A search for periodicity in the x ray spectrum of black hole candidate A0620-00

The archived data from the SAS-3 observations of the X-ray nova A0620-00, the best of the stellar blackhole candidates, were exhaustively examined for evidence of variable phenomena correlated with the orbital motion of the binary system of which it is a member. The original analysis of these data was completed before discovery of the binary companion and determination of the orbital period of the system. New interest was drawn to the task of a reexamination of the archive data by the recent discovery of the massive nature of the X-ray source through analysis of the Doppler variations and ellipsoidal light variations of the faint K-star companion by McClintock and Remillard. The archive research, carried out under the supervision of the principal investigator, was the topic of the thesis submitted to the MIT Department of Physics by Kenneth Plaks in partial fulfillment of the requirements for the degree of Master of Science. Plaks' effort was focused on the elimination of fluctuations in the data due to errors in attitude solutions and other extraneous causes. The first products of his work were long-term light curves of the X-ray intensities in the various energy channels as functions of time during the time from outbursts in August 1975 to quiescence approximately 6 months later. These curves, are refined versions of the preliminary results published in 1976 (Matilsky et al. 1976). Smooth exponentials were fitted to these long term light curves to provide the basis for detrending the data, thereby permitting a calculation of residuals derived by subtracting the fitted curve from the data. The residuals were then analyzed by Fourier analysis to search for variations with the period of the binary orbit, namely 7.75 hours. No evidence of an orbital periodicity was found. However, the refined light curve provides a much clearer picture of the outburst and subsequent decay of the X-ray luminosity. In fact, there were two outbursts, each followed by an exponential decay with similar time constants of about 25 days. Previous evidence of a three-oscillation variation with a 7.8 day period were confirmed. Substantial theoretical effort has been devoted to attempts to account for the decay characteristics as the result of the gradual eating up of an accretion disk by a stellar-mass blackhole (e.g., Huang and Wheeler 1989). The improved decay curves will provide significant new constraints on the theoretical analyses

A spectroscopic analysis of the starburst galaxies Ngc 3395 and Ngc 3396

We have obtained ultraviolet and visible wavelength spectra of 31 bright star forming knots in the interacting galaxies NGC 3395 and NGC 3396 using the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. The knots are possible super star clusters on the order of ∼100 pc diameter with measured metallicities on the order of 0.5--0.6 Z⊙ . The spectra are consistent with a massive production of hot young stars in a starburst; Ages of the starburst knots were calculated using several diagnostics from the Leitherer et al. Starburst 99 code (SB99) using an Initial Mass Function (IMF) with a power law coefficient alpha = 2.35 and an upper mass limit of 100 M⊙ . We modeled our star forming knots as instantaneous starbursts with the measured metallicity and we obtained consistent and reasonable estimates of the starburst age. The UV-brightest knots are ∼5 Myr old in both galaxies. We found no age gradient in the galaxies implying the starburst does not propagate across the galaxy but rather occurs simultaneously everywhere. The data are also consistent with the interpretation that the starburst is not only happening more or less simultaneously within each galaxy, it is also occurring simultaneously in both galaxies. If true, the fact that it is occurring simultaneously in both galaxies gives credence to the interaction being the source of the star formation in line with current theory; While our starforming knots were spatially resolved, at high redshift one cannot resolve individual knots and instead has to rely on spatially unresolved spectra. To assess the representativeness of these spectra of the underlying structure, we simulated the spectra one would observe by defining the entire portion of each galaxy observed as an unresolved knot. We found the metallicities for the unresolved knots were very representative of the resolved knots that made them up. We also found that the ages we derived for the unresolved knots were representative of the underlying resolved knot ages to approximately a factor of 2--3; We measured the flux in the broad He II lambda4686 emission line characteristic of Wolf-Rayet (WR) stars. Uncorrected for reddening, we estimated ∼250 WR and ∼1100 O stars in NGC 3395 and ∼400 WR and ∼2500 O stars in NGC 3396. We were unable to subcategorize the WR stars, although the spectra do have some characteristics of WN stars; We discovered a super bubble in NGC 3395 with a radius of approximately 24 pc containing ∼80 WR stars uncorrected for reddening. We calculate that it also contains ∼25 O stars although we suspect that we have severely underestimated this value and a more representative value may be as many as 420 O stars uncorrected for reddening

Dynamics of longitudinally forced bluff body flames with varying dilatation ratios

This thesis focuses on experimentally measuring the response of varying dilatation ratio bluff body flames under harmonic excitation. Such flames are often encountered in jet engine afterburners and are susceptible to combustion instabilities. Previous work has been done modeling such flames, however, only limited experimental data has been obtained at these conditions and is the motivation for this thesis. The focus of this work is to measure the transfer function of longitudinally forced, varying dilatation ratio bluff body flames. The transfer function is obtained by measuring flame position and flame luminosity fluctuations at the forcing frequency. Specifically, the amplitude and phase of the fluctuations are characterized as a function of flow velocity, axial location, and perturbation amplitude. These measurements are also compared to available theoretical predictions, showing that qualitative measured trends are consistent with theory. In addition, a detailed quantitative comparison is performed at one condition, showing good agreement between predictions and measurements in the near and mid-field of the flame response. However, agreement is not obtained in the far-field, indicating that continued theoretical work is needed to understand the flame response characteristics in this region.M.S.Committee Chair: Tim Lieuwen; Committee Member: Jeff Jagoda; Committee Member: Suresh Meno

Reconfigurable Computing and Hardware/Software Codesign

none3Article ID 731830 - EditorialPLAKS T. P; SANTAMBROGIO M. D; D. SCIUTOPLAKS T., P; Santambrogio, MARCO DOMENICO; Sciuto, Donatell

Hearing loss in the closed head injured population of South Africa, two to five years post closed head injury.

Purpose: The main objective of the current study was to describe auditory function within the closed head injured (CHI) population of South Africa, two to five years post head injury. This was achieved by describing the participants’ medical history, radiological and audiological findings and relating these findings to each other. This enabled the researcher to determine the occurrence of hearing loss within the CHI participants within the current study. Participants: A total of 30 participants formed part of the analysis of which 23 participants were males and 7 participants were females. Purposive sampling was utilized in this study and the participants were selected from specific participant inclusion criteria. Participants were recruited using the records from two private rehabilitation facilities in Gauteng. The total sample of participants was analyzed according to a variety of critical variables which included gender, type of CHI, site of lesion and ratings on the Glasgow Coma Scale. Design: The current research study made use of a non-experimental, descriptive, cross-sectional design. The researcher analyzed adult individuals who had already sustained a CHI at a single point in time, and analyzed their hearing function, while further looking at how variables such as gender, type of injury and site of lesion affected the integrity of the auditory system. The descriptive research design allowed the researcher to observe and describe the participants’ behaviours without manipulating any variables. The data was organised into tables, graphs, and figures to display the results. Methods and materials: Participants were informed telephonically about the study and volunteered to participate. They completed a detailed case history questionnaire, they underwent basic audiological tests including otoscopy and immittance testing, pure tone and speech testing, as well as advanced audiological tests which included otoacoustic emissions (OAEs) and auditory brainstem responses (ABRs). Data analysis: Both descriptive and inferential statistics were used to analyse the data from the study. Inferential statistics in the form of the Wilcoxon Matched Pairs Signed Rank Test and the Kruskal Wallis test were utilized to analyze the data. The Wilcoxon Signed Rank test was used to compare the related samples between all the recorded ABR data. In the current study the Kruskal-Wallis ANOVA test was used to determine if there was any association between the ABR recordings and type of head injury, Glasgow Coma Scale scores and site of lesion. Significance levels were recorded when the p-value was < 0.05. Results: Basic audiometry revealed normal hearing in all 30 closed head injured participants. The results of the OAEs were normal in 25 participants, and are consistent with the basic audiometry findings. However when analyzed individually, OAEs revealed that 5 participants presented with OAE abnormalities on either the distortion product OAE, the transient evoked OAE or both. The neurological ABR revealed abnormalities on 14 participants’ neurological ABR recordings. Almost half of the sample of the closed head injured participants presented with subtle abnormalities on their neurological ABR recordings. All audiological ABR recordings were normal and correlated well with the basic auditory tests. The current study revealed that type of CHI, Glasgow coma scale score or site of lesion will not negatively affect the auditory system. It was revealed that a hearing loss may not be diagnosed by using only basic hearing tests, more advanced hearing tests which include OAE’s and ABR’s must also be considered when analyzing the auditory system in the CHI population. It was also revealed that hearing impairment following CHI is mainly temporary and tends to dissipate during the post-traumatic period

Computational Protein Design for Peptide-Directed Bioconjugation

Proteins enable living organisms to perform many of their critical functions, having been applied over evolutionary time to solve problems of overwhelming diversity and complexity. Protein engineering seeks to deploy these versatile molecules in addressing problems of human concern and would benefit from innovations that improve protein utilization in unnatural environments as well as from increased predictive capability in protein design. Bioconjugation facilitates the use of proteins in unnatural environments by permitting the attachment of molecules, such as polymers, that can modulate protein stability, solubility, and activity and by mediating protein immobilization. We initially explored this propensity of bioconjugation by designing an enzymatic polyurethane-based material in which proteins were covalently immobilized via non-specific, isocyanate reaction chemistries. The resulting material resisted bacterial biofilm formation through the activity of the embedded enzymes, which hydrolyzed signaling molecules involved in quorum sensing.In order to gain better regional and temporal reaction control, we transitioned to working with an enzyme-mediated conjugation system in which lipoic acid ligase functionalizes a specific 13-residue peptide sequence (the LAP sequence) with an azide-bearing lipoic acid derivative. Using GFP as a model protein, we demonstrated that the LAP sequence could be inserted at internal positions within a protein’s structure and successfully ligated and subsequently modified via azide-alkyne click chemistry within that context. Given the ability of the LAP sequence to site-specifically direct conjugation at internal sites within protein structures, we developed a predictive computational approach to facilitate the design of internal LAP insertion sites within diverse protein targets. The kinematic loop modeling application within the Rosetta framework was adapted for rapid scanning and characterization of insertion sites, using Rosetta’s coarse-grained centroid score function for site differentiation. Soluble protein expression of LAP-containing proteins was found to correlate with Rosetta scores, and unintuitive sites were identified relative to B-factor and secondary structure considerations. Our results highlighted the role played by residues in the near-loop environment in determining whether a particular site within a protein accommodates an inserted loop, such as the LAP sequence, and suggest that our computational approach, which is highly user accessible, can usefully predict such sites

Development of a Method and Architecture of the Information System for Automated Collection of Thematic Information on the Internet

The aim of my research is to develop the information system architecture collection of information on the Internet, which will allow to automate the process of information search. It must satisfy with setting the entire region searching and finding documents in accordance with it. Develop information system architecture model, which consists of indexing, searching service and virtual data warehouse that allows the researcher quickly obtain data on the topic of your search from various sources

Mesh shape and anisotropic elements : theory and practice

The relationship between the shape of finite elements in unstructured meshes and the error that results in the numerical solution is of increasing importance as finite elements are used to solve problems with highly anisotropic and, often, very complex solutions. This issue is explored in terms of a priori and a posteriori error estimates, and through consideration of the practical issues associated with assessing element shape quality and implementing an adaptive finite element solver