Self-trapping of dark incoherent light beams

"Dark beams" are nonuniform optical beams that contain either a one-dimensional (1D) dark stripe or a two-dimensional (2D) dark hole resulting from a phase singularity or an amplitude depression in their optical field. Thus far, self-trapped dark beams (dark solitons) have been observed using coherent light only. Here, self-trapped dark incoherent light beams (self-trapped dark incoherent wavepackets) were observed. Both dark stripes and dark holes nested in a broad partially spatially incoherent wavefront were self-trapped to form dark solitons in a host photorefractive medium. These self-trapped 1D and 2D dark beams induced refractive-index changes akin to planar and circular dielectric waveguides. The experiments introduce the possibility of controlling high-power coherent laser beams with low-power incoherent light sources such as light emitting diodes.     

Size and age of the universe

The age of the universe based on abundances of isotopes is in the range 10 billion to 15 billion years. This is consistent with the age range 12 billion to 20 billion years calculated from the evolution of the oldest galactic stars. A third estimate of the age of the universe is based on the Hubble relation between the velocities of galaxies and their distances from us, where the inverse of the Hubble parameter H is a measure of the age of a uniformly expanding universe. Evidence that has been accumulating over the past few years indicates that the expansion of the universe may exhibit a rather large local perturbation due to the gravitational attraction of the Virgo supercluster. Different types of observations still produce conflicting evidence about the velocity with which the Local Group of galaxies (of which our Milky Way system is a member) is falling into the Virgo cluster. The results to date indicate that this velocity lies somewhere in the range 0 to 500 kilometers per second. The resulting ambiguity in the flow pattern for relatively nearby galaxies makes values of H derived from galaxies with radial velocities less than 2000 kilometers per second particularly uncertain, and this restricts determinations of H to distant galaxies, for which distances are particularly uncertain. The best that can be said at present is that H(-1) yields a maximum time scale in the range 10 billion to 20 billion years.     

Venus southern hemisphere: geologic character and age of terrains in the themis-alpha-lada region

Arecibo high-resolution radar images of the southern hemisphere of Venus extending to 78 degrees S show that the surface of the Themis-Alpha-Lada region is characterized by linear deformation zones with volcanoes and corona-like features and by regional volcanic deposits (primarily plains, small shields, and large edifices). Large-scale areal deformation is limited to the tessera of Alpha Regio. Lada Terra, in the southern high latitudes, contains several large coronae, in contrast to Ishtar Terra in the northern high latitudes. The density of craters of possible impact origin is somewhat lower than that observed in the Venera 15 and 16 coverage; these data extend to 43 percent of the areas of the surface of Venus with ages of less than about 1 billion years.     

楠木名称考订

\t\t\t\t\t目的\t\t\t\t\t为了解湖北省兴山县的野生楠木资源分布状况、种群结构及其群落特征。\t\t\t\t\t\t\t\t\t\t\t\t\t方法\t\t\t\t\t采用样方法分别在兴山县的南阳镇、古夫镇和峡口镇对楠木资源分布集中地段进行野外实地调查,并记录其生境条件和群落特征。\t\t\t\t\t\t\t\t\t\t\t\t\t结果\t\t\t\t\t调查区内发现野生楠木类植物9种,共计274株。包括楠属植物4种,润楠属植物5种,其中多脉润楠(Machilus multinervia)、刨花润楠(M. pauhoi)初步确定为兴山县新分布记录种。其楠木总体分布较零散,仅在龙门河村有集中分布。它们较多分布在阴坡,坡度为36°~40°,海拔在680 m左右的生境条件下。其楠木类植物群落的维管束植物共有68种,隶属于34科58属,以樟科植物为最多。\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t结论\t\t\t\t\t调查区内楠属植物的种群年龄结构相比润楠属更合理,呈稳定型,而润楠属植物种群年龄结构为衰退型。\t\t\t\t     

Wind tunnel simulations of light and dark streaks on Mars

Wind tunnel experiments have revealed a characteristic flow field pattern over raised-rim craters which causes distinctive zones of aeolian erosion and deposition. Comparisons of the results with Mariner 9 images of Mars show that some crater-associated dark zones result from wind erosion and that some crater-associated light streaks are depositional.     

篱壁式栽培条件下富士苹果树冠光照分布与果实产量品质的关系

以不同主枝数量的篱壁式栽培富士苹果为试材,研究该条件下树冠内光照分布及其与果实品质的关系。结果表明,随着主枝数量的增加,树冠内相对光照强度小于30%的区域所占比例逐渐增加,而大于85%的区域所占比例逐渐减小,主枝数为16～18个的树冠内相对光照强度为30%～85%的(为优质光照)区域比例最高达到77%。60%～85%区域内果实单果重、可溶性糖及果皮花青苷含量均达较高水平,故该相对光照强度对果实品质形成最有利,30%～60%区域次之;相对光照强度≥85%的区域内果实可溶性糖含量最高,内在品质好,但果皮花青苷含量低(为60%～85%区域的75.6%,)。果实主要集中在相对光照小于85%区域内,30%～60%区域内的果实所占比例最高,可达总果实量的40%以上,60%～85%区域次之。结果表明,蓠壁式栽培苹果树冠内优质光照区域所占比例(最高可达77.2%)高于传统的主干形(50%～60%),有利于果树的生长、果实的发育及品质形成,同时还可以提高株间的生产效率,且单株以16～18个主枝为宜。     

光暗处理对水稻叶片光合关键酶的效应

稻苗置暗中24h后,Rubisco含量及Rubisco与可溶性蛋白的比值随光强的增加而提高;经2h光照后再置黑暗中,Rubisco含量在最初20min下降迅速,说明苗期Rubisco蛋白在光暗交替下周转较快.Rubisco的初始活力在光照下迅速增加,其上升倍数大大高于量的增加,光强越大达到最大活力所需的时间越短.照光后把稻苗置暗中,Rubisco初始羧化活力很快下降,说明Rubisco的光下活化及暗中失活迅速.Rubisco活化酶的含量随光照增加而逐渐上升,光照处理后再置暗中Rubisco活化酶含量不断下降,但速率不如Rubisco.Rubisco活化酶的活化只依赖低光强,光照处理后再置黑暗中,Rubisco活化酶活力迅速下降.     

Size distribution of fine particles from coal combustion

Measurements of the particle size distribution at the outlets of six coal-fired utility boilers showed a peak at a particle diameter near 0.1 micrometer. This submicrometer mode appears to be a general feature of coal combustion that results from a volatilization-condensation process in the boiler. At the boilers tested, the submicrometer mode contained 0.2 to 2.2 percent of the total fly ash mass. The importance of this mode is greater than its small quantity suggests because particles in the submicrometer size range are often much more difficult to collect with conventional particulate control devices than larger particles. Thus, the submicrometer mode may significantly influence the design and selection of future power plant emission controls. The particle mass in the submicrometer mode was correlated with the nitric oxide concentration in the flue gas. This correlation suggests that control of nitric oxide by modification of the combustion conditions may reduce the generation and emission of submicrometer particles.     

糯玉米胚乳淀粉粒的粒度分布特征

以7个糯玉米品种为材料,采用激光衍射粒度分析仪测定其胚乳淀粉粒粒径以及体积、表面积和数目的分布,明确糯玉米胚乳淀粉粒的粒度分布特征。结果表明:糯玉米胚乳淀粉粒的粒径为0.375—30.07μm,其上限为22.73—30.07μm,平均粒径为12.33-14.60μm。淀粉粒的体积和表面积分布呈现三峰曲线,数目分布呈现单峰曲线。以体积分布曲线凹处为界线将糯玉米淀粉粒分为小型(3.519μm)、中型(3.519—7.422μm)和大型(7.422μm)。7个糯玉米品种小型、中型和大型淀粉粒体积分别占总体积的11.25%—12.46%、1.79%—6.98%和80.77%—86.96%,表面积分别占总表面积的54.28%—57.13%、2.50%—8.26%和35.97%—40.38%,数目分别占总数目的98.71%—99.39%、0.20%—0.76%和0.39%—0.53%。可见,糯玉米胚乳淀粉主要由小型淀粉粒组成,其对表面积的贡献最大,而大型淀粉粒对体积的贡献最大。品种间比较,小型淀粉粒的粒度分布差异不显著,中型和大型淀粉粒的粒度分布存在显著差异。     

光暗条件对储藏期辣椒果实中辣椒素含量的影响

试验主要针对采后辣椒果实中辣椒素的变化,采用两个不同的辣椒品种景尖椒3号和家园1号(均为高辣度品种),青熟果采摘,采后分别以室内散射光、无光两种不同的光条件储存,晒干、阴干两种不同光条件干制,对辣椒果实采后辣椒素含量的变化进行了系统研究。发现在辣椒采后储存期中,辣椒素含量随储存期延长先增加后减少,储存第6~9天,辣椒素含量达到最高值;在辣椒果实采后干制过程中,辣椒素含量先增加后减少,在干制第20~25天,辣椒素含量达到最大值。晒干更利于辣椒素含量的增加。     

光暗条件与触角去除对中华通草蛉成虫取食的影响

为了解视觉、嗅觉单一和双重感觉通道的作用,室内研究了光、暗、触角正常和触角去除4种处理对中华通草蛉成虫取食的影响。结果发现:①光条件下触角去除的中华通草蛉平均取食率(13.67%)高于其暗条件下取食率(3.67%),表明光暗条件及与其关联的视觉对其取食率有影响;②触角正常的中华通草蛉暗条件下平均取食率(30.67%)大于触角去除个体的取食率(3.67%),表明嗅觉对其取食率有显著影响;③4种处理中光条件下触角正常平均取食率最高(43.00%),暗条件下触角正常次之(30.67%),光条件下触角去除居三位(10.67%),暗条件下触角去除最低(3.67%),表明触角去除较光暗条件对其取食率的影响更大(依次分别为88.05%、73.18%),且视嗅觉间具有协同作用;④光、暗条件对触角去除的雌、雄虫取食影响率分别达72.73%和73.70%,触角去除对暗条件下的雌、雄虫取食影响率分别为86.67%和89.37%,表明其性别间各处理的影响差异甚小。综上表明光、暗、触角及其相关的视、嗅觉是影响中华通草蛉取食的重要因素,其中嗅觉影响更大。     

肉种蛋鸡啄羽行为在遮光笼中亮区和暗区的频次差异

通过比较盒式笼中肉种蛋鸡啄羽行为在遮光区和非遮光区的频次差异,旨在检验遮光、环境丰富度、啄羽和福利的关系。利用行为观测者摄像分析仪,对相同光周期下遮光的单鸡笼和双鸡笼每组各16只同日龄肉种产蛋鸡的活动同时摄录并分析。结果显示,单鸡笼啄羽频次(4.3±1.13)显著低于双鸡笼的(14.0±2.0)(P<0.01);单鸡笼暗区啄羽相比亮区减少了46%(P>0.05),而双鸡笼啄羽仅发生在亮区(P<0.05);亮区啄羽,单鸡笼较之双鸡笼则显著减小了80%(P<0.01),而暗区啄羽2者水平都很低(0~1.5),无显著差异。本研究中未见剧烈型啄羽,仅有温和型啄羽。本研究表明,虽然啄羽的密度效应大于啄羽的遮光效应,但遮光能够降低密度对啄羽的效应值。遮光提供分化的光环境,而被遮光的环境很可能以减弱视觉信号方式减小羽毛对啄羽行为的刺激作用。这提示对盒式鸡笼进行局部遮光以增大其环境丰富度从而提高动物福利,也有可取之处。     

玉米定向栽植模式下冠层结构及光能分布特征研究

为探讨不同栽植模式下玉米冠层光能利用情况的差异和定向栽植方式的增产机理,以紧凑型玉米品种先玉335和半紧凑型玉米品种吉单50为试验材料,设置定向播种、随机播种、定向移栽、随机移栽4种栽植模式,测定其玉米冠层结构参数、群体内不同高度不同时间的光合有效辐射量等参数。结果表明:吐丝期最大冠层形成时两个品种叶片垂直分布比例存在差异,且不随栽植方式改变而改变。其中,上午时段(10:00~10:15)定向播种和定向移栽的群体有效光能截获率分别比随机种植模式增加10.60和23.50个百分点,但定向种植模式玉米群体的中部光合有效辐射下降快,而群体底部可保证一定的透光率;在机械许可的情况下,定向栽植能够建立合理冠层结构,有效利用光能,为高产栽培提供一条新的途径。