bluuebunny/crossref_metadata_2025 huggingface dataset:
Mean structure and seasonal variability of the poleward undercurrent off southern California
Authors: Gay Peter S. , Chereskin Teresa K.
Published: February 2009

The magnitude, location, and extent of the California Undercurrent (CUC) off southern California is investigated using cruises of the California Cooperative Oceanic Fisheries Investigations (CalCOFI) from 1993 to 2003 which provide hydrographic, biochemical, and acoustic Doppler current profiler (ADCP) velocity data on a quarterly basis. This study is the first use of the decade‐long ADCP time series; it improves on prior geostrophic calculations by providing an absolute velocity reference for estimates of currents and transport. The long‐term mean reveals two undercurrent cores in the region south of Point Conception and north of Baja, California: one in the region of the continental slope within the Southern California Bight (SCB) and a second off the Santa Rosa Ridge (SRR). A single core is observed off Point Conception. Spiciness is found to be a good indicator of the presence of the CUC; however, direct velocity observations or a deep reference level are required to resolve the full strength of the CUC cores. In particular, the core off the SRR would be almost entirely missed by geostrophic calculations relative to 500 m, the maximum depth sampled by CalCOFI. The undercurrent transport off Point Conception is estimated to be about 1.7 ± 0.1 Sv, slightly less than the sum of that estimated for the SCB (1.0 ± 0.1 Sv) and that estimated off the SRR (1.1 ± 0.1 Sv) and consistent with some of the flow turning offshore at Point Conception. The CUC in the SCB is strongest in summer, while that off the SRR is strongest in fall. The CUC off Point Conception is strong in both summer and fall, reflecting the confluence of these two branches. Interannual variability is also present, and the velocity and spiciness of the CUC appear to peak during El Niño periods.
Trends in primary production in the California Current detected with satellite data
Authors: Kahru Mati , Kudela Raphael , Manzano‐Sarabia Marlenne , Mitchell B. Greg
Published: February 2009

Several ocean primary production algorithms using satellite data were evaluated on a large archive of net primary production (NPP) and chlorophyll‐a (Chl‐a) measurements collected by the California Cooperative Fisheries Investigations program in the California Current. The best algorithm matching in situ data was found by empirically adjusting the Behrenfeld‐Falkowski Vertically Generalized Production Model. Satellite‐derived time series of NPP were calculated for the California Current area. Significant increase in NPP and Chl‐a annual peak levels, i.e., the “bloom magnitude,” were found along the coasts of the California Current as well as other major eastern boundary currents for the period of modern ocean color data (1997–2007). The reasons for this increase are not clear but are associated with various environmental conditions.
Interpretation of the propagation of surface altimetric observations in terms of planetary waves and geostrophic turbulence
Authors: Tulloch Ross , Marshall John , Smith K. Shafer
Published: February 2009

The interpretation of surface altimetric signals in terms of Rossby waves is revisited. Rather than make the long‐wave approximation, the horizontal scale of the waves is adjusted to optimally fit the phase speed predicted by linear theory to that observed by altimetry, assuming a first baroclinic mode vertical structure. It is found that in the tropical band the observations can be fit if the wavelength of the waves is assumed to be large, of order 600 km or so. However poleward of ±30°, it is more difficult to fit linear theory to the observations, and the fit is less good than at lower latitudes: the required scale of the waves must be reduced to about 100 km, somewhat larger than the local deformation wavelength. It is argued that these results can be interpreted in terms of Rossby wave, baroclinic instability, and turbulence theory. At low latitudes there is an overlap between geostrophic turbulence and Rossby wave timescales, and so, an upscale energy transfer from baroclinic instability at the deformation scale produces waves. At high latitudes there is no such overlap and waves are not produced by upscale energy transfer. These ideas are tested by using surface drifter data to infer turbulent velocities and timescales that are compared to those of linear Rossby waves. A transition from a field dominated by waves to one dominated by turbulence occurs at about ±30°, broadly consistent with the transition that is required to fit linear theory to altimetric observations.
Analyses of FORMOSAT‐3/COSMIC humidity retrievals and comparisons with AIRS retrievals and NCEP/NCAR reanalyses
Authors: Chou Ming‐Dah , Weng Chun‐Hsiung , Lin Po‐Hsiung
Published: February 2009

The specific humidity retrieved from the FORMOSAT‐3/Constellation Observation System for the Meteorology, Ionosphere, and Climate (COSMIC) (FC) occultation observations of the GPS radiowaves were analyzed and compared with radiosonde observations, aircraft dropsonde observations, Atmospheric Infrared Sounder (AIRS) retrievals, and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses. For the limited number of radio soundings at the sites of small islands near Taiwan coincident in space and time with FC observations, the difference of humidity in individual cases is <40% below ∼7 km without obvious bias. Above this level, the humidity of radiosonde observations is systematically lower than that of FC observations, which is consistent with previous studies showing the dry bias of certain radiosonde observations. The humidity of FC observations differs significantly throughout the troposphere with dropsonde observations surrounding a strong typhoon. The difference reaches 100% in the middle and upper troposphere. The cause of the large discrepancy is likely to be the large horizontal variation of humidity in regions of an active weather system as shown in closely spaced dropsonde observations, where FC observations represent humidity averaged over humid and dry regions in the long path of GPS radiowaves, whereas dropsonde observations are a point measurement. Global distributions of specific humidity were compared between FC retrievals and the AIRS retrievals and NCEP/NCAR reanalyses. There is a good agreement between AIRS and FC humidity retrievals. The discrepancy is generally within 15%. The discrepancy between the NCEP/NCAR and FC humidity is significant, especially in the upper troposphere. For the layer 300–400 hPa, the NCEP/NCAR humidity is higher than the FC humidity by >30% over most of oceanic regions.
Radar‐observed squall line propagation and the diurnal cycle of convection in Niamey, Niger, during the 2006 African Monsoon and Multidisciplinary Analyses Intensive Observing Period
Authors: Rickenbach Thomas , Nieto Ferreira Rosana , Guy Nick , Williams Earle
Published: February 2009

Surface radar observations near Niamey, Niger, during the African Monsoon Multidisciplinary Analyses (AMMA) campaign in 2006 documented the structure, motion, and precipitation of cloud systems during the monsoon season. These unique observations for that part of the Sahel were combined with satellite rain estimates and infrared satellite imagery to study the diurnal cycle of rainfall in Niamey, Niger. This study confirms the bimodal structure of the diurnal rainfall cycle in Niamey during AMMA, seen by previous studies of West African rainfall. Radar analysis of squall line mesoscale convective systems (SLMCS) and non‐MCS isolated convection clearly demonstrated that the nocturnal maximum was associated with the observed arrival time of westward propagating SLMCS. Satellite imagery suggested that these SLMCS formed in elevated terrain to the east of Niamey the prior afternoon. Radar observations showed that local isolated convection produced the smaller afternoon maximum. Early in the monsoon season, locally generated convection produced an afternoon diurnal rainfall maximum that was delayed by several hours compared to midseason when African easterly wave (AEW) activity was much greater. We suggest that the observed greater mean convective inhibition early in the season, perhaps tied to the absence of large‐scale forcing from AEW, played a role in the delayed initiation time.
Modeling the coupled effects of pore space geometry and velocity on colloid transport and retention
Authors: Bradford Scott A. , Torkzaban Saeed , Leij Feike , Šimůnek Jiri , van Genuchten Martinus T.
Published: February 2009

Recent experimental and theoretical work has demonstrated that pore space geometry and hydrodynamics can play an important role in colloid retention under unfavorable attachment conditions. Conceptual models that only consider the average pore water velocity and a single attachment rate coefficient are therefore not always adequate to describe colloid retention processes, which frequently produce nonexponential profiles of retained colloids with distance. In this work, we highlight a dual‐permeability model formulation that can be used to account for enhanced colloid retention in low‐velocity regions of the pore space. The model accounts for different rates of advective and dispersive transport, as well as first‐order colloid retention and release in fast and slow velocity regions of the pore space. The model also includes provisions for the exchange of colloids from fast to slow regions in the aqueous phase and/or on the solid phase. A sensitivity analysis performed with the dual‐permeability model parameters indicated that low rates of advective transport to low‐velocity regions had a pronounced influence on colloid retention profiles, especially near the inlet. The developed model provided a good description of measured colloid breakthrough curves and retention profiles that were collected for a variety of conditions.
A note on the drawdown, diffusive behavior of fractured rocks
Authors: Raghavan Rajagopal
Published: February 2009

Transients in fractured media are described using a model in which permeability depends on space and time. The motivation for the differential equation used here draws on recent results for diffusion on fractals in the asymptotic regime. The solution proposed is consistent with the scaling arguments for diffusion on fractal structures. Known results for transients in fractured rocks may be extracted from the solution given here.
Characteristics of evaporation from partially wettable porous media
Authors: Shokri N. , Lehmann P. , Or D.
Published: February 2009

The evaporation rate from porous media often exhibits an abrupt transition from a high and nearly constant rate supplied by capillary‐induced liquid flow (stage 1) to lower values supported by vapor diffusion. Evidence suggests that evaporation from hydrophobic porous media is suppressed relative to evaporation from similar hydrophilic media. The mechanism for evaporation suppression remains unclear; some implicate effects of partial wettability on liquid phase continuity. Here we examine potential effects of wettability on capillary driving forces required for sustaining liquid flows. Evaporation experiments from sand‐filled columns with different fractions of hydrophobic grains enabled comparisons of evaporative mass loss rates and drying front depths. Results show a gradual reduction in drying front depth at the end of stage 1 (denoted as “evaporation characteristic length”) with an increasing fraction of hydrophobic grains. A model based on the simple averaging of partial wettability effects on capillary driving forces was in good agreement with the experimentally determined drying front depth. Experimental and modeling results suggest that liquid phase continuity was less important in suppressing the duration of stage 1 and reducing the evaporation characteristic length relative to capillarity effects, as is also confirmed in a 3‐D percolation‐based morphological pore network model. Nevertheless, partial wettability significantly modifies phase distribution above the drying front, as shown by spatially resolved observations using neutron radiography and by a pore‐scale percolation model. New insights concerning the effects of partial wettability on evaporation may provide engineering solutions for reducing evaporative losses from porous surfaces.
Regulation of Visceral and Subcutaneous Adipocyte Lipolysis by Acute AICAR‐induced AMPK Activation
Authors: Anthony Nicole M. , Gaidhu Mandeep P. , Ceddia Rolando B.
Published: February 2009

This study investigated the role of adenosine monophosphate–activated protein kinase (AMPK) in the regulation of lipolysis in visceral (VC) and subcutaneous (SC) rat adipocytes and the molecular mechanisms involved in this process. VC (epididymal and retroperitoneal) and SC (inguinal) adipocytes were isolated from male Wistar rats (160–180 g). Adipocytes were incubated either in the absence or in the presence of the AMPK agonist 5‐aminoimidazole‐4‐carboxamide‐1‐β‐d‐ribofuranoside (AICAR, 0–500 µmol/l). AMPK and acetyl‐CoA carboxylase (ACC) phosphorylation, basal and epinephrine‐stimulated (100 nmol/l) glycerol release, and hormone‐sensitive lipase (HSL) phosphorylation and activity were determined. AICAR‐induced (500 µmol/l) AMPK activation inhibited basal glycerol release by ∼42, 41, and 44% in epididymal, retroperitoneal, and inguinal adipocytes, respectively. Epinephrine‐stimulated glycerol release was almost completely prevented by AICAR treatment in adipocytes from all fat depots. The AMPK inhibitor compound C (20 µmol/l) prevented AICAR‐induced phosphorylation of AMPK and significantly increased basal (∼1.3‐, 1.4‐, and 1.7‐fold) and epinephrine‐stimulated (∼1.3‐, 1.2‐, 1.4‐fold) glycerol release in epididymal, retroperitoneal, and inguinal adipocytes, respectively. AICAR increased phosphorylation of HSLSer565 and inhibited epinephrine‐induced phosphorylation of HSLSer563 and HSLSer660. This was also accompanied by a 73% reduction in epinephrine‐stimulated HSL activity. Compound C prevented the phosphorylation of HSLSer565 induced by AICAR and partially prevented the inhibitory effect of this drug on basal and epinephrine‐stimulated lipolysis in adipocytes in VC and SC fat depots. In summary, despite different fat depots eliciting distinct rates of lipolysis, acute AICAR‐induced AMPK activation suppressed HSL phosphorylation/activation and exerted similar antilipolytic effects on both VC and SC adipocytes.
Leptin, Insulin, and Obesity‐related Phenotypes: Genetic Influences on Levels and Longitudinal Changes
Authors: Friedlander Yechiel , Meiner Vardiella , Sharon Nir , Siscovick David S. , Miserez Andre R.
Published: February 2009

This study estimated the genetic and environmental determinants of plasma leptin and insulin levels and of obesity‐related phenotypes. Included in this analysis were family members from 80 families living in kibbutz settlements, who participated in two examinations 8–10 years apart. We estimated that polygenes explained 30–50% of the adjusted leptin and insulin levels and 30–70% of the anthropometric phenotypes. This study demonstrated a significant genetic influence on longitudinal changes in leptin and BMI (h2 = 0.45) and small‐to‐moderate heritability estimates for changes in insulin and other obesity‐related phenotypes. In bivariate genetic analyses, we observed positive genetic correlations between leptin and anthropometric phenotypes, suggesting that shared effects of the same sets of loci account for 20–30% of the additive genetic variance in these pairs of variables. Shared genetic factors also account for 20–25% of the additive genetic variance in insulin—anthropometric pairs of variables.
Lipid phosphate phosphohydrolase type 1 (LPP1) degrades extracellular lysophosphatidic acid in vivo
Authors: Tomsig Jose L. , Snyder Ashley H. , Berdyshev Evgeny V. , Skobeleva Anastasia , Mataya Chifundo , Natarajan Viswanathan , Brindley David N. , Lynch Kevin R.
Published: February 2009

LPA (lysophosphatidic acid) is a lipid mediator that stimulates cell proliferation and growth, and is involved in physiological and pathological processes such as wound healing, platelet activation, angiogenesis and the growth of tumours. Therefore defining the mechanisms of LPA production and degradation are of interest in understanding the regulation of these processes. Extracellular LPA synthesis is relatively well understood, whereas the mechanisms of its degradation are not. One route of LPA degradation is dephosphorylation. A candidate enzyme is the integral membrane exophosphatase LPP1 (lipid phosphate phosphohydrolase type 1). In the present paper, we report the development of a mouse wherein the LPP1 gene (Ppap2a) was disrupted. The homozygous mice, which are phenotypically unremarkable, generally lack Ppap2a mRNA, and multiple tissues exhibit a substantial (35–95%) reduction in LPA phosphatase activity. Compared with wild-type littermates, Ppap2atr/tr animals have increased levels of plasma LPA, and LPA injected intravenously is metabolized at a 4-fold lower rate. Our results demonstrate that LPA is rapidly metabolized in the bloodstream and that LPP1 is an important determinant of this turnover. These results indicate that LPP1 is a catabolic enzyme for LPA in vivo.
Role of the renin–angiotensin–aldosterone system and inflammatory processes in the development and progression of diastolic dysfunction
Authors: Sciarretta Sebastiano , Paneni Francesco , Palano Francesca , Chin Diana , Tocci Giuliano , Rubattu Speranza , Volpe Massimo
Published: February 2009

Left ventricular diastolic dysfunction represents a frequent clinical condition and is associated with increased cardiovascular morbidity and mortality. Diastolic dysfunction is the most common cause of HF-PSF (heart failure with preserved ejection fraction). Therefore it becomes important to understand the pathophysiological mechanisms underlying diastolic dysfunction, as well as the effective therapeutic strategies able to antagonize its development and progression. Among the complex pathophysiological factors that may contribute to the development of diastolic dysfunction, the RAAS (renin–angiotensin–aldosterone system) has been shown to play a significant role. Paracrine and autocrine signals of the RAAS promote structural and functional changes in the heart largely linked to increased myocardial fibrosis. Enhanced and dysregulated activity of the RAAS also contributes to the development of volume overload and vasoconstriction with subsequent increases in left ventricular diastolic filling pressures and a higher susceptibility of developing CHF (congestive heart failure). More recently, it has also been suggested that the RAAS may play a role in triggering myocardial and vascular inflammation through the activation of different cell types and the secretion of cytokines and chemokines. RAAS-induced myocardial inflammation leads to perivascular myocardial fibrosis and to the development or progression of diastolic dysfunction. For these reasons pharmacological blockade of the RAAS has been proposed as a rational approach for the treatment of diastolic dysfunction. In fact, ACEIs (angiotensin-converting enzyme inhibitors), ARBs (angiotensin II receptor blockers) and AAs (aldosterone antagonists) have been demonstrated to delay the development and progression from pre-clinical diastolic dysfunction towards CHF, as well as to reduce the morbidity and mortality associated with this condition.
The Infusion of Interactive Digital Media With Self-Help and Stuttering Treatment
Authors: Reitzes Peter , Snyder Greg
Published: February 2009

Limitations in the science of stuttering and stuttering therapy result in a failure to eradicate the stuttering phenomenon in clients with persistent developmental stuttering. Subsequently, many clients who stutter continue to live with the negative social consequences of stuttered speech, which include the potential for social marginalization and a reduction in quality of life. Consequently, current stuttering treatments, as well as a grass-roots self-help movement, have evolved to address these challenges faced by the stuttering population. This paper discusses the application of self-help styled interactive content over a digital media, in the form of audio and video podcasting, in stuttering support and treatment.
Current-induced domain-wall depinning in curved Permalloy nanowires
Authors: Nahrwold Gesche , Bocklage Lars , Scholtyssek Jan M. , Matsuyama Toru , Krüger Benjamin , Merkt Ulrich , Meier Guido
Published: February 2009

Domain walls in curved Permalloy (Ni80Fe20) nanowires are depinned by nanosecond current pulses and magnetic fields. A significant dependence of the depinning probability on the pulse length is observed. We measure an oscillatory dependence with a characteristic frequency of 270 MHz. The quality of the Permalloy used for the nanowires is crucial for efficient domain-wall depinning. By sputtering Permalloy on heated substrates we are able to considerably decrease the specific resistance that is found to directly correspond to the depinning field of the domain wall.
Magnetic properties and structure of bulk nanocrystalline Sm(CoCuFeZr)7.6 sintered magnet
Authors: Zhang Dongtao , Yue Ming , Yang Jianjun , Xu Gang , Liu Weiqiang , Zhang Jiuxing , Liu Xubo
Published: February 2009

Structure and magnetic properties were studied for Sm(Co0.74Cu0.12Fe0.1Zr0.04)7.6 nanocrystalline ball milled powders and bulk magnet consolidated via spark plasma sintering technique. The amorphous milling powders crystallize to TbCu7 structure or a mixture of Th2Zn17 and CaCu5 structures when annealed below or above 1023 K, respectively. The coercivity of the powders decreases from 1.27 to 0.56 T as the annealed temperature increases from 923 to 1223 K. The bulk magnet also exhibits a TbCu7 structure with an average grain size of 32 nm. Magnetic measurements show that the remanence is 0.49 T and the coercivity reaches as high as 1.42 T. The Mr/Ms ratio of 0.63 demonstrates the existence of intergrain exchange coupling among the nanograins. The magnet exhibits the coercivity of 0.27 T at 773 K.
Micromagnetic simulation by using the fast multipole method specialized for uniform brick elements
Authors: Takahashi Y. , Wakao S. , Iwashita T. , Kanazawa M.
Published: February 2009

This paper describes a large-scale micromagnetic simulation by using the fast multipole method (FMM) specialized for uniform brick elements. The fast Fourier transform (FFT) is widely used to reduce computational costs of the demagnetizing field calculation. However, the FFT still requires operation counts of O(N log N), where N is the number of elements, which results in the huge computational costs in large-scale problems. To overcome the difficulties, we develop an O(N) approach based on the FMM. In a micromagnetic simulation, an analyzed region is usually subdivided into uniform elements. By making the best use of the periodic structure of uniformly distributed elements, the computational costs of the FMM can be reduced drastically. A large-scale micromagnetic simulation of a single-pole-type head demonstrates the effectiveness of the specialized FMM from the viewpoints of calculation time and memory requirements, compared with the FFT.
Annealing of CoFeB/MgO based single and double barrier magnetic tunnel junctions: Tunnel magnetoresistance, bias dependence, and output voltage
Authors: Feng G. , van Dijken Sebastiaan , Feng J. F. , Coey J. M. D. , Leo T. , Smith David J.
Published: February 2009

Co 40 Fe 40 B 20 / MgO single and double barrier magnetic tunnel junctions (MTJs) were grown using target-facing-target sputtering for MgO barriers and conventional dc magnetron sputtering for Co40Fe40B20 ferromagnetic electrodes. Large tunnel magnetoresistance (TMR) ratios, 230% for single barrier MTJs and 120% for the double barrier MTJs, were obtained after postdeposition annealing in a field of 800 mT. The lower TMR ratio for double barrier MTJs can be attributed to the amorphous nature of the middle Co40Fe40B20 free layer, which could not be crystallized during postannealing. A highly asymmetric bias voltage dependence of the TMR can be observed for both single and double barrier MTJs in the as-deposited states and after field annealing at low temperature. The asymmetry decreases with increasing annealing temperature and the bias dependence becomes almost symmetric after annealing at 350 °C. Maximum output voltages of 0.65 and 0.85 V were obtained for both single and double barrier MTJs, respectively, after annealing at 300 °C, a temperature which is high enough for large TMR ratios but insufficient to completely remove asymmetry from the TMR bias dependence.
Microwave absorption measurements using a broad-band meanderline approach
Authors: Tsai C. C. , Choi J. , Cho Sunglae , Lee S. J. , Sarma B. K. , Thompson C. , Chernyashevskyy O. , Nevirkovets I. , Ketterson J. B.
Published: February 2009

We describe a technique that permits broad-band, field-dependent ferromagnetic and electron paramagnetic resonance absorption measurements that is applicable to thin films and patterned micro-/nanostructured arrays and is based on a wire-wound meanderline approach. Techniques to prepare meanderlines and perform microwave measurements are described along with some demonstrations involving an electron paramagnetic resonance calibration/test material, 2,2-diphenyl-1-picryl-hydrazyl, and a ferromagnetic cobalt thin film.
Magnetic properties of thin hard/soft-stacked dot arrays with a large uniaxial magnetic anisotropy
Authors: Mitsuzuka K. , Shimatsu T. , Kikuchi N. , Kitakami O. , Muraoka H. , Aoi H.
Published: February 2009

Magnetic properties of hard/soft stacked dot arrays consisting of thin Co/Pt superlattice hard layers (3.6 nm in thickness, uniaxial magnetic anisotropy, Ku=1.3×107 erg/cm3) and Co soft layers, with dot diameters of 30–40 nm, were investigated as functions of Co soft layer thickness and the interfacial exchange coupling between the hard and soft layers. Pt was used as the control layer of the interfacial exchange coupling, and Co soft layers were sandwiched with Pt layers to induce surface anisotropy on the Co soft layers. The remanence coercivity, Hr, was 2.7 kOe for Co/Pt(3.6 nm)/Co(4 nm) stacked dot arrays and 3.2 kOe for Co/Pt(3.6 nm)/Pt(1.2 nm)/Co(3 nm) stacked dot arrays, and these values were less than half that of single hard layer dot arrays (7.1 kOe). Hr was nearly constant in the ϕ range from 0° to about 45° (ϕ is the applied field angle from the easy axis), and increased significantly as ϕ increased further, as theoretically predicted. Hard/soft dot arrays maintained a relatively large Ku due to the surface anisotropy of the Co soft layers. It was suggested that the ratio of magnetic energy to the thermal energy, KueffV/kT, for Co/Pt(3.6 nm)/Pt(1.2 nm)/Co(3 nm) hard/soft dot arrays was 1.5 times larger than that for Co/Pt(3.6 nm) single dot arrays because of the relatively large Ku.
Nanometer range correlations between molecular orientations in liquids of molecules with perfect tetrahedral shape: CCl4, SiCl4, GeCl4, and SnCl4
Authors: Pothoczki Sz. , Temleitner L. , Jóvári P. , Kohara S. , Pusztai L.
Published: February 2009

Neutron and x-ray weighted total scattering structure factors of liquid carbon, silicon, germanium, and tin tetrachlorides, CCl4, SiCl4, GeCl4, and SnCl4, have been interpreted by means of reverse Monte Carlo modeling. For each material the two sets of diffraction data were modeled simultaneously, thus providing sets of particle coordinates that were consistent with two experimental structure factors within errors. From these particle configurations, partial radial distribution functions, as well as correlation functions characterizing mutual orientations of molecules as a function of distance between molecular centers were calculated. Via comparison with reference systems, obtained by hard sphere Monte Carlo simulations, we demonstrate that orientational correlations characterizing these liquids are much longer ranged than expected, particularly in carbon tetrachloride.
Atomic scale observation and characterization of redox-induced interfacial layers in commercial Si thin film photovoltaics
Authors: Ramasse Quentin , Anapolsky Abraham , Lazik Christopher , Jin Miao , Armstrong Karl , Wang Dapeng
Published: February 2009

Thermodynamics considerations and experimental evidence suggest that redox reactions occur at the interfaces between transparent conductive oxides (TCOs) and the active silicon layers in photovoltaic stacks, with potentially nefarious effects to device efficiency. The presence of interfacial layers of oxidized silicon and reduced metal is confirmed here with analytical depth profiling techniques in industrially produced Si thin film solar cells. Atomic-resolution scanning transmission electron microscopy and energy loss spectroscopy are used to show that the specific chemistry of the interface, the front TCO being Sn-rich while the back TCO is Zn-rich, has a strong influence on the size of the resulting interfacial layer. Furthermore, the morphology of the interface and the impact of annealing treatments are also studied, leading to suggestions for possible improvements of commercial device efficiency.
Colloidal nanocrystal-based light-emitting diodes fabricated on plastic toward flexible quantum dot optoelectronics
Authors: Tan Zhanao , Xu Jian , Zhang Chunfeng , Zhu Ting , Zhang Fan , Hedrick Brittany , Pickering Shawn , Wu Jian , Su Huaipeng , Gao Shuai , Wang Andrew Y. , Kimball Brian , Ruzyllo Jerzy , Dellas Nicholas S. , Mohney Suzanne E.
Published: February 2009

We report the demonstration of mechanically flexible quantum dot light emitting diodes (QD-LEDs) of all three primary colors (red, green, and blue). The QD-LEDs have been fabricated over poly(ethylene-terephthalate) substrates and exhibited high brightness, saturated colors, and pronounced flexibility with a critical bending radius of ∼5 mm. The efficiencies of the flexible QD-LEDs are comparable with the devices fabricated on rigid substrates, suggesting the intrinsic flexibility of quantum dot-based optoelectronic devices.
Remarks on the blow-up criteria for three-dimensional ideal magnetohydrodynamics equations
Authors: Du Yi , Liu Yan , Yao Zhengan
Published: February 2009

In this paper, we establish some improved regularity conditions for the three-dimensional (3D) magnetohydrodynamics equations. We proved the logarithmically improved Caflisch–Klapper–Steele’s criteria [“Remarks on sigularities, dimension and energy dissipation for ideal hydrodynamics and MHD,” Commun. Math. Phys. 184, 443 (1997)] as well as the logarithmically improved He–Xin’s [“On the regularity of weak solutions to the magnetohydrodynamic equations,” J. Differ. Equ. 23, 235 (2005)] and Wu’s [“Bounds and new approach for the 3D MHD equations,” J. Nonlinear Sci. 12, 395 (2002)] results for 3D ideal MHD equations.
Behavior of cylindrical liquid jets evolving in a transverse acoustic field
Authors: Carpentier Jean-Baptiste , Baillot Françoise , Blaisot Jean-Bernard , Dumouchel Christophe
Published: February 2009

This paper presents a theoretical and an experimental investigation of low-velocity cylindrical liquid jets submitted to transverse planar acoustic waves. For this purpose, the behavior of a liquid jet traversing the section of a Kundt tube was examined. Experiments reported that the liquid jet could be either deviated from its trajectory or deformed as a succession of lobes oriented in space and whose length and width depend on the jet acoustic environment. Furthermore, for a sufficient acoustic velocity, the jet deformation increases in such proportion that a premature and vivid atomization mechanism disintegrates the liquid flow. Theoretical models are proposed to understand these behaviors. The first one calls out for acoustic radiation pressure to explain the jet deviation. The second one consists in a modal analysis of the vibrations of a jet when submitted to a transverse stationary acoustic field. As a first approach, a simplified two-dimensional model is proposed. This model reports that a sudden exposition of the jet to an acoustic field triggers two jet eigenmodes. One of them induces jet deformations that were not experimentally observed. This part of the solution emerges due to theoretical deficiencies. However, the second mode reproduces the lobe formation and leads to atomization criteria in good agreement with the experimental results. The paper ends with an extension of the mathematical development in three dimensions in order to provide a basis to a more consistent model.
Large elastic wave amplitude and attenuation in shocked pure aluminum
Authors: Gupta Y. M. , Winey J. M. , Trivedi P. B. , LaLone B. M. , Smith R. F. , Eggert J. H. , Collins G. W.
Published: February 2009

Shock-induced elastic-plastic deformation in pure aluminum was examined at 4 GPa peak stress by measuring wave profiles in thin (40–180 μm) samples under plate impact loading. Unlike past work, large elastic wave amplitudes (∼1 GPa) and rapid elastic wave attenuation with propagation distance were observed. The combination of large elastic wave attenuation in thin samples and differences in sample thicknesses between the present and past work suggest a consistent picture of shock propagation in pure aluminum where time-dependent elastic-plastic response is confined to material very near the impact surface. The present results cannot be fully reconciled with recent shockless compression results.
Tailoring the shape of GaN/AlxGa1−xN nanostructures to extend their luminescence in the visible range
Authors: Brault J. , Huault T. , Natali F. , Damilano B. , Lefebvre D. , Leroux M. , Korytov M. , Massies J.
Published: February 2009

We show that the shape of GaN nanostructures grown by molecular beam epitaxy on AlxGa1−xN (0001) surfaces, for x≥0.4, can be controlled via the ammonia pressure. The nanostructures are obtained from a two dimensional to three dimensional transition of a GaN layer occurring upon a growth interruption. Atomic force microscopy measurements show that depending on the ammonia pressure during the growth interruption, dot or dash-shaped nanostructures can be obtained. Low temperature photoluminescence measurements reveal a large redshift in the emission energy of the quantum dashes, as compared to the quantum dots. By simply adjusting the GaN deposited thickness, it is shown that quantum dashes enable to strongly extend the emission range of GaN/Al0.5Ga0.5N nanostructures from the violet-blue (∼400–470 nm) to the green-orange range (∼500–600 nm).
Effect of pulsed laser irradiation on the structure of GeTe films deposited by metal organic chemical vapor deposition: A Raman spectroscopy study
Authors: Salicio O. , Wiemer C. , Fanciulli M. , Gawelda W. , Siegel J. , Afonso C. N. , Plausinaitiene V. , Abrutis A.
Published: February 2009

Phase changes between amorphous and crystallized states were induced by laser irradiation with nanosecond pulses in GexTey films grown by metal organic chemical vapor deposition. The different phases were obtained by adjusting the pulse energy and could be distinguished by their different optical reflectivities. The corresponding structural changes were studied by Raman spectroscopy, showing marked differences for the two phases. A clear correlation is found between optical reflectivity levels, crystallographic state and the evolution of Ge–Ge, Te–Te, and Ge–Te Raman bands.
Confinement jumps in a non-neutral plasma
Authors: Hahn Michael , Pedersen Thomas Sunn , Brenner Paul W. , Marksteiner Quinn
Published: February 2009

Measurements of confinement jumps in pure electron plasmas confined on magnetic surfaces are presented and discussed. The experiments were performed in the Columbia non-neutral torus stellarator [T. S. Pedersen, J. P. Kremer, R. G. Lefrancois, Q. Marksteiner, N. Pomphrey, W. Reiersen, F. Dahlgren, and X. Sarasola, Fusion Sci. Technol. 50, 372 (2006)]. The jumps exhibit hysteresis and are associated with a negative differential resistance. The jumps occur at particular emission currents of the biased emissive filaments that create and sustain the electron plasmas independent of the methods used to affect the emission current. This observation, as well as other experimental evidence, supports that the jumps are caused by a cathode instability. The jumps can also be triggered by the application of a bias potential on a nearby mesh. In most circumstances, the jumps occur between two stable but measurably different equilibrium states. These different equilibrium states have substantially different confinement times. The cathode physics is important for the jumps because the cathode instability provides the perturbation that triggers the jump of the whole plasma into the other equilibrium state, but as mentioned, an external electrostatic perturbation is also capable of triggering such a jump.
Mean free path effects in the shock-implosion problem
Authors: Goldsworthy M. J. , Pullin D. I.
Published: February 2009

The effects of finite Knudsen number in the problem of a cylindrically imploding shock wave in a monatomic gas are investigated. Numerical solutions of the flow field are obtained with initial conditions in the ranges 1.25≤M0≤5 and 0.005≤Kn0≤0.1 using the direct simulation Monte Carlo method. Results show that as Kn0 decreases and M0 increases, the maximum implosion temperature scales increasingly well with the similarity exponent predicted in the Guderley solution for an imploding strong shock in the Euler limit. When the radius of curvature is large, the cylindrical shock thickness is found to be almost identical to the thickness of a planar shock for a given shock Mach number. For small radii of curvature, the cylindrical shock was found to be thicker than the corresponding planar shock.
Coherence resonance induced by rewiring in complex networks
Authors: Jiang Mi , Ma Ping
Published: February 2009

We report a novel coherent excitation phenomenon in a heterogeneous network of coupled FitzHugh–Nagumo elements. It is demonstrated that dynamical rewiring in the network can play a constructive role to bring on coherent excitations. The coherence factor as the function of rewiring time interval represents a nontrivial phenomenon which is a fingerprint of coherence resonance. We call this resonant behavior caused by dynamical wiring changes the network-rewiring-induced coherence resonance. The mechanism can be understood by the effective noise played by the rewiring process.
Radiating relativistic matter in geodesic motion
Authors: Thirukkanesh S. , Maharaj S. D.
Published: February 2009

We study the gravitational behavior of a spherically symmetric radiating star when the fluid particles are in geodesic motion. We transform the governing equation into a simpler form which allows for a general analytic treatment. We find that Bernoulli, Ricatti, and confluent hypergeometric equations are possible. These admit solutions in terms of elementary functions and special functions. Particular models contain the Minkowski space-time and the Friedmann dust space-time as limiting cases. Our infinite family of solutions contains specific models found previously. For a particular metric we briefly investigate the physical features, derive the temperature profiles, and plot the behavior of the casual and acasual temperatures.
Benefit of H2 surface pretreatment for 4H-SiC oxynitridation using N2O and rapid thermal processing steps
Authors: Constant A. , Camara N. , Godignon P. , Camassel J.
Published: February 2009

The effect of H2 surface pretreatment on the density of interface traps in SiO2 films grown on the Si-face of 4H-SiC has been investigated. With respect to the more conventional oxide grown in nitrous oxide gas by rapid thermal processing but without any preannealing step, we find that the interface trap and fixed oxide charge densities have been reduced by, typically, one order of magnitude. The reasons for such improvement in the properties of the SiO2/SiC interface after preoxidation hydrogen annealing are discussed.
Design and estimated performance of a new neutron guide system for the NCNR expansion project
Authors: Cook J. C.
Published: February 2009

An integral part of the National Institute of Standards and Technology Center for Neutron Research (NCNR) expansion project is the addition of five cold neutron guide tubes serving multiple experimental stations in an expanded guide hall. The guides have curved-straight arrangements in the horizontal plane, employing horizontally or vertically defocusing and focusing sections in some cases to improve transmission efficiency or for beam reshaping. The horizontally curved sections eliminate direct lines of sight between the source and the experimental stations, and the outer (concave) surfaces generally have higher critical angles than the inner (convex) surfaces. These features result in well-filtered cold neutron beams with no intensity losses at shorter wavelengths with respect to curved guides having the higher critical angle coatings on both surfaces. For all guides the critical angle of the outer coating of the curved section is selected to achieve a desirable characteristic wavelength, consistent with the instrument requirements. On guides where the scattering-plane beam divergence must be strictly limited, the inner radial coatings of the curved sections and the side coatings and lengths of the final straight sections are chosen to produce the desired beam divergence while the outer radial coating is selected so as to obtain a spatial-angular uniformity of the transmitted beam that is not achievable using a curved guide alone. The long-wavelength transmission of such guides tends to exceed that of equivalent straight guides using crystal filters.
Improved silicon surface passivation achieved by negatively charged silicon nitride films
Authors: Weber K. J. , Jin H.
Published: February 2009

A corona discharge is used to create and store negative charge in the silicon nitride films of silicon dioxide/silicon nitride stacks. Effective lifetime measurements on both textured and planar, as well as both boron diffused and undiffused silicon samples passivated with silicon oxide/silicon nitride stacks, show that the creation of negative charge in the nitride layer results in an improvement in the surface passivation for all samples, with very low (<2 cm/s) effective surface recombination velocities demonstrated for planar, undiffused samples. The manipulation of charge can be exploited to improve the conversion efficiency of silicon solar cells.
Narrow-band metal-oxide-semiconductor photodetector
Authors: Ho W. S. , Lin C.-H. , Cheng T.-H. , Hsu W. W. , Chen Y.-Y. , Kuo P.-S. , Liu C. W.
Published: February 2009

Si-based photodetectors for narrow-band ultraviolet light (319 nm) and green light (500 nm) detection are demonstrated using a metal-oxide-semiconductor tunneling structure. By using appropriate selection of gate metal, the metal-oxide-semiconductor tunneling diode can detect specific range of light. Due to the spectral dependence of absorption and reflection of the Ag and Au as gate electrodes, the narrow-band detection of ultraviolet and green light can be achieved, respectively. The photodetectors with 130 nm thick Ag gate and 70 nm thick Au gate exhibit peak responsivities of 5.1 and 0.3 mA/W at 319 and 500 nm, respectively.
Automated spin-assisted layer-by-layer assembly of nanocomposites
Authors: Vozar Steven , Poh Yeh-Chuin , Serbowicz Thomas , Bachner Matthew , Podsiadlo Paul , Qin Ming , Verploegen Eric , Kotov Nicholas , Hart A. John
Published: February 2009

We present the design and verification of a desktop system for the automated production of nanostructured thin films via spin-assisted layer-by-layer (spin-LBL) assembly. The utility of this system is demonstrated by fabricating polyvinyl alcohol/clay nanocomposites. Ellipsometry measurements demonstrate that the automated spin-LBL method creates composites with bilayer thickness and growth rate comparable to traditional dip-LBL; however, the cycle time of the spin-LBL method is an order of magnitude faster. Small angle X-ray scattering analysis shows that the clay platelets in spin-LBL nanocomposites are more highly aligned than in dip-LBL composites. This method can significantly increase the throughput of laboratory-scale LBL discovery and processing, can enable testing of functional properties of LBL nanocomposites over wafer-scale areas, and can be scaled to larger substrates for commercial production.
Table-top reflectometer in the extreme ultraviolet for surface sensitive analysis
Authors: Banyay Matus , Juschkin Larissa
Published: February 2009

We suggest a reflectometer for thin film analysis based on a plasma-discharge source utilizing extreme ultraviolet (XUV) radiation in a wavelength region of 4–40 nm. In contrast to other laboratory based reflectometers, which are designed for the near normal incidence case to characterize XUV multilayer optics and maskblanks, in our approach we move to a selectable fixed grazing incidence angle that enables surface sensitive analysis of almost arbitrary ultrathin film systems providing high elemental contrast due to the characteristic absorption of XUV by matter. Most materials (e.g., Si, Al, Gd, and Ag) exhibit characteristic absorption edges allowing not only to determine layer thicknesses, surface or interlayer roughnesses in a stack, but also elemental composition and even analyzing the absorption fine structures. Together with our simulations we show that our polychromatic approach makes it possible to provide all these parameters in one measurement.
Defect formation and annealing behaviors of fluorine-implanted GaN layers revealed by positron annihilation spectroscopy
Authors: Wang M. J. , Yuan L. , Cheng C. C. , Beling C. D. , Chen K. J.
Published: February 2009

Defect formation and annealing behaviors of fluorine-implanted, unintentionally doped GaN layers were studied by positron annihilation spectroscopy (PAS). Single Ga vacancies (VGa) were identified as the main vacancy-type defects detected by PAS after fluorine implantation at 180 keV with a dose of 1×1015 cm−2. Implantation-induced VGa tend to aggregate and form vacancy clusters after postimplantation annealing in N2 ambient at 600 °C. Fluorine ions tend to form F-vacancy complexes quickly after thermal annealing, which is consistent with the proposed diffusion model that predicts the behaviors of fluorine in GaN.
Legislative Support for Urban Land-Use Control in China
Authors: Zhang Sumei , Pearlman Kenneth
Published: February 2009

China is in a transitional period with a decentralized economy operated within a highly centralized governmental structure. With a strong statutory law tradition, the federal government has created a very complicated set of statutes to regulate land-use tenure, land-use rights allocation, and planning activities. Local governments regulate daily land-use transfer activities within the federal framework. China is now looking for a land-use management tool that can effectively regulate individual activities at the local level. The statutory plan framework (local-level land-use plans similar to zoning ordinances) is one of the attempts. Shenzhen is the first city to adopt statutory plans as local bylaws and its experience provides other cities with a good example of how to incorporate public participation into land-use management. However, the experience in Shenzhen also exposes a number of problems related to the overall distribution of power in the current federal structure. With most cities lacking power to issue local bylaws, the statutory plan concept is not universally applicable. China should at least delegate the full power to regulate local land-use activities to local communities. Effective control of local land-use activities calls for such decentralization. Further, the existence of a weak judicial and extremely strong administrative system is another issue of concern. Both systems need to be further reformed to achieve a balanced distribution of power between administrative and judicial implementation of land-use regulation.