bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural characterization and 90° domain contribution to ferroelectricity of epitaxial Pb(Zr0.35,Ti0.65)O3 thin films
Authors: Saito Keisuke , Kurosawa Toshiyuki , Akai Takao , Oikawa Takahiro , Funakubo Hiroshi
Published: December 2002

Remanent polarizations (Pr) of 200-nm-thick epitaxial Pb(Zr0.35,Ti0.65)O3 (PZT) thin films deposited on (001), (110), and (111) SrTiO3 (STO) substrates coated with SrRuO3 (SRO) were compared to the domain configurations that were precisely and quantitatively characterized by high-resolution x-ray diffraction reciprocal space mapping (HRXRD-RSM). (001)/(100), (101)/(110), and (111) oriented domains were obtained for films grown on (001), (110), and (111) STO substrates coated with SRO, respectively. HRXRD-RSM showed that the films grown on (001) and (110) STO substrates mainly consisted of (001) and (101) domains, although they also included about 32% and 25% of (100) and (110) domain, respectively. Tilt growths in the domains were found except for the (001) domain. The tilt growths in the (100), (101), and (110) domains were attributed to the geometrically induced tilt by the 90° domain that had {101} domain walls. On the other hand, the tilt in the (111) domain was attributed to the misfit strain relaxation by introducing tilt growth in the domain but not due to the 90° domain. The Pr ratios of films having different domain configurations were well explained by the estimated Pr ratios from the volume fractions of the domains, based on the assumption that the 90° domain was not reoriented by the externally applied electrical field and did not contribute to the measured Pr values. This indicates that the 90° domain is strongly pinned in epitaxial 200-nm-thick PZT films and the 180° domain switching is the dominant contribution to the total remanent polarization.
A Phase I and Pharmacokinetic Study of Pegylated Camptothecin as a 1-Hour Infusion Every 3 Weeks in Patients With Advanced Solid Malignancies
Authors: Rowinsky Eric K. , Rizzo Jinee , Ochoa Leonel , Takimoto Chris H. , Forouzesh Bahram , Schwartz Garry , Hammond Lisa A. , Patnaik Amita , Kwiatek Joseph , Goetz Andrew , Denis Louis , McGuire Jeffrey , Tolcher Anthony W.
Published: December 2002

Purpose: To assess the feasibility of administering camptothecin (CPT), the prototypic topoisomerase I inhibitor, as polyethylene glycol (PEG)-CPT, a macromolecule consisting of CPT conjugated to chemically modified PEG. The study also sought to determine the maximum-tolerated dose (MTD) of PEG-CPT, characterize its pharmacokinetic behavior, and seek preliminary evidence of anticancer activity.

Patients and Methods: Patients with advanced solid malignancies were treated with escalating doses of PEG-CPT as a 1-hour intravenous (IV) infusion every 3 weeks. A modified continual reassessment method was used for dose-level assignment to determine the MTD, which was defined as the highest dose level at which the incidence of dose-limiting toxicity did not exceed 20%.

Results: Thirty-seven patients were treated with 144 courses of PEG-CPT at seven dose levels ranging from 600 to 8,750 mg/m2. Severe myelosuppression was consistently experienced by heavily pretreated (HP) and minimally pretreated (MP) patients at the highest dose level evaluated, 8,750 mg/m2, whereas both HP and MP patients tolerated repetitive treatment at 7,000 mg/m2. Cystitis, nausea, vomiting, and diarrhea were also observed but were rarely severe. A partial response was noted in a patient with platinum- and etoposide-resistant small-cell lung carcinoma, and minor responses were noted in one patient each with adenocarcinoma of unknown primary type and osteosarcoma. The pharmacokinetics of free CPT were dose proportional. Free CPT accumulated slowly in plasma, with maximal plasma concentrations achieved at 23 ± 12.3 hours; the harmonic mean half-life (t1/2) of free CPT was long (t1/2, 77.46 ± 36.77 hours).

Conclusion: Clinically relevant doses of CPT can be delivered by administering PEG-CPT. The recommended dose for phase II studies in both MP and HP patients is 7,000 mg/m2 as 1-hour IV every 3 weeks. The characteristics of the myelosuppressive effects of PEG-CPT, the paucity of severe nonhematologic toxicities with repetitive treatment, the preliminary antitumor activity noted, and the slow clearance of CPT enabling simulation of desirable pharmacokinetic parameters with a convenient single-dosing regimen warrant further disease-directed evaluations.
Association of JNK1 with p21waf1 and p53: Modulation of JNK1 activity
Authors: Xue Yue , Ramaswamy Nadja T. , Hong Xiaoman , Pelling Jill C.
Published: December 2002

Exposure of mammalian cells to genotoxic stress results in activation of the c‐jun amino‐terminal kinase (JNK)‐stress‐activated protein kinase (SAPK) pathway and induction of DNA repair enzymes and cell cycle–regulatory proteins such as p53 and p21waf1. The p53 tumor suppressor protein transmits signals that activate p21waf1 gene expression. The p21waf1 protein then restricts cell‐cycle progression, thereby allowing time for DNA repair to occur. In this study, we investigated the effects of modulation of the level of wild‐type and mutant p53 protein on basal JNK1 activity in the A1‐5 rat fibroblast cell line. This cell line contains a p53 gene coding for a temperature‐sensitive p53 protein, which allows us to regulate the relative level of wild‐type and mutant p53 protein produced in cells. Using the immune complex kinase assay to measure JNK1 activity, we demonstrated that cells expressing the wild‐type–conformation p53 protein (when grown at 32.5°C) exhibited a very low level of JNK1 activity. When cells were grown at 37°C or 39°C to express predominantly mutant p53 protein, basal level of JNK1 activity was significantly higher than at 32.5°C. We also demonstrated protein‐protein interactions between the p53, p21waf1, and JNK1 proteins in this cell line. Both wild‐type p53 protein (expressed at 32.5°C) and mutant p53val135 protein (expressed at 37°C and 39°C) were present in immunocomplexes of JNK1 protein. Under conditions where wild‐type p53 protein was present to induce p21waf1 expression (at 32.5°C), a higher level of p21waf1 protein was also detected in the JNK1 immunocomplexes than in those at 37°C and 39°C. We next investigated the effect that co‐association of p53 protein and p21waf1 protein would have on JNK1 activity. We measured basal levels of JNK1 activity in cells expressing wild‐type p53 and p21waf1, or in p21waf1‐null cells, and demonstrated that cells expressing both p53 and p21waf1 proteins exhibited an approximately threefold lower basal level of JNK1 activity when compared with p21waf1‐null cells. To confirm that p21waf1 protein expression in cells resulted in reduced JNK1 activity, we transfected p21waf1−/− cells with a p21waf1 expression vector. We observed that JNK1 activity was inhibited after exogenous p21waf1 protein was expressed in these cells. Our results provide evidence for modulation of the JNK1 pathway by p53 and p21waf1 proteins and support the hypothesis that modulation of JNK1 activity occurred through protein‐protein interactions between JNK1, p53, and p21waf1 proteins. © 2002 Wiley‐Liss, Inc.
Climatic Regionalization and the Spatio-Temporal Occurrence of Extreme Single-Year Drought Events (1500–1998) in the Interior Pacific Northwest, USA
Authors: Knapp Paul A. , Grissino-Mayer Henri D. , Soulé Peter T.
Published: December 2002

Tree-ring records from western juniper (Juniperus occidentalis var. occidentalis Hook.) growing throughout the interior Pacific Northwest identify extreme climatic pointer years (CPYs) (i.e., severe single-year droughts) from 1500–1998. Widespread and extreme CPYs were concentrated in the 16th and early part of the 17th centuries and did not occur again until the early 20th century. The 217-yr absence of extreme CPYs may have occurred during an extended period of low variance in the Pacific Decadal Oscillation. We mapped climatic boundaries for the interior Pacific Northwest based on the location of sites with similar precipitation variability indices. Three regions, the Northwest (based on chronologies from nine sites), the Southwest (four sites), and the East (five sites) were identified. Our results suggest that western juniper radial growth indices have substantial interannual variability within the northwestern range of the species (central Oregon), particularly when compared with western juniper growing in its eastern range (eastern Oregon, southeastern Idaho, and northern Nevada) and southwestern range (southern Oregon and northeast California). We suspect that the substantial differences in the variability of western juniper radial growth indices are linked to the influence of ENSO events on winter/spring precipitation amounts.
Pre‐transmembrane sequence of Ebola glycoprotein
Authors: Sáez-Cirión Asier , Gómara Marı́a J , Agirre Aitziber , Nieva José L
Published: December 2002

The membrane‐interacting domain that precedes the transmembrane anchor of Ebola glycoprotein has been characterized. This aromatic‐rich region is predicted to bind the membrane interface adopting an α‐helical structure. Peptides representing either the Ebola glycoprotein pre‐transmembrane sequence, or a ‘scrambled’ control with a different hydrophobic‐at‐interface moment, have been studied. Insertion into lipid monolayers, changes in intrinsic fluorescence and in infrared spectra demonstrated that only the wild‐type peptide bound the interface under equilibrium conditions and adopted an α‐helical conformation. The presence of the raft‐associated lipid sphingomyelin did not affect membrane insertion, but it stimulated highly the membrane‐destabilizing capacity of the pre‐transmembrane sequence. A parallel study of the effects of the viral sequence and of melittin suggests that Ebola glycoprotein pre‐transmembrane sequence might target membranes inherently prone to destabilization by lytic peptides.
Simultaneous vs. sequential biventricular pacing in dilated cardiomyopathy: an acute hemodynamic study
Authors: Perego Giovanni B. , Chianca Roberto , Facchini Mario , Frattola Alessandra , Balla Eva , Zucchi Stefania , Cavaglià Sergio , Vicini Ilaria , Negretto Marco , Osculati Giuseppe
Published: December 2002

Aims:

Simultaneous biventricular pacing improves left ventricular (LV) systolic performance in patients with dilated cardiomyopathy and intraventricular conduction delay. We tested the hypothesis that further improvements can be obtained using sequential biventricular pacing by optimizing both atrioventricular and interventricular delays.

Methods and results:

In 12 patients, LV pressure, right ventricular (RV) pressure and respective rates of change of pressure (dP/dt) were acutely measured during biventricular pacing with different atrioventricular and interventricular (VVi) intervals ranging from −60 to +40 ms. The average increase vs. baseline in maximum LV dP/dt was higher for sequential than for simultaneous biventricular pacing (VDD mode: 35±20 vs. 29±18%, P<0.01; DDD mode: 38±23 vs. 34±25%, P<0.01), with a minority of patients accounting for most of the difference. The mean optimal VVi was −25±21 ms in VDD mode and −25±26 ms in DDD mode. With these settings, RV dP/dt was not significantly different from baseline. QRS shortening was not predictive of LV dP/dt increase.

Conclusion:

A significant increase of LV dP/dt with no change in RV dP/dt can be obtained by sequential biventricular pacing as compared to simultaneous biventricular pacing. The highest LV dP/dt is achieved when LV is stimulated before RV. The hemodynamic advantage might be of clinical significance in selected cases.
Heat Death in Ancient and Modern Thermodynamics
Authors: Kutrovátz Gábor
Published: December 2002

The notion of Heat Death proves to be very useful for the understanding of the behaviour and evolutionary features of various thermodynamic systems. It is closely related to the problems that motivated the birth of modern thermodynamics, but these problems were already present, in different forms, in the scientific and philosophical theories of the distant past. In this paper, I would like to show that one particular and very influential ancient scientific theory, Aristotle's physics, includes a solution to the problem of Heat Death implicitly, and that this solution can fruitfully be compared with the different solution offered by modern thermodynamics.
On Some Nonlinear Measures of Diabetic Autonomic Dysfunction
Authors: Posiewnik Andrzej
Published: December 2002

Beat-to-beat heart rate was measured for 50 normal and 60 diabetic subjects. Autonomic dysfunction in diabetic subject was assessed by the Ewing test. Next we employed two nonlinear measures of cardiac interbeat interval dynamics: entropy-like measure on AIP diagram, and parameter “forbidden words” for symbolic dynamics. We test their performance in detecting diabetic autonomic dysfunction and show that there is a very significant relationship between the measures and the Ewing score.
War‐related trauma and symptoms of posttraumatic stress disorder among adult Kosovar refugees
Authors: Ai Amy L. , Peterson Christopher , Ubelhor David
Published: December 2002

Since 1999, almost 16,000 Kosovar refugees have entered the United States. Few studies have investigated trauma and symptoms of posttraumatic stress disorder (PTSD) in this population. We conducted a caseworker‐assisted survey of 129 Kosovar refugees (aged 18 to 79 years, 55% male). Of these individuals. 78 (60.5%) showed the likely presence of PTSD. The mean number of war‐related traumatic events reported was 15 (SD = 4.5). Higher PTSD scores were associated with more traumatic events and female gender.
The Expectation Value of the Entropy of a Digital Message
Authors: De Vos Alexis
Published: December 2002

If a message can have n different values and all values are equally probable, then the entropy of the message is log(n). In the present paper, we calculate the expectation value of the entropy, for arbitrary probability distribution. For that purpose, we assume ‘the probability of a probability distribution’ being uniformly distributed over Bhattacharyya's statistical space, i.e. the unitary n-dimensional hyperoctant. After some calculations, this turns out to amount to log(n) − [2 − log(2) − γ] = log(n) − 0.7297…, where γ is Buler's constant.
Polymer crystallization on pre-patterned substrates
Authors: Dorenbos G. , Sommer J.-U. , Reiter G.
Published: December 2002

Several aspects of self-ordering are predicted by Monte Carlo simulations for a model system in which crystallization of polymers on a pre-patterned surface is simulated. The pattern consists of parallel lanes which have alternately a high and low affinity with respect to particle adsorption. Prior to crystallization, an anisotropic melt density profile is established. A nucleus located perpendicular to the lanes acts as a seed where crystallization starts. Initially, the anisotropic melt density profile causes each high affinity lane to crystallize. As time proceeds less crystals will be able to continue to grow. Surviving crystals (1) grow at constant speed, (2) do not switch lanes, and (3) are nonrandomly distributed showing a characteristic intercrystal distance, which is represented by a strongly peaked structure function in the direction perpendicular to the lanes. Besides the self-ordering, we also find that the crystal growth velocity on the patterned substrate is higher than for a nonpatterned substrate. We propose underlying mechanisms to be generally applicable for several growth models.
Wave function penetration effects on current–voltage characteristics of ballistic metal–oxide–semiconductor transistors
Authors: Yunus M. , Haque A.
Published: December 2002

Effects of wave function penetration into the gate oxide on the drain current in ballistic metal–oxide–semiconductor field-effect transistors (MOSFETs) are studied. MOS electrostatics is treated by self-consistent solution of one-dimensional Schrödinger and Poisson equations. Schrödinger equation is solved with an open boundary condition applied at the silicon–gate-oxide interface. Two-dimensional effects and inelastic scattering of carriers are neglected in the drain current calculation. Numerical results show that wave function penetration has nontrivial effects on modeling of the drain current. These effects are found to depend on the silicon surface orientation. In devices fabricated on (100) silicon, drain current and transconductance decrease when penetration effects are considered although the gate capacitance increases in the presence of penetration. On the other hand, in devices on (111) silicon, penetration effects increase the drain current and transconductance. An explanation for the opposite dependence of the penetration effects on surface orientation is provided. It also appears that the use of only the lowest subband to describe MOS electrostatics, as done in some studies, will lead to significant error in the calculation of drain currents.
Optical breakdown in aluminum vapor induced by ultraviolet laser radiation
Authors: Mazhukin V. I. , Nossov V. V. , Nickiforov M. G. , Smurov I.
Published: December 2002

Theoretical analysis of the evolution of nonequilibrium plasma induced by ultraviolet laser radiation is carried out. Intensity threshold values are studied by mathematical modeling as a function of laser-pulse wavelength. Basic mechanisms of nonequilibrium ionization of aluminum vapor are analyzed and the dominant role of photo-processes, namely, resonant and nonresonant photoexcitation and photoionization, is shown. The modeling results are in good agreement with experimental data on optical breakdown in aluminum vapor by the excimer laser radiation in nanosecond and microsecond range.
Onset of long-range diffusion and exponent of 1/fα noise in metal films with electromigration damage
Authors: Kar Swastik , Raychaudhuri A. K.
Published: December 2002

Investigations of low-frequency conductance fluctuations have been done on silver films which have been made to undergo electromigration damage. The system shows a clear increase in noise magnitude after electromigration damage. The noise spectral power shows a distinct presence of 1/f3/2 component arising out of long-range diffusion. The temperature dependence of noise (150 K<T<350 K) shows a marked deviation from the Dutta–Horn type behavior with the 1/f3/2 term showing a strong dominance at higher temperatures. We propose that the increase of noise in metal films after electromigration damage arise predominantly from this spectral component.
Raman investigation of amorphous carbon in diamond film treated by laser
Authors: Wu Qihong , Yu Lin , Ma Yurong , Liao Yuan , Fang Rongchuan , Zhang Ligong , Chen Xiangli , Wang Kelvin
Published: December 2002

Micro-Raman spectroscopy was employed to investigate the structural changes of diamond films prepared by hot filament chemical vapor deposition and treated by femtosecond (fs) laser and nanosecond (ns) lasers. Breit–Wigner–Fano and Lorentzian line shape simulations were used to fit the spectra. For 266 nm ns laser treated samples, increasing laser power density results in the transformation of amorphous carbons in diamond films into nanocarbon clusters whose size increases and saturates rapidly at around 5.1 nm. At the same time, the Raman G peak position considerably shifts upwardly with increasing laser power density. The different change behavior of the nanocarbons and G peak is interpreted in light of the charge transfer from the graphite π bands to the localized edge states. As the 266 nm laser power density is high enough, a Raman peak in the range of 1150–1200 cm−1 appears, which is attributed to the presence of amorphous diamond. In the case of fs laser treated samples, much more power density (>15 TW/cm2) is needed to transform the amorphous carbon into nanocarbon phases. With increasing fs laser power density, the diamond peak is broadened and downshifted due to the presence of nanocrystalline diamond produced by the high laser power density.
Chern–Simons field theories with non-semisimple gauge group of symmetry
Authors: Ferrari Franco
Published: December 2002

The subject of this work is a class of Chern–Simons field theories with non-semisimple gauge group, which may well be considered as the most straightforward generalization of an Abelian Chern–Simons field theory. As a matter of fact, these theories, which are characterized by a non-semisimple group of gauge symmetry, have cubic interactions like those of non-Abelian Chern–Simons field theories, but are free from radiative corrections. Moreover, at the tree level in the perturbative expansion, there are only two connected tree diagrams, corresponding to the propagator and to the three vertex originating from the cubic interaction terms. For such theories it is derived here a set of BRST invariant observables, which lead to metric independent amplitudes. The vacuum expectation values of these observables can be computed exactly. From their expressions it is possible to isolate the Gauss linking number and an invariant of the Milnor type, which describes the topological relations among three or more closed curves.
Vortex instability and time effects in I–V curves of superconducting Y1Ba2Cu3O7−δ
Authors: Kiliç A. , Kiliç K. , Çetin O.
Published: December 2002

We have investigated the effect of the current sweep rate (CSR) on the vortex dynamics in a superconducting bulk sample of Y1Ba2Cu3O7−δ. It has been found that the CSR has several effects on vortex motion in that it gives rise to enhancement of dissipation as the CSR decreases, significant time effects and instabilities in current–voltage (I–V) curves. Those anomalies are discussed in terms of depinning/pinning together with disorder in the coupling strength between the superconducting grains. In addition, for a given field and temperature domain, it is shown that the CSR together and a relevant current scale is of importance in the evolution of I–V curves.
Unipolar transport and shot noise in metal–semiconductor–metal structures
Authors: Gomila G. , Cantalapiedra I. R. , Reggiani L.
Published: December 2002

We carry out a self-consistent analytical theory of unipolar current and noise properties of metal–semiconductor–metal structures made of highly resistive semiconductors in the presence of an applied bias of arbitrary strength. By including the effects of the diffusion current we succeed in studying the whole range of carrier injection conditions going from low level injection, where the structure behaves as a linear resistor, to high level injection, where the structure behaves as a space charge limited diode. We show that these structures display shot noise at the highest voltages. Remarkably the crossover from Nyquist noise to shot noise exhibits a complicated behavior with increasing current where an initial square root dependence (double thermal noise) is followed by a cubic power law.
Molecular orientation dependence of ortho-para conversion of a H2 interacting with a metal surface
Authors: Muhida R. , Miura Y. , Diño W. A. , Kasai H. , Nakanishi H. , Okiji A. , Fukutani K. , Okano T.
Published: December 2002

In order to obtain a general conclusion regarding the steric effect on the ortho-para H2 (o-p H2) conversion on solid surfaces, we investigate the molecular orientation dependence of the o-p conversion of a H2 interacting with a metal surface. Taking the H2-surface electron interaction (Coulomb interaction) and Fermi’s contact interaction as perturbations, our calculation results indicate that the o-p H2 conversion yield for a H2 oriented perpendicular to the surface is larger than that for a H2 oriented parallel to the surface. These results and the conclusion thus obtained generalize the steric effect on the o-p H2 conversion on metal oxide surfaces obtained previously.
On the charge overcompensation of quenched polyelectrolyte stars electrostatically adsorbed onto a quenched oppositely charged planar surface
Authors: Leermakers F. A. M. , van den Oever J. M. P. , Zhulina E. B.
Published: December 2002

We present numerical self-consistent field calculations in a two-gradient cylindrical coordinate system for a (translationally restricted) quenched polyelectrolyte star which is electrostatically attracted to an oppositely charged surface with homogeneous surface charge density at a given ionic strength of a 1:1 electrolyte. The results prove that without any additional driving force for adsorption, electrostatic attraction alone can give significant overcompensation of the surface charge provided that the ionic strength is below some critical value. This is demonstrated for the case that the charge density on the surface is lower than the (projected) charge density in the star. In the regime of charge overcompensation, the thickness of the adsorbed layer is of the order of the star size in solution. The adsorbed layer is laterally inhomogeneous and the outer part of the adsorption profile is locally neutralized by the small counterions.
Local electrostatic effects of surface structure on field emission
Authors: Jaeger D. L. , Hren J. J. , Zhirnov V. V.
Published: December 2002

We examined the classical electrostatic effects due to geometric surface structures on conductive field emission needles numerically using the finite element method and compared our results to several commonly applied analytic relations. Analysis of the morphology of electrochemically prepared Mo needles by high-resolution transmission electron microscopy was incorporated in the numerical analysis in the form of small surface protrusions and gross needle shape. We found that the error between the electrostatic potential defined by popular analytic equations and both analytic equations derived in prolate spheroidal coordinates and finite element method results was significant for ellipsoidal needles with and without surface protrusions. The morphology of the surface protrusion was found to introduce a significant nonlinear potential barrier near the needle surface. Finally we numerically analyzed a nonsymmetric, nonhomogeneous experimental needle indicating that even larger errors in the electrostatic potential can be expected relative to analytic equations.
Quantum mechanical and quasi-classical trajectory study of the C(1D)+H2 reaction dynamics
Authors: Bañares L. , Aoiz F. J. , Honvault P. , Bussery-Honvault B. , Launay J.-M.
Published: December 2002

First accurate quantum mechanical (QM) calculations of integral and differential cross sections for the C(1D)+H2(v=0,j=0,1) insertion reaction have been performed on a newly developed ab initio potential energy surface [B. Bussery-Honvault et al., J. Chem. Phys. 115, 10701 (2001)]. These results have been compared with those obtained with a quasi-classical trajectory (QCT) method. A Gaussian-weighted binning procedure to assign product quantum states in the QCT calculations yields vibrational branching ratios and rotational distributions in better agreement with the QM calculations than those obtained when the usual histogramatic binning method is employed. This is the first time that the Gaussian-weighted binning procedure is used for an insertion reaction.
Beneficial effect of a low deposition temperature of hot-wire deposited intrinsic amorphous silicon for solar cells
Authors: van Veen M. K. , Schropp R. E. I.
Published: December 2002

Hot-wire deposited amorphous silicon is an excellent material for incorporation as the absorbing layer in solar cells. We show the beneficial effect of a low deposition temperature of hot-wire deposited intrinsic amorphous silicon for solar cells. The influence of a few specific deposition parameters on the material properties was investigated. It is shown that both the filament history and the deposition pressure are crucial parameters for the material quality. Optimized material, deposited at 250 °C, was incorporated in efficient single- and multijunction solar cells on flexible stainless steel substrates. The n-i-p structure was used to avoid any influence of TCO- and p-layer degradation, which is otherwise present in p-i-n structures. The cells have a high open-circuit voltage and high fill factor, clearly showing the improved performance of hot-wire deposited amorphous silicon made at moderate temperature.
Ion emission from solid surfaces induced by intense electron beam impact
Authors: Vermare C. , Davis H. A. , Moir D. C. , Hughes T. P.
Published: December 2002

Ions or ionized neutrals released from solid surfaces by electron beam impact can be accelerated and trapped in the beam potential causing beam disruption. Experiments have been performed on the DARHT-I accelerator (1.7 kA, 19.8 MeV, 60 ns) to study this phenomenon. The beam, focused to a range of diameters, was transmitted through thin targets made of various materials. The time evolution of the beam radial profile was measured downstream of the target. For low current density, the downstream-beam radial profile was time invariant as expected for a pure electron beam. At higher current density, the downstream beam was clearly disrupted during the pulse followed by a large-amplitude transverse centroid instability. Two-dimensional calculations using the Lsp particle-in-cell code show that if the space-charge-limiting ion current is allowed to flow after the target surface temperature increases by about 400 K, the main features of the experimental observations are replicated. Three-dimensional Lsp calculations show growth of the ion hose instability at a frequency close to that observed in the experiments.
Statistics, pathways and dynamics of single molecule protein folding
Authors: Wang Jin
Published: December 2002

In this paper, we address the important issue of pathways of protein folding. With the statistical energy landscape theory, the folding can be seen as a chemical reaction process from an ensemble of unfolded states to a unique folded state. The Poissoness (non-Poissoness) of statistics of kinetic populations of unfolded states and folded state can be related to the multiple (discrete) pathways of protein folding. In large populations, the statistical fluctuations are suppressed by the number of molecules in the events. In single molecule experiments, fluctuations in general cannot be ignored and different statistics becomes prominent and detectable. From the analytical study, we find that multiple pathways emerge when the bias towards the folded state is large compared to the fluctuations of the energy landscape funnel and the kinetic population is single exponential in time indicating a Poisson process. On the other hand, when fluctuations or roughness of the landscape dominates, discrete pathways of folding emerge and the kinetic population exhibits nonexponential behavior in time indicating a non-Poisson process. The advances in single molecule detection may provide a good opportunity and a new way of statistical analysis of the kinetic data to resolve the multiple pathway versus discrete pathway issue of protein folding.
What causes the carbon nanotubes collapse in a chemical vapor deposition process
Authors: Qian Weizhong , Wei Fei , Liu Tang , Wang Zhanwen , Li Yongdan
Published: December 2002

The formation of the collapsed carbon nanotubes (CNTs) in a chemical vapor deposition process is studied by intentionally adding some toxic materials (sodium carbonate, sodium phosphate, and calcium chloride) of the catalyst into the CNTs growth system. The distorted CNTs and fully collapsed CNTs are observed as compared to the pristine CNTs with relatively perfect morphology. The yield of carbon decreases and the defects inside the CNTs increase with the increasing addition of these poisonous materials. The characterization by Raman spectroscopy shows that the length of in-plane carbon of these carbon products treated by high temperature decreases nearly linearly with the increasing of the amount of poisonous materials. The formation of the collapsed nanotubes is possibly attributed to the decreased yield of carbon and the significant difference between carbon concentrations when the carbon diffuses from the poisoned part and the unaffected part of metal particles to the precipitation interface for the formation of nanotubes.
Nanostructured Co1−xNixSb3 skutterudites: Synthesis, thermoelectric properties, and theoretical modeling
Authors: Bertini Luca , Stiewe Christian , Toprak Muhammet , Williams Simon , Platzek Dieter , Mrotzek Antje , Zhang Yu , Gatti Carlo , Müller Eckhard , Muhammed Mamoun , Rowe Michael
Published: December 2002

Nanostructured skutterudite Co1−xNixSb3 has been synthesized by chemical alloying with Ni substitution for Co up to 27.5 at. %. High concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials and could thus increase their thermoelectric dimensionless figure-of-merit ZT. Material preparation comprises two key stages, coprecipitation of the precursor, and thermal processing to produce the skutterudite. By modeling the chemistry of the metal ions in aqueous solution, optimum coprecipitation conditions were achieved. The precipitated precursor consists of a solid solution of the different intermediate compounds, and exhibits high reactivity. Calcination and reduction of the precursor resulted in the alloying of these elements and in the formation of skutterudite at a temperature as low as 723–773 K. Unfilled CoSb3 skutterudites were prepared by chemical precipitation from aqueous solutions to achieve powders with a very small grain size (∼40 nm). Compacted samples were produced from this powder by uniaxial pressing under various conditions. Thermal conductivity, electrical resistivity and Seebeck coefficient of the resulting compacts were measured in a temperature range from 150 to 575 K. Measurement procedures were standardized for absolute accuracy and reproducibility between the DLR, Cologne and NEDO, Cardiff Laboratories. It was found that the thermal conductivity can be decreased by almost an order of magnitude at the highest concentration of grain boundaries compared to highly annealed CoSb3. Scanning Seebeck microthermoprobe examination, facilitated spatially resolved measurement of Seebeck coefficient S, providing information on samples’ homogeneity and on its effect on local S. Indications on the formation of an additional Ni containing phase were found. The electronic structure of Ni-doped skutterudites has been investigated by means of fully periodic density functional theory calculations and a topological analysis of the resulting electron densities. Ni substitution for Co doubles the electronic charge transfer from the pnicogen ring to the metal frame and fills the region of the CoSb3 band gap with occupied states, thus explaining the increase of electrical conductivity observed experimentally. The effect of the Ni substitution on the thermal conductivity is analyzed. The computed changes of the cell parameter with rising Ni content differ with those found by x-ray powder diffraction, thereby suggesting that the structural hypothesis of Ni replacing Co in the cubic frame of the skutterudite is only approximate or possibly incorrect.
The contribution of charge exchange ions to cylindrical Langmuir probe current
Authors: Sternovsky Z. , Robertson S. , Lampe M.
Published: December 2002

A theory for the collection of ion current by cylindrical Langmuir probes is presented which includes the effect of charge exchange collisions. These collisions replace ions accelerated into the probe sheath with slower ions having a much greater probability of collection, thus increasing the probe current. The probe ion current increase is obtained from the volume integral of the charge exchange rate weighted by the collection probability. The increase is significant even for plasma with a mean free path of ∼103 Debye lengths. The validity of the model is verified experimentally in an Ar plasma of density ∼107 cm−3 created with a hot cathode discharge. The plasma density measured by microwaves is held constant as the pressure and collision frequency are varied. The charge exchange current, obtained by subtracting the calculated orbit-motion-limited current from the measured net ion current, increases nearly linearly with probe bias and with neutral gas pressure.
On the theory of magnetic phase transitions in magnets with a large single-ion anisotropy
Authors: Kalita V. M. , Loktev V. M.
Published: December 2002

For the example of a system with a ferromagnetic exchange interaction between ions with spins S=1, it is shown that the methods of the phenomenological theory based on the use of a Landau potential can be used for a description of processes of ordering and magnetization of magnets with a large single-ion anisotropy.
Structure and photoluminescence of helium-intercalated fullerite C60
Authors: Legchenkova I. V. , Prokhvatilov A. I. , Stetsenko Yu. E. , Strzhemechny M. A. , Yagotintsev K. A. , Avdeenko A. A. , Eremenko V. V. , Zinoviev P. V. , Zoryansky V. N. , Silaeva N. B. , Ruoff R. S.
Published: December 2002

The intercalation of C60 single crystals with helium is studied by powder x-ray diffractometry. It is established that the intercalation is a two-stage process: octahedral cavities are filled first and then tetrahedral ones, the chemical pressure being negative during both stages. The low-temperature (5 K) photoluminescence spectra of helium-intercalated fullerite C60 are studied for the first time. The presence of helium in lattice voids is shown to reduce that part of the luminescent intensity which is due to the emission of covalently bound pairs of C60 molecules, the so-called “deep traps” with the 0–0 transition energy close to 1.69 eV. The mechanism of the effect of intercalation with helium on the pair formation in fullerite C60 is discussed.
Annealing-induced reversible change in optical absorption of Ag nanoparticles
Authors: Bi Huijuan , Cai Weiping , Zhang Lide , Martin D. , Träger F.
Published: December 2002

Optical absorption of silver nanoparticles dispersed within pores of monolithic mesoporous silica was investigated after annealing in different atmospheres. It has been found that treatment in H2 or N2 induces a strong surface plasmon resonance (SPR) as usually expected, but air annealing results in the disappearance of the SPR, which is contrary to the fact that bulk metal silver is stable and not oxidized in air at above 200 °C. The absence and appearance of the SPR absorption can be controlled through alternate annealing in air and H2 (or N2). Thermodynamic analysis for oxidation of Ag nanoparticles, by additionally considering the surface and curvature effects of a particle, shows the existence of critical particle size. Only when a Ag particle size is smaller than the critical value is the oxidation possible in air at above 200 °C. The optical changes are attributed to the occurrence of the redox of the Ag particles in different atmospheres at a high temperature.
Periodic entrainment of power dropouts in mutually coupled semiconductor lasers
Authors: Buldú J. M. , Vicente Raúl , Pérez Toni , Mirasso Claudio R. , Torrent M. C. , Garcı́a-Ojalvo J.
Published: December 2002

We examine the effect of current modulation in the irregular dropout dynamics exhibited by two mutually coupled semiconductor lasers. Our experimental results show that a weak periodic modulation in the injection current of one of the lasers entrains the power dropouts in a very efficient way. It is also observed that the laser with the highest frequency leads the dynamics independent of which laser is modulated. As a result, the entrainment is anticipative when modulation is applied to the laser with lowest frequency. Numerical simulations of a model based on delay-coupled rate equations successfully reproduce the behavior observed.
Intrinsic electron transport properties of carbon nanotube Y-junctions
Authors: Meunier Vincent , Nardelli Marco Buongiorno , Bernholc J. , Zacharia Thomas , Charlier Jean-Christophe
Published: December 2002

The electron transport properties of three-terminal carbon-nanotube junctions are investigated within the Landauer theory of quantum conductance. Using a realistic tight-binding Hamiltonian, we demonstrate that the experimentally observed rectifying behavior is not an intrinsic property of the junction, but rather of the contact geometry. When semiconducting nanotubes are connected to metallic leads, nontransmitting states are induced at the nanotube–metal interface, leading to asymmetric transmission curves and potentially rectifying behavior of the nanodevice.
Edge-coupled membrane terahertz photonic transmitters based on metal–semiconductor–metal traveling-wave photodetectors
Authors: Shi Jin-Wei , Chu Shi-Wei , Tien Ming-Chun , Sun Chi-Kuang , Chiu Yi-Jen , Bowers John E.
Published: December 2002

Ultra-high-speed photodetectors and printed-circuit antennas construct photonic transmitters. In this letter, we demonstrate a terahertz (THz) photonic transmitter: edge-coupled membrane photonic transmitters based on metal–semiconductor–metal traveling-wave photodetectors, which are fabricated with low-temperature-grown GaAs photoabsorption layers. With a membrane-based and edge-coupled structure, the demonstrated photonic transmitters can eliminate the requirement of Si lenses and attain an over 20 times higher optical-to-THz power conversion efficiency 2×10−4 than vertical illuminated photonic transmitters with Si lenses at the same operation frequency.
Three approaches to calculating the velocity profile of a laminar incompressible fluid flow in a hollow tube
Authors: Neipp C. , Hernández A. , Beléndez T. , Rodes J. J. , Beléndez A.
Published: December 2002

We present three ways of treating the problem of fluid flow in a hollow cylinder. One method involves a differential equation, and the other two involve more physical insight. We discuss the relative advantages of each method.
Interrupted aortic arch in a child with trisomy 5q31.1q35.1 due to a maternal (20;5) balanced insertion
Authors: Martin Donna M. , Mindell Margaret H. , Kwierant Christine A. , Glover Thomas W. , Gorski Jerome L.
Published: December 2002

Complex congenital heart defects (CHD) are associated with a variety of single gene abnormalities and chromosomal rearrangements. Of the various forms of CHD, aortic arch interruption, a conotruncal heart defect, is relatively uncommon. Here we report a male neonate with aortic arch interruption type B, secundum atrial septal defect, perimembranous ventricular septal defect, patent ductus arteriosus, aortic and subaortic stenosis, and trisomy 5q31.1q35.1 resulting from a maternal balanced insertion (20;5). Chromosomal deletions, including deletion 22q11, have been reported with interrupted aortic arch (IAA); however, to our knowledge this is the first report of a trisomy of distal chromosome 5q associated with aortic arch interruption. Here we compare this child's features to other cases of trisomy 5q31.1q35.1, and review other causes of IAA. We conclude that gene dosage in this chromosomal region likely influences aortic arch development. © 2003 Wiley‐Liss, Inc.
What do ratings of cancer‐specific distress mean among women at high risk of breast and ovarian cancer?
Authors: Coyne James C. , Kruus Linda , Racioppo Melissa , Calzone Kathleen A. , Armstrong Katrina
Published: December 2002

Women recruited from a hereditary cancer registry provided ratings of distress associated with different aspects of high‐risk status and genetic testing and completed measures of general psychological distress, emotional and social health, and role functioning. Overall, high‐risk status was rated as more distressing than undergoing genetic testing. Women without a personal history of cancer rated the level of distress associated with a positive test result to be greater than that associated with high‐risk status. In contrast, level of distress associated with a positive test result was not significantly different from that associated with high‐risk status for women with a personal history of cancer. Furthermore, women with a personal cancer history also anticipated that if they had an altered gene associated with increased risk of cancer, it would be less distressing than their diagnosis of cancer had been. Women with the highest ratings of cancer‐related stress were less inclined to obtain testing, but were not more generally distressed or maladjusted. The need to interpret psychological distress and the stressfulness of genetic testing among high‐risk women with respect to relevant comparison data is discussed. © 2002 Wiley‐Liss, Inc.
True hermaphroditism with ambiguous genitalia due to a complicated mosaic karyotype: Clinical features, cytogenetic findings, and literature review
Authors: Modan‐Moses Dalit , Litmanovitch Talia , Rienstein Shlomit , Meyerovitch Joseph , Goldman Boleslaw , Aviram‐Goldring Ayala
Published: December 2002

Abnormal recombination between the X and Y chromosomes during meiosis, occurring outside the pseudoautosomal region, can result in translocation of the SRY gene from the Y to the X chromosome, and consequently in abnormal sexual differentiation, such as the development of 46,XX males or true hermaphroditism. In this report we present clinical, cytogenetic, and molecular‐cytogenetic data of a patient with ambiguous genitalia and true hermaphroditism, who had a unique mosaic karyotype, comprising three different cell lines: 46,XXSRY+, 45,XSRY+, and 45,X. The mosaic karyotype of our patient probably represents two different events: abnormal recombination between the X and Y chromosomes during paternal meiosis, and postzygotic loss of one of the X chromosomes. Replication studies demonstrated that in 80% of the XX cells, the SRY sequence was located on the active X chromosome. This finding suggests nonrandom X inactivation and, together with the presence of the SRY gene, explains the male phenotype of our patient. On the other hand, the presence of the 45,X cell line may have contributed to genital ambiguity. We conclude that fluorescence in situ hybridization (FISH) analysis with SRY probes is highly recommended and allows accurate diagnosis and optimal management in cases of 46,XX hermaphroditism and ambiguous genitalia. © 2002 Wiley‐Liss, Inc.
Hypertrichosis terminalis, gingival hyperplasia, and a characteristic face: A new distinct entity
Authors: Canún Sonia , Guevara‐Sanginés E.G. , Elvira‐Morales A. , Sierra‐Romero Ma. del C. , Rodríguez‐Asbun H.
Published: December 2002

Congenital generalized hypertrichosis terminalis has been described in association with other features as gingival hyperplasia, osteochondrodysplasia, and a dysmorphic face. Bondeson and Miles [1993: Am J Med Genet 47:198–212] described a woman with universal congenital hypertrichosis terminalis associated with gingival hyperplasia; the face of this patient was coarse and different from other forms of hypertrichosis described before. We present an 11‐year, 6‐month‐old girl with universal congenital hypertrichosis terminalis, gingival hyperplasia, and a characteristic coarse face resembling the patient described by Bondeson and Miles [1993: Am J Med Genet 47:198–212]. We propose that this type of congenital generalized hypertrichosis terminalis, associated with gingival hyperplasia and a coarse face, is a distinctive new entity. © 2002 Wiley‐Liss, Inc.