13,234 research outputs found
Assessing the impact of prompt corrective action on bank capital and risk
This paper was presented at the conference "Financial services at the crossroads: capital regulation in the twenty-first century" as part of session 1, "Impact of capital requirements on bank risk taking: empirical evidence." The conference, held at the Federal Reserve Bank of New York on February 26-27, 1998, was designed to encourage a consensus between the public and private sectors on an agenda for capital regulation in the new century.Bank capital ; Bank supervision ; Risk ; Bank investments
Immirzi parameter without Immirzi ambiguity : Conformal loop quantization of scalar-tensor gravity
C.W. wishes to thank G. Immirzi and C. Rovelli for early discussions and brief correspondence respectively, and appreciates the EPSRC GG-Top Project and the Cruickshank Trust for financial support. O.V. is grateful to the Aberdeen University College of Physical Sciences for a research studentship.Peer reviewedPublisher PD
A subset solution to the sign problem in random matrix simulations
We present a solution to the sign problem in dynamical random matrix
simulations of a two-matrix model at nonzero chemical potential. The sign
problem, caused by the complex fermion determinants, is solved by gathering the
matrices into subsets, whose sums of determinants are real and positive even
though their cardinality only grows linearly with the matrix size. A detailed
proof of this positivity theorem is given for an arbitrary number of fermion
flavors. We performed importance sampling Monte Carlo simulations to compute
the chiral condensate and the quark number density for varying chemical
potential and volume. The statistical errors on the results only show a mild
dependence on the matrix size and chemical potential, which confirms the
absence of sign problem in the subset method. This strongly contrasts with the
exponential growth of the statistical error in standard reweighting methods,
which was also analyzed quantitatively using the subset method. Finally, we
show how the method elegantly resolves the Silver Blaze puzzle in the
microscopic limit of the matrix model, where it is equivalent to QCD.Comment: 18 pages, 11 figures, as published in Phys. Rev. D; added references;
in Sec. VB: added discussion of model satisfying the Silver Blaze for all N
(proof in Appendix E
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Schwannomatosis of the Spinal Accessory Nerve: A Case Report.
Schwannomatosis is a distinct syndrome characterized by multiple peripheral nerve schwannomas that can be sporadic or familial in nature. Cases affecting the lower cranial nerves are infrequent. Here, the authors present a rare case of schwannomatosis affecting the left spinal accessory nerve. Upon genetic screening, an in-frame insertion at codon p.R177 of the Sox 10 gene was observed. There were no identifiable alterations in NF1, NF2, LZTR1, and SMARCB1. This case demonstrates a rare clinical presentation of schwannomatosis in addition to a genetic aberration that has not been previously reported in this disease context
Robust Adaptive Control Barrier Functions: An Adaptive & Data-Driven Approach to Safety (Extended Version)
A new framework is developed for control of constrained nonlinear systems
with structured parametric uncertainties. Forward invariance of a safe set is
achieved through online parameter adaptation and data-driven model estimation.
The new adaptive data-driven safety paradigm is merged with a recent adaptive
control algorithm for systems nominally contracting in closed-loop. This
unification is more general than other safety controllers as closed-loop
contraction does not require the system be invertible or in a particular form.
Additionally, the approach is less expensive than nonlinear model predictive
control as it does not require a full desired trajectory, but rather only a
desired terminal state. The approach is illustrated on the pitch dynamics of an
aircraft with uncertain nonlinear aerodynamics.Comment: Added aCBF non-Lipschitz example and discussion on approach
implementatio
Natural regulatory (CD4+CD25+FOXP+) T cells control the production of pro-inflammatory cytokines during Plasmodium chabaudi adami infection and do not contribute to immune evasion.
Different functions have been attributed to natural regulatory CD4+CD25+FOXP+ (Treg) cells during malaria infection. Herein, we assessed the role for Treg cells during infections with lethal (DS) and non-lethal (DK) Plasmodium chabaudi adami parasites, comparing the levels of parasitemia, inflammation and anaemia. Independent of parasite virulence, the population of splenic Treg cells expanded during infection, and the absolute numbers of activated CD69+ Treg cells were higher in DS-infected mice. In vivo depletion of CD25+ T cells, which eliminated 80% of CD4+FOXP3+CD25+ T cells and 60â70% of CD4+FOXP3+ T cells, significantly decreased the number of CD69+ Treg cells in mice with lethal malaria. As a result, higher parasite burden and morbidity were measured in the latter, whereas the kinetics of infection with non-lethal parasites remained unaffected. In the absence of Treg cells, parasite-specific IFN-Îł responses by CD4+ T cells increased significantly, both in mice with lethal and non-lethal infections, whereas IL-2 production was only stimulated in mice with non-lethal malaria. Following the depletion of CD25+ T cells, the production of IL-10 by CD90â cells was also enhanced in infected mice. Interestingly, a potent induction of TNF- and IFN-Îł production by CD4+ and CD90â lymphocytes was measured in DS-infected mice, which also suffered severe anaemia earlier than non-depleted infected controls. Taken together, our data suggest that the expansion and activation of natural Treg cells represent a counter-regulatory response to the overwhelming inflammation associated with lethal P.c. adami. This response to infection involves TH1 lymphocytes as well as cells from the innate immune system
Two-slit diffraction with highly charged particles: Niels Bohr's consistency argument that the electromagnetic field must be quantized
We analyze Niels Bohr's proposed two-slit interference experiment with highly
charged particles that argues that the consistency of elementary quantum
mechanics requires that the electromagnetic field must be quantized. In the
experiment a particle's path through the slits is determined by measuring the
Coulomb field that it produces at large distances; under these conditions the
interference pattern must be suppressed. The key is that as the particle's
trajectory is bent in diffraction by the slits it must radiate and the
radiation must carry away phase information. Thus the radiation field must be a
quantized dynamical degree of freedom. On the other hand, if one similarly
tries to determine the path of a massive particle through an inferometer by
measuring the Newtonian gravitational potential the particle produces, the
interference pattern would have to be finer than the Planck length and thus
undiscernable. Unlike for the electromagnetic field, Bohr's argument does not
imply that the gravitational field must be quantized.Comment: 8 pages, 4 figures. To appear in Proc. Natl. Acad. Sc
Fast directional correlation on the sphere with steerable filters
A fast algorithm is developed for the directional correlation of scalar
band-limited signals and band-limited steerable filters on the sphere. The
asymptotic complexity associated to it through simple quadrature is of order
O(L^5), where 2L stands for the square-root of the number of sampling points on
the sphere, also setting a band limit L for the signals and filters considered.
The filter steerability allows to compute the directional correlation uniquely
in terms of direct and inverse scalar spherical harmonics transforms, which
drive the overall asymptotic complexity. The separation of variables technique
for the scalar spherical harmonics transform produces an O(L^3) algorithm
independently of the pixelization. On equi-angular pixelizations, a sampling
theorem introduced by Driscoll and Healy implies the exactness of the
algorithm. The equi-angular and HEALPix implementations are compared in terms
of memory requirements, computation times, and numerical stability. The
computation times for the scalar transform, and hence for the directional
correlation, of maps of several megapixels on the sphere (L~10^3) are reduced
from years to tens of seconds in both implementations on a single standard
computer. These generic results for the scale-space signal processing on the
sphere are specifically developed in the perspective of the wavelet analysis of
the cosmic microwave background (CMB) temperature (T) and polarization (E and
B) maps of the WMAP and Planck experiments. As an illustration, we consider the
computation of the wavelet coefficients of a simulated temperature map of
several megapixels with the second Gaussian derivative wavelet.Comment: Version accepted in APJ. 14 pages, 2 figures, Revtex4 (emulateapj).
Changes include (a) a presentation of the algorithm as directly built on
blocks of standard spherical harmonics transforms, (b) a comparison between
the HEALPix and equi-angular implementation
Collide and Conquer: Constraints on Simplified Dark Matter Models using Mono-X Collider Searches
The use of simplified models as a tool for interpreting dark matter collider
searches has become increasingly prevalent, and while early Run II results are
beginning to appear, we look to see what further information can be extracted
from the Run I dataset. We consider three `standard' simplified models that
couple quarks to fermionic singlet dark matter: an -channel vector mediator
with vector or axial-vector couplings, and a -channel scalar mediator. Upper
limits on the couplings are calculated and compared across three alternate
channels, namely mono-jet, mono- (leptonic) and mono- (hadronic). The
strongest limits are observed in the mono-jet channel, however the
computational simplicity and absence of significant -channel model width
effects in the mono-boson channels make these a straightforward and competitive
alternative. We also include a comparison with relic density and direct
detection constraints.Comment: 32 pages, 8 figures; v2: minor changes, conclusion unchanged, matches
published versio
Dark Matter: Collider vs. direct searches
Effective Field Theories (EFTs) are a useful tool across a wide range of DM searches, including LHC searches and direct detection. Given the current lack of indications about the nature of the DM particle and its interactions, a model independent interpretation of the collider bounds appears mandatory, especially in complementarity with the reinterpretation of the exclusion limits within a choice
of simplified models, which cannot exhaust the set of possible completions of an effective Lagrangian. However EFTs must be used with caution at LHC energies, where the energy scale of the interaction is at a scale where the EFT approximation can no longer be assumed to be valid. Here we introduce some tools that allow the validity of the EFT approximation to be quantified, and provide case studies for
two operators. We also show a technique that allows EFT constraints from collider searches to be made substantially more robust, even at large center-of-mass energies. This allows EFT constraints from different classes of experiment to be compared in a much more robust manner
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