Searching for life on Mars: selection of molecular targets for ESA's aurora ExoMars mission

The European Space Agency's ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pasteur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect specific organic molecules or classes of molecules. Therefore, it is necessary to define and prioritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) organic matter, and contamination. Once organic molecules are detected on Mars, further information is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from unexpected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil biomarkers, but sequential extraction would be required to optimize the analysis of each of these in turn.     

Biomarker and stable isotope characterization of coastal pond-derived organic matter, McMurdo Dry Valleys, Antarctica

Small coastal ponds that contain photosynthetic microbial mat communities represent an extreme environment where a potentially significant source of labile organic carbon can be found within the McMurdo Dry Valleys, Antarctica. To distinguish coastal pond-derived organic matter from other sources of organic matter in the Dry Valleys, bulk organic carbon, nitrogen, and sulfur isotope signatures and phospholipid fatty acid (PLFA) profiles of benthic microbial mats located at two sites--Hjorth Hill coast and Garwood Valley--were investigated. The average isotope values at Hjorth Hill coast and Garwood Valley are, respectively, -10.9 per thousand and -10.2 per thousand for delta(13) C, 3.7 per thousand and -1.3 per thousand for delta(15)N, and 8.1 per thousand and 16.7 per thousand for delta(34)S. Microbial mats from all ponds are dominated by monounsaturated PLFAs (indicative of Gram-negative bacteria) and polyunsaturated PLFAs (indicative of microeukaryotes). Biomarkers specific to aerobic prokaryotes, eukaryotes, and photoautotrophic microeukaryotes, as well as sulfur-reducing bacteria, are present in all samples. Benthic mats at Garwood Valley are thicker and more laminated, have a higher biomass, and have a greater carbon and nitrogen content, which suggests greater productivity than mats at Hjorth Hill coast. Greater productivity is supported, as well, by higher dissolved oxygen contents likely derived from heightened photosynthetic productivity. More productivity at Garwood Valley likely results from a larger influx of terrestrial surface waters together with a concomitant nutrient loading.     

再生型木塑复合材料的研究

为了充分利用城市固体废弃物中的各项资源,本项工作将固体废弃物中的高密度聚乙烯(H igh dens itypo lyethy lene,HDPE)回收后与废弃的木纤维进行复合,成功地制备出再生型木塑复合材料。研究了木纤维长度、含量以及相容剂对木塑复合材料热性能和力学性能的影响。通过扫描电子显微镜观察了复合材料的冲击断口形貌,分析了此类复合材料的断裂机制。结果表明:木纤维的加入使HDPE的结晶温度降低,结晶速度减慢;相容剂的加入大大改善了木纤维与基体树脂之间的界面结合。随着木纤维含量的增加,木塑复合材料的弯曲强度升高,冲击强度下降。     

A history of modern selenogony: Theoretical origins of the Moon,from capture to crash 1955–1984

The development of ideas about the origin of the Moon during the last three decades is reviewed. In the 1950s G. H. Darwin's fission theory was still occasionally mentioned but by the 1960s it had been displaced by the hypothesis of lunar capture. A few scientists favored formation of the Moon from particles in orbit around the growing Earth. Analysis of samples from the Apollo missions did not confirm any of the three theories of lunar origin. Eventually the giant impact theory, proposed by Hartmann and Davis (1974) and by Cameron and Ward (1975), was adopted as the best working hypothesis. But the problem is not yet satisfactorily solved and work continues on other hypotheses such as co-accretion.     

Analysis of the current density characteristics in through-mask electrochemical micromachining (TMEMM) for fabrication of micro-hole arrays on invar alloy film

Invar alloy consisting of 64% iron and 36% nickel has been widely used for the production of shadow masks for organic light emitting diodes(OLEDs) because of its low thermal expansion coefficient(1.86 ? 10à6cm/°C).To fabricate micro-hole arrays on 30 lm invar alloy film,through-mask electrochemical micromachining(TMEMM) was developed and combined with a portion of the photolithography etching process.For precise hole shapes,patterned photoresist(PR) film was applied as an insulating mask.To investigate the relationship between the current density and the material removal rate,the principle of the electrochemical machining was studied with a focus on the equation.The finite element method(FEM) was used to verify the influence of each parameter on the current density on the invar alloy film surface.The parameters considered were the thickness of the PR mask,inter-electrode gap(IEG),and electrolyte concentration.Design of experiments(DOE) was used to figure out the contribution of each parameter.A simulation was conducted with varying parameters to figure out their relationships with the current density.Optimization was conducted to select the suitable conditions.An experiment was carried out to verify the simulation results.It was possible to fabricate micro-hole arrays on invar alloy film using TMEMM,which is a promising method that can be applied to fabrications of OLEDs shadow masks.     

Magnetic Fields in Supernova Remnants and Pulsar-Wind Nebulae

We review the observations of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe) that give information on the strength and orientation of magnetic fields. Radio polarimetry gives the degree of order of magnetic fields, and the orientation of the ordered component. Many young shell supernova remnants show evidence for synchrotron X-ray emission. The spatial analysis of this emission suggests that magnetic fields are amplified by one to two orders of magnitude in strong shocks. Detection of several remnants in TeV gamma rays implies a lower limit on the magnetic-field strength (or a measurement, if the emission process is inverse-Compton upscattering of cosmic microwave background photons). Upper limits to GeV emission similarly provide lower limits on magnetic-field strengths. In the historical shell remnants, lower limits on B range from 25 to 1000?μG. Two remnants show variability of synchrotron X-ray emission with a timescale of years. If this timescale is the electron-acceleration or radiative loss timescale, magnetic fields of order 1?mG are also implied. In pulsar-wind nebulae, equipartition arguments and dynamical modeling can be used to infer magnetic-field strengths anywhere from ～5?μG to 1?mG. Polarized fractions are considerably higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field geometries often suggest a toroidal structure around the pulsar, but this is not universal. Viewing-angle effects undoubtedly play a role. MHD models of radio emission in shell SNRs show that different orientations of upstream magnetic field, and different assumptions about electron acceleration, predict different radio morphology. In the remnant of SN 1006, such comparisons imply a magnetic-field orientation connecting the bright limbs, with a substantial density gradient across the remnant.     

并行子空间设计算法在电动无人机一体化设计中的应用

应用并行子空间设计算法对低雷诺数电动无人机进行了初步设计.电动无人机涉及多门学科,包括气动、重量、推进系统、性能和操稳.首先开发了电动无人机多学科系统分析软件.并行子空间设计算法利用基于人工神经网络的响应面技术作为系统分析的近似模型.电动无人机初步设计中的设计变量共有29个,其中连续设计变量25个,离散设计变量4个.研究表明,并行子空间设计算法能以较少的系统分析次数在可行域内寻找出一个较好的设计点,并在设计过程中具有适应设计要求(约束)可变性的要求,它为飞行器一体化设计提供了一条途径.     

The effect of climber transit on the space elevator dynamics

The space elevator offers an alternate and efficient method for space travel. It will have two main components. The first component is the tether (or the ribbon), which extends from the Earth to an equatorial satellite at an altitude beyond the geostationary orbit, and is fixed to a base on the surface of the Earth at its lower end. The second component is the climber, which scales the ribbon, transporting payloads to space. An important issue for effective operation of the space elevator will be to understand its dynamics. This paper attempts to develop a realistic and yet simple planar model for this purpose. The basic response of the ribbon to climber transit is determined. Both analytical and numerical results are presented. Specific climbing procedures are devised based on these results so as to minimize the adverse effects of climber transit on the ribbon.     

Synchrotron Radiation from Galactic Sources: What We Can Learn About Particle Acceleration

I review the observations of galactic synchrotron sources, focusing on shell supernova remnants (SNRs), with particular attention to attributes that constrain the properties of electron acceleration. Radio observations provide information on source fluxes, spectral index, morphology, and polarization. Recent observations give us strong reason to believe that several young SNRs show synchrotron X-ray emission. Even if X-rays are thermal, however, limits can be set on the maximum energy to which electrons can be accelerated without a spectral break, since no galactic SNR is observed to have X-ray emission (due to any source) as bright as the extrapolation from radio frequencies of radio synchrotron emission. If synchrotron X-rays are detected or inferred, their morphology and spectrum provide important information on mechanisms governing acceleration to the highest energies. I describe models of synchrotron emission from SNRs and their comparison with observations. Finally, I describe the tasks ahead for both observers and theoreticians, to make better use of what SNR synchrotron emission tells us about particle acceleration.     

High accuracy satellite drag model (HASDM)

The dominant error source in force models used to predict low-perigee satellite trajectories is atmospheric drag. Errors in operational thermospheric density models cause significant errors in predicted satellite positions, since these models do not account for dynamic changes in atmospheric drag for orbit predictions. The Air Force Space Battlelab’s High Accuracy Satellite Drag Model (HASDM) estimates and predicts (out three days) a dynamically varying global density field. HASDM includes the Dynamic Calibration Atmosphere (DCA) algorithm that solves for the phases and amplitudes of the diurnal and semidiurnal variations of thermospheric density near real-time from the observed drag effects on a set of Low Earth Orbit (LEO) calibration satellites. The density correction is expressed as a function of latitude, local solar time and altitude. In HASDM, a time series prediction filter relates the extreme ultraviolet (EUV) energy index E_10.7 and the geomagnetic storm index a_p, to the DCA density correction parameters. The E_10.7 index is generated by the SOLAR2000 model, the first full spectrum model of solar irradiance. The estimated and predicted density fields will be used operationally to significantly improve the accuracy of predicted trajectories for all low-perigee satellites.