9,179 research outputs found
The spectral shift function and spectral flow
This paper extends Krein's spectral shift function theory to the setting of
semifinite spectral triples. We define the spectral shift function under these
hypotheses via Birman-Solomyak spectral averaging formula and show that it
computes spectral flow.Comment: 47 page
Development of holistic vs. featural processing in face recognition
According to a classic view developed by Carey and Diamond (1977), young children process faces in a piecemeal fashion before adult-like holistic processing starts to emerge
at the age of around 10 years. This is known as the
encoding switch hypothesis . Since then,a growing body of studies have challenged the theory. This article will provide a critical appraisal of this literature, followed by an analysis of some more recent developments.
We will conclude, quite contrary to the classical view, that holistic processing is not only present in early child development, but could even precede the development of part-based processing
Automatic grid construction for few-body quantum mechanical calculations
An algorithm for generating optimal nonuniform grids for solving the two-body
Schr\"odinger equation is developed and implemented. The shape of the grid is
optimized to accurately reproduce the low-energy part of the spectrum of the
Schr\"odinger operator. Grids constructed this way are applicable to more
complex few-body systems where the number of grid points is a critical
limitation to numerical accuracy. The utility of the grid generation for
improving few-body calculations is illustrated through an application to bound
states of He trimers
The Birman-Schwinger principle in von Neumann algebras of finite type
We introduce a relative index for a pair of dissipative operators in a von
Neumann algebra of finite type and prove an analog of the Birman-Schwinger
principle in this setting. As an application of this result, revisiting the
Birman-Krein formula in the abstract scattering theory, we represent the de la
Harpe-Skandalis determinant of the characteristic function of dissipative
operators in the algebra in terms of the relative index
Extracting individual contributions from their mixture: a blind source separation approach, with examples from space and laboratory plasmas
Multipoint or multichannel observations in plasmas can frequently be modelled
as an instantaneous mixture of contributions (waves, emissions, ...) of
different origins. Recovering the individual sources from their mixture then
becomes one of the key objectives. However, unless the underlying mixing
processes are well known, these situations lead to heavily underdetermined
problems. Blind source separation aims at disentangling such mixtures with the
least possible prior information on the sources and their mixing processes.
Several powerful approaches have recently been developed, which can often
provide new or deeper insight into the underlying physics. This tutorial paper
briefly discusses some possible applications of blind source separation to the
field of plasma physics, in which this concept is still barely known. Two
examples are given. The first one shows how concurrent processes in the
dynamical response of the electron temperature in a tokamak can be separated.
The second example deals with solar spectral imaging in the Extreme UV and
shows how empirical temperature maps can be built.Comment: expanded version of an article to appear in Contributions to Plasma
Physics (2010
Evaluation of the Algorithms and Parameterizations for Ground Thawing and Freezing Simulation in Permafrost Regions
Ground thawing and freezing depths (GTFDs) strongly influence the hydrology and energy balances of permafrost regions. Current methods to simulate GTFD differ in algorithm type, soil parameterization, representation of latent heat, and unfrozen water content. In this study, five algorithms (one semiempirical, two analytical, and two numerical), three soil thermal conductivity parameterizations, and three unfrozen water parameterizations were evaluated against detailed field measurements at four field sites in Canada’s discontinuous permafrost region. Key findings include: (1) de Vries’ parameterization is recommended to determine the thermal conductivity in permafrost soils; (2) the three unfrozen water parameterization methods exhibited little difference in terms of GTFD simulations, yet the segmented linear function is the simplest to be implemented; (3) the semiempirical algorithm reasonably simulates thawing at permafrost sites and freezing at seasonal frost sites with site-specific calibration. However, large interannual and intersite variations in calibration coefficients limit its applicability for dynamic analysis; (4) when driven by surface forcing, analytical algorithms performed marginally better than the semiempirical algorithm. The inclusion of bottom forcing improved analytical algorithm performance, yet their results were still poor compared with those achieved by numerical algorithms; (5) when supplied with the optimal inputs, soil parameterizations, and model configurations, the numerical algorithm with latent heat treated as an apparent heat capacity achieved the best GTFD simulations among all algorithms at all sites. Replacing the observed bottom temperature with a zero heat flux boundary condition did not significantly reduce simulation accuracy, while assuming a saturated profile caused large errors at several sites
Characterisation of a pucBA deletion mutant from Rhodopseudomonas palustris lacking all but the pucBAd genes
Rhodopseudomonas palustris is a species of purple photosynthetic bacteria that has a multigene family of puc genes that encode the alpha and beta apoproteins, which form the LH2 complexes. A genetic dissection strategy has been adopted in order to try and understand which spectroscopic form of LH2 these different genes produce. This paper presents a characterisation of one of the deletion mutants generated in this program, the pucBAd only mutant. This mutant produces an unusual spectroscopic form of LH2 that only has a single large NIR absorption band at 800 nm. Spectroscopic and pigment analyses on this complex suggest that it has basically a similar overall structure as that of the wild-type HL LH2 complex. The mutant has the unique phenotype where the mutant LH2 complex is only produced when cells are grown at LL. At HL the mutant only produces the LH1-RC core complex
Exact solution of a 2D interacting fermion model
We study an exactly solvable quantum field theory (QFT) model describing
interacting fermions in 2+1 dimensions. This model is motivated by physical
arguments suggesting that it provides an effective description of spinless
fermions on a square lattice with local hopping and density-density
interactions if, close to half filling, the system develops a partial energy
gap. The necessary regularization of the QFT model is based on this proposed
relation to lattice fermions. We use bosonization methods to diagonalize the
Hamiltonian and to compute all correlation functions. We also discuss how,
after appropriate multiplicative renormalizations, all short- and long distance
cutoffs can be removed. In particular, we prove that the renormalized two-point
functions have algebraic decay with non-trivial exponents depending on the
interaction strengths, which is a hallmark of Luttinger-liquid behavior.Comment: 59 pages, 3 figures, v2: further references added; additional
subsections elaborating mathematical details; additional appendix with
details on the relation to lattice fermion
- …