bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of neuropilins in cell signalling
Authors: Zachary Ian C. , Frankel Paul , Evans Ian M. , Pellet-Many Caroline
Published: November 2009

NRPs (neuropilins) are receptors for class 3 semaphorins, polypeptides essential for axonal guidance, and for members of the VEGF (vascular endothelial growth factor) family of angiogenic cytokines. While mutant mouse studies show that NRP1 is essential for neuronal and cardiovascular development, little is known concerning the molecular mechanisms through which NRPs mediate the functions of their ligands in different cell types. NRP1 forms complexes with its co-receptors and is required for optimal function, but NRPs lack a clearly defined signalling domain and the role of NRP1 in receptor signalling and the function of the NRP1 cytosolic domain are unclear. Growing evidence indicates, however, that NRP1 plays a selective role in signalling at least in part via its C-terminal domain and interaction with intracellular binding partners.
Protease-activated receptors, cyclo-oxygenases and pro-angiogenic signalling in endothelial cells
Authors: Wheeler-Jones Caroline P.D. , Farrar Charlotte , Garonna Elena
Published: November 2009

COX (cyclo-oxygenase)-2 and members of the PAR (protease-activated receptor) family (PARs 1–4) are highly overexpressed in a number of angiogenesis-dependent pathologies, including advanced atherosclerosis and cancer. An appreciation of the potential role(s) of PARs and COX enzymes in physiological angiogenesis is, however, currently lacking. Exposure of human endothelial cells to serine proteases (e.g. thrombin) or to PAR-selective agonist peptides leads to a wide range of cellular responses, including enhanced expression of COX-2, and we have shown that this induction depends on activation of classic pro-inflammatory signalling elements [e.g. MAPKs (mitogen-activated protein kinases) and NF-κB (nuclear factor κB)]. Our current studies suggest that COX-2-derived mediators are important autocrine regulators of PAR-stimulated angiogenesis. This mechanism could help us to explain how this novel family of receptors couple vascular inflammation with repair and angiogenesis in health and disease.
VEGF-A-stimulated signalling in endothelial cells via a dual receptor tyrosine kinase system is dependent on co-ordinated trafficking and proteolysis
Authors: Bruns Alexander F. , Bao Leyuan , Walker John H. , Ponnambalam Sreenivasan
Published: November 2009

The mammalian endothelium expresses two related but distinct receptor tyrosine kinases, VEGFR1 and VEGFR2 [VEGF (vascular endothelial growth factor) receptor 1 and 2], that regulate the vascular response to a key cytokine, VEGF-A. In the present review, we suggest a model for integrating the signals from these receptor tyrosine kinases by co-ordinating the spatial and temporal segregation of these membrane proteins linked to distinct signalling outputs associated with each intracellular location. Activation of pro-angiogenic VEGFR2 stimulates a programme of tyrosine phosphorylation, ubiquitination and proteolysis. This is linked to ESCRT (endosomal sorting complex required for transport)-mediated recognition of activated VEGFR2 and sorting in endosomes before arrival in lysosomes for terminal degradation. In addition, Rab GTPases regulate key events in VEGFR2 trafficking between the plasma membrane, early and late endosomes, with distinct roles for Rab4a, Rab5a and Rab7a. Manipulation of GTPase levels affects not only VEGFR2 activation and intracellular signalling, but also functional outputs such as VEGF-A-stimulated endothelial cell migration. In contrast, VEGFR1 displays stable Golgi localization that can be perturbed by cell stimuli that elevate cytosolic Ca2+ ion levels. One model is that VEGFR1 translocates from the trans-Golgi network to the plasma membrane via a calcium-sensitive trafficking step. This allows rapid and preferential sequestration of VEGF-A by the higher-affinity VEGFR1, thus blocking further VEGFR2 activation. Recycling or degradation of VEGFR1 allows resensitization of the VEGFR2-dependent signalling pathway. Thus a dual VEGFR system with a built-in negative-feedback loop is utilized by endothelial cells to sense a key cytokine in vascular tissues.
Gene therapy with vascular endothelial growth factors
Authors: Ylä-Herttuala Seppo
Published: November 2009

Therapeutic angiogenesis is a promising new concept for the treatment of myocardial and peripheral ischaemia. Members of the VEGF (vascular endothelial growth factor) family are among the most powerful modulators of angiogenesis. They regulate vascular growth and maintenance during embryogenesis and in adults. The present review summarizes the current status of therapeutic angiogenesis using VEGF, with special reference to preclinical studies.
Thymosin β4 induces epicardium-derived neovascularization in the adult heart
Authors: Riley Paul R. , Smart Nicola
Published: November 2009

The inability of the human heart to effectively repair itself after acute ischaemic injury has driven the search for efficacious means of promoting cardiac regenerative growth. Central to this has been the emergence of cell-based strategies to stimulate and augment both myocardial regeneration and neovascularization. Autologous cell transplantation of a variety of adult progenitor cells has been taken forward in clinical trials and, in parallel, investigators have begun to focus on the activation of resident cardiac cell populations as a means to stimulate endogenous repair. The latter approach depends on characterizing native progenitors with self-renewal, clonality, multipotency and arguably an analogous embryological counterpart. Recently, we have focused on adult EPDCs (epicardium-derived progenitor cells), which, when induced by the actin monomer-binding protein Tβ4 (thymosin β4), are able to revert to their embryonic phenotype and give rise to endothelial cells and vascular smooth muscle cells ex vivo. Studies are ongoing to determine whether activated adult EPDCs can contribute to bona fide neovascularization in the injured adult mammalian heart proper, as a therapeutic means to support surviving cardiac muscle cells and sustain regenerating myocardium.
Neuropilin ligands in vascular and neuronal patterning
Authors: Fantin Alessandro , Maden Charlotte H. , Ruhrberg Christiana
Published: November 2009

Blood vessels and neurons share guidance cues and cell-surface receptors to control their behaviour during embryogenesis. The transmembrane protein NRP1 (neuropilin 1) is present on both blood vessels and nerves and binds two structurally diverse ligands, the class 3 semaphorin SEMA3A and an isoform of the vascular endothelial growth factor VEGF-A termed VEGF165 (VEGF164 in mice). In vitro, SEMA3A competes with VEGF164 for binding to NRP1 to modulate the migration of endothelial cells and neuronal progenitors. It was therefore hypothesized that NRP1 signalling controls neurovascular co-patterning by integrating competing VEGF164 and SEMA3A signals. However, SEMA3A, but not VEGF164, is required for axon patterning of motor and sensory nerves, and, vice versa, VEGF164 rather than SEMA3A is required for blood vessel development. Ligand competition for NRP1 therefore does not explain neurovascular congruence. Instead, these ligands control different aspects of neurovascular patterning that have an impact on cardiovascular function. Thus SEMA3A/NRP1 signalling guides the NCC (neural crest cell) precursors of sympathetic neurons as well as their axonal projections. In addition, VEGF164 and a second class 3 semaphorin termed SEMA3C contribute to the remodelling of the embryonic pharyngeal arch arteries and primitive heart outflow tract by acting on endothelium and NCCs respectively. Consequently, loss of either of these NRP1 ligands disrupts blood flow into and out of the heart. Multiple NRP1 ligands therefore co-operate to orchestrate cardiovascular morphogenesis.
VEGFRs and Notch: a dynamic collaboration in vascular patterning
Authors: Jakobsson Lars , Bentley Katie , Gerhardt Holger
Published: November 2009

ECs (endothelial cells) in the developing vasculature are heterogeneous in morphology, function and gene expression. Inter-endothelial signalling via Dll4 (Delta-like 4) and Notch has recently emerged as a key regulator of endothelial heterogeneity, controlling arterial cell specification and tip versus stalk cell selection. During sprouting angiogenesis, tip cell formation is the default response to VEGF (vascular endothelial growth factor), whereas the stalk cell phenotype is acquired through Dll4/Notch-mediated lateral inhibition. Precisely how Notch signalling represses stalk cells from becoming tip cells remains unclear. Multiple components of the VEGFR (VEGF receptor) system are regulated by Notch, suggesting that quantitative differences in protein expression between adjacent ECs may provide key features in the formation of a functional vasculature. Computational modelling of this selection process in iterations, with experimental observation and validation greatly facilitates our understanding of the integrated processes at the systems level. We anticipate that the study of mosaic vascular beds of genetically modified ECs in dynamic interactions with wild-type ECs will provide a powerful tool for the investigation of the molecular control and cellular mechanisms of EC specification.
Can the biology of VEGF and haem oxygenases help solve pre-eclampsia?
Authors: Ahmed Asif , Cudmore Melissa J.
Published: November 2009

Pre-eclampsia, a pregnancy-specific multi-organ syndrome characterized by widespread endothelial damage, is a new risk factor for cardiovascular disease. No therapies exist to prevent or treat this condition, even to achieve a modest improvement in pregnancy length or birth weight. Co-administration of soluble VEGFR-1 [VEGF (vascular endothelial growth factor) receptor-1; more commonly known as sFlt-1 (soluble Fms-like tyrosine kinase-1)] and sEng (soluble endoglin) to pregnant rats elicits severe pre-eclampsia-like symptoms. These two anti-angiogenic factors are increased dramatically prior to the clinical onset of pre-eclampsia and are quite possibly the ‘final common pathway’ responsible for the accompanying signs of hypertension and proteinuria as they can be reversed by VEGF administration in animal models. HO-1 (haem oxygenase-1), an anti-inflammatory enzyme, and its metabolite, CO (carbon monoxide), exert protective effects in several organs against oxidative stimuli. In a landmark publication, we showed that the HO-1 pathway inhibits sFlt-1 and sEng in cultured cells and human placental tissue explants. Both CO and NO (nitric oxide) promote vascular homoeostasis and vasodilatation, and activation of VEGFR-1 or VEGFR-2 induced eNOS (endothelial nitric oxide synthase) phosphorylation, NO release and HO-1 expression. Our studies established the HO-1/CO pathway as a negative regulator of cytokine-induced sFlt-1 and sEng release and eNOS as a positive regulator of VEGF-mediated vascular morphogenesis. These findings provide compelling evidence for a protective role of HO-1 in pregnancy and identify it as a target for the treatment of pre-eclampsia. Any agent that is known to up-regulate HO-1, such as statins, may have potential as a therapy. Any intervention achieving even a modest prolongation of pregnancy or amelioration of the condition could have a significant beneficial health impact worldwide.
Regulation of angiogenesis by ETS transcription factors
Authors: Randi Anna M. , Sperone Andrea , Dryden Nicola H. , Birdsey Graeme M.
Published: November 2009

Transcription factors of the ETS family are important regulators of endothelial gene expression. Here, we review the evidence that ETS factors regulate angiogenesis and briefly discuss the target genes and pathways involved. Finally, we discuss novel evidence that shows how these transcription factors act in a combinatorial fashion with others, through composite sites that may be crucial in determining endothelial specificity in gene transcription.
Transcriptional dysregulation of coding and non-coding genes in cellular models of Huntington's disease
Authors: Bithell Angela , Johnson Rory , Buckley Noel J.
Published: November 2009

HD (Huntington's disease) is a late onset heritable neurodegenerative disorder that is characterized by neuronal dysfunction and death, particularly in the cerebral cortex and medium spiny neurons of the striatum. This is followed by progressive chorea, dementia and emotional dysfunction, eventually resulting in death. HD is caused by an expanded CAG repeat in the first exon of the HD gene that results in an abnormally elongated polyQ (polyglutamine) tract in its protein product, Htt (Huntingtin). Wild-type Htt is largely cytoplasmic; however, in HD, proteolytic N-terminal fragments of Htt form insoluble deposits in both the cytoplasm and nucleus, provoking the idea that mutHtt (mutant Htt) causes transcriptional dysfunction. While a number of specific transcription factors and co-factors have been proposed as mediators of mutHtt toxicity, the causal relationship between these Htt/transcription factor interactions and HD pathology remains unknown. Previous work has highlighted REST [RE1 (repressor element 1)-silencing transcription factor] as one such transcription factor. REST is a master regulator of neuronal genes, repressing their expression. Many of its direct target genes are known or suspected to have a role in HD pathogenesis, including BDNF (brain-derived neurotrophic factor). Recent evidence has also shown that REST regulates transcription of regulatory miRNAs (microRNAs), many of which are known to regulate neuronal gene expression and are dysregulated in HD. Thus repression of miRNAs constitutes a second, indirect mechanism by which REST can alter the neuronal transcriptome in HD. We will describe the evidence that disruption to the REST regulon brought about by a loss of interaction between REST and mutHtt may be a key contributory factor in the widespread dysregulation of gene expression in HD.
Splicing, cis genetic variation and disease
Authors: Jensen Cathy J. , Oldfield Brian J. , Rubio Justin P.
Published: November 2009

Splicing is a post-transcriptional modification of RNA during which introns are removed and exons are joined. Most of the mammalian genes undergo constitutive and alternative splicing events. In addition to the strong signals of the splice sites, splicing is influenced at a distance by a range of trans factors that interact with cis regulatory elements and influence the spliceosome. The intention of the present mini-review is to give some insights into the complexity of this interaction and to introduce the consequences of some kinds of detrimental genetic variation on alternative splicing and disease.
The physiological properties and therapeutic potential of α5-GABAA receptors
Authors: Martin Loren J. , Bonin Robert P. , Orser Beverley A.
Published: November 2009

The notion that drug treatments can improve memory performance has moved from the realm of science fiction to that of serious investigation. A popular working hypothesis is that cognition can be improved by altering the balance between excitatory and inhibitory neurotransmission. This review focuses on the unique physiological and pharmacological properties of GABAARs [GABA (γ-aminobutyric acid) subtype A receptors] that contain the α5 subunit (α5-GABAAR), as these receptors serve as candidate targets for memory-enhancing drugs.
Regulation of glutamate receptor trafficking by leptin
Authors: Moult Peter R. , Harvey Jenni
Published: November 2009

It is well established that leptin is a circulating hormone that enters the brain and regulates food intake and body weight via its hypothalamic actions. However, it is also known that leptin receptors are widely expressed in the CNS (central nervous system), and evidence is accumulating that leptin modulates many neuronal functions. In particular, recent studies have indicated that leptin plays an important role in the regulation of hippocampal synaptic plasticity. Indeed leptin-insensitive rodents display impairments in hippocampal synaptic plasticity and defects in spatial memory tasks. We have also shown that leptin facilitates the induction of hippocampal LTP (long-term potentiation) via enhancing NMDA (N-methyl-D-aspartate) receptor function and that leptin has the ability to evoke a novel form of NMDA receptor-dependent LTD (long-term depression). In addition, leptin promotes rapid alterations in hippocampal dendritic morphology and synaptic density, which are likely to contribute to the effects of this hormone on excitatory synaptic strength. Recent studies have demonstrated that trafficking of AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) receptors is pivotal for activity-dependent hippocampal synaptic plasticity. However, little is known about how AMPA receptor trafficking processes are regulated by hormonal systems. In the present paper, we discuss evidence that leptin rapidly alters the trafficking of AMPA receptors to and away from hippocampal CA1 synapses. The impact of these leptin-driven changes on hippocampal excitatory synaptic function are discussed.
Regulation of NMDA receptor Ca2+ signalling and synaptic plasticity
Authors: Lau C. Geoffrey , Takeuchi Koichi , Rodenas-Ruano Alma , Takayasu Yukihiro , Murphy Jessica , Bennett Michael V.L. , Zukin R. Suzanne
Published: November 2009

NMDARs (N-methyl-D-aspartate receptors) are critical for synaptic function throughout the CNS (central nervous system). NMDAR-mediated Ca2+ influx is implicated in neuronal differentiation, neuronal migration, synaptogenesis, structural remodelling, long-lasting forms of synaptic plasticity and higher cognitive functions. NMDAR-mediated Ca2+ signalling in dendritic spines is not static, but can be remodelled in a cell- and synapse-specific manner by NMDAR subunit composition, protein kinases and neuronal activity during development and in response to sensory experience. Recent evidence indicates that Ca2+ permeability of neuronal NMDARs, NMDAR-mediated Ca2+ signalling in spines and induction of NMDAR-dependent LTP (long-term potentiation) at hippocampal Schaffer collateral–CA1 synapses are under control of the cAMP/PKA (protein kinase A) signalling cascade. Thus, by enhancing Ca2+ influx through NMDARs in spines, PKA can regulate the induction of LTP. An emerging concept is that activity-dependent regulation of NMDAR-mediated Ca2+ signalling by PKA and by extracellular signals that modulate cAMP or protein phosphatases at synaptic sites provides a dynamic and potentially powerful mechanism for bi-directional regulation of synaptic efficacy and remodelling.
Spare respiratory capacity, oxidative stress and excitotoxicity
Authors: Nicholls David G.
Published: November 2009

Chronic exposure to glutamate (glutamate excitotoxicity) exacerbates neuronal damage in the aftermath of stroke and is implicated in a variety of neurodegenerative disorders. Mitochondria play a central role in the survival or death of the exposed neuron. Calcium, oxidative stress and ATP insufficiency play closely interlocked roles that may be investigated with primary neuronal cultures.
Rapid dendritic and axonal responses to neuronal insults
Authors: Mizielinska Sarah M. , Greenwood Sam M. , Tummala Hemanth , Connolly Christopher N.
Published: November 2009

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system playing critical roles in basal synaptic transmission and mechanisms of learning and memory. Under normal conditions, glutamate is sequestered within synaptic vesicles (~100 mM) with extracellular glutamate concentrations being limited (<1 μM), via retrieval by plasma-membrane transporters on neuronal and glial cells. In the case of central nervous system trauma, stroke, epilepsy, and in certain neurodegenerative diseases, increased concentrations of extracellular glutamate (by vesicular release, cell lysis and/or decreased glutamate transporter uptake/reversal) stimulate the overactivation of local ionotropic glutamate receptors that trigger neuronal cell death (excitotoxicity). Other natural agonists, such as domoic acid, alcohol and auto-antibodies, have also been reported to induce excitotoxicity.
Ca2+-dependent modulation of GABAA and NMDA receptors by extracellular ATP: implication for function of tripartite synapse
Authors: Lalo Ulyana , Andrew Jemma , Palygin Oleg , Pankratov Yuriy
Published: November 2009

The importance of communication between neuronal and glial cells for brain function is recognized by a modern concept of ‘tripartite synapse’. Astrocytes enwrap synapses and can modulate their activity by releasing gliotransmitters such as ATP, glutamate and D-serine. One of the regulatory pathways in the tripartite synapse is mediated by P2X purinoreceptors. Release of ATP from synaptic terminals and astrocytes activates Ca2+ influx via P2X purinoreceptors which co-localize with NMDA (N-methyl-D-aspartate) and GABA (γ-aminobutyric acid) receptors and can modulate their activity via intracellular cascades which involve phosphatase II and PKA (protein kinase A).
Cortical excitability and post-stroke recovery
Authors: Clarkson Andrew N. , Carmichael S. Tomas
Published: November 2009

Stroke is the leading cause of adult disability. Recent studies show that the brain can engage in a limited process of neural repair after stroke: re-mapping of sensory and motor function and sprouting of new connections in peri-infarct cortex surrounding the stroke. Changes in cortical sensory and motor maps and alterations in axonal structure are dependent on patterned neuronal activity. The central cellular process in these events is alteration in neuronal response to incoming inputs – manipulations that increase neuronal firing to a given input are likely to induce changes in neuronal structure and alterations in cortical maps. Because post-stroke neural repair and recovery also involves neuronal sprouting and re-mapping of cortical sensory and motor representations, it has been assumed that changes in neuronal excitability underlie neural repair.
Potential role for ligand-gated ion channels after seizure-induced neurogenesis
Authors: Swijsen Ann , Hoogland Govert , Rigo Jean-Michel
Published: November 2009

Epileptic seizures result in an increased generation of new neurons in the dentate gyrus of the adult mammalian hippocampus. The role of these seizure-induced newborn neurons in the process of epileptogenesis remains largely unknown. Recent work, however, suggests an aberrant incorporation of newborn cells into the existing hippocampal network in such a way that they promote hippocampal hyperexcitability. In the present review, we discuss current knowledge about the possible role of seizure-induced newly generated neurons and the putative involvement of ligand-gated ion channels in the process of epileptogenesis.
On some properties of orthogonal Weingarten functions
Authors: Collins Benoît , Matsumoto Sho
Published: November 2009

We give a Fourier-type formula for computing the orthogonal Weingarten formula. The Weingarten calculus was introduced as a systematic method to compute integrals of polynomials with respect to Haar measure over classical groups. Although a Fourier-type formula was known in the unitary case, the orthogonal counterpart was not known. It relies on the Jack polynomial generalization of both Schur and zonal polynomials. This formula substantially reduces the complexity involved in the computation of Weingarten formulas. We also describe a few more new properties of the Weingarten formula, state a conjecture, and give a table of values.
Influence of C60 morphology on high-order harmonic generation enhancement in fullerene-containing plasma
Authors: Ganeev R. A. , Singhal H. , Naik P. A. , Chakera J. A. , Srivastava A. K. , Dhami T. S. , Joshi M. P. , Gupta P. D.
Published: November 2009

The morphologies of the fullerene targets and the ablated fullerenes to determine the optimal conditions of excitation of the C60-containing targets have been analyzed. The optimization of fullerene-containing plasma conditions allowed the enhanced harmonic generation in these plasmas using laser radiation of different wavelengths, pulse durations, and phase modulation. A comparison between the harmonic generation in single-atom/ion-containing plasmas (using bulk carbon, silver, and indium targets) and fullerene-rich plasma plumes showed better conversion efficiency for the latter medium. The influence of phase modulation of the fundamental radiation in fullerene plasmas on the spectral properties of harmonics has been studied.
Comparison between hot spot modeling and measurement of a superconducting hot electron bolometer mixer at submillimeter wavelengths
Authors: Miao Wei , Delorme Yan , Feret Alexandre , Lefevre Rolland , Lecomte Benoit , Dauplay Fred , Krieg Jean-Michel , Beaudin Gerard , Zhang Wen , Ren Yuan , Shi Sheng-Cai
Published: November 2009

This paper presents the modeling and measurement of a quasioptical niobium nitride superconducting hot electron bolometer mixer at submillimeter wavelengths. The modeling is performed with a distributed hot spot model which is based on solving a heat balance equation for electron temperature along the superconducting microbridge. Particular care has been taken during the modeling concerning the temperature-dependent resistance and the bias current dependence of the critical temperature of the device. The dc and mixing characteristics of this mixer have been computed and we have observed a quite good match between the predicted and the measured results for both dc characteristics and mixing performances at submillimeter wavelengths.
Enhancement of light transmission by coupling to surface plasmon polaritons of a layer-plus-islands silver layer
Authors: Wang Pangpang , Zhang Dongyan , Kim Dong Hun , Qiu Zhiyong , Gao Lumei , Murakami Ri-ichi , Song Xiaoping
Published: November 2009

Enhanced light transmission through coupling incident light with surface plasmon polaritons (SPPs) on a layer-plus-islands nanostructure Ag layer, surrounded by symmetric ZnO dielectrics (ZnO/Ag/ZnO), was investigated. The couple and decouple processes at ZnO/Ag and Ag/ZnO grating interfaces were considered to confine the incident light to SPPs (near field) and then to excite the SPPs to radiate light (far field), which enhanced light transmission. A broad range of light transmission enhancement showed a blueshift with increasing Ag midlayer mass thickness. The physical reasons for light transmission enhancement were theoretically discussed using both the metal/dielectric grating interface model and the Drude–Lorentz free electron model.
Highly mismatched crystalline and amorphous GaN1−xAsx alloys in the whole composition range
Authors: Yu K. M. , Novikov S. V. , Broesler R. , Demchenko I. N. , Denlinger J. D. , Liliental-Weber Z. , Luckert F. , Martin R. W. , Walukiewicz W. , Foxon C. T.
Published: November 2009

Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general, formed of component elements that are well matched in terms of ionicity, atom size, and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN1−xAsx, a highly mismatched, immiscible alloy system that was successfully synthesized in the whole composition range using a nonequilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.17<x<0.75 and crystalline outside this region. The amorphous films have smooth morphology, homogeneous composition, and sharp, well defined optical absorption edges. The band gap energy varies in a broad energy range from ∼3.4 eV in GaN to ∼0.8 eV at x∼0.85. The reduction in the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x>0.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offer an opportunity of using GaN1−xAsx alloys for various types of solar power conversion devices.
Continuous spectrum analysis of roughness-induced transient growth
Authors: Denissen N. A. , White E. B.
Published: November 2009

Continuous spectrum amplitude distributions are calculated for transiently growing roughness-induced perturbations in a flat-plate boundary layer. A direct method is employed when the complete flow is known via direct numerical simulation. A new method using regularizing functionals is developed for calculating the distributions when only partial experimental data are available. These amplitude distributions provide a way of rigorously characterizing the boundary layer receptivity to surface roughness. Contrasting the present results to optimal theory results conclusively demonstrates that roughness-induced disturbances cannot be described by optimal disturbance calculations. The continuous spectrum analysis demonstrates the linearity of the perturbations by correctly reproducing the flow evolution over the measurement domain. Extracting the continuous spectrum amplitudes using the partial data technique reveals the underlying vortex behavior that creates transient growth. The method described is amenable to future work with realistic distributed roughness and complex surface geometries.
A new generic model potential for mesogenic systems: Square well line potential of variable range
Authors: Varga Szabolcs , Vesely Franz J.
Published: November 2009

A single-site pair potential is derived to approximate the linear n-site square well interaction. The resulting square well line (SWL) potential is analytical, fairly smooth, and reproduces the distance and orientation dependence of the multisite pair energy. It contains only three control parameters n, L, and s2, in addition to the units of length s1 and energy ε. The advantages of the new model over the traditional potentials such as Gay–Berne and Kihara are that n, L, and s2 are physically meaningful quantities and that no additional adjustable parameters are introduced. With the SWL potential even very long square well chain molecules may be treated in Monte Carlo (MC) simulations; moreover the model is well suited for perturbation theory. Using Onsager-like theories we test the effect of molecular elongation, temperature, and the range of the square well potential on the vapor-liquid and nematic-smectic A (NS) phase transitions. We find that the vapor-liquid binodal of the SWL fluid is in good agreement with MC results for square well dumbbells. For repulsive SWL particles, varying the interaction range s2 results in a similar effect on the NS transition as the change in the ionic strength in a real suspension of fd viruses.
Electronic properties and open-circuit voltage enhancement in mixed copper phthalocyanine:fullerene bulk heterojunction photovoltaic devices
Authors: Ng T. W. , Lo M. F. , Fung M. K. , Lai S. L. , Liu Z. T. , Lee C. S. , Lee S. T.
Published: November 2009

While bulk heterojunctions (HJ) have been used in organic photovoltaic (OPV) devices, there are few studies on their interface electronics and mechanisms on device performance. Here, we studied the electronic structure of a mixed CuPc:C60 and a discrete CuPc/C60 junctions using photoemission spectroscopy. The HOMOCuPc-LUMOC60 energy offset, which controls the theoretical maximum open-circuit voltage (Voc), was increased from 0.64 to 1.13 eV by mixing CuPc with C60. This Voc increase is attributed to the underlying substrate work function and charge transfer between two molecules. The results provide an understanding of the Voc enhancement in OPV devices with bulk HJ.
Direct measurement of auger recombination in In0.1Ga0.9N/GaN quantum wells and its impact on the efficiency of In0.1Ga0.9N/GaN multiple quantum well light emitting diodes
Authors: Zhang M. , Bhattacharya P. , Singh J. , Hinckley J.
Published: November 2009

The Auger recombination coefficient in In0.1Ga0.9N/GaN quantum wells, emitting at 407 nm has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region. A value of 1.5×10−30 cm6 s−1 is determined for the Auger coefficient at room temperature, which is used to analyze the reported efficiency characteristics of 410 nm In0.1Ga0.9N/GaN quantum wells light emitting diodes. The calculated efficiencies agree remarkably well with the measured ones. It is apparent that Auger recombination is largely responsible for limiting device efficiencies at high injection currents.
Josephson effects in weakly coupled MgB2 intergrain nanobridges prepared by focused ion beam
Authors: Lee Soon-Gul , Hong Sung-Hak , Seong Won Kyung , Kang Won Nam
Published: November 2009

We have fabricated weakly coupled intergrain nanobridges from MgB2 films by a focused ion beam (FIB) patterning technique and studied their transition properties. The bridges were nominally 300 nm wide and 100 nm long, and crossed a single grain boundary perpendicularly. The temperature-dependent resistance data showed a two-step transition after FIB pattern with more-than-two-decade increase in the resistivity. Current-voltage curves showed the characteristics of an ideal Josephson junction. The measured data were perfectly matched with the theory of the resistively shunted junction model with thermal fluctuations at all measured temperatures. At 4.2 K, the measured data showed the effect of hysteresis in agreement with the estimated McCumber parameter βc>0.3. The hysteresis effect disappeared above 6 K. The critical currents obtained from fitting to the RSJ model were linearly dependent on temperature, implying that the grain boundary played an insulating barrier.
Terahertz lasing from silicon by infrared Raman scattering on bismuth centers
Authors: Pavlov S. G. , Böttger U. , Eichholz R. , Abrosimov N. V. , Riemann H. , Shastin V. N. , Redlich B. , Hübers H.-W.
Published: November 2009

Stimulated emission at terahertz frequencies (4.5–5.8 THz) has been realized by electronic Raman scattering of infrared radiation on bismuth donor centers in silicon at low temperatures. The Stokes shift of the observed laser emission is 40.53 meV which corresponds to the bismuth intracenter transition between the 1s(A1) ground state and the excited 1s(E) state. The laser has a low optical threshold and the largest frequency coverage in comparison with other Raman silicon lasers based on shallow donor centers. Time-resolved pump spectra enable the separation of donor and Raman lasing.
Aggregates-induced dynamic negative differential resistance in conducting organic films
Authors: Xie Xian Ning , Wang Junzhong , Loh Kian Ping , Wee Andrew Thye Shen
Published: November 2009

This letter reports the negative differential resistance (NDR) behavior of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride films induced by aggregate formation in the film. It is observed that aggregate-states in the energy gap can by-pass the common charge conduction mode, and electron injection, trapping, and conduction through these states lead to the NDR characteristic. The rate-dependence of NDR is discussed in terms of the transit time and lifetime of the aggregates-states electrons. The quenching of NDR by photoillumination is also observed, and is attributed to the saturation of aggregates-states by photoelectrons.
The Wertheimer–Benary Effect Does Not Invert, and a Nulled Wertheimer–Benary Effect
Authors: Huang Abigail E , Ghosh Shanchita , Hon Alice J , Goris-Rosales Jessica , Altschuler Eric Lewin
Published: November 2009

More than three-quarters of a century ago Wertheimer and Benary demonstrated an ingenious and clear, though, interestingly, small effect: a grey triangle just inside an arm of a black cross on a white background appears slightly lighter than an identical triangle immediately adjacent to the cross, despite both triangles having the same perimeter exposure to black and white. Over a generation ago White discovered an apparently related, but far stronger effect: when short grey (test) bars are placed onto either black or white alternating long bars, the short test bars placed on the long black bars appear much lighter than those placed on the long white bars. A decade ago Spehar, Gilchrist, and Arend found that, enigmatically, if the short test bars in White's effect are the lightest stimulus in a figure, then the relative lightness of the test bars inverts compared with the standard version of White's effect. Here we show that the Wertheimer–Benary effect does not invert, but instead produces a very weak version of the standard effect. We also demonstrate a novel, nulled Wertheimer-Benary effect.
Structure and functional characterization of the atypical human kinase haspin
Authors: Eswaran Jeyanthy , Patnaik Debasis , Filippakopoulos Panagis , Wang Fangwei , Stein Ross L. , Murray James W. , Higgins Jonathan M. G. , Knapp Stefan
Published: November 2009

The protein kinase haspin/Gsg2 plays an important role in mitosis, where it specifically phosphorylates Thr-3 in histone H3 (H3T3). Its protein sequence is only weakly homologous to other protein kinases and lacks the highly conserved motifs normally required for kinase activity. Here we report structures of human haspin in complex with ATP and the inhibitor iodotubercidin. These structures reveal a constitutively active kinase conformation, stabilized by haspin-specific inserts. Haspin also has a highly atypical activation segment well adapted for specific recognition of the basic histone tail. Despite the lack of a DFG motif, ATP binding to haspin is similar to that in classical kinases; however, the ATP γ-phosphate forms hydrogen bonds with the conserved catalytic loop residues Asp-649 and His-651, and a His651Ala haspin mutant is inactive, suggesting a direct role for the catalytic loop in ATP recognition. Enzyme kinetic data show that haspin phosphorylates substrate peptides through a rapid equilibrium random mechanism. A detailed analysis of histone modifications in the neighborhood of H3T3 reveals that increasing methylation at Lys-4 (H3K4) strongly decreases substrate recognition, suggesting a key role of H3K4 methylation in the regulation of haspin activity.
Symbolic gestures and spoken language are processed by a common neural system
Authors: Xu Jiang , Gannon Patrick J. , Emmorey Karen , Smith Jason F. , Braun Allen R.
Published: November 2009

Symbolic gestures, such as pantomimes that signify actions (e.g., threading a needle) or emblems that facilitate social transactions (e.g., finger to lips indicating “be quiet”), play an important role in human communication. They are autonomous, can fully take the place of words, and function as complete utterances in their own right. The relationship between these gestures and spoken language remains unclear. We used functional MRI to investigate whether these two forms of communication are processed by the same system in the human brain. Responses to symbolic gestures, to their spoken glosses (expressing the gestures' meaning in English), and to visually and acoustically matched control stimuli were compared in a randomized block design. General Linear Models (GLM) contrasts identified shared and unique activations and functional connectivity analyses delineated regional interactions associated with each condition. Results support a model in which bilateral modality-specific areas in superior and inferior temporal cortices extract salient features from vocal-auditory and gestural-visual stimuli respectively. However, both classes of stimuli activate a common, left-lateralized network of inferior frontal and posterior temporal regions in which symbolic gestures and spoken words may be mapped onto common, corresponding conceptual representations. We suggest that these anterior and posterior perisylvian areas, identified since the mid-19th century as the core of the brain's language system, are not in fact committed to language processing, but may function as a modality-independent semiotic system that plays a broader role in human communication, linking meaning with symbols whether these are words, gestures, images, sounds, or objects.
Immobilisation of a Large Animal for Imaging Purposes
Authors: Szyszkowski W. , Cai Wei
Published: November 2009

The mobility of a horse in the standing position with its hooves fixed to the ground is investigated to assist designing a minimally obstructing system for restraining large animals. The horse is modelled as a mechanical linkage driven by muscle forces. The linkage′s configuration patterns, active joints and the forces associated with motion initiation are studied by reducing it to a mechanism with a low number of degrees of freedom. A restraint system blocking the motion of active joints with ropes is proposed as an alternative to massive mechanical devices restraining the whole body. The system has been verified experimentally on a sheep.
California—Mexico Collaborations on Social Marketing Campaigns Targeting Mexican Immigrants
Authors: Ojeda Victoria D. , Hiller Sarah P. , Estrada Pamela
Published: November 2009

This pilot study examined whether California public health agencies collaborate with Mexican counterparts when developing and implementing social marketing campaigns that target Mexican immigrants in California. We also examined barriers to collaboration and factors contributing to successful partnerships. We recruited 13 and conducted 8 qualitative interviews (62% response rate) with social marketing staff from California public health agencies and contractors whose activities spanned four priority health areas for Mexican immigrants. Results include a desire to collaborate with Mexican counterparts but limited actual collaboration. Factors stated to affect the quality of binational social marketing collaborations included (1) the importance of communication and a working relationship between both parties, (2) funding issues, (3) evaluation activities, (4) administrative issues, especially travel restrictions, and (5) social stigmatization of the target audience. Policy recommendations include increasing funding available for binational collaborations, reducing administrative barriers, and building capacity on both sides of the U.S.—Mexico border. Such efforts may promote binational discussions that may benefit Mexican immigrants in new and established receiving communities in the United States while potentially promoting continuity of social marketing messages and campaigns. Our data suggest that binational social marketing campaigns may be feasible, though several barriers to their execution must be addressed.
Tailoring Hospital Education Materials for The Period of PURPLE Crying: Keeping Babies Safe in North Carolina Media Campaign
Authors: Hennink-Kaminski Heidi J. , Dougall Elizabeth K.
Published: November 2009

The social marketing approach recognizes the need to tailor message and channel strategies to effectively reach the full range of individuals who must act or exert influence to bring about knowledge, belief, and behavior change. However, repurposing health education materials for additional target audiences and communication channels may at times be rationalized as a necessary response to budgetary constraints. Furthermore, when the materials in question are the outcome of rigorous testing, the experts involved may be reluctant to accept the need for tailoring those materials. This study demonstrates how a rigorously designed and tested shaken baby syndrome prevention program comprising a 10-minute DVD and an 11-page brochure delivered in-hospital to parents of newborns by specially trained health care workers was adapted for a media campaign targeting additional audiences and channels. Focus group research determined which messages and images from The Period of PURPLE Crying DVD and brochure were most salient. Participants were surprised to learn about the normalcy of prolonged infant crying, embraced the PURPLE label, and were keen to share this new knowledge. The volume and quality of advice new parents receive emerged as important. Two campaign concepts, including key messages and visuals, were tested using focus groups and intercept interviews. The normalcy of infant crying as a developmental stage rather than an indication of caregiver incompetence or an unhealthy child resonated with respondents and was adopted for the campaign. This approach underscores the value of tailoring and message testing to provide evidence-based guidance for media campaign decisions.
RFID-enabled business intelligence modules for supply chain optimisation
Authors: Bottani Eleonora , Bertolini Massimo , Montanari Roberto , Volpi Andrea
Published: November 2009

The implementation of radio frequency identification (RFID) for product identification and electronic product code (EPC) for information sharing has the potential to generate a wide amount of data, and to make those data real-time available between supply chain players. However, data need to be interpreted to derive value-added information, which could generate economic benefits from the introduction of RFID technology. This paper aims at addressing the issue of how to exploit EPC data generated by RFID technology to provide value-added information, which could be usefully exploited to optimise supply chain processes. To achieve such aim, a panel of experts, composed of information technology, logistics and supply chain managers of major manufacturers and distributors of fast-moving consumer goods (FMCG), has been involved in the definition of relevant value-added information to be derived from RFID reads. On the basis of the suggestions from the panel members, appropriate business intelligence modules (BIMs) were designed and developed. All BIMs are compliant with EPC standards, and could be in-field implemented to manage logistics processes through RFID technology. The whole work has been carried out inside the RFID Logistics Pilot project, an Italian pilot study aiming at exploiting RFID technology and innovative EPC Network tools, to enable track and trace and product flow plain visibility in the FMCG supply chain.
Arms and Letters: Julius Caesar, theCommentariesof Pope Pius II, and the Politicization of Papal Imagery*
Authors: O'Brien Emily
Published: November 2009

In their title, theCommentariesof Pope Pius II recall the works of Julius Caesar by the same name. The connections between these ancient and humanist histories, however, run much deeper. This article explores this relationship in detail and in the broader historical and historiographical contexts of fifteenth-century Italy. It argues that in both Caesar's histories and in his career more generally, Pius found much that resonated with his own experiences, challenges, and goals. More importantly, he found in these ancientCommentariesvaluable apologetic strategies for constructing his own textual self-portrait as both pope and prince. In choosing Caesar's histories as his models, Pius was following a recent historiographical precedent. Several Italian Renaissance humanists had also turned to Caesar's works as guides for writing histories about leaders of contemporary temporal politics. This article argues that by adopting the same models when shaping his own image, Pius was effectively politicizing his self-portrait in hisCommentaries.
Chaotic motion for the generalized KdV–Burgers equation with external perturbation
Authors: Yu Jun , Li Jieru , Wan Ng Tick
Published: November 2009

The bifurcation and chaos in the generalized KdV–Burgers equation under periodic perturbation are investigated numerically in some detail. It is shown that dynamical chaos can occur when we choose appropriately systematic parameters and initial conditions. Abundant bifurcation structures and different routes to chaos such as period-doubling and inverse period-doubling cascades, intermittent bifurcation and crisis are found by using bifurcation diagrams, Poincaré maps and phase portraits. To characterize the chaotic behavior of this system, the spectrum of the Lyapunov exponent and the Lyapunov dimension of the attractor are also employed.