bluuebunny/crossref_metadata_2025 huggingface dataset:
A spherical-cap bubble moving at terminal velocity in a viscous liquid
Authors: FENG JAMES Q.
Published: May 2007

The nonlinear Navier–Stokes equations governing steady, laminar, axisymmetric flow past a deformable bubble are solved by the Galerkin finite-element method simultaneously with a set of elliptic partial differential equations governing boundary-fitted mesh. For Reynolds number 20 ≤ Re ≤ 500, numerical solutions of spherical-cap bubbles are obtained at capillary number Ca = 1. Increasing Ca to 2 leads to a highly curved, cusp-like bubble rim that seems to correspond to skirt formation. The computed steady, axisymmetric spherical-cap bubbles with closed, laminar wakes compare reasonably with the available experimental results, especially for Re ≤ 100. By exploring the parameter space (for Re ≤ 200), a sufficient condition for steady axisymmetric solutions of bubbles with the spherical-cap shape is found to be roughly Ca > 0.4. The basic characteristics of spherical-cap bubbles of Ca ≥ 0.5, for a given Re ≥ 50, are found to be almost independent of the value of Ca (or Weber number We ≡ Re Ca). At a fixed Re ≥ 50, continuation by increasing Ca (or We) from a spherical bubble solution cannot lead to solutions of spherical-cap bubbles, but rather to a turning point at We slightly greater than 10 where the solution branch folds back to reduced values of Ca (or We). Yet continuation by reducing Ca (or We) from a spherical-cap bubble solution cannot arrive at a spherical bubble solution for Re ≥ 50, but rather at solutions with bubbles having more complicated shapes such as a sombrero, etc. Without thorough examinations of the solution stability, multiple steady axisymmetric solutions are shown to exist in the parameter space for a given set of parameters.
A multi-mode approximation to wave scattering by ice sheets of varying thickness
Authors: BENNETTS L. G. , BIGGS N. R. T. , PORTER D.
Published: May 2007

The problem of linear wave scattering by an ice sheet of variable thickness floating on water of variable quiescent depth is considered by applying the Rayleigh–Ritz method in conjunction with a variational principle. By using a multi-mode expansion to approximate the velocity potential that represents the fluid motion, Porter & Porter (J. Fluid Mech. vol. 509, 2004, p. 145) is extended and the solution of the problem may be obtained to any desired accuracy. Explicit solution methods are formulated for waves that are obliquely incident on two-dimensional geometry, comparisons are made with existing work and a range of new examples that includes both total and partial ice-cover is considered.
The effects of gravity modulation on fluid mixing. Part 2. Stochastic modulation
Authors: SIDDAVARAM V. K. , HOMSY G. M.
Published: May 2007

We study numerically the effects of zero-mean stochastic gravity modulation on the mixing characteristics of two interdiffusing miscible Boussinesq fluids initially separated by a thin diffusion layer. The gravity modulation has a Gaussian probability distribution and is characterized by an exponentially damped cosine autocorrelation function, i.e. $\langle g(t) g(t+\tau)\rangle/\langle g^{2}(t)\rangle\,{=}\,{\rm e}^{-\lambda \tau} \cos (\omega \tau)$. The associated power spectrum is a Lorentzian with peak at ω and width λ. The flow is found to depend on the following parameters: the Grashof number, Gr, based on the viscous length scale, $l_{\nu}\,{=}\,\sqrt{{\nu}/{\omega}}$; the Schmidt number, Sc; the correlation exponent, λ; and other geometric parameters. Even for extremely small Gr, we observe the propagation of gravity currents, Kelvin–Helmholtz (KH) and Rayleigh–Taylor (RT) instabilities. This is in contrast to the case of harmonic modulation considered in Part 1 (Siddavaram & Homsy J. Fluid Mech. vol. 562, 2006, p. 445) wherein these phenomena occur sequentially as Gr increases. The mixed volume is found to vary non-monotonically with the correlation exponent, λ, with narrow-band modulation having the largest mixed volume followed by harmonic modulation and then broadband modulation. This non-monotonicity of the mixed volume with λ is explained on the basis of the competition between the effects of excitation of lower frequencies, which lead to higher mixing, and the effects of the reduction in the energy content at the dominant frequency, which leads to reduced mixing. The value of the correlation coefficient, λ, at which the mixed volume is the largest is found to be independent of Gr. To understand the finer details of the mechanisms, we consider two- and three-frequency modulations. We find that increasing the amplitude of the secondary component when its frequency is smaller than that of the primary component leads to the occurrence of KH and RT instabilities at smaller Gr than that for the case of single-frequency modulation. We have understood the non-monotonic variation in the mixed volume by considering a three-frequency modulation, where one of the frequencies is smaller than the characteristic frequency and the other larger.
A shallow-water model for high-Reynolds-number gravity currents for a wide range of density differences and fractional depths
Authors: UNGARISH MARIUS
Published: May 2007

We consider the propagation of a gravity current of density ρc from a lock of length x0 and height h0 into an ambient fluid of density ρa in a channel of height H. When the Reynolds number is large, the resulting flow is governed by the parameters ρc/ρa and H* = H/h0. We show that the shallow-water one-layer model, combined with a Benjamin-type front condition, provides a versatile formulation for the thickness and speed of the current, without any adjustable constants. The results cover in a continuous manner the range of light ρc/ρa ≪ 1, Boussinesq ρc/ρa ≈ 1, and heavy ρc/ρa ≫ 1 currents in a fairly wide range of depth ratio. We obtain analytical solutions for the initial dam-break or slumping stage of propagation with constant speed, and derive explicitly the trends for small and large values of the governing parameters. This reveals the main features: (a) the heavy current propagates faster and its front is thinner than for the light counterpart; (b) the speed of the heavy current depends little on H*, while that of the light current increases with H*; and (c) in the shallow ambient case (H* close to 1) the light current is choked to move with the thickness of half-channel, while the heavy current typically moves with an unrestricted smaller thickness. These qualitative predictions are in accord with previous observations, and some quantitative comparisons with available experimental and numerical simulations data also show fair agreement. However, given the paucity of the available data, the main deficiency of the model is the unknown practical limit of applicability. For large time, t, a self-similar propagation with t2/3 is feasible for both the heavy and light currents, but the thickness profiles display differences.
A psychosocial skills training approach in Mexican out-patients with schizophrenia
Authors: VALENCIA MARCELO , RASCON MARIA LUISA , JUAREZ FRANCISCO , MUROW ESTHER
Published: May 2007

Background

The effectiveness of a psychosocial skills training (PSST) approach applied to chronic out-patients with schizophrenia was examined. We hypothesized that the PSST programme, which included treatment as usual (TAU), PSST and family therapy (FT), would reduce positive and negative symptoms, prevent relapse and rehospitalization, and improve psychosocial functioning (PSF), global functioning and treatment adherence.

Method

Eighty-two patients were randomly assigned to receive either TAU [antipsychotic medication (AP); n=39] or the PSST approach (TAU+PSST+FT; n=43). The two groups were assessed at intake and after completion of 1 year of treatment.

Results

There were statistically significant differences between the two groups. Patients in the PSST group improved their symptomatology, psychosocial and global functioning (symptoms and psychological, social and occupational functioning), showed lower relapse, rehospitalization and drop-out rates, a higher level of compliance with AP medication, and a high level of therapeutic adherence in comparison with TAU patients, whose symptoms also improved although they showed no improvement in any of the clinical or psychosocial variables. A comparison of the standardized effect sizes showed a medium and a large effect size of PSF and global functioning for the PSST group and a non-effect size for the TAU group.

Conclusions

A higher level of effectiveness was demonstrated when combining TAU, PSST and FT in comparison with AP medication alone. The PSST approach should be recommended for clinical practice.
The role of perinatal problems in risk of co-morbid psychiatric and medical disorders in adulthood
Authors: NOMURA YOKO , BROOKS-GUNN JEANNE , DAVEY CHARLES , HAM JACOB , FIFER WILLIAM P.
Published: May 2007

Background

Perinatal problems may be associated with an increased risk for psychological and physical health problems in adulthood, although it is unclear which perinatal problems (low birthweight, preterm birth, low Apgar scores, and small head circumference), or what clusters of problems, are more likely to be associated with later health problems. It is also not known whether perinatal problems (singly or together) are associated with co-morbidity between psychological and physical health problems.

Method

A regional random sample (from Baltimore) of mothers and their children (n=1525) was followed from birth to adulthood (mean age 29 years). Perinatal conditions were measured at delivery. Psychological problems (depression and suicidal ideation) were measured with the General Health Questionnaire-28 (GHQ-28) and physical problems (asthma and hypertension) with the RAND-36 Health Status Inventory.

Results

Children with perinatal problems were generally at increased risk for depression, suicidal ideation and hypertension, and co-morbid depression and hypertension even after controlling for confounders. One possible underlying condition, preterm low birthweight (LBW), extracted by cluster analysis, considering all of the four perinatal problems, was associated with increased risk for psychological and physical health outcomes as well as co-morbidity of the two.

Conclusions

LBW, preterm birth and small head circumference singly increased the risk for both psychological and physical health problems, as well as co-morbid depression and hypertension, while low Apgar scores were only associated with psychological problems. Delineating different etiological processes, such as preterm LBW, considering various perinatal problems simultaneously, might be of benefit to understanding the fetal origin of adult illness and co-morbidity.
Anti-Inflammatory Effects of the 70 kDa Heat Shock Protein in Experimental Stroke
Authors: Zheng Zhen , Kim Jong Youl , Ma Hualong , Lee Jong Eun , Yenari Midori A
Published: May 2007

The 70-kDa heat shock protein (Hsp70) is involved in protecting the brain from a variety of insults including stroke. Although the mechanism has been largely considered to be because of its chaperone functions, recent work indicates that Hsp70 also modulates inflammatory responses. To explore how and whether Hsp70 regulate immune responses in brain ischemia, mice overexpressing Hsp70 (Hsp Tg) were subjected to 2 h middle cerebral artery occlusion, followed by 24 h reperfusion. Parallel experiments were performed using a brain inflammation model. Hsp Tg microglia cocultured with astrocytes were used to evaluate the direct effects of Hsp70 on cytotoxicity of mcrigolia. Compared with wild-type (Wt) littermates, Hsp Tg mice showed decreased infarct size and improved neurological deficits. The number of activated microglia/macrophages were also reduced in ischemic brains of Hsp Tg mice. Similar observations were made in a model of brain inflammation that does not result in brain cell death. Overexpression of Hsp70 in microglia completely prevented microglia-induced cytotoxicity to astrocytes. Activation of the inflammatory transcription factor, nuclear factor-κB (NF-κB) was inhibited significantly in Hsp Tg mice and microglia. This was associated with decreased phosphorylation of NF-κB inhibitor protein, IκBα, and decreased expression of several NFκB-regulated genes. Co-immunoprecipitation studies revealed an interaction of Hsp70 with NF-κB and IκBα, but not with IkB kinase, IKKγ, suggesting that Hsp70 binds to the NF-κB:IκB complex preventing IκB phosphorylation by IKK. The findings of the present work establish an anti-inflammatory role for Hsp70 in the context of brain ischemia as a novel mechanism of protection.
Perfusion Magnetic Resonance Imaging Correlates of Neuropsychological Impairment in Multiple Sclerosis
Authors: Inglese Matilde , Adhya Sumita , Johnson Glyn , Babb James S , Miles Laura , Jaggi Hina , Herbert Joseph , Grossman Robert I
Published: May 2007

Although cognitive impairment is common in multiple sclerosis (MS), its pathophysiology is still poorly understood. Abnormalities of cerebral blood flow (CBF) have long been acknowledged in MS and advances in perfusion magnetic resonance imaging (MRI) allow for their assessment in vivo. We investigated the relationship between regional perfusion changes and neuropsychological (NP) dysfunctions in patients with relapsing-remitting and primary-progressive MS. Absolute CBF, cerebral blood volume (CBV) and mean transit time were measured in 32 MS patients and 11 healthy controls using dynamic susceptibility contrast-enhanced T2*-weighted MRI. A comprehensive NP test battery was administered to all patients. A mixed model analysis of covariance was performed for group comparisons in terms of perfusion measures in normal-appearing white matter (NAWM) and deep gray matter (GM). Pearson's correlations were used to describe the association of perfusion metrics with NP Z-scores. CBF and CBV values were significantly decreased in both NAWM and deep GM in MS patients compared with controls ( P = 0.01). In all patients, deep GM CBF was significantly associated with Rey Complex Figure Test (RCFT)-Copy ( r = 0.5; P = 0.001) and deep GM CBV and NAWM CBV were significantly associated with Color-Word Interference Inhibition Switching test (D-KEFSIS) ( r = 0.4; P = 0.008 and r = 0.4; P = 0.02). However, the only associations that remained significant after Bonferroni correction were between deep GM CBF and RCFT-Copy ( P =0.006), and deep GM CBV and D-KEFSIS ( P = 0.04). Our results suggest a role for tissue perfusion impairment in NP dysfunction in MS. Large-scale studies are needed to characterize better this association.
Interface atomic structure and magnetic anisotropy in ultrathin Fe films grown by thermal deposition and pulsed laser deposition on GaAs(001)
Authors: Kardasz B. , Zukrowski J. , Mosendz O. , Przybylski M. , Heinrich B. , Kirschner J.
Published: May 2007

Thermal deposition (TD) and pulsed laser deposition (PLD) techniques were used to prepare GaAs∕Fe(001) crystalline ultrathin films. The magnetic environment of Fe at the Fe∕GaAs(001) interface was investigated by means of conversion electron Mössbauer spectroscopy using an Fe57 probe layer having the equivalent thickness of two atomic layers. The magnetic anisotropies were measured using ferromagnetic resonance. PLD samples were affected by an appreciably higher degree of interface alloying compared with the TD films. The interface in-plane fourfold (cubic) anisotropy is significantly increased and the in-plane interface uniaxial anisotropy is significantly decreased in the PLD samples compared to those prepared using TD. The effective perpendicular demagnetizing field in the PLD films is significantly decreased compared to the TD samples due to an unexpected increase in the interface uniaxial perpendicular anisotropy at the Fe∕Au(001) interface.
Ferromagnetic resonance study of thickness-dependent magnetization precession in Ni80Fe20 films
Authors: Chen Yi-Chun , Hung Dung-Shing , Yao Yeong-Der , Lee Shang-Fan , Ji Huan-Pei , Yu Chwen
Published: May 2007

The ferromagnetic resonance (FMR) behaviors for Ni80Fe20 Permalloy films with a wide thickness range from 30to360nm were investigated. The FMR measurements were performed by a vector network analyzer (VNA) technique with scanning frequency at a specified external field. The measured frequency response was fitted well by the theoretical precession conditions. The FMR results show that the effective saturation magnetization, μ0Meff, increases from 1.01to1.36T, while the film thickness varies from 30to360nm. A discontinuous transition is observed at the thickness of 90nm, which corresponds to the transformation boundary of domain wall from Néel to Bloch type in Permalloy films. Meanwhile, the variation of damping coefficient with film thickness also shows a discontinuity at 90nm. For films thinner than 90nm, the dampings vary insignificantly with film thickness. For films thicker than 90nm, the damping coefficient varies linearly with the thickness. The result could be explained by the magnon scattering through nonuniform magnetization.
Magnetic and electromagnetic evaluation of the magnetic nanoparticle filled polyurethane nanocomposites
Authors: Guo Zhanhu , Park Sung , Hahn H. Thomas , Wei Suying , Moldovan Monica , Karki Amar B. , Young David P.
Published: May 2007

The magnetic and electromagnetic wave absorption behavior of a flexible iron-nanoparticle reinforced polyurethane nanocomposite is reported. Surface-initiated-polymerization (SIP) method was utilized to fabricate high-quality nanocomposites with uniform particle distribution and tunable particle loading (up to 65wt%). The enhancement of coercive force is observed when the nanoparticles are embedded into the polymer matrix. Electromagnetic wave absorption performance at a discrete frequency as studied by metal-backed reflection loss indicates that the SIP nanocomposites can save the weight up to 50% compared to the composite counterpart with micron-size particles.
Structure and magnetic properties of Co-rich nanocrystalline soft magnetic alloys with low coercivity
Authors: Heil T. M. , Willard M. A. , Flores J. J.
Published: May 2007

In this study, a series of five nanocrystalline soft magnetic alloys, with compositions equally spaced between (Co0.70Fe0.20Ni0.10)88Zr7B4Cu1 and (Co0.90Fe0.08N0.02)88Zr7B4Cu1, was fabricated by melt spinning and subsequent isothermal annealing. The alloys were annealed at 823 and 1023K for 3600s, and the resulting structure and magnetic properties are reported. X-ray diffraction indicates that 1h isothermal annealing at 823K results in body-centered cubic crystallites in the Fe∕Ni poor alloys and in a mixture of body-centered cubic and face-centered cubic crystallites in most Fe∕Ni rich alloy. The (Co0.90Fe0.08N0.02)88Zr7B4Cu1 alloy annealed at 823K has a low coercivity of 8A∕m and a relatively high saturation magnetization of 131.1Am2∕kg. The magnetic properties of these alloys are discussed in terms of their nanocrystalline microstructures.
X-ray magnetic circular dichroism studies of the enhancement of Fe spin moment in (Fe70Co30∕Pd)n superlattice films with high saturation magnetization
Authors: Noma Kenji , Kanai Hitoshi , Uehara Yuji , Nakamura Tetsuya , Osawa Hitoshi , Doi Shuichi , Nomura Kenji , Awaji Naoki
Published: May 2007

It was reported that magnetic materials reveal a high saturation magnetization above 2.45T, which is known as the highest saturation magnetization of Fe70Co30 alloy in nature. An (Fe70Co30∕Pd)n superlattice film with optimized sublayer thickness showed that the saturation magnetization of the Fe70Co30 sublayers and that of the whole film were 2.66 and 2.57T, respectively. These values were defined as an average of the magnetic moments of Fe, Co, and Pd atoms, and the contribution ratio of each element to the magnetization improvement is still not clear. X-ray magnetic circular dichroism measurement enabled a direct estimation of the individual moments of Fe, Co, and Pd atoms in the superlattice film and it clarified that the magnetization improvement in the superlattice films was induced by an enhancement of Fe spin moment dominantly in the Fe70Co30 sublayers. These results follow the other theoretical and experimental results about an enhancement of the Fe moment of atoms which are laminated with Pd layers.
Charge carriers at organic heterojunction interface: Exciplex emission or electroplex emission?
Authors: Yang Shengyi , Zhang Xiulong , Hou Yanbing , Deng Zhenbo , Xu Xurong
Published: May 2007

We report the electroluminescence (EL) of organic heterojunction devices based on N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′,-diamine (TPD) and 2-(4′-biphenyl)-5-(4″-tert-butylphenyl)-1,3,4-oxadiazole (PBD). Besides monomolecular emissions from TPD, there are two additional EL peaks at around 460 and 480nm from the bilayer device indium tin oxide (ITO)/TPD(100nm)∕PBD(45nm)∕Al. Our experimental data confirmed that the EL emission maximized at around 460nm is from electroplex as the result of charge carriers cross recombination at the TPD/PBD interface and the EL emission maximized at around 480nm originates from (TPD*PBD)-type exciplex.
Thermal effects in plasma-based accelerators
Authors: Esarey E. , Schroeder C. B. , Cormier-Michel E. , Shadwick B. A. , Geddes C. G. R. , Leemans W. P.
Published: May 2007

Finite plasma temperature can modify the structure of the wake field, reduce the wave-breaking field, and lead to self-trapped electrons, which can degrade the electron bunch quality in a plasma-based accelerator. A relativistic warm fluid theory is used to describe the plasma temperature evolution and alterations to the structure of a nonlinear periodic wave exited in a warm plasma. The trapping threshold for a plasma electron and the fraction of electrons trapped from a thermal distribution are examined using a single-particle model. Numerical artifacts in particle-in-cell models that can mimic the physics associated with finite momentum spread are discussed.
Zonal-flow-driven nonlinear energy transfer in experiment and simulation
Authors: Holland C. , Tynan G. R. , Fonck R. J. , McKee G. R. , Candy J. , Waltz R. E.
Published: May 2007

Using a newly developed algorithm, the nonlinear transfer of internal fluctuation energy ∣ñ∣2 due to convection of drift-wave turbulence by a geodesic acoustic mode (GAM, a finite-frequency zonal flow) has now been measured directly in a high-temperature plasma. By combining spatially resolved density fluctuation measurements obtained via an upgraded beam emission spectroscopy system in the edge region of the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] with a velocity inference algorithm, the convection of turbulent fluctuations by the GAM has been measured. Taken together, the results strongly suggest that GAM convection of turbulence leads to a transfer of internal fluctuation energy from low to high frequencies, in agreement with expectations from theory and simulation. In addition, the GAM is found to modulate the intensity of the density fluctuations. Calculations of the measured nonlinear interactions in the gyrokinetic code GYRO are found to be in good qualitative agreement with the experimental observations.
Quantum chemistry calculations for molecules coupled to reservoirs: Formalism, implementation, and application to benzenedithiol
Authors: Arnold A. , Weigend F. , Evers F.
Published: May 2007

Modern quantum chemistry calculations are usually implemented for isolated systems—big molecules or atom clusters; total energy and particle number are fixed. However, in many situations, like quantum transport calculations or molecules in a electrochemical environment, the molecule can exchange particles (and energy) with a reservoir. Calculations for such cases require to switch from the canonical to a grand canonical description, where one fixes the chemical potential rather than particle number. To achieve this goal, the authors propose an implementation in standard quantum chemistry packages. An application to the nonlinear charge transport through 1,4-benzenedithiol will be presented. They explain the leading finite bias effect on the transmission as a consequence of a nonequilibrium Stark effect and discuss the relation to earlier work.
Laser-light diffraction studies on the electric-field response of the helical director configuration in smectic-C* liquid crystals
Authors: Krueger Michael , Giesselmann Frank
Published: May 2007

We report results from laser light diffraction studies on the electric-field-induced dynamic modulation of the helical director configuration of SmC* liquid crystals. In contrast to what is predicted by common theoretical models for bulk samples, we found no increase of the helix pitch with increasing electric fields in planar-aligning cells. This can be explained by the appearance of disclinations that are pinned at the cell surfaces but also the large dimension of the sample cell along the helix axis is expected to play a role. Even more surprisingly, we found a decreasing pitch with an increasing field for one of the compounds investigated and a field-controllable rotation of the diffraction pattern around the sample cell normal in two other materials.
Structural and dielectric properties of (Li0.5Na0.5) doped strontium barium niobate
Authors: Mohiddon Md. Ahamad , Yadav K. L.
Published: May 2007

The alkali (Li0.5Na0.5) modified strontium barium niobate (SBN) was prepared by a conventional mixed oxide method. X-ray diffraction was carried out to study the phase changes developed in the sample. Quantitative x-ray analysis was also carried out to study the effect of (Li0.5Na0.5) on the “extent of reaction” in SBN reaction kinematics. From the surface morphology study it was found that grains preferred to grow in unidirection forming tetragonal shaped grains creating porosity, which in turn affects the dielectric and grain boundary resistance properties. Detailed dielectric analysis revealed that, all the SBN samples show diffuse phase transitions and alkali doping results in increasing the transition temperature along with decreasing maximum dielectric constant. Complex impedance analysis shows that (Li0.5Na0.5) doping in SBN increases its grain boundary resistance.
Theory and particle simulation of nonlinear double layers in a magnetized plasma
Authors: Kim Seung-Shik , Kim Tae-Han , Kim Ho-Yeun
Published: May 2007

Theoretical investigation and particle simulation of obliquely propagating nonlinear double layers (NDLs) of nonmonotonic type are performed in a magnetized plasma, which consists of a positively charged ion fluid and trapped, as well as free electrons. The modified Zakharov-Kuznetsov equation is derived by the usual reductive perturbation technique in a three-dimensional system. A nonlinear double layer solution is presented. Furthermore using Sagdeev’s pseudopotential technique, nonlinear double layer solution, which is associated with a set of nonlinear eigenvalue conditions, is also presented. These solutions are the analytic extensions of the monotonic double layers and solitary holes. The effects of physical parameters of nonlinear double layers are discussed. In particle simulations of a current driven system, physical relations among the obliqueness, the propagating velocity, the inverse scale length, and the maximum potential are investigated. The maximum potential and the width of the NDL decreases as the degree of the angle increases. In a chosen field, a decrease of potential width (or maximum potential) is clearly shown in the case of less than 10°. Variation of propagating velocity is clearly shown in the range of 10°–16°. Particle simulations are performed with an axially bounded electrostatic particle-in-cell code XPDP1, which is a workstation version of a one-dimensional bounded plasma code PDW1 [J. Comput. Phys. 80, 253 (1989)]. These particle simulation results are in good agreement with the qualitative theoretical results.
Nonlinear growth of marginally unstable tearing modes
Authors: Coelho R.
Published: May 2007

In this work, the nonlinear growth of the classical tearing mode is revisited, using reduced magnetohydrodynamic numerical simulations in cylindrical geometry, emphasizing the limiting scenario of a marginally unstable mode, i.e., 0∼Δ′a<4, where a is the minor radius and Δ′ is the stability parameter [H. Furth, J. Killeen, and M. N. Rosenbluth, Phys. Fluids 6, 459 (1963)]. Conventionally, the mode becomes unstable when Δ′>0 and, eventually, a steady state island width (saturated island width) is achieved. It is found that, contrary to theoretical predictions, no steady state solution is obtained for typically low temperature plasmas with perpendicular viscosity and magnetic Reynolds number below a certain threshold. Plasma inertial forces are identified as the physical mechanism behind such nonlinear evolution.
Cavity ring-down spectroscopy measurements of single aerosol particle extinction. I. The effect of position of a particle within the laser beam on extinction
Authors: Butler Timothy J. A. , Miller Johanna L. , Orr-Ewing Andrew J.
Published: May 2007

A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient εmin was determined to be 3×10−6. Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4μm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper.
Adsorption of superheavy elements on metal surfaces
Authors: Sarpe-Tudoran C. , Fricke B. , Anton J. , Persina V.
Published: May 2007

Fully relativistic four-component density functional theory with the general gradient approximation calculations have been performed to determine the adsorption energy and position of the superheavy element 112 on a Au surface. Extended cluster as well as embedded cluster calculations were used to simulate the surface which allow for the top, bridge, and hollow adsorption sites without losing the advantage of symmetry considerations. Comparison with analogous calculations of the adsorption of the homologue element Hg allows to predict the adsorption of element 112 at a bridge site with a binding energy of 0.67eV.
Total dissociative electron attachment cross sections of selected amino acids
Authors: Scheer A. M. , Mozejko P. , Gallup G. A. , Burrow P. D.
Published: May 2007

Total dissociative electron attachment cross sections are presented for the amino acids, glycine, alanine, proline, phenylalanine, and tryptophan, at energies below the first ionization energy. Cross section magnitudes were determined by observation of positive ion production and normalization to ionization cross sections calculated using the binary-encounter-Bethe method. The prominent 1.2eV feature in the cross sections of the amino acids and the closely related HCOOH molecule is widely attributed to the attachment into the –COOH π* orbital. The authors discuss evidence that direct attachment to the lowest σ* orbital may instead be responsible. A close correlation between the energies of the core-excited anion states of glycine, alanine, and proline and the ionization energies of the neutral molecules is found. A prominent feature in the total dissociative electron attachment cross section of these compounds is absent in previous studies using mass analysis, suggesting that the missing fragment is energetic H−.
Periodic orbits in biological molecules: Phase space structures and selectivity in alanine dipeptide
Authors: Farantos Stavros C.
Published: May 2007

Small and large molecules may localize their energy in specific bonds or generally in vibrational modes for extended periods of time, an effect which may have dramatic consequences in reaction dynamics. Periodic orbits offer the means to identify phase space regions with localized motions. The author demonstrate that techniques to locate periodic orbits developed for small molecules can be applied to large molecules such as alanine dipeptide. The widely used empirical force fields are employed and principal families of periodic orbits associated with local-type motions and emanated from the lowest energy minima and saddle points are investigated. Continuation of these families at high energies unravels the stable and unstable regions of phase space as well as elementary bifurcations such as saddle nodes.
Buried interfacial layer of highly oriented molecules in copper phthalocyanine thin films on polycrystalline gold
Authors: Biswas Indro , Peisert Heiko , Nagel Mathias , Casu Maria Benedetta , Schuppler Stefan , Nagel Peter , Pellegrin Eric , Chassé Thomas
Published: May 2007

The growth of copper phthalocyanine thin films evaporated on polycrystalline gold is examined in detail using near edge x-ray absorption fine structure spectroscopy and surface sensitive x-ray photoemission spectroscopy. The combination of both methods allows distinguishing between the uppermost layers and buried interface layers in films up to ∼3nm thickness. An interfacial layer of approximately 3 ML of molecules with an orientation parallel to the substrate surface was found, whereas the subsequent molecules are perpendicular to the metal surface. It was shown that even if the preferred molecular orientation in thin films is perpendicular, the buried interfacial layer can be oriented differently.
Anisotropic phase-mixing in homogeneous turbulence in a rapidly rotating or in a strongly stratified fluid: An analytical study
Authors: Salhi A. , Cambon C.
Published: May 2007

Angular phase mixing in rapidly rotating or in strongly stratified flows is quantified for single-time single-point energy components, using linear theory. In addition to potential energy, turbulent kinetic energy is more easily analyzed in terms of its toroidal and poloidal components, and then in terms of vertical and horizontal components. Since the axial symmetry around the direction n (which bears both the system angular velocity and the mean density gradient) is consistent with basic dynamical equations, the input of initial anisotropy is investigated in the axisymmetric case. A general way to construct axisymmetric initial data is used, with a classical expansion in terms of scalar spherical harmonics for the 3D spectral density of kinetic energy e, and a modified expansion for the polarization anisotropy Z, which reflects the unbalance in terms of poloidal and toroidal energy components. The expansion involves Legendre polynomials of arbitrary order, P2n0(cosθ), (n=0,1,2,…,N0), in which the term [cosθ=(k∙n)∕∣k∣] characterizes the anisotropy in k-wavespace; two sets of parameters, β2n(e) and β2n(z), separately generate the directional anisotropy and the polarization anisotropy. In the rotating case, the phase mixing results in damping the polarization anisotropy, so that toroidal and poloidal energy components asymptotically equilibrate after transient oscillations. Complete analytical solutions are found in terms of Bessel functions. The envelope of these oscillations decay with time like (ft)−2 (f being the Coriolis parameter), whereas those for the vertical and horizontal components decay like (ft)−3. The long-time limit of the ratio of horizontal component to vertical one depends only on β2(e), which is eventually related to a classical component in structure-based modeling, independently of the degree of the expansion of the initial data. For the stratified case, both the degree of initial anisotropy and the initial unbalance in terms of potential and poloidal (or kinetic gravity wave) energy are investigated. The latter unbalance is characterized by a ratio χ∕2, assuming initial proportionality between the kinetic energy spectrum and the potential energy one. The phase mixing yields asymptotic equipartition in terms of poloidal and potential energy components, and analytical solutions are found in terms of Weber functions. At large time, the damped oscillations for poloidal, potential and vertical components decay with time like (Nt)−1∕2 (N is the buoyancy frequency), while the oscillations for the horizontal component decay with time like (Nt)−3∕2. The long-time limit of the ratio of horizontal component to vertical one depends only on the parameters χ, β2(e), β0(z), β2(z), and β4(z).
Size-dependent optical and electrochemical band gaps of ZnS nanorods fabricated through single molecule precursor route
Authors: Geng B. Y. , Liu X. W. , Ma J. Z. , Du Q. B. , Zhang L. D.
Published: May 2007

The colloidal, highly crystalline, and size-controlled ZnS nanorods have been prepared through a thermal decomposition of single-source-precursor approach in oleylamine solution. The length and width of nanorods can be controlled simply by varying the molar ratio of zinc 2-mercaptobenzothiazole complex and oleylamine or prolonging the anneal duration. Optical and electrochemical properties of different sizes of ZnS nanorods are discussed and size-dependent optical and electrochemical band gaps are evidently observed, which show a direct correlation between the electronic spectra and electrochemical band gap.
Coefficient of thermal expansion and biaxial elastic modulus of β phase tantalum thin films
Authors: Knepper Robert , Baker Shefford P.
Published: May 2007

The coefficient of thermal expansion and biaxial elastic modulus of metastable tetragonal β-tantalum thin films were determined from the thermoelastic slopes of films deposited on (100) silicon and fused silica substrates. Measurements were made during heating, when the film was in the β phase, and during cooling, after the film had transformed to the stable bcc α phase. While the thermal expansion coefficients of the two phases were similar, β phase films were much more compliant than α films. The thermal expansion coefficient and biaxial elastic modulus of the α phase were consistent with values reported for bulk α tantalum.
Binary-collision modeling of ion-induced stress relaxation in cubic BN and amorphous C thin films
Authors: Abendroth B. , Jäger H. U. , Möller W. , Bilek M.
Published: May 2007

It is demonstrated that ion-bombardment-induced stress release during physical vapor deposition of cubic boron nitride (cBN) and amorphous carbon (aC) films is related to collisional relocation of atoms. A model based on TRIM and molecular dynamics computer simulations is presented. Experimental results obtained using pulsed substrate bias are in good agreement with the model predictions at adequately chosen threshold energies of atomic relocation. The collisional relaxation model describes the experimental data significantly better than the widely applied thermal spike model.
Broadband surface plasmon resonance spectroscopy for determination of refractive-index dispersion of dielectric thin films
Authors: Qi Zhi-mei , Wei Mingdeng , Matsuda Hirofumi , Honma Itaru , Zhou Haoshen
Published: May 2007

Here the authors report the spectral surface plasmon resonance (SPR) behavior of thin gold films covered with dielectric layers. With the SPR sensor angular dependence of the resonant wavelength and refractive-index (RI) sensitivity at a specific angle were measured by broadband absorption spectroscopy. By fitting the calculated SPR absorption spectrum to the experimental result, RI dispersion of a TiO2-nanoparticle/polymer composite layer was obtained, which was compared with the ellipsometry data. The phase spectra of the sensor were calculated, and a large response of the phase to the solution RI was observed around the resonant wavelength.
Ti(N) thin film resistors for 20dB Π-type attenuator applications
Authors: Cuong Nguyen Duy , Yoon Soon-Gil , Kim Dong-Jin , Kang Byoung-Don
Published: May 2007

The authors report the effect of the film thickness on electrical properties of Ti(N) film resistors. The applications of titanium nitride thin film resistor in Π-type attenuators are also characterized. As film thickness decreases from 100to30nm, the temperature coefficient of resistance significantly decreases from −60to−148ppm∕K, while the sheet resistance increases from 37to270Ω∕◻. The characterizations of 20dB attenuators using thin film resistors are improved in comparison with those using thick film resistors. The Π-type attenuators using Ti(N) thin film resistors exhibit an attenuation of −19.94dB and voltage standing wave ratio of 1.16 at a frequency of 2.7GHz.
Reproducible unipolar resistance switching in stoichiometric ZrO2 films
Authors: Wu X. , Zhou P. , Li J. , Chen L. Y. , Lv H. B. , Lin Y. Y. , Tang T. A.
Published: May 2007

The resistance switching characteristics of stoichiometric ZrO2 film were investigated for nonvolatile memory. The Al∕ZrO2∕Al device presents reliable and reproducible switching behaviors. The on/off ratio of two stable states is larger than 2×103. It is suggested that the current-voltage characteristics are governed by the Schottky conduction mechanism in high voltage region, while the filament conduction is suggested in low voltage region. The switching process is explained in terms of the spontaneous reversible reaction between electrode and ZrO2 films with the contribution of Joule heating effect by the external current. It provides a possible solution for low device yield of nonstoichiometric oxides.
Anodic nanoclusters of GaN
Authors: Kim Keunjoo , Choi Jaeho , Bae Tae Sung
Published: May 2007

The authors report an anodization of the deposited Al layer on a p-GaN surface of InGaN∕GaN multiquantum-well light-emitting-diode structures, which forms the anodic nanoclusters of GaN as well as the disordered alumina nanopore layer. The GaN nanoclusters show the shape of the radial hemisphere similar to an orange. The formation mechanism comes from the nanofluidic channel for supplying the electrolyte in electrochemical etching reaction. The nanorods with a diameter of about 100nm in nanocluster structures enhance the photoluminescence intensity by three times compared to the bare sample without anodization.
Direct writing three-dimensional Ba2TiSi2O8 crystalline pattern in glass with ultrashort pulse laser
Authors: Dai Ye , Zhu Bin , Qiu Jianrong , Ma Hongliang , Lu Bo , Cao Shixun , Yu Binkung
Published: May 2007

The nonlinear optical crystal Ba2TiSi2O8 is induced three-dimensionally inside a glass by a femtosecond pulse laser with 800nm, 250kHz, and 150fs. Micro-Raman and photoluminescence spectra confirm that crystals can grow in the focal point of the laser beam. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate a convenient method to engrave three-dimensional patterns of crystals with nonlinear optical properties for integrated optical devices.
Synthetic single crystal diamond as a fission reactor neutron flux monitor
Authors: Marinelli Marco , Milani E. , Prestopino G. , Tucciarone A. , Verona C. , Verona-Rinati G. , Angelone M. , Lattanzi D. , Pillon M. , Rosa R. , Santoro E.
Published: May 2007

Thermal neutron flux monitors were fabricated using chemical vapor deposited single crystal diamond in a p-type/intrinsic/metal/Li6F layered structure. They were placed 80cm above the core midplane of a 1MW research fission reactor, where the maximum neutron flux is 2.2×109neutrons∕cm2s. Good stability and reproducibility of the device response were observed over the whole reactor power range. A 150000counts∕s count rate was measured at the maximum reactor power with no degradation of the detector signal. As the multiple pile-up process due to the slow readout electronics is accounted for, an excellent linearity of the diamond response is observed.
Enhanced electric field tunable dielectric properties of BaZrxTi1−xO3 relaxor ferroelectrics
Authors: Maiti Tanmoy , Guo R. , Bhalla A. S.
Published: May 2007

The environmental friendly lead-free perovskite BaZrxTi1−xO3 (x=0.35, 0.40, and 0.45) relaxor ceramics are developed for the tunable microwave device applications such as tunable filters, phase shifters, antennas, etc. Electric field dependence of dielectric behavior of the ceramic samples has been studied in the temperature range from 300to15K for the tunable dielectric devices. The results have been analyzed in relation to tunability (%) and K factor of the tunable dielectric materials. Very high tunability (∼93%) as well as extremely high K factor (∼468) has been achieved by manipulating the Zr:Ti concentration in BaZrxTi1−xO3 ceramics.
Photon number resolving detector based on a quantum dot field effect transistor
Authors: Kardynał B. E. , Hees S. S. , Shields A. J. , Nicoll C. , Farrer I. , Ritchie D. A.
Published: May 2007

The authors show that the change in current flowing through the channel of a quantum dot field effect transistor is proportional to the number (N) of photons absorbed from an incident pulse. Distinct features due to photon number state up to N=3 are resolved. With improvement of external quantum efficiency the device may form a useful photon number resolving detector.
Application of Czochralski-grown SiGe bulk crystal as a substrate for luminescent strained quantum wells
Authors: Usami Noritaka , Nihei Ryota , Yonenaga Ichiro , Nose Yoshitaro , Nakajima Kazuo
Published: May 2007

Czochralski-grown Si1−xGex bulk crystal (x=0.085) was utilized as a substrate for strained Si-based quantum wells (QWs). The linewidth of the (400) x-ray rocking curve of the SiGe(100) substrate was comparable with that of the Si(100) substrate, and no peak splitting was observed in the line scan all over the substrate. Epitaxial growth of strained QWs designed as a couple of strained Si/strained Ge QWs have been attempted simultaneously on SiGe(100) and Si(100). Photoluminescence measurements revealed that the sample on SiGe(100) exhibits peaks from excitons confined in QWs without any dislocation-related luminescence in contrast to that on Si(100).
Transmission-type microfocus x-ray tube using carbon nanotube field emitters
Authors: Heo Sung Hwan , Ihsan Aamir , Cho Sung Oh
Published: May 2007

A microfocus x-ray tube that can generate x rays with the focal spot size less than 5μm has been demonstrated using carbon nanotube (CNT) field emitters. A CNT cathode on a sharp tungsten tip, a magnetic solenoid lens, and a transmission-type x-ray target were adopted for the microfocus x-ray tube. The design characteristics and the operation performance of the microfocus x-ray tube are presented. Due to the small focal spot size, clear x-ray radiographic images of 6μm bars and x-ray images with the magnification factor of higher than 230 were obtained.
Conserved region I of human coactivator TAF4 binds to a short hydrophobic motif present in transcriptional regulators
Authors: Wang Xiaoping , Truckses Dagmar M. , Takada Shinako , Matsumura Tatsushi , Tanese Naoko , Jacobson Raymond H.
Published: May 2007

TBP-associated factor 4 (TAF4), an essential subunit of the TFIID complex acts as a coactivator for multiple transcriptional regulators, including Sp1 and CREB. However, little is known regarding the structural properties of the TAF4 subunit that lead to the coactivator function. Here, we report the crystal structure at 2.0-Å resolution of the human TAF4-TAFH domain, a conserved domain among all metazoan TAF4, TAF4b, and ETO family members. The hTAF4-TAFH structure adopts a completely helical fold with a large hydrophobic groove that forms a binding surface for TAF4 interacting factors. Using peptide phage display, we have characterized the binding preference of the hTAF4-TAFH domain for a hydrophobic motif, DΨΨζζΨΦ, that is present in a number of nuclear factors, including several important transcriptional regulators with roles in activating, repressing, and modulating posttranslational modifications. A comparison of the hTAF4-TAFH structure with the homologous ETO-TAFH domain reveals several critical residues important for hTAF4-TAFH target specificity and suggests that TAF4 has evolved in response to the increased transcriptional complexity of metazoans.