86,717 research outputs found
Gamma-ray Emission from Millisecond Pulsars - An Outergap Perspective
In this review paper we explain the following gamma-ray emission features
from the millisecond pulsars. (1)Why is the dipolar field of millisecond
pulsars so weak but the magnetic pair creation process may still be able to
control the size of the outergap? (2)A sub-GeV pulse component could occur in
the vicinity of the radio pulse of millisecond pulsars. (3)Orbital modulated
gamma-rays should exist in the black widow systems for large viewing angle.Comment: This is the proceeding paper of 3rd Fermi Asian Network Workshop and
will be published by Journal of the Korea Space Science Societ
Low carbon manufacturing: Characterization, theoretical models and implementation
Today, the rising of carbon dioxide (CO2) emissions is becoming the crucial factor for global warming especially in industrial sectors. Therefore, the research to reduce carbon intensity and enhance resources utilization in manufacturing industry is starting to be a timely topic. Low carbon manufacturing (LCM) can be referred to the manufacturing process that produces low carbon emissions intensity and uses energy and resources efficiently and effectively during the process as well.
In this paper, the concepts of LCM are discussed and the LCM associated theoretical models, characterization and implementation perspective explored. The paper is structured in four parts. Firstly, the conception of low carbon manufacturing is critically reviewed then the characterization of low carbon manufacturing is discussed and formulated. Third part, the theoretical models are developed with initial models by using the theory from supply chain modeling and linear programming solutions (LP). The models show the relationship of resource utilizations and related variables for LCM in two levels: shop-floor and extended supply chain. Finally, the pilot implementations of LCM are discussed with two approaches: desktop or micro machines and devolved manufacturing. The paper is concluded with further discussions on the potential and application of LCM for manufacturing industry
X-ray/GeV emissions from Crab-like pulsars in LMC
We discuss X-ray and gamma-ray emissions from Crab-like pulsars,
PSRs~J0537-6910 and~J0540-6919, in Large Magellanic Cloud. Fermi-LAT
observations have resolved the gamma-ray emissions from these two pulsars and
found the pulsed emissions from PSR~J0540-6919. The total pulsed radiation in
the X-ray/gamma-ray energy bands of PSR~J0540-6919 is observed with the
efficiency (in 4 sr), which is about a factor of
ten larger than of the Crab pulsar. Although
PSR~J0537-6910 has the highest spin-down power among currently known pulsars,
the efficiency of the observed X-ray emissions is about two orders of magnitude
smaller than that of PSR~J0540-6919. This paper mainly discusses what causes
the difference in the radiation efficiencies of these three energetic Crab-like
pulsars. We discuss electron/positron acceleration and high-energy emission
processes within the outer gap model. By solving the outer gap structure with
the dipole magnetic field, we show that the radiation efficiency decreases as
the inclination angle between the magnetic axis and the rotation axis
increases. To explain the difference in the pulse profile and in the radiation
efficiency, our model suggests that PSR~J0540-6919 has an inclination angle
much smaller than the that of Crab pulsar (here we assume the inclination
angles of both pulsars are ). On the other hand, we
speculate that the difference in the radiation efficiencies between
PSRs~J0537-6910 and J0549-6919 is mainly caused by the difference in the Earth
viewing angle, and that we see PSR~J0537-6910 with an Earth viewing angle
(or ) measured from the spin axis, while we
see PSR~J0540-6919 with .Comment: 23 pages, 7 figures, ApJ in pres
Constraints on extra-dimensions and variable constants from cosmological gamma ray bursts
The observation of the time delay between the soft emission and the
high-energy radiation from cosmological gamma ray bursts can be used as an
important observational test of multi-dimensional physical theories. The main
source of the time delay is the variation of the electromagnetic coupling, due
to dimensional reduction, which induces an energy dependence of the speed of
light. For photons with energies around 1 TeV, the time delay could range from
a few seconds in the case of Kaluza-Klein models to a few days for models with
large extra-dimensions. Based on these results we suggest that the detection of
the 18-GeV photon 4500 s after the keV/MeV burst in GRB 940217 provides
a strong evidence for the existence of extra-dimensions. The time delay of
photons, if observed by the next generation of high energy detectors, like, for
example, the SWIFT and GLAST satellite based detectors, or the VERITAS
ground-based TeV gamma-ray instrument, could differentiate between the
different models with extra-dimensions.Comment: 8 pages, 4 figures, contribution to the proceedings of the II
Workshop on Unidentified Gamma-Ray Sources, Hong Kong, June 1-4, 200
Localization of a Bose-Fermi mixture in a bichromatic optical lattice
We study the localization of a cigar-shaped super-fluid Bose-Fermi mixture in
a quasi-periodic bichromatic optical lattice (OL) for inter-species attraction
and intra-species repulsion. The mixture is described by the Gross-Pitaevskii
equation for the bosons, coupled to a hydrodynamic mean-field equation for
fermions at unitarity. We confirm the existence of the symbiotic localized
states in the Bose-Fermi mixture and Anderson localization of the Bose
component in the interacting Bose-Fermi mixture on a bichromatic OL. The phase
diagram in boson and fermion numbers showing the regions of the symbiotic and
Anderson localization of the Bose component is presented. Finally, the
stability of symbiotic and Anderson localized states is established under small
perturbations
Symmetry breaking in a localized interacting binary BEC in a bi-chromatic optical lattice
By direct numerical simulation of the time-dependent Gross-Pitaevskii
equation using the split-step Fourier spectral method we study different
aspects of the localization of a cigar-shaped interacting binary
(two-component) Bose-Einstein condensate (BEC) in a one-dimensional
bi-chromatic quasi-periodic optical-lattice potential, as used in a recent
experiment on the localization of a BEC [Roati et al., Nature 453, 895 (2008)].
We consider two types of localized states: (i) when both localized components
have a maximum of density at the origin x=0, and (ii) when the first component
has a maximum of density and the second a minimum of density at x=0. In the
non-interacting case the density profiles are symmetric around x=0. We
numerically study the breakdown of this symmetry due to inter-species and
intra-species interaction acting on the two components. Where possible, we have
compared the numerical results with a time-dependent variational analysis. We
also demonstrate the stability of the localized symmetry-broken BEC states
under small perturbation.Comment: 9 page
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