A 12 year comparison of MIDAS and IRI 2007 ionospheric Total Electron Content

Data assimilation in conventional meteorological applications uses measurements in conjunction with a physical model. In the case of the ionised region of the upper atmosphere, the ionosphere, assimilation techniques are much less mature. The empirical model known as the International Reference Ionosphere (IRI) could be used to augment data-sparse regions in an ionospheric now-cast and forecast system. In doing so, it is important that it does not introduce systematic biases to the result. Here, the IRI model is compared to ionospheric observations from the Global Positioning System satellites over Europe and North America. Global Positioning System data are processed into hour-to-hour monthly averages of vertical Total Electron Content using a tomographic technique. A period of twelve years, from January 1998 to December 2009, is analysed in order to capture variations over the whole solar cycle. The study shows that the IRI model underestimates Total Electron Content in the daytime at solar maximum by up to 37% compared to the monthly average of GPS tomographic images, with the greatest differences occurring at the equinox. IRI shows good agreement at other times. Errors in TEC are likely due to peak height and density inaccuracies. IRI is therefore a suitable model for specification of monthly averages of Total Electron Content and can be used to initialise a data assimilation process at times away from solar maximum. It may be necessary to correct for systematic deviations from IRI at solar maximum, and to incorporate error estimation into a data assimilation scheme.     

Cyanobacterial emergence at 2.8 gya and greenhouse feedbacks

Apparent cyanobacterial emergence at about 2.8 Gya coincides with the negative excursion in the organic carbon isotope record, which is the first strong evidence for the presence of atmospheric methane. The existence of weathering feedbacks in the carbonate-silicate cycle suggests that atmospheric and oceanic CO2 concentrations would have been high prior to the presence of a methane greenhouse (and thus the ocean would have had high bicarbonate concentrations). With the onset of a methane greenhouse, carbon dioxide concentrations would decrease. Bicarbonate has been proposed as the preferred reductant that preceded water for oxygenic photosynthesis in a bacterial photosynthetic precursor to cyanobacteria; with the drop of carbon dioxide level, Archean cyanobacteria emerged using water as a reductant instead of bicarbonate (Dismukes et al., 2001). Our thermodynamic calculations, with regard to this scenario, give at least a tenfold drop in aqueous CO2 levels with the onset of a methane-dominated greenhouse, assuming surface temperatures of about 60 degrees C and a drop in the level of atmospheric carbon dioxide from about 1 to 0.1 bars. The buildup of atmospheric methane could have been triggered by the boost in oceanic organic productivity that arose from the emergence of pre-cyanobacterial oxygenic phototrophy at about 2.8-3.0 Gya; high temperatures may have precluded an earlier emergence. A greenhouse transition timescale on the order of 50-100 million years is consistent with results from modeling the carbonate-silicate cycle. This is an alternative hypothesis to proposals of a tectonic driver for this apparent greenhouse transition.     

Plant molecular biology in the space station era: utilization of KSC fixation tubes with RNAlater

Spaceflight experiments involving biological specimens face unique challenges with regard to the on orbit harvest and preservation of material for later ground-based analyses. Preserving plant material for gene expression analyses requires that the tissue be prepared and stored in a manner that maintains the integrity of RNA. The liquid preservative RNAlater (Ambion) provides an effective alternative to conventional freezing strategies, which are limited or unavailable in current spaceflight experiment scenarios. The spaceflight use of RNAlater is enabled by the Kennedy space center fixation tube (KFT), hardware designed to provide the necessary containment of fixatives during the harvest and stowage of biological samples in space. Pairing RNAlater with the KFT system provides a safe and effective strategy for preserving plant material for subsequent molecular analyses, a strategy that has proven effective in several spaceflight experiments. Possible spaceflight scenarios for the use of RNAlater and KFTs are explored and discussed.     

Semiconductor Surface Thermocouples for Determining Heat-Transfer Rates

Possible methods of increasing the sensitivity capabilities for determining heat-transfer rates associated with wind tunnel testing have been investigated. Techniques utilizing surface thermocouples of conventional thermocouple materials do not provide the necessary temperature sensitivity to low heat-transfer rates. This need for increased sensitivity has resulted in development and evaluation of surface thermocouples fabricated from semiconductor materials. Calibration of the semiconductor surface thermocouple has disclosed temperature sensitivity on the order of 35 times that of chromel-constantan thermocouples. This increased sensitivity has established confidence in the potential value of this concept and further investigation and evaluation are presently being conducted.     

GE积极应对防务预算削减

针对防务预算削减的局面,GE公司把准市场发展趋势,集中资金发展重点项目,将商业发动机的运作方式移植到军事领域,力图减小防务预算缩减带来的不利影响。     

美国人眼中的中国5.8枪族

作为冷战时代成长起来的一代．我们很难想象俄国人已经不是我们的最大敌人了，随着时光流逝．有关苏联的记忆已经慢慢淡逝了．现在俄罗斯成了我们的朋友．作为一个轻武器大国．俄罗斯拥有才华横溢的设计师和数十年积累的丰富经验。在了解了大量原苏联／俄罗斯轻武器发展的状况的同时．我们必须关注另一个国家一中国。由于现在公开的中国轻武器资料信息实在是太少了，所以我决定去为大家揭开这个神秘国家轻武器研究的面纱。     

Imprints of small-scale nonadiabatic particle dynamics on large-scale properties of dynamical magnetotail equilibria

We extend our large-scale kinetic (LSK) simulation of the magnetotail by including the global electrostatic effects generated by the field-aligned motion of electrons. Differences in electron and ion dynamics result in significant electrostatic fields near the current sheet (especially near X-lines) and in the auroral zone. In addition, E_ƒ and E alter the ion precipitation profile and affect particle loss from the system through the flanks and downtail. This work provides a basis for including transverse electron currents in our calculations.