Wave-generated 'white hole' boosts Hawking radiation theory: research

In 1974, Hawking predicted that black holes--often thought of having gravitational pulls so strong that nothing escapes from them--emit a very weak level of radiation. According to the theory, pairs of photons are torn apart by a black hole's gravitational field--one photon falls into the black hole, but the other escapes as a form of radiation.

In results outlined in the latest issue ofPhysical Review Letters, a team of UBC researchers led by international postdoctoral researcher Silke Weinfurtner put the test to Hawking's theory by creating a 'white hole' in a six-metre-long flume of flowing water.

Placing an airplane wing-shaped obstacle in the path of the flowing water created a region of high-velocity flow which blocked surface waves, generated downstream, from traveling upstream. The obstruction simulated a white hole, the temporal reverse of a black hole.

The shallow surface waves divided into pairs of deep-water waves, analogous to the photon pairs featured in Hawking's theory. Like inblack holes, they showed that the analog would also emit a thermal spectrum of radiation.

"While this creative simulation obviously doesn't prove Hawking's theory, it does show that his ideas apply broadly,"says UBCtheoretical physicistWilliam Unruh, part of the team which included European Union Marie Curie Fellow Weinfurtner, undergraduate student Matthew Penrice, Civil Engineering post doctoral fellow Edmund Tedford, and Canada Research Chair in Environmental Fluid Mechanics Gregory Lawrence.

"This experiment also exemplifies all of the strengths of UBC's research enterprise--the involvement of students, our international outreach and connections, and a very open, collaborative way of looking at scientific questions,"says Unruh.

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New territory in nuclear fission explored with ISOLDE

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In nuclearfission, the nucleus splits into two fragments (daughter nuclei), releasing a huge amount of energy.Nuclear fissionis exploited in power plants to produce energy. From the fundamental research point of view, fission is not yet fully understood decades after its discovery and its properties can still surprise nuclear physicists.

The way the process occurs can tell us a lot about the internal structure of the nucleus and the interactions taking place inside the complex nuclear structure. In particular, processes in which fission is observed at an energy just above the minimum required are the most likely to tell us which quantum corrections should be applied to the liquid-drop model (classical description) to fully understand nuclear behaviour.

At ISOLDE, an international collaboration involving scientists from nine countries has been studying the 180Tl isotope. Via radioactive decay, the thallium isotope transforms into the 180 isotope of mercury (180Hg), which subsequently fissions.“According to previous experiments and related theoretical models, we were expecting a symmetric mass distribution of the fission fragments,” says A. N. Andreyev, the principal investigator from the KU Leuven team (presently working at the University of the West of Scotland).“However, we measured an asymmetric mass distribution of the fission fragments. This discrepancy is leading us to rethink our theories on the interplay between the macroscopic liquid-drop model and the microscopic single-particle shell corrections to apply in the description of these nuclei.”

The result follows other attempts to understand similar fission processes that were made about 20 years ago by scientists in Dubna.“Previous experiments had to deal with huge amounts of contaminants in the samples of the parent element. Using ISOLDE’s unique laser ion source that makes it possible to selectively ionize elements, we can obtain a high-purity sample of 180Tl (T1/2=1.1 s). This allows us to determine with an unprecedented accuracy the different branching ratios of the various decays,” explains Andreyev.

The unexpected result of ISOLDE’s experiment will stimulate the development of new theoretical approaches to the fission process.“We have worked on a new description of the internal structure of the Hg nucleus, which is able to predict the asymmetric mass splits that we have observed. Further experiments and new theories are needed to elucidate the dynamics of the fission processes, at least for nuclei located in the region around thallium in the nuclei chart,"concludes Mark Huyse, another member of the team from KU Leuven.

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'Electron vortices' have the potential to increase conventional microscopes' capabilities

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The development opens the possibility of adaptingtransmission electron microscopy, which can see tinier details thanoptical microscopyand can study a wider range of materials than scanning probe microscopy, for quick and inexpensive imaging of a larger set of magnetic and biological materials with atomic-scale resolution.

"The spiral shape andangular momentumof these electrons will let us look at a greater variety of materials in ways that were previously inaccessible to TEM users,"said Ben McMorran, one of the authors of the forthcoming research paper."Outfitting a TEM with a nanograting like we used in our experiment could be a low-cost way to dramatically expand the microscope's capabilities."

Although NIST researchers were not the first to manipulate a beam of electrons in this way, their device was much smaller, separated the fanned out beams 10 times more widely than previous experiments, and spun up the electrons with 100 times the orbital momentum. This increase in orbital momentum enabled them to determine that the electron corkscrew, while remarkably stable, gradually spreads out over time. The group's work will be reported in the Jan. 14, 2011, issue of the journalScience.

Electrons in electron beams behave like rippling waves that move through space like a wave of light, McMorran said. Unlike wavefronts of light, which are hundreds of nanometers apart (a distance called the wavelength), the wavelengths of electrons are measured in picometers (trillionths of a meter), which make them excellent for imaging tiny objects such as atoms because of their comparable dimensions. In an ordinary electron beam, the electron wavefronts are relatively flat and uniform.

To spin up the electrons and give them orbital momentum, the NIST researchers twisted the flat electron wavefronts into a fan of helices using a very thin film with a 5-micron-diameter pattern of nanoscale slits. The pattern affects the shape of the electron wavefronts passing through it, amplifying some of the wave peaks and eliminating some of the wave valleys, to create a spiral form similar to a pasta maker extruding rotini. This method produces several electron beams fanning out in different directions, with each beam made of electrons that orbit around the direction of the beam.

The researchers knew they were successful because when they detected the electrons– which were recorded as millions of individual particles building up an image– they had formed donut-like or spiral patterns, indicating a helical shape.

Transmission electron microscopy creates images by shooting trillions of electrons through an object and measuring their absorption, deflection and energy loss. TEMs equipped with corkscrew electron beams could also monitor how the particles exert torque on a material and how a material affects the spiral shape of transmitted electrons, helping scientists build a more complete picture of the material's structure.

For example, these special electron beams have the potential to help obtain more information from magnetic materials.
"Magnetism, at its most fundamental, results from charges spinning and orbiting,"McMorran said."So anelectron beamthat itself carries angular momentum makes a good tool for probing magnetic materials."

A beam of corkscrew-shaped electrons, when interacting with a specimen, can exert torque on the material, by exchanging angular momentum with its atoms. In this way, the corkscrew electrons could obtain more information in the process than beams with ordinary electrons, which do not carry this orbital angular momentum.

This technique could also help improve TEM images of transparent objects like biological specimens. Biological material can be difficult to image in ordinary TEMs because electrons pass through it without deflecting. But by using corkscrew electron beams, researchers hope to provide high-contrast, high-resolution images of biological samples by looking at how the spiral wavefronts get distorted as they pass through such transparent objects.

While these imaging applications have not yet been demonstrated, producing corkscrew electrons with nanogratings in a TEM provides a significant step toward expanding the capabilities of existing microscopes.

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New molecular imaging technologies for detecting cellular processes

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The work carried out by these scientists has ranged from the initial design of an electronic architecture for gamma ray detectors to industry transfer of a completescanner, after having adequately validated a prototype through experimental studies at the Gregorio Marañón Hospital. The results of this research, headed by professors Juan José Vaquero and Manuel Desco, from the Department of de Bioengineering and Aerospace Engineering at UC3M, have been recently published in the journalsIEEE Transactions on Nuclear Science(two articles) andPhysics in Medicine and Biology(one article).

The electronic technology equipment designed by the researchers- which is in patent process-is based on molecular imaging, a type of biomedical imaging capable of detecting livecellular processes."These techniques differ from conventional medical imaging in that the information they show is function not form, which means that they are capable of showing the malfunctioning of an organ before the malfunction turns into an anatomical change", Juan José Vaquero explained."In other words", he added,"they allow for earlier detection of a possible anomaly, which enormously facilitates treatment". In addition to making an earlier diagnosis possible these types of scanners are used in biomedical research and in pharmaceutical laboratories, for example, to speed up the development of new medicines

The growth of molecular imaging in recent years, according to experts, is chiefly due to the narrowing of the gap between molecular biology and imaging technologies, and it is expected that an acceleration of the transfer of these techniques to clinical practice will be produced. In fact, some of the characteristics of molecular imaging itself are already present in techniques for clinical use in humans such as nuclear medicine imaging or magnetic resonance imaging."Computerized tomograhy by a sole photon emission, better known by its Anglo-Saxon acronym SPECT, is probably the most widespread molecular imagining technique in clinical practice, and from there stems the interest in having preclinical systems which allow the study of human illnesses to be carried out on animals", Professor Manuel Desco pointed out.

The Department of Bioengineering and Aerospace Engineering at UC3M focuses on the development of preclinical molecular imaging scanners used in research work on animals. Obtaining good quality in these applications constitutes a much more difficult technical challenge than with humans, due to the large difference in size (with animals being approximately 280 times smaller). The research group has completed the development of SPECT type of system for laboratory animals at University installation, which has features placing it among the top on an international scale in terms of facilities and cost.

This UC3M research group, in addition to carrying out research which leads to scientific publications, focuses a large part of its interest on technology transfer so that it can be commercialized. The company, SEDECAL, the largest domestic manufacturer and exporter of electro-medical imaging equipment, is going to commercialize the system in the immediate future. The research team from this Madrid public university continues to work on new developments in the area of technology, in close contact with national industry. Part of the developments are under the framework of the AMIT (AdvancedMolecular ImagingTechnologies) Project from the most recent CENIT public funding, whose scientific coordination oversees this equipment at the UC3M.

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Car batteries powered by relativity

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The physicists and chemists who performed the study– Rajeev Ahuja, Andreas Blomqvist, and Peter Larsson from Uppsala University in Uppsala, Sweden, and Pekka Pyykkö and Patryk Zaleski-Ejgierd from the University of Helsinki– have published their results in a recent issue ofPhysical Review Letters.

"This is a new, well-documented case of 'everyday relativity,'"Pyykkö toldPhysOrg.com. As the scientists noted in their study, the finding essentially means that"cars start due to relativity."

The lead-acid battery is the oldest type of rechargeable battery, with the main component being lead. With an atomic number of 82, lead is a heavy element. In general, relativistic effects emerge when fast electrons move near a heavy nucleus, such as that of lead. These relativistic effects include anything that depends on the speed of light (or from a mathematical perspective, anything that involves the Dirac or Schrödinger equations).

The lead-acid battery contains a positive electrode made of lead dioxide, a negative electrode made of metallic lead, and an electrolyte made of sulfuric acid. Through their calculations, the scientists found that the battery’s relativistic effects arise mainly from the lead dioxide in the positive electrode, and partly from the lead sulfate created during chemical reactions.

The discovery of relativistic effects in the lead-acid battery also sheds some light on why no corresponding“tin battery” exists. In the periodic table, tin is located directly above lead and has an atomic number of 50, making it lighter than lead. According to the scientists’ calculations, a tin battery would basically be a lead battery with very minimal relativistic effects. Although tin and lead have similar nonrelativistic energy values, tin’s small relativistic effects prohibit it from being used in an efficient battery.

As the scientists noted, relativistic effects have been found in other areas, such as the perennial yellow color of gold and the liquidity of mercury, although the latter is still not very well proven.

Overall, the scientists predicted that this understanding ofrelativity’s importance to the lead-acid battery will probably not help researchers improve thebattery; however, the insight could be useful for exploring better alternatives, especially those that involve any sixth period element (found in the sixth row of the periodic table, like lead).

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A breakthrough for terahertz semiconductor lasers

Light is nothing short of awesome -- it inspires painters and guides a midnight trip to the bathroom. Butvisible lightoccupies just one portion of theelectromagnetic spectrum. Farther along the spectrum,radio wavesenable the world to talk wirelessly. X-rays makemedical imagingpossible. Each region of the spectrum promises new technologies, if it can be harnessed.

A team led by Sushil Kumar, assistant professor of electrical and computer engineering, is helping to develop a largely unexploited region of the electromagnetic spectrum.

Working with researchers at MIT and Sandia National Laboratories, Kumar has made a semiconductor laser, also called a quantum-cascade laser (QCL), that emits terahertz (THz)radiationat higher operating temperatures than ever before. He reported his achievement recently inNature Physics.

The breakthrough moves the technology closer to applications in disease diagnosis; quality control in drug manufacturing; detection of concealed weapons, drugs and explosives; the remote sensing of the earth’s atmosphere; and the study of star and galaxy formation.

It also erases doubts that there is a maximum temperature at which coherent THz radiation can be generated from semiconductor chips.

“Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field,” the researchers wrote inNature Physics.

Progress toward a room-temperature THz laser

“Thus far, their maximum operating temperature has been empirically limited, {which} has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present.”

QCLs are attractive because of their size. Traditionally high-power THz radiation was produced by bulky, expensive lasers fueled by a molecular gas such as methane. Advances in semiconductors have made QCLs as tiny as the diode in a laser pointer, but the lasers require temperatures almost 200 degrees below zero to emit terahertz radiation.

His team has raised the QCL’s operating temperature, says Kumar, by exploiting its“tunability.”

The frequency of light generated in any material is naturally fixed and is determined by the spacing of energy levels at the molecular level. But the spacing of the QCL’s energy levels can be tuned, allowing the laser to emit THz radiation. QCLs are made of alternating layers of different semiconductors (such as gallium arsenide and aluminum gallium arsenide) because the thickness of each layer determines the spacing between the energy levels.

Proper tuning, says Kumar, is achieved by injecting electrons into the correct energy level of the semiconductor layers. The process is analogous to fuel injection in an automobile. Electrons (the fuel) hop from one energy level to another in the layered semiconductor to generate power in the form of THz photons.

But the THz photon energy, says Kumar, is much smaller than the thermal energy of electrons at room temperature.

“This makes it very difficult to selectively put electrons in the required energy levels for them to emit THz photons.”

Fuel injection -- using electrons

To raise QCLs’ operating temperature, Kumar’s group has harnessed the“relaxation process.” Electrons tend to dissipate their energy in the form of lattice vibrations at higher temperatures, called“non-radiative relaxation,” which is typically detrimental to laser operation.

Kumar’s group used this natural phenomenon in a controlled manner to inject electrons into the correctenergy levels. This scattering-assisted injection technique is less sensitive to the thermal energy of electrons and remains efficient at high temperatures as well.

“This tremendous achievement is very promising for the future of THz laser technologies,” says Alessandro Tredicucci, research director at the National Research Council of Italy and inventor of the first THz QCL.“It shows that the power of quantum design has yet to be fully tapped and encourages people to look for new materials and structures whose relaxation times can be slowed down.”

“It is remarkable how the science of QCLs has progressed hand-in-hand with advancements in crystal growth technology to make such an incredibly complex semiconductor device possible,” says John Reno of Sandia’s Center for Integrated Nanotechnologies, who coauthored theNature Physicsarticle.

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Physicists discover how the outer shell of a hornet can harvest solar power

"The interesting thing here is that a living biological creature does a thing like that,"says physicist Prof. David Bergman of Tel Aviv University's School of Physics and Astronomy, who was part of the team that made discovery."The hornet may have discovered things we do not yet know."In partnership with the late Prof. Jacob Ishay of the university's Sackler Faculty of Medicine, Prof. Bergman and his doctoral candidate Marian Plotkin engaged in a truly interdisciplinary research project to explain the biological processes that turn a hornet's abdomen intosolar cells.

The research team made the discovery several years ago, and recently tried to mimic it. The results show that the hornet's body shell, orexoskeleton, is able to harvest solarenergy. They were recently published in the German journalNaturwissenschaften.

Discovering a new system for renewable energy?

Previously, entomologists noted that Orientalwasps, unlike other wasps and bees, are active in the afternoon rather than the morning when the sun is just rising. They also noticed that the hornet digs more intensely as the sun's intensity increases.

Taking this information to the lab, the Tel Aviv University team studied weather conditions like temperature, humidity andsolar radiationto determine if and how these factors also affected the hornet's behavior, but found that UVB radiation alone dictated the change.

In the course of their research, the Tel Aviv University team also found that the yellow and brown stripes on the hornet abdomen enable a photo-voltaic effect: the brown and yellow stripes on the hornet abdomen can absorb solar radiation, and the yellow pigment transforms that into electric power.

The team determined that the brown shell of the hornet was made from grooves that split light into diverging beams. The yellow stripe on the abdomen is made from pinhole depressions, and contains a pigment called xanthopterin. Together, the light diverging grooves, pinhole depressions and xanthopterin change light into electrical energy. The shell traps the light and the pigment does the conversion.

A biological heat pump

The researchers also found a number of energy processes unique to the insect. Like air conditioners and refrigerators, the hornet has a well-developed heat pump system in its body which keeps it cooler than the outside temperature while it forages in the sun. This is something that's not easy to do, says Prof. Bergman.

To see if the solar collecting prowess of the hornet could be duplicated, the team imitated the structure of the hornet's body but had poor results in achieving the same high efficiency rates of energy collection. In the future, they plan to refine the model to see if this"bio-mimicry"can give clues to novel renewable energy solutions.

The research team also discovered that hornets use finely honed acoustic signals to guide them so they can build their combs with extraordinary precision in total darkness. Bees can at least see what they are doing, explains Prof. Bergman, but hornets cannot -- it's totally dark inside a hornet nest.

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