bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulations of a cylinder wake under a strong axial magnetic field
Authors: Dousset Vincent , Pothérat Alban
Published: January 2008

We study the flow of a liquid metal in a square duct past a circular cylinder in a strong externally imposed magnetic field. In these conditions, the flow is quasi-two-dimensional, which allows us to model it using a two-dimensional (2D) model. We perform a parametric study by varying the two control parameters Re and Ha (Ha2 is the ratio of Lorentz to viscous forces) in the ranges [0…6000] and [0…2160], respectively. The flow is found to exhibit a sequence of four regimes. The first three regimes are similar to those of the non-magnetohydrodynamic (non-MHD) 2D circular wake, with transitions controlled by the friction parameter Re∕Ha. The fourth one is characterized by vortices raising from boundary layer separations at the duct side walls, which strongly disturbs the Kármán vortex street. This provides the first explanation for the breakup of the 2D Kármán vortex street first observed experimentally by Frank, Barleon, and Müller [Phys. Fluids 13, 2287 (2001)]. We also show that, for high values of Ha (Ha⩾1120), the transition to the fourth regime occurs for Re∝0.56Ha, and that it is accompanied by a sudden drop in the Strouhal number. In the first three regimes, we show that the drag coefficient and the length of the steady recirculation regions located behind the cylinder are controlled by the parameter Re∕Ha4∕5. Also, the free shear layer that separates the recirculation region from the free stream is similar to a free MHD parallel layer, with a thickness of the order of Ha−1∕2 that is quite different to that of the non-MHD case, and therefore strongly influences the dynamics of this region. We also present one case at Re=3×104 and Ha=1120, where this layer undergoes an instability of the Kelvin–Helmholtz-type.
Physical insights from a penetration depth model of optically pumped NMR
Authors: Mui Stacy , Ramaswamy Kannan , Hayes Sophia E.
Published: January 2008

A model of optically pumped NMR (OPNMR) behavior in GaAs that connects the photon energy dependence of the OPNMR signal intensity for Ga69 with different polarizations of light has been developed. Inputs to this model include experimental conditions—external magnetic field (B0), temperature (T), and optical pumping parameters (τL, laser helicity)—as well as parameters that arise from sample-specific characteristics—electron spin lifetime (T1e), electron lifetime (τe), electron-nuclear correlation time (τc), and sample thickness (z). These various inputs affect the profile of the OPNMR signal intensity as a function of photon energy (E) in a predictable manner. Therefore, the profile can serve as a composite fingerprint by which individual parameters can be inferred when not known. Characteristics of the profile include the photon energy for maximum OPNMR signal intensity and the intensity ratio between σ+ and σ− light.
A technique to measure hydrogen absorption in isolated nanometer structures
Authors: Phillips A. B. , Shivaram B. S.
Published: January 2008

We describe an apparatus assembled to measure hydrogen absorption on a monolayer of isolated nanometer scale entities. Utilizing inexpensive and readily available high frequency surface acoustic wave (SAW) sensors we achieve a sensitivity of 4pg, sufficient to detect hydrogen uptake at less than 1% in nanogram level samples of such entities at room temperature. Results of hydriding rare earth metal nanoparticles and a transition metal–carbon complex measured with 315MHz SAW resonators are presented. However, the design of our apparatus is general and can be used with a wide variety of commercial SAW sensors.
Surface-wave suppression band gap and plane-wave reflection phase band of mushroomlike photonic band gap structures
Authors: Li Long , Chen Qiang , Yuan Qiawei , Liang Changhong , Sawaya Kunio
Published: January 2008

Mushroomlike photonic band gap (PBG) structures exhibit two band gap characteristics: surface-wave suppression and in-phase reflectivity. The fundamental electromagnetic properties and the relationship between the surface-wave suppression band gap and the plane-wave reflection phase band are investigated and clarified by a finite-element full-wave analysis. The results of the plane-wave bistatic reflection experiments on mushroomlike PBG plates in an anechoic chamber are in good agreement with those of numerical simulation, confirming the phenomenon of dual in-phase reflection, i.e., dual-resonant behavior, for a transverse magnetic polarization plane wave at oblique incidence on a mushroomlike PBG surface. A modified local resonance cavity cell model of a PBG structure is presented to provide insight into the physical mechanism of dual-resonant behavior.
An experimental study of charge distribution in crystalline and amorphous Si nanoclusters in thin silica films
Authors: Thøgersen Annett , Diplas Spyros , Mayandi Jeyanthinath , Finstad Terje , Olsen Arne , Watts John F. , Mitome Masanori , Bando Yoshio
Published: January 2008

Crystalline and amorphous nanoparticles of silicon in thin silica layers were examined by transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy (XPS). We used XPS data in the form of the Auger parameter to separate initial and final state contributions to the Si2p energy shift. The electrostatic charging and electron screening issues as well as initial state effects were also addressed. We show that the chemical shift in the nanocrystals is determined by initial state rather than final state effects, and that the electron screening of silicon core holes in nanocrystals dispersed in SiO2 is inferior to that in pure bulk Si.
Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion implantation
Authors: Butenko A. V. , Kahatabi R. , Mogilko E. , Strul R. , Sandomirsky V. , Schlesinger Y. , Dashevsky Z. , Kasiyan V. , Genikhov S.
Published: January 2008

Two types of high-quality PbTe p-n junctions, prepared by thermal diffusion of In4Te3 gas [thermally diffused junction (TDJ)] and by ion implantation [implanted junction (IJ)] of indium (In-IJ) and zinc (Zn-IJ), have been characterized. Capacitance-voltage and current-voltage characteristics have been measured over a temperature range from ∼10to∼180K. The saturation current density J0 in both diode types was ∼10−5A∕cm2 at 80K, while at 180K, J0∼10−1A∕cm2 in TDJ and ∼1A∕cm2 in both IJ diodes. At 80K, the reverse current started to increase markedly at a bias of ∼400mV for TDJ and at ∼550mV for IJ. The ideality factor was about 1.5–2 for both diode types at 80K. Both diode types were linearly graded. The height of the junction barrier, the concentration and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant have been determined. The zero-bias resistance times area product (R0Ae) at 80K is 850Ωcm2 for TDJ, 250Ωcm2 for In-IJ, and ∼80Ωcm2 for Zn-IJ, while at 180K, R0Ae∼0.38Ωcm2 for TDJ and ∼0.1Ωcm2 for both IJ diodes. The estimated detectivity is D*∼1011cmHz1∕2∕W at T=80K, determined mainly by background radiation, while at T=180K, D* decreases to 5×109–1010cmHz1∕2∕W and is determined by the Johnson noise.
Enhancement of magnetic moment of Co-doped ZnO films by postannealing in vacuum
Authors: Li Xiao-Li , Wang Zhu-Liang , Qin Xiu-Fang , Wu Hai-Shun , Xu Xiao-Hong , Gehring G. A.
Published: January 2008

The Co-doped ZnO thin films were prepared on c-cut sapphire substrates by magnetron cosputtering, and then annealed at various temperatures in vacuum. Magnetic measurements indicate that all the films are ferromagnetic at room temperature and the magnetization of the annealed Zn0.88Co0.12O films is increased about one order of magnitude in comparison with the corresponding as-deposited one. The enhancement of magnetization is possibly due to the fact that the generation of oxygen vacancies during annealing in vacuum increases the carrier (electron) concentration, which is consistent with the mechanism of carrier-induced ferromagnetism. Optical spectrometry indicates that Co2+ enters the tetrahedral sites of the wurtzite structure of ZnO host and substitutes for Zn2+.
The influence of metallic particle size on the mechanical properties of polytetraflouroethylene-Al–W powder composites
Authors: Cai J. , Nesterenko V. F. , Vecchio K. S. , Jiang F. , Herbold E. B. , Benson D. J. , Addiss J. W. , Walley S. M. , Proud W. G.
Published: January 2008

The dynamic mechanical properties of high density mixtures of polytetraflouroethylene, aluminum (Al), and tungsten (W) powders are tailored by changing the morphology of the particles and porosity. Powder composites with fine metallic particles exhibited higher ultimate compressive strength, despite higher porosity, than less porous composites containing coarse W particles with equivalent mass fractions. The mesoscale force chains between the fine metallic particles are responsible for this unusual phenomenon. Macrocracks forming in the sample below the critical failure strain in the matrix and a competition between densification and fracture were observed in dynamic tests.
Radiation tolerant polymeric films through the incorporation of small molecule dopants in the polymer matrix
Authors: Lenhart Joseph L. , Cole Phillip J. , Cole Shannon M. , Schroeder John L. , Belcher Michael E.
Published: January 2008

Radiation induced conductivity (RIC) in semicrystalline polyethylene terephthalate (PET) films can be reduced by incorporating small molecule electron traps into the polymer. The electron traps contained an aromatic core with strong electron withdrawing functionality pendant to the core and were incorporated into the PET film by immersing the polymer in a solution of dopant and solvent at elevated temperatures. The chemical functionality of the electron trapping molecule and the number of pendant functional groups had a strong impact on the equilibrium doping level and the most effective doping solvent. In addition, all of the electron traps exhibited effectiveness at reducing the RIC. The technique of incorporating small molecule dopants into the polymer matrix in order to reduce the RIC can potentially be exploited with other polymers films and coatings utilized in electronics devices such as encapsulants, conformal coatings, and polymeric underfills.
Micro∕nanoscopic patterning of polymeric materials by atomic force microscope assisted electrohydrodynamic nanolithography
Authors: Xie Xian Ning , Chung Hong Jing , Bandyopadhyay Dipankar , Sharma Ashutosh , Sow Chorng Haur , Wee Andrew Thye Shen
Published: January 2008

In this work, we address the spatiotemporal evolution of micro∕nanoscopic pattern formation on polymer films by atomic force microscope (AFM) assisted electrohydrodynamic (EHD) nanolithography. This patterning method combines the locality and site specificity of AFM and the surface wave amplification of EHD instability for pattern creation and is capable of generating a series of structures corresponding to the zeroth- to second-order wave patterns. Detailed simulations in the framework of nonlinear three-dimensional analysis are presented to elucidate the localized EHD pattern formation. The experimental and theoretical results are quantitatively compared to address the characteristics of the AFM-assisted EHD pattern formation. The impact of key experimental parameters such as the tip bias voltage and bias duration on the formation rate, morphology, and lateral dimension of the wave patterns are discussed. The AFM assisted EHD nanolithography would open new route to the fabrication of complex polymer nanostructures.
Magnetic properties of La0.6Sr0.4MnO3 thin films on SrTiO3 and buffered Si substrates with varying thickness
Authors: Pradhan A. K. , Hunter D. , Williams T. , Lasley-Hunter B. , Bah R. , Mustafa H. , Rakhimov R. , Zhang J. , Sellmyer D. J. , Carpenter E. E. , Sahu D. R. , Huang J.-L.
Published: January 2008

La 0.60 Sr 0.40 MnO 3 (LSMO) thin films of varying thickness from 12 to 55 nm were deposited using the pulsed-laser deposition technique onto single-crystalline SrTiO3 (STO) and STO-buffered Si substrates. The Tc of LSMO films grown on STO-buffered Si substrates decreases faster than films directly grown on STO with decreasing film thickness. The LSMO/STO film with thickness of 55 nm shows Tc at about 360 K, which is close to the bulk value, whereas Tc LSMO film on STO-buffered Si film of similar thickness is reduced to 320 K. This difference is attributed to the strain and interfacial disorders in LSMO film on STO/Si. The film surface morphology is influenced by the film thickness. Oxygenation of LSMO films on STO-buffered Si affects the Tc minimally but improved the overall magnetization of the films due to better oxygenation, which is also the case for postannealing the sample at elevated temperatures. The thermomagnetic history effects observed in LSMO films of STO-buffered Si indicate the presence of inhomogeneity, mostly at the interface, which influences the magnetic properties significantly.
Sol-gel derived morphotropic phase boundary 0.37BiScO3–0.63PbTiO3 thin films
Authors: Xiao Jingzhong , Wu Aiying , Vilarinho Paula M.
Published: January 2008

Dielectric/ferroelectric properties of morphotropic phase boundary 0.37BiScO3–0.63PbTiO3 thin films with a PbTiO3 seed layer deposited on platinized silicon substrates by sol-gel are examined. Room temperature dielectric constant of >1600 and dielectric loss of 0.02 are achieved (100Hz). A well-defined hysteresis loop was observed with a Pr of ∼23μC∕cm2. In particular, the remarkable low Ec of ∼33kV∕cm of these films adds value to the potential application of BiScO3–PbTiO3 films in high temperature ferroelectric memories. The influence of PbTiO3 seed layer on the electric properties and the relation with the phase formation process, crystallinity, and microstructure of the films is discussed.
Wide-ridge metal-metal terahertz quantum cascade lasers with high-order lateral mode suppression
Authors: Fan Jonathan A. , Belkin Mikhail A. , Capasso Federico , Khanna Suraj P. , Lachab Mohamed , Davies A. Giles , Linfield Edmund H.
Published: January 2008

Terahertz quantum cascade lasers with wide-ridge metal-metal waveguides are prone to lasing in high-order lateral modes, which reduce the maximum light output power from these devices. We have demonstrated, theoretically and experimentally, that the output power can be improved severalfold by introducing “side absorbers” into the waveguide structure, which enforce lasing in the TM00 mode with minor temperature performance deterioration. Lasers without side absorbers operate up to 168K, a current record for devices processed using indium/gold wafer bonding.
Terahertz evanescent field microscopy of dielectric materials using on-chip waveguides
Authors: Cunningham J. , Byrne M. , Upadhya P. , Lachab M. , Linfield E. H. , Davies A. G.
Published: January 2008

We demonstrate an evanescent field modality for terahertz frequency time-domain measurements, based on the interaction between a sample and the evanescent field extending above lithographically defined terahertz waveguides. We quantify this interaction using freely positionable dielectric samples (GaAs) moved in close proximity to the waveguide (a terahertz microstrip line), finding a reduction in the microstrip-propagating pulse amplitude and an increase in its time delay when the dielectric is brought into the microstrip evanescent field. We also show that the frequency response of resonant passive circuit elements (stub band-stop filters), integrated into the microstrip line, can be used to determine the terahertz frequency properties of scanned samples, opening the way for a terahertz subwavelength imaging modality, the resolution of which is limited by lithographic constraints, rather than by free-space diffraction.
Critical clearance and lubricant instability at the head-disk interface of a disk drive
Authors: Ambekar Rohit P. , Bogy David B. , Dai Qing , Marchon Bruno
Published: January 2008

We report experimental data that suggest the existence of a critical clearance between the flying head and the disk in a hard disk drive, below which significant lubricant transfer from the disk to the slider takes place. This phenomenon is interpreted as originating from dewetting instabilities brought about by molecular interactions with the slider. A model that reproduces the onset of instability is presented.
Band alignment between amorphous Ge2Sb2Te5 and prevalent complementary-metal-oxide-semiconductor materials
Authors: Fang Lina Wei-Wei , Pan Ji-Sheng , Zhao Rong , Shi Luping , Chong Tow-Chong , Samudra Ganesh , Yeo Yee-Chia
Published: January 2008

Band alignment of amorphous Ge2Sb2Te5 and various substrates was obtained using high-resolution x-ray photoelectron spectroscopy. The valence band offset of Ge2Sb2Te5 on various complementary-metal-oxide-semiconductor (CMOS) materials, i.e., Si, SiO2, HfO2, Si3N4 and NiSi, were investigated with the aid of the core level, valence band, and energy loss spectra. Energy band lineups of Ge2Sb2Te5 on these materials were thus determined which can be used as for phase change memory device engineering and integration with CMOS technology.
The Geophysics of Venus
Authors: Solomon Sean C.
Published: January 2008

Venus is the planet most similar to the Earth in mass, radius and solar distance. Current theories of the early evolution of the solar system suggest that Earth and Venus each formed by the accretion of planetesimals—small rocky or rock-metal objects—that collectively constituted a well-mixed sample of material condensed from the inner solar nebula. The bulk compositions of the two planets should thus be similar. The rates of internal heat generation and the energy available to drive interior convection should also be similar. An important difference between the two planets, however, is the character of their atmospheres. The mass of the dominantly CO2 atmosphere of Venus is two orders of magnitude greater, as a fraction of planet mass, than that of Earth's atmosphere, and the surface temperature is 450 K higher, a consequence of continuous global cloud cover and a runaway greenhouse effect. The mass of H2O in a vertical column of unit area is four to five orders of magnitude less for Venus's atmosphere than for the atmosphere and hydrosphere on Earth. As a result, the surface of Venus lacks a water cycle, and the processes of weathering, erosion and sediment transport that dominate terrestrial landforms are comparatively unimportant.
Industrial Ecology: Minimizing the Impact of Industrial Waste
Authors: Frosch Robert A.
Published: January 2008

Throughout human history, industry has been an open system of materials flow. People took natural plant, animal and mineral materials and transformed them into tools, clothing and other products of all kinds. When materials were left over from the production process or worn out, they were thrown aside—dumped in the backyard, as it were. Archaeologists find deposits of discarded materials—scrap stone, flints and potsherds—in the rubbish dumps of the Neolithic. Habitations were often moved because the waste that people had piled around them had rendered the old location an unsuitable place to live.
The Summer of 1953: A Watershed for Astrophysics
Authors: Gingerich Owen
Published: January 2008

Beginning in 1927 the University of Michigan's summer school in physics became famous as the international forum for learning about the latest advances in modern physics. Within a decade of its inception perhaps half of the most renowned European physicists had turned up for its sessions—scientists like Fermi, Dirac, Pauli, Sommerfeld, Goudsmit, Uhlenbeck, Ehrenfest and the astrophysicists Robert Atkinson and E. A. Milne.
Physics: A Personal Perspective
Authors: Langenberg Donald N.
Published: January 2008

I want to present a very personal perspective on physics and its current circumstances. I'd like to emphasize the word “personal.” I do not assume my perspective has general validity or global significance. I do hope it will be of some interest to some of you and that it will perhaps provoke some useful thoughts about the compelling calling we share.
Special Issue: Physics and Biology
Authors: Frauenfelder Hans , Berg Howard C.
Published: January 2008

This issue of PHYSICS TODAY is devoted to the interface between physics and biology, commonly termed biological physics or biophysics. Physicists tend to consider biological physics as physics inspired by biology and biophysics as biology revealed by physical methods—or to put it colloquially, what biology can do for physics and what physics can do for biology. Biologists take a broader view. Cells and organisms must know some physics as well as biology because they have evolved in the face of daunting physical constraints. So biophysics includes the physics mastered by living things. Some of this physics is understood by physicists, and some is not. In the former case, one is awed by how much physics organisms know. In the latter case, one is intrigued by how much physics they might yet reveal. The topics addressed in this issue of PHYSICS TODAY deal with these two domains.
The Ear's Gears: Mechanoelectrical Transduction by Hair Cells
Authors: Hudspeth A. J. , Markin Vladislav S.
Published: January 2008

Although we are generally unaware of the fact, our nervous systems constantly monitor a variety of mechanical stimuli. Neurons in the spinal cord and brain stem extend sensory terminals to the body's surface and there provide us with sensitivity to touch. Other such neurons measure the tension in and extension of skeletal muscles. Sensory cells of the autonomic nervous system detect pressures within the body's hollow organs, including blood vessels, the bladder, and the gut. The most sensitive of our mechanical receptors are hair cells, the sensory receptors of the internal ear. Such cells underlie our sensitivities to sound, to linear accelerations (including that due to gravity), and to angular accelerations.
Neurons, Dynamics and Computation
Authors: Hopfield John J.
Published: January 2008

The question “How does it work?” is the motivation of many physicists. Condensed matter physics, chemical physics and nuclear physics can all be thought of as descriptions of the relation between structure and properties. The components of a biological system have functional properties that are particularly relevant to the operation of the system. Thus it is especially important in biology to understand the relation between structure and function. Such understanding can be sought at the level of the molecule, the cell, the organ, the organism or the social group.
Cancer and Power Lines
Authors: Bennett William R.
Published: January 2008

Epidemiologists in Denver, Los Angeles and Sweden are asking us to believe that magnetic fields of 2 milligauss from power distribution lines are a serious cause of childhood leukemia. What started as a series of sensational articles in The New Yorker magazine by Paul Brodeur (later collected into a book), bringing the earliest of these studies to the attention of the general public, has turned into a new growth industry. Several government agencies, not to mention the private electric power industry, have already sponsored multimillion-dollar studies of the problem; a number of small companies selling 60-Hz gaussmeters have sprung into existence and are doing a land-office business; and the public concern over this issue has become a bonanza to groups of people doing epidemiological and biological research on the effects of electromagnetic fields. Hastily contrived legislation in a number of states has legalized the status quo for fields from power lines, and the threat of still more ill-thought-out legislation is on the horizon—mandating, for example, warning labels on toaster ovens and television sets similar to those now found on cigarettes.
The Golden Age of Optical Fiber Amplifiers
Authors: Desurvire Emmanuel
Published: January 2008

After nearly two decades of research in fiber-optics technology, what could possibly remain to be discovered? Clearly, the design of optical fibers cannot be improved forever. With current technology, fibers can transmit infrared (1.5-micron wavelength) light pulses in a single electromagnetic mode with a minimal power loss of 5% per kilometer and without dispersion; such performance is forever fixed by Maxwell's equations and the physics of silica glass waveguides. Yet the field of fiber optics still reserves some surprises. Indeed, the past few years have seen stunning developments in reaction to advances in rare-earth-doped fiber amplifiers and nonlinear (or soliton) pulse propagation in fibers.
The Electron-Beam Ion Trap
Authors: Marrs Roscoe E. , Beiersdorfer Peter , Schneider Dieter
Published: January 2008

The mention of few-electron atoms usually brings to mind hydrogen, helium or other light elements in neutral form. However, these simple atoms are part of a sequence of ions having the same number of electrons but different nuclear charges. For example, the hydrogen-like sequence spans neutral hydrogen through hydrogen-like uranium, U91+. Both the atomic physics and the applications of the most highly charged ions in such isoelectronic sequences are receiving increasing attention. Recently the electronbeam ion trap has made it possible to produce and study any such ion in a modest-sized apparatus (figure 1).
The Ocean's Overturning Circulation
Authors: Toggweiler J. Robert
Published: January 2008

The ocean is a mysterious place. As terrestrial creatures, we are familiar with a small volume of relatively warm ocean water near the surface. The deep ocean is not so familiar. Isolated from the thermal energy of the Sun and the mechanical energy of atmospheric winds, the deep ocean is completely dark and filled with near-freezing water. Yet the deep ocean is far from stagnant. Radioactive tracer measurements show that the ocean's circulation brings its interior water into contact with the atmosphere every 600 years or so.
Xerography: A Study in Innovation and Economic Competitiveness
Authors: Mort Joseph
Published: January 2008

The general consensus is that the US in recent years has progressively lost competitive ground in a number of critical economic areas—this despite the fact that it has been the world's leading scientific and technological power and has spent more on nondefense R&D than any other country. Evidently scientific and technological prowess do not guarantee economic competitiveness.
Ultrafast Switching with Nonlinear Optics
Authors: Islam Mohammed N.
Published: January 2008

Remember when we optimized our computer programs to minimize the memory usage, even at the expense of readability of the code? Now, with an abundance of memory, we no longer worry about the memory requirements. Remember when we minimized the gate count in a circuit by using techniques such as Karnaugh maps? Now, with VLSI and ULSI chips, gate count is no longer an issue. Yet in telecommunications many applications still need to be optimized to fit within bandwidth limitations. Researchers in optics and photonics dream of making bandwidth an inexpensive, virtually limitless commodity, so that we will be able to tailor applications to optimize their functionality without regard to bandwidth.
X Rays in Medicine
Authors: Hendee William R.
Published: January 2008

One hundred years ago this month Wilhelm Röntgen, a professor of physics at the Julius Maximilian University of Würzburg, discovered x rays while experimenting with cathode rays in a Crookes tube. Word of the discovery spread quickly, and by early 1896 the properties of x rays were under investigation in numerous physics laboratories in Europe and North America. By the turn of the century, physicians and physicists were exploiting the penetrating character of x rays to look inside the human body without cutting it open. They were also beginning to explore the therapeutic properties of x radiation.
Special Issue: Magnetoelectronics
Authors: Prinz Gary , Hathaway Kristl
Published: January 2008

Magnetism abounds with dichotomies: It was known to the ancients and yet is the focus of exciting new research; its manifestations are apparent to every schoolchild yet its origins are rooted deep in quantum mechanics and relativity; its applications underlie huge industries yet its understanding—even in iron—is still incomplete.
Helioseismology
Authors: Harvey John
Published: January 2008

What powers the Sun? Why does it have spots? How long will it sustain life on Earth? Efforts to answer these questions about the astrophysical object that is of greatest importance to humanity have produced many advances in physics and helped lay the main foundations of astrophysics. The three questions, however, remain to be answered. For example, the best models of the Sun's nuclear power predict a significantly higher neutrino flux than is observed. (See PHYSICS TODAY April, page 19.) We do not know what causes sunspots and other solar activity or even why the Sun emits x rays. Modeling how stars evolve leads to age estimates for some stars that are greater than recent estimates of the age of the universe.
Wilhelm Conrad Röntgen and the Glimmer of Light
Authors: Seliger Howard H.
Published: January 2008

On Friday evening, 8 November 1895, Wilhelm Conrad Röntgen, a 50-year-old professor of physics and recently elected rector of the Julius Maximilian University of Würzburg, Germany, was unusually late for dinner. And when he did arrive at the family living quarters above his laboratory in the Physical Institute, he did not speak, ate little and then left abruptly to return to the experiments that had so disturbed him that afternoon.
Electronic Structure Calculations for Magnetically Ordered Systems
Authors: Jansen Henri J. F.
Published: January 2008

Although magnetism was known to the ancients, its uses before modern times were very limited. The compass was probably the most important application before the 19th century. After Oersted's discovery, in 1820, that magnets interact with electric currents, the number of applications grew rapidly. The classical union of electricity and magnetism culminated, of course, in Maxwell's beautiful theory of the electromagnetic field.
Spin-Polarized Transport
Authors: Prinz Gary A.
Published: January 2008

A new field that has come to be called “spin-polarized transport” is growing dramatically. Although its roots are in the quantum description of solids, only recently have new material fabrication techniques permitted widespread study of the phenomenon and the development of device applications (see figure 1).
Controlling Chaos
Authors: Ott Edward , Spano Mark
Published: January 2008

Scientists in many fields are recognizing that the systems they study often exhibit a type of time evolution known as chaos. Its hallmark is wild, unpredictable behavior, a state often perplexing and unwelcome to those who encounter it. Indeed this highly structured and deterministic phenomenon was in the past frequently mistaken for noise and viewed as something to be avoided in most applications. Recently researchers have realized that chaos can actually be advantageous in many situations and that when it is unavoidably present, it can often be controlled to obtain desired results. In this article, we present some of the basic ideas behind the feedback control of chaos, review a few illustrative experimental results and assess the status and future promise of the field.
A Lecture on Bomb Physics: February 1942
Authors: Heisenberg Werner , Cassidy David , Sweet William
Published: January 2008

During the waning weeks of World War II in Europe, as Allied armies swept across a defeated, chaotic Germany, two teams of the world's leading nuclear scientists strove to complete their work. One team, sequestered at Los Alamos, hastened to assemble the first of three atomic bombs. The other, a group of German scientists and technicians who had recently fled the Allied bombing of Berlin for southern Germany, worked day and night trying to achieve what, unbeknownst to them, the Allies had achieved nearly two and a half years earlier: a critical self-sustaining nuclear reactor.
Bomb Apologetics: Farm Hall, August 1945
Authors: Bernstein Jeremy , Cassidy David
Published: January 2008

A little over a month after the ten German physicists had settled into Farm Hall, the British manor where they would be held and observed for six months (see the preceding article on page 27), they were astounded by the news of the atomic bombing of Hiroshima. Believing themselves far ahead of the Allies in nuclear research, the German scientists were suddenly shaken by the realization that they were in fact far behind. How had the Allies done it? Why had the Germans made so little progress in comparison? How could they explain this to themselves, to their countrymen, to their former enemies?
Groves and the Scientists: Compartmentalization and the Building of the Bomb
Authors: Goldberg Stanley
Published: January 2008

This month marks the 50th anniversary of the only times that atomic bombs have been used against human targets–at Hiroshima and Nagasaki, Japan. Over the years since those events, secondary histories of the Manhattan Project have made much of the collective virtuoso performance of the scientists, especially at Los Alamos, where scientists were able to design and manufacture the weapons essentially from scratch in less than three years.
What Future Will We Choose for Physics?
Authors: Gruner Sol M. , Langer James S. , Nelson Phil , Vogel Viola
Published: January 2008

Science in the United States is in a time of pain and uncertainty. The pain is felt most acutely by young scientists, who are having great difficulty establishing their careers. The uncertainty about the duration and outcome of the current situation stems from its roots in ponderous events of recent history—the end of the cold war, industrial downsizing, government deficits and demographic trends. Although budget difficulties and lack of jobs plague most of the sciences, the atmosphere of uncertainty about the future is palpably different from one profession to the next. Our concern here is with the profession of physics.
Resonant Ultrasound Spectroscopy
Authors: Maynard Julian
Published: January 2008

When a new crystalline material is discovered, one of the first fundamental properties to be determined is the atomic structure, defined by the minimum in the free energy with respect to the positions of the atoms. Another fundamental characteristic of interest is the curvature of the free energy in the vicinity of the minimum, and this would be manifest in the elastic constants for the material. As derivatives of the free energy, elastic constants are closely connected to thermodynamic properties of the material. They can be related to the specific heat, the Debye temperature and the Gruneisen parameter (which relates the thermal expansion coefficient to the specific heat at constant volume), and they can be used to check theoretical models. Extensive quantitative connections among thermodynamic properties can be made if the elastic constants are known as functions of temperature and pressure. The damping of elastic waves provides information on anharmonicity and on coupling with electrons and other relaxation mechanisms. The elastic properties are perhaps most valuable as probes of phase transitions, such as superconductivity transitions. Clearly precise and accurate measurements of elastic constants furnish significant information about materials.
My Encounters—as a Physicist—with Mathematics
Authors: Jackiw Roman
Published: January 2008

Mathematical physics is not a discipline with its own identity. Rather there is mathematics and there is physics, and their cyclical relationship enjoys periods of cooperation interspersed with periods of mutual indifference. New initiatives leading to rapid development in physics frequently are accompanied by mathematical innovation. Examples from the past are the construction of particle mechanics and differential calculus by Isaac Newton and Gottfried Leibniz, developments in general relativity and differential geometry at the time of Albert Einstein and Hermann Minkowski, and advances in group theory and analysis following the invention of quantum mechanics and quantum field theory.
Inelastic X-Ray Scattering in Condensed Matter Systems
Authors: Isaacs Eric D. , Platzman Phil
Published: January 2008

Scattering experiments have given us much of what we know about the microscopic behavior of an enormous variety of condensed matter systems. Simple but fascinating materials such as solid and liquid helium, transition metals such as iron and nickel, semiconductors such as silicon and gallium arsenide, complex oxides such as V2O3 and high-temperature superconductors, and even more complex solids such as protein crystals have all been investigated by a variety of scattering probes.
The Computing Revolution and the Physics Community
Authors: Brenner Alfred E.
Published: January 2008

By any measure, society—US society in particular—is now in some phase of what is being called the information revolution. This “third wave,” a term introduced by Alvin Toffler, follows the industrial revolution of the 18th century and the agricultural revolution of 10 000 years ago, and is resulting in phenomenal social, cultural and economic transformations. It is changing the ways in which people spend their time at work and at play, and the ways in which they live their lives in general. Inevitably, it will lead to major geopolitical upheavals. This revolution, as were the two previous ones, is technology based, with the seeds being planted over a long period.
Precision Tests Find No Violation of Bose Statistics
Authors: Schwarzschild Bertram
Published: January 2008

The symmetrization postulate of quantum mechanics asserts that the multiparticle wavefunction for any collection of identical particles must be either wholly symmetric or wholly antisymmetric under the exchange of labels between any two particles. In nonrelativistic quantum mechanics, this postulate is a somewhat ad hoc assumption tacked onto the theory; wholly symmetric or antisymmetric wave functions are not the only ways of preserving the indistinguishability of identical particles.
Thermonuclear Milestones: (3) The Race Accelerates
Authors: Goncharov German A.
Published: January 2008

No more than four days after President Harry Truman's January 1950 directive to continue US work on the superbomb, the problem of “measures to ensure the progress of RDS-6” was discussed in the USSR at a meeting of the Special Committee. On 26 February, the Council of Ministers of the USSR adopted a resolution that commissioned the First Central Administration at the Council of Ministers, Laboratory No. 2 of the Academy of Sciences, and KB-11 to organize analytical-theoretical, experimental and design operations on the construction of devices RDS-6s (Sloika, the Layer Cake) and RDS-6t (Truba, the Tube). (See the preceding article for descriptions of these thermonuclear bomb designs.)
Confidence is Growing in Tropospheric OH Measurements
Authors: Levi Barbara Goss
Published: January 2008

There aren't many hydroxyl molecules (OH) in the troposphere, but the few that are there certainly make their presence known. More than any other species in the troposphere (the atmospheric layer between Earth's surface and an altitude of 8–18 km), the OH radical determines the lifetimes of such common atmospheric constituents as carbon monoxide, methane and sulfur dioxide. Yet, because of its short atmospheric lifetime (a single molecule sticks around less than one second) and low concentrations (a few tenths of a part per trillion, compared, for example to carbon dioxide levels, which are a few hundred parts per million), the OH radical has defied accurate measurement. Not any more.
Trinity at Dubna
Authors: Reed Thomas , Kramish Arnold
Published: January 2008

In feudal times, society was viewed as being made up of three estates, a “trinity,” functioning under the king's beneficence: the Lords Spiritual, the Lords Temporal and the Peasants. For all of its modern aspirations, Stalin's Soviet society of the 1940s and '50s was, in fact, feudal. Certainly that was true of the nuclear community. The respect reserved for the clergy in feudal times went to the security services. The nuclear nobility, the designers, lived well and were accorded full honors. And then there were those who did the tough and dirty work, the peasants. Some were recent graduates in chemistry or physics; no one was concerned by the serious overdoses of radiation that many received. Others were engineers, pursuing one blind alley after another with no time for the ordered exploration of alternatives. Still others were prisoners and soldiers, building the foundations and infrastructure that supported the program. They all were “peasants” in this scheme of things.
Detecting the Soviet Bomb: Joe-1 in a Rain Barrel
Authors: Friedman Herbert , Lockhart Luther B. , Blifford Irving H.
Published: January 2008

In April 1947, a former Wall Street banker. Admiral Lewis Strauss, became a member of the newly established Atomic Energy Commission. At the time, both General Leslie Groves and J. Robert Oppenheimer believed that the Soviets were still a decade away from nuclear success; Naval Intelligence estimated the earliest date for a Soviet nuclear weapon as 1952, five years hence. Nevertheless, just one week after Strauss's appointment, he asked Secretary of Defense James E. Forrestal if any measures had been taken for the long-range detection (LRD) of a hypothetical Soviet atomic bomb test, and the one-time banker was surprised by the answer: No. Although he had little scientific knowledge of atomic weapons effects, Strauss felt intuitively that the military could and should have such a detection capability. He therefore pressed his deep concern to the military. The Office of Naval Research responded immediately.
Thermonuclear Milestones
Authors: Goncharov German A.
Published: January 2008

The creation of atomic weapons, and later thermonuclear weapons, was an event of such epochal significance in the 20th century that its history has preoccupied scientists worldwide and the international community at large. Those who have participated directly in nuclear weapons programs do not, and cannot, remain aloof from revealing the facts of that history. Of special interest is the early history of thermonuclear weapons development in the US and the USSR, the first countries to detonate this most dreadful species of nuclear weapon. In these three articles I present a brief survey and analysis of the principal events that make up that early history.
Nobel Prize in Physics to Lee, Osheroff and Richardson for Discovery of Superfluidity in He3
Authors: Lubkin Gloria B.
Published: January 2008

David M. Lee, Douglas D. Osheroff and Robert C. Richardson have been awarded the 1996 Nobel Prize in Physics for their discovery of superfluidity in helium-3. Their experiments, done in the low-temperature physics lab at Cornell University in the early 1970s, showed that below 3 mK liquid He3 has three new phases, with properties very different from the normal phase. Each of the three phases exhibits superfluidity, flowing with zero viscosity. All three are magnetic and have anisotropic behavior, exhibiting an entirely new category of macroscopically observable quantum behavior. Superfluid He3 is the most sophisticated condensed matter system known of which we can claim a quantitative understanding, says Anthony Leggett (University of Illinois), who helped develop the theory of the new phases soon after their discovery.
Topological Ideas and Fluid Mechanics
Authors: Ricca Renzo L. , Berger Mitchell A.
Published: January 2008

The use of topological ideas in physics and fluid mechanics dates back to the very origin of topology as an independent science. In a brief note in 1833 Karl Gauss, while lamenting the lack of progress in the “geometry of position” (or Geometria Situs, as topology was then known I, gives a remarkable example of the relationship between topology and measurable physical quantities such as electric currents. He considers two inseparably linked circuits, each of them a copper wire with ends joined, and flowing electric current. Without comment he puts forward a formula that gives the relationship between the magnetic action induced by the currents and a pure number that depends only on the type of link, and not on the geometry. This number is a topological invariant now known as the linking number. The formula, as well as the very first studies in topology done by Johann Benedict Listing in 1847, became known to Kelvin (then William Thomson), James Clerk Maxwell and Peter Guthrie Tait in Britain.
Follicle stimulating hormone and fibroblast growth factor-2 interact and promote goat primordial follicle development in vitro
Authors: Matos M. H. T. , Lima-Verde I. B. , Bruno J. B. , Lopes C. A. P. , Martins F. S. , Santos K. D. B. , Rocha R. M. P. , Silva J. R. V. , Bão S. N. , Figueiredo J. R.
Published: January 2008

The aims of the present study were to investigate the effects of the interaction between follicle stimulating hormone (FSH) and fibroblast growth factor-2 (FGF-2) on survival, follicular growth initiation and further growth of caprine preantral follicles. Pieces of caprine ovarian cortex were cultured for 1 or 7 days in minimum essential medium (MEM) supplemented with FSH, FGF-2 or FSH + FGF-2. Small fragments from non-cultured ovarian tissue and from those cultured for 1 or 7 days were processed for classical histology and transmission electron microscopy (TEM) to verify follicular morphology and growth. The results showed that, after 7 days culture, the highest percentages of normal follicles were observed in medium supplemented with FSH. After 7 days culture, the interaction between FSH and FGF-2 was most effective to promote the initiation of primordial follicles growth and oocyte growth. TEM showed ultrastructural integrity of follicles after 1 day of culture in MEM and after 7 days in all treatments, except in those follicles cultured for 7 days in MEM. In conclusion, this study demonstrated that the interaction between FSH and FGF-2 stimulates the initiation of primordial follicles growth and the subsequent growth of developing follicles. Furthermore, these data showed that FSH is important to maintain follicular integrity after 7 days culture.