bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoxia-based habitat compression in the Neuse River Estuary: context-dependent shifts in behavioral avoidance thresholds
Authors: Eby Lisa A , Crowder Larry B
Published: October 2002

Anthropogenic activities in estuarine watersheds alter physical and chemical characteristics of these ecosystems. Increased nutrient loading and changes in hydrology affect oxygen budgets and subsequently alter the spatial and temporal extent of hypoxia. We used classification and regression tree analyses to examine behavioral avoidance thresholds over a range of dissolved oxygen concentrations. In an examination of 10 fish species, all avoided areas with dissolved oxygen concentrations of <2.0 mg·L1. Our data suggest that the dissolved oxygen avoidance threshold expressed by fish may be context-dependent. Specifically, the spatial extent of hypoxia significantly affected avoidance thresholds. Fish may occupy poorer quality habitat (areas with lower dissolved oxygen levels) as conditions worsen and the size of the oxygenated refuge shrinks. When the entire estuary is oxygenated, fish utilize all depths. During hypoxic episodes, fish are restricted to oxygenated, shallow, warmer areas. This habitat compression may result in higher densities and greater overlap with potential competitors and predators. Hypoxic zones alter habitat use and may increase bioenergetic costs, potentially resulting in sublethal effects, i.e., decreased growth and condition, on the estuarine fish community.
Estimating rates of fish movement from tag recoveries: conditioning by recapture
Authors: McGarvey Richard , Feenstra John E
Published: October 2002

Tag-recovery data are commonly used to estimate movement rates of fish stocks. Fishers report tagged fish found in their catch; however, not all recoveries are reported to fishery researchers and the rate of nonreporting is usually not known or is imprecisely estimated. To obviate the problem of nonreporting, an estimator of movement rates is proposed that does not use the number originally tagged but is fitted to the relative proportions recaptured in each cell in each time step subsequent to release. Rates of processes that occur in the tag-release spatial cell, such as short-term tagging mortality and survival, cancel from the predicted likelihood probabilities. Similarly, rates in the recapture cell for processes of ongoing tag loss, natural mortality, and tag nonreporting, if they can be reasonably approximated as uniform across cells, also cancel. Estimators are presented assuming one of two levels of auxiliary fishery inputs: (i) total mortality by cell or time step, or (ii) if mortality can be approximated as spatially uniform, effort totals in each cell, by time step. Yearly movement transition matrices were estimated for King George whiting (Sillaginodes punctata) in South Australia among 11 spatial cells from tag recoveries gathered over a period of three decades.
Genetic perspectives on invasions: the case of the Cladocera
Authors: Hebert Paul D.N , Cristescu Melania E.A
Published: October 2002

Using freshwater cladocerans as an example, this paper explores the contributions that genetic analyses are making to the field of invasion biology. Most importantly, this approach enables a quantification of the incidence of both recent and past invasions. By determining genetic divergence between European and North American lineages of cladocerans, it is possible to estimate the natural incidence of past exchange between these continents. The results of this analysis establish that the current pace of species invasions is extraordinary; present rates are nearly 50 000 times higher than historical levels. Genetic studies can also exploit molecular markers to localize the points of origin of invaders. Finally, genetic studies are poised to play an important role in monitoring invasions; the DNA bar-coding of life is now simple and rapid enough to enable the development of molecular identification systems.
The front-form Hamiltonian and BRST formulations of the JackiwRajaraman chiral Schwinger model
Authors: Kulshreshtha U , Kulshreshtha D S
Published: October 2002

The Hamiltonian and BRST formulations of the JackiwRajaraman chiral Schwinger model are investigated in the light-front frame.

PACS No.: 11.15-q
Quantum mechanics of the damped harmonic oscillator
Authors: Blasone M , Jizba P
Published: October 2002

We quantize the system of a damped harmonic oscillator coupled to its time-reversed image, known as Bateman's dual system. By using the FeynmanHibbs method, the time-dependent quantum states of such a system are constructed entirely in the framework of the classical theory. The geometric phase is calculated and found to be proportional to the ground-state energy of the one-dimensional linear harmonic oscillator to which the two-dimensional system reduces under appropriate constraint.

PACS Nos.: 03.65Ta, 03.65Vf, 03.65Ca, 03.65Fd
Diffusive behavior and structural characterization of a hard-sphere fluid through a narrow channel with roughened walls
Authors: Tafreshi H Vahedi , Benedek G , Zamankhan P , Sarkomaa P J
Published: October 2002

A molecular dynamics technique is devised to simulate the flow of a hard-sphere fluid between two parallel roughened walls separated by a 10 particle diameter distance. The structural state of the system in different solid-volume fractions is characterized by analyzing the static-structure factor contour plot. At solids concentrations below [Formula: see text] [Formula: see text] 0.3, the calculations have shown no remarkable signature of the presence of the roughened confining walls similar to the previous unbounded simulation results (wide channel). At high concentrations, walls manifest their presence by reducing the particle diffusion in the direction of velocity gradient. Due to the metastability of the assembly, further increase in the solid fraction, [Formula: see text] [Formula: see text] 0.6, may yield a crystalline phase wherein diffusion coefficients vanish locally.

PACS Nos.: 51.20+d, 61.20-p, 66.10Cb
Contribution à l'étude des effets de charge sur l'émission X des matériaux isolants non métallisés
Authors: Raouadi K , Renoud R , Askri B , Yangui B , Fakhfakh Z
Published: October 2002

The presence of charges perturbs the X-microanalysis on insulator samples. Attempts to suppress these effects have been fruitless and a better understanding of the charge phenomenon is the only way to a clear interpretation of the results of a X-microanalysis. From a simulation of the charges implanted by an electron beam on an insulator target, we compute, as a fuction of the integrated dose, the characteristics of the emitted X-rays, such as the generating function ϕ (ρ z) or the intensity of the characteristic lines. We underline the role of the electric field on the primary beam and on the electron trajectories in the target. These results allow the analysis of experimentally measured X-rays. Our studies on the effects of the diameter of the probe and on the exposure time led us to establish the best conditions for the successful X-microanalysis of an insulator. [Journal translation]
First-quantized electron and photon model of QED and radiative processes
Authors: Yucel M B , Unal N
Published: October 2002

In this study, we combine the classical models of the massive and massless spinning particles, derive the currentcurrent interaction Lagrangian of the particles from the gauge transformations of the classical spinors, and discuss radiative processes in electrodynamics by using the solutions of the Dirac equation and the quantum wave equations of the photon. The longitudinal-polarized photon states give a new idea about the vacuum concept in electrodynamics.

PACS Nos.: 03.75-b, 11.10-z, 12.20-m, 13.40-f, 14.60Cd, 14.70Bh, 32.80Cy
Chemical effects on L X-ray intensity ratios of U and Th
Authors: Küçükönder A
Published: October 2002

The chemical effects on the Lβ/Lα, Ll /Lα, and Lγ/Lα X-ray intensity ratios of U and Th were investigated. Vacancies were produced by heavily filtered 241Am gamma rays. A high-resolution Si(Li) detector system was used in the experiments. The experimental values are given with the theoretical values of the pure U and Th elements.

PACS Nos.: 32.30Rj
Lowest order constrained variational and local density approximation approach to the hot alpha particle
Authors: Modarres M , Moshfegh H R , Mariji H
Published: October 2002

The free energy of an alpha particle is calculated using the local density approximation in the harmonic oscillator basis. The effective two-body interactions are generated from the lowest order constrained variational (LOCV) calculation for nuclear matter at finite temperature, with the Reid and Δ-Reid potentials. The FermiDirac distribution is used to calculate the entropy and the occupation probability of each state of alpha particle at a given temperature. The effective mass is treated as a variational parameter. Our zero temperature results with the Δ-Reid interaction agree well with the experimental saturation data of alpha particle and the other many-body techniques. The flashing temperature of ≈5 MeV is found, which is consistent with experimental evidence. It is concluded that a similar liquidgas phase transition to that of nuclear matter is most probable in the alpha particle and heavier nuclei.

PACS Nos.: 21.65+f, 21.10-k, 21.10Dr, 21.60-n
Biological control of stem canker of greenhouse tomatoes caused by Botrytis cinerea
Authors: Utkhede R S , Mathur S
Published: October 2002

Experiments were conducted to study the effect of various chemical and biological agents on stem canker caused by Botrytis cinerea Pers.: Fr. on tomato plants grown in sawdust under near-commercial greenhouse conditions. Lesion lengths following treatment with RootShield® and strain S33 of Rhodosporidium diobovatum Newell & Hunter, applied as post-inoculation sprays, were significantly smaller than those in inoculated controls. These treatments also increased fruit yield and decreased the number of dead plants compared with inoculated controls. Decree®, Prestop®, and R. diobovatum S33, applied as sprays, prevented the occurrence of stem canker and increased fruit yield in tomato. The number of dead plants was also smaller with these treatments than with the other treatments and in inoculated controls. These results suggest that, in tomato, post-inoculation sprays of RootShield® and R. diobovatum S33 can reduce lesion lengths, and that a preventive spray of Decree®, Prestop®, and R. diobovatum S33 might prevent stem canker, under near-commercial greenhouse conditions.Key words: biological control, Botrytis cinerea, Bacillus subtilis, Rhodosporidium diobovatum, grey mold.
Regulation of indoleacetic acid production inPseudomonas putidaGR12-2 by tryptophan and the stationary-phase sigma factor RpoS
Authors: Patten Cheryl L , Glick Bernard R
Published: October 2002

The phytohormone indole-3-acetic acid (IAA) accumulates in the culture medium of the plant growth-promoting bacterium Pseudomonas putida GR12-2 only when grown in the presence of exogenous tryptophan, suggesting that expression of indolepyruvate decarboxylase, a key enzyme in the IAA biosynthesis pathway in this bacterium, may be regulated by tryptophan. To test this hypothesis, we isolated the promoter region for the ipdc gene encoding indolepyruvate decarboxylase by inverse polymerase chain reaction (PCR) and inserted it upstream of the bioluminescent reporter gene luxAB on a plasmid in P. putida GR12-2. Activity of the ipdc promoter, measured by quantifying light production, increased fivefold in the presence of L-tryptophan, confirming that ipdc expression is induced by tryptophan. In addition, transcription of ipdc is regulated by the stationary phase sigma factor RpoS: the ipdc promoter contains a sequence similar to the RpoS recognition sequence, and transformation of P. putida GR12-2 with a plasmid carrying rpoS under the control of a constitutive promoter induced promoter activity before the onset of stationary phase when RpoS is not normally produced and prolonged a higher level of transcription at the later stages of the cell cycle.Key words: indoleacetic acid, indolepyruvate decarboxylase, regulation, tryptophan, RpoS.
Bacterial diversity associated with subalpine fir (Abies lasiocarpa) ectomycorrhizae following wildfire and salvage-logging in central British Columbia
Authors: Khetmalas Madhukar B , Egger Keith N , Massicotte Hugues B , Tackaberry Linda E , Clapperton M Jill
Published: October 2002

To assess the effect of fire and salvage logging on the diversity of mycorrhizalbacterial communities, bacteria associated with Cenococcum, Thelephora, Tomentella, Russulaceae, and E-strain ectomycorrhizae (ECM) of Abies lasiocarpa seedlings were characterized using two approaches. First, bacteria were isolated and characterized by Biolog©, gas chromatography fatty acid methyl ester (GC-FAME), and amplified 16S rDNA restriction analysis (ARDRA). The bacterial communities retrieved from ECM from both sites were dominated by Proteobacteria (groups gamma and beta). Pseudomonas was the most common genus isolated, followed by Variovorax, Burkholderia, and Xanthomonas. Gram-positive isolates (mostly high-G+C Gram-positive bacteria) were more frequently retrieved on the burned-salvaged site, many commonly associated with the two ascomycete ECM, Cenococcum and E-strain. Pseudomonas species were retrieved more frequently from Thelephora. Although actinomycetes were isolated from all sites, almost no actinomycetes or other Gram-positive bacteria were isolated from either Thelephora or Tomentella. Second, amplified 16S rRNA gene sequences were amplified directly from root tips and then cloned into the plasmid vector pAMP1, followed by restriction analysis. This technique distinguished more genotypes than isolates retrieved by culturing methods, but generally, results were similar in that the largest proportion of the bacteria were putatively Gram-negative; putative Gram-positive bacteria were fewer and most were from the burnedsalvaged site. Direct cloning resulted in many patterns that did not match any identified isolates, suggesting that a large proportion of clones were unique or not culturable by the methods used. Analysis for both protocols showed no significant difference in bacterial diversity between the burnedsalvaged and unburned sites. Key words: rhizosphere bacteria, ARDRA, 16S rDNA, Biolog©, GC-FAME.
Growth and dieback of aspen forests in northwestern Alberta, Canada, in relation to climate and insects
Authors: Hogg E H , Brandt James P , Kochtubajda B
Published: October 2002

Trembling aspen (Populus tremuloides Michx.) is the most important deciduous tree in the Canadian boreal forest, with >1000 Tg of carbon stored in the aboveground biomass of this species. Since the early 1990s, aspen dieback has been noted over parts of the southern boreal forest and aspen parkland in western Canada. In this study, tree-ring analysis and forest health assessments were conducted in 18 aspen stands near Grande Prairie, Alta., to examine causes of reduced growth and dieback. Defoliation histories were reconstructed based on light-colored ("white") tree rings and records of past insect outbreaks. The results indicated that several factors contributed to the observed dieback. Defoliation by forest tent caterpillar (Malacosoma disstria Hbn.) and drought in the 1960s and 1980s led to reduced growth and predisposed some stands to secondary damage by wood-boring insects and fungal pathogens. Thawfreeze events during a period (19841993) of unusually light snow cover in late winter may have also contributed to the observed dieback. Under global change, the severity of these stressors may increase, which would pose a serious concern for the future health, productivity, and carbon sequestration of aspen forests in the region.
Bark beetles and fungal associates colonizing white spruce in the Great Lakes region
Authors: Haberkern Kirsten E , Illman Barbara L , Raffa Kenneth F
Published: October 2002

We examined the major bark beetles and associated fungi colonizing subcortical tissues of white spruce (Picea glauca (Moench) Voss) in the Great Lakes region. Trees were felled at one northwestern Wisconsin site in a preliminary study in 1997 and at 10 sites throughout northern Wisconsin, Minnesota, and Michigan in 1998. Fungal isolations were made from beetles colonizing felled trees, beetles that emerged from felled trees, tissue of colonized trees, and tissue of uncolonized trees. Dryocoetes affaber (Mannerheim) and Polygraphus rufipennis (Kirby) accounted for over 90% of the insects that emerged from logs. Time of colonization had a significant effect on abundance and composition of emerging insects. New records include Dendroctonus rufipennis (Kirby) in Wisconsin and two Michigan counties and Crypturgus borealis (Swaine) in Wisconsin and Minnesota and one Michigan county. Five fungal species from two genera were isolated both from beetles and colonized tree tissue. None were isolated from uncolonized trees. Ten new beetlefungal associations were identified. The association of specific fungi with specific bark beetles, both as they colonize and emerge from hosts and the isolation of these fungi from subcortical tissues of colonized but not uncolonized trees, is consistent with vector relationships. We compare our results with bark beetle  fungal associations reported elsewhere in spruce and suggest possible mechanisms constraining population growth by Dendroctonus rufipennis in the Great Lakes region.
Process and patterns of duff consumption in the mixedwood boreal forest
Authors: Miyanishi K , Johnson E A
Published: October 2002

Postfire tree recruitment in the boreal forest is restricted to patches from which the duff (organic layer) has been removed by fire. Duff consumption occurs by smoldering combustion, propagation of which is determined by bulk density, moisture content, and depth. This study investigated interactions among these factors, their spatial distribution, and spatial patterns of duff consumption in two wildfires. A hypothesized positive relationship between moisture content and depth was supported by a laboratory study. Duff characteristic data were collected from two burns and comparable unburned areas of mixedwood forest in western Canada to describe and explain patterns of duff consumption within and between top-slope Pinus banksiana Lamb.  Picea mariana (Mill.) BSP stands and lower slope pure stands of Picea mariana on glaciofluvial hillslopes. In unburned stands, bulk density did not differ significantly between stands, while depths were significantly greater in Picea stands. With moist duff, consumption was significantly greater in Picea than in PinusPicea stands as depth limited smoldering in the thin duff of PinusPicea stands. With dry duff, smoldering was propagated regardless of depth resulting in no differences between stand types. The spatial correlation between burned patches and fire-killed trees was explained by within-stand spatial variation in duff moisture due to precipitation interception by tree crowns.
WEAKLY REGULAR FLOQUET HAMILTONIANS WITH PURE POINT SPECTRUM
Authors: DUCLOS P. , LEV O. , ŠŤOVÍČEK P. , VITTOT M.
Published: October 2002

We study the Floquet Hamiltonian -i∂t + H + V(ωt), acting in L2([0,T],ℋ, dt), as depending on the parameter ω = 2π/T. We assume that the spectrum of H in ℋ is discrete, [Formula: see text], but possibly degenerate, and that t ↦ V(t) ∈ ℬ(ℋ) is a 2π-periodic function with values in the space of Hermitian operators on ℋ. Let J > 0 and set [Formula: see text]. Suppose that for some σ > 0 it holds true that ∑hm > hnMmMn (hm - hn)-σ < ∞ where Mm is the multiplicity of hm. We show that in that case there exist a suitable norm to measure the regularity of V, denoted ∊V, and positive constants, ∊⋆ and δ⋆, with the property: if ∊V < ∊⋆ then there exists a measurable subset Ω∞ ⊂ Ω0 such that its Lebesgue measure fulfills |Ω∞| ≥ |Ω0| - δ⋆ ∊V and the Floquet Hamiltonian has a pure point spectrum for all ω∈Ω∞.
ON THE DOMAIN OF SINGULAR TRACES
Authors: GUIDO DANIELE , ISOLA TOMMASO
Published: October 2002

The question whether an operator belongs to the domain of some singular trace is addressed, together with the dual question whether an operator does not belong to the domain of some singular trace. We show that the answers are positive in general, namely for any (compact, infinite rank) positive operator A we exhibit two singular traces, the first being zero and the second being infinite on A. However, if we assume that the singular traces are genrated by a "regular" operator, the answers change, namely such traces alway vanish on trace-class, non singularly traceable operators and are always infinite on non trace-class, non singularly traceable operators. These results are achieved on a general semifinite factor and make use of a new characterization of singular traceability (cf. [7]).
CONDITIONALLY EXACTLY SOLVABLE SINGULAR EVEN POWER POTENTIAL IN SUPERSYMMETRIC QUANTUM MECHANICS
Authors: CHAKRABARTI BARNALI , DAS TAPAN KUMAR
Published: October 2002

We solve strongly singular even power potential with inverse quadratic, inverse quartic and inverse sextic terms, using superpotential ansatz technique. We show that our new technique is very powerful and simple compared to traditional wave function ansatz technique. We also point out conditional shape invariance as the underlying symmetry to get conditional exactness. We also generalize the case for two-body Hamiltonian and propose an alternative way to solve Riccati equation instead of solving Schrödinger equation. We present operator formalism which is rather powerful. We also discuss the problem encountered in generalizing the potential for an N-body system.
CREATION OF SCALAR AND DIRAC PARTICLES IN THE PRESENCE OF A TIME VARYING ELECTRIC FIELD IN AN ANISOTROPIC UNIVERSE
Authors: VILLALBA VÍCTOR M.
Published: October 2002

We compute the density of scalar and Dirac particles created by a cosmological anisotropic universe1,2 in the presence of a time dependent homogeneous electric field. In order to compute the rate of particles created we apply a quasiclassical approach that has been used successfully in different scenarios3,4. The idea behind the method is the following: First, we solve the relativistic Hamilton-Jacobi equation and, looking at its solutions, we identify positive and negative frequency modes. Second, after separating variables5,6, we solve the Klein-Gordon and Dirac equations and, after comparing with the results obtained for the quasiclassical limit, we identify the positive and negative frequency states. We show that the particle distribution becomes thermal when one neglects the electric interaction.
ALGORITHM FOR THE EVALUATION OF THE SELF-DIFFUSION COEFFICIENT OF SMALL MOLECULES, USING THE NMR MAGNETIC FIELD GRADIENT METHOD
Authors: TODICA M. , POP A. V.
Published: October 2002

Different methods of investigation of the spin-echo attenuation, in the NMR pulsed field gradient experiments, were analyzed in order to optimize the measurements of the self-diffusion coefficient of the small molecules of simplest liquids. A particular algorithm of representation of the experimental data is proposed in order to eliminate the effect of the residual gradient. This algorithm, tested for pure water, give results in accord with the literature.
MODIFIED EAM POTENTIALS FOR MODELLING STACKING–FAULT BEHAVIOR IN Cu, Al, Au, AND Ni
Authors: SZELESTEY P. , PATRIARCA M. , PERONDI L. F. , KASKI K.
Published: October 2002

In this paper we have developed empirical Embedded Atom Model potentials, following the fitting scheme proposed by Chantasiriwan and Milstein, in order to describe the stacking fault behaviour of copper, gold, nickel and aluminium. We show that the potentials based on this scheme can be modified to provide reasonable stacking-fault energy values and consequently a better description of the plastic properties. Modifications were done by changing the cut-off distance in case of aluminium and nickel, and in case of gold and copper by also modifying the functional form of the pair-potential. In order to validate these modified potentials we have tested them by studying various properties, such as structural, defect, and surface energies, and phonon spectra and comparing results with those from experiments and other model potentials.
STOCK MARKET PREDICTION BY A MIXTURE OF GENETIC-NEURAL EXPERTS
Authors: ARMANO GIULIANO , MURRU ANDREA , ROLI FABIO
Published: October 2002

In this paper, a hybrid approach to stock market forecasting is presented. It entails utilizing a mixture of hybrid experts, each expert embedding a genetic classifier coupled with an artificial neural network. Information retrieved from technical analysis is supplied as input to genetic classifiers, while past stock market prices — together with other relevant data — are used as input to neural networks. In this way it is possible to implement a strategy that resembles the one used by human experts. In particular, genetic classifiers based on technical-analysis domain knowledge are used to identify quasi-stationary regimes within the financial data series, whereas neural networks are designed to perform context-dependent predictions. For this purpose, a novel kind of feedforward artificial neural network has been defined whereby effective stock market predictors can be implemented without the need for complex recurrent neural architectures. Experiments were performed on a major Italian stock market index, also taking into account trading commissions. The results point to the good forecasting capability of the proposed approach, which allowed outperforming the well known buy-and-hold strategy, as well as predictions obtained using recurrent neural networks.
BIFURCATIONS OF PERIODIC ORBITS IN A JOSEPHSON EQUATION WITH A PHASE SHIFT
Authors: JING ZHUJUN , CAO HONGJUN
Published: October 2002

The Josephson equation with constant current and sinusoidal forcings and a phase shift is investigated in detail: the existence and the bifurcations of harmonics and subharmonics under small perturbations are given, by using the second-order averaging method and Melnikov function; the influence on bifurcations of periodic or subharmonics as the phase shift varies is considered; some numerical simulation results are reported in order to prove our theoretical predictions.
EFFECTS OF SPACE IN 2 × 2 GAMES
Authors: HAUERT CH.
Published: October 2002

A systematic analysis of the effects of spatial extension on the equilibrium frequency of cooperators and defectors in 2 × 2 games is presented and compared to well mixed populations where spatial extension can be neglected. We demonstrate that often spatial extension is indeed capable of promoting cooperative behavior. This holds in particular for the prisoner's dilemma for a small but important parameter range. For the hawk–dove game, spatial extension may lead to both, increases of the hawk- as well as the dove-strategy. The outcome subtly depends on the parameters as well as on the degree of stochasticity in the different update rules. For rectangular lattices, the general conclusions are rather robust and hold for different neighborhood types i.e. for the von Neumann as well as the Moore neighborhood and, in addition, they appear to be almost independent of the update rule of the lattice. However, increasing stochasticity for the update rules of the players results in equilibrium frequencies more closely related to the mean field description.
COMPUTATIONAL GEOMETRY COLUMN 43
Authors: O'ROURKE JOSEPH
Published: October 2002

The concept of pointed pseudo-triangulations is defined and a few of its applications described.
SPIKES IN COSMIC CRYSTALLOGRAPHY
Authors: GOMERO G. I. , TEIXEIRA A. F. F. , REBOUÇCAS M. J. , BERNUI A.
Published: October 2002

If the universe is multiply connected and small the sky shows multiple images of cosmic objects, correlated by the covering group of the 3-manifold used to model it. These correlations were originally thought to manifest as spikes in pair separation histograms (PSH) built from suitable catalogues. Using probability theory we derive an expression for the expected pair separation histogram (EPSH) in a rather general topological-geometrical-observational setting. As a major consequence we show that the spikes of topological origin in PSH's are due to translations, whereas other isometries manifest as tiny deformations of the PSH corresponding to the simply connected case. This result holds for all Robertson–Walker spacetimes and gives rise to two basic corollaries: (i) that PSH's of Euclidean manifolds that have the same translations in their covering groups exhibit identical spike spectra of topological origin, making clear that even if the universe is flat the topological spikes alone are not sufficient for determining its topology; and (ii) that PSH's of hyperbolic 3-manifolds exhibit no spikes of topological origin. These corollaries ensure that cosmic crystallography, as originally formulated, is not a conclusive method for unveiling the shape of the universe. We also present a method that reduces the statistical fluctuations in PSH's built from simulated catalogues.
X-RAY RAMAN SCATTERING FROM LOW Z MATERIALS
Authors: KRISCH MICHAEL , SETTE FRANCESCO
Published: October 2002

X-ray Raman scattering from core electrons of low Z materials provides an alternative to soft X-ray absorption spectroscopy in cases where (i) exotic final states will be probed, (ii) the penetrating power of hard X rays is needed to study bulk properties, and (iii) when systems under high pressure are studied. The theoretical background and experimental requirements are discussed. The present capabilities of the technique are illustrated by two experiments, performed on the inelastic X ray scattering beamlines at the European Synchrotron Radiation Facility.
RECENT DEVELOPMENT IN SOFT X-RAY SPECTROSCOPY OF CORRELATED MATERIALS: HIGH RESOLUTION ABSORPTION AND BULK-SENSITIVE PHOTOEMISSION
Authors: SUGA SHIGEMASA
Published: October 2002

An extremely high quality soft X-ray beam line was constructed at BL25SU of SPring-8. A varied line spacing plane grating monochromator (VLSPGM) equipped with gratings with the central groove density of 600 and 1,000/mm can cover the energy region from 0.22 to 2 keV by the use of the fundamental radiation from the twin helical undulator. The energy resolution of VLSPGM is beyond 20,000 at 1 keV. The total resolution of practical photoelectron spectroscopy (PES) of better than 80 meV is achieved at 880 eV. The PES measurements performed above several hundred eV have shown the bulk sensitivity in many materials and provided spectra much different from the surface-sensitive spectra so far obtained below slightly above 100 eV or by He II and I light sources. As a breakthrough, bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) is demonstrated to be a very powerful means of studying the bulk electronic states of correlated electron systems.
RESONANT CORE LEVEL STUDIES OF MOLECULES AND CLUSTERS: ELECTRONIC STRUCTURE AND FEMTOSECOND DYNAMICS
Authors: BJÖRNEHOLM OLLE
Published: October 2002

Core level spectroscopy offers probing of atomic matter localized both in time and space. The temporal localization is due to the short lifetime of core holes, which opens a window from the energy domain to the low femtosecond time domain. The thus enabled studies of dynamic phenomena are exemplified by ultrafast dissociation of molecules. It is shown how information may be obtained about a characteristic dissociation time scale and the fragment velocities. The latter are also shown to be photon-energy-dependent. The spatial localization is due to the atomic character of core levels even in polyatomic systems. Clusters have a high and size-dependent fraction of atoms at the surface, and this leads to size-dependent properties. The spatially local character of core level spectroscopy is shown to be very valuable for separating contributions from surface and bulk atoms in free clusters.
NUCLEAR MOTION, SYMMETRY BREAKING AND DISSOCIATION DYNAMICS OF CORE-EXCITED POLYATOMIC MOLECULES
Authors: UEDA KIYOSHI
Published: October 2002

Recent studies on nuclear dynamics of core-excited and Auger final states are reviewed. Emphasis is given to the nuclear motion of the core-excited states and its influence to the subsequent decay and fragmentation processes. As specific examples we discuss two-dimensional nuclear motion caused by the O 1s → 2b2 excitation in H 2 O and by the C 1s → 2πu excitation in CO 2, as well as out-of-plane motion caused by B [Formula: see text] excitation and asymmetric stretching motion caused by the F 1s ionization in BF 3.
THE FERMI SURFACE IN A MAGNETIC METAL–INSULATOR INTERFACE
Authors: GREBER T. , AUWÄRTER W. , HOESCH M. , GRAD G. , BLAHA P. , OSTERWALDER J.
Published: October 2002

Nickel (111) and the interface of hexagonal boron nitride on Ni(111) serve as model systems for an itinerant ferromagnet that is truncated with vacuum or a single layer insulator. These systems are investigated with angle-scanned He I and He II photoemission. Upon formation of the h-BN/Ni(111) interface the work function drops by 1.8 eV and the minority Ni Λ3d-band shifts by 0.13 eV to higher binding energy. This indicates that the Ni magnetic moment decreases in the interface. Spin-polarized band structure calculations from bulk nickel identify the observed minority and majority bands. The experimental Fermi surface maps show that h-BN distorts a minority d-band in a way which is consistent with the decreasing magnetic moment. It can be seen that h-BN affects the scattering of the electrons. Effects in the photoemission final and initial state are recognized.
GISAXS STUDY OF CADMIUM SULFIDE QUANTUM DOTS
Authors: DUBCEK P. , BERNSTORFF S. , DESNICA U. V. , DESNICA-FRANKOVIC I. D. , SALAMON K.
Published: October 2002

In order to investigate the structure of semiconductor/glass composites prepared by ion implantation, the grazing incidence small angle X-ray scattering (GISAXS) technique was applied to CdS nanocrystals synthesized in SiO 2 by implanting separately the constituent Cd and S atoms with a dose of 1017/ cm 2 each, which resulted in a Gaussian depth density distribution of the dopants. Subsequently the samples were annealed at 700°C in order to form CdS particles. Due to the high concentration of nanocrystalline CdS, the scattered intensity is not following simple homogenous film models. Instead, additional particle scattering contribution is detected, as well as a multiplicative contribution due to inplane (lateral) particle correlation. From the first one, the particle size is estimated to be 4.6 nm, while an interparticle distance of 15–25 nm is deduced from the latter. Taking into account the applied dose, these values suggest that either part of the Cd and S ions are still dissolved in the amorphous substrate after annealing, and thus are not contributing to the CdS nanoparticle formation, or that implanted atoms have diffused deeper into the substrate during annealing.
A SPACE SOLAR PATROL APPARATUS FOR PHOTOMETRIC MEASUREMENTS AT A PHOTON-ENERGY RANGE OF 8 eV TO 8 keV
Authors: AVAKYAN S. V. , ANDREEV E. P. , AFANAS'EV I. M. , LEONOV N. B. , LEBEDINSKAYA M. L. , SAVUSHKIN A. V. , SEROVA A. E. , KUVALDIN E. V. , VORONIN N. A.
Published: October 2002

At the Vavilov State Optical Institute (SOI) a special apparatus and a methodology have been developed which enable one to measure absolute fluxes from the full disk of the Sun in the VUV, the EUV and the soft X-ray spectral ranges (0.14–157 nm). The apparatus allows one to carry out absolute spectral measurements using simultaneous operation of the radiometer and spectrometers. The radiometer is equipped with a special disk on which several filters are fitted (foils, thin films and crystals). This enables one to carry out measurements in the spectral range of 0.14–157 nm. The EUV grating spectrometer with normal incidence provides five spectral channels with a channel width of 35 nm each for measurements in the spectral range under 155 nm. The spectral range of 1.8–60 nm can be covered by a soft X-ray grazing grating spectrometer. All instruments are equipped with the same detectors, namely with the open secondary electron multipliers (SEM) with photocathodes made of BeO which were developed at the SOI. This photocathode has a good sensitivity in the spectral range under 150 nm and its sensitivity falls practically down to zero at wavelengths greater than 160 nm. The SEM has a high amplification (up to 108) and is stable to atmospheric influence. The stability of the SEM could be controlled by the radiation of the isotope 55 Fe (0.2 nm). There are plans to use this complex for mutual calibration of various synchrotron sources. Moreover it is planned to launch the Space Solar Patrol mission at the Russian Module of the International Space Station.
A NOVEL APPARATUS FOR LASER-EXCITED TIME-RESOLVED PHOTOEMISSION SPECTROSCOPY
Authors: PAOLICELLI G. , FONDACARO A. , RUOCCO A. , ATTILI A. , STEFANI G. , FERRINI G. , PELOI M. , PARMIGIANI F. , BANFI G. , CAUTERO G. , TOMMASINI R. , COMELLI G. , ROSEI R.
Published: October 2002

A novel apparatus devoted to time-resolved photoemission experiments in the sub-picosecond regime will be presented. The system is composed of a Ti:sapphire laser source and a time of flight (TOF) electron energy analyzer mounted in a UHV experimental chamber. The laser source is characterized by a pulse duration of 150 fs at a wavelength of 790 nm (1.57 eV) and operates at a repetition rate of 1 kHz. To perform photoemission measurements, UV radiation up to 6.28 eV is produced with sequential steps of frequency conversion by employing crystals with a second order nonlinearity. Photoelectrons are collected by a TOF spectrometer designed to analyze electrons from tenths of eV up to 5 eV. It can be operated in two different angular resolution modes switching on and off an electrostatic collection optics: the high angular resolution mode (Δα = ±2.7°) and the low angular resolution mode (Δα = ±5.6°). Single photon photoemission spectra from the Ag(100) clean surface have been recorded at room temperature using the fourth harmonic light (λ = 200 nm and hν = 6.28 eV). The Fermi edge profile convoluted with a Gaussian-shaped energy transmission function of the TOF spectrometer sets an upper limit for the energy resolution which is about 65 meV (FWHM) at 2 eV of electron energy.
A NEW XUV BEAMLINE ON A MULTI-POLE WIGGLER IN THE SRS
Authors: BOWLER M. , WEST J. B. , QUINN F. M. , HOLLAND D. M. P. , FELL B. , HATHERLY P. A. , HUMPHREY I. , FLAVELL W. R. , HAMILTON B.
Published: October 2002

An XUV beamline has been constructed on the SRS synchrotron radiation source at Daresbury Laboratory, exploiting the output from a 2 T multi-pole wiggler. The beamline is based on an SGM design and produces photons in the energy range 40–350 eV. By taking a 7.5 mrad fan, a high flux of between 1 × 1013 and 1 × 1014 photons/s/300 mA ring current can be delivered, with a resolving power of around 1000. A Kirkpatrick–Baez mirror pair focuses the light onto the entrance slit of the monochromator. Using 10 · m entrance and exit slits, a resolving power of up to 10,000 can be achieved, with a flux of 0.5–2 × 1011 photons/s/300 mA. The calculated and measured performance is presented, with emphasis on the challenges associated with utilizing the XUV output of a high field MPW source. In addition, the scientific research programme is outlined.
AN ANALYSIS OF ELECTRON–HOLE RECOMBINATION IN SOLID KRYPTON USING TIME-RESOLVED VUV-LUMINESCENCE SECTROSCOPY
Authors: KISAND V. , KIRM M. , VIELHAUER S. , ZIMMERER G.
Published: October 2002

For the first time, the free exciton (FE) VUV-luminescence decay curves were systematically investigated in solid Kr using photoexcitation in the energy region above band gap energy. Delayed electron–hole recombination and "prompt" (in terms of the time resolution of the experimental setup) creation of secondary excitons were separated using the time-resolved experimental technique. A detailed model for the dynamics of electron–hole recombination into the FE state was developed. The delayed component of the free exciton decay curve was reproduced with model calculations, including thermalization of the carriers via scattering on acoustic phonons, and the recombination cross-section, which depends on the actual carrier temperatures. A satisfactory agreement between experiment and theory was found.
MCD STUDIES IN 2p AND 3d XAS OF La1-xSrxCoO3
Authors: MIZUMAKI MASAICHIRO , YOSHII KENJI , KAWAMURA NAOMI , NAKAZAWA MAKOTO
Published: October 2002

Magnetic circular dichroism (MCD) spectra of La 1-x Sr x CoO 3 have been measured at Co 1s and 2p XAS, La 3d and 2p XAS. The contribution of the orbital moment to the total magnetic moment of Co ions became larger with the Sr composition of the La 1-x Sr x CoO 3 system increasing. There was no polarization of the 4f orbital in La but the 5d orbital in La was polarized by the hybridization between the Co 3d orbital and the La 5d orbital.
MAGNETIC COUPLING OF ALKALI AND RARE-GAS FILMS ADSORBED ON A FERROMAGNETIC SURFACE
Authors: SCHICKETANZ M. , OELSNER A. , FECHER G. H. , MORAIS J. , SCHÖNHENSE G.
Published: October 2002

The observation of magnetic circular dichroism in the angular distribution of photoelectrons (MCDAD) from alkali and rare-gas films adsorbed on a thin remanently magnetized Co layer is reported. The observation of an antisymmetric MCDAD near normal emission for Co(0001)–Cs 5p semi core level is shown. The reversed magnetization leads to a mirror-image-like distribution. The second system under investigation, physisorbed Co(0001)–Xe 5p, does not give such an but shows significant differences in the MCDAD signal for both directions of magnetization, in particular in the |mj| substates of the p3/2 level. A magnetic coupling between Xe and Co is evident when we take results of spin-resolved photoemission into account.
ELECTRONIC STRUCTURES OF THE METAL-TO-INSULATOR TRANSITION SYSTEM 1T-TaSxSe2-x STUDIED BY ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY
Authors: HORIBA K. , ONO K. , OSHIMA M. , AIURA Y. , SHIINO O.
Published: October 2002

We have investigated the electronic structures of metal-to-insulator transitions (MIT) due to charge-density-wave phase transition in 1T- TaS x Se 2-x by angle-resolved photoemission spectroscopy. In the insulating phase of the sample with x = 1.5, we observe a gap formation at the Fermi energy (E F ), while in the metallic phase of the sample with x = 1.2, we do not observe a drastic change in the spectra between at room temperature and at low temperature. We observe a peak originating from the lower Hubbard band in the insulating phase of the sample with x = 1.5. In the metallic phase of the sample with x = 1.2, the peak intensity is smaller and the peak energy shifts near E F , but the lower Hubbard band peak still remains. These results suggest that MIT in 1T- TaS x Se 2-x is due to the Mott localization.
RELATIVISTIC CALCULATION OF THE TWO-PHOTON BREMSSTRAHLUNG PROCESS
Authors: FEDOROVA T. A. , KOROL A. V. , SOLOVJEV I. A.
Published: October 2002

We present analytical and numerical results on the relativistic calculation of the two-photon bremsstrahlung process. For the approximate calculation of relativistic free–free two-photon matrix elements in the central field, we applied the method based on the accurate treatment of the diagonal singularities in the relativistic free–free single-photon matrix elements. Numerical calculations are carried out with the Furry–Sommerfeld–Maue wave functions. The obtained results are compared with the results of the relativistic Born approximation.
5d STATES AND RESONANT X-RAY SCATTERING FROM CeB6
Authors: NAGAO TATSUYA , IGARASHI JUN-ICHI
Published: October 2002

We study the origin of the resonant X-ray scattering (RXS) signal near the Ce L III absorption edge in the antiferroquadrupolar (AFQ) ordering phase of CeB 6. In this rare-earth metal compound, the intra-atomic Coulomb interaction plays a dominant role to give the large RXS intensities, which shows a sharp contrast with the Jahn–Teller distortion mechanism realized in the transition metal compound such as LaMnO 3. The temperature and magnetic field dependences show good agreement with the recent experiment, indicating that the RXS signal is a direct reflection of the AFQ order parameter.
ELECTRONIC STRUCTURE OF CoSe2
Authors: SATO H. , NAGASAKI F. , KANI Y. , SENBA S. , UEDA Y. , KIMURA A. , TANIGUCHI M.
Published: October 2002

The valence-band and conduction-band electronic structure of pyrite-type CoSe 2 has been investigated by means of ultraviolet-photoemission, synchrotron-radiation-photoemission and inverse-photoemission spectroscopies. The fully occupied Co 3d states with t 2g symmetry are observed as a main peak at -1.0 eV relative to the Fermi level (E F ), and the partially filled Co 3d states with e g symmetry are observed as a shoulder at the E F side of the main peak. On the other hand, the structure due to the unoccupied Co e g states appears at 0.6 eV in the inverse-photoemission spectrum. The electronic structure of CoSe 2 is similar to that of CoS 2. The electron correlation is more important for CoSe 2 than for CoS 2.
COLLAGEN AND ELASTIN CROSSLINKS IN HUMAN INTERVERTEBRAL DISCS AND LIGAMENTUM FLAVUM: AGE, GENDER AND SPINAL LEVEL INFLUENCES
Authors: Tan C. I. , Kent G. N. , Randall A. G. , Edmondston S. J. , Singer K. P.
Published: October 2002

The collagen and elastin content and extent of collagen crosslinks were determined in human formalin-fixed and unfixed intervertebral discs and ligamentum flava. Tissue samples from cadaveric spinal discs (n = 77) and ligamentum flava (n = 364) were obtained from 24 formalin-fixed and 2 fresh spines. The mean age of all cases was 57±26 years. Spinal ligament and disc samples were harvested and analyzed for collagen, and crosslinks of pyridinoline, deoxypyridinoline, and elastin crosslinks isodesmosine and desmosine. Collagen and elastin crosslinks were extracted from hydrolyzed samples by cellulose partition chromatography, and analyzed by reverse-phase HPLC. Elastin crosslinks were only detected in 4 lumbar discs (mean 0.04±0.01 nmol/mg dry wt) but yielded results for all ligamentum flavum samples (mean 20.2±6.4 nmol/mg dry wt). For ligamentum flavum, the collagen and collagen crosslinks increased significantly with age (p < 0.05), whereas elastin content decreased significantly with age but only for the lumbar region (p < 0.05). Collagen and elastin content were significantly higher in females (p < 0.01) and collagen, pyridinoline and isodesmosine were significantly higher in the lumbar region (p < 0.01). Elastin detected in lumbar discs was significantly less than that found in ligamentum flavum. The collagen and elastin content and extent of collagen crosslinks in ligamentum matrix varied significantly depending on the age, gender and spinal region.
SEMI-CLASSICAL LIMIT FOR THE ONE DIMENSIONAL NONLINEAR SCHRÖDINGER EQUATION
Authors: FELMER PATRICIO L. , TORRES JUAN J.
Published: October 2002

In this article we study standing wave solutions for the nonlinear Schrödinger equation, which correspond to solutions of the equation [Formula: see text] We are interested in solutions having a prescribed L2 norm, exhibiting high oscillatory behavior and concentrating in an interval. We prove existence of such solutions and we study their asymptotic behavior as the parameter ε goes to zero. In particular we obtain an envelope function describing the amplitude of the solutions and we identify their asymptotic density.
YBa2Cu3Ox Films Irradiated by 120 MeV Oxygen Ions
Authors: Kazumata Yukio , Satoru Okayasu Satoru Okayasu , Takeo Aruga Takeo Aruga
Published: October 2002

YBa2Cu3O

x

films were irradiated by 120 MeV O7+ ions. No significant change of T
c was found at the highest fluence of 1.3×1014 O+/cm2, but ΔM obtained from hysteresis loops and the irreversibility field appreciably decreased with irradiation. The decrease of zero-field cooling (ZFC) magnetization with irradiation is attributed to the increase of λ, which is caused by the decrease of density of superconducting carriers. Activation energies of flux motion were obtained from the measurements of magnetic relaxation. The decrease of activation energies may be correlated with the reduction of ΔM after the irradiation.