bluuebunny/crossref_metadata_2025 huggingface dataset:
Wachstum: Was ist normal?
Authors: Mullis  , Janner
Published: August 2009

Das Wachstum ist ein zentraler Prozess in der Entwicklung des Kindes; es beginnt mit der Konzeption und endet nach Abschluss des pubertären Wachstumsspurts. Die genaue Verlaufskontrolle des kindlichen Wachstums ist von ausserordentlicher Bedeutung und ihr gebührt im Rahmen der Vorsorgeuntersuchungen eines jeden Grundversorgers eine besondere Rolle, da sie die Früherkennung wichtiger Störungen der Gesundheit und des Wohlbefindens des Kindes ermöglicht.
Seasonal differences in wind‐driven across‐shelf forcing and response relationships in the shelf surface layer of the central Mid‐Atlantic Bight
Authors: Dzwonkowski Brian , Kohut Josh T. , Yan Xiao‐Hai
Published: August 2009

Observations of surface currents, wind stress, and adjusted sea level from August 2002 to January 2004 were used to study across‐shelf forcing and response relationships in the central Mid‐Atlantic Bight (MAB). A commonly observed shelf wide offshore flow pattern was associated with distinctly different wind stress magnitudes and directions during mixed and stratified seasons. During the stratified period, the offshore current flow pattern was associated with relatively weak winds out of the Southwest (upwelling favorable), while the mixed period events were associated with relatively strong across‐shelf winds from the Northwest. To quantify these observations, time series of the spatial mean surface current, wind stress, and coastal sea level were analyzed using several types of correlation analyses. Seasonal vector correlations between the surface current and wind stress revealed very high correlations but distinctly different phase angles and transfer coefficients. The stratified (mixed) period current veered to the right of the wind by 30–40° (6–8°) and had a higher (lower) transfer coefficient. Scalar correlations between across‐shelf wind stress and across‐shelf current showed higher r values than with the along‐shelf wind stress during the mixed period. While this pattern did not hold between wind stress and sea level, the correlations did show a stronger (weaker) relationship with across‐shelf (along‐shelf) wind stress than what was observed in the stratified season. However, conditional sampling of shelf wide events during the weaker stratified periods did show stronger relationships between both across‐shelf wind/across‐shelf current and across‐shelf wind/sea level than with the along‐shelf wind stress.
Climate change and lakes: Estimating sensitivities of water and carbon budgets
Authors: Cardille Jeffrey A. , Carpenter Stephen R. , Foley Jonathan A. , Hanson Paul C. , Turner Monica G. , Vano Julie A.
Published: August 2009

As humanity develops strategies to manage and adapt to climate change, potential changes to carbon cycles are of increasing interest. The potential sensitivity of carbon sources and sinks in lakes may be of global importance, yet the direction and magnitude of possible changes are poorly understood across entire lake‐rich regions. We used a spatially explicit simulation model of water and carbon cycling to explore the potential behavior of 6739 lakes and watersheds to changes in climate. Our study site was the Northern Highland Lake District of northern Wisconsin and the Upper Peninsula of Michigan. We developed two perturbation scenarios built from observed extreme high and low precipitation and evaporation values. Despite a spatially uniform change in precipitation across the region, individual lakes responded differently. Hydrologic responses were mostly predictable at both individual and regional scales, but the routing of carbon in lakes was both more sensitive and varied. We estimate that in today's climate, 7.3E+10 g of carbon are vented annually from lake surfaces in the District to the atmosphere. Compared to today's climate, total regional flux of carbon from lake surfaces was 31% higher in the wet scenario and 45% lower in the dry scenario. Some measures of carbon fluxes (such as net ecosystem production) appear to change uniformly and gradually at the regional scale, though aggregate change was driven primarily by considerable changes in relatively few large lakes. The simulations demonstrate that simple, spatially homogeneous perturbations in these complex connected watersheds can have both predictable and surprising effects.
LitMod3D: An interactive 3‐D software to model the thermal, compositional, density, seismological, and rheological structure of the lithosphere and sublithospheric upper mantle
Authors: Fullea J. , Afonso J. C. , Connolly J. A. D. , Fernàndez M. , García‐Castellanos D. , Zeyen H.
Published: August 2009

We present an interactive 3‐D computer program (LitMod3D) developed to perform combined geophysical‐petrological modeling of the lithosphere and sublithospheric upper mantle. In contrast to other available modeling software, LitMod3D is built within an internally consistent thermodynamic‐geophysical framework, where all relevant properties are functions of temperature, pressure, and composition. By simultaneously solving the heat transfer, thermodynamic, rheological, geopotential, and isostasy (local and flexural) equations, the program outputs temperature, pressure, surface heat flow, density (bulk and single phase), seismic wave velocities, geoid and gravity anomalies, elevation, and lithospheric strength for any given model. These outputs can be used to obtain thermal and compositional models of the lithosphere and sublithospheric upper mantle that simultaneously fit all available geophysical and petrological observables. We illustrate some of the advantages and limitations of LitMod3D using synthetic models and comparing our predictions with those from other modeling methods. In particular, we show that (1) temperature at midlithosphere depths may be overestimated by as much as 200 K when compositional heterogeneities in the mantle and T‐P effects are not considered in lithospheric models and (2) the neglect of mantle phase transformations on gravity‐based models in thin‐crust settings can result in a significant overestimation and underestimation of the derived crustal thickness and its internal density distribution, respectively.
Nd/Ca ratios in plankton‐towed and core top foraminifera: Confirmation of the water column acquisition of Nd
Authors: Martínez‐Botí M. A. , Vance D. , Mortyn P. G.
Published: August 2009

Planktic foraminifera have been used as recorders of the neodymium (Nd) isotopic composition of seawater, although there is still controversy over the precise provenance of the Nd signal. We present an extensive, multispecific plankton tow Nd/Ca data set from several geographic locations (SE Atlantic, NE Atlantic, Norwegian Sea, and western Mediterranean), together with core top samples from the Mediterranean region. The range of Nd/Ca ratios in plankton‐towed foraminifera, cleaned only of organic material, from all regions (0.01–0.7 μmol/mol), is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps, with distribution coefficients (Kd) ranging between 4 and 302. For the Mediterranean, where core top and plankton tow data are both available, the range for plankton tows (0.05–0.7 μmol/mol) is essentially identical to that for the core tops (0.1–0.5 μmol/mol). Readsorption of Nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process. We find a relationship between manganese (Mn) and Nd in plankton tow samples that is mirrored by a similar correlation in core top samples. This relationship suggests that Fe‐Mn coatings are of negligible importance to the Nd budgets of foraminifera as the Nd/Mn ratio it implies is over an order of magnitude greater than that seen in other Fe‐Mn oxide phases. Rather, since both plankton tows and core tops present a similar behavior, the Nd/Mn relationship must originate in the upper water column. The data are consistent with the acquisition of Nd and Mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes. Collectively, the results help to explain two abiding puzzles about Nd in sedimentary planktic foraminifera: their high REE contents and the fact that they record a surface water Nd isotopic signal, regardless of the cleaning procedure used.
Cold‐trapped organic compounds at the poles of the Moon and Mercury: Implications for origins
Authors: Zhang Jo Ann , Paige David A.
Published: August 2009

We have calculated evaporation rates for a range of organic compounds that may be cold‐trapped at the poles of the Moon and Mercury. Organics vary widely in their volatilities and thus can be stable to evaporation at higher and lower temperatures than water. The detection of cold‐trapped organics would point to volatile delivery by impacts, as comets and asteroids are the only plausible sources for organic molecules. The characterization of cold‐trapped organics on both bodies may provide constraints on the thermal evolution of cold traps over time and the history of volatiles in the inner solar system.
Evidence for complete and partial surface renewal at an air‐water interface
Authors: Jessup A. T. , Asher W. E. , Atmane M. , Phadnis K. , Zappa C. J. , Loewen M. R.
Published: August 2009

A wind‐wave flume is used to determine the extent to which the thermal boundary layer (TBL) at a wind‐forced air‐water interface is completely renewed from below. We measure skin temperature, Tskin, radiometrically, temperature immediately below the TBL, Tsubskin, using a temperature profiler, and net heat flux using the gradient flux technique. The Tskin probability density function, p(Tskin), and surface renewal time scale, τ, were measured using passive and active infrared imaging techniques, respectively. We find that the mean percentile rank of Tsubskin in p(Tskin) is 99.90, implying that complete surface renewal occurs. This result suggests an alternative to radiometric measurement of Tskin through the simple combination of an infrared camera and an in situ temperature sensor. Comparison of the temperature difference across the TBL to the expected cooling implies that a significant portion of events only partially renew the TBL. This result should impact efforts to improve air‐sea transfer models.
Magma degassing triggered by static decompression at Kīlauea Volcano, Hawai‘i
Authors: Poland Michael P. , Sutton A. Jeff , Gerlach Terrence M.
Published: August 2009

During mid‐June 2007, the summit of Kīlauea Volcano, Hawai‘i, deflated rapidly as magma drained from the subsurface to feed an east rift zone intrusion and eruption. Coincident with the deflation, summit SO2 emission rates rose by a factor of four before decaying to background levels over several weeks. We propose that SO2 release was triggered by static decompression caused by magma withdrawal from Kīlauea's shallow summit reservoir. Models of the deflation suggest a pressure drop of 0.5–3 MPa, which is sufficient to trigger exsolution of the observed excess SO2 from a relatively small volume of magma at the modeled source depth beneath Kīlauea's summit. Static decompression may also explain other episodes of deflation accompanied by heightened gas emission, including the precursory phases of Kīlauea's 2008 summit eruption. Hazards associated with unexpected volcanic gas emission argue for increased awareness of magma reservoir pressure fluctuations.
Slip distribution from the 1 April 2007 Solomon Islands earthquake: A unique image of near‐trench rupture
Authors: Chen Ting , Newman Andrew V. , Feng Lujia , Fritz Hermann M.
Published: August 2009

We estimate the slip distribution from the MW 8.1 Solomon Islands earthquake in 2007, from two post‐seismic surveys measuring uplifted coral and submerged coastal features. The occurrence of islands extremely proximal to the trench and nucleation of rupture allowed for the collection of unprecedented coseismic deformation dataset along a large megathrust earthquake. Using data from the two surveys along the southeastern half of the slip zone within five weeks of the event, we model the elastic dislocation to identify the optimal (29°), and alternate (20°), dip and distribution of thrust along the southern rupture. The vertical deformation, which includes both coseismic and early postseismic deformation, has highly variable and large slip within 25 km of the trench and straddling Ranongga Island. The shallow focus of slip in the near‐trench area may explain the locally high tsunami run‐up on portions of Simbo Island, however the aseismic contribution of afterslip remains unknown.
Additional stratifications in the equatorial F region at dawn and dusk during geomagnetic storms: Role of electrodynamics
Authors: Sreeja V. , Balan N. , Ravindran Sudha , Pant Tarun Kumar , Sridharan R. , Bailey G. J.
Published: August 2009

The role of electrodynamics in producing additional stratifications in the equatorial F region (F3 layer) at dawn and dusk during geomagnetic storms is discussed. Two cases of F3 layer at dawn (0600–0730 LT on 5 October 2000 and 8 December 2000) and one case of F3 layer at dusk (1600–1730 LT on 5 October 2000) are observed, for the first time, by the digital ionosonde at the equatorial station Trivandrum (8.5°N; 77°E; dip ∼ 0.5°N) in India. The unusual F3 layers occurred during the geomagnetic storms and are associated with southward turning of interplanetary magnetic field Bz, suggesting that eastward prompt penetration electric field could be the main cause of the F3 layers. The dawn F3 layer on 5 October is modeled using the Sheffield University Plasmasphere‐Ionosphere Model by using the E × B drift estimated from the real height variation of the ionospheric peak during the morning period. The model qualitatively reproduces the dawn F3 layer. While the existing F2 layer rapidly drifts upward and forms the F3 layer and topside ledge, a new layer forming at lower heights develops into the normal F2 layer.
High order finite element model for core loss assessment in a hysteresis magnetic lamination
Authors: Zhang Yu , Cheng Ming-C. , Pillay Pragasen , Helenbrook Brian
Published: August 2009

A dynamic model for evaluating core losses in a hysteretic magnetic lamination is developed and then solved using a high-order finite element method that includes time-history effects. It is demonstrated that the dynamic hysteresis effect, previously used to explain the frequency dependence of B−H loops, is not a fundamental phenomenon of magnetic materials but originates from the skin effect. It arises because the measured flux density is an averaged value over the lamination thickness, and this value is influenced strongly by the skin effect. The study verifies that, unlike the observed dynamic hysteresis effect, the local B−H loop is in fact frequency independent. The developed dynamic core loss model is thus derived based on the frequency-independent B−H loop. It is shown that the developed model can accurately evaluate the losses for different frequencies and thicknesses based on only one set of inputs of an experimental B−H loop at one low frequency without a huge database of experimental losses.
A step forward toward smart white lighting: Combination of glass phosphor and light emitting diodes
Authors: Andrade L. H. C. , Lima S. M. , Novatski A. , Steimacher A. , Rohling J. H. , Medina A. N. , Bento A. C. , Baesso M. L. , Guyot Y. , Boulon G.
Published: August 2009

We present our recent achievements of a glass able to produce smart white light combining a glass phosphor with light emitting diodes (LEDs). The combined emissions of Ce3+-doped calcium aluminosilicate glass and the 405 nm LED using the Commission Internationale de l’Éclairage 1931 chromatic diagram showed that this system presents an emission close to the ideal white light and allows tunability. In addition, the glass blue emission overlaps with the spectral range of the retinal photoreceptors involved in circadian responses. This glass combined with UV LED emission is suitable for circadian lights and therefore may contribute to improve environmental lighting and human well being.
Atomic resolution on a metal single crystal with dynamic force microscopy
Authors: König T. , Simon G. H. , Rust H.-P. , Heyde M.
Published: August 2009

Atomically resolved frequency modulation dynamic force microscope (FM-DFM) images taken by a tuning fork setup on an Ag(001) surface are presented. The necessity of well chosen tip surface interaction parameters is demonstrated making atomically resolved FM-DFM images on metal surfaces scarce. The capability of our setup to measure frequency shift and simultaneously tunneling current gives insight into different tip trajectories and possible contrast formation mechanisms in FM-DFM and scanning tunneling microscopy. One explanation is related to local variations in the decaying signals, which may originate from different density of states contributions to tip-sample force and tunneling current.
Ion-mediated interactions in suspensions of oppositely charged nanoparticles
Authors: Dahirel Vincent , Hansen Jean Pierre
Published: August 2009

The structure of oppositely charged spherical nanoparticles (polyions), dispersed in ionic solutions with continuous solvent (primitive model), is investigated by Monte Carlo (MC) simulations, within explicit and implicit microion representations, over a range of polyion valences and densities, and microion concentrations. Systems with explicit microions are explored by semigrand canonical MC simulations, and allow density-dependent effective polyion pair potentials vαβeff(r) to be extracted from measured partial pair distribution functions. Implicit microion MC simulations are based on pair potentials of mean force vαβ(2)(r) computed by explicit microion simulations of two charged polyions, in the low density limit. In the vicinity of the liquid-gas separation expected for oppositely charged polyions, the implicit microion representation leads to an instability against density fluctuations for polyion valences |Z| significantly below those at which the instability sets in within the exact explicit microion representation. Far from this instability region, the vαβ(2)(r) are found to be fairly close to but consistently more repulsive than the effective pair potentials vαβeff(r). This is corroborated by additional calculations of three-body forces between polyion triplets, which are repulsive when one polyion is of opposite charge to the other two. The explicit microion MC data were exploited to determine the ratio of salt concentrations c and co within the dispersion and the reservoir (Donnan effect). c/co is found to first increase before finally decreasing as a function of the polyion packing fraction.
Effect of trehalose on amyloid β (29–40)-membrane interaction
Authors: Reddy Allam S. , Izmitli Aslin , de Pablo J. J.
Published: August 2009

A growing body of experimental evidence indicates that the interaction between amyloid β peptide and lipid bilayer membranes plays an important role in the development of Alzheimer disease. Recent experimental evidence also suggests that trehalose, a simple disaccharide, reduces the toxicity of amyloid β peptide. Molecular simulations are used to examine the effect of trehalose on the conformational stability of amyloid β peptide in aqueous solution and its effect on the interaction between amyloid β peptide and a model phospholipid bilayer membrane. It is found that, in aqueous solution, the peptide exhibits a random coil conformation but, in the presence of trehalose, it adopts an alpha helical conformation. It is then shown that the insertion of amyloid β peptide into a membrane is more favorable when the peptide is folded into an α-helix than in a random coil conformation, thereby suggesting that trehalose promotes the insertion of α-helical amyloid β into biological membranes.
Mechanical properties and electronic structure of superhard diamondlike BC5: A first-principles study
Authors: Wang Yun-Jiang , Wang Chong-Yu
Published: August 2009

The mechanical properties and electronic structure of diamondlike BC5 are studied by ab initio method. The results for elastic moduli, stress-strain relationships, and ideal strengths are presented. The calculated properties agree well with the existing experiments. BC5 possesses very large elastic moduli and ideal strengths, suggesting its intrinsical superhard nature. Its ideal tensile strengths are much larger than ideal shear strengths. Electronic structures show that strong covalent bond network through sp3 hybridization is the origin of excellent mechanical properties of BC5. The failure of BC5 is attributed to the breaking of the B–C bond. BC5 is predicted to be metallic and remains its electronic properties at finite strain. Our results show that BC5 has good prospect in electronic application as a superhard material.
Explosive crystallization of amorphous silicon films by flash lamp annealing
Authors: Ohdaira Keisuke , Fujiwara Tomoko , Endo Yohei , Nishizaki Shogo , Matsumura Hideki
Published: August 2009

Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.
Toward ultrafast time-resolved Debye–Scherrer x-ray diffraction using a laser-plasma source
Authors: Shymanovich U. , Nicoul M. , Lu W. , Kähle S. , Tarasevitch A. , Sokolowski-Tinten K. , von der Linde D.
Published: August 2009

An elliptical glass capillary has been used to focus ultrashort Cu Kα x-ray pulses emitted from a femtosecond laser-produced plasma. Due to its high magnification (7×), the optic transforms the divergent x-ray emission of the plasma into a quasicollimated x-ray beam with a divergence of only 0.18°. As an application we demonstrate the possibility to perform Debye–Scherrer diffraction experiments with the simultaneous detection of several diffraction orders. This will allow one to extend time-resolved x-ray diffraction with femtosecond laser-plasma x-ray sources to a much wider range of materials, which are not easily available as single crystals.
Analysis of nonhydrostatic high-pressure diffraction data (cubic system): Assessment of various assumptions in the theory
Authors: Singh Anil K.
Published: August 2009

The mathematical formulation commonly used to analyze the high-pressure diffraction data from the sample under nonhydrostatic compression is based on three assumptions: A1—a weighted harmonic mean of the diffraction shear moduli under Reuss and Voigt limits with a weight parameter α that lies between 0.5 and 1 describes adequately the diffraction shear modulus; A2—a stress tensor with only the diagonal terms describes the stress state at the center of the sample under nonhydrostatic compression; and A3—the lattice-strain equations derived using only the linear elasticity theory are adequate to derive strength and elastic moduli from the diffraction data. To examine A1 we derive compressive strength, diffraction shear moduli, and single-crystal elastic moduli from the experimental high-pressure x-ray diffraction data on bcc Fe, Au, Mo, and FeO. These data contain plastic deformation effects. The diffraction shear modulus in the limit of small deformation (elastic) is computed using rigorous formulae derived by Kröner [Z. Phys. 151, 504 (1958)] and de Wit [J. Appl. Crystallogr. 30, 510 (1997)]. The elastic moduli are derived from the computed shear moduli assuming the validity of A1. The results show that A1 with α≅0.5 is valid for small deformation in all four cases. The analysis of the experimental data suggests that A1 is valid with α<1 for solids with x>1 where x=2C44/(C11−C12); for solids with x<1, the validity of A1 requires α>1. At least for solids of the cubic system, the effect of plastic deformation appears to be fully contained in a single parameter α. In practice, deviations from A2 of varying magnitudes occur mainly because of the difficulty in avoiding diffraction from regions of stress gradient in the sample. A discussion of A3 is presented.
Magnetic separation and inelastic tunneling in self-doped manganite films
Authors: Markovich V. , Jung G. , Khartsev S. I. , Tsindlekht M. I. , Grishin A. M. , Yuzhelevski Ya. , Gorodetsky G.
Published: August 2009

Magnetic and transport properties of 100 nm thick La0.9MnO3−δ self-doped manganite films have been investigated in the temperature range 5–300 K. The films exhibit a paramagnetic to ferromagnetic transition at TC=194 K. The temperature dependence of the resistivity shows a metal-insulator transition at 204 K and a strong resistivity increase below 160 K. The magnetoresistance was always negative and slightly bias dependent. Variations in resistivity with magnetic field and current are nonhysteretic, while the temperature dependence of the resistivity exhibits unusual inverse thermal hysteresis. The magnetic field independent inverse thermal hysteresis is strongly influenced by a thermal history of the sample. The data suggest that nonlinear low temperature transport is dominated by inelastic tunneling through intrinsic tunnel junctions formed by phase-separated ferromagnetic metallic domains and insulating antiferromagnetic matrix.
Diffusion-controlled and “diffusionless” crystal growth near the glass transition temperature: Relation between liquid dynamics and growth kinetics of seven ROY polymorphs
Authors: Sun Ye , Xi Hanmi , Ediger M. D. , Richert Ranko , Yu Lian
Published: August 2009

The liquid dynamics of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, named ROY for its red, orange, and yellow crystal polymorphs, was characterized by dielectric spectroscopy and differential scanning calorimetry. Four of these polymorphs show fast “diffusionless” crystal growth at low temperatures while three others do not. ROY was found to be a typical fragile organic liquid. Its α relaxation process has time-temperature superposition symmetry across the viscous range (τα=100 s–100 ns) with the width of the relaxation peak characterized by a constant βKWW of 0.73. No secondary relaxation peak was observed, even with glasses made by fast quenching. For the polymorphs not showing fast crystal growth in the glassy state, the growth rate has a power-law relation with τα, u∝τα−ξ, where ξ≈0.7. For the polymorphs showing fast crystal growth in the glassy state, the growth is so fast near and below the glass transition temperature Tg that thousands of molecular layers can be added to the crystalline phase during one structural relaxation time of the liquid. In the glassy state, this mode of growth slows slightly over time. This slowdown is not readily explained by the effect of physical aging on the thermodynamic driving force of crystallization, the glass vapor pressure, or the rate of structural relaxation. This study demonstrates that from the same liquid or glass, the growth of some polymorphs is accurately described as being limited by the rate of structural relaxation or bulk diffusion, whereas the growth of other polymorphs is too fast to be under such control.
Systematic error of diode thermometer
Authors: Iskrenovic Predrag S.
Published: August 2009

Semiconductor diodes are often used for measuring temperatures. The forward voltage across a diode decreases, approximately linearly, with the increase in temperature. The applied method is mainly the simplest one. A constant direct current flows through the diode, and voltage is measured at diode terminals. The direct current that flows through the diode, putting it into operating mode, heats up the diode. The increase in temperature of the diode-sensor, i.e., the systematic error due to self-heating, depends on the intensity of current predominantly and also on other factors. The results of systematic error measurements due to heating up by the forward-bias current have been presented in this paper. The measurements were made at several diodes over a wide range of bias current intensity.
Strain evolution in Si substrate due to implantation of MeV ion observed by extremely asymmetric x-ray diffraction
Authors: Emoto T. , Ghatak J. , Satyam P. V. , Akimoto K.
Published: August 2009

We studied the strain introduced in a Si(111) substrate due to MeV ion implantation using extremely asymmetric x-ray diffraction and measured the rocking curves of asymmetrical 113 diffraction for the Si substrates implanted with a 1.5 MeV Au2+ ion at fluence values of 1×1013, 5×1013, and 1×1014/cm2. The measured curves consisted of a bulk peak and accompanying subpeak with an interference fringe. The positional relationship of the bulk peak to the subpeak and the intensity variation of those peaks with respect to the wavelengths of the x rays indicated that crystal lattices near the surface were strained; the lattice spacing of surface normal (111) planes near the surface was larger than that of the bulk. Detailed strain profiles along the depth direction were successfully estimated using a curve-fitting method based on Darwin’s dynamical diffraction theory. Comparing the shapes of resultant strain profiles, we found that a strain evolution rapidly occurred within a depth of ∼300 nm at fluence values between 1×1013 and 5×1013/cm2. This indicates that formation of the complex defects progressed near the surface when the fluence value went beyond a critical value between 1×1013 and 5×1013/cm2 and the defects brought a large strain to the substrate.
Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
Authors: Ramzan M. , Lebègue S. , Larsson P. , Ahuja R.
Published: August 2009

In this paper, we report on Na2FePO4F and Li2FePO4F, which are materials that are used as cathodes in batteries, using density functional theory with the LDA, LDA+U, GGA, or GGA+U approximations. Specifically, we study their crystal structure, electronic structure, and magnetic properties and provide similar information about the intermediate compounds LiFePO4F and NaFePO4F. Finally, the intercalation voltages of the corresponding batteries are calculated using various exchange-correlation approximations and conclusions are drawn about which one is the most suitable to use for the study of this class of materials.
Effect of Ta migration from sidewall barrier on leakage current in Cu/SiOCH low-k dielectrics
Authors: Tan T. L. , Gan C. L. , Du A. Y. , Cheng C. K.
Published: August 2009

Tantalum migration from the anode sidewall barrier was observed in Cu interconnects/SiOCH low-k dielectrics after voltage ramp and constant voltage stress. This phenomenon was found to contribute to leakage current as observed from the current-voltage (I-V) and current-time (I-t) leakage curves. The mechanism of Ta migration is proposed to be due to the ease of Ta oxidation that converts the Ta atoms into ions, which subsequently drift along with the applied electric field and into the SiOCH low-k dielectric. The Ta ionic drift and diffusion into the dielectric led to an increase in leakage current, although the eventual formation of a stable Ta oxide resulted in a leakage saturation.
Transmission electron microscopy investigation of microtwins and double positioning domains in (111) 3C-SiC in relation with the carbonization conditions
Authors: Roy S. , Portail M. , Chassagne T. , Chauveau J. M. , Vennéguès P. , Zielinski M.
Published: August 2009

In this work, transmission electron microscopy is used to investigate the influence of the carbonization conditions on the formation of crystal defects in 3C-SiC layers deposited on (111) silicon. We focus on two kinds of defects; (1) the stacking faults and microtwins lying in the (1¯1¯1) planes, and (2) the double positioning domains. While the density of the stacking faults and microtwins is found independent on the carbonization conditions, the size of the double positioning domains is strongly influenced by the propane flow rate and can be related to the substrate sealing at the early stage of carbonization.
Acousto-optic interaction in photonic crystals with defects
Authors: Qian Xiao-Shi , Li Jing-Ping , Lu Ming-hui , Lu Yan-qing , Chen Yan-feng
Published: August 2009

The acousto-optic (AO) effects of photonic crystals (PCs) were studied. Both the PCs’ periodicity and their index distribution could be modulated instantly by the propagating acoustic wave. As a consequence, the PCs’ band structure becomes tunable. In addition to band gap shift in an ideal PC, AO frequency modulation was observed in a PC with single defect, which is quite different from normal AO tunable filters and gives rise to some interesting applications. Furthermore, in dual-defect situation, synchronized and desynchronized modulations were realized at different acoustic wavelengths. Interesting phenomena such as dual frequency sweeping and dual frequency Q-switching were demonstrated.
The effect of defects on the electronic structure of long chain ferroelectric polymers
Authors: Xiao Jie , Zhou Xin , Zhang Q. M. , Dowben P. A.
Published: August 2009

The apparent molecular density of states from combined photoemission and inverse photoemission spectroscopies is compared to the bulk conductivity and frequency dependent dielectric measurements for a variety of ferroelectric polymer poly(vinylidene fluoride) (PVDF) copolymers and terpolymers. While some extra chemical groups introduced into the PVDF long chains increase the measured conductivities at room temperature and can cause significant changes in the dielectric properties, few changes are observed in the overall experimental molecular density of states. The exception appears to be the very short polymer chains. The significance of this comparison is that profound changes can occur in the overall dielectric and transport properties of this class of polymers and copolymers through molecular “dopant addition,” without altering the overall density of states of the dominant PVDF polymer host.
The role of elastic anisotropy in poroelastic transport
Authors: Rickman J. M.
Published: August 2009

A poroelastic medium, comprising a deformable solid with a saturating fluid, exhibits pressure-driven fluid transport that, via a solid∕fluid coupling, generates stresses in the surrounding solid. In an elastically anisotropic solid, this coupling may lead to interactions between distant fluid elements and, therefore, to complex transport behavior. To examine the impact of elastic anisotropy on poroelastic transport, a simplified phase-field model of fluid imbibition in a weakly anisotropic poroelastic solid is studied. It is found that the rate of imbibition depends on the strength of the crystalline anisotropy as well as the orientation of the crystallographic axes relative to the direction of a propagating fluid front.
Investigation of self- and in-field dependent n-value of Tb-doped (Bi,Pb)-2212 superconductor
Authors: Sarun P. M. , Vinu S. , Shabna R. , Syamaprasad U.
Published: August 2009

Knowledge of the electric field versus current density (E-J) characteristics is very important for the development of superconducting high-field magnets particularly for operation in the persistent mode. A systematic study of the E-J characteristics and the associated n-indices has been carried out both in self and applied fields in respect of Tb-doped (Bi,Pb)-2212, a promising superconductor for high-field application. The results on n-indices and pinning energy (Uc) show that the flux-lines in (Bi,Pb)-2212 doped with an optimum concentration of Tb (x=0.075–0.100) are in glass-state and hence the material allows maximum current to flow with minimum dissipation of energy. Further, it has been shown that the modified material is a promising candidate for persistent mode superconducting magnets.
Nonlinear kinetics of fast relaxation in solutions with short and lengthy micelles
Authors: Kshevetskiy M. S. , Shchekin A. K.
Published: August 2009

An analytical treatment of the nonlinear kinetic equations for fast relaxation of coexisting short and lengthy micelles in surfactant solutions is presented. The kinetic equations can be written as a hierarchical set of differential equations for the moments of the aggregation number distribution function of micelles. It is shown that the moment equations can be successively integrated. As examples of the general approach, particular cases of short spherical micelles, lengthy cylindrical micelles, and coexisting short and lengthy micelles have been considered and compared to the results of linear kinetic theory of micellar fast relaxation. The results show that there is a strong interplay between coexisting short and lengthy micelles, even in the case when the total number of surfactant molecules aggregated in short micelles is small in comparison with that in lengthy micelles.
Hugoniot temperatures and melting of tantalum under shock compression determined by optical pyrometry
Authors: Dai Chengda , Hu Jianbo , Tan Hua
Published: August 2009

LiF single crystal was used as transparent window (anvil) to tamp the shock-induced free surface expansion of Ta specimen, and the Ta/LiF interface temperature was measured under shock compression using optical pyrometry technique. The shock temperatures and/or melting temperatures of Ta up to ∼400 GPa were extracted from the observed interface temperatures based on the Tan–Ahrens’ model for one-dimensional heat conduction across metal/window ideal interface in which initial melting and subsequent solidification were considered under shock loading. The obtained data within the experimental uncertainties are consistent with the results from high-pressure sound velocity measurements. The temperature of the partial melting on Ta Hugoniot is estimated to be ∼9700 K at 300 GPa, supported by available results from theoretical calculations.
Efficient near-infrared organic light-emitting devices based on low-gap fluorescent oligomers
Authors: Yang Yixing , Farley Richard T. , Steckler Timothy T. , Eom Sang-Hyun , Reynolds John R. , Schanze Kirk S. , Xue Jiangeng
Published: August 2009

We report efficient near-infrared (NIR) organic light-emitting devices (OLEDs) based on fluorescent donor-acceptor-donor conjugated oligomers. The energies of the highest occupied and lowest unoccupied molecular orbitals of these oligomers are controlled by the donor and acceptor components, respectively; hence the energy gap and therefore the emission wavelength can be tuned by changing the strengths of the donor and acceptor components. External quantum efficiencies (EQEs) up to 1.6% and power efficiencies up to 7.0 mW/W are achieved in NIR OLEDs based on 4,9-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-6,7-dimethyl-[1,2,5]thiadiazolo[3,4-g]-quinoxaline (BEDOT-TQMe2), in which the electroluminescence peaks at a wavelength of 692 nm but extends to well above 800 nm. With a stronger acceptor in the oligomer, 4,8-bis(2,3-dihydrothieno-[3,4-b][1,4]dioxin-5-yl)benzo[1,2-c;4,5-c′]bis [1,2,5]thiadiazole (BEDOT-BBT) based devices show longer wavelength emission peaked at 815 nm, although the maximum EQE is reduced to 0.51% due to the lower fluorescent quantum yield of the NIR emitter. The efficiencies of these NIR OLEDs are further increased by two to three times by using the sensitized fluorescent device structure, leading to a maximum EQE of 3.1% for BEDOT-TQMe2 and 1.6% for BEDOT-BBT based devices.
Off-axis stability of intense continuous relativistic beams
Authors: Martins Luciano C. , Rizzato Felipe B. , Pakter Renato
Published: August 2009

This paper investigates the stability of off-axis continuous intense relativistic beams propagating inside a circular conducting pipe. The equations of motion for the centroid and the envelope of slightly off-axis beams are derived and used to determine equilibrium and stability conditions for the beam transport. It is shown that depending on the parameters of the system, beams propagating along the pipe axis may become unstable due to the presence of the wall, imposing a fundamental limitation in the effective area that an equilibrium beam can occupy inside the conductor.
Approximate behavior of arbitrarily unsteady laminar flow in long, straight, flexible tubes
Authors: Brereton G. J.
Published: August 2009

Analytical solutions have been obtained for laminar flows in long, straight tubes with linearly elastic walls that undergo arbitrary spatial/temporal unsteadiness from a known initial state. These initial-boundary value solutions express quantities such as the momentary wall deflection, flow rate, and wall shear stress as functionals of the pressure field’s history under the assumptions that unsteady effects propagate as long-wavelength disturbances at a constant wave speed and produce changes in the wall shear stress that are significantly less than in the pressure. These solutions are particularly useful for analysis of pulsatile periodic and aperiodic flows that come to rest before restarting, for which existing continuously unsteady analytical solutions do not apply. When the arbitrary unsteadiness is given the particular form of a sinusoidally varying pressure field that starts from rest at time zero, the long-time behavior of these approximate solutions is in excellent agreement with existing analytical solutions for continuously unsteady flow at all but low values of the Womersley frequency parameter.
Microgravity compatible equipment for inert gas condensation of metals during parabolic flights
Authors: Lösch S. , Günther B. H. , Iles G. N. , Büngener U.
Published: August 2009

Agglomerates of nanosized metal particles can be deposited onto a variety of substrates using a custom-built, microgravity-compatible evaporation/condensation device. A metal aerosol with high solid loading is produced by rf-induction coil heating of a metal melt in a laminar inert gas flow. Valves and flow controllers operating in hypergravity and microgravity conditions allow powder samples to be prepared from such aerosols suppressing buoyancy and sedimentation effects. We present here the technical details for such a parabolic flight compatible metal aerosol source together with some initial results of nanoscale Ni agglomerates synthesized and deposited under microgravity conditions.
Real time estimation of equivalent cantilever parameters in tapping mode atomic force microscopy
Authors: Agarwal Pranav , Salapaka Murti V.
Published: August 2009

In this article, a method of imaging is developed, where during tapping-mode operation, equivalent resonant frequency and quality factor can be obtained in real time. It involves exciting the cantilever near its resonant frequency and two other frequencies chosen close to the resonant frequency. It is shown that changes in equivalent cantilever parameters can be registered for topography changes that are less than 1 nm in height and within 400 μs of the change occurring. The estimation time is two orders of magnitude better than current techniques.
Drag reduction in turbulent flows over superhydrophobic surfaces
Authors: Daniello Robert J. , Waterhouse Nicholas E. , Rothstein Jonathan P.
Published: August 2009

In this paper, we demonstrate that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain micro- or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to drag reductions approaching 50%. At a given Reynolds number, drag reduction is found to increase with increasing feature size and spacing, as in laminar flows. No observable drag reduction was noted in the laminar regime, consistent with previous experimental results for the channel geometry considered. The onset of drag reduction occurs at a critical Reynolds number where the viscous sublayer thickness approaches the scale of the superhydrophobic microfeatures and performance is seen to increase with further reduction in viscous sublayer height. These results indicate superhydrophobic surfaces may provide a significant drag reducing mechanism for marine vessels.
An extension of Palumbo’s method of solution for the Grad–Shafranov equation
Authors: Hernandes J. A. , Clemente R. A.
Published: August 2009

We present an extension of Palumbo’s method for solving Grad Shafranov equation for ideal axisymmetric magnetohydrodynamic equilibria. The method relies essentially on an expansion in even powers of radius for the square of the gradient of the magnetic stream function and a suitable coordinate transformation that allows reducing the problem of mapping magnetic surface to quadratures. The resulting exact equilibria have magnetic surface contours different from isodynamic ones, allowing modeling flattened or D-shaped plasma tori.
On the effect of Reynolds number for flow around a row of square cylinders
Authors: Sewatkar C. M. , Sharma Atul , Agrawal Amit
Published: August 2009

Flow across a row of identical square cylinders placed side-by-side has been found to show interesting flow patterns which have complex characteristics depending upon the spacing (s/d) between the cylinders and the Reynolds number (Re). The combined effects of cylinder spacing and Reynolds number on the flow across a row of cylinders are numerically studied for 30≤Re≤140 and 1.0≤s/d≤4.0, where s is the surface-to-surface distance between two cylinders and d is the size of cylinder. It is found that the critical Reynolds number for the onset of vortex shedding increases with increase in gap ratio. The Reynolds number is found to have a strong effect on the flow especially at s/d=3.0,4.0. Secondary frequency in the signal for lift and drag coefficients significantly contributes to the forces experienced by the cylinders. It is observed that at s/d=3.0,4.0 the secondary frequency disappears at larger Reynolds number and the primary frequency dominates the flow. This means that the interaction of the wakes behind the cylinders at these gap ratios weakens with an increase in the Reynolds number. It is proposed that wake interaction is strongly influenced by the jets in the gap region, the nature of which alters with spacing and Reynolds number. This is confirmed by computing the average wake size as a function of Reynolds number. Based on this, two critical gap ratios, 2.0 and 4.0 for the range of Reynolds number under consideration are proposed. These gap ratios separate synchronous, quasiperiodic-I and quasiperiodic-II flow regimes depending on the Reynolds number. The mechanism of wake interaction has been studied to bring out these critical gap ratios.
Large Rayleigh number thermal convection: Heat flux predictions and strongly nonlinear solutions
Authors: Chini Gregory P. , Cox Stephen M.
Published: August 2009

We investigate the structure of strongly nonlinear Rayleigh–Bénard convection cells in the asymptotic limit of large Rayleigh number and fixed, moderate Prandtl number. Unlike the flows analyzed in prior theoretical studies of infinite Prandtl number convection, our cellular solutions exhibit dynamically inviscid constant-vorticity cores. By solving an integral equation for the cell-edge temperature distribution, we are able to predict, as a function of cell aspect ratio, the value of the core vorticity, details of the flow within the thin boundary layers and rising/falling plumes adjacent to the edges of the convection cell, and, in particular, the bulk heat flux through the layer. The results of our asymptotic analysis are corroborated using full pseudospectral numerical simulations and confirm that the heat flux is maximized for convection cells that are roughly square in cross section.