Sulfur in Cometary Dust

The computer-intensive project consisted of the analysis and synthesis of existing data on composition of comet Halley dust particles. The main objective was to obtain a complete inventory of sulfur containing compounds in the comet Halley dust by building upon the existing classification of organic and inorganic compounds and applying a variety of statistical techniques for cluster and cross-correlational analyses. A student hired for this project wrote and tested the software to perform cluster analysis. The following tasks were carried out: (1) selecting the data from existing database for the proposed project; (2) finding access to a standard library of statistical routines for cluster analysis; (3) reformatting the data as necessary for input into the library routines; (4) performing cluster analysis and constructing hierarchical cluster trees using three methods to define the proximity of clusters; (5) presenting the output results in different formats to facilitate the interpretation of the obtained cluster trees; (6) selecting groups of data points common for all three trees as stable clusters. We have also considered the chemistry of sulfur in inorganic compounds

Bias correction factors for near-Earth asteroids

Knowledge of the population size and physical characteristics (albedo, size, and rotation rate) of near-Earth asteroids (NEA's) is biased by observational selection effects which are functions of the population's intrinsic properties and the size of the telescope, detector sensitivity, and search strategy used. The NEA population is modeled in terms of orbital and physical elements: a, e, i, omega, Omega, M, albedo, and diameter, and an asteroid search program is simulated using actual telescope pointings of right ascension, declination, date, and time. The position of each object in the model population is calculated at the date and time of each telescope pointing. The program tests to see if that object is within the field of view (FOV = 8.75 degrees) of the telescope and above the limiting magnitude (V = +1.65) of the film. The effect of the starting population on the outcome of the simulation's discoveries is compared to the actual discoveries in order to define a most probable starting population

Modelling polarization properties of comet 1P/Halley using a mixture of compact and aggregate particles

Recently, the result obtained from `Stardust' mission suggests that the overall ratio of compact to aggregate particles is 65:35 (or 13:7) for Comet 81P/Wild 2 (Burchell et al. 2008). In the present work, we propose a model which considers cometary dust as a mixture of compact and aggregate particles, with composition of silicate and organic. We consider compact particles as spheroidal particles and aggregates as BCCA and BAM2 aggregate with some size distribution. For modeling Comet 1P/ Halley, the power-law size distribution n(a)= a^{-2.6}, for both compact and aggregate particles is taken. We take a mixture of BAM2 and BCCA aggregates with a lower and upper cutoff size around 0.20$\mu m$ and 1$\mu m$. We also take a mixture of prolate, spherical and oblate compact particles with axial ratio (E) from 0.8 to 1.2 where a lower and upper cutoff size around 0.1$\mu m$ and 10$\mu m$ are taken. Using T-matrix code, the average simulated polarization curves are generated which can best fit the observed polarization data at the four wavelengths $\lambda$ = 0.365$\mu m$, 0.485$\mu m$, 0.670$\mu m$ and 0.684$\mu m$. The suitable mixing percentage of aggregates emerging out from the present modeling corresponds to 50% BAM2 and 50% BCCA particles and silicate to organic mixing percentage corresponds to 78% silicate and 22% organic in terms of volume. The present model successfully reproduces the observed polarization data, especially the negative branch, more effectively as compared to other work done in the past. It is found that among the aggregates, the BAM2 aggregate plays a major role, in deciding the cross-over angle and depth of negative polarization branch.Comment: 7 pages, 5 figures (accepted for publication in MNRAS on May 4, 2011

The Dust Trail of Comet 67P/Churyumov-Gerasimenko

We report the detection of comet 67P/Churyumov-Gerasimenko's dust trail and nucleus in 24 micron Spitzer Space Telescope images taken February 2004. The dust trail is not found in optical Palomar images taken June 2003. Both the optical and infrared images show a distinct neck-line tail structure, offset from the projected orbit of the comet. We compare our observations to simulated images using a Monte Carlo approach and a dynamical model for comet dust. We estimate the trail to be at least one orbit old (6.6 years) and consist of particles of size >~100 micron. The neck-line is composed of similar sized particles, particles of size but younger in age. Together, our observations and simulations suggest grains 100 micron and larger in size dominate the total mass ejected from the comet. The radiometric effective radius of the nucleus is 1.87 +/- 0.08 km, derived from the Spitzer observation. The Rosetta spacecraft is expected to arrive at and orbit this comet in 2014. Assuming the trail is comprised solely of 1 mm radius grains, we compute a low probability (~10^-3) of a trail grain impacting with Rosetta during approach and orbit insertion.Comment: Accepted for publication in Icaru

Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si

Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin.publishedVersio

Isolation, crystallization, and investigation of ribosomal protein S8 complexed with specific fragments of rRNA of bacterial or archaeal origin. Biochemistry 66

Study of the nature of protein-rRNA complexes is a topical problem of modern molecular biology. Structural studies of rRNA-protein complexes are the most direct and precise method of analysis of these interactions. Because ribosomal proteins are most conservative during evolution, their complexes with specific RNA fragments provide an interesting model for studying RNA-protein interactions. Ribosomal protein S8 from E. coli plays a key role in assembling the small ribosomal subunit The major region of protein S8 binding on 16S rRNA was determined by partial hydrolysis with restric tion endonucleases The binding sites of protein S8 on 16S rRNA are similar in E. coli and T. thermophilus. It was shown that ACCELERATED PUBLICATION 0006 2979/01/6609 0948$25.00 ©2001 MAIK "Nauka / Interperiodica" * To whom correspondence should be addressed. Vol. 66, No. 9, 2001, pp. 948 953. Translated from Biokhimiya, Vol. 66, No. 9, 2001, pp. 1165 1171. Original Russian Text Copyright © 2001 Abstract-The core ribosomal protein S8 binds to the central domain of 16S rRNA independently of other ribosomal proteins and is required for assembling the 30S subunit. It has been shown with E. coli ribosomes that a short rRNA fragment restrict ed by nucleotides 588 602 and 636 651 is sufficient for strong and specific protein S8 binding. In this work, we studied the complexes formed by ribosomal protein S8 from Thermus thermophilus and Methanococcus jannaschii with short rRNA frag ments isolated from the same organisms. The dissociation constants of the complexes of protein S8 with rRNA fragments were determined. Based on the results of binding experiments, rRNA fragments of different length were designed and syn thesized in preparative amounts in vitro using T7 RNA polymerase. Stable S8-RNA complexes were crystallized. Crystals were obtained both for homologous bacterial and archaeal complexes and for hybrid complexes of archaeal protein with bac terial rRNA. Crystals of the complex of protein S8 from M. jannaschii with the 37 nucleotide rRNA fragment from the same organism suitable for X ray analysis were obtained

Клиническое значение парного определения ВИЧ -1 у больных в крови и цереброспинальной жидкости

A comparative investigation has been applied to 100 HIV infected patients with CD4 lymphocytes rate <350 cells/microliter, demanding HAART prescription, divided into two groups: 1 – without clinical features of CNS damage (54 people) and 2 – with features of CNS damage of various etiology (46 people). HIV viral load (VL) indices in blood plasma and cerebrospinal fluid (CSF) have been examined. 45,7% of damages are caused with mixed infections. CSF HIV VL level with the 2 group patients is 7,6 times as high as that of 1 group patients. HIV VL in plasma is considerably higher than in CSF. Eight patients showed increased CSF HIV VL. Brain damages of various etiology with clinical implications violate hematoencephalic barrier integrity, contribute to HIV accumulation in CSF and intensify virus replication in brain tissue. It has been concluded that CSF examination for HIV is expedient.Проведено сравнительное исследование 100 больных с ВИЧ-инфекцией с показателем количества СD4-лимфоцитов <350 кл/мкл, нуждающихся в назначении ВААРТ, разделенных на две группы: 1 – без клинических признаков поражения ЦНС (54 человека) и 2 – имеющих признаки поражения ЦНС различной этиологии (46 человек). Изучались показатели вирусной нагрузки (ВН) ВИЧ в плазме крови и спинномозговой жидкости (СМЖ). В 45,7% случаях поражения вызваны микст-инфекциями. У пациентов 2 группы уровень ВН ВИЧ в СМЖ в 7,6 раз выше, чем у пациентов 1 группы. ВН ВИЧ в плазме значительно выше показателей в СМЖ. У восьми больных установлено превышение ВН ВИЧ в МЖ. Поражения головного мозга различной этиологии с клиническими проявлениями нарушают целостность гематоэнцефалического барьера, способствуют накоплению ВИЧ в СМЖ и усиливают репликацию вируса в мозговой ткани. Сделан вывод о целесообразности проведения исследования на ВИЧ в СМЖ

Current Issues of Antibiotic Use for Acute Infections Treatment in Children

In the article we considered the antibacterial therapy in children with acute respiratory disease: rational of administration, the choice of an initial antibiotic and the selection of methods of antibiotic therapy. 369 case records of children with acute respiratory infection, bronchitis and pneumonias were analyzed. It was detected that the prescription of antibacterial therapy was groundless and timeless in 1/3 children with acute respiratory diseases. The Cephalosporins of the II and III generation dominates as a starting treatment of acute respiratory disease in children. We registered the rare use of sequential therapy and prevailing administration of parenteral antibiotics