高超声速尾流及其气动、物理和化学性质(下)

<正> 七、尾流计算方法和湍流输运系数 有关高超声速尾流的理论分析工作,始于前述Feldman[16]1961年的平衡层流尾流数值解。然而,除非飞行体在低空中以高超声速飞行,高熵的尾流总是处于化学非平衡之中,而在低空时,尾流又总是转捩为湍流,所以Feldman的计算多少有点自相矛盾。 1962年,Lees和Hromas[41]首先对圆球尾流的湍流扩散问题进行了分析,他们采用雷诺相似假设,即假定质量、动量和能量的湍流输运之间存在着相似关系,并根

The effect of low temperature GaAs nucleation on the growth of GaN on Silicon (001) during MOVPE process

High quality cubic GaN was grown on Silicon (001) by metalorganic vapor phase epitaxy (MOVPE) using a GaAs nucleation layer grown at low temperature. The influence of various nucleation conditions on the GaN epilayers' quality was investigated. We found that the GaAs nucleation layer grown by atomic layer epitaxy (ALE) could improve the quality of GaN films by depressing the formation of mixed phase. Photoluminescence (PL) and X-ray diffraction were used to characterize the properties of GaN epilayers. High quality GaN epilayers with PL full width at half maximum (FWHM) of 130meV at room temperature and X-ray FWHM of 70 arc-min were obtained by using 10-20nm GaAs nucleation layer grown by ALE.

Classification of jinjiang oysters Crassostrea rivularis (Gould, 1861) from China, based on morphology and phylogenetic analysis

The jinjiang oyster Crassostrea rivularis [Gould, 1861. Descriptions of Shells collected in the North Pacific Exploring Expedition under Captains Ringgold and Rodgers. Proc. Boston Soc. Nat. Hist. 8 (April) 33-40] is one of the most important and best-known oysters in China. Based on the color of its flesh, two forms of C rivularis are recognized and referred to as the "white meat" and 11 red meat" oysters. The classification of white and red forms of this species has been a subject of confusion and debate in China. To clarify the taxonomic status of the two forms of C. rivularis, we collected and analyzed oysters from five locations along China's coast using both morphological characters and DNA sequences from mitochondrial 16S rRNA and cytochrome oxidase 1, and the nuclear 28S rRNA genes. Oysters were classified as white or red forms according to their morphological characteristics and then subjected to DNA sequencing. Both morphological and DNA sequence data suggest that the red and white oysters are two separate species. Phylogenetic analysis of DNA sequences obtained in this study and existing sequences of reference species show that the red oyster is the same species as C. ariakensis Wakiya [1929. Japanese food oysters. Jpn. J. Zool. 2, 359-367.], albeit the red oysters from north and south China are genetically distinctive. The white oyster is the same species as a newly described species from Hong Kong, C. hongkongensis Lam and Morton [2003. Mitochondrial DNA and identification of a new species of Crassostrea (Bivalvia: Ostreidae) cultured for centuries in the Pearl River Delta, Hong Kong, China. Aqua. 228, 1-13]. Although the name C. rivularis has seniority over C. ariakensis and C. hongkongensis, the original description of Ostrea rivularis by Gould [1861] does not fit shell characteristics of either the red or the white oysters. We propose that the name of C. rivularis Gould [1861] should be suspended, the red oyster should take the name C. ariakensis, and the white oyster should take the name C. hongkongensis. (C) 2004 Elsevier B.V. All rights reserved.

角百灵和小云雀的孵化行为

鸟类的个体发育是在双亲、雏鸟及巢组成的一种特殊环境中完成的，稳定的热环境是它们完成孵化和雏鸟生长发育的必要条件（White et al.，1974；Purdue，1976；Ellis，1982；Haftorn，1983；Morton et al.，1985；Schnace et al.，1991；Vatnick et al.，1998；张晓爱等，1995）。因此亲鸟的伴巢行为及时间是指亲鸟在繁殖期间，为筑巢、防御、抱卵、孵雏及递食而出现在巢中或附近的所有行为（Oppenhaim，1972）。亲鸟拌巢的时间分配与巢环境有密切关系，已有大量的报道（如Purdue，1976；Ellis, 1982；Schnace et al., 1991；张晓爱等，1995）。张晓爱等（1995）比较了高寒草甸地区的地面、灌丛及洞穴3种不同营巢类型亲鸟的伴巢时间分配模式，但是对亲缘关系较近，营巢生境相同鸟类之间的伴巢时间分配模式，以及坐巢行为与巢环境之间关系没有报道，国外对这方面的报道也甚少。本项研究选择高寒草甸的两种百灵科鸟：角百灵（Eremophila alpestris）和小云雀（Alauda gulgula）作为研究对象来比较亲鸟在卵化期坐巢行为与巢址微环境的关系，对研究鸟类繁殖行为与环境关系及从生活史进化角度研究相似种的共存机制提供理论依据。