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.     

基于改进持支向量机的猪肉价格预测研究

针对近年频现“价高伤民,价贱伤农”的“猪周期”现象,尝试使用集成经验模态分解（EEMD） 方法挖掘出 “猪周期”的价格波动机制,并引入遗传算法（GA）改进支持向量机。研究结果发现,通过 EEMD 方法能较好地展示出“猪周期”的循环轨迹;通过对比常用的预测模型,发现基于 EEMD 的 GASVM 模型预测精测更高,是一种更具有科学性的价格预测工具。     

Lattice effects observed in chaotic dynamics of experimental populations

Animals and many plants are counted in discrete units. The collection of possible values (state space) of population numbers is thus a nonnegative integer lattice. Despite this fact, many mathematical population models assume a continuum of system states. The complex dynamics, such as chaos, often displayed by such continuous-state models have stimulated much ecological research; yet discrete-state models with bounded population size can display only cyclic behavior. Motivated by data from a population experiment, we compared the predictions of discrete-state and continuous-state population models. Neither the discrete- nor continuous-state models completely account for the data. Rather, the observed dynamics are explained by a stochastic blending of the chaotic dynamics predicted by the continuous-state model and the cyclic dynamics predicted by the discrete-state models. We suggest that such lattice effects could be an important component of natural population fluctuations.     

Earth's Variable Rotation

Recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the Earth's rotation. The interpretation of these fluctuations is inextricably linked with studies of the dynamics of the Earth-moon system and dynamical processes in the liquid metallic core of the Earth (where the geomagnetic field originates), other parts of the Earth's interior, and the hydrosphere and atmosphere. Fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core-mantle boundary and the electrical, magnetic, and other properties of the core and lower mantle. Investigations of more rapid fluctuations bear on meteorological studies of interannual, seasonal, and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations.     

Chemistry. The motions of an enzyme soloist

Dynamics of proteins are crucial to their function. In his Perspective, Orrit stresses the advantages of studying these dynamics with single-molecule methods--which require no synchronization--rather than with conventional ensemble measurements. He highlights the report by Yang et al., who follow the fluorescence of a single enzyme molecule. Electron transfer from the fluorophore to a quencher induces fluctuations of the fluorescence lifetime along with the fluorophore-quencher distance. The wide range of characteristic times of those fluctuations reveals the complexity of the protein's potential energy landscape. As a new molecular ruler, electron transfer complements other single-molecule methods such as energy transfer (FRET) for distances shorter than a few nanometers.     

黑龙江省粮食产量波动分析与政策建议

黑龙江省的粮食生产对于保障全国粮食安全负有重要责任.本文测算了1987-2007年黑龙江省粮食产量的波动指数、波动周期和波动幅度.研究结果表明,黑龙江省粮食产量波动具有短周期的显著特征,产量波动主要是受自然灾害、农业政策变化、生产性投入等因素的影响.从加快农田水利建设、落实国家粮食保护政策、增加财政对粮食生产的扶持力度等方面,提出稳定粮食产量的政策建议.     

生猪价格波动原因探析

长期趋势、季节性、周期性和不确定因素是影响中国生猪价格波动的主要原因。研究表明,成本上升和需求刚性增长使生猪价格呈现长期上涨的趋势;生产的阶段性使生猪价格呈现一年以上的从低到高、再从高到低周而复始的周期性波动;生产与消费的季节性使生猪价格在一年中拥有规律的季节性特征;自然灾害、疫病等不确定因素使生猪价格在波动幅度和持续时间上出现非常规性波动。由于中长期生产成本持续上涨,近期内养殖周期和季节性不可改变,对于养殖主体来说,控制生产成本、提高养殖技术、加强疫病防范管理水平比预测价格以调整产量更为重要。     

罗非鱼主养池塘水体微生物群落对碳源代谢的动态变化

为摸清养殖池塘水体微生物数量的动态变化和微生物群落对不同碳源物质的代谢性能,跟踪研究了罗非鱼主养池塘水体中微生物的数量变动,并采用Biolog ECO微平板法分析微生物群落对糖类、氨基酸、脂肪、代谢中间产物等四类共31种不同碳源的代谢动态变化。结果显示:在5月至10月的整个养殖季中,水体的异养细菌和芽孢杆菌的数量均较稳定,未出现明显的剧烈变化;水体微生物群落对25种碳源物质的利用较平稳,有9种碳源的利用值高于其他22种碳源,包括糖类中的D-甘露醇、N-乙酰-D-葡萄糖氨和D-纤维二糖,氨基酸类的L-天门冬酰胺和L-丝氨酸,脂肪类的吐温40、吐温80、丙酮酸甲酯,代谢中间产物和次生代谢物中的腐胺等。结果表明,在整个养殖季中,池塘水体微生物的数量和群落对碳源的代谢水平总体均处于相对平稳的状态,但微生物群落对不同种类的碳源选择性存在差异。     

经济增长、产业贡献与农民收入增长波动——基于宏观收入分配计量模型与谱分析的实证

利用收入分配模型导出的计量模型,对改革开放以来(1978—2013年)农民收入增长波动及其宏观影响因素进行实证研究;使用谱分析方法,估计并比较农民收入增长与GDP及各产业增长的波动周期。结果表明:第一产业和第二产业的增长对农民收入增长有显著的贡献,但第三产业增长对农民收入增长影响不显著。农民收入增长波动的主周期与GDP及非农产业增长波动的主周期一致,农民收入增长波动的副周期则与农业产业增长波动的主周期一致。根据实证结果提出以下政策建议:稳定农民收入,一方面需稳定农民的农业收入,另一方面应提高农民工的教育水平和科学文化素质,促进农民进入第三产业就业以获得增收的来源。     

战后美国经济周期再考察

二战后美国经济周期波动发生显著变化。相比二战之前，美国经济周期扩张期拉长，衰退期缩短，二者之间形成剪刀差。经济周期长度、扩张期跨度和紧缩期跨度的离散度远远大于战前。二战后至今，美国经济中周期出现（朱格拉周期）呈拉长的趋势，扩张期远远长于衰退期，中周期（朱格拉周期）和短周期（基钦周期）的波幅经历了从小到大的阶段性变化。     

8O例成人麻疹临床特点分析

目的探讨成人麻疹流行特点、临床特征及防治措施。方法对80例成人麻疹患者的流行病学资料、临床表现、实验室检查及预后、转归等进行回顾性分析。结果相比儿童麻疹,成人麻疹具有热度高、全身中毒症状重、消化道反应明显等临床特征;皮疹出现时间相对晚、皮疹多,且融合疹、异型疹明显,退疹缓慢;合并心、肝、肺等脏器并发症较多,但预后良好。结论成人麻疹发病率升高与接种率低、体内麻疹抗体不足及麻疹病毒基因变异有关。积极有效的隔离、治疗是防治成人麻疹的重要措施。     

鲜活农产品市场价格波动规律研究——基于H-P滤波法的周期性分析

基于时间序列分析理论,将猪肉、鸡肉、鸡蛋、蔬菜和水果等5类鲜活农产品市场价格的变化分解为趋势变动、周期波动(循环变动)、季节波动和随机波动等4个部分。运用X12法和H-P滤波法对5类鲜活农产品市场价格波动规律进行分析,研究结果表明:在价格波动周期长度方面,猪肉呈缩小趋势,鸡肉、鸡蛋和蔬菜呈扩大趋势,水果趋于稳定;在价格波动周期对称性方面,猪肉、鸡肉和鸡蛋呈下跌周期大于上涨周期趋势,蔬菜、水果呈上涨周期大于下跌周期趋势;在价格波动的贡献率方面,猪肉、鸡肉和鸡蛋价格的周期性波动大于季节性波动,蔬菜和水果价格的季节性波动大于周期性波动,果蔬价格受随机波动的影响程度总体大于畜产品。     

Rapid variability of seawater chemistry over the past 130 million years

Fluid inclusion data suggest that the composition of major elements in seawater changes slowly over geological time scales. This view contrasts with high-resolution isotope data that imply more rapid fluctuations of seawater chemistry. We used a non-steady-state box model of the global sulfur cycle to show that the global δ(34)S record can be explained by variable marine sulfate concentrations triggered by basin-scale evaporite precipitation and dissolution. The record is characterized by long phases of stasis, punctuated by short intervals of rapid change. Sulfate concentrations affect several important biological processes, including carbonate mineralogy, microbially mediated organic matter remineralization, sedimentary phosphorous regeneration, nitrogen fixation, and sulfate aerosol formation. These changes are likely to affect ocean productivity, the global carbon cycle, and climate.     

头足类资源评估模型及其影响因素的研究进展

头足类是海洋生态系统的重要组成部分,也是目前世界上最具开发潜力的渔业资源之一,对该资源进行科学评估是实现其可持续利用的关键。不同于传统的鱼类种群,头足类具有生命周期短、生长速度快、种群结构复杂等生物学特点,且其资源量极易受到海洋环境波动的影响,使得头足类种群动力学和资源评估研究与传统鱼类资源相比面临着更多困难和挑战。本文总结了头足类的生活史特征及其资源与海洋环境因子的关系对资源评估的影响,并梳理了主要评估模型对头足类资源评估的适用性。分析认为,当前经过改进的衰减模型和剩余产量模型应用最为广泛,但仍无法制定出具有时效性的渔业管理措施。为此,文章从提高输入参数的准确度和可靠性、开展长期系统的资源环境调查和开发新的评估模型等方面提出了优化头足类资源评估研究的建议。     

Checkpoints: controls that ensure the order of cell cycle events

The events of the cell cycle of most organisms are ordered into dependent pathways in which the initiation of late events is dependent on the completion of early events. In eukaryotes, for example, mitosis is dependent on the completion of DNA synthesis. Some dependencies can be relieved by mutation (mitosis may then occur before completion of DNA synthesis), suggesting that the dependency is due to a control mechanism and not an intrinsic feature of the events themselves. Control mechanisms enforcing dependency in the cell cycle are here called checkpoints. Elimination of checkpoints may result in cell death, infidelity in the distribution of chromosomes or other organelles, or increased susceptibility to environmental perturbations such as DNA damaging agents. It appears that some checkpoints are eliminated during the early embryonic development of some organisms; this fact may pose special problems for the fidelity of embryonic cell division.     

农产品价格波动国内研究现状述评

随着中国农业市场的逐步开放,中国农产品价格波动频繁。有关农产品价格波动问题的研究一直是国内经济学术界的热点。目前的研究主要围绕农产品价格的波动特征、波动成因、农产品价格波动对社会经济的影响以及平抑价格波动的政策等内容展开。为推动研究工作的深入,今后应当加强对农产品价格异常波动的成因、价格波动在不同市场之间及不同产业链条之间传递的量化分析、价格异常波动的机理和平抑价格异常波动各种调控政策的利弊分析等方面的研究。     

Dynamics-driven reaction pathway in an intramolecular rearrangement

A critical role is traditionally assigned to transition states (TSs) and minimum energy pathways, or intrinsic reaction coordinates (IRCs), in interpreting organic reactivity. Such an interpretation, however, ignores vibrational and kinetic energy effects of finite temperature. Recently it has been shown that reactions do not necessarily follow the intermediates along the IRC. We report here molecular dynamics (MD) simulations that show that dynamics effects may alter chemical reactions even more. In the heterolysis rearrangement of protonated pinacolyl alcohol Me3C-CHMe-OH2+ (Me, methyl), the MD pathway involves a stepwise route with C-O bond cleavage followed by methyl group migration, whereas the IRC pathway suggests a concerted mechanism. Dynamics effects may lead to new interpretations of organic reactivity.     

Oscillations and sparsening of odor representations in the mushroom body

In the insect olfactory system, oscillatory synchronization is functionally relevant and reflects the coherent activation of dynamic neural assemblies. We examined the role of such oscillatory synchronization in information transfer between networks in this system. The antennal lobe is the obligatory relay for olfactory afferent signals and generates oscillatory output. The mushroom body is responsible for formation and retrieval of olfactory and other memories. The format of odor representations differs significantly across these structures. Whereas representations are dense, dynamic, and seemingly redundant in the antennal lobe, they are sparse and carried by more selective neurons in the mushroom body. This transformation relies on a combination of oscillatory dynamics and intrinsic and circuit properties that act together to selectively filter and synthesize the output from the antennal lobe. These results provide direct support for the functional relevance of correlation codes and shed some light on the role of oscillatory synchronization in sensory networks.     

丙硫咪唑对猪囊尾蚴酶组织化学影响的研究

本实实验采用酶组织化学方法测定猪囊定蚴发育过程中三磷酸腺苷酶（ATPase)、酸性磷酸酶（ACP）、碱性磷酸酶（AKP）三种酶的活性，并研究了丙硫米唑类药物对不同时期囊尾蚴的三种酶活性的影响。实验结果表明，丙硫咪唑类抗囊药物通过抑制囊虫体内ATPase、ACP、AKP的活性而抑制虫体对糖的吸收和物质转运，阻碍了能量代谢和ATP的产生，从而影响虫体发育和生长，最终导致囊尾蚴死亡。