540 research outputs found
Pattern formation during diffusion limited transformations in solids
We develop a description of diffusion limited growth in solid-solid
transformations, which are strongly influenced by elastic effects. Density
differences and structural transformations provoke stresses at interfaces,
which affect the phase equilibrium conditions. We formulate equations for the
interface kinetics similar to dendritic growth and study the growth of a stable
phase from a metastable solid in both a channel geometry and in free space. We
perform sharp interface calculations based on Green's function methods and
phase field simulations, supplemented by analytical investigations. For pure
dilatational transformations we find a single growing finger with symmetry
breaking at higher driving forces, whereas for shear transformations the
emergence of twin structures can be favorable. We predict the steady state
shapes and propagation velocities, which can be higher than in conventional
dendritic growth.Comment: submitted to Philosophical Magazin
Progress in prevention of mother-to-child transmission of HIV infection in Ukraine: results from a birth cohort study
Background: Ukraine was the epicentre of the HIV epidemic in Eastern Europe, which has the most rapidly accelerating HIV epidemic world-wide today; national HIV prevalence is currently estimated at 1.6%. Our objective was to evaluate the uptake and effectiveness of interventions for prevention of mother-to-child transmission (PMTCT) over an eight year period within operational settings in Ukraine, within the context of an ongoing birth cohort study.Methods: The European Collaborative Study (ECS) is an ongoing birth cohort study in which HIV-infected pregnant women identified before or during pregnancy or at delivery were enrolled and their infants prospectively followed. Three centres in Ukraine started enrolling in 2000, with a further three joining in September 2006.Results: Of the 3356 women enrolled, 21% (689) reported current or past injecting drug use (IDU). Most women were diagnosed antenatally and of those, the proportion diagnosed in the first/second trimester increased from 47% in 2000/01 (83/178) to 73% (776/1060) in 2006/07 (p < 0.001); intrapartum diagnosis was associated with IDU (Adjusted odds ratio 4.38; 95% CI 3.19-6.02). The percentage of women not receiving any antiretroviral prophylaxis declined from 18% (36/205) in 2001 to 7% in 2007 (61/843) p < 0.001). Use of sdNVP alone substantially declined after 2003, with a concomitant increase in zidovudine prophylaxis. Median antenatal zidovudine prophylaxis duration increased from 24 to 72 days between 2000 and 2007. Elective caesarean section (CS) rates were relatively stable over time and 34% overall. Mother-to-child transmission (MTCT) rates decreased from 15.2% in 2001 (95% CI 10.2-21.4) to 7.0% in 2006 (95% CI 2.6-14.6). In adjusted analysis, MTCT risk was reduced by 43% with elective CS versus vaginal delivery and by 75% with zidovudine versus no prophylaxis.Conclusion: There have been substantial improvements in use of PMTCT interventions in Ukraine, including earlier diagnosis of HIV-infected pregnant women and increasing coverage with antiretroviral prophylaxis and the initial MTCT rate has more than halved. Future research should focus on hard-to-reach populations such as IDU and on missed opportunities for further reducing the MTCT rate
Globular clusters as indicators of Galactic evolution
We have studied the system of globular clusters (GCs) that formed in other
galaxies and eventually accreted onto the Milky Way. Thus, the samples of GCs
belonging to different tidal streams, obtained on the basis of the latest data
from the Gaia observatory, were taken from the literature. We measured the
anisotropy of the distribution of these GCs using the gyration tensor and found
that the distribution of GCs in the streams is isotropic. Nevertheless, it can
be seen that some of the accreted GCs included into existing samples actually
belong to the disk of the Galaxy. To clarify the origin of GCs, we investigated
the ``age--metallicity'' relation. This dependence demonstrates bimodality and
its two different branches clearly show the difference between the clusters
formed in the streams and in the disk of the Galaxy. Furthermore, we have
studied the influence of the large--scale environment of the Galaxy (i.e., the
Local Supercluster) on the distribution of satellite galaxies and Galactic GCs.
The satellite galaxies of the Milky Way are known to form an anisotropic planar
structure, so we included them in our analysis too. An inspection has shown
that the plane of the satellite galaxies is perpendicular both to the disk of
the Galaxy and the supergalactic plane. For GCs more distant than 100~Kpc, a
similar picture is observed.Comment: 15 pages, 3 figure
Machine learning techniques for MRI feature-based detection of frontotemporal lobar degeneration
Making a diagnosis of neurodegenerative diseases at an early stage is one of the most significant challenges of modern neuroscience. Although this family of diseases remains without a cure, the effectiveness of their medical treatment largely relies on the timing of their detection. For certain groups of diseases, such as Fronto-Temporal Dementia (FTD), trained professionals can effectively reach a correct diagnosis through the visual analysis of Magnetic Resonance Imaging, in its functional (fMRI) or raw (MRI) version. However, this operation is time-consuming and may be subject to personal interpretation. In this paper, we explore the performance of a group of machine learning algorithms to formulate a correct FTD diagnosis, in order to provide medical professionals with a supporting tool. The dataset consists of MRI data acquired on 30 subjects, and the experiments are carried out by investigating different fMRI techniques based on a Multi-Voxel Pattern Analysis (MVPA) approach. The results obtained show high accuracy in identifying FTD in elderly patients when Support Vector Machine and Random Forest techniques are used, with outcomes varying based on the fMRI methods
Constrained Local UniversE Simulations: A Local Group Factory
Near field cosmology is practiced by studying the Local Group (LG) and its
neighbourhood. The present paper describes a framework for simulating the near
field on the computer. Assuming the LCDM model as a prior and applying the
Bayesian tools of the Wiener filter (WF) and constrained realizations of
Gaussian fields to the Cosmicflows-2 (CF2) survey of peculiar velocities,
constrained simulations of our cosmic environment are performed. The aim of
these simulations is to reproduce the LG and its local environment. Our main
result is that the LG is likely a robust outcome of the LCDM scenario when
subjected to the constraint derived from CF2 data, emerging in an environment
akin to the observed one. Three levels of criteria are used to define the
simulated LGs. At the base level, pairs of halos must obey specific isolation,
mass and separation criteria. At the second level the orbital angular momentum
and energy are constrained and on the third one the phase of the orbit is
constrained. Out of the 300 constrained simulations 146 LGs obey the first set
of criteria, 51 the second and 6 the third. The robustness of our LG factory
enables the construction of a large ensemble of simulated LGs. Suitable
candidates for high resolution hydrodynamical simulations of the LG can be
drawn from this ensemble, which can be used to perform comprehensive studies of
the formation of the LGComment: 13 pages, accepted for publication in MNRA
Crack growth by surface diffusion in viscoelastic media
We discuss steady state crack growth in the spirit of a free boundary
problem. It turns out that mode I and mode III situations are very different
from each other: In particular, mode III exhibits a pronounced transition
towards unstable crack growth at higher driving forces, and the behavior close
to the Griffith point is determined entirely through crack surface dissipation,
whereas in mode I the fracture energy is renormalized due to a remaining finite
viscous dissipation. Intermediate mixed-mode scenarios allow steady state crack
growth with higher velocities, leading to the conjecture that mode I cracks can
be unstable with respect to a rotation of the crack front line
Previous reproductive history and post-natal family planning among HIV-infected women in Ukraine
BACKGROUND: Ukraine has the highest antenatal HIV prevalence in Europe. The national prevention of mother-to-child transmission (MTCT) programme has reduced the MTCT rate, but less attention has been given to the prevention of unintended pregnancy among HIV-positive women. Our objectives were to describe the reproductive health, condom use and family planning (FP) practices of HIV-positive childbearing Ukrainian women and to identify factors associated with different methods of post-natal contraception.
METHODS: HIV-infected childbearing women, diagnosed before or during pregnancy, were enrolled prospectively in a post-natal cohort study in four regional HIV/AIDS centres in Ukraine from December 2007. Logistic regression models were used to identify factors associated with post-natal FP practices.
RESULTS: Data were available for 371 women enrolled by March 2009; 82% (n = 303) were married or cohabiting, 27% (97 of 363) reported a current HIV-negative sexual partner and 69% were diagnosed with HIV during their most recent pregnancy. Overall, 21% (75 of 349) of women were not using contraception post-natally (of whom 80% reported no current sexual activity), 50% (174 of 349) used condoms, 20% (74 of 349) relied solely/partially on coitus interruptus and 4% used hormonal methods or intrauterine device. Among married/cohabiting women, consistent use of condoms in the previous pregnancy [AOR 1.96 (95%CI 1.06â3.62)], having an HIV-positive partner [AOR 0.42 (0.20â0.87)], current sexual activity [AOR 4.53 (1.19â17.3)] and study site were significantly associated with post-natal condom use; 16% of those with HIV-negative partners did not use condoms. Risk factors for non-use of FP were lack of affordability [AOR 6.34 (1.73â23.2)] and inconsistent use of condoms in the previous pregnancy [AOR 7.25 (1.41â37.2)].
CONCLUSIONS: More than 40% of HIV-positive women in this population are at risk of unintended pregnancy and the one in six women in HIV-discordant couples not using barrier methods risk transmitting HIV to their partners. Our study results are limited by the observational nature of the data and the potential for both measured and unmeasured confounding
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