指纹识别的小波变换算法

指纹的唯一性和不变性使其在生物特征识别中占有重要地位,基于指纹识别系统进行身份认证的应用越来越广泛。在分析已有指纹识别算法的基础上,提出了一种利用小波变换的指纹识别算法。通过对指纹图像小波变换系数进行建模,发现其高频子带系数近似服从广义高斯分布。所用算法使用高斯分布的两个参数标识小波子带特征,并以此作为指纹标识参数进行特征匹配。算法的优点在于运行所需数据存储量小,适合实际应用。为验证算法可行性,对指纹库数据进行仿真,实验结果表明,算法计算高效,识别率高。     

Distribution and stable isotopic composition of amino acids from fungal peptaibiotics: assessing the potential for meteoritic contamination

The presence of nonprotein α-dialkyl-amino acids such as α-aminoisobutyric acid (α-AIB) and isovaline (Iva), which are considered to be relatively rare in the terrestrial biosphere, has long been used as an indication of the indigeneity of meteoritic amino acids. However, recent work showing the presence of α-AIB and Iva in peptides produced by a widespread group of filamentous fungi indicates the possibility of a terrestrial biotic source for the α-AIB observed in some meteorites. We measured the amino acid distribution and stable carbon and nitrogen isotopic composition of four α-AIB-containing fungal peptides and compared this data to similar meteoritic measurements. We show that the relatively simple distribution of the C(4) and C(5) amino acids in fungal peptides is distinct from the complex distribution observed in many carbonaceous chondrites. We also identify potentially diagnostic relationships between the stable isotopic compositions of pairs of amino acids from the fungal peptides that may aid in ruling out fungal contamination as a source of meteoritic amino acids.     

The determination of ice composition with instruments on cometary landers

The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as a detector for the MAG and serves to resolve ambiguities between fragments of similar mass such as CO and N2. Because most of the compounds of interest for the volatile ices are simple, a gas chromatograph is not needed and thus more integration time is available to determine isotopic ratios. A gamma-ray spectrometer (GRS) will determine the elemental abundances of the bulk cometary material by determining the flux of gamma rays produced from the interaction of the cometary material with cosmic ray produced neutrons. Because the gamma rays can penetrate a distance of several tens of centimeters a large volume of material is analyzed. The measured composition is, therefore, much more likely to be representative of the bulk comet than a very small sample that might have lost some of its volatiles. Making these measurements on a lander offers substantial advantages over trying to address similar objectives from an orbiter. For example, an orbiter instrument can determine the presence and isotopic composition of CO in the cometary coma, but only a lander can determine the phase(s) in which the CO is located and separately determine the isotopic composition of each reservoir of CO. The bulk composition of the nucleus might be constrained from separate orbiter analyses of dust and gas in the coma, but the result will be very model dependent, as the ratio of gas to dust in the comet will vary and will not necessarily be equal to the bulk value.     

Public school teachers in the U.S. evaluate the educational impact of student space experiments launched by expendable vehicles, aboard Skylab, and aboard Space Shuttle

Space education is a discipline that has evolved at an unprecedented rate over the past 25 years. Although program proceedings, research literature, and historical documentation have captured fragmented pieces of information about student space experiments, the field lacks a valid comprehensive study that measures the educational impact of sounding rockets, Skylab, Ariane, AMSAT, and Space Shuttle. The lack of this information is a problem for space educators worldwide which led to a national study with classroom teachers. Student flown experiments continue to offer a unique experiential approach to teach students thinking and reasoning skills that are imperative in the current international competitive environment in which they live and will work. Understanding the history as well as the current status and educational spin-offs of these experimental programs strengthens the teaching capacity of educators throughout the world to develop problem solving skills and various higher mental processes in the schools. These skills and processes enable students to use their knowledge more effectively and efficiently long after they leave the classroom. This paper focuses on student space experiments as a means of motivating students to meet this educational goal successfully.     

Radiation exposure predictions for short-duration stay Mars missions

The human radiation environment for several short-duration stay manned Mars missions is predicted using the Mission Radiation Calculation (MIRACAL) program, which was developed at NASA Langley Research Center. This program provides dose estimates for galactic cosmic rays (GCR) and large and ordinary solar proton flare events for various amounts of effective spacecraft shielding (both operational and storm shelter thicknesses) and a given time history of the spacecraft's heliocentric position. The results of this study show that most of the missions can survive the most recent large flares (if they were to occur at the missions' perihelion) if a 25 g/cm2 storm shelter is assumed. The dose predictions show that missions during solar minima (when solar flare activity is the lowest) are not necessarily the minimum dose cases, due to increased GCR contribution during this time period. The direct transfer mission studied has slightly lower doses than the outbound Venus swingby mission [on the order of 10-20 centi-Sieverts (cSv) lower], with the greatest dose differences for the assumed worst case scenario (when the large flares occur at perihelion). The GCR dose for a mission can be reduced by having the crew spend some fraction of its day nominally in the storm shelter (other than during flare events).     

基于适航符合性的翼身融合布局客机客舱布置设计

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。     

Role of the ionosphere for the atmospheric evolution of planets

We have synthesized current understanding, mainly observations, with regard to ion escape mechanisms to space from the ionosphere and exosphere of Titan and Earth-type planets, with the intent to provide an improved input for models of atmospheric evolution on early Earth and Earth-type planets and exoplanets. We focus on the role of the ionosphere and its non-linear response to solar parameters, all of which have been underestimated in current models of ancient atmospheric escape (4 billion years ago). Factors that have been overlooked include the following: (1) Much larger variation of O(+) outflow than H(+) outflow from the terrestrial ionosphere, depending on solar and geomagnetic activities (an important consideration when attempting to determine the oxidized state of the atmosphere of early Earth); (2) magnetization of the ionopause, which keeps ionospheric ions from escaping and controls many other escape processes; (3) extra ionization by, for example, the critical ionization velocity mechanism, which expands the ionosphere to greater altitudes than current models predict; and (4) the large escape of cold ions from the dense, expanded ionosphere of Titan. Here we offer, as a guideline for quantitative simulations, a qualitative diagnosis of increases or decreases of non-thermal escape related to the ionosphere for magnetized and unmagnetized planets in response to changes in solar parameters (i.e., solar EUV/FUV flux, solar wind dynamic pressure, and interplanetary magnetic field).     

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。