395 research outputs found
The role of the Berry Phase in Dynamical Jahn-Teller Systems
The presence/absence of a Berry phase depends on the topology of the manifold
of dynamical Jahn-Teller potential minima. We describe in detail the relation
between these topological properties and the way the lowest two adiabatic
potential surfaces get locally degenerate. We illustrate our arguments through
spherical generalizations of the linear T x h and H x h cases, relevant for the
physics of fullerene ions. Our analysis allows us to classify all the spherical
Jahn-Teller systems with respect to the Berry phase. Its absence can, but does
not necessarily, lead to a nondegenerate ground state.Comment: revtex 7 pages, 2 eps figures include
Endocytic recycling via the TGN underlies the polarized hyphal mode of growth
Intracellular traffic in Aspergillus nidulans hyphae must cope with the challenges that the high rates of apical extension (1ÎŒm/min) and the long intracellular distances (>100 ÎŒm) impose. Understanding the ways in which the hyphal tip cell coordinates traffic to meet these challenges is of basic importance, but is also of considerable applied interest, as fungal invasiveness of animals and plants depends critically upon maintaining these high rates of growth. Rapid apical extension requires localization of cell-wall-modifying enzymes to hyphal tips. By combining genetic blocks in different trafficking steps with multidimensional epifluorescence microscopy and quantitative image analyses we demonstrate that polarization of the essential chitin-synthase ChsB occurs by indirect endocytic recycling, involving delivery/exocytosis to apices followed by internalization by the sub-apical endocytic collar of actin patches and subsequent trafficking to TGN cisternae, where it accumulates for ~1 min before being re-delivered to the apex by a RAB11/TRAPPII-dependent pathway. Accordingly, ChsB is stranded at the TGN by Sec7 inactivation but re-polarizes to the apical dome if the block is bypassed by a mutation in geaAgea1 that restores growth in the absence of Sec7. That polarization is independent of RAB5, that ChsB predominates at apex-proximal cisternae, and that upon dynein impairment ChsB is stalled at the tips in an aggregated endosome indicate that endocytosed ChsB traffics to the TGN via sorting endosomes functionally located upstream of the RAB5 domain and that this step requires dynein-mediated basipetal transport. It also requires RAB6 and its effector GARP (Vps51/Vps52/Vps53/Vps54), whose composition we determined by MS/MS following affinity chromatography purification. Ablation of any GARP component diverts ChsB to vacuoles and impairs growth and morphology markedly, emphasizing the important physiological role played by this pathway that, we propose, is central to the hyphal mode of growth
Low-energy excitations of a linearly Jahn-Teller coupled orbital quintet
The low-energy spectra of the single-mode h x (G+H) linear Jahn-Teller model
is studied by means of exact diagonalization. Both eigenenergies and
photoemission spectral intensities are computed. These spectra are useful to
understand the vibronic dynamics of icosahedral clusters with partly filled
orbital quintet molecular shells, for example C60 positive ions.Comment: 14 pages revte
The Fractal Properties of Internet
In this paper we show that the Internet web, from a user's perspective,
manifests robust scaling properties of the type where n
is the size of the basin connected to a given point, represents the density
of probability of finding n points downhill and s a
characteristic universal exponent. This scale-free structure is a result of the
spontaneous growth of the web, but is not necessarily the optimal one for
efficient transport. We introduce an appropriate figure of merit and suggest
that a planning of few big links, acting as information highways, may
noticeably increase the efficiency of the net without affecting its robustness.Comment: 6 pages,2 figures, epl style, to be published on Europhysics Letter
Quantitative description and modeling of real networks
In this letter we present data analysis and modeling of two particular cases
of study in the field of growing networks. We analyze WWW data set and
authorship collaboration networks in order to check the presence of correlation
in the data. The results are reproduced with a pretty good agreement through a
suitable modification of the standard AB model of network growth. In
particular, intrinsic relevance of sites plays a role in determining the future
degree of the vertex.Comment: 4 pages, 3 figure
Scale-free random branching tree in supercritical phase
We study the size and the lifetime distributions of scale-free random
branching tree in which branches are generated from a node at each time
step with probability . In particular, we focus on
finite-size trees in a supercritical phase, where the mean branching number
is larger than 1. The tree-size distribution exhibits a
crossover behavior when ; A characteristic tree size
exists such that for , and for , , where scales as . For , it follows the conventional
mean-field solution, with .
The lifetime distribution is also derived. It behaves as for , and for when branching step , and for all when . The analytic solutions are
corroborated by numerical results.Comment: 6 pages, 6 figure
Usefulness of Housekeeping Genes for the Diagnosis of Helicobacter pylori Infection, Strain Discrimination and Detection of Multiple Infection
Background: Helicobacter pylori infects human stomachs of over half the world's population, evades the immune response and establishes a chronic infection. Although most people remains asymptomatic, duodenal and gastric ulcers, MALT lymphoma and progression to gastric cancer could be developed. Several virulence factors such as flagella, lipopolysaccharide, adhesins and especially the vacuolating cytotoxin VacA and the oncoprotein CagA have been described for H. pylori. Despite the extensive published data on H. pylori, more research is needed to determine new virulence markers, the exact mode of transmission or the role of multiple infection. Materials and Methods: Amplification and sequencing of six housekeeping genes (amiA, cgt, cpn60, cpn70, dnaJ, and luxS) related to H. pylori pathogenesis have been performed in order to evaluate their usefulness for the specific detection of H. pylori, the genetic discrimination at strain level and the detection of multiple infection. A total of 52 H. pylori clones, isolated from 14 gastric biopsies from 11 patients, were analyzed for this purpose. Results: All genes were specifically amplified for H. pylori and all clones isolated from different patients were discriminated, with gene distances ranged from 0.9 to 7.8%. Although most clones isolated from the same patient showed identical gene sequences, an event of multiple infection was detected in all the genes and microevolution events were showed for amiA and cpn60 genes. Conclusions: These results suggested that housekeeping genes could be useful for H. pylori detection and to elucidate the mode of transmission and the relevance of the multiple infection
Extremal dynamics model on evolving networks
We investigate an extremal dynamics model of evolution with a variable number
of units. Due to addition and removal of the units, the topology of the network
evolves and the network splits into several clusters. The activity is mostly
concentrated in the largest cluster. The time dependence of the number of units
exhibits intermittent structure. The self-organized criticality is manifested
by a power-law distribution of forward avalanches, but two regimes with
distinct exponents tau = 1.98 +- 0.04 and tau^prime = 1.65 +- 0.05 are found.
The distribution of extinction sizes obeys a power law with exponent 2.32 +-
0.05.Comment: 4 pages, 5 figure
Comparable quality of bowel preparation with singleâday versus threeâday lowâresidue diet: Randomized controlled trial
Background and aims: There is controversy about the length of low-residue diet (LRD) for colonoscopy preparation. The aim of the study was to compare one-day vs. three-day LRD associated to standard laxative treatment for achieving an adequate colonoscopy preparation in average risk subjects with positive fecal immunochemical test undergoing screening colonoscopy. Methods: A non-inferiority, randomized, controlled, parallel-group clinical trial was performed in the setting of average risk colorectal cancer screening program. Participants were randomized to receive 1-day vs. 3-day LRD in addition to standard polyethilenglicol treatment. Adequacy of preparation was evaluated using the Boston Bowel Preparation Scale (BBPS). Primary outcome was achieving a BBPS â„ 2 in all colon segments. Analysis was performed for a non-inferiority margin of 5%, a 95% statistical power and one-sided 0.05 significance level. Results: A total of 855 patients were randomized. Adequate bowel preparation was similar between groups: 97.9% of patients in the 1-day LRD group vs 96.9% in the 3-day LRD group achieved the primary outcome (P-value for non-inferiority < 0.001). The percentage of patients with BBPS scores â„ 8 was superior in the 1-day LRD group (254 vs 221 in the 3-day LRD group, P = 0.032). The 1-day regimen was better tolerated than the 3-day diet. 47.7% (vs 28.7%, P < 0.05) of patients rated the 1-day LRD as very easy to follow. Conclusion: The 1-day LRD is non-inferior to 3-day LRD for achieving an adequate colon cleansing before average risk screening colonoscopy and it is better tolerated. Keywords: bowel preparation; colonoscopy; colorectal cancer; screening
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