Sexual risk behavior and risk factors for HIV-1 seroconversion in homosexual men participating in the Tricontinental Seroconverter Study, 1982-1994

Trends in sexual behavior associated with incident infection with human immunodeficiency virus (HIV) type 1 are described and a case-control study was conducted to examine risk factors for HIV seroconversion in homosexual men who became infected with HIV between 1982 and 1994 from four geographic sites: Amsterdam, the Netherlands; San Francisco, California; Vancouver, Canada; and Sydney, Australia. Changes in sexual behaviors were evaluated from cohort visits in the preseroconversion, seroconversion, and postseroconversion intervals and were further examined over three time periods: 1982-1984, 1985-1987, and 1988-1994. In a case-control study, sexual behaviors, substance use, and presence of sexually transmitted disease were compared between 345 HIV-positive cases and 345 seronegative controls matched by visit date and site. Receptive anal intercourse was the sexual behavior most highly associated with seroconversion. The odds ratio (OR) per receptive anal intercourse partner increase was 1.05 (95% confidence interval (CI) 1.02-1.09). To more carefully examine risk associated with receptive oral intercourse, analyses were done in a subgroup of men who reported no or one receptive anal intercourse partner. The risk (OR) associated with receptive oral intercourse partner increase was 1.05 (95% CI 1.0-1.11). In multivariate conditional logistic regression analyses, presence of sexually transmitted disease (OR = 3.39, 95% CI 1.95-5.91) and amphetamine use (OR = 2.55, 95% CI 1.26-5.15) were independently associated with seroconversion. Although the prevalence of major risk factors has decreased over time, the associations of these behaviors and HIV infection persist, suggesting that these risk behaviors remain important avenues for public health interventions.     

Pyrochlore Phase Formation in the System Bi2O3–ZnO–Ta2O5

The subsolidus phase diagram of the system Bi₂O₃–ZnO–Ta₂O₅ in the region of the cubic pyrochlore phase has been determined at 1050°C. This phase forms a solid solution area that includes the ideal composition P, Bi₃Zn₂Ta₃O₁₄; possible solid solution mechanisms are proposed, supported by density measurements of Zn-deficient solid solutions. The general formula of the solid solutions is Bi_{3+ y} Zn_{2− x} Ta_{3− y} O_{14− x − y} , based on the creation of Zn²⁺, O²⁻ vacancies in Zn-deficient compositions and a variable Bi/Ta ratio.     

钢筋混凝土烟囱恢复力特性试验研究

从钢筋混凝土烟囱实际特点出发,以四个大尺寸烟囱试件的试验结果为依据,讨论了不同剪跨比、不同轴压比下钢筋混凝土烟囱的滞回特性,提出了能够反映钢筋混凝土烟囱特点的四线型恢复力模型及其特征点的计算方法,有关结论可供烟囱抗震设计参考。     

Some recent developments in polysilane chemistry

(I) Ordered and disordered polysilane copolymers: Condensation of ClSiMe₂Si(n-Hex)₂SiMe₂Cl with Na/K in toluene at 90°C produced a polymer with a strongly bimodal molecular weight distribution. The high-M _w and low-M _w portions were separated by fractional precipitation with 2-propanol, and the properties of the two fractions were investigated.²⁹Si-NMR spectra show that the low-M _w fraction is fully ordered but the high-M _w fraction is randomized. (II) Liquid crystalline polysilanes: Condensation ofn-Bu(n-Hex)SiCl₂ with Na in toluene led to a homopolymer which is a rubbery solid at 25°C. The polymer undergoes a second-order transition at –45°C and a first-order (melt) transition at –20°C. X-ray diffraction shows that the polymer has the same structure, a columnar hexagonal lattice, in all three phases; from –20 to >200°C, it exists in a columnar liquid crystalline mesophase. Similar hexagonal mesophases were observed at 25°C for the family of copolymers, (n-Hex₂Si) _n (Alk₂Si) _m , Alk =n-Pentyl,n-Bu,n-Pr, Et, Me.     

Studies on the release of polymeric Langmuir-Blodgett multilayers from the solid supports on which they were prepared

It has been shown that polymeric Langmuir-Blodgett (LB) multilayers may be released from the supports on which they were prepared by first thermally evaporating thin films of stearic acid onto the support. The acid can subsequently be washed away, so undercutting the film and releasing it to float to the water surface. The films were redeposited onto fresh silicon wafers or onto glass microscope slides. Under the optical microscope, the films on the glass microscope slides were clear and featureless. By XRD the transferred films had the same or fewer orders of Bragg peaks and the corresponding bilayer spacings were the same or slightly larger than those of the original films. Thus, it appears that most films lose a small amount of their order in the transfer process. By second harmonic generation (SHG) the transferred alternating LB films formed from a poly(4-vinylpyridine) partially quaternised by reaction with n-docosyl bromide and from the poly(4-vinylpyridinium bromide) formed by the zwitterionic polymerisation of 4-vinylpyridine with 4(12-bromododecyloxy)-4′-trifluoromethylazobenzene displayed essentially the same SHG properties as the original films. Moreover, the SHG films could be stacked successfully to give thicker films. Several of the transferred films, but not all, contained traces of stearic acid, which appears to be present as small domains of Y-type layers. In one typical case, where the LB film consisted of 100 layers of a poly(4-vinylpyridine), it was shown that the amount of stearic acid present corresponded to an average of one monolayer.     

Influence of inert gas species on the growth of silver and molybdenum films via a magnetron discharge

Argon is the process gas of choice for most magnetron sputtering applications due to its large atomic mass, inert chemistry, and relatively low cost. Other inert gases are available for use in sputtering deposition that have varying mass and hence different momentum behaviour during ion bombardment of solid surfaces — affecting sputter yield, particle implantation and incorporation of process gas into deposited films. The plasma discharges generated from these gases vary in terms of the nature and energy of species incident at both target and substrate. In particular, the contribution from energetic neutrals varies as a consequence of the atomic mass of the process gas in comparison to the target material to be sputtered.Magnetron plasma discharges were generated from neon, argon, krypton and xenon gases in DC and mid-frequency pulsed-DC modes with both silver and molybdenum cathodes. The electrical characteristics, such as potential and current at the target and substrate were measured and compared. Thin metallic films were then deposited and analysed in terms of structure; mechanical, optical and electrical properties; and process gas incorporation. The data generated is used to establish the relationship between process gas species, plasma discharge characteristics of those gases, and the subsequent growth and properties of deposited coatings.     

Estimating black carbon aging time-scales with a particle-resolved aerosol model

Understanding the aging process of aerosol particles is important for assessing their chemical reactivity, cloud condensation nuclei activity, radiative properties and health impacts. In this study we investigate the aging of black carbon containing particles in an idealized urban plume using a new approach, the particle-resolved aerosol model PartMC-MOSAIC. We present a method to estimate aging time-scales using an aging criterion based on cloud condensation nuclei activation. The results show a separation into a daytime regime where condensation dominates and a nighttime regime where coagulation dominates. There is also a strong dependence on supersaturation threshold. For the chosen urban plume scenario and supersaturations ranging from 0.1% to 1%, the aging time-scales vary between 11 and 0.068 h during the day, and between 54 and 6.4 h during the night.     

Adsorption-desorption study of benzotriazole in a phosphate-based electrolyte for Cu electrochemical mechanical planarization

In this article, the adsorption-desorption behavior of benzotriazole (BTA) in a phosphate-based electrolyte developed for Cu electrochemical mechanical planarization (ECMP) is studied. The formation of a continuous BTA passive film adsorbed on the Cu surface has been characterized by atomic force microscopy (AFM). Additionally, the adsorption behavior of BTA was found to be mass-transfer-controlled at lower operating potentials (≤0.7 V vs. Ag/AgCl). Using a microfluidic electrochemical device and electrochemical impedance spectrum (EIS), it was also observed that at low BTA concentrations (≤0.002 M), more time was necessary to form an effective passive film on the Cu surface. Furthermore, the desorption time obtained from a potentiometric response to the removal of BTA from the electrolyte increases with increasing BTA concentration or decreasing applied potential. It is critical to expand the operating potential window and to reduce the usage of inhibitors in the proposed ECMP process to enhance the removal rate and the reduction of organic residues. Therefore, the combined microfluidic and electrochemical methodology is proven useful in finding suitable BTA concentrations and a wider potential window.