Cs feed tests and emittance measurements on a modified MC-SNICS ion source for radiocarbon AMS

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2007. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 49 (2007): 301-306.We report on 2 recent developments in an ongoing program of characterizing and improving the National Electrostatics Corp. (NEC) MC-SNICS ion source at University of California (UC) Irvine’s Keck AMS laboratory. First, we have investigated the possibility of modifying a large-body (134-sample) MC-SNICS to incorporate the UC Irvine Cs oven and vacuum-insulated Cs feed tube, which provide better confinement of Cs than the standard NEC setup. In our 40-sample source, the feed tube enters the source housing directly below the ionizer assembly. This area cannot be accessed for machining on the 134-sample source, but we have successfully tested a modified geometry where the delivery tube enters the body via the source end flange. Second, we recently installed a second beam profile monitor in the injection line of our spectrometer to allow us to make online emittance measurements. At full output (150 μA of C– at 55 keV), the emittance of our source at 8 kV sputtering voltage is approximately 40π mm mrad

A high-performance 14C accelerator mass spectrometry system

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 228-235.A new and unique radiocarbon accelerator mass spectrometry (AMS) facility has been constructed at the Woods Hole Oceanographic Institution. The defining characteristic of the new system is its large-gap optical elements that provide a larger-than-standard beam acceptance. Such a system is ideally suited for high-throughput, high-precision measurements of 14C. Details and performance of the new system are presented

HIV Incidence among Men Who Have Sex with Men in China: A Meta-Analysis of Published Studies

Men who have sex with men (MSM) have now become one of the priority populations for prevention and control of HIV pandemic in China. Information of HIV incidence among MSM is important to describe the spreading of the infection and predict its trends in this population. We reviewed the published literature on the incidence of HIV infection among MSM in China.We identified relevant studies by use of a comprehensive strategy including searches of Medline and two Chinese electronic publication databases from January 2005 to September 2010. Point estimate of random effects incidence with corresponding 95% confidence intervals (CI) of HIV infection was carried out using the Comprehensive Meta-Analysis software. Subgroup analyses were examined separately, stratified by study design and geographic location.Twelve studies were identified, including three cohort studies and nine cross-sectional studies. The subgroup analyses revealed that the sub-overall incidence estimates were 3.5% (95% CI, 1.7%-5.3%) and 6.7% (95% CI, 4.8%-8.6%) for cohort and cross-sectional studies, respectively (difference between the sub-overalls, Q = 5.54, p = 0.02); and 8.3% (95% CI, 6.9%-9.7%) and 4.6% (95% CI, 2.4%-6.9%) for studies in Chongqing and other areas, respectively (difference between the sub-overalls, Q = 7.58, p<0.01). Syphilis infection (RR = 3.33, p<0.001), multiple sex partnerships (RR = 2.81, p<0.001), and unprotected receptive anal intercourse in the past six months (RR = 3.88, p = 0.007) represented significant risk for HIV seroconversion.Findings from this meta-analysis indicate that HIV incidence is substantial in MSM in China. High incidence of HIV infection and unique patterns of sexual risk behaviors in this population serve as a call for action that should be answered with the innovative social and public health intervention strategies, and development of biological prevention strategies

Surface modification of Ni3Al-based alloy IC6 with intense pulsed ion beams

The effects of intense pulsed ion beams (IPIB) irradiation (ions of C+ and H+, accelerating voltage V ¼ 250 kV, ion current density J ¼ 1002200 A/cm2, pulse duration t ¼ 60 ns, and pulse number n ¼ 12224) on the phase and microstructure response of Ni3Al-based alloy IC6 have been studied. It is shown that the deformation texture can be formed on the surface layer of target under IPIB irradiation with a low current density (100 A/cm2). With further increasing ion current density (150–200 A/cm2), the formation of amorphous and new phases occurs. A higher density of dislocations can be observed in the irradiated specimen compared to the unirradiated specimen

Long-Term Exposure to High Altitude Affects Conflict Control in the Conflict-Resolving Stage

The neurocognitive basis of the effect of long-term high altitude exposure on conflict control is unclear. Event related potentials (ERPs) were recorded in a flanker task to investigate the influence of high altitude on conflict control in the high-altitude group (who had lived at high altitude for three years but were born at low altitude) and the low-altitude group (living in low altitude only). Although altitude effect was not significant at the behavioral level, ERPs showed cognitive conflict modulation. The interaction between group and trial type was significant: P3 amplitude was greater in the low-altitude group than in the high-altitude group in the incongruent trial. This result suggests that long-term exposure to high altitude affects conflict control in the conflict-resolving stage, and that attentional resources are decreased to resist the conflict control in the high-altitude group

Effect of intense pulsed ion beams irradiation on the oxidation behavior of γ′-based superalloy

Intense pulsed ion beams (IPIB) with three different power densities (25, 37.5 and 50 MW/cm2) are employed for the surface treatment of c0-based superalloy IC6. The influence of IPIBirradiation on the oxidation behavior of IC6 at 1100 C for up to 100 h is investigated. It is found that the phase states of IC6 are dramatically changed after IPIBirradiation and the oxidation behavior of the irradiated coupons depends greatly on the power density of IPIB. IPIB irradiation with a power density of 25 or 37.5 MW/cm2 significantly reduces the oxidation rate with respect to the unirradiated coupon. The improvement of the oxidation resistance can be attributed to a change in the oxidation products from a three-layered scale of Ni-rich oxides for the unirradiated coupon to a two-layered scale of Mo- and Al-rich oxides. In contrast, IPIBirradiation with a power density of 50 MW/cm2 proves to be detrimental, causing a higher oxidation rate. The oxidation mechanism for IPIBirradiated coupons is discussed

Design improvements to the SNS ion source and diagnostics

The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world's most intense pulsed-neutron beams to a wide array of instruments which are used to conduct investigations in many fields of science and engineering. The accelerator system is fed by an RF-driven, multicusp, H− ion source which nominally provides pulsed beam currents of 50-60 mA (1ms, 60Hz). This report provides a discussion of ongoing design improvements to the SNS ion source and Low Energy Beam Transport (LEBT) as well as diagnostic upgrades undertaken since the previous ICIS conference. These improvements include (i) simple mechanical modifications to the source outlet aperture which resulted in dramatically increased extracted beam current and comparable or lower emittance at similar beam currents, (ii) design improvements to the LEBT chopper target which will enable full power beam-dumping during physics studies, (iii) refinement of the SNS Allison emittance scanner that has enabled the first reliable LEBT beam measurements at full beam power (65kV, 50-100mA, 1ms, 60Hz) on the SNS ion source test stand and (iv) the implementation of a thermal imaging camera for the monitoring the LEBT electrode temperatures. (v) The design of an advanced Cs system, capable of more efficient Cs utilization with significantly lower Cs losses from the source is also presented. Mechanical details, computational simulations and experimental results are discussed within the context of these improvements.peerReviewe

Seropositivity and risk factors for herpes simplex virus type 2 infection among female sex workers in Guangxi, China.

OBJECTIVES: To determine seropositivity of herpes simplex virus type 2 (HSV-2) infection and associated risk factors among female sex workers (FSWs) in Guangxi, China. METHODS: A convenience sample of FSWs was recruited from different types of sex work venues in two cities (Wuzhou and Hezhou) in Guangxi. Blood specimens were collected for ELISA-based detection of HSV-2 antibodies to examine the seropositivity of HSV-2 infection. Socio-demographic and behavioral data were collected through a structured questionnaire interview. Association of HSV-2 seropositivity with socio-demographic and behavioral characteristics and HIV status was analyzed. RESULTS: The overall prevalence of HSV-2 seropositivity among 2453 FSWs was 54.9% (95% confidence interval [CI], 52.9-56.9%). The HSV-2 seropositivity was independently associated with older age, low education level, non-Han minority, migration status, working in lower-tier venues and positive HIV status. CONCLUSIONS: The study indicates a high prevalence of HSV-2 infection among FSWs, particularly in those working in low-tier venues in study areas, suggesting the needs to further emphasize the inclusion of HSV-2 in surveillance and intervention programs in this population