2,264 research outputs found
Cooperative Beamforming for Wireless Ad Hoc Networks
Via collaborative beamforming, nodes in a wireless network are able to
transmit a common message over long distances in an energy efficient fashion.
However, the process of making available the same message to all collaborating
nodes introduces delays. In this paper, a MAC-PHY cross-layer scheme is
proposed that enables collaborative beamforming at significantly reduced
collaboration overhead. It consists of two phases. In the first phase, nodes
transmit locally in a random access time-slotted fashion. Simultaneous
transmissions from multiple source nodes are viewed as linear mixtures of all
transmitted packets. In the second phase, a set of collaborating nodes, acting
as a distributed antenna system, beamform the received analog waveform to one
or more faraway destinations. This step requires multiplication of the received
analog waveform by a complex weight, which is independently computed by each
cooperating node, and which allows packets bound to the same destination to add
coherently at the destination node. Assuming that each node has access to
location information, the proposed scheme can achieve high throughput, which in
certain cases exceeds one. An analysis of the symbol error probability
corresponding to the proposed scheme is provided.Comment: 5 pages, 4 figures. To appear in the Proceedings of the IEEE Global
Communications Conference (GLOBECOM), Washington, DC, November 26 - 30, 200
Cross-layer optimization in TCP/IP networks
TCP-AQM can be interpreted as distributed primal-dual algorithms to maximize aggregate utility over source rates. We show that an equilibrium of TCP/IP, if exists, maximizes aggregate utility over both source rates and routes, provided congestion prices are used as link costs. An equilibrium exists if and only if this utility maximization problem and its Lagrangian dual have no duality gap. In this case, TCP/IP incurs no penalty in not splitting traffic across multiple paths. Such an equilibrium, however, can be unstable. It can be stabilized by adding a static component to link cost, but at the expense of a reduced utility in equilibrium. If link capacities are optimally provisioned, however, pure static routing, which is necessarily stable, is sufficient to maximize utility. Moreover single-path routing again achieves the same utility as multipath routing at optimality
Communication Theoretic Data Analytics
Widespread use of the Internet and social networks invokes the generation of
big data, which is proving to be useful in a number of applications. To deal
with explosively growing amounts of data, data analytics has emerged as a
critical technology related to computing, signal processing, and information
networking. In this paper, a formalism is considered in which data is modeled
as a generalized social network and communication theory and information theory
are thereby extended to data analytics. First, the creation of an equalizer to
optimize information transfer between two data variables is considered, and
financial data is used to demonstrate the advantages. Then, an information
coupling approach based on information geometry is applied for dimensionality
reduction, with a pattern recognition example to illustrate the effectiveness.
These initial trials suggest the potential of communication theoretic data
analytics for a wide range of applications.Comment: Published in IEEE Journal on Selected Areas in Communications, Jan.
201
Polarized positron beams via intense two-color laser pulses
Generation of ultrarelativistic polarized positrons during interaction of an
ultrarelativistic electron beam with a counterpropagating two-color petawatt
laser pulse is investigated theoretically. Our Monte Carlo simulation based on
a semi-classical model, incorporates photon emissions and pair productions,
using spin-resolved quantum probabilities in the local constant field
approximation, and describes the polarization of electrons and positrons for
the pair production and photon emission processes, as well as the classical
spin precession in-between. The main reason of the polarization is shown to be
the spin-asymmetry of the pair production process in strong external fields,
combined with the asymmetry of the two-color laser field. Employing a feasible
scenario, we show that highly polarized positron beams, with a polarization
degree of , can be produced in a femtosecond time scale,
with a small angular divergence, mrad, and high density cm. The laser-driven positron source, along with laser
wakefield acceleration, may pave the way to small scale facilities for high
energy physics studies
Vacuolar ATPase depletion contributes to dysregulation of endocytosis in bloodstream forms of Trypanosoma brucei
BACKGROUND
Vacuolar H-ATPase (V-ATPase) is a highly conserved protein complex which hydrolyzes ATP and pumps protons to acidify vacuolar vesicles. Beyond its role in pH maintenance, the involvement of V-ATPase in endocytosis is well documented in mammals and plants but is less clear in Trypanosoma brucei.
METHODS
In this study, the subcellular localization of V-ATPase subunit B (TbVAB) of T. brucei was assessed via in situ N-terminal YFP-tagging and immunofluorescence assays. Transgenic bloodstream forms (BSF) of T. brucei were generated which comprised either a V-ATPase subunit B (TbVAB) conditional knockout or a V-ATPase subunit A (TbVAA) knockdown. Acridine orange and BCECF-AM were employed to assess the roles of V-ATPase in the pH regulation of BSF T. brucei. The endocytic activities of three markers were also characterized by flow cytometry analyses. Furthermore, trypanosomes were counted from trypanolysis treatment groups (either containing 1% or 5% NHS) and endocytosed trypanosome lytic factor (TLF) was also analyzed by an immunoblotting assay.
RESULTS
TbVAB was found to localize to acidocalcisomes, lysosomes and probably also to endosomes of BSF of T. brucei and was demonstrated to be essential for cell growth. TbVAB depletion neutralized acidic organelles at 24 hours post-tetracycline depletion (hpd), meanwhile the steady state intracellular pH increased from 7.016 ± 0.013 to 7.422 ± 0.058. Trypanosomes with TbVAB depletion at 24 hpd were found to take up more transferrin (2.068 ± 0.277 fold) but less tomato lectin (49.31 ± 22.57%) by endocytosis, while no significant change was detected in dextran uptake. Similar endocytic dysregulated phenotypes were also observed in TbVAA knockdown cells. In addition, TbVAB depleted trypanosomes showed a low uptake of TLF and exhibited less sensitive to lysis in both 1% and 5% NHS treatments.
CONCLUSIONS
TbVAB is a key component of V-ATPase and was found to play a key function in endocytosis as well as exhibiting different effects in a receptor/cargo dependent manner in BSF of T. brucei. Besides vacuolar alkalinization, the dysregulation of endocytosis in TbVAB depleted T. brucei is considered to contribute to the reduced sensitivity to lysis by normal human serum
RF-thermal-structural-RF coupled analysis on the travelling wave disk-loaded accelerating structure
Travelling wave (TW) disk-loaded accelerating structure is one of the key
components in normal conducting (NC) linear accelerators, and has been studied
for many years. In the design process, usually after the dimensions of each
cell and the two couplers are finalized, the structure is fabricated and tuned,
and then the whole structure characteristics can be measured by the vector
network analyzer. Before the structure fabrication, the whole structure
characteristics are less simulated limited by the available computer
capability. In this paper, we described the method to do the
RF-thermal-structural-RF coupled analysis on the TW disk-loaded structure with
one single PC. In order to validate our method, we first analyzed and compared
our RF simulation results on the 3m long BEPCII structure with the
corresponding experimental results, which shows very good consistency. Finally,
the RF-thermal-structure-RF coupled analysis results on the 1.35m long NSC KIPT
linac accelerating structure are presented.Comment: 5 pages, 16 figures, Submitted to the Chinese Physics C (Formerly
High Energy Physics and Nuclear Physics
Human African trypanosomiasis : the current situation in endemic regions and the risks for non-endemic regions from imported cases
Human African trypanosomiasis (HAT) is caused by Trypanosoma brucei
gambiense and T. b. rhodesiense and caused devastating epidemics during the 20th
century. Due to effective control programs implemented in the last two decades, the
number of reported cases has fallen to a historically low level. Although fewer than
977 cases were reported in 2018 in endemic countries, HAT is still a public health
problem in endemic regions until it is completely eliminated. In addition, almost 150
confirmed HAT cases were reported in non-endemic countries in the last three
decades. The majority of non-endemic HAT cases were reported in Europe, United
States and South Africa, due to historical alliances, economic links or geographic
proximity to disease endemic countries. Furthermore, with the implementation of the
“Belt and Road” project, sporadic imported HAT cases have been reported in China
as a warning sign of tropical diseases prevention. In this paper, we explore and
interpret the data on HAT incidence and find no positive correlation between the
number of HAT cases from endemic and non-endemic countries.This data will
provide useful information for better understanding the imported cases of HAT
globally in the post-elimination phase
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Examining the economic impact of transport complex economies
Transport complex economies (TCEs), which comprise both upstream and downstream firms in the transport chain that conduct shipping and trade-related activities, can be desirable locations for port users (e.g., traders, logistics service providers, shipping lines and terminal operators) to perform their business activities. To explore TCEs, this study identifies trade facilitation measures at both the macro and micro levels to enhance regional performance. Hypotheses have been developed to build a theoretical model to illustrate the relationship between trade facilitation activities and trade costs. The economic outcomes are also examined in the theoretical model. To validate the proposed model, we have collected data from the World Bank and employed structural equation modelling. The result suggests that trade facilitation measures are negatively associated with trade cost. The result also suggests that the trade facilitation measures of a region is positively associated with its economic performance. Based on the findings, users can formulate effective and efficient strategies to select a location for their firm to conduct business activities. The findings illustrate the importance of the development of social capital for trade facilitation from the perspective of policy makers
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ADP-Ribosylargininyl reaction of cholix toxin is mediated through diffusible intermediates
Background: Cholix toxin is an ADP-ribosyltransferase found in non-O1/non-O139 strains of Vibrio cholera. The catalytic fragment of cholix toxin was characterized as a diphthamide dependent ADP-ribosyltransferase. Results: Our studies on the enzymatic activity of cholix toxin catalytic fragment show that the transfer of ADP-ribose to toxin takes place by a predominantly intramolecular mechanism and results in the preferential alkylation of arginine residues proximal to the NAD+ binding pocket. Multiple arginine residues, located near the catalytic site and at distal sites, can be the ADP-ribose acceptor in the auto-reaction. Kinetic studies of a model enzyme, M8, showed that a diffusible intermediate preferentially reacted with arginine residues in proximity to the NAD+ binding pocket. ADP-ribosylarginine activity of cholix toxin catalytic fragment could also modify exogenous substrates. Auto-ADP-ribosylation of cholix toxin appears to have negatively regulatory effect on ADP-ribosylation of exogenous substrate. However, at the presence of both endogenous and exogenous substrates, ADP-ribosylation of exogenous substrates occurred more efficiently than that of endogenous substrates. Conclusions: We discovered an ADP-ribosylargininyl activity of cholix toxin catalytic fragment from our studies in auto-ADP-ribosylation, which is mediated through diffusible intermediates. The lifetime of the hypothetical intermediate exceeds recorded and predicted lifetimes for the cognate oxocarbenium ion. Therefore, a diffusible strained form of NAD+ intermediate was proposed to react with arginine residues in a proximity dependent manner. Electronic supplementary material The online version of this article (doi:10.1186/s12858-014-0026-1) contains supplementary material, which is available to authorized users
1+1+2 Electromagnetic perturbations on general LRS space-times: Regge-Wheeler and Bardeen-Press equations
We use the, covariant and gauge-invariant, 1+1+2 formalism developed by
Clarkson and Barrett, and develop new techniques, to decouple electromagnetic
(EM) perturbations on arbitrary locally rotationally symmetric (LRS)
space-times. Ultimately, we derive 3 decoupled complex equations governing 3
complex scalars. One of these is a new Regge-Wheeler (RW) equation generalized
for LRS space-times, whereas the remaining two are new generalizations of the
Bardeen-Press (BP) equations. This is achieved by first using linear algebra
techniques to rewrite the first-order Maxwell equations in a new complex 1+1+2
form which is conducive to decoupling. This new complex system immediately
yields the generalized RW equation, and furthermore, we also derive a decoupled
equation governing a newly defined complex EM 2-vector. Subsequently, a further
decomposition of the 1+1+2 formalism into a 1+1+1+1 formalism is developed,
allowing us to decompose the complex EM 2-vector, and its governing equations,
into spin-weighted scalars, giving rise to the generalized BP equations
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