3,975 research outputs found
Large Chiral Diffeomorphisms on Riemann Surfaces and W-algebras
The diffeomorphism action lifted on truncated (chiral) Taylor expansion of a
complex scalar field over a Riemann surface is presented in the paper under the
name of large diffeomorphisms. After an heuristic approach, we show how a
linear truncation in the Taylor expansion can generate an algebra of symmetry
characterized by some structure functions. Such a linear truncation is
explicitly realized by introducing the notion of Forsyth frame over the Riemann
surface with the help of a conformally covariant algebraic differential
equation. The large chiral diffeomorphism action is then implemented through a
B.R.S. formulation (for a given order of truncation) leading to a more
algebraic set up. In this context the ghost fields behave as holomorphically
covariant jets. Subsequently, the link with the so called W-algebras is made
explicit once the ghost parameters are turned from jets into tensorial ghost
ones. We give a general solution with the help of the structure functions
pertaining to all the possible truncations lower or equal to the given order.
This provides another contribution to the relationship between KdV flows and
W-diffeomorphimsComment: LaTeX file, 31 pages, no figure. Version to appear in J. Math. Phys.
Work partly supported by Region PACA and INF
Monitoring cathodic shielding and corrosion under disbonded coatings
This work presents a novel corrosion monitoring probe designed for simulating the conditions developed under disbonded coatings and for measuring current densities and their distribution over a simulated pipeline surface. The probe’s concept was experimentally evaluated via immersion tests under Cathodic Protection (CP) in high resistivity aqueous solution. Under the disbonded area, anodic currents as well as cathodic currents were both measured. Anodic current densities were used to calculate metal losses by means of Faraday’s law. Calculated corrosion patterns were compared with corrosion damage observed at the probe’s surface after a period of test. The probe’s working principles are explained in terms of simple electrochemistry
Evaluation of discharge prescriptions for secondary prevention in patients with acute coronary syndromes in Iraq
Background: Optimal prescribing of secondary prevention medications after acute coronary syndrome (ACS) events has been shown to reduce morbidity and mortality. However, it is unknown whether these medications are optimally prescribed at discharge from acute care in Iraq. Objective: To evaluate whether patients with ACS received optimal secondary prevention medications: antiplatelets, statins, angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers (ACEI/ARBs), and beta-blockers at discharge from a cardiology unit, and to assess whether statins, ACEI/ARBs and beta-blockers were prescribed at target doses based on the American Heart Association/American College of Cardiology (AHA/ACC) guidelines. Methods: Observational retrospective cross-sectional study of patients with ACS admitted to a hospital in Baghdad and survived to discharge between May 2016 and January 2017. Patient-level data and secondary prevention medications at discharge were extracted from routine medical records. Optimal dosing was defined as ≥75%, moderate dosing as 50–74%, and low dosing a
Motor deficits in schizophrenia quantified by nonlinear analysis of postural sway.
Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural sway area was examined in individuals with schizophrenia under four conditions with different amounts of visual and proprioceptive feedback: eyes open or closed and feet together or shoulder width apart. The nonlinear complexity of postural sway was assessed by detrended fluctuation analysis (DFA). The schizophrenia group (n = 27) exhibited greater sway area compared to controls (n = 37). Participants with schizophrenia showed increased sway area following the removal of visual input, while this pattern was absent in controls. Examination of DFA revealed decreased complexity of postural sway and abnormal changes in complexity upon removal of visual input in individuals with schizophrenia. Additionally, less complex postural sway was associated with increased symptom severity in participants with schizophrenia. Given the critical involvement of the cerebellum and related circuits in postural stability and sensorimotor integration, these results are consistent with growing evidence of motor, cerebellar, and sensory integration dysfunction in the disorder, and with theoretical models that implicate cerebellar deficits and more general disconnection of function in schizophrenia
A review of techniques for the monitoring of cathodic shielding and corrosion under disbonded coatings
The mitigation of external corrosion of energy pipelines by a combination of barrier coatings and Cathodic Protection (CP) is not always effective. Even when design specifications are properly met, the shielding of cathodic protection current from reaching steel surface by disbonded barrier coatings, often referred to as cathodic shielding, may lead to severe corrosion problems such as deep pitting, high and near neutral pH Stress Corrosion Cracking (SCC) and Microbiologically Induced Corrosion (MIC). Unfortunately, current indirect assessment methods used in the pipeline industry have serious difficulties in detecting such corrosion problems. This paper provides a brief review of current techniques and their limitations when being applied under complex buried pipeline environmental conditions. The main purpose is to identify potential methods that could be utilised in the design of new monitoring probes specific for the monitoring of cathodic shielding and corrosion of disbonded coatings in the pipeline industry
Studying the cathodic disbondment of coatings using electrochemical impedance spectroscopy
The disbondment of protective organic coatings is a widely reported pipeline coating failure mode in the oil and gas industry. Traditional methods of evaluating cathodic disbondment of pipeline coatings are based on visual inspection of pipeline conditions, and laboratory testing of cathodic disbondment resistance (CDR) using standard methods such as ASTM G8. Although some other laboratory-based techniques, such as scanning kelvin probe and scanning acoustic microscopy have been used to study the cathodic disbondment (CD) of coatings, these are often difficult to apply in practical testing. Over the past decade, electrochemical impedance spectroscopy (EIS) has been employed as a potential method for measuring CD. This paper reports preliminary results from an EIS study designed to characterise CD behaviour of epoxy coatings under excessive cathodic protection. EIS data correlated well with the area of disbonded coating. Analysis of EIS data can provide valuable information on the initiation and rates of CD
Atomistic simulation of the structure and dynamics of the plastic crystal diethyl(methyl)(isobutyl) phosphonium hexafluorophosphate
Analytical Evaluation of Surface-Mounted PMSG Performances Connected to a Diode Rectifier
This paper analyzes some operational issues of threephase surface-mounted permanent magnet synchronous generators (PMSGs) connected to a diode rectifier. This simple configuration coupled to a single-switch dc–dc converter is used in smallscale wind energy conversion systems, as well as in energy harvesting systems, to reduce costs. The diode rectifier causes an intrinsic limit for the maximum convertible power, which is related to the load impedance matching, and additional joule losses due to the distorted currents. By using an analytical steady-state model of the rectifier and of the PMSG, this paper discusses how to achieve two particularly meaningful operating conditions characterized respectively by the maximum power transfer and the maximum power per ampere. The theory is validated by simulation and test results on a prototype
Parameterization invariance and shape equations of elastic axisymmetric vesicles
The issue of different parameterizations of the axisymmetric vesicle shape
addressed by Hu Jian-Guo and Ou-Yang Zhong-Can [ Phys.Rev. E {\bf 47} (1993)
461 ] is reassesed, especially as it transpires through the corresponding Euler
- Lagrange equations of the associated elastic energy functional. It is argued
that for regular, smooth contours of vesicles with spherical topology,
different parameterizations of the surface are equivalent and that the
corresponding Euler - Lagrange equations are in essence the same. If, however,
one allows for discontinuous (higher) derivatives of the contour line at the
pole, the differently parameterized Euler - Lagrange equations cease to be
equivalent and describe different physical problems. It nevertheless appears to
be true that the elastic energy corresponding to smooth contours remains a
global minimum.Comment: 10 pages, latex, one figure include
The complex multiferroic phase diagram of MnCoWO
The complete magnetic and multiferroic phase diagram of
MnCoWO single crystals is investigated by means of magnetic,
heat capacity, and polarization experiments. We show that the ferroelectric
polarization in the multiferroic state abruptly changes
its direction twice upon increasing Co content, x. At x=0.075,
rotates from the axis into the plane and at
x=0.15 it flips back to the axis. The origin of the multiple
polarization flops is identified as an effect of the Co anisotropy on the
orientation and shape of the spin helix leading to thermodynamic instabilities
caused by the decrease of the magnitude of the polarization in the
corresponding phases. A qualitative description of the ferroelectric
polarization is derived by taking into account the intrachain (axis) as
well as the interchain (axis) exchange pathways connecting the magnetic
ions. In a narrow Co concentration range (0.1x0.15), an
intermediate phase, sandwiched between the collinear high-temperature and the
helical low-temperature phases, is discovered. The new phase exhibits a
collinear and commensurate spin modulation similar to the low-temperature
magnetic structure of MnWO.Comment: 18 pages, 6 figure
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