Metrological characterization of custom-designed 894.6 nm VCSELs for miniature atomic clocks.

We report on the characterization and validation of custom-designed 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), for use in miniature Cs atomic clocks based on coherent population trapping (CPT). The laser relative intensity noise (RIN) is measured to be 1 × 10(-11) Hz(-1) at 10 Hz Fourier frequency, for a laser power of 700 µW. The VCSEL frequency noise is 10(13) · f(-1) Hz(2)/Hz in the 10 Hz < f < 10(5) Hz range, which is in good agreement with the VCSEL's measured fractional frequency instability (Allan deviation) of ≈ 1 × 10(-8) at 1 s, and also is consistent with the VCSEL's typical optical linewidth of 20-25 MHz. The VCSEL bias current can be directly modulated at 4.596 GHz with a microwave power of -6 to +6 dBm to generate optical sidebands for CPT excitation. With such a VCSEL, a 1.04 kHz linewidth CPT clock resonance signal is detected in a microfabricated Cs cell filled with Ne buffer gas. These results are compatible with state-of-the-art CPT-based miniature atomic clocks exhibiting a short-term frequency instability of 2-3 × 10(-11) at τ = 1 s and few 10(-12) at τ = 10(4) s integration time..

Long-term HIV/AIDS-related prevention behaviours among men having sex with men: Switzerland 1992-2000.

The aim of this paper is to present trends in reported HIV-related behaviours among men having sex with men (MSM) in Switzerland. In 1992, 1994, 1997 and 2000 a standardized anonymous questionnaire was placed in gay newspapers and distributed in gay associations. High levels of protection (no anal sex or consistent condom use) with casual partners were found: around 90%, with a peak in 1994 and a slight decrease in 2000 to the level of 1992. With the steady partner, the level of protection was 57% in 1992, 61% in 1997 and decreased in 2000 to the same level as in 1992. The proportion of couples with both HIV statuses known increased from 49% in 1994 to 59% in 2000. In 2000, 26% of concordant HIV negative couples protected themselves compared to 83% of those exposed to an actual or potential risk (HIV status discordant or unknown). Within each category of couples, there was no change over time in the level of reported practice of anal sex and condom use. This slight decrease in prevention behaviour justifies efforts to maintain HIV/AIDS prevention targeted at gay men.

Men having sex with men and HIV/AIDS prevention in Switzerland: 1987-2000.

Although the latest survey on prevention behaviours of men having sex with men (MSMs) in Switzerland shows a decreasing number of HIV cases since 1992, a decrease in the protection level has also been observed. This could lead to a higher rate of HIV notifications in 2001 compared to 2000.

Management of the risk of HIV infection in male homosexual couples.

OBJECTIVES: To study the ways of managing HIV risk within male homosexual steady relationships (gay couples), including factors associated with consistent condom use during anal sex with the steady partner. METHOD: An anonymous and standardized questionnaire completed by a convenience sample of homosexuals in Switzerland in 1997 (n = 1097). Information on the couple was provided by the 74% (n = 786) of male respondents who reported having a steady partner in the past 12 months. Data were analysed by contingency tables and logistic regression. RESULTS: Different ways of managing HIV risk were reported: negotiated safety (both HIV negative, condoms abandoned) was chosen by one quarter of the couples, but the most frequent solution was reliance on condoms for anal sex, chosen by more than four in 10. Altogether 84% of couples exhibited safe management of HIV risk within their partnership. The 16% of couples showing inadequate management of HIV risk within the couple mostly relied on questionable assumptions about past or present risks. A total of 74% of couples had spoken about managing HIV risk with possible casual partners. Reported behaviour with the steady partner and with casual partners was highly consistent with claimed strategies chosen to manage HIV risk. Consistent condom use with the steady partner was mostly associated with variables characterizing the relationship: initial 2 years of the relationship, discordant or unknown serological HIV status, non-exclusivity. CONCLUSION: Gay couples manage HIV risk in a variety of ways. Most strategies provide adequate protection with casual partners, but leave gaps in protection between the steady partners themselves.

Adolescent sexuality: the gender gap.

The aim of this paper is to determine gender differences as regards adolescent sexuality, in order to improve the adjustment of prevention programmes to boys' and girls' specific needs. Data were collected as part of the Swiss Multicentric Adolescent Survey on Health. Anonymous questionnaires were distributed in school classes among a national representative sample of about 9,300 adolescents (15 to 20 years old). About 45% of the total sample reported a previous sexual experience. Differences between boys and girls were identified by means of bivariate and multivariate analyses. A higher proportion of Swiss girls report intra-family discussions about sexuality, having had a previous sexual experience, having sexual intercourse regularly, having had only one partner, and using contraception regularly. A higher proportion of Swiss boys report positive attitudes towards condoms and using condoms regularly. Variables independently associated with the occurrence of first sexual intercourse before 15 years old also show gender differences, notably as regards health behaviours and social adjustment. The findings suggest that prevention programmes should emphasize, among boys, responsibility in contraception and the need for protection in situations of multipartnership, and among girls, a positive attitude towards condom use and an increased familiarity with condoms presented both in a perspective of contraception and prevention of STDs.

[AIDS prevention in homosexuals in Switzerland: adaptation to risks according to type of partner]. / La prévention du sida chez les homosexuels en Suisse: adaptation au risque de sida selon le type de partenaire.

OBJECTIVE: To evaluate the effectiveness of AIDS prevention and modes of adaptation to risk among gay men. Swiss results are presented from an international study conducted in 8 European countries. METHOD: A self-administered questionnaire was published in gay magazines and distributed by gay organizations and clubs. 934 questionnaires were returned in Switzerland. RESULTS: More than 80% of the respondents report no risk behaviours in the last 12 months. Among all respondents three main modes of adaptation to risk were found: avoidance (no partner, no penetration), protection (condom use), non-use of condoms by stable couples (this assumes an agreement between partners). With casual partners 39% avoid penetration, 49% use condoms and 12% do not use them consistently. With stable partners penetration is more frequent; protection and non use of condoms are found with equal frequency. Nevertheless, 10% of those who report always using condoms say that they have been exposed to a risk, while a third of those who do not always use condoms admitted having taken such a risk. CONCLUSIONS: Prevention campaigns must continue and focus especially on factors linked to the non use of condoms in couples in stable relationships (poor communication, exaggerated trust).

[Prevention of AIDS in drug addicts in Switzerland: an encouraging development]. / Prévention du sida chez les toxicomanes en Suisse: une évolution encourageante.

Switzerland has adopted a prevention strategy including the promotion of non-sharing injection material and use of condoms. The access to sterile equipment has been made easier, but regional differences still exist. Studies conducted between 1989 and 1992 among drug users in different Swiss regions are reviewed in order to examine if progress in prevention occurred. Syringe sharing diminished everywhere, but rather high sharing rates persist where sterile material is less accessible. Condom use increased, but the situation is still unsatisfactory considering the high HIV prevalence among i.v. drug users. Where several surveys have been conducted consecutively, a stabilization of HIV prevalence was observed. This suggests a slowing down of the progression of the epidemic among drug users. These results, obtained in few years, are encouraging in the light of the pessimism which prevailed at the beginning of the epidemic about the ability of drug users to adopt preventive behaviour.

Sexual behaviour of gay and bisexual men in eight European countries.

To compare the sexual behaviour and HIV risk reduction strategies of gay and bisexual men in Europe, a survey, disseminated via the gay press and gay associations, was conducted amongst gay and bisexual men in Austria, Switzerland, Germany, Denmark, France, Great Britain, Italy and the Netherlands during the autumn and winter of 1991. By end March of 1992, 12,347 completed questionnaires had been obtained. A preliminary analysis shows striking similarities in patterns of sexual behaviour of gay men in the 8 European countries but indicates that strategies of risk management concerning HIV and AIDS vary widely. While the majority of gay men have multiple partners, and intercourse is more common with stable partners than with causal partners. The proportion of men who, during the past 12 months, engaged in unprotected anal intercourse with a partner with different or unknown HIV-status ranged from 1/3 in East Germany to 1/6 in UK. However, reported incidence over the past 12 months of STDs, other than HIV infection, was similar in all countries (2%-3%). The reported HIV antibody prevalence varied from less than 7% in East Germany, Italy and the United Kingdom to 15% in Denmark and 17% in France. HIV risk reduction strategies appear to be most common in those countries where the gay community had been included in targeted prevention campaigns during the early phase of the AIDS epidemic. Considering the high proportion of gay men engaging in high risk activities it is imperative that prevention efforts are sustained and improved.