Lee, Han Sang; Je, Jin Ho; Kim, Dong Jun; Kim, Yun Jae [Dept. of Mechanical Engineering, Korea University, Seoul (Korea, Republic of)
2015-10-15
This paper estimates the time-dependent crack-tip stress fields under elastic-plastic-creep conditions. We perform Finite-Element (FE) transient creep analyses for a Single-Edge-notched-Bend (SEB) specimen. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step-load. We consider both the same stress exponent and different stress exponent in the power-law creep and plasticity to determine the elastic-plastic-creep behaviour. To estimation of the crack-tip stress fields, we compare FE analysis results with those obtained numerically formulas. In addition, we propose a new equation to predict the crack-tip stress fields when the creep exponent is different from the plastic exponent.
Matsumoto, S.
2016-09-01
The stress field is a key factor controlling earthquake occurrence and crustal evolution. In this study, we propose an approach for determining the stress field in a region using seismic moment tensors, based on the classical equation in plasticity theory. Seismic activity is a phenomenon that relaxes crustal stress and creates plastic strain in a medium because of faulting, which suggests that the medium could behave as a plastic body. Using the constitutive relation in plastic theory, the increment of the plastic strain tensor is proportional to the deviatoric stress tensor. Simple mathematical manipulation enables the development of an inversion method for estimating the stress field in a region. The method is tested on shallow earthquakes occurring on Kyushu Island, Japan.
Geyer, A.; Martí, J.; Villaseñor, A.
2016-06-01
In volcanic areas, the existing stress field is a key parameter controlling magma generation, location and geometry of the magmatic plumbing systems and the distribution of the resulting volcanism at surface. Therefore, knowing the stress configuration in the lithosphere at any scale (i.e. local, regional and plate-scale) is fundamental to understand the distribution of volcanism and, subsequently, to interpret volcanic unrest and potential tectonic controls of future eruptions. The objective of the present work is to provide a first-order estimate of the plate-scale tectonic stresses acting on the Canary Islands, one of the largest active intraplate volcanic regions of the World. In order to obtain the orientation of the minimum and maximum horizontal compressive stresses, we perform a series of 2D finite element models of plate scale kinematics assuming plane stress approximation. Results obtained are used to develop a regional model, which takes into account recognized archipelago-scale structural discontinuities. Maximum horizontal compressive stress directions obtained are compared with available stress, geological and geodynamic data. The methodology used may be easily applied to other active volcanic regions, where a first order approach of their plate/regional stresses can be essential information to be used as input data for volcanic hazard assessment models.
Gómez-Alba, Sebastián; Fajardo-Zarate, Carlos Eduardo; Vargas, Carlos Alberto
2016-11-01
At least 156 earthquakes (Mw 2.8-4.4) were detected in Puerto Gaitán, Colombia (Eastern Llanos Basin) between April 2013 and December 2014. Out of context, this figure is not surprising. However, from its inception in 1993, the Colombian National Seismological Network (CNSN) found no evidence of significant seismic events in this region. In this study, we used CNSN data to model the rupture front and orientation of the highest-energy events. For these earthquakes, we relied on a joint inversion method to estimate focal mechanisms and, in turn, determine the area's fault trends and stress tensor. While the stress tensor defines maximum stress with normal tendency, focal mechanisms generally represent normal faults with NW orientation, an orientation which lines up with the tracking rupture achieved via Back Projection Imaging for the study area. We ought to bear in mind that this anomalous earthquake activity has taken place within oil fields. In short, the present paper argues that, based on the spatiotemporal distribution of seismic events, hydrocarbon operations may induce the study area's seismicity.
Totaro, C.; Orecchio, B.; Presti, D.; Scolaro, S.; Neri, G.
2016-09-01
A new high-quality waveform inversion focal mechanism database of the Calabrian Arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions. The new database has then been used for computation of posterior density distributions of stress tensor components by a Bayesian method never applied in south Italy before the present study. The application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated. Our results well constrain the extensional domain of Calabrian Arc and the compressional one of the southernmost Tyrrhenian Sea. In addition, previously undetected transcurrent regimes have been identified in the Ionian offshore. The new information released here will furnish useful tools and constraints for future geodynamic investigations.
Sidi Ali Ould Abdi
2011-01-01
Full Text Available Given a stationary multidimensional spatial process (i=(i,i∈ℝ×ℝ,i∈ℤ, we investigate a kernel estimate of the spatial conditional quantile function of the response variable i given the explicative variable i. Asymptotic normality of the kernel estimate is obtained when the sample considered is an -mixing sequence.
Global Geopotential Energy & Stress Field
Schiffer, Christian; Nielsen, S.B.
2012-01-01
Knowledge about the Earth's stress field and its sources can provide better understanding and interpretation of geodynamic and tectonic processes and regimes in the Earth's lithosphere. Stresses can be measured with different in-situ techniques and analysed by the study of focal mechanisms and stress induced geological structures. Quantifying single stress sources however remains a difficult and not uncommonly vague procedure. Modelling stress contributions can provide principle insight into ...
Estimation of Motion Vector Fields
Larsen, Rasmus
1993-01-01
This paper presents an approach to the estimation of 2-D motion vector fields from time varying image sequences. We use a piecewise smooth model based on coupled vector/binary Markov random fields. We find the maximum a posteriori solution by simulated annealing. The algorithm generate sample...
Stress field models from Maxwell stress functions: southern California
Bird, Peter
2017-08-01
The lithospheric stress field is formally divided into three components: a standard pressure which is a function of elevation (only), a topographic stress anomaly (3-D tensor field) and a tectonic stress anomaly (3-D tensor field). The boundary between topographic and tectonic stress anomalies is somewhat arbitrary, and here is based on the modeling tools available. The topographic stress anomaly is computed by numerical convolution of density anomalies with three tensor Green's functions provided by Boussinesq, Cerruti and Mindlin. By assuming either a seismically estimated or isostatic Moho depth, and by using Poisson ratio of either 0.25 or 0.5, I obtain four alternative topographic stress models. The tectonic stress field, which satisfies the homogeneous quasi-static momentum equation, is obtained from particular second derivatives of Maxwell vector potential fields which are weighted sums of basis functions representing constant tectonic stress components, linearly varying tectonic stress components and tectonic stress components that vary harmonically in one, two and three dimensions. Boundary conditions include zero traction due to tectonic stress anomaly at sea level, and zero traction due to the total stress anomaly on model boundaries at depths within the asthenosphere. The total stress anomaly is fit by least squares to both World Stress Map data and to a previous faulted-lithosphere, realistic-rheology dynamic model of the region computed with finite-element program Shells. No conflict is seen between the two target data sets, and the best-fitting model (using an isostatic Moho and Poisson ratio 0.5) gives minimum directional misfits relative to both targets. Constraints of computer memory, execution time and ill-conditioning of the linear system (which requires damping) limit harmonically varying tectonic stress to no more than six cycles along each axis of the model. The primary limitation on close fitting is that the Shells model predicts very sharp
Okabe, T. [GERD Geothermal Energy Research and Development Co. Ltd., Tokyo (Japan); Hayashi, K. [Tohoku Univ., Sendai (Japan). Inst. of Fluid Science; Kato, O.; Doi, N.; Miyazaki, S. [Japan Metals and Chemicals Co. Ltd., Tokyo (Japan); Uchida, T. [New Energy and Industrial Technology Development Organization, Tokyo, (Japan)
1997-05-27
This paper describes estimation of a stress field in the earth`s crust in the Kakkonda geothermal field. Formation micro imager (FMI) logging known as a crack detecting logging was performed in the well WD-1. This FMI logging has made observation possible on cracks along well axis thought to indicate size and direction of the crust stress, and drilling-induced tensile fractures (DTF). It was verified that these DTFs are generated initially in an azimuth determined by in-situ stress (an angle up to the DTF as measured counterclockwise with due north as a starting point, expressed in {theta}) in the well`s circumferential direction. It was also confirmed that a large number of cracks incline at a certain angle to the well axis (an angle made by the well axis and the DTF, expressed in {gamma}). The DTF is a crack initially generated on well walls as a result of such tensile stresses as mud pressure and thermal stress acting on the well walls during well excavation, caused by the in-situ stress field. Measurement was made on the {theta} and {gamma} from the FMI logging result, and estimation was given on a three-dimensional stress field. Elucidating the three-dimensional crust stress field in a geothermal reservoir is important in making clear the formation mechanism thereof and the growth of water-permeable cracks. This method can be regarded as an effective method. 9 refs., 8 figs., 1 tab.
Estimating stress heterogeneity from aftershock rate
Helmstetter, A; Helmstetter, Agnes; Shaw, Bruce E.
2005-01-01
We estimate the rate of aftershocks triggered by a heterogeneous stress change, using the rate-and-state model of Dieterich [1994]. We show than an exponential stress distribution P(\\tau)~ exp(-\\tau/\\tau_0) gives an Omori law decay of aftershocks with time ~1/t^p, with an exponent p=1-A\\sigma_n/\\tau_0, where A is a parameter of the rate-and-state friction law, and \\sigma_n the normal stress. Omori exponent p thus decreases if the stress "heterogeneity" \\tau_0 decreases. We also invert the stress distribution P(\\tau) from the seismicity rate R(t), assuming that the stress does not change with time. We apply this method to a synthetic stress map, using the (modified) scale invariant "k^2" slip model [Herrero and Bernard, 1994]. We generate synthetic aftershock catalogs from this stress change. The seismicity rate on the rupture area shows a huge increase at short times, even if the stress decreases on average. This stochastic slip model gives a Gaussian stress distribution, but nevertheless produces an aftersho...
Stress Field of Straight Edge Dislocation in Magnetic Field
LIU Zhao-long; HU Hai-yun; FAN Tian-you
2007-01-01
To study the changes in mechanical properties of materials within magnetic fields and the motion of dislocations,stress fields of dislocation in magnetic field need to be calculated.The straight edge dislocation is of basic importance in various defects.The stress field of straight edge dislocation in an external static magnetic field is determined by the theory of elasticity and electrodynamics according to the Volterra dislocation model for continuous media.This reduces to the known stress field when the magnet field is zero.The results can be used for further study on the strain energy of dislocations and the interactions between dislocations in magnetic fields.
An Estimation Method of Stress in Soft Rock Based on In-situ Measured Stress in Hard Rock
LI Wen-ping; LI Xiao-qin; SUN Ru-hua
2007-01-01
The law of variation of deep rock stress in gravitational and tectonic stress fields is analyzed based on the Hoek-Brown strength criterion. In the gravitational stress field, the rocks in the shallow area are in an elastic state and the deep, relatively soft rock may be in a plastic state. However, in the tectonic stress field, the relatively soft rock in the shallow area is in a plastic state and the deep rock in an elastic state. A method is proposed to estimate stress values in coal and soft rock based on in-situ measurements of hard rock. Our estimation method relates to the type of stress field and stress state. The equations of rock stress in various stress states are presented for the elastic, plastic and critical states. The critical state is a special stress state, which indicates the conversion of the elastic to the plastic state in the gravitational stress field and the conversion of the plastic to the elastic state in the tectonic stress field. Two cases studies show that the estimation method is feasible.
Geostatistical Estimations of Regional Hydraulic Conductivity Fields
Patriarche, D.; Castro, M. C.; Goovaerts, P.
2004-12-01
when estimating both (log T)* and T*. Among univariate procedures using the direct approach, the best prediction performances are obtained using simple kriging of log K with known local means. Cross validation also indicates that the indirect approach leads to smaller prediction errors than the direct approach, which is likely due to fewer available K primary data as well as a weaker correlation between primary and secondary attributes in the direct case. Although all procedures used log-transformed variables and incorporate secondary information derived from specific capacity data, none of the investigated techniques provides systematically better predictions for all scales, which stresses the importance of using cross validation to compare performances of alternative approaches and assess the unbiasedness of the back-transform procedure. Overall, estimation of the hydraulic conductivity field at such large regional scales through the tested geostatistical methods appears to be difficult due to both scarcity of sampling in the deeper portions of the formation (> 1 km) and preferential emplacement of well screens in the most productive portions of the aquifer. For example, in the deepest portions of the aquifer in the model domain, the estimated hydraulic conductivity field is obtained by extrapolation and gives origin to unrealistically high hydraulic conductivity values.
EFFECTS OF ROCK BEHAVIOR AND STRESS CONDITIONON FIELD STRESS DETERMINATION
D.H.（Steve）Zou
1995-01-01
Non-consistency of stress results is often observed during field measurements. In some cases, even the measurements are made at the same location in a massive rockmass, the results can vary widely. In order to solve the problem, extensive research has been carried out to study the major factors which may affect stress determination. They include the rock behaviour and the stress state. For rocks showing non-isotropic behaviour, the values of Young's modulus and Poisson ratio vary with the orientation of loading and measurement. Stress condition in the rock affects the rock behaviour. Furthermore, the loading condition on rock samples during laboratory tests is different from in the field and therefore the determined elastic constants may not represent the field condition. In general, the Young's modulus may depend on the orientation, the loading path, the stress magnitude and the stress ratio. This paper examines in detail the effects of those factors, especially for rocks showing transversely isotropic behaviour. It is found that the discrepancy of stress results from fieldts in this type of rock is mainly due to over simplification of the rock behavior and inadequate use of elastic constants of the rock during stress calculation. A case study is given, which indicates the significance of these factors and demonstrates the proper procedure for stress calculation from
Effect of stress on field dependence.
Sarris, V; Heineken, E; Peters, H
1976-08-01
60 subjects were tested in the rod-and-frame test under flicker conditions (stress). As compared to scores in a control situation (no flicker), the rod-and-frame scores were large under stress and increased monotonically during the session. Futhermore, both intra- and interindividual variability of rod-and-frame performance changed under stress conditions in a consistent manner. The general results, which clearly point to a reliable influence of stress on field dependency, are discussed within the methodological framework of Witkin's theory of perception and personality.
Entropy estimates for simple random fields
Forchhammer, Søren; Justesen, Jørn
1995-01-01
We consider the problem of determining the maximum entropy of a discrete random field on a lattice subject to certain local constraints on symbol configurations. The results are expected to be of interest in the analysis of digitized images and two dimensional codes. We shall present some examples...... of binary and ternary fields with simple constraints. Exact results on the entropies are known only in a few cases, but we shall present close bounds and estimates that are computationally efficient...
Global Geopotential Energy & Stress Field
Schiffer, Christian; Nielsen, S.B.
in the lithosphere, induced by lateral density variation. The leading quantity is the Geopotential Energy, the integrated lithostatic pressure in a rock column, which is related to horizontal stresses by the Equations of Equilibrium. The Geopotential Energy can be furthermore linearly related to the Geoid under...... assumption of local isostasy. Satellite Geoid measurements contain, however, deeper mantle responses of most likely longwavelength. Still after filtering, the Geoid can't be satisfyingly corrected. Existing shallow signals can be hereby extinguished as well, for instance the somewhat age dependent signal...... response to Geopotential Energy and the Geoid. A linearized inverse method fits a lithospheric reference model to reproduce measured data sets, such as topography and surface heat flow, while assuming isostasy and solving the steady state heat equation. A FEM code solves the equations of equilibrium...
Stress theory for classical fields
Kupferman, Raz; Olami, Elihu; Segev, Reuven
2017-01-01
Classical field theories together with the Lagrangian and Eulerian approaches to continuum mechanics are embraced under a geometric setting of a fiber bundle. The base manifold can be either the body manifold of continuum mechanics, space manifold, or space-time. Differentiable sections of the fiber bundle represent configurations of the system and the configuration space containing them is given the structure of an infinite dimensional manifold. Elements of the cotangent bundle of the config...
Confusion and controversy in the stress field.
Selye, H
1975-06-01
An attempt is made to further clarify present areas of controversy in the stress field, in response to a two-part article by Dr. John W. Mason which concludes in this issue of the Journal of Human Stress. The author tries to elucidate each source of confusion enumerated by Dr. Mason. The continued use of the word "stress" for the nonspecific response to any demand is deemed most desirable. The once vague term can now be applied in a well-defined sense and is accepted in all foreign languages as well, including those in which no such word existed previously in any sense. Subdivision of the stress concept has become necessary as more recent work has led to such notions as "eustress," "distress," "systemic stress" and "local stress." Confusion between stress as both an agent and a result can be avoided only by the distinction between "stress" and "stressor". It is explained that the stress syndrome is--by definition--nonspecific in its causation. However, depending upon conditioning factors, which can selectively influence the reactivity of certain organs, the same stressor can elicit different manifestations in different individuals.
ESTIMATION OF INCREASE OF STRESS RESISTANCE AMONG STUDENTS
Drobysheva O. M.
2015-09-01
Full Text Available By results of the estimation of stress resistance on dynamics of the regulation-adaptive status we can observe, that the autogenic training at the end of one academic year did not cause authentic changes in stress resistance in students with high and low levels of stress resistance. At the same time, it raised stress resistance for persons with a moderate level of stress resistance
Luttrell, Karen M.; Tong, Xiaopeng; Sandwell, David T.; Brooks, Benjamin A.; Bevis, Michael G.
2011-11-01
The great 27 February 2010 Mw 8.8 earthquake off the coast of southern Chile ruptured a ˜600 km length of subduction zone. In this paper, we make two independent estimates of shear stress in the crust in the region of the Chile earthquake. First, we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar (InSAR) and GPS to derive a spatially variable estimate of the change in static shear stress along the ruptured fault. Second, we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore-arc topography and the stress orientation indicated by the earthquake focal mechanism. This includes the derivation of a semianalytic solution for the stress field exerted by surface and Moho topography loading the crust. We find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid, with a Poisson ratio of 0.5, and is independent of Young's modulus. This places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography. We estimate the coseismic shear stress change from the Maule event ranged from -6 MPa (stress increase) to 17 MPa (stress drop), with a maximum depth-averaged crustal shear-stress drop of 4 MPa. We separately estimate that the plate-driving forces acting in the region, regardless of their exact mechanism, must contribute at least 27 MPa trench-perpendicular compression and 15 MPa trench-parallel compression. This corresponds to a depth-averaged shear stress of at least 7 MPa. The comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the Maule earthquake is weak, with the seismic cycle relieving much of the total sustained shear stress in the crust.
Stress field reconstruction in an active mudslide
Baroň, Ivo; Kernstocková, Markéta; Melichar, Rostislav
2017-07-01
Meso-scale structures from gravitational slope deformation observed in landslides and deep-seated gravitational slope failures are very similar to those of endogenous ones. Therefore we applied palaeostress analysis of fault-slip data for reconstructing the stress field of an active mudslide in Pechgraben, Austria. This complex compound landslide has developed in clayey colluvium and shale and was activated after a certain period of dormancy in June 2013. During the active motion on June 12, 2013, 73 fault-slip traces at 9 locations were measured within the landslide body. The heterogeneous fault-slip data were processed in term of palaeostresses, the reconstructed palaeostress tensor being characterized by the orientations of the three principal stress axes and the stress ratio (which provides the shape of the stress ellipsoid). The results of the palaeostress analysis were compared to airborne laser scan digital terrain models that revealed dynamics and superficial displacements of the moving mass prior and after our survey. The results were generally in good agreement with the observed landslide displacement pattern and with the anticipated stress regime according to Mohr-Coulomb failure criteria and Anderson's theory. The compressional regime was mostly registered at the toe in areas, where a compressional stress field is expected during previous mass-movement stages, or at margins loaded by subsequent landslide bodies from above. On the other hand, extension regimes were identified at the head scarps of secondary slides, subsequently on bulged ridges at the toe and in the zone of horst-and-graben structures in the lower central part of the main landslide body, where the basal slip surface probably had locally convex character. Strike-slip regimes, as well as oblique normal or oblique reverse regimes were observed at the lateral margins of the landslide bodies. The directions of principal stresses could be used as markers of landslide movement directions
Martinez, P.; Bohnhoff, M.; Kwiatek, G.
2012-12-01
Studying potential spatial and temporal variations of the crustal stress field caused by massive fluid injection during reservoir stimulation is important towards an improved understanding of induced seismicity in different types of reservoirs. However, an accurate and reliable determination of such stress changes is difficult and requires dense local seismic networks with good azimuthal coverage and low magnitude-detection threshold. The Geysers geothermal field is located close to the San Andreas Fault in California, USA. There, induced seismicity associated with the exploitation of the reservoir has been extensively monitored for more than 30 years. While it is evident that seismicity at The Geyser is related to injection and production operations it is difficult to relate the production parameters from individual wells to the spatial and temporal patterns of the crustal stress field and associated seismicity. Earlier attempts to determine the local stress field in the area (Oppenheimer, 1986, J. G. R., 91) estimated the stress orientation by inverting 210 fault plane solutions. He obtained a result that was very consistent with the regional stress field, which might indicate that the regional tectonic stress field dominates over the stresses induced locally by reservoir treatment. In this study we aim at determining potential spatial and temporal variations of the local stress field orientation at The Geysers geothermal site using first motion polarity data provided by a permanent array of 34 stations from Lawrence Berkeley National Laboratory (LBNL) installed in 2007. The network is composed of 3-component short period sensors located at the surface throughout the geothermal field with a sampling frequency of 500 Hz. To determine the stress field orientation we apply different stress inversion methods including non-linear stress inversion algorithms (Abers and Gephart, 2001, J. G. R., 106) with Bayesian uncertainty assessment and a linear approach (Hardebeck
Wall shear stress estimates in coronary artery constrictions
Back, L. H.; Crawford, D. W.
1992-01-01
Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.
Propagating Uncertainties from Source Model Estimations to Coulomb Stress Changes
Baumann, C.; Jonsson, S.; Woessner, J.
2009-12-01
Multiple studies have shown that static stress changes due to permanent fault displacement trigger earthquakes on the causative and on nearby faults. Calculations of static stress changes in previous studies have been based on fault parameters without considering any source model uncertainties or with crude assumptions about fault model errors based on available different source models. In this study, we investigate the influence of fault model parameter uncertainties on Coulomb Failure Stress change (ΔCFS) calculations by propagating the uncertainties from the fault estimation process to the Coulomb Failure stress changes. We use 2500 sets of correlated model parameters determined for the June 2000 Mw = 5.8 Kleifarvatn earthquake, southwest Iceland, which were estimated by using a repeated optimization procedure and multiple data sets that had been modified by synthetic noise. The model parameters show that the event was predominantly a right-lateral strike-slip earthquake on a north-south striking fault. The variability of the sets of models represents the posterior probability density distribution for the Kleifarvatn source model. First we investigate the influence of individual source model parameters on the ΔCFS calculations. We show through a correlation analysis that for this event, changes in dip, east location, strike, width and in part north location have stronger impact on the Coulomb failure stress changes than changes in fault length, depth, dip-slip and strike-slip. Second we find that the accuracy of Coulomb failure stress changes appears to increase with increasing distance from the fault. The absolute value of the standard deviation decays rapidly with distance within about 5-6 km around the fault from about 3-3.5 MPa down to a few Pa, implying that the influence of parameter changes decrease with increasing distance. This is underlined by the coefficient of variation CV, defined as the ratio of the standard deviation of the Coulomb stress
Chatterjee, Sulagna; Chattopadhyay, Sanatan
2016-10-01
An analytical model including the simultaneous impact of lattice and thermo-elastic constant mismatch-induced stress in nanowires on Insulator-on-Silicon substrate is developed. It is used to calibrate the finite-element based software, ANSYS, which is subsequently employed to estimate process-induced stress in the sequential steps of NW-FET fabrication. The model considers crystal structures and orientations for both the nanowires and substrates. In-plane stress components along nanowire-axis are estimated for different radii and fractions of insertion. Nature of longitudinal stress is observed to change when inserted fraction of nanowires is changed. Effect of various high-k gate-dielectrics is also investigated. A longitudinal tensile stress of 2.4 GPa and compressive stress of 1.89 GPa have been obtained for NW-FETs with 1/4th and 3/4th insertions with La2O3 and TiO2 as the gate-dielectrics, respectively. Therefore, it is possible to achieve comparable values of electron and hole mobility in NW-FETs by judiciously choosing gate-dielectrics and fractional insertion of the nanowires.
Recognition of Active Faults and Stress Field
Azuma, T.
2012-12-01
Around the plate-boundary region, the directions of maximum and minimum stress related to the plate motion is one of the key for the recognition of active faults. For example, it is typical idea that there are many N-S trading reverse faults, NE-SW and NW-SE trending strike slip faults and less normal faults (only near volcanoes) in Japan, where the compressional stress with E-W direction is dominant caused by the motion of the subduction of the Pacific Plate beneath the North American Plate. After the 2011 Tohoku earthquake (Mj 9.0), however, many earthquakes with the mechanism of the normal fault type occurred in the coastal region of the northern-east Japan. On 11th April 2011, the Fukushima Hamadori Earthquake (Mj 7.0) occurred accompanying surface faults along two faults, the Idosawa fault and the Yunotake fault, that recognized as active faults by the Research Group for Active Fault of Japan (1980, 1991). It impacted on active fault study by the reason of not only the appearance of two traces of significant surface faults with maximum displacement up to 2.1 m, but also the reactivation of the normal faults under the E-W compressional stress field. When we identify the active faults, it is one of the key whether the direction of slip on the fault consists with the stress field in that area or not. And there is a technique to recognized whether the fault is active or not by using the data of the direction of stress in the field and the geometry of the fault plane. Though it is useful for the fault in the rock without overlain Quaternary deposits, we should care that the active faults may react caused by the temporal stress condition after the generation of large earthquakes.
Bayesian parameter estimation for effective field theories
Wesolowski, S; Furnstahl, R J; Phillips, D R; Thapaliya, A
2015-01-01
We present procedures based on Bayesian statistics for effective field theory (EFT) parameter estimation from data. The extraction of low-energy constants (LECs) is guided by theoretical expectations that supplement such information in a quantifiable way through the specification of Bayesian priors. A prior for natural-sized LECs reduces the possibility of overfitting, and leads to a consistent accounting of different sources of uncertainty. A set of diagnostic tools are developed that analyze the fit and ensure that the priors do not bias the EFT parameter estimation. The procedures are illustrated using representative model problems and the extraction of LECs for the nucleon mass expansion in SU(2) chiral perturbation theory from synthetic lattice data.
Bayesian parameter estimation for effective field theories
Wesolowski, S.; Klco, N.; Furnstahl, R. J.; Phillips, D. R.; Thapaliya, A.
2016-07-01
We present procedures based on Bayesian statistics for estimating, from data, the parameters of effective field theories (EFTs). The extraction of low-energy constants (LECs) is guided by theoretical expectations in a quantifiable way through the specification of Bayesian priors. A prior for natural-sized LECs reduces the possibility of overfitting, and leads to a consistent accounting of different sources of uncertainty. A set of diagnostic tools is developed that analyzes the fit and ensures that the priors do not bias the EFT parameter estimation. The procedures are illustrated using representative model problems, including the extraction of LECs for the nucleon-mass expansion in SU(2) chiral perturbation theory from synthetic lattice data.
Random field estimation approach to robot dynamics
Rodriguez, Guillermo
1990-01-01
The difference equations of Kalman filtering and smoothing recursively factor and invert the covariance of the output of a linear state-space system driven by a white-noise process. Here it is shown that similar recursive techniques factor and invert the inertia matrix of a multibody robot system. The random field models are based on the assumption that all of the inertial (D'Alembert) forces in the system are represented by a spatially distributed white-noise model. They are easier to describe than the models based on classical mechanics, which typically require extensive derivation and manipulation of equations of motion for complex mechanical systems. With the spatially random models, more primitive locally specified computations result in a global collective system behavior equivalent to that obtained with deterministic models. The primary goal of applying random field estimation is to provide a concise analytical foundation for solving robot control and motion planning problems.
Modern tectonic stress field deeply in Xuzhou Coal Mine
Zhen-jie JING; Fu-ren XIE; Xiao-feng CUI; Jing-fei ZHANG
2013-01-01
By inverting fault slip data,the parameters of 12 tectonic stress tensors in the mine region can be determined.The following characteristics can be obtained for recent tectonic stress fields,which are found deep in the study region.The results show that the recent tectonic stress field mainly presents the characteristics of near NWW-SSE maximum compressional stress and near NE-SW minimum extensional stress,while the stress regimes are mainly of strike slip,part of the reverse-fault type.Recent tectonic stress field in the region is characterized by horizontal components.The maximum principal compression stress direction was from NEE to SEE,the average principal compression stress direction was near NWW-SSE maximum compressional stress and near NE-SW minimum extensional.The recent tectonic stress field of the studied area can be controlled by a large tectonic stress area.
Electromagnetic Fields, Oxidative Stress, and Neurodegeneration
Claudia Consales
2012-01-01
Full Text Available Electromagnetic fields (EMFs originating both from both natural and manmade sources permeate our environment. As people are continuously exposed to EMFs in everyday life, it is a matter of great debate whether they can be harmful to human health. On the basis of two decades of epidemiological studies, an increased risk for childhood leukemia associated with Extremely Low Frequency fields has been consistently assessed, inducing the International Agency for Research on Cancer to insert them in the 2B section of carcinogens in 2001. EMFs interaction with biological systems may cause oxidative stress under certain circumstances. Since free radicals are essential for brain physiological processes and pathological degeneration, research focusing on the possible influence of the EMFs-driven oxidative stress is still in progress, especially in the light of recent studies suggesting that EMFs may contribute to the etiology of neurodegenerative disorders. This review synthesizes the emerging evidences about this topic, highlighting the wide data uncertainty that still characterizes the EMFs effect on oxidative stress modulation, as both pro-oxidant and neuroprotective effects have been documented. Care should be taken to avoid methodological limitations and to determine the patho-physiological relevance of any alteration found in EMFs-exposed biological system.
Estimation of bed shear stresses in the pearl river estuary
Liu, Huan; Wu, Jia-xue
2015-03-01
Mean and fluctuating velocities were measured by use of a pulse coherent acoustic Doppler profiler (PC-ADP) and an acoustic Doppler velocimeter in the tidal bottom boundary layer of the Pearl River Estuary. The bed shear stresses were estimated by four different methods: log profile (LP), eddy correlation (EC), turbulent kinetic energy (TKE), and inertial dissipation (ID). The results show that (a) all four methods for estimating bed stresses have advantages and disadvantages, and they should be applied simultaneously to obtain reliable frictional velocity and to identify potential sources of errors; (b) the LP method was found to be the most suitable to estimate the bed stresses in non-stratified, quasi-steady, and homogeneous flows; and (c) in the estuary where the semi-diurnal tidal current is dominant, bed shear stresses exhibit a strong quarter-diurnal variation.
Estimation of Bed Shear Stresses in the Pearl River Estuary
刘欢; 吴加学
2015-01-01
Mean and fluctuating velocities were measured by use of a pulse coherent acoustic Doppler profiler (PC-ADP) and an acoustic Doppler velocimeter in the tidal bottom boundary layer of the Pearl River Estuary. The bed shear stresses were estimated by four different methods: log profile (LP), eddy correlation (EC), turbulent kinetic energy (TKE), and inertial dissipation (ID). The results show that (a) all four methods for estimating bed stresses have advantages and disadvantages, and they should be applied simultaneously to obtain reliable frictional velocity and to identify potential sources of errors; (b) the LP method was found to be the most suitable to estimate the bed stresses in non-stratified, quasi-steady, and homogeneous flows; and (c) in the estuary where the semi-diurnal tidal current is dominant, bed shear stresses exhibit a strong quarter-diurnal variation.
Stress field control during large caldera-forming eruptions
Costa, Antonio; Marti, Joan
2016-10-01
Crustal stress field can have a significant influence on the way magma is channelled through the crust and erupted explosively at the surface. Large Caldera Forming Eruptions (LCFEs) can erupt hundreds to thousands of cubic kilometres of magma in a relatively short time along fissures under the control of a far-field extensional stress. The associated eruption intensities are estimated in the range 109 - 1011 kg/s. We analyse syn-eruptive dynamics of LCFEs, by simulating numerically explosive flow of magma through a shallow dyke conduit connected to a magma chamber that in turn is fed by a deeper magma reservoir, both under the action of an extensional far-field stress. Results indicate that huge amounts of high viscosity silicic magma can be erupted over timescales of a few to several hours. Our study provides answers to outstanding questions relating to the intensity and duration of catastrophic volcanic eruptions in the past. In addition, it presents far-reaching implications for the understanding of dynamics and intensity of large-magnitude volcanic eruptions on Earth and to highlight the necessity of a future research to advance our knowledge of these rare catastrophic events.
Stress field control during large caldera-forming eruptions
Antonio Costa
2016-10-01
Full Text Available Crustal stress field can have a significant influence on the way magma is channelled through the crust and erupted explosively at the surface. Large Caldera Forming Eruptions (LCFEs can erupt hundreds to thousands of cubic kilometres of magma in a relatively short time along fissures under the control of a far-field extensional stress. The associated eruption intensities are estimated in the range 109 - 1011 kg/s. We analyse syn-eruptive dynamics of LCFEs, by simulating numerically explosive flow of magma through a shallow dyke conduit connected to a magma chamber that in turn is fed by a deeper magma reservoir, both under the action of an extensional far-field stress. Results indicate that huge amounts of high viscosity silicic magma can be erupted over timescales of a few to several hours. Our study provides answers to outstanding questions relating to the intensity and duration of catastrophic volcanic eruptions in the past. In addition, it presents far-reaching implications for the understanding of dynamics and intensity of large-magnitude volcanic eruptions on Earth and to highlight the necessity of a future research to advance our knowledge of these rare catastrophic events.
Modern tectonic stress field in Southwest Yunnan, China
谢富仁; 苏刚; 崔效锋; 舒赛兵; 赵建涛
2001-01-01
By means of inversion of fault slip data, the parameters of 20 tectonic stress tensors in Southwest Yunnan region are determined. Compared with the average stress field of the region obtained from focal mechanism solutions, the following characteristics of modern tectonic stress field in this region are obtained. From the west of Zhenyuan- Yingpanshan fault to the south of Longling fault zone, the maximum compressional stress is in NNE direction and the stress regime is mainly of strike-slip type. In Longling fault zone and the area north to it, the direction of maximum compressional stress is near-NS or NNW, the stress regime is of strike-slip type.
Estimating Stresses, Fault Friction and Fluid Pressure from Topography and Coseismic Slip Models
Styron, R. H.; Hetland, E. A.
2014-12-01
Stress is a first-order control on the deformation state of the earth. However, stress is notoriously hard to measure, and researchers typically only estimate the directions and relative magnitudes of principal stresses, with little quantification of the uncertainties or absolute magnitude. To improve upon this, we have developed methods to constrain the full stress tensor field in a region surrounding a fault, including tectonic, topographic, and lithostatic components, as well as static friction and pore fluid pressure on the fault. Our methods are based on elastic halfspace techniques for estimating topographic stresses from a DEM, and we use a Bayesian approach to estimate accumulated tectonic stress, fluid pressure, and friction from fault geometry and slip rake, assuming Mohr-Coulomb fault mechanics. The nature of the tectonic stress inversion is such that either the stress maximum or minimum is better constrained, depending on the topography and fault deformation style. Our results from the 2008 Wenchuan event yield shear stresses from topography up to 20 MPa (normal-sinistral shear sense) and topographic normal stresses up to 80 MPa on the faults; tectonic stress had to be large enough to overcome topography to produce the observed reverse-dextral slip. Maximum tectonic stress is constrained to be >0.3 * lithostatic stress (depth-increasing), with a most likely value around 0.8, trending 90-110°E. Minimum tectonic stress is about half of maximum. Static fault friction is constrained at 0.1-0.4, and fluid pressure at 0-0.6 * total pressure on the fault. Additionally, the patterns of topographic stress and slip suggest that topographic normal stress may limit fault slip once failure has occurred. Preliminary results from the 2013 Balochistan earthquake are similar, but yield stronger constraints on the upper limits of maximum tectonic stress, as well as tight constraints on the magnitude of minimum tectonic stress and stress orientation. Work in progress on
Estimation of Dense Image Flow Fields in Fluids
Larsen, Rasmus; Conradsen, Knut; Ersbøll, Bjarne Kjær
1998-01-01
The estimation of flow fields from time sequences of satellite imagery has a number of important applications. For visualisation of cloud or sea ice movements in sequences of crude temporal sampling a satisfactory non-blurred temporal interpolation can be performed only when the flow field...... images. The estimated flow fields are used in a temporal interpolation scheme....
Stress field near an interface edge of linear hardening materials
许金泉; 付列东
2002-01-01
The elastic-plastic singular stress field near an interface edge of bounded linear hardening material is substantially as same as that of bonded elastic materials whose Young' s modulus and Poisson ratio are substituted by equivalent values, respectively. Further investigation by the elasto-plastic boundary element method (BEM) on the stress field near the interface edge showed that the stress field there can be divided into three regions: the domain region of the elastic-plastic singular stress field, the transitional region and the elastic region. The domain region of the elastic-plastic singular stress becomes larger with the increasing of the linear hardening coefficient. When the linear hardening coefficient decreases to a certain value, the effective stress in most of the yield zone equals approximately the yield stress. The stress distribution in the elastic region under small-scale yielding condition was also investigated.
Stress field near an interface edge of linear hardening materials
无
2002-01-01
The elastic-plastic singular stress field near an interface edge of bounded linear hardening material is substantially as same as that of bonded elastic materials whose Young's modulus and Poisson ratio are substituted by equivalent values, respectively. Further investigation by the elasto-plastic boundary element method (BEM) on the stress field near the interface edge showed that the stress field there can be divided into three regions: the domain region of the elastic-plastic singular stress field, the transitional region and the elastic region. The domain region of the elastic-plastic singular stress becomes larger with the increasing of the linear hardening coefficient. When the linear hardening coefficient decreases to a certain value, the effective stress in most of the yield zone equals approximately the yield stress. The stress distribution in the elastic region under small-scale yielding condition was also investigated.
Stress Recovery and Error Estimation for Shell Structures
Yazdani, A. A.; Riggs, H. R.; Tessler, A.
2000-01-01
The Penalized Discrete Least-Squares (PDLS) stress recovery (smoothing) technique developed for two dimensional linear elliptic problems is adapted here to three-dimensional shell structures. The surfaces are restricted to those which have a 2-D parametric representation, or which can be built-up of such surfaces. The proposed strategy involves mapping the finite element results to the 2-D parametric space which describes the geometry, and smoothing is carried out in the parametric space using the PDLS-based Smoothing Element Analysis (SEA). Numerical results for two well-known shell problems are presented to illustrate the performance of SEA/PDLS for these problems. The recovered stresses are used in the Zienkiewicz-Zhu a posteriori error estimator. The estimated errors are used to demonstrate the performance of SEA-recovered stresses in automated adaptive mesh refinement of shell structures. The numerical results are encouraging. Further testing involving more complex, practical structures is necessary.
Restriction estimates for the paraboloid over finite fields
Lewko, Allison
2010-01-01
We prove certain endpoint restriction estimates for the paraboloid over finite fields in three and higher dimensions. Working in the bilinear setting, we are able to pass from estimates for characteristic functions to estimates for general functions while avoiding the extra logarithmic power of the field size which is introduced by the dyadic pigeonhole approach. This allows us to remove logarithmic factors from the estimates obtained by Mockenhaupt and Tao in three dimensions and those obtained by Iosevich and Koh in higher dimensions.
Uncertainty principle estimates for vector fields
Pérez Moreno, Carlos; Wheeden, Richard L.
2001-01-01
We derive weighted norm estimates for integral operators of potential type and for their related maximal operators. These operators are generalizations of the classical fractional integrals and fractional maximal functions. The norm estimates are derived in the context of a space of homogeneous type. The conditions required of the weight functions involve generalizations of the Fefferman-Phong "r-bump" condition. The results improve some earlier ones of the same kind, and they also extend to ...
Auditory Perception in Open Field: Distance Estimation
2013-07-01
the distance and spaciousness estimation cues can be ambiguous (e.g., sound intensity, sound spectrum) or are fairly weak (e.g., binaural cues...Invariance in Sound Perception. Acta Psychologica Fennica 1951, 1, 9–20. Florentine, M.; Epstein, M. Ecological Loudness. Binaural Loudness Constancy...8, 145–149. 50 Lu, Y-Ch.; Cooke, M. Binaural Estimation of Sound Source Distance via the Direct-to- Reverberant Energy Ratio for Static and Moving
Mothers’ estimates of their preschool children and parenting stress
Benjamin Loader
2011-06-01
Full Text Available The present study investigates whether the results of the study of Willinger and Eisenwort (2005 could also apply to a sample of preschool children not referred to a tertiary medical institution. Moreover, we were interested in the accuracy of maternal estimates of their children’s development regarding vocabulary for parenting stress, regarding behavioural problems, intellectual development, age and gender of the child. 108 children between the ages of three and six and their mothers were investigated by several diagnostic scales concerning child development with respect to language, motor and intellectual development as well as child behavioural problems and parenting stress concering child and parent characteristics. The mothers’ estimates regarding the children`s vocabulary were assessed by the same vocabulary test used for the children by presenting the test as questionnaire to the mothers. There was a significant trend towards an overestimation of a child’s developmental functioning regarding vocabulary. Group comparisons between groups of different levels of maternal overestimations (mild, moderate and severe overestimation of their child’s language development with respect to parenting stress levels considering age, sex, intellectual develoment and child behaviour problems showed the lowest parenting stress level regarding child characteristics in the group of severe overestimation and the highest level of parenting stress regarding parent characteristics in the group of mild overestimation. Significant influences of child behaviour and intellectual level on parenting stress were found. The results showed that mothers should not be used as only source of information about their children’s developmental status, especially with respect to their active vocabulary. However, maternal overestimation seems to have a positive impact on parenting stress regarding child characteristics, which could possibly be explained as a defense
Luttrell, K. M.; Tong, X.; Sandwell, D. T.; Brooks, B. A.
2010-12-01
The great February 27, 2010 Mw 8.8 earthquake off the coast of southern Chile ruptured a 606 km length of subduction zone. In this study we make two independent estimates of shear stress in the crust in the region of the Chile earthquake. First, we use a coseismic slip model constrained by geodetic observations from InSAR and GPS to derive a spatially variable estimate of the change in static shear stress along the ruptured fault. Second, we use a static force balance model to constrain the crustal shear stress required to support observed accretionary wedge topography and the stress orientation indicated by the earthquake focal mechanism. This includes the derivation of a semi-analytic solution for the stress field exerted by surface and Moho topography loading the crust. We find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid, with a Poisson’s ratio of 0.5. This places a lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography. We estimate the shear stress change from the Maule event ranged from -6 MPa (stress increase) to 14 MPa (stress drop), with a maximum depth-averaged shear stress drop of 4 MPa. We separately estimate that the plate driving forces acting in the region, regardless of their exact mechanism, must contribute at least 15 MPa trench-parallel compression, and trench-perpendicular compression must exceed trench-parallel compression by at least 12 MPa. This corresponds to a depth-averaged shear stress of at least 7 MPa. The comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the Maule earthquake is weak, with the seismic cycle relieving much of the total sustained shear stress in the crust, and an equal portion of plate-driving stress being transmitted through the mantle.
Parameter estimation of hidden periodic model in random fields
何书元
1999-01-01
Two-dimensional hidden periodic model is an important model in random fields. The model is used in the field of two-dimensional signal processing, prediction and spectral analysis. A method of estimating the parameters for the model is designed. The strong consistency of the estimators is proved.
Variational multi-valued velocity field estimation for transparent sequences
Ramirez-Manzanares, Alonso; Rivera, Mariano; Kornprobst, Pierre;
2011-01-01
Motion estimation in sequences with transparencies is an important problem in robotics and medical imaging applications. In this work we propose a variational approach for estimating multi-valued velocity fields in transparent sequences. Starting from existing local motion estimators, we derive a...
Failure of Ceramic Composites in Non-Uniform Stress Fields
Rajan, Varun P.
Continuous-fiber ceramic matrix composites (CMCs) are of interest as hot-section components in gas turbine engines due to their refractoriness and low density relative to metallic alloys. In service, CMCs will be subjected to spatially inhomogeneous temperature and stress fields. Robust tools that enable prediction of deformation and fracture under these conditions are therefore required for component design and analysis. Such tools are presently lacking. The present work helps to address this deficiency by developing models for CMC mechanical behavior at two length scales: that of the constituents and that of the components. Problems of interest are further divided into two categories: '1-D loadings,' in which the stresses are aligned with the fiber axes, and '2-D loadings,' in which the stress state is more general. For the former class of problems, the major outstanding issue is material fracture, not deformation. A fracture criterion based on the attainment of a global load maximum is developed, which yields results for pure bending of CMCs in reasonable agreement with available experimental data. For the latter class of problems, the understanding of both the micro-scale and macro-scale behavior is relatively immature. An approach based upon analysis of a unit cell (a single fiber surrounded by a matrix jacket) is pursued. Stress fields in the constituents of the composite are estimated using analytical models, the accuracy of which is confirmed using finite element analysis. As part of a fracture mechanics analysis, these fields enable estimation of the steady-state matrix cracking stress for arbitrary in-plane loading of a unidirectional ply. While insightful at the micro-scale, unit cell models are difficult to extend to coarser scales. Instead, material deformation is typically predicted using phenomenological constitutive models. One such model for CMC laminates is investigated and found to predict material instability where none should exist. Remedies to
Estimating thermal performance curves from repeated field observations
Childress, Evan; Letcher, Benjamin H.
2017-01-01
Estimating thermal performance of organisms is critical for understanding population distributions and dynamics and predicting responses to climate change. Typically, performance curves are estimated using laboratory studies to isolate temperature effects, but other abiotic and biotic factors influence temperature-performance relationships in nature reducing these models' predictive ability. We present a model for estimating thermal performance curves from repeated field observations that includes environmental and individual variation. We fit the model in a Bayesian framework using MCMC sampling, which allowed for estimation of unobserved latent growth while propagating uncertainty. Fitting the model to simulated data varying in sampling design and parameter values demonstrated that the parameter estimates were accurate, precise, and unbiased. Fitting the model to individual growth data from wild trout revealed high out-of-sample predictive ability relative to laboratory-derived models, which produced more biased predictions for field performance. The field-based estimates of thermal maxima were lower than those based on laboratory studies. Under warming temperature scenarios, field-derived performance models predicted stronger declines in body size than laboratory-derived models, suggesting that laboratory-based models may underestimate climate change effects. The presented model estimates true, realized field performance, avoiding assumptions required for applying laboratory-based models to field performance, which should improve estimates of performance under climate change and advance thermal ecology.
Estimating thermal performance curves from repeated field observations.
Childress, Evan S; Letcher, Benjamin H
2017-03-08
Estimating thermal performance of organisms is critical for understanding population distributions and dynamics and predicting responses to climate change. Typically, performance curves are estimated using laboratory studies to isolate temperature effects, but other abiotic and biotic factors influence temperature-performance relationships in nature reducing these models' predictive ability. We present a model for estimating thermal performance curves from repeated field observations that includes environmental and individual variation. We fit the model in a Bayesian framework using MCMC sampling, which allowed for estimation of unobserved latent growth while propagating uncertainty. Fitting the model to simulated data varying in sampling design and parameter values demonstrated that the parameter estimates were accurate, precise, and unbiased. Fitting the model to individual growth data from wild trout revealed high out-of-sample predictive ability relative to laboratory-derived models, which produced more biased predictions for field performance. The field-based estimates of thermal maxima were lower than those based on laboratory studies. Under warming temperature scenarios, field-derived performance models predicted stronger declines in body size than laboratory-derived models, suggesting that laboratory-based models may underestimate climate change effects. The presented model estimates true, realized field performance, avoiding assumptions required for applying laboratory-based models to field performance, which should improve estimates of performance under climate change and advance thermal ecology. This article is protected by copyright. All rights reserved.
Moment analysis of the Delaunay tessellation field estimator
Lieshout, M.N.M. van
2009-01-01
The Campbell-Mecke theorem is used to derive explicit expressions for the mean and variance of Schaap and Van de Weygaert's Delaunay tessellation field estimator. Special attention is paid to Poisson processes.
Lipschitz estimates for convex functions with respect to vector fields
Valentino Magnani
2012-12-01
Full Text Available We present Lipschitz continuity estimates for a class of convex functions with respect to Hörmander vector fields. These results have been recently obtained in collaboration with M. Scienza, [22].
Far-field DOA estimation and near-field localization for multipath signals
Elbir, Ahmet M.; Tuncer, T. Engin
2014-09-01
In direction finding and localization applications, multipath signals are important sources of error for parameter estimation. When the antenna array receives multipath reflections which are coherent with the far-field line-of-sight signal, estimating the far- and near-field components becomes an important problem. In this paper, a new method is proposed to estimate the direction-of-arrival (DOA) of the far-field source and to localize its near-field multipaths. Far-field source DOA is estimated using calibration of the antenna array. A near-to-far transformation is proposed for the estimation of the near-field source DOA angles. In order to estimate the near-field range parameters, a compressive sensing approach is presented where a dictionary with near-field sources with different ranges is employed. As a result, the proposed method estimates the far-field and near-field source DOAs as well as the range and the signal amplitudes of the near-field sources. This method is evaluated using close-to-real world data generated by a numerical electromagnetic tool, where the array and transmitter are placed in an irregular terrain and array data are generated using full 3-D propagation model. It is shown that unknown source parameters can be estimated effectively showing the potential of the proposed approach in applications involving high-frequency direction finding and indoor localization.
Attitude and Trajectory Estimation Using Earth Magnetic Field Data
Deutschmann, Julie; Bar-Itzhack, Itzhack Y.
1996-01-01
The magnetometer has long been a reliable, inexpensive sensor used in spacecraft momentum management and attitude estimation. Recent studies show an increased accuracy potential for magnetometer-only attitude estimation systems. Since the Earth's magnetic field is a function of time and position, and since time is known quite precisely, the differences between the computer and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both the spacecraft trajectory and attitude errors. Therefore, these errors can be used to estimate both trajectory and attitude. Traditionally, satellite attitude and trajectory have been estimated with completely separate system, using different measurement data. Recently, trajectory estimation for low earth orbit satellites was successfully demonstrated in ground software using only magnetometer data. This work proposes a single augmented extended Kalman Filter to simultaneously and autonomously estimate both spacecraft trajectory and attitude with data from a magnetometer and either dynamically determined rates or gyro-measured body rates.
Joint development in perturbed stress fields near faults
Rawnsley, K. D.; Rives, T.; Petti, J.-P.; Hencher, S. R.; Lumsden, A. C.
1992-09-01
Field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms. Joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories. A progressive change in joint direction is observed from unperturbed regions away from faults, to strongly perturbed zones adjacent to faults. This indicates that the joint pattern can reflect perturbations of the regional stress field around faults. In the examples, the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock. The corresponding joints converge at these points and are sub-parallel to the fault along the remainder of the fault plane. The possibility that a fault plane acts as a free surface contained within an elastic body is considered. In this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault. The free surface model seems to explain the metre-scale curvature of joints in the vicinity of existing joints, but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the Earth's surface. Two examples are investigated from the Lias of Great Britain; at Nash Point and Robin Hood's Bay. Both comprise sub-horizontal strata of relatively homogeneous lithology and bed thickness, which provide striking examples of joints developed near faults.
Investigations of some rock stress measuring techniques and the stress field in Norway
Hanssen, Tor Harald
1997-12-31
Rock stresses are important to the safe construction and operation of all man-made structures in rock, whether In mining, civil or petroleum engineering. The crucial issue is their relative magnitude and orientation. This thesis develops equipment and methods for further rock stress assessment and reevaluates existing overcoring rock stress measurements, and relates this information to the present geological setting. Both laboratory work and field work are involved. In the field, rock stresses are measured by the overcoring and the hydraulic fracturing technique. An observation technique for assessing likely high stresses is developed. The field data refer to several hydropower projects and to some offshore hydrocarbon fields. The principal sections are: (1) Tectonic setting in the western Fennoscandia, (2) Triaxial rock stress measurements by overcoring using the NTH cell (a strain gauge cell developed at the Norwegian technical university in Trondheim and based on the CSIR cell of the South African Council for Scientific and Industrial Research), (3) Laboratory testing of the NTH cell, (4) Quality ranking of stresses measured by the NTH cell, (4) Recalculated rock stresses and implications to the regional stress field, (5) Hydraulic fracturing stress measurements. 113 refs., 98 figs., 62 tabs.
Neotectonic stresses in Fennoscandia: field observations and modelling
Pascal, Christophe
2013-04-01
The present-day stress state of Fennoscandia is traditionally viewed as the combination of far field sources and residual glacial loading stresses. Investigations were conducted in different regions of Norway with the purpose of detecting and measuring stress-relief features and to derive from them valuable information on the crustal stress state. Stress-relief features are induced by blasting and sudden rock unloading in road construction and quarrying operations and are common in Norway and very likely in other regions of Fennoscandia. Stress relief at the Earth's surface is diagnostic of anomalously high stress levels at shallow depths in the crust and appears to be a characteristic of the formerly glaciated Baltic and Canadian Precambrian shields. The studied stress-relief features are, in general, indicative of NW-SE compression, suggesting ridge-push as the main source of stress. Our derived stress directions are also in excellent agreement with the ones derived from other kinds of stress indicators, including focal mechanisms from deep earthquakes, demonstrating that stress-relief features are valuable for neotectonic research. As a second step we applied numerical modelling techniques to simulate the neotectonic stress field in Fennoscandia with particular emphasis to southern Norway. A numerical method was used to reconstruct the structure of the Fennoscandian lithosphere. The numerical method involves classical steady-state heat equations to derive lithosphere thickness, geotherm and density distribution and, in addition, requires the studied lithosphere to be isostatically compensated at its base. The a priori crustal structure was derived from previous geophysical studies. Undulations of the geoid were used to calibrate the models. Once the density structure of the Fennoscandian lithosphere is reconstructed it is straightforward to quantify its stress state and compare modelling results with existing stress indicators. The modelling suggests that
Estimation of fluid flow fields and their stagnation points
Larsen, Rasmus
Given a temporal sequence of images of fluids we will use local polynomials to regularise obser-vations of normal flows into smooth flow fields. This technique furthermore allows us to give a qualitative local description of the flow field and to estimate the position of stagnation points...
Estimation of Dense Image Flow Fields in Fluids
Larsen, Rasmus; Conradsen, Knut; Ersbøll, Bjarne Kjær
The estimation of flow fields from time sequences of satellite imagery has a number of important applications. For visualization of cloud or sea ice movements in sequences of crude temporal sampling a satisfactory non blurred temporal interpolation can be performed only when the flow field...... interpolation scheme....
Estimation of viscous dissipative stresses induced by a mechanical heart valve using PIV data.
Li, Chi-Pei; Lo, Chi-Wen; Lu, Po-Chien
2010-03-01
Among the clinical complications of mechanical heart valves (MHVs), hemolysis was previously thought to result from Reynolds stresses in turbulent flows. A more recent hypothesis suggests viscous dissipative stresses at spatial scales similar in size to red blood cells may be related to hemolysis in MHVs, but the resolution of current instrumentation is insufficient to measure the smallest eddy sizes. We studied the St. Jude Medical (SJM) 27 mm valve in the aortic position of a pulsatile circulatory mock loop under physiologic conditions with particle image velocimetry (PIV). Assuming a dynamic equilibrium assumption between the resolved and sub-grid-scale (SGS) energy flux, the SGS energy flux was calculated from the strain rate tensor computed from the resolved velocity fields and the SGS stress was determined by the Smagorinsky model, from which the turbulence dissipation rate and then the viscous dissipative stresses were estimated. Our results showed Reynolds stresses up to 80 N/m2 throughout the cardiac cycle, and viscous dissipative stresses below 12 N/m2. The viscous dissipative stresses remain far below the threshold of red blood cell hemolysis, but could potentially damage platelets, implying the need for further study in the phenomenon of MHV hemolytic complications.
Did stresses from the Cerro Prieto Geothermal Field influence the El Mayor-Cucapah rupture sequence?
Trugman, Daniel T.; Borsa, Adrian A.; Sandwell, David T.
2014-12-01
The Mw 7.2 El Mayor-Cucapah (EMC) earthquake ruptured a complex fault system in northern Baja California that was previously considered inactive. The Cerro Prieto Geothermal Field (CPGF), site of the world's second largest geothermal power plant, is located approximately 15 km to the northeast of the EMC hypocenter. We investigate whether anthropogenic fluid extraction at the CPGF caused a significant perturbation to the stress field in the EMC rupture zone. We use Advanced Land Observing Satellite interferometric synthetic aperture radar data to develop a laterally heterogeneous model of fluid extraction at the CPGF and estimate that this extraction generates positive Coulomb stressing rates of order 15 kPa/yr near the EMC hypocenter, a value which exceeds the local tectonic stressing rate. Although we cannot definitively conclude that production at the CPGF triggered the EMC earthquake, its influence on the local stress field is substantial and should not be neglected in local seismic hazard assessments.
Reverberant shear wave fields and estimation of tissue properties
Parker, Kevin J.; Ormachea, Juvenal; Zvietcovich, Fernando; Castaneda, Benjamin
2017-02-01
The determination of shear wave speed is an important subject in the field of elastography, since elevated shear wave speeds can be directly linked to increased stiffness of tissues. MRI and ultrasound scanners are frequently used to detect shear waves and a variety of estimators are applied to calculate the underlying shear wave speed. The estimators can be relatively simple if plane wave behavior is assumed with a known direction of propagation. However, multiple reflections from organ boundaries and internal inhomogeneities and mode conversions can create a complicated field in time and space. Thus, we explore the mathematics of multiple component shear wave fields and derive the basic properties, from which efficient estimators can be obtained. We approach this problem from the historic perspective of reverberant fields, a conceptual framework used in architectural acoustics and related fields. The framework can be recast for the alternative case of shear waves in a bounded elastic media, and the expected value of displacement patterns in shear reverberant fields are derived, along with some practical estimators of shear wave speed. These are applied to finite element models and phantoms to illustrate the characteristics of reverberant fields and provide preliminary confirmation of the overall framework.
Temperature and stress fields of multi-track laser cladding
ZHAO Hong-yun; ZHANG nong-tao; XU Chun-hua; YANG Xian-qun
2009-01-01
Based on genetic algorithm and neural network algorithm, the finite element analyses on the temperature fields and stress fields of multi-track laser cladding were carried out by using the ANSYS software. The results show that, in the multi-track cladding process, the temperature field ellipse leans to the cladding formed, and the front cladding has preheating function on the following cladding. During cladding, the longitudinal stress is the largest, the lateral stress is the second, and the thickness direction stress is the smallest. The center of the cladding is in the tensile stress condition. The longitudinal tensile stress is higher than the lateral or thickness direction stress by several times, and the tensile stress achieves the maximum at the area of joint between the cladding and substrate. Therefore, it is inferred that transversal crack is the most main crack form in multi-track laser cladding. Moreover, the joint between cladding and substrate is the crack sensitive area, and this is consistent with the actual experiments.
Using stress shadows to invert for changes in local stress field
Latimer, C. D.; Tiampo, K. F.; Rundle, J.
2009-12-01
When a large earthquake occurs, stresses in the crust are redistributed creating regions that experience an increase in stress while others experience a stress decrease which are called stress shadows. In many studies, these stress shadows are said to contain less seismic activity than the average background rate, and so correlations are made between lack of seismicity or a decrease in seismicity rate and the stress shadow locations and magnitudes (the amount of decrease of stress). In this study the opposite procedure is applied: We use seismicity rate changes to determine information about the stress changes due to a large magnitude earthquake, as well as its effect on the stress field itself. We use the Pattern Informatics method to examine the changes in seismicity rate, as it is an objective measure of the rate changes with respect to the regional background rate. The results from this analysis are then used to invert for, with a genetic algorithm, parameters that define the stress field such as the principal stress orientations, the coefficient of friction, and the calculation depth. The modelled stress data is calculated using Coulomb stress change theory and the Coulomb 3 program, and it is trying to produce the same size and location of stress shadows as seen in the seismicity rate change data. Four different Californian earthquakes were chosen in order to determine their effect on the local stress field: (1) 1987 Superstition Hills (2) 1989 Loma Prieta (3) 1992 Landers and (4) 1994 Northridge. In order to find out the effect that each of the parameters have on the modelled results, we performed a Monte Carlo simulation to find the errors associated with each, and a sensitivity analysis to determine the magnitude of change that each one produces. We hope with this new information of the changes incurred due to a large magnitude earthquake occurrence, that modelling of earthquakes can be advanced, and our understanding of their mechanics enhanced.
Analytical maximum likelihood estimation of stellar magnetic fields
González, M J Martínez; Ramos, A Asensio; Belluzzi, L
2011-01-01
The polarised spectrum of stellar radiation encodes valuable information on the conditions of stellar atmospheres and the magnetic fields that permeate them. In this paper, we give explicit expressions to estimate the magnetic field vector and its associated error from the observed Stokes parameters. We study the solar case where specific intensities are observed and then the stellar case, where we receive the polarised flux. In this second case, we concentrate on the explicit expression for the case of a slow rotator with a dipolar magnetic field geometry. Moreover, we also give explicit formulae to retrieve the magnetic field vector from the LSD profiles without assuming mean values for the LSD artificial spectral line. The formulae have been obtained assuming that the spectral lines can be described in the weak field regime and using a maximum likelihood approach. The errors are recovered by means of the hermitian matrix. The bias of the estimators are analysed in depth.
Modelling of the Global Geopotential Energy & Stress Field
Schiffer, Christian; Nielsen, S.B.
Lateral density and topography variations yield in and important contribution to the lithospheric stress field. The leading quantity is the Geopotential Energy, the integrated lithostatic pressure in a rock column. The horizontal gradient of this quantity is related to horizontal stresses through...... the Equations of equilibrium of stresses. The Geopotential Energy furthermore can be linearly related to the Geoid under assumption of local isostasy. Satellite Geoid measurements contain, however, also non-isostatic deeper mantle responses of long wavelength. Unfortunately, high-pass filtering of the Geoid...... flow in the presence of local isostasy and a steady state geotherm. Subsequently we use a FEM code to solve the Equations of equilibrium of stresses for a three dimensional elastic shell. The modelled results are shown and compared with the global stress field and other publications....
A NOVEL METHOD FOR ESTIMATING SOIL PRECOMPRESSION STRESS FROM UNIAXIAL CONFINED COMPRESSION TESTS
Lamandé, Mathieu; Schjønning, Per; Labouriau, Rodrigo
2017-01-01
The concept of precompression stress is used for estimating soil strength of relevance to fieldtraffic. It represents the maximum stress experienced by the soil. The most recently developed fitting method to estimate precompression stress (Gompertz) is based on the assumption of an S-shape stress......-strain curve, which is not always fulfilled. A new simple numerical method was developed to estimate precompression stress from stress-strain curves, based solely on the sharp bend on the stress-strain curve partitioning the curve into an elastic and a plastic section. Our study had three objectives: (i......) Assessing the utility of the numerical method by comparison with the Gompertz method; (ii) Comparing the estimated precompression stress to the maximum preload of test samples; (iii) Determining the influence that soil type, bulk density and soil water potential have on the estimated precompression stress...
Present-day stress field of Southeast Asia
Tingay, Mark; Morley, Chris; King, Rosalind; Hillis, Richard; Coblentz, David; Hall, Robert
2010-02-01
It is now well established that ridge push forces provide a major control on the plate-scale stress field in most of the Earth's tectonic plates. However, the Sunda plate that comprises much of Southeast Asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field. The Cenozoic tectonic evolution of the Sunda plate is usually considered to be controlled by escape tectonics associated with India-Eurasia collision. However, the Sunda plate is bounded by a poorly understood and complex range of convergent and strike-slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region. We compile the first extensive stress dataset for Southeast Asia, containing 275 A-D quality (177 A-C) horizontal stress orientations, consisting of 72 stress indicators from earthquakes (located mostly on the periphery of the plate), 202 stress indicators from breakouts and drilling-induced fractures and one hydraulic fracture test within 14 provinces in the plate interior. This data reveals that a variable stress pattern exists throughout Southeast Asia that is largely inconsistent with the Sunda plate's approximately ESE absolute motion direction. The present-day maximum horizontal stress in Thailand, Vietnam and the Malay Basin is predominately north-south, consistent with the radiating stress patterns arising from the eastern Himalayan syntaxis. However, the present-day maximum horizontal stress is primarily oriented NW-SE in Borneo, a direction that may reflect plate-boundary forces or topographic stresses exerted by the central Borneo highlands. Furthermore, the South and Central Sumatra Basins exhibit a NE-SW maximum horizontal stress direction that is perpendicular to the Indo-Australian subduction front. Hence, the plate-scale stress field in Southeast Asia appears to be controlled by a combination of Himalayan
Stress field modelling from digital geological map data
Albert, Gáspár; Barancsuk, Ádám; Szentpéteri, Krisztián
2016-04-01
To create a model for the lithospheric stress a functional geodatabase is required which contains spatial and geodynamic parameters. A digital structural-geological map is a geodatabase, which usually contains enough attributes to create a stress field model. Such a model is not accurate enough for engineering-geological purposes because simplifications are always present in a map, but in many cases maps are the only sources for a tectonic analysis. The here presented method is designed for field geologist, who are interested to see the possible realization of the stress field over the area, on which they are working. This study presents an application which can produce a map of 3D stress vectors from a kml-file. The core application logic is implemented on top of a spatially aware relational database management system. This allows rapid and geographically accurate analysis of the imported geological features, taking advantage of standardized spatial algorithms and indexing. After pre-processing the map features in a GIS, according to the Type-Property-Orientation naming system, which was described in a previous study (Albert et al. 2014), the first stage of the algorithm generates an irregularly spaced point cloud by emitting a pattern of points within a user-defined buffer zone around each feature. For each point generated, a component-wise approximation of the tensor field at the point's position is computed, derived from the original feature's geodynamic properties. In a second stage a weighted moving average method calculates the stress vectors in a regular grid. Results can be exported as geospatial data for further analysis or cartographic visualization. Computation of the tensor field's components is based on the implementation of the Mohr diagram of a compressional model, which uses a Coulomb fracture criterion. Using a general assumption that the main principal stress must be greater than the stress from the overburden, the differential stress is
Blackwood, R.L.
1980-05-15
There are now available sufficient data from in-situ, pre-mining stress measurements to allow a first attempt at predicting the maximum stress magnitudes likely to occur in a given mining context. The sub-horizontal (lateral) stress generally dominates the stress field, becoming critical to stope stability in many cases. For cut-and-fill mining in particular, where developed fill pressures are influenced by lateral displacement of pillars or stope backs, extraction maximization planning by mathematical modelling techniques demands the best available estimate of pre-mining stresses. While field measurements are still essential for this purpose, in the present paper it is suggested that the worst stress case can be predicted for preliminary design or feasibility study purposes. In the Eurpoean continent the vertical component of pre-mining stress may be estimated by adding 2 MPa to the pressure due to overburden weight. The maximum lateral stress likely to be encountered is about 57 MPa at depths of some 800m to 1000m below the surface.
Estimation of Centers and Stagnation points in optical flow fields
Larsen, Rasmus
1997-01-01
In a topological sense fluid flows are characterised by their stagnation points. Given a temporal sequence of images of fluids we will consider the application of local polynomials to the estimation of smooth fluid flow fields. The normal flow at intensity contours is estimated from the local...... distribution of spatio-temporal energy, which is sampled using a set of spatio-temporal quadrature filters. These observations of normal flows are then integrated into smooth flow fields by locally approximating first order polynomials in the spatial coordinates to the flow vectors. This technique furthermore...... allows us to give a qualitative local description of the flow field and to estimate the position of stagnation points (e.g. nodes, saddles, and centers). We will apply the algorithm to two data sets. The first sequence consists of infrared images from the meteorological satellite Meteosat. Here...
Geological background of the estimation of natural stresses in soil body
Chernyshev Sergey Nikolaevich
2015-01-01
Full Text Available Initial and boundary conditions are always given for solving the problem of calculating the interaction of tunnels and other underground structures with soil and rocks. The same conditions are set for calculating the surface buildings. These initial data for calculation are divided into three groups: 1 the geometrical shape of the layers of rocks (geological structure; 2 the parameters of the strength and compressibility of rocks; 3 compressive stresses in the array. These data all over the world are set with engineering surveys. In engineering surveys there are good methods of determining the source of the data 1 and 2. But there is no available methodology for determining the natural stress state. Therefore, compressive and tensile stresses are usually determined by mathematical modeling. The calculation of the compressive stresses is done on the basis of the following hypotheses: compressive stresses are created by the weight of rocks; they go down in proportion to the density of rocks; the main normal stress is has a vertical direction; normal stress in horizontal direction is smaller. The value of the horizontal stress is was calculated using Poisson’s ratio. This hypothesis of the nineteenth century was used another 50 years ago, when it was not known exactly about the movement of the continents and when compressive stresses in the earth’s crust have not yet been measured. Today a universal application of this hypothesis is not correct. Now the application of this hypothesis in many cases is not correct. In this research paper an attempt is made to specify the area, in which the above hypothesis can be used. This is done on the basis of current scientific evidence. Abroad this way of calculating tunnels and other underground structures and bases of buildings should be done taking into account the real field of natural stresses. The geological characteristics of the location of the axes of stresses in soil body are based on the study of
Medvedev, Sergei; Werner, Stephanie; Steinberger, Bernhard; "African Plate" Working Group
2010-05-01
Several mechanisms control the state of stress within plates on Earth. The list is rather long, but well-known and includes ridge push, mantle drag, stresses invoked by lateral variations of lithospheric density structure and subduction processes. We attempt to quantify the influence of these mechanisms and to construct a reliable model to understand modern and palaeo-stresses using the African plate (TAP) as an example. Previous studies explained stress patterns and their evolution solely by assigning different rheological properties to sub-domains and their boundaries. Such an approach often leads to unrealistically high variations of properties within a modeled plate. In our approach we find the best possible agreement with observations before differentiating between sub-domains of TAP. The finite-element based suite ProShell was utilized to calculate stresses on the real geometry of TAP (non-planar). The approach allows us to combine several data sets and to estimate stresses caused by lateral and vertical distribution of properties within the lithosphere, to quantify the in-plane and bending stresses, to account for forces due to ridge push and mantle heterogeneities and mantle flow. The modeled results are tested and iterated to match the observed stress pattern and potential fields as good as possible. The starting model is based on the CRUST2 data set to construct the model crust and half-space cooling model to approximate properties of the lithospheric mantle. The results however, are not satisfactory, and might be related to oversimplifications in the uniform model of lithosphere or/and to the unrealistic representation of the CRUST2 model in certain areas of TAP. The latter was also shown by simple evaluation using gravity forward modeling of the model boundaries. The model implementation of the crustal structure calculated from simple gravity inversion or derived through isostatical considerations agree better to today's observed stress pattern.
Distributed estimation of a parametric field with random sensor placements
Alkhweldi, Marwan; Cao, Zhicheng; Schmid, Natalia A.
2015-05-01
This paper considers a problem of distributed function estimation in the case when sensor locations are modeled as Gaussian random variables. We consider a scenario where sensors are deployed in clusters with cluster centers known a priori (or estimated by a high performance GPS) and the average quadratic spread of sensors around the cluster center also known. Distributed sensors make noisy observations about an unknown parametric field generated by a physical object of interest (for example, magnetic field generated by a ferrous object and sensed by a network of magnetometers). Each sensor then performs local signal processing of its noisy observation and sends it to a central processor (called fusion center) in the wireless sensor network over parallel channels corrupted by fading and additive noise. The central processor combines the set of received signals to form an estimate of the unknown parametric field. In our numerical analysis, we involve a field shaped as a Gaussian bell. We experiment with the size of sensor clusters and with their number. A mean square error between the estimated parameters of the field and the true parameters used in simulations is involved as a performance measure. It can be shown that a relatively good estimate of the field can be obtained with only a small number of clusters. As the number of clusters increases, the estimation performance steadily improves. The results also indicate that, on the average, the number of clusters has more impact on the performance than the number of sensors per cluster, given the same size of the total network.
Fuzzy logic based ELF magnetic field estimation in substations.
Kosalay, Ilhan
2008-01-01
This paper examines estimation of the extremely low frequency magnetic fields (MF) in the power substation. First, the results of the previous relevant research studies and the MF measurements in a sample power substation are presented. Then, a fuzzy logic model based on the geometric definitions in order to estimate the MF distribution is explained. Visual software, which has a three-dimensional screening unit, based on the fuzzy logic technique, has been developed.
Measurement of electric fields and estimation of dielectric susceptibility
Nogi, Yasuyuki; Suzuki, Kiyomitsu; Ohkuma, Yasunori
2013-05-01
We describe a method of measuring the spatial structures of electric fields produced by charge distributions such as those on strip electrodes, small disk electrodes, and long double-plate electrodes. An electric-field sensor with high sensitivity to ac fields is fabricated for the measurement using a thin copper sheet. The reliability of the sensor is confirmed using a parallel-plate capacitor. The electric fields are oscillated at a frequency of 300 kHz to operate the electric-field sensor successfully. The structures of the measured fields coincide well with those of theoretical fields derived from Coulomb's law. When a dielectric is inserted in an electric field, polarization charges appear on the surface of the dielectric and modify the electric field in empty space. We measure the modified field and confirm the well-known linear relation between the polarization of a dielectric and the electric field. Dielectric susceptibilities are estimated from the linear relation for four types of dielectric.
An inverse finite element method for determining residual and current stress fields in solids
Tartibi, M.; Steigmann, D. J.; Komvopoulos, K.
2016-11-01
The life expectancy of a solid component is traditionally predicted by assessing its expected stress cycle and comparing it to experimentally determined stress states at failure. The accuracy of this procedure is often compromised by unforeseen extremes in the loading cycle or material degradation. Residually stressed parts may either have longer or shorter lifespans than predicted. Thus, determination of the current state of stress (i.e., the residual stress in the absence of external loading) and material properties is particularly important. Typically, the material properties of a solid are determined by fitting experimental data obtained from the measured deformation response in the stress-free configuration. However, the characterization of the mechanical behavior of a residually stressed body requires, in principle, a method that is not restricted to specific constitutive models. Complementing a recently developed technique, known as the reversed updated Lagrangian finite element method (RULFEM), a new method called estimating the current state of stress (ECSS) is presented herein. ECSS is based on three-dimensional full-field displacement and force data of a body perturbed by small displacements and complements the first step of the incremental RULFEM method. The present method generates the current state of stress (or residual stress in the absence of external tractions) and the incremental elasticity tensor of each finite element used to discretize the deformable body. The validity of the ECSS method is demonstrated by two noise-free simulation cases.
An inverse finite element method for determining residual and current stress fields in solids
Tartibi, M.; Steigmann, D. J.; Komvopoulos, K.
2016-08-01
The life expectancy of a solid component is traditionally predicted by assessing its expected stress cycle and comparing it to experimentally determined stress states at failure. The accuracy of this procedure is often compromised by unforeseen extremes in the loading cycle or material degradation. Residually stressed parts may either have longer or shorter lifespans than predicted. Thus, determination of the current state of stress (i.e., the residual stress in the absence of external loading) and material properties is particularly important. Typically, the material properties of a solid are determined by fitting experimental data obtained from the measured deformation response in the stress-free configuration. However, the characterization of the mechanical behavior of a residually stressed body requires, in principle, a method that is not restricted to specific constitutive models. Complementing a recently developed technique, known as the reversed updated Lagrangian finite element method (RULFEM), a new method called estimating the current state of stress (ECSS) is presented herein. ECSS is based on three-dimensional full-field displacement and force data of a body perturbed by small displacements and complements the first step of the incremental RULFEM method. The present method generates the current state of stress (or residual stress in the absence of external tractions) and the incremental elasticity tensor of each finite element used to discretize the deformable body. The validity of the ECSS method is demonstrated by two noise-free simulation cases.
Stress and strain field in the Tatra Mountains
Papco, Juraj; Faskova, Zuzana
2010-05-01
The goal of this poster is to present geodynamic research of the Tatra mountains crust movements. To that goal epoch's GNSS measurements have been performed annually since 1998 with at least 96 hours' duration. The data processing has been made in Bernese software version 5.0 according to CEGRN and EUREF recommendation. The estimate of point's velocity has been done together with the study of stress and strain fields. The finite element method with its linear and quadratic elements has been applied. For that purpose, 3D computational domain has been created. The upper boundary has been the real Earth's surface represented by SRTM and discretized by series of triangles where displacements as boundary condition (BC) were prescribed. The lower boundary has been placed to the Moho surface, in depth 35 km. Additional side boundaries were created here the zero Neumann BC was supposed. The different material properties in different parts of the domain have been taken into account. Finally, there were determined three risk zones with higher posibility of occurring the earthquakes where the detailed study was done.
Estimation of psychological stress in humans: a combination of theory and practice.
Parul Sood
Full Text Available Stress has long been known to increase susceptibility to health disorders. In 2009, American Psychological Association further established association of stress to serious health problems. However, a quantitative and accurate way to evaluate and estimate stress status of individuals is still a big challenge. It has been shown, in large animal models using cattle, that psychological stress can be quantified as well as disease susceptibility could be predicted through biomarker discovery. Taking cue from those studies, we have evaluated and estimated psychological stress level of individuals theoretically and validated experimentally. Various biomarkers have also been identified which can be associated to psychological stress to predict stress status of unknown individuals.
Estimation of psychological stress in humans: a combination of theory and practice.
Sood, Parul; Priyadarshini, Sushri; Aich, Palok
2013-01-01
Stress has long been known to increase susceptibility to health disorders. In 2009, American Psychological Association further established association of stress to serious health problems. However, a quantitative and accurate way to evaluate and estimate stress status of individuals is still a big challenge. It has been shown, in large animal models using cattle, that psychological stress can be quantified as well as disease susceptibility could be predicted through biomarker discovery. Taking cue from those studies, we have evaluated and estimated psychological stress level of individuals theoretically and validated experimentally. Various biomarkers have also been identified which can be associated to psychological stress to predict stress status of unknown individuals.
Estimating neuronal connectivity from axonal and dendritic density fields
van Pelt, Jaap; van Ooyen, Arjen
2013-01-01
Neurons innervate space by extending axonal and dendritic arborizations. When axons and dendrites come in close proximity of each other, synapses between neurons can be formed. Neurons vary greatly in their morphologies and synaptic connections with other neurons. The size and shape of the arborizations determine the way neurons innervate space. A neuron may therefore be characterized by the spatial distribution of its axonal and dendritic “mass.” A population mean “mass” density field of a particular neuron type can be obtained by averaging over the individual variations in neuron geometries. Connectivity in terms of candidate synaptic contacts between neurons can be determined directly on the basis of their arborizations but also indirectly on the basis of their density fields. To decide when a candidate synapse can be formed, we previously developed a criterion defining that axonal and dendritic line pieces should cross in 3D and have an orthogonal distance less than a threshold value. In this paper, we developed new methodology for applying this criterion to density fields. We show that estimates of the number of contacts between neuron pairs calculated from their density fields are fully consistent with the number of contacts calculated from the actual arborizations. However, the estimation of the connection probability and the expected number of contacts per connection cannot be calculated directly from density fields, because density fields do not carry anymore the correlative structure in the spatial distribution of synaptic contacts. Alternatively, these two connectivity measures can be estimated from the expected number of contacts by using empirical mapping functions. The neurons used for the validation studies were generated by our neuron simulator NETMORPH. An example is given of the estimation of average connectivity and Euclidean pre- and postsynaptic distance distributions in a network of neurons represented by their population mean density
Volumetric breast density estimation from full-field digital mammograms.
Engeland, S. van; Snoeren, P.R.; Huisman, H.J.; Boetes, C.; Karssemeijer, N.
2006-01-01
A method is presented for estimation of dense breast tissue volume from mammograms obtained with full-field digital mammography (FFDM). The thickness of dense tissue mapping to a pixel is determined by using a physical model of image acquisition. This model is based on the assumption that the breast
Determining the stress field in active volcanoes using focal mechanisms
Bruno Massa
2016-11-01
Full Text Available Stress inversion of seismological datasets became an essential tool to retrieve the stress field of active tectonics and volcanic areas. In particular, in volcanic areas, it is able to put constrains on volcano-tectonics and in general in a better understanding of the volcano dynamics. During the last decades, a wide range of stress inversion techniques has been proposed, some of them specifically conceived to manage seismological datasets. A modern technique of stress inversion, the BRTM, has been applied to seismological datasets available at three different regions of active volcanism: Mt. Somma-Vesuvius (197 Fault Plane Solutions, FPSs, Campi Flegrei (217 FPSs and Long Valley Caldera (38,000 FPSs. The key role of stress inversion techniques in the analysis of the volcano dynamics has been critically discussed. A particular emphasis was devoted to performances of the BRTM applied to volcanic areas.
Determining the stress field in active volcanoes using focal mechanisms
Massa, Bruno; D'Auria, Luca; Cristiano, Elena; De Matteo, Ada
2016-11-01
Stress inversion of seismological datasets became an essential tool to retrieve the stress field of active tectonics and volcanic areas. In particular, in volcanic areas, it is able to put constrains on volcano-tectonics and in general in a better understanding of the volcano dynamics. During the last decades, a wide range of stress inversion techniques has been proposed, some of them specifically conceived to manage seismological datasets. A modern technique of stress inversion, the BRTM, has been applied to seismological datasets available at three different regions of active volcanism: Mt. Somma-Vesuvius (197 Fault Plane Solutions, FPSs), Campi Flegrei (217 FPSs) and Long Valley Caldera (38,000 FPSs). The key role of stress inversion techniques in the analysis of the volcano dynamics has been critically discussed. A particular emphasis was devoted to performances of the BRTM applied to volcanic areas.
Precise numerical estimation of the magnetic field generated around recombination
Fidler, Christian; Pettinari, Guido; Pitrou, Cyril
2016-05-01
We investigate the generation of magnetic fields from nonlinear effects around recombination. As tight-coupling is gradually lost when approaching z ≃1100 , the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: (i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; (ii) the magnetic field is generated up to z ≃10 ; (iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than 1 Mpc. Finally we confirm that for scales of a few Mpc, this magnetic field is of order 2 ×10-29 G , many orders of magnitude smaller than what is currently observed on intergalactic scales.
High resolution, large dynamic range field map estimation
Dagher, Joseph; Reese, Timothy; Bilgin, Ali
2013-01-01
Purpose We present a theory and a corresponding method to compute high resolution field maps over a large dynamic range. Theory and Methods We derive a closed-form expression for the error in the field map value when computed from two echoes. We formulate an optimization problem to choose three echo times which result in a pair of maximally distinct error distributions. We use standard field mapping sequences at the prescribed echo times. We then design a corresponding estimation algorithm which takes advantage of the optimized echo times to disambiguate the field offset value. Results We validate our method using high resolution images of a phantom at 7T. The resulting field maps demonstrate robust mapping over both a large dynamic range, and in low SNR regions. We also present high resolution offset maps in vivo using both, GRE and MEGE sequences. Even though the proposed echo time spacings are larger than the well known phase aliasing cutoff, the resulting field maps exhibit a large dynamic range without the use of phase unwrapping or spatial regularization techniques. Conclusion We demonstrate a novel 3-echo field map estimation method which overcomes the traditional noise-dynamic range trade-off. PMID:23401245
Hardebeck, Jeanne L.
2010-01-01
It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.
Dynamics of Traction Stress Field during Cell Division
Tanimoto, Hirokazu; Sano, Masaki
2012-12-01
We report a quantitative measurement of traction stress exerted by dividing eukaryotic cells. The stress field was highly dynamic and sequentially changed as follows: (1) strong and localized as two spots, (2) weak and broadly distributed, and (3) strong and localized as four spots. At the final stage of cytokinesis, the dividing cells exerted strong tensile force on the intercellular bridge. The asymmetry of the traction stress and the orientation of the division axis matched throughout the division process, suggesting the possible role of the mechanical force as a “store” of the orientational information.
Modelling of the Global Geopotential Energy & Stress Field
Schiffer, C.; Nielsen, S. B.
2012-04-01
Lateral density and topography variations yield in and important contribution to the lithospheric stress field. The leading quantity is the Geopotential Energy, the integrated lithostatic pressure in a rock column. The horizontal gradient of this quantity is related to horizontal stresses through the Equations of equilibrium of stresses. The Geopotential Energy furthermore can be linearly related to the Geoid under assumption of local isostasy. Satellite Geoid measurements contain, however, also non-isostatic deeper mantle responses of long wavelength. Unfortunately, high-pass filtering of the Geoid does not suppress only the deeper sources. The age-dependent signal of the oceanic lithosphere, for instance, is of long wave length and a prominent representative of in-plane stress, derived from the horizontal gradient of isostatic Geoid anomalies and responsible for the ridge push effect. Therefore a global lithospheric density model is required in order to isolate the shallow Geoid signal and calculate the stress pattern from isostatically compensated lithospheric sources. We use a linearized inverse method to fit a lithospheric reference model to observations such as topography and surface heat flow in the presence of local isostasy and a steady state geotherm. Subsequently we use a FEM code to solve the Equations of equilibrium of stresses for a three dimensional elastic shell. The modelled results are shown and compared with the global stress field and other publications.
Topographical estimation of visual population receptive fields by FMRI.
Lee, Sangkyun; Papanikolaou, Amalia; Keliris, Georgios A; Smirnakis, Stelios M
2015-02-03
Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic resonance imaging allows us to estimate voxel-based population receptive fields (pRF), i.e., the part of the visual field that activates the cells within each voxel. Prior, direct, pRF estimation methods(1) suffer from certain limitations: 1) the pRF model is chosen a-priori and may not fully capture the actual pRF shape, and 2) pRF centers are prone to mislocalization near the border of the stimulus space. Here a new topographical pRF estimation method(2) is proposed that largely circumvents these limitations. A linear model is used to predict the Blood Oxygen Level-Dependent (BOLD) signal by convolving the linear response of the pRF to the visual stimulus with the canonical hemodynamic response function. PRF topography is represented as a weight vector whose components represent the strength of the aggregate response of voxel neurons to stimuli presented at different visual field locations. The resulting linear equations can be solved for the pRF weight vector using ridge regression(3), yielding the pRF topography. A pRF model that is matched to the estimated topography can then be chosen post-hoc, thereby improving the estimates of pRF parameters such as pRF-center location, pRF orientation, size, etc. Having the pRF topography available also allows the visual verification of pRF parameter estimates allowing the extraction of various pRF properties without having to make a-priori assumptions about the pRF structure. This approach promises to be particularly useful for investigating the pRF organization of patients with disorders of the visual system.
Analytical estimation of the Earth's magnetic field scale
Bologna, Mauro
2012-01-01
In this paper we analytically estimate the magnetic field scale of planets with physical core conditions similar to that of Earth from a statistical point of view. We evaluate the magnetic field on the basis of the physical parameters of the center of the planet, such as density, temperature, and core size. We look at the contribution of the Peltier-Seebeck effect on the magnetic field, showing that an electrical thermal current can exist in a rotating fluid sphere. Finally, we apply our calculations to Earth and Jupiter. In each case we show that the thermal generation of currents leads to a magnetic field scale comparable to the observed fields of the two planets.
Displacement and stress fields around rock fractures opened by irregular overpressure variations
Shigekazu eKusumoto
2014-05-01
Full Text Available Many rock fractures are entirely driven open by fluids such as ground water, geothermal water, gas, oil, and magma. These are a subset of extension fractures (mode I cracks; e.g., dikes, mineral veins and joints referred to as hydrofractures. Field measurements show that many hydrofractures have great variations in aperture. However, most analytical solutions for fracture displacement and stress fields assume the loading to be either constant or with a linear variation. While these solutions have been widely used, it is clear that a fracture hosted by heterogeneous and anisotropic rock is normally subject to loading that is neither constant nor with a linear variation. Here we present new general solutions for the displacement and stress fields around hydrofractures, modelled as two-dimensional elastic cracks, opened by irregular overpressure variations given by the Fourier cosine series. Each solution has two terms. The first term gives the displacement and stress fields due to the average overpressure acting inside the crack; it is given by the initial term of the Fourier coefficients expressing the overpressure variation. The second term gives the displacement and stress fields caused by the overpressure variation; it is given by general terms of the Fourier coefficients and solved through numerical integration. Our numerical examples show that the crack aperture variation closely reflects the overpressure variation. Also, that the general displacement and stress fields close to the crack follow the overpressure variation but tend to be more uniform far from the crack. The present solutions can be used to estimate the displacement and stress fields around any fluid-driven crack, that is, any hydrofracture, as well as its aperture, provided the variation in overpressure can be described by Fourier series. The solutions add to our understanding of local stresses, displacements, and fluid transport associated with hydrofractures in the crust.
Estimate of Coronal Magnetic Field Strength Using Plasmoid Acceleration Measurement
Choe, G.; Lee, K.; Jang, M.
2010-12-01
A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. A rather simple calculation shows that the vertical force acting on a cylinder-like volume, whose lateral surface is a flux surface and whose magnetic axis is parallel to the horizontal, is just the difference in total pressure (magnetic pressure plus plasma pressure) below and above the volume. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.
Kazachenko, Maria D; Welsch, Brian T
2014-01-01
Photospheric electric fields, estimated from sequences of vector magnetic field and Doppler measurements, can be used to estimate the flux of magnetic energy (the Poynting flux) into the corona and as time-dependent boundary conditions for dynamic models of the coronal magnetic field. We have modified and extended an existing method to estimate photospheric electric fields that combines a poloidal-toroidal (PTD) decomposition of the evolving magnetic field vector with Doppler and horizontal plasma velocities. Our current, more comprehensive method, which we dub the "{\\bf P}TD-{\\bf D}oppler-{\\bf F}LCT {\\bf I}deal" (PDFI) technique, can now incorporate Doppler velocities from non-normal viewing angles. It uses the \\texttt{FISHPACK} software package to solve several two-dimensional Poisson equations, a faster and more robust approach than our previous implementations. Here, we describe systematic, quantitative tests of the accuracy and robustness of the PDFI technique using synthetic data from anelastic MHD (\\te...
Challenges in estimating insecticide selection pressures from mosquito field data.
Susana Barbosa
2011-11-01
Full Text Available Insecticide resistance has the potential to compromise the enormous effort put into the control of dengue and malaria vector populations. It is therefore important to quantify the amount of selection acting on resistance alleles, their contributions to fitness in heterozygotes (dominance and their initial frequencies, as a means to predict the rate of spread of resistance in natural populations. We investigate practical problems of obtaining such estimates, with particular emphasis on Mexican populations of the dengue vector Aedes aegypti. Selection and dominance coefficients can be estimated by fitting genetic models to field data using maximum likelihood (ML methodology. This methodology, although widely used, makes many assumptions so we investigated how well such models perform when data are sparse or when spatial and temporal heterogeneity occur. As expected, ML methodologies reliably estimated selection and dominance coefficients under idealised conditions but it was difficult to recover the true values when datasets were sparse during the time that resistance alleles increased in frequency, or when spatial and temporal heterogeneity occurred. We analysed published data on pyrethroid resistance in Mexico that consists of the frequency of a Ile1,016 mutation. The estimates for selection coefficient and initial allele frequency on the field dataset were in the expected range, dominance coefficient points to incomplete dominance as observed in the laboratory, although these estimates are accompanied by strong caveats about possible impact of spatial and temporal heterogeneity in selection.
Stress engineering and the applications of inhomogeneously polarized optical fields
Thomas G. BROWN; Amber M. BECKLEY
2013-01-01
Spatial inhomogeneities in the polarization of a light field can show fascinating effects in focusing, propagation, illumination, and imaging. This paper provides examples of these effects and describes how deterministic stress on the periphery of an optical element can be used in fundamental studies of beam propagation, as well as applications such as polarimetry.
Assessing maize foliar water stress levels under field conditions ...
Assessing maize foliar water stress levels under field conditions using in-situ ... is non-destructive to the crops as opposed to other traditional ground-based methods. ... water indices that could monitor the water status at leaf level on maize (Zea ... about AJOL · AJOL's Partners · Contact AJOL · Terms and Conditions of Use.
Time Series Vegetation Aerodynamic Roughness Fields Estimated from MODIS Observations
Borak, Jordan S.; Jasinski, Michael F.; Crago, Richard D.
2005-01-01
Most land surface models used today require estimates of aerodynamic roughness length in order to characterize momentum transfer between the surface and atmosphere. The most common method of prescribing roughness is through the use of empirical look-up tables based solely on land cover class. Theoretical approaches that employ satellite-based estimates of canopy density present an attractive alternative to current look-up table approaches based on vegetation cover type that do not account for within-class variability and are oftentimes simplistic with respect to temporal variability. The current research applies Raupach s formulation of momentum aerodynamic roughness to MODIS data on a regional scale in order to estimate seasonally variable roughness and zero-plane displacement height fields using bulk land cover parameters estimated by [Jasinski, M.F., Borak, J., Crago, R., 2005. Bulk surface momentum parameters for satellite-derived vegetation fields. Agric. For. Meteorol. 133, 55-68]. Results indicate promising advances over look-up approaches with respect to characterization of vegetation roughness variability in land surface and atmospheric circulation models.
Estimating Canopy Nitrogen Concentration in Sugarcane Using Field Imaging Spectroscopy
Marc Souris
2012-06-01
Full Text Available The retrieval of nutrient concentration in sugarcane through hyperspectral remote sensing is widely known to be affected by canopy architecture. The goal of this research was to develop an estimation model that could explain the nitrogen variations in sugarcane with combined cultivars. Reflectance spectra were measured over the sugarcane canopy using a field spectroradiometer. The models were calibrated by a vegetation index and multiple linear regression. The original reflectance was transformed into a First-Derivative Spectrum (FDS and two absorption features. The results indicated that the sensitive spectral wavelengths for quantifying nitrogen content existed mainly in the visible, red edge and far near-infrared regions of the electromagnetic spectrum. Normalized Differential Index (NDI based on FDS_{(750/700} and Ratio Spectral Index (RVI based on FDS_{(724/700} are best suited for characterizing the nitrogen concentration. The modified estimation model, generated by the Stepwise Multiple Linear Regression (SMLR technique from FDS centered at 410, 426, 720, 754, and 1,216 nm, yielded the highest correlation coefficient value of 0.86 and Root Mean Square Error of the Estimate (RMSE value of 0.033%N (n = 90 with nitrogen concentration in sugarcane. The results of this research demonstrated that the estimation model developed by SMLR yielded a higher correlation coefficient with nitrogen content than the model computed by narrow vegetation indices. The strong correlation between measured and estimated nitrogen concentration indicated that the methods proposed in this study could be used for the reliable diagnosis of nitrogen quantity in sugarcane. Finally, the success of the field spectroscopy used for estimating the nutrient quality of sugarcane allowed an additional experiment using the polar orbiting hyperspectral data for the timely determination of crop nutrient status in rangelands without any requirement of prior
Estimation of the Axial Stress in High-Tension Bolt by Acoustoelastic Method
Chun, Hae Hwa; Lee, Tae Hoon; Jhang, Kyung Young [Hanyang University, Seoul (Korea, Republic of); Kim, Noh Yu [Korea University of Technology and Education, Cheonan (Korea, Republic of)
2006-10-15
The evaluation of clamping condition has been regarded as the main issue in the safety-maintenance of the clamped high-tension bolts. For this, this paper proposes a method to estimate the axial stress by measuring the Tofu (Time-Of-Flight) of ultrasonic wave, which is based on the acetylsalicylate or the dependency of sound speed on the stress. In this method, however, the variation of sound speed within the range of stress induced under the field condition is very small, and thus the accuracy of the Tofu measurement is important. We adopted the phase detection method using tone-burst ultrasonic wave to measure the precise Tofu. In order to verify the usefulness of the proposed method experiments are carried out and the results were compared with the stress measured by the strain gage. The results show good agreement with each other, and from these we can conclude that the proposed method is highly useful fnr the evaluation of clamping condition in the clamped high-tension bolts
Cortico-Cortical Receptive Field Estimates in Human Visual Cortex
Koen V Haak
2012-05-01
Full Text Available Human visual cortex comprises many visual areas that contain a map of the visual field (Wandell et al 2007, Neuron 56, 366–383. These visual field maps can be identified readily in individual subjects with functional magnetic resonance imaging (fMRI during experimental sessions that last less than an hour (Wandell and Winawer 2011, Vis Res 718–737. Hence, visual field mapping with fMRI has been, and still is, a heavily used technique to examine the organisation of both normal and abnormal human visual cortex (Haak et al 2011, ACNR, 11(3, 20–21. However, visual field mapping cannot reveal every aspect of human visual cortex organisation. For example, the information processed within a visual field map arrives from somewhere and is sent to somewhere, and visual field mapping does not derive these input/output relationships. Here, we describe a new, model-based analysis for estimating the dependence between signals in distinct cortical regions using functional magnetic resonance imaging (fMRI data. Just as a stimulus-referred receptive field predicts the neural response as a function of the stimulus contrast, the neural-referred receptive field predicts the neural response as a function of responses elsewhere in the nervous system. When applied to two cortical regions, this function can be called the cortico-cortical receptive field (CCRF. We model the CCRF as a Gaussian-weighted region on the cortical surface and apply the model to data from both stimulus-driven and resting-state experimental conditions in visual cortex.
Ageing under Shear: Effect of Stress and Temperature Field
Shukla, Asheesh; Joshi, Yogesh M.
2008-07-01
In this work we studied the effect of oscillatory stress and temperature on the ageing dynamics of aqueous suspension of laponite. At the higher magnitude of stress, elastic and viscous moduli of the system underwent a sharp rise with the ageing time. The age at the onset of rise and the sharpness of the same increased with the magnitude of stress. We propose that at the beginning of ageing, the strain associated with the oscillatory stress field affects the lower modes in the relaxation time distribution. The higher modes, which are not significantly affected by the deformation field, continue to grow increasing the viscosity of the system thereby lowering the magnitude of the deformation field. Progressive decrease in the later reduces the range of relaxation modes affected by it. This dynamics eventually leads to an auto-catalytic increase in the elastic and viscous moduli. An increase in temperature accelerates the ageing process by shifting the ageing dynamics to a lower ageing time. This is due the microscopic relaxation dynamics, which causes ageing, becomes faster with increase in the temperature.
Stress field evaluation by Barkhausen noise on bearing raceway
Desvaux, S.; Gualandri, J.; Duquennoy, M.; Ourak, M.
2002-05-01
The intention of our work is to present a NDT method based on the phenomenon of the Barkhausen noise to identify the stress profiles of loading zones between balls or rollers and raceways. This method is adapted to the industrial imperatives bound to lineally measurements. Indeed, this solution presents the advantage to be without contact, rapid and suitable for the circular geometry's rings. By leaning on the X ray diffraction as method of reference, we showed the efficiency of the Barkhausen noise to estimate the residual stress profiles on raceways after grinding operations, after specific pre-stressing treatment and after operation of an engine. Today the advancement of our works permits us to consider, in a near future, the transfer of this method toward the industrial environment.
Estimating signal loss in regularized GRACE gravity field solutions
Swenson, S. C.; Wahr, J. M.
2011-05-01
Gravity field solutions produced using data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are subject to errors that increase as a function of increasing spatial resolution. Two commonly used techniques to improve the signal-to-noise ratio in the gravity field solutions are post-processing, via spectral filters, and regularization, which occurs within the least-squares inversion process used to create the solutions. One advantage of post-processing methods is the ability to easily estimate the signal loss resulting from the application of the spectral filter by applying the filter to synthetic gravity field coefficients derived from models of mass variation. This is a critical step in the construction of an accurate error budget. Estimating the amount of signal loss due to regularization, however, requires the execution of the full gravity field determination process to create synthetic instrument data; this leads to a significant cost in computation and expertise relative to post-processing techniques, and inhibits the rapid development of optimal regularization weighting schemes. Thus, while a number of studies have quantified the effects of spectral filtering, signal modification in regularized GRACE gravity field solutions has not yet been estimated. In this study, we examine the effect of one regularization method. First, we demonstrate that regularization can in fact be performed as a post-processing step if the solution covariance matrix is available. Regularization then is applied as a post-processing step to unconstrained solutions from the Center for Space Research (CSR), using weights reported by the Centre National d'Etudes Spatiales/Groupe de Recherches de geodesie spatiale (CNES/GRGS). After regularization, the power spectra of the CSR solutions agree well with those of the CNES/GRGS solutions. Finally, regularization is performed on synthetic gravity field solutions derived from a land surface model, revealing that in
Stress relaxation and estimation of activation volume in a commercial hard PZT piezoelectric ceramic
B L Cheng; M J Reece
2001-04-01
The stress relaxation of ferroelectric/piezoelectric material was studied using compression testing. The deformation was produced by the switching of ferroelectric domains. The internal stresses were estimated by decremental stress relaxation during unloading. The results were interpreted in terms of reversible and irreversible switching of the domains.
Oceanic Wind Speed and Wind Stress Estimation from Ambient Noise Measurements.
1977-02-01
it was found that noise records may be used to monitor wind speed and wind stress over the ocean. Time series of wind speeds can be produced from...wind direction, the wind stress has also been estimated and vector-averaged. The monthly mean stress from the authors’ data is higher than values
Cohen, Eliahu; Grossman, Doron; Horwitz, Lawrence; Elitzur, Avshalom C
2013-01-01
An experiment is proposed which can distinguish between two approaches to the reality of the electric field, and whether its lines have physical properties such as rigidity and stress. A charged pendulum swings within the field of another charge. If the curvature of the field-lines is a genuine physical phenomenon, the charge's center of mass must be proportionately shifted, in contrast with the conventional interpretation of the curvature as a mere superposition of different field-lines. Granting reality to the electric field may shed new light on several unresolved issues in electromagnetism, classical as well as quantum and relativistic.
Surface profile and stress field evaluation using digital gradient sensing method
Miao, C.; Sundaram, B. M.; Huang, L.; Tippur, H. V.
2016-09-01
Shape and surface topography evaluation from measured orthogonal slope/gradient data is of considerable engineering significance since many full-field optical sensors and interferometers readily output such a data accurately. This has applications ranging from metrology of optical and electronic elements (lenses, silicon wafers, thin film coatings), surface profile estimation, wave front and shape reconstruction, to name a few. In this context, a new methodology for surface profile and stress field determination based on a recently introduced non-contact, full-field optical method called digital gradient sensing (DGS) capable of measuring small angular deflections of light rays coupled with a robust finite-difference-based least-squares integration (HFLI) scheme in the Southwell configuration is advanced here. The method is demonstrated by evaluating (a) surface profiles of mechanically warped silicon wafers and (b) stress gradients near growing cracks in planar phase objects.
The perturbed magnetic fields caused by mechanical stress
QIN Fei; YAN Dong-mei
2006-01-01
In the framework of the linearized magnetoelastic theory,the perturbed magnetic fields caused by mechanical stress and deformation were investigated theoretically.Governing equations and boundary conditions to determine the perturbed fields were derived.The effect of mechanical deformation on the magnetic fields was taken into account by coupling structural displacement into the perturbed magnetic field continuous conditions on the boundary of the structure.As an example,the perturbed field of a half-plane magnetized structure caused by a point force was calculated by the Fourier transform method.The results show that the calculated magnetic intensity component normal to the boundary of the structure reaches its maximum at the point force acted while the component tangent to the boundary inverses its direction sharply.The magnetic induction of the perturbed field is proportional to the applied force.Magnitude analysis proved that since the applied magnetic field has a relative weak intensity such as the Earth's magnetic field, influence of the magnetic field on deformation of the structure can be neglected.
Bayesian parameter estimation for chiral effective field theory
Wesolowski, Sarah; Furnstahl, Richard; Phillips, Daniel; Klco, Natalie
2016-09-01
The low-energy constants (LECs) of a chiral effective field theory (EFT) interaction in the two-body sector are fit to observable data using a Bayesian parameter estimation framework. By using Bayesian prior probability distributions (pdfs), we quantify relevant physical expectations such as LEC naturalness and include them in the parameter estimation procedure. The final result is a posterior pdf for the LECs, which can be used to propagate uncertainty resulting from the fit to data to the final observable predictions. The posterior pdf also allows an empirical test of operator redundancy and other features of the potential. We compare results of our framework with other fitting procedures, interpreting the underlying assumptions in Bayesian probabilistic language. We also compare results from fitting all partial waves of the interaction simultaneously to cross section data compared to fitting to extracted phase shifts, appropriately accounting for correlations in the data. Supported in part by the NSF and DOE.
Gravitational wave stress tensor from the linearised field equations
Balbus, Steven A
2016-01-01
A conserved stress energy tensor for weak field gravitational waves in standard general relativity is derived directly from the linearised wave equation alone, for an arbitrary gauge. The form of the tensor leads directly to the classical expression for the outgoing wave energy in any harmonic gauge. The method described here, however, is a much simpler, shorter, and more physically motivated approach than is the customary procedure, which involves a lengthy and cumbersome second-order (in wave-amplitude) calculation starting with the Einstein tensor. Our method has the added advantage of exhibiting the direct coupling between the outgoing energy flux in gravitational waves and the work done by the gravitational field on the sources. For nonharmonic gauges, the derived wave stress tensor has an index asymmetry. This coordinate artefact may be removed by techniques similar to those used in classical electrodynamics (where this issue also arises), but only by appeal to a more lengthy calculation. For any harmon...
Stress field evolution in the northwest Himalayan syntaxis, northern Pakistan
Pêcher, A.; Seeber, L.; Guillot, S.; Jouanne, F.; Kausar, A.; Latif, M.; Majid, A.; MahéO, G.; Mugnier, J. L.; Rolland, Y.; van der Beek, P.; van Melle, J.
2008-12-01
We have conducted a systematic inversion of striated fault planes throughout northern Pakistan in order to better depict the temporal and spatial variations in stress patterns. Two domains are evidenced at a regional scale, separated by the active Raikhot fault, the western boundary of the Nanga Parbat spur. West of this fault, a wrench-type stress field with σ1 axis oriented around N-S predominates in the Karakorum and in Kohistan. It predates Pliocene-Quaternary exhumation of Nanga Parbat and corresponds to the Miocene or earlier regional stress field related to Indian-Asian convergence. East of the Raikhot fault, compression parallel to the belt accounts for initiation of the Nanga Parbat anticlinorium after 5 Ma. It is followed by predominant post-2 Ma extension, both parallel to the belt and NNE-SSW oriented. Thus, in the N-W Himalayan syntaxis, multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt. Such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence.
De Matteo, Ada; Massa, Bruno; D'Auria, Luca; Castaldo, Raffaele
2017-04-01
Geological processes are generally very complex and too slow to be directly observed in their completeness; modelling procedures overcome this limit. The state of stress in the upper lithosphere is the main responsible for driving geodynamical processes; in order to retrieve the active stress field in a rock volume, stress inversion techniques can be applied on both seismological and structural datasets. This approach has been successfully applied to active tectonics as well as volcanic areas. In this context the best approach in managing heterogeneous datasets in volcanic environments consists in the analysis of spatial variations of the stress field by applying robust techniques of inversion. The study of volcanic seismicity is an efficient tool to retrieve spatial and temporal pattern of the pre-, syn- and inter-eruptive stress field: magma migration as well as dynamics of magma chamber and hydrothermal system are directly connected to the volcanic seismicity. Additionally, analysis of the temporal variations of stress field pattern in volcanoes could be a useful monitoring tool. Recently the stress field acting on several active volcanoes has been investigated by using stress inversion techniques on seismological datasets (Massa et al., 2016). The Bayesian Right Trihedra Method (BRTM; D'Auria and Massa, 2015) is able to successfully manage heterogeneous datasets allowing the identification of regional fields locally overcame by the stress field due to volcano specific dynamics. In particular, the analysis of seismicity and stress field inversion at the Somma-Vesuvius highlighted the presence of two superposed volumes characterized by different behaviour and stress field pattern: a top volume dominated by an extensional stress field, in accordance with a gravitational spreading-style of deformation, and a bottom volume related to a regional extensional stress field. In addition, in order to evaluate the dynamics of deformation, both analogue and numerical
Stress field modeling of the Carpathian Basin based on compiled tectonic maps
Albert, Gáspár; Ungvári, Zsuzsanna; Szentpéteri, Krisztián
2014-05-01
The estimation of the stress field in the Carpathian Basin is tackled by several authors. Their modeling methods usually based on measurements (borehole-, focal mechanism- and geodesic data) and the result is a possible structural pattern of the region. Our method works indirectly: the analysis is aimed to project a possible 2D stress field over the already mapped/known/compiled lineament pattern. This includes a component-wise interpolation of the tensor-field, which is based on the generated irregular point cloud in the puffer zone of the mapped lineaments. The interpolated values appear on contour and tensor maps, and show the relative stress field of the area. In 2006 Horváth et al. compiled the 'Atlas of the present-day geodynamics of the Pannonian basin'. To test our method we processed the lineaments of the 1:1 500 000 scale 'Map of neotectonic (active) structures' published in this atlas. The geodynamic parameters (i.e. normal, reverse, right- and left lateral strike-slip faults, etc.) of the lines on this map were mostly explained in the legend. We classified the linear elements according to these parameters and created a geo-referenced mapping database. This database contains the polyline sections of the map lineaments as vectors (i.e. line sections), and the directions of the stress field as attributes of these vectors. The directions of the dip-parallel-, strike-parallel- and vertical stress-vectors are calculated from the geodynamical parameters of the line section. Since we created relative stress field properties, the eigenvalues of the vectors were maximized to one. Each point in the point cloud inherits the stress property of the line section, from which it was derived. During the modeling we tried several point-cloud generating- and interpolation methods. The analysis of the interpolated tensor fields revealed that the model was able to reproduce a geodynamic synthesis of the Carpathian Basin, which can be correlated with the synthesis of the
Theoretical and experimental estimates of the Peierls stress
Nabarro, FRN
1997-03-01
Full Text Available an error of a factor of 2 in this exponent in Peierls's original estimate. A revised estimate by Huntington introduced a further factor of 2. Three experimental estimates are available, from the Bordoni peaks (which agrees with the Huntington theory), from...
Revisiting Boltzmann learning: parameter estimation in Markov random fields
Hansen, Lars Kai; Andersen, Lars Nonboe; Kjems, Ulrik
1996-01-01
This article presents a generalization of the Boltzmann machine that allows us to use the learning rule for a much wider class of maximum likelihood and maximum a posteriori problems, including both supervised and unsupervised learning. Furthermore, the approach allows us to discuss regularization...... and generalization in the context of Boltzmann machines. We provide an illustrative example concerning parameter estimation in an inhomogeneous Markov field. The regularized adaptation produces a parameter set that closely resembles the “teacher” parameters, hence, will produce segmentations that closely reproduce...
Two Field Techniques for Estimating Relative Abundance of Galliformes
LuXin; CangjueZhuoma; SuolongCiren; ZhengGuang-mei
2003-01-01
Galliformes are often difficult to count adequately in their natural habitats due to low detectability of them. In the present study, we confirm availability of feather-count and feces-count as two useful field techniques to estimate the relative abundance of eared pheasants (Crossoptilon spp. ). The former is suitable to forest environments during the post-incubation period, whereas the latter is best in areas with dry climate conditions during the fall winter season. With the advantages of reduced survey effort and high repeatability, the two techniques are potentially applicable to other Galliform species in habitat selection studies and long-term population monitoring.
Estimation of probability densities using scale-free field theories.
Kinney, Justin B
2014-07-01
The question of how best to estimate a continuous probability density from finite data is an intriguing open problem at the interface of statistics and physics. Previous work has argued that this problem can be addressed in a natural way using methods from statistical field theory. Here I describe results that allow this field-theoretic approach to be rapidly and deterministically computed in low dimensions, making it practical for use in day-to-day data analysis. Importantly, this approach does not impose a privileged length scale for smoothness of the inferred probability density, but rather learns a natural length scale from the data due to the tradeoff between goodness of fit and an Occam factor. Open source software implementing this method in one and two dimensions is provided.
T-stress estimation by the two-parameter approach for a specimen with a V-shaped notch
Bouledroua, O.; Elazzizi, A.; Hadj Meliani, M.; Pluvinage, G.; Matvienko, Y. G.
2017-05-01
In the present research, T-stress solutions are provided for a V-shaped notch in the case of surface defects in a pressurised pipeline. The V-shaped notch is analyzed with the use of the finite element method by the Castem2000 commercial software to determine the stress distribution ahead of the notch tip. The notch aspect ratio is varied. In contrast to a crack, it is found that the T-stress is not constant and depends on the distance from the notch tip. To estimate the T-stress in the case of a notch, a novel method is developed, inspired by the volumetric method approach proposed by Pluvinage. The method is based on averaging the T-stress over the effective distance ahead of the notch tip. The effective distance is determined by the point with the minimum stress gradient in the fracture process zone. This approach is successfully used to quantify the constraints of the notch-tip fields for various geometries and loading conditions. Moreover, the proposed T-stress estimation creates a basis for analyzing the crack path under mixed-mode loading from the viewpoint of the two-parameter fracture mechanics.
Estimate of the maximum induced magnetic field in relativistic shocks
Ghorbanalilu, M.; Sadegzadeh, S.
2017-01-01
The proton-driven Weibel instability is a crucial process for amplifying the generated magnetic fields in gamma-ray bursts. An expression for the saturation level of magnetic fields is estimated in a relativistic shock consisting of electron-proton plasmas. Within the shock transition layer, the plasma is modelled with the waterbag and Maxwell-Jüttner distribution functions for asymmetric counter-propagating proton beams and isotropic background electrons, respectively. The proton-driven Weibel-type instability in the linear phase is investigated thoroughly and then the instability conditions and the stabilization mechanisms are considered in details just after the shutdown of the electron Weibel instability. The growth rate of the instability and the saturated magnetic field strength are obtained in terms of the effective proton beam Mach number, asymmetry parameter, and the background electron temperature. In this paper, fully relativistic kinetic treatment is used to formulate the dispersion relation for the proton Weibel-type instability. Then, by using the magnetic trapping criteria, the saturated magnetic field strength is computed. In the present scenario, the instability includes two stages: in the first stage the electron Weibel instability evolves very rapidly, but in the second one because of the free energy stored in the slow counter-propagating proton beams, the instability is further amplified in the context of electrons with an isotropic distribution function. Increment of the growth rate and saturated magnetic field by increasing (decreasing) the effective proton beam Mach number (the asymmetry parameter) is deduced from the results. It is shown that at the temperatures around 108 K a maximum magnetic field up to around 56 G can be detected by this mechanism after the saturation time.
Yang, Xiaobin, E-mail: yangxb@lzu.edu.cn; Li, Xiuhong; He, Yafeng; Wang, Xiaojun; Xu, Bo
2017-04-15
Highlights: • The differential equation including temperature and magnetic field was derived for a long cylindrical superconductor. • Thermal stress and electromagnetic stress were studied at the same time under pulse field magnetizing. • The distributions of the magnetic field, the temperature and stresses are studied and compared for two pulse fields of the different duration. • The Role thermal stress and electromagnetic stress play in the process of pulse field magnetizing is discussed. - Abstract: A multiphysics model for the numerical computation of stresses, trapped field and temperature distribution of a infinite long superconducting cylinder is proposed, based on which the stresses, including the thermal stresses and mechanical stresses due to Lorentz force, and trapped fields in the superconductor subjected to pulsed magnetic fields are analyzed. By comparing the results under pulsed magnetic fields with different pulse durations, it is found that the both the mechanical stress due to the electromagnetic force and the thermal stress due to temperature gradient contribute to the total stress level in the superconductor. For pulsed magnetic field with short durations, the thermal stress is the dominant contribution to the total stress, because the heat generated by AC-loss builds up significant temperature gradient in such short durations. However, for a pulsed field with a long duration the gradient of temperature and flux, as well as the maximal tensile stress, are much smaller. And the results of this paper is meaningful for the design and manufacture of superconducting permanent magnets.
Quantum Galileo's experiments and mass estimation in a gravitational field
Seveso, Luigi; Paris, Matteo G A
2016-01-01
We address the problem of estimating the mass of a (quantum) particle interacting with a classical gravitational field. In particular, we analyze in details the ultimate bounds to precision imposed by quantum mechanics and study the effects of gravity in a variety of settings. Our results show that the presence of a gravitational field generally leads to a precision gain, which can be significant in a regime half-way between the quantum and classical domains. We also address quantum enhancement to precision, i.e. the advantages coming from taking into account the quantum nature of the probe particle, and show that non-classicality is indeed a relevant resource for mass estimation. In particular, we suggest schemes for mass-sensing measurements using quantum probes and show that upon employing non-classical states like quantum coherent superpositions one may improve precisions by orders of magnitude. In addition, we discuss the compatibility of the weak equivalence principle (WEP) within the quantum regime usi...
Estimation of field capacity from ring infiltrometer-drainage data
Theophilo Benedicto Ottoni Filho
2014-12-01
Full Text Available Field capacity (FC is a parameter widely used in applied soil science. However, its in situ method of determination may be difficult to apply, generally because of the need of large supplies of water at the test sites. Ottoni Filho et al. (2014 proposed a standardized procedure for field determination of FC and showed that such in situ FC can be estimated by a linear pedotransfer function (PTF based on volumetric soil water content at the matric potential of -6 kPa [θ(6] for the same soils used in the present study. The objective of this study was to use soil moisture data below a double ring infiltrometer measured 48 h after the end of the infiltration test in order to develop PTFs for standard in situ FC. We found that such ring FC data were an average of 0.03 m³ m- 3 greater than standard FC values. The linear PTF that was developed for the ring FC data based only on θ(6 was nearly as accurate as the equivalent PTF reported by Ottoni Filho et al. (2014, which was developed for the standard FC data. The root mean squared residues of FC determined from both PTFs were about 0.02 m³ m- 3. The proposed method has the advantage of estimating the soil in situ FC using the water applied in the infiltration test.
Magnetic field induced strain assisted by stress in Ni-Fe-GaCo single crystals
Chumlyakov Y.
2010-06-01
Full Text Available Ferromagnetic shape memory alloys (FSMA have the possibility to induced a strain by applying a magnetic field. The main advantage of the FSMA is that the strain cycling frequency is two orders of magnitude higher than coventional shape memory alloys. The best alloy showing this effect is the Ni-Mn-Ga system, with a high mobility of its martensite variants and high magnetocrystalline anisotropy constant. Nevertheless, due to the high brittleness of this alloy, other systems (Ni-Fe-Ga, Co-Ni-Al, Co-Ni-Ga, ... are being investigated as an alternative to Ni-Mn-Ga. In the current work, Ni-Fe-Ga-Co single crystals have been studied. In spite of the formation of L10 martensite (low mobility of the variants, the [001] crystals exhibited magnetic-field-induced strains (in tension larger than 2%, under an assisting tensile stress around 16 MPa and fields below 15 kOe. In martensitic samples previously compressed, application of a constant tensile stress along the same axis together with a perpendicular magnetic field produces the elongation of the sample by variant reorientation, as one of the variants rotates its c axis from the field direction to the stress-axis direction. An estimated magnetostress of ~0.8 MPa is in good agreement with the theoretical value given by the ratio of magnetocrystalline anisotropy constant and twinning shear.
Stress-induced piezoelectric field in GaN-based 450-nm light-emitting diodes
Tawfik, Wael Z. [Department of Materials Science and Engineering, Chonnam National University, Yongbong 300 Gwangju 500-757 (Korea, Republic of); Department of Physics, Faculty of Science, Beni-Suef University, Beni-Suef 62511 (Egypt); Hyeon, Gil Yong; Lee, June Key, E-mail: junekey@chonnam.ac.kr [Department of Materials Science and Engineering, Chonnam National University, Yongbong 300 Gwangju 500-757 (Korea, Republic of)
2014-10-28
We investigated the influence of the built-in piezoelectric field induced by compressive stress on the characteristics of GaN-based 450-nm light-emitting diodes (LEDs) prepared on sapphire substrates of different thicknesses. As the sapphire substrate thickness was reduced, the compressive stress in the GaN layer was released, resulting in wafer bowing. The wafer bowing-induced mechanical stress altered the piezoelectric field, which in turn reduced the quantum confined Stark effect in the InGaN/GaN active region of the LED. The flat-band voltage was estimated by measuring the applied bias voltage that induced a 180° phase shift in the electro-reflectance (ER) spectrum. The piezoelectric field estimated by the ER spectra changed by ∼110 kV/cm. The electroluminescence spectral peak wavelength was blue-shifted, and the internal quantum efficiency was improved by about 22% at a high injection current of 100 mA. The LED on the 60-μm-thick sapphire substrate exhibited the highest light output power of ∼59 mW at an injection current of 100 mA, with the operating voltage unchanged.
Yongxiang Xu
2014-01-01
Full Text Available Deep-sea permanent magnet motor equipped with fluid compensated pressure-tolerant system is compressed by the high pressure fluid both outside and inside. The induced stress distribution in stator core is significantly different from that in land type motor. Its effect on the magnetic properties of stator core is important for deep-sea motor designers but seldom reported. In this paper, the stress distribution in stator core, regarding the seawater compressive stress, is calculated by 2D finite element method (FEM. The effect of compressive stress on magnetic properties of electrical steel sheet, that is, permeability, BH curves, and BW curves, is also measured. Then, based on the measured magnetic properties and calculated stress distribution, the stator iron loss is estimated by stress-electromagnetics-coupling FEM. At last the estimation is verified by experiment. Both the calculated and measured results show that stator iron loss increases obviously with the seawater compressive stress.
Solar flare prediction using highly stressed longitudinal magnetic field parameters
Xin Huang; Hua-Ning Wang
2013-01-01
Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions,and their flare productivities are calculated for 1055 active regions.We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples.Using the long-term accumulated MDI data,we build the solar flare prediction model by using a data mining method.Furthermore,the decision boundary,which is used to divide flaring from non-flaring samples,is determined by the decision tree algorithm.Finally,the performance of the prediction model is evaluated by 10-fold cross validation technology.We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.
Estimation of the Level of Residual Stress in Wires with a Magnetic Method
Suliga M.
2015-04-01
Full Text Available Residual stress present in wires after drawing process affects their magnetic properties. The paper presents a concept to estimate the level of residual stress on the basis of measurements of hysteresis loops. In order to describe the effect qualitatively the Jiles-Atherton-Sablik description is adapted. On the basis of variations in hysteresis loop shapes the average values of residual stress in wires for different single draft values are determined. It was found that the estimated average values by magnetic stresses are comparable with the results of numerical modeling and experimental studies.
Estimating Field Scale Crop Evapotranspiration using Landsat and MODIS Satellite Observations
Wong, A.; Jin, Y.; Snyder, R. L.; Daniele, Z.; Gao, F.
2016-12-01
Irrigation accounts for 80% of human freshwater consumption, and most of it return to the atmosphere through Evapotranspiration (ET). Given the challenges of already-stressed water resources and ground water regulation in California, a cost-effective, timely, and consistent spatial estimate of crop ET, from the farm to watershed level, is becoming increasingly important. The Priestley-Taylor (PT) approach, calibrated with field data and driven by satellite observations, shows great promise for accurate ET estimates across diverse ecosystems. We here aim to improve the robustness of the PT approach in agricultural lands, to enable growers and farm managers to tailor irrigation management based on in-field spatial variability and in-season variation. We optimized the PT coefficients for each crop type with available ET measurements from eddy covariance towers and/or surface renewal stations at six crop fields (Alfalfa, Almond, Citrus, Corn, Pistachio and Rice) in California. Good agreement was found between satellite-based estimates and field measurements of net radiation, with a RMSE of less than 36 W m-2. The crop type specific optimization performed well, with a RMSE of 30 W m-2 and a correlation of 0.81 for predicted daily latent heat flux. The calibrated algorithm was used to estimate ET at 30 m resolution over the Sacramento-San Joaquin Delta region for 2015 water year. It captures well the seasonal dynamics and spatial distribution of ET in Sacramento-San Joaquin Delta. A continuous monitoring of the dynamics and spatial heterogeneity of canopy and consumptive water use at a field scale, will help the growers to be well prepared and informed to adaptively manage water, canopy, and grove density to maximize the yield with the least amount of water.
Bordoni, M.; Bittelli, M.; Valentino, R.; Chersich, S.; Meisina, C.
2017-09-01
In this work, Soil Water Characteristic Curves (SWCCs) were reconstructed through simultaneous field measurements of soil pore water pressure and water content. The objective was to evaluate whether field-based monitoring can allow for the improvement of the accuracy in SWCCs estimation with respect to the use of laboratory techniques. Moreover, field assessment of SWCCs allowed to: a) quantify the hydrological hysteresis affecting SWCCs through field data; b) analyze the effect of different temporal resolution of field measures; c) highlight the differences in SWCCs reconstructed for a particular soil during different hydrological years; d) evaluate the reliability of field reconstructed SWCCs, by the comparison between assessed and measured trends of a component of the soil water balance. These aspects were fundamental for assessing the reliability of the field reconstructed SWCCs. Field data at two Italian test-sites were measured. These test-sites were used to evaluate the goodness of field reconstructed SWCCs for soils characterized by different geomorphological, geological, physical and pedological features. Field measured or laboratory measured SWCCs data of 5 soil horizons (3 in a predominantly silty soil, 2 in a predominantly clayey one) were fitted by Van Genuchten model. Different field drying and wetting periods were identified, based on monthly meteorological conditions, in terms of rainfall and evapotranspiration amounts, of different cycles. This method allowed for a correct discrimination of the main drying and the main wetting paths from field data related and for a more reliable quantification of soil hydrological properties with respect to laboratory methodologies. Particular patterns of changes in SWCCs forms along depth could be also identified. Field SWCCs estimation is not affected by the temporal resolution of the acquisition (hours or days), as testified by similar values of Van Genuchten equation fitting parameters. Instead, hourly data
LI Chang-sheng; YU Hai-liang; DENG Guan-yu; LIU Xiang-hua; WANG Guo-dong
2007-01-01
Based on the thermal conduction equations, the three-dimensional (3D) temperature field of a work roll was investigated using finite element method (FEM). The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 ℃, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 145.7 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.
Neimitz A.
2016-06-01
Full Text Available A numerical analysis is performed of the stress field in and around inclusions of various shapes. Inclusions both stiffer and more compliant than the metal matrix are analysed. The critical stresses required for inclusion fracture are estimated after observation of cavities and inclusions by scanning electron microscopy. Real inclusions were observed after performing uniaxial loading to different amounts of overall strain. The material tested was Hardox-400 steel.
Sung Woo Park
2015-03-01
Full Text Available The safety of a multi-span waler beam subjected simultaneously to a distributed load and deflections at its supports can be secured by limiting the maximum stress of the beam to a specific value to prevent the beam from reaching a limit state for failure or collapse. Despite the fact that the vast majority of accidents on construction sites occur at waler beams in retaining wall systems, no safety monitoring model that can consider deflections at the supports of the beam is available. In this paper, a maximum stress estimation model for a waler beam based on average strains measured from vibrating wire strain gauges (VWSGs, the most frequently used sensors in construction field, is presented. The model is derived by defining the relationship between the maximum stress and the average strains measured from VWSGs. In addition to the maximum stress, support reactions, deflections at supports, and the magnitudes of distributed loads for the beam structure can be identified by the estimation model using the average strains. Using simulation tests on two multi-span beams, the performance of the model is evaluated by estimating maximum stress, deflections at supports, support reactions, and the magnitudes of distributed loads.
Klusák J.
2009-12-01
Full Text Available The study of bi-material notches becomes a topical problem as they can model efficiently geometrical or material discontinuities. When assessing crack initiation conditions in the bi-material notches, the generalized stress intensity factors H have to be calculated. Contrary to the determination of the K-factor for a crack in an isotropic homogeneous medium, for the ascertainment of the H-factor there is no procedure incorporated in the calculation systems. The calculation of these fracture parameters requires experience. Direct methods of estimation of H-factors need choosing usually length parameter entering into calculation. On the other hand the method combining the application of the reciprocal theorem (Ψ-integral and FEM does not require entering any length parameter and is capable to extract the near-tip information directly from the far-field deformation.
Effects of the stress field induced by a running tyre on the soil pore system
Berisso, Feto Esimo; Schjønning, Per; Lamandé, Mathieu
2013-01-01
repeated wheelings were performed by a forage harvester (wheel load 6100 kg; tyre width 80 cm). Mean normal and horizontal stresses were measured with Bolling probes (at 10, 20 and 40 cm depth) and load cells (at 40, 50, 60 cm lateral distance from the centreline of the wheel rut at 10, 30 and 50 cm depth...... state in the soil profile beneath the harvester tyre was calculated using the SoilFlex model. Pore continuity index (N) and blocked air-filled porosity (εb) were estimated from the relationship between ka and air-filled porosity (εa) for a range of matric potentials. Calculated and measured stresses...... of the wheel rut. Simulations of the stress field in the soil beneath the tyre indicated that the trends in ka were determined by both the mean normal stress and the shear stress, while the trend in εa was determined by the mean normal stress only. At 10 cm depth, the index of pore continuity (N) supported...
Kazachenko, Maria D.; Fisher, George H.; Welsch, Brian T., E-mail: kazachenko@ssl.berkeley.edu [Space Sciences Laboratory, UC Berkeley, CA 94720 (United States)
2014-11-01
Photospheric electric fields, estimated from sequences of vector magnetic field and Doppler measurements, can be used to estimate the flux of magnetic energy (the Poynting flux) into the corona and as time-dependent boundary conditions for dynamic models of the coronal magnetic field. We have modified and extended an existing method to estimate photospheric electric fields that combines a poloidal-toroidal decomposition (PTD) of the evolving magnetic field vector with Doppler and horizontal plasma velocities. Our current, more comprehensive method, which we dub the 'PTD-Doppler-FLCT Ideal' (PDFI) technique, can now incorporate Doppler velocities from non-normal viewing angles. It uses the FISHPACK software package to solve several two-dimensional Poisson equations, a faster and more robust approach than our previous implementations. Here, we describe systematic, quantitative tests of the accuracy and robustness of the PDFI technique using synthetic data from anelastic MHD (ANMHD) simulations, which have been used in similar tests in the past. We find that the PDFI method has less than 1% error in the total Poynting flux and a 10% error in the helicity flux rate at a normal viewing angle (θ = 0) and less than 25% and 10% errors, respectively, at large viewing angles (θ < 60°). We compare our results with other inversion methods at zero viewing angle and find that our method's estimates of the fluxes of magnetic energy and helicity are comparable to or more accurate than other methods. We also discuss the limitations of the PDFI method and its uncertainties.
Two Field Techniques for Estimating Relative Abundance of Galliformes
Lu Xin; Cangjue Zhuoma; Suolong Ciren; Zheng Guang-mei
2003-01-01
Galliformes are often difficult to count adequate-ly in their natural habitats due to low detectability of them. In the present study, we confirm availability of feather-count and feces-count as two useful field techniques to estimate the rela-tive abundance of eared-pheasants (Crossoptilon spp. ). The former is suitable to forest environments during the post-incu-bation period, whereas the latter is best in areas with dry cli-mate conditions during the fall-winter season. With the ad-vantages of reduced survey effort and high repeatability, the two techniques are potentially applicable to other Galliform species in habitat selection studies and long-term population monitoring.
Comparison of two field tests to estimate maximum aerobic speed.
Berthoin, S; Gerbeaux, M; Turpin, E; Guerrin, F; Lensel-Corbeil, G; Vandendorpe, F
1994-08-01
The measurement of maximal aerobic speed (MAS) and the prediction of maximal oxygen uptake (VO2 max) by means of field tests were carried out on 17 students studying physical education. The subjects underwent a continuous multi-stage track test (Léger and Boucher, 1980), shuttle test (Léger et al., 1984) and VO2 max measurement on a treadmill. The VO2 max values estimated using the track test (56.8 +/- 5.8 ml kg-1 min-1) were not significantly different from the values measured in the treadmill test (56.8 +/- 7.1 ml kg-1 min-1), but were higher than those estimated using the shuttle test (51.1 +/- 5.9 ml kg-1 min-1). The maximal nature of the tests was checked by measurement of heart rate and lactate concentration, taken within 2 min post-test. The means of the MAS observed in the track test (15.8 +/- 1.9 km h-1) and in the treadmill test (15.9 +/- 2.6 km h-1) were not significantly different (P > 0.10). The mean of the shuttle test MAS (13.1 +/- 1 km h-1) was significantly lower (P < 0.01) than those of the other tests. However, the MAS of the shuttle test and track test are linked. The equation for linear regression between MAS values in these two tests is MAStrack = 1.81 x MASshuttle -7.86 (r = 0.91), allowing estimation of one of these MAS values when the other is known. Thus these values may be used within diversified training.
Estimation of turbulent shear stress in free jets: application to valvular regurgitation.
Winoto, S H; Shah, D A; Liu, H
1996-01-01
In an attempt to better assess the severity of valvular regurgitation, an in-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress (uv/Um2) were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of uv/Um2 independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m2, corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.
Magnetic Field Feature Extraction and Selection for Indoor Location Estimation
Carlos E. Galván-Tejada
2014-06-01
Full Text Available User indoor positioning has been under constant improvement especially with the availability of new sensors integrated into the modern mobile devices, which allows us to exploit not only infrastructures made for everyday use, such as WiFi, but also natural infrastructure, as is the case of natural magnetic field. In this paper we present an extension and improvement of our current indoor localization model based on the feature extraction of 46 magnetic field signal features. The extension adds a feature selection phase to our methodology, which is performed through Genetic Algorithm (GA with the aim of optimizing the fitness of our current model. In addition, we present an evaluation of the final model in two different scenarios: home and office building. The results indicate that performing a feature selection process allows us to reduce the number of signal features of the model from 46 to 5 regardless the scenario and room location distribution. Further, we verified that reducing the number of features increases the probability of our estimator correctly detecting the user’s location (sensitivity and its capacity to detect false positives (specificity in both scenarios.
Estimation of Coal Bed Methane Potential of Coal Seams of Margherita Coal Field, Assam, India
Prasenjit Talukdar
2015-06-01
Full Text Available The rapid industrialization and growing energy needs have put a great stress on the conventional energy resources. This is even more concerning for a country like India which is a net importer of oil. To meet the ever increasing need for energy, it is essential that the search for unconventional energy is intensified. This paper deals with the estimation of coal bed methane potential of the Margherita Coal Field of Assam, India. For this purpose, eight coal samples were collected from Tirap O.C.P., Ledo UG Incline and Tikak O.C.P collieries of the Margherita coal field. Proximate analysis, megascopic study and finally qualitative analysis of these eight samples was undertaken. After analysis, the inferred reserves of CBM at Margherita Coalfield, was found to be in the range of 42.5-49.04 Billion Cubic Meter.
A multi-stage 3-D stress field modelling approach exemplified in the Bavarian Molasse Basin
Ziegler, Moritz O.; Heidbach, Oliver; Reinecker, John; Przybycin, Anna M.; Scheck-Wenderoth, Magdalena
2016-09-01
The knowledge of the contemporary in situ stress state is a key issue for safe and sustainable subsurface engineering. However, information on the orientation and magnitudes of the stress state is limited and often not available for the areas of interest. Therefore 3-D geomechanical-numerical modelling is used to estimate the in situ stress state and the distance of faults from failure for application in subsurface engineering. The main challenge in this approach is to bridge the gap in scale between the widely scattered data used for calibration of the model and the high resolution in the target area required for the application. We present a multi-stage 3-D geomechanical-numerical approach which provides a state-of-the-art model of the stress field for a reservoir-scale area from widely scattered data records. Therefore, we first use a large-scale regional model which is calibrated by available stress data and provides the full 3-D stress tensor at discrete points in the entire model volume. The modelled stress state is used subsequently for the calibration of a smaller-scale model located within the large-scale model in an area without any observed stress data records. We exemplify this approach with two-stages for the area around Munich in the German Molasse Basin. As an example of application, we estimate the scalar values for slip tendency and fracture potential from the model results as measures for the criticality of fault reactivation in the reservoir-scale model. The modelling results show that variations due to uncertainties in the input data are mainly introduced by the uncertain material properties and missing SHmax magnitude estimates needed for a more reliable model calibration. This leads to the conclusion that at this stage the model's reliability depends only on the amount and quality of available stress information rather than on the modelling technique itself or on local details of the model geometry. Any improvements in modelling and increases
Reich, Felix A.; Rickert, Wilhelm; Stahn, Oliver; Müller, Wolfgang H.
2017-03-01
Based on the principles of rational continuum mechanics and electrodynamics (see Truesdell and Toupin in Handbuch der Physik, Springer, Berlin, 1960 or Kovetz in Electromagnetic theory, Oxford University Press, Oxford, 2000), we present closed-form solutions for the mechanical displacements and stresses of two different magnets. Both magnets are initially of spherical shape. The first (hard) magnet is uniformly magnetized and deforms due to the field induced by the magnetization. In the second problem of a (soft) linear-magnetic sphere, the deformation is caused by an applied external field, giving rise to magnetization. Both problems can be used for modeling parts of general magnetization processes. We will address the similarities between both settings in context with the solutions for the stresses and displacements. In both problems, the volumetric Lorentz force density vanishes. However, a Lorentz surface traction is present. This traction is determined from the magnetic flux density. Since the obtained displacements and stresses are small in magnitude, we may use Hooke's law with a small-strain approximation, resulting in the Lamé- Navier equations of linear elasticity theory. If gravity is neglected and azimuthal symmetry is assumed, these equations can be solved in terms of a series. This has been done by Hiramatsu and Oka (Int J Rock Mech Min Sci Geomech Abstr 3(2):89-90, 1966) before. We make use of their series solution for the displacements and the stresses and expand the Lorentz tractions of the analyzed problems suitably in order to find the expansion coefficients. The resulting algebraic system yields finite numbers of nonvanishing coefficients. Finally, the resulting stresses, displacements, principal strains and the Lorentz tractions are illustrated and discussed.
Reich, Felix A.; Rickert, Wilhelm; Stahn, Oliver; Müller, Wolfgang H.
2016-12-01
Based on the principles of rational continuum mechanics and electrodynamics (see Truesdell and Toupin in Handbuch der Physik, Springer, Berlin, 1960 or Kovetz in Electromagnetic theory, Oxford University Press, Oxford, 2000), we present closed-form solutions for the mechanical displacements and stresses of two different magnets. Both magnets are initially of spherical shape. The first (hard) magnet is uniformly magnetized and deforms due to the field induced by the magnetization. In the second problem of a (soft) linear-magnetic sphere, the deformation is caused by an applied external field, giving rise to magnetization. Both problems can be used for modeling parts of general magnetization processes. We will address the similarities between both settings in context with the solutions for the stresses and displacements. In both problems, the volumetric uc(Lorentz) force density vanishes. However, a uc(Lorentz) surface traction is present. This traction is determined from the magnetic flux density. Since the obtained displacements and stresses are small in magnitude, we may use uc(Hooke's) law with a small-strain approximation, resulting in the uc(Lamé)-uc(Navier) equations of linear elasticity theory. If gravity is neglected and azimuthal symmetry is assumed, these equations can be solved in terms of a series. This has been done by uc(Hiramatsu) and uc(Oka) (Int J Rock Mech Min Sci Geomech Abstr 3(2):89-90, 1966) before. We make use of their series solution for the displacements and the stresses and expand the uc(Lorentz) tractions of the analyzed problems suitably in order to find the expansion coefficients. The resulting algebraic system yields finite numbers of nonvanishing coefficients. Finally, the resulting stresses, displacements, principal strains and the uc(Lorentz) tractions are illustrated and discussed.
Field evaluation of an acid rain-drought stress interaction.
Banwart, W L
1988-01-01
Various methods have been proposed to simulate natural field conditions for growing agricultural crops while controlling conditions to study specific environmental effects. This report briefly describes the use of moveable rain exclusion shelters (10.4 x 40.9 m) to study the results of the interaction of acid rain and drought stress on corn and soybean yields. The rain exclusion shelters are constructed of galvanized pipe framing and covered with polyethylene film. Movement is automated by a rain switch to protect crops from ambient rainfall and to treat them with simulated acid rain The facility simulates a real environment with respect to variables such as solar exposure, wind movement, dew formation, and insect exposure, while allowing careful control of moisture regimes. Soybeans and corn were treated with average rainfall amounts, and with one-half and one-quarter of these rainfall amounts (drought stress) at two levels of rainfall acidity, pH 5.6 and 3.0. While drought stress resulted in considerable yield reduction for Amsoy and Williams soybeans, no additional reduction in yield was observed with rainfall of pH 3.0, as compared to rainfall of approximately pH 5.6. Similar results were observed for one corn cultivar, Pioneer 3377. For one year of the study however, yield of B73 x Mo17 (corn) was reduced 3139 kg ha(-1) by the most severe drought, and an additional 1883 kg ha(-1) by acid rain of pH 3.0, as compared to the control (pH 5.6). Yield reduction from acidic rain was considerably less at full water rates, resulting in a significant pH by drought stress interaction. However, during the second year of the experiment, no pH effect or drought by pH interaction was observed for this cultivar. The reason for the difference in the two years was not identified.
Contemporary stress field in the area of the 2016 Amatrice seismic sequence (central Italy
Maria Teresa Mariucci
2016-11-01
Full Text Available We update the last present-day stress map for Italy relatively to the area of 2016 Amatrice seismic sequence (central Italy taking into account a large number of earthquakes occurred from August 24 to October 3, 2016. In particular in this paper, we discuss the new stress data from crustal earthquake focal mechanisms selecting those with Magnitude ≥ 4.0; at the same time, we revise the borehole data, analyze the stratigraphic profiles and the relative sonic logs in 4 deep wells located close to the Amatrice sequence along the Apennine belt and toward east along the Adriatic foredeep. From these data we consider the P-wave velocity trend with depth and estimate rock density following an empirical relationship. Then we calculate the overburden stress magnitude for each well. The new present-day stress indicators confirm the presence of prevalent normal faulting regime and better define the local stress field in the area, highlighting a slight rotation from NE-SW to ENE-WSW of extension. The analysis evidences that the lithostatic gradient gradually changes from ~26 MPa/km in the belt to less than 23 MPa/km along the Adriatic foredeep. Finally, at a depth of 5 km we estimate the vertical stress magnitude varying from 130 MPa to 114 moving from the Apennine belt to the Adriatic foredeep. Although the wells are very close each other they show different P wave velocities from the belt to the foredeep with values ~7km/s and ~4 km/s at 5 km depth, respectively.
Holland, Austin Adams
2002-02-01
A digital network of 24 seismograph stations was operated from September 15, 1987 to September 30, 1988, by Lawrence Livermore National Laboratory and Unocal as part of the Salton Sea Scientific Drilling Project to study seismicity related to tectonics and geothermal activity near the drilling site. More than 2001 microearthquakes were relocated in this study in order to image any pervasive structures that may exist within the Salton Sea geothermal field. First, detailed velocity models were obtained through standard 1-D inversion techniques. These velocity models were then used to relocate events using both single event methods and Double-Differencing, a joint hypocenter location method. An anisotropic velocity model was built from anisotropy estimates obtained from well logs within the study area. During the study period, the Superstition wills sequence occurred with two moderate earthquakes of MS 6.2 and MS 6.6. These moderate earthquakes caused a rotation of the stress field as observed from the inversion of first motion data from microearthquakes at the Salton Sea geothermal field. Coulomb failure analysis also indicates that microearthquakes occurring after the Superstition Hills sequence are located within a region of stress increase suggesting stress triggering caused by the moderate earthquakes.
ESTIMATION OF SHEAR STRESS WORKING ON SUBMERGED HOLLOW FIBRE MEMBRANE BY CFD METHOD IN MBRs
Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi
This study was conducted to evaluate shear stress working on submerged hollow fibre membrane by CFD (Computation Fluid Dynamics) method in MBRs. Shear stress on hollow fibre membrane caused by aeration was measured directly using a two-direction load sensor. The measurement of water-phase flow velocity was done also by using laser doppler velocimeter. It was confirmed that the shear stress was possible to be evaluated from the water-phase flow velocityby the result of comparison of time average shear stress actually measured with one hollow fibre membrane and the one calculated by the water-phase flow velocity. In the estimation of the water-phase flow velocity using the CFD method, time average water-phase flow velocity estimated by consideration of the fluid resistance of the membrane module nearly coincided with the measured values, and it was shown that it was possible to be estimated also within the membrane module. Moreover, the measured shear stress and drag force well coincided with the values calculated from the estimated water-phase flow velocity outside of membrane module and in the center of membrane module, and it was suggested that the shear stress on the hollow fibre membrane could be estimated by the CFD method in MBRs.
Yoo, Jejoong; Cui, Qiang
2013-01-08
Using both atomistic and coarse-grained (CG) models, we compute the three-dimensional stress field around a gramicidin A (gA) dimer in lipid bilayers that feature different degrees of negative hydrophobic mismatch. The general trends in the computed stress field are similar at the atomistic and CG levels, supporting the use of the CG model for analyzing the mechanical features of protein/lipid/water interfaces. The calculations reveal that the stress field near the protein-lipid interface exhibits a layered structure with both significant repulsive and attractive regions, with the magnitude of the stress reaching 1000 bar in certain regions. Analysis of density profiles and stress field distributions helps highlight the Trp residues at the protein/membrane/water interface as mechanical anchors, suggesting that similar analysis is useful for identifying tension sensors in other membrane proteins, especially membrane proteins involved in mechanosensation. This work fosters a connection between microscopic and continuum mechanics models for proteins in complex environments and makes it possible to test the validity of assumptions commonly made in continuum mechanics models for membrane mediated processes. For example, using the calculated stress field, we estimate the free energy of membrane deformation induced by the hydrophobic mismatch, and the results for regions beyond the annular lipids are in general consistent with relevant experimental data and previous theoretical estimates using elasticity theory. On the other hand, the assumptions of homogeneous material properties for the membrane and a bilayer thickness at the protein/lipid interface being independent of lipid type (e.g., tail length) appear to be oversimplified, highlighting the importance of annular lipids of membrane proteins. Finally, the stress field analysis makes it clear that the effect of even rather severe hydrophobic mismatch propagates to only about two to three lipid layers, thus putting a
Estimating magnetic field power spectrum using CRRES magnetometer data
Ali, A.; Elkington, S. R.
2013-05-01
Radial diffusion is one of the acceleration mechanisms responsible for populating and depleting the Van Allen radiation belts with high energy charged particles. We use the magnetometer data from the Combined Release and Radiation Effects Satellite (CRRES) to estimate the power spectral density in the compressional component of the geomagnetic field in the frequency range of 0.8mHz-16.3mHz. We see a clear dependence of power spectral density on radial distance L, measure of geomagnetic disturbance Kp, and magnetic local time. Comparing total integrated power, the noon sector contains more power with no significant difference between other sectors during periods of low activity. During high activity the dusk sector has significantly more power than dawn sector with the difference sometimes being an order of magnitude higher with power increasing slightly as we move radially outward to higher L-shells. We then recompute the power spectral density without local time dependence and compute the electromagnetic part of the radial diffusion coefficient. The electromagnetic diffusion coefficients are then compared with the electrostatic coefficients computed by Brautigam et al. (2005). The dependence of the diffusion coefficients is then studied on parameters of L, Kp, and the first invariant. For a fixed first invariant the diffusion coefficient can be up to two orders of magnitude higher as we move from the inner magnetosphere (L=3.5) to the outer magnetosphere (L=6.5). During high activity, radial diffusion is also significantly faster than at quiet times.
Field test on temperature field and thermal stress for prestressed concrete box-girder bridge
Baoguo CHEN; Rui DING; Junjie ZHENG; Shibiao ZHANG
2009-01-01
A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete (PC) box-girder bridge. The change of hydration heat temperature consists of four periods: temperature rising period, constant temperature period, rapid temperature fall period and stow temperature fall period. The peak value of hydration heat temperature increases with the increasing casting temperature of concrete; the relation between them is approximately linear. According to field tests, the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder. Furthermore, the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring. Such results show that the prevailing Chinese Code (2004) is insufficient since it does not take into account the temperature gradient of the bottom slab. Finally, some preventive measures against temperature cracks were proposed based on related studies. The conclusions can provide valuable reference for the design and construction of PC box-girder bridges.
Effects of 60 Hz electric fields on operant and social stress behaviors of nonhuman primates
Rogers, W.R.; Coelho, A.M. Jr.; Easley, S.P.; Lucas, J.H.; Moore, G.T.; Orr, J.L.; Smith, H.D.; Taylor, L.L.; Tuttle, M.L.
1987-10-24
The objective of this program is to investigate, using the baboon as a nonhuman primate surrogate for the human, possible behavioral effects associated with exposure to high intensity 60 Hz electric fields. Results from this program, along with information from experiments conducted elsewhere, will be used by the Department of Energy (DOE) to estimate and evaluate the likelihood of deleterious consequences resulting from exposure of humans to the electric fields associated with power transmission over high voltage lines. This research program consists of four major research projects, all of which have been successfully completed. The first project evaluated the potentially aversive character of exposure to 60 Hz electric fields by determining the threshold intensity that produces escape or avoidance responses. The second project estimated the threshold intensity for detection threshold was 12 kV/m; the range of means was 6 to 16 kV/m. The third project assessed, in separate experiments conducted at 30 and 60 kV/m, effects of chronic exposure to electric fields on the performance of two operant conditioning tasks, fixed ratio (FR), and differential reinforcement of low rate (DRL). In the same two experiments, the fourth project investigated, using the systematic quantitative observational sampling methods of primatology, the possible stress-inducing effects of chronic exposure to 60 Hz electric fields on the behavior of baboons living in small social groups. 131 refs., 87 figs., 123 tabs.
Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves
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.
Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions
CUI Xiao-feng
2006-01-01
In this paper, we analyze the general directional features of regional tectonic stress field in Jiashi, Xinjiang and adjacent regions from the data of focal mechanism solutions, borehole breakouts and fault slip. The direction of maximum horizontal principal stress given by these three sorts of stress data differs slightly, which indicates there is a NS-trending horizontal compression in the tectonic stress field in the region of interest. We also invert and analyze the temporal and spatial changes of recent tectonic stress field in the research region by using 137 focal mechanism solutions. The inverted results show that the maximum principal stress σ1 in Jiashi and adjacent regions is NNW-SSE with an azimuth of 162°. In the period from 1997 to 2003 before the occurrence of Jiashi-Bachu earthquake, the directions of the maximum principal stress σ1 and the minimum principal stress σ3 in Jiashi seismic source zone changed clockwise with respect to the tectonic stress field in the regions around. The maximum principal stress σ1 adjusted to the direction of NNE-SSW with an azimuth of 25°. Under the control of this tectonic stress field, a series of earthquakes happened, including the Jiashi strong earthquake swarm in 1997.Then, the tectonic stress field in the Jiashi seismic source zone might adjust again. And the tectonic stress field controlling the Jiashi-Bachu earthquake in 2003 was in accordance with the regions around.
ESTIMATION OF EFFECTIVE SHEAR STRESS WORKING ON FLAT SHEET MEMBRANE USING FLUIDIZED MEDIA IN MBRs
Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi; Mishima, Iori
This study was aimed at estimating effective shear stress working on flat sheet membrane by the addition of fluidized media in MBRs. In both of laboratory-scale aeration tanks with and without fluidized media, shear stress variations on membrane surface and water phase velocity variations were measured and MBR operation was conducted. For the evaluation of the effective shear stress working on membrane surface to mitigate membrane surface, simulation of trans-membrane pressure increase was conducted. It was shown that the time-averaged absolute value of shear stress was smaller in the reactor with fluidized media than without fluidized media. However, due to strong turbulence in the reactor with fluidized media caused by interaction between water-phase and media and also due to the direct interaction between membrane surface and fluidized media, standard deviation of shear stress on membrane surface was larger in the reactor with fluidized media than without media. Histograms of shear stress variation data were fitted well to normal distribution curves and mean plus three times of standard deviation was defined to be a maximum shear stress value. By applying the defined maximum shear stress to a membrane fouling model, trans-membrane pressure curve in the MBR experiment was simulated well by the fouling model indicting that the maximum shear stress, not time-averaged shear stress, can be regarded as an effective shear stress to prevent membrane fouling in submerged flat-sheet MBRs.
Lee, Rayeon; Chang, Chandong; Hong, Tae-kyung; Lee, Junhyung; Bae, Seong-Ho; Park, Eui-Seob; Park, Chan
2016-04-01
We are characterizing stress fields in Korea using two types of stress data: earthquake focal mechanism inversions (FMF) and hydraulic fracturing stress measurements (HF). The earthquake focal mechanism inversion data represent stress conditions at 2-20 km depths, whereas the hydraulic fracturing stress measurements, mostly conducted for geotechnical purposes, have been carried out at depths shallower than 1 km. We classified individual stress data based on the World Stress Map quality ranking scheme. A total of 20 FMF data were classified into A-B quality, possibly representing tectonic stress fields. A total of 83 HF data out of compiled 226 data were classified into B-C quality, which we use for shallow stress field characterization. The tectonic stress, revealed from the FMF data, is characterized by a remarkable consistency in its maximum stress (σ1) directions in and around Korea (N79±2° E), indicating a quite uniform deep stress field throughout. On the other hand, the shallow stress field, represented by HF data, exhibits local variations in σ1 directions, possibly due to effects of topography and geologic structures such as faults. Nonetheless, there is a general similarity in σ1 directions between deep and shallow stress fields. To investigate the shallow stress field statistically, we follow 'the mean orientation and wavelength analysis' suggested by Reiter et al. (2014). After the stress pattern analysis, the resulting stress points distribute sporadically over the country, not covering the entire region evenly. In the western part of Korea, the shallow σ1directions are generally uniform with their search radius reaching 100 km, where the average stress direction agrees well with those of the deep tectonic stress. We note two noticeable differences between shallow and deep stresses in the eastern part of Korea. First, the shallow σ1 orientations are markedly non-uniform in the southeastern part of Korea with their search radius less than 25 km
Stress Field and Seismicity in the Basin of Mexico
Huesca-Perez, E.; Quintanar, L.; Garcia-Palomo, A.
2007-12-01
Mexico City is located in the basin of Mexico, inside the so called Trans-Mexican Volcanic Belt. The region in general and the basin in particular, is characterized by local low magnitude seismicity (Mc Chalco and 3)- Juchitepec - Milpa Alta outside Mexico City; the rest of the basin presents lower seismic activity. We recorded and located 336 earthquakes with digital seismograms between 1996 and 2007. From them, just 23 focal mechanisms could be evaluated because of low magnitude that creates recording problems in the seismological networks and high frequency background noise. The focal mechanisms are mainly strike-slip and dip-slip (normal) faulting. We used three different techniques (when possible) to calculate the focal mechanisms: simple and composite first motion focal mechanism, Hash's S/P amplitude rate focal mechanism and time domain moment tensor inversion using broadband three components seismograms. The final goal is to find the local and regional stress field for the whole basin.
Comparison of thermal aftereffect models for estimating the fluctuation field
Della Torre, E. [George Washington University, Washington, DC 20052 (United States)], E-mail: edt@gwu.edu; Bennett, L.H.; Korman, C.E. [George Washington University, Washington, DC 20052 (United States)
2008-02-01
The sigmoidal decay of the magnetization in log time, which is geometrically similar to the major loop, starts at the major loop and decays to the anhysteretic magnetization for a given holding field. The linear displacement of these curves after normalization with holding field can be used to compute the fluctuation field. This paper discusses the errors in computing this field.
Wave-induced stress and estimation of its driven effect on currents
SUN Fu; GAO Shan; WANG Wei; QIAN Chengchun
2004-01-01
A genuine geostrophic small amplitude wave solution is deduced for the first time from the general form of linear fluid dynamic equations with the f-plane approximation, where the horizontal component of angular velocity of the earth rotation is taken into account. The Coriolisinduced stress obtained from this solution consists of lateral and reverse component, while its first order approximation is reduced to the result of Hasselmann or Xu Zhigang. Accordingly,combining the Coriolis-induced wave stress with the virtual wave stress proposed by Longuet-Higgins, the ratio of total wave-induced stress to wind stress on the sea surface is estimated, through which the importance of the wave-induced stress is emphasized in the study of the currents in the seas around China, especially in the Bohai Sea and the Yellow Sea.
An estimation method on failure stress of micro thickness Cu film-substrate structure
无
2009-01-01
The failure of thin film-substrate structure occurs mainly at the thin film or the interface. However, the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size, interface and stress state on the failure behavior of thin film-substrate structure. Based on the scanning electron microscope (SEM) in-situ in- vestigation on the failure models of the Cu thin film-substrate structure and the nano scratched testing results, the failure stresses in different thicknesses of the Cu film-substrate were characterized, which were compared and confirmed by other methods, such as Stoney formula and other empiric equations. These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods. The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film. Therefore, the novel estimating method of failure stress assists people to understand the critical interfacial strength and to set up the failure criterion of thin film-substrate structure.
An estimation method on failure stress of micro thickness Cu film-substrate structure
WANG XiShu; LI Ying; MENG XiangKang
2009-01-01
The failure of thin film-substrate structure occurs mainly at the thin film or the interface.However,the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size,interface and stress state on the failure behavior of thin film-substrate structure.Based on the scanning electron microscope(SEM)in-situ investigation on the failure models of the Cu thin film-substrata structure and the nano scratched testing results,the failure stresses in different thicknesses of the Cu film-substrate were characterized,which were compared and confirmed by other methods,such as Stoney formula and other empiric equations.These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods.The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film.Therefore,the novel estimating method of failure stress assists people to understand the critical interracial strength and to set up the failure criterion of thin film-substrate structure.
Shaaran, T; Lewenstein, M
2012-01-01
In strong field laser physics it is a common practice to use the high-order harmonic cutoff to estimate the laser intensity of the pulse that generates the harmonic radiation. Based on the semiclassical arguments it is possible to find a direct relationship between the maximum value of the photon energy and the laser intensity. This approach is only valid if the electric field driving HHG is spatially homogenous. In laser-matter processes driven by plasmonics fields, the enhanced fields present a spatial dependence that strongly modifies the electron motion and consequently the laser driven phenomena. As a result, this method should be revised in order to more realistically estimate the field. In this work, we demonstrate how the inhomogeneity of the fields will effect this estimation. Furthermore, by employing both quantum mechanical and classical calculations, we show how one can obtain a better estimation for the intensity of the enhanced field in plasmonic nanostructure.
Bröde, Peter; Fiala, Dusan; Lemke, Bruno; Kjellstrom, Tord
2017-04-01
With a view to occupational effects of climate change, we performed a simulation study on the influence of different heat stress assessment metrics on estimated workability (WA) of labour in warm outdoor environments. Whole-day shifts with varying workloads were simulated using as input meteorological records for the hottest month from four cities with prevailing hot (Dallas, New Delhi) or warm-humid conditions (Managua, Osaka), respectively. In addition, we considered the effects of adaptive strategies like shielding against solar radiation and different work-rest schedules assuming an acclimated person wearing light work clothes (0.6 clo). We assessed WA according to Wet Bulb Globe Temperature (WBGT) by means of an empirical relation of worker performance from field studies (Hothaps), and as allowed work hours using safety threshold limits proposed by the corresponding standards. Using the physiological models Predicted Heat Strain (PHS) and Universal Thermal Climate Index (UTCI)-Fiala, we calculated WA as the percentage of working hours with body core temperature and cumulated sweat loss below standard limits (38 °C and 7.5% of body weight, respectively) recommended by ISO 7933 and below conservative (38 °C; 3%) and liberal (38.2 °C; 7.5%) limits in comparison. ANOVA results showed that the different metrics, workload, time of day and climate type determined the largest part of WA variance. WBGT-based metrics were highly correlated and indicated slightly more constrained WA for moderate workload, but were less restrictive with high workload and for afternoon work hours compared to PHS and UTCI-Fiala. Though PHS showed unrealistic dynamic responses to rest from work compared to UTCI-Fiala, differences in WA assessed by the physiological models largely depended on the applied limit criteria. In conclusion, our study showed that the choice of the heat stress assessment metric impacts notably on the estimated WA. Whereas PHS and UTCI-Fiala can account for
Maler, Leonard
2009-10-10
The electric fish Apteronotus leptorhynchus emits a high-frequency electric organ discharge (EOD) sensed by specialized electroreceptors (P-units). Amplitude modulations (AMs) of the EOD are caused by objects such as prey as well as by social interactions with conspecifics. The firing rate of P-units is modulated by the AMs due to both objects and communication signals. P-units trifurcate as they enter the medulla; they terminate topographically with three maps of the electrosensory lateral line lobe (ELL): the centromedial (CMS), centrolateral (CLS), and lateral (LS) segments. Within each map P-units terminate onto the basal dendrites of pyramidal cells. Anterograde filling of P-units and retrograde filling of the basal bushes of pyramidal cells were used to estimate their respective spreads and spacing in the three maps. These estimates were used to compute the receptive field structure of the pyramidal cells: receptive fields were small in CMS and very large in LS with intermediate values in CLS. There are several classes of pyramidal cells defined by morphological and functional criteria; these cells are organized into columns such that each column contains one member of each class and all cells within a column receive the same P-unit input.
Flavour Fields in Steady State: Stress Tensor and Free Energy
Banerjee, Avik; Kundu, Sandipan
2015-01-01
The dynamics of a probe brane in a given gravitational background is governed by the Dirac-Born-Infeld action. The corresponding open string metric arises naturally in studying the fluctuations on the probe. In Gauge-String duality, it is known that in the presence of a constant electric field on the worldvolume of the probe, the open string metric acquires an event horizon and therefore the fluctuation modes on the probe experience an effective temperature. In this article, we bring together various properties of such a system to a formal definition and a subsequent narration of the effective thermodynamics and the stress tensor of the corresponding flavour fields, also including a non-vanishing chemical potential. In doing so, we point out a potentially infinitely-degenerate scheme-dependence of regularizing the free energy, which nevertheless yields a universal contribution in certain cases. This universal piece appears as the coefficient of a log-divergence in free energy when a space-filling probe brane ...
Field Phenotyping of Soybean Roots for Drought Stress Tolerance
Berhanu A. Fenta
2014-08-01
Full Text Available Root architecture was determined together with shoot parameters under well watered and drought conditions in the field in three soybean cultivars (A5409RG, Jackson and Prima 2000. Morphology parameters were used to classify the cultivars into different root phenotypes that could be important in conferring drought tolerance traits. A5409RG is a drought-sensitive cultivar with a shallow root phenotype and a root angle of <40°. In contrast, Jackson is a drought-escaping cultivar. It has a deep rooting phenotype with a root angle of >60°. Prima 2000 is an intermediate drought-tolerant cultivar with a root angle of 40°–60°. It has an intermediate root phenotype. Prima 2000 was the best performing cultivar under drought stress, having the greatest shoot biomass and grain yield under limited water availability. It had abundant root nodules even under drought conditions. A positive correlation was observed between nodule size, above-ground biomass and seed yield under well-watered and drought conditions. These findings demonstrate that root system phenotyping using markers that are easy-to-apply under field conditions can be used to determine genotypic differences in drought tolerance in soybean. The strong association between root and nodule parameters and whole plant productivity demonstrates the potential application of simple root phenotypic markers in screening for drought tolerance in soybean.
Basic Study on Estimating Water Stress of a Plant Using Vibration Measurement of Leaf
Sano, Motoaki; Sugimoto, Tsuneyoshi; Hosoya, Hiroshi; Ohaba, Motoyoshi; Shibusawa, Sakae
2013-07-01
A new noninvasive method for estimating the water stress of a plant was proposed. In order to investigate this method, we first examined the characteristic frequency of an individual leaf picked from the plant, and obtained the result that its characteristic frequency decreased in proportion to the reduction in the water content of the leaf. Next, we applied this method to a leaf on a branch and confirmed the same tendency when the water stress was increased by stopping the water supply of a plant cultured in water. From these results, it was suggested that the water stress of the plant could be estimated from the vibration measurement of the leaf. Lastly, the relationship between the water potential of the leaf and its elastic constant was discussed with the soil-plant-atmosphere-continuum model (SPAC model), and Young's modulus of a tomato leaf was roughly estimated.
Using Estimations of Entropy to Optimize Complex Human Dynamic Networks under Stress
2013-12-30
blood components , during various physically and mentally stressful exercises, we will be able to determine the factors that drive overall team success and assemble more effective teams using these factors. Sixteen WVU Air Force ROTC participants were selected, divided into four different teams of four individuals, their biological responses were monitored (some in real-time and some prior to and immediately following) in response to stressful teamwork exercises (mock hostage rescue). Individuals were outfitted with EEG, heart rate, breathing rate, estimated core
Estimation of Korean paddy field soil properties using optical reflectance
An optical sensing approach based on diffuse reflectance has shown potential for rapid and reliable on-site estimation of soil properties. Important sensing ranges and the resulting regression models useful for soil property estimation have been reported. In this study, a similar approach was applie...
An Empirical Approach for Estimating Stress-Coupling Lengths for Marine-Terminating Glaciers
Ellyn Mary Enderlin
2016-12-01
Full Text Available Variability in the dynamic behavior of marine-terminating glaciers is poorly understood, despite an increase in the abundance and resolution of observations. When paired with ice thicknesses, surface velocities can be used to quantify the dynamic redistribution of stresses in response to environmental perturbations through computation of the glacier force balance. However, because the force balance is not purely local, force balance calculations must be performed at the spatial scale over which stresses are transferred within glacier ice, or the stress-coupling length (SCL. Here we present a new empirical method to estimate the SCL for marine-terminating glaciers using high-resolution observations. We use the empirically-determined periodicity in resistive stress oscillations as a proxy for the SCL. Application of our empirical method to two well-studied tidewater glaciers (Helheim Glacier, SE Greenland, and Columbia Glacier, Alaska, USA demonstrates that SCL estimates obtained using this approach are consistent with theory (i.e., can be parameterized as a function of the ice thickness and with prior, independent SCL estimates. In order to accurately resolve stress variations, we suggest that similar empirical stress-coupling parameterizations be employed in future analyses of glacier dynamics.
Evolution of 3D tectonic stress field and fault movement in North China
陈连旺; 陆远忠; 郭若眉; 许桂林; 张杰
2001-01-01
Based on data of fault movement surveying, we simulate the evolution process of three dimensional stress field in North China by three dimensional finite element method. Evolutional patterns in one-year time scale from 1986 to 1997 have been illustrated and the evolution characteristics of stress field have been analyzed. In comparison with the seismic activity among that time interval in North China, we have primarily discussed the relationship between the evolution of stress field and seismic activity.
J. Gogoi
2012-01-01
Full Text Available This paper deals with the stress vs. strength problem incorporating multi-componentsystems viz. standby redundancy. The models developed have been illustrated assuming that allthe components in the system for both stress and strength are independent and follow differentprobability distributions viz. Exponential, Gamma and Lindley. Four different conditions forstress and strength have been considered for this investigation. Under these assumptions thereliabilities of the system have been obtained with the help of the particular forms of densityfunctions of n-standby system when all stress-strengths are random variables. The expressions forthe marginal reliabilities R(1, R(2, R(3 etc. have been derived based on its stress- strengthmodels. Then the corresponding system reliabilities Rn have been computed numerically andpresented in tabular forms for different stress-strength distributions with different values of theirparameters. Here we consider n 3 for estimating the system reliability R3.
Equations for estimating muscle fiber stress in the left ventricular wall.
Rabben, S I; Irgens, F; Angelsen, B
1999-01-01
Left ventricular muscle fiber stress is an important parameter in cardiac energetics. Hence, we developed equations for estimating regional fiber stresses in rotationally symmetric chambers, and equatorial and apical fiber stresses in prolate spheroidal chambers. The myocardium was modeled as a soft incompressible material embedding muscle fibers that support forces only in their longitudinal direction. A thin layer of muscle fibers then contributes with a pressure increment determined by the fiber stress and curvature. The fiber curvature depends on the orientation of the fibers, which varies continuously across the wall. However, by assuming rotational symmetry about the long axis of the ventricle and including a longitudinal force balance, we obtained equations where fiber stress is completely determined by the principal curvatures of the middle wall surface, wall thickness, and cavity pressure. The equations were validated against idealized prolate spheroidal chambers, whose wall thicknesses are such that the fiber stress is uniform from the equator to the apex. Because the apex is free to rotate, the resultant moment about the long axis of the LV must be zero. By using this constraint together with our fiber-stress equations, we were able to estimate a muscle fiber orientation distribution across the wall that was in qualitative agreement with published measurements.
Estimation of the shear stress on the surface of an aortic valve leaflet.
Weston, M W; LaBorde, D V; Yoganathan, A P
1999-01-01
The limited durability of xenograft heart valves and the limited supply of allografts have sparked interest in tissue engineered replacement valves. A bioreactor for tissue engineered valves must operate at conditions that optimize the biosynthetic abilities of seeded cells while promoting their adherence to the leaflet matrix. An important parameter is shear stress, which is known to influence cellular behavior and may thus be crucial in bioreactor optimization. Therefore, an accurate estimate of the shear stress on the leaflet surface would not only improve our understanding of the mechanical environment of aortic valve leaflets, but it would also aid in bioreactor design. To estimate the shear stress on the leaflet surface, two-component laser-Doppler velocimetry measurements have been conducted inside a transparent polyurethane valve with a trileaflet structure similar to the native aortic valve. Steady flow rates of 7.5, 15.0, and 22.5 L/min were examined to cover the complete range possible during the cardiac cycle. The laminar shear stresses were calculated by linear regression of four axial velocity measurements near the surface of the leaflet. The maximum shear stress recorded was 79 dyne/cm2, in agreement with boundary layer theory and previous experimental and computational studies. This study has provided a range of shear stresses to be explored in bioreactor design and has defined a maximum shear stress at which cells must remain adherent upon a tissue engineered construct.
Estimating the diffuseness of sound fields: A wavenumber analysis method
Nolan, Melanie; Davy, John L.; Brunskog, Jonas
2017-01-01
The concept of a diffuse sound field is widely used in the analysis of sound in enclosures. The diffuse sound field is generally described as composed of plane waves with random phases, which wave number vectors are uniformly distributed over all angles of incidence. In this study......, an interpretation in the spatial frequency domain is discussed, with the prospect of evaluating the diffuse field conditions in non-anechoic enclosures. This work examines how theoretical considerations compare with experimental results obtained in rooms with various diffuse field conditions. In addition, the paper...
Multiscale stress field inversion in the crust from focal mechanism datasets
Massa, Bruno; D'Auria, Luca; Cristiano, Elena; De Matteo, Ada
2016-04-01
Earthquake focal mechanisms are an important tool to study spatial and temporal patterns of the stress field within the lithosphere. Nowadays various techniques are able to exploit focal mechanisms dataset to retrieve the orientation of the principal stress tensor axes and a ratio of their respective magnitudes (Bishop's ratio). However these techniques rely on the assumption of a homogeneous stress field responsible for the earthquakes. Within the Earth's lithosphere the stress field is highly variable depending on the geodynamic context, heterogeneities of the mechanical properties and time-varying perturbations (earthquakes, volcanic processes). Various methods have been devised to effectively capture the complexity of the stress field. An important category relies on a clustering approach to identify different contributions to the heterogeneous dataset. However these techniques are effective only when the different stress field components are not so many and are well separated. Other techniques are more appropriated when dealing with smooth varying stress fields. They rely on a damped linearized inversion on a grid and allow imaging the spatial variations in the stress field. We propose a novel approach based on a space-time 4D Discrete Wavelet representation of the stress field. The usage of Discrete Wavelets provides a natural framework to capture the multiscale nature of the stress field. We parameterize the spatial and temporal distribution of the stress field parameters using 4D wavelets, selecting only those constrained by a sufficient numbers of focal mechanisms. This allows reducing the computational efforts of the inverse methods, keeping a greater level of details in regions/intervals more constrained by the data. Using a linearized damped inverse method we are able retrieve the spatial and temporal pattern of the stress field simultaneously at different scales. We show the performances of the method using both synthetic tests as well as example
Methods of gas hydrate concentration estimation with field examples
Kumar, D.; Dash, R.; Dewangan, P.
different methods of gas hydrate concentration estimation that make use of data from the measurements of the seismic properties, electrical resistivity, chlorinity, porosity, density, and temperature are summarized in this paper. We demonstrate the methods...
Field measurement of critical shear stress for erosion and deposition of fine muddy sediments
Salehi, M.; Strom, K. B.; Field Study
2010-12-01
The movement of muddy sediment from one region to another is linked to the fate and transport of pollutants that can be attached to this sediment. Important in understanding this movement is the need to know the critical conditions for erosion and deposition of the fine muddy sediment. For non-cohesion sediment, such as sands and gravels, reasonable estimates for the critical conditions can often be made theoretically without in situ measurements of the critical fluid condition or sediment transport rate. However, the shear stress needed for the incipient motion of the mud (cohesive sediments) is inherently difficult to calculate theoretically or in research flumes due to the influence of (1) flow history; (2) local sediment composition; (3) biological activity within the bed; (4) water content of the bed; and (5) salinity of the water column. The complexity of the combination of these factors makes the field measurement necessary. A field experiment was conducted under tidal flow in the region surrounding the Houston Ship Channel (near Houston, TX) to determine these conditions. Observations were made using single point, simultaneous, in situ measurement of turbulent flow and suspended sediment concentration within bottom boundary layer. Measurements were primarily made with a 6 MHz Nortek Vector velocimeter (ADV). The ADV was programmed to record 3-minute turbulent velocity with 32 Hz frequency every 10 minute. The suspended sediment concentration (SSC) was measured using the calibration of acoustic backscatter recorded by ADV against sample derived SSC. Different methods such as turbulent kinetic energy (TKE), TKEw and direct covariance method (COV) are compared together. TKE showed much more reasonable estimation on bed shear stress. Combination of time varying SSC, distance from the bed to the sampling volume recorded by ADV and calculation of shear stress made the determination of critical conditions for erosion and deposition possible.
Quantifying the heterogeneity of the tectonic stress field using borehole data
Schoenball, Martin; Davatzes, Nicholas C.
2017-01-01
The heterogeneity of the tectonic stress field is a fundamental property which influences earthquake dynamics and subsurface engineering. Self-similar scaling of stress heterogeneities is frequently assumed to explain characteristics of earthquakes such as the magnitude-frequency relation. However, observational evidence for such scaling of the stress field heterogeneity is scarce.We analyze the local stress orientations using image logs of two closely spaced boreholes in the Coso Geothermal Field with sub-vertical and deviated trajectories, respectively, each spanning about 2 km in depth. Both the mean and the standard deviation of stress orientation indicators (borehole breakouts, drilling-induced fractures and petal-centerline fractures) determined from each borehole agree to the limit of the resolution of our method although measurements at specific depths may not. We find that the standard deviation in these boreholes strongly depends on the interval length analyzed, generally increasing up to a wellbore log length of about 600 m and constant for longer intervals. We find the same behavior in global data from the World Stress Map. This suggests that the standard deviation of stress indicators characterizes the heterogeneity of the tectonic stress field rather than the quality of the stress measurement. A large standard deviation of a stress measurement might be an expression of strong crustal heterogeneity rather than of an unreliable stress determination. Robust characterization of stress heterogeneity requires logs that sample stress indicators along a representative sample volume of at least 1 km.
Velocity field statistics and tessellation techniques : Unbiased estimators of Omega
Van de Weygaert, R; Bernardeau, F; Muller,; Gottlober, S; Mucket, JP; Wambsganss, J
1998-01-01
We describe two new - stochastic-geometrical - methods to obtain reliable velocity field statistics from N-body simulations and from any general density and velocity fluctuation field sampled at a discrete set of locations. These methods, the Voronoi tessellation method and Delaunay tessellation met
Donald D. Anderson
2012-01-01
Full Text Available Recent findings suggest that contact stress is a potent predictor of subsequent symptomatic osteoarthritis development in the knee. However, much larger numbers of knees (likely on the order of hundreds, if not thousands need to be reliably analyzed to achieve the statistical power necessary to clarify this relationship. This study assessed the reliability of new semiautomated computational methods for estimating contact stress in knees from large population-based cohorts. Ten knees of subjects from the Multicenter Osteoarthritis Study were included. Bone surfaces were manually segmented from sequential 1.0 Tesla magnetic resonance imaging slices by three individuals on two nonconsecutive days. Four individuals then registered the resulting bone surfaces to corresponding bone edges on weight-bearing radiographs, using a semi-automated algorithm. Discrete element analysis methods were used to estimate contact stress distributions for each knee. Segmentation and registration reliabilities (day-to-day and interrater for peak and mean medial and lateral tibiofemoral contact stress were assessed with Shrout-Fleiss intraclass correlation coefficients (ICCs. The segmentation and registration steps of the modeling approach were found to have excellent day-to-day (ICC 0.93–0.99 and good inter-rater reliability (0.84–0.97. This approach for estimating compartment-specific tibiofemoral contact stress appears to be sufficiently reliable for use in large population-based cohorts.
Estimating of pulsed electric fields using optical measurements.
Flanagan, Timothy McGuire; Chantler, Gary.
2013-09-01
We performed optical electric field measurements ion nanosecond time scales using the electrooptic crystal beta barium borate (BBO). Tests were based on a preliminary bench top design intended to be a proofofprinciple stepping stone towards a modulardesign optical Efield diagnostic that has no metal in the interrogated environment. The long term goal is to field a modular version of the diagnostic in experiments on large scale xray source facilities, or similarly harsh environments.
Castillo, D. A., [Department of Geology and Geophysics, University of Adelaide (Australia); Younker, L.W. [Lawrence Livermore National Lab., CA (United States)
1997-01-30
Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.
Research was conducted in northern Colorado in 2011 to estimate the Crop Water Stress Index (CWSI) and actual water transpiration (Ta) of maize under a range of irrigation regimes. The main goal was to obtain these parameters with minimum instrumentation and measurements. The results confirmed that ...
Yang, Xiaobin; Li, Xiuhong; He, Yafeng; Wang, Xiaojun; Xu, Bo
2017-04-01
A multiphysics model for the numerical computation of stresses, trapped field and temperature distribution of a infinite long superconducting cylinder is proposed, based on which the stresses, including the thermal stresses and mechanical stresses due to Lorentz force, and trapped fields in the superconductor subjected to pulsed magnetic fields are analyzed. By comparing the results under pulsed magnetic fields with different pulse durations, it is found that the both the mechanical stress due to the electromagnetic force and the thermal stress due to temperature gradient contribute to the total stress level in the superconductor. For pulsed magnetic field with short durations, the thermal stress is the dominant contribution to the total stress, because the heat generated by AC-loss builds up significant temperature gradient in such short durations. However, for a pulsed field with a long duration the gradient of temperature and flux, as well as the maximal tensile stress, are much smaller. And the results of this paper is meaningful for the design and manufacture of superconducting permanent magnets.
Estimating relic magnetic fields from CMB temperature correlations
Giovannini, Massimo
2009-01-01
The temperature and polarization inhomogeneities of the Cosmic Microwave Background might bear the mark of pre-decoupling magnetism. The parameters of a putative magnetized background are hereby estimated from the observed temperature autocorrelation as well as from the measured temperature-polarization cross-correlation.
Automatic Pain Intensity Estimation using Heteroscedastic Conditional Ordinal Random Fields
Rudovic, Ognjen; Pavlovic, Vladimir; Pantic, Maja
2013-01-01
Automatic pain intensity estimation from facial images is challenging mainly because of high variability in subject-specific pain expressiveness. This heterogeneity in the subjects causes their facial appearance to vary significantly when experiencing the same pain level. The standard classification
Neural Conditional Ordinal Random Fields for Agreement Level Estimation
Rakicevic, Nemanja; Rudovic, Ognjen; Petridis, Stavros; Rakicevic, N.; Rudovic, O.; Petrids, S.; Pantic, Maja
2015-01-01
We present a novel approach to automated estimation of agreement intensity levels from facial images. To this end, we employ the MAHNOB Mimicry database of subjects recorded during dyadic interactions, where the facial images are annotated in terms of agreement intensity levels using the Likert scal
Automatic Pain Intensity Estimation using Heteroscedastic Conditional Ordinal Random Fields
Rudovic, Ognjen; Pavlovic, Vladimir; Pantic, Maja
Automatic pain intensity estimation from facial images is challenging mainly because of high variability in subject-specific pain expressiveness. This heterogeneity in the subjects causes their facial appearance to vary significantly when experiencing the same pain level. The standard classification
Bed shear stress estimation on an open intertidal flat using in situ measurements
Zhu, Q.; van Prooijen, B. C.; Wang, Z. B.; Ma, Y. X.; Yang, S. L.
2016-12-01
Accurate estimations for the bed shear stress are essential to predict the erosion and deposition processes in estuaries and coasts. This study used high-frequency in situ measurements of water depths and near-bed velocities to estimate bed shear stress on an open intertidal flat in the Yangtze Delta, China. To determine the current-induced bed shear stress (τc) the in situ near-bed velocities were first decomposed from the turbulent velocity into separate wave orbital velocities using two approaches: a moving average (MA) and energy spectrum analysis (ESA). τc was then calculated and evaluated using the log-profile (LP), turbulent kinetic energy (TKE), modified TKE (TKEw), Reynolds stress (RS), and inertial dissipation (ID) methods. Wave-induced bed shear stress (τw) was estimated using classic linear wave theory. The total bed shear stress (τcw) was determined based on the Grant-Madsen wave-current interaction model (WCI). The results demonstrate that when the ratio of significant wave height to water depth (Hs/h) is greater than 0.25, τcw is significantly overestimated because the vertical velocity fluctuations are contaminated by the surface waves generated by high winds. In addition, wind enhances the total bed shear stress as a result of the increases in both τw and τc generated by the greater wave height and reinforcing of vertical turbulence, respectively. From a comparison of these various methods, the TKEw method associated with ESA decomposition was found to be the best approach because: (1) this method generates the highest mean index of agreement; (2) it uses vertical velocities that are less affected by Doppler noise; and (3) it is less sensitive to the near-bed stratification structure and uncertainty in bed location and roughness.
Koo, Young Do; Yoo, Kwae Hwan; Na, Man Gyun [Dept. of Nuclear Engineering, Chosun University, Gwangju (Korea, Republic of)
2017-06-15
Residual stress is a critical element in determining the integrity of parts and the lifetime of welded structures. It is necessary to estimate the residual stress of a welding zone because residual stress is a major reason for the generation of primary water stress corrosion cracking in nuclear power plants. That is, it is necessary to estimate the distribution of the residual stress in welding of dissimilar metals under manifold welding conditions. In this study, a cascaded support vector regression (CSVR) model was presented to estimate the residual stress of a welding zone. The CSVR model was serially and consecutively structured in terms of SVR modules. Using numerical data obtained from finite element analysis by a subtractive clustering method, learning data that explained the characteristic behavior of the residual stress of a welding zone were selected to optimize the proposed model. The results suggest that the CSVR model yielded a better estimation performance when compared with a classic SVR model.
Yu, Guozhu; Carstensen, Carsten
2011-01-01
Assumed stress hybrid methods are known to improve the performance of standard displacement-based finite elements and are widely used in computational mechanics. The methods are based on the Hellinger-Reissner variational principle for the displacement and stress variables. This work analyzes two existing 4-node hybrid stress quadrilateral elements due to Pian and Sumihara [Int. J. Numer. Meth. Engng, 1984] and due to Xie and Zhou [Int. J. Numer. Meth. Engng, 2004], which behave robustly in numerical benchmark tests. For the finite elements, the isoparametric bilinear interpolation is used for the displacement approximation, while different piecewise-independent 5-parameter modes are employed for the stress approximation. We show that the two schemes are free from Poisson-locking, in the sense that the error bound in the a priori estimate is independent of the relevant Lame constant $\\lambda$. We also establish the equivalence of the methods to two assumed enhanced strain schemes. Finally, we derive reliable ...
Reducing thermal mismatch stress in anodically bonded silicon-glass wafers: theoretical estimation
Sinev, Leonid S.; Ryabov, Vladimir T.
2017-01-01
This paper reports the theoretical study and estimations of thermal mismatch stress reduction in anodically bonded silicon-glass stacks by justifiable selection of bonding temperature and glass thickness. This can be done only after prior thorough study of temperature dependence of the linear thermal expansion coefficient of the glass and silicon to be used. We show by analyzing such a dependence of several glass brands that the usual idea of decreasing the bonding process temperature as a solution to the thermal mismatch stress problem can be a failure. Interchanging glass brands during device design is shown to produce very contrasting changes in residual stresses. These results are in good agreement with finite-element modeling. This paper reports there is proportion between glass and silicon wafer thicknesses minimizing thermal mismatch stress at unbonded side of the silicon independently of the bonding or working temperatures chosen.
Earthquakes focal mechanism and stress field pattern in the northeastern part of Egypt
Emad K. Mohamed
2015-12-01
The inversion technique scheme is used also in the present study for determining the regional stress field parameters for earthquake focal mechanism solutions based on the grid search method of Gephart and Forsyth (1984. The Results of the stress tensor using focal mechanisms of recent earthquakes show a prevailed tension stress field in N52°E, N41°E and N52°E for the northern Red Sea, Gulf of Suez and Gulf of Aqaba zone respectively.
Mechanical Pre Stressing a Transducer through a Negative DC Biasing Field
2017-04-21
interesting concept but would not work under high-drive conditions. 17 (18 blank) BIBLIOGRAPHY Butler, S.C., “MLTRT Element FEA Dynamic Stress ...NUWC-NPT Technical Report 12,224 21 April 2017 Mechanical Pre- Stressing a Transducer through a Negative DC Biasing Field Stephen C...TITLE AND SUBTITLE Mechanical Pre- Stressing a Transducer through a Negative DC Biasing Field 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c
Effect of Visual Field Presentation on Action Planning (Estimating Reach) in Children
Gabbard, Carl; Cordova, Alberto
2012-01-01
In this article, the authors examined the effects of target information presented in different visual fields (lower, upper, central) on estimates of reach via use of motor imagery in children (5-11 years old) and young adults. Results indicated an advantage for estimating reach movements for targets placed in lower visual field (LoVF), with all…
Theorems on Estimating Perturbative Coefficients in Quantum Field Theory and Statistical Physics
Samuel, Mark
2003-06-25
The authors present rigorous proofs for several theorems on using Pade approximants to estimate coefficients in Perturbative Quantum Field Theory and Statistical Physics. As a result, they find new trigonometric and other identities where the estimates based on this approach are exact. They discuss hypergeometric functions, as well as series from both Perturbative Quantum Field Theory and Statistical Physics.
GHULAM; Abduwasit; LI; Zhao-Liang; QIN; QiMing; TONG; QingXi; WANG; JiHua; KASIMU; Alimujiang; ZHU; Lin
2007-01-01
In this paper, a new method for canopy water content (FMC) estimation for highly vegetated surfaces- shortwave infrared perpendicular water stress index (SPSI) is developed using NIR, SWIR wavelengths of Enhanced Thematic Mapper Plus (ETM+) on the basis of spectral features and distribution of surface targets with different water conditions in NIR-SWIR spectral space. The developed method is further explored with radiative transfer simulations using PROSPECT, Lillesaeter, SailH and 6S. It is evident from the results of validation derived from satellite synchronous field measurements that SPSI is highly correlated with FMC, coefficient of determination (R squared) and root mean square error are 0.79 and 26.41%. The paper concludes that SPSI has a potential in vegetation water content estimation in terms of FMC.
覃文洁; 张儒华; 左正兴
2004-01-01
The adaptive FEM analysis of the temperature field of the piston in one diesel engine is given by using the ANSYS software. By making full use of the post results provided by the software, the posteriori error estimation and adaptive accuracy meshing algorithm is developed. So the blindness of the mesh design through experiences can be avoided, and the accuracy requirement is adapted to the relative temperature gradient distribution across the entire domain. Therefore the meshes and solutions can be obtained at the same time. Based on the temperature field analysis, the thermal stress and deformation fields are calculated as well. The results show that the stress concentrates on the edge of the piston pin boss and the inside surface of the first ring groove, and the deformation of the head of the piston is greatest. But the difference between the long and short axes of the bottom cross section is greatest.
The DTFE public software: The Delaunay Tessellation Field Estimator code
Cautun, Marius C.; van de Weygaert, Rien
2011-01-01
We present the DTFE public software, a code for reconstructing fields from a discrete set of samples/measurements using the maximum of information contained in the point distribution. The code is written in C++ using the CGAL library and is parallelized using OpenMP. The software was designed for th
The DTFE public software : The Delaunay Tessellation Field Estimator code
Cautun, Marius C.; van de Weygaert, Rien
2011-01-01
We present the DTFE public software, a code for reconstructing fields from a discrete set of samples/measurements using the maximum of information contained in the point distribution. The code is written in C++ using the CGAL library and is parallelized using OpenMP. The software was designed for th
Closed form maximum likelihood estimator of conditional random fields
Zhu, Zhemin; Hiemstra, Djoerd; Apers, Peter M.G.; Wombacher, Andreas
2013-01-01
Training Conditional Random Fields (CRFs) can be very slow for big data. In this paper, we present a new training method for CRFs called {\\em Empirical Training} which is motivated by the concept of co-occurrence rate. We show that the standard training (unregularized) can have many maximum likeliho
Direct magnetic field estimation based on echo planar raw data.
Testud, Frederik; Splitthoff, Daniel Nicolas; Speck, Oliver; Hennig, Jürgen; Zaitsev, Maxim
2010-07-01
Gradient recalled echo echo planar imaging is widely used in functional magnetic resonance imaging. The fast data acquisition is, however, very sensitive to field inhomogeneities which manifest themselves as artifacts in the images. Typically used correction methods have the common deficit that the data for the correction are acquired only once at the beginning of the experiment, assuming the field inhomogeneity distribution B(0) does not change over the course of the experiment. In this paper, methods to extract the magnetic field distribution from the acquired k-space data or from the reconstructed phase image of a gradient echo planar sequence are compared and extended. A common derivation for the presented approaches provides a solid theoretical basis, enables a fair comparison and demonstrates the equivalence of the k-space and the image phase based approaches. The image phase analysis is extended here to calculate the local gradient in the readout direction and improvements are introduced to the echo shift analysis, referred to here as "k-space filtering analysis." The described methods are compared to experimentally acquired B(0) maps in phantoms and in vivo. The k-space filtering analysis presented in this work demonstrated to be the most sensitive method to detect field inhomogeneities.
Developing and evaluating rapid field methods to estimate peat carbon
Rodney A. Chimner; Cassandra A. Ott; Charles H. Perry; Randall K. Kolka
2014-01-01
Many international protocols (e.g., REDD+) are developing inventories of ecosystem carbon stocks and fluxes at country and regional scales, which can include peatlands. As the only nationally implemented field inventory and remeasurement of forest soils in the US, the USDA Forest Service Forest Inventory and Analysis Program (FIA) samples the top 20 cm of organic soils...
Information channel capacity in the field theory estimation
Sładkowski, J., E-mail: jan.sladkowski@us.edu.pl [Department of Astrophysics and Cosmology, Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Syska, J., E-mail: jacek.syska@us.edu.pl [Department of Field Theory and Particle Physics, Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland)
2012-12-03
The construction of the information capacity for the vector position parameter in the Minkowskian space–time is presented. This lays the statistical foundations of the kinematical term of the Lagrangian of the physical action for many field theory models, derived by the extremal physical information method of Frieden and Soffer.
Analysis of fracture patterns and local stress field variations in fractured reservoirs
Deckert, Hagen; Drews, Michael; Fremgen, Dominik; Wellmann, J. Florian
2010-05-01
A meaningful qualitative evaluation of permeabilities in fractured reservoirs in geothermal or hydrocarbon industry requires the spatial description of the existing discontinuity pattern within the area of interest and an analysis how these fractures might behave under given stress fields. This combined information can then be used for better estimating preferred fluid pathway directions within the reservoir, which is of particular interest for defining potential drilling sites. A description of the spatial fracture pattern mainly includes the orientation of rock discontinuities, spacing relationships between single fractures and their lateral extent. We have examined and quantified fracture patterns in several outcrops of granite at the Costa Brava, Spain, and in the Black Forest, Germany, for describing reservoir characteristics. For our analysis of fracture patterns we have used photogrammetric methods to create high-resolution georeferenced digital 3D images of outcrop walls. The advantage of this approach, compared to conventional methods for fracture analysis, is that it provides a better 3D description of the fracture geometry as the entity of position, extent and orientation of single fractures with respect to their surrounding neighbors is conserved. Hence for instance, the method allows generating fracture density maps, which can be used for a better description of the spatial distribution of discontinuities in a given outcrop. Using photogrammetric techniques also has the advantage to acquire very large data sets providing statistically sound results. To assess whether the recorded discontinuities might act as fluid pathways information on the stress field is needed. A 3D model of the regional tectonic structure was created and the geometry of the faults was put into a mechanical 3D Boundary Element (BE) Model. The model takes into account the elastic material properties of the geological units and the orientation of single fault segments. The
Anomalies of Density, Stresses, and the Gravitational Field in the Interior of Mars
Chuikova, N A; Maksimova, T G; 10.3103/S0027134912020075
2012-01-01
We determined the possible compensation depths for relief harmonics of different degrees and orders. The relief is shown to be completely compensated within the depth range of 0 to 1400 km. The lateral distributions of compensation masses are determined at these depths and the maps are constructed. The possible nonisostatic vertical stresses in the crust and mantle of Mars are estimated to be 64 MPa in compression and 20 MPa in tension. The relief anomalies of the Tharsis volcanic plateau and symmetric feature in the eastern hemisphere could have arisen and been maintained dynamically due to two plumes in the mantle substance that are enriched with fluids. The plumes that originate at the core of Mars can arise and be maintained by the anomalies of the inner gravitational field achieving +800 mGal in the region of plume formation, - 1200 mGal above the lower mantle-core transition layer, and -1400 mGal at the crust.
An objective estimation of impurities in oil field stagnant waters
Abashev, R.G.; Runets, S.A.
1984-01-01
Studies and an analysis of published materials are used to establish the predominant role of the mechanical impurities of various origins covered by layers of the heavy components of petroleum products in reducing the injectivity of injection wells for injecting stagnant waters containing concretions. A method is proposed for determining the impurities in the oil field stagnant waters used for flooding; this method makes it possible to obtain more reliable results on the concentration of the concretions responsible in such conditions for the drop in the injectivity of the formation reservoirs. A comparative evaluation of the results from an analysis of the impurities determined by the existing method and the proposed method is given. This method is useful in oil field laboratories in the systematic quality control over injected waters.
Recursion and growth estimates in renormalizable quantum field theory
Kreimer, D; Kreimer, Dirk; Yeats, Karen
2006-01-01
In this paper we show that there is a Lipatov bound for the radius of convergence for superficially divergent one-particle irreducible Green functions in a renormalizable quantum field theory if there is such a bound for the superficially convergent ones. The radius of convergence turns out to be ${\\rm min}\\{\\rho,1/b_1\\}$, where $\\rho$ is the bound on the convergent ones, the instanton radius, and $b_1$ the first coefficient of the $\\beta$-function.
Estimation of cyclic stress-strain curves for low-alloy steel from hardness
R. Basan
2010-04-01
Full Text Available This article describes investigations into the existence of correlation between experimentally determined cyclic parameters and hardness of quenched and tempered representative low-alloy steel 42CrMo4. A good correlation was found to exist between cyclic strength coefficient K’ and Brinell hardness HB, but not between cyclic strain hardening exponent n‘ and hardness HB. Nevertheless, good agreement between calculated and experimental cyclic stress-strain curves shows that cyclic parameters i.e. cyclic stress-strain curves of the investigated steel can be successfully estimated from its hardness.
Huang, Haihong, E-mail: huanghaihong@hfut.edu.cn; Yang, Cheng; Qian, Zhengchun; Han, Gang; Liu, Zhifeng
2016-10-15
Stress can induce a spontaneous magnetic field in ferromagnetic steel under the excitation of geomagnetic field. In order to investigate the impact of applied magnetic field and tensile stress on variation of the residual magnetic signals on the surface of ferromagnetic materials, static tensile tests of Q235 structural steel were carried out, with the normal component of the residual magnetic signals, H{sub p}(y), induced by applied magnetic fields with different intensities measured through the tensile tests. The H{sub p}(y), its slope coefficient K{sub S} and maximum gradient K{sub max} changing with the applied magnetic field H and tensile stress were observed. Results show that the magnitude of H{sub p}(y) and its slope coefficient K{sub S} increase linearly with the increase of stress in the elastic deformation stage. Under yield stress, H{sub p}(y) and K{sub S} reach its maximum, and then decrease slightly with further increase of stress. Applied magnetic field affects the magnitude of H{sub p}(y) instead of changing the signal curve′s profile; and the magnitude of H{sub p}(y), K{sub S}, K{sub max} and the change rate of K{sub S} increase with the increase of applied magnetic field. The phenomenon is also discussed from the viewpoint of magnetic charge in ferromagnetic materials. - Highlights: • We investigated how applied magnetic field and tensile stress impact H{sub p}(y) signals. • Magnitude of H{sub p}(y), K{sub S} and K{sub max} increase with the increase of applied magnetic field. • Both applied magnetic field and tensile stress impact material magnetic permeability. • Applied magnetic field can help to evaluate the stress distribution of components.
End Late Paleozoic tectonic stress field in the southern edge of Junggar Basin
Wei Ju
2012-09-01
Full Text Available This paper presents the end Late Paleozoic tectonic stress field in the southern edge of Junggar Basin by interpreting stress-response structures (dykes, folds, faults with slickenside and conjugate joints. The direction of the maximum principal stress axes is interpreted to be NW–SE (about 325°, and the accommodated motion among plates is assigned as the driving force of this tectonic stress field. The average value of the stress index R′ is about 2.09, which indicates a variation from strike-slip to compressive tectonic stress regime in the study area during the end Late Paleozoic period. The reconstruction of the tectonic field in the southern edge of Junggar Basin provides insights into the tectonic deformation processes around the southern Junggar Basin and contributes to the further understanding of basin evolution and tectonic settings during the culmination of the Paleozoic.
Characteristics of in situ stress field at Qingshui coal mine
Yang Xiaojie; Pang Jiewen; Lou Haopeng; Fan Lipeng
2015-01-01
In this study, the characteristics of geological structure at Qingshui coal mine were analyzed. And the hollow inclusion strain cell overcoring method was used to obtain the in situ stress. The effect of in situ stress on the stability of soft rock roadway was analyzed. The results show that the maximum principal stress is in the horizontal direction with a northeast orientation and has a value of about 1.2–1.9 times larger than gravity; the right side of roadway roof and floor is easily subject to serious deformation and failure, and the in situ stress is found to be a major factor. This paper presents important information for developing countermeasures against the large deformation of the soft rock roadway at Qingshui coal mine.
Prevention of brittle fracture of steel structures by controlling the local stress and strain fields
Moyseychik Evgeniy Alekseevich
Full Text Available In the article the author offers a classification of the methods to increase the cold resistance of steel structural shapes with a focus on the regulation of local fields of internal stresses and strains to prevent brittle fracture of steel structures. The need of a computer thermography is highlighted not only for visualization of temperature fields on the surface, but also to control the fields of residual stresses and strains in a controlled element.
Estimation of Temperature Fields in Local Tissues During Intracavitary Hyperthermia
NanQun; HuZhengjun; 等
1999-01-01
This paper presents a heat transfer model for the hyperthermia treatment of cervix cancer using a intracavitary microwave applicator and based on which the 3-D finite element simulation of the temperature fields have done,Before then the specific absorption rate(SAR) distribution for the transvaginal probe have been measured in a phantom.The variations of the parameters have been investigated.Too,for optimization.At last,the rsults of simulation are compared to that measured in the phantom and some instructive conclusions are presented for critical application.
ESTIMATION OF THE CONCRETE PAVEMENT TEMPERATURE FIELDS AND THEIR GRADIENTS
M. K. Pshembaev
2015-01-01
Full Text Available The heat fluxes impact on the road-dressing concrete surfacing under different regions climatic conditions of the construction and maintenance dramatically degrades their solidity, corroding-, shiftingand frost-resistance, and ultimately – the service durability. The source of deformation processes is the character of the gradient temperature fields in the road dressing materials developing with both protracted (static and short run (dynamic heat-and-mass impacts that forward destruction of the pavement surface layers being in contact with free air. In addition, pulsating hydrodynamic pressures appear in the pores of moisture-laden pavement as a result of the vehicular traffic that foster material structure disruption of the surface layers leading to irreversible deformation incipiency (cracks etc.. The authors report of developing a С++ computer program for temperature and gradient fields engineering evaluations of the road dressings made of materials with various surfacing and free-air thermophysical characteristics in line with boundary conditions of the 3rd kind for semi-bounded body. The paper presents the evaluation results in form of graphical curves of the temperature allocation along the surfacing thickness as function of its initial temperature and thermophysical characteristics of the concrete.
Use of Pyranometers to Estimate PV Module Degradation Rates in the Field: Preprint
Vignola, Frank; Peterson, Josh; Kessler, Rich; Mavromatakis, Fotis; Dooraghi, Mike; Sengupta, Manajit
2016-08-01
This paper describes a methodology that uses relative measurements to estimate the degradation rates of PV modules in the field. The importance of calibration and cleaning is illustrated. The number of years of field measurements needed to measure degradation rates with data from the field is cut in half using relative comparisons.
Use of Pyranometers to Estimate PV Module Degradation Rates in the Field
Vignola, Frank; Peterson, Josh; Kessler, Rich; Mavromatakis, Fotis; Dooraghi, Mike; Sengupta, Manajit
2016-06-05
This poster provides an overview of a methodology that uses relative measurements to estimate the degradation rates of PV modules in the field. The importance of calibration and cleaning is illustrated. The number of years of field measurements needed to measure degradation rates with data from the field is cut in half using relative comparisons.
Use of Pyranometers to Estimate PV Module Degradation Rates in the Field
Vignola, Frank; Peterson, Josh; Kessler, Rich; Mavromatakis, Fotis; Dooraghi, Mike; Sengupta, Manajit
2016-11-21
Methodology is described that uses relative measurements to estimate the degradation rates of PV modules in the field. The importance of calibration and cleaning is discussed. The number of years of field measurements needed to measure degradation rates with data from the field is cut in half using relative comparisons.
Palano, M.; Cannavò, F.; Ferranti, L.; Mattia, M.; Mazzella, M. E.
2011-12-01
We present an improved evaluation of the current strain and stress fields in the Southern Apennines (Italy) obtained through a careful analysis of geodetic, seismological and borehole data. In particular, our analysis provides an updated comparison between the accrued strain recorded by geodetic data, and the strain released by seismic activity in a region hit by destructive historical earthquakes. To this end, we have used nine years of GPS observations (2001-2010) from a dense network of permanent stations, a data set of 73 well-constrained stress indicators (borehole breakouts and focal mechanisms of moderate-to-large earthquakes) and published estimations of the geological strain accommodated by active faults in the region. Although geodetic data are generally consistent with seismic and geological information, previously unknown features of the current deformation in southern Italy emerge from this analysis. The newly obtained GPS velocity field supports the well-established notion of a dominant NE-SW-oriented extension concentrated in a ˜50-km-wide belt along the topographic relief of the Apennines, as outlined by the distribution of seismogenic normal faults. Geodetic deformation is, however, non-uniform along the belt, with two patches of higher strain-rate and shear-stress accumulation in the north (Matese Mountains) and in the south (Irpinia area). Low geodetic strain-rates are found in the Bradano basin and Apulia plateau to the east. Along the Ionian Sea margin of southern Italy, in southern Apulia and eastern Basilicata and Calabria, geodetic velocities indicate NW-SE extension that is consistent with active shallow-crustal gravitational motion documented by geological studies. In the west, along the Tyrrhenian margin of the Campania region, the tectonic geodetic field is disturbed by volcanic processes. Comparison between the magnitude of the geodetic and the seismic strain rates (computed using a long historical seismicity catalogue) allow detecting
Galanti, Eli; Durante, Daniele; Finocchiaro, Stefano; Iess, Luciano; Kaspi, Yohai
2017-07-01
The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulated Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.
Bahman Tarvirdizade
2014-01-01
Full Text Available We consider the estimation of stress-strength reliability based on lower record values when X and Y are independently but not identically inverse Rayleigh distributed random variables. The maximum likelihood, Bayes, and empirical Bayes estimators of R are obtained and their properties are studied. Confidence intervals, exact and approximate, as well as the Bayesian credible sets for R are obtained. A real example is presented in order to illustrate the inferences discussed in the previous sections. A simulation study is conducted to investigate and compare the performance of the intervals presented in this paper and some bootstrap intervals.
An easy and reliable automated method to estimate oxidative stress in the clinical setting.
Vassalle, Cristina
2008-01-01
During the last few years, reliable and simple tests have been proposed to estimate oxidative stress in vivo. Many of them can be easily adapted to automated analyzers, permitting the simultaneous processing of a large number of samples in a greatly reduced time, avoiding manual sample and reagent handling, and reducing variability sources. In this chapter, description of protocols for the estimation of reactive oxygen metabolites and the antioxidant capacity (respectively the d-ROMs and OXY Adsorbent Test, Diacron, Grosseto, Italy) by using the clinical chemistry analyzer SYNCHRON, CX 9 PRO (Beckman Coulter, Brea, CA, USA) is reported as an example of such an automated procedure that can be applied in the clinical setting. Furthermore, a calculation to compute a global oxidative stress index (Oxidative-INDEX), reflecting both oxidative and antioxidant counterparts, and, therefore, a potentially more powerful parameter, is also described.
Nondestructive testing and characterization of residual stress field using an ultrasonic method
Song, Wentao; Xu, Chunguang; Pan, Qinxue; Song, Jianfeng
2016-03-01
To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designed to conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.
Nondestructive Testing and Characterization of Residual Stress Field Using an Ultrasonic Method
SONG Wentao; XU Chunguang; PAN Qinxue; SONG Jianfeng
2016-01-01
To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designedto conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.
A rapid estimation of near field tsunami run-up
Riqueime, Sebastian; Fuentes, Mauricio; Hayes, Gavin; Campos, Jamie
2015-01-01
Many efforts have been made to quickly estimate the maximum run-up height of tsunamis associated with large earthquakes. This is a difficult task, because of the time it takes to construct a tsunami model using real time data from the source. It is possible to construct a database of potential seismic sources and their corresponding tsunami a priori.However, such models are generally based on uniform slip distributions and thus oversimplify the knowledge of the earthquake source. Here, we show how to predict tsunami run-up from any seismic source model using an analytic solution, that was specifically designed for subduction zones with a well defined geometry, i.e., Chile, Japan, Nicaragua, Alaska. The main idea of this work is to provide a tool for emergency response, trading off accuracy for speed. The solutions we present for large earthquakes appear promising. Here, run-up models are computed for: The 1992 Mw 7.7 Nicaragua Earthquake, the 2001 Mw 8.4 Perú Earthquake, the 2003Mw 8.3 Hokkaido Earthquake, the 2007 Mw 8.1 Perú Earthquake, the 2010 Mw 8.8 Maule Earthquake, the 2011 Mw 9.0 Tohoku Earthquake and the recent 2014 Mw 8.2 Iquique Earthquake. The maximum run-up estimations are consistent with measurements made inland after each event, with a peak of 9 m for Nicaragua, 8 m for Perú (2001), 32 m for Maule, 41 m for Tohoku, and 4.1 m for Iquique. Considering recent advances made in the analysis of real time GPS data and the ability to rapidly resolve the finiteness of a large earthquake close to existing GPS networks, it will be possible in the near future to perform these calculations within the first minutes after the occurrence of similar events. Thus, such calculations will provide faster run-up information than is available from existing uniform-slip seismic source databases or past events of pre-modeled seismic sources.
Intraplate stress field in South America from earthquake focal mechanisms
Assumpção, Marcelo; Dias, Fábio L.; Zevallos, Ivan; Naliboff, John B.
2016-11-01
We present an updated compilation of earthquake focal mechanisms in Brazil together with focal mechanisms from the sub-Andean region (mainly from global CMT catalogs). All earthquakes in the sub-Andean region show reverse (majority) or strike-slip faulting mechanisms. Focal mechanisms in Brazil show reverse, strike-slip and normal faulting. Focal mechanisms of nearby earthquakes in the same tectonic environment were grouped and inverted for the stress tensor. In the sub-Andean region, stresses are compressional, as expected, with the principal major compression (S1) roughly E-W, on average. A slight rotation of S1 can be observed and is controlled by the orientation of the Andean plateau. In the sub-Andean region, the intermediate principal stress (S2) is also compressional (i.e., larger than the lithostatic pressure, Sv), a feature that is not always reproduced in numerical models published in the literature. In mid-plate South America stresses seem to vary in nature and orientation. In SE Brazil and the Chaco-Pantanal basins, S1 tends to be oriented roughly E-W with S2 approximately equal to S3. This stress pattern changes to purely compressional (both SHmax and Shmin larger than Sv) in the São Francisco craton. A rotation of SHmax from E-W to SE-NW is suggested towards the Amazon region. Along the Atlantic margin, the regional stresses are very much affected by coastal effects (due to continent/ocean spreading stresses as well as flexural effects from sediment load at the continental margin). This coastal effect tends to make SHmax parallel to the coastline and Shmin (usually S3) perpendicular to the coastline. Few breakout data and in-situ measurements are available in Brazil and are generally consistent with the pattern derived from the earthquake focal mechanisms. Although numerical models of global lithospheric stresses tend to reproduce the main large-scale features in most mid-plate areas, the S1 rotation from ∼E-W in SE Brazil to SE-NW in the Amazon
WANG; Yi; SU; Yanjing; CHU; Wuyang; QIAO; Lijie
2005-01-01
The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen. The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil, i.e. stress corrosion cracking, decrease linearly with the increasing applied electric field, either positive or negative. For the PZT-5 ferroelectric ceramics, delayed fracture in silicone oil under sustained positive or negative field can occur, and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor. The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes fieldenhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.
Jamshidian, M., E-mail: mostafa.jamshidian@gmail.com [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Institute of Structural Mechanics, Bauhaus-University Weimar, Marienstrasse 15, 99423 Weimar (Germany); Rabczuk, T., E-mail: timon.rabczuk@uni-weimar.de [Institute of Structural Mechanics, Bauhaus-University Weimar, Marienstrasse 15, 99423 Weimar (Germany); School of Civil, Environmental and Architectural Engineering, Korea University, Seoul (Korea, Republic of)
2014-03-15
We establish the correlation between the diffuse interface and sharp interface descriptions for stressed grain boundary migration by presenting analytical solutions for stressed migration of a circular grain boundary in a bicrystalline phase field domain. The validity and accuracy of the phase field model is investigated by comparing the phase field simulation results against analytical solutions. The phase field model can reproduce precise boundary kinetics and stress evolution provided that a thermodynamically consistent theory and proper expressions for model parameters in terms of physical material properties are employed. Quantitative phase field simulations are then employed to investigate the effect of microstructural length scale on microstructure and texture evolution by stressed grain growth in an elastically deformed polycrystalline aggregate. The simulation results reveal a transitional behaviour from normal to abnormal grain growth by increasing the microstructural length scale.
Recent tectonic stress field zoning in Sichuan-Yunnan region and its dynamic interest
CUI Xiao-feng; XIE Fu-ren; ZHANG Hong-yan
2006-01-01
In this paper, we have carefully determined the stress zones in the Sichuan-Yunnan region with reference to the in-situ stress data of hydraulic fracturing and the inverted fault slip data by using the step-by-step convergence method for stress zoning based on focal mechanism solutions. The results indicate that the tectonic stress field in the Sichuan-Yunnan region is divided into 3 stress zones by 2 approximately parallel NNW-trending stress transition belts. The area between the 2 belts is the Sichuan-Yunnan stress zone where the maximum principal stress σ1 is just in the NNW direction. The eastern boundary of Sichuan-Yunnan stress zone (the eastern stress transition belt) is basically consistent with the eastern boundary of Sichuan-Yunnan rhombic block. The western boundary of Sichuan-Yunnan stress zone (the western stress transition belt) is not totally consistent with the western boundary of Sichuan-Yunnan rhombic block. The northern segment of the western stress transition belt extends basically along the Jinshajiang fault and accords with the western boundary of Sichuan-Yunnan rhombic block, while its southern segment does not extend along the southwestern boundary of the rhombic block, i.e., Honghe fault and converge with the eastern stress transition belt, but stretches continuously in the NNW direction and accords with the Yingpanshan fault. We therefore consider that under the combined influence from the northward motion of India Plate, the southeastward shift of east Qinghai-Xizang Plateau and the strong obstruction of South China block, the tectonic stress field in the Sichuan-Yunnan region might not be totally controlled by the previous tectonic frame and new stress transition belt may have possibly formed.
Stress-energy of a quantized scalar field in static wormhole spacetimes
Taylor, B E; Anderson, P R; Taylor, Brett E.; Hiscock, William A.; Anderson, Paul R.
1997-01-01
Static traversable wormhole solutions of the Einstein equations require ``exotic'' matter which violates the weak energy condition. The vacuum stress-energy of quantized fields has been proposed as the source for this matter. Using the Dewitt-Schwinger approximation, analytic expressions for the stress-energy of a quantized massive scalar field are calculated in five static spherically symmetric Lorentzian wormhole spacetimes. We find that in all cases, for both minimally and conformally coupled scalar fields, the stress-energy does not have the properties needed to support the wormhole geometry.
Measurement of the stress field of a tunnel through its rock EMR
Qiu, Liming; Wang, Enyuan; Song, Dazhao; Liu, Zhentang; Shen, Rongxi; Lv, Ganggang; Xu, Zhaoyong
2017-08-01
In order to quantitatively study the relationship between the disturbance stress of coal mine roadways and the electromagnetic radiation (EMR) of rocks, and further evaluate their internal stress distributions, we first examined the characteristics of EMR signals emitted from rock mass under uniaxial compression, analyzed the relationship between the stress inside the rock mass and its emitted EMR intensity, and put forward a new disturbance stress testing method by monitoring the EMR from the rock mass to retrieve its surrounding stress field. Then, we applied the method to monitor EMR intensity from the no.11803 rock roadway of the Nuodong coal mine, China, and inversely retrieved its stress field. Lastly, we analyzed the causes of local stress anomalies in the Nuodong area by testing the EMR intensity of its nearby areas, and we examined the geology of the whole region. The results showed that: (1) in the rock roadway and the surrounding area of the Nuodong coal mine, the disturbance stress was in the range of 4.8 ∼ 9.1 MPa, the angle between the direction of the stress field and the horizontal plane of the roadway was 35 ± 2.5°, the lateral pressure coefficient was 1.30 ∼ 1.57 (2) the Laoguishan and Yulong anticlines in the vicinity of the Nuodong coal mine caused great horizontal tectonic stress in the region, and the existence of the auxiliary roadway and F12 normal fault resulted in the formation of two high stress zones in the no.11803 rock roadway. Overall, monitoring the EMR from rock mass could ascertain the state, direction, size and distribution of disturbance stress in a roadway and further obtain the distribution of the stress field of an underground structure.
Schwab, D.; Bidgoli, T.; Taylor, M. H.
2015-12-01
South-central Kansas has experienced an unprecedented increase in seismic activity since 2013. The spatial and temporal relationship of the seismicity with brine disposal operations has renewed interest in the role of fluids in fault reactivation. This study focuses on determining the suitability of CO2 injection into a Cambro-Ordovician reservoir for long-term storage and a Mississippian reservoir for enhanced oil recovery in Wellington Field, Sumner County, Kansas. Our approach for determining the potential for induced seismicity has been to (1) map subsurface faults and estimate in-situ stresses, (2) perform slip and dilation tendency analysis to identify optimally-oriented faults relative to the estimated stress field, and (3) monitor surface deformation through cGPS data and InSAR imaging. Through the use of 3D seismic reflection data, 60 near vertical, NNE-striking faults have been identified. The faults range in length from 140-410 m and have vertical separations of 3-32m. A number of faults appear to be restricted to shallow intervals, while others clearly cut the top basement reflector. Drilling-induced tensile fractures (N=78) identified from image logs and inversion of earthquake focal mechanism solutions (N=54) are consistent with the maximum horizontal stress (SHmax) oriented ~E-W. Both strike-slip and normal-slip fault plane solutions for earthquakes near the study area suggest that SHmax and Sv may be similar in magnitude. Estimates of stress magnitudes using step rate tests (Shmin = 2666 psi), density logs (Sv = 5308 psi), and calculations from wells with drilling induced tensile fractures (SHmax = 4547-6655 psi) are determined at the gauge depth of 4869ft. Preliminary slip and dilation tendency analysis indicates that faults striking 0°-20° are stable, whereas faults striking 26°-44° may have a moderate risk for reactivation with increasing pore-fluid pressure.
Temperature and stress fields produced by ultrasound-induced cavitation in a viscoelastic medium
Mancia, Lauren; Johnsen, Eric
2016-11-01
Ultrasound contrast agents can act as cavitation nuclei that mechanically damage surrounding tissue when they oscillate in diagnostic ultrasound. Encapsulated microbubbles have also been proposed as a means to improve the efficiency and efficacy of therapeutic ultrasound by increasing the rate of tissue heating. However, the thermal and mechanical effects of cavitation are difficult to distinguish from each other and to quantify experimentally as they often occur simultaneously. To address this challenge, we study the cavitation-induced temperature and stress fields produced by a spherical bubble oscillating in a Kelvin-Voigt viscoelastic medium with nonlinear elasticity using a model that also accounts for energy transport inside and outside the bubble. We find that the primary contribution to heating is viscous dissipation, which itself depends on both the material (viscosity) and the bubble dynamics. We examine the rate of viscous heating and the magnitude of stresses over a relevant range of tissue properties and waveform parameters to determine regimes where heating is expected to be dominant. A means of estimating the expected significance of viscous dissipation from given tissue properties and waveform parameters is proposed.
Kosch, Olaf; Steinhoff, Uwe; Trahms, Lutz; Trontelj, Zvonko; Jazbinšek, Vojko
2015-01-01
Comprehensive body surface potential mapping (BSPM) and magnetic field mapping (MFM) measurements have been carried out in order to improve the estimation of the current distribution generated by the human heart. Electric and magnetic fields and also the planar gradient of the magnetic field during the QRS complex were imaged as a time series of field maps. A model of the current distribution should explain the features of both BSPM and MFM. Simulated maps generated by a single dipole or a st...
Frassinetti, L.; Olofsson, K. E. J.; Fridström, R.; Setiadi, A. C.; Brunsell, P. R.; Volpe, F. A.; Drake, J.
2013-08-01
A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.
Stress fields of the San Andreas and Queen Charlotte transform faults
Kilty, Kevin T.
1981-08-01
Analytic solutions to the stress fields resulting from the San Andreas and Queen Charlotte transform faults may be found by applying conformal mappings to the generalized plane stress solution of stresses in a half-plane. The mean stress fields (one-half the trace of the stress tensor) found in this manner show a similarity to the deformation found in western Canada and the western United States. The results refute the hypothesis that Alaska acts as a continental buttress against deformation of the Canadian Cordillera. Moreover, these results imply that the differences in the tectonics of major transform boundaries are caused primarily by differences in lithospheric structure and differences in stress distribution along the plate boundaries.
Huang, Haihong; Yang, Cheng; Qian, Zhengchun; Han, Gang; Liu, Zhifeng
2016-10-01
Stress can induce a spontaneous magnetic field in ferromagnetic steel under the excitation of geomagnetic field. In order to investigate the impact of applied magnetic field and tensile stress on variation of the residual magnetic signals on the surface of ferromagnetic materials, static tensile tests of Q235 structural steel were carried out, with the normal component of the residual magnetic signals, Hp(y), induced by applied magnetic fields with different intensities measured through the tensile tests. The Hp(y), its slope coefficient KS and maximum gradient Kmax changing with the applied magnetic field H and tensile stress were observed. Results show that the magnitude of Hp(y) and its slope coefficient KS increase linearly with the increase of stress in the elastic deformation stage. Under yield stress, Hp(y) and KS reach its maximum, and then decrease slightly with further increase of stress. Applied magnetic field affects the magnitude of Hp(y) instead of changing the signal curve‧s profile; and the magnitude of Hp(y), KS, Kmax and the change rate of KS increase with the increase of applied magnetic field. The phenomenon is also discussed from the viewpoint of magnetic charge in ferromagnetic materials.
Method of estimating mechanical stress on Si body of MOSFET using drain–body junction current
Seo, Ji-Hoon; Kim, Gang-Jun; Son, Donghee; Lee, Nam-Hyun; Kang, Bongkoo
2017-01-01
A simple and accurate method of estimating the mechanical stress σ on the Si body of a MOSFET is proposed. This method measures the doping concentration of the body, N d, and the onset voltage V hl for the high-level injection of the drain–body junction, uses N d, the ideality factor η, and the Fermi potential ϕf ≈ V hl/2η to calculate the intrinsic carrier concentration n i of the Si body, and then uses the calculated n i to obtain the bandgap energy E g of the Si body. σ is estimated from E g using the deformation potential theory. The estimates of σ agree well with those obtained using previous methods. The proposed method requires one MOSFET, whereas the others require at least two MOSFETs, so the proposed method can give an absolute measurement of σ on the Si body of a MOSFET.
Optimal design of anchor cables for slope reinforcement based on stress and displacement fields
Guanghua Yang; Zhihui Zhong; Yucheng Zhang; Xudong Fu
2015-01-01
How to determine reasonable position and length of anchor cable is a frequently encountered but not well addressed problem in slope reinforcement projects. In this paper, the variable-modulus elastoplastic strength reduction method (SRM) is used to obtain the stress field, displacement field, and factor of safety of slope. Slope reinforcement using anchor cables is modeled by surface loading, i.e. different distributions of surface loading represent various reinforcement schemes. Optimal reinforcement scheme of anchor cables can be determined based on slope stress and displacement fields. By comparing the factor of safety and stress field before and after slope reinforcement, it is found that better rein-forcement results can be achieved if strong reinforcement is applied upon the regions with high stress and large displacement. This method can well optimize the arrangement of anchor cables. In addition, several cases are employed to verify the proposed method.
Biofeedback systems for stress reduction : Towards a bright future for a revitalized field
Broek, E.L. van den; Westerink, J.H.D.M.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. This article proposes biofeedback systems as a means to reduce stress. A concise state-of-the-art introduction on biofeedback systems is given. The field of mental
Biofeedback systems for stress reduction: Towards a Bright Future for a Revitalized Field
van den Broek, Egon; Westerink, Joyce H.D.M.; Conchon, E.; Correia, C.; Fred, A.; Gamboa, H.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. This article proposes biofeedback systems as a means to reduce stress. A concise state-ofthe-art introduction on biofeedback systems is given. The field of mental
Biofeedback for stress reduction: towards a brigth future for a revitalized field
Van den Broek, E.L.; Westerink, J.H.D.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. Thisarticle proposes biofeedback systems as a means to reduce stress. Aconcise state-ofthe-art introduction on biofeedback systems is given. The field of mental health
Biofeedback systems for stress reduction: Towards a Bright Future for a Revitalized Field
Broek, van den Egon L.; Westerink, Joyce H.D.M.; Conchon, E.; Correia, C.; Fred, A.; Gamboa, H.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. This article proposes biofeedback systems as a means to reduce stress. A concise state-ofthe-art introduction on biofeedback systems is given. The field of mental healt
Biofeedback for stress reduction: towards a brigth future for a revitalized field
Van den Broek, E.L.; Westerink, J.H.D.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. Thisarticle proposes biofeedback systems as a means to reduce stress. Aconcise state-ofthe-art introduction on biofeedback systems is given. The field of mental health
Biofeedback systems for stress reduction : Towards a bright future for a revitalized field
Broek, E.L. van den; Westerink, J.H.D.M.
2012-01-01
Stress has recently been baptized as the black death of the 21st century, which illustrates its threat to current health standards. This article proposes biofeedback systems as a means to reduce stress. A concise state-of-the-art introduction on biofeedback systems is given. The field of mental heal
Estimation of random fields from network observations. Technical report No. 26
Cabannes, A F
1979-06-01
When one has observed a random field Z at some points and recorded its values (network observations), a natural problem is to estimate Z at points where there are no observations. This dissertation deals first with this problem in an abstract setting, in m dimensions; later, it considers the estimation of a spatial two-dimensional random field. The problem then is one of constructing an estimated map of Z over a geographic area. For a given network of stations the quality of a map depends on the method of estimation. But for the given method of estimation the quality of a map depends on the choice of locations for the stations. This is the problem of network design. Both the study of methods of estimation and the problem of network design are addressed. 16 figures. (RWR)
Estimation of the magnetic field gradient tensor using the Swarm constellation
Kotsiaros, Stavros; Finlay, Chris; Olsen, Nils
2014-01-01
For the first time, part of the magnetic field gradient tensor is estimated in space by the Swarm mission. We investigate the possibility of a more complete estimation of the gradient tensor exploiting the Swarm constellation. The East-West gradients can be approximated by observations from...
Near field phased array DOA and range estimation of UHF RFID tags
Huiting, Jordy; Kokkeler, André B.J.; Smit, Gerard J.M.
2015-01-01
This paper presents a near field localization system based on a phased array for UHF RFID tags. To estimate angle and range the system uses a two-dimensional MUSIC algorithm. A four channel phased array is used to experimentally verify the estimation of angle and range for an EPC gen2 tag. The syste
Near field phased array DOA and range estimation of UHF RFID tags
Huiting, J.; Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria
2015-01-01
This paper presents a near field localization system based on a phased array for UHF RFID tags. To estimate angle and range the system uses a two-dimensional MUSIC algorithm. A four channel phased array is used to experimentally verify the estimation of angle and range for an EPC gen2 tag. The
Approximate stress-energy tensor of the massless spin-1/2 field in Schwarzschild spacetime
Matyjasek, J
2005-01-01
The approximate stress-energy tensor of the conformally invariant massless spin-1/2 field in the Hartle-Hawking state in the Schwarzschild spacetime is constructed. It is shown that by solving the conservation equation in conformal space and utilizing the regularity conditions in a physical metric one obtains the stress-energy tensor that is in a good agreement with the numerical calculations. The back reaction of the quantized field upon the spacetime metric is briefly discussed.
Stress field near interface crack tip of double dissimilar orthotropic composite materials
LI Jun-lin; ZHANG Shao-qin; YANG Wei-yang
2008-01-01
In this paper, double dissimilar orthotropic composite materials interracial crack is studied by constructing new stress functions and employing the method of com- posite material complex. When the characteristic equations' discriminants △1 >0 and △2 > 0, the theoretical formula of the stress field and the displacement field near the mode I interface crack tip are derived, indicating that there is no oscillation and inter- embedding between the interfaces of the crack.
Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs.
Apperson, K D
1991-11-01
Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region.
STUDY ON COUPLING MODEL OF SEEPAGE-FIELD AND STRESS-FIELD FOR ROLLED CONTROL CONCRETE DAM
GU Chong-shi; SU Huai-zhi; ZHOU Hong
2005-01-01
Based on the construction interfaces in rolled control concrete dam(RCCD),the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters.The principle on establishing the coupling model of seepage-field and stress-field for RCCd was presented.A 3-D Finite Element Method(FEM)program was developed.Study shows that such parameters as the thickness of construction interfaces ,the elastic ration and the Poisson's ratio obtained by tests and theoretical analysis are more resasonable ,the coupling model of seepage-field and stress-field for RCCD may indicate the coupling effect between the two fields scientifically,and the develpped 3-D FEM program can feflect the effect of the construction interfaces more adequately.According to the stydy,many scientific opinions are given both to analyze the influence of the construction interfaces to the dam's characteristic,and to reveal the interaction between the stress-field and the seepage-field.
A SO(3)-invariant variational method for depth field estimation based on inertial and camera data
Zarrouati, Nadege; Rouchon, Pierre
2011-01-01
In this paper, we use known camera motion associated to a video sequence of a static scene in order to estimate and incrementally refine the surrounding depth field. We exploit the SO(3)-invariance of brightness and depth fields dynamics to customize standard image processing techniques. Inspired by the Horn-Schunck method, we propose a SO(3)-invariant cost minimized by the depth field. For each time, this provides a diffusion equation on the unit Riemannian sphere that characterizes the estimated depth field. Written in pinhole coordinates, this scalar diffusion equation is numerically solved to provide in real time a depth field estimation of the entire field of view. On synthetic data, quantitative comparison with asymptotic observers merging direct optical flow estimation (by Horn-Schunck and TV-L1 methods) and camera motion illustrate the performance of the proposed method. Implementation on a real sequence of images shows that these estimations are accurate in regions where the depth field is continuous...
ZHOU Xiao; ZHI Guang; XU Yong; WANG Jing; YAN Guo-hui
2012-01-01
Background Coronary microcirculation reserve is an important field in the research of coronary artery disease,but it is difficult to identify clinically.Currently it is widely accepted that myocardial contrast echocardiography (MCE) is a safe,inexpensive method and has comparatively high image resolution.The present study used quantitative low-dose adenosine stress real-time (RT)-MCE to estimate myocardial perfusion and the coronary stenosis.Methods Forty-nine left ventricular (LV) segments from 14 unselected patients were divided into three groups according to the coronary angiography or CT angiography results:group 1 (n=20,41％) without significant stenosis (＜70％),group 2 (n=12,24％)with successful percutaneous coronary intervention (PCI),and group 3 (n=17,35％)with significant stenosis (＞70％).RT-MCE was performed in these patients with low-dose adenosine stress and continuous infusion of Sonovue.The replenishing curves were drawn according to the contrast density measured at the end-diastolic frame of every cardiac circle by ACQ software.Results Forty-nine LV segments with satisfactory image quality were picked for quantitative contrast echo analysis.The replenishing curves were analyzed at baseline and after stress.Perfusion of group 3 did not decrease significantly at baseline,and showed no improvement during adenosine stress and was significantly different from groups 1 and 2 (P ＜0.05).The A·β and β increased more significantly in group 1 than in groups 2 and 3 (P ＜0.05).In a receiver operating characteristic (ROC) curve analysis,A·β under adenosine stress ＜1.74 dB/s had a sensitivity and specificity of 71％ for diagnosis of coronary artery stenosis,reduced adenosine-induced rise (percentage of A·β ＜81％) had a sensitivity and specificity of 83％ and 79％ for the diagnosis of low-reserve,and β ＜54％ had a sensitivity of 86％ and specificity of 79％.Conclusions Rest perfusion of severely stenosed arteries may be normal
Li Jianwei; Liu Changyou; Zhao Tong
2016-01-01
This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain. This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine. The effects of gully ter-rain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress (g) at the location corresponding to the maximum vertical stress. Based on the function g=f(h), the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area, moderately affected area, or non-affected area. Working face 6106 in the Chuancao Gedan Mine had a coal bed depth<80 m and was located in what was identified as a signifi-cantly affected area. Hence, mining may cause sliding of the gully slope and increased loading (including significant dynamic loading) on the roof strata. Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope, and that dynamic loadings were observed upslope of the working face expansion, provided that the expanding direction of the working face is parallel to the gully.
Görgün, Ethem
2017-03-01
15 June 2013 M w 6.1 off-shore southern Crete earthquake and its aftershock sequence along Hellenic Subduction Zone are examined. Centroid moment tensors (CMTs) for 40 earthquakes with moment magnitudes ( M w) between 3.5 and 6.1 are determined by applying a waveform inversion method. The mainshock is shallow focus thrust event with a minor strike-slip component at a depth of 20 km. The seismic moment ( M o) of the mainshock is estimated as 2.07 × 1018 Nm, and rupture duration of the mainshock is 4 s. The focal mechanisms of aftershocks are mainly thrust faulting with a strike-slip component. The geometry of the moment tensors ( M w ≥ 3.5) reveals a thrust faulting regime with N-S trending direction of P axis in the entire activated region. According to high-resolution CMT solutions of the off-shore southern Crete earthquake sequence, one main cluster consisting of 40 events is revealed. The aftershock activity in the observation period between 15 June and 15 July 2013 extends from N to S and NW to SE directions. Seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of two segments. The subduction interface is clearly revealed with high-resolution hypocenter source relocation and moment tensor solution. The best-constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate (depth < 30 km) and is ranging from about 5-28 km depth. A stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the off-shore southern Crete stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NE-SW-oriented maximum horizontal compressive stress ( S H). According to variance of the stress tensor inversion, to first order, the southern Crete region is characterized by a homogeneous interplate stress field. We also investigate the Coulomb stress change associated with the mainshock to evaluate any significant
Preusser, T.; Droske, M.; Garbe, C. S.; Telea, A.; Rumpf, M.
2007-01-01
The estimation of optical flow fields from image sequences is incorporated in a Mumford-Shah approach for image denoising and edge detection. Possibly noisy image sequences are considered as input and a piecewise smooth image intensity, a piecewise smooth motion field, and a joint discontinuity set
Artificial force fields for multi-agent simulations of maritime traffic and risk estimation
Xiao, F.; Ligteringen, H.; Van Gulijk, C.; Ale, B.J.M.
2012-01-01
A probabilistic risk model is designed to estimate probabilities of collisions for shipping accidents in busy waterways. We propose a method based on multi-agent simulation that uses an artificial force field to model ship maneuvers. The artificial force field is calibrated by AIS data (Automatic Id
Sensor selection for parameterized random field estimation in wireless sensor networks
无
2011-01-01
We consider the random field estimation problem with parametric trend in wireless sensor networks where the field can be described by unknown parameters to be estimated. Due to the limited resources, the network selects only a subset of the sensors to perform the estimation task with a desired performance under the D-optimal criterion. We propose a greedy sampling scheme to select the sensor nodes according to the information gain of the sensors. A distributed algorithm is also developed by consensus-based ...
Pu, Yichao; Yang, Chao
2014-09-01
Urban vehicle emission models have been utilized to calculate pollutant concentrations at both microscopic and macroscopic levels based on vehicle emission rates which few researches have been able to validate. The objective of our research is to estimate urban roadside emissions and calibrate it with in-field measurement data. We calculated the vehicle emissions based on localized emission rates, and used an atmospheric dispersion model to estimate roadside emissions. A non-linear regression model was applied to calibrate the localized emission rates using in-field measurement data. With the calibrated emission rates, emissions on urban roadside can be estimated with a high accuracy.
Real-Time Personalized Monitoring to Estimate Occupational Heat Stress in Ambient Assisted Working
Pablo Pancardo
2015-07-01
Full Text Available Ambient Assisted Working (AAW is a discipline aiming to provide comfort and safety in the workplace through customization and technology. Workers’ comfort may be compromised in many labor situations, including those depending on environmental conditions, like extremely hot weather conduces to heat stress. Occupational heat stress (OHS happens when a worker is in an uninterrupted physical activity and in a hot environment. OHS can produce strain on the body, which leads to discomfort and eventually to heat illness and even death. Related ISO standards contain methods to estimate OHS and to ensure the safety and health of workers, but they are subjective, impersonal, performed a posteriori and even invasive. This paper focuses on the design and development of real-time personalized monitoring for a more effective and objective estimation of OHS, taking into account the individual user profile, fusing data from environmental and unobtrusive body sensors. Formulas employed in this work were taken from different domains and joined in the method that we propose. It is based on calculations that enable continuous surveillance of physical activity performance in a comfortable and healthy manner. In this proposal, we found that OHS can be estimated by satisfying the following criteria: objective, personalized, in situ, in real time, just in time and in an unobtrusive way. This enables timely notice for workers to make decisions based on objective information to control OHS.
Real-Time Personalized Monitoring to Estimate Occupational Heat Stress in Ambient Assisted Working.
Pancardo, Pablo; Acosta, Francisco D; Hernández-Nolasco, José Adán; Wister, Miguel A; López-de-Ipiña, Diego
2015-07-13
Ambient Assisted Working (AAW) is a discipline aiming to provide comfort and safety in the workplace through customization and technology. Workers' comfort may be compromised in many labor situations, including those depending on environmental conditions, like extremely hot weather conduces to heat stress. Occupational heat stress (OHS) happens when a worker is in an uninterrupted physical activity and in a hot environment. OHS can produce strain on the body, which leads to discomfort and eventually to heat illness and even death. Related ISO standards contain methods to estimate OHS and to ensure the safety and health of workers, but they are subjective, impersonal, performed a posteriori and even invasive. This paper focuses on the design and development of real-time personalized monitoring for a more effective and objective estimation of OHS, taking into account the individual user profile, fusing data from environmental and unobtrusive body sensors. Formulas employed in this work were taken from different domains and joined in the method that we propose. It is based on calculations that enable continuous surveillance of physical activity performance in a comfortable and healthy manner. In this proposal, we found that OHS can be estimated by satisfying the following criteria: objective, personalized, in situ, in real time, just in time and in an unobtrusive way. This enables timely notice for workers to make decisions based on objective information to control OHS.
The effects of lithospheric thickness and density structure on Earth's stress field
Naliboff, J. B.; Lithgow-Bertelloni, C.; Ruff, L. J.; de Koker, N.
2012-01-01
Lithospheric density and thickness variations are important contributors to the state of stress of the plates. The relationship between the lithosphere's isostatic state, subcrustal structure and stress field, however, remains unresolved due to the uncertainties on its thickness, composition and rheology. To study the influence of lithospheric structure on intraplate stresses, we use a new model of global lithospheric structure (TDL) that accounts for the presence of depleted mantle to explore the effects of isostatic compensation, mantle density structure, lithospheric thickness (base depth) and mechanical coupling within the lithosphere on wavelengths >200 km. We compute the mean lithostatic stress (Ω) of 2°× 2° lithospheric columns and then solve for the resulting global 'tectonic' stress field for a homogeneous elastic lithosphere with the finite element package ABAQUS. For a 100 km base depth, a historically common value for lithospheric thickness, tectonic stress patterns are largely insensitive to mantle density structure and match patterns in the world stress map, for both isostatically compensanted and non-compensated lithospheric structure. Increasing the base depth up to 250 km to account for thick continental roots, however, leads to sharp variations in the stress field between isostatic lithospheric structure models and TDL as the mantle portion of the lithosphere dominates Ω. Decreasing the model base depths up to 25 km as a proxy for vertical strength variations due to low viscosity channels within the crust or lithosphere as a whole, strongly alters stresses in magnitude, azimuth and regime, as the influence of topography and shallow crustal structure increases. We find that restricting spatial changes in Ω to a specified region to mimic lateral variations in strength also has a large effect on the resulting stresses, which leads us to conclude that regional models may not always be adequate for modelling the stress field. Strong deviations
Research on temperature field and temperature stress of prestressed concrete girders
Chen Cheng
2011-02-01
Full Text Available This paper introduces the establishment and simplification of the temperature field and the general calculation method of temperature stress of the prestressed concrete box girders. Three kinds of sunshine temperature gradient models were loaded to a real bridge respectively, and got stress and displacement curves. Research data of several prestressed concrete box girders were selected from different regions of China to compare the relative error of the calculated and measured value. We indicate that the study of temperature field and thermal stress of prestressed concrete box girders is necessary, and will help engineers to solve the problem in structure design.
J. Ray
2014-08-01
Full Text Available We present a sparse reconstruction scheme that can also be used to ensure non-negativity when fitting wavelet-based random field models to limited observations in non-rectangular geometries. The method is relevant when multiresolution fields are estimated using linear inverse problems. Examples include the estimation of emission fields for many anthropogenic pollutants using atmospheric inversion or hydraulic conductivity in aquifers from flow measurements. The scheme is based on three new developments. Firstly, we extend an existing sparse reconstruction method, Stagewise Orthogonal Matching Pursuit (StOMP, to incorporate prior information on the target field. Secondly, we develop an iterative method that uses StOMP to impose non-negativity on the estimated field. Finally, we devise a method, based on compressive sensing, to limit the estimated field within an irregularly shaped domain. We demonstrate the method on the estimation of fossil-fuel CO2 (ffCO2 emissions in the lower 48 states of the US. The application uses a recently developed multiresolution random field model and synthetic observations of ffCO2 concentrations from a limited set of measurement sites. We find that our method for limiting the estimated field within an irregularly shaped region is about a factor of 10 faster than conventional approaches. It also reduces the overall computational cost by a factor of two. Further, the sparse reconstruction scheme imposes non-negativity without introducing strong nonlinearities, such as those introduced by employing log-transformed fields, and thus reaps the benefits of simplicity and computational speed that are characteristic of linear inverse problems.
Estimation of In Situ Stress and Permeability from an Extended Leak-off Test
Nghiep Quach, Quoc; Jo, Yeonguk; Chang, Chandong; Song, Insun
2016-04-01
Among many parameters needed to analyze a variety of geomechanical problems related to subsurface CO2 storage projects, two important ones are in situ stress states and permeability of the storage reservoirs and cap rocks. In situ stress is needed for investigating potential risk of fault slip in the reservoir systems and permeability is needed for assessing reservoir flow characteristics and sealing capability of cap rocks. We used an extended leak-off test (XLOT), which is often routinely conducted to assess borehole/casing integrity as well as fracture gradient, to estimate both in situ least principal stress magnitude and in situ permeability in a CO2 storage test site, offshore southeast Korea. The XLOT was conducted at a casing shoe depth (700 m below seafloor) within the cap rock consisting of mudstone, approximately 50 m above the interface between cap rock and storage reservoir. The test depth was cement-grouted and remained for 4 days for curing. Then the hole was further drilled below the casing shoe to create a 4 m open-hole interval at the bottom. Water was injected using hydraulic pump at an approximately constant flowrate into the bottom interval through the casing, during which pressure and flowrate were recorded continuously at the surface. The interval pressure (P) was increased linearly with time (t) as water was injected. At some point, the slope of P-t curve deviated from the linear trend, which indicates leak-off. Pressure reached its peak upon formation breakdown, followed by a gradual pressure decrease. Soon after the formation breakdown, the hole was shut-in by pump shut-off, from which we determined the instantaneous shut-in pressure (ISIP). The ISIP was taken to be the magnitude of the in situ least principal stress (S3), which was determined to be 12.1 MPa. This value is lower than the lithostatic vertical stress, indicating that the S3 is the least horizontal principal stress. The determined S3 magnitude will be used to characterize the
Propose a Wall Shear Stress Divergence to Estimate the Risks of Intracranial Aneurysm Rupture
Y. Zhang
2013-01-01
Full Text Available Although wall shear stress (WSS has long been considered a critical indicator of intracranial aneurysm rupture, there is still no definite conclusion as to whether a high or a low WSS results in aneurysm rupture. The reason may be that the effect of WSS direction has not been fully considered. The objectives of this study are to investigate the magnitude of WSS (WSS and its divergence on the aneurysm surface and to test the significance of both in relation to the aneurysm rupture. Patient-specific computational fluid dynamics (CFD was used to compute WSS and wall shear stress divergence (WSSD on the aneurysm surface for nineteen patients. Our results revealed that if high WSS is stretching aneurysm luminal surface, and the stretching region is concentrated, the aneurysm is under a high risk of rupture. It seems that, by considering both direction and magnitude of WSS, WSSD may be a better indicator for the risk estimation of aneurysm rupture (154.
On Non-Parametric Field Estimation using Randomly Deployed, Noisy, Binary Sensors
Wang, Ye
2007-01-01
We consider the problem of reconstructing a deterministic data field from binary quantized noisy observations of sensors randomly deployed over the field domain. Our focus is on the extremes of lack of control in the sensor deployment, arbitrariness and lack of knowledge of the noise distribution, and low-precision and unreliability in the sensors. These adverse conditions are motivated by possible real-world scenarios where a large collection of low-cost, crudely manufactured sensors are mass-deployed in an environment where little can be assumed about the ambient noise. We propose a simple estimator that reconstructs the entire data field from these unreliable, binary quantized, noisy observations. Under the assumption of a bounded amplitude field, we prove almost sure and mean-square convergence of the estimator to the actual field as the number of sensors tends to infinity. For fields with bounded-variation, Sobolev differentiable, or finite-dimensionality properties, we derive specific mean squared error...
Multiple void interaction of pipeline steel in triaxial stress fields
Bao-wen QIU; Ze-xi YUAN; Gui-feng ZHOU
2008-01-01
Three-dimensional unit cell models were developed to study the damage induced by void growth in ductile materials. Special emphasis is given to the influence of the void shape and random spatial void arrangements. The periodical void arrays of body cen-tered cubic are investigated by analyzing representative unit cells. The isotropic behavior of the matrix material is modeled using v. Mises plasticity. The cell models are analyzed by the large strain finite element method under monotonic loading while keeping the constant stress triaxiality. Results showed that when void density increased, effects of void aspects on void growth gradu-ally diminished.
The Effect of Stress and Recovery on Field-test Performance in Floorball.
van der Does, H T D; Brink, M S; Visscher, C; Huijgen, B C H; Frencken, W G P; Lemmink, K A P M
2015-06-01
Physical and psychosocial stress and recovery are important performance determinants. A holistic approach that monitors these performance determinants over a longer period of time is lacking. Therefore this study aims to investigate the effect of a player's physical and psychosocial stress and recovery on field-test performance. In a prospective non-experimental cohort design 10 female Dutch floorball players were monitored over 6 months. To monitor physical and psychosocial stress and recovery, daily training-logs and 3-weekly the Recovery-Stress Questionnaire for Athletes (RESTQ-Sport) were filled out respectively. To determine field-test performance 6 Heart rate Interval Monitoring System (HIMS) and 4 Repeated Modified Agility T-test (RMAT) measurements were performed. Multilevel prediction models were applied to account for within-players and between-players field-test performance changes. The results show that more psychosocial stress and less psychosocial recovery over 3-6 weeks before testing decrease HIMS performance (p≤0.05). More physical stress over 6 weeks before testing improves RMAT performance (p≤0.05). In conclusion, physical and psychosocial stress and recovery affect submaximal interval-based running performance and agility up to 6 weeks before testing. Therefore both physical and psychosocial stress and recovery should be monitored in daily routines to optimize performance.
Heat kernel estimates and spectral properties of a pseudorelativistic operator with magnetic field
Jakubassa-Amundsen, D. H.
2008-03-01
Based on the Mehler heat kernel of the Schrödinger operator for a free electron in a constant magnetic field, an estimate for the kernel of EA=∣α(p-eA)+βm∣ is derived, where EA represents the kinetic energy of a Dirac electron within the pseudorelativistic no-pair Brown-Ravenhall model. This estimate is used to provide the bottom of the essential spectrum for the two-particle Brown-Ravenhall operator, describing the motion of the electrons in a central Coulomb field and a constant magnetic field, if the central charge is restricted to Z ⩽86.
Topographical Estimation of Visual Population Receptive Fields by fMRI
Lee, Sangkyun; Papanikolaou, Amalia; Keliris, Georgios A.; Smirnakis, Stelios M.
2015-01-01
Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic resonance imaging allows us to estimate voxel-based population receptive fields (pRF), i.e., the part of the visual field that activates the cells within each voxel. Prior, direct, pRF estimation methods1 suffer from certain limitations: 1) the pRF model is chosen a-priori and may not fully capture the actual pRF shape, and 2) pRF centers are pr...
Measurement of Residual Stress Field of Hardfacing Metal with RE Oxide and Its Numerical Simulation
杨庆祥; 姚枚
2003-01-01
The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the expe rimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic trans formation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.
Estimation of soil moisture in paddy field using Artificial Neural Networks
Arif, Chusnul; Setiawan, Budi Indra; Doi, Ryoichi
2013-01-01
In paddy field, monitoring soil moisture is required for irrigation scheduling and water resource allocation, management and planning. The current study proposes an Artificial Neural Networks (ANN) model to estimate soil moisture in paddy field with limited meteorological data. Dynamic of ANN model was adopted to estimate soil moisture with the inputs of reference evapotranspiration (ETo) and precipitation. ETo was firstly estimated using the maximum, average and minimum values of air temperature as the inputs of model. The models were performed under different weather conditions between the two paddy cultivation periods. Training process of model was carried out using the observation data in the first period, while validation process was conducted based on the observation data in the second period. Dynamic of ANN model estimated soil moisture with R2 values of 0.80 and 0.73 for training and validation processes, respectively, indicated that tight linear correlations between observed and estimated values of s...
Shielding Flowers Developing under Stress: Translating Theory to Field Application.
Chayut, Noam; Sobol, Shiri; Nave, Nahum; Samach, Alon
2014-07-11
Developing reproductive organs within a flower are sensitive to environmental stress. A higher incidence of environmental stress during this stage of a crop plants' developmental cycle will lead to major breaches in food security. Clearly, we need to understand this sensitivity and try and overcome it, by agricultural practices and/or the breeding of more tolerant cultivars. Although passion fruit vines initiate flowers all year round, flower primordia abort during warm summers. This restricts the season of fruit production in regions with warm summers. Previously, using controlled chambers, stages in flower development that are sensitive to heat were identified. Based on genetic analysis and physiological experiments in controlled environments, gibberellin activity appeared to be a possible point of horticultural intervention. Here, we aimed to shield flowers of a commercial cultivar from end of summer conditions, thus allowing fruit production in new seasons. We conducted experiments over three years in different settings, and our findings consistently show that a single application of an inhibitor of gibberellin biosynthesis to vines in mid-August can cause precocious flowering of ~2-4 weeks, leading to earlier fruit production of ~1 month. In this case, knowledge obtained on phenology, environmental constraints and genetic variation, allowed us to reach a practical solution.
Shielding Flowers Developing under Stress: Translating Theory to Field Application
Noam Chayut
2014-07-01
Full Text Available Developing reproductive organs within a flower are sensitive to environmental stress. A higher incidence of environmental stress during this stage of a crop plants’ developmental cycle will lead to major breaches in food security. Clearly, we need to understand this sensitivity and try and overcome it, by agricultural practices and/or the breeding of more tolerant cultivars. Although passion fruit vines initiate flowers all year round, flower primordia abort during warm summers. This restricts the season of fruit production in regions with warm summers. Previously, using controlled chambers, stages in flower development that are sensitive to heat were identified. Based on genetic analysis and physiological experiments in controlled environments, gibberellin activity appeared to be a possible point of horticultural intervention. Here, we aimed to shield flowers of a commercial cultivar from end of summer conditions, thus allowing fruit production in new seasons. We conducted experiments over three years in different settings, and our findings consistently show that a single application of an inhibitor of gibberellin biosynthesis to vines in mid-August can cause precocious flowering of ~2–4 weeks, leading to earlier fruit production of ~1 month. In this case, knowledge obtained on phenology, environmental constraints and genetic variation, allowed us to reach a practical solution.
Huang-bin Lin
2012-01-01
Full Text Available Langmuir Probes attached to plasma-facing components in a Tokamak are used to diagnose high-temperature plasma during fusion experiments. In this work, a finite element model of Langmuir Probe-Cooling Monoblock (LP-CM is established, and structural analysis of the LP-CM is carried out. The maximum von Mises stress during the 400 s incident heat flux has been given in detail, and the relationship between the sliding friction coefficient and thermal stress has been investigated systematically. A contact design is employed between Langmuir Probe and Cooling Monoblock, which is an effective method to lower the thermal stress. The thermal stress reaches the peak on the edge of the aluminium oxide ceramic interlayer. The damaged displacement field of the LP-CM has been examined fully, and the maximum global displacement is 0.444 mm.
HU CaiBo; ZHOU YiJie; CAI YongEn
2009-01-01
In this paper, a new finite element model (FEM) In consideration of regional stress field and an earthquake triggering factor C are proposed for studying earthquake triggering and stress field evolution in an earthquake sequence. The factor C is defined as a ratio between the shear stress and the frictional strength on a slip surface, and it can be used to tell if earthquake is triggered or not. The new FEM and the factor C are used to study the aftershock triggering of the 1976 Tangshan earthquake sequence. The results indicate that the effects of the stress field and the heterogeneity of the Tangshan earthquake fault zone on the aftershock triggering are very important. The affershocks fallen in the earthquake triggering regions predicted by the new FEM are more than those fallen in the regions of △CFS≥0 predicted by seismic dislocation theory.
Research on a system and method of automated whole-field measurement of optical glass stress
Zhang, Li-jun; Tang, Yi; Bai, Ting-zhu
2008-03-01
On the basis of the principle of single quarter wave plate method, a model of automatic whole-field measuring optical glass stress is presented, which is called "4+1steps phase shifting method" including the model for the isoclinic parameter and the stress birefringence. According to this model, an automatic whole-field measuring system is established. The correctness of the model was testified by numeric emulation experiments under the preset conditions of isoclinic angle and stress birefringence. Practical measurement obtained a result coincident with the actual distribution of the isoclinic angle and the birefringence. The automatic whole-field measuring model and system can achieve the whole process intelligently and automatically, and dispose the disadvantages of tradition method about interpreting the stress level by subjective judging birefringence of some selected spots.
无
2009-01-01
In this paper, a new finite element model (FEM) in consideration of regional stress field and an earthquake triggering factor C are proposed for studying earthquake triggering and stress field evolution in an earthquake sequence. The factor C is defined as a ratio between the shear stress and the frictional strength on a slip surface, and it can be used to tell if earthquake is triggered or not. The new FEM and the factor C are used to study the aftershock triggering of the 1976 Tangshan earthquake sequence. The results indicate that the effects of the stress field and the heterogeneity of the Tangshan earthquake fault zone on the aftershock triggering are very important. The aftershocks fallen in the earthquake triggering regions predicted by the new FEM are more than those fallen in the regions of ΔCFS≥ 0 predicted by seismic dislocation theory.
Lowes, F.J.; Olsen, Nils
2004-01-01
Most modern spherical harmonic geomagnetic models based on satellite data include estimates of the variances of the spherical harmonic coefficients of the model; these estimates are based on the geometry of the data and the fitting functions, and on the magnitude of the residuals. However......, led to quite inaccurate variance estimates. We estimate correction factors which range from 1/4 to 20, with the largest increases being for the zonal, m = 0, and sectorial, m = n, terms. With no correction, the OSVM variances give a mean-square vector field error of prediction over the Earth's surface...
Staszek, M.; Orlecka-Sikora, B.; Leptokaropoulos, K.; Kwiatek, G.; Martínez-Garzón, P.
2017-07-01
We use a high-quality data set from the NW part of The Geysers geothermal field to determine statistical significance of temporal static stress drop variations and their relation to injection rate changes. We use a group of 322 seismic events which occurred in the proximity of Prati-9 and Prati-29 injection wells to examine the influence of parameters such as moment magnitude, focal mechanism, hypocentral depth, and normalized hypocentral distances from open-hole sections of injection wells on static stress drop changes. Our results indicate that (1) static stress drop variations in time are statistically significant, (2) statistically significant static stress drop changes are inversely related to injection rate fluctuations. Therefore, it is highly expected that static stress drop of seismic events is influenced by pore pressure in underground fluid injection conditions and depends on the effective normal stress and strength of the medium.
无
2007-01-01
Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA)and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3/Al interface is minimal when Al2O3 layer and Al layer have the same thickness.
Parametrization and stress-energy-momentum tensors in metric field theories
Lopez, Marco Castrillon [Departamento de GeometrIa y TopologIa, Facultad de Ciencias Matematicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Gotay, Mark J [Department of Mathematics, University of Hawai' i, Honolulu, HI 96822 (United States); Marsden, Jerrold E [Control and Dynamical Systems 107-81, California Institute of Technology, Pasadena, CA 91125 (United States)
2008-08-29
We give an exposition of the 1972 parametrization method of Kuchar in the context of the multisymplectic approach to field theory. The purpose of the formalism developed here is to make any classical field theory, containing a metric as a sole background field, generally covariant (that is, parametrized, with the spacetime diffeomorphism group as a symmetry group) as well as fully dynamic. This is accomplished by introducing certain 'covariance fields' as genuine dynamic fields. As we shall see, the multimomenta conjugate to these new fields form the Piola-Kirchhoff version of the stress-energy-momentum tensor field, and their Euler-Lagrange equations are vacuously satisfied. Thus, these fields have no additional physical content; they serve only to provide an efficient means of parametrizing the theory. Our results are illustrated with two examples, namely an electromagnetic field and a Klein-Gordon vector field, both on a background spacetime.
Umriukhin, P E; Grigorchuk, O S
2015-12-01
In the presented study we investigated the possibility to use the open field behavior data for prediction of corticosterone level in rat blood plasma before and after stress. It is shown that the most reliable open field behavior parameters, reflecting high probability of significant upregulation of corticosterone after 3 hours of immobilization, are the short latency of first movement and low locomotor activity during the test. Rats with high corticosterone at normal non-stress conditions are characterized by low locomotor activity and on the contrary long latency period for the entrance of open field center.
Stress management as an enabling technology for high-field superconducting dipole magnets
Holik, Eddie Frank, III
This dissertation examines stress management and other construction techniques as means to meet future accelerator requirement demands by planning, fabricating, and analyzing a high-field, Nb3Sn dipole. In order to enable future fundamental research and discovery in high energy accelerator physics, bending magnets must access the highest fields possible. Stress management is a novel, propitious path to attain higher fields and preserve the maximum current capacity of advanced superconductors by managing the Lorentz stress so that strain induced current degradation is mitigated. Stress management is accomplished through several innovative design features. A block-coil geometry enables an Inconel pier and beam matrix to be incorporated in the windings for Lorentz Stress support and reduced AC loss. A laminar spring between windings and mica paper surrounding each winding inhibit any stress transferral through the support structure and has been simulated with ALGORRTM. Wood's metal filled, stainless steel bladders apply isostatic, surface-conforming preload to the pier and beam support structure. Sufficient preload along with mica paper sheer release reduces magnet training by inhibiting stick-slip motion. The effectiveness of stress management is tested with high-precision capacitive stress transducers and strain gauges. In addition to stress management, there are several technologies developed to assist in the successful construction of a high-field dipole. Quench protection has been designed and simulated along with full 3D magnetic simulation with OPERARTM. Rutherford cable was constructed, and cable thermal expansion data was analysed after heat treatment. Pre-impregnation analysis techniques were developed due to elemental tin leakage in varying quantities during heat treatment from each coil. Robust splicing techniques were developed with measured resistivites consistent with nO joints. Stress management has not been incorporated by any other high field dipole
Hamzeh, Saeid; Naseri, Abd Ali; AlaviPanah, Seyed Kazem; Bartholomeus, Harm; Herold, Martin
2016-10-01
This study evaluates the feasibility of hyperspectral and multispectral satellite imagery for categorical and quantitative mapping of salinity stress in sugarcane fields located in the southwest of Iran. For this purpose a Hyperion image acquired on September 2, 2010 and a Landsat7 ETM+ image acquired on September 7, 2010 were used as hyperspectral and multispectral satellite imagery. Field data including soil salinity in the sugarcane root zone was collected at 191 locations in 25 fields during September 2010. In the first section of the paper, based on the yield potential of sugarcane as influenced by different soil salinity levels provided by FAO, soil salinity was classified into three classes, low salinity (1.7-3.4 dS/m), moderate salinity (3.5-5.9 dS/m) and high salinity (6-9.5) by applying different classification methods including Support Vector Machine (SVM), Spectral Angle Mapper (SAM), Minimum Distance (MD) and Maximum Likelihood (ML) on Hyperion and Landsat images. In the second part of the paper the performance of nine vegetation indices (eight indices from literature and a new developed index in this study) extracted from Hyperion and Landsat data was evaluated for quantitative mapping of salinity stress. The experimental results indicated that for categorical classification of salinity stress, Landsat data resulted in a higher overall accuracy (OA) and Kappa coefficient (KC) than Hyperion, of which the MD classifier using all bands or PCA (1-5) as an input performed best with an overall accuracy and kappa coefficient of 84.84% and 0.77 respectively. Vice versa for the quantitative estimation of salinity stress, Hyperion outperformed Landsat. In this case, the salinity and water stress index (SWSI) has the best prediction of salinity stress with an R2 of 0.68 and RMSE of 1.15 dS/m for Hyperion followed by Landsat data with an R2 and RMSE of 0.56 and 1.75 dS/m respectively. It was concluded that categorical mapping of salinity stress is the best option
Schuelke, J.S.; Quirein, J.A.; Sarg, J.F.
1998-12-31
This case study shows the benefit of using multiple seismic trace attributes and the pattern recognition capabilities of neural networks to predict reservoir architecture and porosity distribution in the Pegasus Field, West Texas. The study used the power of neural networks to integrate geologic, borehole and seismic data. Illustrated are the improvements between the new neural network approach and the more traditional method of seismic trace inversion for porosity estimation. Comprehensive statistical methods and interpretational/subjective measures are used in the prediction of porosity from seismic attributes. A 3-D volume of seismic derived porosity estimates for the Devonian reservoir provide a very detailed estimate of porosity, both spatially and vertically, for the field. The additional reservoir porosity detail provided, between the well control, allows for optimal placement of horizontal wells and improved field development. 6 refs., 2 figs.
Selecting a spatial resolution for estimation of per-field green leaf area index
Curran, Paul J.; Williamson, H. Dawn
1988-01-01
For any application of multispectral scanner (MSS) data, a user is faced with a number of choices concerning the characteristics of the data; one of these is their spatial resolution. A pilot study was undertaken to determine the spatial resolution that would be optimal for the per-field estimation of green leaf area index (GLAI) in grassland. By reference to empirically-derived data from three areas of grassland, the suitable spatial resolution was hypothesized to lie in the lower portion of a 2-18 m range. To estimate per-field GLAI, airborne MSS data were collected at spatial resolutions of 2 m, 5 m and 10 m. The highest accuracies of per-field GLAI estimation were achieved using MSS data with spatial resolutions of 2 m and 5 m.
Optimization by Estimation of Distribution with DEUM Framework Based on Markov Random Fields
Siddhartha Shakya; John McCall
2007-01-01
This paper presents a Markov random field (MRP) approach to estimating and sampling the probability distribution in populations of solutions. The approach is used to define a class of algorithms under the general heading distribution estimation using Markov random fields (DEUM). DEUM is a subclass of estimation of distribution algorithms (EDAs) where interaction between solution variables is represented as an undirected graph and the joint probability of a solution is factorized as a Gibbs distribution derived from the structure of the graph. The focus of this paper will be on describing the three main characteristics of DEUM framework, which distinguishes it from the traditional EDA. They are: 1) use of MRF models, 2) fitness modeling approach to estimating the parameter of the model and 3) Monte Carlo approach to sampling from the model.
Field Evaluation of the System Identification Approach for Tension Estimation of External Tendons
Myung-Hyun Noh
2015-01-01
Full Text Available Various types of external tendons are considered to verify the applicability of tension estimation method based on the finite element model with system identification technique. The proposed method is applied to estimate the tension of benchmark numerical example, model structure, and field structure. The numerical and experimental results show that the existing methods such as taut string theory and linear regression method show large error in the estimated tension when the condition of external tendon is different with the basic assumption used during the derivation of relationship between tension and natural frequency. However, the proposed method gives reasonable results for all of the considered external tendons in this study. Furthermore, the proposed method can evaluate the accuracy of estimated tension indirectly by comparing the measured and calculated natural frequencies. Therefore, the proposed method can be effectively used for field application of various types of external tendons.
Stress, faulting and fluid flow in the Coso Geothermal Field, CA
Davatzes, N. C.; Hickman, S.
2006-12-01
We integrate new geologic mapping and new in situ measurements of stress orientations and magnitudes from studies of wells within and on the flanks of the geothermal system with existing data sets to refine a geomechanical model for the Coso geothermal field. Stress orientations (averaged from several hundred to thousand meters of vertical borehole data) in wells across the field are fairly uniform and are consistent with focal mechanism inversions of earthquake clusters for stress and incremental strain. Active faults trending NNW-SSE to NNE-SSW are well oriented for normal slip in the current stress field, where the mean least principal horizontal compressive stress, Shmin, orientation is 108° ± 24º in a transitional strike-slip to normal faulting stress regime. These structures bound regions of intense micro-seismicity and are complexly associated with surface hydrothermal activity. WNW-ESE trending faults are also associated with distinct regions of enhanced seismicity but are only associated with surface hydrothermal activity where they intersect more northerly trending normal faults. These faults show no evidence for Quaternary slip at the surface and are poorly oriented in the modern stress field. These results together with stress magnitudes measured in the East Flank of the field suggest that the most productive portions of the Coso geothermal field are in high deviatoric stress environments conducive to normal faulting. Recent earthquake relocations and incremental strain inversions map areas of extensional strain located over the southern part of the Main Field and reaching east and north into the East Flank consistent with our borehole analyses. The resulting relatively low mean stress is conducive to dilation and increased permeability accompanying fault slip and coincides with the hottest areas in the geothermal field. Similar regions of locally reduced mean stress might arise from mechanical interaction during slip on intersecting fault segments
W. Friederich
2014-05-01
Full Text Available The lateral variation of the stress field in the southern Aegean plate and the subducting Hellenic slab is determined from recordings of seismicity obtained with the CYCNET and EGELADOS networks in the years from 2002 to 2007. First motions from 7000 well-located microearthquakes were analysed to produce 540 well-constrained focal mechanisms. They were complemented by another 140 derived by waveform matching of records from larger events. Most of these earthquakes fall into 16 distinct spatial clusters distributed over the southern Aegean region. For each cluster, a stress inversion could be carried out yielding consistent estimates of the stress field and its spatial variation. At crustal levels, the stress field is generally dominated by a steeply dipping compressional principal stress direction except in places where coupling of the subducting slab and overlying plate come into play. Tensional principal stresses are generally subhorizontal. Just behind the forearc, the crust is under arc-parallel tension whereas in the volcanic areas around Kos, Columbo and Astypalea tensional and intermediate stresses are nearly degenerate. Further west and north, in the Santorini–Amorgos graben and in the area of the islands of Mykonos, Andros and Tinos, tensional stresses are significant and point around the NW–SE direction. Very similar stress fields are observed in western Turkey with the tensional axis rotated to NNE–SSW. Intermediate-depth earthquakes below 100 km in the Nisyros region indicate that the Hellenic slab experiences slab-parallel tension at these depths. The direction of tension is close to east–west and thus deviates from the local NW-oriented slab dip presumably owing to the segmentation of the slab. Beneath the Cretan sea, at shallower levels, the slab is under NW–SE compression. Tensional principal stresses in the crust exhibit very good alignment with extensional strain rate principal axes derived from GPS velocities except
Tertiary stress field evolution in Sistan (Eastern Iran)
Michael, Jentzer; Marc, Fournier; Philippe, Agard; Jafar, Omrani
2016-04-01
The Sistan orogenic belt in eastern Iran, near the boundary with Afghanistan, results from the closure of a branch of the Neo-Thethys: the Sistan Ocean. It was divided by Tirrul et al. (1983) in five main units: the Lut (1) and Afghan (2) continental blocks where basement is exposed; the Neh (3) and Ratuk (4) complexes which display ophiolitic rocks weakly and highly (HP-BT) metamorphosed, respectively, and the Sefidabeh basin lying over these complexes and interpreted as a fore-arc basin. Sistan is bordered by the Makran and Zagros (formed by the closure of the Neo-Tethys) to the south and by the Kopet Dagh (formed by the closure of Paleo-Tethys) to the North. The aim of this study is to fill the gap between preliminary studies about the overall structure of the Sistan Suture Zone and recent investigations of active tectonics in the region (e.g., Walker et al., 2004 and 2006 a and b). Questions herein addressed are: (1) how are stresses transfered throughout Iran from the Zagros to the Sistan belts? (2) Did the Zagros, Makran and Sistan belts evolve independently through time, or were they mechanically coupled? In order to answer these questions, we have determined paleostress evolution in the Sistan, using a direct inversion method for 42 microtectonic sites in almost all lithologies of the Neh complex and the Sefidabeh basin. We find three successive directions of compression: (1) 87°N for the oldest deformation stage dated of the Late Miocene, (2) 59°N for the intermediate stage probably dated of the Early Pliocene, and (3) 26°N for the youngest stage dated of the Plio-Quaternary. A counterclockwise rotation of about 60° of the main stress (σ1) in less than 10 Ma is therefore documented in Sistan. These same three stages of deformation were also documented by several microtectonic studies in Iran, especially in Makran and Zagros. The direction of the youngest compression is very homogeneous indicating that the mountain belts and continental blocks of Iran
Evaluation of properties and thermal stress field for thermal barrier coatings
王良; 齐红宇; 杨晓光; 李旭
2008-01-01
In order to get thermal stress field of the hot section with thermal barrier coating (TBCs), the thermal conductivity and elastic modulus of top-coat are the physical key properties. The porosity of top-coat was tested and evaluated under different high temperatures. The relationship between the microstructure (porosity of top-coat) and properties of TBCs were analyzed to predict the thermal properties of ceramic top-coat, such as thermal conductivity and elastic modulus. The temperature and stress field of the vane with TBCs were simulated using two sets of thermal conductivity data and elastic modulus, which are from literatures and this work, respectively. The results show that the temperature and stress distributions change with thermal conductivity and elastic modulus. The differences of maximum temperatures and stress are 6.5% and 8.0%, respectively.
Application of nonlocal criteria for destruction in problems with a nonuniform stress field
Chevrychkina, A. A.; Gruzdkov, A. A.; Petrov, Yu. V.
2017-08-01
The dependence of the critical load on the degree of nonuniformity of the stress field is considered on the example of polymethylmethacrylate beams and plates with a round hole or a sharp notch. It is proposed to use nonlocal criteria for brittle fracture to describe the behavior of a nonuniformly stressed material. Among the criteria considered, the structural criterion is the most universal, because, in this case, the distance parameter d is least dependent on the test configuration. The distance parameters in problems with a regular concentrator are of the same order of magnitude, as in problems with a singular stress concentrator. A further modification of the criterion that takes into account the properties of the fracture process will probably make it possible to obtain a unique value for the length parameter for any degree of nonuniformity of the stress field.
Mapping residual stress fields from Vickers hardness indents using Raman microprobe spectroscopy
Sparks, R.G.; Enloe, W.S.; Paesler, M.A.
1988-12-01
Micro-Raman spectroscopy is used to map the residual stress fields in the vicinity of Vickers hardness indents. Both 514.5 and 488.0 nm, light is used to excite the effect and the resulting shifted and broadened Raman peaks are analyzed using computer deconvolution. Half-wave plates are used to vary the orientation of the incident later light`s polarization state with respect to crystal orientation. The Raman scattered light is then analyzed for polarization dependences which are indicative of the various components of the Raman scattering tensor. Such studies can yield valuable information about the orientation of stress components in a well known stress field. The results can then be applied to the determination of stress components in machined semiconductor materials.
Delay Kalman Filter to Estimate the Attitude of a Mobile Object with Indoor Magnetic Field Gradients
Christophe Combettes
2016-05-01
Full Text Available More and more services are based on knowing the location of pedestrians equipped with connected objects (smartphones, smartwatches, etc.. One part of the location estimation process is attitude estimation. Many algorithms have been proposed but they principally target open space areas where the local magnetic field equals the Earth’s field. Unfortunately, this approach is impossible indoors, where the use of magnetometer arrays or magnetic field gradients has been proposed. However, current approaches omit the impact of past state estimates on the current orientation estimate, especially when a reference field is computed over a sliding window. A novel Delay Kalman filter is proposed in this paper to integrate this time correlation: the Delay MAGYQ. Experimental assessment, conducted in a motion lab with a handheld inertial and magnetic mobile unit, shows that the novel filter better estimates the Euler angles of the handheld device with an 11.7° mean error on the yaw angle as compared to 16.4° with a common Additive Extended Kalman filter.
Comprehensive evaluation of attitude and orbit estimation using real earth magnetic field data
Deutschmann, Julie; Bar-Itzhack, Itzhack
1997-01-01
A single, augmented extended Kalman filter (EKF) which simultaneously and autonomously estimates spacecraft attitude and orbit was developed and tested with simulated and real magnetometer and rate data. Since the earth's magnetic field is a function of time and position, and since time is accurately known, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft's orbit, are a function of orbit and attitude errors. These differences can be used to estimate the orbit and attitude. The test results of the EKF with magnetometer and gyro data from three NASA satellites are presented and evaluated.
Zygielbaum, A. I.; Arkebauer, T. J.; Walter-Shea, E.
2013-12-01
Vegetation photoprotective responses impact the reflected spectra in the visible or photosynthetically active (PAR) spectral region. Earlier, we presented a case that the increasing PAR reflectance which accompanies increasing water stress was due to one such response, chloroplast avoidance movement. This increasing reflectance has been reported in published papers for several decades and dismissed as operator error or a result of changes in leaf turgor or optical pathway. We showed, however, that such changes in the PAR region, which occurred with no significant change in chlorophyll content, were caused by decreasing absorption, not changes in light scatter. Further, we demonstrated that the changes in reflectance were correlated with changes in ambient light (downwelling radiance). To further refine the case that chloroplast movement is the basis of these observations, excised leaves were exposed separately to either red light or white light illumination of equal photon flux densities. The transmittance observed as these leaves dried increased in the leaves exposed to white light and remained constant in the leaves exposed to red light. Since chloroplast movement is driven by blue light, our conjecture is strengthened. We have also observed distinct morning vs. afternoon differences in reflectance spectra of greenhouse-grown plants; indices derived from these spectra also vary diurnally--leading us to coin the phase 'apparent chlorophyll'. All observations previously reported were the result of greenhouse experiments. We report herein on observations of leaf and canopy reflectances under field conditions and on the impact the increasing reflectance has on estimation of chlorophyll content using spectral indices. We also present evidence that increasing reflectance which is concomitant with increasing plant stress may not correlate with stress indications using the photochemical reflectance index (PRI) and discuss the implications of that observation.
THEORETICAL COMPUTATION OF A STRESS FIELD IN A CYLINDRICAL GLASS SPECIMEN
NORBERT KREČMER
2011-03-01
Full Text Available This work deals with the computation of the stress field generated in an infinitely high glass cylinder while cooling. The theory of structural relaxation is used in order to compute the heat capacity, the thermal expansion coefficient, and the viscosity. The relaxation of the stress components is solved in the frame of the Maxwell viscoelasticity model. The obtained results were verified by the sensitivity analysis and compared with some experimental data.
Abnormal enhancement of interface trap generation under dynamic oxide field stress at MHz region
Zhu, Shiyang; Nakajima, Anri
2005-01-01
By stressing metal-oxide-semiconductor field-effect transistors with ultrathin silicon dioxide or oxynitride gate dielectrics under square wave form voltage at the MHz region, an abnormal enhancement of interface trap generation in the midchannel region has been observed at some special frequencies. A hypothesis, including self-accelerating interface trap generation originated from the positive feedback of a charge pumping current to be contributed by the stress-induced near-interface oxide t...
Estimation of a planetary magnetic field using a reduced magnetohydrodynamic model
Nabert, Christian; Heyner, Daniel; Glassmeier, Karl-Heinz
2017-03-01
Knowledge of planetary magnetic fields provides deep insights into the structure and dynamics of planets. Due to the interaction of a planet with the solar wind plasma, a rather complex magnetic environment is generated. The situation at planet Mercury is an example of the complexities occurring as this planet's field is rather weak and the magnetosphere rather small. New methods are presented to separate interior and exterior magnetic field contributions which are based on a dynamic inversion approach using a reduced magnetohydrodynamic (MHD) model and time-varying spacecraft observations. The methods select different data such as bow shock location information or magnetosheath magnetic field data. Our investigations are carried out in preparation for the upcoming dual-spacecraft BepiColombo mission set out to precisely estimate Mercury's intrinsic magnetic field. To validate our new approaches, we use THEMIS magnetosheath observations to estimate the known terrestrial dipole moment. The terrestrial magnetosheath provides observations from a strongly disturbed magnetic environment, comparable to the situation at Mercury. Statistical and systematic errors are considered and their dependence on the selected data sets are examined. Including time-dependent upstream solar wind variations rather than averaged conditions significantly reduces the statistical error of the estimation. Taking the entire magnetosheath data along the spacecraft's trajectory instead of only the bow shock location into account further improves accuracy of the estimated dipole moment.
A new estimate of average dipole field strength for the last five million years
Cromwell, G.; Tauxe, L.; Halldorsson, S. A.
2013-12-01
The Earth's ancient magnetic field can be approximated by a geocentric axial dipole (GAD) where the average field intensity is twice as strong at the poles than at the equator. The present day geomagnetic field, and some global paleointensity datasets, support the GAD hypothesis with a virtual axial dipole moment (VADM) of about 80 ZAm2. Significant departures from GAD for 0-5 Ma are found in Antarctica and Iceland where paleointensity experiments on massive flows (Antarctica) (1) and volcanic glasses (Iceland) produce average VADM estimates of 41.4 ZAm2 and 59.5 ZAm2, respectively. These combined intensities are much closer to a lower estimate for long-term dipole field strength, 50 ZAm2 (2), and some other estimates of average VADM based on paleointensities strictly from volcanic glasses. Proposed explanations for the observed non-GAD behavior, from otherwise high-quality paleointensity results, include incomplete temporal sampling, effects from the tangent cylinder, and hemispheric asymmetry. Differences in estimates of average magnetic field strength likely arise from inconsistent selection protocols and experiment methodologies. We address these possible biases and estimate the average dipole field strength for the last five million years by compiling measurement level data of IZZI-modified paleointensity experiments from lava flows around the globe (including new results from Iceland and the HSDP-2 Hawaii drill core). We use the Thellier Gui paleointensity interpreter (3) in order to apply objective criteria to all specimens, ensuring consistency between sites. Specimen level selection criteria are determined from a recent paleointensity investigation of modern Hawaiian lava flows where the expected magnetic field strength was accurately recovered when following certain selection parameters. Our new estimate of average dipole field strength for the last five million years incorporates multiple paleointensity studies on lava flows with diverse global and
An efficient anti-occlusion depth estimation using generalized EPI representation in light field
Zhu, Hao; Wang, Qing
2016-10-01
Light field cameras have been rapidly developed and are likely to appear in mobile devices in near future. It is essential to develop efficient and robust depth estimation algorithm for mobile applications. However, existing methods are either slow or lack of adaptability to occlusion such that they are not suitable to mobile computing platform. In this paper, we present the generalized EPI representation in light field and formulate it using two linear functions. By combining it with the light field occlusion theory, a highly efficient and anti-occlusion depth estimation algorithm is proposed. Our algorithm outperforms the previous local method, especially in occlusion areas. Experimental results on public light field datasets have demonstrated the effectiveness and efficiency of the proposed algorithm.
Recursive Estimation of Gauss-Markov Random Fields Indexed over 1-D Space
Vats, Divyanshu
2009-01-01
This paper presents optimal recursive estimators for vector valued Gauss-Markov random \\emph{fields} taking values in $\\R^M$ and indexed by (intervals of) $\\R$ or $\\Z$. These 1-D fields are often called reciprocal processes. They correspond to two point boundary value fields, i.e., they have boundary conditions given at the end points of the indexing interval. To obtain the recursive estimators, we derive two classes of recursive representations for reciprocal processes. The first class transforms the Gaussian reciprocal process into a Gauss-Markov \\emph{process}, from which we derive forward and backwards recursive representations. The second representation folds the index set and transforms the original \\emph{field} taking values in $\\R^M$ into a Markov \\emph{process} taking values in $\\R^{2M}$. The folding corresponds to recursing the reciprocal process from the boundary points and telescoping inwards. From these recursive representations, Kalman filters and recursive smoothers are promptly derived.
STRESS FIELD AT A TIP OF A PREFABRICATED SPIRAL V-NOTCH
郑周练; 陈山林; 叶晓明
2004-01-01
Based on the tranditional V-notched blasting,a technique of spirally V-notched blasting to loosen earth and rock was presented.Fracture mechanics and Westergaard stress function were adopted to build a complex stress function to derive the plane stress and strain fields at one tip of the crack under a quasi-static pressure.An expression was formulated to define the stress intensity factor of spiral V-notch loosen blasting.Factors that have effects on the stress intensity factor were studied.It is demonstrated that spiral V-notch loosen blasting is an extension of vertical V-notch blasting,straight cracking,and alike theories.
Post-Palbozoic crustal responses to the contemporary stress field in the eastern United States
Staub, W.P.; Hardee, H.K.
1993-08-01
This paper summarizes the current state of knowledge with respect to post-Paleozoic tectonic features and their relationship to the contemporary stress field outside coastal plain regions of the eastern United States. Until the early 1970s very little was known about such features. By the end of 1992 post-Paleozoic faults had been observed in at least five widely separated regions. Pleistocene-Holocene surface ruptures and liquefaction features had been observed over a steadily increasing area of the upper Mississippi embayment and adjacent regions. Ages of most recent ruptures on post-Paleozoic faults range from uncertain to Holocene and their senses of motion are compatible with the contemporary stress field. The cumulative amount of post-Paleozoic displacement on these faults is generally less than three meters. Fracture systems in Paleozoic rocks also are compatible with the contemporary stress field over a wide region of Indiana.
Optimal heat kernel estimates for Schroedinger operators with magnetic fields in two dimensions
Loss, M. [Georgia Inst. of Tech., Atlanta (United States). School of Mathematics; Thaller, B. [Institut fuer Mathematik, Universitaet Graz, A-8010 Graz (Austria)
1997-06-01
Sharp smoothing estimates are proven for magnetic Schroedinger semigroups in two dimensions under the assumption that the magnetic field is bounded below by some positive constant B{sub 0}. As a consequence the L{sup {infinity}} norm of the associated integral kernel is bounded by the L{sup {infinity}} norm of the Mehler kernel of the Schroedinger semigroup with the constant magnetic field B{sub 0}. (orig.)
Estimating magnetic fields of homes near transmission lines in the California Power Line Study.
Vergara, Ximena P; Kavet, Robert; Crespi, Catherine M; Hooper, Chris; Silva, J Michael; Kheifets, Leeka
2015-07-01
The California Power Line Study is a case-control study investigating the relation between residences near transmission lines and risk of childhood leukemia. It includes 5788 childhood leukemia cases and 5788 matched primary controls born between 1986 and 2007. We describe the methodology for estimating magnetic fields at study residences as well as for characterizing sources of uncertainty in these estimates. Birth residences of study subjects were geocoded and their distances to transmission lines were ascertained. 302 residences were deemed sufficiently close to transmission lines to have non-zero magnetic fields attributable to the lines. These residences were visited and detailed data, describing the physical configuration and dimensions of the lines contributing to the magnetic field at the residence, were collected. Phasing, loading, and directional load flow data for years of birth and diagnosis for each subject as well as for the day of site visit were obtained from utilities when available; when yearly average load for a particular year was not available, extrapolated values based on expert knowledge and prediction models were obtained. These data were used to estimate the magnetic fields at the center, closest and farthest point of each residence. We found good correlation between calculated fields and spot measurements of fields taken on site during visits. Our modeling strategies yielded similar calculated field estimates, and they were in high agreement with utility extrapolations. Phasing was known for over 90% of the lines. Important sources of uncertainty included a lack of information on the precise location of residences located within apartment buildings or other complexes. Our findings suggest that we were able to achieve high specificity in exposure assessment, which is essential for examining the association between distance to or magnetic fields from power lines and childhood leukemia risk.
Simplified Atmospheric Dispersion Model andModel Based Real Field Estimation System ofAir Pollution
2015-01-01
The atmospheric dispersion model has been well developed and applied in pollution emergency and prediction. Based on thesophisticated air diffusion model, this paper proposes a simplified model and some optimization about meteorological andgeological conditions. The model is suitable for what is proposed as Real Field Monitor and Estimation system. The principle ofsimplified diffusion model and its optimization is studied. The design of Real Field Monitor system based on this model and itsfundamental implementations are introduced.
A priori estimates for nonvariational operators modeled on Hörmander's vector fields with drift
Marco Bramanti
2013-12-01
Full Text Available For a nonvariational operator structured on Hörmander's vector fields with drift, where the matrix of coffiecients is real, symmetric and uniformly positive, we prove local a priori estimates on the second order derivatives with respect to the vector fields, in Hölder spaces if the coecients are Holder continuous, in Lp spaces if the coefficients are bounded, measurable and locally VMO.
A priori estimates for nonvariational operators modeled on Hörmander's vector fields with drift
Marco Bramanti
2013-01-01
For a nonvariational operator structured on Hörmander's vector fields with drift, where the matrix of coffiecients is real, symmetric and uniformly positive, we prove local a priori estimates on the second order derivatives with respect to the vector fields, in Hölder spaces if the coecients are Holder continuous, in Lp spaces if the coefficients are bounded, measurable and locally VMO.
Numerical Analysis of Frictional Heat-Stress Coupled Field at Dynamic Contact
张一兵; 刘佐民
2004-01-01
A new analysis method was developed to simulate the dynamic process of a frictional heat-stress coupled field.The relationship between the frictional heat and the thermal stress was investigated for concave cylinder contact conditions.The results show that, as a nonlinear contact problem, the frictional heat at the contact areas changes with moving velocity in both value and distribution, and that the transient frictional heat at the dynamic condition has a peak within a cycle.The dynamic process of friction heat and thermal stresses affects diffusion of the frictional effects.The result can be helpful for dynamic simulation of diffusion lubrication of elements at elevated temperatures.
Fracture toughness and evaluation of coating strength with an initial residual stress field
Byakova, A.V.; Gorbach, V.G. [Polytechnic Institute, Kiev (Ukraine)
1994-09-01
The effect of residual elastic stresses on the geometry of cracks which arise with contact and spontaneous failure of brittle coatings made of high-strength compounds is studied. Conditions are established for the correctness of fracture toughness K{sub lc} tests with indentation of a standard Vickers pyramid as applied to surface layers with an inhomogeneous structure and an initial residual stress field. Taking account of the anisotropy of fracture toughness established by experiment a reliable approach is suggested for evaluating the brittle strength of coatings in the presence of residual stresses.
CHEN Qing-fa; ZHOU Ke-ping; WANG Li-li
2010-01-01
For improving global stability of mining environment reconstructing structure,the stress field evolution law of the structure with the filling height change of low-grade backfill was studied by ADINA finite element analysis code.Three kinds of filling schemes were designed and calculated,in which the filling heights were 2,4,and 7 m,separately.The results show that there are some rules in the stress field with the increase of the filling height as follows:(1)the maximum value of tension stress of the roof decreases gradually,and stress conditions are improved gradually;(2)the tension stress status in the vertical pillar is transformed into the compressive stress status,and the carrying capacity is improved gradually; however,when the filling height is beyond 2.8 m,the carrying capacity of the vertical pillar grows very slowly,so,there is little significance to continue to fill the low-grade backfill;(3)the bottom pillar suffers the squeezing action from the vertical pillars at first and then the gravity action of the low-grade backfill,and the maximum value of tension stress of the bottom pillar firstly increases and then decreases.Considering the economic factor,security and other factors,the low-grade backfill has the most reasonable height(2.8 m)in the scope of all filling height.
Limkumnerd, Surachate; Sethna, James P.
2007-06-01
We derive general relations between grain boundaries, rotational deformations, and stress-free states for the mesoscale continuum Nye dislocation density tensor. Dislocations generally are associated with long-range stress fields. We provide the general form for dislocation density fields whose stress fields vanish. We explain that a grain boundary (a dislocation wall satisfying Frank’s formula) has vanishing stress in the continuum limit. We show that the general stress-free state can be written explicitly as a (perhaps continuous) superposition of flat Frank walls. We show that the stress-free states are also naturally interpreted as configurations generated by a general spatially dependent rotational deformation. Finally, we propose a least-squares definition for the spatially dependent rotation field of a general (stressful) dislocation density field.
Douglas, Gregory S; Hardenstine, Jeffery H; Liu, Bo; Uhler, Allen D
2012-08-07
We describe a new and rapid quantitative approach to assess the extent of aerobic biodegradation of volatile and semivolatile hydrocarbons in crude oil, using Shushufindi oil from Ecuador as an example. Volatile hydrocarbon biodegradation was both rapid and complete-100% of the benzene, toluene, xylenes (BTEX) and 98% of the gasoline-range organics (GRO) were biodegraded in less than 2 days. Severe biodegradation of the semivolatile hydrocarbons occurred in the inoculated samples with 67% and 87% loss of the diesel-range hydrocarbons (DRO) in 3 and 20 weeks, respectively. One-hundred percent of the naphthalene, fluorene, and phenanthrene, and 46% of the chrysene in the oil were biodegraded within 3 weeks. Percent depletion estimates based on C(30) 17α,21β(H)-hopane (hopane) underestimated the diesel-range organics (DRO) and USEPA 16 priority pollutant PAH losses in the most severely biodegraded samples. The C(28) 20S-triaromatic steroid (TAS) was found to yield more accurate depletion estimates, and a new hopane stability ratio (HSR = hopane/(hopane + TAS)) was developed to monitor hopane degradation in field samples. Oil degradation within field soil samples impacted with Shushufindi crude oil was 83% and 98% for DRO and PAH, respectively. The gas chromatograms and percent depletion estimates indicated that similar levels of petroleum degradation occurred in both the field and laboratory samples, but hopane degradation was substantially less in the field samples. We conclude that cometabolism of hopane may be a factor during rapid biodegradation of petroleum in the laboratory and may not occur to a great extent during biodegradation in the field. We recommend that the hopane stability ratio be monitored in future field studies. If hopane degradation is observed, then the TAS percent depletion estimate should be computed to correct for any bias that may result in petroleum depletion estimates based on hopane.
Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III
1996-01-01
The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.
An analysis on short-wave components of the global stress field
黄玺瑛; 魏东平; 陈棋福; 陈虹
2003-01-01
The 10 920 stress indicators collected so far by the WSM (World Stress Map) project represent the observed orientations of the maximum horizontal principal stress ((Hmax) in a certain region. Assuming that the long-wave component of (Hmax is expressed by the absolute direction of plate motions, we can get the relative orientation and the magnitude of the short-wave component resulted from the local tectonic process or other factors with vector analytical technique. The global surface was divided into basic element bins by 2.5((2.5( dimensions and the WSM indicators were statistically analyzed for each element by weight coefficient method in order to determine the mean orientation of the stress. We calculated the long-wave component of the global stress field using HS2-NUVEL1 model. The relative magnitude or the direction limitation of short-wave component, which reflect the local contribution to the observed stresses, was determined by the angle between the mean (Hmax and the orientation of the long-wave component. The results of this paper show that the contribution of either the long-wave component or the short-wave component is approximately equal to most of the global plates on the basis of the mean effect of the observed stresses. For some of continental regions, the local active tectonics plays an important role in the observed stresses and controls the generation and occurrence of earthquakes.
Coupling Mechanism of Electromagnetic Field and Thermal Stress on Drosophila melanogaster
Yang, Chuan-Jun; Lian, Hui-Yong; Yu, Hui; Huang, Xiao-Mei; Cai, Peng
2016-01-01
Temperature is an important factor in research on the biological effects of extremely low-frequency electromagnetic field (ELF-EMF), but interactions between ELF-EMF and temperature remain unknown. The effects of ELF-EMF (50 Hz, 3 mT) on the lifespan, locomotion, heat shock response (HSR), and oxidative stress (OS) of Canton-Special (CS) and mutant w1118 flies were investigated at 25°C and 35°C (thermal stress). Results showed that thermal stress accelerated the death rates of CS and w1118 flies, shortened their lifespan, and influenced their locomotion rhythm and activity. The upregulated expression levels of heat shock protein (HSP) 22, HSP26, and HSP70 indicated that HSR was enhanced. Thermal stress-induced OS response increased malondialdehyde content, enhanced superoxide dismutase activity, and decreased reactive oxygen species level. The effects of thermal stress on the death rates, lifespan, locomotion, and HSP gene expression of flies, especially w1118 line, were also enhanced by ELF-EMF. In conclusion, thermal stress weakened the physiological function and promoted the HSR and OS of flies. ELF-EMF aggravated damages and enhanced thermal stress-induced HSP and OS response. Therefore, thermal stress and ELF-EMF elicited a synergistic effect. PMID:27611438
The electrical conductivity of the upper mantle as estimated from satellite magnetic field data
Didwall, E. M.
1984-01-01
The electrical conductivity of the upper mantle is estimated from low-latitude magnetic field variations caused by large fluctuations in the equatorial ring current. The data base is derived from magnetic field magnitude data measured by satellites OGO 2, 4, and 6, which offer better global coverage than land-based observatories. The procedures of analysis consist of: (1) separation of the disturbance field into internal and external parts relative to the surface of the earth, (2) estimation of an electromagnetic response function Q(omega) which relates the internally generated magnetic field variations to the external variations due to the ring current, and (3) interpretation of the estimated response function using theoretical response functions for assumed conductivity profiles. Special consideration is given to possible oceanic and ionospheric effects. Best estimates of the geomagnetic response function Q(omega) for 0.2 to 2.0 cpd indicate an upper mantle conductivity of the order of 0.01 S/m.
New a priori estimates for mean-field games with congestion
Evangelista, David
2016-01-06
We present recent developments in crowd dynamics models (e.g. pedestrian flow problems). Our formulation is given by a mean-field game (MFG) with congestion. We start by reviewing earlier models and results. Next, we develop our model. We establish new a priori estimates that give partial regularity of the solutions. Finally, we discuss numerical results.
Estimating adhesive seed-dispersal distances : field experiments and correlated random walks
Mouissie, AM; Lengkeek, W; van Diggelen, R
1. In this study we aimed to estimate distance distributions of adhesively dispersed seeds and the factors that determine them. 2. Seed attachment and detachment were studied using field experiments with a real sheep, a sheep dummy and a cattle dummy. Seed-retention data were used in correlated
The electrical conductivity of the upper mantle as estimated from satellite magnetic field data
Didwall, E. M.
1984-01-01
The electrical conductivity of the upper mantle is estimated from low-latitude magnetic field variations caused by large fluctuations in the equatorial ring current. The data base is derived from magnetic field magnitude data measured by satellites OGO 2, 4, and 6, which offer better global coverage than land-based observatories. The procedures of analysis consist of: (1) separation of the disturbance field into internal and external parts relative to the surface of the earth, (2) estimation of an electromagnetic response function Q(omega) which relates the internally generated magnetic field variations to the external variations due to the ring current, and (3) interpretation of the estimated response function using theoretical response functions for assumed conductivity profiles. Special consideration is given to possible oceanic and ionospheric effects. Best estimates of the geomagnetic response function Q(omega) for 0.2 to 2.0 cpd indicate an upper mantle conductivity of the order of 0.01 S/m.
Effects of the near field on source-independent q estimation
Shigapov, R.; Kashtan, B.; Droujinine, A.; Mulder, W.A.
2013-01-01
We consider the problem of Q estimation from microseismic and from perforation shot data. Assuming that the source wavelet is not well known, we focused on the spectral ratio method and on source-independent viscoelastic full waveform inversion. We derived 3-D near-field approximations of monopole a
The stress field and its sources in the North Atlantic Realm and Europe
Nielsen, S.B.; Schiffer, Christian; Stephenson, Randell Alexander
in the convecting mantle cause mantle tractions at the base of the lithosphere. The radial component can cause dynamic topography and an anomalous state of lithospheric pressure, whereas the horizontal component might influence the plate movements directly. Relative plate movements and stress transmission through...... the rigid plates result in forces along plate boundaries. The relative importance and absolute magnitudes of the single stress sources is still matter of considerable discussion. Whereas the crustal structure is relatively well constrained for the estimation of the geopotential stress component...... and temperature variations at the base of the lithosphere that result in dynamic topography, and an anomalous geopotential energy. We do not include horizontal basal tractions or plate boundary forces. Nevertheless we can indirectly discuss the importance of additional stress sources for the lithospheric state...
Estimating a Global Hydrological Carrying Capacity Using GRACE Observed Water Stress
An, K.; Reager, J. T.; Famiglietti, J. S.
2013-12-01
Global population is expected to reach 9 billion people by the year 2050, causing increased demands for water and potential threats to human security. This study attempts to frame the overpopulation problem through a hydrological resources lens by hypothesizing that observed groundwater trends should be directly attributed to human water consumption. This study analyzes the relationships between available blue water, population, and cropland area on a global scale. Using satellite data from NASA's Gravity Recovery and Climate Experiment (GRACE) along with land surface model data from the Global Land Data Assimilation System (GLDAS), a global groundwater depletion trend is isolated, the validity of which has been verified in many regional studies. By using the inherent distributions of these relationships, we estimate the regional populations that have exceeded their local hydrological carrying capacity. Globally, these populations sum to ~3.5 billion people that are living in presently water-stressed or potentially water-scarce regions, and we estimate total cropland is exceeding a sustainable threshold by about 80 million km^2. Key study areas such as the North China Plain, northwest India, and Mexico City were qualitatively chosen for further analysis of regional water resources and policies, based on our distributions of water stress. These case studies are used to verify the groundwater level changes seen in the GRACE trend . Tfor the many populous, arid regions of the world that have already begun to experience the strains of high water demand.he many populous, arid regions of the world have already begun to experience the strains of high water demand. It will take a global cooperative effort of improving domestic and agricultural use efficiency, and summoning a political will to prioritize environmental issues to adapt to a thirstier planet. Global Groundwater Depletion Trend (Mar 2003-Dec 2011)
Comprehensive Evaluation of Attitude and Orbit Estimation Using Actual Earth Magnetic Field Data
Deutschmann, Julie K.; Bar-Itzhack, Itzhack Y.
2000-01-01
A single, augmented Extended Kalman Filter (EKF), which simultaneously and autonomously estimates spacecraft attitude and orbit has been developed and successfully tested with real magnetometer and gyro data only. Because the earth magnetic field is a function of time and position, and because time is known quite precisely, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both orbit and attitude errors. Thus, conceivably these differences could be used to estimate both orbit and attitude; an observability study validated this assumption. The results of testing the EKF with actual magnetometer and gyro data, from four satellites supported by the NASA Goddard Space Flight Center (GSFC) Guidance, Navigation, and Control Center, are presented and evaluated. They confirm the assumption that a single EKF can estimate both attitude and orbit when using gyros and magnetometers only.
Optimization of Camera Arrangement Using Correspondence Field to Improve Depth Estimation.
Fu, Shichao; Safaei, Farzad; Li, Wanqing
2017-04-18
Stereo matching algorithms attempt to estimate depth from the images obtained by two cameras. In most cases, the arrangement of cameras (their locations and orientations with respect to the scene) are determined based on human experience. In this paper, it is shown that the camera arrangement can be optimized using the concept of correspondence field (CF) for better acquisition of depth. Specifically, the paper demonstrates the relationship between the correspondence field of a pair of cameras and depth estimation accuracy and presents a method to optimize their arrangement based on the gradient of CF. The experimental results show that a pair of cameras optimized by the proposed method can improve the accuracy of depth estimation by as much as 30% compared to the conventional camera arrangements.
Estimation of GNSS Multiscale Strain Field and Detection of Regional Crustal Deformation
XU Keke
2016-08-01
Full Text Available Using GNSS data,the estimation model for GNSS multiscale strain field was established based on spherical wavelet. The key technologies for wavelet center location, wavelet scale choices and regularization parameter calculation were discussed in detail. For further testing the correctness of the model, the simulated data in locked fault areas was generated according to negative dislocation theory. With spherical wavelet model, the strain field in locked strike-slip fault areas was estimated,and the results agreed well with the characteristics of actual crustal deformation. Meanwhile, the experiments on crustal deformation anomaly detection with multiscale strain field were completed. The results showed that the small fault deformation of 50 km appeared obviously in the small scale(8th scale stain field, but there wasn't signals in the large scale (4 to 7 scale. The large fault deformation of 150 km only showed a part of information in the small scale (8th scale stain field, but showed more completely and clearly in the large scale(4 to 7 scale.So it's concluded that crustal deformation of different spatial coverage scope embody in the different scales strain field, and the small scale strain field have the ability to detect regional deformation anomaly.
Third-order elastic solution of the stress field around a wellbore
Elata, D.
1996-04-01
Within a certain range of strain, consolidated granular materials may be characterized as nonlinear elastic solids. The nonlinearity can be easily observed by examining the effect of stress on the acoustical properties of the material. Ignoring damage evolution and failure that occur in higher strains and the hysteretic behavior due to intercyranular friction, the material can be modeled as a nonlinear hyperelastic solid. A simple example of such a model is formulating the strain energy as a third-order polynomial of the strain invariants. This model is limited in the sense that the material is assumed to be isotropic with respect to the stress free state, and that the mechanical response of the material is described by only five material constants. Nevertheless, this model is appealing because it naturally exhibits stress dependent stiffness and stress induced anisotropy, and it allows a different mechanical response to positive and negative volume changes. In this work, this model is used to calculate the stress field around a wellbore. Many well logging tools use acoustics (e.g., tube, surface, torsion, and flexural waves) to detect pore fluids and ore in the surrounding granular rock. By modeling the rock as an isotropic third-order elastic material the effects of the inhomogeneous stiffness and the stress induced anisotropy may be examined. Analysis of the tangential stress around a wellbore in an isotropic third-order elastic (TOE) material yields different results than the same analysis in the related isotropic linear elastic (LE) material (i.e., both materials have the same stiffness tensor at the stress free state). This difference modifies the far-field stress that is interpreted of from hydraulic fracturing data. The analysis in the present work is static and pore fluid effects are ignored.
Collaborative effects of electric field and fluid shear stress on fibroblast migration.
Song, Sukhyun; Han, Hana; Ko, Ung Hyun; Kim, Jaemin; Shin, Jennifer H
2013-04-21
Cells are inherently exposed to a number of different biophysical stimuli such as electric fields, shear stress, and tensile or compressive stress from the extracellular environment in vivo. Each of these biophysical cues can work simultaneously or independently to regulate cellular functions and tissue integrity in both physiological and pathological conditions. Thus, it is vital to understand the interaction of multiple stimuli on cells by decoupling and coupling the stimuli in simple combinations and by investigating cellular behaviors in response to these cues. Here, we report a novel microfluidic platform to apply the combinatorial stimulation of an electric field and fluid shear stress by controlling two directional cues independently. An integrated microfluidic platform was developed using soft lithography to monitor the cellular migration in real-time in response to an electric field and fluid shear stress in single, simultaneous, and sequential modes. When each of these stimulations is applied separately, normal human dermal fibroblasts migrate toward the anode and in the direction of fluid flow in a dose-dependent manner. Simultaneous stimulation with an electric field and shear stress, which mimics a wound in vivo, enhances the directional migration of fibroblasts by increasing both directedness and trajectory speed, suggesting the plausible scenario of cooperation between two physical cues to promote wound healing. When an electric field and shear stress are applied sequentially, migration behavior is affected by the applied stimulation as well as pre-existing stimulating conditions. This microfluidic platform can be utilized to understand other microenvironments such as embryogenesis, angiogenesis and tumor metastasis.
Hong, Hunsop; Schonfeld, Dan
2008-06-01
In this paper, we propose a maximum-entropy expectation-maximization (MEEM) algorithm. We use the proposed algorithm for density estimation. The maximum-entropy constraint is imposed for smoothness of the estimated density function. The derivation of the MEEM algorithm requires determination of the covariance matrix in the framework of the maximum-entropy likelihood function, which is difficult to solve analytically. We, therefore, derive the MEEM algorithm by optimizing a lower-bound of the maximum-entropy likelihood function. We note that the classical expectation-maximization (EM) algorithm has been employed previously for 2-D density estimation. We propose to extend the use of the classical EM algorithm for image recovery from randomly sampled data and sensor field estimation from randomly scattered sensor networks. We further propose to use our approach in density estimation, image recovery and sensor field estimation. Computer simulation experiments are used to demonstrate the superior performance of the proposed MEEM algorithm in comparison to existing methods.
Ponte Castañeda, Pedro
2016-11-01
This paper presents a variational method for estimating the effective constitutive response of composite materials with nonlinear constitutive behavior. The method is based on a stationary variational principle for the macroscopic potential in terms of the corresponding potential of a linear comparison composite (LCC) whose properties are the trial fields in the variational principle. When used in combination with estimates for the LCC that are exact to second order in the heterogeneity contrast, the resulting estimates for the nonlinear composite are also guaranteed to be exact to second-order in the contrast. In addition, the new method allows full optimization with respect to the properties of the LCC, leading to estimates that are fully stationary and exhibit no duality gaps. As a result, the effective response and field statistics of the nonlinear composite can be estimated directly from the appropriately optimized linear comparison composite. By way of illustration, the method is applied to a porous, isotropic, power-law material, and the results are found to compare favorably with earlier bounds and estimates. However, the basic ideas of the method are expected to work for broad classes of composites materials, whose effective response can be given appropriate variational representations, including more general elasto-plastic and soft hyperelastic composites and polycrystals.
Estimation of soil moisture in paddy field using Artificial Neural Networks
Chusnul Arif
2012-04-01
Full Text Available In paddy field, monitoring soil moisture is required for irrigation scheduling and water resource allocation, management and planning. The current study proposes an Artificial Neural Networks (ANN model to estimate soil moisture in paddy field with limited meteorological data. Dynamic of ANN model was adopted to estimate soil moisture with the inputs of reference evapotranspiration (ETo and precipitation. ETo was firstly estimated using the maximum, average and minimum values of air temperature as the inputs of model. The models were performed under different weather conditions between the two paddy cultivation periods. Training process of model was carried out using the observation data in the first period, while validation process was conducted based on the observation data in the second period. Dynamic of ANN model estimated soil moisture with R2 values of 0.80 and 0.73 for training and validation processes, respectively, indicated that tight linear correlations between observed and estimated values of soil moisture were observed. Thus, the ANN model reliably estimates soil moisture with limited meteorological data.
Nabert, Christian; Othmer, Carsten; Glassmeier, Karl-Heinz
2017-05-01
The interaction of the solar wind with a planetary magnetic field causes electrical currents that modify the magnetic field distribution around the planet. We present an approach to estimating the planetary magnetic field from in situ spacecraft data using a magnetohydrodynamic (MHD) simulation approach. The method is developed with respect to the upcoming BepiColombo mission to planet Mercury aimed at determining the planet's magnetic field and its interior electrical conductivity distribution. In contrast to the widely used empirical models, global MHD simulations allow the calculation of the strongly time-dependent interaction process of the solar wind with the planet. As a first approach, we use a simple MHD simulation code that includes time-dependent solar wind and magnetic field parameters. The planetary parameters are estimated by minimizing the misfit of spacecraft data and simulation results with a gradient-based optimization. As the calculation of gradients with respect to many parameters is usually very time-consuming, we investigate the application of an adjoint MHD model. This adjoint MHD model is generated by an automatic differentiation tool to compute the gradients efficiently. The computational cost for determining the gradient with an adjoint approach is nearly independent of the number of parameters. Our method is validated by application to THEMIS (Time History of Events and Macroscale Interactions during Substorms) magnetosheath data to estimate Earth's dipole moment.
Estimating field scale root zone soil moisture using the cosmic-ray neutron probe
Peterson, A. M.; Helgason, W. D.; Ireson, A. M.
2015-12-01
Many practical hydrological, meteorological and agricultural management problems require estimates of soil moisture with an areal footprint equivalent to "field scale", integrated over the entire root zone. The cosmic-ray neutron probe is a promising instrument to provide field scale areal coverage, but these observations are shallow and require depth scaling in order to be considered representative of the entire root zone. A study to identify appropriate depth-scaling techniques was conducted at a grazing pasture site in central Saskatchewan, Canada over a two year period. Area-averaged soil moisture was assessed using a cosmic-ray neutron probe. Root zone soil moisture was measured at 21 locations within the 5002 m2 area, using a down-hole neutron probe. The cosmic-ray neutron probe was found to provide accurate estimates of field scale surface soil moisture, but accounted for less than 40 % of the seasonal change in root zone storage due to its shallow measurement depth. The root zone estimation methods evaluated were: (1) the coupling of the cosmic-ray neutron probe with a time stable neutron probe monitoring location, (2) coupling the cosmic-ray neutron probe with a representative landscape unit monitoring approach, and (3) convolution of the cosmic-ray neutron probe measurements with the exponential filter. The time stability method provided the best estimate of root zone soil moisture (RMSE = 0.004 cm3 cm-3), followed by the exponential filter (RMSE = 0.012 cm3 cm-3). The landscape unit approach, which required no calibration, had a negative bias but estimated the cumulative change in storage reasonably. The feasibility of applying these methods to field sites without existing instrumentation is discussed. It is concluded that the exponential filter method has the most potential for estimating root zone soil moisture from cosmic-ray neutron probe data.
Liarte, Danilo B; Transtrum, Mark K; Catelani, Gianluigi; Liepe, Matthias; Sethna, James P
2016-01-01
We review our work on theoretical limits to the performance of superconductors in high magnetic fields parallel to their surfaces. These limits are of key relevance to current and future accelerating cavities, especially those made of new higher-$T_c$ materials such as Nb$_3$Sn, NbN, and MgB$_2$. We summarize our calculations of the so-called superheating field $H_{\\mathrm{sh}}$, beyond which flux will spontaneously penetrate even a perfect superconducting surface and ruin the performance. We briefly discuss experimental measurements of the superheating field, comparing to our estimates. We explore the effects of materials anisotropy and disorder. Will we need to control surface orientation in the layered compound MgB$_2$? Can we estimate theoretically whether dirt and defects make these new materials fundamentally more challenging to optimize than niobium? Finally, we discuss and analyze recent proposals to use thin superconducting layers or laminates to enhance the performance of superconducting cavities. T...
The limiting behavior of the estimated parameters in a misspecified random field regression model
Dahl, Christian Møller; Qin, Yu
convenient new uniform convergence results that we propose. This theory may have applications beyond those presented here. Our results indicate that classical statistical inference techniques, in general, works very well for random field regression models in finite samples and that these models succesfully......This paper examines the limiting properties of the estimated parameters in the random field regression model recently proposed by Hamilton (Econometrica, 2001). Though the model is parametric, it enjoys the flexibility of the nonparametric approach since it can approximate a large collection...... of nonlinear functions and it has the added advantage that there is no "curse of dimensionality."Contrary to existing literature on the asymptotic properties of the estimated parameters in random field models our results do not require that the explanatory variables are sampled on a grid. However...
Discussion on rotational tectonic stress field and the genesis of circum-Ordos landmass fault system
谢新生
2004-01-01
When the resultant of applied forces does not pass through the center of an active landmass, the landmass will rotate, giving rise to a rotational tectonic stress field. The motion of a fault along the principal stress plane is determined by the mechanic features of the plane. Tensile fractures occur on the faults in the direction of the principal extensional stress plane, and fault-depression basins will be formed under a long-term action. Thrusting and overthrusting occur on faults in the direction of the principal compressional stress plane, or folds may be formed as a result. Information on geology shows that the North China landmass, which remained stable and intact for a long time, became disjointed in the Eogene period. In the course of disjunction, anticlockwise rotation took place in the Shanxi-Hebei-Shaanxi (Jin-Ji-Shan) landmass, giving rise to the fault-depression system in its periphery. In the Pliocene epoch the landmass lost stability and its eastern boundary moved westward. As a result, the Shanxi graben system appeared and Ordos landmass was formed. Structural and mechanic features of the main faults around Jin-Ji-Shan landmass can be explained with principal stress plane of a rotational tectonic stress field.
The stress field beneath a quiescent stratovolcano: The case of Mount Vesuvius
D'Auria, Luca; Massa, Bruno; Matteo, Ada De
2014-02-01
We have analyzed a focal mechanism data set for Mount Vesuvius, consisting of 197 focal mechanisms of events recorded from 1999 to 2012. Using different approaches and a comparison between observations and numerical models, we have determined the spatial variations in the stress field beneath the volcano. The main results highlight the presence of two seismogenic volumes characterized by markedly different stress patterns. The two volumes are separated by a layer where the seismic strain release shows a significant decrease. Previous studies postulated the existence, at about the same depth, of a ductile layer allowing the spreading of the Mount Vesuvius edifice. We interpreted the difference in the stress pattern within the two volumes as the effect of a mechanical decoupling caused by the aforementioned ductile layer. The stress pattern in the top volume is dominated by a reverse faulting style, which agrees with the hypothesis of a seismicity driven by the spreading process. This agrees also with the persistent character of the seismicity located within this volume. Conversely, the stress field determined for the deep volume is consistent with a background regional field locally perturbed by the effects of the topography and of heterogeneities in the volcanic structure. Since the seismicity of the deep volume shows an intermittent behavior and has shown to be linked to geochemical variations in the fumaroles of the volcano, we hypothesize that it results from the effect of fluid injection episodes, possibly of magmatic origin, perturbing the pore pressure within the hydrothermal system.
Silvestri, Erin E; Yund, Cynthia; Taft, Sarah; Bowling, Charlena Yoder; Chappie, Daniel; Garrahan, Kevin; Brady-Roberts, Eletha; Stone, Harry; Nichols, Tonya L
2017-03-01
In the event of an indoor release of an environmentally persistent microbial pathogen such as Bacillus anthracis, the potential for human exposure will be considered when remedial decisions are made. Microbial site characterization and clearance sampling data collected in the field might be used to estimate exposure. However, there are many challenges associated with estimating environmental concentrations of B. anthracis or other spore-forming organisms after such an event before being able to estimate exposure. These challenges include: (1) collecting environmental field samples that are adequate for the intended purpose, (2) conducting laboratory analyses and selecting the reporting format needed for the laboratory data, and (3) analyzing and interpreting the data using appropriate statistical techniques. This paper summarizes some key challenges faced in collecting, analyzing, and interpreting microbial field data from a contaminated site. Although the paper was written with considerations for B. anthracis contamination, it may also be applicable to other bacterial agents. It explores the implications and limitations of using field data for determining environmental concentrations both before and after decontamination. Several findings were of interest. First, to date, the only validated surface/sampling device combinations are swabs and sponge-sticks on stainless steel surfaces, thus limiting availability of quantitative analytical results which could be used for statistical analysis. Second, agreement needs to be reached with the analytical laboratory on the definition of the countable range and on reporting of data below the limit of quantitation. Finally, the distribution of the microbial field data and statistical methods needed for a particular data set could vary depending on these data that were collected, and guidance is needed on appropriate statistical software for handling microbial data. Further, research is needed to develop better methods to
Roshni Jaiswal
2016-01-01
Full Text Available Background: Stress classically describes a destructive notion that can have a bearing on one's physical and mental health. It may also add to an increased propensity to periodontal disease. Aim: To investigate the association between psychological stress and serum cortisol levels in patients with chronic periodontitis. Materials and Methods: Forty subjects were recruited from the outpatient department at the Department of Periodontics, from a college in Mangalore, divided into two groups, i.e., twenty as healthy controls and twenty were stressed subjects with chronic periodontitis. The clinical examination included the assessment of probing pocket depth, clinical attachment level and oral hygiene index-simplified. Serum cortisol levels were estimated biochemically using the enzyme-linked immunosorbent assay method and the estimation of psychological stress was done by a questionnaire. Results: Descriptive statistics such as mean and standard deviation was used to review the collected data. Independent sample t-test was used for comparison and correlation was evaluation using Pearson's correlation test. As per our observation, high serum cortisol levels and psychological stress are positively linked with chronic periodontitis establishing a risk profile showing a significant correlation (P < 0.05. Conclusion: Routine serum cortisol assessment may be a reasonable and a valuable investigative indicator to rule out stress in periodontitis patients as it should be considered as an imperative risk factor for periodontal disease.
Schall, Mark C; Fethke, Nathan B; Chen, Howard; Gerr, Fred
2015-05-01
The performance of an inertial measurement unit (IMU) system for directly measuring thoracolumbar trunk motion was compared to that of the Lumbar Motion Monitor (LMM). Thirty-six male participants completed a simulated material handling task with both systems deployed simultaneously. Estimates of thoracolumbar trunk motion obtained with the IMU system were processed using five common methods for estimating trunk motion characteristics. Results of measurements obtained from IMUs secured to the sternum and pelvis had smaller root-mean-square differences and mean bias estimates in comparison to results obtained with the LMM than results of measurements obtained solely from a sternum mounted IMU. Fusion of IMU accelerometer measurements with IMU gyroscope and/or magnetometer measurements was observed to increase comparability to the LMM. Results suggest investigators should consider computing thoracolumbar trunk motion as a function of estimates from multiple IMUs using fusion algorithms rather than using a single accelerometer secured to the sternum in field-based studies.
Using thermal tracers to estimate flow velocities of shallow flows: laboratory and field experiments
Lima Rui L.P. de
2015-09-01
Full Text Available Accurate measurement of shallow flows is important for hydraulics, hydrology and water resources management. The objective of this paper is to discuss a technique for shallow flow and overland flow velocity estimation that uses infrared thermography. Laboratory flumes and different bare, vegetated and paved field surfaces were used to test the technique. Results show that shallow flow surface velocities estimated using thermal tracers and infrared technology are similar to estimates obtained using the Acoustic Doppler Velocimeter; similar results were also obtained for overland flow velocity estimates using thermography, here comparing with the dye tracer technique. The thermographic approach revealed some potential as a flow visualization technique, and leaves space for future studies and research.
Dynamic Response in Transient Stress-Field Behavior Induced by Hydraulic Fracturing
Jenkins, Andrew
Hydraulic fracturing is a technique which is used to exploit geologic features and subsurface properties in an effort to increase production in low-permeability formations. The process of hydraulic fracturing provides a greater surface contact area between the producing formation and the wellbore and thus increases the amount of recoverable hydrocarbons from within the reservoir. The use of this stimulation technique has brought on massive applause from the industry due to its widespread success and effectiveness, however the dynamic processes that take part in the development of hydraulic fractures is a relatively new area of research with respect to the massive scale operations that are seen today. The process of hydraulic fracturing relies upon understanding and exploiting the in-situ stress distribution throughout the area of study. These in-situ stress conditions are responsible for directing fracture orientation and propagation paths throughout the period of injection. The relative magnitude of these principle stresses is key in developing a successful stimulation plan. In horizontal well plan development the interpretation of stress within the reservoir is required for determining the azimuth of the horizontal well path. These horizontal laterals are typically oriented in a manner such that the well path lies parallel to the minimum horizontal stress. This allows for vertical fractures to develop transversely to the wellbore, or normal to the least principle stress without the theoretical possibility of fractures overlapping, creating the most efficient use of the fluid energy during injection. The orientation and magnitude of these in-situ stress fields however can be dynamic, controlled by the subsequent fracture propagation and redistribution of the surrounding stresses. That is, that as the fracture propagates throughout the reservoir, the relative stress fields surrounding the fractures may see a shift and deviate from their original direction or
徐明瑜; 谭文长
2001-01-01
The velocity field of generalized second order fluid with fractional anomalous diffusion caused by a plate moving impulsively in its own plane is investigated and the anomalous diffusion problems of the stress field and vortex sheet caused by this process are studied. Many previous and classical results can be considered as particular cases of this paper, such as the solutions of the fractional diffusion equations obtained by Wyss; the classical Rayleigh' s time-space similarity solution; the relationship between stress field and velocity field obtained by Bagley and co-worker and Podlubny' s results on the fractional motion equation of a plate. In addition, a lot of significant results also are obtained. For example, the necessary condition for causing the vortex sheet is that the time fractional diffusion index β must be greater than that of generalized second order fluid α; the establishment of the vorticity distribution function depends on the time history of the velocity profile at a given point, and the time history can be described by the fractional calculus.
Bi-Metallic Composite Structures With Designed Internal Residual Stress Field
Brice, Craig A.
2014-01-01
Shape memory alloys (SMA) have a unique ability to recover small amounts of plastic strain through a temperature induced phase change. For these materials, mechanical displacement can be accomplished by heating the structure to induce a phase change, through which some of the plastic strain previously introduced to the structure can be reversed. This paper introduces a concept whereby an SMA phase is incorporated into a conventional alloy matrix in a co-continuous reticulated arrangement forming a bi-metallic composite structure. Through memory activation of the mechanically constrained SMA phase, a controlled residual stress field is developed in the interior of the structure. The presented experimental data show that the memory activation of the SMA composite component significantly changes the residual stress distribution in the overall structure. Designing the structural arrangement of the two phases to produce a controlled residual stress field could be used to create structures that have much improved durability and damage tolerance properties.
Estimation of the effects of strong static magnetic fields on plants.
Kuznetsov, O.
In our recent studies we extensively used ponderomotive magnetic forces in high gradient magnetic fields (HGMF) for displacing organelles inside plant gravity receptor cells. Such displacement is a convenient tool both for investigating plant gravity perception mechanism and for physical characterization of the cell interior, and can have future practical applications in providing a directional stimulus for plants in microgravity. This method takes advantage of the magnetic heterogeneity of the receptor cells, namely stronger diamagnetism of starch-filled amyloplasts compared to cytoplasm (? æ < 0). Such particles are repelled from the zones of stronger field in a non-uniform field. To exert a force on amyloplasts, which is comparable to the gravity force, the dynamic factor of the field grad(H2 /2) needs to be 109 - 1 01 0 Oe 2 /cm, and the field intensity in the experimental magnetic systems typically varies from 0 to 2.5-104 Oe, while the size of the area of non-uniformity is 10-2 to 1 cm. Possible effects of such static magnetic fields on plants other than magnetophoresis of amyloplasts were estimated theoretically and tested experimentally. No statistically significant differences in growth rates or rates of gravicurvature were observed in experiments with Linum, Arabidopsis, Hordeum, Avena, Ceratodon and Chara between the plants grown in uniform magnetic fields of various intensities (102 to 2.5-104 Oe) and those grown in the Earth's magnetic field. Microscopic studies also did not detect any structural differences between test and control plants. The magnitudes of possible effects of static magnetic fields on plant cells and organs (including effects on ion currents, magneto-hydrodynamic effects in moving cytoplasm, ponderomotive forces on other cellular structures, effects on some biochemical reactions and biomolecules) were estimated theoretically. The estimations have shown, that these effects are small compared to the thermodynamic noise and thus are
Laser cutting of holes in thick sheet metals: Development of stress field
Yilbas, B. S.; Arif, A. F. M.; Aleem, B. J. Abdul
2009-09-01
Laser cutting of hole in a mild steel thick sheet metal is investigated. Temperature and stress fields developed around the cutting section are simulated using the finite element method. An experimental is carried out accommodating the simulation parameters. The residual stress developed in the cutting section is measured using the XRD technique and findings are compared with the predictions. Optical microscopy and SEM are carried out to examine the morphological changes in the cutting sections. It is found that temperature decays sharply in the region of the laser heat source, which results in high temperature gradient in this region. This causes the development of high stress levels around the cut edges. The residual stresses predicted are in agreement with the measured results.
Cecchini, M; Colantoni, A; Massantini, R; Monarca, D
2010-07-01
Agricultural workers are exposed to various risks, including chemical agents, noise, and many other factors. One of the most characteristic and least known risk factors is constituted by the microclimatic conditions in the different phases of work (in field, in greenhouse, etc). A typical condition is thermal stress due to high temperatures during harvesting operations in open fields or in greenhouses. In Italy, harvesting is carried out for many hours during the day, mainly in the summer, with temperatures often higher than 30 degrees C. According to ISO 7243, these conditions can be considered dangerous for workers' health. The aim of this study is to assess the risks of exposure to microclimatic conditions (heat) for fruit and vegetable harvesters in central Italy by applying methods established by international standards. In order to estimate the risk for workers, the air temperature, radiative temperature, and air speed were measured using instruments in conformity with ISO 7726. Thermodynamic parameters and two more subjective parameters, clothing and the metabolic heat production rate related to the worker's physical activity, were used to calculate the predicted heat strain (PHS) for the exposed workers in conformity with ISO 7933. Environmental and subjective parameters were also measured for greenhouse workers, according to ISO 7243, in order to calculate the wet-bulb globe temperature (WBGT). The results show a slight risk for workers during manual harvesting in the field. On the other hand, the data collected in the greenhouses show that the risk for workers must not be underestimated. The results of the study show that, for manual harvesting work in climates similar to central Italy, it is essential to provide plenty of drinking water and acclimatization for the workers in order to reduce health risks. Moreover, the study emphasizes that the possible health risks for greenhouse workers increase from the month of April through July.
Naidu, V.S.
location for discharge of the effluents into the sea by using near-field and far-field models. Near-field dilutions were calculated using a buoyant jet model, whereas far-field dilutions were estimated using a two-dimensional numerical model. As a case...
The University of California Institute of Environmental Stress Marathon Field Studies
Maron, Michael B.
2014-01-01
In 1973, the Institute of Environmental Stress of the University of California-Santa Barbara, under the direction of Steven M. Horvath, began a series of field and laboratory studies of marathon runners during competition. As one of Horvath's graduate students, many of these studies became part of my doctoral dissertation. The rationale for…
The University of California Institute of Environmental Stress Marathon Field Studies
Maron, Michael B.
2014-01-01
In 1973, the Institute of Environmental Stress of the University of California-Santa Barbara, under the direction of Steven M. Horvath, began a series of field and laboratory studies of marathon runners during competition. As one of Horvath's graduate students, many of these studies became part of my doctoral dissertation. The rationale for…
Vortex configuration in the presence of local magnetic field and locally applied stress
Wissberg, Shai; Kremen, Anna; Shperber, Yishai; Kalisky, Beena
2017-02-01
Vortex configuration is determined by the repulsive interaction, which becomes dominant with increasing vortex density, by the pinning potential, and by other considerations such as the local magnetic fields, currents flowing in the sample, or as we showed recently, by local stress applied on the sample. In this work we describe different ways to control vortex configuration using scanning SQUID microscopy.
Field performance of timber bridges. 11, Spearfish Creek stress-laminated box-beam bridge
J. P. Wacker; M. A. Ritter; K. Stanfill-McMillan
The Spearfish Creek bridge was constructed in 1992 in Spearfish, South Dakota. It is a single-span, stress-laminated, box-beam superstructure. Performance of the bridge is being monitored for 5 years, beginning at installation. This report summarizes results for the first 3-1/2 years of monitoring and includes information on the design, construction, and field...
Monaco, James P; Madabhushi, Anant
2012-12-01
Many estimation tasks require Bayesian classifiers capable of adjusting their performance (e.g. sensitivity/specificity). In situations where the optimal classification decision can be identified by an exhaustive search over all possible classes, means for adjusting classifier performance, such as probability thresholding or weighting the a posteriori probabilities, are well established. Unfortunately, analogous methods compatible with Markov random fields (i.e. large collections of dependent random variables) are noticeably absent from the literature. Consequently, most Markov random field (MRF) based classification systems typically restrict their performance to a single, static operating point (i.e. a paired sensitivity/specificity). To address this deficiency, we previously introduced an extension of maximum posterior marginals (MPM) estimation that allows certain classes to be weighted more heavily than others, thus providing a means for varying classifier performance. However, this extension is not appropriate for the more popular maximum a posteriori (MAP) estimation. Thus, a strategy for varying the performance of MAP estimators is still needed. Such a strategy is essential for several reasons: (1) the MAP cost function may be more appropriate in certain classification tasks than the MPM cost function, (2) the literature provides a surfeit of MAP estimation implementations, several of which are considerably faster than the typical Markov Chain Monte Carlo methods used for MPM, and (3) MAP estimation is used far more often than MPM. Consequently, in this paper we introduce multiplicative weighted MAP (MWMAP) estimation-achieved via the incorporation of multiplicative weights into the MAP cost function-which allows certain classes to be preferred over others. This creates a natural bias for specific classes, and consequently a means for adjusting classifier performance. Similarly, we show how this multiplicative weighting strategy can be applied to the MPM
Kim, M. C.; Cho, H.; Son, M.
2014-12-01
To determine current regional stress field and to characterize the resultant crustal deformation in SE Korea, Quaternary fault, focal mechanism, and geotechnical in-situ stress data were synthetically analyzed. The Quaternary faults are extensively observed along major inherited fault zones and show compatible orientations with general trends of the inherited faults. Most of the Quaternary faults have a top-to-the-west thrust geometry and kinematics and show a tendency of upward-decreasing dip angle and upward-narrowing gouge zone. Slip-sense indicators and paleo-stress field reconstructions indicate that the faults resulted from reverse or transpressional faulting under an E-W compression. All the magnetic fabrics (AMS) of the fault gouges also indicate the prevailing reverse-slip faulting under an ENE-WNW compression. The dominant oblate magnetic fabrics parallel to fault plane and the degrees of anisotropy increasing in proportion to their oblatenesses indicate that the fabrics have formed by a progressive deformation due to continuous simple shear during the last reactivation stage as reverse faulting. The focal mechanism study in and around the Korean Peninsula show the horizontally clustered P-axes in ENE-WSW direction and the girdle-distributed T-axes in NNW trend. The geotechnical in-situ stress data in south Korea also show NE- or ENE-trending maximum horizontal stress. The current crustal deformation in Korea thus can be characterized by contractional structures produced under a regional E-W or ENE-WSW compression stress field, and most of the Quaternary faults resulted from the local re-activation of appropriately oriented inherited major faults. Considering the tectonic setting and structural features in Asia during the Neogene, the current stress regime is interpreted to have been caused by the cooperation of westward shallow subduction of Pacific Plate and collision of Indian and Eurasian continents since about 5-3.5 Ma.
Source mechanism of small-moderate earthquakes and tectonic stress field in Yunnan Province
吴建平; 明跃红; 王椿镛
2004-01-01
In the paper, source mechanisms of 33 small-moderate earthquakes occurred in Yunnan are determined by modeling of regional waveforms from Yunnan digital seismic network. The result shows that most earthquakes occurred within or near the Chuandian rhombic block have strike-slip mechanism. The orientations of maximum compressive stresses obtained from source mechanism are changed from NNW-SSN to NS in the areas from north to south of the block, and tensile stresses are mainly in ENE-WSW or NE-SE. In the eastern Tibetan Plateau, the orientations of maximum compressive stress radiate toward outside from the plateau, and the tensile stress orientations mostly parallel to arc structures. Near 28°N the orientations of both maximum compressive stress and tensile stress changed greatly, and the boundary seems to correspond to the southwestern extended line of Longmenshan fault. Outside of the Chuandian rhombic block, the orientations of P and T axes are some different from those within the block. The comparison shows that the source mechanism of small-moderate events presented in the paper is consistence with that of moderate-strong earthquakes determined by Harvard University, which means the source mechanism of small-moderate events can be used to study the tectonic stress field in this region.
Dose estimation outside radiation field using Pinpoint and Semiflex ionization chamber detectors
Abdelaal, Ahmed M.; Attalla, Ehab M.; Elshemey, Wael M.
2017-10-01
This work aims to provide a comparison between two important detectors (Pinpoint and Semiflex) that are frequently used in radiation dosimetery in radiotherapy. This is carried out through the employment of both detectors in a quantitative estimation of the change in out-of-field dose with important dosimetric parameters such as field size (from 5×5 cm2 to 30×30 cm2) and depth (from 1.5 cm to 30 cm) at two different energies (6 MV and 15 MV) and two different collimator angles (0-90°). The change in out-of-field dose with Source-Skin-Distance (SSD) from 80 to 115 cm is also studied using both detectors. Results show that, the Pinpoint and Semiflex detectors both reported an increase in out-of-field dose with field size, depth, energy and SSD. In almost all measurements, Pinpoint detector reported considerably higher out-of-field dose values compared to Semiflex. For 6 MV and 0° collimator angle, the out-of-field dose at field size of 30×30 cm2 and at a depth of 1.5 cm is 7.3% for Pinpoint detector compared to 4.3% for Semiflex. At collimator angle of 90°, the out-of-field dose is 6.5% for Pinpoint detector compared to 5.5% for semiflex. The out-of-field dose for a depth of 30 cm and field size of 10×10 cm is 7.9% for Pinpoint detector compared to 5.9% for Semiflex. For 15 MV and 0° collimator angle, the out-of-field dose at field size of 30×30 cm2 and at a depth of 1.5 cm is 7.5% for Pinpoint detector compared 5.1% for Semiflex. At 6 MV, field size of 10×10 cm2 and depth of 1.5 cm, the out-of-field dose at SSD 115 cm is 3.7% for Pinpoint detector compared to 3.4% for Semiflex. The considerably higher out-of-field dose values reported by Pinpoint detector compared to Semiflex may be attributed to the relatively higher sensitivity of Pinpoint detector for low doses (such as out-of-field doses). Therefore, for reliable out-of-field dose measurements a Pinpoint detector is highly recommended.
Zech, Alraune; Arnold, Sven; Schneider, Christoph; Attinger, Sabine
2015-09-01
The knowledge of subsurface heterogeneity is a prerequisite to describe flow and transport in porous media. Of particular interest are the variance and the correlation scale of hydraulic conductivity. In this study, we present how these aquifer parameters can be inferred using empirical steady state pumping test data. We refer to a previously developed analytical solution of "effective well flow" and examine its applicability to pumping test data as under field conditions. It is examined how the accuracy and confidence of parameter estimates of variance and correlation length depend on the number and location of head measurements. Simulations of steady state pumping tests in a confined virtual aquifer are used to systematically reduce sampling size while determining the rating of the estimates at each level of data density. The method was then applied to estimate the statistical parameters of a fluvial heterogeneous aquifer at the test site Horkheimer Insel, Germany. We conclude that the "effective well flow" solution is a simple alternative to laboratory investigations to estimate the statistical heterogeneity parameter using steady state pumping tests. However, the accuracy and uncertainty of the estimates depend on the design of the field study. In this regard, our results can help to improve the conceptual design of pumping tests with regard to the parameter of interest.
PSF Estimation of Space-Variant Ultra-Wide Field of View Imaging Systems
Petr Janout
2017-02-01
Full Text Available Ultra-wide-field of view (UWFOV imaging systems are affected by various aberrations, most of which are highly angle-dependent. A description of UWFOV imaging systems, such as microscopy optics, security camera systems and other special space-variant imaging systems, is a difficult task that can be achieved by estimating the Point Spread Function (PSF of the system. This paper proposes a novel method for modeling the space-variant PSF of an imaging system using the Zernike polynomials wavefront description. The PSF estimation algorithm is based on obtaining field-dependent expansion coefficients of the Zernike polynomials by fitting real image data of the analyzed imaging system using an iterative approach in an initial estimate of the fitting parameters to ensure convergence robustness. The method is promising as an alternative to the standard approach based on Shack–Hartmann interferometry, since the estimate of the aberration coefficients is processed directly in the image plane. This approach is tested on simulated and laboratory-acquired image data that generally show good agreement. The resulting data are compared with the results of other modeling methods. The proposed PSF estimation method provides around 5% accuracy of the optical system model.
Goncharov, Yu P
2014-01-01
The paper is devoted to applying the confinement mechanism proposed earlier by one of the authors to estimate the possible parameters of the confining SU(3)-gluonic field in vector $\\phi$-meson. The estimates obtained are consistent with the leptonic widths of the given meson. The corresponding estimates of the gluon concentrations, electric and magnetic colour field strengths are also adduced for the mentioned field at the scales of the meson under consideration.
Li, Chunming; Gore, John C; Davatzikos, Christos
2014-09-01
This paper proposes a new energy minimization method called multiplicative intrinsic component optimization (MICO) for joint bias field estimation and segmentation of magnetic resonance (MR) images. The proposed method takes full advantage of the decomposition of MR images into two multiplicative components, namely, the true image that characterizes a physical property of the tissues and the bias field that accounts for the intensity inhomogeneity, and their respective spatial properties. Bias field estimation and tissue segmentation are simultaneously achieved by an energy minimization process aimed to optimize the estimates of the two multiplicative components of an MR image. The bias field is iteratively optimized by using efficient matrix computations, which are verified to be numerically stable by matrix analysis. More importantly, the energy in our formulation is convex in each of its variables, which leads to the robustness of the proposed energy minimization algorithm. The MICO formulation can be naturally extended to 3D/4D tissue segmentation with spatial/sptatiotemporal regularization. Quantitative evaluations and comparisons with some popular softwares have demonstrated superior performance of MICO in terms of robustness and accuracy.
ESTIMATE OF METHANE EMISSIONS FROM RICE FIELDS IN CHINA BY CLIMATE-BASED NET PRIMARY PRODUCTIVITY
KANG Guo-ding; CAI Zu-cong; ZHANG Zi-heng; XIAO Peng-feng
2004-01-01
Rice fields provide food for over half of the world population but are also an important source of atmospheric CH4. Using the climate-based GIS empirical model and the meteorological data collected from 600 meteorological stations in China, with county as the basic unit, the net primary productivity (NPP) of rice fields in China in 1990, 1995, 1998, and 2000 were estimated to be in the range from 202.19×1012g C in 1990 to 163.46×1012g C in 2000. From the measured data of the factors affecting CH4 emission and NPP, the conversion ratio of the NPP into CH4 emission for the rice fields of China was determined to be 1.8%. Using this ratio and estimated NPP, the CH4 emissions from rice fields of China in 1990, 1995, 1998, and 2000 were estimated to be 7.24×1012, 6.31×1012, 6.77×1012 and 5.85×1012g CH4, respectively.
A precise numerical estimation of the magnetic field generated around recombination
Fidler, Christian; Pitrou, Cyril
2015-01-01
We investigate the generation of magnetic fields from non-linear effects around recombination. As tight-coupling is gradually lost when approaching $z\\simeq 1100$, the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; ii) the magnetic field is generated up to $z\\simeq ...
An Algorithm for Joint Estimating Range, DOA and Frequency of Near-Field Sources
CHENJianfeng; ZHANGXianda; WUYuntao
2004-01-01
Most of the existing eigen-decomposition based localization methods make the plane wave assumption in order to estimate the signal parameters of multiple sources. This paper proposes a novel joint algorithm for ranges, DOA's and frequencies of multiple narrow-band sources with the sources in the near field. This algorithm uses the Estimating signal parameters via rotational invariance technique (ESPRIT) based on cumulant-domain signal subspaces. The new algorithm does not require searching spectral peak or pairing among parameters, and has the power to resist an additive Gaussian noise due to use of the fourth-order cumulants. The performance of the new algorithm is confirmed by computer simulations.
Field Oriented Control for Rotor Position Estimation of IPM Drives over a Wide Speed Range
Ekhlas Kadhum
2013-01-01
Full Text Available Field oriented control strategy of Interior Permanent Magnet IPM Synchronous Motor drives over a wide speed range applications is presented. Rotor position estimation using model reference adaptive system method for IPM Drive without using a mechanical sensor is illustrated considering the effects of cross-saturation between the d and q axes. The cross saturation between d and q axes has been calculated by finite-element analysis. The inductance measurement regards the cross saturation which is used to obtain the suitable id - characteristics in base and flux weakening regions. The simulation results show that rotor position estimation error accuracy was improved. Various dynamic conditions have been investigated
A New Algorithm for Joint Range-DOA-Frequency Estimation of Near-Field Sources
Jian-Feng Chen
2004-03-01
Full Text Available This paper studies the joint estimation problem of ranges, DOAs, and frequencies of near-field narrowband sources and proposes a new computationally efficient algorithm, which employs a symmetric uniform linear array, uses eigenvalues together with the corresponding eigenvectors of two properly designed matrices to estimate signal parameters, and does not require searching for spectral peak or pairing among parameters. In addition, the proposed algorithm can be applied in arbitrary Gaussian noise environment since it is based on the fourth-order cumulants, which is verified by extensive computer simulations.
TENG Pengxiao; MA Chizhou; YANG Yichun; LI Xiaodong
2007-01-01
A robust algorithm of direction of arrival (DOA) estimation for coherent wideband sources in unknown correlated noise fields was investigated. The noise is usually unknown and correlated among sensors in practical applications, especially for arrays with comparatively small apertures. The spatially correlated noise incurs an increase in focusing error and a severe degradation in the DOA estimation, and therefore a method of focusing transformation based on differentiating covariance matrix was proposed to eliminate noise, hence reduce the focusing error. The simulation and experimental results demonstrate the effectiveness of the proposed method.
A New Method for Radar Rainfall Estimation Using Merged Radar and Gauge Derived Fields
Hasan, M. M.; Sharma, A.; Johnson, F.; Mariethoz, G.; Seed, A.
2014-12-01
Accurate estimation of rainfall is critical for any hydrological analysis. The advantage of radar rainfall measurements is their ability to cover large areas. However, the uncertainties in the parameters of the power law, that links reflectivity to rainfall intensity, have to date precluded the widespread use of radars for quantitative rainfall estimates for hydrological studies. There is therefore considerable interest in methods that can combine the strengths of radar and gauge measurements by merging the two data sources. In this work, we propose two new developments to advance this area of research. The first contribution is a non-parametric radar rainfall estimation method (NPZR) which is based on kernel density estimation. Instead of using a traditional Z-R relationship, the NPZR accounts for the uncertainty in the relationship between reflectivity and rainfall intensity. More importantly, this uncertainty can vary for different values of reflectivity. The NPZR method reduces the Mean Square Error (MSE) of the estimated rainfall by 16 % compared to a traditionally fitted Z-R relation. Rainfall estimates are improved at 90% of the gauge locations when the method is applied to the densely gauged Sydney Terrey Hills radar region. A copula based spatial interpolation method (SIR) is used to estimate rainfall from gauge observations at the radar pixel locations. The gauge-based SIR estimates have low uncertainty in areas with good gauge density, whilst the NPZR method provides more reliable rainfall estimates than the SIR method, particularly in the areas of low gauge density. The second contribution of the work is to merge the radar rainfall field with spatially interpolated gauge rainfall estimates. The two rainfall fields are combined using a temporally and spatially varying weighting scheme that can account for the strengths of each method. The weight for each time period at each location is calculated based on the expected estimation error of each method
Switches in the Stress Field Induced by Fluid Overpressures Below a Low-Permeability Fault Zone
Collettini, C.; de Paola, N.; Goulty, N. R.
2005-12-01
The geological structure of Elba comprises thrust sheets stacked during the Apennine orogeny that are cross-cut by later Neogene extensional faults. The Zuccale fault is a gently east-dipping normal fault that offsets part of the thrust stack eastwards. Stratigraphic separations imply an offset of 7-8 km and exhumation of 3-6 km. A complex hydrofracture system exposed in the footwall of Palaeozoic schists and Triassic sediments at Punta di Zuccale consists of three vein sets: two vertical sets trending N-S and E-W and one sub-horizontal. The veins show a crack-and-seal texture and are characterized by mutual crosscutting relationships. The regional stress field throughout the period when the Zuccale fault was active, evidenced by numerous kinematic indicators, was extensional with the minimum principal stress oriented E-W, consistent with the N-S trending set of vertical hydrofractures. We interpret the vertical E-W trending and sub-horizontal hydrofractures as the result of overpressure development, due to exhumation, below the low-permeability, phyllosilicate-rich fault core. In our proposed mechanical model, exhumation reduced the vertical stress and also the horizontal stresses which responded poroelastically. The N-S trending vertical hydrofractures formed when the pore pressure exceeded the minimum principal stress by the tensile strength of the rock. Continued exhumation further reduced the vertical and N-S principal stresses, whilst the E-W principal stress remained equal to the pore pressure, until the pore pressure exceeded the N-S principal stress by the tensile strength of the rock, causing the E-W hydrofractures to form. Yet more exhumation further reduced the vertical stress, while the horizontal stresses remained equal to the pore pressure, until the pore pressure exceeded the vertical stress by the tensile strength of the rock, causing the sub-horizontal hydrofractures to form. The reduced normal effective stress across the fault encouraged fault
Uncertainty in global groundwater storage estimates in a Total Groundwater Stress framework
Richey, Alexandra S.; Thomas, Brian F.; Lo, Min‐Hui; Swenson, Sean; Rodell, Matthew
2015-01-01
Abstract Groundwater is a finite resource under continuous external pressures. Current unsustainable groundwater use threatens the resilience of aquifer systems and their ability to provide a long‐term water source. Groundwater storage is considered to be a factor of groundwater resilience, although the extent to which resilience can be maintained has yet to be explored in depth. In this study, we assess the limit of groundwater resilience in the world's largest groundwater systems with remote sensing observations. The Total Groundwater Stress (TGS) ratio, defined as the ratio of total storage to the groundwater depletion rate, is used to explore the timescales to depletion in the world's largest aquifer systems and associated groundwater buffer capacity. We find that the current state of knowledge of large‐scale groundwater storage has uncertainty ranges across orders of magnitude that severely limit the characterization of resilience in the study aquifers. Additionally, we show that groundwater availability, traditionally defined as recharge and redefined in this study as total storage, can alter the systems that are considered to be stressed versus unstressed. We find that remote sensing observations from NASA's Gravity Recovery and Climate Experiment can assist in providing such information at the scale of a whole aquifer. For example, we demonstrate that a groundwater depletion rate in the Northwest Sahara Aquifer System of 2.69 ± 0.8 km3/yr would result in the aquifer being depleted to 90% of its total storage in as few as 50 years given an initial storage estimate of 70 km3. PMID:26900184
Reynolds stress flow shear and turbulent energy transfer in reversed field pinch configuration
Vianello, Nicola; Spolaore, Monica; Serianni, Gianluigi; Regnoli, Giorgio; Spada, Emanuele; Antoni, Vanni; Bergsåker, Henric; Drake, James R.
2003-10-01
The role of Reynolds Stress tensor on flow generation in turbulent fluids and plasmas is still an open question and the comprehension of its behavior may assist the understanding of improved confinement scenario. It is generally believed that shear flow generation may occur by an interaction of the turbulent Reynolds stress with the shear flow. It is also generally believed that this mechanism may influence the generation of zonal flow shears. The evaluation of the complete Reynolds Stress tensor requires contemporary measurements of its electrostatic and magnetic part: this requirement is more restrictive for Reversed Field Pinch configuration where magnetic fluctuations are larger than in tokamak . A new diagnostic system which combines electrostatic and magnetic probes has been installed in the edge region of Extrap-T2R reversed field pinch. With this new probe the Reynolds stress tensor has been deduced and its radial profile has been reconstructed on a shot to shot basis exploring differen plasma conditions. These profiles have been compared with the naturally occurring velocity flow profile, in particular during Pulsed Poloidal Current Drive experiment, where a strong variation of ExB flow radial profile has been registered. The study of the temporal evolution of Reynolds stress reveals the appearance of strong localized bursts: these are considered in relation with global MHD relaxation phenomena, which naturally occur in the core of an RFP plasma sustaining its configuration.
The limiting behavior of the estimated parameters in a misspecified random field regression model
Dahl, Christian Møller; Qin, Yu
, as a consequence the random field model specification introduces non-stationarity and non-ergodicity in the misspecified model and it becomes non-trivial, relative to the existing literature, to establish the limiting behavior of the estimated parameters. The asymptotic results are obtained by applying some...... convenient new uniform convergence results that we propose. This theory may have applications beyond those presented here. Our results indicate that classical statistical inference techniques, in general, works very well for random field regression models in finite samples and that these models succesfully...
Kemp, Brandon A.; Sheppard, Cheyenne J.
2016-09-01
The momentum of light in media has been one of the most debated topics in physics over the past one hundred years. Originally a theoretical debate over the electrodynamics of moving media, practical applications have emerged over the past few decades due to interest in optical manipulation and nanotechnology. Resolution of the debate identifies a kinetic momentum as the momentum of the fields responsible for center of mass translations and a canonical momentum related to the coupled field and material system. The optical momentum resolution has been considered incomplete because it did not uniquely identify the full stress-energy-momentum (SEM) tensor of the field-kinetic subsystem. A consequence of this partial resolution is that the field-kinetic momentum could be described by three of the leading formulations found in the literature. The Abraham, Einstein-Laub, and Chu SEM tensors share the field-kinetic momentum, but their SEM tensors differ resulting in competing force densities. We can show now that the Abraham and Einstein-Laub formulations are invalid since their SEM tensors are not frame invariant, whereas the Chu SEM tensor satisfies relativistic principles as the field-kinetic formulation. However, a number of reports indicate that the force distribution in matter may not accurately represent experimental observations. In this correspondence, we show that the field-kinetic SEM tensor can be used along with the corresponding material subsystem to accurately predict experimental force and stress distributions. We model experimental examples from optical and static manipulation of particles and fluids.
Stochastic estimation of hydraulic transmissivity fields using flow connectivity indicator data
Freixas, G.; FernÃ ndez-Garcia, D.; Sanchez-Vila, X.
2017-01-01
Most methods for hydraulic test interpretation rely on a number of simplified assumptions regarding the homogeneity and isotropy of the underlying porous media. This way, the actual heterogeneity of any natural parameter, such as transmissivity (T), is transferred to the corresponding estimates in a way heavily dependent on the interpretation method used. An example is a long-term pumping test interpreted by means of the Cooper-Jacob method, which implicitly assumes a homogeneous isotropic confined aquifer. The estimates obtained from this method are not local values, but still have a clear physical meaning; the estimated T represents a regional-scale effective value, while the log-ratio of the normalized estimated storage coefficient, indicated by ω', is an indicator of flow connectivity, representative of the scale given by the distance between the pumping and the observation wells. In this work we propose a methodology to use ω', together with sampled local measurements of transmissivity at selected points, to map the expected value of local T values using a technique based on cokriging. Since the interpolation involves two variables measured at different support scales, a critical point is the estimation of the covariance and crosscovariance matrices. The method is applied to a synthetic field displaying statistical anisotropy, showing that the inclusion of connectivity indicators in the estimation method provide maps that effectively display preferential flow pathways, with direct consequences in solute transport.
Sunita Deswal
2013-01-01
Full Text Available The aim of this paper is to study magneto-thermoelastic interactions in an initially stressed isotropic homogeneous half-space in the context of fractional order theory of generalized thermoelasticity. State space formulation with the Laplace transform technique is used to obtain the general solution, and the resulting formulation is applied to the ramp type increase in thermal load and zero stress. Solutions of the problem in the physical domain are obtained by using a numerical method of the Laplace inverse transform based on the Fourier expansion technique, and the expressions for the displacement, temperature, and stress inside the half-space are obtained. Numerical computations are carried out for a particular material for illustrating the results. Results obtained for the field variables are displayed graphically. Some comparisons have been shown in figures to present the effect of fractional parameter, ramp parameter, magnetic field, and initial stress on the field variables. Some particular cases of special interest have been deduced from the present investigation.
Influence of stress on the stray field signals of ferromagnetic materials
Lihong Dong; Binshi Xu; Shiyun Dong; Qunzhi Chen; Dan Wang
2008-01-01
To investigate the influence of stress alone on the stray field signals of ferromagnetic materials, the static tensile tests of 0.45%C steel and 45CrNiMoVA steel fiat-shaped specimens were performed on an MTSSI0 hydraulic testing machine. Hp(y) signals,the normal component of spontaneous stray field, were measured during the testing process by an EMS-2003 metal magnetic mem-ory diagnostic apparatus cooperated with a non-magnetic electric control displacement instrument. Fracture and microstructure were observed by a scanning electronic microscope and a transmission electron microscope, respectively. The relationships between axial applied stress or residual stress measured by X-ray diffraction method and Hp(y) were analyzed. The results indicate that some regu-lar pattern of the magnetic curve is displayed only between applied stress and stray field signals. The magnetic ordering process stops due to dislocation pinning magnetic domain structure, and Hp(y) value unvaried nearly with applied load increasing in the plastic de-formation stage.
Conservation laws and stress-energy-momentum tensors for systems with background fields
Gratus, Jonathan, E-mail: j.gratus@lancaster.ac.uk [Lancaster University, Lancaster LA1 4YB (United Kingdom); The Cockcroft Institute, Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Obukhov, Yuri N., E-mail: yo@thp.uni-koeln.de [Institute for Theoretical Physics, University of Cologne, 50923 Koeln (Germany); Tucker, Robin W., E-mail: r.tucker@lancaster.ac.uk [Lancaster University, Lancaster LA1 4YB (United Kingdom); The Cockcroft Institute, Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)
2012-10-15
This article attempts to delineate the roles played by non-dynamical background structures and Killing symmetries in the construction of stress-energy-momentum tensors generated from a diffeomorphism invariant action density. An intrinsic coordinate independent approach puts into perspective a number of spurious arguments that have historically lead to the main contenders, viz the Belinfante-Rosenfeld stress-energy-momentum tensor derived from a Noether current and the Einstein-Hilbert stress-energy-momentum tensor derived in the context of Einstein's theory of general relativity. Emphasis is placed on the role played by non-dynamical background (phenomenological) structures that discriminate between properties of these tensors particularly in the context of electrodynamics in media. These tensors are used to construct conservation laws in the presence of Killing Lie-symmetric background fields. - Highlights: Black-Right-Pointing-Pointer The role of background fields in diffeomorphism invariant actions is demonstrated. Black-Right-Pointing-Pointer Interrelations between different stress-energy-momentum tensors are emphasised. Black-Right-Pointing-Pointer The Abraham and Minkowski electromagnetic tensors are discussed in this context. Black-Right-Pointing-Pointer Conservation laws in the presence of nondynamic background fields are formulated. Black-Right-Pointing-Pointer The discussion is facilitated by the development of a new variational calculus.
Modelling of stress fields during LFEM DC casting of aluminium billets by a meshless method
Mavrič, B.; Šarler, B.
2015-06-01
Direct Chill (DC) casting of aluminium alloys is a widely established technology for efficient production of aluminium billets and slabs. The procedure is being further improved by the application of Low Frequency Electromagnetic Field (LFEM) in the area of the mold. Novel LFEM DC processing technique affects many different phenomena which occur during solidification, one of them being the stresses and deformations present in the billet. These quantities can have a significant effect on the quality of the cast piece, since they impact porosity, hot-tearing and cold cracking. In this contribution a novel local radial basis function collocation method (LRBFCM) is successfully applied to the problem of stress field calculation during the stationary state of DC casting of aluminium alloys. The formulation of the method is presented in detail, followed by the presentation of the tackled physical problem. The model describes the deformations of linearly elastic, inhomogeneous isotropic solid with a given temperature field. The temperature profile is calculated using the in-house developed heat and mass transfer model. The effects of low frequency EM casting process parameters on the vertical, circumferential and radial stress and on the deformation of billet surface are presented. The application of the LFEM appears to decrease the amplitudes of the tensile stress occurring in the billet.
Akhtar, Sohail; Kardas, Omer Ozgur; Keles, Omer; Yilbas, Bekir Sami
2014-10-01
Laser cutting of a rectangular geometry into aluminum alloy 2024 is carried out. Temperature and stress fields are predicted in the cutting section using the ABAQUS finite element code in line with the experimental conditions. Effect of the size of the rectangular geometry on the thermal stress fields is examined in the cutting section. Temperature predictions are validated through the thermocouple data. To identify the morphological changes in the cutting section, an experiment is carried out and the resulting cutting sections are examined under optical and scanning electron microscopes. It is found that temperature and stress fields are affected by the size of the rectangular cut geometry. Temperature and von Mises stress attains higher values for small size rectangular geometry as compared to its counterpart corresponding to the large size geometry. Laser cut sections are free from large size asperities including sideways burning and out-off flatness at the cut edges. Locally scattered some small dross attachments are observed at the kerf exit.
Rogers, W.R.
1986-01-03
This research program will evaluate the aversive character of exposure to 60 Hz electric fields by determining the threshold intensity which produces avoidance or escape responses, will estimate the threshold intensity for detection of 60 Hz electric fields, will assess effects of chronic exposure to 60 Hz electric fields on the performance of two operant conditioning tasks, fixed ratio and differential reinforcement of low rate responding, will investigate, using the systematic quantitative observational sampling methods of primatology, the possible stress-inducing effects of chronic exposure to 60 Hz electric fields on the behavior of baboons living in small social groups. In all experiments, the electric fields will be described, characterized, and controlled to account for recognized artifacts associated with high intensity 60 Hz electric fields and the health of all subjects will be described using the methods of primate veterinary medicine.
Orientation effect on the giant stress field induced in a single Ni nanowire by mechanical strain
Melilli, G.; Madon, B.; Clochard, M.-C.; Wegrowe, J.-E.
2015-09-01
The change of magnetization (i.e. using the inverse magnetostriction effect) allows to investigate at the nanoscale the effects of thermoelastic and piezoelectric strain of an active track-etched β-PVDF polymer matrix on an electrodeposited single-contacted Ni nanowire (NW). The magnetization state is measured locally by anisotropic magnetoresitance (AMR). The ferromagnetic NW plays thus the role of a mechanical probe that allows the effects of mechanical strain to be characterized and described qualitatively and quantitatively. Due to the inverse magnetostriction, a quasi-disappearance of the AMR signal for a variation of the order of ΔT ≍ 10 K has been evidenced. The coplanarity of the vectors between the magnetization and the magnetic field is broken. A way of studying the effect of the geometry on such a system, is to fabricate oriented polymer templates. Track-etched polymer membranes were thus irradiated at various angles (αirrad) leading, after electrodeposition, to embedded Ni NWs of different orientations. With cylindrical Ni NW oriented normally to the template surface, the induced stress field in a single Ni NW was found 1000 time higher than the bulk stress field (due to thermal expansion measured on the PVDF). This amplification results in three nanoscopic effects: (1) a stress mismatch between the Ni NW and the membrane, (2) a non-negligible role of the surface tension on Ni NW Young modulus, and (3) the possibility of non-linear stress-strain law. When the Ni NWs are tilted from the polymer template surface normality, the induced stress field is reduced and the amplification phenomenon is less important.
Determination of the Micro Stress Field in Composite by Homogenization Method
无
2006-01-01
The objective of this study is to investigate the local stress fluctuation in two-phase composite by homogenization method.The composite was described by homogeneous macro structure and periodical micro structure simultaneously and the mechanical response of the composite can be described based on both macro and micro dimensional scales.Micro and macro homogenization problems can be formulated.The effective material properties of the composite and the local stress field in the microstructure of the composite can be determined by solving these equations.
Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress
Mathijssen, S. G. J.; Cölle, M.; Mank, A. J. G.; Kemerink, M.; Bobbert, P. A.; de Leeuw, D. M.
2007-05-01
The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current.
Investigation of stress and displacement fields in a planar model of Y type seals
Huang, Z.; Yang, M.; Zhang, B.; Huang, H.
1986-01-01
To provide necessary information for working out the national standard for Y type seals, the authors investigated the stress and displacement fields of Y type seals under load. Models used as seals for the test were made of polyurethane rubber. Photoelastic method was used to measure stress and a new moire-grid method, which requires a grating with dragging along system was used to measure displacement under limited deformation. The test has shown that the sealing behavior is mainly dependent on the structure of the sealing lip, which is liable to wearing out. 6 references, 9 figures.
Quantitative assessments of residual stress fields at the surface of alumina hip joints.
Pezzotti, Giuseppe; Munisso, Maria Chiara; Lessnau, Kristina; Zhu, Wenliang
2010-11-01
In-depth and in-plane response functions of photo- and electro-stimulated probes have been modeled and quantitatively evaluated in order to assess their suitability to detect the highly graded residual stress fields generated at the surface of alumina hip joints. Optical calibrations revealed large differences in probe size, which strongly affected the detected magnitude of residual stress. A comparison between the responses of Raman and fluorescence probes in polycrystalline alumina showed that the depth of those probes spread to an extent in the order of the tens of microns even with using a confocal probe configuration. On the other hand, the electro-stimulated luminescence emitted by oxygen vacancy sites (F(+) center) in the alumina lattice represented the most suitable choice for confining to a shallow volume the stress probe. This latter probe enabled us to reduce the measurement depth to the order of the tens of nanometers. We show maps of surface residual stress as collected on both main-wear and nonwear zones of an alumina femoral head. A comparison among stress maps taken at exactly the same location, but employing different probes, revealed averaging effects on the stress magnitude detected with photo-stimulated probes, while proving the superior spatial resolution of the electron probe.
Field investigations of high stress soft surrounding rocks and deformation control
Weijian Yu
2015-08-01
Full Text Available Field investigations of high stress soft rock deformations show that the high stress soft rock roadway can slide with large deformation. Severe extrusion and floor heave can also be subsequently observed. The supported roadway can be locally damaged or completely fail, where the floor has a large deformation and/or is seriously damaged. The factors inducing large deformation of surrounding rocks in deep roadway are rock strengths, structure face cutting types, stress states, stress release, support patterns, and construction methods. Based on the deformation characteristics of high stress soft rock roadway, a comprehensive support scheme is proposed. The overall support technology of “step-by-step and joint, hierarchical reinforcement” for roadway is presented, and the anchor cable and bolt parameters to check the design methods are also given. Finally, the proposed comprehensive support method “bolt + metal mesh + U-steel arch + shortcrete + grouting and cable” is used in the extension section of east main haulage roadway at −850 m level of Qujiang coal mine. The 173-day monitoring results show that the average convergence of sidewalls reaches 208 mm, and the average relative convergence of roof and floor reaches 448 mm, suggesting that this kind of support technology for controlling large deformation of high stress soft surrounding rock roadway is effective.
Quercitol and osmotic adaptation of field-grown Eucalyptus under seasonal drought stress.
Arndt, Stefan K; Livesley, Stephen J; Merchant, Andrew; Bleby, Timothy M; Grierson, Pauline F
2008-07-01
This study investigated the role of quercitol in osmotic adjustment in field-grown Eucalyptus astringens Maiden subject to seasonal drought stress over the course of 1 year. The trees grew in a native woodland and a farm plantation in the semi-arid wheatbelt region of south Western Australia. Plantation trees allocated relatively more biomass to leaves than woodland trees, but they suffered greater drought stress over summer, as indicated by lower water potentials, CO(2)assimilation rates and stomatal conductances. In contrast, woodland trees had relatively fewer leaves and suffered less drought stress. Plantation trees under drought stress engaged in osmotic adjustment, but woodland trees did not. Quercitol made a significant contribution to osmotic adjustment in drought-stressed trees (25% of total solutes), and substantially more quercitol was measured in the leaves of plantation trees (5% dry matter) than in the leaves of woodland trees (2% dry matter). We found no evidence that quercitol was used as a carbon storage compound while starch reserves were depleted under drought stress. Differences in stomatal conductance, biomass allocation and quercitol production clearly indicate that E. astringens is both morphologically and physiologically 'plastic' in response to growth environment, and that osmotic adjustment is only one part of a complex strategy employed by this species to tolerate drought.
Internal stress field at Mount Vesuvius: A model for background seismicity at a central volcano
de Natale, Giuseppe; Petrazzuoli, Stefano M.; Troise, Claudia; Pingue, Folco; Capuano, Paolo
2000-07-01
We propose a model to explain the background seismicity occurring at Somma-Vesuvius in its present, mostly quiescent period. A finite element procedure has been used to simulate the stress field due to gravitational body forces in an axisymmetric volcano characterized by a central high-rigidity anomaly. Results emphasize the important effect of axial high-rigidity, which concentrates at its borders stresses resulting from the gravitational load of the volcanic edifice, as well as external (regional) stresses. The joint effect of the gravitational loading and of the presence of the anomaly produces stresses very close to or above the critical rupture threshold. The observed spatial concentrations of seismicity and moment release correlate well with peaks of computed maximum shear stress. Seismicity is then interpreted as due to small stress perturbations concentrated around the high-rigidity core and added to a system already close, to the failure threshold. This model can explain the widely observed occurrence of background seismicity at central volcanoes worldwide.
Sensorless Stator Field-Oriented Controlled IM Drive at Low Speed with Rr Estimator
Wen-Cheng Pu
2014-01-01
Full Text Available This paper pertains to a technique of a sensorless indirect stator field-oriented induction motor control, which prevents the accumulative errors incurred by the integrator and the problem relating to the stability of the control system caused by the stator resistance susceptible to temperature variations while conducting the flux estimation directly and computing the synchronous rotary speed. The research adds an adaptive flux observer to estimate the speed of the rotor and uses the fixed trace algorithm (FTA to execute an online estimation of the slip difference, thereby improving the system of stability under the low rotary speed at regenerating mode and the influence of the rotor resistance on the slip angle. Finally, the paper conducts simulations by Simulink of MATLAB and practices to verify the correctness of the result the paper presents.
Stegemann, Robert; Cabeza, Sandra; Lyamkin, Viktor; Bruno, Giovanni; Pittner, Andreas; Wimpory, Robert; Boin, Mirko; Kreutzbruck, Marc
2017-03-01
The residual stress distribution of tungsten inert gas welded S235JRC+C plates was determined by means of neutron diffraction (ND). Large longitudinal residual stresses with maxima around 600 MPa were found. With these results as reference, the evaluation of residual stress with high spatial resolution GMR (giant magneto resistance) sensors was discussed. The experiments performed indicate a correlation between changes in residual stresses (ND) and the normal component of local residual magnetic stray fields (GMR). Spatial variations in the magnetic field strength perpendicular to the welds are in the order of the magnetic field of the earth.
Prevalence estimates of combat-related post-traumatic stress disorder: critical review.
Richardson, Lisa K; Frueh, B Christopher; Acierno, Ronald
2010-01-01
The aim of the present study was to provide a critical review of prevalence estimates of combat-related post-traumatic stress disorder (PTSD) among military personnel and veterans, and of the relevant factors that may account for the variability of estimates within and across cohorts, including methodological and conceptual factors accounting for differences in prevalence rates across nations, conflicts/wars, and studies. MEDLINE and PsycINFO databases were examined for literature on combat-related PTSD. The following terms were used independently and in combinations in this search: PTSD, combat, veterans, military, epidemiology, prevalence. The point prevalence of combat-related PTSD in US military veterans since the Vietnam War ranged from approximately 2% to 17%. Studies of recent conflicts suggest that combat-related PTSD afflicts between 4% and 17% of US Iraq War veterans, but only 3-6% of returning UK Iraq War veterans. Thus, the prevalence range is narrower and tends to have a lower ceiling among combat veterans of non-US Western nations. Variability in prevalence is likely due to differences in sampling strategies; measurement strategies; inclusion and measurement of the DSM-IV clinically significant impairment criterion; timing and latency of assessment and potential for recall bias; and combat experiences. Prevalence rates are also likely affected by issues related to PTSD course, chronicity, and comorbidity; symptom overlap with other psychiatric disorders; and sociopolitical and cultural factors that may vary over time and by nation. The disorder represents a significant and costly illness to veterans, their families, and society as a whole. Further carefully conceptualized research, however, is needed to advance our understanding of disorder prevalence, as well as associated information on course, phenomenology, protective factors, treatment, and economic costs.
Estimating the correlation between bursty spike trains and local field potentials.
Li, Zhaohui; Ouyang, Gaoxiang; Yao, Li; Li, Xiaoli
2014-09-01
To further understand rhythmic neuronal synchronization, an increasingly useful method is to determine the relationship between the spiking activity of individual neurons and the local field potentials (LFPs) of neural ensembles. Spike field coherence (SFC) is a widely used method for measuring the synchronization between spike trains and LFPs. However, due to the strong dependency of SFC on the burst index, it is not suitable for analyzing the relationship between bursty spike trains and LFPs, particularly in high frequency bands. To address this issue, we developed a method called weighted spike field correlation (WSFC), which uses the first spike in each burst multiple times to estimate the relationship. In the calculation, the number of times that the first spike is used is equal to the spike count per burst. The performance of this method was demonstrated using simulated bursty spike trains and LFPs, which comprised sinusoids with different frequencies, amplitudes, and phases. This method was also used to estimate the correlation between pyramidal cells in the hippocampus and gamma oscillations in rats performing behaviors. Analyses using simulated and real data demonstrated that the WSFC method is a promising measure for estimating the correlation between bursty spike trains and high frequency LFPs.
Estimation of emissions from field burning of crop straw in China
CAO GuoLiang; ZHANG XiaoYe; WANG YaQiang; Zheng FangCheng
2008-01-01
Emissions resulting from crop straw field burning in China, which have caused serious environmental problems in China, are estimated in this paper. From the county-level data of crop production in 2000-2003 from the government statistics, taking into account the ratio of residue and grain, the total amount of crop straw production is estimated to be about 600 Tg per year, 76% of which are rice, wheat and corn straw. With reference to the data of living standards, the percentage of crop straw burnt in fields for counties are obtained and consequently the total amount of burnt straws is approximately 140 Tg/year. With the emission factors from literature and experiments, appropriate emission factors have been obtained. The total amounts of PM, SO2, NOx, NH3, CH4, BC, OC, VOC, CO, CO2 emissions from field burning of crop straw in China are estimated. All emissions are presented at county level. Some pollutants, such as BC, VOC, OC, CO and CO2, are contributing a major portion to the total emissions of China. This paper uses a map with resolution of 0.2°×0.2° to present the PM emissions distribution from crop straw burnt in 2003. The results show a significant regional unevenness of emissions, with larger amounts of pollutions coming from the provinces in eastern and northeast China. The regions with higher emissions per unit area are located as a belt stretching from northeast China to eastern China.
Liarte, Danilo B.; Posen, Sam; Transtrum, Mark K.; Catelani, Gianluigi; Liepe, Matthias; Sethna, James P.
2017-03-01
Theoretical limits to the performance of superconductors in high magnetic fields parallel to their surfaces are of key relevance to current and future accelerating cavities, especially those made of new higher-T c materials such as Nb3Sn, NbN, and MgB2. Indeed, beyond the so-called superheating field {H}{sh}, flux will spontaneously penetrate even a perfect superconducting surface and ruin the performance. We present intuitive arguments and simple estimates for {H}{sh}, and combine them with our previous rigorous calculations, which we summarize. We briefly discuss experimental measurements of the superheating field, comparing to our estimates. We explore the effects of materials anisotropy and the danger of disorder in nucleating vortex entry. Will we need to control surface orientation in the layered compound MgB2? Can we estimate theoretically whether dirt and defects make these new materials fundamentally more challenging to optimize than niobium? Finally, we discuss and analyze recent proposals to use thin superconducting layers or laminates to enhance the performance of superconducting cavities. Flux entering a laminate can lead to so-called pancake vortices; we consider the physics of the dislocation motion and potential re-annihilation or stabilization of these vortices after their entry.
Distance estimation in a dynamic simulated environment: a visual field dependence problem?
Vianin, Pascal; Baumberger, Bernard; Flückiger, Michelangelo
2004-01-01
Egocentric distance estimation implies that the subject perceives his own location in the environment. In a simulated environment, subjects have to transpose perceptively their own observation point in order to assume their virtual body position. As only visual information specifies this position, their ability to perceive the camera viewpoint should be linked to the field dependence independence factor (FDI). Field-independent subjects underestimated the mid-distance between their own virtual body position and a far-located target; their bisection was located between the projective (2-D) and the simulated (3-D) mid-distance which indicates their difficulty in considering the in-depth simulated spatial references. High correlations between the vertical estimation in the rod-and-frame test and the egocentric-distance-estimation task (with shifted camera) suggest a similar perceptive process in both tasks. This result is confirmed by the better performances of the field-dependent subjects in this condition. In conclusion, we discuss the relationship between FDI and the sense of presence in virtual environments.
Heat flux estimates from the Gakkel Ridge 85E vent field from the AGAVE 2007 expedition
Stranne, C.; Winsor, P.; Sohn, R. A.; Liljebladh, B.
2009-04-01
During the Arctic Gakkel Vents Expedition (AGAVE) 2007, abundant hydrothermal venting was discovered on the Gakkel Ridge at 85E. Hydrothermal vents on the sea floor give rise to buoyant plumes which, when reaching neutral buoyancy, spreads horizontally over areas with length scales on the order of several kilometres and are therefore easily detected with a CTD rosette. The detected anomalies are consistent with the findings 6 years earlier during the Arctic Mid-Ocean Ridge Expedition (AMORE) 2001. The horizontal and vertical distribution of the anomalies is considered in order to establish the number of individual plumes detected. The objective of this paper is to estimate the minimum heat input required to reproduce the observed plumes, using a turbulent entrainment model. The model was run with a large number of combinations of boundary conditions (nozzle area, vertical velocity and temperature) in order to see which combinations that give rise to the observed plume characteristics (level of neutral buoyancy and temperature anomaly). For each individual plume, we estimate the minimum heat flux required to obtain the observed temperature anomaly. Adding the minimum heat flux from each vent together, the total heat flux for the vent field is estimated to be ~ 2 GW. The estimated value is comparable or larger than any other known vent field.
Limkumnerd, Surachate; Sethna, James P.
2007-01-01
We derive general relations between grain boundaries, rotational deformations, and stress-free states for the mesoscale continuum Nye dislocation density tensor. Dislocations generally are associated with long-range stress fields. We provide the general form for dislocation density fields whose stre
Flood control and loss estimation for paddy field at midstream of Chao Phraya River Basin, Thailand
Cham, T. C.; Mitani, Y.
2015-09-01
2011 Thailand flood has brought serious impact to downstream of Chao Phraya River Basin. The flood peak period started from August, 2011 to the end of October, 2011. This research focuses on midstream of Chao Phraya River Basin, which is Nakhon Sawan area includes confluence of Nan River and Yom River, also confluence of Ping River and Nan River. The main purpose of this research is to understand the flood generation, estimate the flood volume and loss of paddy field, also recommends applicable flood counter measurement to ease the flood condition at downstream of Chao Phraya River Basin. In order to understand the flood condition, post-analysis is conducted at Nakhon Sawan. The post-analysis consists of field survey to measure the flood marks remained and interview with residents to understand living condition during flood. The 2011 Thailand flood generation at midstream is simulated using coupling of 1D and 2D hydrodynamic model to understand the flood generation during flood peak period. It is calibrated and validated using flood marks measured and streamflow data received from Royal Irrigation Department (RID). Validation of results shows good agreement between simulated result and actual condition. Subsequently, 3 scenarios of flood control are simulated and Geographic Information System (GIS) is used to assess the spatial distribution of flood extent and reduction of loss estimation at paddy field. In addition, loss estimation for paddy field at midstream is evaluated using GIS with the calculated inundation depth. Results show the proposed flood control at midstream able to minimize 5% of the loss of paddy field in 26 provinces.
Mukhopadhyay, Banibrata
2016-01-01
We show that the removal of angular momentum is possible in the presence of large scale magnetic stresses, arisen by fields much stronger than that required for magnetorotational instability, in geometrically thick, advective, sub-Keplerian accretion flows around black holes in steady-state, in the complete absence of alpha-viscosity. The efficiency of such angular momentum transfer via Maxwell stress, with the field well below its equipartition value, could be equivalent to that of alpha-viscosity, arisen via Reynolds stress, with $\\alpha=0.01-0.08$. We find in our simpler vertically averaged advective disk model that stronger the magnetic field and/or larger the vertical-gradient of azimuthal component of magnetic field, stronger the rate of angular momentum transfer is, which in turn may lead to a faster rate of outflowing matter, which has important implications to describe the hard spectral states of black hole sources. When the generic origin of alpha-viscosity is still being explored, mechanism of effi...
Subsidence and Stress Change in the Cerro Prieto Geothermal Field, B. C., Mexico
Glowacka, E.; Sarychikhina, O.; Nava, F. A.
2005-11-01
Previous works have shown that ground deformation and seismicity in the Cerro Prieto geothermal field (CPGF) are due to both tectonics and field exploitation. Here, we use information about current tectonics and data from precision leveling surveys, to model tectonic and anthropogenic subsidence. Our results show that tectonic subsidence constitutes only ˜4% of the measured subsidence. Anthropogenic subsidence was evaluated using a model of rectangular tensional cracks, based on the hydrological model of the field, together with the Coulomb 2.0 program. From the resulting values of the fissure parameters and from extraction and injection data, we calculate that the volume changes caused by closure of the geothermal and cold water reservoirs account for only ˜3% and ˜7%, respectively, of the volume change which should occur due to extraction. Since 18% of the extracted fluids are reinjected, external recharge must compensate for about 72% of the expected volume reduction. An analysis of the changes in Coulomb stress caused by exploitation of the geothermal field suggest that even though the anthropogenic stresses account for only a fraction of tectonic stresses, they are large enough to trigger seismicity.
Multilayer stress field interference in sandstone and mudstone thin interbed reservoir
Guo, Jian-Chun; Luo, Bo; Zhu, Hai-Yan; Yuan, Shu-Hang; Deng, Yan; Duan, You-Jing; Duan, Wei-Gang; Chen, Li
2016-10-01
General fracturing and separate layer fracturing play an important role in sandstone and mudstone thin interbed (SMTI) reservoirs, where one of the main issues is to control the excessive height growth of fracturing. The fracture propagation at the interface depends on the induced stress produced by the hydraulic fracturing construction. This paper employed a poroelastic coupled damage element with the cohesive zone method (CZM) to establish a 2D fracture quasi-static propagation model. A parametric study was performed under different fracture height, fracture width, pumping rate, fluid viscosity, in situ stress, elastic modulus and tensile strength with this model. General fracturing and separate layer fracturing are compared with each other through fracture morphology and induced stress. The simulation results show that the absolute value of induced stress increases with the decrease in matrix stress near the fracture tip. As a result, the propagation of the fractures is much easier due to the weakened degree of compression. The growth of fracture height and width, the increase in pumping rate and the excessively large or small value of fluid viscosity lead to larger induced stress on the interface. Higher in situ stress, lower elastic modulus, and higher tensile strength of the interlayers can control the excessive height growth of fracturing. The simulated results also show that the fractures are more likely to be overlapped with each other in general fracturing compared to that in separate-layer fracturing. Results of the simulations suggest that lower pumping rates, the proper value of fluid viscosity, separate layer fracturing and interlayers with higher in situ stress, lower elastic modulus and higher tensile strength tend to limit fracture height. Finally, the proposed model was applied to a practical oil field case to verify its effectiveness.
Rogers, W.R.; Coelho, A.M. Jr.; Easley, S.P.; Orr, J.L.; Smith, H.D.; Taylor, L.L.; Tuttle, M.L.
1987-01-01
The objective of this program is to investigate, using the baboon as a nonhuman primate surrogate for the human, possible hehavioral effects associated with exposure to high intensity 60 Hz electric fields. Results from this program, along with information from experiments conducted elsewhere, will be used by the Department of Energy (DOE) to estimate and evaluate the likelihood of deleterious consequences resulting from exposure of humans to the electric fields associated with power transmission over high voltage lines. This research program consists of four major research projects, all of which have been successfully completed. The third project assessed, in separate experiments conducted at 30 and 60 kV/m, effects of chronic exposure to electric fields on the performance of two operant conditioning tasks, fixed ratio (FR), and differential reinforcement of low rate (DRL). In the same two experiments, the fourth project investigated, using the systematic quantitative observational sampling methods of primatology, the possible stress-inducing effects of chronic exposure to 60 Hz electric fields on the behavior of baboons living in small social groups. This volume contains only appendices for projects 3 and 4. 81 figs., 67 tabs.
Estimation of Radiated Fields of Small Horizontal Submodules Based on a Lumped-Element Model
M. Leone
2006-12-01
Full Text Available A novel approach to the estimation of radiated electric field of small horizontal submodules is presented. The principle idea is to describe the radiating submodule-on-motherboard structure with a lumped-element equivalent circuit which includes both the geometrical and the electrical parameters. The electromagnetic emission from the structure is approximated by the radiation characteristics of a Hertzian dipole driven by the antenna voltage resulting from the connector equivalent circuit. Therefore, no time consuming numerical field simulations are needed to evaluate the radiated electric field. Instead, a fast frequency circuit analysis with e.g. PSPICE is sufficient. Moreover, this modeling approach provides a clear insight concerning the influence of geometrical and electrical parameters with respect to radiated emissions. Finally, the computational solutions are compared with experimental results, demonstrating a good correspondence regarding engineering purposes.
Estimates on Functional Integrals of Quantum Mechanics and Non-relativistic Quantum Field Theory
Bley, Gonzalo A.; Thomas, Lawrence E.
2017-01-01
We provide a unified method for obtaining upper bounds for certain functional integrals appearing in quantum mechanics and non-relativistic quantum field theory, functionals of the form {E[{exp}(A_T)]} , the (effective) action {A_T} being a function of particle trajectories up to time T. The estimates in turn yield rigorous lower bounds for ground state energies, via the Feynman-Kac formula. The upper bounds are obtained by writing the action for these functional integrals in terms of stochastic integrals. The method is illustrated in familiar quantum mechanical settings: for the hydrogen atom, for a Schrödinger operator with {1/|x|^2} potential with small coupling, and, with a modest adaptation of the method, for the harmonic oscillator. We then present our principal applications of the method, in the settings of non-relativistic quantum field theories for particles moving in a quantized Bose field, including the optical polaron and Nelson models.
A field test of the extent of bias in selection estimates after accounting for emigration
Letcher, B.H.; Horton, G.E.; Dubreuil, T.L.; O'Donnell, M. J.
2005-01-01
Question: To what extent does trait-dependent emigration bias selection estimates in a natural system? Organisms: Two freshwater cohorts of Atlantic salmon (Salmo salar) juveniles. Field site: A 1 km stretch of a small stream (West Brook) in western Massachusetts. USA from which emigration could be detected continuously. Methods: Estimated viability selection differentials for body size either including or ignoring emigration (include = emigrants survived interval, ignore = emigrants did not survive interval) for 12 intervals. Results: Seasonally variable size-related emigration from our study site generated variable levels of bias in selection estimates for body size. The magnitude of this bias was closely related with the extent of size-dependent emigration during each interval. Including or ignoring the effects of emigration changed the significance of selection estimates in 5 of the 12 intervals, and changed the estimated direction of selection in 4 of the 12 intervals. These results indicate the extent to which inferences about selection in a natural system can be biased by failing to account for trait-dependent emigration. ?? 2005 Benjamin H. Letcher.
Quaternionic Spatiotemporal Filtering for Dense Motion Field Estimation in Ultrasound Imaging
Adrien Marion
2010-01-01
Full Text Available Blood motion estimation provides fundamental clinical information to prevent and detect pathologies such as cancer. Ultrasound imaging associated with Doppler methods is often used for blood flow evaluation. However, Doppler methods suffer from shortcomings such as limited spatial resolution and the inability to estimate lateral motion. Numerous methods such as block matching and decorrelation-based techniques have been proposed to overcome these limitations. In this paper, we propose an original method to estimate dense fields of vector velocity from ultrasound image sequences. Our proposal is based on a spatiotemporal approach and considers 2D+t data as a 3D volume. Orientation of the texture within this volume is related to velocity. Thus, we designed a bank of 3D quaternionic filters to estimate local orientation and then calculate local velocities. The method was applied to a large set of experimental and simulated flow sequences with low motion (≈1 mm/s within small vessels (≈1 mm. Evaluation was conducted with several quantitative criteria such as the normalized mean error or the estimated mean velocity. The results obtained show the good behaviour of our method, characterizing the flows studied.
Quaternionic Spatiotemporal Filtering for Dense Motion Field Estimation in Ultrasound Imaging
Marion Adrien
2010-01-01
Full Text Available Abstract Blood motion estimation provides fundamental clinical information to prevent and detect pathologies such as cancer. Ultrasound imaging associated with Doppler methods is often used for blood flow evaluation. However, Doppler methods suffer from shortcomings such as limited spatial resolution and the inability to estimate lateral motion. Numerous methods such as block matching and decorrelation-based techniques have been proposed to overcome these limitations. In this paper, we propose an original method to estimate dense fields of vector velocity from ultrasound image sequences. Our proposal is based on a spatiotemporal approach and considers 2D+t data as a 3D volume. Orientation of the texture within this volume is related to velocity. Thus, we designed a bank of 3D quaternionic filters to estimate local orientation and then calculate local velocities. The method was applied to a large set of experimental and simulated flow sequences with low motion ( 1 mm/s within small vessels ( 1 mm. Evaluation was conducted with several quantitative criteria such as the normalized mean error or the estimated mean velocity. The results obtained show the good behaviour of our method, characterizing the flows studied.
Formulation of Deformation Stress Fields and Constitutive Equations in Rational Mechanics
Jianhua, Xiao
2010-01-01
In continuum mechanics, stress concept plays an essential role. For complicated materials, different stress concepts are used with ambiguity or different understanding. Geometrically, a material element is expressed by a closed region with arbitral shape. The internal region is acted by distance dependent force (internal body force), while the surface is acted by surface force. Further more, the element as a whole is in a physical background (exterior region) which is determined by the continuum where the element is embedded (external body force). Physically, the total energy can be additively decomposed as three parts: internal region energy, surface energy, and the background energy. However, as forces, they cannot be added directly. After formulating the general forms of physical fields, the deformation tensor is introduced to formulate the force variations caused by deformation. As the force variation is expressed by the deformation tensor, the deformation stress concept is well formulated. Furthermore, a...
Field-based observations confirm linear scaling of sand flux with wind stress
Martin, Raleigh L
2016-01-01
Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the sand flux scales with wind speed, largely because models do not agree on how particle speed changes with wind shear velocity. Here, we present comprehensive measurements from three new field sites and three published studies, showing that characteristic saltation layer heights, and thus particle speeds, remain approximately constant with shear velocity. This result implies a linear dependence of saltation flux on wind shear stress, which contrasts with the nonlinear 3/2 scaling used in most aeolian process predictions. We confirm the linear flux law with direct measurements of the stress-flux relationship occurring at each site. Models for dust generation, dune migration, and other processes driven by wind-blown sand on Earth, Mars, and several other planetary surfaces should be modified to account for linear stress-flux scaling.
Conservation Laws and Stress-energy-momentum Tensors for Systems with Background Fields
Gratus, Jonathan; Tucker, Robin W
2012-01-01
This article attempts to delineate the roles played by non-dynamical background structures and Killing symmetries in the construction of stress-energy-momentum tensors generated from a diffeomorphism invariant action density. An intrinsic coordinate independent approach puts into perspective a number of spurious arguments that have historically lead to the main contenders, viz the Belinfante-Rosenfeld stress-energy-momentum tensor derived from a Noether current and the Einstein-Hilbert stress-energy-momentum tensor derived in the context of Einstein's theory of general relativity. Emphasis is placed on the role played by non-dynamical background (phenomenological) structures that discriminate between properties of these tensors particularly in the context of electrodynamics in media. These tensors are used to construct conservation laws in the presence of Killing Lie-symmetric background fields.
Asifa Khurram
2013-03-01
Full Text Available Fillet welds are extensively used in shipbuilding, automobile and other industries. Heat concentrated at a small area during welding induces distortions and residual stresses, affecting the structural strength. In this study, indirect coupled-field method is used to predict welding residual stresses and deformation in a fillet joint due to welding on both sides. 3-D nonlinear thermal finite element analysis is performed in ANSYS software followed by a structural analysis. Symmetrical boundary conditions are applied on half of the model for simplification. Results of FE structure analysis predict residual stresses in the specimen. A comparison of simulation results with experimental values proves the authenticity of the technique. The present study can be extended for complex structures and welding techniques.
Influence of fractality of fracture surfaces on stress and displacement fields at crack tips
2008-01-01
In the classic theory of fracture mechanics,expressions for calculating the stresses and displacements in the vicinity of the crack tip are deduced on the basis of the assumption that a fracture surface is a smooth surface or that a crack is a smooth crack.In fact,the surface of a crack formed during the fracture is usually very irregular.So the real asymptotic form of the stress and displacement fields at the crack tip is different from the classic one.Considering the irregularity of a real fracture surface or a real crack profile,the crack is taken as a fractal one,and then the real asymptotic form at the crack tip is developed by applying Griffith’s energy balance principle and fractal geometry.Through the developed asymptotic form,it is discovered that the fractality of the crack reduces the stress singularity at the crack tip.
De Guidi, Giorgio; Caputo, Riccardo; Scudero, Salvatore; Perdicaro, Vincenzo
2013-04-01
An intense tectonic activity in eastern Sicily and southern Calabria is well documented by the differential uplift of Late Quaternary coastlines and by the record of the strong historical earthquakes. The extensional belt that crosses this area is dominated by a well established WNW-ESE-oriented extensional direction. However, this area is largely lacking of any structural analysis able to define the tectonics at a more local scale. In the attempt to fill this gap of knowledge, we carried out a systematic analysis of extension joint sets. In fact, the systematic field collection of these extensional features, coupled with an appropriate inversion technique, allows to determine the characteristic of the causative tectonic stress field. Joints are defined as outcrop-scale mechanical discontinuities showing no evidence of shear motion and being originated as purely extensional fractures. Such tectonic features are one of the most common deformational structures in every tectonic environment and particularly abundant in the study area. A particular arrangement of joints, called "fracture grid-lock system", and defined as an orthogonal joint system where mutual abutting and crosscutting relationships characterize two geologically coeval joint sets, allow to infer the direction and the magnitude of the tectonic stress field. We performed the analyses of joints only on Pleistocene deposits of Eastern Sicily and Southern Calabria. Moreover we investigated only calcarenite sediments and cemented deposits, avoiding claysh and loose matrix-supported clastic sediments where the deformation is generally accomodated in a distributed way through the relative motion between the single particles. In the selection of the sites, we also took into account the possibility to clearly observe the geometric relationships among the joints. For this reason we chose curvilinear road cuts or cliffs, wide coastal erosional surfaces and quarries. The numerical inversions show a similar stress
Satoshi Suzuki
2013-01-01
Full Text Available For an establishment of a skill evaluation method for human support systems, development of an estimating equation of the machine operational skill is presented. Factors of the eye movement such as frequency, velocity, and moving distance of saccade were computed using the developed eye gaze measurement system, and the eye movement features were determined from these factors. The estimating equation was derived through an outlier test (to eliminate nonstandard data and a principal component analysis (to find dominant components. Using a cooperative carrying task (cc-task simulator, the eye movement and operational data of the machine operators were recorded, and effectiveness of the derived estimating equation was investigated. As a result, it was confirmed that the estimating equation was effective strongly against actual simple skill levels (r=0.56–0.84. In addition, effects of internal condition such as fatigue and stress on the estimating equation were analyzed. Using heart rate (HR and coefficient of variation of R-R interval (Cvrri. Correlation analysis between these biosignal indexes and the estimating equation of operational skill found that the equation reflected effects of stress and fatigue, although the equation could estimate the skill level adequately.
Leaf Area Index Estimation Using Chinese GF-1 Wide Field View Data in an Agriculture Region.
Wei, Xiangqin; Gu, Xingfa; Meng, Qingyan; Yu, Tao; Zhou, Xiang; Wei, Zheng; Jia, Kun; Wang, Chunmei
2017-07-08
Leaf area index (LAI) is an important vegetation parameter that characterizes leaf density and canopy structure, and plays an important role in global change study, land surface process simulation and agriculture monitoring. The wide field view (WFV) sensor on board the Chinese GF-1 satellite can acquire multi-spectral data with decametric spatial resolution, high temporal resolution and wide coverage, which are valuable data sources for dynamic monitoring of LAI. Therefore, an automatic LAI estimation algorithm for GF-1 WFV data was developed based on the radiative transfer model and LAI estimation accuracy of the developed algorithm was assessed in an agriculture region with maize as the dominated crop type. The radiative transfer model was firstly used to simulate the physical relationship between canopy reflectance and LAI under different soil and vegetation conditions, and then the training sample dataset was formed. Then, neural networks (NNs) were used to develop the LAI estimation algorithm using the training sample dataset. Green, red and near-infrared band reflectances of GF-1 WFV data were used as the input variables of the NNs, as well as the corresponding LAI was the output variable. The validation results using field LAI measurements in the agriculture region indicated that the LAI estimation algorithm could achieve satisfactory results (such as R² = 0.818, RMSE = 0.50). In addition, the developed LAI estimation algorithm had potential to operationally generate LAI datasets using GF-1 WFV land surface reflectance data, which could provide high spatial and temporal resolution LAI data for agriculture, ecosystem and environmental management researches.
Analytical Solution for Stress Field and Intensity Factor in CSTBD under Mixed Mode Conditions
Najaf Ali Ghavidel
2014-06-01
Full Text Available Considering the fact that rocks fail faster under tensile stress, rock tensile strength is of greatimportance in applications such as blasting, rock fragmentation, slope stability, hydraulic fracturing,caprock integrity, and geothermal energy extraction. There are two direct and indirect methods tomeasure tensile strength. Since direct methods always encompass difficulties in test setup, indirectmethods, specifically the Brazilian test, have often been employed for tensile strength measurement.Tensile failure is technically attributed to crack propagation in rock. Fracture mechanics hassignificant potential for the determination of crack behaviour as well as propagation pattern. To applyBrazilian tests, cracked disc geometry has been suggested by the International Society for RockMechanics ISRM. Accordingly, a comprehensive study is necessary to evaluate stress field and stressintensity factor (SIF around the crack in the centre of the specimen. In this paper, superpositionprinciple is employed to solve the problem of cracked straight-through Brazilian disc (CSTBD, usingtwo methods of dislocation and complex stress function. Stress field and SIF in the vicinity of thecrack tip are then calculated. With the proposed method, the magnitude of critical load for crackinitiation in structures can be predicted. This method is valid for any crack of any arbitrary length andangle. In addition, numerical modelling has been carried out for the Brazilian disc. Finally, theanalytical solution has been compared with numerical modelling results showing the same outcomefor both methods.
THERMAL STRESS FIELD WHEN CRACK ARREST IN AN AXIAL SYMMETRY METAL DIE USING ELECTROMAGNETIC HEATING
无
2006-01-01
In order to solve the thermal stress field around crack tip in metal die when crack prevention using electromagnetic heating, a metal die with a half-embedded round crack was selected as the study object. The complex function method was used as a basis for the theoretical model of the space crack prevention in metal dies using electromagnetic heating. The crack arrest was accomplished by a pulse current discharge through the inner and outer. The theoretical analysis results show that the temperature around the crack tip rises instantly above the melting point of the metal. Small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect when the current pulse discharged. The thermal compressive stress field appears around the crack tip at the moment. The research results show that the crack prevention using electromagnetic heating can decrease the stress concentration and forms a compressive stress area around the crack tip, and also prevents the main crack from propagating further, and the goal of crack preventing can be reached.
On the spatial distribution of seismicity and the 3D tectonic stress field in western Greece
Kassaras, Ioannis; Kapetanidis, Vasilis; Karakonstantis, Andreas
2016-10-01
We analyzed a large number of focal mechanisms and relocated earthquake hypocenters to investigate the geodynamics of western Greece, the most seismically active part of the Aegean plate-boundary zone. This region was seismically activated multiple times during the last decade, providing a large amount of enhanced quality new information that was obtained by the Hellenic Unified Seismological Network (HUSN). Relocated seismicity using a double-difference method appears to be concentrated above ∼35 km depth, exhibiting spatial continuity along the convergence boundary and being clustered elsewhere. Earthquakes are confined within the accreted sediments escarpment of the down-going African plate against the un-deformed Eurasian hinterland. The data arrangement shows that Pindos constitutes a seismic boundary along which large stress heterogeneities occur. In Cephalonia no seismicity is found to be related with the offshore Cephalonia Transform Fault (CTF). Onshore, Nsbnd S crustal extension dominates, while in central and south Peloponnesus the stress field appears rotated by 90°. Shearing-stress obliquity by 30° is indicated along the major strike-slip faults, consistent with clockwise crustal rotation. Within the lower crust, the stress field appears affected by plate kinematics and distributed deformation of the lower crust and upper mantle, which guide the regional geodynamics.
Blad, B. L.; Norman, J. M.; Gardner, B. R.
1983-01-01
The experimental design, data acquisition and analysis procedures for agronomic and reflectance data acquired over corn and soybeans at the Sandhills Agricultural Laboratory of the University of Nebraska are described. The following conclusions were reached: (1) predictive leaf area estimation models can be defined which appear valid over a wide range of soils; (2) relative grain yield estimates over moisture stressed corn were improved by combining reflectance and thermal data; (3) corn phenology estimates using the model of Badhwar and Henderson (1981) exhibited systematic bias but were reasonably accurate; (4) canopy reflectance can be modelled to within approximately 10% of measured values; and (5) soybean pubescence significantly affects canopy reflectance, energy balance and water use relationships.
Stress-energy-momentum tensors in Lagrangian field theory; 2, gravitational superpotential
Giachetta, G
1995-01-01
Our investigation of differential conservation laws in Lagrangian field theory is based on the first variational formula which provides the canonical decomposition of the Lie derivative of a Lagrangian density by a projectable vector field on a bundle (Part 1: gr-qc/9510061). If a Lagrangian density is invariant under a certain class of bundle isomorphisms, its Lie derivative by the associated vector fields vanishes and the corresponding differential conservation laws take place. If these vector fields depend on derivatives of parameters of bundle transformations, the conserved current reduces to a superpotential. This Part of the work is devoted to gravitational superpotentials. The invariance of a gravitational Lagrangian density under general covariant transformations leads to the stress-energy-momentum conservation law where the energy-momentum flow of gravity reduces to the corresponding generalized Komar superpotential. The associated energy-momentum (pseudo) tensor can be defined and calculated on solu...
Evaluation of uncertainty in field soil moisture estimations by cosmic-ray neutron sensing
Scheiffele, Lena Maria; Baroni, Gabriele; Schrön, Martin; Ingwersen, Joachim; Oswald, Sascha E.
2017-04-01
Cosmic-ray neutron sensing (CRNS) has developed into a valuable, indirect and non-invasive method to estimate soil moisture at the field scale. It provides continuous temporal data (hours to days), relatively large depth (10-70 cm), and intermediate spatial scale measurements (hundreds of meters), thereby overcoming some of the limitations in point measurements (e.g., TDR/FDR) and of remote sensing products. All these characteristics make CRNS a favorable approach for soil moisture estimation, especially for applications in cropped fields and agricultural water management. Various studies compare CRNS measurements to soil sensor networks and show a good agreement. However, CRNS is sensitive to more characteristics of the land-surface, e.g. additional hydrogen pools, soil bulk density, and biomass. Prior to calibration the standard atmospheric corrections are accounting for the effects of air pressure, humidity and variations in incoming neutrons. In addition, the standard calibration approach was further extended to account for hydrogen in lattice water and soil organic material. Some corrections were also proposed to account for water in biomass. Moreover, the sensitivity of the probe was found to decrease with distance and a weighting procedure for the calibration datasets was introduced to account for the sensors' radial sensitivity. On the one hand, all the mentioned corrections showed to improve the accuracy in estimated soil moisture values. On the other hand, they require substantial additional efforts in monitoring activities and they could inherently contribute to the overall uncertainty of the CRNS product. In this study we aim (i) to quantify the uncertainty in the field soil moisture estimated by CRNS and (ii) to understand the role of the different sources of uncertainty. To this end, two experimental sites in Germany were equipped with a CRNS probe and compared to values of a soil moisture network. The agricultural fields were cropped with winter
SUN; Longde; SONG; Wenjie; JIANG; Tongwen
2004-01-01
Kela 2 Gas Field, with high formation pressure (74.35MPa), high pressure coefficient (2.022) and difficulty of potential test and evaluation, is the largest integrated proved dry gas reservoir in China so far and the principal source for West-East Gas Development Project. In order to correctly evaluate the elastic-plastic deformation of rocks caused by the pressure decline during production, some researches, as the experiment on reservoir sensitivity to stress of gas filed with abnormal high pressure, are made. By testing the rock mechanic properties, porosities and permeabilities at different temperature and pressure of 342 core samples from 5 wells in this area, the variations of petro-physical properties at changing pressure are analyzed, and the applicable inspection relationship is concluded. The average productivity curve with the reservoir sensitivity to stress is plotted on the basis of the research, integrated with the field-wide productivity equation. The knowledge lays a foundation for the gas well productivity evaluation in the field and the gas field development plan, and provides effective techniques and measures for basic research on the development of similar gas fields.
Perrone, John A.; Stone, Leland S.
1997-01-01
We have previously proposed a computational neural-network model by which the complex patterns of retinal image motion generated during locomotion (optic flow) can be processed by specialized detectors acting as templates for specific instances of self-motion. The detectors in this template model respond to global optic flow by sampling image motion over a large portion of the visual field through networks of local motion sensors with properties similar to neurons found in the middle temporal (MT) area of primate extrastriate visual cortex. The model detectors were designed to extract self-translation (heading), self-rotation, as well as the scene layout (relative distances) ahead of a moving observer, and are arranged in cortical-like heading maps to perform this function. Heading estimation from optic flow has been postulated by some to be implemented within the medial superior temporal (MST) area. Others have questioned whether MST neurons can fulfill this role because some of their receptive-field properties appear inconsistent with a role in heading estimation. To resolve this issue, we systematically compared MST single-unit responses with the outputs of model detectors under matched stimulus conditions. We found that the basic physiological properties of MST neurons can be explained by the template model. We conclude that MST neurons are well suited to support heading estimation and that the template model provides an explicit set of testable hypotheses which can guide future exploration of MST and adjacent areas within the primate superior temporal sulcus.
A multimodal detection model of dolphins to estimate abundance validated by field experiments.
Akamatsu, Tomonari; Ura, Tamaki; Sugimatsu, Harumi; Bahl, Rajendar; Behera, Sandeep; Panda, Sudarsan; Khan, Muntaz; Kar, S K; Kar, C S; Kimura, Satoko; Sasaki-Yamamoto, Yukiko
2013-09-01
Abundance estimation of marine mammals requires matching of detection of an animal or a group of animal by two independent means. A multimodal detection model using visual and acoustic cues (surfacing and phonation) that enables abundance estimation of dolphins is proposed. The method does not require a specific time window to match the cues of both means for applying mark-recapture method. The proposed model was evaluated using data obtained in field observations of Ganges River dolphins and Irrawaddy dolphins, as examples of dispersed and condensed distributions of animals, respectively. The acoustic detection probability was approximately 80%, 20% higher than that of visual detection for both species, regardless of the distribution of the animals in present study sites. The abundance estimates of Ganges River dolphins and Irrawaddy dolphins fairly agreed with the numbers reported in previous monitoring studies. The single animal detection probability was smaller than that of larger cluster size, as predicted by the model and confirmed by field data. However, dense groups of Irrawaddy dolphins showed difference in cluster sizes observed by visual and acoustic methods. Lower detection probability of single clusters of this species seemed to be caused by the clumped distribution of this species.
Tommaso Julitta
2016-02-01
Full Text Available Remote Sensing of Sun-Induced Chlorophyll Fluorescence (SIF is a research field of growing interest because it offers the potential to quantify actual photosynthesis and to monitor plant status. New satellite missions from the European Space Agency, such as the Earth Explorer 8 FLuorescence EXplorer (FLEX mission—scheduled to launch in 2022 and aiming at SIF mapping—and from the National Aeronautics and Space Administration (NASA such as the Orbiting Carbon Observatory-2 (OCO-2 sampling mission launched in July 2014, provide the capability to estimate SIF from space. The detection of the SIF signal from airborne and satellite platform is difficult and reliable ground level data are needed for calibration/validation. Several commercially available spectroradiometers are currently used to retrieve SIF in the field. This study presents a comparison exercise for evaluating the capability of four spectroradiometers to retrieve SIF. The results show that an accurate far-red SIF estimation can be achieved using spectroradiometers with an ultrafine resolution (less than 1 nm, while the red SIF estimation requires even higher spectral resolution (less than 0.5 nm. Moreover, it is shown that the Signal to Noise Ratio (SNR plays a significant role in the precision of the far-red SIF measurements.
Particle tracking velocimetry applied to estimate the pressure field around a Savonius turbine
Murai, Yuichi; Nakada, Taishi; Suzuki, Takao; Yamamoto, Fujio
2007-08-01
Particle tracking velocimetry (PTV) is applied to flows around a Savonius turbine. The velocity vector field measured with PTV is utilized to estimate the pressure field around the turbine, as well as to evaluate the torque performance. The main objective of the work is the establishment of the pressure estimation scheme required to discuss the turbine performance. First, the PTV data are interpolated on a regular grid with a fourth-order ellipsoidal differential equation to generate velocity vectors satisfying the third-order spatio-temporal continuity both in time and space. Second, the phase-averaged velocity vector information with respect to the turbine angle is substituted into three different types of pressure-estimating equations, i.e. the Poisson equation, the Navier-Stokes equation and the sub-grid scale model of turbulence. The results obtained based on the Navier-Stokes equation are compared with those based on the Poisson equation, and have shown several merits in employing the Navier-Stokes-based method for the PTV measurement. The method is applied to a rotating turbine with the tip-speed ratio of 0.5 to find the relationship between torque behaviour and flow structure in a phase-averaged sense. We have found that a flow attached to the convex surface of the blades induces low-pressure regions to drive the turbine, namely, the lift force helps the turbine blades to rotate even when the drag force is insufficient. Secondary mechanisms of torque generation are also discussed.
Evaluation of Scattered Wave and Stress Concentration Field in a Damaged Solder Joint
Dineva, P.; Gross, D.; Rangelov, T.
1999-06-01
Two different, but equally important problems for solder joint reliability are solved. The evaluation of the dynamic stress concentration field in the thin base layer of a damaged solder joint is the first one. It is considered as a rectangular plate with a central macro-crack surrounded with randomly distributed micro-cracks, subjected to uniform time-harmonic tension. The damaged solder joint state is described by the model of Gross and Zhang [1] (International Journal of Solids and Structures29, 1763-1779). The information of the stress concentration field in a damaged solder joint is important to understand the mechanisms in the base components of all electronic packages.The second problem is ultrasonic wave scattering in a solder joint damaged by micro-cracks, considered as a two-dimensional finite multi-layered system. The solution of this problem may aid the creation of the modern non-destructive evaluation method (NDEM) for a high quality control of products in electronic industry.The method of the solution of both boundary-value problems is a direct BIEM (boundary integral equation method). The numerical results obtained for a solder joint with real geometry and physical properties show how the acoustic and stress concentration fields depend on the solder joint damage state. The character of this dependence is discussed.
1986-01-24
The objective was to investigate, using baboons (superspecies Papio cynocephalus) as surrogates, possible behavioral effects associated with exposure to high intensity 60 Hz electric fields. This program consists of four major projects. The first will evaluate the potential aversive character of exposure to 60 Hz electric fields by determining the threshold intensity which produces avoidance or escape responses. The second project will estimate the threshold intensity for detection of 60 Hz electric fields. The third will assess effects of chronic exposure to 60 Hz electric fields on the performance of two operant conditioning tasks, fixed ratio (FR) and differential reinforcement of low rate responding (DRL). The fourth will investigate the possible stress-inducing effects of chronic exposure to 60 Hz electric fields on the behavior of baboons living in small social groups.
Kohei Arai
2016-10-01
Full Text Available Method for Near Infrared: NIR reflectance estimation with visible camera data based on regression for Normalized Vegetation Index: NDVI estimation is proposed together with its application for insect damage detection of rice paddy fields. Through experiments at rice paddy fields which is situated at Saga Prefectural Agriculture Research Institute SPARI in Saga city, Kyushu, Japan, it is found that there is high correlation between NIR reflectance and Green color reflectance. Therefore, it is possible to estimate NIR reflectance with visible camera data which results in possibility of estimation of NDVI with drone mounted visible camera data. As is well known that the protein content in rice crops is highly correlated with NIR intensity, or reflectance of rice leaves, it is possible to estimate rice crop quality with drone based visible camera data.
Assessing the effect of vegetation in the estimation of soil properties with field VNIR radiometry
Melendez-Pastor, I.; Córdoba-Sola, P.; Navarro-Pedreño, J.; Gómez, I.; Koch, M.
2009-04-01
Spectroradiometric soil surveys (field radiometry) are a valuable technique for soil classification and properties estimation. Field radiometry combines -in a relatively easy-to-use procedure- a fast, accurate and non-destructive sampling method. A wide range of soil properties have been quantitatively estimated with field or laboratory radiometry. In addition, field radiometry is a basic stage in remote sensing studies. It allows the up-scaling process of soil, vegetation or water parameters from the ground level to the airborne or spaceborne sensors level. Field radiometry plays a crucial role in training and validation stages of quantitative remote sensing. A complex problem in remote sensing appears when several components are mixed within a pixel and the resulting pixel's spectrum is a combination of the individual components. This work assess the effect of vegetation in soil properties estimation with linear regression models. Field spectra were taken from soil-vegetation mixtures under natural illumination with a portable spectroradiometer in the visible and near-infrared (VNIR) spectral range. Soil and vegetation samples for each radiometric sampling point were taken and analyzed in laboratory. Soil moisture content and soil organic carbon measured by the LOI (Loss-On-Ignition) method (Konen et al. 2002) were used in this approach. A derivative analysis of field spectra was used to determine the position and magnitude of absorption bands according to the method employed by Melendez-Pastor et al. (2008). Pearson correlations between soil parameters and each spectral band were computed and correlograms for the first and second derivate were obtained. Maximum (approximates to +1) and minimum (approximates to -1) Pearson correlations were used to normalize correlograms between 0 to 1. High relatively correlated bands (with values ranging from 0 to 0.1 or from 0-9 to 1 for the normalized correlograms) were identified and used as explicative variables in the
Jubany-Marí, T; Munné-Bosch, S; Alegre, L
2010-05-01
Abiotic stresses, such as drought, can increase the production of reactive oxygen species (ROS) in plants. An increase in ROS levels can provoke a partial or severe oxidation of cellular components inducing redox status changes, so continuous control of ROS and therefore of their metabolism is decisive under stress conditions. The present work focuses on the contribution of one pro-oxidant, hydrogen peroxide (H(2)O(2)) and one antioxidant, ascorbate (AA) and its redox status, in the control of plant responses to drought-oxidative stress in resistant plants growing in field conditions. After a general introduction to the concept of drought and oxidative stress and its relationship, we describe the role of H(2)O(2) in drought stress responses, emphasizing the importance of studies in H(2)O(2) subcellular localization, needed for a better understanding of its role in plant responses to stress. Although more studies are needed in the study of changes of redox status in plants subjected to stress, the AA pools and its redox status can be indicative of its involvement as a part of cellular mechanisms by which the plant respond to drought-induced oxidative stress. The mechanism of resistance and/or tolerance to drought-oxidative stress is complex, especially when studies are carried out in plants growing in field conditions, where an interaction of stresses occurs. This study sheds light on the mechanisms of plant responses to water-oxidative stress in plants growing in the field.
Estimation of Reserves of Tula Horizon Oil Deposits of Severo-Yurmanskoye Field, Perm Kray
V I Nabiullin
2015-09-01
Full Text Available This article presents an estimation of reserves of the Tula horizon oil-bearing layers Tl2-a and Tl2-b at the Severo-Yurmanskoye oil field. Research was carried out in order to prospect the unestimated oil reserves at the previously drilled but not commercially producing areas of Perm kray. The opportunity of reserve calculation for this oil field was provided by the sufficient oil encroachment rate achieved during testing of Tula horizon layers in the borehole 174, reliable mapping of oil-bearing horizons using seismic and borehole data, existence of updated stratigraphic information, results of study of uniformity of oil-bearing layers throughout the area of the Severo-Yurmanskoye oil field, reliable estimate of the position of water-oil contact, defining the effective oil-bearing thickness of oil-bearing layers using results of borehole geophysical survey, study of lithological composition and reservoir properties, study of physical and chemical properties of oil in borehole and in laboratory, and reliability of statistical evaluation of oil recovery factor.
Estimation of the Required Amount of Superconductors for High-field Accelerator Dipole Magnets
Schwerg, N
2007-01-01
The coil size and the corresponding amount of superconducting material that is used during the design process of a magnet cross-section have direct impacts on the overall magnet cost. It is therefore of interest to estimate the minimum amount of conductors needed to reach the defined field strength before a detailed design process starts. Equally, it is useful to evaluate the efficiency of a given design by calculating the amount of superconducting cables that are used to reach the envisaged main field by simple rule. To this purpose, the minimum amount of conductors for the construction of a dipole of given main field strength and aperture size is estimated taking the actual critical current density of the used strands into account. Characteristic curves applicable for the NED Nb3Sn strand specification are given and some of the recently studied different dipole configurations are compared. Based on these results, it is shown how the required amount of conductors changes due to the iron yoke contribution and...
Effect of visual field presentation on action planning (estimating reach) in children.
Gabbard, Carl; Cordova, Alberto
2012-01-01
In this article, the authors examined the effects of target information presented in different visual fields (lower, upper, central) on estimates of reach via use of motor imagery in children (5-11 years old) and young adults. Results indicated an advantage for estimating reach movements for targets placed in lower visual field (LoVF), with all groups having greater difficulty in the upper visual field (UpVF) condition, especially 5- and 7-year-olds. Complementing these results was an overall age-related increase in accuracy. Based in part on the equivalence hypothesis suggesting that motor imagery and motor planning and execution are similar, the findings support previous work of executed behaviors showing that there is a LoVF bias for motor skill actions of the hand. Given that previous research hints that the UpVF may be bias for visuospatial (perceptual) qualities, research in that area and its association with visuomotor processing (LoVF) should be considered.
Slab stress field in the Hellenic subduction zone as inferred from intermediate depth earthquakes
Rontogianni, S.; Konstantinou, K.; Melis, N. S.; Evangelidis, C.
2010-12-01
In this study we investigate the stress regime of the subducting slab beneath the Hellenic Arc aiming to answer two fundamental questions; a) How does the slab deformation vary horizontally and vertically along this large curvature arc? b) Which are the mechanisms inferred from global observations that can explain this deformation and have not been identified previously due to dataset limitations. The data are selected from various seismic networks, global and local seismic catalogues and the newly established Hellenic broadband seismic network (http://bbnet.gein.noa.gr/). An updated view of the geometry of the Hellenic Wadati-Benioff zone (WBZ) is gained by the spatial distribution of intermediate depth earthquakes (40 km≤ depth ≤ 180km). Stress tensor inversion is performed on 100 fault plane solutions of intermediate depth earthquakes after quality control has been applied. The stress field parameters are determined along the arc for several depth ranges. The slab is divided into four subsets, each containing enough focal mechanisms for stress inversion to be performed successfully. The Peloponnese segment shows for depths 50-80 km σ1 almost normal to the slab and σ3 steeper than the slab dip that might indicate suction force-the component of the slab pull force that is unbalanced by the subduction resistance. The Kithira-Western Crete segment shows for depths 50-100 km a biaxial deviatoric compression or a state of confined compression with the σ1 along strike. The stress regime in this section of the slab might be related to its complex shape and geometry (width, curvature) reflecting changes in the slab dip between the Peloponnese-Kithira strait and the Crete region as has also been identified by teleseimic receiver functions. The third segment below Crete shows σ1 along strike and σ3 almost subvertical to slab direction. The stress field for the forth segment below Karpathos and Rhodos has been divided into two depth ranges. The shallow subset (50
Pan, Xinpeng; Zhang, Guangzhi; Yin, Xingyao
2017-10-01
Estimation of effective geostress parameters is fundamental to the trajectory design and hydraulic fracturing in shale-gas reservoirs. Considering the shale characteristics of excellent stratification, well-developed cracks or fractures and small-scale pores, an effective or suitable shale anisotropic rock-physics model contributes to achieving the accurate prediction of effective geostress parameters in shale-gas reservoirs. In this paper, we first built a shale anisotropic rock-physics model with orthorhombic symmetry, which helps to calculate the anisotropic and geomechanical parameters under the orthorhombic assumption. Then, we introduced an anisotropic stress model with orthorhombic symmetry compared with an isotropic stress model and a transversely isotropic stress model. Combining the effective estimation of the pore pressure and the vertical stress parameters, we finally obtained the effective geostress parameters including the minimum and maximum horizontal stress parameters, providing a useful guide for the exploration and development in shale-gas reservoirs. Of course, ultimately the optimal choice of the hydraulic-fracturing area may also take into consideration other multi-factors such as the rock brittleness, cracks or fractures, and hydrocarbon distribution.
Zordan, Jessica; Schleiss, Anton J.; Franca, Mário J.
2016-04-01
Density or gravity currents are geophysical flows driven by density gradients between two contacting fluids. The physical trigger mechanism of these phenomena lays in the density differences which may be caused by differences in the temperature, dissolved substances or concentration of suspended sediments. Saline density currents are capable to entrain bed sediments inducing signatures in the bottom of sedimentary basins. Herein, saline density currents are reproduced in laboratory over a movable bed. The experimental channel is of the lock-exchange type, it is 7.5 m long and 0.3 m wide, divided into two sections of comparable volumes by a sliding gate. An upstream reach serves as a head tank for the dense mixture; the current propagates through a downstream reach where the main measurements are made. Downstream of the channel a tank exist to absorb the reflection of the current and thus artifacts due to the limited length of the channel. High performance thermoplastic polyurethane simulating fine sediments forms the movable bed. Measures of 3D instantaneous velocities will be made with the use of the non-intrusive technique of the ADV (Acoustic Doppler Current Profiler). With the velocity measurements, the evolution in time of the channel-bed shear stress due the passage of gravity currents is estimated. This is in turn related to the observed erosion and to such parameters determinant for the dynamics of the current as initial density difference, lock length and channel slope. This work was funded by the ITN-Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7-PEOPLE-2013-ITN under REA grant agreement n_607394-SEDITRANS.
See, M T; Mabry, J W; Bertrand, J K
1993-11-01
Variance components for number of pigs born alive (NBA) were estimated from sow productivity field records collected by purebred breed associations. Data sets analyzed were as follows: Hampshire (n = 13,537), Landrace (n = 10,822), and Spotted (n = 3,949). Variance components for service sire, sire of sow, dam of sow, and residual effects on NBA (adjusted for parity) were estimated. The single-trait model included relationships between service sires, sires of sows, and dams of sows. The model was implemented using an expectation maximization (EM) REML algorithm. A sparse-matrix solver was also used. Heritability estimates for NBA were .13, .13, and .12 for Hampshire, Spotted, and Landrace, respectively. Estimates of maternal genetic (co)variances (m2) expressed as a proportion of the phenotypic variance were .05, .01, and .03 for Hampshire, Spotted, and Landrace, respectively. Results indicated that service sires account for 1 to 2% of the total variation for NBA. Genetic effects influencing NBA seem to be small in these data sets, but selection for increased NBA should be effective.
Scaling of semivariograms and the kriging estimation of field-measured properties
S. R. Vieira
1997-12-01
Full Text Available Two methods were evaluated for scaling a set of semivariograms into a unified function for kriging estimation of field-measured properties. Scaling is performed using sample variances and sills of individual semivariograms as scale factors. Theoretical developments show that kriging weights are independent of the scaling factor which appears simply as a constant multiplying both sides of the kriging equations. The scaling techniques were applied to four sets of semivariograms representing spatial scales of 30 x 30 m to 600 x 900 km. Experimental semivariograms in each set successfully coalesced into a single curve by variances and sills of individual semivariograms. To evaluate the scaling techniques, kriged estimates derived from scaled semivariogram models were compared with those derived from unscaled models. Differences in kriged estimates of the order of 5% were found for the cases in which the scaling technique was not successful in coalescing the individual semivariograms, which also means that the spatial variability of these properties is different. The proposed scaling techniques enhance interpretation of semivariograms when a variety of measurements are made at the same location. They also reduce computational times for kriging estimations because kriging weights only need to be calculated for one variable. Weights remain unchanged for all other variables in the data set whose semivariograms are scaled.
Linear Track Estimation Using Double Pulse Sources for Near-Field Underwater Moving Target
Zhifei Chen; Hong Hou; Jianhua Yang; Jincai Sun; Qian Wang
2013-01-01
The double pulse sources (DPS) method is presented for linear track estimation in this work.In the field of noise identification of underwater moving target,the Doppler will distort the frequency and amplitude of the radiated noise.To eliminate this,the track estimation is necessary.In the DPS method,we first estimate bearings of two sinusoidal pulse sources installed in the moving target through baseline positioning method.Meanwhile,the emitted and recorded time of each pulse are also acquired.Then the linear track parameters will be achieved based on the geometry pattern with the help of double sources spacing.The simulated results confirm that the DPS improves the performance of the previous double source spacing method.The simulated experiments were carried out using a moving battery car to further evaluate its performance.When the target is 40-60m away,the experiment results show that biases of track azimuth and abeam distance of DPS are under 0.6° and 3.4m,respectively.And the average deviation of estimated velocity is around 0.25m/s.
Potential-field estimation from satellite data using scalar and vector Slepian functions
Plattner, Alain
2013-01-01
In the last few decades a series of increasingly sophisticated satellite missions has brought us gravity and magnetometry data of ever improving quality. To make optimal use of this rich source of information on the structure of Earth and other celestial bodies, our computational algorithms should be well matched to the specific properties of the data. In particular, inversion methods require specialized adaptation if the data are only locally available, their quality varies spatially, or if we are interested in model recovery only for a specific spatial region. Here, we present two approaches to estimate potential fields on a spherical Earth, from gradient data collected at satellite altitude. Our context is that of the estimation of the gravitational or magnetic potential from vector-valued measurements. Both of our approaches utilize spherical Slepian functions to produce an approximation of local data at satellite altitude, which is subsequently transformed to the Earth's spherical reference surface. The ...
Scene estimation from speckled synthetic aperture radar imagery: Markov-random-field approach.
Lankoande, Ousseini; Hayat, Majeed M; Santhanam, Balu
2006-06-01
A novel Markov-random-field model for speckled synthetic aperture radar (SAR) imagery is derived according to the physical, spatial statistical properties of speckle noise in coherent imaging. A convex Gibbs energy function for speckled images is derived and utilized to perform speckle-compensating image estimation. The image estimation is formed by computing the conditional expectation of the noisy image at each pixel given its neighbors, which is further expressed in terms of the derived Gibbs energy function. The efficacy of the proposed technique, in terms of reducing speckle noise while preserving spatial resolution, is studied by using both real and simulated SAR imagery. Using a number of commonly used metrics, the performance of the proposed technique is shown to surpass that of existing speckle-noise-filtering methods such as the Gamma MAP, the modified Lee, and the enhanced Frost.
Theory of Distribution Estimation of Hyperparameters in Markov Random Field Models
Sakamoto, Hirotaka; Nakanishi-Ohno, Yoshinori; Okada, Masato
2016-06-01
We investigated the performance of distribution estimation of hyperparameters in Markov random field models proposed by Nakanishi-Ohno et al., http://doi.org/10.1088/1751-8113/47/4/045001, J. Phys. A 47, 045001 (2014) when used to evaluate the confidence of data. We analytically calculated the configurational average, with respect to data, of the negative logarithm of the posterior distribution, which is called free energy based on an analogy with statistical mechanics. This configurational average of free energy shrinks as the amount of data increases. Our results theoretically confirm the numerical results from that previous study.
Genetic Variation in Response to Salt Stress of Quinoa Grown under Controlled and Field Conditions
Nguyen Long
2016-04-01
Full Text Available The objective of this study was to understand the change in response of quinoa genotypes to divers salinity stress conditions e.g in controlled (net-house and in the different saline fields. The pot experiment was conducted in a net-house at Vietnam National University of Agriculture, Hanoi, Vietnam in spring cropping season to characterize the growth and yield of six quinoa genotypes under four NaCl concentrations (0, 10, 20 and 30 dS m-1. At the same time, in Nam Dinh and Hai Phong provinces, two coastal provinces that are most affected by seawater intrusion in the North of Vietnam, same genotypes were studied under two plant densities (20 x 5cm and 50 x 5cm. The results showed that salinity stresses reduced growth and yield characteristics of quinoa plant and varying due to different saline conditions. Plant density of quinoa grown under saline fields was not associated with difference in morphological traits but might relate to the change in yield characteristics. Salinity stresses reduced plant height, the number of leaves on main stem, the number of branches on plant, head panicle length, the number of branches per panicle, dry matter accumulation, 1000-seed weight, individual and grain yield of all quinoa genotypes. However, most of quinoa genotypes produced acceptable yield even under high salt conditions in the field. Among quinoa genotypes, Moradas and Verde adapted well to salt stress conditions with high potential for the number of leaves on main stem, the number of branches on plant, dry matter accumulation and yield than others. These should be recommended varieties for cultivation in saline areas in Vietnam as well as be useful to improve genetic resources in breeding program for salt tolerant quinoa varieties.
Estimation of the rice-planting field in Bangladesh by satellite remote sensing
Furuta, E.; Suzuki, G.; Yamassaki, M.; Teraoka, T.; Fujiwara, H.; Ogino, Y.; Akashi, M.; Lahrita, L.; Naruse, N.; Takahashi, Y.
2016-12-01
In Bangladesh, price of rice has been unstable due to a large increase in production. To control the price can become a political issue, because rice agriculture is one of the most important industries in Bangladesh, whereas the total area of the paddy field is accurately unknown, owing to unsustainable and on-site surveys for the area (1). Satellite remote sensing is an effective solution to research the all area of domestic paddy field. Microwave satellite imaging has a large merit to be observable regardless of the weather conditions, however, research institutions have been limited to observing continuously since the cost is high for developing countries, such as Bangladesh. This study aims to establish the way to grasp the paddy field using optical satellite images for free of charge (Landsat-8). We have focused on seasonal changes in the water and the vegetation indices obtained from paddy fields. We have performed image calculations of Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) of the well-known paddy field in Bangladesh Rice Research Institute. We found that there are seasonal changes of NDVI and NDWI calculated from paddy field. The characteristics are as follows; the NDVI and the NDWI values varies by 0.17-0.25 up and 0.11-0.19 down, respectively, at the transition from the dry to the rainy season, on the other hand, the NDVI and the NDWI changes by 0.21-0.29 down and 0.09-0.17 up from the rainy to the dry season. These features make us to distinguish the paddy field from the other cultivated area. The decrease of NDVI means that rice bares, The increase of NDWI can be interpreted that the paddy field is covered with water for the preparation for planting it. Our estimated area of paddy field in Bangladesh (85,900km ) corresponds well with the previous reported value of 117,700km (1). We have established the way to grasp the paddy field using optical satellite images for free of charge, on the bases of the
A new estimate of the mass of the gravitational scalar field for Dark Energy
Fujii, Yasunori
2015-01-01
A new estimate of the mass of the pseudo dilaton is offered by following the funda- mental nature that a massless Nambu-Goldstone boson, called a dilaton, in the Einstein frame acquires a nonzero mass through the loop effects which occur with the Higgs field in the relativistic quantum field theory as described by poles of D, spacetime dimensionality off the physical value D = 4. Naturally the technique of dimensional regulairzation is fully used to show this pole structure to be suppressed to be finite by what is called a Classical-Quantum-Interplay, to improve our previous attempt. Basically the same anal- ysis is extended to derive also the coupling of a pseudo dilaton to two photons.
Axonal and dendritic density field estimation from incomplete single-slice neuronal reconstructions
Jaap evan Pelt
2014-06-01
Full Text Available Neuronal information processing in cortical networks critically depends on the organization of synaptic connectivity. Synaptic connections can form when axons and dendrites come in close proximity of each other. The spatial innervation of neuronal arborizations can be described by their axonal and dendritic density fields. Recently we showed that potential locations of synapses between neurons can be estimated from their overlapping axonal and dendritic density fields. However, deriving density fields from single-slice neuronal reconstructions is hampered by incompleteness because of cut branches.Here, we describe a method for recovering the lost axonal and dendritic mass. This so-called completion method is based on an estimation of the mass inside the slice and an extrapolation to the space outside the slice, assuming axial symmetry in the mass distribution. We validated the method using a set of neurons generated with our NETMORPH simulator. The model-generated neurons were artificially sliced and subsequently recovered by the completion method. Depending on slice thickness and arbor extent, branches that have lost their outside parents (orphan branches may occur inside the slice. Not connected anymore to the contiguous structure of the sliced neuron, orphan branches result in an underestimation of neurite mass. For 300 m thick slices, however, the validation showed a full recovery of dendritic and an almost full recovery of axonal mass.The completion method was applied to three experimental data sets of reconstructed rat cortical L2/3 pyramidal neurons. The results showed that in 300 m thick slices intracortical axons lost about 50% and dendrites about 16% of their mass. The completion method can be applied to single-slice reconstructions as long as axial symmetry can be assumed in the mass distribution. This opens up the possibility of using incomplete neuronal reconstructions from open-access data bases to determine population mean
Olga A. Kuchay
2015-09-01
Full Text Available The cataclastic method developed by Yu.L. Rebetsky is applied to reconstruct the recent field of stresses related to aftershock sequences of earthquakes that occurred in the Altai-Sayan mountainous region, specifically the Altai earthquake of 27 September 2003 (М=7.3; φ=50.061o; λ=87.966o and the Busingol earthquake of 27 December 1991 (М=5.0; φ=51.1o; λ=98.13o. Upon reconstruction of the field of stresses from data on aftershocks of different magnitudes, it is revealed that orientations of maximum stresses are misaligned, and this may suggest a lack of similarity of fields of stresses in different scale ranks. The fields of stresses reconstructed from data on sequences of weak aftershocks of the Altai and Busingol earthquakes show changes in orientations of major stress axes at opposite sides of the shear faults under study. The orientation of the maximum deviation stress axes due to strong aftershocks is consistent with the regional field of stresses and does not change in the vicinity of the fault plane associated with the strong earthquakes the Altai and Sayan regions.
Jiménez, Juan de la Cruz; Cardoso, Juan A; Leiva, Luisa F; Gil, Juanita; Forero, Manuel G; Worthington, Margaret L; Miles, John W; Rao, Idupulapati M
2017-01-01
Brachiaria grasses are sown in tropical regions around the world, especially in the Neotropics, to improve livestock production. Waterlogging is a major constraint to the productivity and persistence of Brachiaria grasses during the rainy season. While some Brachiaria cultivars are moderately tolerant to seasonal waterlogging, none of the commercial cultivars combines superior yield potential and nutritional quality with a high level of waterlogging tolerance. The Brachiaria breeding program at the International Center for Tropical Agriculture, has been using recurrent selection for the past two decades to combine forage yield with resistance to biotic and abiotic stress factors. The main objective of this study was to test the suitability of normalized difference vegetation index (NDVI) and image-based phenotyping as non-destructive approaches to identify Brachiaria hybrids tolerant to waterlogging stress under field conditions. Nineteen promising hybrid selections from the breeding program and three commercial checks were evaluated for their tolerance to waterlogging under field conditions. The waterlogging treatment was imposed by applying and maintaining water to 3 cm above soil surface. Plant performance was determined non-destructively using proximal sensing and image-based phenotyping and also destructively via harvesting for comparison. Image analysis of projected green and dead areas, NDVI and shoot biomass were positively correlated (r ≥ 0.8). Our results indicate that image analysis and NDVI can serve as non-destructive screening approaches for the identification of Brachiaria hybrids tolerant to waterlogging stress.
Fukada Saiji
2015-01-01
Full Text Available The prestressed concrete (PC stress ribbon footbridge is a type of suspension bridge without towers, which has been applied in Japan and all over the world for years in light of its low construction cost and aesthetic merit. It generally consists of the precast concrete slabs with embedded cables. However, the walking-induced lateral vibration trouble of the Millennium Bridge in London in 2000 gave a lesson to the engineers that the lateral vibration feature must be taken into consideration for the footbridge vibration evaluation. In this sense, the field investigations on the lateral vibration features of 14 pre-stressed concrete stress ribbon footbridge in Japan was carried out by artificial impact and damping free vibration tests. According to the investigations, the larger the bridge span, the lower the frequencies of lateral-related vibration modes. In addition, based on the damping-free vibration field tests, there was a tendency toward the damping constant degradation when bridge span became larger.
Jiménez, Juan de la Cruz; Cardoso, Juan A.; Leiva, Luisa F.; Gil, Juanita; Forero, Manuel G.; Worthington, Margaret L.; Miles, John W.; Rao, Idupulapati M.
2017-01-01
Brachiaria grasses are sown in tropical regions around the world, especially in the Neotropics, to improve livestock production. Waterlogging is a major constraint to the productivity and persistence of Brachiaria grasses during the rainy season. While some Brachiaria cultivars are moderately tolerant to seasonal waterlogging, none of the commercial cultivars combines superior yield potential and nutritional quality with a high level of waterlogging tolerance. The Brachiaria breeding program at the International Center for Tropical Agriculture, has been using recurrent selection for the past two decades to combine forage yield with resistance to biotic and abiotic stress factors. The main objective of this study was to test the suitability of normalized difference vegetation index (NDVI) and image-based phenotyping as non-destructive approaches to identify Brachiaria hybrids tolerant to waterlogging stress under field conditions. Nineteen promising hybrid selections from the breeding program and three commercial checks were evaluated for their tolerance to waterlogging under field conditions. The waterlogging treatment was imposed by applying and maintaining water to 3 cm above soil surface. Plant performance was determined non-destructively using proximal sensing and image-based phenotyping and also destructively via harvesting for comparison. Image analysis of projected green and dead areas, NDVI and shoot biomass were positively correlated (r ≥ 0.8). Our results indicate that image analysis and NDVI can serve as non-destructive screening approaches for the identification of Brachiaria hybrids tolerant to waterlogging stress. PMID:28243249
Balbus, Steven A
2016-10-18
A conserved stress energy tensor for weak field gravitational waves propagating in vacuum is derived directly from the linearized general relativistic wave equation alone, for an arbitrary gauge. In any harmonic gauge, the form of the tensor leads directly to the classical expression for the outgoing wave energy. The method described here, however, is a much simpler, shorter, and more physically motivated approach than is the customary procedure, which involves a lengthy and cumbersome second-order (in wave-amplitude) calculation starting with the Einstein tensor. Our method has the added advantage of exhibiting the direct coupling between the outgoing wave energy flux and the work done by the gravitational field on the sources. For nonharmonic gauges, the directly derived wave stress tensor has an apparent index asymmetry. This coordinate artifact may be straightforwardly removed, and the symmetrized (still gauge-invariant) tensor then takes on its widely used form. Angular momentum conservation follows immediately. For any harmonic gauge, however, the stress tensor found is manifestly symmetric from the start, and its derivation depends, in its entirety, on the structure of the linearized wave equation.
Asgharzadeh Sadegh, Parisa
Earthquakes in western Quebec and southern Ontario present a major contribution to the natural hazards in south eastern Canada due to their proximity to major population centres. However, the seismic characteristics of the events in these regions have not been well documented. Improved knowledge of earthquake distribution and seismic controlling mechanisms provides a great benefit for earthquake hazard analysis in eastern Canada. The available information about the tectonic stress indicators, including focal mechanisms, was compiled for Canada prior to 1994. The present research is concentrated mainly on determination of the focal mechanisms and hypocentre locations of the earthquakes after 1993 with M > 3.5 to characterize the present-day regional and local stress fields in southern Ontario and western Quebec. An attempt was also made to differentiate local zones with comparatively homogeneous tectonic stresses orientation and seismic regimes, thus providing information for future re-assessment of the seismic hazard in each region. Considering seismic parameters such as the trend of the epicentres, focal depths and the state of stress of the events along with their tectonic settings, ten distinct clusters have been proposed for western Quebec and two clusters of events were determined for southern Ontario with comparatively consistent focal mechanisms. The locations and characteristics of seismicity clusters appear to be consistent with the hypothesis that they are near the locations of large historic and prehistoric events, and represent exceptionally persistent aftershocks of past large earthquakes.
Bias stress effect and recovery in organic field effect transistors: proton migration mechanism
Sharma, A.; Mathijssen, Simon G. J.; Kemerink, M.; de Leeuw, Dago M.; Bobbert, Peter A.
2010-08-01
Organic field-effect transistors exhibit operational instabilities when a gate bias is applied. For a constant gate bias the threshold voltage shifts towards the applied gate bias voltage, an effect known as the bias-stress effect. We have performed a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric. We propose a mechanism in which holes in the semiconductor are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric to explain the instabilities in organic transistors. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we explain in detail the recovery of a pres-stressed transistor on applying zero gate bias. We show that recovery dynamics depends strongly on the extent of stressing. Our mechanism is consistent with the known aspects of bias-stress effect like acceleration due to humidity, constant activation energy and reversibility.
Ju, Sanghyun; Janes, David B.; Lu, Gang; Facchetti, Antonio; Marks, Tobin J.
2006-11-01
The effects of bias stress (gate stress or drain stress) on nanowire field-effect transistor (NW-FET) stability were investigated as a function of stress bias and stress time. The n-channel NW-FETs used a nanoscopic self-assembled organic gate insulator, and each device contained a single ZnO nanowire. Before stress, the off current is limited by a leakage current in the 1nA range, which increases as the gate to source bias becomes increasingly negative. The devices also exhibited significant changes in threshold voltage (Vth) and off current over 500 repeated measurement sweeps. The leakage current was significantly reduced after gate stress, but not after drain stress. Vth variations observed upon successive bias sweeps for devices following gate stress or drain stress were smaller than the Vth variation of unstressed devices. These observations suggest that gate stress and drain stress modify the ZnO nanowire-gate insulator interface, which can reduce electron trapping at the surface and therefore reduce the off current levels and variations in Vth. These results confirm that gate and drain stresses are effective means to stabilize device operation and provide high performance transistors with impressive reliabilities.
Ritchie, R O; Lubock, P
1986-05-01
Projected fatigue life analyses are performed to estimate the endurance of a cardiac valve prosthesis under physiological environmental and mechanical conditions. The analyses are conducted using both the classical stress-strain/life and the fracture mechanics-based damage-tolerant approaches, and provide estimates of expected life in terms of initial flaw sizes which may pre-exist in the metal prior to the valve entering service. The damage-tolerant analysis further is supplemented by consideration of the question of "short cracks," which represents a developing area in metal fatigue research, not commonly applied to data in standard engineering design practice.
A label field fusion bayesian model and its penalized maximum rand estimator for image segmentation.
Mignotte, Max
2010-06-01
This paper presents a novel segmentation approach based on a Markov random field (MRF) fusion model which aims at combining several segmentation results associated with simpler clustering models in order to achieve a more reliable and accurate segmentation result. The proposed fusion model is derived from the recently introduced probabilistic Rand measure for comparing one segmentation result to one or more manual segmentations of the same image. This non-parametric measure allows us to easily derive an appealing fusion model of label fields, easily expressed as a Gibbs distribution, or as a nonstationary MRF model defined on a complete graph. Concretely, this Gibbs energy model encodes the set of binary constraints, in terms of pairs of pixel labels, provided by each segmentation results to be fused. Combined with a prior distribution, this energy-based Gibbs model also allows for definition of an interesting penalized maximum probabilistic rand estimator with which the fusion of simple, quickly estimated, segmentation results appears as an interesting alternative to complex segmentation models existing in the literature. This fusion framework has been successfully applied on the Berkeley image database. The experiments reported in this paper demonstrate that the proposed method is efficient in terms of visual evaluation and quantitative performance measures and performs well compared to the best existing state-of-the-art segmentation methods recently proposed in the literature.
Estimating aboveground biomass in interior Alaska with Landsat data and field measurements
Ji, Lei; Wylie, Bruce K.; Nossov, Dana R.; Peterson, Birgit E.; Waldrop, Mark P.; McFarland, Jack W.; Rover, Jennifer R.; Hollingsworth, Teresa N.
2012-01-01
Terrestrial plant biomass is a key biophysical parameter required for understanding ecological systems in Alaska. An accurate estimation of biomass at a regional scale provides an important data input for ecological modeling in this region. In this study, we created an aboveground biomass (AGB) map at 30-m resolution for the Yukon Flats ecoregion of interior Alaska using Landsat data and field measurements. Tree, shrub, and herbaceous AGB data in both live and dead forms were collected in summers and autumns of 2009 and 2010. Using the Landsat-derived spectral variables and the field AGB data, we generated a regression model and applied this model to map AGB for the ecoregion. A 3-fold cross-validation indicated that the AGB estimates had a mean absolute error of 21.8 Mg/ha and a mean bias error of 5.2 Mg/ha. Additionally, we validated the mapping results using an airborne lidar dataset acquired for a portion of the ecoregion. We found a significant relationship between the lidar-derived canopy height and the Landsat-derived AGB (R2 = 0.40). The AGB map showed that 90% of the ecoregion had AGB values ranging from 10 Mg/ha to 134 Mg/ha. Vegetation types and fires were the primary factors controlling the spatial AGB patterns in this ecoregion.
Field Application of Cable Tension Estimation Technique Using the h-SI Method
Myung-Hyun Noh
2015-01-01
Full Text Available This paper investigates field applicability of a new system identification technique of estimating tensile force for a cable of long span bridges. The newly proposed h-SI method using the combination of the sensitivity updating algorithm and the advanced hybrid microgenetic algorithm can allow not only avoiding the trap of local minimum at initial searching stage but also finding the optimal solution in terms of better numerical efficiency than existing methods. First, this paper overviews the procedure of tension estimation through a theoretical formulation. Secondly, the validity of the proposed technique is numerically examined using a set of dynamic data obtained from benchmark numerical samples considering the effect of sag extensibility and bending stiffness of a sag-cable system. Finally, the feasibility of the proposed method is investigated through actual field data extracted from a cable-stayed Seohae Bridge. The test results show that the existing methods require precise initial data in advance but the proposed method is not affected by such initial information. In particular, the proposed method can improve accuracy and convergence rate toward final values. Consequently, the proposed method can be more effective than existing methods in terms of characterizing the tensile force variation for cable structures.
Estimate of Methane Emission from Rice Paddy Fields in Taihu Region,China
CAIZU－CONG; JINJI－SHENG; 等
1994-01-01
Methane fluxes from late rice and single cropping rice fields in Taihu region were measured using closed chamber method in 1992 and 1993 and CH4 emission from this region (total area of paddy soils was about 1.88 million hectares,of which 0.63 million hectares are distibuted in the south of Jiangsu province) was estimated on the basis of the meam CH4 fluxes observed.The results showed that the mean CH4 flaxes from late rice and single cropping rice field were quite similar under the prevailing cultivation practices in the region,being around 5 mg CH4/m2/h(4.31-5.31mg CH4/m2/h for various cultivars of the late rice and 3.20-6.22mg CH4/m2/h for various treatments of the single cropping rice).Total CH4 emission from paddy soils in the region was estimated to e 0.185-0.359 Tg CH4 per year.Continuously flooding the soil with a water layer till ripening caused higher mean CH4 flux;and addition of nitrification inhibitor(thiourea) stimulated CH4 emission.There was no simple repationship between CH4 flux and either soil temperature or soil Eh.
Diaz, P. M. A.; Feitosa, R. Q.; Sanches, I. D.; Costa, G. A. O. P.
2016-06-01
This paper presents a method to estimate the temporal interaction in a Conditional Random Field (CRF) based approach for crop recognition from multitemporal remote sensing image sequences. This approach models the phenology of different crop types as a CRF. Interaction potentials are assumed to depend only on the class labels of an image site at two consecutive epochs. In the proposed method, the estimation of temporal interaction parameters is considered as an optimization problem, whose goal is to find the transition matrix that maximizes the CRF performance, upon a set of labelled data. The objective functions underlying the optimization procedure can be formulated in terms of different accuracy metrics, such as overall and average class accuracy per crop or phenological stages. To validate the proposed approach, experiments were carried out upon a dataset consisting of 12 co-registered LANDSAT images of a region in southeast of Brazil. Pattern Search was used as the optimization algorithm. The experimental results demonstrated that the proposed method was able to substantially outperform estimates related to joint or conditional class transition probabilities, which rely on training samples.
Robust estimation of error covariance functions in GRACE gravity field determination
Behzadpour, Saniya; Mayer-Gürr, Torsten; Flury, Jakob
2016-04-01
The accurate modelling of the stochastic behaviour of the GRACE mission observations is an important task in the time variable gravity field determination. After fitting a model in the least-squares sense, it is necessary to determine whether all the necessary model assumptions, i.e., independence, normality, and homoscedasticity of the residuals, are valid before performing inference. Checking the model assumptions for the range rate residuals, it has been concluded that one of the major problems in the range rate observations is the outliers in the data. One way to deal with this problem is to implement a robust estimation procedure to dampen the effect of observations that would be highly influential if least squares were used. In addition to insensitivity to outliers, such a procedure tends to leave the residuals associated with outliers large, therefore making the identification of outliers much easier. Implementation of this procedure using robust error covariance functions, comparison of different robust estimators, e.g., Huber's and Tukey's estimators, and assessing the detected outliers with respect to temporal and spatial patterns are discussed.
Vibol, S; Towprayoon, S
2010-02-01
To estimate the greenhouse gas emissions from paddy fields of Cambodia, the methodology of the Intergovernmental Panel on Climate Change (IPCC) guidelines, IPCC coefficients, and emission factors from the experiment in Thailand and another country were used. Total area under rice cultivation during the years 2005-2006 was 2,048,360 ha in the first crop season and 298,529 ha in the second crop season. The emission of methane from stubble incorporation with manure plus fertilizer application areas in the first crop season was estimated to be 192,783.74 ton higher than stubble with manure, stubble with fertilizer, and stubble without fertilizer areas. The fields with stubble burning emitted the highest emission of methane (75,771.29 ton) followed by stubble burning with manure (22,251.08 ton), stubble burning with fertilizer (13,213.27 ton), and stubble burning with fertilizer application areas (3,222.22 ton). The total emission of methane from rice field in Cambodia for the years 2005-2006 was approximately 342,649.26 ton (342.65 Gg) in the first crop season and 36,838.88 ton (36.84 Gg) in the second crop season. During the first crop season in the years 2005-2006, Battambang province emitted the highest amount of CH(4) (38,764.48 ton) and, in the second crop season during the years 2005-2006, the highest emission (8,262.34 ton) was found in Takeo province (8,262.34 ton). Nitrous oxide emission was between 2.70 and 1,047.92 ton in the first crop season and it ranged from 0 to 244.90 ton in the second crop season. Total nitrous oxide emission from paddy rice field was estimated to be 9,026.28 ton in the first crop season and 1,091.93 ton in the second crop season. Larger area under cultivation is responsible for higher emission of methane and nitrous oxide. Total emission of nitrous oxide by using IPCC default emission coefficient was approximately 2,328.85 ton. The total global warming potential of Cambodian paddy rice soil is 11,723,217.03 ton (11,723 Gg
Galanti, Eli; Durante, Daniele; Iess, Luciano; Kaspi, Yohai
2017-04-01
The ongoing Juno spacecraft measurements are improving our knowledge of Jupiter's gravity field. Similarly, the Cassini Grand Finale will improve the gravity estimate of Saturn. The analysis of the Juno and Cassini Doppler data will provide a very accurate reconstruction of spacial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity fields of Jupiter and Saturn, additional information needs to be incorporated into the analysis, especially with regards to the planets' wind structures. In this work we propose a new iterative approach for the estimation of Jupiter and Saturn gravity fields, using simulated measurements, a trajectory estimation model, and an adjoint based inverse thermal wind model. Beginning with an artificial gravitational field, the trajectory estimation model is used to obtain the gravitational moments. The solution from the trajectory model is then used as an initial guess for the thermal wind model, and together with an optimization method, the likely penetration depth of the winds is computed, and its uncertainty is evaluated. As a final step, the gravity harmonics solution from the thermal wind model is given back to the trajectory model, along with an estimate of their uncertainties, to be used as a priori for a new calculation of the gravity field. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that by using this method some of the gravitational moments are fitted better to the `observed' ones, mainly due to the added information from the dynamical model which includes the wind structure and its depth. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity moments estimated from the Juno and Cassini radio science experiments.
A. N. Avramenko
2016-01-01
Full Text Available Performance tuning improvement of modern diesel engines exerts an influence on technical and economic, ecological and resource indices of an internal combustion engine (ICE. In its turn, that requires a complex estimation and improvement of engine indices. As is known, working process and thermal intensity of combustion chamber parts are interconnected between themselves. Changes in design, operating and adjustment parameters of systems and structural elements of internal combustion engines that enable air-fuel mixing and combustions processes stressed state of combustion chamber parts. Joint estimation of operating cycle parameters and strength indices of ICE parts makes it possible to solve a number of problems originating in the process of designing new engine models and further development of the existing ones. The paper provides results of comparative estimation on heat-stressed state of a cylinder head for a high-speed diesel engine Д21A (2Ч10,5/12 while operating a rated power mode. In order to simulate and specify a heat-stressed state for description of boundary heat conductivity conditions the following adjoint “gas – wall” problems have been solved: the first one – for combustion chamber of a diesel engine (an internal problem – simulation of a working cycle for a diesel engine; the second one – for cooling edges while blowing over them by air flow (an external problem. Calculations have been made in three-dimensional non-stationary presentation within the Cartesian coordinates. In order to simulate a working cycle of the diesel engine a computational grid describing combustion chamber configuration, inlet and outlet channels has been used in the paper. Solution of the external problem for cooling edge surface in case of blowing over them by air flow has permitted to specify temperatures and heat-transfer coefficient and later to improve an accuracy while estimating level of temperatures and stresses of the cylinder head.
A simplified sampling procedure for the estimation of methane emission in rice fields.
Khokhar, Nadar Hussain; Park, Jae-Woo
2017-08-24
Manual closed chamber methods are widely used for CH4 measurement from rice paddies. Despite diurnal and seasonal variations in CH4 emissions, fixed sampling times, usually during the day, are used. Here, we monitored CH4 emission from rice paddies for one complete rice-growing season. Daytime CH4 emission increased from 0800 h, and maximal emission was observed at 1200 h. Daily averaged CH4 flux increased during plant growth or fertilizer application and decreased upon drainage of plants. CH4 measurement results were linearly interpolated and matched with the daily averaged CH4 emission calculated from the measured results. The time when daily averaged emission and the interpolated CH4 curve coincided during the daytime was largely invariant within each of the five distinctive periods. One-hourly sampling during each of these five periods was utilized to estimate the emission during each period, and we found that five one-hourly samples during the season accurately reflected the CH4 emission calculated based on all 136 hourly samples. This new sampling scheme is simple and more efficient than current sampling practices. Previously reported sampling schemes yielded estimates 9 to 32% higher than the measured CH4 emission, while our suggested scheme yielded an estimate that was only 5% different from that based on all 136-h samples. The sampling scheme proposed in this study can be used in rice paddy fields in Korea and extended worldwide to countries that use similar farming practices. This sampling scheme will help in producing more accurate global methane budget from rice paddy fields.
Origin of magnetic field effect enhancement by electrical stress in organic light emitting diodes
Bagnich, S. A.; Niedermeier, U.; Melzer, C.; Sarfert, W.; von Seggern, H.
2009-06-01
Recently, it has been discovered that the magnetic field effect (MFE) in organic light emitting diodes (OLEDs) based on poly(para-phenylene vinylene) can be enhanced by exposing the diode to moderate electrical stress. Here, we disclose the mechanism behind this way of improving the MFE. We first show that electronic traps in general play an important role for the MFE. Optical depletion of available trap states by infrared illumination leads to a decrease in the MFE. Furthermore, we demonstrate that annealing of the OLED at high temperatures eliminates the MFE improvement of the previously performed electrical conditioning. However, the improvement can be restored by subsequent conditioning at higher current or voltage. Thus it is likely that electrical stress is accompanied by a transformation of the polymer morphology or conformation resulting in a formation of energetic traps for charge carriers.
Development of an algebraic stress/two-layer model for calculating thrust chamber flow fields
Chen, C. P.; Shang, H. M.; Huang, J.
1993-01-01
Following the consensus of a workshop in Turbulence Modeling for Liquid Rocket Thrust Chambers, the current effort was undertaken to study the effects of second-order closure on the predictions of thermochemical flow fields. To reduce the instability and computational intensity of the full second-order Reynolds Stress Model, an Algebraic Stress Model (ASM) coupled with a two-layer near wall treatment was developed. Various test problems, including the compressible boundary layer with adiabatic and cooled walls, recirculating flows, swirling flows and the entire SSME nozzle flow were studied to assess the performance of the current model. Detailed calculations for the SSME exit wall flow around the nozzle manifold were executed. As to the overall flow predictions, the ASM removes another assumption for appropriate comparison with experimental data, to account for the non-isotropic turbulence effects.
NUMERICAL SIMULATION OF THE STRUCTURAL STRESS FIELD OF BEIYA GOLD DEPOSIT
MA Deyun; GAO Zhenmin
2003-01-01
Based on the study about the geological background of Beiya Gold Deposit, numerical simulation was conducted about the three-dimensional structural stress field for Beiya Gold Deposit by applying finite element theory and by employing a linear elasticity model. Results of the simulation indicate that the Beiya syncline is a faulted basin, and a hidden fracture occurs in the west wing of the syncline.Under the action of the EW-trending compressive force, four nearly NS-trending fractures (groups) were generated in the stress stretching areas of the two wings of the syncline, and these fractures constitute favorable tectonic positions for the upward intrusion of porphyry magma and the occurrence of Au-Pb-Zn polymetallic deposits.
Vacuum stress tensor of a scalar field in a rectangular waveguide
Rodrigues, R.B.; Svaiter, N.F. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]. E-mail: robson@cbpf.br; svaiter@lns.mit.edu; Paola, R.D.M. de [Escola Federal de Engenharia de Itajuba, MG (Brazil). Inst. de Ciencias]. E-mail: rpaola@efei.br
2001-11-01
Using the heat Kernel method and the analytical continuation of the zeta function, we calculate the canonical and improved vacuum stress tensors, {l_brace}T{sub {mu}}{sub {nu}}(vector x){r_brace} and {l_brace}{theta}{sub {mu}}{sub {nu}} (vector x){r_brace}, associated with a massless scalar field confined in the interior of an infinity long rectangular waveguide. The local depence of the renormalized energy for two special configurations when the total energy is positive and negative are presented using {l_brace}T{sub 00}(vector x){r_brace} and {l_brace}{theta}{sub 00}(vector x){r_brace}. From the stress tensors we obtain the local casimir forces in all walls by introducing a particular external configuration. It is hown that this external configuration cannot give account of the edge divergences of the local forces. The local form of the forces is obtained for three special configurations. (author)
Application of magnetic Barkhausen noise in non-destructive testing fields of residual stress
Yin Hechi; Zhang Guangye; Chen Ligong; Ni Chunzhen
2007-01-01
Magnetic Barkhausen noise (MBN) is a phenomenon of electromagnetic energy due to the movement of magnetic domain walls inside ferromagnetic materials when they are locally magnetized by an alternating magnetic fields. According to Faraday's law of electromagnetic induction, the noise can be received by the coil attached to the surface of the material being magnetized and the noise carries the message of the characteristics of the material such as stresses, hardness, phase content, etc. Based on the characteristic of the noise, researching about the relationship between the residual stress in the welding assembly and the noise are carried out. Furthermore, data process is performed by RMS (Root Mean Square) equation and Power Spectrum analysis.
Poss, J A; Russell, W B; Grieve, C M
2006-01-01
In arid irrigated regions, the proportion of crop production under deficit irrigation with poorer quality water is increasing as demand for fresh water soars and efforts to prevent saline water table development occur. Remote sensing technology to quantify salinity and water stress effects on forage yield can be an important tool to address yield loss potential when deficit irrigating with poor water quality. Two important forages, alfalfa (Medicago sativa L.) and tall wheatgrass (Agropyron elongatum L.), were grown in a volumetric lysimeter facility where rootzone salinity and water content were varied and monitored. Ground-based hyperspectral canopy reflectance in the visible and near infrared (NIR) were related to forage yields from a broad range of salinity and water stress conditions. Canopy reflectance spectra were obtained in the 350- to 1000-nm region from two viewing angles (nadir view, 45 degrees from nadir). Nadir view vegetation indices (VI) were not as strongly correlated with leaf area index changes attributed to water and salinity stress treatments for both alfalfa and wheatgrass. From a list of 71 VIs, two were selected for a multiple linear-regression model that estimated yield under varying salinity and water stress conditions. With data obtained during the second harvest of a three-harvest 100-d growing period, regression coefficients for each crop were developed and then used with the model to estimate fresh weights for preceding and succeeding harvests during the same 100-d interval. The model accounted for 72% of the variation in yields in wheatgrass and 94% in yields of alfalfa within the same salinity and water stress treatment period. The model successfully predicted yield in three out of four cases when applied to the first and third harvest yields. Correlations between indices and yield increased as canopy development progressed. Growth reductions attributed to simultaneous salinity and water stress were well characterized, but the
Wen-Jie Wu
2017-01-01
Full Text Available We established a stress-history-dependent porosity model of potential target rocks for CO2 geosequestration based on rock sample porosity measurements under various effective stresses (5 - 120 MPa. The measured samples were collected from shallow boreholes (< 300 m depth drilled at the frontal fold in northern Taiwan. The lithology, density, and the stress-history-dependent porosity derived from shallow boreholes enabled us to predict the porosity-depth relationship of given rock formations at (burial depths of approximately 3170 - 3470 m potential sites for CO2 geosequestration located near the Taoyuan Tableland coastline. Our results indicate that the porosity of samples derived from laboratory tests under atmospheric pressure is significantly greater than the porosity measured under stress caused by sediment burial. It is therefore strongly recommended that CO2 storage capacity assessment not be estimated from the porosity measured under atmospheric pressure. Neglecting the stress history effect on the porosity of compacted and uplifted rocks may induce a percentage error of 7.7% at a depth of approximately 1000 m, where the thickness of the eroded, formerly overlying formation is 2.5 km in a synthetic case. The CO2 injection pressure effect on the porosity was also evaluated using the stress-history-dependent porosity model. As expected, the pore pressure buildup during CO2 injection will induce an increase in the rock porosity. For example, a large injection pressure of 13 MPa at a depth of approximately 1000 m will increase the rock porosity by a percentage error of 6.7%. Our results have implications for CO2 storage capacity injection pressure estimates.
Koike, Narihiko; Ii, Satoshi; Yoshinaga, Tsukasa; Nozaki, Kazunori; Wada, Shigeo
2017-09-14
This paper presents a novel inverse estimation approach for the active contraction stresses of tongue muscles during speech. The proposed method is based on variational data assimilation using a mechanical tongue model and 3D tongue surface shapes for speech production. The mechanical tongue model considers nonlinear hyperelasticity, finite deformation, actual geometry from computed tomography (CT) images, and anisotropic active contraction by muscle fibers, the orientations of which are ideally determined using anatomical drawings. The tongue deformation is obtained by solving a stationary force-equilibrium equation using a finite element method. An inverse problem is established to find the combination of muscle contraction stresses that minimizes the Euclidean distance of the tongue surfaces between the mechanical analysis and CT results of speech production, where a signed-distance function represents the tongue surface. Our approach is validated through an ideal numerical example and extended to the real-world case of two Japanese vowels, /ʉ/ and /ɯ/. The results capture the target shape completely and provide an excellent estimation of the active contraction stresses in the ideal case, and exhibit similar tendencies as in previous observations and simulations for the actual vowel cases. The present approach can reveal the relative relationship among the muscle contraction stresses in similar utterances with different tongue shapes, and enables the investigation of the coordination of tongue muscles during speech using only the deformed tongue shape obtained from medical images. This will enhance our understanding of speech motor control. Copyright © 2017. Published by Elsevier Ltd.
刘波; 高玉臣
1995-01-01
Using Gao’s constitutive relation, the stress fieid has been analyzed near the notch tip and the crack tip of an incompressible rubber-like specimen under the condition of plane strain. The asymptotic equation of the notch tip field is solved numerically; the stress and strain singularities are calculated for various notch angles and different material constant values; the stress variation with the angle coordinate is also analyzed.
Grazulis, Alexandra K.
In Wattenberg Field the Niobrara Formation is the primary productive zone for horizontal drilling and completions. It is an unconventional reservoir made up of alternating chalk and marl layers which require hydraulic fracturing for completion. The main study area for this project is a four square mile region where time-lapse multicomponent seismic surveys have been acquired. This area includes the Wishbone section, where 11 horizontal wells have been drilled, and is the focus of dynamic reservoir characterization. The primary goal of this research study is to investigate relationships between geomechanics, stress and fractures. Determining the geomechanical properties of the reservoir is essential for better reservoir management. Geology is the main driver controlling production, due to the presence of fault compartmentalization in the field. The central graben, within the Wishbone section, causes geologic heterogeneity and displays signs of high net pressure. This is due to a larger increase in pore pressure, ultimately decreasing effective stress. Outside of the graben, naturally fractured areas, displaying decreasing net pressure trends, will maximize fracture network surface area during completions. This allows for a larger volume of rock to be stimulated, and a greater chance of opening pre-existing fractures. As far as re-fracturing efforts are concerned, areas outside of the graben which are brittle and have low stress anisotropy should be targeted to create complex fracture networks. Geomechanical and stress information about the reservoir is vital for predicting fracture propagation. After investigation of fracture characterization trends, we have a better understanding of stimulated areas within the Wishbone section. Specific completion techniques can be applied to stages based on geomechanical properties and geologic location. Fracture networks defined through the integrated dynamic reservoir characterization process provide targets for future re
Kaplan David L
2011-01-01
Full Text Available Abstract Background Electric fields are integral to many biological events, from maintaining cellular homeostasis to embryonic development to healing. The application of electric fields offers substantial therapeutic potential, while optimal dosing regimens and the underlying mechanisms responsible for the positive clinical impact are poorly understood. Methods The purpose of this study was to track the differentiation profile and stress response of human bone marrow derived mesenchymal stem cells (hMSCs undergoing osteogenic differentiation during exposure to a 20 mV/cm, 60 kHz electric field. Morphological and biochemical changes were imaged using endogenous two-photon excited fluorescence (TPEF and quantitatively assessed through eccentricity calculations and extraction of the redox ratio from NADH, FAD and lipofuscin contributions. Real time reverse transcriptase-polymerase chain reactions (RT-PCR were used to track osteogenic differentiation markers, namely alkaline phosphatase (ALP and collagen type 1 (col1, and stress response markers, such as heat shock protein 27 (hsp27 and heat shock protein 70 (hsp70. Comparisons of collagen deposition between the stimulated hMSCs and controls were examined through second harmonic generation (SHG imaging. Results Quantitative differences in cell morphology, as described through an eccentricity ratio, were found on days 2 and days 5 (p Conclusions Electrical stimulation is a useful tool to improve hMSC osteogenic differentiation, while heat shock proteins may reveal underlying mechanisms, and optical non-invasive imaging may be used to monitor the induced morphological and biochemical changes.
HUOZongliang; WEIJianlin; MAOLingfeng; TANChanghua; XUMingzhen
2003-01-01
In this paper, the change in parameters of FN tunneling current has been investigated. Experiments show that parameters (I ln(A)l and B) decrease during ini-tial stress stage and then saturates after long stress time.By fitting method based on two exponential decay func-tions, we found that there exist two types of traps at least and a threshold electric field. Both types of traps might be natural traps and will play different roles according to stress electric field. When the stress electric field is higher than the threshold electric field, the traps play a role of electronic trap; whereas the traps play a role of hole trap.
Levitas, Valery I.; Warren, James A.
2016-06-01
A thermodynamically consistent, large-strain, multi-phase field approach (with consequent interface stresses) is generalized for the case with anisotropic interface (gradient) energy (e.g. an energy density that depends both on the magnitude and direction of the gradients in the phase fields). Such a generalization, if done in the "usual" manner, yields a theory that can be shown to be manifestly unphysical. These theories consider the gradient energy as anisotropic in the deformed configuration, and, due to this supposition, several fundamental contradictions arise. First, the Cauchy stress tensor is non-symmetric and, consequently, violates the moment of momentum principle, in essence the Herring (thermodynamic) torque is imparting an unphysical angular momentum to the system. In addition, this non-symmetric stress implies a violation of the principle of material objectivity. These problems in the formulation can be resolved by insisting that the gradient energy is an isotropic function of the gradient of the order parameters in the deformed configuration, but depends on the direction of the gradient of the order parameters (is anisotropic) in the undeformed configuration. We find that for a propagating nonequilibrium interface, the structural part of the interfacial Cauchy stress is symmetric and reduces to a biaxial tension with the magnitude equal to the temperature- and orientation-dependent interface energy. Ginzburg-Landau equations for the evolution of the order parameters and temperature evolution equation, as well as the boundary conditions for the order parameters are derived. Small strain simplifications are presented. Remarkably, this anisotropy yields a first order correction in the Ginzburg-Landau equation for small strains, which has been neglected in prior works. The next strain-related term is third order. For concreteness, specific orientation dependencies of the gradient energy coefficients are examined, using published molecular dynamics
J. Olakunle Onaolapo
2016-07-01
Conclusion: Repeated caffeine consumption and/or acute sleep-deprivation led to significant changes in pattern of open-field behaviour and stress/antioxidant response in mice. Responses seen in the study are probably due to modulatory effects of caffeine on the total body response to stressful stimuli.
A simplified dynamic method for field capacity estimation and its parameter analysis
Zhen-tao CONG; Hua-fang LÜ; Guang-heng NI
2014-01-01
This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey (BC) model and the van Genuchten (vG) model, and four soil data groups were used in this study. The relative drainage rate, which is a unique parameter and independent of the soil type in the simplified dynamic method, was analyzed using the pressure-based method with a matric potential of−1/3 bar and the flux-based method with a drainage flux of 0.005 cm/d. As a result, the relative drainage rate of the simplified dynamic method was determined to be 3% per day. This was verified by the similar field capacity results estimated with the three methods for most soils suitable for cultivating plants. In addition, the drainage time calculated with the simplified dynamic method was two to three days, which agrees with the classical definition of field capacity. We recommend the simplified dynamic method with a relative drainage rate of 3% per day due to its simple application and clearly physically-based concept.
Reale, Marcella; Kamal, Mohammad A; Patruno, Antonia; Costantini, Erica; D'Angelo, Chiara; Pesce, Miko; Greig, Nigel H
2014-01-01
Neurodegenerative diseases comprise both hereditary and sporadic conditions characterized by an identifying progressive nervous system dysfunction and distinctive neuopathophysiology. The majority are of non-familial etiology and hence environmental factors and lifestyle play key roles in their pathogenesis. The extensive use of and ever increasing worldwide demand for electricity has stimulated societal and scientific interest on the environmental exposure to low frequency electromagnetic fields (EMFs) on human health. Epidemiological studies suggest a positive association between 50/60-Hz power transmission fields and leukemia or lymphoma development. Consequent to the association between EMFs and induction of oxidative stress, concerns relating to development of neurodegenerative diseases, such as Alzheimer disease (AD), have been voiced as the brain consumes the greatest fraction of oxygen and is particularly vulnerable to oxidative stress. Exposure to extremely low frequency (ELF)-EMFs are reported to alter animal behavior and modulate biological variables, including gene expression, regulation of cell survival, promotion of cellular differentiation, and changes in cerebral blood flow in aged AD transgenic mice. Alterations in inflammatory responses have also been reported, but how these actions impact human health remains unknown. We hence evaluated the effects of an electromagnetic wave (magnetic field intensity 1 mT; frequency, 50-Hz) on a well-characterized immortalized neuronal cell model, human SH-SY5Y cells. ELF-EMF exposure elevated the expession of NOS and O2(-), which were countered by compensatory changes in antioxidant catylase (CAT) activity and enzymatic kinetic parameters related to CYP-450 and CAT activity. Actions of ELF-EMFs on cytokine gene expression were additionally evaluated and found rapidly modified. Confronted with co-exposure to H2O2-induced oxidative stress, ELF-EMF proved not as well counteracted and resulted in a decline in CAT
Szulc Andrzej
2007-01-01
Full Text Available Abstract Background Adolescent girls treated with a brace for scoliosis are submitted to prolonged stress related to both the disease and the therapy. Currently proposed quality of life questionnaires are focused on the outcome of therapy. Bad Sobernheim Stress Questionnaire (BSSQ enables monitoring of patients being under treatment with a brace or exercises. The aim of the study was to assess the stress level in conservatively managed scoliotic girls using BSSQ. Materials and methods 111 girls, aged 14,2 ± 2,2 years, mean Cobb angle of the primary curve 42,8° ± 17,0° and mean Bunnell angle of 11,4° ± 4,5° were examined with two versions of BSSQ (Deformity and Brace. The analysis considered the type of treatment, curve location, correlation of the total score with age, Cobb angle and Bunnell rotation angle. Results The BSSQ Deformity revealed the median of 17 points in patients managed with exercises (from 4 to 24 points, 18 in patients managed with a brace (from 8 to 24 points and 12 in patients before surgery (from 3 to 21 points. Braced patients who completed both questionnaires (n = 50 revealed significantly higher score with BSSQ Deformity (median = 18 comparing to BSSQ Brace (median = 9. There was a correlation between the total score of BSSQ Deformity and the Cobb angle (r = -0,34, Bunnell primary curve rotation (r = -0,34 and Bunnell sum of rotation (r = -0,33 but not with the age of patients. Conclusion Scoliotic adolescents managed with exercises and brace suffered little stress from the deformity. The brace increased the level of stress over the stress induced by the deformity. The stress level correlated with clinical deformity (Bunnell angle, radiological deformity (Cobb angle and the type of treatment (exercises, bracing, surgery. Bad Sobernheim Stress Questionnaires are simple and helpful in the management of girls treated conservatively for idiopathic scoliosis.
Real-Time Personalized Monitoring to Estimate Occupational Heat Stress in Ambient Assisted Working
Pablo Pancardo; Acosta, Francisco D.; José Adán Hernández-Nolasco; Miguel A. Wister; Diego López-de-Ipiña
2015-01-01
Ambient Assisted Working (AAW) is a discipline aiming to provide comfort and safety in the workplace through customization and technology. Workers’ comfort may be compromised in many labor situations, including those depending on environmental conditions, like extremely hot weather conduces to heat stress. Occupational heat stress (OHS) happens when a worker is in an uninterrupted physical activity and in a hot environment. OHS can produce strain on the body, which leads to discomfort and eve...
Phase-Field Relaxation of Topology Optimization with Local Stress Constraints
Stainko, Roman; Burger, Martin
2006-01-01
We introduce a new relaxation scheme for structural topology optimization problems with local stress constraints based on a phase-field method. In the basic formulation we have a PDE-constrained optimization problem, where the finite element and design analysis are solved simultaneously...... parameter decreases to zero. A major advantage of this kind of relaxation opposed to standard approaches is a uniform constraint qualification that is satisfied for any positive value of the penalization parameter. The relaxation scheme yields a large-scale optimization problem with a high number of linear...
Reynolds and Maxwell stress measurements in the reversed field pinch experiment Extrap-T2R
Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Cavazzana, R.; Bergsåker, H.; Cecconello, M.; Drake, J. R.
2005-08-01
The complete Reynolds stress (RS) has been measured in the edge region of the Extrap-T2R reversed field pinch experiment. The RS exhibits a strong gradient in the region where a high E × B shear takes place. Experimental results show this gradient to be almost entirely due to the electrostatic contribution. This has been interpreted as experimental evidence of flow generation via turbulence mechanism. The scales involved in flow generation are deduced from the frequency decomposition of RS tensor. They are found related to magnetohydrodynamic activity but are different with respect to the scales responsible for turbulent transport.
Genetic Variation in Response to Salt Stress of Quinoa Grown under Controlled and Field Conditions
Nguyen Long
2016-01-01
The objective of this study was to understand the change in response of quinoa genotypes to divers salinity stress conditions e.g in controlled (net-house) and in the different saline fields. The pot experiment was conducted in a net-house at Vietnam National University of Agriculture, Hanoi, Vietnam in spring cropping season to characterize the growth and yield of six quinoa genotypes under four NaCl concentrations (0, 10, 20 and 30 dS m-1). At the same time, in Nam Dinh and Hai Phong provin...
Numerical simulation of stress field in inclusions of large rudder arm steel castings
Yang Dixin; Xie Jingpei; Zhang Kefeng; Liu Zongfa; Wang Aiqin; Wang Wenyan
2009-01-01
The influence of non-metallic inclusions on quality and performance of steel depends on not only the quantity of inclusions,but also the type,shape,size,distribution,and deformation behavior. In this paper,ANSYS finite element analysis software is used to simulate the stress field of inclusions appearing in heavy rudder arm steel castings,the effects of inclusion type,shape,distribution,and various loading conditions were studied. The micromechanics of inclusions in such castings were also analyzed. Such research provides further cladficetion on reaction mechanism of inclusions under complex loading conditions.
Estimating ecological water stress caused by anthropogenic uses in the US Great Lakes region
Alian, S.; Mayer, A. S.; Maclean, A.; Watkins, D. W., Jr.; Gyawali, R.; Mirchi, A.
2016-12-01
Anthropocentric water resources management that prioritizes socio-economic growth can cause harmful ecological water stress by depriving aquatic ecosystems of the water needed to sustain habitats. It is important to better understand the impacts of water withdrawal by different economic sectors (e.g., agriculture, power utilities, manufacturing, etc.), withdrawal sources, and extent of return flow (i.e., return of water to river system) at different spatial and temporal scales in order to characterize potentially harmful streamflow disturbances, and to inform water management. Herein, GIS technology is used to characterize and map ecological water stress in the Great Lakes region by compiling and analyzing water withdrawal data for different use categories. An integrative geospatial method is developed to quantify catchment scale streamflow disturbance as the sum of flow depletion and return flow, and propagate it along the stream network in order to calculate water stress index as function of consumptive use and impacted streamflow. Results for the Kalamazoo River Watershed, Michigan, illustrate that although average annual and July water stress is generally relatively low, protective management actions may be necessary in a significant number of catchments, especially in urban catchments with very high water stress. Water stress is significantly higher under low flow conditions, indicating the need to adjust withdrawals to reduce adverse resource impacts on sensitive streams.
Estimate of CH4 Emissions from Year-Round Flooded Rice Fields During Rice Growing Season in China
CAI Zu-Cong; KANG Guo-Ding; H. TSURUTA; A. MOSIER
2005-01-01
A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season. CH4 emission factors were used to estimate the CH4 emissions from year-round flooded rice fields during the rice-growing season in China.The CH4 emissions for the year-round flooded rice fields in China for the rice growing season over a total area of 2.66Mha were estimated to be 2.44 Tg CH4 year-1. The uncertainties of these estimations are discussed as well. However,the emissions during the non-rice growing season could not be estimated because of limited available data. Nevertheless,methane emissions from rice fields that were flooded year-round could be several times higher than those from the rice fields drained in the non-rice-growing season. Thus, the classification of "continuously flooded rice fields" in the IPCC(International Panel on Climate Change) Guidelines for National Greenhouse Gas Inventories is suggested to be revised and divided into "continuously flooded rice fields during the rice growing season" and "year-round flooded rice fields".