2,790 research outputs found
Microfluidic generation and optical manipulation of ultra-low interfacial tension droplets
Density-dependent processes in the transmission of human onchocerciasis: relationship between the numbers of microfilariae ingested and successful larval development in the simuliid vector
A previous paper reported that the intake of Onchocerca volvulus microfilariae (mff) by different species of Simulium is essentially proportional to the parasite load in the skin of infected carriers. This paper examines the fate of the ingested mff in susceptible vectors to assess the relationship between parasite intake and infective larval output in blackfly species with and without well-developed cibarial armatures. Analysis is based on data from 3 onchocerciasis endemic areas: Guatemala (S. ochraceum s.l.), West Africa (S. damnosum s.l./S. sirbanum) and the Amazonian focus between South Venezuela and Northern Brazil (S. guianense and S. oyapockense s.l.). The data, which include published and unedited information collected in the field, record experimental studies of parasite uptake by wild flies maintained in captivity until the completion of the extrinsic incubation period. The relationship between L3 output (measured as the mean number of successful larvae/fly or, as the proportion of flies with infective larvae) and average microfilarial intake, was strongly non-linear. This non-linearity was best represented by a sigmoid function in case of armed simuliids (S. ochraceum s.l., S. oyapockense s.l.), or by a hyperbolic expression in that of unarmed flies (S. damnosum s.l., S. guianense). These results are compatible, respectively, with the patterns of ‘initial facilitation' and ‘limitation' described in culicid vectors of lymphatic filariases. A maximum mean number of 1-3 L3/fly was observed in all 4 vectors. It is concluded that O. volvulus larval development to the infective stage is regulated by density-dependent mechanisms acting at the early phase of microfilarial migration out of the blackfly's bloodmeal. Damage by the bucco-pharyngeal armature may also be density dependent. A hypothesis, based on this density dependence is forwarded to explain initial facilitation, so far only recorded in vectors with well-developed cibarial teeth. Our results provide quantitative support for the conjecture that chemotherapy alone is likely to have a greater impact on reducing onchocerciasis transmission in endemic areas where the main vector has a toothed fore-gut than in foci where the vectors have unarmed cibari
p-branes on the waves
We present a large family of simple, explicit ten-dimensional supergravity
solutions describing extended extremal supersymmetric Ramond-Ramond p-branes
embedded into time-dependent dilaton-gravity plane waves of an arbitrary
(isotropic) profile, with the brane world-volume aligned parallel to the
propagation direction of the wave. Generalizations to the non-extremal case are
not analyzed explicitly, but can be pursued as indicated.Comment: 11 pages; v.2 minor notation changes, minor typos corrected
(published version
A Note on D-brane - Anti-D-brane Interactions in Plane Wave Backgrounds
We study aspects of the interaction between a D-brane and an anti-D-brane in
the maximally supersymmetric plane wave background of type IIB superstring
theory, which is equipped with a mass parameter mu. An early such study in flat
spacetime (mu=0) served to sharpen intuition about D-brane interactions,
showing in particular the key role of the ``stringy halo'' that surrounds a
D-brane. The halo marks the edge of the region within which tachyon
condensation occurs, opening a gateway to new non-trivial vacua of the theory.
It seems pertinent to study the fate of the halo for non--zero mu. We focus on
the simplest cases of a Lorentzian brane with p=1 and an Euclidean brane with
p=-1, the D--instanton. For the Lorentzian brane, we observe that the halo is
unaffected by the presence of non--zero mu. This most likely extends to other
(Lorentzian) p. For the Euclidean brane, we find that the halo is affected by
non-zero mu. As this is related to subtleties in defining the exchange
amplitude between Euclidean branes in the open string sector, we expect this to
extend to all Euclidean branes in this background.Comment: 14 pages, LaTeX, 2 eps figures. v2: a reference and some clarifying
remarks added; v3: Considerably revised version; halo unaffected by plane
wave background for Lorentzian branes, but Euclidean branes' halo is modifie
Extended WKB method, resonances and supersymmetric radial barriers
Semiclassical approximations are implemented in the calculation of position
and width of low energy resonances for radial barriers. The numerical
integrations are delimited by t/T<<8, with t the period of a classical particle
in the barrier trap and T the resonance lifetime. These energies are used in
the construction of `haired' short range potentials as the supersymmetric
partners of a given radial barrier. The new potentials could be useful in the
study of the transient phenomena which give rise to the Moshinsky's diffraction
in time.Comment: 12 pages, 4 figures, 3 table
Two-proton events in the 17F(p,2p)16O reaction
In a recent experimental study (Gomez del Campo et al, PRL 86, 43 (2001)) of
the reaction 17F(p,2p)16O, two-proton events were measured from excitations
near a 1-, E*=6.15 MeV state in 18Ne. We calculate by means of R-matrix theory
the resonant two-proton production cross section and branching ratios. We
conclude that it is unlikely that two-proton production via population of the
1- state is sufficient to explain the observed two-proton events. Alternative
sources of such events are discussed.Comment: 4 pages, 4 figures. Resubmission to Physical Review C (first received
6 March 2001
D terms from D-branes, gauge invariance and moduli stabilization in flux compactifications
We elucidate the structure of D terms in N=1 orientifold compactifications
with fluxes. As a case study, we consider a simple orbifold of the type-IIA
theory with D6-branes at angles, O6-planes and general NSNS, RR and
Scherk-Schwarz geometrical fluxes. We examine in detail the emergence of D
terms, in their standard supergravity form, from an appropriate limit of the
D-brane action. We derive the consistency conditions on gauged symmetries and
general fluxes coming from brane-localized Bianchi identities, and their
relation with the Freed-Witten anomaly. We extend our results to other N=1
compactifications and to non-geometrical fluxes. Finally, we discuss the
possible role of U(1) D terms in the stabilization of the untwisted moduli from
the closed string sector.Comment: 1+31 pages, 1 figur
Sigma-phase in Fe-Cr and Fe-V alloy systems and its physical properties
A review is presented on physical properties of the sigma-phase in Fe-Cr and
Fe-V alloy systems as revealed both with experimental -- mostly with the
Mossbauer spectroscopy -- and theoretical methods. In particular, the following
questions relevant to the issue have been addressed: identification of sigma
and determination of its structural properties, kinetics of alpha-to-sigma and
sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon
density of states, Curie temperature and magnetization, hyperfine fields,
isomer shifts and electric field gradients.Comment: 26 pages, 23 figures and 83 reference
An example of localized D-branes solution on PP-wave backgrounds
In this note we provide an explicit example of type IIB supersymmetric
D3-branes solution on a pp-wave like background, consisting in the product of
an eight-dimensional pp-wave times a two-dimensional flat space. An interesting
property of our solution is the fully localization of the D3-branes (i.e. the
solution depends on all the transverse coordinates). Then we show the
generalization to other Dp-branes and to the D1/D5 system.Comment: 14 pages, 1 table; v2. references adde
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