bluuebunny/crossref_metadata_2025 huggingface dataset:
Upregulation of cathepsin D expression in the dedifferentiating salamander limb regenerates and enhancement of its expression by retinoic acid
Authors: Ju Bong‐Gun , Kim Won‐Sun
Published: July 2002

In the regenerating urodele limb, catheptic activity has been known to be present in the stump tissue undergoing histolysis, and it has been implicated in the modification of some intracellular and extracellular matrix molecules. In this study, we compared spatial and temporal gene expression profiles of cathepsin D in normal, retinoic acid‐treated, or denervated larval limb regenerates of Hynobius leechii and compared cathepsin D activities between normal and retinoic acid‐treated limb regenerates. The results showed that the expression of cathepsin D increased markedly in the vicinity of an amputation site under the wound epidermis at dedifferentiation stage, whereas the expression level of cathepsin D was low in the denervated limb. With retinoic acid treatment, the expression of cathepsin D was elevated in terms of both level and duration. In addition, the profile of cathepsin D activity coincided well with the expression profile of cathepsin D in normal and retinoic acid‐treated limb regenerates. These results suggest that the increase of cathepsin D activity during the dedifferentiation period is due to the upregulation of cathepsin D transcription, and nerve factors are involved in this process. Furthermore, retinoic acid appears to upregulate cathepsin D expression, which might be linked to the enhanced dedifferentiation in the retinoic acid‐treated limb regenerates.
A target of thrombin activation promotes cell cycle re‐entry by urodele muscle cells
Authors: Tanaka Elly M. , Brockes Jeremy P.
Published: July 2002

A key early event of newt limb regeneration is the local dedifferentiation of cells to form dividing progenitor cells. This involves the plasticity of differentiation and the ability to re‐enter the cell cycle. In culture, differentiated newt myotubes are able to re‐enter S‐phase in response to serum stimulation. Here, we analyzed the intracellular and extracellular requirements for this process. Cell cycle re‐entry depends on the phosphorylation of the retinoblastoma protein, which is a key regulator of the G1‐S transition. This is in contrast to mammalian myotubes, which are refractory to serum stimulation and cannot phosphorylate retinoblastoma protein in response to serum. The serum factor responsible for this phosphorylation appears to be distinct from common polypeptide growth factors and is enriched in crude preparations of bovine thrombin. Fractionation and analysis of this preparation indicate that the factor is regulated by thrombin and plasmin proteolysis. These results indicate that factors involved in acute responses to wounding such as clotting may be important initiators of the regenerative response.
General Anesthesia and the Ketogenic Diet: Clinical Experience in Nine Patients
Authors: Valencia Ignacio , Pfeifer Heidi , Thiele Elizabeth A.
Published: July 2002

Summary: Purpose:To determine if children actively on the ketogenic diet (KD) can safely undergo general anesthesia (GA) for surgical procedures.

Methods:The records of children treated with the KD at Children's Hospital (Boston, Massachusetts) from 1995 to the present were reviewed. The charts of children who had received GA while on the diet were evaluated with regard to demographics, procedure information, anesthesia records, blood chemistries, and perioperative course. Of 71 children on the KD during the period of the study, nine (12.7%) had procedures requiring GA while on the diet.

Results:Nine children received GA for surgical procedures ranging from central line placement to hemispherectomy while on the KD. At the time of GA, the children ranged from age 1 to 6 years, and had been on the KD for 2–60 months. The patients received carbohydrate‐free intravenous solutions perioperatively. Anesthesia duration ranged from 20 min to 11.5 h; for longer procedures, serum pH, glucose, and electrolyte levels were monitored. Serum glucose levels remained stable in all patients, but serum pH typically decreased; the largest reduction was to 7.16. In three procedures, patients received intravenous bicarbonate because of level of acidosis. There were no perioperative complications.

Conclusions:Children on the KD can safely undergo GA for surgical procedures. Although serum glucose levels appear to remain stable, serum pH or bicarbonate levels should be monitored because of the risk of metabolic acidosis.
Suppressive Efficacies by Adaptive Temporal Filtering System on Photoparoxysmal Response Elicited by Flickering Pattern Stimulation
Authors: Takahashi Takeo , Kamijo Ken‐ichi , Takaki Yoko , Yamazaki Toshimasa
Published: July 2002

Summary:  Purpose: Based on our previous study that validated efficacies of an adaptive temporal filtering system (ATFS) suppressing a photoparoxysmal response (PPR) elicited by a chromatic flicker stimulation, we further studied ATFS efficacies on PPRs elicited by pattern‐flicker stimulation in 13 photosensitive epilepsy patients.

Methods: Subjects were 13 photosensitive epilepsy patients (two male and 11 female patients; mean age ± SD, 20.9 ± 8.9 years) who were all sensitive to a flickering geometric‐pattern scene. We used a scene consisting of 15‐Hz flickering 4 c/deg stripe images lasting for 4 s. With a 14‐inch television set 2 m before a subject, we displayed the following video scenes: nonfiltered and filtered flickering‐stripe scenes; for the latter, two kinds of ATFSs with mild efficacy and strong efficacy were used. Three flickering‐stripe scenes altogether, each of which lasted for 4 s, were given at random with a 10‐s interval.

Results: A nonfiltered flickering‐stripe scene elicited generalized PPRs in all patients; a filtered scene by use of an ATFS with mild efficacy elicited generalized PPRs in six patients (46%), whereas that by an ATFS with strong efficacy exhibited no PPRs.

Conclusions: This study, using an ATFS, again shows suppressive efficacy on PPRs elicited by flickering‐pattern stimulation. Therefore a series of our studies suggested that ATFS may be useful as a preventive measure for photosensitive seizures triggered by stimulative flickering images from televisions or other displays.
Economic Evaluation of Antiepileptic Drug Therapy: A Methodologic Review
Authors: Levy Pierre
Published: July 2002

Summary:  Purpose: The increasing number of antiepileptic drugs (AEDs) fostered the development of economic studies in epilepsy. We reviewed this literature to identify and discuss methodologic issues.

Methods: We included all studies devoted to cost‐based evaluation in epilepy, published in English from 1989 to 2001, and identified via a Medline search.

Results: We identified a series of methodologic problems. First, we reconsidered heterogeneity of concepts and estimating methods, often cited as the most critical problem, as they do not necessarily result from a failure to apply standard methods. One must distinguish “natural” sources of heterogeneity arising from the many unconstrained choices left open in the implementation of economic evaluation on the one hand, and imperfect information and observation‐based sources of heterogeneity leading to constrained choices on the other hand. By their very nature, cost‐of‐illness studies are subject to this variety of choices and were used to illustrate our purpose. Second, cost‐minimization studies were reviewed, as they raise additional problems related to study design and choice of an outcome measure. Finally, deficiencies were also identified in cost‐effectiveness and cost–utility studies concerning attempts to incorporate patient's point of view in outcome measurement.

Conclusions: We agreed with previous reviews on the difficulty of compare results from economic studies in epilepsy due to heterogeneity in methods and concepts used. This is partly due to imperfect information and limits in observation as sources for data collection, as well as to unavailability of refined outcome measures. Therefore, improvements are possible in this field.
Are Nectar Sugar Composition and Corolla Tube Length Related to the Diversity of Insects that Visit Asteraceae Flowers?
Authors: Torres C. , Galetto L.
Published: July 2002

Abstract: In this work, we analysed interspecific variation in nectar sugar composition, corolla tube length, and the diversity of floral visitors of 35 Asteraceae species. The potential correlations between these variables could arise either as a result of selection to improve pollinator attractiveness or simply as a consequence of phylogenetic constraints. Samples of nectar and flowers, and data on floral visitors, were obtained from living plants in natural populations from Argentina. Asteraceae species showed a large variability in corolla tube length. Nectar of most species presented a larger proportion of hexoses than sucrose. All species were visited by numerous insects belonging to 2 different orders. Results showed that floral traits are not significantly correlated with the diversity of floral visitors. These characters seem to be linked to the phylogeny of the species. Early branching species (species phylogenetically close to the root of the Asteraceae tree) tend to have longer corollas, higher sucrose proportions and lesser diversity of floral visitors than late branching species. Considering that longer corolla tubes and higher nectar sucrose percentages may indicate some specialization in the pollination system, we suggest that there is an evolutionary tendency toward generalist pollination systems within the family.
Sporulation of Plasmopara viticola: Differentiation and Light Regulation
Authors: Rumbolz J. , Wirtz S. , Kassemeyer H.‐H. , Guggenheim R. , Schäfer E. , Büche C.
Published: July 2002

Abstract: The development of grape downy mildew (Plasmopara viticola) was followed histologically during the entire latent period until the appearance of mature sporangia. Production of sporangiophores and sporangia was assessed using low‐temperature scanning electron (LTSEM) and fluorescent light microscopy. Time‐course studies using attached leaves of Vitis vinifera cv. Müller‐Thurgau revealed that the production of sporangiophores and sporangia is a highly coordinated process and is completed within 7 h. As this differentiation is assumed to occur only in darkness, the influence of light was investigated. For this purpose, different light regimes were applied to infected leaf discs of V. viniferacv. Müller‐Thurgau. White light irradiation prevented formation of sporangia, although the growth of the mycelium was not affected. Many sporangiophores were observed that were abnormally shaped, i.e., short hyphae in clusters or thin, extremely elongated hyphae. For the formation of mature sporangia, a prolonged dark period was necessary. Light experiments suggest photosensitivity at the end of the latent period. A terminal white light irradiation caused an inhibitory effect, whereas a final phase of darkness promoted sporangium development. Different light qualities were tested, revealing an inhibition of sporangium development by blue light whereas neither red nor far‐red light were effective.
Subthreshold carrier losses from GaInP quantum wells measured by time resolved photoluminescence
Authors: Dekker J. , Dumitrescu M. , Tukiainen A. , Orsila S. , Uusimaa P. , Pessa M. , Tkachenko N. V. , Lemmetyinen H.
Published: July 2002

We report here on measurements of carrier loss processes in GaInP quantum wells made using time resolved photoluminescence spectroscopy. Measurements were made as a function of temperature and excitation intensity on quantum wells with different confinement barrier heights. The measurements reveal three distinct lifetime components identifiable by their activation energy and excitation intensity dependence. The lifetime components are assigned to thermionic emission of holes from the quantum well, nonradiative recombination at deep level defects, and radiative band-to-band recombination. The valence band offsets between GaInP and AlGaInP have been determined from the activation energy for thermionic emission of holes and are found to increase from 0.096 to 0.147 eV as the Al content in the waveguide layer increased from 50% to 70%. The relative contributions of the different carrier loss mechanisms to the subthreshold current of GaInP quantum well lasers is also discussed.
Disruption of a compressed vortex
Authors: Borée J. , Maurel S. , Bazile R.
Published: July 2002

The generation and breakdown of a tumbling motion are measured with particle image velocimetry in a model compression machine. The tumbling motion is a rotating flow which axis is perpendicular to the cylinder axis. The experimental set-up and the measurement procedure are described. The analysis of intake and compression strokes is presented. We first analyze the data by using phase averaging. Balances of mean and turbulent kinetic energy, of mean vorticity are presented. Effects of curvature and flow separation are clear during intake. The disruption of the vortex during the compression is a gradual process. Two three-dimensional separated regions appear first and are due to adverse pressure gradients induced by the vortex. Beyond a volumetric ratio of order two, the mean kinetic energy is transferred to turbulence within a short time scale, which is of the order of the vortex turnover time scale. The turbulence then decreases at the beginning of the expansion stroke. By analyzing instantaneous flow fields and by using proper orthogonal decomposition, we identify the fluctuations of the vortex correlated at a large scale. These fluctuations are amplified during the compression stroke. During the breakdown, they are correlated with fluid ejection from the vortex to the separated regions. We thus show that the vortex breakdown may involve several types of instability (elliptical instability but also centrifugal instability).
Quantum jump dynamics in cavity QED
Authors: Spehner D. , Orszag M.
Published: July 2002

We study the stochastic dynamics of the electromagnetic field in a lossless cavity interacting with a beam of two-level atoms, given that the atomic states are measured after they have crossed the cavity. The atoms first interact at the exit of the cavity with a classical laser field ℰ and then enter into a detector which measures their states. Each measurement disentangles the field and the atoms and changes in a random way the state |ψ(t)〉 of the cavity field. For weak atom-field coupling, the evolution of |ψ(t)〉 when many atoms cross the cavity and the detector is characterized by a succession of quantum jumps occurring at random times, separated by quasi-Hamiltonian evolutions, both of which depend on the laser field ℰ. For ℰ=0, the dynamics is the same as in the Monte Carlo wave function model of Dalibard et al. [Phys. Rev. Lett. 68, 580 (1992)] and Carmichael, An Open System Approach to Quantum Optics, Lecture Notes in Physics Vol. 18 (Springer, Berlin, 1991)]. The density matrix of the quantum field, obtained by averaging the projector |ψ(t)〉〈ψ(t)| over all results of the measurements, is independent of ℰ and follows the master equation of the damped harmonic oscillator at finite temperature. We provide numerical evidence showing that for large ℰ, an arbitrary initial field state |ψ(0)〉 evolves under the monitoring of the atoms and the measurements toward squeezed states |α,re2iφ〉, moving in the α-complex plane but with almost constant squeezing parameters r and φ. The values of r and φ are determined analytically. On the other hand, for ℰ=0, the dynamics transforms the initial state into Fock states |n〉 with fluctuating numbers of photons n, as shown in Kist et al. [J. Opt. B: Quantum Semiclassical Opt. 1, 251 (1999)]. In the last part, we derive the quantum jump dynamics from the linear quantum jump model proposed in Spehner and Bellissard [J. Stat. Phys. 104, 525 (2001)], for arbitrary open quantum systems having a Lindblad-type evolution. A careful derivation of the infinite jump rates limit, where the dynamics can be approximated by a diffusion process of the quantum state, is also presented.
Fourth-order nonlinear evolution equations for counterpropagating capillary-gravity wave packets on the surface of water of infinite depth
Authors: Debsarma Suma , Das K. P.
Published: July 2002

Asymptotically exact nonlocal fourth-order nonlinear evolution equations are derived for two counterpropagating capillary-gravity wave packets on the surface of water of infinite depth. On the basis of these equations a stability analysis is made for a uniform standing capillary-gravity wave for longitudinal perturbation. The instability conditions and an expression for the maximum growth rate of instability are obtained. Significant deviations are noticed between the results obtained from third-order and fourth-order nonlinear evolution equations.
A mathematical problem of the theory of gelation
Authors: Batisheva J. G. , Vedenyapin V. V. , Kuchanov S. I.
Published: July 2002

Current theory of gelation describes this process in terms of a set of nonlinear integral equations. In this article the uniqueness of nontrivial solutions of these equations within the unit functional hypercube has been proved. Besides, the convergence to this solution of iterations from an arbitrary point of the above hypercube has been established, which is of utmost importance for calculations of particular gelation processes.
Numerical investigations of small-amplitude disturbances in a boundary layer with impinging shock wave at Ma=4.8
Authors: Pagella Alessandro , Rist Ulrich , Wagner Siegfried
Published: July 2002

The stability behavior of a laminar boundary layer with shock boundary layer interaction and small amplitude disturbances is investigated by linear stability theory and direct numerical simulation. By a complex interaction of several physical properties, the impinging shock wave locally influences stability behavior of the boundary layer, dependent on its shock strength, applied disturbance frequency, and disturbance propagation angle with respect to the flow direction (obliqueness angle). Due to the displacement of the boundary layer near shock impingement and the according Reynolds number effect in this area, the boundary layer is locally destabilized. The displacement of the boundary layer also produces an increase of the thickness of local regions of relative supersonic speed, which promotes second mode instability. For the results obtained by direct numerical simulation nonparallel effects could be identified and quantified. Taking these nonparallel effects into account, linear stability theory is able to represent the stability behavior of wall distant disturbance amplitude maxima having small obliqueness angles for the cases investigated here. For larger obliqueness angles and disturbance amplitudes at or close to the wall the agreement between linear stability theory and direct numerical simulation declines considerably.
The effect of weak inertia on the emptying of a tube
Authors: de Ryck Alain
Published: July 2002

We present an extension of the classical axisymmetric Bretherton theory giving the thickness of the liquid film left on the walls of a drained tube, treating the case of weak inertia by a regular perturbation method. The results obtained by numerical integration fit Taylor’s [J. Fluid Mech. 10, 161 (1961)] experiments, obtained with viscous fluids (glycerine and strong sucrose solutions), and Aussillous and Quéré’s [Phys. Fluids 12, 2367 (2000)] experiments with low viscosity liquids (hexamethyldisiloxane and water) when inertia becomes important. The discrepancies observed between the theory and high Reynolds numbers experiments (Re>1000) are commented on.
Conservation laws for a class of nonlinear equations with variable coefficients on discrete and noncommutative spaces
Authors: Klimek M.
Published: July 2002

The conservation laws for a class of nonlinear equations with variable coefficients on discrete and noncommutative spaces are derived. For discrete models the conserved charges are constructed explicitly. The applications of the general method include equations on quantum plane, supersymmetric equations for chiral and antichiral supermultiplets, auxiliary equations of integrable models which means various cases of nonlinear Toda lattice equations and anomalous diffusion equation.
Specific heat and magnetocaloric effect measurements using commercial heat-flow sensors
Authors: Plackowski Tomasz , Wang Yuxing , Junod Alain
Published: July 2002

We present a technique for measuring the specific heat (C) and the isothermal magnetocaloric effect (MT) in the temperature range from 30 to 300 K. The method consists of precise measurements of the heat flux between the sample and its surroundings. This design, which uses commercially available Peltier elements as heat-flow meters, is simple and robust. A high density of statistically independent data can be obtained, e.g., 30 points/K in specific heat measurements at 1 K/min heating rate, or 150 points/T in magnetocaloric experiments at 0.2 T/min sweep rate. The signal/noise ratio is in the range of 103 to 104. C can be measured with increasing or with decreasing temperature. Test runs with Cu, NdBa2Cu3O7, and UAs samples show that this method provides measurements of the specific heat in magnetic fields up to ⩾14 T with 2% accuracy, is able to characterize small anomalies at the ∼0.1% level (e.g., melting of the flux line lattice in a superconductor), can detail sharp first-order anomalies, and detect their hysteresis. The magnetocaloric effect in NdBa2Cu3O7 shows clear signatures of vortex melting, crossover to irreversibility, and the “fishtail” effect.
Valence band electronic structure of carbon nitride from x-ray photoelectron spectroscopy
Authors: Chen Z. Y. , Zhao J. P. , Yano T. , Ooie T.
Published: July 2002

This article reviews the valence band (VB) electronic structure of carbon nitride and reports on results obtained from carbon nitride films prepared by pulsed laser deposition (PLD). In the present work, two series of carbon nitride films have been synthesized by nitrogen-ion-beam-assisted PLD and reactive PLD in nitrogen atmosphere, respectively. X-ray photoelectron spectroscopy (XPS) is applied to determine the VB electronic structures. XPS VB spectra reveal that the electronic structures of the prepared carbon nitride films depend on nitrogen supply manner. In the case of nitrogen-ion-beam-assisted deposition, four bands in the regions ∼0–6.2, ∼6.2–13.7, ∼13.7–20.8, and ∼20.8–30 eV are clearly observed in the VB electronic structure, which stem from C 2p electrons associated with π bonds and sp2N in a planar graphite structure, C 2p and N 2p electrons associated with σ bonds, a mixture of 2s and 2p electrons, and C 2s and N 2s electrons, respectively. For the films deposited by reactive PLD in a nitrogen atmosphere at room temperature, a new band that results from N lone pairs of β-C3N4 structure appears at ∼5 eV in region ∼1.0–7.4 eV, instead of the band at ∼2.3 eV in region ∼0–6.2 eV in the case of nitrogen-ion-beam deposited films. At elevated deposition temperature, the evolution of carbon nitride films towards amorphous carbon structure is observed. Furthermore, both nitrogen content and substrate temperature have a strong influence on the VB electronic structures of carbon nitride films. The evolution of VB electronic structure is also discussed by relating to the XPS core-level spectra of the carbon nitride films.
Near-criticality in dilute binary mixtures: Distribution of azulene between coexisting liquid and vapor carbon dioxide
Authors: Bronstein Leandro , Fernández Diego P. , Fernández-Prini Roberto
Published: July 2002

The equilibrium distribution of dilute solutes between vapor and liquid coexisting phases of near-critical solvents exhibits a simple dependence on the solvent’s liquid density which extends over a wide temperature range; however, theory predicts this dependence only as an asymptotic limit. In order to test quantitatively the extension of this behavior and compare it with the value predicted from the asymptotic relationship, a novel high-pressure apparatus with a sampling manifold, which avoids perturbing the system during sampling, was used to measure the equilibrium concentrations of azulene in coexisting liquid and vapor carbon dioxide contained in a high pressure sapphire cell. The density and composition of the two phases under equilibrium were determined between 283 and 301 K. The linearity of RT ln KD(KD being the distribution equilibrium constant) in the solvent’s liquid density was verified over the entire experimental temperature range, and the value of the slope was close to that corresponding to the asymptotic description as calculated with the hydrostatic hypernetted chain theory. An explanation for this observation lies in the weak temperature dependence of the Krichevskii function for this system; however a full quantitative description of the observed phenomenon remains a challenge, which should be provided by crossover theory.
Network viscoelastic behavior in poly(ethylene oxide) melts: Effects of temperature and dissolved LiClO4 on network structure and dynamic behavior
Authors: Walter R. , Selser J. C. , Smith M. , Bogoslovov R. , Piet G.
Published: July 2002

The “wet gel” model used earlier to describe the results of dynamic light scattering studies of neat poly(ethylene oxide) (PEO) melts has now been successfully applied to PEO-melt/LiClO4 solutions. The results of static light scattering and viscometry measurements along with measurements from dynamic light scattering revealed that with or without salt, the melt/gel was an overdamped system whose network diffusive relaxations were controlled by the damping liquid component of the gel. Important features of the melt/gel were significantly affected by the addition of LiClO4. Examples of important changes included increases in the network mesh size even as “petrification” of the network by the salt rendered it less elastic. Nevertheless, for 1 K PEO melts the essential nature of the melt/gel remained uneffected.
Investigation of transparent and conductive undoped Zn2In2O5−x films deposited on n-type GaN layers
Authors: Lo Cheng-Yao , Hsu Che-Lung , Yu Qing-Xuan , Lee Hsin-Ying , Lee Ching-Ting
Published: July 2002

Transparent, conductive, multicomponent oxide films composed of undoped Zn2In2O5−x were deposited on n-type GaN layer using rf sputtering. We investigated the dependence of the surface, electrical, and optical properties on the sputtering parameters, including rf power, total pressure, and the post-deposition annealing process. We obtained high transparency (>80% in the visible and near-infrared ranges) and low electrical resistivity (2.58×10−4 Ω cm). Atomic force microscopy and optical transmittance measurements of Zn2In2O5−x films were used to investigate the mechanisms of resistivity variation in the films. The ohmic performances of Zn2In2O5−x contacts to the n-type GaN layer are also demonstrated.
Bessel discrete variable representation bases
Authors: Littlejohn Robert G. , Cargo Matthew
Published: July 2002

Discrete variable representation (DVR) basis sets on the radial half-line, based on Bessel functions, are presented. These are Hankel transforms of the eigenfunctions of the particle in a spherical box in k space, but there is no box or bound on the radial variable r. The grid points extend to infinity on the r axis. The DVR functions are exactly orthonormal and exactly satisfy the interpolation properties usually associated with DVR functions. The exact matrix elements of the kinetic energy are computed, and the use of the Bessel DVR functions in radial eigenvalue problems is illustrated. The phase space or semiclassical interpretation of the Bessel DVR functions is presented, and variations on these functions, corresponding to alternative boundary conditions in k space, are discussed. An interesting feature of Bessel DVR functions is that they are based on a finite basis representation that is continuously infinite.
Photodissociation dynamics of cyclopropane at 157 nm
Authors: Wang Chia C. , Lee Yuan T. , Lin Jim J. , Shu Jinian , Lee Ying-Yu , Yang Xueming
Published: July 2002

Photodissociation dynamics of cyclopropane at 157 nm has been investigated using a new molecular beam apparatus based on vacuum ultraviolet ionization by synchrotron radiation. Four distinct dissociation pathways have been observed. The observed channels are the H formation process, the H2 formation process, the CH2+C2H4 formation process, and the CH3+C2H3 formation process. Experimental results indicate that the H atom products are possibly produced via a synchronous, concerted 2H elimination process, while other channels are all binary dissociation processes. Product kinetic energy distribution of each dissociation channel has been determined from simulating the experimental time of flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products.
Characterization of S centers generated by thermal degradation in SiO2 on (100)Si
Authors: Stesmans A. , Nouwen B. , Pierreux D. , Afanas’ev V. V.
Published: July 2002

The structural degradation of thermal SiO2 on (100)Si under isochronal vacuum annealing in the range Tan=950 °C–1250 °C was monitored by electron spin resonance (ESR) in terms of point defect creation, including Eγ′, Eδ′, EX and the elusive predominant degradation-center S. Depth profiling after heating at 1200 °C shows that the S centers predominantly reside near the oxide borders, generally in anticorrelation with the Eγ′ distribution. The resulting anisotropic demagnetization effect has enabled inference of the S center susceptibility. As to the nature of the S center, an observed weak hyperfine structure may comply with the S center being of the type SinO3−n≡Si⋅ either the single n=1 or a mix of both the n=1,2 variants.
Dispersionless scalar integrable hierarchies, Whitham hierarchy, and the quasiclassical ∂̄-dressing method
Authors: Konopelchenko B. , Martinez Alonso L.
Published: July 2002

The quasiclassical limit of the scalar nonlocal ∂̄-problem is derived and a quasiclassical version of the ∂̄-dressing method is presented. Dispersionless Kadomtsev–Petviashvili (KP), modified KP, and dispersionless two-dimensional Toda lattice (2DTL) hierarchies are discussed as illustrative examples. It is shown that the universal Whitham hierarchy is nothing but the ring of symmetries for the quasiclassical ∂̄-problem. The reduction problem is discussed and, in particular, the d2DTL equation of B type is derived.
Low- and high-mode separation of short wavelength turbulence in dithering Wendelstein 7-AS plasmas
Authors: Basse N. P. , Zoletnik S. , Saffman M. , Baldzuhn J. , Endler M. , Hirsch M. , Knauer J. P. , Kühner G. , McCormick K. , Werner A. ,   W7-AS Team
Published: July 2002

In this article measurements of small scale electron density fluctuations in dithering high confinement (H)-mode plasmas obtained by collective scattering of infrared light are presented. A scan of the fluctuation wavenumber was made in a series of similar discharges in the Wendelstein 7-AS (W7-AS) stellarator [H. Renner et al., Plasma Phys. Control. Fusion 31, 1579 (1989)]. The experimental setup and discharge properties are described. Hα-light observing an inner limiter was used to separate low confinement (L)- and H-mode phases of the plasma; the separated density fluctuations are characterized. It was found that L- (H-) mode fluctuations dominate at high (low) frequencies, respectively, and that they possess well-defined and distinguishable scaling properties. Wavenumber spectra for L- and H-mode measurements are calculated and fitted by power-laws and exponential functions. The separated measurements can be fitted with the same exponents in L- and H-mode. Correlations between the density fluctuations, the Hα-signal and magnetic fluctuations as measured by Mirnov coils were analyzed. Correlation calculations using 50 ms time windows (several dithering periods) with time lag steps of 100 μs showed that all the fluctuating quantities are highly correlated and that the maximum correlation occurs for high frequency density fluctuations. Performing separate L- and H-mode correlations on a 20 μs time scale between magnetic and density fluctuations leads to the result that the minimum correlation time scale in L-mode is of order 100 μs, while no correlation exists for H-mode.
On the oscillator strength sums S(±1) of atoms and ions
Authors: Koga Toshikatsu , Matsuyama Hisashi
Published: July 2002

Using rigorous relations discovered recently, the Hartree–Fock limit values of the dipole oscillator strength sums S(−1) and S(+1) are obtained for the 102 neutral atoms He through Lr, singly charged 53 cations Li+ through Cs+, and 43 stable anions H− through I− in their experimental ground states. The present results for the ionic species are the first compilation of the sums. For heavy neutral atoms, the literature S(+1) values are found to be insufficiently accurate.
Concentration fluctuation in binary polymer blends: χ parameter, spinodal and Ginzburg criterion
Authors: Wang Zhen-Gang
Published: July 2002

A theory for concentration fluctuations in binary polymer blends is developed using field-theoretic techniques. The theory provides a simple, unified framework for addressing a number of important issues. First, consideration of the fluctuation and correlation effects on different length scales leads to a clarification of three different χ parameters and their interrelationship. By incorporating interaction (modeled by the bare χb) and packing effects up to the polymer size, an effective χe emerges as the natural parameter for characterizing the molecular compatibility of the two polymer species. The measured quantity in small-angle neutron scattering (SANS) experiments is an apparent χa that includes long wavelength critical and spinodal fluctuations, and is related to χe through a self-consistent equation. χa exhibits the typical upward parabolic composition dependence observed in experiments and computer simulations. Second, a unified Ginzburg criterion involving both the composition and temperature (or temperaturelike variable) is derived that is applicable to both the critical and the off-critical spinodal regimes. The common characterization of the Ginzburg criterion in terms of a range of temperature (or temperaturelike variable) alone is generally inadequate. The molecular weight scaling proposed by de Gennes and Binder in the respective critical and off-critical spinodal regimes are recovered as special cases in the limit of large molecular weights. For typical molecular weights used in experiments the Ginzburg region is larger than commonly believed. Finally, the nature of the thermodynamic spinodal is examined. It is shown that a true off-critical thermodynamic spinodal does not exist in spatial dimensions less than 4. In its place, a pseudo-spinodal can be defined where the susceptibility reaches a finite maximum. The pseudo-spinodal precedes the mean-field spinodal but approaches the latter in the limit of infinite molecular weights. The pseudo-spinodal correlates strongly with the free energy barrier for nucleation becoming order kT. Thus it provides a kinetic limit for the physically accessible metastable state, beyond which phase separation may exhibit features characteristic of spinodal decomposition. The calculated location of the pseudo-spinodal for two samples used in a recent experiment of Balsara and co-workers agrees with the onset of spinodal-decomposition-like nucleation observed in the experiement.
Temperature dependence of magnetoresistance and nonlinear conductance of the bicrystal grain boundary in epitaxial La0.67Ba0.33MnO3 thin films
Authors: Khare Neeraj , Moharil U. P. , Gupta A. K. , Raychaudhuri A. K. , Pai S. P. , Pinto R.
Published: July 2002

We investigated conduction through an artificial grain-boundary junction made in La0.67Ba0.33MnO3 thin films, deposited on a 36.7° SrTiO3 bicrystal substrate using a laser ablation technique. The grain boundary exhibits substantial magnetoresistance at low temperatures and also shows nonlinear I–V characteristics. Analysis of temperature dependence of the dynamic conductance allows us to identify three carrier transport mechanisms across the grain boundary. These mechanisms exist in parallel, and at a given temperature one mechanism may dominate. Particularly, at higher temperatures (T>175 K) the transport across the grain boundary involves spin–flip scattering, which we establish leads to decrease of the bicrystal grain-boundary contribution in magnetoresistance. At lower temperature (4.2–45 K), tunneling through a disordered oxide at the grain boundary dominates, whereas in the temperature range from 100 to 175 K, carrier transport is dominated by inelastic tunneling via pairs of manganese atoms.
Stability of ZrO2 layers on Si (001) during high-temperature anneals under reduced oxygen partial pressures
Authors: Stemmer Susanne , Chen Zhiqiang , Keding Ralf , Maria Jon-Paul , Wicaksana Dwi , Kingon Angus I.
Published: July 2002

Electron energy-loss spectroscopy and high-resolution transmission electron microscopy were used to investigate ZrO2 layers grown by electron-beam evaporation in a molecular-beam epitaxy system. ZrO2/Si layers were investigated before and after uncapped annealing at 1000 °C under different oxygen partial pressures. The thickness of a SiO2-like, low-dielectric constant layer at the silicon interface was found to depend on the oxygen partial pressure during annealing. At oxygen partial pressures of about 10−4 torr the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO2 layer and silicon consumption at the interface. At oxygen partial pressures in the range of approximately 10−5 torr, only a thin (1 nm) interfacial silicon oxide layer was present, as required for low-equivalent oxide thicknesses of gate stacks incorporating alternative oxides. Further reduction of the oxygen partial pressures (about 10−7 torr) during annealing resulted in zirconium silicide formation at the interface. ZrO2 films annealed at the optimal partial pressure for a thin interfacial oxide were found to crystallize and contain no silicon. High-resolution analytical capabilities afforded by scanning transmission electron microscopy techniques proved essential in analyzing the stability of these ultrathin layers.
Plasma characterization during laser ablation of graphite in nitrogen for the growth of fullerene-like CNx films
Authors: Voevodin A. A. , Jones J. G. , Zabinski J. S. , Hultman L.
Published: July 2002

Chemistry, energy, and spatial distributions of species in carbon–nitrogen plasma plumes were investigated to define plasma conditions for growth of carbon nitride CNx films with a fullerene-like structure. Plumes were generated by ablation of graphite using a 248 nm excimer laser in the presence of low-pressure nitrogen. The plumes were investigated using element specific imaging, time-of-flight experiments, fluorescence spectroscopy, and molecular vibration sequence analyses. Studies showed the importance of plume/substrate interaction in causing secondary excitation phenomena. For N2 pressures within the 5–50 mTorr range, plasmas at the substrate vicinity were found to consist mostly of atomic carbon, CN and C2 molecules. Kinetic energies were calculated within 10–20 eV for mono atomic carbon, 30–55 eV for CN, and 20–40 eV for C2. Excited CN and C2 molecules were generated by laser ablation and by collisions of the plume with the substrate surface. Their vibrational energies were strongly influenced by nitrogen pressure and time after a laser pulse. For pressures below 30 mTorr, vibrational energy was as high as 4.0 eV at 2–4 μs for CN and 2.5 eV at 8–10 μs for C2. This low pressure was suggested for the growth of fullerene-like CNx films based on correlations between plasma parameters and film composition and bonding. Synthesis of the fullerene-like structure required high molecular temperatures at the condensation surface. High concentrations of CN radicals in the plasma promoted nitrogen incorporation into the films. Correlations among CNx film composition/bonding, excitation maximums, and kinetic/vibrational energies of atomic carbon, CN and C2 species located near the condensation surface are discussed.
Structural and electronic properties of Genm− and KGen− Zintl anions (n=3–10;m=2–4) from density functional theory
Authors: Li Si-Dian , Guo Qiao-Ling , Zhao Xiu-Feng , Wu Hai-Shun , Jin Zhi-Hao
Published: July 2002

Structural optimizations and frequency analyses have been performed on free Genm− and KGen− (n=3–10, m=2–4) Zintl anions and ionization potentials and electron affinities calculated for KGen using the density functional theory (DFT) of Becke’s three-parameter hybrid functional with the Perdew/Wang 91 expression. The DFT results obtained for small clusters (n=3–5) are further checked with both the second-order Møller–Plesset perturbation theory (MP2) and the configuration interaction calculations with all single and double substitutions from the Hartree–Fock reference determinant (CISD). Free Gen2− anions are found to share the same geometries as naked Zintl anions observed in solids with a systematical expansion in bond lengths within about 5%. Intensive searches indicate that two isomers, a tricapped trigonal prism (D3h) and a slightly distorted tricapped trigonal prism (C2v), exist for Ge92− and Ge93−, while nido-Ge94− clearly favors the monocapped antisquare prism (C4v) structure. HOMO-LUMO energy gaps >2.23 eV are obtained for Genm− series at the DFT level, except Ge93− which has a much narrower energy gap of 1.16 eV. The calculated Gibbs free energy change of Ge92−+Ge94−=2 Ge93− conversion reaction involving nonagermanides has the value of ΔG°=−2.91×105 J mol−1, providing the first quantum chemistry evidence that the geometrically deduced mixed valent couple of Ge92− and Ge94− in a previous study is thermodynamically unstable compared to two Ge93− anions. The calculated stabilization energies of Gen2−, Gen−, and Gen exhibit similar variation trends, clearly indicating a maximum at n=7, a minimum at n=8, and an obvious recovery at n=9 and 10. The calculated normal vibrational frequencies reproduce the six observed Raman peaks of naked Ge52− with an averaged discrepancy of 11 cm−1. Face-capped or edge-capped deltahedral structures are predicted for binary KGen− anions and KGen and K2Gen neutrals. The magic numbers at n=5, 9, and 10 obtained in both stabilization energies and ionization potentials well reproduce the abundance distributions of KGen− observed in time-of-flight mass spectra. The validity of the Zintl–Klemm–Busmann principle in KGen and K2Gen neutrals is supported by the finding that sizable electron transfers from K atoms to Gen nuclei occur in these clusters and the Gen nuclei approach corresponding structures of free closo-Gen2− anions.
Generalization of cylindrical spheromak solution to finite beta and large reversed shear
Authors: Bellan P. M.
Published: July 2002

The well-known analytic solution for a spheromak in a cylindrical flux conserver is generalized to the situation of finite β with the shape of the flux conserver now being a dependent quantity. Analytic expressions are found for the poloidal flux surfaces, beta, the safety factors at both the magnetic axis and the wall, and the wall profile. A large reversed shear (i.e., ratio of safety factor on magnetic axis to safety factor at the wall) can be obtained at finite beta. This feature may be important because reversed shear in the core of tokamaks has been shown to permit stable operation at high β.
Single molecule tracking scheme using a near-field scanning optical microscope
Authors: Decca R. S. , Lee C.-W. , Lall S. , Wassall S. R.
Published: July 2002

The use of a near-field scanning optical microscope (NSOM) to measure the diffusion of fluorescently tagged molecules on a quasi-two-dimensional system is described. The heart of the apparatus lies in the circular motion of the NSOM probe, allowing the detection of small displacements on single molecules. Using a 100 nm tip, and a simulated diffusion coefficient of D∼1×10−12 m2/s, we found that molecules can be tracked within ∼40 nm over several seconds. We foresee that D as large as ∼5×10−12 m2/s can be measured with minor modifications to the experimental setup. These values of D encompass those found in many liquid crystalline systems, particularly lipids in bilayer membranes.
Rotation sector mounted in front of the screen and outside the vacuum chamber for the observation of reflection high-energy electron diffraction
Authors: Takami Tomohide
Published: July 2002

A fan-type rotation sector, mounted in front of a reflection high-energy electron diffraction (RHEED) screen and between the screen and a camera, was demonstrated to compensate for the intensity of RHEED patterns. The r1/2 sector is preferable for a digital charge-coupled device camera, whereas the r3 sector is suitable for an analog camera.
Hole transport in coupled SiGe quantum dots for quantum computation
Authors: Cain Paul A. , Ahmed Haroon , Williams David A.
Published: July 2002

We describe transport measurements on double quantum dot structures formed by trench isolation in a SiGe:Si heterostructure. Three different device geometries are described, and a number of phenomena are observed. Transport measurements at 4.2 K reveal a carrier energy filtering effect accompanying a period doubling in Coulomb oscillations, showing that tunnel barriers can be raised and lowered by application of a gate voltage. Peak splitting in Coulomb oscillations is also observed at 4.2 K, indicating interdot capacitive coupling. The stability diagram for a double dot is mapped out at dilution refrigerator temperatures. In another device, single hole electrometers are fabricated 50 nm away from a double quantum dot, and the ability to measure a single excess charge on the double dot is demonstrated at dilution refrigerator temperatures.
Influence of interface relaxation on passivation kinetics in H2 of coordination Pb defects at the (111)Si/SiO2 interface revealed by electron spin resonance
Authors: Stesmans A.
Published: July 2002

Electron spin resonance studies have been carried out on the isothermal passivation kinetics in 1 atm molecular H2 of trivalent Si traps (Pbs;Si3≡Si•) at the interface of thermal (111)/Si/SiO2 as a function of oxidation temperature Tox in the range 250–1100 °C. Interpretation within the generalized simple thermal (GST) passivation model, based on first-order interaction kinetics, reveals a distinct increase in spread σEf in the activation energy for passivation Ef with decreasing Tox (∼3 times in the covered Tox window), while the other key kinetic parameters (Ef, preexponential factor) remain essentially unchanged. The variation in σEf is ascribed to differently relaxed interfacial stress, affecting the spread in Pb defect morphology. In a second analytic part, the impact of the variation in Ef, and correlatively in the activation energy Ed for PbH dissociation, on Pb–hydrogen interaction kinetics is assessed within the GST-based full interaction scheme, describing parallel competing action of passivation and dissociation. In particular, the passivation behavior in 1 atm H2 of an initially exhaustively depassivated Pb system, is analyzed exposing, as a major result, that growing spreads σEf, σEd result in a drastic reduction in passivation efficiency (drop by four orders of magnitude for a threefold increase in σEf). For σEf/Ef≳20%, the Pb system cannot be inactivated beyond the 90% level, incompatible with device quality requirements. Heating time/temperature vs spread conditions for optimum passivation in H2 have been established, and the technological impact of altering σEf, σEd is discussed. At film edges and trench corners, which are vulnerable local regions of exces stress, and hence enhanced σEf, σEd, an edge defeat effect with respect to passivation is exposed. Within the relentless scaling of Si-based integrated circuit devices, the growing relative impact of edge regions may jeopardize proper passivation of interface traps in the conventional way in future device generations.