Solar wind interaction with lunar crustal magnetic anomalies

Using Lunar Prospector data, we review the magnetic field and electron signatures of solar wind interaction with lunar crustal magnetic sources. Magnetic field amplifications, too large to represent direct measurements of crustal fields, appear in the solar wind over strong crustal sources, with the chance of observing these amplifications depending on upstream solar wind parameters. We often observe increases in low-energy (?100 eV) electron energy fluxes simultaneously with large magnetic field amplifications, consistent with an increase in plasma density across a shock surface. We also often observe low frequency wave activity in the magnetic field data (both broadband turbulence and monochromatic waves), often associated with electron energization, sometimes up to keV energies. Electron energization appears to be correlated more closely with wave activity than with magnetic amplifications. Detailed studies of the interaction region will be necessary in order to understand the physics of the Moon–solar wind interaction. At present, the Moon represents the only natural laboratory available to us to study solar wind interaction with small-scale crustal magnetic fields, though simulation results and theoretical work can also help us understand the physical processes at work.     

A Sequential Detector

The PRSD detector improves radar performance by controlling the distribution of energy in space, thus making a radar adaptive to its environment. An increase in performance over classical detectors may be realized in any of several ways: 1) greater maximum range; 2) smaller minimum detectable targets; 3) higher data rates; 4) lower average transmitted power, which allows smaller size and weight of equipment. The model of the PRSD detector described herein was tested with a semi-agile beam radar, and gave measured field performance improvement (for this particular radar) equivalent to an S/N increase ranging from 5 to 22 dB with a mean of 9.5 dB. This increase is greater than the 5-dB improvement predicted for the system in a white noise environment because many of the field tests were at locations subjected to heavy interference. The PRSD detector was extremely effective reducing the interference. In this paper, we will briefly review the theory of operation, describe the equipment and the method of test, and present experimental data. The data presented here are essential to a complete understanding of sequential detection since a rigorous theory encompassing multiple range bin radar has not been developed at this time. Finally, an extensive bibliography is appended.     

不一样的浪漫 上海约会圣地

<正>每一年情人节,现代的牛郎和织女们都会为了选择合适的"鹊桥"相会而伤透脑筋。其实,上海不止高楼林立,上海还是一座浪漫的城市,让我们钩织一张浪漫地图,为你在平凡的每一天谱写一出浪漫的‘爱情偶像剧"。     

A 12 year comparison of MIDAS and IRI 2007 ionospheric Total Electron Content

Data assimilation in conventional meteorological applications uses measurements in conjunction with a physical model. In the case of the ionised region of the upper atmosphere, the ionosphere, assimilation techniques are much less mature. The empirical model known as the International Reference Ionosphere (IRI) could be used to augment data-sparse regions in an ionospheric now-cast and forecast system. In doing so, it is important that it does not introduce systematic biases to the result. Here, the IRI model is compared to ionospheric observations from the Global Positioning System satellites over Europe and North America. Global Positioning System data are processed into hour-to-hour monthly averages of vertical Total Electron Content using a tomographic technique. A period of twelve years, from January 1998 to December 2009, is analysed in order to capture variations over the whole solar cycle. The study shows that the IRI model underestimates Total Electron Content in the daytime at solar maximum by up to 37% compared to the monthly average of GPS tomographic images, with the greatest differences occurring at the equinox. IRI shows good agreement at other times. Errors in TEC are likely due to peak height and density inaccuracies. IRI is therefore a suitable model for specification of monthly averages of Total Electron Content and can be used to initialise a data assimilation process at times away from solar maximum. It may be necessary to correct for systematic deviations from IRI at solar maximum, and to incorporate error estimation into a data assimilation scheme.     

Impulse Response Determination by Cross Correlation

This paper describes the design of a digital cross correlator and its application in determining the impulse response in linear systems. The output of the cross correlator, which correlates the input and the output of a linear system excited by noise, is the same as the response of the linear system to a pulse which is identical to the noise autocorrelation. The impulse response error is defined as the normalized mean-square deviation of the actual from the true impulse response. A digital computer simulation confirms that the conventional technique yields the same impulse error as the correlation technique, when the width of the input rectangular pulse is equivalent to the width of the noise autocorrelation function. The operation and design of the digital correlator are discussed. An advantage of the specially designed digital correlator over a general-purpose digital computer is to operate in real time without problems of software and storage. The presented experimental and digitally computed results show that the digital correlator can accurately determine the impulse response, even in presence of perturbations. Only the correlation technique allows measurement of system impulse response without disturbing normal operation. Suggestions are made to simplify the design and improve the speed (bandwidth capability).     

Recursive Methods for Computing Detection Probabilities

Recursive methods are drived for computing detection probabilities for general fluctuating targets in Gaussian noise. For the generalized chi-square family of fluctuating targets, very simple and convenient recursive algrithms result. The methods are also extended to cell-averaging CFAR. Although the detection probability is expressed iw: terms of an infinite series, a convenient expression is derived for the resulting error when the series is truncated. Cell-averaging CFAR results are computed for nonfluctuating, Swering case I, and Swerling case II fluctuating targets.     

Domain evolution and functional diversification of sulfite reductases

Sulfite reductases are key enzymes of assimilatory and dissimilatory sulfur metabolism, which occur in diverse bacterial and archaeal lineages. They share a highly conserved domain "C-X5-C-n-C-X3-C" for binding siroheme and iron-sulfur clusters that facilitate electron transfer to the substrate. For each sulfite reductase cluster, the siroheme-binding domain is positioned slightly differently at the N-terminus of dsrA and dsrB, while in the assimilatory proteins the siroheme domain is located at the C-terminus. Our sequence and phylogenetic analysis of the siroheme-binding domain shows that sulfite reductase sequences diverged from a common ancestor into four separate clusters (aSir, alSir, dsr, and asrC) that are biochemically distinct; each serves a different assimilatory or dissimilatory role in sulfur metabolism. The phylogenetic distribution and functional grouping in sulfite reductase clusters (dsrA and dsrB vs. aSiR, asrC, and alSir) suggest that their functional diversification during evolution may have preceded the bacterial/archaeal divergence.     

Prefolding and zero fill in FFT processing

An efficient operation applied prior to fast Fourier transform (FFT) processing is described that enables one to obtain the same spectral resolution with shorter FFTs. This so-called prefolding operation is complementary to zero fill. Both techniques are described