bluuebunny/crossref_metadata_2025 huggingface dataset:
An investigation of dissolution methods for Lu‐Hf and Sm‐Nd isotope studies in zircon‐ and garnet‐bearing whole‐rock samples
Authors: Mahlen Nancy J. , Beard Brian L. , Johnson Clark M. , Lapen Thomas J.
Published: January 2008

The distinct chemical behavior of Lu and Hf can limit complete sample dissolution and spike‐sample equilibration. Here we investigate the effects that four dissolution methods (hotplate, low‐temperature microwave, high‐temperature microwave, and steel‐jacketed Parr bomb) have on the Sm‐Nd and Lu‐Hf isotope compositions of rocks. Any of the dissolution methods produce high‐quality Sm‐Nd isotope data, and hotplate dissolution of young, volcanic rocks produces adequate Lu‐Hf data. However, low‐temperature microwave and hotplate dissolution methods produce significantly different Lu/Hf and 176Hf/177Hf ratios as compared to Parr‐bomb dissolution data for old samples or those that contain garnet, rutile, or zircon. A characteristic feature of incomplete spike‐sample equilibration and sample dissolution for garnet‐bearing samples is anomalously high 176Lu/177Hf ratios relative to 176Hf/177Hf ratios. Our results show that for Lu‐Hf isotope studies of rocks of any significant age, the errors in calculated initial ɛHf values may exceed 10 ɛHf units if complete dissolution and spike‐sample equilibration are not attained for garnet‐ or zircon‐bearing rocks. High‐temperature and pressure dissolution such as that which can be achieved through Parr‐bomb dissolution is critical to ensure complete dissolution of refractory phases such as garnet or zircon.
A doubling in snow accumulation in the western Antarctic Peninsula since 1850
Authors: Thomas Elizabeth R. , Marshall Gareth J. , McConnell Joseph R.
Published: January 2008

We present results from a new medium depth (136 metres) ice core drilled in a high accumulation site (73.59°S, 70.36°W) on the south‐western Antarctic Peninsula during 2007. The Gomez record reveals a doubling of accumulation since the 1850s, from a decadal average of 0.49 mweq y−1 in 1855–1864 to 1.10 mweq y−1 in 1997–2006, with acceleration in recent decades. Comparison with published accumulation records indicates that this rapid increase is the largest observed across the region. Evaluation of the relationships between Gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong, temporally stable and positive relationship with the Southern Annular Mode (SAM). Furthermore, the SAM is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site (r = 0.66). The association between Gomez accumulation and ENSO is complex: while sometimes statistically significant, the relationship is not temporally stable. Thus, at decadal scales we can utilise the Gomez accumulation as a suitable proxy for SAM variability but not for ENSO.
Flux transfer events simultaneously observed by Polar and Cluster: Flux rope in the subsolar region and flux tube addition to the polar cusp
Authors: Le G. , Zheng Y. , Russell C. T. , Pfaff R. F. , Slavin J. A. , Lin N. , Mozer F. , Parks G. , Wilber M. , Petrinec S. M. , Lucek E. A. , Rème H.
Published: January 2008

In this paper we present observational evidence of a flux transfer event observed simultaneously at low‐latitude by Polar and at high‐latitude by Cluster. This event occurs on 21 March 2002, when both Cluster and Polar are located near local noon but with a large latitudinal separation. During the event, Cluster is moving outbound from the polar cusp to the magnetosheath and Polar is in the magnetosheath near the equatorial magnetopause. The observations show that a flux transfer event occurs between the equator and the northern cusp. Polar and Cluster observe the FTE's two open flux tubes: Polar encounters the southward moving flux tube near the equator and Cluster encounters the northward moving flux tube at high latitude. The low‐latitude FTE appears to be a flux rope with helical magnetic field lines as it has a strong core field and the magnetic field component in the boundary normal direction exhibits a strong bipolar variation. Unlike the low‐latitude FTE, the high‐latitude FTE observed by Cluster does not exhibit the characteristic bipolar perturbation in the magnetic field. However, the plasma data clearly reveal its open flux tube configuration. It shows that the magnetic field lines have straightened inside the FTE and become more aligned to the neighboring flux tubes as it moves to the cusp. Enhanced electrostatic fluctuations have been observed within the FTE core, both at low and high latitudes. This event provides a unique opportunity to understand high‐latitude FTE signatures and the nature of time‐varying reconnection. It shows that existing FTE models cannot accommodate all the features in global observations, and coordinated measurements from largely spaced multiple spacecraft place important constraints which are crucial to the development and refinement of FTE models.
A numerical model for the transport of a boulder by tsunami
Authors: Imamura Fumihiko , Goto Kazuhisa , Ohkubo Shigeki
Published: January 2008

We have conducted hydraulic experiments in an open channel with cubic and rectangular shaped solid blocks on the slope for investigating the boulder transport process by tsunami. In our experiments, the block was mainly seen to be transported by a bore due to rolling or saltation rather than by sliding. Previous models for the boulder transport by tsunamis assumed sliding as a mode of transport for the boulder. Therefore, these models underestimated the distance of the boulder moved by the tsunami when it was transported due to rolling or saltation. In this study, we have developed a practical model for the transport of a boulder by tsunami, which takes into account the various transport modes. We introduce an empirical variable coefficient of friction by assuming that the coefficient decreases with decrease in ground contact time when the block was transported by rolling or saltation. With the aid of this parameter, the model can explain various modes of transport, i.e., sliding, rolling, and saltation, and reproduces the experimental results well. We further applied this improved model to a tsunami boulder at Inoda area in Ishigaki Island, Japan, which was transported by the 1771 Meiwa tsunami. The calculated distance of transport of the boulder was approximately 650 m, which is consistent with the description in the historical document. Based on our calculations, we estimated hydraulic values of the tsunamis. Estimation of such hydraulic values is important for understanding the behavior and power of the historical tsunamis, besides aiding future disaster mitigation efforts.
Detailed characterization of a cold Antarctic eddy
Authors: Swart Neil C. , Ansorge Isabelle J. , Lutjeharms Johann R. E.
Published: January 2008

Eddy formation in the Southern Ocean plays a critical role in meridional exchanges of heat and salt. It has also been shown to have a significant impact on primary productivity and on the creation of preferred feeding regions for birds and other predators. This eddy formation is not geographically uniform, but is concentrated in certain specific regions, particularly where the Antarctic Circumpolar Current crosses shallow bathymetry. One such region is at the South‐West Indian Ridge where eddies are formed that subsequently drift past the Prince Edward Islands. We have studied such an eddy in detail. It was at least 1000 m deep, had a radius of 60–90 km, a heat content of 5.40 × 1019 J and rotated at a rate of 1 revolution every 5 days. Altimetric observations show that it was formed at 51°S; 32°E and that its intensity–as expressed as its sea level anomaly–declined by ∼40% of the original value within 144 days. This relatively rapid dissipation suggests that these eddies do not have a lifetime of more than 14 months. During that period they will have carried their anomalous heat and salt content about 1.5 degrees of latitude.
A note on the theoretical foundations of particle tracking methods in heterogeneous porous media
Authors: Ramirez Jorge M. , Thomann Enrique A. , Waymire Edward C. , Chastanet Juliette , Wood Brian D.
Published: January 2008

In this technical note the stochastic process for the path of particles undergoing convection dispersion in a heterogeneous media with sharp interfaces is derived. The derived process is shown to correspond to the numerical particle tracking scheme introduced on a more heuristic basis by Hoteit et al. (2002) who validated the accuracy of their numerical method in controlled laboratory experiments. Specifically, it is shown that in the direction transverse to the flow U(y) and across an interface where the diffusion coefficient is discontinuous the stochastic particle path t → Y*(t) is given by a rescaled version of Itô and McKean's (1963) α‐skew Brownian motion for a uniquely determined value of α that depends on the values of the diffusion coefficient at either side of the interface. These results help supply a theoretical foundation that supports the numerical schemes and experimental findings of Hoteit et al. (2002).
Melting behavior of an idealized membrane model
Authors: Del Pópolo M. G. , Ballone P.
Published: January 2008

The melting behavior of an idealized model giving rise to two-dimensional (2D) structures at low temperature and low density is investigated by Monte Carlo simulations. The system is made of particles carrying a spin of constant length and variable orientation, whose potential energy is the sum of a repulsive spherical pair interaction, and of a spin-spin contribution, reminiscent of but essentially different from the electrostatic dipole-dipole interaction. The simulation results show that the model phase diagram is determined by the interplay of a ferro- to paraelectric transition in the spin part and of the solid to fluid transition found in simple pair-potential models. The 2D solid melts into a three-dimensional (3D) fluid when the spin-spin interaction is weak. Strong spin-spin interactions give rise to two transitions, the first one corresponding to the melting of the 2D solid into a 2D fluid, and the second one corresponding to the crossover from a 2D to a 3D fluid. The fluid phase stable in between these two transitions provides a model for the liquid state arising in organic and biological membranes across their main transition.
Probing the electronic and structural properties of doped aluminum clusters: MAl12− (M=Li, Cu, and Au)
Authors: Pal R. , Cui Li-Feng , Bulusu S. , Zhai Hua-Jin , Wang Lai-Sheng , Zeng X. C.
Published: January 2008

Photoelectron spectroscopy (PES) is combined with theoretical calculations to investigate the electronic and atomic structures of three doped aluminum clusters, MAl12− (M=Li, Cu, and Au). Well-resolved PES spectra have been obtained at two detachment photon energies, 266nm (4.661eV) and 193nm (6.424eV). Basin-hopping global optimization method in combination with density-functional theory calculations has been used for the structural searches. Good agreement between the measured PES spectra and theoretical simulations helps to identify the global minimum structures. It is found that LiAl12− (C5v) can be viewed as replacing a surface Al atom by Li on an icosahedral Al13−, whereas Cu prefers the central site to form the encapsulated D3d-Cu@Al12−. For AuAl12− (C1), Au also prefers the central site, but severely distorts the Al12 cage due to its large size.
Supernova Distance Measurements Suggest an Older, Larger Universe
Authors: Schwarzschild Bertram
Published: January 2008

The Hubble constant, the conversion factor that translates the recessional velocities of remote galaxies into distances, is the only fundamental parameter of cosmology that astronomers think they know to within a factor of two. In the 1970s H0 was thought to be somewhere around 50 km/sec per megaparsec. (A megaparsec is 3.3 million light years.) Then in the next decade, measurements of H0 seemed to be converging on 80 or 90 km/sec-Mpc. But in just the last few months, three novel determinations of H0 based on the observation of supernovae have placed the Hubble constant back down in the regime 50–60 km/sec-Mpc.
Experiments Provide Evidence for the Fractional Charge of Quasiparticles
Authors: Khurana Anil
Published: January 2008

In the fractional quantum Hall effect, the Hall conductance is quantized. In the most common manifestation of the effect, which was first observed in the two-dimensional electron gas sandwiched between the semiconducting layers of a GaAs-AlGaAs heterostructure, the magnetic field dependence of the Hall resistance shows an ascending-staircase-type behavior with increasing field strength. The steps in the staircase correspond to Hall conductance values of the form (p/q)e2/h, and they occur around the magnetic field values for which the number of electrons per magnetic field quantum is p/q, with p and q integers and q usually odd.
New Technology Telescope Actively Corrects for Misalignments
Authors: Levi Barbara Goss
Published: January 2008

Of the 15 optical instruments scanning the heavens from the La Silla Observatory in Chile, the recently completed New Technology Telescope is neither the biggest nor the most expensive. But its resolution does exceed that of its neighbors. It owes its sharp images to so-called active optics that adjust during observations for distortions due to maladjustments or misalignments. Astronomers are quite excited about the fresh detail in pictures emerging from NTT as its observing program gets under way. They were especially impressed that the telescope performed so well from the moment it saw its first light. (The telescope was dedicated in March after one year of commissioning.)
Evidence Accumulates at Last for the Wigner Crystal
Authors: Khurana Anil
Published: January 2008

Experimenters may finally have observed the crystalline phase of a degenerate electron gas. Electrons in such a phase do not move freely through the available space; they are confined to the sites of a lattice and their quantum mechanical zero-point motions are limited to small oscillations about their mean positions. Eugene Wigner had proposed this phase based on his theoretical analyses in the 1930s. The “Wigner crystal” phase has been the focus of much discussion for twenty years, since experimenters have been able to fabricate a variety of systems where the phase might be realized.
A second-order Markov process for modeling diffusive motion through spatial discretization
Authors: Sant Marco , Papadopoulos George K. , Theodorou Doros N.
Published: January 2008

A new “mesoscopic” stochastic model has been developed to describe the diffusive behavior of a system of particles at equilibrium. The model is based on discretizing space into slabs by drawing equispaced parallel planes along a coordinate direction. A central role is played by the probability that a particle exits a slab via the face opposite to the one through which it entered (transmission probability), as opposed to exiting via the same face through which it entered (reflection probability). A simple second-order Markov process invoking this probability is developed, leading to an expression for the self-diffusivity, applicable for large slab widths, consistent with a continuous formulation of diffusional motion. This model is validated via molecular dynamics simulations in a bulk system of soft spheres across a wide range of densities.
Postscript: Reviewers and Authors Comment on Report
Authors: Lubkin Gloria B.
Published: January 2008

The review committee for the DEW study, headed by George Pake, transmitted the report to the APS Council on 20 April. In his transmittal letter, Pake noted that recent statements from the Strategic Defense Initiative Organization indicated that kineticenergy weapons, not directed-energy weapons, are being emphasized as a short-term strategy for ballistic missile defense. Under such plans DEWs are largely relegated to discriminating against decoys, he wrote. Although the study dealt with both decoy discrimination and target destruction, it emphasized the latter. The study group had not been charged with examining kineticenergy weapons components or systems; while the study was under way, SDIO shifted its emphasis.
Free-Electron Lasers Take Small Steps Toward Distant Goal
Authors: Levi Barbara Goss
Published: January 2008

Until recently, no free-electron laser was able to convert more than 5% of the energy from an electron beam into microwave radiation. Last fall, however, a team from Lawrence Livermore National Laboratory and the University of California at Berkeley published a (previously classified) report that they had operated a free-electron laser with an unprecedented 40% efficiency at a wavelength of 8.6 mm. The peak power exceeded 1 gigawatt. Meanwhile, researchers at Los Alamos National Laboratory who operate a free-electron laser of different design at a shorter wavelength (10 microns) have reported a modest increase in efficiency from 1.3% to 2% with peak power output of 20 MW, as well as development of several promising enhancements of their laser operation. In yet another experiment, a Stanford-TRW team has operated an FEL in the visible region of the spectrum (525 nm) with a peak power as high as 170 kW.
Massive Objects in Galactic Nuclei May Be Black Holes
Authors: Andersen Per H.
Published: January 2008

New evidence indicates that there is much hidden matter in galactic nuclei. Quasars are thought to be galaxies with active nuclei, often characterized by nonthermal radio emission and oppositely directed colinear jets. About 1970 Donald Lynden-Bell and Martin Rees (both Institute of Astronomy, Cambridge, UK) proposed the paradigmatic quasar model: a supermassive black hole surrounded by an accretion disk. In this model a disk overloaded with infalling matter spurts out oppositely directed jets perpendicular to the plane of the disk. “The new work is exciting evidence for how long the quasar phenomenon lasts,” Rees tells us.
Probing the Early Universe with Quasar Light
Authors: Schwarzschild Bertram
Published: January 2008

A powerful new cosmological probe is coming of age, giving us access to regions so remote that we have seen nothing of them less luminous than their quasars. But quasars are as atypical as they are wondrous. We've only seen a few thousand. To study the structure and evolution of the cosmos, one wants to look at the less ostentatious, ordinary inhabitants of the distant realms—galaxies and aggregates of hydrogen gas.
Bednorz and Müller Win Nobel Prize for New Superconducting Materials
Authors: Khurana Anil
Published: January 2008

Georg Bednorz and Alex Müller (IBM Zurich Research Laboratory at Rüschlikon, Switzerland) share this year's Nobel Prize in Physics for “their discovery of new superconducting materials.” The announcement of the prize, worth $340 000 this year, caused little surprise among physicists. Few doubted that the discovery by Bednorz and Müller merited the Nobel Prize; speculations on what year the prize would be awarded have abounded since last January.
Two-Neutrino Double β-Decay Seen; Neutrinoless Decay Sought
Authors: Levi Barbara Goss
Published: January 2008

Many nuclei with even numbers of protons and neutrons can undergodouble beta decay, emitting two electrons and two neutrinos, but the halflife for this process is so long that it had been deduced until recently only by measuring the abundance of daughter nuclei from double beta decay of elements in geologic materials. Now Steven Elliott, Alan Hahn and Michael Moe of the University of California at Irvine have observed the double beta decay of selenium-82 in their laboratory and determined its half life to be 1.1−0.3+0.8×1020 years, a time interval that is orders of magnitude longer than any previously detected in a laboratory. Besides being a feat in its own right, the Irvine measurement is a milestone en route to a more elusive goal—observation of a double beta decay in which two electrons but no neutrinos emerge. This neutrinoless decay, which proceeds by the exchange of a virtual neutrino between the two neutrons, can occur only if neutrinos have mass. It is strictly forbidden by the standard theory of electroweak interactions but is predicted as a manifestation of the small symmetry breaking that arises in some grand unified field theories.
Structure, microstructure, and high-temperature transport properties of La1−xCaxMnO3−δ thin films and polycrystalline bulk materials
Authors: Aguirre M. H. , Canulescu S. , Robert R. , Homazava N. , Logvinovich D. , Bocher L. , Lippert Th. , Döbeli M. , Weidenkaff A.
Published: January 2008

Single-phase samples of La1−xCaxMnO3−δ (LCMO), x≈0.3, prepared by pulsed reactive crossed beam laser ablation on SrTiO3 (STO) substrates, and soft chemistry synthesized powders were studied by various methods. The precise study of the crystal structure and microstructures by a combination of electron diffraction and high-resolution electron microscopy revealed a monoclinic distortion of the GdFeO3-type structure, P21/c space group, in both types of materials, i.e., the thin films and powder compound. The analysis of the LCMO/STO interface showed nonhomogeneous stress states and a composition that results in a different superstructure from the usual detected structure. The temperature-dependent thermoelectric power in the case of thin films presented an anomalous behavior compared to those from the powder compound. A structural transition at high temperature (T≈750 K) influences the thermopower behavior as well as the thermal conductivity values.
A high-voltage pulse transformer with a modular ferrite core
Authors: Liu Z. , Winands G. J. J. , Yan K. , Pemen A. J. M. , Van Heesch E. J. M.
Published: January 2008

A high ratio (winding ratio of 1:80) pulse transformer with a modular ferrite core was developed for a repetitive resonant charging system. The magnetic core is constructed from 68 small blocks of ferrites, glued together by epoxy resin. This allows a high degree of freedom in choosing core shape and size. Critical issues related to this modular design are the size tolerance of the individual ferrite blocks, the unavoidable air gap between the blocks, and the saturation of the core. To evaluate the swing of the flux density inside the core during the charging process, an equivalent circuit model was introduced. It was found that when a transformer is used in a resonant charging circuit, the minimal required volume of the magnetic material to keep the core unsaturated depends on the coupling coefficient of the transformer and is independent of the number of turns of the primary winding. Along the flux path, 17 small air gaps are present due to the inevitable joints between the ferrite blocks. The total air gap distance is about 0.67mm. The primary and secondary windings have 16 turns and 1280 turns, respectively, and the actually obtained ratio is about 1:75.4. A coupling coefficient of 99.6% was obtained. Experimental results are in good agreement with the model, and the modular ferrite core works well. Using this transformer, the high-voltage capacitors can be charged up to more than 70kV from a low-voltage capacitor with an initial charging voltage of about 965V. With 26.9J energy transfer, the increased flux density inside the core was about 0.23T, and the core remains unsaturated. The energy transfer efficiency from the primary to the secondary was around 92%.
Special Issue: Complexity And Materials Research
Authors: Chaudhari Praveen
Published: January 2008

In physics, simplicity has always been equated with beauty. Today in physics related to research in materials, however, a single broad trend is clear: The degree of complexity is increasing. This is evident not only in the structure of the materials but also in the techniques used for their characterization, in their synthesis and in their properties, which frequently need to satisfy diverse requirements. Our traditional metaphor, it appears, may need to be complemented with another observation: Complexity is seductive.
Modern Tests of Special Relativity
Authors: Haugan Mark P. , Will Clifford M.
Published: January 2008

From our perspective one hundred years after the fact, the null result of the Michelson-Morley ether-drift experiment clearly marked the beginning of the end for the Newtonian notions of absolute space and time. At the time, however, it took 20 years of work by H. A. Lorentz, Henri Poincaré and others for most physicists to come to the same conclusion. In 1887, fundamental physics appeared to be essentially complete. Newtonian mechanics and Maxwell's electrodynamics were in hand, and a grand unification of physics seemed within reach. It was expected that a purely mechanistic basis for the ether interpretation of Maxwell's equations could be constructed and would provide a final unity of physics. This was a concise and powerful world view that was not easily discarded, but the null result of Michelson-Morley challenged its very heart.
Reminiscences of the Early Days of Fission
Authors: Barschall Henry H.
Published: January 2008

Roger Stuewer has described how Léon Rosenfeld brought the news that uranium undergoes fission to Princeton's Physics Journal Club on the evening of 16 January 1939—the day on which Niels Bohr and Rosenfeld had arrived in New York from Denmark. (See Stuewer's article in PHYSICS TODAY, October 1985, page 48). Bohr had first learned of the discovery of fission from Otto Frisch on 3 January 1939, and Rosenfeld's report was the first information received by physicists in the United States. I was in the audience and the news had an immediate impact on my own activities, and it continued to affect my work for the next six years. The following are some of my recollections of that period.
Laser Cooling
Authors: Wineland David J. , Itano Wayne M.
Published: January 2008

In the photograph on the opposite page we see a single mercury ion held nearly at rest in an electromagnetic “trap.” Physicists have seen individual atoms before, in arrays imaged by field ion microscopes and more recently by vacuum tunneling microscopes, but what we see here is different. It graphically demonstrates a physicist's ideal: holding a single isolated atom nearly at rest for careful examination.
Thoughts of a Retiring APS President
Authors: Drell Sidney D.
Published: January 2008

I view this talk as an occasion for a bit of self-indulgence. It is an opportunity to say a number of things that have been on my mind on a broad range of subjects.
The Birth of Neutron Stars and Black Holes
Authors: Burrows Adam
Published: January 2008

Neutron stars are nothing if not exotic. Most are the residues of massive stars that, after exhausting their thermonuclear fuel, die spectacularly as supernovae. Fifty percent more massive than our Sun, but only 20 kilometers in diameter, they are the densest objects in the universe. At the surface of a neutron star, the acceleration due to gravity is in excess of 1011 times that at the surface of Earth, so that the binding energy of a parcel of matter in a neutron star is about 10% of its rest mass. Hence mass accretion onto a neutron star, which releases over 100 MeV/nucleon, is a far more efficient energy conversion process than thermonuclear fusion, which releases approximately 8 MeV/nucleon. Theory suggests that neutron stars are about 95% neutrons in “chemical” equilibrium with a small admixture of protons and electrons: n⇄p++e−. Some investigators have likened a neutron star to a giant nucleus with atomic mass about 1057. The pressure of strongly interacting degenerate neutrons at supranuclear densities is balanced by gravity to maintain a hydrostatic equilibrium in the canonical configuration described above. Neutron stars therefore are laboratories for both nuclear physics and general relativity.
The Surface of Crystalline Helium-4
Authors: Maris Humphrey J. , Andreev Aleksander F.
Published: January 2008

Although solid helium was first produced over 60 years ago, by Willem H. Keesom at Leiden, it is only in the last few years that physicists have studied the surface of this solid. They have discovered that the surface has remarkable properties of great scientific interest:

▸ It is extraordinarily pure chemically, and can be made isotopically pure and free of crystal defects.

▸ Its growth is easily manipulated (as the cover of this magazine indicates) because it is more a mechanical proćess than a thermal process. In this article we examine these properties and explain the consequent unique opportunities that the helium surface gives us for studying problems that are of general interest in surface physics. Most of the findings that we discuss come from the four countries where research on the surface of solid helium is most active: the United States, the Soviet Union (see figure 1), France and Israel.
Electrons and Ions at the Helium Surface
Authors: Dahm Arnold J. , Vinen W. F.
Published: January 2008

In the last two decades, two-dimensional systems have been found to exhibit phases and phase transitions unlike any seen in their three-dimensional counterparts. Quantization of the Hall conductance of an electron gas in a strong magnetic field, localization of electronic wavefunctions in the presence of infinitesimally small amounts of impurities, and infinite-order phase transitions in magnets and crystals are some examples of unusual phenomena in two dimensions. However, it was not merely a pursuit of the novel and the unexpected that got physicists interested in two-dimensional systems. In fact, studies of two-dimensional systems are useful for understanding surfaces of three-dimensional solids, interfaces between two three-dimensional phases and anisotropic solids in which the interactions in a plane of symmetry are much stronger than interplane couplings. Moreover, our understanding of why and how behavior of physical systems depends on spatial dimensionality has been enhanced considerably by studies of two-dimensional systems.
Quantized Vortices in Superfluid Helium-4
Authors: Glaberson William I. , Schwarz Klaus W.
Published: January 2008

When liquid helium-4 is cooled to 2.17 K it changes from an ordinary fluid to a superfluid somewhat similar in nature to superfluid helium-3 and to the electron fluid in superconductors. Extensive investigation over the last five decades has given us a highly refined phenomenological description of how superfluid He4 behaves, even though the underlying quantum theory is only partially understood. Much of the current research on superfluid He4 is part of a continuing effort to work out the implications of this phenomenological description, in the same way as classical fluid dynamicists are still working out the implications of the Navier-Stokes equations.
The Formation of Galaxies
Authors: Silk Joseph
Published: January 2008

Galaxies are beacons that cosmologists use to chart the universe out to its remotest depths. Yet unlike a lighthouse, built on a sturdy pillar of rock, a galaxy resembles an island of light constructed on quicksand in a continuous state of flux. Galaxies are not isolated objects, but are surrounded by close companions, with whom they often maintain intimate and ongoing relationships. The oldest stars in a galaxy are nearly as old as the universe itself, and a study of their properties yields clues about how galaxies evolved in the distant past. The galaxies themselves define space in the expanding universe. In this article, I will describe current ideas on how galaxies originated and acquired their observed forms, and how this knowledge promises to lead to insights into the evolution of the large-scale structure of the universe.
Leo Dana: Cryogenic Science and Technology
Authors: Donnelly Russell J.
Published: January 2008

Progress in low-temperature physics is so rapid today that it is difficult to realize that the field scarcely existed 100 years ago. Leo Isadore Dana is not a familiar name to many physicists, but his contributions during the years 1920–64, a period of many important advances in cryogenics, span a remarkable range of phenomena in low-temperature physics and technology. This article recalls some of the important projects, from basic research on liquid helium to a wide range of activities in cryogenic and other technology.
Asymptotic Freedom
Authors: Gross David J.
Published: January 2008

Nuclei are very strongly bound aggregates of protons and neutrons. The nucleons in turn, we now believe, are extremely strongly bound aggregates of quarks: so strongly bound that we have never seen a free quark. The nuclear force is not a constant, however, but varies with the distance between the quarks. The dynamics of the vacuum enhance the force at large distances, while at short distances the interaction grows weaker. The notion that the force between quarks becomes vanishingly small as the quarks come close together, or, equivalently, that the quarks become free particles at very large energies, is called asymptotic freedom. I was very fortunate to be able to contribute to the discovery of asymptotic freedom, so I shall start with a few historical remarks, describing my own personal road to this discovery, and then discuss the current status and significance of asymptotic freedom.
Special Issue: Nanoscale and Ultrafast Devices
Authors: Capasso Federico
Published: January 2008

This special issue explores some of the most exciting recent trends in semiconductor electron devices. These developments have been characterized by a strong interplay among three areas: the physical understanding of electronic transport, materials science techniques, particularly epitaxial growth of semiconductor thin films, and device fabrication technologies such as nanolithography. The interdependence of these factors has been the hallmark of this field since the invention of the transistor.
Probing Semiconductors with Femtosecond Pulses
Authors: Auston David H.
Published: January 2008

In semiconductor microelectronics, small distances and high speeds are closely related. Transistors with base lengths of only a few tens of nanometers have electron transit times that can be less than 1 picosecond. Indeed, this very fact has motivated much of the intense interest in very-small-scale electronic devices: To make something faster, one generally must make it smaller.
Ultrahigh-Speed Bipolar Transistors
Authors: Levi A. F. J. , Nottenburg R. N. , Chen Y. K. , Panish M. B.
Published: January 2008

The invention of the transistor in the late 1940s has had tremendous technological ramifications, heralding as it did an era of semiconductor microelectronics. At the heart of the transistor's device applications are its ability to amplify and the ease with which it can be fabricated in very complex integrated circuits.
Ultrafast Reaction Dynamics
Authors: Gruebele Martin , Zewail Ahmed H.
Published: January 2008

A decade ago this magazine devoted a special issue to laser chemistry (see PHYSICS TODAY, November 1980). One of the articles emphasized the importance of time scales in chemical reactions and the possible use of ultrashort lasser pulses to induce chemistry. Over the past 10 years new laser techniques, and gas-phase and molecular-beam experiments, have revealed much about the fundamental steps of elementary chemical reactions. These approaches and the tremendous detail they have exposed about the dynamics of chemical reactions are the subject of the present article.
Dynamics of Confined Molecular Systems
Authors: Drake J. M. , Klafter J.
Published: January 2008

The dynamic and thermodynamic properties of molecular systems are known to be modified by confinement in very small spaces. However, making explicit and unambiguous connections between the geometry of the confining space and the molecular behavior has proven to be difficult, and the connections, when made, are frequently controversial. Nonetheless studies show that within a family of similarly prepared porous materials, the effect of finite size on the behavior of confined liquids and gases scales with a single geometric property of the pore space.
On the Road to Tomsk
Authors: Kristiansen Magne , Guenther Arthur H. , Thompson James E.
Published: January 2008

From 25 June to 4 July 1989, a group of 20 US scientists and engineers from industry, academia and Federal research facilities had a singular opportunity to visit several previously “closed” Soviet scientific installationswhere research in pulsed-power technology is conducted. These installations, many of which had never been seen by a Westerner, included the Institute of High Current Electronics and the Nuclear Physics Institute, both in Tomsk; the Leningrad Polytechnic Institute; and the Kurchatov Institute for Atomic Energy's facility at Troitsk, near Moscow. Various members of the US group also visited the Yefremov Institute for Electro-Physical Apparatus (Leningrad), the Lebedev Institute (Moscow), the USSR Research Center for Surface and Vacuum Investigation (Moscow), the Institute of High Temperatures (Moscow), the Institute of Nuclear Physics (Novosibirsk) and others. Throughout our journey, Soviet researchers conveyed the spirit of glasnost through their candor and their interest in a genuine exchange of ideas, a spirit often missing from earlier US-Soviet scientific interactions.
Structured Fluids
Authors: Witten Thomas A.
Published: January 2008

Water, gasoline, pancake syrup, mucus, salad oil, cornstarch-and-water paste, Silly Putty, liquid dishwashing soap, egg white, glycerin, Vaseline, ketchup, model airplane glue, paint, toothpaste—this motley list of substances seems to defy scientific classification. Water, gasoline, salad oil and glycerin are clearly liquids. The other substances, strictly speaking, are also liquids, since they all flow on the application of stress. But the name “liquid” hardly captures the variety of behavior in these substances. The substances differ from one another in their mechanical responses almost as much as they differ from solids. In the first place, they differ enormously from one another in viscosity, the quantitative measure of a liquid's flow response. Furthermore, many of them have striking properties whose description requires variables besides viscosity. Syrup becomes sticky as it dries. Liquid dishwashing soap has the same consistency as syrup, but it does not become sticky on drying. Mucus, egg white and model airplane glue are springy and rubbery. Silly Putty and cornstarch paste flow on a tilted surface but shatter like a brittle solid on sudden impact. Dishwashing soap in water easily forms masses of long-lived foam. Even the simplest flow properties of toothpaste are qualitatively unliquid-like: It comes out of its tube as a plug rather unlike an ordinary liquid, which flows fastest in the middle of the opening.
Disorder, Dynamical Chaos and Structures
Authors: Gaponov-Grekhov Andrei V. , Robinovich Mikhail I.
Published: January 2008

Science, like life itself, often poses questions whose answers are so sophisticated and indefinite that one must either rely on the opinion established by the majority or refer to some article of “faith” rather than deductive knowledge. “Where does randomness come from?” “How does order arise from disorder?” These are perhaps the oldest questions of this kind. Anyone who has thought about the principles governing nature has surely faced such questions. Everyday life, as well as conventional learning in physics, has almost persuaded us that complex, irregular and intricate behavior is possible only in very complex systems and that the study of some of these very complex systems may be beyond the scope of physical theory. The vast multitude of molecules in a bottle filled with gas or a crowd of infuriated fans reacting to the news that a football match has been canceled suddenly, are both examples of complex systems. In such systems we usually fail to relate cause and effect uambigously—that is, we cannot predict the behavior of the system in detail and therefore conclude that it is random. Of course, there is always the hope that it might be possible to eliminate such seeming randomness and unpredictability if one had more precise knowledge about the system. Would having a detailed knowledge of the interaction among the elements of a complex system and comprehensive and precise information about their initial states allow one to make precise predictions about the system's behavior at large times, so that the system will not appear to be random? The answer is yes only if one believes in Laplacian determinism, which was one of the earliest dogmas of science.
Voyager 2's Encounter with the Gas Giants
Authors: Miner Ellis D.
Published: January 2008

It was 3:40 am Pacific daylight time, 25 August 1989. I had watched with fascination a video display of Voyager 2's radio signal after the spacecraft had passed through Neptune's thick atmosphere, and for the last 90 minutes I had been attempting to nap in a sleeping bag on the floor of my office at JPL. My computer had just awakened me with a reminder that the first of 23 high-resolution pictures of Neptune's moon Triton was about to appear on the small monitor on my desk. The adjacent office was crowded with a dozen or so of my coworkers excitedly anticipating the same pictures. The first image appeared on my screen; boisterous cheering simultaneously erupted from next door. All thoughts of sleep fled, and for the next two hours I, along with dozens of other Voyager personnel and millions of interested onlookers around the world, exulted in the amazing scenes being transmitted by a small robot more than 4.4 billion km (4.1 light-hours) away. Humanity was seeing for the first time the surface features of the most distant moon in our solar system.
Andrei Dmitrievich Sakharov
Authors: Drell Sidney , Okun Lev
Published: January 2008

At the time of his death from a heart attack on 14 December 1989, Andrei Dmitrievich Sakharov was recognized both as a great scientist and as a persistent and uncompromising fighter for human rights and political freedom for all. He lived to see his Russian homeland start on the path toward implementing the principles of democracy to which he had devoted the last two decades of his life. His leadership in the struggle of conscience and principle against raw political power earned him worldwide accolades as the conscience of humanity. Gentle and modest in person, but of unconquerable persistence in his commitment to principle and opposition to injustice, he had become, in the memorial words of a Russian commentator, both “the saint and martyr of perestroika.” With the end of his life, the curtain fell on a morality play with the dimensions of a historical epic.
Processing Digital Color Images: From Capture to Display
Authors: Allebach Jan P.
Published: January 2008

Color is a vital part of our everyday experience. It provides essential cues about our environment, adds aesthetic value to the world around us and even has a strong effect on our mood. Yet the role of color in this age of electronic information processing is surprisingly incomplete. We use color in separate and isolated systems and have no way to connect them. We photograph our families and look at the prints in albums; we view time-varying color images on our television sets; we sit in front of computer monitors that display multicolor windows and icons and perhaps some color pictures. How do we take the family photographs and display them on our televisions, or grab snapshots from television broadcasts and put them into our personal computers, or combine those images with those in the photo albums and print them as color images in a newsletter? These scenarios and others that involve capture, manipulation and display or printing of color images in heretofore unimagined ways are becoming realized in the workplace and home thanks to digital color. (Figure 1 shows a monitor display of one of the window-based products for processing digital color images, in this case Adobe Systems' Adobe-Photoshop.)
Stability and Transport Processes in Tokamak Plasmas
Authors: Callen James D. , Carreras Benjamin A. , Stambaugh Ronald D.
Published: January 2008

Tokamak experiments have made dramatic progress over the past two decades, and today plasma parameters are nearing the values needed for a fusion reactor. (See the article by J. Geoffrey Cordey, Robert J. Goldston and Ronald R. Parker on page 22.) In November 1991 the first deuterium-tritium experiments in the Joint European Torus in Abingdon, England, generated a peak fusion power of almost 2 megawatts and a total energy release of 2 megajoules in a 2-second pulse. Concomitant progress has been made in understanding the basic physics of tokamak plasmas; this was made possible by major developments in plasma science, nonlinear theory, plasma diagnostic capabilities and supercomputer calculations.
Consultant to Industry, Adviser to Government
Authors: Poke George
Published: January 2008

John Bardeen spent more than 80% of his post-PhD years in university positions, including his last 40 years at the University of Illinois. He might therefore justifiably be considered an academic scientist. But it was at the Bell Telephone Laboratories that John coinvented the transistor, which because of its enormous impact on modern technology was the work for which he was most widely known. Consequently, throughout John's career his views and advice on science and technology were continually sought by industry and government. John's work and ideas in these nonacademic spheres are the focus of this article.
Impaired cytoadherence of
Plasmodium falciparum
-infected erythrocytes containing sickle hemoglobin
Authors: Cholera Rushina , Brittain Nathaniel J. , Gillrie Mark R. , Lopera-Mesa Tatiana M. , Diakité Séidina A. S. , Arie Takayuki , Krause Michael A. , Guindo Aldiouma , Tubman Abby , Fujioka Hisashi , Diallo Dapa A. , Doumbo Ogobara K. , Ho May , Wellems Thomas E. , Fairhurst Rick M.
Published: January 2008

Sickle trait, the heterozygous state of normal hemoglobin A (HbA) and sickle hemoglobin S (HbS), confers protection against malaria in Africa. AS children infected with
Plasmodium falciparum
are less likely than AA children to suffer the symptoms or severe manifestations of malaria, and they often carry lower parasite densities than AA children. The mechanisms by which sickle trait might confer such malaria protection remain unclear. We have compared the cytoadherence properties of parasitized AS and AA erythrocytes, because it is by these properties that parasitized erythrocytes can sequester in postcapillary microvessels of critical tissues such as the brain and cause the life-threatening complications of malaria. Our results show that the binding of parasitized AS erythrocytes to microvascular endothelial cells and blood monocytes is significantly reduced relative to the binding of parasitized AA erythrocytes. Reduced binding correlates with the altered display of
P. falciparum
erythrocyte membrane protein-1 (PfEMP-1), the parasite's major cytoadherence ligand and virulence factor on the erythrocyte surface. These findings identify a mechanism of protection for HbS that has features in common with that of hemoglobin C (HbC). Coinherited hemoglobin polymorphisms and naturally acquired antibodies to PfEMP-1 may influence the degree of malaria protection in AS children by further weakening cytoadherence interactions.
Pediatric Acupuncture: A Review of Clinical Research
Authors: Gold Jeffrey I. , Nicolaou Colette D. , Belmont Katharine A. , Katz Aaron R. , Benaron Daniel M. , Yu Wendy
Published: January 2008

Practiced in China for more than 2000 years, acupuncture has recently gained increased attention in the United States as an alternative treatment approach for a variety of medical conditions. Despite its growing prevalence and anecdotal reports of success among pediatric populations, few empirically based studies have assessed the efficacy of acupuncture for children and adolescents. This article presents a review of the current literature, including a systematic appraisal of the methodological value of each study and a discussion of potential benefits and adverse effects of acupuncture. While acupuncture holds great promise as a treatment modality for diverse pediatric conditions, a significant amount of additional research is necessary to establish an empirical basis for the incorporation of acupuncture into standard care.