bluuebunny/crossref_metadata_2025 huggingface dataset:
Perinatal mortality in an English health region: geographical distribution and association with socio‐economic factors
Authors: Martuzzi Marco , Grundy Christopher , Elliott Paul
Published: July 2002

Although the international and regional variability of perinatal mortality rates have been widely studied, less is known about the variability at the small‐area level. The geographical distribution of perinatal mortality in the former North‐West Thames Health Region, England, during 1981–90, and its association with small‐area socio‐economic factors, as measured by the Carstairs index of deprivation, were studied. Recently developed methods of analysis, including use of Bayesian statistics, were applied to obtain descriptive results and maps, and for fitting regression models that allowed for the presence of unmeasured risk factors. Significant heterogeneity (P < 0.001) of perinatal mortality across census wards and districts was found. The 5% of wards with the highest mortality experienced a risk more than 1.7 times that of the 5% with lowest mortality. Significant, positive association between deprivation and perinatal mortality was also found. Assuming causality, social differentials at the small‐area level accounted for between 1.3% and 14.1% of all perinatal deaths, depending on which level of the Carstairs index was selected as reference. Although a proportion of such variability might be explained by social characteristics, a better understanding of the nature of the association is necessary.
Dose‐dependent hyperbaric oxygen stimulation of human fibroblast proliferation
Authors: Hehenberger Karin , Brismar Kerstin , Lind Folke , Kratz Gunnar
Published: July 2002

Diabetic wounds are characterized by a prolonged wound healing process with insufficient formation of granulation tissue. Systemic hyperbaric oxygen therapy has been observed to improve the healing of these wounds. However, the mechanism(s) responsible for these findings are not yet fully elucidated. In the present study we have studied the in vitro effects of hyperbaric oxygen on proliferation of human fibroblasts from normal skin and from chronic foot ulcers in non‐insulin‐dependent diabetics. A 1‐hour exposure to hyperbaric oxygen at oxygen pressures between 106 and 300 kPa (795 to 2250 mm Hg) increased the proliferation in both diabetic and normal fibroblasts. The stimulatory effect was dose‐dependent, with a peak increase in cell proliferation at 250 kPa and 200 kPa for normal and diabetic cells, respectively. The effects were not due to hydrostatic pressure per se. These results suggest that hyperbaric oxygen could stimulate fibroblast activity in the diabetic wound, a finding that could explain the enhanced formation of granulation tissue seen clinically in wounds treated with hyperbaric oxygen. We also speculate that mechanisms other than just increased oxygen availability may be responsible for our findings.
Proteolytic activity in human burn wounds
Authors: Neely Alice N. , Brown Rebeccah L. , Clendening Chris E. , Orloff Mary M. , Gardner Jason , Greenhalgh David G.
Published: July 2002

Wound healing is the result of a dynamic balance between synthetic and degradative processes. After a burn, proteolytic activity increases at the wound site. Excised burn wounds and donor skin were examined from 20 pediatric burn patients, to determine which of two classes of neutral proteinases, serine or metalloproteinases, accounts for the majority of this proteolytic activity in these tissues; to examine messenger RNA expression of three of the principal enzymes and inhibitors of this class; and to measure enzymatic activity of two of these metalloproteinases. The majority of the increased proteolysis was due to metalloproteinases. By polymerase chain reaction assays, messenger RNAs for matrix metalloproteinase‐1, ‐3, and ‐9 were strongly expressed in burn tissue and absent or weakly expressed in unburned skin. Messenger RNA for tissue inhibitor of metalloproteinase‐1 and ‐2 was consistently present in burned and unburned skin. By zymography, there was a significant increase in matrix metalloproteinase‐2 (twofold to threefold) and matrix metalloproteinase‐9 (20‐ to 30‐fold) activity in burned versus unburned skin. We suggest that postburn there is an upregulation of some matrix metalloproteinases that exceeds the level of inhibitors with the net result of an increase in proteolysis in burned tissue. This increased proteolysis may play a role in wound repair and scar formation.
Epidemiological study of chronic dermal ulcers in China
Authors: Fu Xiaobing , Sheng Zhiyong , Cherry George W. , Li Quanyue
Published: July 2002

A total of 30,000 hospitalized surgical patients in 15 hospitals were screened for chronic ulcers. A total of 489 patients with chronic dermal ulcers were found with their major causes of ulceration including traumatic wounds, infections, diabetes mellitus, and venous diseases. Patients with chronic ulcers following trauma and infection comprised 67.48% of the total patient population. The incidence of diabetic ulcers and venous ulcers was 4.91% and 6.54% respectively. Sites of ulceration differed with different etiological factors. The percentage of chronic dermal ulcers in the lower extremities, upper extremities, thorax and abdomen, back, and head was 63.10%, 17.93%, 7.76%, 4.83% and 6.38% respectively. Of the 489 patients with chronic ulcers, 183 were farmers (37.42%), and 131 were workers (26.79%). Chronic dermal ulcers were more common in men than in women, but there was no significant difference in the sex‐related prevalence. According to these data from different hospitals, the incidence of chronic ulcers in patients hospitalized for surgery was 1.5% to 3.0%. These data have primarily shown the prevalence and clinical characteristics of chronic ulcers in hospitalized patients in China. These data may not be consistent with reports from other countries. Significant differences in etiological factors of ulceration, professional distribution of patients with chronic dermal ulcers, and treatment methods were found when compared with reports of studies conducted in developed countries. Our results will benefit not only additional basic research, but these data will also be useful in preventing and managing chronic wounds in developing countries.
Thyroid hormone induces a reprogramming of gene expression in the liver of premetamorphic Rana catesbeiana tadpoles
Authors: Atkinson Burr G. , Warkman Andrew S. , Chen Yuqing
Published: July 2002

During spontaneous or thyroid hormone‐induced metamorphosis of the Rana catesbeiana tadpole, postembryonic changes occur in its liver that are permanent and necessary for the transition of this organism from an aquatic, ammonotelic larva to a semiterrestrial, ureotelic adult. These changes include the coordinated expression of genes encoding the urea cycle enzymes carbamyl phosphate synthetase and ornithine transcarbamylase. Although these changes are dependent on thyroid hormone and occur within the resident hepatocytes, the mechanism(s) by which this hormone reprograms gene expression in these cells and initiates the tissue‐specific expression of these genes is poorly understood. Our contention is that the thyroid hormone—induced expression of these genes is an indirect effect of thyroid hormone and involves an early, thyroid hormone‐induced upregulation of a gene(s) encoding a tissue‐specific transcription factor(s), which in turn, upregulates in a coordinated fashion, the expression of these urea cycle enzyme genes. Herein, we present results that demonstrate a role for a Rana homologue of a mammalian transcription factor, C/EBPα (designated as RcC/EBP‐1), in the thyroid hormone‐induced cascade of gene activity responsible for reprogramming gene expression and initiating the coordinated expression of genes, such as carbamyl phosphate synthetase‐I and ornithine transcarbamylase, which are characteristic of the adult liver phenotype.
Evaluation of linear polyethyleneimine/nitric oxide adduct on wound repair: therapy versus toxicity
Authors: Bauer Joseph A. , Rao Weisun , Smith Daniel J.
Published: July 2002

A full‐thickness wound model was used to evaluate the effects of a topically applied polyethyleneimine‐based nitric oxide donor on wound repair in aged rats. Polymer applications were applied over a 10‐day period on days 0, 2, 4, 6, and 8 comparing treatment (linear polyethyleneimine‐nitric oxide) and control groups (linear polyethyleneimine). Urinary nitrate excretion was quantified as a measure of nitric oxide released. The nitric oxide released from the linear polyethyleneimine‐nitric oxide group was significant compared with controls (p≤0.001), with a maximal nitrate level of 40 µmol on day 1 and an average sustained delivery of 34 µmol/day for the remainder of the study. Wound closure was examined using a computer‐based video‐imaging analysis system. The wounds of both the linear polyethyleneimine‐nitric oxide treatment and linear polyethyleneimine control groups exhibited minimal wound closure; however, the wound closure of the treatment group was significant as compared with the control group (p≤0.05). A phosphate‐buffered saline solution‐wounded control was performed that showed cleaner and faster healing wounds, similar to normal healing, than either of the polymer application groups. The histological data showed very little wound healing, on a cellular level, implicating the linear polyethyleneimine‐nitric oxide as well as the carrier compound as contributing to the adverse tissue reactions that occurred in the wound bed. Thus, we report the toxic effects of a polyethyleneimine‐based compound, as well as the toxic effects of sustained delivery of excess levels of nitric oxide on the wound‐repair process. Our findings suggest that there exists indeterminate parameters between therapy and toxicity of nitric oxide delivery to wounds.
Stabilized viral nucleic acids in plasma as an alternative shipping method for NAT
Authors: Lee Dong‐Hun , Li Liping , Andrus Linda , Prince Alfred M.
Published: July 2002

BACKGROUND: Preservation of the integrity of viral nucleic acids in blood specimens during shipping and handling is crucial for NAT and viral load monitoring. An economical and convenient method is described for nucleic acid stabilization by using an RNA stabilizing solution (RNAlater, Ambion) in plasma that is designed for the shipment of samples to tropical countries.

STUDY DESIGN AND METHODS: HCV, HIV, and HBV FFP were compared with RNAlater‐treated plasma and dried plasma spots (DPSs) after incubation at 37°C, which was chosen as an upper limit of ambient shipping temperature, for up to 28 days. HCV‐infected chimpanzee plasma was shipped at either room temperature after RNAlater treatment or as frozen plasma in liquid nitrogen from Liberia to New York City. They were then compared for HCV RNA levels. The nucleic acid stabilities were determined by quantitative PCR by using a molecular beacon assay on a sequence detection system (ABI 7700, PE‐Biosystems) and by visualizing the PCR components on an acrylamide gel.

RESULTS: Quantitative PCR data showed that a 60:40 or greater ratio of RNAlater:plasma volume successfully stabilized HCV RNA and HIV RNA in plasma for up to 28 days at 37°C. HBV DNA in plasma was stable for up to 14 days at 37°C without any stabilizing solution. DPSs on filter paper stabilized viral nucleic acids, but the recoveries were 3 to 10 times less than those with frozen plasma. The integrity of the 5′ UTR region of HCV RNA in RNA later‐treated chimpanzee plasma was intact when its PCR component was viewed on an acrylamide gel.

CONCLUSION: The DPS method stabilized nucleic acids, at least with the extraction method used, was less sensitive than use of RNAlater, and required tedious manual handling. RNAlater provides a convenient way of stabilizing viral nucleic acid in plasma at ambient temperature during sample transportation.
Lack of SCN1A Mutations in Familial Febrile Seizures
Authors: Malacarne Michela , Madia Francesca , Gennaro Elena , Vacca Daniela , Güney A. Ilter , Buono Salvatore , Bernardina Bernardo Dalla , Gaggero Roberto , Gobbi Giuseppe , Lispi Maria Luisa , Malamaci Daniela , Melideo Giustino , Roccella Maurizio , Sferro Caterina , Tiberti Alessandra , Vanadia Francesca , Vigevano Federico , Viri Franco , Vitali Maria Rosa , Bricarelli Franca Dagna , Bianchi Amedeo , Zara Federico
Published: July 2002

Summary:  Purpose: Mutations in the voltage‐gated sodium channel subunit gene SCN1A have been associated with febrile seizures (FSs) in autosomal dominant generalized epilepsy with febrile seizures plus (GEFS+) families and severe myoclonic epilepsy of infancy. The present study assessed the role of SCN1A in familial typical FSs.

Methods: FS families were selected throughout a collaborative study of the Italian League Against Epilepsy. For each index case, the entire coding region of SCN1A was screened by denaturant high‐performance liquid chromatography. DNA fragments showing variant chromatograms were subsequently sequenced.

Results: Thirty‐two FS families accounting for 91 affected individuals were ascertained. Mutational analysis detected a single coding variant (A3169G) on exon 16. The extended analysis of all family members and 78 normal controls demonstrated that A3169G did not contribute to the FS phenotype.

Conclusions: Our study demonstrated that SCN1A is not frequently involved in common FSs and suggested the involvement of specific FS genes.
Serum Insulin and Leptin Levels in Valproate‐associated Obesity
Authors: Pylvänen Virpi , Knip Mikael , Pakarinen Arto , Kotila Mervi , Turkka Jukka , Isojärvi Jouko I. T.
Published: July 2002

Summary:  Purpose: Weight gain is an important adverse effect of valproate (VPA) therapy, and it is associated with hyperinsulinemia and hyperandrogenism in women with epilepsy. Leptin is considered a signaling factor regulating body weight and energy metabolism. In human subjects, obesity is in general associated with elevated serum leptin levels, suggesting decreased sensitivity to leptin. The present study aimed at evaluating the role of insulin and leptin in VPA‐related obesity.

Methods: Body mass index (BMI) was calculated, and serum insulin and leptin levels were measured in 81 patients with epilepsy taking VPA and in 51 healthy control subjects.

Results: Forty (49%) of the patients taking VPA and 25 (49%) of the control subjects were obese. The mean insulin levels were higher in VPA‐treated patients than in the control subjects despite similar BMI values, when all subjects were included in the comparison. Both obese male and female patients taking VPA had higher serum insulin levels than the respective control subjects with similar BMI values. Serum insulin levels also were higher in lean male and lean female patients compared with the lean control subjects of same sex. Serum leptin levels did not differ between the VPA‐treated patients and the control subjects.

Conclusions: Both obese and lean patients taking VPA for epilepsy have hyperinsulinemia, suggesting development of insulin resistance. This may be one of the factors leading to weight gain during VPA treatment. However, the results of the present study do not suggest an independent role for leptin in the pathogenesis of VPA‐related obesity.
Seizure Reduction and Quality of Life Improvements in People with Epilepsy
Authors: Birbeck Gretchen L. , Hays Ron D. , Cui Xinping , Vickrey Barbara G.
Published: July 2002

Summary:  Purpose: Previous research suggests that seizure freedom may be necessary to improve health‐related quality of life (HRQOL) for epilepsy surgery patients, but little is known regarding the seizure‐frequency reduction needed to improve HRQOL among medically treated individuals.

Methods: With data from 134 adults with refractory complex partial seizures participating in a randomized controlled antiepileptic drug (AED) trial, we compared the change in HRQOL across groups having different levels of change in seizure frequency: 100%, 75–99%, 50–74% reduction, and 0–50% increase or decrease. Changes over time within each seizure‐reduction group also were assessed. HRQOL was measured by the QOLIE‐31, QOLIE‐89, and SF‐36.

Results: Subjects who became seizure free reported significantly more positive change than those who did not on the QOLIE‐31 and QOLIE‐89 overall scores, the QOLIE‐89 mental health, physical health, and epilepsy‐targeted composites, as well as the SF‐36 mental health summary score. Changes over time in overall QOLIE‐31 and QOLIE‐89 scores were significantly more positive for subjects who achieved seizure freedom (i.e., 100% reduction in seizure frequency) than for those who did not. No significant change in QOLIE‐31 and QOLIE‐89 overall scores was observed for subjects who did not achieve seizure freedom.

Conclusions: In this study, HRQOL improvement occurred primarily among patients who achieved complete seizure freedom. Many AED trials use a 50% seizure‐frequency reduction criterion as a trial end point, but measurable impacts of this degree of reduction in seizure frequency on HRQOL in this sample were not observed. These results further support striving for seizure freedom as an epilepsy care goal.
Do Structural Properties Explain the Anticonvulsant Activity of Valproate Metabolites? A QSAR Analysis
Authors: Bello‐Ramírez Angélica M. , Carreón‐Garabito Blanca Y. , Nava‐Ocampo Alejandro A.
Published: July 2002

Summary:  Purpose: Differences in potency among valproate (VPA) metabolites could be explained by structural properties. Therefore, a quantitative structure–activity relation (QSAR) analysis was performed to study the relation between structural parameters and the effect of the following VPA metabolites: 4‐en‐VPA, 2‐en‐VPA, 3‐en‐VPA, 2,4'‐dien‐VPA, 4,4'‐dien‐VPA, 4‐hydroxy‐VPA, 3‐ceto‐VPA, 3‐hydroxy‐VPA, 5‐hydroxy‐VPA, and propylglutaric acid.

Methods: By using the CAChe program package for biomolecules (Oxford Molecular, Ltd), we performed molecular modeling. The anticonvulsant activity determined on the threshold for maximal electroconvulsions in mice was obtained from a study of Löscher and Nau. Structural parameters were compared between metabolites with a double bond and metabolites with oxygen at either side chain (unpaired Student's t test). A single linear regression analysis between each structural parameter and the relative anticonvulsant potency was also performed.

Results: Similar parameters were found between the cis and trans and R and S isomers. Biologic activity and most of the structural parameters were significantly different between metabolites with a double bond and metabolites with oxygen at either side chain. Activity was directly related to log Poct (r2 = 0.77) and to reactivity parameters and was inversely related to stability parameters and to molecular weight and surface. The most potent metabolites had a log Poct value of higher than 2 units.

Conclusions: Similar data were identified between cis and trans, and R and S isomers of VPA metabolites. Anticonvulsant activity was mainly related to log Poct, probably reflecting the ability of VPA metabolites to cross the blood–brain barrier.
Effects of Drought on the Competitive Interference of an Early Successional Species (Rubus fruticosus) on Fagus sylvatica L. Seedlings: 15N Uptake and Partitioning, Responses of Amino Acids and other N Compounds
Authors: Fotelli M. N. , Rennenberg H. , Geβler A.
Published: July 2002

Abstract: We assessed the role of water availability as a factor regulating the ability of beech seedlings to cope with competitive interference for nitrogen resources by an early successional species (Rubus fruticosus). A glasshouse experiment was performed with two levels of interference (beech with and without R. fruticosus) and three levels of irrigation (high, intermediate, none). 15N uptake and partitioning of both species, and composition of N pools in leaves, roots and phloem of beech, were determined. Under all irrigation regimes, 15N uptake by beech seedlings decreased when grown together with R. fruticosus. R. fruticosus had higher 15N uptake rates than beech, under all water supply levels. When irrigation was reduced, a substantial decrease in 15N uptake of beech seedlings and a concurrent increase in 15N uptake by R. fruticosus were observed. Interference by R. fruticosus and low irrigation also affected the 15N partitioning in beech seedlings and resulted in reduced allocation of 15N to the roots. The combination of competitive interference and lack of irrigation led to an increase in soluble non‐protein N in roots and leaves of beech, due to protein degradation. This response was attributed to an increase in levels of amino acids serving as osmoprotectants under these conditions. The concentration of proline in leaves of beech was negatively correlated to shoot water potential. A competition‐induced reduction of total N in leaves of beech under high and intermediate irrigation was found. These results illustrate (1) the advantage of R. fruticosus in terms of N uptake when compared to young beech, particularly under inadequate water supply, and (2) the changes in N composition of beech seedlings in order to cope with reduced soil water and interference by R. fruticosus.
On the multiple time scales in solvation dynamics: A mode-coupling theory approach
Authors: Egorov S. A. , Denny R. Aldrin , Reichman David R.
Published: July 2002

A microscopic statistical mechanical theory of solvation dynamics is presented. The theory is capable of reproducing the characteristic multiphasic behavior of the solvation correlation function typically observed in the time-resolved spectroscopic studies. The fast initial decay of the solvation correlation function is modeled on the basis of a short-time expansion, while the slowly varying long-time tail is computed within the mode-coupling theory formalism. Comparison with simulation for nonpolar solvation shows that the present theory provides a very substantial improvement over the commonly used time-dependent density functional and surrogate Hamiltonian treatments of the slow component of solvation dynamics. In addition, the range of applicability of the results obtained in this study is much wider compared to the other theories. The mode-coupling theory of solvation is tested for model nonpolar systems consisting of both a neat fluid and a system, where the chromophore size is significantly different from that of the solvent particles. A systematic study of the dependence of the solvation time scales on the size of the chromophore is carried out.
Application of a “slice” proper orthogonal decomposition to the far field of an axisymmetric turbulent jet
Authors: Gamard Stephan , George William K. , Jung Daehan , Woodward Scott
Published: July 2002

Instantaneous measurements of the streamwise velocity component were obtained in the far field region of an axisymmetric turbulent jet at exit Reynolds numbers ranging from 40 000 to 84 700. The data were taken from 20 to 69 diameters downstream of the jet exit using 138 hot-wires. The proper orthogonal decomposition was applied to a double Fourier transform in time and azimuthal direction of the two-point velocity correlation tensor. The first eigenspectrum, which contains more than 60% of the kinetic energy, has two peaks: A dominant peak at azimuthal mode-2 at near zero frequency, and a secondary peak at mode-1 at a local Strouhal number (fx/Uc) of approximately 1. The most striking feature was the general behavior of the eigenspectra: when normalized to reflect the energy repartition per mode number only, they peaked at mode-2, and were independent of downstream position in the experiment considered. They were also similar in nature to those obtained in earlier experiments at x/D=6, just past the end of the potential core, but distinctly different from those closer to the jet exit where mode-0 and higher modes dominated.
Structure and scales in turbulence modeling
Authors: Reynolds W. C. , Langer C. A. , Kassinos S. C.
Published: July 2002

The enstrophy of the large-scale energy-containing turbulence is proposed as the second turbulence scale for use, in conjunction with the turbulence energy, in two-scale one-point engineering turbulence models. Its transport equation is developed in general and modeled for homogeneous turbulence in terms of the two scales and our new one-point structure tensors. The model produces the correct behavior of the scales for both two- and three-dimensional turbulence. Constants in the high Reynolds number model are evaluated only by reference to asymptotic analysis for decaying turbulence in stationary and rotating frames, and this model is then shown to provide an excellent prediction of homogeneous turbulent shear flow when used with the structure tensors for that flow. The low Reynolds number constant in the model is evaluated using the asymptotic decay rate for isotropic turbulence at zero Reynolds number, and numerical simulations of decay for intermediate Reynolds numbers are used to establish one remaining constant, the value of which does not affect high Reynolds number predictions.
Optimal rotary control of the cylinder wake in the laminar regime
Authors: Protas B. , Styczek A.
Published: July 2002

In this paper we develop the Optimal Control Approach to the rotary control of the cylinder wake. We minimize the functional which represents the sum of the work needed to resist the drag force and the work needed to control the flow, where the rotation rate φ̇(t) is the control variable. Sensitivity of the functional to control is determined using the adjoint equations. We solve them in the “vorticity” form, which is a novel approach and leads to computational advantages. Simulations performed at Re=75 and Re=150 reveal systematic decrease of the total power and drag achieved using a very small amount of control effort. We investigate the effect of the optimization horizon on the performance of the algorithm and the correlation of the optimal controls with the changes of the flow pattern. The algorithm was also applied to the control of the subcritical flow at Re=40, however, no drag reduction was achieved in this case. Based on this, limits of the performance of the algorithm are discussed.
Time-energy coherent states and adiabatic scattering
Authors: Avron J. E. , Elgart A. , Graf G. M. , Sadun L.
Published: July 2002

Coherent states in the time-energy plane provide a natural basis to study adiabatic scattering. We relate the (diagonal) matrix elements of the scattering matrix in this basis with the frozen on-shell scattering data. We describe an exactly solvable model, and show that the error in the frozen data cannot be estimated by the Wigner time delay alone. We introduce the notion of energy shift, a conjugate of Wigner time delay, and show that for incoming state ρ(H0) the energy shift determines the outgoing state.
Quantum models related to fouled Hamiltonians of the harmonic oscillator
Authors: Tempesta P. , Alfinito E. , Leo R. A. , Soliani G.
Published: July 2002

We study a pair of canonoid (fouled) Hamiltonians of the harmonic oscillator which provide, at the classical level, the same equation of motion as the conventional Hamiltonian. These Hamiltonians, say K1 and K2, result to be explicitly time dependent and can be expressed as a formal rotation of two cubic polynomial functions, H1 and H2, of the canonical variables (q,p). We investigate the role of these fouled Hamiltonians at the quantum level. Adopting a canonical quantization procedure, we construct some quantum models and analyze the related eigenvalue equations. One of these models is described by a Hamiltonian admitting infinite self-adjoint extensions, each of them has a discrete spectrum on the real line. A self-adjoint extension is fixed by choosing the spectral parameter ε of the associated eigenvalue equation equal to zero. The spectral problem is discussed in the context of three different representations. For ε=0, the eigenvalue equation is exactly solved in all these representations, in which square-integrable solutions are explicitly found. A set of constants of motion corresponding to these quantum models is also obtained. Furthermore, the algebraic structure underlying the quantum models is explored. This turns out to be a nonlinear (quadratic) algebra, which could be applied for the determination of approximate solutions to the eigenvalue equations.
Coherent state realizations of su(n+1) on the n-torus
Authors: de Guise Hubert , Bertola Marco
Published: July 2002

We obtain a new family of coherent state representations of SU(n+1), in which the coherent states are Wigner functions over a subgroup of SU(n+1). For representations of SU(n+1) of the type (λ, 0, 0,…), the basis functions are simple products of n exponential. The corresponding coherent state representations of the algebra su(n+1) are also obtained, and provide a polar decomposition of su(n+1) for any n+1. The su(n+1) modules thus obtained are useful in understanding contractions of su(n+1) and su(n+1)-phase states of quantum optics.
Superconductor strip near a magnetic wall of finite thickness
Authors: Genenko Yu. A. , Snezhko A. V.
Published: July 2002

Transport current distributions in a flux-free superconductor strip located near a soft magnet wall of arbitrary thickness were studied numerically for different magnetic permeabilities using the method of surface magnetic charge. It was established that the reduction of the edge current peaks caused by magnetic shielding saturates rapidly with increasing thickness of the magnet. This makes possible the use of thin magnetic films for shielding of superconductor strips with the aim of improving their current-carrying capability so that a small thickness of shields may be compensated by a large magnetic permeability.
In situ structural properties of N2-, O2-, and air-clathrates by neutron diffraction
Authors: Chazallon Bertrand , Kuhs Werner F.
Published: July 2002

The crystal structures of type II N2-,O2-, and air-clathrate hydrates have been studied under their thermodynamic conditions of stability by neutron powder diffraction. The isothermal compressibilities were deduced from the refined lattice constants and found to be significantly different for N2 and O2 clathrate hydrates. The water host lattice structure rearranges as a function of pressure with a resulting change of the volume ratio of small and large cages. The cage fillings were established on an absolute scale for the first time. The large cages were found to be partly occupied by two molecules. The results are compared with predictions based on the statistical thermodynamic theory of van der Waals and Platteeuw. While the filling follows the predicted trend significant differences exist in detail.
Electronic structure and bonding in metal porphyrins, metal=Fe, Co, Ni, Cu, Zn
Authors: Liao Meng-Sheng , Scheiner Steve
Published: July 2002

A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of [MTPP]x ions (x=2+, 1+, 1−, 2−, 3−, 4−), which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as A2g3, which arises from the configuration (dxy)2(dz2)2(dxz)1(dyz)1. The calculated M–TPP binding energies, ionization potentials, and electron affinities are in good agreement with available experimental data. The influence of axial ligands and peripheral substitution by fluorine are in accord with the experimental observation that not only half-wave potentials (E1/2) of electrode reactions, but also the site of oxidation/reduction, may be dependent on the porphyrin basicity and the type of axial ligand coordination.
The hydration structure of the lithium ion
Authors: Loeffler Hannes H. , Rode Bernd M.
Published: July 2002

The hydration structure of Li+ has been studied by means of hybrid quantum-mechanical molecular mechanical molecular dynamics simulations at Hartree–Fock and density-functional level of theory. The size of the quantum-mechanical region and the form of the potential function are shown to be of crucial importance for reliable results. Radial distribution functions, coordination number distributions, and various angular distributions have been used to discuss details of the hydration structure, together with bond lengths and bond angles of the water molecules in the first hydration shell. The lithium ion is found to be mainly fourfold coordinated with some smaller amounts of fivefold coordination. The lithium–water cluster exhibits a nearly perfect tetrahedral but still very flexible structure, in which coordinated water molecules are considerably tilted away from planarity. Water molecules in the first hydration shell are shown to be considerably polarized compared to gas-phase structures.
Small gold clusters on stoichiometric and defected TiO2 anatase (101) and their interaction with CO: A density functional study
Authors: Vittadini Andrea , Selloni Annabella
Published: July 2002

We have studied the interaction of small Aun (n=1–3) particles with the defect-free (stoichiometric) and defected (partially reduced) TiO2 anatase (101) surface using density functional calculations within a slab geometry. On the stoichiometric surface, gold particles prefer anion sites and “standing” geometries, in agreement with simple MO theory arguments. On the defected surface, Au strongly binds to the two cations close to the bridging oxygen vacancy. For both Au2 and Au3, “lying” adsorption geometries are now more likely, and starting from n=3 there is a tendency towards mixed binding, where cation and anion sites are simultaneously involved. Clustering of Au atoms is favored on both the stoichiometric and the reduced surfaces. CO strongly interacts with gold particles adsorbed on the stoichiometric surface. As found in previous gas-phase investigations, the CO-cluster bond is stronger when the cluster carries a positive charge. Accordingly, a weak interaction is computed for a gold atom supported on the reduced surface.
Interparticle correlations due to electrostatic interactions: A small angle x-ray and dynamic light scattering study. I. Apoferritin
Authors: Häußler W. , Wilk A. , Gapinski J. , Patkowski A.
Published: July 2002

The structure and dynamics of the spherical protein Apoferritin in aqueous solution are studied over a wide range of protein concentrations and ionic strengths. At high ionic strength and low protein concentration, the intermolecular forces are screened and, therefore, the proteins behave like uncharged molecules. Under these conditions, the form factor of Apoferritin was measured by means of small angle x-ray scattering (SAXS) and the hydrodynamic radius was determined by means of dynamic light scattering (DLS). The sample was found to be highly monodisperse. By decreasing the content of salt added, interactions between the Apoferritin particles were initiated. These intermolecular forces lead to a pronounced maximum in the SAXS intensity. At the same time, a slow mode appears in the relaxation time distribution, additionally to the diffusive mode. The relative amplitudes and correlation times of the diffusive and the slow mode were investigated and compared with predictions of the coupled mode theory. By assuming the slow mode to be related to the correlated motion of ordered domains, the size of these domains was derived from the slow relaxation time. From the x-ray data and the Apoferritin form factor, structure factors of ordered solutions were calculated. The shape of the structure factor peaks was studied as a function of Apoferritin and salt concentration. Finally, by using the DLS information regarding the size of correlated domains, we analyzed the degree of polyelectrolyte ordering within the paracrystalline domains in Apoferritin solutions.
Tearing mode stability studies near ideal stability boundaries in DIII-D
Authors: Brennan D. P. , Strait E. J. , Turnbull A. D. , Chu M. S. , La Haye R. J. , Luce T. C. , Taylor T. S. , Kruger S. , Pletzer A.
Published: July 2002

For high β, highly shaped plasmas in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], the value of the tearing stability index Δ′ calculated at a rational surface can be especially sensitive to the pressure and current profiles. Near marginal stability for a global ideal mode, a pole in Δ′ exists in equilibrium parameter space, as predicted by analytic theory. The proximity of an equilibrium reconstruction to this pole in parameter space strongly decreases the accuracy of the Δ′ calculations. Tearing stability calculations on kinetic equilibrium reconstructions of a series of times in three DIII-D discharges are presented, which indicate that the tearing modes in these discharges are classically unstable at the time of onset. The onset mechanism of two of these discharges (which are in H-mode) is related to the approach of ideal stability boundaries and the occurrence of poles in Δ′. Several ideal modes (sawteeth, edge localized modes, and resistive wall modes) are thought to seed neoclassical tearing modes (NTMs) through forced reconnection, after the ideal mode is unstable. However, tearing modes often appear suddenly and grow quickly without an obvious ideal mode causing a seed island through forced reconnection, which could be explained by this mechanism. This is proposed as an alternative mechanism for the onset of NTMs in tokamaks, which is not incompatible with forced reconnection.
Screening in anisotropic plasmas
Authors: Shokri B.
Published: July 2002

The connection between electrostatics and magnetostatics is investigated in both anisotropic classical and isotropic quantum systems and it is shown that in such media, static exponential screening is changed. Moreover, it is shown that, under special circumstances, two electrons in such media may attract each other.
Modifying fractal basin boundaries by reshaping periodic terms
Authors: Chacón R. , Garcı́a-Hoz A. Martı́nez
Published: July 2002

A generic route is described for the modification of fractal basin boundaries in nonlinear systems by changing only the shape of a periodic (autonomous or non-autonomous) term in the dynamics equations. Two examples are used to illustrate the route: a non-invertible two-dimensional map, and a driven dissipative oscillator with a cubic potential that typically models a metastable system close to a fold.
Resonant and Kelvin–Helmholtz instabilities on the magnetopause
Authors: Taroyan Y. , Erdélyi R.
Published: July 2002

The Kelvin–Helmholtz instability (KHI) of magnetohydrodynamic surface waves on the magnetopause is examined and the resonant flow instability (RFI) of these waves is studied under the assumption that the plasma density decreases in the direction from the magnetosheath towards the magnetosphere. It is found that when a finite plasma temperature is taken into account, three different kinds of surface modes (labeled as “primary” modes and “β” modes on sides 1 and 2) may exist. The β modes remain almost unaffected by the flow in the corresponding rest frames and can be excited in certain velocity intervals which are determined. These modes do not interact with each other, but their interaction with primary modes leads to KHIs confined to narrow velocity intervals when the mode energies are of opposite signs. Only primary mode can be resonantly unstable with growth rates smaller than those typical for KHIs. Starting with the slow resonant instability the negative energy primary and β modes are subject to several RF and KH instabilities which are separated from each other by narrow velocity intervals of stability. The growth rates of these instabilities tend to increase with increasing velocity shear. Possible applications to, e.g., observations in the terrestrial magnetosphere, are discussed.
Field emission from open ended aluminum nitride nanotubes
Authors: Tondare V. N. , Balasubramanian C. , Shende S. V. , Joag D. S. , Godbole V. P. , Bhoraskar S. V. , Bhadbhade M.
Published: July 2002

This letter reports the field emission measurements from the nanotubes of aluminum nitride which were synthesized by gas phase condensation using the solid-vapor equilibria. A dc arc plasma reactor was used for producing the vapors of aluminum in a reactive nitrogen atmosphere. Nanoparticles and nanotubes of aluminum nitride were first characterized by transmission electron microscope and tube dimensions were found to be varying from 30 to 200 nm in diameter and 500 to 700 nm in length. These tubes were mixed with nanoparticles of size range between 5 and 200 nm in diameter. Tungsten tips coated with these nanoparticles and tubes were used as a field emitter. The field emission patterns display very interesting features consisting of sharp rings which were often found to change their shapes. The patterns are attributed to the open ended nanotubes of aluminum nitride. A few dot patterns corresponding to the nanoparticles were also seen to occur. The Fowler–Nordheim plots were seen to be nonlinear in nature, which reflects the semi-insulating behavior of the emitter. The field enhancement factor is estimated to be 34 500 indicating that the field enhancement due to the nanometric size of the emitter is an important cause for the observed emission.
A moving-mirror frequency modulator for cold atom spectroscopy
Authors: Jones P. H. , Saunders-Singer H. , Bergamini S. , Meacher D. R.
Published: July 2002

We have investigated the use of a moving or “Doppler” mirror to probe laser cooled atoms. The device uses the Doppler shift induced on reflection at a moving surface to modulate the frequency of a probing laser beam, with a modulation bandwidth and frequency resolution sufficient for the narrow spectral features typically encountered. We anticipate that the device could be a simple and cost-effective alternative to acousto-optic modulators for cold atom spectroscopy, and demonstrate its usefulness by performing stimulated optical Compton scattering on an optical molasses.
Velocity map imaging of ion-molecule reaction products: Co+(3F4)+isobutane
Authors: Reichert Emily L. , Thurau Gert , Weisshaar James C.
Published: July 2002

The velocity map imaging technique is applied to mass-selected CoC3H6++CH4 and CoC4H8++H2 elimination products from the Co+(3F4)+isobutane reaction studied under crossed-beam conditions at 0.21 eV collision energy. For both reactions we obtain the joint scattering probability distribution P(E,Θ), where E and Θ are the product translational energy and scattering angle. The fraction of available energy deposited into product translation is 0.4 for H2, compared with 0.1 for CH4. For the CH4 product, the angular distribution is forward-backwards symmetric and sharply peaked at Θ=0 and 180°. P(E,Θ) is not separable into the product of an energy and an angular function; rather, the angular distribution peaks more sharply at higher translational energy. Evidently, incipient CoC3H6++CH4 products equilibrate in the Co+(C3H6)(CH4) exit-channel well, from which they decay statistically. The product translational energy distribution P(E) is consistent with orbiting-transition state phase-space theory with no exit-channel barrier. In addition, the energy-integrated angular distribution T(Θ) is consistent with the predictions of the early statistical complex decay model of Miller and Herschbach for fragmentation from a transition state that is a prolate top. In sharp contrast, P(E) for the CoC4H8++H2 products exhibits a substantial hot, nonstatistical tail towards high energy. Perhaps the H2 channel has a late potential energy barrier some 0.5 eV above products, but we view this explanation as highly unlikely. Instead, we suggest that the potential energy from an earlier multicenter transition state is funneled efficiently, and highly nonstatistically, into product translation. This surprising conclusion may apply to H2 products for the entire family of reactions of the late-3D series transition metal cations Fe+, Co+, and Ni+ with alkanes.
The lowest 1(3PJ) and 2(3P2) ion-pair states of ClF: Nonadiabatic effects and emission spectra
Authors: Kokh Daria B. , Alekseyev Aleksey B. , Li Yan , Buenker Robert J.
Published: July 2002

The structure of the Ω=1,2 states correlating with the F−(1S0)+Cl+(3PJ) ionic products and their emission are studied. Ab initio potential energy curves of ClF published recently and computed electronic dipole moments for parallel transitions between the Ω=1,2 ion pair and valence states, as reported in the present work, are used to calculate vibrational energies and emission spectra in the adiabatic and nonadiabatic approximations. It is shown that spectroscopic and emission properties of the D′2(3P2) state can be quite accurately described in the adiabatic approximation. On the contrary, the G1(3P1) and β1(3P2) states are nonadiabatically mixed due to the strong radial coupling caused by significant variation of the Σ−3 and Π3 Λ–S contributions, similar to that observed for the E0+(3P2) and f0+(3P0) states. Nonadiabatic calculations carried out for the G1(3P1) and β1(3P2) ion-pair states clearly demonstrate the influence of the radial coupling on the emission spectra, although do not reproduce quantitatively the entire range of experimental vibrational energies.
Rayleigh–Taylor instability in plasmas with shear flow
Authors: Mikhailenko Vladimir S. , Mikhailenko Vladimir V. , Weiland Jan
Published: July 2002

The temporal evolution of the Rayleigh–Taylor instability in plasma with homogeneous shear flow is studied. It is found that shear flow leads to the suppression of nonlinearly excited perturbations of the electrostatic potential for a value of the velocity shear parameter, which is larger than the ones obtained earlier for the stabilization of the linearly unstable solution. However, even in this case the stabilization of the electrostatic potential is a real physical process, not a mathematical artifact. At the same time, the perturbation of the electron density is not suppressed by flow shear. After the stage of the temporal algebraic growth, oscillations of the electron density perturbations with permanent amplitudes are settled.
Squeezed superbananas and improved superbanana transport in stellarators
Authors: Shaing K. C.
Published: July 2002

It is well known that the size of the superbananas in stellarators scales with the minor radius. Thus, in some stellarator configurations superbananas may not be confined. To improve stellarator confinement, a theory is developed to include the effects of the magnetic well and the radial gradient of the radial electric field to squeeze superbananas. It is found that the size of the superbananas is reduced by a factor of S1/2, where S is the superbanana squeezing factor that depends on the magnetic well depth and the radial gradient of the radial electric field. The corresponding fraction of the superbanana is increased by a factor of S1/2. The diffusive loss is thus reduced by a factor of S−3/2.
Normal-incidence intersubband absorption in AlGaSb quantum wells
Authors: Jancu Jean-Marc , Bassani Franco , Voisin Paul
Published: July 2002

Intersubband optical properties of AlGaSb multiple-valley quantum-well (QW) heterostructures are analyzed. Our calculations are based on an improved tight-binding model to consider contributions from different points of the QW Brillouin zone. We show that strong normal-incidence electron absorption is achieved within asymmetrically stepped QWs in contrast to rectangular wells. Structures suited to infrared detection in the 10 μm spectral range are discussed.