bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal wave packets in a boundary layer and initial phases of a turbulent spot
Authors: CHERUBINI S. , ROBINET J.-C. , BOTTARO A. , DE PALMA P.
Published: May 2010

The three-dimensional global optimal dynamics of a flat-plate boundary layer is studied by means of an adjoint-based optimization in a spatial domain of long – but finite – streamwise dimension. The localized optimal initial perturbation is characterized by a pair of streamwise-modulated counter-rotating vortices, tilted upstream, yielding at the optimal time elongated streaks of alternating sign in the streamwise direction. This indicates that perturbations with non-zero streamwise wavenumber have a role in the transient dynamics of a boundary layer. A scaling law is provided, describing the variation of the streamwise modulation of the optimal initial perturbation with respect to the streamwise domain length and to the Reynolds number. For spanwise-extended domains, a near-optimal three-dimensional perturbation is extracted during the optimization process; it is localized also in the spanwise direction, resulting in a wave packet of elongated disturbances modulated in the spanwise and streamwise directions. The nonlinear evolution of the optimal and near-optimal perturbations is investigated by means of direct numerical simulations. Both perturbations are found to induce transition at lower levels of the initial energy than local optimal and suboptimal perturbations. Moreover, it is observed that transition occurs in a well-defined region of the convected wave packet, close to its centre, via a mechanism including at the same time oscillations of the streaks of both quasi-sinuous and quasi-varicose nature. Hairpin vortices are observed before transition; they have an active role in the breakdown of the streaks and result in a turbulent spot which spreads out in the boundary layer.
Sexual conflict inNeptunea arthritica: the power asymmetry and female resistance
Authors: Roberto Carlos Lombardo , Seiji Goshima
Published: May 2010

Copula trials inNeptunea arthriticawere conducted to provide possible hypotheses explaining the outcomes of reproductive interaction with regards to size differences and female resistance in the context of conflict over copula duration between the sexes. Size asymmetry predicted the outcome of copula duration to favour the largest individuals. Female resistance was expressed consistently and increased with consecutive copulas, generating variation in copula duration. When resistance was removed, copula duration increased in contrast with natural trials suggesting intense conflict. Overall, males showed a tendency to mate with large females, which represents higher rejection risk, indicating that benefits from mating with large females might offset the risk of failure against resistance. Conflict possibly stems from a ‘power asymmetry’ in which individuals of one sex could sequester control over some aspects of mating to the detriment of the opposite sex.
Misattribution of facial expressions of emotion in adolescents at increased risk of psychosis: the role of inhibitory control
Authors: van Rijn S. , Aleman A. , de Sonneville L. , Sprong M. , Ziermans T. , Schothorst P. , van Engeland H. , Swaab H.
Published: May 2010

Background

By studying behavior, cognitive abilities and brain functioning in adolescents at high risk for psychosis, we can gain an insight into the vulnerability markers or protective factors in the development of psychotic symptoms. Although many high-risk studies have focused on impairments in neurocognitive functions, such as memory and attention, very few studies have investigated problems in processing social cues such as facial expressions as a possible vulnerability marker for psychosis.

Method

Thirty-six adolescents at ultra-high risk (UHR) for psychosis and 21 non-clinical controls completed a face recognition test, a facial affect labeling test and an inhibitory control test. Schizotypal traits and schizophrenia symptoms were assessed using a schizotypy questionnaire and the Positive and Negative Syndrome Scale (PANSS).

Results

The UHR group showed impairments in labeling facial expressions of others, in addition to a spared ability to recognize facial identity. More specifically, the UHR group made more errors in labeling neutral expressions compared to the controls, and an analysis of error types indicated that neutral faces were misattributed as being angry. The degree of misattribution of neutral-as-angry faces correlated significantly with reduced inhibitory control.

Conclusions

Our findings suggest that misattributing social cues might contribute to vulnerability for psychosis. This social cognitive deficit may be related to problems in inhibitory control, which potentially plays an important role in the selection of appropriate social meaning. These findings may have relevance for understanding the mechanisms underlying prodromal social dysfunction, which should be targeted in future remediation interventions.
Undue influence of weight and shape: is it distinct from body dissatisfaction and concern about weight and shape?
Authors: Wade T. D. , Zhu G. , Martin N. G.
Published: May 2010

Background

Three cognitive constructs are risk factors for eating disorders: undue influence of weight and shape, concern about weight and shape, and body dissatisfaction (BD). Undue influence, a diagnostic criterion for eating disorders, is postulated to be closely associated with self-esteem whereas BD is postulated to be closely associated with body mass index (BMI). We understand less about the relationships with concern about weight and shape. The aim of the current investigation was examine the degree of overlap across these five phenotypes in terms of latent genetic and environmental risk factors in order to draw some conclusions about the similarities and differences across the three cognitive variables.

Method

A sample of female Australian twins (n=1056, including 348 complete pairs), mean age 35 years (s.d.=2.11, range 28–40), completed a semi-structured interview about eating pathology and self-report questionnaires. An independent pathways model was used to investigate the overlap of genetic and environmental risk factors for the five phenotypes.

Results

In terms of variance that was not shared with other phenotypes, self-esteem emerged as being separate, with 100% of its variance unshared with the other phenotypes, followed by undue influence (51%) and then concern (34%), BD (28%) and BMI (32%).

Conclusions

In terms of shared genetic risk, undue influence and concern were more closely related than BD, whereas BMI and BD were found to share common sources of risk. With respect to environmental risk factors, concern, BMI and BD were more closely related to each other than to undue influence.
The Demon's Nun: FOMMA and the Embodied Politics of Gendered Visibility in Mayan Mexico
Authors: UNDERINER TAMARA
Published: May 2010

This contribution to the performance dossier situates this 2003 play within the larger body of FOMMA's work and within the sociopolitical context of neoliberalism within Mexico, which has disproportionately affected indigenous communities in general, and indigenous women in particular.
A solution of the uniform word problem for ortholattices
Authors: MEINANDER ANDREA
Published: May 2010

The uniform word problem for finitely presented ortholattices is shown to be solvable through a method of terminating proof search. The axioms of ortholattices are all Harrop formulas, and thus can be expressed in natural deduction style as single succedent rules. A system of natural deduction style rules for orthologic is given as an extension of the system for lattices presented by Negri and von Plato. By considering formal derivations of atomic formulas from a finite number of given atomic formulas, it is shown that proof search is bounded, and thus that the question of derivability of any atomic formula from any finite set of given atomic formulas is decidable.
The molecular mediators of type 2 epithelial to mesenchymal transition (EMT) and their role in renal pathophysiology
Authors: Burns Wendy C. , Thomas Merlin C.
Published: May 2010

Common to all forms of chronic kidney disease is the progressive scarring of the tubulo-interstitial space, associated with the acquisition and accumulation of activated myofibroblasts. Many of these myofibroblasts are generated when tubular epithelial cells progressively lose their epithelial characteristics (cell–cell contact, microvilli, tight-junction proteins, apical–basal polarity) and acquire features of a mesenchymal lineage, including stress fibres, filopodia and augmented matrix synthesis. This process, known as epithelial to mesenchymal transition (EMT), plays an important role in progressive kidney disease. For EMT to occur in tubular cells, the transcriptional activation (and derepression) of genes required to sustain mesenchymal-type structures and functions (e.g. vimentin, α-smooth muscle actin) must occur alongside repression (or deactivation) of genes that act to maintain the epithelial phenotype (e.g. E-cadherin, bone morphogenic protein 7). Several factors have been suggested as potential initiators of EMT. With a few key exceptions, these triggers require the induction of transforming growth factor β (TGF-β) and downstream mediators, including SMADs, CTGF, ILK and SNAI1. Activation of TGF-β receptors is also able to stimulate a range of additional pathways (so-called non-SMAD activation), including RhoA, mitogen-activated protein kinase and phosphoinositide 3-kinase signalling cascades, that also contribute to EMT and renal fibrogenesis. This review examines in detail the molecular mediators of EMT in tubular cells and its potential role as a long-lasting mediator of metabolic stress.
The entropy principle, and the influence of sociological pressures on SETI
Authors: Bozhilov V. , Forgan Duncan H.
Published: May 2010

We begin with the premise that the law of entropy could prove to be fundamental for the evolution of intelligent life and the advent of technological civilization. Building on recent theoretical results, we combine a modern approach to evolutionary theory with Monte Carlo realization techniques. A numerical test for a proposed significance of the law of entropy within the evolution of intelligent species is performed and results are compared with a neutral test hypothesis. Some clarifying aspects on the emergence of intelligent species arise and are discussed in the framework of contemporary astrobiology.
Effect of multiyear drought on upland sediment yield and subsequent impacts on flood control reservoir storage
Authors: Dunbar John A. , Allen Peter M. , Bennett Sean J.
Published: May 2010

Since the early 1950s, the U.S. Soil Conservation Service (SCS) and later the U.S. Department of Agriculture Natural Resources Conservation Service has built over 11,000 flood control reservoirs (FCR) in 47 states. FCR built in Texas and Oklahoma in the early 1950s to mid‐1950s were impounded during the most severe drought on record in the region. In this study, the sediment trapped in FCR is used to reconstruct the variation in sediment yield through the drought years to the present. New sediment surveys of four FCR in McCulloch County, Texas, are combined with three previous surveys by the SCS. The new surveys are conducted using acoustic profiling to map water depth and sediment thickness in submerged areas of the reservoirs and real‐time kinematic GPS in the dry areas. Sediment coring is used to determine sediment dry bulk density. The survey results are used to construct a composite history of the normalized sediment yield for the study area. Normalized sediment yield is the annual sediment yield normalized by the soil erodability factor K and the combined slope length and steepness factor LS of the watershed. The results indicate that sediment yield was lowest during the relatively drought‐free period from 1971 to 2007, averaging 4.2 t/ha/yr/unit K/unit LS and over 70 times higher during the early part of the 1950s drought from 1951 to 1953, averaging 300.3 t/ha/yr/unit K/unit LS. These results have important implications for predicting the remaining useful life of FCR in the region and planning for future droughts.
Observation of magnetic diffusion in the Earth's outer core from Magsat, Ørsted, and CHAMP data
Authors: Chulliat A. , Olsen N.
Published: May 2010

The frozen flux assumption consists in neglecting magnetic diffusion in the core. It has been widely used to compute core flows from geomagnetic observations. Here we investigate the validity of this assumption over the time interval 1980–2005, using high‐precision magnetic data from the Magsat, Ørsted, and CHAMP satellites. A detectable change of magnetic fluxes through patches delimited by curves of zero radial magnetic field at the core‐mantle boundary is associated with a failure of the frozen flux assumption. For each epoch (1980 and 2005), we calculate spatially regularized models of the core field which we use to investigate the change of reversed magnetic flux at the core surface. The largest and most robust change of reversed flux is observed for two patches: one located under St. Helena Island (near 20°S, 15°E); the other, much larger, is located under the South Atlantic Ocean. We next calculate frozen‐flux‐constrained field models (i.e., pairs of models for epoch 1980 and 2005 having the same flux through patches delimited by curves of zero radial magnetic field), using a penalty method. We find that the frozen flux constraint does not lead to any significant increase of the global misfit. However, applying the constraint leads to a detectable increase of the scalar residuals at satellite altitude in the region of St. Helena, strongly suggesting a local failure of the frozen flux assumption. The observed flux expulsion within the St. Helena patch could result from the formation of a pair of “core spots,” as predicted by numerical simulations of the geodynamo.
Examining the impact of overlying aerosols on the retrieval of cloud optical properties from passive remote sensing
Authors: Coddington O. M. , Pilewskie P. , Redemann J. , Platnick S. , Russell P. B. , Schmidt K. S. , Gore W. J. , Livingston J. , Wind G. , Vukicevic T.
Published: May 2010

Haywood et al. (2004) show that an aerosol layer above a cloud can cause a bias in the retrieved cloud optical thickness and effective radius. Monitoring for this potential bias is difficult because space‐based passive remote sensing cannot unambiguously detect or characterize aerosol above cloud. We show that cloud retrievals from aircraft measurements above cloud and below an overlying aerosol layer are a means to test this bias. The data were collected during the Intercontinental Chemical Transport Experiment (INTEX‐A) study based out of Portsmouth, New Hampshire, United States, above extensive, marine stratus cloud banks affected by industrial outflow. Solar Spectral Flux Radiometer (SSFR) irradiance measurements taken along a lower level flight leg above cloud and below aerosol were unaffected by the overlying aerosol. Along upper level flight legs, the irradiance reflected from cloud top was transmitted through an aerosol layer. We compare SSFR cloud retrievals from below‐aerosol legs to satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) in order to detect an aerosol‐induced bias. In regions of small variation in cloud properties, we find that SSFR and MODIS‐retrieved cloud optical thickness compares within the uncertainty range for each instrument while SSFR effective radius tend to be smaller than MODIS values (by 1–2 μm) and at the low end of MODIS uncertainty estimates. In regions of large variation in cloud properties, differences in SSFR and MODIS‐retrieved cloud optical thickness and effective radius can reach values of 10 and 10 μm, respectively. We include aerosols in forward modeling to test the sensitivity of SSFR cloud retrievals to overlying aerosol layers. We find an overlying absorbing aerosol layer biases SSFR cloud retrievals to smaller effective radii and optical thickness while nonabsorbing aerosols had no impact.
Black carbon aerosols over coastal Antarctica and its scavenging by snow during the Southern Hemispheric summer
Authors: Chaubey Jai Prakash , Moorthy K. Krishna , Babu S. Suresh , Nair Vijayakumar S. , Tiwari Anoop
Published: May 2010

Mass concentrations of aerosol black carbon (BC) and of the composite (total) aerosols (MB and MT, respectively) were measured over two Antarctic locations, Maitri [70°S, 12°E, 123 m mean sea level (msl)] and Larsemann Hills (LH; 69°S, 77°E, 48 m msl) as a part of the twenty‐eighth Indian Scientific Expedition to Antarctica during the Southern Hemispheric summer of 2009. Despite being very low compared to Northern Hemisphere locations, MB and its mass mixing ratio to the total aerosols were much high over Maitri (∼75 ng m−3 and 2%) compared to LH (13 ng m−3 and 0.2%). At both locations, MB fell abruptly after blizzards, after which the values reduced to nearly half the pre‐blizzard values. This BC scavenging by snow can lead to change in snow albedo and has strong climate implications. The Angstrom exponent (αabs) estimated from the spectral values of absorption coefficients (σabs) is found to vary from 0.5 to 1, indicating higher a BC‐to‐organic carbon ratio typical of fossil fuel origin.
Evaluating hillslope diffusion and terrace riser degradation in New Zealand and Idaho
Authors: Clarke Brian A. , Burbank Douglas W.
Published: May 2010

The relationship of sediment flux to surface slope is a predominant control on the evolution of transport‐limited hillslopes. Although both linear and nonlinear sediment flux models have been proposed and widely debated, this functional relationship remains one of the outstanding questions in geomorphology. We examine degradation of fluvial terrace risers in New Zealand and Idaho in order to test the linear diffusion model and to better understand the relationship between sediment flux and slope. We implement three techniques based on the linear diffusion model, as well as a geometric scaling method that uses proportional relationships in riser geometry rather than a specific transport equation model, to assess rates of degradation. We show that techniques that utilize the riser midpoint slope as the primary metric of degradation, as opposed to the full scarp profile, offer the simplest and most reliable assessment of riser degradation. Our findings suggest that the linear diffusion model does not accurately describe terrace riser degradation, except for low‐angle risers for which linear and nonlinear forms are indistinguishable. Results from the geometric scaling method show that degradation rates in both regions differ by a factor of two between equator‐ and pole‐facing risers and that diffusion ages of Idaho risers are approximately 2 times those of New Zealand risers. Similar geometric trends in riser evolution from both regions reveal that terrace riser degradation is governed by a widely applicable relationship between sediment flux and slope.
Cause of super‐thermal electron heating during magnetotail reconnection
Authors: Egedal J. , Lê A. , Zhu Y. , Daughton W. , Øieroset M. , Phan T. , Lin R. P. , Eastwood J. P.
Published: May 2010

We present a candidate mechanism for the energization of super‐thermal electrons during magnetic reconnection in the Earth's magnetotail. By analyzing in‐situ measurements of electron distribution functions we characterize the relative energy gain of the electrons as a function of energy, Δ(). For all the events considered the high energy part of Δ() is nearly independent of . This is the signature of energization in an acceleration potential, Φ∥, which is caused by parallel electric fields in the vicinity of the reconnection region. The same acceleration mechanism is also documented for a kinetic simulation of reconnection.
Pericardial Fat and Atrial Conduction Abnormalities in the Multiethnic Study of Atherosclerosis (MESA)
Authors: Babcock Michael J. , Soliman Elsayed Z. , Ding Jingzhong , Kronmal Richard A. , Goff‐Jr David C.
Published: May 2010

Pericardial fat (Pfat) overlies the cardiac surface including atria and their inter‐ and intra‐conduction system. Through its local inflammatory effects, Pfat may predispose to atrial abnormalities that could be detected as changes in P‐wave morphology in the 12‐lead electrocardiogram (ECG). We evaluated the association between Pfat and ECG measurements of P wave and PR interval (referred to as P‐wave indexes): PR duration (PR‐dur), P‐wave duration (P‐dur), and P‐wave terminal force (P‐term), in the Multiethnic Study of Atherosclerosis (MESA). Participants with available Pfat measured by computed tomography (CT) and P‐wave indexes measured by ECG were included (N = 996). Differences in P‐wave indexes per 1 standard deviation difference in Pfat were tested in unadjusted linear regression analysis first, then adjusted for demographics (age, sex, and ethnicity), and further adjusted for measures of adiposity (BMI or waist circumference (WC)), or cardiovascular risk factors (hypertension (HTN), diabetes, and smoking). All P‐wave indexes were significantly associated with Pfat in unadjusted analyses (regression‐coefficient (β) (95% CI): PR‐dur (ms) 2.53 (1.02, 4.04), P‐dur (ms) 2.59 (1.84, 3.35), P‐term (µV·s) 0.25 (0.13, 0.36)). After demographics adjustment, P‐dur (1.68 (0.87, 2.49)) and P‐term (0.16 (0.04,0.28)), but not PR‐dur (1.11 (−0.52, 2.74)) were associated with Pfat. No associations were significant after adjustment for BMI, WC, or cardiovascular disease (CVD) risk factors. BMI and WC, separately, were significantly associated with P‐wave indexes in all models, including those that included Pfat as a covariate. BMI, but not WC, was associated with P‐wave indexes when the two were entered into the same model. In conclusion, Pfat is associated with P‐wave indexes, but not after adjusting for measures of adiposity or CVD risk factors. Among Pfat, BMI and WC, BMI had the most robust association with P‐wave indexes. These findings raise doubts about potential local effects of Pfat on atrial electrophysiology and morphology
Human mitochondrial import receptor Tom70 functions as a monomer
Authors: Fan Anna C. Y. , Gava Lisandra M. , Ramos Carlos H. I. , Young Jason C.
Published: May 2010

The mitochondrial import receptor Tom70 (translocase of the mitochondrial outer membrane 70) interacts with chaperone–preprotein complexes through two domains: one that binds Hsp70 (heat-shock protein 70)/Hsc70 (heat-shock cognate 70) and Hsp90, and a second that binds preproteins. The oligomeric state of Tom70 has been controversial, with evidence for both monomeric and homodimeric forms. In the present paper, we report that the functional state of human Tom70 appears to be a monomer with mechanistic implications for its function in mitochondrial protein import. Based on analytical ultracentrifugation, cross-linking, size-exclusion chromatography and multi-angle light scattering, we found that the soluble cytosolic fragment of human Tom70 exists in equilibrium between monomer and dimer. A point mutation introduced at the predicted dimer interface increased the percentage of monomeric Tom70. Although chaperone docking to the mutant was the same as to the wild-type, the mutant was significantly more active in preprotein targeting. Cross-linking also demonstrated that the mutant formed stronger contacts with preprotein. However, cross-linking of full-length wild-type Tom70 on the mitochondrial membrane showed little evidence of homodimers. These results indicate that the Tom70 monomers are the functional form of the receptor, whereas the homodimers appear to be a minor population, and may represent an inactive state.
Functions for pro-opiomelanocortin-derived peptides in obesity and diabetes
Authors: Mountjoy Kathleen G.
Published: May 2010

Melanocortin peptides, derived from POMC (pro-opiomelanocortin) are produced in the ARH (arcuate nucleus of the hypothalamus) neurons and the neurons in the commissural NTS (nucleus of the solitary tract) of the brainstem, in anterior and intermediate lobes of the pituitary, skin and a wide range of peripheral tissues, including reproductive organs. A hypothetical model for functional roles of melanocortin receptors in maintaining energy balance was proposed in 1997. Since this time, there has been an extraordinary amount of knowledge gained about POMC-derived peptides in relation to energy homoeostasis. Development of a Pomc-null mouse provided definitive proof that POMC-derived peptides are critical for the regulation of energy homoeostasis. The melanocortin system consists of endogenous agonists and antagonists, five melanocortin receptor subtypes and receptor accessory proteins. The melanocortin system, as is now known, is far more complex than most of us could have imagined in 1997, and, similarly, the importance of this system for regulating energy homoeostasis in the general human population is much greater than we would have predicted. Of the known factors that can cause human obesity, or protect against it, the melanocortin system is by far the most significant. The present review is a discussion of the current understanding of the roles and mechanism of action of POMC, melanocortin receptors and AgRP (agouti-related peptide) in obesity and Type 2 diabetes and how the central and/or peripheral melanocortin systems mediate nutrient, leptin, insulin, gut hormone and cytokine regulation of energy homoeostasis.
The cutting edge: membrane-anchored serine protease activities in the pericellular microenvironment
Authors: Antalis Toni M. , Buzza Marguerite S. , Hodge Kathryn M. , Hooper John D. , Netzel-Arnett Sarah
Published: May 2010

The serine proteases of the trypsin-like (S1) family play critical roles in many key biological processes including digestion, blood coagulation, and immunity. Members of this family contain N- or C-terminal domains that serve to tether the serine protease catalytic domain directly to the plasma membrane. These membrane-anchored serine proteases are proving to be key components of the cell machinery for activation of precursor molecules in the pericellular microenvironment, playing vital functions in the maintenance of homoeostasis. Substrates activated by membrane-anchored serine proteases include peptide hormones, growth and differentiation factors, receptors, enzymes, adhesion molecules and viral coat proteins. In addition, new insights into our understanding of the physiological functions of these proteases and their involvement in human pathology have come from animal models and patient studies. The present review discusses emerging evidence for the diversity of this fascinating group of membrane serine proteases as potent modifiers of the pericellular microenvironment through proteolytic processing of diverse substrates. We also discuss the functional consequences of the activities of these proteases on mammalian physiology and disease.
Shock equation of state of a multi-phase epoxy-based composite (Al–MnO2-epoxy)
Authors: Jordan Jennifer L. , Dattelbaum Dana M. , Sutherland Gerrit , Richards D. Wayne , Sheffield Stephen A. , Dick Richard D.
Published: May 2010

There are several studies in the literature regarding the equation of state of alumina-epoxy composites. Although these single component systems interact in a complex manner with shock waves, the addition of a second metal or ceramic particulate can result in even more complex interactions. This paper presents the shock equation of state results on a multi-phase composite Al–MnO2-epoxy. Equation of state experiments were conducted using three different loading techniques—single stage light gas gun, two stage light gas gun, and explosive loading—with multiple diagnostic techniques. The Us−up relationship is shown to be linear, with deviations from linearity at low, and possibly high, pressures due to the behavior of the epoxy binder. The experimental equation of state data is compared to volume averaged and mesoscale mixture models.
Control of asymmetric strain relaxation in InGaAs grown by molecular-beam epitaxy
Authors: France R. , Ptak A. J. , Jiang C.-S. , Ahrenkiel S. P.
Published: May 2010

InGaAs strain relaxation is studied by an in situ multibeam optical stress sensor (MOSS). Strain relaxation during growth of InGaAs on GaAs occurs at different thicknesses and rates along the directions perpendicular to its misfit dislocations, [110] and [11¯0]. We show the asymmetry of relaxation between these directions in real time by aligning the MOSS laser array along [110] and [11¯0]. This asymmetric relaxation data from the MOSS correlates with both x-ray diffraction relaxation analysis and an estimation of the misfit dislocation density from transmission electron microscopy images. Lowering the V/III ratio or raising the growth temperature lowers the thickness of the onset of dislocation formation, changes the relaxation rate, lowers the final relaxation during 2 μm of growth, and shifts the initial direction of relaxation from [110] to [11¯0]. We identify two phases of relaxation that occur at different growth thicknesses. Lowering the V/III ratio changes the relative contribution of each of these phases to the total relaxation of the epilayer.
First-principles study of GaAs(001)-β2(2×4) surface oxidation and passivation with H, Cl, S, F, and GaO
Authors: Wang Weichao , Lee Geunsik , Huang Min , Wallace Robert M. , Cho Kyeongjae
Published: May 2010

The interactions of oxygen atoms on the GaAs(001)-β2(2×4) surface and the passivation of oxidized GaAs(001)-β2(2×4) surface were studied by density functional theory. The results indicate that oxygen atoms adsorbed at back-bond sites satisfy the bond saturation conditions and do not induce surface gap states. However, due to the oxygen replacement of an As dimer atom at a trough site or row site, the As–As bond is broken, and gap states are produced leading to the Fermi level pinning because of unsaturated As dangling bonds. Atomic H, Cl, S, F, and the molecular species GaO were examined to passivate the unsaturated As dangling bond. The results show that H, Cl, F, and GaO can remove such gap states. It is also found that the interaction of S with the unsaturated As dangling bond does not remove the gap states, and new gap states are generated upon single S adsorption. A higher S coverage forms S–S dimer pairs which passivate two unsaturated As atoms, and removes the As-induced gap states.
Affine extension of Galilean conformal algebra in 2+1 dimensions
Authors: Hosseiny Ali , Rouhani Shahin
Published: May 2010

We show that a class of nonrelativistic algebras including noncentrally extended Schrödinger algebra and Galilean conformal algebra (GCA) has an affine extension in 2+1 hitherto unknown. This extension arises out of the conformal symmetries of the two dimensional complex plane. We suggest that this affine form may be the symmetry that explains the relaxation of some classical phenomena toward their critical point. This affine algebra admits a central extension and maybe realized in the bulk. The bulk realization suggests that this algebra may be derived by looking at the asymptotic symmetry of an Anti-de Sitter (AdS) theory. This suggests that AdS/CFT (conformal field theory) duality may take on a special form in four dimensions.
Thermal diffusivity of oxide perovskite compounds at elevated temperature
Authors: Hofmeister Anne M.
Published: May 2010

The phonon component of thermal diffusivity (D) for eleven compounds (synthetic SrTiO3, SrTiO3:Fe3+, BaTiO3, KTaO3, KNbO3, NdGaO3, YAlO3, YAlO3:Tm, LaAlO3, La0.29Sr0.66Al0.65Ta0.35O3, and natural Ca1.01Mn0.001Fe0.007Ti0.99O3) with various perovskite structures was measured from ambient temperature (T) up to ∼2000 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. Structural transitions (e.g., orthorhombic to tetragonal) below 800 K were manifest as sharp steps in 1/D. Above 800 K, structural transitions occur over intervals of ∼150 K. Similarly broad peaks accompany changes from colorless to black, attributable to partial reduction in Ti, Nb, or Ta from contact with graphite coatings. Otherwise, D decreases with increasing T and, if substitutional disorder exists, approaches a constant (Dsat) near 1600 K. Our data are best described as D−1 following a low order polynomial in T. Ordered, cubic perovskites occupy a single trend for D(T)−1, defining the contribution of the ideal lattice. Distortion, disorder, and polymorphism affect D−1 in a manner that is consistent with the damped harmonic oscillator-phonon gas model which relates phonon lifetimes to infrared peak widths. Calculated D-values at ambient and high T agree with measurements. The behavior of D is simple compared to that of thermal conductivity, k=ρCPD, where ρ is density and CP is heat capacity. Combining our data with cryogenic measurements of YAlO3 and LaAlO3 shows that D−1 depends on T similarly to CP, consistent with phonon lifetime depending on the density of states but, the best description for D−1(T) is a proportionality to αT from ∼0 K up to the limit of measurements, where α is thermal expansivity, a strongly anharmonic property. At low T, D−1 due to phonon scattering follows that of CP, generally∝T3, so klat=k0+k1T. Defects being present preclude scattering at sample walls, adding a small constant D0−1 ∼0.0001 mm−2 s as T→0, and an additional contribution of kdfctT3. Forms previously inferred for thermal insulators include systematic errors stemming from ballistic radiative transfer and/or interface resistance. Our results show that optical phonons largely govern heat transport of complex insulators.
Spatial localization of quantized states responsible for sharp optical transition in AlGaN/GaN superlattice
Authors: Cai Duanjun , Guo Guang-Yu
Published: May 2010

We present atomic level studies of the quantized electronic states in AlGaN/GaN superlattice by employing first-principles calculations. Based on the complete band profile, distribution of the discrete energy levels inside the GaN quantum well is obtained and the well-in-well confinement is observed. This second-level well introduces the spatial localization of quantized states. The calculated envelopes of the quantized state densities reveal the spatial overlap between certain electron and hole states. This, together with theoretical absorption spectra, enables us to assign the origin of band-edge peak to the e0-h2 intersubband transition, which governs the optical band gap in the superlattice structure.
Stress in (110)-textured phosphorus-doped polycrystalline diamond studied by Raman and cathodoluminescence spectroscopies
Authors: Habka N. , Barjon J. , Lazea A. , Haenen K.
Published: May 2010

In this work, we investigate the stress developed in phosphorus-doped layers grown on (110)-textured polycrystalline diamond templates. To that end, we follow the shifts of the diamond Raman diffusion and the exciton recombination energies by Raman and cathodoluminescence spectroscopies, respectively. With each approach, a high tensile strain of several gigapascal is evidenced. Moreover, Raman mapping performed in cross section shows (i) at the grain boundaries, a strain in tension that propagates along the growth direction from the template to the deposited layer and (ii) at the center of each grain, a tensile strain of the phosphorus-doped layer with respect to the underlying undoped grain. Concerning the second, we observe also an increase in strain effects at high phosphorus incorporation, together with a structural degradation. The possible origins of such high lattice deformation of phosphorus-doped layers are discussed.
Thermal conductance and phonon transmissivity of metal–graphite interfaces
Authors: Schmidt Aaron J. , Collins Kimberlee C. , Minnich Austin J. , Chen Gang
Published: May 2010

The thermal boundary conductances between c-axis oriented highly ordered pyrolytic graphite and several metals have been measured in the temperature range 87–300 K and are found to be similar to those of metal–diamond interfaces. The values obtained are indicative of the thermal interface conductance between metals and the sidewalls of multiwall carbon nanotubes (CNTs) and, therefore, have relevance for the accurate characterization of the thermal properties of CNTs, graphene, and the design and performance of composite materials and electronic devices based on these structures. A modified diffuse mismatch model is used to interpret the data and extract the phonon transmissivity at the interface. The results indicate that metal–graphite adhesion forces and interfacial mixing effects play important roles in determining the boundary conductance.
Improved micro x-ray fluorescence spectrometer for light element analysis
Authors: Smolek Stephan , Streli Christina , Zoeger Norbert , Wobrauschek Peter
Published: May 2010

Since most available micro x-ray fluorescence (micro-XRF) spectrometers operate in air, which does not allow the analysis of low-Z elements (Z≤14), a special micro-XRF spectrometer has been designed to extend the analytical range down to light elements (Z≥6). It offers improved excitation and detection conditions necessary for light element analysis. To eliminate absorption of the exciting and fluorescent radiation, the system operates under vacuum condition. Sample mapping is automated and controlled by specialized computer software developed for this spectrometer. Several different samples were measured to test and characterize the spectrometer. The spot size has been determined by scans across a 10 μm Cu wire which resulted in a full width at half maximum of 31 μm for Mo Kα line (17.44 keV) and 44 μm effective beam size for the Cu K edge and 71 μm effective beam size for the Cu L edge. Lower limits of detection in the picogram range for each spot (or μg/cm2) were obtained by measuring various thin metal foils under different conditions. Furthermore, detection limits in the parts per million range were found measuring NIST621 standard reference material. Area scans of a microscopic laser print and NaF droplet were performed to show mapping capabilities.
From boundary to thin film lubrication under water: Influence of surface hydrophilicity on adsorbed water layer
Authors: Liu Shuhai , Xie Guoxin , Guo Dan , Liu Yonghe
Published: May 2010

The influence of surface hydrophilicity on adsorbed water layer was investigated using a thin film interferometry and a microtribometer based on laser interferometers. Experimental results indicate that, in the mixed film lubrication from the boundary lubrication to the thin film lubrication, the hydrophilic surface promotes the forming of thinner water film and the higher friction. It is thought that a layer of water adjacent to the surface forms an ordered water layer whose characteristic determines the properties of adsorbed water layer in the contact area.
Nanofluid-based direct absorption solar collector
Authors: Otanicar Todd P. , Phelan Patrick E. , Prasher Ravi S. , Rosengarten Gary , Taylor Robert A.
Published: May 2010

Solar energy is one of the best sources of renewable energy with minimal environmental impact. Direct absorption solar collectors have been proposed for a variety of applications such as water heating; however the efficiency of these collectors is limited by the absorption properties of the working fluid, which is very poor for typical fluids used in solar collectors. It has been shown that mixing nanoparticles in a liquid (nanofluid) has a dramatic effect on the liquid thermophysical properties such as thermal conductivity. Nanoparticles also offer the potential of improving the radiative properties of liquids, leading to an increase in the efficiency of direct absorption solar collectors. Here we report on the experimental results on solar collectors based on nanofluids made from a variety of nanoparticles (carbon nanotubes, graphite, and silver). We demonstrate efficiency improvements of up to 5% in solar thermal collectors by utilizing nanofluids as the absorption mechanism. In addition the experimental data were compared with a numerical model of a solar collector with direct absorption nanofluids. The experimental and numerical results demonstrate an initial rapid increase in efficiency with volume fraction, followed by a leveling off in efficiency as volume fraction continues to increase.
Electric field control of a quantum dot molecule through optical excitation
Authors: Garrido Mauricio , Wijesundara Kushal C. , Ramanathan Swati , Stinaff E. A. , Bracker A. S. , Gammon D.
Published: May 2010

Nonresonant optical excitation of a coupled quantum dot system was seen to generate a shift in the electric-field-dependent photoluminescence spectra. By monitoring the interdot recombination associated with an electron and hole in different dots we were able to precisely monitor the internal electric field generated. Power, wavelength, and applied field dependence of the charging was studied. Such an optically generated electric field may provide a means for applying local oscillating voltages, allowing for optical tuning of the device parameters.
Anomalous memory effects on transport of inertial particles in turbulent jets
Authors: Picano F. , Sardina G. , Gualtieri P. , Casciola C. M.
Published: May 2010

The letter focuses on a new phenomenology found in the far field of turbulent-free jets, where small inertial particles exhibit a local concentration peak on the axis. This finding contrasts with the prediction of classical models based on turbulent kinetic energy gradient transport assumptions, whereby particles should move away from the local kinetic energy maxima. This behavior is universal, i.e., it occurs no matter the details of the specific jet, and takes place irrespective of the inertia of the particles. As anomalous signature of the near field dynamics, it cannot be predicted on purely dimensional grounds. A new form of similarity allows to collapse the local particle flux profile on a universal curve.
Photochemical control of the carrier mobility in pentacene-based organic thin-film transistors
Authors: Marchl Marco , Golubkov Andrej W. , Edler Matthias , Griesser Thomas , Pacher Peter , Haase Anja , Stadlober Barbara , Belegratis Maria R. , Trimmel Gregor , Zojer Egbert
Published: May 2010

We use a photoreactive interfacial layer of poly(endo,exo-bis(2-nitrobenzyl) bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) (PBHND) between the gate dielectric and the pentacene active layer to tune the effective hole mobility in organic thin film transistors over approximately one order of magnitude. This can be explained by the photoconversion of the PBHND layer changing its surface energy and thus strongly impacting pentacene growth. A linear relationship between the mobility and the grain size is observed.
Photocurrent increase in n-i-p thin film silicon solar cells by guided mode excitation via grating coupler
Authors: Söderström Karin , Haug Franz-Josef , Escarré Jordi , Cubero Oscar , Ballif Christophe
Published: May 2010

Angle resolved measurements of the external quantum efficiency of n-i-p single junction amorphous solar cell deposited on a grating structure show clearly defined peaks of enhanced photocurrent in the weakly absorbing region between 1.6 and 2.15 eV. We explain these absorption phenomena and their angular variation with the excitation of guided modes via grating coupling. Calculation using an equivalent flat multilayer system permits to relate the theoretical values with the experimental data.
Monte Carlo simulation of photon scattering in x-ray absorption imaging of high-intensity discharge lamps
Authors: Curry J J
Published: May 2010

Coherent and incoherent scattering of x-rays during x-ray absorption imaging of high-intensity discharge lamps have been studied with Monte Carlo simulations developed specifically for this purpose. The Monte Carlo code is described and some initial results are discussed. Coherent scattering, because of its angular concentration in the forward direction, is found to be the most significant scattering mechanism. Incoherent scattering, although comparably strong, is not as significant because it results primarily in photons being scattered in the rearward direction and therefore out of the detector. Coherent scattering interferes with the detected absorption signal because the path of a scattered photon through the object to be imaged is unknown. Although scattering is usually a small effect, it can be significant in regions of high contrast. At the discharge/wall interface, as many as 50% of the detected photons are scattered photons. The effect of scattering on analysis of Hg distributions has not yet been quantified.
Non-destructive measurement of Xe filling pressure in mercury-free metal halide lamp
Authors: Motomura Hideki , Enoki Kyosuke , Jinno Masafumi
Published: May 2010

Mercury-free metal halide lamps (MHLs) for automotive purposes have been developing in the market. When mercury is not used, the electric and emission characteristics of the lamp strongly depend on the xenon filling pressure. Therefore a non-destructive gas pressure estimation technique is required to obtain stable performance of the lamps as commercial products. The authors have developed an estimation method by which the gas pressure is estimated from the current peak value at the initial stage of ignition under pulsed operation. It is shown that accuracy of the order of ±(0.1–0.3) atm is obtained using an empirical formula.
Modification of light sources for appropriate biological action
Authors: Kozakov R , Schöpp H , Franke St , Stoll C , Kunz D
Published: May 2010

The impact of the non-visual action of light on the design of novel light sources is discussed. Therefore possible modifications of lamps dealing with spectral tailoring and their action on melatonin suppression in usual life situations are investigated. The results of melatonin suppression by plasma lamps are presented. It is shown that even short-time exposure to usual light levels in working areas has an influence on the melatonin onset.
The Interferon-γ–induced Murine Guanylate-Binding Protein-2 Inhibits Rac Activation during Cell Spreading on Fibronectin and after Platelet-derived Growth Factor Treatment: Role for Phosphatidylinositol 3-Kinase
Authors: Messmer-Blust Angela F. , Balasubramanian Sujata , Gorbacheva Victoria Y. , Jeyaratnam Jonathan A. , Vestal Deborah J.
Published: May 2010

Exposure of cells to certain cytokines can alter how these same cells respond to later cues from other agents, such as extracellular matrix or growth factors. Interferon (IFN)-γ pre-exposure inhibits the spreading of fibroblasts on fibronectin. Expression of the IFN-γ–induced GTPase murine guanylate-binding protein-2 (mGBP-2) can phenocopy this inhibition and small interfering RNA knockdown of mGBP-2 prevents IFN-γ–mediated inhibition of cell spreading. Either IFN-γ treatment or mGBP-2 expression inhibits Rac activation during cell spreading. Rac is required for cell spreading. mGBP-2 also inhibits the activation of Akt during cell spreading on fibronectin. mGBP-2 is incorporated into a protein complex containing the catalytic subunit of phosphatidylinositol 3-kinase (PI3-K), p110. The association of mGBP-2 with p110 seems important for the inhibition of cell spreading because S52N mGBP-2, which does not incorporate into the protein complex with p110, is unable to inhibit cell spreading. PI3-K activation during cell spreading on fibronectin was inhibited in the presence of mGBP-2. Both IFN-γ and mGBP-2 also inhibit cell spreading initiated by platelet-derived growth factor treatment, which is also accompanied by inhibition of Rac activation by mGBP-2. This is the first report of a novel mechanism by which IFN-γ can alter how cells respond to subsequent extracellular signals, by the induction of mGBP-2.