14,318 research outputs found
Urban Lymphatic Filariasis in the Metropolis of\ud Dar es Salaam, Tanzania
The last decades have seen a considerable increase in urbanization in Sub-Saharan Africa, and it is estimated that over 50% of the population will live in urban areas by 2040. Rapid growth of cities combined with limited economic resources often result in informal settlements and slums with favorable conditions for proliferation of vectors of lymphatic filariasis (LF). In Dar es Salaam, which has grown more than 30 times in population during the past 55 years (4.4 million inhabitants in 2012), previous surveys have indicated high prevalences of LF. This study investigated epidemiological aspects of LF in Dar es Salaam, as a background for planning and implementation of control. Six sites with varying distance from the city center (3â30 km) and covering different population densities, socioeconomic characteristics, and water, sewerage and sanitary facilities were selected for the study. Pupils from one public primary school at each site were screened for circulating filarial antigen (CFA; marker of adult worm infection) and antibodies to Bm14 (marker of exposure to transmission). Community members were examined for CFA, microfilariae and chronic manifestations. Structured questionnaires were administered to pupils and heads of community households, and vector surveys were carried out in selected households. The study indicated that a tremendous decrease in the burden of LF infection had occurred, despite haphazard urbanisation. Contributing factors may be urban malaria control targeting Anopheles vectors, short survival time of the numerous Culex quinquefasciatus vectors in the urban environment, widespread use of bed nets and other mosquito proofing measures, and mass drug administration (MDA) in 2006 and 2007. Although the level of ongoing transmission was low, the burden of chronic LF disease was still high. The development has so far been promising, but continued efforts are necessary to ensure elimination of LF as a public health problem. These will include improving the awareness of people about the role of mosquitoes in transmission of LF, more thorough implementation of environmental sanitation to reduce Cx. Quinquefasciatus breeding, continued MDA to high-risk areas, and set-up of programmes for management of chronic LF disease
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals
is theoretically studied. Using a scattering-matrix approach and the
Wigner-Smith delay time concept, we show that optical absorbance benefits both
from slow-light phenomena as well as a high filling factor of the energy
residing in the liquid. Utilizing strongly dispersive photonic crystal
structures, we numerically demonstrate how liquid-infiltrated photonic crystals
facilitate enhanced light-matter interactions, by potentially up to an order of
magnitude. The proposed concept provides strong opportunities for improving
existing miniaturized absorbance cells for optical detection in lab-on-a-chip
systems.Comment: Paper accepted for the "Special Issue OWTNM 2007" edited by A.
Lavrinenko and P. J. Robert
Optical and near-infrared observations of the GRB 970616 error box
We report on near-infrared and optical observations of the GRB 970616 error
box and of the X-ray sources discovered by ASCA and ROSAT in the region. No
optical transient was found either within the IPN band or in the X-ray error
boxes, similarly to other bursts, and we suggest that either considerable
intrinsic absorption was present (like GRB 970828) or that the optical
transient displayed a very fast decline (like GRB 980326 and GRB 980519).Comment: 2 pages with one encapsulated PostScript figure included. Uses
Astronomy & Astrophysics LaTeX macros. Accepted for publication in Astronomy
& Astrophysics Supplement Serie
Correlation-induced conductance suppression at level degeneracy in a quantum dot
The large, level-dependent g-factors in an InSb nanowire quantum dot allow
for the occurrence of a variety of level crossings in the dot. While we observe
the standard conductance enhancement in the Coulomb blockade region for aligned
levels with different spins due to the Kondo effect, a vanishing of the
conductance is found at the alignment of levels with equal spins. This
conductance suppression appears as a canyon cutting through the web of direct
tunneling lines and an enclosed Coulomb blockade region. In the center of the
Coulomb blockade region, we observe the predicted correlation-induced
resonance, which now turns out to be part of a larger scenario. Our findings
are supported by numerical and analytical calculations.Comment: 5 pages, 4 figure
Antigens in human glioblastomas and meningiomas: Search for tumour and onco-foetal antigens. Estimation of S-100 and GFA protein.
Extracts of glioblastomas and meningiomas were analysed by quantitative immunoelectrophoresis for the presence of foetal brain antigens and tumour-associated antigens, and levels of 2 normal brain-specific proteins were also determined. The following antibodies were used: monospecific anti-S-100 (glia specific); monospecific anti-GFA (glial fibrillary acidic protein), (astroglia specific); polyspecific anti-foetal brain (12-16th week of gestation); a polyspecific anti-glioblastoma antiserum, absorbed with insolubilized serum, haemolysate and normal brain extract; polyspecific anti-alpha-foetoprotein; and monospecific anti-ferritin. Using the antibodies raised against the tumours, several antigens not present in foetal or adult normal brain were found in the glioblastomas and the meningiomas. These antigens cross-reacted with antigens present in normal liver and were therefore not tumour-associated. S-100 was found in glioblastomas in approximately one tenth the amount in whole brain homogenate, whereas GFA was found 2-4 times enriched. The 2 proteins were absent in meningiomas. The possible use of the GFA protein as a marker for astroglial neoplasia is discussed. Five foetal antigens were found in foetal brain, but none in the tumours. alpha-Foetoprotein could only be demonstrated in foetal tissue extracts, including foetal brain, but not in tumours. Ferritin was detected in all tumour extracts, although the amounts determined were unrelated to histological tumour type
Spin-orbit interaction and the 'metal-insulator' transition observed in two-dimensional hole systems
We present calculations of the spin and phase relaxation rates in GaAs/AlGaAs
-type quantum wells. These rates are used to derive the temperature
dependence of the weak-localization correction to the conductivity. In -type
quantum wells both weak localization and weak anti-localization are present due
to the strong spin-orbit interaction. When determining the total conductivity
correction one also have to include the term due to hole-hole interaction. The
magnitude of the latter depends on the ratio between the thermal energy and the
Fermi energy, and whether the system can be considered
as ballistic or diffusive (). We argue that due to the relatively low Fermi energy
and the moderate mobilities, in the -type systems in question, the
conductivity correction arising from hole-hole interactions is negligible at
the highest temperatures accessible in the experiments. Hence the
'metal-insulator' transition observed at these relatively high temperatures
could be caused by interference effects. We compare our calculations of the
weak anti-localization correction with the experimental results from different
independent groups with special emphasis on the experiments by Simmons et al.
We find good agreement between predicted and observed transistion density
.Comment: 6 pages, 4 figures. Accepted to PRB (15 June, 2002
Volume-energy correlations in the slow degrees of freedom of computer-simulated phospholipid membranes
Constant-pressure molecular-dynamics simulations of phospholipid membranes in
the fluid phase reveal strong correlations between equilibrium fluctuations of
volume and energy on the nanosecond time-scale. The existence of strong
volume-energy correlations was previously deduced indirectly by Heimburg from
experiments focusing on the phase transition between the fluid and the ordered
gel phases. The correlations, which are reported here for three different
membranes (DMPC, DMPS-Na, and DMPSH), have volume-energy correlation
coefficients ranging from 0.81 to 0.89. The DMPC membrane was studied at two
temperatures showing that the correlation coefficient increases as the phase
transition is approached
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
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