294 research outputs found
High Density Effective Theory Confronts the Fermi Liquid
The high density effective theory recently introduced by Hong and Hsu to
describe ultradense relativistic fermionic matter is used to calculate the
tree-level forward scattering amplitude between two particles at the Fermi
surface. While the direct term correctly reproduces that of the underlying
gauge theory, the exchange term has the wrong sign. The physical consequences
are discussed in the context of Landau's theoretical description of the Fermi
liquid.Comment: 15 pages, 2 figures; conclusion expanded, reference adde
A way to estimate the heavy quark thermalization rate from the lattice
The thermalization rate of a heavy quark is related to its momentum diffusion
coefficient. Starting from a Kubo relation and using the framework of the heavy
quark effective theory, we argue that in the large-mass limit the momentum
diffusion coefficient can be defined through a certain Euclidean correlation
function, involving color-electric fields along a Polyakov loop. Furthermore,
carrying out a perturbative computation, we demonstrate that the spectral
function corresponding to this correlator is relatively flat at small
frequencies. Therefore, unlike in the case of several other transport
coefficients, for which the narrowness of the transport peak makes analytic
continuation from Euclidean lattice data susceptible to severe systematic
uncertainties, it appears that the determination of the heavy quark
thermalization rate could be relatively well under control.Comment: 17 pages. v2: clarifications and references added, published versio
Symmetry of bound and antibound states in the semiclassical limit
We consider one dimensional scattering and show how the presence of a mild
positive barrier separating the interaction region from infinity implies that
the bound and antibound states are symmetric modulo exponentially small errors
in 1/h. This simple result was inspired by a numerical experiment and we
describe the numerical scheme for an efficient computation of resonances in one
dimension
Decision problem structuring method for the specification and selection of active fire protection systems
The UK along with the EU has witnessed a recent proliferation of designs for potential active
fire suppression systems for the mitigation of fire risks in buildings and equipment; from five
in 1986 (BSI, 1986) to eleven in 2011 (BSI, 2011a). However, each technology remains
limited to the protection of certain types of application only, rather than offering a solution to
guard against all possible hazards. This trend occurs at the same time as a transition from
prescriptive to performance based standards and against the backdrop of the current nonprescriptive
regulatory frameworks including the Building Regulations (HMSO, 2010), The
Regulatory (fire) Reform Order (HMSO, 2005) and associated guidance (Approved
Documents, standards, codes of practice and guides). Hazards can be difficult to assess and
describe and the inequality or absence of satisfactory methods is notable in many recently
published guidance documents.
Active fire protection systems are installed to meet legislative requirements (to protect life),
and / or when identified as appropriate by a cost-benefit analysis (e.g. to achieve risk
reduction for business resilience purposes or to historic assets). There are many guidance
documents available to assist users and designers in choosing and specifying appropriate
active fire protection. These documents vary in age, relevance, scope, quality, impartiality
and suitability.
The Fire Protection Association (FPA) and several leading insurers who participate in its risk
management work, have identified the requirement for assistance with the decision making
process of analysing fire hazards and matching them to appropriate candidate systems, in
order to make informed and impartial recommendations. This has led to the undertaking of a
four year research project aimed at developing a decision problem structuring method and a
software tool (Expert System), for the specification and selection of Active Fire Protection
Systems. The research aim is to develop a tool that will assist users in making an informed
selection of a system that is likely to best suit their needs and thereby contribute to overall
improvements in fire safety and outcomes. This paper presents a summary of the work to
date, focusing on the demand for the work, development of the methodology and practical
application of the emerging Expert System
On the Lieb-Thirring constants L_gamma,1 for gamma geq 1/2
Let denote the negative eigenvalues of the one-dimensional
Schr\"odinger operator on . We prove the inequality \sum_i|E_i(H)|^\gamma\leq L_{\gamma,1}\int_{\Bbb
R} V^{\gamma+1/2}(x)dx, (1) for the "limit" case This will imply
improved estimates for the best constants in (1), as
$1/2<\gamma<3/2.Comment: AMS-LATEX, 15 page
Development of a fixed firefighting system selection tool for improved outcomes
The UK along with the European Union has experienced a recent proliferation in design
approaches for potential fixed firefighting systems. Such systems are installed to mitigate fire hazards in
buildings and equipment. In the UK, for example there were five general design approaches to fixed firefighting
systems protection in 1986. This had increased to eleven in 2011. This is against the backdrop of the current
non-prescriptive regulatory frameworks including the Building Regulations, the repeal of so-called âlocal actsâ,
the Regulatory (fire) Reform Order and associated guidance (Approved Documents, standards, codes of practice
and guides).
In response to this trend, as was intended, the market place is becoming increasingly competitive. However, the
capability of each technology remains limited to protection against certain hazards, rather than offering a
solution to guard against all possible scenarios. When selecting a fixed firefighting system, fire hazards and
interactions can be difficult to assess and describe and the inequality or absence of satisfactory methods is
notable in many recently published guidance documents. The absence of good quality guidance for non-expert
practitioners (specifiers) and regulatory changes means a good quality source of impartial and expert
knowledge is increasingly desirable. The challenge is to amass this knowledge and render it in an accessible
format to the non-expert user. This paper reports on progress to-date; understanding the problem, amassing and
structuring the knowledge base and developing a suitable knowledge management tool
Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes
Iron oxide-apatite (IOA) deposits are an important source of iron and other elements (e.g., REE, P, U, Ag and Co) vital to modern society. However, their formation, including the namesake Kiruna-type IOA deposit (Sweden), remains controversial. Working hypotheses include a purely magmatic origin involving separation of an Fe-, P-rich, volatile-rich oxide melt from a Si-rich silicate melt, and precipitation of magnetite from an aqueous ore fluid, which is either of magmatic-hydrothermal or non-magmatic surface or metamorphic origin. In this study, we focus on the geochemistry of magnetite from the Cretaceous Kiruna-type Los Colorados IOA deposit (~350. Mt Fe) located in the northern Chilean Iron Belt. Los Colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in IOA deposits. Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) transects and electron probe micro-analyzer (EPMA) wavelength-dispersive X-ray (WDX) spectrometry mapping demonstrate distinct chemical zoning in magnetite grains, wherein cores are enriched in Ti, Al, Mn and Mg. The concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt, whereas magnetite rims show a pronounced depletion in these elements, consistent with magnetite grown from an Fe-rich magmatic-hydrothermal aqueous fluid. Further, magnetite grains contain polycrystalline inclusions that re-homogenize at magmatic temperatures (>850. °C). Smaller inclusions (500. ppm) concentrations
Schwinger Terms and Cohomology of Pseudodifferential Operators
We study the cohomology of the Schwinger term arising in second quantization
of the class of observables belonging to the restricted general linear algebra.
We prove that, for all pseudodifferential operators in 3+1 dimensions of this
type, the Schwinger term is equivalent to the ``twisted'' Radul cocycle, a
modified version of the Radul cocycle arising in non-commutative differential
geometry. In the process we also show how the ordinary Radul cocycle for any
pair of pseudodifferential operators in any dimension can be written as the
phase space integral of the star commutator of their symbols projected to the
appropriate asymptotic component.Comment: 19 pages, plain te
Nontrivial eigenvalues of the Liouvillian of an open quantum system
We present methods of finding complex eigenvalues of the Liouvillian of an
open quantum system. The goal is to find eigenvalues that cannot be predicted
from the eigenvalues of the corresponding Hamiltonian. Our model is a T-type
quantum dot with an infinitely long lead. We suggest the existence of the
non-trivial eigenvalues of the Liouvillian in two ways: one way is to show that
the original problem reduces to the problem of a two-particle Hamiltonian with
a two-body interaction and the other way is to show that diagram expansion of
the Green's function has correlation between the bra state and the ket state.
We also introduce the integral equations equivalent to the original eigenvalue
problem.Comment: 5 pages, 2 figures, proceeding
The signed loop approach to the Ising model: foundations and critical point
The signed loop method is a beautiful way to rigorously study the
two-dimensional Ising model with no external field. In this paper, we explore
the foundations of the method, including details that have so far been
neglected or overlooked in the literature. We demonstrate how the method can be
applied to the Ising model on the square lattice to derive explicit formal
expressions for the free energy density and two-point functions in terms of
sums over loops, valid all the way up to the self-dual point. As a corollary,
it follows that the self-dual point is critical both for the behaviour of the
free energy density, and for the decay of the two-point functions.Comment: 38 pages, 7 figures, with an improved Introduction. The final
publication is available at link.springer.co
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