846 research outputs found
Anisotropic dark energy and CMB anomalies
We investigate the breaking of global statistical isotropy caused by a dark
energy component with an energy-momentum tensor which has point symmetry, that
could represent a cubic or hexagonal crystalline lattice. In such models
Gaussian, adiabatic initial conditions created during inflation can lead to
anisotropies in the cosmic microwave background whose spherical harmonic
coefficients are correlated, contrary to the standard assumption. We develop an
adaptation of the line of sight integration method that can be applied to
models where the background energy-momentum tensor is isotropic, but whose
linearized perturbations are anisotropic. We then show how this can be applied
to the cases of cubic and hexagonal symmetry. We compute quantities which show
that such models are indistinguishable from isotropic models even in the most
extreme parameter choices, in stark contrast to models with anisotropic initial
conditions based on inflation. The reason for this is that the dark energy
based models contribute to the CMB anistropy via the inegrated Sachs-Wolfe
effect, which is only relevent when the dark energy is dominant, that is, on
the very largest scales. For inflationary models, however, the anisotropy is
present on all scales.Comment: 18 pages, 9 figure
Social Communication Patterns of Attention-Deficit-Disordered Boys
This study was designed to compare the social communication patterns of attention-deficit-disordered (ADD) and normal boys. This was accomplished by employing a TV Talk Show social role-playing procedure in which the task required different strategies for the roles of host and guest. Groups of ADD and normal elementary-age boys were formed, and each boy was paired with a normal classmate. Measures of communication competence were coded from videotapes made of subject and partner social interactions while performing both roles. Results indicated that the ADD boys, in contrast to the control group, failed to modulate their social communication behaviors as task demands shifted. Additionally, the behavior of the ADD boys resulted in their normal partners\u27\u27 altering their response patterns in order to maintain the equilibrium in the dyadic interaction. These results suggest that the social behavior of ADD children is relatively independent of environmental requirements and may contribute to the inappropriate responding of others
Selecting Efficient and Reliable Preservation Strategies
This article addresses the problem of formulating efficient and reliable operational preservation policies that ensure bit-level information integrity over long periods, and in the presence of a diverse range of real-world technical, legal, organizational, and economic threats. We develop a systematic, quantitative prediction framework that combines formal modeling, discrete-event-based simulation, hierarchical modeling, and then use empirically calibrated sensitivity analysis to identify effective strategies.
Specifically, the framework formally defines an objective function for preservation that maps a set of preservation policies and a risk profile to a set of preservation costs, and an expected collection loss distribution. In this framework, a curator’s objective is to select optimal policies that minimize expected loss subject to budget constraints. To estimate preservation loss under different policy conditions optimal policies, we develop a statistical hierarchical risk model that includes four sources of risk: the storage hardware; the physical environment; the curating institution; and the global environment. We then employ a general discrete event-based simulation framework to evaluate the expected loss and the cost of employing varying preservation strategies under specific parameterization of risks.
The framework offers flexibility for the modeling of a wide range of preservation policies and threats. Since this framework is open source and easily deployed in a cloud computing environment, it can be used to produce analysis based on independent estimates of scenario-specific costs, reliability, and risks.
We present results summarizing hundreds of thousands of simulations using this framework. This exploratory analysis points to a number of robust and broadly applicable preservation strategies, provides novel insights into specific preservation tactics, and provides evidence that challenges received wisdom
Selecting efficient and reliable preservation strategies: modeling long-term information integrity using large-scale hierarchical discrete event simulation
This article addresses the problem of formulating efficient and reliable
operational preservation policies that ensure bit-level information integrity
over long periods, and in the presence of a diverse range of real-world
technical, legal, organizational, and economic threats. We develop a
systematic, quantitative prediction framework that combines formal modeling,
discrete-event-based simulation, hierarchical modeling, and then use
empirically calibrated sensitivity analysis to identify effective strategies.
The framework offers flexibility for the modeling of a wide range of
preservation policies and threats. Since this framework is open source and
easily deployed in a cloud computing environment, it can be used to produce
analysis based on independent estimates of scenario-specific costs,
reliability, and risks.Comment: Fortcoming IDCC 202
Target search on a dynamic DNA molecule
We study a protein-DNA target search model with explicit DNA dynamics
applicable to in vitro experiments. We show that the DNA dynamics plays a
crucial role for the effectiveness of protein "jumps" between sites distant
along the DNA contour but close in 3D space. A strongly binding protein that
searches by 1D sliding and jumping alone, explores the search space less
redundantly when the DNA dynamics is fast on the timescale of protein jumps
than in the opposite "frozen DNA" limit. We characterize the crossover between
these limits using simulations and scaling theory. We also rationalize the slow
exploration in the frozen limit as a subtle interplay between long jumps and
long trapping times of the protein in "islands" within random DNA
configurations in solution.Comment: manuscript and supplementary material combined into a single documen
Excitation spectra and rf-response near the polaron-to-molecule transition from the functional renormalization group
A light impurity in a Fermi sea undergoes a transition from a polaron to a
molecule for increasing interaction. We develop a new method to compute the
spectral functions of the polaron and molecule in a unified framework based on
the functional renormalization group with full self-energy feedback. We discuss
the energy spectra and decay widths of the attractive and repulsive polaron
branches as well as the molecular bound state and confirm the scaling of the
excited state decay rate near the transition. The quasi-particle weight of the
polaron shifts from the attractive to the repulsive branch across the
transition, while the molecular bound state has a very small residue
characteristic for a composite particle. We propose an experimental procedure
to measure the repulsive branch in a Li6 Fermi gas using rf-spectroscopy and
calculate the corresponding spectra.Comment: 15 pages, 13 figures; v2: version published in Phys. Rev.
The Vertical Structure of Planet-induced Gaps in Proto-Planetary Discs
Giant planets embedded in circumstellar discs are expected to open gaps in
these discs. We examine the vertical structure of the gap edges. We find that
the planet excites spiral arms with significant (Mach number of a half)
vertical motion of the gas, and discuss the implications of these motions. In
particular, the spiral arms will induce strong vertical stirring of the dust,
making the edge appeared `puffed up' relative to the bulk of the disc.
Infra-red observations (sensitive to dust) would be dominated by the light from
the thick inner edge of the disc. Sub-millimetre observations (sensitive to gas
velocities) would appear to be hot in `turbulent' motions (actually the ordered
motion caused by the passage of the spiral arms), but cold in chemistry.
Resolved sub-millimetre maps of circumstellar discs might even be able to
detect the spiral arms directly.Comment: Revision adds new data, and corrects physical intepretatio
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