bluuebunny/crossref_metadata_2025 huggingface dataset:
Far ultraviolet remote sensing of the isotropy boundary and magnetotail stretching
Authors: Blockx C. , Gérard J.‐C. , Meurant M. , Hubert B. , Coumans V.
Published: November 2005

Several studies have attempted to identify the isotropy boundary (IB) defining the limit between the adiabatic and nonadiabatic trajectories of the trapped protons along closed magnetic field lines. This boundary is an indicator of the amount of magnetic field line stretching in the magnetotail. Previous studies were based on in situ measurements, resulting in spatially and temporally restricted samples. To overcome these limitations, we propose to use global data obtained with the FUV spectrographic proton auroral imager (SI12) on board the IMAGE satellite. We determine at each magnetic local time the position of an optical boundary related to the IB and thereby to the stretching of the magnetic field lines. We show that the correspondence between the latitude of the maximum proton precipitation observed by SI12 and the IB measured by Defense Meteorological Satellite Program satellites is statistically established and depends on the magnetic local time. The relation between the position of the maximum proton precipitation as well as the intensity of this maximum and the magnetic field distortion is determined by comparison with GOES 8 data. We suggest that SI12 images can be used as a tool to globally determine the isotropy boundary and to monitor the level of stretching in the magnetotail.
Ion precipitation in the dawn sector during geomagnetic storms
Authors: Huang C. Y. , Burke W. J. , Lin C. S.
Published: November 2005

Three southward turnings of the IMF during the magnetic storm of 29–31 October 2003 led to ring current intensifications characterized by Dst minima. Defense Meteorological Satellite Program (DMSP) satellites detected low‐energy ions precipitating equatorward of auroral electrons in the dawn/morning local time sector. These ion fluxes weakened and/or vanished subsequent to Dst recoveries. A survey of the DMSP database reveals that near‐dawn ion precipitation is a main‐phase characteristic of all large magnetic storms. DMSP and Combined Release and Radiation Effects Satellite (CRRES) satellites also detected similar ion precipitation during the main phase of the March 1991 magnetic storm. To reconcile these observations with elementary concepts of ion drifts, the data suggest two source populations. The lowest‐energy ions were initially energized earthward of the plasma sheet electron boundary in the evening sector then corotated eastward. Higher‐energy ions originated in the plasma sheet and drifted close to the Earth under the combined influences of time‐varying convective electric fields and azimuthal gradients in the Earth's magnetic field. We developed a modified Volland Stern model to study test‐particle trajectories in asymmetric magnetic fields and variable electric fields compatible with CRRES measurements. Ions with magnetic moments μ ≥ μc ≈ 14 eV/nT drift duskward. Ions with μ < μc are injected to low L shells during a spike in the convective electric field. As the electric field diminishes and shielding increases, these ions drift toward dawn much closer to Earth than any test electron trajectories. Precipitation in the dawn sector results from a combination of pitch‐angle scattering by intense ambient waves and the dictates of ion drift paths.
Forecast evaluation of the coronal mass ejection (CME) geoeffectiveness using halo CMEs from 1997 to 2003
Authors: Kim R.‐S. , Cho K.‐S. , Moon Y.‐J. , Kim Y.‐H. , Yi Y. , Dryer M. , Bong Su‐Chan , Park Y.‐D.
Published: November 2005

In this study we have made a forecast evaluation of geoeffective coronal mass ejections (CMEs) by using frontside halo CMEs and the magnetospheric ring current index, Dst. This is the first time, to our knowledge, that an attempt has been made to construct contingency tables depending on the geoeffectiveness criteria as well as to estimate the probability of CME geoeffectiveness depending on CME location and/or speed. For this, we consider 7742 CMEs observed by SOHO/LASCO and select 305 frontside halo CMEs with their locational information from 1997 to 2003 using SOHO/EIT images and GOES data. To select CME‐geomagnetic storm (Dst < −50 nT) pairs, we adopt a CME propagation model for estimating the arrival time of each CME at the Earth and then choose the nearest Dst minimum value within the window of ±24 hours. For forecast evaluation, we present contingency tables to estimate statistical parameters such as probability of detection yes (PODy) and false alarm ratio (FAR). We examine the probabilities of CME geoeffectiveness according to their locations, speeds, and their combination. From these studies, we find that (1) the total probability of geoeffectiveness for frontside halo CMEs is 40% (121/305); (2) PODys for the location (L < ∣50°∣) and the speed (>400 km s−1) are estimated to be larger than 80% but their FARs are about 60%; (3) the most probable areas (or coverage combinations) whose geoeffectiveness fraction is larger than the mean probability (∼40%), are 0° < L < +30° for slower speed CMEs (≤800 km s−1), and −30° < L < +60° for faster CMEs (>800 km s−1); (4) when the most probable area is adopted as the new criteria, the PODy becomes slightly lower, but all other statistical parameters such as FAR and bias are significantly improved. Our results can give us some criteria to select geoeffective CMEs with the probability of geoeffectiveness depending on the location, speed, and their combination.
Open flux estimates in Saturn's magnetosphere during the January 2004 Cassini‐HST campaign, and implications for reconnection rates
Authors: Badman S. V. , Bunce E. J. , Clarke J. T. , Cowley S. W. H. , Gérard J.‐C. , Grodent D. , Milan S. E.
Published: November 2005

During 8–30 January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated for the first time with measurements of the upstream interplanetary conditions made by the Cassini spacecraft. Using the poleward edge of the observed aurora as a proxy for the open‐closed field line boundary, the open flux content of the southern polar region has been estimated. It is found to range from ∼15 to ∼50 GWb during the interval, such a large variation providing evidence of a significant magnetospheric interaction with the solar wind, in particular with the interplanetary structures associated with corotating interaction regions (CIRs). The open flux is found to decline slowly during a rarefaction region in which the interplanetary magnetic field remained very weak, while decreasing sharply in association with the onset of CIR‐related solar wind compressions. Such decreases are indicative of the dominating role of open flux closure in Saturn's tail during these intervals. Increases in open flux are found to occur in the higher‐field compression regions after the onsets, and in a following rarefaction region of intermediate field strength. These increases are indicative of the dominating role of open flux production at Saturn's magnetopause during these intervals. The rate of open flux production has been estimated from the upstream interplanetary data using an empirical formula based on experience at Earth, with typical values varying from ∼10 kV during the weak‐field rarefaction region, to ∼200 kV during the strong‐field compression. These values have been integrated over time between individual HST image sets to estimate the total open flux produced during these intervals. Comparison with the changes in open flux obtained from the auroral images then allows us to estimate the amount of open flux closed during these intervals, and hence the averaged tail reconnection rates. Intermittent intervals of tail reconnection at rates of ∼30–60 kV are inferred in rarefaction regions, while compression regions are characterised by rates of ∼100–200 kV, these values representing averages over the ∼2‐day intervals between HST image sequences. The forms of the aurorae observed are also discussed in relation to the deduced voltage values.
A wave equation migration method for receiver function imaging: 2. Application to the Japan subduction zone
Authors: Chen Ling , Wen Lianxing , Zheng Tianyu
Published: November 2005

The newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the Japan subduction zone using the Fundamental Research on Earthquakes and Earth's Interior Anomalies (FREESIA) broadband data. Three profiles are chosen in the subsurface imaging, two in northeast (NE) Japan to study the subducting Pacific plate and one in southwest (SW) Japan to study the Philippine Sea plate. The descending Pacific plate in NE Japan is well imaged within a depth range of 50–150 km. The slab image exhibits a little more steeply dipping angle (∼32°) in the south than in the north (∼27°), although the general characteristics between the two profiles in NE Japan are similar. The imaged Philippine Sea plate in eastern SW Japan, in contrast, exhibits a much shallower subduction angle (∼19°) and is only identifiable at the uppermost depths of no more than 60 km. Synthetic tests indicate that the top 150 km of the migrated images of the Pacific plate is well resolved by our seismic data, but the resolution of deep part of the slab images becomes poor due to the limited data coverage. Synthetic tests also suggest that the breakdown of the Philippine Sea plate at shallow depths reflects the real structural features of the subduction zone, rather than caused by insufficient coverage of data. Comparative studies on both synthetics and real data images show the possibility of retrieval of fine‐scale structures from high‐frequency contributions if high‐frequency noise can be effectively suppressed and a small bin size can be used in future studies. The derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure. The observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates. Moreover, the deep extent of the Pacific plate image and the shallow breakdown of the Philippine Sea plate image are observed to correlate well with the depth extent of the seismicity beneath NE and SW Japan. Such a correlation supports the inference that the specific appearance of slabs and intermediate‐depth earthquakes are a consequence of temperature‐dependent dehydration induced metamorphism occurring in the hydrated descending oceanic crust.
Constraints on the Martian lithosphere from gravity and topography data
Authors: Belleguic V. , Lognonné P. , Wieczorek M.
Published: November 2005

Localized spectral admittances of the large Martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere. In order to model the case where the load density differs from that of the crust, a new method for calculating gravity anomalies and lithospheric deflections is developed. The modeled gravity anomalies depend upon the elastic thickness, crustal thickness, load density, and crustal density, and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function. We find that the densities of the Martian volcanoes are generally well constrained with values of 3200 ± 100 kg m−3, which is considerably greater than those reported previously. These higher densities are consistent with those of the Martian basaltic meteorites, which are believed to originate from the Tharsis and Elysium volcanic provinces. The crustal density is constrained only beneath the Elysium rise to be 3270 ± 150 kg m−3. If this value is representative of the northern lowlands, then Pratt compensation is likely responsible for the approximately 6‐km elevation difference between the northern and southern hemispheres. The elastic thicknesses of the major Martian volcanoes (when subsurface loads are ignored) are found to be the following: Elysium rise (56 ± 20 km), Olympus Mons (93 ± 40 km), Alba Patera (66 ± 20 km), and Ascraeus Mons (105 ± 40 km). We have also investigated the effects of subsurface loads, allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material. We found that all volcanoes except Pavonis are better modeled with the presence of less dense material in the upper mantle, which is indicative of either a mantle plume or a depleted mantle composition. An active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on Olympus Mons and the Elysium rise, which indicate that some lava flows are as young as 10–30 Myr, as well as with the crystallization ages of the Shergottites, of which some are as young as 180 Myr.
Drainage of a horizontal Boussinesq aquifer with a power law hydraulic conductivity profile
Authors: Rupp David E. , Selker John S.
Published: November 2005

Solutions to the Boussinesq equation describing drainage into a fully penetrating channel have been used for aquifer characterization. Two analytical solutions exist for early‐ and late‐time drainage from a saturated, homogeneous, and horizontal aquifer following instantaneous drawdown. The solutions for discharge Q can be expressed as dQ/dt = −aQb, where a is constant and b takes on the value 3 and 3/2 for early and late time, respectively. Though many factors can contribute to departures from the two predictions, we explore the effect of having permeability decrease with depth, as it is known that many natural soils exhibit this characteristic. We derive a new set of analytical solutions to the Boussinesq equation for k ∝ zn, where k is the saturated hydraulic conductivity, z is the height above an impermeable base, and n is a constant. The solutions reveal that in early time, b retains the value of 3 regardless of the value of n, while in late time, b ranges from 3/2 to 2 as n varies from 0 to ∞. Similar to discharge, water table height h in late time can be expressed as dh/dt = −chd, where d = 2 for constant k and d → ∞ as n → ∞. In theory, inclusion of a power law k profile does not complicate aquifer parameter estimation because n can be solved for when fitting b to the late‐time data, whereas previously b was assumed to be 3/2. However, if either early‐ or late‐time data are missing, there is an additional unknown. Under appropriate conditions, water table height measurements can be used to solve for an unknown parameter.
Effect of bottom curvature on mudflow dynamics: Theory and experiments
Authors: Siviglia A. , Cantelli A.
Published: November 2005

A one‐dimensional mathematical model of mudflow dynamics is formulated assuming mud to behave rheologically as a Herschel‐Bulkley fluid. Novel features of the present contribution regard the propagation of mudflows over a curvilinear bottom. A set of nonlinear partial differential equations is found to govern the unsteady, nonuniform flow of such fluids. Following the approach of Huang and Garcìa (1998), a depth‐integrated form of the continuity equation and shear‐integrated and plug‐integrated forms of the momentum equations are derived. A perturbation analysis is also carried out under the assumption of “slender” flow. The leading‐order problem takes the form of a kinematic wave equation. One straightforward application of this simplified model is the evaluation of the maximum run‐out extension of a mud which flows over a bed with a variable topography. This solution is obtained by solving the steady state problem. Dynamics information are obtained by numerically solving the hyperbolic conservative equation by means of a free oscillating numerical method. The effects of bottom curvature either on the equilibrium solution or mudflow dynamics are analyzed. Experiments are also performed releasing a given volume of kaoline and water mixture from a reservoir into both a constant slope and an upward concave channel. Comparisons between the numerical solution and the experimental data are generally satisfactory, though suggesting limitations typical of any approach that neglects convective accelerations and assumes gradually varied flow.
ARE‐mRNA degradation requires the 5′–3′ decay pathway
Authors: Stoecklin Georg , Mayo Thomas , Anderson Paul
Published: November 2005

As an important mode of suppressing gene expression, messenger RNAs containing an AU‐rich element (ARE) in the 3′ untranslated region are rapidly degraded in the cytoplasm. ARE‐mediated mRNA decay (AMD) is initiated by deadenylation, and in vitro studies have indicated that subsequent degradation occurs in the 3′–5′ direction through a complex of exonucleases termed the exosome. An alternative pathway of mRNA degradation occurs at processing bodies, cytoplasmic foci that contain decapping enzymes, the 5′–3′ exonuclease Xrn1 and the Lsm1–7 heptamer. To determine which of the two pathways is important for AMD in live cells, we targeted components of both pathways using short interfering RNA in human HT1080 cells. We show that Xrn1 and Lsm1 are essential for AMD. On the other side, out of three exosome components tested, only knockdown of PmScl‐75 caused a strong inhibition of AMD. Our results show that mammalian cells, similar to yeast, require the 5′–3′ Xrn1 pathway to degrade ARE‐mRNAs.
Building a better snail: Lubrication and adhesive locomotion
Authors: Chan Brian , Balmforth N. J. , Hosoi A. E.
Published: November 2005

Many gastropods, such as slugs and snails, crawl via an unusual mechanism known as adhesive locomotion. We investigate this method of propulsion using two mathematical models: one for direct waves and one for retrograde waves. We then test the effectiveness of both proposed mechanisms by constructing two mechanical crawlers. Each crawler uses a different mechanical strategy to move on a thin layer of viscous fluid. The first uses a flexible flapping sheet to generate lubrication pressures in a Newtonian fluid, which in turn propel the mechanical snail. The second generates a wave of compression on a layer of Laponite, a non-Newtonian, finite-yield stress fluid with characteristics similar to those of snail mucus. This second design can climb smooth vertical walls and perform an inverted traverse.
Multiple time scale dynamics of distance fluctuations in a semiflexible polymer: A one-dimensional generalized Langevin equation treatment
Authors: Debnath Pallavi , Min Wei , Xie X. Sunney , Cherayil Binny J.
Published: November 2005

Time-dependent fluctuations in the distance x(t) between two segments along a polymer are one measure of its overall conformational dynamics. The dynamics of x(t), modeled as the coordinate of a particle moving in a one-dimensional potential well in thermal contact with a reservoir, is treated with a generalized Langevin equation whose memory kernel K(t) can be calculated from the time-correlation function of distance fluctuations C(t)≡⟨x(0)x(t)⟩. We compute C(t) for a semiflexible continuum model of the polymer and use it to determine K(t) via the GLE. The calculations demonstrate that C(t) is well approximated by a Mittag-Leffler function and K(t) by a power-law decay on time scales of several decades. Both functions depend on a number of parameters characterizing the polymer, including chain length, degree of stiffness, and the number of intervening residues between the two segments. The calculations are compared with the recent observation of a nonexponential C(t) and a power law K(t) in the conformational dynamics within single molecule proteins [Min et al., Phys. Rev. Lett. 94, 198302 (2005)].
Hamiltonian multivector fields and Poisson forms in multisymplectic field theory
Authors: Forger Michael , Paufler Cornelius , Römer Hartmann
Published: November 2005

We present a general classification of Hamiltonian multivector fields and of Poisson forms on the extended multiphase space appearing in the geometric formulation of first order classical field theories. This is a prerequisite for computing explicit expressions for the Poisson bracket between two Poisson forms.
Free-energy calculations for the cubic ZrO2 crystal as an example of a system with a soft mode
Authors: Sternik M. , Parlinski K.
Published: November 2005

We calculate the free energy for a crystalline ZrO2 with a soft mode by the first-principles method, using the double-well energy-displacement relation. The soft-mode branch is considered as an ensemble of independent anharmonic oscillators of the parabola-plus-Gaussian or of the 2-4 polynomial forms. The anharmonic contributions are included to reproduce the cubic-to-tetragonal phase transition, however, it appears that the cubic phase does not become the most stable within the framework of the independent oscillators approach.
Two-color pump-probe laser spectroscopy instrument with picosecond time-resolved electronic delay and extended scan range
Authors: Yu Anchi , Ye Xiong , Ionascu Dan , Cao Wenxiang , Champion Paul M.
Published: November 2005

An electronically delayed two-color pump-probe instrument was developed using two synchronized laser systems. The instrument has picosecond time resolution and can perform scans over hundreds of nanoseconds without the beam divergence and walk-off effects that occur using standard spatial delay systems. A unique picosecond Ti:sapphire regenerative amplifier was also constructed without the need for pulse stretching and compressing optics. The picosecond regenerative amplifier has a broad wavelength tuning range, which suggests that it will make a significant contribution to two-color pump-probe experiments. To test this instrument we studied the rotational correlation relaxation of myoglobin (τr=8.2±0.5ns) in water as well as the geminate rebinding kinetics of oxygen to myoglobin (kg1=1.7×1011s−1, kg2=3.4×107s−1). The results are consistent with, and improve upon, previous studies.
Ab initio configuration-interaction study of the ground and low-lying electronic states of NiI
Authors: Yang Chuan-Lu , Gao Feng , Zhang Xiao-Yan , Han Ke-Li
Published: November 2005

For the first time, we have studied the potential-energy curves, spectroscopic terms, vibrational levels, and the spectroscopic constants of the ground and low-lying excited states of NiI by employing the complete active space self-consistent-field method with relativistic effective core potentials followed by multireference configuration-interaction calculations. We have identified six low-lying electronic states of NiI with doublet spin multiplicities, including three states of Δ symmetry and three states of Π symmetry of the molecule within 15000cm−1. The lowest Δ2 state is identified as the ground state of NiI, and the lowest Π2 state is found at 2174.56cm−1 above it. These results fully support the previous conclusion of the observed spectra although our computational energy separation of the two states is obviously larger than that of the experimental values. The present calculations show that the low-lying excited states [13.9]Π2 and [14.6]Δ2 are 3Π2 and 3Δ2 electronic states of NiI, respectively. Our computed spectroscopic terms, vibrational levels, and spectroscopic constants for them are in good agreement with the experimental data available at present. In the present work we have not only suggested assignments for the observed states but also computed more electronic states that are yet to be observed experimentally.
Variable gain detection strategy for time-of-flight multiphoton ionization spectroscopy experiments
Authors: Pasquini M. , Piani G. , Pietraperzia G. , Demtroeder W. , Giuntini M. , Becucci M.
Published: November 2005

This note presents a new, simple approach to measure time-of-flight mass spectra containing ions in a wide concentration range as generated by laser photoionization studies of van der Waals complexes. Real-time control of the gain of the microchannel plate detector, applying to it fast-rising high-voltage pulses like in slice imaging experiments, is suggested. Results are presented for a model system study.
Experimental measurement of lattice strain pole figures using synchrotron x rays
Authors: Miller M. P. , Bernier J. V. , Park J.-S. , Kazimirov A.
Published: November 2005

This article describes a system for mechanically loading test specimens in situ for the determination of lattice strain pole figures and their evolution in multiphase alloys via powder diffraction. The data from these experiments provide insight into the three-dimensional mechanical response of a polycrystalline aggregate and represent an extremely powerful material model validation tool. Relatively thin (0.5mm) iron/copper specimens were axially strained using a mechanical loading frame beyond the macroscopic yield strength of the material. The loading was halted at multiple points during the deformation to conduct a diffraction experiment using a 0.5×0.5mm2 monochromatic (50keV) x ray beam. Entire Debye rings of data were collected for multiple lattice planes ({hkl}’s) in both copper and iron using an online image plate detector. Strain pole figures were constructed by rotating the loading frame about the specimen transverse direction. Ideal powder patterns were superimposed on each image for the purpose of geometric correction. The chosen reference material was cerium (IV) oxide powder, which was spread in a thin layer on the downstream face of the specimen using petroleum jelly to prevent any mechanical coupling. Implementation of the system at the A2 experimental station at the Cornell High Energy Synchrotron Source (CHESS) is described. The diffraction moduli measured at CHESS were shown to compare favorably to in situ data from neutron-diffraction experiments conducted on the same alloys.
Optical properties of tetrapod-shaped CdTe nanocrystals
Authors: Tarì Davide , De Giorgi Milena , Sala Fabio Della , Carbone Luigi , Krahne Roman , Manna Liberato , Cingolani Roberto , Kudera Stefan , Parak Wolfgang J.
Published: November 2005

We studied the carrier confinement in tetrapod-shaped colloidal CdTe nanocrystals by means of absorption, photoluminescence, and photoluminescence excitation spectroscopy at room and cryogenic temperatures. The spectra show features characteristic of the tetrapod shape together with a clear dependence on the dominant confinement parameter, i.e., the diameter of the tetrapod arm. Theoretical calculations based on an envelope-function approximation and using the exact tetrapod shape have been performed to assign the observed spectral features. Oscillator strength and size dependence of the transitions energy have been calculated showing a direct correlation between the oscillator strength and the nanocrystal shape.
A high-frequency method for determining winding faults in transformers and electrical machines
Authors: Florkowski Marek , Furgał Jakub
Published: November 2005

Improvement of diagnostic methods of both power transformers and electrical machines is crucial considering the function they play in electrical networks and industry as well as the cost of those devices. High-frequency measurements are used more and more frequently as a diagnostic tool for the investigation of transformer and machine windings. They are also used for identifying winding faults. As a base are measurement results of frequency dependencies of the winding admittance or the transfer function. Therefore, relations between different kinds of winding faults and changes of frequency dependencies of winding admittances or transfer functions should be determined. Much research work is done in that field, which aims to determine the sensitivity of this method and to develop the recognition criteria with regard to the type and range of faults. This article presents the comparison of measurement results of the admittance performed on the medium-voltage transformer winding. The quantitative results of detecting deformations and dislocations of windings by means of frequency response analysis are described. Of particular importance is the early detection of winding failures in electrical machines, both during the manufacturing process and in operation. The results of investigations of winding faults in electrical machines of different construction are presented. The influence of turn-to-turn faults between adjacent winding wires on the admittance wave form has been also investigated.
Reformulating and quantifying the generalized added mass in filtered gas-solid flow models
Authors: De Wilde Juray
Published: November 2005

To account for mesoscale phenomena in coarse grid simulations, Reynolds stress terms appearing in the filtered gas-solid flow equations have to be modeled. A generalized added mass approach previously proposed by Zhang and VanderHeyden [Int. J. Multiphase Flow 28, 805 (2002)] to model the acoustic gas-solid interaction Reynolds stress term is analyzed. Theoretically, it is shown that a generalized added mass term appears directly from the filtered acoustic gas-solid interaction term and that it corresponds to a redistribution of the filtered gas phase pressure gradient over the phases. This direct contribution scales according to the mean square of the solid volume fraction fluctuations. Two-dimensional dynamic mesoscale simulations over a broad solid volume fraction range and for two domain sizes and two grid resolutions are carried out to calculate the magnitude of the generalized added mass effect. Calculated values of the mean square of the solid volume fraction fluctuations are qualitatively in agreement with the experimental observations of Zenit and Hunt [Int. J. Multiphase Flow 26, 763 (2000)]. A second, indirect contribution to the generalized added mass term from the filtered acoustic gas-solid interaction term is shown to be statistically significant, but one order of magnitude smaller than the direct contribution. A further quantification of the maximum generalized added mass effect as a function of the filter frequency is obtained from a mixture speed of sound test. The results show that a large generalized added mass coefficient, as previously reported by Zhang and VanderHeyden [Int. J. Multiphase Flow 28, 805 (2002)], is justified only in case the filter frequency is low (<20Hz), i.e., if the grid is, either spatially or temporally, sufficiently coarse.
Simple, adjustable beam splitting element for differential interferometers based on photoelastic birefringence of a prismatic bar
Authors: Sanderson S. R.
Published: November 2005

We examine the prototypical Toepler optical arrangement for the visualization of phase objects and consider the effect of different contrast elements placed at the focus of the source. In particular, Wollaston prism beam splitting elements based on the crystallographic birefringence of calcite or quartz find application in differential interferometry systems based on the Toepler arrangement. The focus of the current article is a simple low cost alternative to the Wollaston prism that is realized by inserting a prismatic bar constructed of a photoelastic material into the optical path. It is shown that, under the action of an applied bending moment, the prismatic bar functions as a first-order approximation to a Wollaston prism. Results are derived for the divergence angle of the beam splitter for orthogonally polarized rays. The implementation of a practical device is discussed and representative experimental results are presented, taken from the field of shock wave visualization in supersonic flow.
Diagnostics of nitrogen plasma by trace rare-gas–optical emission spectroscopy
Authors: Qayyum A. , Zeb Shaista , Naveed M. A. , Ghauri S. A. , Zakaullah M. , Waheed A.
Published: November 2005

Trace rare-gas–optical emission spectroscopy is carried out to characterize the nitrogen plasma as a function of discharge parameters. The functional dependence of N2(CΠu3) and N2+(BΣu+2) excited states is monitored by measuring the emission intensities of the bandheads of second positive and first negative systems. The excited-state population density of N atoms and N2 molecules, extracted from their optical emission, is related to the ground-state population density after normalizing the changes for excitation cross section and electron energy distribution function by optical actinometry. The electron temperature is determined from the plasma-induced optical emission of trace rare gas by the line-to-line method. The obtained data may help us to adjust the optimum discharge conditions for the production of active species, which are considered to be important for the desired treatment of the samples.
The effects of uniaxial compressive stress on the terahertz emission from phosphorus-doped silicon devices
Authors: Lv P.-C. , Zhang X. , Kolodzey J. , Odnoblyudov M. A. , Yassievich I. N.
Published: November 2005

The effects of uniaxial compressive stress on the terahertz electroluminescence from P-doped silicon devices have been studied. A shift by ∼0.5THz in the emission peaks of donor state transitions: 2p0→1s(E) and 3p+∕−→1s(E) has been observed for a stress of ∼0.1GPa along the [100] direction. Transitions from excited states to the strain split states of 1s(E) showed a pronounced polarization effect. Transitions involving the 1s(T1) ground state, however, showed no polarization effect. These results suggest that it may be possible to realize a tunable impurity-doped silicon terahertz emitter by externally applied stress.
Diagnostics of hydrogen plasma with in situ optical emission and silicon probes
Authors: Lee Szetsen , Chung Yi-Jie
Published: November 2005

In this work, an approach has been adopted to explore plasma properties by combining an in situ optical emission technique with a contact angle measurement. Hydrogen plasma was generated with a radio-frequency power source. The plasma parameters such as number densities and temperatures were derived from the optical emission spectroscopic data. Small silicon chips were placed at various positions inside a discharge tube as probes for the plasma conditions. The hydrogen-plasma-treated silicon chip surfaces were characterized with the contact angle measurement method. The change of wettability on the silicon surface was observed with various plasma treatment times. The spectroscopic information about the plasma is correlated with the results of the surface characterization. It is found that the rate of the increasing hydrophilicity is sensitive to the amount of helium added and the location in the discharge tube. A simple model describing the relation between the surface coverage area of water droplet and the variation of contact angle has been established. We have proposed plasma excitation and reaction mechanisms for the observed correlation between plasma temperatures and the wettability of the silicon surface. It shows that small silicon chips can serve as “litmus tests” for the plasma conditions without introducing too much perturbation.
Si
O
x
F
y
passivation layer in silicon cryoetching
Authors: Mellhaoui X. , Dussart R. , Tillocher T. , Lefaucheux P. , Ranson P. , Boufnichel M. , Overzet L. J.
Published: November 2005

The SiOxFy passivation layer created on structure sidewalls during silicon cryoetching is investigated. This SiOxFy passivation layer formation strongly depends on O2 content, temperature and bias. It is a fragile layer, which mostly disappears when the wafer is warmed up to ambient temperature. A mass spectrometer was used to analyze the desorbed species during the warm-up and using this instrument allowed us to find a large signal increase in SiF3+ between −80°C and −50°C. SiF4 etching products can participate in the formation of the passivation layer as it is shown by a series of test experiments. SiF4∕O2 plasmas are used to form a thin SiOxFy layer on a cooled silicon wafer. Thickness and optical index of this thin film can be determined by in situ spectroscopic ellipsometry. It is shown that the passivation layer spontaneously desorbs when the silicon wafer temperature increases in good agreement with the mass spectrometry analysis. Two physical mechanisms are proposed to explain the SiOxFy passivation layer buildup involving either the etching products or the SiFx sites created during etching. In both cases, oxygen radicals react at the surface to form the SiOxFy layer.
In situ vapor sorption apparatus for small-angle neutron scattering and its application
Authors: Kim Man-Ho , Glinka Charles J. , Carter Robert N.
Published: November 2005

An in situ vapor sorption apparatus has been constructed for use in small-angle neutron scattering (SANS) measurements. The apparatus adapts two independent operating mechanisms, with and without a carrier gas, to control relative or absolute pressure, respectively, in the SANS sorption cell. By controlling the absolute pressure, a target relative vapor pressure between 0% and 90% can be reached within 1–2 min. The short response time makes it possible to correlate diffusion kinetics and/or sorption/desorption isotherms with structure evolution during wetting/drying, which is not possible in gravimetric methods. Also, one can extract diffusion coefficients and interaction parameters. Other uses include the enhancement of scattering contrast in the study of semicrystalline polymers by the preferential vapor sorption of deuterated vapor into the amorphous regions. Thus, one can obtain the same structural information as small-angle x-ray scattering measurements on dry samples. Also, the apparatus has the capability to inject a pore-masking liquid into the sample cell while under vacuum to ensure the filling of all open porosities in a sample. The capability to mix two vapors in various ratios facilitates the determination of a contrast-matching point using a single sample, which also eliminates a major source of systematic error. The performance of the apparatus is demonstrated using a polyelectrolyte membrane and semicrystalline polyethylene. Additionally, technical points relating to controlling the relative vapor pressure, relative humidity, and regarding the vapor distribution in the cell are discussed.
Temporal instability of a capillary jet with a source of mass
Authors: Savtchenko Serguei , Ashgriz Nasser
Published: November 2005

The temporal linear instability of an inviscid capillary liquid jet with a source of mass is investigated. Two different spatial mass distributions are considered. In the first case, mass is added uniformly everywhere in the jet. In the second case, mass is added uniformly in the radial direction, but allowed to change along the axial direction. The problem is solved using a one-dimensional approximation for the capillary jet. An analytical solution for the steady basic flow of a jet with a small source of mass is obtained. The dispersion relation and the growth rate of the disturbances are obtained analytically for small source terms. The influence of the mass addition on the instability characteristics, the breakup time, and the breakup length of a jet are presented. It is shown that the mass addition decreases the rate of growth of the disturbances. The mass addition increases the breakup time and decreases the breakup length. Also, the sizes of the generated drops increase with increasing the source of mass.
Absolute energy reference calorimeter with bismuth telluride thermocouples for laser energy standard
Authors: Fukuda Daiji , Kimura Shinji , Endo Mitiyuki
Published: November 2005

A highly sensitive calorimeter has been developed for measuring the absolute energy of single laser pulses. The calorimeter, which consists of a solid volume absorber, a copper absorption cavity, and bismuth telluride thermocouples, is operated at room temperature with no vacuum window. The absorption of the laser energy in the calorimeter leads to a temperature increase of the cavity. The time-dependent temporal temperature change was measured as voltage signals with highly sensitive bismuth telluride semiconductor thermocouples. The calorimeter was calibrated by injecting a known Joule heat with a heater on the cavity. The experimental results showed a linear relationship in an energy range from 5to100mJ. The standard deviation of the calibrated sensitivity was less than 0.1%. The systematic errors of the laser energy measurement are estimated to be as small as 0.32%.
Beneficial effects of annealing on amorphous Nb–Si thin-film thermometers
Authors: Querlioz D. , Helgren E. , Queen D. R. , Hellman F. , Islam R. , Smith David. J.
Published: November 2005

Amorphous Nb–Si alloys have a temperature-dependent resistivity which can be tuned over many decades by controlling composition and are used for thin-film thermometers. Annealing at temperatures from 100 to 500 °C produces dramatic but easily controlled increases in resistivity, both magnitude and temperature dependence, for insulating and metallic samples with compositions ranging from 8–15 at. %Nb. A transition from metal to insulator is induced by annealing an initially metallic sample. Annealing produces thermal stability against subsequent heat treatment, allowing annealed films to be used as low-temperature thermometers even when they are cycled to temperatures as high as 500 °C. Cross-section transmission electron microscopy and energy-dispersive x-ray analysis show that the initially amorphous films develop Nb-rich clusters within an amorphous Nb-depleted matrix, explaining the observed resistivity increase.
Trapping-detrapping defects in single crystal diamond films grown by chemical vapor deposition
Authors: Balducci A. , Marinelli Marco , Milani E. , Morgada M. E. , Prestopino G. , Scoccia M. , Tucciarone A. , Verona-Rinati G.
Published: November 2005

High-quality single-crystal diamond films were homoepitaxially grown by chemical vapor deposition onto low cost high-pressure high-temperature diamond substrates. The transport properties of the obtained samples were studied by photoresponse characterization. Fast ultraviolet (5 ns) laser pulses at 215 nm were used as a probe. The time evolution of the photoinduced current was observed to closely reproduce the laser pulse shape, thus indicating a time response lower than the adopted laser pulse duration. Very stable and reproducible response was measured, so that neither priming nor memory effects are observed. However, a minor slow component shows up in the charge-integrated sample response, whose temperature dependence was investigated in a −25–+50°C range. A systematic speed up of this slow component of the sample signal is observed, indicating the presence of shallow centers producing trapping-detrapping effects. The experimental results are discussed in the framework of a trapping-detrapping model affecting the charge transport mechanism and an activation energy of Ea=0.4eV was derived for the shallow trapping centers.
Modeling of dual frequency liquid crystal materials and devices
Authors: Brimicombe P. D. , Parry-Jones L. A. , Elston S. J. , Raynes E. P.
Published: November 2005

We present a director-based model of the dual frequency nature of liquid crystals based on a Debye-type relaxation of the permittivity in the direction parallel to the director. This relaxation is governed by a first order differential equation in terms of the polarization and electric field along the long axis. We demonstrate that this equation can be used as an extension to the well-known Eriksen-Leslie-Parodi theory. Since solution is in the time domain, the frequency response of the applied waveform need not be calculated. Consequently, the device response to arbitrary applied waveforms can be modeled. As an example, we present the switching response of a dual frequency addressed hybrid-aligned nematic cell, and suggest some optimization of the addressing scheme.
Comparison of the layered semiconductors GaSe, GaS, and GaSe1−xSx by Raman and photoluminescence spectroscopy
Authors: León C. Pérez , Kador L. , Allakhverdiev K. R. , Baykara T. , Kaya A. A.
Published: November 2005

The room-temperature Raman spectra of single crystals of GaSe, GaS, and mixed compounds GaSe1−xSx with 0.02⩽x⩽0.8 were measured with a HeNe laser in confocal configuration. The changes in the spectra indicate changes of the crystal structure. The spectra of pure GaSe and of the mixed compound with x=0.02 show pronounced photoluminescence signals blueshifted from the laser line, whereas these signals do not appear for higher sulfur content. Their origin is interpreted as second-harmonic generation in the laser focus causing the formation and radiative decay of Wannier excitons. Two-photon absorption is ruled out, since the effect is absent in the centrosymmetric crystals with x>0.02. With a green laser whose photon energy is larger than the band gap, strong photoluminescence is also observed in crystals with higher sulfur content.
Average energy dissipated by mega-electron-volt hydrogen and helium ions per electron-hole pair generation in 4H-SiC
Authors: Lo Giudice Alessandro , Fizzotti Franco , Manfredotti Claudio , Vittone Ettore , Nava Filippo
Published: November 2005

The pulse height response for He and H ions with energies between 1 and 6 MeV incident upon n-type 4H-SiC epitaxial Schottky diodes has been investigated. The average amount of energy, ε, given up by the incident radiation to form electron-hole pair in this material was obtained by comparison with the average energy loss per pair in silicon detectors and it was found to be (7.78±0.05)eV at room temperature. This value is smaller than that foreseen by Klein’s semiempirical linear relationship between ε and the semiconductor band gap.
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nanowires: Synthesis, characterization, and p-channel field-effect transistor
Authors: Chang Pai-Chun , Fan Zhiyong , Tseng Wei-Yu , Rajagopal A. , Lu Jia G.
Published: November 2005

Quasione-dimensional Ga2O3 nanowires are synthesized via catalytic chemical vapor deposition method. Their morphology and crystal structure are characterized by electron microscopy and x-ray diffraction techniques, and their optical property is studied by photoluminescence measurement. To develop their future application in nanoelectronic devices, the as-grown Ga2O3 nanowires are doped with zinc to increase its carrier concentration and subsequently fabricated into field-effect transistors. Electron transport measurements show that the doped nanowires exhibit p-type semiconducting behavior with a significant enhancement of conductivity.
Kinetic control of Ge(Si)∕Si(100) dome cluster composition
Authors: McDaniel E. P. , Jiang Qian , Crozier P. A. , Drucker Jeff , Smith David J.
Published: November 2005

The Ge content of dome clusters grown by molecular beam epitaxy of pure Ge onto Si(100) rises with increasing deposition rate. The rising Ge content is manifested by a decrease in the volume at which clusters change shape from pyramids to domes and is quantitatively confirmed using nm spatial resolution electron-energy-loss spectroscopy in a scanning transmission electron microscope. The areal density of dome clusters is controlled by the ratio between the deposition and surface diffusion rates whereas their composition is controlled by the ratio between the deposition and Si interdiffusion rates.
Steady-state and transient electron transport within bulk wurtzite indium nitride: An updated semiclassical three-valley Monte Carlo simulation analysis
Authors: O’Leary Stephen K. , Foutz Brian E. , Shur Michael S. , Eastman Lester F.
Published: November 2005

Recent experimentation, performed on bulk wurtzite InN, suggests that the energy gap, the effective mass of the electrons in the lowest-energy valley, and the nonparabolicity coefficient of the lowest-energy valley are not as originally believed for this material. Using a semiclassical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk wurtzite InN using a revised set of material parameters, this revised set of parameters taking into account this recently observed phenomenology. We find that the peak electron drift velocity is considerably greater than that found previously. The impact that this revised set of parameters has upon the transient electron transport is also found to be significant.