bluuebunny/crossref_metadata_2025 huggingface dataset:
Steepened channels upstream of knickpoints: Controls on relict landscape response
Authors: Berlin Maureen M. , Anderson Robert S.
Published: September 2009

The morphology of a relict landscape provides important insight into erosion rates and processes prior to base level fall. Fluvial knickpoints are commonly thought to form a leak‐proof moving boundary between a rejuvenated landscape below and a relict landscape above. We argue that fluvial rejuvenation may leak farther upstream, depending on the rate and style of knickpoint migration. The outer margin of a relict landscape should therefore be used with caution in tectonic geomorphology studies, as channel steepening upstream of knickpoints could reduce the relict area. We explore the response of the Roan Plateau to knickpoint retreat triggered by late Cenozoic upper Colorado River incision. Multiple knickpoints (100‐m waterfalls) separate a low‐relief, upper landscape from incised canyons below. Two digital elevation model data sets (10‐m U.S. Geological Survey and 1‐m Airborne Laser Swath Mapping) indicate steeper channels above waterfalls relative to concave channels farther upstream. The steepened reaches are several kilometers long, correspond to doubling of slope, and exhibit channel narrowing and an increase in hillslope angle. We compare two mechanisms for generating steepened reaches. The first uses a recent model for erosion amplification due to flow acceleration at the waterfall lip. The second acknowledges that waterfall lips may be limited to the outcrop of a resistant formation. Subtle structural warping of the stratigraphy can lead to lowering of the waterfall lip as it retreats, thus lowering base level for upstream channels. Results of numerical modeling experiments suggest the latter mechanism is more consistent with our observations of long, mildly steepened reaches.
A Regional Climate Change Assessment Program for North America
Authors: Mearns Linda O. , Gutowski William , Jones Richard , Leung Ruby , McGinnis Seth , Nunes Ana , Qian Yun
Published: September 2009

There are two main uncertainties in determining future climate: the trajectories of future emissions of greenhouse gases and aerosols, and the response of the global climate system to any given set of future emissions [Meehl et al., 2007]. These uncertainties normally are elucidated via application of global climate models, which provide information at relatively coarse spatial resolutions. Greater interest in, and concern about, the details of climate change at regional scales has provided the motivation for the application of regional climate models, which introduces additional uncertainty [Christensen et al., 2007a].

These uncertainties in fine‐scale regional climate responses, in contrast to uncertainties of coarser spatial resolution global models in which regional models are nested, now have been documented in numerous contexts [Christensen et al., 2007a] and have been found to extend to uncertainties in climate impacts [Wood et al., 2004; Oleson et al., 2007]. While European research in future climate projections has moved forward systematically to examine combined uncertainties from global and regional models [Christensen et al., 2007b], North American climate programs have lagged behind.
First Scholarship at AGU Established by David E. Lumley
Authors: Tahar Joanna G.
Published: September 2009

Shortly after AGU launched its annual voluntary contribution campaign last year— the theme was “Building Tomorrow's Talent Today”—the Union's development office received an e‐mail message from David E. Lumley about establishing a scholarship for a high‐school student or undergraduate. Many scientific societies and associations have quite a few named scholarships, but for AGU this was a new concept. Lumley was sure of what he wanted to do and even more excited when he learned that his scholarship would be a first for AGU.

“I want to help inspire today's young minds to work on problems of global importance in both the energy and environment sectors of industry and academia,” Lumley said. Recipients of the David E. Lumley Young Scientist Scholarship for Energy and Environmental Science will be expected to present a paper and to participate in various student activities at Fall Meeting. “Meeting some of the ‘giants’ of geoscience and getting their feedback on research is a big deal for these young students. We sometimes lose sight of this,” he said.
AGU Members to Vote on Governance Changes
Authors: Anonymous
Published: September 2009

Like all nonprofit organizations, AGU's structure is contained in “formation” documents (articles of incorporation or “charter”) and “governance” documents (bylaws, policies and procedures). At AGU, the bylaws are currently known as the “statutes and bylaws.” Members are required to give a majority affirmative vote on any changes to the statutes and a two‐thirds affirmative vote to amend the articles of incorporation.
Nominees for AGU 2010–2012 Election of Officers
Authors: Anonymous
Published: September 2009

The nominees listed below constitute the slate approved by the AGU Council for the election of officers for the next biennium.
Fostering Interdisciplinary Science to Improve Resilience to Natural Hazards: Characterization, Communication and Mitigation of Risks Arising From Multiple Hazards; Norwich, UK, 7–8 May 2009
Authors: Darnell Amii , Barclay Jean
Published: September 2009

Despite great scientific advances and humanitarian efforts, economic and human losses from natural hazards have increased in recent decades. This is largely a result of the growth in size and vulnerability of populations. Scientists additionally face the complexities of dealing with a broad range of hazards, including the seemingly inevitable increase in the severity and frequency of hydrometeorological events. To address these issues, the U.K. Natural Environment Research Council and the Economic and Social Research Council, together with the Department for Environment, Food and Rural Affairs, sponsored a meeting to assess how the societal cost of natural disasters could be reduced through the development of new, integrated approaches to research.
Comparison of CALIOP level 2 aerosol subtypes to aerosol types derived from AERONET inversion data
Authors: Mielonen T. , Arola A. , Komppula M. , Kukkonen J. , Koskinen J. , de Leeuw G. , Lehtinen K. E. J.
Published: September 2009

Identification of aerosol types is important, because different aerosol types have different effects on health, visibility and climate change. The space‐borne lidar CALIOP on‐board the CALIPSO satellite provides information on the types of aerosols in the separate layers that can be detected with this instrument. In this study, the aerosol subtypes of CALIOP measurements are compared with daily aerosol types derived from AERONET level 2.0 inversion data. AERONET aerosol types are categorized by single scattering albedo and Ångström exponent values. The comparison shows that 70% of the CALIOP and AERONET aerosol types are in agreement. Best agreement is achieved for dust and polluted dust types.
LDL Receptor‐Related Proteins in Neurodevelopment
Authors: May Petra , Herz Joachim
Published: September 2009

Low‐density lipoprotein receptor‐related proteins (LRPs) are evolutionarily ancient cell‐surface receptors with diverse biological functions. All are expressed in the central nervous system and, for most receptors, animal models have shown that they are indispensable for successful neurodevelopment. The mechanisms by which they regulate the formation of the nervous system are varied and include the transduction of extracellular signals and the modulation of intracellular signal propagation, as well as cargo transport, the function most commonly attributed to this gene family. Here, we will summarize recent advances in our understanding of the molecular basis on which these receptors function during development.
Differential Requirements of Rab5 and Rab7 for Endocytosis of Influenza and Other Enveloped Viruses
Authors: Sieczkarski Sara B. , Whittaker Gary R.
Published: September 2009

Enveloped viruses often enter cells via endocytosis; however, specific endocytic trafficking pathway(s) for many viruses have not been determined. Here we demonstrate, through the use of dominant‐negative Rab5 and Rab7, that influenza virus (Influenza A/WSN/33 (H1N1) and A/X‐31 (H3N2)) requires both early and late endosomes for entry and subsequent infection in HeLa cells. Time‐course experiments, monitoring viral ribonucleoprotein colocalization with endosomal markers, indicated that influenza exhibits a conventional endocytic uptake pattern – reaching early endosomes after approximately 10 min, and late endosomes after 40 min. Detection with conformation‐specific hemagglutinin antibodies indicated that hemagglutinin did not reach a fusion‐competent form until the virus had trafficked beyond early endosomes. We also examined two other enveloped viruses that are also pH‐dependent for entry – Semliki Forest virus and vesicular stomatitis virus. In contrast to influenza virus, infection with both Semliki Forest virus and vesicular stomatitis virus was inhibited only by the expression of dominant negative Rab5 and not by dominant negative Rab7, indicating an independence of late endosome function for infection by these viruses. As a whole, these data provide a definitive characterization of influenza virus endocytic trafficking and show differential requirements for endocytic trafficking between pH‐dependent enveloped viruses.
Dual‐energy X‐ray Absorptiometry and Anthropometric Estimates of Visceral Fat in Black and White South African Women
Authors: Micklesfield Lisa K. , Evans Juliet , Norris Shane A. , Lambert Estelle V. , Jennings Courtney , Joffe Yael , Levitt Naomi S. , Goedecke Julia H.
Published: September 2009

Visceral adipose tissue (VAT) is associated with increased risk for cardiovascular disease, and therefore, accurate methods to estimate VAT have been investigated. Computerized tomography (CT) is the gold standard measure of VAT, but its use is limited. We therefore compared waist measures and two dual‐energy X‐ray absorptiometry (DXA) methods (Ley and Lunar) that quantify abdominal regions of interest (ROIs) to CT‐derived VAT in 166 black and 143 white South African women. Anthropometry, DXA ROI, and VAT (CT at L4–L5) were measured. Black women were younger (P < 0.001), shorter (P < 0.001), and had higher body fat (P < 0.05) than white women. There were no ethnic differences in waist (89.7 ± 18.2 cm vs. 90.1 ± 15.6 cm), waist:height ratio (WHtR, 0.56 ± 0.12 vs. 0.54 ± 0.09), or DXA ROI (Ley: 2.2 ± 1.5 vs. 2.1 ± 1.4; Lunar: 2.3 ± 1.4 vs. 2.3 ± 1.5), but black women had less VAT, after adjusting for age, height, weight, and fat mass (76 ± 34 cm2 vs. 98 ± 35 cm2; P < 0.001). Ley ROI and Lunar ROI were correlated in black (r = 0.983) and white (r = 0.988) women. VAT correlated with DXA ROI (Ley: r = 0.729 and r = 0.838, P < 0.01; Lunar: r = 0.739 and r = 0.847, P < 0.01) in black and white women, but with increasing ROI android fatness, black women had less VAT. Similarly, VAT was associated with waist (r = 0.732 and r = 0.836, P < 0.01) and WHtR (r = 0.721 and r = 0.824, P < 0.01) in black and white women. In conclusion, although DXA‐derived ROIs correlate well with VAT as measured by CT, they are no better than waist or WHtR. Neither DXA nor anthropometric measures are able to accurately distinguish between high and low levels of VAT between population groups.
Development and Validation of a Toddler Silhouette Scale
Authors: Hager Erin R. , McGill Adrienne E. , Black Maureen M.
Published: September 2009

The purpose of this study is to develop and validate a toddler silhouette scale. A seven‐point scale was developed by an artist based on photographs of 15 toddlers (6 males, 9 females) varying in race/ethnicity and body size, and a list of phenotypic descriptions of toddlers of varying body sizes. Content validity, age‐appropriateness, and gender and race/ethnicity neutrality were assessed among 180 pediatric health professionals and 129 parents of toddlers. Inter‐ and intrarater reliability and concurrent validity were assessed by having 138 pediatric health professionals match the silhouettes with photographs of toddlers. Assessments of content validity revealed that most health professionals (74.6%) and parents of toddlers (63.6%) ordered all seven silhouettes correctly, and interobserver agreement for weight status classification was high (κ = 0.710, r = 0.827, P < 0.001). Most respondents reported that the scale represented toddlers aged 12–36 months (89%) and was gender (68.5%) and race/ethnicity (77.3%) neutral. The inter‐rater reliability, based on matching silhouettes with photographs, was 0.787 (Cronbach's α) and the intrarater reliability was 0.855 (P < 0.001). The concurrent validity, based on the correlation between silhouette choice and the weight‐for‐length percentile of each toddler's photograph, was 0.633 (P < 0.001). In conclusion, a valid and reliable toddler silhouette scale that may be used for male or female toddlers, aged 12–36 months, of varying race/ethnicity was developed and evaluated. This scale may be used clinically or in research settings to assess parents' perception of and satisfaction with their toddler's body size. Interventions can be targeted toward parents who have inaccurate perceptions of or are dissatisfied with their toddler's body size.
Estrogen Reduces 11β‐Hydroxysteroid Dehydrogenase Type 1 in Liver and Visceral, but Not Subcutaneous, Adipose Tissue in Rats
Authors: Andersson Therése , Söderström Ingegerd , Simonyté Kotryna , Olsson Tommy
Published: September 2009

Following menopause, body fat is redistributed from peripheral to central depots. This may be linked to the age related decrease in estrogen levels. We hypothesized that estrogen supplementation could counteract this fat redistribution through tissue‐specific modulation of glucocorticoid exposure. We measured fat depot masses and the expression and activity of the glucocorticoid‐activating enzyme 11β‐hydroxysteroid dehydrogenase type 1 (11βHSD1) in fat and liver of ovariectomized female rats treated with or without 17β‐estradiol. 11βHSD1 converts inert cortisone, or 11‐dehydrocorticosterone in rats into active cortisol and corticosterone. Estradiol‐treated rats gained less weight and had significantly lower visceral adipose tissue weight than nontreated rats (P < 0.01); subcutaneous adipose weight was unaltered. In addition, 11βHSD1 activity/expression was downregulated in liver and visceral, but not subcutaneous, fat of estradiol‐treated rats (P < 0.001 for both). This downregulation altered the balance of 11βHSD1 expression and activity between adipose tissue depots, with higher levels in subcutaneous than visceral adipose tissue of estradiol‐treated animals (P < 0.05 for both), opposite the pattern in ovariectomized rats not treated with estradiol (P < 0.001 for mRNA expression). Thus, estrogen modulates fat distribution, at least in part, through effects on tissue‐specific glucocorticoid metabolism, suggesting that estrogen replacement therapy could influence obesity related morbidity in postmenopausal women.
Optimal Waist Circumference for Prediction of Metabolic Syndrome in Young Korean Women With Polycystic Ovary Syndrome
Authors: Oh Jee‐Young , Sung Yeon‐Ah , Lee Hye Jin , Oh Ji Young , Chung Hye Won , Park Hyesook
Published: September 2009

The International Diabetes Federation consensus proposed an ethnically specific criteria of waist circumference (WC) for central obesity, but, the nationwide definition is still debated in Korea. For the detection of the optimal WC cutoff value, the nonadipose components of the metabolic syndrome (MS) were defined by modification of revised 2003 Rotterdam consensus as having two or more risk factors such as hypertension, hyperglycemia, and dyslipidemia without consideration of abdominal obesity. By using receiver‐operating characteristic (ROC) curve analysis, cutoff points of WC and visceral fat area (VFA) for prediction of MS were 80 cm and 53.1 cm2. WC cutoff points corresponding to VFA >53.1 and 100 cm2 were 73.3 and 77.8 cm. The sensitivity and specificity of currently used value of WC 88 cm were 41.9 and 91.5%, suggesting that it could be too high in Korean population. Central obesity defined as WC >80 cm was significantly associated with nonadipose components of MS after adjustment for age, BMI, cholesterol, triglycerides, fasting insulin, and free testosterone levels. Central obesity with WC of >80 cm predicted the presence of nonadipose MS (odds ratio 16.6; 95% confidence interval (CI) 6.5–42.6). It was also significant (odds ratio 14.7; 95% CI 3.4–64.3) when we applied the WC value of 70 cm instead of 80 cm. In conclusion, WC of 80 and 70 cm could be appropriate cutoff points to identify the MS and visceral adiposity in Korean women with polycystic ovary syndrome (PCOS), respectively. Therefore, PCOS women with a WC over 70 cm should be closely monitored for the development of MS.
Crossover from nucleation to spinodal decomposition in a condensing vapor
Authors: Wedekind Jan , Chkonia Guram , Wölk Judith , Strey Reinhard , Reguera David
Published: September 2009

The mechanism controlling the initial step of a phase transition has a tremendous influence on the emerging phase. We study the crossover from a purely nucleation-controlled transition toward spinodal decomposition in a condensing Lennard-Jones vapor using molecular dynamics simulations. We analyze both the kinetics and at the same time the thermodynamics by directly reconstructing the free energy of cluster formation. We estimate the location of the spinodal, which lies at much deeper supersaturations than expected. Moreover, the nucleation barriers we find differ only by a constant from the classical nucleation theory predictions and are in very good agreement with semiempirical scaling relations. In the regime from very small barriers to the spinodal, growth controls the rate of the transition but not its nature because the activation barrier has not yet vanished. Finally, we discuss in detail the influence of the chosen reaction coordinate on the interpretation of such simulation results.
Structural characterization of (C2H2)1–6+ cluster ions by vibrational predissociation spectroscopy
Authors: Relph Rachael A. , Bopp Joseph C. , Roscioli Joseph R. , Johnson Mark A.
Published: September 2009

Vibrational predissociation spectra are reported for the cationic acetylene clusters, (C2H2)n+, n=1–6, in the region of the C–H stretching fundamentals. For n=1 and 2, predissociation could only be observed for the Ar-tagged clusters. These were prepared by charge-transfer collisions of Ark+ with C2H2 to create C2H2+⋅Arm clusters, which were then converted into larger members of the (C2H2)n+⋅Ar series by sequential addition of acetylene molecules. The (C2H2)2+⋅Ar spectrum indicates that this species is predominantly present as the cyclobutadiene cation. Although mobility measurements on the electron-impact-generated (C2H2)3+ ion indicated that it primarily occurs as the benzene cation, [P. O. Momoh, J. Am. Chem. Soc. 128, 12408 (2006)] photofragmentation of (C2H2)3+⋅Ar in the C–H stretching region is dominated by the loss of C2H2 in addition to the weakly bound Ar atom. This suggests that the dominant n=3 species formed by sequential addition of C2H2 is based on a covalently bound C4H4+ core ion. Interestingly, the spectrum of this core C4H4+ species is different from that found for the cyclobutadiene cation, displaying instead a new band pattern that is retained in the higher (C2H2)3–6+ clusters. Multiple isomers are clearly involved, as yet another pattern of bands is recovered when the (C2H2)3+⋅Ar action spectrum is recorded in the (minor) Ar loss fragmentation channel. One of these features does appear in the location of the single band characteristic of the Ar-tagged benzene cation reported earlier [Phys. Chem. Chem. Phys. 4, 24 (2002)], supporting a scenario where the benzene cation is one of the isomers present. We then compare the Ar predissociation results with (C2H2)n+ spectra obtained when the ions are prepared by electron impact ionization of neutral acetylene clusters. The photofragmentation behavior and vibrational spectra indicate that the dominant species formed in this way also occur with a covalently bound C4H4+ core. There are absorptions, however, which are consistent with a minor contribution from (C2H2)n+ clusters based on the benzene cation.
The characteristics of four ratcheting states in cellular flames
Authors: Gorman M. , el-Hamdi M. , Pearson B.
Published: September 2009

A premixed flat flame on a circular porous plug burner can form patterns of one or two concentric rings of cells in which brighter, hotter regions are separated by darker, cooler cusps and folds. Dynamic states are found at parameter values that are interleaved between those of the ordered states. Rotating states, modulated rotating states, hopping states, and intermittently ordered states have all been observed with motions of ∼100°/s. These states have been described using the ideas of dynamical systems. Their characteristics have been analyzed using modal decomposition techniques. Ratcheting states are qualitatively and quantitatively different from these other dynamic states. In ratcheting states one or both of the concentric rings rotate very slowly, ∼0.8°/s, each speeding up and slowing down in a manner unique to that state. Measurements of the angular displacement and computed values of the angular velocity are presented for four ratcheting states. The experimental results are discussed in the context of the physical characteristics of the flame front and in terms of bifurcations of systems with symmetry. Many of the principal features of ratcheting motion are not yet understood.
Extracting phonon thermal conductance across atomic junctions: Nonequilibrium Green’s function approach compared to semiclassical methods
Authors: Hopkins Patrick E. , Norris Pamela M. , Tsegaye Mikiyas S. , Ghosh Avik W.
Published: September 2009

The thermal conductance of nanoscale phonon modes is typically calculated using the Boltzmann transport equation. A particular implementation of this method is the acoustic mismatch model (AMM) that compares impedance ratios at a mathematically abrupt transition between two equilibrium regions. The shortcomings of this model can be rectified by starting from a microscopic physics based equation describing the propagation of phonon waves across an extended junction, with carefully computed thermal boundary conditions on either side. The resulting nonequilibrium Green’s function (NEGF) formalism provides an accurate yet physically transparent machinery to calculate energy transfer, especially in nanosystems where the concept of thermal equilibrium breaks down readily. The purpose of this paper is to establish the NEGF formalism of thermal conductivity with a few simple examples and illustrate its particular strengths compared to the AMM.
Study on mechanism of crystallization in HfO2 films on Si substrates by in-depth profile analysis using photoemission spectroscopy
Authors: Toyoda Satoshi , Takahashi Haruhiko , Kumigashira Hiroshi , Oshima Masaharu , Lee Dong-Ick , Sun Shiyu , Liu Zhi , Sun Yun , Pianetta Piero A. , Oshiyama Itaru , Tai Kaori , Fukuda Seiichi
Published: September 2009

We have investigated the effect of HfO2 layer thickness on crystallization in thin HfO2 films using photoemission spectroscopy and x-ray absorption spectroscopy (XAS). O K-edge XAS spectra depending on annealing temperature indicate that crystallization in thin HfO2 films is suppressed upon annealing for thin HfO2 film, which in turn has a beneficial effect on the performance of devices. The annealing-temperature dependence of the depth profile of HfO2 films suggests that diffusion of Si atoms into the HfO2 layer plays only a minor role in the suppression of crystallization, indicating that HfO2 films can restrain a decrease in dielectric constant.
Dielectric properties and phase transition behaviors in (1−x)PbZrO3–xPb(Mg1/2W1/2)O3 ceramics
Authors: Vittayakorn Naratip , Charoonsuk Piyanut , Kasiansin Panisara , Wirunchit Supamas , Boonchom Banjong
Published: September 2009

The solid solution of lead zirconate [PbZrO3 (PZ)] and lead magnesium tungstate [Pb(Mg1/2W1/2)O3 (PMW)] has been synthesized by the wolframite precursor method. The crystal structure, phase transformations, dielectric and thermal properties of (1−x)PZ-xPMW, where x=0.00–0.10, were investigated. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. Phase-pure perovskite was obtained for all compositions. Furthermore, a change from orthorhombic to rhombohedral symmetry was observed as the mole fraction of increased PMW. As a result, it was found that PbZrO3–Pb(Mg1/2W1/2)O3 undergoes successive transitions from the antiferroelectric phase to the ferroelectric phase to the paraelectric state. The coexistence of orthorhombic and rhombohedral phases in this binary system is located near the composition x=0.1.
Effect of biaxial strain on the electrical and magnetic properties of (001) La0.7Sr0.3MnO3 thin films
Authors: Adamo C. , Ke X. , Wang H. Q. , Xin H. L. , Heeg T. , Hawley M. E. , Zander W. , Schubert J. , Schiffer P. , Muller D. A. , Maritato L. , Schlom D. G.
Published: September 2009

We have studied the effect of biaxial strain on thin films of (001) La0.7Sr0.3MnO3. We deposited films by reactive molecular-beam epitaxy on different single crystalline substrates, varying the substrate-induced biaxial strain from −2.3% to +3.2%. Magnetization and electrical transport measurements reveal that the dependence of the Curie temperature on biaxial strain is in very good agreement with the theoretical predictions of Millis et al. [J. Appl. Phys. 83, 1588 (1998)].
An auxiliary capacitor based ultrafast drive circuit for shear piezoelectric motors
Authors: Chatterjee Kamalesh , Boyer M. C. , Wise W. D. , Hudson E. W.
Published: September 2009

Shear piezoelectric motors frequently require large voltage changes on very short time scales. Since piezos behave electrically as capacitors, this requires a drive circuit capable of quickly sourcing or sinking a large amount of current at high voltages. Here we describe a novel circuit design using a high voltage amplifier, transistor switching stage, and auxiliary capacitor. This circuit can drive piezoelectric motors at higher speeds and lower costs than conventional methods and with greater flexibility for computer automation. We illustrate its application in a controller for a scanning tunneling microscope coarse approach mechanism and discuss other possible applications and modifications of this circuit.
Diversity of kinetic pathways in amyloid fibril formation
Authors: Bellesia Giovanni , Shea Joan-Emma
Published: September 2009

The kinetics of peptide oligomerization was investigated using Langevin Dynamics simulations and a coarse-grained peptide model. The simulations show a rich diversity of aggregation pathways, modulated by the β-sheet propensity (flexibility) of the peptide. Aggregation into amyloidlike fibrils occurs via three main mechanisms: (i) formation of fibrils directly from the assembly of early ordered oligomers, (ii) fibril formation via the formation of on-pathway, nonfibrillar aggregates high in β-sheet content, and (iii) formation of amorphous aggregates followed by reorganization to β-sheet aggregates and to fibrils. β-sheet, nonfibrillar aggregates also appeared as long-lived, “off-pathway” end-product species.
On the dielectric conductivity of molecular ionic liquids
Authors: Schröder Christian , Steinhauser Othmar
Published: September 2009

The contribution of the conductivity to the spectrum of the generalized dielectric constant or susceptibility of molecular ionic liquids is analyzed, both in theoretical terms and computationally by means of molecular dynamics simulation of the concrete system 1-ethyl-3-methyl-imidazolium dicyanoamide at 300 K. As a central quantity the simulated current autocorrelation function is modeled by a carefully designed fit function. This not only gives a satisfactory numerical representation but yields the correct conductivity upon integration. In addition the fit function can be Fourier–Laplace transformed analytically. Both, the real and imaginary parts of the transform show expected behavior, in particular, the right limits for zero frequency. This altogether demonstrates that the components of the fit function are of physical relevance.
Analysis of magnetic response of critical state in second-generation high temperature superconductor YBa2Cu3Ox wire
Authors: Youssef Ahmed , Švindrych Zdeněk , Janů Zdeněk
Published: September 2009

We have measured magnetic response of second-generation high temperature superconductor YBa2Cu3Ox wire in perpendicular ac field as a function of temperature. We compare complex ac susceptibility to the calculated susceptibility based on the model of Bean’s critical-state response in two-dimensional (2D) disk in perpendicular field and infinitely long cylinder in parallel field. We present a method of linking model and experimental susceptibility. Good agreement of experimental susceptibility with model susceptibility of 2D disk allows noncontact estimation of critical depinning current density and its temperature dependence.
Six-fold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles
Authors: Thevenard L. , Zeng H. T. , Petit D. , Cowburn R. P.
Published: September 2009

Six-fold configurational anisotropy was studied in Permalloy triangles, in which the shape symmetry order yields two energetically non-degenerate micromagnetic configurations of the spins, the so-called Y and “buckle” states. A 12-pointed switching astroid was measured using magneto-optical experiments and well reproduced numerically. Switching fields in different polar sectors were shown to reflect the different possible energy paths dictated by the configurational anisotropy during a 180° reversal of the magnetization, thereby giving a comprehensive view of the switching mechanism in these structures. A detailed analysis moreover highlighted the necessity to include the physical rounding of the structures in the simulations to account for the instability of the Y state.
Generation of polarized shear Alfvén waves by a rotating magnetic field source
Authors: Gigliotti A. , Gekelman W. , Pribyl P. , Vincena S. , Karavaev A. , Shao X. , Sharma A. Surjalal , Papadopoulos D.
Published: September 2009

Experiments are performed in the Large Plasma Device at the University of California, Los Angeles to study the propagation of field-aligned, polarized kinetic shear Alfvén waves radiated from a rotating magnetic field source created via a novel phased orthogonal loop antenna. Both right and left hand circular polarizations are generated at a wide range of frequencies from 0.21≤ω/Ωci<0.93. Propagation parallel to the background magnetic field near the Alfvén velocity is observed along with a small parallel wave magnetic field component implying a shear mode. The peak-to-peak magnitude of the wave magnetic field, 33 cm away from the antenna, is on the order of 0.8% of the background field and drops off in the far field. The full width at half maximum of the wave energy changes little over a distance of 2.5 parallel wavelengths while the exponential decrease in wave energy as a function of distance can be attributed to collisional damping. Evidence of electron heating and ionization is observed during the pulse.
Postionization fragmentation of rare-gas trimers revisited with new theoretical approaches
Authors: Janeček Ivan , Cintavá Silvie , Hrivňák Daniel , Kalus René , Fárník Michal , Gadea Florent Xavier
Published: September 2009

A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics (mixing classical and quantum approach) and applied to the postionization of rare-gas trimers. There was an important disagreement between trajectory surface hopping (TSH) or mean field (MF) approaches and the experimental results; noteworthy, with the new method qualitative and almost quantitative agreement is found for the fragmentation ratios of ionic monomers and dimers. For the first time in the theory as in the experiment, the dimers prevail for argon while monomers strongly dominate for the heavier rare gases, krypton and xenon. A new compromise between MF and TSH approaches is proposed and the new method is found quite robust with results not too sensitive to various possible implementations.
Controlled growth of InGaAs/InGaAsP quantum dots on InP substrates employing diblock copolymer lithography
Authors: Park J. H. , Kirch J. , Mawst L. J. , Liu C.-C. , Nealey P. F. , Kuech T. F.
Published: September 2009

Selective metalorganic chemical vapor deposition growth with diblock copolymer nanopatterning is utilized to produce InGaAsP(Q1.15 μm)/In0.53Ga0.47As/InGaAsP(Q1.15 μm) and InP/In0.53Ga0.47As/InP quantum dots (QDs) on InP substrates. The QD patterning is prepared by dense nanoscale diblock copolymer lithography followed by pattern-transfer onto a dielectric template mask and reactive ion etching is utilized to form nanosized openings exposing the underlying InGaAsP layer. By varying the In0.53Ga0.47As layer thickness within the QDs, the emission wavelength can be selected within the 1.4–1.6 μm region. Strongest photoluminescence (PL) intensity is observed from QDs employing InP rather than InGaAsP barriers, demonstrating room temperature PL near 1.6 μm.
Effects of large-scale free stream turbulence on a turbulent boundary layer
Authors: Sharp N. S. , Neuscamman S. , Warhaft Z.
Published: September 2009

Results of a wind tunnel experiment in which there are systematic variations of free stream turbulence above a flat-plate boundary layer are presented. Upstream of the plate, an active grid generates free stream turbulence varying in intensity from 0.25% to 10.5%. The momentum thickness Reynolds number of the boundary layer varies from 550 to nearly 3000. In all cases, the ratio of the free stream turbulence length scale to the boundary layer depth is greater than unity. Hotwire measurements show that, at high turbulence intensities, the effects of the free stream turbulence extend deep into the boundary layer, affecting the wall stress as well as the small-scale (derivative) statistics. Premultiplied energy spectra show a double peak. At very low free stream turbulence intensities these peaks are associated with the inner and outer scales of the turbulent boundary layer, but at high turbulence intensities the free stream energy peak dominates over the boundary layer’s outer scale. The implications of the effect of the large free stream turbulence scales on the small, near-wall scales is discussed with reference to recent high Reynolds number experiments in a turbulent boundary layer without free stream turbulence [Hutchins and Marusic, Philos. Trans. R. Soc. London, Ser. A 365, 647 (2007)].
On the stabilizing effect of the Coriolis force on the turbulent wake of a normal flat plate
Authors: Khaledi Hatef A. , Barri Mustafa , Andersson Helge I.
Published: September 2009

The turbulent Karman vortex street behind a flat plate in a rotating fluid is explored by means of direct numerical simulations. The effect of the Coriolis force is often said to be stabilizing on the cyclonic side of the wake and destabilizing on the anticyclonic side. The present computer experiments reveal a more subtle influence of the system rotation. The turbulence is suppressed at the cyclonic side of the wake at Rossby numbers of about unity whereas the cyclonic Karman roller eddies persist. The anticyclonic vortex cells which are blurred by the enhanced turbulence level are scarcely visible. The Strouhal number of this asymmetric vortex shedding is slightly higher than in the absence of rotation. At even higher rotation rates, the three-dimensional turbulence is suppressed also along the anticyclonic side of the wake and a nearly symmetric vortex street is observed at Rossby number of 0.16 with the Strouhal number significantly lower than for the nonrotating wake. At this rotation rate, the anticyclonically shed cells appeared as high-pressure zones. At even lower Rossby numbers, not only the turbulence but also the periodic vortex shedding is suppressed, in accordance with the demarcation line in a Rossby–Ekman number flow regime map.
Wide range and tunable linear magnetic tunnel junction sensor using two exchange pinned electrodes
Authors: Negulescu B. , Lacour D. , Montaigne F. , Gerken A. , Paul J. , Spetter V. , Marien J. , Duret C. , Hehn M.
Published: September 2009

A magnetic tunnel junction sensor with both the detection and the reference layers pinned by IrMn is fabricated. Using the differences in the blocking temperatures of the IrMn films with different thicknesses, crossed anisotropies can be induced between the detection and the reference electrodes. The pinning of the sensing electrode ensures a linear and reversible output. It also allows tuning both the sensitivity and the linear range of the sensor. The sensitivity varies linearly with the ferromagnetic thickness of the detection electrode. It is demonstrated that an increased thickness leads to a rise of sensitivity and a reduction of the operating range.
Noise measurement system at electron temperature down to 20 mK with combinations of the low pass filters
Authors: Hashisaka Masayuki , Yamauchi Yoshiaki , Chida Kensaku , Nakamura Shuji , Kobayashi Kensuke , Ono Teruo
Published: September 2009

We developed a quantum noise measurement system in a dilution refrigerator by using three kinds of cryogenic low pass filters. One of them is a commercial low pass filter inserted into the noise measurement lines instead of the conventional powder filter, which assures well-defined circuit parameters necessary for the noise measurement at a finite frequency. We checked that this filter gives sufficiently large attenuation up to 20 GHz at room temperature, 77 and 4.2 K. The electron temperature of the mesoscopic device placed in the present system was confirmed to be down to around 20 mK by measuring the thermal noise of the device.
Charging dust particles in plasmas with two-temperature distributions of electrons and with cold ions
Authors: Filippov A. V. , Pal’ A. F. , Starostin A. N. , Gavrikov A. V. , Fortov V. E. , Petrov O. F. , Vasil’ev M. N.
Published: September 2009

Supercharging of dust particles in a plasma with a two-temperature energy distribution of electrons is studied. Influence of the thermal-field emission and the secondary electron emission on the charge of dust particles is investigated. The maximum possible charge in view of the limited tensile strength of dust particles, which can be disintegrated under the action of the ponderomotive force, is determined. It is experimentally and theoretically demonstrated that the charge of micron-sized particles can be as high as 106 electron charges.
Force modulation of tunnel gaps in metal oxide memristive nanoswitches
Authors: Miao Feng , Yang J. Joshua , Strachan John Paul , Stewart Duncan , Williams R. Stanley , Lau Chun Ning
Published: September 2009

Electron tunneling plays a key role in computing devices. Tunneling is, however, notoriously difficult to characterize inside real device structures. Using pressure modulated conductance microscopy, we demonstrate in situ angstrom-scale tuning and estimation of tunnel gaps with ∼10 nm lateral resolution. By modulating tunnel gaps in Pt/TiOx/Pt memristive oxide nanoswitches, we establish that these devices switch via 2–9 Å modification of the tunnel gap.
Effect of the introduction of H atoms on magnetic properties and magnetic entropy change in metamagnetic Heusler alloys Ni–Mn–In
Authors: Hu F. X. , Wang J. , Chen L. , Zhao J. L. , Sun J. R. , Shen B. G.
Published: September 2009

By hydrogen insertion into Ni51Mn49−xInx (x=16.2,16.6) Heusler alloys, the interstitial compounds Ni51Mn49−xInxHδ were fabricated. The introduction of H atoms does not change the L21 structure of the alloys but shifts martensitic temperature (TM) to lower temperature. Magnetic measurements indicated the hydrogenated Ni51Mn49−xInxHδ compounds retain the metamagnetic properties although the ferromagnetic behavior of martensitic phases is slightly enhanced due to the introduction of H atoms. The strong metamagnetic behaviors result in large magnetocaloric effect (MCE). By controlling H content an extended temperature range having large MCE can be achieved.
Cross sections for electron impact excitation of the C Π1 and D Σ1+ electronic states in N2O
Authors: Kawahara H. , Suzuki D. , Kato H. , Hoshino M. , Tanaka H. , Ingólfsson O. , Campbell L. , Brunger M. J.
Published: September 2009

Differential and integral cross sections for electron-impact excitation of the dipole-allowed C Π1 and D Σ1+ electronic states of nitrous oxide have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at six electron energies in the range 15–200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to check both the validity of the only other comprehensive experimental study into these excitation processes [Marinković et al., J. Phys. B 32, 1949 (1998)] and to extend the energy range of those data. Agreement with the earlier data, particularly at the lower common energies, was typically found to be fair. In addition, the BEf-scaling approach [Kim, J. Chem. Phys. 126, 064305 (2007)] is used to calculate integral cross sections for the C Π1 and D Σ1+ states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, the only exception being at the lowest energies of this study. Finally, optical oscillator strengths, also determined as a part of the present investigations, were found to be in fair accordance with previous corresponding determinations.
Entraining synthetic genetic oscillators
Authors: Wagemakers Alexandre , Buldú Javier M. , Sanjuán Miguel A. F. , de Luis Oscar , Izquierdo Adriana , Coloma Antonio
Published: September 2009

We propose a new approach for synchronizing a population of synthetic genetic oscillators, which consists in the entrainment of a colony of repressilators by external modulation. We present a model where the repressilator dynamics is affected by periodic changes in temperature. We introduce an additional plasmid in the bacteria in order to correlate the temperature variations with the enhancement of the transcription rate of a certain gene. This can be done by introducing a promoter that is related to the heat shock response. This way, the expression of that gene results in a protein that enhances the overall oscillations. Numerical results show coherent oscillations of the population for a certain range of the external frequency, which is in turn related to the natural oscillation frequency of the modified repressilator. Finally we study the transient times related with the loss of synchronization and we discuss possible applications in biotechnology of large-scale production coupled to synchronization events induced by heat shock.
Determination of colloidal interaction potentials from small angle scattering data
Authors: Fritz-Popovski Gerhard
Published: September 2009

The scattering curves of monodisperse, globular particles measured by small angle scattering are products of a form factor and of a structure factor. The form factor contains the information on particle shape and size and can often be measured for dilute samples. The structure factor contains the contributions due to particle interactions. It should be approximated by a structure factor model based on the Percus–Yevik, hypernetted chain, or soft mean spherical approximation closure relations. Combining these relations with a flexible model for the interaction potential, it is possible to determine the interaction potential from the scattering data. Scattering curves of charged spherical colloids and of spheres interacting by depletion forces are therefore simulated and evaluated, resulting in potentials that are close to the ones used for the simulation. The applicability of the approach is finally tested on a 5% solution of lysozyme at pH 4.5, which gave an interaction potential that agreed well with the one expected for such a sample.
Enhancing the magnetoelectric response of Metglas/polyvinylidene fluoride laminates by exploiting the flux concentration effect
Authors: Fang Z. , Lu S. G. , Li F. , Datta S. , Zhang Q. M. , El Tahchi M.
Published: September 2009

Magnetic flux concentration effect of Metglas as a function of its sheet aspect ratio was investigated for Metglas/polyvinylidene fluoride laminates. Taking advantage of this effect, the magnetoelectric voltage coefficient of 21.46 V/cm∙Oe for a laminate with 1 mm wide and 30 mm long Metglas sheet (25 μm thick) is achieved, which is much higher than those reported earlier in similar laminates without making use of the flux concentration effect. The results demonstrate an effective means to significantly enhance the sensitivity of magnetostrictive/piezoelectric composite laminates as weak magnetic field sensors.
Influence of surface morphology on the optical property of vertically aligned ZnO nanorods
Authors: Das Sachindra Nath , Kar Jyoti Prakash , Choi Ji-Hyuk , Byeon S. , Jho Y. D. , Myoung Jae-Min
Published: September 2009

In this letter we have studied an influence of surface morphology on the optical property of vertically aligned ZnO nanorods. At low temperature the near band edge excitonic emission shows a strong dependence on surface morphology. A prominent and well resolved near band edge photoluminescence (PL) peak was obtained for nanowires with decreasing diameter and thus assigned due to the contributions to the optical properties of individual nanorods. Depending on surface morphology, the difference in low temperature PL property is attributed to the tailing of the density of states due to the potential fluctuations in randomly distributed intrinsic defects.
The dynamics of nonlinear instability waves in laminar heated and unheated compressible mixing layers
Authors: Cheung Lawrence C. , Lele Sanjiva K.
Published: September 2009

Previous studies have shown that when using instability wave theories to model compressible laminar mixing layers, explicitly accounting for nonlinear processes such as the mean flow correction and modal interactions is necessary in order to properly capture vortex roll-up and pairing phenomena. In this study, we examine the effects of heating when using the nonlinear instability wave formulation on two-dimensional compressible mixing layers. We compare the results of both heated and unheated, supersonic and subsonic laminar mixing layer calculations using both the nonlinear parabolized stability equations (PSE) and Navier–Stokes equations. For all supersonic mixing layers, we find that the nonlinear stability method adequately captures the roll-up process and agrees well with direct calculations. While the same is true for the unheated subsonic mixing layer, in the heated subsonic mixing layer, we find that baroclinic vorticity generation, in addition to nonlinear interactions, plays a significant role in governing the vorticity dynamics. We observe that in the presence of large density stratifications in subsonic flows, approximations made in the streamwise pressure gradient of the PSE formulation can lead to discrepancies in the vortex dynamics. Error estimates for the approximations to the baroclinic term show that discrepancies are directly proportional to the temperature difference and inversely proportional to the Reynolds number.
Diterpenoid Hydroperoxides from the Far-Eastern Brown Alga Dictyota dichotoma
Authors: Kolesnikova Sophia A. , Lyakhova Ekaterina G. , Kalinovsky Anatoly I. , Dmitrenok Pavel S. , Dyshlovoy Sergei A. , Stonik Valentin A.
Published: September 2009

Two new compounds, dictyohydroperoxide 1 and hydroperoxyacetoxycrenulide 2, (Scheme 1) containing hydroperoxyl groups rarely found in algal terpenoids were isolated from the Russian population of brown alga Dictyota dichotoma. The known compounds acetoxycrenulide 4 and squalene were also found in this algal species for the first time. Some of the isolated compounds showed moderate cytoxicity against human cancer cell lines.