12 research outputs found
A re-visit of the phase-resolved X-ray and \gamma-ray spectra of the Crab pulsar
We use a modified outer gap model to study the multi-frequency phase-resolved
spectra of the Crab pulsar. The emissions from both poles contribute to the
light curve and the phase-resolved spectra. Using the synchrotron self-Compton
mechanism and by considering the incomplete conversion of curvature photons
into secondary pairs, the observed phase-averaged spectrum from 100 eV - 10 GeV
can be explained very well. The predicted phase-resolved spectra can match the
observed data reasonably well, too. We find that the emission from the north
pole mainly contributes to Leading Wing 1. The emissions in the remaining
phases are mainly dominated by the south pole. The widening of the azimuthal
extension of the outer gap explains Trailing Wing 2. The complicated
phase-resolved spectra for the phases between the two peaks, namely Trailing
Wing 1, Bridge and Leading Wing 2, strongly suggest that there are at least two
well-separated emission regions with multiple emission mechanisms, i.e.
synchrotron radiation, inverse Compton scattering and curvature radiation. Our
best fit results indicate that there may exist some asymmetry between the south
and the north poles. Our model predictions can be examined by GLAST.Comment: 35 pages, 13 figures, accepted to publish in Ap
Thermal X-Ray Pulses Resulting From Pulsar Glitches
The non-spherically symmetric transport equations and exact thermal evolution
model are used to calculate the transient thermal response to pulsars. The
three possible ways of energy release originated from glitches, namely the
`shell', `ring' and `spot' cases are compared. The X-ray light curves resulting
from the thermal response to the glitches are calculated. Only the `spot' case
and the `ring' case are considered because the `shell' case does not produce
significant modulative X-rays. The magnetic field () effect, the
relativistic light bending effect and the rotational effect on the photons
being emitted in a finite region are considered. Various sets of parameters
result in different evolution patterns of light curves. We find that this
modulated thermal X-ray radiation resulting from glitches may provide some
useful constraints on glitch models.Comment: 48 pages, 20 figures, submitted to Ap
Three-dimensional Two-Layer Outer Gap Model: Fermi Energy Dependent Light Curves of the Vela Pulsar
We extend the two-dimensional two-layer outer gap model to a
three-dimensional geometry and use it to study the high-energy emission of the
Vela pulsar. In this model, the outer gap is divided into two parts, i.e. the
main acceleration region on the top of last-open field lines and the screening
region around the upper boundary of the gap. In the main acceleration region,
the charge density is much lower than the Goldreich-Julian charge density and
the charged particles are accelerated by the electric field along the magnetic
field to emit multi-GeV photons. In the screening region, the charge density is
larger than the Goldreich-Julian value to close the gap and particles in this
region are responsible for multi-100MeV photon emission. We apply this three
dimensional two-layer model to the Vela pulsar and compare the model light
curves, the phase-averaged spectrum and the phase-resolved spectra with the
recent Fermi observations, which also reveals the existence of the third peak
between two main peaks. The phase position of the third peak moves with the
photon energy, which cannot be explained by the geometry of magnetic field
structure and the caustic effects of the photon propagation. We suggest that
the existence of the third peak and its energy dependent movement results from
the azimuthal structure of the outer gap.Comment: 11 pages, 15 figures, accepted for publication in MNRA
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Texture spectrum coupled with entropy and homogeneity image features for myocardium muscle characterization
People in middle/later age often suffer from heart muscle damage due to coronary artery disease associated to myocardial infarction. In young people, the genetic forms of cardiomyopathies (heart muscle disease) are the utmost protuberant cause of myocardial disease. Accurate early detected information regarding the myocardial tissue structure is a key answer for tracking the progress of several myocardial diseases. The present work proposes a new method for myocardium muscle texture classification based on entropy, homogeneity and on the texture unit-based texture spectrum approaches. Entropy and homogeneity are generated in moving windows of size 3x3 and 5x5 to enhance the texture features and to create the premise of differentiation of the myocardium structures. Texture is then statistically analyzed using the texture spectrum approach. Texture classification is achieved based on a fuzzy câmeans descriptive classifier. The noise sensitivity of the fuzzy câmeans classifier is overcome by using the image features. The proposed method is tested on a dataset of 80 echocardiographic ultrasound images in both short-axis and long-axis in apical two chamber view representations, for normal and infarct pathologies. The results established that the entropy-based features provided superior clustering results compared to homogeneity
Aktualisasi Nilai Keimanan dalam Konteks Masyarakat Berkeadilan
Agama, dalam pengertian tradisional yang sering dipresentasikan dalam ensiklopedi, kamus maupun sejarah agama-agarna, identik dengan sebuah kekuatan supernatural, magic, ritual, persembahan, dogma, kitab suci, ataupun tempat-rempat suci. Akan tetapi Islam sebagai agama, nampaknya tidak tepat jika sekadar dideskripsikan dalam frame kategori-kategori tradisional tersebul. Islam lebih cocok dengan apa yang kemudian hari dikenalkan oleh filsafat modem, yaitu agama kehidupan (a religion of nature), bukan supernatural, agama yang dapat dicerna oleh akal manusia (a religion of reason), dan bukan agama Tuhan yang tak terjangkau akal manusia (super-reason). Dalam Islam, wahyu dan kehidupan adalah sejajar, sebab wahyu diturunkan untuk kehidupan, sebagai ajakan untuk melakukan Perubahan sosial (social change) dan gerakan pembebasan. Dalam Islam, wahyu dan akal adalah sejawat, sebab tidak ada satupun wahyu yang kontradiktif terhadap akal. Tidak ada misteri dalam keyakinan Islam. wahyu, akal dan kehidupan merupakan tiga esensi Islam yang saling berdialektika
Polyphosphate Stores Enhance the Ability of Vibrio cholerae To Overcome Environmental Stresses in a Low-Phosphate Environment
Vibrio cholerae, the causative agent of Asiatic cholera, has been reported to make large quantities of polyphosphate. Inorganic polyphosphate is a ubiquitous molecule with a variety of functions in prokaryotic and eukaryotic cells. We constructed a V. cholerae mutant with a deletion in the polyphosphate kinase (ppk) gene. The mutant was defective in polyphosphate biosynthesis. Deletion of ppk had no significant effect on production of cholera toxin, hemagglutinin/protease, motility, biofilm formation, and colonization of the suckling mouse intestine. The wild type and mutant had similar growth rates in rich and minimal medium and exhibited similar phosphate uptake and alkaline phosphatase induction. In contrast to ppk mutants from other gram-negative bacteria, the V. cholerae mutant survived prolonged starvation in LB medium and artificial seawater basal salts. The ppk mutant was significantly more sensitive to low pH, high salinity, and oxidative stress when it was cultured in low-phosphate minimal medium. The ppk mutant failed to induce catalase when it was downshifted to phosphorus-limiting conditions. Furthermore, the increased sensitivity of the ppk mutant to environmental stressors in phosphate-limited medium correlated with a diminished capacity to synthesize ATP from intracellular reservoirs. We concluded that polyphosphate protects V. cholerae from environmental stresses under phosphate limitation conditions. It has been proposed that toxigenic V. cholerae can survive in estuaries and brackish waters in which phosphorus and/or nitrogen can be a limiting nutrient. Thus, synthesis of large polyphosphate stores could enhance the ability of V. cholerae to survive in the aquatic environment