scholarly journals Observations in statistically homogeneous, locally inhomogeneous cosmological toy models without FLRW backgrounds

2020 ◽  
Vol 498 (1) ◽  
pp. L135-L139 ◽  
Author(s):  
S M Koksbang
Keyword(s):  
Einstein Equation ◽  
A Priori ◽  
Spatial Curvature ◽  
General Space ◽  
Redshift Drift ◽  
Light Rays ◽  
Cosmological Solutions ◽  
Good Reproduction ◽  
The Mean ◽  
Distance Relation

ABSTRACT We study observations in toy models that constitute exact cosmological solutions to the Einstein equation. These models are statistically homogeneous but locally inhomogeneous, without an a priori introduced Friedmann–Lemaître–Roberston–Walker (FLRW) background and with ‘structures’ evolving fairly slowly. The mean redshift–distance relation and redshift drift along 500 light rays in each of two models are compared with relations based on spatial averages. The relations based on spatial averages give a good reproduction of the mean redshift–distance relation, although most convincingly in the model where the kinematical backreaction and average spatial curvature cancel each other to a subpercentage precision. In both models, the mean redshift drift clearly differs from the drift of the mean redshift. This indicates that redshift drift could be an important tool for testing the backreaction conjecture as redshift drift appears to distinguish between local and global effects. The method presented for computing the redshift drift is straightforward to generalize and can thus be utilized to fairly easily compute this quantity in a general space–time.

Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

2003 ◽  
Vol 81 (2) ◽  
pp. 340-348 ◽  
Author(s):  
Linda L Milette ◽  
Andrew W Trites
Keyword(s):  
Prey Availability ◽  
A Priori ◽  
Population Decline ◽  
Perinatal Period ◽  
Eumetopias Jubatus ◽  
Steller Sea Lions ◽  
Sea Lions ◽  
First Feeding ◽  
Attendance Patterns ◽  
The Mean

Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

A Geometric Model of the Beating Heart

2007 ◽  
Vol 46 (03) ◽  
pp. 282-286 ◽  
Author(s):  
C. Lorenz ◽  
J. von Berg
Keyword(s):  
Computed Tomography ◽  
A Priori ◽  
Anatomical Landmarks ◽  
Motion Model ◽  
A Priori Information ◽  
Average Accuracy ◽  
Tomography Image ◽  
The Mean ◽  
Priori Information ◽  
Computed Tomography Image

Summary Objectives : A comprehensive model of the human heart that covers multiple surfaces, like those of the four chambers and the attached vessels, is presented. It also contains the coronary arteries and a set of 25 anatomical landmarks. The statistical model is intended to provide a priori information for automated diagnostic and interventional procedures. Methods : The end-diastolic phase of the model was adapted to fit 27 clinical multi-slice computed tomography images, thus reflecting the anatomical variability to be observed in that sample. A mean cardiac motion model was also calculated from a set of eleven multi-phase computed tomography image sets. A number of experiments were performed to determine the accuracy of model-based predictions done on unseen cardiac images. Results : Using an additional deformable surface technique, the model allows for determination of all chambers and the attached vessels on the basis of given anatomical landmarks with an average accuracy of 1.1 mm. After such an individualization of the model by surface adaptation the centerlines of the three main coronary arteries may be estimated with an average accuracy of 5.2 mm. The mean motion model was used to estimate the cardiac phase of an unknown multislice computed tomography image. Conclusion : The mean shape model of the human heart as presented here complements automated image analysis methods with the required a priori information about anatomical constraints to make them work fast and robustly.

scholarly journals Estimation of the mean normal measure from flat sections

2008 ◽  
Vol 40 (01) ◽  
pp. 31-48
Author(s):  
Markus Kiderlen
Keyword(s):  
A Priori ◽  
The Other ◽  
Consistent Estimator ◽  
Random Set ◽  
Normal Measure ◽  
Mild Assumption ◽  
The Mean ◽  
Vertical Sections ◽  
Almost All

We discuss the determination of the mean normal measure of a stationary random set Z ⊂ ℝ d by taking measurements at the intersections of Z with k-dimensional planes. We show that mean normal measures of sections with vertical planes determine the mean normal measure of Z if k ≥ 3 or if k = 2 and an additional mild assumption holds. The mean normal measures of finitely many flat sections are not sufficient for this purpose. On the other hand, a discrete mean normal measure can be verified (i.e. an a priori guess can be confirmed or discarded) using mean normal measures of intersections with m suitably chosen planes when m ≥ ⌊d / k⌋ + 1. This even holds for almost all m-tuples of k-dimensional planes are viable for verification. A consistent estimator for the mean normal measure of Z, based on stereological measurements in vertical sections, is also presented.

scholarly journals How to tell about errors not boringly: methodological analysis of expounding the basis of data processing

2020 ◽  
Vol 2020 (2 (131)) ◽  
pp. 104-115
Author(s):  
Oksana Lozovenko ◽  
Yevgeny Sokolov
Keyword(s):  
Confidence Interval ◽  
Experimental Research ◽  
Basic Skills ◽  
A Priori ◽  
Teaching Experience ◽  
Measured Quantity ◽  
General View ◽  
True Value ◽  
Training Interval ◽  
The Mean

The authors continue to report about results they have obtained in the process of creating a special introductory one-semester Laboratory Physics course «Search for Physics laws». It is known that the teaching experience and the results of the performed tests show that most students do not acquire the basic skills for conducting an experimental research. This course was built on the basis of the algorithm of systematic construction of students’ skills for carrying out an experimental research. The authors have used Galperin’s stepwise teaching procedure which was developed on the assumption that learning any kind of knowledge involves different kinds of actions. The authors have analysed different ways of how to expound the basic ideas of data analysis, and shown their connection with the point, syncretic and training-interval paradigms. Action diagrams are provided for each type of expounding. As an example of using the training-interval paradigm for teaching first-year students of a technical university, a specially designed lab session is presented in the article. The topic of the session is “The concept of a confidence interval”. Laboratory Work 1 “The Buffon-de Morgan Experiment”. This lab session meets several important requirements: a) the number of computations is minimised; b) a directly measurable quantity is considered; c) students are provided with a “fulcrum” in the form of a priori known true value of a quantity. A general view on measuring physics quantities is summarised in four quite unexpected for students “unpleasant axioms”: 1) none of measured values coincides with the true value of a quantity; 2) the mean of measured values does not coincide with the true value of a quantity; 3) even if, by a lucky chance, one of measured values or the mean coincided with the true value of a quantity, we would never know about it; 4) a confidence interval catches the true value of a measured quantity only in 68% of cases. The authors claim that the presented lab lesson allows demonstrating the equity of these “axioms” clearly and vividly, and that the organised laboratory sessions in the new way are significantly more successful in improving students’ basic skills of error analysis than traditional laboratory sessions.

scholarly journals Tropical Cyclone Rain Retrievals from FY-3B MWRI Brightness Temperatures Using the Goddard Profiling Algorithm (GPROF)

2019 ◽  
Vol 36 (5) ◽  
pp. 849-864 ◽  
Author(s):  
Ruanyu Zhang ◽  
Christian D. Kummerow ◽  
David L. Randel ◽  
Paula J. Brown ◽  
Wesley Berg ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
A Priori ◽  
Dual Frequency ◽  
Ancillary Data ◽  
Light Rain ◽  
Brightness Temperatures ◽  
The Mean ◽  
Microwave Imager ◽  
Rain Rates ◽  
Global Precipitation

AbstractThis study focuses on the tropical cyclone rainfall retrieval using FY-3B Microwave Radiation Imager (MWRI) brightness temperatures (Tbs). The GPROF, a fully parametric approach based on the Bayesian scheme, is adapted for use by the MWRI sensor. The MWRI GPROF algorithm is an ocean-only scheme used to estimate rain rates and hydrometeor vertical profiles. An a priori database is constructed from MWRI simulated Tbs, the GPM Microwave Imager (GMI) and Dual-Frequency Precipitation Radar (DPR) combined data, and ancillary data resulting in about 100 000 rainfall profiles. The performance of MWRI retrievals is consistent with DPR observations, even though MWRI retrievals slightly overestimate low rain rates and underestimate high rain rates. The total bias of MWRI retrievals is less than 13% of the mean rain rate of DPR precipitation. Statistical comparisons over GMI GPROF, GMI Hurricane GPROF (HGPROF), and MWRI GPROF retrievals show MWRI GPROF retrievals are consistent in terms of spatial distribution and rain estimates for TCs compared with the other two estimates. In terms of the global precipitation, the mean rain rates at different distances from best track locations for five TC categories are used to identify substantial differences between mean MWRI and GMI GPROF retrievals. After correcting the biases between MWRI and GMI retrievals, the performance of MWRI retrievals shows slight overestimate for light rain rates while underestimating rain rates near the eyewall for category 4 and 5 only.

scholarly journals Spontaneous formation of geysers at only one pole on Enceladus’s ice shell

2020 ◽  
Vol 117 (26) ◽  
pp. 14764-14768 ◽  
Author(s):  
Wanying Kang ◽  
Glenn Flierl
Keyword(s):  
Symmetry Breaking ◽  
Shell Thickness ◽  
A Priori ◽  
Icy Moons ◽  
The North ◽  
Fracture Formation ◽  
Breaking Mechanism ◽  
The Mean ◽  
Ice Shell ◽  
North And South

The ice shell on Enceladus, an icy moon of Saturn, exhibits strong asymmetry between the northern and southern hemispheres, with all known geysers concentrated over the south pole, even though the expected pattern of tidal forced deformation should be symmetric between the north and south poles. Using an idealized ice-evolution model, we demonstrate that this asymmetry may form spontaneously, without any noticeable a priori asymmetry (such as a giant impact or a monopole structure of geological activity), in contrast to previous studies. Infinitesimal asymmetry in the ice shell thickness due to random perturbations are found to be able to grow indefinitely, ending up significantly thinning the ice shell at one of the poles, thereby allowing fracture formation there. Necessary conditions to trigger this hemispheric symmetry-breaking mechanism are found analytically. A rule of thumb we find is that, for Galilean and Saturnian icy moons, the ice shell can undergo hemispheric symmetry breaking only if the mean shell thickness is around 10 to 30 km.

scholarly journals Method for Quantitative Broadband Diffuse Optical Spectroscopy of Tumor-Like Inclusions

2020 ◽  
Vol 10 (4) ◽  
pp. 1419 ◽  
Author(s):  
Sandhya Vasudevan ◽  
Farnoush Forghani ◽  
Chris Campbell ◽  
Savannah Bedford ◽  
Thomas D. O’Sullivan
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Near Infrared ◽  
Continuous Wave ◽  
A Priori ◽  
Hybrid Technique ◽  
Scattering Spectra ◽  
Heterogeneous Tissue ◽  
The Mean ◽  
Homogeneous Background

A hybrid reflectance-based diffuse optical imaging (DOI) technique combining discrete wavelength frequency-domain (FD) near-infrared spectroscopy (NIRS) with broadband continuous wave NIRS measurements was developed to quantify the broadband optical properties of deep tumor-like inclusions. This method was developed to more accurately measure the broadband optical properties of human tumors using a compact handheld imaging probe and without requiring a priori spectral constraints. We simulated the reconstruction of absorption and scattering spectra (650–1000 nm) of human breast tumors in a homogeneous background at depths of 0 to 10 mm. The hybrid DOI technique demonstrated enhanced performance in reconstruction of optical absorption with a mean accuracy over all 71 wavelengths of 8.39% versus 32.26% for a 10 mm deep tumor with the topographic DOI method. The new hybrid technique was also tested and validated on two heterogeneous tissue-simulating phantoms with inclusion depths of 2, 7, and 9 mm. The mean optical absorption accuracy over all wavelengths was similarly improved up to 5x for the hybrid DOI method versus topographic DOI for the deepest inclusions.

Changes Over Time in the Determinants of Sport Commitment

1998 ◽  
Vol 10 (4) ◽  
pp. 356-365 ◽  
Author(s):  
Paul J. Carpenter ◽  
Tara K. Scanlan
Keyword(s):  
High School ◽  
Regression Analysis ◽  
Multiple Regression Analysis ◽  
A Priori ◽  
Soccer Players ◽  
Male And Female ◽  
Sport Commitment ◽  
The Mean ◽  
Changes Over Time ◽  
Over Time

The purpose of this study was to examine whether changes over time in the determinants of sport commitment would be related to predicted changes in commitment. Male and female (N = 103) high school soccer players completed surveys toward the middle and at the end of their regular season. A simultaneous multiple regression analysis indicated that commitment was significantly predicted by changes in involvement opportunities. Examination of the mean magnitude of changes in the determinants and corresponding changes in commitment using a series of correlated t-tests revealed significant effects for sport enjoyment and involvement opportunities. For those players whose sport enjoyment and involvement opportunities had declined, there was a corresponding decrease in their commitment. For those players whose involvement opportunities had increased, there was a corresponding increase in their commitment. Combined, these results provided support for a priori hypotheses regarding changes in the determinants of commitment over time and corresponding changes in commitment.

scholarly journals Counterexamples to C2 Boundary Estimates for a Fully Nonlinear Yamabe Problem on Manifolds with Boundary

2012 ◽  
Vol 12 (4) ◽  
Author(s):  
YanYan Li ◽  
Luc Nguyen
Keyword(s):  
Mean Curvature ◽  
A Priori Estimates ◽  
A Priori ◽  
Gradient Estimates ◽  
Manifolds With Boundary ◽  
Fully Nonlinear ◽  
Priori Estimates ◽  
Hessian Estimates ◽  
The Mean ◽  
Boundary Estimates

AbstractOn closed manifolds, gradient and Hessian a priori estimates for fully nonlinear Yamabe problems are known to hold. On manifolds with boundary, gradient estimates are known to hold, while Hessian estimates hold if the prescribed mean curvature is positive. Examples are given here which show that Hessian estimates can fail when the mean curvature is negative.

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