bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of Mediterranean aerosol radiative forcing and influence of the single scattering albedo
Authors: Di Biagio Claudia , di Sarra Alcide , Meloni Daniela , Monteleone Francesco , Piacentino Salvatore , Sferlazzo Damiano
Published: March 2009

Ground‐based measurements of aerosol optical depth and surface shortwave irradiance carried out at the Mediterranean island of Lampedusa during 2004–2007 are used to estimate the surface aerosol direct radiative forcing for desert dust (DD), urban/industrial‐biomass burning (UI‐BB), and mixed aerosols (MA). The aerosol single scattering albedo, ω, at 415.6 and 868.7 nm is derived at 60° solar zenith angle, θ, from measurements of global and diffuse radiation using radiative transfer model calculations. The shortwave forcing efficiency (FES) is derived, for θ between 20° and 75°, for the three identified classes of aerosol and for all the observed data (AD). The absolute value of FES decreases for increasing θ for all the aerosol types. FES varies between −185 and −81.7 W m−2 for DD, −168 and −84 W m−2 for UI‐BB, −251 and −120.2 W m−2 for MA, and −208 and −106.5 W m−2 for AD. The daily average forcing efficiency (FEd) at the equinox is −67.2 W m−2 for DD, −59.0 W m−2 for UI‐BB, and −93.2 W m−2 for MA. The forcing efficiency of DD, UI‐BB, and MA at θ = 60° was calculated for three intervals of single scattering albedo (0.7 ≤ ω < 0.8, 0.8 ≤ ω < 0.9, 0.9 ≤ ω ≤ 1) at 415.6 and 868.7 nm. The absolute value of FES decreases with increasing ω at 868.7 nm for all aerosol types, while it decreases with increasing ω at 415.6 nm for UI‐BB and MA and increases for DD. A 0.1 increment in the single scattering albedo at 868.7 nm produces a reduction in FES by 25–30 W m−2, and a reduction by 10–15 W m−2 in FEd.
Annual accumulation for Greenland updated using ice core data developed during 2000–2006 and analysis of daily coastal meteorological data
Authors: Bales Roger C. , Guo Qinghua , Shen Dayong , McConnell Joseph R. , Du Guoming , Burkhart John F. , Spikes Vandy B. , Hanna Edward , Cappelen John
Published: March 2009

An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950–2000 is better represented by the data than are earlier periods. Ice‐sheet‐wide accumulation was estimated based on kriging. The average accumulation (95% confidence interval, or ±2 times standard error) over the Greenland ice sheet is 30.0 ± 2.4 g cm−2 a−1, with the average accumulation above 2000‐m elevation being essentially the same, 29.9 ± 2.2 g cm−2 a−1. At higher elevations the new accumulation map maintains the main features shown in previous maps. However, there are five coastal areas with obvious differences: southwest, northwest, and eastern regions, where the accumulation values are 20–50% lower than previously estimated, and southeast and northeast regions, where the accumulation values are 20–50% higher than previously estimated. These differences are almost entirely due to new coastal data. The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long‐term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland. A significant and sustained precipitation measurement program will be needed to resolve this uncertainty.
Unique archaeal assemblages in the Arctic Ocean unveiled by massively parallel tag sequencing
Authors: Galand Pierre E , Casamayor Emilio O , Kirchman David L , Potvin Marianne , Lovejoy Connie
Published: March 2009

The Arctic Ocean plays a critical role in controlling nutrient budgets between the Pacific and Atlantic Ocean. Archaea are key players in the nitrogen cycle and in cycling nutrients, but their community composition has been little studied in the Arctic Ocean. Here, we characterize archaeal assemblages from surface and deep Arctic water masses using massively parallel tag sequencing of the V6 region of the 16S rRNA gene. This approach gave a very high coverage of the natural communities, allowing a precise description of archaeal assemblages. This first taxonomic description of archaeal communities by tag sequencing reported so far shows that it is possible to assign an identity below phylum level to most (95%) of the archaeal V6 tags, and shows that tag sequencing is a powerful tool for resolving the diversity and distribution of specific microbes in the environment. Marine group I Crenarchaeota was overall the most abundant group in the Arctic Ocean and comprised between 27% and 63% of all tags. Group III Euryarchaeota were more abundant in deep-water masses and represented the largest archaeal group in the deep Atlantic layer of the central Arctic Ocean. Coastal surface waters, in turn, harbored more group II Euryarchaeota. Moreover, group II sequences that dominated surface waters were different from the group II sequences detected in deep waters, suggesting functional differences in closely related groups. Our results unveiled for the first time an archaeal community dominated by group III Euryarchaeota and show biogeographical traits for marine Arctic Archaea.
Extracellular polysaccharide-protein complexes of a harmful alga mediate the allelopathic control it exerts within the phytoplankton community
Authors: Yamasaki Yasuhiro , Shikata Tomoyuki , Nukata Atsushi , Ichiki Satoko , Nagasoe Sou , Matsubara Tadashi , Shimasaki Yohei , Nakao Miki , Yamaguchi Kenichi , Oshima Yuji , Oda Tatsuya , Ito Makoto , Jenkinson Ian R , Asakawa Makio , Honjo Tsuneo
Published: March 2009

The goal of this study was to examine the significance of allelopathy by the raphidophyte Heterosigma akashiwo in a multispecies phytoplankton community in the field. Towards this aim, we sought allelochemicals of H. akashiwo, which had allelopathic effect both in laboratory experiments and in the field. As an initial step, we showed that the allelopathic effects of H. akashiwo filtrate were both species-specific and dependent upon the cell density of the target species. Secondly, we found for the first time that extracellular, high-molecular weight allelochemicals [that is, polysaccharide-protein complexes (APPCs)] were produced by a marine phytoplankton species, H. akashiwo. Thirdly, we indicated that the purified APPCs selectively inhibited the growth of the diatom Skeletonema costatum that is a major competitor of H. akashiwo, and thereby tended to promote the formation of monospecific H. akashiwo blooms. Furthermore, we demonstrated that the inhibitory effect of APPCs on the growth of the diatoms was determined by binding to the cell surface of the target species. Finally, we succeeded in the detection of APPCs in the field samples at concentrations exceeding their experimentally determined action threshold during the H. akashiwo bloom. Strategies for ecosystem control, including mitigation of harmful algal blooms (HABs), should take into account that red-tide organisms like H. akashiwo are already part of complex webs involving inter-specific allelopathic inhibition and ecosystem control during their dense blooms.
Obesity, End‐stage Renal Disease, and Survival in an Elderly Cohort With Cardiovascular Disease
Authors: Lea Janice P. , Crenshaw Daryl O. , Onufrak Stephen J. , Newsome Britt B. , McClellan William M.
Published: March 2009

Obesity is highly prevalent in African Americans and is associated with increased risk of End‐Stage Renal Disease (ESRD) and death. It is not known if the effect of obesity is similar among blacks and whites. The aim of this study is to examine racial differences in the association of obesity with ESRD and survival in elderly patients (age >65). Data were obtained for 74,167 Medicare patients with acute myocardial infarction (AMI) between February 1994 and July 1995. BMI was calculated as weight (kg) divided by height (m2). We evaluated the association of BMI class with ESRD incidence and death using multivariable Cox proportional hazards models, testing for race‐BMI interactions. Compared to whites, African Americans had higher BMI (26.9 vs. 26.0, P < 0.0001) and estimated glomerular filtration rate (72.4 ml/min/1.73 m2 vs. 66.6 ml/min/1.73 m2, P < 0.0001). Crude ESRD rates increased with increasing obesity among whites but not among blacks. However, after adjusting for age, sex, and other comorbidities, obesity was not associated with increased ESRD rate among blacks or whites and the interaction between race and BMI was not significant. Furthermore, for both races, patients classified as overweight, class 1 obese, or class 2 obese had similar, significantly better survival abilities compared to normal weight patients and the race BMI interaction was not significant. In conclusion, obesity does not increase risk of ESRD among black or white elderly subjects with cardiovascular disease (CVD). However, both obese blacks and whites, in this population, experience a survival benefit. Further studies need to explore this obesity paradox.
Characterization of Obese Phenotypes in a Small Nonhuman Primate, the Common Marmoset (Callithrix jacchus)
Authors: Tardif Suzette D. , Power Michael L. , Ross Corinna N. , Rutherford Julienne N. , Layne‐Colon Donna G. , Paulik Mark A.
Published: March 2009

This report explores aspects of developing obesity in two captive populations of common marmosets (Callithrix jacchus), a small primate with a short lifespan that may be of value in modeling chronic aspects of obesity acquisition and its lifetime effects. Two populations were examined. In study 1, body composition, lipid parameters, and glucose metabolic parameters were measured in a population of 64 adult animals. Animals classified as obese (>80th percentile relative fat based on sex) displayed both dyslipidemia (higher triglyceride and very low–density lipoprotein (VLDL)) and altered glucose metabolism (higher fasting glucose and HbA1c). Using operational definitions of atypical values for factors associated with metabolic syndrome in humans, five subjects (7.8%) had at least three atypical factors and five others had two atypical factors. A previously unreported finding in these normally sexually monomorphic primates was higher body weight, fat weights, and percent fat in females compared to males. In a second study, longitudinal weight data for a larger population (n = 210) were analyzed to evaluate the development of high weight animals. Differences in weights for animals that would exceed the 90th percentile in early adulthood were evident from infancy, with a 15% difference in weight between future‐large weight vs. their future‐normal weight litter mates as early as 4–6 months of age. The marmoset, therefore, demonstrates similar suites of obesity‐related alterations to those seen in other primates, including humans, suggesting that this species is worthy of consideration for obesity studies in which its fast maturity, high fertility, relatively short lifespan, and small size may be of advantage.
Gender‐specific Effect of Obesity on Balance
Authors: Menegoni Francesco , Galli Manuela , Tacchini Elena , Vismara Luca , Cavigioli Marco , Capodaglio Paolo
Published: March 2009

Obesity modifies the body geometry by adding mass to different regions and it influences the biomechanics of activities of daily living. Weight influences postural stability, but there is no consensus as to whether the different fat distribution in males and females produces gender‐related effects on balance. The aim of this study was to investigate the effect of body weight increases on postural performance in males and females. A total of 22 obese females (BMI: 41.1 ± 4.1 kg/m2) and 22 obese males (BMI: 40.2 ± 5 kg/m2) were analyzed during a static posture trial on a force platform in standardized conditions. Twenty healthy subjects (10 females, 10 males) constituted the control group. We computed the following parameters related to the center of pressure (CoP): velocity and displacements along the antero‐posterior (AP) and medio‐lateral axis (ML). We found several statistically significant differences between healthy and obese men, in particular regarding the AP and ML CoP parameters, which were correlated to body weight (r = 0.36–0.58). The comparison between healthy and obese females pointed out statistically significant differences in AP parameters and no significant differences in ML displacements. Body weight was found to correlate with AP parameters (r = 0.36–0.74), but not with ML displacements. The increased body mass seems to produce AP instability in both genders and ML destabilization only in males. Rehabilitation programs should take these findings into account by adopting specific interventions to improve ML control in obese males, and through weight loss and strengthening of ankle flexors/extensors in both genders.
The Transcription Factor TFAP2B Is Associated With Insulin Resistance and Adiposity in Healthy Adolescents
Authors: Nordquist Niklas , Göktürk Camilla , Comasco Erika , Eensoo Diva , Merenäkk Liis , Veidebaum Toomas , Oreland Lars , Harro Jaanus
Published: March 2009

Insulin resistance and central adiposity are strong risk indicators for type 2 diabetes and coronary heart disease. An important role for adipose tissue in the etiology and progression of these conditions has recently become more evident. A transcription factor, TFAP2B, has been shown to participate in the regulation of adipocyte metabolism, by facilitating glucose uptake and lipid accumulation, while simultaneously reducing insulin sensitivity, and recently a direct function for TFAP2B as an inhibitor of adiponectin expression was observed. In this study, we have investigated how insulin resistance, plasma adiponectin, and central adiposity, in a normal population of adolescents, are affected by genetic variability in TFAP2B. Our results show that both insulin sensitivity, as measured from levels of fasting glucose and insulin, and central adiposity, estimated by subscapular skinfold thickness, were significantly associated to genetic variability in TFAP2B. This association was restricted to males only, where carriers of the 4‐repeat allele of intron 2 had higher insulin sensitivity and lower subscapular skinfold thickness. Levels of adiponectin did not show any association to the TFAP2B polymorphism, but was negatively correlated to central adiposity in females. These results suggest that reduction of TFAP2B expression could have a protective effect against future risk of complications associated with decreased insulin sensitivity and central adiposity, such as type 2 diabetes and coronary heart disease.
Increased Carbohydrate Induced Ghrelin Secretion in Obese vs. Normal‐weight Adolescent Girls
Authors: Misra Madhusmita , Tsai Patrika M. , Mendes Nara , Miller Karen K. , Klibanski Anne
Published: March 2009

Orexigenic and anorexigenic pathways mediate food intake and may be affected by meal composition. Our objective was to determine whether changes in levels of active ghrelin and peptide YY (PYY) differ in obese vs. normal‐weight adolescent girls following specific macronutrient intake and predict hunger and subsequent food intake. We enrolled 26 subjects: 13 obese and 13 normal‐weight girls, 12–18 years old, matched for maturity (as assessed by bone age) and race. Subjects were assigned a high‐carbohydrate, high‐protein, and high‐fat breakfast in random order. Active ghrelin and PYY were assessed for 4 h after breakfast and 1 h after intake of a standardized lunch. Hunger was assessed using a standardized visual analog scale (VAS). No suppression in active ghrelin levels was noted following macronutrient intake in obese or normal‐weight girls. Contrary to expectations, active ghrelin increased in obese girls following the high‐carbohydrate breakfast, and the percent increase was higher than in controls (P = 0.046). Subsequent food intake at lunch was also higher (P = 0.03). Following the high‐fat breakfast, but not other breakfasts, percent increase in PYY was lower (P = 0.01) and subsequent lunch intake higher (P = 0.005) in obese compared with normal‐weight girls. In obese adolescents, specific intake of high‐carbohydrate and high‐fat breakfasts is associated with greater increases in ghrelin, lesser increases in PYY, and higher intake at a subsequent meal than in controls. Changes in anorexigenic and orexigenic hormones in obese vs. normal‐weight adolescents following high‐carbohydrate and high‐fat meals may influence hunger and satiety signals and subsequent food intake.
Hydrodynamic interactions in protein folding
Authors: Cieplak Marek , Niewieczerzał Szymon
Published: March 2009

We incorporate hydrodynamic interactions (HIs) in a coarse-grained and structure-based model of proteins by employing the Rotne–Prager hydrodynamic tensor. We study several small proteins and demonstrate that HIs facilitate folding. We also study HIV-1 protease and show that HIs make the flap closing dynamics faster. The HIs are found to affect time correlation functions in the vicinity of the native state even though they have no impact on same time characteristics of the structure fluctuations around the native state.
Study on microwave properties of low temperature fired NiZnCu gyromagnetic ferrite
Authors: Liu Yingli , Li Yuanxun , Zhang Huaiwu , Yang Qinghui
Published: March 2009

This paper describes the microwave properties of low temperature fired Ni0.6CuxZn(0.4−x)Fe1.96+δO4 gyromagnetic ferrite material synthesized by conventional oxide process with Bi2O3 additives. It is found that 60–63 mol % Ni and 5 mol % Cu contents have the advantage to keep the material with both low-fired characteristic and high saturated magnetization with 3 wt % Bi2O3 additives. Considering the conditions of milling, calcination, and sintering process, the low temperature fired NiCuZn gyromagnetic material was prepared with excellent microwave performances. The saturated magnetization Ms of the sample is 337 kA/m, the ferromagnetic resonance linewidth ΔH and dielectric loss tgδε less than 16 kA/m and 5.7×10−4, respectively, which has the potential applications for low temperature cofired ceramics technology to develop microwave chip circulator/isolator and passive integrated substrate.
Viscosity and relaxation processes in the phonon-roton system of He II
Authors: Zadorozhko A. A. , Rudavskiĭ É. Ya. , Chagovets V. K. , Sheshin G. A. , Kitsenko Yu. A.
Published: March 2009

The viscosity of He4 in the temperature range 0.1–2.2K has been measured using a vibrating quartz tuning fork. A quantitative comparison is made of the experimental data and the conclusions of the modern theory of the phonon-roton system of superfluid helium. The complex hierarchy of relaxation processes is analyzed and the role and contribution of each process to the coefficient of viscosity are determined. Agreement between the experiments and theory is obtained in the hydrodynamic region. The transition from the hydrodynamic to the ballistic regime of phonon flow is analyzed and the effective viscosity of He II at such temperatures is found. It is shown that the position of the maximum of the temperature dependence of the effective viscosity, obtained using different methods of measurement, correlates with the characteristic size of the measuring apparatus.
Complex permeability of granular textured YBa2Cu2O7−δ superconducting ceramic
Authors: Alekseev F. O. , Zalutskiĭ M. V.
Published: March 2009

Measurements of the complex permeability of the granular textured YBa2Cu3O7−δ ceramic as a function of the temperature in a weak ac magnetic field in the presence of a constant magnetic field have been performed. The experimental ceramic consisted of ∼3mm macrograins which formed in the process of texturization. The orientation of the c axis of the macrograins was chaotically distributed. A three-peak structure of the absorption of the ac magnetic field was observed in the imaginary part of the complex permeability in a weak constant magnetic field ∼0.1T. The behavior of this absorption structure as a function of the magnitude and orientation of the constant magnetic field, frequency, and amplitude of the ac magnetic field is analyzed. It is shown that the three-peak absorption structure in the imaginary part of the complex permeability is due to the influence of two mechanisms of the dissipation of the ac magnetic field energy: volume energy dissipation associated with pinning and surface energy dissipation associated with a Bean-Livingston surface barrier. It is found that as the constant magnetic field increases, this three-peak absorption structure transforms into a single-peak structure, described well in a linear model of thermally activated flow of magnetic flux.
NMR Investigation of the local diamagnetic properties of carbon structures with multilayer nanotubes
Authors: Nikolaev E. G. , Omel’yanovskiĭ O. E. , Prudkovskiĭ V. S. , Sadakov A. V. , Tsebro V. I.
Published: March 2009

The reasons for the high diamagnetic susceptibility of carbon columns, which are covered with a nanotube mesh, from the interior part of cathode deposits have been studied by means of NMR. A comparative study is made of the C13 NMR spectra and the magnetic susceptibility of carbon columns before and after ultrasonic processing as well as of finely dispersed material, obtained as a result of such processing, enriched with multilayer nanotubes. The strong diamagnetism of the carbon columns is apparently associated with a quite dense conglomerate of graphite particles, nanotubes, and multilayer polyhedral particles present in their core and not with the surface mesh of multilayer nanotubes. To make a more accurate determination of the character of the anisotropy of the magnetic susceptibility of multilayer carbon nanotubes, the form of the C13 NMR spectra of samples enriched with multilayer nanotubes, where the nanotubes are either not oriented or only partially oriented, is analyzed. It is shown that the diamagnetic susceptibility of multilayer carbon nanotubes is highest when the magnetic field is oriented perpendicular to their axis.
Changes of the electronic structure of a (8, 0) zigzag nanotube due to doping with potassium
Authors: But’ko V. G. , Gusev A. A. , Shevtsova T. N. , Pashkevich Yu. G.
Published: March 2009

Density functional methods are used to calculate the band structure of an ideal and potassium-filled (8, 0) zigzag carbon nanotube. The calculations are performed taking account of the optimization of the parameters of the tube. It is shown that doping changes the characteristic bond lengths, and as a result of these changes the absorption spectra of the doped tubes are substantially different from those of the undoped tubes. The change of the character of the conductivity of a doped tube from semiconductor to metallic is largely due to the shift of the Fermi level. It is shown that doping decreases the frequency of the radial mode of the Raman scattering spectrum.
Shubnikov-de Haas oscillations of the conductivity of a two-dimensional gas in quantum wells based on germanium and silicon. Determination of the effective mass and g factor
Authors: Berkutov I. B. , Andrievskiĭ V. V. , Komnik Yu. F. , Mironov O. A. , Mironov M. , Leadley D. R.
Published: March 2009

The Shubnikov-de Haas oscillations of the conductivity of a two-dimensional gas of holes in quantum wells consisting of pure germanium and silicon with low germanium content (13%) are analyzed to determine the effective masses and the g factor in these regions. The magnetic-field dependences of the resistivity ρxx obtained at temperatures from 33mKto4K in magnetic fields up to 11T are used for the analysis.
Fermi-liquid anomaly of the concentration dependence of the g-factor of the conduction electrons in a semiconductor with hybridized impurity states
Authors: Okulov V. I. , Pamyatnykh E. A. , Al’shanskiĭ G. A.
Published: March 2009

A theoretical description is given of the concentration dependence of the g factor of the conduction electrons in hybridized states on donor impurities in a semiconductor taking account of the effect of the interelectronic interaction within the framework of the Fermi-liquid approach. It is shown that the theoretically predicted dependence due to the Fermi-liquid interaction is non-monotonic in the resonance interval because of partial electron localization on impurities.
Low-temperature thermodynamics of two-dimensional electron gas on disordered host lattice
Authors: Slavin V. V.
Published: March 2009

The low-temperature thermodynamic properties of two-dimensional electron ensemble on ordered and disordered host lattice are studied numerically by the transfer-matrix method. It is shown that at low temperatures and weak disordering of host lattice site positions a change in chemical potential leads to successive transitions of the system from ordered phases (like the generalized Wigner crystal) to disordered states. The ranges of stability of these crystals as functions of temperature, chemical potential and disorder parameter are established.
Flexural rigidity of layers and its manifestation in the vibrational characteristics of strongly anisotropic layered crystals. Characteristic frequencies and stability conditions in quasi-two-dimensional systems
Authors: Syrkin E. S. , Feodos’ev S. B. , Kravchenko K. V. , Eremenko A. V. , Kantor B. Ya. , Kosevich Yu. A.
Published: March 2009

The reasons for the appearance of flexural rigidity of layers in strongly anisotropic layered crystals are investigated. Structures consisting of loosely bound monatomic layers (specifically, graphite) as well as formed loosely bound structural elements each consisting of several monolayers which are coupled much more strongly with one another (for example, in dichalcogenide transition metals) are examined. The effect of the flexural rigidity on the phonon spectra of these compounds—quasi-flexural bending of the dispersion curves of phonon modes polarized in a direction normal to the layers—and the particularities appearing in the phonon densities of states as a result of quasi-flexural vibrational branches crossing low-frequency optical modes are analyzed.
On the character of the scattering of wide-band x-ray radiation in the low-temperature phase of 2H-NbSe2
Authors: Eremenko V. V. , Ibulaev V. V. , Sirenko V. A. , Shvedun M. Yu.
Published: March 2009

The intensity of x-ray scattering in the layered metal 2H-NbSe2 has been investigated experimentally in the temperature range below the temperature of the transition into the charge-density wave state. It is shown that the relation I∼(TC−T)−γ with TC∼30K and γ=1.6±0.2, as is characteristic for quasi-elastic (quasi-Bragg) scattering, describes the scattering intensity. Such scattering is strong when the width ΔεXR of the spectral distribution of the x-ray radiation is greater than the spectral width of the fluctuations Δεf of the order parameter. The inequality Δεf<Δεf holds for scattering of slow neutrons, for which quasi-elastic scattering is immeasurably weak.
Analysis of a magnetostrictive power harvesting device with hysteretic characteristics
Authors: Davino Daniele , Giustiniani Alessandro , Visone Ciro
Published: March 2009

A model for the description of the energy harvesting in magnetostriction devices is discussed. In particular, the effects of hysteresis, normally observed in these materials, are highlighted and compared to the predictions of the linear modeling. The coupling of the model to the circuit equations leads to a differential equation with hysteresis, which could provide an effective macroscopic description of the energy conversion mechanism taking place in these devices. Numerical tests are performed in order to show the effect of a magnetic field bias on the generated electric power.
Theory of magnetism with temporal disorder applied to magnetically doped ZnO
Authors: Gehring Gillian A. , Ahmed Mahrous R. , Crombie Alex J.
Published: March 2009

A dynamic model of the asymmetric Ising glass is presented: an Ising model with antiferromagnet bonds, −J, and ferromagnetic bonds, +J, with probabilities q and 1−q. The dynamics is introduced by changing the arrangement of the antiferromagnetic bonds after n Monte Carlo steps but keeping the same value of q and spin configuration. In the region where there is a second order transition between the ferromagnetic and paramagnetic states at Tc(q) for qq0 where there is a first order transition between the ferromagnetic and spin glass states where it shows no effects of motional narrowing. The implications of this are discussed. This model is devised to explain the properties of doped ZnO where the magnetization is reduced when the exchange interactions change with time.
Isothermal oxidation behaviors of FeCoV and FeCoVNb alloys
Authors: Turgut Zafer , Horwath John C. , Huang Meiqing , Coate Jack E.
Published: March 2009

The present study investigates the isothermal oxidation of two iron-cobalt based alloys at 500 °C for up to 5000 h. Both alloys exhibit crack-free oxide layers consist of a porosity-free iron rich outer layer and a solute rich inner layer populated with islands of solute oxides and porosities. X-ray diffraction measurements reveal the presence of MO–Fe2O3-type (where M=Co, Nb, and/or V) spinel structures along with Fe2O3. Analysis shows that the oxidation follows the parabolic rate law for both alloys with niobium containing alloy exhibiting a higher oxidation rate. Comparison of yield strengths (σ0) of oxidized specimens to those aged similarly under an inert atmosphere indicates that two competing mechanisms occur. Surface oxidation decreases the yield strength while precipitation reactions inside the iron-cobalt matrix increase the yield strength of the matrix.
Rational design of ion force fields based on thermodynamic solvation properties
Authors: Horinek Dominik , Mamatkulov Shavkat I. , Netz Roland R.
Published: March 2009

Most aqueous biological and technological systems contain solvated ions. Atomistic explicit-water simulations of ionic solutions rely crucially on accurate ionic force fields, which contain most commonly two adjustable parameters: the Lennard-Jones diameter and the interaction strength. Assuming these parameters to be properly optimized, the plethora of parameters one finds in the literature for one and the same ion is surprising. In principle, the two parameters should be uniquely determined by matching two ionic properties obtained for a particular water model and within a given simulation protocol with the corresponding experimental observables. Traditionally, ion parameters were chosen in a somewhat unsystematic way to reproduce the solvation free energy and to give the correct ion size when compared with scattering results. Which experimental observable one chooses to reproduce should in principle depend on the context within which the ionic force field is going to be used. In the present work we suggest to use the solvation free energy in conjunction with the solvation entropy to construct thermodynamically sound force fields for the alkali and halide ions for the simulation of ion-specific effects in aqueous environment. To that end we determine the solvation free energy and entropy of both cations and anions in the entire relevant parameter space. As an independent check on the quality of the resulting force fields we also determine the effective ionic radius from the first peak of the radial ion-water distribution function. Several difficulties during parameter optimization are discussed in detail. (i) Single-ion solvation depends decisively on water-air surface properties, which experimentally becomes relevant when introducing extrathermodynamic assumptions on the hydronium (H3O+) solvation energy. Fitting ion pairs circumvents this problem but leaves the parameters of one reference ion (here we choose chloride) undetermined. (ii) For the halides the problem is almost underdetermined, i.e., there is a whole set of degenerate parameters that equally well describe, e.g., chloride and bromide ions. (iii) For the heavy cations the problem is overdetermined, i.e., no combination of Lennard-Jones parameters is able to reproduce simultaneously energy and entropy of solvation. We discuss various possibilities to deal with these problems and finally present an optimized force field for the halide anions that reproduces the free energy and the entropy of solvation. For the alkali metal cations there is no unambiguous choice of parameters. Therefore, we give three different parameter sets for every ion with a small, intermediate, or large Lennard-Jones interaction strength, where the Lennard-Jones diameters are optimized to reproduce the solvation free energy. The ionic radius is reproduced with acceptable accuracy by this optimization strategy, meaning that the proposed force fields are reliable beyond the target observables (i.e., free energy and entropy of solvation).
Temperature dependence of the performance of charge-sensitive infrared phototransistors
Authors: Ueda Takeji , Komiyama Susumu , An Zhenghua , Nagai Naomi , Hirakawa Kazuhiko
Published: March 2009

The performance of charge-sensitive infrared phototransistors (λ∼14.7 μm) is studied at temperatures of up to 30 K. The devices, with a 16×4 μm2 photoactive area, are fabricated in GaAs/AlGaAs double-quantum-well structure. An excellent specific detectivity D∗=9.6×1014 cm Hz1/2/W is derived in a T range of up to T=23 K. Experimental results are theoretically studied based on WKB approximation, in which photogenerated holes in the floating gate (FG) are recombined with thermal emission or thermally assisted tunneling from the outside of FG through the barriers. The model well reproduces the experimental results, including the vanishing of photosignal at 30 K under 280 fW incident radiation. The model is used to predict a temperature-dependent specific detectivity D∗ in ideal devices free from 1/f noise.
“Seedless” vapor-liquid-solid growth of Si and Ge nanowires: The origin of bimodal diameter distributions
Authors: Dailey Eric , Drucker Jeff
Published: March 2009

We identify a previously uncharacterized vapor-liquid-solid growth mode that can produce small diameter, epitaxial ⟨110⟩ oriented Si and Ge nanowires (NWs). Disilane or digermane pyrolysis evolves H2 causing the monolayer thick Au/Si(111) layer between three dimensional Au seeds to dewet and form small Au islands. Under some conditions, these small islands facilitate “seedless” growth of small diameter NWs distinct from larger NWs that grow from the deposited seeds leading to a bimodal diameter distribution. We identify the precursor pressures and growth temperature regimes for which Si and Ge NW growth occurs in the absence of deposited seeds from the dewetted Au/Si(111) layer.
Phase transitions in Ge–Sb phase change materials
Authors: Raoux Simone , Cabral Cyril , Krusin-Elbaum Lia , Jordan-Sweet Jean L. , Virwani Kumar , Hitzbleck Martina , Salinga Martin , Madan Anita , Pinto Teresa L.
Published: March 2009

Thin films of the phase change material Ge–Sb with Ge concentrations between 7.3 and 81.1 at. % were deposited by cosputtering from elemental targets. Their crystallization behavior was studied using time-resolved x-ray diffraction, Auger electron spectroscopy, differential scanning calorimetry, x-ray reflectivity, profilometry, optical reflectivity, and resistivity versus temperature measurements. It was found that the crystallization temperature increases with Ge content. Calculations of the glass transition temperature (which is a lower limit for the crystallization temperature Tx) also show an increase with Ge concentration closely tracking the measured values of Tx. For low Ge content samples, Sb x-ray diffraction peaks occurred during a heating ramp at lower temperature than Ge diffraction peaks. The appearance of Ge peaks is related to Ge precipitation and agglomeration. For Ge concentrations of 59.3 at. % and higher, Sb and Ge peaks occurred at the same temperature. Upon crystallization, film mass density and optical reflectivity increase as well as electrical contrast (ratio of resistivity in amorphous phase to crystalline phase) all showed a maximum for the eutectic alloy (14.5 at. % Ge). For the alloy with 59.3 at. % Ge there was very little change in any of these parameters, while the alloy with 81.1 at. % Ge behaved opposite to a typical phase change alloy and showed reduced mass density and reflectivity and increased resistivity.
Self-consistent-field calculations of core excited states
Authors: Besley Nicholas A. , Gilbert Andrew T. B. , Gill Peter M. W.
Published: March 2009

The accuracy of core excitation energies and core electron binding energies computed within a Δself-consistent-field framework is assessed. The variational collapse of the core excited state is prevented by maintaining a singly occupied core orbital using an overlap criterion called the maximum overlap method. When applied to a wide range of small organic molecules, the resulting core excitation energies are not systematically underestimated as observed in time-dependent density functional theory and agree well with experiment. The accuracy of this approach for core excited states is illustrated by the calculation of the pre-edge features in x-ray absorption spectra of plastocyanin, which shows that accurate results can be achieved with Δself-consistent-field calculations when used in conjunction with uncontracted basis functions.
Self-organization processes in highly epitaxial La2/3Sr1/3MnO3 thin films grown on SrTiO3 (001) substrates
Authors: Konstantinović Z. , Santiso J. , Colson D. , Forget A. , Balcells Ll. , Martínez B.
Published: March 2009

We report on the growth of highly epitaxial La2/3Sr1/3MnO3 thin films on SrTiO3 (001) oriented substrates by rf magnetron sputtering. It is shown that structural strain caused by lattice mismatch between film and substrate and kinetics growing instabilities may offer unique opportunities to control the film morphologies. By increasing growth rate, the surface morphology undergoes a dramatic transformation: from very smooth surface through arrays of mounds or antidots to hatched morphology. All nano-objects form long-range ordered arrays running in the steps direction defined by the miscut angle of underlying substrate. These self-assembled structures are of high interest envisaging a new route for the fabrication of oxide-based magnetoelectronic devices by using a bottom-up approach.
Atomic layer deposition of Cu2S for future application in photovoltaics
Authors: Martinson Alex B. F. , Elam Jeffrey W. , Pellin Michael J.
Published: March 2009

Alternating exposure to bis(N,N′-di-sec-butylacetamidinato)dicopper(I) and hydrogen sulfide is shown to produce high quality chalcocite (Cu2S) thin films by atomic layer deposition on silicon and fused silica substrates. The layer-by-layer chemical vapor deposition method enables conformal growth of the phase-pure material at 130 °C. X-ray diffraction reveals that polycrystalline high-chalcocite films are deposited preferentially oriented in the ⟨00l⟩ plane. The optical properties of this naturally p-type absorber compare well with previous reports on single crystals, highlighting the applicability of the technique to nanostructured photovoltaics.
Modeling of chemical processes in the low pressure capacitive radio frequency discharges in a mixture of Ar/C2H2
Authors: Ariskin D. A. , Schweigert I. V. , Alexandrov A. L. , Bogaerts A. , Peeters F. M.
Published: March 2009

We study the properties of a capacitive 13.56 MHz discharge with a mixture of Ar/C2H2 taking into account the plasmochemistry and growth of heavy hydrocarbons. A hybrid model was developed to combine the kinetic description for electron motion and the fluid approach for negative and positive ion transports and plasmochemical processes. A significant change in plasma parameters related to injection of 5.8% portion of acetylene in argon was observed and analyzed. We found that the electronegativity of the mixture is about 30%. The densities of negatively and positively charged heavy hydrocarbons are sufficiently large to be precursors for the formation of nanoparticles in the discharge volume.
Comment on “Turbulent equipartition theory of toroidal momentum pinch” [Phys. Plasmas 15, 055902 (2008)]
Authors: Peeters A. G. , Angioni C. , Strintzi D.
Published: March 2009

The comment addresses questions raised on the derivation of the momentum pinch velocity due to the Coriolis drift effect [A. G. Peeters et al., Phys. Rev. Lett. 98, 265003 (2007)]. These concern the definition of the gradient, and the scaling with the density gradient length. It will be shown that the turbulent equipartition mechanism is included within the derivation using the Coriolis drift, with the density gradient scaling being the consequence of drift terms not considered in [T. S. Hahm et al., Phys. Plasmas 15, 055902 (2008)]. Finally the accuracy of the analytic models is assessed through a comparison with the full gyrokinetic solution.
A high energy density shock driven Kelvin–Helmholtz shear layer experiment
Authors: Hurricane O. A. , Hansen J. F. , Robey H. F. , Remington B. A. , Bono M. J. , Harding E. C. , Drake R. P. , Kuranz C. C.
Published: March 2009

Radiographic data from a novel and highly successful high energy density Kelvin–Helmholtz (KH) instability experiment is presented along with synapses of the theory and simulation behind the target design. Data on instability growth are compared to predictions from simulation and theory. The key role played by baroclinic vorticity production in the functioning of the target and the key design parameters are also discussed. The data show the complete evolution of large distinct KH eddies, from formation to turbulent break-up. Unexpectedly, low density bubbles comparable to the vortex size are observed forming in the free-stream region above each vortex at late time. These bubbles have the appearance of localized shocks, possibly supporting a theoretical fluid dynamics conjecture about the existence of supersonic bubbles over the vortical structure [transonic convective Mach numbers, D. Papamoschou and A. Roshko, J. Fluid Mech. 197, 453 (1988)] that support localized shocks (shocklets) not extending into the free stream (P. E. Dimotakis, Proceedings of the 22nd Fluid Dynamics, Plasma Dynamics and Lasers Conference, 1991, Paper No. AIAA 91-1724). However, it is also possible that these low density bubbles are the result of a cavitationlike effect. Hypothesis that may explain the appearance of low density bubbles will be discussed.
Computational studies of aqueous interfaces of RbBr salt solutions
Authors: Sun Xiuquan , Dang Liem X.
Published: March 2009

We computed the structure factor and the corresponding x-ray reflectivity of an aqueous interface of RbBr salt solution and used molecular dynamics techniques to compare polarizable and nonpolarizable potential models for molecular interaction. Our computed electron and number density profiles clearly demonstrate that the polarizable Br− anions are enhanced at the water/vapor surface while the nonpolarizable Br− anions are depleted from it. The observation of Br− ions at the interface contradicts a recent interpretation that was based on experimentally measured x-ray reflectivity data.
Roughness effects on fine-scale anisotropy and anomalous scaling in atmospheric flows
Authors: Katul G. G. , Porporato A. , Poggi D.
Published: March 2009

The effects of surface roughness on various measures of fine-scale intermittency within the inertial subrange were analyzed using two data sets that span the roughness “extremes” encountered in atmospheric flows, an ice sheet and a tall rough forest, and supplemented by a large number of existing literature data. Three inter-related problems pertaining to surface roughness effects on (i) anomalous scaling in higher-order structure functions, (ii) generalized dimensions and singularity spectra of the componentwise turbulent kinetic energy, and (iii) scalewise measures such local flatness factors and stretching exponents were addressed. It was demonstrated that surface roughness effects do not impact the fine-scale intermittency in u (the longitudinal velocity component), consistent with previous laboratory experiments. However, fine-scale intermittency in w (the vertical velocity component) increased with decreasing roughness. The consequence of this external intermittency (i.e., surface roughness induced) is that the singularity spectra of the scaling exponents are much broader for w when compared u in the context of the multifractal formalism for the local kinetic energy (instead of the usual conservative cascade studied for the dissipation rate). The scalewise evolution of the flatness factors and stretching exponents collapse when normalized using a global Reynolds number Rt=σLI/ν, where σ is the velocity standard deviation, LI is the integral length scale, and ν is the fluid viscosity.
On turbulent entrainment and dissipation in dilute polymer solutions
Authors: Liberzon A. , Holzner M. , Lüthi B. , Guala M. , Kinzelbach W.
Published: March 2009

We present a comparative experimental study of a turbulent flow developing in clear water and dilute polymer solutions (25 and 50 wppm polyethylene oxide). The flow is forced by a planar grid that oscillates vertically with stroke S and frequency f in a square container of initially still fluid. Two-component velocity fields are measured in a vertical plane passing through the center of the tank by using time resolved particle image velocimetry. After the forcing is initiated, a turbulent layer develops that is separated from the initially irrotational fluid by a sharp interface, the so-called turbulent/nonturbulent interface (TNTI). The turbulent region grows in time through entrainment of surrounding fluid until the fluid in the whole container is in turbulent motion. From the comparison of the experiments in clear water and polymer solutions we conclude: (i) Polymer additives modify the large scale shape of the TNTI. (ii) Both, in water and in the polymer solution the mean depth of the turbulent layer, H(t), follows the theoretical prediction for Newtonian fluids H(t)∝Kt, where K∝S2f is the “grid action.” (iii) We find a larger grid action for dilute polymer solutions than for water. As a consequence, the turbulent kinetic energy of the flow increases and the rate of energy input becomes higher. (iv) The entrainment rate β=ve/vrms (where ve=dH/dt is the interface propagation velocity and vrms is the root mean square of the vertical velocity) is lower for polymers (βp≈0.7) than for water (βw≈0.8). The measured values for β are in good agreement with similarity arguments, from which we estimate that in our experiment about 28% of the input energy is dissipated by polymers.