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161.
162.
N Desai M Durante Z W Lin F Cucinotta H Wu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(2):236-242
We investigated the spatial distribution of the induction of the phosphorylated form of the histone protein H2AX (gamma-H2AX), known to be activated by DSBs. Following irradiation of human fibroblast cells with 600 MeV/nucleon silicon and 600 MeV/nucleon iron ions we observed the formation of gamma-H2AX aggregates in the shape of streaks stretching over several micrometers in an x/y plane. Polyethylene shielding was used to achieve a Bragg curve distribution with beam geometry parallel to the monolayer of cells. We present data that highlights the formation of immunofluorescent gamma-H2AX tracks showing the ion trajectories across the Bragg peak of irradiated human fibroblast cells. Qualitative analyses of these distributions indicated potentially increased clustering of DNA damage before the Bragg peak, enhanced gamma-H2AX distribution at the peak, and provided visual evidence of high-linear energy transfer particle traversal of cells beyond the Bragg peak in agreement with one-dimensional transport approximations. Spatial assessment of gamma-H2AX fluorescence may provide direct insights into DNA damage across the Bragg curve for high charge and energy ions including the biological consequences of shielding and possible contributors to bystander effects. 相似文献
163.
Has the current US space policy improved the USA's overall strategic position? Does it affect favorably international partnerships? These questions are examined in terms of security, political economy, and influence. In today's context, where there are more space players, more options, more potential for unintended consequences, and higher stakes, unilateral action is more limited in its effectiveness than in earlier times. Surveying current US space policy, it is not clear that data-driven, analytically based decisions are being made to affect positively national independence, innovation, market creation, and international perceptions of the USA as a trustworthy partner. More promising are the steps taken to bolster a predictable space operational environment and economic competitiveness. Ultimately, in order to achieve American excellence and leadership, a ‘closed loop’ on the policy system is needed, to gauge regularly and systematically whether the US is achieving the desired national outcomes. 相似文献
164.
Adaptive boosting for SAR automatic target recognition 总被引:3,自引:0,他引:3
Sun Y. Liu Z. Todorovic S. Li J. 《IEEE transactions on aerospace and electronic systems》2007,43(1):112-125
The paper proposed a novel automatic target recognition (ATR) system for classification of three types of ground vehicles in the moving and stationary target acquisition and recognition (MSTAR) public release database. First MSTAR image chips are represented as fine and raw feature vectors, where raw features compensate for the target pose estimation error that corrupts fine image features. Then, the chips are classified by using the adaptive boosting (AdaBoost) algorithm with the radial basis function (RBF) network as the base learner. Since the RBF network is a binary classifier, the multiclass problem was decomposed into a set of binary ones through the error-correcting output codes (ECOC) method, specifying a dictionary of code words for the set of three possible classes. AdaBoost combines the classification results of the RBF network for each binary problem into a code word, which is then "decoded" as one of the code words (i.e., ground-vehicle classes) in the specified dictionary. Along with classification, within the AdaBoost framework, we also conduct efficient fusion of the fine and raw image-feature vectors. The results of large-scale experiments demonstrate that our ATR scheme outperforms the state-of-the-art systems reported in the literature 相似文献
165.
166.
Michael Potter 《Space Policy》1991,7(2)
The signing of an INF arms control treaty in 1987 and the reduction in East-West tension has resulted in a surplus of missiles. Getting rid of them remains a problem, but two distinct initiatives have been advanced in the USA and the USSR for their conversion into low-cost launchers. The author describes these two initiatives and discusses the political and economic issues they raise before speculating on the likelihood of their achievement. 相似文献
167.
B.Z. Siegel S.M. Siegel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(14):27-36
The adsorptive and/or catalytic properties of clays, silicates in general, and other minerals are well known. More recently, their probable role in prebiotic syntheses of bio-organic compounds has become a matter of record. We demonstrate that, in addition to their role in formation of important biomolecules, clays, micas, fibrous silicates and other minerals mimick the activities of contemporary enzymes including oxidases, esterases, phosphatases and glucosidases. The existence of such capabilities in substances likely to be represented on the surfaces of Earth-like planets may offer a challenge to the technology and design of remote life detection systems which must then distinguish between bona fide biological chemistry and mineral-base pseudometabolism. It also raises questions about the importance of mineral surfaces in post-mortem transformations of organic metabolites in our own biosphere. 相似文献
168.
169.
F.B. McDonald Z. Fujii P. Ferrando B. Heber A. Raviart H. Kunow N. Lal R. Mller-Mellin G. Wibberenz R. McGuire C. Paizis 《Space Science Reviews》2001,97(1-4):321-325
The combination of Voyager 1 (77.9 AU, 34.4° N) and Voyager 2 (61.2 AU, 24.5° S) at moderate heliolatitudes in the distant heliosphere and Ulysses with its unique latitudinal surveys in the inner heliosphere along with IMP 8 and other satellites at 1 AU constitutes a
network of observatories that are ideally suited to study cosmic rays over the solar minimum of cycle 22 and the onset of
solar activity and the long term cosmic ray modulation of cycle 23. Through 2000.7 there have been three well-defined step
decreases in the cosmic ray intensity at 1 AU with the cumulative effect being in good agreement with the net decrease in
cycle 21 at a comparable time in the solar cycle. Over this period the intensity changes at Ulysses are similar to those at 1 AU. In the distant heliosphere the initial decreases appear to be smaller than those at 1 AU. However
the full effects of the interplanetary disturbances producing the most recent and largest step decrease in the inner heliosphere
have not yet reached V-2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
170.
Z. Chvoj P. Demo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(5):21-24
The basic thermodynamical equations for values which characterize the surface (as curvatures, thickness, surface density of extensive value and its fluxes) are derived with real thickness of the surface being taken into consideration. The terms in the equations connect the thickness with the curvature as well as with the fluxes, surface densities and production of extensive properties. The extended thermodynamical fluxes contain terms in which the thickness and curvature of surface are explicitly expressed. 相似文献