bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical investigation of coherent structures and mass exchange processes in channel flow with two lateral submerged groynes
Authors: McCoy Andrew , Constantinescu George , Weber Larry
Published: May 2007

Large eddy simulation is used to investigate the dynamics of the main coherent structures present in the flow around two vertical submerged groynes situated in a long flatbed open channel. The mass exchange processes between the embayment region and the main channel are investigated by studying the ejection of a contaminant introduced instantaneously inside the embayment. The instantaneous and mean structure of the horseshoe vortex system forming at the base of the upstream groyne and the bed shear distributions that determine the evolution of the scour in the groyne region are investigated. It is found that the amplification of the bed shear stress in the accelerating region around the tip of the upstream groyne is around one order of magnitude larger relative to the mean bed shear stress in the incoming flow. Analysis of the instantaneous flow fields shows that the eddies that are shed inside the horizontal and vertical detached shear layers play an important role in controlling the mass exchange at the lateral and roof interfaces. It is found that most of the pollutant leaves the embayment through the roof and bottom lateral sections. The overall mass exchange process is qualitatively different and substantially accelerated compared to the case when the groynes are emerged. However, it is shown that similar to the emerged case, the decay of the mass of contaminant within the embayment cannot be characterized by a unique value of the exchange coefficient used in simple dead zone theory models.
Modeling reference evapotranspiration over complex terrains from minimum climatological data
Authors: Diodato Nazzareno , Bellocchi Gianni
Published: May 2007

This work presents methods where monthly based climate data are used to estimate reference evapotranspiration (ET0). The objective was to evaluate two monthly ET0 models (Hargreaves‐Samani, HS; Droogers‐Allen HS, DAHS) and compare the results with an improved model (reference evapotranspiration model for complex terrains, REMCT). HS and DAHS are both based on the monthly temperature range (ΔT), while REMCT replaces ΔT with a monthly adjusted function (reference minimum air temperature). The test area was peninsular‐insular Italy, where 13 stations with sufficient data to calculate FAO‐56 Penman‐Monteith ET0 were available. The three models were evaluated against FAO‐56 over a validation data set of six stations, using a multiple‐statistics indicator: 0 (best) ≤ IET ≤ 1 (worst). The REMCT estimates generally compared well with the FAO‐56 estimates (mean IET = 0.029 against 0.187 and 0.255 with HS and DAHS, respectively). The three models performed similarly at low‐altitude sites. REMCT was superior at sites higher than 500 m above sea level, where the ET0 − ΔT relationship was distorted (e.g., by an asymmetric lapse rate between maximum and minimum air temperatures).
Bystin in human cancer cells: intracellular localization and function in ribosome biogenesis
Authors: Miyoshi Masaya , Okajima Tetsuya , Matsuda Tsukasa , Fukuda Michiko N. , Nadano Daita
Published: May 2007

Although bystin has been identified as a protein potentially involved in embryo implantation (a process unique to mammals) in humans, the bystin gene is evolutionarily conserved from yeast to humans. DNA microarray data indicates that bystin is overexpressed in human cancers, suggesting that it promotes cell growth. We undertook RT (reverse transcription)–PCR and immunoblotting, and confirmed that bystin mRNA and protein respectively are expressed in human cancer cell lines, including HeLa. Subcellular fractionation identified bystin protein as nuclear and cytoplasmic, and immunofluorescence showed that nuclear bystin localizes mainly in the nucleolus. Sucrose gradient ultracentrifugation of total cytoplasmic ribosomes revealed preferential association of bystin with the 40S subunit fractions. To analyse its function, bystin expression in cells was suppressed by RNAi (RNA interference). Pulse–chase analysis of ribosomal RNA processing suggested that bystin knockdown delays processing of 18S ribosomal RNA, a component of the 40S subunit. Furthermore, this knockdown significantly inhibited cell proliferation. Our findings suggest that bystin may promote cell proliferation by facilitating ribosome biogenesis, specifically in the production of the 40S subunit. Localization of bystin to the nucleolus, the site of ribosome biogenesis, was blocked by low concentrations of actinomycin D, a reagent that causes nucleolar stress. When bystin was transiently overexpressed in HeLa cells subjected to nucleolar stress, nuclear bystin was included in particles different from the nuclear stress granules induced by heat shock. In contrast, cytoplasmic bystin was barely affected by nucleolar stress. These results suggest that, while bystin may play multiple roles in mammalian cells, a conserved function is to facilitate ribosome biogenesis required for cell growth.
Autophosphorylation-dependent degradation of Pak1, triggered by the Rho-family GTPase, Chp
Authors: Weisz Hubsman Monika , Volinsky Natalia , Manser Edward , Yablonski Deborah , Aronheim Ami
Published: May 2007

The Paks (p21-activated kinases) Pak1, Pak2 and Pak3 are among the most studied effectors of the Rho-family GTPases, Rac, Cdc42 (cell division cycle 42) and Chp (Cdc42 homologous protein). Pak kinases influence a variety of cellular functions, but the process of Pak down-regulation, following activation, is poorly understood. In the present study, we describe for the first time a negative-inhibitory loop generated by the small Rho-GTPases Cdc42 and Chp, resulting in Pak1 inhibition. Upon overexpression of Chp, we unexpectedly observed a T-cell migration phenotype consistent with Paks inhibition. In line with this observation, overexpression of either Chp or Cdc42 caused a marked reduction in the level of Pak1 protein in a number of different cell lines. Chp-induced degradation was accompanied by ubiquitination of Pak1, and was dependent on the proteasome. The susceptibility of Pak1 to Chp-induced degradation depended on its p21-binding domain, kinase activity and a number of Pak1 autophosphorylation sites, whereas the PIX- (Pak-interacting exchange factor) and Nck-binding sites were not required. Together, these results implicate Chp-induced kinase autophosphorylation in the degradation of Pak1. The N-terminal domain of Chp was found to be required for Chp-induced degradation, although not for Pak1 activation, suggesting that Chp provides a second function, distinct from kinase activation, to trigger Pak degradation. Collectively, our results demonstrate a novel mechanism of signal termination mediated by the Rho-family GTPases Chp and Cdc42, which results in ubiquitin-mediated degradation of one of their direct effectors, Pak1.
PhosphoethanolamineN-methyltransferase (PMT-1) catalyses the first reaction of a new pathway for phosphocholine biosynthesis inCaenorhabditis elegans
Authors: Brendza Katherine M. , Haakenson William , Cahoon Rebecca E. , Hicks Leslie M. , Palavalli Lavanya H. , Chiapelli Brandi J. , McLaird Merry , McCarter James P. , Williams D. Jeremy , Hresko Michelle C. , Jez Joseph M.
Published: May 2007

The development of nematicides targeting parasitic nematodes of animals and plants requires the identification of biochemical targets not found in host organisms. Recent studies suggest that Caenorhabditis elegans synthesizes phosphocholine through the action of PEAMT (S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferases) that convert phosphoethanolamine into phosphocholine. Here, we examine the function of a PEAMT from C. elegans (gene: pmt-1; protein: PMT-1). Our analysis shows that PMT-1 only catalyses the conversion of phosphoethanolamine into phospho-monomethylethanolamine, which is the first step in the PEAMT pathway. This is in contrast with the multifunctional PEAMT from plants and Plasmodium that perform multiple methylations in the pathway using a single enzyme. Initial velocity and product inhibition studies indicate that PMT-1 uses a random sequential kinetic mechanism and is feedback inhibited by phosphocholine. To examine the effect of abrogating PMT-1 activity in C. elegans, RNAi (RNA interference) experiments demonstrate that pmt-1 is required for worm growth and development and validate PMT-1 as a potential target for inhibition. Moreover, providing pathway metabolites downstream of PMT-1 reverses the RNAi phenotype of pmt-1. Because PMT-1 is not found in mammals, is only distantly related to the plant PEAMT and is conserved in multiple parasitic nematodes of humans, animals and crop plants, inhibitors targeting it may prove valuable in human and veterinary medicine and agriculture.
The reductase NCB5OR is responsive to the redox status in β-cells and is not involved in the ER stress response
Authors: Larade Kevin , Jiang Zhi-gang , Dejam Andre , Zhu Hao , Bunn H. Franklin
Published: May 2007

The novel reductase NCB5OR (NADPH cytochrome b5 oxidoreductase) resides in the ER (endoplasmic reticulum) and may protect cells against ER stress. Levels of BiP (immunoglobulin heavy-chain-binding protein), CHOP (CCAAT/enhancer-binding protein homologous protein) and XBP-1 (X-box-binding protein-1) did not differ in WT (wild-type) and KO (Ncb5or-null) tissues or MEFs (mouse embryonic fibroblasts), and XBP-1 remained unspliced. MEFs treated with inducers of ER stress demonstrated no change in Ncb5or expression and expression of ER-stress-induced genes was not enhanced. Induction of ER stress in β-cell lines did not change Ncb5or expression or promoter activity. Transfection with Ncb5or-specific siRNA (small interfering RNA) yielded similar results. Microarray analysis of mRNA from islets and liver of WT and KO animals revealed no significant changes in ER-stress-response genes. Induction of oxidative stress in βTC3 cells did not alter Ncb5or mRNA levels or promoter activity. However, KO islets were more sensitive to streptozotocin when compared with WT islets. MEFs incubated with nitric oxide donors showed no difference in cell viability or levels of nitrite produced. No significant differences in mRNA expression of antioxidant enzymes were observed when comparing WT and KO tissues; however, microarray analysis of islets indicated slightly enhanced expression of some antioxidant enzymes in the KO islets. Short-term tBHQ (t-butylhydroquinone) treatment increased Ncb5or promoter activity, although longer incubation times yielded a dose-dependent decrease in activity. This response appears to be due to a consensus ARE (antioxidant-response element) present in the Ncb5or promoter. In summary, NCB5OR does not appear to be involved in ER stress, although it may be involved in maintaining or regulating the redox status in β-cells.
The protective and destructive roles played by molecular chaperones during ERAD (endoplasmic-reticulum-associated degradation)
Authors: Brodsky Jeffrey L.
Published: May 2007

Over one-third of all newly synthesized polypeptides in eukaryotes interact with or insert into the membrane or the lumenal space of the ER (endoplasmic reticulum), an event that is essential for the subsequent folding, post-translational modification, assembly and targeting of these proteins. Consequently, the ER houses a large number of factors that catalyse protein maturation, but, in the event that maturation is aborted or inefficient, the resulting aberrant proteins may be selected for ERAD (ER-associated degradation). Many of the factors that augment protein biogenesis in the ER and that mediate ERAD substrate selection are molecular chaperones, some of which are heat- and/or stress-inducible and are thus known as Hsps (heat-shock proteins). But, regardless of whether they are constitutively expressed or are inducible, it has been assumed that all molecular chaperones function identically. As presented in this review, this assumption may be false. Instead, a growing body of evidence suggests that a chaperone might be involved in either folding or degrading a given substrate that transits through the ER. A deeper appreciation of this fact is critical because (i) the destruction of some ERAD substrates results in specific diseases, and (ii) altered ERAD efficiency might predispose individuals to metabolic disorders. Moreover, a growing number of chaperone-modulating drugs are being developed to treat maladies that arise from the synthesis of a unique mutant protein; therefore it is critical to understand how altering the activity of a single chaperone will affect the quality control of other nascent proteins that enter the ER.
Synaptophysin I selectively specifies the exocytic pathway of synaptobrevin 2/VAMP2
Authors: Bonanomi Dario , Rusconi Laura , Colombo Chiara Agnese , Benfenati Fabio , Valtorta Flavia
Published: May 2007

Biogenesis and recycling of synaptic vesicles are accompanied by sorting processes that preserve the molecular composition of the compartments involved. In the present study, we have addressed the targeting of synaptobrevin 2/VAMP2 (vesicle-associated membrane protein 2), a critical component of the synaptic vesicle­-fusion machinery, in a heterotypic context where its sorting is not confounded by the presence of other neuron-specific molecules. Ectopically expressed synaptophysin I interacts with VAMP2 and alters its default surface targeting to a prominent vesicular distribution, with no effect on the targeting of other membrane proteins. Protein–protein interaction is not sufficient for the control of VAMP2 sorting, which is mediated by the C-terminal domain of synaptophysin I. Synaptophysin I directs the sorting of VAMP2 to vesicles before surface delivery, without influencing VAMP2 endocytosis. Consistent with this, dynamin and α-SNAP (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein) mutants which block trafficking at the plasma membrane do not abrogate the effect of synaptophysin I on VAMP2 sorting. These results indicate that the sorting determinants of synaptic vesicle proteins can operate independently of a neuronal context and implicate the association of VAMP2 with synaptophysin I in the specification of the pathway of synaptic vesicle biogenesis.
Evidence for functional redundancy of class IA PI3K isoforms in insulin signalling
Authors: Chaussade Claire , Rewcastle Gordon W. , Kendall Jackie D. , Denny William A. , Cho Kitty , Grønning Line M. , Chong Mei Ling , Anagnostou Sasha H. , Jackson Shaun P. , Daniele Nathalie , Shepherd Peter R.
Published: May 2007

Recent genetic knock-in and pharmacological approaches have suggested that, of class IA PI3Ks (phosphatidylinositol 3-kinases), it is the p110α isoform (PIK3CA) that plays the predominant role in insulin signalling. We have used isoform-selective inhibitors of class IA PI3K to dissect further the roles of individual p110 isoforms in insulin signalling. These include a p110α-specific inhibitor (PIK-75), a p110α-selective inhibitor (PI-103), a p110β-specific inhibitor (TGX-221) and a p110δ-specific inhibitor (IC87114). Although we find that p110α is necessary for insulin-stimulated phosphorylation of PKB (protein kinase B) in several cell lines, we find that this is not the case in HepG2 hepatoma cells. Inhibition of p110β or p110δ alone was also not sufficient to block insulin signalling to PKB in these cells, but, when added in combination with p110α inhibitors, they are able to significantly attenuate insulin signalling. Surprisingly, in J774.2 macrophage cells, insulin signalling to PKB was inhibited to a similar extent by inhibitors of p110α, p110β or p110δ. These results provide evidence that p110β and p110δ can play a role in insulin signalling and also provide the first evidence that there can be functional redundancy between p110 isoforms. Further, our results indicate that the degree of functional redundancy is linked to the relative levels of expression of each isoform in the target cells.
Chemical structure of the cell-wall mannan of Candida albicans serotype A and its difference in yeast and hyphal forms
Authors: Shibata Nobuyuki , Suzuki Akifumi , Kobayashi Hidemitsu , Okawa Yoshio
Published: May 2007

The structure of the cell-wall mannan from the J-1012 (serotype A) strain of the polymorphic yeast Candida albicans was determined by acetolysis under mild conditions followed by HPLC and sequential NMR experiments. The serotype A mannan contained β-1,2-linked mannose residues attached to α-1,3-linked mannose residues and α-1,6-linked branching mannose residues. Using a β-1,2-mannosyltransferase, we synthesized a three-β-1,2-linkage-containing mannoheptaose and used it as a reference oligosaccharide for 1H-NMR assignment. On the basis of the results obtained, we derived an additivity rule for the 1H-NMR chemical shifts of the β-1,2-linked mannose residues. The morphological transformation of Candida cells from the yeast form to the hyphal form induced a significant decrease in the phosphodiesterified acid-labile β-1,2-linked manno-oligosaccharides, whereas the amount of acid-stable β-1,2 linkage-containing side chains did not change. These results suggest that the Candida mannan in candidiasis patients contains β-1,2-linked mannose residues and that they behave as a target of the immune system.
Temporal Intraspeech Masking of Plosive Bursts: Effects of Hearing Loss and Frequency Shaping
Authors: Mackersie Carol L.
Published: May 2007

Purpose

The purposes were (a) to compare masking of consonant bursts by adjacent vowels for listeners with and without hearing loss and (b) to determine the extent to which the temporal intraspeech masking can be reduced by a simulated hearing-aid frequency-response shaping.

Method

Fourteen adults with sensorineural hearing loss and 10 with normal hearing participated. Seven of the participants with hearing loss had flat or gradually sloping audiograms, and 7 had steeply sloping losses. Stimuli consisted of 3 consonant bursts (/t/, /p/, /k/) presented in isolation and in vowel-consonant-vowel combinations using the vowel /a/ with formant transition information removed. Normal-hearing listeners were tested using unfiltered stimuli. Listeners with hearing loss were tested using unfiltered stimuli and stimuli filtered to approximate a hearing aid frequency response prescribed by NAL-R. All listeners were tested under earphones at the most comfortable level for the vowel stimulus. Temporal intraspeech masking was quantified as the threshold shift produced by the adjacent vowels.

Results

Average intraspeech masking for listeners with steeply sloping hearing loss was significantly higher than that of normal-hearing listeners and those with flat/gradually sloping losses. Greater intraspeech masking was observed for /t/ and /p/ than for /k/. On average, frequency shaping significantly reduced the amount of intraspeech masking for listeners with steeply sloping hearing losses. Even with appropriate amplification/spectral shaping, however, temporal intraspeech masking remained greater than normal for several individuals.

Conclusion

Findings suggest that some individuals with steeply sloping losses may need additional signal processing to supplement frequency shaping to overcome the effect of temporal intraspeech masking.
Effects of Cueing in Auditory Temporal Masking
Authors: Zhang Ting , Formby Craig
Published: May 2007

Purpose

In a landmark study, B. A. Wright et al. (1997) reported an apparent backward-masking deficit in language-learning-impaired children. Subsequently, the controversial interpretation of those results has been influential in guiding treatments for childhood language problems. This study revisited the temporal-masking paradigm reported by B. A. Wright et al. to evaluate adult listener signal/masker uncertainty effects for some of their key stimulus conditions. New signal conditions presented off frequency from the masker also were evaluated to assess conditions of reduced signal/masker confusion.

Method

Masked detection was measured for 20-ms sinusoids (480, 1000, or 1680 Hz) presented at temporal positions before, during, or after a gated narrowband (bandwidth = 600–1400 Hz) masker. Listener uncertainty was investigated by cueing various stimulus temporal properties with a 6000-Hz sinusoid presented contralateral to the test ear.

Results

The primary cueing effect was measured in the backward-masking condition for the cue gated simultaneously with the on-frequency 1000-Hz signal. The resulting cued masked-detection threshold was reduced to quiet threshold. No significant cueing effects were obtained for other signal temporal positions in the masker or for any off-frequency signal conditions.

Conclusions

These results for normal adult listeners indicate that on-frequency backward masking can be eliminated by cueing the signal, and thus, these findings raise the possibility that the deficit reported by B. A. Wright et al. for language-learning-impaired children may reflect inordinate signal/masker confusion, rather than a temporal-processing deficit per se.
Basic Auditory Processing Skills and Specific Language Impairment: A New Look at an Old Hypothesis
Authors: Corriveau Kathleen , Pasquini Elizabeth , Goswami Usha
Published: May 2007

Purpose

To explore the sensitivity of children with specific language impairment (SLI) to amplitude-modulated and durational cues that are important for perceiving suprasegmental speech rhythm and stress patterns.

Method

Sixty-three children between 7 and 11 years of age were tested, 21 of whom had a diagnosis of SLI, 21 of whom were matched for chronological age to the SLI sample, and 21 of whom were matched for language age to the SLI sample. All children received a battery of nonspeech auditory processing tasks along with standardized measures of phonology and language.

Results

As many as 70%–80% of children diagnosed with SLI were found to perform below the 5th percentile of age-matched controls in auditory processing tasks measuring sensitivity to amplitude envelope rise time and sound duration. Furthermore, individual differences in sensitivity to these cues predicted unique variance in language and literacy attainment, even when age, nonverbal IQ, and task-related (attentional) factors were controlled.

Conclusion

Many children with SLI have auditory processing difficulties, but for most children, these are not specific to brief, rapidly successive acoustic cues. Instead, sensitivity to durational and amplitude envelope cues appear to predict language and literacy outcomes more strongly. This finding now requires replication and exploration in languages other than English.
Fast Mapping Skills in the Developing Lexicon
Authors: Gershkoff-Stowe Lisa , Hahn Erin R.
Published: May 2007

Purpose

This preliminary investigation was a longitudinal study of fast mapping skills in normally developing children, 16–18 months of age. The purpose was to examine the effects of practice on the accessibility of words in lexical memory.

Method

Eight children were taught the names of 24 unfamiliar objects over 12 weekly training sessions. The amount of practice children had with individual words varied as a function of session. Data were compared to a control group of children—matched on productive vocabulary—who were exposed to the same experimental words at the first and last sessions only.

Results

The results showed that for children in the experimental group, extended practice with a novel set of high-practice words led to the rapid acquisition of a second set of low-practice words. Children in the control group did not show the same lexical advantage.

Conclusions

The data suggest that learning some words primes the system to learn more words. Vocabulary development can thus be conceptualized as a continual process of fine-tuning the lexical system to enable increased accessibility to information. Implications for the treatment of children with word-finding difficulties are considered.
Intrinsic ferromagnetism versus phase segregation in Mn-doped Ge
Authors: Biegger E. , Stäheli L. , Fonin M. , Rüdiger U. , Dedkov Yu. S.
Published: May 2007

We report on a detailed study of structural, magnetic, and electronic properties of MnxGe1−x single crystals (0<x<0.1) prepared by the Bridgman’s crystal growth technique. The chemical distribution of Mn in a Ge matrix investigated by means of energy dispersive x-ray spectroscopy indicates a strong phase separation in the Ge/Mn system. Temperature-dependent magnetization [M(T)] measurements performed on the Mn-poor part containing 1%–3% of Mn reveal magnetic properties similar to those of a Mn11Ge8 reference sample as well as to those of the highly inhomogeneous Mn-rich parts of the sample. X-ray absorption spectroscopy (XAS) at the Mn L2,3 absorption edge shows that Mn ions in Mn-rich and Mn-poor parts are in the divalent high-spin state. Resonant valence-band photoelectron spectroscopy (ResPES) was performed at the Mn 2p3∕2 absorption edge for the Mn-poor part. The obtained Mn 3d PDOS shows a feature centered at 4.8 eV which is characteristic for the Mn5Ge3 phase. We identify the formation of ferromagnetic intermetallic compounds as the most possible origin of ferromagnetism in both Mn-rich and Mn-poor regions of the MnxGe1−x samples.
Effect of high pressure on the magnetocaloric property of LaFe11.5Si1.5
Authors: Jia L. , Sun J. R. , Shen B. G. , Li D. X. , Nimori S.
Published: May 2007

A field-induced magnetic entropy change under high pressure has been experimentally studied for the LaFe11.5Si1.5 compound. High pressure causes a linear decrease of the Curie temperature from ~194 to ~88 K, corresponding to a variation of the pressure from ~0 to 1 GPa. Appropriate pressures enhance the magnetic entropy change significantly in the meantime depressing the Curie temperature. A spike-shaped peak, followed by a plateau with a width of ~20 K, of the entropy change emerges and grows rapidly with the increase of pressure, and its maximum value is 138 J∕kg K, obtained under the pressure of 1 GPa for a field change of 0−5 T. The pressure effect is also obvious on the entropy plateau. It results in an increase of the plateau height from ~23.8 J∕kg K, without pressure, to ~29 J∕kg K, when the pressure is 0.45 GPa. These results demonstrate the effectiveness of high pressure in modifying the entropy of LaFe11.5Si1.5.
Characterization and microwave resonance in nanocrystalline FeCoNi flake composite
Authors: Deng L. J. , Zhou P. H. , Xie J. L. , Zhang L.
Published: May 2007

To explore the resonance mechanism of nanocrystalline FeCoNi flake composites, characterization of the flakes was investigated. The structural and magnetic properties of flakes manifestly tailored the features of microwave permeability spectrum of flake composites, relating to the physical effects of nanograins. The exchange mode with a few modifications was used to explain the origin of composite microwave performance, and the computed results were close to the experiment. It is believed that the exchange energy, dominating in the microwave resonance of spherical nanoparticles, plays an equally important role in nanocrystalline flakes.
Magnetoresistance in granular CrO2: Effects of variation in crystallographic and magnetic microstructure
Authors: Bajpai A. , Nigam A. K.
Published: May 2007

We report magnetotransport measurements up to 5 Tesla on high purity sintered samples of granular CrO2 with a significantly enhanced grain size. The negative magnetoresistance (MR) as derived from RH isotherms is observed to be unhysteretic up to temperatures as high as 200 K. RH isotherms exhibit some unusual features between 240 and 290 K, including a positive MR and strong pinning effects. These features disappear above 290 K and are apparently related with the magnetic state of the insulating grain boundary. Qualitatively similar features with significantly enhanced MR are also observed when CrO2 is diluted with two antiferromagnetic oxides, Cr2O3 or Cr2O5. These results bring out the role played by the magnetic and crystallographic microstructure on the magnitude, sign, and hysteresis of the magnetoresistance in this technologically important material.
Role of substrate bias on the magnetic properties and microstructure of CoCrPt:SiO2 perpendicular recording media
Authors: Piramanayagam S. N. , Mah C. S. , Ong C. Y. , Shi J. Z. , Dumaya Jo Alvin , Onoue T. , Ishibashi S.
Published: May 2007

The role of substrate bias during the sputter deposition of various layers of double-layered CoCrPt−SiO2 perpendicular recording media has been investigated in order to understand the physical mechanisms behind the various effects observed. Perpendicular recording media with dual Ru intermediate layers were investigated using several magnetic and microstructural characterization techniques. It was observed that, in general, the application of a bias voltage during the deposition of the seedlayer (Ta) and the first intermediate layer (Ru) is helpful in reducing the c-axis dispersion of the recording layer. For the other layers, application of bias voltage leads to deterioration in the magnetic properties. It was also observed that the application of a bias voltage during the deposition of the first intermediate layer (especially Ru) may not enhance the preferred growth of Ru hexagonal-close-packed (00.2) planes parallel to the disk surface, as predicted before. However, the bias voltage on the Ru layer still reduces the c-axis dispersion of the magnetic layer. From the omega-offset x-ray diffraction investigations, it is estimated that the lattice parameter “a” of the Ru layer is reduced slightly with bias voltage, which could probably lead to a reduction in the lattice mismatch between the Ru layer and Co-alloy layer. Bias conditions also could lead to improved interface condition. Such an improvement in the lattice matching or interface conditions could probably be the cause of the reduction of c-axis dispersion of the recording layer.
Propagation of thermal waves in multilayered spheres
Authors: Madariaga Nora , Salazar Agustín
Published: May 2007

In the last years there has been a growing interest in the application of photothermal techniques to samples with nonflat surfaces, in particular cylinders and spheres. In this work the surface temperature oscillation of multilayered spherical samples which are heated by a modulated light beam is calculated by using the quadrupole method. Several illumination geometries have been studied. Moreover, the lack of adherence between layers, as well as heat losses at the surface, has been considered in the model. This theoretical approach allows photothermal techniques to be used to characterize the thermal properties of spherical samples with continuously varying in-depth thermal conductivity.
Characteristics of flow over traveling wavy foils in a side-by-side arrangement
Authors: Dong Gen-Jin , Lu Xi-Yun
Published: May 2007

Flow over traveling wavy foils in a side-by-side arrangement has been numerically investigated using the space-time finite element method to solve the two-dimensional incompressible Navier-Stokes equations. The midline of each foil undergoes lateral motion in the form of a streamwise traveling wave, which is similar to the backbone undulation of swimming fish. Based on the phase difference between the adjacent undulating foils, two typical cases, i.e., in-phase and anti-phase traveling wavy movements, are considered in the present study. The effects of lateral interference among the foils on the forces, power consumption, propeller efficiency, and flow structures are analyzed. It is revealed that the lateral interference is of benefit to saving the swimming power in the in-phase case and enhancing the forces in the anti-phase case. Some typical vortex structures, e.g., vortex-pair row, single vortex row, and in-phase and anti-phase synchronized vortex-street, are observed in the wake of the traveling wavy foils. The results obtained in this study provide physical insight into the understanding of hydrodynamics and flow structures for flow over the traveling wavy foils and swimming mechanisms relevant to fish schooling.
Car-Parrinello simulation of an O–H stretching envelope and potential of mean force of an intramolecular hydrogen bonded system: Application to a Mannich base in solid state and in vacuum
Authors: Jezierska Aneta , Panek Jarosław J. , Koll Aleksander , Mavri Janez
Published: May 2007

Car-Parrinello molecular dynamics (CPMD) study was performed for an anharmonic system—an intramolecularly hydrogen bonded Mannich-base-type compound, 4,5-dimethyl-2(N,N-dimethylaminemethyl)phenol, to investigate the vibrational spectrum associated with the O–H stretching. Calculations were carried out for the solid state and for an isolated molecule. The classical CPMD simulation was performed and then the proton potential snapshots were extracted from the trajectory. The vibrational Schrödinger equation for the snapshots was solved numerically, and the (O–H) envelope was calculated as a superposition of the 0→1 transitions. The potential of mean force for the proton stretching mode was calculated from the proton vibrational eigenfunctions and eigenvalues incorporating statistical sampling, nuclear quantum effects, and effects of the environment. Perspectives for application of the presented methodology in the computational support of biocatalysis are given in the study.
Interdiffusion in narrow InGaAsN∕GaAs quantum wells
Authors: Liu W. , Zhang D. H. , Huang Z. M. , Wang S. Z. , Yoon S. F. , Fan W. J. , Liu C. J. , Wee A. T. S.
Published: May 2007

Interdiffusion in In0.32Ga0.68As0.984N0.016∕GaAs multiple quantum wells with well widths of 2 and 4nm, respectively, was investigated both experimentally and theoretically. Maximum blueshifts of 206 and 264meV in the photoluminescence spectra were observed. Secondary ion mass spectrometry showed that both In–Ga and N–As interdiffusions played key roles for the large blueshifts. The significant In–Ga interdiffusion occurred at 650°C while the N diffusion occurred at a temperature above 700°C. The theoretical results are in good agreement with the experimental observations.
Characterization of spherical Si by photoluminescence measurement
Authors: Nagai Takehiko , Liu Zhengxin , Masuda Atsushi , Kondo Michio
Published: May 2007

Spherical silicon (Si) with a size of ∼1mm diameter was fabricated by the dropping method for the applications of spherical Si solar cells. In this research work, we characterized spherical Si by means of photoluminescence (PL) measurement at 4 and 18K. The horn-type spherical Si crystals, formed under large undercooled conditions without a seeding technique, showed D-band luminescence originating from dislocations, whereas intrinsic PL bands of Si were not observed. In contrast, for the tear-type spherical Si crystals, formed under shadow undercooling by a seeding technique with Si powder, the boron (B) bound and Si intrinsic phonon-assisted PL bands were clearly observed both at 4 and 18K. Moreover, the intensity ratio of B bound exciton band to Si intrinsic phonon-assisted PL band showed good correlation to the minority carrier lifetime measured with microwave photoconductance decay method. These experimental results suggested that the crystallinity of the tear-type spherical Si is significantly improved by the seeding technique compared with the horn-type ones, which contain a large amount of B-related defects.
Lindemann measures for the solid-liquid phase transition
Authors: Chakravarty Charusita , Debenedetti Pablo G. , Stillinger Frank H.
Published: May 2007

A set of Lindemann measures, based on positional deviations or return distances, defined with respect to mechanically stable inherent structure configurations, is applied to understand the solid-liquid phase transition in a Lennard-Jones-type system. The key quantity is shown to be the single-particle return distance-squared distribution. The first moment of this distribution is related to the Lindemann parameter which is widely used to predict the melting temperature of a variety of solids. The correlation of the single-particle return distance and local bond orientational order parameter in the liquid phase provides insights into mechanisms for melting. These generalized Lindemann measures, especially the lower order moments of the single-particle return distance distribution, show clear signatures of the transition of the liquid from the stable to the metastable, supercooled regime and serve as landscape-based indicators of the thermodynamic freezing transition for the Lennard-Jones-type system investigated.
Free field realization of current superalgebra gl(m∣n)k
Authors: Yang Wen-Li , Zhang Yao-Zhong , Liu Xin
Published: May 2007

We construct the free field representation of the affine currents, energy-momentum tensor, and screening currents of the first kind of the current superalgebra gl(m∣n)k uniformly for m=n and m≠n. The energy-momentum tensor is given by a linear combination of two Sugawara tensors associated with the two independent quadratic Casimir elements of gl(m∣n).
Amorphous and crystalline phases in thermal quench simulations of alumina
Authors: Rosen J. , Warschkow O. , McKenzie D. R. , Bilek M. M. M.
Published: May 2007

The authors report molecular dynamics simulations of alumina (Al2O3) during crystallization from the melt. Using liquid quench methods, they investigate the effect of cooling rate on the structural evolution of the α, κ, and the bixbyite phases. A critical temperature window is identified, where the time spent in this window is crucial in determining the extent to which the systems approach crystallinity. A strong dependence is observed between the final structure and the quench rate, which is most pronounced for the α phase and to lesser extent for the other phases. The results show that the different phases have different tendencies to crystallize that are determined by energetics, complexity of crystal structure, and the number of metastable states.
Instrument and technique for the in vitro screening of platelet activation from whole blood samples
Authors: Martin Yves , Lépine Mariette , Bannari Abdelfettah , Vermette Patrick
Published: May 2007

The measurement of platelet activation is very difficult to accomplish clinically as platelets are readily activated by in vitro manipulations. Although techniques such as platelet aggregation and flow cytometry exist to estimate platelet function, important limitations prevent these techniques to be widely accepted. In this study, low-fouling surfaces used to limit ex vivo platelet activation were locally bioactivated to rapidly detect platelet activation from whole blood through the selective local adhesion and aggregation of artificially activated platelets. To achieve this result, a fabrication method was developed to create arrays of anti-CD62 and anti-CD61 proteins covalently immobilized on substrates covered by low-fouling graft layers. Moreover, to further limit ex vivo platelet activation and to obtain reproducible results, a custom-made flow chamber was designed and fabricated with the help of computer-assisted mathematical modeling to create defined shear environments. This diagnostic instrument has the potential to allow the rapid estimation of platelet activation levels in whole blood.
Enhanced performance of cylindrical Hall thrusters
Authors: Raitses Y. , Smirnov A. , Fisch N. J.
Published: May 2007

The cylindrical thruster differs significantly in its underlying physical mechanisms from the conventional annular Hall thruster. It features high ionization efficiency, quiet operation, ion acceleration in a large volume-to-surface ratio channel, and performance comparable with the state-of-the-art conventional Hall thrusters. Very significant plume narrowing, accompanied by the increase of the energetic ion fraction and improvement of ion focusing, led to 50%–60% increase of the thruster anode efficiency. These improvements were achieved by overrunning the discharge current in the magnetized thruster plasma.
Canonical averaging in the second order quantized Hamilton dynamics by extension of the coherent state thermodynamics of the harmonic oscillator
Authors: Heatwole Eric , Prezhdo Oleg V.
Published: May 2007

A conceptually simple approximation to quantum mechanics, quantized Hamilton dynamics (QHD) includes zero-point energy, tunneling, dephasing, and other important quantum effects in a classical-like description. The hierarchy of coupled differential equations describing the time evolution of observables in QHD can be mapped in the second order onto a classical system with double the dimensionality of the original system. While QHD excels at dynamics with a single initial condition, the correct method for generating thermal initial conditions in QHD remains an open question. Using the coherent state representation of thermodynamics of the harmonic oscillator (HO) [Schnack, Europhys. Lett. 45, 647 (1999)], we develop canonical averaging for the second order QHD [Prezhdo, J. Chem. Phys. 117, 2995 (2002)]. The methodology is exact for the free particle and HO, and shows good agreement with quantum results for a variety of quartic potentials.
First-principles study on ZnO nanoclusters with hexagonal prism structures
Authors: Li Chun , Guo Wanlin , Kong Yong , Gao Huajian
Published: May 2007

Size-dependent ground state energies and electronic structures of ZnO nanoclusters with wurtzite structures are investigated using density-functional theory calculations. After structural optimizations, the initial Zn–O double layers merge into single layers. Particularly, a phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure is found in the ZnO cluster with 48 atoms, which indicates that clusters with too many dangling bonds will significantly change their configurations during the relaxations. The calculations also show that on the whole both the energy gap and the binding energy approach to the corresponding bulk values with increasing cluster size.
Pr
2
O
3
on Si(001): A commensurate interfacial layer overgrown by silicate
Authors: Libralesso L. , Lee T.-L. , Zegenhagen J.
Published: May 2007

The growth of Pr2O3 on Si(001) for film thicknesses up to 3nm was studied in situ in ultrahigh vacuum without exposure to ambient by x-ray reflectivity, grazing incident x-ray diffraction, and angle-resolved x-ray photoelectron spectroscopy using synchrotron radiation. The electron density and chemical composition profiles as well as the in-plane superstructure deduced from the present analysis reveal the development of a 0.5nm thick transition layer at the interface that exhibits a cubic Pr2O3 structure and is commensurate to the Si substrate. This layer is overgrown by disordered Pr silicate.
Nanophotonic switch using ZnO nanorod double-quantum-well structures
Authors: Yatsui Takashi , Sangu Suguru , Kawazoe Tadashi , Ohtsu Motoichi , An Sung Jin , Yoo Jinkyoung , Yi Gyu-Chul
Published: May 2007

The authors report on time-resolved near-field spectroscopy of ZnO∕ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices.
Cellular solids with tunable positive or negative thermal expansion of unbounded magnitude
Authors: Lakes Roderic
Published: May 2007

Material microstructures are presented with a coefficient of thermal expansion larger in magnitude than that of either constituent. Thermal expansion can be large positive, zero, or large negative. Three-dimensional lattices with void space exceed two-phase bounds but obey three-phase bounds; lattices and normal materials have a trend of expansion decreasing with modulus. Two-phase composites with a negative stiffness phase exceed bounds that assume positive strain energy density. The author determined Young’s modulus and its relation to thermal expansion. Behavior of these composites is compared with that of homogeneous solids in expansion-modulus maps.
Deviations from the reciprocity theory of McCumber at low temperature in Nd3+-doped glasses
Authors: Martin R. M. , Quimby R. S.
Published: May 2007

The reciprocity theory of McCumber [Phys. Rev. 136, A954 (1964)], which relates optical absorption and emission spectra between two energy level manifolds, was tested at temperatures down to 130K on the F3∕24→I9∕24 transition in Nd-doped glass. Deviations between calculated and measured spectra were observed for temperatures below 230K in Nd:silicate and below 170K in Nd:fluorozirconate glass. Below these temperatures, the calculated absorption is skewed to shorter wavelength and the calculated emission is skewed to longer wavelength. The magnitude of the deviation depends on the ratio of inhomogeneous linewidth to thermal energy kBT.
Lagrangian approach to molecular vibrational Raman intensities using time-dependent hybrid density functional theory
Authors: Rappoport Dmitrij , Furche Filipp
Published: May 2007

The authors propose a new route to vibrational Raman intensities based on analytical derivatives of a fully variational polarizability Lagrangian. The Lagrangian is constructed to recover the negative frequency-dependent polarizability of time-dependent Hartree-Fock or adiabatic (hybrid) density functional theory at its stationary point. By virtue of the variational principle, first-order polarizability derivatives can be computed without using derivative molecular orbital coefficients. As a result, the intensities of all Raman-active modes within the double harmonic approximation are obtained at approximately the same cost as the frequency-dependent polarizability itself. This corresponds to a reduction of the scaling of computational expense by one power of the system size compared to a force constant calculation and to previous implementations. Since the Raman intensity calculation is independent of the harmonic force constant calculation more, computationally demanding density functionals or basis sets may be used to compute the polarizability gradient without much affecting the total time required to compute a Raman spectrum. As illustrated for fullerene C60, the present approach considerably extends the domain of molecular vibrational Raman calculations at the (hybrid) density functional level. The accuracy of absolute and relative Raman intensities of benzene obtained using the PBE0 hybrid functional is assessed by comparison with experiment.
40
J
class laser oscillation of Nd-doped silica glass with high thermal shock parameter
Authors: Sato Takahiro , Fujimoto Yasushi , Okada Hajime , Yoshida Hidetsugu , Nakatsuka Masahiro , Ueda Tetsuji , Fujinoki Akira
Published: May 2007

The authors demonstrated a 40J class laser oscillation from a bulk-type Nd-doped silica glass with a high thermal shock parameter. A maximum output energy of 37.3J was obtained from a laser oscillator that consisted of a 30% output coupler with a 30mm diameter and 300mm length laser medium. The thermal shock parameter, a figure of merit for the thermal toughness of the materials, was estimated to be 12.0W∕cm, which is 1.5 times larger than neodymium-doped yttrium aluminum garnet (7.9W∕cm). These results show that the Nd-doped silica glass has the potential to be installed in high-average-power or high-peak-power lasers.