Neutron spectral measurements in the upper atmosphere

An experiment to measure neutrons in the upper atmosphere was performed on a balloon flight from Palestine, Texas, at an altitude of about 32 km. The experimental arrangement is discussed briefly, and results of a preliminary analysis of the data for neutrons in the energy range 3 to 30 MeV are given

Excitation sources for fuel assembly vibrations in a PWR

Noise measurements from in-core neutron detectors have been utilized previously to monitor in-plant vibrations of pressurized water reactor (PWR) fuel assemblies. Fuel assembly resonant frequencies and mode shapes were obtained from these in-core measurements by observing resonances in the neutron noise power spectral density (PSD) and then plotting the axial dependence of the root mean square (rms) neutron noise over frequency ranges containing these resonances. In order to determine the fuel assembly mode shapes and their relationship to core barrel motion, we performed simultaneous measurements of in-core and ex-core neutron noise at the Sequoyah-1 reactor, a Westinghouse 1150 MW(e) PWR. Analysis of this data indicates that there are two different sources of vibrational excitation for the fuel in the 6- to 8-Hz frequency range. 7 refs., 2 figs

Intracellular Bacteria Encode Inhibitory SNARE-Like Proteins

Pathogens use diverse molecular machines to penetrate host cells and manipulate intracellular vesicular trafficking. Viruses employ glycoproteins, functionally and structurally similar to the SNARE proteins, to induce eukaryotic membrane fusion. Intracellular pathogens, on the other hand, need to block fusion of their infectious phagosomes with various endocytic compartments to escape from the degradative pathway. The molecular details concerning the mechanisms underlying this process are lacking. Using both an in vitro liposome fusion assay and a cellular assay, we showed that SNARE-like bacterial proteins block membrane fusion in eukaryotic cells by directly inhibiting SNARE-mediated membrane fusion. More specifically, we showed that IncA and IcmG/DotF, two SNARE-like proteins respectively expressed by Chlamydia and Legionella, inhibit the endocytic SNARE machinery. Furthermore, we identified that the SNARE-like motif present in these bacterial proteins encodes the inhibitory function. This finding suggests that SNARE-like motifs are capable of specifically manipulating membrane fusion in a wide variety of biological environments. Ultimately, this motif may have been selected during evolution because it is an efficient structural motif for modifying eukaryotic membrane fusion and thus contribute to pathogen survival

The peroxisome: still a mysterious organelle

More than half a century of research on peroxisomes has revealed unique features of this ubiquitous subcellular organelle, which have often been in disagreement with existing dogmas in cell biology. About 50 peroxisomal enzymes have so far been identified, which contribute to several crucial metabolic processes such as β-oxidation of fatty acids, biosynthesis of ether phospholipids and metabolism of reactive oxygen species, and render peroxisomes indispensable for human health and development. It became obvious that peroxisomes are highly dynamic organelles that rapidly assemble, multiply and degrade in response to metabolic needs. However, many aspects of peroxisome biology are still mysterious. This review addresses recent exciting discoveries on the biogenesis, formation and degradation of peroxisomes, on peroxisomal dynamics and division, as well as on the interaction and cross talk of peroxisomes with other subcellular compartments. Furthermore, recent advances on the role of peroxisomes in medicine and in the identification of novel peroxisomal proteins are discussed

A host specialized form of Ceratocystis fimbriata causes seed and seedling blight on native Carapa guianensis (andiroba) in Amazonian rainforests.

Ceratocystis fimbriata Ellis & Halsted recently was recorded causing seed and seedling blight on Carapa guianensis Aubl. (andiroba), a tree species native to the Amazon Rainforest and prized for its valuable timber and medicinal seed oil. C. fimbriata more commonly causes wilt type diseases in woody hosts, especially on non-native host trees. However, on andiroba the disease occurs on seedlings and seeds, affecting the species regeneration. We studied 73 isolates of C. fimbriata on andiroba from three regions of the Amazon Basin to see if they represented natural or introduced populations. Analysis of ITS rDNA sequences and phylogenetic analysis of mating type genes revealed new haplotypes of C. fimbriata from the Latin American Clade that were closely related to other Brazilian populations of the fungus. In mating experiments, andiroba isolates were inter-fertile with tester strains of C. fimbriata from Brazil and elsewhere, confirming that they belong to a single biological species. Using microsatellite markers, 14 genotypes and populations with intermediate levels of genetic variability were found, suggesting that the fungus is indigenous to the Amazon Basin. Inoculation tests indicated that the andiroba isolates are host-specialized on andiroba, supporting the proposition of the special form C. fimbriata f. sp. carapa.Made available in DSpace on 2019-03-20T00:43:38Z (GMT). No. of bitstreams: 1 26788.pdf: 3260751 bytes, checksum: e216b037faec9a95d9551042e8f53907 (MD5) Previous issue date: 2019bitstream/item/194519/1/26788.pd

Sec18p and Vam7p remodel trans-SNARE complexes to permit a lipid-anchored R-SNARE to support yeast vacuole fusion

Intracellular membrane fusion requires SNARE proteins in a trans-complex, anchored to apposed membranes. Proteoliposome studies have suggested that SNAREs drive fusion by stressing the lipid bilayer via their transmembrane domains (TMDs), and that SNARE complexes require a TMD in each docked membrane to promote fusion. Yeast vacuole fusion is believed to require three Q-SNAREs from one vacuole and the R-SNARE Nyv1p from its fusion partner. In accord with this model, we find that fusion is abolished when the TMD of Nyv1p is replaced by lipid anchors, even though lipid-anchored Nyv1p assembles into trans-SNARE complexes. However, normal fusion is restored by the addition of both Sec18p and the soluble SNARE Vam7p. In restoring fusion, Sec18p promotes the disassembly of trans-SNARE complexes, and Vam7p enhances their assembly. Thus, either the TMD of this R-SNARE is not essential for fusion, and TMD-mediated membrane stress is not the only mode of trans-SNARE complex action, or these SNAREs have more flexibility than heretofore appreciated to form alternate functional complexes that violate the 3Q:1R rule

Non-parametric Modelling of Spatial Price Relationships

We apply non-parametric methods to a consideration of price transmission processes within US egg markets at the turn of the nineteenth century. Gordon (National Bureau of Economic Research Working Paper 7833, 2000) labelled this as an era of 'Great Inventions' which contributed to the subsequent years of significant productivity growth and noted that the development of mechanical refrigeration and transportation technologies played an important role in this growth. Our models present certain advantages relative to parametric models traditionally employed in price transmission analyses. We compare results derived from local polynomial modelling with those obtained using non-linear threshold models. Both techniques suggest that US egg markets were interrelated at the turn of the nineteenth century. However, non-parametric techniques often suggest a higher degree of price transmission than that implied by threshold models. Results also suggest that threshold models may have difficulties in adequately capturing price relationship dynamics, especially when these are of a highly nonlinear nature. Copyright 2006 Blackwell Publishing Ltd.