Induction of pancreatic differentiation by signals from blood vessels

Blood vessels supply developing organs with metabolic sustenance. Here, we demonstrate a role for blood vessels as a source of developmental signals during pancreatic organogenesis. In vitro experiments with embryonic mouse tissues demonstrate that blood vessel endothelium induces insulin expression in isolated endoderm. Removal of the dorsal aorta in Xenopus laevis embryos results in the failure of insulin expression in vivo. Furthermore, using transgenic mice, we show that ectopic vascularization in the posterior foregut leads to ectopic insulin expression and islet hyperplasia. These results indicate that vessels not only provide metabolic sustenance, but also provide inductive signals for organ development.     

Fish population and behavior revealed by instantaneous continental shelf-scale imaging

Until now, continental shelf environments have been monitored with highly localized line-transect methods from slow-moving research vessels. These methods significantly undersample fish populations in time and space, leaving an incomplete and ambiguous record of abundance and behavior. We show that fish populations in continental shelf environments can be instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide. The technique has revealed the instantaneous horizontal structural characteristics and volatile short-term behavior of very large fish shoals, containing tens of millions of fish and stretching for many kilometers.     

Shadows cast by retinal blood vessels mapped in primary visual cortex

The mammalian eye is a remarkable optical device, but its design is not perfect. The blood vessels that supply the inner retina are located in front of the photoreceptor layer, blocking access to light. Their shadows create a pattern of blindness in the field of vision that corresponds precisely to the location of the largest vessels in the eye. We show here that in squirrel monkeys, focal deprivation by blood vessels leads to rewiring of the eye's geniculocortical projections, imprinting an image of the retinal vascular tree onto the primary visual cortex. This process illustrates vividly that local imbalances in neuronal activity can influence column formation during normal development.     

Life histories, blood revenge, and warfare in a tribal population

Blood revenge is one of the most commonly cited causes of violence and warfare in tribal societies, yet it is largely ignored in recent anthropological theories of primitive warfare. A theory of tribal violence is presented showing how homicide, revenge, kinship obligations, and warfare are linked and why reproductive variables must be included in explanations of tribal violence and warfare. Studies of the Yanomam? Indians of Amazonas during the past 23 years show that 44 percent of males estimated to be 25 or older have participated in the killing of someone, that approximately 30 percent of adult male dealths are due to violence, and that nearly 70 percent of all adults over an estimated 40 years of age have lost a close genetic relative due to violence. Demographic data indicate that men who have killed have more wives and offspring than men who have not killed.     

家兔亚硒酸钠中毒的血液和组织硒含量变化

２组家兔分别肌肉注射不同剂量的亚硒酸钠,连续８周,测定血液和组织中的硒含量．结果表明：血硒含量高于０．５ｍｇＬ－１,临床症状明显,可作为家兔硒中毒的早期诊断指标;血硒含量高于０．９ｍｇＬ－１,临床症状严重,可作为家兔硒中毒的诊断指标．组织硒含量以肾脏最高,肝脏次之,提示肝肾硒含量的测定可作为硒中毒病死后诊断参考指标     

草莓苗圃主要昆虫种群动态监测

在草莓(Fragaria ananassa Duch.)苗圃采用黄色粘虫板和随机抽样法系统调查方法了解主要昆虫种群的季节性动态,监测到的昆虫种群动态有单一的前峰型、中峰型及后峰型、双峰型和三峰型等5种季节性动态格局。主要害虫烟粉虱Bemisia tabacci表现为三峰型、外来入侵生物西花蓟马Frankliniella occidentalis为双峰型、桃蚜Aphis persicae则为后峰型。同一露地植株上的主要害虫烟粉虱数量动态与其黄色粘虫板上的数量有很好的一致性。露地和网室内草莓植株上的害虫组成上有较大的差异,前者有较高数量的烟粉虱,后者则有较高数量的桃蚜。网室环境似乎更有利于蜘蛛类天敌的增长。     

基于超声波的母猪产前行为监测系统设计

针对目前养殖业对母猪分娩时间的判断主要通过人工观察,不仅工作繁杂,而且易受饲养员主观经验影响等问题,设计一种基于超声波传感器和无线传感网络的母猪产前行为监测系统。该系统通过节点采集母猪产前头部、背部、尾部活动量的距离信息,将采集到的距离数据实时发送到网关节点,网关节点将距离信息转发到服务器。服务器端采用K-means聚类算法进行行为识别与分类。试验结果表明:系统能够快速采集母猪身体活动量的距离信息并对母猪行为进行分类,能够检测出母猪筑窝、站立、躺卧等行为,正确率为90.47%,系统工作稳定。提出了一种非接触式监测母猪产前行为的方法,为母猪分娩时间的预测提供基础。     

Reduction of a larval herring population by jellyfish predator

The scyphomedusa Aurelia aurita consumes large amounts of yolk-sac herring larvae in Kiel Fjord. The decline of the larval herring population in late spring coincides with a major population growth of the jellyfish. The size of the larval herring population seems to be more significantly affected by the size of the predator stock than by the size of the parental herring stock.     

A single progenitor population switches behavior to maintain and repair esophageal epithelium

Diseases of the esophageal epithelium (EE), such as reflux esophagitis and cancer, are rising in incidence. Despite this, the cellular behaviors underlying EE homeostasis and repair remain controversial. Here, we show that in mice, EE is maintained by a single population of cells that divide stochastically to generate proliferating and differentiating daughters with equal probability. In response to challenge with all-trans retinoic acid (atRA), the balance of daughter cell fate is unaltered, but the rate of cell division increases. However, after wounding, cells reversibly switch to producing an excess of proliferating daughters until the wound has closed. Such fate-switching enables a single progenitor population to both maintain and repair tissue without the need for a "reserve" slow-cycling stem cell pool.     

Food intake controlled by a blood factor

Intake of food by hungry rats was reduced 50 percent below normal after their blood had been mixed with that of satiated rats. Intake of food by deprived rats was not reduced when the donor rat was deprived of food for 24 hours prior to mixing of the blood or when a deprived donor was fed to satiety immediately before such transfusion.     

Effect of neuropeptides on production of inflammatory cytokines by human monocytes

Two groups of mediators, the neuropeptides substance P and K and the monocyte-derived cytokines, interact in the neural regulation of immunological and inflammatory responses. Substance P, substance K, and the carboxyl-terminal peptide SP(4-11) induce the release of interleukin-1, tumor necrosis factor-alpha, and interleukin-6 from human blood monocytes. The neuropeptide effects occur at low doses, are specific as shown by inhibition studies with a substance P antagonist, and require de novo protein synthesis. Since monocyte-derived cytokines regulate multiple cellular functions in inflammation and immunity and since neuropeptides can be released from peripheral nerve endings into surrounding tissues, these findings identify a potent mechanism for nervous system regulation of host defense responses.     

拖网渔船曳纲的运动建模及仿真

在拖拽系统水动力理论研究的基础上,根据集中质量法建立曳纲的三维动力学数学模型,将曳纲在空间上离散为一系列节点,同时忽略曳纲的扭转、抖动等,计入张力、重力、浮力和流体阻力的作用,建立曳纲的动态运动数学模型,并通过四阶龙格库塔方法积分求解,得到曳纲的位置和速度信息,最后利用三维图形引擎OSG(Open Scene Graph)实现拖曳系统的三维可视化。数值计算结果与相关试验数据比较表明,曳纲模型的求解方法是可靠的,同时又保证了仿真的实时性。     

拖网渔船曳纲的运动建模及仿真

在拖拽系统水动力理论研究的基础上,根据集中质量法建立曳纲的三维动力学数学模型,将曳纲在空间上离散为一系列节点,同时忽略曳纲的扭转、抖动等,计入张力、重力、浮力和流体阻力的作用,建立曳纲的动态运动数学模型,并通过四阶龙格库塔方法积分求解,得到曳纲的位置和速度信息,最后利用三维图形引擎OSG(Open Scene Graph)实现拖曳系统的三维可视化。数值计算结果与相关试验数据比较表明,曳纲模型的求解方法是可靠的,同时又保证了仿真的实时性。     

Monitoring Earth and sun by satellite

Researchers attending the spring meeting of the American Geophysical Union held 18 to 21 May in Baltimore have grown familiar with doing geophysical studies by satellite. Here are three current examples discussed at the meeting: gauging the output of the sun, measuring crustal movement, and deciphering the mineral composition of surface rocks.     

鱼类年龄硬组织鉴定方法研究应用进展

鱼类年龄鉴定是鱼类生态学与渔业资源评估的基础和前提。不同鱼类的年龄鉴定方法目前还无统一标准,通常是几种方法相互补充与验证,但应用最广泛的仍是硬组织年轮法,即基于耳石、鳞片等钙化组织的生长纹结构鉴定年龄。近几年,利用眼晶状体鉴定鱼类年龄有了新的进展,特别是在软骨鱼类中有些新的应用。本文系统梳理了基于鱼体不同硬组织(包括钙化组织和晶状体)鉴定年龄的原理与应用,综述了鱼类硬组织年龄鉴定领域的最新进展,并就鱼类年龄鉴定的精度评价、潜在新方法、数据读取可视化等方面提出未来研究建议,以期为鱼类生长与年龄鉴定研究及应用提供借鉴。     

合成孔径雷达水稻识别和监测研究进展

合成孔径雷达（SAR）具有全天时、全天候、高分辨率、大幅面监测地物的特征,利用SAR在阴雨天气多、云量大的水稻种植地区开展水稻识别、监测和估产具有光学遥感无可比拟的优势。目前基于雷达对水稻进行识别和监测的研究多用ERS/SAR、RADARSAT/SAR、ENVISATASAR等,其多是以民用或军民两用为主的星载合成孔径雷达。在用SAR数据监测水稻时,其后向散射系数来自4个方面：①入射波直接被水稻散射回去,即直接散射项（D-BS）;②入射波经水稻层的散射到达水面后,经水面反射到水稻层,经水稻层衰减回到雷达（SRE）;③入射波经水稻层衰减到达水面,经水面反射回到水稻层,经水稻层散射回去（ERS）;④入射波经水稻层衰减到达水面,经水面反射到水稻层,经水稻层的散射改变方向下行,再次经水面反射到水稻层,并经水稻层的衰减后回到雷达（W-R-W）。其中,后向散射系数的主要来源是SRE项和ERS项。SAR数据后向散射系数不仅要受到水稻物候期、植株高度、生物量、含水量等的影响,也受到自身入射角、波段、极化方式等的影响。一般地,水稻后向散射系数总体上是先随水稻生长增大,然后略有下降;水稻生长早期,后向散射系数随入射角波动的幅度较小,在水稻生长后期,后向散射系数随入射角波动的幅度变大,波动起伏次数增加;L波段和C波段的后向散射系数表现基本类同,但值要小很多,X波段则与L、C波段的表现相差较大。已有研究中大部分采用同极极化方式的后向散射系数作为研究对象。VV极化的后向散射系数变化比较平滑,HH极化的后向散射系数变化比较复杂。随着雷达卫星技术的发展,多极化、多模式、特殊波段将更能突出星载SAR的优势,拓宽SAR的应用范围,为进一步分析、识别和检测目标提供更有力的工具。