Performance of Photosensors in the PandaX-I Experiment

We report the long term performance of the photosensors, 143 one-inch R8520-406 and 37 three-inch R11410-MOD photomultipliers from Hamamatsu, in the first phase of the PandaX dual-phase xenon dark matter experiment. This is the first time that a significant number of R11410 photomultiplier tubes were operated in liquid xenon for an extended period, providing important guidance to the future large xenon-based dark matter experiments.Comment: v3 as accepted by JINST with modifications based on reviewers' comment

Spacelike hypersurfaces with negative total energy in de Sitter spacetime

De Sitter spacetime can be separated into two parts along two kinds of hypersurfaces and the half-de Sitter spacetimes are covered by the planar and hyperbolic coordinates respectively. Two positive energy theorems were proved previously for certain $\P$-asymptotically de Sitter and \H-asymptotically de Sitter initial data sets by the second author and collaborators. These initial data sets are asymptotic to time slices of the two kinds of half-de Sitter spacetimes respectively, and their mean curvatures are bounded from above by certain constants. While the mean curvatures violate these conditions, the spacelike hypersurfaces with negative total energy in the two kinds of half-de Sitter spacetimes are constructed in this short paper.Comment: 11 pages, final version, to appear in J. Math. Phy

A connection-level call admission control using genetic algorithm for MultiClass multimedia services in wireless networks

Call admission control in a wireless cell in a personal communication system (PCS) can be modeled as an M/M/C/C queuing system with m classes of users. Semi-Markov Decision Process (SMDP) can be used to optimize channel utilization with upper bounds on handoff blocking probabilities as Quality of Service constraints. However, this method is too time-consuming and therefore it fails when state space and action space are large. In this paper, we apply a genetic algorithm approach to address the situation when the SMDP approach fails. We code call admission control decisions as binary strings, where a value of “1” in the position i (i=1,…m) of a decision string stands for the decision of accepting a call in class-i; a value of “0” in the position i of the decision string stands for the decision of rejecting a call in class-i. The coded binary strings are feed into the genetic algorithm, and the resulting binary strings are founded to be near optimal call admission control decisions. Simulation results from the genetic algorithm are compared with the optimal solutions obtained from linear programming for the SMDP approach. The results reveal that the genetic algorithm approximates the optimal approach very well with less complexity

Three essays on macroeconomics and monetary economics

University of Technology, Sydney. Faculty of Business.The thesis includes three essays on macroeconomics and monetary economics. The first essay is my work in macroeconomics, particularly Chinese economy. The rest two essays are my work in monetary economics, and also the focus of my doctoral thesis. After the Global Financial Crisis, the Quantitative Easing (or unconventional monetary policy) in the U.S., Japan and other advanced economies have inspired theoretical interest in the questions of how monetary policy can affect the interest rates of money and other assets, and further affect the real economy. In the second and third essays, I build micro-founded models with money and government bonds to address those questions. The first essay studies the real exchange rate appreciation caused by non-traded factor misallocation in China. The departure of a factor in excess supply in the non-traded sector leads to a real exchange rate appreciation, in a setup that combines the canonical Lewis Model with a Balassa-Samuelson traded/non-traded dichotomy. China is an ideal case for non-traded factor appreciation, since it has not completed its structural transformation. My model identifies non-traded goods with rural output produced in the West of China, and traded goods with manufactures produced on the Eastern Seaboard using overseas capital. According to the model, China’s real exchange rate should appreciate as the hukou system, which acts to trap labor in the rural West, is dismantled. The second essay develops a micro-founded model of money and bonds to address effects of monetary policy on output and unemployment. The baseline model considers both money and short-term government bonds serving as media of exchange. We analyze the effects of conventional monetary policy when Central Bank conducts open market operations (OMOs) by adjusting short-term bonds holdings. Conventional monetary policy is effective only when the short-term interest rate is positive. Then we introduce long-term government bonds to address the effects of unconventional monetary policy, particularly when the short-term interest rate hits the zero-lower bound. Quantitative analysis shows that unconventional monetary policy can reduce unemployment only when the fraction of households holding the portfolio of money and bonds is not too big. In the third essay, we extend standard models of monetary exchange to include, in addition to currency, government bonds. We then study monetary policy, including OMOs, under various assumptions about market structure, and about the liquidity of money and bonds — i.e., their acceptability or pledgeability as media of exchange or collateral. OMOs matter because the supply of liquid assets matters. Theory delivers sharp policy predictions. It can also generate novel phenomena, like negative nominal interest rates, endogenous market segmentation, and outcomes resembling liquidity traps. We also explore explanations for differences in the liquidity of money and bonds using information theory

Effects of genetically modified herbicide-tolerant (GMHT) rice on biodiversity of weed in paddy fields

To detect potential changes in properties of weed communities in fields of GMHT rice Bar68-1, trials were carried out from 2007-2008 at Changsha, China with conventional indica rice D68 served as control. The average richness of weed community measured by species accumulation curve tended to be identical in the fields of Bar68-1 and D68 as the number of sampling points increased. There were no significant differences (p > 0.05) in diversity indices which included numbers of species(S), Shannon-Wiener (H’), Pielou evenness (J’), Simpson diversity (D) and evenness (E) indices. Species composition for these two weed communities was roughly comparable. The top four weed species, sorted by individual abundance, were Monochoria vaginalis (Burm. f.) Presl ex Kunth, Lindernia procumbens(Krock.) Philcox, Cyperus diformis L. and Juncellus serotinus (Rottb.) .B. Clarke in the fields of Bar68-1 and D68. ABC curves showed that the weed communities were “unpolluted”. The data above confirm the hypothesis that the difference between the effect of GMHT rice Bar68-1 on biodiversity of weed in paddy fields and that of non-GM rice D68 was not significant