322 research outputs found
Charge fluctuations and electron-phonon interaction in the finite- Hubbard model
In this paper we employ a gaussian expansion within the finite-
slave-bosons formalism to investigate the momentum structure of the
electron-phonon vertex function in the Hubbard model as function of and
. The suppression of large momentum scattering and the onset a small- peak structure, parametrized by a cut-off , are shown to be
essentially ruled by the band narrowing factor due to the
electronic correlation. A phase diagram of and in the whole
- space is presented. Our results are in more than qualitative agreement
with a recent numerical analysis and permit to understand some anomalous
features of the Quantum Monte Carlo data.Comment: 4 pages, eps figures include
Statistical analysis of magnetic divertor configuration influence on H-mode transitions
DIII-D plasmas are compared for two upper divertor configurations: with the outer strike point on the small angle slot (SAS) divertor target and with the outer strike point on the horizontal divertor target (HT). Scanning the vertical distance between the magnetic null point and the divertor target over a range 0.10–0.16 m is shown to increase the threshold power, Pth , and edge plasma power, PLoss , for the low-to-high confinement (L–H) and H–L transitions respectively, by up to a factor of 1.4. The X-point height scans were performed at three L-mode core plasma line average electron densities, n¯e= 1.2, 2.2 and 3.6 ×1019m−3 , to investigate the density dependence of divertor magnetic configuration influence on Pth . The X-point height, Zx-pt , was further extended across the range 0.16–0.22 m with the more open HT divertor configuration, for which a clear decrease in Pth with increasing Zx-pt is observed. The dependence of Pth on divertor magnetic geometry is further investigated using a time-dependent probability density function (PDF) model and information geometry to elucidate the roles played by pedestal plasma turbulence and perpendicular velocity flows. The degree of stochasticity of the plasma turbulence is observed to be sensitive to the plasma heating rate. The calculated square of the information rate shows changes in the relative density fluctuations and perpendicular velocity PDFs begin 2–5 ms prior to the L–H transition for three plasmas; providing a crucial measurement of the dynamic timescale of external transport barrier formation. Additionally, both information length and rate provide potential predictors of the L–H transition for these plasmas
Application of Hansch’s Model to Capsaicinoids and Capsinoids: A Study Using the Quantitative Structure−Activity Relationship. A Novel Method for the Synthesis of Capsinoids
We describe a synthetic approach for two families of compounds, the capsaicinoids and capsinoids,
as part of a study of the quantitative relationship between structure and activity
Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors
Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to
highlight an anomalously large band renormalization at high binding energies in
cuprate superconductors: the high energy 'waterfall' or high energy anomaly
(HEA). This paper demonstrates, using a combination of new ARPES measurements
and quantum Monte Carlo simulations, that the HEA is not simply the by-product
of matrix element effects, but rather represents a cross-over from a
quasiparticle band at low binding energies near the Fermi level to valence
bands at higher binding energy, assumed to be of strong oxygen character, in
both hole- and electron-doped cuprates. While photoemission matrix elements
clearly play a role in changing the aesthetic appearance of the band
dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate
description for the physics that underlies the strong band renormalization
giving rise to the HEA. Model calculations of the single-band Hubbard
Hamiltonian showcase the role played by correlations in the formation of the
HEA and uncover significant differences in the HEA energy scale for hole- and
electron-doped cuprates. In addition, this approach properly captures the
transfer of spectral weight accompanying both hole and electron doping in a
correlated material and provides a unifying description of the HEA across both
sides of the cuprate phase diagram.Comment: Original: 4 pages, 4 figures; Replaced: changed and updated content,
12 pages, 6 figure
The periodic Anderson model from the atomic limit and FeSi
The exact Green's functions of the periodic Anderson model for
are formally expressed within the cumulant expansion in terms of an effective
cumulant. Here we resort to a calculation in which this quantity is
approximated by the value it takes for the exactly soluble atomic limit of the
same model. In the Kondo region a spectral density is obtained that shows near
the Fermi surface a structure with the properties of the Kondo peak.
Approximate expressions are obtained for the static conductivity
and magnetic susceptibility of the PAM, and they are employed to fit
the experimental values of FeSi, a compound that behaves like a Kondo insulator
with both quantities vanishing rapidly for . Assuming that the system
is in the intermediate valence region, it was possible to find good agreement
between theory and experiment for these two properties by employing the same
set of parameters. It is shown that in the present model the hybridization is
responsible for the relaxation mechanism of the conduction electrons.Comment: 26 pages and 8 figure
Condition Indices as Surrogates of Energy Density and Lipid Content in Juveniles of Three Fish Species
To guide the selection of condition indices for juvenile fishes, we compared the ability of several indirect condition indices (those based on length-mass relationships, the hepatosomatic index, and relative lipid estimates from the Distell fish fatmeter) to assess energy density and lipid content of Summer Flounder Paralichthys dentatus, Striped BassMorone saxatilis, and Atlantic Croakers Micropogonias undulatus. These species use estuarine areas as nurseries, but they have different life history strategies and ecological niches that affect their energy storage strategies. We tested hypotheses that differences in the distribution and role of lipids as energy stores among species would influence the suitability of condition indices for estimating energy and lipid content. Length-based indices were most suitable for estimating energy and lipid content of juvenile Summer Flounder and Striped Bass, suggesting that length-based indices may be appropriate for juveniles that store energy as proteins (i.e., juveniles with low lipid content). The fatmeter suitably predicted energy and lipid content of Atlantic Croakers, indicating its potential for assessing condition of juveniles that store lipids for migration and that display a high range of observed lipid content. Even though a small size range was examined, fish length improved predictions of energy and lipid content for some of the indirect condition indices for Atlantic Croakers and Summer Flounder, suggesting that fish length should be considered when developing relationships among measures of condition. The selection of condition indices should be tailored to the life stage and species of interest based on the energy and lipid storage strategies used by the fish
Influence of processing on the volatile profile of strawberry spreads made with isomaltulose
[EN] A new strawberry spread formulated with fructose and isomaltulose (replacing sucrose partially or totally) and a high percentage of fruit was developed in line with the new trend of healthier products. This work studies the influence of some process variables (percentage of sugar, pectin and citric acid, and time of thermal treatment) on the volatile profile of these spreads with different formulations. The ripeness of the raw strawberries influences the concentrations of some of the compounds in the spreads, such as isobutyl acetate, butyl butyrate, 3-hexen-1-yl acetate or propan-2-ol. The process conditions have an important effect on the volatile profiles. Most of the esters and alcohols decreased whereas 13 new compounds appear, mostly furans (furfural, 2-acetylfurane, 5-methyl furfural, mesifurane) and aldehydes (octanal, nonanal, decanal and benzaldeyhde). In general, the spreads formulated with sucrose-isomaltulose that contained higher levels of pectin and citric acid gave better results in the preservation of the original aromatic compounds in raw strawberries.Authors would like to thank Direccion General de Investigacion del Ministerio de Ciencia y Tecnologia (AGL2008-01745/ALI) as well as the Universitat Politecnica de Valencia for the financial support given to this investigation.Peinado Pardo, I.; Rosa Barbosa, EM.; Heredia Gutiérrez, AB.; Escriche Roberto, MI.; Andrés Grau, AM. (2013). Influence of processing on the volatile profile of strawberry spreads made with isomaltulose. Food Chemistry. 138(1):621-629. https://doi.org/10.1016/j.foodchem.2012.09.104S621629138
Use of isomaltulose to formulate healthy spreadable strawberry products. Application of response surface methodology
Response surface methodology (RSM) was applied to optimize the formulation of a 50 Brix spreadable strawberry product with healthier sugars and a high percentage of fruit. A central composite design was applied to analyse the influence of four independent
variables on the quality parameters. Each of the variables was analysed at five different levels (X1: % of isomaltulose (0, 12.5, 25, 37.5 and 50%), X2: % of pectin (0.5, 1, 1.5, 2 and
2.5%), X3: % of citric acid (0, 0.25, 0.5, 0.75 and 1%) and X4: time of thermal treatment (0, 5 10, 15 and 20 min). Physicochemical properties, microbiological stability, antioxidant
properties (anthocyanin content and antioxidant activity) as well as optical and mechanical
properties were considered for the optimization. The influence of storage time on the
above parameters was also evaluated. Percentages of pectin and citric acid were the
variables that most influenced the measured parameters. In general terms, high levels of
these two variables (2% pectin; 0.75% citric acid) resulted in greater antioxidant activity,
consistency and adhesiveness values. The optimal formulation to obtain a spreadable
strawberry product was fresh strawberry, 50% fructose, 50% isomaltulose, 1% citric acid and 1.5% pectin; the ingredients were mixed, and heated to 85 1C, and the product was stable after 90 days stored at room temperature.Authors would like to thank Direccion General de Investigacion del Ministerio de Ciencia y Tecnologia (AGL2008-01745/ALI) as well as the Universitat Politecnica de Valencia for the financial support given to this investigation.Peinado Pardo, I.; Rosa Barbosa, EM.; Heredia Gutiérrez, AB.; Andrés Grau, AM. (2015). Use of isomaltulose to formulate healthy spreadable strawberry products. Application of response surface methodology. Food Bioscience. 9:47-59. https://doi.org/10.1016/j.fbio.2014.08.002S4759
Adjacent single-stranded regions mediate processing of tRNA precursors by RNase E direct entry
The RNase E family is renowned for being central to
the processing and decay of all types of RNA in
many species of bacteria, as well as providing the
first examples of endonucleases that can recognize
50
-monophosphorylated ends thereby increasing
the efficiency of cleavage. However, there is
increasing evidence that some transcripts can be
cleaved efficiently by Escherichia coli RNase E via
direct entry, i.e. in the absence of the recognition of
a 50
-monophosphorylated end. Here, we provide
biochemical evidence that direct entry is central to
the processing of transfer RNA (tRNA) in E. coli, one
of the core functions of RNase E, and show that it is
mediated by specific unpaired regions that are
adjacent, but not contiguous to segments cleaved
by RNase E. In addition, we find that direct entry at a
site on the 50 side of a tRNA precursor triggers a
series of 50
-monophosphate-dependent cleavages.
Consistent with a major role for direct entry
in tRNA processing, we provide additional evidence
that a 50
-monophosphate is not required to
activate the catalysis step in cleavage. Other
examples of tRNA precursors processed via direct
entry are also provided. Thus, it appears increasingly
that direct entry by RNase E has a major role
in bacterial RNA metabolism
Multidimensional Proteomics Analysis of Amniotic Fluid to Provide Insight into the Mechanisms of Idiopathic Preterm Birth
Though recent advancement in proteomics has provided a novel perspective on several distinct pathogenetic mechanisms leading to preterm birth (inflammation, bleeding), the etiology of most preterm births still remains elusive. We conducted a multidimensional proteomic analysis of the amniotic fluid to identify pathways related to preterm birth in the absence of inflammation or bleeding.A proteomic fingerprint was generated from fresh amniotic fluid using surface-enhanced laser desorbtion ionization time of flight (SELDI-TOF) mass spectrometry in a total of 286 consecutive samples retrieved from women who presented with signs or symptoms of preterm labor or preterm premature rupture of the membranes. Inflammation and/or bleeding proteomic patterns were detected in 32% (92/286) of the SELDI tracings. In the remaining tracings, a hierarchical algorithm was applied based on descriptors quantifying similarity/dissimilarity among proteomic fingerprints. This allowed identification of a novel profile (Q-profile) based on the presence of 5 SELDI peaks in the 10-12.5 kDa mass area. Women displaying the Q-profile (mean+/-SD, gestational age: 25+/-4 weeks, n = 40) were more likely to deliver preterm despite expectant management in the context of intact membranes and normal amniotic fluid clinical results. Utilizing identification-centered proteomics techniques (fluorescence two-dimensional differential gel electrophoresis, robotic tryptic digestion and mass spectrometry) coupled with Protein ANalysis THrough Evolutionary Relationships (PANTHER) ontological classifications, we determined that in amniotic fluids with Q-profile the differentially expressed proteins are primarily involved in non-inflammatory biological processes such as protein metabolism, signal transduction and transport.Proteomic profiling of amniotic fluid coupled with non-hierarchical bioinformatics algorithms identified a subgroup of patients at risk for preterm birth in the absence of intra-amniotic inflammation or bleeding, suggesting a novel pathogenetic pathway leading to preterm birth. The altered proteins may offer opportunities for therapeutical intervention and future drug development to prevent prematurity
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