Sinusoidal phase-modulating laser diode interferometer for measuring angular displacement

We propose a sinusoidal phase-modulating laser diode interferometer for measuring small angular displacement. The interferometer is based on a Fabry-Perot plate. It has a simple structure and is insensitive to external disturbance. Sinusoidal phase-modulating interferometry is used for improving the measurement accuracy. A charge-coupled device (CCD) image sensor is used for measuring the distance between the reflected beams from two faces of the Fabry-Perot plate. From the distance, the initial angle of incidence is calculated. Compared with Michelson interferometers and autocollimators, this interferometer has the advantage of compact size and simple structure. The numerical calculation and experimental results verify the usefulness of this novel interferometer. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

El comercio de noticias y Noticias del Nuevo Mundo descubierto en la Luna

En fecha tan temprana como 1622 aparece en Inglaterra la primera publicación periódica. Ese mismo año Ben Jonson, escritor teatral contemporáneo de William Shakespeare, compone una mascarada, la primera obra literaria que alude al fenómeno del periodismo. Cuatro años después, en 1626, escribe y hace representar toda una comedia cuyo tema central y escenario es un periódico. Por primera vez en español damos ahora en traducción ambas obras, Noticias del Nuevo Mundo descubierto en la Luna (News from the New World discover’d in the Moon) y El comercio de noticias (The staple of news). Especialmente esta última es, además de una apreciable pieza dramática, un excelente retrato de un fenómeno emergente que no solamente describe las características del incipiente periodismo, sino además una reflexión sobre cuestiones tales como la democracia, la participación ciudadana, la monarquía, la estructura empresarial o los derechos de autor. La obra de Jonson es el retrato de una época oscura, apenas dos décadas de albores del periodismo, y su literatura es la única capaz de devolvernos algo de su efímero esplendor. Pero es también el retrato de una profesión cuyas principales características, que el escalpelo crítico de Jonson tan ácidamente pone de manifiesto, siguen siendo contemporáneas. Con sus casi cuatro siglos de solera, en la oficina de noticias que Jonson nos pinta está teniendo lugar una escena que no ha perdido su vigencia.

基于孔径耦合带状线的激光脉冲整形系统

实现了一种新型的激光脉冲整形系统，该系统使用了一个由孔径耦合带状线（ACSL）电脉冲整形器驱动的电光调制器。一个电脉冲整形器由两条通过其公共接地板上的耦合孔径发生耦合作用的带状传输线所组成的四端口装置。更换具有不同耦合孔径的公共接地板，该电脉冲整形发生器可以具有150ps时间结构的任意整形电脉冲。将任意整形的电脉冲输入到电光调制器上，就可以得到任意整形的激光脉冲。利用该系统，激光脉冲整形系统能够产生具有150ps前后沿，1～3ns脉冲宽度可调、高对比度、光滑过渡以及任意整形的激光脉冲。

Temperature characteristics of optical parameters of phthalocyanine LB films and spin-coated films

The LB films and spin-coated films of tetra-neopentoxy phthalocyanine zinc (TNPPcZn) were prepared and annealed at different temperatures. Their refractive index (n) and extinction coefficient (k) were measured by p-polarized reflectance. The similar value of n and k, as well as similar changing tendency of it and k at varied annealing temperatures, was found between LB films and spin-coated films. In addition, the absorption curves of TNPPcZn LB films and spin-coated films in visible range at different annealing temperature were investigated. The results indicate that the changing tendency of the extinction coefficient of two kinds of TNPPcZn films obtained from two methods mentioned above were coincident. When the annealing temperature increased to 150 degrees C, the monomers of TNPPcZn films transformed to aggregates, n(f) and k(f) of the films increased. Further, n(f) and k(f) decreased as aggregates changed back to monomers again at the annealing temperature of 300 degrees C. The experimental results coincide well with the theoretical analysis. (C) 2004 Elsevier B.V. All rights reserved.

Population structure and variance effective size of red snapper (Lutjanus campechanus) in the northern Gulf of Mexico*

We assayed allelic variation at 19 nuclear-encoded microsatellites among 1622 Gulf red snapper (Lutjanus campechanus) sampled from the 1995 and 1997 cohorts at each of three offshore localities in the northern Gulf of Mexico (Gulf). Localities represented western, central, and eastern subregions within the northern Gulf. Number of alleles per microsatellite per sample ranged from four to 23, and gene diversity ranged from 0.170 to 0.917. Tests of conformity to Hardy-Weinberg equilibrium expectations and of genotypic equilibrium between pairs of micro-satellites were generally nonsignificant following Bonferroni correction. Significant genic or genotypic heterogeneity (or both) among samples was detected at four microsatellites and over all microsatellites. Levels of divergence among samples were low (FST ≤0.001). Pairwise exact tests revealed that six of seven “significant” comparisons involved temporal rather than spatial heterogeneity. Contemporaneous or variance effective size (NeV) was estimated from the temporal variance in allele frequencies by using a maximum-likelihood method. Estimates of NeV ranged between 1098 and >75,000 and differed significantly among localities; the NeV estimate for the sample from the northcentral Gulf was >60 times as large as the estimates for the other two localities. The differences in variance effective size could ref lect differences in number of individuals successfully reproducing, differences in patterns and intensity of immigration, or both, and are consistent with the hypothesis, supported by life-history data, that different “demographic stocks” of red snapper are found in the northern Gulf. Estimates of NeV for red snapper in the northern Gulf were at least three orders of magnitude lower than current estimates of census size (N). The ratio of effective to census size (Ne/N) is far below that expected in an ideal population and may reflect high variance in individual reproductive success, high temporal and spatial variance in productivity among subregions or a combination of the two.

Growth, mortality, and hatchdate distributions of larval and juvenile spotted seatrout (Cynoscion nebulosus) in Florida Bay, Everglades National Park

Life history aspects of larval and, mainly, juvenile spotted seatrout (Cynoscion nebulosus) were studied in Florida Bay, Everglades National Park, Florida. Collections were made in 1994−97, although the majority of juveniles were collected in 1995. The main objective was to obtain life history data to eventually develop a spatially explicit model and provide baseline data to understand how Everglades restoration plans (i.e. increased freshwater flows) could influence spotted seatrout vital rates. Growth of larvae and juveniles (<80 mm SL) was best described by the equation loge standard length = –1.31 + 1.2162 (loge age). Growth in length of juveniles (12–80 mm SL) was best described by the equation standard length = –7.50 + 0.8417 (age). Growth in wet weight of juveniles (15–69 mm SL) was best described by the equation loge wet-weight = –4.44 + 0.0748 (age). There were no significant differences in juvenile growth in length of spotted seatrout in 1995 between three geographical subdivisions of Florida Bay: central, western, and waters adjacent to the Gulf of Mexico. We found a significant difference in wet-weight for one of six cohorts categorized by month of hatchdate in 1995, and a significant difference in length for another cohort. Juveniles (i.e. survivors) used to calculate weekly hatchdate distributions during 1995 had estimated spawning times that were cyclical and protracted, and there was no correlation between spawning and moon phase. Temperature influenced otolith increment widths during certain growth periods in 1995. There was no evidence of a relationship between otolith growth rate and temperature for the first 21 increments. For increments 22–60, otolith growth rates decreased with increasing age and the extent of the decrease depended strongly in a quadratic fashion on the temperature to which the fish was exposed. For temperatures at the lower and higher range, increment growth rates were highest. We suggest that this quadratic relationship might be influenced by an environmental factor other than temperature. There was insufficient information to obtain reliable inferences on the relationship of increment growth rate to salinity.

紫茎泽兰入侵的生态学研究

存在明显的季节性干旱的实验地的自然生境（无遮荫不补水处理）对于1年生紫茎泽兰来说具有胁迫作用，而对于本地草本植物群落来说，这样的季节性干旱并不存在胁迫作用;在单层遮荫不补水的处理中，紫茎泽兰具有竞争优势，而单层遮荫补水处理对紫茎泽兰的竞争不利。在双层遮荫补水的处理中，紫茎泽兰表现出对本地植物较大的相对竞争优势，但双层覆盖对于二者的生长均构成了较严重的胁迫。 在无覆盖不补水的处理中，紫茎泽兰定居期的死亡率最高，而定居后的生长指标（平均高和平均单株干重）在补水和不补水条件之间没有明显差异;在双层覆盖条件下，紫茎泽兰存活率在补水和不补水条件下，绝对值都较高，而平均单株干重在补水和不补水条件下都比较低;在单层覆盖条件下，紫茎泽兰存活率在补水和不补水条件下都较高，紫茎泽兰的平均高和平均单株干重在不补水处理都显著高于补水处理，而且明显高于其他不覆盖、双层覆盖的补水和不补水处理。说明在实验地的自然生境中，本地群落对紫茎泽兰早期（侵入定居）具有一定的抵抗力，但在这样的生境中的本地植物群落对紫茎泽兰的后期（定居之后）的发展的抵抗力较低;双层覆盖条件（相当于郁闭度高的林下生境）对紫茎泽兰的早期侵入定居虽然抵抗力较差，但是对紫茎泽兰的后期（定居之后）的发展具有较强的抑制作用;单层覆盖条件（相当于受到人畜干扰的郁闭度较低的林下生境）下，本地群落对紫茎泽兰早期侵入定居和后期（定居之后）的发展抵抗力都很低，这一结果提醒我们，紫茎泽兰易于侵入受到过人为干扰的郁闭度较低的林下生境并产生严重危害。 刈割干扰对紫茎泽兰的入侵具有明显的促进作用，高强度刈割的促进作用主要体现在促进紫茎泽兰的个体生长速度和群体生物量上，但低强度刈割的促进作用主要体现在入侵定居的个体数量和群体生物量上。低强度刈割处理中的紫茎泽兰的密度为高强度刈割处理的5倍，单位面积上的紫茎泽兰的生物量最高，达到高强度刈割处理的2.5倍，可见对于紫茎泽兰的入侵而言，低强度的刈割干扰比高强度刈割干扰具有更大的促进作用。 本地植物雀麦、豆科植物、鱼眼草和香薷在与紫茎泽兰混栽后，它们的根际土壤微生物群落结构与紫茎泽兰根际土壤微生物相似性更高，而偏相关分析结果表明，豆科植物和鱼眼草的根际土壤微生物群落结构的变化与它们的生物量生长具有一定的关联性，而对于雀麦和香薷的根际土壤微生物群落结构的变化与它们的生物量生长的关联性不明显，说明紫茎泽兰入侵本地植物群落后可以对生态系统的土壤微生物群落结构造成较大的影响，而微生物的改变并不是对所有的本地植物来说都是非常严峻的。虽然我们实验中的4种本地植物中只有2种本地植物的生长表现出与其根际土壤微生物变化的显著相关性，但这对于本地植物群落已经是非常严重的威胁。