61,222 research outputs found
Voice Service Support in Mobile Ad Hoc Networks
Mobile ad hoc networks are expected to support voice traffic. The requirement
for small delay and jitter of voice traffic poses a significant challenge for
medium access control (MAC) in such networks. User mobility makes it more
complex due to the associated dynamic path attenuation. In this paper, a MAC
scheme for mobile ad hoc networks supporting voice traffic is proposed. With
the aid of a low-power probe prior to DATA transmissions, resource reservation
is achieved in a distributed manner, thus leading to small delay and jitter.
The proposed scheme can automatically adapt to dynamic path attenuation in a
mobile environment. Simulation results demonstrate the effectiveness of the
proposed scheme.Comment: To appear in the Proceedings of the IEEE Global Communications
Conference (GLOBECOM), Washington, DC, November 26 - 30, 200
The effect of activity-related meridional flow modulation on the strength of the solar polar magnetic field
We studied the effect of the perturbation of the meridional flow in the
activity belts detected by local helioseismology on the development and
strength of the surface magnetic field at the polar caps. We carried out
simulations of synthetic solar cycles with a flux transport model, which
follows the cyclic evolution of the surface field determined by flux emergence
and advective transport by near-surface flows. In each hemisphere, an
axisymmetric band of latitudinal flows converging towards the central latitude
of the activity belt was superposed onto the background poleward meridional
flow. The overall effect of the flow perturbation is to reduce the latitude
separation of the magnetic polarities of a bipolar magnetic region and thus
diminish its contribution to the polar field. As a result, the polar field
maximum reached around cycle activity minimum is weakened by the presence of
the meridional flow perturbation. For a flow perturbation consistent with
helioseismic observations, the polar field is reduced by about 18% compared to
the case without inflows. If the amplitude of the flow perturbation depends on
the cycle strength, its effect on the polar field provides a nonlinearity that
could contribute to limiting the amplitude of a Babcock-Leighton type dynamo.Comment: 16 pages, 5 figures, accepted by Ap
The evolution-dominated hydrodynamic model and the pseudorapidity distributions in high energy physics
By taking into account the effects of leading particles, we discuss the
pseudorapidity distributions of the charged particles produced in high energy
heavy ion collisions in the context of evolution-dominated hydrodynamic model.
The leading particles are supposed to have a Gaussian rapidity distribution
normalized to the number of participants. A comparison is made between the
theoretical results and the experimental measurements performed by BRAHMS and
PHOBOS Collaboration at BNL-RHIC in Au-Au and Cu-Cu collisions at sqrt(s_NN)
=200 GeV and by ALICE Collaboration at CERN-LHC in Pb-Pb collisions at
sqrt(s_NN) =2.76 TeV.Comment: 17 pages,4 figures, 2 table
Cyber Insurance for Heterogeneous Wireless Networks
Heterogeneous wireless networks (HWNs) composed of densely deployed base
stations of different types with various radio access technologies have become
a prevailing trend to accommodate ever-increasing traffic demand in enormous
volume. Nowadays, users rely heavily on HWNs for ubiquitous network access that
contains valuable and critical information such as financial transactions,
e-health, and public safety. Cyber risks, representing one of the most
significant threats to network security and reliability, are increasing in
severity. To address this problem, this article introduces the concept of cyber
insurance to transfer the cyber risk (i.e., service outage, as a consequence of
cyber risks in HWNs) to a third party insurer. Firstly, a review of the
enabling technologies for HWNs and their vulnerabilities to cyber risks is
presented. Then, the fundamentals of cyber insurance are introduced, and
subsequently, a cyber insurance framework for HWNs is presented. Finally, open
issues are discussed and the challenges are highlighted for integrating cyber
insurance as a service of next generation HWNs.Comment: IEEE Communications Magazine (Heterogeneous Ultra Dense Networks
A dynamic information transfer and feedback model for reuse-oriented redesign of used mechanical equipment
- …