168 research outputs found
Measures and outcomes of a psychosocial group approach in Rwanda
This thesis presents different aspects of a quasi-experimental, longitudinal study on a psychosocial intervention (sociotherapy) in northern Rwanda, combining measurements on mental health, social functioning, intimate partner violence and social capital
The role of turbulent coherent structures on microalgal mixing for nutrient removal in jet and paddlewheel raceway ponds
Outdoor studies were conducted on microalgae cultures in two raceway ponds (kept in constant motion with either jet or paddlewheel) with a flatbed to treat anaerobic digestion piggery effluent and to observe the characteristics of turbulence on microalgal mixing and growth. Acoustic Doppler Velocimeters (ADV) were deployed to record the instantaneous velocity components and acoustic backscatter as a substitution of microalgae concentration. The present research on microalgal mixing considers the effect of event-based turbulent features such as the widely known âturbulent burstingâ phenomenon. This is an important aspect, as turbulent coherent structures can result in microalgal mixing, which can lead to significant changes in microalgal growth. The experimental results presented in this paper of two contrasting environments of jet- and paddlewheel-driven ponds suggested that: (1) turbulent bursting events significantly contributed to microalgal mixing when paddlewheels and jets were used; (2) among four type of turbulent bursting events, ejections and sweeps contributed more to the total microalgal mixing; and, (3) a correlation was revealed using wavelet transform between the momentum and microalgal mixing flux when either jet or paddlewheel were used. Such similarities in jet and paddlewheel raceway ponds highlight the need to introduce turbulent coherent structures as an essential parameter for microalgal mixing studies
Identification of Burkholderia spp. in the clinical microbiology laboratory: comparison of conventional and molecular methods
Cystic fibrosis (CF) predisposes patients to bacterial colonization and
infection of the lower airways. Several species belonging to the genus
Burkholderia are potential CF-related pathogens, but microbiological
identification may be complicated. This situation is not in the least due
to the poorly defined taxonomic status of these bacteria, and further
validation of the available diagnostic assays is required. A total of 114
geographically diverse bacterial isolates, previously identified in
reference laboratories as Burkholderia cepacia (n = 51), B. gladioli (n =
14), Ralstonia pickettii (n = 6), B. multivorans (n = 2), Stenotrophomonas
maltophilia (n = 3), and Pseudomonas aeruginosa (n = 11), were collected
from environmental, clinical, and reference sources. In addition, 27
clinical isolates putatively identified as Burkholderia spp. were
recovered from the sputum of Dutch CF patients. All isolates were used to
evaluate the accuracy of two selective growth media, four systems for
biochemical identification (API 20NE, Vitek GNI, Vitek NFC, and
MicroScan), and three different PCR-based assays. The PCR assays amplify
different parts of the ribosomal DNA operon, either alone or in
combination with cleavage by various restriction enzymes (PCR-restriction
fragment length polymorphism [RFLP] analysis). The best system for the
biochemical identification of B. cepacia appeared to be the API 20NE test.
None of the biochemical assays successfully grouped the B. gladioli
strains. The PCR-RFLP method appeared to be the optimal method for
accurate nucleic acid-mediated identification of the different
Burkholderia spp. With this method, B. gladioli was also reliably
classified in a separate group. For the laboratory diagnosis of B.
cepacia, we recommend parallel cultures on blood agar medium and selective
agar plates. Further identification of colonies with a Burkholderia
phenotype should be performed with the API 20NE test. For final
confirmation of species identities, PCR amplification of the small-subunit
rRNA gene followed by RFLP analysis with various enzymes is recommended
Comparative simulation study of colloidal gels and glasses
Using computer simulations, we identify the mechanisms causing aggregation
and structural arrest of colloidal suspensions interacting with a short-ranged
attraction at moderate and high densities. Two different non-ergodicity
transitions are observed. As the density is increased, a glass transition takes
place, driven by excluded volume effects. In contrast, at moderate densities,
gelation is approached as the strength of the attraction increases. At high
density and interaction strength, both transitions merge, and a logarithmic
decay in the correlation function is observed. All of these features are
correctly predicted by mode coupling theory
Evidence for Unusual Dynamical Arrest Scenario in Short Ranged Colloidal Systems
Extensive molecular dynamics simulation studies of particles interacting via
a short ranged attractive square-well (SW) potential are reported. The
calculated loci of constant diffusion coefficient in the
temperature-packing fraction plane show a re-entrant behavior, i.e. an increase
of diffusivity on cooling, confirming an important part of the high
volume-fraction dynamical-arrest scenario earlier predicted by theory for
particles with short ranged potentials. The more efficient localization
mechanism induced by the short range bonding provides, on average, additional
free volume as compared to the hard-sphere case and results in faster dynamics.Comment: 4 pages, 3 figure
Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study
Previous theoretical, along with early simulation and experimental, studies
have indicated that particles with a short-ranged attraction exhibit a range of
new dynamical arrest phenomena. These include very pronounced reentrance in the
dynamical arrest curve, a logarithmic singularity in the density correlation
functions, and the existence of `attractive' and `repulsive' glasses. Here we
carry out extensive molecular dynamics calculations on dense systems
interacting via a square-well potential. This is one of the simplest systems
with the required properties, and may be regarded as canonical for interpreting
the phase diagram, and now also the dynamical arrest. We confirm the
theoretical predictions for re-entrance, logarithmic singularity, and give the
first direct evidence of the coexistence, independent of theory, of the two
coexisting glasses. We now regard the previous predictions of these phenomena
as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.
Nonergodicity transitions in colloidal suspensions with attractive interactions
The colloidal gel and glass transitions are investigated using the idealized
mode coupling theory (MCT) for model systems characterized by short-range
attractive interactions. Results are presented for the adhesive hard sphere and
hard core attractive Yukawa systems. According to MCT, the former system shows
a critical glass transition concentration that increases significantly with
introduction of a weak attraction. For the latter attractive Yukawa system, MCT
predicts low temperature nonergodic states that extend to the critical and
subcritical region. Several features of the MCT nonergodicity transition in
this system agree qualitatively with experimental observations on the colloidal
gel transition, suggesting that the gel transition is caused by a low
temperature extension of the glass transition. The range of the attraction is
shown to govern the way the glass transition line traverses the phase diagram
relative to the critical point, analogous to findings for the fluid-solid
freezing transition.Comment: 11 pages, 7 figures; to be published in Phys. Rev. E (1 May 1999
The effect on mental health of a large scale psychosocial intervention for survivors of mass violence: A quasi-experimental study in Rwanda
Background: War has serious and prolonged mental health consequences. It is argued that post-emergency mental health interventions should not only focus on psychological factors but also address the social environment. No controlled trials of such interventions exist. We studied the effect on mental health of a large scale p
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