STEADY-STATE THERMAL-HYDRAULIC ANALYSIS OF A PLATE TYPE REACTOR

ABSTRACT In the plate type fuel reactor, all the fuel elements are arranged in parallel in the subassembly and set in the core, which create many isolated parallel rectangular channels. The arrangements of the fuel elements may have significant impact on the thermal-hydraulics of the core. In order to fully understand the geometry impact on the steady-state thermalhydraulic characteristics, based on the mass, momentum and energy conservation equations, a multi-channel code was developed to estimate the steady-state thermal-hydraulic characteristics. Two different types of fuel elements arrangements in the subassembly were proposed and studied, one was uniform distribution with the same gap sizes between each fuel elements, and the other was nonuniform distribution with different clearances among boundary fuel elements. The mass flux distribution, the temperature field and the DNBR were obtained by the developed code. It showed that the mass flux distribution was affected by the flow area of the channel and the given power distribution. The flow area of the channel has bigger influence than the second. In addition, the results of the two different types of fuel elements arrangements were compared, and it could be found that the asymmetrical cooling of the fuel elements occurred when fuel elements were nonuniformly arranged, which leaded to the decrease of the maximum temperature in the asymmetrically cooled fuel elements and the increase of the maximum temperature in the core. Furthermore, the DNBR calculated by the Sudo model indicated that the safety margin of the reactor under the present conditions is sufficient. All the obtained results served some valuable information for the design of the new type research reactor

Efficacy of modified thoraco-laparoscopic Ivor-Lewis versus traditional thoraco-laparoscopic Ivor-Lewis for esophageal cancer: Propensity score-matched analysis

ObjectiveTo compare the clinical results of the modified Ivor-Lewis procedure, which preserves the azygous vein, thoracic duct and surrounding tissues, with the traditional Ivor-Lewis procedure, which removes these tissues, for treating esophageal squamous cell carcinoma, and evaluating whether the azygous vein, thoracic duct and surrounding tissues are required to be removed for the surgery of esophageal cancer.MethodsTo retrospectively analyze the clinical data of patients suffering from esophageal cancer treated by thoracic-laparoscopic Ivor-Lewis procedure admitted to the Department of Thoracic Surgery of Gansu Provincial People’s Hospital from September 2017 to September 2019. According to the surgical method, they were divided into the modified thoracolaparoscopic Ivor-Lewis (modified group) and the traditional thoracolaparoscopic Ivor-Lewis (traditional group). Propensity score matching analysis (PSM) was applied to reduce the selection bias of confounding factors.ResultsA total of 245 patients who suffered from esophageal cancer and underwent thoracic-laparoscopic Ivor-Lewis were enrolled in the study. There were 124 cases in the modified group and 121 cases in the traditional group. The discrepancies in the age and T-stage among patients in the traditional and modified groups were statistically significant. After PSM, the above-mentioned factors became statistically insignificant. There were 86 patients in each group after PSM. Compared with the traditional group, the modified group has shorter operative time (p=0.007), less intraoperative bleeding (p=0.003) and less postoperative 3 days chest drainage(p=0.001), with a statistically significant difference. No significant difference in local recurrence (p=0.721) and distant metastasis (p=0.742) after surgery were found in the two groups, and the difference was not statistically significant. There was also no statistically significant difference in the 3-year postoperative survival rate (44.2% vs. 41.9%, p=0.605) between the modified and traditional groups.ConclusionThe modified Ivor-Lewis procedure, which preserves the azygous vein, thoracic duct, and surrounding tissue, reduces surgical trauma in esophageal cancer, has not increased postoperative recurrent metastases, while achieved the same long-term outcomes as expanded surgery

Essays on trade and export development

The dynamics between industrial development and export activities have been the interest of research for the past two decades, especially those related to services activities and global value chain activities. This thesis contributes to the literature by examining the relationships between industrial upgrading, the similarity of countries’ exports, and the economic development of countries. The thesis also explores the factors that promote export upgrading and policy barriers in services trade across different economies. The thesis is organized as follows. Chapter 1 provides the motivation for the thesis. Chapter 2 highlights the literature on export activities (export similarity index and export quality index) foreign direct investment (FDI), and services activities in global economic development. Chapter 3 investigates the links between export similarity and bilateral FDI of Japan and host countries, exploring in particular how multinational activities (FDI) could increase the export activities of domestic countries. The empirical analysis is conducted using a panel data of 70 countries based on SITC (Standard International Trade Classification) 4- and 5-digit products. The results suggest that: (1) outward FDI from Japan increases export similarity between host and source countries, however, inward FDI to Japan shows no evidence of promoting similarity; (2) bilateral FDI positively promotes similarity in the manufactured exports, but to a lesser extent in primary sector exports; and (3) geographic distances and differences in per capita income have significant negative effects on export similarity. In Chapter 4, the empirical framework is developed to study the impact of policy restrictions on services trade across countries. Recent studies highlight that services are essential for manufacturing productivity improvement and economic development. This chapter examines the relationship between policy restrictions (measured by the services trade restrictiveness index (STRI)) and services trade across countries using data from UN Comtrade. A log-linear gravity model is developed to explain variations in bilateral services-trade volumes. The main results show that: (1) a 1% percent increase in the overall STRI leads to a 0.3% decrease in bilateral services trade and around 0.04% decrease in services export; and (2) both goods-trade networks and merchandise exports similarity have statistically significant and positive influences on services trade. In Chapter 5, the determinants of variations in export quality across countries are investigated. The study empirically examines the dynamic pattern of export upgrading and its main influencers based on a panel framework. The results imply that service imports, FDI inflows and the level of per capita income have positive effects on export quality growth. The last chapter, Chapter 6, provides the policy discussion and conclusion of the thesis, as well as discussing how the study could be extended as part of further research in this area.Thesis (Ph.D.) -- University of Adelaide, School of Economics, 201

Surrogate Model Application to the Identification of Optimal Groundwater Exploitation Scheme Based on Regression Kriging Method—A Case Study of Western Jilin Province

This paper introduces a surrogate model to identify an optimal exploitation scheme, while the western Jilin province was selected as the study area. A numerical simulation model of groundwater flow was established first, and four exploitation wells were set in the Tongyu county and Qian Gorlos county respectively so as to supply water to Daan county. Second, the Latin Hypercube Sampling (LHS) method was used to collect data in the feasible region for input variables. A surrogate model of the numerical simulation model of groundwater flow was developed using the regression kriging method. An optimization model was established to search an optimal groundwater exploitation scheme using the minimum average drawdown of groundwater table and the minimum cost of groundwater exploitation as multi-objective functions. Finally, the surrogate model was invoked by the optimization model in the process of solving the optimization problem. Results show that the relative error and root mean square error of the groundwater table drawdown between the simulation model and the surrogate model for 10 validation samples are both lower than 5%, which is a high approximation accuracy. The contrast between the surrogate-based simulation optimization model and the conventional simulation optimization model for solving the same optimization problem, shows the former only needs 5.5 hours, and the latter needs 25 days. The above results indicate that the surrogate model developed in this study could not only considerably reduce the computational burden of the simulation optimization process, but also maintain high computational accuracy. This can thus provide an effective method for identifying an optimal groundwater exploitation scheme quickly and accurately

Land Use Change Impacts on Hydrology in the Nenjiang River Basin, Northeast China

The objectives of this study were to assess land use changes and their hydrological impacts in the Nenjiang River Basin (NRB). The Soil and Water Assessment Tool (SWAT) model was employed to evaluate the impacts of land use changes. The Cellular Automata-Markov model was used to predict a land use map in 2038. Streamflow under each land use state was simulated by the SWAT model. The results showed that there was a significant expansion of agriculture area at the expense of large areas of grassland, wetland, and forest during 1975–2000. The land use changes during the period of 1975 to 2000 had decreased the water yield (3.5%), surface runoff (1.7%), and baseflow (19%) while they increased the annual evapotranspiration (2.1%). For impacts of individual land use type, the forest proved to have reduced streamflow in the flood season (10%–28%) and increased surface runoff in the drought season (20%–38%). Conversely, grassland, dry land, and paddy land scenarios resulted in increase of streamflow during summer months by 7%–37% and a decrease of streamflow in the cold seasons by 11.7%–59.7%. When the entire basin was changed to wetland, streamflow reduced over the whole year, with the largest reduction during January to March. The 2038 land use condition is expected to increase the annual water yield, surface runoff and wet season flow, and reduce evapotranspiration and baseflow. These results could help to improve sustainable land use management and water utilization in the NRB