1,114 research outputs found
The Use and Impact of Manufacturing Productivity Improvement Tools and Methodologies within the Automotive Component Industry
Promising Practices: Supporting Transition of Youth Served by the Foster Care System
A continuation of the 1997 study funded by the Annie E. Casey Foundation, this collaborative effort with the National Resource Center for Youth Services presents findings of a study of approximately 100 independent living and transitional living programs. It identifies "promising practices" linked with positive outcomes for youth leaving foster care-and presents information drawn from interviews with program staff and participating youth
Cold, warm, and composite (cool) cosmic string models
The dynamical behaviour of a cosmic string is strongly affected by any
reduction of the effective string tension below the constant value
say that characterizes the simple, longitudinally Lorentz invariant, Goto Nambu
string model in terms of a fixed mass scale whose magnitude depends on that
of the Higgs field responsible for the existence of the string. Such a
reduction occurs in the standard "hot" cosmic string model in which the effect
of thermal perturbations of a simple Goto Nambu model is expressed by the
formula , where is the string
temperature. A qualitatively similar though analytically more complicated
tension reduction phenomenon occurs in "cold" conducting cosmic string models
where the role of the temperature is played by an effective chemical potential
that is constructed as the magnitude of the phase of a bosonic
condensate of the kind whose existence was first proposed by Witten. The
present article describes the construction and essential mechanical properties
of a category of "warm" cosmic string models that are intermediate between
these "hot" and "cold" extremes. These "warm" models are the string analogues
of the standard Landau model for a 2-constituent finite temperature superfluid,
and as such involve two independent currents interpretable as that of the
entropy on one hand and that of the bosonic condensate on the other. It is
surmised that the stationary (in particular ring) equilibrium states of such
"warm" cosmic strings may be of cosmological significance.Comment: 31 pages, Tex preprint version of manuscript subsequently published
(with editorial modifications) in Nuclear Physics
Radial acceleration relation from symmetron fifth forces
We show that the radial acceleration relation for rotationally supported galaxies may be explained, in the absence of cold dark matter, by a nonminimally coupled scalar field, whose fifth forces are partially screened on galactic scales by the symmetron mechanism. In addition, we show that sufficient energy is stored in the symmetron field to explain the dynamic stability of galactic disks
40Ar/39Ar ages of muscovites from modern Himalayan rivers: Himalayan evolution and the relative contribution of tectonicsand climate
International audience40Ar/39Ar ages from detrital muscovites have been analyzed from six modern rivers in central and western Nepal; the size of the drainage basins associated with these samples ranges from a few square kilometers to >40,000 km2. These data, when combined with previously published ages of detrital muscovites from other modern rivers in the region, suggest that a good correspondence between normalized age and normalized topography (the comparison of t* and z*) is rare, due to either nonuniform rates of passage through the ∼400 °C isotherm or subsequent faulting in the drainage area. The closure temperature of Ar in muscovite is perhaps too high to make meaningful comparisons to modern topography in tectonic analysis of active orogens.The distribution of 40Ar/39Ar ages from detrital muscovites from the Karnali basin in western Nepal is much older than that for the Narayani basin in central Nepal. The Karnali muscovites, when combined with previously published muscovites from the Siwalik Group in western Nepal and zircon fission track ages from modern and ancient samples from the region, suggest a thermal history for western Nepal consistent with vigorous tectonics (and attendant erosion) before the middle Miocene but a significant diminution in the rate of erosion since ca. 10 Ma.40Ar/39Ar ages of detrital muscovites from the Narayani basin in central Nepal suggest a markedly different history with an acceleration of the rate of erosion since ca. 10 Ma and reactivation of major faults; this is consistent with the abundant bedrock data from the Narayani basin.The strong difference in the erosional history of the adjacent Karnali and Narayani basins, as evidenced by the 40Ar/39Ar ages from detrital muscovites, is not likely to have been due to variations in climate, but rather due to strain partitioning within the Himalaya during and after the Miocene
Fifth forces, Higgs portals and broken scale invariance
© 2018 IOP Publishing Ltd and Sissa Medialab. We study the relationship between the strength of fifth forces and the origin of scale breaking in the Standard Model (SM) of particle physics. We start with a light scalar field that is conformally coupled to a toy SM matter sector through a Weyl rescaling of the metric. After appropriately normalizing the fields, the conformally coupled scalar only interacts directly with the would-be Higgs field through kinetic-mixing and Higgs-portal terms. Thus, for the first time, we describe the equivalence of conformally coupled scalar-tensor modifications of gravity and Higgs-portal theories, and we find that the usual tree-level fifth forces only emerge if there is mass mixing between the conformally coupled scalar and the Higgs field. The strength of the fifth force, mediated by the light scalar, then depends on whether the mass of the Higgs arises from an explicit symmetry-breaking term or a spontaneous mechanism of scale breaking. Solar System tests of gravity and the non-observation of fifth forces therefore have the potential to provide information about the structure of the Higgs sector and the origin of its symmetry breaking, setting an upper bound on the magnitude of any explicit scale-breaking terms. These results demonstrate the phenomenological importance (both for cosmology and high-energy physics) of considering how scalar-tensor modifications of gravity are embedded within extensions of the SM
A Memorial for Bosnia: Framework of Legal Arguments Concerning the Lawfulness of the Maintenance of the United Nations Security Council Arms Embargo on Bosnia and Herzegovina
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
Radiative screening of fifth forces
We describe a symmetron model in which the screening of fifth forces arises at the one-loop level through the Coleman-Weinberg mechanism of spontaneous symmetry breaking. We show that such a theory can avoid current constraints on the existence of fifth forces but still has the potential to give rise to observable deviations from general relativity, which could be seen in cold atom experiments
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