7,761 research outputs found
Analysis of General Power Counting Rules in Effective Field Theory
We derive the general counting rules for a quantum effective field theory
(EFT) in dimensions. The rules are valid for strongly and weakly
coupled theories, and predict that all kinetic energy terms are canonically
normalized. They determine the energy dependence of scattering cross sections
in the range of validity of the EFT expansion. We show that the size of cross
sections is controlled by the power counting of EFT, not by chiral
counting, even for chiral perturbation theory (PT). The relation between
and is generalized to dimensions. We show that the
naive dimensional analysis counting is related to counting. The
EFT counting rules are applied to PT, low-energy weak interactions,
Standard Model EFT and the non-trivial case of Higgs EFT.Comment: V2: more details and examples added; version published in journal. 17
pages, 4 figures, 2 table
Assessment of average muscle fiber conduction velocity from surface EMG signals during fatiguing dynamic contractions
Metabolic modeling and analysis of the metabolic switch in Streptomyces coelicolor
Background
The transition from exponential to stationary phase in Streptomyces coelicolor is accompanied by a major metabolic switch and results in a strong activation of secondary metabolism. Here we have explored the underlying reorganization of the metabolome by combining computational predictions based on constraint-based modeling and detailed transcriptomics time course observations.
Results
We reconstructed the stoichiometric matrix of S. coelicolor, including the major antibiotic biosynthesis pathways, and performed flux balance analysis to predict flux changes that occur when the cell switches from biomass to antibiotic production. We defined the model input based on observed fermenter culture data and used a dynamically varying objective function to represent the metabolic switch. The predicted fluxes of many genes show highly significant correlation to the time series of the corresponding gene expression data. Individual mispredictions identify novel links between antibiotic production and primary metabolism.
Conclusion
Our results show the usefulness of constraint-based modeling for providing a detailed interpretation of time course gene expression data
Luteal Blood Flow and progesterone concentration during first and second postpartum estrous cycle in lactating dairy cows
The aim of the present study was to determine the differences in corpus luteum (CL) functionality between the first postpartum estrous cycle and the following cycle in lactating dairy cows. Luteal blood flow (LBF), luteal size and blood progesterone (P4) concentration were monitored during the first and second postpartum estrous cycle. During the first and second postpartum estrous cycle, the mean LBF value increased (p < .05) from early to late dioestrus, while it decreased rapidly in proestrus, resulting statistically lower (p < .05) than those registered in all previous phases. Statistically significant differences were not observed between overall LBF during first and second postpartum estrous cycle (p > .05). During the first postpartum estrous cycle, P4 blood concentrations showed a significant reduction (p < .05) from dioestrus to proestrus. A different trend of P4 concentrations was observed during the second postpartum estrous cycle, where mean P4 value registered in proestrus resulted statistically lower than those registered in the previous cycle phases (p < .05). The mean P4 concentration registered over the first postpartum estrous cycle resulted statistically lower (p < .05) than that registered during the second one. A significant correlation between P4 concentrations and LBF was registered only during the second postpartum estrous cycle. Results indicate that during the first postpartum estrous cycle, P4 concentration was independent of luteal blood flow and luteal size
Phonon distributions of a single bath mode coupled to a quantum dot
The properties of an unconventional, single mode phonon bath coupled to a
quantum dot, are investigated within the rotating wave approximation. The
electron current through the dot induces an out of equilibrium bath, with a
phonon distribution qualitatively different from the thermal one. In selected
transport regimes, such a distribution is characterized by a peculiar selective
population of few phonon modes and can exhibit a sub-Poissonian behavior. It is
shown that such a sub-Poissonian behavior is favored by a double occupancy of
the dot. The crossover from a unequilibrated to a conventional thermal bath is
explored, and the limitations of the rotating wave approximation are discussed.Comment: 21 Pages, 7 figures, to appear in New Journal of Physics - Focus on
Quantum Dissipation in Unconventional Environment
Composite Fermions with Spin at
to be published in proceedings of Varenna Summer School "E. Fermi": Course CLI "Quantum phenomena in mesoscopic systems", July 2002This is the author accepted manuscript. The final version is available from IOS press via the DOI in this record.The model of Composite Fermions for describing interacting electrons in two dimensions in the presence of a magnetic field is described. In this model, charged Fermions are combined with an even number of magnetic flux quanta in such a way that the external magnetic field is compensated on the average for half filling of Landau levels and the interaction is incorporated into an effective mass of the new composite particles. The fluctuations of the Chern-Simons gauge field, which describes formally the flux attachment, induce new interactions between the Composite Fermions. The effective interaction is investigated with particular emphasis on the role of the electron spin at filling factor . For a system with equal numbers of spin-up and spin-down electrons it is found that the dominant effective interaction is attractive in the spin-singlet channel. This can induce a ground state consisting of Cooper pairs of Composite Fermions that is separated from the excited states by a gap. The results are used to understand recent spin polarization measurements done in the region of the Fractional Quantum Hall Effect at different constant filling factors.Acknowledgment This work has been supported by the European Union via the TMR
and RTN programmes (FMRX-CT98-0180, HPRN-CT2000-00144), by the Deutsche
Forschungsgemeinschaft within the Schwerpunkt âQuanten-Hall-Effektâ of the Universitšat
Hamburg, and by the Italian MURST via PRIN00
Parametrization and Stress-Energy-Momentum Tensors in Metric Field Theories
We give an exposition of the parametrization method of Kuchar [1973] in the
context of the multisymplectic approach to field theory, as presented in Gotay
and Marsden [2008a]. The purpose of the formalism developed herein is to make
any classical field theory, containing a metric as a sole background field,
generally covariant (that is, "parametrized," with the spacetime diffeomorphism
group as a symmetry group) as well as fully dynamic. This is accomplished by
introducing certain "covariance fields" as genuine dynamic fields. As we shall
see, the multimomenta conjugate to these new fields form the Piola-Kirchhoff
version of the stress-energy-momentum tensor field, and their Euler-Lagrange
equations are vacuously satisfied. Thus, these fields have no additional
physical content; they serve only to provide an efficient means of
parametrizing the theory. Our results are illustrated with two examples, namely
an electromagnetic field and a Klein-Gordon vector field, both on a background
spacetime.Comment: 13 pages, 1 figur
El sĂndrome de caquexia tumoral
En este trabajo realizamos una revisiĂłn de los mecanismos patogĂ©nicos que intervienen en el desarrollo de la caquexia tumoral, asĂ como de sus consecuencias clĂnicas y de las medidas terapĂ©uticas que podemos establecer para su tratamiento.This paper is a review of the pathogenesis of tumoral cachexia. Also, we present the main clinical signs of this syndrome and the therapeutic protocols to treat it
Comparison between adult and foetal adnexa derived equine post-natal mesenchymal stem cells
Background Little is known about the differences among adult and foetal equine mesenchymal stem cells (MSCs), and no data exist about their comparative ultrastructural morphology. The aim of this study was to describe and compare characteristics, immune properties, and ultrastructural morphology of equine adult (bone marrow: BM, and adipose tissue: AT) and foetal adnexa derived (umbilical cord blood: UCB, and Wharton's jelly: WJ) MSCs. Results No differences were observed in proliferation during the first 3 passages. While migration ability was similar among cells, foetal MSCs showed a higher adhesion ability, forming smaller spheroids after hanging drop culture (P < 0.05). All MSCs differentiated toward adipogenic, chondrogenic and osteogenic lineages, only tenogenic differentiation was less evident for WJ-MSCs. Data obtained by PCR confirmed MHC1 expression and lack of MHC2 expression in all four cell types. Foetal adnexa MSCs were positive for genes specific for anti-inflammatory and angiogenic factors (IL6, IL8, IL beta 1) and WJ-MSCs were the only positive for OCT4 pluripotency gene. At immunofluorescence all cells expressed typical mesenchymal markers (alpha-SMA, N-cadherin), except for BM-MSCs, which did not express N-cadherin. By transmission electron microscopy, it was observed that WJ-MSCs had a higher (P < 0.05) number of microvesicles compared to adult MSCs, and UCB-MSCs showed more microvesicles than BM-MSCs (P < 0.05). AT-MSCs had a lower number of mitochondria than WJ-MSCs (P < 0.05), and mitochondrial area was higher for WJ-MSCs compared to UCB and AT-MSCs (P < 0.05). Conclusions Results demonstrate that MSCs from adult and foetal tissues have different characteristics, and foetal MSCs, particularly WJ derived ones, seem to have some charactestics that warrant further investigation into potential advantages for clinical application
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