4,386 research outputs found
Stress-Energy Tensor and Ultraviolet Behaviour in Massive Integrable Quantum Field Theories
The short distance behaviour of massive integrable quantum field theories is
analyzed in terms of the form factor approach. We show that the on-shell
dynamics is compatible with different definitions of the stress-energy tensor
of the theory. In terms of form factors, this is equivalent to
having a possible non-zero matrix element of the trace of on
one-particle state. Each choice of induces a different scaling behaviour
of the massive theory in the ultraviolet limit.Comment: 32 pages LATEX file (Three figures not included in the text)
ISAS/EP/93/6
"Nonlinear" covariance matrix and portfolio theory for non-Gaussian multivariate distributions
This paper offers a precise analytical characterization of the distribution
of returns for a portfolio constituted of assets whose returns are described by
an arbitrary joint multivariate distribution. In this goal, we introduce a
non-linear transformation that maps the returns onto gaussian variables whose
covariance matrix provides a new measure of dependence between the non-normal
returns, generalizing the covariance matrix into a non-linear fractional
covariance matrix. This nonlinear covariance matrix is chiseled to the specific
fat tail structure of the underlying marginal distributions, thus ensuring
stability and good-conditionning. The portfolio distribution is obtained as the
solution of a mapping to a so-called phi-q field theory in particle physics, of
which we offer an extensive treatment using Feynman diagrammatic techniques and
large deviation theory, that we illustrate in details for multivariate Weibull
distributions. The main result of our theory is that minimizing the portfolio
variance (i.e. the relatively ``small'' risks) may often increase the large
risks, as measured by higher normalized cumulants. Extensive empirical tests
are presented on the foreign exchange market that validate satisfactorily the
theory. For ``fat tail'' distributions, we show that an adequete prediction of
the risks of a portfolio relies much more on the correct description of the
tail structure rather than on their correlations.Comment: Latex, 76 page
Determination of steviol glycosides in commercial extracts of Stevia rebaudiana and sweeteners by ultra-high performance liquid chromatography Orbitrap mass spectrometry
Stevia rebaudiana extracts are used as sweeteners in several countries worldwide. Several extracts of diverse composition are available on the market, and their taste depends on the contents of the various steviol glycosides. This study presents an accurate method for the qualitative and quantitative determination of steviol glycosides in 40 Stevia extracts, 7 sweeteners and 3 Stevia-sweetened beverages by a UHPLC coupled to an Orbitrap mass spectrometer. The sub-2 \u3bcm amide column provided the separation of all the target analytes in a run time of 30 min with high resolution. The effect of different eluent compositions on the ionisation efficiency of the steviol glycosides was studied. The optimal ionisation conditions were achieved in negative mode using 0.05% formic acid. Under this condition, adducts were not found, [M-H]- were the main ions and the spontaneous loss of a glucose residue at C19 was reduced. The %RSD for intra- and inter-day precision for all eleven analytes varied from 2.1\u20134.2% and 3.0\u20135.1%, respectively. The recoveries from spiked Stevia extract samples were greater than 95% for all analytes. Rebaudioside A was the most abundant, ranging from 23\u2013102%. Nine Stevia extracts and one drink were not compliant with the European Regulation. Isosteviol was under the LOD in all samples and steviol was found in four samples in quantities in the range 0.01\u20130.03%
Peripheral Facial Nerve Palsy in Severe Systemic Hypertension: A Systematic Review
BACKGROUND Signs of nervous system dysfunction such as headache or convulsions often occur in severe systemic hypertension. Less recognized is the association between severe hypertension and peripheral facial nerve palsy. The aim of this study was to systematically review the literature on the association of peripheral facial palsy with severe hypertension. METHODS Systematic review of Medline, Embase, Web of Science, and Google Scholar from 1960 through December 2011 and report of two cases. RESULTS The literature review revealed 24 cases to which we add two cases with severe hypertension and peripheral facial palsy. Twenty-three patients were children. Palsy was unilateral in 25 cases, bilateral in one case, and recurred in nine. The time between the first facial symptoms and diagnosis of hypertension was a median of 45 days (range, 0 days-2 years). In five case series addressing the complications of severe hypertension in children, 41 further cases of peripheral facial palsy were listed out of 860 patients (4.8%). CONCLUSIONS The association between severe hypertension and peripheral facial palsy is mainly described in children. Arterial hypertension is diagnosed with a substantial delay. Outcome is favorable with adequate antihypertensive treatment. The pathophysiology is still debate
De-noising of dynamic magnetic resonance images by the combined application of wavelet filtering and Karhunen-Loeve Transform (KLT)
Guided Microwave Detection of Corrosion Product in Insulated Pipelines
Corrosion under insulation (CUI) is a common cause of pipeline failure in the oil and gas industry. Its detection with conventional inspection techniques is challenging due to the presence of the insulation layer and a protective metallic cladding that prevent direct access to the pipe surface. Guided microwave testing has been proposed as a cost-effective approach to screen an extended length of a pipeline for the presence of water, which is a necessary precursor for CUI. The pipe and metallic cladding naturally form a large coaxial transmission line in which the insulation acts as a dielectric and supports the propagation of microwave signals. The inspection is performed by launching the signal from an array of antennas permanently installed at one location along the pipeline. Wet insulation is then detected according to the radar principle since water results in the partial reflection of the incident microwave owing to the permittivity contrast between dry and wet insulation. This paper reviews the underpinning principles of longrange guided microwave testing and presents a new study aimed at enhancing the selectivity of the technique by detecting corrosion product inside the insulation which is more reliable indicator of CUI progression
Improved real-time blood flow velocity quantification via application of the Karhunen-Loeve transform for increased signal-to-noise ratio
Oxidative potential associated with urban aerosol deposited into the respiratory system and relevant elemental and ionic fraction contributions
Size-segregated aerosol measurements were carried out at an urban and at an industrial site. Soluble and insoluble fractions of elements and inorganic ions were determined. Oxidative potential (OP) was assessed on the soluble fraction of Particulate Matter (PM) by ascorbic acid (AA), dichlorofluorescein (DCFH) and dithiothreitol (DTT) assays. Size resolved elemental, ion and OP doses in the head (H), tracheobronchial (TB) and alveolar (Al) regions were estimated using the Multiple-Path Particle Dosimetry (MPPD) model. The total aerosol respiratory doses due to brake and soil resuspension emissions were higher at the urban than at the industrial site. On the contrary, the doses of anthropic combustion tracers were generally higher at the industrial site. In general, the insoluble fraction was more abundantly distributed in the coarse than in the fine mode and vice versa for the soluble fraction. Consequently, for the latter, the percent of the total respiratory dose deposited in TB and Al regions increased. Oxidative potential assay (OPAA) doses were distributed in the coarse region; therefore, their major contribution was in the H region. The contribution in the TB and Al regions increased for OPDTT and OPDCFH
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