bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of cortical contractility during cytokinesis
Authors: Werner Michael , Glotzer Michael
Published: June 2008

Cleavage furrow formation in animal cells results from a local increase in cortical contractility. During anaphase, the spindle contains, in addition to astral arrays of microtubules, a set of bundled microtubules known as the central spindle. Each of these populations of microtubules, the astral arrays and the central spindle bundles, is sufficient to direct cleavage furrow formation, yet in wild-type situations these sets of microtubules co-operate to induce furrow formation at the same site, between the segregating chromosomes. These pathways have distinct genetic requirements that reflect their differential control of cortical actomyosin. We review our current understanding of the molecular mechanisms of furrow formation, with particular emphasis on the central spindle-independent pathway.
Mechanical and genetic separation of aster- and midzone-positioned cytokinesis
Authors: Bringmann Henrik
Published: June 2008

The mitotic spindle positions the cytokinesis furrow. The cytokinesis furrow then forms and ingresses at the site of the mitotic spindle, between the spindle poles. Two populations of spindle microtubules are implicated in cytokinesis furrow positioning: radial microtubule arrays called asters and bundled non-kinetochore microtubules called the spindle midzone. Here I will discuss our recent results that provided examples of how aster-positioned and midzone-positioned cytokinesis can be mechanically and genetically separated. These experiments illustrate how asters and midzone contribute to cytokinesis. ASS (asymmetric spindle severing) is a mechanical way to spatially separate the aster and midzone signals. In Caenorhabditis elegans embryos, asters and midzone provide two consecutive signals that position the cytokinesis furrow. The first signal is positioned midway between the microtubule asters; the second signal is positioned over the spindle midzone. Aster and midzone contribution can also be genetically separated. Mutants in spd-1 have no detectable midzone and are defective in midzone-positioned but not aster-positioned cytokinesis. Disruption of the function of LET-99 and the heterotrimeric G-proteins GOA-1/GPA-16 and their regulator GPR-1/2 causes defects in aster-positioned cytokinesis but not in midzone-positioned cytokinesis. In order to understand aster-positioned cytokinesis we have to understand how microtubule asters spatially control the activity of LET-99, GPR-1/2 and GOA-1/GPA-16 and how the activity of these G-protein pathway components control the assembly of a contractile ring.
Mechanisms regulating targeting of recycling endosomes to the cleavage furrow during cytokinesis
Authors: Simon Glenn C. , Prekeris Rytis
Published: June 2008

Recently, recycling endosomes have emerged as a key components required for the successful completion of cytokinesis. Furthermore, FIP3 (family of Rab11-interacting protein 3), a Rab11 GTPase-binding protein, has been implicated in targeting the recycling endosomes to the midbody of dividing cells. Previously, we have shown that FIP3/Rab11-containing endosomes associate with centrosomes until anaphase, at which time they translocate to the cleavage furrow. At telophase, FIP3/Rab11-containing endosomes move from the furrow into the midbody, and this step is required for abscission. While several other proteins were implicated in regulating FIP3 targeting to the cleavage furrow, the mechanisms regulating the dynamics of FIP3-containing endosomes during mitosis have not been defined. To identify the factors regulating FIP3 targeting to the furrow, we used a combination of siRNA (small interfering RNA) screens and proteomic analysis to identify Cyk-4/MgcRacGAP (GTPase-activating protein) and kinesin I as FIP3-binding proteins. Furthermore, kinesin I mediates the transport of FIP3-containing endosomes to the cleavage furrow. Once in the furrow, FIP3 binds to Cyk-4 as part of centralspindlin complex and accumulates at the midbody. Finally, we demonstrated that ECT2 regulates FIP3 association with the centralspindlin complex. Thus we propose that kinesin I, in concert with centralspindlin complex, plays a role in temporal and spatial regulation of endosome transport to the cleavage furrow during cytokinesis.
An overview of the fission yeast septation initiation network (SIN)
Authors: Krapp Andrea , Simanis Viesturs
Published: June 2008

The fission yeast septation initiation network, or SIN, is a signal transduction network that is required for septum formation in Schizosaccharomyces pombe. Its activity is tightly regulated through the cell cycle, to ensure proper co-ordination of mitosis and cytokinesis. SIN signalling requires three protein kinases for its function and is mediated by a ras-superfamily GTPase. We discuss the elements of the SIN and how they are regulated.
Progress towards understanding the mechanism of cytokinesis in fission yeast
Authors: Pollard Thomas D.
Published: June 2008

We use fission yeast to study the molecular mechanism of cytokinesis. We benefit from a long history in genetic analysis of the cell cycle in fission yeast, which provided the most complete inventory of cytokinesis proteins. We used fluorescence microscopy of proteins tagged with fluorescent proteins to establish the temporal and spatial pathway for the assembly and constriction of the contractile ring. We combined biochemical analysis of purified proteins (myosin-II, profilin, formin Cdc12p and cofilin), observations of fluorescent fusion proteins in live cells and mathematical modelling to formulate and test a simple hypothesis for the assembly of the contractile ring. This model involves the formation of 65 nodes containing myosin-II and formin Cdc12p around the equator of the cell. As a cell enters anaphase, actin filaments grow from formin Cdc12p in these nodes. Myosin captures actin filaments from adjacent nodes and pulls intermittently to condense the nodes into a contractile ring.
The role of Cdc14 phosphatases in the control of cell division
Authors: Clifford Dawn M. , Chen Chun-Ti , Roberts Rachel H. , Feoktistova Anna , Wolfe Benjamin A. , Chen Jun-Song , McCollum Dannel , Gould Kathleen L.
Published: June 2008

The periodicity of CDKs (cyclin-dependent kinases) regulates most cell cycle transitions including cytokinesis. High Cdk1 activity promotes cytoskeletal rearrangements necessary for cell division while at the same time ensuring that cytokinesis does not begin before the separation of sister chromatids during anaphase. The conserved Cdc14 (cell division cycle 14)-family of phosphatases reverses Cdk phosphorylation events and therefore Cdc14 phosphatases promote the process of cytokinesis. Here, we review the elucidated roles of Cdc14 phosphatases in cytokinesis and the current outstanding questions regarding their function in this process.
Anillin: a pivotal organizer of the cytokinetic machinery
Authors: Hickson Gilles R.X. , O'Farrell Patrick H.
Published: June 2008

Cytokinesis is a dynamic and plastic process involving the co-ordinated regulation of many components. Accordingly, many proteins, including the putative scaffold protein anillin, localize to the cleavage furrow and are required for cytokinesis, but how they function together is poorly understood. Anillin can bind to numerous other furrow components, including F-actin, septins and myosin II, but its molecular functions are unclear. Recent data suggest that anillin participates in a previously unrecognized Rho-dependent pathway that can promote the association of anillin with the plasma membrane, septins, myosin II and microtubules. Studies using the inhibitor of F-actin assembly, Lat A (Latrunculin A), have revealed that these associations occur independently of F-actin; indeed they appear to be stabilized by the loss of F-actin. This pathway may explain previously described requirements for anillin in maintaining stable furrow positioning and for forming a stable midbody, and supports the notion that anillin is a central organizer at the hub of the cytokinetic machinery.
Targeting IRFs by ubiquitination: regulating antiviral responses
Authors: Higgs Rowan , Jefferies Caroline A.
Published: June 2008

The IRF [IFN (interferon) regulatory factor] family of transcription factors control many cellular processes, including induction of key antiviral cytokines, type I IFNs, following viral infection. Recent studies have revealed several endogenous and viral proteins involved in ubiquitin-mediated regulation of IRF activity and thus having an impact on type I IFN signalling. Through the ubiquitin pathway, these proteins can manipulate the antiviral response either by initiating proteasomal degradation of the IRFs or, in contrast, by promoting activation of the IRFs.
Natural killer cell evasion by an E3 ubiquitin ligase from Kaposi's sarcoma-associated herpesvirus
Authors: Thomas Mair , Wills Mark , Lehner Paul J.
Published: June 2008

Viruses exploit the ubiquitin system by targeting cell-surface receptors recognized by immune cells for internalization, thereby evading recognition. We have characterized the KSHV (Kaposi's sarcoma-associated herpesvirus)-encoded E3 ubiquitin ligases, K3 and K5. We find their activities not only prevent recognition by cytotoxic T-lymphocytes, but also promote evasion of NK (natural killer) cells. NK cells recognize and lyse virus-infected cells expressing ligands for activatory receptors such as NKG2D (NK group 2D). K5 down-regulates cell-surface expression of the NKG2D ligands MICA/B (MHC class I-related chains A and B) by ubiquitination of MIC cytoplasmic tail lysine residues. Ubiquitination results in redistribution of MICA from the plasma membrane to an intracellular compartment, but does not result in an increased rate of degradation. Furthermore, K5 down-regulates cell-surface expression of another NK cell activatory receptor ligand, AICL (activation-induced C-type lectin). This activity requires the K5 RING (really interesting new gene)-CH domain and AICL cytoplasmic tail lysine residues. MICA and AICL down-regulation by K5 reduces NK cell-mediated cytotoxicity towards target cells, thus providing KSHV with an NK cell evasion mechanism.
The suppressors of cytokine signalling E3 ligases behave as tumour suppressors
Authors: Elliott Joanne , Hookham Michelle B. , Johnston James A.
Published: June 2008

Many studies have suggested that E3 ubiquitin ligases can behave as either oncogenes or tumour suppressor genes and, recently, it has become clear that the SOCS (suppressor of cytokine signalling) E3 ligases fit this mould. While most cancer-associated E3s regulate the cell cycle or DNA repair, the SOCS proteins inhibit growth factor responses by degrading signalling intermediates such as JAKs (Janus kinases) via the SOCS-box-associated ECS (Elongin–Cullin–SOCS) E3 ligase. Clinical studies have found that (epi)genetic (mutation or methylation) phenomena can occur in many solid tumours and a growing number of clinical findings reveal post-translational modifications that disrupt SOCS function in haematological malignancy. In the present review, we provide a summary of the functions of the SOCS E3s and propose the potential use of members of this family as diagnostic markers and therapeutic targets in cancer.
Disruption of ubiquitin-mediated processes in diseases of the brain and bone
Authors: Layfield Robert , Searle Mark S.
Published: June 2008

A role for ubiquitin in the pathogenesis of human diseases was first suggested some two decades ago, from studies that localized the protein to intracellular protein aggregates, which are a feature of the major human neurodegenerative disorders. Although several different mechanisms have been proposed to connect impairment of the UPS (ubiquitin–proteasome system) to the presence of these ‘ubiquitin inclusions’ within diseased neurones, their significance in the disease process remains to be fully clarified. Ubiquitin inclusions also contain ubiquitin-binding proteins, such as the p62 protein [also known as SQSTM1 (sequestosome 1)], which non-covalently interacts with the ubiquitinated protein aggregates and may serve to mediate their autophagic clearance. p62 is a multifunctional protein and, in the context of bone-resorbing osteoclasts, is an important scaffold in the RANK [receptor activator of NF-κB (nuclear factor κB)]–NF-κB signalling pathway. Further, mutations affecting the UBA domain (ubiquitin-associated domain) of p62 are commonly found in patients with the skeletal disorder PDB (Paget's disease of bone). These mutations impair the ability of p62 to bind to ubiquitin and result in disordered osteoclast NF-κB signalling that may underlie the disease aetiology. Recent structural insights into the unusual mechanism of ubiquitin recognition by the p62 UBA domain have helped rationalize the mechanisms by which different PDB mutations exert their negative effects on ubiquitin binding by p62, as well as providing an indication of the ubiquitin-binding selectivity of p62 and, by extension, its normal biological functions.
Control of mRNA decay by phosphorylation of tristetraprolin
Authors: Sandler Heike , Stoecklin Georg
Published: June 2008

TTP (tristetraprolin) is an RNA-binding protein that suppresses inflammation by accelerating the degradation of cytokine mRNAs. TTP binds to an AU-rich element in the 3′-untranslated region of its target mRNAs. In macrophages, the induction of cytokine expression requires activation of the p38-MAPK (mitogen-activated protein kinase)–MK2 [MAPKAP (MAPK-activated protein) kinase-2] kinase cascade. MK2 directly phosphorylates TTP and thereby contributes to transient stabilization of cytokine mRNAs. In the present review, we address the target specificity of TTP, summarize TTP-interacting proteins and discuss how phosphorylation regulates the activity, localization and stability of TTP.
Regulation of gene expression by the RNA-binding protein Sam68 in cancer
Authors: Rajan Prabhakar , Gaughan Luke , Dalgliesh Caroline , El-Sherif Amira , Robson Craig N. , Leung Hing Y. , Elliott David J.
Published: June 2008

Sam68 (Src-associated in mitosis 68 kDa) is the prototypical member of the STAR (signal transducer and activator of RNA) family of RNA-binding proteins. Sam68 is implicated in a number of cellular processes including signal transduction, transcription, RNA metabolism, cell cycle regulation and apoptosis. In the present review, we summarize the functions of Sam68 as a transcriptional and post-transcriptional regulator of gene expression, with particular relevance to cancer.
Regulation of B- and T-cell differentiation by a single microRNA
Authors: Turner Martin , Vigorito Elena
Published: June 2008

miRs (microRNAs) post-transcriptionally regulate gene expression mainly by repressing translation or by inducing mRNA degradation. Dicer, an enzyme responsible for miR biogenesis, is required for T-cell function, suggesting regulatory roles for miRs in lymphocytes. However, specific roles for individual miRs are only just beginning to emerge. miR-155 is encoded within an exon of the non-coding RNA known as bic (B-cell integration cluster) and high levels of bic expression are induced upon antigen receptor stimulation of B- and T-cells, as well as TLR (Toll-like receptor) stimulation of macrophages and dendritic cells. High levels of bic/miR-155 are found in B-cell lymphomas and solid tumours, indicating that this locus may also be linked to cancer. Indeed, transgenic mice overexpressing miR-155 develop B-cell malignancies. To define the in vivo role of bic/miR-155 (bic), we have studied bic-deficient mice. These mice are immunodeficient and fail to generate high levels of class-switched antibody upon immunization with thymus-dependent and thymus-independent antigens. This defect is intrinsic to B-cells and manifested at the level of differentiation of switched plasmablasts into mature antibody secreting plasma cells. In addition, bic-deficient T-cells show skewed differentiation into the Th2 lineage under a variety of in vitro culture conditions. Microarray analysis of bic-deficient B- and T-cells under different conditions has revealed a wide spectrum of targets regulated by an miR-155 and suggested mechanisms for the regulation of lymphocyte differentiation by a single miR.
Gene expression is reduced in trans by inosine-containing dsRNA
Authors: Scadden A.D.J.
Published: June 2008

Inosine residues may be introduced into long dsRNA (double-stranded RNA) molecules by the action of a family of editing enzymes, ADARs (adenosine deaminases that act on RNA). Furthermore, hyperediting of dsRNA by ADARs may result in up to 50% of adenosine residues being converted into inosine. While the effect of hyperediting has traditionally been thought to be limited to the edited dsRNA, we have recently shown that hyperedited dsRNA [I-dsRNA (inosine-containing dsRNA)] is able to down-regulate the expression of both reporter and endogenous mRNAs in cells, in trans. Down-regulation by I-dsRNA occurs both by reducing mRNA levels and by inhibiting of translation. This finding has important functional consequences for hyperediting by ADARs.
Role of the C-terminal domain of RNA polymerase II in expression of small nuclear RNA genes
Authors: Egloff Sylvain , Murphy Shona
Published: June 2008

Pol II (RNA polymerase II) transcribes the genes encoding proteins and non-coding snRNAs (small nuclear RNAs). The largest subunit of Pol II contains a distinctive CTD (C-terminal domain) comprising a repetitive heptad amino acid sequence, Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7. This domain is now known to play a major role in the processes of transcription and co-transcriptional RNA processing in expression of both snRNA and protein-coding genes. The heptapeptide repeat unit can be extensively modified in vivo and covalent modifications of the CTD during the transcription cycle result in the ordered recruitment of RNA-processing factors. The most studied modifications are the phosphorylation of the serine residues in position 2 and 5 (Ser2 and Ser5), which play an important role in the co-transcriptional processing of both mRNA and snRNA. An additional, recently identified CTD modification, phosphorylation of the serine residue in position 7 (Ser7) of the heptapeptide, is however specifically required for expression of snRNA genes. These findings provide interesting insights into the control of gene-specific Pol II function.
Complexity of COX-2 gene regulation
Authors: Harper Kelly A. , Tyson-Capper Alison J.
Published: June 2008

Overexpression of the enzyme COX-2 (cyclo-oxygenase-2) is associated with various pathophysiological conditions, including inflammatory diseases and different cancers. Increased synthesis of COX-2 in fetal membranes and the myometrium is also linked with the onset of term and preterm labour. COX-2 gene regulation is controlled at various levels including gene transcription and post-transcriptional events. The present article focuses on the complexity of COX-2 gene regulation and reviews current concepts that highlight: (i) transcription of COX-2 is induced rapidly and transiently in response to a plethora of stimuli; (ii) COX-2 mRNA stability and translational efficiency is governed by multiple regulatory elements within the 3′-untranslated region; (iii) specific microRNAs and RNA-binding proteins influence COX-2 mRNA stability; and (iv) regulation of COX-2 involves alternative polyadenylation.
Can donor splice site recognition occur without the involvement of U1 snRNP?
Authors: Raponi Michela , Baralle Diana
Published: June 2008

Many disease-causing mutations affecting donor splice site recognition are reported in the literature. One of the more frequently observed nucleotide changes causing aberrant splicing are due to mutations in the donor splice site which lower the strength of base pairing with U1 snRNA (small nuclear RNA). However, recent data have highlighted the possibility of a recognition mechanism for weak donor splice sites that are at least partially U1-independent. This is important as most of the donor splice site prediction programs currently in use are based on the U1 snRNA 5′-splice site base pairing and would not pick this up. We review these mechanisms and how an up-to-date donor splice site mutation repertoire indicates the heterogeneity of the molecular mechanism. We suggest that, in clinical molecular genetics, it is important to evaluate sequence variants for aberrant splicing even in those cases where the variant is not thought to alter the U1 snRNA interaction.
Fructose modifies the hormonal response and modulates lipid metabolism during aerobic exercise after glucose supplementation
Authors: Fernández Juan M. , da Silva-Grigoletto Marzo E. , Ruano-Ruíz Juan A. , Caballero-Villarraso Javier , Moreno-Luna Rafael , Túnez-Fiñana Isaac , Tasset-Cuevas Inmaculada , Pérez-Martínez Pablo , López-Miranda José , Pérez-Jiménez Francisco
Published: June 2008

The metabolic response when aerobic exercise is performed after the ingestion of glucose plus fructose is unclear. In the present study, we administered two beverages containing GluF (glucose+fructose) or Glu (glucose alone) in a randomized cross-over design to 20 healthy aerobically trained volunteers to compare the hormonal and lipid responses provoked during aerobic exercise and the recovery phase. After ingesting the beverages and a 15-min resting period, volunteers performed 30 min of moderate aerobic exercise. Urinary and blood samples were taken at baseline (t−15), during the exercise (t0, t15 and t30) and during the recovery phase (t45, t75 and t105). Plasma insulin concentrations were higher halfway through the exercise period and during acute recuperation (t15 and t75; P<0.05) following ingestion of GluF than after Glu alone, without any differences between the effects of either intervention on plasma glucose concentrations. Towards the end of the exercise period, urinary catecholamine concentrations were lower following GluF (t45; P<0.05). Plasma triacylglycerol (triglyceride) concentrations were higher after the ingestion of GluF compared with Glu (t15, t30, t45 and t105; P<0.05). Furthermore, with GluF, we observed higher levels of lipoperoxides (t15, t30, t45 and t105; P<0.05) and oxidized LDL (low-density lipoprotein; t30; P<0.05) compared with after the ingestion of Glu alone. In conclusion, hormonal and lipid alterations are provoked during aerobic exercise and recovery by the addition of a dose of fructose to the pre-exercise ingestion of glucose.
Streaming instabilities of intense charged particle beams propagating along a solenoidal magnetic field in a background plasma
Authors: Startsev Edward A. , Davidson Ronald C. , Dorf Mikhail
Published: June 2008

Streaming instabilities of intense charged particle beams propagating along a solenoidal magnetic field in a background plasma are studied analytically and numerically. It is shown that the growth rate of the electromagnetic Weibel instability is modified by a relatively weak solenoidal magnetic field such that ωce>βbωpe, where ωce is the electron gyrofrequency, ωpe is the electron plasma frequency, and βb is the ion-beam velocity relative to the speed of light. Moreover, the Weibel instability is limited to very small propagation angles and long longitudinal wavelengths satisfying k∥2⪡k⊥2 and c2k∥2⪡ωpb2ωpi2∕(ωpb2+ωpi2), where ωpb and ωpi are the plasma frequencies of the beam ions and the background plasma ions, respectively. For shorter longitudinal wavelengths, the electrostatic lower-hybrid instability becomes dominant. In this paper, the growth rates of various electrostatic beam-plasma instabilities and the electromagnetic Weibel instability are compared, and the space-time development of the modified two-stream instability is studied in detail and compared with numerical simulations.
Water line lists close to experimental accuracy using a spectroscopically determined potential energy surface for H2O16, H2O17, and H2O18
Authors: Shirin Sergei V. , Zobov Nikolay F. , Ovsyannikov Roman I. , Polyansky Oleg L. , Tennyson Jonathan
Published: June 2008

Line lists of vibration-rotation transitions for the H2O16, H2O17, and H2O18 isotopologues of the water molecule are calculated, which cover the frequency region of 0–20000cm−1 and with rotational states up to J=20 (J=30 for H2O16). These variational calculations are based on a new semitheoretical potential energy surface obtained by morphing a high accuracy ab initio potential using experimental energy levels. This potential reproduces the energy levels with J=0, 2, and 5 used in the fit with a standard deviation of 0.025cm−1. Linestrengths are obtained using an ab initio dipole moment surface. That these line lists make an excellent starting point for spectroscopic modeling and analysis of rotation-vibration spectra is demonstrated by comparison with recent measurements of Lisak and Hodges [J. Mol. Spectrosc. (unpublished)]: assignments are given for the seven unassigned transitions and the intensity of the strong lines are reproduced to with 3%. It is suggested that the present procedure may be a better route to reliable line intensities than laboratory measurements.
Self-gravitating rotating anisotropic pressure plasma in presence of Hall current and electrical resistivity using generalized polytrope laws
Authors: Prajapati R. P. , Soni G. D. , Chhajlani R. K.
Published: June 2008

The effects of uniform rotation, finite electrical resistivity, electron inertia, and Hall current on the self-gravitational instability of anisotropic pressure plasma with generalized polytrope laws have been studied. A general dispersion relation is obtained with the help of the relevant linearized perturbed magnetohydrodynamic (MHD) equations incorporating the relevant contributions of various effects of the problem using the method of normal mode analysis. The general dispersion relation is further reduced for the special cases of rotation; i.e., parallel and perpendicular to the direction of the magnetic field. The longitudinal and transverse modes of propagation are discussed separately for investigation of condition of instability. The effects of rotation, Hall current, finite electron inertia, and polytropic indices are discussed on the gravitational, “firehose,” and “mirror” instabilities. The numerical calculations have been performed to obtain the dependence of the growth rate of the gravitational unstable mode on the various physical parameters involved. The finite electrical resistivity, rotation, and Hall current have a stabilizing influence on the growth rate of the unstable mode of wave propagation. The finite electrical resistivity removes the effect of magnetic field and polytropic index from the condition of instability in the transverse mode of propagation for both the cases of rotation. It is also found that the Jeans criterion of gravitational instability depends upon rotation, electron inertia, and polytropic indices. In the case of transverse mode of propagation with the axis of rotation parallel to the magnetic field, it is observed that the region of instability and the value of the critical Jeans wavenumber are larger for the Chew–Goldberger–Low set of equations in comparison with the MHD set of equations. The stability of the system is discussed by applying Routh–Hurwitz criterion. The inclusion of rotation or Hall current or both together depresses the growth rate of mirror instability. We also note that the condition of mirror instability depends upon polytropic indices.
A method for determining Stokes flow around particles near a wall or in a thin film bounded by a wall and a gas-liquid interface
Authors: Ozarkar Shailesh S. , Sangani Ashok S.
Published: June 2008

A method for determining Stokes flow around particles near a wall or in a thin film bounded by a wall on one side and a nondeformable gas-liquid interface on the other side is developed. The no-slip boundary conditions at the wall are satisfied by constructing an image system based on Lamb’s multipoles. Earlier results for the image systems for the flow due to a point force or a force dipole are extended to image systems for force or source multipoles of arbitrary orders. For the case of a film, the image system consists of an infinite series of multipoles on both sides of the film. Accurate evaluation of the flow due to these images is discussed, including the use of Shanks transforms. The method is applied to several problems including chains of particles, radially expanding particles, drops, and porous particles.
Photoreflectance and photoluminescence study of Ga0.76In0.24Sb/GaSb single quantum wells: Band structure and thermal quenching of photoluminescence
Authors: Motyka M. , Kudrawiec R. , Misiewicz J. , Hümmer M. , Rößner K. , Lehnhardt T. , Müller M. , Forchel A.
Published: June 2008

Photoreflectance (PR) and photoluminescence (PL) have been applied to study the band structure and PL thermal quenching for Ga0.24In0.76Sb/GaSb quantum wells (QWs) of the widths varying from 10 to 21 nm. In the case of PR spectra, a strong GaSb-related resonance followed by Franz–Keldysh oscillations and PR resonances associated with optical transitions between the QW ground and the excited states have been clearly observed. The QW transitions have been identified on the basis of theoretical calculations which were performed in the framework of the effective mass model. Satisfactory agreement between theoretical calculations and experimental data has been found for the conduction band offset of ∼80%–85% that is consistent with the theoretical predictions, which were obtained within the “model-solid” theory. In the case of PL measurements, a very efficient QW emission without any localization features has been observed in the temperature range of 10–280 K. It has been concluded that the thermal quenching of PL can be described by a standard expression with two characteristic activation energies, which can be attributed to an electron escape and a heavy-hole escape to the conduction and valence continua in GaSb barriers, respectively. The obtained activation energies are in the range of 20–30 and 80–100 meV for the first and the second quenching mechanism, respectively. The Varshni parameters for the QW ground state transition have been determined to be α=0.36–0.39 meV/K and β=155–175 K.
Electrical detection of the biological interaction of a charged peptide via gallium arsenide junction-field-effect transistors
Authors: Lee Kangho , Nair Pradeep R. , Alam Muhammad A. , Janes David B. , Wampler Heeyeon P. , Zemlyanov Dmitry Y. , Ivanisevic Albena
Published: June 2008

GaAs junction-field-effect transistors (JFETs) are utilized to achieve label-free detection of biological interaction between a probe transactivating transcriptional activator (TAT) peptide and the target trans-activation-responsive (TAR) RNA. The TAT peptide is a short sequence derived from the human immunodeficiency virus-type 1 TAT protein. The GaAs JFETs are modified with a mixed adlayer of 1-octadecanethiol (ODT) and TAT peptide, with the ODT passivating the GaAs surface from polar ions in physiological solutions and the TAT peptide providing selective binding sites for TAR RNA. The devices modified with the mixed adlayer exhibit a negative pinch-off voltage (VP) shift, which is attributed to the fixed positive charges from the arginine-rich regions in the TAT peptide. Immersing the modified devices into a TAR RNA solution results in a large positive VP shift (>1 V) and a steeper subthreshold slope (∼80 mV/decade), whereas “dummy” RNA induced a small positive VP shift (∼0.3 V) without a significant change in subthreshold slopes (∼330 mV/decade). The observed modulation of device characteristics is analyzed with analytical modeling and two-dimensional numerical device simulations to investigate the electronic interactions between the GaAs JFETs and biological molecules.
State-selective predissociation dynamics of methylamines: The vibronic and H∕D effects on the conical intersection dynamics
Authors: Ahn Doo-Sik , Lee Jeongmook , Choi Jeong-Mo , Lee Kyoung-Seok , Baek Sun Jong , Lee Kunhye , Baeck Kyoung-Koo , Kim Sang Kyu
Published: June 2008

The photodissociation dynamics of methylamines (CH3NH2 and CD3ND2) on the first electronically excited state has been investigated using the velocity map ion imaging technique probing the H or D fragment. Two distinct velocity components are found in the H(D) translational energy distribution, implying the existence of two different reaction pathways for the bond dissociation. The high H(D) velocity component with the small internal energy of the radical fragment is ascribed to the N–H(D) fragmentation via the coupling of S1 to the upper-lying S2 repulsive potential energy surface along the N–H(D) bond elongation axis. Dissociation on the ground S0 state prepared via the nonadiabatic dynamics at the conical intersection should be responsible for the slow H(D) fragment. Several S1 vibronic states of methylamines including the zero-point level and nν9 states (n=1, 2, or 3) are exclusively chosen in order to explore the effect of the initial quantum content on the chemical reaction dynamics. The branching ratio of the fast and slow components is found to be sensitive to the initial vibronic state for the N–H bond dissociation of CH3NH2, whereas it is little affected in the N–D dissociation event of CD3ND2. The fast component is found to be more dominant in the translational distribution of D from CD3ND2 than it is in that of H from CH3NH2. The experimental result is discussed with a plausible mechanism of the conical intersection dynamics.
Magnetic force microscopy study of the training effect in polycrystalline Co/CoO bilayers
Authors: Brems Steven , Volodin Alexander , Van Haesendonck Chris , Temst Kristiaan
Published: June 2008

The training effect in polycrystalline exchange bias Co/CoO bilayers has been investigated with low-temperature magnetic force microscopy (MFM). After field cooling the bilayer to 13 K, no MFM contrast was detected but a clear MFM contrast related to the domain structure appears after the first magnetization reversal of the ferromagnetic Co layer. Once formed, the ferromagnetic domains survive even at very large fields and cannot be erased by the application of a magnetic field along the cooling field direction. On the other hand, it is possible to partially remove the magnetic domains by performing a hysteresis loop with a magnetic field perpendicular to the cooling field direction.
Low-temperature inelastic collisions between hydrogen molecules and helium atoms
Authors: Tejeda G. , Thibault F. , Fernández J. M. , Montero S.
Published: June 2008

Inelastic H2:He collisions are studied from the experimental and theoretical points of view between 22 and 180K. State-to-state cross sections and rates are calculated at the converged close-coupling level employing recent potential energy surfaces (PES): The MR-PES [J. Chem. Phys. 100, 4336 (1994)], and the MMR-PES and BMP-PESs [J. Chem. Phys. 119, 3187 (2003)]. The fundamental rates k2→0 and k3→1 for H2:He collisions are assessed experimentally on the basis of a master equation describing the time evolution of rotational populations of H2 in the vibrational ground state. These populations are measured in the paraxial region of supersonic jets of H2+He mixtures by means of high-sensitivity and high spatial resolution Raman spectroscopy. Good agreement between theory and experiment is found for the k2→0 rate derived from the MR-PES, but not for the BMP-PES. For the k3→1 rate, which is about one-third to one-half of k2→0, the result is less conclusive. The experimental k3→1 rate is compatible within experimental error with the values calculated from both PESs. In spite of this uncertainty, the global consistence of experiment and theory in the framework of Boltzmann equation supports the MR-PES and MMR-PESs, and the set of gas-dynamic equations employed to describe the paraxial region of the jet at a molecular level.
Analysis of current-driven domain wall motion from pinning sites in nanostrips with perpendicular magnetic anisotropy
Authors: Suzuki T. , Fukami S. , Ohshima N. , Nagahara K. , Ishiwata N.
Published: June 2008

Current-driven domain wall motion from pinning sites in nanostrips with perpendicular magnetic anisotropy is studied by using micromagnetic simulations, supported by a one-dimensional model of wall dynamics. The threshold current density of perpendicular anisotropy strips is much smaller than that of in-plane anisotropy strips, and is almost independent of the pinning potential strength. This results from the narrower domain wall width, smaller hard-axis anisotropy, and the larger ratio of the depinning field and hard-axis anisotropy. In the one-dimensional model with a zero damping constant, the threshold current density is found to be about 0.72 of the intrinsic threshold current density for a perfect strip in a strong pinning regime that corresponds to strips with perpendicular magnetic anisotropy. The fact that the threshold current density from the pinning sites is smaller than the intrinsic current density is because the effective field, equivalent to the pinning potential, enhances a breakdown in the pinning site. Moreover, in the strong pinning regime, an opposite-direction depinning hardly ever occurs after current pulse is turned off. These features of strips with perpendicular magnetic anisotropy are attractive for magnetic random access memories where the domain wall should be moved stably between the pinning sites with the small current pulse.
Temperature-pressure-volume equation of state of the B2 phase of sodium chloride
Authors: Ueda Yasuhiro , Matsui Masanori , Yokoyama Ayako , Tange Yoshinori , Funakoshi Ken-ichi
Published: June 2008

The temperature-pressure-volume (T-P-V) data of the B2 phase of sodium chloride (NaCl) were measured at high temperatures between 1023 and 1973K, and high pressures between 22.9 and 26.3GPa, using synchrotron powder x-ray diffraction experiments with a Kawai-type multianvil high pressure apparatus. The Mie–Grüneisen-type thermal pressure analysis was made to obtain the high temperature and high pressure T-P-V equation of state (EOS) of the B2 phase based on the present measured T-P-V data together with the 300K volume compression data previously reported using diamond-anvil-cell experiments. Some molecular dynamics calculations using a breathing shell model interionic potential, recently developed for the NaCl system, were also carried out to investigate the behavior of thermal pressure of the B2 phase at high temperatures and high pressures. The resulting T-P-V EOS agrees very well with recently measured volume compression data at 1000K. Here we present the T-P-V EOS of the B2 phase up to 3000K and more than 150GPa, as a reliable pressure standard at high temperatures and high pressures.
Metal-oxide-junction, triple point cathodes in a relativistic magnetron
Authors: Jordan N. M. , Gilgenbach R. M. , Hoff B. W. , Lau Y. Y.
Published: June 2008

Triple point, defined as the junction of metal, dielectric, and vacuum, is the location where electron emission is favored in the presence of a sufficiently strong electric field. To exploit triple point emission, metal-oxide-junction (MOJ) cathodes consisting of dielectric “islands” over stainless steel substrates have been fabricated. The two dielectrics used are hafnium oxide (HfOx) for its high dielectric constant and magnesium oxide (MgO) for its high secondary electron emission coefficient. The coatings are deposited by ablation-plasma-ion lithography using a KrF laser (0–600mJ at 248nm) and fluence ranging from 3to40J∕cm2. Composition and morphology of deposited films are analyzed by scanning electron microscopy coupled with x-ray energy dispersive spectroscopy, as well as x-ray diffraction. Cathodes are tested on the Michigan Electron Long-Beam Accelerator with a relativistic magnetron, at parameters V=−300kV, I=1–15kA, and pulse lengths of 0.3–0.5μs. Six variations of the MOJ cathode are tested, and are compared against five baseline cases. It is found that particulate formed during the ablation process improves the electron emission properties of the cathodes by forming additional triple points. Due to extensive electron back bombardment during magnetron operation, secondary electron emission also may play a significant role. Cathodes exhibit increases in current densities of up to 80A∕cm2, and up to 15% improvement in current start up time, as compared to polished stainless steel cathodes.
Suppressing series resistance in organic solar cells by oxygen plasma treatment
Authors: Lin Chien-Hung , Tseng Shao-Chin , Liu Yuan-Kui , Tai Yian , Chattopadhyay Surojit , Lin Chi-Feng , Lee Jiun-Haw , Hwang Jih-Shang , Hsu Yung-Yu , Chen Li-Chyong , Chen Wei-Chao , Chen Kuei-Hsien
Published: June 2008

We demonstrate a low series resistance contact of gold (anode)/zinc-phthalocyznine in a reverse organic photovoltaic device aided by oxygen plasma treatment. The power conversion efficiency appreciated from 0.2% to 2.13%, post O2 plasma treatment, predominantly due to the reduction in the series resistance of the device. A depth profile of zinc from x-ray photoelectron spectroscopy study revealed a gold layer with graded zinc composition, instead of pure gold, to be an efficient hole-collector from the organic interface. The zinc alloying of the gold layer has clearly been promoted by the oxygen plasma treatment.
Semiconductor charge transport driven by a picosecond strain pulse
Authors: Fowler D. R. , Akimov A. V. , Balanov A. G. , Greenaway M. T. , Henini M. , Fromhold T. M. , Kent A. J.
Published: June 2008

We demonstrate that a picosecond strain pulse can be used to drive an electric current through both thin-film epilayer and heterostructure semiconductor crystals in the absence of an external electric field. By measuring the transient current pulses, we are able to clearly distinguish the effects of the coherent and incoherent components of the acoustic packet. The properties of the strain induced signal suggest a technique for exciting picosecond current pulses, which may be used to probe semiconductor devices.
Broadband electrical detection of spin excitations in Ga0.98Mn0.02As using a photovoltage technique
Authors: Wirthmann André , Hui Xiong , Mecking N. , Gui Y. S. , Chakraborty T. , Hu C.-M. , Reinwald M. , Schüller C. , Wegscheider W.
Published: June 2008

We report on microwave photovoltage and simultaneous magnetotransport measurements in a (Ga, Mn) As film oriented normal to the magnetic field. We detect the ferromagnetic resonance over a broad frequency range of 2–18.5GHz and determine the spectroscopic g-factor and separate the Gilbert from the inhomogeneous contribution to magnetization relaxation. Temperature dependent measurements below the saturation magnetization indicate that the photovoltage signal can serve as a sensitive tool to study the crystal anisotropy. We demonstrate that the combination of spin dynamics with charge transport is a promising tool to study microstructured ferromagnetic semiconductor samples.
Dynamics of magnetization, reversal, and ultrafast demagnetization of TbFeCo amorphous films
Authors: Liu Xiaodong , Xu Zhen , Gao Ruixin , Hu Haining , Chen Zhifeng , Wang Zixin , Du Jun , Zhou Shiming , Lai Tianshu
Published: June 2008

Static and dynamic hysteresis loops of TbFeCo amorphous films are measured by vibrating sample magnetometry (VSM) and magneto-optical Kerr rotation. The static VSM loop shows a faster magnetization reversal than the static Kerr loop does. The dynamic Kerr hysteresis loop in a sinusoidal alternating magnetic field at 1.14kHz shows a large increase in coercivity with respect to the static coercivity. The ultrafast dynamics of laser-induced demagnetization and magnetization recovery is studied by femtosecond time-resolved polar Kerr rotation spectroscopy, and shows a subpicosecond demagnetization and several hundreds of picosecond magnetization recovery process, which suggests gigahertz writing rate possible.
The p110β isoform of phosphoinositide 3-kinase signals downstream of G protein-coupled receptors and is functionally redundant with p110γ
Authors: Guillermet-Guibert Julie , Bjorklof Katja , Salpekar Ashreena , Gonella Cristiano , Ramadani Faruk , Bilancio Antonio , Meek Stephen , Smith Andrew J. H. , Okkenhaug Klaus , Vanhaesebroeck Bart
Published: June 2008

The p110 isoforms of phosphoinositide 3-kinase (PI3K) are acutely regulated by extracellular stimuli. The class IA PI3K catalytic subunits (p110α, p110β, and p110δ) occur in complex with a Src homology 2 (SH2) domain-containing p85 regulatory subunit, which has been shown to link p110α and p110δ to Tyr kinase signaling pathways. The p84/p101 regulatory subunits of the p110γ class IB PI3K lack SH2 domains and instead couple p110γ to G protein-coupled receptors (GPCRs). Here, we show, using small-molecule inhibitors with selectivity for p110β and cells derived from a p110β-deficient mouse line, that p110β is not a major effector of Tyr kinase signaling but couples to GPCRs. In macrophages, both p110β and p110γ contributed to Akt activation induced by the GPCR agonist complement 5a, but not by the Tyr kinase ligand colony-stimulating factor-1. In fibroblasts, which express p110β but not p110γ, p110β mediated Akt activation by the GPCR ligands stromal cell-derived factor, sphingosine-1-phosphate, and lysophosphatidic acid but not by the Tyr kinase ligands PDGF, insulin, and insulin-like growth factor 1. Introduction of p110γ in these cells reduced the contribution of p110β to GPCR signaling. Taken together, these data show that p110β and p110γ can couple redundantly to the same GPCR agonists. p110β, which shows a much broader tissue distribution than the leukocyte-restricted p110γ, could thus provide a conduit for GPCR-linked PI3K signaling in the many cell types where p110γ expression is low or absent.
Infused Fc-tagged β-glucuronidase crosses the placenta and produces clearance of storagein uteroin mucopolysaccharidosis VII mice
Authors: Grubb Jeffrey H. , Vogler Carole , Tan Yun , Shah Gul N. , MacRae Amy F. , Sly William S.
Published: June 2008

Glycosaminoglycan storage begins in prenatal life in patients with mucopolysaccharidosis (MPS). In fact, prenatal hydrops is a common manifestation of MPS VII because of β-glucuronidase (GUS) deficiency. One way to address prenatal storage might be to deliver the missing enzyme across the placenta into the fetal circulation. Maternal IgG is transported across the placenta by the neonatal Fc receptor (FcRn), which recognizes the Fc domain of IgG and mediates transcytosis from maternal to fetal circulation. We hypothesized that we could exploit this process to deliver corrective enzyme to the fetus. To test this hypothesis, the C-terminal fusion protein, GUS-Fc, was compared with native, untagged, recombinant GUS for clearance from the maternal circulation, delivery to the fetus, and reduction of lysosomal storage in offspring of MPS VII mice. We observed that GUS-Fc, infused into pregnant mothers on embryonic days 17 and 18, was transported across the placenta. Similarly infused untagged GUS was not delivered to the fetus. GUS-Fc plasma enzyme activity in newborn MPS VII mice was 1,000 times that seen after administration of untagged GUS and ≈100 times that of untreated WT newborns. Reduced lysosomal storage in heart valves, liver, and spleen provided evidence thatin uteroenzyme replacement therapy with GUS-Fc targeted sites of storage in the MPS VII fetus. We hypothesize that this noninvasive approach could deliver the missing lysosomal enzyme to a fetus with any lysosomal storage disease. It might also provide a method for inducing immune tolerance to the missing enzyme or another foreign protein.
Predictors of Mortality From Community-Onset Bloodstream Infections Due to Extended-Spectrum β-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae
Authors: Apisarnthanarak Anucha , Kiratisin Pattarachai , Mundy Linda M.
Published: June 2008

In a cohort study of 36 patients with community-onset extended-spectrum β-lactamase (ESBL)–producing Escherichia coli or Klebsiella pneumoniae bloodstream infections, we found that predictors of mortality were community-onset infection with ESBL-producing K. pneumoniae pathogens (P = .02) and failure to receive an initial empirical regimen that included either β-lactam and β-lactamase–inhibitors or a carbapenem (P = .04).