bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind‐driven inner‐shelf circulation off central Oregon during summer
Authors: Kirincich Anthony R. , Barth John A. , Grantham Brian A. , Menge Bruce A. , Lubchenco Jane
Published: October 2005

Velocity measurements from 17 deployments of moored acoustic Doppler current profilers obtained during four summer upwelling seasons are used to describe the cross‐shelf divergence of Ekman transport in the inner shelf off Oregon. For each deployment the measured surface and bottom cross‐shelf transports were compared with estimates of the theoretical Ekman transports to find the fraction of full theoretical Ekman transport present. In general, in 15 m of water at 1–2 km offshore, measured transport was 25% of the full Ekman transport. Measured transports reached full Ekman transport 5–6 km offshore in 50 m of water. This result indicates that the region of active upwelling marked by the divergence of Ekman transport was limited to a narrow region along the coast. With small wind stress curl and no major headlands in the region, no along‐shelf trends in the transport fractions were observed. Average transport fractions at each station were similar from year to year with one exception. The interannual variability seen at this particular site was most likely a result of local along‐shelf bathymetric features. In addition, a weak linear relationship was found between the ambient stratification and the fraction of full Ekman transport. Reduced cross‐shelf transport occurred at times of decreased stratification. This type of “shutdown” of the inner‐shelf cross‐shelf circulation has significant biological implications, sequestering production in the nearshore and reducing larval cross‐shelf transport.
Determination of diapycnal diffusion rates in the upper thermocline in the North Atlantic Ocean using sulfur hexafluoride
Authors: Kim Dae‐Oak , Lee Kitack , Choi Sung‐Deuk , Kang Hee‐Sook , Zhang Jia‐Zhong , Chang Yoon‐Seok
Published: October 2005

The apparent diapycnal diffusivity below the wind‐driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern North Atlantic using sulfur hexafluoride (SF6) tracer data collected in June 1998. In this tracer experiment the downward penetration of SF6 was measured for 3 weeks following the deliberate injection of SF6 in the surface mixed layer. The resulting data were used to constrain the one‐dimensional Fickian diffusion model to estimate the diapycnal diffusivity. The model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the SF6 concentrations along the isopycnal surface. This affects the estimation of the diapycnal diffusivity. For the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0.3 ± 0.2 cm2 s−1 at a buoyancy frequency of 8.2 cph.
A flume experiment on the development of subaqueous fine‐gravel dunes from a lower‐stage plane bed
Authors: Carling P. A. , Richardson K. , Ikeda H.
Published: October 2005

Determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability. In addition, estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of, for example, oil‐ and gas‐bearing geological strata. Consequently, a series of experiments considered dune initiation. In these experiments, defects and latterly incipient dunes developed from lower‐stage plane gravel beds during near‐threshold conditions of motion (θ/θcrit = 1.0–1.016) and long periods of marginal bed load transport rates. The three‐dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters. After 17 hours of flow, incipient, low‐amplitude, simple two‐dimensional dunes developed from the defects, with heights ranging between 0.029 and 0.055 m, nonequilibrium wavelengths of 1–4 m and spans of 0.6–0.9 m. Continued development over several days, with θ/θcrit ratios of around 1.3, resulted in near‐equilibrium two‐dimensional dunes with wavelengths averaging 2.6–3.5 m and spans equal to the flume width (4 m). The inception of incipient dunes could be predicted using bulk flow models; however, this approach was not suitable for the prediction of defect development. Near‐bed turbulence, in the form of small‐scale sweep events of limited breadth, controls the initiation of defects, but larger‐scale, coherent turbulent structures in the outer flow are related to dune development. Significantly, both defects and incipient dunes can exist at the same time, which indicates that the effects of sweeps on the bed morphology persist at the same time as larger‐scale turbulent structures are beginning to effect sediment transport.
Three‐dimensionality of sand ripples under steady laminar shear flow
Authors: Langlois V. , Valance A.
Published: October 2005

We investigate the formation of three‐dimensional sand patterns under a steady laminar shear flow using a process‐based stability approach. The hydrodynamics of the problem is solved in the infinite depth case and in the long‐wavelength approximation. The sand transport is described using two different models. The first one is based on a semiempirical law in terms of both the local bed shear stress and the local bed slope. The second one accounts for an additional mechanism depending on grain inertia. A three‐dimensional linear stability analysis reveals that within both models, the most unstable mode is a longitudinal mode, thus corresponding to a ripple pattern with crests perpendicular to the flow direction. In the first model, the destabilizing effect of fluid inertia is counterbalanced by the stabilizing mechanism due to gravity, whereas in the second one, the effect of grain inertia on sand transport is found to be the pertinent stabilizing process for sufficiently large particle Reynolds number. In addition, we find that a range of oblique modes is unstable and can couple to longitudinal modes in the nonlinear regime. A weakly nonlinear analysis indeed shows that the coupling between two oblique modes and a longitudinal one gives birth to complex three‐dimensional sand ripples, which migrate in the flow direction at constant speed, preserving their shape. As a direct consequence, the three‐dimensionality of the phenomenon cannot be neglected.
Electromagnetic interaction in dipole grids and prospective high‐impedance surfaces
Authors: Simovski C. R. , Zouhdi S. , Yatsenko V. V.
Published: October 2005

A two‐dimensional grid of isotropic dipole scatterers excited by an obliquely incident plane wave is considered. Analytical formulas are obtained for the so‐called interaction constant of the grid. To validate our theory, a comparison is done between the obtained approximate relation for the interaction constant, the result of the numerical summation of dipole fields, and a known accurate result for a special case. The theory results in the grid impedance of arrays which does not depend on the wave incidence angle. We show that the grid of nearly resonant electric dipoles turns out to be prospective as a constitutive element of novel high‐impedance surfaces whose impedance is unique for the whole angular spectrum of plane waves.
Straining of colloids at textural interfaces
Authors: Bradford Scott A. , Simunek Jirka , Bettahar Mehdi , Tadassa Yadata F. , van Genuchten Martinus T. , Yates Scott R.
Published: October 2005

Although natural soil and aquifer systems often contain layers and lenses of contrasting soil texture, relatively little research has focused on the mechanisms of colloid deposition at textural interfaces. Saturated column studies were undertaken to characterize the straining behavior of negatively charged latex colloids (1.1 and 3.0 μm) at textural interfaces. Mechanisms of colloid transport and retention were deduced from measured effluent concentration curves, final spatial distributions in the columns, mass balance information, microscopic examination of deposition behavior in micromodel experiments, and numerical modeling. Transport and deposition of colloids were found to be highly dependent upon the textural interface. Deposition of colloids in a given sand was always most pronounced at the sand (inlet) surface. Here colloids enter a new pore network and are more likely to encounter smaller pores or dead‐end regions of the pore space that contribute to straining. Less deposition occurred at textural interfaces within the column than at the sand surface. We believe that this is due to the fact that advection, dispersion, and size exclusion tend to confine colloid transport to the larger pore networks, thus limiting accessibility to straining sites. Increasing the textural contrast at an interface produced greater colloid deposition when water flowed from coarser‐ to finer‐textured sands. Conversely, when water flowed from finer‐ to coarser‐textured sands, little deposition occurred. Numerical modeling indicates the need to account for blocking (filling) and accessibility of straining sites in layered systems. A previously developed straining model was modified to account for this behavior.
Effect on flow structure of sand deposition on a gravel bed: Results from a two‐dimensional flume experiment
Authors: Sambrook Smith Gregory H. , Nicholas Andrew P.
Published: October 2005

Particle imaging velocimetry (PIV) was used to quantify the entire two‐dimensional flow field over a series of fixed test beds in a laboratory flume. The test beds used in the experiments provide a two‐dimensional representation of gravel beds with contrasting roughness. The two‐dimensional form of the beds, combined with the nonintrusive nature of PIV, allowed the velocity field to be quantified right down to the bed surface. The three beds used were designed to simulate the progressive effect of sand deposition on a gravel bed with median grain size (D50) of 25 mm. Such a situation is common in bimodal beds, but, as compared with gravel and sand cases, little work has been done to investigate the interaction between the variable roughness of a bimodal bed and the flow structure above it. The results demonstrate that as the effective roughness decreases the reverse flow often found in the lee of gravel particles is eliminated. Furthermore, near‐bed velocities increase, while shear stress and turbulent kinetic energy decrease. Turbulent properties are also diminished higher up in the profile, although this is not the case for the mean downstream velocity, which remains unaffected except at the bed. Quadrant analysis reveals that Q2 and Q4 events become less frequent around high points as effective roughness decreases. All these responses to the changing bed conditions are most pronounced in areas where the effective roughness height (h) approaches 10 mm or less (h/D50 = 0.4). Such a situation is often found immediately upstream of gravel‐sand transitions in natural rivers. It is hypothesized that the hydraulic response outlined here provides a detailed physically based explanation for the gravel‐sand transition; the combination of reduced bed shear stress and Q2/Q4 events around gravel particles will result in greater mobility of the sand fraction relative to gravel. These experiments thus appear to demonstrate that there is a fundamental threshold between gravel bed and sand bed states that has not previously been quantified.
Three‐dimensional multi‐fluid simulations of Pluto's magnetosphere: A comparison to 3D hybrid simulations
Authors: Harnett E. M. , Winglee R. M. , Delamere P. A.
Published: October 2005

Results from 3D multi‐fluid simulations of the solar wind interaction with Pluto are compared to 3D hybrid simulations of the same interaction. The results from the multi‐fluid simulations are similar to the hybrid results in both the overall size of the magnetosphere as well as predicting pick‐up of ionospheric ions by the solar wind. The results from the multi‐fluid simulations also show how an increase in the mass of the pick‐up ion leads to a larger pick‐up region and an asymmetric bow shock. When the solar wind speed is doubled, but its dynamic pressure is held constant, the size of the magnetosphere more than doubles and the asymmetry of the bow shock and pick up region are enhanced. This effect is not present in MHD simulations since ion cyclotron effects are neglected. The results illustrate the ability of the multi‐fluid technique to capture ion cyclotron effects, like the hybrid technique.
Denitrification in the Arctic mid‐winter 2004/2005 observed by airborne submillimeter radiometry
Authors: Kleinböhl Armin , Bremer Holger , Küllmann Harry , Kuttippurath Jayanarayanan , Browell Edward V. , Canty Timothy , Salawitch Ross J. , Toon Geoffrey C. , Notholt Justus
Published: October 2005

We present measurements of unusually low mixing ratios of HNO3 in the exceptionally cold Arctic vortex of late‐January and early‐February 2005. The measurements were obtained by the airborne submillimeter radiometer ASUR during the polar aura validation experiment (PAVE). The distribution of HNO3 inside the vortex reaches minima below 4 ppbv around 22 km altitude and maxima above 13 ppbv around 16 km altitude, with a considerable spatial variability. We estimate a vortex averaged denitrification of 3.1 ± 0.8 ppbv around 20 km altitude, and slight renitrification below ∼15.5 km altitude. The observed HNO3 deficit is largest (∼6 ppbv) near the center of the vortex, where the air masses had experienced temperatures below the NAT formation threshold for 80–100% of the previous 20 days according to back trajectories. This suggests that the main denitrification mechanism is based on sedimenting nitric acid trihydrate particles.
Shielding effects of trees on the measurement of the Earth's electric field: Implications for secular variations of the global electrical circuit
Authors: Williams Earle , Markson Ralph , Heckman Stan
Published: October 2005

The perturbation of the natural atmospheric electric field by growing trees is considered with both measurements and electrostatic calculations. It is concluded that tree growth alone can account for the decline in measured field strength over four decades at Nagycenk, Hungary, with no need for a decrease in intensity in the global electrical circuit.
Orbital control of long‐term moisture in the southwestern USA
Authors: Polyak Victor J. , Asmerom Yemane
Published: October 2005

Regional lake sediment records, including late Pleistocene Lake Estancia, New Mexico, show that the southwestern USA was wetter than present over the last glacial maximum and drier during the Holocene. Chronology of speleothems that mark groundwater levels in Cavenee Caverns near Lake Estancia, indicates water‐level lowering through the cave during the early to middle Holocene (8500 yr BP) consistent with the timing of desiccation of Lake Estancia and deflation of the basin floor. The speleothem record also shows the same wetter to drier climatic shift during the penultimate glacial and interglacial transition at 134 kyr BP (subaqueous crusts formed when cave submerged) to 121 kyr BP (cave rafts formed during water table drop). Our data support wet glacials and dry interglacials as being a general feature of Pleistocene climate in the southwestern USA. The timing suggests that the process is orbitally controlled.
The U‐tube: A novel system for acquiring borehole fluid samples from a deep geologic CO2 sequestration experiment
Authors: Freifeld Barry M. , Trautz Robert C. , Kharaka Yousif K. , Phelps Tommy J. , Myer Larry R. , Hovorka Susan D. , Collins Daniel J.
Published: October 2005

A novel system has been deployed to obtain geochemical samples of water and gas, at in situ pressure, during a geologic CO2 sequestration experiment conducted in the Frio brine aquifer in Liberty County, Texas. Project goals required high‐frequency recovery of representative and uncontaminated aliquots of a rapidly changing two‐phase fluid (supercritical CO2 and brine) fluid from 1.5 km depth. The data sets collected, using both the liquid and gas portions of the downhole samples, provide insights into the coupled hydrogeochemical issues affecting CO2 sequestration in brine‐filled formations. While the basic premise underlying the U‐tube sampler is not new, the system is unique because careful consideration was given to the processing of the recovered two‐phase fluids. In particular, strain gauges mounted beneath the high‐pressure surface sample cylinders measured the ratio of recovered brine to supercritical CO2. A quadrupole mass spectrometer provided real‐time gas analysis for perfluorocarbon and noble gas tracers that were injected along with the CO2. The U‐tube successfully acquired frequent samples, facilitating accurate delineation of the arrival of the CO2 plume, and on‐site analysis revealed rapid changes in geochemical conditions.
On molecular transport effects in real gas laminar diffusion flames at large pressure
Authors: Palle Sridhar , Nolan Christopher , Miller Richard S.
Published: October 2005

Direct numerical simulations are conducted of unsteady, exothermic and one-dimensional laminar diffusion flames at large pressures. The simulations are used to assess the impact of molecular diffusion and real gas effects under high pressure conditions with simplified chemical kinetics. The formulation includes the fully compressible form of the governing equations, real gas effects modeled by the cubic Peng–Robinson equation of state, and a generalized form of the Soret and Dufour mass and heat diffusion vectors derived from nonequilibrium thermodynamics and fluctuation theory. The cross diffusion fluxes are derived for a ternary species system and include the effects of both heat and mass diffusion in the presence of temperature, concentration and pressure gradients (i.e., Soret and Dufour diffusion). The ternary species formulation is applied to a simplified single step reaction elucidating molecular and thermodynamic effects apparent in general combustion. Realistic models for pressure, temperature and species dependent heat capacities, viscosities, thermal conductivities and mass diffusivities are also included. Three different model reactions are simulated both including and neglecting Soret and Dufour cross diffusion. The simulation results show that Soret and Dufour effects are negligible for reactions comprised of species with equal or near equal molecular weights. However, Soret diffusion effects are apparent when species with nonequal molecular weights are involved in the reaction and result in reductions of the peak flame temperature. In addition, it is shown that neglect of cross diffusion leads to deviations in the predicted flame thicknesses, with under predictions for a hydrogen-oxygen system and over predictions for a heavy hydrocarbon reaction. These effects are explained in detail through examinations of the individual heat and mass flux vectors as well as through associated thermodynamic properties. A parametric study addresses the effects of the ambient pressure, the initial “flame Reynolds number,” the Damkohler number and the heat release parameter.
Resonances of polyatomic molecules in the Born-Oppenheimer approximation
Authors: Messirdi B. , Senoussaoui A. , Djellouli G.
Published: October 2005

We study the spectral properties of polyatomic molecules near a scattering level. We prove that in the Born-Oppenheimer approximation this study can be reduced to the one of a family of finite matrices of semiclassical pseudodifferential operators. More precisely, we show that any resonance of the molecule which is close enough to the real axis can be obtained from the discrete spectrum of one of these matrixes.
Second order superintegrable systems in conformally flat spaces. III. Three-dimensional classical structure theory
Authors: Kalnins E. G. , Kress J. M. , Miller W.
Published: October 2005

This paper is part of a series that lays the groundwork for a structure and classification theory of second-order superintegrable systems, both classical and quantum, in real or complex conformally flat spaces. Here we consider classical superintegrable systems with nondegenerate potentials in three dimensions. We show that there exists a standard structure for such systems, based on the algebra of 3×3 symmetric matrices, and that the quadratic algebra always closes at order 6. We show that the spaces of truly second-, third-, fourth-, and sixth-order constants of the motion are of dimension 6, 4, 21, and 56, respectively, and we construct explicit bases for the fourth- and sixth order constants in terms of products of the second order constants.
A recursive parametrization of unitary matrices
Authors: Jarlskog C.
Published: October 2005

A simple recursive scheme for parametrization of n-by-n unitary matrices is presented. The n-by-n matrix is expressed as a product containing the (n−1)-by-(n−1) matrix and a unitary matrix that contains the additional parameters needed to go from n−1 to n. The procedure is repeated to obtain recursion formulas for n-by-n unitary matrices.
End-evaporation dynamics revisited
Authors: Dubbeldam Johan L. A. , van der Schoot Paul
Published: October 2005

We present analytical results on the so-called end-evaporation kinetics in equilibrium polymeric systems following a temperature jump (T jump). A T jump prepares the system with a nonequilibrium length distribution, after which it relaxes back to its equilibrium state. Starting from a master equation, we develop a mean-field analytical theory based on a generating function approach, which allows explicit approximate expressions for the monomer and dimer concentrations to be derived in a discrete setting; the concentrations of the other chains as well as the average chain length were shown to be entirely expressible in terms of the monomer and dimer concentrations. We find that the calculated monomer and dimer concentrations as well as the average chain length are in good agreement with numerical simulation results and do not suffer from some of the defects of earlier continuum theories. Furthermore, the relaxation was shown to take place in three different stages. The first stage comprises the very fast relaxation of the monomers to almost their equilibrium concentration; the other polymer chains have hardly relaxed. During the second stage, which is highly nonlinear, a redistribution of material at practically constant monomer density takes place. Only in the final stage of the relaxation process the chain concentrations approach their true equilibrium values. In this stage there are only very small shifts in the concentrations of chains, which are governed by extremely slow “indirect” monomer-mediated processes.
Overcoming stiffness in stochastic simulation stemming from partial equilibrium: A multiscale Monte Carlo algorithm
Authors: Samant A. , Vlachos D. G.
Published: October 2005

In this paper the problem of stiffness in stochastic simulation of singularly perturbed systems is discussed. Such stiffness arises often from partial equilibrium or quasi-steady-state type of conditions. A multiscale Monte Carlo method is discussed that first assesses whether partial equilibrium is established using a simple criterion. The exact stochastic simulation algorithm (SSA) is next employed to sample among fast reactions over short time intervals (microscopic time steps) in order to compute numerically the proper probability distribution function for sampling the slow reactions. Subsequently, the SSA is used to sample among slow reactions and advance the time by large (macroscopic) time steps. Numerical examples indicate that not only long times can be simulated but also fluctuations are properly captured and substantial computational savings result.
Molecular ionization energies and ground- and ionic-state properties using a non-Dyson electron propagator approach
Authors: Trofimov A. B. , Schirmer J.
Published: October 2005

An earlier proposed propagator method for the treatment of molecular ionization is tested in first applications. The method referred to as the non-Dyson third-order algebraic-diagrammatic construction [nD-ADC(3)] approximation for the electron propagator represents a computationally promising alternative to the existing Dyson ADC(3) method. The advantage of the nD-ADC(3) scheme is that the (N±1)-electronic parts of the one-particle Green’s function are decoupled from each other and the corresponding equations can be solved separately. For a test of the method the nD-ADC(3) results for the vertical ionization transitions in C2H4, CO, CS, F2, H2CO, H2O, HF, N2, and Ne are compared with available experimental and theoretical data including results of full configuration interaction (FCI) and coupled cluster computations. The mean error of the nD-ADC(3) ionization energies relative to the experimental and FCI results is about 0.2eV. The nD-ADC(3) method, scaling as n5 with the number of orbitals, requires the solution of a relatively simple Hermitian eigenvalue problem. The method renders access to ground-state properties such as dipole moments. Moreover, also one-electron properties of (N±1) electron states can now be studied as a consequence of a specific intermediate-state representation (ISR) formulation of the nD-ADC approach. Corresponding second-order ISR equations are presented.
Direct numerical simulation of turbulent supercritical flows with heat transfer
Authors: Bae Joong Hun , Yoo Jung Yul , Choi Haecheon
Published: October 2005

Turbulent heat transfer to CO2 at supercritical pressure flowing in heated vertical tubes is investigated using direct numerical simulation at the inlet Reynolds number Re0=5400, which is based on inlet bulk velocity and tube diameter. Temperature range within the flow field covers the pseudocritical region, where very significant fluid property variations are involved. Both upward and downward flows are considered. The wall temperature distribution shows well-known heat transfer deterioration characterized by the localized peak in upward flows, while no such anomaly is observed in downward flows. The deterioration occurs at the region where turbulence is attenuated significantly, and is followed by the enhancement with restoration of turbulence caused by complicated interactions with a buoyancy effect. Further investigation of turbulence statistics indicates that ρux″ux″¯, ρux″ur″¯, and ρux″h″¯ are significantly affected by their respective buoyancy production terms due to ρ′ux′¯, ρ′ur′¯, and ρ′h′¯ which are proven to be significant in vertical supercritical flows. Combined with the deformation of mean velocity profile into an M-shaped one in upward flow, ρ′ux′¯ becomes negatively correlated from a certain downstream region so that ρux″h″¯ undergoes a very complicated transition changing both in sign and magnitude, causing severe impairment of heat transfer in upward supercritical flows.
Optimal molecular alignment and orientation through rotational ladder climbing
Authors: Salomon Julien , Dion Claude M. , Turinici Gabriel
Published: October 2005

We study the control by electromagnetic fields of molecular alignment and orientation in a linear, rigid-rotor model. With the help of a monotonically convergent algorithm, we find that the optimal field is in the microwave part of the spectrum and acts by resonantly exciting the rotation of the molecule progressively from the ground state, i.e., by rotational ladder climbing. This mechanism is present not only when maximizing orientation or alignment, but also when using prescribed target states that simultaneously optimize the efficiency of orientation/alignment and its duration. The extension of the optimization method to consider a finite rotational temperature is also presented.
Interactions between nanocolloidal particles in polymer solutions: Effect of attractive interactions
Authors: Patel N. , Egorov S. A.
Published: October 2005

We present a density-functional theory study of nanoparticle interactions in a concentrated polymer solution. The polymers are modeled as freely jointed tangent chains; all nonbonded interactions between polymer segments and nanoparticles are described by Lennard-Jones potentials. We test several recently proposed methods of treating attractive interactions within the density-functional theory framework by comparing theoretical results with recent simulation data. We find that the simple van der Waals approach provides the most accurate results for the polymer-mediated potential of mean force between two dilute nanoparticles. We employ this approach to study nanoparticle interactions as a function of nanoparticle-segment interaction strength and polymer solution density and temperature.
Brownian dynamics investigation of magnetization and birefringence relaxations in ferrofluids
Authors: Mériguet G. , Jardat M. , Turq P.
Published: October 2005

Brownian dynamics simulations are used to investigate the dynamics of orientational properties of real charge-stabilized ferrofluids, i.e. stable colloidal dispersions of magnetic nanoparticles. The relaxation times of the magnetization and of the birefringence, data accessible by experimental techniques, have been computed at several volume fractions. Besides, the effect of hydrodynamic interactions has been investigated. Equilibrium simulations without field are found to be inadequate to determine the aforementioned relaxation times for the systems under study, the dipolar interaction being too weak. Thus a nonequilibrium simulation procedure that mimics the experimental operating mode has been developed. After equilibrium simulations under a magnetic field, both birefringence and magnetization decays are recorded once the field is suppressed. Birefringence and magnetization decays are markedly impeded as the volume fraction increases, whereas they are barely enhanced when the intensity of the initial magnetic field is increased at a fixed volume fraction. Eventually, hydrodynamic interactions exhibit a slight but systematic lengthening of the relaxation times.
An interfacial energy mechanism for the complete inhibition of crystal growth by inhibitor adsorption
Authors: Anklam Mark R. , Firoozabadi Abbas
Published: October 2005

We present a unified model for complete crystal-growth inhibition based on the thermodynamics of interfaces. The premise for our model is that the adsorption of inhibitor leads to a reduction in interfacial tension or edge energy for the crystal surface or step, respectively. In our formulation, the work to add a layer or grow a step increases due to the difference in interfacial tensions or edge energies for surfaces with and without an adsorbed inhibitor. For a large enough difference in interfacial tensions or edge energies, complete inhibition of growth is realized when the total work does not decrease as more crystals are formed. We demonstrate that our model can provide a theoretical description of critical subcooling data for ice with antifreeze proteins and glycoproteins, critical subcooling data for hydrates and ionic crystals, and critical supersaturation data for various crystal systems.
A fluid cell with integrated acoustic radiation pressure actuator for atomic force microscopy
Authors: Onaran A. G. , Degertekin F. L.
Published: October 2005

The development of a fluid cell with an acoustic radiation pressure (ARP) actuator for atomic force microscopy (AFM) is reported. The ARP actuator uses a zinc oxide thin film transducer fabricated on a silicon substrate to generate acoustic waves in the 120–180 MHz range. These waves are coupled to the liquid and are reflected off of the AFM cantilever exerting radiation pressure to move the AFM cantilevers in the dc-MHz frequency range, providing a fast actuation scheme. Since the ARP actuator is remotely located on the fluid cell, it can be used with virtually any type of cantilever. The design, fabrication, and characterization of the AFM fluid cell with an ARP actuator are discussed and the performance of the device is compared with theoretical predictions. ARP actuator electronics and its integration to a commercial AFM system are described. Tapping mode images and molecular adhesion measurements are presented as illustrative examples.
First-principles T-matrix calculations of double-ionization energy spectra of atoms and molecules
Authors: Noguchi Yoshifumi , Kudo Yohei , Ishii Soh , Ohno Kaoru
Published: October 2005

Strong electron correlation plays an important role in the determination of double ionization energy, which is required for removing or adding two electrons, particularly in small-sized systems. Starting from the state-of-the-art GW approximation, we evaluate the particle-particle ladder diagrams up to the infinite order by solving the Bethe-Salpeter equation of the T-matrix theory to calculate the double-ionization energy spectra of atoms and molecules (Be, Mg, Ca, Ne, Ar, Kr, CO, C2H2, Li2, Na2, and K2) from first principles. The ladder diagrams up to the infinite order are significant to calculations of double-ionization energy spectra. The present results are in good agreement with available experimental data as well as the previous calculations using, e.g., the configuration-interaction method.
A study of the partitioning of the first-order reduced density matrix according to the theory of atoms in molecules
Authors: Alcoba Diego R. , Lain Luis , Torre Alicia , Bochicchio Roberto C.
Published: October 2005

This work describes a simple spatial decomposition of the first-order reduced density matrix corresponding to an N-electron system into first-order density matrices, each of them associated to an atomic domain defined in the theory of atoms in molecules. A study of the representability of the density matrices arisen from this decomposition is reported and analyzed. An appropriate treatment of the eigenvectors of the matrices defined over atomic domains or over unions of these domains allows one to describe satisfactorily molecular properties and chemical bondings within a determined molecule and among its fragments. Numerical determinations, performed in selected molecules, confirm the reliability of our proposal.
Site-directed deep electronic tunneling through a molecular network
Authors: Caspary Maytal , Peskin Uri
Published: October 2005

Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The “deep” tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors.
Epitaxial growth mechanism of L10 FePt thin films on Pt∕Cr bilayer with amorphous glass substrate
Authors: Sun An-Cheng , Kuo P. C. , Hsu Jen-Hwa , Huang H. L. , Sun Jui-Ming
Published: October 2005

Ordered L10 FePt films with magnetic perpendicular anisotropy were fabricated with a Pt∕Cr bilayer. The squareness of the L10 FePt film with a Cr underlayer and a Pt buffer was close to one when a magnetic field was applied perpendicular to the film’s plane, because a semicoherent epitaxial growth was initiated from the Cr (002) underlayer; continued through the Pt buffer layer, and extended into the L10 FePt (001) magnetic layer. Without the Pt buffer layer, the Cr atoms may diffuse directly into the FePt magnetic layer. Consequently, an epitaxial barrier of the Cr-rich FePtCr alloy formed between the Cr underlayer and the FePt magnetic layer, degrading the magnetic performance and epitaxial growth of the latter.
Controlled large-scale synthesis and magnetic properties of single-crystal cobalt nanorods
Authors: Aslam M. , Bhobe R. , Alem N. , Donthu S. , Dravid V. P.
Published: October 2005

We report detailed synthesis studies of large-scale fabrication of single-crystalline cobalt nanorods using thermally evaporated gold as a conducting electrode on a nanoporous anodized aluminum oxide (AAO) template. By varying the time (i.e., adjusting the current density), it is possible to control the length of the nanorods and these rods grow in highly anisotropic face-centered (L10) phase. The large-scale isolation of these nanorods was achieved using a mild HF solution to dissolve the AAO membranes, leaving behind large scale ensemble of the isolated Co nanorods. Scanning electron microscopy and transmission electron microscopy examinations show clear evidence for metallic Co nanorods (about 100 nm in diameter) formed inside an array of AAO nanopores. We observe more uniform length of nanorods when an external magnetic field is applied during synthesis. A preferred perpendicular (shape) anisotropy is observed in these nanorod arrays. Magnetic properties indicate both coercivity and thermal activation volume increase with increasing nanorod length.
O
2
(
Δ
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production in flowing He∕O2 plasmas. I. Axial transport and pulsed power formats
Authors: Stafford D. Shane , Kushner Mark J.
Published: October 2005

Chemical oxygen-iodine lasers (COILs) have promising applications due to their high efficiency and ease of scaling to multikilowatt powers. Recent research has focused on pumping the iodine with O2(Δ1) produced by electric discharges. In a previous work, a global model was used to develop reaction mechanisms and determine the specific energy deposition (eV∕O2) required to obtain high O2(Δ1) yields for electric discharge COILs. Experiments have recently achieved positive laser gain and oscillation with these energy depositions and have highlighted the importance of axial expansion of the plasma in optimizing excitation of the O2(Δ1). In this work, the consequences of axial transport on O2(Δ1) yields have been computationally investigated in flowing He∕O2 plasmas at a few Torrs using a one-dimensional plasma hydrodynamics and kinetics model. We show that the experimentally observed extension of the plasma glow upstream and downstream of the electrodes is due to electron diffusion and capacitive coupling of the radio-frequency power source. We also show that ≈50% higher O2(Δ1) yields can be achieved with a pulsed discharge combined with continuous-wave discharge.
O
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Δ
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production in flowing He∕O2 plasmas. II. Two-dimensional modeling
Authors: Arakoni Ramesh , Stafford D. Shane , Babaeva Natalia Y. , Kushner Mark J.
Published: October 2005

In conventional chemical oxygen-iodine lasers (COIL) the 1.315μm transition in atomic iodine is pumped by a sequence of reactions of I2 and I with O2(Δ1) which is generated using liquid chemistry. Ongoing studies are investigating means to produce the O2(Δ1) precursor with an electric discharge (eCOIL) to enable a totally gas phase system. Due to the thermodynamic and power loading requirements, the plasma in eCOIL systems is sustained in a flow of a rare-gas diluent and the O2. In previous investigations, the scaling of production of O2(Δ1) was investigated using global-kinetics and one-dimensional (1D) models. It was found that the production of O2(Δ1) scaled linearly with energy deposition for moderate loadings (a few eV∕O2 molecule). In this paper, these previous investigations are extended to two-dimensions using a plasma hydrodynamics model. The goal of this investigation is to determine if multidimensional considerations affect energy scalings for production of O2(Δ1). We found that O2(Δ1) production generally does scale linearly with energy loading, however, the saturation of O2(Δ1) production occurs at lower-energy loadings than predicted with global and 1D models. This trend is a result of the more accurately depicted and more localized energy deposition afforded by the two-dimensional model, and emphasizes the need for volumetrically uniform power deposition to optimize O2(Δ1) production.
Nanostructured ZnO coatings grown by pulsed laser deposition for optical gas sensing of butane
Authors: Mazingue T. , Escoubas L. , Spalluto L. , Flory F. , Socol G. , Ristoscu C. , Axente E. , Grigorescu S. , Mihailescu I. N. , Vainos N. A.
Published: October 2005

We report the detection of 100ppm of butane in superatmospheric N2 or air with an m-lines setup. The sensing elements are ZnO-nanostructured coatings prepared by pulsed laser deposition. The deposition technique was optimized to obtain highly transparent films of 1cm2 in area and several hundreds nanometer thick. ZnO structures preserve gas sensitivity even when deposited at room temperature. Refractive index variations down to 0.005 were detected and typical variations of about 20% were induced during ZnO film-butane contact.
Calculation of electric field and optical transitions in InGaN∕GaN quantum wells
Authors: Christmas Ursula M. E. , Andreev A. D. , Faux D. A.
Published: October 2005

We present analytical expressions for internal electric field and strain in single and multiple quantum wells, incorporating electromechanical coupling, spontaneous polarization, and periodic boundary conditions. Internal fields are typically 2% lower than the fields calculated using an uncoupled model. We point out two possible interpolation routes to calculate the piezoelectric (PZ) constants eij of an alloy from the PZ constants of the constituent materials and show that, for an In0.2Ga0.8N∕GaN quantum well system, the respective internal electric fields differ by 10%. Using an effective-mass model, we explore the effect of the uncertainty in the elastic and PZ constants of GaN on the internal field and optical transitions of InGaN∕GaN quantum wells, and find that the range of published values of eij produces an uncertainty of more than ±20% in the internal field and of more than ±30% in the blueshift in optical transition energy between zero bias and flatband conditions (when the applied field is equal and opposite to the internal field). Using the PZ constants of Shimada et al. [J. Appl. Phys. 84, 4951 (1998)] in our model gives the best fit to results in the literature for internal field and optical transition energy in InGaN∕GaN quantum wells. We find that a well with a smooth In gradient along the growth direction has similar optical properties to a well with constant composition, if the average In content of the two wells is the same.
Deaging in Gd2(MoO4)3 by cyclic motion of a single planar domain wall
Authors: Shur V. Ya. , Nikolaeva E. V. , Shishkin E. I. , Baturin I. S. , Shur A. G. , Utschig T. , Schlegel T. , Lupascu D. C.
Published: October 2005

The motion of a single planar 180° domain wall was studied in single-crystalline gadolinium molybdate, Gd2(MoO4)3. The switching current and the instantaneous wall positions were recorded using polarized light in an optical microscope and subsequent image processing. A pronounced deaging (wake-up) effect is observed represented by an increase of domain-wall shift during cyclic switching at constant voltage amplitude. The experimental data are compared to computer simulations taking into account the kinetic imprint effect under ac cycling. The latter is the change of the spatial distribution of the internal bias field during cycling. It is shown that deaging (wake-up) arises for aged (screened) initial states. After long enough cycling, the spatial distribution of the internal bias field becomes steady state and the wall motion becomes reproducible in all its details. The final distribution of the internal bias field does not depend on the initial state of the sample. The activation energies for deaging and aging are equal within the experimental uncertainty and thus very likely stem from the same micromechanism.
Room-temperature hydrogen gas sensor
Authors: Raissi Farshid , Farivar Rashid
Published: October 2005

The hydrogen gas sensing ability of n-type PtSi∕porous Si Schottky junctions is investigated at room temperature. These junctions exhibit a breakdown-type current-voltage curve, whose breakdown voltage depends on the gas content inside the pores. Hydrogen replaces gases with an inherent dipole moment and increases the breakdown voltage. The response time is very fast, around 6 s, and the recovery time is about 60 s. Concentrations as low as 10 ppm have been detected in the presence of methanol and acetone. Detection has been tested at different temperatures ranging from 273 to 300 K.
Interface states in polymer metal-insulator-semiconductor devices
Authors: Torres I. , Taylor D. M.
Published: October 2005

The admittance of polymer metal-insulator-semiconductor (MIS) capacitors has been measured as a function of frequency and applied voltage. The results reveal the presence of hole trapping states at the interface of the polysilsesquioxane insulator and the poly(3-hexylthiophene) semiconductor. The states appear to be distributed in two bands: one close to the equilibrium Fermi level at the semiconductor surface, the other ∼0.5eV above. Annealing the devices under vacuum for several hours at 90°C increases the concentration of the shallower traps to ∼3×1012cm−2eV−1, while decreasing the concentration of deep traps to ∼1×1010cm−2eV−1. Annealing improves the bulk hole mobility to ∼1×10−4cm2V−1s−1 while reducing the field-effect mobility in MIS field-effect transistors (FETs) slightly to ∼7×10−3cm2V−1s−1. Although the concentration of interface states is sufficiently great to account for gate-bias-induced threshold voltage instability in MISFETs, their associated time constants are much too short to explain the long term nature of the instability.
Effect of an external excitation on the flow structure in a circular impinging jet
Authors: Vejrazka J. , Tihon J. , Marty Ph. , Sobolík V.
Published: October 2005

The effect of an external excitation on circular impinging jet flow is studied experimentally. Velocity fields in moderate air flows (Re=10000) are investigated by hot-wire anemometry. The basic flow is excited by a small sinusoidal modulation of the nozzle exit velocity. The phase-averaging technique is used to study the behavior of vortex structures in the jet, specifically rolling-up, pairing, and interaction with the wall. The jet is found to be sensitive to excitation in the frequency range characterized by a Strouhal number, Ste=feD∕U, from 0.3 to 3. Different flow regimes are identified in the excited impinging jet: a periodic flow regime with the same frequency as the excitation, a regime with a frequency corresponding to a subharmonic of the excitation frequency, a regime alternating between these two frequencies, and two border regimes with more complicated behavior. The low-frequency excitation leads to the formation of vortices, which are larger than those occurring in an unexcited jet. Consequently, the near-wall velocity fluctuations are enhanced and the unsteady flow separation induced by vortex impingement is more pronounced. By contrast, excitation at higher frequencies, characterized by value 0.017 of a Strouhal number based on the shear layer thickness θ, Stθ=feθ∕U, leads to the roll-up of small vortices and hence to the attenuation of the near-wall velocity fluctuations. In this case, the flow separation is suppressed because the small vortices are unable to induce it. Finally, the vortex merging process is sensitive to the double-frequency excitation with subharmonic components. For example, a combined excitation at Ste=1.60 and 0.53 leads to the merging of three vortices.