bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the relative proportion of ferromagnetic and charge-ordered phases on the metal–insulator transition temperature in La0.5Ca0.5Mn1−xGexO3
Authors: Li Run-Wei , Sun Ji-Rong , Wang Zhi-Hong , Zhang Shao-Ying , Tang Ning , Shen Bao-Gen
Published: July 2002

Magnetic and transport properties of rare-earth manganites La0.5Ca0.5Mn1−xGexO3 with 0⩽x⩽0.1 have been investigated systematically. Doping Ge at Mn sites increases the metal–insulator transition temperature (TP) from 124 to 210 K with increasing x from 0 to 0.08. The introduction of Ge severely destroys the charge-ordered state and hardly affects the ferromagnetic ordering. For low-doped samples, TP is also increased dramatically by the magnetic field, especially in the field-cooled mode. Magnetic analysis suggests the coexistence of the charge-ordered antiferromagnetic phase and the ferromagnetic phase. We propose that the proportion of the ferromagnetic phase and the charge-ordered phase can affect TP in phase-separated compounds. The phase diagram of La0.5Ca0.5Mn1−xGexO3 with 0⩽x⩽0.1 is presented.
Be-enhanced CdSe island formation in CdSe/ZnSe heterostructures
Authors: Keim M. , Korn M. , Seufert J. , Bacher G. , Forchel A. , Landwehr G. , Ivanov S. , Sorokin S. , Sitnikova A. A. , Shubina T. V. , Toropov A. , Waag A.
Published: July 2002

The Be-enhanced formation of CdSe quantum dots in CdSe/ZnSe heterostructures grown by migration enhanced epitaxy on (001)GaAs substrates has been investigated using photoluminescence spectroscopy, x-ray techniques (diffraction and reflectometry), and transmission electron microscopy. Coverage of the ZnSe starting surface with a fractional monolayer of beryllium selenide leads to enhanced island formation well below the CdSe thickness of 0.6 monolayer corresponding to the onset of the CdSe-rich island formation in the Be-free structures. The effect of the fractional Be coverage is demonstrated by observation of sharp lines in the photoluminescence signal from patterned mesas with dimensions down to 60 nm, which is due to the emission from individual exciton localization sites attributed to quantum dots. X-ray diffraction and reflectometry measurements on CdSe/ZnSe short-period superlattices with the submonolayer CdSe insertions confirm an enhanced roughening of the CdSe layer morphology in the case of beryllium coverage. Cross-sectional transmission electron microscopy on the SLs with BeSe fractional monolayer exhibits Cd-induced stress modulation along the CdSe sheets with a lateral scale of ∼4 nm, that can also be interpreted in favor of the BeSe-nucleated CdSe-based quantum dots.
Ion-assisted deposition of MoSx films from laser-generated plume under pulsed electric field
Authors: Fominski V. Yu. , Nevolin V. N. , Romanov R. I. , Smurov I.
Published: July 2002

The thickness profiles and compositional distributions of MoSx films deposited from a plume generated by pulsed laser irradiation of the MoS2 target were investigated at a varying fluence and constant laser pulse energy. It was shown that films with stoichiometric composition were formed at sufficiently low fluence (near the ionization threshold), and increasing fluence caused intricate nonmonotonic variations of the compositional distribution. A substantial deviation of the film composition from stoichiometric and a significant radial gradient of the sulfur concentration over the substrate surface (1<x<3, where x is the ratio of concentrations of S and Mo atoms, x=S/Mo) were found. These phenomena were caused by: (1) the incongruent target evaporation; (2) the mass dependence of the angular distribution of the ablated particles; and (3) the selective sulfur sputtering and desorption induced by energetic particles (ions, excited atoms) of the laser-generated plume. When the laser fluence was low, films of stoichiometric composition were bombarded by energetic particles with a low intensity, and the number of displacements was inadequate for formation of the basal-oriented structure (≪1 displacement per atom). Raising the laser fluence, it is possible to increase the bombardment dose; however, the effect of the factors (1)–(3) has turned the selection of optimal conditions for stoichiometric film deposition into a rather complicated problem. A new technique is proposed for pulsed laser deposition of high-purity MoSx films with varying sulfur concentration and the required ion-irradiation dose. The technique consists in accelerating the ion component of the plume by a pulsed electric field up to an energy of a few tens of kilo-electron-volts, thus making it possible to significantly increase the number of displaced atoms in the MoSx film without noticeable change in its composition and to induce ion mixing at the MoSx-substrate interface. The positive voltage pulse of up to 100 kV amplitude was applied to the target during the plume expansion from the target towards the substrate which was grounded. The modification of the MoSx films by accelerated ions resulted in noticeable improvement of their lubrication performance.
Photoinduced processes in Sn-doped silica fiber preforms
Authors: Chiodini N. , Ghidini S. , Paleari A. , Brambilla G. , Pruneri V.
Published: July 2002

Effects induced by KrF ultraviolet excimer laser on Sn-doped silica fiber performs were analyzed by means of optical and electron paramagnetic resonance (EPR) techniques. Bond breaking in substitutional Sn sites was evidenced by the Sn–E′ EPR signal due to sp3 unpaired electrons in threefold coordinated Sn sites. Red photoluminescence excited at 633 nm, due to nonbridging-oxygen sites, was also observed after laser exposure. The intensity of this emission did not follow the Sn concentration profile, being observed at the core–cladding interface and in the core center. Birefringence data showed that these effects are accompanied by stress relief in the Sn-doped region. Different structural features of core and cladding were evidenced by micro-Raman measurements and related to the observed photosensitivity.
Size dependence of the exchange bias field in NiO/Ni nanostructures
Authors: Fraune M. , Rüdiger U. , Güntherodt G. , Cardoso S. , Freitas P.
Published: July 2002

NiO/Ni wires have been investigated as a function of their width in order to investigate the size dependence of exchange bias. The samples have been prepared by e-beam lithography and ion milling of ion beam sputtered thin films. For NiO/Ni wires narrower than 3 μm, the exchange bias field significantly depends on the wire width. A NiO/Ni film shows an exchange bias field of −78 Oe whereas the exchange bias field of wires narrower than 200 nm is reduced to approximately −40 Oe. The coercive field of the NiO/Ni film is 28 Oe and increases to 210 Oe for the narrowest wires. The decrease of the exchange bias field for the narrowest wires is consistent with a recent microscopic model of exchange bias where the appearance of a unidirectional anisotropy in ferromagnet/antiferromagnet bilayers has been attributed to the presence of antiferromagnetic domains in the bulk of the antiferromagnet. A possible onset of a transition from a multidomain to a single-domain state of the antiferromagnet as a function of the NiO/Ni wire width seems to be the origin for the observed decrease of the exchange bias field for narrow wires.
Quantum wavepacket method for state-to-state reactive cross sections
Authors: Althorpe Stuart C.
Published: July 2002

We present a 3D quantum wavepacket method for calculating state-to-state reactive cross sections for the A+BC→AC+B reaction. The method avoids the coordinate problem (of A+BC arrangements being difficult to represent by AC+B coordinates, and vice versa) by solving the reactant-product decoupling (RPD) equations [T. Peng and J. Z. H. Zhang, J. Chem. Phys. 105, 6072 (1996)] in their further partitioned form [S. C. Althorpe, D. J. Kouri, and D. K. Hoffman, J. Chem. Phys. 107, 7816 (1997)]. These equations decouple the nuclear dynamics Schrödinger equation into separate reactant, strong-interaction, and product regions, permitting different coordinates to be used in each region. We solve the equations using A+BC Jacobi coordinates in the reactant region, and AC+B Jacobi coordinates in the strong-interaction and product regions. In test calculations on the J=0 H+H2 reaction, we show that this partitioning of coordinate systems is much more efficient than using A+BC coordinates in the strong-interaction region (as was done in all previous applications of the RPD equations). We apply the method to the H+H2 reaction (for J=0–24), and obtain the first state-to-state differential cross sections to be calculated by an exact quantum wavepacket method. The method will allow state-to-state cross sections to be calculated for the same reactions for which wavepacket methods can currently calculate total cross sections.
Effect of uniaxial stress on the electromechanical properties of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals and ceramics
Authors: Viehland D. , Powers J.
Published: July 2002

The electromechanical performance characteristics of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 ceramics and 〈001〉-oriented crystals have been investigated under uniaxial stress (σ). The results demonstrate that 〈001〉-oriented crystals have an electromechanical coupling coefficient of ∼0.9 for σ less than 4×107 N/m2. The results also demonstrate that the acoustical energy density of ceramics and 〈001〉-oriented crystals are not significantly different at field levels below 15 kV/cm.
Temperature and partial oxygen pressure role on the electrical conductivity of Bi12Ti0.7Ga0.3O20 single crystal
Authors: Lanfredi S. , Carvalho J. F. , Hernandes A. C.
Published: July 2002

The electrical conduction properties of Bi12Ti0.7Ga0.3O20 (BTGaO) single crystal was investigated by impedance spectroscopy. The measurements were performed in the range of 100–400 °C and in a frequency range of 5–1.3×107 Hz. The effect of partial oxygen pressure on the electric conductivity was investigated from 1 to 10−6 atm. The data are presented in a Nyquist diagram plot, from which the electric resistance was determined. The electric conductivity follows the Arrhenius law, with an activation energy of 0.55 eV. The change in conductivity caused by oxygen pressure showed that BTGaO is a p-type semiconductor, according to the relation σ α PO2+1/4. The dielectric constant value was equal to 50. The dielectric behavior of BTGaO does not depend on the temperature and the partial oxygen pressure.
Stopping cross sections for 0.3–2.5 MeV protons in GaN and InP
Authors: Ahlgren T. , Rauhala E.
Published: July 2002

The stopping cross sections of the III–V semiconductor materials GaN and InP for 0.3–2.5 MeV H1 have been studied by the Rutherford backscattering technique. The data are given with an estimated uncertainty better than 2% and the agreement with earlier data existing for InP below 500 keV is good. A commonly used model ZBL-85 predicts the data correctly at the high energy end of our energy interval, but overestimates the stopping values by 7% and 4% for GaN and InP, respectively, at the lower energies.
Conformation-dependent environments in folding proteins
Authors: Fernández Ariel
Published: July 2002

We introduce a semiempirical approach to ab initio prediction of expeditious pathways and native backbone geometries of proteins folding under in vitro renaturation conditions. The algorithm incorporates a discretized codification of local steric hindrances which constrain the movements of the peptide backbone. Thus, torsional motion is shown to be conditioned by the hopping from one basin of attraction (R-basin) to another in the Ramachandran map or local potential energy surface associated with each residue. Rather than simulating detailed dynamics, we simulate the time evolution of such torsional constraints. The semiempirical potential needed to obtain geometric realizations of such “modulo R-basin” topologies is rescaled with each iteration of the simulation in order to incorporate the role of conformation-dependent local environments. Thus, the extent of local desolvation within which a specific interaction occurs is computed for each iteration using an effective local “solvophobic field” determined by two-body interactions emerging from the previous iteration. The predictive power of the algorithm is established by (a) computing ab initio folding pathways for mammalian ubiquitin that yield a stable structural pattern reproducing all of its native features in spite of some adverse local propensities associated with those features when taken in isolation; (b) determining the nucleating event that triggers the hydrophobic collapse of the chain; and (c) comparing coarse predictions of stable folds of moderate size proteins (N∼100) with structures from the Protein Data Bank.
Ionic distribution around simple B-DNA models. III. The effect of ionic charge
Authors: Abascal José L. F. , Montoro Juan Carlos Gil
Published: July 2002

The effect of the ionic charge on the ionic distribution around a simple B-DNA model at the continuum solvent level is investigated using Monte Carlo simulation. In the model, the DNA shape is approximated by a set of simple geometric elements with charges at the canonical phosphate positions. Three series of simulations for an infinitely diluted polyion with added salt have been carried out. In each of them the ionic strength is kept constant. At low ionic strength, the behavior of monovalent, divalent, and trivalent cations is studied. It is shown that the number of counterions within the grooves depend only weakly on its valence so the fraction of DNA charge canceled out at small distances increases with the charge of the cation. This results in a deeper penetration of the coions, which, for systems with highly charged counterions as a 3:1 salt, may even surpass the bulk concentration in the vicinity of the polyelectrolyte. Nevertheless, no overscreening of the DNA charge has been observed in this system. On the contrary, the charge reversal phenomenon appeared in the simulations at high ionic strength irrespective of the ionic valences. It seems that this feature occurs when the bulk concentration of the mobile ions is of the same order as the local concentration in the vicinity of DNA with no added salt. Finally, the competition between monovalent and divalent cations is studied at concentrations close to those of biological media. It is shown that the divalent cations push the monovalent ions out of the DNA surroundings even if their concentration is much lower.
Development of a Blumlein based on helical line storage elements
Authors: Singal V. P. , Narayan B. S. , Nanu K. , Ron P. H.
Published: July 2002

A Blumlein based on helical line storage elements was conceived and developed for generation of a rectangular pulse of 150 kV, 5 μs duration and which can drive a load of about 1 kΩ impedance. The helical line consisting of an aluminum tube of 750 mm length and 100 mm diam, wound with mylar film insulation to withstand 200 kV and then wound with copper wire was built and tested in our laboratory. It has a capacitance of 1.2 nF and has a characteristic impedance of 2 kΩ. The pulse generator built here, uses ten such coils in Blumlein configuration with five elements in parallel in each section giving total capacitance of about 10 nF. It has the advantages of compactness, simplicity, low cost, reliability, and high performance towards good flat top, low rise time, and small jitter. It can be designed to match load impedances in the range of a few ohms to several kilo ohms. This pulse power system was built and successfully tested for accelerating electrons in the gun chamber of an electron beam controlled CO2 laser operating in the single shot mode. This article describes the design, fabrication, and performance of the pulse power system.
Low propagation losses of an Er:Y2O3 planar waveguide grown by alternate-target pulsed laser deposition
Authors: Korzenski M. B. , Lecoeur Ph. , Mercey B. , Camy P. , Doualan J.-L.
Published: July 2002

We report on waveguiding properties in epitaxial Er:Y2O3 films grown by pulsed-laser deposition on sapphire [0001] substrate. Characterization of the as-grown films by x-ray diffraction, atomic force microscopy, and Rutherford backscattering revealed that the films were highly crystalline and textured along the [111] direction and possessed an average surface roughness of 2 nm for a 0.69-μm-thick film. The investigation of the emission spectra confirms the proper structural position for the Er3+ ions in the Y2O3 matrix and that the films guide optical waves along the entire length (5 mm) of the film yielding a propagation loss of <1 dB/cm at 800 nm.
Inelastic electron tunneling spectroscopy measurements using adjustable oxide-free tunnel junctions
Authors: Zimmerman Darin T. , Agnolet Glenn
Published: July 2002

We report an adjustable, oxide-free tunnel junction for inelastic electron tunneling spectroscopy that is capable of detecting the vibrational modes of molecules adsorbed on clean metal surfaces. In this article, we describe the details of these junctions and the procedure by which the tunneling data is obtained and analyzed. We also describe a compact He4 cryostat that was built to test the properties of these junctions. The performance of the junctions is demonstrated with tunneling data taken with a neon–hydrogen film adsorbed on platinum.
Stress-stimulated luminescence from ZnAl2O4:Mn
Authors: Matsui Hiroaki , Xu Chao-Nan , Tateyama Hiroshi
Published: July 2002

We have investigated the stress-stimulated luminescence (SSL) from ZnAl2O4:Mn. Two kinds of ZnAl2O4:Mn samples were synthesized at different reduction conditions to clarify the influence of the structure defects on the SSL property. The SSL intensity was found to be greatly increased by reducing ZnAl2O4:Mn at a high temperature of 1300 °C. The luminescence integrated intensity was about two magnitudes larger than that of conventional ZnAl2O4:Mn. This enhancement is attributed to a large number of trapped carriers in the reduced ZnAl2O4:Mn from the results of thermoluminescence. The SSL spectrum was consistent with the photoluminescence spectrum as well as the afterglow one. It is suggested that the trapped carriers can be excited by stress, and the resultant recombination between excited electrons and holes give rise to an energy which can be transferred to Mn2+ centers to create emission according to the transitions of T14 to A16.
Theory and simulation of the available volume for adsorption in a chain molecule templated porous material
Authors: Cheng Songyin , Van Tassel Paul R.
Published: July 2002

Molecular templating offers a means of tailoring the pore space geometry of disordered materials. We present here a theoretical description of the available volume (porosity) for adsorption created by chain molecule templates. Our model material is a quenched, equilibrated hard-sphere/tangent hard-sphere chain mixture configuration with the chain molecules removed. We extend a diagrammatic theory [P. R. Van Tassel, Phys. Rev. E. 60, R25 (1999)], previously used for a hard-sphere template, to this system and obtain the required correlation functions from the polymer Percus–Yevick theory of a sticky two-point associating fluid mixture within an ideal chain approximation. We also apply Monte Carlo simulation. We find that the available volume increases with template length and that this is most pronounced for a small chain length (n⩽4), a large template:matrix ratio, and a large adsorbate size.
Matrix effects on the mobility of oxygen atoms in different states
Authors: Ning Xi-Jing , Qin Qi-Zong
Published: July 2002

The trapping site structures for ozone molecules isolated in Xe matrices are simulated by a technique of time-going-backwards, showing that single substitutional sites are the most probable. Based on this understanding, molecular dynamics simulations of ultraviolet photolysis of O3 molecules in Xe matrices are carried out for various trapping sites for temperatures of 10, 20, and 30 K. By examining thousands of trajectories, we found that the photolysis quantum yield in Xe matrices is about ten times higher than that in Ar matrices, and solid Xe can serve as atomic sieve for selecting oxygen atoms in the D1 state. Our theoretical results are essentially in agreement with the available experimental data.
Element-specific imaging of magnetic domains at 25 nm spatial resolution using soft x-ray microscopy
Authors: Fischer P. , Eimüller T. , Schütz G. , Denbeaux G. , Pearson A. , Johnson L. , Attwood D. , Tsunashima S. , Kumazawa M. , Takagi N. , Köhler M. , Bayreuther G.
Published: July 2002

The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb25(Fe75Co25)75 layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined.
First physics results from the MAST Mega-Amp Spherical Tokamak
Authors: Sykes A. , Ahn J.-W. , Akers R. , Arends E. , Carolan P. G. , Counsell G. F. , Fielding S. J. , Gryaznevich M. , Martin R. , Price M. , Roach C. , Shevchenko V. , Tournianski M. , Valovic M. , Walsh M. J. , Wilson H. R. ,   MAST Team
Published: July 2002

First physics results are presented from MAST (Mega-Amp Spherical Tokamak), one of the new generation of purpose built spherical tokamaks (STs) now commencing operation. Some of these results demonstrate, for the first time, the novel effects of low aspect ratio, for example, the enhancement of resistivity due to neo-classical effects. H-mode is achieved and the transition to H-mode is accompanied by a tenfold steepening of the edge density gradient which may enable the successful application of electron Bernstein wave heating in STs. Studies of halo currents show that these less than expected from conventional tokamak results, and measurements of divertor power loading confirm that most of the power flows to the outer strike points, easing the power handling on the inner points (a critical issue for STs).
Computational study of molecular hydrogen in zeolite Na–A. II. Density of rotational states and inelastic neutron scattering spectra
Authors: MacKinnon Jennifer A. , Eckert Juergen , Coker David F. , Bug Amy L. R.
Published: July 2002

Part I of this series [J. Chem. Phys. 111, 7599 (1999)] describes a simulation of H2 adsorbed within zeolite Na–A in which a block Lanczos procedure is used to generate the first several (9) rotational eigenstates of H2, modeled as a rigid rotor, and equilibrated at a given temperature via Monte Carlo sampling. Here, we show that rotational states are strongly perturbed by the electrostatic fields in the solid. Wave functions and densities of rotational energy states are presented. Simulated neutron spectra are compared with inelastic neutron scattering data. Comparisons are made with IR spectra in which rotational levels may appear due to rovibrational coupling.
A simple optical patternator for evaluating spray symmetry
Authors: Ullom M. J. , Sojka P. E.
Published: July 2002

An optical instrument for measuring spray patternation in research and quality control applications is described. The instrument uses a light sheet generated by a diode laser and collimating lens to probe the spray throughout a plane perpendicular to its centerline. After passing through the spray, the light sheet is condensed onto a linear array detector, corrected for laser power fluctuations using a reference photodiode detector, and then used to measure extinction by the spray. The instrument was used to collect spray patterns from gas turbine atomizers (pressure-swirl and airblast), residential pressure-swirl atomizers, and consumer product trigger sprayers (pressure-swirl) in order to demonstrate its performance. Examples from consumer product and gas turbine pressure-swirl sprays are presented to illustrate the versatility of the patternator, along with the speed and ease with which spray pattern information can be obtained. Results demonstrate that the instrument provides simple, fast, high-resolution patternation data for the quality control of sprays and spray processes. It could be easily combined with a forward light diffraction based particle-sizing instrument to determine spatial mass variations throughout symmetric sprays.
Polarizable dielectric model of solvation with inclusion of charge penetration effects
Authors: Cossi Maurizio , Rega Nadia , Scalmani Giovanni , Barone Vincenzo
Published: July 2002

An approximate method, recently proposed to include in continuum solvation models the effects of electronic charge lying outside the solute cavity, has been adapted and implemented in the framework of the polarizable continuum model (PCM). This formulation exploits all the features already developed for the other PCM versions; it provides molecular free energies, gradients and second derivatives with respect to nuclear coordinates. The performances of this method have been tested in comparison with other PCM versions, in particular, we examined the reliability of this technique to reproduce actual volume charge distribution effects, compared to traditional procedures based on Gauss’ Law.
Neutral atom temperature and flow measurements in the edge region of the Alcator C-mod tokamak
Authors: Welch B. L. , Weaver J. L. , Griem H. R. , Noonan W. A. , Terry J. , Lipschultz B. , Pitcher C. S.
Published: July 2002

Spectral line shifts have been observed in the Dα transition of neutral deuterium in the Alcator C-mod [I. H. Hutchinson, Proceedings of the IEEE 13th Symposium on Fusion Engineering (IEEE, Piscataway, 1990), Vol. 1, p. 13] tokamak and interpreted as Doppler shifts due to a neutral flow of approximately 5×103 m/s. The emission originates from plasma at the inner wall, as indicated by the Zeeman patterns of the transition. The direction of the flow changes when the plasma transitions from a limited to a diverted configuration. In all cases, the flows are directed toward the point of contact with the wall or divertor plate. Narrow spectral profiles have been observed for the Dα transition near the midplane and within the divertor. Temperatures not higher than 0.86 eV are indicated for the divertor measurements. A difference in plasma conditions for separate locations along a single line of sight has been observed.
Piezo- and pyroelectricity of a polymer-foam space-charge electret
Authors: Neugschwandtner Gerhard S. , Schwödiauer Reinhard , Bauer-Gogonea Simona , Bauer Siegfried , Paajanen Mika , Lekkala Jukka
Published: July 2002

Charged closed-cell polypropylene polymer foams are highly sensitive and broadband piezoelectric materials with a quasistatic piezoelectric d33 coefficient about 250 pC/N and a dynamic d33 coefficient of 140 pC/N at 600 kHz. The piezoelectric coefficient is much larger than that of ferroelectric polymers, like polyvinylidene fluoride, and compares favorably with ferroelectric ceramics, such as lead zirconate titanate. The pyroelectric coefficient p3=0.25 μC/m2 K is small in comparison to ferroelectric polymers and ferroelectric ceramics. The low density, small pyroelectric coefficient and high piezoelectric sensitivity make charged polymer foams attractive for a wide range of sensor and transducer applications in acoustics, air-borne ultrasound, medical diagnostics, and nondestructive testing.
Diode-less operation of a resonantly charged repetitive high voltage pulser circuit
Authors: Biswas Dhruba J. , Nilaya J. Padma
Published: July 2002

We report here that the unique geometry of the rotating dielectric spark gap allows the diode-less operation of a command resonant charging pulser network. An average power of about 3.5 kW with a peak value of 75 MW was switched at a repetition rate of 600 Hz into a dummy load resembling a typical TEA CO2 laser.
IUPAC-NIST Solubility Data Series. 74. Actinide Carbon Compounds
Authors: Hála Jiri , Hála Jiri , Navratil James D.
Published: July 2002

This volume presents solubility data of the carbonates, salts of carboxylic acids, and other carbon containing compounds of actinides. Covered are compounds of thorium, uranium, neptunium, plutonium, americium, and one system for curium. No solubility data on carbonates or other carbon containing compounds have been found for other actinide elements. The literature has been covered up to the end of 1999, and there was a great effort to have the literature survey as complete as possible. Only those published results that report meaningful data were considered for the volume. Papers that reported qualitative results with statements like “sparingly soluble” or “insoluble,” etc. were not considered. In addition to papers that published numerical data, some papers that presented data in graphical form only were considered as well. They were considered for the volume either if no other data were available for the system, if the data were published in difficult to obtain older literature, or if the data were considered to be of importance for other reasons. For many compounds it was not possible to provide the Chemical Abstracts Registry Numbers since these have not yet been assigned. For this reason, the Registry Number index is incomplete.
Large dynamic range technique for magnetoacoustic measurements
Authors: Gavenda J. D. , Foegelle Michael D.
Published: July 2002

We show how the acoustic transmission through a specimen, measured as a function of frequency, can be Fourier transformed to the time domain to yield magnetoacoustic data quite similar to those produced by the conventional pulse-echo technique. Because continuous waves are employed, very precise measurements can be made over a wide dynamic range.
Telescopic refractive index gradient diagnostic of an ion diode anode plasma
Authors: Knyazev B. A. , Greenly J. B. , Hammer D. A. , Krastelev E. G. , Cuneo M. E.
Published: July 2002

We present a general analysis of possible variants of refractive index gradient (RING) diagnostics with a laser beam probe. Using a differential bicell photodiode as a detector, the sensitivity, dynamic range, and geometric restrictions of RING deflectometry have been found for lensless, one lens, and “three-telescope” optical schemes. The three-telescope method is found to be the most flexible and easily aligned. If the refracted/deflected laser beam cross section in the back focal plane of the output lens is also recorded using a fast framing camera, measurements of the beam deflection and its spatial frequency spectrum after passing through the refractive medium can be obtained simultaneously. A general relation is presented between the Fourier transform of a Gaussian beam by the output lens and the spatial frequency spectrum of the inhomogeneities. From these considerations, we present the specific design of a RING diagnostic for study of anode plasma evolution in a magnetically insulated ion diode on the Cornell Beam Research Accelerator (COBRA) (800 kV, 80 ns pulse). The maximum density gradient was found to be located about 0.4 mm from the anode surface at the peak of the diode voltage pulse. The electron density at this position was about 2×1015 cm−3. The transverse spatial frequency distribution of the probe laser beam after passing through the anode plasma was recorded using the optical Fourier transform technique. This experiment demonstrates that the combined integrated deflection. (RING) and Fourier transform optical techniques can give a great deal of information about this thin (∼1 mm) anode plasma layer.
Experimental observation of ion-acoustic waves in an inhomogeneous dusty plasma
Authors: Liang Xiaoping , Zheng Jian , Ma J. X. , Liu W. D. , Xie Jinlin , Zhuang Ge , Yu C. X.
Published: July 2002

The propagation of a dust-ion-acoustic wave (DIAW) wave down the steep density gradient in an inhomogeneous diffusive dusty plasma is experimentally studied. It is observed that the presence of the dust enhances the plasma inhomogeneity. The phase velocity of the DIAW increases rapidly with distance and becomes supersonic. The interplay between the effects of the density nonuniformity and collisional damping results in the continuous transition of the relative amplitude of the DIAW from damping to growth. The experimental data are in agreement with theoretical prediction and confirm the importance of density-dependent ion–dust collisions.
Measuring the camber deformation of a dragonfly wing using projected comb fringe
Authors: Song Deqiang , Wang Hao , Zeng Lijiang , Yin Chunyong
Published: July 2002

The camber deformations of the flapping insect wing provide important information for lift force analysis. Recent measurements are nearly all based on the hypothesis of the rigid wing, neglecting the camber deformation. In this article, a measurement system based on fringe pattern projection is introduced. Projected comb fringes, whose intensity function is near a comb function, were used instead of conventional sine fringes because of their high intensity and sharpness, allowing us to take the distorted fringes on the transparent dragonfly wing easily. The camber deformation and torsion angle of a flapping dragonfly wing can be measured without hypothesizing that the wing is a rigid plate. The experimental result shows that the camber deformation is different during upstroke and downstroke. It is very important for the explanation of the lift force.
Responsive biomimetic hydrogel valve for microfluidics
Authors: Yu Qing , Bauer Joseph M. , Moore Jeffrey S. , Beebe David J.
Published: July 2002

A biomimetic hydrogel valve capable of directional flow control in response to the local fluid environment in microfluidic channels is described. The valve consists of a pair of photopolymerized hydrogel bistrips with different pH sensitivities, and becomes activated or deactivated reversibly based on local pH as a result of volume and shape changes. When activated at pH 8, the valve mimics anatomic venous valves both functionally and structurally, allowing fluid flow in one direction under forward pressure while restricting flow in the opposite direction. At an applied pressure of 0.71 psi, the forward flow rate was 140 μL/min, compared to a backward leakage rate of 2.3 μL/min.
Nonlinear phenomena in hybrid Couette flow composed of planar and circular shear
Authors: Kobine J. J. , Mullin T.
Published: July 2002

Results are presented from an experimental investigation of a novel shear flow. Two parallel sections of planar Couette flow are connected by two semicircular sections of circular Couette flow to give a flow domain with the shape of a running track. Driving the flow with a moving inner boundary leads to centrifugal instability in the curved regions as in conventional Taylor–Couette flow. This is in contrast to the planar regions, which are linearly stable and are characterized instead by finite-amplitude instability. In the steady regime, the entire flow field is dominated by structures akin to Taylor vortices. The mechanism of exchange between a four-cell and a six-cell flow over a range of aspect ratio is qualitatively the same as for the standard Taylor–Couette problem. In the unsteady regime, the flow is characterized by various spatiotemporal modes, the selection of which is dependent on the manner of flow evolution. Quasistatic increase of the Reynolds number from zero typically results in flow with a banded spatial structure and low-dimensional dynamics, both of which are associated with instability in the semicircular regions. However, an abrupt step-like increase of Reynolds number produces a persistent flow state with strong spatial disorder and a broadband dynamical spectrum. The results of this study have implications for the conventional distinctions between the properties of open and closed flows, and suggest the possibility of intermediate flows which are worthy of investigation in their own right.
Hollow cathode ion lasers for deep ultraviolet Raman spectroscopy and fluorescence imaging
Authors: Storrie-Lombardi M. C. , Hug W. F. , McDonald G. D. , Tsapin A. I. , Nealson K. H.
Published: July 2002

This article describes the development of hollow cathode ion lasers and their use in constructing an ultraviolet micro-Raman spectrograph with native fluorescence imaging capability. Excitation at 224.3 nm is provided by a helium–silver hollow cathode metal ion laser and at 248.6 nm by a neon–copper hollow cathode metal ion laser. Refractive microscope objectives focus chopped continuous wave laser light on a sample and collect 180° scattered photons. Imaging is accomplished by broadband visible illumination and by deep ultraviolet laser induced excitation of visible wavelength native fluorescence in untagged micro-organisms. This makes possible a detection strategy employing rapid imaging with laser excitation to locate regions of native fluorescence activity, followed by deep ultraviolet resonance Raman spectroscopy of the identified fluorescent sites. We have employed this probe for in situ detection of micro-organisms on mineral and soil substrates. We present here the deep ultraviolet resonance Raman spectra for the gram negative iron reducing bacterium Shewanella oneidensis obtained while the micro-organism remains in situ on the unpolished surface of the mineral calcite and in a Mars soil analog, JSC1. In the current configuration the in situ mineral surface limit of detection for fluorescence is one organism in 2×104 μm2 field of view and of order 20–30 micro-organisms for Raman spectra. For the Mars soil sample analog fluorescent target selection gives an effective ultraviolet resonance Raman spectral detection limit of 6×104cells/gm or ∼60 ppb.
Quenching of excited P11 state atomic zinc by molecular nitrogen: A matrix-isolation spectroscopy/quantum chemical calculation study
Authors: Colmenares Fernando , McCaffrey John G. , Novaro Octavio
Published: July 2002

A concentration study is used to identify the optical absorption of zinc atoms isolated in solid nitrogen. Photoexcitation of the threefold-split, atomic 4p 1P1 singlet absorption band did not produce any emission from either the singlet or triplet states. Hartree–Fock (relativistic effective core potentials) plus variational and multireference perturbational configuration-interaction calculations are performed to analyze this very efficient quenching of excited state atomic zinc by molecular nitrogen. Of the two geometries considered in energy calculations of the approach of Zn(1P1) to N2, the collinear exhibited a slightly greater stabilization than the perpendicular approach. However, the collinear is identified as of no significance in the excited state quenching due to the absence of low energy crossings with the ground state. In contrast, for the perpendicular approach a crossing between the repulsive ground A11(1S0) state and the strongly attractive B12(1P1) state occurs close to the energy minimum of the B12 state. The efficiency of crossing between these states is analyzed in the framework of one-dimensional Landau–Zener (LZ) theory. A hopping probability of 0.07 is obtained for a single crossing, considered important in a rapidly relaxing solid state system, such as present in a low temperature matrix. Crossings found between the repulsive B31(3P1) and A31(3P1) states with the strongly bound B12(1P1) state are expected to play a role in gas phase Zn(1P1) quenching leading to the production of Zn(3PJ) states. LZ calculations indicate a small hopping probability for these crossings, consistent with the small P11→3PJ quenching cross sections observed in the gas phase work.
Surface alignment bistability of nematic liquid crystals by orientationally frustrated surface patterns
Authors: Kim Jong-Hyun , Yoneya Makoto , Yamamoto Jun , Yokoyama Hiroshi
Published: July 2002

We demonstrate a robust in-plane bistability of liquid-crystal surface alignment based on tailored submicrometer-sized surface domains imposing a frustrated alignment. By a nanorubbing technique utilizing the atomic force microscope, we prepared an orientational checkerboard pattern on polyimide layer, consisting of square unit domains on which the alignment is locally constrained to be planar yet orthogonal between the neighboring domains. Due to the four-fold rotational symmetry of the pattern, the two diagonal axes of the square domain become equally stable directions for the macroscopic liquid crystal alignment. The alignment could be switched between these two states by an in-plane electric field above a certain threshold, determined by the local azimuthal anchoring.
Phase transitional behavior and piezoelectric properties of the orthorhombic phase of Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals
Authors: Lu Yu , Jeong D.-Y. , Cheng Z.-Y. , Zhang Q. M. , Luo Hao-Su , Yin Zhi-Wen , Viehland D.
Published: July 2002

We report on the observation of an orthorhombic ferroelectric phase in 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals, whose polarization is along 〈011〉 direction and stability can be altered by poling conditions. We studied the piezoelectric properties on poled 〈011〉 crystals, in both monodomain and polydomain states, and found that the piezoelectric d32 coefficient, which is the piezoelectric response in perpendicular to the poling direction, is positive in both cases. Based on the phenomenological theory, we show that this is possible in a crystal with the electrostrictive coefficients Q11>Q44–Q12.
Dissociation kinetics of metal clusters on multiple electronic states including electronic level statistics into the vibronic soup
Authors: Shvartsburg Alexandre A. , Siu K. W. Michael
Published: July 2002

Modeling the delayed dissociation of clusters had been over the last decade a frontline development area in chemical physics. It is of fundamental interest how statistical kinetics methods previously validated for regular molecules and atomic nuclei may apply to clusters, as this would help to understand the transferability of statistical models for disintegration of complex systems across various classes of physical objects. From a practical perspective, accurate simulation of unimolecular decomposition is critical for the extraction of true thermochemical values from measurements on the decay of energized clusters. Metal clusters are particularly challenging because of the multitude of low-lying electronic states that are coupled to vibrations. This has previously been accounted for assuming the average electronic structure of a conducting cluster approximated by the levels of electron in a cavity. While this provides a reasonable time-averaged description, it ignores the distribution of instantaneous electronic structures in a “boiling” cluster around that average. Here we set up a new treatment that incorporates the statistical distribution of electronic levels around the average picture using random matrix theory. This approach faithfully reflects the completely chaotic “vibronic soup” nature of hot metal clusters. We found that the consideration of electronic level statistics significantly promotes electronic excitation and thus increases the magnitude of its effect. As this excitation always depresses the decay rates, the inclusion of level statistics results in slower dissociation of metal clusters.
Cascaded resonant tunneling diode quantizer for analog-to-digital flash conversion
Authors: Kholod Alexandre N. , Liniger M. , Zaslavsky A. , d’Avitaya F. Arnaud
Published: July 2002

We propose and model an application of cascaded resonant tunneling diodes to flash analog-to-digital conversion. We connect diodes of linearly increasing area in series, with separate contacts to interconnecting doped layers between the diodes. When a voltage is applied to the structure, the linearly changing diode size determines which of the diodes switch to the valley current, while the interconnecting contacts allow for a differential voltage measurement that accomplishes the signal quantization. The resulting flash quantizer has an estimated frequency operating limit in the gigahertz range.
Self-consistent hybrid approach for complex systems: Application to the spin-boson model with Debye spectral density
Authors: Thoss Michael , Wang Haobin , Miller William H.
Published: July 2002

The self-consistent hybrid approach [H. Wang, M. Thoss, and W. H. Miller, J. Chem. Phys. 115, 2979 (2001), preceding paper] is applied to the spin-boson problem with Debye spectral density as a model for electron-transfer reactions in a solvent exhibiting Debye dielectric relaxation. The population dynamics of the donor and acceptor states in this system is studied for a broad range of parameters, including the adiabatic (slow bath), nonadiabatic (fast bath), as well as the intermediate regime. Based on illustrative examples we discuss the transition from damped coherent dynamics to purely incoherent decay. Using the numerically exact results of the self-consistent hybrid approach as a benchmark, several approximate theories that have been widely used to describe the dynamics in the spin-boson model are tested: the noninteracting blip approximation, the Bloch–Redfield theory, the Smoluchowski-equation treatment of the reaction coordinate (Zusman equations), and the classical path approach (Ehrenfest model). The parameter range where the different methods are applicable are discussed in some detail.
Axial motion and scalar transport in stretched spiral vortices
Authors: Pullin D. I. , Lundgren T. S.
Published: July 2002

We consider the dynamics of axial velocity and of scalar transport in the stretched-spiral vortex model of turbulent fine scales. A large-time asymptotic solution to the scalar advection-diffusion equation, with an azimuthal swirling velocity field provided by the stretched spiral vortex, is used together with appropriate stretching transformations to determine the evolution of both the axial velocity and a passive scalar. This allows calculation of the shell-integrated three-dimensional spectra of these quantities for the spiral-vortex flow. The dominant term in the velocity (energy) spectrum contributed by the axial velocity is found to be produced by the stirring of the initial distribution of axial velocity by the axisymmetric component of the azimuthal velocity. This gives a k−7/3 spectrum at large wave numbers, compared to the k−5/3 component for the azimuthal velocity itself. The spectrum of a passive scalar being mixed by the vortex velocity field is the sum of two power laws. The first is a k−1 Batchelor spectrum for wave numbers up to the inverse Batchelor scale. This is produced by the axisymmetric component of the axial vorticity but is independent of the detailed radial velocity profile. The second is a k−5/3 Obukov–Corrsin spectrum for wave numbers less than the inverse Kolmogorov scale. This is generated by the nonaxisymmetric axial vorticity and depends on initial correlations between this vorticity and the initial scalar field. The one-dimensional scalar spectrum for the composite model is in satisfactory agreement with experimental measurement.
Dynamic permeability in soft magnetic composite materials
Authors: Chevalier A. , Le Floc’h M.
Published: July 2002

This article reports on an isotropic model of the magnetic susceptibility based on an average field theory and proposes to predict the dynamic behaviors of powder magnetic materials. It was essentially built around a so-called effective demagnetizing factor capable of taking the particle shapes into account. So, for a population of randomly distributed particles of anisotropic shapes like, for instance, needles or flakes, we show that the effective demagnetizing factor of this population of particles can be significantly lowered with regard to the well known value of 1/3 classically used to represent the isotropy state. This phenomenon is interpreted as the natural tendency of particles to form clusters to which a moving demagnetizing factor must be assigned. Taking then the aggregation process of particles into account, the ability of the model to predict the dynamic properties of many composite magnetic materials is successfully demonstrated. Our development is illustrated by experimental results concerning a nickel–zinc ferrimagnetic (Ni0.7Zn0.3Fe2O4) powder.