bluuebunny/crossref_metadata_2025 huggingface dataset:
Postsurgical intraperitoneal exposure to glove powders modulates inflammatory and immune‐related cytokine production
Authors: Rong Hui , Tang Xin‐Min , Zhao Yong , Juneja Subhash C. , Fay Margaret F. , Williams R. Stan , Chegini Nasser
Published: September 2002

The objective of the present study was to determine whether intraperitoneal exposure to glove powders modulates the inflammatory and immune responses by altering the influx of inflammatory and immune cells and peritoneal fluid cytokines and thus the outcome of surgically induced peritoneal wound healing. Peritoneal wall injuries were made by scraping the tissue until bleeding occurred in 360 mice. One of the following fluids was then introduced into the peritoneal cavity: phosphate‐buffered saline solution, phosphate‐buffered saline solution containing glove powders (Biosorb and Keoflo, 100 µg/ml), Hydrocote (Hydrogel film, Biogel 100 µg/ml), latex proteins (1 mg/ml), or lipopolysaccharides (12.5 µg/ml). At intervals of 1 to 28 days after injury, 10 mice per treatment per day and 10 uninjured mice were killed, peritoneal fluids were collected to determine the cytokine levels, the rate of fibrous adhesions formed at the site of injuries was graded, and peritoneal walls with attached fibrous adhesions were removed to determine the degree of inflammatory and immune cell infiltration into the wound. The results indicated that, with the exception of interferon‐γ, the peritoneal fluid levels of transforming growth factor‐β1, tumor necrosis factor‐α, interleukin‐1β, and granulocyte‐macrophage‐colony stimulating factor in the phosphate‐buffered saline solution‐treated injured group significantly increased, reaching maximum between days 4 and 7 (p < 0.05) compared with the uninjured group and returned to uninjured values by day 14 after injury. The level of transforming growth factor‐β1 was higher in glove powders and Hydrocote‐treated groups than in latex, liposaccharides, or phosphate‐buffered saline solution‐treated groups until day 14 after surgery (p < 0.05). The levels of tumor necrosis factor‐α and interleukin‐1β increased in all treatment groups during the first week after injury compared with uninjured controls, with the exception of Hydrocote. The number of T helper/inducers (CD4), total leukocytes (CD11a), B lymphocytes (CD45R), granulocytes (Gr‐1), and mononuclear phagocytes (Mac‐3) in the wound increased during the first week after peritoneal wounding with no significant difference between treated and untreated groups. The rate of adhesion formation was not significantly altered in treated compared with untreated groups. These data suggest that a mechanism which mediates glove powder‐induced peritoneal inflammatory and immune reactions in the postsurgical setting involves augmentation of cytokine production without influencing the influx of inflammatory and immune cells or adhesion formation.
Clinical Results of Intraarticular Fractures of the Base of the Fifth Metacarpal Treated by Closed Reduction and Cast Immobilization
Authors: LUNDEEN J. M. , SHIN A. Y.
Published: September 2002

This retrospective study evaluated the results of closed reduction and cast immobilization for isolated intraarticular fractures of the base of the fifth metacarpal. Twenty-two of 37 such fractures were available for follow-up at an average of 43 months, and these had all healed at an average of 5 weeks without any cast complications. Twenty patients reported excellent or good results, and two reported fair or poor results. At follow-up, 13 had no arthrosis and nine had mild arthrosis of the carpometacarpal joint. However, outcome was not influenced by fracture type, the degree of subluxation or articular step off, or the presence of arthrosis. We conclude that isolated fractures of the base of the fifth metacarpal can be reliably treated with closed reduction and cast immobilization.
Control of Nitrate Uptake by Phloem‐Translocated Glutamine in Zea mays L. Seedlings
Authors: Pal'ove‐Balang P. , Mistrík I.
Published: September 2002

Abstract: The putative role of glutamine, exported from leaves to roots, as a negative feedback signal for nitrate uptake was investigated in Zea mays L. seedlings. Glutamine (Gln) was supplied by immersion of the tip‐cut leaves in a concentrated solution. Nitrate (NO3−) uptake was measured by its depletion in amino acid‐free medium. The treatment with Gln resulted in a strong inhibition of nitrate uptake rate, accompanied by a significant enrichment of amino compounds in root tissue. The effect of N‐availability on NO3− uptake was determined in split‐root cultures. The plants were subjected to complete or localized N supply. Inducible NO3− uptake systems were also induced in N‐deprived roots when the opposite side of the root system was supplied with KNO3. The inhibitory effect of Gln was unaffected by localized N supply on one side of the split‐root. The potential role of Gln in the shoot‐to‐root control of NO3− uptake is discussed.
The nonlinear behavior of a sheared immiscible fluid interface
Authors: Tauber Warren , Unverdi Salih Ozen , Tryggvason Gretar
Published: September 2002

The two-dimensional Kelvin–Helmholtz instability of a sheared fluid interface separating immiscible fluids is studied by numerical simulations. The evolution is determined by the density ratio of the fluids, the Reynolds number in each fluid, and the Weber number. Unlike the Kelvin–Helmholtz instability of miscible fluids, where the sheared interface evolves into well-defined concentrated vortices if the Reynolds number is high enough, the presence of surface tension leads to the generation of fingers of interpenetrating fluids. In the limit of a small density ratio the evolution is symmetric, but for a finite density difference the large amplitude stage consists of narrow fingers of the denser fluid penetrating into the lighter fluid. The initial growth rate is well predicted by inviscid theory when the Reynolds numbers are sufficiently high, but the large amplitude behavior is strongly affected by viscosity and the mode that eventually leads to fingers is longer than the inviscidly most unstable one.
Charged polymer membrane translocation
Authors: Ambjörnsson T. , Apell S. P. , Konkoli Z. , Di Marzio E. A. , Kasianowicz J. J.
Published: September 2002

We study the process of charged polymer translocation, driven by an external electric potential, through a narrow pore in a membrane. We assume that the number of polymer segments, m, having passed the entrance pore mouth, is a slow variable governing the translocation process. Outside the pore the probability that there is an end segment at the entrance pore mouth, is taken as the relevant parameter. In particular we derive an expression for the free energy as a function of m, F(m). F(m) is used in the Smoluchowski equation in order to obtain the flux of polymers through the pore. In the low voltage regime we find a thresholdlike behavior and exponential dependence on voltage. Above this regime the flux depends linearly on the applied voltage. At very high voltages the process is diffusion limited and the flux saturates to a constant value. The model accounts for all features of the recent experiments by Henrickson et al. [Phys. Rev. Lett. 85, 3057 (2000)] for the flux of DNA molecules through an α-hemolysin pore as a function of applied voltage.
Dynamics and characteristics of a 215-eV dynamic-hohlraum x-ray source on Z
Authors: Sanford T. W. L. , Lemke R. W. , Mock R. C. , Chandler G. A. , Leeper R. J. , Ruiz C. L. , Peterson D. L. , Chrien R. E. , Idzorek G. C. , Watt R. G. , Chittenden J. P.
Published: September 2002

A radiation source has been developed on the 20-MA Z facility that produces a high-power x-ray pulse, generated in the axial direction primarily from the interior of a collapsing dynamic hohlraum (DH). The hohlraum is created from a solid cylindrical CH2 target centered within an imploding tungsten wire-array Z pinch. Analyses and interpretation of measurements made of the x-ray generation within and radiated from the hohlraum target have been done using radiation-magnetohydrodynamic-code simulations in the r-z plane that take account of the magnetic Rayleigh–Taylor (RT) instability. These analyses suggest that a significantly reduced RT seed (relative to that used to explain targetless Z-pinch data on Z) is required to explain the observations. Although some quantitative and qualitative agreement with the measurements is obtained with the reduced RT seed, differences remain. Initial attempts to include into the simulations a precursor plasma, arising from wire material driven ahead of the main implosion, did not ameliorate the differences. Modification of the simulated W/CH2 interface may be required to properly explain the measured axial radiation pulse. This pulse, which exits a 4.5-mm2 hole centered above the target, begins ∼5 ns prior to stagnation (as defined by peak radial radiation power). The 5-ns interval leading to stagnation represents the duration when the imploding tungsten plasma acts as a hohlraum wall, trapping radiation within the interior of the foam target. The hohlraum radiation exiting the hole at 6 degrees to the z-axis reaches a maximum intensity of 3.1±0.6 TW/str (associated with an average hohlraum temperature of 215±10 eV), 1.4±0.4 ns prior to stagnation. (The uncertainties represent rms shot-to-shot variations.) This radiation pulse, characterized here, is useful for performing radiation-transport experiments with drive temperatures in excess of 200 eV.
A merging criterion for two-dimensional co-rotating vortices
Authors: Meunier Patrice , Ehrenstein Uwe , Leweke Thomas , Rossi Maurice
Published: September 2002

We propose a quantitative criterion for the merging of a pair of equal two-dimensional co-rotating vortices. A cross-validation between experimental and theoretical analyses is performed. Experimental vortices are generated by the roll-up of a vortex sheet originating from the identical and impulsive rotation of two plates. The phenomenon is then followed up in time until a rapid pairing transition occurs for which critical parameters are measured. In the theoretical approach, the nonlinear Euler solution representing a pair of equal vortices is computed for various nonuniform vorticity distributions. The stability analysis of such a configuration then provides critical values for the onset of merging. From this data set, a criterion depending on global impulse quantities is extracted for different shapes of the vorticity distribution. This theoretical statement agrees well with our experimentally based criterion.
Rayleigh–Taylor instability of violently collapsing bubbles
Authors: Lin Hao , Storey Brian D. , Szeri Andrew J.
Published: September 2002

In a classical paper Plesset has determined conditions under which a bubble changing in volume maintains a spherical shape. The stability analysis was further developed by Prosperetti to include the effects of liquid viscosity on the evolving shape modes. In the present work the theory is further modified to include the changing density of the bubble contents. The latter is found to be important in violent collapses where the densities of the gas and vapor within a bubble may approach densities of the liquid outside. This exerts a stabilizing influence on the Rayleigh–Taylor mechanism of shape instability of spherical bubbles. A comparison with experimental data shows good agreement with the new theory; the Rayleigh–Taylor instability does provide an extinction threshold for violently collapsing bubbles. It is also explained why earlier works did not produce a slope in the Rayleigh–Taylor stability curve that conforms with that of the present work.
N
2
O
and NO2 formation on Pt(111): A density functional theory study
Authors: Burch R. , Daniells S. T. , Hu P.
Published: September 2002

Catalytic formation of N2O and NO2 were studied employing density functional theory with generalized gradient approximations, in order to investigate the microscopic reaction pathways of these catalytic processes on a Pt(111) surface. Transition states and reaction barriers for the addition of chemisorbed N or chemisorbed O to NO(ads) producing N2O and NO2, respectively, were calculated. The N2O transition state involves bond formation across the hcp hollow site with an associated reaction barrier of 1.78 eV. NO2 formation favors a fcc hollow site transition state with a barrier of 1.52 eV. The mechanisms for both reactions are compared to CO oxidation on the same surface. The activation of the chemisorbed NO and the chemisorbed N or O from the energetically stable initial state to the transition state are both significant contributors to the overall reaction barrier Ea, in contrast to CO oxidation in which the activation of the O(ads) is much greater than CO(ads) activation.
Thermal decomposition of ethanol. I. Ab Initio molecular orbital/Rice–Ramsperger–Kassel–Marcus prediction of rate constant and product branching ratios
Authors: Park J. , Zhu R. S. , Lin M. C.
Published: September 2002

The unimolecular decomposition of CH3CH2OH has been investigated at the G2M (RCC2) level of theory. The decomposition reaction was found to be dependent strongly on pressure and temperature. Among the eight product channels identified, the H2O-elimination process (1) via a four-member-ring transition state is dominant below 10 atm in the temperature range of 700–2500 K. At the high—pressure limit and over 1500 K, cleavage of the C–C bond by reaction (2) producing CH3+CH2OH is predicted to be dominant while the CH3CH2+OH channel (8) also becomes competitive. The predicted high-pressure rate constants for the two major product channels can be given by k1=7.0×1013 exp(−34 200/T) and k2=3.7×1026 T−2.95 exp(−45 600/T) s−1, which compare reasonably with earlier data and with our preliminary experimental result obtained in a shock tube and static cell study. At the internal energy corresponding to the O(1D)+C2H6 reaction (140.7 kcal/mol above C2H5OH), the predicted branching ratios for the production of CH3, C2H5, and H2 are in qualitative agreement with the result of a recent cross-molecular beam experiment.
Model and probe measurements of inductively coupled CF4 discharges
Authors: Kimura T. , Ohe K.
Published: September 2002

A global model for electronegative plasma, in which the negative ion distribution is assumed to be a parabolic profile in the axial direction with a flat central region and a similar edge profile in the radial direction in the electronegative region, is applied to study the power and pressure dependences of plasma parameters in low-pressure CF4 discharges. The electron density increases approximately linearly with the power. The electron temperature also increases with the power due to the decrease in neutral number density with increase in power, resulting in the increase in plasma potential. The density of CF3+ is a weak function of the power, while the densities of CF2+, CF+, and F+, which are strongly correlated to the densities of the respective radicals, depend on the power. On the other hand, the decrease in electron temperature with the pressure significantly results in a decrease in the degree of dissociation. The electron density also decreases gradually with the pressure except for the case of pressure lower than 5 mTorr. The densities of CF2+, CF+, and F+ decrease gradually with the pressure at pressures higher than 5 mTorr, while the density of CF3+ increases gradually with the pressure. The electron energy probability function (EEPF) is measured with a Langmuir probe in an inductively coupled rf (13.56 MHz) CF4 discharge over a pressure range from 2 to 30 mTorr, while keeping the power injected into the plasma at about 70 W. The measured EEPFs are approximately Maxwellian at any pressure, although there is a slight deviation from a Maxwellian distribution at pressures higher than 10 mTorr. The results estimated from the measured EEPF are compared to the model and show reasonably good agreement.
Lagrangian simulation of the unsteady near field dynamics of planar buoyant plumes
Authors: Soteriou M. C. , Dong Y. , Cetegen B. M.
Published: September 2002

The unsteady dynamics of planar plumes is investigated numerically with particular emphasis on the pulsating instability characterizing the source (nozzle) near field. This instability manifests itself as the periodic shedding of vortical structures from the nozzle. The Lagrangian Transport Element Method is used to provide high resolution two-dimensional simulations of the unaveraged variable density flow. Comparison with experimental results verifies that the simulations capture the plume instantaneous behavior and reproduce the pulsation frequency. The latter is controlled by a Strouhal–Richardson number correlation which implies that the instability is inviscid in nature with a frequency that is mainly dependent on the gravitational acceleration and the nozzle width, f∼g/w. The presence of a horizontal wall surrounding the nozzle exit does not affect these results. Numerical results indicate that transition from nonpulsatile to pulsatile behavior obeys a Reynolds–Richardson number correlation of the form Re∼Ri−0.627 implying a balance between buoyant and viscous forces. Arguments based on vorticity dynamics trace the origin of the instability to the mechanism of vorticity generation by buoyancy. In the nonpulsatile flow, the circulation generated by buoyancy increases monotonically with height at a rate that is approximately constant. This arrangement can be altered via perturbations that create local circulation maxima and can lead to vortex formation. Once a first vortex pair is created, a subsequent pair precipitates via a mechanism that yields circulation maxima near the nozzle exit through the interaction of the local vorticity generation by buoyancy with the strain field induced by the preceding vortex pair. This mechanism is complex enough to suggest that simple theoretical models that predict the pulsation frequency are unlikely. It does help explain, however, the relative simplicity of the functionality of the frequency and its lack of sensitivity on a variety of boundary conditions and external parameters.
A simple model of the resistive wall mode in tokamaks
Authors: Fitzpatrick Richard
Published: September 2002

A simple set of evolution equations is derived for the resistive wall mode in a large aspect-ratio, rotating, viscous, tokamak plasma. The equations take into account the nonlinear deceleration of the plasma rotation generated by mode interaction with both the resistive wall and a static error field. Furthermore, the equations are largely able to explain resistive wall mode data recently obtained from the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. In particular, the role of the error field in triggering plasma deceleration is elucidated.
Bound states in straight quantum waveguides with combined boundary conditions
Authors: Dittrich J. , Křı́ž J.
Published: September 2002

We investigate the discrete spectrum of the Hamiltonian describing a quantum particle living in the two-dimensional straight strip. We impose the combined Dirichlet and Neumann boundary conditions on different parts of the boundary. Several statements on the existence or the absence of the discrete spectrum are compared for two models with combined boundary conditions. Examples of eigenfunctions and eigenvalues are computed numerically.
Temperature dependence of water dynamics at an aqueous micellar surface: Atomistic molecular dynamics simulation studies of a complex system
Authors: Pal Subrata , Balasubramanian Sundaram , Bagchi Biman
Published: September 2002

In order to study the temperature dependence of water dynamics at the surface of a self-organized assembly, we perform long atomistic molecular dynamics simulations of a micelle of cesium pentadecafluorooctanoate in water at two different temperatures, 300 and 350 K. Since this micellar system is stable over a range of temperature, a detailed study of the microscopic dynamics of water at the surface of the micelle at both temperatures could be performed. The diffusion and dipolar orientational correlation function of the water molecules and the polar solvation dynamics of cesium ions at the micellar surface are calculated as a function of their location from the micellar surface. Our study reveals a strong temperature dependence. The relaxation of both the time correlation functions are highly nonexponential, and become very slow at 300 K. It is found that while the slowness in the orientational time correlation function originates partly from the formation of bridge hydrogen bonds between the polar head groups (PHG) of the micelle and the water molecules, the solvation dynamics slows down primarily due to the interaction of the positive cesium ions with the negatively charged PHGs.
Rate of diffusion-limited reactions for a fractal aggregate of reactive spheres
Authors: Tseng Chin-Yao , Tsao Heng-Kwong
Published: September 2002

We study the reaction rate for a fractal cluster of perfectly absorbing, stationary spherical sinks in a medium containing a mobile reactant. The effectiveness factor η, which is defined as the ratio of the total reaction rate of the cluster to that without diffusional interactions, is calculated. The scaling behavior of η is derived for arbitrary fractal dimension based on the Kirkwood–Riseman approximation. The asymptotic as well as the finite size scaling of η are confirmed numerically by the method of multipole expansion, which has been proven to be an excellent approximation. The fractal assembly is made of N spheres with its dimension varying from D<1 to D=3. The number of sinks can be as high as N∼O(104). The asymptotic scaling behavior of the effectiveness factor is η∼N1/D−1 for D>1, η∼(ln N)−1 for D=1, and η∼N0 for D<1. The crossover behavior indicates that while in the regime of D>1 the screening effect of diffusive interactions grows with the size, for D<1 it is limited in a finite range and decays with decreasing D. The conclusion is also applicable to transport phenomena like dissolution, heat conduction, and sedimentation.
The formation and ejection of endohedral Cs@C60+ by low energy collisions (35–220 eV) of Cs+ ions with surface adsorbed C60 molecules
Authors: Kaplan A. , Bekkerman A. , Tsipinyuk B. , Kolodney E.
Published: September 2002

The collisional insertion of Cs+ ions into surface adsorbed C60 molecules was studied by scattering Cs+ ion beams from a C60 layer deposited on gold over the 35–220 eV impact energy range. Both Cs@C60+ and C60+ ions were ejected from the surface following the Cs+ impact but each species was characterized by different impact energy dependent yields and internal temperatures. Clear evidence for the endohedral nature of the complex is given. Both the scattering dynamics (at impact energies up to ∼100 eV) and the instant rise of the Cs@C60+ signal with the Cs+ beam onset clearly demonstrate that the insertion/ejection process is basically a single collision event. The outgoing Cs@C60+ and C60+ ions fragment during their flight time, after leaving the surface, via sequential emission of C2 units down to Cs@C50+ and C44+, respectively. Relative impact energy dependent yields were measured for both parent species and for all fragments. The yield curves are kinetically shifted with respect to each other as expected. Comparing the impact energy dependent fragmentation patterns of C60+ and Cs@C60+ we conclude that the ejected Cs@C60+ ion is much hotter than the C60+ ion. The internal vibrational excitation for both species is reaching a maximal value around 90–110 eV impact energy and than gradually decreases with increase in impact energy. The integrated Cs@C60+ yield is strongly peaked at around 80±5 eV impact energy. At impact energies above 120 eV also a C60− signal is observed but no Cs@C60− could be detected.
Robustness of laser phase fronts in backward Raman amplifiers
Authors: Fraiman G. M. , Yampolsky N. A. , Malkin V. M. , Fisch N. J.
Published: September 2002

The backward Raman amplification (BRA) of short laser pulses in plasma is studied numerically in two space dimensions. A high quality prefocused seed pulse is shown to remain well-focused through the entire process of the seed amplification by a high quality pump. In addition, it is shown that the BRA is not sensitive to a broad class of pump and seed fluctuations. The BRA length at which self-focusing and self-phase-modulation effects appear is determined numerically.
S-mixing contributions to the high-order anisotropy terms in the effective spin Hamiltonian for magnetic clusters
Authors: Liviotti E. , Carretta S. , Amoretti G.
Published: September 2002

The magnetic clusters are usually described by an effective Hamiltonian acting in a fixed S space. This single-spin description neglects the mixing between states with different total spin S produced by anisotropic interactions, such as the local crystal field and the magnetic dipole-dipole coupling. We have developed a general and simple procedure, based on a perturbational approach, where the S-mixing effects are included in some new terms to be added to the original effective Hamiltonian. These terms contain some new operators, which depend on the anisotropic interactions and on the difference ΔS between the spin of the states involved in the mixing. Interestingly, these operators are very similar (in some specific cases equal) to the well known Stevens operator equivalents. A list of them for ΔS=1 and ΔS=2 and for second-order anisotropic interactions is presented. The method has been applied to study the S-mixing in two iron nanomagnets, Fe4 and Fe8.
Measurement of energetic electrons from atomic clusters irradiated by intense femtosecond laser pulses
Authors: Chen L. M. , Park J. J. , Hong K. H. , Choi I. W. , Kim J. L. , Zhang J. , Nam C. H.
Published: September 2002

Spectra of energetic electrons in the 100 keV range were measured from the interaction of intense femtosecond laser pulses with clusters of xenon or argon. The interaction of 28 fs pulses with cluster targets revealed quite different results with respect to applied laser intensity. At the laser intensity of 1×1016 W/cm2, the absorption by xenon clusters was about 25%; however, at the laser intensity of 1×1017 W/cm2, the laser energy absorption drastically increased to 78%, and the efficient coupling between the laser pulse and cluster target produced electrons with energy as high as 500 keV. The estimated hot electron temperatures ranged from about 30 to 90 keV depending on atoms and backing pressures.
Effect of high rotation rates on the laminar flow around a circular cylinder
Authors: Stojković D. , Breuer M. , Durst F.
Published: September 2002

A two-dimensional numerical study on the laminar flow past a circular cylinder rotating with a constant angular velocity was carried out. The objectives were to obtain a consistent set of data for the drag and lift coefficients for a wide range of rotation rates not available in the literature and a deeper insight into the flow field and vortex development behind the cylinder. First, a wide range of Reynolds numbers (0.01⩽Re⩽45) and rotation rates (0⩽α⩽6) were considered for the steady flow regime, where α is the circumferential velocity at the cylinder surface normalized by the free-stream velocity. Furthermore, unsteady flow calculations were carried out for one characteristic Reynolds number (Re=100) in the typical two-dimensional (2D) vortex shedding regime with α varying in the range 0⩽α⩽2. Additionally, the investigations were extended to very high rotation rates (α⩽12) for which no data exist in the literature. The numerical investigations were based on a finite-volume flow solver enhanced by multi-grid acceleration and the local grid refinement technique to achieve efficient computations and accurate numerical results. The predictions show that the rotation of the cylinder suppresses the vortex development in both the steady and the unsteady flow regimes and significantly changes the flow field close to the cylinder. For very low Reynolds numbers, the drag force is not affected by rotation and the lift force is a linear function of α. For higher Re in the steady flow regime, the drag force decreases with increasing rotational velocities even leading to negative values. The lift force is almost a linear function of the rotational velocity and nearly independent of Re for low rotational speeds of α<2. However, for higher α values and larger Reynolds numbers (Re>1), a progressive increase in the lift force is observed. A very interesting phenomenon was found in the unsteady flow regime at Re=100. For low rotation rates (α⩽2) the flow exhibits the behavior known from the literature, e.g., a linear increase of the mean lift coefficient with increasing α and the suppression of vortex shedding beyond a critical α value of about αL≈1.8. However, for α≈5, an unsteady periodic flow motion was found in the wake which is characterized by a frequency much lower than that known for normal vortex shedding. The change in the flow structure also leads to a distinct change in the mean lift coefficients which exhibits a linear relation of very high rotations rates and asymptotically converges to the values known from the potential flow theory.
Optical response of one-dimensional (Si/SiO2)m photonic crystals
Authors: Patrini M. , Galli M. , Belotti M. , Andreani L. C. , Guizzetti G. , Pucker G. , Lui A. , Bellutti P. , Pavesi L.
Published: September 2002

One-dimensional photonic crystals made of (Si/SiO2)m multilayers with m=2,…8 have been grown on SiO2 4-in. wafers by repeated polysilicon low-pressure chemical vapor deposition, oxidation, and wet etching steps. The poly-Si and SiO2 layers were about 220 and 660 nm thick, respectively, thus realizing λ/4 distributed Bragg reflectors. Spectroscopic ellipsometry in the 1.4–5 eV range was used to determine the dielectric function of poly-Si and the actual layer thicknesses, as well as to check the structural and compositional homogeneity of the structures. In order to measure the photonic crystal properties, specular reflectance and transmittance measurements were performed from 0.2 to 6 eV at different angles of incidence θ⩽50° and for transverse electric and transverse magnetic polarizations. The stop-bands characteristic of Bragg reflector multilayers appear up to the fifth order and become more pronounced with increasing m, reaching almost complete rejection for m=4 periods. The experimental spectra were fitted by the transfer-matrix method, both versus θ and m. Moreover, the experimental stop bands of the finite multilayers matched the calculated photonic band gaps of an infinite one-dimensional photonic crystal very well.
Deconvolving two-dimensional images of three-dimensional momentum trajectories
Authors: Zhao K. , Colvin T. , Hill W. T. , Zhang G.
Published: September 2002

A deconvolution technique to eliminate the azimuthal contribution from two-dimensional (2D) images of three-dimensional momentum trajectories is presented. The technique, which in some respects is superior to Abel and similar numerical inversion methods, exploits numerical simulation to generate a 2D polar representation of the dynamics where the radius from the center of the image is proportional to the magnitude of the momentum and the angle is the ejection angle relative to the polarization axis of the laser. A sample deconvolution for the three-body Coulomb explosion of NO2 is shown.
Influence of growth temperature on properties of zirconium dioxide films grown by atomic layer deposition
Authors: Kukli Kaupo , Ritala Mikko , Aarik Jaan , Uustare Teet , Leskelä Markku
Published: September 2002

ZrO 2 films were grown by atomic layer deposition from ZrCl4 and H2O or a mixture of H2O and H2O2 on Si(100) substrates in the temperature range of 180–600  °C. The films were evaluated in the as-deposited state, in order to follow the effect of deposition temperature on the film quality. The rate of crystal growth increased and the content of residual impurities decreased with increasing temperature. The zirconium-to-oxygen atomic ratio, determined by ion-beam analysis, corresponded to the stoichiometric dioxide regardless of the growth temperature. The effective permittivity of ZrO2 in Al/ZrO2/Si capacitor structures increased from 13–15 in the films grown at 180  °C to 19 in the films grown at 300–600  °C, measured at 100 kHz. The permittivity was relatively high in the crystallized films, compared to the amorphous ones, but rather insensitive to the crystal structure. The permittivity was higher in the films grown using water. The leakage current density tended to be lower and the breakdown field higher in the films grown using hydrogen peroxide.
Three-halves harmonic emission from femtosecond laser produced plasmas
Authors: Veisz L. , Theobald W. , Feurer T. , Schillinger H. , Gibbon P. , Sauerbrey R. , Jovanović M. S.
Published: September 2002

Measurements of three-halves harmonic radiation (3ω0/2) produced by femtosecond, Ti:sapphire laser pulses (⩽2×1017 W/cm2) in long density scale length plasmas generated from solid aluminum targets are presented. The 3ω0/2 emission yield shows excellent agreement with theories of the two-plasmon decay instability in the predominantly linear regime.
Coupled cluster study of the energetic and spectroscopic properties of OPOx (x=O,+1,−1)
Authors: Francisco Joseph S.
Published: September 2002

Ab initio electronic structure calculations are reported for OPO, its ions OPO+ and OPO−. Geometric parameters and rotational constants are calculated using the singles and doubles coupled cluster method, including a perturbational correction for connected triple excitations, CCSD(T), together with systematic sequences of correlation consistent basis sets. Energetic and structural properties of the OPO cation are reported for the first time. The 0 K adiabatic ionization potential and electron affinity are predicted to be 247.5±1 kcal mol−1 and 79.2±1 kcal mol−1, respectively.
Thermopower enhancement in misfit cobaltites
Authors: Maignan A. , Hébert S. , Pelloquin D. , Michel C. , Hejtmanek J.
Published: September 2002

The isovalent substitution of Ca2+ for Sr2+ substitution in the recently discovered misfit cobaltite [Pb0.7Co0.3Sr2O3] [CoO2]1.79 has been investigated for its very attractive thermopower properties. Starting from the pure Sr cobaltite with a thermopower S value at 300 K in the range from 100 to 130 μV K−1, it is found that the calcium substitution enhances the thermopower value up to +165 μV K−1 for the pure calcium phase, [Pb0.4Co0.6Ca2O3] [CoO2]1.61. Since these thermoelectric materials are studied for the high T applications, it should be pointed out that this S improvement induced by chemical substitution is even more pronounced for T≫300 K with S700 K=+210 μV K−1. This beneficial effect is interpreted in the light of the clear modification in the geometry of CoO2 layers which could play a role on the cobalt electronic configurations.
Intrinsic tensile stress and grain boundary formation during Volmer–Weber film growth
Authors: Rajamani Ashok , Sheldon Brian W. , Chason Eric , Bower Allan F.
Published: September 2002

The finite element calculations in this letter present a detailed picture of tensile stress evolution during island coalescence in polycrystalline films. Earlier models suggest that these stresses are produced only when islands initially coalesce. In contrast, our model predicts that stress evolution is an inherent part of the growth process when two neighboring surfaces grow together to form a grain boundary. This view of coalescence stress is also consistent with experimental observations.
Polarizability anisotropy relaxation in liquid ethanol: A molecular dynamics study
Authors: Paolantoni Marco , Ladanyi Branka M.
Published: September 2002

Molecular dynamics simulation is used to study the relaxation of the polarizability anisotropy in liquid ethanol at temperatures of 298 and 348 K. Ethanol molecules are represented by a four-site semi-flexible model in which the internal degree of freedom, corresponding to the torsional motion around the C–O bond, is taken into consideration. The molecular polarizability is calculated using an interaction-site model, based on the modified dipole-induced dipole model developed by Thole. The collective polarizability induced by intermolecular interactions is included using first-order perturbation theory and calculated considering both center–center and site–site models. Results are analyzed in terms of projected variables that allow the decomposition of the total relaxation into orientational and collision-induced components, both of which are influenced by molecular flexibility. We compare our data with the results of low-frequency depolarized Rayleigh light scattering experiments, examining the possibility of separating different relaxation processes from spectroscopic signals in the time and frequency domains. We find that even though the largest contributor to polarizability anisotropy dynamics is orientational relaxation, collision-induced contributions are important, especially at shorter times. Moreover, we show that torsional motion also plays a significant role in the fast decay of the polarizability anisotropy of the system. Although liquid ethanol is strongly associated and its dipolar relaxation is highly collective, we find orientational pair correlation effects on polarizability relaxation to be negligible. A comparison with simulation data previously obtained for methanol suggests that increasing the alcohol chain length decreases the relative importance of OH dynamics in polarizability relaxation. We further show that, as expected for such a structured liquid composed of strongly asymmetric molecules, polarizability and dipole relaxation processes exhibit marked differences.
Intermolecular vibrations of large ammonia clusters from helium atom scattering
Authors: Beu Titus A. , Steinbach Christof , Buck Udo
Published: September 2002

The excitation of the low-energy intermolecular modes of ammonia clusters by helium atom scattering has been calculated using classical trajectories. The energy transfer is investigated as a function of scattering angle (from 10° to 90°), collision energy (94.8 and 50.5 meV), cluster size (n=18, 100, 1000), and cluster temperature (Tc=1 K, 30–50 K, and 105 K). It is observed that predominantly the mode at 7 meV and to a lesser extent also the one at 12 meV are excited. These are surface modes that mainly originate from the angular motion of three adjacent N atoms. The excitation is nearly independent of the cluster size and the probability for multiphonon excitation steadily increases with increasing deflection angle. This trend is even strengthened by increasing the collision energy. The role of the cluster temperature is to broaden the energy transfer distribution with increasing values. The calculations are compared with previous and new measurements presented here of the double-differential cross sections (dσ/dω)ΔE of ammonia clusters of average size 〈n〉=92 at two collision energies and 〈n〉=1040 at one energy. While the general trends in the angular and energy dependence could be well reproduced, the correct cluster temperature was crucial in getting good agreement at the lower collision energy for n=100. At the higher collision energy, the large energy transfer is not reproduced, probably a shortcoming of the potential models to account correctly for the anharmonicity of the strong multiquantum excitations.
Nondipole bound anions: Be2− and Be3−
Authors: Kaplan Ilya G. , Dolgounitcheva Olga , Watts John D. , Ortiz J. V.
Published: September 2002

Electron affinities (EAs) of beryllium clusters are calculated up to the complete coupled-cluster single double triple (CCSDT) level using reasonably large basis sets with many diffuse functions. At all levels of theory, the obtained values for the adiabatic EA are large enough to be observed with standard photodetachment techniques. The vertical electron detachment energy is 0.341 eV for Be2− and is 1.470 eV for Be3− at the most precise CCSDT level. All studied beryllium anions are valence bound but the nature of binding is different in Be2− and the two Be3− isomers. The only factor of stabilization of the excess electron in Be2− is the relaxation energy. Be3−(D∞h) is stabilized by the relaxation energy and the Koopmans electrostatic and exchange energies; in Be3−(D3h), the main factors of stabilization are the correlation and relaxation energies. As was revealed in our study, in linear molecules the correlation contribution to the electron binding energy is negative, i.e., it decreases the EA.
Microwave magnetoabsorption in glass-coated amorphous microwires with radii close to skin depth
Authors: Lofland S. E. , Garcia-Miquel H. , Vazquez M. , Bhagat S. M.
Published: September 2002

We present the frequency dependence of microwave magnetoabsorption in glass-coated amorphous microwires of (Co100−xFex)72.5Si12.5B15. The data were taken at room temperature in the frequency range of 1–60 GHz for fields up to 15 kOe by either a cavity perturbation technique or a coaxial transmission line. The resulting spectra strongly depend upon the local microwave magnetic and electric fields. We have found that we can simulate the spectra using an analytic solution to the problem of electromagnetic scattering from a cylinder. We demonstrate that these unusual spectra can be interpreted in terms of ferromagnetic resonance and antiferromagnetic resonance. However, because the electromagnetic skin depth is comparable to the radius, the resonance and antiresonance fields do not follow the conventional equations.
Spin valves using insulating cobalt ferrite exchange-spring pinning layers
Authors: Carey M. J. , Maat S. , Rice P. , Farrow R. F. C. , Marks R. F. , Kellock A. , Nguyen P. , Gurney B. A.
Published: September 2002

Cobalt ferrite, CoFe2O4, thin films are explored as pinning layers for read sensor applications. High ΔR/R values, 12.8%, and high pinning fields, 1500 Oe, are observed. Unlike other coercivity based pinning layers, the soft properties of the free layer are not compromised. The properties of the cobalt ferrite layers are strongly dependent on the microstructure, which, in turn, depends on the reactive sputtering process.
Magnetron sputtered epitaxial single-phase Ti3SiC2 thin films
Authors: Palmquist J.-P. , Jansson U. , Seppänen T. , Persson P. O. Å. , Birch J. , Hultman L. , Isberg P.
Published: September 2002

We report on the synthesis and characterization of epitaxial single-crystalline Ti3SiC2 films (Mn+1AXn-phase). Two original deposition techniques are described, (i) magnetron sputtering from Ti3SiC2 compound target and (ii) sputtering from individual titanium and silicon targets with co-evaporated C60 as carbon source. Epitaxial Ti3SiC2 films of single-crystal quality were grown at 900 °C with both techniques. Epitaxial TiC(111) deposited in situ on MgO(111) by Ti sputtering using C60 as carbon source was used to nucleate the Ti3SiC2 films. The epitaxial relationship was found to be Ti3SiC2(0001)//TiC(111)//MgO(111) with the in-plane orientation Ti3SiC2[100]//TiC[101]//MgO[101].
A cell for combined UV-visible and x-ray absorption spectroscopy studies under low-temperature and air exclusion conditions
Authors: Sprakel V. S. I. , Feiters M. C. , Nolte R. J. M. , Hombergen P. M. F. M. , Groenen A. , De Haas H. J. R.
Published: September 2002

A measuring system that integrates a low-temperature optical cell UV-visible (UV-Vis) for air exclusion experiments with a liquid x-ray absorption spectroscopy (XAS) cell (x-ray absorption near-edge spectroscopy and extended x-ray absorption fine structure) is reported here together with its application in studies of organometallic complexes. UV-Vis measurements are performed in a three-compartment glass vessel, fitted with an external fiber optics probe. This UV-Vis cell is suitable for the measurement of oxygen- and air-sensitive compounds at variable temperatures (RT to −78 °C). The liquid XAS cell is filled with the UV-Vis solution at low temperature and can be used in both fluorescence- or transmission-mode measurements with (frozen) solutions. The complete measuring system is reusable and easy to clean and handle. To test the performance of these cells the oxygenation behavior of a dinuclear organometallic copper(I) complex was studied in acetone by UV-Vis and XAS. It is shown that direct correlation of low-temperature UV-Vis and XAS data is possible in organic solvents.
S
1
–S
vibronic spectra of benzene clusters revisited. II. The trimer
Authors: Iimori Toshifumi , Aoki Yasuhito , Ohshima Yasuhiro
Published: September 2002

We present a reexamination of the S1–S0 transition of the (benzene)n cluster that appears only in the dimer ion channel and thus has been assigned to an isomer of the neutral dimer other than the extensively studied T-shaped form. Mass-selective resonantly enhanced two-photon ionization (R2PI) excitation and UV–UV (ultraviolet) hole burning spectra are measured in the 000 and 601 vibronic regions. It is established from the observed spectra monitoring three isotopomer channels, (C6H6)2+, [(C6H6)(C6D6)]+, and (C6D6)2+, that efficient fragmentation following ionization prohibits one to observe the two-color R2PI spectra in the parent ion channels, similar to the case for the benzene tetramer as presented in Paper I [J. Chem. Phys. 117, 3656 (2002)]. Three neutral isotopomers containing at least one C6H6 moiety are identified, and this result argues the reassignment of the band system to the neutral benzene trimer with a cyclic form, where the three benzene sites are equivalent. The spectra of the homo isotopomers [(C6H6)3 and (C6D6)3] in the two vibronic regions exhibit small splittings due to the excitation exchange interactions, and this observation is discussed on the symmetry of the cluster geometry. Energetics pertaining to neutral and ionic benzene clusters are also discussed with previous experimental studies to assess a reason of the efficient fragmentation in the ionic states after R2PI for the trimer and larger clusters but not for the dimer.
Temperature and pressure dependences of the Mn2+ and donor–acceptor emissions in ZnS:Mn2+ nanoparticles
Authors: Chen Wei , Su Fuhai , Li Guohua , Joly Alan G. , Malm Jan-Olle , Bovin Jan-Olov
Published: September 2002

Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn2+ nanoparticles. As temperature increases, the donor–acceptor (DA) emission of ZnS:Mn2+ nanoparticles at 440 nm shifts to longer wavelengths while the Mn2+ emission (4T1–6A1) shifts to shorter wavelengths. Both the DA and Mn2+ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn2+ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn2+ nanoparticles is approximately −3.2 meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn2+ emission in ZnS:Mn2+ nanoparticles is roughly −34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn2+ ions is mainly from the recombination of carriers localized at Mn2+ ions.