150 research outputs found
Kidney Function in Patients With Neuromuscular Disease:Creatinine Versus Cystatin C
Background: Accurate measurement of kidney function in patients with neuromuscular disorders is challenging. Cystatin C, a marker not influenced by skeletal muscle degradation, might be of clinical value in these patients.Methods: We consecutively enrolled 39 patients with neuromuscular disorders. We investigated the association of the eGFR, based on plasma creatinine and Cystatin C, with clinical and biochemical variables associated with kidney function, namely age and galectin-3.Results: Creatinine-based eGFR was 242 (±80) and Cystatin C-based eGFR was 110 (±23) mL/min/1.73 m2. Cystatin C-based eGFR was associated with age (ÎČ â0.63 p < 0.0001) and galectin-3 levels (ÎČ â0.43 p < 0.01), while creatinine-based eGFR was not (ÎČ â0.22 p = 0.20; ÎČ â0.28 p = 0.10). Sensitivity analyses in Duchenne and Becker patients revealed the same results: Cystatin C-based eGFR was associated with age (ÎČ â0.61 p < 0.01) and galectin-3 levels (ÎČ â0.43 p = 0.05), while creatinine-based eGFR was not (ÎČ â0.32 p = 0.13; ÎČ â0.34 p = 0.14).Conclusions: These data indicate that estimation of renal function in patients with neuromuscular disorders cannot reliably be achieved with creatinine, while Cystatin C appears a reasonable alternative. Since a large proportion of patients with neuromuscular disorders develops heart failure, and requires heart failure medication, adequate monitoring of renal function is warranted
Hypermagnetic Field Effects in the Thermal Bath of Chiral Fermions
The dispersion relations for leptons in the symmetric phase of the
electroweak model in the presence of a constant hypermagnetic field are
investigated. The one-loop fermion self-energies are calculated in the lowest
Landau level approximation and used to show that the hypermagnetic field
forbids the generation of the ''effective mass'' found as a pole of the
fermions' propagators at high temperature and zero fields. In the considered
approximation leptons behave as massless particles propagating only along the
direction of the external field. The reported results can be of interest for
the cosmological implications of primordial hypermagnetic fields.Comment: 5 page
D-terms and D-strings in open string models
We study the Fayet-Iliopoulos (FI) D-terms on D-branes in type II Calabi-Yau
backgrounds. We provide a simple worldsheet proof of the fact that, at tree
level, these terms only couple to scalars in closed string hypermultiplets. At
the one-loop level, the D-terms get corrections only if the gauge group has an
anomalous spectrum, with the anomaly cancelled by a Green-Schwarz mechanism. We
study the local type IIA model of D6-branes at SU(3) angles and show that, as
in field theory, the one-loop correction suffers from a quadratic divergence in
the open string channel. By studying the closed string channel, we show that
this divergence is related to a closed string tadpole, and is cancelled when
the tadpole is cancelled. Next, we study the cosmic strings that arise in the
supersymmetric phases of these systems in light of recent work of Dvali et. al.
In the type IIA intersecting D6-brane examples, we identify the D-term strings
as D4-branes ending on the D6-branes. Finally, we use N=1 dualities to relate
these results to previous work on the FI D-term of heterotic strings.Comment: 29 pages, 5 figures; v2: improved referencin
Neutrino Propagation in a Strongly Magnetized Medium
We derive general expressions at the one-loop level for the coefficients of
the covariant structure of the neutrino self-energy in the presence of a
constant magnetic field. The neutrino energy spectrum and index of refraction
are obtained for neutral and charged media in the strong-field limit () using the lowest Landau level
approximation. The results found within the lowest Landau level approximation
are numerically validated, summing in all Landau levels, for strong and weakly-strong fields. The neutrino energy in
leading order of the Fermi coupling constant is expressed as the sum of three
terms: a kinetic-energy term, a term of interaction between the magnetic field
and an induced neutrino magnetic moment, and a rest-energy term. The leading
radiative correction to the kinetic-energy term depends linearly on the
magnetic field strength and is independent of the chemical potential. The other
two terms are only present in a charged medium. For strong and weakly-strong
fields, it is found that the field-dependent correction to the neutrino energy
in a neutral medium is much larger than the thermal one. Possible applications
to cosmology and astrophysics are considered.Comment: 23 pages, 4 figures. Corrected misprints in reference
Detecting Damage on Wind Turbine Bearings Using Acoustic Emissions and Gaussian Process Latent Variable Models
This paper presents a study into the use of Gaussian Process Latent Variable Models (GP-LVM) and Probabilistic Principal Component Analysis (PPCA) for detection of defects on wind turbine bearings using Acoustic Emission (AE) data. The results presented have been taken from an experimental rig with a seeded defect, to attempt to replicate an AE burst generated from a developing crack. Some of the results for both models are presented and compared, and it is shown that the GP-LVM, which is a nonlinear extension of PPCA, outperforms it in distinguishing AE bursts generated from a defect over those generated by other mechanisms
A probabilistic approach for acoustic emission based monitoring techniques: with application to structural health monitoring
It has been demonstrated that acoustic-emission (AE), inspection of structures can offer advantages over other types of monitoring techniques in the detection of damage; namely, an increased sensitivity to damage, as well as an ability to localise its source. There are, however, numerous challenges associated with the analysis of AE data. One issue is the high sampling frequencies required to capture AE activity. In just a few seconds, a recording can generate very high volumes of data, of which a significant portion may be of little interest for analysis. Identifying the individual AE events in a recorded time-series is therefore a necessary procedure for reducing the size of the dataset and projecting out the influence of background noise from the signal. In this paper, a state-of-the-art technique is presented that can automatically identify cluster the AE events from a probabilistic perspective. A nonparametric Bayesian approach, based on the Dirichlet process (DP), is employed to overcome some of the challenges associated with this task. Additionally, the developed model is applied for damage detection using AE data collected from an experimental setup. Two main sets of AE data are considered in this work: (1) from a journal bearing in operation, and (2) from an Airbus A320 main landing gear subjected to fatigue testing
Axially asymmetric fermion scattering off electroweak phase transition bubble walls with hypermagnetic fields
We show that in the presence of large scale primordial hypermagnetic fields,
it is possible to generate an axial asymmetry for a first order electroweak
phase transition. This happens during the reflection and transmission of
fermions off the true vacuum bubbles, due to the chiral nature of the fermion
coupling with the background field in the symmetric phase. We derive and solve
the Dirac equation for such fermions and compute the reflection and
transmission coefficients for the case when these fermions move from the
symmetric to the symmetry broken phase. We also comment on the possible
implications of such axial charge segregation processes for baryon number
generation.Comment: 8 pages, 2 Encapsulated Postscript figures, uses ReVTeX and
epsfig.sty, expanded discussion, version to appear in Phys. Rev.
Branes on Generalized Calibrated Submanifolds
We extend previous results on generalized calibrations to describe
supersymmetric branes in supergravity backgrounds with diverse fields turned
on, and provide several new classes of examples. As an important application,
we show that supersymmetric D-branes in compactifications with field strength
fluxes, and on SU(3)-structure spaces, wrap generalized calibrated
submanifolds, defined by simple conditions in terms of the underlying globally
defined, but non-closed, 2- and 3-forms. We provide examples where the
geometric moduli of D-branes (for instance D7-branes in 3-form flux
configurations) are lifted by the generalized calibration condition. In
addition, we describe supersymmetric D6-branes on generalized calibrated
3-submanifolds of half-flat manifolds, which provide the mirror of B-type
D-branes in IIB CY compactifications with 3-form fluxes. Supersymmetric sets of
such D-branes carrying no homology charges are mirror to supersymmetric sets of
D-branes which are homologically non-trivial, but trivial in K-theory. As an
additional application, we describe models with chiral gauge sectors, realized
in terms of generalized calibrated brane box configurations of NS- and
D5-branes, which are supersymmetric but carry no charges, so that no
orientifold planes are required in the compactification.Comment: 40 pages, 3 figures, references adde
Dark Energy from structure: a status report
The effective evolution of an inhomogeneous universe model in any theory of
gravitation may be described in terms of spatially averaged variables. In
Einstein's theory, restricting attention to scalar variables, this evolution
can be modeled by solutions of a set of Friedmann equations for an effective
volume scale factor, with matter and backreaction source terms. The latter can
be represented by an effective scalar field (`morphon field') modeling Dark
Energy.
The present work provides an overview over the Dark Energy debate in
connection with the impact of inhomogeneities, and formulates strategies for a
comprehensive quantitative evaluation of backreaction effects both in
theoretical and observational cosmology. We recall the basic steps of a
description of backreaction effects in relativistic cosmology that lead to
refurnishing the standard cosmological equations, but also lay down a number of
challenges and unresolved issues in connection with their observational
interpretation.
The present status of this subject is intermediate: we have a good
qualitative understanding of backreaction effects pointing to a global
instability of the standard model of cosmology; exact solutions and
perturbative results modeling this instability lie in the right sector to
explain Dark Energy from inhomogeneities. It is fair to say that, even if
backreaction effects turn out to be less important than anticipated by some
researchers, the concordance high-precision cosmology, the architecture of
current N-body simulations, as well as standard perturbative approaches may all
fall short in correctly describing the Late Universe.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 59
pages, 2 figures; matches published versio
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