bluuebunny/crossref_metadata_2025 huggingface dataset:
On hydrologic similarity: 3. A dimensionless flood frequency model using a generalized geomorphologic unit hydrograph and partial area runoff generation
Authors: Sivapalan Murugesu , Wood Eric F. , Beven Keith J.
Published: February 2008

One of the shortcomings of the original theory of the geomorphologic unit hydrograph (GUH) is that it assumes that runoff is generated uniformly from the entire catchment area. It is now recognized that in many catchments much of the runoff during storm events is produced on partial areas which usually form on narrow bands along the stream network. A storm response model that includes runoff generation on partial areas by both Hortonian and Dunne mechanisms was recently developed by the authors. In this paper a methodology for integrating this partial area runoff generation model with the GUH‐based runoff routing model is presented; this leads to a generalized GUH. The generalized GUH and the storm response model are then used to estimate physically based flood frequency distributions. In most previous work the initial moisture state of the catchment had been assumed to be constant for all the storms. In this paper we relax this assumption and allow the initial moisture conditions to vary between storms. The resulting flood frequency distributions are cast in a scaled dimensionless framework where issues such as catchment scale and similarity can be conveniently addressed. A number of experiments are performed to study the sensitivity of the flood frequency response to some of the “similarity” parameters identified in this formulation. The results indicate that one of the most important components of the derived flood frequency model relates to the specification of processes within the runoff generation model; specifically the inclusion of both saturation excess (Dunne) and Horton infiltration excess runoff production mechanisms. The dominance of these mechanisms over different return periods of the flood frequency distribution can significantly affect the distributional shape and confidence limits about the distribution. Comparisons with observed flood distributions seem to indicate that such mixed runoff production mechanisms influence flood distribution shape. The sensitivity analysis also indicated that the incorporation of basin and rainfall storm scale also greatly influences the distributional shape of the flood frequency curve.
First‐ and third‐type boundary conditions in two‐dimensional solute transport modeling
Authors: Batu Vedat , van Genuchten Martinus T.
Published: February 2008

This paper presents a general analytical solution for convective‐dispersive solute transport in a two‐dimensional, semiinfinite porous medium. The solute is assumed to be subject to linear equilibrium sorption and first‐order decay. Solutions are derived for several third‐type (Cauchy) or flux‐type boundary conditions at the input surface. After presenting a generally applicable solution a special solution is given for a strip‐type solute source. It is shown that the third‐type boundary condition correctly conserves mass in the two‐dimensional system and that the first‐type (Dirichlet) or concentration‐type boundary condition corresponds to a situation that the solute flux at the source decreases with time and at large time approaches to the solute flux of the third‐type boundary condition. This can lead to significant discrepancies in the calculated concentrations, especially near the source boundaries.
Advective‐dispersive transport of dense organic vapors in the unsaturated zone: 2. Sensitivity analysis
Authors: Mendoza Carl A. , Frind Emil O.
Published: February 2008

In the migration of dense organic vapors in the unsaturated zone, advection due to density gradients can play an important or even dominant role under certain conditions. Advective transport can distribute contaminants over a wide area within the unsaturated zone, thus increasing the potential for groundwater contamination. The controls on gas phase advective‐dispersive transport from a residual source of a generic organic compound are investigated using a numerical model. A sensitivity analysis reveals that, for compounds with high vapor pressures and molecular weights, in high permeability environments (coarse sands or gravels), the mass transported by density‐dependent advection may greatly exceed that transported by diffusion alone. If density‐dependent advection is the dominant transport mechanism, the extent of the contaminated area is increased if the ground surface is open to the atmosphere, rather than covered. The opposite is true for a diffusion‐controlled system. For either case an open ground surface contributes to a more rapid depletion of the residual liquid source. The advective mass flux caused by the release of vapor due to vaporization at the source is seen to be of minor importance.
Simulating physical processes and economic behavior in saline, irrigated agriculture: model development
Authors: Lefkoff L. Jeff , Gorelick Steven M.
Published: February 2008

A model of an irrigated, saline stream‐aquifer system is constructed to simulate economic, agronomic, and hydrologic processes. The model is applied to a section of the Arkansas Valley in southeastern Colorado and is used to examine the effect of crop‐mixing strategies on long‐term profits. Mixing in excess of crop rotation requirements provides an index of farmers' willingness to exchange some profit for a reduction in the risk of short‐term loss. The model contains three components. The economic component simulates water use decisions that maximize annual profit for each farm. The hydrologic component simulates salt transport by employing regression equations that predict changes in groundwater salinity as a function of hydrologic conditions and water use decisions. The agronomic component approximates changes in corn and alfalfa production in response to the depth and salinity of irrigation applications. Results from the entire economic‐hydrologic‐agronomic model are consistent with the few historical observations available for the site.
Inverse solution for one‐dimensional infiltration, and the ratio A/K1
Authors: Philip J. R.
Published: February 2008

The inverse method of solving the nonlinear diffusion equation is extended to give exactly the two leading terms of the infiltration series solution of the nonlinear Fokker‐Planck equation of unsaturated flow. We use the method, together with a new integral result for the ratio A/K, to investigate the, hitherto imperfectly understood, physical determinants of A/K1. K1 is the saturated conductivity, and A the second coefficient of the two‐term infiltration equation i = St1/2 + At. We separate out the relatively superficial direct effect of the initial moisture content θ0 (important only when θ0 is very large) from the more complicated effect, dependent both on soil texture and on θ0, of the shapes of the diffusivity D and the conductivity derivative dK/dθ. Normalized first moments of these functions measure the steepness of their variation. We explore the full range of combinations of shapes of D and dK/dθ from essentially flat to essentially infinitely steep. For soils with K0/K1 negligibly small (K0 = K(θ0)), A/K1 lies in the range 0 to ⅔. The dominant physical effect is that A/K1 decreases monotonically as dK/dθ increases in steepness. On the other hand, A/K1 increases (relatively slowly) with the steepness of D.
Analysis of Outflow Experiments Subject to Significant Plate Impedance
Authors: Valiantzas John D.
Published: February 2008

A new method is developed for the determination of the diffusivity‐water content relationship from pressure‐outflow experiments when the impedance of the supporting porous plate has to be taken into account. The classic one‐step outflow procedure for the determination of soil water diffusivity does not use the early linear part of the outflow versus the square root of time,
, curve, where the effect of plate impedance is not negligible. The present method can be applied also to the linear part of the outflow curve which is considerably extended when the effect of the plate impedance is significant. The suggested procedure requires additional information, namely, the retention curve and the plate impedance value. The method was tested by simulating outflow experiments with significant plate impedance and using data obtained to calculate diffusivities, as well as by analyzing experimental outflow data for a real soil.
Inner Region Humidity Characteristics of the Neutral Boundary Layer Over Prairie Terrain
Authors: Brutsaert Wilfried , Sugita Michiaki , Fritschen Leo J.
Published: February 2008

Radiosonde observations were carried out over prairie terrain in the Flint Hills region of eastern Kansas during the FIFE (First ISLSCP Field Experiment, International Satellite Land Surface Climatology Project) experiments in 1987. Analysis of 13 specific humidity profiles measured under neutral conditions revealed that they can be described by a logarithmic dependency on (z − d0), where z is the height above the zero‐plane reference at 330 m above sea level and d0 = 26.9 m the assumed displacement height. With a roughness height z0 = 1.05 m, this logarithmic layer was found to occupy the range 52(±28) ≤ (z − 0)/z0 ≤ 104(±37), which is consistent with previous experimental results. Good agreement was obtained (r = 0.87) between the evaporation values derived from the radiosonde profiles and mean values determined independently at six ground stations distributed over the 15 × 15 km experimental region. On the basis of only one profile the scalar roughness for water vapor z0υ was found to be 3 to 5 orders of magnitude smaller than z0.
Acute Neurodegeneration and the Inflammasome: Central Processor for Danger Signals and the Inflammatory Response?
Authors: Trendelenburg George
Published: January 2008

Activation of the inflammatory response is a crucial event in the adverse outcome of cerebral ischemia, which is promoted by proinflammatory cytokines such as interleukin (IL)-1β. Although caspase-1 is necessary for IL-1β processing, the ‘upstream’ signaling pathways were, until recently, essentially unknown. Fortunately, the inflammasome, a multiprotein complex responsible for activating caspase-1 and caspase-5, has recently been characterized. The activation of the inflammasome can result in one of several consequences such as cytokine secretion, cell death, or the development of a stress-resistant state. The significance of the inflammasome for the initiation of the inflammatory response during systemic diseases has already been shown and members of the inflammasome complex were recently found to be induced in acute brain injury. However, the specific pathophysiologic role of the inflammasome in neurodegenerative disorders still remains to be clarified. The underlying theories (e.g., danger signal theory) along with the signaling pathways that link the inflammasome to acute neurodegeneration will be discussed here. Furthermore, the stimuli that potentially activate the inflammasome in cerebral ischemia will be specified, as well as their relation to well-known pathways activating the innate immune response (e.g., Toll-like receptor signaling) and the consequences that result from their activation (beneficial versus deleterious).
ROS-Independent Preconditioning in Neurons via Activation of mitoKATPChannels by BMS-191095
Authors: Gáspár Tamás , Snipes James A , Busija Anna R , Kis Béla , Domoki Ferenc , Bari Ferenc , Busija David W
Published: January 2008

Previously, we have shown that the selective mitochondrial ATP-sensitive potassium (mitoKATP) channel opener BMS-191095 (BMS) induces neuronal preconditioning (PC); however, the exact mechanism of BMS-induced neuroprotection remains unclear. In this study, we have identified key components of the cascade resulting in delayed neuronal PC with BMS using isolated rat brain mitochondria and primary cultures of rat cortical neurons. BMS depolarized isolated mitochondria without an increase in reactive oxygen species (ROS) generation and induced rapid phosphorylation of Akt and glycogen synthase kinase-3β. Long-term (3 days) treatment of neurons with BMS resulted in sustained mitochondrial depolarization, decreased basal ROS generation, and elevated ATP levels. This treatment also elicited almost complete protection against glutamate excitotoxicity, which could be abolished using the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin, but not with the superoxide dismutase (SOD) mimetic M40401. Long-term BMS treatment induced a PI3K-dependent increase in the expression and activity of catalase without affecting manganese SOD and copper/zinc-dependent SOD. Finally, the catalase inhibitor 3-aminotriazole dose-dependently antagonized the neuroprotective effect of BMS-induced PC. In summary, BMS depolarizes mitochondria without ROS generation, activates the PI3K—Akt pathway, improves ATP content, and increases catalase expression. These mechanisms appear to play important roles in the neuroprotective effect of BMS.
LEP Collider Moves Beyond the Z0
Authors: Ladbury Ray
Published: January 2008

Last year, after six years of precisely mapping out the physics of Z0-boson production and decay, CERN's Large Electron-Positron collider completed its role as the Z0 factory called LEP 1 and began to metamorphose into LEP 2—a W+W− or W-pair factory. The transformation, scheduled for completion in June, involves replacing 32 of the conventional copper 1.4-mega-volt/meter accelerating elements in the 27-km-circumference collider with superconducting cavities having an accelerating gradient of 6.0 MV/m.
New Compound Brightens Outlook for Photorefractive Polymers
Authors: Levi Barbara Goss
Published: January 2008

A picture is worth a thousand—no, hundreds of thousands—of bits of information. If that picture can be optically stored and retrieved, with the data bits moving in and out in parallel, one has a very fast way to transfer information. So goes one of the motivations for research on optical holography: One can record data as a pattern of 0's and 1's on a page and rapidly store an image of that page.
Horseradish Can Clean Industrial Wastewater
Authors: Lubkin Gloria B.
Published: January 2008

Horseradish is so potent that it clears clogged sinuses, tickles taste-buds when dabbed on gefilte fish or roast beef… and now, it can clean up industrial wastewater. Jean-Mare Bol-lag, codirector of Penn State's Center for Bioremediation and Detoxification, and Jerzy Dec, a research associate there, report that minced horseradish root can clean wastewater containing phenols a lot more cheaply than other chemical and physical treatments.
Los Alamos Accelerator Group Reports Its Evidence for Neutrino Oscillation
Authors: Schwarzschild Bertram
Published: January 2008

Despite its somewhat hectic provenance, the paper submitted to Physical Review Letters in June by the Liquid Scintillator Neutrino Detector collaboration at Los Alamos brings us the first serious evidence of neutrino oscillation in an accelerator experiment. All previous substantial hints of neutrino oscillation have come from astrophysical sources, over which experimenters have no control. (See PHYSICS TODAY, April, page 19.) The LSND result, like all the astrophysical evidence, is still inconclusive. But it has set the particle physics and cosmological communities abuzz.
Researchers Report Evidence for Lasing Without Inversion
Authors: Levi Barbara Goss
Published: January 2008

We have come to think that lasing requires an inversion of population between atoms in an excited state and those in a lower state: Normally the probability of absorption from the lower state equals the probability of emission from the higher state, so that the only way to have more photons coming out than going in is to start with more atoms in the upper state. It would be useful to decouple the probabilities of emission and absorption, so that one could lower the loss associated with absorption without reducing the emission.
Satellite Mapping of Terra Incognita Provides Welcome Relief
Authors: Ladbury Ray
Published: January 2008

The topography of the Earth is less well known than that of Mars or Venus, largely because about three-fourths of it is hidden beneath the oceans, out of reach of direct observation by satellites. Now, however, the ocean-floor topography of much of Earth's Southern Hemisphere has been revealed in an innovative map (see the figure on page 22), created by Walter Smith of the National Oceanographic and Atmospheric Administration and David Sandwell of Scripps Institution of Oceanography. Using the abundant gravimetric data collected by the ERS-1 and GEOSAT satellites in combination with the few available ships' depth soundings, they have mapped the region between latitudes 30° S and 70° S with a finer resolution (better than 10 kilometers) than previously available. On the map, variations in hue represent altitude variations, or depth below sea level, as identified in the map scale, while changes in color saturation highlight the topography in light and shadow as it would appear when illuminated from longitude 0°.
Oscillating Granular Layers Produce Stripes, Squares, Hexagons…
Authors: Lubkin Gloria B.
Published: January 2008

Take a bunch of granular particles, put them in a container on a rigid platform and shake the system vertically. You might find heaping, convective rolls, size segregation or traveling waves. Recent experiments with several layers of particles have produced, at a critical acceleration, a sharp transition from a flat surface to standing-wave patterns oscillating at either one-half or one-quarter the excitation frequency.
German Neutron Source Gets Go-Ahead
Authors: Levi Barbara Goss
Published: January 2008

Neutron scattering research in Germany should get a boost from the construction of a new research reactor, called the FRM-2, at the Technical University of Munich. The German federal government and the state of Bavaria have approved funding for the reactor, which, together with the beam hall and instruments, is expected to cost DM720 million. Although the reactor will have only about one-third the power of the 57-megawatt facility at the Institut Laue-Langevin in Grenoble, France—the research reactor with the highest neutron flux—the FRM-2 will have somewhat over half its flux (8×1014 neutrons per square centimeter per second compared to 1.5×1015 cm−2 s−1 at the ILL). With a capacity for 30-35 instruments, the reactor will provide additional neutron capability at a time when beam lines at ILL and other reactors are heavily oversubscribed. FRM-2 will have a cold source to provide neutrons whose temperatures are below 60 K; the flux of these cold neutrons will be comparable to that at the ILL. A unique feature of the FRM-2 will be a built-in facility for treating human cancer with fission neutrons. The chief designer of the FRM-2 is Klaus Boning of the Technical University of Munich.
STM Gets to the Core of the Matter in a High-Tc Superconductor
Authors: Levi Barbara Goss
Published: January 2008

Since the 1986 discovery of high-temperature superconductors, researchers have been struggling to understand the nature of the magnetic flux lines that thread through these copper-oxide materials when the field is above a few tens of gauss. the flux lines take the form of vortices, swirling supercurrents that confine the magnetic field to a cylindrical region around a quiescent center. Understanding them is more than an academic exercise: Motion of the vortices, when pushed by a high enough current, introduces resistivity and limits the long-sought high-field applications. (See PHYSICS TODAY, October 1992, page 17.
…and Martin Perl Wins for Discovering the Tau Lepton
Authors: Schwarzshild Bertram
Published: January 2008

Sharing this year's physics Nobel Prize with Frederick Reines (see the previous news story) is Martin L. Perl, a professor at the Stanford Linear Accelerator Center (SLAC). The Swedish academy cites Perl “for the discovery of the tau lepton,” in 1975.
Nobel Chemistry Prize Gives a Stratospheric Boost to Atmospheric Scientists
Authors: Levi Barbara Goss
Published: January 2008

Reaching out in an interdisciplinary direction, the Royal Swedish Academy of Sciences has awarded the 1995 Nobel Prize in Chemistry to Paul Crutzen, Mario Molina and F. Sherwood Rowland for “their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone.” The award comes on the eve of the 1996 global ban on ozone-depleting chemicals, mandated by the 1987 Montreal Protocol and its later updates.
Serving the Physics Community: AIP's Physics Programs
Authors: Rigden John S.
Published: January 2008

The place of physics in our society, in the workplace and in academic institutions is undergoing change, and we physicists need to be agile and responsive to the challenges and opportunities we face. The professional staff at the American Institute of Physics wants to be responsive; for this reason, advisory committees meet regularly to help staff members evaluate and improve their activities.
Near-Field Optical Microscopes Take a Close Look at Individual Molecules
Authors: Collins Graham P.
Published: January 2008

Researchers have recently looked at individual dye molecules with a resolution of about 50 nanometers, about six times finer than the diffraction limit for the 600-nm light they are using. They achieved these unprecedented optical resolutions and the sensitivity needed for single-molecule detection with nearfield scanning optical microscopy. This technique surpasses the diffraction limit by placing a subwavelength-sized optical element within tens of nanometers of the sample: Traveling over such short distances, light has no opportunity to diffract and take on its asymptotic far-field characteristics. And unlike other high-resolution imaging techniques, such as electron microscopy and scanning tunneling microscopy, the technique allows the study of fluorescence in molecules’ natural biochemical environments, such as the biological membranes responsible for photosynthesis.
Astronomers are Poised for the ‘Crash of 1994’: Boom Or Bust?
Authors: Benka Stephen G.
Published: January 2008

If comets are like “dirty snowballs,” as Fred Whipple proposed in the early 1950s, then Jupiter is about to suffer the embarrassment of being hit by a boomerang snowball as astronomers around the world watch. Like many snowballs, Comet Shoemaker-Levy 9 broke apart in mid-flight. Comet SL9 was first seen, already in orbit around Jupiter, in March 1993, by a trio of avid comet hunters: Carolyn and Gene Shoemaker of the US Geological Survey in Flagstaff, Arizona, and David Levy, a contributing editor to Sky & Telescope magazine. By May of last year the comet's orbit had been determined. It was realized by Brian Marsden (Smithsonian Astrophysical Observatory, Cambridge, Massachusetts) that in July 1992, SL9 had come within 95 000 km of Jupiter's center of mass, where it experienced tidal forces sufficient to rip it apart. On its next pass, SL9 will aim to come within 30 000 km of Jupiter's center of mass. Because the planet's radius is about 71 000 km, Jupiter will suffer a direct hit. Astronomers will be on hand to evaluate its injuries, if any.
Experiment Reveals a New Type of Electron System
Authors: Levi Barbara Goss
Published: January 2008

In most metals, the electrons behave as if they were independent of one another. Although each electron really does interact with the other electrons and phonons, the net effect is felt only as a kind of molasses through which the otherwise freely moving electron must slog. Thus one an usually treat metallic systems as a low-density gas of weakly interacting particles, accounting for the average interactions simply by assigning an effective mass to the electrons. Such a model is commonly called a Fermi liquid. In one-dimensional systems, however, the Coulomb forces between the electrons intervene more strongly and produce quite a different behavior.
Repaired Hubble Sees Strong Evidence of a Supermassive Black Hole in M87
Authors: Collins Graham P.
Published: January 2008

Researchers using the refurbished Hubble Space Telescope to study the galaxy M87 have seen new and compelling dynamical evidence that a supermassive black hole lurks at the galaxy's core. Using the Wide Field-Planetary Camera, the astronomers obtained an image of what seems to be a gaseous accretion disk centered on the point of origin of a relativistic jet that emanates from M87. (See the figure at right.) Spectrographic measurements reveal that relative to M87's overall motion, one side of the disk is receding from us at about 500 km/sec and the other is approaching at a similar velocity, strongly suggesting that the gas is orbiting the center of M87 at that velocity. (See the figure on page 18.) Given the 60-light-year distance of the two points from the center of the motion and assuming stable circular orbits, one readily deduces with ordinary Newtonian mechanics that material amounting to about 2.4×109 solar masses (M⊙) lurks at the center of M87, in a volume that contains far too few visible stars to account for so much matter.
New Hubble Camera Finds Many Protoplanetary Disks in Orion Nebula
Authors: Schwarzschild Bertram
Published: January 2008

The Orion nebula, a glowing gas cloud studded with brilliant young stars, was discovered in the sword of Orion by Nicolas Fabri de Peiresc just one year after Galileo first looked at the night sky through a telescope. Ever since then, astronomers have hastened to train every new kind of instrument on this spectacular stellar nursery. So that's what NASA did last December, just after the second-generation Wide Field-Planetary Camera was put aboard the Hubble Space Telescope by visiting astronauts. (See PHYSICS TODAY, March, page 42.) Outfitted with corrective optics designed to compensate for the much-lamented flaw in Hubble's primary mirror, the new camera was promptly pointed at a portion of the Orion nebula that its predecessor had imaged two years earlier.
Veil of Secrecy is Lifted from Parts of Livermore's Laser Fusion Program
Authors: Levi Barbara Goss
Published: January 2008

Researchers from Japan, Germany and elsewhere are finally getting a more detailed look at the results of experiments on inertial confinement fusion done at the Nova facility at Lawrence Livermore National Laboratory, site of the most powerful laser devoted to fusion research. Although Livermore scientists have reported on their progress in general terms over the years, significant aspects of their experiments and models remained classified because the information had potential relevance to nuclear weapons as well as to the development of a commercial energy source. But a Department of Energy spokesperson told us that the department decided last December to declassify portions of the program as part of Secretary Hazel O'Leary's “openness initiative.” The announcement of the declassification noted that researchers in other countries were publishing their own work, which in many cases duplicated results developed earlier in the US but never made public because of classification restrictions.
Magneto-Optic Traps are Set for Radioactive Atoms
Authors: Ladbury Ray
Published: January 2008

For years atomic and nuclear physicists have dreamed of doing experiments with dense, trapped gases of cold, neutral, radioactive atoms. With such samples they could perform precision spectroscopy of radioactive atoms, search for electric dipole moments (indicative of time-reversalsymmetry violation), study parity violation and electroweak effects in atomic transitions and β decay, and more. As reported in a recent issue of Physical Review Letters, such experiments took a step (or perhaps three) closer to reality when groups at the Lawrence Berkeley Laboratory, the State University of New York at Stony Brook and the University of Colorado demonstrated the feasibility of quickly and efficiently transporting and capturing large numbers of atoms from a vapor or an atomic beam.
Bolivian Quake Gives a Rare Glimpse of Earth's Interior
Authors: Ladbury Ray
Published: January 2008

The most challenging paradox of the magnitude-8.2 earthquake that struck the Bolivian Alteplano (literally, “high plane”) on 9 June is not that it caused minimal damage while still being strong enough to be felt throughout most of the Western Hemisphere, to excite normal modes of vibration of the Earth never before seen and potentially to enable geophysicists to map the Earth's interior with 50 km resolution. Rather it is that the earthquake could occur at all. That is because the depth of the Bolivian quake (640 km) puts it in a rare class of earthquakes called “deep focus” quakes, whose foci lie between 75 km and 670 km beneath the Earth's surface. How such deep-focus quakes occur in the mantle, where high pressures and temperatures cause rock under stress to flow rather than fracture, has been a subject of intense interest and controversy ever since their existence was established in the late 1920s. The importance of the Bolivian quake is further increased because it is the first really large, very deep event to occur since the deployment of modern global networks of digital seismographs. Three networks of portable broadband seismographs recently deployed in South America promise to provide an unprecedented close-up view of the quake. (The color relief map on the cover of this issue shows the positions of the stations in these networks in relation to the quake's epicenter.) Researchers hope that data from the earthquake will yield a wealth of information on the Earth's interior as well as shed light on how deep-focus events occur.
Tabletop Capillary-Discharge Soft-X-Ray Laser Demonstrated
Authors: Collins Graham P.
Published: January 2008

Optical-wavelength lasers are ubiquitous, from the checkout scanner at the supermarket to the CD player in your Discman. They come in all sizes, all the way down to microelectronic scales. Lasers operating at wavelengths shorter than 100 nanometers, however, have been rare and expensive behemoths ever since their first demonstration a decade ago; they rely on bulky, high-powered optical lasers to produce the plasma conditions needed for x-ray lasing.
Anomalous Cosmic-Ray Data Suggest Oscillation Between Neutrino Flavors
Authors: Schwarzschild Bertram
Published: January 2008

When high-energy cosmic ray protons and nuclei hit the top of the atmosphere, they generate showers of mesons that quickly decay to muons, electrons, positrons and neutrinos. A few kilometers below the surface of the Earth, nothing remains but the most energetic muons and almost all of the neutrinos. Irrespective of the complicated details, unimpeachable particle theory dictates that these hadronic showers produce, on average, twice as many muon-flavored neutrinos (νμ and ν̄μ) as electron-flavored neutrinos (νe and ν̄e). The details leave wiggle room for only a few percent departure from this predicted 2:1 ratio.
HERA is Now Running with Longitudinally Polarized Positrons
Authors: Schwarzschild Bertram
Published: January 2008

Recently there have been some interesting developments at HERA, the Hadron-Electron Ring Accelerator that wends its circular way for 6 kilometers beneath the streets and parks of Hamburg. Since the fall of 1992 this uniquely asymmetric pair of storage rings has been providing experimenters with collisions between 820-GeV protons and 30-GeV electrons. (See PHYSICS TODAY March 1992, page 21.) Since July, however, HERA has been running with positrons instead of electrons, and will continue to do so at least until the end of 1995. And more importantly, the circulating HERA positron (or electron) beam can now be longitudinally polarized at will. That's an important first: No other electron storage ring has ever achieved longitudinal polarization.
Is the Noise of Overhead Neighbors Inescapable?
Authors: Benka Stephen G.
Published: January 2008

If you have ever lived in an apartment and had overhead neighbors, you have probably been anoyed by the noise they made just walking. This can be a problem even in luxury condominiums designed with acoustic privacy in mind. Now we know why.
Nobelists Brockhouse and Shull Gave Neutron Scattering a Jump Start
Authors: Levt Barbara Goss
Published: January 2008

More than 40 years ago Bertram N. Brockhouse and Clifford G. Shull started working separately at two of the world's first nuclear reactors, exploiting the opportunities to do basic research with the relatively large fluxes of neutrons from those machines. Their efforts helped launch the technique of neutron scattering, which is now widely used to study materials: Being uncharged, neutrons penetrate deeply to interact with the atomic nuclei of a sample, and having a magnetic moment, they also probe its magnetic structure. Today neutron scattering occupies thousands of researchers in condensed matter, materials physics, chemistry, biology and engineering (see PHYSICS TODAY, November, page 17).
Stirring Things Up in Waste Tank at Hanford
Authors: Levi Barbara Goss
Published: January 2008

At the Hanford Nuclear Reservation in Richland, Washington first steps are being taken toward mitigation of the threat posed by hydrogen buildup in a milliongallon tank of radioactive waste. Shown in the photograph is a 64-foothigh pump being lowered on 4 July through a 40-inch-diameter pipe into tank 101-SY, which is buried below ground. Of the 177 tanks of high-level waste stored at Hanford, 101-SY is the most notorious, because of the high concentrations of hydrogen that are produced by its mixture of radioactive materials and organic chemicals. (See PHYSICS TODAY, March 1992, page 17.) The material in the tank forms a viscous slurry at the bottom, covered by a liquid layer and topped by thick pieces of crust. As the hydrogen is generated, it is trapped in the slurry, and about every three months it is released in a giant “burp.” Hydrodynamic models have indicated that the pump should be able to stir the tank contents enough to promote a continual release of hydrogen gas and prevent the accumulation of explosive concentrations.
High-frequency dynamic nuclear polarization using biradicals: A multifrequency EPR lineshape analysis
Authors: Hu Kan-Nian , Song Changsik , Yu Hsiao-hua , Swager Timothy M. , Griffin Robert G.
Published: January 2008

To date, the cross effect (CE) and thermal mixing (TM) mechanisms have consistently provided the largest enhancements in dynamic nuclear polarization (DNP) experiments performed at high magnetic fields. Both involve a three-spin electron-electron-nucleus process whose efficiency depends primarily on two electron-electron interactions—the interelectron distance R and the correct electron paramagnetic resonance (EPR) frequency separation that matches the nuclear Larmor frequency, ∣ωe2−ωe1∣=ωn. Biradicals, for example, two 2,2,6,6-tetramethyl-piperidine-1-oxyls (TEMPOs) tethered with a molecular linker, can in principle constrain both the distance and relative g-tensor orientation between two unpaired electrons, allowing these two spectral parameters to be optimized for the CE and TM. To verify this hypothesis, we synthesized a series of biradicals—bis-TEMPO tethered by n ethylene glycol units (a.k.a. BTnE)—that show an increasing DNP enhancement with a decreasing tether length. Specifically at 90K and 5T, the enhancement grew from ∼40 observed with 10mM monomeric TEMPO, where the average R∼56Å corresponding to electron-electron dipolar coupling constant ωd∕2π=0.3MHz, to ∼175 with 5mM BT2E (10mM electrons) which has R∼13Å with ωd∕2π=24MHz. In addition, we compared these DNP enhancements with those from three biradicals having shorter and more rigid tethers—bis-TEMPO tethered by oxalyl amide, bis-TEMPO tethered by the urea structure, and 1-(TEMPO-4-oxyl)-3-(TEMPO-4-amino)-propan-2-ol (TOTAPOL) TOTAPOL is of particular interest since it is soluble in aqueous media and compatible with DNP experiments on biological systems such as membrane and amyloid proteins. The interelectron distances and relative g-tensor orientations of all of these biradicals were characterized with an analysis of their 9 and 140GHz continuous-wave EPR lineshapes. The results show that the largest DNP enhancements are observed with BT2E and TOTAPOL that have shorter tethers and the two TEMPO moieties are oriented so as to satisfy the matching condition for the CE.
The structure of aqueous sodium hydroxide solutions: A combined solution x-ray diffraction and simulation study
Authors: Megyes Tünde , Bálint Szabolcs , Grósz Tamás , Radnai Tamás , Bakó Imre , Sipos Pál
Published: January 2008

To determine the structure of aqueous sodium hydroxide solutions, results obtained from x-ray diffraction and computer simulation (molecular dynamics and Car-Parrinello) have been compared. The capabilities and limitations of the methods in describing the solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in describing the hydration spheres of the sodium ion and yield structural information on the anion’s hydration structure. Classical molecular dynamics simulations were not able to correctly describe the bulk structure of these solutions. However, Car-Parrinello simulation proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions and bulk structure of solutions. The results of Car-Parrinello simulations were compared with the findings of diffraction experiments.
Viscoelasticity and primitive path analysis of entangled polymer liquids: From F-actin to polyethylene
Authors: Uchida Nariya , Grest Gary S. , Everaers Ralf
Published: January 2008

We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide range of reduced polymer densities: (i) semidilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semiflexible (bio)polymers such as F-actin or suspensions of rodlike viruses. Together, these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts.
Saturation of backward stimulated scattering of laser in kinetic regime: Wavefront bowing, trapped particle modulational instability, and trapped particle self-focusing of plasma waves
Authors: Yin L. , Albright B. J. , Bowers K. J. , Daughton W. , Rose H. A.
Published: January 2008

Backward stimulated Raman and Brillouin scattering (SRS and SBS) of laser are examined in the kinetic regime using particle-in-cell simulations. The SRS reflectivity measured as a function of the laser intensity in a single hot spot from two-dimensional (2D) simulations shows a sharp onset at a threshold laser intensity and a saturated level at higher intensities, as obtained previously in Trident experiments [D. S. Montgomery et al., Phys. Plasmas 9, 2311 (2002)]. In these simulations, wavefront bowing of electron plasma waves (ion acoustic waves) due to the trapped particle nonlinear frequency shift, which increases with laser intensity, is observed in the SRS (SBS) regime for the first time. Self-focusing from trapped particle modulational instability (TPMI) [H. A. Rose, Phys. Plasmas 12, 12318 (2005)] is shown to occur in both two- and three-dimensional SRS simulations. The key physics underlying nonlinear saturation of SRS is identified as a combination of wavefront bowing, TPMI, and self-focusing of electron plasma waves. The wavefront bowing marks the beginning of SRS saturation and self-focusing alone is sufficient to terminate the SRS reflectivity, both effects resulting from cancellation of the source term for SRS and from greatly increased dissipation rate of the electron plasm waves. Ion acoustic wave bowing also contributes to the SBS saturation. Velocity diffusion by transverse modes and rapid loss of hot electrons in regions of small transverse extent formed from self-focusing lead to dissipation of the wave energy and an increase in the Landau damping rate in spite of strong electron trapping that reduces Landau damping initially. The ranges of wavelength and growth rate associated with transverse breakup of the electron-plasma wave are also examined in 2D speckle simulations as well as in 2D periodic systems from Bernstein–Greene–Kruskal equilibrium and are compared with theory predictions.
Flexible metal grating based optical fiber probe for photonic integrated circuits
Authors: Scheerlinck Stijn , Taillaert Dirk , Van Thourhout Dries , Baets Roel
Published: January 2008

An optical probe for photonic integrated circuits is proposed and demonstrated. The device is based on a single-mode fiber containing a subwavelength period metal grating on the facet. When approaching an integrated waveguide, light can be efficiently coupled between probe and waveguide without the need for integrated coupling structures, paving the way for wafer-scale circuit testing. A nanoimprint-and-transfer process were developed for fabricating this probe in a single step. We report 15% coupling efficiency between a gold grating fiber probe and a 220nm×3μm silicon-on-insulator waveguide and demonstrate testing of an integrated microring resonator using two probes.
Microstructure and magnetic properties of FePt-SiO2 granular films with Ag addition
Authors: Seki T. O. , Takahashi Y. K. , Hono K.
Published: January 2008

Perpendicularly anisotropic L10-ordered FePt-SiO2 granular films with an average grain size of 15 nm and a relatively narrow size distribution were prepared by cosputtering Fe, Pt, and SiO2 on MgO (001) substrates at 700 °C. By reducing the substrate temperature to 500 °C, the average grain size was further refined to 6.2 nm with a standard deviation of 1.7 nm; however, the FePt particles remained as an A1 disordered phase. Alloying Ag to the FePt particles and increasing the Ar gas pressure in the sputtering chamber were found to be both beneficial for enhancing the L10 ordering while keeping the fine granular structure.
Thermal and spontaneous remagnetization in the bulk amorphous ferromagnets Nd60Fe30Al10 and Nd60Fe20Co10Al10
Authors: Collocott S. J. , Dunlop J. B. , Watterson P. A.
Published: January 2008

Bulk amorphous Nd60Fe30Al10 and Nd60Fe20Co10Al10 alloys, which display hard magnetic properties, have been prepared by arc melting and quenching into a copper mould. Following magnetic saturation and dc demagnetization, at room temperature, both materials are seen to exhibit the phenomena of thermal and spontaneous remagnetizations. The behavior of the observed thermal and spontaneous remagnetizations is similar to that exhibited in nucleation controlled sintered permanent magnets. The thermal remagnetization data are fitted using a model, developed from the theory of Schumann and Jahn [J. Magn. Magn. Mater. 232, 231 (2001)] for explaining thermal remagnetization in polycrystalline magnets, to gauge its usefulness when applied to amorphous ferromagnets. The spontaneous remagnetization behavior is interpreted in the context of the Preisach model.
Room temperature organic spintronics
Authors: Morley N. A. , Rao A. , Dhandapani D. , Gibbs M. R. J. , Grell M. , Richardson T.
Published: January 2008

The magnetoresistance (MR) of organic spin valves containing the spacer layer regioregular poly(3-hexylthiophene) (RR-P3HT), which is a conjugated polymer, has been studied at room temperature. Investigations have been made of the influence of the thickness of organic spacer layer on the magnetoresistance of Fe50Co50∕RR-P3HT∕Ni81Fe19 spin valves. It was determined that the MR decreased as the layer thickness increased, consistent with the spin coherence length in this material. It has been observed at room temperature that there is the co-occurrence of two magnetoresistance effects, the spin-valve magnetoresistance, and anisotropic magnetoresistance in the magnetic electrodes.
Thin-film superparamagnetic resonance in a γ-Fe2O3 nanoparticle array
Authors: Zohar S. , Hultman K. , O’Brien S. , Bailey W. E.
Published: January 2008

We have investigated the microwave properties of monodisperse, superparamagnetic γ-Fe2O3 nanoparticle arrays using broadband ferromagnetic resonance. We identify a novel field for resonance relationship in the films. Compared with ferromagnetic films of equal magnetization, resonance frequencies are suppressed for in-plane magnetization and enhanced for out-of-plane magnetization, over the range of 0–8Ghz. The behavior identified is that of a superparamagnetic thin film, where thin-film dipolar fields act on a gradually saturating magnetization described by the Langevin function. Resonance linewidths can be described by the natural thermal dispersion in properties of the system.
Structural and soft magnetic properties of a new nanocrystalline Fe-based and B-free alloy
Authors: Long Jianguo , Laughlin D. E. , McHenry M. E.
Published: January 2008

A new nanocrystalline Fe-based soft magnetic alloy is discussed here. Ingots of nanocrystalline alloys (FeCu)80ZrxSi20−x (x=5, 6, and 8) were prepared by arc melting. The ingots were remelted and cast into 25–30μm thick ribbons by a single roller melt spinning method. X-ray diffraction (XRD) revealed the as-spun ribbons to be amorphous. The structural evolution of these samples was studied by XRD and transmission electron microscopy (TEM) after annealing at 450, 480, and 550°C. XRD shows the primary nanocrystallization product to be the α-Fe(Si) phase. The grain size was observed by TEM to be ∼10nm after annealing at 480°C for 1h and 14nm after 550°C for 1h. ac soft magnetic properties were measured using a Walker AMH 401 ac permeameter. The core loss at an exciting frequency f=100kHz and maximum induction Bm=1kG was determined to be less than 19W∕kg.
The possible origin of RE–Fe–B thin films with c-axis texture
Authors: Tang S. L. , Gibbs M. R. J. , Davies H. A. , Mateen N. E. , Nie B. , Du Y. W.
Published: January 2008

RE–Fe–B (RE-rare earth) films are prepared on a Nb buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The crystal structure, magnetic structure, and magnetic properties of RE–Fe–B films are studied. The results show that after annealing at 590°C, the c-axis texture and perpendicular anisotropy of RE–Fe–B films increase strongly with the increase of deposition temperature from 300to470°C. We suggest that the texture of the RE2Fe14B phase or the texture of the amorphous phase created in the first deposition process is a potential origin of the strong c-axis texture in the crystallized films.
Crossover of electron transmission mechanism and spin filtering effect at Fe∕GaAs(001) interfaces
Authors: Wada E. , Itoh M. , Taniyama T.
Published: January 2008

A clear correlation between the spin filtering effect of optically pumped spin-polarized electrons at Fe∕GaAs(001) Schottky interfaces and its electron transmission mechanism is reported. Current-voltage (I-V) characteristics of the Schottky diode demonstrate tunneling and thermionic emission transmission processes in the low and high bias voltage regions, respectively. A spin filtering current contribution, on the other hand, exhibits a significant peak at a particular bias voltage while spin selectivity shows a shoulder at the same bias voltage. The bias voltage where the features occur corresponds well to the crossover regime of the electron transmission mechanisms. The spin selectivity also shows a field dependence similar to the magnetization curve, assuring that the spin selectivity has its origin in the spin filtering effect.