1,196 research outputs found
A sticky business: the status of the conjectured viscosity/entropy density bound
There have been a number of forms of a conjecture that there is a universal
lower bound on the ratio, eta/s, of the shear viscosity, eta, to entropy
density, s, with several different domains of validity. We examine the various
forms of the conjecture. We argue that a number of variants of the conjecture
are not viable due to the existence of theoretically consistent
counterexamples. We also note that much of the evidence in favor of a bound
does not apply to the variants which have not yet been ruled out.Comment: 23 pages, 4 figures, added references, corrected typos, added
subsection in response to Son's comments in arXiv:0709.465
A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
We present a self-consistent three-dimensional Monte-Carlo radiative transfer
model of the stellar and dust emission in the Milky-Way, and have computed
synthetic observations of the 3.6 to 100 microns emission in the Galactic
mid-plane. In order to compare the model to observations, we use the GLIMPSE,
MIPSGAL, and IRAS surveys to construct total emission spectra, as well as
longitude and latitude profiles for the emission. The distribution of stars and
dust is taken from the SKY model, and the dust emissivities includes an
approximation of the emission from polycyclic aromatic hydrocarbons in addition
to thermal emission. The model emission is in broad agreement with the
observations, but a few modifications are needed to obtain a good fit. Firstly,
by adjusting the model to include two major and two minor spiral arms rather
than four equal spiral arms, the fit to the longitude profiles for |l|>30
degrees can be improved. Secondly, introducing a deficit in the dust
distribution in the inner Galaxy results in a better fit to the shape of the
IRAS longitude profiles at 60 and 100 microns. With these modifications, the
model fits the observed profiles well, although it systematically
under-estimates the 5.8 and 8.0 microns fluxes. One way to resolve this
discrepancy is to increase the abundance of PAH molecules by 50% compared to
the original model, although we note that changes to the dust distribution or
radiation field may provide alternative solutions. Finally, we use the model to
quantify which stellar populations contribute the most to the heating of
different dust types, and which stellar populations and dust types contribute
the most to the emission at different wavelengths.Comment: Published in A&A. This version has been revised (compared to the
published version) to include additional references to previous work. Scripts
to reproduce the results in this paper can be found as supplementary material
on the A&A site, or at https://github.com/hyperion-rt/paper-galaxy-rt-mode
Subconjunctival Injection of XG-102, a JNK Inhibitor Peptide, in Patients with Intraocular Inflammation: A Safety and Tolerability Study.
Abstract Purpose: We aimed to investigate the safety, tolerability, and systemic diffusion of a single escalating dose of XG-102 (a 31-D-amino-acid peptide inhibiting JNK pathway activation), administered subconjunctivally in the treatment of post-surgery or post-trauma intraocular inflammation. Methods: This is a dose-escalating, tolerance Phase Ib study. Twenty patients with post-surgery or post-traumatic intraocular inflammation were assigned to 1 of the 4 dose escalating (45, 90, 450, or 900 μg XG-102) groups of 5 patients each. Patients were evaluated at 24, 48 h, 8, and 28 days following the administration of XG-102, including laboratory tests, standard eye examinations, vital signs, and occurrence of adverse events. A single plasma quantification of XG-102 was performed 30 min after administration, according to previous pharmacokinetics studies performed on volunteers. Results: A total of 17 non-serious adverse events, considered unrelated to the study treatment, were reported for 10 patients. The adverse event incidence was not related to the drug dose. All patients experienced a decrease in intraocular inflammation as of 24 h post-administration and this decrease was sustained up to 28 days thereafter. No patient required local injection or systemic administration of corticoids following the administration of XG-102. XG-102 was undetectable in the first 3 dose groups. In the fourth-dose group (900 μg) the XG-102 plasma levels were above the limit of detection for 3 patients and above the limit of quantification for 1 patient. Conclusions: In this first clinical trial using XG-102, administered as a single subconjunctival injection as adjunct therapy, in patients with recent post-surgery or post-trauma intraocular inflammation is safe and well tolerated. Further studies are required to evaluate its efficacy
Coherent information analysis of quantum channels in simple quantum systems
The coherent information concept is used to analyze a variety of simple
quantum systems. Coherent information was calculated for the information decay
in a two-level atom in the presence of an external resonant field, for the
information exchange between two coupled two-level atoms, and for the
information transfer from a two-level atom to another atom and to a photon
field. The coherent information is shown to be equal to zero for all
full-measurement procedures, but it completely retains its original value for
quantum duplication. Transmission of information from one open subsystem to
another one in the entire closed system is analyzed to learn quantum
information about the forbidden atomic transition via a dipole active
transition of the same atom. It is argued that coherent information can be used
effectively to quantify the information channels in physical systems where
quantum coherence plays an important role.Comment: 24 pages, 7 figs; Final versiob after minor changes, title changed;
to be published in Phys. Rev. A, September 200
Knot soliton in Weinberg-Salam model
We study numerically the topological knot solution suggested recently in the
Weinberg-Salam model. Applying the SU(2) gauge invariant Abelian projection we
demonstrate that the restricted part of the Weinberg-Salam Lagrangian
containing the interaction of the neutral boson with the Higgs scalar can be
reduced to the Ginzburg-Landau model with the hidden SU(2) symmetry. The energy
of the knot composed from the neutral boson and Higgs field has been evaluated
by using the variational method with a modified Ward ansatz. The obtained
numerical value is 39 Tev which provides the upper bound on the electroweak
knot energy.Comment: 6 pages, 3 figures, analysis of stability adde
Optical response of superfluid state in dilute atomic Fermi-Dirac gases
We theoretically study the propagation of light in a Fermi-Dirac gas in the
presence of a superfluid state. BCS pairing between atoms in different
hyperfine levels may significantly increase the optical linewidth and line
shift of a quantum degenerate Fermi-Dirac gas and introduce a local-field
correction that, under certain conditions, dramatically dominates over the
Lorentz-Lorenz shift. These optical properties could possibly unambiguously
sign the presence of the superfluid state and determine the value of the BCS
order parameter.Comment: 5 pages, 2 figure
Chaperone-mediated native folding of a β-scorpion toxin in the periplasm of E.coli
Background: Animal neurotoxin peptides are valuable probes for investigating ion channel structure/function relationships and represent lead compounds for novel therapeutics and insecticides. However, misfolding and aggregation are common outcomes when toxins containing multiple disulfides are expressed in bacteria.
Methods: The ß-scorpion peptide toxin Bj-xtrIT from Hottentotta judaica and four chaperone enzymes (DsbA, DsbC, SurA and FkpA) were co-secreted into the oxidizing environment of the E.coli periplasm. Expressed Bj-xtrIT was purified and analyzed by HPLC and FPLC chromatography. Its thermostability was assessed using synchrotron radiation circular dichroism spectroscopy and its crystal structure was determined.
Results: Western blot analysis showed that robust expression was only achieved when cells co-expressed the chaperones. The purified samples were homogenous and monodisperse and the protein was thermostable. The crystal structure of the recombinant toxin confirmed that it adopts the native disulfide connectivity and fold.
Conclusions: The chaperones enabled correct folding of the four-disulfide-bridged Bj-xtrIT toxin. There was no apparent sub-population of misfolded Bj-xtrIT, which attests to the effectiveness of this expression method.
General Significance: We report the first example of a disulfide-linked scorpion toxin natively folded during bacterial expression. This method eliminates downstream processing steps such as oxidative refolding or cleavage of a fusion-carrier and therefore enables efficient production of insecticidal Bj-xtrIT. Periplasmic chaperone activity may produce native folding of other extensively disulfide-reticulated proteins including animal neurotoxins. This work is therefore relevant to venomics and studies of a wide range of channels and receptors
What are communities of practice? A comparative review of four seminal works
This paper is a comparative review of four seminal works on communities of practice. It is argued that the ambiguities of the terms community and practice are a source of the concept's reusability allowing it to be reappropriated for different purposes, academic and practical. However, it is potentially confusing that the works differ so markedly in their conceptualizations of community, learning, power and change, diversity and informality. The three earlier works are underpinned by a common epistemological view, but Lave and Wenger's 1991 short monograph is often read as primarily about the socialization of newcomers into knowledge by a form of apprenticeship, while the focus in Brown and Duguid's article of the same year is, in contrast, on improvising new knowledge in an interstitial group that forms in resistance to management. Wenger's 1998 book treats communities of practice as the informal relations and understandings that develop in mutual engagement on an appropriated joint enterprise, but his focus is the impact on individual identity. The applicability of the concept to the heavily individualized and tightly managed work of the twenty-first century is questionable. The most recent work by Wenger – this time with McDermott and Snyder as coauthors – marks a distinct shift towards a managerialist stance. The proposition that managers should foster informal horizontal groups across organizational boundaries is in fact a fundamental redefinition of the concept. However it does identify a plausible, if limited, knowledge management (KM) tool. This paper discusses different interpretations of the idea of 'co-ordinating' communities of practice as a management ideology of empowerment
Novel Approach to Confront Electroweak Data and Theory
A novel approach to study electroweak physics at one-loop level in generic
theories is introduced. It separates the 1-loop
corrections into two pieces: process specific ones from vertex and box
contributions, and universal ones from contributions to the gauge boson
propagators. The latter are parametrized in terms of four effective form
factors , , and corresponding to the , , and
propagators. Under the assumption that only the Standard Model contributes to
the process specific corrections, the magnitudes of the four form factors are
determined at and at q^2=\mmz by fitting to all available precision
experiments. These values are then compared systematically with predictions of
theories. In all fits \alpha_s(\mz) and
\bar{\alpha}(\mmz) are treated as external parameters in order to keep the
interpretation as flexible as possible. The treatment of the electroweak data
is presented in detail together with the relevant theoretical formulae used to
interpret the data. No deviation from the Standard Model has been identified.
Ranges of the top quark and Higgs boson masses are derived as functions of
\alpha_s(\mz) and \bar{\alpha}(\mmz). Also discussed are consequences of
the recent precision measurement of the left-right asymmetry at SLC as well as
the impact of a top quark mass and an improved mass measurement.Comment: 123 pages, LaTeX (33 figures available via anonymous ftp),
KEK-TH-375, KEK preprint 93-159, KANAZAWA-94-19, DESY 94-002, YUMS 94-22,
SNUTP 94-82, to be published in Z.Phys.
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