分类: 核科学技术 >> 核科学与技术 提交时间: 2024-03-28
摘要: Due to their excellent safety performance, dispersion fuels are widely used in advanced reactors, such as high-temperature gas-cooled reactors (HTGRs). Compared with deterministic methods, the Monte Carlo method has more advantages in the geometric modeling of stochastic media. The explicit modeling method has high computational accuracy and high computational cost. The chord length sampling (CLS) method can improve computational efficiency by sampling the chord length during neutron transport using the matrix chord length’s probability density function (PDF). This study shows that the excluded-volume effect in realistic stochastic media can introduce significant deviations into the CLS. A chord length correction approach is proposed to obtain the chord length correction factor by developing the Particle code based on equivalent transmission probability. Through numerical analysis against reference solutions from explicit modeling in the RMC code, it was demonstrated that CLS with the proposed correction method provides good accuracy for addressing the excluded-volume effect in realistic infinite stochastic media.
分类: 物理学 >> 核物理学 提交时间: 2024-03-28
摘要: 中能区电荷交换反应可以从自旋-同位旋激发的角度研究原子核复杂结构。利用中国科学院近代物理研究所的放射性束流线,利用逆运动学方法进行电荷交换反应实验,可以将研究的对象核素拓展至丰中子核乃至不稳定核。基于此,设计了用于电荷交换反应实验的探测器系统,该系统主要包括了3He气体靶、TPC和CsI(Tl) 阵列,其中TPC和CsI(Tl) 阵列构成ΔE-E系统。利用Geant4、Garfield++等模拟软件,优化了TPC的工作条件,确定了实验研究的运动学区间和探测器的基本设计,考察了探测系统的粒子鉴别能力。基于模拟优化,搭建了探测系统。
分类: 交通运输工程 >> 船舶、舰船工程 提交时间: 2024-03-28
摘要: With rapidly increasing consumption of energy, shipping industry has imposed a huge burden on the marine environment. It is a general trend to increase the use of renewable energy on ships to improve the ship sustainability. This article summarized the current development and application of solar energy, wind energy and fuel cell in ship power systems. Furthermore, in order to investigate the advantages of sustainable design for the ships, for the first time, a hybrid PV, wind and fuel cell energy system was established for an oil tanker, and the economic and environmental analyses of the hybrid system were performed. The analysis results demonstrate that the optimal hybrid energy system can reduce 151,467kg emission of CO2 and provide 2.92% electricity for the ship gird per year.
分类: 能源科学 >> 能源(综合) 提交时间: 2024-03-28
摘要: Considering the huge consumption of traditional energy and the rising demand for electricity, the development of renewable energy is very necessary. In this paper, an energy system integrating biomass energy, solar and two-stage organic Rankine cycle (ORC) is proposed, which uses the stable energy output of biomass energy to compensate for the volatility of solar modules. The proposed system comprises a biomass boiler, photovoltaic thermal panels (PV/T), evaporators, condensers, working medium pumps, turbines, a preheater and an air preheater. In addition, conventional and advanced exergy, exergoeconomic and exergoenvironmental (3E) analyses are carried out. Conventional 3E analyses reveal two components that require priority improvement. They are respectively evaporator 1 with the largest exergy destruction (708.2kW) and exergy destruction environmental impact rate (775.3 mPt/h) and evaporator 2 with the largest exergy destruction cost rate (19.15$/h). The results of advanced 3E analyses show that the largest avoidable endogenous exergy destruction is condenser 1 (136.6kW), the largest avoidable endogenous exergy destruction cost rate is condenser 2 (3.377$/h), and the largest avoidable endogenous exergy destruction environmental impact rate is condenser 1 (196.1mPt/h). These mean that these components have great potential for improvement in reducing exergy destruction, saving cost and protecting the environment. In addition, the avoidable endogenous exergy destruction/cost/environmental impact rate of evaporator 2 are negative, so evaporator 2 is not suitable as a priority component for improvement, which is contrary to the conclusions of conventional 3E analyses. It is found that conventional 3E analyses can only point out the biggest exergy destruction point, but cannot indicate whether the components with the greatest exergy destruction have the greatest potential for improvement. However, advanced 3E analyses can show the improvement potential of each component by improving its own performance and the external conditions. Therefore, it is necessary to conduct advanced 3E analyses.
分类: 医学、药学 >> 预防医学与公共卫生学 提交时间: 2024-03-28 合作期刊: 《中国全科医学》
摘要: 中医药是我国传统文化的重要组成部分,亦是我国重要的卫生、经济、科技、文化和生态资源,中医药国际化发展是传承创新发展中医药的重要内容。在全球传统医学体系中,印度传统医学具有极大影响力,印度传统医药的发展现状、国际化发展战略及影响等方面与中医药具有可比性。本文从国际化发展视角出发,从卫生服务、卫生人力资源、传统药物生产能力、卫生系统财政拨款及医保政策、健康治理、产品出口规模及目标市场、国际化发展及影响七个方面对中印传统医学进行对比,旨在借鉴其国际化发展的成功经验,对中医药国际化发展提出思考,从而积极推动中医药国际化发展,为加深海外中医药文化认同及推进中医药参与全球健康治理贡献重要力量。
分类: 机械工程 >> 机械工程其他学科 提交时间: 2024-03-28
摘要: Increasing the transfer (HT) coefficient used in thermal industries is very important. Various methods are used to improve the efficiency of thermal heat HT so that maximum HT takes place in a smaller space. Ethylene glycol (EG) is generally used as an agent for convective HT. EG obtains energy from a hot source and discharges it to the required location. At present, the most consumption of EG is to produce engine cooling fluid. In the upcoming research, the TB of EG fluid in two-dimensional microchannels (MCs) has been investigated using molecular dynamics (MD) simulations, and the effect of variables such as MC dimensions and MC wall temperature (Temp) on the TB of the simulated fluid has been investigated. The results revealed that by increasing the Temp difference of the MC wall from 10 to 50 K, the maximum temperature (Max-Temp) and velocity (Max-Vel) of the target sample increased to 640.94 K and 0.024 Å/ps. It can be concluded that the increase in the cross-sectional area and the wall Temp difference leads to an increase in the HT rate in the MC.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 天文学 >> 天文学 分类: 信息科学与系统科学 >> 信息科学与系统科学基础学科 提交时间: 2024-03-27
摘要: The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类: 数学 >> 离散数学和组合数学 提交时间: 2024-03-27
摘要: Let f(n) be the maximum number of edges in a graph on n vertices in which no two cycles have the same length. Erd¨os raised the problem of determining f(n). Erd¨os conjectured that there exists a positive constant c such that ex(n, C2k) ≥ cn1+1/k. Haj´os conjecture that every simple even graph on n vertices can be decomposed into at most n/2 cycles. We present the problems, conjectures related to these problems and we summarize the know results. We do not think Haj´os conjecture is true.
分类: 数学 >> 离散数学和组合数学 提交时间: 2024-03-27
摘要: The set of all non-increasing nonnegative integers sequence π = (d(v1), d(v2), ..., d(vn)) is denoted by NSn. A sequence π ∈ NSn is said to be graphic if it is the degree sequence of a simple graph G on n vertices, and such a graph G is called a realization of π. The set of all graphic sequences in NSn is denoted by GSn. A graphical sequence π is potentially H-graphical if there is a realization of π containing H as a subgraph, while π is forcibly H-graphical if every realization of π contains H as a subgraph. Let Kk denote a complete graph on k vertices. Let Km −H be the graph obtained from Km by removing the edges set E(H) of the graph H (H is a subgraph of Km). This paper summarizes briefly some recent results on potentially Km −G-graphic sequences and give a useful classification for determining σ(H, n).
分类: 医学、药学 >> 临床医学 提交时间: 2024-03-27 合作期刊: 《中国全科医学》
摘要: 背景 左心疾病相关肺动脉高压(PH-LHD)是肺动脉高压(PH)中最常见的一种。研究表明,血钠水平与 1 类 PH 的严重程度和不良预后相关,然而,其对 PH-LHD 的影响鲜有报道。目的 探讨 PH-LHD 患者的血钠水平与 N 末端脑利钠肽前体(NT-proBNP)、超声心动图指标的关系,评价血钠水平对 PH-LHD 严重程度及住院时间的影响,为 PH-LHD 患者的临床诊疗及提高医院周转率提供理论依据。方法 收集 2020 年 1 月—2022 年 2 月在山西医科大学第一医院住院的 360 例 PH-LHD 患者的临床资料,依据患者的中位血钠水平 139 mmol/L(血钠 <135 mmol/L为低血钠),将患者分为 3 组:血钠 <135 mmol/L 组(50 例)、血钠 135~139 mmol/L(136 例)、血钠 140~145 mmol/L(174 例)。采用 Spearman 秩相关分析探讨血钠水平与住院时间、NT-proBNP 及超声心动图指标的相关性;采用 Kaplan-Meier 生存曲线分析比较不同血钠水平 PH-LHD 患者的住院时间;采用二元 Logistic 回归分析探讨血钠水平对 PH-LHD 患者住院时间的影响。结果 3 组 PH-LHD 患者年龄、住院时间、NT-proBNP、左心房前后径、右心房面积、左心室射血分数、缩短分数比较,差异有统计学意义(P<0.05);其中血钠 140~145 mmol/L 组患者的住院时间、NT-proBNP 低于血钠 <135 mmol/L 组及血钠 135~139 mmol/L 组(P<0.05)。Spearman 秩相关分析结果显示,PH-LHD 患者血钠水平与住院时间(r=-0.176)、NT-proBNP(r=-0.135)、右心室前后径(r=-0.110)、肺动脉收缩压(r=-0.105)均呈负相关(P<0.05)。Kaplan-Meier 生存曲线分析结果显示,3 组血钠水平的 PH-LHD 患者住院时间比较,差异有统计学意义(χ2=12.469,P=0.002)。二元 Logistic 回归分析校正各控制变量后结果显示,血钠水平升高是 PH-LHD 患者住院时间延长的保护因素(OR=0.916,95%CI=0.859~0.977,P=0.008);与血钠 140~145 mmol/L 患者相比,血钠 <135 mmol/L(OR=2.268,95%CI=1.049~4.903,P=0.037)及血钠 135~139 mmol/L(OR=2.056,95%CI=1.163~3.635,P=0.013)患者住院时间延长的风险均升高。结论 血钠水平与 PH-LHD 严重程度密切相关,血钠水平降低是 PH-LHD 患者住院时间的独立危险因素,是一种潜在的治疗考虑因素,为 PH-LHD 的诊疗及医院周转提供新策略。
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2024-03-27
摘要: Electron-diffraction patterns with5-fold rotational symmetry of experimental alloy phases are assumedto be produced by periodic structures. Two three-dimensionalperiodic structures are presented based on regular pentagonaldodecahedrons. These structures can be used as atomic models todescribe the alloy phases. The Fourier-transform patterns of themodels are found to be similar to the correspondingelectron-diffraction patterns of these alloy phases. Details of themotivations and approaches that lead to thesemodels are also discussed.
分类: 计算机科学 >> 计算机应用技术 提交时间: 2024-03-27
摘要: 大语言模型 (LLMs, Large Language Models) 能够从大量语料的上下文中学习到模式,其包括词语之间的关系、句子的结构甚至更复杂的语义和语用信息。然而,让预训练语言模型生成结构化、严格遵循约定的内容仍然是一项挑战。我们提出了一种引导大模型生成计算机高可用内容的方案,无需微调和额外的神经网络推理,通过提前约定的上下文无关文法 (CFG, Context-Free Grammar) 构建一个采用协程的约束装置,在自回归模型Transformer的解码阶段引导模型采样正确的词元,以构成符合程序约定的形式语言。这将保证计算机程序每次都能把语言模型生成内容解析为期望的数据结构、类型或指令,以便开发人员更容易地将大语言模型纳入具体应用程序。我们在多个任务数据集上进行了实验,包括JSON、Mermaid框图和函数调用表达式生成等任务,结果表明我们的方法能够有效地提高LLMs生成内容对计算机程序的可用性。
分类: 医学、药学 >> 预防医学与公共卫生学 提交时间: 2024-03-27 合作期刊: 《中国全科医学》
摘要: 背景急性心肌梗死(AMI)是威胁全球公众健康的主要原因之一。虽然已有相应的再灌注治疗策略,但AMI相关的主要不良心脑血管事件(MACCEs)仍然是全世界人口死亡的原因之一。尤其合并糖尿病的AMI患者,因冠状动脉病变复杂,病变程度严重,尽早发现和判断该部分患者远期预后相对困难,因此寻找相对简便、易获得的实验室指标,有利于为2型糖尿病(T2DM)合并AMI患者经皮冠状动脉介入(PCI)术后MACCEs的预测提供依据。目的 探讨血清C反应蛋白(CRP)/白蛋白(Alb)比值(CAR)对T2DM合并AMI患者PCI术后远期MACCEs的预测价值。方法 纳入2014—2019年就诊于宁夏医科大学总医院心血管内科的1683例T2DM合并AMI患者为研究对象,收集患者的一般临床资料与检查检验结果。对所有患者进行电话或门诊随访,中位随访时间为5.6年,以全因死亡、非致死性心肌梗死、再发不稳定型心绞痛、非致死性脑卒中、新发心力衰竭或心力衰竭加重再入院、再次血运重建作为MACCES。根据患者随访期间是否发生主要不良心血管事件分为MACCEs组508例和非MACCEs组1175例。采用单因素及多因素Logistic回归分析T2DM合并AMI患者MACCEs事件的影响因素。采用Kaplan-Meier法绘制患者的生存曲线,生存曲线的比较采用Log-rank检验。采用受试者工作特征(ROC)曲线分析CAR对T2DM合并AMI患者远期MACCEs的预测效能,使用净重分类改善指标(NRI)和综合判别指数(IDI)评价CAR对T2DM合并AMI患者预后评估的改善效果。结果 1683例患者中508例(30.18%)患者出现MACCEs。多因素Logistic回归分析表明高血压病[OR(95%CI)=1.994(1.142~3.483)]、冠状动脉植入支架长度[OR(95%CI)=1.031(1.002~1.062)]、CRP[OR(95%CI)=0.950(0.915~0.986)]、Alb[OR(95%CI)=0.933(0.880~0.989)]及CAR[OR(95%CI)=5.582(1.705~18.277)]是T2DM合并AMI患者PCI术后MACCEs的影响因素(P<0.05)。根据CAR中位表达水平(0.86),将患者分为CAR<0.86组和CAR≥0.86组,Log-rank检验结果显示,CAR≥0.86组MACCEs发生率高于CAR<0.86组(52.68%与22.92%;χ2=65.65,P<0.001)。ROC曲线显示CAR预测患者发生MACCEs的ROC曲线下面积为0.728(95%CI=0.702~0.754),最佳截断值为0.576,灵敏度为0.617,特异度0.747。在基线模型基础上,与CRP、Alb相比,CAR能明显改善患者不良心脑血管事件的预测效果[C指数=0.149,P<0.01;NRI=0.377(0.067,0.597),P<0.05;IDI=0.166(0.025,0.257),P<0.05]。结论 CAR是T2DM合并AMI患者PCI术后远期MACCEs发生风险的有效预测指标。