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Topic Review

Ionizing Irradiations in Food Industry

The ionizing radiations are particles or waves containing enough energy to ionize the matter when coming in contact. Their mode of action in living cells involves either the direct destruction of nucleic acid or by creating free radicals that can attack the cellular components. This cellular destruction and inactivation can be used to reduce the microbial burden in food items to increase the shelf life and safety of food, meanwhile maintaining the quality of the product. Although this technology is accepted by more than 60 countries, some consumers are reluctant to buy such products thinking that radiations might have modified their food which can also induce changes in their body after consumption. The proper scientific communication regarding the safety of ionization irradiations can change consumer behavior, and it requires the collaboration of all stakeholders in the food production chain.

2.7K
05 Nov 2020

Topic Review

Tensile Testing

Tensile testing, also known as tension testing, is a fundamental materials science and engineering test in which a sample is subjected to a controlled tension until failure. Properties that are directly measured via a tensile test are ultimate tensile strength, breaking strength, maximum elongation and reduction in area. From these measurements the following properties can also be determined: Young's modulus, Poisson's ratio, yield strength, and strain-hardening characteristics. Uniaxial tensile testing is the most commonly used for obtaining the mechanical characteristics of isotropic materials. Some materials use biaxial tensile testing. The main difference between these testing machines being how load is applied on the materials.

2.7K
23 Nov 2022

Topic Review

A Message from Earth (2008)

A Message from Earth (AMFE) is a high-powered digital radio signal that was sent on 9 October 2008 towards Gliese 581c, a large terrestrial extrasolar planet orbiting within the Gliese 581 system. The signal is a digital time capsule containing 501 messages that were selected through a competition on the social networking site Bebo. The message was sent using the RT-70 radar telescope. The signal will reach the planet Gliese 581c in early 2029. More than half a million people including celebrities and politicians participated in the AMFE project, which was the world's first digital time capsule where the content was selected by the public. As of 1 February 2018, the message has traveled 62.43 trillion kilometers of the total 192 trillion kilometers, which is 33.5% of the distance to the Gliese 581 system. On 13 February 2015, scientists (including David Grinspoon, Seth Shostak, and David Brin) at an annual meeting of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea; That same week, a statement was released, signed by many in the SETI community, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent". However neither Frank Drake, nor Seth Shostak signed this appeal. On 28 March 2015, a related essay with some different point of view was written by Seth Shostak and published in The New York Times .

2.7K
21 Oct 2022

Topic Review

Gyrotrons are among the most powerful sources of coherent radiation that operate in CW and long pulse regimes in the sub-THz and the THz frequency ranges of the electromagnetic spectrum, i.e. between 0.3 THz and 3.0 THz (corresponding to wavelengths from 1.0 to 0.1 mm). This region, which spans between the frequency bands occupied by various electronic and photonic devices, respectively, is habitually called a THz power gap. The underlying mechanism of the operation of the gyrotron involves a formation of bunches of electrons gyrating in a helical electron beam and their synchronous interaction with a fast (i.e. having a superluminal phase velocity) electromagnetic wave, producing a bremsstrahlung radiation. In contrast to the slow-wave tubes, which utilize tiny structures with dimensions comparable to the wavelength of the radiation, the gyrotrons have a simpler resonant system (cavity resonator) with dimensions that are much greater than the wavelength. This allows much more powerful electron beams to be used and thus higher output powers to be achieved. Although in comparison with the classical microwave tubes the gyrotrons are characterized by greater volume and weight due to the presence of bulky parts (such as superconducting magnets and massive collectors where the energy of the spent electron beam is dissipated) they are much more compact and can easily be embedded in a sophisticated laboratory equipment (e.g. spectrometers, technological systems, etc.) than other devices such as free-electron lasers (FEL) and radiation sources based on electron accelerators. Nowadays, the gyrotrons are used as powerful sources of coherent radiation in the wide fields of high-power sub-THz and THz science and technologies [1][2][3].

2.6K
29 Oct 2020

Topic Review

In orbital mechanics (subfield of celestial mechanics), Gauss's method is used for preliminary orbit determination from at least three observations (more observations increases the accuracy of the determined orbit) of the orbiting body of interest at three different times. The required information are the times of observations, the position vectors of the observation points (in Equatorial Coordinate System), the direction cosine vector of the orbiting body from the observation points (from Topocentric Equatorial Coordinate System) and general physical data. Carl Friedrich Gauss developed important mathematical techniques (summed up in Gauss's methods) which were specifically used to determine the orbit of Ceres. The method shown following is the orbit determination of an orbiting body about the focal body where the observations were taken from, whereas the method for determining Ceres' orbit requires a bit more effort because the observations were taken from Earth while Ceres orbits the Sun.

2.6K
10 Nov 2022

Topic Review

In physics, a homogeneous material or system has the same properties at every point; it is uniform without irregularities. A uniform electric field (which has the same strength and the same direction at each point) would be compatible with homogeneity (all points experience the same physics). A material constructed with different constituents can be described as effectively homogeneous in the electromagnetic materials domain, when interacting with a directed radiation field (light, microwave frequencies, etc.). Mathematically, homogeneity has the connotation of invariance, as all components of the equation have the same degree of value whether or not each of these components are scaled to different values, for example, by multiplication or addition. Cumulative distribution fits this description. "The state of having identical cumulative distribution function or values".

2.6K
15 Nov 2022

Topic Review

In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Others define it as the magnitude of the reaction force exerted on a body by mechanisms that keep it in place: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of free fall, the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, and about one-sixth as much on the Moon. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (i.e. comparing and converting force weight in pounds to mass in kilograms and vice versa). Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to which gravity is modeled as a consequence of the curvature of spacetime. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.

2.6K
19 Oct 2022

Topic Review

Emergency Position-Indicating Radiobeacon Station

An emergency position-indicating radiobeacon (EPIRB) is a type of emergency locator beacon, a portable battery powered radio transmitter used in emergencies to locate airplanes, vessels, and persons in distress and in need of immediate rescue. In the event of an emergency, such as the ship sinking or an airplane crash, the transmitter is activated and begins transmitting a continuous radio signal which is used by search and rescue teams to quickly locate the emergency and render aid. The signal is detected by satellites operated by an international consortium of rescue services, COSPAS-SARSAT. The basic purpose of this system is to help rescuers find survivors within the so-called "golden day" (the first 24 hours following a traumatic event) during which the majority of survivors can usually be saved. The feature distinguishing modern EPIRBs, often called GPIRBs, from other types of emergency beacon is that it contains a GPS receiver and broadcasts its position, usually accurate within 100 metres (330 ft), to facilitate location. The standard frequency of a modern EPIRB is 406 MHz. It is an internationally regulated mobile radiocommunication service that aids search and rescue operations to detect and locate distressed boats, aircraft, and people. It is distinct from a Satellite emergency position-indicating radiobeacon station. The first form of these beacons was the 121.500 MHz ELT, which was designed as an automatic locator beacon for crashed military aircraft. These beacons were first used in the 1950s by the U.S. military and were mandated for use on many types of commercial and general aviation aircraft beginning in the early 1970s. The frequency and signal format used by the ELT beacons was not designed for satellite detection, which resulted in a system with poor location detection abilities and with long delays in detection of activated beacons. The satellite detection network was built after the ELT beacons were already in general use, with the first satellite not being launched until 1982, and even then, the satellites only provided detection, with location accuracy being roughly 20 kilometres (12 mi). The technology was later expanded to cover use on vessels at sea (EPIRB), individual persons (PLB and, starting in 2016, MSLD). All have migrated from using 121.500 MHz as their primary frequency to using 406 MHz, which was designed for satellite detection and location. Since the inception of Cospas-Sarsat in 1982, distress radiobeacons have assisted in the rescue of over 28,000 people in more than 7,000 distress situations. In 2010 alone, the system provided information used to rescue 2,388 persons in 641 distress situations.

2.5K
27 Oct 2022

Biography

Mani Lal Bhaumik

Mani Lal Bhaumik is an Indian-born American physicist and a bestselling author.[1] Bhaumik was born on March 30, 1931 in a small village in Siuri, Medinipore, West Bengal, India and attended the Krishnagang krishi silpa vidyalaya school.[2][3] As a teenager, Bhaumik spent some time with Mahatma Gandhi in his Mahisadal camp. He received a Bachelor of Science degree from Scottish Church College

2.5K
22 Nov 2022

Topic Review

Carbon-Burning Process

The carbon-burning process or carbon fusion is a set of nuclear fusion reactions that take place in the cores of massive stars (at least 8 [math]\displaystyle{ \begin{smallmatrix}M \odot\end{smallmatrix} }[/math] at birth) that combines carbon into other elements. It requires high temperatures (> 5×108 K or 50 keV) and densities (> 3×109 kg/m3). These figures for temperature and density are only a guide. More massive stars burn their nuclear fuel more quickly, since they have to offset greater gravitational forces to stay in (approximate) hydrostatic equilibrium. That generally means higher temperatures, although lower densities, than for less massive stars. To get the right figures for a particular mass, and a particular stage of evolution, it is necessary to use a numerical stellar model computed with computer algorithms. Such models are continually being refined based on nuclear physics experiments (which measure nuclear reaction rates) and astronomical observations (which include direct observation of mass loss, detection of nuclear products from spectrum observations after convection zones develop from the surface to fusion-burning regions – known as dredge-up events – and so bring nuclear products to the surface, and many other observations relevant to models).

2.5K
17 Nov 2022

Topic Review

Asymmetric Conductivity in Heavy-Fermion Metals

We consider the time reversal T and particle-antiparticle C symmetries that, being most fundamental, can be violated at microscopic level by a weak interaction. The notable example here is from condensed matter, where strongly correlated Fermi systems like HF metals and high-Tc superconductors (or HF compounds) exhibit C and T symmetries violation due to the so-called non-Fermi liquid (NFL) behavior rather than to microscopic inter-particle interaction. When a HF compound is near the topological fermion condensation quantum phase transition (FCQPT), it exhibits the NFL properties, so that the C symmetry breaks down, making the differential tunneling conductivity to be an asymmetric function of the bias voltage V. This asymmetry does not take place in normal metals, where Landau Fermi liquid (LFL) theory holds. Under the application of magnetic field, a HF compound transits to the LFL state, and σ(V) becomes symmetric function of V. These findings are in good agreement with experimental observations. We suggest that the same topological FCQPT defines the baryon asymmetry in the Universe. Thus, the most fundamental features of the nature are defined by its topological and symmetry properties.

2.5K
29 Apr 2021

Topic Review

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. These can detect a change in the 4 km mirror spacing of less than a ten-thousandth the charge diameter of a proton, equivalent to measuring the distance from Earth to Proxima Centauri (4.0208x1013km) with an accuracy smaller than the width of a human hair. The initial LIGO observatories were funded by the National Science Foundation (NSF) and were conceived, built, and are operated by Caltech and MIT. They collected data from 2002 to 2010 but no gravitational waves were detected. The Advanced LIGO Project to enhance the original LIGO detectors began in 2008 and continues to be supported by the NSF, with important contributions from the UK Science and Technology Facilities Council, the Max Planck Society of Germany, and the Australian Research Council. The improved detectors began operation in 2015. The detection of gravitational waves was reported in 2016 by the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration with the international participation of scientists from several universities and research institutions. Scientists involved in the project and the analysis of the data for gravitational-wave astronomy are organized by the LSC, which includes more than 1000 scientists worldwide, as well as 440,000 active Einstein@Home users (As of December 2016). LIGO is the largest and most ambitious project ever funded by the NSF. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry C. Barish "for decisive contributions to the LIGO detector and the observation of gravitational waves." "The Nobel Prize in Physics 2017". Nobel Foundation. https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html. As of March 2018, LIGO has made six detections of gravitational waves, of which the first five were colliding black-hole pairs. The sixth detected event, on August 17, 2017, was the first detection of a collision of two neutron stars, which simultaneously produced optical signals detectable by conventional telescopes.

2.5K
25 Oct 2022

Topic Review

The Hum is a phenomenon, or collection of phenomena, involving widespread reports of a persistent and invasive low-frequency humming, rumbling, or droning noise not audible to all people. Hums have been widely reported by national media in the UK and the United States. The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the "Bristol Hum" or the "Taos Hum". It is unclear whether it is a single phenomenon; different causes have been attributed. In some cases, it may be a manifestation of tinnitus.

2.4K
27 Oct 2022

Topic Review

In 1851, George Gabriel Stokes derived an expression, now known as Stokes's law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers in a viscous fluid. Stokes's law is derived by solving the Stokes flow limit for small Reynolds numbers of the Navier–Stokes equations.

2.4K
24 Nov 2022

Topic Review

Rooftop Photovoltaic Power Station

A rooftop photovoltaic power station, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters and other electrical accessories. Rooftop mounted systems are small compared to ground-mounted photovoltaic power stations with capacities in the megawatt range, hence being a form of distributed generation. Most rooftop PV stations in developed countries are Grid-connected photovoltaic power systems. Rooftop PV systems on residential buildings typically feature a capacity of about 5 to 20 kilowatts (kW), while those mounted on commercial buildings often reach 100 kilowatts to 1 Megawatt (MW). Very large roofs can house industrial scale PV systems in the range of 1-10 Megawatts.

2.4K
17 Nov 2022

Topic Review

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number. Even though the ultimate cause of drag is viscous friction, turbulent drag is independent of viscosity. Drag forces always tend to decrease fluid velocity relative to the solid object in the fluid's path.

2.4K
22 Nov 2022

Topic Review

Solid Oxide Electrolysis Cells and SOFCs Components

Solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs) are the leading high-temperature devices to realize the global “Hydrogen Economy”. These devices are inherently multi-material (ceramic and cermets). They have multi-scale, multilayer configurations (a few microns to hundreds of microns) and different morphology (porosity and densification) requirements for each layer. Adjacent layers should exhibit chemical and thermal compatibility and high-temperature mechanical stability.

2.4K
20 Oct 2022

Topic Review

Reconnaissance Satellite

A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications. The first generation type (i.e., Corona and Zenit) took photographs, then ejected canisters of photographic film which would descend back down into Earth's atmosphere. Corona capsules were retrieved in mid-air as they floated down on parachutes. Later, spacecraft had digital imaging systems and downloaded the images via encrypted radio links. In the United States, most information available is on programs that existed up to 1972, as this information has been declassified due to its age. Some information about programs prior to that time is still classified, and a small amount of information is available on subsequent missions. A few up-to-date reconnaissance satellite images have been declassified on occasion, or leaked, as in the case of KH-11 photographs which were sent to Jane's Defence Weekly in 1984.

2.4K
03 Nov 2022

Topic Review

In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. The scale is logarithmic and defined such that a magnitude 1 star is exactly 100 times brighter than a magnitude 6 star. Thus each step of one magnitude is [math]\displaystyle{ \sqrt{100} \approx 2.512 }[/math] times brighter than the next faintest. The brighter an object appears, the lower the value of its magnitude, with the brightest objects reaching negative values. Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude. The apparent magnitude (m) is the brightness of an object as it appears in the night sky from Earth. Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness. The absolute magnitude (M) describes the intrinsic luminosity emitted by an object and is defined to be equal to the apparent magnitude that the object would have if it were placed at a certain distance from Earth, 10 parsecs for stars. A more complex definition of absolute magnitude is used for planets and small Solar System bodies, based on its brightness at one astronomical unit from the observer and the Sun. The Sun has an apparent magnitude of −27 and Sirius, the brightest visible star in the night sky, −1.46. Venus at its brightest is -5. The International Space Station (ISS) sometimes reaches a magnitude of −6.

2.4K
28 Sep 2022

Topic Review

Space and Upper Atmosphere Research Commission

Established in its modern form on 16 September 1961 by an executive order of President of Pakistan, it is headquartered in Karachi, Sindh Province of Pakistan. Part of the Strategic Plans Division (SPD) of Pakistan Armed Forces, which is currently headquartered at the Chakalala Military District under the control of the Pakistan Air Force ; the space programmes recorded number of pioneering accomplishments in space flight during the initial years of its establishment. The country's first satellite, Badr-I, was built by the SUPARCO and launched from the Xichang Satellite Launch Center, China on July 16, 1990. However, during the meantime, the space programme suffered many setbacks, difficulties, and problems that partly slowed the progress of the space programme. The bureaucratic influence and politicization further lagged the space programme and many projects were cancelled by the superior authorities. Over the years, SUPARCO expanded and it now has several installations all over the country. It has multi-lateral and bilateral international agreements. SUPARCO has been quite dormant in recent years and also have failed to make any breakthroughs. SUPARCO's science and research is mainly focused and concentrated on understanding of the Solar system, Space weather, astrophysics, astronomical observation, climatic studies, space and telemedicine, remote sensing and the Earth observation.

2.3K
02 Nov 2022

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