1,795 research outputs found
Is Turing's Thesis the Consequence of a More General Physical Principle?
We discuss historical attempts to formulate a physical hypothesis from which
Turing's thesis may be derived, and also discuss some related attempts to
establish the computability of mathematical models in physics. We show that
these attempts are all related to a single, unified hypothesis.Comment: 10 pages, 0 figures; section 1 revised, other minor change
Inflation near a metastable de Sitter vacuum from moduli stabilisation
We study the cosmological properties of a metastable de Sitter vacuum
obtained recently in the framework of type IIB flux compactifications in the
presence of three D7-brane stacks, based on perturbative quantum corrections at
both world-sheet and string loop level that are dominant at large volume and
weak coupling. In the simplest case, the model has one effective parameter
controlling the shape of the potential of the inflaton which is identified with
the volume modulus. The model provides a phenomenological successful
small-field inflation for a value of the parameter that makes the minimum very
shallow and near the maximum. The horizon exit is close to the inflection point
while most of the required e-folds of the Universe expansion are generated near
the minimum, with a prediction for the ratio of tensor-to-scalar primordial
fluctuations . Despite its shallowness, the minimum
turns out to be practically stable. We show that it can decay only through the
Hawking-Moss instanton leading to an extremely long decay rate. Obviously, in
order to end inflation and obtain a realistic model, new low-energy physics is
needed around the minimum, at intermediate energy scales of order
GeV. An attractive possibility is by introducing a "waterfall"' field within
the framework of hybrid inflation.Comment: 25 pages, 9 figures; v2: published version, minor correction
On the nature of the residual meson-meson interaction from simulations with a QED model
A potential between mesons is extracted from 4-point functions within lattice
gauge theory taking 2+1 dimensional QED as an example. This theory possesses
confinement and dynamical fermions. The resulting meson-meson potential has a
short-ranged hard repulsive core and the expected dipole-dipole forces lead to
attraction at intermediate distances. Sea quarks lead to a softer form of the
total potential.Comment: 4 pages, uuencoded tar-compressed postscript file, contribution to
Lattice'9
Baryon-Baryon Potentials on the Lattice
The interaction of spatially extended heavy baryons is investigated in the
framework of lattice QCD with dynamical quarks. It is shown that the expected
dipole forces have a very short range and that the baryon-antibaryon
interaction is more attractive than the baryon-baryon interaction. Sea quarks
play a minor important role.Comment: 8 pages, uuencoded postscript file; Physics Letters B, in pres
Content validation of a new measure of patient-reported barriers to antiretroviral therapy adherence, the I-Score: results from a Delphi study
Background
Over a third of people living with HIV (PLHIV) have suboptimal adherence to antiretroviral therapy (ART). Measures of barriers to ART adherence often lack comprehensiveness. To help manage ART adherence barriers in HIV care, we are developing a new patient-reported outcome measure (PROM) of these barriers (the I-Score).
Methods
We assessed the content validity of 100 items (distinct barriers) to retain only those most relevant to both PLHIV and HIV health/social service providers. A web-based Delphi was conducted in Canada and France, collecting data from December 2018 to October 2019. Items were evaluated on relevance (the combined rated importance and actionability for HIV care of items among both PLHIV and providers); comprehensibility (rated item clarity); comprehensiveness (examined against our conceptual framework); cross-cultural equivalence (based on comparisons by questionnaire language (English, French) and country of residence). Pearsonâs chi-square tests were used for comparisons by language, country, gender, and stakeholder group (PLHIV, providers).
Results
Panelists included 40 PLHIV and 57 providers (66% response rate). Thirty-one items were retained based on consensus thresholds for relevance (minimum: 50% for PLHIV, 60% for providers) and showed good comprehensibility and comprehensiveness, when compared to our conceptual framework (representation of: 6/6 domains, 15/20 subdomains). No significant difference in relevance based on language or country was found among retained items, suggestive of cross-cultural equivalence. Among all 100 items, only 6 significant differences on relevance were observed for gender. For 62 items, the relevance ratings of PLHIV and providers differed significantly, with providers showing greater endorsement of all items but one.
Discussion
The Delphi led to a much-needed item reduction. Remaining items highlight the panelâs multidimensional priorities for the PROM on ART adherence barriers, with few, if any, differences by language, country, and gender. While the analyses may lack generalizability and power, the sample size is considered adequate for a PROM validation study.
Conclusion
Retained items showed good content validity. The different patterns of item endorsement observed underscore the utility of engaging multiple stakeholder groups in PROM development for use in clinical practice. The greater endorsement of items by providers versus patients merits further investigation, including the implications of such differentials for measure development.KE is partially supported by a SPOR Mentorship Chair in Innovative Clinical Trials awarded by the CIHR to BL (Grant No. 383427). BL is supported by a career award, LE 250, from the Quebec Ministry of Health for researchers in Family Medicine. The Delphi benefited from methodological expertise and funding from the Quebec SPOR Support Unit -McGill Methodological Developments Platform (Grant No. M006). The Delphi is a subproject of the PROM development study, the I-Score Study, which is supported, in part, by the CIHR HIV Clinical Trials Network (CTN 283) and by a research Grant from the Investigator Initiated Studies Program of Merck Canada Inc. (Grant No. IISP-53538), neither of which had a hand in the design, conduct, or writing up of this work. The opinions expressed in this study are those of the authors and do not necessarily represent those of Merck Canada Inc or its affiliates or related companies
Extraction of hadron-hadron potentials on the lattice within 2+1 dimensional QED
A potential between mesons is extracted from 4-point functions within lattice
gauge theory taking 2+1 dimensional QED as an example. This theory possesses
confinement and dynamical fermions. The resulting meson-meson potential has a
short-ranged hard repulsive core due to antisymmetrization. The expected
dipole-dipole forces lead to attraction at intermediate distances. Sea quarks
lead to a softer form of the total potential.Comment: 12 pages, uuencoded tar-compressed postscript fil
Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration
We consider stochastic particle acceleration in plasmas around stellar mass
black holes to explain the emissions above 1 MeV from Galactic black hole
candidates. We show that for certain parameter regimes, electrons can overcome
Coulomb losses and be accelerated beyond the thermal distribution to form a new
population, whose distribution is broad and usually not a power law; the peak
energy of the distribution is determined by the balance between acceleration
and cooling, with particles piling up around it. Radiation by inverse Compton
scattering off the thermal (from background) and non-thermal (produced by
acceleration) particles can in principle explain the hard X-ray to gamma-ray
emissions from black hole candidates. We present model fits of Cyg X-1 and GRO
J0422 in 50 keV -- 5 MeV region observed with OSSE and COMPTEL.Comment: 2 figures, to appear in March 20 of ApJ
Nonlocal Kinetic Equation and Simulations of Heavy Ion Reactions
A kinetic equation which combines the quasiparticle drift of Landau's
equation with a dissipation governed by a nonlocal and noninstantaneous
scattering integral in the spirit of Enskog corrections is discussed. Numerical
values of the off-shell contribution to the Wigner distribution, of the
collision duration and of the collision nonlocality are presented for different
realistic potentials. On preliminary results we show that simulations of
quantum molecular dynamics extended by the nonlocal treatment of collisions
leads to a broader proton distribution bringing the theoretical spectra closer
towards the experimental values than the local approach.Comment: Proceedings of the Erice School, published as Vol. 42 of "Progress in
Particle and Nuclear Physics" by ELSEVIE
The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM
The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low
Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based
multi-band astronomical Variable Objects Monitor), a French-Chinese mission
with Italian contribution. Observations are expected to start in 2013. It has
been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent
sources of the sky, thanks to its wide field of view (about 2 sr) and its
remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging
sensitivity in the 4-70 keV energy band. These characteristics are well suited
to detect highly redshifted GRBs, and consequently to provide fast and accurate
triggers to other onboard or ground-based instruments able to follow-up the
detected events in a very short time from the optical wavelength bands up to
the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008,
Nanjing, Chin
- âŠ