Showing papers by "Aoyama Gakuin University published in 2014"

Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

Abstract: The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest gamma-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

The international integrated reporting framework : key issues and future research opportunities

Abstract: This paper has three main aims. First, the paper introduces the concept of integrated reporting ( ) as described by the International Integrated Reporting Council (IIRC). A background to the development of the concept over the 4-year period from the inception of the IIRC in 2010 is provided, culminating in the release by the IIRC of a Consultation Draft (CD) of the framework in March 2013. Second, the paper discusses key issues currently being debated relating to the CD that the IIRC will need to resolve prior to the expected release of their framework in late 2013. This discussion is based on issues identified and reported to the IIRC by a subcommittee of the International Association for Accounting Education and Research (IAAER) comprised of international accounting academics. Finally, the paper identifies a range of potential research issues relating to the development and implementation of .

Thermally driven ratchet motion of a skyrmion microcrystal and topological magnon Hall effect.

Abstract: Remarkably stable excitations known as skyrmions have recently garnered significant attention in condensed-matter systems. It is now shown that skyrmions in thin films of MnSi and Cu2OSeO3 can be made to rotate as a result of thermal fluctuations.

GRB 130427A: A Nearby Ordinary Monster

Abstract: Long-duration gamma-ray bursts (GRBs) are an extremely rare outcome of the collapse of massive stars and are typically found in the distant universe. Because of its intrinsic luminosity (L ∼ 3 × 1053 ergs per second) and its relative proximity (z = 0.34), GRB 130427A reached the highest fluence observed in the γ-ray band. Here, we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-meter Liverpool and Faulkes telescopes, and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs, suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early universe and over the full range of GRB isotropic energies.

The ASTRO-H X-ray astronomy satellite

Abstract: The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of ΔE ≤ 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.

Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Abstract: A flare from the TeV blazar Mrk 421, occurring in March 2010, was observed for 13 consecutive days from radio to very high energy (VHE, E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We model the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigate the physical parameters, and evaluate whether the observed broadband SED variability can be associated to variations in the relativistic particle population. Flux variability was remarkable in the X-ray and VHE bands while it was minor or not significant in the other bands. The one-zone SSC model can describe reasonably well the SED of each day for the 13 consecutive days. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission while the other smaller zone, which is spatially separated from the first one, contributes to the daily-variable emission occurring in X-rays and VHE gamma-rays. Both the one-zone SSC and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly to the underlying particle population. This shows that the particle acceleration and cooling mechanism producing the radiating particles could be the main one responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement to the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by the variation of the parameters related to the emitting region itself ($\delta$, $B$ and $R$), in addition to the parameters related to the particle population.

In Search of Homo economicus

Abstract: Homo economicus, a model for humans in neoclassical economics, is a rational maximizer of self-interest. However, many social scientists regard such a person as a mere imaginary creature. We found that 31 of 446 residents of relatively wealthy Tokyo suburbs met the behavioral definition of Homo economicus. In several rounds of economic games, participants whose behavior was consistent with this model always apportioned the money endowed by the experimenter to themselves, leaving no share for their partners. These participants had high IQs and a deliberative decision style. An additional 39 participants showed a similar disregard for other people’s welfare, although they were slightly more altruistic than those in the Homo economicus group. The psychological composition of these quasi–Homo economicus participants was distinct from that of participants in the Homo economicus group. Although participants in the latter group behaved selfishly on the basis of rational calculations, those in the former group ma...

Fast graspability evaluation on single depth maps for bin picking with general grippers

Abstract: We present a method that estimates graspability measures on a single depth map for grasping objects randomly placed in a bin. Our method represents a gripper model by using two mask images, one describing a contact region that should be filled by a target object for stable grasping, and the other describing a collision region that should not be filled by other objects to avoid collisions during grasping. The graspability measure is computed by convolving the mask images with binarized depth maps, which are thresholded differently in each region according to the minimum height of the 3D points in the region and the length of the gripper. Our method does not assume any 3-D model of objects, thus applicable to general objects. Our representation of the gripper model using the two mask images is also applicable to general grippers, such as multi-finger and vacuum grippers. We apply our method to bin picking of piled objects using a robot arm and demonstrate fast pick-and-place operations for various industrial objects.

Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope

Abstract: The gamma-ray burst (GRB) rate is essential for revealing the connection between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at high redshift provides a strong probe of star formation history in the early universe. While hundreds of GRBs are observed by Swift, it remains difficult to determine the intrinsic GRB rate due to the complex trigger algorithm of Swift. Current studies of the GRB rate usually approximate the Swift trigger algorithm by a single detection threshold. However, unlike the previously own GRB instruments, Swift has over 500 trigger criteria based on photon count rate and additional image threshold for localization. To investigate possible systematic biases and explore the intrinsic GRB properties, we develop a program that is capable of simulating all the rate trigger criteria and mimicking the image threshold. Our simulations show that adopting the complex trigger algorithm of Swift increases the detection rate of dim bursts. As a result, our simulations suggest bursts need to be dimmer than previously expected to avoid over-producing the number of detections and to match with Swift observations. Moreover, our results indicate that these dim bursts are more likely to be high redshift events than low-luminosity GRBs. This would imply an even higher cosmic GRB rate at large redshifts than previous expectations based on star-formation rate measurements, unless other factors, such as the luminosity evolution, are taken into account. The GRB rate from our best result gives a total number of 4568 +825 -1429 GRBs per year that are beamed toward us in the whole universe.

Accelerometry-Based Gait Analysis and Its Application to Parkinson's Disease Assessment— Part 1: Detection of Stride Event

Abstract: Gait analysis is widely recognized as a promising tool for obtaining objective information on the walking behavior of Parkinson's disease (PD) patients. It is especially useful in clinical practices if gait properties can be captured with minimal instrumentation that does not interfere with the subject's usual behavioral pattern under ambulatory conditions. In this study, we propose a new gait analysis system based on a trunk-mounted acceleration sensor and automatic gait detection algorithm. The algorithm identifies the acceleration signal with high intensity, periodicity, and biphasicity as a possible gait sequence, from which gait peaks due to stride events are extracted by utilizing the cross-correlation and anisotropy properties of the signal. A total of 11 healthy subjects and 12 PD patients were tested to evaluate the performance of the algorithm. The result indicates that gait peaks can be detected with an accuracy of more than 94%. The proposed method may serve as a practical component in the accelerometry-based assessment of daily gait characteristics.

The many sides of RCW 86: a type Ia supernova remnant evolving in its progenitor's wind bubble

Abstract: We present the results of a detailed investigation of the Galactic supernova remnant RCW 86 using the XMM-Newton X-ray telescope. RCW 86 is the probable remnant of SN 185 A.D., a supernova that likely exploded inside a wind-blown cavity. We use the XMM-Newton Reflection Grating Spectrometer to derive precise temperatures and ionization ages of the plasma, which are an indication of the interaction history of the remnant with the presumed cavity. We find that the spectra are well fitted by two non-equilibrium ionization models, which enables us to constrain the properties of the ejecta and interstellar matter plasma. Furthermore, we performed a principal component analysis on EPIC MOS and pn data to find regions with particular spectral properties. We present evidence that the shocked ejecta, emitting Fe K and Si line emission, are confined to a shell of approximately 2 pc width with an oblate spheroidal morphology. Using detailed hydrodynamical simulations, we show that general dynamical and emission properties at different portions of the remnant can be well reproduced by a Type Ia supernova that exploded in a non-spherically symmetric wind-blown cavity. We also show that this cavity can be created using general wind properties for a single degenerate system. Our data and simulations provide further evidence that RCW 86 is indeed the remnant of SN 185, and is the likely result of a Type Ia explosion of single degenerate origin.

Control of the Single‐Molecule Magnet Behavior of Lanthanide‐Diarylethene Photochromic Assemblies by Irradiation with Light

Abstract: Lanthanide-based extended coordination frameworks showing photocontrolled single-molecule magnet (SMM) behavior were prepared by combining highly anisotropic Dy(III) and Ho(III) ions with the carboxylato-functionalized photochromic molecule 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H2 dae), which acts as a bridging ligand. As a result, two new compounds of the general formula [{Ln(III) 2 (dae)3 (DMSO)3 (MeOH)}⋅10 MeOH]n (M=Dy for 1 a and Ho for 2) and two additional pseudo-polymorphs [{Dy(III) 2 (dae)3 (DMSO)3 (H2 O)}⋅x MeOH]n (1 b) and [{Dy(III) 2 (dae)3 (DMSO)3 (DMSO)}⋅x MeOH]n (1 c) were obtained. All four compounds have 2D coordination-layer topologies, in which carboxylate-bridged Ln2 units are linked together by dae(2-) anions into grid-like frameworks. All four compounds exhibited a strong reversible photochromic response to UV/Vis light. Moreover, both 1 a and 2 show field-induced SMM behavior. The slow magnetic relaxation of 1 a is influenced by the photoisomerization reaction leading to the observation of the cross-effect: photocontrolled SMM behavior.

Effects of combined heat and light soaking on device performance of Cu(In,Ga)Se2 solar cells with ZnS(O,OH) buffer layer

Abstract: The impacts of air annealing, light soaking (LS), and heat–light soaking (HLS) on cell performances were investigated for ZnS(O,OH)/Cu(In,Ga)Se2 (CIGS) thin-film solar cells. It was found that the HLS post-treatment, a combination of LS and air annealing at 130 °C, is the most effective process for improving the cell performances of ZnS(O,OH)/CIGS devices. The best solar cell yielded a total area efficiency of 18.4% after the HLS post-treatment. X-ray photoelectron spectroscopy showed that the improved cell performance was attributable to the decreased S/(S + O) atomic ratio, not only in the surface region but also the interface region between the ZnS(O,OH) and CIGS layers, implying the shift to an adequate conduction-band offset at the ZnS(O,OH)/CIGS interface. Copyright © 2013 John Wiley & Sons, Ltd.

The effect of oxytocin on cooperation in a prisoner’s dilemma depends on the social context and a person’s social value orientation

Abstract: The interactionist approach to the study of exogenous oxytocin (OT) effects on prosocial behavior has emphasized the need to consider both contextual cues and individual differences. Therefore, an experiment was set up to examine the joint effect of intranasal OT, a salient social cue and the personality trait social value orientation on cooperative behavior in one-shot prisoner’s dilemma games. The outcome of these mixed-motive games is known to be highly dependent on values and on social information that might reveal the partner’s intent. Consistent with an a priori hypothesis, OT and social information interact significantly to affect the behavior of individuals with a proself value orientation: after prior contact with the game partner, OT enhances cooperative behavior, whereas in anonymous conditions, it exacerbates their intrinsic self-interested behavior. These effects of OT do not hold for individuals with a prosocial value orientation, whose cooperation levels appear to be more influenced by prior contact with the game partner. Follow-up hypotheses for why prosocial and proself individuals respond differently to exogenous OT were developed.

The ‘amplitude’ parameter of gamma-ray bursts and its implications for GRB classification

Abstract: Traditionally gamma-ray bursts (GRBs) are classified in the $T_{90}$-hardness ratio two-dimensional plane into long/soft and short/hard GRBs. In this paper, we suggest to add the "amplitude" of GRB prompt emission as the third dimension as a complementary criterion to classify GRBs, especially those of short durations. We define three new parameters $f$, $f_{\rm eff}$ and $f_{\rm eff,z}$ as ratios between the measured/simulated peak flux of a GRB/pseudo-GRB and the flux background, and discuss the applications of these parameters to GRB classification. We systematically derive these parameters to find that most short GRBs are likely not "tip-of-iceberg" of long GRBs. However, one needs to be cautious if a short GRB has a relatively small $f$ (e.g. $f<1.5$), since the chance for an intrinsically long GRB to appear as a "disguised" short GRB is higher. Based on avaialble data, we quantify the probability of a disguised short GRB below a certain $f$ value is as $P (

The Effects of Using Corpora on Revision Tasks in L2 Writing with Coded Error Feedback.

Abstract: This study reports on the results of classroom research investigating the effects of corpus use in the process of revising compositions in English as a foreign language. Our primary aim was to investigate the relationship between the information extracted from corpus data and how that information actually helped in revising different types of errors in the essays. In ‘data-driven learning’, previous research has often failed to provide rigorous criteria for choosing the words or phrases suitable for correction with corpus data. By investigating the above relationship, this study aims to clarify what should be corrected by looking at corpus data. 93 undergraduate students from two universities in Tokyo wrote a short essay in 20 minutes without a dictionary, and the instructors gave coded error feedback for two lexical or grammatical errors. They deliberately selected one error which should be appropriate for checking against corpus data and one that was more likely to be corrected without using any reference resource. Three weeks later, a short hands-on instruction of the corpus query tool was given, followed by revision activities in which the participants were instructed to revise their first drafts, with or without the tool depending on the codes given to each error. 188 errors were automatically classified into three different categories (omission, addition and misformation) using natural language processing techniques. All words and phrases tagged for errors were further annotated for part-of-speech (POS) information. The results show that there was a significant difference in the accuracy rate among the three error types when the students consulted the corpus: omission and addition errors were easily identified and corrected, whereas misformation errors were low in correction accuracy. This reveals that certain errors are more suitable for checking against corpus data than others.

Soft x-ray spectrometer (SXS): the high-resolution cryogenic spectrometer onboard ASTRO-H

Abstract: We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.

A novel mucosal vaccine targeting Peyer's patch M cells induces protective antigen-specific IgA responses.

Abstract: Mucosal vaccines can induce mucosal immunity, including antigen-specific secretory IgA production, to protect from invasion by pathogens and to neutralize toxins at mucosal surfaces. We established an effective antigen-delivering fusion protein, anti-GP2-SA, as a mucosal vaccine. The anti-GP2-SA consists of streptavidin (SA) fused to the antigen-binding fragment region from a mAb against glycoprotein 2 (GP2), an antigen-uptake receptor specifically expressed on M cells. Anti-GP2-SA targets antigen-sampling M cells in the follicle-associated epithelium covering Peyer's patches. Immunofluorescence showed that anti-GP2-SA specifically bound to M cells. Orally administered biotinylated ovalbumin peptide (bOVA) conjugated with anti-GP2-SA more efficiently induced OVA-specific fecal IgA secretion compared with bOVA alone or bOVA conjugated with SA. Furthermore, mice immunized by oral administration of the biotinylated Salmonella enterica serovar Typhimurium (S. Typhimurium) lysate conjugated with anti-GP2-SA were significantly better protected from subsequent infection by virulent S. Typhimurium than mice treated with the bacterial lysate alone or conjugated with SA. These results suggest that anti-GP2-SA-based M-cell-targeting vaccines are a novel strategy for inducing efficient mucosal immunity.

Probing intergalactic neutral hydrogen by the Lyman alpha red damping wing of gamma-ray burst 130606A afterglow spectrum at z = 5.913

Abstract: The unprecedentedly bright optical afterglow of GRB 130606A located by Swift at a redshift close to the reionization era (z = 5.913) provides a new opportunity to probe the ionization status of the intergalactic medium (IGM). Here we present an analysis of the red Lyα damping wing of the afterglow spectrum taken by Subaru/FOCAS during 10.4–13.2 hr after the burst. We find that the minimal model including only the baseline power-law and H i absorption in the host galaxy does not give a good fit, leaving residuals showing concave curvature in 8400–8900 A with an amplitude of about 0.6% of the flux. Such a curvature in the short wavelength range cannot be explained either by extinction at the host with standard extinction curves, intrinsic curvature of afterglow spectra, or by the known systematic uncertainties in the observed spectrum. The red damping wing by intervening H i gas outside the host can reduce the residual by about 3 σ statistical significance. We find that a damped Lyα system is not favored as the origin of this intervening H i absorption, from the observed Lyβ and metal absorption features. Therefore absorption by diffuse IGM remains as a plausible explanation. A fit by a simple uniform IGM model requires an H i neutral fraction of fH i ∼ 0.1–0.5 depending on the distance to the GRB host, implying high fH i IGM associated with the observed dark Gunn–Peterson (GP) troughs. This gives new evidence that the reionization is not yet complete at z = 6.

Detailed Investigation of the Gamma-Ray Emission in the Vicinity of SNR W28 with FERMI-LAT

Abstract: We present a detailed investigation of the Gamma-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4−0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ -ray emission spatially coincident with TeV sources HESS J1800−240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2-100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides with radio emission from the western part of W28. All of the GeV Gamma-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s (exp−1). Under the assumption that the Gamma-ray emission toward HESS J1800−240A, B, and C comes from 3.14(exp0) decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. The total energy of the CRs escaping from W28 is constrained through the same modeling to be larger than is approximately 2 × 10(exp49) erg. The emission from Source W can also be explained with the same CR escape scenario.

Beyond horizontal location context: measuring elevation using smartphone's barometer

Abstract: Accurate estimation of elevation is important for many location based services. Although, it is possible to obtain altitude from GPS, its accuracy is unreliable and applicable in outdoors only. It is possible to use barometers on smartphones to estimate elevation in both indoor and outdoor scenarios. To this end, we proposed an integrated framework to provide ubiquitous and accurate elevation measurement using smartphones. Experiments conducted in both indoor and outdoor with different geographical characteristics reveal that our system can provide elevation with an error less than 5 meters in 90 % of the cases and less than 3 meters in 75 % of the cases, which is sufficient for most practical applications.

Evaluating J-integral from Displacement Fields Measured by Digital Image Correlation

Abstract: Path integral, domain integral and least squares methods for evaluating J-integral from measured displacement fields for a power-law hardening material are described in this paper. The values of the J-integral are evaluated by applying the path and domain integral methods to the displacement fields obtained by elastoplastic finite element analysis and the displacement fields obtained through the measurement using digital image correlation. Results show that the values obtained by the domain integral method are slightly better than those by the path integral method, because the domain integral method efficiently uses the full-field measurement data. The values of the J-integral are also evaluated by the least squares method with the Hutchinson, Rice, and, Rosengren displacement fields. Results show that the J-integral can be obtained by the least squares method simply and easily without any calculation of the integration. The J-integral values obtained by the least squares method agree well with the values obtained using other methods. Because J-integral can be evaluated easily by any method described in this paper, it is expected that these methods are applicable to various fracture problems during experimental evaluation of structural components.

Enhancing the Versatility and Functionality of Fast Photochromic Bridged Imidazole Dimers by Flipping Imidazole Rings

Abstract: The widely tunable optical properties and the visible sensitivity have been required for fast photochromic molecules whose coloration–decoloration cycle completes in μs to ms time scale not only for practical applications such as full-color holographic displays but also for fundamental researches in biochemistry. However, the so far developed [2.2]paracyclophane-bridged imidazole dimers, which are one of the best candidates for fast photochromic molecules, have their weaknesses for these requirements. Herein, we overcome the issues with sustaining fast photochromism and high durability by flipping the two imidazole rings (the head-to-tail and tail-to-tail forms). The alteration in the relative configuration of the imidazole rings suppresses the broad absorption band resulting from the radical–radical interaction. The substitution to the 2-position of the imidazole ring of the tail-to-tail form gives the drastic changes in the steady-state and the transient absorption spectra. The pyrene-substituted tail-t...

Luminescence behaviour in acetonitrile and in the solid state of a series of lanthanide complexes with a single helical ligand

Abstract: Luminescence mechanisms of EuIII, TbIII, GdIII and NdIII complexes with a hexadentate ligand (abbreviated to EuL, TbL, GdL, and NdL, respectively), which have two bipyridine moieties bridged by an ethylenediamine unit, have been examined. Our molecular design is that each complex forms a single helical polar structure based on the chelate ring to retain solubility in solutions. EuL and NdL show comparably bright emission from ff transitions both in acetonitrile solution and in the solid state. To understand the mechanism of the emission in detail, the energy level of the triplet (T) state of the ligand L has been estimated based on the phosphorescence measurements of GdL, because GdIII shows no ff emission. The donor level of the T state of L and the acceptor level of EuIII or NdIII can overlap, indicating that the excited photon localized on L has been used for the efficient ff emission, while not for ππ* emission. For TbL, the luminescence quantum yield is significantly dependent on temperature and the state: in the solid state of TbL, the quantum yield of ff emission is over 90% at 77 K, while no luminescence is observed at room temperature, and in solution TbL shows no emission. This observation suggests that the emissive f-level of TbIII and the energy donor level of the excited T state of L are in thermal equilibrium. The described lanthanide complexes are stable and retain their molecular structure even in solutions and show characteristic luminescence behaviour based on the energy relaxation process of each lanthanide ion. Furthermore the HoIII complex with L (HoL) has been prepared and its structure has been analyzed. HoL has a twisted arrangement of the bipyridine moiety surrounding HoIII due to the small ionic radius of HoIII.

Effects of stretching on mechanical properties of aligned multi-walled carbon nanotube/epoxy composites

Abstract: Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechanical stretching of the MWCNT sheets and their prepregs was conducted for this study. Mechanical stretching of the MWCNT sheets and hot stretching of the MWCNT/epoxy prepregs markedly improved the mechanical properties of the composites. The improved mechanical properties of stretched composites derived from the increased MWCNT volume fraction and the reduced MWCNT waviness caused by stretching. With a 3% stretch ratio, the MWCNT/epoxy composites achieved their best mechanical properties in this study. Although hot stretching of the prepregs increased the tensile strength and modulus of the composites considerably, its efficiency was lower than that of stretching the MWCNT sheets.

Long-lasting X-ray emission from type IIb supernova 2011dh and mass-loss history of the yellow supergiant progenitor

Abstract: Type IIb supernova (SN) 2011dh, with conclusive detection of an unprecedented yellow supergiant (YSG) progenitor, provides an excellent opportunity to deepen our understanding on the massive star evolution in the final centuries toward the SN explosion. In this paper, we report on detection and analyses of thermal X-ray emission from SN IIb 2011dh at ∼500 days after the explosion on Chandra archival data, providing a solidly derived mass-loss rate of a YSG progenitor for the first time. We find that the circumstellar media should be dense, more than that expected from a Wolf-Rayet (W-R) star by one order of magnitude. The emission is powered by a reverse shock penetrating into an outer envelope, fully consistent with the YSG progenitor but not with a W-R progenitor. The density distribution at the outermost ejecta is much steeper than that expected from a compact W-R star, and this finding must be taken into account in modeling the early UV/optical emission from SNe IIb. The derived mass-loss rate is ∼3 × 10{sup –6} M {sub ☉} yr{sup –1} for the mass-loss velocity of ∼20 km s{sup –1} in the final ∼1300 yr before the explosion. The derived mass-loss properties are largely consistent with themore » standard wind mass-loss expected for a giant star. This is not sufficient to be a main driver to expel nearly all the hydrogen envelope. Therefore, the binary interaction, with a huge mass transfer having taken place at ≳ 1300 yr before the explosion, is a likely scenario to produce the YSG progenitor.« less