176 research outputs found
Chiral Lagrangians and Quark Condensate in Nuclei
We study the evolution with density of the quark condensate in the nuclear
medium with interacting nucleons and including the short range correlations. We
work with two chiral models, the linear sigma model and the non-linear one. For
the last one we use two versions, one which does not satisfy PCAC, and another
one which does. We show that the quark condensate, as other observables, is
independent on the variant selected. The application to physical pions excludes
the linear sigma model as a credible one. In the non-linear models our
conclusions are: first there is no systematic reaction imposed by chiral
symmetry against symmetry restoration, second, if one keeps only the s-wave
pion-nucleon interaction, the quark condensate evolves essentially linearly
with density, as if the nucleons were non interacting. The main correction
arises from the p-wave pion-nucleon interaction. Last, in the s-wave optical
potential, chiral symmetry tolerates but does not impose two body terms. On the
other hand the effect of correlations linked to the isospin symmetric amplitude
is negligible.Comment: 24 pages, LaTex, 7 PostScript Figures, a couple of misprints
corrected , 2 references added, a few modifications of the main text and
conclusion, to be published in Nucl. Phys.
Virtual Pion Scattering
We propose a theory which exploits the charge-exchange reactions
(He,H) and (p,n) as effective sources of virtual pions.
We consider processes in which the creation of virtual pions is followed by
conventional coupled-channel pion scattering to discrete nuclear states. This
picture allows us to incorporate successful theories of pion scattering and
utilize virtual pions as probes of the nuclear matter. For coherent pion
production we clearly demonstrate that the shift of the coherent peak position
in the excitation function of He-A relative to He-N scattering is
determined entirely by the pion nucleus rescattering.Comment: 10 pages, revtex 3, 2 figures attached in file figures.u
Kaon-Nucleon Scattering from Chiral Lagrangians
The s-wave scattering amplitude is computed up to one-loop order
corresponding to next-to-next-to-leading order (or NLO in short) with a
heavy-baryon effective chiral Lagrangian. Constraining the low-energy constants
by on-shell scattering lengths, we obtain contributions of each chiral order up
to NLO and find that the chiral corrections are ``natural" in the sense of
viable effective field theories. We have also calculated off-shell -wave
scattering amplitudes relevant to kaonic atoms and condensation in
``nuclear star" matter including the effect of . The
amplitude is found to be quite sensitive to the intermediate
contribution, while the amplitude varies smoothly with the C.M. energy.
The crossing-even one-loop corrections are found to play an important role in
determining the higher-order chiral corrections.Comment: 14 pages and 2 figures(LaTeX), SNUTP-93-81. (References are added in
the reference [21]
Architecture et urbanisme de villégiature : un état de la recherche
Dix ans après le précédent numéro d’In Situ consacré à la villégiature, les points de vue sur la question ne semblent pas fondamentalement différents, même si, comme le montre Claude Mignot, les perspectives se sont sensiblement élargies. Si changement il y a, il serait peut-être plus patrimonial que scientifique, davantage lié à la perception des « objets » de la villégiature qu’aux préoccupations des chercheurs. Il faut bien reconnaître que désormais, même si le combat patrimonial est toujo..
Architecture et urbanisme de villégiature : un état de la recherche
Dix ans après le précédent numéro d’In Situ consacré à la villégiature, les points de vue sur la question ne semblent pas fondamentalement différents, même si, comme le montre Claude Mignot, les perspectives se sont sensiblement élargies. Si changement il y a, il serait peut-être plus patrimonial que scientifique, davantage lié à la perception des « objets » de la villégiature qu’aux préoccupations des chercheurs. Il faut bien reconnaître que désormais, même si le combat patrimonial est toujo..
Neutron-proton mass difference in isospin asymmetric nuclear matter
Isospin-breaking effects in the baryonic sector are studied in the framework
of a medium-modified Skyrme model. The neutron-proton mass difference in
infinite, asymmetric nuclear matter is discussed. In order to describe the
influence of the nuclear environment on the skyrmions, we include
energy-dependent charged and neutral pion optical potentials in the s- and
p-wave channels. The present approach predicts that the neutron-proton mass
difference is mainly dictated by its strong part and that it strongly decreases
in neutron matter.Comment: 11 pages, 6 figures; some new references adde
Remarks on N N -> N N pi beyond leading order
In recent years a two-scale expansion was established to study reactions of
the type N N -> N N pi within chiral perturbation theory. Then the diagrams of
some subclasses that are invariant under the choice of the pion field no longer
appear at the same chiral order. In this letter we show that the proposed
expansion still leads to well defined results. We also discuss the appropriate
choice of the heavy baryon propagator.Comment: 16 pages, 4 figures, minor correction
Interconnect Capacitance Modelling in a VDSM CMOS Technology
International audienceThis paper introduces a set of analytical formulations for 3D modelling of inter- and intra-layer capacitance. Based on real silicon data, we have developed and validated efficient and accurate analytical models that are an helpful alternative to lookup tables or numerical simulations
SETD2 transcriptional control of ATG14L/S isoforms regulates autophagosome-lysosome fusion
Macroautophagy/autophagy is an evolutionarily conserved and tightly regulated catabolic process involved in the maintenance of cellular homeostasis whose dysregulation is implicated in several pathological processes. Autophagy begins with the formation of phagophores that engulf cytoplasmic cargo and mature into double-membrane autophagosomes; the latter fuse with lysosomes/vacuoles for cargo degradation and recycling. Here, we report that yeast Set2, a histone lysine methyltransferase, and its mammalian homolog, SETD2, both act as positive transcriptional regulators of autophagy. However, whereas Set2 regulates the expression of several autophagy-related (Atg) genes upon nitrogen starvation, SETD2 effects in mammals were found to be more restricted. In fact, SETD2 appears to primarily regulate the differential expression of protein isoforms encoded by the ATG14 gene. SETD2 promotes the expression of a long ATG14 isoform, ATG14L, that contains an N-terminal cysteine repeats domain, essential for the efficient fusion of the autophagosome with the lysosome, that is absent in the short ATG14 isoform, ATG14S. Accordingly, SETD2 loss of function decreases autophagic flux, as well as the turnover of aggregation-prone proteins such as mutant HTT (huntingtin) leading to increased cellular toxicity. Hence, our findings bring evidence to the emerging concept that the production of autophagy-related protein isoforms can differentially affect core autophagy machinery bringing an additional level of complexity to the regulation of this biological process in more complex organisms.Peer reviewe
Meson Condensation in Dense Matter Revisited
The results for meson condensation in the literature vary markedly depending
on whether one uses chiral perturbation theory or the current-algebra-plus-PCAC
approach. To elucidate the origin of this discrepancy, we re-examine the role
of the sigma-term in meson condensation. We find that the resolution of the
existing discrepancy requires a knowledge of terms in the Lagrangian that are
higher order in density than hitherto considered.Comment: 10pages, USC(NT)-94-
- …