bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient dynamic bipedal walking using effects of semicircular feet
Authors: Asano Fumihiko , Luo Zhi-Wei
Published: May 2010

Achieving energy-efficient and high-speed dynamic walking has become one of the main subjects of research in the area of robotic biped locomotion, and passive dynamic walking has attracted a great deal of attention as a solution to this. It is empirically known that the convex curve of the foot, which characterizes passive–dynamic walkers, has an important effect on increasing the walking speed.

This paper mainly discusses our investigations into the driving mechanism for compass-like biped robots and the rolling effect of semicircular feet. We first analyze the mechanism for a planar fully actuated compass-like biped model to clarify the importance of ankle-joint torque by introducing a generalized virtual-gravity concept. A planar underactuated biped model with semicircular feet is then introduced and we demonstrate that virtual passive dynamic walking only by hip-joint torque can be accomplished based on the rolling effect. We then compare the rolling effect with a flat feet model through linear approximation, and show that the rolling effect is equivalent to virtual ankle-joint torque. Throughout this paper, we provide novel insights into how zero-moment-point-free robots can generate a dynamic bipedal gait.
The International Conference of the Red Cross and Red Crescent: challenges, key issues and achievements
Authors: Bugnion François
Published: May 2010

Since the constituent Conference in October 1863, which gave birth to the Red Cross,1 the International Conference of the Red Cross and Red Crescent has met on thirty occasions. The first meeting took place in Paris in 1867 and the thirtieth in Geneva in November 2007. What contribution has the Conference made to the development of international humanitarian law and humanitarian action? What are the main challenges that the Conference has had to face? Where has it succeeded and where has it failed? These are the questions that this article seeks to answer.
Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge
Authors: Smit Jeroen , Burg Jean‐Pierre , Dolati Asghar , Sokoutis Dimitrios
Published: May 2010

Olistostromes cover large portions of active thrust wedges like Makran, Gulf of Cadiz, and offshore Borneo. Olistostrome emplacement by submarine mass flow represents an instantaneous and massive mass redistribution that may influence thrust wedge mechanics. Different scenarios are experimentally tested. They show that the postolistostrome wedge development depends on the thickness and extent of the added load. These results are discussed after the example of the Iranian Makran wedge, situated between the Arabian and Eurasian plates. Mass redistribution caused by a late Miocene mass flow may explain a change in deformation style from intense folding and thrusting to gentle folding and eventually a jump of thrust imbrication toward the frontal offshore part of this active accretionary wedge.
Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs
Authors: Rioux Matthew , Mattinson James , Hacker Bradley , Kelemen Peter , Blusztajn Jurek , Hanghøj Karen , Gehrels George
Published: May 2010

Seismic profiles of several modern arcs have identified thick, low‐velocity midcrustal layers (Vp= 6.0–6.5 km/s) that are interpreted to represent intermediate to felsic plutonic crust. The presence of this silicic crust is surprising given the mafic composition of most primitive mantle melts and could have important implications for the chemical evolution and bulk composition of arcs. However, direct studies of the middle crust are limited by the restricted plutonic exposures in modern arcs. The accreted Talkeetna arc, south central Alaska, exposes a faulted crustal section from residual subarc mantle to subaerial volcanic rocks of a Jurassic intraoceanic arc and is an ideal place to study the intrusive middle crust. Previous research on the arc, which has provided insight into a range of arc processes, has principally focused on western exposures of the arc in the Chugach Mountains. We present new U‐Pb zircon dates, radiogenic isotope data, and whole‐rock geochemical analyses that provide the first high‐precision data on large intermediate to felsic plutonic exposures on Kodiak Island and the Alaska Peninsula. A single chemical abrasion–thermal ionization mass spectrometry analysis from the Afognak pluton yielded an age of 212.87 ± 0.19 Ma, indicating that the plutonic exposures on Kodiak Island represent the earliest preserved record of Talkeetna arc magmatism. Nine new dates from the extensive Jurassic batholith on the Alaska Peninsula range from 183.5 to 164.1 Ma and require a northward shift in the Talkeetna arc magmatic axis following initial emplacement of the Kodiak plutons, paralleling the development of arc magmatism in the Chugach and Talkeetna mountains. Radiogenic isotope data from the Alaska Peninsula and the Kodiak archipelago range from ɛNd(t) = 5.2 to 9.0 and87Sr/86Srint= 0.703515 to 0.703947 and are similar to age‐corrected data from modern intraoceanic arcs, suggesting that the evolved Alaska Peninsula plutons formed by extensive differentiation of arc basalts with little or no involvement of preexisting crustal material. The whole‐rock geochemical data and calculated seismic velocities suggest that the Alaska Peninsula represents an analogue for the low‐velocity middle crust observed in modern arcs. The continuous temporal record and extensive exposure of intermediate to felsic plutonic rocks in the Talkeetna arc indicate that evolved magmas are generated by repetitive or steady state processes and play a fundamental role in the growth and evolution of intraoceanic arcs.
Cluster observations of EMIC triggered emissions in association with Pc1 waves near Earth's plasmapause
Authors: Pickett J. S. , Grison B. , Omura Y. , Engebretson M. J. , Dandouras I. , Masson A. , Adrian M. L. , Santolík O. , Décréau P. M. E. , Cornilleau‐Wehrlin N. , Constantinescu D.
Published: May 2010

The Cluster spacecraft were favorably positioned on the nightside near the equatorial plasmapause of Earth at L ∼ 4.3 on 30 March 2002 to observe electromagnetic ion cyclotron (EMIC) rising tone emissions in association with Pc1 waves at 1.5 Hz. The EMIC rising tone emissions were found to be left‐hand, circularly polarized, dispersive, and propagating away from the equator. Their burstiness and dispersion of ∼30s/Hz rising out of the 1.5 Hz Pc1 waves are consistent with their identification as EMIC triggered chorus emissions, the first to be reported through in situ observations near the plasmapause. Along with the expected H+ ring current ions seen at higher energies (>300 eV), lower energy ions (300 eV and less) were observed during the most intense EMIC triggered emission events. Nonlinear wave‐particle interactions via cyclotron resonance between the ∼2–10 keV H+ ions with temperature anisotropy and the linearly‐amplified Pc1 waves are suggested as a possible generation mechanism for the EMIC triggered emissions.
Levoglucosan stability in biomass burning particles exposed to hydroxyl radicals
Authors: Hennigan Christopher J. , Sullivan Amy P. , Collett Jeffrey L. , Robinson Allen L.
Published: May 2010

Experiments were carried out in a smog chamber to investigate the oxidation of levoglucosan in biomass burning particles exposed to gas‐phase hydroxyl radicals (OH). The experiments featured atmospherically‐relevant particle and oxidant concentrations and both high and low relative humidity conditions. In every experiment, we observed levoglucosan decay in particles exposed to OH. The extent of decay ranged from ∼20% to ∼90% and was strongly correlated to the integrated OH exposure. Increased relative humidity did not enhance or impede reaction. Relative kinetics indicate that levoglucosan has an atmospheric lifetime of 0.7–2.2 days when biomass burning particles are exposed to 1 × 106 molecules cm−3 of OH (typical average summertime conditions). This implies that levoglucosan reacts with OH on a timescale similar to that of transport and deposition, which has important implications for the use of levoglucosan as a tracer for biomass burning emissions in source apportionment studies.
Molecular origin of plasma membrane citrate transporter in human prostate epithelial cells
Authors: Mazurek Maciej P , Prasad Puttur D , Gopal Elangovan , Fraser Scott P , Bolt Leszek , Rizaner Nahit , Palmer Christopher P , Foster Christopher S , Palmieri Ferdinando , Ganapathy Vadivel , Stühmer Walter , Djamgoz Mustafa B A , Mycielska Maria E
Published: May 2010

The prostate is a highly specialized mammalian organ that produces and releases large amounts of citrate. However, the citrate release mechanism is not known. Here, we present the results of molecular cloning of a citrate transporter from human normal prostate epithelial PNT2‐C2 cells shown previously to express such a mechanism. By using rapid amplification of cDNA ends PCR, we determined that the prostatic carrier is an isoform of the mitochondrial transporter SLC25A1 with a different first exon. We confirmed the functionality of the clone by expressing it in human embryonic kidney cells and performing radiotracer experiments and whole‐cell patch‐clamp recordings. By using short interfering RNAs targeting different parts of the sequence, we confirmed that the cloned protein is the main prostatic transporter responsible for citrate release. We also produced a specific antibody and localized the cloned transporter protein to the plasma membrane of the cells. By using the same antibody, we have shown that the cloned transporter is expressed in non‐malignant human tissues.
Functional modularity of nuclear hormone receptors in a Caenorhabditis elegans metabolic gene regulatory network
Authors: Arda H Efsun , Taubert Stefan , MacNeil Lesley T , Conine Colin C , Tsuda Ben , Van Gilst Marc , Sequerra Reynaldo , Doucette‐Stamm Lynn , Yamamoto Keith R , Walhout Albertha J M
Published: May 2010

Gene regulatory networks (GRNs) provide insights into the mechanisms of differential gene expression at a systems level. GRNs that relate to metazoan development have been studied extensively. However, little is still known about the design principles, organization and functionality of GRNs that control physiological processes such as metabolism, homeostasis and responses to environmental cues. In this study, we report the first experimentally mapped metazoan GRN of Caenorhabditis elegans metabolic genes. This network is enriched for nuclear hormone receptors (NHRs). The NHR family has greatly expanded in nematodes: humans have 48 NHRs, but C. elegans has 284, most of which are uncharacterized. We find that the C. elegans metabolic GRN is highly modular and that two GRN modules predominantly consist of NHRs. Network modularity has been proposed to facilitate a rapid response to different cues. As NHRs are metabolic sensors that are poised to respond to ligands, this suggests that C. elegans GRNs evolved to enable rapid and adaptive responses to different cues by a concurrence of NHR family expansion and modular GRN wiring.
Gas phase homolytic bond dissociation enthalpies of common laboratory solvents: A G4 theoretical study
Authors: Rayne Sierra , Forest Kaya
Published: May 2010

Gas phase standard state (298.15 K, 1 atm) calculations were conducted at the Gaussian-4 (G4) composite method level of theory to estimate the bond dissociation enthalpies (BDEs) of various common laboratory solvents. Excellent agreement was obtained between experimental and G4 estimated BDEs. The current study demonstrates the BDE prediction accuracy of the G4 method, and is also intended to function as a potentially useful resource in any reevaluations of the preferred BDEs for these common laboratory solvents.
Affibody molecule‐mediated depletion of HSA and IgG using different buffer compositions: a 15 min protocol for parallel processing of 1–48 samples
Authors: Eriksson Cecilia , Schwenk Jochen M. , Sjöberg Anna , Hober Sophia
Published: May 2010

High‐abundant plasma proteins pose a challenge in a large number of proteomics‐based technologies. Depletion of these high‐abundant proteins has proven to be a fruitful strategy to circumvent masking of lower‐abundant proteins that could serve as valuable biomarker candidates. However, current strategies often do not meet the throughput requirements of large‐scale proteomic studies. In the present paper, a flexible and parallelized method for the depletion of high‐abundant proteins is described, allowing the removal of the two most abundant proteins from 48 blood‐derived samples in less than 15 min using Affibody molecules as affinity ligands. A sample‐processing platform like this should be suitable for a number of proteomics technologies; its flexibility in buffer composition allows for different types of downstream applications.
The identification of the SNARE complex required for the fusion of VLDL-transport vesicle with hepaticcis-Golgi
Authors: Siddiqi Shaila , Mani Arul M. , Siddiqi Shadab A.
Published: May 2010

VLDLs (very-low-density lipoproteins) are synthesized in the liver and play an important role in the pathogenesis of atherosclerosis. Following their biogenesis in hepatic ER (endoplasmic reticulum), nascent VLDLs are exported to the Golgi which is a physiologically regulatable event. We have previously shown that a unique ER-derived vesicle, the VTV (VLDL-transport vesicle), mediates the targeted delivery of VLDL to the Golgi lumen. Because VTVs are different from other ER-derived transport vesicles in their morphology and biochemical composition, we speculated that a distinct set of SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins would form a SNARE complex which would eventually facilitate the docking/fusion of VTVs with Golgi. Our results show that Sec22b is concentrated in VTVs as compared with the ER. Electron microscopic results show that Sec22b co-localizes with p58 and Sar1 on the VTV surface. Pre-treatment of VTV with antibodies against Sec22b inhibited VTV–Golgi fusion, indicating its role as a v-SNARE (vesicle SNARE). To isolate the SNARE complex, we developed an in vitro docking assay in which VTVs were allowed to dock with the Golgi, but fusion was prevented to stabilize the SNARE complex. After the docking reaction, VTV–Golgi complexes were collected, solubilized in 2% Triton X-100 and the SNARE complex was co-immunoprecipitated using anti-Sec22b or GOS28 antibodies. A ~110 kDa complex was identified in non-boiled samples that was dissociated upon boiling. The components of the complex were identified as Sec22b, syntaxin 5, rBet1 and GOS28. Antibodies against each SNARE component significantly inhibited VTV–Golgi fusion. We conclude that the SNARE complex required for VTV–Golgi fusion is composed of Sec22b, syntaxin 5, rBet1 and GOS28.
The glycosylation of human synovial lubricin: implications for its role in inflammation
Authors: Estrella Ruby P. , Whitelock John M. , Packer Nicolle H. , Karlsson Niclas G.
Published: May 2010

Acidic proteins were isolated from synovial fluid from two osteoarthritic and two rheumatoid arthritic patients and identified by MS. It was found that the most abundant protein in all of the samples was the mucin-like protein lubricin. Further characterization of lubricin from the different patients by LC (liquid chromatography)–MS of released oligosaccharides showed that the core 1 O-linked oligosaccharides NeuAcα2–3Galβ1–3GalNAc and NeuAcα2–3Galβ1–3(NeuAcα2–6)GalNAc were the dominating structures on lubricin. The latter was found to be more prevalent in the rheumatoid arthritis samples, indicating that sialylation is up-regulated as part of the inflammatory response. In addition to these dominating structures, core 2 structures were also found in low amounts, where the largest was the disialylated hexasaccharide corresponding to the sequence NeuAcα2–3Galβ1–3(NeuAcα2–3Galβ1–3/4GlcNAcβ1–6)GalNAc. It was also found that a small proportion of the core 2 oligosaccharides carried sulfate. The ability of lubricin to present complex glycosylation reflecting the state of the joint tissue makes lubricin a candidate as a carrier of inflammatory oligosaccharide epitopes. In particular, it was shown that lubricin from inflamed arthritic tissue was recognized by the antibody MECA-79 and thus carried the sulfated epitope proposed to be part of the L-selectin ligand that is responsible for recruitment of leucocytes to inflammatory sites.
Role of conservative mutations in protein multi-property adaptation
Authors: Rodriguez-Larrea David , Perez-Jimenez Raul , Sanchez-Romero Inmaculada , Delgado-Delgado Asuncion , Fernandez Julio M. , Sanchez-Ruiz Jose M.
Published: May 2010

Protein physicochemical properties must undergo complex changes during evolution, as a response to modifications in the organism environment, the result of the proteins taking up new roles or because of the need to cope with the evolution of molecular interacting partners. Recent work has emphasized the role of stability and stability–function trade-offs in these protein adaptation processes. In the present study, on the other hand, we report that combinations of a few conservative, high-frequency-of-fixation mutations in the thioredoxin molecule lead to largely independent changes in both stability and the diversity of catalytic mechanisms, as revealed by single-molecule atomic force spectroscopy. Furthermore, the changes found are evolutionarily significant, as they combine typically hyperthermophilic stability enhancements with modulations in function that span the ranges defined by the quite different catalytic patterns of thioredoxins from bacterial and eukaryotic origin. These results suggest that evolutionary protein adaptation may use, in some cases at least, the potential of conservative mutations to originate a multiplicity of evolutionarily allowed mutational paths leading to a variety of protein modulation patterns. In addition the results support the feasibility of using evolutionary information to achieve protein multi-feature optimization, an important biotechnological goal.
(–)-Epigallocatechin-3-gallate down-regulates EGFR, MMP-2, MMP-9 and EMMPRIN and inhibits the invasion of MCF-7 tamoxifen-resistant cells
Authors: Farabegoli Fulvia , Papi Alessio , Orlandi Marina
Published: May 2010

The activation of the EGFR (epidermal growth factor receptor) signalling pathway is one of the key mechanisms underlying the development of resistance to tamoxifen in breast cancer patients. As EGCG [(–)-epigallocatechin-3-gallate], the most active catechin present in green tea, has been shown to down-regulate EGFR, we studied the effects of 10–100 μg/ml EGCG treatment on growth and invasion in a breast carcinoma cell line resistant to tamoxifen [MCF-7Tam (MCF-7 breast carcinoma cell line resistant to tamoxifen) cells] and parental MCF-7. A dose-dependent down-regulation of EGFR mRNA expression and protein level occurred after 50 μg/ml EGCG treatment of MCF-7Tam cells. EGFR molecules on the plasma membrane surface of MCF-7Tam cells significantly decreased. EGFR phosphorylation (Tyr-992, Tyr-1045 and Tyr-1068) was higher in MCF-7Tam than in MCF-7 and it was reduced by EGCG treatment. ERK (extracellular regulated kinase) and phospho-ERK p42/44 were also down-regulated by EGCG treatment and in vitro cell growth and invasion decreased. MMP-2 (matrix metalloproteinase-2) and MMP-9, which are implicated in cell invasion and metastasis, and EMMPRIN (extracellular matrix metalloproteinase inducer), a glycoprotein able to activate MMPs, were significantly reduced after 50 μg/ml EGCG treatment. In keeping with this, TIMP-1 (tissue inhibitor of metalloproteinases-1) and TIMP-2, which down-regulate MMPs, increased after EGCG treatment. Altogether, the present data demonstrated that EGCG could attenuate the tamoxifen-resistant phenotype of MCF-7Tam cells. EGCG could stop MCF-7Tam cell growth and in vitro invasion through down-regulation of EGFR and other molecules implicated in aggressive biological behaviour. The present data support the hypothesis that EGCG is an interesting molecule to be investigated in tamoxifen-resistant breast carcinoma.
Hydrogen sulfide attenuates cardiac dysfunction in a rat model of heart failure: a mechanism through cardiac mitochondrial protection
Authors: Wang Xianli , Wang Qian , Guo Wei , Zhu Yi Zhun
Published: May 2010

HF (heart failure) after MI (myocardial infarction) is a major cause of morbidity and mortality worldwide. Recent studies have shown that hydrogen sulfide (H2S) has cardioprotective effects. Hence, we aimed to elucidate the potential effects of H2S on HF after MI in rats. The HF model after MI was made by ligating the left anterior descending coronary artery. HF groups and sham-operated groups of rats were treated with vehicle, sodium hydrosulfide (NaHS) or PAG (propagylglycine). Equal volumes of saline, 3.136 mg·kg−1·day−1 NaHS or 37.5 mg·kg−1·day−1 PAG, were intraperitoneally injected into rats for 6 weeks after operation. Survival, lung-to-body weight ratio and left ventricular haemodynamic parameters were measured. The protein and gene expression of Bcl-2, Bax, caspase 3 and cytochrome c were analysed by Western blotting and RT–PCR (reverse transcription–PCR). TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) and EM (electron microscopy) were used to examine apoptosis of heart tissues. NaHS was found to improve the survival and lower the lung-to-body weight ratio. It increased the LVSP (left ventricular systolic pressure) and the maximum rate of pressure and decreased LVEDP (left ventricular end-diastolic pressure). Furthermore, NaHS promoted Bcl-2 protein and mRNA expression and demoted Bax, caspase 3 protein and mRNA expression in HF rats. We also showed that NaHS decreased the leakage of cytochrome c protein from the mitochondria to the cytoplasm. Histological observation by TUNEL and EM proved that NaHS inhibited cardiac apoptosis in HF hearts and improved mitochondrial derangements, but that PAG aggravated those indices. Hence, H2S has protective effects in HF rats.
The value of MG7‐Ag and COX‐2 for predicting malignancy in gastric precancerous lesions
Authors: Hong Liu , Li Shujun , Liu Lin , Shi Yongquan , Wu Kaichun , Fan Daiming
Published: May 2010

Here we aimed to first investigate the clinical value of combined detection of MG7‐Ag and COX‐2 (cyclo‐oxygenase 2) in prediction of advances in gastric precancerous lesions. Immunohistochemical analysis was used to examine the expression of MG7‐Ag and COX‐2 in 396 cases of patients with gastric precancerous lesions, including 66 cases of atrophic gastritis, 106 cases of intestinal metaplasia, 174 cases of low‐moderate‐grade dysplasia and 50 cases of high‐grade dysplasia. The relation of MG7‐Ag and COX‐2 staining with various clinicopathological features was analysed by follow‐up study. The positive rates of MG7‐Ag and COX‐2 were increased gradually from atrophic gastritis (21.2%, 28.8%), intestinal metaplasia (36.8%, 44.3%), low‐moderate‐grade dysplasia (51.4%, 58.6%) to high‐grade dysplasia (72%, 80%). Double positive staining of MG7‐Ag and COX‐2 in gastric precancerous lesions had an increased risk of precancerous progression over 22 times, compared with negative ones. However, the expression of MG7‐Ag and COX‐2 was not significantly correlated with age and gender of patients. MG7‐Ag and COX‐2 might play an important role in the process of carcinogenesis and progression of gastric cancer. Combined detection of MG7‐Ag and COX‐2 was of value of predicting early gastric cancer from precancerous lesions.
Scalings of energetic particle transport by ion temperature gradient microturbulence
Authors: Zhang Wenlu , Decyk Viktor , Holod Ihor , Xiao Yong , Lin Zhihong , Chen Liu
Published: May 2010

Transport scaling of energetic particles by ion temperature gradient microturbulence in magnetized plasmas is studied in massively paralleled gyrokinetic particle-in-cell simulations. It is found that the diffusivity decreases drastically at high particles energy (E) to plasma temperature (T) ratio because of the averaging effects of the large gyroradius and drift-orbit width, and the fast wave-particle decorrelation. At high energy, the diffusivity follows a (E/T)−1 scaling for purely passing particles, a (E/T)−2 scaling for deeply trapped particles and a (E/T)−1 scaling for particles with an isotropic velocity distribution since the diffusivity therein is contributed mostly by the passing particles.
Comparison between cylindrical model and experimental observation on the study of resistive wall mode in reversed field pinch plasmas
Authors: Wang Z. R. , Guo S. C. , Shi L. , Bolzonella T. , Baruzzo M. , Wang X. G.
Published: May 2010

A cylindrical magnetohydrodynamic model including plasma pressure and longitudinal flow has been employed for the study of resistive wall mode (RWM) in reversed field pinch (RFP) plasmas. In order to validate the model, a careful comparison with the experimental measurements in RFX-mod [P. Sonato et al., Fusion Eng. Des. 66–68, 161 (2003)] on the mode growth rates has been made by well matching the equilibrium parameters F, Θ, and βp. The RWM instability spectrum, which varies with the equilibrium parameters, is also calculated for comparison. The sensitivity of the mode growth rate to the equilibrium parameters is studied in details. It is concluded that the model can provide consistent accuracy in studies of RWM in RFP plasmas. The analysis based on the balance of the potential energy components has been carried out in order to obtain the physical understanding on the mode behavior.
Test particle analysis in L- and H-mode simulations
Authors: Sánchez Burillo G. , van Milligen B. Ph. , Thyagaraja A.
Published: May 2010

In this work, the radial transport of tracers in an H-mode run in the CUTIE code [A. Thyagaraja et al., Phys. Plasmas 12, 090907 (2005)] is analyzed globally. Several techniques are applied to the study of the trajectories performed by the tracers, measuring the degree of self-similarity in the motion and searching for long range spatial and temporal correlations. The results are compared to those of an L-mode run [G. Sánchez Burillo et al., Phys. Plasmas 16, 042319 (2009)] in order to highlight the changes between L and H. The analysis of self-similarity parameters of the motion reveals that changes, if any, are slight, although the reliability of the results is limited. Nevertheless, the study of the mean step size indicates that transport is more local (or rather less global) and the anomalous diffusion contribution is less dominant. Namely, the variance of the radial distribution of tracers is smaller in H-mode and the strong asymmetry in the positive/negative steps performed by the tracers vanishes.
Effective recombination velocity of textured surfaces
Authors: Xiong Kanglin , Lu Shulong , Jiang Desheng , Dong Jianrong , Yang Hui
Published: May 2010

Surface texturization is an effective way to enhance the absorption of light for optoelectronic devices but it also aggravates the surface recombination by enlarging the surface area. In order to evaluate the influence of texture structures on the surface recombination, an effective surface recombination velocity is defined which is assumed to have an equivalent recombination effect on a flat surface. Based on numerical and analytical calculation, the dependences of effective surface recombination on the pattern geometry, the surface recombination velocity, and the diffusion length are analyzed.
Resonant cavity-enhanced absorption for optical refrigeration
Authors: Seletskiy D. V. , Hasselbeck M. P. , Sheik-Bahae M.
Published: May 2010

A 20-fold increase over the single path optical absorption is demonstrated with a low loss medium placed in a resonant cavity. This is applied to laser cooling of ytterbium-doped fluorozirconate glass resulting in 90% absorption of the incident pump light. A coupled-cavity scheme to achieve active optical impedance matching is analyzed.
Spheromak formation and sustainment by tangential boundary flows
Authors: García-Martínez Pablo Luis , Farengo Ricardo
Published: May 2010

The nonlinear, resistive, three-dimensional magnetohydrodynamic equations are solved numerically to demonstrate the possibility of forming and sustaining a spheromak by forcing tangential flows at the plasma boundary. The method can be explained in terms of helicity injection. Several features previously observed in dc helicity injection experiments are reproduced and analyzed.
Striation and plasma bullet propagation in an atmospheric pressure plasma jet
Authors: Kim Sun Ja , Chung T. H. , Bae S. H.
Published: May 2010

An atmospheric pressure plasma jet source driven by pulsed wave of several tens of kilohertz and by sinusoidal wave was designed and characterized. A newly designed jet consists of a sharpened tungsten pin electrode covered with a cone type Teflon layer confined in a Pyrex tube. This structure provides an efficient ignition since the electric field is concentrated on the end of electrode. Using the electrical and optical characterization, the properties of plasma bullet were explored. For the Ar plasma jet driven by a pulsed wave at low duty cycles, the volume, the speed, and the luminosity of the plasma bullet became larger, and the striation behavior was observed.
Photonic band gap and x-ray optics in warm dense matter
Authors: Ku S. , Son S. , Moon Sung Joon
Published: May 2010

Photonic band gaps for the soft x rays, formed in the periodic structures of solids or dense plasmas, are theoretically investigated. Optical manipulation mechanisms for the soft x rays, which are based on these band gaps, are computationally demonstrated. The reflection and amplification of the soft x rays and the compression and stretching of chirped soft x-ray pulses are discussed. A scheme for lasing with atoms with two energy levels, utilizing the band gap, is also studied.
Impact of perovskite layer stacking on dielectric responses in KCa2Nan−3NbnO3n+1 (n=3–6) Dion–Jacobson homologous series
Authors: Li Bao-Wen , Osada Minoru , Ebina Yasuo , Ozawa Tadashi C. , Ma Renzhi , Sasaki Takayoshi
Published: May 2010

The dielectric properties of KCa2Nan−3NbnO3n+1 (n=3–6) Dion–Jacobson homologous series have been investigated. The dielectric constants (ε) increase with the number of octahedral units (n), and the n=6 compound (KCa2Na3Nb6O19) exhibits a stable dielectric response with ε=∼500 between 1 kHz and 1 MHz. This n-dependent behavior is similar to those observed in other layered perovskites such as Ruddlesden–Popper and Aurivillius phases. Raman scattering studies reveal that increase in n in KCa2Nan−3NbnO3n+1 leads to higher polarizability of the lattice and softening of the lowest-frequency phonon mode, which is responsible for the observed enhancement in ε with n.
Structures of diffusion regions in collisionless magnetic reconnection
Authors: Umeda Takayuki , Togano Kentaro , Ogino Tatsuki
Published: May 2010

Detailed structures of diffusion regions in two-dimensional collisionless magnetic reconnection are studied by using an electromagnetic Vlasov simulation. It has been well known that plasma number density decreases near the X-point of the reconnection. However, numerical thermal fluctuations exist in particle-in-cell simulations, and there is a possibility that detailed structures near the X-point diffuse numerically when the number of particles per cell is not enough. In the present study, a high-resolution two-dimensional Vlasov simulation is performed. It is found that electron number density in the electron diffusion region decreases to a hundredth of the initial value. Structures of electron diffusion region are determined by the local electron inertial length.
Structure and effective interactions in parallel monolayers of charged spherical colloids
Authors: Contreras-Aburto C. , Méndez-Alcaraz J. M. , Castañeda-Priego R.
Published: May 2010

We study the microstructure and the effective interactions of model suspensions consisting of Yukawa-like colloidal particles homogeneously distributed in equally spaced parallel planar monolayers. All the particles interact with each other, but particle transfer between monolayers is not allowed. The spacing between the layers defines the effective system dimensionality. When the layer spacing is comparable to the particle size, the system shows quasi-three-dimensional behavior, whereas for large distances the layers behave as effective two-dimensional systems. We find that effective attractions between like-charged particles can be triggered by adjusting the interlayer spacing, showing that the distance between adjacent layers is an excellent control parameter for the effective interparticle interactions. Our study is based on Brownian dynamics simulations and the integral equations theory of liquids. The effective potentials are accounted for by exploiting the invariance of the Ornstein–Zernike matrix equation under contractions of the description, and on assuming that the difference between bare and effective bridge functions can be neglected. We find that the hypernetted chain approximation does not account properly for the effective interactions in layered systems.
Effect of self-focusing on resonant third harmonic generation of laser in a rippled density plasma
Authors: Kaur Sukhdeep , Yadav Sushila , Sharma A. K.
Published: May 2010

Resonant third harmonic generation by a Gaussian laser beam in a rippled density plasma is studied. The laser ponderomotive force induces second harmonic longitudinal velocity on electrons that couples with the static density ripple to produce a density perturbation at 2ω,2k+q, where ω and k are the frequency and wave number of the laser and q is the ripple wave number of the laser. This density perturbation beats with electron oscillatory velocity at ω,k⃗ to produce a nonlinear current driving the third harmonic generation. In the regime of quadratic nonlinearity, the self-focusing of the laser enhances the third harmonic power. However, at higher intensity, plasma density is significantly reduced on the axis, detuning the third harmonic resonance and weakening the harmonic yield. Self-focusing causes enhancement in the efficiency of harmonic generation.
Thermal convective and rotational instability in dissipative magnetohydrodynamics
Authors: Ren Haijun , Wu Zhengwei , Dong Chao , Chu Paul K.
Published: May 2010

The thermal convective and magnetorotational instability is investigated by means of magnetohydrodynamic equations including anisotropic viscosity and resistivity dissipative effects. Magnetic force lines are assumed to be initially isothermal and the heat is restricted to being primarily transported along the magnetic force lines. To obtain the analytic expressions for the growth rate and instability criteria, we neglect the cross-field resistivity by applying our result to the weakly ionized environment. Under this assumption, the general dispersion relation describing the local thermal convective and magnetorotational instability is derived. The effects on the dispersion relation due to anisotropic resistivity and viscosity are discussed. Both the resistivity and viscosity show stabilizing effect on the thermal convective and rotational instability but do not affect the instability criterion. The analytic expression governing the growth rate is presented for Prandtl number Pm=1 case.
On the calculation of rotational anisotropy decay, as measured by ultrafast polarization-resolved vibrational pump-probe experiments
Authors: Lin Y.-S. , Pieniazek P. A. , Yang Mino , Skinner J. L.
Published: May 2010

Polarization-resolved vibrational pump-probe experiments are useful for measuring the dynamics of molecular reorientation. The rotational anisotropy observable is usually modeled by the second-Legendre-polynomial time-correlation function of the appropriate molecule-fixed unit vector. On the other hand, more elaborate calculations that include non-Condon effects, excited-state absorption, and spectral diffusion, can be performed using the infrastructure of the nonlinear response formalism. In this paper we present “exact” (within the impulsive limit) results from the nonlinear response formalism, and also a series of approximations that ultimately recover the traditional result mentioned above. To ascertain the importance of these effects not included in the traditional approach, we consider the specific case of dilute HOD in H2O. We find that for the frequency-integrated anisotropy decay, it is important to include non-Condon effects. For the frequency-resolved anisotropy decay, non-Condon effects, excited-state absorption, and spectral diffusion are all important. We compare our results with recent experiments.
Rotational dependence of the proton-transfer reaction HBr++CO2→HOCO++Br. I. Energy versus angular momentum effects
Authors: Paetow Lisa , Unger Franziska , Beichel Witali , Frenking Gernot , Weitzel Karl-Michael
Published: May 2010

Cross sections for the endothermic proton-transfer reactions of rotationally state-selected HBr+ and DBr+ ions with CO2 were measured in a guided ion beam apparatus in order to determine the influence of rotational excitation and collision energy in the center of mass (c.m.) system on the cross section. Ab initio calculations were performed to obtain energetic information about reactants, intermediates, and products. In the experiment HBr+ and DBr+ ions were prepared with the same mean rotational quantum number but different mean rotational energies as the rotational constants differ by about a factor of two. The mean rotational energy was varied from 1.4 to 66.3 meV for HBr+ and from 0.7 to 43.0 meV for DBr+. Collision energies (Ec.m.) ranged from 0.32 to 1.00 eV. Under all conditions considered, an increase in the rotational excitation leads to a decrease in the cross section for both reactions. However, the effect is more pronounced for the higher collision energies. For Ec.m.=1.00 and 0.85 eV; a comparison between the results for HBr+ and DBr+ indicates that the cross section is dominated by effects of rotational energy rather than angular momentum. For lower collision energies the cross sections for the deuteron transfer and the proton transfer are in best agreement if not compared for the same c.m. collision energy but for the same value of the difference between the collision energy and the reaction enthalpy.
The role of elastic flap deformation on fluid mixing in a microchannel
Authors: Lambert Ruth A. , Rangel Roger H.
Published: May 2010

We explore the capacity of a flexible flap to increase mixing in a microchannel for a flap Reynolds number Ref ranging from 0.3–80. The fictitious-domain (DLM) method is used to model the fluid and solid interactions. The momentum equations for the fluid and solid are solved individually using the finite-volume and finite-difference methods. The equations are coupled using distributed Lagrange multipliers. The stress in the solid is derived from the nonlinear beam equations. Fluid mixing is quantified by solving the mass transport equation for a solute with low molecular diffusivity and calculating a global mixing fraction M. The flap is actuated using a distributed follower force along the length of the flap. The results show that mixing is enhanced for larger flap displacements and for dimensionless frequencies Sl between 1 and 2. Optimal mixing occurs when the flap length is 2/3 the microchannel height. The influence of the hydrodynamic force on the beam bending motion enhances the mixing process. Under optimal conditions the flap behaves as a rapid mixing device where 80% of the long time mixing fraction is reached during an initial time interval of 3.8 s.
Effects of patch size and number within a simple model of patchy colloids
Authors: Giacometti Achille , Lado Fred , Largo Julio , Pastore Giorgio , Sciortino Francesco
Published: May 2010

We report on a computer simulation and integral equation study of a simple model of patchy spheres, each of whose surfaces is decorated with two opposite attractive caps, as a function of the fraction χ of covered attractive surface. The simple model explored—the two-patch Kern–Frenkel model—interpolates between a square-well and a hard-sphere potential on changing the coverage χ. We show that integral equation theory provides quantitative predictions in the entire explored region of temperatures and densities from the square-well limit χ=1.0 down to χ≈0.6. For smaller χ, good numerical convergence of the equations is achieved only at temperatures larger than the gas-liquid critical point, where integral equation theory provides a complete description of the angular dependence. These results are contrasted with those for the one-patch case. We investigate the remaining region of coverage via numerical simulation and show how the gas-liquid critical point moves to smaller densities and temperatures on decreasing χ. Below χ≈0.3, crystallization prevents the possibility of observing the evolution of the line of critical points, providing the angular analog of the disappearance of the liquid as an equilibrium phase on decreasing the range for spherical potentials. Finally, we show that the stable ordered phase evolves on decreasing χ from a three-dimensional crystal of interconnected planes to a two-dimensional independent-planes structure to a one-dimensional fluid of chains when the one-bond-per-patch limit is eventually reached.
Asymptotic solution of Fokker–Planck equation for plasma in Paul traps
Authors: Shah Kushal
Published: May 2010

An exact analytic solution of the Vlasov equation for the plasma distribution in a Paul trap is known to be a Maxwellian and thus, immune to collisions under the assumption of infinitely fast relaxation [K. Shah and H. S. Ramachandran, Phys. Plasmas 15, 062303 (2008)]. In this paper, it is shown that even for a more realistic situation of finite time relaxation, solutions of the Fokker–Planck equation lead to an equilibrium solution of the form of a Maxwellian with oscillatory temperature. This shows that the rf heating observed in Paul traps cannot be caused due to collisional effects alone.
Study on structures and properties of ammonia clusters (NH3)n (n=1–5) and liquid ammonia in terms of ab initio method and atom-bond electronegativity equalization method ammonia-8P fluctuating charge potential model
Authors: Yu Ling , Yang Zhong-Zhi
Published: May 2010

Structures, binding energies, and vibrational frequencies of (NH3)n (n=2–5) isomers and dynamical properties of liquid ammonia have been explored using a transferable intermolecular potential eight point model including fluctuating charges and flexible body based on a combination of the atom-bond electronegativity equalization and molecular (ABEEM) mechanics (ABEEM ammonia-8P) in this paper. The important feature of this model is to divide the charge sites of one ammonia molecule into eight points region containing four atoms, three σ bonds, and a lone pair, and allows the charges in system to fluctuate responding to the ambient environment. Due to the explicit descriptions of charges and special treatment of hydrogen bonds, the results of equilibrium geometries, dipole moments, cluster interaction energies, vibrational frequencies for the gas phase of small ammonia clusters, and radial distribution function for liquid ammonia calculated with the ABEEM ammonia-8P potential model are in good agreement with those measured by available experiments and those obtained from high level ab initio calculations. The properties of ammonia dimer are studied in detail involving the structure and one-dimensional, two-dimensional potential energy surface. As for interaction energies, the root mean square deviation is 0.27 kcal/mol, and the linear correlation coefficient reaches 0.994.
Mesoscale hydrodynamics via stochastic rotation dynamics: Comparison with Lennard-Jones fluid
Authors: Petersen Matt K. , Lechman Jeremy B. , Plimpton Steven J. , Grest Gary S. , in ’t Veld Pieter J. , Schunk P. R.
Published: May 2010

Stochastic rotation dynamics (SRD) is a relatively recent technique, closely related to lattice Boltzmann, for capturing hydrodynamic fluid flow at the mesoscale. The SRD method is based on simple constituent fluid particle interactions and dynamics. Here we parametrize the SRD fluid to provide a one to one match in the shear viscosity of a Lennard-Jones fluid and present viscosity measurements for a range of such parameters. We demonstrate how to apply the Müller-Plathe reverse perturbation method for determining the shear viscosity of the SRD fluid and discuss how finite system size and momentum exchange rates effect the measured viscosity. The implementation and performance of SRD in a parallel molecular dynamics code is also described.
Measurement of diffusion and thermal diffusion in ternary fluid mixtures using a two-color optical beam deflection technique
Authors: Königer A. , Wunderlich H. , Köhler W.
Published: May 2010

We have developed a highly sensitive two-color beam deflection setup to measure diffusion and thermal diffusion in ternary fluid mixtures following a suggestion of Haugen and Firoozabadi [J. Phys. Chem. B 110, 17678 (2006)]. Simultaneous detection of two laser beams with different wavelengths makes it possible to determine the time dependent concentration profiles of all three components. By comparing the measured beam deflection signals to a numerical solution of the coupled heat and mass transport equations, the diffusion matrix, the thermal diffusion, and the Soret coefficients are obtained by a numerical model combined with a nonlinear least-squares fitting routine. The results can be improved by additional thermal diffusion forced Rayleigh scattering experiments, which yield a contrast-weighted average thermal diffusion coefficient. The three Soret coefficients can be obtained independently from the stationary beam deflection amplitudes. Measurements have been performed on the symmetric (equal weight fractions) ternary mixtures dodecane/isobutylbenzene/1,2,3,4-tetrahydronaphthalene and 1-methylnaphthalene/octane/decane. There is only partial agreement between our results and literature data.
The impact of the Fermi–Dirac distribution on charge injection at metal/organic interfaces
Authors: Wang Z. B. , Helander M. G. , Greiner M. T. , Lu Z. H.
Published: May 2010

The Fermi level has historically been assumed to be the only energy-level from which carriers are injected at metal/semiconductor interfaces. In traditional semiconductor device physics, this approximation is reasonable as the thermal distribution of delocalized states in the semiconductor tends to dominate device characteristics. However, in the case of organic semiconductors the weak intermolecular interactions results in highly localized electronic states, such that the thermal distribution of carriers in the metal may also influence device characteristics. In this work we demonstrate that the Fermi–Dirac distribution of carriers in the metal has a much more significant impact on charge injection at metal/organic interfaces than has previously been assumed. An injection model which includes the effect of the Fermi–Dirac electron distribution was proposed. This model has been tested against experimental data and was found to provide a better physical description of charge injection. This finding indicates that the thermal distribution of electronic states in the metal should, in general, be considered in the study of metal/organic interfaces.