872 research outputs found
Post-Newtonian expansions for perfect fluids
We prove the existence of a large class of dynamical solutions to the
Einstein-Euler equations that have a first post-Newtonian expansion. The
results here are based on the elliptic-hyperbolic formulation of the
Einstein-Euler equations used in \cite{Oli06}, which contains a singular
parameter \ep = v_T/c, where is a characteristic velocity associated
with the fluid and is the speed of light. As in \cite{Oli06}, energy
estimates on weighted Sobolev spaces are used to analyze the behavior of
solutions to the Einstein-Euler equations in the limit \ep\searrow 0, and to
demonstrate the validity of the first post-Newtonian expansion as an
approximation
The usability of description logics: understanding the cognitive difficulties presented by description logics
Description Logics have been extensively studied from the viewpoint of decidability and computational tractability. Less attention has been given to their usability and the cognitive difficulties they present, in particular for those who are not specialists in logic. This paper reports on a study into the difficulties associated with the most commonly used Description Logic features. Psychological theories are used to take account of these. Whilst most of the features presented no difficulty to participants, the comprehension of some was affected by commonly occurring misconceptions. The paper proposes explanations and remedies for some of these difficulties. In addition, the time to confirm stated inferences was found to depend both on the maximum complexity of the relations involved and the number of steps in the argument
Shadowing in photo-production : role of in-medium hadrons
We study the effects of in-medium hadronic properties on shadowing in
photon-nucleus interactions in Glauber model as well as in the multiple
scattering approach. A reasonable agreement with the experimental data is
obtained in a scenario of downward spectral shift of the hadrons. Shadowing is
found to be insensitive to the broadening of the spectral functions. An impact
parameter dependent analysis of shadowing might shed more light on the role of
in-medium properties of hadrons.Comment: Title modified; version to appear in PRC, Rapid Communication
Nonfactorizable contributions in B decays to charmonium: the case of
Nonleptonic to charmonium decays generally show deviations from the
factorization predictions. For example, the mode has
been experimentally observed with sizeable branching fraction while its
factorized amplitude vanishes. We investigate the role of rescattering effects
mediated by intermediate charmed meson production in this class of decay modes,
and consider with the meson.
Using an effective lagrangian describing interactions of pairs of heavy-light
mesons with a quarkonium state, we relate this mode to the
analogous mode with in the final state. We find large enough to be measured at the factories, so that this decay
mode could be used to study the poorly known .Comment: RevTex, 16 pages, 2 eps figure
Strangeness nuclear physics: a critical review on selected topics
Selected topics in strangeness nuclear physics are critically reviewed. This
includes production, structure and weak decay of --Hypernuclei, the
nuclear interaction and the possible existence of bound
states in nuclei. Perspectives for future studies on these issues are also
outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical
Journal
Tuning the cross-linking density and cross-linker in core cross-linked polymeric micelles and its effects on the particle stability in human blood plasma and mice
Core cross-linked polymeric micelles (CCPMs) are designed to improve the therapeutic profile of hydrophobic drugs, reduce or completely avoid protein corona formation, and offer prolonged circulation times, a prerequisite for passive or active targeting. In this study, we tuned the CCPM stability by using bifunctional or trifunctional cross-linkers and varying the cross-linkable polymer block length. For CCPMs, amphiphilic thiol-reactive polypept(o)ides of polysarcosine-block-poly(S-ethylsulfonyl-l-cysteine) [pSar-b-pCys(SO2Et)] were employed. While the pCys(SO2Et) chain lengths varied from Xn = 17 to 30, bivalent (derivatives of dihydrolipoic acid) and trivalent (sarcosine/cysteine pentapeptide) cross-linkers have been applied. Asymmetrical flow field-flow fraction (AF4) displayed the absence of aggregates in human plasma, yet for non-cross-linked PM and CCPMs cross-linked with dihydrolipoic acid at [pCys(SO2Et)]17, increasing the cross-linking density or the pCys(SO2Et) chain lengths led to stable CCPMs. Interestingly, circulation time and biodistribution in mice of non-cross-linked and bivalently cross-linked CCPMs are comparable, while the trivalent peptide cross-linkers enhance the circulation half-life from 11 to 19 h.Biopharmaceutic
A Phenomenological Analysis of Heavy Hadron Lifetimes
A phenomenological analysis of lifetimes of bottom and charmed hadrons within
the framework of the heavy quark expansion is performed. The baryon matrix
element is evaluated using the bag model and the nonrelativistic quark model.
We find that bottom-baryon lifetimes follow the pattern
.
However, neither the lifetime ratio nor the
absolute decay rates of the baryon and mesons can be explained.
One way of solving both difficulties is to allow the presence of linear
corrections by scaling the inclusive nonleptonic width with the fifth power of
the hadron mass rather than the heavy quark mass . The hierarchy
of bottom baryon lifetimes is dramatically modified to
: The
longest-lived among bottom baryons in the OPE prescription now
becomes shortest-lived. The replacement of by in nonleptonic
widths is natural and justified in the PQCD-based factorization approach
formulated in terms of hadron-level kinematics. For inclusive charmed baryon
decays, we argue that since the heavy quark expansion does not converge, local
duality cannot be tested in this case. We show that while the ansatz of
substituting the heavy quark mass by the hadron mass provides a much better
description of the charmed-baryon lifetime {\it ratios}, it appears unnatural
and unpredictive for describing the {\it absolute} inclusive decay rates of
charmed baryons, contrary to the bottom case.Comment: 35 pages, to appear in Phys. Rev. The CDF result on the lifetime
ratio of Lambda_b and B_d is discusse
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
Photocleavable core cross-linked polymeric micelles of polypept(o)ides and ruthenium(II) complexes
Core cross-linking of polymeric micelles has been demonstrated to contribute to enhanced stability that can improve the therapeutic efficacy. Photochemistry has the potential to provide spatial resolution and on-demand drug release. In this study, light-sensitive polypyridyl-ruthenium(II) complexes were combined with polypept(o)ides for photocleavable core cross-linked polymeric micelles. Block copolymers of polysarcosine-block-poly(glutamic acid) were synthesized by ring-opening N-carboxyanhydride polymerization and modified with aromatic nitrile-groups on the glutamic acid side chain. The modified copolymers self-assembled into micelles and were cross-linked by cis-diaquabis(2,2'-bipyridine)-ruthenium(II) ([Ru(bpy)2(H2O)2]2+) or cis-diaquabis(2,2'-biquinoline)-ruthenium(II) ([Ru(biq)2(H2O)2]2+). Depending on the flexibility and hydrophobicity of the nitrile linker, either small spherical structures (Dh 45 nm, PDI 0.11) or worm-like micelles were obtained. The cross-linking reaction did not affect the overall size distribution but induced a change in the metal-to-ligand charge transfer peak from 482 to 420 nm and 592 to 548 nm. The cross-linked micelles displayed colloidal stability after incubation with human blood plasma and during gel permeation chromatography in hexafluoroisopropanol. Light-induced cleavage of [Ru(bpy)2(H2O)2]2+ was accomplished within 300 s, while [Ru(biq)2(H2O)2]2+ could not be completely released. Analysis in HuH-7 cells revealed increased cytotoxicity via micellar delivery of [Ru(bpy)2(H2O)2]2+ but mostly irradiation damage for [Ru(biq)2(H2O)2]2+. Further evaluation in ovo confirmed stable circulation pointing towards the future development of quick-release complexes.Drug Delivery Technolog
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