A Resistive Wideband Space Beam Splitter

We present the design, construction and measurements of the electromagnetic performance of a wideband space beam splitter. The beam splitter is designed to power divide the incident radiation into reflected and transmitted components for interferometer measurement of spectral features in the mean cosmic radio background. Analysis of a 2-element interferometer configuration with a vertical beam splitter between a pair of antennas leads to the requirement that the beam splitter be a resistive sheet with sheet resistance {\eta}o /2, where {\eta}o is the impedance of free space. The transmission and reflection properties of such a sheet is computed for normal and oblique incidences and for orthogonal polarizations of the incident electric field. We have constructed such an electromagnetic beam splitter as a square soldered grid of resistors of value 180 Ohms (approximately {\eta}o /2) and a grid size of 0.1 m, and present measurements of the reflection and transmission coefficients over a wide frequency range between 50 and 250 MHz in which the wavelength well exceeds the mesh size. Our measurements of the coefficients for voltage transmission and reflection agree to within 5% with physical optics modeling of the wave propagation, which takes into account edge diffraction.Comment: 14 pages,17 figure

Divergent Metabolic Effects of Metformin Merge to Enhance Eicosapentaenoic Acid Metabolism and Inhibit Ovarian Cancer In Vivo

Metformin is being actively repurposed for the treatment of gynecologic malignancies including ovarian cancer. We investigated if metformin induces analogous metabolic changes across ovarian cancer cells. Functional metabolic analysis showed metformin caused an immediate and sustained decrease in oxygen consumption while increasing glycolysis across A2780, C200, and SKOV3ip cell lines. Untargeted metabolomics showed metformin to have differential effects on glycolysis and TCA cycle metabolites, while consistent increased fatty acid oxidation intermediates were observed across the three cell lines. Metabolite set enrichment analysis showed alpha-linolenic/linoleic acid metabolism as being most upregulated. Downstream mediators of the alpha-linolenic/linoleic acid metabolism, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were abundant in all three cell lines. EPA was more effective in inhibiting SKOV3 and CaOV3 xenografts, which correlated with inhibition of inflammatory markers and indicated a role for EPA-derived specialized pro-resolving mediators such as Resolvin E1. Thus, modulation of the metabolism of omega-3 fatty acids and their anti-inflammatory signaling molecules appears to be one of the common mechanisms of metformin\u27s antitumor activity. The distinct metabolic signature of the tumors may indicate metformin response and aid the preclinical and clinical interpretation of metformin therapy in ovarian and other cancers

The epidemiology and transmission of methicillin-resistant Staphylococcus aureus in the community in Singapore: study protocol for a longitudinal household study.

BACKGROUND/AIM: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common multidrug-resistant organisms in healthcare settings worldwide, but little is known about MRSA transmission outside of acute healthcare settings especially in Asia. We describe the methods for a prospective longitudinal study of MRSA prevalence and transmission. METHODS: MRSA-colonized individuals were identified from MRSA admission screening at two tertiary hospitals and recruited together with their household contacts. Participants submitted self-collected nasal, axilla and groin (NAG) swabs by mail for MRSA culture at baseline and monthly thereafter for 6 months. A comparison group of households of MRSA-negative patients provided swab samples at one time point. In a validation sub-study, separate swabs from each site were collected from randomly selected individuals, to compare MRSA detection rates between swab sites, and between samples collected by participants versus those collected by trained research staff. Information on each participant's demographic information, medical status and medical history, past healthcare facilities usage and contacts, and personal interactions with others were collected using a self-administered questionnaire. DISCUSSION/CONCLUSION: Understanding the dynamics of MRSA persistence and transmission in the community is crucial to devising and evaluating successful MRSA control strategies. Close contact with MRSA colonized patients may to be important for MRSA persistence in the community; evidence from this study on the extent of community MRSA could inform the development of household- or community-based interventions to reduce MRSA colonization of close contacts and subsequent re-introduction of MRSA into healthcare settings. Analysis of longitudinal data using whole-genome sequencing will yield further information regarding MRSA transmission within households, with significant implications for MRSA infection control outside acute hospital settings

EPIDEMIOLOGY AND TRANSMISSION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS IN THE COMMUNITY IN SINGAPORE

Ph.DDOCTOR OF PHILOSOPHY (SPH

STUDY OF VITAMIN D LEVELS IN EPILEPTIC CHILDREN IN AGE GROUP OF 2-16 YEARS

 Objective: Epilepsy is a common neurological disorder in childhood. A number of medications are used in the treatment of epilepsy. Antiepilepticdrugs (AEDs) are known to exert deleterious effects on vitamin D metabolism. Its deficiency state in epileptics can lead to difficult seizure control asvitamin D is said to have anti-epileptogenic activity in addition to its known role in calcium metabolism. Correction of vitamin D deficiency may helpin decreasing the morbidity as well as seizure frequency. The purpose of this prospective observational study was to determine vitamin D status inthese children.Methods: Seventy children aged 2-16 years with epilepsy on AEDs were assessed for vitamin D levels.Results: The results showed that the vitamin D levels in this study population were significantly low.Conclusion: Vitamin D levels were significantly low in children with epilepsy and hence, it is recommended that vitamin D supplementation in thesechildren is necessary to reduce the seizure frequency and vitamin D deficiency related morbidity.Keywords: 25OH vitamin D, Epilepsy, Antiepileptic drugsÂ

A wideband resistive beam-splitter screen

We present the design, construction and measurements of the electromagnetic performance of a wideband space beam splitter. The beam splitter is a sheet in free space that is designed to divide incident radiation into reflected and transmitted components for interferometer measurement of spectral features in the mean cosmic radio background. Analysis of a two-element interferometer configuration with a vertical beam splitter between a pair of antennas leads to the requirement that the beam splitter be a resistive sheet with sheet resistance η_o/2, where η_o is the impedance of free space. The transmission and reflection properties of such a sheet are computed for normal and oblique incidences and for orthogonal polarizations of the incident electric field. We have constructed such an electromagnetic beam splitter as a square-soldered grid of resistors of value 180 Ohms (approximately η_o/2) and a grid size of 0.1 m. We measured the reflection and transmission coefficients over a wide frequency range between 50 and 250 MHz in which the wavelength well exceeds the mesh size. Measurements of the coefficients for voltage transmission and reflection agree to within 5% with physical optics modeling of the wave propagation, which takes into account edge diffraction

Antennas, space beam splitters and receivers for precision radiometers exploring the reionization and recombination epochs

The challenging goal of detecting faint and wideband spectral features arising from cosmological evolution in the thermal state of the baryons has driven recent progress in radiometer technology. Because these faint signals are received with foregrounds and terrestrial RFI that are overwhelmingly larger in power, the design of sensors of the EM field and associated receiver configuration need special care to minimize contaminations into the spectral domain and in particular into the spectral modes where the cosmological signatures reside. We present recent progress at the Raman Research Institute in the design of wideband frequency independent antennas, space beam splitters, and receiver configurations that are designed to self-calibrate spectral structures arising from self-generated receiver noise. All these innovative elements are purpose built for precision radiometers. We present engineering test and measurement results from prototypes as well as results of astronomy measurements of the cosmic radio background from field deployment

Signatures in the cosmic radio background from spin flip and recombination in cosmological hydrogen

The cosmological evolution of baryons through recombination and reionization are predicted to manifest as faint spectral features in the cosmic radio background. Pathfinder experiments that aim to detect global phase transitions in the ionization state of the gas in redshifted 21-cm may well be the first radio wavelength constraints on the astrophysics that drive the thermal evolution during reionization and the timing of critical events as first stars and galaxies form. This challenging problem is a motivation for innovative design in radio astronomy receivers. We present progress at the Raman Research Institute in the system design of precision radiometers for detecting spectral deviations in the radio background, design and test measurements of novel antennas, space beam splitters and receiver configurations, and present results from observations to date. The precision radiometer elements developed for the detection of cosmological phase transitions is a step towards building out SKA arrays that operate as interferometers to detect the spatial fluctuations in hydrogen during these critical epochs

Experimental Persistent Infection of BALB/c Mice with Small-Colony Variants of Burkholderia pseudomallei Leads to Concurrent Upregulation of PD-1 on T Cells and Skewed Th1 and Th17 Responses.

Burkholderia pseudomallei (B. pseudomallei), the causative agent of melioidosis, is a deadly pathogen endemic across parts of tropical South East Asia and Northern Australia. B. pseudomallei can remain latent within the intracellular compartment of the host cell over prolonged periods of time, and cause persistent disease leading to treatment difficulties. Understanding the immunological mechanisms behind persistent infection can result in improved treatment strategies in clinical melioidosis.Ten-day LD50 was determined for the small-colony variant (SCV) and its parental wild-type (WT) via intranasal route in experimental BALB/c mice. Persistent B. pseudomallei infection was generated by administrating sub-lethal dose of the two strains based on previously determined LD50. After two months, peripheral blood mononuclear cells (PBMCs) and plasma were obtained to investigate host immune responses against persistent B. pseudomallei infection. Lungs, livers, and spleens were harvested and bacterial loads in these organs were determined.Based on the ten-day LD50, the SCV was ~20-fold less virulent than the WT. The SCV caused higher bacterial loads in spleens compared to its WT counterparts with persistent B. pseudomallei infection. We found that the CD4+ T-cell frequencies were decreased, and the expressions of PD-1, but not CTLA-4 were significantly increased on the CD4+ and CD8+ T cells of these mice. Notably, persistent infection with the SCV led to significantly higher levels of PD-1 than the WT B. pseudomallei. Plasma IFN-γ, IL-6, and IL-17A levels were elevated only in SCV-infected mice. In addition, skewed plasma Th1 and Th17 responses were observed in SCV-infected mice relative to WT-infected and uninfected mice.B. pseudomallei appears to upregulate the expression of PD-1 on T cells to evade host immune responses, which likely facilitates bacterial persistence in the host. SCVs cause distinct pathology and immune responses in the host as compared to WT B. pseudomallei