Linear Stability Analysis of Convection in Two-Layer System with an Evaporating Vapor-Liquid Interface

Classical theories have successfully provided an explanation for convection in a liquid layer heated from below without evaporation. However, these theories are inadequate to account for the convective instabilities in an evaporating liquid layer, especially in the case when it is cooled from below. In the present paper, we study the onset of Marangoni convection in a liquid layer being overlain by a vapor layer.A new two-sided model is put forward instead of the one-sided model in previous studies. Marangoni-Bénard instabilities in evaporating liquid thin layers are investigated with a linear instability analysis. We define a new evaporation Biot number, which is different from that in previous studies and discuss the influences of reference evaporating velocity and evaporation Biot number on the vapor-liquid system. At the end, we explain why the instability occurs even when an evaporating liquid layer is cooled from below.

Two new species of Rotifera from China

Two new rotifera species, Brachionus huangi n. sp, and Lecane chinesensis n. sp. are described and illustrated from different localities in China. The main distinguishing taxonomic features of B. huangi are three pairs of apical spines, a pair of symmetrical caudal spines and a wide caudal projection. For L. chinesensis, the main characteristics are the two-sided small extentions of the foot pseudosegment, the long and innercurved apical spines and ventral lorica anteriorly narrower than the dorsal one.

Marangoni-Benard instability with the exchange of evaporation at liquid-vapour interface

A new two-sided model rather than the one-sided model in previous works is put forward. The linear instability analysis is performed on the Marangoni-Benard convection in the two-layer system with an evaporation interface. We define a new evaporation Biot number which is different from that in the one-sided model, and obtain the curves of critical Marangoni number versus wavenumber. The influence of evaporation velocity and Biot number on the system is discussed and a new phenomenon uninterpreted before is now explained from our numerical results.

Influence of Evaporation on Marangoni-Benard Instability

Evaporative convection and instability give rise to both scientific and technological interests. Practically, a number of the industrial applications such as thin-film evaporators, boiling technologies and heat pipes concern with the evaporation process of which through the vapor-liquid interface the heat and mass transfer occur. From a physical viewpoint, one of interesting questions is the mechanisms of convection instability in thin-liquid layers induced by the coupling of evaporation phenomenon and Marangoni effect at the mass exchanged interface. Classical theories, including Rayleigh’s and Pearson’s, have only successfully explained convection in a liquid layer heated from below without evaporation. However these theories are unable to explain the convection in an evaporating thin layer, especially liquid layer is cooled from below. In present paper, a new two-sided model is put forward rather than the one-sided model in previous works. In previous works, the vapor is treated as passive gas and dynamics of vapor has been ignored. In this case, the vapor liquid system can be described by one-sided model. In our two-sided model, the dynamics of vapor should be considered. Linear instability analysis of the Marangoni-Bénard convection in the two-layer system with an evaporation interface is performed. We define a new evaporating Biot number which is different from the Biot number in one-sided model and obtain the curves of critical Marangoni number versus wave number. In our theoretical results, the Biot number and the evaporating velocity play a major role in the stability of the vapor-liquid system.

Instabilities of a liquid film flowing down an inclined porous plane

The problem of a film flowing down an inclined porous layer is considered. The fully developed basic flow is driven by gravitation. A careful linear instability analysis is carried out. We use Darcy's law to describe the porous layer and solve the coupling equations of the fluid and the porous medium rather than the decoupled equations of the one-sided model used in previous works. The eigenvalue problem is solved by means of a Chebyshev collocation method. We compare the instability of the two-sided model with the results of the one-sided model. The result reveals a porous mode instability which is completely neglected in previous works. For a falling film on an inclined porous plane there are three instability modes, i.e., the surface mode, the shear mode, and the porous mode. We also study the influences of the depth ratio d, the Darcy number delta, and the Beavers-Joseph coefficient alpha(BJ) on the instability of the system.

The Kiloparsec-scale structure of 3C 286

We present radio images of the compact steep spectrum (CSS) quasar 3C 286 acquired with the Very Large Array (VLA) at 8.4 and 22.5 GHz. The source exhibits a two-sided core-jet structure with a bright central component and two extended components one to the east (P.A. 100degrees) and another to the southwest (P.A. -116degrees). From the compact core, an extension runs towards the southwest component up to similar to 0.7 arcsecond. The emission between the primary central component and the southwest component exhibits a knotty structure. A gradual change of the jet position angles from -135degrees to -120degrees in the inner southwest jet suggests a local bend. The position angle changes of the major eastern components E2 and E1 suggest that the eastern jet likely follows a curved trace. The bends in the jet trace may be associated with a relativistic precession or some interaction between the jet and the ambient matter. A mean spectral index of alpha(8.4)(22.5) similar to -0.76 (S-nu proportional to nu(alpha)) is estimated for the core component. Steep spectra are also obtained for the extended southwest component (2.6", P.A. -116degrees) and eastern component (0.8", P.A. 100degrees), with alpha(8.4)(22.5) similar to -0.88 and alpha(8.4)(22.5) similar to -1.79, respectively. The radio morphologies and spectral index distributions suggest that the core seen in our images is likely to be the beamed inner jet while the real nucleus is dimmed by it beaming away from us.

Status of sturgeon aquaculture and sturgeon trade in China: a review based on two recent nationwide surveys

The authors reviewed the aquacultural history of Acipenseriformes in China, related the legal status and examined the current status of the cultured species or hybrids, origins of seedlings, quantities of production, geographic distribution in farming, and the sustainability for both restocking programmes and human consumption. The census shows that since 2000, the production of cultured sturgeons in China appears to have become the largest in the world. As of 2000, the rapid growth of sturgeon farming in China mainly for commercial purposes has shifted harvests in the Amur River from caviar production to the artificial culture of sturgeon seedlings. This dramatic development has also caused a series of extant and potential problems, including insufficient market availability and the impact of exotic sturgeons on indigenous sturgeon species. Annual preservation of sufficient higher-age sturgeons should be a national priority in order to establish a sustainable sturgeon-culture industry and to preserve a gene pool of critically endangered sturgeon species to prevent their extinction.

基于Internet的力反馈技术研究

论述了基于Internet的力反馈技术及其相关技术的发展和研究意义 ,综合机器人遥操作控制领域的理论方法 ,结合多媒体技术的最新发展 ,构建了一种基于事件的系统结构及其设计方法 .基于该方法 ,分析了系统的可靠性、稳定性及力媒体传输的透明性 ,并设计了一个基于Internet的力反馈技术的系统实例