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

Association of overall diet quality with falls and physical function among community dwelling older adults - results from MrOS study

Falls among people aged 65 and older are recognized as an issue of public health significance in the United States which faces an increasingly aging society. The current study tests the hypothesis that lower diet quality is prospectively associated with incident falls and whether physical function as assessed by gait speed is a mediator of this association. For our prospective analysis, we studied 5849 men enrolled in the Osteoporotic Fractures in men study (MrOS). All men in MrOS were ≥ age 65 at baseline. Overall diet quality as assessed by Healthy Eating Index (HEI-2010) scores were calculated from a reduced version Block 98 food-frequency questionnaire and categorized into quartiles. An indicator variable for incident falls was computed using falls categorized by a yes/no response and number of falls reported at follow-up of 12 months. Recurrent falls were classified as (≥ 2) vs single (1) or no fall (0). Gait speed was measured in meters/second on a standard six meter walking course. Multiple logistic regression methods were used to test the association between HEI-2010 scores and incident falls after adjusting for age, race, clinic site, smoking status, physical activity, Body Mass Index, diabetes, stroke, parkinson’s disease, glaucoma, selective serotonin reuptake inhibitor antidepressants, tricyclic antidepressants, antidepressants, benzodiazepines and gait speed. At the end of the follow-up period of 1 year, 1473 (25.7%) experienced a fall (≥ 1), 685 (11.7%) experienced recurrent falls (≥ 2). Compared to older men with the highest HEI-2010 scores, those with the lower HEI-2010 scores had a similar risk of falls. There was no significant association with falls in the unadjusted or adjusted models. Additional adjustment for gait speed showed similar associations. For recurrent falls, compared to men with the highest HEI-2010 scores, older men with the lower HEI-2010 scores had a higher risk of recurrent falls in the unadjusted model which remained significant after adjustment for age, race, clinic site (p trend=0.02), lifestyle factors including smoking status and physical activity (p trend=0.03) and BMI (p trend=0.04). Further adjustments for comorbidities reduced the overall significance of the trend (p trend=0.07). Finally adjusting for gait speed, there was no significant association although the risk for falls marginally increased (p trend=0.12). We concluded that there was no significant association between diet quality and incident falls

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

Paper-PDMS hybrid microchannel: a platform for rapid fluid-transport and mixing

The functionalities of a paper-PDMS hybrid microchannel, as a potential fluidic transport platform, are presented. The setup consists of a PDMS microchannel with one of its walls covered by paper. In contrast to the available microfluidic platforms, the capillary filling is found to occur at much faster speed in the hybrid channel. Moreover, experimentation using two dye solutions shows mixing enhancement at a significantly faster rate and at a shorter distance in the hybrid channel as compared to the other available counterparts. The paper attachment is found to induce an effective slip during liquid transport, and thereby allows faster transport and capillary filling. The liquid slippage further modifies the shear flow behavior near the wall leading to a slip-enhanced mixing within the hybrid channel. These fundamental understandings correspond to the experimental results quantitatively in terms of corroborating scaling laws. Further mixing enhancement is introduced through spiral, curved and elliptical–spiral geometries of the channel. Apart from the above benefits, the enclosed arrangement protects sensitive reagents from external environment and offers better control over their transport, thus giving a stable mixing and reaction performance inside the channel

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

Wideband antennas for precision spectral radiometers for cosmology

Precision cosmology has been made possible by differential microwave radiometers that have imaged the anisotropy in the cosmic microwave background radiation. Continued progress is expected from measurement of spectral distortions in this cosmic radiation. A key distortion in the global sky spectrum is in the 40-250 MHz band and expected from variations in the hydrogen spin temperature and ionization state during Cosmic Dawn and Epoch of Reionization when the first stars and galaxies form. Electrically-small shaped ultra-wideband antennas are described that have been designed for the detection of these global or all-sky spectral distortions; a key design feature is the making of the transfer function Maximally Smooth

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

The association between social support through contacts with Accredited Social Health Activists (ASHAs) and antenatal anxiety among women in Mysore, India: a cross-sectional study

Purpose In India, antenatal anxiety prevalence estimates range from 6 to 48%. Social support is strongly associated with mental wellbeing, yet most studies have examined the impact of support from partners and family members rather than peers, community members, or health care providers. This study explores the supportive role of Accredited Social Health Activists (ASHA) contacts for antenatal anxiety. Methods Data were analyzed from the Saving Children, Improving Lives project, a quasi-experimental study conducted among rural, pregnant women in India. Regression models were used to estimate adjusted prevalence ratios (aPRs) and 95% confidence intervals for the relationship frequency of ASHA contacts and antenatal anxiety. Antenatal anxiety was measured using a subscale of the Edinburgh Postnatal Depression Scale. Results The sample consisted of 480 pregnant women. Reported antenatal anxiety prevalence was 27% (95% CI 23%, 31%). Participants who were more frequently visited by ASHAs at home (aPR: 0.90; 95% CI 0.76, 0.98) and more frequently accompanied by ASHAs to their antenatal care visits (aPR: 0.86, 95% CI 0.78, 0.95) were less likely to report antenatal anxiety. ASHA home visits were protective for the most vulnerable women (primigravida and those experiencing domestic violence) and ASHA accompaniment to antenatal care visits was equally protective for all women. Conclusions ASHAs are valued for their contribution towards maternal health education and linking women of reproductive age to healthcare services. Our findings additionally suggest the important role ASHAs play in providing social support to pregnant women, particularly those who are most vulnerable to experiencing antenatal anxiety.12 month embargo; published: 07 March 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]