bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of transforming growth factor‐β1 on extracellular matrix gene expression by human fibroblasts from a laryngeal stenotic lesion
Authors: Macauley Shawn P. , Schultz Gregory S. , Bruckner Brian A. , Krawetz Stephen A. , Yang Thomas P.
Published: September 2002

Transforming growth factor‐β1 appears to play important roles in normal wound healing by increasing synthesis of extracellular matrix components. However, the role of transforming growth factor‐β1 in the production of excessive scar tissue by fibroblasts from stenotic lesions of the larynx has not been evaluated. We examined the effect of transforming growth factor‐β1 on the steady‐state messenger RNA levels of elastin, α2(l) procollagen, and lysyl oxidase (the enzyme that cross‐links both of these structural proteins) in cell cultures of diploid human fibroblasts established from fetal skin, newborn foreskin, and an adult laryngeal stenotic lesion. Time‐course and dose‐response experiments demonstrated that treatment with 500 pmol/L transforming growth factor‐β1 for 20 hours induced maximal levels of mRNA for elastin (7‐ to 59‐fold) and α2(l) procollagen (1.7‐ to 2.4‐fold) in all three cultures of fibroblasts. Transforming growth factor‐β1 also increased levels of lysyl oxidase mRNA in fibroblasts cultured from newborn foreskin (2.4‐fold) and a stenotic lesion (10‐fold) but had minimal effects on the fibroblasts cultured from fetal skin (1.1‐fold), which constitutively expressed high levels of lysyl oxidase mRNA. Furthermore, the fibroblast culture established from a laryngeal stenotic lesion responded with the highest fold‐induction for all three mRNAs. Inhibition of mRNA synthesis by acti‐nomycin D showed that transcription was required for transforming growth factor‐β1 induction of elastin, α2(l) procollagen, and lysyl oxidase mRNA in all three cultures of fibroblasts. Inhibition of protein synthesis by cycloheximide showed that translation was required for maximal induction by transforming growth factor‐β1 of elastin mRNA but had no observable effect on α2(l) procollagen mRNA in all three cultures of fibroblasts. In addition, translation was required for maximal induction of the lysyl oxidase mRNA by transforming growth factor‐β1 in the fibroblasts cultured from a stenotic lesion but not for fibroblast cultures established from fetal and adult skin. These results show that transforming growth factor‐β1 coordinately increases mRNA levels for the structural extracellular matrix proteins collagen and elastin, as well as for the cross‐linking enzyme, lysyl oxidase. These data also support the hypothesis that transforming growth factor‐β1 may contribute to the formation of laryngeal stenotic lesions.
Hyaluronic acid‐dependent pericellular matrices in fetal fibroblasts: implication for scar‐free wound repair
Authors: Moriarty Kevin P. , Crombleholme Timothy M. , Kerry Gallivan E. , O'Donnell Cathleen
Published: September 2002

Fetal fibroblasts are intrinsically different from postnatal fibroblasts. We studied the differences in expression, size, and assembly of pericellular matrices in human fetal and postnatal fibroblasts, as well as the effect of fetal fibroblast‐conditioned media as a source of migration stimulating factor on pericellular matrix formation. Fibroblasts in their fifth to fifteenth passages were cultured for 24 hours before analysis. Streptomyces hyaluronidase (0.1 U/ml), monoclonal mouse anti‐human CD‐44std, or anti‐human CD‐4 antibodies were added and incubated for 1 hour (at 4° and 37° C) before analysis of the pericellular matrices with the use of a particle exclusion technique. The pericellular matrix/cell body ratio of fetal fibroblasts was significantly larger than that of newborn (p < 0.002) and adult (p < 0.001) fibroblasts. Hyaluronidase disrupted the pericellular matrices in all three cell lines. Assembly of the pericellular matrices was blocked by anti‐human CD‐44std antibody but not by anti‐human CD‐4 antibody at both 4° and 37° C. Incubation of fibroblast cell lines in fetal fibroblast‐conditioned media did not increase pericellular matrix/cell body ratio but did increase the percentage of fibroblasts expressing a detectable pericellular matrix in adult (p < 0.01), newborn (p < 0.001), and fetal (p < 0.005) fibroblasts. We conclude that fibroblasts produce hyaluronic acid‐dependent pericellular matrices which require interaction with a hyaluronic acid‐binding protein for assembly. Large pericellular matrices are one intrinsic factor characterizing a unique fetal fibroblast phenotype.
Recombinant human bone morphogenetic proteins‐2 and ‐4 induce several mesenchymal phenotypes in culture
Authors: Dixon Karen P. , Murphy Rick W. , Southerland Sheila S. , Young Henry E. , Lucas Paul A.
Published: September 2002

Bone morphogenetic protein has previously been shown to induce the formation of cartilage and bone in vivo. We have isolated a population of mesenchymal stem cells from rat skeletal muscle capable of forming multiple mesodermal morphologies in vitro. These cells were treated with recombinant human bone morphogenetic proteins‐2 and ‐4 to determine the differentiation‐inducing activities of bone morphogenetic protein on these cells. The mesenchymal stem cells were cultured in medium with 10% preselected horse serum containing 0 to 100 ng/ml recombinant human bone morphogenetic proteins‐2 or ‐4 for a maximum of 4 weeks. Control cultures maintained the stellate morphology of mesenchymal stem cells. Cultures treated with recombinant human bone morphogenetic protein‐2 exhibited discrete cartilage nodules and mineralized bone nodules. The first increase in chondrogenesis was seen at 0.5 ng/ml. Cultures treated with recombinant human bone morphogenetic protein‐4 also exhibited an increase in chondrogenesis at the higher concentration of 2 ng/ml. Skeletal myotubes and adipocytes also appeared in cultures treated with either bone morphogenetic protein. Mesenchymal stem cells do respond to inductive factors, but bone morphogenetic proteins‐2 and ‐4 were not specific for the induction of cartilage and bone.
Low‐frequency ultrasound treatment of chronic venous ulcers
Authors: Weichenthal Michael , Mohr Peter , Stegmann W. , Breitbart Eckhard W.
Published: September 2002

In a randomized controlled clinical trial, the properties of low‐frequency ultrasound in the treatment of chronic venous ulcers were investigated. Thirty‐eight patients with chronic ulcerations of the legs caused by chronic venous insufficiency were randomly assigned to receive either conventional therapy alone or conventional therapy plus additional 30 kHz ultrasound treatment. Patients with other conditions that may impair wound healing such as diabetes mellitus or arterial disease were excluded. The ultrasound treatment consisted of 10 minutes of foot bathing with application of 30 kHz ultrasound 100 mW/cm2 three times a week. Response was evaluated with the use of planimetry of the ulcer area and compared with controls after 3 and 8 weeks. After 3 weeks of treatment (and to a greater extent after 8 weeks of treatment) the ultrasound group showed a markedly better response than the control group. Although the control group showed a mean decrease of 11% in the ulcerated area after 8 weeks, in the ultrasound group the mean ulcerated area decreased by 41% (p < 0.05). There were only mild side effects in some of the patients treated with ultrasound. In conclusion, application of low‐frequency ultrasound may be a helpful treatment option in chronic venous leg ulcers.
Seasonal Direct Light Availability Affects Mean Leaf Orientation in a Herbaceous Multi‐Species Canopy
Authors: Zobel K. , Eek L.
Published: September 2002

Abstract:Relationship between leaf orientation in natural or semi‐natural herbaceous communities and the local abundance of direct light has rarely been investigated. We present evidence from a permanent plot experiment that seasonal direct light availability in 40 × 40 cm plots significantly affects mean leaf orientation in a semi‐natural wooded meadow. In sunny years and in well‐illuminated conditions, the leaf surface is exposed predominantly to the north, andvice versa. Two groups of species are responsible for such a response: of the variation in leaf orientation, 41 % is explainable through direct light availability for light‐demanding species, and 26 % for graminoid species. In shade‐tolerant species and in forbs there is no sign of a regression between leaf orientation and direct light abundance. Ability to plastically react to variation in seasonal and local direct light availability appears to be a trait under considerable selective pressure only in light‐demanding plants, and more characteristic of species with graminoid growth form.
Comparison of Isoprene Emission, Intercellular Isoprene Concentration and Photosynthetic Performance in Water‐Limited Oak (Quercus pubescens Willd. and Quercus robur L.) Saplings
Authors: Brüggemann N. , Schnitzler J.‐P.
Published: September 2002

Abstract: The influence of prolonged water limitation on leaf gas exchange, isoprene emission, isoprene synthase activities and intercellular isoprene concentrations was investigated under standard conditions (30 °C leaf temperature and 1000 μmol photons m‐2 s‐1 PPFD) in greenhouse experiments with five‐year‐old pubescent oak (Quercus pubescens Willd.) and four‐year‐old pedunculate oak (Quercus robur L.) saplings. Net assimilation rates proved to be highly sensitive to moderate drought in both oak species, and were virtually zero at water potentials (Ψpd) below ‐ 1.3 MPa in Q. robur and below ‐ 2.5 MPa in Q. pubescens. The response of stomatal conductance to water stress was slightly less distinct. Isoprene emission was much more resistant to drought and declined significantly only at Ψpd below ‐ 2 MPa in Q. robur and below ‐ 3.5 MPa in Q. pubescens. Even during the most severe water stress, isoprene emission of drought‐stressed saplings was still approximately one‐third of the control in Q. robur and one‐fifth in Q. pubescens. Isoprene synthase activities were virtually unaffected by drought stress. Re‐watering led to partial recovery of leaf gas exchange and isoprene emission. Intercellular isoprene concentrations were remarkably enhanced in water‐limited saplings of both oak species during the first half of the respective drought periods with maximum mean values up to ca. 16 μl l‐1 isoprene for Q. pubescens and ca. 11 μl l‐1 isoprene for pedunculate oak, supporting the hypothesis that isoprene serves as a short‐term thermoprotective agent in isoprene‐emitting plant species.
Polarization switching of ferroelectric ceramics with grain boundary effect: A simple continuum model
Authors: Kim Sang-Joo
Published: September 2002

A one-dimensional continuum model is proposed to simulate the polarization switching of ferroelectric ceramics and investigate the effects of the presence of grain boundaries on the switching behavior. A ceramic bar is modeled as a composite system of grains and grain boundaries. A grain element consists of a material characterized by a Helmholtz free energy function and a grain boundary element consists of a linear dielectric material. A polarization switching in a grain element starts and proceeds according to a switching criterion and a kinetic relation, respectively. Electric conduction effects in both grain and grain boundary elements are included in the model. A system of differential equations is derived from the law of charge conservation and solved using the finite difference method. The predicted change of hysteresis loops with electrical loading rates is qualitatively consistent with experiments. The effects of the grain boundary on polarization switching are also calculated and discussed.
Spectrum analysis, correlation crystal-field effects and f–f transition intensities of U3+ in LaCl3
Authors: Karbowiak M. , Drożdżyński J. , Sobczyk M.
Published: September 2002

High resolution polarized absorption spectra of U3+:LaCl3 single crystals were recorded in the 4000–50 000 cm−1 range at 7 K. The experimental crystal-field energy levels of the U3+ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators. The performed analysis of the spectra enabled the determination of crystal-field parameters and reassignment of some of the observed 5f3→5f3 transitions. The effects of selected CCF operators on the splitting of some specific U3+ multiplets have been investigated. On the basis of the obtained electronic wave functions the electric-dipole intensity parameters of the total transition dipole strength were determined by fitting the calculated and experimental transition intensities. Among 67 transitions observed in the 4000–22 000 cm−1 range 56 were sufficiently well resolved for quantitative calculations.
The hierarchical reference theory as applied to square well fluids of variable range
Authors: Reiner Albert , Kahl Gerhard
Published: September 2002

Continuing our investigation into the numerical properties of the hierarchical reference theory, we study the square well fluid of range λ from slightly above unity up to 3.6. After briefly touching upon the core condition and the related decoupling assumption necessary for numerical calculations, we shed some light on the way an inappropriate choice of the boundary condition imposed at high density may adversely affect the numerical results; we also discuss the problem of the partial differential equation becoming stiff for close-to-critical and subcritical temperatures. While agreement of the theory’s predictions with simulational and purely theoretical studies of the square well system is generally satisfactory for λ≳2, the combination of stiffness and the closure chosen is found to render the critical point numerically inaccessible in the current formulation of the theory for most of the systems with narrower wells. The mechanism responsible for some deficiencies is illuminated at least partially and allows us to conclude that the specific difficulties encountered for square wells are not likely to resurface for continuous potentials.
Global ballooning instabilities in a Heliotron J plasma
Authors: Yamagishi Osamu , Nakamura Yuji , Kondo Katsumi , Nakajima Noriyoshi
Published: September 2002

The global ballooning stability in a Heliotron J plasma [M. Wakatani et al., Nucl. Fusion 40, 569 (2000)] is studied by use of the CAS3D code (code for analysis of stability in three-dimensional systems) [C. Schwab, Phys. Fluids 5, 3195 (1993)]. The global mode has strong toroidal mode coupling so that the mode structure is typically a helical type. The mode structure of the pressure driven modes, including the interchange mode, is discussed. The comparison between the local and global modes is also shown. The eigenvalue as well as eigenfunction shows good agreement.
The angular momentum equation for a finite element of a fluid: A new representation and application to turbulent modeling
Authors: Iovieno M. , Tordella D.
Published: September 2002

The equation for the intrinsic moment of momentum averaged over small volumes of linear dimension δ has been considered. A representation of it is given as an infinite sequence of independent equations using a series expansion in terms of δ2. The equations of different orders are obtained through linear antisymmetric operators—with a structure that is similar to that of the curl—acting on the momentum equation. The first-order term of the sequence is the Helmholtz equation; the remaining terms can be considered as balances for a kind of higher-orders vorticity. It has been shown that the coupling between the momentum and the angular momentum equation, based on a supposed antisymmetrical part of the stress tensor—which has sometimes been assumed by authors who deal with turbulent flow of a homogeneous fluid—is devoid of physical rationale. A different form of coupling is proposed that may be used to describe a turbulent flow of a homogeneous medium, using a large eddy simulation technique. In the authors model the coupling is given by a functional dependence of the turbulent eddy diffusivity over the angular momentum of a finite volume of a fluid.
Nonlinear dynamics of temporally excited falling liquid films
Authors: Oron Alexander , Gottlieb O.
Published: September 2002

The two-dimensional spatiotemporal dynamics of falling thin liquid films on a solid vertical wall periodically oscillating in its own plane is studied within the framework of long-wave theory. A pertinent nonlinear evolution equation referred to as the temporally modulated Benney equation (TMBE) is derived and its solutions are investigated numerically. The bifurcation diagram of the Benney equation (BE) describing the film dynamics in the unforced regime is computed depicting the domains of linearly stable, linearly unstable bounded, and unbounded behaviors. The solutions obtained for film dynamics via the BE are compared to those documented for direct numerical simulations of the Navier–Stokes equations (NSE). The comparison demonstrates that the BE constitutes an accurate asymptotic reduction of the NSE in the domain preceding the transition to the regime of its unbounded solutions. It is found that periodic planar boundary excitation does not alter the fundamental unforced bifurcation structure and the spatial topological structure of the interfacial waves. The film evolution as described by TMBE is found to be primarily of quasiperiodic tori complemented by several types of strange attractors. In the case of relatively thick films increase of either the amplitude or the frequency of wall oscillation results in significant decrease of the peak-to-peak size of interfacial waves.
Response function of a Hall magnetosensor in the diffusive regime
Authors: Cornelissens Y. G. , Peeters F. M.
Published: September 2002

Two-dimensional electron gas systems patterned into micrometer Hall bars can be used as Hall magnetosensors. In this way, ballistic Hall probes have already been studied and used successfully. Here, the response function of a Hall sensor is determined in the diffusive regime, which allows this device to be used as a magnetosensor for the determination of inhomogeneous magnetic field distributions. Furthermore, the influence of the geometry of the Hall bar on this response function, such as circular corners and asymmetry in the probes, is also investigated and appears to be non-negligible.
Kinetics of thermalization in shock waves
Authors: Beylich Alfred E.
Published: September 2002

The recently developed interlaced system which can be employed for the numerical calculation of flow problems with arbitrary cell-Knudsen numbers, Knc=λ/Δx (λ=mean free path length, Δx=typical computational cell dimension), has been extended by introducing a Lennard–Jones (LJ) interaction potential. The scattering behavior of the LJ-model is quite different from that of the previously used hard-sphere (HS) model: The HS-model has a symmetric dipole-type scattering lobe, whereas the scattering lobe of the LJ-model shows a strong forward scattering, due to the large cross sections for low energy collisions. The influence of this scattering behavior on the collisional loss frequency ν and the gain function fg=G/ν (with G being the gain rate) in the kinetic equation is considerable and may be roughly stated as follows: For the HS-model the loss rate is small but the collisional redistribution is very efficient, for the LJ-model the situation is reversed. The kinetics of thermalization controlled by the loss and gain terms is studied, in a first step, using a pseudo-shock (with space homogeneity). In a second step, the structure of normal shock waves is calculated by using both models (HS; LJ for helium and argon). Comparison of density profiles with existing shock tube experiments show fair agreement for the LJ-model but too small shock thickness for the HS-model. Results for the stress term σxx and the heat flux qx are in good agreement with simple estimates for large Mach numbers, M1≫1, where we find, for the extrema of these moments, that |σxx|∼M12 and |qx|∼M13. The complex interaction of loss and gain terms and their dependence on the energy of the interacting particles has some influence on the shock thickness. We find that, with decreasing upstream temperature T1, also the shock wave thickness decreases, while the minima of σxx and qx practically remain unchanged. When testing the collisional terms used in the BGK-model, with a constant loss term ν and a gain function fg=fM (M=Maxwellian), we find the typical upstream tail in the density and temperature profiles, as it was calculated before.
Total cross sections and molecular frame photoelectron angular distributions in the N 1s photoionization of N2: An investigation of electron correlation effects
Authors: Lin Ping , Lucchese Robert R.
Published: September 2002

Multichannel scattering calculations have been performed to study the electron correlation effects in the N 1s photoionization of nitrogen molecules. Both the Hartree–Fock and configuration–interaction methods were applied in the calculations of target states, therefore the role of electron correlation effects in the target states can be investigated. Both single- and multichannel calculations have been performed to study the interchannel coupling effects. With correlated target states and coupled channels in the calculations, our calculated cross sections and asymmetry parameters are in good agreement with the experiments. The shape resonance is very well reproduced in our calculation, and we found weak coupling between channels leading to the 1σg−1 and 1σu−1 states, which agrees well with more recent experimental results by Hergenhahn et al. [J. Phys. Chem. 105, 5704 (2001)], but contradicts the random phase approximation results. The molecular frame photoelectron angular distributions obtained from our calculations are also in agreement with experiments. Our calculations also suggest an autoionization process via a double-excited state of the character of 1σg−11πu−11πg2, which is located near the threshold as observed by the experiments. Dynamics of the shake-up channels are also studied and compared with the experiments.
A field-theoretical approach to simulation in the classical canonical and grand canonical ensemble
Authors: Baeurle Stephan A. , Martoňák Roman , Parrinello Michele
Published: September 2002

In this paper we present a new approach to simulation methods for classical statistical mechanics relying on a field-theoretical formalism. It is based on applying the complex Hubbard–Stratonovich transformation to the canonical and grand-canonical partition function, which allows one to reexpress their particle representation in terms of a functional integral over a fluctuating auxiliary field. The thermodynamic averages from the resulting field representations can then be calculated with a conventional Monte Carlo algorithm. We explored the applicability of the auxiliary field methodology for both the canonical and grand-canonical ensemble using a system of particles interacting through a purely repulsive Gaussian pair potential in a broad range of external parameters. In the grand-canonical case this technique represents an alternative to standard grand-canonical Monte Carlo methods. Generally providing a framework for simulating classical particle systems within a continuum formalism can be useful for multiscale modeling where the field or continuum description naturally appears within quantum mechanics on smaller length scales and within classical mechanics on larger ones.
On a low energy bound in a class of chiral field theories with solitons
Authors: Shabanov Sergei V.
Published: September 2002

A low energy bound for static classical solutions in a class of chiral solitonic field theories related to the infrared physics of the SU(N) Yang–Mills theory is established.
Characterization and application of an externally mounted catalytic converter for aircraft measurements of NOy
Authors: Lange L. , Fischer H. , Parchatka U. , Gurk C. , Zenker T. , Harris G. W.
Published: September 2002

A novel design for an airborne NOy converter was implemented, characterized in the laboratory, and used extensively for in situ tropospheric and stratospheric measurements of total reactive nitrogen (NOy). During field deployments, the converter is mounted outside the aircraft fuselage, avoiding the need for an inlet line. In flight, the converter can be calibrated by the addition of standard gases close to the sample inlet, compensating for any changes in the instrument sensitivity caused by changing operating conditions. The system has been used successfully during several Stratosphere Troposphere Experiments by Aircraft Measurements campaigns in the lowermost stratosphere and upper troposphere for the measurement of total reactive nitrogen. The detection limit of the system is approximately 100 pptv for 10 s integrated data (2σ). The precision, deduced from the reproducibility of the in-flight calibrations, is 7% and the accuracy is about 30%. Laboratory studies demonstrate that interference from HCN, NH3, and CH3CN is negligible for background conditions.
A high-resolution mixed field immersion lens attachment for conventional scanning electron microscopes
Authors: Khursheed A. , Karuppiah N.
Published: September 2002

This article deals with a compact mixed field add-on lens attachment for conventional scanning electron microscopes (SEMs). By immersing the specimen in a mixed electric–magnetic field combination, the add-on lens is able to provide high image resolution at relatively low landing energies (<1 keV). Experimental results show that the add-on lens unit enables a tungsten gun SEM to acquire images with a resolution of better than 4 nm at a landing energy of 600 eV, which lies close to simulation predictions. Normally, this type of SEM would only be able to provide this kind of resolution at high voltages (30 kV).
Pseudo-Hermiticity versus PT-symmetry III: Equivalence of pseudo-Hermiticity and the presence of antilinear symmetries
Authors: Mostafazadeh Ali
Published: September 2002

We show that a diagonalizable (non-Hermitian) Hamiltonian H is pseudo-Hermitian if and only if it has an antilinear symmetry, i.e., a symmetry generated by an invertible antilinear operator. This implies that the eigenvalues of H are real or come in complex conjugate pairs if and only if H possesses such a symmetry. In particular, the reality of the spectrum of H implies the presence of an antilinear symmetry. We further show that the spectrum of H is real if and only if there is a positive-definite inner-product on the Hilbert space with respect to which H is Hermitian or alternatively there is a pseudo-canonical transformation of the Hilbert space that maps H into a Hermitian operator.
High-voltage pulse switching hardware for electro-optic studies of conducting aqueous solutions
Authors: Riley Scott A. , May Skipp , Augustine Matthew P.
Published: September 2002

The hardware necessary for the electro-optic study of conducting polyelectrolyte solutions is frequently not commercially available or financially practical. The designs of an electrical rectangular pulse switch and polarity-reversing relay switch capable of producing 3 kV 5 A direct current pulses lasting longer than 100 μs are presented. As an example of the operation of this equipment, the electric birefringence of an aqueous solution of the Pseudomonas bacteriophage Pf1 in tris/EDTA buffer is presented.
Thermoelectric power measurement under hydrostatic pressure using a self-clamped pressure cell
Authors: Choi E. S. , Kang Haeyong , Jo Y. J. , Kang W.
Published: September 2002

A thermoelectric power (TEP) measurement technique in a self-clamped pressure cell is presented. Thermal and electrical contacts were glued to heaters by Stycast epoxy, which enhances thermal integration. The pressure effect of Chromel–Constantan and Chromel–AuFe0.07% thermocouples are compared to Chromel–Alumel thermocouples, which are known to be pressure insensitive between 4.2 and 300 K. The investigated thermocouples are found to have a small pressure effect; ∼±4% at maximum in the measured temperature and pressure range. Any pressure effect on Au wires was also found to be very small from the pressure-dependent TEP measurement of YBCO superconductor below Tc.
Experimental evidence for the heat capacity maximum during a melt’s polymerization
Authors: Johari G. P. , Tombari E. , Presto S. , Salvetti G.
Published: September 2002

The equilibrium heat capacity Cp of a liquid whose molecules polymerized to form a linear chain structure at a fixed temperature has been measured at a fixed frequency of 3.33 mHz in real time simultaneously with the extent of polymerization α. The polymerization temperatures and this frequency were chosen such that the fully polymerized state remained a liquid and no heat capacity relaxation occurred. The plots of Cp against α show a maximum. This confirms the recent theoretical conclusions based on the polymer chain statistics [J. Wang and G. P. Johari, J. Chem. Phys. 116, 2310 (2002)] that during the course of a melt’s polymerization, the configurational heat capacity of the equilibrium liquid reaches a maximum value at a certain α, and then decreases to the finite value of the fully polymerized melt. The results are also discussed in terms of the potential energy landscape at a fixed temperature where each new covalent bond formed and/or a new molecular weight distribution causes the state of the sample to enter a new landscape with a new set of potential energy minima of different depths and widths.
Properties of the symplectic structure of general relativity for spatially bounded space–time regions
Authors: Anco Stephen C. , Tung Roh S.
Published: September 2002

We continue a previous analysis of the covariant Hamiltonian symplectic structure of general relativity for spatially bounded regions of space–time. To allow for wide generality, the Hamiltonian is formulated using any fixed hypersurface, with a boundary given by a closed spacelike two-surface. A main result is that we obtain Hamiltonians associated with Dirichlet and Neumann boundary conditions on the gravitational field coupled to matter sources, in particular a Klein–Gordon field, an electromagnetic field, and a set of Yang–Mills–Higgs fields. The Hamiltonians are given by a covariant form of the Arnowitt–Deser–Misner (ADM) Hamiltonian modified by a surface integral term that depends on the particular boundary conditions. The general form of this surface integral involves an underlying “energy-momentum” vector in the space–time tangent space at the spatial boundary two-surface. We give examples of the resulting Dirichlet and Neumann vectors for topologically spherical two-surfaces in Minkowski space–time, spherically symmetric space–times, and stationary axisymmetric space–times. Moreover, we establish the relation between these vectors and the ADM energy-momentum vector for a two-surface taken in a limit to be spatial infinity in asymptotically flat space–times. We also discuss the geometrical properties of the Dirichlet and Neumann vectors and obtain several striking results relating these vectors to the mean curvature and normal curvature connection of the two-surface. Most significantly, the part of the Dirichlet vector normal to the two-surface depends only on the space–time metric at this surface and thereby defines a geometrical normal vector field on the two-surface. We show that this normal vector is orthogonal to the mean curvature vector, and its norm is the mean null extrinsic curvature, while its direction is such that there is zero expansion of the two-surface, i.e., the Lie derivative of the surface volume form in this direction vanishes. This leads to a direct relation between the Dirichlet vector and the condition for a spacelike two-surface to be (marginally) trapped.
Band structure, Born effective charges, and lattice dynamics of CuInS2 from ab initio calculations
Authors: Łażewski J. , Jochym P. T. , Parlinski K.
Published: September 2002

The first principles plane-wave pseudopotential calculations based on density functional theory were used to determine structural and electronic properties of CuInS2 semiconducting chalcopyrite. The Born effective charges were obtained using Berry phase method. Phonon dispersion relations were evaluated from Hellmann–Feynman forces with the direct method. The elastic constants were derived from the stress–strain relationships. The calculated quantities agree well with available experimental data.
Theoretical study of proton transfer in ammonium nitrate clusters
Authors: Alavi Saman , Thompson Donald L.
Published: September 2002

Proton transfer in ammonia–nitric acid clusters containing up to four component units are subject to theoretical calculation in this work. In a single ammonium nitrate unit, proton transfer between the nitric acid and ammonia unit does not occur but the two molecules are strongly hydrogen-bonded. In a cluster of two ammonium nitrate formula units [NH3HNO3]2, proton transfer does occur and the components are stabilized by ionic interactions. Ammonium nitrate solvated with single ammonia [NH3HNO3]NH3 or nitric acid [NH3HNO3]HNO3 molecules are also studied. Structural changes in the various clusters relative to the free molecules are discussed. Using population analysis, the total electrostatic interaction between the components of each cluster are calculated. It is argued that the magnitude of the total electrostatic interactions within the cluster determines whether proton transfer and ion formation takes place. Binding energies alone do not give a reliable indication of the occurrence of proton transfer.
Control of stretching rate in time-periodic chaotic flows
Authors: Vikhansky A.
Published: September 2002

In this study we consider a method for enhancement of mixing in time-periodic laminar flows. The stretching rate along unstable manifold of the chaotic flow is considered as a quantitative criterion of mixing quality. Optimal control theory is applied for improving the stretching rate in a prototypic cavity flow. It is demonstrated that the optimal flow field tends to stretch the infinitesimally small vectors that are distributed along the material interface. The higher is the length of a vector at the final moment of time the more effective is the stretching along this vector. It is shown that a high stretching rate does not imply uniformity of mixing. In the periodic flows with the relatively short periods the chaotic region does not span over the entire flow, and the increase of a stretching rate in the chaotic region leads to expansion of regular islands. Thus, the proposed method for enhancement of mixing is applicable for the flows without regular unmixed islands.
On the collision rate of particles in turbulent flow with gravity
Authors: Dodin Z. , Elperin T.
Published: September 2002

Formula for the collision rate of inertial particles in a homogeneous isotropic stationary turbulent flow with gravity is derived. The obtained formula yields correct results for two special cases, where the formula by Saffman and Turner [J. Fluid Mech. 1, 16 (1956)] fails. In the case of the particles with the same size, the collision rate predicted by Saffman and Turner is 29% higher than that predicted by the obtained formula. Turbulence effects on the collision rate are estimated for the conditions pertinent to droplets in atmospheric clouds.
Mechanism for linear and nonlinear optical effects in SrBe3O4 crystal
Authors: Lin Zheshuai , Wang Zhizhong , Yang Huatong , Chen Chuangtian , Lee Ming-Hsien
Published: September 2002

Electronic and band structure calculations of SrBe3O4 crystal from first principles are performed based on a plane-wave pseudopotential method for the first time. The linear refractive indices and the static second-harmonic generation (SHG) coefficients are also calculated by the SHG formula improved by our group. The calculated values are in good agreement with the experimental values. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to the optical response. The results show that the contribution of the (SrO9) group to the SHG coefficients is more pronounced than that of (BeO3)4− and (BeO4)6− groups. Because the plane BeO3 and tetrahedral BeO4 groups have a little covalent bonding, they only give a tenth of the contribution of the SrO9 group.
Spectral difference methods for solving the differential equations of chemical physics
Authors: Mazziotti David A.
Published: September 2002

Spectral differences [D. A. Mazziotti, Chem. Phys. Lett. 299, 473 (1999)] is a family of techniques for solving differential equations in which the summation in the numerical derivative is accelerated to produce a matrix representation that is not only exponentially convergent like the discrete variable representation (DVR) and other spectral methods but also sparse like traditional finite differences and finite elements. Building upon important work by Boyd [Comput. Methods Appl. Mech. Eng. 116, 1 (1994)] and Gray and Goldfield [J. Chem. Phys. 115, 8331 (2001)], we explore a new class of spectral difference methods which yields solutions that are more accurate than high-order finite differences by several orders of magnitude. With the generating weight for Gegenbauer polynomials we design a new spectral difference method where the limits of an adjustable parameter α generate both finite differences (α=∞), emphasizing the low Fourier frequencies, and a truncated sinc-DVR (α=0), emphasizing all Fourier frequencies below the aliasing limit of the grid. A range of choices for α∈[0,∞] produces solutions which are significantly better than the equivalent order of finite differences. We compare the Gegenbauer-weighted spectral differences with methods by Boyd as well as Gray and Goldfield which employ a hyperbolic secant and a step function as frequency weights, respectively. The solutions from the Gegenbauer- and the sech-weighted differences are shown to be less sensitive to parameter selection than the step-weighted differences. We illustrate all of the spectral difference methods through vibrational and quantum control calculations with diatomic iodine and the van der Waals cluster NeCO. Spectral differences also have important applications in molecular dynamics and electronic structure as well as other areas of science and engineering.
(2+1)-dimensional (M+N)-component AKNS system: Painlevé integrability, infinitely many symmetries, similarity reductions and exact solutions
Authors: Lou Sen-yue , Chen Chun-li , Tang Xiao-yan
Published: September 2002

The (2+1)-dimensional (M+N)-component AKNS system that is derived from the inner parameter dependent symmetry constraint of the KP equation is studied in detail. First, the Painlevé integrability of the model is proved by using the standard WTC and Kruskal approach. Using the formal series symmetry approach, the generalized KMV symmetry algebra and the related symmetry group are found. The two-dimensional similarity partial differential equation reductions and the ordinary differential equation reductions are obtained from the generalized KMV symmetry algebra and the direct method. Abundant localized coherent structures are revealed by the variable separation approach. Some special types of the localized excitations like the multiple solitoffs, dromions, lumps, ring solitons, breathers and instantons are plotted also.
Boundary-layer theory, strong-coupling series, and large-order behavior
Authors: Bender Carl M. , Pelster Axel , Weissbach Florian
Published: September 2002

The introduction of a lattice converts a singular boundary-layer problem in the continuum into a regular perturbation problem. However, the continuum limit of the discrete problem is extremely nontrivial and is not completely understood. This article examines two singular boundary-layer problems taken from mathematical physics, the instanton problem and the Blasius equation, and in each case examines two strategies, Padé resummation and variational perturbation theory, to recover the solution to the continuum problem from the solution to the associated discrete problem. Both resummation procedures produce good and interesting results for the two cases, but the results still deviate from the exact solutions. To understand the discrepancy a comprehensive large-order behavior analysis of the strong-coupling lattice expansions for each of the two problems is done.
A fast low noise charge preamplifier for position sensitive detectors
Authors: Beltrán David , Perlas Josep Antoni
Published: September 2002

We present the design and the results of the evaluation of a fast, low noise, charge preamplifier. This device uses commercial circuits; the advantages over classical circuits based on transistors are presented. These include short development time, high reliability and reproducibility, and easy maintenance. The amplifier has been tested with a position sensitive multiwire proportional counter with a readout system based on delay lines. With an input impedance of 50 Ω, we have obtained a signal to noise ratio better than 40 dB, a gain of 0.42 μV per electron, a pulse rise time of 9.4 ns, and a total pulse duration lower than 120 ns. These values allow detector data acquisition rates in excess of 1 MHz, and a spatial resolution better than 300 μm.
Gamma radiation resistant Fabry–Perot fiber optic sensors
Authors: Liu Hanying , Miller Don W. , Talnagi Joseph
Published: September 2002

The Nuclear Regulatory Commission (NRC) in 1998 completed a study of emerging technologies that could be applicable to measurement systems in nuclear power plants [H. M. Hashemian et al., “Advanced Instrumentation and Maintenance Technologies for Nuclear Power Plants,” NUREG/CR-5501 (1998)]. This study concluded that advanced fiber optic sensing technology is an emerging technology that should be investigated. It also indicated that there had been very little research related to performance evaluation of fiber optic sensors in nuclear plant harsh environments, although substantial research has been performed on nuclear radiation effects on optical fibers in the last two decades. A type of Fabry–Perot fiber optic temperature sensor, which is manufactured by Fiso Technologies in Canada, is qualified to be a candidate for potential applications in nuclear radiation environment due to its unique signal processing technique and its resistance to power loss. The gamma irradiation effects on this type of sensors are investigated in this article. Two sensors were irradiated in a gamma irradiation field and one of them was irradiated up to a total gamma dose of 133 Mrad. The sensor on-line performance was monitored during each gamma irradiation test. Furthermore, the sensor static and dynamic performance before and after each irradiation test were evaluated according to the Standard ISA-dS67.06.01 (“Performance Monitoring for Nuclear Safety-Related Instrument Channels in Nuclear Power Plants”, Standard ISA-dS67.06.01, Draft 7, Instrument Society of America, 1999). Although several abnormal phenomena were observed, analysis shows that gamma irradiation is not accredited to the abnormal behavior, which implies that this type of sensor is suitable to a gamma irradiation environment with a high gamma dose.
Dynamics of immersed molecules in superfluids
Authors: Quist Michael J. , Elser Veit
Published: September 2002

The dynamics of a molecule immersed in a superfluid medium are considered. Results are derived using a classical hydrodynamic approach followed by canonical quantization. The classical model, a rigid body immersed in incompressible fluid, permits a thorough analysis; its effective Hamiltonian generalizes the usual rigid-rotor Hamiltonian. In contrast to the free rigid rotor, the immersed body is shown to have chaotic dynamics. Quantization of the classical model leads to new and experimentally verifiable features. It is shown, for instance, that chiral molecules can behave as “quantum propellers:” the rotational-translational coupling induced by the superfluid leads to a nonzero linear momentum in the ground state. Hydrogen peroxide is a strong candidate for experimental detection of this effect. The signature is a characteristic splitting of rotational absorption lines. The 101→110 line in hydrogen peroxide, for example, is predicted to split into three lines separated by as much as 0.01 cm−1, which is about the experimental linewidth.
The rate of electrochemical electron-transfer reactions
Authors: Schmickler W. , Mohr J.
Published: September 2002

Electrochemical electron-transfer reactions form the basis of such important devices as fuel cells and sensors. Previous theories of these reactions were limited either to the case of weak electronic interaction between the electrode and the reactants, or to strong interactions. In this work the rate of electron exchange is calculated by a combination of quantum mechanics and computer simulations. This method is valid for all strengths of the electronic interaction, so that the dependence of the reaction rate on the interaction strength could be obtained. Our results encompass three different regimes; in the order of increasing interaction these are: (i) a linear region, in which first-order perturbation theory holds; (ii) a weakly adiabatic region, in which the rate is limited by solvent dynamics; (iii) a strongly adiabatic region, in which the interaction lowers the energy of activation.
Flow-independent drop deformation with zero surface tension
Authors: Cristini Vittorio
Published: September 2002

We derive exact solutions describing three-dimensional ellipsoidal drop deformation with zero surface tension in steady, planar linear flows. We apply the analysis to study the development of lamellar drop morphologies as observed in recent experiments.
Study of carrier dynamics in indirect transition-type (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP superlattices by transient photoluminescence and photocurrent measurements
Authors: Ishitani Yoshihiro , Matsuya Kouhei , Fujita Toshiaki , Nakasa Keijiro , Harima Yutaka
Published: September 2002

The time resolved photoluminescence (TRPL) and the time resolved photocurrent (TRPC) are simultaneously measured for undoped (Al0.7Ga0.3)0.5In0.5P/AlxIn1−xP (x=0.53 and 0.57) superlattices. The bias voltage is applied on the semitransparent Au electrode on the epitaxial layer. From the measurement of the sample with x=0.53 (lattice matched to the GaAs substrate), most of the carriers are recombined by nonradiative processes under the bias voltage of +0.3–−1.0 V. The increase of the electric field causes the increase of electron flow from the surface region of the SL and the decrease in PL intensity. From the bias voltage dependence of the TRPL and TRPC properties, the amount of the radiatively recombined carriers are found to be less than 1×109 when 1.4×1011 photons are incident on the sample. The surface electric field of the sample without the electrode is estimated to be less than 3×103 V/cm during the PL measurement. For the sample with x=0.57, the energy states originating from the crystal defects act as the carrier traps under a low-electric field and the levels which contribute to the tunneling of electrons through the potential barriers under a high-electric field.
Arc erosion characteristics of pseudospark discharge in multiaperture geometry
Authors: Naweed Ahmer , Kiefer Jochen , Gavrilescu Constantin , Neff Willi
Published: September 2002

Analysis of discharge mechanism in especially designed pseudosparks that facilitate pseudospark characteristic low-erosive conduction at very high currents is presented. The alternate formulation of criterion for transition to arc discharge phase developed here enables us to account for the emergence of arcs at each aperture after a threshold electric charge is transmitted in these devices. The use of a large number of apertures is found to have no influence on discharge condition that initiates arc formation at individual apertures.