Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.     

Discrimination of aqueous and aeolian paleoenvironments by atomic force microscopy-- a database for the characterization of martian sediments

In the search for aqueous habitats on Mars direct proof of (ancient) flowing water is still lacking, although remote sensing has provided indications of young fluvial systems. To demonstrate that such proof can be given, we examined surface marks on recent terrestrial sand grains by atomic force microscopy (AFM) and applied a quantitative three-dimensional analysis that can numerically distinguish between aeolian and aquatic transport mechanisms in sedimentary deposits on Earth. The surfaces of natural quartz grains as well as olivine, feldspar pyroxene, and monazite sands of known origin were imaged, each image yielding a three-dimensional map of the mineral surface. A fully automated analysis of distribution patterns of the structural elements that constitute the grain surfaces shows that wind-transported quartz grains have short linear elements irregularly distributed on the surface. Linear elements on water-transported grains, however, are longer with orientations that reflect the mineral symmetry. Because the surface patterns found on aqueous grains are due to preferential etching, they can be used as diagnostic fingerprints for the existence of past or present aqueous transport systems. We used a cluster analysis of the cross-correlation distance of distribution patterns in the structures of aeolian and aquatic sand grains to build a phenogram that provides a map for the relationship of the various sediments found on earth. The analysis shows that the method is highly significant and that water and wind transport can clearly be differentiated. In particular, feldspar and olivine sands contributed even more to the discrimination than quartz grains, which indicated that the method is promising for its application on future missions to Mars. Assuming that martian aqueous sand grains exhibit similar erosional patterns to mineral grains on Earth, simple AFM experiments on a Mars lander would be capable of proving the activity of flowing water in modern runoff systems and of analyzing the paleoenvironments of Mars.     

DASIG:一种多处理机的数据和信号处理体系结构

本文介绍了一种称为DASIG机的灵活的计算机体系结构,准备用于数据和信号处理。该机实际上包括任意数量并行工作的可编微程序数字和/或信号处理部件。每一部件具有4K高速缓冲存贮器和三个长为16的队列。这些队列用于部件问的通信。利用4K高速缓冲存贮器可在部件问或从主存贮器成块传送数据,所以各部件在完成各自任务中与其它部件的交互影响很少。数字处理部件由可编微程序的位片数字硬件结构组成,这些硬件结构能够级联一至八个位组。信号处理部件由专门用于极快信号处理的高速可编微程序的位片数字信号处理硬件组成。典型的DASIG机配置能为很多种数字和信号处理提供杰出的性能,它包括三个部件:全局接口部件、数据处理部件和信号处理部件。本文介绍了DASIG机的总体结构,然后介绍数字处理部件和信号处理部件的结构以及处理机的同步问题。最后讨论DASIG机的性能和灵活性。     

屏蔽室用的新型铁氧体栅格状吸收体

1 引言 符合CISPR(国际无线电干扰特别委员会)标准的辐射发射测量一般在开阔的测试场内进行。但这种方法有几个主要的缺限,或是它需要一个RF透明的、大的防风雨的封闭罩,不然,测量受气候的不可预测因素影响。这一防风雨的密封罩本身可能会引起测试场的误差[1]。更     

NON-DIMENSIONAL DESIGN PARAMETERS FOR FOD TOLERANT FAN BLADES

Non-dimensional design concept for FOD tolerant fan blades is introduced based on the analyses of simplified impact models. The fan blades arc idealized as either beams or plates of elastic or rigid-plastic materials. The case of constant force impact as well as that of mass impact is analyzed. The centrifugal force effects are also considered in the beam models. The critical fracture conditions arc shown in simple npn-dimensional formulae or diagrams for each case.     

带微处理器的超声流速测量系统

本文介绍了带微处理器的超声流速测量系统,该系统仅采用一个传送器和接收器装置,它是以测量流体处于静止状态和运动状态时,在设定的时间间隔中所传送的脉冲数之差为基础的.     

端羧基聚丁二烯(CTPB)推进剂的进展

用作优良粘合剂组份的端羧基聚丁二稀聚合物,由于其均匀的分子结构和化学反应性提供给推进剂良好的力学性能。本文是关于新的端羧基聚丁二稀和推进剂的进展。作者们共同研究的新CTPB 已从工业基地日本合成橡胶公司推荐给推进剂制造者。对日本合成橡胶公司的端羧基聚丁二稀的特性,特别是关于分子结构和粘合剂性能方面已进行了试验研究。     

Engineering challenges to the long term operation of the International Space Station

The U.S. Congress has maintained an intense interest in the ISS program since its inception. In the Appropriations Act of 1997, the Senate of the United States included language directing National Aeronautics and Space Administration (NASA) to have the National Research Council (NRC) under take a study that evaluates the engineering challenges posed by extravehicular activity (EVA) requirements, United States and non-United States space launch requirements, the potential need to upgrade or replace equipment and components after Assembly Complete, and the requirement to decommission and disassemble the facility. NASA and the NRC decided the focus should be on the anticipated challenges in the continuous operation and maintenance of the ISS after assembly of the on-orbit facility has been completed. This would encompass the operational years, from late 2004 (if the current schedule holds) to 2020-2025. This executive summary overviews the results of this NRC study. It focuses on the U.S. operation of the ISS after Assembly Complete, including cooperative efforts by the United States and Russia. The paper summarizes the primary findings and recommendations in each of the areas considered during this two-year NRC study.     

Detailed modeling of aluminum particle combustion——From single particles to cloud combustion in Bunsen flames

A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer, phase change, heterogeneous surface reactions, homogeneous combustion,oxide cap growth and radiation within the Euler–Lagrange framework is proposed. The model is validated in single particle configurations with varying particle diameters. The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the v...