6,532 research outputs found
The Fundamental Plane of Gamma-ray Globular Clusters
We have investigated the properties of a group of -ray emitting
globular clusters (GCs) which have recently been uncovered in our Galaxy. By
correlating the observed -ray luminosities with various
cluster properties, we probe the origin of the high energy photons from these
GCs. We report is positively correlated with the encounter rate
and the metalicity which place an
intimate link between the gamma-ray emission and the millisecond pulsar
population. We also find a tendency that increase with the energy
densities of the soft photon at the cluster location. Furthermore, the
two-dimensional regression analysis suggests that , soft photon
densities, and / possibly span fundamental
planes which potentially provide better predictions for the -ray
properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap
Observing two dark accelerators around the Galactic Centre with Fermi Large Area Telescope
We report the results from a detailed ray investigation in the field
of two "dark accelerators", HESS J1745-303 and HESS J1741-302, with years
of data obtained by the Fermi Large Area Telescope. For HESS J1745-303, we
found that its MeV-GeV emission is mainly originated from the "Region A" of the
TeV feature. Its ray spectrum can be modeled with a single power-law
with a photon index of from few hundreds MeV to TeV. Moreover,
an elongated feature, which extends from "Region A" toward northwest for
, is discovered for the first time. The orientation of this
feature is similar to that of a large scale atomic/molecular gas distribution.
For HESS J1741-302, our analysis does not yield any MeV-GeV counterpart for
this unidentified TeV source. On the other hand, we have detected a new point
source, Fermi J1740.1-3013, serendipitously. Its spectrum is apparently curved
which resembles that of a ray pulsar. This makes it possibly
associated with PSR B1737-20 or PSR J1739-3023.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in MNRA
A sandpile model with tokamak-like enhanced confinement phenomenology
Confinement phenomenology characteristic of magnetically confined plasmas
emerges naturally from a simple sandpile algorithm when the parameter
controlling redistribution scalelength is varied. Close analogues are found for
enhanced confinement, edge pedestals, and edge localised modes (ELMs), and for
the qualitative correlations between them. These results suggest that tokamak
observations of avalanching transport are deeply linked to the existence of
enhanced confinement and ELMs.Comment: Manuscript is revtex (latex) 1 file, 7 postscript figures Revised
version is final version accepted for publication in PRL Revisions are mino
Persistence in Cluster--Cluster Aggregation
Persistence is considered in diffusion--limited cluster--cluster aggregation,
in one dimension and when the diffusion coefficient of a cluster depends on its
size as . The empty and filled site persistences are
defined as the probabilities, that a site has been either empty or covered by a
cluster all the time whereas the cluster persistence gives the probability of a
cluster to remain intact. The filled site one is nonuniversal. The empty site
and cluster persistences are found to be universal, as supported by analytical
arguments and simulations. The empty site case decays algebraically with the
exponent . The cluster persistence is related to the
small behavior of the cluster size distribution and behaves also
algebraically for while for the behavior is
stretched exponential. In the scaling limit and with fixed the distribution of intervals of size between
persistent regions scales as , where is the average interval size and . For finite the
scaling is poor for , due to the insufficient separation of the two
length scales: the distances between clusters, , and that between
persistent regions, . For the size distribution of persistent regions
the time and size dependences separate, the latter being independent of the
diffusion exponent but depending on the initial cluster size
distribution.Comment: 14 pages, 12 figures, RevTeX, submitted to Phys. Rev.
Life at high Deborah number
In many biological systems, microorganisms swim through complex polymeric
fluids, and usually deform the medium at a rate faster than the inverse fluid
relaxation time. We address the basic properties of such life at high Deborah
number analytically by considering the small-amplitude swimming of a body in an
arbitrary complex fluid. Using asymptotic analysis and differential geometry,
we show that for a given swimming gait, the time-averaged leading-order
swimming kinematics of the body can be expressed as an integral equation on the
solution to a series of simpler Newtonian problems. We then use our results to
demonstrate that Purcell's scallop theorem, which states that time-reversible
body motion cannot be used for locomotion in a Newtonian fluid, breaks down in
polymeric fluid environments
On geometric problems related to Brown-York and Liu-Yau quasilocal mass
We discuss some geometric problems related to the definitions of quasilocal
mass proposed by Brown-York \cite{BYmass1} \cite{BYmass2} and Liu-Yau
\cite{LY1} \cite{LY2}. Our discussion consists of three parts. In the first
part, we propose a new variational problem on compact manifolds with boundary,
which is motivated by the study of Brown-York mass. We prove that critical
points of this variation problem are exactly static metrics. In the second
part, we derive a derivative formula for the Brown-York mass of a smooth family
of closed 2 dimensional surfaces evolving in an ambient three dimensional
manifold. As an interesting by-product, we are able to write the ADM mass
\cite{ADM61} of an asymptotically flat 3-manifold as the sum of the Brown-York
mass of a coordinate sphere and an integral of the scalar curvature plus
a geometrically constructed function in the asymptotic region outside
. In the third part, we prove that for any closed, spacelike, 2-surface
in the Minkowski space for which the Liu-Yau mass is
defined, if bounds a compact spacelike hypersurface in ,
then the Liu-Yau mass of is strictly positive unless lies on
a hyperplane. We also show that the examples given by \'{O} Murchadha, Szabados
and Tod \cite{MST} are special cases of this result.Comment: 28 page
Persistence with Partial Survival
We introduce a parameter , called partial survival, in the persistence of
stochastic processes and show that for smooth processes the persistence
exponent changes continuously with , being the usual
persistence exponent. We compute exactly for a one-dimensional
deterministic coarsening model, and approximately for the diffusion equation.
Finally we develop an exact, systematic series expansion for , in
powers of , for a general Gaussian process with finite density of
zero crossings.Comment: 5 pages, 2 figures, references added, to appear in Phys.Rev.Let
Halogen ligth thermogravimetric technique for determining the retained water in fine aggregates used for concrete mixing design
[EN] Measuring the rate of water retention of the aggregates used in mortars and concrete is required to achieve a good mix design. The water retention, specifically absorption, is used to keep constant the water/cement ratio. This paper focuses on the study of a new technique for measuring retained water in fine aggregates. In order to obtain results, the procedure described in the existing standards takes more than 24 h. Additionally, it involves high consumption of heat energy due to the use of drying ovens. Furthermore, the results obtained remain highly variable and therefore discussed by the scientific community.In this research, a novel technique based on a halogen moisture analyzer was implemented. The technique was assessed using an experiment design with a surface response model. The most important factors and levels were identified together with the interactions between them. Finally, the model was validated and the results
obtained with this technique were compared with those obtained by conventional techniques in order to verify that they were equivalent.Arias Jaramillo, Y.; Paya Bernabeu, JJ.; Ochoa Botero, JC. (2015). Halogen ligth thermogravimetric technique for determining the retained water in fine aggregates used for concrete mixing design. Journal of Thermal Analysis and Calorimetry: an international forum for thermal studies. 123:127-134. doi:10.1007/s10973-015-4902-8S127134123Djerbi Tegguer A. Determining the water absorption of recycled aggregates utilizing hydrostatic weighing approach. Constr Build Mater. 2012;27:112–6.Kasemchaisiri R, Tangtermsirikul S. A method to determine water retainability of porous fine aggregate for design and quality control of fresh concrete. Constr Build Mater. 2007;21:1322–34.Gonilho Pereira C, Castro-Gomes J, Pereira de Oliveira L. Influence of natural coarse aggregate size, mineralogy and water content on the permeability of structural concrete. Constr Build Mater. 2009;23:602–8.Cortas R, Roiziére E, Staquet S, Hamami A, Delplancke-Ogletree M. Effect of the water saturation of aggregates on the shrinkage induced cracking risk of concrete at early age. Cem Concr Compos. 2014;50:1–9.Black R. The determination of specific gravity using Siphon-Can method. Cem Concr Aggreg. 1986;8:46–50.Saxer E. A direct method of determining absorption and specific gravity of aggregates. 1956;2.Hughes B, Famili H., Part 1—Absorption of concrete aggregates, Part 2—saturated air techniques for determining the absorption of aggregates. In: Absorptions of concrete aggregates. Birmingham University; 1971.Tam VWY, Gao XF, Tam CM, Chan CH. New approach in measuring water absorption of recycled aggregates. Constr Build Mater. 2008;22:364–9.Balcedowiak W. Phase analysis of high-calcium line by TG. J Therm Anal Calorim. 2000;60:70–7.Mendoza O, Tobón JI. An alternative thermal method for identification of pozzolanic activity in Ca(OH)2/pozzolan pastes. J Therm Anal Calorim. 2013;114:589–96.Kosmatka SH, Kerkhoff B, Panarese W, MacLeod NF, McGrath RJ, Design and control of concrete mixtures. 7rd ed. Cement association of Canada. 2002. pp. 88.Cárdenas JI, Restrepo C. Patrimonio geológico y patrimonio minero de la cuenca carbonífera del suroeste antioqueño, Colombia. Boletín de ciencias de la tierra. 2006;18:91–102 ISSN 0120-3630 .Klein NS, Aguado A, Tollares-Carbonari BM, Real LV. Prediction of the water absorption by aggregates over time: modelling through the use of value function and experimental validation. Constr Build Mater. 2014;69:213–20
Managing aging effects on dry cask storage systems for extended long-term storage and transportation of used fuel - rev. 0
The cancellation of the Yucca Mountain repository program in the United States raises the prospect of extended long-term storage (i.e., >120 years) and deferred transportation of used fuel at operating and decommissioned nuclear power plant sites. Under U.S. federal regulations contained in Title 10 of the Code of Federal Regulations (CFR) 72.42, the initial license term for an Independent Spent Fuel Storage Installation (ISFSI) must not exceed 40 years from the date of issuance. Licenses may be renewed by the U.S. Nuclear Regulatory Commission (NRC) at the expiration of the license term upon application by the licensee for a period not to exceed 40 years. Application for ISFSI license renewals must include the following: (1) Time-limited aging analyses (TLAAs) that demonstrate that structures, systems, and components (SSCs) important to safety will continue to perform their intended function for the requested period of extended operation; and (2) a description of the aging management program (AMP) for management of issues associated with aging that could adversely affect SSCs important to safety. In addition, the application must also include design bases information as documented in the most recent updated final safety analysis report as required by 10 CFR 72.70. Information contained in previous applications, statements, or reports filed with the Commission under the license may be incorporated by reference provided that those references are clear and specific. The NRC has recently issued the Standard Review Plan (SRP) for renewal of used-fuel dry cask storage system (DCSS) licenses and Certificates of Compliance (CoCs), NUREG-1927, under which NRC may renew a specific license or a CoC for a term not to exceed 40 years. Both the license and the CoC renewal applications must contain revised technical requirements and operating conditions (fuel storage, surveillance and maintenance, and other requirements) for the ISFSI and DCSS that address aging effects that could affect the safe storage of the used fuel. The information contained in the license and CoC renewal applications will require NRC review to verify that the aging effects on the SSCs in DCSSs/ ISFSIs are adequately managed for the period of extended operation. To date, all of the ISFSIs located across the United States with more than 1,500 dry casks loaded with used fuel have initial license terms of 20 years; three ISFSIs (Surry, H.B. Robinson and Oconee) have received their renewed licenses for 20 years, and two other ISFSIs (Calvert Cliffs and Prairie Island) have applied for license renewal for 40 years. This report examines issues related to managing aging effects on the SSCs in DCSSs/ISFSIs for extended long-term storage and transportation of used fuels, following an approach similar to that of the Generic Aging Lessons Learned (GALL) report, NUREG-1801, for the aging management and license renewal of nuclear power plants. The report contains five chapters and an appendix on quality assurance for aging management programs for used-fuel dry storage systems. Chapter I of the report provides an overview of the ISFSI license renewal process based on 10 CFR 72 and the guidance provided in NUREG-1927. Chapter II contains definitions and terms for structures and components in DCSSs, materials, environments, aging effects, and aging mechanisms. Chapter III and Chapter IV contain generic TLAAs and AMPs, respectively, that have been developed for managing aging effects on the SSCs important to safety in the dry cask storage system designs described in Chapter V. The summary descriptions and tabulations of evaluations of AMPs and TLAAs for the SSCs that are important to safety in Chapter V include DCSS designs (i.e., NUHOMS{reg_sign}, HI-STORM 100, Transnuclear (TN) metal cask, NAC International S/T storage cask, ventilated storage cask (VSC-24), and the Westinghouse MC-10 metal dry storage cask) that have been and continue to be used by utilities across the country for dry storage of used fuel to date. The goal of this report is to help establish the technical basis for extended long-term storage and transportation of used fuel
BNL-201^5 RECENT EXPERIMENTS ON THE SURFACE OF LIQUID 4 He: ELASTIC SCATTERING OF 4 He ATOMS
repulsive. This is unfavorable for a low-temperature superfluid condensation. The bulk of the paper discusses the implications of a recent experiment on the elastic scattering of free 4 He atoms at the surface of pure liquid He. The elasticscattering probability R(k,9) has been measured as a function of the momentum of the atom ftk and of the angle of incidence 9. In addition the probability of inelastic scattering was found to be very small (less than 2 x 10~3 ). With the simplifying assumption that the scattered atoms can be treated as distinguishable from those in the liquid it is found that R(k,0) can be calculated from the density profile p(z) at the surface of the liquid. The relation between the scattering data and the spectrum of atoms evaporated from the liquid at finite temperature is also discussed
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