1,731 research outputs found
Refractive error sensing from wavefront slopes
15 pĂĄginas, 8 figuras, 2 tablas.The problem of measuring the objective refractive error with an aberrometer has shown to be more elusive than expected.
Here, the formalism of differential geometry is applied to develop a theoretical framework of refractive error sensing. At each
point of the pupil, the local refractive error is given by the wavefront curvature, which is a 2 2 symmetric matrix, whose
elements are directly related to sphere, cylinder, and axis. Aberrometers usually measure the local gradient of the
wavefront. Then refractive error sensing consists of differentiating the gradient, instead of integrating as in wavefront
sensing. A statistical approach is proposed to pass from the local to the global (clinically meaningful) refractive error, in\ud
which the best correction is assumed to be the maximum likelihood estimation. In the practical implementation, this
corresponds to the mode of the joint histogram of the 3 different elements of the curvature matrix. Results obtained both in
computer simulations and with real data provide a close agreement and consistency with the main optical image quality
metrics such as the Strehl ratio.This research has been supported by the Spanish
CICyT, Grant FIS2008-00697, and Red Española de
OptometrĂa (Ministerio de Ciencia e InnovaciĂłn,
SAF2008-01114-E).Peer reviewe
On inversions and Doob -transforms of linear diffusions
Let be a regular linear diffusion whose state space is an open interval
. We consider a diffusion which probability law is
obtained as a Doob -transform of the law of , where is a positive
harmonic function for the infinitesimal generator of on . This is the
dual of with respect to where is the speed measure of
. Examples include the case where is conditioned to stay above
some fixed level. We provide a construction of as a deterministic
inversion of , time changed with some random clock. The study involves the
construction of some inversions which generalize the Euclidean inversions.
Brownian motion with drift and Bessel processes are considered in details.Comment: 19 page
Validity and reliability of total body volume and relative body fat mass from a 3-dimensional photonic body surface scanner
OBJECTIVE: Three-dimensional photonic body surface scanners (3DPS) feature a tool to estimate total body volume (BV) from 3D images of the human body, from which the relative body fat mass (%BF) can be calculated. However, information on validity and reliability of these measurements for application in epidemiological studies is limited. METHODS: Validity was assessed among 32 participants (men, 50%) aged 20-58 years. BV and %BF were assessed using a 3DPS (VitusSmart XXL) and air displacement plethysmography (ADP) with a BOD POD(R) device using equations by Siri and Brozek. Three scans were obtained per participant (standard, relaxed, exhaled scan). Validity was evaluated based on the agreement of 3DPS with ADP using Bland Altman plots, correlation analysis and Wilcoxon signed ranks test for paired samples. Reliability was investigated in a separate sample of 18 participants (men, 67%) aged 25-66 years using intraclass correlation coefficients (ICC) based on two repeated 3DPS measurements four weeks apart. RESULTS: Mean BV and %BF were higher using 3DPS compared to ADP, (3DPS-ADP BV difference 1.1 +/- 0.9 L, p<0.01; %BF difference 7.0 +/- 5.6, p<0.01), yet the disagreement was not associated with gender, age or body mass index (BMI). Reliability was excellent for 3DPS BV (ICC, 0.998) and good for 3DPS %BF (ICC, 0.982). Results were similar for the standard scan and the relaxed scan but somewhat weaker for the exhaled scan. CONCLUSIONS: Although BV and %BF are higher than ADP measurements, our data indicate good validity and reliability for an application of 3DPS in epidemiological studies
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3D Quantification of Vascular-Like Structures in z Stack Confocal Images
Optical slice microscopy is commonly used to characterize the morphometric features of 3D cellular cultures, such as in vitro vascularization. However, the quantitative analysis of those structures is often performed on a single 2D maximum intensity projection image, limiting the accuracy of data obtained from 3D cultures. Here, we present a protocol for the quantitative analysis of z stack images, utilizing Fiji, Amira, and WinFiber3D. This protocol facilitates the in-depth examination of vascular-like structures within 3D cell culture models
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Techniques for RNA extraction from cells cultured in starPEG-heparin hydrogels
Three-dimensional (3D) cell culture models that provide a biologically relevant microenvironment are imperative to investigate cellâcell and cellâmatrix interactions in vitro. Semi-synthetic star-shaped poly(ethylene glycol) (starPEG)âheparin hydrogels are widely used for 3D cell culture due to their highly tuneable biochemical and biomechanical properties. Changes in gene expression levels are commonly used as a measure of cellular responses. However, the isolation of high-quality RNA presents a challenge as contamination of the RNA with hydrogel residue, such as polymer or glycosaminoglycan fragments, can impact template quality and quantity, limiting effective gene expression analyses. Here, we compare two protocols for the extraction of high-quality RNA from starPEGâheparin hydrogels and assess three subsequent purification techniques. Removal of hydrogel residue by centrifugation was found to be essential for obtaining high-quality RNA in both isolation methods. However, purification of the RNA did not result in further improvements in RNA quality. Furthermore, we show the suitability of the extracted RNA for cDNA synthesis of three endogenous control genes confirmed via quantitative polymerase chain reaction (qPCR). The methods and techniques shown can be tailored for other hydrogel models based on natural or semi-synthetic materials to provide robust templates for all gene expression analyses
Critical appraisal skills of family physicians in Ontario, Canada
BACKGROUND: Our primary objective in this study was to measure family physicians' knowledge of the key elements that go into assessing the validity and interpreting the results in three different types of studies: i) a randomized controlled trial (RCT); ii) a study evaluating a diagnostic test; and iii) a systematic review (SR). Our secondary objectives were to determine the relationship between the above skills and age, gender, and type of practice. METHODS: We obtained a random sample of 1000 family physicians in Ontario from the College of Family Physicians of Canada database. These physicians were sent a questionnaire in the mail with follow-up mailings to non-responders at 3 and 8 weeks. The questionnaire was designed to measure knowledge and understanding of the basic concepts of critical appraisal skills. Based on the responses to the questions an Evidence Based Medicine (EBM) Knowledge Score was determined for each physician. RESULTS: A response rate of 30.2% was achieved. The respondents were younger and more likely to be recent graduates than the population of Ontario Family Physicians as a whole. This was an expected outcome. Just over 50% of respondents were able to answer questions concerning the critical appraisal of methods and the interpretation of results of research articles satisfactorily. The average score on the 12-point EBM Knowledge Scale was 6.4. The younger physicians scored higher than the older physicians, and academic physicians scored higher than community-based physicians. Scores of male and female physicians did not differ. CONCLUSIONS: We have shown that in a population of physicians which is younger than the general population of physicians, about 50% have reasonable knowledge regarding the critical appraisal of the methods and the interpretation of results of a research article. In general, younger physicians were more knowledgeable than were older physicians. EBM principles were felt to be important to the practice of medicine by 95% of respondents
Non-intersecting squared Bessel paths and multiple orthogonal polynomials for modified Bessel weights
We study a model of non-intersecting squared Bessel processes in the
confluent case: all paths start at time at the same positive value , remain positive, and are conditioned to end at time at . In
the limit , after appropriate rescaling, the paths fill out a
region in the -plane that we describe explicitly. In particular, the paths
initially stay away from the hard edge at , but at a certain critical
time the smallest paths hit the hard edge and from then on are stuck to
it. For we obtain the usual scaling limits from random matrix
theory, namely the sine, Airy, and Bessel kernels. A key fact is that the
positions of the paths at any time constitute a multiple orthogonal
polynomial ensemble, corresponding to a system of two modified Bessel-type
weights. As a consequence, there is a matrix valued
Riemann-Hilbert problem characterizing this model, that we analyze in the large
limit using the Deift-Zhou steepest descent method. There are some novel
ingredients in the Riemann-Hilbert analysis that are of independent interest.Comment: 59 pages, 11 figure
Comparison of Gonadotropin-Releasing Hormone versus Estrogen-Based Fixed-Time Artificial Insemination Protocols in Grazing Bos taurus Suckled Beef Cows
Fixed-timed artificial insemination (FTAI) protocols for beef cattle in South America are primarily based on estradiol esters and intravaginal progesterone-releasing devices (IVPD). The objective of this study was to determine the optimal gonadotropin-releasing hormone (GnRH)-based protocol as an alternative to the use of estrogen-based protocols in grazing Bos taurus suckling beef cows. All cows received an IVPD on the day of protocol initiation and prostaglandin F2α (PG) plus equine chorionic gonadotropin (eCG) treatments at the time of IVPD removal. In Experiment 1, cows (n = 235) were randomly assigned to one of four treatments: (i) 7-day estradiol = 2 mg of estradiol benzoate (EB) at IVPD insertion on Day 9 and 1 mg of estradiol cypionate (ECP) at IVPD removal on Day 2; (ii) 7-day GnRH = 10 ”g of GnRH at IVPD insertion on Day 10, IVPD removal on Day 3 and GnRH at FTAI; (iii) 7 & 7 estradiol = PG at IVPD insertion on Day 16, EB on Day 9 and ECP at IVPD removal on Day 2; (iv) 7 & 7 GnRH = PG at IVPD insertion on Day 17, GnRH on Day 10, IVPD removal on Day 3 and GnRH at FTAI. In Experiment 2, cows (n = 462) were randomly assigned to one of four treatments: (i) 6-day estradiol = EB at IVPD insertion on Day 9, IVPD removal on Day 3 and GnRH at FTAI; (ii) 7-day estradiol; (iii) 7-day GnRH; (iv) 7 & 7 GnRH. In Experiment 1, plasma progesterone concentrations and percentage of cows with a corpus luteum (CL) at IVPD removal, and pregnancy per AI (P/AI) were greater for cows subjected to GnRH-based protocols compared with cows subjected to estrogen-based protocols (p < 0.01). In Experiment 2, cows subjected to the 7 & 7 GnRH protocol had the greatest P/AI (p < 0.01). In summary, GnRH-based FTAI protocols resulted in similar or greater P/AI compared to estrogen-based FTAI protocols in grazing postpartum Bos taurus suckled beef cows. The greatest P/AI was attained with the 7 & 7 GnRH protocol.Fil: FerrĂ©, Luis B.. Instituto Nacional de TecnologĂa Agropecuaria; ArgentinaFil: Jaeschke, Julian. BiogĂ©nesis BagĂł; ArgentinaFil: Gatti, Juliana. BiogĂ©nesis BagĂł; ArgentinaFil: BaladĂłn, Gerardo. BiogĂ©nesis BagĂł; ArgentinaFil: Bellocq, Ezequiel. BiogĂ©nesis BagĂł; ArgentinaFil: FernĂĄndez, Gustavo. No especifĂca;Fil: Rearte, Ramiro. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de ClĂnica. CĂĄtedra de ReproducciĂłn Animal; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata; ArgentinaFil: Kjelland, Michael E.. Mayville State University; Estados UnidosFil: Colazo, Marcos G.. University of Alberta; CanadĂĄFil: Thomas, Jordan M.. University of Missouri; Estados Unido
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