377 research outputs found
Restoration of Macroscopic Isotropy on -Simplex Fractal Conductor Networks
Restoration of macroscopic isotropy has been investigated in (d+1)-simplex
fractal conductor networks via exact real space renormalization group
transformations. Using some theorems of fixed point theory, it has been shown
very rigoroursly that the macroscopic conductivity becomes isotropic for large
scales and anisotropy vanishes with a scaling exponent which is computed
exactly for arbitrary values of d and decimation numbers b=2,3,4 and
5.Comment: 27 Pages, 3 Figure
Epidemiology: Back to the Future
In 2018, the Society for Epidemiologic Research and its partner journal, the American Journal of Epidemiology, assembled a working group to develop a set of papers devoted to the "future of epidemiology." These 14 papers covered a wide range of topic areas and perspectives, from thoughts on our profession, teaching, and methods to critical areas of substantive research. The authors of those papers considered current challenges and future opportunities for research and education. In light of past commentaries, 4 papers also include reflections on the discipline at present and in the future
Interface roughening with nonlinear surface tension
Using stability arguments, this Brief Report suggests that a term that
enhances the surface tension in the presence of large height fluctuations
should be included in the Kardar-Parisi-Zhang equation. A one-loop
renormalization group analysis then shows for interface dimensions larger than
an unstable strong-coupling fixed point that enters the system
from infinity. The relevance of these results to the roughening transition is
discussed.Comment: 4 pages RevTeX, 1 figur
Coarse-grained simulation of transmembrane peptides in the gel phase
We use Dissipative Particle Dynamics simulations, combined with parallel tempering and umbrella sampling, to investigate the potential of mean force between model transmembrane peptides in the various phases of a lipid bilayer, including the low-temperature gel phase.
The observed oscillations in the effective interaction between peptides are consistent with the different structures of the surrounding lipid phases
Geology, geochemistry and SrâNd constraints of selected metavolcanic rocks from the eastern boundary of the Saharan Metacraton, southern Sudan : a possible revision of the eastern boundary
Neoproterozoic, Pan-African low-grade metavolcanic rocks and associated mafic and ultramafic rocks of
ophiolitic origin have long been identified within the pre-Neoproterozoic Saharan Metacraton (SMC).
These low-grade rocks within generally high-grade (upper amphibolite facies) gneiss and schist have
not yet been fully investigated, and their geological and geotectonic significance have been recognised
only in a very few localities: (1) the DelgoâAtmur ophiolite and low-grade volcano-sedimentary belt,
(2) the Rahib ophiolite and low-grade sedimentary fold and thrust belt, both in northern Sudan along
the eastern boundary of the Saharan Metacraton and (3) the low-grade volcano-sedimentary rocks in
the Central African Republic.
Dismembered and low-grade metamorphosed occurrences of mafic extrusive and intrusive and minor
ultramafic rocks, grouped as the Arid unit, similar to those of the Arabian Nubian Shield (ANS), are
reported here for the first time in the westernmost part of the Nuba Mountains, southeastern Sudan.
These occurrences are interpreted to represent part of an ophiolite sequence with a lower cumulate layer
composed of layered gabbro and minor cumulate hornblendite and a top layer of thick massive gabbro,
pillowed basalt and basaltic andesite. The Arid unit is structurally underlain by basaltic-andesite and
andesite and a metasedimentary sequence identified as turbidite and both grouped as the Abutulu unit.
All of the rocks are slightly sheared, deformed and metamorphosed under low-grade greenschist facies
to epidote amphibolite sub-facies. New geochemical and SrâNd isotope data reveal that the low-grade
metavolcanic rocks of the westernmost Nuba Mountains represent a Neoproterozoic oceanic arc/backarc
assemblage. The massive gabbro and pillowed basalt of the Arid unit show the geochemical characteristics
of HFSE-depleted tholeiitic basalt while the co-genetic and more evolved meta-andesite of Abutulu
unit show a calc-alkaline signature. Both units display a REE pattern characterized by LILE enrichment
indicating formation in an arc/back-arc environment. This arc was active at around 778 ± 90 Ma (Smâ
Nd 12 WR isochron) that is similar in age to the arc magmatism in the ANS. The close interval between
the TDM Nd model age (average of 10 metavolcanic samples is 814 Ma) and the crystallization age
(778 ± 90 Ma) is indicative of little or no involvement of older material. The western Nuba Mountains
metavolcanic rocks have eNd values of +5.9 at 778 Ma (average of 12 samples) indicating a depleted mantle
source similar to that of the ANS (published range from +6.5 to +8.4). The eNd values of the metavolcanic
rocks are different from previously published ages of high-grade basement rocks that occupy the
area west of the Kabus suture and east of Abutulu (+2.2 and +3.5 for the Rashad and Abbassyia).
It is proposed that the metavolcanic and associated plutonic mafic rocks represent a unique
Neoproterozoic entity named the Abutulu terrane that developed in a marginal back-arc basin west of
the medium-grade gneiss of the Nuba Mountains. If the Abutulu terrane is included as a part of the
ANS, then the eastern boundary of the SMC is adjacent to the western edge of the ANS along the
Abutulu suture.http://www.elsevier.com/locate/precamres2017-08-31hb2016Geolog
Interface Depinning in the Absence of External Driving Force
We study the pinning-depinning phase transition of interfaces in the quenched
Kardar-Parisi-Zhang model as the external driving force goes towards zero.
For a fixed value of the driving force we induce depinning by increasing the
nonlinear term coefficient , which is related to lateral growth, up to
a critical threshold. We focus on the case in which there is no external force
applied (F=0) and find that, contrary to a simple scaling prediction, there is
a finite value of that makes the interface to become depinned. The
critical exponents at the transition are consistent with directed percolation
depinning. Our results are relevant for paper wetting experiments, in which an
interface gets moving with no external driving force.Comment: 4 pages, 3 figures included, uses epsf. Submitted to PR
Genomics and transcriptomics of Xanthomonas campestris species challenge the concept of core type III effectome
The bacterial species Xanthomonas campestris infects a wide range of Brassicaceae. Specific pathovars of this species cause black rot (pv. campestris), bacterial blight of stock (pv. incanae) or bacterial leaf spot (pv. raphani).
In this study, we extended the genomic coverage of the species by sequencing and annotating the genomes of strains from pathovar incanae (CFBP 1606R and CFBP 2527R), pathovar raphani (CFBP 5828R) and a pathovar formerly named barbareae (CFBP 5825R). While comparative analyses identified a large core ORFeome at the species level, the core type III effectome was limited to only three putative type III effectors (XopP, XopF1 and XopAL1). In Xanthomonas, these effector proteins are injected inside the plant cells by the type III secretion system and contribute collectively to virulence. A deep and strand-specific RNA sequencing strategy was adopted in order to experimentally refine genome annotation for strain CFBP 5828R. This approach also allowed the experimental definition of novel ORFs and non-coding RNA transcripts. Using a constitutively active allele of hrpG, a master regulator of the type III secretion system, a HrpG-dependent regulon of 141 genes co-regulated with the type III secretion system was identified. Importantly, all these genes but seven are positively regulated by HrpG and 56 of those encode components of the Hrp type III secretion system and putative effector proteins.
This dataset is an important resource to mine for novel type III effector proteins as well as for bacterial genes which could contribute to pathogenicity of X. campestris
Circulating pancreatic polypeptide concentrations predict visceral and liver fat content
CONTEXT AND OBJECTIVE: No current biomarker can reliably predict visceral and liver fat content, both of which are risk factors for cardiovascular disease. Vagal tone has been suggested to influence regional fat deposition. Pancreatic polypeptide (PP) is secreted from the endocrine pancreas under vagal control. We investigated the utility of PP in predicting visceral and liver fat.
PATIENTS AND METHODS: Fasting plasma PP concentrations were measured in 104 overweight and obese subjects (46 men and 58 women). In the same subjects, total and regional adipose tissue, including total visceral adipose tissue (VAT) and total subcutaneous adipose tissue (TSAT), were measured using whole-body magnetic resonance imaging. Intrahepatocellular lipid content (IHCL) was quantified by proton magnetic resonance spectroscopy.
RESULTS: Fasting plasma PP concentrations positively and significantly correlated with both VAT (r = 0.57, P < .001) and IHCL (r = 0.51, P < .001), but not with TSAT (r = 0.02, P = .88). Fasting PP concentrations independently predicted VAT after controlling for age and sex. Fasting PP concentrations independently predicted IHCL after controlling for age, sex, body mass index (BMI), waist-to-hip ratio, homeostatic model assessment 2-insulin resistance, (HOMA2-IR) and serum concentrations of triglyceride (TG), total cholesterol (TC), and alanine aminotransferase (ALT). Fasting PP concentrations were associated with serum ALT, TG, TC, low- and high-density lipoprotein cholesterol, and blood pressure (P < .05). These associations were mediated by IHCL and/or VAT. Fasting PP and HOMA2-IR were independently significantly associated with hepatic steatosis (P < .01).
CONCLUSIONS: Pancreatic polypeptide is a novel predictor of visceral and liver fat content, and thus a potential biomarker for cardiovascular risk stratification and targeted treatment of patients with ectopic fat deposition
Avalanche Dynamics in Evolution, Growth, and Depinning Models
The dynamics of complex systems in nature often occurs in terms of
punctuations, or avalanches, rather than following a smooth, gradual path. A
comprehensive theory of avalanche dynamics in models of growth, interface
depinning, and evolution is presented. Specifically, we include the Bak-Sneppen
evolution model, the Sneppen interface depinning model, the Zaitsev flux creep
model, invasion percolation, and several other depinning models into a unified
treatment encompassing a large class of far from equilibrium processes. The
formation of fractal structures, the appearance of noise, diffusion with
anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be
related to the same underlying avalanche dynamics. This dynamics can be
represented as a fractal in spatial plus one temporal dimension. We develop
a scaling theory that relates many of the critical exponents in this broad
category of extremal models, representing different universality classes, to
two basic exponents characterizing the fractal attractor. The exact equations
and the derived set of scaling relations are consistent with numerical
simulations of the above mentioned models.Comment: 27 pages in revtex, no figures included. Figures or hard copy of the
manuscript supplied on reques
Development of a transgenic early flowering pear (Pyrus communis L.) genotype by RNAi silencing of PcTFL1-1 and PcTFL1-2
Trees require a long maturation period, known as juvenile phase, before they can reproduce, complicating their genetic improvement as compared to annual plants. âSpadonaâ, one of the most important European pear (Pyrus communis L.) cultivars grown in Israel, has a very long juvenile period, up to 14 years, making breeding programs extremely slow. Progress in understanding the molecular basis of the transition to flowering has revealed genes that accelerate reproductive development when ectopically expressed in transgenic plants. A transgenic line of âSpadonaâ, named Early Flowering-Spadona (EF-Spa), was produced using a MdTFL1 RNAi cassette targeting the native pear genes PcTFL1-1 and PcTFL1-2. The transgenic line had three T-DNA insertions, one assigned to chromosome 2 and two to chromosome 14 PcTFL1-1 and PcTFL1-2 were completely silenced, and EF-Spa displayed an early flowering phenotype: flowers developed already in tissue culture and on most rooted plants 1â8 months after transfer to the greenhouse. EF-Spa developed solitary flowers from apical or lateral buds, reducing vegetative growth vigor. Pollination of EF-Spa trees generated normal-shaped fruits with viable F1 seeds. The greenhouse-grown transgenic F1 seedlings formed shoots and produced flowers 1â33 months after germination. Sequence analyses, of the non-transgenic F1 seedlings, demonstrated that this approach can be used to recover seedlings that have no trace of the T-DNA. Thus, the early flowering transgenic line EF-Spa obtained by PcTFL1 silencing provides an interesting tool to accelerate pear breeding
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