An Approach of Reducing Overall Level of Export Fluctuations of the Export-oriented Countries

Overall level of export fluctuations of the export-oriented countries with rising export volume partly stem from the market failure caused by free choice of export enterprises, some government intervention thus may be necessary. To reduce the level of fluctuations of the export growth rates in these countries, this paper, taking the significant differences of the exports among various markets into account and thus using a new index named relative variance to measure the export volatility risks, proposes a model of merchandise market portfolio, a modified version of Markowitz model, available to provide explicit guidelines for the firms, the industries and even the whole country to optimize the structure of their export markets. An application of this model to the case of China's apple is then discussed. The results show that the market share of China’s apple in 7 sub-markets should be redistributed drastically

Evaluating The Environmental Impacts of U.S. Historical Oil Spill Incidents

The adverse impacts of extremely large oil spill incidents such as Deepwater Horizon Oil Spill have been widely studied in recent years. Catastrophic oil spill disasters such as Deepwater Horizon Oil Spill have been widely studied. While vast smaller oil spills, which also could result in significant amount of oil release, still lack attention. This research assessed distributions and environmental impacts caused by historical oil spill incidents in U.S. We first analyzed the spatial and temporal characteristics of oil spills. Then the relationship between spillage amount and spill frequency is evaluated via statistical approaches. Last, based on a thorough literature review of environmental, ecological, and economic impacts of oil spill, we proposed a framework to estimate the impact of oil spill incidents

New insights into the sign problem of QCD and heavy tetraquarks

Quantum Chromodynamics (QCD) describes strong interactions among the fundamental particles known as quarks and gluons. In principle, QCD can be used to explain complicated phenomena in the strong sector. However, at the energy scale of hadronic physics, the strong coupling constant is so large that the traditional perturbative method is not applicable. There are two powerful alternative approaches utilized in the non-pertubative regime: (1) lattice QCD, which discretizes space-time and utilizes Monte Carlo computer simulations, and (2) finding new systematic expansion regimes to obtain physical insights in certain limits. In this dissertation, three problems are studied in the context of these two approaches. In Chapter 2, a notorious numeric problem in lattice QCD known as the sign problem is explored. A subtle phenomenon caused by the interplay between the sign problem and the infinite volume limit is discussed and explained using the saddle point approximation. This work provides insight into the sign problem and the physics of the QCD theta-vacuum. Chapter 3 and Chapter 4 focus on tetraquarks, which are unconventional hadrons containing four valence quarks. Despite numerous tetraquark candidates seen in experiments, there is no unified and well-accepted theoretical descriptions of the tetraquark state yet. This dissertation examines the existence of tetraquarks in the heavy quark mass limit. A powerful systematic expansion regime can be built when the heavy quark mass is extremely large. In Chapter 3, a framework is established to analyze tetraquarks in the heavy quark mass limit. It is shown in a model-independent way that multiple parametrically narrow doubly heavy tetraquarks must exist in this limit. Many of these states will be parametrically close to the threshold of decaying into two heavy mesons. In Chapter 4, based on a modification of the framework in Chapter 3, it is shown that tetraquarks containing a heavy quark and a heavy antiquark with appropriate large angular momentum must exist in the heavy quark mass limit. This may provide insights into the experimentally-observed narrow near-threshold tetraquarks which contain a heavy quark and a heavy antiquark

New Explanations to Law of Resource Utilization

Abstract. The serious problems of resources and environment arising in development of human society have important ties with the scientific understanding of mankind toward the law of resource utilization. The author has demonstrated, based on the division of human resource utilization in depth and breadth spaces, the material form and nature of the depth and breadth space resources; and put forward the time model of the depth and breadth space resource utilization--a time demarcation and analysis of human resource utilization, with which we can see in the other sphere the various states of the influences of resource utilization by mankind to the environment. The continuous extension and utilization of depth space resource at one point is the core content of new explanation to resource utilization in phenomenon of "work". The time model of the breadth space takes the carbon cycling as the example and divides the resource material cycling into three stages. The analysis by the author offers us an audio-visual and comparatively new "cross-section" in the research of depth and breadth space resource utilization, also a new and systematic explanation to the law of resource utilization

Generation of Short Laser Pulses by Using Hollow Fibre and Chirped Mirror Compressor System

A FEMTOLASERS hollow core silicon fibre of length 1 m and 250μm inner diameter was set up in the lab in Waterloo with the purpose of generating sub 10fs pulses for Coulomb Explosion Imaging (CEI). The input laser was a new Ti: sapphire regenerative amplifier system providing energy of 1mJ per pulse at a duration of the 35fs with 1kHZ repetition rate. Modifications to the initial setup were crucial in achieving the desired goal. A new, angled, incident window was made to eliminate reflective damage to the mirrors, and a new delivery beamline was built to minimize unwanted nonlinear effects. The pressure dependence of spectral broadening in argon gas was studied to find the best performance and found to be p=0.43atm. A chirped mirror system was set up to compensate the group delay dispersion in the beam line to the CEI experiment and compress the pulse, and MATLAB programs were written to carefully estimate how much material was necessary to minimise total dispersion of the system. The optimal input beam duration was determined by comparing the setting of the compressor with the output spectrum of the fibre and it was found that a spectrum capable of generating a 7.49fs laser pulse was produced if group delay dispersion and higher order dispersions were assumed to be zero. However, after calculating the higher order dispersion present in the system, which can not be compensated by the chirped mirrors, a laser pulse with a duration of 9.76fs is feasible with an average power of 0.45W. This result if verified by CEI will result in near equilibrium imaging of small molecules in the Waterloo lab for the first time