42 research outputs found

    Are there superposed Mohos in the south-western Alps? New seismic data from fan-profiling reflections

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    International audienceThe Moho preserves imprints of the regional geodynamic evolution of the lithosphere. As such, its detailed topography in divergence or convergence zones has a strong bearing on any geodynamic model. This is still more critical where 3D effects are expected, as in the case of the Alpine chain which exhibits in its western part a short radius of curvature while its trend rotates by 180°. The deep structure of this zone, characterized by a peculiar imbrication of highdensity material of lower crust or mantle origin, remains a puzzle. In September 1999 a new controlled-source-seismology experiment was carried out in the south-western Alps, in the area between the Pelvoux, Dora Maira and Argentera massifs. Five shots were recorded with 130 seismic stations deployed on a total of nine fan- and one in-line profiles. It aimed at getting information on the Moho depth in a hitherto blank area, and discussing the existence of the hypothetical Briançonnais mantle flake mapped in 1986 by the ECORS-CROP experiment. Fan profiles recorded at critical distance for reflections from the European Moho allowed us to map in detail the thickening of the crust from the Mediterranean coastline (27 km) to the root zone (55 km). The zone just south of the Pelvoux massif is characterized by a rather flat, 40-km-deep Moho, which distorts the isobaths in thickening the crust along the Durance valley. Beneath the Argentera massif and just north of it, we evidence a strong dip of the Moho down to 51 km, whereas previous maps predicted depths of 40–46 km only. A new, detailed map of the European Moho can be drawn, which integrates depth data measured at ~ 300 reflection midpoints. However the experiment could not establish the continuity of the Briançonnais mantle flake over a large area in the internal Alps. We observed several reflectors in the 15–31-km depth range. One of them is the Ubaye reflector, a 20-km-long, 23–31-km-deep structure. It might correspond to the Briançonnais mantle flake, although it is located much farther south than the reflector mapped in 1986. New investigations will be necessary to state whether its origin is crustal or due to wedging of mantle material

    Experimental pressure solution compaction of synthetic halite/calcite aggregates.

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    Experimental observations are reported of weakening of sediment-like aggregates by addition of hard particles. Sieved mixtures of calcite and halite grains are experimentally compacted in drained pressure cells in the presence of a saturated aqueous solution. The individual halite grains deform easily by pressure solution creep whereas calcite grains act as hard objects and resist compaction. The fastest rate of compaction of the mixed aggregate is not obtained for a 100% halite aggregate but for a content of halite grains between 45% and 75%. We propose that this unusual compaction behavior reflects the competition between two mechanisms at the grain scale: intergranular pressure solution at grain contacts and grain boundary healing between halite grains that prevent further compaction

    HIV Testing and Diagnosis Rates in Kiev, Ukraine: April 2013-March 2014

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    Data from Ukraine on risk factors for HIV acquisition are limited. We describe the characteristics of individuals testing for HIV in the main testing centres of the Ukrainian capital Kiev, including HIV risk factors, testing rates, and positivity rates. As part of a larger study to estimate HIV incidence within Kiev City, we included questions on possible risk factors for HIV acquisition and testing history to existing systems in 4 infectious disease clinics. Data were provided by the person requesting an HIV test using a handheld electronic tablet. All persons (≥16 yrs) presenting for an HIV test April 2013-March 2014 were included. Rates per 100,000 were calculated using region-specific denominators for Kiev. During the study period 6370 individuals tested for HIV, equivalent to a testing rate of 293.2 per 100,000. Of these, 467 (7.8%) were HIV-positive, with the highest proportion positive among 31-35 year olds (11.2%), males (9.4%), people who inject drugs (PWID) (17.9%) and men who have sex with men (MSM) (24.1%). Using published population size estimates of MSM, diagnosis rates for MSM ranged from 490.6 to 1548.3/100,000. A higher proportion of heterosexual women compared to heterosexual men reported contact with PWID, (16% vs. 4.7%) suggesting a bridging in risk between PWID and their sexual partners. Collection of HIV risk factor information in Kiev, essential for the purposes of developing effective HIV prevention and response tools, is feasible. The high percentage of MSM among those testing positive for HIV, may indicate a significant level of undisclosed sex between men in national figures

    A Phylogenetic Analysis of Human Immunodeficiency Virus Type 1 Sequences in Kiev: Findings Among Key Populations

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    Background: The human immunodeficiency virus (HIV) epidemic in Ukraine has been driven by a rapid rise among people who inject drugs, but recent studies have shown an increase through sexual transmission. Methods: Protease and reverse transcriptase sequences from 876 new HIV diagnoses (April 2013–March 2015) in Kiev were linked to demographic data. We constructed phylogenetic trees for 794 subtype A1 and 64 subtype B sequences and identified factors associated with transmission clustering. Clusters were defined as ≥2 sequences, ≥80% local branch support, and maximum genetic distance of all sequence pairs in the cluster ≤2.5%. Recent infection was determined through the limiting antigen avidity enzyme immunoassay. Sequences were analyzed for transmitted drug resistance mutations. Results Thirty percent of subtype A1 and 66% of subtype B sequences clustered. Large clusters (maximum 11 sequences) contained mixed risk groups. In univariate analysis, clustering was significantly associated with subtype B compared to A1 (odds ratio [OR], 4.38 [95% confidence interval {CI}, 2.56–7.50]); risk group (OR, 5.65 [95% CI, 3.27–9.75]) for men who have sex with men compared to heterosexual males; recent, compared to long-standing, infection (OR, 2.72 [95% CI, 1.64–4.52]); reported sex work contact (OR, 1.93 [95% CI, 1.07–3.47]); and younger age groups compared with age ≥36 years (OR, 1.83 [95% CI, 1.10–3.05] for age ≤25 years). Females were associated with lower odds of clustering than heterosexual males (OR, 0.49 [95% CI, .31–.77]). In multivariate analysis, risk group, subtype, and age group were independently associated with clustering (P < .001, P = .007, and P = .033, respectively). Eighteen sequences (2.1%) indicated evidence of transmitted drug resistance. Conclusions Our findings suggest high levels of transmission and bridging between risk groups

    Impact of CD4 and CD8 dynamics and viral rebounds on loss of virological control in HIV controllers

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    Objective: HIV controllers (HICs) spontaneously maintain HIV viral replication at low level without antiretroviral therapy (ART), a small number of whom will eventually lose this ability to control HIV viremia. The objective was to identify factors associated with loss of virological control. Methods: HICs were identified in COHERE on the basis of \ue2\u89\ua55 consecutive viral loads (VL) \ue2\u89\ua4500 copies/mL over \ue2\u89\ua51 year whilst ART-naive, with the last VL \ue2\u89\ua4500 copies/mL measured \ue2\u89\ua55 years after HIV diagnosis. Loss of virological control was defined as 2 consecutive VL &gt;2000 copies/mL. Duration of HIV control was described using cumulative incidence method, considering loss of virological control, ART initiation and death during virological control as competing outcomes. Factors associated with loss of virological control were identified using Cox models. CD4 and CD8 dynamics were described using mixed-effect linear models. Results: We identified 1067 HICs; 86 lost virological control, 293 initiated ART, and 13 died during virological control. Six years after confirmation of HIC status, the probability of losing virological control, initiating ART and dying were 13%, 37%, and 2%. Current lower CD4/CD8 ratio and a history of transient viral rebounds were associated with an increased risk of losing virological control. CD4 declined and CD8 increased before loss of virological control, and before viral rebounds. Discussion: Expansion of CD8 and decline of CD4 during HIV control may result from repeated low-level viremia. Our findings suggest that in addition to superinfection, other mechanisms, such as low grade viral replication, can lead to loss of virological control in HICs

    The 16,000-event 2003–2004 earthquake swarm in Ubaye (French Alps)

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    International audienceThe Ubaye valley, one of the most active seismic zones in the French Alps, was visited in 2003–2004 by a prolific and protracted earthquake swarm with a maximum magnitude M L = 2.7. The seismic activity clustered along a 9-km-long, 3- to 8-km-deep rupture zone which trends NW-SE across the valley and dips 80°SW. Focal mechanisms for the larger shocks show either normal faulting with a SW-NE trending extension direction or NW-SE strike slip with right lateral displacement. The activity initiated in the central part of the rupture zone, diffused to its periphery, and eventually concentrated in its southeastern deeper part. A permanent station situated above the swarm allowed us to monitor the entire phenomenon from its inception to its conclusion. The complete time series includes more than 16,000 events, with shocks down to magnitude M L = −1.3. It shows bursts of activity, separated by quiescent periods, with no well-defined subswarms as observed in other similar studies. The Gutenberg-Richter b value significantly varied between 1.0 and 1.5 in the course of the phenomeno
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