bluuebunny/crossref_metadata_2025 huggingface dataset:
COGNITIVE THERAPY IN EARLY PSYCHOSIS: A PILOT RANDOMIZED CONTROLLED TRIAL
Authors: Jolley Suzanne , Garety Philippa , Craig Tom , Dunn Graham , White Jo , Aitken Melissa
Published: February 2004

A pilot RCT of cognitive therapy (CT; based on Fowler, Garety, and Kuipers, 1995) for early psychosis adjunctive to treatment as usual (TAU) compared to TAU alone is presented. Recruitment is problematic and numbers are small. Levels of symptomatology are low at baseline; and both CT (n = 12) and TAU (n = 9) groups improve, with few significant group differences and high levels of individual variation. This pattern is common to other studies (Jackson et al., 1998; Lewis et al., 2002). The body of evidence to date seems to suggest that CT for early psychosis is not strongly indicated as an adjunctive treatment for all people with early psychosis, but should perhaps focus on the sub-group of patients whose recovery is incomplete.
The impact of feral horses on grassland bird communities in Argentina
Authors: Zalba Sergio M. , Cozzani Natalia C.
Published: February 2004

The impact of introduced herbivores on the composition and structure of plant communities has been widely studied. However, little is known about how they affect wildlife. We studied the impact of feral horses under different grazing regimes on the communities of birds in a nature reserve in the Pampas grasslands in Argentina. The areas that had predominantly tall grass (enclosures and areas of moderate grazing intensity) showed the greatest species richness and total abundance of birds. Some species, e.g. the southern lapwing (Vanellus chilensis), were associated with the presence of horses, while others, e.g. pipits (Anthus spp), were more common in lesser grazed areas. The presence of feral horses was associated with an increase in the rate of predation of eggs which varied from 12.5% within the enclosures to 70% in grazed areas. It is suggested that the increase in predation rate was due to the increased visibility of the nests and an increase in the density of opportunist carnivores. Small areas of grassland in a good state of conservation could serve as sources that would maintain communities of birds in the more transformed sections.
Strategic planning for captive populations: projecting changes in genetic diversity
Authors: Earnhardt Joanne M. , Thompson Steven D. , Schad Kristine
Published: February 2004

Maintenance of genetic diversity is critical for the preservation of small populations. Most captive populations are small and managers focus their efforts on reducing extinction risks by minimising loss of genetic diversity. To project changes in genetic diversity, managers use a genetic drift model. We used data from 40 managed captive populations to test whether this drift model is a good predictor of change in genetic diversity by comparing projected 10‐year trajectories of annual loss in expected heterozygosity with the changes estimated from pedigree analysis. We found that the drift model frequently overestimated the rate at which genetic diversity would be lost and could not predict increases, which we observed in 22 species. We suggest that the drift model does not adequately reflect the potential for management strategies, such as prioritised breeding recommendations and recruitment of potential founders, to slow the loss of genetic diversity. In many cases, the drift model may be overly pessimistic, leading managers to seek solutions such as importation, increased population size or the abandonment of a captive population, that may be unnecessary or premature. Managers should be cautious when interpreting results from genetic drift models, taking care to assess how management actions might lead to more optimistic prognoses.
Carnivore re‐colonisation: reality, possibility and a non‐equilibrium century for grizzly bears in the southern Yellowstone ecosystem
Authors: Pyare Sanjay , Cain Steve , Moody Dave , Schwartz Chuck , Berger Joel
Published: February 2004

Most large native carnivores have experienced range contractions due to conflicts with humans, although neither rates of spatial collapse nor expansion have been well characterised. In North America, the grizzly bear (Ursus arctos) once ranged from Mexico northward to Alaska, however its range in the continental USA has been reduced by 95–98%. Under the U. S. Endangered Species Act, the Yellowstone grizzly bear population has re‐colonised habitats outside Yellowstone National Park. We analysed historical and current records, including data on radio‐collared bears, (1) to evaluate changes in grizzly bear distribution in the southern Greater Yellowstone Ecosystem (GYE) over a 100‐year period, (2) to utilise historical rates of re‐colonisation to project future expansion trends and (3) to evaluate the reality of future expansion based on human limitations and land use. Analysis of distribution in 20‐year increments reflects range reduction from south to north (1900–1940) and expansion to the south (1940–2000). Expansion was exponential and the area occupied by grizzly bears doubled approximately every 20 years. A complementary analysis of bear occurrence in Grand Teton National Park also suggests an unprecedented period of rapid expansion during the last 20–30 years. The grizzly bear population currently has re‐occupied about 50% of the southern GYE. Based on assumptions of continued protection and ecological stasis, our model suggests total occupancy in 25 years. Alternatively, extrapolation of linear expansion rates from the period prior to protection suggests total occupancy could take >100 years. Analyses of historical trends can be useful as a restoration tool because they enable a framework and timeline to be constructed to pre‐emptively address the social challenges affecting future carnivore recovery.
Wer liest Zeitung? Einflussfaktoren auf die Zeitungsnutzung Jugendlicher
Authors: Rager Günther , Graf-Szczuka Karola , Bodin Michael , Thiele Martina
Published: February 2004

Zusammenfassung. Im vorliegenden Beitrag wird eine Studie vorgestellt, die Merkmale zur Unterscheidung von jugendlichen Zeitungsleser/inne/n und Nichtleser/inne/n identifiziert. Auf der Basis von Mittelwertsunterschieden beschreiben wir zunächst vier unterschiedliche Typen von Leser/inne/n und Nichtleser/inne/n anhand von Sozialisations- und Einstellungsfaktoren sowie Personenmerkmale wie Interessen, Wissensdurst, verbale Fertigkeiten und Lesefertigkeiten. Die Beziehung der einzelnen Variablen untereinander und deren Zusammenhang mit der Zeitungsnutzung werden mittels multipler Regressionsanalysen und einer Faktorenanalyse genauer untersucht, dargestellt und diskutiert.
Comparison of photometric measurements and charge moment estimations in two sprite‐producing storms
Authors: Gerken E. A. , Inan U. S.
Published: February 2004

In one relatively small storm on July 2, 2000, 276 sprites were observed between 04:00–07:00 UT. These sprites were largely confined to 70–85 km altitude, were relatively faint and diffuse, and were typically associated with very high peak currents and short time duration. A second storm, on July 4, 2000, had a much larger spatial extent and 27 sprites were observed between 04:00–07:00 UT in a wide range of shapes and time scales spanning 40–90 km altitude. These sprites were produced by 20–120 kA CG's, had complex optical signatures, and were frequently associated with observed ELF radiation. We hypothesize that relatively small storms mainly produce sprites in the form of diffuse glow whereas larger storms with higher cloud tops can initiate streamer discharges leading to more spectacular sprites.
Growth of the hemispheric dichotomy and the cessation of plate tectonics on Mars
Authors: Lenardic A. , Nimmo F. , Moresi L.
Published: February 2004

Although Mars is currently not tectonically active, it may have experienced plate tectonics early in its history. The southern hemisphere of Mars possesses a thick crust which probably renders the lithosphere positively buoyant. In this paper we present numerical and scaling arguments which show that if the area of positively buoyant lithosphere grows beyond a critical fraction (≈50% for Mars), plate tectonics will stop. Heat transfer through the buoyant lithosphere is inefficient, which causes mean mantle temperatures to increase as the surface area of buoyant lithosphere increases. The resulting reduction in mantle viscosity reduces shear stresses; if these shear stresses drop below the yield strength of the lithosphere, plate motions will cease and the planet will behave as a one‐plate system. Thus the end of plate tectonics on Mars is a natural consequence of the growth of the southern highlands. Similar arguments for the Earth predict that it should operate in the plate tectonic regime now but that it may have experienced stagnant lid convection in the past.
Mitochondrial cytochrome c release may occur by volume-dependent mechanisms not involving permeability transition
Authors: GOGVADZE Vladimir , ROBERTSON John D. , ENOKSSON Mari , ZHIVOTOVSKY Boris , ORRENIUS Sten
Published: February 2004

The mechanisms regulating mitochondrial outer-membrane permeabilization and the release of cytochrome c during apoptosis remain controversial. In the present study, we show in an in vitro model system that the release of cytochrome c may occur via moderate modulation of mitochondrial volume, irrespective of the mechanism leading to the mitochondrial swelling. In contrast with mitochondrial permeability transition-dependent release of cytochrome c, in the present study mitochondria remain intact and functionally active.
Latrophilin is required for toxicity of black widow spider venom in Caenorhabditis elegans
Authors: MEE Christopher J. , TOMLINSON Simon R. , PERESTENKO Pavel V. , de POMERAI David , DUCE Ian R. , USHERWOOD Peter N. R. , BELL David R.
Published: February 2004

Black widow spider venom (BWSV) kills Caenorhabditis elegans after injection owing to the presence of heat- and detergent-sensitive components, which are high-molecular-mass latrotoxins. A C. elegans homologue of latrophilin/CIRL (calcium-independent receptor for latrotoxin), B0457.1, was identified and shown to have five conserved domains. RNAi (RNA interference) of this gene rendered C. elegans resistant to BWSV, whereas RNAi for CYP37A1 or a neurexin I homologue, and a deletion mutant of the related B0286.2 gene, had no effect on BWSV toxicity. The latrophilin RNAi mutants exhibit changes in defaecation cycle and alterations in drug sensitivity. These results demonstrate that latrophilin mediates the toxicity of BWSV and provide evidence for a physiological function of this receptor.
Hormonal regulation of phospholipase Cepsilon through distinct and overlapping pathways involving G12 and Ras family G-proteins
Authors: KELLEY Grant G. , REKS Sarah E. , SMRCKA Alan V.
Published: February 2004

PLC∊ (phospholipase C∊) is a novel PLC that has a CDC25 guanine nucleotide exchange factor domain and two RA (Ras-association) domains of which the second (RA2) is critical for Ras activation of the enzyme. In the present studies, we examined hormonal stimulation to elucidate receptor-mediated pathways that functionally regulate PLC∊. We demonstrate that EGF (epidermal growth factor), a receptor tyrosine kinase agonist, and LPA (lysophosphatidic acid), S1P (sphingosine 1-phosphate) and thrombin, GPCR (G-protein-coupled receptor) agonists, stimulate PLC∊ overexpressed in COS-7 cells. EGF stimulated PLC∊ in an RA2-dependent manner through Ras and Rap. In contrast, LPA, S1P and thrombin stimulated PLC∊ by both RA2-independent and -dependent mechanisms. To determine the G-proteins that mediate the effects of these GPCR agonists, we co-expressed constitutively active G-proteins with PLC∊ and found that Gα12, Gα13, Rho, Rac and Ral stimulate PLC∊ in an RA2-independent manner; whereas TC21, Rap1A, Rap2A and Rap2B stimulate PLC∊ in an RA2-dependent manner similar to H-Ras. Of these G-proteins, we show that Gα12/Gα13 and Rap partly mediate the effects of LPA, S1P and thrombin to stimulate PLC∊. In addition, the stimulation by LPA and S1P is also partly sensitive to pertussis toxin. These studies demonstrate diverse hormonal regulation of PLC∊ by distinct and overlapping pathways.
Importin beta1 mediates the glucose-stimulated nuclear import of pancreatic and duodenal homeobox-1 in pancreatic islet beta-cells (MIN6)
Authors: GUILLEMAIN Ghislaine , da SILVA XAVIER Gabriela , RAFIQ Imran , LETURQUE Armelle , RUTTER Guy A.
Published: February 2004

The transcription factor PDX-1 (pancreatic and duodenal homeobox-1) is essential for pancreatic development and the maintainence of expression of islet β-cell-specific genes. In an previous study [Rafiq, Kennedy and Rutter (1998) J. Biol. Chem. 273, 23241–23247] we demonstrated that PDX-1 may be activated at elevated glucose concentrations by translocation from undefined binding sites in the cytosol and nuclear membrane into the nucleoplasm. In the present study, we show that PDX-1 interacts directly and specifically in vitro with the nuclear import receptor family member, importin β1, and that this interaction is mediated by the PDX-1 homeodomain (amino acids 146–206). Demonstrating the functional importance of the PDX-1–importin β1 interaction, microinjection of MIN6 β-cells with anti-(importin β1) antibodies blocked both the nuclear translocation of PDX-1, and the activation by glucose (30 mM versus 3 mM) of the pre-proinsulin promoter. However, treatment with extracts from pancreatic islets incubated at either low or high glucose concentrations had no impact on the ability of PDX-1 to interact with importin β1 in vitro. Furthermore, importin β1 also interacted with SREBP1c (sterol-regulatory-element-binding protein 1c) in vitro, and microinjection of importin β1 antibodies blocked the activation by glucose of SREBP1c target genes. Since the subcellular distribution of SREBP1c is unaffected by glucose, these findings suggest that a redistribution of importin β1 is unlikely to explain the glucose-stimulated nuclear uptake of PDX-1. Instead, we conclude that the uptake of PDX-1 into the nucleoplasm, as glucose concentrations increase, may be mediated by release of the factor both from sites of retention in the cytosol and from non-productive complexes with importin β1 at the nuclear membrane.
WNK1, the kinase mutated in an inherited high-blood-pressure syndrome, is a novel PKB (protein kinase B)/Akt substrate
Authors: VITARI Alberto C. , DEAK Maria , COLLINS Barry J. , MORRICE Nick , PRESCOTT Alan R. , PHELAN Anne , HUMPHREYS Sian , ALESSI Dario R.
Published: February 2004

Recent evidence indicates that mutations in the gene encoding the WNK1 [with no K (lysine) protein kinase-1] results in an inherited hypertension syndrome called pseudohypoaldosteronism type II. The mechanisms by which WNK1 is regulated or the substrates it phosphorylates are currently unknown. We noticed that Thr-60 of WNK1, which lies N-terminal to the catalytic domain, is located within a PKB (protein kinase B) phosphorylation consensus sequence. We found that PKB phosphorylated WNK1 efficiently compared with known substrates, and both peptide map and mutational analysis revealed that the major PKB site of phosphorylation was Thr-60. Employing a phosphospecific Thr-60 WNK1 antibody, we demonstrated that IGF1 (insulin-like growth factor) stimulation of HEK-293 cells induced phosphorylation of endogenously expressed WNK1 at Thr-60. Consistent with PKB mediating this phosphorylation, inhibitors of PI 3-kinase (phosphoinositide 3-kinase; wortmannin and LY294002) but not inhibitors of mammalian target of rapamycin (rapamycin) or MEK1 (mitogen-activated protein kinase kinase-1) activation (PD184352), inhibited IGF1-induced phosphorylation of endogenous WNK1 at Thr-60. Moreover, IGF1-induced phosphorylation of endogenous WNK1 did not occur in PDK1−/− ES (embryonic stem) cells, in which PKB is not activated. In contrast, IGF1 still induced normal phosphorylation of WNK1 in PDK1L155E/L155E knock-in ES cells in which PKB, but not S6K (p70 ribosomal S6 kinase) or SGK1 (serum- and glucocorticoid-induced protein kinase 1), is activated. Our study provides strong pharmacological and genetic evidence that PKB mediates the phosphorylation of WNK1 at Thr-60 in vivo. We also performed experiments which suggest that the phosphorylation of WNK1 by PKB is not regulating its kinase activity or cellular localization directly. These results provide the first connection between the PI 3-kinase/PKB pathway and WNK1, suggesting a mechanism by which this pathway may influence blood pressure.
TAB3, a new binding partner of the protein kinase TAK1
Authors: CHEUNG Peter C. F. , NEBREDA Angel R. , COHEN Philip
Published: February 2004

We have identified a new binding partner of the TGFβ (transforming growth factor-β)-activated protein kinase (TAK1), termed TAB3 (TAK1-binding protein-3), which shares 48% amino acid sequence identity with TAB2. Our results indicate that two distinct TAK1 complexes are present in cells. One comprises TAK1 complexed with TAB1 and TAB2, and the other TAK1 complexed with TAB1 and TAB3. Both complexes are activated in response to tumour necrosis factor-α or interleukin-1 in human epithelial KB cells or bacterial lipopolysaccharide in RAW264.7 macrophages, and are subject to feedback control by stress-activated protein kinase 2a (SAPK2a; also called p38α). The electrophoretic mobility of TAB2 and TAB3 decreases in response to these agonists or osmotic shock, and is reversed by treatment with protein phosphatase-1. The decrease in mobility of TAB3 is prevented if the cells are incubated with SB 203580 before stimulation, but treatment with SB 203580 produces forms of TAB2 with a mobility intermediate between that observed for TAB2 in unstimulated and stimulated cells. Similar results were obtained in embryonic fibroblasts from mice deficient in SAPK2a/p38α. Our results indicate that TAB3 is phosphorylated via the SAPK2a/p38α pathway, whereas TAB2 is phosphorylated at two or more sites by both an SAPK2a/p38α-dependent and an SB 203580-independent kinase. The SAPK2a/p38α-mediated phosphorylation of TAB2 and TAB3 may contribute to the SAPK2a/p38α-mediated feedback control of TAK1 activity that also involves the phosphorylation of TAB1. We also show that the agonist-induced activation of TAK1 complexes requires the phosphorylation of the TAK1 catalytic subunit at a serine/threonine residue(s).
Field and laboratory biology of the stem‐feeding beetle Thamnurgus euphorbiae (Küster) (Col., Scolytidae) in Italy, a potential biological control candidate of leafy spurge in the USA and Canada
Authors: Campobasso G. , Terragitti G. , Mann K. , Quimby P. C.
Published: February 2004

Thamnurgus euphorbiae overwinters as adults in dry stems of Euphorbia characias until the end of March before exiting through circular holes cut with their mandibles. Females and males appeared in the field at the same time, and the first pairs were observed on 28 March on new stems of E. characias having the open‐flower at the beginning of its development. Throughout the rest of April it was possible to find and collect the fairly abundant adults. Mating occurs on new stems of the host plant and females walk up towards the top of the stem and start to mine the centre of it in order to penetrate. Oviposition occurs in new stems and eggs are laid singly along the interior of the stem; females laid 35–85 eggs. Upon hatching, larvae started feeding on vascular bundles and the inner cortex. There are three larval instars, and pupation occurred in the stem of the host plant; this insect is univoltine. Thamnurgus euphorbiae has been accepted by the Technical Advisory Group for Biological Control Agents of Weeds for release as a biological control agent of leafy spurge in the US. Prior to this study the biology of T. euphorbiae was unknown.
Comparative growth inhibitory and antifeedant effects of plant extracts and pure allelochemicals on four phytophagous insect species
Authors: Akhtar Y. , Isman M. B.
Published: February 2004

Antifeedant and growth inhibitory effects of crude plant extracts (Melia volkensii and Origanum vulgare) and pure allelochemicals (digitoxin, cymarin, xanthotoxin, toosendanin, thymol and trans‐anethole) were investigated in the cabbage looper (Trichoplusia ni), and in the armyworm (Pseudaletia unipuncta) using different bioassays. Antifeedant effects of M. volkensii, O. vulgare and thymol were investigated in larvae of the diamondback moth (Plutella xylostella), and of O. vulgare and thymol in the Mexican bean beetle (Epilachna varivestis), using leaf disc choice bioassays. M. volkensii was the most potent growth inhibitor for T. ni and P. unipuncta (dietary EC50 = 7.6 and 12.5 p.p.m., respectively) of all the test substances. Cymarin was the second most potent growth inhibitor (EC50 = 132.0 p.p.m.) for T. ni. The most effective feeding deterrents for third instar T. ni larvae were xanthotoxin andM. volkensii (DC50 = 0.9 and 8.3 μg/cm2, respectively). M. volkensii was also the most potent feeding deterrent for third instar P. unipuncta, P. xylostella and adult E. varivestis (DC50 = 10.5, 20.7 and 2.3 μg/cm2, respectively). Because of interspecific differences in response to feeding deterrents and the lack of a strong relationship between EC50 and DC50 values, we recommend testing a battery of bioassay species with candidate compounds and the use of more than one bioassay. Based on their growth inhibitory and feeding deterrent properties, some of these plant extracts and pure allelochemicals have potential for use as alternative crop protectants against a number of pest species.
Third-order Douglas–Kroll relativistic coupled-cluster theory through connected single, double, triple, and quadruple substitutions: Applications to diatomic and triatomic hydrides
Authors: Hirata So , Yanai Takeshi , de Jong Wibe A. , Nakajima Takahito , Hirao Kimihiko
Published: February 2004

Coupled-cluster methods including through and up to the connected single, double, triple, and quadruple substitutions have been derived and implemented automatically for sequential and parallel executions by an algebraic and symbolic manipulation program TCE (TENSOR CONTRACTION ENGINE) for use in conjunction with a one-component third-order Douglas–Kroll approximation for relativistic corrections. A combination of the converging electron-correlation methods, the accurate relativistic reference wave functions, and the use of systematic basis sets tailored to the relativistic approximation has been shown to predict the experimental singlet–triplet separations within 0.02 eV (0.5 kcal/mol) for five triatomic hydrides (CH2, NH2+, SiH2, PH2+, and AsH2+), the experimental bond lengths (re or r0) within 0.002 Å, rotational constants (Be or B0) within 0.02 cm−1, vibration–rotation constants (αe) within 0.01 cm−1, centrifugal distortion constants (De) within 2%, harmonic vibration frequencies (ωe) within 8 cm−1 (0.4%), anharmonic vibrational constants (xωe) within 2 cm−1, and dissociation energies (D00) within 0.02 eV (0.4 kcal/mol) for twenty diatomic hydrides (BH, CH, NH, OH, FH, AlH, SiH, PH, SH, ClH, GaH, GeH, AsH, SeH, BrH, InH, SnH, SbH, TeH, and IH) containing main-group elements across the second through fifth rows of the periodic table. In these calculations, spin–orbit effects on dissociation energies, which were assumed to be additive, were estimated from the measured spin–orbit coupling constants of atoms and diatomic molecules, and an electronic energy in the complete-basis-set, complete-electron-correlation limit has been extrapolated in two ways to verify the robustness of the results: One assuming Gaussian-exponential dependence of total energies on double through quadruple ζ basis sets and the other assuming n−3 dependence of correlation energies on double through quintuple ζ basis sets.
Sticking of CO to crystalline and amorphous ice surfaces
Authors: Al-Halabi A. , van Dishoeck E. F. , Kroes G. J.
Published: February 2004

We present results of classical trajectory calculations on the sticking of hyperthermal CO to the basal plane (0001) face of crystalline ice Ih and to the surface of amorphous ice Ia. The calculations were performed for normal incidence at a surface temperature Ts=90 K for ice Ia, and at Ts=90 and 150 K for ice Ih. For both surfaces, the sticking probability can be fitted to a simple exponentially decaying function of the incidence energy, Ei: Ps=1.0e−Ei(kJ/mol)/90(kJ/mol) at Ts=90 K. The energy transfer from the impinging molecule to the crystalline and the amorphous surface is found to be quite efficient, in agreement with the results of molecular beam experiments on the scattering of the similar molecule, N2, from crystalline and amorphous ice. However, the energy transfer is less efficient for amorphous than for crystalline ice. Our calculations predict that the sticking probability decreases with Ts for CO scattering from crystalline ice, as the energy transfer from the impinging molecule to the warmer surfaces becomes less efficient. At high Ei (up to 193 kJ/mol), no surface penetration occurs in the case of crystalline ice. However, for CO colliding with the amorphous surface, a penetrating trajectory was observed to occur into a large water pore. The molecular dynamics calculations predict that the average potential energy of CO adsorbed to ice Ih is −10.1±0.2 and −8.4±0.2 kJ/mol for CO adsorbed to ice Ia. These values are in agreement with previous experimental and theoretical data. The distribution of the potential energy of CO adsorbed to ice Ia was found to be wider (with a standard deviation σ of 2.4 kJ/mol) than that of CO interacting with ice Ih (σ=2.0 kJ/mol). In collisions with ice Ia, the CO molecules scatter at larger angles and over a wider distribution of angles than in collisions with ice Ih.
Time-resolved spectroscopic behavior of Fe2O3 and ZnFe2O4 nanocrystals
Authors: Fu Limin , Wu Zhenyu , Ai Xicheng , Zhang Jianping , Nie Yuxin , Xie Sishen , Yang Guozhen , Zou Bingsuo
Published: February 2004

Using nanosecond (ns) and femtosecond (fs) time-resolved absorption spectroscopies (pump–probe technique), the carrier dynamics in transition metal oxide nanocrystals of α-Fe2O3 and ZnFe2O4 was studied during the photolysis process. For Fe2O3 and ZnFe2O4 nanocrystals, the fs measurements detect similar profiles of a positive nonlinear absorption in their capped nanocrystals, whereas much weak signals in the naked particles. In the nanosecond measurements Fe2O3 and ZnFe2O4 nanocrystals show obvious excitation-power dependent absorption properties and at the low pump power they show weak photobleaching, but at high pump power they produce positive nonlinear absorptions. For Fe2O3 nanocrystals, the threshold power of negative absorption (bleach) to positive absorption increases with reducing size, whereas for the ZnFe2O4 samples, the threshold powers reach minimum at a critical size of 11 nm, grow for both the bigger and the smaller nanocrystals. These results reflect the influences of their microscopic magnetic couplings and carrier correlation on biexciton absorption in Fe2O3 and ZnFe2O4 nanocrystals. All the results indicate that the time resolved photoabsorption techniques are useful to study the microscopic spin interactions and carrier correlations in transition metal oxide nanocrystals.
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spin–spin coupling constant surfaces for (HF)2 clusters: The orientation and distance dependence of the sign and magnitude of JF–F
Authors: Del Bene Janet E. , Elguero José , Alkorta Ibon , Yáñez Manuel , Mó Otilia
Published: February 2004

Ab initio calculations using the equation-of-motion coupled cluster method have been carried out to investigate F19–19F spin–spin coupling constants for a pair of HF molecules. The overall features of the JF–F coupling surface with respect to the F–F distance and the orientation of the pair of HF molecules reflect those of the Fermi-contact (FC) surface, although the FC term may not be a good quantitative estimate of JF–F. The hydrogen-bonded HF dimer exhibits unusual behavior compared to other hydrogen-bonded complexes, since both the FC term and JF–F2h exhibit variations in sign and magnitude as the F–F distance changes and the linearity of the hydrogen bond is destroyed. The FC term for F–F coupling is relative small and negative for the equilibrium dimer. At the dimer F–F distance, the maximum negative value for the FC term is found for the linear arrangement F–H⋯H–F, while the maximum positive value is found for the linear H–F⋯F–H arrangement, despite the fact that neither of these structures is bound. Changes in the sign and magnitude of the FC term are analyzed using the nuclear magnetic resonance triplet wave function model, which relates the orientation of magnetic nuclei to the phases of the wave functions for excited triplet states that couple to the ground state. The FC term for a particular orientation is a result of competing positive and negative contributions from different triplet states, the sign of each contribution being determined by the alignment of the nuclear magnetic moments in that state. Factors are identified which must play a role in determining which types of wave functions dominate.
Spin and charge distribution in iron porphyrin models: A coupled cluster and density-functional study
Authors: Johansson Mikael P. , Sundholm Dage
Published: February 2004

We recently performed detailed analyses of the electronic structure of low-spin iron porphyrins using density-functional theory (DFT). Both the spin-density distributions of the oxidized, ferric forms, as well as the changes in total charge density upon reduction to the ferrous forms have been explored. Here, we compare the DFT results with wave-function theory, more specifically, with the approximate singles and doubles coupled-cluster method (CC2). Different spin states are considered by studying representative models of low spin, intermediate spin, and high spin species. The CC2 calculations corroborate the DFT results; the spin density exhibits the same amount of molecular spin polarization, and the charge delocalization is of comparable magnitude. Slight differences in the descriptions are noted and discussed.
Four-color hole burning spectra of phenol/ammonia 1:3 and 1:4 clusters
Authors: Ishiuchi Shun-ichi , Daigoku Kota , Hashimoto Kenro , Fujii Masaaki
Published: February 2004

The hole burning spectra of phenol/ammonia (1:3 and 1:4) clusters were measured by a newly developed four-color (UV–near-IR–UV–UV) hole burning spectroscopy, which is a kind of population labeling spectroscopy. From the hole burning spectra, it was found that single species is observed in an n=3 cluster, while three isomers are observed simultaneously for n=4. A possibility was suggested that the reaction efficiency of the hydrogen transfer from the electronically excited phenol/ammonia clusters, which was measured by a comparison with the action spectra of the corresponding cluster, depends on the initial vibronic levels.
Density functional study on the circular dichroism of photoelectron angular distribution from chiral derivatives of oxirane
Authors: Stener M. , Fronzoni G. , Tommaso D. Di , Decleva P.
Published: February 2004

The linear combination of atomic orbitals B-spline density functional method has been successfully applied to a series of four chiral derivatives of oxirane, to calculate the photoionization dynamical parameters, the circular dichroism in the angular distribution effect, and to identify trends along the series. The computational algorithm has proven numerically stable and computationally competitive. The photoionization cross section, asymmetry, and dichroic parameter profiles relative to valence orbitals have been systematically studied for the states which retain their nature along the series: the identified trends have been ascribed to the different electronic properties of the substituents. A rather unexpected sensitivity of the dichroic parameter to changes in the electronic structure has been found in many instances, making this dynamical property suitable to investigate the electronic structure of chiral compounds. The magnitude of the circular dichroism in the angular distribution effect does not seem to be associated with the initial state chirality, but rather to be governed by the ability of the delocalized photoelectron wave function to probe the asymmetry of the molecular effective potential.
Pressure-induced formation of diblock copolymer “micelles” in supercritical fluids. A combined study by small angle scattering experiments and mean-field theory. II. Kinetics of the unimer–aggregate transition
Authors: Raudino A. , Lo Celso F. , Triolo A. , Triolo R.
Published: February 2004

We developed a simple time-dependent mean-field theory to describe the phase separation kinetics of either homopolymers or AB-diblock copolymers in supercritical (SC) fluids. The model, previously used to describe the phase behavior of AB-block copolymers under the assumption of strong solvent selectivity for just one copolymer chain, has been extended to study the kinetics of the phase separation process. Time resolved small angle x-ray scattering (TR–SAXS) measurements have been performed on different AB-diblock copolymers containing a perfluorinated chain and dissolved in SC–CO2. The data obtained over a wide range of pressure and temperature confirm our theoretical predictions. Particularly interesting is the presence of two relaxation frequencies for the homogeneous solution→spherical aggregate transition, where the two relaxation processes depend on the depth of the pressure jump and on temperature. The whole phenomenon could be explained as an initial SC solvent/polymer phase separation followed by a slow reorientation process to form spherical aggregates driven by the copolymer solvophilic moiety.
Path integral calculation of thermal rate constants within the quantum instanton approximation: Application to the H+CH4→H2+CH3 hydrogen abstraction reaction in full Cartesian space
Authors: Zhao Yi , Yamamoto Takeshi , Miller William H.
Published: February 2004

The quantum instanton approximation for thermal rate constants of chemical reactions [Miller, Zhao, Ceotto, and Yang, J. Chem. Phys. 119, 1329 (2003)], which is modeled after the earlier semiclassical instanton approach, is applied to the hydrogen abstraction reaction from methane by a hydrogen atom, H+CH4→H2+CH3, using a modified and recalibrated version of the Jordan–Gilbert potential surface. The quantum instanton rate is evaluated using path integral Monte Carlo approaches based on the recently proposed implementation schemes [Yamamoto and Miller, J. Chem. Phys. 120, 3086 (2004)]. The calculations were carried out using the Cartesian coordinates of all the atoms (thus involving 18 degrees of freedom), thereby taking explicit account of rotational effects of the whole system and also allowing the equivalent treatment of the four methane hydrogens. To achieve such a treatment, we present extended forms of the path integral estimators for relevant quantities that may be used for general N-atom systems with any generalized reaction coordinates. The quantum instanton rates thus obtained for the temperature range T=200–2000 K show good agreement with available experimental data, which gives support to the accuracy of the underlying potential surface used.
Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
Authors: Chiang Su-Yu , Fang Yung-Sheng , Sankaran K. , Lee Yuan-Pern
Published: February 2004

The dissociative photoionization of CH2Br2 in a region ∼10–24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of ΔHf,2980(CHBr+)⩽300.7±1.5 kcal mol−1 is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be ⩽9.17±0.23 eV. Literature values for ΔHf,2980(CBr+)=362.5 kcal mol−1 and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol−1 and 9.11 eV, respectively. Also based on a new experimental ionization energy, ΔHf,2980(CH2Br2+) is revised to be 236.4±1.5 kcal mol−1.
Nuclear magnetic shielding and chirality IV. The odd and even character of the shielding response to a chiral potential
Authors: Sears Devin N. , Jameson Cynthia J. , Harris Robert A.
Published: February 2004

We investigate the odd and even character of the shielding response in a chiral molecule (modeled by a Ne8 helix) when subjected to a chiral potential. We establish that the diastereomeric splittings are a measure of odd powers of Vodd. Implications for diastereomeric, splittings of Xe in handed cages with handed tethers are discussed.
Phenomenological description of the multidomain state of the easy-plane antiferromagnet NiCl2
Authors: Kalita V. M. , Lozenko A. F. , Trotsenko P. A. , Yatkevich T. M.
Published: February 2004

An analysis is made of the experimental data on the magnetic-field dependence of the magnetostriction and magnetization of the NiCl2 crystal at its transition from the multidomain antiferromagnetic state to a uniform state. It is shown that their field dependence is determined by the mean orientation of the domains, which is characterized by a domain coalignment parameter. That parameter is used to give a phenomenological description of the multidomain state of the antiferromagnet NiCl2.
Reinvestigation of CS2 dissociation at 193 nm by means of product state-selective vacuum ultraviolet laser ionization and velocity imaging
Authors: Xu Dadong , Huang Jianhua , Jackson William M.
Published: February 2004

A branching ratio of 1.6±0.3 for S(3P)/S(1D) is obtained for the dissociation of CS2 with very low fluence 193 nm laser (less than 2 mJ/cm2), in which the S(3P) and S(1D) have been state-selectively ionized using VUV lasers at different wavelengths. The anisotropy parameters βmax(3P)=0.8 and βmax(1D)=1.9 indicate that these channels are preferentially populated at different geometries and the lifetime is very short.
On the dynamics of coupled Bohmian and phase-space variables: A new hybrid quantum-classical approach
Authors: Burghardt Irene , Parlant Gérard
Published: February 2004

A new approach to the coupling of quantum and classical dynamics is developed, by combining a hydrodynamic, Bohmian description for the quantum subsystem with a Liouville-space description for the classical subsystem. To this end, partial hydrodynamic moments are introduced, the dynamics of which is determined by a hierarchy of equations derived from the quantum Liouville equation. We focus on pure states (wave functions) and introduce a trajectory representation in a hybrid hydrodynamic-Liouvillian phase space. The interleaved trajectory dynamics is guided by a new type of quantum force. For illustration, we consider a pair of bilinearly coupled harmonic oscillators, for which the method is exact.
Symmetrized Tensor ``Trace'' Operations
Authors: Tompkins Donald R.
Published: February 2004

Extracting the ``trace'' from a Cartesian tensor requires working with the whole tensor. Extracting the trace from a symmetrized tensor is shown to allow one to work with separate invariant subspaces (hence yielding more convenient analytical results), and thus, reduces the number of coupled equations to be solved. Symmetrized trace extraction is described for extended symmetrization procedures based respectively on modified Young symmetrizers, Wigner projection operator symmetrizers, and Young symmetrizers. Symmetrized traceless tensors usually need to be further symmetrized to obtain fully symmetrized traceless tensors. Also described is a method where each rank of trace extraction is performed in a separate step and is accompanied by a step of symmetrization. This method yields fully symmetrized traceless tensors and the least coupling of equations.
Unitary Representations of the Homogeneous Lorentz Group in an O(2, 1) Basis
Authors: Mukunda N.
Published: February 2004

Unitary irreducible representations of the homogeneous Lorentz group, SO(3, 1), belonging to the principal series and containing integral angular momenta, are reduced with respect to the subgroup SO(2, 1). It is found that the representation {j0, ρ} of SO(3, 1), where j0 is a nonnegative integer and ρ a real number, contains each representation of SO(2, 1) of the continuous class (nonexceptional and integral) twice, and each of the discrete representations Dk(±) of SO(2, 1) once, for k = 1, 2, ⋯, j0. The latter representations are absent for j0 = 0. It is shown that the basis states of the representation Dk(±) (for k ≥ 2) lie in the domain of those generators of SO(3, 1) that are outside the SO(2, 1) subalgebra, while the states of the representations D1(±) do not lie in this domain. It is further shown that from the point of view of the nature of this domain, the representations D1(±) of SO(2, 1) are very intimately connected to the continuous class representations of SO(2, 1), and that these two discrete representations act as a bridge between the remaining discrete representations on the one hand, and the continuous class representations on the other.
Weyl Transformation and the Classical Limit of Quantum Mechanics
Authors: Leaf Boris
Published: February 2004

The Weyl correspondence for obtaining quantum operators from functions of classical coordinates and momenta is known to be incorrect. To calculate quantum-mechanical expectation values as phase-space averages with the Wigner density function, one cannot use classical functions but must use Weyl transforms. These transforms are defined and their properties derived from quantum mechanics. Their properties are expressed in terms of a Hermitian operator Δ(Q, K) whose Weyl transform is a δ function. The Wigner function is the transform of the density operator. Every Weyl transform is exhibited as a difference of two functions which are nonnegative on the phase spece. Weyl transforms do not obey the algebra of classical functions. In the classical limit ℏ → 0, Weyl transforms become classical functions, the Wigner function becomes nonnegative throughout the phase space, and the Hilbert space is spanned by an orthonormal set of vectors which are simultaneous eigenkets of the commuting coordinate and momentum operators.
Limitable Dynamical Groups in Quantum Mechanics. I. General Theory and a Spinless Model
Authors: Doebner H. D. , Melsheimer O.
Published: February 2004

A pure group-theoretical description of nonrelativistic interacting systems in terms of irreducible representations U(D) of a so-called dynamical group D is investigated. The description is assumed to be complete in the sense that all observable quantities of the system can be calculated from U(D) in the same way as the nonrelativistic free particle can be identified with an irreducible representation U(GE) of the central extension of the inhomogeneous Galilei group GE. D depends on the interaction. It is a noninvariance group and it contains a spectrum-generating algebra. Our problem is to connect a representation of an arbitrary abstract group with a complete description of an interacting system. This needs some physically motivated principles. Some such principles are proposed. We assume that the interaction can be turned off, which implies that U(D) and the physical representation U(GE) of the free-particle group GE can be limited into each other. If this limitation can be formulated without violating super-selection rules, i.e., mass and spin conservation in nonrelativistic systems, the group Dt is called a limitable group. Properties of these groups are derived. An explicit construction of a limitable Dt is given by embedding the free-particle group GE into a larger group. A discussion of all embeddings leads to the special choice Dt≈GE0(N)[multiplication in left half circle]Sp(2N, R). GE0(N) is the central extension of the pure inhomogeneous Galilei group in N dimensions and Sp(2N, R) the noncompact real form of the symplectic group. A representation theory for Dt is established using the technique of Nelson extensions, together with some properties of the universal enveloping algebra of the Lie algebra of GE0(N). Our main success is that Dt is a limitable dynamical group and that the physical system described by Dt and the physical representation can be calculated uniquely from the proposed principles. The group-theoretical description is equivalent to nonrelativistic quantum mechanics for a spinless particle in N dimensions with an arbitrary second-order polynomial in Pi, Qi, i = 1, ⋯, N as Hamiltonian. The possibility of further models is discussed.
Electro-Optical Effects. II
Authors: Carroll M. M. , Rivlin R. S.
Published: February 2004

The constitutive equations governing the propagation of electromagnetic waves of small amplitude in a centro-symmetric isotropic material to which a static electric field is applied involve, in general, six scalar functions of the static field strength and wave frequency. It is shown that if the material is nondissipative, four of these functions are real, while the remaining two are complex conjugates. Conditions are also derived such that the material shall be nonabsorptive with respect to plane-electromagnetic waves and it is seen that a nonabsorptive material is not necessarily nondissipative, but is necessarily stable. It is shown that for a stable, nondissipative material, there are four real velocities corresponding to any direction of propagation. If it is assumed that these are neither zero nor infinite for any direction of propagation, then for each direction of propagation two of these velocities are positive and two are negative.
Generating Functions for the Exact Solution of the Transport Equation. I
Authors: Abu-Shumays I. K. , Bareiss E. H.
Published: February 2004

Generating functions are used as analytic tools for the transformation of the integro-differential transport equations to partial differential equations. The transformations are constructed so that their inverses are known. Therefore, the problem of solving the integro-differential equations is reduced to the more familiar problem of solving partial differential equations. Part I of this series introduces the general method in detail for slab geometry. The general solution is given in analytic form, and the one-to-one correspondence with Case's method of elementary solutions is demonstrated. The results are extended to slab geometry without axial symmetry. Part II extends the method to the general time-dependent, anisotropic case for slab geometry. Parts III and IV treat the stationary and time-dependent problems in one and three space dimensions, introduce in addition the method of characteristics, and include numerical results.
Spinor Structure of Space-Times in General Relativity. I
Authors: Geroch Robert
Published: February 2004

In order to define spinor fields on a space-time M, it is necessary first to endow M with some further structure in addition to its Lorentz metric. This is the spinor structure. The definition and the elementary implications of the existence of a spinor structure are discussed. It is proved that a necessary and sufficient condition for a noncompact space-time M to admit a spinor structure is that M have a global field of orthonormal tetrads.