arXiv subjects

Hong Xu

Publications and source records attributed to Hong Xu.

103 records · Page 6Linked to original sources

arXiv2013

RepFlow: Minimizing Flow Completion Times with Replicated Flows in Data Centers

Short TCP flows that are critical for many interactive applications in data centers are plagued by large flows and head-of-line blocking in switches. Hash-based load balancing schemes such as ECMP aggravate the matter and result in long-tailed flow completion times (FCT). Previous work on reducing FCT usually requires custom switch hardware and/or protocol changes. We propose RepFlow, a simple yet practically effective approach that replicates each short flow to reduce the completion times, without any change to switches or host kernels. With ECMP the original and replicated flows traverse distinct paths with different congestion levels, thereby reducing the probability of having long queueing delay. We develop a simple analytical model to demonstrate the potential improvement of RepFlow. Extensive NS-3 simulations and Mininet implementation show that RepFlow provides 50%--70% speedup in both mean and 99-th percentile FCT for all loads, and offers near-optimal FCT when used with DCTCP.

cs.NI↗

arXiv2013

Spot Transit: Cheaper Internet Transit for Elastic Traffic

We advocate to create a \emph{spot} Internet transit market, where transit is sold using the under-utilized backbone capacity at a lower price. The providers can improve profit by capitalizing the perishable capacity, and customers can buy transit on-demand without a minimum commitment level for elastic traffic, and as a result improve its surplus (i.e. utility gains). We conduct a systematic study of the economical benefits of spot transit both theoretically and empirically. We propose a simple analytical framework with a general demand function, and solve the pricing problem of maximizing the expected profit, taking into account the revenue loss of regular transit when spot transit traffic hikes. We rigorously prove the price advantage of spot transit, as well as profit and surplus improvements for tier-1 ISPs and customers, respectively. Using real-world price data and traffic statistics of 6 IXPs with more than 1000 ISPs, we quantitatively evaluate spot transit and show that significant financial benefits can be achieved in both absolute and relative terms, robust to parameter values.

cs.NI↗

arXiv2013

Experimental studies of THGEM in different Ar/CO2 mixtures

In this paper, the performances of a type of the domestic THGEM (THick Gaseous Electron Multiplier) working in the Ar/CO2 mixtures are reported in details. This kind of single THGEM can provide the gain range from 100 to 1000, which is very suitable for the application in the neutron detection. In order to study its basic characteristics as the references for the development of THGEM based neutron detector, the counting rate plateau, the energy resolution and the gain of the THGEM have been measured in the different Ar/CO2 mixtures with the change of the electrical fields. For the Ar/CO2(90%/10%) gas mixture, a wide counting rate plateau is got from 720V to 770V with the plateau slope of 2.4% / 100 V and the excellent energy resolution about 22% is obtained at the 5.9keV full energy peak of the 55Fe X-ray source.

physics.ins-det↗

arXiv2013

An Efficient Implementation of Belief Function Propagation

The local computation technique (Shafer et al. 1987, Shafer and Shenoy 1988, Shenoy and Shafer 1986) is used for propagating belief functions in so called a Markov Tree. In this paper, we describe an efficient implementation of belief function propagation on the basis of the local computation technique. The presented method avoids all the redundant computations in the propagation process, and so makes the computational complexity decrease with respect to other existing implementations (Hsia and Shenoy 1989, Zarley et al. 1988). We also give a combined algorithm for both propagation and re-propagation which makes the re-propagation process more efficient when one or more of the prior belief functions is changed.

cs.AI↗

arXiv2013

A Decision Calculus for Belief Functions in Valuation-Based Systems

Valuation-based system (VBS) provides a general framework for representing knowledge and drawing inferences under uncertainty. Recent studies have shown that the semantics of VBS can represent and solve Bayesian decision problems (Shenoy, 1991a). The purpose of this paper is to propose a decision calculus for Dempster-Shafer (D-S) theory in the framework of VBS. The proposed calculus uses a weighting factor whose role is similar to the probabilistic interpretation of an assumption that disambiguates decision problems represented with belief functions (Strat 1990). It will be shown that with the presented calculus, if the decision problems are represented in the valuation network properly, we can solve the problems by using fusion algorithm (Shenoy 1991a). It will also be shown the presented decision calculus can be reduced to the calculus for Bayesian probability theory when probabilities, instead of belief functions, are given.

cs.AI↗

arXiv2013

A Belief-Function Based Decision Support System

In this paper, we present a decision support system based on belief functions and the pignistic transformation. The system is an integration of an evidential system for belief function propagation and a valuation-based system for Bayesian decision analysis. The two subsystems are connected through the pignistic transformation. The system takes as inputs the user's "gut feelings" about a situation and suggests what, if any, are to be tested and in what order, and it does so with a user friendly interface.

cs.AI↗

arXiv2013

Evidential Reasoning with Conditional Belief Functions

In the existing evidential networks with belief functions, the relations among the variables are always represented by joint belief functions on the product space of the involved variables. In this paper, we use conditional belief functions to represent such relations in the network and show some relations of these two kinds of representations. We also present a propagation algorithm for such networks. By analyzing the properties of some special evidential networks with conditional belief functions, we show that the reasoning process can be simplified in such kinds of networks.

cs.AI↗

arXiv2013

Generating Explanations for Evidential Reasoning

In this paper, we present two methods to provide explanations for reasoning with belief functions in the valuation-based systems. One approach, inspired by Strat's method, is based on sensitivity analysis, but its computation is simpler thus easier to implement than Strat's. The other one is to examine the impact of evidence on the conclusion based on the measure of the information content in the evidence. We show the property of additivity for the pieces of evidence that are conditional independent within the context of the valuation-based systems. We will give an example to show how these approaches are applied in an evidential network.

cs.AI↗

arXiv2011

Developments of a 2D Position Sensitive Neutron Detector

Chinese Spallation Neutron Source (CSNS), one project of the 12th five-year-plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will be installed at the first phase of the project, where two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detector, a prototype of two-dimensional 200 mmx200 mm Multi-wire Proportional Chamber (MWPC) with the flowing gas of Ar/CO2 (90/10) has been constructed and tested with the 55Fe X-Ray using part of the electronics in 2009, which showed a good performance. Following the test in 2009, the neutron detector has been constructed with the complete electronics and filled with the 6atm.3He + 2.5atm.C3H8 gas mixture in 2010. The neutron detector has been primarily tested with an Am/Be source. In this paper, some new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper.

physics.ins-det↗

arXiv2009

Tuning parameter selection for penalized likelihood estimation of inverse covariance matrix

In a Gaussian graphical model, the conditional independence between two variables are characterized by the corresponding zero entries in the inverse covariance matrix. Maximum likelihood method using the smoothly clipped absolute deviation (SCAD) penalty (Fan and Li, 2001) and the adaptive LASSO penalty (Zou, 2006) have been proposed in literature. In this article, we establish the result that using Bayesian information criterion (BIC) to select the tuning parameter in penalized likelihood estimation with both types of penalties can lead to consistent graphical model selection. We compare the empirical performance of BIC with cross validation method and demonstrate the advantageous performance of BIC criterion for tuning parameter selection through simulation studies.

stat.ME↗

arXiv2006

Further Results on the Distinctness of Decimations of l-sequences

Let $\underline{a}$ be an \textit{l}-sequence generated by a feedback-with-carry shift register with connection integer $q=p^{e}$, where $ p$ is an odd prime and $e\geq 1$. Goresky and Klapper conjectured that when $ p^{e}\notin \{5,9,11,13\}$, all decimations of $\underline{a}$ are cyclically distinct. When $e=1$ and $p>13$, they showed that the set of distinct decimations is large and, in some cases, all deciamtions are distinct. In this article, we further show that when $e\geq 2$ and$ p^{e}\neq 9$, all decimations of $\underline{a}$ are also cyclically distinct.

cs.CR↗

arXiv2000

The plasma-insulator transition of spin-polarized Hydrogen

A mixed classical-quantum density functional theory is used to calculate pair correlations and the free energy of a spin-polarized Hydrogen plasma. A transition to an atomic insulator phase is estimated to occur around r_s=2.5 at T=10^4K, and a pressure $P\approx0.5Mbar$. Spin polarization is imposed to prevent the formation of H_2 molecules.

cond-mat.stat-mech↗

arXiv2000

Density functional theory of phase coexistence in weakly polydisperse fluids

The recently proposed universal relations between the moments of the polydispersity distributions of a phase-separated weakly polydisperse system are analyzed in detail using the numerical results obtained by solving a simple density functional theory of a polydisperse fluid. It is shown that universal properties are the exception rather than the rule.

cond-mat.stat-mech↗