Mood-congruent free recall bias in anxious individuals is not a consequence of response bias.

Science.gov (United States)

Russo, Riccardo; Whittuck, Dora; Roberson, Debi; Dutton, Kevin; Georgiou, George; Fox, Elaine

2006-05-01

The status of mood-congruent free recall bias in anxious individuals was evaluated following incidental encoding of target words. Individuals with high and low levels of trait anxiety completed a modified Stroop task, which revealed an attentional bias for threat-related stimuli in anxious individuals. This group was significantly slower in naming the colour in which threat-related words were displayed compared to neutral words. In a subsequent free recall test for the words used in the modified Stroop task, anxious individuals recalled more threat-related words compared to low-anxious people. This difference was significant even when controlling for the false recall of items that had not been presented during study. These results support the view put forward by Russo, Fox, Bellinger, and Nguyen-Van-Tam (2001) that mood-congruent free recall bias in anxious individuals can be observed if the target material is encoded at a relatively shallow level. Moreover, contrary to Dowens and Calvo (2003), the current results show that the memory advantage for threat-related information in anxious individuals is not a consequence of response bias.

Spatial Bias in Field-Estimated Unsaturated Hydraulic Properties

Energy Technology Data Exchange (ETDEWEB)

HOLT,ROBERT M.; WILSON,JOHN L.; GLASS JR.,ROBERT J.

2000-12-21

Hydraulic property measurements often rely on non-linear inversion models whose errors vary between samples. In non-linear physical measurement systems, bias can be directly quantified and removed using calibration standards. In hydrologic systems, field calibration is often infeasible and bias must be quantified indirectly. We use a Monte Carlo error analysis to indirectly quantify spatial bias in the saturated hydraulic conductivity, K{sub s}, and the exponential relative permeability parameter, {alpha}, estimated using a tension infiltrometer. Two types of observation error are considered, along with one inversion-model error resulting from poor contact between the instrument and the medium. Estimates of spatial statistics, including the mean, variance, and variogram-model parameters, show significant bias across a parameter space representative of poorly- to well-sorted silty sand to very coarse sand. When only observation errors are present, spatial statistics for both parameters are best estimated in materials with high hydraulic conductivity, like very coarse sand. When simple contact errors are included, the nature of the bias changes dramatically. Spatial statistics are poorly estimated, even in highly conductive materials. Conditions that permit accurate estimation of the statistics for one of the parameters prevent accurate estimation for the other; accurate regions for the two parameters do not overlap in parameter space. False cross-correlation between estimated parameters is created because estimates of K{sub s} also depend on estimates of {alpha} and both parameters are estimated from the same data.

Mood-congruent free recall bias in anxious individuals is not a consequence of response bias

OpenAIRE

Russo, Riccardo; Whittuck, Dora; Roberson, Debi; Dutton, Kevin; Georgiou, George; Fox, Elaine

2006-01-01

The status of mood-congruent free recall bias in anxious individuals was evaluated following incidental encoding of target words. Individuals with high and low levels of trait anxiety completed a modified Stroop task, which revealed an attentional bias for threat-related stimuli in anxious individuals. This group was significantly slower in naming the colour in which threat-related words were displayed compared to neutral words. In a subsequent free recall test for the words used in the modif...

Comparison of erythrocyte dynamics in shear flow under different stress-free configurations

Science.gov (United States)

Cordasco, Daniel; Yazdani, Alireza; Bagchi, Prosenjit

2014-04-01

An open question that has persisted for decades is whether the cytoskeleton of a red blood cell is stress-free or under a stress. This question is important in the context of theoretical modeling of cellular motion under a flowing condition where it is necessary to make an assumption about the stress-free state. Here, we present a 3D numerical study to compare the cell dynamics in a simple shear flow under two different stress-free states, a biconcave discocyte representing the resting shape of the cell, and a nearly spherical oblate shape. We find that whether the stress-free states make a significant difference or not depends on the viscosity of the suspending medium. If the viscosity is close to that of blood plasma, the two stress-free states do not show any significant difference in cell dynamics. However, when the suspending medium viscosity is well above that of the physiological range, as in many in vitro studies, the shear rate separating the tank-treading and tumbling dynamics is observed to be higher for the biconcave stress-free state than the spheroidal state. The former shows a strong shape oscillation with repeated departures from the biconcave shape, while the latter shows a nearly stable biconcave shape. It is found that the cell membrane in the biconcave stress-free state is under a compressive stress and a weaker bending force density, leading to a periodic compression of the cell. The shape oscillation then leads to a higher energy barrier against membrane tank-tread leading to an early transition to tumbling. However, if the cells are released with a large off-shear plane angle, the oscillations can be suppressed due to an azimuthal motion of the membrane along the vorticity direction leading to a redistribution of the membrane points and lowering of the energy barrier, which again results in a nearly similar behavior of the cells under the two different stress-free states. A variety of off-shear plane dynamics is observed, namely, rolling

Turbulent transport reduction by E x B velocity shear during edge plasma biasing in tokamaks

Energy Technology Data Exchange (ETDEWEB)

Van Oost, G. [Dept. of Applied Physics, Ghent Univ., Ghent (Belgium); Adamek, J.; Antoni, V.; Balan, P.; Boedo, J.A.; Devynck, P.; Duran, I.; Eliseev, L.; Gunn, J.P.; Hron, M.; Ionita, C.; Jachmich, S.; Kirnev, G.S.; Martines, E.; Melnikov, A.; Peleman, P.; Schrittwieser, R.; Silva, C.; Stoeckel, J.; Tendler, M.; Varandas, C.; Van Schoor, M.; Vershkov, V.; Weynants, R.R.

2004-07-01

Experiments in the tokamaks TEXTOR, CASTOR, T-10 and ISTTOK have provided new and complementary evidence on the physics of the universal mechanism of E x B velocity shear stabilization of turbulence, concomitant transport barrier formation and radial conductivity by using various edge biasing techniques. (orig.)

BIASED BEARINGS-ONIKY PARAMETER ESTIMATION FOR BISTATIC SYSTEM

Institute of Scientific and Technical Information of China (English)

Xu Benlian; Wang Zhiquan

2007-01-01

According to the biased angles provided by the bistatic sensors,the necessary condition of observability and Cramer-Rao low bounds for the bistatic system are derived and analyzed,respectively.Additionally,a dual Kalman filter method is presented with the purpose of eliminating the effect of biased angles on the state variable estimation.Finally,Monte-Carlo simulations are conducted in the observable scenario.Simulation results show that the proposed theory holds true,and the dual Kalman filter method can estimate state variable and biased angles simultaneously.Furthermore,the estimated results can achieve their Cramer-Rao low bounds.

The shear-free condition and constant-mean-curvature hyperboloidal initial data

International Nuclear Information System (INIS)

Allen, Paul T; Allen, Iva Stavrov; Isenberg, James; Lee, John M

2016-01-01

We consider the Einstein–Maxwell-fluid constraint equations, and make use of the conformal method to construct and parametrize constant-mean-curvature hyperboloidal initial data sets that satisfy the shear-free condition. This condition is known to be necessary in order that a spacetime development admit a regular conformal boundary at future null infinity; see (Andersson and Chruściel 1994 Commun. Math. Phys. 161 533–68). We work with initial data sets in a variety of regularity classes, primarily considering those data sets whose geometries are weakly asymptotically hyperbolic , as defined in (Allen et al 2015 arXiv:1506.03399). These metrics are C 1,1 conformally compact, but not necessarily C 2 conformally compact. In order to ensure that the data sets we construct are indeed shear-free, we make use of the conformally covariant traceless Hessian introduced in (Allen et al 2015 arXiv:1506.03399). We furthermore construct a class of initial data sets with weakly asymptotically hyerbolic metrics that may be only C 0,1 conformally compact; these data sets are insufficiently regular to make sense of the shear-free condition. (paper)

Maxwell, Yang-Mills, Weyl and eikonal fields defined by any null shear-free congruence

Science.gov (United States)

Kassandrov, Vladimir V.; Rizcallah, Joseph A.

We show that (specifically scaled) equations of shear-free null geodesic congruences on the Minkowski space-time possess intrinsic self-dual, restricted gauge and algebraic structures. The complex eikonal, Weyl 2-spinor, SL(2, ℂ) Yang-Mills and complex Maxwell fields, the latter produced by integer-valued electric charges (“elementary” for the Kerr-like congruences), can all be explicitly associated with any shear-free null geodesic congruence. Using twistor variables, we derive the general solution of the equations of the shear-free null geodesic congruence (as a modification of the Kerr theorem) and analyze the corresponding “particle-like” field distributions, with bounded singularities of the associated physical fields. These can be obtained in a straightforward algebraic way and exhibit nontrivial collective dynamics simulating physical interactions.

Estimation of viscoelastic parameters in Prony series from shear wave propagation

Energy Technology Data Exchange (ETDEWEB)

Jung, Jae-Wook; Hong, Jung-Wuk, E-mail: j.hong@kaist.ac.kr, E-mail: jwhong@alum.mit.edu [Department of Civil and Environmental Engineering, KAIST, 291 Deahak-ro, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Lee, Hyoung-Ki; Choi, Kiwan [Health and Medical Equipment, Samsung Electronics, 1003 Daechi-dong, Gangnam-gu, Seoul 135-280 (Korea, Republic of)

2016-06-21

When acquiring accurate ultrasonic images, we must precisely estimate the mechanical properties of the soft tissue. This study investigates and estimates the viscoelastic properties of the tissue by analyzing shear waves generated through an acoustic radiation force. The shear waves are sourced from a localized pushing force acting for a certain duration, and the generated waves travel horizontally. The wave velocities depend on the mechanical properties of the tissue such as the shear modulus and viscoelastic properties; therefore, we can inversely calculate the properties of the tissue through parametric studies.

A simple model to understand the role of membrane shear elasticity and stress-free shape on the motion of red blood cells in shear flow

Science.gov (United States)

Viallat, Annie; Abkarian, Manouk; Dupire, Jules

2015-11-01

The analytical model presented by Keller and Skalak on the dynamics of red blood cells in shear flow described the cell as a fluid ellipsoid of fixed shape. It was extended to introduce shear elasticity of the cell membrane. We further extend the model when the cell discoid physiological shape is not a stress-free shape. We show that spheroid stress-free shapes enables fitting experimental data with values of shear elasticity typical to that found with micropipettes and optical tweezers. For moderate shear rates (when RBCs keep their discoid shape) this model enables to quantitatively determine an effective cell viscosity, that combines membrane and hemoglobin viscosities and an effective shear modulus of the membrane that combines shear modulus and stress-free shape. This model allows determining RBC mechanical parameters both in the tanktreading regime for cells suspended in a high viscosity medium, and in the tumbling regime for cells suspended in a low viscosity medium. In this regime,a transition is predicted between a rigid-like tumbling motion and a fluid-like tumbling motion above a critical shear rate, which is directly related to the mechanical parameters of the cell. A*MIDEX (n ANR-11-IDEX-0001-02) funded by the ''Investissements d'Avenir'', Region Languedoc-Roussillon, Labex NUMEV (ANR-10-LABX-20), BPI France project DataDiag.

Free Speech Tensions: Responding to Bias on College and University Campuses

Science.gov (United States)

Miller, Ryan A.; Guida, Tonia; Smith, Stella; Ferguson, S. Kiersten; Medina, Elizabeth

2018-01-01

Despite the increasing development of bias response teams on college and university campuses, little scholarship has examined these teams and, in particular, team leaders' approaches to understanding the role of free speech in responding to bias. Through semi-structured interviews, administrators who served on bias response teams at 19…

Practical Weak-lensing Shear Measurement with Metacalibration

Energy Technology Data Exchange (ETDEWEB)

Sheldon, Erin S. [Brookhaven National Laboratory, Bldg. 510, Upton, NY 11973 (United States); Huff, Eric M. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 (United States)

2017-05-20

Metacalibration is a recently introduced method to accurately measure weak gravitational lensing shear using only the available imaging data, without need for prior information about galaxy properties or calibration from simulations. The method involves distorting the image with a small known shear, and calculating the response of a shear estimator to that applied shear. The method was shown to be accurate in moderate-sized simulations with galaxy images that had relatively high signal-to-noise ratios, and without significant selection effects. In this work we introduce a formalism to correct for both shear response and selection biases. We also observe that for images with relatively low signal-to-noise ratios, the correlated noise that arises during the metacalibration process results in significant bias, for which we develop a simple empirical correction. To test this formalism, we created large image simulations based on both parametric models and real galaxy images, including tests with realistic point-spread functions. We varied the point-spread function ellipticity at the five-percent level. In each simulation we applied a small few-percent shear to the galaxy images. We introduced additional challenges that arise in real data, such as detection thresholds, stellar contamination, and missing data. We applied cuts on the measured galaxy properties to induce significant selection effects. Using our formalism, we recovered the input shear with an accuracy better than a part in a thousand in all cases.

Two biased estimation techniques in linear regression: Application to aircraft

Science.gov (United States)

Klein, Vladislav

1988-01-01

Several ways for detection and assessment of collinearity in measured data are discussed. Because data collinearity usually results in poor least squares estimates, two estimation techniques which can limit a damaging effect of collinearity are presented. These two techniques, the principal components regression and mixed estimation, belong to a class of biased estimation techniques. Detection and assessment of data collinearity and the two biased estimation techniques are demonstrated in two examples using flight test data from longitudinal maneuvers of an experimental aircraft. The eigensystem analysis and parameter variance decomposition appeared to be a promising tool for collinearity evaluation. The biased estimators had far better accuracy than the results from the ordinary least squares technique.

A new energy transfer model for turbulent free shear flow

Science.gov (United States)

Liou, William W.-W.

1992-01-01

A new model for the energy transfer mechanism in the large-scale turbulent kinetic energy equation is proposed. An estimate of the characteristic length scale of the energy containing large structures is obtained from the wavelength associated with the structures predicted by a weakly nonlinear analysis for turbulent free shear flows. With the inclusion of the proposed energy transfer model, the weakly nonlinear wave models for the turbulent large-scale structures are self-contained and are likely to be independent flow geometries. The model is tested against a plane mixing layer. Reasonably good agreement is achieved. Finally, it is shown by using the Liapunov function method, the balance between the production and the drainage of the kinetic energy of the turbulent large-scale structures is asymptotically stable as their amplitude saturates. The saturation of the wave amplitude provides an alternative indicator for flow self-similarity.

An equation satisfied by the tangent to a shear-free, geodesic, null congruence

International Nuclear Information System (INIS)

Hogan, P.A.; Dublin Inst. for Advanced Studies

1987-01-01

A tensorial equation satisfied by the tangent to a shear-free geodesic, null congruence is presented. If the congruence is neither twist-free nor expansion-free then the equation defines a second, unique, null direction previously obtained, using the spinor formalism, by Somers. Some further properties of the equation are discussed. (orig.)

Bias in estimating food consumption of fish from stomach-content analysis

DEFF Research Database (Denmark)

Rindorf, Anna; Lewy, Peter

2004-01-01

This study presents an analysis of the bias introduced by using simplified methods to calculate food intake of fish from stomach contents. Three sources of bias were considered: (1) the effect of estimating consumption based on a limited number of stomach samples, (2) the effect of using average......, a serious positive bias was introduced by estimating food intake from the contents of pooled stomach samples. An expression is given that can be used to correct analytically for this bias. A new method, which takes into account the distribution and evacuation of individual prey types as well as the effect...... of other food in the stomach on evacuation, is suggested for estimating the intake of separate prey types. Simplifying the estimation by ignoring these factors biased estimates of consumption of individual prey types by up to 150% in a data example....

Estimation of bias shifts in a steam-generator water-level controller

International Nuclear Information System (INIS)

Tylee, J.L.

1983-01-01

A method for detecting and estimating the value of sudden bias shifts in a U-tube steam-generator water-level controller is described and evaluated. Generalized likelihood ratios (GLR) are used to perform both the bias detection and bias estimation. Simulation results using a seventh-order, linear, discrete steam-generator model demonstrate the capabilities of the GLR detection/estimation approach

Estimates of bias and uncertainty in recorded external dose

International Nuclear Information System (INIS)

Fix, J.J.; Gilbert, E.S.; Baumgartner, W.V.

1994-10-01

A study is underway to develop an approach to quantify bias and uncertainty in recorded dose estimates for workers at the Hanford Site based on personnel dosimeter results. This paper focuses on selected experimental studies conducted to better define response characteristics of Hanford dosimeters. The study is more extensive than the experimental studies presented in this paper and includes detailed consideration and evaluation of other sources of bias and uncertainty. Hanford worker dose estimates are used in epidemiologic studies of nuclear workers. A major objective of these studies is to provide a direct assessment of the carcinogenic risk of exposure to ionizing radiation at low doses and dose rates. Considerations of bias and uncertainty in the recorded dose estimates are important in the conduct of this work. The method developed for use with Hanford workers can be considered an elaboration of the approach used to quantify bias and uncertainty in estimated doses for personnel exposed to radiation as a result of atmospheric testing of nuclear weapons between 1945 and 1962. This approach was first developed by a National Research Council (NRC) committee examining uncertainty in recorded film badge doses during atmospheric tests (NRC 1989). It involved quantifying both bias and uncertainty from three sources (i.e., laboratory, radiological, and environmental) and then combining them to obtain an overall assessment. Sources of uncertainty have been evaluated for each of three specific Hanford dosimetry systems (i.e., the Hanford two-element film dosimeter, 1944-1956; the Hanford multi-element film dosimeter, 1957-1971; and the Hanford multi-element TLD, 1972-1993) used to estimate personnel dose throughout the history of Hanford operations. Laboratory, radiological, and environmental sources of bias and uncertainty have been estimated based on historical documentation and, for angular response, on selected laboratory measurements

Estimation and correction of visibility bias in aerial surveys of wintering ducks

Science.gov (United States)

Pearse, A.T.; Gerard, P.D.; Dinsmore, S.J.; Kaminski, R.M.; Reinecke, K.J.

2008-01-01

Incomplete detection of all individuals leading to negative bias in abundance estimates is a pervasive source of error in aerial surveys of wildlife, and correcting that bias is a critical step in improving surveys. We conducted experiments using duck decoys as surrogates for live ducks to estimate bias associated with surveys of wintering ducks in Mississippi, USA. We found detection of decoy groups was related to wetland cover type (open vs. forested), group size (1?100 decoys), and interaction of these variables. Observers who detected decoy groups reported counts that averaged 78% of the decoys actually present, and this counting bias was not influenced by either covariate cited above. We integrated this sightability model into estimation procedures for our sample surveys with weight adjustments derived from probabilities of group detection (estimated by logistic regression) and count bias. To estimate variances of abundance estimates, we used bootstrap resampling of transects included in aerial surveys and data from the bias-correction experiment. When we implemented bias correction procedures on data from a field survey conducted in January 2004, we found bias-corrected estimates of abundance increased 36?42%, and associated standard errors increased 38?55%, depending on species or group estimated. We deemed our method successful for integrating correction of visibility bias in an existing sample survey design for wintering ducks in Mississippi, and we believe this procedure could be implemented in a variety of sampling problems for other locations and species.

Post-mortem virtual estimation of free abdominal blood volume

International Nuclear Information System (INIS)

Ampanozi, Garyfalia; Hatch, Gary M.; Ruder, Thomas D.; Flach, Patricia M.; Germerott, Tanja; Thali, Michael J.; Ebert, Lars C.

2012-01-01

Purpose: The purpose of this retrospective study was to examine the reliability of virtually estimated abdominal blood volume using segmentation from postmortem computed tomography (PMCT) data. Materials and methods: Twenty-one cases with free abdominal blood were investigated by PMCT and autopsy. The volume of the blood was estimated using a manual segmentation technique (Amira, Visage Imaging, Germany) and the results were compared to autopsy data. Six of 21 cases had undergone additional post-mortem computed tomographic angiography (PMCTA). Results: The virtually estimated abdominal blood volumes did not differ significantly from those measured at autopsy. Additional PMCTA did not bias data significantly. Conclusion: Virtual estimation of abdominal blood volume is a reliable technique. The virtual blood volume estimation is a useful tool to deliver additional information in cases where autopsy is not performed or in cases where a postmortem angiography is performed

Investigation of particle-laden turbulent flow in free shear turbulent combustion

International Nuclear Information System (INIS)

Buckingham, A.C.; Siekhaus, W.J.; Ellzey, J.; Daily, J.W.

1983-01-01

Explicit numerical mixed phase simulations are described which couple random gasdynamic motions to inertiallly interactive gas borne particles. Theses simulations are numerical experiments intended to provide data for investigating the interaction between a developing turbulent free shear layer and gas borne solid particles it entrains. The simulations predict most probable distributions of dispersed phase trajectories, standard deviations, and gas phase mixing dynamics which include the concomitant back-influences of the particle phase on the carrier gas flow. Data for refinement of the computational scheme and physical verification are provided by experiment. The experimental evidence is developed in a splitter plate divided, two-channel free shear mixing combustion tube. A variety of particle concentrations and particle size distributions are admitted into non-combusting or combusting flows with selected heat release levels. The computations, in turn, provide guidance on design and selection of new experiments

Network Structure and Biased Variance Estimation in Respondent Driven Sampling.

Science.gov (United States)

Verdery, Ashton M; Mouw, Ted; Bauldry, Shawn; Mucha, Peter J

2015-01-01

This paper explores bias in the estimation of sampling variance in Respondent Driven Sampling (RDS). Prior methodological work on RDS has focused on its problematic assumptions and the biases and inefficiencies of its estimators of the population mean. Nonetheless, researchers have given only slight attention to the topic of estimating sampling variance in RDS, despite the importance of variance estimation for the construction of confidence intervals and hypothesis tests. In this paper, we show that the estimators of RDS sampling variance rely on a critical assumption that the network is First Order Markov (FOM) with respect to the dependent variable of interest. We demonstrate, through intuitive examples, mathematical generalizations, and computational experiments that current RDS variance estimators will always underestimate the population sampling variance of RDS in empirical networks that do not conform to the FOM assumption. Analysis of 215 observed university and school networks from Facebook and Add Health indicates that the FOM assumption is violated in every empirical network we analyze, and that these violations lead to substantially biased RDS estimators of sampling variance. We propose and test two alternative variance estimators that show some promise for reducing biases, but which also illustrate the limits of estimating sampling variance with only partial information on the underlying population social network.

Balancing anisotropic curvature with gauge fields in a class of shear-free cosmological models

Science.gov (United States)

Thorsrud, Mikjel

2018-05-01

We present a complete list of general relativistic shear-free solutions in a class of anisotropic, spatially homogeneous and orthogonal cosmological models containing a collection of n independent p-form gauge fields, where p\\in\\{0, 1, 2, 3\\} , in addition to standard ΛCDM matter fields modelled as perfect fluids. Here a (collection of) gauge field(s) balances anisotropic spatial curvature on the right-hand side of the shear propagation equation. The result is a class of solutions dynamically equivalent to standard FLRW cosmologies, with an effective curvature constant Keff that depends both on spatial curvature and the energy density of the gauge field(s). In the case of a single gauge field (n  =  1) we show that the only spacetimes that admit such solutions are the LRS Bianchi type III, Bianchi type VI0 and Kantowski–Sachs metric, which are dynamically equivalent to open (Keff0 ) FLRW models, respectively. With a collection of gauge fields (n  >  1) also Bianchi type II admits a shear-free solution (Keff>0 ). We identify the LRS Bianchi type III solution to be the unique shear-free solution with a gauge field Hamiltonian bounded from below in the entire class of models.

Estimates of Shear Stress and Measurements of Water Levels in the Lower Fox River near Green Bay, Wisconsin

Science.gov (United States)

Westenbroek, Stephen M.

2006-01-01

Turbulent shear stress in the boundary layer of a natural river system largely controls the deposition and resuspension of sediment, as well as the longevity and effectiveness of granular-material caps used to cover and isolate contaminated sediments. This report documents measurements and calculations made in order to estimate shear stress and shear velocity on the Lower Fox River, Wisconsin. Velocity profiles were generated using an acoustic Doppler current profiler (ADCP) mounted on a moored vessel. This method of data collection yielded 158 velocity profiles on the Lower Fox River between June 2003 and November 2004. Of these profiles, 109 were classified as valid and were used to estimate the bottom shear stress and velocity using log-profile and turbulent kinetic energy methods. Estimated shear stress ranged from 0.09 to 10.8 dynes per centimeter squared. Estimated coefficients of friction ranged from 0.001 to 0.025. This report describes both the field and data-analysis methods used to estimate shear-stress parameters for the Lower Fox River. Summaries of the estimated values for bottom shear stress, shear velocity, and coefficient of friction are presented. Confidence intervals about the shear-stress estimates are provided.

Estimating Climatological Bias Errors for the Global Precipitation Climatology Project (GPCP)

Science.gov (United States)

Adler, Robert; Gu, Guojun; Huffman, George

2012-01-01

A procedure is described to estimate bias errors for mean precipitation by using multiple estimates from different algorithms, satellite sources, and merged products. The Global Precipitation Climatology Project (GPCP) monthly product is used as a base precipitation estimate, with other input products included when they are within +/- 50% of the GPCP estimates on a zonal-mean basis (ocean and land separately). The standard deviation s of the included products is then taken to be the estimated systematic, or bias, error. The results allow one to examine monthly climatologies and the annual climatology, producing maps of estimated bias errors, zonal-mean errors, and estimated errors over large areas such as ocean and land for both the tropics and the globe. For ocean areas, where there is the largest question as to absolute magnitude of precipitation, the analysis shows spatial variations in the estimated bias errors, indicating areas where one should have more or less confidence in the mean precipitation estimates. In the tropics, relative bias error estimates (s/m, where m is the mean precipitation) over the eastern Pacific Ocean are as large as 20%, as compared with 10%-15% in the western Pacific part of the ITCZ. An examination of latitudinal differences over ocean clearly shows an increase in estimated bias error at higher latitudes, reaching up to 50%. Over land, the error estimates also locate regions of potential problems in the tropics and larger cold-season errors at high latitudes that are due to snow. An empirical technique to area average the gridded errors (s) is described that allows one to make error estimates for arbitrary areas and for the tropics and the globe (land and ocean separately, and combined). Over the tropics this calculation leads to a relative error estimate for tropical land and ocean combined of 7%, which is considered to be an upper bound because of the lack of sign-of-the-error canceling when integrating over different areas with a

Bias-Corrected Estimation of Noncentrality Parameters of Covariance Structure Models

Science.gov (United States)

Raykov, Tenko

2005-01-01

A bias-corrected estimator of noncentrality parameters of covariance structure models is discussed. The approach represents an application of the bootstrap methodology for purposes of bias correction, and utilizes the relation between average of resample conventional noncentrality parameter estimates and their sample counterpart. The…

Bias-corrected estimation of stable tail dependence function

DEFF Research Database (Denmark)

Beirlant, Jan; Escobar-Bach, Mikael; Goegebeur, Yuri

2016-01-01

We consider the estimation of the stable tail dependence function. We propose a bias-corrected estimator and we establish its asymptotic behaviour under suitable assumptions. The finite sample performance of the proposed estimator is evaluated by means of an extensive simulation study where...

Shear Elasticity and Shear Viscosity Imaging in Soft Tissue

Science.gov (United States)

Yang, Yiqun

In this thesis, a new approach is introduced that provides estimates of shear elasticity and shear viscosity using time-domain measurements of shear waves in viscoelastic media. Simulations of shear wave particle displacements induced by an acoustic radiation force are accelerated significantly by a GPU. The acoustic radiation force is first calculated using the fast near field method (FNM) and the angular spectrum approach (ASA). The shear waves induced by the acoustic radiation force are then simulated in elastic and viscoelastic media using Green's functions. A parallel algorithm is developed to perform these calculations on a GPU, where the shear wave particle displacements at different observation points are calculated in parallel. The resulting speed increase enables rapid evaluation of shear waves at discrete points, in 2D planes, and for push beams with different spatial samplings and for different values of the f-number (f/#). The results of these simulations show that push beams with smaller f/# require a higher spatial sampling rate. The significant amount of acceleration achieved by this approach suggests that shear wave simulations with the Green's function approach are ideally suited for high-performance GPUs. Shear wave elasticity imaging determines the mechanical parameters of soft tissue by analyzing measured shear waves induced by an acoustic radiation force. To estimate the shear elasticity value, the widely used time-of-flight method calculates the correlation between shear wave particle velocities at adjacent lateral observation points. Although this method provides accurate estimates of the shear elasticity in purely elastic media, our experience suggests that the time-of-flight (TOF) method consistently overestimates the shear elasticity values in viscoelastic media because the combined effects of diffraction, attenuation, and dispersion are not considered. To address this problem, we have developed an approach that directly accounts for all

Counteracting estimation bias and social influence to improve the wisdom of crowds.

Science.gov (United States)

Kao, Albert B; Berdahl, Andrew M; Hartnett, Andrew T; Lutz, Matthew J; Bak-Coleman, Joseph B; Ioannou, Christos C; Giam, Xingli; Couzin, Iain D

2018-04-01

Aggregating multiple non-expert opinions into a collective estimate can improve accuracy across many contexts. However, two sources of error can diminish collective wisdom: individual estimation biases and information sharing between individuals. Here, we measure individual biases and social influence rules in multiple experiments involving hundreds of individuals performing a classic numerosity estimation task. We first investigate how existing aggregation methods, such as calculating the arithmetic mean or the median, are influenced by these sources of error. We show that the mean tends to overestimate, and the median underestimate, the true value for a wide range of numerosities. Quantifying estimation bias, and mapping individual bias to collective bias, allows us to develop and validate three new aggregation measures that effectively counter sources of collective estimation error. In addition, we present results from a further experiment that quantifies the social influence rules that individuals employ when incorporating personal estimates with social information. We show that the corrected mean is remarkably robust to social influence, retaining high accuracy in the presence or absence of social influence, across numerosities and across different methods for averaging social information. Using knowledge of estimation biases and social influence rules may therefore be an inexpensive and general strategy to improve the wisdom of crowds. © 2018 The Author(s).

Noise Induces Biased Estimation of the Correction Gain.

Directory of Open Access Journals (Sweden)

Jooeun Ahn

Full Text Available The detection of an error in the motor output and the correction in the next movement are critical components of any form of motor learning. Accordingly, a variety of iterative learning models have assumed that a fraction of the error is adjusted in the next trial. This critical fraction, the correction gain, learning rate, or feedback gain, has been frequently estimated via least-square regression of the obtained data set. Such data contain not only the inevitable noise from motor execution, but also noise from measurement. It is generally assumed that this noise averages out with large data sets and does not affect the parameter estimation. This study demonstrates that this is not the case and that in the presence of noise the conventional estimate of the correction gain has a significant bias, even with the simplest model. Furthermore, this bias does not decrease with increasing length of the data set. This study reveals this limitation of current system identification methods and proposes a new method that overcomes this limitation. We derive an analytical form of the bias from a simple regression method (Yule-Walker and develop an improved identification method. This bias is discussed as one of other examples for how the dynamics of noise can introduce significant distortions in data analysis.

Bespoke Bias for Obtaining Free Energy Differences within Variationally Enhanced Sampling.

Science.gov (United States)

McCarty, James; Valsson, Omar; Parrinello, Michele

2016-05-10

Obtaining efficient sampling of multiple metastable states through molecular dynamics and hence determining free energy differences is central for understanding many important phenomena. Here we present a new biasing strategy, which employs the recent variationally enhanced sampling approach (Valsson and Parrinello Phys. Rev. Lett. 2014, 113, 090601). The bias is constructed from an intuitive model of the local free energy surface describing fluctuations around metastable minima and depends on only a few parameters which are determined variationally such that efficient sampling between states is obtained. The bias constructed in this manner largely reduces the need of finding a set of collective variables that completely spans the conformational space of interest, as they only need to be a locally valid descriptor of the system about its local minimum. We introduce the method and demonstrate its power on two representative examples.

Basic MR sequence parameters systematically bias automated brain volume estimation

International Nuclear Information System (INIS)

Haller, Sven; Falkovskiy, Pavel; Roche, Alexis; Marechal, Benedicte; Meuli, Reto; Thiran, Jean-Philippe; Krueger, Gunnar; Lovblad, Karl-Olof; Kober, Tobias

2016-01-01

Automated brain MRI morphometry, including hippocampal volumetry for Alzheimer disease, is increasingly recognized as a biomarker. Consequently, a rapidly increasing number of software tools have become available. We tested whether modifications of simple MR protocol parameters typically used in clinical routine systematically bias automated brain MRI segmentation results. The study was approved by the local ethical committee and included 20 consecutive patients (13 females, mean age 75.8 ± 13.8 years) undergoing clinical brain MRI at 1.5 T for workup of cognitive decline. We compared three 3D T1 magnetization prepared rapid gradient echo (MPRAGE) sequences with the following parameter settings: ADNI-2 1.2 mm iso-voxel, no image filtering, LOCAL- 1.0 mm iso-voxel no image filtering, LOCAL+ 1.0 mm iso-voxel with image edge enhancement. Brain segmentation was performed by two different and established analysis tools, FreeSurfer and MorphoBox, using standard parameters. Spatial resolution (1.0 versus 1.2 mm iso-voxel) and modification in contrast resulted in relative estimated volume difference of up to 4.28 % (p < 0.001) in cortical gray matter and 4.16 % (p < 0.01) in hippocampus. Image data filtering resulted in estimated volume difference of up to 5.48 % (p < 0.05) in cortical gray matter. A simple change of MR parameters, notably spatial resolution, contrast, and filtering, may systematically bias results of automated brain MRI morphometry of up to 4-5 %. This is in the same range as early disease-related brain volume alterations, for example, in Alzheimer disease. Automated brain segmentation software packages should therefore require strict MR parameter selection or include compensatory algorithms to avoid MR parameter-related bias of brain morphometry results. (orig.)

Basic MR sequence parameters systematically bias automated brain volume estimation

Energy Technology Data Exchange (ETDEWEB)

Haller, Sven [University of Geneva, Faculty of Medicine, Geneva (Switzerland); Affidea Centre de Diagnostique Radiologique de Carouge CDRC, Geneva (Switzerland); Falkovskiy, Pavel; Roche, Alexis; Marechal, Benedicte [Siemens Healthcare HC CEMEA SUI DI BM PI, Advanced Clinical Imaging Technology, Lausanne (Switzerland); University Hospital (CHUV), Department of Radiology, Lausanne (Switzerland); Meuli, Reto [University Hospital (CHUV), Department of Radiology, Lausanne (Switzerland); Thiran, Jean-Philippe [LTS5, Ecole Polytechnique Federale de Lausanne, Lausanne (Switzerland); Krueger, Gunnar [Siemens Medical Solutions USA, Inc., Boston, MA (United States); Lovblad, Karl-Olof [University of Geneva, Faculty of Medicine, Geneva (Switzerland); University Hospitals of Geneva, Geneva (Switzerland); Kober, Tobias [Siemens Healthcare HC CEMEA SUI DI BM PI, Advanced Clinical Imaging Technology, Lausanne (Switzerland); LTS5, Ecole Polytechnique Federale de Lausanne, Lausanne (Switzerland)

2016-11-15

Automated brain MRI morphometry, including hippocampal volumetry for Alzheimer disease, is increasingly recognized as a biomarker. Consequently, a rapidly increasing number of software tools have become available. We tested whether modifications of simple MR protocol parameters typically used in clinical routine systematically bias automated brain MRI segmentation results. The study was approved by the local ethical committee and included 20 consecutive patients (13 females, mean age 75.8 ± 13.8 years) undergoing clinical brain MRI at 1.5 T for workup of cognitive decline. We compared three 3D T1 magnetization prepared rapid gradient echo (MPRAGE) sequences with the following parameter settings: ADNI-2 1.2 mm iso-voxel, no image filtering, LOCAL- 1.0 mm iso-voxel no image filtering, LOCAL+ 1.0 mm iso-voxel with image edge enhancement. Brain segmentation was performed by two different and established analysis tools, FreeSurfer and MorphoBox, using standard parameters. Spatial resolution (1.0 versus 1.2 mm iso-voxel) and modification in contrast resulted in relative estimated volume difference of up to 4.28 % (p < 0.001) in cortical gray matter and 4.16 % (p < 0.01) in hippocampus. Image data filtering resulted in estimated volume difference of up to 5.48 % (p < 0.05) in cortical gray matter. A simple change of MR parameters, notably spatial resolution, contrast, and filtering, may systematically bias results of automated brain MRI morphometry of up to 4-5 %. This is in the same range as early disease-related brain volume alterations, for example, in Alzheimer disease. Automated brain segmentation software packages should therefore require strict MR parameter selection or include compensatory algorithms to avoid MR parameter-related bias of brain morphometry results. (orig.)

Inflationary perturbations in anisotropic, shear-free universes

International Nuclear Information System (INIS)

Pereira, Thiago S.; Carneiro, Saulo; Marugan, Guillermo A. Mena

2012-01-01

In this work, the linear and gauge-invariant theory of cosmological perturbations in a class of anisotropic and shear-free spacetimes is developed. After constructing an explicit set of complete eigenfunctions in terms of which perturbations can be expanded, we identify the effective degrees of freedom during a generic slow-roll inflationary phase. These correspond to the anisotropic equivalent of the standard Mukhanov-Sasaki variables. The associated equations of motion present a remarkable resemblance to those found in perturbed Friedmann-Robertson-Walker spacetimes with curvature, apart from the spectrum of the Laplacian, which exhibits the characteristic frequencies of the underlying geometry. In particular, it is found that the perturbations cannot develop arbitrarily large super-Hubble modes

Individuals With OCD Lack Unrealistic Optimism Bias in Threat Estimation.

Science.gov (United States)

Zetsche, Ulrike; Rief, Winfried; Exner, Cornelia

2015-07-01

Overestimating the occurrence of threatening events has been highlighted as a central cognitive factor in the maintenance of obsessive-compulsive disorder (OCD). The present study examined the different facets of this cognitive bias, its underlying mechanisms, and its specificity to OCD. For this purpose, threat estimation, probabilistic classification learning (PCL) and psychopathological measures were assessed in 23 participants with OCD, 30 participants with social phobia, and 31 healthy controls. Whereas healthy participants showed an optimistic expectation bias regarding positive and negative future events, OCD participants lacked such a bias. This lack of an optimistic expectation bias was not specific to OCD. Compared to healthy controls, OCD participants overestimated their personal risk for experiencing negative events, but did not differ from controls in their risk estimation regarding other people. Finally, OCD participants' biases in the prediction of checking-related events were associated with their impairments in learning probabilistic cue-outcome associations in a disorder-relevant context. In sum, the present results add to a growing body of research demonstrating that cognitive biases in OCD are context-dependent. Copyright © 2015. Published by Elsevier Ltd.

The Effect of Amplifier Bias Drift on Differential Magnitude Estimation in Multiple-Star Systems

Science.gov (United States)

Tyler, David W.; Muralimanohar, Hariharan; Borelli, Kathy J.

2007-02-01

We show how the temporal drift of CCD amplifier bias can cause significant relative magnitude estimation error in speckle interferometric observations of multiple-star systems. When amplifier bias varies over time, the estimation error arises if the time between acquisition of dark-frame calibration data and science data is long relative to the timescale over which the bias changes. Using analysis, we show that while detector-temperature drift over time causes a variation in accumulated dark current and a residual bias in calibrated imagery, only amplifier bias variations cause a residual bias in the estimated energy spectrum. We then use telescope data taken specifically to investigate this phenomenon to show that for the detector used, temporal bias drift can cause residual energy spectrum bias as large or larger than the mean value of the noise energy spectrum. Finally, we use a computer simulation to demonstrate the effect of residual bias on differential magnitude estimation. A supplemental calibration technique is described in the appendices.

Compressibility effects in the shear layer over a rectangular cavity

Energy Technology Data Exchange (ETDEWEB)

Beresh, Steven J.; Wagner, Justin; Casper, Katya Marie

2016-10-26

we studied the influence of compressibility on the shear layer over a rectangular cavity of variable width in a free stream Mach number range of 0.6–2.5 using particle image velocimetry data in the streamwise centre plane. As the Mach number increases, the vertical component of the turbulence intensity diminishes modestly in the widest cavity, but the two narrower cavities show a more substantial drop in all three components as well as the turbulent shear stress. Furthermore, this contrasts with canonical free shear layers, which show significant reductions in only the vertical component and the turbulent shear stress due to compressibility. The vorticity thickness of the cavity shear layer grows rapidly as it initially develops, then transitions to a slower growth rate once its instability saturates. When normalized by their estimated incompressible values, the growth rates prior to saturation display the classic compressibility effect of suppression as the convective Mach number rises, in excellent agreement with comparable free shear layer data. The specific trend of the reduction in growth rate due to compressibility is modified by the cavity width.

Ultrasound viscoelasticity assessment using an adaptive torsional shear wave propagation method

Energy Technology Data Exchange (ETDEWEB)

Ouared, Abderrahmane [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9, Canada and Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4 (Canada); Kazemirad, Siavash; Montagnon, Emmanuel [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9 (Canada); Cloutier, Guy, E-mail: guy.cloutier@umontreal.ca [Laboratory of Biorheology and Medical Ultrasonics, University of Montréal Hospital Research Center (CRCHUM), Montréal, Québec H2X 0A9 (Canada); Department of Radiology, Radio-Oncology and Nuclear Medicine, University of Montréal, Montréal, Québec H3T 1J4 (Canada); Institute of Biomedical Engineering, University of Montréal, Montréal, Québec H3T 1J4 (Canada)

2016-04-15

Purpose: Different approaches have been used in dynamic elastography to assess mechanical properties of biological tissues. Most techniques are based on a simple inversion based on the measurement of the shear wave speed to assess elasticity, whereas some recent strategies use more elaborated analytical or finite element method (FEM) models. In this study, a new method is proposed for the quantification of both shear storage and loss moduli of confined lesions, in the context of breast imaging, using adaptive torsional shear waves (ATSWs) generated remotely with radiation pressure. Methods: A FEM model was developed to solve the inverse wave propagation problem and obtain viscoelastic properties of interrogated media. The inverse problem was formulated and solved in the frequency domain and its robustness to noise and geometric constraints was evaluated. The proposed model was validated in vitro with two independent rheology methods on several homogeneous and heterogeneous breast tissue-mimicking phantoms over a broad range of frequencies (up to 400 Hz). Results: Viscoelastic properties matched benchmark rheology methods with discrepancies of 8%–38% for the shear modulus G′ and 9%–67% for the loss modulus G″. The robustness study indicated good estimations of storage and loss moduli (maximum mean errors of 19% on G′ and 32% on G″) for signal-to-noise ratios between 19.5 and 8.5 dB. Larger errors were noticed in the case of biases in lesion dimension and position. Conclusions: The ATSW method revealed that it is possible to estimate the viscoelasticity of biological tissues with torsional shear waves when small biases in lesion geometry exist.

Estimating Gravity Biases with Wavelets in Support of a 1-cm Accurate Geoid Model

Science.gov (United States)

Ahlgren, K.; Li, X.

2017-12-01

Systematic errors that reside in surface gravity datasets are one of the major hurdles in constructing a high-accuracy geoid model at high resolutions. The National Oceanic and Atmospheric Administration's (NOAA) National Geodetic Survey (NGS) has an extensive historical surface gravity dataset consisting of approximately 10 million gravity points that are known to have systematic biases at the mGal level (Saleh et al. 2013). As most relevant metadata is absent, estimating and removing these errors to be consistent with a global geopotential model and airborne data in the corresponding wavelength is quite a difficult endeavor. However, this is crucial to support a 1-cm accurate geoid model for the United States. With recently available independent gravity information from GRACE/GOCE and airborne gravity from the NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project, several different methods of bias estimation are investigated which utilize radial basis functions and wavelet decomposition. We estimate a surface gravity value by incorporating a satellite gravity model, airborne gravity data, and forward-modeled topography at wavelet levels according to each dataset's spatial wavelength. Considering the estimated gravity values over an entire gravity survey, an estimate of the bias and/or correction for the entire survey can be found and applied. In order to assess the accuracy of each bias estimation method, two techniques are used. First, each bias estimation method is used to predict the bias for two high-quality (unbiased and high accuracy) geoid slope validation surveys (GSVS) (Smith et al. 2013 & Wang et al. 2017). Since these surveys are unbiased, the various bias estimation methods should reflect that and provide an absolute accuracy metric for each of the bias estimation methods. Secondly, the corrected gravity datasets from each of the bias estimation methods are used to build a geoid model. The accuracy of each geoid model

estimation of shear strength parameters of lateritic soils using

African Journals Online (AJOL)

user

... a tool to estimate the. Nigerian Journal of Technology (NIJOTECH). Vol. ... modeling tools for the prediction of shear strength parameters for lateritic ... 2.2 Geotechnical Analysis of the Soils ... The back propagation learning algorithm is the most popular and ..... [10] Alsaleh, M. I., Numerical modeling for strain localization in ...

Change-in-ratio density estimator for feral pigs is less biased than closed mark-recapture estimates

Science.gov (United States)

Hanson, L.B.; Grand, J.B.; Mitchell, M.S.; Jolley, D.B.; Sparklin, B.D.; Ditchkoff, S.S.

2008-01-01

Closed-population capture-mark-recapture (CMR) methods can produce biased density estimates for species with low or heterogeneous detection probabilities. In an attempt to address such biases, we developed a density-estimation method based on the change in ratio (CIR) of survival between two populations where survival, calculated using an open-population CMR model, is known to differ. We used our method to estimate density for a feral pig (Sus scrofa) population on Fort Benning, Georgia, USA. To assess its validity, we compared it to an estimate of the minimum density of pigs known to be alive and two estimates based on closed-population CMR models. Comparison of the density estimates revealed that the CIR estimator produced a density estimate with low precision that was reasonable with respect to minimum known density. By contrast, density point estimates using the closed-population CMR models were less than the minimum known density, consistent with biases created by low and heterogeneous capture probabilities for species like feral pigs that may occur in low density or are difficult to capture. Our CIR density estimator may be useful for tracking broad-scale, long-term changes in species, such as large cats, for which closed CMR models are unlikely to work. ?? CSIRO 2008.

Estimation of time-delayed mutual information and bias for irregularly and sparsely sampled time-series

International Nuclear Information System (INIS)

Albers, D.J.; Hripcsak, George

2012-01-01

Highlights: ► Time-delayed mutual information for irregularly sampled time-series. ► Estimation bias for the time-delayed mutual information calculation. ► Fast, simple, PDF estimator independent, time-delayed mutual information bias estimate. ► Quantification of data-set-size limits of the time-delayed mutual calculation. - Abstract: A method to estimate the time-dependent correlation via an empirical bias estimate of the time-delayed mutual information for a time-series is proposed. In particular, the bias of the time-delayed mutual information is shown to often be equivalent to the mutual information between two distributions of points from the same system separated by infinite time. Thus intuitively, estimation of the bias is reduced to estimation of the mutual information between distributions of data points separated by large time intervals. The proposed bias estimation techniques are shown to work for Lorenz equations data and glucose time series data of three patients from the Columbia University Medical Center database.

Spectroscopic failures in photometric redshift calibration: cosmological biases and survey requirements

Energy Technology Data Exchange (ETDEWEB)

Cunha, Carlos E. [KIPAC, Menlo Park; Huterer, Dragan [Michigan U.; Lin, Huan [Fermilab; Busha, Michael T. [Zurich U.; Wechsler, Risa H. [SLAC

2014-10-11

We use N-body-spectro-photometric simulations to investigate the impact of incompleteness and incorrect redshifts in spectroscopic surveys to photometric redshift training and calibration and the resulting effects on cosmological parameter estimation from weak lensing shear-shear correlations. The photometry of the simulations is modeled after the upcoming Dark Energy Survey and the spectroscopy is based on a low/intermediate resolution spectrograph with wavelength coverage of 5500{\\AA} < {\\lambda} < 9500{\\AA}. The principal systematic errors that such a spectroscopic follow-up encounters are incompleteness (inability to obtain spectroscopic redshifts for certain galaxies) and wrong redshifts. Encouragingly, we find that a neural network-based approach can effectively describe the spectroscopic incompleteness in terms of the galaxies' colors, so that the spectroscopic selection can be applied to the photometric sample. Hence, we find that spectroscopic incompleteness yields no appreciable biases to cosmology, although the statistical constraints degrade somewhat because the photometric survey has to be culled to match the spectroscopic selection. Unfortunately, wrong redshifts have a more severe impact: the cosmological biases are intolerable if more than a percent of the spectroscopic redshifts are incorrect. Moreover, we find that incorrect redshifts can also substantially degrade the accuracy of training set based photo-z estimators. The main problem is the difficulty of obtaining redshifts, either spectroscopically or photometrically, for objects at z > 1.3. We discuss several approaches for reducing the cosmological biases, in particular finding that photo-z error estimators can reduce biases appreciably.

Improving multisensor estimation of heavy-to-extreme precipitation via conditional bias-penalized optimal estimation

Science.gov (United States)

Kim, Beomgeun; Seo, Dong-Jun; Noh, Seong Jin; Prat, Olivier P.; Nelson, Brian R.

2018-01-01

A new technique for merging radar precipitation estimates and rain gauge data is developed and evaluated to improve multisensor quantitative precipitation estimation (QPE), in particular, of heavy-to-extreme precipitation. Unlike the conventional cokriging methods which are susceptible to conditional bias (CB), the proposed technique, referred to herein as conditional bias-penalized cokriging (CBPCK), explicitly minimizes Type-II CB for improved quantitative estimation of heavy-to-extreme precipitation. CBPCK is a bivariate version of extended conditional bias-penalized kriging (ECBPK) developed for gauge-only analysis. To evaluate CBPCK, cross validation and visual examination are carried out using multi-year hourly radar and gauge data in the North Central Texas region in which CBPCK is compared with the variant of the ordinary cokriging (OCK) algorithm used operationally in the National Weather Service Multisensor Precipitation Estimator. The results show that CBPCK significantly reduces Type-II CB for estimation of heavy-to-extreme precipitation, and that the margin of improvement over OCK is larger in areas of higher fractional coverage (FC) of precipitation. When FC > 0.9 and hourly gauge precipitation is > 60 mm, the reduction in root mean squared error (RMSE) by CBPCK over radar-only (RO) is about 12 mm while the reduction in RMSE by OCK over RO is about 7 mm. CBPCK may be used in real-time analysis or in reanalysis of multisensor precipitation for which accurate estimation of heavy-to-extreme precipitation is of particular importance.

Large biases in regression-based constituent flux estimates: causes and diagnostic tools

Science.gov (United States)

Hirsch, Robert M.

2014-01-01

It has been documented in the literature that, in some cases, widely used regression-based models can produce severely biased estimates of long-term mean river fluxes of various constituents. These models, estimated using sample values of concentration, discharge, and date, are used to compute estimated fluxes for a multiyear period at a daily time step. This study compares results of the LOADEST seven-parameter model, LOADEST five-parameter model, and the Weighted Regressions on Time, Discharge, and Season (WRTDS) model using subsampling of six very large datasets to better understand this bias problem. This analysis considers sample datasets for dissolved nitrate and total phosphorus. The results show that LOADEST-7 and LOADEST-5, although they often produce very nearly unbiased results, can produce highly biased results. This study identifies three conditions that can give rise to these severe biases: (1) lack of fit of the log of concentration vs. log discharge relationship, (2) substantial differences in the shape of this relationship across seasons, and (3) severely heteroscedastic residuals. The WRTDS model is more resistant to the bias problem than the LOADEST models but is not immune to them. Understanding the causes of the bias problem is crucial to selecting an appropriate method for flux computations. Diagnostic tools for identifying the potential for bias problems are introduced, and strategies for resolving bias problems are described.

Local linear density estimation for filtered survival data, with bias correction

DEFF Research Database (Denmark)

Nielsen, Jens Perch; Tanggaard, Carsten; Jones, M.C.

2009-01-01

it comes to exposure robustness, and a simple alternative weighting is to be preferred. Indeed, this weighting has, effectively, to be well chosen in a 'pilot' estimator of the survival function as well as in the main estimator itself. We also investigate multiplicative and additive bias-correction methods...... within our framework. The multiplicative bias-correction method proves to be the best in a simulation study comparing the performance of the considered estimators. An example concerning old-age mortality demonstrates the importance of the improvements provided....

Local Linear Density Estimation for Filtered Survival Data with Bias Correction

DEFF Research Database (Denmark)

Tanggaard, Carsten; Nielsen, Jens Perch; Jones, M.C.

it comes to exposure robustness, and a simple alternative weighting is to be preferred. Indeed, this weighting has, effectively, to be well chosen in a ‘pilot' estimator of the survival function as well as in the main estimator itself. We also investigate multiplicative and additive bias correction methods...... within our framework. The multiplicative bias correction method proves to be best in a simulation study comparing the performance of the considered estimators. An example concerning old age mortality demonstrates the importance of the improvements provided....

A Method for Estimating BeiDou Inter-frequency Satellite Clock Bias

Directory of Open Access Journals (Sweden)

LI Haojun

2016-02-01

Full Text Available A new method for estimating the BeiDou inter-frequency satellite clock bias is proposed, considering the shortage of the current methods. The constant and variable parts of the inter-frequency satellite clock bias are considered in the new method. The data from 10 observation stations are processed to validate the new method. The characterizations of the BeiDou inter-frequency satellite clock bias are also analyzed using the computed results. The results of the BeiDou inter-frequency satellite clock bias indicate that it is stable in the short term. The estimated BeiDou inter-frequency satellite clock bias results are molded. The model results show that the 10 parameters of model for each satellite can express the BeiDou inter-frequency satellite clock bias well and the accuracy reaches cm level. When the model parameters of the first day are used to compute the BeiDou inter-frequency satellite clock bias of the second day, the accuracy also reaches cm level. Based on the stability and modeling, a strategy for the BeiDou satellite clock service is presented to provide the reference of our BeiDou.

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation.

Science.gov (United States)

Tie, Junbo; Cao, Juliang; Chang, Lubing; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-03-16

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method.

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation

Science.gov (United States)

Cao, Juliang; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-01-01

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method. PMID:29547552

Attitude and gyro bias estimation by the rotation of an inertial measurement unit

International Nuclear Information System (INIS)

Wu, Zheming; Sun, Zhenguo; Zhang, Wenzeng; Chen, Qiang

2015-01-01

In navigation applications, the presence of an unknown bias in the measurement of rate gyros is a key performance-limiting factor. In order to estimate the gyro bias and improve the accuracy of attitude measurement, we proposed a new method which uses the rotation of an inertial measurement unit, which is independent from rigid body motion. By actively changing the orientation of the inertial measurement unit (IMU), the proposed method generates sufficient relations between the gyro bias and tilt angle (roll and pitch) error via ridge body dynamics, and the gyro bias, including the bias that causes the heading error, can be estimated and compensated. The rotation inertial measurement unit method makes the gravity vector measured from the IMU continuously change in a body-fixed frame. By theoretically analyzing the mathematic model, the convergence of the attitude and gyro bias to the true values is proven. The proposed method provides a good attitude estimation using only measurements from an IMU, when other sensors such as magnetometers and GPS are unreliable. The performance of the proposed method is illustrated under realistic robotic motions and the results demonstrate an improvement in the accuracy of the attitude estimation. (paper)

HIERARCHICAL PROBABILISTIC INFERENCE OF COSMIC SHEAR

International Nuclear Information System (INIS)

Schneider, Michael D.; Dawson, William A.; Hogg, David W.; Marshall, Philip J.; Bard, Deborah J.; Meyers, Joshua; Lang, Dustin

2015-01-01

Point estimators for the shearing of galaxy images induced by gravitational lensing involve a complex inverse problem in the presence of noise, pixelization, and model uncertainties. We present a probabilistic forward modeling approach to gravitational lensing inference that has the potential to mitigate the biased inferences in most common point estimators and is practical for upcoming lensing surveys. The first part of our statistical framework requires specification of a likelihood function for the pixel data in an imaging survey given parameterized models for the galaxies in the images. We derive the lensing shear posterior by marginalizing over all intrinsic galaxy properties that contribute to the pixel data (i.e., not limited to galaxy ellipticities) and learn the distributions for the intrinsic galaxy properties via hierarchical inference with a suitably flexible conditional probabilitiy distribution specification. We use importance sampling to separate the modeling of small imaging areas from the global shear inference, thereby rendering our algorithm computationally tractable for large surveys. With simple numerical examples we demonstrate the improvements in accuracy from our importance sampling approach, as well as the significance of the conditional distribution specification for the intrinsic galaxy properties when the data are generated from an unknown number of distinct galaxy populations with different morphological characteristics

Operator Bias in the Estimation of Arc Efficiency in Gas Tungsten Arc Welding

Directory of Open Access Journals (Sweden)

Fredrik Sikström

2015-03-01

Full Text Available In this paper the operator bias in the measurement process of arc efficiency in stationary direct current electrode negative gas tungsten arc welding is discussed. An experimental study involving 15 operators (enough to reach statistical significance has been carried out with the purpose to estimate the arc efficiency from a specific procedure for calorimetric experiments. The measurement procedure consists of three manual operations which introduces operator bias in the measurement process. An additional relevant experiment highlights the consequences of estimating the arc voltage by measuring the potential between the terminals of the welding power source instead of measuring the potential between the electrode contact tube and the workpiece. The result of the study is a statistical evaluation of the operator bias influence on the estimate, showing that operator bias is negligible in the estimate considered here. On the contrary the consequences of neglecting welding leads voltage drop results in a significant under estimation of the arc efficiency.

Bias Errors due to Leakage Effects When Estimating Frequency Response Functions

Directory of Open Access Journals (Sweden)

Andreas Josefsson

2012-01-01

Full Text Available Frequency response functions are often utilized to characterize a system's dynamic response. For a wide range of engineering applications, it is desirable to determine frequency response functions for a system under stochastic excitation. In practice, the measurement data is contaminated by noise and some form of averaging is needed in order to obtain a consistent estimator. With Welch's method, the discrete Fourier transform is used and the data is segmented into smaller blocks so that averaging can be performed when estimating the spectrum. However, this segmentation introduces leakage effects. As a result, the estimated frequency response function suffers from both systematic (bias and random errors due to leakage. In this paper the bias error in the H1 and H2-estimate is studied and a new method is proposed to derive an approximate expression for the relative bias error at the resonance frequency with different window functions. The method is based on using a sum of real exponentials to describe the window's deterministic autocorrelation function. Simple expressions are derived for a rectangular window and a Hanning window. The theoretical expressions are verified with numerical simulations and a very good agreement is found between the results from the proposed bias expressions and the empirical results.

Bias correction for the least squares estimator of Weibull shape parameter with complete and censored data

International Nuclear Information System (INIS)

Zhang, L.F.; Xie, M.; Tang, L.C.

2006-01-01

Estimation of the Weibull shape parameter is important in reliability engineering. However, commonly used methods such as the maximum likelihood estimation (MLE) and the least squares estimation (LSE) are known to be biased. Bias correction methods for MLE have been studied in the literature. This paper investigates the methods for bias correction when model parameters are estimated with LSE based on probability plot. Weibull probability plot is very simple and commonly used by practitioners and hence such a study is useful. The bias of the LS shape parameter estimator for multiple censored data is also examined. It is found that the bias can be modeled as the function of the sample size and the censoring level, and is mainly dependent on the latter. A simple bias function is introduced and bias correcting formulas are proposed for both complete and censored data. Simulation results are also presented. The bias correction methods proposed are very easy to use and they can typically reduce the bias of the LSE of the shape parameter to less than half percent

Sense of shear and displacement estimates in the Abeibara-Rarhous late Pan-African shear zone, Adrar des Iforas, Mali

Science.gov (United States)

Boullier, Anne-Marie

The late Pan-African Abeibara-Rarhous shear zone in the Adrar des Iforas (Mali) is described and studied with the aim of defining the direction, sense of movement and amount of displacement along the zone. It is a strike-slip shear zone, the dextral sense of which is demonstrated at the scale of the map by the rotation of the related mylonitic foliation and at the scale of the thin section with characteristic microstructures. Preferred orientation of quartz c-axes is tentatively used; three quartz-rich samples of 35% or more quartz indicate dextral strike-slip movement, but other samples do not show preferred orientation of quartz c-axes. Strain measurements have been performed on one half of the shear zone using established techniques and a new technique using the thickness of mylonitic layering. The results vary along the length of the shear zone when using the same method and for the same cross-section when using the three methods together. A mean value of 4 km is obtained for total displacement which is low when considering the apparent width of the shear zone. This result is discussed in view of the assumptions involved in the strain estimation. The tectonic history of the Abeibara-Rarhous shear zone and its significance in the Trans-Saharan Pan-African collisional belt are discussed.

Bias-corrected Pearson estimating functions for Taylor's power law applied to benthic macrofauna data

DEFF Research Database (Denmark)

Jørgensen, Bent; Demétrio, Clarice G. B.; Kristensen, Erik

2011-01-01

Estimation of Taylor’s power law for species abundance data may be performed by linear regression of the log empirical variances on the log means, but this method suffers from a problem of bias for sparse data. We show that the bias may be reduced by using a bias-corrected Pearson estimating...

Spatial Working Memory Capacity Predicts Bias in Estimates of Location

Science.gov (United States)

Crawford, L. Elizabeth; Landy, David; Salthouse, Timothy A.

2016-01-01

Spatial memory research has attributed systematic bias in location estimates to a combination of a noisy memory trace with a prior structure that people impose on the space. Little is known about intraindividual stability and interindividual variation in these patterns of bias. In the current work, we align recent empirical and theoretical work on…

Wingtip Vortices and Free Shear Layer Interaction in the Vicinity of Maximum Lift to Drag Ratio Lift Condition

Science.gov (United States)

Memon, Muhammad Omar

Cost-effective air-travel is something everyone wishes for when it comes to booking flights. The continued and projected increase in commercial air travel advocates for energy efficient airplanes, reduced carbon footprint, and a strong need to accommodate more airplanes into airports. All of these needs are directly affected by the magnitudes of drag these aircraft experience and the nature of their wingtip vortex. A large portion of the aerodynamic drag results from the airflow rolling from the higher pressure side of the wing to the lower pressure side, causing the wingtip vortices. The generation of this particular drag is inevitable however, a more fundamental understanding of the phenomenon could result in applications whose benefits extend much beyond the relatively minuscule benefits of commonly-used winglets. Maximizing airport efficiency calls for shorter intervals between takeoffs and landings. Wingtip vortices can be hazardous for following aircraft that may fly directly through the high-velocity swirls causing upsets at vulnerably low speeds and altitudes. The vortex system in the near wake is typically more complex since strong vortices tend to continue developing throughout the near wake region. Several chord lengths distance downstream of a wing, the so-called fully rolled up wing wake evolves into a combination of a discrete wingtip vortex pair and a free shear layer. Lift induced drag is generated as a byproduct of downwash induced by the wingtip vortices. The parasite drag results from a combination of form/pressure drag and the upper and lower surface boundary layers. These parasite effects amalgamate to create the free shear layer in the wake. While the wingtip vortices embody a large portion of the total drag at lifting angles, flow properties in the free shear layer also reveal their contribution to the aerodynamic efficiency of the aircraft. Since aircraft rarely cruise at maximum aerodynamic efficiency, a better understanding of the balance

Structural Estimation of Expert Strategic Bias: The Case of Movie Reviewers

OpenAIRE

Camara, Fanny; Dupuis, Nicolas

2014-01-01

We develop the first structural estimation of reputational cheap-talk games using data on movie reviews released in the US between 2004 and 2013. We identify and estimate movies' priors, as well as movie reviewers' abilities and strategic biases. We find that reviewers adopt reporting strategies that are consistent with the predictions of the literature on reputational cheap-talk. The average conservatism bias for low prior movies lies between 8 and 11%, depending on the specifications of the...

Hydrodynamic characterization and molecular weight estimation of ultrasonically sheared DNA

International Nuclear Information System (INIS)

Casal, J. I.; Garces, F.; Garcia-Sacristan, A.

1981-01-01

The sedimentation coefficients and intrinsic viscosities of ultrasonically sheared calf thymus DNA have been determined. The molecular weight estimation according to this parameters have been compared with the ones obtained from the electrophoretic migration rates based on the calibration proposed using the known molecular weight restriction fragments of X-ENA. (Author) 35 refs

Modified free volume theory of self-diffusion and molecular theory of shear viscosity of liquid carbon dioxide.

Science.gov (United States)

Nasrabad, Afshin Eskandari; Laghaei, Rozita; Eu, Byung Chan

2005-04-28

In previous work on the density fluctuation theory of transport coefficients of liquids, it was necessary to use empirical self-diffusion coefficients to calculate the transport coefficients (e.g., shear viscosity of carbon dioxide). In this work, the necessity of empirical input of the self-diffusion coefficients in the calculation of shear viscosity is removed, and the theory is thus made a self-contained molecular theory of transport coefficients of liquids, albeit it contains an empirical parameter in the subcritical regime. The required self-diffusion coefficients of liquid carbon dioxide are calculated by using the modified free volume theory for which the generic van der Waals equation of state and Monte Carlo simulations are combined to accurately compute the mean free volume by means of statistical mechanics. They have been computed as a function of density along four different isotherms and isobars. A Lennard-Jones site-site interaction potential was used to model the molecular carbon dioxide interaction. The density and temperature dependence of the theoretical self-diffusion coefficients are shown to be in excellent agreement with experimental data when the minimum critical free volume is identified with the molecular volume. The self-diffusion coefficients thus computed are then used to compute the density and temperature dependence of the shear viscosity of liquid carbon dioxide by employing the density fluctuation theory formula for shear viscosity as reported in an earlier paper (J. Chem. Phys. 2000, 112, 7118). The theoretical shear viscosity is shown to be robust and yields excellent density and temperature dependence for carbon dioxide. The pair correlation function appearing in the theory has been computed by Monte Carlo simulations.

Shear behavior of thermoformed woven-textile thermoplastic prepregs: An analysis combining bias-extension test and X-ray microtomography

Science.gov (United States)

Gassoumi, M.; Rolland du Roscoat, S.; Casari, P.; Dumont, P. J. J.; Orgéas, L.; Jacquemin, F.

2017-10-01

Thermoforming allows the manufacture of structural parts for the automotive and aeronautical domains using long fiber thermoplastic prepregs with short cycle times. During this operation, several sheets of molten prepregs are stacked and subjected to large macroscale strains, mainly via in-plane shear, out-of-plane consolidation or dilatation, and bending of the fibrous reinforcement. These deformation modes and the related meso and microstructure evolutions are still poorly understood. However, they can drastically alter the end-use macroscale properties of fabricated parts. To better understand these phenomena, bias extension tests were performed using specimens made of several stacked layers of glass woven fabrics and polyamide matrix. The macroscale shear behavior of these prepregs was investigated at various temperatures. A multiscale analysis of deformed samples was performed using X-ray microtomography images of the deformed specimens acquired at two different spatial resolutions. The low-resolution images were used to analyze the deformation mechanisms and the structural characteristics of prepregs at the macroscale and bundle scales. It was possible to analyze the 3D shapes of deformed samples and, in particular, the spatial variations of their thickness so as to quantify the out-of-plane dilatancy or consolidation phenomena induced by the in-plane shear of prepregs. At a lower scale, the analysis of the high-resolution images showed that these mechanisms were accompanied by the growth of pores and the deformation of fiber bundles. The orientation of the fiber bundles and its through-thickness evolution were measured along the weft and warp directions in the deformed samples, allowing the relevance of geometrical models currently used to analyze bias extension tests to be discussed. Results can be used to enhance the current rheological models for the prediction of thermoforming of thermoplastic prepregs.

Exploration, Sampling, And Reconstruction of Free Energy Surfaces with Gaussian Process Regression.

Science.gov (United States)

Mones, Letif; Bernstein, Noam; Csányi, Gábor

2016-10-11

Practical free energy reconstruction algorithms involve three separate tasks: biasing, measuring some observable, and finally reconstructing the free energy surface from those measurements. In more than one dimension, adaptive schemes make it possible to explore only relatively low lying regions of the landscape by progressively building up the bias toward the negative of the free energy surface so that free energy barriers are eliminated. Most schemes use the final bias as their best estimate of the free energy surface. We show that large gains in computational efficiency, as measured by the reduction of time to solution, can be obtained by separating the bias used for dynamics from the final free energy reconstruction itself. We find that biasing with metadynamics, measuring a free energy gradient estimator, and reconstructing using Gaussian process regression can give an order of magnitude reduction in computational cost.

Reviving the shear-free perfect fluid conjecture in general relativity

Science.gov (United States)

Sikhonde, Muzikayise E.; Dunsby, Peter K. S.

2017-12-01

Employing a Mathematica symbolic computer algebra package called xTensor, we present (1+3) -covariant special case proofs of the shear-free perfect fluid conjecture in general relativity. We first present the case where the pressure is constant, and where the acceleration is parallel to the vorticity vector. These cases were first presented in their covariant form by Senovilla et al. We then provide a covariant proof for the case where the acceleration and vorticity vectors are orthogonal, which leads to the existence of a Killing vector along the vorticity. This Killing vector satisfies the new constraint equations resulting from the vanishing of the shear. Furthermore, it is shown that in order for the conjecture to be true, this Killing vector must have a vanishing spatially projected directional covariant derivative along the velocity vector field. This in turn implies the existence of another basic vector field along the direction of the vorticity for the conjecture to hold. Finally, we show that in general, there exists a basic vector field parallel to the acceleration for which the conjecture is true.

Maxwell fields and shear-free null geodesic congruences

International Nuclear Information System (INIS)

Newman, Ezra T

2004-01-01

We study and report on the class of vacuum Maxwell fields in Minkowski space that possess a non-degenerate, diverging, principal null vector field (null eigenvector field of the Maxwell tensor) that is tangent to a shear-free null geodesics congruence. These congruences can be either surface forming (the tangent vectors being proportional to gradients) or not, i.e., the twisting congruences. In the non-twisting case, the associated Maxwell fields are precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from an electric monopole moving on an arbitrary worldline. The null geodesic congruence is given by the generators of the light-cones with apex on the worldline. The twisting case is much richer, more interesting and far more complicated. In a twisting subcase, where our main interests lie, the following strange interpretation can be given. If we allow the real Minkowski space to be complexified so that the real Minkowski coordinates x a take complex values, i.e., x a → z a = x a + iy a with complex metric g η ab dz a dz b , the real vacuum Maxwell equations can be extended into the complex space and rewritten as curl W=i W radical, div W=0 with W=E+iB. This subcase of Maxwell fields can then be extended into the complex space so as to have as source, a complex analytic worldline, i.e., to now become complex Lienard-Wiechart fields. When viewed as real fields on the real Minkowski space (z a = x a ), they possess a real principal null vector that is shear-free but twisting and diverging. The twist is a measure of how far the complex worldline is from the real 'slice'. Most Maxwell fields in this subcase are asymptotically flat with a time-varying set of electric and magnetic moments, all depending on the complex displacements and the complex velocities

Estimating low-bias frequency response using random decrement

DEFF Research Database (Denmark)

Brincker, Rune; Brandt, Anders

2011-01-01

It is well known that in order to minimize the influence of leakage bias in frequency response function (FRF) estimates, smooth windows should be applied in the FFT processing. It is also normal practice to use self windowing excitation signals whenever possible. However, in many cases FRFs have...

Hemolysis in a laminar flow-through Couette shearing device: an experimental study.

Science.gov (United States)

Boehning, Fiete; Mejia, Tzahiry; Schmitz-Rode, Thomas; Steinseifer, Ulrich

2014-09-01

Reducing hemolysis has been one of the major goals of rotary blood pump development and in the investigational phase, the capability of hemolysis estimation for areas of elevated shear stresses is valuable. The degree of hemolysis is determined by the amplitude of shear stress and the exposure time, but to date, the exact hemolytic behavior at elevated shear stresses and potential thresholds for subcritical shear exposure remain vague. This study provides experimental hemolysis data for a set of shear stresses and exposure times to allow better estimations of hemolysis for blood exposed to elevated shearing. Heparinized porcine blood with a hematocrit of 40% was mechanically damaged in a flow-through laminar Couette shear flow at a temperature of 23°C. Four levels of shear stress, 24, 592, 702, and 842 Pa, were replicated at two exposure times, 54 and 873 ms. For the calculation of the shear stresses, an apparent viscosity of 5 mPas was used, which was verified in an additional measurement of the blood viscosity. The hemolysis measurements were repeated four times, whereby all conditions were measured once within the same day and with blood from the same source. Samples were taken at the inlet and outlet of the shear region and an increase in plasma-free hemoglobin was measured. An index of hemolysis (IH) was thereby calculated giving the ratio of free to total hemoglobin. The results are compared with data from previously published studies using a similar shearing device. Hemolysis was found to increase exponentially with shear stress, but high standard deviations existed at measurements with elevated IH. At short exposure times, the IH remained low at under 0.5% for all shear stress levels. For high exposure times, the IH increased from 0.84% at 592 Pa up to 3.57% at the highest shear stress level. Hemolysis was significant for shear stresses above ∼600 Pa at the high exposure time of 873 ms. Copyright © 2014 International Center for Artificial

The Role of Shearing Energy and Interfacial Gibbs Free Energy in the Emulsification Mechanism of Waxy Crude Oil

Directory of Open Access Journals (Sweden)

Zhihua Wang

2017-05-01

Full Text Available Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process particularly, both in terms of transportation energy consumption and separation efficiency. To deal with the production and operational problems which are related to crude oil emulsions, especially to ensure the separation and transportation of crude oil-water systems, it is necessary to better understand the emulsification mechanism of crude oil under different conditions from the aspects of bulk and interfacial properties. The concept of shearing energy was introduced in this study to reveal the driving force for emulsification. The relationship between shearing stress in the flow field and interfacial tension (IFT was established, and the correlation between shearing energy and interfacial Gibbs free energy was developed. The potential of the developed correlation model was validated using the experimental and field data on emulsification behavior. It was also shown how droplet deformation could be predicted from a random deformation degree and orientation angle. The results indicated that shearing energy as the energy produced by shearing stress working in the flow field is the driving force activating the emulsification behavior. The deformation degree and orientation angle of dispersed phase droplet are associated with the interfacial properties, rheological properties and the experienced turbulence degree. The correlation between shearing stress and IFT can be quantified if droplet deformation degree vs. droplet orientation angle data is available. When the water cut is close to the inversion point of waxy crude oil emulsion, the interfacial Gibbs free energy change decreased and the shearing energy increased. This feature is also presented in the special regions where

A MORET tool to assist code bias estimation

International Nuclear Information System (INIS)

Fernex, F.; Richet, Y.; Letang, E.

2003-01-01

This new Graphical User Interface (GUI) developed in JAVA is one of the post-processing tools for MORET4 code. It aims to help users to estimate the importance of the k eff bias due to the code in order to better define the upper safety limit. Moreover, it allows visualizing the distance between an actual configuration case and evaluated critical experiments. This tool depends on a validated experiments database, on sets of physical parameters and on various statistical tools allowing interpolating the calculation bias of the database or displaying the projections of experiments on a reduced base of parameters. The development of this tool is still in progress. (author)

Bias Correction for the Maximum Likelihood Estimate of Ability. Research Report. ETS RR-05-15

Science.gov (United States)

Zhang, Jinming

2005-01-01

Lord's bias function and the weighted likelihood estimation method are effective in reducing the bias of the maximum likelihood estimate of an examinee's ability under the assumption that the true item parameters are known. This paper presents simulation studies to determine the effectiveness of these two methods in reducing the bias when the item…

Non-response bias in physical activity trend estimates

Directory of Open Access Journals (Sweden)

Bauman Adrian

2009-11-01

Full Text Available Abstract Background Increases in reported leisure time physical activity (PA and obesity have been observed in several countries. One hypothesis for these apparently contradictory trends is differential bias in estimates over time. The purpose of this short report is to examine the potential impact of changes in response rates over time on the prevalence of adequate PA in Canadian adults. Methods Participants were recruited in representative national telephone surveys of PA from 1995-2007. Differences in PA prevalence estimates between participants and those hard to reach were assessed using Student's t tests adjusted for multiple comparisons. Results The number of telephone calls required to reach and speak with someone in the household increased over time, as did the percentage of selected participants who initially refused during the first interview attempt. A higher prevalence of adequate PA was observed with 5-9 attempts to reach anyone in the household in 1999-2002, but this was not significant after adjustment for multiple comparisons. Conclusion No significant impact on PA trend estimates was observed due to differential non response rates. It is important for health policy makers to understand potential biases and how these may affect secular trends in all aspects of the energy balance equation.

A thin rivulet or ridge subject to a uniform transverse shear stress at its free surface due to an external airflow

KAUST Repository

Sullivan, J. M.

2012-01-01

We use the lubrication approximation to analyze three closely related problems involving a thin rivulet or ridge (i.e., a two-dimensional droplet) of fluid subject to a prescribed uniform transverse shear stress at its free surface due to an external airflow, namely a rivulet draining under gravity down a vertical substrate, a rivulet driven by a longitudinal shear stress at its free surface, and a ridge on a horizontal substrate, and find qualitatively similar behaviour for all three problems. We show that, in agreement with previous numerical studies, the free surface profile of an equilibrium rivulet/ridge with pinned contact lines is skewed as the shear stress is increased from zero, and that there is a maximum value of the shear stress beyond which no solution with prescribed semi-width is possible. In practice, one or both of the contact lines will de-pin before this maximum value of the shear stress is reached, and so we consider situations in which the rivulet/ridge de-pins at one or both contact lines. In the case of de-pinning only at the advancing contact line, the rivulet/ridge is flattened and widened as the shear stress is increased from its critical value, and there is a second maximum value of the shear stress beyond which no solution with a prescribed advancing contact angle is possible. In contrast, in the case of de-pinning only at the receding contact line, the rivulet/ridge is thickened and narrowed as the shear stress is increased from its critical value, and there is a solution with a prescribed receding contact angle for all values of the shear stress. In general, in the case of de-pinning at both contact lines there is a critical "yield" value of the shear stress beyond which no equilibrium solution is possible and the rivulet/ridge will evolve unsteadily. In the Appendix, we show that an equilibrium rivulet/ridge with prescribed flux/area is quasi-statically stable to two-dimensional perturbations. © 2012 American Institute of Physics.

Potential for Bias When Estimating Critical Windows for Air Pollution in Children's Health.

Science.gov (United States)

Wilson, Ander; Chiu, Yueh-Hsiu Mathilda; Hsu, Hsiao-Hsien Leon; Wright, Robert O; Wright, Rosalind J; Coull, Brent A

2017-12-01

Evidence supports an association between maternal exposure to air pollution during pregnancy and children's health outcomes. Recent interest has focused on identifying critical windows of vulnerability. An analysis based on a distributed lag model (DLM) can yield estimates of a critical window that are different from those from an analysis that regresses the outcome on each of the 3 trimester-average exposures (TAEs). Using a simulation study, we assessed bias in estimates of critical windows obtained using 3 regression approaches: 1) 3 separate models to estimate the association with each of the 3 TAEs; 2) a single model to jointly estimate the association between the outcome and all 3 TAEs; and 3) a DLM. We used weekly fine-particulate-matter exposure data for 238 births in a birth cohort in and around Boston, Massachusetts, and a simulated outcome and time-varying exposure effect. Estimates using separate models for each TAE were biased and identified incorrect windows. This bias arose from seasonal trends in particulate matter that induced correlation between TAEs. Including all TAEs in a single model reduced bias. DLM produced unbiased estimates and added flexibility to identify windows. Analysis of body mass index z score and fat mass in the same cohort highlighted inconsistent estimates from the 3 methods. © The Author(s) 2017. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Dilatancy of Shear Transformations in a Colloidal Glass

Science.gov (United States)

Lu, Y. Z.; Jiang, M. Q.; Lu, X.; Qin, Z. X.; Huang, Y. J.; Shen, J.

2018-01-01

Shear transformations, as fundamental rearrangement events operating in local regions, hold the key of plastic flow of amorphous solids. Despite their importance, the dynamic features of shear transformations are far from clear, which is the focus of the present study. Here, we use a colloidal glass under shear as the prototype to directly observe the shear-transformation events in real space. By tracing the colloidal-particle rearrangements, we quantitatively determine two basic properties of shear transformations: local shear strain and dilatation (or free volume). It is revealed that the local free volume undergoes a significantly temporary increase prior to shear transformations, eventually leading to a jump of local shear strain. We clearly demonstrate that shear transformations have no memory of the initial free volume of local regions. Instead, their emergence strongly depends on the dilatancy ability of these local regions, i.e., the dynamic creation of free volume. More specifically, the particles processing the high dilatancy ability directly participate in subsequent shear transformations. These results experimentally enrich Argon's statement about the dilatancy nature of shear transformations and also shed insight into the structural origin of amorphous plasticity.

Fat fraction bias correction using T1 estimates and flip angle mapping.

Science.gov (United States)

Yang, Issac Y; Cui, Yifan; Wiens, Curtis N; Wade, Trevor P; Friesen-Waldner, Lanette J; McKenzie, Charles A

2014-01-01

To develop a new method of reducing T1 bias in proton density fat fraction (PDFF) measured with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). PDFF maps reconstructed from high flip angle IDEAL measurements were simulated and acquired from phantoms and volunteer L4 vertebrae. T1 bias was corrected using a priori T1 values for water and fat, both with and without flip angle correction. Signal-to-noise ratio (SNR) maps were used to measure precision of the reconstructed PDFF maps. PDFF measurements acquired using small flip angles were then compared to both sets of corrected large flip angle measurements for accuracy and precision. Simulations show similar results in PDFF error between small flip angle measurements and corrected large flip angle measurements as long as T1 estimates were within one standard deviation from the true value. Compared to low flip angle measurements, phantom and in vivo measurements demonstrate better precision and accuracy in PDFF measurements if images were acquired at a high flip angle, with T1 bias corrected using T1 estimates and flip angle mapping. T1 bias correction of large flip angle acquisitions using estimated T1 values with flip angle mapping yields fat fraction measurements of similar accuracy and superior precision compared to low flip angle acquisitions. Copyright © 2013 Wiley Periodicals, Inc.

Fractal aspects of the flow and shear behaviour of free-flowable particle size fractions of pharmaceutical directly compressible excipient sorbitol.

Science.gov (United States)

Hurychová, Hana; Lebedová, Václava; Šklubalová, Zdenka; Dzámová, Pavlína; Svěrák, Tomáš; Stoniš, Jan

Flowability of powder excipients is directly influenced by their size and shape although the granulometric influence of the flow and shear behaviour of particulate matter is not studied frequently. In this work, the influence of particle size on the mass flow rate through the orifice of a conical hopper, and the cohesion and flow function was studied for four free-flowable size fractions of sorbitol for direct compression in the range of 0.080-0.400 mm. The particles were granulometricaly characterized using an optical microscopy; a boundary fractal dimension of 1.066 was estimated for regular sorbitol particles. In the particle size range studied, a non-linear relationship between the mean particle size and the mass flow rate Q10 (g/s) was detected having amaximum at the 0.245mm fraction. The best flow properties of this fraction were verified with aJenike shear tester due to the highest value of flow function and the lowest value of the cohesion. The results of this work show the importance of the right choice of the excipient particle size to achieve the best flow behaviour of particulate material.Key words: flowability size fraction sorbitol for direct compaction Jenike shear tester fractal dimension.

Correcting the bias of empirical frequency parameter estimators in codon models.

Directory of Open Access Journals (Sweden)

Sergei Kosakovsky Pond

2010-07-01

Full Text Available Markov models of codon substitution are powerful inferential tools for studying biological processes such as natural selection and preferences in amino acid substitution. The equilibrium character distributions of these models are almost always estimated using nucleotide frequencies observed in a sequence alignment, primarily as a matter of historical convention. In this note, we demonstrate that a popular class of such estimators are biased, and that this bias has an adverse effect on goodness of fit and estimates of substitution rates. We propose a "corrected" empirical estimator that begins with observed nucleotide counts, but accounts for the nucleotide composition of stop codons. We show via simulation that the corrected estimates outperform the de facto standard estimates not just by providing better estimates of the frequencies themselves, but also by leading to improved estimation of other parameters in the evolutionary models. On a curated collection of sequence alignments, our estimators show a significant improvement in goodness of fit compared to the approach. Maximum likelihood estimation of the frequency parameters appears to be warranted in many cases, albeit at a greater computational cost. Our results demonstrate that there is little justification, either statistical or computational, for continued use of the -style estimators.

Effect of soft mode on shear viscosity of quark matter

International Nuclear Information System (INIS)

Fukutome, Takahiko; Iwasaki, Masaharu

2008-01-01

We calculate the shear viscosity of quark matter at finite temperature and density. If we assume that the quark interacts with the soft mode, which is a collective mode of a quark-antiquark pair, the self-energy of the quark is calculated by quasi-particle random phase approximation. It is shown that its imaginary part is large and its mean free path is short. With the use of the Kubo formula, the shear viscosity of quark matter decreases. The Reynolds number of quark matter is estimated to be about 10. As temperature increases, shear viscosity increases gradually for T>200 MeV. Moreover it is shown that the shear viscosity also increases with the chemical potential for μ>200 MeV. (author)

Velocity-pressure correlation measurements in complex free shear flows

International Nuclear Information System (INIS)

Naka, Yoshitsugu; Obi, Shinnosuke

2009-01-01

Simultaneous measurements of fluctuating velocity and pressure were performed in various turbulent free shear flows including a turbulent mixing layer and the wing-tip vortex trailing from a NACA0012 half-wing. Two different methods for fluctuating static pressure measurement were considered: a direct method using a miniature Pitot tube and an indirect method where static pressure was calculated from total pressure. The pressure obtained by either of these methods was correlated with the velocity measured by an X-type hot-wire probe. The results from these two techniques agreed with each other in the turbulent mixing layer. In the wing-tip vortex case, however, some discrepancies were found, although overall characteristics of the pressure-related statistics were adequately captured by both methods.

On the estimation of bias in post-closure performance assessment of underground radioactive waste disposal

International Nuclear Information System (INIS)

Thompson, B.G.J.; Gralewski, Z.A.; Grindrod, P.

1995-01-01

This paper proposes a systematic method for recording and evaluating bias in performance assessments for underground radioactive waste disposal facilities. The bias estimation approach comprises three principal components: (1) creation of a relational database containing historical assumptions and decisions made during the assessment, (2) investigation of the impact of some identified sources of internal bias through alternative assessment calculations, and (3) investigation of the impact of some identified sources of external bias by estimating degrees of belief probability. Bias corrections may help avoid unnecessary concerns by explaining and scoping the impacts of principal differences without the need to undertake additional site investigation, research, and performance analysis

EFFECTS OF BIASES IN VIRIAL MASS ESTIMATION ON COSMIC SYNCHRONIZATION OF QUASAR ACCRETION

International Nuclear Information System (INIS)

Steinhardt, Charles L.

2011-01-01

Recent work using virial mass estimates and the quasar mass-luminosity plane has yielded several new puzzles regarding quasar accretion, including a sub-Eddington boundary (SEB) on most quasar accretion, near-independence of the accretion rate from properties of the host galaxy, and a cosmic synchronization of accretion among black holes of a common mass. We consider how these puzzles might change if virial mass estimation turns out to have a systematic bias. As examples, we consider two recent claims of mass-dependent biases in Mg II masses. Under any such correction, the surprising cosmic synchronization of quasar accretion rates and independence from the host galaxy remain. The slope and location of the SEB are very sensitive to biases in virial mass estimation, and various mass calibrations appear to favor different possible physical explanations for feedback between the central black hole and its environment. The alternative mass estimators considered do not simply remove puzzling quasar behavior, but rather replace it with new puzzles that may be more difficult to solve than those using current virial mass estimators and the Shen et al. catalog.

Bias correction for the estimation of sensitivity indices based on random balance designs

International Nuclear Information System (INIS)

Tissot, Jean-Yves; Prieur, Clémentine

2012-01-01

This paper deals with the random balance design method (RBD) and its hybrid approach, RBD-FAST. Both these global sensitivity analysis methods originate from Fourier amplitude sensitivity test (FAST) and consequently face the main problems inherent to discrete harmonic analysis. We present here a general way to correct a bias which occurs when estimating sensitivity indices (SIs) of any order – except total SI of single factor or group of factors – by the random balance design method (RBD) and its hybrid version, RBD-FAST. In the RBD case, this positive bias has been recently identified in a paper by Xu and Gertner [1]. Following their work, we propose a bias correction method for first-order SIs estimates in RBD. We then extend the correction method to the SIs of any order in RBD-FAST. At last, we suggest an efficient strategy to estimate all the first- and second-order SIs using RBD-FAST. - Highlights: ► We provide a bias correction method for the global sensitivity analysis methods: RBD and RBD-FAST. ► In RBD, first-order sensitivity estimates are corrected. ► In RBD-FAST, sensitivity indices of any order and closed sensitivity indices are corrected. ► We propose an efficient strategy to estimate all the first- and second-order indices of a model.

Eliminating Survivor Bias in Two-stage Instrumental Variable Estimators.

Science.gov (United States)

Vansteelandt, Stijn; Walter, Stefan; Tchetgen Tchetgen, Eric

2018-07-01

Mendelian randomization studies commonly focus on elderly populations. This makes the instrumental variables analysis of such studies sensitive to survivor bias, a type of selection bias. A particular concern is that the instrumental variable conditions, even when valid for the source population, may be violated for the selective population of individuals who survive the onset of the study. This is potentially very damaging because Mendelian randomization studies are known to be sensitive to bias due to even minor violations of the instrumental variable conditions. Interestingly, the instrumental variable conditions continue to hold within certain risk sets of individuals who are still alive at a given age when the instrument and unmeasured confounders exert additive effects on the exposure, and moreover, the exposure and unmeasured confounders exert additive effects on the hazard of death. In this article, we will exploit this property to derive a two-stage instrumental variable estimator for the effect of exposure on mortality, which is insulated against the above described selection bias under these additivity assumptions.

Endothelial shear stress estimation in the human carotid artery based on Womersley versus Poiseuille flow

NARCIS (Netherlands)

Schwarz, Janina C. V.; Duivenvoorden, Raphaël; Nederveen, Aart J.; Stroes, Erik S. G.; VanBavel, Ed

2015-01-01

Endothelial shear stress (ESS) dynamics are a major determinant of atherosclerosis development. The frequently used Poiseuille method to estimate ESS dynamics has important limitations. Therefore, we investigated whether Womersley flow may provide a better alternative for estimation of ESS while

A forecasting method to reduce estimation bias in self-reported cell phone data.

Science.gov (United States)

Redmayne, Mary; Smith, Euan; Abramson, Michael J

2013-01-01

There is ongoing concern that extended exposure to cell phone electromagnetic radiation could be related to an increased risk of negative health effects. Epidemiological studies seek to assess this risk, usually relying on participants' recalled use, but recall is notoriously poor. Our objectives were primarily to produce a forecast method, for use by such studies, to reduce estimation bias in the recalled extent of cell phone use. The method we developed, using Bayes' rule, is modelled with data we collected in a cross-sectional cluster survey exploring cell phone user-habits among New Zealand adolescents. Participants recalled their recent extent of SMS-texting and retrieved from their provider the current month's actual use-to-date. Actual use was taken as the gold standard in the analyses. Estimation bias arose from a large random error, as observed in all cell phone validation studies. We demonstrate that this seriously exaggerates upper-end forecasts of use when used in regression models. This means that calculations using a regression model will lead to underestimation of heavy-users' relative risk. Our Bayesian method substantially reduces estimation bias. In cases where other studies' data conforms to our method's requirements, application should reduce estimation bias, leading to a more accurate relative risk calculation for mid-to-heavy users.

A Copula-Based Method for Estimating Shear Strength Parameters of Rock Mass

Directory of Open Access Journals (Sweden)

Da Huang

2014-01-01

Full Text Available The shear strength parameters (i.e., the internal friction coefficient f and cohesion c are very important in rock engineering, especially for the stability analysis and reinforcement design of slopes and underground caverns. In this paper, a probabilistic method, Copula-based method, is proposed for estimating the shear strength parameters of rock mass. The optimal Copula functions between rock mass quality Q and f, Q and c for the marbles are established based on the correlation analyses of the results of 12 sets of in situ tests in the exploration adits of Jinping I-Stage Hydropower Station. Although the Copula functions are derived from the in situ tests for the marbles, they can be extended to be applied to other types of rock mass with similar geological and mechanical properties. For another 9 sets of in situ tests as an extensional application, by comparison with the results from Hoek-Brown criterion, the estimated values of f and c from the Copula-based method achieve better accuracy. Therefore, the proposed Copula-based method is an effective tool in estimating rock strength parameters.

Measurement Error in Income and Schooling and the Bias of Linear Estimators

DEFF Research Database (Denmark)

Bingley, Paul; Martinello, Alessandro

2017-01-01

and Retirement in Europe data with Danish administrative registers. Contrary to most validation studies, we find that measurement error in income is classical once we account for imperfect validation data. We find nonclassical measurement error in schooling, causing a 38% amplification bias in IV estimators......We propose a general framework for determining the extent of measurement error bias in ordinary least squares and instrumental variable (IV) estimators of linear models while allowing for measurement error in the validation source. We apply this method by validating Survey of Health, Ageing...

Measurement error in income and schooling, and the bias of linear estimators

DEFF Research Database (Denmark)

Bingley, Paul; Martinello, Alessandro

The characteristics of measurement error determine the bias of linear estimators. We propose a method for validating economic survey data allowing for measurement error in the validation source, and we apply this method by validating Survey of Health, Ageing and Retirement in Europe (SHARE) data...... with Danish administrative registers. We find that measurement error in surveys is classical for annual gross income but non-classical for years of schooling, causing a 21% amplification bias in IV estimators of returns to schooling. Using a 1958 Danish schooling reform, we contextualize our result...

Chiral Biases in Solids by Effect of Shear Gradients: A Speculation on the Deterministic Origin of Biological Homochirality

International Nuclear Information System (INIS)

Arteaga, O.; Canillas, A.; Crusats, Joaquim; Hachemi, Zoubir; Jellison, Gerald Earle Jr.; Llorca, Jordi; Ribo, Josep M.

2010-01-01

We present an experimental approach to the study of the chirality of three CM2 meteorite solid samples by direct measurement of the optical activity (circular birefringence; CB). The measurements are based on transmission two modulator generalized ellipsometry in conjuction with microscope optics to map the CB of the samples. In spite of the complexity of such optical analysis, these first results indicate the presence of optically active areas in the meteorite solid matrix. In the case of the Murchison sample the statistics of the CB mapping shows a bimodal distribution with a bias to negative CB values. The composition of the active areas probably corresponds to serpentines and other poorly identified phyllosilicate phases. The results are compatible with the hypothesis that in a mineral-based scenario for the origin of life a CB sign bias in the chiral fractures originated by mechanical and flow shear gradients on clays could be later transferred to the reactions of the absorbed organic compounds.

Insights into the growth rate of spatially evolving plane turbulent free-shear layers from 2D vortex-gas simulations

Science.gov (United States)

Suryanarayanan, Saikishan; Narasimha, Roddam

2017-02-01

Although the free-shear or mixing layer has been a subject of extensive research over nearly a century, there are certain fundamental issues that remain controversial. These include the influence of initial and downstream conditions on the flow, the effect of velocity ratio across the layer, and the nature of any possible coupling between small scale dynamics and the large scale evolution of layer thickness. In the spirit of the temporal vortex-gas simulations of Suryanarayanan et al. ["Free turbulent shear layer in a point vortex gas as a problem in nonequilibrium statistical mechanics," Phys. Rev. E 89, 013009 (2014)], we revisit the simple 2D inviscid vortex-gas model with extensive computations and detailed analysis, in order to gain insights into some of the above issues. Simulations of the spatially evolving vortex-gas shear layer are carried out at different velocity ratios using a computational model based on the work of Basu et al. ["Vortex sheet simulation of a plane canonical mixing layer," Comput. Fluids 21, 1-30 (1992) and "Modelling plane mixing layers using vortex points and sheets," Appl. Math. Modell. 19, 66-75 (1995)], but with a crucial improvement that ensures conservation of global circulation. The simulations show that the conditions imposed at the origin of the free shear layer and at the exit to the computational domain can affect flow evolution in their respective downstream and upstream neighbourhoods, the latter being particularly strong in the single stream limit. In between these neighbourhoods at the ends is a regime of universal self-preserving growth rate given by a universal function of velocity ratio. The computed growth rates are generally located within the scatter of experimental data on plane mixing layers and closely agree with recent high Reynolds number experiments and 3D large eddy simulation studies. These findings support the view that observed free-shear layer growth can be largely explained by the 2D vortex dynamics of

Sheared-flow induced confinement transition in a linear magnetized plasma

International Nuclear Information System (INIS)

Zhou, S.; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Friedman, B.; Schaffner, D.

2012-01-01

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn/n∼eδφ/kT e ∼0.5) are observed at the plasma edge, accompanied by a large density gradient (L n =∇lnn -1 ∼2cm) and shearing rate (γ∼300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V bias ) on the obstacle and the axial magnetic field (B z ) strength. In cases with low V bias and large B z , improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by ExB drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B z , large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m=1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

Adaptive enhanced sampling by force-biasing using neural networks

Science.gov (United States)

Guo, Ashley Z.; Sevgen, Emre; Sidky, Hythem; Whitmer, Jonathan K.; Hubbell, Jeffrey A.; de Pablo, Juan J.

2018-04-01

A machine learning assisted method is presented for molecular simulation of systems with rugged free energy landscapes. The method is general and can be combined with other advanced sampling techniques. In the particular implementation proposed here, it is illustrated in the context of an adaptive biasing force approach where, rather than relying on discrete force estimates, one can resort to a self-regularizing artificial neural network to generate continuous, estimated generalized forces. By doing so, the proposed approach addresses several shortcomings common to adaptive biasing force and other algorithms. Specifically, the neural network enables (1) smooth estimates of generalized forces in sparsely sampled regions, (2) force estimates in previously unexplored regions, and (3) continuous force estimates with which to bias the simulation, as opposed to biases generated at specific points of a discrete grid. The usefulness of the method is illustrated with three different examples, chosen to highlight the wide range of applicability of the underlying concepts. In all three cases, the new method is found to enhance considerably the underlying traditional adaptive biasing force approach. The method is also found to provide improvements over previous implementations of neural network assisted algorithms.

Systematic Biases in Parameter Estimation of Binary Black-Hole Mergers

Science.gov (United States)

Littenberg, Tyson B.; Baker, John G.; Buonanno, Alessandra; Kelly, Bernard J.

2012-01-01

Parameter estimation of binary-black-hole merger events in gravitational-wave data relies on matched filtering techniques, which, in turn, depend on accurate model waveforms. Here we characterize the systematic biases introduced in measuring astrophysical parameters of binary black holes by applying the currently most accurate effective-one-body templates to simulated data containing non-spinning numerical-relativity waveforms. For advanced ground-based detectors, we find that the systematic biases are well within the statistical error for realistic signal-to-noise ratios (SNR). These biases grow to be comparable to the statistical errors at high signal-to-noise ratios for ground-based instruments (SNR approximately 50) but never dominate the error budget. At the much larger signal-to-noise ratios expected for space-based detectors, these biases will become large compared to the statistical errors but are small enough (at most a few percent in the black-hole masses) that we expect they should not affect broad astrophysical conclusions that may be drawn from the data.

Reynolds-Averaged Navier-Stokes Modeling of Turbulent Free Shear Layers

Science.gov (United States)

Schilling, Oleg

2017-11-01

Turbulent mixing of gases in free shear layers is simulated using a weighted essentially nonoscillatory implementation of ɛ- and L-based Reynolds-averaged Navier-Stokes models. Specifically, the air/air shear layer with velocity ratio 0.6 studied experimentally by Bell and Mehta (1990) is modeled. The detailed predictions of turbulent kinetic energy dissipation rate and lengthscale models are compared to one another, and to the experimental data. The role of analytical, self-similar solutions for model calibration and physical insights is also discussed. It is shown that turbulent lengthscale-based models are unable to predict both the growth parameter (spreading rate) and turbulent kinetic energy normalized by the square of the velocity difference of the streams. The terms in the K, ɛ, and L equation budgets are compared between the models, and it is shown that the production and destruction mechanisms are substantially different in the ɛ and L equations. Application of the turbulence models to the Brown and Roshko (1974) experiments with streams having various velocity and density ratios is also briefly discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Reconsidering Cluster Bias in Multilevel Data: A Monte Carlo Comparison of Free and Constrained Baseline Approaches.

Science.gov (United States)

Guenole, Nigel

2018-01-01

The test for item level cluster bias examines the improvement in model fit that results from freeing an item's between level residual variance from a baseline model with equal within and between level factor loadings and between level residual variances fixed at zero. A potential problem is that this approach may include a misspecified unrestricted model if any non-invariance is present, but the log-likelihood difference test requires that the unrestricted model is correctly specified. A free baseline approach where the unrestricted model includes only the restrictions needed for model identification should lead to better decision accuracy, but no studies have examined this yet. We ran a Monte Carlo study to investigate this issue. When the referent item is unbiased, compared to the free baseline approach, the constrained baseline approach led to similar true positive (power) rates but much higher false positive (Type I error) rates. The free baseline approach should be preferred when the referent indicator is unbiased. When the referent assumption is violated, the false positive rate was unacceptably high for both free and constrained baseline approaches, and the true positive rate was poor regardless of whether the free or constrained baseline approach was used. Neither the free or constrained baseline approach can be recommended when the referent indicator is biased. We recommend paying close attention to ensuring the referent indicator is unbiased in tests of cluster bias. All Mplus input and output files, R, and short Python scripts used to execute this simulation study are uploaded to an open access repository.

Unbiased multi-fidelity estimate of failure probability of a free plane jet

Science.gov (United States)

Marques, Alexandre; Kramer, Boris; Willcox, Karen; Peherstorfer, Benjamin

2017-11-01

Estimating failure probability related to fluid flows is a challenge because it requires a large number of evaluations of expensive models. We address this challenge by leveraging multiple low fidelity models of the flow dynamics to create an optimal unbiased estimator. In particular, we investigate the effects of uncertain inlet conditions in the width of a free plane jet. We classify a condition as failure when the corresponding jet width is below a small threshold, such that failure is a rare event (failure probability is smaller than 0.001). We estimate failure probability by combining the frameworks of multi-fidelity importance sampling and optimal fusion of estimators. Multi-fidelity importance sampling uses a low fidelity model to explore the parameter space and create a biasing distribution. An unbiased estimate is then computed with a relatively small number of evaluations of the high fidelity model. In the presence of multiple low fidelity models, this framework offers multiple competing estimators. Optimal fusion combines all competing estimators into a single estimator with minimal variance. We show that this combined framework can significantly reduce the cost of estimating failure probabilities, and thus can have a large impact in fluid flow applications. This work was funded by DARPA.

Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves

Science.gov (United States)

Chen, Andrew; Schumacher, Thomas

2014-02-01

Ultrasonic testing is commonly used to detect flaws, estimate geometries, and characterize properties of materials and structures. Acoustoelasticity refers to the dependency of stress wave velocity with applied stresses and is a phenomenon that has been known by geophysicists since the 1960s. A way to capitalize on this effect for concrete applications is by using ultrasonic shear waves which are particularly sensitive to applied stresses when polarized in the direction of the applied stress. The authors conducted an experiment on a 150 mm (6 in.) diameter concrete cylinder specimen with a length of 305 mm (12 in.) that was loaded in discrete load steps to failure. At each load step two ultrasonic shear waves were transmitted through the specimen, one with the polarization perpendicular and the other transverse to the applied stress. The velocity difference between the two sets of polarized shear waves was found to correlate with the applied stress in the specimen. Two potential applications for this methodology include estimation of stresses in pre-stressed concrete bridge girders and investigation of load redistribution in structural support elements after extreme events. This paper introduces the background of the methodology, presents an analysis of the collected data, and discusses the relationship between the recorded signals and the applied stress.

Systematic Biases in Weak Lensing Cosmology with the Dark Energy Survey

Energy Technology Data Exchange (ETDEWEB)

Samuroff, Simon [Manchester U.

2017-01-01

This thesis sets out a practical guide to applying shear measurements as a cosmological tool. We first present one of two science-ready galaxy shape catalogues from Year 1 of the Dark Energy Survey (DES Y1), which covers 1500 square degrees in four bands $griz$, with a median redshift of $0.59$. We describe the shape measurement process implemented by the DES Y1 imshape catalogue, which contains 21.9 million high-quality $r$-band bulge/disc fits. In Chapter 3 a new suite of image simulations, referred to as Hoopoe, are presented. The Hoopoe dataset is tailored to DES Y1 and includes realistic blending, spatial masks and variation in the point spread function. We derive shear corrections, which we show are robust to changes in calibration method, galaxy binning and variance within the simulated dataset. Sources of systematic uncertainty in the simulation-based shear calibration are discussed, leading to a final estimate of the $1\\sigma$ uncertainties in the residual multiplica tive bias after calibration of 0.025. Chapter 4 describes an extension of the analysis on the Hoopoe simulations into a detailed investigation of the impact of galaxy neighbours on shape measurement and shear cosmology. Four mechanisms by which neighbours can have a non-negligible influence on shear measurement are identified. These effects, if ignored, would contribute a net multiplicative bias of $m \\sim 0.03 - 0.09$ in DES Y1, though the precise impact will depend on both the measurement code and the selection cuts applied. We use the cosmological inference pipeline of DES Y1 to explore the cosmological implications of neighbour bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude $S_8 \\equiv \\sigma_8 (\\omegam /0.3)^{0.5}$ by $1.5 \\sigma$ towards low values. Finally, we use the Hoopoe simulations to test the effect of neighbour-induced spatial correlations in the multiplicative bias. We find the cosmo logical

How and how much does RAD-seq bias genetic diversity estimates?

Science.gov (United States)

Cariou, Marie; Duret, Laurent; Charlat, Sylvain

2016-11-08

RAD-seq is a powerful tool, increasingly used in population genomics. However, earlier studies have raised red flags regarding possible biases associated with this technique. In particular, polymorphism on restriction sites results in preferential sampling of closely related haplotypes, so that RAD data tends to underestimate genetic diversity. Here we (1) clarify the theoretical basis of this bias, highlighting the potential confounding effects of population structure and selection, (2) confront predictions to real data from in silico digestion of full genomes and (3) provide a proof of concept toward an ABC-based correction of the RAD-seq bias. Under a neutral and panmictic model, we confirm the previously established relationship between the true polymorphism and its RAD-based estimation, showing a more pronounced bias when polymorphism is high. Using more elaborate models, we show that selection, resulting in heterogeneous levels of polymorphism along the genome, exacerbates the bias and leads to a more pronounced underestimation. On the contrary, spatial genetic structure tends to reduce the bias. We confront the neutral and panmictic model to "ideal" empirical data (in silico RAD-sequencing) using full genomes from natural populations of the fruit fly Drosophila melanogaster and the fungus Shizophyllum commune, harbouring respectively moderate and high genetic diversity. In D. melanogaster, predictions fit the model, but the small difference between the true and RAD polymorphism makes this comparison insensitive to deviations from the model. In the highly polymorphic fungus, the model captures a large part of the bias but makes inaccurate predictions. Accordingly, ABC corrections based on this model improve the estimations, albeit with some imprecisions. The RAD-seq underestimation of genetic diversity associated with polymorphism in restriction sites becomes more pronounced when polymorphism is high. In practice, this means that in many systems where

MASKED AREAS IN SHEAR PEAK STATISTICS: A FORWARD MODELING APPROACH

International Nuclear Information System (INIS)

Bard, D.; Kratochvil, J. M.; Dawson, W.

2016-01-01

The statistics of shear peaks have been shown to provide valuable cosmological information beyond the power spectrum, and will be an important constraint of models of cosmology in forthcoming astronomical surveys. Surveys include masked areas due to bright stars, bad pixels etc., which must be accounted for in producing constraints on cosmology from shear maps. We advocate a forward-modeling approach, where the impacts of masking and other survey artifacts are accounted for in the theoretical prediction of cosmological parameters, rather than correcting survey data to remove them. We use masks based on the Deep Lens Survey, and explore the impact of up to 37% of the survey area being masked on LSST and DES-scale surveys. By reconstructing maps of aperture mass the masking effect is smoothed out, resulting in up to 14% smaller statistical uncertainties compared to simply reducing the survey area by the masked area. We show that, even in the presence of large survey masks, the bias in cosmological parameter estimation produced in the forward-modeling process is ≈1%, dominated by bias caused by limited simulation volume. We also explore how this potential bias scales with survey area and evaluate how much small survey areas are impacted by the differences in cosmological structure in the data and simulated volumes, due to cosmic variance

Extended Adaptive Biasing Force Algorithm. An On-the-Fly Implementation for Accurate Free-Energy Calculations.

Science.gov (United States)

Fu, Haohao; Shao, Xueguang; Chipot, Christophe; Cai, Wensheng

2016-08-09

Proper use of the adaptive biasing force (ABF) algorithm in free-energy calculations needs certain prerequisites to be met, namely, that the Jacobian for the metric transformation and its first derivative be available and the coarse variables be independent and fully decoupled from any holonomic constraint or geometric restraint, thereby limiting singularly the field of application of the approach. The extended ABF (eABF) algorithm circumvents these intrinsic limitations by applying the time-dependent bias onto a fictitious particle coupled to the coarse variable of interest by means of a stiff spring. However, with the current implementation of eABF in the popular molecular dynamics engine NAMD, a trajectory-based post-treatment is necessary to derive the underlying free-energy change. Usually, such a posthoc analysis leads to a decrease in the reliability of the free-energy estimates due to the inevitable loss of information, as well as to a drop in efficiency, which stems from substantial read-write accesses to file systems. We have developed a user-friendly, on-the-fly code for performing eABF simulations within NAMD. In the present contribution, this code is probed in eight illustrative examples. The performance of the algorithm is compared with traditional ABF, on the one hand, and the original eABF implementation combined with a posthoc analysis, on the other hand. Our results indicate that the on-the-fly eABF algorithm (i) supplies the correct free-energy landscape in those critical cases where the coarse variables at play are coupled to either each other or to geometric restraints or holonomic constraints, (ii) greatly improves the reliability of the free-energy change, compared to the outcome of a posthoc analysis, and (iii) represents a negligible additional computational effort compared to regular ABF. Moreover, in the proposed implementation, guidelines for choosing two parameters of the eABF algorithm, namely the stiffness of the spring and the mass

Computed and experimental interactions between eddy structure and dispersed particles in developing free shear layers

International Nuclear Information System (INIS)

Buckingham, A.C.; Siekhaus, W.J.; Keller, J.O.; Ellzey, J.; Hubbard, G.; Daily, J.W.

1982-01-01

We are investigating the interactive process between turbulent flow and dispersed phase particles. We are focusing on the mechanisms that appear to result in a reduction of local turbulent intensity and a corresponding reduction in wall heat transfer and subsequent wall erosion in turbulent solid propellant combustion flow. We apply computational simulations and physical experiments specialized to a developing free shear layer over a rearward facing step and over a parallel splitter plate. The flow configuration evolves in a two-dimensional, steady, combustion and non-combustion turbulent free shear mixing region, with and without particle additives. The computational simulations combine three basic components: gas phase Navier-Stokes solutions, Lagrange particle field solutions and a Monte Carlo technique for the random encounters, forces and accelerations between the two fields. We concentrate here on relatively large sized additive particles (of the order of tens of microns to 100 microns mean diameter). We examine their apparent influence in breaking up the larger, energy bearing eddy structures into smaller structures which are more readily dissipated

Simultaneous Estimation of Model State Variables and Observation and Forecast Biases Using a Two-Stage Hybrid Kalman Filter

Science.gov (United States)

Pauwels, V. R. N.; DeLannoy, G. J. M.; Hendricks Franssen, H.-J.; Vereecken, H.

2013-01-01

In this paper, we present a two-stage hybrid Kalman filter to estimate both observation and forecast bias in hydrologic models, in addition to state variables. The biases are estimated using the discrete Kalman filter, and the state variables using the ensemble Kalman filter. A key issue in this multi-component assimilation scheme is the exact partitioning of the difference between observation and forecasts into state, forecast bias and observation bias updates. Here, the error covariances of the forecast bias and the unbiased states are calculated as constant fractions of the biased state error covariance, and the observation bias error covariance is a function of the observation prediction error covariance. In a series of synthetic experiments, focusing on the assimilation of discharge into a rainfall-runoff model, it is shown that both static and dynamic observation and forecast biases can be successfully estimated. The results indicate a strong improvement in the estimation of the state variables and resulting discharge as opposed to the use of a bias-unaware ensemble Kalman filter. Furthermore, minimal code modification in existing data assimilation software is needed to implement the method. The results suggest that a better performance of data assimilation methods should be possible if both forecast and observation biases are taken into account.

Simultaneous estimation of model state variables and observation and forecast biases using a two-stage hybrid Kalman filter

Directory of Open Access Journals (Sweden)

V. R. N. Pauwels

2013-09-01

Full Text Available In this paper, we present a two-stage hybrid Kalman filter to estimate both observation and forecast bias in hydrologic models, in addition to state variables. The biases are estimated using the discrete Kalman filter, and the state variables using the ensemble Kalman filter. A key issue in this multi-component assimilation scheme is the exact partitioning of the difference between observation and forecasts into state, forecast bias and observation bias updates. Here, the error covariances of the forecast bias and the unbiased states are calculated as constant fractions of the biased state error covariance, and the observation bias error covariance is a function of the observation prediction error covariance. In a series of synthetic experiments, focusing on the assimilation of discharge into a rainfall-runoff model, it is shown that both static and dynamic observation and forecast biases can be successfully estimated. The results indicate a strong improvement in the estimation of the state variables and resulting discharge as opposed to the use of a bias-unaware ensemble Kalman filter. Furthermore, minimal code modification in existing data assimilation software is needed to implement the method. The results suggest that a better performance of data assimilation methods should be possible if both forecast and observation biases are taken into account.

Practical estimate of gradient nonlinearity for implementation of apparent diffusion coefficient bias correction.

Science.gov (United States)

Malkyarenko, Dariya I; Chenevert, Thomas L

2014-12-01

To describe an efficient procedure to empirically characterize gradient nonlinearity and correct for the corresponding apparent diffusion coefficient (ADC) bias on a clinical magnetic resonance imaging (MRI) scanner. Spatial nonlinearity scalars for individual gradient coils along superior and right directions were estimated via diffusion measurements of an isotropicic e-water phantom. Digital nonlinearity model from an independent scanner, described in the literature, was rescaled by system-specific scalars to approximate 3D bias correction maps. Correction efficacy was assessed by comparison to unbiased ADC values measured at isocenter. Empirically estimated nonlinearity scalars were confirmed by geometric distortion measurements of a regular grid phantom. The applied nonlinearity correction for arbitrarily oriented diffusion gradients reduced ADC bias from 20% down to 2% at clinically relevant offsets both for isotropic and anisotropic media. Identical performance was achieved using either corrected diffusion-weighted imaging (DWI) intensities or corrected b-values for each direction in brain and ice-water. Direction-average trace image correction was adequate only for isotropic medium. Empiric scalar adjustment of an independent gradient nonlinearity model adequately described DWI bias for a clinical scanner. Observed efficiency of implemented ADC bias correction quantitatively agreed with previous theoretical predictions and numerical simulations. The described procedure provides an independent benchmark for nonlinearity bias correction of clinical MRI scanners.

Free vibration analysis of a cracked shear deformable beam on a two-parameter elastic foundation using a lattice spring model

Science.gov (United States)

Attar, M.; Karrech, A.; Regenauer-Lieb, K.

2014-05-01

The free vibration of a shear deformable beam with multiple open edge cracks is studied using a lattice spring model (LSM). The beam is supported by a so-called two-parameter elastic foundation, where normal and shear foundation stiffnesses are considered. Through application of Timoshenko beam theory, the effects of transverse shear deformation and rotary inertia are taken into account. In the LSM, the beam is discretised into a one-dimensional assembly of segments interacting via rotational and shear springs. These springs represent the flexural and shear stiffnesses of the beam. The supporting action of the elastic foundation is described also by means of normal and shear springs acting on the centres of the segments. The relationship between stiffnesses of the springs and the elastic properties of the one-dimensional structure are identified by comparing the homogenised equations of motion of the discrete system and Timoshenko beam theory.

Estimated strength of shear keys in concrete dams

Energy Technology Data Exchange (ETDEWEB)

Curtis, D.D. [Hatch Energy, Niagara Falls, ON (Canada); Lum, K.K.Y. [BC Hydro, Burnaby, BC (Canada)

2008-07-01

BC Hydro requested that Hatch Energy review the seismic stability of Ruskin Dam which was constructed in 1930 at Hayward Lake in British Columbia. The concrete gravity dam is founded nearly entirely on rock in a narrow valley. The vertical joints between blocks are keyed and grouted. The strength of the shear keys was assessed when a non-linear finite element model found that significant forces were being transferred laterally to the abutments during an earthquake. The lateral transfer of loads to the abutment relies on the strength of the shear keys. The dynamic finite element analysis was used to determine the stability of the dam. A review of the shear strength measurements reported in literature showed that the measurements compared well to those obtained by BC Hydro from cores taken from Ruskin Dam. The cohesive strength obtained using the Griffith failure criteria was also in good agreement with both sets of measurements. A simple ultimate shear strength equation was developed using the Mohr-Coulomb failure criteria to determine combined cohesive and frictional strength of shear keys. Safety factors of 2.0 for static loads and 1.5 for seismic loads were proposed to reduce the ultimate strength to allowable values. It was concluded that given the relatively high shear strength established for the shear keys, the abutment rock or dam/abutment contact will control the amount of load which can arch to the abutments. 8 refs., 4 tabs., 5 figs.

Adjusting forest density estimates for surveyor bias in historical tree surveys

Science.gov (United States)

Brice B. Hanberry; Jian Yang; John M. Kabrick; Hong S. He

2012-01-01

The U.S. General Land Office surveys, conducted between the late 1700s to early 1900s, provide records of trees prior to widespread European and American colonial settlement. However, potential and documented surveyor bias raises questions about the reliability of historical tree density estimates and other metrics based on density estimated from these records. In this...

Estimating the price elasticity of beer: meta-analysis of data with heterogeneity, dependence, and publication bias.

Science.gov (United States)

Nelson, Jon P

2014-01-01

Precise estimates of price elasticities are important for alcohol tax policy. Using meta-analysis, this paper corrects average beer elasticities for heterogeneity, dependence, and publication selection bias. A sample of 191 estimates is obtained from 114 primary studies. Simple and weighted means are reported. Dependence is addressed by restricting number of estimates per study, author-restricted samples, and author-specific variables. Publication bias is addressed using funnel graph, trim-and-fill, and Egger's intercept model. Heterogeneity and selection bias are examined jointly in meta-regressions containing moderator variables for econometric methodology, primary data, and precision of estimates. Results for fixed- and random-effects regressions are reported. Country-specific effects and sample time periods are unimportant, but several methodology variables help explain the dispersion of estimates. In models that correct for selection bias and heterogeneity, the average beer price elasticity is about -0.20, which is less elastic by 50% compared to values commonly used in alcohol tax policy simulations. Copyright © 2013 Elsevier B.V. All rights reserved.

KiDS-450: cosmological constraints from weak-lensing peak statistics - II: Inference from shear peaks using N-body simulations

Science.gov (United States)

Martinet, Nicolas; Schneider, Peter; Hildebrandt, Hendrik; Shan, HuanYuan; Asgari, Marika; Dietrich, Jörg P.; Harnois-Déraps, Joachim; Erben, Thomas; Grado, Aniello; Heymans, Catherine; Hoekstra, Henk; Klaes, Dominik; Kuijken, Konrad; Merten, Julian; Nakajima, Reiko

2018-02-01

We study the statistics of peaks in a weak-lensing reconstructed mass map of the first 450 deg2 of the Kilo Degree Survey (KiDS-450). The map is computed with aperture masses directly applied to the shear field with an NFW-like compensated filter. We compare the peak statistics in the observations with that of simulations for various cosmologies to constrain the cosmological parameter S_8 = σ _8 √{Ω _m/0.3}, which probes the (Ωm, σ8) plane perpendicularly to its main degeneracy. We estimate S8 = 0.750 ± 0.059, using peaks in the signal-to-noise range 0 ≤ S/N ≤ 4, and accounting for various systematics, such as multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic alignment, and shear-position coupling. These constraints are ˜ 25 per cent tighter than the constraints from the high significance peaks alone (3 ≤ S/N ≤ 4) which typically trace single-massive haloes. This demonstrates the gain of information from low-S/N peaks. However, we find that including S/N KiDS-450. Combining shear peaks with non-tomographic measurements of the shear two-point correlation functions yields a ˜20 per cent improvement in the uncertainty on S8 compared to the shear two-point correlation functions alone, highlighting the great potential of peaks as a cosmological probe.

Bias Corrections for Standardized Effect Size Estimates Used with Single-Subject Experimental Designs

Science.gov (United States)

Ugille, Maaike; Moeyaert, Mariola; Beretvas, S. Natasha; Ferron, John M.; Van den Noortgate, Wim

2014-01-01

A multilevel meta-analysis can combine the results of several single-subject experimental design studies. However, the estimated effects are biased if the effect sizes are standardized and the number of measurement occasions is small. In this study, the authors investigated 4 approaches to correct for this bias. First, the standardized effect…

A bias correction for covariance estimators to improve inference with generalized estimating equations that use an unstructured correlation matrix.

Science.gov (United States)

Westgate, Philip M

2013-07-20

Generalized estimating equations (GEEs) are routinely used for the marginal analysis of correlated data. The efficiency of GEE depends on how closely the working covariance structure resembles the true structure, and therefore accurate modeling of the working correlation of the data is important. A popular approach is the use of an unstructured working correlation matrix, as it is not as restrictive as simpler structures such as exchangeable and AR-1 and thus can theoretically improve efficiency. However, because of the potential for having to estimate a large number of correlation parameters, variances of regression parameter estimates can be larger than theoretically expected when utilizing the unstructured working correlation matrix. Therefore, standard error estimates can be negatively biased. To account for this additional finite-sample variability, we derive a bias correction that can be applied to typical estimators of the covariance matrix of parameter estimates. Via simulation and in application to a longitudinal study, we show that our proposed correction improves standard error estimation and statistical inference. Copyright © 2012 John Wiley & Sons, Ltd.

Estimating Free and Added Sugar Intakes in New Zealand

Directory of Open Access Journals (Sweden)

Rachael Kibblewhite

2017-11-01

Full Text Available The reduction of free or added sugar intake (sugars added to food and drinks as a sweetener is almost universally recommended to reduce the risk of obesity-related diseases and dental caries. The World Health Organisation recommends intakes of free sugars of less than 10% of energy intake. However, estimating and monitoring intakes at the population level is challenging because free sugars cannot be analytically distinguished from naturally occurring sugars and most national food composition databases do not include data on free or added sugars. We developed free and added sugar estimates for the New Zealand (NZ food composition database (FOODfiles 2010 by adapting a method developed for Australia. We reanalyzed the 24 h recall dietary data collected for 4721 adults aged 15 years and over participating in the nationally representative 2008/09 New Zealand Adult Nutrition Survey to estimate free and added sugar intakes. The median estimated intake of free and added sugars was 57 and 49 g/day respectively and 42% of adults consumed less than 10% of their energy intake from free sugars. This approach provides more direct estimates of the free and added sugar contents of New Zealand foods than previously available and will enable monitoring of adherence to free sugar intake guidelines in future.

Estimating Free and Added Sugar Intakes in New Zealand.

Science.gov (United States)

Kibblewhite, Rachael; Nettleton, Alice; McLean, Rachael; Haszard, Jillian; Fleming, Elizabeth; Kruimer, Devonia; Te Morenga, Lisa

2017-11-27

The reduction of free or added sugar intake (sugars added to food and drinks as a sweetener) is almost universally recommended to reduce the risk of obesity-related diseases and dental caries. The World Health Organisation recommends intakes of free sugars of less than 10% of energy intake. However, estimating and monitoring intakes at the population level is challenging because free sugars cannot be analytically distinguished from naturally occurring sugars and most national food composition databases do not include data on free or added sugars. We developed free and added sugar estimates for the New Zealand (NZ) food composition database (FOODfiles 2010) by adapting a method developed for Australia. We reanalyzed the 24 h recall dietary data collected for 4721 adults aged 15 years and over participating in the nationally representative 2008/09 New Zealand Adult Nutrition Survey to estimate free and added sugar intakes. The median estimated intake of free and added sugars was 57 and 49 g/day respectively and 42% of adults consumed less than 10% of their energy intake from free sugars. This approach provides more direct estimates of the free and added sugar contents of New Zealand foods than previously available and will enable monitoring of adherence to free sugar intake guidelines in future.

Estimating Free and Added Sugar Intakes in New Zealand

Science.gov (United States)

Kibblewhite, Rachael; Nettleton, Alice; McLean, Rachael; Haszard, Jillian; Fleming, Elizabeth; Kruimer, Devonia

2017-01-01

The reduction of free or added sugar intake (sugars added to food and drinks as a sweetener) is almost universally recommended to reduce the risk of obesity-related diseases and dental caries. The World Health Organisation recommends intakes of free sugars of less than 10% of energy intake. However, estimating and monitoring intakes at the population level is challenging because free sugars cannot be analytically distinguished from naturally occurring sugars and most national food composition databases do not include data on free or added sugars. We developed free and added sugar estimates for the New Zealand (NZ) food composition database (FOODfiles 2010) by adapting a method developed for Australia. We reanalyzed the 24 h recall dietary data collected for 4721 adults aged 15 years and over participating in the nationally representative 2008/09 New Zealand Adult Nutrition Survey to estimate free and added sugar intakes. The median estimated intake of free and added sugars was 57 and 49 g/day respectively and 42% of adults consumed less than 10% of their energy intake from free sugars. This approach provides more direct estimates of the free and added sugar contents of New Zealand foods than previously available and will enable monitoring of adherence to free sugar intake guidelines in future. PMID:29186927

Estimation of satellite position, clock and phase bias corrections

Science.gov (United States)

Henkel, Patrick; Psychas, Dimitrios; Günther, Christoph; Hugentobler, Urs

2018-05-01

Precise point positioning with integer ambiguity resolution requires precise knowledge of satellite position, clock and phase bias corrections. In this paper, a method for the estimation of these parameters with a global network of reference stations is presented. The method processes uncombined and undifferenced measurements of an arbitrary number of frequencies such that the obtained satellite position, clock and bias corrections can be used for any type of differenced and/or combined measurements. We perform a clustering of reference stations. The clustering enables a common satellite visibility within each cluster and an efficient fixing of the double difference ambiguities within each cluster. Additionally, the double difference ambiguities between the reference stations of different clusters are fixed. We use an integer decorrelation for ambiguity fixing in dense global networks. The performance of the proposed method is analysed with both simulated Galileo measurements on E1 and E5a and real GPS measurements of the IGS network. We defined 16 clusters and obtained satellite position, clock and phase bias corrections with a precision of better than 2 cm.

Bias analysis applied to Agricultural Health Study publications to estimate non-random sources of uncertainty.

Science.gov (United States)

Lash, Timothy L

2007-11-26

The associations of pesticide exposure with disease outcomes are estimated without the benefit of a randomized design. For this reason and others, these studies are susceptible to systematic errors. I analyzed studies of the associations between alachlor and glyphosate exposure and cancer incidence, both derived from the Agricultural Health Study cohort, to quantify the bias and uncertainty potentially attributable to systematic error. For each study, I identified the prominent result and important sources of systematic error that might affect it. I assigned probability distributions to the bias parameters that allow quantification of the bias, drew a value at random from each assigned distribution, and calculated the estimate of effect adjusted for the biases. By repeating the draw and adjustment process over multiple iterations, I generated a frequency distribution of adjusted results, from which I obtained a point estimate and simulation interval. These methods were applied without access to the primary record-level dataset. The conventional estimates of effect associating alachlor and glyphosate exposure with cancer incidence were likely biased away from the null and understated the uncertainty by quantifying only random error. For example, the conventional p-value for a test of trend in the alachlor study equaled 0.02, whereas fewer than 20% of the bias analysis iterations yielded a p-value of 0.02 or lower. Similarly, the conventional fully-adjusted result associating glyphosate exposure with multiple myleoma equaled 2.6 with 95% confidence interval of 0.7 to 9.4. The frequency distribution generated by the bias analysis yielded a median hazard ratio equal to 1.5 with 95% simulation interval of 0.4 to 8.9, which was 66% wider than the conventional interval. Bias analysis provides a more complete picture of true uncertainty than conventional frequentist statistical analysis accompanied by a qualitative description of study limitations. The latter approach is

Bias analysis applied to Agricultural Health Study publications to estimate non-random sources of uncertainty

Directory of Open Access Journals (Sweden)

Lash Timothy L

2007-11-01

Full Text Available Abstract Background The associations of pesticide exposure with disease outcomes are estimated without the benefit of a randomized design. For this reason and others, these studies are susceptible to systematic errors. I analyzed studies of the associations between alachlor and glyphosate exposure and cancer incidence, both derived from the Agricultural Health Study cohort, to quantify the bias and uncertainty potentially attributable to systematic error. Methods For each study, I identified the prominent result and important sources of systematic error that might affect it. I assigned probability distributions to the bias parameters that allow quantification of the bias, drew a value at random from each assigned distribution, and calculated the estimate of effect adjusted for the biases. By repeating the draw and adjustment process over multiple iterations, I generated a frequency distribution of adjusted results, from which I obtained a point estimate and simulation interval. These methods were applied without access to the primary record-level dataset. Results The conventional estimates of effect associating alachlor and glyphosate exposure with cancer incidence were likely biased away from the null and understated the uncertainty by quantifying only random error. For example, the conventional p-value for a test of trend in the alachlor study equaled 0.02, whereas fewer than 20% of the bias analysis iterations yielded a p-value of 0.02 or lower. Similarly, the conventional fully-adjusted result associating glyphosate exposure with multiple myleoma equaled 2.6 with 95% confidence interval of 0.7 to 9.4. The frequency distribution generated by the bias analysis yielded a median hazard ratio equal to 1.5 with 95% simulation interval of 0.4 to 8.9, which was 66% wider than the conventional interval. Conclusion Bias analysis provides a more complete picture of true uncertainty than conventional frequentist statistical analysis accompanied by a

A new method for estimating UV fluxes at ground level in cloud-free conditions

Science.gov (United States)

Wandji Nyamsi, William; Pitkänen, Mikko R. A.; Aoun, Youva; Blanc, Philippe; Heikkilä, Anu; Lakkala, Kaisa; Bernhard, Germar; Koskela, Tapani; Lindfors, Anders V.; Arola, Antti; Wald, Lucien

2017-12-01

A new method has been developed to estimate the global and direct solar irradiance in the UV-A and UV-B at ground level in cloud-free conditions. It is based on a resampling technique applied to the results of the k-distribution method and the correlated-k approximation of Kato et al. (1999) over the UV band. Its inputs are the aerosol properties and total column ozone that are produced by the Copernicus Atmosphere Monitoring Service (CAMS). The estimates from this new method have been compared to instantaneous measurements of global UV irradiances made in cloud-free conditions at five stations at high latitudes in various climates. For the UV-A irradiance, the bias ranges between -0.8 W m-2 (-3 % of the mean of all data) and -0.2 W m-2 (-1 %). The root mean square error (RMSE) ranges from 1.1 W m-2 (6 %) to 1.9 W m-2 (9 %). The coefficient of determination R2 is greater than 0.98. The bias for UV-B is between -0.04 W m-2 (-4 %) and 0.08 W m-2 (+13 %) and the RMSE is 0.1 W m-2 (between 12 and 18 %). R2 ranges between 0.97 and 0.99. This work demonstrates the quality of the proposed method combined with the CAMS products. Improvements, especially in the modeling of the reflectivity of the Earth's surface in the UV region, are necessary prior to its inclusion into an operational tool.

Effects of social organization, trap arrangement and density, sampling scale, and population density on bias in population size estimation using some common mark-recapture estimators.

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Manan Gupta

Full Text Available Mark-recapture estimators are commonly used for population size estimation, and typically yield unbiased estimates for most solitary species with low to moderate home range sizes. However, these methods assume independence of captures among individuals, an assumption that is clearly violated in social species that show fission-fusion dynamics, such as the Asian elephant. In the specific case of Asian elephants, doubts have been raised about the accuracy of population size estimates. More importantly, the potential problem for the use of mark-recapture methods posed by social organization in general has not been systematically addressed. We developed an individual-based simulation framework to systematically examine the potential effects of type of social organization, as well as other factors such as trap density and arrangement, spatial scale of sampling, and population density, on bias in population sizes estimated by POPAN, Robust Design, and Robust Design with detection heterogeneity. In the present study, we ran simulations with biological, demographic and ecological parameters relevant to Asian elephant populations, but the simulation framework is easily extended to address questions relevant to other social species. We collected capture history data from the simulations, and used those data to test for bias in population size estimation. Social organization significantly affected bias in most analyses, but the effect sizes were variable, depending on other factors. Social organization tended to introduce large bias when trap arrangement was uniform and sampling effort was low. POPAN clearly outperformed the two Robust Design models we tested, yielding close to zero bias if traps were arranged at random in the study area, and when population density and trap density were not too low. Social organization did not have a major effect on bias for these parameter combinations at which POPAN gave more or less unbiased population size estimates

CFD simulation of estimating critical shear stress for cleaning flat ...

Indian Academy of Sciences (India)

Sumit Kawale

2017-11-22

Nov 22, 2017 ... Jet impingement; wall shear stress; cleaning of flat plate; turbulence model; critical shear stress; ... On comparing the theoretical predictions with wall shear ... distance and Reynolds number on peak value of local shear stress ...

Examples of invasive and non-invasive methods for estimation of shear-wave velocity profile in Bucharest

International Nuclear Information System (INIS)

Aldea, A.; Albota, E.; Yamanaka, H.; Fukumoto, S.; Poiata, N.

2007-01-01

The estimation of subsurface shear-wave velocity is of major importance for understanding and modelling site-response and surface ground motion. The shear-wave velocity profile strongly influence the shear-wave part of the seismic motion that proved to be the most damaging one. The improvement of input seismic ground motion for design is one of the long-term objectives within the Japan International Cooperation Agency (JICA) Project in Romania. Two approaches were used: installation of a digital seismic network and soil investigations (in situ and in laboratory). National Center for Seismic Risk Reduction (NCSRR, Romania), the implementing agency of JICA Project, performed these activities in cooperation with Japanese partner institutions, and an efficient know-how transfer was achieved. Between the soil investigation activities, a special importance was given to the estimation of shear-wave velocity profile. The present paper presents results from PS logging tests at NCSRR seismic station sites, and from single-station and array microtremor measurements. Other results from PS logging tests, surface-wave method and in situ and laboratory geotechnical investigations are presented in other papers in these proceedings. In future, a joint-collaborative effort of Romanian institutions may allow an improved characterisation of the soil profile beneath Bucharest. (authors)

Competing risk bias was common in Kaplan-Meier risk estimates published in prominent medical journals.

Science.gov (United States)

van Walraven, Carl; McAlister, Finlay A

2016-01-01

Risk estimates from Kaplan-Meier curves are well known to medical researchers, reviewers, and editors. In this study, we determined the proportion of Kaplan-Meier analyses published in prominent medical journals that are potentially biased because of competing events ("competing risk bias"). We randomly selected 100 studies that had at least one Kaplan-Meier analysis and were recently published in prominent medical journals. Susceptibility to competing risk bias was determined by examining the outcome and potential competing events. In susceptible studies, bias was quantified using a previously validated prediction model when the number of outcomes and competing events were given. Forty-six studies (46%) contained Kaplan-Meier analyses susceptible to competing risk bias. Sixteen studies (34.8%) susceptible to competing risk cited the number of outcomes and competing events; in six of these studies (6/16, 37.5%), the outcome risk from the Kaplan-Meier estimate (relative to the true risk) was biased upward by 10% or more. Almost half of Kaplan-Meier analyses published in medical journals are susceptible to competing risk bias and may overestimate event risk. This bias was found to be quantitatively important in a third of such studies. Copyright © 2016 Elsevier Inc. All rights reserved.

Improving RNA-Seq expression estimates by correcting for fragment bias

Science.gov (United States)

2011-01-01

The biochemistry of RNA-Seq library preparation results in cDNA fragments that are not uniformly distributed within the transcripts they represent. This non-uniformity must be accounted for when estimating expression levels, and we show how to perform the needed corrections using a likelihood based approach. We find improvements in expression estimates as measured by correlation with independently performed qRT-PCR and show that correction of bias leads to improved replicability of results across libraries and sequencing technologies. PMID:21410973

FRACTURE MECHANICS APPROACH TO ESTIMATE FATIGUE LIVES OF WELDED LAP-SHEAR SPECIMENS

Energy Technology Data Exchange (ETDEWEB)

Lam, P.; Michigan, J.

2014-04-25

A full range of stress intensity factor solutions for a kinked crack is developed as a function of weld width and the sheet thickness. When used with the associated main crack solutions (global stress intensity factors) in terms of the applied load and specimen geometry, the fatigue lives can be estimated for the laser-welded lap-shear specimens. The estimations are in good agreement with the experimental data. A classical solution for an infinitesimal kink is also employed in the approach. However, the life predictions tend to overestimate the actual fatigue lives. The traditional life estimations with the structural stress along with the experimental stress-fatigue life data (S-N curve) are also provided. In this case, the estimations only agree with the experimental data under higher load conditions.

Improving real-time estimation of heavy-to-extreme precipitation using rain gauge data via conditional bias-penalized optimal estimation

Science.gov (United States)

Seo, Dong-Jun; Siddique, Ridwan; Zhang, Yu; Kim, Dongsoo

2014-11-01

A new technique for gauge-only precipitation analysis for improved estimation of heavy-to-extreme precipitation is described and evaluated. The technique is based on a novel extension of classical optimal linear estimation theory in which, in addition to error variance, Type-II conditional bias (CB) is explicitly minimized. When cast in the form of well-known kriging, the methodology yields a new kriging estimator, referred to as CB-penalized kriging (CBPK). CBPK, however, tends to yield negative estimates in areas of no or light precipitation. To address this, an extension of CBPK, referred to herein as extended conditional bias penalized kriging (ECBPK), has been developed which combines the CBPK estimate with a trivial estimate of zero precipitation. To evaluate ECBPK, we carried out real-world and synthetic experiments in which ECBPK and the gauge-only precipitation analysis procedure used in the NWS's Multisensor Precipitation Estimator (MPE) were compared for estimation of point precipitation and mean areal precipitation (MAP), respectively. The results indicate that ECBPK improves hourly gauge-only estimation of heavy-to-extreme precipitation significantly. The improvement is particularly large for estimation of MAP for a range of combinations of basin size and rain gauge network density. This paper describes the technique, summarizes the results and shares ideas for future research.

Peak Measurement for Vancomycin AUC Estimation in Obese Adults Improves Precision and Lowers Bias.

Science.gov (United States)

Pai, Manjunath P; Hong, Joseph; Krop, Lynne

2017-04-01

Vancomycin area under the curve (AUC) estimates may be skewed in obese adults due to weight-dependent pharmacokinetic parameters. We demonstrate that peak and trough measurements reduce bias and improve the precision of vancomycin AUC estimates in obese adults ( n = 75) and validate this in an independent cohort ( n = 31). The precision and mean percent bias of Bayesian vancomycin AUC estimates are comparable between covariate-dependent ( R 2 = 0.774, 3.55%) and covariate-independent ( R 2 = 0.804, 3.28%) models when peaks and troughs are measured but not when measurements are restricted to troughs only ( R 2 = 0.557, 15.5%). Copyright © 2017 American Society for Microbiology.

How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model.

Science.gov (United States)

Starrfelt, Jostein; Liow, Lee Hsiang

2016-04-05

The fossil record is a rich source of information about biological diversity in the past. However, the fossil record is not only incomplete but has also inherent biases due to geological, physical, chemical and biological factors. Our knowledge of past life is also biased because of differences in academic and amateur interests and sampling efforts. As a result, not all individuals or species that lived in the past are equally likely to be discovered at any point in time or space. To reconstruct temporal dynamics of diversity using the fossil record, biased sampling must be explicitly taken into account. Here, we introduce an approach that uses the variation in the number of times each species is observed in the fossil record to estimate both sampling bias and true richness. We term our technique TRiPS (True Richness estimated using a Poisson Sampling model) and explore its robustness to violation of its assumptions via simulations. We then venture to estimate sampling bias and absolute species richness of dinosaurs in the geological stages of the Mesozoic. Using TRiPS, we estimate that 1936 (1543-2468) species of dinosaurs roamed the Earth during the Mesozoic. We also present improved estimates of species richness trajectories of the three major dinosaur clades: the sauropodomorphs, ornithischians and theropods, casting doubt on the Jurassic-Cretaceous extinction event and demonstrating that all dinosaur groups are subject to considerable sampling bias throughout the Mesozoic. © 2016 The Authors.

Effect of shear stress and free radicals induced by ultrasound on erythrocytes

International Nuclear Information System (INIS)

Kondo, T.; Fukushima, Y.; Kon, H.; Riesz, P.

1989-01-01

The present study was undertaken to elucidate the mechanism of hemolysis induced by ultrasound. Ar or N2O gas was used to distinguish between cavitation with or without free radical formation (hydroxyl radicals and hydrogen atoms). Free radical formation was examined by the method of spin trapping combined with ESR. After sonication of erythrocyte suspensions, several structural and functional parameters of the erythrocyte membrane--hemolysis, membrane fluidity, membrane permeability, and membrane deformability--were examined. Although free radical formation was observed in the erythrocyte suspensions sonicated in the presence of Ar, no free radical formation was observed in the presence of N2O. However, the hemolysis behavior induced by ultrasound was similar in the presence of Ar or N2O. The membrane fluidity, permeability, and deformability of the remaining unlysed erythrocytes after sonication in the presence of Ar or N2O were unchanged and identical to those of the control cells. On the other hand, after gamma irradiation (700 Gy), the hemolysis behavior was quite different from that after sonication, and the membrane properties were significantly changed. These results suggest that hemolysis induced by sonication was due to mechanical shearing stress arising from cavitation, and that the membrane integrity of the remaining erythrocytes after sonication was the same as that of control cells without sonication. The triatomic gas, N2O, may be useful for ultrasonically disrupting cells without accompanying free radical formation

Comparison of direct shear and simple shear responses of municipal solid waste in USA

KAUST Repository

Fei, Xunchang; Zekkos, Dimitrios

2017-01-01

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (τ ) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between

Learning free energy landscapes using artificial neural networks.

Science.gov (United States)

Sidky, Hythem; Whitmer, Jonathan K

2018-03-14

Existing adaptive bias techniques, which seek to estimate free energies and physical properties from molecular simulations, are limited by their reliance on fixed kernels or basis sets which hinder their ability to efficiently conform to varied free energy landscapes. Further, user-specified parameters are in general non-intuitive yet significantly affect the convergence rate and accuracy of the free energy estimate. Here we propose a novel method, wherein artificial neural networks (ANNs) are used to develop an adaptive biasing potential which learns free energy landscapes. We demonstrate that this method is capable of rapidly adapting to complex free energy landscapes and is not prone to boundary or oscillation problems. The method is made robust to hyperparameters and overfitting through Bayesian regularization which penalizes network weights and auto-regulates the number of effective parameters in the network. ANN sampling represents a promising innovative approach which can resolve complex free energy landscapes in less time than conventional approaches while requiring minimal user input.

Learning free energy landscapes using artificial neural networks

Science.gov (United States)

Sidky, Hythem; Whitmer, Jonathan K.

2018-03-01

Existing adaptive bias techniques, which seek to estimate free energies and physical properties from molecular simulations, are limited by their reliance on fixed kernels or basis sets which hinder their ability to efficiently conform to varied free energy landscapes. Further, user-specified parameters are in general non-intuitive yet significantly affect the convergence rate and accuracy of the free energy estimate. Here we propose a novel method, wherein artificial neural networks (ANNs) are used to develop an adaptive biasing potential which learns free energy landscapes. We demonstrate that this method is capable of rapidly adapting to complex free energy landscapes and is not prone to boundary or oscillation problems. The method is made robust to hyperparameters and overfitting through Bayesian regularization which penalizes network weights and auto-regulates the number of effective parameters in the network. ANN sampling represents a promising innovative approach which can resolve complex free energy landscapes in less time than conventional approaches while requiring minimal user input.

Estimated time of arrival and debiasing the time saving bias.

Science.gov (United States)

Eriksson, Gabriella; Patten, Christopher J D; Svenson, Ola; Eriksson, Lars

2015-01-01

The time saving bias predicts that the time saved when increasing speed from a high speed is overestimated, and underestimated when increasing speed from a slow speed. In a questionnaire, time saving judgements were investigated when information of estimated time to arrival was provided. In an active driving task, an alternative meter indicating the inverted speed was used to debias judgements. The simulated task was to first drive a distance at a given speed, and then drive the same distance again at the speed the driver judged was required to gain exactly 3 min in travel time compared with the first drive. A control group performed the same task with a speedometer and saved less than the targeted 3 min when increasing speed from a high speed, and more than 3 min when increasing from a low speed. Participants in the alternative meter condition were closer to the target. The two studies corroborate a time saving bias and show that biased intuitive judgements can be debiased by displaying the inverted speed. Practitioner Summary: Previous studies have shown a cognitive bias in judgements of the time saved by increasing speed. This simulator study aims to improve driver judgements by introducing a speedometer indicating the inverted speed in active driving. The results show that the bias can be reduced by presenting the inverted speed and this finding can be used when designing in-car information systems.

Thermophysical Property Estimation by Transient Experiments: The Effect of a Biased Initial Temperature Distribution

Directory of Open Access Journals (Sweden)

Federico Scarpa

2015-01-01

Full Text Available The identification of thermophysical properties of materials in dynamic experiments can be conveniently performed by the inverse solution of the associated heat conduction problem (IHCP. The inverse technique demands the knowledge of the initial temperature distribution within the material. As only a limited number of temperature sensors (or no sensor at all are arranged inside the test specimen, the knowledge of the initial temperature distribution is affected by some uncertainty. This uncertainty, together with other possible sources of bias in the experimental procedure, will propagate in the estimation process and the accuracy of the reconstructed thermophysical property values could deteriorate. In this work the effect on the estimated thermophysical properties due to errors in the initial temperature distribution is investigated along with a practical method to quantify this effect. Furthermore, a technique for compensating this kind of bias is proposed. The method consists in including the initial temperature distribution among the unknown functions to be estimated. In this way the effect of the initial bias is removed and the accuracy of the identified thermophysical property values is highly improved.

Partial verification bias and incorporation bias affected accuracy estimates of diagnostic studies for biomarkers that were part of an existing composite gold standard.

Science.gov (United States)

Karch, Annika; Koch, Armin; Zapf, Antonia; Zerr, Inga; Karch, André

2016-10-01

To investigate how choice of gold standard biases estimates of sensitivity and specificity in studies reassessing the diagnostic accuracy of biomarkers that are already part of a lifetime composite gold standard (CGS). We performed a simulation study based on the real-life example of the biomarker "protein 14-3-3" used for diagnosing Creutzfeldt-Jakob disease. Three different types of gold standard were compared: perfect gold standard "autopsy" (available in a small fraction only; prone to partial verification bias), lifetime CGS (including the biomarker under investigation; prone to incorporation bias), and "best available" gold standard (autopsy if available, otherwise CGS). Sensitivity was unbiased when comparing 14-3-3 with autopsy but overestimated when using CGS or "best available" gold standard. Specificity of 14-3-3 was underestimated in scenarios comparing 14-3-3 with autopsy (up to 24%). In contrast, overestimation (up to 20%) was observed for specificity compared with CGS; this could be reduced to 0-10% when using the "best available" gold standard. Choice of gold standard affects considerably estimates of diagnostic accuracy. Using the "best available" gold standard (autopsy where available, otherwise CGS) leads to valid estimates of specificity, whereas sensitivity is estimated best when tested against autopsy alone. Copyright © 2016 Elsevier Inc. All rights reserved.

CPI Bias in Korea

Directory of Open Access Journals (Sweden)

Chul Chung

2007-12-01

Full Text Available We estimate the CPI bias in Korea by employing the approach of Engel’s Law as suggested by Hamilton (2001. This paper is the first attempt to estimate the bias using Korean panel data, Korean Labor and Income Panel Study(KLIPS. Following Hamilton’s model with non­linear specification correction, our estimation result shows that the cumulative CPI bias over the sample period (2000-2005 was 0.7 percent annually. This CPI bias implies that about 21 percent of the inflation rate during the period can be attributed to the bias. In light of purchasing power parity, we provide an interpretation of the estimated bias.

Absolute/convective secondary instabilities and the role of confinement in free shear layers

Science.gov (United States)

Arratia, Cristóbal; Mowlavi, Saviz; Gallaire, François

2018-05-01

We study the linear spatiotemporal stability of an infinite row of equal point vortices under symmetric confinement between parallel walls. These rows of vortices serve to model the secondary instability leading to the merging of consecutive (Kelvin-Helmholtz) vortices in free shear layers, allowing us to study how confinement limits the growth of shear layers through vortex pairings. Using a geometric construction akin to a Legendre transform on the dispersion relation, we compute the growth rate of the instability in different reference frames as a function of the frame velocity with respect to the vortices. This approach is verified and complemented with numerical computations of the linear impulse response, fully characterizing the absolute/convective nature of the instability. Similar to results by Healey on the primary instability of parallel tanh profiles [J. Fluid Mech. 623, 241 (2009), 10.1017/S0022112008005284], we observe a range of confinement in which absolute instability is promoted. For a parallel shear layer with prescribed confinement and mixing length, the threshold for absolute/convective instability of the secondary pairing instability depends on the separation distance between consecutive vortices, which is physically determined by the wavelength selected by the previous (primary or pairing) instability. In the presence of counterflow and moderate to weak confinement, small (large) wavelength of the vortex row leads to absolute (convective) instability. While absolute secondary instabilities in spatially developing flows have been previously related to an abrupt transition to a complex behavior, this secondary pairing instability regenerates the flow with an increased wavelength, eventually leading to a convectively unstable row of vortices. We argue that since the primary instability remains active for large wavelengths, a spatially developing shear layer can directly saturate on the wavelength of such a convectively unstable row, by

Considerations about expected a posteriori estimation in adaptive testing: adaptive a priori, adaptive correction for bias, and adaptive integration interval.

Science.gov (United States)

Raiche, Gilles; Blais, Jean-Guy

2009-01-01

In a computerized adaptive test, we would like to obtain an acceptable precision of the proficiency level estimate using an optimal number of items. Unfortunately, decreasing the number of items is accompanied by a certain degree of bias when the true proficiency level differs significantly from the a priori estimate. The authors suggest that it is possible to reduced the bias, and even the standard error of the estimate, by applying to each provisional estimation one or a combination of the following strategies: adaptive correction for bias proposed by Bock and Mislevy (1982), adaptive a priori estimate, and adaptive integration interval.

Estimation of gas wall shear stress in horizontal stratified gas-liquid pipe flow

International Nuclear Information System (INIS)

Newton, C.H.; Behnia, M.

1996-01-01

Two-phase pipe flows occur in many industrial applications, such as condensers and evaporators, chemical processing equipment, nuclear reactors, and oil pipelines. A variety of basic mechanistic flow models for predicting the pressure gradient and liquid loading characteristics of these types of flows to assist in design calculations has emerged over the past two decades, especially for the stratified and slug flow regimes. These models generally rely on a number of basic assumptions and empirical closure equations. Possibly the most notable of these relates to the evaluation of interfacial shear stresses. However, one of the most important yet least discussed assumptions used in most of these models is that the phase wall shear stresses can be accurately estimated from correlations developed for single-phase pipe flows. The object of this article is to present measurements of gas wall shear up to locations in close proximity to the gas-liquid interface for a variety of interface conditions in developed flow, and to determine the effects of the interface on average gas wall friction factors. In this context the interface may be smooth, rippled or wavy

Platelet-free shear flow assay facilitates analysis of shear-dependent functions of VWF and ADAMTS13.

Science.gov (United States)

Kraus, Emma; Kraus, Kristina; Obser, Tobias; Oyen, Florian; Klemm, Ulrike; Schneppenheim, Reinhard; Brehm, Maria A

2014-12-01

The multimeric form of von Willebrand factor (VWF), is the largest soluble protein in mammals and exhibits a multidomain structure resulting in multiple functions. Upon agonist stimulation endothelial cells secrete VWF multimers from Weibel-Palade bodies into the blood stream where VWF plays an essential role in platelet-dependent primary hemostasis. Elongation of VWF strings on the cells' surface leads to accessibility of VWF binding sites for proteins, such as platelet membrane glycoprotein Ib. The prothrombotic strings are size-regulated by the metalloprotease ADAMTS13 by shear force-activated proteolytic cleavage. VWF string formation was induced by histamine stimulation of HUVEC cells under unidirectional shear flow and VWF strings were detected employing the VWF binding peptide of platelet glycoprotein Ib coupled to latex beads. VWF strings were then used as substrate for kinetic studies of recombinant and plasma ADAMTS13. To investigate specific aspects of the shear-dependent functions of VWF and ADAMTS13, we developed a shear flow assay that allows observation of VWF string formation and their degradation by ADAMTS13 without the need for isolated platelets. Our assay specifically detects VWF strings, can be coupled with fluorescent applications and allows semi-automated, quantitative assessment of recombinant and plasma ADAMTS13 activity. Our assay may serve as a valuable research tool to investigate the biochemical characteristics of VWF and ADAMTS13 under shear flow and could complement diagnostics of von Willebrand Disease and Thrombotic Thrombocytopenic Purpura as it allows detection of shear flow-dependent dysfunction of VWD-associated VWF mutants as well as TTP-associated ADAMTS13 mutants. Copyright © 2014 Elsevier Ltd. All rights reserved.

Estimation of shear wave speed in the human uterine cervix.

Science.gov (United States)

Carlson, L C; Feltovich, H; Palmeri, M L; Dahl, J J; Munoz del Rio, A; Hall, T J

2014-04-01

To explore spatial variability within the cervix and the sensitivity of shear wave speed (SWS) to assess softness/stiffness differences in ripened (softened) vs unripened tissue. We obtained SWS estimates from hysterectomy specimens (n = 22), a subset of which were ripened (n = 13). Multiple measurements were made longitudinally along the cervical canal on both the anterior and posterior sides of the cervix. Statistical tests of differences in the proximal vs distal, anterior vs posterior and ripened vs unripened cervix were performed with individual two-sample t-tests and a linear mixed model. Estimates of SWS increase monotonically from distal to proximal longitudinally along the cervix, they vary in the anterior compared to the posterior cervix and they are significantly different in ripened vs unripened cervical tissue. Specifically, the mid position SWS estimates for the unripened group were 3.45 ± 0.95 m/s (anterior; mean ± SD) and 3.56 ± 0.92 m/s (posterior), and 2.11 ± 0.45 m/s (anterior) and 2.68 ± 0.57 m/s (posterior) for the ripened group (P < 0.001). We propose that SWS estimation may be a valuable research and, ultimately, diagnostic tool for objective quantification of cervical stiffness/softness. Copyright © 2013 ISUOG. Published by John Wiley & Sons Ltd.

Redshift distributions of galaxies in the Dark Energy Survey Science Verification shear catalogue and implications for weak lensing

Energy Technology Data Exchange (ETDEWEB)

Bonnett, C.; Troxel, M. A.; Hartley, W.; Amara, A.; Leistedt, B.; Becker, M. R.; Bernstein, G. M.; Bridle, S. L.; Bruderer, C.; Busha, M. T.; Carrasco Kind, M.; Childress, M. J.; Castander, F. J.; Chang, C.; Crocce, M.; Davis, T. M.; Eifler, T. F.; Frieman, J.; Gangkofner, C.; Gaztanaga, E.; Glazebrook, K.; Gruen, D.; Kacprzak, T.; King, A.; Kwan, J.; Lahav, O.; Lewis, G.; Lidman, C.; Lin, H.; MacCrann, N.; Miquel, R.; O’Neill, C. R.; Palmese, A.; Peiris, H. V.; Refregier, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sánchez, C.; Sheldon, E.; Uddin, S.; Wechsler, R. H.; Zuntz, J.; Abbott, T.; Abdalla, F. B.; Allam, S.; Armstrong, R.; Banerji, M.; Bauer, A. H.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Fausti Neto, A.; Fernandez, E.; Flaugher, B.; Fosalba, P.; Gerdes, D. W.; Gruendl, R. A.; Honscheid, K.; Jain, B.; James, D. J.; Jarvis, M.; Kim, A. G.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Martini, P.; Melchior, P.; Miller, C. J.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Santiago, B.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Vikram, V.; Walker, A. R.

2016-08-01

We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based photometric redshift methods { annz2, bpz calibrated against BCC-U fig simulations, skynet, and tpz { are analysed. For training, calibration, and testing of these methods, we also construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evalu-ated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ±0.01 over the range 0:3 < z < 1:3, we construct three tomographic bins with means of z = {0.45; 0.67,1.00g}. These bins each have systematic uncertainties δ_z ≲ 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ₈ of approx. 3%. This shift is within the one sigma statistical errors on σ8 for the DES SV shear catalog. We also found that further study of the potential impact of systematic differences on the critical surface density, Σ_crit, contained levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0:05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.

Shear-limited test particle diffusion in 2-dimensional plasmas

International Nuclear Information System (INIS)

Anderegg, Francois; Driscoll, C. Fred; Dubin, Daniel H.E.

2002-01-01

Measurements of test-particle diffusion in pure ion plasmas show 2D enhancements over the 3D rates, limited by shear in the plasma rotation ω E (r). The diffusion is due to 'long-range' ion-ion collisions in the quiescent, steady-state Mg + plasma. For short plasma length L p and low shear S≡r∂ω E /∂r, thermal ions bounce axially many times before shear separates them in θ, so the ions move in (r,θ) as bounce averaged 'rods' of charge (i.e. 2D point vortices). Experimentally, we vary the number of bounces over the range 0.2≤N b ≤10,000. For long plasmas with N b ≤1, we observe diffusion in quantitative agreement with the 3D theory of long-range ExB drift collisions. For shorter plasmas or lower shear, with N b >1, we measure diffusion rates enhanced by up to 100x. For exceedingly small she0ar, i.e. N b ≥1000, we observe diffusion rates consistent with the Taylor-McNamara estimates for a shear-free thermal plasma. Overall, the data shows fair agreement with Dubin's new theory of 2D diffusion in shear, which predicts an enhancement of D 2D /D 3D ≅N b up to the Taylor-McNamara limit

Joint optimization of MIMO radar waveform and biased estimator with prior information in the presence of clutter

Directory of Open Access Journals (Sweden)

Liu Hongwei

2011-01-01

Full Text Available Abstract In this article, we consider the problem of joint optimization of multi-input multi-output (MIMO radar waveform and biased estimator with prior information on targets of interest in the presence of signal-dependent noise. A novel constrained biased Cramer-Rao bound (CRB based method is proposed to optimize the waveform covariance matrix (WCM and biased estimator such that the performance of parameter estimation can be improved. Under a simplifying assumption, the resultant nonlinear optimization problem is solved resorting to a convex relaxation that belongs to the semidefinite programming (SDP class. An optimal solution of the initial problem is then constructed through a suitable approximation to an optimal solution of the relaxed one (in a least squares (LS sense. Numerical results show that the performance of parameter estimation can be improved considerably by the proposed method compared to uncorrelated waveforms.

Sheared-flow induced confinement transition in a linear magnetized plasma

Science.gov (United States)

Zhou, S.; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Friedman, B.; Schaffner, D.

2012-01-01

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn /n~eδφ/kTe~0.5) are observed at the plasma edge, accompanied by a large density gradient (Ln=|∇lnn |-1~2cm) and shearing rate (γ ~300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (Vbias) on the obstacle and the axial magnetic field (Bz) strength. In cases with low Vbias and large Bz, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E ×B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller Bz, large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m =1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

Excited waves in shear layers

Science.gov (United States)

Bechert, D. W.

1982-01-01

The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

A thin rivulet or ridge subject to a uniform transverse shear stress at its free surface due to an external airflow

KAUST Repository

Sullivan, J. M.; Paterson, C.; Wilson, S. K.; Duffy, B. R.

2012-01-01

We use the lubrication approximation to analyze three closely related problems involving a thin rivulet or ridge (i.e., a two-dimensional droplet) of fluid subject to a prescribed uniform transverse shear stress at its free surface due

Refining estimates of availability bias to improve assessments of the conservation status of an endangered dolphin.

Science.gov (United States)

Sucunza, Federico; Danilewicz, Daniel; Cremer, Marta; Andriolo, Artur; Zerbini, Alexandre N

2018-01-01

Estimation of visibility bias is critical to accurately compute abundance of wild populations. The franciscana, Pontoporia blainvillei, is considered the most threatened small cetacean in the southwestern Atlantic Ocean. Aerial surveys are considered the most effective method to estimate abundance of this species, but many existing estimates have been considered unreliable because they lack proper estimation of correction factors for visibility bias. In this study, helicopter surveys were conducted to determine surfacing-diving intervals of franciscanas and to estimate availability for aerial platforms. Fifteen hours were flown and 101 groups of 1 to 7 franciscanas were monitored, resulting in a sample of 248 surface-dive cycles. The mean surfacing interval and diving interval times were 16.10 seconds (SE = 9.74) and 39.77 seconds (SE = 29.06), respectively. Availability was estimated at 0.39 (SE = 0.01), a value 16-46% greater than estimates computed from diving parameters obtained from boats or from land. Generalized mixed-effects models were used to investigate the influence of biological and environmental predictors on the proportion of time franciscana groups are visually available to be seen from an aerial platform. These models revealed that group size was the main factor influencing the proportion at surface. The use of negatively biased estimates of availability results in overestimation of abundance, leads to overly optimistic assessments of extinction probabilities and to potentially ineffective management actions. This study demonstrates that estimates of availability must be computed from suitable platforms to ensure proper conservation decisions are implemented to protect threatened species such as the franciscana.

Shear strength estimation of the concrete beams reinforced with FRP; comparison of artificial neural network and equations of regulations

Directory of Open Access Journals (Sweden)

Mahmood Akbari

2017-12-01

Full Text Available In recent years, numerous experimental tests were done on the concrete beams reinforced with the fiber-reinforced polymer (FRP. In this way, some equations were proposed to estimate the shear strength of the beams reinforced with FRP. The aim of this study is to explore the feasibility of using a feed-forward artificial neural network (ANN model to predict the ultimate shear strength of the beams strengthened with FRP composites. For this purpose, a database consists of 304 reinforced FRP concrete beams have been collected from the available articles on the analysis of shear behavior of these beams. The inputs to the ANN model consists of the 11 variables including the geometric dimensions of the section, steel reinforcement amount, FRP amount and the properties of the concrete, steel reinforcement and FRP materials while the output variable is the shear strength of the FRP beam. To assess the performance of the ANN model for estimating the shear strength of the reinforced beams, the outputs of the ANN are compared to those of equations of the Iranian code (Publication No. 345 and the American code (ACI 440. The comparisons between the outputs of Iran and American regulations with those of the proposed model indicates that the predictive power of this model is much better than the experimental codes. Specifically, for under study data, mean absolute relative error (MARE criteria is 13%, 34% and 39% for the ANN model, the American and the Iranian codes, respectively.

Ligation bias in illumina next-generation DNA libraries: implications for sequencing ancient genomes.

Directory of Open Access Journals (Sweden)

Andaine Seguin-Orlando

Full Text Available Ancient DNA extracts consist of a mixture of endogenous molecules and contaminant DNA templates, often originating from environmental microbes. These two populations of templates exhibit different chemical characteristics, with the former showing depurination and cytosine deamination by-products, resulting from post-mortem DNA damage. Such chemical modifications can interfere with the molecular tools used for building second-generation DNA libraries, and limit our ability to fully characterize the true complexity of ancient DNA extracts. In this study, we first use fresh DNA extracts to demonstrate that library preparation based on adapter ligation at AT-overhangs are biased against DNA templates starting with thymine residues, contrarily to blunt-end adapter ligation. We observe the same bias on fresh DNA extracts sheared on Bioruptor, Covaris and nebulizers. This contradicts previous reports suggesting that this bias could originate from the methods used for shearing DNA. This also suggests that AT-overhang adapter ligation efficiency is affected in a sequence-dependent manner and results in an uneven representation of different genomic contexts. We then show how this bias could affect the base composition of ancient DNA libraries prepared following AT-overhang ligation, mainly by limiting the ability to ligate DNA templates starting with thymines and therefore deaminated cytosines. This results in particular nucleotide misincorporation damage patterns, deviating from the signature generally expected for authenticating ancient sequence data. Consequently, we show that models adequate for estimating post-mortem DNA damage levels must be robust to the molecular tools used for building ancient DNA libraries.

Bias correction of risk estimates in vaccine safety studies with rare adverse events using a self-controlled case series design.

Science.gov (United States)

Zeng, Chan; Newcomer, Sophia R; Glanz, Jason M; Shoup, Jo Ann; Daley, Matthew F; Hambidge, Simon J; Xu, Stanley

2013-12-15

The self-controlled case series (SCCS) method is often used to examine the temporal association between vaccination and adverse events using only data from patients who experienced such events. Conditional Poisson regression models are used to estimate incidence rate ratios, and these models perform well with large or medium-sized case samples. However, in some vaccine safety studies, the adverse events studied are rare and the maximum likelihood estimates may be biased. Several bias correction methods have been examined in case-control studies using conditional logistic regression, but none of these methods have been evaluated in studies using the SCCS design. In this study, we used simulations to evaluate 2 bias correction approaches-the Firth penalized maximum likelihood method and Cordeiro and McCullagh's bias reduction after maximum likelihood estimation-with small sample sizes in studies using the SCCS design. The simulations showed that the bias under the SCCS design with a small number of cases can be large and is also sensitive to a short risk period. The Firth correction method provides finite and less biased estimates than the maximum likelihood method and Cordeiro and McCullagh's method. However, limitations still exist when the risk period in the SCCS design is short relative to the entire observation period.

Naesliden Project: direct shear tests of filled and unfilled joints

Energy Technology Data Exchange (ETDEWEB)

Ludvig, B.

1980-05-15

Joints from the Naesliden mine have been tested in a small field shear box and in a large shear rig. The large shear rig is described in detail, and its ability to test joints with an area of 600 mc/sup 2/ at a maximum normal stress of up to 20 MPa is emphasized. The stiffness and shear strength of the discontinuities in the Naesliden mine is presented. The values estimated at direct shear tests are compared with results from in situ measurements and tests on drillcores. The results show that the in situ measurements give lower values for the shear resistance than the direct shear tests. Estimation of the normal stiffness for joints in drill cores gave much higher stiffness than the estimations in the shear rig.

Mean wall-shear stress measurements using the micro-pillar shear-stress sensor MPS3

International Nuclear Information System (INIS)

Große, S; Schröder, W

2008-01-01

A new sensor to measure the mean turbulent wall-shear stress in turbulent flows is described. The wall-shear stress sensor MPS 3 has been tested in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re b based on the bulk velocity U b and the pipe diameter D in the range of Re b = 10 000–20 000. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. The sensor device consists of a flexible micro-pillar that extends from the wall into the viscous sublayer. Bending due to the exerting fluid forces, the pillar-tip deflection serves as a measure for the local wall-shear stress. The sensor concept, calibration techniques, the achievable accuracy and error estimates, the fields of application and the sensor limits will be discussed. Furthermore, a first estimate of the pillar dynamic response will be derived showing the potential of the sensor to also measure the turbulent fluctuating wall-shear stress

Comparison of some biased estimation methods (including ordinary subset regression) in the linear model

Science.gov (United States)

Sidik, S. M.

1975-01-01

Ridge, Marquardt's generalized inverse, shrunken, and principal components estimators are discussed in terms of the objectives of point estimation of parameters, estimation of the predictive regression function, and hypothesis testing. It is found that as the normal equations approach singularity, more consideration must be given to estimable functions of the parameters as opposed to estimation of the full parameter vector; that biased estimators all introduce constraints on the parameter space; that adoption of mean squared error as a criterion of goodness should be independent of the degree of singularity; and that ordinary least-squares subset regression is the best overall method.

Mean size estimation yields left-side bias: Role of attention on perceptual averaging.

Science.gov (United States)

Li, Kuei-An; Yeh, Su-Ling

2017-11-01

The human visual system can estimate mean size of a set of items effectively; however, little is known about whether information on each visual field contributes equally to the mean size estimation. In this study, we examined whether a left-side bias (LSB)-perceptual judgment tends to depend more heavily on left visual field's inputs-affects mean size estimation. Participants were instructed to estimate the mean size of 16 spots. In half of the trials, the mean size of the spots on the left side was larger than that on the right side (the left-larger condition) and vice versa (the right-larger condition). Our results illustrated an LSB: A larger estimated mean size was found in the left-larger condition than in the right-larger condition (Experiment 1), and the LSB vanished when participants' attention was effectively cued to the right side (Experiment 2b). Furthermore, the magnitude of LSB increased with stimulus-onset asynchrony (SOA), when spots on the left side were presented earlier than the right side. In contrast, the LSB vanished and then induced a reversed effect with SOA when spots on the right side were presented earlier (Experiment 3). This study offers the first piece of evidence suggesting that LSB does have a significant influence on mean size estimation of a group of items, which is induced by a leftward attentional bias that enhances the prior entry effect on the left side.

Calibration of colour gradient bias in shear measurement using HST/CANDELS data

Science.gov (United States)

Er, X.; Hoekstra, H.; Schrabback, T.; Cardone, V. F.; Scaramella, R.; Maoli, R.; Vicinanza, M.; Gillis, B.; Rhodes, J.

2018-06-01

Accurate shape measurements are essential to infer cosmological parameters from large area weak gravitational lensing studies. The compact diffraction-limited point spread function (PSF) in space-based observations is greatly beneficial, but its chromaticity for a broad-band observation can lead to new subtle effects that could hitherto be ignored: the PSF of a galaxy is no longer uniquely defined and spatial variations in the colours of galaxies result in biases in the inferred lensing signal. Taking Euclid as a reference, we show that this colour gradient bias (CG bias) can be quantified with high accuracy using available multicolour Hubble Space Telescope (HST) data. In particular we study how noise in the HST observations might impact such measurements and find this to be negligible. We determine the CG bias using HST observations in the F606W and F814W filters and observe a correlation with the colour, in line with expectations, whereas the dependence with redshift is weak. The biases for individual galaxies are generally well below 1 per cent, which may be reduced further using morphological information from the Euclid data. Our results demonstrate that CG bias should not be ignored, but it is possible to determine its amplitude with sufficient precision, so that it will not significantly bias the weak lensing measurements using Euclid data.

Detectability of migrating raptors and its effect on bias and precision of trend estimates

Directory of Open Access Journals (Sweden)

Eric G. Nolte

2016-12-01

Full Text Available Annual counts of migrating raptors at fixed observation points are a widespread practice, and changes in numbers counted over time, adjusted for survey effort, are commonly used as indices of trends in population size. Unmodeled year-to-year variation in detectability may introduce bias, reduce precision of trend estimates, and reduce power to detect trends. We conducted dependent double-observer surveys at the annual fall raptor migration count at Lucky Peak, Idaho, in 2009 and 2010 and applied Huggins closed-capture removal models and information-theoretic model selection to determine the relative importance of factors affecting detectability. The most parsimonious model included effects of observer team identity, distance, species, and day of the season. We then simulated 30 years of counts with heterogeneous individual detectability, a population decline (λ = 0.964, and unexplained random variation in the number of available birds. Imperfect detectability did not bias trend estimation, and increased the time required to achieve 80% power by less than 11%. Results suggested that availability is a greater source of variance in annual counts than detectability; thus, efforts to account for availability would improve the monitoring value of migration counts. According to our models, long-term trends in observer efficiency or migratory flight distance may introduce substantial bias to trend estimates. Estimating detectability with a novel count protocol like our double-observer method is just one potential means of controlling such effects. The traditional approach of modeling the effects of covariates and adjusting the index may also be effective if ancillary data is collected consistently.

Direct estimation and correction of bias from temporally variable non-stationary noise in a channelized Hotelling model observer.

Science.gov (United States)

Fetterly, Kenneth A; Favazza, Christopher P

2016-08-07

Channelized Hotelling model observer (CHO) methods were developed to assess performance of an x-ray angiography system. The analytical methods included correction for known bias error due to finite sampling. Detectability indices ([Formula: see text]) corresponding to disk-shaped objects with diameters in the range 0.5-4 mm were calculated. Application of the CHO for variable detector target dose (DTD) in the range 6-240 nGy frame(-1) resulted in [Formula: see text] estimates which were as much as 2.9×  greater than expected of a quantum limited system. Over-estimation of [Formula: see text] was presumed to be a result of bias error due to temporally variable non-stationary noise. Statistical theory which allows for independent contributions of 'signal' from a test object (o) and temporally variable non-stationary noise (ns) was developed. The theory demonstrates that the biased [Formula: see text] is the sum of the detectability indices associated with the test object [Formula: see text] and non-stationary noise ([Formula: see text]). Given the nature of the imaging system and the experimental methods, [Formula: see text] cannot be directly determined independent of [Formula: see text]. However, methods to estimate [Formula: see text] independent of [Formula: see text] were developed. In accordance with the theory, [Formula: see text] was subtracted from experimental estimates of [Formula: see text], providing an unbiased estimate of [Formula: see text]. Estimates of [Formula: see text] exhibited trends consistent with expectations of an angiography system that is quantum limited for high DTD and compromised by detector electronic readout noise for low DTD conditions. Results suggest that these methods provide [Formula: see text] estimates which are accurate and precise for [Formula: see text]. Further, results demonstrated that the source of bias was detector electronic readout noise. In summary, this work presents theory and methods to test for the

Accurate shear measurement with faint sources

International Nuclear Information System (INIS)

Zhang, Jun; Foucaud, Sebastien; Luo, Wentao

2015-01-01

For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys

Estimating Sampling Biases and Measurement Uncertainties of AIRS-AMSU-A Temperature and Water Vapor Observations Using MERRA Reanalysis

Science.gov (United States)

Hearty, Thomas J.; Savtchenko, Andrey K.; Tian, Baijun; Fetzer, Eric; Yung, Yuk L.; Theobald, Michael; Vollmer, Bruce; Fishbein, Evan; Won, Young-In

2014-01-01

We use MERRA (Modern Era Retrospective-Analysis for Research Applications) temperature and water vapor data to estimate the sampling biases of climatologies derived from the AIRS/AMSU-A (Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit-A) suite of instruments. We separate the total sampling bias into temporal and instrumental components. The temporal component is caused by the AIRS/AMSU-A orbit and swath that are not able to sample all of time and space. The instrumental component is caused by scenes that prevent successful retrievals. The temporal sampling biases are generally smaller than the instrumental sampling biases except in regions with large diurnal variations, such as the boundary layer, where the temporal sampling biases of temperature can be +/- 2 K and water vapor can be 10% wet. The instrumental sampling biases are the main contributor to the total sampling biases and are mainly caused by clouds. They are up to 2 K cold and greater than 30% dry over mid-latitude storm tracks and tropical deep convective cloudy regions and up to 20% wet over stratus regions. However, other factors such as surface emissivity and temperature can also influence the instrumental sampling bias over deserts where the biases can be up to 1 K cold and 10% wet. Some instrumental sampling biases can vary seasonally and/or diurnally. We also estimate the combined measurement uncertainties of temperature and water vapor from AIRS/AMSU-A and MERRA by comparing similarly sampled climatologies from both data sets. The measurement differences are often larger than the sampling biases and have longitudinal variations.

Communication: Estimating the initial biasing potential for λ-local-elevation umbrella-sampling (λ-LEUS) simulations via slow growth

Energy Technology Data Exchange (ETDEWEB)

Bieler, Noah S.; Hünenberger, Philippe H., E-mail: phil@igc.phys.chem.ethz.ch [Laboratory of Physical Chemistry, ETH Zürich, CH-8093 Zürich (Switzerland)

2014-11-28

In a recent article [Bieler et al., J. Chem. Theory Comput. 10, 3006–3022 (2014)], we introduced a combination of the λ-dynamics (λD) approach for calculating alchemical free-energy differences and of the local-elevation umbrella-sampling (LEUS) memory-based biasing method to enhance the sampling along the alchemical coordinate. The combined scheme, referred to as λ-LEUS, was applied to the perturbation of hydroquinone to benzene in water as a test system, and found to represent an improvement over thermodynamic integration (TI) in terms of sampling efficiency at equivalent accuracy. However, the preoptimization of the biasing potential required in the λ-LEUS method requires “filling up” all the basins in the potential of mean force. This introduces a non-productive pre-sampling time that is system-dependent, and generally exceeds the corresponding equilibration time in a TI calculation. In this letter, a remedy is proposed to this problem, termed the slow growth memory guessing (SGMG) approach. Instead of initializing the biasing potential to zero at the start of the preoptimization, an approximate potential of mean force is estimated from a short slow growth calculation, and its negative used to construct the initial memory. Considering the same test system as in the preceding article, it is shown that of the application of SGMG in λ-LEUS permits to reduce the preoptimization time by about a factor of four.

Communication: Estimating the initial biasing potential for λ-local-elevation umbrella-sampling (λ-LEUS) simulations via slow growth

International Nuclear Information System (INIS)

Bieler, Noah S.; Hünenberger, Philippe H.

2014-01-01

In a recent article [Bieler et al., J. Chem. Theory Comput. 10, 3006–3022 (2014)], we introduced a combination of the λ-dynamics (λD) approach for calculating alchemical free-energy differences and of the local-elevation umbrella-sampling (LEUS) memory-based biasing method to enhance the sampling along the alchemical coordinate. The combined scheme, referred to as λ-LEUS, was applied to the perturbation of hydroquinone to benzene in water as a test system, and found to represent an improvement over thermodynamic integration (TI) in terms of sampling efficiency at equivalent accuracy. However, the preoptimization of the biasing potential required in the λ-LEUS method requires “filling up” all the basins in the potential of mean force. This introduces a non-productive pre-sampling time that is system-dependent, and generally exceeds the corresponding equilibration time in a TI calculation. In this letter, a remedy is proposed to this problem, termed the slow growth memory guessing (SGMG) approach. Instead of initializing the biasing potential to zero at the start of the preoptimization, an approximate potential of mean force is estimated from a short slow growth calculation, and its negative used to construct the initial memory. Considering the same test system as in the preceding article, it is shown that of the application of SGMG in λ-LEUS permits to reduce the preoptimization time by about a factor of four

Design-related bias in estimates of accuracy when comparing imaging tests: examples from breast imaging research

International Nuclear Information System (INIS)

Houssami, Nehmat; Ciatto, Stefano

2010-01-01

This work highlights concepts on the potential for design-related factors to bias estimates of test accuracy in comparative imaging research. We chose two design factors, selection of eligible subjects and the reference standard, to examine the effect of design limitations on estimates of accuracy. Estimates of sensitivity in a study of the comparative accuracy of mammography and ultrasound differed according to how subjects were selected. Comparison of a new imaging test with an existing test should distinguish whether the new test is to be used as a replacement for, or as an adjunct to, the conventional test, to guide the method for subject selection. Quality of the reference standard, examined in a meta-analysis of preoperative breast MRI, varied across studies and was associated with estimates of incremental accuracy. Potential solutions to deal with the reference standard are outlined where an ideal reference standard may not be available in all subjects. These examples of breast imaging research demonstrate that design-related bias, when comparing a new imaging test with a conventional imaging test, may bias accuracy in a direction that favours the new test by overestimating the accuracy of the new test or by underestimating that of the conventional test. (orig.)

Temperature dependence of grain boundary free energy and elastic constants

International Nuclear Information System (INIS)

Foiles, Stephen M.

2010-01-01

This work explores the suggestion that the temperature dependence of the grain boundary free energy can be estimated from the temperature dependence of the elastic constants. The temperature-dependent elastic constants and free energy of a symmetric Σ79 tilt boundary are computed for an embedded atom method model of Ni. The grain boundary free energy scales with the product of the shear modulus times the lattice constant for temperatures up to about 0.75 the melting temperature.

Influence of Plasma Biasing on Coherent Structures in TJ-K

Science.gov (United States)

Ramisch, M.; Greiner, F.; Lechte, C.; Mahdizadeh, N.; Rahbarnia, K.; Stroth, U.

2003-10-01

Poloidal shear flows play an important role in the improvement of plasma confinement in fusion devices. They limit the radial correlation length via the shear decorrelation mechanism [1] and can trigger transitions into transport barriers. External biasing can be used to drive poloidal shear flows [2] in order to study the decorrelation mechanism. The torsatron TJ-K is operated with low-temperature plasmas produced by ECRH. Coherent and quasi-coherent structures have been observed [3]. Their structure size varies according to the drift scale ρ_s. The influence of biasing on these structures is investigated by means of electrostatic probes. Electron density fluctuations as well as fluctuations of the floating potential tend to decrease in the presence of a positively biased probe. The evolution of radial electric field, poloidal flow and radial transport are investigated for different plasma parameters using a 2D Langmuir probe array with 64 tips in comparison with two-point correlation measurements. First results are presented. [1] H. Biglari et al., Phys. Fluids B 2, p. 1 (1990); [2] R. J. Taylor et al., Phys. Rev. Lett. 63, 21, p. 2365 (1989); [3] C. Lechte, PhD-Thesis, CAU Kiel (2003)

Approximate Bias Correction in Econometrics

OpenAIRE

James G. MacKinnon; Anthony A. Smith Jr.

1995-01-01

This paper discusses ways to reduce the bias of consistent estimators that are biased in finite samples. It is necessary that the bias function, which relates parameter values to bias, should be estimable by computer simulation or by some other method. If so, bias can be reduced or, in some cases that may not be unrealistic, even eliminated. In general, several evaluations of the bias function will be required to do this. Unfortunately, reducing bias may increase the variance, or even the mea...

A practical method for estimating maximum shear modulus of cemented sands using unconfined compressive strength

Science.gov (United States)

Choo, Hyunwook; Nam, Hongyeop; Lee, Woojin

2017-12-01

The composition of naturally cemented deposits is very complicated; thus, estimating the maximum shear modulus (Gmax, or shear modulus at very small strains) of cemented sands using the previous empirical formulas is very difficult. The purpose of this experimental investigation is to evaluate the effects of particle size and cement type on the Gmax and unconfined compressive strength (qucs) of cemented sands, with the ultimate goal of estimating Gmax of cemented sands using qucs. Two sands were artificially cemented using Portland cement or gypsum under varying cement contents (2%-9%) and relative densities (30%-80%). Unconfined compression tests and bender element tests were performed, and the results from previous studies of two cemented sands were incorporated in this study. The results of this study demonstrate that the effect of particle size on the qucs and Gmax of four cemented sands is insignificant, and the variation of qucs and Gmax can be captured by the ratio between volume of void and volume of cement. qucs and Gmax of sand cemented with Portland cement are greater than those of sand cemented with gypsum. However, the relationship between qucs and Gmax of the cemented sand is not affected by the void ratio, cement type and cement content, revealing that Gmax of the complex naturally cemented soils with unknown in-situ void ratio, cement type and cement content can be estimated using qucs.

Estimate of Radiosonde Dry Bias From Far-Infrared Measurements on the Antarctic Plateau

Science.gov (United States)

Rizzi, R.; Maestri, T.; Arosio, C.

2018-03-01

The experimental data set of downwelling radiance spectra measured at the ground in clear conditions during 2013 by a Far-Infrared Fourier Transform Spectrometer at Dome-C, Antarctica, presented in Rizzi et al. (2016, https://doi.org/10.1002/2016JD025341) is used to estimate the effect of solar heating of the radiosonde humidity sensor, called dry bias. The effect is quite evident comparing residuals for the austral summer and winter clear cases and can be modeled by an increase of the water vapor concentration at all levels by about 15%. Such an estimate has become possible only after a new version of the simulation code and spectroscopic data has become available, which has substantially improved the modeling of water vapor absorption in the far infrared. The negative yearly spectral bias reported in Rizzi et al. (2016, https://doi.org/10.1002/2016JD025341) is in fact greatly reduced when compared to the same measurement data set.

Biased limiter experiments on text

International Nuclear Information System (INIS)

Phillips, P.E.; Wootton, A.J.; Rowan, W.L.; Ritz, C.P.; Rhodes, T.L.; Bengtson, R.D.; Hodge, W.L.; Durst, R.D.; McCool, S.C.; Richards, B.; Gentle, K.W.; Schoch, P.; Forster, J.C.; Hickok, R.L.; Evans, T.E.

1987-01-01

Experiments using an electrically biased limiter have been performed on the Texas Experimental Tokamak (TEXT). A small movable limiter is inserted past the main poloidal ring limiter (which is electrically connected to the vacuum vessel) and biased at V Lim with respect to it. The floating potential, plasma potential and shear layer position can be controlled. With vertical strokeV Lim vertical stroke ≥ 50 V the plasma density increases. For V Lim Lim > 0 the results obtained are inconclusive. Variation of V Lim changes the electrostatic turbulence which may explain the observed total flux changes. (orig.)

Estimation of shear viscosity based on transverse momentum correlations

International Nuclear Information System (INIS)

Sharma, Monika

2009-01-01

Event anisotropy measurements at RHIC suggest the strongly interacting matter created in heavy ion collisions flows with very little shear viscosity. Precise determination of 'shear viscosity-to-entropy' ratio is currently a subject of extensive study [S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97 (2006) 162302]. We present preliminary results of measurements of the evolution of transverse momentum correlation function with collision centrality of Au+Au interactions at √(s NN )=200 GeV. We compare two differential correlation functions, namely inclusive [J. Adams et al. (STAR Collaboration), Phys. Rev. C 72 (2005) 044902] and a differential version of the correlation measure C introduced by Gavin et al. [S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97 (2006) 162302; M. Sharma and C. A. Pruneau, Phys. Rev. C 79 (2009) 024905.]. These observables can be used for the experimental study of the shear viscosity per unit entropy.

Estimation of shear viscosity based on transverse momentum correlations

Science.gov (United States)

STAR Collaboration; Sharma, Monika; STAR Collaboration

2009-11-01

Event anisotropy measurements at RHIC suggest the strongly interacting matter created in heavy ion collisions flows with very little shear viscosity. Precise determination of “shear viscosity-to-entropy” ratio is currently a subject of extensive study [S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97 (2006) 162302]. We present preliminary results of measurements of the evolution of transverse momentum correlation function with collision centrality of Au+Au interactions at s=200 GeV. We compare two differential correlation functions, namely inclusive [J. Adams et al. (STAR Collaboration), Phys. Rev. C 72 (2005) 044902] and a differential version of the correlation measure C˜ introduced by Gavin et al. [S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97 (2006) 162302; M. Sharma and C. A. Pruneau, Phys. Rev. C 79 (2009) 024905.]. These observables can be used for the experimental study of the shear viscosity per unit entropy.

Person-Independent Head Pose Estimation Using Biased Manifold Embedding

Directory of Open Access Journals (Sweden)

Sethuraman Panchanathan

2008-02-01

Full Text Available Head pose estimation has been an integral problem in the study of face recognition systems and human-computer interfaces, as part of biometric applications. A fine estimate of the head pose angle is necessary and useful for several face analysis applications. To determine the head pose, face images with varying pose angles can be considered to be lying on a smooth low-dimensional manifold in high-dimensional image feature space. However, when there are face images of multiple individuals with varying pose angles, manifold learning techniques often do not give accurate results. In this work, we propose a framework for a supervised form of manifold learning called Biased Manifold Embedding to obtain improved performance in head pose angle estimation. This framework goes beyond pose estimation, and can be applied to all regression applications. This framework, although formulated for a regression scenario, unifies other supervised approaches to manifold learning that have been proposed so far. Detailed studies of the proposed method are carried out on the FacePix database, which contains 181 face images each of 30 individuals with pose angle variations at a granularity of 1∘. Since biometric applications in the real world may not contain this level of granularity in training data, an analysis of the methodology is performed on sparsely sampled data to validate its effectiveness. We obtained up to 2∘ average pose angle estimation error in the results from our experiments, which matched the best results obtained for head pose estimation using related approaches.

An empirical study on memory bias situations and correction strategies in ERP effort estimation

NARCIS (Netherlands)

Erasmus, I.P.; Daneva, Maia; Amrahamsson, Pekka; Corral, Luis; Olivo, Markku; Russo, Barbara

2016-01-01

An Enterprise Resource Planning (ERP) project estimation process often relies on experts of various backgrounds to contribute judgments based on their professional experience. Such expert judgments however may not be biasfree. De-biasing techniques therefore have been proposed in the software

Efficient Determination of Free Energy Landscapes in Multiple Dimensions from Biased Umbrella Sampling Simulations Using Linear Regression.

Science.gov (United States)

Meng, Yilin; Roux, Benoît

2015-08-11

The weighted histogram analysis method (WHAM) is a standard protocol for postprocessing the information from biased umbrella sampling simulations to construct the potential of mean force with respect to a set of order parameters. By virtue of the WHAM equations, the unbiased density of state is determined by satisfying a self-consistent condition through an iterative procedure. While the method works very effectively when the number of order parameters is small, its computational cost grows rapidly in higher dimension. Here, we present a simple and efficient alternative strategy, which avoids solving the self-consistent WHAM equations iteratively. An efficient multivariate linear regression framework is utilized to link the biased probability densities of individual umbrella windows and yield an unbiased global free energy landscape in the space of order parameters. It is demonstrated with practical examples that free energy landscapes that are comparable in accuracy to WHAM can be generated at a small fraction of the cost.

Tree imbalance causes a bias in phylogenetic estimation of evolutionary timescales using heterochronous sequences.

Science.gov (United States)

Duchêne, David; Duchêne, Sebastian; Ho, Simon Y W

2015-07-01

Phylogenetic estimation of evolutionary timescales has become routine in biology, forming the basis of a wide range of evolutionary and ecological studies. However, there are various sources of bias that can affect these estimates. We investigated whether tree imbalance, a property that is commonly observed in phylogenetic trees, can lead to reduced accuracy or precision of phylogenetic timescale estimates. We analysed simulated data sets with calibrations at internal nodes and at the tips, taking into consideration different calibration schemes and levels of tree imbalance. We also investigated the effect of tree imbalance on two empirical data sets: mitogenomes from primates and serial samples of the African swine fever virus. In analyses calibrated using dated, heterochronous tips, we found that tree imbalance had a detrimental impact on precision and produced a bias in which the overall timescale was underestimated. A pronounced effect was observed in analyses with shallow calibrations. The greatest decreases in accuracy usually occurred in the age estimates for medium and deep nodes of the tree. In contrast, analyses calibrated at internal nodes did not display a reduction in estimation accuracy or precision due to tree imbalance. Our results suggest that molecular-clock analyses can be improved by increasing taxon sampling, with the specific aims of including deeper calibrations, breaking up long branches and reducing tree imbalance. © 2014 John Wiley & Sons Ltd.

Bias correction for estimated QTL effects using the penalized maximum likelihood method.

Science.gov (United States)

Zhang, J; Yue, C; Zhang, Y-M

2012-04-01

A penalized maximum likelihood method has been proposed as an important approach to the detection of epistatic quantitative trait loci (QTL). However, this approach is not optimal in two special situations: (1) closely linked QTL with effects in opposite directions and (2) small-effect QTL, because the method produces downwardly biased estimates of QTL effects. The present study aims to correct the bias by using correction coefficients and shifting from the use of a uniform prior on the variance parameter of a QTL effect to that of a scaled inverse chi-square prior. The results of Monte Carlo simulation experiments show that the improved method increases the power from 25 to 88% in the detection of two closely linked QTL of equal size in opposite directions and from 60 to 80% in the identification of QTL with small effects (0.5% of the total phenotypic variance). We used the improved method to detect QTL responsible for the barley kernel weight trait using 145 doubled haploid lines developed in the North American Barley Genome Mapping Project. Application of the proposed method to other shrinkage estimation of QTL effects is discussed.

Strength Estimation for Hydrate-Bearing Sediments From Direct Shear Tests of Hydrate-Bearing Sand and Silt

Science.gov (United States)

Liu, Zhichao; Dai, Sheng; Ning, Fulong; Peng, Li; Wei, Houzhen; Wei, Changfu

2018-01-01

Safe and economic methane gas production, as well as the replacement of methane while sequestering carbon in natural hydrate deposits, requires enhanced geomechanical understanding of the strength and volume responses of hydrate-bearing sediments during shear. This study employs a custom-made apparatus to investigate the mechanical and volumetric behaviors of carbon dioxide hydrate-bearing sediments subjected to direct shear. The results show that both peak and residual strengths increase with increased hydrate saturation and vertical stress. Hydrate contributes mainly the cohesion and dilatancy constraint to the peak strength of hydrate-bearing sediments. The postpeak strength reduction is more evident and brittle in specimens with higher hydrate saturation and under lower stress. Significant strength reduction after shear failure is expected in silty sediments with high hydrate saturation Sh ≥ 0.65. Hydrate contribution to the residual strength is mainly by increasing cohesion at low hydrate saturation and friction at high hydrate saturation. Stress state and hydrate saturation are dominating both the stiffness and the strength of hydrate-bearing sediments; thus, a wave velocity-based peak strength prediction model is proposed and validated, which allows for precise estimation of the shear strength of hydrate-bearing sediments through acoustic logging data. This method is advantageous to geomechanical simulators, particularly when the experimental strength data of natural samples are not available.

MRI non-uniformity correction through interleaved bias estimation and B-spline deformation with a template.

Science.gov (United States)

Fletcher, E; Carmichael, O; Decarli, C

2012-01-01

We propose a template-based method for correcting field inhomogeneity biases in magnetic resonance images (MRI) of the human brain. At each algorithm iteration, the update of a B-spline deformation between an unbiased template image and the subject image is interleaved with estimation of a bias field based on the current template-to-image alignment. The bias field is modeled using a spatially smooth thin-plate spline interpolation based on ratios of local image patch intensity means between the deformed template and subject images. This is used to iteratively correct subject image intensities which are then used to improve the template-to-image deformation. Experiments on synthetic and real data sets of images with and without Alzheimer's disease suggest that the approach may have advantages over the popular N3 technique for modeling bias fields and narrowing intensity ranges of gray matter, white matter, and cerebrospinal fluid. This bias field correction method has the potential to be more accurate than correction schemes based solely on intrinsic image properties or hypothetical image intensity distributions.

MRI Non-Uniformity Correction Through Interleaved Bias Estimation and B-Spline Deformation with a Template*

Science.gov (United States)

Fletcher, E.; Carmichael, O.; DeCarli, C.

2013-01-01

We propose a template-based method for correcting field inhomogeneity biases in magnetic resonance images (MRI) of the human brain. At each algorithm iteration, the update of a B-spline deformation between an unbiased template image and the subject image is interleaved with estimation of a bias field based on the current template-to-image alignment. The bias field is modeled using a spatially smooth thin-plate spline interpolation based on ratios of local image patch intensity means between the deformed template and subject images. This is used to iteratively correct subject image intensities which are then used to improve the template-to-image deformation. Experiments on synthetic and real data sets of images with and without Alzheimer’s disease suggest that the approach may have advantages over the popular N3 technique for modeling bias fields and narrowing intensity ranges of gray matter, white matter, and cerebrospinal fluid. This bias field correction method has the potential to be more accurate than correction schemes based solely on intrinsic image properties or hypothetical image intensity distributions. PMID:23365843

Shear-free perfect fluids with zero magnetic Weyl tensor

International Nuclear Information System (INIS)

Collins, C.B.

1984-01-01

Rotating, shear-free general-relativistic perfect fluids are investigated. It is first shown that, if the fluid pressure, p, and energy density, μ, are related by a barotropic equation of state p = p( μ) satifying μ+pnot =0, and if the magnetic part of the Weyl tensor (with respect to the fluid flow) vanishes, then the fluid's volume expansion is zero. The class of all such fluids is subsequently characterized. Further analysis of the solutions shows that, in general, the space-times may be regarded as being locally stationary and axisymmetric (they admit a two-dimensional Abelian isometry group with timelike orbits, which is in fact orthogonally transistive), although various specializations can occur, with the ''most special'' case being the well-known Goedel model, which is space-time homogeneous (it admits a five-dimensional isometry group acting multiply transitively on the space-time). all solutions are of Petrov type D. The fact that there are any solutions in the class at all means that a theorem appearing in the literature is invalid, and the existence of some special solutions in which the fluid's vorticity vector is orthogonal to the acceleration reveals the incompleteness of a previous study of a class of space-times, in which there are Killing vectors parallel to the fluid four-velocity and to the vorticity vector

Evolution of allowable stresses in shear for lumber

Science.gov (United States)

Robert L. Ethington; William L. Galligan; Henry M. Montrey; Alan D. Freas

1979-01-01

This paper surveys research leading to allowable shear stress parallel to grain for lumber. In early flexure tests of lumber, some pieces failed in shear. The estimated shear stress at time of failure was generally lower than shear strength measured on small, clear, straight-grained specimens. This and other engineering observations gave rise to adjustments that...

Estimation of noise-free variance to measure heterogeneity.

Directory of Open Access Journals (Sweden)

Tilo Winkler

Full Text Available Variance is a statistical parameter used to characterize heterogeneity or variability in data sets. However, measurements commonly include noise, as random errors superimposed to the actual value, which may substantially increase the variance compared to a noise-free data set. Our aim was to develop and validate a method to estimate noise-free spatial heterogeneity of pulmonary perfusion using dynamic positron emission tomography (PET scans. On theoretical grounds, we demonstrate a linear relationship between the total variance of a data set derived from averages of n multiple measurements, and the reciprocal of n. Using multiple measurements with varying n yields estimates of the linear relationship including the noise-free variance as the constant parameter. In PET images, n is proportional to the number of registered decay events, and the variance of the image is typically normalized by the square of its mean value yielding a coefficient of variation squared (CV(2. The method was evaluated with a Jaszczak phantom as reference spatial heterogeneity (CV(r(2 for comparison with our estimate of noise-free or 'true' heterogeneity (CV(t(2. We found that CV(t(2 was only 5.4% higher than CV(r2. Additional evaluations were conducted on 38 PET scans of pulmonary perfusion using (13NN-saline injection. The mean CV(t(2 was 0.10 (range: 0.03-0.30, while the mean CV(2 including noise was 0.24 (range: 0.10-0.59. CV(t(2 was in average 41.5% of the CV(2 measured including noise (range: 17.8-71.2%. The reproducibility of CV(t(2 was evaluated using three repeated PET scans from five subjects. Individual CV(t(2 were within 16% of each subject's mean and paired t-tests revealed no difference among the results from the three consecutive PET scans. In conclusion, our method provides reliable noise-free estimates of CV(t(2 in PET scans, and may be useful for similar statistical problems in experimental data.

Migration in the shearing sheet and estimates for young open cluster migration

Science.gov (United States)

Quillen, Alice C.; Nolting, Eric; Minchev, Ivan; De Silva, Gayandhi; Chiappini, Cristina

2018-04-01

Using tracer particles embedded in self-gravitating shearing sheet N-body simulations, we investigate the distance in guiding centre radius that stars or star clusters can migrate in a few orbital periods. The standard deviations of guiding centre distributions and maximum migration distances depend on the Toomre or critical wavelength and the contrast in mass surface density caused by spiral structure. Comparison between our simulations and estimated guiding radii for a few young supersolar metallicity open clusters, including NGC 6583, suggests that the contrast in mass surface density in the solar neighbourhood has standard deviation (in the surface density distribution) divided by mean of about 1/4 and larger than measured using COBE data by Drimmel and Spergel. Our estimate is consistent with a standard deviation of ˜0.07 dex in the metallicities measured from high-quality spectroscopic data for 38 young open clusters (<1 Gyr) with mean galactocentric radius 7-9 kpc.

Nonlinear unbiased minimum-variance filter for Mars entry autonomous navigation under large uncertainties and unknown measurement bias.

Science.gov (United States)

Xiao, Mengli; Zhang, Yongbo; Fu, Huimin; Wang, Zhihua

2018-05-01

High-precision navigation algorithm is essential for the future Mars pinpoint landing mission. The unknown inputs caused by large uncertainties of atmospheric density and aerodynamic coefficients as well as unknown measurement biases may cause large estimation errors of conventional Kalman filters. This paper proposes a derivative-free version of nonlinear unbiased minimum variance filter for Mars entry navigation. This filter has been designed to solve this problem by estimating the state and unknown measurement biases simultaneously with derivative-free character, leading to a high-precision algorithm for the Mars entry navigation. IMU/radio beacons integrated navigation is introduced in the simulation, and the result shows that with or without radio blackout, our proposed filter could achieve an accurate state estimation, much better than the conventional unscented Kalman filter, showing the ability of high-precision Mars entry navigation algorithm. Copyright © 2018 ISA. Published by Elsevier Ltd. All rights reserved.

Mood-congruent attention and memory bias in dysphoria: Exploring the coherence among information-processing biases.

Science.gov (United States)

Koster, Ernst H W; De Raedt, Rudi; Leyman, Lemke; De Lissnyder, Evi

2010-03-01

Recent studies indicate that depression is characterized by mood-congruent attention bias at later stages of information-processing. Moreover, depression has been associated with enhanced recall of negative information. The present study tested the coherence between attention and memory bias in dysphoria. Stable dysphoric (n = 41) and non-dysphoric (n = 41) undergraduates first performed a spatial cueing task that included negative, positive, and neutral words. Words were presented for 250 ms under conditions that allowed or prevented elaborate processing. Memory for the words presented in the cueing task was tested using incidental free recall. Dysphoric individuals exhibited an attention bias for negative words in the condition that allowed elaborate processing, with the attention bias for negative words predicting free recall of negative words. Results demonstrate the coherence of attention and memory bias in dysphoric individuals and provide suggestions on the influence of attention bias on further processing of negative material. 2009 Elsevier Ltd. All rights reserved.

The skewed weak lensing likelihood: why biases arise, despite data and theory being sound.

Science.gov (United States)

Sellentin, Elena; Heymans, Catherine; Harnois-Déraps, Joachim

2018-04-01

We derive the essentials of the skewed weak lensing likelihood via a simple Hierarchical Forward Model. Our likelihood passes four objective and cosmology-independent tests which a standard Gaussian likelihood fails. We demonstrate that sound weak lensing data are naturally biased low, since they are drawn from a skewed distribution. This occurs already in the framework of ΛCDM. Mathematically, the biases arise because noisy two-point functions follow skewed distributions. This form of bias is already known from CMB analyses, where the low multipoles have asymmetric error bars. Weak lensing is more strongly affected by this asymmetry as galaxies form a discrete set of shear tracer particles, in contrast to a smooth shear field. We demonstrate that the biases can be up to 30% of the standard deviation per data point, dependent on the properties of the weak lensing survey and the employed filter function. Our likelihood provides a versatile framework with which to address this bias in future weak lensing analyses.

Shear and loading in channels: Oscillatory shearing and edge currents of superconducting vortices

Science.gov (United States)

Wambaugh, J. F.; Marchesoni, F.; Nori, Franco

2003-04-01

Via computer simulations we study the motion of quantized magnetic flux-lines, or vortices, confined to a straight pin-free channel in a strong-pinning superconducting sample. We find that, when a constant current is applied across this system, a very unusual oscillatory shearing appears, in which the vortices moving at the edges of the channel periodically trail behind and then suddenly leapfrog past the vortices moving in the inner rows. For small enough driving forces, this oscillatory shearing dynamic phase is replaced by a continuous shearing phase in which the distance between initially-nearby vortices grows in time, quickly destroying the order of the lattice. An animation of this novel “oscillatory leapfrogging shear” effect of the vortex edge currents appears in http://www-personal.engin.umich.edu/˜nori/channel/

ExB flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

International Nuclear Information System (INIS)

Chapman, B.E.; Almagri, A.F.; Anderson, J.K.; Chiang, C.; Craig, D.; Fiksel, G.; Lanier, N.E.; Prager, S.C.; Sarff, J.S.; Stoneking, M.R.; Terry, P.W.

1998-01-01

Strong ExB flow shear occurs in the edge of three types of enhanced confinement discharge in the Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch. Measurements in standard (low confinement) discharges indicate that global magnetic fluctuations drive particle and energy transport in the plasma core, while electrostatic fluctuations drive particle transport in the plasma edge. This paper explores possible contributions of ExB flow shear to the reduction of both the magnetic and electrostatic fluctuations and, thus, the improved confinement. In one case, shear in the ExB flow occurs when the edge plasma is biased. Biased discharges exhibit changes in the edge electrostatic fluctuations and improved particle confinement. In two other cases, the flow shear emerges (1) when auxiliary current is driven in the edge and (2) spontaneously, following sawtooth crashes. Both edge electrostatic and global magnetic fluctuations are reduced in these discharges, and both particle and energy confinement improve. copyright 1998 American Institute of Physics

Bias in tensor based morphometry Stat-ROI measures may result in unrealistic power estimates.

Science.gov (United States)

Thompson, Wesley K; Holland, Dominic

2011-07-01

A series of reports have recently appeared using tensor based morphometry statistically-defined regions of interest, Stat-ROIs, to quantify longitudinal atrophy in structural MRIs from the Alzheimer's Disease Neuroimaging Initiative (ADNI). This commentary focuses on one of these reports, Hua et al. (2010), but the issues raised here are relevant to the others as well. Specifically, we point out a temporal pattern of atrophy in subjects with Alzheimer's disease and mild cognitive impairment whereby the majority of atrophy in two years occurs within the first 6 months, resulting in overall elevated estimated rates of change. Using publicly-available ADNI data, this temporal pattern is also found in a group of identically-processed healthy controls, strongly suggesting that methodological bias is corrupting the measures. The resulting bias seriously impacts the validity of conclusions reached using these measures; for example, sample size estimates reported by Hua et al. (2010) may be underestimated by a factor of five to sixteen. Copyright © 2011 Elsevier Inc. All rights reserved.

The Effectiveness of Using Limited Gauge Measurements for Bias Adjustment of Satellite-Based Precipitation Estimation over Saudi Arabia

Science.gov (United States)

Alharbi, Raied; Hsu, Kuolin; Sorooshian, Soroosh; Braithwaite, Dan

2018-01-01

Precipitation is a key input variable for hydrological and climate studies. Rain gauges are capable of providing reliable precipitation measurements at point scale. However, the uncertainty of rain measurements increases when the rain gauge network is sparse. Satellite -based precipitation estimations appear to be an alternative source of precipitation measurements, but they are influenced by systematic bias. In this study, a method for removing the bias from the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) over a region where the rain gauge is sparse is investigated. The method consists of monthly empirical quantile mapping, climate classification, and inverse-weighted distance method. Daily PERSIANN-CCS is selected to test the capability of the method for removing the bias over Saudi Arabia during the period of 2010 to 2016. The first six years (2010 - 2015) are calibrated years and 2016 is used for validation. The results show that the yearly correlation coefficient was enhanced by 12%, the yearly mean bias was reduced by 93% during validated year. Root mean square error was reduced by 73% during validated year. The correlation coefficient, the mean bias, and the root mean square error show that the proposed method removes the bias on PERSIANN-CCS effectively that the method can be applied to other regions where the rain gauge network is sparse.

Dual-electrode biasing experiments in KT-5C device

International Nuclear Information System (INIS)

Yu Yi; Lu Ronghua; Wang Chen; Pan Geshen; Wen Yizhi; Yu Changxuan; Ma Jinxiu; Wan Shude; Liu Wandong

2005-01-01

Based on the single biasing electrode experiments to optimize the confinement of plasma in the device of KT-5C tokamak, dual-biasing electrodes were inserted into the KT5C plasma for the first time to explore the enhancement of the effects of biasing and the mechanisms of the biasing. By means of applying different combinations of biasing voltages to the dual electrodes, the changes in E r , which is the key factor for boosting up the Er x B flow shear, were observed. The time evolution showed the inner electrode played a major role in dual-biasing, for it always drew a larger current than the outer one. The outer electrode made little influence. It turned out that the dual-biasing electrodes were as effective as a single one, in improving plasma confinement, for the mechanism of biasing was essentially an edge effect. (author)

Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes

DEFF Research Database (Denmark)

Wood, Lesley; Egger, Matthias; Gluud, Lise Lotte

2008-01-01

To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome....

A Mesoscopic Analytical Model to Predict the Onset of Wrinkling in Plain Woven Preforms under Bias Extension Shear Deformation

Directory of Open Access Journals (Sweden)

Abbas Hosseini

2017-10-01

Full Text Available A mesoscopic analytical model of wrinkling of Plain-Woven Composite Preforms (PWCPs under the bias extension test is presented, based on a new instability analysis. The analysis is aimed to facilitate a better understanding of the nature of wrinkle formation in woven fabrics caused by large in-plane shear, while it accounts for the effect of fabric and process parameters on the onset of wrinkling. To this end, the mechanism of wrinkle formation in PWCPs in mesoscale is simplified and an equivalent structure composed of bars and different types of springs is proposed, mimicking the behavior of a representative PWCP element at the post-locking state. The parameters of this equivalent structure are derived based on geometric and mechanical characteristics of the PWCP. The principle of minimum total potential energy is employed to formluate the model, and experimental validation is carried out to reveal the effectiveness of the derived wrinkling prediction equation.

Correcting estimators of theta and Tajima's D for ascertainment biases caused by the single-nucleotide polymorphism discovery process

DEFF Research Database (Denmark)

Ramírez-Soriano, Anna; Nielsen, Rasmus

2009-01-01

Most single-nucleotide polymorphism (SNP) data suffer from an ascertainment bias caused by the process of SNP discovery followed by SNP genotyping. The final genotyped data are biased toward an excess of common alleles compared to directly sequenced data, making standard genetic methods of analysis...... the variances and covariances of these estimators and provide a corrected version of Tajima's D statistic. We reanalyze a human genomewide SNP data set and find substantial differences in the results with or without ascertainment bias correction....

Maximum likelihood estimation and EM algorithm of Copas-like selection model for publication bias correction.

Science.gov (United States)

Ning, Jing; Chen, Yong; Piao, Jin

2017-07-01

Publication bias occurs when the published research results are systematically unrepresentative of the population of studies that have been conducted, and is a potential threat to meaningful meta-analysis. The Copas selection model provides a flexible framework for correcting estimates and offers considerable insight into the publication bias. However, maximizing the observed likelihood under the Copas selection model is challenging because the observed data contain very little information on the latent variable. In this article, we study a Copas-like selection model and propose an expectation-maximization (EM) algorithm for estimation based on the full likelihood. Empirical simulation studies show that the EM algorithm and its associated inferential procedure performs well and avoids the non-convergence problem when maximizing the observed likelihood. © The Author 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Re-constructing historical Adélie penguin abundance estimates by retrospectively accounting for detection bias.

Science.gov (United States)

Southwell, Colin; Emmerson, Louise; Newbery, Kym; McKinlay, John; Kerry, Knowles; Woehler, Eric; Ensor, Paul

2015-01-01

Seabirds and other land-breeding marine predators are considered to be useful and practical indicators of the state of marine ecosystems because of their dependence on marine prey and the accessibility of their populations at breeding colonies. Historical counts of breeding populations of these higher-order marine predators are one of few data sources available for inferring past change in marine ecosystems. However, historical abundance estimates derived from these population counts may be subject to unrecognised bias and uncertainty because of variable attendance of birds at breeding colonies and variable timing of past population surveys. We retrospectively accounted for detection bias in historical abundance estimates of the colonial, land-breeding Adélie penguin through an analysis of 222 historical abundance estimates from 81 breeding sites in east Antarctica. The published abundance estimates were de-constructed to retrieve the raw count data and then re-constructed by applying contemporary adjustment factors obtained from remotely operating time-lapse cameras. The re-construction process incorporated spatial and temporal variation in phenology and attendance by using data from cameras deployed at multiple sites over multiple years and propagating this uncertainty through to the final revised abundance estimates. Our re-constructed abundance estimates were consistently higher and more uncertain than published estimates. The re-constructed estimates alter the conclusions reached for some sites in east Antarctica in recent assessments of long-term Adélie penguin population change. Our approach is applicable to abundance data for a wide range of colonial, land-breeding marine species including other penguin species, flying seabirds and marine mammals.

Re-constructing historical Adélie penguin abundance estimates by retrospectively accounting for detection bias.

Directory of Open Access Journals (Sweden)

Colin Southwell

Full Text Available Seabirds and other land-breeding marine predators are considered to be useful and practical indicators of the state of marine ecosystems because of their dependence on marine prey and the accessibility of their populations at breeding colonies. Historical counts of breeding populations of these higher-order marine predators are one of few data sources available for inferring past change in marine ecosystems. However, historical abundance estimates derived from these population counts may be subject to unrecognised bias and uncertainty because of variable attendance of birds at breeding colonies and variable timing of past population surveys. We retrospectively accounted for detection bias in historical abundance estimates of the colonial, land-breeding Adélie penguin through an analysis of 222 historical abundance estimates from 81 breeding sites in east Antarctica. The published abundance estimates were de-constructed to retrieve the raw count data and then re-constructed by applying contemporary adjustment factors obtained from remotely operating time-lapse cameras. The re-construction process incorporated spatial and temporal variation in phenology and attendance by using data from cameras deployed at multiple sites over multiple years and propagating this uncertainty through to the final revised abundance estimates. Our re-constructed abundance estimates were consistently higher and more uncertain than published estimates. The re-constructed estimates alter the conclusions reached for some sites in east Antarctica in recent assessments of long-term Adélie penguin population change. Our approach is applicable to abundance data for a wide range of colonial, land-breeding marine species including other penguin species, flying seabirds and marine mammals.

Mixture models reveal multiple positional bias types in RNA-Seq data and lead to accurate transcript concentration estimates.

Directory of Open Access Journals (Sweden)

Andreas Tuerk

2017-05-01

Full Text Available Accuracy of transcript quantification with RNA-Seq is negatively affected by positional fragment bias. This article introduces Mix2 (rd. "mixquare", a transcript quantification method which uses a mixture of probability distributions to model and thereby neutralize the effects of positional fragment bias. The parameters of Mix2 are trained by Expectation Maximization resulting in simultaneous transcript abundance and bias estimates. We compare Mix2 to Cufflinks, RSEM, eXpress and PennSeq; state-of-the-art quantification methods implementing some form of bias correction. On four synthetic biases we show that the accuracy of Mix2 overall exceeds the accuracy of the other methods and that its bias estimates converge to the correct solution. We further evaluate Mix2 on real RNA-Seq data from the Microarray and Sequencing Quality Control (MAQC, SEQC Consortia. On MAQC data, Mix2 achieves improved correlation to qPCR measurements with a relative increase in R2 between 4% and 50%. Mix2 also yields repeatable concentration estimates across technical replicates with a relative increase in R2 between 8% and 47% and reduced standard deviation across the full concentration range. We further observe more accurate detection of differential expression with a relative increase in true positives between 74% and 378% for 5% false positives. In addition, Mix2 reveals 5 dominant biases in MAQC data deviating from the common assumption of a uniform fragment distribution. On SEQC data, Mix2 yields higher consistency between measured and predicted concentration ratios. A relative error of 20% or less is obtained for 51% of transcripts by Mix2, 40% of transcripts by Cufflinks and RSEM and 30% by eXpress. Titration order consistency is correct for 47% of transcripts for Mix2, 41% for Cufflinks and RSEM and 34% for eXpress. We, further, observe improved repeatability across laboratory sites with a relative increase in R2 between 8% and 44% and reduced standard deviation.

An Improved BeiDou-2 Satellite-Induced Code Bias Estimation Method

Directory of Open Access Journals (Sweden)

Jingyang Fu

2018-04-01

Full Text Available Different from GPS, GLONASS, GALILEO and BeiDou-3, it is confirmed that the code multipath bias (CMB, which originate from the satellite end and can be over 1 m, are commonly found in the code observations of BeiDou-2 (BDS IGSO and MEO satellites. In order to mitigate their adverse effects on absolute precise applications which use the code measurements, we propose in this paper an improved correction model to estimate the CMB. Different from the traditional model which considering the correction values are orbit-type dependent (estimating two sets of values for IGSO and MEO, respectively and modeling the CMB as a piecewise linear function with a elevation node separation of 10°, we estimate the corrections for each BDS IGSO + MEO satellite on one hand, and a denser elevation node separation of 5° is used to model the CMB variations on the other hand. Currently, the institutions such as IGS-MGEX operate over 120 stations which providing the daily BDS observations. These large amounts of data provide adequate support to refine the CMB estimation satellite by satellite in our improved model. One month BDS observations from MGEX are used for assessing the performance of the improved CMB model by means of precise point positioning (PPP. Experimental results show that for the satellites on the same orbit type, obvious differences can be found in the CMB at the same node and frequency. Results show that the new correction model can improve the wide-lane (WL ambiguity usage rate for WL fractional cycle bias estimation, shorten the WL and narrow-lane (NL time to first fix (TTFF in PPP ambiguity resolution (AR as well as improve the PPP positioning accuracy. With our improved correction model, the usage of WL ambiguity is increased from 94.1% to 96.0%, the WL and NL TTFF of PPP AR is shorten from 10.6 to 9.3 min, 67.9 to 63.3 min, respectively, compared with the traditional correction model. In addition, both the traditional and improved CMB model have

Estimating the residential demand function for natural gas in Seoul with correction for sample selection bias

International Nuclear Information System (INIS)

Yoo, Seung-Hoon; Lim, Hea-Jin; Kwak, Seung-Jun

2009-01-01

Over the last twenty years, the consumption of natural gas in Korea has increased dramatically. This increase has mainly resulted from the rise of consumption in the residential sector. The main objective of the study is to estimate households' demand function for natural gas by applying a sample selection model using data from a survey of households in Seoul. The results show that there exists a selection bias in the sample and that failure to correct for sample selection bias distorts the mean estimate, of the demand for natural gas, downward by 48.1%. In addition, according to the estimation results, the size of the house, the dummy variable for dwelling in an apartment, the dummy variable for having a bed in an inner room, and the household's income all have positive relationships with the demand for natural gas. On the other hand, the size of the family and the price of gas negatively contribute to the demand for natural gas. (author)

Adaptive Disturbance Estimation for Offset-Free SISO Model Predictive Control

DEFF Research Database (Denmark)

Huusom, Jakob Kjøbsted; Poulsen, Niels Kjølstad; Jørgensen, Sten Bay

2011-01-01

Offset free tracking in Model Predictive Control requires estimation of unmeasured disturbances or the inclusion of an integrator. An algorithm for estimation of an unknown disturbance based on adaptive estimation with time varying forgetting is introduced and benchmarked against the classical...

Prediction of shear wave velocity using empirical correlations and artificial intelligence methods

Science.gov (United States)

Maleki, Shahoo; Moradzadeh, Ali; Riabi, Reza Ghavami; Gholami, Raoof; Sadeghzadeh, Farhad

2014-06-01

Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR) and Back-Propagation Neural Network (BPNN). Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.

Prediction of shear wave velocity using empirical correlations and artificial intelligence methods

Directory of Open Access Journals (Sweden)

Shahoo Maleki

2014-06-01

Full Text Available Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR and Back-Propagation Neural Network (BPNN. Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.

Observation of self-organized criticality (SOC) behavior during edge biasing experiment on TEXTOR

Energy Technology Data Exchange (ETDEWEB)

Xu, Y.H.; Jachmich, S.; Weynants, R.R. [Ecole Royale Militaire/Koninklijke Militaire School, Laboratory for Plasma Physics, Euratom-Belgian State Association, Brussels, Belgium, Partner in the Trilateral Euregio Cluster (Belgium)

2004-07-01

The self-organized criticality (SOC) behavior of the edge plasma transport has been investigated using the fluctuation data measured in the plasma edge and the scrape-off layer of TEXTOR tokamak before and during the edge electrode biasing experiments. In the 'non-shear' discharge phase before biasing, both the potential and density fluctuations clearly exhibit some of the characteristics associated with SOC: (1) existence of f{sup -1} power-law dependence in the frequency spectrum, (2) slowly decaying long tails in the autocorrelation function, (3) values of Hurst parameters larger than 0.5 at all the detected radial locations, (4) non-Gaussian probability density function of fluctuations and (5) radial propagation of avalanche-like events in the edge plasma area. During the biasing phase, with the generation of an edge radial electric field E{sub r} and hence a sheared E{sub r} x B flow, the local turbulence is found to be well de-correlated by the E{sub r} x B velocity shear, consistent with theoretical predictions. Nevertheless, it is concomitantly found that the Hurst parameters are substantially enhanced in the negative flow shear region and in the scrape-off layer as well, which is contrary to theoretical expectation. Implication of these observations to our understanding of plasma transport mechanisms is discussed. (authors)

Estimating Free and Added Sugar Intakes in New Zealand

OpenAIRE

Rachael Kibblewhite; Alice Nettleton; Rachael McLean; Jillian Haszard; Elizabeth Fleming; Devonia Kruimer; Lisa Te Morenga

2017-01-01

The reduction of free or added sugar intake (sugars added to food and drinks as a sweetener) is almost universally recommended to reduce the risk of obesity-related diseases and dental caries. The World Health Organisation recommends intakes of free sugars of less than 10% of energy intake. However, estimating and monitoring intakes at the population level is challenging because free sugars cannot be analytically distinguished from naturally occurring sugars and most national food composition...

Measurement of tritium in the free water of milk : spotting and quantifying some biases and proposing ways of improvement

International Nuclear Information System (INIS)

Le Goff, Pierre; Duda, Jean-Marie; Guétat, Philippe; Rambaud, Pauline; Mavon, Christophe; Vichot, Laurent; Badot, Pierre-Marie; Fromm, Michel

2014-01-01

As one of the three natural isotopes of hydrogen, tritium is ubiquitous and may potentially be present in any water or organic molecule that constitutes a biological matrix. Milk is one of the most frequently monitored foodstuffs in the vicinity of chronic release of radionuclides, as it is a very common food product and also because it integrates deposition on large areas of grass or crops at a local scale. Different parameters have been studied to assess their impact on the reliability of tritium measurements in the free water of milk. The volume of the sample, the technique used to extract the water and the level of dehydration modulate the results but in different ways: dispersion of results and under- or over-estimation of the tritium activity. The influence of sample storage and preparation has also been investigated. Methodological improvements of tritium measurements in the free water of milk are proposed. An original fractionation effect during distillation of milk is also described. -- Highlights: • Biases in tritium assay are caused by the conditions in which the water is extracted. • Isotopic fractionation does not fit with the Rayleigh formula when milk is distilled. • Recommendations are made to improve tritium activity measurement

Bias in estimating the cross-sectional smoking, alcohol, obesity and diabetes associations with moderate-severe periodontitis in the Atherosclerosis Risk in Communities study: comparison of full versus partial-mouth estimates.

Science.gov (United States)

Akinkugbe, Aderonke A; Saraiya, Veeral M; Preisser, John S; Offenbacher, Steven; Beck, James D

2015-07-01

To assess whether partial-mouth protocols (PRPs) result in biased estimates of the associations between smoking, alcohol, obesity and diabetes with periodontitis. Using a sample (n = 6129) of the 1996-1998 Atherosclerosis Risk in Communities study, we used measures of probing pocket depth and clinical attachment level to identify moderate-severe periodontitis. Adjusting for confounders, unconditional binary logistic regression estimated prevalence odds ratios (POR) and 95% confidence limits. Specifically, we compared POR for smoking, alcohol, obesity and diabetes with periodontitis derived from full-mouth to those derived from 4-PRPs (Ramfjörd, National Health and Nutrition Examination survey-III, modified-NHANES-IV and 42-site-Random-site selection-method). Finally, we conducted a simple sensitivity analysis of periodontitis misclassification by changing the case definition threshold for each PRP. In comparison to full-mouth PORs, PRP PORs were biased in terms of magnitude and direction. Holding the full-mouth case definition at moderate-severe periodontitis and setting it at mild-moderate-severe for the PRPs did not consistently produce POR estimates that were either biased towards or away from the null in comparison to full-mouth estimates. Partial-mouth protocols result in misclassification of periodontitis and may bias epidemiologic measures of association. The magnitude and direction of this bias depends on choice of PRP and case definition threshold used. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Estimation bias from using nonlinear Fourier plane correlators for sub-pixel image shift measurement and implications for the binary joint transform correlator

Science.gov (United States)

Grycewicz, Thomas J.; Florio, Christopher J.; Franz, Geoffrey A.; Robinson, Ross E.

2007-09-01

When using Fourier plane digital algorithms or an optical correlator to measure the correlation between digital images, interpolation by center-of-mass or quadratic estimation techniques can be used to estimate image displacement to the sub-pixel level. However, this can lead to a bias in the correlation measurement. This bias shifts the sub-pixel output measurement to be closer to the nearest pixel center than the actual location. The paper investigates the bias in the outputs of both digital and optical correlators, and proposes methods to minimize this effect. We use digital studies and optical implementations of the joint transform correlator to demonstrate optical registration with accuracies better than 0.1 pixels. We use both simulations of image shift and movies of a moving target as inputs. We demonstrate bias error for both center-of-mass and quadratic interpolation, and discuss the reasons that this bias is present. Finally, we suggest measures to reduce or eliminate the bias effects. We show that when sub-pixel bias is present, it can be eliminated by modifying the interpolation method. By removing the bias error, we improve registration accuracy by thirty percent.

Optimized Free Energies from Bidirectional Single-Molecule Force Spectroscopy

Science.gov (United States)

Minh, David D. L.; Adib, Artur B.

2008-05-01

An optimized method for estimating path-ensemble averages using data from processes driven in opposite directions is presented. Based on this estimator, bidirectional expressions for reconstructing free energies and potentials of mean force from single-molecule force spectroscopy—valid for biasing potentials of arbitrary stiffness—are developed. Numerical simulations on a model potential indicate that these methods perform better than unidirectional strategies.

Out-of-plane ultimate shear strength of RC mat-slab foundations

International Nuclear Information System (INIS)

Kumagai, Hitoshi; Nukui, Yasushi; Imamura, Akira; Terayama, Takeshi; Hagiwara, Tetsuya; Kojima, Isao

2011-01-01

There have been few studies on the out-of-plane shear in RC mat-slab foundations, and the reasonable method has been demanded to estimate ultimate shear strength of RC mat-slab foundations in the nuclear facilities. In the previous study, the out-of-plane loading tests on the 20 square slab specimens had been performed to collect the fundamental data. In this study, the test results were successfully predicted by 3D non-linear Finite Element Analysis. It has been confirmed that the ultimate shear stress in the slab specimen can be estimated by the Arakawa's formula, which is commonly used to estimate the shear strength of RC beams. (author)

Is it feasible to estimate radiosonde biases from interlaced measurements?

Science.gov (United States)

Kremser, Stefanie; Tradowsky, Jordis S.; Rust, Henning W.; Bodeker, Greg E.

2018-05-01

Upper-air measurements of essential climate variables (ECVs), such as temperature, are crucial for climate monitoring and climate change detection. Because of the internal variability of the climate system, many decades of measurements are typically required to robustly detect any trend in the climate data record. It is imperative for the records to be temporally homogeneous over many decades to confidently estimate any trend. Historically, records of upper-air measurements were primarily made for short-term weather forecasts and as such are seldom suitable for studying long-term climate change as they lack the required continuity and homogeneity. Recognizing this, the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) has been established to provide reference-quality measurements of climate variables, such as temperature, pressure, and humidity, together with well-characterized and traceable estimates of the measurement uncertainty. To ensure that GRUAN data products are suitable to detect climate change, a scientifically robust instrument replacement strategy must always be adopted whenever there is a change in instrumentation. By fully characterizing any systematic differences between the old and new measurement system a temporally homogeneous data series can be created. One strategy is to operate both the old and new instruments in tandem for some overlap period to characterize any inter-instrument biases. However, this strategy can be prohibitively expensive at measurement sites operated by national weather services or research institutes. An alternative strategy that has been proposed is to alternate between the old and new instruments, so-called interlacing, and then statistically derive the systematic biases between the two instruments. Here we investigate the feasibility of such an approach specifically for radiosondes, i.e. flying the old and new instruments on alternating days. Synthetic data sets are used to explore the

Evaluating interfacial shear stresses in composite hollo

Directory of Open Access Journals (Sweden)

Aiham Adawi

2016-09-01

Full Text Available Analytical evaluation of the interfacial shear stresses for composite hollowcore slabs with concrete topping is rare in the literature. Adawi et al. (2014 estimated the interfacial shear stiffness coefficient (ks that governs the behavior of the interface between hollowcore slabs and the concrete topping using push-off tests. This parameter is utilized in this paper to provide closed form solutions for the differential equations governing the behavior of simply supported composite hollowcore slabs. An analytical solution based on the deformation compatibility of the composite section and elastic beam theory, is developed to evaluate the shear stresses along the interface. Linear finite element modeling of the full-scale tests presented in Adawi et al. (2015 is also conducted to validate the developed analytical solution. The proposed analytical solution was found to be adequate in estimating the magnitude of horizontal shear stress in the studied composite hollowcore slabs.

National HIV prevalence estimates for sub-Saharan Africa: controlling selection bias with Heckman-type selection models

Science.gov (United States)

Hogan, Daniel R; Salomon, Joshua A; Canning, David; Hammitt, James K; Zaslavsky, Alan M; Bärnighausen, Till

2012-01-01

Objectives Population-based HIV testing surveys have become central to deriving estimates of national HIV prevalence in sub-Saharan Africa. However, limited participation in these surveys can lead to selection bias. We control for selection bias in national HIV prevalence estimates using a novel approach, which unlike conventional imputation can account for selection on unobserved factors. Methods For 12 Demographic and Health Surveys conducted from 2001 to 2009 (N=138 300), we predict HIV status among those missing a valid HIV test with Heckman-type selection models, which allow for correlation between infection status and participation in survey HIV testing. We compare these estimates with conventional ones and introduce a simulation procedure that incorporates regression model parameter uncertainty into confidence intervals. Results Selection model point estimates of national HIV prevalence were greater than unadjusted estimates for 10 of 12 surveys for men and 11 of 12 surveys for women, and were also greater than the majority of estimates obtained from conventional imputation, with significantly higher HIV prevalence estimates for men in Cote d'Ivoire 2005, Mali 2006 and Zambia 2007. Accounting for selective non-participation yielded 95% confidence intervals around HIV prevalence estimates that are wider than those obtained with conventional imputation by an average factor of 4.5. Conclusions Our analysis indicates that national HIV prevalence estimates for many countries in sub-Saharan African are more uncertain than previously thought, and may be underestimated in several cases, underscoring the need for increasing participation in HIV surveys. Heckman-type selection models should be included in the set of tools used for routine estimation of HIV prevalence. PMID:23172342

Shear-induced inflation of coronal magnetic fields

International Nuclear Information System (INIS)

Klimchuk, J.A.

1990-01-01

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes. 38 refs

Estimates of bottom roughness length and bottom shear stress in South San Francisco Bay, California

Science.gov (United States)

Cheng, R.T.; Ling, C.-H.; Gartner, J.W.; Wang, P.-F.

1999-01-01

A field investigation of the hydrodynamics and the resuspension and transport of participate matter in a bottom boundary layer was carried out in South San Francisco Bay (South Bay), California, during March-April 1995. Using broadband acoustic Doppler current profilers, detailed measurements of turbulent mean velocity distribution within 1.5 m above bed have been obtained. A global method of data analysis was used for estimating bottom roughness length zo and bottom shear stress (or friction velocities u*). Field data have been examined by dividing the time series of velocity profiles into 24-hour periods and independently analyzing the velocity profile time series by flooding and ebbing periods. The global method of solution gives consistent properties of bottom roughness length zo and bottom shear stress values (or friction velocities u*) in South Bay. Estimated mean values of zo and u* for flooding and ebbing cycles are different. The differences in mean zo and u* are shown to be caused by tidal current flood-ebb inequality, rather than the flooding or ebbing of tidal currents. The bed shear stress correlates well with a reference velocity; the slope of the correlation defines a drag coefficient. Forty-three days of field data in South Bay show two regimes of zo (and drag coefficient) as a function of a reference velocity. When the mean velocity is >25-30 cm s-1, the ln zo (and thus the drag coefficient) is inversely proportional to the reference velocity. The cause for the reduction of roughness length is hypothesized as sediment erosion due to intensifying tidal currents thereby reducing bed roughness. When the mean velocity is <25-30 cm s-1, the correlation between zo and the reference velocity is less clear. A plausible explanation of scattered values of zo under this condition may be sediment deposition. Measured sediment data were inadequate to support this hypothesis, but the proposed hypothesis warrants further field investigation.

Bias-Free Chemically Diverse Test Sets from Machine Learning.

Science.gov (United States)

Swann, Ellen T; Fernandez, Michael; Coote, Michelle L; Barnard, Amanda S

2017-08-14

Current benchmarking methods in quantum chemistry rely on databases that are built using a chemist's intuition. It is not fully understood how diverse or representative these databases truly are. Multivariate statistical techniques like archetypal analysis and K-means clustering have previously been used to summarize large sets of nanoparticles however molecules are more diverse and not as easily characterized by descriptors. In this work, we compare three sets of descriptors based on the one-, two-, and three-dimensional structure of a molecule. Using data from the NIST Computational Chemistry Comparison and Benchmark Database and machine learning techniques, we demonstrate the functional relationship between these structural descriptors and the electronic energy of molecules. Archetypes and prototypes found with topological or Coulomb matrix descriptors can be used to identify smaller, statistically significant test sets that better capture the diversity of chemical space. We apply this same method to find a diverse subset of organic molecules to demonstrate how the methods can easily be reapplied to individual research projects. Finally, we use our bias-free test sets to assess the performance of density functional theory and quantum Monte Carlo methods.

Improved Correction of Misclassification Bias With Bootstrap Imputation.

Science.gov (United States)

van Walraven, Carl

2018-07-01

Diagnostic codes used in administrative database research can create bias due to misclassification. Quantitative bias analysis (QBA) can correct for this bias, requires only code sensitivity and specificity, but may return invalid results. Bootstrap imputation (BI) can also address misclassification bias but traditionally requires multivariate models to accurately estimate disease probability. This study compared misclassification bias correction using QBA and BI. Serum creatinine measures were used to determine severe renal failure status in 100,000 hospitalized patients. Prevalence of severe renal failure in 86 patient strata and its association with 43 covariates was determined and compared with results in which renal failure status was determined using diagnostic codes (sensitivity 71.3%, specificity 96.2%). Differences in results (misclassification bias) were then corrected with QBA or BI (using progressively more complex methods to estimate disease probability). In total, 7.4% of patients had severe renal failure. Imputing disease status with diagnostic codes exaggerated prevalence estimates [median relative change (range), 16.6% (0.8%-74.5%)] and its association with covariates [median (range) exponentiated absolute parameter estimate difference, 1.16 (1.01-2.04)]. QBA produced invalid results 9.3% of the time and increased bias in estimates of both disease prevalence and covariate associations. BI decreased misclassification bias with increasingly accurate disease probability estimates. QBA can produce invalid results and increase misclassification bias. BI avoids invalid results and can importantly decrease misclassification bias when accurate disease probability estimates are used.

Comparison of direct shear and simple shear responses of municipal solid waste in USA

KAUST Repository

Fei, Xunchang

2017-10-25

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (τ ) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between the shear responses of MSW obtained from the two testing methods is lacking. In this study, a large-size shear device was used to test identical MSW specimens sampled in USA in DS and SS. Eight DS tests and 11 SS tests were conducted at vertical effective stresses of 50–500 kPa. The stress–displacement response of MSW in SS testing was hyperbolic and a maximum shear stress was reached, whereas a maximum shear stress was not reached in most DS tests. The τ, effective friction angle (ϕ ′) and cohesion (c ′) of MSW were obtained from DS and SS tests by using a displacement failure criterion of 40 mm. τ in SS testing was found to be equal to or lower than τ in DS testing with ratios of τ between 73 and 101%. SS testing resulted in higher ϕ ′ but lower c ′ than DS testing. The shear strength parameters were lower than those obtained in previous studies from DS tests at 55 mm displacement.

Gibbs Sampler-Based λ-Dynamics and Rao-Blackwell Estimator for Alchemical Free Energy Calculation.

Science.gov (United States)

Ding, Xinqiang; Vilseck, Jonah Z; Hayes, Ryan L; Brooks, Charles L

2017-06-13

λ-dynamics is a generalized ensemble method for alchemical free energy calculations. In traditional λ-dynamics, the alchemical switch variable λ is treated as a continuous variable ranging from 0 to 1 and an empirical estimator is utilized to approximate the free energy. In the present article, we describe an alternative formulation of λ-dynamics that utilizes the Gibbs sampler framework, which we call Gibbs sampler-based λ-dynamics (GSLD). GSLD, like traditional λ-dynamics, can be readily extended to calculate free energy differences between multiple ligands in one simulation. We also introduce a new free energy estimator, the Rao-Blackwell estimator (RBE), for use in conjunction with GSLD. Compared with the current empirical estimator, the advantage of RBE is that RBE is an unbiased estimator and its variance is usually smaller than the current empirical estimator. We also show that the multistate Bennett acceptance ratio equation or the unbinned weighted histogram analysis method equation can be derived using the RBE. We illustrate the use and performance of this new free energy computational framework by application to a simple harmonic system as well as relevant calculations of small molecule relative free energies of solvation and binding to a protein receptor. Our findings demonstrate consistent and improved performance compared with conventional alchemical free energy methods.

GPS receiver phase biases estimable in PPP-RTK networks: dynamic characterization and impact analysis

Science.gov (United States)

Zhang, Baocheng; Liu, Teng; Yuan, Yunbin

2018-06-01

The integer ambiguity resolution enabled precise point positioning (PPP-RTK) has been proven advantageous in a wide range of applications. The realization of PPP-RTK concerns the isolation of satellite phase biases (SPBs) and other corrections from a network of Global Positioning System (GPS) reference receivers. This is generally based on Kalman filter in order to achieve real-time capability, in which proper modeling of the dynamics of various types of unknowns remains crucial. This paper seeks to gain insight into how to reasonably deal with the dynamic behavior of the estimable receiver phase biases (RPBs). Using dual-frequency GPS data collected at six colocated receivers over days 50-120 of 2015, we analyze the 30-s epoch-by-epoch estimates of L1 and wide-lane (WL) RPBs for each receiver pair. The dynamics observed in these estimates are a combined effect of three factors, namely the random measurement noise, the multipath and the ambient temperature. The first factor can be overcome by turning to a real-time filter and the second by considering the use of a sidereal filtering. The third factor has an effect only on the WL, and this effect appears to be linear. After accounting for these three factors, the low-pass-filtered, sidereal-filtered, epoch-by-epoch estimates of L1 RPBs follow a random walk process, whereas those of WL RPBs are constant over time. Properly modeling the dynamics of RPBs is vital, as it ensures the best convergence of the Kalman-filtered, between-satellite single-differenced SPB estimates to their correct values and, in turn, shortens the time-to-first-fix at user side.

GPS receiver phase biases estimable in PPP-RTK networks: dynamic characterization and impact analysis

Science.gov (United States)

Zhang, Baocheng; Liu, Teng; Yuan, Yunbin

2017-11-01

The integer ambiguity resolution enabled precise point positioning (PPP-RTK) has been proven advantageous in a wide range of applications. The realization of PPP-RTK concerns the isolation of satellite phase biases (SPBs) and other corrections from a network of Global Positioning System (GPS) reference receivers. This is generally based on Kalman filter in order to achieve real-time capability, in which proper modeling of the dynamics of various types of unknowns remains crucial. This paper seeks to gain insight into how to reasonably deal with the dynamic behavior of the estimable receiver phase biases (RPBs). Using dual-frequency GPS data collected at six colocated receivers over days 50-120 of 2015, we analyze the 30-s epoch-by-epoch estimates of L1 and wide-lane (WL) RPBs for each receiver pair. The dynamics observed in these estimates are a combined effect of three factors, namely the random measurement noise, the multipath and the ambient temperature. The first factor can be overcome by turning to a real-time filter and the second by considering the use of a sidereal filtering. The third factor has an effect only on the WL, and this effect appears to be linear. After accounting for these three factors, the low-pass-filtered, sidereal-filtered, epoch-by-epoch estimates of L1 RPBs follow a random walk process, whereas those of WL RPBs are constant over time. Properly modeling the dynamics of RPBs is vital, as it ensures the best convergence of the Kalman-filtered, between-satellite single-differenced SPB estimates to their correct values and, in turn, shortens the time-to-first-fix at user side.

Optimal classifier selection and negative bias in error rate estimation: an empirical study on high-dimensional prediction

Directory of Open Access Journals (Sweden)

Boulesteix Anne-Laure

2009-12-01

Full Text Available Abstract Background In biometric practice, researchers often apply a large number of different methods in a "trial-and-error" strategy to get as much as possible out of their data and, due to publication pressure or pressure from the consulting customer, present only the most favorable results. This strategy may induce a substantial optimistic bias in prediction error estimation, which is quantitatively assessed in the present manuscript. The focus of our work is on class prediction based on high-dimensional data (e.g. microarray data, since such analyses are particularly exposed to this kind of bias. Methods In our study we consider a total of 124 variants of classifiers (possibly including variable selection or tuning steps within a cross-validation evaluation scheme. The classifiers are applied to original and modified real microarray data sets, some of which are obtained by randomly permuting the class labels to mimic non-informative predictors while preserving their correlation structure. Results We assess the minimal misclassification rate over the different variants of classifiers in order to quantify the bias arising when the optimal classifier is selected a posteriori in a data-driven manner. The bias resulting from the parameter tuning (including gene selection parameters as a special case and the bias resulting from the choice of the classification method are examined both separately and jointly. Conclusions The median minimal error rate over the investigated classifiers was as low as 31% and 41% based on permuted uninformative predictors from studies on colon cancer and prostate cancer, respectively. We conclude that the strategy to present only the optimal result is not acceptable because it yields a substantial bias in error rate estimation, and suggest alternative approaches for properly reporting classification accuracy.

Asymmetric free vibrations of laminated annular cross-ply circular plates including the effects of shear deformation and rotary inertia. Spline method

Energy Technology Data Exchange (ETDEWEB)

Viswanathan, K.K.; Kim, Kyung Su; Lee, Jang Hyun [Inha Univ., Incheon (Korea). Dept. of Naval Architecture and Ocean Engineering

2009-12-15

Asymmetric free vibrations of annular cross-ply circular plates are studied using spline function approximation. The governing equations are formulated including the effects of shear deformation and rotary inertia. Assumptions are made to study the cross-ply layered plates. A system of coupled differential equations are obtained in terms of displacement functions and rotational functions. These functions are approximated using Bickley- type spline functions of suitable order. Then the system is converted into the eigenvalue problem by applying the point collocation technique and suitable boundary conditions. Parametric studies have been made to investigate the effect of transverse shear deformation and rotary inertia on frequency parameter with respect to the circumferential node number, radii ratio and thickness to radius ratio for both symmetric and anti-symmetric cross-ply plates using various types of material properties. (orig.)

Combined estimation of kappa and shear-wave velocity profile of the Japanese rock reference

Science.gov (United States)

Poggi, Valerio; Edwards, Benjamin; Fäh, Donat

2013-04-01

The definition of a common soil or rock reference is a key issue in probabilistic seismic hazard analysis (PSHA), microzonation studies, local site-response analysis and, more generally, when predicted or observed ground motion is compared for sites of different characteristics. A scaling procedure, which accounts for a common reference, is then necessary to avoid bias induced by the differences in the local geology. Nowadays methods requiring the definition of a reference condition generally prescribe the characteristic of a rock reference, calibrated using indirect estimation methods based on geology or on surface proxies. In most cases, a unique average shear-wave velocity value is prescribed (e.g. Vs30 = 800m/s as for class A of the EUROCODE8). Some attempts at defining the whole shape of a reference rock velocity profile have been described, often without a clear physical justification of how such a selection was performed. Moreover, in spite of its relevance in affecting the high-frequency part of the spectrum, the definition of the associated reference attenuation is in most cases missing or, when present, still remains quite uncertain. In this study we propose an approach that is based on the comparison between empirical anelastic amplification functions from spectral modeling of earthquakes and average S-wave velocities computed using the quarter-wavelength approach. The method is an extension of the approach originally proposed by Poggi et al. (2011) for Switzerland, and is here applied to Japan. For the analysis we make use of a selection of 36 stiff-soil and rock sites from the Japanese KiK-net network, for which a measured velocity profile is available. With respect to the previous study, however, we now analyze separately the elastic and anelastic contributions of the estimated empirical amplification. In a first step - which is consistent with the original work - only the elastic part of the amplification spectrum is considered. This procedure allows

Divergence-free smoothing for MRV data on stenosed carotid artery phantom flows

Science.gov (United States)

Im, Chaehyuk; Ko, Seungbin; Song, Simon

2017-11-01

Magnetic Resonance Velocimetry (MRV) is a versatile technique for measuring flow velocity using an MRI machine. It is frequently used for visualization and analysis of blood flows. However, it is difficult to accurately estimate hemodynamics parameters like wall shear stress (WSS) and oscillatory shear index (OSI) due to its low spatial resolution and low signal-to-noise ratio. We suggest a divergence-free smoothing (DFS) method to correct the erroneous velocity vectors obtained with MRV and improve the estimation accuracy of those parameters. Unlike previous studies on DFS for a wall-free flow, we developed a house code to apply a DFS method to a wall-bounded flow. A Hagen-Poiseuille flow and stenosed carotid artery phantom flows were measured with MRV. Each of them was analyzed for validation of the DFS code and confirmation on the accuracy improvement of hemodynamic parameters. We will discuss the effects of DFS on the improvement of the estimation accuracy of velocity vectors, WSS, OSI and etc in detail This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korea government(MSIP) (No. 2016R1A2B3009541).

Joint estimation of vertical total electron content (VTEC) and satellite differential code biases (SDCBs) using low-cost receivers

Science.gov (United States)

Zhang, Baocheng; Teunissen, Peter J. G.; Yuan, Yunbin; Zhang, Hongxing; Li, Min

2018-04-01

Vertical total electron content (VTEC) parameters estimated using global navigation satellite system (GNSS) data are of great interest for ionosphere sensing. Satellite differential code biases (SDCBs) account for one source of error which, if left uncorrected, can deteriorate performance of positioning, timing and other applications. The customary approach to estimate VTEC along with SDCBs from dual-frequency GNSS data, hereinafter referred to as DF approach, consists of two sequential steps. The first step seeks to retrieve ionospheric observables through the carrier-to-code leveling technique. This observable, related to the slant total electron content (STEC) along the satellite-receiver line-of-sight, is biased also by the SDCBs and the receiver differential code biases (RDCBs). By means of thin-layer ionospheric model, in the second step one is able to isolate the VTEC, the SDCBs and the RDCBs from the ionospheric observables. In this work, we present a single-frequency (SF) approach, enabling the joint estimation of VTEC and SDCBs using low-cost receivers; this approach is also based on two steps and it differs from the DF approach only in the first step, where we turn to the precise point positioning technique to retrieve from the single-frequency GNSS data the ionospheric observables, interpreted as the combination of the STEC, the SDCBs and the biased receiver clocks at the pivot epoch. Our numerical analyses clarify how SF approach performs when being applied to GPS L1 data collected by a single receiver under both calm and disturbed ionospheric conditions. The daily time series of zenith VTEC estimates has an accuracy ranging from a few tenths of a TEC unit (TECU) to approximately 2 TECU. For 73-96% of GPS satellites in view, the daily estimates of SDCBs do not deviate, in absolute value, more than 1 ns from their ground truth values published by the Centre for Orbit Determination in Europe.

An experimental verification of laser-velocimeter sampling bias and its correction

Science.gov (United States)

Johnson, D. A.; Modarress, D.; Owen, F. K.

1982-01-01

The existence of 'sampling bias' in individual-realization laser velocimeter measurements is experimentally verified and shown to be independent of sample rate. The experiments were performed in a simple two-stream mixing shear flow with the standard for comparison being laser-velocimeter results obtained under continuous-wave conditions. It is also demonstrated that the errors resulting from sampling bias can be removed by a proper interpretation of the sampling statistics. In addition, data obtained in a shock-induced separated flow and in the near-wake of airfoils are presented, both bias-corrected and uncorrected, to illustrate the effects of sampling bias in the extreme.

An estimation of the height system bias parameter N (0) using least squares collocation from observed gravity and GPS-levelling data

DEFF Research Database (Denmark)

Sadiq, Muhammad; Tscherning, Carl C.; Ahmad, Zulfiqar

2009-01-01

This paper deals with the analysis of gravity anomaly and precise levelling in conjunction with GPS-Levelling data for the computation of a gravimetric geoid and an estimate of the height system bias parameter N-o for the vertical datum in Pakistan by means of least squares collocation technique...... covariance parameters has facilitated to achieve gravimetric height anomalies in a global geocentric datum. Residual terrain modeling (RTM) technique has been used in combination with the EGM96 for the reduction and smoothing of the gravity data. A value for the bias parameter N-o has been estimated...... with reference to the local GPS-Levelling datum that appears to be 0.705 m with 0.07 m mean square error. The gravimetric height anomalies were compared with height anomalies obtained from GPS-Levelling stations using least square collocation with and without bias adjustment. The bias adjustment minimizes...

Advanced Biasing Experiments on the C-2 Field-Reversed Configuration Device

Science.gov (United States)

Thompson, Matthew; Korepanov, Sergey; Garate, Eusebio; Yang, Xiaokang; Gota, Hiroshi; Douglass, Jon; Allfrey, Ian; Valentine, Travis; Uchizono, Nolan; TAE Team

2014-10-01

The C-2 experiment seeks to study the evolution, heating and sustainment effects of neutral beam injection on field-reversed configuration (FRC) plasmas. Recently, substantial improvements in plasma performance were achieved through the application of edge biasing with coaxial plasma guns located in the divertors. Edge biasing provides rotation control that reduces instabilities and E × B shear that improves confinement. Typically, the plasma gun arcs are run at ~ 10 MW for the entire shot duration (~ 5 ms), which will become unsustainable as the plasma duration increases. We have conducted several advanced biasing experiments with reduced-average-power plasma gun operating modes and alternative biasing cathodes in an effort to develop an effective biasing scenario applicable to steady state FRC plasmas. Early results show that several techniques can potentially provide effective, long-duration edge biasing.

Experimental investigation of separated shear layer from a leading ...

Indian Academy of Sciences (India)

Shear layer development over a thick flat plate with a semi-circular leading edge is investigated for a range of angles of attack under different pressure gradients for a Reynolds number of 2.44×105 (based on chord and free-stream velocity). The characteristics of the separated shear layer are very well documented through ...

Bias-correction in vector autoregressive models

DEFF Research Database (Denmark)

Engsted, Tom; Pedersen, Thomas Quistgaard

2014-01-01

We analyze the properties of various methods for bias-correcting parameter estimates in both stationary and non-stationary vector autoregressive models. First, we show that two analytical bias formulas from the existing literature are in fact identical. Next, based on a detailed simulation study......, we show that when the model is stationary this simple bias formula compares very favorably to bootstrap bias-correction, both in terms of bias and mean squared error. In non-stationary models, the analytical bias formula performs noticeably worse than bootstrapping. Both methods yield a notable...... improvement over ordinary least squares. We pay special attention to the risk of pushing an otherwise stationary model into the non-stationary region of the parameter space when correcting for bias. Finally, we consider a recently proposed reduced-bias weighted least squares estimator, and we find...

Design and implementation of a shearing apparatus for the experimental study of shear displacement in rocks

Science.gov (United States)

Moore, Johnathan; Crandall, Dustin; Gill, Magdalena; Brown, Sarah; Tennant, Bryan

2018-04-01

Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via shear to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between shearing and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize shear, they do not characterize the intermediate stages during shear. We present an experimental apparatus based on slight modifications to a commonly available Hassler core holder that allows for shearing of rocks, while measuring the hydraulic and mechanical changes to geomaterials during intermediate steps. The core holder modification employs the use of semi-circular end caps and structural supports for the confining membrane that allow for free movement of the sheared material while preventing membrane collapse. By integrating this modified core holder with a computed tomography scanner, we show a new methodology for understanding the interdependent behavior between fracture structure and flow properties during intermediate steps in shearing. We include a case study of this device function which is shown here through shearing of a fractured shale core and simultaneous observation of the mechanical changes and evolution of the hydraulic properties during shearing.

Semiparametric efficient and robust estimation of an unknown symmetric population under arbitrary sample selection bias

KAUST Repository

Ma, Yanyuan

2013-09-01

We propose semiparametric methods to estimate the center and shape of a symmetric population when a representative sample of the population is unavailable due to selection bias. We allow an arbitrary sample selection mechanism determined by the data collection procedure, and we do not impose any parametric form on the population distribution. Under this general framework, we construct a family of consistent estimators of the center that is robust to population model misspecification, and we identify the efficient member that reaches the minimum possible estimation variance. The asymptotic properties and finite sample performance of the estimation and inference procedures are illustrated through theoretical analysis and simulations. A data example is also provided to illustrate the usefulness of the methods in practice. © 2013 American Statistical Association.

Considerations for analysis of time-to-event outcomes measured with error: Bias and correction with SIMEX.

Science.gov (United States)

Oh, Eric J; Shepherd, Bryan E; Lumley, Thomas; Shaw, Pamela A

2018-04-15

For time-to-event outcomes, a rich literature exists on the bias introduced by covariate measurement error in regression models, such as the Cox model, and methods of analysis to address this bias. By comparison, less attention has been given to understanding the impact or addressing errors in the failure time outcome. For many diseases, the timing of an event of interest (such as progression-free survival or time to AIDS progression) can be difficult to assess or reliant on self-report and therefore prone to measurement error. For linear models, it is well known that random errors in the outcome variable do not bias regression estimates. With nonlinear models, however, even random error or misclassification can introduce bias into estimated parameters. We compare the performance of 2 common regression models, the Cox and Weibull models, in the setting of measurement error in the failure time outcome. We introduce an extension of the SIMEX method to correct for bias in hazard ratio estimates from the Cox model and discuss other analysis options to address measurement error in the response. A formula to estimate the bias induced into the hazard ratio by classical measurement error in the event time for a log-linear survival model is presented. Detailed numerical studies are presented to examine the performance of the proposed SIMEX method under varying levels and parametric forms of the error in the outcome. We further illustrate the method with observational data on HIV outcomes from the Vanderbilt Comprehensive Care Clinic. Copyright © 2017 John Wiley & Sons, Ltd.

Estimation of shear stress in counter-current gas-liquid annular two-phase flow

International Nuclear Information System (INIS)

Abe, Yutaka; Akimoto, Hajime; Murao, Yoshio

1991-01-01

The accuracy of the correlations of the friction factor is important for the counter-current flow (CCF) analysis with two-fluid model. However, existing two fluid model codes use the correlations of friction factors for co-current flow or correlation developed based on the assumption of no wall shear stress. The assessment calculation for two fluid model code with those existing correlations of friction factors shows the falling water flow rate is overestimated. Analytical model is developed to calculate the shear stress distribution in water film at CCF in order to get the information on the shear stress at the interface and the wall. The analytical results with the analysis model and Bharathan's CCF data shows that the wall shear stress acting on the falling water film is almost same order as the interfacial shear stress and the correlations for co-current flow cannot be applied to the counter-current flow. Tentative correlations of the interfacial and the wall friction factors are developed based on the results of the present study. (author)

Shear Behavior Models of Steel Fiber Reinforced Concrete Beams Modifying Softened Truss Model Approaches.

Science.gov (United States)

Hwang, Jin-Ha; Lee, Deuck Hang; Ju, Hyunjin; Kim, Kang Su; Seo, Soo-Yeon; Kang, Joo-Won

2013-10-23

Recognizing that steel fibers can supplement the brittle tensile characteristics of concrete, many studies have been conducted on the shear performance of steel fiber reinforced concrete (SFRC) members. However, previous studies were mostly focused on the shear strength and proposed empirical shear strength equations based on their experimental results. Thus, this study attempts to estimate the strains and stresses in steel fibers by considering the detailed characteristics of steel fibers in SFRC members, from which more accurate estimation on the shear behavior and strength of SFRC members is possible, and the failure mode of steel fibers can be also identified. Four shear behavior models for SFRC members have been proposed, which have been modified from the softened truss models for reinforced concrete members, and they can estimate the contribution of steel fibers to the total shear strength of the SFRC member. The performances of all the models proposed in this study were also evaluated by a large number of test results. The contribution of steel fibers to the shear strength varied from 5% to 50% according to their amount, and the most optimized volume fraction of steel fibers was estimated as 1%-1.5%, in terms of shear performance.

Masking in reports of "most serious" events: bias in estimators of sports injury incidence in Canadian children

Directory of Open Access Journals (Sweden)

A. Gupta

2016-08-01

Full Text Available Introduction: Surveys that collect information on injuries often focus on the single "most serious" event to help limit recall error and reduce survey length. However, this can mask less serious injuries and result in biased incidence estimates for specific injury subcategories. Methods: Data from the 2002 Health Behaviour in School-aged Children (HBSC survey and from the Canadian Hospitals Injury Reporting and Prevention Program (CHIRPP were used to compare estimates of sports injury incidence in Canadian children. Results: HBSC data indicate that 6.7% of children report sustaining a sports injury that required an emergency department (ED visit. However, details were only collected on a child's "most serious" injury, so children who had multiple injuries requiring an ED visit may have had sports injuries that went unreported. The rate of 6.7% can be seen to be an underestimate by as much as 4.3%. Corresponding CHIRPP surveillance data indicate an incidence of 9.9%. Potential masking bias is also highlighted in our analysis of injuries attended by other health care providers. Conclusion: The "one most serious injury" line of questioning induces potentially substantial masking bias in the estimation of sports injury incidence, which limits researchers' ability to quantify the burden of sports injury. Longer survey recall periods naturally lead to greater masking. The design of future surveys should take these issues into account. In order to accurately inform policy decisions and the direction of future research, researchers must be aware of these limitations.

Diabat Interpolation for Polymorph Free-Energy Differences.

Science.gov (United States)

Kamat, Kartik; Peters, Baron

2017-02-02

Existing methods to compute free-energy differences between polymorphs use harmonic approximations, advanced non-Boltzmann bias sampling techniques, and/or multistage free-energy perturbations. This work demonstrates how Bennett's diabat interpolation method ( J. Comput. Phys. 1976, 22, 245 ) can be combined with energy gaps from lattice-switch Monte Carlo techniques ( Phys. Rev. E 2000, 61, 906 ) to swiftly estimate polymorph free-energy differences. The new method requires only two unbiased molecular dynamics simulations, one for each polymorph. To illustrate the new method, we compute the free-energy difference between face-centered cubic and body-centered cubic polymorphs for a Gaussian core solid. We discuss the justification for parabolic models of the free-energy diabats and similarities to methods that have been used in studies of electron transfer.

Imaging Shear Strength Along Subduction Faults

Science.gov (United States)

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-11-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Imaging shear strength along subduction faults

Science.gov (United States)

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-01-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Estimation of free-hydrocarbon recovery from dual-pump systems

International Nuclear Information System (INIS)

Charbeneau, R.J.

1995-01-01

Free-product hydrocarbon which floats on the water table may be recovered using single-pump and dual-pump systems. The factors that affect the long-term free-product recovery using dual-pump systems include the free-product thickness as measured in monitoring wells, the ground-water pumping rate, hydrocarbon density and viscosity, and the soil permeability. This paper presents a simple model for prediction of free-product recovery using dual-pump systems. The model predicts the long-term rather than short-term recovery rates, and lends itself to spreadsheet calculations on microcomputers. A particularly simple form arises for cases where the drawdown is small. An application for estimating recovery from a dual-pump system is presented, and limitations of the model are summarized

Estimating Production Potentials: Expert Bias in Applied Decision Making

International Nuclear Information System (INIS)

Matthews, L.J.; Burggraf, L.K.; Reece, W.J.

1998-01-01

A study was conducted to evaluate how workers predict manufacturing production potentials given positively and negatively framed information. Findings indicate the existence of a bias toward positive information and suggest that this bias may be reduced with experience but is never the less maintained. Experts err in the same way non experts do in differentially processing negative and positive information. Additionally, both experts and non experts tend to overestimate production potentials in a positive direction. The authors propose that these biases should be addressed with further research including cross domain analyses and consideration in training, workplace design, and human performance modeling

Two-dimensional Shear Wave Elastography on Conventional Ultrasound Scanners with Time Aligned Sequential Tracking (TAST) and Comb-push Ultrasound Shear Elastography (CUSE)

Science.gov (United States)

Song, Pengfei; Macdonald, Michael C.; Behler, Russell H.; Lanning, Justin D.; Wang, Michael H.; Urban, Matthew W.; Manduca, Armando; Zhao, Heng; Callstrom, Matthew R.; Alizad, Azra; Greenleaf, James F.; Chen, Shigao

2014-01-01

Two-dimensional (2D) shear wave elastography presents 2D quantitative shear elasticity maps of tissue, which are clinically useful for both focal lesion detection and diffuse disease diagnosis. Realization of 2D shear wave elastography on conventional ultrasound scanners, however, is challenging due to the low tracking pulse-repetition-frequency (PRF) of these systems. While some clinical and research platforms support software beamforming and plane wave imaging with high PRF, the majority of current clinical ultrasound systems do not have the software beamforming capability, which presents a critical challenge for translating the 2D shear wave elastography technique from laboratory to clinical scanners. To address this challenge, this paper presents a Time Aligned Sequential Tracking (TAST) method for shear wave tracking on conventional ultrasound scanners. TAST takes advantage of the parallel beamforming capability of conventional systems and realizes high PRF shear wave tracking by sequentially firing tracking vectors and aligning shear wave data in the temporal direction. The Comb-push Ultrasound Shear Elastography (CUSE) technique was used to simultaneously produce multiple shear wave sources within the field-of-view (FOV) to enhance shear wave signal-to-noise-ratio (SNR) and facilitate robust reconstructions of 2D elasticity maps. TAST and CUSE were realized on a conventional ultrasound scanner (the General Electric LOGIQ E9). A phantom study showed that the shear wave speed measurements from the LOGIQ E9 were in good agreement to the values measured from other 2D shear wave imaging technologies. An inclusion phantom study showed that the LOGIQ E9 had comparable performance to the Aixplorer (Supersonic Imagine) in terms of bias and precision in measuring different sized inclusions. Finally, in vivo case analysis of a breast with a malignant mass, and a liver from a healthy subject demonstrated the feasibility of using the LOGIQ E9 for in vivo 2D shear wave

Eliminating bias in rainfall estimates from microwave links due to antenna wetting

Science.gov (United States)

Fencl, Martin; Rieckermann, Jörg; Bareš, Vojtěch

2014-05-01

Commercial microwave links (MWLs) are point-to-point radio systems which are widely used in telecommunication systems. They operate at frequencies where the transmitted power is mainly disturbed by precipitation. Thus, signal attenuation from MWLs can be used to estimate path-averaged rain rates, which is conceptually very promising, since MWLs cover about 20 % of surface area. Unfortunately, MWL rainfall estimates are often positively biased due to additional attenuation caused by antenna wetting. To correct MWL observations a posteriori to reduce the wet antenna effect (WAE), both empirically and physically based models have been suggested. However, it is challenging to calibrate these models, because the wet antenna attenuation depends both on the MWL properties (frequency, type of antennas, shielding etc.) and different climatic factors (temperature, due point, wind velocity and direction, etc.). Instead, it seems straight forward to keep antennas dry by shielding them. In this investigation we compare the effectiveness of antenna shielding to model-based corrections to reduce the WAE. The experimental setup, located in Dübendorf-Switzerland, consisted of 1.85-km long commercial dual-polarization microwave link at 38 GHz and 5 optical disdrometers. The MWL was operated without shielding in the period from March to October 2011 and with shielding from October 2011 to July 2012. This unique experimental design made it possible to identify the attenuation due to antenna wetting, which can be computed as the difference between the measured and theoretical attenuation. The theoretical path-averaged attenuation was calculated from the path-averaged drop size distribution. During the unshielded periods, the total bias caused by WAE was 0.74 dB, which was reduced by shielding to 0.39 dB for the horizontal polarization (vertical: reduction from 0.96 dB to 0.44 dB). Interestingly, the model-based correction (Schleiss et al. 2013) was more effective because it reduced

Performance of bias corrected MPEG rainfall estimate for rainfall-runoff simulation in the upper Blue Nile Basin, Ethiopia

Science.gov (United States)

Worqlul, Abeyou W.; Ayana, Essayas K.; Maathuis, Ben H. P.; MacAlister, Charlotte; Philpot, William D.; Osorio Leyton, Javier M.; Steenhuis, Tammo S.

2018-01-01

In many developing countries and remote areas of important ecosystems, good quality precipitation data are neither available nor readily accessible. Satellite observations and processing algorithms are being extensively used to produce satellite rainfall products (SREs). Nevertheless, these products are prone to systematic errors and need extensive validation before to be usable for streamflow simulations. In this study, we investigated and corrected the bias of Multi-Sensor Precipitation Estimate-Geostationary (MPEG) data. The corrected MPEG dataset was used as input to a semi-distributed hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) for simulation of discharge of the Gilgel Abay and Gumara watersheds in the Upper Blue Nile basin, Ethiopia. The result indicated that the MPEG satellite rainfall captured 81% and 78% of the gauged rainfall variability with a consistent bias of underestimating the gauged rainfall by 60%. A linear bias correction applied significantly reduced the bias while maintaining the coefficient of correlation. The simulated flow using bias corrected MPEG SRE resulted in a simulated flow comparable to the gauge rainfall for both watersheds. The study indicated the potential of MPEG SRE in water budget studies after applying a linear bias correction.

Normalization Approaches for Removing Systematic Biases Associated with Mass Spectrometry and Label-Free Proteomics

Energy Technology Data Exchange (ETDEWEB)

Callister, Stephen J.; Barry, Richard C.; Adkins, Joshua N.; Johnson, Ethan T.; Qian, Weijun; Webb-Robertson, Bobbie-Jo M.; Smith, Richard D.; Lipton, Mary S.

2006-02-01

Central tendency, linear regression, locally weighted regression, and quantile techniques were investigated for normalization of peptide abundance measurements obtained from high-throughput liquid chromatography-Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR MS). Arbitrary abundances of peptides were obtained from three sample sets, including a standard protein sample, two Deinococcus radiodurans samples taken from different growth phases, and two mouse striatum samples from control and methamphetamine-stressed mice (strain C57BL/6). The selected normalization techniques were evaluated in both the absence and presence of biological variability by estimating extraneous variability prior to and following normalization. Prior to normalization, replicate runs from each sample set were observed to be statistically different, while following normalization replicate runs were no longer statistically different. Although all techniques reduced systematic bias, assigned ranks among the techniques revealed significant trends. For most LC-FTICR MS analyses, linear regression normalization ranked either first or second among the four techniques, suggesting that this technique was more generally suitable for reducing systematic biases.

SEDflume - High Shear Stress Flume

Data.gov (United States)

Federal Laboratory Consortium — The U.S. Army Corps of Engineers High Shear Stress flume (SEDflume) is designed for estimating erosion rates of fine-grained and mixed fine/coarse grained sediments...

Role of E x B Shear and Magnetic Shear in the Formation of Transport Barriers in DIII-D

International Nuclear Information System (INIS)

Burrell, K.H.

2005-01-01

Development of the E x B shear stabilization model to explain the formation of transport barriers in magnetic confinement devices is a major achievement of fusion research. This concept has the universality needed to explain the H-mode edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines; the broader edge transport barrier seen in VH-mode plasmas; and the core transport barriers formed in tokamaks with low or negative magnetic shear. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to reduce transport when an additional source of free energy is applied to it. The transport decrease associated with E x B velocity shear is also of great practical benefit to fusion research. The fundamental physics involved in transport reduction is the effect of E x B shear on the growth, radial extent, and phase correlation of turbulent eddies in the plasma. The same basic transport reduction process can be operational in various portions of the plasma because there are a number of ways to change the radial electric field E r . An important theme in this area is the synergistic effect of E x B velocity shear and magnetic shear. Although the E x B velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of E x B velocity shear and facilitate turbulence stabilization. The experimental results on DIII-D and other devices are generally consistent with the basic theoretical models

On biases in precise point positioning with multi-constellation and multi-frequency GNSS data

International Nuclear Information System (INIS)

El-Mowafy, A; Deo, M; Rizos, C

2016-01-01

Various types of biases in Global Navigation Satellite System (GNSS) data preclude integer ambiguity fixing and degrade solution accuracy when not being corrected during precise point positioning (PPP). In this contribution, these biases are first reviewed, including satellite and receiver hardware biases, differential code biases, differential phase biases, initial fractional phase biases, inter-system receiver time biases, and system time scale offset. PPP models that take account of these biases are presented for two cases using ionosphere-free observations. The first case is when using primary signals that are used to generate precise orbits and clock corrections. The second case applies when using additional signals to the primary ones. In both cases, measurements from single and multiple constellations are addressed. It is suggested that the satellite-related code biases be handled as calibrated quantities that are obtained from multi-GNSS experiment products and the fractional phase cycle biases obtained from a network to allow for integer ambiguity fixing. Some receiver-related biases are removed using between-satellite single differencing, whereas other receiver biases such as inter-system biases are lumped with differential code and phase biases and need to be estimated. The testing results show that the treatment of biases significantly improves solution convergence in the float ambiguity PPP mode, and leads to ambiguity-fixed PPP within a few minutes with a small improvement in solution precision. (paper)

A method of estimating GPS instrumental biases with a convolution algorithm

Science.gov (United States)

Li, Qi; Ma, Guanyi; Lu, Weijun; Wan, Qingtao; Fan, Jiangtao; Wang, Xiaolan; Li, Jinghua; Li, Changhua

2018-03-01

This paper presents a method of deriving the instrumental differential code biases (DCBs) of GPS satellites and dual frequency receivers. Considering that the total electron content (TEC) varies smoothly over a small area, one ionospheric pierce point (IPP) and four more nearby IPPs were selected to build an equation with a convolution algorithm. In addition, unknown DCB parameters were arranged into a set of equations with GPS observations in a day unit by assuming that DCBs do not vary within a day. Then, the DCBs of satellites and receivers were determined by solving the equation set with the least-squares fitting technique. The performance of this method is examined by applying it to 361 days in 2014 using the observation data from 1311 GPS Earth Observation Network (GEONET) receivers. The result was crosswise-compared with the DCB estimated by the mesh method and the IONEX products from the Center for Orbit Determination in Europe (CODE). The DCB values derived by this method agree with those of the mesh method and the CODE products, with biases of 0.091 ns and 0.321 ns, respectively. The convolution method's accuracy and stability were quite good and showed improvements over the mesh method.

Impedance method for measuring shear elasticity of liquids

Science.gov (United States)

Badmaev, B. B.; Dembelova, T. S.; Damdinov, B. B.; Gulgenov, Ch. Zh.

2017-11-01

Experimental results of studying low-frequency (74 kHz) shear elasticity of polymer liquids by the impedance method (analogous to the Mason method) are presented. A free-volume thick liquid layer is placed on the horizontal surface of a piezoelectric quartz crystal with dimensions 34.7 × 12 × 5.5 cm. The latter performs tangential vibrations at resonance frequency. The liquid layer experiences shear strain, and shear waves should propagate in it. From the theory of the method, it follows that, with an increase in the layer thickness, both real and imaginary resonance frequency shifts should exhibit damped oscillations and tend to limiting values. For the liquids under study, the imaginary frequency shift far exceeds the real one, which testifies to the presence of bulk shear elasticity.

Bed shear stress distribution in straight channels with arbitrary cross section

DEFF Research Database (Denmark)

Christensen, Henrik Bo; Fredsøe, Jørgen

1998-01-01

The bed shear stress distribution in straight open channels is affected by mechanisms as bed curvature of the cross section profile, shear diffusion, and secondary currents. This paper compares some analytical and numerical methods to estimate the bed shear stress distribution. The methods...

Edge-Induced Shear Banding in Entangled Polymeric Fluids.

Science.gov (United States)

Hemingway, Ewan J; Fielding, Suzanne M

2018-03-30

Despite decades of research, the question of whether solutions and melts of highly entangled polymers exhibit shear banding as their steady state response to a steadily imposed shear flow remains controversial. From a theoretical viewpoint, an important unanswered question is whether the underlying constitutive curve of shear stress σ as a function of shear rate γ[over ˙] (for states of homogeneous shear) is monotonic, or has a region of negative slope, dσ/dγ[over ˙]<0, which would trigger banding. Attempts to settle the question experimentally via velocimetry of the flow field inside the fluid are often confounded by an instability of the free surface where the sample meets the outside air, known as "edge fracture." Here we show by numerical simulation that in fact even only very modest edge disturbances-which are the precursor of full edge fracture but might well, in themselves, go unnoticed experimentally-can cause strong secondary flows in the form of shear bands that invade deep into the fluid bulk. Crucially, this is true even when the underlying constitutive curve is monotonically increasing, precluding true bulk shear banding in the absence of edge effects.

Gas Near a Wall: Shortened Mean Free Path, Reduced Viscosity, and the Manifestation of the Knudsen Layer in the Navier-Stokes Solution of a Shear Flow

Science.gov (United States)

Abramov, Rafail V.

2018-06-01

For the gas near a solid planar wall, we propose a scaling formula for the mean free path of a molecule as a function of the distance from the wall, under the assumption of a uniform distribution of the incident directions of the molecular free flight. We subsequently impose the same scaling onto the viscosity of the gas near the wall and compute the Navier-Stokes solution of the velocity of a shear flow parallel to the wall. Under the simplifying assumption of constant temperature of the gas, the velocity profile becomes an explicit nonlinear function of the distance from the wall and exhibits a Knudsen boundary layer near the wall. To verify the validity of the obtained formula, we perform the Direct Simulation Monte Carlo computations for the shear flow of argon and nitrogen at normal density and temperature. We find excellent agreement between our velocity approximation and the computed DSMC velocity profiles both within the Knudsen boundary layer and away from it.

Shear Behavior Models of Steel Fiber Reinforced Concrete Beams Modifying Softened Truss Model Approaches

Directory of Open Access Journals (Sweden)

Joo-Won Kang

2013-10-01

Full Text Available Recognizing that steel fibers can supplement the brittle tensile characteristics of concrete, many studies have been conducted on the shear performance of steel fiber reinforced concrete (SFRC members. However, previous studies were mostly focused on the shear strength and proposed empirical shear strength equations based on their experimental results. Thus, this study attempts to estimate the strains and stresses in steel fibers by considering the detailed characteristics of steel fibers in SFRC members, from which more accurate estimation on the shear behavior and strength of SFRC members is possible, and the failure mode of steel fibers can be also identified. Four shear behavior models for SFRC members have been proposed, which have been modified from the softened truss models for reinforced concrete members, and they can estimate the contribution of steel fibers to the total shear strength of the SFRC member. The performances of all the models proposed in this study were also evaluated by a large number of test results. The contribution of steel fibers to the shear strength varied from 5% to 50% according to their amount, and the most optimized volume fraction of steel fibers was estimated as 1%–1.5%, in terms of shear performance.

Estimation of Physical Activity Energy Expenditure during Free-Living from Wrist Accelerometry in UK Adults.

Directory of Open Access Journals (Sweden)

Tom White

Full Text Available Wrist-worn accelerometers are emerging as the most common instrument for measuring physical activity in large-scale epidemiological studies, though little is known about the relationship between wrist acceleration and physical activity energy expenditure (PAEE.1695 UK adults wore two devices simultaneously for six days; a combined sensor and a wrist accelerometer. The combined sensor measured heart rate and trunk acceleration, which was combined with a treadmill test to yield a signal of individually-calibrated PAEE. Multi-level regression models were used to characterise the relationship between the two time-series, and their estimations were evaluated in an independent holdout sample. Finally, the relationship between PAEE and BMI was described separately for each source of PAEE estimate (wrist acceleration models and combined-sensing.Wrist acceleration explained 44-47% between-individual variance in PAEE, with RMSE between 34-39 J•min-1•kg-1. Estimations agreed well with PAEE in cross-validation (mean bias [95% limits of agreement]: 0.07 [-70.6:70.7] but overestimated in women by 3% and underestimated in men by 4%. Estimation error was inversely related to age (-2.3 J•min-1•kg-1 per 10y and BMI (-0.3 J•min-1•kg-1 per kg/m2. Associations with BMI were similar for all PAEE estimates (approximately -0.08 kg/m2 per J•min-1•kg-1.A strong relationship exists between wrist acceleration and PAEE in free-living adults, such that irrespective of the objective method of PAEE assessment, a strong inverse association between PAEE and BMI was observed.

Estimation of shear velocity contrast for dipping or anisotropic medium from transmitted Ps amplitude variation with ray-parameter

Science.gov (United States)

Kumar, Prakash

2015-12-01

Amplitude versus offset analysis of P to P reflection is often used in exploration seismology for hydrocarbon exploration. In the present work, the feasibility to estimate crustal velocity structure from transmitted P to S wave amplitude variation with ray-parameter has been investigated separately for dipping layer and anisotropy medium. First, for horizontal and isotropic medium, the approximation of P-to-s conversion is used that is expressed as a linear form in terms of slowness. Next, the intercept of the linear regression has been used to estimate the shear wave velocity contrast (δβ) across an interface. The formulation holds good for isotropic and horizontal layer medium. Application of such formula to anisotropic medium or dipping layer data may lead to erroneous estimation of δβ. In order to overcome this problem, a method has been proposed to compensate the SV-amplitude using shifted version of SH-amplitude, and subsequently transforming SV amplitudes equivalent to that from isotropic or horizontal layer medium as the case may be. Once this transformation has been done, δβ can be estimated using isotropic horizontal layer formula. The shifts required in SH for the compensation are π/2 and π/4 for dipping layer and anisotropic medium, respectively. The effectiveness of the approach has been reported using various synthetic data sets. The methodology is also tested on real data from HI-CLIMB network in Himalaya, where the presence of dipping Moho has already been reported. The result reveals that the average shear wave velocity contrast across the Moho is larger towards the Indian side compared to the higher Himalayan and Tibetan regions.

Coherent drift wave structures in sheared magnetic fields

International Nuclear Information System (INIS)

Morrison, P.J.; Horton, W.

1993-01-01

For the problem of calculating the coherent drift wave structures in sheared magnetic fields, the authors have found it useful to derive the governing nonlinear pde from a variational principle. The variational principle is based on the free energy functional F[var-phi] = ∫ V F(var-phi, ∇ var-phi, x)dx dy. The method is applied to the vortex with speed u derived in Su et al., given by ∇ 2 var-phi = (1 - v d /u) var-phi - S m 2 /u 2 (x - var-phi/u) (x - var-phi/2u) var-phi where space is measured in units of ρ s , var-phi = (eΦ/T e )(L n /ρ s ) and the magnetic shear parameter is S m . While the linearized problem (var-phi much-lt ux) describes the usual shear induced damping, nonlinear solutions with trapped flow (var-phi > ur 0 ) form nonlinear self-bound states, which are maxima of the free energy F. The authors discuss the analytic properties and the numerical procedures for solving these types of nonlinear pde's

Bootstrap confidence intervals and bias correction in the estimation of HIV incidence from surveillance data with testing for recent infection.

Science.gov (United States)

Carnegie, Nicole Bohme

2011-04-15

The incidence of new infections is a key measure of the status of the HIV epidemic, but accurate measurement of incidence is often constrained by limited data. Karon et al. (Statist. Med. 2008; 27:4617–4633) developed a model to estimate the incidence of HIV infection from surveillance data with biologic testing for recent infection for newly diagnosed cases. This method has been implemented by public health departments across the United States and is behind the new national incidence estimates, which are about 40 per cent higher than previous estimates. We show that the delta method approximation given for the variance of the estimator is incomplete, leading to an inflated variance estimate. This contributes to the generation of overly conservative confidence intervals, potentially obscuring important differences between populations. We demonstrate via simulation that an innovative model-based bootstrap method using the specified model for the infection and surveillance process improves confidence interval coverage and adjusts for the bias in the point estimate. Confidence interval coverage is about 94–97 per cent after correction, compared with 96–99 per cent before. The simulated bias in the estimate of incidence ranges from −6.3 to +14.6 per cent under the original model but is consistently under 1 per cent after correction by the model-based bootstrap. In an application to data from King County, Washington in 2007 we observe correction of 7.2 per cent relative bias in the incidence estimate and a 66 per cent reduction in the width of the 95 per cent confidence interval using this method. We provide open-source software to implement the method that can also be extended for alternate models.

Control of cracking in R.C. Structures: Numerical simulation of a squat shear wall

NARCIS (Netherlands)

Damoni, C.; Belletti, B.; Lilliu, G.

2013-01-01

In this paper the behavior of a squat shear wall subjected to monotonic shear loading is investigated. The study fits into the experimental program driven by CEOS.fr on modeling of the behavior of the tested mocks-ups (monotonic and cycling loading-under prevented or free shrinkage). The shear wall

FLUID EVOLUTION AND MINERAL REACTIONS DURING SHEAR ZONE FORMATION AT NUSFJORD, LOFOTEN, NORWAY (Invited)

Science.gov (United States)

Kullerud, K.

2009-12-01

At Nusfjord in Lofoten, Norway, three 0.3 - 3 m thick shear zones occur in a gabbro-anorthosite. During deformation, the shear zones were infiltrated by a hydrous fluid enriched in Cl. In the central parts of the shear zones, fluid-rock interaction resulted in complete break-down of the primary mafic silicates. Complete hydration of these minerals to Cl-free amphibole and biotite suggests that the hydrous fluid was present in excess during deformation in these parts of the shear zones. Along the margins of the shear zones, however, the igneous mafic silicates (Cpx, Bt, Opx) were only partly overgrown by hydrous minerals. Here, Cl-enriched minerals (Amph, Bt, Scp, Ap) can be observed. Amphibole shows compositions covering the range 0.1 - 4.0 wt % Cl within single thin sections. Mineral textures and extreme compositional variations of the Cl-bearing minerals indicate large chemical gradients of the fluid phase. Relics of primary mafic silicates and compositionally zoned reaction coronas around primary mafic silicates suggest that the free fluid was totally consumed before the alteration of the primary phases were completed. The extreme variations in the Cl-content of amphibole are inferred to monitor a gradual desiccation of the Cl-bearing grain-boundary fluid during fluid-mineral reactions accordingly: 1) The first amphibole that formed during the reactions principally extracted water from the fluid, resulting in a slight increase in the Cl content of the fluid. 2) Continued amphibole-forming reactions resulted in gradual consumption of the free fluid phase, principally by extracting water from the fluid, resulting in an increase in its Cl-content. Higher Cl-content of the fluid resulted in higher Cl-content of the equilibrium amphibole. 3) The most Cl-enriched amphibole (4 wt % Cl) formed in equilibrium with the last volumes of the grain-boundary fluid, which had evolved to a highly saline solution. Mineral reactions within a 1-2 thick zone of the host rock along

Shear and Turbulence Estimates for Calculation of Wind Turbine Loads and Responses Under Hurricane Strength Winds

Science.gov (United States)

Kosovic, B.; Bryan, G. H.; Haupt, S. E.

2012-12-01

Schwartz et al. (2010) recently reported that the total gross energy-generating offshore wind resource in the United States in waters less than 30m deep is approximately 1000 GW. Estimated offshore generating capacity is thus equivalent to the current generating capacity in the United States. Offshore wind power can therefore play important role in electricity production in the United States. However, most of this resource is located along the East Coast of the United States and in the Gulf of Mexico, areas frequently affected by tropical cyclones including hurricanes. Hurricane strength winds, associated shear and turbulence can affect performance and structural integrity of wind turbines. In a recent study Rose et al. (2012) attempted to estimate the risk to offshore wind turbines from hurricane strength winds over a lifetime of a wind farm (i.e. 20 years). According to Rose et al. turbine tower buckling has been observed in typhoons. They concluded that there is "substantial risk that Category 3 and higher hurricanes can destroy half or more of the turbines at some locations." More robust designs including appropriate controls can mitigate the risk of wind turbine damage. To develop such designs good estimates of turbine loads under hurricane strength winds are essential. We use output from a large-eddy simulation of a hurricane to estimate shear and turbulence intensity over first couple of hundred meters above sea surface. We compute power spectra of three velocity components at several distances from the eye of the hurricane. Based on these spectra analytical spectral forms are developed and included in TurbSim, a stochastic inflow turbulence code developed by the National Renewable Energy Laboratory (NREL, http://wind.nrel.gov/designcodes/preprocessors/turbsim/). TurbSim provides a numerical simulation including bursts of coherent turbulence associated with organized turbulent structures. It can generate realistic flow conditions that an operating turbine

Application of a hybrid model to reduce bias and improve precision in population estimates for elk (Cervus elaphus) inhabiting a cold desert ecosystem

Science.gov (United States)

Schoenecker, Kathryn A.; Lubow, Bruce C.

2016-01-01

Accurately estimating the size of wildlife populations is critical to wildlife management and conservation of species. Raw counts or “minimum counts” are still used as a basis for wildlife management decisions. Uncorrected raw counts are not only negatively biased due to failure to account for undetected animals, but also provide no estimate of precision on which to judge the utility of counts. We applied a hybrid population estimation technique that combined sightability modeling, radio collar-based mark-resight, and simultaneous double count (double-observer) modeling to estimate the population size of elk in a high elevation desert ecosystem. Combining several models maximizes the strengths of each individual model while minimizing their singular weaknesses. We collected data with aerial helicopter surveys of the elk population in the San Luis Valley and adjacent mountains in Colorado State, USA in 2005 and 2007. We present estimates from 7 alternative analyses: 3 based on different methods for obtaining a raw count and 4 based on different statistical models to correct for sighting probability bias. The most reliable of these approaches is a hybrid double-observer sightability model (model MH), which uses detection patterns of 2 independent observers in a helicopter plus telemetry-based detections of radio collared elk groups. Data were fit to customized mark-resight models with individual sighting covariates. Error estimates were obtained by a bootstrapping procedure. The hybrid method was an improvement over commonly used alternatives, with improved precision compared to sightability modeling and reduced bias compared to double-observer modeling. The resulting population estimate corrected for multiple sources of undercount bias that, if left uncorrected, would have underestimated the true population size by as much as 22.9%. Our comparison of these alternative methods demonstrates how various components of our method contribute to improving the final

The Selective Advantage of Synonymous Codon Usage Bias in Salmonella.

Directory of Open Access Journals (Sweden)

Gerrit Brandis

2016-03-01

Full Text Available The genetic code in mRNA is redundant, with 61 sense codons translated into 20 different amino acids. Individual amino acids are encoded by up to six different codons but within codon families some are used more frequently than others. This phenomenon is referred to as synonymous codon usage bias. The genomes of free-living unicellular organisms such as bacteria have an extreme codon usage bias and the degree of bias differs between genes within the same genome. The strong positive correlation between codon usage bias and gene expression levels in many microorganisms is attributed to selection for translational efficiency. However, this putative selective advantage has never been measured in bacteria and theoretical estimates vary widely. By systematically exchanging optimal codons for synonymous codons in the tuf genes we quantified the selective advantage of biased codon usage in highly expressed genes to be in the range 0.2-4.2 x 10-4 per codon per generation. These data quantify for the first time the potential for selection on synonymous codon choice to drive genome-wide sequence evolution in bacteria, and in particular to optimize the sequences of highly expressed genes. This quantification may have predictive applications in the design of synthetic genes and for heterologous gene expression in biotechnology.

Effects of ExB velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices

International Nuclear Information System (INIS)

Burrell, K.H.

1996-11-01

One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization

Optimum biasing of integral equations in Monte Carlo calculations

International Nuclear Information System (INIS)

Hoogenboom, J.E.

1979-01-01

In solving integral equations and estimating average values with the Monte Carlo method, biasing functions may be used to reduce the variancee of the estimates. A simple derivation was used to prove the existence of a zero-variance collision estimator if a specific biasing function and survival probability are applied. This optimum biasing function is the same as that used for the well known zero-variance last-event estimator

Interfacial shear stress in stratified flow in a horizontal rectangular duct

International Nuclear Information System (INIS)

Lorencez, C.; Kawaji, M.; Murao, Y.

1995-01-01

Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods

Interfacial shear stress in stratified flow in a horizontal rectangular duct

Energy Technology Data Exchange (ETDEWEB)

Lorencez, C.; Kawaji, M. [Univ. of Toronto (Canada); Murao, Y. [Tokushima Univ. (Japan)] [and others

1995-09-01

Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods.

Estimates of Gibbs free energies of formation of chlorinated aliphatic compounds

NARCIS (Netherlands)

Dolfing, Jan; Janssen, Dick B.

1994-01-01

The Gibbs free energy of formation of chlorinated aliphatic compounds was estimated with Mavrovouniotis' group contribution method. The group contribution of chlorine was estimated from the scarce data available on chlorinated aliphatics in the literature, and found to vary somewhat according to the

Effects of self-calibration of intrinsic alignment on cosmological parameter constraints from future cosmic shear surveys

International Nuclear Information System (INIS)

Yao, Ji; Ishak, Mustapha; Lin, Weikang; Troxel, Michael

2017-01-01

Intrinsic alignments (IA) of galaxies have been recognized as one of the most serious contaminants to weak lensing. These systematics need to be isolated and mitigated in order for ongoing and future lensing surveys to reach their full potential. The IA self-calibration (SC) method was shown in previous studies to be able to reduce the GI contamination by up to a factor of 10 for the 2-point and 3-point correlations. The SC method does not require the assumption of an IA model in its working and can extract the GI signal from the same photo-z survey offering the possibility to test and understand structure formation scenarios and their relationship to IA models. In this paper, we study the effects of the IA SC mitigation method on the precision and accuracy of cosmological parameter constraints from future cosmic shear surveys LSST, WFIRST and Euclid. We perform analytical and numerical calculations to estimate the loss of precision and the residual bias in the best fit cosmological parameters after the self-calibration is performed. We take into account uncertainties from photometric redshifts and the galaxy bias. We find that the confidence contours are slightly inflated from applying the SC method itself while a significant increase is due to the inclusion of the photo-z uncertainties. The bias of cosmological parameters is reduced from several-σ, when IA is not corrected for, to below 1-σ after SC is applied. These numbers are comparable to those resulting from applying the method of marginalizing over IA model parameters despite the fact that the two methods operate very differently. We conclude that implementing the SC for these future cosmic-shear surveys will not only allow one to efficiently mitigate the GI contaminant but also help to understand their modeling and link to structure formation.

Effects of self-calibration of intrinsic alignment on cosmological parameter constraints from future cosmic shear surveys

Energy Technology Data Exchange (ETDEWEB)

Yao, Ji; Ishak, Mustapha; Lin, Weikang [Department of Physics, The University of Texas at Dallas, Dallas, TX 75080 (United States); Troxel, Michael, E-mail: jxy131230@utdallas.edu, E-mail: mxi054000@utdallas.edu, E-mail: wxl123830@utdallas.edu, E-mail: michael.a.troxel@gmail.com [Department of Physics, Ohio State University, Columbus, OH 43210 (United States)

2017-10-01

Intrinsic alignments (IA) of galaxies have been recognized as one of the most serious contaminants to weak lensing. These systematics need to be isolated and mitigated in order for ongoing and future lensing surveys to reach their full potential. The IA self-calibration (SC) method was shown in previous studies to be able to reduce the GI contamination by up to a factor of 10 for the 2-point and 3-point correlations. The SC method does not require the assumption of an IA model in its working and can extract the GI signal from the same photo-z survey offering the possibility to test and understand structure formation scenarios and their relationship to IA models. In this paper, we study the effects of the IA SC mitigation method on the precision and accuracy of cosmological parameter constraints from future cosmic shear surveys LSST, WFIRST and Euclid. We perform analytical and numerical calculations to estimate the loss of precision and the residual bias in the best fit cosmological parameters after the self-calibration is performed. We take into account uncertainties from photometric redshifts and the galaxy bias. We find that the confidence contours are slightly inflated from applying the SC method itself while a significant increase is due to the inclusion of the photo-z uncertainties. The bias of cosmological parameters is reduced from several-σ, when IA is not corrected for, to below 1-σ after SC is applied. These numbers are comparable to those resulting from applying the method of marginalizing over IA model parameters despite the fact that the two methods operate very differently. We conclude that implementing the SC for these future cosmic-shear surveys will not only allow one to efficiently mitigate the GI contaminant but also help to understand their modeling and link to structure formation.

Critical bed shear stress and threshold of motion of maerl biogenic gravel

Science.gov (United States)

Joshi, Siddhi; Duffy, Garret Patrick; Brown, Colin

2017-07-01

A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s-1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.

Viscoelastic properties of soft gels: comparison of magnetic resonance elastography and dynamic shear testing in the shear wave regime

Science.gov (United States)

Okamoto, R. J.; Clayton, E. H.; Bayly, P. V.

2011-10-01

Magnetic resonance elastography (MRE) is used to quantify the viscoelastic shear modulus, G*, of human and animal tissues. Previously, values of G* determined by MRE have been compared to values from mechanical tests performed at lower frequencies. In this study, a novel dynamic shear test (DST) was used to measure G* of a tissue-mimicking material at higher frequencies for direct comparison to MRE. A closed-form solution, including inertial effects, was used to extract G* values from DST data obtained between 20 and 200 Hz. MRE was performed using cylindrical 'phantoms' of the same material in an overlapping frequency range of 100-400 Hz. Axial vibrations of a central rod caused radially propagating shear waves in the phantom. Displacement fields were fit to a viscoelastic form of Navier's equation using a total least-squares approach to obtain local estimates of G*. DST estimates of the storage G' (Re[G*]) and loss modulus G'' (Im[G*]) for the tissue-mimicking material increased with frequency from 0.86 to 0.97 kPa (20-200 Hz, n = 16), while MRE estimates of G' increased from 1.06 to 1.15 kPa (100-400 Hz, n = 6). The loss factor (Im[G*]/Re[G*]) also increased with frequency for both test methods: 0.06-0.14 (20-200 Hz, DST) and 0.11-0.23 (100-400 Hz, MRE). Close agreement between MRE and DST results at overlapping frequencies indicates that G* can be locally estimated with MRE over a wide frequency range. Low signal-to-noise ratio, long shear wavelengths and boundary effects were found to increase residual fitting error, reinforcing the use of an error metric to assess confidence in local parameter estimates obtained by MRE.

Electrode and limiter biasing experiments on the tokamak ISTTOK

International Nuclear Information System (INIS)

Silva, C.; Figueiredo, H.; Cabral, J.A.C.; Nedzelsky, I.; Varandas, C.A.F.

2003-01-01

In this contribution limiter and electrode biasing experiments are compared, in particular in what concerns their effects on the edge plasma parameters. For electrode AC bias a substantial increase (>50%) in the average plasma density is observed with positive voltage, without significant changes in the edge density, leading to steeper profiles. The ratio n e /Hα also increases significantly (>20%), indicating an improvement in gross particle confinement. The plasma potential profile is strongly modified as both the edge E r and its shear increase significantly. For positive limiter bias an increase in the average plasma density and the radiation losses is observed, resulting in almost no modification, or a slight, in particle confinement. Preliminary results of simultaneous electrode and limiter bias experiments show that the control of the plasma potential profile is very limited, since negative voltages do not modify the plasma parameters significantly. (author)

Laser reflection method for determination of shear stress in low density transitional flows

Science.gov (United States)

Sathian, Sarith P.; Kurian, Job

2006-03-01

The details of laser reflection method (LRM) for the determination of shear stress in low density transitional flows are presented. The method is employed to determine the shear stress due to impingement of a low density supersonic free jet issuing out from a convergent divergent nozzle on a flat plate. The plate is smeared with a thin oil film and kept parallel to the nozzle axis. For a thin oil film moving under the action of aerodynamic boundary layer, the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope generated by the shear force is done using a position sensing detector (PSD). The thinning rate of the oil film is directly measured which is the major advantage of the LRM. From the oil film slope history, calculation of the shear stress is done using a three-point formula. The range of Knudsen numbers investigated is from 0.028 to 0.516. Pressure ratio across the nozzle varied from 3,500 to 8,500 giving highly under expanded free jets. The measured values of shear, in the overlapping region of experimental parameters, show fair agreement with those obtained by force balance method and laser interferometric method.

On the linear stability of sheared and magnetized jets without current sheets - relativistic case

Science.gov (United States)

Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

2018-03-01

In our prior series of papers, we studied the non-relativistic and relativistic linear stability analysis of magnetized jets that do not have current sheets. In this paper, we extend our analysis to relativistic jets with a velocity shear and a similar current sheet free structure. The jets that we study are realistic because we include a velocity shear, a current sheet free magnetic structure, a relativistic velocity and a realistic thermal pressure so as to achieve overall pressure balance in the unperturbed jet. In order to parametrize the velocity shear, we apply a parabolic profile to the jets' 4-velocity. We find that the velocity shear significantly improves the stability of relativistic magnetized jets. This fact is completely consistent with our prior stability analysis of non-relativistic, sheared jets. The velocity shear mainly plays a role in stabilizing the short wavelength unstable modes for the pinch as well as the kink instability modes. In addition, it also stabilizes the long wavelength fundamental pinch instability mode. We also visualize the pressure fluctuations of each unstable mode to provide a better physical understanding of the enhanced stabilization by the velocity shear. Our overall conclusion is that combining velocity shear with a strong and realistic magnetic field makes relativistic jets even more stable.

Self-biased broadband magnet-free linear isolator based on one-way space-time coherency

Science.gov (United States)

Taravati, Sajjad

2017-12-01

This paper introduces a self-biased broadband magnet-free and linear isolator based on one-way space-time coherency. The incident wave and the space-time-modulated medium share the same temporal frequency and are hence temporally coherent. However, thanks to the unidirectionally of the space-time modulation, the space-time-modulated medium and the incident wave are spatially coherent only in the forward direction and not in the opposite direction. As a consequence, the energy of the medium strongly couples to the propagating wave in the forward direction, while it conflicts with the propagating wave in the opposite direction, yielding strong isolation. We first derive a closed-form solution for the wave scattering from a spatiotemporally coherent medium and then show that a perfectly coherent space-time-modulated medium provides a moderate isolation level which is also subject to one-way transmission gain. To overcome this issue, we next investigate the effect of space-coherency imperfection between the medium and the wave, while they are still perfectly temporally coherent. Leveraging the spatial-coherency imperfection, the medium exhibits a quasiarbitrary and strong nonreciprocal transmission. Finally, we present the experimental demonstration of the self-biased version of the proposed broadband isolator, exhibiting more than 122 % fractional operation bandwidth.

3-D FDTD simulation of shear waves for evaluation of complex modulus imaging.

Science.gov (United States)

Orescanin, Marko; Wang, Yue; Insana, Michael

2011-02-01

The Navier equation describing shear wave propagation in 3-D viscoelastic media is solved numerically with a finite differences time domain (FDTD) method. Solutions are formed in terms of transverse scatterer velocity waves and then verified via comparison to measured wave fields in heterogeneous hydrogel phantoms. The numerical algorithm is used as a tool to study the effects on complex shear modulus estimation from wave propagation in heterogeneous viscoelastic media. We used an algebraic Helmholtz inversion (AHI) technique to solve for the complex shear modulus from simulated and experimental velocity data acquired in 2-D and 3-D. Although 3-D velocity estimates are required in general, there are object geometries for which 2-D inversions provide accurate estimations of the material properties. Through simulations and experiments, we explored artifacts generated in elastic and dynamic-viscous shear modulus images related to the shear wavelength and average viscosity.

Good practices for quantitative bias analysis.

Science.gov (United States)

Lash, Timothy L; Fox, Matthew P; MacLehose, Richard F; Maldonado, George; McCandless, Lawrence C; Greenland, Sander

2014-12-01

Quantitative bias analysis serves several objectives in epidemiological research. First, it provides a quantitative estimate of the direction, magnitude and uncertainty arising from systematic errors. Second, the acts of identifying sources of systematic error, writing down models to quantify them, assigning values to the bias parameters and interpreting the results combat the human tendency towards overconfidence in research results, syntheses and critiques and the inferences that rest upon them. Finally, by suggesting aspects that dominate uncertainty in a particular research result or topic area, bias analysis can guide efficient allocation of sparse research resources. The fundamental methods of bias analyses have been known for decades, and there have been calls for more widespread use for nearly as long. There was a time when some believed that bias analyses were rarely undertaken because the methods were not widely known and because automated computing tools were not readily available to implement the methods. These shortcomings have been largely resolved. We must, therefore, contemplate other barriers to implementation. One possibility is that practitioners avoid the analyses because they lack confidence in the practice of bias analysis. The purpose of this paper is therefore to describe what we view as good practices for applying quantitative bias analysis to epidemiological data, directed towards those familiar with the methods. We focus on answering questions often posed to those of us who advocate incorporation of bias analysis methods into teaching and research. These include the following. When is bias analysis practical and productive? How does one select the biases that ought to be addressed? How does one select a method to model biases? How does one assign values to the parameters of a bias model? How does one present and interpret a bias analysis?. We hope that our guide to good practices for conducting and presenting bias analyses will encourage

Estimation and correction of surface wind-stress bias in the Tropical Pacific with the Ensemble Kalman Filter

NARCIS (Netherlands)

Leeuwenburgh, O.

2008-01-01

The assimilation of high-quality in situ data into ocean models is known to lead to imbalanced analyses and spurious circulations when the model dynamics or the forcing contain systematic errors. Use of a bias estimation and correction scheme has been shown to significantly improve the balance of

Assessing the Regional/Diurnal Bias between Satellite Retrievals and GEOS-5/MERRA Model Estimates of Land Surface Temperature

Science.gov (United States)

Scarino, B. R.; Smith, W. L., Jr.; Minnis, P.; Bedka, K. M.

2017-12-01

Atmospheric models rely on high-accuracy, high-resolution initial radiometric and surface conditions for better short-term meteorological forecasts, as well as improved evaluation of global climate models. Continuous remote sensing of the Earth's energy budget, as conducted by the Clouds and Earth's Radiant Energy System (CERES) project, allows for near-realtime evaluation of cloud and surface radiation properties. It is unfortunately common for there to be bias between atmospheric/surface radiation models and Earth-observations. For example, satellite-observed surface skin temperature (Ts), an important parameter for characterizing the energy exchange at the ground/water-atmosphere interface, can be biased due to atmospheric adjustment assumptions and anisotropy effects. Similarly, models are potentially biased by errors in initial conditions and regional forcing assumptions, which can be mitigated through assimilation with true measurements. As such, when frequent, broad-coverage, and accurate retrievals of satellite Ts are available, important insights into model estimates of Ts can be gained. The Satellite ClOud and Radiation Property retrieval System (SatCORPS) employs a single-channel thermal-infrared method to produce anisotropy-corrected Ts over clear-sky land and ocean surfaces from data taken by geostationary Earth orbit (GEO) satellite imagers. Regional and diurnal changes in model land surface temperature (LST) performance can be assessed owing to the somewhat continuous measurements of the LST offered by GEO satellites - measurements which are accurate to within 0.2 K. A seasonal, hourly comparison of satellite-observed LST with the NASA Goddard Earth Observing System Version 5 (GEOS-5) and the Modern-Era Retrospective Analysis for Research and Applications (MERRA) LST estimates is conducted to reveal regional and diurnal biases. This assessment is an important first step for evaluating the effectiveness of Ts assimilation, as well for determining the

Bulk and shear viscosities of hot and dense hadron gas

International Nuclear Information System (INIS)

Kadam, Guru Prakash; Mishra, Hiranmaya

2015-01-01

We estimate the bulk and the shear viscosity at finite temperature and baryon densities of hadronic matter within a hadron resonance gas model which includes a Hagedorn spectrum. The parameters of the Hagedorn spectrum are adjusted to fit recent lattice QCD simulations at finite chemical potential. For the estimation of the bulk viscosity we use low energy theorems of QCD for the energy momentum tensor correlators. For the shear viscosity coefficient, we estimate the same using molecular kinetic theory to relate the shear viscosity coefficient to average momentum of the hadrons in the hot and dense hadron gas. The bulk viscosity to entropy ratio increases with chemical potential and is related to the reduction of velocity of sound at nonzero chemical potential. The shear viscosity to entropy ratio on the other hand, shows a nontrivial behavior with the ratio decreasing with chemical potential for small temperatures but increasing with chemical potential at high temperatures and is related to decrease of entropy density with chemical potential at high temperature due to finite volume of the hadrons

Bias and efficiency loss in regression estimates due to duplicated observations: a Monte Carlo simulation

Directory of Open Access Journals (Sweden)

Francesco Sarracino

2017-04-01

Full Text Available Recent studies documented that survey data contain duplicate records. We assess how duplicate records affect regression estimates, and we evaluate the effectiveness of solutions to deal with duplicate records. Results show that the chances of obtaining unbiased estimates when data contain 40 doublets (about 5% of the sample range between 3.5% and 11.5% depending on the distribution of duplicates. If 7 quintuplets are present in the data (2% of the sample, then the probability of obtaining biased estimates ranges between 11% and 20%. Weighting the duplicate records by the inverse of their multiplicity, or dropping superfluous duplicates outperform other solutions in all considered scenarios. Our results illustrate the risk of using data in presence of duplicate records and call for further research on strategies to analyze affected data.

Comparative shear tests of some low temperature lead-free solder pastes

Science.gov (United States)

Branzei, Mihai; Plotog, Ioan; Varzaru, Gaudentiu; Cucu, Traian C.

2016-12-01

The range of electronic components and as a consequence, all parts of automotive electronic equipment operating temperatures in a vehicle is given by the location of that equipment, so the maximum temperature can vary between 358K and 478K1. The solder joints could be defined as passive parts of the interconnection structure of automotive electronic equipment, at a different level, from boards of electronic modules to systems. The manufacturing costs reduction necessity and the RoHS EU Directive3, 7 consequences generate the trend to create new Low-Temperature Lead-Free (LTLF) solder pastes family9. In the paper, the mechanical strength of solder joints and samples having the same transversal section as resistor 1206 case type made using the same LTLF alloys into Vapour Phase Soldering (VPS) process characterized by different cooling rates (slow and rapid) and two types of test PCBs pads finish, were benchmarked at room temperature. The presented work extends the theoretical studies and experiments upon heat transfer in VPSP in order to optimize the technology for soldering process (SP) of automotive electronic modules and could be extended for home and modern agriculture appliances industry. The shear forces (SF) values of the LTLF alloy samples having the same transversal section as resistor 1206 case type will be considered as references values of a database useful in the new solder alloy creation processes and their qualification for automotive electronics domain.

A review on the inter-frequency biases of GLONASS carrier-phase data

Science.gov (United States)

Geng, Jianghui; Zhao, Qile; Shi, Chuang; Liu, Jingnan

2017-03-01

GLONASS ambiguity resolution (AR) between inhomogeneous stations requires correction of inter-frequency phase biases (IFPBs) (a "station" here is an integral ensemble of a receiver, an antenna, firmware, etc.). It has been elucidated that IFPBs as a linear function of channel numbers are not physical in nature, but actually originate in differential code-phase biases (DCPBs). Although IFPBs have been prevalently recognized, an unanswered question is whether IFPBs and DCPBs are equivalent in enabling GLONASS AR. Besides, general strategies for the DCPB estimation across a large network of heterogeneous stations are still under investigation within the GNSS community, such as whether one DCPB per receiver type (rather than individual stations) suffices, as tentatively suggested by the IGS (International GNSS Service), and what accuracy we are able to and ought to achieve for DCPB products. In this study, we review the concept of DCPBs and point out that IFPBs are only approximate derivations from DCPBs, and are potentially problematic if carrier-phase hardware biases differ by up to several millimeters across frequency channels. We further stress the station and observable specific properties of DCPBs which cannot be thoughtlessly ignored as conducted conventionally. With 212 days of data from 200 European stations, we estimated DCPBs per stations by resolving ionosphere-free ambiguities of ˜ 5.3 cm wavelengths, and compared them to the presumed truth benchmarks computed directly with L1 and L2 data on ultra-short baselines. On average, the accuracy of our DCPB products is around 0.7 ns in RMS. According to this uncertainty estimates, we could unambiguously confirm that DCPBs can typically differ substantially by up to 30 ns among receivers of identical types and over 10 ns across different observables. In contrast, a DCPB error of more than 6 ns will decrease the fixing rate of ionosphere-free ambiguities by over 20 %, due to their smallest frequency spacing and

Elucidation of covariant proofs in general relativity: example of the use of algebraic software in the shear-free conjecture in MAPLE

Science.gov (United States)

Huf, P. A.; Carminati, J.

2018-01-01

In this paper we explore the use of a new algebraic software package in providing independent covariant proof of a conjecture in general relativity. We examine the proof of two sub-cases of the shear-free conjecture σ =0 => ω Θ =0 by Senovilla et al. (Gen. Relativ. Gravit 30:389-411, 1998): case 1: for dust; case 2: for acceleration parallel to vorticity. We use TensorPack, a software package recently released for the Maple environment. In this paper, we briefly summarise the key features of the software and then demonstrate its use by providing and discussing examples of independent proofs of the paper in question. A full set of our completed proofs is available online at http://www.bach2roq.com/science/maths/GR/ShearFreeProofs.html. We are in agreeance with the equations provided in the original paper, noting that the proofs often require many steps. Furthermore, in our proofs we provide fully worked algebraic steps in such a way that the proofs can be examined systematically, and avoiding hand calculation. It is hoped that the elucidated proofs may be of use to other researchers in verifying the algebraic consistency of the expressions in the paper in question, as well as related literature. Furthermore we suggest that the appropriate use of algebraic software in covariant formalism could be useful for developing research and teaching in GR theory.

Effect of Bias Correction of Satellite-Rainfall Estimates on Runoff Simulations at the Source of the Upper Blue Nile

Directory of Open Access Journals (Sweden)

Emad Habib

2014-07-01

Full Text Available Results of numerous evaluation studies indicated that satellite-rainfall products are contaminated with significant systematic and random errors. Therefore, such products may require refinement and correction before being used for hydrologic applications. In the present study, we explore a rainfall-runoff modeling application using the Climate Prediction Center-MORPHing (CMORPH satellite rainfall product. The study area is the Gilgel Abbay catchment situated at the source basin of the Upper Blue Nile basin in Ethiopia, Eastern Africa. Rain gauge networks in such area are typically sparse. We examine different bias correction schemes applied locally to the CMORPH product. These schemes vary in the degree to which spatial and temporal variability in the CMORPH bias fields are accounted for. Three schemes are tested: space and time-invariant, time-variant and spatially invariant, and space and time variant. Bias-corrected CMORPH products were used to calibrate and drive the Hydrologiska Byråns Vattenbalansavdelning (HBV rainfall-runoff model. Applying the space and time-fixed bias correction scheme resulted in slight improvement of the CMORPH-driven runoff simulations, but in some instances caused deterioration. Accounting for temporal variation in the bias reduced the rainfall bias by up to 50%. Additional improvements were observed when both the spatial and temporal variability in the bias was accounted for. The rainfall bias was found to have a pronounced effect on model calibration. The calibrated model parameters changed significantly when using rainfall input from gauges alone, uncorrected, and bias-corrected CMORPH estimates. Changes of up to 81% were obtained for model parameters controlling the stream flow volume.

Impact of Selection Bias on Estimation of Subsequent Event Risk

NARCIS (Netherlands)

Hu, Yi Juan; Schmidt, Amand F.; Dudbridge, Frank; Holmes, Michael V; Brophy, James M.; Tragante, Vinicius; Li, Ziyi; Liao, Peizhou; Quyyumi, Arshed A.; McCubrey, Raymond O.; Horne, Benjamin D.; Hingorani, Aroon D; Asselbergs, Folkert W; Patel, Riyaz S.; Long, Qi; Åkerblom, Axel; Algra, Ale; Allayee, Hooman; Almgren, Peter; Anderson, Jeffrey L.; Andreassi, Maria G.; Anselmi, Chiara V.; Ardissino, Diego; Arsenault, Benoit J.; Ballantyne, Christie M.; Baranova, Ekaterina V.; Behloui, Hassan; Bergmeijer, Thomas O; Bezzina, Connie R; Bjornsson, Eythor; Body, Simon C.; Boeckx, Bram; Boersma, Eric H.; Boerwinkle, Eric; Bogaty, Peter; Braund, Peter S; Breitling, Lutz P.; Brenner, Hermann; Briguori, Carlo; Brugts, Jasper J.; Burkhardt, Ralph; Cameron, Vicky A.; Carlquist, John F.; Carpeggiani, Clara; Carruthers, Kathryn F.; Casu, Gavino; Condorelli, Gianluigi; Cresci, Sharon; Danchin, Nicolas; de Faire, Ulf; Deanfield, John; Delgado, Graciela; Deloukas, Panos; Direk, Kenan; Doughty, Robert N.; Drexel, Heinz; Duarte, Nubia E.; Dubé, Marie Pierre; Dufresne, Line; Engert, James C; Eriksson, Niclas; Fitzpatrick, Natalie; Foco, Luisa; Ford, Ian; Fox, Keith A; Gigante, Bruna; Gijsberts, Crystel M.; Girelli, Domenico; Gong, Yan; Gudbjartsson, Daniel F.; Hagström, Emil; Hartiala, Jaana; Hazen, Stanley L.; Held, Claes; Helgadottir, Anna; Hemingway, Harry; Heydarpour, Mahyar; Hoefer, Imo E.; Hovingh, G. Kees; Hubacek, Jaroslav A; James, Stefan; Johnson, Julie A; Jukema, J Wouter; Kaczor, Marcin P.; Kaminski, Karol A.; Kettner, Jiri; Kiliszek, Marek; Kleber, Marcus; Klungel, Olaf H.; Kofink, Daniel; Kohonen, Mika; Kotti, Salma; Kuukasjärvi, Pekka; Lagerqvist, Bo; Lambrechts, Diether; Lang, Chim C; Laurikka, Jari O.; Leander, Karin; Lee, Vei Vei; Lehtimäki, Terho; Leiherer, Andreas; Lenzini, Petra A.; Levin, Daniel; Lindholm, Daniel; Lokki, Marja-Liisa; Lotufo, Paulo A; Lyytikäinen, Leo-Pekka; Mahmoodi, B. Khan; Maitland-Van Der Zee, Anke H.; Martinelli, Nicola; März, Winfried; Marziliano, Nicola; McPherson, Ruth; Melander, Olle; Mons, Ute; Muehlschlegel, Jochen D.; Muhlestein, Joseph B.; Nelson, Cristopher P.; Cheh, Chris Newton; Olivieri, Oliviero; Opolski, Grzegorz; Palmer, Colin Na; Pare, Guillaume; Pasterkamp, Gerard; Pepine, Carl J; Pepinski, Witold; Pereira, Alexandre C.; Pilbrow, Anna P.; Pilote, Louise; Pitha, Jan; Ploski, Rafal; Richards, A. Mark; Saely, Christoph H.; Samani, Nilesh J; Samman-Tahhan, Ayman; Sanak, Marek; Sandesara, Pratik B.; Sattar, Naveed; Scholz, Markus; Siegbahn, Agneta; Simon, Tabassome; Sinisalo, Juha; Smith, J. Gustav; Spertus, John A.; Stefansson, Kari; Stewart, Alexandre F R; Stott, David J.; Szczeklik, Wojciech; Szpakowicz, Anna; Tanck, Michael W.T.; Tang, Wilson H.; Tardif, Jean-Claude; Ten Berg, Jur M.; Teren, Andrej; Thanassoulis, George; Thiery, Joachim; Thorgeirsson, Gudmundur; Thorleifsson, Gudmar; Thorsteinsdottir, Unnur; Timmis, Adam; Trompet, Stella; Van de Werf, Frans; van der Graaf, Yolanda; Van Der Haarst, Pim; van der Laan, Sander W; Vilmundarson, Ragnar O.; Virani, Salim S.; Visseren, Frank L J; Vlachopoulou, Efthymia; Wallentin, Lars; Waltenberger, Johannes; Wauters, Els; Wilde, Arthur A M

2017-01-01

Background - Studies of recurrent or subsequent disease events may be susceptible to bias caused by selection of subjects who both experience and survive the primary indexing event. Currently, the magnitude of any selection bias, particularly for subsequent time-to-event analysis in genetic

Codon Deviation Coefficient: a novel measure for estimating codon usage bias and its statistical significance

Directory of Open Access Journals (Sweden)

Zhang Zhang

2012-03-01

Full Text Available Abstract Background Genetic mutation, selective pressure for translational efficiency and accuracy, level of gene expression, and protein function through natural selection are all believed to lead to codon usage bias (CUB. Therefore, informative measurement of CUB is of fundamental importance to making inferences regarding gene function and genome evolution. However, extant measures of CUB have not fully accounted for the quantitative effect of background nucleotide composition and have not statistically evaluated the significance of CUB in sequence analysis. Results Here we propose a novel measure--Codon Deviation Coefficient (CDC--that provides an informative measurement of CUB and its statistical significance without requiring any prior knowledge. Unlike previous measures, CDC estimates CUB by accounting for background nucleotide compositions tailored to codon positions and adopts the bootstrapping to assess the statistical significance of CUB for any given sequence. We evaluate CDC by examining its effectiveness on simulated sequences and empirical data and show that CDC outperforms extant measures by achieving a more informative estimation of CUB and its statistical significance. Conclusions As validated by both simulated and empirical data, CDC provides a highly informative quantification of CUB and its statistical significance, useful for determining comparative magnitudes and patterns of biased codon usage for genes or genomes with diverse sequence compositions.

Two-dimensional interaction of a shear flow with a free surface in a stratified fluid and its solitary-wave solutions via mathematical methods

Science.gov (United States)

Seadawy, Aly R.

2017-12-01

In this study, we presented the problem formulations of models for internal solitary waves in a stratified shear flow with a free surface. The nonlinear higher order of extended KdV equations for the free surface displacement is generated. We derived the coefficients of the nonlinear higher-order extended KdV equation in terms of integrals of the modal function for the linear long-wave theory. The wave amplitude potential and the fluid pressure of the extended KdV equation in the form of solitary-wave solutions are deduced. We discussed and analyzed the stability of the obtained solutions and the movement role of the waves by making graphs of the exact solutions.

Estimated levels of gluten incidentally present in a Canadian gluten-free diet.

Science.gov (United States)

La Vieille, Sébastien; Dubois, Sheila; Hayward, Stephen; Koerner, Terence B

2014-02-21

Avoiding exposure to gluten is currently the only effective treatment for celiac disease. However, the evidence suggests that for most affected individuals, exposure to less than 10 mg/day is unlikely to cause histological changes to the intestinal mucosa. The daily diet of people with celiac disease does not rely solely on gluten-free pre-packaged foods, but also on naturally gluten-free grains (e.g., rice, buckwheat, ...) and foods with grain-derived ingredients (i.e., flour and starches) used for cooking and baking at home. The objective of this study was to estimate the level of incidental gluten potentially present in gluten-free diets from a Canadian perspective. We have conducted gluten exposure estimations from grain-containing foods and foods with grain-derived ingredients, taking into consideration the various rates of food consumption by different sex and age groups. These estimates have concluded that if gluten was present at levels not exceeding 20 ppm, exposure to gluten would remain below 10 mg per day for all age groups studied. However, in reality the level of gluten found in naturally gluten-free ingredients is not static and there may be some concerns related to the flours made from naturally gluten-free cereal grains. It was found that those containing a higher level of fiber and that are frequently used to prepare daily foods by individuals with celiac disease could be a concern. For this category of products, only the flours and starches labelled "gluten-free" should be used for home-made preparations.

Interfacial shear behavior of composite flanged concrete beams

Directory of Open Access Journals (Sweden)

Moataz Awry Mahmoud

2014-08-01

Full Text Available Composite concrete decks are commonly used in the construction of highway bridges due to their rapid constructability. The interfacial shear transfer between the top slab and the supporting beams is of great significance to the overall deck load carrying capacity and performance. Interfacial shear capacity is directly influenced by the distribution and the percentage of shear connectors. Research and design guidelines suggest the use of two different approaches to quantify the required interfacial shear strength, namely based on the maximum compressive forces in the flange at mid span or the maximum shear flow at the supports. This paper investigates the performance of flanged reinforced concrete composite beams with different shear connector’s distribution and reinforcing ratios. The study incorporated both experimental and analytical programs for beams. Key experimental findings suggest that concentrating the connectors at the vicinity of the supports enhances the ductility of the beam. The paper proposes a simple and straight forward approach to estimate the interfacial shear capacity that was proven to give good correlation with the experimental results and selected code provisions. The paper presents a method to predict the horizontal shear force between precast beams and cast in-situ slabs.

Repetitive Supra-Physiological Shear Stress Impairs Red Blood Cell Deformability and Induces Hemolysis.

Science.gov (United States)

Horobin, Jarod T; Sabapathy, Surendran; Simmonds, Michael J

2017-11-01

The supra-physiological shear stress that blood is exposed to while traversing mechanical circulatory assist devices affects the physical properties of red blood cells (RBCs), impairs RBC deformability, and may induce hemolysis. Previous studies exploring RBC damage following exposure to supra-physiological shear stress have employed durations exceeding clinical instrumentation, thus we explored changes in RBC deformability following exposure to shear stress below the reported "hemolytic threshold" using shear exposure durations per minute (i.e., duty-cycles) reflective of that employed by circulatory assist devices. Blood collected from 20 male donors, aged 18-38 years, was suspended in a viscous medium and exposed to an intermittent shear stress protocol of 1 s at 100 Pa, every 60 s for 60 duty-cycles. During the remaining 59 s/min, the cells were left at stasis until the subsequent duty-cycle commenced. At discrete time points (15/30/45/60 duty-cycles), an ektacytometer measured RBC deformability immediately after shear exposure at 100 Pa. Plasma-free hemoglobin, a measurement of hemolysis, was quantified via spectrophotometry. Supra-physiological shear stress impaired RBC properties, as indicated by: (1) decreased maximal elongation of RBCs at infinite shear stress following 15 duty-cycles (P supra-physiological shear stress protocol (100 Pa) following exposure to 1 duty-cycle (F (1.891, 32.15) = 12.21, P = 0.0001); and (3) increased plasma-free hemoglobin following 60 duty-cycles (P supra-physiological shear stress, impairs RBC deformability, with the extent of impairment exacerbated with each duty-cycle, and ultimately precipitates hemolysis. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Shear machines

International Nuclear Information System (INIS)

Astill, M.; Sunderland, A.; Waine, M.G.

1980-01-01

A shear machine for irradiated nuclear fuel elements has a replaceable shear assembly comprising a fuel element support block, a shear blade support and a clamp assembly which hold the fuel element to be sheared in contact with the support block. A first clamp member contacts the fuel element remote from the shear blade and a second clamp member contacts the fuel element adjacent the shear blade and is advanced towards the support block during shearing to compensate for any compression of the fuel element caused by the shear blade (U.K.)

Calibration and assessment of channel-specific biases in microarray data with extended dynamical range.

Science.gov (United States)

Bengtsson, Henrik; Jönsson, Göran; Vallon-Christersson, Johan

2004-11-12

Non-linearities in observed log-ratios of gene expressions, also known as intensity dependent log-ratios, can often be accounted for by global biases in the two channels being compared. Any step in a microarray process may introduce such offsets and in this article we study the biases introduced by the microarray scanner and the image analysis software. By scanning the same spotted oligonucleotide microarray at different photomultiplier tube (PMT) gains, we have identified a channel-specific bias present in two-channel microarray data. For the scanners analyzed it was in the range of 15-25 (out of 65,535). The observed bias was very stable between subsequent scans of the same array although the PMT gain was greatly adjusted. This indicates that the bias does not originate from a step preceding the scanner detector parts. The bias varies slightly between arrays. When comparing estimates based on data from the same array, but from different scanners, we have found that different scanners introduce different amounts of bias. So do various image analysis methods. We propose a scanning protocol and a constrained affine model that allows us to identify and estimate the bias in each channel. Backward transformation removes the bias and brings the channels to the same scale. The result is that systematic effects such as intensity dependent log-ratios are removed, but also that signal densities become much more similar. The average scan, which has a larger dynamical range and greater signal-to-noise ratio than individual scans, can then be obtained. The study shows that microarray scanners may introduce a significant bias in each channel. Such biases have to be calibrated for, otherwise systematic effects such as intensity dependent log-ratios will be observed. The proposed scanning protocol and calibration method is simple to use and is useful for evaluating scanner biases or for obtaining calibrated measurements with extended dynamical range and better precision. The

Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 2. Biases and homogenization

Science.gov (United States)

Kennedy, J. J.; Rayner, N. A.; Smith, R. O.; Parker, D. E.; Saunby, M.

2011-07-01

Changes in instrumentation and data availability have caused time-varying biases in estimates of global and regional average sea surface temperature. The size of the biases arising from these changes are estimated and their uncertainties evaluated. The estimated biases and their associated uncertainties are largest during the period immediately following the Second World War, reflecting the rapid and incompletely documented changes in shipping and data availability at the time. Adjustments have been applied to reduce these effects in gridded data sets of sea surface temperature and the results are presented as a set of interchangeable realizations. Uncertainties of estimated trends in global and regional average sea surface temperature due to bias adjustments since the Second World War are found to be larger than uncertainties arising from the choice of analysis technique, indicating that this is an important source of uncertainty in analyses of historical sea surface temperatures. Despite this, trends over the twentieth century remain qualitatively consistent.

Reflecting Equity and Diversity. Part I: Guidelines and Procedure for Evaluating Bias in Instructional Materials. Part II: Bias Awareness Training Worksheets. Part III: Bias Awareness and Procedure Training Course.

Science.gov (United States)

Bebermeyer, Jim; Edmond, Mary, Ed.

Reflecting a need to prepare students for working in diverse organizations, this document was developed to increase school officials' awareness of bias in instructional materials and help them select bias-free materials. A number of the examples illustrate situations dealing with diversity in the workplace. The guide is divided into three parts:…

Research on definition of hard rock shear wave velocity of site for nuclear power plant

International Nuclear Information System (INIS)

Ding Zhenkun; Xia Zufeng

2013-01-01

Background: The definition of hard rock shear wave velocity is one of the most critical issues in the work of site selection. Purpose: To make a definition of hard rock site on which the model can be assumed as fixed-base condition, a series of research had been done. Several possible hard rock site soil models were developed. Methods: Shear wave velocity of hard rock had been assumed from 1100 m/s to 3200 m/s. For each case, free field analysis and soil structure analysis had been performed. And responses in soil and key nodes of structure were compared. Results: In free field analysis, responses of models that shear wave velocity below 2400 m/s decreased a lot. In SSI analysis, structure responses didn't change much when shear wave velocity was above 2400 m/s. Conclusions: 2400 m/s was the lowest shear wave velocity for hard rock site for fixed-base assumption. (authors)

Model-based control of observer bias for the analysis of presence-only data in ecology.

Directory of Open Access Journals (Sweden)

David I Warton

Full Text Available Presence-only data, where information is available concerning species presence but not species absence, are subject to bias due to observers being more likely to visit and record sightings at some locations than others (hereafter "observer bias". In this paper, we describe and evaluate a model-based approach to accounting for observer bias directly--by modelling presence locations as a function of known observer bias variables (such as accessibility variables in addition to environmental variables, then conditioning on a common level of bias to make predictions of species occurrence free of such observer bias. We implement this idea using point process models with a LASSO penalty, a new presence-only method related to maximum entropy modelling, that implicitly addresses the "pseudo-absence problem" of where to locate pseudo-absences (and how many. The proposed method of bias-correction is evaluated using systematically collected presence/absence data for 62 plant species endemic to the Blue Mountains near Sydney, Australia. It is shown that modelling and controlling for observer bias significantly improves the accuracy of predictions made using presence-only data, and usually improves predictions as compared to pseudo-absence or "inventory" methods of bias correction based on absences from non-target species. Future research will consider the potential for improving the proposed bias-correction approach by estimating the observer bias simultaneously across multiple species.

An interactive website for analytical method comparison and bias estimation.

Science.gov (United States)

Bahar, Burak; Tuncel, Ayse F; Holmes, Earle W; Holmes, Daniel T

2017-12-01

Regulatory standards mandate laboratories to perform studies to ensure accuracy and reliability of their test results. Method comparison and bias estimation are important components of these studies. We developed an interactive website for evaluating the relative performance of two analytical methods using R programming language tools. The website can be accessed at https://bahar.shinyapps.io/method_compare/. The site has an easy-to-use interface that allows both copy-pasting and manual entry of data. It also allows selection of a regression model and creation of regression and difference plots. Available regression models include Ordinary Least Squares, Weighted-Ordinary Least Squares, Deming, Weighted-Deming, Passing-Bablok and Passing-Bablok for large datasets. The server processes the data and generates downloadable reports in PDF or HTML format. Our website provides clinical laboratories a practical way to assess the relative performance of two analytical methods. Copyright © 2017 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Determination of Shear Properties in the Upper Seafloor Using Seismo-acoustic Interface Waves

Energy Technology Data Exchange (ETDEWEB)

Frivik, Svein Arne

1998-12-31

This thesis develops methods for recording and analysis of seismo-acoustic interface waves for determination of shear wave velocity as a function of depth and includes this in standard refraction seismic surveying. It investigates different techniques for estimation of dispersion characteristics of the interface waves and demonstrates that multi sensor spectral estimation techniques improve the dispersion estimates. The dispersion estimate of the fundamental interface wave mode is used as input to an object function for a model based linearized inversion. The inversion scheme provides an estimate of the shear wave velocity as a function of depth. Three field surveys were performed. Data were acquired with a standard bottom deployed refraction seismic hydrophone array containing 24 or 48 receivers, with a receiver spacing of 2.5 m. Explosive charges were used as sources. The recording time was increased from 0.5 to 8 s, compared to standard refraction seismic surveys. Shear wave velocity and shear modulus estimates were obtained from all the sites. At one of the sites, geotechnically obtained shear wave parameters were available, and a comparison between the two techniques were performed. the result of the comparison is promising and shows the potential of the technique. Although the result of applying the processing scheme to all three data sets is promising, it appears that survey parameters, like source-array spacing, receiver spacing and type of source might have been optimized for better performance. Based on this limitation, a new processing scheme and a new array configuration is proposed for surveys which integrates the recording and processing of both compressional waves and shear waves. 89 refs., 65 refs., 19 tabs.

Estimating Physical Activity and Sedentary Behavior in a Free-Living Context: A Pragmatic Comparison of Consumer-Based Activity Trackers and ActiGraph Accelerometry.

Science.gov (United States)

Gomersall, Sjaan R; Ng, Norman; Burton, Nicola W; Pavey, Toby G; Gilson, Nicholas D; Brown, Wendy J

2016-09-07

Activity trackers are increasingly popular with both consumers and researchers for monitoring activity and for promoting positive behavior change. However, there is a lack of research investigating the performance of these devices in free-living contexts, for which findings are likely to vary from studies conducted in well-controlled laboratory settings. The aim was to compare Fitbit One and Jawbone UP estimates of steps, moderate-to-vigorous physical activity (MVPA), and sedentary behavior with data from the ActiGraph GT3X+ accelerometer in a free-living context. Thirty-two participants were recruited using convenience sampling; 29 provided valid data for this study (female: 90%, 26/29; age: mean 39.6, SD 11.0 years). On two occasions for 7 days each, participants wore an ActiGraph GT3X+ accelerometer on their right hip and either a hip-worn Fitbit One (n=14) or wrist-worn Jawbone UP (n=15) activity tracker. Daily estimates of steps and very active minutes were derived from the Fitbit One (n=135 days) and steps, active time, and longest idle time from the Jawbone UP (n=154 days). Daily estimates of steps, MVPA, and longest sedentary bout were derived from the corresponding days of ActiGraph data. Correlation coefficients and Bland-Altman plots with examination of systematic bias were used to assess convergent validity and agreement between the devices and the ActiGraph. Cohen's kappa was used to assess the agreement between each device and the ActiGraph for classification of active versus inactive (≥10,000 steps per day and ≥30 min/day of MVPA) comparable with public health guidelines. Correlations with ActiGraph estimates of steps and MVPA ranged between .72 and .90 for Fitbit One and .56 and .75 for Jawbone UP. Compared with ActiGraph estimates, both devices overestimated daily steps by 8% (Fitbit One) and 14% (Jawbone UP). However, mean differences were larger for daily MVPA (Fitbit One: underestimated by 46%; Jawbone UP: overestimated by 50%). There was

Hydrodynamic characterization and molecular weight estimation of ultrasonically sheared DNA; Caracterizacion hidrodinamica y estimacion de pesos moleculares de DNA degradado por ultrasonidos

Energy Technology Data Exchange (ETDEWEB)

Casal, J I; Garces, F; Garcia-Sacristan, A

1981-07-01

The sedimentation coefficients and intrinsic viscosities of ultrasonically sheared calf thymus DNA have been determined. The molecular weight estimation according to this parameters have been compared with the ones obtained from the electrophoretic migration rates based on the calibration proposed using the known molecular weight restriction fragments of X-ENA. (Author) 35 refs.

A New Estimate for Total Offset on the Southern San Andreas Fault: Implications for Cumulative Plate Boundary Shear in the Northern Gulf of California

Science.gov (United States)

Darin, M. H.; Dorsey, R. J.

2012-12-01

Development of a consistent and balanced tectonic reconstruction for the late Cenozoic San Andreas fault (SAF) in southern California has been hindered for decades by incompatible estimates of total dextral offset based on different geologic cross-fault markers. The older estimate of 240-270 km is based on offset fluvial conglomerates of the middle Miocene Mint Canyon and Caliente Formations west of the SAF from their presumed source area in the northern Chocolate Mountains NE of the SAF (Ehlig et al., 1975; Ehlert, 2003). The second widely cited offset marker is a distinctive Triassic megaporphyritic monzogranite that has been offset 160 ± 10 km between Liebre Mountain west of the SAF and the San Bernadino Mountains (Matti and Morton, 1993). In this analysis we use existing paleocurrent data and late Miocene clockwise rotation in the eastern Transverse Ranges (ETR) to re-assess the orientation of the piercing line used in the 240 km-correlation, and present a palinspastic reconstruction that satisfies all existing geologic constraints. Our reconstruction of the Mint Canyon piercing line reduces the original estimate of 240-270 km to 195 ± 15 km of cumulative right-lateral slip on the southern SAF (sensu stricto), which is consistent with other published estimates of 185 ± 20 km based on correlative basement terranes in the Salton Trough region. Our estimate of ~195 km is consistent with the lower estimate of ~160 km on the Mojave segment because transform-parallel extension along the southwestern boundary of the ETR during transrotation produces ~25-40 km of displacement that does not affect offset markers of the Liebre/San Bernadino correlation located northwest of the ETR rotating domain. Reconciliation of these disparate estimates places an important new constraint on the total plate boundary shear that is likely accommodated in the adjacent northern Gulf of California. Global plate circuit models require ~650 km of cumulative Pacific-North America (PAC

Evaluation of Bias Correction Method for Satellite-Based Rainfall Data

Science.gov (United States)

Bhatti, Haris Akram; Rientjes, Tom; Haile, Alemseged Tamiru; Habib, Emad; Verhoef, Wouter

2016-01-01

With the advances in remote sensing technology, satellite-based rainfall estimates are gaining attraction in the field of hydrology, particularly in rainfall-runoff modeling. Since estimates are affected by errors correction is required. In this study, we tested the high resolution National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Centre (CPC) morphing technique (CMORPH) satellite rainfall product (CMORPH) in the Gilgel Abbey catchment, Ethiopia. CMORPH data at 8 km-30 min resolution is aggregated to daily to match in-situ observations for the period 2003–2010. Study objectives are to assess bias of the satellite estimates, to identify optimum window size for application of bias correction and to test effectiveness of bias correction. Bias correction factors are calculated for moving window (MW) sizes and for sequential windows (SW’s) of 3, 5, 7, 9, …, 31 days with the aim to assess error distribution between the in-situ observations and CMORPH estimates. We tested forward, central and backward window (FW, CW and BW) schemes to assess the effect of time integration on accumulated rainfall. Accuracy of cumulative rainfall depth is assessed by Root Mean Squared Error (RMSE). To systematically correct all CMORPH estimates, station based bias factors are spatially interpolated to yield a bias factor map. Reliability of interpolation is assessed by cross validation. The uncorrected CMORPH rainfall images are multiplied by the interpolated bias map to result in bias corrected CMORPH estimates. Findings are evaluated by RMSE, correlation coefficient (r) and standard deviation (SD). Results showed existence of bias in the CMORPH rainfall. It is found that the 7 days SW approach performs best for bias correction of CMORPH rainfall. The outcome of this study showed the efficiency of our bias correction approach. PMID:27314363

Evaluation of Bias Correction Method for Satellite-Based Rainfall Data.

Science.gov (United States)

Bhatti, Haris Akram; Rientjes, Tom; Haile, Alemseged Tamiru; Habib, Emad; Verhoef, Wouter

2016-06-15

With the advances in remote sensing technology, satellite-based rainfall estimates are gaining attraction in the field of hydrology, particularly in rainfall-runoff modeling. Since estimates are affected by errors correction is required. In this study, we tested the high resolution National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Centre (CPC) morphing technique (CMORPH) satellite rainfall product (CMORPH) in the Gilgel Abbey catchment, Ethiopia. CMORPH data at 8 km-30 min resolution is aggregated to daily to match in-situ observations for the period 2003-2010. Study objectives are to assess bias of the satellite estimates, to identify optimum window size for application of bias correction and to test effectiveness of bias correction. Bias correction factors are calculated for moving window (MW) sizes and for sequential windows (SW's) of 3, 5, 7, 9, …, 31 days with the aim to assess error distribution between the in-situ observations and CMORPH estimates. We tested forward, central and backward window (FW, CW and BW) schemes to assess the effect of time integration on accumulated rainfall. Accuracy of cumulative rainfall depth is assessed by Root Mean Squared Error (RMSE). To systematically correct all CMORPH estimates, station based bias factors are spatially interpolated to yield a bias factor map. Reliability of interpolation is assessed by cross validation. The uncorrected CMORPH rainfall images are multiplied by the interpolated bias map to result in bias corrected CMORPH estimates. Findings are evaluated by RMSE, correlation coefficient (r) and standard deviation (SD). Results showed existence of bias in the CMORPH rainfall. It is found that the 7 days SW approach performs best for bias correction of CMORPH rainfall. The outcome of this study showed the efficiency of our bias correction approach.

Evaluation of Bias Correction Method for Satellite-Based Rainfall Data

Directory of Open Access Journals (Sweden)

Haris Akram Bhatti

2016-06-01

Full Text Available With the advances in remote sensing technology, satellite-based rainfall estimates are gaining attraction in the field of hydrology, particularly in rainfall-runoff modeling. Since estimates are affected by errors correction is required. In this study, we tested the high resolution National Oceanic and Atmospheric Administration’s (NOAA Climate Prediction Centre (CPC morphing technique (CMORPH satellite rainfall product (CMORPH in the Gilgel Abbey catchment, Ethiopia. CMORPH data at 8 km-30 min resolution is aggregated to daily to match in-situ observations for the period 2003–2010. Study objectives are to assess bias of the satellite estimates, to identify optimum window size for application of bias correction and to test effectiveness of bias correction. Bias correction factors are calculated for moving window (MW sizes and for sequential windows (SW’s of 3, 5, 7, 9, …, 31 days with the aim to assess error distribution between the in-situ observations and CMORPH estimates. We tested forward, central and backward window (FW, CW and BW schemes to assess the effect of time integration on accumulated rainfall. Accuracy of cumulative rainfall depth is assessed by Root Mean Squared Error (RMSE. To systematically correct all CMORPH estimates, station based bias factors are spatially interpolated to yield a bias factor map. Reliability of interpolation is assessed by cross validation. The uncorrected CMORPH rainfall images are multiplied by the interpolated bias map to result in bias corrected CMORPH estimates. Findings are evaluated by RMSE, correlation coefficient (r and standard deviation (SD. Results showed existence of bias in the CMORPH rainfall. It is found that the 7 days SW approach performs best for bias correction of CMORPH rainfall. The outcome of this study showed the efficiency of our bias correction approach.

Simulating publication bias

DEFF Research Database (Denmark)

Paldam, Martin

is censoring: selection by the size of estimate; SR3 selects the optimal combination of fit and size; and SR4 selects the first satisficing result. The last four SRs are steered by priors and result in bias. The MST and the FAT-PET have been developed for detection and correction of such bias. The simulations......Economic research typically runs J regressions for each selected for publication – it is often selected as the ‘best’ of the regressions. The paper examines five possible meanings of the word ‘best’: SR0 is ideal selection with no bias; SR1 is polishing: selection by statistical fit; SR2...... are made by data variation, while the model is the same. It appears that SR0 generates narrow funnels much at odds with observed funnels, while the other four funnels look more realistic. SR1 to SR4 give the mean a substantial bias that confirms the prior causing the bias. The FAT-PET MRA works well...

Validating the absolute reliability of a fat free mass estimate equation in hemodialysis patients using near-infrared spectroscopy.

Science.gov (United States)

Kono, Kenichi; Nishida, Yusuke; Moriyama, Yoshihumi; Taoka, Masahiro; Sato, Takashi

2015-06-01

The assessment of nutritional states using fat free mass (FFM) measured with near-infrared spectroscopy (NIRS) is clinically useful. This measurement should incorporate the patient's post-dialysis weight ("dry weight"), in order to exclude the effects of any change in water mass. We therefore used NIRS to investigate the regression, independent variables, and absolute reliability of FFM in dry weight. The study included 47 outpatients from the hemodialysis unit. Body weight was measured before dialysis, and FFM was measured using NIRS before and after dialysis treatment. Multiple regression analysis was used to estimate the FFM in dry weight as the dependent variable. The measured FFM before dialysis treatment (Mw-FFM), and the difference between measured and dry weight (Mw-Dw) were independent variables. We performed Bland-Altman analysis to detect errors between the statistically estimated FFM and the measured FFM after dialysis treatment. The multiple regression equation to estimate the FFM in dry weight was: Dw-FFM = 0.038 + (0.984 × Mw-FFM) + (-0.571 × [Mw-Dw]); R(2)  = 0.99). There was no systematic bias between the estimated and the measured values of FFM in dry weight. Using NIRS, FFM in dry weight can be calculated by an equation including FFM in measured weight and the difference between the measured weight and the dry weight. © 2015 The Authors. Therapeutic Apheresis and Dialysis © 2015 International Society for Apheresis.

The response of dense dry granular material to the shear reversal

Science.gov (United States)

Zhang, Jie; Ren, Jie; Farhadi, Somayeh; Behringer, Robert

2008-11-01

We have performed two dimensional granular experiments under pure shear using bidisperse photo-elastic disks. Starting from a stress free state, a square box filled with granular particles is subject to shear. The forward shears involved various number of steps, leading to maximum strains between 0.1 and 0.3. The area is kept constant during the shear. The network of force chains gradually built up as the strain increased, leading to increased pressure and shear stress. Reverse shear was then applied to the system. Depending on the initial packing fraction and the strain at which the shear is reversed, the force chain network built prior to the shear reversal may be destroyed completely or partially destroyed. Following the force chain weakening, when the reserve shear is continuously applied to the system, there is a force chain strengthening. Following each change of the system, contact forces of individual disks were measured by applying an inverse algorithm. We also kept track of the displacement and angle of rotation of every particle from frame to frame. We present the results for the structure failure and reconstruction during shear reversals. We also present data for stresses, contact force distributions and other statistical measures.

Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study

DEFF Research Database (Denmark)

Wood, L.; Egger, M.; Gluud, L.L.

2008-01-01

OBJECTIVE: To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome. DESIGN: Combined analysis of data from three meta-epidemiological studies based o...

Resolution of axial shear strain elastography

International Nuclear Information System (INIS)

Thitaikumar, Arun; Righetti, Raffaella; Krouskop, Thomas A; Ophir, Jonathan

2006-01-01

The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 45 0 to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift (ΔW) on the estimated resolution were investigated. The results show that the resolution (at 45 0 orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift

Bias-corrected estimation in potentially mildly explosive autoregressive models

DEFF Research Database (Denmark)

Haufmann, Hendrik; Kruse, Robinson

This paper provides a comprehensive Monte Carlo comparison of different finite-sample bias-correction methods for autoregressive processes. We consider classic situations where the process is either stationary or exhibits a unit root. Importantly, the case of mildly explosive behaviour is studied...... that the indirect inference approach oers a valuable alternative to other existing techniques. Its performance (measured by its bias and root mean squared error) is balanced and highly competitive across many different settings. A clear advantage is its applicability for mildly explosive processes. In an empirical...

Motional Effect on Wall Shear Stresses

DEFF Research Database (Denmark)

Kock, Samuel Alberg; Torben Fründ, Ernst; Yong Kim, Won

Atherosclerosis is the leading cause of death and severe disability. Wall Shear Stress (WSS), the stress exerted on vessel walls by the flowing blood is a key factor in the development of atherosclerosis. Computational Fluid Dynamics (CFD) is widely used for WSS estimations. Most CFD simulations...... are based on static models to ease computational burden leading to inaccurate estimations. The aim of this work was to estimate the effect of vessel wall deformations (expansion and bending) on WSS levels....

Shear wave elastography with a new reliability indicator

Directory of Open Access Journals (Sweden)

Christoph F. Dietrich

2016-09-01

Full Text Available Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s. The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed. The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France, point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France. More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Shear wave elastography with a new reliability indicator.

Science.gov (United States)

Dietrich, Christoph F; Dong, Yi

2016-09-01

Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Identification of the Viscous Superlayer on the Low-Speed Side of a Single-Stream Shear Layer

Science.gov (United States)

Foss, John; Peabody, Jason

2010-11-01

Image pairs (elevation/plan views) have been acquired of a smoke streakline originating in the irrotational region on the low-speed side of a high Re single-stream shear layer of Morris and Foss (2003). The viscous superlayer (VSL) is identified as the terminus of the streak; 1800 such images provide VSL position statistics. Hot-wire data acquired concurrently at the shear layer edge and interior are used to investigate the relationship between these velocity magnitudes and the large-scale motions. Distinctive features (plumes) along the streakline are tracked between images to provide discrete irrotational region velocity magnitudes and material trajectories. A non-diffusive marker, introduced in the separating (high speed) boundary layer and imaged at x/θo=352, has revealed an unexpected bias in the streak-defined VSL locations. The interpretation of this bias clarifies the induced flow patterns in the entrainment region. The observations are consistent with a conception of the large-scale shear layer motions as "billows" of vortical fluid separated by re-entrant "wedges" of irrotational fluid, per Phillips (1972). Morris, S.C. and Foss, J.F. (2003). "Turbulent Boundary Layer to Single Stream Shear Layer: The Transition Region." Journal of Fluid Mechanics. Vol. 494, pp. 187-221. Phillips, O. M. (1972). "The Entrainment Interface." Journal of Fluid Mechanics. Vol. 51, pp. 97-118.

Cognitive constraints increase estimation biases: Cognitive load and delay in judgments

OpenAIRE

Allred, Sarah; Crawford, L. Elizabeth; Duffy, Sean; Smith, John

2014-01-01

Previous work has demonstrated that memory for simple stimuli can be biased by information about the category of which the stimulus is a member. These biases have been interpreted as optimally integrating noisy sensory information with category information. A separate literature has demonstrated that cognitive load can lead to biases in social cognition. Here we link the two, asking whether delay (Experiment 1) and cognitive load (Experiment 2) affect the extent to which observers' memories f...

Codon Deviation Coefficient: A novel measure for estimating codon usage bias and its statistical significance

KAUST Repository

Zhang, Zhang

2012-03-22

Background: Genetic mutation, selective pressure for translational efficiency and accuracy, level of gene expression, and protein function through natural selection are all believed to lead to codon usage bias (CUB). Therefore, informative measurement of CUB is of fundamental importance to making inferences regarding gene function and genome evolution. However, extant measures of CUB have not fully accounted for the quantitative effect of background nucleotide composition and have not statistically evaluated the significance of CUB in sequence analysis.Results: Here we propose a novel measure--Codon Deviation Coefficient (CDC)--that provides an informative measurement of CUB and its statistical significance without requiring any prior knowledge. Unlike previous measures, CDC estimates CUB by accounting for background nucleotide compositions tailored to codon positions and adopts the bootstrapping to assess the statistical significance of CUB for any given sequence. We evaluate CDC by examining its effectiveness on simulated sequences and empirical data and show that CDC outperforms extant measures by achieving a more informative estimation of CUB and its statistical significance.Conclusions: As validated by both simulated and empirical data, CDC provides a highly informative quantification of CUB and its statistical significance, useful for determining comparative magnitudes and patterns of biased codon usage for genes or genomes with diverse sequence compositions. 2012 Zhang et al; licensee BioMed Central Ltd.

Phylogenetic uncertainty can bias the number of evolutionary transitions estimated from ancestral state reconstruction methods.

Science.gov (United States)

Duchêne, Sebastian; Lanfear, Robert

2015-09-01

Ancestral state reconstruction (ASR) is a popular method for exploring the evolutionary history of traits that leave little or no trace in the fossil record. For example, it has been used to test hypotheses about the number of evolutionary origins of key life-history traits such as oviparity, or key morphological structures such as wings. Many studies that use ASR have suggested that the number of evolutionary origins of such traits is higher than was previously thought. The scope of such inferences is increasing rapidly, facilitated by the construction of very large phylogenies and life-history databases. In this paper, we use simulations to show that the number of evolutionary origins of a trait tends to be overestimated when the phylogeny is not perfect. In some cases, the estimated number of transitions can be several fold higher than the true value. Furthermore, we show that the bias is not always corrected by standard approaches to account for phylogenetic uncertainty, such as repeating the analysis on a large collection of possible trees. These findings have important implications for studies that seek to estimate the number of origins of a trait, particularly those that use large phylogenies that are associated with considerable uncertainty. We discuss the implications of this bias, and methods to ameliorate it. © 2015 Wiley Periodicals, Inc.

Estimated Levels of Gluten Incidentally Present in a Canadian Gluten-Free Diet

Directory of Open Access Journals (Sweden)

Sébastien La Vieille

2014-02-01

Full Text Available Avoiding exposure to gluten is currently the only effective treatment for celiac disease. However, the evidence suggests that for most affected individuals, exposure to less than 10 mg/day is unlikely to cause histological changes to the intestinal mucosa. The daily diet of people with celiac disease does not rely solely on gluten-free pre-packaged foods, but also on naturally gluten-free grains (e.g., rice, buckwheat, ... and foods with grain-derived ingredients (i.e., flour and starches used for cooking and baking at home. The objective of this study was to estimate the level of incidental gluten potentially present in gluten-free diets from a Canadian perspective. We have conducted gluten exposure estimations from grain-containing foods and foods with grain-derived ingredients, taking into consideration the various rates of food consumption by different sex and age groups. These estimates have concluded that if gluten was present at levels not exceeding 20 ppm, exposure to gluten would remain below 10 mg per day for all age groups studied. However, in reality the level of gluten found in naturally gluten-free ingredients is not static and there may be some concerns related to the flours made from naturally gluten-free cereal grains. It was found that those containing a higher level of fiber and that are frequently used to prepare daily foods by individuals with celiac disease could be a concern. For this category of products, only the flours and starches labelled “gluten-free” should be used for home-made preparations.

Nonlinear vs. linear biasing in Trp-cage folding simulations

Energy Technology Data Exchange (ETDEWEB)

Spiwok, Vojtěch, E-mail: spiwokv@vscht.cz; Oborský, Pavel; Králová, Blanka [Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague, Technická 3, Prague 6 166 28 (Czech Republic); Pazúriková, Jana [Institute of Computer Science, Masaryk University, Botanická 554/68a, 602 00 Brno (Czech Republic); Křenek, Aleš [Institute of Computer Science, Masaryk University, Botanická 554/68a, 602 00 Brno (Czech Republic); Center CERIT-SC, Masaryk Univerzity, Šumavská 416/15, 602 00 Brno (Czech Republic)

2015-03-21

Biased simulations have great potential for the study of slow processes, including protein folding. Atomic motions in molecules are nonlinear, which suggests that simulations with enhanced sampling of collective motions traced by nonlinear dimensionality reduction methods may perform better than linear ones. In this study, we compare an unbiased folding simulation of the Trp-cage miniprotein with metadynamics simulations using both linear (principle component analysis) and nonlinear (Isomap) low dimensional embeddings as collective variables. Folding of the mini-protein was successfully simulated in 200 ns simulation with linear biasing and non-linear motion biasing. The folded state was correctly predicted as the free energy minimum in both simulations. We found that the advantage of linear motion biasing is that it can sample a larger conformational space, whereas the advantage of nonlinear motion biasing lies in slightly better resolution of the resulting free energy surface. In terms of sampling efficiency, both methods are comparable.

Thermal flexural analysis of cross-ply laminated plates using trigonometric shear deformation theory

Directory of Open Access Journals (Sweden)

Yuwaraj Marotrao Ghugal

Full Text Available Thermal stresses and displacements for orthotropic, two-layer antisymmetric, and three-layer symmetric square cross-ply laminated plates subjected to nonlinear thermal load through the thickness of laminated plates are presented by using trigonometric shear deformation theory. The in-plane displacement field uses sinusoidal function in terms of thickness co-ordinate to include the shear deformation effect. The theory satisfies the shear stress free boundary conditions on the top and bottom surfaces of the plate. The present theory obviates the need of shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The validity of present theory is verified by comparing the results with those of classical plate theory and first order shear deformation theory and higher order shear deformation theory.

Estimation of soil properties and free product volume from baildown tests

International Nuclear Information System (INIS)

Zhu, J.L.; Parker, J.C.; Lundy, D.A.; Zimmerman, L.M.

1993-01-01

Baildown tests, involving measurement of water and free product levels in a monitoring well after bailing, are often performed at spill sites to estimate the oil volume per unit area -- which the authors refer to as ''oil specific volume.'' Spill volume is estimated by integrating oil specific volume over the areal domain of the spill. Existing methods for interpreting baildown tests are based on grossly simplistic approximations of soil capillary properties that cannot accurately describe the transient well response. A model for vertical equilibrium oil distributions based on the van Genuchten capillary model has been documented and verified in the laboratory and in the field by various authors. The model enables oil specific volume and oil transmissivity to be determined as functions of well product thickness. This paper describes a method for estimating van Genuchten capillary parameters, as well as aquifer hydraulic conductivity, from baildown tests. The results yield the relationships of oil specific volume and oil transmissivity to apparent product thickness, which may be used, in turn, to compute spill volume and to model free product plume movement and free product recovery. The method couples a finite element model for radial flow of oil and water to a well with a nonlinear parameter estimation algorithm. Effects of the filter pack around the well in the fluid level response are considered explicitly by the model. The method, which is implemented in the program BAILTEST, is applied to field data from baildown tests. The results indicate that hydrographs of water and oil levels are accurately described by the model

Bias correction of nutritional status estimates when reported age is used for calculating WHO indicators in children under five years of age.

Science.gov (United States)

Quezada, Amado D; García-Guerra, Armando; Escobar, Leticia

2016-06-01

To assess the performance of a simple correction method for nutritional status estimates in children under five years of age when exact age is not available from the data. The proposed method was based on the assumption of symmetry of age distributions within a given month of age and validated in a large population-based survey sample of Mexican preschool children. The main distributional assumption was consistent with the data. All prevalence estimates derived from the correction method showed no statistically significant bias. In contrast, failing to correct attained age resulted in an underestimation of stunting in general and an overestimation of overweight or obesity among the youngest. The proposed method performed remarkably well in terms of bias correction of estimates and could be easily applied in situations in which either birth or interview dates are not available from the data.

Can free-viewing perceptual asymmetries be explained by scanning, pre-motor or attentional biases?

Science.gov (United States)

Nicholls, Michael E R; Roberts, Georgina R

2002-04-01

Judgments of relative magnitude between the left and right sides of a stimulus are generally weighted toward the features contained on the left side. This leftward perceptual bias could be the result of, (a) left-to-right scanning biases, (b) pre-motor activation of the right hemisphere, or (c) a left hemispatial attentional bias. The relative merits of these explanations of perceptual asymmetry were investigated. In Experiment 1, English and Hebrew readers made luminance judgements for two left/right mirror-reversed luminance gradients (greyscales task). Despite different reading/scanning habits, both groups exhibited a leftward perceptual bias. English and Hebrew readers also performed a line bisection task. Scanning biases were controlled by asking participants to follow a marker as it moved left-to-right or right-to-left and then stop it as it reached the midpoint of the line. Despite controlling scanning, a leftward bias was observed in both groups. In Experiment 2, peripheral spatial cues were presented prior to the greyscales stimuli. English readers showed a reduction in the leftward bias for right-sided cues as compared to left-sided and neutral cues. Right-side cues presumably overcame a pre-existing leftward attentional bias. In both experiments, pre-motor activation was controlled using bimanual responses. Despite this control, a leftward bias was observed throughout the study. The data support the attentional bias account of leftward perceptual biases over the scanning and pre-motor activation accounts. Whether or not unilateral hemispheric activation provides an adequate account of this attentional bias is discussed.

Practical Considerations about Expected A Posteriori Estimation in Adaptive Testing: Adaptive A Priori, Adaptive Correction for Bias, and Adaptive Integration Interval.

Science.gov (United States)

Raiche, Gilles; Blais, Jean-Guy

In a computerized adaptive test (CAT), it would be desirable to obtain an acceptable precision of the proficiency level estimate using an optimal number of items. Decreasing the number of items is accompanied, however, by a certain degree of bias when the true proficiency level differs significantly from the a priori estimate. G. Raiche (2000) has…

Bias-correction in vector autoregressive models: A simulation study

DEFF Research Database (Denmark)

Engsted, Tom; Pedersen, Thomas Quistgaard

We analyze and compare the properties of various methods for bias-correcting parameter estimates in vector autoregressions. First, we show that two analytical bias formulas from the existing literature are in fact identical. Next, based on a detailed simulation study, we show that this simple...... and easy-to-use analytical bias formula compares very favorably to the more standard but also more computer intensive bootstrap bias-correction method, both in terms of bias and mean squared error. Both methods yield a notable improvement over both OLS and a recently proposed WLS estimator. We also...... of pushing an otherwise stationary model into the non-stationary region of the parameter space during the process of correcting for bias....

A basis for bias in geographical judgments.

Science.gov (United States)

Friedman, Alinda; Brown, Norman R; McGaffey, Aaron P

2002-03-01

To determine why North Americans tend to locate European cities south of North American cities at similar latitudes (Tversky, 1981), we had observers provide bearing estimates between cities in the U.S. and Europe. Earlier research using latitude estimates of these cities has indicated that each continent has several subjective regions (Friedman & Brown, 2000a). Participants judged cities from two subjectively northern regions (Milwaukee-Munich), two subjectively southern regions (Memphis-Lisbon), and the two "crossed" regions (Albuquerque-Geneva; Minneapolis-Rome). Estimates were biased only when cities from the subjectively northern regions of North America were paired with cities from the subjectively southern region of Europe. In contrast to the view that biases are derived from distorted or aligned map-like representations, the data provide evidence that the subjective representation of global geography is principally categorical. Biases in numerical location estimates of individual cities and in bearing estimates between city pairs are derived from plausible reasoning processes operating on the same categorical representations.

Seismic cycle feedbacks in a mid-crustal shear zone

Science.gov (United States)

Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Smit, Louis; Macey, Paul

2018-07-01

Mid-crustal fault rheology is controlled by alternating brittle and plastic deformation mechanisms, which cause feedback cycles that influence earthquake behavior. Detailed mapping and microstructural observations in the Pofadder Shear Zone (Namibia and South Africa) reveal a lithologically heterogeneous shear zone core with quartz-rich mylonites and ultramylonites, plastically overprinted pseudotachylyte and active shear folds. We present evidence for a positive feedback cycle in which coseismic grain size reduction facilitates active shear folding by enhancing competency contrasts and promoting crystal plastic flow. Shear folding strengthens a portion of a shear zone by limb rotation, focusing deformation and promoting plastic flow or brittle slip in resulting areas of localized high stress. Using quartz paleopiezometry, we estimate strain and slip rates consistent with other studies of exhumed shear zones and modern plate boundary faults, helping establish the Pofadder Shear Zone as an ancient analogue to modern, continental-scale, strike-slip faults. This feedback cycle influences seismicity patterns at the scale of study (10s of meters) and possibly larger scales as well, and contributes to bulk strengthening of the brittle-plastic transition on modern plate boundary faults.

Shearing single crystal magnesium in the close-packed basal plane at different temperatures

Science.gov (United States)

Han, Ming; Li, Lili; Zhao, Guangming

2018-05-01

Shear behaviors of single crystal magnesium (Mg) in close-packed (0001) basal plane along the [ 1 bar 2 1 bar 0 ], [ 1 2 bar 10 ], [ 10 1 bar 0 ] and [ 1 bar 010 ] directions were studied using molecular dynamics simulations via EAM potential. The results show that both shear stress-strain curves along the four directions and the motion path of free atoms during shearing behave periodic characteristics. It reveals that the periodic shear displacement is inherently related to the crystallographic orientation in single crystal Mg. Moreover, different temperatures in a range from 10 to 750 K were considered, demonstrating that shear modulus decreases with increasing temperatures. The results agree well with the MTS model. It is manifested that the modulus is independent with the shear direction and the size of the atomic model. This work also demonstrates that the classical description of shear modulus is still effective at the nanoscale.

Reducing bias in rainfall estimates from microwave links by considering variable drop size distribution

Science.gov (United States)

Fencl, Martin; Jörg, Rieckermann; Vojtěch, Bareš

2015-04-01

Commercial microwave links (MWL) are point-to-point radio systems which are used in backhaul networks of cellular operators. For several years, they have been suggested as rainfall sensors complementary to rain gauges and weather radars, because, first, they operate at frequencies where rain drops represent significant source of attenuation and, second, cellular networks almost completely cover urban and rural areas. Usually, path-average rain rates along a MWL are retrieved from the rain-induced attenuation of received MWL signals with a simple model based on a power law relationship. The model is often parameterized based on the characteristics of a particular MWL, such as frequency, polarization and the drop size distribution (DSD) along the MWL. As information on the DSD is usually not available in operational conditions, the model parameters are usually considered constant. Unfortunately, this introduces bias into rainfall estimates from MWL. In this investigation, we propose a generic method to eliminate this bias in MWL rainfall estimates. Specifically, we search for attenuation statistics which makes it possible to classify rain events into distinct groups for which same power-law parameters can be used. The theoretical attenuation used in the analysis is calculated from DSD data using T-Matrix method. We test the validity of our approach on observations from a dedicated field experiment in Dübendorf (CH) with a 1.85-km long commercial dual-polarized microwave link transmitting at a frequency of 38 GHz, an autonomous network of 5 optical distrometers and 3 rain gauges distributed along the path of the MWL. The data is recorded at a high temporal resolution of up to 30s. It is further tested on data from an experimental catchment in Prague (CZ), where 14 MWLs, operating at 26, 32 and 38 GHz frequencies, and reference rainfall from three RGs is recorded every minute. Our results suggest that, for our purpose, rain events can be nicely characterized based on

Drag reduction by the introduction of shear-free surfaces in a ...

Indian Academy of Sciences (India)

2D simulations have been carried out for aturbulent channel flow using shear stress transport (SST) Reynolds-averaged Navier–Stokes (RANS) model and validated with the available experimental results. The interaction between the plates and the fluid is two way,and is enforced either by the use of a rigid body solver with ...

SSI response of a typical shear wall structure

International Nuclear Information System (INIS)

Johnson, J.J.; Maslenikov, O.R.; Schewe, E.C.

1985-01-01

The seismic response of a typical shear structure in a commercial nuclear power plant was investigated for a series of site and foundation conditions using best estimate and design procedures. The structure selected is a part of the Zion AFT complex which is a connected group of reinforced concrete shear wall buildings, typical of nuclear power plant structures. Comparisons between best estimate responses quantified the effects of placing the structure on different sites and founding it in different manners. Calibration factors were developed by comparing simplified SSI design procedure responses to responses calculated by best estimate procedures. Nineteen basic cases were analyzed - each case was analyzed for ten earthquakes targeted to the NRC R.G. 1.60 design response spectra. The structure is a part of the Zion auxiliary-fuel handling turbine building (AFT) complex to the Zion nuclear power plants. (orig./HP)

Divertor plasma modification by divertor biasing and edge ergodization in JFT-2M

International Nuclear Information System (INIS)

Shoji, T.; Nagashima, K.; Tamai, H.; Ohdachi, S.; Miura, Y.; Ohasa, K.; Maeda, H.; Ohyabu, N.; Leonard, A.W.; Aikawa, H.; Fujita, T.; Hoshino, K.; Kawashima, H.; Matsuda, T.; Maeno, M.; Mori, M.; Ogawa, H.; Shimada, M.; Uehara, K.; Yamauchi, T.

1995-01-01

The effects of divertor biasing and edge ergodization on the divertor plasma have been investigated in the JFT-2M tokamak. Experimental results show; (1) The differential divertor biasing can change the in/out asymmetry of the divertor plasma. It especially changes the density on the ion side divertor plasma. The in/out electron pressure difference has a good correlation with the biasing current. (2) The unipolar divertor biasing can change the density profile of divertor plasma. The radial electric field and shear flow are the cause for this change. (3) The electron temperature of the divertor plasma in the H-mode with frequent ELMs induced by edge ergodization is lower than that of usual H-mode. That is due to the enhancement of the radial particle flux by frequent ELMs, ((orig.))

Estimation of Radiation Limit from a Huygens' Box under Non-Free-Space Conditions

DEFF Research Database (Denmark)

Franek, Ondrej; Sørensen, Morten; Bonev, Ivan Bonev

2013-01-01

The recently studied Huygens' box method has difficulties when radiation of an electronic module is to be determined under non-free-space conditions, i.e. with an enclosure. We propose an estimate on radiation limit under such conditions based only on the Huygens' box data from free...

Bias Correction with Jackknife, Bootstrap, and Taylor Series

OpenAIRE

Jiao, Jiantao; Han, Yanjun; Weissman, Tsachy

2017-01-01

We analyze the bias correction methods using jackknife, bootstrap, and Taylor series. We focus on the binomial model, and consider the problem of bias correction for estimating $f(p)$, where $f \\in C[0,1]$ is arbitrary. We characterize the supremum norm of the bias of general jackknife and bootstrap estimators for any continuous functions, and demonstrate the in delete-$d$ jackknife, different values of $d$ may lead to drastically different behavior in jackknife. We show that in the binomial ...

Bias-Correction in Vector Autoregressive Models: A Simulation Study

Directory of Open Access Journals (Sweden)

Tom Engsted

2014-03-01

Full Text Available We analyze the properties of various methods for bias-correcting parameter estimates in both stationary and non-stationary vector autoregressive models. First, we show that two analytical bias formulas from the existing literature are in fact identical. Next, based on a detailed simulation study, we show that when the model is stationary this simple bias formula compares very favorably to bootstrap bias-correction, both in terms of bias and mean squared error. In non-stationary models, the analytical bias formula performs noticeably worse than bootstrapping. Both methods yield a notable improvement over ordinary least squares. We pay special attention to the risk of pushing an otherwise stationary model into the non-stationary region of the parameter space when correcting for bias. Finally, we consider a recently proposed reduced-bias weighted least squares estimator, and we find that it compares very favorably in non-stationary models.

Bias correction of nutritional status estimates when reported age is used for calculating WHO indicators in children under five years of age

Directory of Open Access Journals (Sweden)

Amado D Quezada

2016-05-01

Full Text Available Objective.To assess the performance of a simple correction method for nutritional status estimates in children under five years of age when exact age is not available from the data. Materials and methods. The proposed method was ba- sed on the assumption of symmetry of age distributions within a given month of age and validated in a large population-based survey sample of Mexican preschool children. Results. The main distributional assumption was consistent with the data. All prevalence estimates derived from the correction method showed no statistically significant bias. In contrast, failing to correct attained age resulted in an underestimation of stunting in general and an overestimation of overweight or obesity among the youngest. Conclusions. The proposed method performed remarkably well in terms of bias correction of estimates and could be easily applied in situations in which either birth or interview dates are not available from the data.

bcROCsurface: an R package for correcting verification bias in estimation of the ROC surface and its volume for continuous diagnostic tests.

Science.gov (United States)

To Duc, Khanh

2017-11-18

Receiver operating characteristic (ROC) surface analysis is usually employed to assess the accuracy of a medical diagnostic test when there are three ordered disease status (e.g. non-diseased, intermediate, diseased). In practice, verification bias can occur due to missingness of the true disease status and can lead to a distorted conclusion on diagnostic accuracy. In such situations, bias-corrected inference tools are required. This paper introduce an R package, named bcROCsurface, which provides utility functions for verification bias-corrected ROC surface analysis. The shiny web application of the correction for verification bias in estimation of the ROC surface analysis is also developed. bcROCsurface may become an important tool for the statistical evaluation of three-class diagnostic markers in presence of verification bias. The R package, readme and example data are available on CRAN. The web interface enables users less familiar with R to evaluate the accuracy of diagnostic tests, and can be found at http://khanhtoduc.shinyapps.io/bcROCsurface_shiny/ .

Conductivity of an inverse lyotropic lamellar phase under shear flow

Science.gov (United States)

Panizza, P.; Soubiran, L.; Coulon, C.; Roux, D.

2001-08-01

We report conductivity measurements on solutions of closed compact monodisperse multilamellar vesicles (the so-called ``onion texture'') formed by shearing an inverse lyotropic lamellar Lα phase. The conductivity measured in different directions as a function of the applied shear rate reveals a small anisotropy of the onion structure due to the existence of free oriented membranes. The results are analyzed in terms of a simple model that allows one to deduce the conductivity tensor of the Lα phase itself and the proportion of free oriented membranes. The variation of these two parameters is measured along a dilution line and discussed. The high value of the conductivity perpendicular to the layers with respect to that of solvent suggests the existence of a mechanism of ionic transport through the insulating solvent.

Estimation of Shear Wave Speed in the Rhesus Macaques Uterine Cervix

Science.gov (United States)

Huang, Bin; Drehfal, Lindsey C.; Rosado-Mendez, Ivan M.; Guerrero, Quinton W.; Palmeri, Mark L.; Simmons, Heather A.; Feltovich, Helen; Hall, Timothy J.

2016-01-01

Cervical softness is a critical parameter in pregnancy. Clinically, preterm birth is associated with premature cervical softening and post-dates birth is associated with delayed cervical softening. In practice, the assessment of softness is subjective, based on digital examination. Fortunately, objective, quantitative techniques to assess softness and other parameters associated with microstructural cervical change are emerging. One of these is shear wave speed (SWS) estimation. In principle, this allows objective characterization of stiffness because waves travel more slowly in softer tissue. We are studying SWS in humans and rhesus macaques, the latter in order to accelerate translation from bench to bedside. For the current study, we estimated SWS in ex vivo cervices of rhesus macaques, n=24 nulliparous (never given birth) and n=9 multiparous (delivered at least 1 baby). Misoprostol (a prostaglandin used to soften human cervices prior to gynecological procedures) was administered to 13 macaques prior to necropsy (nulliparous: 7, multiparous: 6). SWS measurements were made at predetermined locations from the distal to proximal end of the cervix on both the anterior and posterior cervix, with 5 repeat measures at each location. The intent was to explore macaque cervical microstructure, including biological and spatial variability, to elucidate the similarities and differences between the macaque and the human cervix in order to facilitate future in vivo studies. We found that SWS is dependent on location in the normal nonpregnant macaque cervix, as in the human cervix. Unlike the human cervix, we detected no difference between ripened and unripened rhesus macaque cervix samples, nor nulliparous versus multiparous samples, although we observed a trend toward stiffer tissue in nulliparous samples. We found rhesus macaque cervix to be much stiffer than human, which is important for technique refinement. These findings are useful for guiding study of cervical

The global mean energy balance under cloud-free conditions

Science.gov (United States)

Wild, Martin; Hakuba, Maria; Folini, Dois; Ott, Patricia; Long, Charles

2017-04-01

A long standing problem of climate models is their overestimation of surface solar radiation not only under all-sky, but also under clear-sky conditions (Wild et al. 1995, Wild et al. 2006). This overestimation reduced over time in consecutive model generations due to the simulation of stronger atmospheric absorption. Here we analyze the clear sky fluxes of the latest climate model generation from the Coupled Model Intercomparison Project Phase 5 (CMIP5) against an expanded and updated set of direct observations from the Baseline Surface Radiation Network (BSRN). Clear sky climatologies from these sites have been composed based on the Long and Ackermann (2000) clear sky detection algorithm (Hakuba et al. 2017), and sampling issues when comparing with model simulated clear sky fluxes have been analyzed in Ott (2017). Overall, the overestimation of clear sky insolation in the CMIP5 models is now merely 1-2 Wm-2 in the multimodel mean, compared to 4 Wm-2 in CMIP3 and 6 Wm-2 in AMIPII (Wild et al. 2006). Still a considerable spread in the individual model biases is apparent, ranging from -2 Wm-2 to 10 Wm-2 when averaged over 53 globally distributed BSRN sites. This bias structure is used to infer best estimates for present day global mean clear sky insolation, following an approach developped in Wild et al. (2013, 2015, Clim. Dyn.) for all sky fluxes. Thereby the flux biases in the various models are linearly related to their respective global means. A best estimate can then be inferred from the linear regression at the intersect where the bias against the surface observations becomes zero. This way we obtain a best estimate of 247 Wm-2 for the global mean insolation at the Earth surface under cloud free conditions, and a global mean absorbed solar radiation of 214 Wm-2 in the cloud-free atmosphere, assuming a global mean surface albedo of 13.5%. Combined with a best estimate for the net influx of solar radiation at the Top of Atmosphere under cloud free conditions

Permanent-Magnet Free Biasing of MR Sensors with Tunable Sensitivity

Science.gov (United States)

Halloran, Sean; Dasilva, Fabio; Pappas, David

2007-03-01

Exchange coupling^1 has been previously observed in a trilayer structure of ferromagnet (FM)/non-magnetic/antiferromagnet (AFM) and the exchange bias was found to be a function of the thickness of the buffer layer.^2,3,4 This unique coupling is used as a stabilizing bias for the sense layer with the additional ability to tailor the magnetic gain of the sensor for various applications. The elimination of permanent magnet bias results in the elimination of one patterning and one deposition step. Ruthenium (Ru) is used as the buffer layer and is self aligned with the FM and AFM layers and the thickness is varied to change the slope of the transfer curve in the linear region. Sensor devices are fabricated with a bipolar output, a medium sensitivity, and a wide field range. The results show that this biasing scheme is well suited for barber pole and soft adjacent layer (SAL) anisotropic magnetoresistance (AMR) stripes used in magnetic field sensors with a FM layer of Permalloy (NiFe) and an AFM layer of Iridium-Manganese (IrMn). Applications include a 256 channel read head used for magnetic forensics. 1N.J. Gokemeijer, T. Ambrose, C.L. Chien, N. Wang and K.K. Fung, J. Appl. Phys. 81 (8), 4999, 15 April 1997. 2W.H. Meiklejohn and C.P. Bean, Phys. Rev. 102, 1413 1956; 105, 904, 1957. 3L. Thomas, A.J. Kellock and S.S.P. Parkin, J. Appl. Phys. 87 (9), 5061, 1 May 2000. 4D. Wang, J. Daughton, C. Nordman, P. Eames and J. Fink, J. Appl. Phys. 99, 2006.

Enabling real-time ultrasound imaging of soft tissue mechanical properties by simplification of the shear wave motion equation.

Science.gov (United States)

Engel, Aaron J; Bashford, Gregory R

2015-08-01

Ultrasound based shear wave elastography (SWE) is a technique used for non-invasive characterization and imaging of soft tissue mechanical properties. Robust estimation of shear wave propagation speed is essential for imaging of soft tissue mechanical properties. In this study we propose to estimate shear wave speed by inversion of the first-order wave equation following directional filtering. This approach relies on estimation of first-order derivatives which allows for accurate estimations using smaller smoothing filters than when estimating second-order derivatives. The performance was compared to three current methods used to estimate shear wave propagation speed: direct inversion of the wave equation (DIWE), time-to-peak (TTP) and cross-correlation (CC). The shear wave speed of three homogeneous phantoms of different elastic moduli (gelatin by weight of 5%, 7%, and 9%) were measured with each method. The proposed method was shown to produce shear speed estimates comparable to the conventional methods (standard deviation of measurements being 0.13 m/s, 0.05 m/s, and 0.12 m/s), but with simpler processing and usually less time (by a factor of 1, 13, and 20 for DIWE, CC, and TTP respectively). The proposed method was able to produce a 2-D speed estimate from a single direction of wave propagation in about four seconds using an off-the-shelf PC, showing the feasibility of performing real-time or near real-time elasticity imaging with dedicated hardware.

Shear failure of granular materials

Science.gov (United States)

Degiuli, Eric; Balmforth, Neil; McElwaine, Jim; Schoof, Christian; Hewitt, Ian

2012-02-01

Connecting the macroscopic behavior of granular materials with the microstructure remains a great challenge. Recent work connects these scales with a discrete calculus [1]. In this work we generalize this formalism from monodisperse packings of disks to 2D assemblies of arbitrarily shaped grains. In particular, we derive Airy's expression for a symmetric, divergence-free stress tensor. Using these tools, we derive, from first-principles and in a mean-field approximation, the entropy of frictional force configurations in the Force Network Ensemble. As a macroscopic consequence of the Coulomb friction condition at contacts, we predict shear failure at a critical shear stress, in accordance with the Mohr-Coulomb failure condition well known in engineering. Results are compared with numerical simulations, and the dependence on the microscopic geometric configuration is discussed. [4pt] [1] E. DeGiuli & J. McElwaine, PRE 2011. doi: 10.1103/PhysRevE.84.041310

Shear Resistance Variations in Experimentally Sheared Mudstone Granules: A Possible Shear-Thinning and Thixotropic Mechanism

Science.gov (United States)

Hu, Wei; Xu, Qiang; Wang, Gonghui; Scaringi, Gianvito; Mcsaveney, Mauri; Hicher, Pierre-Yves

2017-11-01

We present results of ring shear frictional resistance for mudstone granules of different size obtained from a landslide shear zone. Little rate dependency of shear resistance was observed in sand-sized granules in any wet or dry test, while saturated gravel-sized granules exhibited significant and abrupt reversible rate-weakening (from μ = 0.6 to 0.05) at about 2 mm/s. Repeating resistance variations occurred also under constant shear displacement rate. Mudstone granules generate mud as they are crushed and softened. Shear-thinning and thixotropic behavior of the mud can explain the observed behavior: with the viscosity decreasing, the mud can flow through the coarser soil pores and migrate out from the shear zone. This brings new granules into contact which produces new mud. Thus, the process can start over. Similarities between experimental shear zones and those of some landslides in mudstone suggest that the observed behavior may play a role in some landslide kinematics.

Impact of relativistic effects on cosmological parameter estimation

Science.gov (United States)

Lorenz, Christiane S.; Alonso, David; Ferreira, Pedro G.

2018-01-01

Future surveys will access large volumes of space and hence very long wavelength fluctuations of the matter density and gravitational field. It has been argued that the set of secondary effects that affect the galaxy distribution, relativistic in nature, will bring new, complementary cosmological constraints. We study this claim in detail by focusing on a subset of wide-area future surveys: Stage-4 cosmic microwave background experiments and photometric redshift surveys. In particular, we look at the magnification lensing contribution to galaxy clustering and general-relativistic corrections to all observables. We quantify the amount of information encoded in these effects in terms of the tightening of the final cosmological constraints as well as the potential bias in inferred parameters associated with neglecting them. We do so for a wide range of cosmological parameters, covering neutrino masses, standard dark-energy parametrizations and scalar-tensor gravity theories. Our results show that, while the effect of lensing magnification to number counts does not contain a significant amount of information when galaxy clustering is combined with cosmic shear measurements, this contribution does play a significant role in biasing estimates on a host of parameter families if unaccounted for. Since the amplitude of the magnification term is controlled by the slope of the source number counts with apparent magnitude, s (z ), we also estimate the accuracy to which this quantity must be known to avoid systematic parameter biases, finding that future surveys will need to determine s (z ) to the ˜5 %- 10 % level. On the contrary, large-scale general-relativistic corrections are irrelevant both in terms of information content and parameter bias for most cosmological parameters but significant for the level of primordial non-Gaussianity.

Number-counts slope estimation in the presence of Poisson noise

Science.gov (United States)

Schmitt, Juergen H. M. M.; Maccacaro, Tommaso

1986-01-01

The slope determination of a power-law number flux relationship in the case of photon-limited sampling. This case is important for high-sensitivity X-ray surveys with imaging telescopes, where the error in an individual source measurement depends on integrated flux and is Poisson, rather than Gaussian, distributed. A bias-free method of slope estimation is developed that takes into account the exact error distribution, the influence of background noise, and the effects of varying limiting sensitivities. It is shown that the resulting bias corrections are quite insensitive to the bias correction procedures applied, as long as only sources with signal-to-noise ratio five or greater are considered. However, if sources with signal-to-noise ratio five or less are included, the derived bias corrections depend sensitively on the shape of the error distribution.

The impact of response bias on estimates of health care utilization in a metropolitan area: The use of administrative data

NARCIS (Netherlands)

Reijneveld, S.A.; Stronks, K.

1999-01-01

Background. Surveys among the general population are an important method for collecting epidemiological data on health and utilization of health care in that population. Selective non-response may affect the validity of these data. This study examines the impact of response bias on estimates of

Lichen forage ingestion rates of free-roaming caribou estimated with fallout cesium-137

International Nuclear Information System (INIS)

Hanson, W.C.; Whicker, F.W.; Lipscomb, J.F.

1975-01-01

Lichen forage ingestion rates of free-roaming caribou herds in northern Alaska during 1963 to 1970 were estimated by applying a two-compartment, eight parameter cesium-137 kinetics model to measured fallout 137 Cs concentrations in lichen and caribou. Estimates for winter equilibrium periods (January to April) for each year ranged from 3.7 to 6.9 kg dry weight lichens per day for adult female caribou. Further refinement of these estimations were obtained by calculating probabilistic distributions of intake rates by stochastic processes based upon the mean and standard error intervals of the eight parameters during 1965 and 1968. A computer program generated 1,000 randomly sampled values within each of the eight parameter distributions. Results substantiate the contention that lichen forage ingestion rates by free-roaming caribou are significantly greater than previously held

On the Limitations of Variational Bias Correction

Science.gov (United States)

Moradi, Isaac; Mccarty, Will; Gelaro, Ronald

2018-01-01

Satellite radiances are the largest dataset assimilated into Numerical Weather Prediction (NWP) models, however the data are subject to errors and uncertainties that need to be accounted for before assimilating into the NWP models. Variational bias correction uses the time series of observation minus background to estimate the observations bias. This technique does not distinguish between the background error, forward operator error, and observations error so that all these errors are summed up together and counted as observation error. We identify some sources of observations errors (e.g., antenna emissivity, non-linearity in the calibration, and antenna pattern) and show the limitations of variational bias corrections on estimating these errors.

The central tendency bias in color perception: effects of internal and external noise.

Science.gov (United States)

Olkkonen, Maria; McCarthy, Patrice F; Allred, Sarah R

2014-09-05

Perceptual estimates can be biased by previously seen stimuli in delayed estimation tasks. These biases are often toward the mean of the whole stimulus set. Recently, we demonstrated such a central tendency bias in delayed color estimation. In the Bayesian framework of perceptual inference, perceptual biases arise when noisy sensory measurements are combined with prior information about the world. Here, we investigate this idea in color perception by manipulating stimulus range and stimulus noise while characterizing delayed color estimates. First, we manipulated the experimental prior for stimulus color by embedding stimuli in collections with different hue ranges. Stimulus range affected hue bias: Hue estimates were always biased toward the mean of the current set. Next, we studied the effect of internal and external noise on the amount of hue bias. Internal noise was manipulated by increasing the delay between the reference and test from 0.4 to 4 s. External noise was manipulated by increasing the amount of chromatic noise in the reference stimulus, while keeping the delay between the reference and test constant at 2 s. Both noise manipulations had a reliable effect on the strength of the central tendency bias. Furthermore, there was a tendency for a positive relationship between variability of the estimates and bias in both noise conditions. In conclusion, observers are able to learn an experimental hue prior, and the weight on the prior can be manipulated by introducing noise in the estimation process. © 2014 ARVO.

Sensor for Boundary Shear Stress in Fluid Flow

Science.gov (United States)

Bao, Xiaoqi; Badescu, Mircea; Sherrit, Stewart; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Chang, Zensheu; Trease, Brian P.; Kerenyi, Kornel; Widholm, Scott E.; Ostlund, Patrick N.

2012-01-01

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.

Grouted Connections with Shear Keys

DEFF Research Database (Denmark)

Pedersen, Ronnie; Jørgensen, M. B.; Damkilde, Lars

2012-01-01

This paper presents a finite element model in the software package ABAQUS in which a reliable analysis of grouted pile-to-sleeve connections with shear keys is the particular purpose. The model is calibrated to experimental results and a consistent set of input parameters is estimated so that dif...... that different structural problems can be reproduced successfully....

Geological and structural characterization and microtectonic study of shear zones Colonia

International Nuclear Information System (INIS)

Gianotti, V.; Oyhantcabal, P.; Spoturno, J.; Wemmer, K.

2010-01-01

The “Colonia Shear Zone System”, characterized by a transcurrent system of predominant sinistral shear sense, is defined by two approximately parallel shear zones, denominated Isla San Gabriel-Juan Lacaze Shear Zone (ISG-JL S.Z.) and Islas de Hornos-Arroyo Riachuelo Shear Zone (IH-AºR S. Z.). Represented by rocks with ductile and brittle deformation, are defined as a strike slip fault system, with dominant subvertical foliation orientations: 090-100º (dip-direction 190º) and 090-100º (dip-direction 005º). The K/Ar geochronology realized, considering the estimates temperatures conditions for shear zones (450-550º), indicate that 1780-1812 Ma should be considered a cooling age and therefore a minimum deformation age. The observed microstructures suggest deformation conditions with temperatures between 450-550º overprinted by cataclastic flow structures (reactivation at lower temperature)

Brownian dynamics simulations of an order-disorder transition in sheared sterically stabilized colloidal suspensions

International Nuclear Information System (INIS)

Rigos, A.A.; Wilemski, G.

1992-01-01

The shear thinning behavior of a sterically stabilized nonaqueous colloidal suspension was investigated using nonequilibrium Brownian dynamics simulations of systems with 108 and 256 particles. At a volume fraction of 0.4, the suspension is thixotropic: it has a reversible shear thinning transition from a disordered state to an ordered, lamellar state with triangularly packed strings of particles. The time scale for the transition is set by the free particle diffusion constant. For the smaller system, the transition occurs gradually with increasing shear rate. For the larger system, the transition is sharp and discontinuous shear thinning is found. 34 refs., 9 figs., 1 tab

Improving Estimation of Betweenness Centrality for Scale-Free Graphs

Energy Technology Data Exchange (ETDEWEB)

Bromberger, Seth A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Klymko, Christine F. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Henderson, Keith A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pearce, Roger [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Sanders, Geoff [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2017-11-07

Betweenness centrality is a graph statistic used to nd vertices that are participants in a large number of shortest paths in a graph. This centrality measure is commonly used in path and network interdiction problems and its complete form requires the calculation of all-pairs shortest paths for each vertex. This leads to a time complexity of O(jV jjEj), which is impractical for large graphs. Estimation of betweenness centrality has focused on performing shortest-path calculations on a subset of randomly- selected vertices. This reduces the complexity of the centrality estimation to O(jSjjEj); jSj < jV j, which can be scaled appropriately based on the computing resources available. An estimation strategy that uses random selection of vertices for seed selection is fast and simple to implement, but may not provide optimal estimation of betweenness centrality when the number of samples is constrained. Our experimentation has identi ed a number of alternate seed-selection strategies that provide lower error than random selection in common scale-free graphs. These strategies are discussed and experimental results are presented.

Shear strength of clay and silt embankments.

Science.gov (United States)

2009-09-01

Highway embankment is one of the most common large-scale geotechnical facilities constructed in Ohio. In the past, the design of these embankments was largely based on soil shear strength properties that had been estimated from previously published e...

Relationship between enamel bond fatigue durability and surface free-energy characteristics with universal adhesives.

Science.gov (United States)

Nagura, Yuko; Tsujimoto, Akimasa; Barkmeier, Wayne W; Watanabe, Hidehiko; Johnson, William W; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

2018-04-01

The relationship between enamel bond fatigue durability and surface free-energy characteristics with universal adhesives was investigated. The initial shear bond strengths and shear fatigue strengths of five universal adhesives to enamel were determined with and without phosphoric acid pre-etching. The surface free-energy characteristics of adhesive-treated enamel with and without pre-etching were also determined. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were higher than those to ground enamel. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were material dependent, unlike those to ground enamel. The surface free-energy of the solid (γ S ) and the hydrogen-bonding force (γSh) of universal adhesive-treated enamel were different depending on the adhesive, regardless of the presence or absence of pre-etching. The bond fatigue durability of universal adhesives was higher to pre-etched enamel than to ground enamel. In addition, the bond fatigue durability to pre-etched enamel was material dependent, unlike that to ground enamel. The surface free-energy characteristics of universal adhesive-treated enamel were influenced by the adhesive type, regardless of the presence or absence of pre-etching. The surface free-energy characteristics of universal adhesive-treated enamel were related to the results of the bond fatigue durability. © 2018 Eur J Oral Sci.

Gamma-point lattice free energy estimates from O(1) force calculations

DEFF Research Database (Denmark)

Voss, Johannes; Vegge, Tejs

2008-01-01

We present a new method for estimating the vibrational free energy of crystal (and molecular) structures employing only a single force calculation, for a particularly displaced configuration, in addition to the calculation of the ground state configuration. This displacement vector is the sum...

Correction of stream quality trends for the effects of laboratory measurement bias

Science.gov (United States)

Alexander, Richard B.; Smith, Richard A.; Schwarz, Gregory E.

1993-01-01

We present a statistical model relating measurements of water quality to associated errors in laboratory methods. Estimation of the model allows us to correct trends in water quality for long-term and short-term variations in laboratory measurement errors. An illustration of the bias correction method for a large national set of stream water quality and quality assurance data shows that reductions in the bias of estimates of water quality trend slopes are achieved at the expense of increases in the variance of these estimates. Slight improvements occur in the precision of estimates of trend in bias by using correlative information on bias and water quality to estimate random variations in measurement bias. The results of this investigation stress the need for reliable, long-term quality assurance data and efficient statistical methods to assess the effects of measurement errors on the detection of water quality trends.

Measuring Local Strain Rates In Ductile Shear Zones: A New Approach From Deformed Syntectonic Dykes

Science.gov (United States)

Sassier, C.; Leloup, P.; Rubatto, D.; Galland, O.; Yue, Y.; Ding, L.

2006-12-01

At the Earth surface, deformation is mostly localized in fault zones in between tectonic plates. In the upper crust, the deformation is brittle and the faults are narrow and produce earthquakes. In contrast, deformation in the lower ductile crust results in larger shear zones. While it is relatively easy to measure in situ deformation rates at the surface using for example GPS data, it is more difficult to determinate in situ values of strain rate in the ductile crust. Such strain rates can only be estimated in paleo-shear zones. Various methods have been used to assess paleo-strain rates in paleo-shear zones. For instance, cooling and/or decompression rates associated with assumptions on geothermic gradients and shear zone geometry can lead to such estimates. Another way to estimate strain rates is the integration of paleo-stress measurements in a power flow law. But these methods are indirect and imply strong assumptions. Dating of helicitic garnets or syntectonic fibres are more direct estimates. However these last techniques have been only applied in zones of low deformation and not in major shear zones. We propose a new direct method to measure local strain rates in major ductile shear zones from syntectonic dykes by coupling quantification of deformation and geochronology. We test our method in a major shear zone in a well constrained tectonic setting: the Ailao-Shan - Red River Shear Zone (ASRRsz) located in SE Asia. For this 10 km wide shear zone, large-scale fault rates, determined in three independent ways, imply strain rates between 1.17×10^{-13 s-1 and 1.52×10^{-13 s-1 between 35 and 16 Ma. Our study focused on one outcrop where different generations of syntectonic dykes are observed. First, we quantified the minimum shear strain γ for each dyke using several methods: (1) by measuring the stretching of dykes with a surface restoration method (2) by measuring the final angle of the dykes with respect to the shear direction and (3) by combining the two

Asymptotic stability of shear-flow solutions to incompressible viscous free boundary problems with and without surface tension

Science.gov (United States)

Tice, Ian

2018-04-01

This paper concerns the dynamics of a layer of incompressible viscous fluid lying above a rigid plane and with an upper boundary given by a free surface. The fluid is subject to a constant external force with a horizontal component, which arises in modeling the motion of such a fluid down an inclined plane, after a coordinate change. We consider the problem both with and without surface tension for horizontally periodic flows. This problem gives rise to shear-flow equilibrium solutions, and the main thrust of this paper is to study the asymptotic stability of the equilibria in certain parameter regimes. We prove that there exists a parameter regime in which sufficiently small perturbations of the equilibrium at time t=0 give rise to global-in-time solutions that return to equilibrium exponentially in the case with surface tension and almost exponentially in the case without surface tension. We also establish a vanishing surface tension limit, which connects the solutions with and without surface tension.

The proportionator: unbiased stereological estimation using biased automatic image analysis and non-uniform probability proportional to size sampling

DEFF Research Database (Denmark)

Gardi, Jonathan Eyal; Nyengaard, Jens Randel; Gundersen, Hans Jørgen Gottlieb

2008-01-01

examined, which in turn leads to any of the known stereological estimates, including size distributions and spatial distributions. The unbiasedness is not a function of the assumed relation between the weight and the structure, which is in practice always a biased relation from a stereological (integral......, the desired number of fields are sampled automatically with probability proportional to the weight and presented to the expert observer. Using any known stereological probe and estimator, the correct count in these fields leads to a simple, unbiased estimate of the total amount of structure in the sections...... geometric) point of view. The efficiency of the proportionator depends, however, directly on this relation to be positive. The sampling and estimation procedure is simulated in sections with characteristics and various kinds of noises in possibly realistic ranges. In all cases examined, the proportionator...

Study on shear properties of coral sand under cyclic simple shear condition

Science.gov (United States)

Ji, Wendong; Zhang, Yuting; Jin, Yafei

2018-05-01

In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement.

TH-A-207B-00: Shear-Wave Imaging and a QIBA US Biomarker Update

International Nuclear Information System (INIS)

2016-01-01

Imaging of tissue elastic properties is a relatively new and powerful approach to one of the oldest and most important diagnostic tools. Imaging of shear wave speed with ultrasound is has been added to most high-end ultrasound systems. Understanding this exciting imaging mode aiding its most effective use in medicine can be a rewarding effort for medical physicists and other medical imaging and treatment professionals. Assuring consistent, quantitative measurements across the many ultrasound systems in a typical imaging department will constitute a major step toward realizing the great potential of this technique and other quantitative imaging. This session will target these two goals with two presentations. A. Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity - Shigao Chen, Ph.D. Learning objectives-To understand: Introduction: Importance of tissue elasticity measurement Strain vs. shear wave elastography (SWE), beneficial features of SWE The link between shear wave speed and material properties, influence of viscosity Generation of shear waves External vibration (Fibroscan) ultrasound radiation force Point push Supersonic push (Aixplorer) Comb push (GE Logiq E9) Detection of shear waves Motion detection from pulse-echo ultrasound Importance of frame rate for shear wave imaging Plane wave imaging detection How to achieve high effective frame rate using line-by-line scanners Shear wave speed calculation Time to peak Random sample consensus (RANSAC) Cross correlation Sources of bias and variation in SWE Tissue viscosity Transducer compression or internal pressure of organ Reflection of shear waves at boundaries B. Elasticity Imaging System Biomarker Qualification and User Testing of Systems – Brian Garra, M.D. Learning objectives-To understand: Goals Review the need for quantitative medical imaging Provide examples of quantitative imaging biomarkers Acquaint the participant with the purpose of the RSNA Quantitative Imaging

TH-A-207B-00: Shear-Wave Imaging and a QIBA US Biomarker Update

Energy Technology Data Exchange (ETDEWEB)

NONE

2016-06-15

Imaging of tissue elastic properties is a relatively new and powerful approach to one of the oldest and most important diagnostic tools. Imaging of shear wave speed with ultrasound is has been added to most high-end ultrasound systems. Understanding this exciting imaging mode aiding its most effective use in medicine can be a rewarding effort for medical physicists and other medical imaging and treatment professionals. Assuring consistent, quantitative measurements across the many ultrasound systems in a typical imaging department will constitute a major step toward realizing the great potential of this technique and other quantitative imaging. This session will target these two goals with two presentations. A. Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity - Shigao Chen, Ph.D. Learning objectives-To understand: Introduction: Importance of tissue elasticity measurement Strain vs. shear wave elastography (SWE), beneficial features of SWE The link between shear wave speed and material properties, influence of viscosity Generation of shear waves External vibration (Fibroscan) ultrasound radiation force Point push Supersonic push (Aixplorer) Comb push (GE Logiq E9) Detection of shear waves Motion detection from pulse-echo ultrasound Importance of frame rate for shear wave imaging Plane wave imaging detection How to achieve high effective frame rate using line-by-line scanners Shear wave speed calculation Time to peak Random sample consensus (RANSAC) Cross correlation Sources of bias and variation in SWE Tissue viscosity Transducer compression or internal pressure of organ Reflection of shear waves at boundaries B. Elasticity Imaging System Biomarker Qualification and User Testing of Systems – Brian Garra, M.D. Learning objectives-To understand: Goals Review the need for quantitative medical imaging Provide examples of quantitative imaging biomarkers Acquaint the participant with the purpose of the RSNA Quantitative Imaging

Shear strength of non-shear reinforced concrete elements

DEFF Research Database (Denmark)

Hoang, Cao linh

1997-01-01

The paper deals with the plastic shear strength of non shear reinforced T-beams.The influence of an un-reinforced flange on the shear capacity is investigated by considering a failure mechanism involving crack sliding in the web and a kind of membrane action over an effective width of the flange...

Constructing a multidimensional free energy surface like a spider weaving a web.

Science.gov (United States)

Chen, Changjun

2017-10-15

Complete free energy surface in the collective variable space provides important information of the reaction mechanisms of the molecules. But, sufficient sampling in the collective variable space is not easy. The space expands quickly with the number of the collective variables. To solve the problem, many methods utilize artificial biasing potentials to flatten out the original free energy surface of the molecule in the simulation. Their performances are sensitive to the definitions of the biasing potentials. Fast-growing biasing potential accelerates the sampling speed but decreases the accuracy of the free energy result. Slow-growing biasing potential gives an optimized result but needs more simulation time. In this article, we propose an alternative method. It adds the biasing potential to a representative point of the molecule in the collective variable space to improve the conformational sampling. And the free energy surface is calculated from the free energy gradient in the constrained simulation, not given by the negative of the biasing potential as previous methods. So the presented method does not require the biasing potential to remove all the barriers and basins on the free energy surface exactly. Practical applications show that the method in this work is able to produce the accurate free energy surfaces for different molecules in a short time period. The free energy errors are small in the cases of various biasing potentials. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Empirical single sample quantification of bias and variance in Q-ball imaging.

Science.gov (United States)

Hainline, Allison E; Nath, Vishwesh; Parvathaneni, Prasanna; Blaber, Justin A; Schilling, Kurt G; Anderson, Adam W; Kang, Hakmook; Landman, Bennett A

2018-02-06

The bias and variance of high angular resolution diffusion imaging methods have not been thoroughly explored in the literature and may benefit from the simulation extrapolation (SIMEX) and bootstrap techniques to estimate bias and variance of high angular resolution diffusion imaging metrics. The SIMEX approach is well established in the statistics literature and uses simulation of increasingly noisy data to extrapolate back to a hypothetical case with no noise. The bias of calculated metrics can then be computed by subtracting the SIMEX estimate from the original pointwise measurement. The SIMEX technique has been studied in the context of diffusion imaging to accurately capture the bias in fractional anisotropy measurements in DTI. Herein, we extend the application of SIMEX and bootstrap approaches to characterize bias and variance in metrics obtained from a Q-ball imaging reconstruction of high angular resolution diffusion imaging data. The results demonstrate that SIMEX and bootstrap approaches provide consistent estimates of the bias and variance of generalized fractional anisotropy, respectively. The RMSE for the generalized fractional anisotropy estimates shows a 7% decrease in white matter and an 8% decrease in gray matter when compared with the observed generalized fractional anisotropy estimates. On average, the bootstrap technique results in SD estimates that are approximately 97% of the true variation in white matter, and 86% in gray matter. Both SIMEX and bootstrap methods are flexible, estimate population characteristics based on single scans, and may be extended for bias and variance estimation on a variety of high angular resolution diffusion imaging metrics. © 2018 International Society for Magnetic Resonance in Medicine.

Attention, interpretation, and memory biases in subclinical depression: a proof-of-principle test of the combined cognitive biases hypothesis.

Science.gov (United States)

Everaert, Jonas; Duyck, Wouter; Koster, Ernst H W

2014-04-01

Emotional biases in attention, interpretation, and memory are viewed as important cognitive processes underlying symptoms of depression. To date, there is a limited understanding of the interplay among these processing biases. This study tested the dependence of memory on depression-related biases in attention and interpretation. Subclinically depressed and nondepressed participants completed a computerized version of the scrambled sentences test (measuring interpretation bias) while their eye movements were recorded (measuring attention bias). This task was followed by an incidental free recall test of previously constructed interpretations (measuring memory bias). Path analysis revealed a good fit for the model in which selective orienting of attention was associated with interpretation bias, which in turn was associated with a congruent bias in memory. Also, a good fit was observed for a path model in which biases in the maintenance of attention and interpretation were associated with memory bias. Both path models attained a superior fit compared with path models without the theorized functional relations among processing biases. These findings enhance understanding of how mechanisms of attention and interpretation regulate what is remembered. As such, they offer support for the combined cognitive biases hypothesis or the notion that emotionally biased cognitive processes are not isolated mechanisms but instead influence each other. Implications for theoretical models and emotion regulation across the spectrum of depressive symptoms are discussed.

Estimating the shear strength of concrete with coarse aggregate replacement

OpenAIRE

Folagbade Olusoga Peter ORIOLA; George MOSES; Jacob Oyeniyi AFOLAYAN; John Engbonye SANI

2017-01-01

For economic, environmental and practical reasons, it is desirable to replace the constituents of concrete with wastes and cheaper alternative materials. However, it is best when such replacements are done at optimum replacement levels. In view of this, a laboratory investigative test was carried out to evaluate the shear strength of concrete with coarse aggregate replacement by Coconut Shell and by Waste Rubber Tyre. The coarse aggregate replacement was done at recommended optimum proportion...

Consistent Parameter and Transfer Function Estimation using Context Free Grammars

Science.gov (United States)

Klotz, Daniel; Herrnegger, Mathew; Schulz, Karsten

2017-04-01

This contribution presents a method for the inference of transfer functions for rainfall-runoff models. Here, transfer functions are defined as parametrized (functional) relationships between a set of spatial predictors (e.g. elevation, slope or soil texture) and model parameters. They are ultimately used for estimation of consistent, spatially distributed model parameters from a limited amount of lumped global parameters. Additionally, they provide a straightforward method for parameter extrapolation from one set of basins to another and can even be used to derive parameterizations for multi-scale models [see: Samaniego et al., 2010]. Yet, currently an actual knowledge of the transfer functions is often implicitly assumed. As a matter of fact, for most cases these hypothesized transfer functions can rarely be measured and often remain unknown. Therefore, this contribution presents a general method for the concurrent estimation of the structure of transfer functions and their respective (global) parameters. Note, that by consequence an estimation of the distributed parameters of the rainfall-runoff model is also undertaken. The method combines two steps to achieve this. The first generates different possible transfer functions. The second then estimates the respective global transfer function parameters. The structural estimation of the transfer functions is based on the context free grammar concept. Chomsky first introduced context free grammars in linguistics [Chomsky, 1956]. Since then, they have been widely applied in computer science. But, to the knowledge of the authors, they have so far not been used in hydrology. Therefore, the contribution gives an introduction to context free grammars and shows how they can be constructed and used for the structural inference of transfer functions. This is enabled by new methods from evolutionary computation, such as grammatical evolution [O'Neill, 2001], which make it possible to exploit the constructed grammar as a

Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

DEFF Research Database (Denmark)

Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

2006-01-01

We have simulated plastic deformation of a model Mg-Cu metallic glass in order to study shear banding. In uniaxial tension, we find a necking instability occurs rather than shear banding. We can force the latter to occur by deforming in plane strain, forbidding the change of length in one...... of the transverse directions. Furthermore, in most of the simulations a notch is used to initiate shear bands, which lie at a 45 degrees angle to the tensile loading direction. The shear bands are characterized by the Falk and Langer local measure of plastic deformation D-min(2), averaged here over volumes...... observe a slight decrease in density, up to 1%, within the shear band, which is consistent with notions of increased free volume or disorder within a plastically deforming amorphous material....

Three calculations of free cortisol versus measured values in the critically ill.

Science.gov (United States)

Molenaar, Nienke; Groeneveld, A B Johan; de Jong, Margriet F C

2015-11-01

To investigate the agreement between the calculated free cortisol levels according to widely applied Coolens and adjusted Södergård equations with measured levels in the critically ill. A prospective study in a mixed intensive care unit. We consecutively included 103 patients with treatment-insensitive hypotension in whom an adrenocorticotropic hormone (ACTH) test (250μg) was performed. Serum total and free cortisol (equilibrium dialysis), corticosteroid-binding globulin and albumin were assessed. Free cortisol was estimated by the Coolens method (C) and two adjusted Södergård (S1 and S2) equations. Bland Altman plots were made. The bias for absolute (t=0, 30 and 60min after ACTH injection) cortisol levels was 38, -24, 41nmol/L when the C, S1 and S2 equations were used, with 95% limits of agreement between -65-142, -182-135, and -57-139nmol/L and percentage errors of 66, 85, and 64%, respectively. Bias for delta (peak-baseline) cortisol was 14, -31 and 16nmol/L, with 95% limits of agreement between -80-108, -157-95, and -74-105nmol/L, and percentage errors of 107, 114, and 100% for C, S1 and S2 equations, respectively. Calculated free cortisol levels have too high bias and imprecision to allow for acceptable use in the critically ill. Copyright © 2015 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Prediction of wall shear stresses in transitional boundary layers using near-wall mean velocity profiles

International Nuclear Information System (INIS)

Jeon, Woo Pyung; Shin, Sung Ho; Kang, Shin Hyoung

2000-01-01

The local wall shear stress in transitional boundary layer was estimated from the near-wall mean velocity data using the principle of Computational Preston tube Method(CPM). The previous DNS and experimental databases of transitional boundary layers were used to demonstrate the accuracy of the method and to provide the applicable range of wall unit y + . The skin friction coefficients predicted by the CPM agreed well with those from previous studies. To reexamine the applicability of the CPM, near-wall hot-wire measurements were conducted in developing transitional boundary layers on a flat plate with different freestream turbulence intensities. The intermittency profiles across the transitional boundary layers were reasonably obtained from the conditional sampling technique. An empirical correlation between the representative intermittency near the wall and the free parameter K 1 of the extended wall function of CPM has been newly proposed using the present and other experimental data. The CPM has been verified as a useful tool to measure the wall shear stress in transitional boundary layer with reasonable accuracy

Constraining primordial non-Gaussianity with cosmological weak lensing: shear and flexion

International Nuclear Information System (INIS)

Fedeli, C.; Bartelmann, M.; Moscardini, L.

2012-01-01

We examine the cosmological constraining power of future large-scale weak lensing surveys on the model of the ESA planned mission Euclid, with particular reference to primordial non-Gaussianity. Our analysis considers several different estimators of the projected matter power spectrum, based on both shear and flexion. We review the covariance and Fisher matrix for cosmic shear and evaluate those for cosmic flexion and for the cross-correlation between the two. The bounds provided by cosmic shear alone are looser than previously estimated, mainly due to the reduced sky coverage and background number density of sources for the latest Euclid specifications. New constraints for the local bispectrum shape, marginalized over σ 8 , are at the level of Δf NL ∼ 100, with the precise value depending on the exact multipole range that is considered in the analysis. We consider three additional bispectrum shapes, for which the cosmic shear constraints range from Δf NL ∼ 340 (equilateral shape) up to Δf NL ∼ 500 (orthogonal shape). Also, constraints on the level of non-Gaussianity and on the amplitude of the matter power spectrum σ 8 are almost perfectly anti-correlated, except for the orthogonal bispectrum shape for which they are correlated. The competitiveness of cosmic flexion constraints against cosmic shear ones depends by and large on the galaxy intrinsic flexion noise, that is still virtually unconstrained. Adopting the very high value that has been occasionally used in the literature results in the flexion contribution being basically negligible with respect to the shear one, and for realistic configurations the former does not improve significantly the constraining power of the latter. Since the shear shot noise is white, while the flexion one decreases with decreasing scale, by considering high enough multipoles the two contributions have to become comparable. Extending the analysis up to l max = 20,000 cosmic flexion, while being still subdominant

An importance biasing for 1-D deep-penetration problem by Monte Carlo

International Nuclear Information System (INIS)

Gupta, H.C.; Dwivedi, S.R.

1988-01-01

Using the itegral equations for the first and second moments of the 'total score' in an analogue and non-analogue simulations zero-variance biasing schemes have been obtained for all the commonly used reaction rate estimators. For partial score estimators a new zero-variance biasing scheme has been obtained as a special case. The new zero-variance scheme developed for partial score estimators has been used to develop an importance biasing scheme for use with expectation estimator in one dimensional deep-penetration problems with isotropic scattering. The importance biasing scheme has been studied for variance reduction in shields with anisotropic scattering. It is observed that the scheme not only results into a significant reduction in variance over the exponential biasing but also simplifies the complicated sampling procedure for the particle's outgoing direction at collision point. (author). 27 tables, 79 refs

Assessing the Magnitude of Non-Consent Biases in Linked Survey and Administrative Data

Directory of Open Access Journals (Sweden)

Joseph W. Sakshaug