Posts by Jai Ganesh

Jai Ganesh · This is Cool

Nuclear Power

Gist

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants.

Nuclear power is generated through a process called nuclear fission, where the heat produced is used to create steam that spins turbines to generate electricity. First, neutrons split uranium atoms in a reactor's core, releasing more neutrons and heat. This heat boils water into steam, which then turns a turbine connected to an electric generator.

Summary

Nuclear power is electricity generated by power plants that derive their heat from fission in a nuclear reactor. Except for the reactor, which plays the role of a boiler in a fossil-fuel power plant, a nuclear power plant is similar to a large coal-fired power plant, with pumps, valves, steam generators, turbines, electric generators, condensers, and associated equipment.

World nuclear power

Nuclear power provides almost 15 percent of the world’s electricity. The first nuclear power plants, which were small demonstration facilities, were built in the 1960s. These prototypes provided “proof-of-concept” and laid the groundwork for the development of the higher-power reactors that followed.

The nuclear power industry went through a period of remarkable growth until about 1990, when the portion of electricity generated by nuclear power reached a high of 17 percent. That percentage remained stable through the 1990s and began to decline slowly around the turn of the 21st century, primarily because of the fact that total electricity generation grew faster than electricity from nuclear power while other sources of energy (particularly coal and natural gas) were able to grow more quickly to meet the rising demand. This trend appears likely to continue well into the 21st century. The Energy Information Administration (EIA), a statistical arm of the U.S. Department of Energy, has projected that world electricity generation between 2005 and 2035 will roughly double (from more than 15,000 terawatt-hours to 35,000 terawatt-hours) and that generation from all energy sources except petroleum will continue to grow.

In 2012 more than 400 nuclear reactors were in operation in 30 countries around the world, and more than 60 were under construction. The United States has the largest nuclear power industry, with more than 100 reactors; it is followed by France, which has more than 50. Of the top 15 electricity-producing countries in the world, all but two, Italy and Australia, utilize nuclear power to generate some of their electricity. The overwhelming majority of nuclear reactor generating capacity is concentrated in North America, Europe, and Asia. The early period of the nuclear power industry was dominated by North America (the United States and Canada), but in the 1980s that lead was overtaken by Europe. The EIA projects that Asia will have the largest nuclear capacity by 2035, mainly because of an ambitious building program in China.

A typical nuclear power plant has a generating capacity of approximately one gigawatt (GW; one billion watts) of electricity. At this capacity, a power plant that operates about 90 percent of the time (the U.S. industry average) will generate about eight terawatt-hours of electricity per year. The predominant types of power reactors are pressurized water reactors (PWRs) and boiling water reactors (BWRs), both of which are categorized as light water reactors (LWRs) because they use ordinary (light) water as a moderator and coolant. LWRs make up more than 80 percent of the world’s nuclear reactors, and more than three-quarters of the LWRs are PWRs.

Details

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Reactors producing controlled fusion power have been operated since 1958 but have yet to generate net power and are not expected to be commercially available in the near future.

The first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. Nuclear power plants supplied 2,602 terawatt hours (TWh) of electricity in 2023, equivalent to about 9% of global electricity generation, and were the second largest low-carbon power source after hydroelectricity. As of November 2025, there are 416 civilian fission reactors in the world, with overall capacity of 376 GW, 63 under construction and 87 planned, with a combined capacity of 66 GW and 84 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh per year with an average capacity factor of 92%. The average global capacity factor is 89%. Most new reactors under construction are generation III reactors in Asia.

Nuclear power is a safe, sustainable energy source that reduces carbon emissions. This is because nuclear power generation causes one of the lowest levels of fatalities per unit of energy generated compared to other energy sources. "Economists estimate that each nuclear plant built could save more than 800,000 life years." Coal, petroleum, natural gas and hydroelectricity have each caused more fatalities per unit of energy due to air pollution and accidents. Nuclear power plants also emit no greenhouse gases and result in less life-cycle carbon emissions than common sources of renewable energy. The radiological hazards associated with nuclear power are the primary motivations of the anti-nuclear movement, which contends that nuclear power poses threats to people and the environment, citing the potential for accidents like the Fukushima nuclear disaster in Japan in 2011, and is too expensive to deploy when compared to alternative sustainable energy sources.

Additional Information

As the world’s second-largest source of low-emissions electricity after hydropower, nuclear power today produces just under 10% of global electricity supply. Now, fresh momentum around the world has the potential to open a new era for nuclear energy.

Power generation from the global fleet of nearly 420 active nuclear reactors is set to reach a record high in 2025 as Japan restarts production, maintenance works are completed in France, and new reactors begin commercial operations in various markets, including China, Europe, India and Korea. Meanwhile, more than 60 nuclear reactors are currently under construction – representing over 70 gigawatts (GW) of capacity – and governments’ interest in nuclear power is at its highest level since the oil crisis in the 1970s, reflecting efforts to bolster energy security, accelerate clean energy transitions and meet rising demand for electricity. Over 40 countries now have plans to expand its use.

Nuclear power is an important low-emission source of electricity, providing about 10% of global electricity generation. For those countries where it is accepted, it can complement renewables in reducing power sector emissions while also contributing to electricity security as a dispatchable power source. It is also an option for producing low-emission heat and hydrogen.

More efforts are needed to get nuclear power on track with the Net Zero Emissions by 2050 Scenario. Lifetime extensions of existing nuclear power plants are one of the most cost-effective sources of low-emission electricity, and there have been several positive policy developments to take full advantage of these opportunities including in the United States, France and Japan. Additional effort is needed to accelerate new constructions – 8 GW of new nuclear capacity was brought online in 2022, but the Net Zero Scenario calls for over four-times as much annual deployment by 2030. Support for innovation in nuclear power, including small modular reactors, will also help expand the range of low-emission options and widen the path to net zero power.

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Jai Ganesh · Science HQ

Metal

Gist

A metal is a material that is typically hard, strong, shiny, and an excellent conductor of heat and electricity. It can be shaped by hammering (malleability) or drawn into wires (ductility). The term can refer to a chemical element (like iron, copper, or gold), a mixture of elements (like steel), or the music genre, heavy metal.

A metal is a material that is typically hard, shiny, and an excellent conductor of heat and electricity. Common characteristics include being malleable (can be hammered into sheets), ductile (can be drawn into wires), and having a high melting point. Metals are elements found on the periodic table that readily lose electrons to form positive ions. Examples include iron, copper, aluminum, and gold.

Summary

A metal is any of a class of substances characterized by high electrical and thermal conductivity as well as by malleability, ductility, and high reflectivity of light.

Approximately three-quarters of all known chemical elements are metals. The most abundant varieties in the Earth’s crust are aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority of metals are found in ores (mineral-bearing substances), but a few such as copper, gold, platinum, and silver frequently occur in the free state because they do not readily react with other elements.

Metals are usually crystalline solids. In most cases, they have a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry. Typically, the atoms of metals contain less than half the full complement of electrons in their outermost shell. Because of this characteristic, metals tend not to form compounds with each other. They do, however, combine more readily with nonmetals (e.g., oxygen and sulfur), which generally have more than half the maximum number of valence electrons. Metals differ widely in their chemical reactivity. The most reactive include lithium, potassium, and radium, whereas those of low reactivity are gold, silver, palladium, and platinum.

The high electrical and thermal conductivities of the simple metals (i.e., the non-transition metals of the periodic table) are best explained by reference to the free-electron theory. According to this concept, the individual atoms in such metals have lost their valence electrons to the entire solid, and these free electrons that give rise to conductivity move as a group throughout the solid. In the case of the more complex metals (i.e., the transition elements), conductivities are better explained by the band theory, which takes into account not only the presence of free electrons but also their interaction with so-called d electrons.

The mechanical properties of metals, such as hardness, ability to resist repeated stressing (fatigue strength), ductility, and malleability, are often attributed to defects or imperfections in their crystal structure. The absence of a layer of atoms in its densely packed structure, for example, enables a metal to deform plastically, and prevents it from being brittle.

Details

A metal is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as opposed to nonmetallic materials which do not. Metals are typically ductile (can be drawn into a wire) and malleable (can be shaped via hammering or pressing).

A metal may be a chemical element such as iron; an alloy such as stainless steel; or a molecular compound such as polymeric sulfur nitride. The general science of metals is called metallurgy, a subtopic of materials science; aspects of the electronic and thermal properties are also within the scope of condensed matter physics and solid-state chemistry, it is a multidisciplinary topic. In colloquial use materials such as steel alloys are referred to as metals, while others such as polymers, wood or ceramics are nonmetallic materials.

A metal conducts electricity at a temperature of absolute zero, which is a consequence of delocalized states at the Fermi energy. Many elements and compounds become metallic under high pressures, for example, iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure.

When discussing the periodic table and some chemical properties, the term metal is often used to denote those elements which in pure form and at standard conditions are metals in the sense of electrical conduction mentioned above. The related term metallic may also be used for types of dopant atoms or alloying elements.

The strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, and railroad tracks. Precious metals were historically used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements. There is also extensive use of multi-element metals such as titanium nitride or degenerate semiconductors in the semiconductor industry.

The history of refined metals is thought to begin with the use of copper about 11,000 years ago. Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. Subsequent developments include the production of early forms of steel; the discovery of sodium—the first light metal—in 1809; the rise of modern alloy steels; and, since the end of World War II, the development of more sophisticated alloys.

Additional Information

The term “metal” applies to a large portion of the periodic table of elements. Metals are typically characterized by high electrical and thermal conductivity, luster, and, in many cases, notable malleability, ductility, and tensile strength. Most are solid at room temperature and readily form metallic bonds. They are a core pillar of most product market segments thanks to their advantageous properties and broad versatility.

What Is Metal?

Metal elements are characterized by several distinct physical and chemical properties. They are typically found toward the left side of the periodic table and are distinguished by their ability to form positive ions (cations) via the loss of electrons. These cations form metallic bonds with free electrons, allowing them to move freely among the metal atoms. This bonding structure contributes to their unique properties, such as ductility, conductivity, and strength.

What Are the Different Properties of Metal?

The common properties of metals are listed and discussed below:

1. Density

Density is a fundamental physical property, quantifying mass per unit volume. Metals, on average, exhibit higher densities than non-metals, influenced by factors like atomic structure, atomic number/mass, and crystalline/atomic packing arrangement. Variations in composition, temperature, and pressure impact metal density; pure metals often boast higher densities than alloys.

2. Electronegativity

Electronegativity is a measure of an atom's electron-attracting capability when forming molecular bonds. In metals, it underpins their chemical behaviors and interactions. Metals typically exhibit low electronegativity compared to non-metals, signifying weaker electron attractions during bond formation. Consequently, metals readily donate electrons to nearby atoms, yielding positively charged ions (cations) that can then form ionic compounds or metallic bonds.

When forming bonds, metal ions are enveloped by a sea of delocalized electrons, enabling efficient electricity and heat conduction. Metals react with non-metals, forming ionic compounds with high melting points. Some such reactions generate impermeable oxide coatings like aluminum oxide or chromium oxide, while others, like iron oxide (rust), allow further degradation. Almost all metals oxidize readily when conditions allow.

3. Luster

Luster defines how light interacts with a material's surface and how well it reflects to the observer. Metals' electron configuration and metallic bonding enable strong electromagnetic (EM) reflection. Incident light interacts with delocalized electrons in the lattice. They’re easily absorbed and re-emitted, imparting a characteristic brilliance to the macroscopic surface.

Luster varies with surface finish, purity, and crystal structure, with polished surfaces exhibiting greater reflectivity. Beyond aesthetics, luster holds practical significance because it reflects infrared and radio frequencies in addition to visible light.

4. Malleability

Malleability denotes a material's ability to endure compressive stress and deform without fracturing. This trait defines metals’ utility and adaptability. Metallic bonding and regular crystalline structure enable metal atoms to glide over one another under pressure, remaining in lattice contact by delocalized electrons circulating among metal ions.

Malleability varies based on microscopic crystal structure, temperature, and purity. Metals with the closest-packed microstructure, like gold and silver, are the most malleable. Malleability facilitates forging, stamping, and rolling, among other processes.

5. Opacity

Metals’ electronic structure makes them opaque in the visible spectrum. When light interacts with a metal surface, it encounters free electrons, which absorb and scatter photons. This scattering prevents light from passing through in a straight line, resulting in opacity. Metals absorb many wavelengths of light, including the visible spectrum, so they’re highly opaque.

Overall, electronic structure, electron mobility, and light scattering within the lattice combine to make metals opaque at all visible frequencies and more or less reflective across most spectra. This property influences laser-based machining methods, thermal control/dissipation applications, and aesthetic roles.

6. Ductility

A metal’s intrinsic ductility determines how it can be formed into useful shapes. Metallic bonding fosters high ductility, as atomic layers slide over each other under stress. Ductility varies across metals, and it is affected by purity, crystalline structure, and other factors. More densely packed crystal structures, like those in gold and silver, show higher ductility.

This is a key property for metals drawn into wires, rods, or thin sheets for electrical wiring, cables, and metal foils. Ductility also enables intricate component shaping via forging, extrusion, and rolling.

7. Hardness

Hardness gauges a material's resistance to deformation, scratching, or penetration. In metals, it has functional significance, dictating the products’ durability. Standardized tests like Rockwell, Vickers, or Brinell measure hardness.

Atomic structure and bonding have the biggest influence on metal hardness — densely packed crystal structures like face-centered cubic (FCC) or body-centered cubic (BCC) translate into harder metals. Alloying elements, grain size, and heat treatment also impact hardness. Hardness guides material selection — hard metals find use in tools and wear-resistant coatings, while softer ones are critical in resilient structural components for buildings and vehicles.

8. Conductivity

Conductivity describes a material's ability to conduct electricity or heat. Both are crucial features in many metal applications.

The free electrons in a metal’s crystal structure enable excellent electrical current flow. This property is found in wiring, circuits, and electronics. For the same reason, metals generally exhibit high thermal conductivity, facilitating heat transfer via lattice vibrations and free electron movement. Applications span from heat exchangers to cooking utensils. Conductivity hinges on factors like crystal structure and purity; dense structures like copper and silver exhibit superior conductivity. These inherent conductive qualities are important factors in material selection for electronics and thermal management items.

9. High Tensile Strength

Tensile strength describes a material's ability to resist tensile forces without permanent deformation. It's key for structural and load-bearing applications, and metals are usually far stronger in tension than are polymers or ceramics.

Metallic bonding underpins this strength — the atoms shift elastically under tension. Tensile strength varies with factors like composition, crystal structure, grain size, and processing. Metals with greater crystallinity, smaller grains, and higher purity exhibit superior tensile strength.

10. High Reflectivity

Reflectivity defines a material's ability to reflect light or other electromagnetic radiation. It is essentially the same as luster but applies to a larger frequency range, from X-ray/UV to long-wave radio. Nevertheless, the mechanisms of reflectivity are the same as those describing luster.

11. Sonorousness

Sonorousness characterizes a material's ability to produce resonant sound upon impact, a hallmark of most metals. This property stems from the fact that sound waves propagate easily through metallic crystalline structures. Sound reflection further extends the sound effects. Striking a metal object, like a bell or plate, induces highly elastic vibrations that travel through the lattice, resulting in clear, ringing tones. The macro effect is shape oscillations that induce sound waves in the surrounding air.

Practical applications abound, particularly in musical instruments where metals produce rich, resonant sounds. Additionally, sonorous metals are used in acoustic engineering, enhancing sound reflection and architectural acoustics in buildings and performance spaces.

12. High Melting and Boiling Points

Most metals exhibit very high melting and boiling points (MP and BP). The most notable exceptions are lead, tin, gallium, and mercury. Metallic bonding is responsible for these characteristics, with variations in atomic size and packing density affecting specific values.

Tungsten and molybdenum have high MPs and may be added as alloying agents to raise the MP of various materials for high-temperature machinery. Tantalum also has a high BP, benefiting vacuum systems.

13. Corrosion Resistance

Corrosion resistance describes the material’s durability amid exposure to corrosive elements like moisture, chlorides, acids, and alkalis. It safeguards structural integrity and aesthetics for all types of products.

Metals can corrode via oxidation or other chemical reactions, leading to surface defects and weakened structures. Factors like composition, treatments, and environment influence resistance.

Stainless steel, nickel, chromium, zinc, aluminum, and titanium excel because they form impermeable and self-healing oxide layers on their surfaces. Many cheaper but high-performing metals, like steel, require coatings or alloying. Steel can be coated in zinc or alloyed with chromium to resist oxidation. Gold and silver are both highly resistant to corrosion under typical conditions, with gold being virtually immune to most corrosive agents.

14. Magnetic Properties

Metals’ magnetic properties arise from their electron configuration and atomic arrangement. They are categorized into three types: ferromagnetic, paramagnetic, and diamagnetic metals. Ferromagnetic metals exhibit strong magnetic responses to external magnetic fields and will retain their magnetic alignment after being exposed to a magnetic field. Paramagnetic metals, on the other hand, are weakly attracted to magnetic fields but lose magnetization once the field is removed. Diamagnetic metals are repelled by magnetic fields and possess no net magnetization.

These three properties enable applications in magnetic storage, electromagnets, magnetic shielding, magnetic braking, and MRI machines.

15. Solid State at Room Temperature

Metals typically remain solid at room temperature due to the robust metallic bonds between atoms. The arrangement and strength of metallic bonds, influenced by factors like valence electrons and atomic size, dictate the melting point.

What Is the Use of Metal?

Metals have a plethora of applications owing to their physical, mechanical, and chemical properties. They are ideal for structural applications like construction and transportation, enduring heavy loads and harsh loading conditions. Their electrical and thermal conductivity makes metals vital in electrical wiring, electronics, and heating/cooling systems. Metals' malleability and ductility allow easy shaping and fabrication. Some offer excellent corrosion resistance, ideal for outdoor, marine, and chemically aggressive environments. High recyclability means metals can be reused, reducing the environmental impact of primary extraction and waste disposal. Some metals are visually appealing enough for jewelry and architectural finishes. Metals' high melting and boiling points ensure they retain mechanical strength, demanding high-temperature applications.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10677. What does the term in Geography Col mean?

#10678. What does the term in Geography Colatitude mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5873. What does the adjective confederate mean?

#5874. What does the verb (used without object) confer mean?

Jai Ganesh · Dark Discussions at Cafe Infinity

2399) Charles H. Townes

Gist:

Work

Stimulated emission means that a light packet, a photon, coming in contact with an atom can cause an electron to descend to a lower energy level so that an additional photon with the same amount of energy is emitted. If electrons are elevated to higher energy levels with the help of heat or light, an avalanche-like effect occurs when they fall to lower levels. In the 1950s Charles Townes, Nicolay Basov, and Aleksandr Prokhorov contributed to putting this phenomenon into practical use in masers and lasers, which produce concentrated and coherent beams of microwaves and light, respectively.

Summary

Charles Hard Townes (born July 28, 1915, Greenville, South Carolina, U.S.—died January 27, 2015, Oakland, California) was an American physicist, joint winner (with the Soviet physicists Aleksandr M. Prokhorov and Nikolay G. Basov) of the Nobel Prize for Physics in 1964 for his role in the invention of the maser and the laser.

Townes studied at Furman University (B.A., B.S., 1935), Duke University (M.A., 1937), and the California Institute of Technology (Ph.D., 1939). In 1939 he joined the technical staff of Bell Telephone Laboratories, Inc., where he worked until 1948, when he joined the faculty of Columbia University. Three years later he conceived the idea of using ammonia molecules to amplify microwave radiation. Townes and two students completed the first such device in December 1953 and gave it the name maser, an acronym for “microwave amplification by stimulated emission of radiation.” In 1958 Townes and A.L. Schawlow showed that it was possible to construct a similar device using light—i.e., a laser.

From 1959 to 1961 Townes served as vice president and director of research of the Institute for Defense Analyses, Washington, D.C. He then was appointed provost and professor of physics at the Massachusetts Institute of Technology, Cambridge. In 1967 he became a professor at the University of California, Berkeley, where he initiated a program of radio and infrared astronomy leading to the discovery of complex molecules (ammonia and water) in the interstellar medium. He became professor emeritus in 1986.

Details

Charles Hard Townes (July 28, 1915 – January 27, 2015) was an American physicist. Townes worked on the theory and application of the maser, for which he obtained the fundamental patent, and other work in quantum electronics associated with both maser and laser devices. He shared the 1964 Nobel Prize in Physics with Nikolay Basov and Alexander Prokhorov. Townes was an adviser to the United States Government, meeting every US president from Harry S. Truman (1945) to Bill Clinton (1999).

He directed the US government's Science and Technology Advisory Committee for the Apollo lunar landing program. After becoming a professor of the University of California, Berkeley in 1967, he began an astrophysical program that produced several important discoveries, for example, the black hole at the center of the Milky Way galaxy.

Townes was religious and believed that science and religion are converging to provide a greater understanding of the nature and purpose of the universe.

Early life and education

Townes had German, Scottish, English, Welsh, Huguenot French, and Scotch Irish ancestry, Townes was born in Greenville, South Carolina, the son of Henry Keith Townes (1876–1958), an attorney, and Ellen Sumter Townes (née Hard; 1881–1980). His brother, Henry Keith Townes Jr., (January 20, 1913 – May 2, 1990), was a renowned entomologist who was a world authority on Ichneumon wasps. Charles earned his B.S. in Physics and B.A. in Modern Languages at Furman University, where he graduated in 1935. Townes completed work for the Master of Arts degree in physics at Duke University in 1937, and then began graduate school at the California Institute of Technology, from which he received a Ph.D. degree in 1939. During World War II, he worked on radar bombing systems at Bell Labs.

Career and research

In 1950, Townes was appointed professor at Columbia University. He served as executive director of the Columbia Radiation Laboratory from 1950 to 1952. He was Chairman of the Physics Department from 1952 to 1955.

In 1951, Townes conceived a new way to create intense, precise beams of coherent radiation, for which he invented the acronym maser (for Microwave Amplification by Stimulated Emission of Radiation). When the same principle was applied to higher frequencies, the term laser was used (the word "light" substituting for the word "microwave").

During 1953, Townes, James P. Gordon, and Herbert J. Zeiger built the first ammonia maser at Columbia University. This device used stimulated emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24.0 gigahertz.

From 1959 to 1961, he was on leave of absence from Columbia University to serve as vice president and director of research of the Institute for Defense Analyses in Washington, D.C., a nonprofit organization, which advised the U.S. government and was operated by eleven universities. Between 1961 and 1967, Townes served as both provost and professor of physics at the Massachusetts Institute of Technology. Then, during 1967, he was appointed as a professor of physics at the University of California at Berkeley, where he remained for almost 50 years; his status was as professor emeritus by the time of his death during 2015. Between 1966 and 1970, he was chairman of the NASA Science Advisory Committee for the Apollo lunar landing program.

For his creation of the maser, Townes along with Nikolay Basov and Alexander Prokhorov received the 1964 Nobel Prize in Physics. Townes also developed the use of masers and lasers for astronomy, was part of a team that first discovered complex molecules in space, and determined the mass of the supermassive black hole at the center of the Milky Way galaxy.

During 2002–2003, Townes served as a Karl Schwarzschild Lecturer in Germany and the Birla Lecturer and Schroedinger Lecturer in India.

Townes is one of the 20 American recipients of the Nobel Prize in Physics to sign a letter addressed to President George W. Bush in May 2008, urging him to "reverse the damage done to basic science research in the Fiscal Year 2008 Omnibus Appropriations Bill" by requesting additional emergency funding for the Department of Energy's Office of Science, the National Science Foundation, and the National Institute of Standards and Technology.

Jai Ganesh · This is Cool

2451) Ozone

Gist

Ozone (O3) is a gas with a distinct odor that exists in two layers of the atmosphere: the protective stratospheric ozone layer and the harmful ground-level ozone. While stratospheric ozone is beneficial because it shields the Earth from the sun's harmful ultraviolet (UV) radiation, ground-level ozone is a major air pollutant and a key component of smog that can cause serious health problems. Ground-level ozone forms when pollutants from sources like car exhaust and industrial emissions react with sunlight.

Ozone (O3) is a gas with a chemical formula of O3, meaning it has three oxygen atoms instead of the two in the oxygen we breathe (O2). It can be "good" or "bad" depending on its location in the atmosphere: "good" stratospheric ozone forms a protective layer that shields Earth from the sun's harmful ultraviolet (UV) radiation, while "bad" ground-level ozone is a pollutant that can damage lungs and crops.

Summary

Ozone, also called trioxygen, is an inorganic molecule with the chemical formula O3. It is a pale-blue gas with a distinctively pungent odour. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O2, breaking down in the lower atmosphere to O2 (dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the atmosphere, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.

Ozone's odour is reminiscent of chlorine, and detectable by many people at concentrations of as little as 0.1 ppm in air. Ozone's O3 structure was determined in 1865. The molecule was later proven to have a bent structure and to be weakly diamagnetic. At standard temperature and pressure, ozone is a pale blue gas that condenses at cryogenic temperatures to a dark blue liquid and finally a violet-black solid. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively at elevated temperatures, physical shock, or fast warming to the boiling point. It is therefore used commercially only in low concentrations.

Ozone is a powerful oxidising agent (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. This same high oxidising potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about 0.1 ppm. While this makes ozone a potent respiratory hazard and pollutant near ground level, a higher concentration in the ozone layer (from two to eight ppm) is beneficial, preventing damaging UV light from reaching the Earth's surface.

Details

Ozone, (O3), triatomic allotrope of oxygen (a form of oxygen in which the molecule contains three atoms instead of two as in the common form) that accounts for the distinctive odor of the air after a thunderstorm or around electrical equipment. The odor of ozone around electrical machines was reported as early as 1785; ozone’s chemical constitution was established in 1872. Ozone is an irritating pale blue gas that is explosive and toxic, even at low concentrations. It occurs naturally in small amounts in Earth’s stratosphere, where it absorbs solar ultraviolet radiation, which otherwise could cause severe damage to living organisms on Earth’s surface. Under certain conditions, photochemical reactions between nitrogen oxides and hydrocarbons in the lower atmosphere can produce ozone in concentrations high enough to cause irritation of the eyes and mucous membranes. Such ground-level ozone is considered a major air pollutant.

Ozone usually is manufactured by passing an electric discharge through a current of oxygen or dry air. The resulting mixtures of ozone and original gases are suitable for most industrial purposes, although purer ozone may be obtained from them by various methods; for example, upon liquefaction, an oxygen-ozone mixture separates into two layers, of which the denser one contains about 75 percent ozone. The extreme instability and reactivity of concentrated ozone makes its preparation both difficult and hazardous.

Ozone is 1.5 times as dense as oxygen; at −112 °C (−170 °F) it condenses to a dark blue liquid, which freezes at −251.4 °C (−420 °F). The gas decomposes rapidly at temperatures above 100 °C (212 °F) or, in the presence of certain catalysts, at room temperatures. Although it resembles oxygen in many respects, ozone is much more reactive; hence, it is an extremely powerful oxidizing agent, particularly useful in converting olefins into aldehydes, ketones, or carboxylic acids. Because it can decolorize many substances, it is used commercially as a bleaching agent for organic compounds; as a strong germicide it is used to sterilize drinking water as well as to remove objectionable odors and flavors.

Additional Information

Ozone (O3) is a highly reactive gas composed of three oxygen atoms. It is both a natural and a man-made product that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere). Depending on where it is in the atmosphere, ozone affects life on Earth in either good or bad ways.

Stratospheric ozone is formed naturally through the interaction of solar ultraviolet (UV) radiation with molecular oxygen (O2). The "ozone layer," approximately 6 through 30 miles above the Earth's surface, reduces the amount of harmful UV radiation reaching the Earth's surface.

Tropospheric or ground-level ozone – what we breathe – is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOx). These reactions have traditionally been viewed as depending upon the presence of heat and sunlight, resulting in higher ambient ozone concentrations in summer months. Within the last decade, however, high ozone concentrations have also been observed under specific circumstances in cold months, where a few high elevation areas in the Western U.S. with high levels of local VOC and NOx emissions have formed ozone when snow is on the ground and temperatures are near or below freezing. Ozone contributes to what we typically experience as "smog" or haze, which still occurs most frequently in the summertime, but can occur throughout the year in some southern and mountain regions.

Although some stratospheric ozone is transported into the troposphere, and some VOC and NOx occur naturally, the majority of ground-level ozone is the result of reactions of man-made VOC and NOx. Significant sources of VOC are chemical plants, gasoline pumps, oil-based paints, autobody shops, and print shops. Nitrogen oxides result primarily from high temperature combustion. Significant sources are power plants, industrial furnaces and boilers, and motor vehicles.

Ozone has two properties of interest to human health. First, it absorbs UV light, reducing human exposure to harmful UV radiation that causes skin cancer and cataracts. Second, when inhaled, it reacts chemically with many biological molecules in the respiratory tract, leading to a number of adverse health effects. This course addresses this second property.

Ozone (O3) is a gas molecule composed of three oxygen atoms which occur both in the Earth's upper atmosphere and at ground level. There is both a "good" and "bad" Ozone.

Bad Ozone - Ground-level Ozone is an air pollutant that is harmful to breathe and damages crops, trees, and other vegetation. It is the main ingredient of urban smog. The Centers for Disease Control and Prevention (CDC) states that breathing ground-level ozone can be harmful to your health.

Good Ozone - Ozone is produced naturally in the stratosphere. But this "good" ozone layer is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances (ODS). Essentially, Ozone is only good for our stratosphere, which is a layer of the earth's protective barrier.

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - VI

1. We're no longer in the Cold War. Eavesdropping on friends is unacceptable. - Vladimir Putin

2. Construction of the first gas pipeline system was started during the 1960s, at the height of the Cold War, and for all those years, from the 1960s until this day, Russia has been fulfilling its contract obligations in a very consistent and reliable way, regardless of the political situation. - Vladimir Putin

3. Well, my friend, this earth will one day be that cold corpse; it will become uninhabitable and uninhabited like the moon, which has long since lost all its vital heat. - Jules Verne

4. I don't plan to take a formal, cold approach with my children, but I expect a lot. I don't want my children to view me as their best friend. I want to be their mom. - Ivanka Trump

5. The cold, commercial word 'market' disguises its human character - a market is a collection of our aspirations, exertions, choices and desires. - Rupert Murdoch

6. If a patient is cold, if a patient is feverish, if a patient is faint, if he is sick after taking food, if he has a bed-sore, it is generally the fault not of the disease, but of the nursing. - Florence Nightingale

7. We've always had this experience that things take long, but I'm 100% convinced that our principles will in the end prevail. No one knew how the Cold War would end at the time, but it did end. This is within our living experience... I'm surprised at how fainthearted we sometimes are and how quickly we lose courage. - Angela Merkel

8. I think I'm teaching my teammates that they can still be successful while having fun and enjoying the moment rather than being a stone cold brick. - Simone Biles.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2531. What does the medical term Microkeratome mean (instrument)?

Jai Ganesh · Jokes

Q: What water yields award winning cabbage heads?
A: Perspiration!
* * *
Q: What is another name for brussels sprouts?
A: Cabbage patch kids.
* * *
Q: What does a cabbage outlaw have?
A: A price on his head.
* * *
Q: What do you call a cabbage that's in love?
A: Head over heels.
* * *
Q: What do you tell a cabbage that's down in the dumps?
A: Hold your head up high.
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9811.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6305.

Jai Ganesh · Exercises

Hi,

2656.

Jai Ganesh · Dark Discussions at Cafe Infinity

2398) Jacques Monod

Gist:

Work

The biochemical processes that take place within an organism's cells are controlled by the genes found inside DNA molecules. Jacques Monod and François Jacob proved how the genetic information is converted during the formation of proteins by means of a messenger, which proved to the substance we now know as RNA. Different cells work in different ways at different times, however. This too is regulated by genes. In the early 1960s Monod and Jacob mapped the intricate processes that determine how genes are expressed or suppressed in a self-regulating process.

Summary

Jacques Monod (born Feb. 9, 1910, Paris, France—died May 31, 1976, Cannes) was a French biochemist who, with François Jacob, did much to elucidate how genes regulate cell metabolism by directing the biosynthesis of enzymes. The pair shared, along with André Lwoff, the Nobel Prize for Physiology or Medicine in 1965.

In 1961 Jacob and Monod proposed the existence of a messenger ribonucleic acid (mRNA), a substance whose base sequence is complementary to that of deoxyribonucleic acid (DNA) in the cell. They postulated that the messenger carries the “information” encoded in the base sequence to ribosomes, the sites of protein synthesis; here the base sequence of the messenger RNA is translated into the amino acid sequence of a proteinaceous enzyme (biological catalyst).

In advancing the concept of gene complexes that they called operons, Jacob and Monod postulated the existence of a class of genes that regulate the function of other genes by affecting the synthesis of messenger RNA. For this work, which has been proved generally correct for bacteria, the two men were awarded a Nobel Prize.

Monod’s book-length essay Le Hasard et la nécessité (1970; Chance and Necessity) argued that the origin of life and the process of evolution are the result of chance. Monod joined the staff of the Pasteur Institute in Paris in 1945 and became its director in 1971.

Details

Jacques Lucien Monod (9 February 1910 – 31 May 1976) was a French biochemist who won the Nobel Prize in Physiology or Medicine in 1965, sharing it with François Jacob and André Lwoff "for their discoveries concerning genetic control of enzyme and virus synthesis".

Monod and Jacob became famous for their work on the E. coli lac operon, which encodes proteins necessary for the transport and breakdown of the sugar lactose (lac). From their own work and the work of others, they came up with a model for how the levels of some proteins in a cell are controlled. In their model, the manufacture of a set of related proteins, such as the ones encoded within the lac (lactose) operon, is prevented when a repressor protein, encoded by a regulatory gene, binds to its operator, a specific site in the DNA sequence that is close to the genes encoding the proteins. (It is now known that a repressor bound to an operator physically blocks RNA polymerase from binding to the promoter, the site where transcription of the adjacent genes begins.)

Study of the control of expression of genes in the lac operon provided the first example of a system for the regulation of transcription. Monod also suggested the existence of messenger RNA molecules that link the information encoded in DNA and proteins. For these contributions he is widely regarded as one of the founders of molecular biology.

Jai Ganesh · This is Cool

2450) Tunnel

Gist

A tunnel is a passage that runs underground or through something, like a train tunnel that cuts through a mountain. Some theme parks have networks of underground tunnels so that employees can move around out of sight of visitors.

Some tunnels, like New York's Lincoln Tunnel and the Holland Tunnel, which connect New York City to New Jersey, are large and solid enough to drive cars through. Others are much smaller, like the tunnels small animals dig through snow or soil for safety and shelter.

Summary

A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along the length. A pipeline differs significantly from a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.

A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.

Secret tunnels are built for military purposes, or by civilians for smuggling of weapons, contraband, or people. Special tunnels, such as wildlife crossings, are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in tunnel networks.

A tunnel is relatively long and narrow; the length is often much greater than twice the diameter, although similar shorter excavations can be constructed, such as cross passages between tunnels. The definition of what constitutes a tunnel can vary widely from source to source. For example, in the United Kingdom, a road tunnel is defined as "a subsurface highway structure enclosed for a length of 150 metres (490 ft) or more." In the United States, the NFPA definition of a tunnel is "An underground structure with a design length greater than 23 m (75 ft) and a diameter greater than 1,800 millimetres (5.9 ft)."

Details

Tunnels and underground excavations are horizontal underground passageway produced by excavation or occasionally by nature’s action in dissolving a soluble rock, such as limestone. A vertical opening is usually called a shaft. Tunnels have many uses: for mining ores, for transportation—including road vehicles, trains, subways, and canals—and for conducting water and sewage. Underground chambers, often associated with a complex of connecting tunnels and shafts, increasingly are being used for such things as underground hydroelectric-power plants, ore-processing plants, pumping stations, vehicle parking, storage of oil and water, water-treatment plants, warehouses, and light manufacturing; also command centres and other special military needs.

True tunnels and chambers are excavated from the inside—with the overlying material left in place—and then lined as necessary to support the adjacent ground. A hillside tunnel entrance is called a portal; tunnels may also be started from the bottom of a vertical shaft or from the end of a horizontal tunnel driven principally for construction access and called an adit. So-called cut-and-cover tunnels (more correctly called conduits) are built by excavating from the surface, constructing the structure, and then covering with backfill. Tunnels underwater are now commonly built by the use of an immersed tube: long, prefabricated tube sections are floated to the site, sunk in a prepared trench, and covered with backfill. For all underground work, difficulties increase with the size of the opening and are greatly dependent upon weaknesses of the natural ground and the extent of the water inflow.

History:

Ancient tunnels

It is probable that the first tunneling was done by prehistoric people seeking to enlarge their caves. All major ancient civilizations developed tunneling methods. In Babylonia, tunnels were used extensively for irrigation; and a brick-lined pedestrian passage some 3,000 feet (900 metres) long was built about 2180 to 2160 bce under the Euphrates River to connect the royal palace with the temple. Construction was accomplished by diverting the river during the dry season. The Egyptians developed techniques for cutting soft rocks with copper saws and hollow reed drills, both surrounded by an abrasive, a technique probably used first for quarrying stone blocks and later in excavating temple rooms inside rock cliffs. Abu Simbel Temple on the Nile, for instance, was built in sandstone about 1250 bce for Ramses II (in the 1960s it was cut apart and moved to higher ground for preservation before flooding from the Aswān High Dam). Even more elaborate temples were later excavated within solid rock in Ethiopia and India.

The Greeks and Romans both made extensive use of tunnels: to reclaim marshes by drainage and for water aqueducts, such as the 6th-century-bce Greek water tunnel on the isle of Samos driven some 3,400 feet through limestone with a cross section about 6 feet square. Perhaps the largest tunnel in ancient times was a 4,800-foot-long, 25-foot-wide, 30-foot-high road tunnel (the Pausilippo) between Naples and Pozzuoli, executed in 36 bce. By that time surveying methods (commonly by string line and plumb bobs) had been introduced, and tunnels were advanced from a succession of closely spaced shafts to provide ventilation. To save the need for a lining, most ancient tunnels were located in reasonably strong rock, which was broken off (spalled) by so-called fire quenching, a method involving heating the rock with fire and suddenly cooling it by dousing with water. Ventilation methods were primitive, often limited to waving a canvas at the mouth of the shaft, and most tunnels claimed the lives of hundreds or even thousands of the slaves used as workers. In ad 41 the Romans used some 30,000 men for 10 years to push a 3.5-mile (6-kilometre) tunnel to drain Lacus Fucinus. They worked from shafts 120 feet apart and up to 400 feet deep. Far more attention was paid to ventilation and safety measures when workers were freemen, as shown by archaeological diggings at Hallstatt, Austria, where salt-mine tunnels have been worked since 2500 bce.

From the Middle Ages to the present

Canal and railroad tunnels

Because the limited tunneling in the Middle Ages was principally for mining and military engineering, the next major advance was to meet Europe’s growing transportation needs in the 17th century. The first of many major canal tunnels was the Canal du Midi (also known as Languedoc) tunnel in France, built in 1666–81 by Pierre Riquet as part of the first canal linking the Atlantic and the Mediterranean. With a length of 515 feet and a cross section of 22 by 27 feet, it involved what was probably the first major use of explosives in public-works tunneling, gunpowder placed in holes drilled by handheld iron drills. A notable canal tunnel in England was the Bridgewater Canal Tunnel, built in 1761 by James Brindley to carry coal to Manchester from the Worsley mine. Many more canal tunnels were dug in Europe and North America in the 18th and early 19th centuries. Though the canals fell into disuse with the introduction of railroads about 1830, the new form of transport produced a huge increase in tunneling, which continued for nearly 100 years as railroads expanded over the world. Much pioneer railroad tunneling developed in England. A 3.5-mile tunnel (the Woodhead) of the Manchester-Sheffield Railroad (1839–45) was driven from five shafts up to 600 feet deep. In the United States, the first railroad tunnel was a 701-foot construction on the Allegheny Portage Railroad. Built in 1831–33, it was a combination of canal and railroad systems, carrying canal barges over a summit. Though plans for a transport link from Boston to the Hudson River had first called for a canal tunnel to pass under the Berkshire Mountains, by 1855, when the Hoosac Tunnel was started, railroads had already established their worth, and the plans were changed to a double-track railroad bore 24 by 22 feet and 4.5 miles long. Initial estimates contemplated completion in 3 years; 21 were actually required, partly because the rock proved too hard for either hand drilling or a primitive power saw. When the state of Massachusetts finally took over the project, it completed it in 1876 at five times the originally estimated cost. Despite frustrations, the Hoosac Tunnel contributed notable advances in tunneling, including one of the first uses of dynamite, the first use of electric firing of explosives, and the introduction of power drills, initially steam and later air, from which there ultimately developed a compressed-air industry.

Simultaneously, more spectacular railroad tunnels were being started through the Alps. The first of these, the Mont Cenis Tunnel (also known as Fréjus), required 14 years (1857–71) to complete its 8.5-mile length. Its engineer, Germain Sommeiller, introduced many pioneering techniques, including rail-mounted drill carriages, hydraulic ram air compressors, and construction camps for workers complete with dormitories, family housing, schools, hospitals, a recreation building, and repair shops. Sommeiller also designed an air drill that eventually made it possible to move the tunnel ahead at the rate of 15 feet per day and was used in several later European tunnels until replaced by more durable drills developed in the United States by Simon Ingersoll and others on the Hoosac Tunnel. As this long tunnel was driven from two headings separated by 7.5 miles of mountainous terrain, surveying techniques had to be refined. Ventilation became a major problem, which was solved by the use of forced air from water-powered fans and a horizontal diaphragm at mid-height, forming an exhaust duct at top of the tunnel. Mont Cenis was soon followed by other notable Alpine railroad tunnels: the 9-mile St. Gotthard Pass (1872–82), which introduced compressed-air locomotives and suffered major problems with water inflow, weak rock, and bankrupt contractors; the 12-mile Simplon (1898–1906); and the 9-mile Lötschberg (1906–11), on a northern continuation of the Simplon railroad line.

Simplon Tunnel

Nearly 7,000 feet below the mountain crest, Simplon encountered major problems from highly stressed rock flying off the walls in rock bursts; high pressure in weak schists and gypsum, requiring 10-foot-thick masonry lining to resist swelling tendencies in local areas; and from high-temperature water (130° F [54° C]), which was partly treated by spraying from cold springs. Driving Simplon as two parallel tunnels with frequent crosscut connections considerably aided ventilation and drainage.

Lötschberg was the site of a major disaster in 1908. When one heading was passing under the Kander River valley, a sudden inflow of water, gravel, and broken rock filled the tunnel for a length of 4,300 feet, burying the entire crew of 25 men. Though a geologic panel had predicted that the tunnel here would be in solid bedrock far below the bottom of the valley fill, subsequent investigation showed that bedrock lay at a depth of 940 feet, so that at 590 feet the tunnel tapped the Kander River, allowing it and soil of the valley fill to pour into the tunnel, creating a huge depression, or sink, at the surface. After this lesson in the need for improved geologic investigation, the tunnel was rerouted about one mile (1.6 kilometres) upstream, where it successfully crossed the Kander Valley in sound rock.

Most long-distance rock tunnels have encountered problems with water inflows. One of the most notorious was the first Japanese Tanna Tunnel, driven through the Takiji Peak in the 1920s. The engineers and crews had to cope with a long succession of extremely large inflows, the first of which killed 16 men and buried 17 others, who were rescued after seven days of tunneling through the debris. Three years later another major inflow drowned several workers. In the end, Japanese engineers hit on the expedient of digging a parallel drainage tunnel the entire length of the main tunnel. In addition, they resorted to compressed-air tunneling with shield and air lock, a technique almost unheard-of in mountain tunneling.

Subaqueous tunnels

Tunneling under rivers was considered impossible until the protective shield was developed in England by Marc Brunel, a French émigré engineer. The first use of the shield, by Brunel and his son Isambard, was in 1825 on the Wapping-Rotherhithe Tunnel through clay under the Thames River. The tunnel was of horseshoe section 22.25 by 37.5 feet and brick-lined. After several floodings from hitting sand pockets and a seven-year shutdown for refinancing and building a second shield, the Brunels succeeded in completing the world’s first true subaqueous tunnel in 1841, essentially nine years’ work for a 1,200-foot-long tunnel. In 1869 by reducing to a small size (8 feet) and by changing to a circular shield plus a lining of cast-iron segments, Peter W. Barlow and his field engineer, James Henry Greathead, were able to complete a second Thames tunnel in only one year as a pedestrian walkway from Tower Hill. In 1874, Greathead made the subaqueous technique really practical by refinements and mechanization of the Brunel-Barlow shield and by adding compressed air pressure inside the tunnel to hold back the outside water pressure. Compressed air alone was used to hold back the water in 1880 in a first attempt to tunnel under New York’s Hudson River; major difficulties and the loss of 20 lives forced abandonment after only 1,600 feet had been excavated.

The first major application of the shield-plus-compressed-air technique occurred in 1886 on the London subway with an 11-foot bore, where it accomplished the unheard-of record of seven miles of tunneling without a single fatality. So thoroughly did Greathead develop his procedure that it was used successfully for the next 75 years with no significant change. A modern Greathead shield illustrates his original developments: miners working under a hood in individual small pockets that can be quickly closed against inflow; shield propelled forward by jacks; permanent lining segments erected under protection of the shield tail; and the whole tunnel pressurized to resist water inflow.

Once subaqueous tunneling became practical, many railroad and subway crossings were constructed with the Greathead shield, and the technique later proved adaptable for the much larger tunnels required for automobiles. A new problem, noxious gases from internal-combustion engines, was successfully solved by Clifford Holland for the world’s first vehicular tunnel, the Holland Tunnel, completed in 1927 under the Hudson River. Holland and his chief engineer, Ole Singstad, solved the ventilation problem with huge-capacity fans in ventilating buildings at each end, forcing air through a supply duct below the roadway, with an exhaust duct above the ceiling. Such ventilation provisions significantly increased the tunnel size, requiring about a 30-foot diameter for a two-lane vehicular tunnel.

Lincoln Tunnel

Many similar vehicular tunnels were built by shield-and-compressed-air methods—including Lincoln and Queens tunnels in New York City, Sumner and Callahan in Boston, and Mersey in Liverpool. Since 1950, however, most subaqueous tunnelers preferred the immersed-tube method, in which long tube sections are prefabricated, towed to the site, sunk in a previously dredged trench, connected to sections already in place, and then covered with backfill. This basic procedure was first used in its present form on the Detroit River Railroad Tunnel between Detroit and Windsor, Ontario (1906–10). A prime advantage is the avoidance of high costs and the risks of operating a shield under high air pressure, since work inside the sunken tube is at atmospheric pressure (free air).

Seikan Tunnel

Japan’s impressive undersea tunnel, the Seikan Tunnel, is the world’s second longest tunnel (after the Gotthard Base Tunnel in Switzerland) and links the main island of Honshu with the northern neighbouring island of Hokkaido. Much of the tunnel lies under the Tsugaru Strait that separates the two islands. Construction of the tunnel began in 1964 and was completed in 1988. The digging employed as many as 3,000 workers at one time and took 34 lives in all because of cave-ins, flooding, and other mishaps. The tunnel remains one of the most formidable engineering feats of the 20th century.

Machine-mined tunnels

Sporadic attempts to realize the tunnel engineer’s dream of a mechanical rotary excavator culminated in 1954 at Oahe Dam on the Missouri River near Pierre, in South Dakota. With ground conditions being favourable (a readily cuttable clay-shale), success resulted from a team effort: Jerome O. Ackerman as chief engineer, F.K. Mittry as initial contractor, and James S. Robbins as builder of the first machine—the “Mittry Mole.” Later contracts developed three other Oahe-type moles, so that all the various tunnels here were machine-mined—totaling eight miles of 25- to 30-foot diameter. These were the first of the modern moles that since 1960 have been rapidly adopted for many of the world’s tunnels as a means of increasing speeds from the previous range of 25 to 50 feet per day to a range of several hundred feet per day. The Oahe mole was partly inspired by work on a pilot tunnel in chalk started under the English Channel for which an air-powered rotary cutting arm, the Beaumont borer, had been invented. A 1947 coal-mining version followed, and in 1949 a coal saw was used to cut a circumferential slot in chalk for 33-foot-diameter tunnels at Fort Randall Dam in South Dakota. In 1962 a comparable breakthrough for the more difficult excavation of vertical shafts was achieved in the American development of the mechanical raise borer, profiting from earlier trials in Germany.

In 2016 the Gotthard Base Tunnel, the world’s longest and deepest railway tunnel, opened under the Saint-Gotthard Massif in the Lepontine Alps in southern Switzerland. The two tunnels were primarily constructed with four massive tunnel boring machines, Herrenknecht Gripper TBMs; blasting was used for only about 25 percent of the project. An incredible feat of engineering, the tunnel provided a high-speed rail link between northern and southern Europe, forming a mainline rail connection between Rotterdam in the Netherlands and Genoa in Italy.

Ferrin-Knob-Tunnel-3-MP-402-Steven-Freedman-web.jpg?maxwidth=1300&maxheight=1300&autorotate=false&format=webp

Jai Ganesh · Science HQ

Electrovalent Bond

Gist

An electrovalent bond, also known as an ionic bond, is a type of chemical bond formed by the transfer of one or more electrons from one atom to another, resulting in the formation of oppositely charged ions that are held together by strong electrostatic attraction. This process typically occurs between a metal and a non-metal, where the metal atom loses electrons to become a positive ion (cation) and the non-metal atom gains electrons to become a negative ion (anion).

There is no difference between ionic and electrovalent bonds; the terms are synonymous and both describe a bond formed by the complete transfer of electrons between atoms, typically a metal and a non-metal. This transfer creates oppositely charged ions (a cation and an anion) that are then held together by a strong electrostatic force of attraction.

Summary

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds. It is one of the main types of bonding, along with covalent bonding and metallic bonding. Ions are atoms (or groups of atoms) with an electrostatic charge. Atoms that gain electrons make negatively charged ions (called anions). Atoms that lose electrons make positively charged ions (called cations).

Clean ionic bonding – in which one atom or molecule completely transfers an electron to another – cannot exist: all ionic compounds have some degree of covalent bonding or electron sharing. Thus, the term "ionic bonding" is given when the ionic character is greater than the covalent character – that is, a bond in which there is a large difference in electronegativity between the cation and anion, causing the bonding to be more polar (ionic) than in covalent bonding where electrons are shared more equally. Bonds with partially ionic and partially covalent characters are called polar covalent bonds.

Ionic compounds conduct electricity when molten or in solution, typically not when solid. Ionic compounds generally have a high melting point, depending on the charge of the ions they consist of. The higher the charges the stronger the cohesive forces and the higher the melting point. They also tend to be soluble in water; the stronger the cohesive forces, the lower the solubility.

Overview

Atoms that have an almost full or almost empty valence shell tend to be very reactive. Strongly electronegative atoms (such as halogens) often have only one or two empty electron states in their valence shell, and frequently bond with other atoms or gain electrons to form anions. Weakly electronegative atoms (such as alkali metals) have relatively few valence electrons, which can easily be lost to strongly electronegative atoms. As a result, weakly electronegative atoms tend to distort their electron cloud and form cations.

Properties of ionic bonds

* They are considered to be among the strongest of all types of chemical bonds. This often causes ionic compounds to be very stable.
* Ionic bonds have high bond energy. Bond energy is the mean amount of energy required to break the bond in the gaseous state.
* Most ionic compounds exist in the form of a crystal structure, in which the ions occupy the corners of the crystal. Such a structure is called a crystal lattice.
* Ionic compounds lose their crystal lattice structure and break up into ions when dissolved in water or any other polar solvent. This process is called solvation. The presence of these free ions makes aqueous ionic compound solutions good conductors of electricity. The same occurs when the compounds are heated above their melting point in a process known as melting.

Details

Ionic bond is the type of linkage formed from the electrostatic attraction between oppositely charged ions in a chemical compound. Such a bond forms when the valence (outermost) electrons of one atom are transferred permanently to another atom. The atom that loses the electrons becomes a positively charged ion (cation), while the one that gains them becomes a negatively charged ion (anion). A brief treatment of ionic bonds follows. For full treatment, see chemical bonding: The formation of ionic bonds.

Ionic bonding results in compounds known as ionic, or electrovalent, compounds, which are best exemplified by the compounds formed between nonmetals and the alkali and alkaline-earth metals. In ionic crystalline solids of this kind, the electrostatic forces of attraction between opposite charges and repulsion between similar charges orient the ions in such a manner that every positive ion becomes surrounded by negative ions and vice versa. In short, the ions are so arranged that the positive and negative charges alternate and balance one another, the overall charge of the entire substance being zero. The magnitude of the electrostatic forces in ionic crystals is considerable. Accordingly, these substances tend to be hard and nonvolatile.

An ionic bond is actually the extreme case of a polar covalent bond, the latter resulting from unequal sharing of electrons rather than complete electron transfer. Ionic bonds typically form when the difference in the electronegativities of the two atoms is great, while covalent bonds form when the electronegativities are similar.

Additional Information

An electrovalent bond, also known as an ionic bond, is a type of chemical bond that occurs between two atoms when one atom transfers one or more of its electrons to another atom. This transfer of electrons leads to the formation of ions: the atom that loses electrons becomes a positively charged ion (cation), while the atom that gains electrons becomes a negatively charged ion (anion). The electrostatic attraction between these oppositely charged ions results in the formation of the electrovalent bond. Electrovalent bonds typically form between metals and non-metals, such as sodium (Na) and chlorine (Cl), where sodium donates an electron to chlorine, resulting in the formation of sodium chloride (NaCl).

Ionic-Bond-and-Ionic-Bond-Formation-Definition-Properties-in-Chemistry.png

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - V

1. In the euphoria after the Cold War, there was a misplaced notion that the UN could solve every problem anywhere. - Atal Bihari Vajpayee

2. You will never have great tennis champions from England because of the cold and dark, but most of all because people only care about the sport for two weeks a year, and then they're on to something else. There's just not a great love of the sport there. - Monica Seles

3. Overcoming the Cold War required courage from the people of Central and Eastern Europe and what was then the German Democratic Republic, but it also required the steadfastness of Western partner over many decades when many had long lost hope of integration of the two Germanys and Europe. - Angela Merkel

4. I mean, I have done scenes with animals, with owls, with bats, with cats, with special effects, with thespians, in the freezing cold, in the pouring rain, boiling hot; I've done press with every syndication, every country; I've done interviews with people dressed up as cows - there's honestly nothing that's gonna intimidate me! - Emma Watson

5. The threat today is not that of the 1930s. It's not big powers going to war with each other. The ravages which fundamentalist political ideology inflicted on the 20th century are memories. The Cold war is over. Europe is at peace, if not always diplomatically. - Tony Blair

6. The politicians always told us that the Cold War stand-off could only change by way of nuclear war. None of them believed that such systemic change was possible. - Lech Walesa

7. Even during the years of the Cold War, the intense confrontation between the Soviet Union and the United States, we always avoided any direct clash between our civilians and, most certainly, between our military. - Vladimir Putin

8. I would prefer to abandon the terminology of the past. 'Superpower' is something which we used during the cold war time. Why use it now? - Vladimir Putin.

Jai Ganesh · Jokes

Q: What do you get when you cross a hamburger with a computer?
A: A big mac!
* * *
Q: What did Sushi A say to Sushi B?
A: Wasabi!
* * *
Q: My bookish kid asked me why we have to go to B-Dubs for his birthday?
A: I told them it's "Where the Wild Wings Are".
* * *
Q: What did the hamburger say to the pickle?
A: You're dill-icious!
* * *
Q: What are the best days of the week in FastFoodland?
A: Fry-day and Sundae!
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10675. What does the term in Geography Climax community mean?

#10676. What does the term in Geography Coast mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5871. What does the adjective centripetal mean?

#5872. What does the adjective cerebral mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2530. Where are the Bitot's spots situated?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9810.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6304.

Jai Ganesh · Exercises

Hi,

2655.

Jai Ganesh · Dark Discussions at Cafe Infinity

2397) André Michel Lwoff

Gist:

Work

Bacteriophages are viruses that attach themselves to bacteria, emptying their genetic material into them. At times, many new phage are created quickly, while at other times, new phage are formed only several bacterial generations later. In the early 1950s André Lwoff successfully explained how this process, known as lysogeny, works. The bacteriophage's genes are incorporated into the bacteria's genetic material, but remain latent until a trigger factor causes new phage to be formed. Lwoff also showed that ultraviolet light can be one such factor.

Summary

André Lwoff (born May 8, 1902, Ainay-le-Château, France—died Sept. 30, 1994, Paris) was a French biologist who contributed to the understanding of lysogeny, in which a bacterial virus, or bacteriophage, infects bacteria and is transmitted to subsequent bacterial generations solely through the cell division of its host. Lwoff’s discoveries brought him (with François Jacob and Jacques Monod) the Nobel Prize for Medicine or Physiology in 1965.

Lwoff, born of Russian-Polish parents, was educated at the University of Paris. He spent most of his research career at the Pasteur Institute in Paris, serving on the board of directors from 1966 to 1972. From 1959 to 1968 he was also a professor of microbiology at the Sorbonne in Paris. When he retired from the Pasteur Institute in 1968, he served as director of the Cancer Research Institute at nearby Villejuif until 1972.

In his prizewinning research, Lwoff showed that, after infection, the virus is passed on to succeeding generations of bacteria in a noninfective form called a prophage. He demonstrated that under certain conditions this prophage gives rise to an infective form that causes lysis, or disintegration, of the bacterial cell; the viruses that are released upon the cell’s destruction are capable of infecting other bacterial hosts. Lwoff also discovered that vitamins serve both as growth factors for microbes and as coenzymes. Among his written works are Problems of Morphogenesis in Ciliates (1950) and Biological Order (1962).

After World War II Lwoff won the Medal of the Resistance for work in the French underground. He was also made an officer of the Legion of Honour.

Details

André Michel Lwoff (8 May 1902 – 30 September 1994) was a French microbiologist and Nobel laureate.

Education, early life and career

Lwoff was born in Ainay-le-Château, Allier, in Auvergne, France, into a Jewish family of Russian-Polish origin, the son of Marie (Siminovitch), an artist, and Solomon Lwoff, a psychiatrist. He joined the Institute Pasteur in Paris when he was 19 years old. In 1932, he finished his PhD and, with the help of a grant from the Rockefeller Foundation, moved with his wife and co-researcher Marguerite Lwoff to the Kaiser Wilhelm Institute for Medical Research of Heidelberg to Otto Meyerhof, where he did research on the development of flagellates. Another Rockefeller grant allowed him go to the University of Cambridge in 1937. In 1938, he was appointed departmental head at the Institut Pasteur, where he did groundbreaking research on bacteriophages, microbiota and on the poliovirus.

Awards and honors

He was awarded numerous prizes from the French Académie des Sciences, the Grand Prix Charles-Leopold Mayer, the Leeuwenhoek Medal of the Royal Netherlands Academy of Arts and Sciences in 1960 and the Keilin Medal of the British Biochemical Society in 1964. He was awarded a Nobel Prize in Medicine in 1965 for the discovery of the mechanism that some viruses (which he named proviruses) use to infect bacteria. He was an elected member of the United States National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society. Throughout his career he partnered with his wife Marguerite Lwoff although he gained considerably more recognition. Lwoff was elected a Foreign Member of the Royal Society in 1958. Lwoff was also president of the FEMS for a term of two years from 1974. The FEMS-Lwoff Award in microbiology is named in his honour.

Personal life

Lwoff was married to the microbiologist and virologist Marguerite Lwoff with whom he published many works. He was also a humanist against capital punishment.

Jai Ganesh · Dark Discussions at Cafe Infinity

Cold Quotes - IV

1. Living indoors without fresh air quickly poisons the blood and makes people feel tired and seedy when they don't know why. For myself, I sleep out of doors in winter as well as summer. I only feel tired or seedy when I have been indoors a lot. I only catch cold when I sleep in a room. - Robert Baden-Powell

2. Here at the Cold Spring Harbor Laboratory, we have genetically rearranged various viruses and bacteria as part of our medical research. In fact, we have been able to create entirely new types of DNA molecules by splicing together the genetic information from different organisms - recombinant DNA. - James D. Watson

3. If a patient is cold, if a patient is feverish, if a patient is faint, if he is sick after taking food, if he has a bed-sore, it is generally the fault not of the disease, but of the nursing. - Florence Nightingale

4. A small cold and cough can actually stop you from going where you are. - P. V. Sindhu

5. I can see that, without being excited, mathematics can look pointless and cold. - Maryam Mirzakhani

6. The smartest thing I did was to stop going online. I'm the sort of person who will just look for the negative - Michael really can't understand it, but that's just the way I am. And with my bipolar thing, that's poison. So I just stopped. Cold turkey. And it's so liberating. - Catherine Zeta-Jones

7. I get cold really quickly, but I don't care. I like weather. I never understand why people move someplace so that they can avoid weather. - Holly Hunter

8. Would not the child's heart break in despair when the first cold storm of the world sweeps over it, if the warm sunlight of love from the eyes of mother and father did not shine upon him like the soft reflection of divine light and love? - Max Muller.

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