19,528 research outputs found
Potential value of triple drug therapy with ivermectin, diethylcarbamazine, and albendazole (IDA) to accelerate elimination of lymphatic filariasis and onchocerciasis in Africa
High pressure freezing/freeze substitution fixation improves the ultrastructural assessment of Wolbachia endosymbiont – filarial nematode host interaction
Wolbachia α-proteobacteria are essential for growth, reproduction and survival for many filarial nematode parasites of medical and veterinary importance. Endobacteria were discovered in filarial parasites by transmission electron microscopy in the 1970's using chemically fixed specimens. Despite improvements of fixation and electron microscopy techniques during the last decades, methods to study the Wolbachia/filaria interaction on the ultrastructural level remained unchanged and the mechanisms for exchange of materials and for motility of endobacteria are not known.We used high pressure freezing/freeze substitution to improve fixation of Brugia malayi and its endosymbiont, and this led to improved visualization of different morphological forms of Wolbachia. The three concentric, bilayer membranes that surround the endobacterial cytoplasm were well preserved. Vesicles with identical membrane structures were identified close to the endobacteria, and multiple bacteria were sometimes enclosed within a single outer membrane. Immunogold electron microscopy using a monoclonal antibody directed against Wolbachia surface protein-1 labeled the membranes that enclose Wolbachia and Wolbachia-associated vesicles. High densities of Wolbachia were observed in the lateral chords of L4 larvae, immature, and mature adult worms. Extracellular Wolbachia were sometimes present in the pseudocoelomic cavity near the developing female reproductive organs. Wolbachia-associated actin tails were not observed. Wolbachia motility may be explained by their residence within vacuoles, as they may co-opt the host cell's secretory pathway to move within and between cells.High pressure freezing/freeze substitution significantly improved the preservation of filarial tissues for electron microscopy to reveal membranes and sub cellular structures that could be crucial for exchange of materials between Wolbachia and its host
Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions
The occupation of more than one single-particle state and hence the emergence
of fragmentation is a many-body phenomenon universal to systems of spatially
confined interacting bosons. In the present study, we investigate the effect of
the range of the interparticle interactions on the fragmentation degree of one-
and two-dimensional systems. We solve the full many-body Schr\"odinger equation
of the system using the recursive implementation of the multiconfigurational
time-dependent Hartree for bosons method, R-MCTDHB. The dependence of the
degree of fragmentation on dimensionality, particle number, areal or line
density and interaction strength is assessed. It is found that for contact
interactions, the fragmentation is essentially density independent in two
dimensions. However, fragmentation increasingly depends on density the more
long-ranged the interactions become. The degree of fragmentation is increasing,
keeping the particle number fixed, when the density is decreasing as
expected in one spatial dimension. We demonstrate that this remains,
nontrivially, true also for long-range interactions in two spatial dimensions.
We, finally, find that within our fully self-consistent approach, the
fragmentation degree, to a good approximation, decreases universally as
when only is varied.Comment: 8 pages of RevTex4-1, 5 figure
Cyanobacterial mats: Microanalysis of community metabolism
The microbial communities in two sites were studied using several approaches: (1) light microscopy; (2) the measurement of microprofiles of oxygen and sulfide at the surface of the microbial mat; (3) the study of diurnal variation of oxygen and sulfides; (4) in situ measurement of photosynthesis and sulfate reduction and study of the coupling of these two processes; (5) measurement of glutathione in the upper layers of the microbial mat as a possible oxygen quencher; (6) measurement of reduced iron as a possible intermediate electron donor along the established redoxcline in the mats; (7) measurement of dissolved phosphate as an indicator of processes of break down of organic matter in these systems; and (8) measurement of carbon dioxide in the interstitial water and its delta C-13 in an attempt to understand the flow of CO2 through the systems. Microbial processes of primary production and initial degradation at the most active zone of the microbial mat were analyzed
Renormalization flow of Yang-Mills propagators
We study Landau-gauge Yang-Mills theory by means of a nonperturbative vertex
expansion of the quantum effective action. Using an exact renormalization group
equation, we compute the fully dressed gluon and ghost propagators to lowest
nontrivial order in the vertex expansion. In the mid-momentum regime,
, we probe the propagator flow with various
{\em ans\"atze} for the three- and four-point correlations. We analyze the
potential of these truncation schemes to generate a nonperturbative scale. We
find universal infrared behavior of the propagators, if the gluon dressing
function has developed a mass-like structure at mid-momentum. The resulting
power laws in the infrared support the Kugo-Ojima confinement scenario.Comment: 28 pages, 5 figures. V2: Typos corrected and reference adde
Tissue and Stage-Specific Distribution of Wolbachia in Brugia malayi
Most filarial nematodes contain Wolbachia endobacteria that are essential for development and reproduction. An antibody against a Wolbachia surface protein was used to monitor the distribution of endobacteria during the B. malayi life cycle. In situ hybridization with probes binding to Wolbachia 16S rRNA were used to confirm results. Only a few cells contain Wolbachia in microfilariae and vector stage larvae; this suggests that the bacteria need to be maintained, but may have limited importance for these stages. Large numbers of Wolbachia were detected in the lateral chords of L4 larvae and of young adult worms, but not in the developing reproductive tissue. Confocal laser scanning and transmission electron microscopy showed that Wolbachia are aligned towards the developing germline. It can be hypothesized that Wolbachia invade developing ovaries from the lateral chords. In inseminated females, Wolbachia were detected in the ovaries and embryos. In young males, Wolbachia were found in parts of the testis and in the lateral chords in the vicinity of testicular tissue but never in mature spermatids or spermatozoa. The process of overcoming tissue boundaries to ensure transovarial transmission of Wolbachia could be an Achilles heel in the life cycle of B. malayi
Creep motion in a random-field Ising model
We analyze numerically a moving interface in the random-field Ising model
which is driven by a magnetic field. Without thermal fluctuations the system
displays a depinning phase transition, i.e., the interface is pinned below a
certain critical value of the driving field. For finite temperatures the
interface moves even for driving fields below the critical value. In this
so-called creep regime the dependence of the interface velocity on the
temperature is expected to obey an Arrhenius law. We investigate the details of
this Arrhenius behavior in two and three dimensions and compare our results
with predictions obtained from renormalization group approaches.Comment: 6 pages, 11 figures, accepted for publication in Phys. Rev.
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