Glycine identification in natural jarosites using laser desorption Fourier transform mass spectrometry: implications for the search for life on Mars

The jarosite group minerals have received increasing attention since the discovery of jarosite on the martian surface by the Mars Exploration Rover Opportunity. Given that jarosite can incorporate foreign ions within its structure, we have investigated the use of jarosite as an indicator of aqueous and biological processes on Earth and Mars. The use of laser desorption Fourier transform mass spectrometry has revealed the presence of organic matter in several jarosite samples from various locations worldwide. One of the ions from the natural jarosites has been attributed to glycine because it was systematically observed in combinations of glycine with synthetic ammonium and potassium jarosites, Na(2)SO(4) and K(2)SO(4). The ability to observe these organic signatures in jarosite samples with an in situ instrumental technique, such as the one employed in this study, furthers the goals of planetary geologists to determine whether signs of life (e.g., the presence of biomolecules or biomolecule precursors) can be detected in the rock record of terrestrial and extraterrestrial samples.     

Ground-Based and Space-Based Radio Observations of Planetary Lightning

We review radio detection of planetary lightning performed by Voyager, Galileo (including in-situ probe measurements), Cassini, and other spacecraft, and compare the information on the underlying physics derived from these observations—especially the discharge duration, at Jupiter and Saturn—with our knowledge of terrestrial lightning. The controversial evidence at Venus is discussed, as well as the prospects for lightning-like discharges in Martian dust-storms (and studies on terrestrial analogues). In addition, lightning sources provide radio beacons that allow us to probe planetary ionospheres. Ground-based observations of Saturn’s lightning have been attempted several times in the past and have been recently successful. They will be the subject of observations by the new generation of giant radio arrays. We review past results and future studies, focussing on the detection challenges and on the interest of ground-based radio monitoring, in conjunction with spacecraft observations or in standalone mode.     

Processing throughput estimation for radar intercept receivers

Analytical expressions for the computational requirements of broad classes of radar pulse deinterleaving algorithms are developed. The analysis applies to block collection systems and is principally intended for systems with insufficient monopulse resolution to uniquely sort emitters on monopulse parameters alone. The analysis begins with triplet sequence search approaches and is confirmed by simulation. It is also shown that this approach generalizes to more complex deinterleaving schemes, including M-tuple search and time of arrival (TOA) difference histogramming. All cases exhibit the same basic functional form of quadratic dependence on the number of emitters, linear dependence on the collection time, and complex dependence on the pulse deletion (or dropping) probability     

A hardware-efficient, multirate, digital channelized receiverarchitecture

An approach is presented to realizing a digital channelized receiver for signal intercept applications that provides a hardware efficient implementation of a uniform filter bank in which the number of filters K is greater than the decimation factor M. The proposed architecture allows simple channel arbitration logic to be used and provides reliable instantaneous frequency measurements, even in adjacent channel crossover regions. In the proposed implementation of the filter bank, K is related to M by K=FM where F is an integer. It is shown that the optimum selection of F allows the instantaneous frequency measurement to be made in the channel crossover region and the arbitration function to be based solely on the instantaneous frequency measurement. The development of a filter bank structure which combines the flexibility of the short-time Fourier transform (STFT) with the implementation efficiency of the polyphase filter bank decomposition, meeting these requirements and leading to a hardware-efficient implementation, is presented     

Replacement strategy for aging avionics computers

With decreasing defense dollars available to purchase new military aircraft, the inventory of existing aircraft will have to last many more years than originally anticipated. As the avionics computers on these aging aircraft get older, they become more expensive to maintain due to parts obsolescence. In addition, expanding missions and changing requirements lead to growth in the embedded software which, in turn, requires additional processing and memory capacity. Both factors, parts obsolescence and new processing capacity, result in the need to replace the old computer hardware with newer, more capable microprocessor technology. New microprocessors, however, are not compatible with the older computer instruction set architectures. This generally requires the embedded software in these computers to be rewritten. A significant savings-estimated in the billions of dollars-could be achieved in these upgrades if the new computers could execute the old embedded code along with any new code to be added. This paper describes a commercial-off-the-shelf (COTS)-based form, fit, function, and interface (F³I) replacement strategy for legacy avionics computers that can reuse existing avionics code “as is” while providing a flexible framework for incremental upgrades and managed change. It is based on a real-time embedded software technology that executes legacy binary code on the latest generation COTS microprocessors. This technology promises performance improvements of 5-10 times that of the legacy avionics computer that it replaces. It also promises a 4× decrease in cost and schedule over rewriting the code and provides a “known good” starting point for incremental upgrades of the embedded flight software. Code revalidation cost and risk are minimized since the structure of the embedded code is not changed, allowing the replacement computer to be retested at the “blackbox” level using existing qualification tests     

X-ray spectroscopy and variability of AGN detected in the 2 Ms Chandra Deep Field-North Survey

We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 active galactic nuclei (AGN) detected in the 2 Ms Chandra Deep Field-North Survey with >200 background-subtracted 0.5–8.0 keV counts [F_{0.5–8.0 keV} = (1.4−200) × 10⁻¹⁵ erg cm⁻² s⁻¹]. Our preliminary spectral analyses yield median spectral parameters of Γ = 1.61 and intrinsic N_H = 6.2 × 10²¹ cm⁻² (z = 1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived JVH distribution and, to a lesser extent, the X-ray luminosity distribution. We also find that among the 136 AGN, 10 (≈7%) show significant Fe K emission-line features with equivalent widths in the range 0.1–1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Γ < 1.0 and large Fe K equivalent width). Finally, we find that 81 (≈60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (≈80–90%) when better photon statistics are available.     

模糊控制算法分析及改进

基于E.H.Mamdai等人的模糊控制算法,本文讨论了模糊控制器参数的选择及对系统输出性能的影响。与已有的方法不同,本文注重物理概念的分析,并研究了模糊控制器参数的自调整问题。这是因为基本模糊控制器参数的选择难以同时兼顾控制系统的动静态性能,一般只好采取折衷的方法。为了改善控制系统性能,一种实用的方法是在线调整模糊控制器的参数。文中提出了一种分段式自调参方案,仿真结果表明该方案优于已有的自调参方案。为了达到有效的调参目的,本文给出了模糊控制器参数初始配置的一种关系,并通过仿真,验证了该关系是确切的。最后,基于模糊控制算法的特点,探讨了一种新的模糊控制算法的构思,作为今后进一步研究的问题。     

A study of a long duration B9 flare-CME event and associated shock

We present and discuss here the observations of a small long duration GOES B-class flare associated with a quiescent filament eruption, a global EUV wave and a CME on 2011 May 11. The event was well observed by the Solar Dynamics Observatory (SDO), GONG H$\alpha$, STEREO and Culgoora spectrograph. As the filament erupted, ahead of the filament we observed the propagation of EIT wave fronts, as well as two flare ribbons on both sides of the polarity inversion line (PIL) on the solar surface. The observations show the co-existence of two types of EUV waves, i.e., a fast and a slow one. A type II radio burst with up to the third harmonic component was also associated with this event. The evolution of photospheric magnetic field showed flux emergence and cancellation at the filament site before its eruption.     

Enhancing the ATIC charge resolution

The Advanced Thin Ionization Calorimeter (ATIC) experiment is designed to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10¹¹ to 10¹⁴ eV during Long Duration Balloon (LDB) flights from McMurdo, Antarctica. Currently, analysis from the ATIC-1 test flight and ATIC-2 science flight is underway and preparation for a second science flight is in progress. Charge identification of the incident cosmic ray is accomplished, primarily, by a pixilated Silicon Matrix detector located at the very top of the instrument. While it has been shown that the Silicon Matrix detector provides good charge identification even in the presence of electromagnetic shower backscatter from the calorimeter, the detector only measures the charge once. In this paper, we examine use of the top scintillator hodoscope detector to provide a second measure of the cosmic ray charge and, thus, improve the ATIC charge identification.