On the Pronunciation of the Japanese Consonantal Length Contrast by Italian, French and English Native Speakers

国際基督教大学2018年

On the non-detection of gamma-rays from energetic millisecond pulsars -- dependence on viewing geometry

Millisecond pulsars (MSPs) and normal non-recycled pulsars are both detected in $\gamma$-rays. However, it appears that a much larger fraction of known energetic and nearby MSPs are detected in $\gamma$-rays, in comparison with normal pulsars, thereby making undetected $\gamma$-ray MSPs exceptions. In this paper, we demonstrate that the viewing angles (i.e. between the pulsar spin axis and the line of sight) are well described by the orbital inclination angles which, for binary MSPs with helium white dwarf companions, can be determined using the relationship between the orbital period and the white dwarf mass. We use the predicted viewing angles, in complement with values obtained from other constraints when available, to identify the causes of non-detection of energetic and nearby MSPs from the point of view of beaming geometry and orientation. We find evidence for slightly different viewing angle distributions, and postulate that energetic and nearby MSPs are mainly undetected in $\gamma$-rays simply because they are seen under unfavourable (i.e. small) viewing angles. We finally discuss the magnetic fields of $\gamma$-ray detected pulsars and show that pulsars which are efficient at converting their rotational energy into $\gamma$-ray emission may have overestimated dipolar magnetic field strengths.Comment: 11 pages, 6 figures. MNRAS, in press. Updated to reflect changes made at the proof stag

Rate distortion optimized graph partitioning for omnidirectional image coding

International audienceOmnidirectional images are spherical signals captured by cameras with 360-degree field of view. In order to be compressed using existing encoders, these signals are mapped to planar domain. A commonly used planar representation is the equirectangular one, which corresponds to a non uniform sampling pattern on the spherical surface. This particularity is not explored in traditional image compression schemes, which treat the input signal as a classical perspective image. In this work, we build a graph-based coder adapted to the spherical surface. We build a graph directly on the sphere. Then, to have computationally feasible graph transforms, we propose a rate-distortion optimized graph partitioning algorithm to achieve an effective trade-off between the distortion of the reconstructed signals, the smoothness of the signal on each subgraph, and the cost of coding the graph partitioning description. Experimental results demonstrate that our method outperforms JPEG coding of planar equirectangular images

Polynomial kernelization for removing induced claws and diamonds

A graph is called (claw,diamond)-free if it contains neither a claw (a $K_{1,3}$) nor a diamond (a $K_4$ with an edge removed) as an induced subgraph. Equivalently, (claw,diamond)-free graphs can be characterized as line graphs of triangle-free graphs, or as linear dominoes, i.e., graphs in which every vertex is in at most two maximal cliques and every edge is in exactly one maximal clique. In this paper we consider the parameterized complexity of the (claw,diamond)-free Edge Deletion problem, where given a graph $G$ and a parameter $k$, the question is whether one can remove at most $k$ edges from $G$ to obtain a (claw,diamond)-free graph. Our main result is that this problem admits a polynomial kernel. We complement this finding by proving that, even on instances with maximum degree $6$, the problem is NP-complete and cannot be solved in time $2^{o(k)}\cdot |V(G)|^{O(1)}$ unless the Exponential Time Hypothesis fai

Fermi Large Area Telescope observations of GRB 110625A

Gamma-ray bursts (GRBs) that emit photons at GeV energies form a small but significant population of GRBs. However, the number of GRBs whose GeV-emitting period is simultaneously observed in X-rays remains small. We report gamma-ray observations of GRB 110625A using Fermi's Large Area Telescope (LAT) in the energy range 100 MeV to 20 GeV. Gamma-ray emission at these energies was clearly detected using data taken between 180s and 580s after the burst, an epoch after the prompt emission phase. The GeV light curve differs from a simple power-law decay, and probably consists of two emission periods. Simultaneous Swift/XRT observations did not show flaring behaviors as in the case of GRB 100728A. We discuss the possibility that the GeV emission is the synchrotron self-Compton radiation of underlying ultraviolet flares.Comment: 6 pages, 3 figures, 1 table; accepted for publication in the ApJ on May 31, 201

Five New Millisecond Pulsars From a Radio Survey of 14 Unidentified Fermi-LAT Gamma-ray Sources

We have discovered five millisecond pulsars (MSPs) in a survey of 14 unidentified Fermi-LAT sources in the southern sky using the Parkes radio telescope. PSRs J0101-6422, J1514-4946, and J1902-5105 reside in binaries, while PSRs J1658-5324 and J1747-4036 are isolated. Using an ephemeris derived from timing observations of PSR J0101-6422 (P =2.57 ms, DM=12 pc cm-3), we have detected {\gamma}-ray pulsations and measured its proper motion. Its {\gamma}-ray spectrum (a power law of {\Gamma} = 0.9 with a cutoff at 1.6 GeV) and efficiency are typical of other MSPs, but its radio and {\gamma}-ray light curves challenge simple geometric models of emission. The high success rate of this survey-enabled by selecting {\gamma}-ray sources based on their detailed spectral characteristics-and other similarly successful searches indicate that a substantial fraction of the local population of MSPs may soon be known.Comment: 6 pages, 3 figures, 2 tables, accepted by ApJ

The VELA-X-Pulsar Wind Nebula Revisited with Four Years of Fermi Large Area Telescope Observations

The Vela supernova remnant (SNR) is the closest SNR to Earth containing an active pulsar, the Vela pulsar (PSR B0833-45). This pulsar is an archetype of the middle-aged pulsar class and powers a bright pulsar wind nebula (PWN), Vela-X, spanning a region of 2deg 3deg south of the pulsar and observed in the radio, X-ray, and very high energy -ray domains. The detection of the Vela-X PWN by the Fermi Large Area Telescope (LAT) was reported in the first year of the mission. Subsequently, we have reinvestigated this complex region and performed a detailed morphological and spectral analysis of this source using 4 yr of Fermi-LAT observations. This study lowers the threshold for morphological analysis of the nebula from 0.8 GeV to 0.3 GeV, allowing for the inspection of distinct energy bands by the LAT for the first time. We describe the recent results obtained on this PWN and discuss the origin of the newly detected spatial features

Positron annihilation in latex templated macroporous silica films: pore size and ortho-positronium escape

International audienceDepth profling of positron annihilation characteristics has been used to investigate the pore size distribution in macroporous PMMA latex templated SiO2 films deposited on glass or Si and prepared with 11-70% porosity. The correlation between the annihilation characteristics shows that o-Ps escape (re-emission) into vacuum occurs in all films with a porosity threshold that is pore size dependent. For 60 ± 2% porosity, the o-Ps reemission yield decreases from ~ 0:25 to ~ 0:11 as the pore size increases from 32 to 75 nm. The o-Ps reemission yield is shown to vary linearly with the specific surface area per mass unit and the slope is independent of pore size, 9:1±0:4 g cm-1. For 32 nm pores, the o-Ps annihilation lifetimes in the films, 17(2)ns and 106(5) ns, show that o-Ps annihilates from micropores with small effective size (1:4 ± 4 nm) and from macropores with large effective size (~ 32 nm). Above the porosity threshold, the o-Ps-escape model predicts the annihilation lifetime in the films to be 19±2 ns. Our results imply that o-Ps effciently detects the microporosity present in the silica walls. At low porosity, its capture into the micropores competes with its capture into the macropores. At higher porosity (when the distance between micropores and macropores become small), this capture into the micropores assists the capture into the macropores

Transient developmental imbalance of cortical interneuron subtypes presages long-term changes in behavior

Cortical GABAergic interneurons are generated in large numbers in the ganglionic eminences and migrate into the cerebral cortex during embryogenesis. At early postnatal stages, during neuronal circuit maturation, autonomous and activity-dependent mechanisms operate within the cortex to adjust cell numbers by eliminating naturally occurring neuron excess. Here, we show that when cortical interneurons are generated in aberrantly high numbers—due to a defect in precursor cell proliferation during embryogenesis—extra parvalbumin interneurons persist in the postnatal mouse cortex during critical periods of cortical network maturation. Even though cell numbers are subsequently normalized, behavioral abnormalities remain in adulthood. This suggests that timely clearance of excess cortical interneurons is critical for correct functional maturation of circuits that drive adult behavior