The Detector System for the Stratospheric Kinetic Inductance Polarimeter (SKIP)

The Stratospheric Kinetic Inductance Polarimeter (SKIP) is a proposed balloon-borne experiment designed to study the cosmic microwave background, the cosmic infrared background and Galactic dust emission by observing 1133 square degrees of sky in the Northern Hemisphere with launches from Kiruna, Sweden. The instrument contains 2317 single-polarization, horn-coupled, aluminum lumped-element kinetic inductance detectors (LEKID). The LEKIDs will be maintained at 100 mK with an adiabatic demagnetization refrigerator. The polarimeter operates in two configurations, one sensitive to a spectral band centered on 150 GHz and the other sensitive to 260 and 350 GHz bands. The detector readout system is based on the ROACH-1 board, and the detectors will be biased below 300 MHz. The detector array is fed by an F/2.4 crossed-Dragone telescope with a 500 mm aperture yielding a 15 arcmin FWHM beam at 150 GHz. To minimize detector loading and maximize sensitivity, the entire optical system will be cooled to 1 K. Linearly polarized sky signals will be modulated with a metal-mesh half-wave plate that is mounted at the telescope aperture and rotated by a superconducting magnetic bearing. The observation program consists of at least two, five-day flights beginning with the 150 GHz observations.Comment: J Low Temp Phys DOI 10.1007/s10909-013-1014-3 The final publication is available at link.springer.co

A Titanium Nitride Absorber for Controlling Optical Crosstalk in Horn-Coupled Aluminum LEKID Arrays for Millimeter Wavelengths

We discuss the design and measured performance of a titanium nitride (TiN) mesh absorber we are developing for controlling optical crosstalk in horn-coupled lumped-element kinetic inductance detector arrays for millimeter-wavelengths. This absorber was added to the fused silica anti-reflection coating attached to previously-characterized, 20-element prototype arrays of LEKIDs fabricated from thin-film aluminum on silicon substrates. To test the TiN crosstalk absorber, we compared the measured response and noise properties of LEKID arrays with and without the TiN mesh. For this test, the LEKIDs were illuminated with an adjustable, incoherent electronic millimeter-wave source. Our measurements show that the optical crosstalk in the LEKID array with the TiN absorber is reduced by 66\% on average, so the approach is effective and a viable candidate for future kilo-pixel arrays.Comment: 7 pages, 5 figures, accepted for publication in the Journal of Low Temperature Physic

Horn-Coupled, Commercially-Fabricated Aluminum Lumped-Element Kinetic Inductance Detectors for Millimeter Wavelengths

We discuss the design, fabrication, and testing of prototype horn-coupled, lumped-element kinetic inductance detectors (LEKIDs) designed for cosmic microwave background (CMB) studies. The LEKIDs are made from a thin aluminum film deposited on a silicon wafer and patterned using standard photolithographic techniques at STAR Cryoelectronics, a commercial device foundry. We fabricated twenty-element arrays, optimized for a spectral band centered on 150 GHz, to test the sensitivity and yield of the devices as well as the multiplexing scheme. We characterized the detectors in two configurations. First, the detectors were tested in a dark environment with the horn apertures covered, and second, the horn apertures were pointed towards a beam-filling cryogenic blackbody load. These tests show that the multiplexing scheme is robust and scalable, the yield across multiple LEKID arrays is 91%, and the noise-equivalent temperatures (NET) for a 4 K optical load are in the range 26\thinspace\pm6 \thinspace \mu \mbox{K} \sqrt{\mbox{s}}

A LEKID-based CMB instrument design for large-scale observations in Greenland

We present the results of a feasibility study, which examined deployment of a ground-based millimeter-wave polarimeter, tailored for observing the cosmic microwave background (CMB), to Isi Station in Greenland. The instrument for this study is based on lumped-element kinetic inductance detectors (LEKIDs) and an F/2.4 catoptric, crossed-Dragone telescope with a 500 mm aperture. The telescope is mounted inside the receiver and cooled to $<\,4$ K by a closed-cycle $^4$He refrigerator to reduce background loading on the detectors. Linearly polarized signals from the sky are modulated with a metal-mesh half-wave plate that is rotated at the aperture stop of the telescope with a hollow-shaft motor based on a superconducting magnetic bearing. The modular detector array design includes at least 2300 LEKIDs, and it can be configured for spectral bands centered on 150~GHz or greater. Our study considered configurations for observing in spectral bands centered on 150, 210 and 267~GHz. The entire polarimeter is mounted on a commercial precision rotary air bearing, which allows fast azimuth scan speeds with negligible vibration and mechanical wear over time. A slip ring provides power to the instrument, enabling circular scans (360 degrees of continuous rotation). This mount, when combined with sky rotation and the latitude of the observation site, produces a hypotrochoid scan pattern, which yields excellent cross-linking and enables 34\% of the sky to be observed using a range of constant elevation scans. This scan pattern and sky coverage combined with the beam size (15~arcmin at 150~GHz) makes the instrument sensitive to $5 < \ell < 1000$ in the angular power spectra

The Green Bank Northern Celestial Cap Pulsar Survey - I: Survey Description, Data Analysis, and Initial Results

We describe an ongoing search for pulsars and dispersed pulses of radio emission, such as those from rotating radio transients (RRATs) and fast radio bursts (FRBs), at 350 MHz using the Green Bank Telescope. With the Green Bank Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided into 4,096 channels every 81.92 $\mu s$. This survey will cover the entire sky visible to the Green Bank Telescope ($\delta > -40^\circ$, or 82% of the sky) and outside of the Galactic Plane will be sensitive enough to detect slow pulsars and low dispersion measure ($<$30 $\mathrm{pc\,cm^{-3}}$) millisecond pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a spectral index of $-$1.6, we will be 2.5 times more sensitive than previous and ongoing surveys over much of our survey region. Here we describe the survey, the data analysis pipeline, initial discovery parameters for 62 pulsars, and timing solutions for 5 new pulsars. PSR J0214$+$5222 is an MSP in a long-period (512 days) orbit and has an optical counterpart identified in archival data. PSR J0636$+$5129 is an MSP in a very short-period (96 minutes) orbit with a very low mass companion (8 $M_\mathrm{J}$). PSR J0645$+$5158 is an isolated MSP with a timing residual RMS of 500 ns and has been added to pulsar timing array experiments. PSR J1434$+$7257 is an isolated, intermediate-period pulsar that has been partially recycled. PSR J1816$+$4510 is an eclipsing MSP in a short-period orbit (8.7 hours) and may have recently completed its spin-up phase.Comment: 18 pages, 10 figures, 5 tables, accepted by Ap

The Right Diagnosis: The Role of Pathology in Health System Strengthening

Background: The drive to Universal Health Care coverage, and the need for strengthening health systems, has led to the examination of the role of core elements of the system such as surgery and radiology. Until recently, pathology (which, along with radiology, is key to correct diagnosis and treatment), has been relatively neglected within the global health framework. Resource-constrained governments and patients paying out-ofpocket have tended to underestimate the importance of laboratory testing. International donors have looked to point-of-care tests as a way to overcome the difficult task of strengthening national laboratory networks. Without strong pathology systems, however, there is the danger of development of multi-drug resistance, inaccurate tissue diagnosis and delays in identifying new emerging epidemics. Diagnosis and treatment of cancer and other non-communica

Clinical Impact and Cost-Effectiveness of Expanded Voluntary HIV Testing in India

Background: Despite expanding access to antiretroviral therapy (ART), most of the estimated 2.3 to 2.5 million HIV-infected individuals in India remain undiagnosed. The questions of whom to test for HIV and at what frequency remain unclear. Methods: We used a simulation model of HIV testing and treatment to examine alternative HIV screening strategies: 1) current practice, 2) one-time, 3) every five years, and 4) annually; and we applied these strategies to three population scenarios: 1) the general Indian population (“national population”), i.e. base case (HIV prevalence 0.29%; incidence 0.032/100 person-years [PY]); 2) high-prevalence districts (HIV prevalence 0.8%; incidence 0.088/100 PY), and 3) high-risk groups (HIV prevalence 5.0%; incidence 0.552/100 PY). Cohort characteristics reflected Indians reporting for HIV testing, with a median age of 35 years, 66% men, and a mean CD4 count of 305 cells/µl. The cost of a rapid HIV test was $3.33. Outcomes included life expectancy, HIV-related direct medical costs, incremental cost-effectiveness ratios (ICERs), and secondary transmission benefits. The threshold for “cost-effective” was defined as 3x the annual per capita GDP of India ($3,900/year of life saved [YLS]), or for “very cost-effective” was <1x the annual per capita GDP ($1,300/YLS). Results: Compared to current practice, one-time screening was very cost-effective in the national population (ICER:$1,100/YLS), high-prevalence districts (ICER: $800/YLS), and high-risk groups (ICER:$800/YLS). Screening every five years in the national population (ICER: $1,900/YLS) and annual screening in high-prevalence districts (ICER:$1,900/YLS) and high-risk groups (ICER: $1,800/YLS) were also cost-effective. Results were most sensitive to costs of care and linkage-to-care. Conclusions: In India, voluntary HIV screening of the national population every five years offers substantial clinical benefit and is cost-effective. Annual screening is cost-effective among high-risk groups and in high-prevalence districts nationally. Routine HIV screening in India should be implemented

The Green Bank Northern Celestial Cap Pulsar Survey II: The Discovery and Timing of Ten Pulsars

We present timing solutions for ten pulsars discovered in 350 MHz searches with the Green Bank Telescope. Nine of these were discovered in the Green Bank Northern Celestial Cap survey and one was discovered by students in the Pulsar Search Collaboratory program in analysis of drift-scan data. Following discovery and confirmation with the Green Bank Telescope, timing has yielded phase-connected solutions with high precision measurements of rotational and astrometric parameters. Eight of the pulsars are slow and isolated, including PSR J0930$-$2301, a pulsar with nulling fraction lower limit of $\sim$30\% and nulling timescale of seconds to minutes. This pulsar also shows evidence of mode changing. The remaining two pulsars have undergone recycling, accreting material from binary companions, resulting in higher spin frequencies. PSR J0557$-$2948 is an isolated, 44 \rm{ms} pulsar that has been partially recycled and is likely a former member of a binary system which was disrupted by a second supernova. The paucity of such so-called `disrupted binary pulsars' (DRPs) compared to double neutron star (DNS) binaries can be used to test current evolutionary scenarios, especially the kicks imparted on the neutron stars in the second supernova. There is some evidence that DRPs have larger space velocities, which could explain their small numbers. PSR J1806+2819 is a 15 \rm{ms} pulsar in a 44 day orbit with a low mass white dwarf companion. We did not detect the companion in archival optical data, indicating that it must be older than 1200 Myr.Comment: 9 pages, 5 figure

The Green Bank North Celestial Cap Pulsar Survey. IV: Four New Timing Solutions

We present timing solutions for four pulsars discovered in the Green Bank Northern Celestial Cap (GBNCC) survey. All four pulsars are isolated with spin periods between 0.26$\,$s and 1.84$\,$s. PSR J0038$-$2501 has a 0.26$\,$s period and a period derivative of ${7.6} \times {10}^{-19}\,{\rm s\,s}^{-1}$, which is unusually low for isolated pulsars with similar periods. This low period derivative may be simply an extreme value for an isolated pulsar or it could indicate an unusual evolution path for PSR J0038$-$2501, such as a disrupted recycled pulsar (DRP) from a binary system or an orphaned central compact object (CCO). Correcting the observed spin-down rate for the Shklovskii effect suggests that this pulsar may have an unusually low space velocity, which is consistent with expectations for DRPs. There is no X-ray emission detected from PSR J0038$-$2501 in an archival swift observation, which suggests that it is not a young orphaned CCO. The high dispersion measure of PSR J1949+3426 suggests a distance of 12.3$\,$kpc. This distance indicates that PSR J1949+3426 is among the most distant 7% of Galactic field pulsars, and is one of the most luminous pulsars.Comment: 7 pages, 5 figure