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A search for Galactic transients disguised as gamma-ray bursts
摘要： Context. A signi?cant fraction of cosmological gamma-ray bursts (GRBs) are characterised by a fast rise and exponential decay (FRED) temporal structure. This is not a distinctive feature of this class, since it is observed in many Galactic transients and is likely descriptive of a sudden release of energy followed by a di?usion process. Possible evidence has recently been reported for a Galactic contamination in the sample of FRED GRBs discovered with Swift. Aims. We searched for possible Galactic intruders disguised as FRED GRBs in the Swift catalogue up to September 2014. Methods. We selected 181 FRED GRBs (2/3 with unknown redshift) and considered di?erent subsamples. We tested the degree of isotropy through the dipole and quadrupole moment distributions, both with reference to the Galaxy and independent of any coordinate system as well as with the two-point angular autocovariance function. In addition, we searched for possible indicators of a Galactic origin among the spectral and temporal properties of individual GRBs. Results. We found marginal (～3σ) evidence for an excess of FREDs with unknown redshift towards the Galactic plane compared with what is expected for an isotropic distribution corrected for the non-uniform sky exposure. However, when we account for the observational bias against optical follow-up observations of low-Galactic latitude GRBs, the evidence for anisotropy decreases to ～2σ. In addition, we found no statistical evidence for di?erent spectral or temporal properties from the bulk of cosmological GRBs. Conclusions. We found marginal evidence for the presence of a disguised Galactic population among Swift GRBs with unknown redshift. The estimated fraction is f = (19 ± 11)%, with an upper limit of 34% (90% con?dence).
关键词： gamma-ray burst: general,methods: statistical
更新于2025-09-04 15:30:14
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Annealing effects on recombinative activity of nickel at direct silicon bonded interface
摘要： By performing capacitance transient analyses, the recombination activity at a (110)/(100) direct silicon bonded (DSB) interface contaminated with nickel diffused at different temperatures, as a model of grain boundaries in multicrystalline silicon, was studied. The trap level depth from the valence band, trap density of states, and hole capture cross section peaked at an annealing temperature of 300 ?C. At temperatures (cid:62)400 ?C, the hole capture cross section increased with temperature, but the density of states remained unchanged. Further, synchrotron-based X-ray analyses, microprobe X-ray fluorescence (μ-XRF), and X-ray absorption near edge structure (XANES) analyses were performed. The analysis results indicated that the chemical phase after the sample was annealed at 200 ?C was a mixture of NiO and NiSi2.
关键词： direct silicon bonded interface,recombination activity,annealing effects,X-ray analyses,nickel,capacitance transient analyses
更新于2025-09-04 15:30:14
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Investigation of low temperature bonding process using indium bumps
摘要： Hybrid pixel detector modules are state of the art components of X-ray cameras in synchrotron radiation experiments. Temperature-sensitive, high-Z sensor materials like Germanium, Cadmium-Telluride, Cadmium-Zinc-Telluride and MCT-sensors require an especially low temperature bonding process. The investigation presented in this paper focuses on a low temperature compression bonding process using a ductile bump material, like indium, and a dedicated UBM surface that is able to form intermetallic compounds with this bump metal. The test samples are based on a test chip design with the size of the MEDIPIX3 readout chip and an identical number of bumps, arranged in a 256 × 256 bump matrix with 55 μm pitch in X- and Y-directions. In addition to the indium bumped test chip, two typical UBM-pad configurations were investigated on the corresponding interconnect side: a pad-defined electroplated Ni-Au-UBM and a passivation opening-defined, PVD-deposited NiV-Au pad. Daisy chain structures, 4-Point-probe resistance measurement structures and isolation test structures were implemented to characterize the influence of bonding pressure, bonding temperature and dwell time of bonding pressure on the electrical interconnection resistance. Good bonding results and a corresponding minimum electrical resistance of daisy chains and individual interconnects were achieved at temperatures of 80?C and 100?C. A minimum bonding pressure of 3.2 MPa was necessary to achieve reliable bonding results. Daisy chain failures occurred especially in the corner of the chips. After electrical characterization, pull tests were performed to investigate the corresponding bonding area. Pull test results showed a larger bonding area for the pad-defined, electroplated UBM pad configuration in comparison to the passivation opening defined bonding pad.
关键词： Hybrid detectors,X-ray detectors,Solid state detectors
更新于2025-09-04 15:30:14
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Demonstration of resonant inelastic x-ray scattering as a probe of exciton-phonon coupling
摘要： Resonant inelastic x-ray scattering (RIXS) is a promising technique for obtaining electron-phonon coupling constants. However, the ability to extract these coupling constants throughout the Brillouin zone for crystalline materials remains limited. To address this need, we developed a Green’s function formalism to capture electron-phonon contributions to core-level spectroscopies without explicitly solving the full vibronic problem. Our approach is based on the cumulant expansion of the Green’s function combined with many-body theory calculated vibrational coupling constants. The methodology is applied to x-ray photoemission spectroscopy, x-ray absorption spectroscopy (XAS), and RIXS. In the case of the XAS and RIXS, we use a two-particle exciton Green’s function, which accounts implicitly for particle-hole interference effects that have previously proved difficult. To demonstrate the methodology and gain a deeper understanding of the experimental technique, we apply our formalism to small molecules, for which unambiguous experimental data exist. This comparison reveals that the vibronic coupling constant probed by RIXS is in fact related to exciton-phonon coupling rather than electron-phonon coupling, challenging the conventional interpretation of the experiment.
关键词： electron-phonon coupling,Green’s function formalism,exciton-phonon coupling,Resonant inelastic x-ray scattering,vibronic coupling
更新于2025-09-04 15:30:14
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PHOTOMETRIC ANALYSIS OF PI OF THE SKY DATA
摘要： Pi of the Sky is a system of two wide ?eld of view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical GRB emissions. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m–13m range and time resolution of the order of 1–10 seconds. Two fully automatic Pi of the Sky detectors located in Spain (INTA — INTA El Arenosillo Test Centre in Mazagón, near Huelva.) and Chile (SPDA — San Pedro de Atacama Observatory.) have been observing the sky almost every night in search of rare optical phenomena. They also collect a lot of useful observations which include e.g. many kinds of variable stars. To be able to draw proper conclusions from the data received, adequate quality of the data is very important. Pi of the Sky data is subject to systematic errors caused by various factors, such as cloud cover, seen as signi?cant ?uctuations in the number of stars observed by the detector, problems with conducting mounting, a strong background of the moon or the passing of a bright object, e.g., a planet, near the observed star. Some of these adverse e?ects have already been detected during the cataloging of individual measurements, but the quality of our data was still not satisfactory for us. In order to improve the quality of our data, we have developed two new procedures based on two di?erent approaches. In this article we will report on these procedures, give some examples, and we will show how these procedures improve the quality of our data[1].
关键词： variable stars,photometry,data quality,robotic telescopes,astrometry,photometric corrections,Gamma Ray Burst (GRB)
更新于2025-09-04 15:30:14
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA, USA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Detector response function of a HPGe detector to photon energies between 200 keV and 1.5 MeV for Gamma-ray nondestructive assay instrument
摘要： A semi-empirical detector response function (DRF) model of HPGe detector was proposed to fit gamma-ray nondestructive assay transmission spectra. The model for each single peak contained a step function, a Gaussian function, and an exponential tail function. The Gaussian standard deviation obtained by electronic noise and Fano factor, so our DRF only had 4 parameters and they were obtained by the weighted nonlinear least-squares fitting method. In the application, 152Eu spectra were obtained by using the 30%, 50%, 70% HPGe detector, and fitted by the established DRF model. Reduced chi- square values were at the interval of 0.039-0.202. Its validity that the model had good versatility, can be applicable to different detection efficiency of HPGe detectors.
关键词： gamma-ray nondestructive assay,HPGe detector,semi-empirical model,detector response function
更新于2025-09-04 15:30:14
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Deposition of Amorphous Carbon Thin Films by RF Magnetron Sputtering using Woodceramics as Target
摘要： Woodceramics, a substance based on woody materials carbonized at elevated temperatures after impregnating with phenolic resin, have been developed as a new kind of porous carbonaceous material. To expand the industrial application, we attempted to produce amorphous carbon films were RF magnetron sputtering using woodceramics as its target. As a result, typical amorphous carbon films were successfully produced using woodceramics, and the films were characterized by X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The films produced were composed of carbon turbostratic structure or amorphous whose electron configurations consisted of sp2 and sp3. The ratio of sp3 bonding in the films were about 53% just after the sputtering, but the number increased to about 82% after etching the material using argon ions. Fundamental mechanical properties such as hardness and friction coefficient were also measured and taken into account.
关键词： magnetron sputtering,Raman spectroscopy,X-ray photoelectron spectroscopy,amorphous carbon film,woodceramics
更新于2025-09-04 15:30:14
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Enhancement of Localization Systems in NLOS Urban Scenario with Multipath Ray Tracing Fingerprints and Machine Learning
摘要： A hybrid technique is proposed to enhance the localization performance of a time difference of arrival (TDOA) deployed in non-line-of-sight (NLOS) suburban scenario. The idea was to use Machine Learning framework on the dataset, produced by the ray tracing simulation, and the Channel Impulse Response estimation from the real signal received by each sensor. Conventional localization techniques mitigate errors trying to avoid NLOS measurements in processing emitter position, while the proposed method uses the multipath fingerprint information produced by ray tracing (RT) simulation together with calibration emitters to refine a Machine Learning engine, which gives an extra layer of information to improve the emitter position estimation. The ray-tracing fingerprints perform the target localization embedding all the reflection and diffraction in the propagation scenario. A validation campaign was performed and showed the feasibility of the proposed method, provided that the buildings can be appropriately included in the scenario description.
关键词： time difference of arrival localization,machine learning,cooperative positioning,multipath exploitation,hybrid positioning,ray tracing fingerprints,wireless positioning
更新于2025-09-04 15:30:14
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Structural and optical properties of (Cu6PS5Br)1-(Cu7PS6) mixed crystals
摘要： The structure and optical properties of Bridgman-grown (Cu6PS5Br)1-x(Cu7PS6)x mixed crystals are reported. X-ray diffraction data reveal a face-centred cubic lattice (Fm-34 space group) for Cu6PS5Br-rich crystals (0<x<0.4) and a primitive cubic lattice (P213 space group) for Cu7PS6-rich (0.4<x<1) crystals. These structural data correlate with the Raman spectra where, besides the common features typical for the argyrodite-type Cu6PS5Br and Cu7PS6 crystals, weaker bands characteristic only for the end-point compounds are observed in the corresponding compositional intervals. Based on the spectral position of the short-wavelength edge of diffuse reflection spectra, the compositional dependence of the energy gap is studied exhibiting a nonlinear behaviour.
关键词： Inorganic materials,crystal growth,diffuse reflection,Raman scattering,X-ray diffraction,crystal structure
更新于2025-09-04 15:30:14
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Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers
摘要： Plastic strain relaxation in epitaxial layers is one of the crucial factors that limit the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important towards the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.
关键词： X-ray diffraction,cracks,graded layers,epitaxy,strain relaxation,AlGaN
更新于2025-09-04 15:30:14