404 research outputs found
Temporal variability of the telluric sodium layer
The temporal variability of the telluric sodium layer is investigated by
analyzing 28 nights of data obtained with the Colorado State University LIDAR
experiment. The mean height power spectrum of the sodium layer was found to be
well fit by a power law over the observed range of frequencies, 10 microhertz
to 4 millhertz. The best fitting power law was found to be 10^\beta \nu^\alpha,
with \alpha = -1.79 +/- 0.02 and \beta = 1.12 +/- 0.40. Applications to
wavefront sensing require knowledge of the behavior of the sodium layer at kHz
frequencies. Direct measurements at these frequencies do not exist.
Extrapolation from low-frequency behavior to high frequencies suggests that
this variability may be a significant source of error for laser-guide-star
adaptive optics on large-aperture telescopes.Comment: 3 pages, 3 figures, accepted for publication in Optics Letter
Reliability of Intra-Retinal Layer Thickness Estimates
Purpose Measurement of intra-retinal layer thickness using optical coherence
tomography (OCT) has become increasingly prominent in multiple sclerosis (MS)
research. Nevertheless, the approaches used for determining the mean layer
thicknesses vary greatly. Insufficient data exist on the reliability of
different thickness estimates, which is crucial for their application in
clinical studies. This study addresses this lack by evaluating the
repeatability of different thickness estimates. Methods Studies that used
intra-retinal layer segmentation of macular OCT scans in patients with MS were
retrieved from PubMed. To investigate the repeatability of previously applied
layer estimation approaches, we generated datasets of repeating measurements
of 15 healthy subjects and 13 multiple sclerosis patients using two OCT
devices (Cirrus HD-OCT and Spectralis SD-OCT). We calculated each thickness
estimate in each repeated session and analyzed repeatability using intra-class
correlation coefficients and coefficients of repeatability. Results We
identified 27 articles, eleven of them used the Spectralis SD-OCT, nine Cirrus
HD-OCT, two studies used both devices and two studies applied RTVue-100.
Topcon OCT-1000, Stratus OCT and a research device were used in one study
each. In the studies that used the Spectralis, ten different thickness
estimates were identified, while thickness estimates of the Cirrus OCT were
based on two different scan settings. In the simulation dataset, thickness
estimates averaging larger areas showed an excellent repeatability for all
retinal layers except the outer plexiform layer (OPL). Conclusions Given the
good reliability, the thickness estimate of the 6mm-diameter area around the
fovea should be favored when OCT is used in clinical research. Assessment of
the OPL was weak in general and needs further investigation before OPL
thickness can be used as a reliable parameter
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State-of-the-art stochastic data assimilation methods for high-dimensional non-Gaussian problems
This paper compares several commonly used state-of-the-art ensemble-based data assimilation methods in a coherent mathematical notation. The study encompasses different methods that are applicable to high-dimensional geophysical systems, like ocean and atmosphere, and provide an uncertainty estimate. Most variants of Ensemble Kalman Filters, Particle Filters and second-order exact methods are discussed, including Gaussian Mixture Filters, while methods that require an adjoint model or a tangent linear formulation of the model are excluded. The detailed description of all the methods in a mathematically coherent way provides both novices and experienced researchers with a unique overview and new insight in the workings and relative advantages of each method, theoretically and algorithmically, even leading to new filters. Furthermore, the practical implementation details of all ensemble and particle filter methods are discussed to show similarities and differences in the filters aiding the users in what to use when. Finally, pseudo-codes are provided for all of the methods presented in this paper
Trifluoromethyl Fluorosulfonate (CF3OSO2F) and Trifluoromethoxy Sulfur Pentafluoride (CF3OSF5) – Two Gaseous Sulfur(VI) Compounds with Insulating Properties
In this work, we analyzed trifluoromethyl fluorosulfonate (CF3OSO2F) and trifluoromethoxy sulfur pentafluoride (CF3OSF5) regarding their potential use as dielectrics by investigating some of their intrinsic and extrinsic properties. Both compounds show a higher breakdown voltage than SF6 with averaged relative breakdown voltages of 1.3±0.2 for CF3OSO2F and 1.4±0.2 for CF3OSF5 compared to SF6 with 1.0. Like the dielectric (CF3)2CFCN, both compounds decompose during the breakdown process. The decomposition products were analyzed by IR spectroscopy and GCIR methods. Furthermore, the molecular structures of both gaseous compounds CF3OSO2F and CF3OSF5 have been determined by in situ crystallization, and their physical properties were determined as well
Does in vitro protocol predict the nutritional value of thermally treated cereals?
Several in vitro protocols were proposed to rapidly evaluate the nutritional value of cereal and food ingredients. These In vitro protocols are based on restricted parameters and may involve results differing to the reality once assessed in vivo. Moreover, information about some in vitro parameters is sometimes insufficiently described.
In the present study, a three steps in vitro digestion simulation developed by Tervila-Wilo et al. (1996) to mimic digestion in poultry digestive tract was assessed and compared with in vivo digestibility of corn grain harvest at two moisture contents and dried at three temperatures. In vitro digestion simulation showed that increasing drying temperature led to an increase in in vitro digestibility of dry matter (IVDMD) while in vivo digestibility of dry matter (DM) measured on force fed broilers chickens decreased in the same conditions.
To improve this in vitro digestion model, the effect of amylase activity of pancreatin, substrate concentration, corn flour particles reduction and agitation were investigated. Results showed that increasing amylase activity of pancreatin and decreasing substrate concentration improved DM digestibility through starch digestibility while corn flour particles reduction had little effect on its final DM digestibility. Rotational agitation greatly improved starch digestibility and therefore DM digestibility, even at low speed. This increase in DM digestibility reached 20% and was attributed to the better contact between substrate and enzymes and a reduction in solution viscosity under constant agitation. A good adjustment of these parameters would improve the ability of in vitro digestion simulation to accurately predict nutritional value of thermally treated cereals. They have to be taken into account on the implementation of in vitro digestion simulation aiming to predict in vivo performances of consumers.Maïsecvol:Optimisation des modalités de séchage du maïs grain cultivé en Wallonie au regard des performances zootechniques du poulet de chai
A geometric approach to time evolution operators of Lie quantum systems
Lie systems in Quantum Mechanics are studied from a geometric point of view.
In particular, we develop methods to obtain time evolution operators of
time-dependent Schrodinger equations of Lie type and we show how these methods
explain certain ad hoc methods used in previous papers in order to obtain exact
solutions. Finally, several instances of time-dependent quadratic Hamiltonian
are solved.Comment: Accepted for publication in the International Journal of Theoretical
Physic
A Comparison of Atrial Fibrillation Monitoring Strategies After Cryptogenic Stroke (from the Cryptogenic Stroke and Underlying AF Trial)
Ischemic stroke cause remains undetermined in 30% of cases, leading to a diagnosis of cryptogenic stroke. Paroxysmal atrial fibrillation (AF) is a major cause of ischemic stroke but may go undetected with short periods of ECG monitoring. The Cryptogenic Stroke and Underlying Atrial Fibrillation trial (CRYSTAL AF) demonstrated that long-term electrocardiographic monitoring with insertable cardiac monitors (ICM) is superior to conventional follow-up in detecting AF in the population with cryptogenic stroke. We evaluated the sensitivity and negative predictive value (NPV) of various external monitoring techniques within a cryptogenic stroke cohort. Simulated intermittent monitoring strategies were compared to continuous rhythm monitoring in 168 ICM patients of the CRYSTAL AF trial. Short-term monitoring included a single 24-hour, 48-hour, and 7-day Holter and 21-day and 30-day event recorders. Periodic monitoring consisted of quarterly monitoring through 24-hour, 48-hour, and 7-day Holters and monthly 24-hour Holters. For a single monitoring period, the sensitivity for AF diagnosis was lowest with a 24-hour Holter (1.3%) and highest with a 30-day event recorder (22.8%). The NPV ranged from 82.3% to 85.6% for all single external monitoring strategies. Quarterly monitoring with 24-hour Holters had a sensitivity of 3.1%, whereas quarterly 7-day monitors increased the sensitivity to 20.8%. The NPVs for repetitive periodic monitoring strategies were similar at 82.6% to 85.3%. Long-term continuous monitoring was superior in detecting AF compared to all intermittent monitoring strategies evaluated (p <0.001). Long-term continuous electrocardiographic monitoring with ICMs is significantly more effective than any of the simulated intermittent monitoring strategies for identifying AF in patients with previous cryptogenic stroke
Exercise training and high-sensitivity cardiac troponin T in patients with heart failure with reduced ejection fraction
Plasma cell disorders (PCDs) are identified in the clinical lab by detecting the monoclonal immunoglobulin (M-protein) which they produce. Traditionally, serum protein electrophoresis methods have been utilized to detect and isotype Mproteins. Increasing demands to detect low-level disease and new therapeutic monoclonal immunoglobulin treatments have stretched the electrophoretic methods to their analytical limits. Newer techniques based on mass spectrometry (MS) are emerging which have improved clinical and analytical performance. MS is gaining traction into clinical laboratories, and has replaced immunofixation electrophoresis (IFE) in routine practice at one institution. The International Myeloma Working Group (IMWG) Mass Spectrometry Committee reviewed the literature in order to summarize current data and to make recommendations regarding the role of mass spectrometric methods in diagnosing and monitoring patients with myeloma and related disorders. Current literature demonstrates that immune-enrichment of immunoglobulins coupled to intact light chain MALDI-TOF MS has clinical characteristics equivalent in performance to IFE with added benefits of detecting additional risk factors for PCDs, differentiating Mprotein from therapeutic antibodies, and is a suitable replacement for IFE for diagnosing and monitoring multiple myeloma and related PCDs. In this paper we discuss the IMWG recommendations for the use of MS in PCDs.publishedVersio
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