2,698 research outputs found
Multidimensional Quasi-Monte Carlo Malliavin Greeks
We investigate the use of Malliavin calculus in order to calculate the Greeks
of multidimensional complex path-dependent options by simulation. For this
purpose, we extend the formulas employed by Montero and Kohatsu-Higa to the
multidimensional case. The multidimensional setting shows the convenience of
the Malliavin Calculus approach over different techniques that have been
previously proposed. Indeed, these techniques may be computationally expensive
and do not provide flexibility for variance reduction. In contrast, the
Malliavin approach exhibits a higher flexibility by providing a class of
functions that return the same expected value (the Greek) with different
accuracies. This versatility for variance reduction is not possible without the
use of the generalized integral by part formula of Malliavin Calculus. In the
multidimensional context, we find convenient formulas that permit to improve
the localization technique, introduced in Fourni\'e et al and reduce both the
computational cost and the variance. Moreover, we show that the parameters
employed for variance reduction can be obtained \textit{on the flight} in the
simulation. We illustrate the efficiency of the proposed procedures, coupled
with the enhanced version of Quasi-Monte Carlo simulations as discussed in
Sabino, for the numerical estimation of the Deltas of call, digital Asian-style
and Exotic basket options with a fixed and a floating strike price in a
multidimensional Black-Scholes market.Comment: 22 pages, 6 figure
Pricing and Hedging Asian Basket Options with Quasi-Monte Carlo Simulations
In this article we consider the problem of pricing and hedging
high-dimensional Asian basket options by Quasi-Monte Carlo simulation. We
assume a Black-Scholes market with time-dependent volatilities and show how to
compute the deltas by the aid of the Malliavin Calculus, extending the
procedure employed by Montero and Kohatsu-Higa (2003). Efficient
path-generation algorithms, such as Linear Transformation and Principal
Component Analysis, exhibit a high computational cost in a market with
time-dependent volatilities. We present a new and fast Cholesky algorithm for
block matrices that makes the Linear Transformation even more convenient.
Moreover, we propose a new-path generation technique based on a Kronecker
Product Approximation. This construction returns the same accuracy of the
Linear Transformation used for the computation of the deltas and the prices in
the case of correlated asset returns while requiring a lower computational
time. All these techniques can be easily employed for stochastic volatility
models based on the mixture of multi-dimensional dynamics introduced by Brigo
et al. (2004).Comment: 16 page
General Relativistic Dynamics of Irrotational Dust: Cosmological Implications
The non--linear dynamics of cosmological perturbations of an irrotational
collisionless fluid is analyzed within General Relativity. Relativistic and
Newtonian solutions are compared, stressing the different role of boundary
conditions in the two theories. Cosmological implications of relativistic
effects, already present at second order in perturbation theory, are studied
and the dynamical role of the magnetic part of the Weyl tensor is elucidated.Comment: 12 pages , DFPD 93/A/6
Perturbations of spacetime: gauge transformations and gauge invariance at second order and beyond
We consider in detail the problem of gauge dependence that exists in
relativistic perturbation theory, going beyond the linear approximation and
treating second and higher order perturbations. We first derive some
mathematical results concerning the Taylor expansion of tensor fields under the
action of one-parameter families (not necessarily groups) of diffeomorphisms.
Second, we define gauge invariance to an arbitrary order . Finally, we give
a generating formula for the gauge transformation to an arbitrary order and
explicit rules to second and third order. This formalism can be used in any
field of applied general relativity, such as cosmological and black hole
perturbations, as well as in other spacetime theories. As a specific example,
we consider here second order perturbations in cosmology, assuming a flat
Robertson-Walker background, giving explicit second order transformations
between the synchronous and the Poisson (generalized longitudinal) gauges.Comment: slightly revised version, accepted for publication in Classical and
Quantum Gravity. 27 pages including 4 figures, latex using 2 CQG style files:
ioplppt.sty, iopl10.st
Depression and conservative surgery for breast cancer
BACKGROUND: Depression is prevalent among women and associated with reduced quality of life, and therefore it is important to determine its incidence in adult women, especially in those with breast cancer. OBJECTIVE: To determine the occurrence of depression in women who underwent conservative surgery for breast cancer with or without breast reconstruction. METHODS: Seventy-five women aged between 18 and 65 years were enrolled. Patients had undergone conservative surgery for breast cancer with immediate breast reconstruction (n = 25) or without breast reconstruction (n = 25) at least one year before the study. The control group consisted of 25 women without cancer, but of similar age and educational level distribution as the other two groups. The Beck Depression Inventory was used to measure depression. The collected data were assessed using analysis of variance and the χ2 test. RESULTS: There were no significant differences between groups in age (p = 0.72) or educational level (p = 0.20). A smaller number of patients had undergone the menopause (p = 0.02) in the control group than in other groups. There were no significant differences in occurrence of depression between groups (χ2=9.97; p = 0.126). CONCLUSĂŤON: Conservative surgery for breast cancer did not affect the occurrence of depression in women, regardless of whether breast reconstruction was performed
Yellow fever vaccine viremia following ablative BM suppression in AML
Univ SĂŁo Paulo, Sch Med, Dept Infect & Parasit Dis, SĂŁo Paulo, BrazilHosp Sirio Libanes, SĂŁo Paulo, BrazilUniv SĂŁo Paulo, Sch Med, Div Clin Immunol & Allergy, SĂŁo Paulo, BrazilFundacao Prosangue Hemoctr SĂŁo Paulo, SĂŁo Paulo, BrazilUniversidade Federal de SĂŁo Paulo, Infect Dis Div DIPA, SĂŁo Paulo, BrazilFundacao Oswaldo Cruz, Rio de Janeiro, BrazilUniversidade Federal de SĂŁo Paulo, Infect Dis Div DIPA, SĂŁo Paulo, BrazilWeb of Scienc
Cosmic Microwave Background anisotropies from second order gravitational perturbations
This paper presents a complete analysis of the effects of second order
gravitational perturbations on Cosmic Microwave Background anisotropies, taking
explicitly into account scalar, vector and tensor modes. We also consider the
second order perturbations of the metric itself obtaining them, for a universe
dominated by a collision-less fluid, in the Poisson gauge, by transforming the
known results in the synchronous gauge. We discuss the resulting second order
anisotropies in the Poisson gauge, and analyse the possible relevance of the
different terms. We expect that, in the simplest scenarios for structure
formation, the main effect comes from the gravitational lensing by scalar
perturbations, that is known to give a few percent contribution to the
anisotropies at small angular scales.Comment: 15 pages, revtex, no figures. Version to be published in Phys. Rev.
Signatures of Primordial non-Gaussianities in the Matter Power-Spectrum and Bispectrum: the Time-RG Approach
We apply the time-renormalization group approach to study the effect of
primordial non-Gaussianities in the non-linear evolution of cosmological dark
matter density perturbations. This method improves the standard perturbation
approach by solving renormalization group-like equations governing the dynamics
of gravitational instability. The primordial bispectra constructed from the
dark matter density contrast and the velocity fields represent initial
conditions for the renormalization group flow. We consider local, equilateral
and folded shapes for the initial non-Gaussianity and analyze as well the case
in which the non-linear parameter f_{NL} parametrizing the strength of the
non-Gaussianity depends on the momenta in Fourier space through a power-law
relation, the so-called running non-Gaussianity. For the local model of
non-Gaussianity we compare our findings for the power-spectrum with those of
recent N-body simulations and find that they accurately fit the N-body data up
to wave-numbers k \sim 0.25 h/Mpc at z=0. We also present predictions for the
(reduced) matter bispectra for the various shapes of non-Gaussianity.Comment: 27 pages, 12 figures. Results and discussion for a particular case
added. One figure and one reference added. Matches with the version accepted
for publication in the JCAP
Relativistic effects and primordial non-Gaussianity in the galaxy bias
When dealing with observables, one needs to generalize the bias relation
between the observed galaxy fluctuation field to the underlying matter
distribution in a gauge-invariant way. We provide such relation at second-order
in perturbation theory adopting the local Eulerian bias model and starting from
the observationally motivated uniform-redshift gauge. Our computation includes
the presence of primordial non-Gaussianity. We show that large scale-dependent
relativistic effects in the Eulerian bias arise independently from the presence
of some primordial non-Gaussianity. Furthermore, the Eulerian bias inherits
from the primordial non-Gaussianity not only a scale-dependence, but also a
modulation with the angle of observation when sources with different biases are
correlated.Comment: 12 pages, LaTeX file; version accepted for publication in JCA
A device-independent approach to evaluate the heating performance during magnetic hyperthermia experiments: peak analysis and zigzag protocol
Accurate knowledge of the heating performance of magnetic nanoparticles
(MNPs) under AC fields is critical for the development of hyperthermia-mediated
applications. Usually reported in terms of the specific loss power (SLP)
obtained from the temperature variation () vs. time (t) curve, such
estimate is subjected to a huge uncertainty. Thus, very different SLP values
are reported for the same particles when measured on different
equipment/laboratories. This lack of control clearly hampers the further
development of MNP-mediated heat-triggered technologies. Here we report a
device-independent approach to calculate the SLP value of a suspension of MNPs:
the SLP is obtained from the analysis of the peak at the field on/off switch of
the curve. The measurement procedure, which itself constitutes a
change of paradigm within the field, is based on fundamental physics
considerations: specifically to guarantee the applicability of Newton's law of
cooling, as i) it corresponds to the ideal scenario in which the temperature
profiles of the system during heating and cooling are the same; and ii) it
diminishes the role of coexistence of various heat dissipation channels. Such
an approach is supported by theoretical and computational calculations to
increase the reliability and reproducibility of SLP determination. This is
experimentally confirmed, demonstrating a reduction in SLP variation across 3
different devices located in 3 different laboratories. Furthermore, the
application of this peak analysis method (PAM) to a rapid succession of field
on/off switches that result in a zigzag-like , which we term the
zigzag protocol, allows evaluating possible variations of the SLP values with
time or temperature.Comment: main text: 30 pages, 9 figure
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