bluuebunny/crossref_metadata_2025 huggingface dataset:
Piecewise linear fitting and trend changing points of climate parameters
Authors: Tomé A. R. , Miranda P. M. A.
Published: January 2004

Finding an overall linear trend is a common method in scientific studies. It is almost a requirement when one intends to study variability. Nevertheless, when dealing with long climate temporal series, fitting a straight line only seldom has a relevant meaning. This paper proposes and describes a new methodology for finding overall trends, and, simultaneously, for computing a new set of climate parameters: the breakpoints between periods with significantly different trends. The proposed methodology uses a least‐squares approach to compute the best continuous set of straight lines that fit a given time series, subject to a number of constraints on the minimum distance between breakpoints and on the minimum trend change at each breakpoint. The method is tested with three climate time series.
Ionospheric solar flare effects monitored by the ground‐based GPS receivers: Theory and observation
Authors: Liu J. Y. , Lin C. H. , Tsai H. F. , Liou Y. A.
Published: January 2004

The ionosphere responses to a solar flare observed by using ground‐based receivers of the global positioning system (GPS) are investigated in this paper. Two quantities, the total electron content (TEC) and its time rate of change (rTEC), can be derived from the receivers. The theoretical studies show that the rTEC is related to the frequency deviation of the GPS signals. Meanwhile, worldwide ground‐based GPS receivers are employed to derive the TEC and associated rTEC to monitor the ionospheric solar flare effect on 14 July (Bastille Day) 2000. It is found that ionospheric solar flare effects can be observed from predawn to postdusk regions, and the most pronounced signatures appear in the midday area. The agreement between theoretical predications and observations demonstrates that the TEC is suitable to monitor the overall variations of flare radiations while the rTEC is capable to detect sudden changes in the flare radiations.
Polar cap bifurcation during steady‐state northward interplanetary magnetic field with ∣BY∣ ∼ BZ
Authors: Watanabe Masakazu , Sofko George J. , André Dieter A. , Tanaka Takashi , Hairston Marc R.
Published: January 2004

In this paper, for steady‐state northward interplanetary magnetic field (IMF) with ∣BY∣ ∼ BZ, we describe a new merging sequence that results in polar cap bifurcation and accompanying paired “exchange cells” in the ionospheric convection pattern. Although the IMF is northward, it reconnects with the closed geomagnetic field on the dayside high‐latitude magnetopause, creating two types of open geomagnetic field lines. For the first type the neutral point and the foot point are in the same hemisphere; for the second type the neutral point and the foot point are in opposite hemispheres. The latter type of field lines slips on the magnetopause in the azimuthal direction opposite to the normal BY‐ associated flux transport and forms an overdraped tail lobe. The ionospheric signature of this overdraped lobe is the appearance of an open magnetic flux island inside the dawn/dusk plasma sheet (i.e., polar cap bifurcation). For BY > 0 the island emerges in the duskside (dawnside) plasma sheet in the northern (southern) ionosphere and conversely for BY < 0. The overdraped field lines which have slipped on the magnetopause then reconnect with closed geomagnetic field lines in the opposite hemisphere to the foot points, thereby transferring the open magnetic flux to the nightside convection system and maintaining the steady‐state magnetic flux circulation. As a result, paired ionospheric convection cells form which exchange magnetic flux. For BY > 0 the pair is located in the noon‐dusk and midnight‐dawn (dawn‐noon and dusk‐midnight) quadrants of the northern (southern) ionosphere; for BY < 0 a mirror image with respect to the noon‐midnight meridian applies to the convection pattern. We demonstrate observational evidence that supports this model.
Schumann resonance frequency increase during solar X‐ray bursts
Authors: Roldugin V. C. , Maltsev Y. P. , Vasiljev A. N. , Schokotov A. Y. , Belyajev G. G.
Published: January 2004

Variations of the first mode Schumann resonance frequency in the Kola Peninsula and of the first and second mode frequencies in Kamchatka during seven days of March–April 2001, when the intensive solar X‐ray bursts occurred, are studied with 5 min averaging. All X‐ray bursts were accompanied by ∼0.2 Hz increase in the first mode frequency, at least in one of the magnetic components. Duration of the increases coincided with that of the bursts. For the second mode the increase (in average by ∼0.3 Hz) was registered in most events, when the ELF noise level was not very high.
Nonlinear waveform and delay time analysis of triplicated core phases
Authors: Garcia R. , Chevrot S. , Weber M.
Published: January 2004

We introduce a new method to measure differential travel times and attenuation of seismic body waves. The problem is formulated as a nonlinear inverse problem, which is solved by simulated annealing. Using this technique, we have analyzed triplicated PKP waves recorded by the temporary Eifel array in central Europe. These examples demonstrate the potential of the technique, which is able to determine differential travel times and waveforms of the core phases, even when they interfere on the seismograms or when additional depth phases are present. The PKP differential travel times reveal the presence of large‐amplitude and small‐scale heterogeneities along the PKP(AB) ray paths and favor a local radial inner core model with ∼0.9% velocity perturbation in its top 150 km and small velocity perturbations below. The quality factor in the top 300 km of this inner core region is estimated from PKP differential attenuation. Its preferred value is 330 with a lower bound of 75.
Absolute geomagnetic paleointensity after the Cretaceous Normal Superchron and just prior to the Cretaceous‐Tertiary transition
Authors: Goguitchaichvili Avto , Alva‐Valdivia Luis M. , Rosas‐Elguera José , Urrutia‐Fucugauchi Jaime , Solé Jesús
Published: January 2004

We report a detailed rock magnetic and Thellier paleointensity study from Autlan volcanic succession in western Mexico. The whole rock K‐Ar age obtained for these lavas, 67.4 ± 1.2 Ma, together with the magnetostratigraphy results indicates that the lava flows were erupted during chron 30n just prior to Cretaceous‐Tertiary transition. Thirty‐nine samples from eight cooling units were preselected for paleointensity experiments on the basis of their low‐viscosity index, stable remanent magnetization, and close to reversible continuous thermomagnetic curves. High‐quality determinations were obtained for 18 individual samples from four independent lava flows. The mean virtual dipole moment (VDM) obtained in this study is 4.9 ± 0.6 × 1022 A m2, which is significantly lower than the present geomagnetic field strength but in reasonably good accord with other comparable quality determinations between 35 and 80 Ma. Our data are not significantly different from almost all published paleointensities between 5 and 90 Ma. Moreover, rigorously selected worldwide paleointensity data in the same interval better fit trend 2 of Heller et al. [2000]. A careful examination of high‐quality paleointensity data from Cretaceous indicates that there is no simple relation between magnitude of Earth's magnetic field and reversal rate.
Multifractal dimension andbvalue analysis of the 1998–1999 Quito swarm related to Guagua Pichincha volcano activity, Ecuador
Authors: Legrand D. , Villagómez D. , Yepes H. , Calahorrano A.
Published: January 2004

Temporal variations of spatial multifractal dimensions of Quito swarm seismicity (Ecuador) are related to the August 1998 to December 1999 Guagua Pichincha volcanic activity. Multifractal dimensions decrease a few days before the five main seismic energy peaks and increase again before or just after these peaks. This behavior reveals a self‐organization of earthquakes that precedes main seismic energy peaks. The Quito swarm is also characterized by a bimodal Gutenberg‐Richter law with twobvalues:b1= 0.95 ± 0.15 andb2= 1.48 ± 0.15. This bimodality may reveal the superposition of two different processes: one related to a classical elastic rupture and the other related to hydraulic fracture (leading to highbvalues) resulting from magma and overpressurized groundwater movements. Groundwater expulsion may be driven by heat released from deeper upgoing magma and manifested on the surface by the occurrence of phreatic explosions (beginning 7 August 1998) and by the formation of eight dacitic lava domes (beginning 25 September 1999).
Initiation of subduction by small‐scale convection
Authors: Solomatov V. S.
Published: January 2004

The possibility of initiation of subduction by sublithospheric small‐scale convection is investigated with the help of Fowler's theory, numerical constraints on the lithospheric stresses generated by convection, and direct numerical simulations of subduction. The derived scaling laws show that the critical yield stress for initiation of subduction by small‐scale convection is of the order of 30 MPa. This value is comparable with the critical yield stress required for initiation of subduction by plate forces and with the estimates of stresses in the subduction zone. This implies that small‐scale convection can play an important role in the initiation of subduction on the present‐day Earth. This also implies that small‐scale convection can initiate subduction in the absence of already occurring plate tectonics and thus can be a trigger mechanism for plate tectonics on the early Earth and other terrestrial planets. The critical yield stress for initiation of subduction by either mechanism is at least one order of magnitude smaller than the estimates of the lithospheric strength suggested by laboratory experiments on rock deformation. Such a low lithospheric strength is most likely caused by a relatively high abundance of water in the interior of the Earth. Since the critical yield stress depends only weakly on planetary parameters, water seems to be the key condition required for plate tectonics to occur on a terrestrial planet.
Vertical profiles of mass flux for windblown sand movement at steady state
Authors: Zheng Xiaojing , He Lihong , Wu Jianjun
Published: January 2004

A profile pattern different from the generally accepted one that mass flux exponentially decreases with the height is indicated by several experimental and theoretical studies and field observations on aeolian sediment transports; however, a theoretical explanation for such a pattern is still absent. To overcome this difficulty, a new model is suggested in this paper, in which the interaction between the saltation of sand grains and the winds is considered, the probability distribution function of vertical liftoff velocities of grains is used to obtain all probable trajectories of saltating grains, and the steady state of the windblown sand movement is reached by adjusting the surface ejection flux (the number ejected per unit area of the bed per unit time). The validity of the model is confirmed by comparing the numerical results of streamwise sand transport versus wind velocity with those calculated from the well‐known empirical formulas of Bagnold and Kawamura in their respective effective regions and by comparing the mass flux profile with Yin's observation in the gravel desert. The vertical profile of the mass flux of windblown sand movement obtained obviously displays a stratification pattern composed of a linear increment layer, a saturation layer, and a monotonic decrement layer. The numerical results also elucidate that the stratification patterns of the steady mass flux profiles are not influenced by the electrification force, the wind velocity, and the distributions of vertical liftoff velocities of sand grains, while the peak value of mass flux may occur at different heights, and tend to shift upward with increasing wind velocity.
Water flux estimates in the central Mediterranean Sea from an inverse box model
Authors: Vetrano Anna , Gasparini Gian Pietro , Molcard Robert , Astraldi Mario
Published: January 2004

Seasonal hydrological surveys and long‐term current measurements carried out during a wide investigation of the central Mediterranean, connecting the eastern and western parts of the basin with the Tyrrhenian Sea, are used to estimate the absolute geostrophic flow through the region applying an inverse methodology. The inverse box model prescribes conservation of water properties (mass, heat, and salt) inside closed boxes of water, as well as the imposition of mean fluxes by direct current measurements. The model result is a mean circulation of the region during four different periods, along with simultaneous evaluation of water fluxes through the three boundary sections and the associated uncertainties. The overall situation, besides confirming previous qualitative knowledge on the mean circulation at all levels, provides a novel quantitative pattern of the water mass exchange in a region that is crucial for the assessment of a more realistic budget for the whole basin. The positive results obtained indicate that the inverse method may be considered an effective powerful tool for successful applications at regional scale.
Numerical simulations of convection in Europa's ice shell: Implications for surface features
Authors: Showman Adam P. , Han Lijie
Published: January 2004

Europa's icy surface displays numerous small (5‐ to 30‐km‐diameter) pits, spots, and uplifts that have been suggested to result from convection in the ice shell. To test this hypothesis, we present numerical simulations of convection in Europa's ice shell, including temperature‐dependent viscosity and tidal heating. Ice shells 15 and 50 km thick are considered, consistent with several estimates of the shell thickness on Europa. The convection produces deep pits (consistent with some of the observed features) when the lithospheric viscosity is 103–105 times greater than that of the underlying ice, but greater viscosity contrasts lead to topography insufficient to explain the observed pits. If ductile creep is the only deformation mechanism, these results imply that convection cannot produce the observed pits and uplifts because in that case the predicted surface viscosity exceeds that of the warm underlying ice by at least a factor of 1010. However, the strength of Europa's surface may be low enough for plastic deformation to play a role in the convection, opening the possibility that convection could produce some of Europa's pits. For plausible viscosities (1013 Pa s at the melting temperature), the pits are 100–300 m deep and 10–20 km in diameter; greater or lesser viscosities lead to wider or narrower pits, respectively. None of our simulations produced isolated uplifts of any diameter, however, so these probably formed by another mechanism. The convection can induce surface stresses >1 bar, which exceeds the inferred strength of Europa's crust and indicates the likelihood of surface disruption. The maximum tidal heat fluxes that can be transported by convection at realistic ice viscosities are 0.05–0.07 W m−2.
Thickness of the Martian crust: Improved constraints from geoid‐to‐topography ratios
Authors: Wieczorek Mark A. , Zuber Maria T.
Published: January 2004

The average crustal thickness of the southern highlands of Mars was investigated by calculating geoid‐to‐topography ratios (GTRs) and interpreting these in terms of an Airy compensation model appropriate for a spherical planet. We show that (1) if GTRs were interpreted in terms of a Cartesian model, the recovered crustal thickness would be underestimated by a few tens of kilometers, and (2) the global geoid and topography signals associated with the loading and flexure of the Tharsis province must be removed before undertaking such a spatial analysis. Assuming a conservative range of crustal densities (2700–3100 kg m−3), we constrain the average thickness of the Martian crust to lie between 33 and 81 km (or 57 ± 24 km). When combined with complementary estimates based on crustal thickness modeling, gravity/topography admittance modeling, viscous relaxation considerations, and geochemical mass balance modeling, we find that a crustal thickness between 38 and 62 km (or 50 ± 12 km) is consistent with all studies. Isotopic investigations based on Hf‐W and Sm‐Nd systematics suggest that Mars underwent a major silicate differentiation event early in its evolution (within the first ∼30 Ma) that gave rise to an “enriched” crust that has since remained isotopically isolated from the “depleted” mantle. In comparing estimates of the thickness of this primordial crust with those obtained in this study, we find that at least one third of the Martian crust has an origin dating from the time of accretion and primary differentiation. Subsequent partial melting of the depleted mantle would have given rise to the remaining portion of the crust. While we predict that a large portion of the crust should be composed of ancient “enriched” materials, a representative sample of this primordial crust does not currently exist among the known Martian meteorites.
Estimating bulk rheological properties of flowing snow avalanches from field data
Authors: Ancey C. , Meunier M.
Published: January 2004

Knowing the path profile and the avalanche velocity variations with downstream distance makes it possible to deduce the bulk frictional force experienced by an avalanche during its course. This derivation was applied to 15 documented events reported in the literature. Three types of rheological behavior were identified: (1) the inertial regime, where the frictional force drops to zero; (2) the Coulombic frictional force, where the force is fairly independent of the avalanche velocity; and (3) the velocity‐dependent regime, where the force exhibits a complicated (nonlinear and hysteretic) dependence on velocity. During its course an avalanche can experience one or several regimes. Interestingly, the Coulomb model can provide predictions of the velocity and run‐out distance in good agreement with field data for most events, even though for some path sections the bulk frictional force departs from the Coulomb model. This result is of primary importance in zoning applications since it makes it possible to deduce avalanche velocities from a knowledge of the run‐out distance. Its physical meaning is, however, not clearly demonstrated in this paper due to the lack of suitable data.
A panel data analysis of commercial customers' water price responsiveness under block rates
Authors: Moeltner Klaus , Stoddard Shawn
Published: January 2004

The existing literature on nonresidential water demand has primarily employed cross‐sectional models based on time‐aggregated data. In this study, we analyze panel data models of commercial water demand that build on monthly observations of water use and marginal prices for individual customers. This allows for a closer investigation of the temporal aspects of commercial water demand. We show that commercial water demand can exhibit strong seasonal patterns. These temporal consumption patterns aggravate simultaneity problems associated with block pricing if they are not explicitly accounted for in demand specifications.
The physics basis for ignition using indirect-drive targets on the National Ignition Facility
Authors: Lindl John D. , Amendt Peter , Berger Richard L. , Glendinning S. Gail , Glenzer Siegfried H. , Haan Steven W. , Kauffman Robert L. , Landen Otto L. , Suter Laurence J.
Published: January 2004

The 1990 National Academy of Science final report of its review of the Inertial Confinement Fusion Program recommended completion of a series of target physics objectives on the 10-beam Nova laser at the Lawrence Livermore National Laboratory as the highest-priority prerequisite for proceeding with construction of an ignition-scale laser facility, now called the National Ignition Facility (NIF). These objectives were chosen to demonstrate that there was sufficient understanding of the physics of ignition targets that the laser requirements for laboratory ignition could be accurately specified. This research on Nova, as well as additional research on the Omega laser at the University of Rochester, is the subject of this review. The objectives of the U.S. indirect-drive target physics program have been to experimentally demonstrate and predictively model hohlraum characteristics, as well as capsule performance in targets that have been scaled in key physics variables from NIF targets. To address the hohlraum and hydrodynamic constraints on indirect-drive ignition, the target physics program was divided into the Hohlraum and Laser–Plasma Physics (HLP) program and the Hydrodynamically Equivalent Physics (HEP) program. The HLP program addresses laser–plasma coupling, x-ray generation and transport, and the development of energy-efficient hohlraums that provide the appropriate spectral, temporal, and spatial x-ray drive. The HEP experiments address the issues of hydrodynamic instability and mix, as well as the effects of flux asymmetry on capsules that are scaled as closely as possible to ignition capsules (hydrodynamic equivalence). The HEP program also addresses other capsule physics issues associated with ignition, such as energy gain and energy loss to the fuel during implosion in the absence of alpha-particle deposition. The results from the Nova and Omega experiments approach the NIF requirements for most of the important ignition capsule parameters, including drive temperature, drive symmetry, and hydrodynamic instability. This paper starts with a review of the NIF target designs that have formed the motivation for the goals of the target physics program. Following that are theoretical and experimental results from Nova and Omega relevant to the requirements of those targets. Some elements of this work were covered in a 1995 review of indirect-drive [J. D. Lindl, “Development of the indirect-drive approach to inertial confinement fusion and the target physics basis for ignition and gain,” Phys. Plasmas 2, 3933 (1995)]. In order to present as complete a picture as possible of the research that has been carried out on indirect drive, key elements of that earlier review are also covered here, along with a review of work carried out since 1995.
Sheath-lens probe for negative ion detection in reactive plasmas
Authors: Stamate E. , Sugai H. , Takai O. , Ohe K.
Published: January 2004

A method that allows easy and inexpensive detection of negative ions is introduced. The method is based upon the electrostatic lens effect of the sheath layer evolving to a positively biased planar probe that focuses the negative charges to distinct regions on the surface. Trajectories of negative ions inside the sheath are obtained after computing the potential and electric field distribution by solving in three dimensions the nonlinear Poisson equation. The negative ions’ flux to square and disk probes is developed in Ar/SF6 and O2 plasmas. The method allows negative ion detection with sensitivity higher than that of Langmuir probes.
Lorentz microscopy studies of the variation with temperature and processing conditions of free layer reversal mechanisms in spin valves
Authors: Lim C. K. , Chapman J. N. , Rahman M. , Johnston A. B. , O’Donnell D. O.
Published: January 2004

The reversal process of the free layer of two spin valves (SVs) with crossed anisotropy was studied as a function of temperature by transmission electron microscopy. In situ magnetizing experiments were carried out using the Fresnel imaging mode at room temperature, 100 °C, and 200 °C. The two SVs studied had slightly different synthetic antiferromagnetic (SAF) structures, the magnetic layers being thicker in one than the other. It was found that the SV with the thinner SAF layer was less thermally stable. Moreover, a change in the reversal process was observed at elevated temperature while no changes were seen for the SV with thicker SAF. Insight into why the reversal mode varied in the way it did was obtained using a modified Stoner–Wohlfarth model.
Landau damping
Authors: Drummond W. E.
Published: January 2004

The damping of a longitudinal plasma wave of finite amplitude is considered. It is shown that the Landau result is the first term in a systematic expansion in a small parameter, and the corrections for finite wave amplitude are shown to be fifth order in the small parameter. The contributions to the damping from particles with different velocities near the phase velocity are explicitly calculated and this leads to a simple physical picture of the damping process.
Molecular dynamics study of the n-hexane–water interface: Towards a better understanding of the liquid–liquid interfacial broadening
Authors: Nicolas J. P. , de Souza N. R.
Published: January 2004

By molecular dynamics simulations, we have studied the hydrophilic–hydrophobic interface between water and n-hexane liquid phases. For all temperatures studied our computed interfacial tension agrees very well with the experimental value. However, the interfacial width calculated from capillary wave theory systematically overestimates the width obtained from fitting either the total density or composition profile. We rationalize the applicability of capillary wave theory for our system by reconsidering the usual value taken for the correlation length. This is motivated by the presence of order at the interface. Possible implications for recent experimental studies on the structure of model alkane–water interfaces are discussed, including the significance of the intrinsic width parameter.
Exchange coupling in a half-metallic and hard-magnetic Fe3O4–antiferromagnetic CrMnPt system, and unidirectional anisotropy enhancement with the induction of stress-induced anisotropy in the CrMnPt film
Authors: Soeya Susumu , Takahashi Hiromasa
Published: January 2004

Exchange coupling between half-metallic Fe3O4 and antiferromagnetic CrMnPt films was investigated, with the goal of inducing unidirectional anisotropy in the Fe3O4 film having hard magnetic properties. We succeeded in obtaining a large unidirectional anisotropy constant of ∼0.15 erg/cm2, a high blocking temperature of ∼320 °C, and an almost unidirectionally shifted M–H curve. The unidirectional anisotropy constant of the Fe3O4–CrMnPt system increased to ∼0.18 erg/cm2, while the high blocking temperature and the nearly unidirectionally shifted M–H curve were retained, when a NiO film was deposited by sputtering onto the CrMnPt film, and the resulting system was annealed at 230 °C for 3 h. This strong unidirectional anisotropy constant is thought to have been caused by large stress relief in the NiO film resulting from the thermal annealing that acted to increase the c/a ratio in the CrMnPt film (the a and c are lattice constants), inducing so-called stress-induced anisotropy in the CrMnPt film.
Broadband optical characterization and modeling of photonic crystal waveguides for silicon optical interconnects
Authors: Zelsmann M. , Picard E. , Charvolin T. , Hadji E. , Heitzmann M. , Dal’zotto B. , Nier M. E. , Seassal C. , Rojo-Romeo P. , Letartre X.
Published: January 2004

Optical properties of a straight 50-row-long photonic crystal waveguide (PCW) are reported. This waveguide is obtained by removing one row of air holes in a triangular lattice two-dimensional photonic crystal etched on a silicon-on-insulator substrate. Transmission measurements are performed on a wide wavelength range (1.15–1.75 μm) with an external white light source. It is found that the experimental data are in very good agreement with both the theoretical transmission calculated by a two-dimensional finite difference time domain method and the theoretical photonic band structure. We show a coupling factor higher than 60% between a monomode ridge waveguide and the PCW.
Collision processes of C2,3Hy and C2,3Hy+ hydrocarbons with electrons and protons
Authors: Janev R. K. , Reiter D.
Published: January 2004

Cross sections and rate coefficients are provided for inelastic collision processes of electrons and protons with CxHy and CxHy+ (x=2,3; 1⩽y⩽2x+2) hydrocarbon species in a wide range of collision energies and plasma (gas) temperatures. The considered processes include electron-impact ionization and dissociation of CxHy, dissociative excitation, ionization and recombination of CxHy+ with electrons, and both charge transfer and atom exchange in proton channels are considered separately. The presented cross sections are based upon a critical assessment of available experimental data and upon an extensive use of a number of semi-empirical, physically well grounded cross section scaling relationships. Information is also provided for the energetics of each individual reaction channel. The cross sections and rate coefficients are presented in compact analytic forms.
Statistico-probabilistic approach to taking account of the vapor depletion in the kinetics of homogeneous nucleation: A free-molecular regime of droplet growth
Authors: Grinin A. P. , Kuni F. M. , Djikaev Y. S.
Published: January 2004

We propose a statistico-probabilistic approach to investigate the process of homogeneous formation of droplets in a vapor phase in the presence of an already formed and growing droplet under free-molecular regime of droplet growth after the instantaneous creation of initial vapor supersaturation. We find the probability density for the formation of a new, nearest (neighbor) droplet in the vicinity of an initially formed droplet. The mean distance between two neighboring droplets is also determined, as well as the average time lag for the formation of the nearest (neighbor) droplet; the latter quantity serves as an estimate for the duration of the nucleation stage. An estimate for the average number of droplets forming in unit volume by the end of the nucleation stage is also given. Our results are compared with the predictions of classical nucleation theory which assumes the density uniformity of a metastable phase. Where the proposed appoach is applicable, there is observed qualitative agreement between the results. The underlying cause of this agreement is analyzed and the limits of applicability of the uniformity approximation are clarified.
Space charge limited transport and time of flight measurements in tetracene single crystals: A comparative study
Authors: de Boer R. W. I. , Jochemsen M. , Klapwijk T. M. , Morpurgo A. F. , Niemax J. , Tripathi A. K. , Pflaum J.
Published: January 2004

We report on a systematic study of electronic transport in tetracene single crystals by means of space charge limited current spectroscopy and time of flight measurements. Both I–V and time of flight measurements show that the room-temperature effective hole mobility reaches values close to μ≃1 cm2/V s and that, within a range of temperatures, the mobility increases with decreasing temperature. The experimental results further allow the characterization of different aspects of the tetracene crystals. In particular, the effects of both deep and shallow traps are clearly visible and can be used to estimate their densities and characteristic energies. The results presented in this article show that the combination of I–V measurements and time of flight spectroscopy is very effective in characterizing several different aspects of electronic transport through organic crystals.
Quantum transport in carbon nanotube transistors: Complex band structure effects
Authors: Xia T.-S. , Register L. F. , Banerjee S. K.
Published: January 2004

We report the subthreshold characteristics of ballistic carbon nanotube field effect transistors (CNTFETs) showing the complex band structure effect. The tunneling of carriers from source to drain through a looped complex band structure increases the subthreshold drain current, reducing the on–off current ratio. We find that nanoscale CNTFETs can perform better with a larger on–off current ratio and better subthreshold swing if the CNT has a larger band gap.
Water in nanopores. I. Coexistence curves from Gibbs ensemble Monte Carlo simulations
Authors: Brovchenko I. , Geiger A. , Oleinikova A.
Published: January 2004

Coexistence curves of water in cylindrical and slitlike nanopores of different size and water–substrate interaction strength were simulated in the Gibbs ensemble. The two-phase coexistence regions cover a wide range of pore filling level and temperature, including ambient temperature. Five different kinds of two-phase coexistence are observed. A single liquid–vapor coexistence is observed in hydrophobic and moderately hydrophilic pores. Surface transitions split from the main liquid–vapor coexistence region, when the water–substrate interaction becomes comparable or stronger than the water–water pair interaction. In this case prewetting, one and two layering transitions were observed. The critical temperature of the first layering transition decreases with strengthening water–substrate interaction towards the critical temperature expected for two-dimensional systems and is not sensitive to the variation of pore size and shape. Liquid–vapor phase transition in a pore with a wall which is already covered with two water layers is most typical for hydrophilic pores. The critical temperature of this transition is very sensitive to the pore size, in contrast to the liquid–vapor critical temperature in hydrophobic pores. The observed rich phase behavior of water in pores evidences that the knowledge of coexistence curves is of crucial importance for the analysis of experimental results and a prerequiste of meaningful simulations.
New coupled-cluster methods with singles, doubles, and noniterative triples for high accuracy calculations of excited electronic states
Authors: Kowalski Karol , Piecuch Piotr
Published: January 2004

The single-reference ab initio methods for high accuracy calculations of potential energy surfaces (PESs) of excited electronic states, termed the completely renormalized equation-of-motion coupled-cluster approaches with singles, doubles, and noniterative triples [CR-EOMCCSD(T)], are developed. In the CR-EOMCCSD(T) methods, which are based on the formalism of the method of moments of coupled-cluster equations [P. Piecuch et al., Int. Rev. Phys. Chem. 21, 527 (2002)], the suitably designed corrections due to triple excitations are added, in a state-selective manner, to the excited-state energies obtained in the standard equation-of-motion coupled-cluster calculations with singles and doubles (EOMCCSD). It is demonstrated that the CR-EOMCCSD(T) approaches, which can be regarded as the excited-state analogs of the ground-state CR-CCSD(T) theory [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 18 (2000)], provide a highly accurate description of excited states dominated by double excitations, excited states displaying a manifestly multireference character, and PESs of excited states along bond breaking coordinates with the ease of the ground-state CCSD(T) or CR-CCSD(T) calculations. The performance of the CR-EOMCCSD(T) methods is illustrated by the results of calculations for the excited states of CH+, HF, N2, C2, and ozone.
Spectroscopy of the conformational disorder in molecular films: Tetracosane and squalane on Pt(111)
Authors: Fuhrmann D. , Graham A. P.
Published: January 2004

The spectroscopic investigation of the molecular vibrations of adsorbed branched and unbranched alkane molecules using helium atom scattering (HAS) provides evidence for the thermal formation of gauche defects in tetracosane (C24H50) monolayers above 200 K. HAS results for the vibration of tetracosane molecules perpendicular to the Pt(111) surface reveal a strong frequency decrease and peak broadening above the transition temperature which can be related to a reduction of the force holding the molecules to the surface. This reduction of the force is interpreted as being due to the thermal formation of gauche defects within the tetracosane molecules.
Multipole induced splitting of metal-cage vibrations in crystalline endohedral D2d-M2@C84 dimetallofullerenes
Authors: Krause M. , Popov V. N. , Inakuma M. , Tagmatarchis N. , Shinohara H. , Georgi P. , Dunsch L. , Kuzmany H.
Published: January 2004

Metal-carbon cage vibrations of crystalline endohedral D2d-M2@C84 (M=Sc,Y,Dy) dimetallofullerenes were analyzed by temperature dependent Raman scattering and a dynamical force field model. Three groups of metal-carbon cage modes were found at energies of 35–200 cm−1 and assigned to metal-cage stretching and deformation vibrations. They exhibit a textbook example for the splitting of molecular vibrations in a crystal field. Induced dipole–dipole and quadrupole–quadrupole interactions account quantitatively for the observed mode splitting. Based on the metal-cage vibrational structure it is demonstrated that D2d-Y2@C84 dimetallofullerene retains a monoclinic crystal structure up to 550 K and undergoes a transition from a disordered to an ordered orientational state at a temperature of approximately 150 K.
Polarization switch using thick holographic polymer-dispersed liquid crystal grating
Authors: Lu Yan-qing , Du Fang , Wu Shin-Tson
Published: January 2004

Theoretical study of the optical diffraction properties of holographic polymer-dispersed liquid crystal (HPDLC)-based thick volume grating was presented. It is found that the HPDLC grating can selectively diffract the s-polarized light only, p-polarized light only, or both s and p beams by selecting suitable grating parameters. When an electric field is applied, the s- and p-polarized lights exhibit different diffraction behaviors and, thus, the tunable dual-state or three-state polarization switching could be realized.
Annealing effect on the property of ultraviolet and green emissions of ZnO thin films
Authors: Kang Hong Seong , Kang Jeong Seok , Kim Jae Won , Lee Sang Yeol
Published: January 2004

The mechanism of ultraviolet (UV) and green emission of ZnO thin films deposited on (001) sapphire substrates by pulsed laser deposition was investigated by using postannealing treatment at various annealing temperatures after deposition. Structural, electrical, and optical properties of ZnO films have been also observed. As the postannealing temperature increased, the intensity of UV (380 nm) peak and the carrier concentration were decreased while the intensity of the visible (about 490–530 nm) peak and the resistivity were increased. The role of oxygen in ZnO thin film during the annealing process was important to the change of optical properties. The mechanism of the luminescence suggested that UV luminescence of ZnO thin film was related to the transition from near band edge to valence band, and green luminescence of ZnO thin film was caused by the transition from deep donor level to valence band due to oxygen vacancies. The activation energy derived by using the variation of green emission intensity was 1.19 eV.
Stability of drift waves in the presence of dust
Authors: Sen S.
Published: January 2004

In the presence of dust particles in the plasma, it is shown that the well-known stability of the drift wave in a sheared slab geometry does not hold. Due to the presence of dust particles in tokamaks, the magnetic shear damping is reduced drastically. As a result, both the collisionless and collisional (dissipative) drift modes become unstable under the typical parameter regimes of a tokamak. Consequently, drift waves must still be considered as an underlying dynamic of anomalous transport in tokamak edges, where dust particles are found to be abundant.
Interaction of powerful laser pulse with magnetized plasma
Authors: Krasovitskii V. B. , Dorofeenko V. G. , Sotnikov V. I. , Bauer B. S.
Published: January 2004

In this paper the generation of electrostatic wake field and electron acceleration in this field by intense laser pulse propagating in plasma in the presence of external magnetic field is investigated. It is shown that if the change in the laser pulse wave amplitude (approximation of the constant laser pulse wave field) is not taken into account, it is possible by switching to Lagrangian variables to reduce the system of equations describing excitation of the wake field and electron acceleration to a simplified system of ordinary differential equations (ODE), which can be easily integrated. This makes it possible to find the energy, transferred to electron oscillations in the wake field for different angles between the direction of laser pulse propagation and magnetic field. Stability of the laser pulse propagating with arbitrary angle to external magnetic field towards excitation of parametric and decay instabilities with involvement of upper hybrid and lower hybrid waves is investigated, as well. Equations describing these instabilities are derived and growth rates are found analytically for a small amplitude wake field and with the help of numerical calculations in the case of the finite wake field amplitude.
Jamming in hard sphere and disk packings
Authors: Donev Aleksandar , Torquato Salvatore , Stillinger Frank H. , Connelly Robert
Published: January 2004

Hard-particle packings have provided a rich source of outstanding theoretical problems and served as useful starting points to model the structure of granular media, liquids, living cells, glasses, and random media. The nature of “jammed” hard-particle packings is a current subject of keen interest. Elsewhere, we introduced rigorous and efficient linear-programming algorithms to assess whether a hard-sphere packing is locally, collectively, or strictly jammed, as defined by Torquato and Stillinger [J. Phys. Chem. B 105, 11849 (2001)]. One algorithm applies to ideal packings in which particles form perfect contacts. Another algorithm treats the case of jamming in packings with significant interparticle gaps. We have applied these algorithms to test jamming categories of ordered lattices as well as random packings of circular disks and spheres under periodic boundary conditions. The random packings were produced computationally with a variety of packing generation algorithms, all of which should, in principle, produce at least collectively jammed packings. Our results highlight the importance of jamming categories in characterizing particle packings. One important and interesting conclusion is that the amorphous monodisperse sphere packings with density φ≈0.64 were for practical purposes strictly jammed in three dimensions, but in two dimensions the monodisperse disk packings at previously reported “random close packed” densities of φ≈0.83 were not even collectively jammed. On the other hand, amorphous bidisperse disk packings with density of φ≈0.84 were virtually strictly jammed. This clearly demonstrates one cannot judge “stability” in packings based solely on local criteria. Numerous interactive visualization models are provided on the authors’ webpage.
Absorption loss at nanorough silver back reflector of thin-film silicon solar cells
Authors: Springer J. , Poruba A. , Müllerova L. , Vanecek M. , Kluth O. , Rech B.
Published: January 2004

Absorption losses at a nanorough silver back reflector of a solar cell were measured with high accuracy by photothermal deflection spectroscopy. Roughness was characterized by atomic force microscopy. The observed increase of absorption, compared to the smooth silver, was explained by the surface plasmon absorption. Two series of silver back reflectors (one covered with thin ZnO layer) were investigated and their absorption related to surface morphology.
Transport and exchange of hydrogen isotopes in silicon-device-related stacks
Authors: Krug C. , Gusev E. P. , Cartier E. A. , Zabel T. H.
Published: January 2004

Thermally driven transport and exchange of hydrogen and deuterium in silicon-based metal-oxide-semiconductor (MOS) device-related structures were experimentally investigated using elastic recoil detection analysis. The samples were planar stacks of different materials on crystalline silicon. The materials studied included silicon oxide prepared by thermal growth, polycrystalline silicon silicon nitride, silicon oxynitride, and borophosphosilicate glass (BPSG) prepared by chemical vapor deposition (CVD). CVD was performed using either standard (hydrogen-containing) or deuterated precursors. Thermal annealing was carried out at 350–800 °C for 10–300 min in argon or in forming gas, either standard (90 vol. % N2,10 vol. % H2) or deuterated. All materials except silicon nitride were permeable to hydrogen and deuterium in the temperature range studied. Isotope exchange in the polycrystalline Si/SiO2 structure was observed above 450 °C. BPSG showed very little relative isotope exchange. Implications to MOS device processing are discussed.
Numerical analysis of space charge layers and electrical conductivity in mesoscopic cerium oxide crystals
Authors: Tschöpe Andreas , Bäuerle Christof , Birringer Rainer
Published: January 2004

The electrical conductivity of mesoscopic cubic cerium oxide crystals with space charge layers along their external boundaries has been calculated as a function of grain size. The equilibrium distribution of electronic and ionic charge carriers in this mixed conductor were obtained by numerical solution of the three-dimensional Poisson–Boltzmann equation in finite-difference approximation. At grain sizes comparable to the screening length λ, space charge layers overlap and penetrate the entire crystallite. Taking into account the inhomogeneous distribution of charge carriers, the partial electronic and ionic conductivities were calculated by numerical solution of the drift-diffusion equations in first-order expansion of the electrical potential under the non-equilibrium conditions imposed by an applied external voltage. Assuming a positive space charge potential, a characteristic grain-size-dependent increase of electronic and decrease of ionic conductivity was found. The obtained numerical results were combined with results from analytic solutions and compared with experimental data on the electrical conductivity of nanocrystalline cerium oxide.
Electrical, microstructural, and thermal stability characteristics of Ta/Ti/Ni/Au contacts to n-GaN
Authors: Motayed Abhishek , Jones Kenneth A. , Derenge Michael A. , Wood Mark C. , Zakharov D. N. , Liliental-Weber Z. , Smith David J. , Davydov Albert V. , Anderson Wallace T. , Iliadis Agis A. , Noor Mohammad S.
Published: January 2004

A metallization technique has been developed for obtaining low resistance Ohmic contact to n-GaN. The metallization technique involves the deposition of a metal layer combination Ta/Ti/Ni/Au on an n-GaN epilayer. It is observed that annealing at 750 °C for 45 s leads to low contact resistivity. Corresponding to a doping level of 5×1017 cm−3, the contact resistivity of the contact ρS=5.0×10−6 Ω cm2. The physical mechanisms underlying the realization of low contact resistivity is investigated using current–voltage characteristics, x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry.
Modeling of magnetically enhanced capacitively coupled plasma sources: Ar/C4F8/O2 discharges
Authors: Vasenkov Alex V. , Kushner Mark J.
Published: January 2004

Magnetically enhanced, capacitively coupled radio frequency plasma sources are finding continued use for etching of materials for microelectronics fabrication. MERIE (magnetically enhanced reactive ion etching) sources typically use magnetic fields of tens to hundreds of gauss parallel to the substrate to either increase the plasma density at a given pressure or to lower the operating pressure. The use of MERIEs for etching of dielectric materials, such as SiO2, often involves the use of complex gas mixtures, such as Ar/C4F8/O2/CO. In this paper results from a two-dimensional hybrid-fluid computational investigation of MERIE reactors operating in such mixtures are discussed. Fluxes and energy distributions for ions incident on the wafer are discussed for an industrially relevant geometry. The reduction in transverse electron mobility as the magnetic field increases produces a decrease in the sheath electric fields and a decrease in the dc bias (becoming more positive) at large magnetic fields thereby decreasing ion energies and increasing the angular spread of ions. These trends affect heavier ions more acutely than lighter ions. Subtle variations in the electrical geometrical layout of the reactor significantly affect the spatial uniformity of ion energy distributions.