New ion trap for atomic frequency standard applications

A novel linear ion trap that permits storage of a large number of ions with reduced susceptibility to the second-order Doppler effect caused by the radio frequency (RF) confining fields has been designed and built. This new trap should store about 20 times the number of ions a conventional RF trap stores with no corresponding increase in second-order Doppler shift from the confining field. In addition, the sensitivity of this shift to trapping parameters, i.e., RF voltage, RF frequency, and trap size, is greatly reduced

Atomic frequency standards for ultra-high-frequency stability

The general features of the Hg-199(+) trapped-ion frequency standard are outlined and compared to other atomic frequency standards, especially the hydrogen maser. The points discussed are those which make the trapped Hg-199(+) standard attractive: high line Q, reduced sensitivity to external magnetic fields, and simplicity of state selection, among others

Simple analytic potentials for linear ion traps

A simple analytical model was developed for the electric and ponderomotive (trapping) potentials in linear ion traps. This model was used to calculate the required voltage drive to a mercury trap, and the result compares well with experiments. The model gives a detailed picture of the geometric shape of the trapping potenital and allows an accurate calculation of the well depth. The simplicity of the model allowed an investigation of related, more exotic trap designs which may have advantages in light-collection efficiency

The JPL trapped mercury ion frequency standard

In order to provide frequency standards for the Deep Space Network (DSN) which are more stable than present-day hydrogen masers, a research task was established under the Advanced Systems Program of the TDA to develop a Hg-199(+) trapped ion frequency standard. The first closed-loop operation of this kind is described. Mercury-199 ions are confined in an RF trap and are state-selected through the use of optical pumping with 194 nm UV light from a Hg-202 discharge lamp. Absorption of microwave radiation at the hyperfine frequency (40.5 GHz) is signaled by atomic fluorescence of the UV light. The frequency of a 40.5 GHz oscillator is locked to a 1.6 Hz wide atomic absorption line of the trapped ions. The measured Allan variance of this locked oscillator is currently gamma sub y (pi) = 4.4 x 10 to the minus 12th/square root of pi for 20 is less than pi is less than 320 seconds, which is better stability than the best commercial cesium standards by almost a factor of 2. This initial result was achieved without magnetic shielding and without regulation of ion number

An apparatus for the electrodynamic containment of charged macroparticles

The dynamic moition of the ions contained in the trapped (199)Hg+ frequency standard contributes to the stability of the standard. In order to study these dynamics, a macroscopic analog of the (199)Hg+ trap is constructed. Containment of micron-sized particles in this trap allows direct visual observation of the particles' motion. Influenced by the confining fields and their own Coulomb repulsion, the particles can form stable arrays

Domestic mobility and experiences of disconnection from sexual health care among gay and bisexual men in Australia: Insights from a qualitative study

Previous research on mobility and HIV acquisition among gay and bisexual men (GBM) has focused on: (1) changed sexual practices in the context of travel; and (2) the association between migration and increased HIV risk. To date, little attention has been given to continuity of sexual health and HIV-prevention services in the context of relocating between different cities or regions within the same country. Methods: Drawing on in-depth interviews with 17 GBM recently diagnosed with HIV, we explored these men's access to sexual health care in the period prior to diagnosis. Results: At least five of these 17 men's accounts provided examples of becoming disconnected from sexual health care because of mobility within Australia. For some men, this disconnection from care also included loss of access to pre-exposure prophylaxis (PrEP). In all these men's accounts, reconnection with services only came about at the time of seeking the HIV test associated with their diagnosis. The fact that men who had previously been well connected to sexual health services (as indicated by early uptake of PrEP, or regular HIV/STI testing) did not easily access similar services after relocating suggest that there are other factors - such as the social and physical environment - that have an important bearing on retention in sexual health care. Conclusions: There is a need for more comprehensive data collection related to mobility in order to ascertain its relative importance. Regarding policy and practice, there are also opportunities for a more formalised process for interstate referral of clients of sexual health services

Sexual negotiation in the AIDS era: negotiated safety revisited

Objective: To test the safety of the 'negotiated safety' strategy - the strategy of dispensing with condoms within HIV-seronegative concordant regular sexual relationships under certain conditions. Method: Data from a recently recruited cohort of homosexually active men (Sydney Men and Sexual Health cohort, n = 1037) are used to revisit negotiated safety. The men were surveyed using a structured questionnaire and questions addressing their sexual relationships and practice, their own and their regular partner's serostatus, agreements entered into by the men concerning sexual practice within and outside their regular relationship, and contextual and demographic variables. Results: The findings indicate that a significant number of men used negotiated safety as an HIV prevention strategy. In the 6 months prior to interview, of the 181 men in seroconcordant HIV-negative regular relationships, 62% had engaged in unprotected anal intercourse within their relationship, and 91% (165 men) had not engaged in unprotected anal intercourse outside their relationship. Of these 165 men, 82% had negotiated agreements about sex outside their relationship. The safety of negotiation was dependent not only on seroconcordance but also on the presence of an agreement; 82% of the men who had not engaged in unprotected anal intercourse outside their regular relationship had entered into an agreement with their partner, whereas only 56% of those who had engaged in unprotected anal intercourse had an agreement. The safety of negotiation was also related to the nature of the safety agreement reached between the men and on the acceptability of condoms. Agreements between HIV-negative seroconcordant regular partners prohibiting anal intercourse with casual partners or any form of sex with a casual partner were typically complied with, and men who had such negotiated agreements were at low risk of HIV infection. Conclusions: The adoption of the strategy of negotiated safety among men in HIV-seronegative regular relationships may help such men sustain the safety of their sexual practice

“…not some young tourist”: The male overseas-acquired HIV social research study

As with the trend in the rest of Australia, the majority of HIV diagnoses in Western Australia (WA) over the past 20 years have been amongst men who have sex with men in Australia. However, a differing trend seen more recently in WA has been the number of HIV diagnoses among heterosexual and homosexual men who acquired HIV while overseas compared to other states. The number of Western Australians acquiring HIV overseas has increased from 41 people in 2002-2004 to 91 people in 2005-2007. The upward trend of overseas acquired notifications continued in 2008-2009 (Combs and Giele 2009; DoH (WA) 2009). While the epidemiological data clearly showed an increase in overseas acquired HIV, there was little information on why the increase was occurring. The Male Overseas Acquired HIV Social Research Study investigated the social, cultural, behavioural and cognitive factors which may have contributed to the overseas-acquisition of HIV by male WA residents. The study used a qualitative approach to collecting and analysing data from in depth interviews with men who had acquired HIV while travelling or working overseas. The study was a joint project of the WA Centre for Health Promotion Research, National Centre in HIV Social Research, National Centre in HIV Epidemiology and Clinical Research and the Australian Research Centre in Sex, Health and Society and funded by the Western Australian Department of Health, Sexual Health and Blood Borne Virus Program. Men were recruited through the WA AIDS Council, Royal Perth Hospital, Fremantle Hospital, Northern Territory AIDS and Hepatitis Council and Clinic 34, Darwin. Fourteen men participated in the study during 2008 and 2009

“…not some young tourist”: The male overseas-acquired HIV social research study

As with the trend in the rest of Australia, the majority of HIV diagnoses in Western Australia (WA) over the past 20 years have been amongst men who have sex with men in Australia. However, a differing trend seen more recently in WA has been the number of HIV diagnoses among heterosexual and homosexual men who acquired HIV while overseas compared to other states. The number of Western Australians acquiring HIV overseas has increased from 41 people in 2002-2004 to 91 people in 2005-2007. The upward trend of overseas acquired notifications continued in 2008-2009 (Combs and Giele 2009; DoH (WA) 2009). While the epidemiological data clearly showed an increase in overseas acquired HIV, there was little information on why the increase was occurring. The Male Overseas Acquired HIV Social Research Study investigated the social, cultural, behavioural and cognitive factors which may have contributed to the overseas-acquisition of HIV by male WA residents. The study used a qualitative approach to collecting and analysing data from in depth interviews with men who had acquired HIV while travelling or working overseas. The study was a joint project of the WA Centre for Health Promotion Research, National Centre in HIV Social Research, National Centre in HIV Epidemiology and Clinical Research and the Australian Research Centre in Sex, Health and Society and funded by the Western Australian Department of Health, Sexual Health and Blood Borne Virus Program. Men were recruited through the WA AIDS Council, Royal Perth Hospital, Fremantle Hospital, Northern Territory AIDS and Hepatitis Council and Clinic 34, Darwin. Fourteen men participated in the study during 2008 and 2009

Sex in Two Cities - Gay Men, Risk and HIV in Perth and Sydney

After massive and sustained reductions in HIV risk behaviour amongst Australian gay men in the 1980's and early 1990's, since 1996 there have been signs of small but significant increases in unprotected anal intercourse. Gay communities are responding to a post crisis context. However, is this response constant across different locations? This paper investigates changes in sexual negotiation and behaviour amongst gay men in the relatively small Australian city of Perth between 1998 and 2002 and compares these results to similar studies in Sydney, an Australian HIV epicentre city. A number of important similarities and differences between the Perth and Sydney samples are identified, particularly in casual contexts and disclosure of HIV status, identifying that isolated or smaller cities may experience similar phenomena to larger cities, but these may be due to different reasons. The findings point to the need for complementary qualitative research and cautions health promotion practitioners to test their assumptions when developing responses to prevent HIV transmission