339 research outputs found
Perturbations of moving membranes in AdS_7
We study the stability of uniformly moving membrane-like objects in seven
dimensional Anti-de Sitter space. This is approached by a linear perturbation
analysis and a search for growing modes. We examine both analytic and numerical
configurations previously found in [1].Comment: 20 pages, 6 figure
Moving Defects in AdS/CFT
We study defects of various dimensions moving through Anti-de Sitter space.
Using the AdS/CFT correspondence this allows us to probe aspects of the dual
quantum field theory. We focus on the energy loss experienced by these defects
as they move through the CFT plasma. We find that the behavior of these
physical quantities is governed by induced world-volume horizons. We identify
world-volume analogs for several gravitational phenomena including black holes,
the Hawking-Page phase transition and expanding cosmological horizons.Comment: 24 pages, 7 figures. Version 2 contains two added reference
Dressed spectral densities for heavy quark diffusion in holographic plasmas
We analyze the large frequency behavior of the spectral densities that govern
the generalized Langevin diffusion process for a heavy quark in the context of
the gauge/gravity duality. The bare Langevin correlators obtained from the
trailing string solution have a singular short-distance behavior. We argue that
the proper dressed spectral functions are obtained by subtracting the
zero-temperature correlators. The dressed spectral functions have a
sufficiently fast fall-off at large frequency so that the Langevin process is
well defined and the dispersion relations are satisfied. We identify the cases
in which the subtraction does not modify the associated low-frequency transport
coefficients. These include conformal theories and the non-conformal,
non-confining models. We provide several analytic and numerical examples in
conformal and non-conformal holographic backgrounds.Comment: 51 pages, 2 figure
Electronic Structure of a Hydrogenic Acceptor Impurity in Semiconductor Nano-structures
The electronic structure and binding energy of a hydrogenic acceptor impurity in 2, 1, and 0-dimensional semiconductor nano-structures (i.e. quantum well (QW), quantum well wire (QWW), and quantum dot (QD)) are studied in the framework of effective-mass envelope-function theory. The results show that (1) the energy levels monotonically decrease as the quantum confinement sizes increase; (2) the impurity energy levels decrease more slowly for QWWs and QDs as their sizes increase than for QWs; (3) the changes of the acceptor binding energies are very complex as the quantum confinement size increases; (4) the binding energies monotonically decrease as the acceptor moves away from the nano-structures’ center; (5) as the symmetry decreases, the degeneracy is lifted, and the first binding energy level in the QD splits into two branches. Our calculated results are useful for the application of semiconductor nano-structures in electronic and photoelectric devices
Holographic Brownian Motion in Magnetic Environments
Using the gauge/gravity correspondence, we study the dynamics of a heavy
quark in two strongly-coupled systems at finite temperature: Super-Yang-Mills
in the presence of a magnetic field and non-commutative Super-Yang-Mills. In
the former, our results agree qualitatively with the expected behavior from
weakly-coupled theories. In the latter, we propose a Langevin equation that
accounts for the effects of non-commutativity and we find new interesting
features. The equation resembles the structure of Brownian motion in the
presence of a magnetic field and implies that the fluctuations along
non-commutative directions are correlated. Moreover, our results show that the
viscosity is smaller than the commutative case and that the diffusion
properties of the quark are unaffected by non-commutativity. Finally, we
compute the random force autocorrelator and verify that the
fluctuation-dissipation theorem holds in the presence of non-commutativity.Comment: 34 pages. v2: typos corrected. v3: title and abstract slightly
modified in order to better reflect the contents of the paper; footnote 3 and
one reference were also added; version accepted for publication in JHE
Background risk of breast cancer and the association between physical activity and mammographic density
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Using differential mobility spectrometry to measure ion solvation: An examination of the roles of solvents and ionic structures in separating quinoline-based drugs
Understanding the mechanisms and energetics of ion solvation is critical in many scientific areas. Here, we present a methodlogy for studying ion solvation using differential mobility spectrometry (DMS) coupled to mass spectrometry. While in the DMS cell, ions experience electric fields established by a high frequency asymmetric waveform in the presence of a desired pressure of water vapor. By observing how a specific ion's behavior changes between the high- and low-field parts of the waveform, we gain knowledge about the aqueous microsolvation of that ion. In this study, we applied DMS to investigate the aqueous microsolvation of protonated quinoline-based drug candidates. Owing to their low binding energies with water, the clustering propensity of 8-substituted quinolinium ions was less than that of the 6- or 7-substituted analogues. We attribute these differences to the steric hinderance presented by subtituents in the 8-position. In addition, these experimental DMS results were complemented by extensive computational studies that determined cluster structures and relative thermodynamic stabilities.We gratefully acknowledge high performance computing support from the SHARCNET consortium of Compute Canada. We are also grateful to Professor Terry McMahon (University of Waterloo) and Drs. Bradley Schneider and Tom Covey (AB SCIEX) for helpful conversations. We thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support through the ENGAGE grant (EGP #449354- 13) and ENGAGE Plus grant (EGP #463974-14)
Identifying source populations for the reintroduction of the Eurasian beaver, Castor fiber L. 1758, into Britain: evidence from ancient DNA
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POLETOWN NEIGHBORHOOD COUNCIL, a voluntary unincorporated association
Corporation as a site for construction of an assembly plant. The plaintiffs, a neighborhood association and several individual residents of the affected area, brought suit in Wayne Circuit Court to challenge the project on a number of grounds, not all of which have been argued to this Court. Defendants' motions for summary judgment were denied pending trial on a single question of fact: whether, under 1980 PA 87; M.C.L. § 213.51 et seq ; M.S.A. § 8.265(1) et seq, the city abused its discretion in determining that condemnation of plaintiffs' property was necessary to complete the project
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