bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous measurement of absorption coefficient, thermal diffusivity, and flow velocity in a gas jet with pulsed photothermal deflection spectroscopy
Authors: Li B. C. , Gupta R.
Published: July 2002

Simultaneous measurement of the absolute optical absorption coefficient or species concentration, thermal diffusivity, and flow velocity in a gaseous medium has been demonstrated by using pulsed photothermal deflection spectroscopy (PTDS) and a multiparameter fitting procedure. The spatial distribution of the three parameters in a laminar flow has been simultaneously determined and the influence of velocity gradient on the measurement has been discussed. Saturation behavior of the PTDS signals was observed and found to influence significantly the fitted results. The saturation influences most significantly the absorption coefficient determination, somewhat less significantly the thermal diffusivity determination, and only negligibly the flow velocity determination. For an absolute and accurate measurement of the absorption coefficient or species concentration, the saturation-induced error has to be corrected by using a model taking into account the effects of the saturation. The influence of saturation on the thermal diffusivity determination can be significantly accounted for by using a simple model in which the pump beam radius is set as a free parameter in the multiparameter fitting procedure. Both multipulse and single-pulse measurements are performed. For multipulse measurement, the estimated measurement uncertainties are ±2% for the flow velocity, and ±5% for the thermal diffusivity and absorption coefficient, while for single-pulse measurement, the estimated uncertainties are ±2% and ±10%, respectively.
Multiwall carbon nanotubes: Self-organization and inhibition of step-flow growth kinetics
Authors: Louchev Oleg A. , Sato Yoichiro , Kanda Hisao
Published: July 2002

In this article the results of a numerical study on the self-organization and inhibition of step-flow growth of carbon nanotubes viewed within the framework of the continuum surface diffusion equation are given. Incorporation constants of C atoms, which differ depending on what side of the step the atom has been chemisorbed prior to incorporation, are considered. These differences can lead to the onset of surface multi-island nucleation in front of a propagating step with decrease in the growth temperature. This effect is able to cause formation of defects in the growing layer and even to inhibit stable step-flow modes of nanotube growth, leading to the formation of misoriented surface nuclei which may be likened to amorphous matter. A diagram distinguishing three characteristic temperature regions for nanotube formation is given: (i) the region where there is no secondary layer nucleation because the surface concentration of adsorbate on the surface of the first layer is not sufficiently high, (ii) the region of successive nucleation and propagation of one layer after another, i.e., stable step-flow growth, and (iii) the region where the nanotube surface is prone to multi-island nucleation, which inhibits stable step-flow growth and causes “amorphization” of the external surface of the nanotube. The simultaneous propagation of multilayer steps coupled by lip–lip interaction is shown to be feasible only if a microkinetic mechanism exists, which effectively redistributes to the edges of internal layers the atoms arriving initially by surface diffusion at the edge of the external layer
Laser printing of active optical microstructures
Authors: Koundourakis G. , Rockstuhl C. , Papazoglou D. , Klini A. , Zergioti I. , Vainos N. A. , Fotakis C.
Published: July 2002

Optically activated indium oxide diffractive optical microstructures are demonstrated through a two step laser based fabrication method. Nonstoichiometric indium oxide thin film material grown by reactive pulsed laser deposition has been selectively transferred onto glass substrates by ultrashort pulse laser microprinting to form surface relief microstructures. Subsequent ultraviolet illumination has induced dynamic refractive index changes, which result in all optical control of the grating diffraction efficiency. The direct materials transfer process enables reproduction of the structural and physical properties of the oxide.
Probing spin currents in semiconductors
Authors: Zhang Shufeng
Published: July 2002

A novel device for spin-current detection in semiconductors, based on the extraordinary Hall effect, is proposed. When a spin current is injected into a nonmagnetic semiconductor, it is found that a transverse electric field, or Hall voltage, is generated. The Hall voltage is proportional to the spin current in the nonmagnetic semiconductor. The proposed device can be used as a tool to investigate the fundamental spin-diffusion length and spin-dependent Hall coefficients in a semiconductor.
Magnetic properties of nanocrystalline Fe3O4 films
Authors: Tang Jinke , Wang Kai-Ying , Zhou Weilie
Published: July 2002

Nanocrystalline magnetite Fe3O4 films of about 180 nm thick have been deposited on Si(100) substrates by pulsed laser deposition. Zero-field-cooled magnetization shows clearly the Verwey transition near 120 K by an abrupt change, which is absent from the field-cooled magnetization. This is correlated to its hysteresis curves where the loops remain open until a high field of 2 T. The magnetization does not saturate in field 2 orders of magnitude higher than its coercive field. Such behaviors may result from the existence of antiphase domains. Antiphase boundaries inside the grains are clearly observed with transmission electron microscopy. Negative magnetoresistance of about 12% has been observed near 120 K in a field of 9 T.
Permeability and giant magnetoimpedance in Co69Fe4.5X1.5Si10B15 (X=Cr, Mn, Ni) amorphous ribbons
Authors: Byon Kwang Seok , Yu Seong-Cho , Kim Cheol Gi
Published: July 2002

The magnetoimpedance (MI) has been measured in the amorphous ribbons of the soft ferromagnetic alloy Co69Fe4.5X1.5Si10B15 (X=Cr, Mn, Ni) as functions of frequency (f ). For all of the three samples, at low frequency, f⩽5 MHz, the MI ratio increases with increasing frequency, but the MI ratio decreases at high frequency, f⩾5 MHz. The MI profiles are not changed at low frequency regions of f⩽1 MHz in the amorphous ribbons. The MI ratio at high frequency of f=5 MHz becomes 57% in Co69Fe4.5Cr1.5Si10B15, but the MI ratio becomes 30% in Co69Fe4.5Mn1.5Si10B15 and Co69Fe4.5Ni1.5Si10B15. The MI ratio at f=10 MHz becomes 45% in Co69Fe4.5Cr1.5Si10B15 and the MI ratio becomes 23% in Co69Fe4.5Mn1.5Si10B15 and Co69Fe4.5Ni1.5Si10B15, respectively. The maximum values of field sensitivity are 2.7(X=Cr), 2.5(X=Mn), 2.2(X=Ni)%/Oe for f=5 MHz.
A general expression of the exact kinetic energy operator in polyspherical coordinates
Authors: Gatti Fabien , Muñoz Claudio , Iung Christophe
Published: July 2002

This paper aims at presenting a general and compact matrix expression of the exact kinetic energy operator in polyspherical coordinates adapted to the study of semirigid molecules. The internal coordinates of an N atom system are expressed by a set of N−1 relative position vectors. The operator can be applied to whatever the set of vectors (Jacobi, Radau, valence, satellite, etc., or a combination of these vectors), and whatever the number of atoms. It includes the rotation and the Coriolis coupling. Such a formulation gives the opportunity to develop a general code for calculating the ro-vibrational spectra in a curvilinear description including all the vibrational, rotational, and Coriolis couplings.
Anatase TiO2 thin films grown on lattice-matched LaAlO3 substrate by laser molecular-beam epitaxy
Authors: Murakami M. , Matsumoto Y. , Nakajima K. , Makino T. , Segawa Y. , Chikyow T. , Ahmet P. , Kawasaki M. , Koinuma H.
Published: July 2002

Epitaxial anatase thin films were fabricated on lattice-matched (−0.2%) LaAlO3 (001) substrates in the layer-by-layer fashion by laser molecular-beam epitaxy. X-ray diffraction and transmission electron microscope show the films to exhibit high crystallinity and atomically defined interfaces. By virtue of the adoption of LaAlO3 substrate, which is transparent to photoexcitation of TiO2, optical band gaps could be determined to be 3.3 eV at room temperature. A photoluminescence band due to recombination of self-trapped excitons was observed at 5 K to give the peak maximum at 2.2 eV. As a result of the high degree of orientation of the epitaxial films, anisotropic optical absorption was clearly observed.
Ab initio potentials and the equation of state of condensed helium at high pressure
Authors: Chang Soon-Yong , Boninsegni Massimo
Published: July 2002

The equation of state of condensed 4He, at room temperature and at pressures between ∼10 and ∼50 GPa, is computed by Path Integral Monte Carlo simulations. Recently proposed, ab initio pair and three-body potentials are utilized. Results are compared to available experimental data, as well as to predictions obtained with two- and three-body potentials used in previous studies. If only two-body interactions are included, the pressure is overestimated by as much as 56% at the highest compression considered here. A relatively modest improvement is offered by the recently developed SAPT over the more commonly adopted Aziz potential. The introduction of three-body forces, modeled using two different potentials, causes instead a significant underestimation of the pressure. In the range of density explored here, agreement with experiment cannot be obtained simply by rescaling the strength of the attractive part of the three-body potential, as had been empirically found in previous work. The results suggest that either four-body terms are more important than previously thought, or, possibly, that the entire approach based on a static potential may be inadequate. Three-body forces are found to have a negligible effect on structural properties and on the single-particle kinetic energy, for which estimates are provided.
Electrolytic formation of nanoapertures for scanning near-field optical microscopy
Authors: Bouhelier A. , Toquant J. , Tamaru H. , Güntherodt H.-J. , Pohl D. W. , Schider G.
Published: July 2002

Aperture probes for near-field optical microscopy were produced by controlled all solid state electrolysis. Control of both the ionic current and light transmission provided reproducible probe tips with aperture diameters in the sub-50 nm range and flat end faces. High resolution scanning near-field optical microscopy images were obtained with these probes. As a by-product, the formation of an electrolytic nanometer-sized contact was observed.
Effects of Nb addition on icosahedral quasicrystalline phase formation and glass-forming ability of Zr–Ni–Cu–Al metallic glasses
Authors: Fan Cang , Li Chunfei , Inoue Akihisa , Haas Volker
Published: July 2002

This work shows that the crystallization process of Zr–Ni–Cu–Al metallic glass is greatly influenced by adding Nb as an alloying element. Based on the results of the differential scanning calorimetry experiments for metallic glasses Zr69−xNbxNi10Cu12Al9 (x=0–15 at. %), the crystallization process takes place through two individual stages. For Zr69Ni10Cu12Al9 (x=0), metastable hexagonal ω-Zr and a small fraction of tetragonal Zr2Cu are precipitated upon completion of the first exothermic reaction. Contrary to this alloy, the precipitation of a nanoquasicrystalline phase is detected when 5–10 at. % Nb is added. Furthermore, the crystallization temperature Tx, supercooled liquid region ΔTx and reduced temperature Tg/TL (Tg is the glass transition temperature, TL the liquidus temperature) increase with increasing Nb content. These results indicate that adding Nb content to Zr–Ni–Cu–Al metallic glasses not only induces quasicrystalline phase formation, but also enhances glass-forming ability.
High-resolution imaging of a single circular surface acoustic wave source: Effects of crystal anisotropy
Authors: Hesjedal T. , Behme G.
Published: July 2002

We present an experimental method for the high-resolution imaging of the excitation and propagation of surface acoustic waves (SAWs) on anisotropic piezoelectric substrates. By employing a scanning acoustic force microscope (SAFM), we are able to image acoustic waves that are excitable by a single circular electrode pair source through the mixing with well-defined reference plane waves. We show amplitude and phase images of the point-source wave field, containing the angular dependence of the phase velocity of these modes, as well as their electromechanical coupling strength. The SAFM allows easy access to acoustic material properties, which are important for the design of commercial SAW devices.
Ultraviolet-infrared optical properties of highly (100)-oriented LaNiO3 thin films on Pt–Ti–SiO2–Si wafer
Authors: Yu J. , Sun J. L. , Meng X. J. , Huang Z. M. , Chu J. H. , Tang D. Y. , Jin C. Y. , Li G. , Li W. Y. , Liang Q.
Published: July 2002

The optical constants of highly (100)-oriented LaNiO3 thin films on Pt(111)-Ti–SiO2–Si substrate derived by metalorganic deposition have been obtained using spectroscopic ellipsometry techniques in the wide wavelength range from ultraviolet to far infrared. In fitting the dielectric functions of LaNiO3, two harmonic oscillators are observed, one is believed to come from the valence–conduction interband transition and the other is attributed to the transition from a donor band to the conduction. Simultaneously the frequency of plasmon is also obtained, which results from the strong electron–electron interaction. Based on these optical and electrical properties, a promising application of LaNiO3 thin films in infrared microsensors has been proposed.
Extreme ultraviolet emission from Xe clusters excited by high-intensity lasers
Authors: Mori M. , Shiraishi T. , Takahashi E. , Suzuki H. , Sharma L. B. , Miura E. , Kondo K.
Published: July 2002

The property of extreme ultraviolet (EUV) generation from Xe clusters irradiated with intense lasers was studied. The Xe cluster jet was well characterized by the interferometric method. In order to obtain the adequate irradiation condition for strong EUV generation, EUV spectra were taken with various laser systems. Then, the wavelength, the pulse width, and the pump energy were widely varied. Through this survey, even with the comparatively low-density Xe jet of ⩽5×1018 cm−3 average atomic density, the highest conversion efficiency of over 10% from laser energy to EUV (5–18 nm) was obtained with a subpicosecond KrF laser pulse, where a 4π source was assumed. This EUV source is considered to be attractive as an EUV lithography light source because of its low average atomic density and small Xe cluster.
Electron energy-loss spectroscopy study of a (LaMnO3)8(SrMnO3)4 heterostructure
Authors: Verbeeck J. , Lebedev O. I. , Van Tendeloo G. , Silcox J. , Mercey B. , Hervieu M. , Haghiri-Gosnet A. M.
Published: July 2002

An epitaxially grown heterostructure consisting of alternating layers of LaMnO3 (8 unit cells) and SrMnO3 (4 unit cells) on a SrTiO3 substrate has been studied by a combination of electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) on an atomic scale. Excitation edges of all elements are captured with subnanometer spatial accuracy, and parametrized to obtain chemical profiles. The fine-edge structure of O K and Mn L2,3 edges are interpreted as signatures of the local electronic structure and show a spatial modulation of the concentration of holes with O 2p character. The chemical concentration is found to be different for the bottom and top interface of a SrMnO3 layer. HRTEM complements the EELS results and confirms the asymmetry of the interfaces.
Time-resolved confocal scanning device for ultrasensitive fluorescence detection
Authors: Böhmer Martin , Pampaloni Francesco , Wahl Michael , Rahn Hans-Jürgen , Erdmann Rainer , Enderlein Jörg
Published: July 2002

A confocal laser-scanning microscope for ultrasensitive fluorescence lifetime imaging on surfaces is presented. The system employs a compact electronics for time-correlated single-photon counting (TCSPC), allowing for measuring fluorescence lifetime with 40 ps time resolution, and for continuously recording photon arrival times with 100 ns time resolution. Additionally developed driver electronics serve for synchronization of scanning and data acquisition, which is significant for achieving high spatial image resolution. The capabilities of the measurement system are demonstrated on imaging single molecules immobilized on glass substrates. Finally, it is shown how the TCSPC capabilities of the system can be used not only for lifetime imaging but also for multichannel measurements.
Inhomogeneous incorporation of In and Al in molecular beam epitaxial AlInGaN films
Authors: Cremades A. , Navarro V. , Piqueras J. , Lima A. P. , Ambacher O. , Stutzmann M.
Published: July 2002

Plasma-induced molecular beam epitaxial AlInGaN heterostructures have been characterized by spatial resolved cathodoluminescence and x-ray energy dispersive microanalysis. Competitive incorporation of Al and In has been observed, with the formation of In-rich regions, showing enhanced luminescence around surface pinholes. These island-like In-rich regions are favored by growth at lower temperature due to the higher incorporation of indium into the alloy. The elastic strain relaxation associated to pinhole formation induces preferential local indium incorporation. The diffusion of carriers to these areas with reduced band gap enhances the luminescence emission of the quaternary film. The width and intensity of the luminescence appear to be sensitive to the mismatch between the quaternary film and the GaN layer below.
Capillary flow in interior corners: The infinite column
Authors: Weislogel M. M.
Published: July 2002

Capillary flow of a sinusoidally perturbed liquid column in an interior corner of infinite extent is solved using lubrication theory. Due primarily to the length scales selected to nondimensionalize the momentum equation, an analytic time scale governing the settling of the perturbation is determined. The time scale, which is shown to be independent of a steady base state flow, proves useful in rapidly predicting transients for surface settling in certain liquid-bearing tanks of spacecraft employing interior corners for fluids management purposes. The asymptotic analysis is extended to address flows along interior corners whose faces are slightly nonplanar. The generalized formulation is presented for the case of a perfectly wetting fluid in a second-order polynomial corner. A leading-order analytic solution for small corner angles is provided. It is shown that a “convex corner” decreases the response time of the liquid and increases the capillary flow rate along the corner by increasing both the driving force and cross-sectional area of the flow. Gravity acting normal to the corner axis along the bisector of the corner angle is also considered and is found to accelerate, decelerate, or destabilize such flows depending on its sign and magnitude.
Schottky diodes with a δ-doped near-surface layer
Authors: Osvald J.
Published: July 2002

The influence of planar δ-doping on effective parameters of Schottky diodes has been studied by simulations of I–V curves within a drift-diffusion approximation. It is shown that an inserted δ layer with the same type of conductivity as that of the base semiconductor material has no significant influence on the effective Schottky diode parameters. The change of the potential barrier shape with the insertion of the δ-doped layer with the same type of conductivity as the base semiconductor material influences the diode current only slightly. On the other hand, significant changes were found for the Schottky diodes with the opposite type of δ-doped layer conductivity compared to the base semiconductor. The resultant barriers and the ideality factors both increase with increasing distance of the δ-doped layer from the metal–semiconductor interface.
Electrokinetic displacement of air bubbles in microchannels
Authors: Takhistov Pavlo , Indeikina Alexandra , Chang Hsueh-Chia
Published: July 2002

Displacement of air bubbles in a circular capillary by electrokinetic flow is shown to be possible when the film flow around the bubble is less than the bulk flow behind it. In our experiments, film flow reduction is achieved by a surfactant-endowed interfacial double layer with an opposite charge from the wall double layer. Increase in the film conductivity relative to the bulk due to expansion of the double layers at low electrolyte concentrations decreases the field strength in the film and further reduces film flow. Within a large window in the total ionic concentration Ct, these mechanisms conspire to induce fast bubble motion. The speed of short bubbles (about the same length as the capillary diameter) can exceed the electro-osmotic velocity of liquid without bubble and can be achieved with a low voltage drop. Both mechanisms disappear at high Ct with thin double layers and very low values of zeta potentials. Since the capillary and interfacial zeta potentials at low concentrations scale as log Ct−1 and log Ct−1/3, respectively, film flow resumes and bubble velocity vanishes in that limit despite a higher relative film conductivity. The bubble velocity within the above concentration window is captured with a matched asymptotic Bretherton analysis which yields the proper scaling with respect to a large number of experimental parameters.
Flat conduction-band alignment at the CdS/CuInSe2 thin-film solar-cell heterojunction
Authors: Morkel M. , Weinhardt L. , Lohmüller B. , Heske C. , Umbach E. , Riedl W. , Zweigart S. , Karg F.
Published: July 2002

By combining ultraviolet and x-ray photoelectron spectroscopy with inverse photoemission spectroscopy, we find that the conduction-band alignment at the CdS/CuInSe2 thin-film solar-cell heterojunction is flat (0.0±0.2 eV). Furthermore, we observe a valence-band offset of 0.8±0.2 eV. The electronic level alignment is dominated by (1) an unusually large surface band gap of the CuInSe2 thin film (1.4 eV), (2) by a reduced surface band gap of the CdS overlayer (2.2 eV) due to intermixing effects, and (3) by a general influence of the intermixing on the chemical state near the interface.
A mass spectrometer system for analysis of polar stratospheric aerosols
Authors: Schreiner J. , Voigt C. , Zink P. , Kohlmann A. , Knopf D. , Weisser C. , Budz P. , Mauersberger K.
Published: July 2002

A balloon-borne mass spectrometer system has been flown successfully to determine the chemical composition of polar stratospheric aerosols over northern Scandinavia. The experiment combines an aerodynamic lens which collimates the aerosols into a narrow beam, a small sphere in which they evaporate, and a mass spectrometer for gas analysis. High-speed differential pumping by two liquid helium pumps effectively lowers the presence of ambient gases without affecting the particles of the beam. Field measurements and aerosol studies inside a large cryo-chamber have shown that the concept of particle focusing, evaporation and subsequent mass spectrometric gas analysis is a reliable technique to determine the molecular composition of aerosols especially in polar stratospheric clouds.
Large remanent polarization and coercive force by 100% 180° domain switching in epitaxial Pb(Zr0.5Ti0.5)O3 capacitor
Authors: Ishida Junichi , Yamada Takatoshi , Sawabe Atsuhito , Okuwada Kumi , Saito Keisuke
Published: July 2002

Pb ( Zr 0.5 Ti 0.5 ) O 3 (PZT) thin film was heteroepitaxially grown on an iridium/magnesium oxide (Ir/MgO) (001) substrate using the metalo-organic decomposition method, and its crystal orientation and ferroelectric properties were investigated. The Ir film by rf-magnetron sputtering on a MgO single crystal showed high crystallinity with the full width at half maximum of 0.2°. The obtained PZT film has a tetragonal structure. Reciprocal space mapping revealed that it consisted of only c-axis orientation. The Ir/PZT/Ir capacitor showed the remanent polarization of 45 μ C/cm2 and a coercive force of 100 kV/cm. These large values were derived from 100% 180° domain switching, which state is difficult to realize in bulky single crystal and ceramics because of piezostress relaxation.
Radial response of individual bubbles subjected to shock wave lithotripsy pulses in vitro
Authors: Matula Thomas J. , Hilmo Paul R. , Storey Brian D. , Szeri Andrew J.
Published: July 2002

Direct measurements of individual bubble oscillations in lithotripsy fields have been performed using light-scattering techniques. Studies were performed with bubble clouds in gassy water as well as single levitated bubbles in degassed water. There is direct evidence that the bubble survives the inertial collapse, rebounding several times before breaking up. Bubble dynamics calculations agree well with the observations, provided that vapor trapping (a reduction in condensation during bubble collapse) is included. Furthermore, the afterbounces are dominated by vapor diffusion, not gas diffusion. Vapor trapping is important in limiting the collapse strength of bubbles, and in sonochemical activity.
Polymorphism in CuInS2 epilayers: Origin of additional Raman modes
Authors: A̧lvarez-Garcı́a J. , Pérez-Rodrı́guez A. , Barcones B. , Romano-Rodrı́guez A. , Morante J. R. , Janotti A. , Wei Su-Huai , Scheer R.
Published: July 2002

CuInS 2 epitaxial films grown on Si(111) substrates at different conditions have been investigated. Transmission electron diffraction shows the coexistence of domains having the Cu–Au and chalcopyrite structure. X-ray diffraction analysis allows the estimation of the relative amount of the phase domains, which is dependent on the growth conditions of the films. The films also present additional modes in the Raman spectra, together with the ones that are chalcopyrite related. The relative intensity of the additional modes directly correlates with the estimated amount of Cu–Au ordered phase. This supports the interpretation that the additional Raman modes are related to Cu–Au ordered domains. Group theory analysis is in agreement with the symmetry of the observed modes. The phonon frequency of the Cu–Au assigned Raman mode is also in excellent agreement with the first-principles frozen-phonon calculations.
Simulation of gallium arsenide electroluminescence spectra in avalanche breakdown using self-absorption and recombination models
Authors: Lahbabi M. , Ahaitouf A. , Abarkan E. , Fliyou M. , Hoffmann A. , Charles J.-P. , Bhuva Bharat L. , Kerns S. E. , Kerns D. V.
Published: July 2002

Light emission from gallium arsenide (GaAs) p–n junctions biased in avalanche breakdown have been modeled over the range of 1.4–3.4 eV. The model emphasizes direct and indirect recombination processes and bulk self-absorption. Comparisons between measured and simulated spectra for sample junctions from custom and commercially fabricated GaAs devices demonstrate that the model is simple, accurate, and consistent with fundamental physical device theory. The model also predicts the junction depth with accuracy.
Femtosecond data storage, processing, and search using collective excitations of a macroscopic quantum state
Authors: Mihailovic D. , Dvorsek D. , Kabanov V. V. , Demsar J. , Forró L. , Berger H.
Published: July 2002

An ultrafast parallel data processor is described in which amplitude mode excitations of a charge density wave are used to encode data on the surface of a 1 T-TaS2 crystal. The data are written, manipulated, and read using parallel femtosecond laser pulse beams, and the operation of a database search algorithm is demonstrated on a two-element array.
Effects of structural memory in protein reactions
Authors: Barabash Yu. M. , Berezetskaya N. M. , Christophorov L. N. , Goushcha A. O. , Kharkyanen V. N.
Published: July 2002

Specific effects of the coupling of protein reactions to slow protein structure dynamics are studied. We focus on accumulation of structural changes produced in consecutive protein cycles and eventually modifying the cycle itself. We showed previously [Christophorov et al., Chem. Phys. 256, 45 (2000); Goushcha et al., Biophys. J. 79, 1273 (2000)] that such an effective interaction between cycles can cause the thresholdlike emergence of a new stable functional state of the protein macromolecule. To elucidate this mechanism, we have performed numerical modeling of the reaction kinetics in a two-state system coupled to diffusion in the corresponding conformational potentials. Specifically, the model is related to the charge separation and recombination processes in photosynthetic reaction centers (RCs). It is shown that the percentage of RCs remaining structurally deformed after recombination, until the next photoexcitation event (“memory-bearing” centers), can be quite low. Nonetheless, under prolonged photoexcitation it is sufficient for driving eventually all the RCs to a state of high charge-separation efficiency. The dependence of this efficiency on quasistationary photoexcitation intensity is pronouncedly hysteretic. The conformation potentials anharmonicity extends the bistability range noticeably, thereby improving RC adaptation properties. Experimental protocols to detect the memory-bearing centers in the RC ensemble are proposed, simulated and tested, disqualifying the electron escape to hypothetical redox traps. The technique proposed can be used in the studies of cooperative effects under repeated cycling of biomolecules.
Magnetic and neutron diffraction studies on PrMnSb2
Authors: Malik S. K. , Chu Z. , Joshi Amish G. , Yang J. B. , Yelon W. B. , Cai Q. , James W. J. , Kamaraju K.
Published: July 2002

Magnetic and neutron diffraction studies have been carried out on PrMnSb2. Magnetization data in the temperature range of 5–400 K show two magnetic transitions: one at ∼175 K attributed to the antiferromagnetic ordering of the Mn moments, and the other at ∼35 K possibly due to the antiferromagnetic ordering of the Pr moments. The magnetization-field isotherms at various temperatures are consistent with the above. Neutron diffraction data obtained at various temperatures can be fitted with a nearly antiferromagnetically coupled Mn moment of ∼3μB at 70 K. At 10 K, moments both on Mn (∼3.5μB) and Pr (∼0.94μB) are ordered antiferromagnetically with small canting angles.
Ionized physical vapor deposition of titanium nitride: A global plasma model
Authors: Tao K. , Mao D. , Hopwood J.
Published: July 2002

A global plasma model for an ionized physical vapor deposition (IPVD) system is described. The model predicts the density of electrons, excited state, Ar and N2, ironized Ar, N2, and Ti, the density of atomic N and N+, and the electron temperature. The computed results are compared to experimental measurements of a titanium nitride IPVD reactor to confirm the validity of the model. The reactor consists of an inductively coupled plasma source that is fed by argon, nitrogen, and sputtered titanium. The dissociation of nitrogen in the discharge is typically found to be in the range of 10%–30%. The electron temperature is 1.8 eV, and the ion density is between 2×1011 and 6×1011 cm−3. The ion density is found to decrease as nitrogen is added to the Ar discharge due to collisional losses associated with molecular states. In the metal mode of operation, the atomic nitrogen density is suppressed by the Ti-rich reactor walls. As the nitrogen flow rate is increased, the target and walls become nitrided and the density of N increases an order of magnitude to 2–4×1012 cm−3. The ionization fraction for the depositing flux of titanium is typically 0.4–0.7. The model is easily adapted to other technologically relevant diffusion barrier layer materials such as WN and TaN.
Radial structure of a low-frequency atmospheric-pressure glow discharge in helium
Authors: Mangolini L. , Orlov K. , Kortshagen U. , Heberlein J. , Kogelschatz U.
Published: July 2002

The spatial structure of a low-frequency atmospheric-pressure glow discharge was studied experimentally. The radial current distribution and discharge light emission were simultaneously measured at different phases during the ac voltage cycle. The glow discharge is formed by a radially propagating ionization wave. We also observed discharge regimes with several current pulses per half cycle corresponding to the successive, spatially separated breakdowns.
Effect of ambient-pressure reduction on multibubble sonochemiluminescence
Authors: Tuziuti Toru , Hatanaka Shin-ichi , Yasui Kyuichi , Kozuka Teruyuki , Mitome Hideto
Published: July 2002

The effect of ambient-pressure reduction on multibubble sonochemiluminescence (MBSCL) is studied experimentally with a luminol solution through measurements of MBSCL intensity as a function of ultrasound irradiation time, applied voltage to a transducer and ultrasonic frequencies to accomplish high efficiency in chemical reactions. From the measurement of ambient-pressure dependence, it is shown that there is an ambient pressure that produces the maximum intensity of the MBSCL and the maximum intensity appears at higher ambient pressure as the applied voltage to the transducer increases. The highest intensity of MBSCL is obtained by appropriate reduction of ambient pressure both for various applied voltages and frequencies. This is caused by both the number of bubbles induced with supersaturation of the gas in a luminol solution and the variation in bubble dynamics.
In-plane control of morphology and tunable photoluminescence in porous silicon produced by metal-assisted electroless chemical etching
Authors: Chattopadhyay Soma , Li Xiuling , Bohn Paul W.
Published: July 2002

Photoluminescent porous silicon (PSi) was produced by Pt-assisted electroless etching of p−-Si (100) in a 1:2:1 solution of HF, H2O2, and methanol. The peak emission wavelength of the PSi could be tuned in the range 500 nm⩽λ⩽600 nm simply by changing the time of etching. The luminescence is sufficiently intense at all wavelengths to be visible by eye. Furthermore, by patterning the metal areas on the surface prior to etching, the luminescence can be controlled spatially. To investigate the relationship among processing variables — principally etch time and spatial proximity to Pt — and morphology, scanning electron microscopy (SEM), true color fluorescence microscopy, and spatially resolved phonon line shape studies were undertaken. SEM images show nanocrystalline features in the region where the luminescence originates, a region which shifts spatially as a function of etch time, as indicated by fluorescence microscopy. Raman scattering measurements of the shift and broadening of the longitudinal optical phonon band interpreted in the context of the phonon confinement model were used to estimate crystallite sizes. As with the luminescence, the crystallite sizes were found to vary as a function of distance from the Pt patterned area and etch time. These results are interpreted in light of an etching mechanism in which H2O2 reduction results in hole injection deep into the valence band, which then drifts spatially and plays a critical role in determining the rate at which Si is removed from the surface.
Ag nanoparticle induced surface enhanced Raman spectroscopy of chemical vapor deposition diamond thin films prepared by hot filament chemical vapor deposition
Authors: Roy D. , Barber Z. H. , Clyne T. W.
Published: July 2002

Surface enhanced Raman spectroscopy was performed by depositing Ag particles by dc sputtering on thin diamond films prepared by hot filament chemical vapor deposition. Enhancement of Raman signal by a factor up to 100 could be obtained by controlling the Ag particle size. Raman spectra from different locations through the thickness of diamond films indicate a variation in the carbon structures. Phonon density of states of diamond and graphite are considered along with previously reported observations, to analyze the additional bands which appear in the SERS scattering as a consequence of the presence of the Ag particles.
High-efficiency green phosphorescence from spin-coated single-layer dendrimer light-emitting diodes
Authors: Markham J. P. J. , Lo S.-C. , Magennis S. W. , Burn P. L. , Samuel I. D. W.
Published: July 2002

We demonstrate very high-efficiency green phosphorescence from a single-layer dendrimer organic light-emitting diode formed by spin-coating. A first generation fac-tris(2-phenylpyridine) iridium cored dendrimer doped into a wide-gap 4,4′-bis(N-carbazole) biphenyl host displays a peak external quantum efficiency of 8.1% (28 Cd/A) at a brightness of 3450 Cd/m2 and a current density of 13.1 mA/cm2. A peak power efficiency of 6.9 lm/W was measured at 1475 Cd/m2 and 5 mA/cm2. We attribute this exceptionally high quantum efficiency for a single-layer device to the excellent film forming properties and high photoluminescence quantum yield of the dendrimer blend and efficient injection of charge into the emissive layer. These results suggest that dendrimers are an effective method for producing efficient phosphorescent devices by spin-coating.
Vaporization thermodynamics of MgB2 and MgB4
Authors: Brutti S. , Ciccioli A. , Balducci G. , Gigli G. , Manfrinetti P. , Palenzona A.
Published: July 2002

The vaporization behavior of MgB2 and MgB4 under thermodynamic conditions has been studied by the Knudsen effusion-mass spectrometry technique. In the temperature range explored (883–1154 K), magnesium borides are observed to decompose by loss of gaseous Mg only. The equilibrium pressures of Mg(g) have been measured during high-temperature decompositions involving MgB2/MgB4 and MgB4/MgB7 two-phase mixtures and the corresponding standard reaction enthalpies were determined. The decomposition temperatures for MgB2 and MgB4 were also inferred by the relevant Van’t Hoff plots.
Formation of a single interface-near, δ-like Ge nanocluster band in thin SiO2 films using ion-beam synthesis
Authors: Klimenkov M. , von Borany J. , Matz W. , Grötzschel R. , Herrmann F.
Published: July 2002

The possibility to create a δ-like, interface-near Ge nanocluster band in a 20 nm thin SiO2 layer by ion-beam synthesis is demonstrated. The role of the post-implantation annealing conditions for the formation of Ge nanoclusters in the center of the layer, near the interface, or in both regions is discussed. The presence of hydrogen in the annealing atmosphere accelerates the redistribution of Ge in SiO2. By applying a two-step annealing process, preannealing in hydrogen containing atmosphere at low temperature followed by a rapid thermal annealing at high temperature, the controlled fabrication of a single δ-like, interface-near Ge nanocluster band was achieved. In some clusters 〈100〉 lattice planes of Ge were observed. From this and the similar contrast situation for amorphous clusters it is concluded that the interface-near clusters consist of elementary germanium.
Improved efficiency by a graded emissive region in organic light-emitting diodes
Authors: Ma Dongge , Lee C. S. , Lee S. T. , Hung L. S.
Published: July 2002

Electrical and optical properties of organic light-emitting diodes (OLEDs) with a stepwise graded bipolar transport emissive layer for a better control of charge transport and recombination are presented. The graded bipolar transport layer was formed by co-evaporating a hole-transporting material N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) and an electron-transporting/emissive material tris-(8-hydroxyquinoline) aluminum (Alq3) in steps, where each step has a different concentration ratio of NPB to Alq3. Compared to a conventional heterojunction OLED, electroluminescence efficiency was enhanced by a factor of more than 1.5, whereas the turn-on voltage remained unchanged in the graded structure.
Laser diode structure for the generation of high-power picosecond optical pulses
Authors: Vainshtein Sergey , Kostamovaara Juha , Shestak Larisa , Sverdlov Mikhail , Tretyakov Vladimir
Published: July 2002

A laser diode structure is designed and tested that permits the generation of high-power (∼100 W) picosecond-range optical pulses. Direct current pumping is used with a current pulse duration of a few nanoseconds and a current amplitude of ∼105 A/cm2. The main distinguishing feature of the structure is separation of the electron injector (p–n junction) from the active region by a potential barrier. The optical gain in the active region is controlled by the transverse electric field, which is determined by the magnitude of the current at each instant. The design allows emission wavelength control by means of band gap engineering.
Phenomenology of boiling: A coupled map lattice model
Authors: Yanagita Tatsuo
Published: July 2002

A minimal model for boiling is proposed. With increasing temperature of a bottom plate, the model shows three successive phases; conduction, nucleate, and film boiling. In the nucleate regime the heat flux increases with the temperature of the bottom plate, while it decreases in the film boiling regime. In the boiling phase, the maximum Lyapunov exponent is positive, implying that the boiling phenomena are spatiotemporally chaotic.
Thermal heat reservoirs via Gauss’ principle of least constraint; Dissipation, chaos, and phase-space dimensionality loss in one-dimensional chains
Authors: Hoover William G. , Posch Harald A. , Campbell Luke W.
Published: July 2002

We use Gauss’ principle of least constraint to impose different kinetic temperatures on the two halves of a periodic one-dimensional chain. The thermodynamic result is heat flow, as predicted by the Second Law of Thermodynamics. The statistical-mechanical result can be either a phase-space limit cycle or a strange attractor, depending on the chain length and the size of the temperature difference. We document the sensitivity of the Lyapunov spectrum and the underlying phase-space topology by varying the chain length and the size of the kinetic-temperature difference.
Effect of an externally applied electric field on excitation propagation in the cardiac muscle
Authors: Pumir Alain , Plaza Frédéric , Krinsky Valentin I.
Published: July 2002

Classical theory of potential distribution in cardiac muscle (cable theory) postulates that all effects of electric field (internally or externally applied) should decay exponentially with a space constant of the order of the tissue space constant (∼1 mm). Classical theory does not take into account the cellular structure of the heart. Here, we formulate a mathematical model of excitation propagation taking into account cellular gap junctions. Investigation of the model has shown that the classical description is correct on the macroscopic scale only. At microscopic scale, electric field is modulated with a spatial period equal to the cell size (Plonsey and Barr), with the zero average. A very important new feature found here is that this effect of electric field does not decay at arbitrary big distances from the electrode. It opens the new way to control the excitation propagation in the cardiac muscle. In particular, we show that electric field can modify the velocity of propagation of an impulse in cardiac tissue at arbitrary big distances from electrode. In 2-dimensions, it can make rotating waves drift. To test these predictions, experiments with cardiac preparations are proposed.
Regular and chaotic motions in applied dynamics of a rigid body
Authors: Beletskiĭ V. V. , Pivovarov M. L. , Starostin E. L.
Published: July 2002

Periodic and regular motions, having a predictable functioning mode, play an important role in many problems of dynamics. The achievements of mathematics and mechanics (beginning with Poincaré) have made it possible to establish that such motion modes, generally speaking, are local and form ‘‘islands’’ of regularity in a ‘‘chaotic sea’’ of essentially unpredictable trajectories. The development of computer techniques together with theoretical investigations makes it possible to study the global structure of the phase space of many problems having applied significance. A review of a number of such problems, considered by the authors in the past four or five years, is given in this paper. These include orientation and rotation problems of artificial and natural celestial bodies and the problem of controlling the motion of a locomotion robot. The structure of phase space is investigated for these problems. The phase trajectories of the motion are constructed by a numerical implementation of the Poincaré point map method. Distinctions are made between regular (or resonance), quasiregular (or conditionally periodic), and chaotic trajectories. The evolution of the phase picture as the parameters are varied is investigated. A large number of ‘‘phase portraits’’ gives a notion of the arrangement and size of the stability islands in the ‘‘sea’’ of chaotic motions, about the appearance and disappearance of these islands as the parameters are varied, etc.
Threshold, excitability and isochrones in the Bonhoeffer–van der Pol system
Authors: Rabinovitch A. , Rogachevskii I.
Published: July 2002

Some new insight is obtained for the structure of the Bonhoeffer–van der Pol system. The problems of excitability and threshold are discussed for all three types of the system classified according to the existing attractors: a focus only, a limit cycle only and a limit cycle together with a focus. These problems can be treated by the T-repellers and the T-attractors of the system which are mutually reciprocal under time inversion. The threshold depends on the structure of the T-repeller (unstable part of integral manifold). This structure is then used to understand the behavior and the properties of the two different types of isochrones: Winfree isochrones (W-isochrones) and regular isochrones. Winfree’s description of a W-isochrone is extended to excitable systems. Both W-isochrones and regular isochrones are calculated for the Bonhoeffer–van der Pol system in its limit cycle and excitable regimes. The important role of the T-repeller as an asymptotic limit for both types of isochrones is manifested.
Evaluation of the smoothed interference pattern under conditions of ray chaos
Authors: Virovlyansky A. L. , Zaslavsky G. M.
Published: July 2002

A ray-based approach has been considered for evaluation of the coarse-grained Wigner function. From the viewpoint of wave propagation theory this function represents the local spectrum of the wave field smoothed over some spatial and angular scales. A very simple formula has been considered which expresses the smoothed Wigner function through parameters of ray trajectories. Although the formula is ray-based, it nevertheless has no singularities at caustics and its numerical implementation does not require looking for eigenrays. These advantages are especially important under conditions of ray chaos when fast growing numbers of eigenrays and caustics are the important factors spoiling applicability of standard semiclassical approaches already at short ranges. Similar factors restrict applicability of some semiclassical predictions in quantum mechanics at times exceeding the so-called “logarithm break time.” Numerical calculations have been carried out for a particular model of range-dependent waveguide where ray trajectories exhibit chaotic motion. These calculations have confirmed our conjecture that by choosing large enough smoothing scales, i.e., by sacrificing small details of the interference pattern, one can substantially enhance the validity region of ray theory.
Elastic stiffness and thermal expansion coefficient of boron nitride films
Authors: Williams D. S.
Published: July 2002

The temperature-dependent stress of boron-nitride (BN) films deposited by low-pressure chemical vapor deposition was measured using an optically leveraged laser apparatus. The measurements were used to calculate values of E/1−ν and α for BN as a function of the NH3/B2H6 ratio. Values of E/1-ν≂1×1012 dynes/cm2 and α≂5×10−6  °K−1 were obtained independent of the NH3/B2H6 ratio. The intrinsic-stress and the thermal-stress contributions to the room-temperature stress were estimated for different substrates and the values were used to rationalize the strong dependence of the room temperature stress on chemical vapor deposition processing variables.