bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain wave evolution equation for nonlinear propagation in materials with mesoscopic mechanical elements
Authors: Gusev Vitalyi , Aleshin Vladislav
Published: December 2002

Nonlinear wave propagation in materials, where distribution function of mesoscopic mechanical elements has very different scales of variation along and normally to diagonal of Preisach–Mayergoyz space, is analyzed. An evolution equation for strain wave, which takes into account localization of element distribution near the diagonal and its slow variation along the diagonal, is proposed. The evolution equation provides opportunity to model propagation of elastic waves with strain amplitudes comparable to and even higher than characteristic scale of element localization near Preisach–Mayergoyz space diagonal. Analytical solutions of evolution equation predict nonmonotonous dependence of wave absorption on its amplitude in a particular regime. The regime of self-induced absorption for small-amplitude nonlinear waves is followed by the regime of self-induced transparency for high-amplitude waves. The developed theory might be useful in seismology, in high-pressure nonlinear acoustics, and in nonlinear acoustic diagnostics of damaged and fatigued materials.
Computation of scattering from N spheres using multipole reexpansion
Authors: Gumerov Nail A. , Duraiswami Ramani
Published: December 2002

A computational technique for the solution of problems of wave scattering from multiple spheres is developed. This technique, based on the T-matrix method, uses the theory for the translation and reexpansion of multipole solutions of the Helmholtz equation for fast and exact recursive computation of the matrix elements. The spheres can have prescribed radii, impedances, and locations. Results are validated by comparison with boundary element calculations, and by convergence analyses. The method is much faster than numerical methods based on discretization of space, or of the sphere surfaces. An even faster method is presented for the case when the spheres are aligned coaxially.
Humans detect gaps in broadband noise according to effective gap duration without additional cues from abrupt envelope changes
Authors: Allen Paul D. , Virag Tracy M. , Ison James R.
Published: December 2002

Previous studies of behavior and IC single units in the mouse support theoretical expectations that gaps with ramped trailing markers have reduced detectability compared to equivalent gaps with ramped leading markers. In experiment 1, detection probability and response speeds of humans listening for gaps in broadband noise were investigated by independently varying either leading marker fall-time (FT) or trailing marker rise-time (RT). Gaps with silent duration of 1, 4, or 12 ms were presented 2 s into a 3-s noise burst, with either abrupt marker onsets and offsets or linearly ramped RT/FT of 2, 4, or 8 ms durations. Addition of a nonzero RT or FT to the gap silent period increased detectability and also increased reaction speed on trials with “Yes” response, but there was no difference in detectability or response speeds between RT and FT conditions. Experiment 2 extended this finding to gaps having two, one, or no abrupt marker edges. These findings suggest that human listeners do not make use of abrupt onset or offset information to enhance gap detection, but seem to rely on the effective sound level reduction associated with the gap for detection.
Volumetric imaging with an amplitude-steered array
Authors: Frazier Catherine H. , Hughes W. Jack , O’Brien William D.
Published: December 2002

Volumetric acoustic imaging is desirable for the visualization of underwater objects and structures; however, the implementation of a volumetric imaging system is difficult due to the high channel count of a fully populated two-dimensional array. Recently, a linear amplitude-steered array with a reduced electronics requirement was presented, which is capable of collecting a two-dimensional set of data with a single transmit pulse. In this study, we demonstrate the use of the linear amplitude-steered array and associated image formation algorithms for collecting and displaying volumetric data; that is, proof of principle of the amplitude-steering concept and the associated image formation algorithms is demonstrated. Range and vertical position are obtained by taking advantage of the frequency separation of a vertical linear amplitude-steered array. The third dimension of data is obtained by rotating the array such that the mainlobe is mechanically steered in azimuth. Data are collected in a water tank at the Pennsylvania State University Applied Research Laboratory for two targets: a ladder and three pipes. These data are the first experimental data collected with an amplitude-steered array for the purposes of imaging. The array is 10 cm in diameter and is operated in the frequency range of 80 to 304 kHz. Although the array is small for high-resolution imaging at these frequencies, the rungs of the ladder are recognizable in the images. The three pipes are difficult to discern in two of the projection images; however, the pipes separated in range are clear in the image showing vertical position versus range. The imaging concept is demonstrated on measured data, and the simulations agree well with the experimental results.
Cluster control of a distributed-parameter planar structure—Middle authority control
Authors: Tanaka Nobuo , Snyder Scott D.
Published: December 2002

This paper proposes a generalized active vibration control approach, “cluster control,” that explicitly targets sets of structural modes with some common property. The approach falls into a category of MAC (middle authority control) between conventionally used LAC (low authority control) and HAC (high authority control), possessing the benefit of stability and control law simplicity analogous to LAC, while providing high control performance as well as some flexibility of control gain assignment similar to HAC. The structure of a cluster control system is outlined, showing that it is possible to control a target cluster without affecting the other clusters. A design procedure for the cluster control system is then proposed. Experimental results are also presented.
Laser ultrasonics in copy paper: Bending stiffness dependence on temperature and moisture content
Authors: Cornwell Matthew A. , Berthelot Yves H.
Published: December 2002

The A0 Lamb mode in copy paper is generated and detected by using laser ultrasonics. The frequency dependence of the group velocity of the A0 mode is found from the wavelet transform of the measured signal. A best fit of the dispersion curve against predictions based on orthotropic plate theory yields an estimate of the bending stiffness of the sample. The sample is enclosed in an environmental chamber so that the effects of temperature and humidity can be controlled. Results indicate that the bending stiffness decreases with increasing temperature at an approximate rate of 4×10−6 N m/°C, and that it decreases with increasing percent moisture content (PMC) at an approximate rate of 2×10−5 (N m)/PMC.
Antimasking aspects of harp seal (Pagophilus groenlandicus) underwater vocalizations
Authors: Serrano Arturo , Terhune John M.
Published: December 2002

Underwater sounds are very important in social communication of harp seals (Pagophilus groenlandicus) because they are the main means of long- and short-distance communication. Individual harp seals must try to avoid being masked and emit only those calls that will benefit them. Underwater vocalizations of harp seals were recorded during the breeding season. The physical characteristics associated with antimasking attributes of 16 call types were examined. Rising frequency or increasing amplitude within calls were not common. Most of the calls ended abruptly (range 145–966 dB/s), but call onset was more gradual. At high calling rates (95.1–135 calls/min) there were significantly more calls overlapping temporally than at medium (75.1–95 calls/min) or low (35–75 calls/min) calling rates, but even at the highest calling rates, 79.1% of the calls were not overlapped. When 2, 3, or 4 calls overlapped, there were significantly fewer frequency separations of less than 1/3 octave than would be expected by chance. This is important because sounds that are separated by less than 1/3 octave likely mask each other. When 2–4 calls are occurring simultaneously, only 4.5% to 14.2% are masked by virtue of being within 1/3 octave from their nearest neighbor. None of the overlappping calls was of the same type. This suggests that the seals are actively listening to each other’s calls and are not randomly using the different call types. Harp seals use frequency and temporal separation in conjunction with a wide vocal repertoire to avoid masking each other.
Pressure and velocity profiles in a static mechanical hemilarynx model
Authors: Alipour Fariborz , Scherer Ronald C.
Published: December 2002

This study examined pressure and velocity profiles in a hemilarynx mechanical model of phonation. The glottal section had parallel walls and was fabricated from hard plastic. Twelve pressure taps were created in the vocal fold surface and connected to a differential pressure transducer through a pressure switch. The glottal gap was measured with feeler gauges and the uniform glottal duct was verified by use of a laser system. Eight pressure transducers were placed in the flat wall opposite the vocal fold. Hot-wire anemometry was used to obtain velocity profiles upstream and downstream of the glottis. The results indicate that the pressure distribution on the vocal fold surface was consistent with pressure change along a parallel duct, whereas the pressures on the opposite flat wall typically were lower (by 8%–40% of the transglottal pressure just past mid-glottis). The upstream velocity profiles were symmetric regardless of the constriction shape and size. The jet flow downstream of the glottis was turbulent even for laminar upstream conditions. The front of the jet was consistently approximately 1.5 mm from the flat wall for glottal gaps of 0.4, 0.8 and 1.2 mm. The turbulence intensity also remained approximately at the same location of about 4 mm from the flat wall for the two larger gaps.
Measurement of urban traffic noise due to heavy cargo transport services
Authors: Ruffa Francisco , Gavinowich Daniel S. , Barkasz Erica A. , Ciccarella Pablo R.
Published: December 2002

The Acoustic and Electroacoustic Laboratory of the Buenos Aires University is working on a Traffic Noise Recommendation to be used in Argentina. To that end, measurements of traffic noise due to heavy cargo transport services were taken in a Buenos Aires neighbourhood, especially asked for by a neighborhood association. The goal of this measurement was to try to define a correct standard set for the annoyance level in order to pass that information to the city government and work together to improve the living standard of the inhabitants. The measured indexes were Leq, L90 and L10, as well as octave measurement focused on frequencies under 250 Hz. This paper will show the results of the measurements and the conclusions that were made.
Intonational phonology and the domain of liaison in French
Authors: Brown Rebecca , Jun Sun-Ah
Published: December 2002

French liaison is a phenomenon where certain word final consonants are pronounced as the onset of a following vowel-initial word. The application of liaison varies depending on a number of factors including morphological, phonological, syntactic, and sociolinguistic factors. For the cases where liaison applies postlexically, prosodic phonologists have claimed that liaison applies within a phonological phrase (PhP), a prosodic domain indirectly defined by syntax. However, many of the empirical studies (e.g., Morin and Kaye, 1982; de Jong, 1994; Post, 2000) have found data that cannot be accounted for by this view, suggesting that this characterization is inadequate. In the current study, liaison data were examined to see if the domain of liaison matches a prosodic unit defined by intonation under the framework of intonational phonology. Data were taken from Post (2000): 27 sentences [nine each in three conditions: the target sequence (C♯V) being inside a PhP, across optional PhPs and obligatory PhPs]. Sentences were randomized and printed with no internal punctuation. Intonation was analyzed using Jun and Fougerons (1995, 2000, in press) model of French intonation. Preliminary results show that the domain of liaison matches an accentual phrase, 91% (including all the optional PhPs), higher than the results predicted by PhP.
Source levels of impulsive sound sources in underwater acoustics
Authors: Chapman N. Ross
Published: December 2002

Impulsive sound sources have been used extensively in underwater acoustics for many different research applications. Since the initial work by Weston in developing a simple analytical model for an underwater explosion, there have been several theoretical and experimental programs designed to determine source levels. More recently, other types of sources such as air guns and water guns have been introduced from marine seismic research, and there is renewed interest in knowing accurate source levels for assessing the impact on marine environments. In this paper the results of a series of experiments carried out to measure the source levels of several different types of impulsive sources are summarized. These included traditional 0.82-kg SUS charges, small and medium sized air guns from 5–185 cu. in., and a 160 cu. in. water gun. The SUS charges were exploded at shot depths from 18–200 m, and the air guns and water guns were fired at shallow depths from 1–5 m, corresponding to the conventional operating depths. The experiments provided high-quality shot waveforms that were processed to determine calibrated source levels in 1/3 octave frequency bands from 10–600 Hz. The measured values are compared to predictions from Weston’s simple model.
The influence of spatialized background noise on ease of hearing in rooms
Authors: Shimizu Yasushi , Stefaniw Abigail , Smith Dana , Torres Rendell
Published: December 2002

The influence of irrelevant noise on worker’s performance has not yet been studied from the standpoint of spatialized background noise in rooms. This paper presents the detriment to Ease of Hearing due to spatial auditory events produced by intruding sound in open plan offices. Auralization is used to represent a generic open plan office noise environment that includes HVAC noise, an intruding voice, and a focus voice. Two different speech communication environments are presented to the listener. In the first presentation, the intruding voice is located far from the listener’s workstation (in the reverberant field) and is not localizable. In the second presentation, the intruding voice is localized near the listener’s workstation. The focus voice is localized in front of the listener for both presentations. These sounds are played over a five-channel auralization system. Listeners are tested for the degree of Ease of Hearing (EOH) of the focus voice. Psycho-acoustical test results are presented to show the difference between the Ease of Hearing in each case. Improvement strategies to keep high quality communication are also presented based on the results.
A theoretical analysis of the AWSUM fluctuation-based processors
Authors: Gilbert Kenneth E. , Talmadge Carrick L.
Published: December 2002

Nonlinear signal processing schemes developed originally by R. A. Wagstaff for ocean acoustics and named ‘‘AWSUM,’’ have been applied in this laboratory to atmospheric acoustic signals in the presence of wind noise. It has been found that the AWSUM processors can provide dramatic gains in the signal-to-noise ratio for narrow-band acoustic signals strongly degraded by wind noise. This paper presents a theoretical analysis of the AWSUM processors for narrow-band acoustic signals in the presence of Raleigh and non-Raleigh (intermittent) noise. The theory quantitatively explains the observed systematic behaviors of the AWSUM processors. In particular, it is shown that in the limit of large sample number, the signal-to-noise gain for AWSUM processors approaches the ratio N(0)/S(0), where N and S are the probability density distributions for the acoustic pressure squared, for noise alone and for noise-plus-signal, respectively. For a steady narrow-band signal in Raleigh noise, the ratio N(0)/S(0) is given by exp(SNR), where SNR is the usual linear signal-to-noise ratio (e.g., SNR=1 corresponds to 0 dB). For wind noise, which is intermittent noise, the ratio N(0)/P(0) is greater than exp(SNR), so that greater gain is predicted. The predictions are in accord with both simulated data and field data.
Soil Warming and Carbon-Cycle Feedbacks to the Climate System
Authors: Melillo J. M. , Steudler P. A. , Aber J. D. , Newkirk K. , Lux H. , Bowles F. P. , Catricala C. , Magill A. , Ahrens T. , Morrisseau S.
Published: December 2002

In a decade-long soil warming experiment in a mid-latitude hardwood forest, we documented changes in soil carbon and nitrogen cycling in order to investigate the consequences of these changes for the climate system. Here we show that whereas soil warming accelerates soil organic matter decay and carbon dioxide fluxes to the atmosphere, this response is small and short-lived for a mid-latitude forest, because of the limited size of the labile soil carbon pool. We also show that warming increases the availability of mineral nitrogen to plants. Because plant growth in many mid-latitude forests is nitrogen-limited, warming has the potential to indirectly stimulate enough carbon storage in plants to at least compensate for the carbon losses from soils. Our results challenge assumptions made in some climate models that lead to projections of large long-term releases of soil carbon in response to warming of forest ecosystems.
A Late Triassic Impact Ejecta Layer in Southwestern Britain
Authors: Walkden Gordon , Parker Julian , Kelley Simon
Published: December 2002

Despite the 160 or so known terrestrial impact craters of Phanerozoic age, equivalent ejecta deposits within distal sedimentary successions are rare. We report a Triassic deposit in southwestern Britain that contains spherules and shocked quartz, characteristic of an impact ejecta layer. Inter- and intragranular potassium feldspar from the deposit yields an argon-argon age of 214 ± 2.5 million years old. This is within the age range of several known Triassic impact craters, the two closest of which, both in age and location, are Manicouagan in northeastern Canada and Rochechouart in central France. The ejecta deposit provides an important sedimentary record of an extraterrestrial impact in the Mesozoic that will help to decipher the number and effect of impact events, the source and dynamics of the event that left this distinctive sedimentary marker, and the relation of this ejecta layer to the timing of extinctions in the fossil record.
The Cortical Topography of Tonal Structures Underlying Western Music
Authors: Janata Petr , Birk Jeffrey L. , Van Horn John D. , Leman Marc , Tillmann Barbara , Bharucha Jamshed J.
Published: December 2002

Western tonal music relies on a formal geometric structure that determines distance relationships within a harmonic or tonal space. In functional magnetic resonance imaging experiments, we identified an area in the rostromedial prefrontal cortex that tracks activation in tonal space. Different voxels in this area exhibited selectivity for different keys. Within the same set of consistently activated voxels, the topography of tonality selectivity rearranged itself across scanning sessions. The tonality structure was thus maintained as a dynamic topography in cortical areas known to be at a nexus of cognitive, affective, and mnemonic processing.
Melanopsin (
Opn4
) Requirement for Normal Light-Induced Circadian Phase Shifting
Authors: Panda Satchidananda , Sato Trey K. , Castrucci Ana Maria , Rollag Mark D. , DeGrip Willem J. , Hogenesch John B. , Provencio Ignacio , Kay Steve A.
Published: December 2002

The master circadian oscillator in the hypothalamic suprachiasmatic nucleus is entrained to the day/night cycle by retinal photoreceptors. Melanopsin (
Opn4
), an opsin-based photopigment, is a primary candidate for photoreceptor-mediated entrainment. To investigate the functional role of melanopsin in light resetting of the oscillator, we generated melanopsin-null mice (
Opn4
−/−
). These mice entrain to a light/dark cycle and do not exhibit any overt defect in circadian activity rhythms under constant darkness. However, they display severely attenuated phase resetting in response to brief pulses of monochromatic light, highlighting the critical role of melanopsin in circadian photoentrainment in mammals.
Alcohol Consumption Impairs Detection of Performance Errors in Mediofrontal Cortex
Authors: Ridderinkhof K. Richard , de Vlugt Yolande , Bramlage Aldo , Spaan Marcus , Elton Martin , Snel Jan , Band Guido P. H.
Published: December 2002

The anterior cingulate cortex (ACC) is a critical component of the human mediofrontal neural circuit that monitors ongoing processing in the cognitive system for signs of erroneous outcomes. Here, we show that the consumption of alcohol in moderate doses induces a significant deterioration of the ability to detect the activation of erroneous responses as reflected in the amplitude of brain electrical activity associated with the ACC. This impairment was accompanied by failures to instigate performance adjustments after these errors. These findings offer insights into how the effects of alcohol on mediofrontal brain function may result in compromised performance.
Increasing River Discharge to the Arctic Ocean
Authors: Peterson Bruce J. , Holmes Robert M. , McClelland James W. , Vörösmarty Charles J. , Lammers Richard B. , Shiklomanov Alexander I. , Shiklomanov Igor A. , Rahmstorf Stefan
Published: December 2002

Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 ± 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate.
Small Nuclear Ribonucleoprotein Remodeling During Catalytic Activation of the Spliceosome
Authors: Makarov Evgeny M. , Makarova Olga V. , Urlaub Henning , Gentzel Marc , Will Cindy L. , Wilm Matthias , Lührmann Reinhard
Published: December 2002

Major structural changes occur in the spliceosome during its activation just before catalyzing the splicing of pre–messenger RNAs (pre-mRNAs). Whereas changes in small nuclear RNA (snRNA) conformation are well documented, little is known about remodeling of small nuclear ribonucleoprotein (snRNP) structures during spliceosome activation. Here, human 45
S
activated spliceosomes and a previously unknown 35
S
U5 snRNP were isolated by immunoaffinity selection and were characterized by mass spectrometry. Comparison of their protein components with those of other snRNP and spliceosomal complexes revealed a major change in protein composition during spliceosome activation. Our data also suggest that the U5 snRNP is dramatically remodeled at this stage, with the Prp19 complex and other factors tightly associating, possibly in exchange for other U5 proteins, and suggest that after catalysis the remodeled U5 is eventually released from the postsplicing complex as a 35
S
snRNP particle.
Experimental Identification of Downhill Protein Folding
Authors: Garcia-Mira Maria M. , Sadqi Mourad , Fischer Niels , Sanchez-Ruiz Jose M. , Muñoz Victor
Published: December 2002

Theory predicts the existence of barrierless protein folding. Without barriers, folding should be noncooperative and the degree of native structure should be coupled to overall protein stability. We investigated the thermal unfolding of the peripheral subunit binding domain from
Escherichia coli
's 2-oxoglutarate dehydrogenase multienzyme complex (termed BBL) with a combination of spectroscopic techniques and calorimetry. Each technique probed a different feature of protein structure. BBL has a defined three-dimensional structure at low temperatures. However, each technique showed a distinct unfolding transition. Global analysis with a statistical mechanical model identified BBL as a downhill-folding protein. Because of BBL's biological function, we propose that downhill folders may be molecular rheostats, in which effects could be modulated by altering the distribution of an ensemble of structures.
Antioxidants in Photosynthesis and Human Nutrition
Authors: Demmig-Adams Barbara , Adams William W.
Published: December 2002

The harnessing of solar energy by photosynthesis depends on a safety valve that effectively eliminates hazardous excess energy and prevents oxidative damage to the plant cells. Many of the compounds that protect plant cells also protect human cells. Improving plant resistance to stress may thus have the beneficial side effect of also improving the nutritional quality of plants in the human diet. The pathways that synthesize these compounds are becoming amenable to genetic manipulation, which may yield benefits as widespread as improved plant stress tolerance and improved human physical and mental health.
Discounting and Reciprocity in an Iterated Prisoner's Dilemma
Authors: Stephens D. W. , McLinn C. M. , Stevens J. R.
Published: December 2002

The Iterated Prisoner's Dilemma (IPD) is a central paradigm in the study of animal cooperation. According to the IPD framework, repeated play (repetition) and reciprocity combine to maintain a cooperative equilibrium. However, experimental studies with animals suggest that cooperative behavior in IPDs is unstable, and some have suggested that strong preferences for immediate benefits (that is, temporal discounting) might explain the fragility of cooperative equilibria. We studied the effects of discounting and strategic reciprocity on cooperation in captive blue jays. Our results demonstrate an interaction between discounting and reciprocity. Blue jays show high stable levels of cooperation in treatments with reduced discounting when their opponent reciprocates, but their levels of cooperation decline in all other treatment combinations. This suggests that stable cooperation requires both reduced discounting and reciprocity, and it offers an explanation of earlier failures to find cooperation in controlled payoff games.
Evo-Devo Branches Out
Authors: Irish Vivian F.
Published: December 2002

Developmental Genetics and Plant Evolution
. Quentin C. B. Cronk, Richard M. Bateman, and Julie A. Hawkins, Eds. Taylor and Francis, London, 2002. 559 pp. $168, £105. ISBN 0-415-25790-5. Paper, $72, £45. ISBN 0-415-25791-3.

Combining contributions from the fields of molecular genetics, systematics, morphology, and evolution, the authors offer an "evo-devo" perspective on the diversification of terrestrial plants.
Observation of a Strongly Interacting Degenerate Fermi Gas of Atoms
Authors: O'Hara K. M. , Hemmer S. L. , Gehm M. E. , Granade S. R. , Thomas J. E.
Published: December 2002

We report on the observation of a highly degenerate, strongly interacting Fermi gas of atoms. Fermionic lithium-6 atoms in an optical trap are evaporatively cooled to degeneracy using a magnetic field to induce strong, resonant interactions. Upon abruptly releasing the cloud from the trap, the gas is observed to expand rapidly in the transverse direction while remaining nearly stationary in the axial direction. We interpret the expansion dynamics in terms of collisionless superfluid and collisional hydrodynamics. For the data taken at the longest evaporation times, we find that collisional hydrodynamics does not provide a satisfactory explanation, whereas superfluidity is plausible.
MONODROMY APPROACH TO QUANTUM COMPUTING
Authors: GIORGADZE G.
Published: December 2002

In this work, a gauge approach to quantum computing is considered. It is assumed that there exists a classical procedure for placing certain classical system in a state described by a holomorphic vector bundle with connection with logarithmic singularities. This bundle and its connection are constructed with the aid of unitary operators realizing the given algorithm using methods of the monodromic Riemann–Hilbert problem. Universality is understood in the sense that for any collection of unitary matrices there exists a connection with logarithmic singularities whose monodromy representation involves these matrices.
BOSE-EINSTEIN CONDENSATION IN A DILUTE GAS: THE FIRST 70 YEARS AND SOME RECENT EXPERIMENTS
Authors: CORNELL E. A. , WIEMAN C. E.
Published: December 2002

Bose-Einstein condensation, or BEC, has a long and rich history dating from the early 1920s. In this article we will trace briefly over this history and some of the developments in physics that made possible our successful pursuit of BEC in a gas. We will then discuss what was involved in this quest. In this discussion we will go beyond the usual technical description to try and address certain questions that we now hear frequently, but are not covered in our past research papers. These are questions along the lines of "How did you get the idea and decide to pursue it? Did you know it was going to work? How long did it take you and why?" We will review some of our favorites from among the experiments we have carried out with BEC. There will then be a brief encore on why we are optimistic that BEC can be created with nearly any species of magnetically trappable atom. Throughout this article we will try to explain what makes BEC in a dilute gas so interesting, unique, and experimentally challenging.
ACOUSTIC PROPERTIES OF MgB2 SUPERCONDUCTOR UNDER PRESSURE
Authors: LI FENG-YING , WANG RU-JU , YU RI-CHENG , LIU ZHEN-XING , JIN CHANG-QING
Published: December 2002

The pressure dependence of sound velocity of longitudinal and shear waves were measured up to 0.5 GPa using a pulse echo overlap method on polycrystalline single-phase MgB 2 superconductor which was high pressure synthesized and with a T c of 39 K. The pressure dependence of Debye temperature and specific heat were calculated based on sound velocity data. The results indicate that Debye temperature increases with the applied pressures while specific heat decreases. The Grüneisen constant was calculated as well. From the sound velocities, the pressure coefficient of the averaged phonon frequency was obtained, which is consistent with the value estimated by Vogt et al. This indicates that the importance of phonon hardening in the variation of T c under pressure. Upon changing the Debye temperature, unit cell volume and transition temperature with the pressure, volume dependence of electron-phonon coupling constant are also calculated.
COMPETITIVE LEARNING OF FUZZY MODELS
Authors: ANDRECUT M. , ALI M. K.
Published: December 2002

In general, fuzzy modeling requires two stages: structure identification (generating the fuzzy rule base) and parameter learning (optimizing parameters in fuzzy rules). Here, we present an on-line algorithm for competitive learning and optimization of fuzzy models. Differing from existing methods, in this approach the structure identification and parameter optimization of the fuzzy model can be carried out automatically, using on-line acquisition of data. We demonstrate this approach by applying it to different types of nonlinear system modeling.
LEVEL CORRELATIONS IN INTEGRABLE SYSTEMS
Authors: SEROTA R. A. , WICKRAMASINGHE J. M. A. S. P.
Published: December 2002

We derive a simple analytical expression for the level correlation function of an integrable system. It accounts for both the lack of correlations at smaller energy scales and for global rigidity (level number conservation) at larger scales. We apply our results to a rectangle with incommensurate sides and show that they are in excellent agreement with the limiting cases established in the semiclassical theory of level rigidity.
RESONANT TUNNELING IN SEMICONDUCTOR MULTIBARRIER HETEROSTRUCTURES
Authors: GONG JIAN , BAN SHI LIANG , LIANG XI XIA
Published: December 2002

The effect of coupling between the electronic transverse motion and longitudinal motion is considered in the theoretical investigation of the resonant tunneling in a semiconductor multi-barriers heterostructure. A numerical calculation is carried out for rectangular and parabolic-well heterostructures consisting of ZnSe/Zn 1-x Cd x Se . The result indicates that the coupling effect results in not only a movement of the resonant peaks but also a reduction of the peak-to-valley ratio in the transmission spectrum. The effect of the electronic transverse motion on the higher-lying resonant states for the resonant tunneling is more remarkable for both the zero and non-zero bias voltages. The J-V characteristic formula of tunneling current density, which is different from Esaki's result, is given by using a two-dimensional approximation. The influence of temperature and mixed crystal effect on the J-V characteristic is also investigated.
THE 3d-TO-4s-BY-2p HIGHWAY TO SUPERCONDUCTIVITY IN CUPRATES
Authors: MISHONOV TODOR M. , INDEKEU JOSEPH O. , PENEV EVGENI S.
Published: December 2002

High-temperature superconductors are nowadays found in great variety and hold technological promise. It is still an unsolved mystery that the critical temperature T c of the basic cuprates is so high. The answer might well be hidden in a conventional corner of theoretical physics, overlooked in the recent hunt for exotic explanations of new effects in these materials. A forgotten intra-atomic s–d two-electron exchange in the Cu atom is found to provide a strong (~ eV) electron pairing interaction. A Bardeen–Cooper–Schrieffer approach can explain the main experimental observations and predict the correct dx2-y2 symmetry of the gap.
SELF-AVERAGING IN TIME REVERSAL FOR THE PARABOLIC WAVE EQUATION
Authors: BAL GUILLAUME , PAPANICOLAOU GEORGE , RYZHIK LEONID
Published: December 2002

We analyze the self-averaging properties of time-reversed solutions of the paraxial wave equation with random coefficients, which we take to be Markovian in the direction of propagation. This allows us to construct an approximate martingale for the phase space Wigner transform of two wave fields. Using a prioriL2-bounds available in the time-reversal setting, we prove that the Wigner transform in the high frequency limit converges in probability to its deterministic limit, which is the solution of a transport equation.
ONSAGER–MACHLUP FUNCTIONAL FOR VOLTERRA EQUATIONS PERTURBED BY NOISE
Authors: BONACCORSI STEFANO
Published: December 2002

The Onsager–Machlup operator is a useful tool in order to study the regularity of the trajectories of the solution to a stochastic differential equation. In this paper, we prove the existence of this operator for the solution of a stochastic Volterra equation in bounded domain. This kind of equation has relevant interest in the applications, as discussed in [6] or [18].
EXPONENTIALLY STRONG CONVERGENCE OF NON-CLASSICAL MULTIDIMENSIONAL CONTINUED FRACTION ALGORITHMS
Authors: NAKAISHI KENTARO
Published: December 2002

Convergence properties of multidimensional continued fraction algorithms introduced by V. Baladi and A. Nogueira are studied. The paper contains an arithmetic proof of almost everywhere exponentially strong convergence of some two-dimensional Markovian random algorithms and dynamically defined ones. A special three-dimensional deterministic case is also discussed.
CONVERGENCE IN DISTRIBUTION OF THE PERIODOGRAM OF CHAOTIC PROCESSES
Authors: LOPES ARTUR O. , LOPES SÍLVIA R. C.
Published: December 2002

In this work we analyze the convergence in distribution sense of the periodogram function (to the spectral density function) based on a time series of a stationary process Xt = (φ ◦ Tt)(X0) obtained from the iterations of a continuous transformation T invariant for an ergodic probability μ and a continuous function φ taking values in ℝ. We only assume a certain rate of convergence to zero for the autocovariance coefficient of the stochastic process, i.e. we assume there exist C > 0 and β > 2 such that |γX(h)| ≤ C|h|-β, for all h ∈ ℕ, where γX(h) = ∫(φ ◦ Th)(x) φ(x)dμ(x) - (∫ φ(x)dμ(x))2 is the h-autocovariance of the process. Our result applies to the case of exponential decay of correlation (or covariance), as it happens for a continuous expanding transformation T on the circle and a Holder potential φ. It can also be applied to the case when the transformation T has a fixed point with derivative equal to one.
Quantitative analysis of mineralized white Portland clinkers: The structure of Fluorellestadite
Authors: Pajares Isabel , De la Torre Ángeles G. , Martínez-Ramírez Sagrario , Puertas Francisca , Blanco-Varela María-Teresa , Aranda Miguel A. G.
Published: December 2002

Fluorellestadite, Ca10(SiO4)3(SO4)3F2, has been synthesized as single phase. This compound crystallizes in the apatite type structure, s.g. P63/m, with parameters a=9.4417(1) Å, c=6.9396(1) Å and V=535.76(1) Å3. The refinement of its crystal structure converged to RWP=12.33% and RF=4.58%. The atomic parameters have been used to analyze the phase content of mineralized white Portland clinkers. These clinkers contain Ca3SiO5, Ca2SiO4, Ca12Al14O32F2 and Ca10(SiO4)3(SO4)3F2. The agreement between the elemental composition inferred from the Rietveld phase analysis and that measured by XRF is noteworthy. This comparison does not take into account the presence of amorphous phases and unmodeled elemental substitutions in crystalline phases. Similar Rietveld studies on commercial white Portland clinkers are also shown to be feasible.
A structural study of the (Na1−xKx)0.5Bi0.5TiO3 perovskite series as a function of substitution (x) and temperature
Authors: Jones G. O. , Kreisel J. , Thomas P. A.
Published: December 2002

Rietveld neutron powder profile analysis of the (Na1−xKx)0.5Bi0.5TiO3 (NKBT) series (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) is reported over the temperature range 293–993 K. A detailed characterization of the structures and phase transitions occurring across this series as a function of temperature has been made. Room-temperature refinements have revealed a rhombohedral phase, space group R3c for x=0, 0.2, and 0.4, which exhibits an antiphase, a−a−a− oxygen tilt system with parallel cation displacements along [111]p. An intermediate zero-tilt rhombohedral phase, space group R3m possessing cation displacements along [111]p, has been established for x=0.5 and 0.6. At the potassium-rich end of the series at x=0.8 and 1.0, a tetragonal phase, space group P4mm is observed possessing cation displacements along [001]. At the sodium-rich end of the series for x=0.2, the unusual tetragonal structure with space group P4bm is seen for Na0.5Bi0.5TiO3 which possesses a combination of in-phase a0a0c+ tilts and antiparallel cation displacements along the polar axis. Temperature-induced phase transitions are reported and structural modifications are discussed.
A neutron diffraction study on a typical highly defective ceria–yttria solid solution
Authors: Chakraborty Keka R. , Chavan S. V. , Tyagi A. K.
Published: December 2002

It was seen during the phase relation studies on the CeO2–YO1.5 system that the ceria is able to accommodate a large anion deficiency caused by aliovalent substitution. A neutron powder diffraction study has been carried out at room temperature for the titled solid solution, Ce1−xYxO2−x/2 with x=0.32, which is an anion-deficient variant of the ideal fluorite structure. The structure has been found to be face centered cubic. No superlattice reflections have been observed indicating that the vacancies occupy the random positions in this highly defective solid solution. The bond distances and angles are also being reported.
Structural characterization of a porous zinc vanadate: Zn3(VO4)2⋅3H2O
Authors: Hoyos Dora Ángela , Echavarría Adriana , Palacio Luz Amparo , Saldarriaga Carlos
Published: December 2002

A novel porous material of composition Zn3(VO4)2⋅3H2O was prepared hydrothermally. The solid crystallizes in the hexagonal space group P6, with a=6.078 77(8), c=7.1827(2) Å, and V=229.857 Å3.
Powder data for synthetic analogue of a mineral nickelphosphide
Authors: Skála Roman , Drábek Milan
Published: December 2002

All known occurrences of nickelphosphide (Ni,Fe)3P—a mineral encountered mainly in meteoritic irons—represent relatively small grains, which prevents acquiring powder data of a reasonable quality. Synthetic analogues of this mineral, corresponding chemically to that found in the meteorite Vicenice, have been synthesized. Powder data collected using a standard laboratory diffractometer in the Bragg–Brentano geometry are presented. The space group of nickelphosphide is identical to that of schreibersite (Fe,Ni,Co)3P and synthetic Ni3P—I4. The unit-cell dimensions refined from the powder data are a=9.0168(1) Å, c=4.4501(1) Å, and V=361.80(1) Å3, with Z=8.
A study of nanocrystalline yttrium oxide from diffraction-line-profile analysis: comparison of methods and crystallite growth
Authors: Louër D. , Bataille T. , Roisnel T. , Rodriguez-Carvajal J.
Published: December 2002

An analysis of the microstructure of nanocrystalline yttrium oxide produced by thermal decomposition of a double oxalate yttrium and ammonium, at temperatures in the range 600 °C to 900 °C, is described. The study is based on line broadening analysis carried out with the (Voigt/Langford) integral breadth and Fourier methods combined with the pattern decomposition technique. Due to the line overlap arising from the density of diffraction lines, the whole pattern refinement method (pattern matching and Rietveld approaches) is also applied. No marked line broadening anisotropy is observed in the patterns. It is shown that for the two samples prepared at the highest temperatures the results are similar whatever the method used and the material can be considered as strain free. For the two lowest temperatures only the whole pattern refinement method is applied. The results suggest that a small amount of lattice microdistortion is present in these two last samples. It is shown that the crystallite growth varies exponentially with temperature. The results obtained from line broadening analysis are compared to those observed with scanning electron microscopy, from which a good accordance is noted between the two techniques.
Influence of planar defects on powder diffractograms of fcc metals
Authors: Ustinov A. I. , Budarina N. M.
Published: December 2002

X-ray powder diffractograms from fcc crystals containing high concentration (more than 1%) of planar defects [deformation stacking faults (SF), double deformation SF, twin boundaries (TB)] have been simulated by Monte Carlo method in kinematic approach. It was shown that the characteristics of powder diffraction peak profiles (except peaks with indexes H00) dependent nonmonotonically on PD concentration, during which peak maximums stay in Bragg positions. An addition point to emphasize is that an appearance of TB only in the crystal not affects on position of all peaks. Several types of PD to be occurred simultaneously in the crystal influence on powder diffractograms additively. Peculiarities of the powder diffraction pattern inherent in different types of PD have been revealed to permit predominant PD type to be found with a high degree of accuracy based on experimental data.
Synthesis and structural elucidation of Ba4Nd3F17: A powder XRD study
Authors: Grover V. , Achary S. N. , Patwe S. J. , Tyagi A. K.
Published: December 2002

The compound Ba4Nd3F17 was prepared by heating predried BaF2 and EuF3 (4:3) at 900 °C for 8 h in static vacuum. The polycrystalline sample obtained was characterized by Rietveld refinement of the observed powder diffraction data with the starting model of Ba4Y3F17. This compound crystallizes in a rhombohedral lattice with unit-cell parameters, a=11.2818(3) and c=20.7788(11) Å, Z=6, (Space group R 3, No. 148). The Rp, Rwp and Rexp factors were 9.5%, 12.9% and 10.9%, respectively.
Powder diffraction data on BaClI and BaBrI
Authors: Lenus A. Jestin , Sornadurai D. , Rajan K. Govinda , Purniah B.
Published: December 2002

The two mixed halides of barium, barium chloroiodide and barium bromoiodide, were synthesized via a solid-state reaction route. In this article, their powder XRD data are reported. A careful analysis of the X-ray data shows that both BaClI and BaBrI crystallize in the orthorhombic structure. The lattice parameters obtained are a=17.841±0.003 Å, b=8.441±0.001 Å and c=5.642±0.001 Å for BaClI (SG. Pbam, No. 55) and a=13.667±0.002 Å, b=12.012±0.001 Å and c=10.871±0.002 Å for BaBrI (SG. P2221 No. 17).
Eyewitness memory for arousing events: putting things into context
Authors: Brown Jeffrey M.
Published: December 2002

If attention is focused on central details at high levels of arousal, memory for peripheral details should be diminished (Easterbrook, 1959). If this is the case, contextual reinstatement (CR) procedures should not enhance memory because these procedures specifically use peripheral information to cue memory. The present experiment tested how arousal influenced eyewitness memory for an event and how it interacts with CR procedures. Participants first viewed one of three series of slides (neutral, arousal, or unusual/control). Memory for central and peripheral details was tested via photo lineups and recognition tests. Although CR procedures enhanced recognition memory for non‐arousing and unusual events, they did not affect recognition memory for arousing events. Analyses of the peripheral photo lineup and peripheral recognition test data revealed that CR enhanced the hit rate for the neutral and unusual conditions but not for the arousal condition. Although CR procedures tended to enhance recognition of central information (increasing the hit rate and decreasing the false alarm rate), CR had a smaller enhancement effect in the arousal condition relative to the neutral and unusual conditions. The present experiment also replicates the Christianson and Loftus (1991) finding that peripheral information is not remembered as well in an arousing event, as compared to memory of neutral and unusual events. The theoretical and applied implications of these results are discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Gaucher disease: In vivo evidence for allele dose leading to neuronopathic and nonneuronopathic phenotypes
Authors: Zhao Huiquan , Bailey Laurie A. , Elsas Louis J. , Grinzaid Karen A. , Grabowski Gregory A.
Published: December 2002

Gaucher disease, a common lysosomal storage disorder, is associated with mutations at the acid β‐glucosidase (GCase) locus. Two affected individuals are described to share a common mutant allele, but manifest different clinical categorical phenotypes. A 57‐year‐old female, with Gaucher disease type 1 and Cherokee ancestry, was homozygous for a rare mutant allele encoding Lys79Asn (K79N). A 2‐year‐old Caucasian male, with Gaucher disease type 3 and Cherokee ancestry, was a heteroallelic homozygote for this same allele (K79N) and a novel complex mutation (null allele). The shared alleles were identical as determined by complete gene sequencing, suggesting a founder effect. The discrepant phenotypes (types 1 and 3) in these two patients provide support for a threshold of residual activity necessary to “protect” the central nervous system (CNS) from the pathogenic effects of Gaucher disease, indicating an allele dose‐effect. Designation of genotype associations with specific phenotypes must be assessed with this perspective. © 2003 Wiley‐Liss, Inc.