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Formaldehyde in the far outer galaxy: constraining the outer boundary of the galactic habitable zone
We present results from an initial survey of the 2(12)-1(11) transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG >or= 16 kpc). Formaldehyde is a key prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit of the Galactic Habitable Zone, the region where conditions for the formation of life are thought to be most favorable. We surveyed 69 molecular clouds in the outer Galaxy, ranging from 12 to 23.5 kpc in galactocentric radius. Formaldehyde emission at 140.8 GHz was detected in 65% of the clouds. The H2CO spectral line was detected in 26 of the clouds with RG > 16 kpc (detection rate of 59%), including 6 clouds with RG > 20 kpc (detection rate of 55%). Formaldehyde is readily found in the far outer Galaxy-even beyond the edge of the old stellar disk. Determining the relatively widespread distribution of H2CO in the far outer Galaxy is a first step in establishing how favorable an environment this vast region of the Galaxy may be toward the formation of life. 相似文献
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Atreya SK Wong AS Renno NO Farrell WM Delory GT Sentman DD Cummer SA Marshall JR Rafkin SC Catling DC 《Astrobiology》2006,6(3):439-450
We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Mars. Large-scale electrostatic fields generated by charged sand and dust in the martian dust devils and storms, as well as during normal saltation, can induce chemical changes near and above the surface of Mars. The most dramatic effect is found in the production of H2O2 whose atmospheric abundance in the "vapor" phase can exceed 200 times that produced by photochemistry alone. With large electric fields, H2O2 abundance gets large enough for condensation to occur, followed by precipitation out of the atmosphere. Large quantities of H2O2 would then be adsorbed into the regolith, either as solid H2O2 "dust" or as re-evaporated vapor if the solid does not survive as it diffuses from its production region close to the surface. We suggest that this H2O2, or another superoxide processed from it in the surface, may be responsible for scavenging organic material from Mars. The presence of H2O2 in the surface could also accelerate the loss of methane from the atmosphere, thus requiring a larger source for maintaining a steady-state abundance of methane on Mars. The surface oxidants, together with storm electric fields and the harmful ultraviolet radiation that readily passes through the thin martian atmosphere, are likely to render the surface of Mars inhospitable to life as we know it. 相似文献
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卫星IP交换技术是实现星上IP网络的关键技术,在卫星IP交换系统中,通过ICMP协议可报告差错报文信息,并可对卫星IP网络中的不同节点进行连通性测试,因此ICMP协议在卫星IP交换系统中起着重要作用。针对星上模块化设计及处理能力有限的特点,提出一种星上ICMP协议的FPGA实现方法,将ICMP报文的判断和生成流程分开,判断部分可在各个端口处理模块完成,生成部分采用单独模块完成,不需要在每个端口模块都完成ICMP报文生成处理操作,不仅优化了星上ICMP协议处理流程,并且节约了星上存储及处理资源。 相似文献
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基于适航符合性的翼身融合布局客机客舱布置设计 总被引:1,自引:0,他引:1
基于适航符合性,结合结构空间限制,从过道宽度、最大并排座椅数、应急出口布置、应急撤离、乘务员座椅布置、洗手间和厨房布置等方面,对某翼身融合布局客机方案的客舱布置开展设计,得到了382座典型两舱布置方案,该方案具有2对机头A型出口和4个机腹A型出口,4条纵向通道和5条横向通道。该布局可以满足适航标准对过道宽度、最大并排座椅数、应急出口类型、应急出口均布性、应急出口通路、乘务员数量、乘务员视界等相关要求。通过与座级相当的常规客机对比,该布局纵向和垂向空间舒适性较高,公务舱座椅排距约多出58%,靠近舱室壁板的乘客头部空间约多出4%~18%;但横向空间舒适性稍差。通过应急撤离仿真系统分析,该布局满足"90 s应急撤离"要求。 相似文献
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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。 相似文献
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