1,266 research outputs found
Optimization in First-Passage Resetting
We investigate classic diffusion with the added feature that a diffusing
particle is reset to its starting point each time the particle reaches a
specified threshold. In an infinite domain, this process is non-stationary and
its probability distribution exhibits rich features. In a finite domain, we
define a non-trivial optimization in which a cost is incurred whenever the
particle is reset and a reward is obtained while the particle stays near the
reset point. We derive the condition to optimize the net gain in this system,
namely, the reward minus the cost.Comment: 4 pages, 3 figures, revtex 4-1 format. Version 1 contains changes in
response to referee comments. Version 2: A missing factor of 2 in an inline
formula has been correcte
Aspects of solar coronal stability theory
Solar coronal stability theory is a powerful tool for understanding the complex behaviour of the Sun's atmosphere. It enables one to discover the driving forces behind some intriguing phenomena and to gauge the soundness of theoretical models for observed structures. In this thesis, the linear stability analysis of line-tied symmetric magnetohydrostatic equilibria is studied within the framework of ideal MHD, aimed at its application to the solar corona. Firstly, a tractable stability procedure based on a variational method is devised. It provides a necessary condition for stability to disturbances localised about a particular flux surface, and a sufficient condition for stability to all accessible perturbations that vanish at the photosphere. The tests require the minimisation of a line integral along the magnetic field lines. For 1-D equilibria, this can be performed analytically, and simple stability criteria are obtained. The necessary condition then serves as an extended Suydam criterion, incorporating the stabilising effect of line-tying. For 2-D equilibria, the minimisation requires the integration of a system of ordinary differential equations along the field lines. This stability technique is applied to arcade, loop, and prominence models, yielding tight bounds on the equilibrium parameters. Secondly, global modes in 1-D coronal loops are investigated using a normal mode method, in order to clarify their link with localised interchange modes. For nearly force-free fields it is shown that instability to localised modes implies the existence of a fast growing global kink mode driven in the neighbourhood of the radius predicted by the local analysis. This confers a new significance on the study of localised interchange modes and the associated extended Suydam criterion
Quantification of valvular regurgitation by cardiac blood pool scintigraphy: correlation with catheterization
The diagnosis of valvular regurgitation (R) is usually based on clinical signs. Quantification conventionally requires catheterization (C). We have quantified R with cardiac blood pool scintigraphy (CBPS) and compared the results with those obtained by C. Regurgitant fraction (RF) determined by C was calculated with the technique of Dodge. Forward output was measured by thermodilution or cardiogreen dilution. The RF at CBPS was obtained by the stroke index ratio (SIR) minus 1.2 divided by SIR, where SIR is the ratio of the stroke counts of left venticle over those of the right ventricle. Stroke counts are calculated directly from the time-activity curves. Each time-activity curve was obtained by drawing one region of interest around each diastolic image. The correction factor (1.2) was calculated from a large normal population. 22 patients had aortic R, 7 mitral R, 12 both, 8 patients had no evidence of regurgitation. RF of the patients with R varied from 27 to 71% (x = 42%) at C and from 26 to 74% (Y = 41%) at CBPS. Linear regression shows a good correlation coefficient (r = 0.82). The regression equation is y = 0.93x + 1.8. No correlation was found between RF (CBPS or C) and the severity of R assessed visually from angiography. In conclusion: CBPS, a non-invasive method, allows easy and repeatable determination of RF and correlates well with data obtained at catheterizatio
The Odor Specificities of a Subset of Olfactory Receptor Neurons Are Governed by Acj6, a POU-Domain Transcription Factor
AbstractLittle is known about how the odor specificities of olfactory neurons are generated, a process essential to olfactory coding. We have found that neuronal identity relies on the abnormal chemosensory jump 6 (acj6) gene, originally identified by a defect in olfactory behavior. Physiological analysis of individual olfactory neurons shows that in acj6 mutants, a subset of neurons acquires a different odorant response profile. Certain other neurons do not respond to any tested odors in acj6. Molecular analysis of acj6 shows that it encodes a POU-domain transcription factor expressed in olfactory neurons. Our data suggest that the odor response spectrum of an olfactory neuron, and perhaps the choice of receptor genes, is determined through a process requiring the action of Acj6
Comparative efficacy of materials used in patients undergoing pulpotomy or direct pulp capping in carious teeth: A systematic review and meta-analysis.
OBJECTIVES
Different materials have been used for capping the pulp after exposure during caries removal in permanent teeth. The purpose of this study was to collate and analyze all pertinent evidence from randomized controlled trials (RCTs) on different materials used in patients undergoing pulpotomy or direct pulp capping in carious teeth.
MATERIALS AND METHODS
Trials comparing two or more capping agents used for direct pulp capping (DPC) or pulpotomy were considered eligible. An electronic search of four databases and two clinical trial registries was carried out up to February 28, 2021 using a search strategy properly adapted to the PICO framework. Screening, data extraction, and risk of bias (RoB) assessment of primary studies were performed in duplicate and independently. The primary outcome was clinical and radiological success; secondary outcomes included continued root formation, tooth discoloration, and dentin bridge formation.
RESULTS
21 RCTs were included in the study. The RoB assessment indicated a moderate risk among the studies. Due to significant clinical and statistical heterogeneity among the studies, performing network meta-analysis (NMA) was not possible. An ad hoc subgroup analysis revealed strong evidence of a higher success of DPC with Mineral Trioxide Aggregate (MTA) compared to calcium hydroxide (CH) (odds ratio [OR] = 3.10, 95% confidence interval [CI]: 1.66-5.79). MTA performed better than CH in pulp capping (both DPC and pulpotomy) of mature compared to immature teeth (OR = 3.34, 95% CI: 1.81-6.17). The GRADE assessment revealed moderate strength of evidence for DPC and mature teeth, and low to very low strength of evidence for the remaining subgroups.
CONCLUSIONS
Considerable clinical and statistical heterogeneity among the trials did not allow NMA. The ad hoc subgroup analysis indicated that the clinical and radiographic success of MTA was higher than that of CH but only in mature teeth and DPC cases where the strength of evidence was moderate. PROSPERO Registration: number CRD42020127239
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