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V Pokrovsky

Publications and source records attributed to V Pokrovsky.

At least 19 recordsLinked to original sources

Domain wall depinning in random media by ac fields.

The viscous motion of an interface driven by an ac external field of frequency omega(0) in a random medium is considered here in the nonadiabatic regime. The velocity exhibits a smeared depinning transition showing a double hysteresis which is absent in the adiabatic case omega(0)-->0. Using scaling arguments and an approximate renormalization group calculation we explain the main characteristics of the hysteresis loop. In the low frequency limit these can be expressed in terms of the depinning threshold and the critical exponents of the adiabatic case.

Journal Article↗

Hysteretic dynamics of domain walls at finite temperatures.

Theory of domain wall motion in a random medium is extended to the case when the driving field is below the zero-temperature depinning threshold and the creep of the domain wall is induced by thermal fluctuations. Subject to an ac drive, the domain wall starts to move when the driving force exceeds an effective threshold which is temperature and frequency dependent. Similar to the case of zero temperature, the hysteresis loop displays three dynamical phase transitions at increasing ac field amplitude h(0). The phase diagram in the 3D phase space of temperature, driving force amplitude, and frequency is investigated.

Journal Article↗

An HIV type 1 subtype A strain of low genetic diversity continues to spread among injecting drug users in Russia: study of the new local outbreaks in Moscow and Irkutsk.

An explosive epidemic of human immunodeficiency virus type 1 (HIV-1) has been documented among injecting drug users (IDUs) in the former Soviet Union republics. In 1999, the two largest local IDU outbreaks of HIV-1 infection in the Russian Federation were registered in the Moscow and Irkutsk regions, where 13,004 HIV-1 cases were identified (44% of the total number of HIV-1 infections in Russia in 1999). To study the prevailing genetic variants and to estimate the genetic diversity of HIV-1 in these outbreaks, 60 samples from Moscow (n = 36) and from Irkutsk (n = 24) were analyzed using the gag/env heteroduplex mobility assay, and the env gp120 V3 encoding regions obtained from 23 individuals were sequenced. Both virus populations were highly homogeneous (the means of pairwise nucleotide distance were 1.75 +/- 0.83 and 2.35 +/- 1.59 for Irkutsk and Moscow, respectively), and similar to the subtype A viruses obtained earlier from IDUs in the former Soviet Union. The subtype A HIV-1 variant thus dominates in the largest HIV-1 outbreaks among IDUs in the Russian Federation.

Adolescent↗

An AB recombinant and its parental HIV type 1 strains in the area of the former Soviet Union: low requirements for sequence identity in recombination. UNAIDS Virus Isolation Network.

In the former Soviet Union (SU) increasing numbers of HIV-1 infections among injecting drug users (IDU) have been reported, especially in the Ukraine. The main subtype transmitted among the IDUs seems to be subtype A, but limited numbers of subtype B cases have also been reported. In Kaliningrad, Russia, an AB recombinant strain was earlier shown to be responsible for the local outbreak. Here we describe the genetic relationship of HIV-1 strains circulating among IDUs in the former SU. For subtype A and the AB recombinant strains nearly full-length genomes were sequenced, and for one subtype B strain the entire envelope gene was cloned. The relationship between the AB recombinant strain and the subtype A and subtype B strains and the mosaic structure of the recombinant was studied by phylogenetic analysis. Ukrainian A and B strains were shown to be the probable parental viruses of the Kaliningrad AB recombinant strain. In the envelope gene the recombination breakpoint could also be precisely mapped to a region of similarity of only 14 base pairs. This suggests that only short stretches of absolute sequence identity may be needed for efficient RNA recombination between HIV-1 subtypes.

Base Sequence↗

HIV infection associated with drug injecting in the newly independent states, eastern Europe: the social and economic context of epidemics.

AIMS: We review recent trends in HIV associated with injecting drug use (IDU) in the Newly Independent States (NIS) in eastern Europe, including Belarus, Moldova, Russia, Ukraine, and Kazakhstan in central Asia. We aim to draw attention to the social and economic "risk environments" in which rapid HIV spread among IDUs has occurred. METHODS: Findings draw on centrally registered HIV surveillance data, published research studies and assessment reports funded by international development agencies. FINDINGS: Since 1995, there is evidence of rapid HIV spread in Belarus, Kazakhstan, Moldova, Russia and Ukraine, with estimates suggesting between 50% and 90% of new HIV infections among IDUs. At the same time, there have been rapid increases in the incidence of syphilis and declines in health and welfare status, including outbreaks of diphtheria, tuberculosis and cholera. Findings emphasize the potential influence of the social and economic context in creating the "risk environments" conducive to HIV and epidemic spread. Key factors include: rapid diffusions in IDU; population migration and mixing; economic transition and decline; increasing unemployment and impoverishment; the growth of informal economies; modes of drug production, distribution and consumption; declines in public health revenue and infrastructure; and political, ideological and cultural transition. CONCLUSIONS: An understanding of the social and economic contexts mediating HIV spread is a prerequiste to identifying the environmental "pre-conditions" of epidemic outbreaks, and thus also, for predicting and preventing HIV transmission. The "risk environment" may influence the efficacy of individual and community-level HIV prevention and highlights the concomitant urgency for interventions targeting social and environmental change.

Europe, Eastern↗

A sudden epidemic of HIV type 1 among injecting drug users in the former Soviet Union: identification of subtype A, subtype B, and novel gagA/envB recombinants.

The former Soviet Union republics have experienced an explosive human immunodeficiency virus type 1 (HIV-1) epidemic among injecting drug users (IDUs), consisting mainly of subtype A viruses originated from a point source (Bobkov et al.: AIDS Res Hum Retroviruses 1997;13:1195-1201). To determine whether new HIV-1 subtypes have entered the IDU population, 46 samples derived from IDUs in Russia (n = 39) and the Ukraine (n = 7) were genotyped by heteroduplex mobility assay (HMA). It was shown that 83% of IDU HIV-1 strains found in both countries belong to genetic subtype A. However, env subtype B was also found in 17% of cases. The sequence data showed a marked intrasubtype homogeneity of HIV-1 (the average means of interpatient genetic distance were 1.1 and 1.7% [in the gag gene] or 1.8 and 2.3% [in the env gene] for subtype A and subtype B, respectively), confirming the hypothesis of a point source of virus for each subtype variant. Moreover, recombinant gagA/envB variants originating from those two strains were also found in two samples collected in the Kaliningrad region of Russia. In conclusion, our results suggest that two strains of HIV-1 belonging to different genetic subtypes, A and B, as well as gagA/envB recombinants between genomes of these strains, are now circulating simultaneously among IDUs in the former Soviet Union.

Adult↗

An HIV type 1 epidemic among injecting drug users in the former Soviet Union caused by a homogeneous subtype A strain.

Epidemiological data have demonstrated rapid growth of HIV-1 infections among injecting drug users (IDUs) in the Ukraine and Russia, during 1996. Here we describe the results of genetic analysis of isolates derived from 12 HIV-1-infected IDUs in different sites of Russia and the Ukraine. The blood samples were taken within a 1- to 2-month period after the first HIV-1-positive test. The results of the heteroduplex mobility assay as well as gag/env phylogenetic analysis reveal that all sequences belong to gag/env genetic subtype A. Moreover, interpatient genetic distances between the nucleotide sequences encompassing the C2-V3, the V4-V5, and p17-encoding regions within this group were low (the average means were 0.9, 1.3, and 0.4%, respectively). These data show a marked homogeneity of HIV-1, probably spreading during primary infection. It is possible that the current epidemic of subtype A HIV-1 among IDUs in the former Soviet Union is caused by a point source exposure.

Adolescent↗

Infections in hospitalised Russian children with AIDS.

OBJECTIVES: (1) To determine the most common infections in hospitalised children with AIDS. (2) To identify the pathogens causing the above infections. (3) To investigate the possibility of nosocomial transmission of potential pathogens in a Russian AIDS hospital. SETTING: Russian AIDS Hospital for Children. SUBJECTS AND METHODS: Swabs/samples of skin, mouth, nose, urine and stool were collected from 95 hospitalised children with AIDS, 12 of their mothers and 11 health care workers in contact with the children. Hospital objects were also sampled. The predominant isolates from the infection sites were speciated. Antibiotic sensitivity profiles, phagotyping and gel electrophoresis of cell lysates were used for the epidemiological marking of Candida albicans, Staphylococcus aureus and Klebsiella pneumoniae. RESULTS: Oral infections were the most prevalent infections in this study group. The most frequently isolated micro-organisms were C. albicans, S. aureus, K. pneumoniae and Escherichia coli. The results of the epidemiological study suggests nosocomial transmission of these strains. CONCLUSIONS: The present chemoprophylaxis programme for opportunistic oral infections requires revision. Systems of microbiological surveillance and cross-infection control monitoring in relation to immunocompromised patients need to be developed to decrease the possibility of nosocomial transmission of potential pathogens between hospitalised children with AIDS, their mothers and health care providers.

AIDS-Related Opportunistic Infections↗

Genetic heterogeneity of HIV type 1 in Russia: identification of H variants and relationship with epidemiological data.

HIV-genetic subtypes were analyzed in 130 subjects from the Russian Federation, by the HMA technique. Six subtypes were identified in heterosexuals, including A, B, C, D, G, and H; however, homosexual men were infected predominantly with the B subtype (33 of 35). The subtype A isolates were found in population of intravenous drug users. HMA successfully identifies 128/130 DNA samples; the phylogenetic analysis of the V1/V5 gp120 encoding region derived from another two samples demonstrated that these isolate belong to subtype H.

Amino Acid Sequence↗