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We used fMRI to investigate competition and on-line attentional selection between targets and distractors in opposite visual hemifields. Displays comprised a high-contrast square-wave grating, defined as target by its orientation, presented alone (unilateral) or with a similar distractor of orthogonal orientation in the opposite hemifield (bilateral displays). The target appeared unpredictably on the left or right, precluding anticipatory attention to one side. We found greater activation in target-contralateral superior occipital gyrus for unilateral than for bilateral displays, indicating suppression of the target’s visual representation by distractor presence despite the competing distractor projecting to a different occipital hemisphere. Several frontal and parietal regions showed greater activation for bilateral than unilateral trials, suggesting involvement in on-line attentional selection. This was particularly pronounced for regions in bilateral intraparietal sulcus (IPS), which also showed greater functional coupling with occipital cortex specifically on bilateral trials that required selection plus some repetition-suppression effects when target side was repeated, but again only on bilateral trials requiring selection. Our results indicate that competition between visual stimuli in opposite hemifields can influence occipital cortex, and implicate IPS in resolution of this competition by selection. [ABSTRACT FROM AUTHOR]

Flux pumping provides a method of inductively magnetizing superconducting coils and can provide thermal, electrical and mechanical isolation between cryogenic environment and power supply. This offers the possibility of lower cryogenic loading and more flexible arrangements for superconducting magnet systems. This paper reports on the performance and analysis of a high-temperature superconducting (HTS) half-bridge transformer–rectifier type flux pump using two switching elements formed by applying AC magnetic field to sections of HTS. Theory of operation is presented followed by results from an experimental prototype which are compared with SPICE simulation. There is good qualitative agreement between simulation and experiment and all current, voltage and power waveforms from experiment are presented. This work represents a step forward in the understanding of the operation of HTS transformer–rectifier flux pumps and shows that SPICE simulation can provide designers of future HTS flux pumping systems with a useful tool for making design decisions. [ABSTRACT FROM AUTHOR]

High Tc superconducting (HTS) coils are ideal candidates in the use of high field magnets. HTS coils carrying a direct current, however, suffer a non-negligible loss when they are exposed to an external AC magnetic field. Although this phenomenon is well known, no study concerning AC magnetic field angular dependence of direct current decay has ever been shown. In this work, we experimentally investigate the direct current decay characteristics in a closed double pancake coil made of a YBCO coated conductor under external AC field. AC field of different angles with respect to the coil plane is applied. Results show that the current decay rate presents a strong angular dependence. The fastest decay occurs when the field is parallel to the coil plane, in which case the surface of the tape in the outermost layer experiences most flux variation. To reduce the decay rate, we propose wrapping superconducting tapes around the outermost layer of the coil to shield external AC field. This method significantly reduces direct current decay rate under parallel field, without affecting the perpendicular self-field of the coil. [ABSTRACT FROM AUTHOR]

Optical rebrightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical rebrightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron–positron pairs through some magnetic dissipation processes. As proposed by Dai, this wind will catch up with the GRB outflow and a long-lasting reverse shock (RS) would form. By applying this scenario to GRB afterglows, we find that the RS propagating back into the electron–positron wind can lead to an observable optical rebrightening and a simultaneous X-ray plateau (or X-ray shallow decay). In our study, we select four GRBs (i.e., GRB 080413B, GRB 090426, GRB 091029, and GRB 100814A), of which the optical afterglows are well observed and show clear rebrightenings. We find that they can be well interpreted. In our scenario, the spin-down timescale of the magnetar should be slightly smaller than the peak time of the rebrightening, which can provide a clue to the characteristics of the magnetar. [ABSTRACT FROM AUTHOR]

Superconducting flux pumps are the kind of devices which can generate direct current into superconducting circuit using external magnetic field. The key point is how to induce a dc voltage across the superconducting load by ac fields. Giaever (1966 IEEE Spectr. 3 117) pointed out flux motion in superconductors will induce a dc voltage, and demonstrated a rectifier model which depended on breaking superconductivity. van de Klundert et al (1981 Cryogenics21 195, 267) in their review(s) described various configurations for flux pumps all of which relied on inducing the normal state in at least part of the superconductor. In this letter, following their work, we reveal that a variation in the resistivity of type II superconductors is sufficient to induce a dc voltage in flux pumps and it is not necessary to break superconductivity. This variation in resistivity is due to the fact that flux flow is influenced by current density, field intensity, and field rate of change. We propose a general circuit analogy for travelling wave flux pumps, and provide a mathematical analysis to explain the dc voltage. Several existing superconducting flux pumps which rely on the use of a travelling magnetic wave can be explained using the analysis enclosed. This work can also throw light on the design and optimization of flux pumps. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are newly discovered radio transient sources. Their high dispersion measures indicate an extragalactic origin. However, due to the lack of observational data in other wavelengths, their progenitors still remain unclear. Here we suggest that the collisions between neutron stars (NSs) and asteroids/comets are promising mechanisms for FRBs. During the impact process, a hot plasma fireball forms after the material of the small body penetrates into the NS surface. The ionized matter inside the fireball then expands along the magnetic field lines. Coherent radiation from the thin shell at the top of the fireball will account for the observed FRBs. Our scenario can reasonably explain the main features of FRBs, such as their durations, luminosities, and the event rate. We argue that for a single NS, FRBs are not likely to happen repeatedly in a forseeable timespan since such impacts are of low probability. We predict that faint remnant X-ray emissions should be associated with FRBs, but it may be too faint to be detected by detectors at work. [ABSTRACT FROM AUTHOR]

Strange-quark matter (SQM) may be the true ground state of hadronic matter, indicating that the observed pulsars may actually be strange stars (SSs), but not neutron stars. According to the SQM hypothesis, the existence of a hydrostatically stable sequence of SQM stars has been predicted, ranging from 1 to 2 solar mass SSs, to smaller strange dwarfs and even strange planets. While gravitational wave (GW) astronomy is expected to open a new window to the universe, it will shed light on the search for SQM stars. Here we show that due to their extreme compactness, strange planets can spiral very close to their host SSs without being tidally disrupted. Like inspiraling neutron stars or black holes, these systems would serve as new sources of GW bursts, producing strong GWs at the final stage. The events occurring in our local universe can be detected by upcoming GW detectors, such as Advanced LIGO and the Einstein Telescope. This effect provides a unique probe to SQM objects and is hopefully a powerful tool for testing the SQM hypothesis. [ABSTRACT FROM AUTHOR]

We report on the delay of optical pulses using electromagnetically induced transparency (EIT) in an ensemble of cold atoms with an optical depth exceeding 500. To identify the regimes in which four-wave mixing (4WM) impacts on EIT behaviour, we conduct the experiment in both 85Rb and 87Rb. Comparison with theory shows excellent agreement in both isotopes. In 87Rb negligible 4WM was observed and we obtained one pulse-width of delay with 50% efficiency. In 85Rb 4WM contributes to the output. In this regime we achieve a delay-bandwidth product of 3.7 at 50% efficiency, allowing temporally multimode delay, which we demonstrate by compressing two pulses into the memory medium. [ABSTRACT FROM AUTHOR]

The optimal culture conditions of exopolysaccharides (EPS) production in sub-merged culture medium by Xylaria nigl4pes were determined using orthogonal matrix method. The optimal medium (per liter) EPS was 60.0 g L-1 maltose, 1.0 g L-1 peptone 5 mmol L-1 KH2PO4, and initial pH 7.0 at 28 °C. In the optimal culture medium, the maximum EPS production was 11.967 g L-1 in shake flask. Two groups of EPSs (designated as Fr-I and Fr-II) were obtained from the culture filtrates by size exclusion chromatography (SEC), and their molecular characteristics were examined by a multiangle laser-light scattering (MALLS) and refractive index (RI) detector system. The weight-average molar masses of Fr-I and Fr-II of EPS were determined to be 6.327 x 104 and 1.478 x 104 g mo1-1, respectively. The SEC/MALLS analysis revealed that the molecular formation of Fr-I is of nearly globular shape. Furthermore, the experiments in vitro indicated that X. nigripes EPS exhibited high antioxidative effects though its antitumour activity was limited. [ABSTRACT FROM AUTHOR]

Covalent immobilization of a range of carbohydrate derivatives onto polymeric resin beads is described. Copper-catalyzed Huisgen 2 3 cycloaddition (often termed click chemistry) was used to graft mannose-containing azides to complementarily functionalized alkyne surfaces, namely (a) Wang resin or (b) Rasta particles consisting of a clickable alkyne polymer loose outer shell and a Wang resin inner core. For the second approach, Wang resin beads were first converted into immobilized living radical polymerization initiators with subsequent polymerization of trimethylsilanyl-protected propargyl methacrylate followed by deprotection with TBAF to yield the desired polyalkyne clickable scaffold. The appropriate -mannopyranoside azide was then clicked onto the bead to give a mannose functionalized Rasta resin. IR, gel-phase 1H NMR, and elemental analysis have been used to characterize the modified resins. The binding abilities of these d-mannose-modified particles were subsequently tested using fluorescein-labeled Concanavalin A (Con A), a lectin that binds certain mannose-containing molecules. Preliminary results indicated that the novel glyco-hybrid materials presented in this work are able to efficiently recognize mannose-binding model lectins such as Con A, opening the way for their potential application in affinity chromatography, sensors, and other protein recognition/separation fields. [ABSTRACT FROM AUTHOR]

Increased signaling by transforming growth factor β (TGFβ) has been implicated in systemic sclerosis (SSc; scleroderma), a complex disorder of connective tissues characterized by excessive accumulation of collagen and other extracellular matrix components in systemic organs. To directly assess the effect of sustained TGFβ signaling in SSc, we established a novel mouse model in which the TGFβ signaling pathway is activated in fibroblasts postnatally.The mice we used (termed TBR1CA; Cre‐ER mice) harbor both the DNA for an inducible constitutively active TGFβ receptor I (TGFβRI) mutation, which has been targeted to the ROSA locus, and a Cre‐ER transgene that is driven by a fibroblast‐specific promoter. Administration of 4‐hydroxytamoxifen 2 weeks after birth activates the expression of constitutively active TGFβRI.These mice recapitulated clinical, histologic, and biochemical features of human SSc, showing pronounced and generalized fibrosis of the dermis, thinner epidermis, loss of hair follicles, and fibrotic thickening of small blood vessel walls in the lung and kidney. Primary skin fibroblasts from these mice showed elevated expression of downstream TGFβ targets, reproducing the hallmark biochemical phenotype of explanted SSc dermal fibroblasts. The mouse fibroblasts also showed elevated basal expression of the TGFβ‐regulated promoters plasminogen activator inhibitor 1 and 3TP, increased Smad2/3 phosphorylation, and enhanced myofibroblast differentiation.Constitutive activation of TGFβ signaling in fibroblastic cells of mice after birth caused a marked fibrotic phenotype characteristic of SSc. These mice should be excellent models with which to test therapies aimed at correcting excessive TGFβ signaling in human scleroderma. [ABSTRACT FROM AUTHOR]

Applications of carbon nanotubes such as field emission or microelectrode sensor arrays require a patterning of vertically aligned carbon nanotubes over large areas. A highly purified and concentrated monodisperse cobalt colloid was produced for use as a catalyst for growth of carbon nanotubes. Nanocontact printing was employed to deposit the cobalt nanoparticles in regular patterns with feature sizes at the 100 nm scale onto silicon wafers at low cost over large areas. Vertically aligned carbon nanotubes were grown by direct current plasma enhanced chemical vapour deposition at temperatures ranging from 300 to 640 °C. [ABSTRACT FROM AUTHOR]

The physical understanding and numerical modelling of superconducting devices which exploit the high performance of second generation high temperature superconducting tapes (2G-HTS), is commonly hindered by the lack of accurate functions which allow the consideration of the in-field dependence of the critical current. This is true regardless of the manufacturer of the superconducting tape. In this paper, we present a general approach for determining a unified function Ic(B, θ), ultimately capable of describing the magneto-angular dependence of the in-field critical current of commercial 2G-HTS tapes in the Lorentz configuration. Five widely different superconducting tapes, provided by three different manufacturers, have been tested in a liquid nitrogen bath and external magnetic fields of up to 400 mT. The critical current was recorded at 90 different orientations of the magnetic field ranging from θ = 0°, i.e., with B aligned with the crystallographic ab-planes of the YBCO layer, towards ±90°, i.e., with B perpendicular to the wider surfaces of the 2G-HTS tape. The whole set of experimental data has been analysed using a novel multi-objective model capable of predicting a sole function Ic(B, θ). This allows an accurate validation of the experimental data regardless of the fabrication differences and widths of the superconducting tapes. It is shown that, in spite of the wide set of differences between the fabrication and composition of the considered tapes, at liquid nitrogen temperature the magneto-angular dependence of the in-field critical current of YBCO-based 2G-HTS tapes, can be described by a universal function Ic(f(B), θ), with a power law field dependence dominated by the Kim’s factor B/B0, and an angular dependence moderated by the electron mass anisotropy ratio of the YBCO layer. [ABSTRACT FROM AUTHOR]

In recent years, more and more gamma-ray bursts (GRBs) with late rebrightenings in their multi-band afterglows have revealed the late-time activity of their central engines. GRB 100814A is a special case among the well-sampled events, with complex temporal and spectral evolution. The single power-law shallow decay index of the optical light curve observed by GROND between 640 s and 10 ks is , which apparently conflicts with expectations from the simple external shock model. In particular, there is remarkable rebrightening in the optical to near-infrared bands at late times, challenging the external shock model with synchrotron emission coming from the interaction of the blast wave with the surrounding interstellar medium. In this paper, we invoke a magnetar with spin evolution to explain the complex multi-band afterglow emission of GRB 100814A. The initial shallow decay phase in the optical bands and the plateau in the X-ray can be explained as being due to energy injection from a spin-down magnetar. At late times, with materials from the fall-back disk falling onto the central object of the burster, the angular momentum of the accreted materials is transferred to the magnetar, which leads to a spin up process. As a result, the magnetic dipole radiation luminosity will increase, resulting in significant rebrightening of the optical afterglow. We show that the model can well reproduce the observed multi-band afterglow emission. [ABSTRACT FROM AUTHOR]