21,964 research outputs found
On finite volume effects in the chiral extrapolation of baryon masses
We perform an analysis of the QCD lattice data on the baryon octet and
decuplet masses based on the relativistic chiral Lagrangian. The baryon self
energies are computed in a finite volume at next-to-next-to-next-to leading
order (NLO), where the dependence on the physical meson and baryon masses
is kept. The number of free parameters is reduced significantly down to 12 by
relying on large- sum rules. Altogether we describe accurately more than
220 data points from six different lattice groups, BMW, PACS-CS, HSC, LHPC,
QCDSF-UKQCD and NPLQCD. Values for all counter terms relevant at NLO are
predicted. In particular we extract a pion-nucleon sigma term of 39
MeV and a strangeness sigma term of the nucleon of MeV. The flavour SU(3) chiral limit of the baryon octet and
decuplet masses is determined with MeV and MeV.
Detailed predictions for the baryon masses as currently evaluated by the ETM
lattice QCD group are made.Comment: 44 pages, 10 figures and 6 tables - the revised manuscript contains
the results of additional fits at the N^2LO level - 4 additional figures show
the size of finite volume corrections for each lattice point - more technical
details on the evaluation of finite volume effects are give
Scale dependence of cosmological backreaction
Due to the non-commutation of spatial averaging and temporal evolution,
inhomogeneities and anisotropies (cosmic structures) influence the evolution of
the averaged Universe via the cosmological backreaction mechanism. We study the
backreaction effect as a function of averaging scale in a perturbative approach
up to higher orders. We calculate the hierarchy of the critical scales, at
which 10% effects show up from averaging at different orders. The dominant
contribution comes from the averaged spatial curvature, observable up to scales
of 200 Mpc. The cosmic variance of the local Hubble rate is 10% (5%) for
spherical regions of radius 40 (60) Mpc. We compare our result to the one from
Newtonian cosmology and Hubble Space Telescope Key Project data.Comment: 6 pages, 2 figures; v3: substantial modifications, new figure
Polarizations and Nullcone of Representations of Reductive Groups
The paper starts with the following simple observation. Let V be a representation of a reductive group G, and let f_1,f_2,...,f_n be homogeneous invariant functions. Then the polarizations of f_1,f_2,...,f_n define the nullcone of k 0} h(t) x = 0 for all x in L. This is then applied to many examples. A surprising result is about the group SL(2,C) where almost all representations V have the property that all linear subspaces of the nullcone are annihilated. Again, this has interesting applications to the invariants on several copies. Another result concerns the n-qubits which appear in quantum computing. This is the representation of a product of n copies of on the n-fold tensor product C^2 otimes C^2 otimes ... otimes C^2. Here we show just the opposite, namely that the polarizations never define the nullcone of several copies if n <= 3. (An earlier version of this paper, distributed in 2002, was split into two parts; the first part with the title ``On the nullcone of representations of reductive groups'' is published in Pacific J. Math. {bf 224} (2006), 119--140.
Extrasolar Trojan Planets close to Habitable Zones
We investigate the stability regions of hypothetical terrestrial planets
around the Lagrangian equilibrium points L4 and L5 in some specific extrasolar
planetary systems. The problem of their stability can be treated in the
framework of the restricted three body problem where the host star and a
massive Jupiter-like planet are the primary bodies and the terrestrial planet
is regarded as being massless. From these theoretical investigations one cannot
determine the extension of the stable zones around the equilibrium points.
Using numerical experiments we determined their largeness for three test
systems chosen from the table of the know extrasolar planets, where a giant
planet is moving close to the so-called habitable zone around the host star in
low eccentric orbits. The results show the dependence of the size and structure
of this region, which shrinks significantly with the eccentricity of the known
gas giant.Comment: 4 pages, 4 figures, submitted to A&
VP24-Karyopherin alpha binding affinities differ between Ebolavirus species, nfluencing interferon inhibition and VP24 stability
Zaire ebolavirus (EBOV), Bundibugyo ebolavirus (BDBV), and Reston ebolavirus (RESTV) belong to the same genus but exhibit different virulence properties. VP24 protein, a structural protein present in all family members, blocks interferon (IFN) signaling and likely contributes to virulence. Inhibition of IFN signaling by EBOV VP24 (eVP24) involves its interaction with the NPI-1 subfamily of karyopherin alpha (KPNA) nuclear transporters. Here, we evaluated eVP24, BDBV VP24 (bVP24), and RESTV VP24 (rVP24) interactions with three NPI-1 subfamily KPNAs (KPNA1, KPNA5, and KPNA6). Using purified proteins, we demonstrated that each VP24 binds to each of the three NPI-1 KPNAs. bVP24, however, exhibited approximately 10-fold-lower KPNA binding affinity than either eVP24 or rVP24. Cell-based assays also indicate that bVP24 exhibits decreased KPNA interaction, decreased suppression of IFN induced gene expression, and a decreased half-life in transfected cells compared to eVP24 or rVP24. Amino acid sequence alignments between bVP24 and eVP24 also identified residues within and surrounding the previously defined eVP24-KPNA5 binding interface that decrease eVP24-KPNA affinity or bVP24-KPNA affinity. VP24 mutations that lead to reduced KPNA binding affinity also decrease IFN inhibition and shorten VP24 half-lives. These data identify novel functional differences in VP24-KPNA interaction and reveal a novel impact of the VP24-KPNA interaction on VP24 stability. IMPORTANCE The interaction of Ebola virus (EBOV) VP24 protein with host karyopherin alpha (KPNA) proteins blocks type I interferon (IFN) signaling, which is a central component of the host innate immune response to viral infection. Here, we quantitatively compared the interactions of VP24 proteins from EBOV and two members of the Ebolavirus genus, Bundibugyo virus (BDBV) and Reston virus (RESTV). The data reveal lower binding affinity of the BDBV VP24 (bVP24) for KPNAs and demonstrate that the interaction with KPNA modulates inhibition of IFN signaling and VP24 stability. The effect of KPNA interaction on VP24 stability is a novel functional consequence of this virus-host interaction, and the differences identified between viral species may contribute to differences in pathogenesis
Reconnection and acoustic emission of quantized vortices in superfluid by the numerical analysis of the Gross-Pitaevskii equation
We study numerically the reconnection of quantized vortices and the
concurrent acoustic emission by the analysis of the Gross-Pitaevskii equation.
Two quantized vortices reconnect following the process similar to classical
vortices; they approach, twist themselves locally so that they become
anti-parallel at the closest place, reconnect and leave separately.The
investigation of the motion of the singular lines where the amplitude of the
wave function vanishes in the vortex cores confirms that they follow the above
scenario by reconnecting at a point. This reconnection is not contradictory to
the Kelvin's circulation theorem, because the potential of the superflow field
becomes undefined at the reconnection point. When the locally anti-parallel
part of the vortices becomes closer than the healing length, it moves with the
velocity comparable to the sound velocity, emits the sound waves and leads to
the pair annihilation or reconnection; this phenomena is concerned with the
Cherenkov resonance. The vortices are broken up to smaller vortex loops through
a series of reconnection, eventually disappearing with the acoustic emission.
This may correspond to the final stage of the vortex cascade process proposed
by Feynman. The change in energy components, such as the quantum, the
compressible and incompressible kinetic energy is analyzed for each dynamics.
The propagation of the sound waves not only appears in the profile of the
amplitude of the wave function but also affects the field of its phase,
transforming the quantum energy due to the vortex cores to the kinetic energy
of the phase field.Comment: 11 pages, 16 figures, LaTe
Ion-neutral sympathetic cooling in a hybrid linear rf Paul and magneto-optical trap
Long range polarization forces between ions and neutral atoms result in large
elastic scattering cross sections, e.g., 10^6 a.u. for Na+ on Na or Ca+ on Na
at cold and ultracold temperatures. This suggests that a hybrid ion-neutral
trap should offer a general means for significant sympathetic cooling of atomic
or molecular ions. We present SIMION 7.0 simulation results concerning the
advantages and limitations of sympathetic cooling within a hybrid trap
apparatus, consisting of a linear rf Paul trap concentric with a Na
magneto-optical trap (MOT). This paper explores the impact of various heating
mechanisms on the hybrid system and how parameters related to the MOT, Paul
trap, number of ions, and ion species affect the efficiency of the sympathetic
cooling
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