疫病如何影响猪肉产销价格波动关联?——基于滚动协整的分析

非洲猪瘟发生以来,中国猪肉市场波动剧烈,产销价格分化明显。为探究疫病如何影响不同区域产销价格变动,本文以北京及其主要外埠产区(河北、河南、辽宁、吉林)为例,基于滚动协整分析方法构建动态误差修正模型,从区域流通视角探究生猪及猪肉价格空间动态传导机制。结果表明:(1)产销价格长期均衡关系表现出显著的时变特征和阶段性差异,在受到疫病冲击时,价格波动的关联性大幅降低;(2)产销价格传导机制存在空间非对称溢出效应,主要表现为"产区—销区"单向传导,但在误差修正机制作用下,疫病对销区价格的间接冲击有所减弱。因此,有必要优化疫病预警机制,完善环保与生猪产业发展规划,构建产销协调的生态养殖模式。     

动物疫病预报预测模式初探

随着北京市密云地区畜牧业不断发展,可以说畜牧业是密云农村、农民增收致富的支柱产业,在经济中发挥越来越大的作用。但是,过去动物疫病的发生及传播曾给密云县畜牧业造成了一定的经济损失。因此,动物疫病的预测预报工作对保障畜产品质量安全以及动物和人类健康具有重要意义。以流行病学调查、免疫效果评价、临床病例汇总分析、国内外信息收集,以及本地区曾发生疫病情况分析为基础的动物疫病预测预报工作技术模式的构建,是当前基层防疫工作需求,提出存在动物疫病的风险点和采取防治措施的建议,将动物疫病带来的损失降到最低。     

钢筋锈蚀对混凝土梁破坏模式影响的试验研究

研究钢筋锈蚀对混凝土梁破坏模式的影响.对4组共21根不同剪跨比、不同锈蚀程度的混凝土梁进行了试验，研究发现，纵向配筋率及剪跨比相同的情况下，随着纵筋、箍筋锈蚀程度的变化，梁会产生弯曲、剪压、剪切-粘结3种不同形态的破坏.针对此现象，基于试验研究结果并结合相关文献的试验结果，根据现行规范中的分析理念建立了考虑剪跨比、箍筋锈蚀率、纵筋锈蚀率及粘结退化等因素影响的锈蚀混凝土梁受剪承载力计算公式.据此再考虑弯剪区的平衡条件，分析讨论得出了试验梁产生破坏形态转变的临界条件和锈蚀混凝土梁构件的综合承载能力的变化规律，从而建立了锈蚀混凝土梁破坏模式转变的分析模型.据此模型分别以纵筋锈蚀率和箍筋锈蚀率为横、纵轴，考虑剪跨比等因素得出临界曲线划分的破坏形态区域与试验结果吻合较好.     

The Phase Composition of Triton's Polar Caps

Triton's polar caps are modeled as permanent nitrogen deposits hundreds of meters thick. Complex temperature variations on Triton's surface induce reversible transitions between the cubic and hexagonal phases of solid nitrogen, often with two coexisting propagating transition fronts. Subsurface temperature distributions are calculated using a two-dimensional thermal model with phase changes. The phase changes fracture the upper nitrogen layer, increasing its reflectivity and thus offering an explanation for the surprisingly high southern polar cap albedo (approximately 0.8) seen during the Voyager 2 flyby. The model has other implications for the phase transition phenomena on Triton, such as a plausible mechanism for the origin of geyser-like plume vent areas and a mechanism of energy transport toward them.     

汉中地区小麦条锈病流行因子分析

利用陕西汉中地区２４ａ（１９７４－１９９７年）的病情气象资料,采用逐步回归法分析了影响汉中小麦条锈病流行的因子,求得最优回归子集,包括秋苗菌量、春苗菌量、４月份平均温度、４月份降雨量、感病品种比例。用所得关键因子（１９７４－１９９３,共２０ａ资料）建立了多元线性回归方程,并用１９９４－１９９７年的资料检验方程的可靠程度,结果表明,方程预测的准确率为７５％。     

A reversibly switching surface

We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.     

Ecological context influences epidemic size and parasite-driven evolution

The occurrence and magnitude of disease outbreaks can strongly influence host evolution. In particular, when hosts face a resistance-fecundity trade-off, they might evolve increased resistance to infection during larger epidemics but increased susceptibility during smaller ones. We tested this theoretical prediction by using a zooplankton-yeast host-parasite system in which ecological factors determine epidemic size. Lakes with high productivity and low predation pressure had large yeast epidemics; during these outbreaks, hosts became more resistant to infection. However, with low productivity and high predation, epidemics remained small and hosts evolved increased susceptibility. Thus, by modulating disease outbreaks, ecological context (productivity and predation) shaped host evolution during epidemics. Consequently, anthropogenic alteration of productivity and predation might strongly influence both ecological and evolutionary outcomes of disease.     

汉中地区小麦条锈病流行程度预测研究

利用陕西汉中地区 2 4年 ( 1 974～ 1 997年 )的小麦条锈病病情、菌量、品种和气象资料 ,采用逐步回归法分析了影响汉中小麦条锈病流行的因子 ,求得最优回归子集 ,包括春季菌量、秋季菌量、感病品种面积比例、4月份降雨量和 4月份平均温度。用前 2 0年资料建立了多元线性回归方程 ,对 1 994～ 1 997年小麦条锈病的流行程度作短期预测 (以残差绝对值≤ 0 .5为标准统计 ) ,结果表明 ,方程预测的准确率为 75%     

Explaining seasonal fluctuations of measles in Niger using nighttime lights imagery

Measles epidemics in West Africa cause a significant proportion of vaccine-preventable childhood mortality. Epidemics are strongly seasonal, but the drivers of these fluctuations are poorly understood, which limits the predictability of outbreaks and the dynamic response to immunization. We show that measles seasonality can be explained by spatiotemporal changes in population density, which we measure by quantifying anthropogenic light from satellite imagery. We find that measles transmission and population density are highly correlated for three cities in Niger. With dynamic epidemic models, we demonstrate that measures of population density are essential for predicting epidemic progression at the city level and improving intervention strategies. In addition to epidemiological applications, the ability to measure fine-scale changes in population density has implications for public health, crisis management, and economic development.     

Quantum criticality: competing ground states in low dimensions

Small changes in an external parameter can often lead to dramatic qualitative changes in the lowest energy quantum mechanical ground state of a correlated electron system. In anisotropic crystals, such as the high-temperature superconductors where electron motion occurs primarily on a two-dimensional square lattice, the quantum critical point between two such lowest energy states has nontrivial emergent excitations that control the physics over a significant portion of the phase diagram. Nonzero temperature dynamic properties near quantum critical points are described, using simple theoretical models. Possible quantum phases and transitions in the two-dimensional electron gas on a square lattice are discussed.     

小麦条锈病流行程度趋势预测专家系统雏型

本文运用知识工程语言 M·1构造了一个用于小麦条锈病流行程度趋势预测的专家系统雏型。专家的知识用产生式规则来表示。知识库中的知识规则可相对独立,便于知识库的扩充和完善。     

南方樱桃谷种鸭主要流行疫病的调查及分析

为了解樱桃谷种鸭不同生长饲养阶段主要传染病的流行情况,对中国南方地区饲养的不同日龄的樱桃谷种鸭开展了重要病原的感染调查。结果显示,4周龄内的育雏期樱桃谷种鸭主要发生鸭传染性浆膜炎、鸭Ⅰ型病毒性肝炎和鸭大肠杆菌病,5~21周龄的育成期樱桃谷种鸭主要为鸭大肠杆菌、鸭疫里默氏杆菌、鸭圆环病毒感染,鸭霍乱和新城疫也时有发生,产蛋期樱桃谷种鸭主要发生鸭大肠杆菌病,同时还有坦布苏病毒病和鸭圆环病毒感染。可见,近年来中国南方樱桃谷鸭群疫病发生日趋复杂,形势严峻,且不同生长阶段的疫病发生情况不尽相同,为樱桃谷种鸭主要流行疫病的防控提供科学依据。     

渭北旱塬苹果黑星病流行程度预测

利用渭北旱塬1997~2003年的温度、相对湿度、降雨量和苹果黑星病流行程度等资料,采用逐步回归法分析了影响渭北旱塬苹果黑星病流行的气象因子,求得了最优回归子集,并用前5年资料建立了多元线性回归模型,用该模型对2002和2003年苹果黑星病的流行程度进行了预测。结果表明,4月份和8月份的降雨量、前一年12月份的平均相对湿度及1月份和7月份的平均温度是影响苹果黑星病流行的主要因子。研究建立的回归模型预测准确率高,对渭北旱塬苹果黑星病的防治具有一定指导作用。     

浅析近代史上水旱灾害对农村社会的影响

中国近代史上灾害频发，水灾、旱灾、虫灾以及疫灾等，这些灾害或多或少都对人民生命财产 安全产生了危害，其中水旱灾害的发生更是对农村社会产生了巨大的影响。本文从水旱灾害发生的 原因探析中国近代史上水旱灾害对农村社会以及农村人民产生的危害，进而探讨中国近代史上乡村 在水旱灾害打击下的农业经济、社会冲突及农民生活状况的改变。     

基于 Fuzzy-IPA 的西南大学校园植物景观满意度测评研究

以西南大学校园植物景观为研究对象,运用三角模糊评价理论,采用三角模糊值表示被调查对象的感知表现,用连续性的变化更为客观地描述被调查对象感知值,并结合IPA分析法,构建基于Fuzzy-IPA分析法的满意度测评模型,不仅可筛选出影响西南大学校园植物景观的关键因子,而且可以找出相关因子的重要程度与表现程度.     

Abrupt climate change and extinction events in Earth history

Slowly changing boundary conditions can sometimes cause discontinuous responses in climate models and result in relatively rapid transitions between different climate states. Such terrestrially induced abrupt climate transitions could have contributed to biotic crises in earth history. Ancillary events associated with transitions could disperse unstable climate behavior over a longer but still geologically brief interval and account for the stepwise nature of some extinction events. There is a growing body of theoretical and empirical support for the concept of abrupt climate change, and a comparison of paleoclimate data with the Phanerozoic extinction record indicates that climate and biotic transitions often coincide. However, more stratigraphic information is needed to precisely assess phase relations between the two types of transitions. The climate-life comparison also suggests that, if climate change is significantly contributing to biotic turnover, ecosystems may be more sensitive to forcing during the early stages of evolution from an ice-free to a glaciated state. Our analysis suggests that a terrestrially induced climate instability is a viable mechanism for causing rapid environmental change and biotic turnover in earth history, but the relation is not so strong that other sources of variance can be excluded.     

Surface-driven switching of liquid crystals using redox-active groups on electrodes

Electrochemical control of the oxidation state of ferrocene-decorated electrodes leads to surface-driven changes in the orientations of thermotropic liquid crystals. When the electrodes possess nanometer-scale topography, voltages of 0.0 to 0.3 volts (versus a counter electrode in a two-electrode cell) can drive changes in the orientation of the liquid crystals in the plane and/or out of the plane of the electrodes. Electrodes not supporting ferrocene do not lead to surface-driven orientational transitions. The in-plane transitions are driven by the reorganization of the monolayer of ferrocene upon oxidation of ferrocene to ferrocenium. The out-of-plane transition reflects a dielectric coupling between the liquid crystal and the diffuse part of an electrical double layer that evolves upon oxidation of ferrocene to ferrocenium. These results suggest new ways to couple the orientations of liquid crystals to chemical and electrical stimuli in electro-optical devices and chemical sensors.     

New prospects for epidemiologic investigations

Epidemiology has evolved from its historic origins as the study of major epidemics and vital statistics to a contemporary focus on the study of the distribution and determinants of health and disease in humans. This evolution reflects changes in the patterns of diseases and deaths that have occurred in our time and has placed new emphasis on preventing avoidable, premature deaths. Advances in clinical medicine, laboratory science, statistical and data handling methods, and in our basic understanding of the pathogenesis of disease have enabled epidemiologists to better examine causes of disease and to propose more effective strategies for prevention and control.     

Climate warming and disease risks for terrestrial and marine biota

Infectious diseases can cause rapid population declines or species extinctions. Many pathogens of terrestrial and marine taxa are sensitive to temperature, rainfall, and humidity, creating synergisms that could affect biodiversity. Climate warming can increase pathogen development and survival rates, disease transmission, and host susceptibility. Although most host-parasite systems are predicted to experience more frequent or severe disease impacts with warming, a subset of pathogens might decline with warming, releasing hosts from disease. Recently, changes in El Ni?o-Southern Oscillation events have had a detectable influence on marine and terrestrial pathogens, including coral diseases, oyster pathogens, crop pathogens, Rift Valley fever, and human cholera. To improve our ability to predict epidemics in wild populations, it will be necessary to separate the independent and interactive effects of multiple climate drivers on disease impact.