2,942 research outputs found
Quantum astrometric observables II: time delay in linearized quantum gravity
A clock synchronization thought experiment is modeled by a diffeomorphism
invariant "time delay" observable. In a sense, this observable probes the
causal structure of the ambient Lorentzian spacetime. Thus, upon quantization,
it is sensitive to the long expected smearing of the light cone by vacuum
fluctuations in quantum gravity. After perturbative linearization, its mean and
variance are computed in the Minkowski Fock vacuum of linearized gravity. The
na\"ive divergence of the variance is meaningfully regularized by a length
scale , the physical detector resolution. This is the first time vacuum
fluctuations have been fully taken into account in a similar calculation.
Despite some drawbacks this calculation provides a useful template for the
study of a large class of similar observables in quantum gravity. Due to their
large volume, intermediate calculations were performed using computer algebra
software. The resulting variance scales like , where
is the Planck length and is the distance scale separating the ("lab" and
"probe") clocks. Additionally, the variance depends on the relative velocity of
the lab and the probe, diverging for low velocities. This puzzling behavior may
be due to an oversimplified detector resolution model or a neglected second
order term in the time delay.Comment: 30 pages, 8 figures, revtex4-1; v3: minor updates and corrections,
close to published versio
Coupled structural, thermal, phase-change and electromagnetic analysis for superconductors, volume 1
This research program has dealt with the theoretical development and computer implementation of reliable and efficient methods for the analysis of coupled mechanical problems that involve the interaction of mechanical, thermal, phase-change and electromagnetic subproblems. The focus application has been the modeling of superconductivity and associated quantum-state phase-change phenomena. In support of this objective the work has addressed the following issues: (1) development of variational principles for finite elements; (2) finite element modeling of the electromagnetic problem; (3) coupling of thermal and mechanical effects; and (4) computer implementation and solution of the superconductivity transition problem. The research was carried out over the period September 1988 through March 1993. The main accomplishments have been: (1) the development of the theory of parametrized and gauged variational principles; (2) the application of those principled to the construction of electromagnetic, thermal and mechanical finite elements; and (3) the coupling of electromagnetic finite elements with thermal and superconducting effects; and (4) the first detailed finite element simulations of bulk superconductors, in particular the Meissner effect and the nature of the normal conducting boundary layer. The grant has fully supported the thesis work of one doctoral student (James Schuler, who started on January 1989 and completed on January 1993), and partly supported another thesis (Carmelo Militello, who started graduate work on January 1988 completing on August 1991). Twenty-three publications have acknowledged full or part support from this grant, with 16 having appeared in archival journals and 3 in edited books or proceedings
Families of L-functions and their Symmetry
In [90] the first-named author gave a working definition of a family of
automorphic L-functions. Since then there have been a number of works [33],
[107], [67] [47], [66] and especially [98] by the second and third-named
authors which make it possible to give a conjectural answer for the symmetry
type of a family and in particular the universality class predicted in [64] for
the distribution of the zeros near s=1/2. In this note we carry this out after
introducing some basic invariants associated to a family
Spectral functions of charmonium with 2+1 flavours of dynamical quarks
Finite temperature charmonium spectral functions in the pseudoscalar(PS) and
vector(V) channels are studied in lattice QCD with 2+1 flavours of dynamical
Wilson quarks, on fine isotropic lattices (with a lattice spacing of 0.057fm),
with a non-physical pion mass of 545MeV. The highest temperature studied is
approximately 1.4Tc. Up to this temperature no significant variation of the
spectral function is seen in the PS channel. The V channel shows some
temperature dependence, which seems to be consistent with a temperature
dependent low frequency peak related to heavy quark transport, plus a
temperature independent term at omega > 0. These results are in accord with
previous calculations using the quenched approximation.Comment: Conference proceedings: The 32nd International Symposium on Lattice
Field Theory - Lattice 2014 June 23-28, 2014 Columbia University, New York,
New York This conference contribution draws heavily from the paper:
arXiv:1401.5940 [hep-lat
Reduction of dynamical biochemical reaction networks in computational biology
Biochemical networks are used in computational biology, to model the static
and dynamical details of systems involved in cell signaling, metabolism, and
regulation of gene expression. Parametric and structural uncertainty, as well
as combinatorial explosion are strong obstacles against analyzing the dynamics
of large models of this type. Multi-scaleness is another property of these
networks, that can be used to get past some of these obstacles. Networks with
many well separated time scales, can be reduced to simpler networks, in a way
that depends only on the orders of magnitude and not on the exact values of the
kinetic parameters. The main idea used for such robust simplifications of
networks is the concept of dominance among model elements, allowing
hierarchical organization of these elements according to their effects on the
network dynamics. This concept finds a natural formulation in tropical
geometry. We revisit, in the light of these new ideas, the main approaches to
model reduction of reaction networks, such as quasi-steady state and
quasi-equilibrium approximations, and provide practical recipes for model
reduction of linear and nonlinear networks. We also discuss the application of
model reduction to backward pruning machine learning techniques
- …