Josephus refers to Magog son of Japheth as progenitor of Scythians, or peoples north of the Black Sea.[2] According to him, the Greeks called Scythia Magogia.[3]
- Josephus, Antiquities of the Jews, Book I, Chapter 6., Interhack Library
- ^ Josephus, Antiquities of the Jews, Book I, Chapter 6., Interhack Library
Vimāna are mythological flying palaces or chariots described in Hindu texts and Sanskrit epics. The “Pushpaka Vimana” of Ravana (who took it from Kubera; Rama returned it to Kubera) is the most quoted example of a vimana. Vimanas are also mentioned in Jain texts.
Science Newsfrom research organizations
A better way to control crystal vibrations
By introducing impurities to a material, researchers can control the speed and frequency of phonons, potentially leading to more energy-efficient devices.
Date:May 21, 2018Source:American Institute of PhysicsSummary:The vibrational motion of an atom in a crystal propagates to neighboring atoms, which leads to wavelike propagation of the vibrations throughout the crystal. The way in which these natural vibrations travel through the crystalline structure determine fundamental properties of the material. Now, researchers have shown that by swapping out just a small fraction of a material’s atoms with atoms of a different element, they can control the speed and frequencies of these vibrations.
FULL STORY
The vibrational motion of an atom in a crystal propagates to neighboring atoms, which leads to wavelike propagation of the vibrations throughout the crystal. The way in which these natural vibrations travel through the crystalline structure determine fundamental properties of the material. For example, these vibrations determine how well heat and electrons can traverse the material, and how the material interacts with light.
Now, researchers have shown that by swapping out just a small fraction of a material’s atoms with atoms of a different element, they can control the speed and frequencies of these vibrations. This demonstration, published in Applied Physics Letters, by AIP Publishing, provides a potentially simpler and cheaper way to tune a material’s properties, allowing for a wide range of new and more efficient devices, such as in solid-state lighting and electronics.
The natural vibrations of a crystalline material travel as particles called phonons. These phonons carry heat, scatter electrons, and affect electrons’ interactions with light. Previously, researchers controlled phonons by dividing the material into smaller pieces whose boundaries can scatter the phonons, limiting their movement. More recently, researchers have engineered nanoscale structures, such as nanowires, into the material to manipulate phonons’ speed and frequencies.
A team of researchers from the University of California, Riverside and the University of California, San Diego has now found that by doping — introducing different elements into the material — you can control phonons. The researchers doped aluminum oxide with neodymium, which replaces some of the aluminum atoms. Because neodymium is larger and more massive than aluminum, it alters the vibrational properties of the material, changing how phonons can travel.
“It introduces distortion to the lattice, which persists over a large distance compared to the atomic size, and affects the whole vibrational spectrum,” said Alexander Balandin of the University of California, Riverside.
Using a new method of producing evenly doped crystals and new sensitive instruments to measure the phonon spectrum, the researchers showed, for the first time, that even a small number of certain dopants can have a big impact. “This approach provides a new way of tuning the vibrational spectrum of materials,” Balandin said.
Previously, researchers assumed that any significant effect on phonons would require a very high concentration of dopants. But, the team found that doped aluminum oxide with a neodymium density of only 0.1 percent was enough to lower the phonon frequency by a few gigahertz and the speed by 600 meters per second.
Boosting phonon speeds increases a material’s thermal conductivity, allowing tiny transistors to cool faster. Slowing phonons, on the other hand, would be useful in making more efficient thermoelectric devices, which convert electricity into heat and vice versa. Furthermore, in optical devices such as light-emitting diodes, slowing phonons and suppressing phonon interactions with electrons would mean more energy is used to produce photons (light) and less is lost as heat.
The researchers are now applying their strategy to other dopants and materials, such as gallium arsenide, with an eye toward developing energy-efficient devices, Balandin said.
Story Source:
Materials provided by American Institute of Physics. Note: Content may be edited for style and length.
Journal Reference:
- Fariborz Kargar, Elias H. Penilla, Ece Aytan, Jacob S. Lewis, Javier E. Garay, Alexander A. Balandin. Acoustic phonon spectrum engineering in bulk crystals via incorporation of dopant atoms. Applied Physics Letters, 2018; 112 (19): 191902 DOI: 10.1063/1.5030558
New way to absorb electromagnetic radiation demonstrated
Scientists show that it is possible to fully absorb electromagnetic radiation using an anisotropic crystal
Date:January 14, 2016Source:Moscow Institute of Physics and TechnologySummary:It is possible to fully absorb electromagnetic radiation using an anisotropic crystal, report scientists. Electromagnetic energy harvesting in the visible spectrum is very important for photovoltaics — the conversion of solar energy into direct current electricity. Absorbing materials in the microwave range of frequencies have an application that is equally as important, say scientists who are now able to reduce the radar visibility of an aircraft.
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A team of authors from MIPT, Kansas State University, and the U.S. Naval Research Laboratory have demonstrated that it is possible to fully absorb electromagnetic radiation using an anisotropic crystal. The observations are of fundamental importance for electrodynamics and will provide researchers with an entirely new method of absorbing the energy of electromagnetic waves. The paper has been published in Physical Review B.
Effective absorption of the energy of electromagnetic radiation is the cornerstone of a wide range of practical applications. Electromagnetic energy harvesting in the visible spectrum is very important for photovoltaics — the conversion of solar energy into direct current electricity. Absorbing materials in the microwave range of frequencies have an application that is equally as important — they are able to reduce the radar visibility of an aircraft. Effective absorption of electromagnetic waves is also important for use in sensing, nanochemistry, and photodynamic therapy.
A classic example of an electromagnetic absorber that is familiar to many people is ordinary black paint. It looks black because a significant amount of the light that falls on it is absorbed in the layer of paint and does not reach the observer. However, black paint is a relatively poor absorber — a certain amount of energy from the incident light (typically a few percent) is still reflected back into the surrounding space.
In order to absorb incident radiation completely, we need to use interference. A layer of absorbing material is placed on a reflective substrate or is combined with a specially designed anti-reflective coating. According to the laws of classical electrodynamics, there emerges a sequence of waves having different amplitudes and phases that are reflected from the structure. Such series of reflections also occurs in a soap film. When white light falls on the film, we see reflected light of a certain colour depending on the thickness of the film. When light falls on an absorbing system, if the coating parameters have been chosen properly, the reflected waves cancel each other out — reflected radiation vanishes completely and the absorption becomes perfect. This type of interference is called destructive interference. Absorption in such systems is very sensitive to the geometry of the structure. With the slightest variation in thickness or refractive indices of the layers the absorption is no longer perfect and reflected radiation reappears.
In their paper, the researchers from Russia and the US showed that destructive interference is not a necessary requirement for perfect absorption. The scientists used an anisotropic crystal — hexagonal boron nitride — as their specific absorbing system.
This medium belongs to the class of unique van der Waals crystals which consist of atomic layers bound together by van der Waals forces from adjacent layers. Van der Waals forces occur between atoms and molecules that are electrically neutral but possess a dipole moment — the charges in them are not uniformly distributed. Due to this arrangement of the lattice, the dielectric permittivity of the crystal in the mid-infrared range (wavelength of about 10 microns) differs considerably for the in- and out-of-plane directions — it becomes anisotropic and is not described by a single number, but by a tensor — a matrix of numbers (each number is responsible for its own direction). It is the dielectric permittivity tensor that determines how light is reflected from the surface of any substance.
Due to the unusual properties of its crystal lattice, hexagonal boron nitride has already found a number of applications in optics and nanoelectronics. In this particular case, the strong anisotropy of dielectric permittivity works in our favour and helps to absorb electromagnetic waves. Incident infrared radiation at a certain wavelength enters the crystal without reflections and is completely absorbed within the medium. There is no need for any anti-reflective layers or a substrate to provide destructive interference — reflected radiation simply does not occur, unlike in an isotropic (i.e. identical in all directions) absorbing medium.
“The ability to fully absorb electromagnetic radiation is one of the key areas of focus in electrodynamics. It is believed that destructive interference is needed to do this, which therefore requires the use of anti-reflective coatings, substrates and other structures. Our observations indicate that interference is not a compulsory requirement and perfect absorption can be achieved using simpler systems,” says Denis Baranov, the corresponding author of the paper.
For the experimental observation of the predicted phenomenon, the researchers grew an optically thick sample of hexagonal boron nitride and measured the reflectance spectrum in the mid-infrared range. At the wavelengths and angles of incidence predicted analytically, the authors observed a strong drop in the reflected signal — less than 10-4 of the incident energy was reflected from the system. In other words, more than 99.99% of the incident wave energy was absorbed in the anisotropic crystal.
The approach proposed by the researchers is currently only able to achieve perfect absorption for a fixed wavelength and angle of incidence, both of which are determined by the electronic properties of the material. However, for practical applications the possibility of energy absorption in a wide range of wavelengths and angles of incidence is of more interest. The use of alternative strongly anisotropic materials such as biaxial absorbing media will likely help to bypass these limitations in the future, making this approach more flexible.
Nevertheless, this experiment is of interest from a fundamental point of view. It demonstrates that it is possible to completely absorb radiation without the incorporation of destructive interference. This effect offers a new tool for controlling electromagnetic absorption. In the future, these materials could give a greater level of flexibility when designing absorbing devices and sensors that operate in the infrared range.
Story Source:
Materials provided by Moscow Institute of Physics and Technology. Note: Content may be edited for style and length.
Journal Reference:
- D. G. Baranov, J. H. Edgar, Tim Hoffman, Nabil Bassim, Joshua D. Caldwell. Perfect interferenceless absorption at infrared frequencies by a van der Waals crystal. Physical Review B, 2015; 92 (20) DOI: 10.1103/PhysRevB.92.201405
The 5G appeal
Scientists and doctors call for a moratorium on the roll-out of 5G.
5G will substantially increase exposure to radiofrequency electromagnetic fields RF-EMF, that has been proven to be harmful for humans and the environment.
International Appeal
Scientists call for Protection from Non-ionizing Electromagnetic Field Exposure
Non-ionizing radiation includes the spectrum of ultraviolet (UV), visible light, infrared (IR), microwave (MW), radio frequency (RF), and extremely low frequency (ELF).
Health risks from radiofrequency radiation, including 5G, should be assessed by experts with no conflicts of interest
Lennart Hardell and Michael Carlberg
Additional article information Associated Data Data Availability Statement
Abstract The fifth generation, 5G, of radiofrequency (RF) radiation is about to be implemented globally without investigating the risks to human health and the environment. This has created debate among concerned individuals in numerous countries. In an appeal to the European Union (EU) in September 2017, currently endorsed by >390 scientists and medical doctors, a moratorium on 5G deployment was requested until proper scientific evaluation of potential negative consequences has been conducted. This request has not been acknowledged by the EU. The evaluation of RF radiation health risks from 5G technology is ignored in a report by a government expert group in Switzerland and a recent publication from The International Commission on Non-Ionizing Radiation Protection. Conflicts of interest and ties to the industry seem to have contributed to the biased reports. The lack of proper unbiased risk evaluation of the 5G technology places populations at risk. Furthermore, there seems to be a cartel of individuals monopolizing evaluation committees, thus reinforcing the no-risk paradigm. We believe that this activity should qualify as scientific misconduct.Keywords: Switzerland, European Union, World Health Organization, International Commission on Non-Ionizing Radiation Protection, Scientific Committee on Emerging and Newly Identified Health Risks, Swedish Radiation Safety Authority, 5G, electromagnetic field, appeals, moratorium, microwave radiation, radiofrequency electromagnetic field, health risks, non-ionizing radiation guidelines, conflicts of interest
What 5G means for our health
Mobile speeds are soon to reach ten times today’s performance. Swinburne researchers are racing to ensure that the technology’s impact on our bodies is understood.
Fast 5G networks are supposed to take hold in 2019, as phones, providers and networks all begin to come online. Behind the scenes, studies modelling the absorption patterns of 5G electromagnetic energy in human tissue, authored by Professor Andrew Wood’s Swinburne team, has helped form the basis for international discussions on safety regulation and design.
Wood’s team, which is part of the multi-institutional Australian Centre for Electromagnetic Bioeffects Research (ACEBR), is a key contributor to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) review, which is expected to be released in 2019.
“We believe the main biological effect of the electromagnetic radiation from mobile phones is a rise in temperature,” Wood explains. “There are also concerns that there could be more subtle effects, such as links between long-term exposure and certain types of cancer, but while there is some evidence from epidemiological and animal studies, these remain controversial.”
“As the frequency goes up, the depth of penetration into biological tissues goes down, so the skin and eyes, rather than the brain, become the main organs of health concern,” Wood says. “The major hurdle is that the power levels involved in mobile and wireless telecommunications are incredibly low, which, at most, produce temperature rises in tissue of a few tenths of a degree. Picking up unambiguous biological changes is therefore very difficult.”
However, it will be important to balance the risk and reward, he notes. “Wireless technologies bring enormous benefits, and being over-cautious would potentially deny these benefits to needy communities.”
ICTHEALTH
Is 5G bad for your health? It’s complicated, say researchers
07 October 2019by Tom Cassauwers
In September 2017, doctors and scientists launched the 5G Appeal, a petition which calls for the EU to impose a moratorium on 5G rollout, citing imminent health dangers like increased cancer risks, cellular stress and genetic damage. The petition now has more than 250 signatories. In March this year, then Brussels minister of environment Céline Fremault blocked a 5G rollout saying she wouldn’t turn the city’s inhabitants into ‘laboratory mice’. In Bern, Switzerland, a protest in May led some administrative areas to block the construction of 5G antennas.
So how different is 5G and could it impact our health? The reality, experts say, is complex.
‘We have been involved in hundreds of studies about electromagnetic radiation and human health,’ said Professor Niels Kuster, founder and director of the Swiss IT’IS Foundation. He was project coordinator for ARIMMORA, a study into the relation between the electromagnetic radiation emitted by power lines and childhood leukaemia.
Both mobile phones and telecom antennas emit electromagnetic radiation, regardless of what network generation they are used for. They send out non-ionising radiation, which is located at the lower end of the frequency spectrum. Most electrical gear emits this type of radiation, from microwave ovens to power lines.
Non-ionising radiation has completely different health effects from ionising radiation, which is higher up the spectrum and includes X-Rays or nuclear radiation, which have proven harmful effects for human health.
Radiation Non-ionising radiation can affect us in two ways, according to Prof. Kuster. Just like a microwave oven heats food using non-ionising radiation, telecom gear can do the same to the human body if it emits too much.
Some animal or lab-based cell studies have shown certain negative health effects from radiation. This eventually led the International Agency for Research on Cancer (IARC) to classify electromagnetic radiation as ‘possibly carcinogenic to humans.’
Millimetre waves
Ever since we’ve had mobile phones, there have been concerns about their negative health effects. In most areas, the 5G debate is a continuation of all of this, which is logical. The radiation 5G emits will largely be the same as it was for 4G, 3G and 2G before, except for one area: millimetre waves.
These waves are higher up the spectrum than the frequencies we have so far used for mobile telecommunications, although they are still non-ionising radiation.
Millimetre waves are a sub-technology of 5G, which can transfer more information, although for shorter distances. For now, these frequencies aren’t being implemented or even auctioned in Europe, although in the US operators have been using them to build their 5G networks. There has been little research about their health effects.
We know, for example, that they don’t penetrate our skin as much as lower frequency waves, yet that could also mean a different risk assessment, with more attention placed on the skin.
‘I don’t claim we need to be concerned about millimetre wave exposure,’ said Prof. Kuster. ‘But it’s irresponsible to not have much data and expose large groups of people to these fields. So, there should be more investment into tests about this.’
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