853 research outputs found
Closed Universes With Black Holes But No Event Horizons As a Solution to the Black Hole Information Problem
We show it is possible for the information paradox in black hole evaporation
to be resolved classically. Using standard junction conditions, we attach the
general closed spherically symmetric dust metric to a spacetime satisfying all
standard energy conditions but with a single point future c-boundary. The
resulting Omega Point spacetime, which has NO event horizons, nevertheless has
black hole type trapped surfaces and hence black holes. But since there are no
event horizons, information eventually escapes from the black holes. We show
that a scalar quintessence field with an appropriate exponential potential near
the final singularity would give rise to an Omega Point final singularity.Comment: 27 pages in LaTex2e, no figure
Entropic Stochastic Resonance
We present a novel scheme for the appearance of Stochastic Resonance when the
dynamics of a Brownian particle takes place in a confined medium. The presence
of uneven boundaries, giving rise to an entropic contribution to the potential,
may upon application of a periodic driving force result in an increase of the
spectral amplification at an optimum value of the ambient noise level. This
Entropic Stochastic Resonance (ESR), characteristic of small-scale systems, may
constitute a useful mechanism for the manipulation and control of
single-molecules and nano-devices.Comment: 4 pages, 3 figure
Embedded-Cluster Calculations in a Numeric Atomic Orbital Density-Functional Theory Framework
We integrate the all-electron electronic structure code FHI-aims into the
general ChemShell package for solid-state embedding (QM/MM) calculations. A
major undertaking in this integration is the implementation of pseudopotential
functionality into FHI-aims to describe cations at the QM/MM boundary through
effective core potentials and therewith prevent spurious overpolarization of
the electronic density. Based on numeric atomic orbital basis sets, FHI-aims
offers particularly efficient access to exact exchange and second order
perturbation theory, rendering the established QM/MM setup an ideal tool for
hybrid and double-hybrid level DFT calculations of solid systems. We illustrate
this capability by calculating the reduction potential of Fe in the
Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for
(photo-)catalytic water oxidation at TiO2(110).Comment: 12 pages, 4 figure
Entropically-induced asymmetric passage times of charged tracers across corrugated channels
We analyze the diffusion of charged and neutral tracers suspended in an electrolyte embedded in a channel of varying cross section. Making use of systematic approximations, the diffusion equation governing the motion of tracers is mapped into an effective 1D equation describing the dynamics along the longitudinal axis of the channel where its varying-section is encoded as an effective entropic potential. This simplified approach allows us to characterize tracer diffusion under generic confinement by measuring their mean first passage time (MFPT). In particular, we show that the interplay between geometrical confinement and electrostatic interactions strongly affect the MFTP of tracers across corrugated channels hence leading to alternative means to control tracers translocation across charged pores. Finally, our results show that the MFPTs of a charged tracer in opposite directions along an asymmetric channel may differ We expect our results to be relevant for biological as well synthetic devices whose dynamics is controlled by the detection of diluted tracer
On the elastic constants of the zeolite chlorosodalite
The use of force-field based molecular modeling to predict the elastic constants of the zeolite chlorosodalite is described. Theoretical predictions of the on-axis and off-axis elastic constants strongly suggest that an error exists in the published elastic constants of the material. When the previous experimental data are corrected by transposing the published directional ultrasound velocities, excellent agreement is observed between the off-axis plots of sodalite produced by experiment and modeling. Further confirmation of the prediction is supplied by considering the Zener ratios of other inorganic materials that possess cubic symmetry. ©2006 American Institute of Physics
Mass fractionation of noble gases in synthetic methane hydrate : implications for naturally occurring gas hydrate dissociation
This paper is not subject to U.S. copyright. The definitive version was published in Chemical Geology 339 (2013): 242-250, doi:10.1016/j.chemgeo.2012.09.033.As a consequence of contemporary or longer term (since 15 ka) climate warming, gas hydrates in some settings may presently be dissociating and releasing methane and other gases to the ocean–atmosphere system. A key challenge in assessing the impact of dissociating gas hydrates on global atmospheric methane is the lack of a technique able to distinguish between methane recently released from gas hydrates and methane emitted from leaky thermogenic reservoirs, shallow sediments (some newly thawed), coal beds, and other sources. Carbon and deuterium stable isotopic fractionation during methane formation provides a first-order constraint on the processes (microbial or thermogenic) of methane generation. However, because gas hydrate formation and dissociation do not cause significant isotopic fractionation, a stable isotope-based hydrate-source determination is not possible. Here, we investigate patterns of mass-dependent noble gas fractionation within the gas hydrate lattice to fingerprint methane released from gas hydrates. Starting with synthetic gas hydrate formed under laboratory conditions, we document complex noble gas fractionation patterns in the gases liberated during dissociation and explore the effects of aging and storage (e.g., in liquid nitrogen), as well as sampling and preservation procedures. The laboratory results confirm a unique noble gas fractionation pattern for gas hydrates, one that shows promise in evaluating modern natural gas seeps for a signature associated with gas hydrate dissociation.Partial support for this research was provided by Interagency Agreements
DE-FE0002911 and DE-NT0006147 between the U.S. Geological
Survey Gas Hydrates Project and the U.S. Department of Energy's Methane
Hydrates Research and Development Program
Density of mechanisms within the flexibility window of zeolites
By treating idealized zeolite frameworks as periodic mechanical trusses, we
show that the number of flexible folding mechanisms in zeolite frameworks is
strongly peaked at the minimum density end of their flexibility window. 25 of
the 197 known zeolite frameworks exhibit an extensive flexibility, where the
number of unique mechanisms increases linearly with the volume when long
wavelength mechanisms are included. Extensively flexible frameworks therefore
have a maximum in configurational entropy, as large crystals, at their lowest
density. Most real zeolites do not exhibit extensive flexibility, suggesting
that surface and edge mechanisms are important, likely during the nucleation
and growth stage. The prevalence of flexibility in real zeolites suggests that,
in addition to low framework energy, it is an important criterion when
searching large databases of hypothetical zeolites for potentially useful
realizable structures.Comment: 11 pages, 3 figure
Permeability of Noble Gases through Kapton, Butyl, Nylon, and "Silver Shield"
Noble gas permeabilities and diffusivities of Kapton, butyl, nylon, and
"Silver Shield" are measured at temperatures between 22C and 115C. The
breakthrough times and solubilities at 22C are also determined. The
relationship of the room temperature permeabilities to the noble gas atomic
radii is used to estimate radon permeability for each material studied. For the
noble gases tested, Kapton and Silver Shield have the lowest permeabilities and
diffusivities, followed by nylon and butyl, respectively.Comment: 14 pages, 7 figure
Numerical study of multilayer adsorption on fractal surfaces
We report a numerical study of van der Waals adsoprtion and capillary
condensation effects on self-similar fractal surfaces. An assembly of uncoupled
spherical pores with a power-law distributin of radii is used to model fractal
surfaces with adjustable dimensions. We find that the commonly used fractal
Frankel-Halsey-Hill equation systematically fails to give the correct dimension
due to crossover effects, consistent with the findings of recent experiments.
The effects of pore coupling and curvature dependent surface tension were also
studied.Comment: 11 pages, 3 figure
Canterbury game industry action plan 2022
This report reviews the video game and interactive media industry landscape, and is intended for game studios, local and international investors in the games industry, regional policy makers, central government, local government agencies, Christchurch City Council, and sector stakeholders
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