36,557 research outputs found
Implications of Fermi-LAT observations on the origin of IceCube neutrinos
The IceCube (IC) collaboration recently reported the detection of TeV-PeV
extraterrestrial neutrinos whose origin is yet unknown. By the photon-neutrino
connection in and interactions, we use the \fermi-LAT
observations to constrain the origin of the IC detected neutrinos. We find that
Galactic origins, i.e., the diffuse Galactic neutrinos due to cosmic ray (CR)
propagation in the Milky Way, and the neutrinos from the Galactic point
sources, may not produce the IC neutrino flux, thus these neutrinos should be
of extragalactic origin. Moreover, the extragalactic gamma-ray bursts (GRBs)
may not account for the IC neutrino flux, the jets of active galactic nuclei
may not produce the IC neutrino spectrum, but the starburst galaxies (SBGs) may
be promising sources. As suggested by the consistency between the IC detected
neutrino flux and the Waxman-Bahcall bound, GRBs in SBGs may be the sources of
both the ultrahigh energy, eV, CRs and the ~PeV CRs that
produce the IC detected TeV-PeV neutrinos.Comment: JCAP accepted version; 8 pages, 2 figs; discussion on blazar origin
added; conclusion unchange
Pumping Current in a Quantum Dot by an Oscillating Magnetic Field
We investigate spin and charge current through a quantum dot pumped by a
time-varying magnetic field. Using the density matrix method, quantum rate
equations for the electronic occupation numbers in the quantum dot are obtained
and solved in the stationary state limit for a wide set of setup parameters.
Both charge and spin current are expressed explicitly in terms of several
relevant parameters and analyzed in detail. The results suggest a way of
optimizing experimental setup parameters to obtain an maximal spin current
without the charge current flow.Comment: to appear in the proceedings of the international conference on
frontiers in nonlinear and complex systems as a special issue in the
International Journal of Modern Physics B, vol. 21
Entanglement spectrum: Identification of the transition from vortex-liquid to vortex-lattice state in a weakly interacting rotating Bose-Einstein condensate
We use entanglement to investigate the transition from vortex liquid phase to
vortex lattice phase in weakly interacting rotating Bose-Einstein condensate
(BEC). Ground state entanglement spectrum is analyzed to distinguish these two
different phases. For the torus geometry, the low-lying part of ground state
entanglement spectrum, as well as the behavior of its lowest level change
clearly when the transition occurs. For the sphere geometry, the disappearance
of entanglement gap in the conformal limit (CL) can indicate this transition.
We also show that the decrease of entanglement between particles can be
regarded as a signal of the transition.Comment: published versio
Probing for the Cosmological Parameters with PLANCK Measurement
We investigate the constraints on cosmological parameters especially for EoS
of dark energy, inflationary parameters, neutrino mass and curvature of
universe using simulated Planck data. Firstly we determine cosmological
parameters with current observations including ESSENCE, WMAP3, Boomerang-2K2,
CBI, VSA, ACBAR, SDSS LRG and 2dFGRS, and take best-fit model as the fiducial
model in simulations. In simulations we pay attention to the effects of
dynamical dark energy in determination of cosmological parameters. We add
simulated SNAP data to do all the simulations. Using present data, we find
Quintom dark energy model is mildly favored while \LambdaCDM remains a good
fit. In the framework of dynamical dark energy, the constraints on inflationary
parameters, m_{\nu} and \Omega_{K} become weak compared with the constraints in
\LambdaCDM. Intriguingly, we find that the inflationary models with a "blue"
tilt, which are excluded about 2\sigma in \LambdaCDM model, are well within
2\sigma region with the presence of the dynamics of dark energy. The upper
limits of neutrino mass are weakened by a factor of 2 (95% C.L.), say,
m_{\nu}<1.59 eV and m_{\nu}<1.53 eV for two forms of parametrization of the
equation of state of dark energy. The flat universe is a good fit to the
current data, namely, |\Omega_{K}|<0.03 (95% C.L.). With the simulated Planck
and SNAP data, dynamical dark energy and \LambdaCDM might be distinguished at
4\sigma. And uncertainties of inflationary parameters, m_{\nu} and \Omega_{K}
can be reduced obviously. We also constrain the rotation angle \Delta\alpha,
denoting possible cosmological CPT violation, with simulated Planck and CMBpol
data and find that our results are much more stringent than current constraint
and will verify cosmological CPT symmetry with a higher precision. (Abridged)Comment: 15 pages, 8 figures and 3 tables, Accepted for publication in
Int.J.Mod.Phys.
Research on the Influence of Perceived Risk in Consumer On-line Purchasing Decision
AbstractPerceived risk is an important factor that affects consumer's on-line shopping purchasing decision, through the perceived theories the consumer can know clearly which step owns higher risk in the whole shopping process, then learn how to prevent it, this process also strengthen the consumer confidence, thus lowering to know that the risk adjudicate to the feeling, so the essay has important and realistic meaning for further expand the electronic commerce. At first, investigate, collect, tidy up, analyze the questionnaire information, and thus get the primary data. Finally try to find out the influence of perceived risk to each stage of purchasing decision during consumer on-line shopping process with data and personal analytical. The paper is a complement to the local and existing perceived theories. The result of the study manifests that, the order of main perceived risks which felt by consumer during on-line shopping process are as follow: financial risk, the performance risk and service risk
How Can Self-regulated Learning Be Supported in E-learning 2.0 Environment: a Comparative Study
As a critical factor that affects the learning performance in distance education, self-regulated learning (SRL) has elicited considerable interest. Self-regulated learners can manage their learning activities efficiently but researchers indicate that learners have difficulties in SRL behavior. Thus, providing support to facilitate self-regulatory processes is important. E-learning has the potential to be a learning tool to examine students’ self-regulatory skills. New advances in technology, especially the development of Web 2.0 technology, have provided effective support for self-regulated learning. This study addresses the following research question: How can SRL be supported properly in E-learning environment? Because learning processes cannot be conceptualized without the sociocultural context this study investigate environmental variations between two samples of Mainland China and Hong Kong distance learners (N=289). The purpose is to chart the underlying relationships between learner self-regulation and distance education environments using regression analysis and to find differences of environmental factors and self-regulation in different cultural orientations. The study has found significant differences between Mainland China and Hong Kong distance students on demography variables except age characteristics. In the relation model however, no difference has been found. Self-regulation is to be equivalent in the two cultures and can be influenced by the same environmental factors
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