A human galaxy: a prehistory of the future

In the very long term, how could humans colonise the Galaxy? Colonisation cannot be centrally controlled; deeper drives must be tapped. It may take centuries to colonise the nearest stars: it may be a 'programme' like the Industrial Revolution, fuelled by entrepreneurship. To build a respectable interstellar empire may take millennia. Religions are similar multigenerational projects. Perhaps colonists will be motivated by appropriate creeds. To win the Galaxy, starship technology must persist for tens or hundreds of millennia. Homo erectus made the same hand-axe for a million years. The driver was biological, not conscious. Perhaps to our descendants starships will be like peacock tails.     

Power plant selection in a carbon constrained world the TERA(technoeconomic environmental risk analysis)

There is an increasing concern that current trends of consumption of natural resources cannot continue.It is imperative that major targeted investments are made into economical and reliable environment friendly propulsion and power solutions.Many novel and promising concepts are being proposed.The selection of the best candidates to pursue for investment becomes a very difficult choice.A detailed TERA(techno-economic environmental risk analysis) framework is described here to quantify risks and to compare and rank competing schemes on a formal and consistent basis.This technique is based on detailed and rigorous thermodynamic representations of power plants.A layer of environment,economic,weather and other models to describe the appropriate local conditions is superimposed to this.The outcome is a techno-economic environmental risk analysis framework with appropriate detail of each power plant as applied to the appropriate conditions.The results for each concept can then be compared and contrasted to make appropriate selections.      

复合结构梁断面的扭转中心

一、引言 精确地计算梁断面的弯心和扭心位置是研究梁或叶片结构的弹性静、动力学的基础。一些特殊断面,如开口或闭口薄壁断面的弯心和扭心,已有许多研究。相反,复合结构梁或复合材料梁断面的研究还相当少。Muskhelishvili把圣文南扭转理论推广到非均匀介质梁,并求得了几种简单形状断面梁的扭转函数。近年来相继发表了一些用差分法和有限元法求解扭转函数和扭转刚度的文章。     

Assessment of depth to magnetic sources using high resolution aeromagnetic data of some parts of the Lower Benue Trough and adjoining areas,Southeast Nigeria

High resolution airborne magnetic data acquired between 2005 and 2010 were used to determine depth to shallow and deep magnetic sources in some parts of Southeastern Nigeria. Various depth estimation methods such as standard Euler deconvolution (SED), source parameter imaging (SPI), spectral depth analysis (SDA) and two dimensional (2-D) forward modeling were applied. Results obtained from SED, SPI and models of profiles 1 and 2 indicate that the Abakaliki Anticlinorium (AA) and Ikom-Mamfe Rift (IMR) regions are dominated by short wavelength magnetic anomalies caused by extensive tectonic events. The SED map showed depth to shallow and deep magnetic sources ranging from ~ 16.6 to ~ 338.3 m and ~ 394.3 to ~ 5748.1 m respectively. Likewise, depth estimates from the SPI map varies from ~ 147.1 to ~ 554.2 m (shallow magnetic sources) and ~ 644.2 to ~ 6141.6 m (deep magnetic sources). The result obtained from SDA revealed depths to deep magnetic basement in the range of ~ 769 to ~ 6666 m with an average of ~ 3449 m. Also, it showed that depth to shallow magnetic sources vary between ~ 119 and ~ 434 m with mean of ~ 269 m. The 2-D forward modelling showed maximum depth values of ~ 4700, ~4600 and ~ 6500 m in the models of profiles 1, 2 and 3 within the Anambra Basin (AB), Afikpo Syncline (AS) and Calabar Flank (CF) respectively. Generally, from all the various methods applied the results indicate that AB, AS and CF are dominated by long wavelength anomalies. The 2-D models indicated that the basement framework is undulant. Also, depth estimates involving the various methods used in this study correlate strongly with each other in the AB, AS and CF geological regions.     

Modeled microgravity increases filamentation, biofilm formation, phenotypic switching, and antimicrobial resistance in Candida albicans

Candida albicans is an opportunistic fungal pathogen responsible for a variety of cutaneous and systemic human infections. Virulence of C. albicans increases upon exposure to some environmental stresses; therefore, we explored phenotypic responses of C. albicans following exposure to the environmental stress of low-shear modeled microgravity. Upon long-term (12-day) exposure to low-shear modeled microgravity, C. albicans transitioned from yeast to filamentous forms at a higher rate than observed under control conditions. Consistently, genes associated with cellular morphology were differentially expressed in a time-dependent manner. Biofilm communities, credited with enhanced resistance to environmental stress, formed in the modeled microgravity bioreactor and had a more complex structure than those formed in control conditions. In addition, cells exposed to low-shear modeled microgravity displayed phenotypic switching, observed as a near complete transition from smooth to "hyper" irregular wrinkle colony morphology. Consistent with the presence of biofilm communities and increased rates of phenotypic switching, cells exposed to modeled microgravity were significantly more resistant to the antifungal agent Amphotericin B. Together, these data indicate that C. albicans adapts to the environmental stress of low-shear modeled microgravity by demonstrating virulence-associated phenotypes.     

The Solar Wind Interaction With the Martian Ionosphere/Atmosphere

The interaction of the solar wind with the Martian exosphere and ionosphere leads to significant loss of atmosphere from the planet. Spacecraft data confirm that this is the case. However, the issue is how much is actually lost. Given that spacecraft coverage is sparse, simulation is one of the few ways for these estimates to be made. In this paper the evolution of our attempts to place bounds on this loss rate will be addressed. Using a hybrid particle code the loss rate with respect to solar EUV flux is addressed as well as a variety of numerical and chemical issues. The progress made has been of an evolutionary nature, with one approach tried and tested followed by another as the simulations are improved and better estimates are produced. The results to be reported suggest that the ion loss rates are high enough to explain the loss of water from Mars during earlier solar epochs.     

Editorial

Spatial Cognition and Computation -     

Polarization studies of magnetic cataclysmic variables

I discuss methods and results in the use of photo-polarimetry and spectro-polarimetry in the studies of magnetic cataclysmic variables. In particular I show how polarimetry can be used to derive the geometry of the accretion region on the surface of the white dwarf, the accreting geometry of the system as a whole and how polarimetry aides in the interpretation of X-ray/optical photometry and spectroscopy. I finish by describing the high speed spectro-polarimetric capabilities of SALT (Southern African Large Telescope) due for completion in 2005.     

Collisional and Radiative Processes in Optically Thin Plasmas

Most of our knowledge of the physical processes in distant plasmas is obtained through measurement of the radiation they produce. Here we provide an overview of the main collisional and radiative processes and examples of diagnostics relevant to the microphysical processes in the plasma. Many analyses assume a time-steady plasma with ion populations in equilibrium with the local temperature and Maxwellian distributions of particle velocities, but these assumptions are easily violated in many cases. We consider these departures from equilibrium and possible diagnostics in detail.