The geomagnetic field gradient tensor
DEFF Research Database (Denmark)
Kotsiaros, Stavros; Olsen, Nils
2012-01-01
We develop the general mathematical basis for space magnetic gradiometry in spherical coordinates. The magnetic gradient tensor is a second rank tensor consisting of 3 × 3 = 9 spatial derivatives. Since the geomagnetic field vector B is always solenoidal (∇ · B = 0) there are only eight independent...... tensor elements. Furthermore, in current free regions the magnetic gradient tensor becomes symmetric, further reducing the number of independent elements to five. In that case B is a Laplacian potential field and the gradient tensor can be expressed in series of spherical harmonics. We present properties...... of the magnetic gradient tensor and provide explicit expressions of its elements in terms of spherical harmonics. Finally we discuss the benefit of using gradient measurements for exploring the Earth’s magnetic field from space, in particular the advantage of the various tensor elements for a better determination...
Estimation of the magnetic field gradient tensor using the Swarm constellation
DEFF Research Database (Denmark)
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...... the lower pair of Swarm satellites, whereas the North-South gradients can be approximated by the first differences in the along-track direction. As a preliminary test, here we will present an analysis of along track differences of CHAMP vector observations. These show considerably smaller standard...
Lattice energy-momentum tensor from the Yang-Mills gradient flow -- inclusion of fermion fields
Makino, Hiroki; Suzuki, Hiroshi
2014-01-01
Local products of fields deformed by the so-called Yang--Mills gradient flow become renormalized composite operators. This fact has been utilized to construct a correctly normalized conserved energy--momentum tensor in the lattice formulation of the pure Yang--Mills theory. In the present paper, this construction is further generalized for vector-like gauge theories containing fermions.
International Nuclear Information System (INIS)
Bull, James N.; Fitchett, Christopher M.; Tennant, W. Craighead
2010-01-01
This paper reports the determination of the electric-field-gradient and mean-squared-displacement tensors in 57 Fe symmetry-related sites of 1-bar Laue class in monoclinic FeCl 2 .4H 2 O at room temperature by single-crystal Mössbauer spectroscopy. Contrary to all previous work, the mean-squared-displacement matrix (tensor), , is not constrained to be isotropic resulting in the determination of physically meaningful estimates of microscopic (local) electric-field gradient (efg) and tensors. As a consequence of anisotropy in the tensor the absorber recoilless fractions are also anisotropic. As expected of a low-symmetry site, Laue class 1-bar in this case, no two principal axes of the efg and tensors are coaxial, within the combined errors in the two. Further, no principal direction of the efg tensor seems related to bond directions in the unit cell. Within error, and in agreement with an earlier study of sodium nitroprusside, it appears that the tensor principal directions lie close to the crystallographic axes suggesting that they are determined by long wavelength (phonon) vibrations in the crystal rather than by approximate local symmetry about the 57 Fe nucleus. Concurrent with the Mössbauer measurements, we determined as part of a new X-ray structural determination, precise atomic displacement parameters (ADPs) leading to an alternative determination of the matrix (tensor). The average of the eigenvalues of the Mössbauer-determined exceeds that of the average of the X-ray-determined eigenvalues by a factor of around 2.2. Assuming isotropic absorber recoilless fractions leads to substantially the same (macroscopic) efg tensor as had been determined in earlier work. Taking 1/3 x the trace of the anisotropic absorber recoilless fractions leads to an isotropic value of 0.304 in good agreement with earlier single crystal studies where isotropy was assumed.
International Nuclear Information System (INIS)
Aghazadeh, Mustafa; Mirzaei, Mahmoud
2008-01-01
Hydrogen bond (HB) interactions are studied in the real crystalline structure of sulfamerazine by density functional theory (DFT) calculations of the electric field gradient (EFG) tensors at the sites of O-17, N-14, and H-2 nuclei. One-molecule (single) and four-molecule (cluster) models of sulfamerazine are created by available crystal coordinates and the EFG tensors are calculated in both models to indicate the influence of HB interactions on the tensors. Directly relate to the experiments, the calculated EFG tensors are converted to the experimentally measurable nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant (qcc) and asymmetry parameter (η Q ). The evaluated NQR parameters reveal that due to contribution of the target molecule to N-H...N and N-H...O types of HB interactions, the EFG tensors at the sites of various nuclei are influenced from single model to the target molecule in cluster. Additionally, O2, N4, and H2 nuclei of the target molecule are significantly influenced by HB interactions, consequently, they have the major contributions to HB interactions in cluster model of sulfamerazine. The calculations are performed employing B3LYP method and 6-311++G** basis set using GAUSSIAN 98 suite of program
Lu, Biao; Luo, Zhicai; Zhong, Bo; Zhou, Hao; Flechtner, Frank; Förste, Christoph; Barthelmes, Franz; Zhou, Rui
2017-11-01
Based on tensor theory, three invariants of the gravitational gradient tensor (IGGT) are independent of the gradiometer reference frame (GRF). Compared to traditional methods for calculation of gravity field models based on the gravity field and steady-state ocean circulation explorer (GOCE) data, which are affected by errors in the attitude indicator, using IGGT and least squares method avoids the problem of inaccurate rotation matrices. The IGGT approach as studied in this paper is a quadratic function of the gravity field model's spherical harmonic coefficients. The linearized observation equations for the least squares method are obtained using a Taylor expansion, and the weighting equation is derived using the law of error propagation. We also investigate the linearization errors using existing gravity field models and find that this error can be ignored since the used a-priori model EIGEN-5C is sufficiently accurate. One problem when using this approach is that it needs all six independent gravitational gradients (GGs), but the components V_{xy} and V_{yz} of GOCE are worse due to the non-sensitive axes of the GOCE gradiometer. Therefore, we use synthetic GGs for both inaccurate gravitational gradient components derived from the a-priori gravity field model EIGEN-5C. Another problem is that the GOCE GGs are measured in a band-limited manner. Therefore, a forward and backward finite impulse response band-pass filter is applied to the data, which can also eliminate filter caused phase change. The spherical cap regularization approach (SCRA) and the Kaula rule are then applied to solve the polar gap problem caused by GOCE's inclination of 96.7° . With the techniques described above, a degree/order 240 gravity field model called IGGT_R1 is computed. Since the synthetic components of V_{xy} and V_{yz} are not band-pass filtered, the signals outside the measurement bandwidth are replaced by the a-priori model EIGEN-5C. Therefore, this model is practically a
Gradients estimation from random points with volumetric tensor in turbulence
Watanabe, Tomoaki; Nagata, Koji
2017-12-01
We present an estimation method of fully-resolved/coarse-grained gradients from randomly distributed points in turbulence. The method is based on a linear approximation of spatial gradients expressed with the volumetric tensor, which is a 3 × 3 matrix determined by a geometric distribution of the points. The coarse grained gradient can be considered as a low pass filtered gradient, whose cutoff is estimated with the eigenvalues of the volumetric tensor. The present method, the volumetric tensor approximation, is tested for velocity and passive scalar gradients in incompressible planar jet and mixing layer. Comparison with a finite difference approximation on a Cartesian grid shows that the volumetric tensor approximation computes the coarse grained gradients fairly well at a moderate computational cost under various conditions of spatial distributions of points. We also show that imposing the solenoidal condition improves the accuracy of the present method for solenoidal vectors, such as a velocity vector in incompressible flows, especially when the number of the points is not large. The volumetric tensor approximation with 4 points poorly estimates the gradient because of anisotropic distribution of the points. Increasing the number of points from 4 significantly improves the accuracy. Although the coarse grained gradient changes with the cutoff length, the volumetric tensor approximation yields the coarse grained gradient whose magnitude is close to the one obtained by the finite difference. We also show that the velocity gradient estimated with the present method well captures the turbulence characteristics such as local flow topology, amplification of enstrophy and strain, and energy transfer across scales.
Calibration of magnetic gradient tensor measurement array in magnetic anomaly detection
Chen, Jinfei; Zhang, Qi; Pan, Mengchun; Weng, Feibing; Chen, Dixiang; Pang, Hongfeng
2013-01-01
Magnetic anomaly detection based on magnetic gradient tensor has become more and more important in civil and military applications. Compared with methods based on magnetic total field or components measurement, magnetic gradient tensor has some unique advantages. Usually, a magnetic gradient tensor measurement array is constituted by four three-axis magnetometers. The prominent problem of magnetic gradient tensor measurement array is the misalignment of sensors. In order to measure the magnetic gradient tensor accurately, it is quite essential to calibrate the measurement array. The calibration method, which is proposed in this paper, is divided into two steps. In the first step, each sensor of the measurement array should be calibrated, whose error is mainly caused by constant biases, scale factor deviations and nonorthogonality of sensor axes. The error of measurement array is mainly caused by the misalignment of sensors, so that triplets' deviation in sensors array coordinates is calibrated in the second step. In order to verify the effectiveness of the proposed method, simulation was taken and the result shows that the proposed method improves the measurement accuracy of magnetic gradient tensor greatly.
Antisymmetric tensor generalizations of affine vector fields.
Houri, Tsuyoshi; Morisawa, Yoshiyuki; Tomoda, Kentaro
2016-02-01
Tensor generalizations of affine vector fields called symmetric and antisymmetric affine tensor fields are discussed as symmetry of spacetimes. We review the properties of the symmetric ones, which have been studied in earlier works, and investigate the properties of the antisymmetric ones, which are the main theme in this paper. It is shown that antisymmetric affine tensor fields are closely related to one-lower-rank antisymmetric tensor fields which are parallelly transported along geodesics. It is also shown that the number of linear independent rank- p antisymmetric affine tensor fields in n -dimensions is bounded by ( n + 1)!/ p !( n - p )!. We also derive the integrability conditions for antisymmetric affine tensor fields. Using the integrability conditions, we discuss the existence of antisymmetric affine tensor fields on various spacetimes.
Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method
Sun, Yong; Meng, Zhaohai; Li, Fengting
2018-03-01
Following the development of gravity gradiometer instrument technology, the full tensor gravity (FTG) data can be acquired on airborne and marine platforms. Large-scale geophysical data can be obtained using these methods, making such data sets a number of the "big data" category. Therefore, a fast and effective inversion method is developed to solve the large-scale FTG data inversion problem. Many algorithms are available to accelerate the FTG data inversion, such as conjugate gradient method. However, the conventional conjugate gradient method takes a long time to complete data processing. Thus, a fast and effective iterative algorithm is necessary to improve the utilization of FTG data. Generally, inversion processing is formulated by incorporating regularizing constraints, followed by the introduction of a non-monotone gradient-descent method to accelerate the convergence rate of FTG data inversion. Compared with the conventional gradient method, the steepest descent gradient algorithm, and the conjugate gradient algorithm, there are clear advantages of the non-monotone iterative gradient-descent algorithm. Simulated and field FTG data were applied to show the application value of this new fast inversion method.
The Topology of Symmetric Tensor Fields
Levin, Yingmei; Batra, Rajesh; Hesselink, Lambertus; Levy, Yuval
1997-01-01
Combinatorial topology, also known as "rubber sheet geometry", has extensive applications in geometry and analysis, many of which result from connections with the theory of differential equations. A link between topology and differential equations is vector fields. Recent developments in scientific visualization have shown that vector fields also play an important role in the analysis of second-order tensor fields. A second-order tensor field can be transformed into its eigensystem, namely, eigenvalues and their associated eigenvectors without loss of information content. Eigenvectors behave in a similar fashion to ordinary vectors with even simpler topological structures due to their sign indeterminacy. Incorporating information about eigenvectors and eigenvalues in a display technique known as hyperstreamlines reveals the structure of a tensor field. The simplify and often complex tensor field and to capture its important features, the tensor is decomposed into an isotopic tensor and a deviator. A tensor field and its deviator share the same set of eigenvectors, and therefore they have a similar topological structure. A a deviator determines the properties of a tensor field, while the isotopic part provides a uniform bias. Degenerate points are basic constituents of tensor fields. In 2-D tensor fields, there are only two types of degenerate points; while in 3-D, the degenerate points can be characterized in a Q'-R' plane. Compressible and incompressible flows share similar topological feature due to the similarity of their deviators. In the case of the deformation tensor, the singularities of its deviator represent the area of vortex core in the field. In turbulent flows, the similarities and differences of the topology of the deformation and the Reynolds stress tensors reveal that the basic addie-viscosity assuptions have their validity in turbulence modeling under certain conditions.
Seamless warping of diffusion tensor fields
DEFF Research Database (Denmark)
Xu, Dongrong; Hao, Xuejun; Bansal, Ravi
2008-01-01
To warp diffusion tensor fields accurately, tensors must be reoriented in the space to which the tensors are warped based on both the local deformation field and the orientation of the underlying fibers in the original image. Existing algorithms for warping tensors typically use forward mapping...... of seams, including voxels in which the deformation is extensive. Backward mapping, however, cannot reorient tensors in the template space because information about the directional orientation of fiber tracts is contained in the original, unwarped imaging space only, and backward mapping alone cannot...... transfer that information to the template space. To combine the advantages of forward and backward mapping, we propose a novel method for the spatial normalization of diffusion tensor (DT) fields that uses a bijection (a bidirectional mapping with one-to-one correspondences between image spaces) to warp DT...
Inflationary cosmology and 4-index tensor fields
International Nuclear Information System (INIS)
Moorhouse, R.G.; Nixon, J.
1985-01-01
We show how an arbitrarily large expansion of the ordinary dimensions in the very early universe can be achieved in the d=11 supergravity theory where the 4-index anti-symmetric tensor field supplies the energy-momentum tensor. However, the decrease of the extra dimensions is too fast to give a satisfactory inflationary cosmology. If a 4-index tensor field is similar used to provide the energy-momentum tensor in dimensions significantly greater than 11 the inflationary outlook is more hopeful. (orig.)
Abelian gauge theories with tensor gauge fields
International Nuclear Information System (INIS)
Kapuscik, E.
1984-01-01
Gauge fields of arbitrary tensor type are introduced. In curved space-time the gravitational field serves as a bridge joining different gauge fields. The theory of second order tensor gauge field is developed on the basis of close analogy to Maxwell electrodynamics. The notion of tensor current is introduced and an experimental test of its detection is proposed. The main result consists in a coupled set of field equations representing a generalization of Maxwell theory in which the Einstein equivalence principle is not satisfied. (author)
Conformal field theories and tensor categories. Proceedings
Energy Technology Data Exchange (ETDEWEB)
Bai, Chengming [Nankai Univ., Tianjin (China). Chern Institute of Mathematics; Fuchs, Juergen [Karlstad Univ. (Sweden). Theoretical Physics; Huang, Yi-Zhi [Rutgers Univ., Piscataway, NJ (United States). Dept. of Mathematics; Kong, Liang [Tsinghua Univ., Beijing (China). Inst. for Advanced Study; Runkel, Ingo; Schweigert, Christoph (eds.) [Hamburg Univ. (Germany). Dept. of Mathematics
2014-08-01
First book devoted completely to the mathematics of conformal field theories, tensor categories and their applications. Contributors include both mathematicians and physicists. Some long expository articles are especially suitable for beginners. The present volume is a collection of seven papers that are either based on the talks presented at the workshop ''Conformal field theories and tensor categories'' held June 13 to June 17, 2011 at the Beijing International Center for Mathematical Research, Peking University, or are extensions of the material presented in the talks at the workshop. These papers present new developments beyond rational conformal field theories and modular tensor categories and new applications in mathematics and physics. The topics covered include tensor categories from representation categories of Hopf algebras, applications of conformal field theories and tensor categories to topological phases and gapped systems, logarithmic conformal field theories and the corresponding non-semisimple tensor categories, and new developments in the representation theory of vertex operator algebras. Some of the papers contain detailed introductory material that is helpful for graduate students and researchers looking for an introduction to these research directions. The papers also discuss exciting recent developments in the area of conformal field theories, tensor categories and their applications and will be extremely useful for researchers working in these areas.
Seamless warping of diffusion tensor fields
DEFF Research Database (Denmark)
Xu, Dongrong; Hao, Xuejun; Bansal, Ravi
2008-01-01
of seams, including voxels in which the deformation is extensive. Backward mapping, however, cannot reorient tensors in the template space because information about the directional orientation of fiber tracts is contained in the original, unwarped imaging space only, and backward mapping alone cannot......To warp diffusion tensor fields accurately, tensors must be reoriented in the space to which the tensors are warped based on both the local deformation field and the orientation of the underlying fibers in the original image. Existing algorithms for warping tensors typically use forward mapping...... deformations in an attempt to ensure that the local deformations in the warped image remains true to the orientation of the underlying fibers; forward mapping, however, can also create "seams" or gaps and consequently artifacts in the warped image by failing to define accurately the voxels in the template...
Why are tensor field theories asymptotically free?
Rivasseau, V.
2015-09-01
In this pedagogic letter we explain the combinatorics underlying the generic asymptotic freedom of tensor field theories. We focus on simple combinatorial models with a 1/p2 propagator and quartic interactions and on the comparison between the intermediate field representations of the vector, matrix and tensor cases. The transition from asymptotic freedom (tensor case) to asymptotic safety (matrix case) is related to the crossing symmetry of the matrix vertex, whereas in the vector case, the lack of asymptotic freedom (“Landau ghost”), as in the ordinary scalar φ^44 case, is simply due to the absence of any wave function renormalization at one loop.
Esrafili, Mehdi D.; Behzadi, Hadi; Hadipour, Nasser L.
2008-06-01
Nuclear quadrupole coupling tensors of 14N and 17O nuclei in benzamide clusters (up to n = 6) were calculated via density functional theory. Results revealed that N-H⋯O hydrogen bonds around the benzamide molecule in crystalline lattice have significant influence on 14N and 17O nuclear quadrupole coupling tensors. n-dependent trend in 14N quadrupole coupling tensors significantly correlates with cooperative effects of R(N-H⋯O) hydrogen bond distance. Natural bonding orbital analysis, NBO, was used to rationalize the quadrupole coupling results in terms of substantial n→σN-H∗ charge transfer in (benzamide) n=1-6 clusters. It was found that intermolecular n→σN-H∗ interactions play a key role in cooperative change of 14N and 17O quadrupole coupling tensors. There is an acceptable linear correlation between 14N or 17O quadrupole coupling tensors with strength of Fock matrix elements (Fij). This suggests that both 14N and 17O quadrupole coupling measurements can provide a useful probe for electron delocalization effects in both gaseous and condensed media.
(Ln-bar, g)-spaces. Special tensor fields
International Nuclear Information System (INIS)
Manoff, S.; Dimitrov, B.
1998-01-01
The Kronecker tensor field, the contraction tensor field, as well as the multi-Kronecker and multi-contraction tensor fields are determined and the action of the covariant differential operator, the Lie differential operator, the curvature operator, and the deviation operator on these tensor fields is established. The commutation relations between the operators Sym and Asym and the covariant and Lie differential operators are considered acting on symmetric and antisymmetric tensor fields over (L n bar, g)-spaces
Seamless warping of diffusion tensor fields
DEFF Research Database (Denmark)
Xu, Dongrong; Hao, Xuejun; Bansal, Ravi
2008-01-01
transfer that information to the template space. To combine the advantages of forward and backward mapping, we propose a novel method for the spatial normalization of diffusion tensor (DT) fields that uses a bijection (a bidirectional mapping with one-to-one correspondences between image spaces) to warp DT...
Visualization and processing of tensor fields
Weickert, Joachim
2007-01-01
Presents information on the visualization and processing of tensor fields. This book serves as an overview for the inquiring scientist, as a basic foundation for developers and practitioners, and as a textbook for specialized classes and seminars for graduate and doctoral students.
Relativistic particles with spin and antisymmetric tensor fields
International Nuclear Information System (INIS)
Sandoval Junior, L.
1990-09-01
A study is made on antisymmetric tensor fields particularly on second order tensor field as far as his equivalence to other fields and quantization through the path integral are concerned. Also, a particle model is studied which has been recently proposed and reveals to be equivalent to antisymmetric tensor fields of any order. (L.C.J.A.)
Hoefnagels, Friso W. A.; de Witt Hamer, Philip C.; Pouwels, Petra J. W.; Barkhof, Frederik; Vandertop, W. Peter
2017-01-01
To explore quantitatively and qualitatively how the number of gradient directions (NGD) and spatial resolution (SR) affect diffusion tensor imaging (DTI) tractography in patients planned for brain tumor surgery, using routine clinical magnetic resonance imaging protocols. Of 67 patients with
Feature Surfaces in Symmetric Tensor Fields Based on Eigenvalue Manifold.
Palacios, Jonathan; Yeh, Harry; Wang, Wenping; Zhang, Yue; Laramee, Robert S; Sharma, Ritesh; Schultz, Thomas; Zhang, Eugene
2016-03-01
Three-dimensional symmetric tensor fields have a wide range of applications in solid and fluid mechanics. Recent advances in the (topological) analysis of 3D symmetric tensor fields focus on degenerate tensors which form curves. In this paper, we introduce a number of feature surfaces, such as neutral surfaces and traceless surfaces, into tensor field analysis, based on the notion of eigenvalue manifold. Neutral surfaces are the boundary between linear tensors and planar tensors, and the traceless surfaces are the boundary between tensors of positive traces and those of negative traces. Degenerate curves, neutral surfaces, and traceless surfaces together form a partition of the eigenvalue manifold, which provides a more complete tensor field analysis than degenerate curves alone. We also extract and visualize the isosurfaces of tensor modes, tensor isotropy, and tensor magnitude, which we have found useful for domain applications in fluid and solid mechanics. Extracting neutral and traceless surfaces using the Marching Tetrahedra method can cause the loss of geometric and topological details, which can lead to false physical interpretation. To robustly extract neutral surfaces and traceless surfaces, we develop a polynomial description of them which enables us to borrow techniques from algebraic surface extraction, a topic well-researched by the computer-aided design (CAD) community as well as the algebraic geometry community. In addition, we adapt the surface extraction technique, called A-patches, to improve the speed of finding degenerate curves. Finally, we apply our analysis to data from solid and fluid mechanics as well as scalar field analysis.
Glyph-Based Comparative Visualization for Diffusion Tensor Fields.
Zhang, Changgong; Schultz, Thomas; Lawonn, Kai; Eisemann, Elmar; Vilanova, Anna
2016-01-01
Diffusion Tensor Imaging (DTI) is a magnetic resonance imaging modality that enables the in-vivo reconstruction and visualization of fibrous structures. To inspect the local and individual diffusion tensors, glyph-based visualizations are commonly used since they are able to effectively convey full aspects of the diffusion tensor. For several applications it is necessary to compare tensor fields, e.g., to study the effects of acquisition parameters, or to investigate the influence of pathologies on white matter structures. This comparison is commonly done by extracting scalar information out of the tensor fields and then comparing these scalar fields, which leads to a loss of information. If the glyph representation is kept, simple juxtaposition or superposition can be used. However, neither facilitates the identification and interpretation of the differences between the tensor fields. Inspired by the checkerboard style visualization and the superquadric tensor glyph, we design a new glyph to locally visualize differences between two diffusion tensors by combining juxtaposition and explicit encoding. Because tensor scale, anisotropy type, and orientation are related to anatomical information relevant for DTI applications, we focus on visualizing tensor differences in these three aspects. As demonstrated in a user study, our new glyph design allows users to efficiently and effectively identify the tensor differences. We also apply our new glyphs to investigate the differences between DTI datasets of the human brain in two different contexts using different b-values, and to compare datasets from a healthy and HIV-infected subject.
Energy-momentum tensor of the electromagnetic field
International Nuclear Information System (INIS)
Horndeski, G.W.; Wainwright, J.
1977-01-01
In this paper we investigate the energy-momentum tensor of the most general second-order vector-tensor theory of gravitation and electromagnetism which has field equations which are (i) derivable from a variational principle, (ii) consistent with the notion of conservation of charge, and (iii) compatible with Maxwell's equations in a flat space. This energy-momentum tensor turns out to be quadratic in the first partial derivatives of the electromagnetic field tensor and depends upon the curvature tensor. The asymptotic behavior of this energy-momentum tensor is examined for solutions to Maxwell's equations in Minkowski space, and it is demonstrated that this energy-momentum tensor predicts regions of negative energy density in the vicinity of point sources
Statistics of the perceived velocity gradient tensor in a rotating turbulent flow
International Nuclear Information System (INIS)
Naso, Aurore; Godeferd, Fabien S
2012-01-01
The dynamics and structure of rotating homogeneous turbulence is investigated through the statistical properties of the ‘perceived’ velocity gradient tensor, defined by interpolation from the locations and velocities of a set of four particles. The results of direct numerical simulations of forced homogeneous rotating turbulence at different Rossby numbers are presented. We thus provide a multi-scale analysis of the dynamics of rotating turbulence and some of its important features. We present scaling laws for second- and third-order moments of the perceived velocity gradient tensor. We relate the distribution of the enstrophy and strain variance, and of their production terms, to the topology of the flow, thanks to conditional probability density functions. These quantities demonstrate the role played by the Zeman scale in the elementary processes of rotating turbulence, when compared to the scale at which the perceived velocity gradient tensor is measured. (paper)
Energy-momentum tensor in the quantum field theory
International Nuclear Information System (INIS)
Azakov, S.I.
1977-01-01
An energy-momentum tensor in the scalar field theory is built. The tensor must satisfy the finiteness requirement of the Green function. The Green functions can always be made finite by renormalizations in the S-matrix by introducing counter terms into the Hamiltonian (or Lagrangian) of the interaction. Such a renormalization leads to divergencies in the Green functions. Elimination of these divergencies requires the introduction of new counter terms, which must be taken into account in the energy-momentum tensor
Renormalization of nonabelian gauge theories with tensor matter fields
Energy Technology Data Exchange (ETDEWEB)
Lemes, Vitor; Renan, Ricardo [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Sorella, Silvio Paolo [Universidade do Estado, Rio de Janeiro, RJ (Brazil). Inst. de Fisica
1996-03-01
The renormalizability of a nonabelian model describing the coupling between antisymmetric second rank tensor matter fields and Yang-Mills gauge fields is discussed within the BRS algebraic framework. (author). 12 refs.
Renormalization of nonabelian gauge theories with tensor matter fields
International Nuclear Information System (INIS)
Lemes, Vitor; Renan, Ricardo; Sorella, Silvio Paolo
1996-03-01
The renormalizability of a nonabelian model describing the coupling between antisymmetric second rank tensor matter fields and Yang-Mills gauge fields is discussed within the BRS algebraic framework. (author). 12 refs
On energy-momentum tensors of gravitational field
International Nuclear Information System (INIS)
Nikishov, A.I.
2001-01-01
The phenomenological approach to gravitation is discussed in which the 3-graviton interaction is reduced to the interaction of each graviton with the energy-momentum tensor of two others. If this is so, (and in general relativity this is not so), then the problem of choosing the correct energy-momentum tensor comes to finding the right 3-graviton vertex. Several energy-momentum tensors od gravitational field are considered and compared in the lowest approximation. Each of them together with the energy-momentum tensor of point-like particles satisfies the conservation laws when equations of motion of particles are the same as in general relativity. It is shown that in Newtonian approximation the considered tensors differ one from other in the way their energy density is distributed between energy density of interaction (nonzero only at locations of particles) and energy density of gravitational field. Stating from Lorentz invariance, the Lagrangians for spin-2, mass-0 field are considered [ru
Pajevic, Sinisa; Aldroubi, Akram; Basser, Peter J
2002-01-01
The effective diffusion tensor of water, D, measured by diffusion tensor MRI (DT-MRI), is inherently a discrete, noisy, voxel-averaged sample of an underlying macroscopic effective diffusion tensor field, D(x). Within fibrous tissues this field is presumed to be continuous and smooth at a gross anatomical length scale. Here a new, general mathematical framework is proposed that uses measured DT-MRI data to produce a continuous approximation to D(x). One essential finding is that the continuous tensor field representation can be constructed by repeatedly performing one-dimensional B-spline transforms of the DT-MRI data. The fidelity and noise-immunity of this approximation are tested using a set of synthetically generated tensor fields to which background noise is added via Monte Carlo methods. Generally, these tensor field templates are reproduced faithfully except at boundaries where diffusion properties change discontinuously or where the tensor field is not microscopically homogeneous. Away from such regions, the tensor field approximation does not introduce bias in useful DT-MRI parameters, such as Trace(D(x)). It also facilitates the calculation of several new parameters, particularly differential quantities obtained from the tensor of spatial gradients of D(x). As an example, we show that they can identify tissue boundaries across which diffusion properties change rapidly using in vivo human brain data. One important application of this methodology is to improve the reliability and robustness of DT-MRI fiber tractography.
Effective field theory approaches for tensor potentials
Energy Technology Data Exchange (ETDEWEB)
Jansen, Maximilian
2016-11-14
Effective field theories are a widely used tool to study physical systems at low energies. We apply them to systematically analyze two and three particles interacting via tensor potentials. Two examples are addressed: pion interactions for anti D{sup 0}D{sup *0} scattering to dynamically generate the X(3872) and dipole interactions for two and three bosons at low energies. For the former, the one-pion exchange and for the latter, the long-range dipole force induce a tensor-like structure of the potential. We apply perturbative as well as non-perturbative methods to determine low-energy observables. The X(3872) is of major interest in modern high-energy physics. Its exotic characteristics require approaches outside the range of the quark model for baryons and mesons. Effective field theories represent such methods and provide access to its peculiar nature. We interpret the X(3872) as a hadronic molecule consisting of neutral D and D{sup *} mesons. It is possible to apply an effective field theory with perturbative pions. Within this framework, we address chiral as well as finite volume extrapolations for low-energy observables, such as the binding energy and the scattering length. We show that the two-point correlation function for the D{sup *0} meson has to be resummed to cure infrared divergences. Moreover, next-to-leading order coupling constants, which were introduced by power counting arguments, appear to be essential to renormalize the scattering amplitude. The binding energy as well as the scattering length display a moderate dependence on the light quark masses. The X(3872) is most likely deeper bound for large light quark masses. In a finite volume on the other hand, the binding energy significantly increases. The dependence on the light quark masses and the volume size can be simultaneously obtained. For bosonic dipoles we apply a non-perturbative, numerical approach. We solve the Lippmann-Schwinger equation for the two-dipole system and the Faddeev
STATISTICS OF THE VELOCITY GRADIENT TENSOR IN SPACE PLASMA TURBULENT FLOWS
Energy Technology Data Exchange (ETDEWEB)
Consolini, Giuseppe; Marcucci, Maria Federica; Pallocchia, Giuseppe [INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma (Italy); Materassi, Massimo, E-mail: giuseppe.consolini@iaps.inaf.it [Istituto dei Sistemi Complessi, CNR, Sesto Fiorentino (Italy)
2015-10-10
In the last decade, significant advances have been presented for the theoretical characterization and experimental techniques used to measure and model all of the components of the velocity gradient tensor in the framework of fluid turbulence. Here, we attempt the evaluation of the small-scale velocity gradient tensor for a case study of space plasma turbulence, observed in the Earth's magnetosheath region by the CLUSTER mission. In detail, we investigate the joint statistics P(R, Q) of the velocity gradient geometric invariants R and Q, and find that this P(R, Q) is similar to that of the low end of the inertial range for fluid turbulence, with a pronounced increase in the statistics along the so-called Vieillefosse tail. In the context of hydrodynamics, this result is referred to as the dissipation/dissipation-production due to vortex stretching.
Tensor fields on orbits of quantum states and applications
Energy Technology Data Exchange (ETDEWEB)
Volkert, Georg Friedrich
2010-07-19
On classical Lie groups, which act by means of a unitary representation on finite dimensional Hilbert spaces H, we identify two classes of tensor field constructions. First, as pull-back tensor fields of order two from modified Hermitian tensor fields, constructed on Hilbert spaces by means of the property of having the vertical distributions of the C{sub 0}-principal bundle H{sub 0} {yields} P(H) over the projective Hilbert space P(H) in the kernel. And second, directly constructed on the Lie group, as left-invariant representation-dependent operator-valued tensor fields (LIROVTs) of arbitrary order being evaluated on a quantum state. Within the NP-hard problem of deciding whether a given state in a n-level bi-partite quantum system is entangled or separable (Gurvits, 2003), we show that both tensor field constructions admit a geometric approach to this problem, which evades the traditional ambiguity on defining metrical structures on the convex set of mixed states. In particular by considering manifolds associated to orbits passing through a selected state when acted upon by the local unitary group U(n) x U(n) of Schmidt coefficient decomposition inducing transformations, we find the following results: In the case of pure states we show that Schmidt-equivalence classes which are Lagrangian submanifolds define maximal entangled states. This implies a stronger statement as the one proposed by Bengtsson (2007). Moreover, Riemannian pull-back tensor fields split on orbits of separable states and provide a quantitative characterization of entanglement which recover the entanglement measure proposed by Schlienz and Mahler (1995). In the case of mixed states we highlight a relation between LIROVTs of order two and a class of computable separability criteria based on the Bloch-representation (de Vicente, 2007). (orig.)
Energy-momentum tensor in quantum field theory
International Nuclear Information System (INIS)
Fujikawa, Kazuo.
1980-12-01
The definition of the energy-momentum tensor as a source current coupled to the background gravitational field receives an important modification in quantum theory. In the path integral approach, the manifest covariance of the integral measure under general coordinate transformations dictates that field variables with weight 1/2 should be used as independent integration variables. An improved energy-momentum tensor is then generated by the variational derivative, and it gives rise to well-defined gravitational conformal (Weyl) anomalies. In the flat space-time limit, all the Ward-Takahashi identities associate with space-time transformations including the global dilatation become free from anomalies, reflecting the general covariance of the integral measure; the trace of this energy-momentum tensor is thus finite at the zero momentum transfer. The Jacobian for the local conformal transformation however becomes non-trivial, and it gives rise to an anomaly for the conformal identity. All the familiar anomalies are thus reduced to either chiral or conformal anomalies. The consistency of the dilatation and conformal identities at the vanishing momentum transfer determines the trace anomaly of this energy-momentum tensor in terms of the renormalization group β-function and other parameters. In contrast, the trace of the conventional energy-momentum tensor generally diverges even at the vanishing momentum transfer depending on the regularization scheme, and it is subtractively renormalized. We also explain how the apparently different renormalization properties of the chiral and trace anomalies arise. (author)
Causal structure in the scalar–tensor theory with field derivative coupling to the Einstein tensor
Directory of Open Access Journals (Sweden)
Masato Minamitsuji
2015-04-01
Full Text Available We investigate the causal structure in the scalar–tensor theory with the field derivative coupling to the Einstein tensor, which is a class of the Horndeski theory in the four-dimensional spacetime. We show that in general the characteristic hypersurface is non-null, which admits the superluminal propagations. We also derive the conditions that the characteristic hypersurface becomes null and show that a Killing horizon can be the causal edge for all the propagating degrees of freedom, if the additional conditions for the scalar field are satisfied. Finally, we find the position of the characteristic hypersurface in the dynamical spacetime with the maximally symmetric space, and that the fastest propagation can be superluminal, especially if the coupling constant becomes positive. We also argue that the superluminality itself may not lead to the acausality of the theory.
Tensor Fields for Use in Fractional-Order Viscoelasticity
Freed, Alan D.; Diethelm, Kai
2003-01-01
To be able to construct viscoelastic material models from fractional0order differentegral equations that are applicable for 3D finite-strain analysis requires definitions for fractional derivatives and integrals for symmetric tensor fields, like stress and strain. We define these fields in the body manifold. We then map them ito spatial fields expressed in terms of an Eulerian or Lagrangian reference frame where most analysts prefer to solve boundary problems.
Leone, Frank A., Jr.
2015-01-01
A method is presented to represent the large-deformation kinematics of intraply matrix cracks and delaminations in continuum damage mechanics (CDM) constitutive material models. The method involves the additive decomposition of the deformation gradient tensor into 'crack' and 'bulk material' components. The response of the intact bulk material is represented by a reduced deformation gradient tensor, and the opening of an embedded cohesive interface is represented by a normalized cohesive displacement-jump vector. The rotation of the embedded interface is tracked as the material deforms and as the crack opens. The distribution of the total local deformation between the bulk material and the cohesive interface components is determined by minimizing the difference between the cohesive stress and the bulk material stress projected onto the cohesive interface. The improvements to the accuracy of CDM models that incorporate the presented method over existing approaches are demonstrated for a single element subjected to simple shear deformation and for a finite element model of a unidirectional open-hole tension specimen. The material model is implemented as a VUMAT user subroutine for the Abaqus/Explicit finite element software. The presented deformation gradient decomposition method reduces the artificial load transfer across matrix cracks subjected to large shearing deformations, and avoids the spurious secondary failure modes that often occur in analyses based on conventional progressive damage models.
Gradient flow and energy-momentum tensor in lattice gauge theory
Kitazawa, Masakiyo; Asakawa, Masayuki; Hatsuda, Tetsuo; Iritani, Takumi; Itou, Etsuko; Suzuki, Hiroshi
2014-09-01
Defining the energy-momentum tensor (EMT) in lattice gauge theory is a nontrivial problem, because of the explicit breaking of the Poincare invariance in lattice regularization. Recently, on the basis of the Yang-Mills gradient flow a construction of the EMT on the lattice is proposed. We apply this EMT to the analysis of the bulk thermodynamics of the SU(3) gauge theory. It is shown that the energy density and pressure measured by taking the thermal expectation values of the EMT well agree with the previous results. Applications to the measurement of correlation functions will also be discussed.
Dilaton and second-rank tensor fields as supersymmetric compensators
International Nuclear Information System (INIS)
Nishino, Hitoshi; Rajpoot, Subhash
2007-01-01
We formulate a supersymmetric theory in which both a dilaton and a second-rank tensor play roles of compensators. The basic off-shell multiplets are a linear multiplet (B μν ,χ,φ) and a vector multiplet (A μ ,λ;C μνρ ), where φ and B μν are, respectively, a dilaton and a second-rank tensor. The third-rank tensor C μνρ in the vector multiplet is ''dual'' to the conventional D field with 0 on-shell or 1 off-shell degree of freedom. The dilaton φ is absorbed into one longitudinal component of A μ , making it massive. Initially, B μν has 1 on-shell or 3 off-shell degrees of freedom, but it is absorbed into the longitudinal components of C μνρ . Eventually, C μνρ with 0 on-shell or 1 off-shell degree of freedom acquires in total 1 on-shell or 4 off-shell degrees of freedom, turning into a propagating massive field. These basic multiplets are also coupled to chiral multiplets and a supersymmetric Dirac-Born-Infeld action. Some of these results are also reformulated in superspace. The proposed mechanism may well provide a solution to the long-standing puzzle of massless dilatons and second-rank tensors in supersymmetric models inspired by string theory
Multiscale analysis of the invariants of the velocity gradient tensor in isotropic turbulence
Danish, Mohammad; Meneveau, Charles
2018-04-01
Knowledge of local flow-topology, the patterns of streamlines around a moving fluid element as described by the velocity-gradient tensor, is useful for developing insights into turbulence processes, such as energy cascade, material element deformation, or scalar mixing. Much has been learned in the recent past about flow topology at the smallest (viscous) scales of turbulence. However, less is known at larger scales, for instance, at the inertial scales of turbulence. In this work, we present a detailed study on the scale dependence of various quantities of interest, such as the population fraction of different types of flow-topologies, the joint probability distribution of the second and third invariants of the velocity gradient tensor, and the geometrical alignment of vorticity with strain-rate eigenvectors. We perform the analysis on a simulation dataset of isotropic turbulence at Reλ=433 . While quantities appear close to scale invariant in the inertial range, we observe a "bump" in several quantities at length scales between the inertial and viscous ranges. For instance, the population fraction of unstable node-saddle-saddle flow topology shows an increase when reducing the scale from the inertial entering the viscous range. A similar bump is observed for the vorticity-strain-rate alignment. In order to document possible dynamical causes for the different trends in the viscous and inertial ranges, we examine the probability fluxes appearing in the Fokker-Plank equation governing the velocity gradient invariants. Specifically, we aim to understand whether the differences observed between the viscous and inertial range statistics are due to effects caused by pressure, subgrid-scale, or viscous stresses or various combinations of these terms. To decompose the flow into small and large scales, we mainly use a spectrally compact non-negative filter with good spatial localization properties (Eyink-Aluie filter). The analysis shows that when going from the inertial
Measurement of gradient magnetic field temporal characteristics
International Nuclear Information System (INIS)
Bartusek, K.; Jflek, B.
1994-01-01
We describe a technique of measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique makes use of a large volume sample and selective RF excitation pulses and free induction decay (FID) (or a spin or gradient echo) to measure the out-of-phase component of the FID, which is proportional to γδB, i.e. the amount the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and used for determining pre-emphasis compensation parameters
Directory of Open Access Journals (Sweden)
Jibing Wu
2017-01-01
Full Text Available Clustering analysis is a basic and essential method for mining heterogeneous information networks, which consist of multiple types of objects and rich semantic relations among different object types. Heterogeneous information networks are ubiquitous in the real-world applications, such as bibliographic networks and social media networks. Unfortunately, most existing approaches, such as spectral clustering, are designed to analyze homogeneous information networks, which are composed of only one type of objects and links. Some recent studies focused on heterogeneous information networks and yielded some research fruits, such as RankClus and NetClus. However, they often assumed that the heterogeneous information networks usually follow some simple schemas, such as bityped network schema or star network schema. To overcome the above limitations, we model the heterogeneous information network as a tensor without the restriction of network schema. Then, a tensor CP decomposition method is adapted to formulate the clustering problem in heterogeneous information networks. Further, we develop two stochastic gradient descent algorithms, namely, SGDClus and SOSClus, which lead to effective clustering multityped objects simultaneously. The experimental results on both synthetic datasets and real-world dataset have demonstrated that our proposed clustering framework can model heterogeneous information networks efficiently and outperform state-of-the-art clustering methods.
Integral Field Spectroscopy Surveys: Oxygen Abundance Gradients
Sánchez, S. F.; Sánchez-Menguiano, L.
2017-07-01
We present here the recent results on our understanding of oxygen abundance gradients derived using Integral Field Spectroscopic surveys. In particular we analyzed more than 2124 datacubes corresponding to individual objects observed by the CALIFA (˜ 734 objects) and the public data by MaNGA (˜ 1390 objects), deriving the oxygen abundance gradient for each galaxy. We confirm previous results that indicate that the shape of this gradient is very similar for all galaxies with masses above 109.5M⊙, presenting in average a very similar slope of ˜ -0.04 dex within 0.5-2.0 re, with a possible drop in the inner regions (r109.5M⊙) the gradient seems to be flatter than for more massive ones. All these results agree with an inside-out growth of massive galaxies and indicate that low mass ones may still be growing in an outside in phase.
Kitazawa, Masakiyo; Iritani, Takumi; Asakawa, Masayuki; Hatsuda, Tetsuo
2017-12-01
Euclidean two-point correlators of the energy-momentum tensor (EMT) in SU(3) gauge theory on the lattice are studied on the basis of the Yang-Mills gradient flow. The entropy density and the specific heat obtained from the two-point correlators are shown to be in good agreement with those from the one-point functions of EMT. These results constitute a first step toward the first principle simulations of the transport coefficients with the gradient flow.
Tensor gauge field localization on a string-like defect
Sousa, L. J. S.; Cruz, W. T.; Almeida, C. A. S.
2012-05-01
This work is devoted to the study of tensor gauge fields on a string-like defect in six dimensions. This model is very successful in localizing fields of various spins only by gravitational interaction. Due to problems of field localization in membrane models we are motivated to investigate if a string-like defect localizes the Kalb-Ramond field. In contrast to what happens in Randall-Sundrum and thick brane scenarios we find a localized zero mode without the addition of other fields in the bulk. Considering the local string defect we obtain analytical solutions for the massive modes. Also, we take the equations of motion in a supersymmetric quantum mechanics scenario in order to analyze the massive modes. The influence of the mass as well as the angular quantum number in the solutions is described. An additional analysis on the massive modes is performed by the Kaluza-Klein decomposition, which provides new details about the KK masses.
A Review of Tensors and Tensor Signal Processing
Cammoun, L.; Castaño-Moraga, C. A.; Muñoz-Moreno, E.; Sosa-Cabrera, D.; Acar, B.; Rodriguez-Florido, M. A.; Brun, A.; Knutsson, H.; Thiran, J. P.
Tensors have been broadly used in mathematics and physics, since they are a generalization of scalars or vectors and allow to represent more complex properties. In this chapter we present an overview of some tensor applications, especially those focused on the image processing field. From a mathematical point of view, a lot of work has been developed about tensor calculus, which obviously is more complex than scalar or vectorial calculus. Moreover, tensors can represent the metric of a vector space, which is very useful in the field of differential geometry. In physics, tensors have been used to describe several magnitudes, such as the strain or stress of materials. In solid mechanics, tensors are used to define the generalized Hooke’s law, where a fourth order tensor relates the strain and stress tensors. In fluid dynamics, the velocity gradient tensor provides information about the vorticity and the strain of the fluids. Also an electromagnetic tensor is defined, that simplifies the notation of the Maxwell equations. But tensors are not constrained to physics and mathematics. They have been used, for instance, in medical imaging, where we can highlight two applications: the diffusion tensor image, which represents how molecules diffuse inside the tissues and is broadly used for brain imaging; and the tensorial elastography, which computes the strain and vorticity tensor to analyze the tissues properties. Tensors have also been used in computer vision to provide information about the local structure or to define anisotropic image filters.
Analytical gradients for tensor hyper-contracted MP2 and SOS-MP2 on graphical processing units
Song, Chenchen; Martínez, Todd J.
2017-10-01
Analytic energy gradients for tensor hyper-contraction (THC) are derived and implemented for second-order Møller-Plesset perturbation theory (MP2), with and without the scaled-opposite-spin (SOS)-MP2 approximation. By exploiting the THC factorization, the formal scaling of MP2 and SOS-MP2 gradient calculations with respect to system size is reduced to quartic and cubic, respectively. An efficient implementation has been developed that utilizes both graphics processing units and sparse tensor techniques exploiting spatial sparsity of the atomic orbitals. THC-MP2 has been applied to both geometry optimization and ab initio molecular dynamics (AIMD) simulations. The resulting energy conservation in micro-canonical AIMD demonstrates that the implementation provides accurate nuclear gradients with respect to the THC-MP2 potential energy surfaces.
Gradient field microscopy of unstained specimens.
Kim, Taewoo; Sridharan, Shamira; Popescu, Gabriel
2012-03-12
We present a phase derivative microscopy technique referred to as gradient field microscopy (GFM), which provides the first-order derivatives of the phase associated with an optical field passing through a transparent specimen. GFM utilizes spatial light modulation at the Fourier plane of a bright field microscope to optically obtain the derivatives of the phase and increase the contrast of the final image. The controllable spatial modulation pattern allows us to obtain both one component of the field gradient (derivative along one direction) and the gradient intensity, which offers some advantages over the regular differential interference contrast (DIC) microscopy. Most importantly, unlike DIC, GFM does not use polarizing optics and, thus, it is applicable to birefringent samples. We demonstrate these features of GFM with studies of static and dynamic biological cells (HeLa cells and red blood cells). We show that GFM is capable of qualitatively providing information about cell membrane fluctuations. Specifically, we captured the disappearance of the bending mode of fluctuations in osmotically swollen red blood cells.
Minamitsuji, Masato
2014-01-01
We investigate the quasinormal modes of a test massless, minimally coupled scalar field on a static and spherically symmetric black hole in the scalar-tensor theory with field derivative coupling to the Einstein tensor, which is a part of the Horndeski theory with the shift symmetry. In our solution, the spacetime is asymptotically AdS (anti-de Sitter), where the effective AdS curvature scale is determined solely by the derivative coupling constant. The metric approaches the AdS spacetime in ...
Hoefnagels, Friso W A; de Witt Hamer, Philip C; Pouwels, Petra J W; Barkhof, Frederik; Vandertop, W Peter
2017-09-01
To explore quantitatively and qualitatively how the number of gradient directions (NGD) and spatial resolution (SR) affect diffusion tensor imaging (DTI) tractography in patients planned for brain tumor surgery, using routine clinical magnetic resonance imaging protocols. Of 67 patients with intracerebral lesions who had 2 different DTI scans, 3 DTI series were reconstructed to compare the effects of NGD and SR. Tractographies for 4 clinically relevant tracts (corticospinal tract, superior longitudinal fasciculus, optic radiation, and inferior fronto-occipital fasciculus) were constructed with a probabilistic tracking algorithm and automated region of interest placement and compared for 3 quantitative measurements: tract volume, median fiber density, and mean fractional anisotropy, using linear mixed-effects models. The mean tractography volume and intersubject reliability were visually compared across scanning protocols, to assess the clinical relevance of the quantitative differences. Both NGD and SR significantly influenced tract volume, median fiber density, and mean fractional anisotropy, but not to the same extent. In particular, higher NGD increased tract volume and median fiber density. More importantly, these effects further increased when tracts were affected by disease. The effects were tract specific, but not dependent on threshold. The superior longitudinal fasciculus and inferior fronto-occipital fasciculus showed the most significant differences. Qualitative assessment showed larger tract volumes given a fixed confidence level, and better intersubject reliability for the higher NGD protocol. SR in the range we considered seemed less relevant than NGD. This study indicates that, under time constraints of clinical imaging, a higher number of diffusion gradients is more important than spatial resolution for superior DTI probabilistic tractography in patients undergoing brain tumor surgery. Copyright © 2017 Elsevier Inc. All rights reserved.
Wallace, James M.
2009-02-01
Twenty years ago there was no experimental access to the velocity gradient tensor for turbulent flows. Without such access, knowledge of fundamental and defining properties of turbulence, such as vorticity dissipation, and strain rates and helicity, could not be studied in the laboratory. Although a few direct simulations at very low Reynolds numbers had been performed, most of these did not focus on properties of the small scales of turbulence defined by the velocity gradient tensor. In 1987 the results of the development and first successful use of a multisensor hot-wire probe for simultaneous measurements of all the components of the velocity gradient tensor in a turbulent boundary layer were published by Balint et al. [Advances in Turbulence: Proceedings of the First European Turbulence Conference (Springer-Verlag, New York, 1987), p. 456]. That same year measurements of all but one of the terms in the velocity gradient tensor were carried out, although not simultaneously, in the self-preserving region of a turbulent circular cylinder wake by Browne et al. [J. Fluid Mech. 179, 307 (1987)], and the first direct numerical simulation (DNS) of a turbulent channel flow was successfully carried out and reported by Kim et al. [J. Fluid Mech. 177, 133 (1987)], including statistics of the vorticity field. Also in that year a DNS of homogeneous shear flow by Rogers and Moin [J. Fluid Mech. 176, 33 (1987)] was published in which the authors examined the structure of the vorticity field. Additionally, Ashurst et al. [Phys. Fluids 30, 2343 (1987)] examined the alignment of the vorticity and strainrate fields using this homogeneous shear flow data as well as the DNS of isotropic turbulence of Kerr [J. Fluid Mech. 153, 31 (1985)] who had initiated such studies. Furthermore, Metcalfe et al. [J. Fluid Mech. 184, 207 (1987)] published results from their direct simulation of a temporally developing planar mixing layer in which they examined coherent vortical states resulting from
Gonçalves, J N; Correia, J G; Butz, T; Picozzi, S; Fenta, A S; Amaral, V S
2012-01-01
The hyperfine interaction between the quadrupole moment of atomic nuclei and the electric field gradient (EFG) provides information on the electronic charge distribution close to a given atomic site. In ferroelectric materials, the loss of inversion symmetry of the electronic charge distribution is necessary for the appearance of the electric polarization. We present first-principles density functional theory calculations of ferroelectrics such as BaTiO$_{3}$, KNbO$_{3}$, PbTiO$_{3}$ and other oxides with perovskite structures, by focusing on both EFG tensors and polarization. We analyze the EFG tensor properties such as orientation and correlation between components and their relation with electric polarization. This work supports previous studies of ferroelectric materials where a relation between EFG tensors and polarization was observed, which may be exploited to study the ferroelectric order when standard techniques to measure polarization are not easily applied.
Frames, the Loewner order and eigendecomposition for morphological operators on tensor fields
van de Gronde, Jasper; Roerdink, Jos B. T. M.
2014-01-01
Rotation invariance is an important property for operators on tensor fields, but up to now, most methods for morphology on tensor fields had to either sacrifice rotation invariance, or do without the foundation of mathematical morphology: a lattice structure. Recently, we proposed a framework for
Electric field gradients in copper alloys
International Nuclear Information System (INIS)
Whalley, L.R.
1974-02-01
The electric field gradients at Cu atoms which are near neighbors to the nickel impurity in a dilute CuNi alloy were measured. The technique used is zero field pure quadrupole resonance which was first demonstrated by Redfield [Redfield, Phys. Rev. 130, 589 (1963)]. The measured electric field gradients for this alloy system are 4.1 x 10 23 cm -3 , 0.84 x 10 23 cm -3 , 0.46 x 10 23 cm -3 and 0.146 x 10 23 cm -3 . These measured values are compared with the values calculated by Beal-Monod [Beal-Monod, Phys. Rev. 164, 360 (1967)]. In addition the following alloy systems were measured; CuCo, CuFe, and CuV. The nuclear relaxation of the alloys was measured but no satellite structure was detected. Results of these measurements show the similarity of the interactions measured here to the interactions in CuZn measured by Redfield. Since nickel has an unfilled 3d shell in its electronic structure, magnetic interactions in the CuNi alloy might be expected. Magnetic interactions were not found. Like the nickel alloy, the zinc alloy with copper exhibits no magnetic effects. (U.S.)
Gauge theories of Yang-Mills vector fields coupled to antisymmetric tensor fields
International Nuclear Information System (INIS)
Anco, Stephen C.
2003-01-01
A non-Abelian class of massless/massive nonlinear gauge theories of Yang-Mills vector potentials coupled to Freedman-Townsend antisymmetric tensor potentials is constructed in four space-time dimensions. These theories involve an extended Freedman-Townsend-type coupling between the vector and tensor fields, and a Chern-Simons mass term with the addition of a Higgs-type coupling of the tensor fields to the vector fields in the massive case. Geometrical, field theoretic, and algebraic aspects of the theories are discussed in detail. In particular, the geometrical structure mixes and unifies features of Yang-Mills theory and Freedman-Townsend theory formulated in terms of Lie algebra valued curvatures and connections associated to the fields and nonlinear field strengths. The theories arise from a general determination of all possible geometrical nonlinear deformations of linear Abelian gauge theory for one-form fields and two-form fields with an Abelian Chern-Simons mass term in four dimensions. For this type of deformation (with typical assumptions on the allowed form considered for terms in the gauge symmetries and field equations), an explicit classification of deformation terms at first-order is obtained, and uniqueness of deformation terms at all higher orders is proven. This leads to a uniqueness result for the non-Abelian class of theories constructed here
On the energy-momentum tensors for field theories in spaces with affine connection and metric
International Nuclear Information System (INIS)
Manoff, S.
1991-01-01
Generalized covariant Bianchi type identities are obtained and investigated for Lagrangian densities, depending on co- and contravariant tensor fields and their first and second covariant derivatives in spaces with affine connection and metric (L n -space). The notions of canonical, generalized canonical, symmetric and variational energy-momentum tensor are introduced and necessary and sufficient conditions for the existence of the symmetric energy-momentum tensor as a local conserved quantity are obtained. 19 refs.; 1 tab
Migration transformation of two-dimensional magnetic vector and tensor fields
DEFF Research Database (Denmark)
Zhdanov, Michael; Cai, Hongzhu; Wilson, Glenn
2012-01-01
We introduce a new method of rapid interpretation of magnetic vector and tensor field data, based on ideas of potential field migration which extends the general principles of seismic and electromagnetic migration to potential fields. 2-D potential field migration represents a direct integral...... to the downward continuation of a well-behaved analytical function. We present case studies for imaging of SQUID-based magnetic tensor data acquired over a magnetite skarn at Tallawang, Australia. The results obtained from magnetic tensor field migration agree very well with both Euler deconvolution and the known...
The fermionic energy-momentum tensor in terms of currents in an external gauge field
International Nuclear Information System (INIS)
Bos, M.
1986-01-01
It is shown that for two-dimensional massless Dirac fields interacting with external gauge fields, the energy-momentum tensor can be expressed in terms of the current via the Sugawara-Sommerfield formula. (orig.)
Stress-energy tensors for vector fields outside a static black hole
International Nuclear Information System (INIS)
Barrios, F.A.; Vaz, C.
1989-01-01
We obtain new, approximate stress-energy tensors to describe gauge fields in the neighborhood of a Schwarzschild black hole. We assume that the coefficient of ∇ 2 R in the trace anomaly is correctly given by ζ-function regularization. Our approximation differs from that of Page and of Brown and Ottewill and relies upon a new, improved ansatz for the form of the stress-energy tensor in the ultrastatic optical metric of the black hole. The Israel-Hartle-Hawking thermal tensor is constructed to be regular on the horizon and possess the correct asymptotic behavior. Our approximation of Unruh's tensor is likewise constructed to be regular on the future horizon and exhibit a luminosity which agrees with Page's numerically obtained value. Geometric expressions for the approximate tensors are given, and the approximate energy density of the thermal tensor on the horizon is compared with recent numerical estimates
Field of a charged particle in a scalar-tensor theory of gravitation
Reddy, D. R. K.; Vidyasagar, T.; Satyanarayana, B.
2012-11-01
Field equations in the scalar-tensor theory of gravitation, proposed by Saez and Ballester (Phys. Lett. A 113: 467, 1986), are obtained for a static charged point mass with the aid of a spherically symmetric metric. A closed form exact solution of the field equations is presented and may be considered as describing the field due to a charged mass point at the origin surrounded by a scalar-tensor field.
Energy-momentum tensor of the gravitational field for material spheres
International Nuclear Information System (INIS)
Sokolov, S.N.
1990-01-01
Density of the energy-momentum tensor of a gravitational field which can be defined in the general relativity theory with the help of ideas of the relativistic gravitational theory is found for the case of material spheres. A relationship of this quantity with the Riemann tensor R αβγδ is discussed
Dynamic pulsed-field-gradient NMR
Sørland, Geir Humborstad
2014-01-01
Dealing with the basics, theory and applications of dynamic pulsed-field-gradient NMR NMR (PFG NMR), this book describes the essential theory behind diffusion in heterogeneous media that can be combined with NMR measurements to extract important information of the system being investigated. This information could be the surface to volume ratio, droplet size distribution in emulsions, brine profiles, fat content in food stuff, permeability/connectivity in porous materials and medical applications currently being developed. Besides theory and applications it will provide the readers with background knowledge on the experimental set-ups, and most important, deal with the pitfalls that are numerously present in work with PFG-NMR. How to analyze the NMR data and some important basic knowledge on the hardware will be explained, too.
Tensor categories and the mathematics of rational and logarithmic conformal field theory
International Nuclear Information System (INIS)
Huang, Yi-Zhi; Lepowsky, James
2013-01-01
We review the construction of braided tensor categories and modular tensor categories from representations of vertex operator algebras, which correspond to chiral algebras in physics. The extensive and general theory underlying this construction also establishes the operator product expansion for intertwining operators, which correspond to chiral vertex operators, and more generally, it establishes the logarithmic operator product expansion for logarithmic intertwining operators. We review the main ideas in the construction of the tensor product bifunctors and the associativity isomorphisms. For rational and logarithmic conformal field theories, we review the precise results that yield braided tensor categories, and in the rational case, modular tensor categories as well. In the case of rational conformal field theory, we also briefly discuss the construction of the modular tensor categories for the Wess–Zumino–Novikov–Witten models and, especially, a recent discovery concerning the proof of the fundamental rigidity property of the modular tensor categories for this important special case. In the case of logarithmic conformal field theory, we mention suitable categories of modules for the triplet W-algebras as an example of the applications of our general construction of the braided tensor category structure. (review)
arXiv Tensor to scalar ratio from single field magnetogenesis
Giovannini, Massimo
2017-08-10
The tensor to scalar ratio is affected by the evolution of the large-scale gauge fields potentially amplified during an inflationary stage of expansion. After deriving the exact evolution equations for the scalar and tensor modes of the geometry in the presence of dynamical gauge fields, it is shown that the tensor to scalar ratio is bounded from below by the dominance of the adiabatic contribution and it cannot be smaller than one thousands whenever the magnetogenesis is driven by a single inflaton field.
Analytic continuation of tensor fields along geodesics by means of covariant Taylor series
International Nuclear Information System (INIS)
Tsirulev, A.N.
1995-01-01
It is shown that covariant derivatives of all orders of arbitrary tensor field, curvature and torsion on a submanifold in the directions of normal geodesics to the submanifold, together with analytical conditions, define the tensor field in a normal neighbourhood of the submanifold introduced analogously to a normal neighbourhood of a point, by means of Taylor series with tensor coefficients. Evident formulae defined a recurrent procedure for calculation of the series coefficient in any order are obtain. Particular cases of the expansions of a pseudo-Riemannian metric by relation to the metric connection without torsion are considered for a point and a hypersurface. 6 refs
New topological invariants for non-abelian antisymmetric tensor fields from extended BRS algebra
International Nuclear Information System (INIS)
Boukraa, S.; Maillet, J.M.; Nijhoff, F.
1988-09-01
Extended non-linear BRS and Gauge transformations containing Lie algebra cocycles, and acting on non-abelian antisymmetric tensor fields are constructed in the context of free differential algebras. New topological invariants are given in this framework. 6 refs
Evaluation of the Field Gradient Lattice Detector
AUTHOR|(CDS)2072983
A novel Micro Pattern Gas Detector, named the Field Gradient Lattice Detector, has been implemented using technologies available to CERN’s Printed Circuit Workshop. Numerous prototypes based on various materials were constructed in different geometries and their gain performance has been studied using 55Fe and 109Cd X-ray sources in Argon-CO2 gas mixtures. Two axis (2D) prototype structures have been shown to provide stable gains of around 1000 while a 3D design, based on the same polyimide foils used in other MPGD elements, holds a gain of 5000 for 8.9 keV X-rays even at high rates of 22 kHz/mm2. At a gain of 3100, the device has been tested up to 1 MHz/mm2 and shows no signs of degradation in performance. The energy resolution of the 3D-in-polyimide is modest, around 40% for 5.9 keV X-rays and 30% if the source is collimated indicating a variation in gain over the 3x3 cm2 active area. Having the most promise for future applications, the 3D-in-polyimide design has been selected for testing with a custom-bu...
Infrared image detail enhancement based on the gradient field specification.
Zhao, Wenda; Xu, Zhijun; Zhao, Jian; Zhao, Fan; Han, Xizhen
2014-07-01
Human vision is sensitive to the changes of local image details, which are actually image gradients. To enhance faint infrared image details, this article proposes a gradient field specification algorithm. First we define the image gradient field and gradient histogram. Then, by analyzing the characteristics of the gradient histogram, we construct a Gaussian function to obtain the gradient histogram specification and therefore obtain the transform gradient field. In addition, subhistogram equalization is proposed based on the histogram equalization to improve the contrast of infrared images. The experimental results show that the algorithm can effectively improve image contrast and enhance weak infrared image details and edges. As a result, it can give qualified image information for different applications of an infrared image. In addition, it can also be applied to enhance other types of images such as visible, medical, and lunar surface.
Tolman temperature gradients in a gravitational field
Santiago, Jessica; Visser, Matt
2018-01-01
Tolman's relation for the temperature gradient in an equilibrium self-gravitating general relativistic fluid is broadly accepted within the general relativity community. However, the concept of temperature gradients in thermal equilibrium continues to cause confusion in other branches of physics, since it contradicts naive versions of the laws of classical thermodynamics. In this paper we discuss the crucial role of the universality of free fall, and how thermodynamics emphasises the great di...
Noether symmetries, energy-momentum tensors, and conformal invariance in classical field theory
International Nuclear Information System (INIS)
Pons, Josep M.
2011-01-01
In the framework of classical field theory, we first review the Noether theory of symmetries, with simple rederivations of its essential results, with special emphasis given to the Noether identities for gauge theories. With this baggage on board, we next discuss in detail, for Poincare invariant theories in flat spacetime, the differences between the Belinfante energy-momentum tensor and a family of Hilbert energy-momentum tensors. All these tensors coincide on shell but they split their duties in the following sense: Belinfante's tensor is the one to use in order to obtain the generators of Poincare symmetries and it is a basic ingredient of the generators of other eventual spacetime symmetries which may happen to exist. Instead, Hilbert tensors are the means to test whether a theory contains other spacetime symmetries beyond Poincare. We discuss at length the case of scale and conformal symmetry, of which we give some examples. We show, for Poincare invariant Lagrangians, that the realization of scale invariance selects a unique Hilbert tensor which allows for an easy test as to whether conformal invariance is also realized. Finally we make some basic remarks on metric generally covariant theories and classical field theory in a fixed curved background.
Study of the tensor correlation in oxygen isotopes using mean-field-type and shell model methods
International Nuclear Information System (INIS)
Sugimoto, Satoru
2007-01-01
The tensor force plays important roles in nuclear structure. Recently, we have developed a mean-field-type model which can treat the two-particle-two-hole correlation induced by the tensor force. We applied the model to sub-closed-shell oxygen isotopes and found that an sizable attractive energy comes from the tensor force. We also studied the tensor correlation in 16O using a shell model including two-particle-two-hole configurations. In this case, quite a large attractive energy is obtained for the correlation energy from the tensor force
DUCASSE , Eric; YAACOUBI , Slah
2010-01-01
International audience; A tensor Hankel transform'' (THT) is defined for vector fields, such as displacement, and second-order tensor fields, such as stress or strain. The THT establishes a bijection between the real space and the wave-vector domain, and, remarkably, cannot be reduced to a scalar transform applied separately to each component. One of the advantages of this approach is that some standard elasticity problems can be concisely rewritten by applying this tensor integral transform ...
Naohito, NAKAZAWA; Research Institute for Theoretical Physics Hiroshima University
1985-01-01
We formulate a field-theoretical method at finite temperature to calculate a thermal energy-momentum tensor in arbitrary curved space-times using a momentum-space representation of the thermal Green's function in terms of Riemann normal coordinates. In particular, the thermal energy-momentum tensor for a massive scalar field is calculated by the high-temperature expansion. A locally observed temperature is obtained by requiring the conservation law of the thermal energy-momentum tensor.
ion in crossed gradient electric and magnetic fields
Indian Academy of Sciences (India)
Photodetachment cross-section for variousexternal fields and the laser polarization are calculated and displayed. A comparison with the photodetachment cross-section in crossed uniform electric and magnetic fields or in a single gradient electric field has been made.The agreement of our results with the above two special ...
Gradient Field Imploding Liner Fusion Propulsion System
National Aeronautics and Space Administration — An innovative modification to magneto-inertial fusion is proposed in which the pulsed, high current magnetic field coil and stationary central fuel target are...
Magnetic field and gradient analysis around matrix for HGMS
International Nuclear Information System (INIS)
Baik, S.K.; Ha, D.W.; Ko, R.K.; Kwon, J.M.
2010-01-01
A High Gradient Magnetic Separator (HGMS) uses matrix to make high magnetic field gradient so that ferro- or para-magnetic particles can be attracted to them by high magnetic force. These matrixes are usually composed of stainless wires having high magnetization characteristics. This paper deals with superconducting HGMS which is aimed for purifying wastewater by using stainless steel matrix. Background magnetic field up to 6 T is generated by a superconducting solenoid and the stainless steel matrix are arranged inside of the solenoid. In order to calculate magnetic forces exerting on magnetic particles in wastewater, it is important to calculate magnetic field and magnetic field gradient those are proportional to the magnetic force acting on the particle. So we presents magnetic field distribution analysis result and estimates how many times of magnetic force will act on a particle when the matrix are arranged or not.
Visualizing MR diffusion tensor fields by dynamic fiber tracking and uncertainty mapping
Ehricke, HH; Klose, U; Grodd, W
Recent advances in magnetic resonance imaging have provided methods for the acquisition of high-resolution diffusion tensor fields. Their 3D-visualization with streamline-based techniques-called fiber tracking-allow analysis of cerebral white matter tracts for diagnostic, therapeutic as well as
An analysis of the intermediate field theory of T{sup 4} tensor model
Energy Technology Data Exchange (ETDEWEB)
Nguyen, Viet Anh [Laboratoire de Physique Théorique, CNRS UMR 8627, Université Paris 11, Bat 210, Faculté des Sciences, Orsay Cedex, 91405 (France); IPhT, Institut de Physique Théorique, CEA/DSM/IPhT, CEA/Saclay,Orme des Merisiers batiment 774, Point courrier 136, Gif-sur-Yvette Cedex, 91191 (France); LAREMA, CNRS UMR 6093, Université d’Anger, Département de mathématiques,Faculté des Sciences, 2 Boulevard Lavoisier, Angers, 49045 (France); Dartois, Stéphane [Laboratoire de Physique Théorique, CNRS UMR 8627, Université Paris 11, Bat 210, Faculté des Sciences, Orsay Cedex, 91405 (France); LIPN, Institut Galilée, CNRS UMR, Université Paris 13,99 avenue Jean Baptiste Clément, Villetaneuse, 93430 (France); Eynard, Bertrand [IPhT, Institut de Physique Théorique, CEA/DSM/IPhT, CEA/Saclay,Orme des Merisiers batiment 774, Point courrier 136, Gif-sur-Yvette Cedex, 91191 (France); Centre de Recherches Mathématiques, Université de Montréal, Pavillon André-Aisenstadt,2920, Chemin de la tour, bur. 5357, Montréal, Québec, H3T 1J4 (Canada)
2015-01-07
In this paper we analyze the multi-matrix model arising from the intermediate field representation of the tensor model with all quartic melonic interactions. We derive the saddle point equation and the Schwinger-Dyson constraints. We then use them to describe the leading and next-to-leading eigenvalues distribution of the matrices.
Two-Dimensional Interactions in a Class of Tensor Gauge Fields from Local BRST Cohomology
Babalic, E M; Cioroianu, E M; Negru, I; Sararu, S C
2003-01-01
Lagrangian interactions in a class of two-dimensional tensor gauge field theory are derived by means of deforming the solution to the master equation with specific cohomological techniques. Both the gauge transformations and their algebra are deformed. The gauge algebra of the coupled model is open.
Bergan, Andrew C.; Leone, Frank A., Jr.
2016-01-01
A new model is proposed that represents the kinematics of kink-band formation and propagation within the framework of a mesoscale continuum damage mechanics (CDM) model. The model uses the recently proposed deformation gradient decomposition approach to represent a kink band as a displacement jump via a cohesive interface that is embedded in an elastic bulk material. The model is capable of representing the combination of matrix failure in the frame of a misaligned fiber and instability due to shear nonlinearity. In contrast to conventional linear or bilinear strain softening laws used in most mesoscale CDM models for longitudinal compression, the constitutive response of the proposed model includes features predicted by detailed micromechanical models. These features include: 1) the rotational kinematics of the kink band, 2) an instability when the peak load is reached, and 3) a nonzero plateau stress under large strains.
Gradient Boosting for Conditional Random Fields
2014-09-23
On-line Handwritten Character Recognition. PhD thesis, Cambridge, MA, USA, 1995. [9] J. Lafferty, A. McCallum, and F. Pereira . Conditional random...ICML ’01), pages 282–289, 2001. [10] D. Levin, Y. Peres, and E. Wilmer . Markov Chains and Mixing Times. American Mathematical Society, 2008. [11] P. Li...1097–1104. [16] F. Sha and F. Pereira . Shallow parsing with conditional random fields. In Proceedings of the 2003 Conference of the North American
Velocity Gradients as a Tracer for Magnetic Fields
González-Casanova, Diego F.; Lazarian, A.
2017-01-01
Strong Alfvénic turbulence develops eddy-like motions perpendicular to the local direction of magnetic fields. This local alignment induces velocity gradients perpendicular to the local direction of the magnetic field. We use this fact to propose a new technique of studying the direction of magnetic fields from observations, which we call the velocity gradient technique. We test our idea by employing the synthetic observations obtained via 3D magnetohydrodynamical (MHD) numerical simulations for different sonic and Alfvén Mach numbers. We calculate the velocity gradient, {\\boldsymbol{Ω }}, using the velocity centroids. We find that {\\boldsymbol{Ω }} traces the projected magnetic field best for the synthetic maps obtained with sub-Alfvénic simulations and provides good point-wise correspondence between the magnetic field direction and the direction of {\\boldsymbol{Ω }}. The reported alignment is much better than the alignment between the density gradients and the magnetic field, and we demonstrate that it can be used to find the magnetic field strength with an analog of the Chandrasekhar-Fermi method. This new technique does not require dust polarimetry, and our study opens up a new way of studying magnetic fields using spectroscopic data.
Stress-energy tensor of quantized massive fields in static wormhole spacetimes
Kocuper, Ewa; Matyjasek, Jerzy; Zwierzchowska, Kasia
2017-11-01
In order to be traversable, the static Lorentzian wormhole must be made out of some exotic matter that violates the weak energy condition. The quantized fields are the natural candidates as their stress-energy tensor, in many cases, possesses desired properties. In this paper we construct and examine the stress-energy tensor of the quantized massive scalar, spinor and vector fields in six static wormhole spacetimes. We find that in all considered cases the quantum fields violate the Morris-Thorne conditions and do not have the form necessary to support the wormhole throat. This is in concord with the previous results and indicates that the massive quantum fields make the wormholes less operable.
Large tensor mode, field range bound and consistency in generalized G-inflation
Energy Technology Data Exchange (ETDEWEB)
Kunimitsu, Taro; Suyama, Teruaki; Watanabe, Yuki; Yokoyama, Jun' ichi, E-mail: kunimitsu@resceu.s.u-tokyo.ac.jp, E-mail: suyama@resceu.s.u-tokyo.ac.jp, E-mail: watanabe@resceu.s.u-tokyo.ac.jp, E-mail: yokoyama@resceu.s.u-tokyo.ac.jp [Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, Tokyo 113-0033 (Japan)
2015-08-01
We systematically show that in potential driven generalized G-inflation models, quantum corrections coming from new physics at the strong coupling scale can be avoided, while producing observable tensor modes. The effective action can be approximated by the tree level action, and as a result, these models are internally consistent, despite the fact that we introduced new mass scales below the energy scale of inflation. Although observable tensor modes are produced with sub-strong coupling scale field excursions, this is not an evasion of the Lyth bound, since the models include higher-derivative non-canonical kinetic terms, and effective rescaling of the field would result in super-Planckian field excursions. We argue that the enhanced kinetic term of the inflaton screens the interactions with other fields, keeping the system weakly coupled during inflation.
Large tensor mode, field range bound and consistency in generalized G-inflation
International Nuclear Information System (INIS)
Kunimitsu, Taro; Suyama, Teruaki; Watanabe, Yuki; Yokoyama, Jun'ichi
2015-01-01
We systematically show that in potential driven generalized G-inflation models, quantum corrections coming from new physics at the strong coupling scale can be avoided, while producing observable tensor modes. The effective action can be approximated by the tree level action, and as a result, these models are internally consistent, despite the fact that we introduced new mass scales below the energy scale of inflation. Although observable tensor modes are produced with sub-strong coupling scale field excursions, this is not an evasion of the Lyth bound, since the models include higher-derivative non-canonical kinetic terms, and effective rescaling of the field would result in super-Planckian field excursions. We argue that the enhanced kinetic term of the inflaton screens the interactions with other fields, keeping the system weakly coupled during inflation
International Nuclear Information System (INIS)
Beleggia, M.; Graef, M. de
2003-01-01
A method is presented to compute the demagnetization tensor field for uniformly magnetized particles of arbitrary shape. By means of a Fourier space approach it is possible to compute analytically the Fourier representation of the demagnetization tensor field for a given shape. Then, specifying the direction of the uniform magnetization, the demagnetizing field and the magnetostatic energy associated with the particle can be evaluated. In some particular cases, the real space representation is computable analytically. In general, a numerical inverse fast Fourier transform is required to perform the inversion. As an example, the demagnetization tensor field for the tetrahedron will be given
The stress-energy tensor of flavor fields from AdS/CFT
Karch, Andreas; O'Bannon, Andy; Thompson, Ethan
2009-04-01
We use the AdS/CFT correspondence to study the transport properties of massive Script N = 2 hypermultiplet fields in an Script N = 4 SU(Nc) super-Yang-Mills theory plasma in the large Nc, large 't Hooft coupling limit, and in the presence of a baryon number chemical potential and external electric and magnetic fields. In particular, we compute the flavor fields' contribution to the stress-energy tensor. We find infrared divergences in the stress-energy tensor, arising from the flavor fields' constant rate of energy and momentum loss. We regulate these divergences and extract the energy and momentum loss rates from the divergent terms. We also check our result in various limits in which the divergences are absent. The supergravity dual is a system of D7-branes, with a particular configuration of worldvolume fields, probing an AdS-Schwarzschild background. The supergravity calculation amounts to computing the stress-energy tensor of the D7-branes.
Josephson tunnel junctions in a magnetic field gradient
DEFF Research Database (Denmark)
Monaco, R.; Mygind, Jesper; Koshelets, V.P.
2011-01-01
We measured the magnetic field dependence of the critical current of high-quality Nb-based planar Josephson tunnel junctions in the presence of a controllable nonuniform field distribution. We found skewed and slowly changing magnetic diffraction patterns quite dissimilar from the Fraunhofer......-like ones typical of a homogeneous field. Our findings can be well interpreted in terms of recent theoretical predictions [R. Monaco, J. Appl. Phys. 108, 033906 (2010)] for a uniform magnetic field gradient, leading to Fresnel-like magnetic diffraction patterns. We also show that Fiske resonances can...... be suppressed by an asymmetric magnetic field profile. © 2011 American Institute of Physics....
Notes on Translational and Rotational Properties of Tensor Fields in Relativistic Quantum Mechanics
Dvoeglazov, V. V.
Recently, several discussions on the possible observability of 4-vector fields have been published in literature. Furthermore, several authors recently claimed existence of the helicity=0 fundamental field. We re-examine the theory of antisymmetric tensor fields and 4-vector potentials. We study the massless limits. In fact, a theoretical motivation for this venture is the old papers of Ogievetskiĭ and Polubarinov, Hayashi, and Kalb and Ramond. Ogievetskiĭ and Polubarinov proposed the concept of the notoph, whose helicity properties are complementary to those of the photon. We analyze the quantum field theory with taking into account mass dimensions of the notoph and the photon. It appears to be possible to describe both photon and notoph degrees of freedom on the basis of the modified Bargmann-Wigner formalism for the symmetric second-rank spinor. Next, we proceed to derive equations for the symmetric tensor of the second rank on the basis of the Bargmann-Wigner formalism in a straightforward way. The symmetric multispinor of the fourth rank is used. Due to serious problems with the interpretation of the results obtained on using the standard procedure we generalize it and obtain the spin-2 relativistic equations, which are consistent with the general relativity. Thus, in fact we deduced the gravitational field equations from relativistic quantum mechanics. The relations of this theory with the scalar-tensor theories of gravitation and f(R) are discussed. Particular attention has been paid to the correct definitions of the energy-momentum tensor and other Nöther currents in the electromagnetic theory, the relativistic theory of gravitation, the general relativity, and their generalizations. We estimate possible interactions, fermion-notoph, graviton-notoph, photon-notoph, and we conclude that they can probably be seen in experiments in the next few years.
Diffusion with finite-helicity field tensor: A mechanism of generating heterogeneity
Sato, N.; Yoshida, Z.
2018-02-01
Topological constraints on a dynamical system often manifest themselves as breaking of the Hamiltonian structure; well-known examples are nonholonomic constraints on Lagrangian mechanics. The statistical mechanics under such topological constraints is the subject of this study. Conventional arguments based on phase spaces, Jacobi identity, invariant measure, or the H theorem are no longer applicable since all these notions stem from the symplectic geometry underlying canonical Hamiltonian systems. Remembering that Hamiltonian systems are endowed with field tensors (canonical 2-forms) that have zero helicity, our mission is to extend the scope toward the class of systems governed by finite-helicity field tensors. Here, we introduce a class of field tensors that are characterized by Beltrami vectors. We prove an H theorem for this Beltrami class. The most general class of energy-conserving systems are non-Beltrami, for which we identify the "field charge" that prevents the entropy to maximize, resulting in creation of heterogeneous distributions. The essence of the theory can be delineated by classifying three-dimensional dynamics. We then generalize to arbitrary (finite) dimensions.
The total energy-momentum tensor for electromagnetic fields in a dielectric
Crenshaw, Michael E.
2017-08-01
Radiation pressure is an observable consequence of optically induced forces on materials. On cosmic scales, radiation pressure is responsible for the bending of the tails of comets as they pass near the sun. At a much smaller scale, optically induced forces are being investigated as part of a toolkit for micromanipulation and nanofabrication technology [1]. A number of practical applications of the mechanical effects of light-matter interaction are discussed by Qiu, et al. [2]. The promise of the nascent nanophotonic technology for manufacturing small, low-power, high-sensitivity sensors and other devices has likely motivated the substantial current interest in optical manipulation of materials at the nanoscale, see, for example, Ref. [2] and the references therein. While substantial progress toward optical micromanipulation has been achieved, e.g. optical tweezers [1], in this report we limit our consideration to the particular issue of optically induced forces on a transparent dielectric material. As a matter of electromagnetic theory, these forces remain indeterminate and controversial. Due to the potential applications in nanotechnology, the century-old debate regarding these forces, and the associated momentums, has ramped up considerably in the physics community. The energy-momentum tensor is the centerpiece of conservation laws for the unimpeded, inviscid, incompressible flow of non-interacting particles in the continuum limit in an otherwise empty volume. The foundations of the energy-momentum tensor and the associated tensor conservation theory come to electrodynamics from classical continuum dynamics by applying the divergence theorem to a Taylor series expansion of a property density field of a continuous flow in an otherwise empty volume. The dust tensor is a particularly simple example of an energy-momentum tensor that deals with particles of matter in the continuum limit in terms of the mass density ρm, energy density ρmc 2 , and momentum density
Electric-field gradients at Ta donor impurities in Cr2O3(Ta) semiconductor
International Nuclear Information System (INIS)
Darriba, G.N.; Errico, L.A.; Munoz, E.L; Richard, D.; Eversheim, P.D.; Renteria, M.
2009-01-01
We report perturbed-angular-correlation (PAC) experiments on 181 Hf(→ 181 Ta)-implanted corundum Cr 2 O 3 powder samples in order to determine the magnitude and symmetry of the electric-field gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbitals (FP-APW+lo) calculations. The results are also compared with EFG results coming from PAC experiments in isomorphous α-Al 2 O 3 and α-Fe 2 O 3 doped with 111 In→ 111 Cd and 181 Hf→ 181 Ta tracers. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.
Tensor hierarchy and generalized Cartan calculus in SL(3)×SL(2) exceptional field theory
Energy Technology Data Exchange (ETDEWEB)
Hohm, Olaf; Wang, Yi-Nan [Center for Theoretical Physics, Massachusetts Institute of Technology,77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
2015-04-10
We construct exceptional field theory for the duality group SL(3)×SL(2). The theory is defined on a space with 8 ‘external’ coordinates and 6 ‘internal’ coordinates in the (3,2) fundamental representation, leading to a 14-dimensional generalized spacetime. The bosonic theory is uniquely determined by gauge invariance under generalized external and internal diffeomorphisms. The latter invariance can be made manifest by introducing higher form gauge fields and a so-called tensor hierarchy, which we systematically develop to much higher degree than in previous studies. To this end we introduce a novel Cartan-like tensor calculus based on a covariant nil-potent differential, generalizing the exterior derivative of conventional differential geometry. The theory encodes the full D=11 or type IIB supergravity, respectively.
Control of colloids with gravity, temperature gradients, and electric fields
Sullivan, M; Harrison, C; Austin, R H; Megens, M; Hollingsworth, A; Russel, W B; Cheng Zhen; Mason, T; Chaikin, P M
2003-01-01
We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.
Fugacity and concentration gradients in a gravity field
May, C. E.
1986-01-01
Equations are reviewed which show that at equilibrium fugacity and concentration gradients can exist in gravitational fields. At equilibrium, the logarithm of the ratio of the fugacities of a species at two different locations in a gravitational field is proportional to the difference in the heights of the two locations and the molecular weight of the species. An analogous relation holds for the concentration ratios in a multicomponent system. The ratio is calculated for a variety of examples. The kinetics for the general process are derived, and the time required to approach equilibrium is calculated for several systems. The following special topics are discussed: ionic solutions, polymers, multiphase systems, hydrostatic pressure, osmotic pressure, and solubility gradients in a gravity field.
Synchrotron Intensity Gradients as Tracers of Interstellar Magnetic Fields
International Nuclear Information System (INIS)
Lazarian, A.; Yuen, Ka Ho; Lee, Hyeseung; Cho, J.
2017-01-01
On the basis of the modern understanding of MHD turbulence, we propose a new way of using synchrotron radiation: using synchrotron intensity gradients (SIGs) for tracing astrophysical magnetic fields. We successfully test the new technique using synthetic data obtained with 3D MHD simulations and provide the demonstration of the practical utility of the technique by comparing the directions of magnetic fields that are obtained with PLANCK synchrotron intensity data to the directions obtained with PLANCK synchrotron polarization data. We demonstrate that the SIGs can reliably trace magnetic fields in the presence of noise and can provide detailed maps of magnetic field directions. We also show that the SIGs are relatively robust for tracing magnetic fields while the low spatial frequencies of the synchrotron image are removed. This makes the SIGs applicable to the tracing of magnetic fields using interferometric data with single-dish measurement absent. We discuss the synergy of using the SIGs together with synchrotron polarization in order to find the actual direction of the magnetic fields and quantify the effects of Faraday rotation as well as with other ways of studying astrophysical magnetic fields. We test our method in the presence of noise and the resolution effects. We stress the complementary nature of the studies using the SIG technique and those employing the recently introduced velocity gradient techniques that trace magnetic fields using spectroscopic data.
Synchrotron Intensity Gradients as Tracers of Interstellar Magnetic Fields
Lazarian, A.; Yuen, Ka Ho; Lee, Hyeseung; Cho, J.
2017-06-01
On the basis of the modern understanding of MHD turbulence, we propose a new way of using synchrotron radiation: using synchrotron intensity gradients (SIGs) for tracing astrophysical magnetic fields. We successfully test the new technique using synthetic data obtained with 3D MHD simulations and provide the demonstration of the practical utility of the technique by comparing the directions of magnetic fields that are obtained with PLANCK synchrotron intensity data to the directions obtained with PLANCK synchrotron polarization data. We demonstrate that the SIGs can reliably trace magnetic fields in the presence of noise and can provide detailed maps of magnetic field directions. We also show that the SIGs are relatively robust for tracing magnetic fields while the low spatial frequencies of the synchrotron image are removed. This makes the SIGs applicable to the tracing of magnetic fields using interferometric data with single-dish measurement absent. We discuss the synergy of using the SIGs together with synchrotron polarization in order to find the actual direction of the magnetic fields and quantify the effects of Faraday rotation as well as with other ways of studying astrophysical magnetic fields. We test our method in the presence of noise and the resolution effects. We stress the complementary nature of the studies using the SIG technique and those employing the recently introduced velocity gradient techniques that trace magnetic fields using spectroscopic data.
Synchrotron Intensity Gradients as Tracers of Interstellar Magnetic Fields
Energy Technology Data Exchange (ETDEWEB)
Lazarian, A.; Yuen, Ka Ho; Lee, Hyeseung; Cho, J. [Department of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 North Charter Street, Madison, WI 53706-1507 (United States)
2017-06-10
On the basis of the modern understanding of MHD turbulence, we propose a new way of using synchrotron radiation: using synchrotron intensity gradients (SIGs) for tracing astrophysical magnetic fields. We successfully test the new technique using synthetic data obtained with 3D MHD simulations and provide the demonstration of the practical utility of the technique by comparing the directions of magnetic fields that are obtained with PLANCK synchrotron intensity data to the directions obtained with PLANCK synchrotron polarization data. We demonstrate that the SIGs can reliably trace magnetic fields in the presence of noise and can provide detailed maps of magnetic field directions. We also show that the SIGs are relatively robust for tracing magnetic fields while the low spatial frequencies of the synchrotron image are removed. This makes the SIGs applicable to the tracing of magnetic fields using interferometric data with single-dish measurement absent. We discuss the synergy of using the SIGs together with synchrotron polarization in order to find the actual direction of the magnetic fields and quantify the effects of Faraday rotation as well as with other ways of studying astrophysical magnetic fields. We test our method in the presence of noise and the resolution effects. We stress the complementary nature of the studies using the SIG technique and those employing the recently introduced velocity gradient techniques that trace magnetic fields using spectroscopic data.
Energy momentum tensor and marginal deformations in open string field theory
International Nuclear Information System (INIS)
Sen, Ashoke
2004-01-01
Marginal boundary deformations in a two dimensional conformal field theory correspond to a family of classical solutions of the equations of motion of open string field theory. In this paper we develop a systematic method for relating the parameter labelling the marginal boundary deformation in the conformal field theory to the parameter labelling the classical solution in open string field theory. This is done by first constructing the energy-momentum tensor associated with the classical solution in open string field theory using Noether method, and then comparing this to the answer obtained in the conformal field theory by analysing the boundary state. We also use this method to demonstrate that in open string field theory the tachyon lump solution on a circle of radius larger than one has vanishing pressure along the circle direction, as is expected for a co-dimension one D-brane. (author)
International Nuclear Information System (INIS)
Stachel, J.
1977-01-01
A first-order Lagrangian is given, from which follow the definitions of the fully covariant form of the Riemann tensor Rsub(μνkappalambda) in terms of the affine connection and metric; the definition of the affine connection in terms of the metric; the Einstein field equations; and the definition of a set of gravitational 'superpotentials' closely connected with the Komar conservation laws (Phys. Rev.; 113:934 (1959)). Substitution of the definition of the affine connection into this Lagrangian results in a second-order Lagrangian, from which follow the definition of the fully covariant Riemann tensor in terms of the metric, the Einstein equations, and the definition of the gravitational 'superpotentials'. (author)
Wu, Bofeng; Huang, Chao-Guang
2018-04-01
The 1 /r expansion in the distance to the source is applied to the linearized f (R ) gravity, and its multipole expansion in the radiation field with irreducible Cartesian tensors is presented. Then, the energy, momentum, and angular momentum in the gravitational waves are provided for linearized f (R ) gravity. All of these results have two parts, which are associated with the tensor part and the scalar part in the multipole expansion of linearized f (R ) gravity, respectively. The former is the same as that in General Relativity, and the latter, as the correction to the result in General Relativity, is caused by the massive scalar degree of freedom and plays an important role in distinguishing General Relativity and f (R ) gravity.
Quantum stress tensor fluctuations of a conformal field and inflationary cosmology
International Nuclear Information System (INIS)
Ford, L. H.; Miao, S. P.; Ng, Kin-Wang; Woodard, R. P.; Wu, C.-H.
2010-01-01
We discuss the additional perturbation introduced during inflation by quantum stress tensor fluctuations of a conformally invariant field such as the photon. We consider both a kinematical model, which deals only with the expansion fluctuations of geodesics, and a dynamical model which treats the coupling of the stress tensor fluctuations to a scalar inflaton. In neither model do we find any growth at late times, in accordance with a theorem due to Weinberg. What we find instead is a correction which becomes larger the earlier one starts inflation. This correction is non-Gaussian and highly scale dependent, so the absence of such effects from the observed power spectra may imply a constraint on the total duration of inflation. We discuss different views about the validity of perturbation theory at very early times during which currently observable modes are trans-Planckian.
Vacuum stress tensor of a scalar field in a rectangular waveguide
International Nuclear Information System (INIS)
Rodrigues, R.B.; Svaiter, N.F.; Paola, R.D.M. de
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, {T μν (vector x)} and {Θ μν (vector x)}, 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 {T 00 (vector x)} and {Θ 00 (vector x)}. 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)
Novel Techniques for Pulsed Field Gradient NMR Measurements
Brey, William Wallace
Pulsed field gradient (PFG) techniques now find application in multiple quantum filtering and diffusion experiments as well as in magnetic resonance imaging and spatially selective spectroscopy. Conventionally, the gradient fields are produced by azimuthal and longitudinal currents on the surfaces of one or two cylinders. Using a series of planar units consisting of azimuthal and radial current elements spaced along the longitudinal axis, we have designed gradient coils having linear regions that extend axially nearly to the ends of the coil and to more than 80% of the inner radius. These designs locate the current return paths on a concentric cylinder, so the coils are called Concentric Return Path (CRP) coils. Coils having extended linear regions can be made smaller for a given sample size. Among the advantages that can accrue from using smaller coils are improved gradient strength and switching time, reduced eddy currents in the absence of shielding, and improved use of bore space. We used an approximation technique to predict the remaining eddy currents and a time-domain model of coil performance to simulate the electrical performance of the CRP coil and several reduced volume coils of more conventional design. One of the conventional coils was designed based on the time-domain performance model. A single-point acquisition technique was developed to measure the remaining eddy currents of the reduced volume coils. Adaptive sampling increases the dynamic range of the measurement. Measuring only the center of the stimulated echo removes chemical shift and B_0 inhomogeneity effects. The technique was also used to design an inverse filter to remove the eddy current effects in a larger coil set. We added pulsed field gradient and imaging capability to a 7 T commercial spectrometer to perform neuroscience and embryology research and used it in preliminary studies of binary liquid mixtures separating near a critical point. These techniques and coil designs will find
Quantum fields interacting with colliding plane waves: the stress-energy tensor and backreaction
International Nuclear Information System (INIS)
Dorca, M.; Verdaguer, E.
1997-01-01
Following a previous work on the quantization of a massless scalar field in a space-time representing the head on collision of two plane waves which focus into a Killing-Cauchy horizon, we compute the renormalized expectation value of the stress-energy tensor of the quantum field near that horizon in the physical state which corresponds to the Minkowski vacuum before the collision of the waves. It is found that for minimally coupled and conformally coupled scalar fields the respective stress-energy tensors are unbounded in the horizon. The specific form of the divergences suggests that when the semiclassical Einstein equations describing the backreaction of the quantum fields on the space-time geometry are taken into account, the horizon will acquire a curvature singularity. Thus the Killing-Cauchy horizon which is known to be unstable under ''generic'' classical perturbations is also unstable by vacuum polarization. The calculation is done following the point-splitting regularization technique. The dynamical colliding wave space-time has four quite distinct space-time regions, namely, one flat region, two single plane wave regions, and one interaction region. Exact mode solutions of the quantum field equation cannot be found exactly, but the blueshift suffered by the initial modes in the plane wave and interaction regions makes the use of the WKB expansion a suitable method of solution. To ensure the correct regularization of the stress-energy tensor, the initial flat modes propagated into the interaction region must be given to a rather high adiabatic order of approximation. (orig.)
Temperature dependency of silicon structures for magnetic field gradient sensing
Dabsch, Alexander; Rosenberg, Christoph; Stifter, Michael; Keplinger, Franz
2018-02-01
This work describes the temperature dependence of two sensors for magnetic field gradient sensors and demonstrates a structure to compensate for the drift of resonance frequency over a wide temperature range. The temperature effect of the sensing element is based on internal stresses induced by the thermal expansion of material, therefore FEM is used to determine the change of the eigenvalues of the sensing structure. The experimental setup utilizes a Helmholtz coil system to generate the magnetic field and to excite the MEMS structure with Lorentz forces. The MEMS structure is placed on a plate heated with resistors and cooled by a Peltier element to control the plate temperature. In the second part, we describe how one can exploit temperature sensitivity for temperature measurements and we show the opportunity to include the temperature effect to increase the sensitivity of single-crystal silicon made flux density gradient sensors.
Design of a nonscaling fixed field alternating gradient accelerator
Directory of Open Access Journals (Sweden)
D. Trbojevic
2005-05-01
Full Text Available We present a design of nonscaling fixed field alternating gradient accelerators (FFAG minimizing the dispersion action function H. The design is considered both analytically and via computer modeling. We present the basic principles of a nonscaling FFAG lattice and discuss optimization strategies so that one can accelerate over a broad range of momentum with reasonable apertures. Acceleration schemes for muons are discussed.
Tao, Chenyang; Nichols, Thomas E; Hua, Xue; Ching, Christopher R K; Rolls, Edmund T; Thompson, Paul M; Feng, Jianfeng
2017-01-01
We propose a generalized reduced rank latent factor regression model (GRRLF) for the analysis of tensor field responses and high dimensional covariates. The model is motivated by the need from imaging-genetic studies to identify genetic variants that are associated with brain imaging phenotypes, often in the form of high dimensional tensor fields. GRRLF identifies from the structure in the data the effective dimensionality of the data, and then jointly performs dimension reduction of the covariates, dynamic identification of latent factors, and nonparametric estimation of both covariate and latent response fields. After accounting for the latent and covariate effects, GRLLF performs a nonparametric test on the remaining factor of interest. GRRLF provides a better factorization of the signals compared with common solutions, and is less susceptible to overfitting because it exploits the effective dimensionality. The generality and the flexibility of GRRLF also allow various statistical models to be handled in a unified framework and solutions can be efficiently computed. Within the field of neuroimaging, it improves the sensitivity for weak signals and is a promising alternative to existing approaches. The operation of the framework is demonstrated with both synthetic datasets and a real-world neuroimaging example in which the effects of a set of genes on the structure of the brain at the voxel level were measured, and the results compared favorably with those from existing approaches. Copyright © 2016. Published by Elsevier Inc.
TensorLy: Tensor Learning in Python
Kossaifi, Jean; Panagakis, Yannis; Pantic, Maja
2016-01-01
Tensor methods are gaining increasing traction in machine learning. However, there are scant to no resources available to perform tensor learning and decomposition in Python. To answer this need we developed TensorLy. TensorLy is a state of the art general purpose library for tensor learning.
International Nuclear Information System (INIS)
Barber, D.P.
2015-10-01
I extend and update earlier work, summarised in an earlier paper (D.P. Barber, M. Voigt, AIP Conference Proceedings 1149 (28)), whereby the invariant polarisation-tensor field (ITF) for deuterons in storage rings was introduced to complement the invariant spin field (ISF). Taken together, the ITF and the ISF provide a definition of the equilibrium spin density-matrix field which, in turn, offers a clean framework for describing equilibrium spin-1 ensembles in storage rings. I show how to construct the ITF by stroboscopic averaging, I give examples, I discuss adiabatic invariance and I introduce a formalism for describing the effect of noise and damping.
International Nuclear Information System (INIS)
Xia Zhicheng; Nguyen, Bao D.; La Mar, Gerd N.
2000-01-01
The use of dipolar shifts as important constraints in refining molecular structure of paramagnetic metalloproteins by solution NMR is now well established. A crucial initial step in this procedure is the determination of the orientation of the anisotropic paramagnetic susceptibility tensor in the molecular frame which is generated interactively with the structure refinement. The use of dipolar shifts as constraints demands knowledge of the diamagnetic shift, which, however, is very often not directly and easily accessible. We demonstrate that temperature gradients of dipolar shifts can serve as alternative constraints for determining the orientation of the magnetic axes, thereby eliminating the need to estimate the diamagnetic shifts. This approach is tested on low-spin, ferric sperm whale cyanometmyoglobin by determining the orientation, anisotropies and anisotropy temperature gradients by the alternate routes of using dipolar shifts and dipolar shift gradients as constraints. The alternate routes ultimately lead to very similar orientation of the magnetic axes, magnetic anisotropies and magnetic anisotropy temperature gradients which, by inference, would lead to an equally valid description of the molecular structure. It is expected that the use of the dipolar shift temperature gradients, rather than the dipolar shifts directly, as constraints will provide an accurate shortcut in a solution structure determination of a paramagnetic metalloprotein
Constant fields and constant gradients in open ionic channels.
Chen, D P; Barcilon, V; Eisenberg, R S
1992-05-01
Ions enter cells through pores in proteins that are holes in dielectrics. The energy of interaction between ion and charge induced on the dielectric is many kT, and so the dielectric properties of channel and pore are important. We describe ionic movement by (three-dimensional) Nemst-Planck equations (including flux and net charge). Potential is described by Poisson's equation in the pore and Laplace's equation in the channel wall, allowing induced but not permanent charge. Asymptotic expansions are constructed exploiting the long narrow shape of the pore and the relatively high dielectric constant of the pore's contents. The resulting one-dimensional equations can be integrated numerically; they can be analyzed when channels are short or long (compared with the Debye length). Traditional constant field equations are derived if the induced charge is small, e.g., if the channel is short or if the total concentration gradient is zero. A constant gradient of concentration is derived if the channel is long. Plots directly comparable to experiments are given of current vs voltage, reversal potential vs. concentration, and slope conductance vs. concentration. This dielectric theory can easily be tested: its parameters can be determined by traditional constant field measurements. The dielectric theory then predicts current-voltage relations quite different from constant field, usually more linear, when gradients of total concentration are imposed. Numerical analysis shows that the interaction of ion and channel can be described by a mean potential if, but only if, the induced charge is negligible, that is to say, the electric field is spatially constant.
International Nuclear Information System (INIS)
Beig, Robert; Krammer, Werner
2004-01-01
For a conformally flat 3-space, we derive a family of linear second-order partial differential operators which sends vectors into trace-free, symmetric 2-tensors. These maps, which are parametrized by conformal Killing vectors on the 3-space, are such that the divergence of the resulting tensor field depends only on the divergence of the original vector field. In particular, these maps send source-free electric fields into TT tensors. Moreover, if the original vector field is the Coulomb field on R 3 {0}, the resulting tensor fields on R 3 {0} are nothing but the family of TT tensors originally written by Bowen and York
Hess, Siegfried
2015-01-01
This book presents the science of tensors in a didactic way. The various types and ranks of tensors and the physical basis is presented. Cartesian Tensors are needed for the description of directional phenomena in many branches of physics and for the characterization the anisotropy of material properties. The first sections of the book provide an introduction to the vector and tensor algebra and analysis, with applications to physics, at undergraduate level. Second rank tensors, in particular their symmetries, are discussed in detail. Differentiation and integration of fields, including generalizations of the Stokes law and the Gauss theorem, are treated. The physics relevant for the applications in mechanics, quantum mechanics, electrodynamics and hydrodynamics is presented. The second part of the book is devoted to tensors of any rank, at graduate level. Special topics are irreducible, i.e. symmetric traceless tensors, isotropic tensors, multipole potential tensors, spin tensors, integration and spin-...
The stress energy tensor of a locally supersymmetric quantum field on a curved spacetime
International Nuclear Information System (INIS)
Koehler, M.
1995-04-01
For an analogon of the free Wess-Zumino model on Ricci flat spacetimes, the relation between a conserved 'supercurrent' and the point-separated improved energy momentum tensor is investigated and a similar relation as on Minkowski space is established. The expectation value of the latter in any globally Hadamard product state is found to be a priori finite in the coincidence limit if the theory is massive. On arbitrary globally hyperbolic spacetimes the 'supercurrent' is shown to be a well defined operator valued distribution on the GNS Hilbertspace of any globally Hadamard product state. Viewed as a new field, all n-point distributions exist, giving a new example for a Wightman field on that manifold. Moreover, it is shown that this field satisfies a new wave front set spectrum condition in a nontrivial way. (orig.)
Dilaton, antisymmetric tensor and gauge fields in string effective theories at the one-loop level
International Nuclear Information System (INIS)
Mayr, P.; Stieberger, S.
1994-01-01
We investigate the dependence of the gauge couplings on the dilaton field in string effective theories at the one-loop level. First we resolve the discrepancies between statements based on symmetry considerations and explicit calculations in string effective theories on this subject. A calculation of the relevant one-loop scattering amplitudes in string theory gives us further information and allows us to derive the exact form of the corresponding effective lagrangian. In particular there is no dilaton dependent one-loop correction to the holomorphic f - function arising from massive string modes in the loop. In addition we address the coupling of the antisymmetric tensor field to the gauge bosons at one loop. While the string S-matrix elements are not reproduced using the usual supersymmetric lagrangian with the chiral superfield representation for the dilaton field, the analogue lagrangian with the dilaton in a linear multiplet naturally gives the correct answer. (orig.)
International Nuclear Information System (INIS)
Joglekar, S.D.; Misra, A.
1989-01-01
In this paper, we generalize our earlier discussion of renormalization of the energy-momentum tensor in scalar QED to that in non-Abelian gauge theories involving scalar fields. We show the need for adding an improvement term to the conventional energy-momentum tensor. We consider two possible forms for the improvement term: (i) one in which the improvement coefficient is a finite function of bare parameters of the theory (so that the energy-momentum tensor can be derived from an action that is a finite function of bare quantities); (ii) one in which the improvement coefficient is a finite quantity, i.e., a finite function of renormalized parameters. We establish a negative result; viz., neither form leads to a finite energy-momentum tensor to O(e 2 λ/sup n/)
International Nuclear Information System (INIS)
Ikhdair, Sameer M.; Hamzavi, Majid
2013-01-01
Approximate analytical solutions of the Dirac equation for Tietz—Hua (TH) potential including Coulomb-like tensor (CLT) potential with arbitrary spin—orbit quantum number κ are obtained within the Pekeris approximation scheme to deal with the spin—orbit coupling terms κ(κ ± 1)r −2 . Under the exact spin and pseudospin symmetric limitation, bound state energy eigenvalues and associated unnormalized two-component wave functions of the Dirac particle in the field of both attractive and repulsive TH potential with tensor potential are found using the parametric Nikiforov—Uvarov (NU) method. The cases of the Morse oscillator with tensor potential, the generalized Morse oscillator with tensor potential, and the non-relativistic limits have been investigated. (general)
Enhancement of electric and magnetic wave fields at density gradients
Directory of Open Access Journals (Sweden)
A. Reiniusson
2006-03-01
Full Text Available We use Freja satellite data to investigate irregular small-scale density variations. The observations are made in the auroral region at about 1000-1700 km. The density variations are a few percent, and the structures are found to be spatial down to a scale length of a few ion gyroradii. Irregular density variations are often found in an environment of whistler mode/lower hybrid waves and we show that at the density gradients both the electric and magnetic wave fields are enhanced.
Buchner, Abel-John; Lozano-Durán, Adrián; Kitsios, Vassili; Atkinson, Callum; Soria, Julio
2016-04-01
Previous works have shown that momentum transfer in the wall-normal direction within turbulent wall-bounded flows occurs primarily within coherent structures defined by regions of intense Reynolds stress [1]. Such structures may be classified into wall-attached and wall-detached structures with the latter being typically weak, small-scale, and isotropically oriented, while the former are larger and carry most of the Reynolds stresses. The mean velocity fluctuation within each structure may also be used to separate structures by their dynamic properties. This study aims to extract information regarding the scales, kinematics and dynamics of these structures within the topological framework of the invariants of the velocity gradient tensor (VGT). The local topological characteristics of these intense Reynolds stress structures are compared to the topological characteristics of vortex clusters defined by the discriminant of the velocity gradient tensor. The alignment of vorticity with the principal strain directions within these structures is also determined, and the implications of these findings are discussed.
TensorLy: Tensor Learning in Python
Kossaifi, Jean; Panagakis, Yannis; Pantic, Maja
2016-01-01
Tensor methods are gaining increasing traction in machine learning. However, there are scant to no resources available to perform tensor learning and decomposition in Python. To answer this need we developed TensorLy. TensorLy is a state of the art general purpose library for tensor learning. Written in Python, it aims at following the same standard adopted by the main projects of the Python scientific community and fully integrating with these. It allows for fast and straightforward tensor d...
ESTIMATION OF THE CONCRETE PAVEMENT TEMPERATURE FIELDS AND THEIR GRADIENTS
Directory of Open Access Journals (Sweden)
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.
Study of the characteristics of crust stress field in East China by inversion of stress tensor
International Nuclear Information System (INIS)
Huilan, Z.; Rugang, D.
1991-12-01
This paper combines the search procedure with the optimization procedure to inverse the average stress tensor, and applies this method to study the crustal stress field using data of the solution of P wave first motion. By dealing with the data of Haicheng, Tangshan, Xingtai, Anyang, Liyang, Taiwan, Fujian and Guangdong areas, we obtain the characteristics of crust stress field of East China. The directions of the principal pressure stress always possess a small dip angle, but the azimuths vary from NEE (in north part of East China) to SEE (in the south part). This frame probably is related to the push-extrusive effects of the northwestern Pacific plate from NEE and the Philippine plate from SEE. (author). 5 refs, 8 figs, 4 tabs
Dudarev, S. L.; Ma, Pui-Wai
2018-03-01
Density functional theory (DFT) calculations show that self-interstitial atom (SIA) defects in nonmagnetic body-centered-cubic (bcc) metals adopt strongly anisotropic configurations, elongated in the direction [S. Han et al., Phys. Rev. B 66, 220101 (2002), 10.1103/PhysRevB.66.220101; D. Nguyen-Manh et al., Phys. Rev. B 73, 020101 (2006), 10.1103/PhysRevB.73.020101; P. M. Derlet et al., Phys. Rev. B 76, 054107 (2007), 10.1103/PhysRevB.76.054107; S. L. Dudarev, Annu. Rev. Mater. Res. 43, 35 (2013), 10.1146/annurev-matsci-071312-121626]. Elastic distortions, associated with such anisotropic atomic structures, appear similar to distortions around small prismatic dislocation loops, although the extent of this similarity has never been quantified. We derive analytical formulas for the dipole tensors of SIA defects, which show that, in addition to the prismatic dislocation looplike character, the elastic field of a SIA defect also has a significant isotropic dilatation component. Using empirical potentials and DFT calculations, we parametrize dipole tensors of defects for all the nonmagnetic bcc transition metals. This enables a quantitative evaluation of the energy of elastic interaction between the defects, which also shows that in a periodic three-dimensional simple cubic arrangement of crowdions, long-range elastic interactions between a defect and all its images favor a orientation of the defect.
Linear Invariant Tensor Interpolation Applied to Cardiac Diffusion Tensor MRI
Gahm, Jin Kyu; Wisniewski, Nicholas; Kindlmann, Gordon; Kung, Geoffrey L.; Klug, William S.; Garfinkel, Alan; Ennis, Daniel B.
2015-01-01
Purpose Various methods exist for interpolating diffusion tensor fields, but none of them linearly interpolate tensor shape attributes. Linear interpolation is expected not to introduce spurious changes in tensor shape. Methods Herein we define a new linear invariant (LI) tensor interpolation method that linearly interpolates components of tensor shape (tensor invariants) and recapitulates the interpolated tensor from the linearly interpolated tensor invariants and the eigenvectors of a linearly interpolated tensor. The LI tensor interpolation method is compared to the Euclidean (EU), affine-invariant Riemannian (AI), log-Euclidean (LE) and geodesic-loxodrome (GL) interpolation methods using both a synthetic tensor field and three experimentally measured cardiac DT-MRI datasets. Results EU, AI, and LE introduce significant microstructural bias, which can be avoided through the use of GL or LI. Conclusion GL introduces the least microstructural bias, but LI tensor interpolation performs very similarly and at substantially reduced computational cost. PMID:23286085
Currents and the energy-momentum tensor in classical field theory: a fresh look at an old problem
International Nuclear Information System (INIS)
Forger, Michael; Roemer, Hartmann
2004-01-01
We give a comprehensive review of various methods to define currents and the energy-momentum tensor in classical field theory, with emphasis on a geometric point of view. The necessity of 'improving' the expressions provided by the canonical Noether procedure is addressed and given an adequate geometric framework. The main new ingredient is the explicit formulation of a principle of 'ultralocality' with respect to the symmetry generators, which is shown to fix the ambiguity inherent in the procedure of improvement and guide it towards a unique answer: when combined with the appropriate splitting of the fields into sectors, it leads to the well-known expressions for the current as the variational derivative of the matter field Lagrangian with respect to the gauge field and for the energy-momentum tensor as the variational derivative of the matter field Lagrangian with respect to the metric tensor. In the second case, the procedure is shown to work even when the matter field Lagrangian depends explicitly on the curvature, thus establishing the correct relation between scale invariance, in the form of local Weyl invariance 'on shell', and tracelessness of the energy-momentum tensor, required for a consistent definition of the concept of a conformal field theory
Bossa, Matías Nicolás; Zacur, Ernesto; Olmos, Salvador
2009-01-01
Tensor-based morphometry (TBM) is an analysis technique where anatomical information is characterized by means of the spatial transformations between a customized template and observed images. Therefore, accurate inter-subject non-rigid registration is an essential prerrequisite. Further statistical analysis of the spatial transformations is used to highlight some useful information, such as local statistical differences among populations. With the new advent of recent and powerful non-rigid registration algorithms based on the large deformation paradigm, TBM is being increasingly used. In this work we evaluate the statistical power of TBM using stationary velocity field diffeomorphic registration in a large population of subjects from Alzheimer's Disease Neuroimaging Initiative project. The proposed methodology provided atrophy maps with very detailed anatomical resolution and with a high significance compared with results published recently on the same data set.
Choi, Bup Kyung; Oh, Tong In; Sajib, Saurav Zk; Kim, Jin Woong; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je
2017-04-01
To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation. Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor. The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy. An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through in vivo and in situ experiments.
Local nematic susceptibility in stressed BaFe2As2 from NMR electric field gradient measurements
Kissikov, T.; Sarkar, R.; Lawson, M.; Bush, B. T.; Timmons, E. I.; Tanatar, M. A.; Prozorov, R.; Bud'ko, S. L.; Canfield, P. C.; Fernandes, R. M.; Goh, W. F.; Pickett, W. E.; Curro, N. J.
2017-12-01
The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe2As2 . We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.
Electric-field gradient characterization at 181Ta impurities in sapphire single crystals
International Nuclear Information System (INIS)
Renteria, M.; Darriba, G.N.; Errico, L.A.; Munoz, E.L.; Eversheim, P.D.
2005-01-01
We report Perturbed-Angular-Correlation (PAC) experiments on corundum Al 2 O 3 single crystals implanted with 181 Hf/ 181 Ta ions at the ISKP at Bonn and measured at La Plata with high efficiency and time-resolution. The magnitude, asymmetry, and orientation (with respect to the crystalline axes) of the electric-field gradient (EFG) tensor were determined measuring the spin-rotation curves as a function of different orientations of the single crystals relative to the detector system. These results are analyzed in the framework of point-charge model and ab initio Full-Potential Linearized-Augmented Plane Wave calculations, and compared with EFG results coming from PAC experiments with 111 In/ 111 Cd impurities. This combined study enables the determination of lattice relaxations induced by the presence of the impurity and the state of charge of a deep impurity donor level in the band gap of the semiconductor. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Electric-field gradient characterization at {sup 181}Ta impurities in sapphire single crystals
Energy Technology Data Exchange (ETDEWEB)
Renteria, M.; Darriba, G.N.; Errico, L.A.; Munoz, E.L. [Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Eversheim, P.D. [Helmholtz-Institut fuer Strahlen-und Kernphysik (ISKP), Universitaet Bonn, Nussallee 14-16, 53115 Bonn (Germany)
2005-07-01
We report Perturbed-Angular-Correlation (PAC) experiments on corundum Al{sub 2}O{sub 3} single crystals implanted with {sup 181}Hf/{sup 181}Ta ions at the ISKP at Bonn and measured at La Plata with high efficiency and time-resolution. The magnitude, asymmetry, and orientation (with respect to the crystalline axes) of the electric-field gradient (EFG) tensor were determined measuring the spin-rotation curves as a function of different orientations of the single crystals relative to the detector system. These results are analyzed in the framework of point-charge model and ab initio Full-Potential Linearized-Augmented Plane Wave calculations, and compared with EFG results coming from PAC experiments with {sup 111}In/{sup 111}Cd impurities. This combined study enables the determination of lattice relaxations induced by the presence of the impurity and the state of charge of a deep impurity donor level in the band gap of the semiconductor. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Calculation of electric-field gradient in a dilute alloy of Al-Mg
Rao, K. K.; Mohapatra, N. C.
1980-10-01
The existing calculations of electric-field gradient (EFG) in dilute Al-based alloys with nonmagnetic substitutional impurities are unsatisfactory on two accounts. First, the magnitudes of the calculated EFG are very different from the experimental results. Second, these calculations predict an axially symmetric EFG at the nearest-neighbor host sites from the impurity ion, contrary to experimental observations. The discrepancy between experiments and these calculations is largely due to the neglect of the size-effect EFG in the latter. In the present paper, we have calculated in the case of Al-Mg alloy contributions to EFG from both the valence effect and the size effect. The EFG from the valence effect has been calculated from a free-electron-screening charge distribution assumed for the alloy. The size-effect EFG tensor, linear in local strain around the impurity, has been evaluated in the elastic continuum approximation. The present result not only provides improved values for the magnitudes of EFG but also predicts a nonzero asymmetry parameter at the nearest-neighbor host sites from the impurity ion, in fair agreement with experiment.
Continuity equations for bound electromagnetic field and the electromagnetic energy-momentum tensor
International Nuclear Information System (INIS)
Kholmetskii, A L; Missevitch, O V; Yarman, T
2011-01-01
We analyze the application of the Poynting theorem to the bound (velocity-dependent) electromagnetic (EM) field and show that an often-used arbitrary elimination of the term of self-interaction in the product j·E (where j is the current density and E the electric field) represents, in general, an illegitimate operation, which leads to incorrect physical consequences. We propose correct ways of eliminating the terms of self-interaction from the Poynting theorem to transform it into the form that is convenient for problems with bound EM field, which yield the continuity equations for the proper EM energy density, the interaction part of EM energy density and the total EM energy density of bound fields, respectively. These equations indicate the incompleteness of the common EM energy-momentum tensor, and in our analysis, we find a missed term in its structure, which makes its trace non-vanished. Some implications of these results are discussed, in particular, in view of the notion of EM mass of charged particles.
Continuity equations for bound electromagnetic field and the electromagnetic energy-momentum tensor
Energy Technology Data Exchange (ETDEWEB)
Kholmetskii, A L [Department of Physics, Belarusian State University, 4 Nezavisimosti Avenue, 220030 Minsk (Belarus); Missevitch, O V [Institute for Nuclear Problems, Belarusian State University, 11 Bobruiskaya Street, 220030 Minsk (Belarus); Yarman, T, E-mail: khol123@yahoo.com [Department of Engineering, Okan University, Akfirat, Istanbul, Turkey and Savronik, Eskisehir (Turkey)
2011-05-01
We analyze the application of the Poynting theorem to the bound (velocity-dependent) electromagnetic (EM) field and show that an often-used arbitrary elimination of the term of self-interaction in the product j{center_dot}E (where j is the current density and E the electric field) represents, in general, an illegitimate operation, which leads to incorrect physical consequences. We propose correct ways of eliminating the terms of self-interaction from the Poynting theorem to transform it into the form that is convenient for problems with bound EM field, which yield the continuity equations for the proper EM energy density, the interaction part of EM energy density and the total EM energy density of bound fields, respectively. These equations indicate the incompleteness of the common EM energy-momentum tensor, and in our analysis, we find a missed term in its structure, which makes its trace non-vanished. Some implications of these results are discussed, in particular, in view of the notion of EM mass of charged particles.
Milton, Kimball A.; Fulling, Stephen A.; Parashar, Prachi; Kalauni, Pushpa; Murphy, Taylor
2016-04-01
Motivated by a desire to understand quantum fluctuation energy densities and stress within a spatially varying dielectric medium, we examine the vacuum expectation value for the stress tensor of a scalar field with arbitrary conformal parameter, in the background of a given potential that depends on only one spatial coordinate. We regulate the expressions by incorporating a temporal-spatial cutoff in the (imaginary) time and transverse-spatial directions. The divergences are captured by the zeroth- and second-order WKB approximations. Then the stress tensor is "renormalized" by omitting the terms that depend on the cutoff. The ambiguities that inevitably arise in this procedure are both duly noted and restricted by imposing certain physical conditions; one result is that the renormalized stress tensor exhibits the expected trace anomaly. The renormalized stress tensor exhibits no pressure anomaly, in that the principle of virtual work is satisfied for motions in a transverse direction. We then consider a potential that defines a wall, a one-dimensional potential that vanishes for z 0 , for z >0 . Previously, the stress tensor had been computed outside of the wall, whereas now we compute all components of the stress tensor in the interior of the wall. The full finite stress tensor is computed numerically for the two cases where explicit solutions to the differential equation are available, α =1 and 2. The energy density exhibits an inverse linear divergence as the boundary is approached from the inside for a linear potential, and a logarithmic divergence for a quadratic potential. Finally, the interaction between two such walls is computed, and it is shown that the attractive Casimir pressure between the two walls also satisfies the principle of virtual work (i.e., the pressure equals the negative derivative of the energy with respect to the distance between the walls).
International Nuclear Information System (INIS)
Choudhury, Sayantan
2015-01-01
In this paper my prime objective is to explain the generation of large tensor-to-scalar ratio from the single field sub-Planckian inflationary paradigm within Randall–Sundrum (RS) single braneworld scenario in a model independent fashion. By explicit computation I have shown that the effective field theory prescription of brane inflation within RS single brane setup is consistent with sub-Planckian excursion of the inflaton field, which will further generate large value of tensor-to-scalar ratio, provided the energy density for inflaton degrees of freedom is high enough compared to the brane tension in high energy regime. Finally, I have mentioned the stringent theoretical constraint on positive brane tension, cut-off of the quantum gravity scale and bulk cosmological constant to get sub-Planckian field excursion along with large tensor-to-scalar ratio as recently observed by BICEP2 or at least generates the tensor-to-scalar ratio consistent with the upper bound of Planck (2013 and 2015) data and Planck+BICEP2+Keck Array joint constraint
International Nuclear Information System (INIS)
Sohnius, M.; West, P.
1982-01-01
The tensor calculus for the new alternative minimal auxiliary field formulation of N = 1 supergravity is given. It is used to construct the couplings of this formulation of supergravity to matter. These couplings are found to be different, in several respects to those of the old minimal formulation of N = 1 supergravity. (orig.)
Electromagnetic Field Theory in (N+1)-Space-Time : AModern Time-Domain Tensor/Array Introduction
De Hoop, A.T.
2012-01-01
In this paper, a modern time-domain introduction is presented for electromagnetic field theory in (N+1)-spacetime. It uses a consistent tensor/array notation that accommodates the description of electromagnetic phenomena in N-dimensional space (plus time), a requirement that turns up in present-day
Energy Technology Data Exchange (ETDEWEB)
Polak, R., E-mail: rudolf.polak@jh-inst.cas.cz [J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejskova 3, 182 23 Prague 8 (Czech Republic); Fiser, J. [Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2 (Czech Republic)
2010-09-14
Graphical abstract: Nitroxyl, nitrosomethane and nitrosoethylene were studied using high level ab initio methods with the main aim to provide a description of the nitrogen electric field gradients, relate them to the field gradient values of the free NO radical and use them for the evaluation of the {sup 14}N quadrupole coupling tensor elements. - Abstract: Electric field gradients (EFGs) at the nitrogen nuclei of nitroxyl, nitrosomethane and nitrosoethylene were calculated by employing the complete-active-space self-consistent field (CASSCF), internally contracted multireference configuration interaction (icMRCI) and single-configuration coupled-cluster (CC) methods with correlation-consistent basis sets at the levels of attainable accuracy. Changes in the p{sigma} and p{pi} atomic orbital populations were used to rationalize the differences between the N EFG tensor components related to the nitroso compound and separate nitric oxide. Calculated {sup 14}N nuclear quadrupole coupling constants were found in reasonable accord with experimental values. Comparison of electric dipole moments and potential energy characteristics with external values served to testify to good overall quality of the wave functions used in our calculations.
Energy Technology Data Exchange (ETDEWEB)
Bongaarts, P.J.M.
1977-07-01
An approach to the investigation of the Maxwell field in the framework of axiomatic quantum field theory is presented which employs Borchers' algebraic reformulation of Wightman theory in a modified form adapted to the special features of the electromagnetic field. This makes it possible to clarify the relation between tensor and potential field operators, the meaning and properties of different gauges, the sense in which field equations hold and the properties of state spaces with their special subspaces.
Anderson, David; Yunes, Nicolás
2017-09-01
Scalar-tensor theories of gravity modify general relativity by introducing a scalar field that couples nonminimally to the metric tensor, while satisfying the weak-equivalence principle. These theories are interesting because they have the potential to simultaneously suppress modifications to Einstein's theory on Solar System scales, while introducing large deviations in the strong field of neutron stars. Scalar-tensor theories can be classified through the choice of conformal factor, a scalar that regulates the coupling between matter and the metric in the Einstein frame. The class defined by a Gaussian conformal factor with a negative exponent has been studied the most because it leads to spontaneous scalarization (i.e. the sudden activation of the scalar field in neutron stars), which consequently leads to large deviations from general relativity in the strong field. This class, however, has recently been shown to be in conflict with Solar System observations when accounting for the cosmological evolution of the scalar field. We here study whether this remains the case when the exponent of the conformal factor is positive, as well as in another class of theories defined by a hyperbolic conformal factor. We find that in both of these scalar-tensor theories, Solar System tests are passed only in a very small subset of coupling parameter space, for a large set of initial conditions compatible with big bang nucleosynthesis. However, while we find that it is possible for neutron stars to scalarize, one must carefully select the coupling parameter to do so, and even then, the scalar charge is typically 2 orders of magnitude smaller than in the negative-exponent case. Our study suggests that future work on scalar-tensor gravity, for example in the context of tests of general relativity with gravitational waves from neutron star binaries, should be carried out within the positive coupling parameter class.
Higher groupoid bundles, higher spaces, and self-dual tensor field equations
Energy Technology Data Exchange (ETDEWEB)
Jurco, Branislav [Charles University in Prague, Faculty of Mathematics and Physics, Mathematical Institute, Prague (Czech Republic); Saemann, Christian [Maxwell Institute for Mathematical Sciences, Department of Mathematics, Heriot-Watt University, Edinburgh (United Kingdom); Wolf, Martin [Department of Mathematics, University of Surrey, Guildford (United Kingdom)
2016-08-15
We develop a description of higher gauge theory with higher groupoids as gauge structure from first principles. This approach captures ordinary gauge theories and gauged sigma models as well as their categorifications on a very general class of (higher) spaces comprising presentable differentiable stacks, as e.g. orbifolds. We start off with a self-contained review on simplicial sets as models of (∞, 1)-categories. We then discuss principal bundles in terms of simplicial maps and their homotopies. We explain in detail a differentiation procedure, suggested by Severa, that maps higher groupoids to L{sub ∞}-algebroids. Generalising this procedure, we define connections for higher groupoid bundles. As an application, we obtain six-dimensional superconformal field theories via a Penrose-Ward transform of higher groupoid bundles over a twistor space. This construction reduces the search for non-Abelian self-dual tensor field equations in six dimensions to a search for the appropriate (higher) gauge structure. The treatment aims to be accessible to theoretical physicists. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Electric-field gradients at Ta impurities in Sc{sub 2}O{sub 3} semiconductor
Energy Technology Data Exchange (ETDEWEB)
Richard, Diego, E-mail: richard@fisica.unlp.edu.ar [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Munoz, Emiliano L. [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Errico, Leonardo A. [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, 2700 Pergamino, Argentina. (Argentina); Renteria, Mario [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina)
2012-08-15
In this work we present an ab initio study of Ta-doped Sc{sub 2}O{sub 3} semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential {gamma}-{gamma} Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor.
Non-ionic contributions to the electric-field gradient at 111Cd/181Ta impurities in bixbyites
International Nuclear Information System (INIS)
Renteria, Mario; Freitag, Kristian; Errico, Leonardo A.
1999-01-01
The electric-field-gradient (EFG) tensor at both cation sites of the bixbyite structure in 181 Hf-implanted Lu- and Sm-sesquioxides was determined by the PAC technique. The cumulated EFG data at Ta-impurity sites in binary oxides enable us to discuss the 'universal' character of the empirical correlation between local and ionic contributions to the EFG in these systems. An EFG factorization in terms of the electronic characteristics of the probe and the geometry of the cation coordination is proposed, which explains the experimental EFG results at Ta/Cd impurity sites in bixbyites and agrees with a simplified decomposition of the EFG valence contribution coming from ab-initio calculations
International Nuclear Information System (INIS)
Dappiagi, Claudio; Hack, Thomas-Paul; Pinamonti, Nicola
2009-03-01
We discuss from scratch the classical structure of Dirac spinors on an arbitrary globally hyperbolic, Lorentzian spacetime, their formulation as a locally covariant quantum field theory, and the associated notion of a Hadamard state. Eventually, we develop the notion of Wick polynomials for spinor fields, and we employ the latter to construct a covariantly conserved stress-energy tensor suited for back-reaction computations. We explicitly calculate its trace anomaly in particular. (orig.)
Bossa, Matias; Zacur, Ernesto; Olmos, Salvador
2010-07-01
Tensor-based morphometry (TBM) is an analysis technique where anatomical information is characterized by means of the spatial transformations mapping a customized template with the observed images. Therefore, accurate inter-subject non-rigid registration is an essential prerequisite for both template estimation and image warping. Subsequent statistical analysis on the spatial transformations is performed to highlight voxel-wise differences. Most of previous TBM studies did not explore the influence of the registration parameters, such as the parameters defining the deformation and the regularization models. In this work performance evaluation of TBM using stationary velocity field (SVF) diffeomorphic registration was performed in a subset of subjects from Alzheimer's Disease Neuroimaging Initiative (ADNI) study. A wide range of values of the registration parameters that define the transformation smoothness and the balance between image matching and regularization were explored in the evaluation. The proposed methodology provided brain atrophy maps with very detailed anatomical resolution and with a high significance level compared with results recently published on the same data set using a non-linear elastic registration method. Copyright (c) 2010 Elsevier Inc. All rights reserved.
On the large N limit, Wilson Loops, Confinement and Composite Antisymmetric Tensor Field theories
Castro, C
2004-01-01
A novel approach to evaluate the Wilson loops asociated with a $ SU ( \\infty )$ gauge theory in terms of pure string degrees of freedom is presented. It is based on the Guendelman-Nissimov-Pacheva formulation of composite antisymmetric tensor field theories of area (volume ) preserving diffeomorphisms which admit $p$-brane solutions and which provide a $new$ route to scale symmetry breaking and confinement in Yang-Mills theory. The quantum effects are discussed and we evaluate the vacuum expectation values (vev) of the Wilson loops in the large $N$ limit of the $quenched$ reduced $SU(N)$ Yang-Mills theory in terms of a path integral involving pure string degrees of freedom. The $quenched$ approximation is necessary to avoid a crumpling of the string world-sheet giving rise to very large Hausdorff dimensions as pointed out by Olesen. The approach is also consistent with the recent results based on the AdS/CFT correspondence and dual QCD models (dual Higgs model with dual Dirac strings ). More general Loop wav...
Photodetachment of negative ion in a gradient electric field near a metal surface
International Nuclear Information System (INIS)
Liu Tian-Qi; Wang De-Hua; Han Cai; Liu Jiang; Liang Dong-Qi; Xie Si-Cheng
2012-01-01
Based on closed-orbit theory, the photodetachment of H − in a gradient electric field near a metal surface is studied. It is demonstrated that the gradient electric field has a significant influence on the photodetachment of negative ions near a metal surface. With the increase of the gradient of the electric field, the oscillation in the photodetachment cross section becomes strengthened. Besides, in contrast to the photodetachment of H − near a metal surface in a uniform electric field, the oscillating amplitude and the oscillating region in the cross section of a gradient electric field also become enlarged. Therefore, we can use the gradient electric field to control the photodetachment of negative ions near a metal surface. We hope that our results will be useful for understanding the photodetachment of negative ions in the vicinity of surfaces, cavities, and ion traps. (atomic and molecular physics)
Tensor spherical harmonics and tensor multipoles. II. Minkowski space
International Nuclear Information System (INIS)
Daumens, M.; Minnaert, P.
1976-01-01
The bases of tensor spherical harmonics and of tensor multipoles discussed in the preceding paper are generalized in the Hilbert space of Minkowski tensor fields. The transformation properties of the tensor multipoles under Lorentz transformation lead to the notion of irreducible tensor multipoles. We show that the usual 4-vector multipoles are themselves irreducible, and we build the irreducible tensor multipoles of the second order. We also give their relations with the symmetric tensor multipoles defined by Zerilli for application to the gravitational radiation
Bouchard, Louis-Serge; Pines, Alexander; Demas, Vasiliki
2014-01-21
A system and method for Fourier encoding a nuclear magnetic resonance (NMR) signal is disclosed. A static magnetic field B.sub.0 is provided along a first direction. An NMR signal from the sample is Fourier encoded by applying a rotating-frame gradient field B.sub.G superimposed on the B.sub.0, where the B.sub.G comprises a vector component rotating in a plane perpendicular to the first direction at an angular frequency .omega.in a laboratory frame. The Fourier-encoded NMR signal is detected.
Salinas-Muciño, G.; Torres-García, E.; Hidalgo-Tobon, S.
2012-10-01
The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. MRI requires the use of gradient coils that generate magnetic fields, which vary linearly with position over the imaging volume. Safety issues have been a motivation to study deeply the relation between the interaction of gradient magnetic field and the peripheral nerve stimulation. In this work is presented a numerical modeling between the concomitant magnetic fields produced by the gradient coils and the electric field induced in a cube with σ conductivity by the gradient field switching in pulse sequences as Eco planar Imaging (EPI), due to this kind of sequence is the most used in advance applications of magnetic resonance imaging as functional MRI, cardiac imaging or diffusion.
Ducasse, Éric; Yaacoubi, Slah
2010-01-01
A tensor Hankel transform (THT) is defined for vector fields, such as displacement, and second-order tensor fields, such as stress or strain. The THT establishes a bijection between the real space and the wave-vector domain, and, remarkably, cannot be reduced to a scalar transform applied separately to each component. One of the advantages of this approach is that some standard elasticity problems can be concisely rewritten by applying this tensor integral transform coupled with an azimuthal Fourier series expansion. A simple and compact formulation of the boundary conditions is also achieved. Thanks to the THT, we obtain for each azimuthal wavenumber and each azimuthal direction exactly the same wave equation as for a standard 2D model of elastic wave propagation. Thus, waves similar to the standard plane P, SV and SH waves are naturally found. Lastly, the THT is used to calculate the ultrasonic field in an isotropic cylindrical leaky waveguide, the walls of which radiating into a surrounding elastic medium, by using a standard scattering approach.
A Test for Tensor Lorentz Violating Fields Using a Rotating Comagnetometer
Smiciklas, Marc; Brown, Justin; Romalis, Michael
2011-05-01
The effective low-energy model of Lorentz violation described by the Standard Model Extension (SME) includes a number of tensor spin interactions that violate Lorentz symmetry but not CPT. Such interactions could be induced in popular Lorentz-violating theories, such as Horava theory of gravity and doubly-special relativity. We are performing a search for Lorentz-violating tensor spin interactions using a K-Rb-21Ne comagnetometer. Compared to our previous work with a K-3He comagnetometer, we expect to achieve significant improvements in energy sensitivity due to the smaller magnetic moment of 21Ne and use of hybrid optical pumping. Preliminary results searching for semisidereal modulations of the comagnetometer signal indicate that limits on tensor Lorentz violation can be improved by more than an order of magnitude. This research funded by NSF grant PHY-0969862
Evaporation rate of water as a function of a magnetic field and field gradient.
Guo, Yun-Zhu; Yin, Da-Chuan; Cao, Hui-Ling; Shi, Jian-Yu; Zhang, Chen-Yan; Liu, Yong-Ming; Huang, Huan-Huan; Liu, Yue; Wang, Yan; Guo, Wei-Hong; Qian, Ai-Rong; Shang, Peng
2012-12-11
The effect of magnetic fields on water is still a highly controversial topic despite the vast amount of research devoted to this topic in past decades. Enhanced water evaporation in a magnetic field, however, is less disputed. The underlying mechanism for this phenomenon has been investigated in previous studies. In this paper, we present an investigation of the evaporation of water in a large gradient magnetic field. The evaporation of pure water at simulated gravity positions (0 gravity level (ab. g), 1 g, 1.56 g and 1.96 g) in a superconducting magnet was compared with that in the absence of the magnetic field. The results showed that the evaporation of water was indeed faster in the magnetic field than in the absence of the magnetic field. Furthermore, the amount of water evaporation differed depending on the position of the sample within the magnetic field. In particular, the evaporation at 0 g was clearly faster than that at other positions. The results are discussed from the point of view of the evaporation surface area of the water/air interface and the convection induced by the magnetization force due to the difference in the magnetic susceptibility of water vapor and the surrounding air.
Evaporation Rate of Water as a Function of a Magnetic Field and Field Gradient
Guo, Yun-Zhu; Yin, Da-Chuan; Cao, Hui-Ling; Shi, Jian-Yu; Zhang, Chen-Yan; Liu, Yong-Ming; Huang, Huan-Huan; Liu, Yue; Wang, Yan; Guo, Wei-Hong; Qian, Ai-Rong; Shang, Peng
2012-01-01
The effect of magnetic fields on water is still a highly controversial topic despite the vast amount of research devoted to this topic in past decades. Enhanced water evaporation in a magnetic field, however, is less disputed. The underlying mechanism for this phenomenon has been investigated in previous studies. In this paper, we present an investigation of the evaporation of water in a large gradient magnetic field. The evaporation of pure water at simulated gravity positions (0 gravity level (ab. g), 1 g, 1.56 g and 1.96 g) in a superconducting magnet was compared with that in the absence of the magnetic field. The results showed that the evaporation of water was indeed faster in the magnetic field than in the absence of the magnetic field. Furthermore, the amount of water evaporation differed depending on the position of the sample within the magnetic field. In particular, the evaporation at 0 g was clearly faster than that at other positions. The results are discussed from the point of view of the evaporation surface area of the water/air interface and the convection induced by the magnetization force due to the difference in the magnetic susceptibility of water vapor and the surrounding air. PMID:23443127
International Nuclear Information System (INIS)
Witalis, E.A.
1965-12-01
Rigorous derivations are given of the basic equations and methods available for the analysis of transverse MHD flow when Hall currents are not suppressed. The gas flow is taken to be incompressible and viscous with uniform tensor conductivity and arbitrary magnetic Reynold's number. The magnetic field is perpendicular to the flow and has variable strength. Analytical solutions can be obtained either in terms of the induced magnetic field or from two types of electric potential. The relevant set of suitable simplifications, restrictive conditions and boundary value considerations for each method is given
International Nuclear Information System (INIS)
Antoci, S.; Mihich, L.
1997-01-01
Given the present status of the problem of the electromagnetic energy tensor in matter, there is perhaps use in recalling a forgotten argument given in 1923 by W. Gordon. Let us consider a material medium which is homogeneous and isotropic when observed in its rest frame. For such a medium, Gordon's argument allows to reduce the above-mentioned problem to an analogous one, defined in a general relativistic vacuum. For the latter problem the form of the Lagrangian is known already, hence the determination of the energy tensor is a straightforward matter. One just performs the Hamiltonian derivative of the Lagrangian chosen in this way with respect to the true metric g ik . Abraham's tensor is thus selected as the electromagnetic energy tensor for a medium which is homogeneous and isotropic in its rest frame
Energy Technology Data Exchange (ETDEWEB)
Xu, Fei [Key Laboratory of Fiber Optic Sensing Technology and Information Processing, Ministry of Education, Wuhan University of Technology, Wuhan 430070 (China); Huang, Jiahao, E-mail: hjiahao@mail2.sysu.edu.cn [TianQin Research Center & School of Physics and Astronomy, Sun Yat-Sen University, SYSU Zhuhai Campus, Zhuhai 519082 (China); Liu, Quan [Key Laboratory of Fiber Optic Sensing Technology and Information Processing, Ministry of Education, Wuhan University of Technology, Wuhan 430070 (China)
2017-03-03
Highlights: • A scheme for detecting magnetic field gradients via a double-well two-component Bose–Einstein condensate interferometer. • The magnetic field gradient can be extracted by either the spin population or the external state. • Our proposal is potentially sensitive to weak magnetic field inhomogeneity due to its small sensor size. - Abstract: We have proposed a scheme to detect magnetic field gradients via an interferometer based on a double-well two-component Bose–Einstein condensate (BEC). Utilizing a sequence of quantum control operations on both external and internal degree of the BEC, one can extract the magnetic field gradients by measuring either the population in one component or the fidelity between the final external state and the initial ground state. Our scheme can be implemented by current experimental techniques of manipulating ultracold atoms.
PHASE GRADIENT METHOD OF MAGNETIC FIELD MEASUREMENTS IN ELECTRIC VEHICLES
Directory of Open Access Journals (Sweden)
N. G. Ptitsyna
2013-01-01
Full Text Available Operation of electric and hybrid vehicles demands real time magnetic field control, for instance, for fire and electromagnetic safety. The article deals with a method of magnetic field measurements onboard electric cars taking into account peculiar features of these fields. The method is based on differential methods of measurements, and minimizes the quantity of magnetic sensors.
Near field plasmonic gradient effects on high vacuum tip-enhanced Raman spectroscopy.
Fang, Yurui; Zhang, Zhenglong; Chen, Li; Sun, Mengtao
2015-01-14
Near field gradient effects in high vacuum tip-enhanced Raman spectroscopy (HV-TERS) are a recent developing ultra-sensitive optical and spectral analysis technology on the nanoscale, based on the plasmons and plasmonic gradient enhancement in the near field and under high vacuum. HV-TERS can not only be used to detect ultra-sensitive Raman spectra enhanced by surface plasmon, but also to detect clear molecular IR-active modes enhanced by strongly plasmonic gradient. Furthermore, the molecular overtone modes and combinational modes can also be experimentally measured, where the Fermi resonance and Darling-Dennison resonance were successfully observed in HV-TERS. Theoretical calculations using electromagnetic field theory firmly supported experimental observation. The intensity ratio of the plasmon gradient term over the linear plasmon term can reach values greater than 1. Theoretical calculations also revealed that with the increase in gap distance between tip and substrate, the decrease in the plasmon gradient was more significant than the decrease in plasmon intensity, which is the reason that the gradient Raman can be only observed in the near field. Recent experimental results of near field gradient effects on HV-TERS were summarized, following the section of the theoretical analysis.
Soibelman, Yan
1997-01-01
We introduce the notion of meromorphic tensor category and illustrate it in several examples. They include representations of quantum affine algebras, chiral algebras of Beilinson and Drinfeld, G-vertex algebras of Borcherds, and representations of GL over a local field. Hopefully the formalism will accomodate various tensor structures arising in relation to the quantized Knizhnik-Zamolodchikov equations and deformed CFT
Spin imaging in solids using synchronously rotating field gradients and samples
International Nuclear Information System (INIS)
Wind, R.A.; Yannoni, C.S.
1983-01-01
A method for spin-imaging in solids using nuclear magnetic resonance (NMR) spectroscopy is described. With this method, the spin density distribution of a two- or three-dimensional object such as a solid can be constructed resulting in an image of the sample. This method lends itself to computer control to map out an image of the object. This spin-imaging method involves the steps of placing a solid sample in the rf coil field and the external magnetic field of an NMR spectrometer. A magnetic field gradient is superimposed across the sample to provide a field gradient which results in a varying DC field that has different values over different parts of the sample. As a result, nuclei in different parts of the sample have different resonant NMR frequencies. The sample is rotated about an axis which makes a particular angle of 54.7 degrees with the static external magnetic field. The magnetic field gradient which has a spatial distribution related to the sample spinning axis is then rotated synchronously with the sample. Data is then collected while performing a solid state NMR line narrowing procedure. The next step is to change the phase relation between the sample rotation and the field gradient rotation. The data is again collected as before while the sample and field gradient are synchronously rotated. The phase relation is changed a number of times and data collected each time. The spin image of the solid sample is then reconstructed from the collected data
Energy Technology Data Exchange (ETDEWEB)
Armas-Pérez, Julio C.; Londono-Hurtado, Alejandro [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Guzmán, Orlando [Departamento de Física, Universidad Autónoma Metropolitana, Iztapalapa, DF 09340, México (Mexico); Hernández-Ortiz, Juan P. [Departamento de Materiales y Minerales, Universidad Nacional de Colombia, Sede Medellín, Medellín (Colombia); Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Pablo, Juan J. de, E-mail: depablo@uchicago.edu [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
2015-07-28
A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.
Energy Technology Data Exchange (ETDEWEB)
Armas-Perez, Julio C.; Londono-Hurtado, Alejandro; Guzman, Orlando; Hernandez-Ortiz, Juan P.; de Pablo, Juan J.
2015-07-27
A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.
Bianchi Type-II String Cosmological Model with Magnetic Field in Scalar-tensor Theory of Gravitation
Sharma, N. K.; Singh, J. K.
2015-03-01
The spatially homogeneous and totally anisotropic Bianchi type-II cosmological solutions of massive strings have been investigated in the presence of the magnetic field in the framework of scalar-tensor theory of gravitation formulated by Saez and Ballester (Phys. Lett. A 113:467, 1986). With the help of special law of variation for Hubble's parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) string cosmological model is obtained in this theory. Some physical and kinematical properties of the model are also discussed.
International Nuclear Information System (INIS)
Zhou, J. F.; Shao, C. L.; Gu, B. Q.
2016-01-01
Magnetic particles (MPs) are known to respond to a magnetic field and can be moved by magnetic force, which make them good carriers in bioengineering and pharmaceutical engineering. In this paper, a pose control method for the straight chain composed of MPs is proposed, and the chain with one pose can be moved to another position with another pose using alternately employed uniform and gradient magnetic fields. Based on computer simulations, it is revealed that in the uniform magnetic field, the MPs form a straight chain with the same separation space along the field lines, and once the uniform magnetic field rotates, the chain also rotates with the field. In the gradient magnetic field, the MPs move toward the higher field so that the translation of the chain can be realized. The simulation results indicate that while the uniform magnetic field is rotating, there exists certain hysteresis between the chain and the field, and the chain is not straight anymore. So the uniform magnetic field should rest at the target angle for a period to make the chain fully relax to be straight. For nanoMP, its magnetic moment directly determines the gradient magnetic force which is much smaller than the dipole–dipole force among MPs. Therefore, the translation of the chain is much more time-consuming than rotation. To enlarge the translational velocity, it is suggested to increase the size of MPs or the magnetic field gradient
Jiang, Limei; Xu, Xiaofei; Zhou, Yichun
2016-12-01
With the development of the integrated circuit technology and decreasing of the device size, ferroelectric films used in nano ferroelectric devices become thinner and thinner. Along with the downscaling of the ferroelectric film, there is an increasing influence of two strain gradient related terms. One is the strain gradient elasticity and the other one is flexoelectricity. To investigate the interrelationship between flexoelectricity and strain gradient elasticity and their combined effect on the domain structure in ferroelectric nanofilms, a phase field model of flexoelectricity and strain gradient elasticity on the ferroelectric domain evolution is developed based on Mindlin's theory of strain-gradient elasticity. Weak form is derived and implemented in finite element formulations for numerically solving the model equations. The simulation results show that upper bounds for flexoelectric coefficients can be enhanced by increasing strain gradient elasticity coefficients. While a large flexoelectricity that exceeds the upper bound can induce a transition from a ferroelectric state to a modulated/incommensurate state, a large enough strain gradient elasticity may lead to a conversion from an incommensurate state to a ferroelectric state. Strain gradient elasticity and the flexoelectricity have entirely opposite effects on polarization. The observed interrelationship between the strain gradient elasticity and flexoelectricity is rationalized by an analytical solution of the proposed theoretical model. The model proposed in this paper could help us understand the mechanism of phenomena observed in ferroelectric nanofilms under complex electromechanical loads and provide some guides on the practical application of ferroelectric nanofilms.
Symmetric Tensor Decomposition
DEFF Research Database (Denmark)
Brachat, Jerome; Comon, Pierre; Mourrain, Bernard
2010-01-01
We present an algorithm for decomposing a symmetric tensor, of dimension n and order d, as a sum of rank-1 symmetric tensors, extending the algorithm of Sylvester devised in 1886 for binary forms. We recall the correspondence between the decomposition of a homogeneous polynomial in n variables...... of polynomial equations of small degree in non-generic cases. We propose a new algorithm for symmetric tensor decomposition, based on this characterization and on linear algebra computations with Hankel matrices. The impact of this contribution is two-fold. First it permits an efficient computation...... of the decomposition of any tensor of sub-generic rank, as opposed to widely used iterative algorithms with unproved global convergence (e.g. Alternate Least Squares or gradient descents). Second, it gives tools for understanding uniqueness conditions and for detecting the rank....
Communication: Control of chemical reactions using electric field gradients.
Deshmukh, Shivaraj D; Tsori, Yoav
2016-05-21
We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.
Variational infrared image enhancement based on adaptive dual-threshold gradient field equalization
Zhao, Wenda; Xu, Zhijun; Zhao, Jian; Zhao, Fan; Han, Xizhen
2014-09-01
Infrared images are characterized by low signal to noise ratio (SNR) and fuzzy texture edges. This article introduces the variational infrared image enhancement algorithm based on gradient field equalization with adaptive dual thresholds. Firstly, we transform the image into gradient domain and get the gradient histogram. Then, we do the gradient histogram equalization. By setting adaptive dual thresholds to qualify the gradients, the image is prevented from over enhancement. The total variation (TV) model is adopted in the reconstruction of the enhanced image to suppress noise. It is shown from experimental results that the image edge details are significantly enhanced, and therefore the algorithm is qualified for enhancement of infrared images in different applications.
Susceptibility tensor imaging (STI) of the brain.
Li, Wei; Liu, Chunlei; Duong, Timothy Q; van Zijl, Peter C M; Li, Xu
2017-04-01
Susceptibility tensor imaging (STI) is a recently developed MRI technique that allows quantitative determination of orientation-independent magnetic susceptibility parameters from the dependence of gradient echo signal phase on the orientation of biological tissues with respect to the main magnetic field. By modeling the magnetic susceptibility of each voxel as a symmetric rank-2 tensor, individual magnetic susceptibility tensor elements as well as the mean magnetic susceptibility and magnetic susceptibility anisotropy can be determined for brain tissues that would still show orientation dependence after conventional scalar-based quantitative susceptibility mapping to remove such dependence. Similar to diffusion tensor imaging, STI allows mapping of brain white matter fiber orientations and reconstruction of 3D white matter pathways using the principal eigenvectors of the susceptibility tensor. In contrast to diffusion anisotropy, the main determinant factor of the susceptibility anisotropy in brain white matter is myelin. Another unique feature of the susceptibility anisotropy of white matter is its sensitivity to gadolinium-based contrast agents. Mechanistically, MRI-observed susceptibility anisotropy is mainly attributed to the highly ordered lipid molecules in the myelin sheath. STI provides a consistent interpretation of the dependence of phase and susceptibility on orientation at multiple scales. This article reviews the key experimental findings and physical theories that led to the development of STI, its practical implementations, and its applications for brain research. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Goora, Frédéric G; Colpitts, Bruce G; Balcom, Bruce J
2014-01-01
The time-varying magnetic fields used in magnetic resonance applications result in the induction of eddy currents on conductive structures in the vicinity of both the sample under investigation and the gradient coils. These eddy currents typically result in undesired degradations of image quality for MRI applications. Their ubiquitous nature has resulted in the development of various approaches to characterize and minimize their impact on image quality. This paper outlines a method that utilizes the magnetic field gradient waveform monitor method to directly measure the temporal evolution of the magnetic field gradient from a step-like input function and extracts the system impulse response. With the basic assumption that the gradient system is sufficiently linear and time invariant to permit system theory analysis, the impulse response is used to determine a pre-equalized (optimized) input waveform that provides a desired gradient response at the output of the system. An algorithm has been developed that calculates a pre-equalized waveform that may be accurately reproduced by the amplifier (is physically realizable) and accounts for system limitations including system bandwidth, amplifier slew rate capabilities, and noise inherent in the initial measurement. Significant improvements in magnetic field gradient waveform fidelity after pre-equalization have been realized and are summarized. Copyright © 2013 Elsevier Inc. All rights reserved.
Pellegrini, Yves-Patrick; Lazar, Markus
2015-01-01
The two-dimensional elastodynamic Green tensor is the primary building block of solutions of linear elasticity problems dealing with nonuniformly moving rectilinear line sources, such as dislocations. Elastodynamic solutions for these problems involve derivatives of this Green tensor, which stand as hypersingular kernels. These objects, well defined as distributions, prove cumbersome to handle in practice. This paper, restricted to isotropic media, examines some of their representations in th...
Magnetic-Field-Gradient-Coil System for Solid-State MAS and Cramps NMR Imaging
Buszko, M.; Maciel, G. E.
The idea of combining cylindrical coils for producing a longitudinal gradient with respect to the MAS axis with quadrupole (straight wire) magnetic-field-gradient coils for producing two transverse gradients for 3D MAS and CRAMPS imaging has been demonstrated. A modified set of a double Maxwell pair and two sets of quadrupole (eight-wire) coils were combined in a compact way and adapted for a 5 mm MAS rotor, achieving gradients of high efficiency (4.3 and 2.9 G/cm A for longitudinal and transverse coils, respectively), low inductance (3.5 and 1.9 μH, respectively), and very good linearity(1%). A 60 μm spatial resolution in a TREV-CRAMPS imaging experiment on solid polyethylene oxide was demonstrated; gradient pulses of 12 μs duration were generated by applying currents of 2.3 and 1.5 A to longitudinal and transverse coils, respectively. This magnetic-field-gradient-coil configuration could also be applied in other areas of NMR where time-dependent gradients are required.
AN INTEGRAL FIELD STUDY OF ABUNDANCE GRADIENTS IN NEARBY LUMINOUS INFRARED GALAXIES
International Nuclear Information System (INIS)
Rich, J. A.; Kewley, L. J.; Dopita, M. A.; Torrey, P.; Rupke, D. S. N.
2012-01-01
We present for the first time metallicity maps generated using data from the Wide Field Spectrograph on the ANU 2.3 m of 10 luminous infrared galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low-metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models that trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.
Hiramatsu, Y.; Matsumoto, N.; Sawada, A.
2016-12-01
We analyze gravity anomalies in the focal area of the 2016 Kumamoto earthquake, evaluate the continuity, segmentation and faulting type of the active fault zones, and discuss relationships between those features and the aftershock distribution. We compile the gravity data published by the Gravity Research Group in Southwest Japan (2001), the Geographical Survey Institute (2006), Yamamoto et al. (2011), Honda et al. (2012), and the Geological Survey of Japan, AIST (2013). We apply terrain corrections with 10 m DEM and a low-pass filter, then remove a linear trend to obtain Bouguer anomalies. We calculate the first horizontal derivative (HD), the first vertical derivative (VD), the normalized total horizontal derivative (TDX) (Cooper and Cowan, 2006), the dimensionality index (Di) (Beki and Pedersen, 2010), and dip angle (β) (Beki, 2013) from a gravity gradient tensor. The HD, VD and TDX show the existence of the continuous fault structure along the Futagawa fault zone, extending from the Uto peninsula to the Beppu Bay except Mt. Aso area. Aftershocks are distributed along this structural boundary from the confluence of the Futagawa and the Hinagu fault zones to the east end of the Aso volcano. The distribution of dip angle β along the Futagawa fault zone implies a normal faulting, which corresponds to the coseismic faulting estimated geologically and geomorphologically. We observe the S-shaped distribution of the Bouguer anomalies around the southern part of the Hinagu segment, indicating a right lateral faulting. The VD and TDX support the existence of the fault structure along the segment but it is not so clear. We can recognize no clear structural boundaries along the Takano-Shirahata segment. TDX implies the existence of a structural boundary with a NW-SE trend around the boundary between the Hinagu and Takano-Shirahata segments. The Di shows that this boundary has a 3D-like structure rather than a 2D-like one, suggesting the discontinuity of 2D-like fault
Ab-initio calculations of electric field gradient in Ru compounds and ...
Indian Academy of Sciences (India)
S N Mishra
2017-07-11
Jul 11, 2017 ... useful for the precise determination of quadrupole moment of high spin states in other Ru isotopes and is likely to stimulate further shell model calculations for an improved understanding of nuclear shape in these nuclei. Keywords. Hyperfine field; electric field gradient; density functional calculation; nuclear ...
Tensor surgery and tensor rank
M. Christandl (Matthias); J. Zuiddam (Jeroen)
2018-01-01
textabstractWe introduce a method for transforming low-order tensors into higher-order tensors and apply it to tensors defined by graphs and hypergraphs. The transformation proceeds according to a surgery-like procedure that splits vertices, creates and absorbs virtual edges and inserts new vertices
Electric-field gradients at Ta donor impurities in Cr{sub 2}O{sub 3}(Ta) semiconductor
Energy Technology Data Exchange (ETDEWEB)
Darriba, G.N. [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Errico, L.A. [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, 2700 Pergamino (Argentina); Munoz, E.L; Richard, D. [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Eversheim, P.D. [Helmholtz-Institut fuer Strahlen-und Kernphysik (H-ISKP), Universitaet Bonn, Nussallee 14-16, 53115 Bonn (Germany); Renteria, M., E-mail: renteria@fisica.unlp.edu.a [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina)
2009-10-01
We report perturbed-angular-correlation (PAC) experiments on {sup 181}Hf(->{sup 181}Ta)-implanted corundum Cr{sub 2}O{sub 3} powder samples in order to determine the magnitude and symmetry of the electric-field gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbitals (FP-APW+lo) calculations. The results are also compared with EFG results coming from PAC experiments in isomorphous alpha-Al{sub 2}O{sub 3} and alpha-Fe{sub 2}O{sub 3} doped with {sup 111}In->{sup 111}Cd and {sup 181}Hf->{sup 181}Ta tracers. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.
Electric-field gradients at 181Ta impurity sites in Ho2O3 and Eu2O3 bixbyites
International Nuclear Information System (INIS)
Errico, Leonardo A.; Renteria, Mario; Bibiloni, Anibal G.; Freitag, Kristian
2007-01-01
The time-differential γ-γ perturbed-angular-correlation (PAC) technique with ion-implanted 181 Hf tracers has been applied to study the hyperfine interactions of 181 Ta impurities in the cubic bixbyite structure of Ho 2 O 3 and Eu 2 O 3 . The PAC experiments were performed in air in the temperature range 300-1373 K (in the case of Ho 2 O 3 ) and 77-1273 K (in the case of Eu 2 O 3 ). For both oxides, two electric-quadrupole interactions were found and attributed to the electric-field gradients (EFGs) acting on 181 Ta probes substitutionally located at the two free-of-defects nonequivalent cation sites of the bixbyite structure. In the case of Ho 2 O 3 , two additional interactions were found in the temperature range 300-573 K. These results, as well as previous characterizations of the EFG at 181 Ta sites in bixbyites, were compared to those obtained in experiments using 111 Cd as probe, and to point-charge model calculations. Very recent ab initio predictions for the EFG tensor at impurities sites in binary oxides are also discussed. All these results enable us to discuss the validity of the widely used ionic model to describe the EFG in these highly ionic compounds
International Nuclear Information System (INIS)
Renteria, M.; Requejo, F.G.; Bibiloni, A.G.; Pasquevich, A.F.; Shitu, J.; Freitag, K.
1997-01-01
We studied the hyperfine interactions of 181 Ta in In 2 O 3 by means of perturbed-angular-correlation (PAC) measurements. We prepared thin films of indium sesquioxide with different degrees of initial amorphism and implanted them with 181 Hf. Chemically prepared indium-sesquioxide powder samples were also made starting from neutron-irradiated HfCl 4 , which provides the 181 Hf PAC probes. PAC experiments were performed on each sample at room temperature, after each step of annealing programs at increasing temperatures up to the full crystallization of the samples. The results indicate that the PAC probe occupies preferentially the axially symmetric cation site. Point-charge-model calculations were performed. The calculated asymmetry parameters η were compared with those obtained in 181 Hf PAC experiments performed also on other binary oxides, showing that the symmetry of the electric-field-gradient (EFG) tensor at 181 Ta cation sites in binary oxides is mainly determined by the nearest-neighbor oxygen-ion distribution around the probe. Comparisons of the experimental results in bixbyites obtained for both PAC probes, 111 Cd and 181 Ta, show that the local EFG in bixbyites, are strongly dependent on the geometry of the sites and the electronic configuration of the probes. copyright 1997 The American Physical Society
On the relation between phase-field crack approximation and gradient damage modelling
Steinke, Christian; Zreid, Imadeddin; Kaliske, Michael
2017-05-01
The finite element implementation of a gradient enhanced microplane damage model is compared to a phase-field model for brittle fracture. Phase-field models and implicit gradient damage models share many similarities despite being conceived from very different standpoints. In both approaches, an additional differential equation and a length scale are introduced. However, while the phase-field method is formulated starting from the description of a crack in fracture mechanics, the gradient method starts from a continuum mechanics point of view. At first, the scope of application for both models is discussed to point out intersections. Then, the analysis of the employed mathematical methods and their rigorous comparison are presented. Finally, numerical examples are introduced to illustrate the findings of the comparison which are summarized in a conclusion at the end of the paper.
150 MeV fixed field alternating gradient (FFAG) accelerator
International Nuclear Information System (INIS)
Nakano, Joe
2002-01-01
150 MeV FFAG accelerator is prototype for practical use. Fundamental development of FFAG, research of FFAG accelerator and its application for therapy are investigated. 150 MeV ring consists of 12 sector magnets. The distribution of magnetic field of 12 sector magnets is almost same. 12 MeV proton beam is generated by cyclotron and injection to 150 MeV FFAG. The injection system consists of 2 bump magnets, kicker magnet and septum electrode. RF accelerating cavity system using high-permeability magnetic substance with high magnetic permeability accelerates proton beam to 150 MeV, then the first operation aims at 250 Hz. Return Yoke Free magnet was developed for adjustment. 150 MeV FFAG magnet is constructed and 12 MeV proton beam acceleration is conformed. The final state of 150 MeV FFAG magnet is explained by calculation results. On cancer therapy by proton beam, the three dimensions spot scan method is proposed. (S.Y.)
Reversal of Magnetisation in Ising Ferromagnet by the Field Having Gradient
International Nuclear Information System (INIS)
Dhar, Abyaya; Acharyya, Muktish
2016-01-01
We have studied the reversal of magnetisation in Ising ferromagnet by the field having gradient along a particular direction. We employed the Monte Carlo simulation with Metropolis single spin flip algorithm. The average lifetime of the metastable state was observed to increase with the magnitude of the gradient of applied field. In the high gradient regime, the system was observed to show two distinct region of up and down spins. The interface or the domain wall was observed to move as one increases the gradient. The displacement of the mean position of the interface was observed to increase with the gradient as hyperbolic tangent function. The roughness of the interface was observed to decay exponentially as the gradient increases. The number of spin flip per site was observed to show a discontinuity in the vicinity of the domain wall. The amount of the discontinuity was found to diverge with the system size as a power law fashion with an exponent 5/3. (paper)
Measurement of asymmetric optical pumping of ions accelerating in a magnetic-field gradient
International Nuclear Information System (INIS)
Sun Xuan; Scime, Earl; Miah, Mahmood; Cohen, Samuel; Skiff, Frederick
2004-01-01
We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic-field gradient. The signature is a difference in the laser-induced-fluorescence emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities
Measurement of Asymmetric Optical Pumping of Ions Accelerating in a Magnetic-field Gradient
Energy Technology Data Exchange (ETDEWEB)
Xuan Sun; Earl Scime; Mahmood Miah; Samuel Cohen; Frederick Skiff
2004-10-28
We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic field gradient. The signature is a difference in the laser-induced-fluorescence (LIF) emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities.
Gould, Harvey; Maddi, Jason; Dinneen, Timothy
2000-06-01
Time-invariant electric field gradients have long been used to deflect beams of molecules and neutral atoms. However, time-varying electric field gradients can also be used to accelerate, slow [1,2], cool [2], or bunch these same beams. The possible applications include slowing and cooling thermal beams of molecules and atoms, launching cold atoms from a trap into a fountain, beam transport, and measuring atomic dipole polarizabilities. [1] H.L. Bethlem, G. Berden, and G Meijer, Phys. Rev. Lett. 83, 1588 (1999). [2] J. A. Maddi, T.P. Dinneen, and H. Gould, Phys. Rev. A60, 3882 (1999).
González, Lina M; Ruder, Warren C; Mitchell, Aaron P; Messner, William C; LeDuc, Philip R
2015-06-01
Many motile unicellular organisms have evolved specialized behaviors for detecting and responding to environmental cues such as chemical gradients (chemotaxis) and oxygen gradients (aerotaxis). Magnetotaxis is found in magnetotactic bacteria and it is defined as the passive alignment of these cells to the geomagnetic field along with active swimming. Herein we show that Magnetospirillum magneticum (AMB-1) show a unique set of responses that indicates they sense and respond not only to the direction of magnetic fields by aligning and swimming, but also to changes in the magnetic field or magnetic field gradients. We present data showing that AMB-1 cells exhibit sudden motility reversals when we impose them to local magnetic field gradients. Our system employs permalloy (Ni(80)Fe(20)) islands to curve and diverge the magnetic field lines emanating from our custom-designed Helmholtz coils in the vicinity of the islands (creating a drop in the field across the islands). The three distinct movements we have observed as they approach the permalloy islands are: unidirectional, single reverse and double reverse. Our findings indicate that these reverse movements occur in response to magnetic field gradients. In addition, using a permanent magnet we found further evidence that supports this claim. Motile AMB-1 cells swim away from the north and south poles of a permanent magnet when the magnet is positioned less than ∼30 mm from the droplet of cells. All together, these results indicate previously unknown response capabilities arising from the magnetic sensing systems of AMB-1 cells. These responses could enable them to cope with magnetic disturbances that could in turn potentially inhibit their efficient search for nutrients.
Feasibility of Imaging Tissue Electrical Conductivity by Switching Field Gradients with MRI.
Gibbs, Eric; Liu, Chunlei
2015-12-01
Tissue conductivity is a biophysical marker of tissue structure and physiology. Present methods of measuring tissue conductivity are limited. Electrical impedance tomography, and magnetic resonance electrical impedance tomography rely on passing external current through the object being imaged, which prevents its use in most human imaging. Recently, the RF field used for MR excitation has been used to non-invasively measure tissue conductivity. This technique is promising, but conductivity at higher frequencies is less sensitive to tissue structure. Measuring tissue conductivity non-invasively at low frequencies remains elusive. It has been proposed that eddy currents generated during the rise and decay of gradient pulses could act as a current source to map low-frequency conductivity. This work centers on a gradient echo pulse sequence that uses large gradients prior to excitation to create eddy currents. The electric and magnetic fields during a gradient pulse are simulated by a finite-difference time-domain simulation. The sequence is also tested with a phantom and an animal MRI scanner equipped with gradients of high gradient strengths and slew rate. The simulation demonstrates that eddy currents in materials with conductivity similar to biological tissue decay with a half-life on the order of nanoseconds and any eddy currents generated prior to excitation decay completely before influencing the RF signal. Gradient-induced eddy currents can influence phase accumulation after excitation but the effect is too small to image. The animal scanner images show no measurable phase accumulation. Measuring low-frequency conductivity by gradient-induced eddy currents is presently unfeasible.
Lagrangian formulation of massive fermionic totally antisymmetric tensor field theory in AdSd space
International Nuclear Information System (INIS)
Buchbinder, I.L.; Krykhtin, V.A.; Ryskina, L.L.
2009-01-01
We apply the BRST approach, developed for higher spin field theories, to Lagrangian construction for totally antisymmetric massive fermionic fields in AdS d space. As well as generic higher spin massive theories, the obtained Lagrangian theory is a reducible gauge model containing, besides the basic field, a number of auxiliary (Stueckelberg) fields and the order of reducibility grows with the value of the rank of the antisymmetric field. However, unlike the generic higher spin theory, for the special case under consideration we show that one can get rid of all the auxiliary fields and the final Lagrangian for fermionic antisymmetric field is formulated only in terms of basic field.
Diffusion tensor image registration using hybrid connectivity and tensor features.
Wang, Qian; Yap, Pew-Thian; Wu, Guorong; Shen, Dinggang
2014-07-01
Most existing diffusion tensor imaging (DTI) registration methods estimate structural correspondences based on voxelwise matching of tensors. The rich connectivity information that is given by DTI, however, is often neglected. In this article, we propose to integrate complementary information given by connectivity features and tensor features for improved registration accuracy. To utilize connectivity information, we place multiple anchors representing different brain anatomies in the image space, and define the connectivity features for each voxel as the geodesic distances from all anchors to the voxel under consideration. The geodesic distance, which is computed in relation to the tensor field, encapsulates information of brain connectivity. We also extract tensor features for every voxel to reflect the local statistics of tensors in its neighborhood. We then combine both connectivity features and tensor features for registration of tensor images. From the images, landmarks are selected automatically and their correspondences are determined based on their connectivity and tensor feature vectors. The deformation field that deforms one tensor image to the other is iteratively estimated and optimized according to the landmarks and their associated correspondences. Experimental results show that, by using connectivity features and tensor features simultaneously, registration accuracy is increased substantially compared with the cases using either type of features alone. Copyright © 2013 Wiley Periodicals, Inc.
Estimation of pore size distribution using concentric double pulsed-field gradient NMR.
Benjamini, Dan; Nevo, Uri
2013-05-01
Estimation of pore size distribution of well calibrated phantoms using NMR is demonstrated here for the first time. Porous materials are a central constituent in fields as diverse as biology, geology, and oil drilling. Noninvasive characterization of monodisperse porous samples using conventional pulsed-field gradient (PFG) NMR is a well-established method. However, estimation of pore size distribution of heterogeneous polydisperse systems, which comprise most of the materials found in nature, remains extremely challenging. Concentric double pulsed-field gradient (CDPFG) is a 2-D technique where both q (the amplitude of the diffusion gradient) and φ (the relative angle between the gradient pairs) are varied. A recent prediction indicates this method should produce a more accurate and robust estimation of pore size distribution than its conventional 1-D versions. Five well defined size distribution phantoms, consisting of 1-5 different pore sizes in the range of 5-25 μm were used. The estimated pore size distributions were all in good agreement with the known theoretical size distributions, and were obtained without any a priori assumption on the size distribution model. These findings support that in addition to its theoretical benefits, the CDPFG method is experimentally reliable. Furthermore, by adding the angle parameter, sensitivity to small compartment sizes is increased without the use of strong gradients, thus making CDPFG safe for biological applications. Copyright © 2013 Elsevier Inc. All rights reserved.
Directory of Open Access Journals (Sweden)
Yao Huang
2015-01-01
Full Text Available Light scattering material with gradient refractive index was prepared under the electrical field by taking methyl methacrylate (MMA monomer as the matrix with the addition of a little preheated styrene (ST and peroxidation benzoin formyl (BPO. The material obtained under electrical field presented different transmittance and molecular weight at different parts of the cylindrical sample along the axis of the direction of electric field which led to the layering phenomenon and gradient refractive index. The disparity of molecular weight between different layers can be as much as 230 thousand. There were several peaks in the figure of GPC test of the sample under electric field. This proved that there were polymers with different molecular weights in the sample. Therefore, it can be concluded that electrical field has a significant effect on polymerization.
Sharan, Surabhi; Gupta, Prateek; Bahga, Supreet Singh
2017-02-01
We describe the physical mechanism responsible for electrohydrodynamic (EHD) instability of a fluid layer with collinear conductivity gradient and electric field. In particular, we resolve the ambiguity in literature regarding the cause for switching between stationary and oscillatory modes of EHD instability. Using linear stability analysis, we show that a small perturbation in conductivity field perturbs the local electric field and also induces a perturbation charge. The coupling of base-state electric field with the perturbation charge leads to a force which causes overstability. Whereas, the coupling of base-state free charge with perturbation electric field leads to a force which causes EHD instability via a stationary mode. The proposed mechanism correctly explains the existence of stationary and oscillatory modes for varying conductivity gradients and wave number of disturbances, depending upon the relative magnitude of these two forces.
Validation of buoyancy driven spectral tensor model using HATS data
DEFF Research Database (Denmark)
Chougule, A.; Mann, Jakob; Kelly, Mark C.
2016-01-01
We present a homogeneous spectral tensor model for wind velocity and temperature fluctuations, driven by mean vertical shear and mean temperature gradient. Results from the model, including one-dimensional velocity and temperature spectra and the associated co-spectra, are shown in this paper....... The model also reproduces two-point statistics, such as coherence and phases, via cross-spectra between two points separated in space. Model results are compared with observations from the Horizontal Array Turbulence Study (HATS) field program (Horst et al. 2004). The spectral velocity tensor in the model...
Evaluation of Bayesian tensor estimation using tensor coherence
Kim, Dae-Jin; Kim, In-Young; Jeong, Seok-Oh; Park, Hae-Jeong
2009-06-01
Fiber tractography, a unique and non-invasive method to estimate axonal fibers within white matter, constructs the putative streamlines from diffusion tensor MRI by interconnecting voxels according to the propagation direction defined by the diffusion tensor. This direction has uncertainties due to the properties of underlying fiber bundles, neighboring structures and image noise. Therefore, robust estimation of the diffusion direction is essential to reconstruct reliable fiber pathways. For this purpose, we propose a tensor estimation method using a Bayesian framework, which includes an a priori probability distribution based on tensor coherence indices, to utilize both the neighborhood direction information and the inertia moment as regularization terms. The reliability of the proposed tensor estimation was evaluated using Monte Carlo simulations in terms of accuracy and precision with four synthetic tensor fields at various SNRs and in vivo human data of brain and calf muscle. Proposed Bayesian estimation demonstrated the relative robustness to noise and the higher reliability compared to the simple tensor regression.
Evaluation of Bayesian tensor estimation using tensor coherence
Energy Technology Data Exchange (ETDEWEB)
Kim, Dae-Jin; Park, Hae-Jeong [Laboratory of Molecular Neuroimaging Technology, Brain Korea 21 Project for Medical Science, Yonsei University, College of Medicine, Seoul (Korea, Republic of); Kim, In-Young [Department of Biomedical Engineering, Hanyang University, Seoul (Korea, Republic of); Jeong, Seok-Oh [Department of Statistics, Hankuk University of Foreign Studies, Yongin (Korea, Republic of)], E-mail: parkhj@yuhs.ac
2009-06-21
Fiber tractography, a unique and non-invasive method to estimate axonal fibers within white matter, constructs the putative streamlines from diffusion tensor MRI by interconnecting voxels according to the propagation direction defined by the diffusion tensor. This direction has uncertainties due to the properties of underlying fiber bundles, neighboring structures and image noise. Therefore, robust estimation of the diffusion direction is essential to reconstruct reliable fiber pathways. For this purpose, we propose a tensor estimation method using a Bayesian framework, which includes an a priori probability distribution based on tensor coherence indices, to utilize both the neighborhood direction information and the inertia moment as regularization terms. The reliability of the proposed tensor estimation was evaluated using Monte Carlo simulations in terms of accuracy and precision with four synthetic tensor fields at various SNRs and in vivo human data of brain and calf muscle. Proposed Bayesian estimation demonstrated the relative robustness to noise and the higher reliability compared to the simple tensor regression.
Energy Technology Data Exchange (ETDEWEB)
Renteria, Mario [Universidad Nacional de La Plata, Departamento de Fisica, Facultad de Ciencias Exactas (Argentina); Freitag, Kristian [Universitaet Bonn, Institut fuer Strahlen- und Kernphysik (ISKP) (Germany); Errico, Leonardo A. [Universidad Nacional de La Plata, Departamento de Fisica, Facultad de Ciencias Exactas (Argentina)
1999-09-15
The electric-field-gradient (EFG) tensor at both cation sites of the bixbyite structure in {sup 181}Hf-implanted Lu- and Sm-sesquioxides was determined by the PAC technique. The cumulated EFG data at Ta-impurity sites in binary oxides enable us to discuss the 'universal' character of the empirical correlation between local and ionic contributions to the EFG in these systems. An EFG factorization in terms of the electronic characteristics of the probe and the geometry of the cation coordination is proposed, which explains the experimental EFG results at Ta/Cd impurity sites in bixbyites and agrees with a simplified decomposition of the EFG valence contribution coming from ab-initio calculations.
Static high-gradient magnetic fields affect the functionality of monocytic cells
Czech Academy of Sciences Publication Activity Database
Syrovets, T.; Schmidt, Z.; Buechele, B.; Zablotskyy, Vitaliy A.; Dejneka, Alexandr; Dempsey, N.; Simmet, T.
2014-01-01
Roč. 28, č. 1 (2014), s. 1-2 ISSN 0892-6638 Institutional support: RVO:68378271 Keywords : static high-gradient * magnet ic fields * affect the functionality * monocytic cells Subject RIV: BM - Solid Matter Physics ; Magnet ism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.)
Microscopic Displacement Imaging with Pulsed Field Gradient Turbo Spin-Echo NMR
Scheenen, T.W.J.; Dusschoten, van D.; Jager, de P.A.; As, van H.
2000-01-01
We present a pulse sequence that enables the accurate and spatially resolved measurements of the displacements of spins in a variety of (biological) systems. The pulse sequence combines pulsed field gradient (PFG) NMR with turbo spin–echo (TSE) imaging. It is shown here that by ensuring that the
Effects of high-gradient magnetic fields on living cell machinery
Czech Academy of Sciences Publication Activity Database
Zablotskyy, V.; Lunov, O.; Kubinová, Šárka; Polyakova, T.; Syková, Eva; Dejneka, A.
2016-01-01
Roč. 49, č. 2016 (2016), s. 493003 ISSN 0022-3727 R&D Projects: GA MŠk(CZ) LO1309 Institutional support: RVO:68378041 Keywords : living cell * magnetic gradient force * cell mechanics * stem cell * magnetic field Subject RIV: FP - Other Medical Disciplines Impact factor: 2.588, year: 2016
Ab-initio calculations of electric field gradient in Ru compounds and ...
Indian Academy of Sciences (India)
S N Mishra
2017-07-11
Jul 11, 2017 ... Abstract. The nuclear quadrupole moments, Q, for the ground and first excited states in 99Ru and ground state of 101Ru have been determined by comparing the experimentally observed quadrupole interaction frequencies νQ with calculated electric field gradient (EFG) for a large number of Ru-based ...
Pilling evaluation of patterned fabrics based on a gradient field method
Czech Academy of Sciences Publication Activity Database
Techniková, L.; Tunák, M.; Janáček, Jiří
2016-01-01
Roč. 41, č. 1 (2016), s. 97-101 ISSN 0971-0426 Institutional support: RVO:67985823 Keywords : 3D surface reconstruction * fabric pilling * gradient field method * patterned fabric * pills detection Subject RIV: JS - Reliability ; Quality Management, Testing Impact factor: 0.430, year: 2016
Ab-initio calculations of electric field gradient in Ru compounds and ...
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 89; Issue 2. A b − i n i t i o calculations of electric field gradient in Ru compounds and their implication on the nuclear quadrupole moments of 99 Ru and 101 Ru. S N MISHRA. Research Article Volume 89 Issue 2 August 2017 Article ID 22 ...
How a high-gradient magnetic field could affect cell life
Czech Academy of Sciences Publication Activity Database
Zablotskyy, Vitaliy A.; Polyakova, Tetyana; Lunov, Oleg; Dejneka, Alexandr
2016-01-01
Roč. 6, Nov (2016), 1-12, č. článku 37407. ISSN 2045-2322 Grant - others:AV ČR(CZ) Fellowship J. E. Purkyně Institutional support: RVO:68378271 Keywords : high-gradient magnetic field * cell Subject RIV: BO - Biophysics Impact factor: 4.259, year: 2016
The Effect of a Spiral Gradient Magnetic Field on the Ionic Conductivity of Water
Czech Academy of Sciences Publication Activity Database
Bartušek, Karel; Marcon, P.; Fiala, P.; Máca, J.; Dohnal, P.
2017-01-01
Roč. 9, č. 9 (2017), s. 1-8, č. článku 664. ISSN 2073-4441 R&D Projects: GA ČR(CZ) GA17-00607S Institutional support: RVO:68081731 Keywords : gradient field * demineralized water * conductivity * ionic conductivity * magnetic field Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Electrochemistry (dry cells, batteries, fuel cells, corrosion metals, electrolysis) Impact factor: 1.832, year: 2016
Origin and orientation of electric field gradient in ordered FeNi
International Nuclear Information System (INIS)
Guenzburger, D.J.R.; Ellis, D.E.
1987-01-01
The electronic structure of tetrataenite, the ordered phase of Fe Ni, has been studied in the molecular cluster approximation using local density theory. Clusters containing 13 and 19 atoms were embedded in the fcc host lattice and spin-unrestricted potentials were iterated to self-consistency. Local moments, magnetic hyperfine fields and electric field gradients (EFG) at the iron sites were determined for comparison with experiment. (Author) [pt
Magnetic resonance imaging with nonlinear gradient fields signal encoding and image reconstruction
Schultz, Gerrit
2013-01-01
Within the past few decades magnetic resonance imaging has become one of the most important imaging modalities in medicine. For a reliable diagnosis of pathologies further technological improvements are of primary importance. This text deals with a radically new approach of image encoding: The fundamental principle of gradient linearity is challenged by investigating the possibilities of acquiring anatomical images with the help of nonlinear gradient fields. Besides a thorough theoretical analysis with a focus on signal encoding and image reconstruction, initial hardware implementations are tested using phantom as well as in-vivo measurements. Several applications are presented that give an impression about the implications that this technological advancement may have for future medical diagnostics. Contents n Image Reconstruction in MRI n Nonlinear Gradient Encoding: PatLoc Imaging n Presentation of Initial Hardware Designs n Basics of Signal Encoding and Image Reconstruction in PatLoc Imaging n ...
Damping of Solute Convection During Crystal Growth by Applying Magnetic Field Gradients
Wakayama, Nobuko I.
2005-06-01
One of the advantages of crystal growth under microgravity conditions is the damping of solute convection that affects crystal quality. The mechanism of the dampening effect of magnetic field gradients, B(dB/dz), on solute convection was studied, and the magnitude of B(dB/dz) required for dampening was calculated. When the absolute value of mass magnetic susceptibility, χg, of a solute is about 70% of that of a solvent (e.g., KCl crystal growth from an aqueous solution) and the weight ratio is 0.26, the gradient to damp convection considerably is estimated to be -3018 T2/m. On the other hand, when the χg of the solute is nearly equal to that of the solvent [protein crystal growth (lysozyme)], a gradient of -1394 T2/m damps convection completely on the earth.
Liu, Yong-Ming; Chen, Rui-Qing; Wu, Zi-Qing; Zhu, Jing; Shi, Jian-Yu; Lu, Hui-Meng; Shang, Peng; Yin, Da-Chuan
2016-09-01
The contact angle is an important parameter that is essential for studying interfacial phenomena. The contact angle can be measured using commercially available instruments. However, these well-developed instruments may not function or may be unsuitable for use in some special environments. A simulated microgravity generated by a large gradient magnetic field is such an environment in which the current measurement instruments cannot be installed. To measure the contact angle in this environment, new tools must be designed and manufactured to be compatible with the size and physical environment. In this study, we report the development and construction of a new setup that was specifically designed for use in a strong magnetic field to measure the contact angle between a levitated droplet and a solid surface. The application of the setup in a large gradient magnetic field was tested, and the contact angles were readily measured.
Image reconstruction in k-space from MR data encoded with ambiguous gradient fields.
Schultz, Gerrit; Gallichan, Daniel; Weber, Hans; Witschey, Walter R T; Honal, Matthias; Hennig, Jürgen; Zaitsev, Maxim
2015-02-01
In this work, the limits of image reconstruction in k-space are explored when non-bijective gradient fields are used for spatial encoding. The image space analogy between parallel imaging and imaging with non-bijective encoding fields is partially broken in k-space. As a consequence, it is hypothesized and proven that ambiguities can only be resolved partially in k-space, and not completely as is the case in image space. Image-space and k-space based reconstruction algorithms for multi-channel radiofrequency data acquisitions are programmed and tested using numerical simulations as well as in vivo measurement data. The hypothesis is verified based on an analysis of reconstructed images. It is found that non-bijective gradient fields have the effect that densely sampled autocalibration data, used for k-space reconstruction, provide less information than a separate scan of the receiver coil sensitivity maps, used for image space reconstruction. Consequently, in k-space only the undersampling artifact can be unfolded, whereas in image space, it is also possible to resolve aliasing that is caused by the non-bijectivity of the gradient fields. For standard imaging, reconstruction in image space and in k-space is nearly equivalent, whereas there is a fundamental difference with practical consequences for the selection of image reconstruction algorithms when non-bijective encoding fields are involved. © 2014 Wiley Periodicals, Inc.
Effects of high-gradient magnetic fields on living cell machinery
International Nuclear Information System (INIS)
Zablotskii, V; Lunov, O; Kubinova, S; Polyakova, T; Dejneka, A; Sykova, E
2016-01-01
A general interest in biomagnetic effects is related to fundamental studies of the influence of magnetic fields on living objects on the cellular and whole organism levels. Emerging technologies offer new directions for the use of high-gradient magnetic fields to control cell machinery and to understand the intracellular biological processes of the emerging field of nanomedicine. In this review we aim at highlighting recent advances made in identifying fundamental mechanisms by which magnetic gradient forces act on cell fate specification and cell differentiation. The review also provides an analysis of the currently available magnetic systems capable of generating magnetic fields with spatial gradients of up to 10 MT m −1 , with the focus on their suitability for use in cell therapy. Relationships between experimental factors and underlying biophysical mechanisms and assumptions that would ultimately lead to a deeper understanding of cell machinery and the development of more predictive models for the evaluation of the effects of magnetic fields on cells, tissue and organisms are comprehensively discussed. (topical review)
Tensors and their applications
Islam, Nazrul
2006-01-01
About the Book: The book is written is in easy-to-read style with corresponding examples. The main aim of this book is to precisely explain the fundamentals of Tensors and their applications to Mechanics, Elasticity, Theory of Relativity, Electromagnetic, Riemannian Geometry and many other disciplines of science and engineering, in a lucid manner. The text has been explained section wise, every concept has been narrated in the form of definition, examples and questions related to the concept taught. The overall package of the book is highly useful and interesting for the people associated with the field. Contents: Preliminaries Tensor Algebra Metric Tensor and Riemannian Metric Christoffel`s Symbols and Covariant Differentiation Riemann-Christoffel Tensor The e-Systems and the Generalized Krönecker Deltas Geometry Analytical Mechanics Curvature of a Curve, Geodesic Parallelism of Vectors Ricci`s Coefficients of Rotation and Congruence Hyper Surfaces
Contribution of Field Strength Gradients to the Net Vertical Current of Active Regions
Vemareddy, P.
2017-12-01
We examined the contribution of field strength gradients for the degree of net vertical current (NVC) neutralization in active regions (ARs). We used photospheric vector magnetic field observations of AR 11158 obtained by Helioseismic and Magnetic Imager on board SDO and Hinode. The vertical component of the electric current is decomposed into twist and shear terms. The NVC exhibits systematic evolution owing to the presence of the sheared polarity inversion line between rotating and shearing magnetic regions. We found that the sign of shear current distribution is opposite in dominant pixels (60%–65%) to that of twist current distribution, and its time profile bears no systematic trend. This result indicates that the gradient of magnetic field strength contributes to an opposite signed, though smaller in magnitude, current to that contributed by the magnetic field direction in the vertical component of the current. Consequently, the net value of the shear current is negative in both polarity regions, which when added to the net twist current reduces the direct current value in the north (B z > 0) polarity, resulting in a higher degree of NVC neutralization. We conjecture that the observed opposite signs of shear and twist currents are an indication, according to Parker, that the direct volume currents of flux tubes are canceled by their return currents, which are contributed by field strength gradients. Furthermore, with the increase of spatial resolution, we found higher values of twist, shear current distributions. However, the resolution effect is more useful in resolving the field strength gradients, and therefore suggests more contribution from shear current for the degree of NVC neutralization.
Gu, Chen; Marzouk, Youssef M.; Toksöz, M. Nafi
2018-03-01
Small earthquakes occur due to natural tectonic motions and are induced by oil and gas production processes. In many oil/gas fields and hydrofracking processes, induced earthquakes result from fluid extraction or injection. The locations and source mechanisms of these earthquakes provide valuable information about the reservoirs. Analysis of induced seismic events has mostly assumed a double-couple source mechanism. However, recent studies have shown a non-negligible percentage of non-double-couple components of source moment tensors in hydraulic fracturing events, assuming a full moment tensor source mechanism. Without uncertainty quantification of the moment tensor solution, it is difficult to determine the reliability of these source models. This study develops a Bayesian method to perform waveform-based full moment tensor inversion and uncertainty quantification for induced seismic events, accounting for both location and velocity model uncertainties. We conduct tests with synthetic events to validate the method, and then apply our newly developed Bayesian inversion approach to real induced seismicity in an oil/gas field in the sultanate of Oman—determining the uncertainties in the source mechanism and in the location of that event.
Charged tensor matter fields and Lorentz symmetry violation via spontaneous symmetry breaking
International Nuclear Information System (INIS)
Colatto, L.P.; Penna, A.L.A.; Santos, W.C.
2003-10-01
We consider a model with a charged vector field along with a Cremmer-Scherk-Kalb-Ramond (CSKR) matter field coupled to a U(1) gauge potential. We obtain a natural Lorentz symmetry violation due to the local U(1) spontaneous symmetry breaking mechanism triggered by the imaginary part of the vector matter. The choice of the unitary gauge leads to the decoupling of the gauge-Kr sector from the Higgs-Kr sector. The excitation spectrum is carefully analyzed and the physical modes are identified. We propose an identification of the neutral massive spin-1 Higgs-like field with the massive Z' boson of the so-called mirror matter models. (author)
Weyl tensors for asymmetric complex curvatures
International Nuclear Information System (INIS)
Oliveira, C.G.
Considering a second rank Hermitian field tensor and a general Hermitian connection the associated complex curvature tensor is constructed. The Weyl tensor that corresponds to this complex curvature is determined. The formalism is applied to the Weyl unitary field theory and to the Moffat gravitational theory. (Author) [pt
Czech Academy of Sciences Publication Activity Database
Plocková, Jana; Chmelík, Josef
2001-01-01
Roč. 918, č. 2 (2001), s. 361-370 ISSN 0021-9673 R&D Projects: GA AV ČR IAA4031805 Institutional research plan: CEZ:AV0Z4031919 Keywords : field-flow fractionation * field programming * flow-rate gradients Subject RIV: CB - Analytical Chemistry, Separation Impact factor: 2.793, year: 2001
The 'gravitating' tensor in the dualistic theory
International Nuclear Information System (INIS)
Mahanta, M.N.
1989-01-01
The exact microscopic system of Einstein-type field equations of the dualistic gravitation theory is investigated as well as an analysis of the modified energy-momentum tensor or so called 'gravitating' tensor is presented
A Genealogy of Convex Solids Via Local and Global Bifurcations of Gradient Vector Fields
Domokos, Gábor; Holmes, Philip; Lángi, Zsolt
2016-12-01
Three-dimensional convex bodies can be classified in terms of the number and stability types of critical points on which they can balance at rest on a horizontal plane. For typical bodies, these are non-degenerate maxima, minima, and saddle points, the numbers of which provide a primary classification. Secondary and tertiary classifications use graphs to describe orbits connecting these critical points in the gradient vector field associated with each body. In previous work, it was shown that these classifications are complete in that no class is empty. Here, we construct 1- and 2-parameter families of convex bodies connecting members of adjacent primary and secondary classes and show that transitions between them can be realized by codimension 1 saddle-node and saddle-saddle (heteroclinic) bifurcations in the gradient vector fields. Our results indicate that all combinatorially possible transitions can be realized in physical shape evolution processes, e.g., by abrasion of sedimentary particles.
Gurau, Razvan
2017-01-01
Written by the creator of the modern theory of random tensors, this book is the first self-contained introductory text to this rapidly developing theory. Starting from notions familiar to the average researcher or PhD student in mathematical or theoretical physics, the book presents in detail the theory and its applications to physics. The recent detections of the Higgs boson at the LHC and gravitational waves at LIGO mark new milestones in Physics confirming long standing predictions of Quantum Field Theory and General Relativity. These two experimental results only reinforce today the need to find an underlying common framework of the two: the elusive theory of Quantum Gravity. Over the past thirty years, several alternatives have been proposed as theories of Quantum Gravity, chief among them String Theory. While these theories are yet to be tested experimentally, key lessons have already been learned. Whatever the theory of Quantum Gravity may be, it must incorporate random geometry in one form or another....
Effects of high-gradient magnetic fields on living cell machinery
Czech Academy of Sciences Publication Activity Database
Zablotskyy, Vitaliy A.; Lunov, Oleg; Kubinová, Šárka; Polyakova, Tetyana; Syková, E.; Dejneka, Alexandr
2016-01-01
Roč. 49, č. 49 (2016), s. 1-23, č. článku 493003. ISSN 0022-3727 R&D Projects: GA MŠk LO1409 Grant - others:FUNBIO(XE) CZ.2.16/3.1.00/21568 Institutional support: RVO:68378271 Keywords : living cell * magnetic gradient force * cell mechanics * stem cell * magnetic field Subject RIV: BO - Biophysics Impact factor: 2.588, year: 2016
Solid-State 1H CRAMPS NMR Imaging with Pulsed Rotating Magnetic Field Gradients
Sun, Y. H.; Xiong, J. C.; Lock, H.; Buszko, M. L.; Haase, J. A.; Maciel, G. E.
By synchronizing a pulsed rotating magnetic field gradient with the rotation of a sample undergoing magic-angle spinning, a series of transverse-plane 1H NMR images was obtained. Both spatial-spatial two-dimensional images and spatial-spectral two-dimensional images are presented. The TREV-8 and BR-24 CRAMPS techniques were used for line narrowing in obtaining these images. Results are shown for both "soft" and "hard" solids.
Electric field gradients in cuprtaes: Does LDA+U give the correct charge distribution?
Czech Academy of Sciences Publication Activity Database
Blaha, P.; Schwarz, K.; Novák, Pavel
2005-01-01
Roč. 101, - (2005), s. 550-566 ISSN 0020-7608 R&D Projects: GA ČR(CZ) GA202/03/0552 Institutional research plan: CEZ:AV0Z10100521 Keywords : cuprtaes * electric field gradients (EFG) * density fuctional theory (DFT) * LDA+U * band structure Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.192, year: 2005
Czech Academy of Sciences Publication Activity Database
Kortunov, P.; Vasenkov, S.; Kärger, J.; Fé Elía, M.; Perez, M.; Stöcker, M.; Papadopoulos, G. K.; Theodorou, D.; Drescher, B.; McElhiney, G.; Bernauer, B.; Krystl, V.; Kočiřík, Milan; Zikánová, Arlette; Jirglová, Hana; Berger, C.; Gläser, R.; Weitkamp, J.; Hansen, E. W.
2005-01-01
Roč. 23, č. 2 (2005), s. 233-237 ISSN 0730-725X Grant - others:TROCAT project - European Community(DE) G5RD-CT-2001-00520 Institutional research plan: CEZ:AV0Z40400503 Keywords : pulsed-field gradient * nuclear magnetic resonance * fluid catalytic cracking catalyst Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.361, year: 2005
Orbit correction in a linear nonscaling fixed field alternating gradient accelerator
Directory of Open Access Journals (Sweden)
D. J. Kelliher
2014-11-01
Full Text Available In a linear nonscaling fixed field alternating gradient accelerator, the large natural chromaticity of the machine results in a betatron tune that varies by several integers over the momentum range. Orbit correction is complicated by the consequent variation of the phase advance between lattice elements. Here we investigate how the correction of multiple closed orbit harmonics allows correction of both the closed orbit distortion and the accelerated orbit distortion over the momentum range.
Multiconfiguration SCF electric field gradients in (NO).sub.2./sub. and its singly charged ions
Czech Academy of Sciences Publication Activity Database
Polák, Rudolf; Fišer, J.
2006-01-01
Roč. 326, 2-3 (2006), s. 611-619 ISSN 0301-0104 R&D Projects: GA AV ČR 1ET400400410; GA AV ČR IAA400400504; GA AV ČR KSK4040110 Institutional research plan: CEZ:AV0Z40400503 Keywords : nitric oxides * electric field gradient * 14N nuclear quadrupole coupling constant * electric dipole moment Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.984, year: 2006
A downstream algorithm based on extended gradient vector flow field for object segmentation.
Chuang, Cheng-Hung; Lie, Wen-Nung
2004-10-01
For object segmentation, traditional snake algorithms often require human interaction; region growing methods are considerably dependent on the selected homogeneity criterion and initial seeds; watershed algorithms, however, have the drawback of over segmentation. A new downstream algorithm based on a proposed extended gradient vector flow (E-GVF) field model is presented in this paper for multiobject segmentation. The proposed flow field, on one hand, diffuses and propagates gradients near object boundaries to provide an effective guiding force and, on the other hand, presents a higher resolution of direction than traditional GVF field. The downstream process starts with a set of seeds scored and selected by considering local gradient direction information around each pixel. This step is automatic and requires no human interaction, making our algorithm more suitable for practical applications. Experiments show that our algorithm is noise resistant and has the advantage of segmenting objects that are separated from the background, while ignoring the internal structures of them. We have tested the proposed algorithm with several realistic images (e.g., medical and complex background images) and gained good results.
Processing the image gradient field using a topographic primal sketch approach.
Gambaruto, A M
2015-03-01
The spatial derivatives of the image intensity provide topographic information that may be used to identify and segment objects. The accurate computation of the derivatives is often hampered in medical images by the presence of noise and a limited resolution. This paper focuses on accurate computation of spatial derivatives and their subsequent use to process an image gradient field directly, from which an image with improved characteristics can be reconstructed. The improvements include noise reduction, contrast enhancement, thinning object contours and the preservation of edges. Processing the gradient field directly instead of the image is shown to have numerous benefits. The approach is developed such that the steps are modular, allowing the overall method to be improved and possibly tailored to different applications. As presented, the approach relies on a topographic representation and primal sketch of an image. Comparisons with existing image processing methods on a synthetic image and different medical images show improved results and accuracy in segmentation. Here, the focus is on objects with low spatial resolution, which is often the case in medical images. The methods developed show the importance of improved accuracy in derivative calculation and the potential in processing the image gradient field directly. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.
Method of formation of a high gradient magnetic field and the device for division of substances
International Nuclear Information System (INIS)
Il'yashenko, E. I.; Glebov, V. A.; Skeltorp, A. T.
2005-01-01
Full text: The method and the device [1] are intended for use as a high-sensitivity magnetic separator for different types of paramagnetic substances and materials from diamagnetic ones, for division of paramagnetic substances and materials on the magnitudes of their paramagnetic susceptibility, for division of diamagnetic substances and materials on magnitudes of their diamagnetic susceptibility. Scopes: to produce pure and super pure substances and materials in electronics, metallurgy and chemistry, separation of biological objects (red blood cells, magnetic bacteria, etc.) in biology and medicine, water treatment removing heavy metals and organic impurities, etc. The main condition for magnetic separation is the magnetic force which acts on a particle of the substance and which is proportional to the magnetic susceptibility of the substance, magnetic induction B and gradient ∇B of the applied magnetic field. Therefore, to increase the sensitivity and selectivity of magnetic separation it will be required to use the largest possible values of the magnetic induction and the gradient of a magnetic field, or their product - B∇B. The device declared in the present work includes the magnetic system such as the open domain structure, consisting of permanent magnets with magnetic anisotropy much greater than the induction of a material of magnets. However, the declared device differs from the open domain structure in that [1]: *the surface of the neighbor poles of magnets is covered with a mask made from sheets of adjustable thickness of a soft magnetic material; *the soft magnetic material of the mask is selected on the basis of the magnitudes of the induction of saturation and magnetic permeability for achievement of the required magnitude of the induction and gradient of the magnetic field; *between the sheets of the mask there is an adjustable gap located symmetrically relative to the junction line of the magnets; *the size and the form of the gap between the
Fixed field alternating gradient accelerator with small orbit shift and tune excursion
Directory of Open Access Journals (Sweden)
Suzanne L. Sheehy
2010-04-01
Full Text Available A new design principle of a nonscaling fixed field alternating gradient accelerator is proposed. It is based on optics that produce approximate scaling properties. A large field index k is chosen to squeeze the orbit shift as much as possible by setting the betatron oscillation frequency in the second stability region of Hill’s equation. Then, the lattice magnets and their alignment are simplified. To simplify the magnets, we expand the field profile of r^{k} into multipoles and keep only a few lower order terms. A rectangular-shaped magnet is assumed with lines of constant field parallel to the magnet axis. The lattice employs a triplet of rectangular magnets for focusing, which are parallel to one another to simplify alignment. These simplifications along with fringe fields introduce finite chromaticity and the fixed field alternating gradient accelerator is no longer a scaling one. However, the tune excursion of the whole ring can be within half an integer and we avoid the crossing of strong resonances.
A new deteriorated energy-momentum tensor
International Nuclear Information System (INIS)
Duff, M.J.
1982-01-01
The stress-tensor of a scalar field theory is not unique because of the possibility of adding an 'improvement term'. In supersymmetric field theories the stress-tensor will appear in a super-current multiplet along with the sypersymmetry current. The general question of the supercurrent multiplet for arbitrary deteriorated stress tensors and their relationship to supercurrent multiplets for models with gauge antisymmetric tensors is answered for various models of N = 1, 2 and 4 supersymmetry. (U.K.)
Compartmentalization of the Coso East Flank geothermal field imaged by 3-D full-tensor MT inversion
Lindsey, Nathaniel J.; Kaven, Joern; Davatzes, Nicholas C.; Newman, Gregory A.
2017-01-01
Previous magnetotelluric (MT) studies of the high-temperature Coso geothermal system in California identified a subvertical feature of low resistivity (2–5 Ohm m) and appreciable lateral extent (>1 km) in the producing zone of the East Flank field. However, these models could not reproduce gross 3-D effects in the recorded data. We perform 3-D full-tensor inversion and retrieve a resistivity model that out-performs previous 2-D and 3-D off-diagonal models in terms of its fit to the complete 3-D MT data set as well as the degree of modelling bias. Inclusion of secondary Zxx and Zyy data components leads to a robust east-dip (60†) to the previously identified conductive East Flank reservoir feature, which correlates strongly with recently mapped surface faults, downhole well temperatures, 3-D seismic reflection data, and local microseismicity. We perform synthetic forward modelling to test the best-fit dip of this conductor using the response at a nearby MT station. We interpret the dipping conductor as a fractured and fluidized compartment, which is structurally controlled by an unmapped blind East Flank fault zone.
Compartmentalization of the Coso East Flank geothermal field imaged by 3-D full-tensor MT inversion
Lindsey, Nathaniel J.; Kaven, Joern Ole; Davatzes, Nicholas; Newman, Gregory A.
2017-02-01
Previous magnetotelluric (MT) studies of the high-temperature Coso geothermal system in California identified a subvertical feature of low resistivity (2-5 Ohm m) and appreciable lateral extent (>1 km) in the producing zone of the East Flank field. However, these models could not reproduce gross 3-D effects in the recorded data. We perform 3-D full-tensor inversion and retrieve a resistivity model that out-performs previous 2-D and 3-D off-diagonal models in terms of its fit to the complete 3-D MT data set as well as the degree of modelling bias. Inclusion of secondary Zxx and Zyy data components leads to a robust east-dip (60†) to the previously identified conductive East Flank reservoir feature, which correlates strongly with recently mapped surface faults, downhole well temperatures, 3-D seismic reflection data, and local microseismicity. We perform synthetic forward modelling to test the best-fit dip of this conductor using the response at a nearby MT station. We interpret the dipping conductor as a fractured and fluidized compartment, which is structurally controlled by an unmapped blind East Flank fault zone.
Effects of multiple-helicity fields on ion temperature gradient modes
Energy Technology Data Exchange (ETDEWEB)
Kuroda, T. [National Inst. for Fusion Science, Toki, Gifu (Japan); Sugama, H. [Graduate Univ. for Advanced Studies, Toki, Gigu (Japan)
2001-04-01
Effects of multiple-helicity magnetic fields on ion temperature gradient (ITG) modes in toroidal helical systems like the Large Helical Device (LHD) are studied by means of the linear gyrokinetic theory. Especially, dependence of the real frequency, growth rate, and the eigenfunction of the ITG mode on sideband-helicity fields added to the main helical component is investigated. Comparison between multiple-helicity effects on the ITG mode with those on the neoclassical ripple transport is presented, and optimization of the magnetic configuration for better plasma confinement is discussed. (author)
Tensor calculus for physics a concise guide
Neuenschwander, Dwight E
2015-01-01
Understanding tensors is essential for any physics student dealing with phenomena where causes and effects have different directions. A horizontal electric field producing vertical polarization in dielectrics; an unbalanced car wheel wobbling in the vertical plane while spinning about a horizontal axis; an electrostatic field on Earth observed to be a magnetic field by orbiting astronauts—these are some situations where physicists employ tensors. But the true beauty of tensors lies in this fact: When coordinates are transformed from one system to another, tensors change according to the same rules as the coordinates. Tensors, therefore, allow for the convenience of coordinates while also transcending them. This makes tensors the gold standard for expressing physical relationships in physics and geometry. Undergraduate physics majors are typically introduced to tensors in special-case applications. For example, in a classical mechanics course, they meet the "inertia tensor," and in electricity and magnetism...
A magnetically shielded room with ultra low residual field and gradient
Altarev, I.; Babcock, E.; Beck, D.; Burghoff, M.; Chesnevskaya, S.; Chupp, T.; Degenkolb, S.; Fan, I.; Fierlinger, P.; Frei, A.; Gutsmiedl, E.; Knappe-Grüneberg, S.; Kuchler, F.; Lauer, T.; Link, P.; Lins, T.; Marino, M.; McAndrew, J.; Niessen, B.; Paul, S.; Petzoldt, G.; Schläpfer, U.; Schnabel, A.; Sharma, S.; Singh, J.; Stoepler, R.; Stuiber, S.; Sturm, M.; Taubenheim, B.; Trahms, L.; Voigt, J.; Zechlau, T.
2014-07-01
A versatile and portable magnetically shielded room with a field of (700 ± 200) pT within a central volume of 1 m × 1 m × 1 m and a field gradient less than 300 pT/m, achieved without any external field stabilization or compensation, is described. This performance represents more than a hundredfold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus. This has implications for developments of magnetometry beyond the femto-Tesla scale in, for example, biomagnetism, geosciences, and security applications and in general low-field nuclear magnetic resonance (NMR) measurements.
A magnetically shielded room with ultra low residual field and gradient
Energy Technology Data Exchange (ETDEWEB)
Altarev, I.; Chesnevskaya, S.; Gutsmiedl, E.; Kuchler, F.; Lins, T.; Marino, M.; McAndrew, J.; Niessen, B.; Paul, S.; Petzoldt, G.; Singh, J.; Stoepler, R.; Stuiber, S.; Sturm, M.; Taubenheim, B. [Physikdepartment, Technische Universität München, D-85748 Garching (Germany); Babcock, E. [Jülich Center for Neutron Science, Lichtenbergstrasse 1, D-85748 Garching (Germany); Beck, D.; Sharma, S. [Physics Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Burghoff, M.; Fan, I. [Physikalisch-Technische Bundesanstalt Berlin, D-10587 Berlin (Germany); and others
2014-07-15
A versatile and portable magnetically shielded room with a field of (700 ± 200) pT within a central volume of 1 m × 1 m × 1 m and a field gradient less than 300 pT/m, achieved without any external field stabilization or compensation, is described. This performance represents more than a hundredfold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus. This has implications for developments of magnetometry beyond the femto-Tesla scale in, for example, biomagnetism, geosciences, and security applications and in general low-field nuclear magnetic resonance (NMR) measurements.
Robust tensor estimation in diffusion tensor imaging
Maximov, Ivan I.; Grinberg, Farida; Jon Shah, N.
2011-12-01
The signal response measured in diffusion tensor imaging is subject to detrimental influences caused by noise. Noise fields arise due to various contributions such as thermal and physiological noise and sources related to the hardware imperfection. As a result, diffusion tensors estimated by different linear and non-linear least squares methods in absence of a proper noise correction tend to be substantially corrupted. In this work, we propose an advanced tensor estimation approach based on the least median squares method of the robust statistics. Both constrained and non-constrained versions of the method are considered. The performance of the developed algorithm is compared to that of the conventional least squares method and of the alternative robust methods proposed in the literature. Two examples of simulated diffusion attenuations and experimental in vivo diffusion data sets were used as a basis for comparison. The robust algorithms were shown to be advantageous compared to the least squares method in the cases where elimination of the outliers is desirable. Additionally, the constraints were applied in order to prevent generation of the non-positive definite tensors and reduce related artefacts in the maps of fractional anisotropy. The developed method can potentially be exploited also by other MR techniques where a robust regression or outlier localisation is required.
International Nuclear Information System (INIS)
Gunell, H.; Loefgren, T.
1997-02-01
In the electron beam-plasma interaction at an electric double layer the beam density is much higher than in the classical beam-plasma experiments. The wave propagation takes place along the density gradient, that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp 'spike' with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward travelling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. 9 refs
Electric field spikes formed by electron beam endash plasma interaction in plasma density gradients
International Nuclear Information System (INIS)
Gunell, H.; Loefgren, T.
1997-01-01
In the electron beam endash plasma interaction at an electric double layer the beam density is much higher than in the classical beam endash plasma experiments. The wave propagation takes place along the density gradient that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp open-quotes spikeclose quotes with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward traveling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. copyright 1997 American Institute of Physics
Directory of Open Access Journals (Sweden)
Kang Ma
2017-01-01
Full Text Available Coherent gradient sensing (CGS method can be used to measure the slope of a reflective surface, and has the merits of full-field, non-contact, and real-time measurement. In this study, the thermal stress field of thermal barrier coating (TBC structures is measured by CGS method. Two kinds of powders were sprayed onto Ni-based alloy using a plasma spraying method to obtain two groups of film–substrate specimens. The specimens were then heated with an oxy-acetylene flame. The resulting thermal mismatch between the film and substrate led to out-of-plane deformation of the specimen. The deformation was measured by the reflective CGS method and the thermal stress field of the structure was obtained through calibration with the help of finite element analysis. Both the experiment and numerical results showed that the thermal stress field of TBC structures can be successfully measured by CGS method.
Phase-field simulations of pore migration and morphology change in thermal gradients
International Nuclear Information System (INIS)
Vance, Ian W.; Millett, Paul C.
2017-01-01
Here we present a phase-field simulation model that captures the thermal-gradient-driven migration of pores in oxide fuel associated with fuel restructuring. The model utilizes a Cahn-Hilliard equation supplemented with an advection term to describe the vapor transport of fuel material through the pore interior due to gradients in vapor pressure. Simulations demonstrate that the model not only predicts pore migration towards the centerline of the fuel, but also a concurrent change in pore shape during migration from an initially isotropic morphology to either a lenticular morphology or a prolate morphology depending on the vapor transport conditions. This model is a necessary first step to conducting accurate simulations of the microscopic changes that occur during the complicated process of oxide fuel restructuring.
Maynes, Daniel; Tenny, Joseph; Webbd, Brent W; Lee, Milton L
2008-02-01
Recently the use electric field gradient focusing (EFGF) to enhance focusing of proteins has been proposed and explored to provide significant improvement in separation resolution. The objective of EFGF is to focus proteins of specific electrophoretic mobilities at distinct stationary locations in a column or channel. This can be accomplished in a capillary by allowing the electric potential to vary in the streamwise direction. Because the electric field is varying, so also is the electrokinetic force exerted on the proteins and the electroosmotic velocity of the buffer solution. Due to the varying electric field, the Taylor diffusion characteristics will also vary along the column, causing a degradation of peak widths of some proteins, dependent on their equilibrium positions and local velocity distributions. The focus of this paper is an analysis that allows characterization of the local Taylor diffusion and resulting protein band peak width as a function of the local magnitude of the EOF relative to the average fluid velocity for both cylindrical and rectangular channels. In general the analysis shows that as the ratio of the local electroosmotic velocity to the average velocity deviates from unity, the effective diffusion increases significantly. The effectiveness of EFGF devices over a range of protein diffusivities, capillary diameters, flow velocities, and electric field gradient is discussed.
Sedimentation and aggregation of magnetite nanoparticles in water by a gradient magnetic field
International Nuclear Information System (INIS)
Medvedeva, I.; Bakhteeva, Yu.; Zhakov, S.; Revvo, A.; Byzov, I.; Uimin, M.; Yermakov, A.; Mysik, A.
2013-01-01
Magnetite (γ-Fe 3 O 4 ) nanoparticles are promising effective sorbents for water cleaning of heavy metal, radionuclides, organic and biological materials. A good sorption capacity can be achieved due to their high specific surface area. Application of gradient magnetic fields helps to separate the magnetic nanoparticles from the water suspension, which is rather hard to do using the conventional mechanical filtration and sedimentation methods without coagulants. The sedimentation dynamics of magnetite nanoparticles with sizes of 10–20 nm in aqueous media in the presence of a gradient magnetic field was studied by optical and NMR relaxometry methods. The gradient magnetic field was produced by a series of strip permanent magnets with B ≤ 0.5 T, dB/dz ≤ 0.13 T/cm and in some cases enhanced by a steel grid with sharp edges (dB/dz ≤ 5 T/cm). Dynamic Light Scattering in the water suspension with different nanoparticle concentrations (c 0 = 0.1–1 g/l) revealed the characteristic features in the aggregate formation, which is reflected in the sedimentation behavior. The sedimentation rate of the nanoparticles in water and in magnetic fields is higher for less concentrated suspensions (c 0 = 0.1 g/l) than for more concentrated ones (c 0 = 1 g/l), which might be connected with the formation of a gel structures due to a strong magnetic attraction between ferromagnetic nanoparticles. In 180 min this resulted in the reduction of the iron concentration in water down to 0.4 mg/l, which is close to hygienic and environmental norms for drinking water and fishery
Optimal Weighting of Multi-Spacecraft Data to Estimate Gradients of Physical Fields
Chanteur, G. M.; Le Contel, O.; Sahraoui, F.; Retino, A.; Mirioni, L.
2016-12-01
Multi-spacecraft missions like the ESA mission CLUSTER and the NASA mission MMS are essential to improve our understanding of physical processes in space plasmas. Several methods were designed in the 90's during the preparation phase of the CLUSTER mission to estimate gradients of physical fields from simultaneous multi-points measurements [1, 2]. Both CLUSTER and MMS involve four spacecraft with identical full scientific payloads including various sensors of electromagnetic fields and different type of particle detectors. In the standard methods described in [1, 2], which are presently in use, data from the four spacecraft have identical weights and the estimated gradients are most reliable when the tetrahedron formed by the four spacecraft is regular. There are three types of errors affecting the estimated gradients (see chapter 14 in [1]) : i) truncature errors are due to local non-linearity of spatial variations, ii) physical errors are due to instruments, and iii) geometrical errors are due to uncertainties on the positions of the spacecraft. An assessment of truncature errors for a given observation requires a theoretical model of the measured field. Instrumental errors can easily be taken into account for a given geometry of the cluster but are usually less than the geometrical errors which diverge quite fast when the tetrahedron flattens, a circumstance occurring twice per orbit of the cluster. Hence reliable gradients can be estimated only on part of the orbit. Reciprocal vectors of the tetrahedron were presented in chapter 4 of [1], they have the advantage over other methods to treat the four spacecraft symmetrically and to allow a theoretical analysis of the errors (see chapters 4 of [1] and 4 of [2]). We will present Generalized Reciprocal Vectors for weighted data and an optimization procedure to improve the reliability of the estimated gradients when the tetrahedron is not regular. A brief example using CLUSTER or MMS data will be given. This approach
Shemesh, Noam; Ozarslan, Evren; Komlosh, Michal E; Basser, Peter J; Cohen, Yoram
2010-08-01
One of the hallmarks of diffusion NMR and MRI is its ability to utilize restricted diffusion to probe compartments much smaller than the excited volume or the MRI voxel, respectively, and to extract microstructural information from them. Single-pulsed field gradient (s-PFG) MR methodologies have been employed with great success to probe microstructures in various disciplines, ranging from chemistry to neuroscience. However, s-PFG MR also suffers from inherent shortcomings, especially when specimens are characterized by orientation or size distributions: in such cases, the microstructural information available from s-PFG experiments is limited or lost. Double-pulsed field gradient (d-PFG) MR methodology, an extension of s-PFG MR, has attracted attention owing to recent theoretical studies predicting that it can overcome certain inherent limitations of s-PFG MR. In this review, we survey the microstructural features that can be obtained from conventional s-PFG methods in the different q regimes, and highlight its limitations. The experimental aspects of d-PFG methodology are then presented, together with an overview of its theoretical underpinnings and a general framework for relating the MR signal decay and material microstructure, affording new microstructural parameters. We then discuss recent studies that have validated the theory using phantoms in which the ground truth is well known a priori, a crucial step prior to the application of d-PFG methodology in neuronal tissue. The experimental findings are in excellent agreement with the theoretical predictions and reveal, inter alia, zero-crossings of the signal decay, robustness towards size distributions and angular dependences of the signal decay from which accurate microstructural parameters, such as compartment size and even shape, can be extracted. Finally, we show some initial findings in d-PFG MR imaging. This review lays the foundation for future studies, in which accurate and novel microstructural
3D field-shaping lens using all-dielectric gradient refractive index materials.
Ding, Tongyu; Yi, Jianjia; Li, Haoyu; Zhang, Hailin; Burokur, Shah Nawaz
2017-04-10
A novel three-dimensional (3D) optical lens structure for electromagnetic field shaping based on spatial light transformation method is proposed at microwave frequencies. The lens is capable of transforming cylindrical wavefronts into planar ones, and generating a directive emission. Such manipulation is simulated and analysed by solving Laplace's equation, and the deformation of the medium during the transformation is theoretically described in detail. The two-dimensional (2D) design method producing quasi-isotropic parameters is further extended to a potential 3D realization with all-dielectric gradient refractive index metamaterials. Numerical full-wave simulations are performed on both 2D and 3D models to verify the functionality and broadband characteristics of the calculated lens. Far-field radiation patterns and near-field distributions demonstrate a highly radiated directive beam when the lens is applied to a conical horn antenna.
Permanent Magnet Spiral Motor for Magnetic Gradient Energy Utilization: Axial Magnetic Field
Valone, Thomas F.
2010-01-01
The Spiral Magnetic Motor, which can accelerate a magnetized rotor through 90% of its cycle with only permanent magnets, was an energy milestone for the 20th century patents by Kure Tekkosho in the 1970's. However, the Japanese company used old ferrite magnets which are relatively weak and an electrically-powered coil to jump start every cycle, which defeated the primary benefit of the permanent magnet motor design. The principle of applying an inhomogeneous, anisotropic magnetic field gradient force Fz = μ cos φ dB/dz, with permanent magnets is well-known in physics, e.g., Stern-Gerlach experiment, which exploits the interaction of a magnetic moment with the aligned electron spins of magnetic domains. In this case, it is applied to dB/dθ in polar coordinates, where the force Fθ depends equally on the magnetic moment, the cosine of the angle between the magnetic moment and the field gradient. The radial magnetic field increases in strength (in the attractive mode) or decreases in strength (in the repulsive mode) as the rotor turns through one complete cycle. An electromagnetic pulsed switching has been historically used to help the rotor traverse the gap (detent) between the end of the magnetic stator arc and the beginning (Kure Tekko, 1980). However, alternative magnetic pulse and switching designs have been developed, as well as strategic eddy current creation. This work focuses on the switching mechanism, novel magnetic pulse methods and advantageous angular momentum improvements. For example, a collaborative effort has begun with Toshiyuki Ueno (University of Tokyo) who has invented an extremely low power, combination magnetostrictive-piezoelectric (MS-PZT) device for generating low frequency magnetic fields and consumes "zero power" for static magnetic field production (Ueno, 2004 and 2007a). Utilizing a pickup coil such as an ultra-miniature millihenry inductor with a piezoelectric actuator or simply Wiegand wire geometry, it is shown that the necessary
Temperature dependence of the electric field gradient in AgPd and AgPt alloys
International Nuclear Information System (INIS)
Krolas, K.
1977-07-01
The measurements of temperature dependence of the electric field gradient (EFG) on 111 Cd nuclei in AgPd and AgPt alloys were performed using the time dependent perturbed angular correlation method. The EFG caused by impurities distributed in further coordination shells decrease stronaer with increasing temperature than the EFG due to single impurity being the nearest neighbour of the probe atom. These results were explained assuming different modes of thermal vibrations of single impurity atoms and impurity complexes in silver host lattice. (author)
Tune-stabilized, non-scaling, fixed-field, alternating gradient accelerator
Johnstone, Carol J [Warrenville, IL
2011-02-01
A FFAG is a particle accelerator having turning magnets with a linear field gradient for confinement and a large edge angle to compensate for acceleration. FODO cells contain focus magnets and defocus magnets that are specified by a number of parameters. A set of seven equations, called the FFAG equations relate the parameters to one another. A set of constraints, call the FFAG constraints, constrain the FFAG equations. Selecting a few parameters, such as injection momentum, extraction momentum, and drift distance reduces the number of unknown parameters to seven. Seven equations with seven unknowns can be solved to yield the values for all the parameters and to thereby fully specify a FFAG.
Non-scaling fixed field alternating gradient permanent magnet cancer therapy accelerator
Trbojevic, Dejan
2017-05-23
A non-scaling fixed field alternating gradient accelerator includes a racetrack shape including a first straight section connected to a first arc section, the first arc section connected to a second straight section, the second straight section connected to a second arc section, and the second arc section connected to the first straight section; an matching cells configured to match particle orbits between the first straight section, the first arc section, the second straight section, and the second arc section. The accelerator includes the matching cells and an associated matching procedure enabling the particle orbits at varying energies between an arc section and a straight section in the racetrack shape.
Single and Multiple-Selective Excitation Combined with Pulsed Field Gradients
Dalvit, Claudio; Ko, Soo Young; Böhlen, Jean Marc
1996-02-01
Applications of selective, multiselective, and semiselective pulses with pulsed field gradients are described. The use of multiple-selective excitation and PFGs for coherence selection in the selective one-dimensional experiments results in spectra devoid of artifacts and with remarkable solvent suppression. Multiple-selective excitation is also employed in an experiment called Multigate, a variant of the well-known WATERGATE experiment, in order to achieve multiple solvent signal suppression. Finally, new pulse sequences are shown for recording pure absorption ω1semiselective PFG NOESY, ROESY, and TOCSY experiments. The merits and limitations of these experiments are discussed.
Meng, Lingyan; Yang, Zhilin; Chen, Jianing; Sun, Mengtao
2014-01-01
Tip-enhanced Raman spectroscopy (TERS) with sub-nanometer spatial resolution has been recently demonstrated experimentally. However, the physical mechanism underlying is still under discussion. Here, we theoretically investigate the electric field gradient of a coupled tip-substrate system. Our calculations suggest that the ultra-high spatial resolution of TERS can be partially attributed to the electric field gradient effect owning to its tighter spatial confinement and sensitivity to the in...
Nayak, Avinash; Taira, Taka'aki; Dreger, Douglas S.; Gritto, Roland
2018-04-01
We retrieve empirical Green's functions in the frequency range (˜0.2-0.9 Hz) for interstation distances ranging from ˜1 to ˜30 km (˜0.22 to ˜6.5 times the wavelength) at The Geysers geothermal field, Northern California, from coherency of ambient seismic noise being recorded by a variety of sensors (broad-band, short-period surface and borehole sensors, and one accelerometer). The applied methodology preserves the intercomponent relative amplitudes of the nine-component Green's tensor that allows us to directly compare noise-derived Green's functions (NGFs) with normalized displacement waveforms of complete single-force synthetic Green's functions (SGFs) computed with various 1-D and 3-D velocity models using the frequency-wavenumber integration method and a 3-D finite-difference wave propagation method, respectively. These comparisons provide an effective means of evaluating the suitability of different velocity models to different regions of The Geysers, and assessing the quality of the sensors and the NGFs. In the T-Tangential, R-Radial, Z-Vertical reference frame, the TT, RR, RZ, ZR and ZZ components (first component: force direction, second component: response direction) of NGFs show clear surface waves and even body-wave phases for many station pairs. They are also broadly consistent in phase and intercomponent relative amplitudes with SGFs for the known local seismic velocity structure that was derived primarily from body-wave traveltime tomography, even at interstation distances less than one wavelength. We also find anomalous large amplitudes in TR, TZ, RT and ZT components of NGFs at small interstation distances (≲4 km) that can be attributed to ˜10°-30° sensor misalignments at many stations inferred from analysis of longer period teleseismic waveforms. After correcting for sensor misalignments, significant residual amplitudes in these components for some longer interstation distance (≳8 km) paths are better reproduced by the 3-D velocity
Khan, Sajid; Yazdani-Kachoei, Majid; Jalali-Asadabadi, Saeid; Farooq, Muhammad Bilal; Ahmad, Iftikhar
2018-02-01
Cubic uranium compounds such as UX3 (X is a non-transition element of groups IIIA or IVA) exhibit highly diverse magnetic properties, including Pauli paramagnetism, spin fluctuation and anti-ferromagnetism. In the present paper, we explore the structural, electronic and magnetic properties as well as the hyperfine fields (HFFs) and electric field gradients (EFGs) with quadrupole coupling constant of UX3 (X = In, Tl, Pb) compounds using local density approximation, Perdew-Burke-Ernzerhof parametrization of generalized gradient approximation (PBE-GGA) including the Hubbard U parameter (GGA + U), a revised version of PBE-GGA that improves equilibrium properties of densely packed solids and their surfaces (PBEsol-GGA), and a hybrid functional (HF-PBEsol). The spin orbit-coupling calculations have been added to investigate the relativistic effect of electrons in these materials. The comparison between the experimental parameters and our calculated structural parameters we confirm the consistency and effectiveness of our theoretical tools. The computed magnetic moments show that magnetic moment increases from indium to lead in the UX3 family, and all these compounds are antiferromagnetic in nature. The EFGs and HFFs, as well as the quadrupole coupling constant of UX3 (X = In, Tl, Pb), are discussed in detail. These properties primarily originate from f and p states of uranium and post-transition sites.
Primordial vorticity and gradient expansion
Giovannini, Massimo
2012-01-01
The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the $\\Lambda$CDM paradigm the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the or...
Conformal correlators of mixed-symmetry tensors
Costa, Miguel S
2015-01-01
We generalize the embedding formalism for conformal field theories to the case of general operators with mixed symmetry. The index-free notation encoding symmetric tensors as polynomials in an auxiliary polarization vector is extended to mixed-symmetry tensors by introducing a new commuting or anticommuting polarization vector for each row or column in the Young diagram that describes the index symmetries of the tensor. We determine the tensor structures that are allowed in n-point conformal correlation functions and give an algorithm for counting them in terms of tensor product coefficients. We show, with an example, how the new formalism can be used to compute conformal blocks of arbitrary external fields for the exchange of any conformal primary and its descendants. The matching between the number of tensor structures in conformal field theory correlators of operators in d dimensions and massive scattering amplitudes in d+1 dimensions is also seen to carry over to mixed-symmetry tensors.
Separation of yeast chromosome-sized DNAs by pulsed field gradient gel electrophoresis.
Schwartz, D C; Cantor, C R
1984-05-01
A new type of gel electrophoresis separates DNA molecules up to 2000 kb with resolutions exceeding the logarithmic molecular weight dependence of conventional electrophoresis. The technique uses 1.5% agarose, 10 to 20 micrograms of DNA per well, and low ionic strength buffers. It employs alternately pulsed, perpendicularly oriented electrical fields, at least one of which is inhomogeneous. The duration of the applied electrical pulses is varied from 1 sec to 90 sec to achieve optimal separations for DNAs with sizes from 30 to 2000 kb. This pulsed field gradient gel electrophoresis fractionates intact S. cerevisiae chromosomal DNA, producing a molecular karyotype that greatly facilitates the assignment of genes to yeast chromosomes. Each yeast chromosome consists of a single piece of DNA; the chromosome sizes are consistent with the genetic linkage map. We also describe a general method for preparing spheroplasts, and cell lysates, without significant chromosomal DNA breakage.
Wide-field schematic eye models with gradient-index lens.
Goncharov, Alexander V; Dainty, Chris
2007-08-01
We propose a wide-field schematic eye model, which provides a more realistic description of the optical system of the eye in relation to its anatomical structure. The wide-field model incorporates a gradient-index (GRIN) lens, which enables it to fulfill properties of two well-known schematic eye models, namely, Navarro's model for off-axis aberrations and Thibos's chromatic on-axis model (the Indiana eye). These two models are based on extensive experimental data, which makes the derived wide-field eye model also consistent with that data. A mathematical method to construct a GRIN lens with its iso-indicial contours following the optical surfaces of given asphericity is presented. The efficiency of the method is demonstrated with three variants related to different age groups. The role of the GRIN structure in relation to the lens paradox is analyzed. The wide-field model with a GRIN lens can be used as a starting design for the eye inverse problem, i.e., reconstructing the optical structure of the eye from off-axis wavefront measurements. Anatomically more accurate age-dependent optical models of the eye could ultimately help an optical designer to improve wide-field retinal imaging.
Energy Technology Data Exchange (ETDEWEB)
Im, Sang Hyuk; Lee, Su Jin [Kyung Hee University, Yongin (Korea, Republic of); Suh, Duck Jong; Park, O Ok [Korea Advanced Institute of Science and Technology (KAIST), Daejeon (Korea, Republic of); Kwon, Moo Hyun [Woosuk University, Wanju (Korea, Republic of)
2015-07-15
We investigated whether a graded-index profile, specified by the polymer compositional gradient, could be formed using shear-induced polymer migration phenomenon in a polymer solution. For the presented model system, we generated a shear flow by rotating a glass rod at the center of a polystyrene/methylmethacrylate (PS/MMA) solution and measured the degree of polymer migration by the shear flow field by examining the concentration of polymer solution along the radial direction from the rotating axis to the periphery. Through model experiments, we formed a compositional gradient and controlled its profile in the solution by varying the concentration of polymer solution, molecular weight of polymer, and shear rate. Finally, we solidified the gradient profiles by the polymerization of the PS/MMA solution and confirmed that the gradient profiles were maintained with a compositional gradient twice larger than the mother PS/MMA solution.
Extensive strain along gradient trajectories in the turbulent kinetic energy field
Gampert, Markus; Goebbert, Jens Henrik; Schaefer, Philip; Gauding, Michael; Peters, Norbert; Aldudak, Fettah; Oberlack, Martin
2011-04-01
Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor-based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution \\skew3\\tilde{P}(\\tilde{l}) of dissipation elements, the conditional mean scalar difference langΔkmidlrang at the extreme points as well as the scaling of the two-point velocity difference along gradient trajectories langΔunrang are studied. Using the field of the instantaneous turbulent kinetic energy k as a scalar, we find good agreement between the model equation for \\skew3\\tilde{P}(\\tilde{l}) as proposed by Wang and Peters (2008 J. Fluid Mech. 608 113-38) and the results obtained in the different direct numerical simulation cases. This confirms the independence of the model solution from both the Reynolds number and the type of turbulent flow, so that it can be considered universally valid. In addition, we show a 2/3 scaling for the mean conditional scalar difference. In the second part of the paper, we examine the scaling of the conditional two-point velocity difference along gradient trajectories. In particular, we compare the linear s/τ scaling, where τ denotes an integral time scale and s the separation arclength along a gradient trajectory in the inertial range as derived by Wang (2009 Phys. Rev. E 79 046325) with the s·a∞ scaling, where a∞ denotes the asymptotic value of the conditional mean strain rate of large dissipation elements.
Magnetophoretic immunoassay of allergen-specific IgE in an enhanced magnetic field gradient.
Hahn, Young Ki; Jin, Zongwen; Kang, Joo H; Oh, Eunkeu; Han, Min-Kyu; Kim, Hak-Sung; Jang, Jung-Tak; Lee, Jae-Hyun; Cheon, Jinwoo; Kim, Seung Hyun; Park, Hae-Sim; Park, Je-Kyun
2007-03-15
We demonstrate a novel magnetophoretic immunoassay of allergen-specific immunoglobulin E (IgE) based on the magnetophoretic deflection velocity of a microbead that is proportional to the associated magnetic nanoparticles under enhanced magnetic field gradient in a microchannel. In this detection scheme, two types of house dust mites, Dermatophagoides farinae (D. farinae) and Dermatophagoides pteronyssinus (D. pteronyssinus), were used as the model allergens. Polystyrene microbeads were conjugated with each of the mite extracts followed by incubation with serum samples. The resulting mixture was then reacted with magnetic nanoparticle-conjugated anti-human IgE for detection of allergen-specific IgE by using sandwich immuno-reactions. A ferromagnetic microstructure combined with a permanent magnet was employed to increase the magnetic field gradient ( approximately 10(4) T/m) in a microfluidic device. The magnetophoretic velocities of microbeads were measured in a microchannel under applied magnetic field, and the averaged velocity was well correlated with the concentration of allergen-specific IgE in serum. From the analysis of pooled sera obtained from 44 patients, the detection limits of the allergen-specific human IgEs for D. farinae and D. pteronyssinus were determined to be 565 (0.045 IU/mL) and 268 fM (0.021 IU/mL), respectively. These values are 1 order of magnitude lower than those by a conventional CAP system. For evaluation of reproducibility and accuracy, unknown sera were subjected to a blind test by using the developed assay system, and they were compared with the CAP system. As a result, coefficient of variance was less than 10%, and the developed method enabled a fast assay with a tiny amount of serum ( approximately 10 microL).
Local recovery of lithospheric stress tensor from GOCE gravitational tensor
Eshagh, Mehdi
2017-04-01
The sublithospheric stress due to mantle convection can be computed from gravity data and propagated through the lithosphere by solving the boundary-value problem of elasticity for the Earth's lithosphere. In this case, a full tensor of stress can be computed at any point inside this elastic layer. Here, we present mathematical foundations for recovering such a tensor from gravitational tensor measured at satellite altitudes. The mathematical relations will be much simpler in this way than the case of using gravity data as no derivative of spherical harmonics (SHs) or Legendre polynomials is involved in the expressions. Here, new relations between the SH coefficients of the stress and gravitational tensor elements are presented. Thereafter, integral equations are established from them to recover the elements of stress tensor from those of the gravitational tensor. The integrals have no closed-form kernels, but they are easy to invert and their spatial truncation errors are reducible. The integral equations are used to invert the real data of the gravity field and steady-state ocean circulation explorer mission (GOCE), in 2009 November, over the South American plate and its surroundings to recover the stress tensor at a depth of 35 km. The recovered stress fields are in good agreement with the tectonic and geological features of the area.
Geometric decomposition of the conformation tensor in viscoelastic turbulence
Hameduddin, Ismail; Meneveau, Charles; Zaki, Tamer A.; Gayme, Dennice F.
2018-05-01
This work introduces a mathematical approach to analysing the polymer dynamics in turbulent viscoelastic flows that uses a new geometric decomposition of the conformation tensor, along with associated scalar measures of the polymer fluctuations. The approach circumvents an inherent difficulty in traditional Reynolds decompositions of the conformation tensor: the fluctuating tensor fields are not positive-definite and so do not retain the physical meaning of the tensor. The geometric decomposition of the conformation tensor yields both mean and fluctuating tensor fields that are positive-definite. The fluctuating tensor in the present decomposition has a clear physical interpretation as a polymer deformation relative to the mean configuration. Scalar measures of this fluctuating conformation tensor are developed based on the non-Euclidean geometry of the set of positive-definite tensors. Drag-reduced viscoelastic turbulent channel flow is then used an example case study. The conformation tensor field, obtained using direct numerical simulations, is analysed using the proposed framework.
Qiu, Haijun; Cui, Peng; Regmi, Amar Deep; Hu, Sheng; Wang, Xingang; Zhang, Yuzhu
2018-01-01
In this study, we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides. To carry out this study, we employ data on 275 loess slides within Zhidan County, Central Loess Plateau, China. These data were collected in the field and supplemented by the interpretation of remote sensing images. Both the field observations and slope stability analysis show that loess slide size increases with the slope length. Slide sizes is significantly correlated with slope length, showing a power law relationship in both cases. However, the simulation results show that slope gradient is not associated with loess slide size. The main part of the link between slope gradient and slide size seen in the observations is only apparent, as indicated by the strong connection between slope gradient and length. Statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length, and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations. In addition, the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation. This analysis shows that slope length controls the rollover of the frequency-size distribution of loess slides. The scaling exponent increases with slope length.
Delay Kalman Filter to Estimate the Attitude of a Mobile Object with Indoor Magnetic Field Gradients
Directory of Open Access Journals (Sweden)
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.
In situ correction of field errors induced by temperature gradient in cryogenic undulators
Directory of Open Access Journals (Sweden)
Takashi Tanaka
2009-12-01
Full Text Available A new technique of undulator field correction for cryogenic permanent magnet undulators (CPMUs is proposed to correct the phase error induced by temperature gradient. This technique takes advantage of two important instruments: one is the in-vacuum self-aligned field analyzer with laser instrumentation system to precisely measure the distribution of the magnetic field generated by the permanent magnet arrays placed in vacuum, and the other is the differential adjuster to correct the local variation of the magnet gap. The details of the two instruments are described together with the method of how to analyze the field measurement data and deduce the gap variation along the undulator axis. The correction technique was applied to the CPMU with a length of 1.7 m and a magnetic period of 14 mm. It was found that the phase error induced during the cooling process was attributable to local gap variations of around 30 μm, which were then corrected by the differential adjuster.
The Physical Interpretation of the Lanczos Tensor
Roberts, Mark D.
1999-01-01
The field equations of general relativity can be written as first order differential equations in the Weyl tensor, the Weyl tensor in turn can be written as a first order differential equation in a three index tensor called the Lanczos tensor. The Lanczos tensor plays a similar role in general relativity to that of the vector potential in electro-magnetic theory. The Aharonov-Bohm effect shows that when quantum mechanics is applied to electro-magnetic theory the vector potential is dynamicall...
International Nuclear Information System (INIS)
Darling, T.W.; Migliori, A.; Moshopoulou, E.G.; Trugman, S.A.; Neumeier, J.J.; Sarrao, J.L.; Bishop, A.R.; Thompson, J.D.
1998-01-01
We have measured the (cubic-lattice-approximation) elastic moduli of optical melt-zone-grown single-crystal La 0.83 Sr 0.17 MnO 3 using resonant ultrasound spectroscopy. We observe the structural transition at 285 K to be hysteretic in the ambient (almost zero) magnetic field. A second elastic feature at the ferromagnetic T c 265 K, a third at 252 K, and a fourth in magnetic field at 220 K are also observed in this sample, which sits in a particularly complex region in composition space. The application of a magnetic field changes some of the elastic moduli significantly between 220 K and 285 K. By determining the complete elastic tensor, we identify which cubic crystallographic distortions are strongest at each elastic anomaly and which are sensitive to magnetic field. We also determine which bonds play a role in each of the observed features. copyright 1998 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Kaufmann, Delia
2012-02-03
Strings of laser cooled ions stored in microstructured Paul traps (microtraps) have promising potential for quantum information science. They provide a system which can be screened from a decohering environment, accurately prepared, manipulated and state selectively detected with efficiency close to unity. Magnetic field gradients allow for addressing trapped ions in frequency space. Furthermore, coupling of the ions' motional and spin states and long range spin-spin coupling of the ions' internal states are induced by such a gradient. This method is called Magnetic Gradient Induced Coupling, MAGIC. In this thesis, the design, construction and first characterization of a novel microtrap with an integrated solenoid is reported. The solenoid is designed to create a high magnetic field gradient per dissipated heat. The microtrap consists of three layers stacked onto each other. The outer layers provide a trapping potential, while the inner layer creates the switchable magnetic field gradient. Another specialty of this trap is the 33 pairs of DC-electrodes, allowing to move the ions along the trap axis and to adjust the range and the strength of the ions' spin-spin interactions. The microtrap is fixed on top of a ceramic block that provides the necessary electrical connections via thick film printed wires, a technique adopted in the context of microtraps for the first time, and in addition acts as a vacuum interface. The volume of the vacuum chamber is quite small, allowing for pressures in the low 10{sup -11} mbar range. In this microtrap, {sup 172}Yb{sup +}-ions are trapped, cooled and shuttled over a distance of about 2 mm. Trapped ions are used as magnetic field gradient probes, with a relative magnetic field precision of {delta}B/B{sub 0}=7.10{sup -6}. The addressing of two ions with the MAGIC method in the solenoid's magnetic field gradient is demonstrated.
The double-gradient magnetic instability: Stabilizing effect of the guide field
Energy Technology Data Exchange (ETDEWEB)
Korovinskiy, D. B., E-mail: daniil.korovinskiy@gmail.com; Semenov, V. S.; Ivanova, V. V. [Saint Petersburg State University, 198504, Ulyanovskaya 1, Petrodvoretz (Russian Federation); Divin, A. V. [Saint Petersburg State University, 198504, Ulyanovskaya 1, Petrodvoretz (Russian Federation); Swedish Institute of Space Physics, SE-751 21 Uppsala (Sweden); Erkaev, N. V. [Institute of Computational Modelling, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Siberian Federal University, 660041 Krasnoyarsk (Russian Federation); Artemyev, A. V. [Space Research Institute RAS, Profsoyuznaya 84/32, Moscow 117997 (Russian Federation); Ivanov, I. B. [Saint Petersburg State University, 198504, Ulyanovskaya 1, Petrodvoretz (Russian Federation); Theoretical Physics Division, Petersburg Nuclear Physics Institute, 188300 Gatchina (Russian Federation); Lapenta, G. [Centrum voor Plasma-Astrofysica, Departement Wiskunde, Katholieke Universiteit Leuven, B-3001 Leuven (Belgium); Markidis, S. [PDC Center for High Performance Computing, KTH Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Biernat, H. K. [Space Research Institute, Austrian Academy of Sciences, 8042 Graz (Austria); Institute of Physics, University of Graz, 8010 Graz (Austria)
2015-01-15
The role of the dawn-dusk magnetic field component in stabilizing of the magnetotail flapping oscillations is investigated in the double-gradient model framework (Erkaev et al., Phys. Rev. Lett. 99, 235003 (2007)), extended for the magnetotail-like configurations with non-zero guide field B{sub y}. Contribution of the guide field is examined both analytically and by means of linearized 2-dimensional (2D) and non-linear 3-dimensional (3D) MHD modeling. All three approaches demonstrate the same properties of the instability: stabilization of current sheet oscillations for short wavelength modes, appearing of the typical (fastest growing) wavelength λ{sub peak} of the order of the current sheet width, decrease of the peak growth rate with increasing B{sub y} value, and total decay of the mode for B{sub y}∼0.5 in the lobe magnetic field units. Analytical solution and 2D numerical simulations claim also the shift of λ{sub peak} toward the longer wavelengths with increasing guide field. This result is barely visible in 3D simulations. It may be accounted for the specific background magnetic configuration, the pattern of tail-like equilibrium provided by approximated solution of the conventional Grad-Shafranov equation. The configuration demonstrates drastically changing radius of curvature of magnetic field lines, R{sub c}. This, in turn, favors the “double-gradient” mode (λ > R{sub c}) in one part of the sheet and classical “ballooning” instability (λ < R{sub c}) in another part, which may result in generation of a “combined” unstable mode.
Template-assisted nano-patterning of magnetic core-shell particles in gradient fields.
Xue, Xiaozheng; Furlani, Edward P
2014-07-14
A method is proposed for controlling the assembly of colloidal magnetic core-shell nanoparticles into patterned monolayer structures with nanoscale feature resolution. The method is based on magnetic field-directed self-assembly that is enhanced using soft-magnetic template elements. The elements are embedded in a nonmagnetic substrate and magnetized using a uniform bias field. A key feature of this approach is the combined use of a uniform field with induced gradient-fields produced by the template elements. This enables the customization of a force field with localized regions of attractive and repulsive magnetic forces that provide extraordinary control of particle motion during assembly. The method is demonstrated using a computational model that simulates the assembly process taking into account magnetic and hydrodynamic forces including interparticle interactions, Brownian diffusion, van der Waals force and effects of surfactants. The analysis shows that extended geometric patterns of particles can be assembled with nanoscale resolution, beyond that of the template elements, within milliseconds. This is achieved by tailoring key parameters including the template geometry to produce a force field that focuses the particles into prescribed patterns; the thickness of the dielectric particle shell to control the magnetic dipole-dipole force upon contact and the particle volume fraction to suppress undesired aggregation during assembly. The proposed method broadly applies to arbitrary template geometries and multi-layered core-shell particles with at least one magnetic component. It can enable the self-assembly of complex patterns of nanoparticles and open up opportunities for the scalable fabrication of multifunctional nanostructured materials for a broad range of applications.
Park, Tyler; Adams, Mike; Bunker, Austin; Hodges, Jeffery; Stufflebeam, Michael; Evenson, William; Matheson, Phil; Zacate, Matthew
2009-10-01
Materials contain defects, which affect crystal properties such as damping of the correlation signal,G2(t), in time and broadening of the frequency spectrum in perturbed angular correlation (PAC) experiments. We attribute this inhomogeneous broadening (IHB) to the random static defects that produce a distribution of electric field gradients (EFGs). Our goal is to find a relationship between the amount of broadening and the concentration of defects. After simulating the EFGs from random configurations of defects, we map our results from the Vzz-Vxx plane to a coordinate system optimized for the EFG distribution through a Czjzek transformation, followed by a conformal mapping. From histograms in this space, we can define probability distribution functions with parameters that vary according to defect concentration. This allows us to calculate the broadened G2(t) spectrum for any concentration, and, in reverse, identify concentrations given a broadened G2(t) spectrum.
The attainment of large accelerating gradients using near field synchrotron radiation
International Nuclear Information System (INIS)
Decker, G.
1989-01-01
Lienard-Wiechert potentials are used to find the electromagnetic field everywhere in free space resulting from a point charge moving on a helical trajectory. The total power emitted as synchrotron radiation from a particle on a circular path is calculated. The point charge results are generalized to the case of a line charge, and formulae are presented which can easily be evaluated numerically. A useful gradient of 80 MeV/m per kA of peak driving beam current over a distance of 1 cm is calculated using two 5 MeV driving beams moving on 1 cm radius helical orbits with bunch length 1 mm. 11 refs., 5 figs
Pelcé, Pierre
2018-02-07
It has been reported that the ionic patterns of hyphal growth can be explained by a weakening of the active transport at the tip at the expense of other biosynthesis processes, from which results energy transport from the proximal cells to the apical ones (Potapova et al. 1988). We present here a theory to support this hypothesis, whose extent is much more general than the initial frame where it has been formulated. It can be summarized in two basics mechanisms, one coupling active transport of the plasma membrane, electric potential and vesicle fusion, the other coupling the Ca 2+ -ATPase of the endoplasmic reticulum and vesicle fusion. For some values of parameters introduced in the theory, the uniform state of the cell becomes unstable, at the origin of intracellular gradient fields. Theoretical ionic patterns are spontaneously produced, which can be satisfactorily compared to several observed in and around tip-growing cells. Copyright © 2017 Elsevier Ltd. All rights reserved.
International Nuclear Information System (INIS)
Ozaki, Hideaki
2004-01-01
Using the closed-time-path formalism, we construct perturbative frameworks, in terms of quasiparticle picture, for studying quasiuniform relativistic quantum field systems near equilibrium and non-equilibrium quasistationary systems. We employ the derivative expansion and take in up to the second-order term, i.e., one-order higher than the gradient approximation. After constructing self-energy resumed propagator, we formulated two kinds of mutually equivalent perturbative frameworks: The first one is formulated on the basis of the 'bare' number density function, and the second one is formulated on the basis of 'physical' number density function. In the course of construction of the second framework, the generalized Boltzmann equations directly come out, which describe the evolution of the system. (author)
Phase transition in tensor models
Energy Technology Data Exchange (ETDEWEB)
Delepouve, Thibault [Laboratoire de Physique Théorique, CNRS UMR 8627, Université Paris Sud,91405 Orsay Cedex (France); Centre de Physique Théorique, CNRS UMR 7644, École Polytechnique,91128 Palaiseau Cedex (France); Gurau, Razvan [Centre de Physique Théorique, CNRS UMR 7644, École Polytechnique,91128 Palaiseau Cedex (France); Perimeter Institute for Theoretical Physics,31 Caroline St. N, N2L 2Y5, Waterloo, ON (Canada)
2015-06-25
Generalizing matrix models, tensor models generate dynamical triangulations in any dimension and support a 1/N expansion. Using the intermediate field representation we explicitly rewrite a quartic tensor model as a field theory for a fluctuation field around a vacuum state corresponding to the resummation of the entire leading order in 1/N (a resummation of the melonic family). We then prove that the critical regime in which the continuum limit in the sense of dynamical triangulations is reached is precisely a phase transition in the field theory sense for the fluctuation field.
Mitchell, J; Chandrasekera, T C; Johns, M L; Gladden, L F; Fordham, E J
2010-02-01
It is known that internal magnetic field gradients in porous materials, caused by susceptibility differences at the solid-fluid interfaces, alter the observed effective Nuclear Magnetic Resonance transverse relaxation times T2,eff. The internal gradients scale with the strength of the static background magnetic field B0. Here, we acquire data at various magnitudes of B0 to observe the influence of internal gradients on T2-T2 exchange measurements; the theory discussed and observations made are applicable to any T2-T2 analysis of heterogeneous materials. At high magnetic field strengths, it is possible to observe diffusive exchange between regions of local internal gradient extrema within individual pores. Therefore, the observed exchange pathways are not associated with pore-to-pore exchange. Understanding the significance of internal gradients in transverse relaxation measurements is critical to interpreting these results. We present the example of water in porous sandstone rock and offer a guideline to determine whether an observed T2,eff relaxation time distribution reflects the pore size distribution for a given susceptibility contrast (magnetic field strength) and spin echo separation. More generally, we confirm that for porous materials T1 provides a better indication of the pore size distribution than T2,eff at high magnetic field strengths (B0>1 T), and demonstrate the data analysis necessary to validate pore size interpretations of T2,eff measurements.
Expected performance of time-gradient magnetic field SESANS diffractometer at pulsed reactor IBR-2
Bodnarchuk, V.; Sadilov, V.; Manoshin, S.; Erhan, R. V.; Ioffe, A.
2017-06-01
The application of the time-gradient magnetic field neutron spin-echo technique (TGF-NSE) aiming to extend the possibilities of the REFLEX reflectometer at the pulsed reactor IBR-2 (Dubna, Russia) towards a high and medium resolution small-angle scattering is considered. This technique requires the use of a linearly increasing magnetic field in the form of the sequence of saw-teeth pulses. Such a technique is well-suited to the pulsed structure of the neutron beam at the IBR-2 reactor. The wide range of neutron wavelengths employed in the time-of-flight (TOF) operation mode allows for the simultaneous coverage of a wide range of spin-echo lengths (corresponding to a wide Q-range in conventional SANS). Virtual experiments carried out using the VITESS simulation package demonstrate that such a setup at IBR-2 will allow for the coverage of the length scales from 100 Å to 6000 Å in a single instrument setting. The use of the TGF-NSE technique in the TOF mode leads to gaps in the measured SANS curves due to the jumps of magnetic field at the end of saw-teeth pulses. However, crucially, these do not harm the quality of the data. Moreover, the lost data can be retrieved by an additional measurement with a delayed start of the magnetic pulse sequence.
Directory of Open Access Journals (Sweden)
E. Keil
2007-05-01
Full Text Available Nonscaling fixed field alternating gradient (FFAG rings for cancer hadron therapy offer reduced physical aperture and large dynamic aperture as compared to scaling FFAGs. The variation of tune with energy implies the crossing of resonances during acceleration. Our design avoids intrinsic resonances, although imperfection resonances must be crossed. We consider a system of three nonscaling FFAG rings for cancer therapy with 250 MeV protons and 400 MeV/u carbon ions. Hadrons are accelerated in a common radio frequency quadrupole and linear accelerator, and injected into the FFAG rings at v/c=0.1294. H^{+}/C^{6+} ions are accelerated in the two smaller/larger rings to 31 and 250 MeV/68.8 and 400 MeV/u kinetic energy, respectively. The lattices consist of doublet cells with a straight section for rf cavities. The gantry with triplet cells accepts the whole required momentum range at fixed field. This unique design uses either high-temperature superconductors or superconducting magnets reducing gantry magnet size and weight. Elements with a variable field at the beginning and at the end set the extracted beam at the correct position for a range of energies.
Energy Technology Data Exchange (ETDEWEB)
Renteria, M.; Requejo, F.G.; Bibiloni, A.G.; Pasquevich, A.F.; Shitu, J. [Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC N67, 1900 La Plata (Argentina); Freitag, K. [Institut fuer Strahlen- und Kernphysik der Universitaet Bonn, Nussallee 14-16, 5300 Bonn (Germany)
1997-06-01
We studied the hyperfine interactions of {sup 181}Ta in In{sub 2}O{sub 3} by means of perturbed-angular-correlation (PAC) measurements. We prepared thin films of indium sesquioxide with different degrees of initial amorphism and implanted them with {sup 181}Hf. Chemically prepared indium-sesquioxide powder samples were also made starting from neutron-irradiated HfCl{sub 4}, which provides the {sup 181}Hf PAC probes. PAC experiments were performed on each sample at room temperature, after each step of annealing programs at increasing temperatures up to the full crystallization of the samples. The results indicate that the PAC probe occupies preferentially the axially symmetric cation site. Point-charge-model calculations were performed. The calculated asymmetry parameters {eta} were compared with those obtained in {sup 181}Hf PAC experiments performed also on other binary oxides, showing that the symmetry of the electric-field-gradient (EFG) tensor at {sup 181}Ta cation sites in binary oxides is mainly determined by the nearest-neighbor oxygen-ion distribution around the probe. Comparisons of the experimental results in bixbyites obtained for both PAC probes, {sup 111}Cd and {sup 181}Ta, show that the local EFG in bixbyites, are strongly dependent on the geometry of the sites and the electronic configuration of the probes. {copyright} {ital 1997} {ital The American Physical Society}
HIGH-GRADIENT, HIGH-TRANSFORMER-RATIO, DIELECTRIC WAKE FIELD ACCELERATOR
Energy Technology Data Exchange (ETDEWEB)
Hirshfield, Jay L
2012-04-12
The Phase I work reported here responds to DoE'ss stated need "...to develop improved accelerator designs that can provide very high gradient (>200 MV/m for electrons...) acceleration of intense bunches of particles." Omega-P's approach to this goal is through use of a ramped train of annular electron bunches to drive a coaxial dielectric wakefield accelerator (CDWA) structure. This approach is a direct extension of the CDWA concept from acceleration in wake fields caused by a single drive bunch, to the more efficient acceleration that we predict can be realized from a tailored (or ramped) train of several drive bunches. This is possible because of a much higher transformer ratio for the latter. The CDWA structure itself has a number of unique features, including: a high accelerating gradient G, potentially with G > 1 GeV/m; continuous energy coupling from drive to test bunches without transfer structures; inherent transverse focusing forces for particles in the accelerated bunch; highly stable motion of high charge annular drive bunches; acceptable alignment tolerances for a multi-section system. What is new in the present approach is that the coaxial dielectric structure is now to be energized by-not one-but by a short train of ramped annular-shaped drive bunches moving in the outer coaxial channel of the structure. We have shown that this allows acceleration of an electron bunch traveling along the axis in the inner channel with a markedly higher transformer ratio T than for a single drive bunch. As described in this report, the structure will be a GHz-scale prototype with cm-scale transverse dimensions that is expected to confirm principles that can be applied to the design of a future THz-scale high gradient (> 500 MV/m) accelerator with mm-scale transverse dimensions. We show here a new means to significantly increase the transformer ratio T of the device, and thereby to significantly improve its suitability as a flexible and effective component in
Sun, Qi; Fu, Shujun
2017-09-20
Fringe orientation is an important feature of fringe patterns and has a wide range of applications such as guiding fringe pattern filtering, phase unwrapping, and abstraction. Estimating fringe orientation is a basic task for subsequent processing of fringe patterns. However, various noise, singular and obscure points, and orientation data degeneration lead to inaccurate calculations of fringe orientation. Thus, to deepen the understanding of orientation estimation and to better guide orientation estimation in fringe pattern processing, some advanced gradient-field-based orientation estimation methods are compared and analyzed. At the same time, following the ideas of smoothing regularization and computing of bigger gradient fields, a regularized singular-value decomposition (RSVD) technique is proposed for fringe orientation estimation. To compare the performance of these gradient-field-based methods, quantitative results and visual effect maps of orientation estimation are given on simulated and real fringe patterns that demonstrate that the RSVD produces the best estimation results at a cost of relatively less time.
International Nuclear Information System (INIS)
Yoon, Seokchan; Choi, Youngwoon; Park, Sangbum; Ji, Wangxi; Lee, Jai-Hyung; An, Kyungwon
2007-01-01
A quantitative study on characteristics of a magneto-optical trap with a single or a few atoms is presented. A very small number of 85 Rb atoms were trapped in a micron-size magneto-optical trap with a high magnetic-field gradient. In order to find the optimum condition for a single-atom trap, we have investigated how the number of atoms and the size of atomic cloud change as various experimental parameters, such as a magnetic-field gradient and the trapping laser intensity and detuning. The averaged number of atoms was measured very accurately with a calibration procedure based on the single-atom saturation curve of resonance fluorescence. In addition, the number of atoms in a trap could be controlled by suppressing stochastic loading events by means of a real-time active feedback on the magnetic-field gradient
Karoly, Kis; Taylor, Patrick T.; Geza, Wittmann
2014-01-01
We computed magnetic field gradients at satellite altitude, over Europe with emphasis on the Kursk Magnetic Anomaly (KMA). They were calculated using the CHAMP satellite total magnetic anomalies. Our computations were done to determine how the magnetic anomaly data from the new ESA/Swarm satellites could be utilized to determine the structure of the magnetization of the Earths crust, especially in the region of the KMA. Since the ten years of 2 CHAMP data could be used to simulate the Swarm data. An initial East magnetic anomaly gradient map of Europe was computed and subsequently the North, East and Vertical magnetic gradients for the KMA region were calculated. The vertical gradient of the KMA was determined using Hilbert transforms. Inversion of the total KMA was derived using Simplex and Simulated Annealing algorithms. Our resulting inversion depth model is a horizontal quadrangle with upper 300-329 km and lower 331-339 km boundaries.
The energy–momentum tensor(s in classical gauge theories
Directory of Open Access Journals (Sweden)
Daniel N. Blaschke
2016-11-01
Full Text Available We give an introduction to, and review of, the energy–momentum tensors in classical gauge field theories in Minkowski space, and to some extent also in curved space–time. For the canonical energy–momentum tensor of non-Abelian gauge fields and of matter fields coupled to such fields, we present a new and simple improvement procedure based on gauge invariance for constructing a gauge invariant, symmetric energy–momentum tensor. The relationship with the Einstein–Hilbert tensor following from the coupling to a gravitational field is also discussed.
The energy–momentum tensor(s) in classical gauge theories
Energy Technology Data Exchange (ETDEWEB)
Blaschke, Daniel N., E-mail: dblaschke@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Gieres, François, E-mail: gieres@ipnl.in2p3.fr [Institut de Physique Nucléaire de Lyon, Université de Lyon, Université Claude Bernard Lyon 1 and CNRS/IN2P3, Bat. P. Dirac, 4 rue Enrico Fermi, F-69622 Villeurbanne (France); Reboud, Méril, E-mail: meril.reboud@ens-lyon.fr [Institut de Physique Nucléaire de Lyon, Université de Lyon, Université Claude Bernard Lyon 1 and CNRS/IN2P3, Bat. P. Dirac, 4 rue Enrico Fermi, F-69622 Villeurbanne (France); Ecole Normale Supérieure de Lyon, 46 allée d' Italie, F-69364 Lyon CEDEX 07 (France); Schweda, Manfred, E-mail: mschweda@tph.tuwien.ac.at [Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8-10, A-1040 Vienna (Austria)
2016-11-15
We give an introduction to, and review of, the energy–momentum tensors in classical gauge field theories in Minkowski space, and to some extent also in curved space–time. For the canonical energy–momentum tensor of non-Abelian gauge fields and of matter fields coupled to such fields, we present a new and simple improvement procedure based on gauge invariance for constructing a gauge invariant, symmetric energy–momentum tensor. The relationship with the Einstein–Hilbert tensor following from the coupling to a gravitational field is also discussed.
Miehe, C; Teichtmeister, S; Aldakheel, F
2016-04-28
This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic-plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. © 2016 The Author(s).
International Nuclear Information System (INIS)
Rebane, T.K.; Ivanov, A.I.; Budanov, G.I.
1985-01-01
General formulas have previously been described for approximating the dependence of the electric field gradient at a nucleus on the configuration of the nuclear core in the molecule, and these are applied to simple diatomic molecules, mainly hydrides of XH type
Cao, Quanliang; Li, Zhenhao; Wang, Zhen; Qi, Fan; Han, Xiaotao
2018-05-01
How to prevent particle aggregation in the magnetic separation process is of great importance for high-purity separation, while it is a challenging issue in practice. In this work, we report a novel method to solve this problem for improving the selectivity of size-based separation by use of a gradient alternating magnetic field. The specially designed magnetic field is capable of dynamically adjusting the magnetic field direction without changing the direction of magnetic gradient force acting on the particles. Using direct numerical simulations, we show that particles within a certain center-to-center distance are inseparable under a gradient static magnetic field since they are easy aggregated and then start moving together. By contrast, it has been demonstrated that alternating repulsive and attractive interaction forces between particles can be generated to avoid the formation of aggregations when the alternating gradient magnetic field with a given alternating frequency is applied, enabling these particles to be continuously separated based on size-dependent properties. The proposed magnetic separation method and simulation results have the significance for fundamental understanding of particle dynamic behavior and improving the separation efficiency.
Gravitational Metric Tensor Exterior to Rotating Homogeneous ...
African Journals Online (AJOL)
The covariant and contravariant metric tensors exterior to a homogeneous spherical body rotating uniformly about a common φ axis with constant angular velocity ω is constructed. The constructed metric tensors in this gravitational field have seven non-zero distinct components.The Lagrangian for this gravitational field is ...
Tensor Transpose and Its Properties
Pan, Ran
2014-01-01
Tensor transpose is a higher order generalization of matrix transpose. In this paper, we use permutations and symmetry group to define? the tensor transpose. Then we discuss the classification and composition of tensor transposes. Properties of tensor transpose are studied in relation to tensor multiplication, tensor eigenvalues, tensor decompositions and tensor rank.
Colored Tensor Models - a Review
Directory of Open Access Journals (Sweden)
Razvan Gurau
2012-04-01
Full Text Available Colored tensor models have recently burst onto the scene as a promising conceptual and computational tool in the investigation of problems of random geometry in dimension three and higher. We present a snapshot of the cutting edge in this rapidly expanding research field. Colored tensor models have been shown to share many of the properties of their direct ancestor, matrix models, which encode a theory of fluctuating two-dimensional surfaces. These features include the possession of Feynman graphs encoding topological spaces, a 1/N expansion of graph amplitudes, embedded matrix models inside the tensor structure, a resumable leading order with critical behavior and a continuum large volume limit, Schwinger-Dyson equations satisfying a Lie algebra (akin to the Virasoro algebra in two dimensions, non-trivial classical solutions and so on. In this review, we give a detailed introduction of colored tensor models and pointers to current and future research directions.
Some effects of high- gradient magnetic field on tropism of roots of higher plants
Kondrachuk, A.; Belyavskaya, N.
The perception of gravity in living organisms is mostly based on the response of the gravisensing system to displacement of some specific mass caused by gravitational force. According to the starch-statolith hypothesis the amyloplasts play the role of specific mass in gravisensing cells of higher plants. Kuznetsov & Hasenstein (1996) have demonstrated that the high-gradient magnetic field (HGMF) exerts a directional ponderomotive force on diamagnetic substances, in particular, statoliths. This effect of the HGMF causes root response similar to that produced by the change in gravity vector. Their studies supported the starch-statolith hypothesis and showed that ponderomotive force can be used to modify force acting on statoliths by manipulating statolith locations within gravisensing cells. We have designed the HGMF facility that allows for generating the HGMF and analyzing its effects on higher plants' roots. It records by videosystem and measures with the help of image analysis software the parameters of kinetics of root bending under both the HGMF action and gravistimulation. Two species of plants (pea and cress) have been examined. The main results of the work are the following: 1) The magnetotropic effect of HGMF on root growth was found for both species. 2) The critical value of ponderomotive force that caused the magnetotropic effect was estimated by modeling the magnetic field spatial distribution in the region of root apex. 3) The electron-microscopic analysis of statocytes after the HGMF treatment was carried out. The displacement of amyloplasts in root statocytes of two species of plants in HGMF was firstly demonstrated at the ultrastructural level. 4) Spatial distribution of exogenous proton fluxes (pH) along the roots was studied. The changes in pH distribution along curvature zone and apices of roots were revealed in the HGMF. It is known that application of HGMFs or strong uniform magnetic fields may influence ion transport due to Ampere force. It
The Energy-Momentum Tensor(s) in Classical Gauge Theories
Blaschke, Daniel N.; Gieres, Francois; Reboud, Meril; Schweda, Manfred
2016-01-01
We give an introduction to, and review of, the energy–momentum tensors in classical gauge field theories in Minkowski space, and to some extent also in curved space–time. For the canonical energy–momentum tensor of non-Abelian gauge fields and of matter fields coupled to such fields, we present a new and simple improvement procedure based on gauge invariance for constructing a gauge invariant, symmetric energy–momentum tensor. The relationship with the Einstein–Hilbert tensor following from t...
Fixed Field Alternating Gradient (FFAG)accelerators and their medical application in proton therapy
International Nuclear Information System (INIS)
Fourrier, J.
2008-10-01
Radiotherapy uses particle beams to irradiate and kill cancer tumors while sparing healthy tissues. Bragg peak shape of the proton energy loss in matter allows a ballistic improvement of the dose deposition compared with X rays. Thus, the irradiated volume can be precisely adjusted to the tumour. This thesis, in the frame of the RACCAM project, aims to the study and the design of a proton therapy installation based on a fixed field alternating gradient (FFAG) accelerator in order to build a spiral sector FFAG magnet for validation. First, we present proton therapy to define medical specifications leading to the technical specifications of a proton therapy installation. Secondly, we introduce FFAG accelerators through their past and on-going projects which are on their way around the world before developing the beam dynamic theories in the case of invariant focusing optics (scaling FFAG). We describe modelling and simulation tools developed to study the dynamics in a spiral scaling FFAG accelerator. Then we explain the spiral optic parameter search which has leaded to the construction of a magnet prototype. Finally, we describe the RACCAM project proton therapy installation starting from the injector cyclotron and ending with the extraction system. (author)
Electric field gradients at 181Ta sites in HfOx
International Nuclear Information System (INIS)
Darriba, G.N.; Rodriguez, A.M.; Saitovitch, H.; Silva, P.R.J.; Pasquevich, A.F.
2007-01-01
In the present work we report preliminary results about the possibility to study properties of the order-disorder transition in HfO x solid solutions via the determination of the electric field gradient (EFG) at 181 Ta radioactive probes. Oxygen solution into the metal was achieved by arc melting stoichiometric amounts of metallic Hf and HfO 2 under argon atmosphere. Samples of HfO x with x=0.1 and 0.2 were prepared. Two types of samples were used for the perturbed angular correlation (PAC) experiments by doping alternatively with 181 Ta, by neutron irradiation, the metallic Hf or the hafnium oxide. The PAC results on both samples were identical, with disappearing hyperfine signals of the metal and the oxide, showing a complete diffusion of the probes independent of the way of doping. The PAC signal of the HfO x solid solution consisted in a wide distribution of EFGs due to the oxygen disorder. This scheme held even after long thermal treatments at high temperature (several days at 1273K). Annealing treatments at moderate temperature (600K) were also made. In these cases the samples were cooling at a very low rate. These results, together with those obtained by measuring samples below and above the order temperature are reported
Geier, Oliver; Snurr, Randall Q.; Stallmach, Frank; Kärger, Jörg
2004-01-01
The boundary conditions of intraparticle diffusion in nanoporous materials may be chosen to approach the limiting cases of either absorbing or reflecting boundaries, depending on the host-guest system under study and the temperature of measurement. Pulsed field gradient nuclear magnetic resonance is applied to monitor molecular diffusion of n-hexane and of an n-hexane-tetrafluoromethane mixture adsorbed in zeolite crystallites of type NaX under either of these limiting conditions. Taking advantage of the thus-established peculiarities of mass transfer at the interface between the zeolite bulk phase and the surrounding atmosphere, three independent routes for probing the crystal size are compared. These techniques are based on (i) the measurement of the effective diffusivity under complete confinement, (ii) the application of the so-called NMR tracer desorption technique, and (iii) an analysis of the time dependence of the effective diffusivity in the short-time limit where, by an appropriate variation of the adsorbate and the measuring conditions, the limiting cases of reflecting and adsorbing boundaries could be considered. All these techniques are found to yield coinciding results, which are in excellent agreement with the crystal sizes determined by microscopy.
Correlated displacement-T2 MRI by means of a pulsed field gradient - milti spin echo method
Windt, C.W.; Vergeldt, F.J.; As, van H.
2007-01-01
A method for correlated displacement-T2 imaging is presented. A Pulsed Field Gradient-Multi Spin Echo (PFG-MSE) sequence is used to record T2 resolved propagators on a voxel-by-voxel basis, making it possible to perform single voxel correlated displacement-T2 analyses. In spatially heterogeneous
Directory of Open Access Journals (Sweden)
Yuan Jiang
Full Text Available We surveyed the Trichoderma (Hypocreales, Ascomycota biodiversity in agricultural fields in four major agricultural provinces of East China. Trichoderma strains were identified based on molecular approaches and morphological characteristics. In three sampled seasons (spring, summer and autumn, 2078 strains were isolated and identified to 17 known species: T. harzianum (429 isolates, T. asperellum (425, T. hamatum (397, T. virens (340, T. koningiopsis (248, T. brevicompactum (73, T. atroviride (73, T. fertile (26, T. longibrachiatum (22, T. pleuroticola (16, T. erinaceum (16, T. oblongisporum (2, T. polysporum (2, T. spirale (2, T. capillare (2, T. velutinum (2, and T. saturnisporum (1. T. harzianum, T. asperellum, T. hamatum, and T. virens were identified as the dominant species with dominance (Y values of 0.057, 0.052, 0.048, and 0.039, respectively. The species amount, isolate numbers and the dominant species of Trichoderma varied between provinces. Zhejiang Province has shown the highest diversity, which was reflected in the highest species amount (14 and the highest Shannon-Wiener diversity index of Trichoderma haplotypes (1.46. We observed that relative frequencies of T. hamatum and T. koningiopsis under rice soil were higher than those under wheat and maize soil, indicating the preference of Trichoderma to different crops. Remarkable seasonal variation was shown, with summer exhibiting the highest biodiversity of the studied seasons. These results show that Trichoderma biodiversity in agricultural fields varies by region, crop, and season. Zhejiang Province (the southernmost province in the investigated area had more T. hamatum than Shandong Province (the northernmost province, not only in isolate amounts but also in haplotype amounts. Furthermore, at haplotype level, only T. hamatum showed a gradient distribution from south to north in correspondence analysis among the four dominant species. The above results would contribute to the
Fotin, Sergei V.; Yin, Yin; Periaswamy, Senthil; Kunz, Justin; Haldankar, Hrishikesh; Muradyan, Naira; Cornud, François; Turkbey, Baris; Choyke, Peter L.
2012-02-01
Fully automated prostate segmentation helps to address several problems in prostate cancer diagnosis and treatment: it can assist in objective evaluation of multiparametric MR imagery, provides a prostate contour for MR-ultrasound (or CT) image fusion for computer-assisted image-guided biopsy or therapy planning, may facilitate reporting and enables direct prostate volume calculation. Among the challenges in automated analysis of MR images of the prostate are the variations of overall image intensities across scanners, the presence of nonuniform multiplicative bias field within scans and differences in acquisition setup. Furthermore, images acquired with the presence of an endorectal coil suffer from localized high-intensity artifacts at the posterior part of the prostate. In this work, a three-dimensional method for fast automated prostate detection based on normalized gradient fields cross-correlation, insensitive to intensity variations and coil-induced artifacts, is presented and evaluated. The components of the method, offline template learning and the localization algorithm, are described in detail. The method was validated on a dataset of 522 T2-weighted MR images acquired at the National Cancer Institute, USA that was split in two halves for development and testing. In addition, second dataset of 29 MR exams from Centre d'Imagerie Médicale Tourville, France were used to test the algorithm. The 95% confidence intervals for the mean Euclidean distance between automatically and manually identified prostate centroids were 4.06 +/- 0.33 mm and 3.10 +/- 0.43 mm for the first and second test datasets respectively. Moreover, the algorithm provided the centroid within the true prostate volume in 100% of images from both datasets. Obtained results demonstrate high utility of the detection method for a fully automated prostate segmentation.
3D reconstruction of tensors and vectors
Energy Technology Data Exchange (ETDEWEB)
Defrise, Michel; Gullberg, Grant T.
2005-02-17
Here we have developed formulations for the reconstruction of 3D tensor fields from planar (Radon) and line-integral (X-ray) projections of 3D vector and tensor fields. Much of the motivation for this work is the potential application of MRI to perform diffusion tensor tomography. The goal is to develop a theory for the reconstruction of both Radon planar and X-ray or line-integral projections because of the flexibility of MRI to obtain both of these type of projections in 3D. The development presented here for the linear tensor tomography problem provides insight into the structure of the nonlinear MRI diffusion tensor inverse problem. A particular application of tensor imaging in MRI is the potential application of cardiac diffusion tensor tomography for determining in vivo cardiac fiber structure. One difficulty in the cardiac application is the motion of the heart. This presents a need for developing future theory for tensor tomography in a motion field. This means developing a better understanding of the MRI signal for diffusion processes in a deforming media. The techniques developed may allow the application of MRI tensor tomography for the study of structure of fiber tracts in the brain, atherosclerotic plaque, and spine in addition to fiber structure in the heart. However, the relations presented are also applicable to other fields in medical imaging such as diffraction tomography using ultrasound. The mathematics presented can also be extended to exponential Radon transform of tensor fields and to other geometric acquisitions such as cone beam tomography of tensor fields.
Energy Technology Data Exchange (ETDEWEB)
Le Caer, Gerard [Institut de Physique de Rennes, UMR UR1-CNRS 6251, Universite de Rennes I, Campus de Beaulieu, Batiment 11A, 35042 Rennes Cedex (France); Bureau, Bruno [Equipe Verres et Ceramiques, UMR-CNRS 6226 Sciences Chimiques de Rennes, Universite de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex (France); Massiot, Dominique, E-mail: gerard.le-caer@univ-rennes1.f, E-mail: bruno.bureau@univ-rennes1.f, E-mail: dominique.massiot@cnrs-orleans.f [Centre de Recherches sur les Materiaux a Hautes Temperatures, UPR 4212 CNRS, 1D avenue de la Recherche Scientifique, 45071 Orleans Cedex 2 (France)
2010-02-17
First, the basis and the characteristics of the Czjzek model for the distribution of electric field gradient (EFG) tensor in disordered solids, some of which are still unnoticed, are depicted. That model results from the statistical invariance by rotation of the structure of the considered disordered solid and from the applicability of a central limit theorem to the EFG tensor. These two conditions, which are physically realistic for a wealth of disordered solids, simplify tremendously the derivation of the EFG distribution but at the cost of a complete loss of structural information about the investigated solid. Next, we describe a simple extension of it which is intended to mimic a well-defined local environment, with given values of the asymmetry parameter and of the principal component V{sub zz} of the EFG tensor, perturbed by the disorder of more remote atoms. The effect of disorder is rendered by a Gaussian (Czjzek) noise with an adjustable weight relative to V{sub zz}. The number of free parameters is limited to three, as compared to a sole scale factor for the Czjzek model. Its characteristics are described as a function of the given asymmetry parameter and of the strength of the noise. The aim is to lead to a practical tool which may help to retrieve, as far as possible, the information about the local environment perturbed by disorder from hyperfine measurements and notably from NMR spectra of quadrupolar nuclei. As an example, that extension is applied to some static NMR spectra of {sup 71}Ga in covalent glasses. Calculated static {sup 71}Ga NMR lineshapes are shown as a function of the parameters of the extended model.
Tensor rank is not multiplicative under the tensor product
M. Christandl (Matthias); A. K. Jensen (Asger Kjærulff); J. Zuiddam (Jeroen)
2018-01-01
textabstractThe tensor rank of a tensor t is the smallest number r such that t can be decomposed as a sum of r simple tensors. Let s be a k-tensor and let t be an ℓ-tensor. The tensor product of s and t is a (k+ℓ)-tensor. Tensor rank is sub-multiplicative under the tensor product. We revisit the
Tensor rank is not multiplicative under the tensor product
M. Christandl (Matthias); A. K. Jensen (Asger Kjærulff); J. Zuiddam (Jeroen)
2017-01-01
textabstractThe tensor rank of a tensor is the smallest number r such that the tensor can be decomposed as a sum of r simple tensors. Let s be a k-tensor and let t be an l-tensor. The tensor product of s and t is a (k + l)-tensor (not to be confused with the "tensor Kronecker product" used in
Yablonskiy, Dmitriy A; Sukstanskii, Alexander L; Luo, Jie; Wang, Xiaoqi
2012-01-01
Purpose Macroscopic magnetic field inhomogeneities adversely affect different aspects of MRI images. In quantitative MRI when the goal is to quantify biological tissue parameters, they bias and often corrupt such measurements. The goal of this paper is to develop a method for correction of macroscopic field inhomogeneities that can be applied to a variety of quantitative gradient-echo-based MRI techniques. Methods We have re-analyzed a basic theory of gradient echo (GE) MRI signal formation in the presence of background field inhomogeneities and derived equations that allow for correction of magnetic field inhomogeneity effects based on the phase and magnitude of GE data. We verified our theory by mapping R2* relaxation rate in computer simulated, phantom, and in vivo human data collected with multi-GE sequences. Results The proposed technique takes into account voxel spread function (VSF) effects and allowed obtaining virtually free from artifacts R2* maps for all simulated, phantom and in vivo data except of the edge areas with very steep field gradients. Conclusion The VSF method, allowing quantification of tissue specific R2*-related tissue properties, has a potential to breed new MRI biomarkers serving as surrogates for tissue biological properties similar to R1 and R2 relaxation rate constants widely used in clinical and research MRI. PMID:23233445
Characteristics of magnetic resonance imaging with partial flip angle and gradient field echo
International Nuclear Information System (INIS)
Hamada, Tatsumi; Uto, Tatsurou; Okafuji, Tatsumasa; Ookusa, Akihiko; Oonishi, Takuya; Mabuchi, Nobuhisa; Fujii, Kouichi; Yoshioka, Hiroyasu; Ishida, Osamu
1988-01-01
Characteristics of a magnetic resonance (MR) imaging pulse sequence with short repetition time (Tr), short echo time (Te), partial flip angle and gradient field echo, at 0.5 T, were studied. A series of sagittal images of the cerebrospinal region was obtained with varied Tr, Te and flip angle, signal intensities were measured by means of a region of interest (ROI) function, and optimal parameters to achieve maximum tissue contrast were found. Of the parameters flip angle had the greatest effect on tissue contrast. Flip angles less than 20 or more than 60 degrees were necessary to discriminate between spinal cord and cerebrospinal fluid. So called MR myelography was obtained with the flip angle of 15 degrees. Opposed and inphase images were obtained at the Te levels of 21 and 28 ms, respectively. Likewise, a series of transverse images of the abdomen with short Tr, short Te and varied flip angles was obtained in a breath-holding interval, and signal intensities of ROIs were measured. Maximum intensities of the liver, the spleen and perirenal fat were obtained at the flip angles of 40, 30 and 60 degrees, respectively. Although maximum intensity was found at the flip angle of 30 degrees for both of the renal cortex and medulla, the maximum contrast between the two tissues was obtained at the flip angles of 50-60 degrees. The image contrast obtained by these pulse sequences was also theoretically predictable, and so it is thought possible that flip angle, Tr and Te are manipulated to yield a desired contrast. (author)
Directory of Open Access Journals (Sweden)
Lijing Shao
2017-10-01
Full Text Available Pulsar timing and laser-interferometer gravitational-wave (GW detectors are superb laboratories to study gravity theories in the strong-field regime. Here, we combine these tools to test the mono-scalar-tensor theory of Damour and Esposito-Farèse (DEF, which predicts nonperturbative scalarization phenomena for neutron stars (NSs. First, applying Markov-chain Monte Carlo techniques, we use the absence of dipolar radiation in the pulsar-timing observations of five binary systems composed of a NS and a white dwarf, and eleven equations of state (EOSs for NSs, to derive the most stringent constraints on the two free parameters of the DEF scalar-tensor theory. Since the binary-pulsar bounds depend on the NS mass and the EOS, we find that current pulsar-timing observations leave scalarization windows, i.e., regions of parameter space where scalarization can still be prominent. Then, we investigate if these scalarization windows could be closed and if pulsar-timing constraints could be improved by laser-interferometer GW detectors, when spontaneous (or dynamical scalarization sets in during the early (or late stages of a binary NS (BNS evolution. For the early inspiral of a BNS carrying constant scalar charge, we employ a Fisher-matrix analysis to show that Advanced LIGO can improve pulsar-timing constraints for some EOSs, and next-generation detectors, such as the Cosmic Explorer and Einstein Telescope, will be able to improve those bounds for all eleven EOSs. Using the late inspiral of a BNS, we estimate that for some of the EOSs under consideration, the onset of dynamical scalarization can happen early enough to improve the constraints on the DEF parameters obtained by combining the five binary pulsars. Thus, in the near future, the complementarity of pulsar timing and direct observations of GWs on the ground will be extremely valuable in probing gravity theories in the strong-field regime.
The effects of noise over the complete space of diffusion tensor shape.
Gahm, Jin Kyu; Kindlmann, Gordon; Ennis, Daniel B
2014-01-01
Diffusion tensor magnetic resonance imaging (DT-MRI) is a technique used to quantify the microstructural organization of biological tissues. Multiple images are necessary to reconstruct the tensor data and each acquisition is subject to complex thermal noise. As such, measures of tensor invariants, which characterize components of tensor shape, derived from the tensor data will be biased from their true values. Previous work has examined this bias, but over a narrow range of tensor shape. Herein, we define the mathematics for constructing a tensor from tensor invariants, which permits an intuitive and principled means for building tensors with a complete range of tensor shape and salient microstructural properties. Thereafter, we use this development to evaluate by simulation the effects of noise on characterizing tensor shape over the complete space of tensor shape for three encoding schemes with different SNR and gradient directions. We also define a new framework for determining the distribution of the true values of tensor invariants given their measures, which provides guidance about the confidence the observer should have in the measures. Finally, we present the statistics of tensor invariant estimates over the complete space of tensor shape to demonstrate how the noise sensitivity of tensor invariants varies across the space of tensor shape as well as how the imaging protocol impacts measures of tensor invariants. Copyright © 2013 Elsevier B.V. All rights reserved.
Bayesian regularization of diffusion tensor images
DEFF Research Database (Denmark)
Frandsen, Jesper; Hobolth, Asger; Østergaard, Leif
2007-01-01
Diffusion tensor imaging (DTI) is a powerful tool in the study of the course of nerve fibre bundles in the human brain. Using DTI, the local fibre orientation in each image voxel can be described by a diffusion tensor which is constructed from local measurements of diffusion coefficients along...... several directions. The measured diffusion coefficients and thereby the diffusion tensors are subject to noise, leading to possibly flawed representations of the three dimensional fibre bundles. In this paper we develop a Bayesian procedure for regularizing the diffusion tensor field, fully utilizing...
Radiative corrections in a vector-tensor model
International Nuclear Information System (INIS)
Chishtie, F.; Gagne-Portelance, M.; Hanif, T.; Homayouni, S.; McKeon, D.G.C.
2006-01-01
In a recently proposed model in which a vector non-Abelian gauge field interacts with an antisymmetric tensor field, it has been shown that the tensor field possesses no physical degrees of freedom. This formal demonstration is tested by computing the one-loop contributions of the tensor field to the self-energy of the vector field. It is shown that despite the large number of Feynman diagrams in which the tensor field contributes, the sum of these diagrams vanishes, confirming that it is not physical. Furthermore, if the tensor field were to couple with a spinor field, it is shown at one-loop order that the spinor self-energy is not renormalizable, and hence this coupling must be excluded. In principle though, this tensor field does couple to the gravitational field
Annat, Gary; Macfarlane, Douglas R; Forsyth, Maria
2007-08-02
Pulsed field gradient NMR is a powerful method for the measurement of diffusion coefficients in liquids and solids and has begun to attract much attention in the ionic liquids field. However, aspects of the methodology as traditionally applied to solutions may not be uniformly applicable in these more viscous and chemically complex systems. In this paper we present data which shows that the Pulsed Gradient Spin Echo (PGSE) method in particular suffers from intrinsic internal gradients and can produce apparent diffusion coefficients which vary by as much as 20% for different 1H nuclei within a given molecule--an obvious anomaly. In contrast, we show that the Pulsed Gradient Stimulated Echo method does not suffer from this problem to the same extent and produces self-consistent data to a high degree of accuracy (better than 1%). This level of significance has allowed the detection, in this work, of subtle mixing effects in [C(3)mpyr][NTf(2)] and [C(4)mpyr][NTf(2)] mixtures.
Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji
2017-11-15
Spin-orbit contributions to the zero-field splitting (ZFS) tensor (D SO tensor) of M III (acac) 3 complexes (M = V, Cr, Mn, Fe and Mo; acac = acetylacetonate anion) are evaluated by means of ab initio (a hybrid CASSCF/MRMP2) and DFT (Pederson-Khanna (PK) and natural orbital-based Pederson-Khanna (NOB-PK)) methods, focusing on the behaviour of DFT-based approaches to the D SO tensors against the valence d-electron configurations of the transition metal ions in octahedral coordination. Both the DFT-based approaches reproduce trends in the D tensors. Significantly, the differences between the theoretical and experimental D (D = D ZZ - (D XX + D YY )/2) values are smaller in NOB-PK than in PK, emphasising the usefulness of the natural orbital-based approach to the D tensor calculations of transition metal ion complexes. In the case of d 2 and d 4 electronic configurations, the D SO (NOB-PK) values are considerably underestimated in the absolute magnitude, compared with the experimental ones. The D SO tensor analysis based on the orbital region partitioning technique (ORPT) revealed that the D SO contributions attributed to excitations from the singly occupied region (SOR) to the unoccupied region (UOR) are significantly underestimated in the DFT-based approaches to all the complexes under study. In the case of d 3 and d 5 configurations, the (SOR → UOR) excitations contribute in a nearly isotropic manner, which causes fortuitous error cancellations in the DFT-based D SO values. These results indicate that more efforts to develop DFT frameworks should be directed towards the reproduction of quantitative D SO tensors of transition metal complexes with various electronic configurations and local symmetries around metal ions.
König, Jörg; Tschulik, Kristina; Büttner, Lars; Uhlemann, Margitta; Czarske, Jürgen
2013-03-19
To experimentally reveal the correlation between electrodeposited structure and electrolyte convection induced inside the concentration boundary layer, a highly inhomogeneous magnetic field, generated by a magnetized Fe-wire, has been applied to an electrochemical system. The influence of Lorentz and magnetic field gradient force to the local transport phenomena of copper ions has been studied using a novel two-component laser Doppler velocity profile sensor. With this sensor, the electrolyte convection within 500 μm of a horizontally aligned cathode is presented. The electrode-normal two-component velocity profiles below the electrodeposited structure show that electrolyte convection is induced and directed toward the rim of the Fe-wire. The measured deposited structure directly correlates to the observed boundary layer flow. As the local concentration of Cu(2+) ions is enhanced due to the induced convection, maximum deposit thicknesses can be found at the rim of the Fe-wire. Furthermore, a complex boundary layer flow structure was determined, indicating that electrolyte convection of second order is induced. Moreover, the Lorentz force-driven convection rapidly vanishes, while the electrolyte convection induced by the magnetic field gradient force is preserved much longer. The progress for research is the first direct experimental proof of the electrolyte convection inside the concentration boundary layer that correlates to the deposited structure and reveals that the magnetic field gradient force is responsible for the observed structuring effect.
Directory of Open Access Journals (Sweden)
Cordula V Mora
Full Text Available It has long been thought that birds may use the Earth's magnetic field not only as a compass for direction finding, but that it could also provide spatial information for position determination analogous to a map during navigation. Since magnetic field intensity varies systematically with latitude and theoretically could also provide longitudinal information during position determination, birds using a magnetic map should be able to discriminate magnetic field intensity cues in the laboratory. Here we demonstrate a novel behavioural paradigm requiring homing pigeons to identify the direction of a magnetic field intensity gradient in a "virtual magnetic map" during a spatial conditioning task. Not only were the pigeons able to detect the direction of the intensity gradient, but they were even able to discriminate upward versus downward movement on the gradient by differentiating between increasing and decreasing intensity values. Furthermore, the pigeons typically spent more than half of the 15 second sampling period in front of the feeder associated with the rewarded gradient direction indicating that they required only several seconds to make the correct choice. Our results therefore demonstrate for the first time that pigeons not only can detect the presence and absence of magnetic anomalies, as previous studies had shown, but are even able to detect and respond to changes in magnetic field intensity alone, including the directionality of such changes, in the context of spatial orientation within an experimental arena. This opens up the possibility for systematic and detailed studies of how pigeons could use magnetic intensity cues during position determination as well as how intensity is perceived and where it is processed in the brain.
(Ln-bar, g)-spaces. Ordinary and tensor differentials
International Nuclear Information System (INIS)
Manoff, S.; Dimitrov, B.
1998-01-01
Different types of differentials as special cases of differential operators acting on tensor fields over (L n bar, g)-spaces are considered. The ordinary differential, the covariant differential as a special case of the covariant differential operator, and the Lie differential as a special case of the Lie differential operator are investigated. The tensor differential and its special types (Covariant tensor differential, and Lie tensor differential) are determined and their properties are discussed. Covariant symmetric and antisymmetric (external) tensor differentials, Lie symmetric, and Lie antisymmetric (external) tensor differentials are determined and considered over (L n bar, g)-spaces
International Nuclear Information System (INIS)
Mitamura, Yoshinori; Okamoto, Eiji
2015-01-01
This study was carried out to clarify the effect of a high gradient magnetic field on pressure characteristics of blood in a hollow fiber membrane oxygenator in a solenoid coil by means of numerical analysis. Deoxygenated erythrocytes are paramagnetic, and oxygenated erythrocytes are diamagnetic. Blood changes its magnetic susceptibility depending on whether it is carrying oxygen or not. Motion of blood was analyzed by solving the continuous equation and the Navier–Stokes equation. It was confirmed that oxygenation of deoxygenated blood in the downstream side of the applied magnetic field was effective for pressure rise in a non-uniform magnetic field. The pressure rise was enhanced greatly by an increase in magnetic field intensity. The results suggest that a membrane oxygenator works as an actuator and there is a possibility of self-circulation of blood through an oxygenator in a non-uniform magnetic field. - Highlights: • Effects of a gradient magnetic field on erythrocytes in an oxygenator were analyzed. • Blood changes magnetic susceptibility depending on if it is carrying oxygen or not. • Oxygenation of deoxygenated blood is effective for pressure rise in a magnetic field. • A membrane oxygenator works as an actuator. • There is a possibility of self-circulation of blood through an oxygenator
Ye, Qian; Lin, Haoze
2017-07-01
Though extensively used in calculating optical force and torque acting on a material object illuminated by laser, the Maxwell stress tensor (MST) method follows the electromagnetic linear and angular momentum balance that is usually derived in most textbooks for a continuous volume charge distribution in free space, if not resorting to the application of Noether’s theorem in electrodynamics. To cast the conservation laws into a physically appealing form involving the current densities of linear and angular momentum, on which the MST method is based, the divergence theorem is employed to transform a volume integral into a surface integral. When a material object of finite volume is put into the field, it brings about a discontinuity of field across its surface, due to the presence of induced surface charge and surface current. Ambiguity arises among students in whether the divergence theorem can still be directly used without any justification. By taking into account the effect of the induced surface charge and current, we present a simple pedagogical derivation for the MST method for calculating the optical force and torque on an object immersed in monochromatic optical field, without resorting to Noether’s theorem. Although the results turn out to be identical to those given in the standard textbooks, our derivation avoids the direct use of the divergence theorem on a discontinuous function.
Tensor rank is not multiplicative under the tensor product
Christandl, Matthias; Jensen, Asger Kjærulff; Zuiddam, Jeroen
2017-01-01
The tensor rank of a tensor t is the smallest number r such that t can be decomposed as a sum of r simple tensors. Let s be a k-tensor and let t be an l-tensor. The tensor product of s and t is a (k + l)-tensor. Tensor rank is sub-multiplicative under the tensor product. We revisit the connection between restrictions and degenerations. A result of our study is that tensor rank is not in general multiplicative under the tensor product. This answers a question of Draisma and Saptharishi. Specif...
Weyl curvature tensor in static spherical sources
International Nuclear Information System (INIS)
Ponce de Leon, J.
1988-01-01
The role of the Weyl curvature tensor in static sources of the Schwarzschild field is studied. It is shown that in general the contribution from the Weyl curvature tensor (the ''purely gravitational field energy'') to the mass-energy inside the body may be positive, negative, or zero. It is proved that a positive (negative) contribution from the Weyl tensor tends to increase (decrease) the effective gravitational mass, the red-shift (from a point in the sphere to infinity), as well as the gravitational force which acts on a constituent matter element of a body. It is also proved that the contribution from the Weyl tensor always is negative in sources with surface gravitational potential larger than (4/9. It is pointed out that large negative contributions from the Weyl tensor could give rise to the phenomenon of gravitational repulsion. A simple example which illustrates the results is discussed
Tensor structure for Nori motives
Barbieri-Viale, Luca; Huber, Annette; Prest, Mike
2018-01-01
We construct a tensor product on Freyd's universal abelian category attached to an additive tensor category or a tensor quiver and establish a universal property. This is used to give an alternative construction for the tensor product on Nori motives.
Tensor eigenvalues and their applications
Qi, Liqun; Chen, Yannan
2018-01-01
This book offers an introduction to applications prompted by tensor analysis, especially by the spectral tensor theory developed in recent years. It covers applications of tensor eigenvalues in multilinear systems, exponential data fitting, tensor complementarity problems, and tensor eigenvalue complementarity problems. It also addresses higher-order diffusion tensor imaging, third-order symmetric and traceless tensors in liquid crystals, piezoelectric tensors, strong ellipticity for elasticity tensors, and higher-order tensors in quantum physics. This book is a valuable reference resource for researchers and graduate students who are interested in applications of tensor eigenvalues.
Bracken, Robert E.; Brown, Philip J.
2006-01-01
On March 12, 2003, data were gathered at Yuma Proving Grounds, in Arizona, using a Tensor Magnetic Gradiometer System (TMGS). This report shows how these data were processed and explains concepts required for successful TMGS data reduction. Important concepts discussed include extreme attitudinal sensitivity of vector measurements, low attitudinal sensitivity of gradient measurements, leakage of the common-mode field into gradient measurements, consequences of thermal drift, and effects of field curvature. Spatial-data collection procedures and a spin-calibration method are addressed. Discussions of data-reduction procedures include tracking of axial data by mathematically matching transfer functions among the axes, derivation and application of calibration coefficients, calculation of sensor-pair gradients, thermal-drift corrections, and gradient collocation. For presentation, the magnetic tensor at each data station is converted to a scalar quantity, the I2 tensor invariant, which is easily found by calculating the determinant of the tensor. At important processing junctures, the determinants for all stations in the mapped area are shown in shaded relief map-view. Final processed results are compared to a mathematical model to show the validity of the assumptions made during processing and the reasonableness of the ultimate answer obtained.
Lacoste-Collin, Laetitia; Castiella, Marion; Franceries, Xavier; Cassol, Emmanuelle; Vieillevigne, Laure; Pereda, Veronica; Bardies, Manuel; Courtade-Saïdi, Monique
2015-01-01
The study of cell survival following exposure to nonuniform radiation fields is taking on particular interest because of the increasing evidence of a nonlinear relationship at low doses. We conducted in vitro experiments using the MCF7 breast cancer cell line. A 2.4 × 2.4 cm(2) square area of a T25 flask was irradiated by a Varian Novalis accelerator delivering 6 MV photons. Cell survival inside the irradiation field, in the dose gradient zone and in the peripheral zone, was determined using a clonogenic assay for different radiation doses at the isocenter. Increased cell survival was observed inside the irradiation area for doses of 2, 10, and 20 Gy when nonirradiated cells were present at the periphery, while the cells at the periphery showed decreased survival compared to controls. Increased survival was also observed at the edge of the dose gradient zone for cells receiving 0.02 to 0.01 Gy when compared with cells at the periphery of the same flask, whatever the isocenter dose. These data are the first to report cell survival in the dose gradient zone. Radiotherapists must be aware of this nonlinearity in dose response.
Comon, Pierre
2014-01-01
International audience; Tensor decompositions are at the core of many Blind Source Separation (BSS) algorithms, either explicitly or implicitly. In particular, the Canonical Polyadic (CP) tensor decomposition plays a central role in identification of underdetermined mixtures. Despite some similarities, CP and Singular value Decomposition (SVD) are quite different. More generally, tensors and matrices enjoy different properties, as pointed out in this brief survey.
Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Kitagawa, Masahiro; Takui, Takeji
2014-05-21
The CASSCF and the hybrid CASSCF-MRMP2 methods are applied to the calculations of spin-spin and spin-orbit contributions to the zero-field splitting tensors (D tensors) of the halogen-substituted spin-septet 2,4,6-trinitrenopyridines, focusing on the heavy atom effects on the spin-orbit term of the D tensors (D(SO) tensors). The calculations reproduced experimentally determined |D| values within an error of 15%. Halogen substitutions at the 3,5-positions are less influential in the spin-spin dipolar (D(SS)) term of 2,4,6-trinitrenopyridines, although the D(SO) terms are strongly affected by the introduction of heavier halogens. The absolute sign of the D(SO) value (D = D(ZZ) - (D(XX) + D(YY))/2) of 3,5-dibromo derivative 3 is predicted to be negative, which contradicts the Pederson-Khanna (PK) DFT result previously reported. The large negative contributions to the D(SO) value of 3 arise from the excited spin-septet states ascribed mainly to the excitations of in-plane lone pair of bromine atoms → SOMO of π nature. The importance of the excited states involving electron transitions from the lone pair orbital of the halogen atom is also confirmed in the D(SO) tensors of halogen-substituted para-phenylnitrenes. A new scheme based on the orbital region partitioning is proposed for the analysis of the D(SO) tensors as calculated by means of the PK-DFT approach.
Massless and massive quanta resulting from a mediumlike metric tensor
International Nuclear Information System (INIS)
Soln, J.
1985-01-01
A simple model of the ''primordial'' scalar field theory is presented in which the metric tensor is a generalization of the metric tensor from electrodynamics in a medium. The radiation signal corresponding to the scalar field propagates with a velocity that is generally less than c. This signal can be associated simultaneously with imaginary and real effective (momentum-dependent) masses. The requirement that the imaginary effective mass vanishes, which we take to be the prerequisite for the vacuumlike signal propagation, leads to the ''spontaneous'' splitting of the metric tensor into two distinct metric tensors: one metric tensor gives rise to masslesslike radiation and the other to a massive particle. (author)
Hunt, Katharine L. C.; Harris, Robert A.
1991-06-01
Motion of nuclei within a molecule induces a magnetic moment me in the electronic charge distribution, giving a nonzero electronic contribution to the magnetic transition dipole that produces vibrational circular dichroism. In this paper, we develop a new susceptibility density theory for the induced magnetic moment. The theory is based on the response of the electrons to changes in the nuclear Coulomb field, due to shifts in nuclear positions. The electronic response to these changes depends on the same susceptibility densities that determine response to external fields. Our analysis suggests a new physical picture of vibrational circular dichroism. It yields an equation for the density of the induced electronic magnetic moment within a molecule; it also yields a new relation connecting the electric-field shielding at nucleus I of a molecule in an applied magnetic field of frequency ω to the derivative of me with respect to the velocity of nucleus I, regarded as a parameter in the electronic wave function. Within our theory, the derivative of me with respect to nuclear velocity separates into quantum-mechanical and classical components in close analogy with the Hellmann-Feynman theorem for forces on nuclei. In matrix-element form, results from our theory are identical to those obtained with nonadiabatic perturbation theory, to leading order. In general, the leading nonadiabatic corrections to electronic properties are determined directly by the electrons' response to the changes in the nuclear Coulomb field, when the nuclei move.
International Nuclear Information System (INIS)
Blum, A.S.; Mancebo, L.
1976-01-01
Direct energy converters for use on controlled fusion reactors utilize electrodes operated at elevated voltages and temperatures. The insulating elements that position these electrodes must support large voltages and under some circumstances large thermal gradients. It is shown that even modest thermal gradients can cause major alterations of the electric-field distribution within the insulating element
Compact fluxgate magnetic full-tensor gradiometer with spherical feedback coil.
Sui, Yangyi; Li, Guang; Wang, Shilong; Lin, Jun
2014-01-01
The magnetic tensor gradiometer, which is used for measuring the spatial derivatives of three orthogonal magnetic field components, is an important magnetic field characterization tool. Here, the construction of a magnetic full-tensor gradiometer is described, which utilizes four fluxgates arranged on a planar cross structure, and a single, triaxial, spherical feedback coil assembly. In this arrangement, one of the fluxgates is used as a reference, controlling the currents through the feedback coils. Since the fluxgates are working in the near-zero magnetic field environment, the magnetic tensor gradiometer is stable and of an improved accuracy. This design avoids the crosstalk normally caused by individual feedback coils for each fluxgate, and reduces the orthogonality and orientation errors. Moreover, the calibration parameters can be directly inferred using the spherical feedback coil. The measured gradient tensor magnitude can reach 0.52 nT/m/Hz(1/2) @ 1 Hz in unshielded laboratory conditions, while exhibiting good noise immunity. The functionality of the system is verified by locating a small, single, permanent, and dipole magnet in space. The gradiometer is compact, while employing global feedback, and therefore it is especially suitable for deployment on space-constrained moving platforms.
International Nuclear Information System (INIS)
Regions with steep dose gradients are often encountered in clinical x-ray beams, especially with the growing use of intensity modulated radiotherapy (IMRT). Such regions are present both at field edges and, for IMRT, in the vicinity of the projection of sensitive anatomical structures in the treatment field. Dose measurements in these regions are often difficult and labour intensive, while dose prediction may be inaccurate. A dedicated algorithm developed in our institution for conversion of pixel values, measured with a charged coupled device camera based fluoroscopic electronic portal imaging device (EPID), into absolute absorbed doses at the EPID plane has an accuracy of 1-2% for flat and smoothly modulated fields. However, in the current algorithm there is no mechanism to correct for the (short-range) differences in lateral electron transport between water and the metal plate with the fluorescent layer in the EPID. Moreover, lateral optical photon transport in the fluorescent layer is not taken into account. This results in large deviations (>10%) in the penumbra region of these fields. We have investigated the differences between dose profiles measured in water and with the EPID for small heavily peaked fields. A convolution kernel has been developed to empirically describe these differences. After applying the derived kernel to raw EPID images, a general agreement within 2% was obtained with the water measurements in the central region of the fields, and within 0.03 cm in the penumbra region. These results indicate that the EPID is well suited for accurate dosimetric verification of steep gradient x-ray fields
DEFF Research Database (Denmark)
Nevald, Rolf; Hansen, P. E.
1978-01-01
The fluorine and lithium NMR line shifts have been followed in temperature from 300 to 1.3 K and in fields up to 40 kG for LiTbF4 and LiHoF4. The Tb3+ and Ho3+ ionic moments cause these shifts. The Li shifts are dominated by dipole interactions, whereas the F shifts also have transferred hyperfine...... contributions of comparable sizes. The transferred hyperfine interactions turn out to be almost isotropic and exhibiting no temperature or field dependence. In LiHoF4 the line shifts are detectable within the entire temperature range. In LiTbF4 the fluorine and lithium lines broaden to such an extent...
International Nuclear Information System (INIS)
Friedt, J.M.
1976-01-01
The change in the hyperfine line intensities is discussed for various Moessbauer transitions in cases involving axial vibrational lattice anisotropy and axial electric field gradient at the resonant nucleus. The change in the relative intensities of the spectral components has been calculed numerically for the different types of Moessbauer transitions. Polynomial expansions are given to describe the functional dependence of the relative intensities on the magnitude of the vibration anisotropy. They may be used to extract the relevant parameters from experimental data without requiring the numerical integrations implied in the description of the Goldanskii-Karyagin effect [fr
Algebraic and computational aspects of real tensor ranks
Sakata, Toshio; Miyazaki, Mitsuhiro
2016-01-01
This book provides comprehensive summaries of theoretical (algebraic) and computational aspects of tensor ranks, maximal ranks, and typical ranks, over the real number field. Although tensor ranks have been often argued in the complex number field, it should be emphasized that this book treats real tensor ranks, which have direct applications in statistics. The book provides several interesting ideas, including determinant polynomials, determinantal ideals, absolutely nonsingular tensors, absolutely full column rank tensors, and their connection to bilinear maps and Hurwitz-Radon numbers. In addition to reviews of methods to determine real tensor ranks in details, global theories such as the Jacobian method are also reviewed in details. The book includes as well an accessible and comprehensive introduction of mathematical backgrounds, with basics of positive polynomials and calculations by using the Groebner basis. Furthermore, this book provides insights into numerical methods of finding tensor ranks through...
di Lauro, C.
2018-03-01
Transformations of vector or tensor properties from a space-fixed to a molecule-fixed axis system are often required in the study of rotating molecules. Spherical components λμ,ν of a first rank irreducible tensor can be obtained from the direction cosines between the two axis systems, and a second rank tensor with spherical components λμ,ν(2) can be built from the direct product λ × λ. It is shown that the treatment of the interaction between molecular rotation and the electric quadrupole of a nucleus is greatly simplified, if the coefficients in the axis-system transformation of the gradient of the electric field of the outer charges at the coupled nucleus are arranged as spherical components λμ,ν(2). Then the reduced matrix elements of the field gradient operators in a symmetric top eigenfunction basis, including their dependence on the molecule-fixed z-angular momentum component k, can be determined from the knowledge of those of λ(2) . The hyperfine structure Hamiltonian Hq is expressed as the sum of terms characterized each by a value of the molecule-fixed index ν, whose matrix elements obey the rule Δk = ν. Some of these terms may vanish because of molecular symmetry, and the specific cases of linear and symmetric top molecules, orthorhombic molecules, and molecules with symmetry lower than orthorhombic are considered. Each ν-term consists of a contraction of the rotational tensor λ(2) and the nuclear quadrupole tensor in the space-fixed frame, and its matrix elements in the rotation-nuclear spin coupled representation can be determined by the standard spherical tensor methods.
Gauge theories, duality relations and the tensor hierarchy
Bergshoeff, Eric A.; Hartong, Jelle; Hohm, Olaf; Huebscher, Mechthild; Ortin, Tomas; Hübscher, Mechthild
We compute the complete 3- and 4-dimensional tensor hierarchies, i.e. sets of p-form fields, with 1 We construct gauge-invariant actions that include all the fields in the tensor hierarchies. We elucidate the relation between the gauge transformations of the p-form fields in the action and those of
a tensor theory of gravitation in a curved metric on a flat background
International Nuclear Information System (INIS)
Drummond, J.E.
1979-01-01
A theory of gravity is proposed using a tensor potential for the field on a flat metric. This potential cannot be isolated by local observations, but some details can be deduced from measurements at a distance. The requirement that the field equations for the tensor potential shall be deducible from an action integral, that the action and field equations are gauge invariant, and, conversely, that the Lagrangian in the action integral can be integrated from the field equations leads to Einstein's field equations. The requirement that the field energy-momentum tensor exists leads to a constraint on the tensor potential. If the constraint is a differential gauge condition, then it can only be the Hilbert condition giving a unique background tensor, metric tensor and tensor potential. For a continuous field inside a solid sphere the metric must be homogeneous in the spatial coordinates, and the associated field energy-momentum tensor has properties consistent with Newtonian dynamics. (author)
International Nuclear Information System (INIS)
Wang Hua; Liu Feng; Crozier, Stuart; Xia Ling
2008-01-01
This paper presents a stabilized Bi-conjugate gradient algorithm (BiCGstab) that can significantly improve the performance of the impedance method, which has been widely applied to model low-frequency field induction phenomena in voxel phantoms. The improved impedance method offers remarkable computational advantages in terms of convergence performance and memory consumption over the conventional, successive over-relaxation (SOR)-based algorithm. The scheme has been validated against other numerical/analytical solutions on a lossy, multilayered sphere phantom excited by an ideal coil loop. To demonstrate the computational performance and application capability of the developed algorithm, the induced fields inside a human phantom due to a low-frequency hyperthermia device is evaluated. The simulation results show the numerical accuracy and superior performance of the method.
Karami, Behrouz; Shahsavari, Davood; Li, Li
2018-03-01
A size-dependent model is developed for the hygrothermal wave propagation analysis of an embedded viscoelastic single layer graphene sheet (SLGS) under the influence of in-plane magnetic field. The bi-Helmholtz nonlocal strain gradient theory involving three small scale parameters is introduced to account for the size-dependent effects. The size-dependent model is deduced based on Hamilton's principle. The closed-form solution of eigenfrequency relation between wave number and phase velocity is achieved. By studying the size-dependent effects on the flexural wave of SLGS, the dispersion relation predicted by the developed size-dependent model can show a good match with experimental data. The influence of in-plane magnetic field, temperature and moisture of environs, structural damping, damped substrate, lower and higher order nonlocal parameters and the material characteristic parameter on the phase velocity of SLGS is explored.
International Nuclear Information System (INIS)
Recoskie, Bryan J; Chronik, Blaine A; Scholl, Timothy J
2009-01-01
Peripheral nerve stimulation (PNS) resulting from electric fields induced from the rapidly changing magnetic fields of gradient coils is a concern in MRI. Nerves exposed to either electric fields or changing magnetic fields would be expected to display consistent threshold characteristics, motivating the direct application of electric field exposure criteria from the literature to guide the development of gradient magnetic field exposure criteria for MRI. The consistency of electric and magnetic field exposures was tested by comparing chronaxie times for electric and magnetic PNS curves for 22 healthy human subjects. Electric and magnetic stimulation thresholds were measured for exposure of the forearm using both surface electrodes and a figure-eight magnetic coil, respectively. The average chronaxie times for the electric and magnetic field conditions were 109 ± 11 μs and 651 ± 53 μs (±SE), respectively. We do not propose that these results call into question the basic mechanism, namely that rapidly switched gradient magnetic fields induce electric fields in human tissues, resulting in PNS. However, this result does motivate us to suggest that special care must be taken when using electric field exposure data from the literature to set gradient coil PNS safety standards in MRI.
Tensor rank is not multiplicative under the tensor product
DEFF Research Database (Denmark)
Christandl, Matthias; Jensen, Asger Kjærulff; Zuiddam, Jeroen
2018-01-01
The tensor rank of a tensor t is the smallest number r such that t can be decomposed as a sum of r simple tensors. Let s be a k-tensor and let t be an ℓ-tensor. The tensor product of s and t is a (k+ℓ)-tensor. Tensor rank is sub-multiplicative under the tensor product. We revisit the connection...... between restrictions and degenerations. A result of our study is that tensor rank is not in general multiplicative under the tensor product. This answers a question of Draisma and Saptharishi. Specifically, if a tensor t has border rank strictly smaller than its rank, then the tensor rank of t...... is not multiplicative under taking a sufficiently hight tensor product power. The “tensor Kronecker product” from algebraic complexity theory is related to our tensor product but different, namely it multiplies two k-tensors to get a k-tensor. Nonmultiplicativity of the tensor Kronecker product has been known since...
Cartesian tensors an introduction
Temple, G
2004-01-01
This undergraduate text provides an introduction to the theory of Cartesian tensors, defining tensors as multilinear functions of direction, and simplifying many theorems in a manner that lends unity to the subject. The author notes the importance of the analysis of the structure of tensors in terms of spectral sets of projection operators as part of the very substance of quantum theory. He therefore provides an elementary discussion of the subject, in addition to a view of isotropic tensors and spinor analysis within the confines of Euclidean space. The text concludes with an examination of t
Near-field radiative heat transfer under temperature gradients and conductive transfer
Energy Technology Data Exchange (ETDEWEB)
Jin, Weiliang; Rodriguez, Alejandro W. [Princeton Univ., NJ (United States). Dept. of Electrical Engineering; Messina, Riccardo [CNRS-Univ. de Montpellier (France). Lab. Charles Coulomb
2017-05-01
We describe a recently developed formulation of coupled conductive and radiative heat transfer (RHT) between objects separated by nanometric, vacuum gaps. Our results rely on analytical formulas of RHT between planar slabs (based on the scattering-matrix method) as well as a general formulation of RHT between arbitrarily shaped bodies (based on the fluctuating-volume current method), which fully captures the existence of temperature inhomogeneities. In particular, the impact of RHT on conduction, and vice versa, is obtained via self-consistent solutions of the Fourier heat equation and Maxwell's equations. We show that in materials with low thermal conductivities (e.g. zinc oxides and glasses), the interplay of conduction and RHT can strongly modify heat exchange, exemplified for instance by the presence of large temperature gradients and saturating flux rates at short (nanometric) distances. More generally, we show that the ability to tailor the temperature distribution of an object can modify the behaviour of RHT with respect to gap separations, e.g. qualitatively changing the asymptotic scaling at short separations from quadratic to linear or logarithmic. Our results could be relevant to the interpretation of both past and future experimental measurements of RHT at nanometric distances.
Malyarenko, Dariya I; Ross, Brian D; Chenevert, Thomas L
2014-03-01
Gradient nonlinearity of MRI systems leads to spatially dependent b-values and consequently high non-uniformity errors (10-20%) in apparent diffusion coefficient (ADC) measurements over clinically relevant field-of-views. This work seeks practical correction procedure that effectively reduces observed ADC bias for media of arbitrary anisotropy in the fewest measurements. All-inclusive bias analysis considers spatial and time-domain cross-terms for diffusion and imaging gradients. The proposed correction is based on rotation of the gradient nonlinearity tensor into the diffusion gradient frame where spatial bias of b-matrix can be approximated by its Euclidean norm. Correction efficiency of the proposed procedure is numerically evaluated for a range of model diffusion tensor anisotropies and orientations. Spatial dependence of nonlinearity correction terms accounts for the bulk (75-95%) of ADC bias for FA = 0.3-0.9. Residual ADC non-uniformity errors are amplified for anisotropic diffusion. This approximation obviates need for full diffusion tensor measurement and diagonalization to derive a corrected ADC. Practical scenarios are outlined for implementation of the correction on clinical MRI systems. The proposed simplified correction algorithm appears sufficient to control ADC non-uniformity errors in clinical studies using three orthogonal diffusion measurements. The most efficient reduction of ADC bias for anisotropic medium is achieved with non-lab-based diffusion gradients. Copyright © 2013 Wiley Periodicals, Inc.
Lepore, N; Brun, C; Chou, Y Y; Chiang, M C; Dutton, R A; Hayashi, K M; Luders, E; Lopez, O L; Aizenstein, H J; Toga, A W; Becker, J T; Thompson, P M
2008-01-01
This paper investigates the performance of a new multivariate method for tensor-based morphometry (TBM). Statistics on Riemannian manifolds are developed that exploit the full information in deformation tensor fields. In TBM, multiple brain images are warped to a common neuroanatomical template via 3-D nonlinear registration; the resulting deformation fields are analyzed statistically to identify group differences in anatomy. Rather than study the Jacobian determinant (volume expansion factor) of these deformations, as is common, we retain the full deformation tensors and apply a manifold version of Hotelling's $T(2) test to them, in a Log-Euclidean domain. In 2-D and 3-D magnetic resonance imaging (MRI) data from 26 HIV/AIDS patients and 14 matched healthy subjects, we compared multivariate tensor analysis versus univariate tests of simpler tensor-derived indices: the Jacobian determinant, the trace, geodesic anisotropy, and eigenvalues of the deformation tensor, and the angle of rotation of its eigenvectors. We detected consistent, but more extensive patterns of structural abnormalities, with multivariate tests on the full tensor manifold. Their improved power was established by analyzing cumulative p-value plots using false discovery rate (FDR) methods, appropriately controlling for false positives. This increased detection sensitivity may empower drug trials and large-scale studies of disease that use tensor-based morphometry.
Scattering of charged tensor bosons in gauge and superstring theories
Antoniadis, Ignatios
2010-01-01
We calculate the leading-order scattering amplitude of one vector and two tensor gauge bosons in a recently proposed non-Abelian tensor gauge field theory and open superstring theory. The linear in momenta part of the superstring amplitude has identical Lorentz structure with the gauge theory, while its cubic in momenta part can be identified with an effective Lagrangian which is constructed using generalized non-Abelian field strength tensors.
Hugon, Cedric; Aubert, Guy; Sakellariou, Dimitris
2012-01-01
Mapping (or plotting) the magnetic field has a critical importance for the achievement of the homogeneous magnetic field necessary to standard MR experiments. A powerful tool for this purpose is the Spherical Harmonic Expansion (SHE), which provides a simple way to describe the spatial variations of a field in free space. Well-controlled non-zero spatial variations of the field are critical to MRI. The resolution of the image is directly related to the strength of the gradient used to encode space. As a result, it is desirable to have strong variations of the field. In that case, the SHE cannot be used as is, because the field modulus variations are affected by the variations of all components of the field. In this paper, we propose a method based on the SHE to characterize such variations, theoretically and experimentally, in the limit of an axisymmetric magnetic field. Practical applications of this method are proposed through the examples of single-sided magnet design and characterization, along with Stray-Field Imaging (STRAFI). Copyright © 2011 Elsevier Inc. All rights reserved.
Using Magnetic Field Gradients to Simulate Variable Gravity in Fluids and Materials Experiments
Ramachandran, Narayanan
2006-01-01
Fluid flow due to a gravitational field is caused by sedimentation, thermal buoyancy, or solutal buoyancy induced convection. During crystal growth, for example, these flows are undesirable and can lead to crystal imperfections. While crystallization in microgravity can approach diffusion limited growth conditions (no convection), terrestrially strong magnetic fields can be used to control fluid flow and sedimentation effects. In this work, a theory is presented on the stability of solutal convection of a magnetized fluid(weak1y paramagnetic) in the presence of a magnetic field. The requirements for stability are developed and compared to experiments performed within the bore of a superconducting magnet. The theoretical predictions are in good agreement with the experiments. Extension of the technique can also be applied to study artificial gravity requirements for long duration exploration missions. Discussion of this application with preliminary experiments and application of the technique to crystal growth will be provided.
MR Measurement Technique of Rapidly Switched Gradient Magnetic Fields in MR Tomography
Czech Academy of Sciences Publication Activity Database
Bartušek, Karel; Gescheidtová, E.
2005-01-01
Roč. 29, č. 4 (2005), s. 675-686 ISSN 0937-9347 Institutional research plan: CEZ:AV0Z20650511 Keywords : MR tomography * gradiernt magnet ic field * IF method * IFSE method * IFSES method * spin echo Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 0.743, year: 2005
influence of pressure gradients and fracturing in oil field rocks on ...
African Journals Online (AJOL)
Admin
migration/accumulation in porous and fractured rocks, particularly oil field rocks, are reviewed; some drilling ... faults as hydrocarbon migration/leakage pathways, and as seals or barriers in hydrocarbon traps. Naturally ..... Formation Fracturing, In: Petroleum Engineering. Handbook (H.B Bradley, Ed.) SPE, Richardson.
Radiation Forces and Torques without Stress (Tensors)
Bohren, Craig F.
2011-01-01
To understand radiation forces and torques or to calculate them does not require invoking photon or electromagnetic field momentum transfer or stress tensors. According to continuum electromagnetic theory, forces and torques exerted by radiation are a consequence of electric and magnetic fields acting on charges and currents that the fields induce…
Direct tensor rendering using a bidirectional reflectance model
Nagasawa, Mikio; Suzuki, Yoshio
2000-02-01
For the multi variable volumetric tensor field visualization, an efficient direct rendering technique without using geometrical primitive is proposed. The bi- directional reflectance shading model is used to map the anisotropy stress shear tensor components in direct volume rendering. We model the sub-pixel-sized microfacet at tensor sampling points. The nine component of 3D tensor field are mapped onto grid deformation, opacity mapping, color specification, and normal directions of these microfacets. The ray integration is executed though these irregular infinitesimal microfacets distribution. This direct tensor rendering was applied for at-a-glance tensor visualization of earthquake simulation. That realized a view of deformed structure, stress distribution, local shear discontinuity and the shock front, integrated in a single image. The characteristic P- and S-wave modes are distinguished in the rendered earthquake simulations. Compared with the glyph representation of tensor features, the direct tensor rendering gives the general and total image of tensor field even for the low resolution pixel planes, because the sampling object is assumed as infinitesimally small. the computational cost of direct tensor rendering is not so high than that of scalar volume rendering because the modifications are only ins hading calculation but not in the ray integration.
Particle-Based Microfluidic Device for Providing High Magnetic Field Gradients
Lin, Adam Y. (Inventor); Wong, Tak S. (Inventor)
2013-01-01
A microfluidic device for manipulating particles in a fluid has a device body that defines a main channel therein, in which the main channel has an inlet and an outlet. The device body further defines a particulate diverting channel therein, the particulate diverting channel being in fluid connection with the main channel between the inlet and the outlet of the main channel and having a particulate outlet. The microfluidic device also has a plurality of microparticles arranged proximate or in the main channel between the inlet of the main channel and the fluid connection of the particulate diverting channel to the main channel. The plurality of microparticles each comprises a material in a composition thereof having a magnetic susceptibility suitable to cause concentration of magnetic field lines of an applied magnetic field while in operation. A microfluidic particle-manipulation system has a microfluidic particle-manipulation device and a magnet disposed proximate the microfluidic particle-manipulation device.
Lepore, Natasha; Brun, Caroline; Chou, Yi-Yu; Chiang, Ming-Chang; Dutton, Rebecca A.; Hayashi, Kiralee M.; Luders, Eileen; Lopez, Oscar L.; Aizenstein, Howard J.; Toga, Arthur W.; Becker, James T.; Thompson, Paul M.
2008-01-01
This paper investigates the performance of a new multivariate method for tensor-based morphometry (TBM). Statistics on Riemannian manifolds are developed that exploit the full information in deformation tensor fields. In TBM, multiple brain images are warped to a common neuroanatomical template via 3-D nonlinear registration; the resulting deformation fields are analyzed statistically to identify group differences in anatomy. Rather than study the Jacobian determinant (volume expansion factor...
Karimi, Kurosh; Shirzaditabar, Farzad
2017-08-01
The analytic signal of magnitude of the magnetic field’s components and its first derivatives have been employed for locating magnetic structures, which can be considered as point-dipoles or line of dipoles. Although similar methods have been used for locating such magnetic anomalies, they cannot estimate the positions of anomalies in noisy states with an acceptable accuracy. The methods are also inexact in determining the depth of deep anomalies. In noisy cases and in places other than poles, the maximum points of the magnitude of the magnetic vector components and Az are not located exactly above 3D bodies. Consequently, the horizontal location estimates of bodies are accompanied by errors. Here, the previous methods are altered and generalized to locate deeper models in the presence of noise even at lower magnetic latitudes. In addition, a statistical technique is presented for working in noisy areas and a new method, which is resistant to noise by using a ‘depths mean’ method, is made. Reduction to the pole transformation is also used to find the most possible actual horizontal body location. Deep models are also well estimated. The method is tested on real magnetic data over an urban gas pipeline in the vicinity of Kermanshah province, Iran. The estimated location of the pipeline is accurate in accordance with the result of the half-width method.
DEFF Research Database (Denmark)
Jespersen, Sune Nørhøj; Lundell, Henrik; Sønderby, Casper Kaae
2013-01-01
pairs of diffusion wave vectors (the d-PFG 5-design) facilitating a theoretically exact determination of the fourth order Taylor or cumulant expansion of the orientationally averaged signal. The d-PFG 5-design is evaluated with numerical simulations and ex vivo high field diffusion MRI experiments...... orientation dispersion when applied to macroscopically anisotropic systems. Here we propose a new framework, the d-PFG 5-design, to enable rotationally invariant estimation of double wave vector diffusion metrics (d-PFG). The method is based on the idea that an appropriate orientational average of the signal...
Couplings of self-dual tensor multiplet in six dimensions
Bergshoeff, E.; Sezgin, E.; Sokatchev, E.
1996-01-01
The (1, 0) supersymmetry in six dimensions admits a tensor multiplet which contains a second-rank antisymmetric tensor field with a self-dual field strength and a dilaton. We describe the fully supersymmetric coupling of this multiplet to a Yangâ€“Mills multiplet, in the absence of supergravity. The
Energy-momentum tensor correlation function in Nf = 2 + 1 full QCD at finite temperature
Directory of Open Access Journals (Sweden)
Taniguchi Yusuke
2018-01-01
Full Text Available We measure correlation functions of the nonperturbatively renormalized energy-momentum tensor in Nf = 2 + 1 full QCD at finite temperature by applying the gradient flow method both to the gauge and quark fields. Our main interest is to study the conservation law of the energy-momentum tensor and to test whether the linear response relation is properly realized for the entropy density. By using the linear response relation we calculate the specific heat from the correlation function. We adopt the nonperturba-tively improved Wilson fermion and Iwasaki gauge action at a fine lattice spacing = 0:07 fm. In this paper the temperature is limited to a single value T ≃ 232 MeV. The u, d quark mass is rather heavy with mπ=mρ ≃ 0:63 while the s quark mass is set to approximately its physical value.
Transverse beam dynamics in non-linear Fixed Field Alternating Gradient accelerators
Energy Technology Data Exchange (ETDEWEB)
Haj, Tahar M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Meot, F. [Brookhaven National Lab. (BNL), Upton, NY (United States)
2016-03-02
In this paper, we present some aspects of the transverse beam dynamics in Fixed Field Ring Accelerators (FFRA): we start from the basic principles in order to derive the linearized transverse particle equations of motion for FFRA, essentially FFAGs and cyclotrons are considered here. This is a simple extension of a previous work valid for linear lattices that we generalized by including the bending terms to ensure its correctness for FFAG lattice. The space charge term (contribution of the internal coulombian forces of the beam) is contained as well, although it is not discussed here. The emphasis is on the scaling FFAG type: a collaboration work is undertaken in view of better understanding the properties of the 150 MeV scaling FFAG at KURRI in Japan, and progress towards high intensity operation. Some results of the benchmarking work between different codes are presented. Analysis of certain type of field imperfections revealed some interesting features about this machine that explain some of the experimental results and generalize the concept of a scaling FFAG to a non-scaling one for which the tune variations obey a well-defined law.
Spectral Tensor-Train Decomposition
DEFF Research Database (Denmark)
Bigoni, Daniele; Engsig-Karup, Allan Peter; Marzouk, Youssef M.
2016-01-01
discretizations of the target function. We assess the performance of the method on a range of numerical examples: a modified set of Genz functions with dimension up to 100, and functions with mixed Fourier modes or with local features. We observe significant improvements in performance over an anisotropic......The accurate approximation of high-dimensional functions is an essential task in uncertainty quantification and many other fields. We propose a new function approximation scheme based on a spectral extension of the tensor-train (TT) decomposition. We first define a functional version of the TT.......e., the “cores”) comprising the functional TT decomposition. This result motivates an approximation scheme employing polynomial approximations of the cores. For functions with appropriate regularity, the resulting spectral tensor-train decomposition combines the favorable dimension-scaling of the TT...
Energy Technology Data Exchange (ETDEWEB)
Errico, Leonardo A. [Departamento de Fisica-IFLP(CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, 1900 La Plata (Argentina); Renteria, Mario [Departamento de Fisica-IFLP(CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, 1900 La Plata (Argentina)]. E-mail: renteria@fisica.unlp.edu.ar; Bibiloni, Anibal G. [Departamento de Fisica-CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, 1900 La Plata (Argentina); Freitag, Kristian [Helmholtz-Institut fuer Strahlen-und Kernphysik (H-ISKP) der Universitaet Bonn, Nussallee 14-16, D 53115 Bonn (Germany)
2007-02-01
The time-differential {gamma}-{gamma} perturbed-angular-correlation (PAC) technique with ion-implanted {sup 181}Hf tracers has been applied to study the hyperfine interactions of {sup 181}Ta impurities in the cubic bixbyite structure of Ho{sub 2}O{sub 3} and Eu{sub 2}O{sub 3}. The PAC experiments were performed in air in the temperature range 300-1373 K (in the case of Ho{sub 2}O{sub 3}) and 77-1273 K (in the case of Eu{sub 2}O{sub 3}). For both oxides, two electric-quadrupole interactions were found and attributed to the electric-field gradients (EFGs) acting on {sup 181}Ta probes substitutionally located at the two free-of-defects nonequivalent cation sites of the bixbyite structure. In the case of Ho{sub 2}O{sub 3}, two additional interactions were found in the temperature range 300-573 K. These results, as well as previous characterizations of the EFG at {sup 181}Ta sites in bixbyites, were compared to those obtained in experiments using {sup 111}Cd as probe, and to point-charge model calculations. Very recent ab initio predictions for the EFG tensor at impurities sites in binary oxides are also discussed. All these results enable us to discuss the validity of the widely used ionic model to describe the EFG in these highly ionic compounds.
Schouten tensor equations in conformal geometry with prescribed boundary metric
Directory of Open Access Journals (Sweden)
Oliver C. Schnuerer
2005-07-01
Full Text Available We deform the metric conformally on a manifold with boundary. This induces a deformation of the Schouten tensor. We fix the metric at the boundary and realize a prescribed value for the product of the eigenvalues of the Schouten tensor in the interior, provided that there exists a subsolution. This problem reduces to a Monge-Ampere equation with gradient terms. The main issue is to obtain a priori estimates for the second derivatives near the boundary.
Particles Sorting in Micro Channel Using Designed Micro Electromagnets of Magnetic Field Gradient
Energy Technology Data Exchange (ETDEWEB)
Chung, Yung-Chiang; Wu, Chen-Ming; Lin, Shih-Hao
2016-06-01
In this study, microelectromagnet, microchannel, syringe pump, and controlling devices were integrated to form a particle sorting system. A simple, two-dimensional, relatively quick fabricating and easily operating microelectromagnet was designed. Polystyrene particles and magnetic beads were pumped into the microchannel with the syringe pump, and it was observed that the magnetic beads were attracted to one of two outlets by the microelectromagnet, which features a gradually changing magnetic field. The polystyrene particles would move to another outlet because of different-width micro channel, and it completed the separation of the particles. Based on experimental results, the magnetic flux density of the microelectromagnet was 2.3 Gauss for a 12.5-μm average distance between electrodes at 1.0-μm increments, and the magnetic force was 0.22 pN for 2.8-μm magnetic beads. The separating rate was greater for larger distance increment and smaller average distance between the electrodes. The separating rate of the magnetic beads increased as the electric current increased and flow velocity decreased. When the flow velocity was 0.333 μm/s and electric current was 1 A, the separating rate was 90%. The separating rate of the polystyrene particles increased as the flow velocity increased and was 85% when the flow velocity was 0.6 μm/s. These results demonstrate that this particle sorting system has potential applications in bio-molecular studies. - Highlights: • We proposed a method for separating polystyrene particles and magnetic beads by the different-width outlets and microelectromagnet with gradually changing magnetic field, which is simple, two-dimensional and easily operating. • The separating rate was greater for larger distance increment and smaller average distance between the electrodes. • The separating rate of the magnetic beads increased as the electric current increased and flow velocity decreased, and the maximum value is 90%.
ERL with non-scaling fixed field alternating gradient lattice for eRHIC
Energy Technology Data Exchange (ETDEWEB)
Trbojevic, D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Berg, J. S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Brooks, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Hao, Y. [Brookhaven National Lab. (BNL), Upton, NY (United States); Litvinenko, V. N. [Brookhaven National Lab. (BNL), Upton, NY (United States); Liu, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Meot, F. [Brookhaven National Lab. (BNL), Upton, NY (United States); Minty, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ptitsyn, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Roser, T. [Brookhaven National Lab. (BNL), Upton, NY (United States); Thieberger, P. [Brookhaven National Lab. (BNL), Upton, NY (United States); Tsoupas, N. [Brookhaven National Lab. (BNL), Upton, NY (United States)
2015-05-03
The proposed eRHIC electron-hadron collider uses a "non-scaling FFAG" (NS-FFAG) lattice to recirculate 16 turns of different energy through just two beam lines located in the RHIC tunnel. This paper presents lattices for these two FFAGs that are optimized for low magnet field and to minimize total synchrotron radiation across the energy range. The higher number of recirculations in the FFAG allows a shorter linac (1.322GeV) to be used, drastically reducing cost, while still achieving a 21.2 GeV maximum energy to collide with one of the existing RHIC hadron rings at up to 250GeV. eRHIC uses many cost-saving measures in addition to the FFAG: the linac operates in energy recovery mode, so the beams also decelerate via the same FFAG loops and energy is recovered from the interacted beam. All magnets will be constructed from NdFeB permanent magnet material, meaning chillers and large magnet power supplies are not needed. This paper also describes a small prototype ERL-FFAG accelerator that will test all of these technologies in combination to reduce technical risk for eRHIC.
A gradient stable scheme for a phase field model for the moving contact line problem
Gao, Min
2012-02-01
In this paper, an efficient numerical scheme is designed for a phase field model for the moving contact line problem, which consists of a coupled system of the Cahn-Hilliard and Navier-Stokes equations with the generalized Navier boundary condition [1,2,4]. The nonlinear version of the scheme is semi-implicit in time and is based on a convex splitting of the Cahn-Hilliard free energy (including the boundary energy) together with a projection method for the Navier-Stokes equations. We show, under certain conditions, the scheme has the total energy decaying property and is unconditionally stable. The linearized scheme is easy to implement and introduces only mild CFL time constraint. Numerical tests are carried out to verify the accuracy and stability of the scheme. The behavior of the solution near the contact line is examined. It is verified that, when the interface intersects with the boundary, the consistent splitting scheme [21,22] for the Navier Stokes equations has the better accuracy for pressure. © 2011 Elsevier Inc.
Renormalizability of the gradient flow in the 2D O(N) non-linear sigma model
Makino, Hiroki; Suzuki, Hiroshi
2015-03-01
It is known that the gauge field and its composite operators evolved by the Yang-Mills gradient flow are ultraviolet (UV) finite without any multiplicative wave function renormalization. In this paper, we prove that the gradient flow in the 2D O(N) non-linear sigma model possesses a similar property: The flowed N-vector field and its composite operators are UV finite without multiplicative wave function renormalization. Our proof in all orders of perturbation theory uses a (2+1)-dimensional field theoretical representation of the gradient flow, which possesses local gauge invariance without gauge field. As an application of the UV finiteness of the gradient flow, we construct the energy-momentum tensor in the lattice formulation of the O(N) non-linear sigma model that automatically restores the correct normalization and the conservation law in the continuum limit.
FLAPW Study of the EFG Tensor at Cd Impurities in In2O3
International Nuclear Information System (INIS)
Errico, L. A.; Renteria, M.; Fabricius, G.; Darriba, G. N.
2004-01-01
We report an ab initio study of the electric-field gradient tensor (EFG) at Cd impurities located at both nonequivalent cationic sites in the semiconductor In 2 O 3 . Calculations were performed with the FLAPW method that allows us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way. From our results for the EFG (in excellent agreement with the experiments), it is clear that the problem of the EFG at Cd impurities in In 2 O 3 cannot be described by the point-charge model and antishielding factors.
Energy Technology Data Exchange (ETDEWEB)
Beaumelle, Léa [INRA, UR 251 PESSAC, 78026 Versailles Cedex (France); Gimbert, Frédéric [Laboratoire Chrono-Environnement, UMR 6249 University of Franche-Comté/CNRS Usc INRA, 16 route de Gray, 25030 Besançon Cedex (France); Hedde, Mickaël [INRA, UR 251 PESSAC, 78026 Versailles Cedex (France); Guérin, Annie [INRA, US 0010 LAS Laboratoire d' analyses des sols, 273 rue de Cambrai, 62000 Arras (France); Lamy, Isabelle, E-mail: lamy@versailles.inra.fr [INRA, UR 251 PESSAC, 78026 Versailles Cedex (France)
2015-07-01
Subcellular fractionation of metals in organisms was proposed as a better way to characterize metal bioaccumulation. Here we report the impact of a laboratory exposure to a wide range of field-metal contaminated soils on the subcellular partitioning of metals in the earthworm Aporrectodea caliginosa. Soils moderately contaminated were chosen to create a gradient of soil metal availability; covering ranges of both soil metal contents and of several soil parameters. Following exposure, Cd, Pb and Zn concentrations were determined both in total earthworm body and in three subcellular compartments: cytosolic, granular and debris fractions. Three distinct proxies of soil metal availability were investigated: CaCl{sub 2}-extractable content dissolved content predicted by a semi-mechanistic model and free ion concentration predicted by a geochemical speciation model. Subcellular partitionings of Cd and Pb were modified along the gradient of metal exposure, while stable Zn partitioning reflected regulation processes. Cd subcellular distribution responded more strongly to increasing soil Cd concentration than the total internal content, when Pb subcellular distribution and total internal content were similarly affected. Free ion concentrations were better descriptors of Cd and Pb subcellular distribution than CaCl{sub 2} extractable and dissolved metal concentrations. However, free ion concentrations and soil total metal contents were equivalent descriptors of the subcellular partitioning of Cd and Pb because they were highly correlated. Considering lowly contaminated soils, our results raise the question of the added value of three proxies of metal availability compared to soil total metal content in the assessment of metal bioavailability to earthworm. - Highlights: • Earthworms were exposed to a wide panel of historically contaminated soils • Subcellular partitioning of Cd, Pb and Zn was investigated in earthworms • Three proxies of soil metal availability were
Avilova, I. A.; Vasil'ev, S. G.; Rimareva, L. V.; Serba, E. M.; Volkova, L. D.; Volkov, V. I.
2015-04-01
The self-diffusion of water in cells of Saccharomyces cerevisiae of races Y-3137 and Y-3327 is studied by means of pulsed-field gradient (PFG) NMR. Three types of water are detected that differ by their self-diffusion coefficients (SDCs): free, intercellular, and intracellular. It is found that the self-diffusion of intercellular and intracellular water is restricted. The size and permeability of the cells of yeasts with different cultivation times (24 and 48 h) is determined by analyzing the dependences of the self-diffusion coefficients of intracellular water on the interval between pulses of the magnetic field gradient.
Diffusion tensor MR microscopy of tissues with low diffusional anisotropy.
Bajd, Franci; Mattea, Carlos; Stapf, Siegfried; Sersa, Igor
2016-06-01
Diffusion tensor imaging exploits preferential diffusional motion of water molecules residing within tissue compartments for assessment of tissue structural anisotropy. However, instrumentation and post-processing errors play an important role in determination of diffusion tensor elements. In the study, several experimental factors affecting accuracy of diffusion tensor determination were analyzed. Effects of signal-to-noise ratio and configuration of the applied diffusion-sensitizing gradients on fractional anisotropy bias were analyzed by means of numerical simulations. In addition, diffusion tensor magnetic resonance microscopy experiments were performed on a tap water phantom and bovine articular cartilage-on-bone samples to verify the simulation results. In both, the simulations and the experiments, the multivariate linear regression of the diffusion-tensor analysis yielded overestimated fractional anisotropy with low SNRs and with low numbers of applied diffusion-sensitizing gradients. An increase of the apparent fractional anisotropy due to unfavorable experimental conditions can be overcome by applying a larger number of diffusion sensitizing gradients with small values of the condition number of the transformation matrix. This is in particular relevant in magnetic resonance microscopy, where imaging gradients are high and the signal-to-noise ratio is low.
Measuring Nematic Susceptibilities from the Elastoresistivity Tensor
Hristov, A. T.; Shapiro, M. C.; Hlobil, Patrick; Maharaj, Akash; Chu, Jiun-Haw; Fisher, Ian
The elastoresistivity tensor mijkl relates changes in resistivity to the strain on a material. As a fourth-rank tensor, it contains considerably more information about the material than the simpler (second-rank) resistivity tensor; in particular, certain elastoresistivity coefficients can be related to thermodynamic susceptibilities and serve as a direct probe of symmetry breaking at a phase transition. The aim of this talk is twofold. First, we enumerate how symmetry both constrains the structure of the elastoresistivity tensor into an easy-to-understand form and connects tensor elements to thermodynamic susceptibilities. In the process, we generalize previous studies of elastoresistivity to include the effects of magnetic field. Second, we describe an approach to measuring quantities in the elastoresistivity tensor with a novel transverse measurement, which is immune to relative strain offsets. These techniques are then applied to BaFe2As2 in a proof of principle measurement. This work is supported by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract DE-AC02-76SF00515.
International Nuclear Information System (INIS)
Scheunert, M.
1982-10-01
We develop a graded tensor calculus corresponding to arbitrary Abelian groups of degrees and arbitrary commutation factors. The standard basic constructions and definitions like tensor products, spaces of multilinear mappings, contractions, symmetrization, symmetric algebra, as well as the transpose, adjoint, and trace of a linear mapping, are generalized to the graded case and a multitude of canonical isomorphisms is presented. Moreover, the graded versions of the classical Lie algebras are introduced and some of their basic properties are described. (orig.)
Visualizing Tensor Normal Distributions at Multiple Levels of Detail.
Abbasloo, Amin; Wiens, Vitalis; Hermann, Max; Schultz, Thomas
2016-01-01
Despite the widely recognized importance of symmetric second order tensor fields in medicine and engineering, the visualization of data uncertainty in tensor fields is still in its infancy. A recently proposed tensorial normal distribution, involving a fourth order covariance tensor, provides a mathematical description of how different aspects of the tensor field, such as trace, anisotropy, or orientation, vary and covary at each point. However, this wealth of information is far too rich for a human analyst to take in at a single glance, and no suitable visualization tools are available. We propose a novel approach that facilitates visual analysis of tensor covariance at multiple levels of detail. We start with a visual abstraction that uses slice views and direct volume rendering to indicate large-scale changes in the covariance structure, and locations with high overall variance. We then provide tools for interactive exploration, making it possible to drill down into different types of variability, such as in shape or orientation. Finally, we allow the analyst to focus on specific locations of the field, and provide tensor glyph animations and overlays that intuitively depict confidence intervals at those points. Our system is demonstrated by investigating the effects of measurement noise on diffusion tensor MRI, and by analyzing two ensembles of stress tensor fields from solid mechanics.
Ozarslan, Evren; Shemesh, Noam; Basser, Peter J
2009-03-14
Based on a description introduced by Robertson, Grebenkov recently introduced a powerful formalism to represent the diffusion-attenuated NMR signal for simple pore geometries such as slabs, cylinders, and spheres analytically. In this work, we extend this multiple correlation function formalism by allowing for possible variations in the direction of the magnetic field gradient waveform. This extension is necessary, for example, to incorporate the effects of imaging gradients in diffusion-weighted NMR imaging scans and in characterizing anisotropy at different length scales via double pulsed field gradient (PFG) experiments. In cylindrical and spherical pores, respectively, two- and three-dimensional vector operators are employed whose form is deduced from Grebenkov's results via elementary operator algebra for the case of cylinders and the Wigner-Eckart theorem for the case of spheres. The theory was validated by comparison with known findings and with experimental double-PFG data obtained from water-filled microcapillaries.
Özarslan, Evren; Shemesh, Noam; Basser, Peter J.
2009-03-01
Based on a description introduced by Robertson, Grebenkov recently introduced a powerful formalism to represent the diffusion-attenuated NMR signal for simple pore geometries such as slabs, cylinders, and spheres analytically. In this work, we extend this multiple correlation function formalism by allowing for possible variations in the direction of the magnetic field gradient waveform. This extension is necessary, for example, to incorporate the effects of imaging gradients in diffusion-weighted NMR imaging scans and in characterizing anisotropy at different length scales via double pulsed field gradient (PFG) experiments. In cylindrical and spherical pores, respectively, two- and three-dimensional vector operators are employed whose form is deduced from Grebenkov's results via elementary operator algebra for the case of cylinders and the Wigner-Eckart theorem for the case of spheres. The theory was validated by comparison with known findings and with experimental double-PFG data obtained from water-filled microcapillaries.
Karl, Stephan; Woodward, Robert C.; Davis, Timothy M. E.; St. Pierre, Tim G.
2010-12-01
Plasmodium falciparum is the most dangerous of the human malaria parasite species and accounts for millions of clinical episodes of malaria each year in tropical countries. The pathogenicity of Plasmodium falciparum is a result of its ability to infect erythrocytes where it multiplies asexually over 48 h or develops into sexual forms known as gametocytes. If sufficient male and female gametocytes are taken up by a mosquito vector, it becomes infectious. Therefore, the presence and density of gametocytes in human blood is an important indicator of human-to-mosquito transmission of malaria. Recently, we have shown that high field gradient magnetic fractionation improves gametocyte detection in human blood samples. Here we present two important new developments. Firstly we introduce a quantitative approach to replace the previous qualitative method and, secondly, we describe a novel method that enables cost-effective production of the magnetic fractionation equipment required to carry out gametocyte quantification. We show that our custom-made magnetic fractionation equipment can deliver results with similar sensitivity and convenience but for a small fraction of the cost.
Barreda, Jorge L; Keiper, Timothy D; Zhang, Mei; Xiong, Peng
2017-04-05
In comparison to conventional (channel-limited) field-effect transistors (FETs), Schottky barrier-limited FETs possess some unique characteristics which make them attractive candidates for some electronic and sensing applications. Consequently, modulation of the nano Schottky barrier at a metal-semiconductor interface promises higher performance for chemical and biomolecular sensor applications when compared to conventional FETs with ohmic contacts. However, the fabrication and optimization of devices with a combination of ideal ohmic and Schottky contacts as the source and drain, respectively, present many challenges. We address this issue by utilizing Si nanowires (NWs) synthesized by a chemical vapor deposition process which yields a pronounced doping gradient along the length of the NWs. Devices with a series of metal contacts on a single Si NW are fabricated in a single lithography and metallization process. The graded doping profile of the NW is manifested in monotonic increases in the channel and junction resistances and variation of the nature of the contacts from ohmic to Schottky of increasing effective barrier height along the NW. Hence multiple single Schottky junction-limited FETs with extreme asymmetry and high reproducibility are obtained on an individual NW. A definitive correlation between increasing Schottky barrier height and enhanced gate modulation is revealed. Having access to systematically varying Schottky barrier contacts on the same NW device provides an ideal platform for identifying optimal device characteristics for sensing and electronic applications.
Yin, Yin; Fotin, Sergei V.; Periaswamy, Senthil; Kunz, Justin; Haldankar, Hrishikesh; Muradyan, Naira; Cornud, François; Turkbey, Baris; Choyke, Peter
2012-02-01
Manual delineation of the prostate is a challenging task for a clinician due to its complex and irregular shape. Furthermore, the need for precisely targeting the prostate boundary continues to grow. Planning for radiation therapy, MR-ultrasound fusion for image-guided biopsy, multi-parametric MRI tissue characterization, and context-based organ retrieval are examples where accurate prostate delineation can play a critical role in a successful patient outcome. Therefore, a robust automated full prostate segmentation system is desired. In this paper, we present an automated prostate segmentation system for 3D MR images. In this system, the prostate is segmented in two steps: the prostate displacement and size are first detected, and then the boundary is refined by a shape model. The detection approach is based on normalized gradient fields cross-correlation. This approach is fast, robust to intensity variation and provides good accuracy to initialize a prostate mean shape model. The refinement model is based on a graph-search based framework, which contains both shape and topology information during deformation. We generated the graph cost using trained classifiers and used coarse-to-fine search and region-specific classifier training. The proposed algorithm was developed using 261 training images and tested on another 290 cases. The segmentation performance using mean DSC ranging from 0.89 to 0.91 depending on the evaluation subset demonstrates state of the art performance. Running time for the system is about 20 to 40 seconds depending on image size and resolution.
DEFF Research Database (Denmark)
Arcisauskaité, Vaida; Knecht, Stefan; Sauer, Stephan P. A.
2012-01-01
We investigate the magnitude and interplay of relativistic and electron correlation effects on the electric field gradient (EFG) at the position of Hg in linear and bent HgL2 (L=CH3, Cl, Br, I) and trigonal planar [HgCl3]- complexes using four-component relativistic Dirac-Coulomb (DC) and non...... on an equal footing. DC-MP2 overestimates the electron correlation correction by 0.48-0.56 a.u. for Hg-halides and by 0.8 a.u. for Hg(CH3)2, respectively, while DC-CCSD underestimates the correlation correction by 0.57-0.66 a.u. compared to the reference DC-CCSD-T data. EFGs obtained at DC-DFT level vary...... considerably with the functional; DC-CAMB3LYP and DC-BH&H reproduce DC-CCSD-T results within 0.08-0.24 a.u. (1% - 3%) for Hg(CH3)2 and Hg-halides, respectively. We finally provide a new standard value for the nuclear quadrupole moment of the I=5/2 state in 199Hg, Q(199Hg)=0.650 b, based on our reference EFG...
DEFF Research Database (Denmark)
Arcisauskaite, V.; Knecht, S.; Sauer, Stephan P. A.
2012-01-01
We examine the performance of Density Functional Theory (DFT) approaches based on the Zeroth-Order Regular Approximation (ZORA) Hamiltonian (with and without inclusion of spin-orbit coupling) for predictions of electric field gradients (EFGs) at the heavy atom Hg nucleus. This is achieved...... by comparing with benchmark DFT and CCSD-T data (Arcisauskaite et al., Phys. Chem. Chem. Phys., 2012, 14, 2651-2657) obtained from 4-component Dirac-Coulomb Hamiltonian calculations. The investigated set of molecules comprises linear HgL2 (L = Cl, Br, I, CH3) and bent HgCl2 mercury compounds as well...... as the trigonal planar [HgCl3](-) system. In 4-component calculations we used the dyall. cv3z basis set for Hg, Br, I and the cc-pCVTZ basis set for H, C, Cl, whereas in ZORA calculations we used the QZ4P basis set for all the atoms. ZORA-4 reproduces the fully relativistic 4-component DFT reference values within...
Czech Academy of Sciences Publication Activity Database
Bartušek, Karel; Gescheidtová, E.
2006-01-01
Roč. 17, č. 8 (2006), s. 2256-2262 ISSN 0957-0233 R&D Projects: GA AV ČR IAA2065201 Institutional research plan: CEZ:AV0Z20650511 Keywords : nuclear magnetic resonance * diffusion coefficients * gradient pulse * spin echo * gradient pulses symmetry Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.228, year: 2006
Arts, M.S.J.; Schill, R.O.; Knigge, T.; Eckwert, H.; Kammenga, J.E.; Köhler, H.R.
2004-01-01
Heat shock proteins (hsps) are potential biomarkers for monitoring environmental pollution. In this study, the use of hsps as biomarkers in field bioassays was evaluated in terrestrial invertebrates exposed to a metal gradient near Avonmouth, UK. We investigated the hsp70 response in resident and
Energy Technology Data Exchange (ETDEWEB)
Ogura, M., E-mail: agura@phys.sci.osaka-u.ac.jp; Akai, H. [Osaka University, Department of Physics, Graduate School of Science (Japan)
2004-11-15
The electric field gradients (EFGs) of B, N, O and Na in TiO{sub 2} were calculated by the full potential Korringa-Kohn-Rostoker (KKR) Greens function method in the framework of the density functional theory. The agreement with the experiments was much improved from the previous calculations that were based on the muffin-tin potential model.
On the energy-momentum tensor in Moyal space
International Nuclear Information System (INIS)
Balasin, Herbert; Schweda, Manfred; Blaschke, Daniel N.; Gieres, Francois
2015-01-01
We study the properties of the energy-momentum tensor of gauge fields coupled to matter in non-commutative (Moyal) space. In general, the non-commutativity affects the usual conservation law of the tensor as well as its transformation properties (gauge covariance instead of gauge invariance). It is well known that the conservation of the energy-momentum tensor can be achieved by a redefinition involving another star-product. Furthermore, for a pure gauge theory it is always possible to define a gauge invariant energy-momentum tensor by means of a Wilson line. We show that the last two procedures are incompatible with each other if couplings of gauge fields to matter fields (scalars or fermions) are considered: The gauge invariant tensor (constructed via Wilson line) does not allow for a redefinition assuring its conservation, and vice versa the introduction of another star-product does not allow for gauge invariance by means of a Wilson line. (orig.)
(2, 0) tensor multiplets and conformal supergravity in D = 6
Bergshoeff, Eric; Sezgin, Ergin; Proeyen, Antoine Van
1999-01-01
We construct the supercurrent multiplet that contains the energyâ€“momentum tensor of the (2, 0) tensor multiplet. By coupling this multiplet of currents to the fields of conformal supergravity, we first construct the linearized superconformal transformations rules of the (2, 0) Weyl multiplet.
A tensor approach to the estimation of hydraulic conductivities in ...
African Journals Online (AJOL)
Based on the field measurements of the physical properties of fractured rocks, the anisotropic properties of hydraulic conductivity (HC) of the fractured rock aquifer can be assessed and presented using a tensor approach called hydraulic conductivity tensor. Three types of HC values, namely point value, axial value and flow ...
Diffusion tensor imaging using multiple coils for mouse brain connectomics.
Nouls, John C; Badea, Alexandra; Anderson, Robert B J; Cofer, Gary P; Allan Johnson, G
2018-04-19
The correlation between brain connectivity and psychiatric or neurological diseases has intensified efforts to develop brain connectivity mapping techniques on mouse models of human disease. The neural architecture of mouse brain specimens can be shown non-destructively and three-dimensionally by diffusion tensor imaging, which enables tractography, the establishment of a connectivity matrix and connectomics. However, experiments on cohorts of animals can be prohibitively long. To improve throughput in a 7-T preclinical scanner, we present a novel two-coil system in which each coil is shielded, placed off-isocenter along the axis of the magnet and connected to a receiver circuit of the scanner. Preservation of the quality factor of each coil is essential to signal-to-noise ratio (SNR) performance and throughput, because mouse brain specimen imaging at 7 T takes place in the coil-dominated noise regime. In that regime, we show a shielding configuration causing no SNR degradation in the two-coil system. To acquire data from several coils simultaneously, the coils are placed in the magnet bore, around the isocenter, in which gradient field distortions can bias diffusion tensor imaging metrics, affect tractography and contaminate measurements of the connectivity matrix. We quantified the experimental alterations in fractional anisotropy and eigenvector direction occurring in each coil. We showed that, when the coils were placed 12 mm away from the isocenter, measurements of the brain connectivity matrix appeared to be minimally altered by gradient field distortions. Simultaneous measurements on two mouse brain specimens demonstrated a full doubling of the diffusion tensor imaging throughput in practice. Each coil produced images devoid of shading or artifact. To further improve the throughput of mouse brain connectomics, we suggested a future expansion of the system to four coils. To better understand acceptable trade-offs between imaging throughput and connectivity
Measurement of mean rotation and strain-rate tensors by using stereoscopic PIV
DEFF Research Database (Denmark)
Özcan, Oktay; Meyer, Knud Erik; Larsen, Poul Scheel
2005-01-01
A technique is described for measuring the mean velocity gradient (rate-of-displacement) tensor by using a conventional stereoscopic particle image velocimetry (SPIV) system. Planar measurement of the mean vorticity vector, rate-of-rotation and rate-of-strain tensors and the production of turbule...
Tensor analysis for physicists
Schouten, J A
1989-01-01
This brilliant study by a famed mathematical scholar and former professor of mathematics at the University of Amsterdam integrates a concise exposition of the mathematical basis of tensor analysis with admirably chosen physical examples of the theory. The first five chapters incisively set out the mathematical theory underlying the use of tensors. The tensor algebra in EN and RN is developed in Chapters I and II. Chapter II introduces a sub-group of the affine group, then deals with the identification of quantities in EN. The tensor analysis in XN is developed in Chapter IV. In chapters VI through IX, Professor Schouten presents applications of the theory that are both intrinsically interesting and good examples of the use and advantages of the calculus. Chapter VI, intimately connected with Chapter III, shows that the dimensions of physical quantities depend upon the choice of the underlying group, and that tensor calculus is the best instrument for dealing with the properties of anisotropic media. In Chapte...
Tensor algebra and tensor analysis for engineers with applications to continuum mechanics
Itskov, Mikhail
2015-01-01
This is the fourth and revised edition of a well-received book that aims at bridging the gap between the engineering course of tensor algebra on the one side and the mathematical course of classical linear algebra on the other side. In accordance with the contemporary way of scientific publications, a modern absolute tensor notation is preferred throughout. The book provides a comprehensible exposition of the fundamental mathematical concepts of tensor calculus and enriches the presented material with many illustrative examples. In addition, the book also includes advanced chapters dealing with recent developments in the theory of isotropic and anisotropic tensor functions and their applications to continuum mechanics. Hence, this monograph addresses graduate students as well as scientists working in this field. In each chapter numerous exercises are included, allowing for self-study and intense practice. Solutions to the exercises are also provided.
Gasilov, Sergei; Mittone, Alberto; Brun, Emmanuel; Bravin, Alberto; Grandl, Susanne; Mirone, Alessandro; Coan, Paola
2014-03-10
The refractive-index gradient vector field approach establishes a connection between a tomographic data set of differential phase contrast images and the distribution of the partial spatial derivatives of the refractive index in an object. The reconstruction of the refractive index in a plane requires the integration of its gradient field. This work shows how this integration can be efficiently performed by converting the problem to the Poisson equation, which can be accurately solved even in the case of noisy and large datasets. The performance of the suggested method is discussed and demonstrated experimentally by computing the refractive index distribution in both a simple plastic phantom and a complex biological sample. The quality of the reconstruction is evaluated through the direct comparison with other commonly used methods. To this end, the refractive index is retrieved from the same data set using also (1) the filtered backprojection algorithm for gradient projections, and (2) the regularized phase-retrieval procedure. Results show that the gradient vector field approach combined with the developed integration technique provides a very accurate depiction of the sample internal structure. Contrary to the two other techniques, the considered method does not require a preliminary phase-retrieval and can be implemented with any advanced computer tomography algorithm. In this work, analyzer-based phase contrast images are used for demonstration. Results, however, are generally valid and can be applied for processing differential phase-contrast tomographic data sets obtained with other phase-contrast imaging techniques.
Killing tensors and conformal Killing tensors from conformal Killing vectors
International Nuclear Information System (INIS)
Rani, Raffaele; Edgar, S Brian; Barnes, Alan
2003-01-01
Koutras has proposed some methods to construct reducible proper conformal Killing tensors and Killing tensors (which are, in general, irreducible) when a pair of orthogonal conformal Killing vectors exist in a given space. We give the completely general result demonstrating that this severe restriction of orthogonality is unnecessary. In addition, we correct and extend some results concerning Killing tensors constructed from a single conformal Killing vector. A number of examples demonstrate that it is possible to construct a much larger class of reducible proper conformal Killing tensors and Killing tensors than permitted by the Koutras algorithms. In particular, by showing that all conformal Killing tensors are reducible in conformally flat spaces, we have a method of constructing all conformal Killing tensors, and hence all the Killing tensors (which will in general be irreducible) of conformally flat spaces using their conformal Killing vectors
Tensor network state correspondence and holography
Singh, Sukhwinder
2018-01-01
In recent years, tensor network states have emerged as a very useful conceptual and simulation framework to study quantum many-body systems at low energies. In this paper, we describe a particular way in which any given tensor network can be viewed as a representation of two different quantum many-body states. The two quantum many-body states are said to correspond to each other by means of the tensor network. We apply this "tensor network state correspondence"—a correspondence between quantum many-body states mediated by tensor networks as we describe—to the multi-scale entanglement renormalization ansatz (MERA) representation of ground states of one dimensional (1D) quantum many-body systems. Since the MERA is a 2D hyperbolic tensor network (the extra dimension is identified as the length scale of the 1D system), the two quantum many-body states obtained from the MERA, via tensor network state correspondence, are seen to live in the bulk and on the boundary of a discrete hyperbolic geometry. The bulk state so obtained from a MERA exhibits interesting features, some of which caricature known features of the holographic correspondence of String theory. We show how (i) the bulk state admits a description in terms of "holographic screens", (ii) the conformal field theory data associated with a critical ground state can be obtained from the corresponding bulk state, in particular, how pointlike boundary operators are identified with extended bulk operators. (iii) We also present numerical results to illustrate that bulk states, dual to ground states of several critical spin chains, have exponentially decaying correlations, and that the bulk correlation length generally decreases with increase in central charge for these spin chains.
Tensors, relativity, and cosmology
Dalarsson, Mirjana
2015-01-01
Tensors, Relativity, and Cosmology, Second Edition, combines relativity, astrophysics, and cosmology in a single volume, providing a simplified introduction to each subject that is followed by detailed mathematical derivations. The book includes a section on general relativity that gives the case for a curved space-time, presents the mathematical background (tensor calculus, Riemannian geometry), discusses the Einstein equation and its solutions (including black holes and Penrose processes), and considers the energy-momentum tensor for various solutions. In addition, a section on relativistic astrophysics discusses stellar contraction and collapse, neutron stars and their equations of state, black holes, and accretion onto collapsed objects, with a final section on cosmology discussing cosmological models, observational tests, and scenarios for the early universe. This fully revised and updated second edition includes new material on relativistic effects, such as the behavior of clocks and measuring rods in m...
DEFF Research Database (Denmark)
Ziegel, Johanna; Nyengaard, Jens Randel; Jensen, Eva B. Vedel
In the present paper, statistical procedures for estimating shape and orientation of arbitrary three-dimensional particles are developed. The focus of this work is on the case where the particles cannot be observed directly, but only via sections. Volume tensors are used for describing particle...... shape and orientation, and stereological estimators of the tensors are derived. It is shown that these estimators can be combined to provide consistent estimators of the moments of the so-called particle cover density. The covariance structure associated with the particle cover density depends...... may be analysed using a generalized methods of moments in which the volume tensors enter. The developed methods are used to study the cell organization in the human brain cortex....
Liu, Limei; Trakic, Adnan; Sanchez-Lopez, Hector; Liu, Feng; Crozier, Stuart
2014-01-01
MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) with a linear accelerator (LINAC) in a single unit. One drawback is that the pulsing of the split gradient coils of the system induces an electric field and currents in the patient which need to be predicted and evaluated for patient safety. In this novel numerical study the in situ electric fields and associated current densities were evaluated inside tissue-accurate male and female human voxel models when a number of different split-geometry gradient coils were operated. The body models were located in the MRI-LINAC system along the axial and radial directions in three different body positions. Each model had a region of interest (ROI) suitable for image-guided radiotherapy. The simulation results show that the amplitudes and distributions of the field and current density induced by different split x-gradient coils were similar with one another in the ROI of the body model, but varied outside of the region. The fields and current densities induced by a split classic coil with the surface unconnected showed the largest deviation from those given by the conventional non-split coils. Another finding indicated that the distributions of the peak current densities varied when the body position, orientation or gender changed, while the peak electric fields mainly occurred in the skin and fat tissues.
Directory of Open Access Journals (Sweden)
J. De Keyser
2007-05-01
Full Text Available This paper describes a general-purpose algorithm for computing the gradients in space and time of a scalar field, a vector field, or a divergence-free vector field, from in situ measurements by one or more spacecraft. The algorithm provides total error estimates on the computed gradient, including the effects of measurement errors, the errors due to a lack of spatio-temporal homogeneity, and errors due to small-scale fluctuations. It also has the ability to diagnose the conditioning of the problem. Optimal use is made of the data, in terms of exploiting the maximum amount of information relative to the uncertainty on the data, by solving the problem in a weighted least-squares sense. The method is illustrated using Cluster magnetic field and electron density data to compute various gradients during a traversal of the inner magnetosphere. In particular, Cluster is shown to cross azimuthal density structure, and the existence of field-aligned currents in the plasmasphere is demonstrated.
Hosseini, A; Philpott, D N; Soleymani, L
2017-11-21
The active transport of analytes inside biosensing systems is important for reducing the response time and enhancing the limit-of-detection of these systems. Due to the ease of functionalization with bio-recognition agents and manipulation with magnetic fields, magnetic particles are widely used for active and directed transport of biological analytes. On-chip active electromagnets are ideally suited for manipulating magnetic particles in an automated and miniaturized fashion inside biosensing systems. Unfortunately, the magnetic force exerted by these devices decays rapidly as we move away from the device edges, and increasing the generated force to the levels necessary for particle manipulation requires a parallel increase in the applied current and the resultant Joule heating. In this paper, we designed a study to understand the combined role of thermal and magnetic forces on the movement of magnetic particles in order to extend the interaction distance of on-chip magnetic devices beyond the device edges. For this purpose, we used a rapid prototyping method to create an active/passive on-chip electromagnet with a micro/nano-structured active layer and a patterned ferromagnetic passive layer. We demonstrated that the measured terminal velocities of particles positioned near the electromagnet edge (∼5.5 μm) closely reflect the values obtained by multi-physics modelling. Interestingly, we observed a two orders of magnitude deviation between the experimental and modelling results for the terminal velocities of particles far from the electromagnet edge (∼55.5 μm). Heat modelling of the system using experimentally-measured thermal gradients indicates that this discrepancy is related to the enhanced fluid movement caused by thermal forces. This study enables the rational design of thermo-magnetic systems for thermally driving and magnetically capturing particles that are positioned at distances tens to hundreds of microns away from the edges of on-chip magnetic
Magnetic hydrodynamics with asymmetric stress tensor
Billig, Yuly
2005-04-01
In this paper we study equations of magnetic hydrodynamics with a stress tensor. We interpret this system as the generalized Euler equation associated with an Abelian extension of the Lie algebra of vector fields with a nontrivial 2-cocycle. We use the Lie algebra approach to prove the energy conservation law and the conservation of cross-helicity.
Magnetic hydrodynamics with asymmetric stress tensor
Billig, Yuly
2004-01-01
In this paper we study equations of magnetic hydrodynamics with a stress tensor. We interpret this system as the generalized Euler equation associated with an abelian extension of the Lie algebra of vector fields with a non-trivial 2-cocycle. We use the Lie algebra approach to prove the energy conservation law and the conservation of cross-helicity.
Superstrings with tensor degrees of freedom
Energy Technology Data Exchange (ETDEWEB)
Amorim, R. (Inst. de Fisica, Univ. Federal do Rio de Janeiro, Rio de Janeiro, RJ (Brazil)); Barcelos-Neto, J. (Inst. de Fisica, Univ. Federal do Rio de Janeiro, Rio de Janeiro, RJ (Brazil))
1994-10-01
We add antisymmetric tensor degrees of freedom to the usual superstring coordinates. We show that super and kappa symmetries are only achieved for the spacetime dimension D = 4. We also address problems related to the quantization of the model and discuss the influences of this extended spacetime in the usual quantum field theory. (orig.)
Tensor modes in pure natural inflation
Nomura, Yasunori; Yamazaki, Masahito
2018-05-01
We study tensor modes in pure natural inflation [1], a recently-proposed inflationary model in which an axionic inflaton couples to pure Yang-Mills gauge fields. We find that the tensor-to-scalar ratio r is naturally bounded from below. This bound originates from the finiteness of the number of metastable branches of vacua in pure Yang-Mills theories. Details of the model can be probed by future cosmic microwave background experiments and improved lattice gauge theory calculations of the θ-angle dependence of the vacuum energy.
Magnetic resonance temporal diffusion tensor spectroscopy of disordered anisotropic tissue
DEFF Research Database (Denmark)
Nielsen, Jonathan Scharff; Dyrby, Tim Bjørn; Lundell, Henrik
2018-01-01
of the oscillating gradient spin echo (OGSE) experiment, giving a basic contrast mechanism closely linked to both the temporal diffusion spectrum and the compartment anisotropy. We demonstrate our new method on post mortem brain tissue and show that we retrieve the correct temporal diffusion tensor spectrum...
Larmor radius expansion for the inhomogeneous plasma dielectric tensor
International Nuclear Information System (INIS)
Ottaviani, M.
1984-01-01
A larmour radius expansion for the dielectric tensor of an inhomogeneous plasma with perpendicular gradients is derived directly from the relativistic Vlasov equation. Various wave equations are derived from relevant radio frequency heating problems together with a generalized Poynting theorem. The validity of Kadomtev's assumption is discussed
Tensor calculus for engineers and physicists
de Souza Sánchez Filho, Emil
2016-01-01
This textbook provides a rigorous approach to tensor manifolds in several aspects relevant for Engineers and Physicists working in industry or academia. With a thorough, comprehensive, and unified presentation, this book offers insights into several topics of tensor analysis, which covers all aspects of N dimensional spaces. The main purpose of this book is to give a self-contained yet simple, correct and comprehensive mathematical explanation of tensor calculus for undergraduate and graduate students and for professionals. In addition to many worked problems, this book features a selection of examples, solved step by step. Although no emphasis is placed on special and particular problems of Engineering or Physics, the text covers the fundamentals of these fields of science. The book makes a brief introduction into the basic concept of the tensorial formalism so as to allow the reader to make a quick and easy review of the essential topics that enable having the grounds for the subsequent themes, without need...
Tensor Calculus: Unlearning Vector Calculus
Lee, Wha-Suck; Engelbrecht, Johann; Moller, Rita
2018-01-01
Tensor calculus is critical in the study of the vector calculus of the surface of a body. Indeed, tensor calculus is a natural step-up for vector calculus. This paper presents some pitfalls of a traditional course in vector calculus in transitioning to tensor calculus. We show how a deeper emphasis on traditional topics such as the Jacobian can…
The evolution of tensor polarization
International Nuclear Information System (INIS)
Huang, H.; Lee, S.Y.; Ratner, L.
1993-01-01
By using the equation of motion for the vector polarization, the spin transfer matrix for spin tensor polarization, the spin transfer matrix for spin tensor polarization is derived. The evolution equation for the tensor polarization is studied in the presence of an isolate spin resonance and in the presence of a spin rotor, or snake
Tensor B mode and stochastic Faraday mixing
Giovannini, Massimo
2014-01-01
This paper investigates the Faraday effect as a different source of B mode polarization. The E mode polarization is Faraday rotated provided a stochastic large-scale magnetic field is present prior to photon decoupling. In the first part of the paper we discuss the case where the tensor modes of the geometry are absent and we argue that the B mode recently detected by the Bicep2 collaboration cannot be explained by a large-scale magnetic field rotating, through the Faraday effect, the well established E mode polarization. In this case, the observed temperature autocorrelations would be excessively distorted by the magnetic field. In the second part of the paper the formation of Faraday rotation is treated as a stationary, random and Markovian process with the aim of generalizing a set of scaling laws originally derived in the absence of the tensor modes of the geometry. We show that the scalar, vector and tensor modes of the brightness perturbations can all be Faraday rotated even if the vector and tensor par...
Iinuma, Takeshi
2018-04-01
A monitoring method to grasp the spatio-temporal change in the interplate coupling in a subduction zone based on the spatial gradients of surface displacement rate fields is proposed. I estimated the spatio-temporal change in the interplate coupling along the plate boundary in northeastern (NE) Japan by applying the proposed method to the surface displacement rates based on global positioning system observations. The gradient of the surface velocities is calculated in each swath configured along the direction normal to the Japan Trench for time windows such as 0.5, 1, 2, 3 and 5 yr being shifted by one week during the period of 1997-2016. The gradient of the horizontal velocities is negative and has a large magnitude when the interplate coupling at the shallow part (less than approximately 50 km in depth) beneath the profile is strong, and the sign of the gradient of the vertical velocity is sensitive to the existence of the coupling at the deep part (greater than approximately 50 km in depth). The trench-parallel variation of the spatial gradients of a displacement rate field clearly corresponds to the trench-parallel variation of the amplitude of the interplate coupling on the plate interface, as well as the rupture areas of previous interplate earthquakes. Temporal changes in the trench-parallel variation of the spatial gradient of the displacement rate correspond to the strengthening or weakening of the interplate coupling. We can monitor the temporal change in the interplate coupling state by calculating the spatial gradients of the surface displacement rate field to some extent without performing inversion analyses with applying certain constraint conditions that sometimes cause over- and/or underestimation at areas of limited spatial resolution far from the observation network. The results of the calculation confirm known interplate events in the NE Japan subduction zone, such as the post-seismic slip of the 2003 M8.0 Tokachi-oki and 2005 M7.2 Miyagi
Hall, Jennifer B; Fushman, David
2006-06-21
We applied a combination of 15N relaxation and CSA/dipolar cross-correlation measurements at five magnetic fields (9.4, 11.7, 14.1, 16.4, and 18.8 T) to determine the 15N chemical shielding tensors for backbone amides in protein G in solution. The data were analyzed using various model-independent approaches and those based on Lipari-Szabo approximation, all of them yielding similar results. The results indicate a range of site-specific values of the anisotropy (CSA) and orientation of the 15N chemical shielding tensor, similar to those in ubiquitin (Fushman, et al. J. Am. Chem. Soc. 1998, 120, 10947; J. Am. Chem. Soc. 1999, 121, 8577). Assuming a Gaussian distribution of the 15N CSA values, the mean anisotropy is -173.9 to -177.2 ppm (for 1.02 A NH bond length) and the site-to-site CSA variability is +/-17.6 to +/-21.4 ppm, depending on the method used. This CSA variability is significantly larger than derived previously for ribonuclease H (Kroenke, et al. J. Am. Chem. Soc. 1999, 121, 10119) or recently, using "meta-analysis" for ubiquitin (Damberg, et al. J. Am. Chem. Soc. 2005, 127, 1995). Standard interpretation of 15N relaxation studies of backbone dynamics in proteins involves an a priori assumption of a uniform 15N CSA. We show that this assumption leads to a significant discrepancy between the order parameters obtained at different fields. Using the site-specific CSAs obtained from our study removes this discrepancy and allows simultaneous fit of relaxation data at all five fields to Lipari-Szabo spectral densities. These findings emphasize the necessity of taking into account the variability of 15N CSA for accurate analysis of protein dynamics from 15N relaxation measurements.
Vectors, tensors and the basic equations of fluid mechanics
Aris, Rutherford
1962-01-01
Introductory text, geared toward advanced undergraduate and graduate students, applies mathematics of Cartesian and general tensors to physical field theories and demonstrates them in terms of the theory of fluid mechanics. 1962 edition.
A generalization of tensor calculus and its application to physics
International Nuclear Information System (INIS)
Ashtekar, A.
1982-01-01
Penrose's abstract index notation and axiomatic introduction of covariant derivatives in tensor calculus is generalized to fields with internal degrees of freedom. The result provides, in particular, an intrinsic formulation of gauge theories without the use of bundles. (author)
Tensor modes on the string theory landscape
Energy Technology Data Exchange (ETDEWEB)
Westphal, Alexander
2012-06-15
We attempt an estimate for the distribution of the tensor mode fraction r over the landscape of vacua in string theory. The dynamics of eternal inflation and quantum tunneling lead to a kind of democracy on the landscape, providing no bias towards large-field or small-field inflation regardless of the class of measure. The tensor mode fraction then follows the number frequency distributions of inflationary mechanisms of string theory over the landscape. We show that an estimate of the relative number frequencies for small-field vs large-field inflation, while unattainable on the whole landscape, may be within reach as a regional answer for warped Calabi-Yau flux compactifications of type IIB string theory.
Tensor modes on the string theory landscape
International Nuclear Information System (INIS)
Westphal, Alexander
2012-06-01
We attempt an estimate for the distribution of the tensor mode fraction r over the landscape of vacua in string theory. The dynamics of eternal inflation and quantum tunneling lead to a kind of democracy on the landscape, providing no bias towards large-field or small-field inflation regardless of the class of measure. The tensor mode fraction then follows the number frequency distributions of inflationary mechanisms of string theory over the landscape. We show that an estimate of the relative number frequencies for small-field vs large-field inflation, while unattainable on the whole landscape, may be within reach as a regional answer for warped Calabi-Yau flux compactifications of type IIB string theory.
International Nuclear Information System (INIS)
Nguyen, Thien Duy; Wells, John Craig; Mokhasi, Paritosh; Rempfer, Dietmar
2010-01-01
In this paper, particle image velocimetry (PIV) results from the recirculation zone of a backward-facing step flow, of which the Reynolds number is 2800 based on bulk velocity upstream of the step and step height (h = 16.5 mm), are used to demonstrate the capability of proper orthogonal decomposition (POD)-based measurement models. Three-component PIV velocity fields are decomposed by POD into a set of spatial basis functions and a set of temporal coefficients. The measurement models are built to relate the low-order POD coefficients, determined from an ensemble of 1050 PIV fields by the 'snapshot' method, to the time-resolved wall gradients, measured by a near-wall measurement technique called stereo interfacial PIV. These models are evaluated in terms of reconstruction and prediction of the low-order temporal POD coefficients of the velocity fields. In order to determine the estimation coefficients of the measurement models, linear stochastic estimation (LSE), quadratic stochastic estimation (QSE), principal component regression (PCR) and kernel ridge regression (KRR) are applied. We denote such approaches as LSE-POD, QSE-POD, PCR-POD and KRR-POD. In addition to comparing the accuracy of measurement models, we introduce multi-time POD-based estimations in which past and future information of the wall-gradient events is used separately or combined. The results show that the multi-time estimation approaches can improve the prediction process. Among these approaches, the proposed multi-time KRR-POD estimation with an optimized window of past wall-gradient information yields the best prediction. Such a multi-time KRR-POD approach offers a useful tool for real-time flow estimation of the velocity field based on wall-gradient data
Coordinate independent expression for transverse trace-free tensors
International Nuclear Information System (INIS)
Conboye, Rory
2016-01-01
The transverse and trace-free (TT) part of the extrinsic curvature represents half of the dynamical degrees of freedom of the gravitational field in the 3 + 1 formalism. As such, it is part of the freely specifiable initial data for numerical relativity. Though TT tensors in three-space possess only two component degrees of freedom, they cannot ordinarily be given solely by two scalar potentials. Such expressions have been derived, however, in coordinate form, for all TT tensors in flat space which are also translationally or axially symmetric (Conboye and Murchadha 2014 Class. Quantum Grav. 31 085019). Since TT tensors are conformally covariant, these also give TT tensors in conformally flat space. In this article, the work above has been extended by giving a coordinate-independent expression for these TT tensors. The translational and axial symmetry conditions have also been generalized to invariance along any hypersurface orthogonal Killing vector. (paper)
Coupling the antisymmetric tensor to the supergravity-matter system
International Nuclear Information System (INIS)
Binetruy, P.; Girardi, G.; Mueller, M.
1987-06-01
The description of the antisymmetric tensor gauge field with Chern-Simons forms in Kaehler superspace is used to derive a particular coupling of the antisymmetric tensor to the general supergravity-matter system in terms of superfields as well as component fields. The construction is performed directly in terms of the linear multiplet. The proper duality transformations are presented at the full superfield level. General couplings are shortly discussed
Gogny interactions with tensor terms
Energy Technology Data Exchange (ETDEWEB)
Anguiano, M.; Lallena, A.M.; Bernard, R.N. [Universidad de Granada, Departamento de Fisica Atomica, Molecular y Nuclear, Granada (Spain); Co' , G. [INFN, Lecce (Italy); De Donno, V. [Universita del Salento, Dipartimento di Matematica e Fisica ' ' E. De Giorgi' ' , Lecce (Italy); Grasso, M. [Universite Paris-Sud, Institut de Physique Nucleaire, IN2P3-CNRS, Orsay (France)
2016-07-15
We present a perturbative approach to include tensor terms in the Gogny interaction. We do not change the values of the usual parameterisations, with the only exception of the spin-orbit term, and we add tensor terms whose only free parameters are the strengths of the interactions. We identify observables sensitive to the presence of the tensor force in Hartree-Fock, Hartree-Fock-Bogoliubov and random phase approximation calculations. We show the need of including two tensor contributions, at least: a pure tensor term and a tensor-isospin term. We show results relevant for the inclusion of the tensor term for single-particle energies, charge-conserving magnetic excitations and Gamow-Teller excitations. (orig.)
Diffusion tensor smoothing through weighted Karcher means
Carmichael, Owen; Chen, Jun; Paul, Debashis; Peng, Jie
2014-01-01
Diffusion tensor magnetic resonance imaging (MRI) quantifies the spatial distribution of water Diffusion at each voxel on a regular grid of locations in a biological specimen by Diffusion tensors– 3 × 3 positive definite matrices. Removal of noise from DTI is an important problem due to the high scientific relevance of DTI and relatively low signal to noise ratio it provides. Leading approaches to this problem amount to estimation of weighted Karcher means of Diffusion tensors within spatial neighborhoods, under various metrics imposed on the space of tensors. However, it is unclear how the behavior of these estimators varies with the magnitude of DTI sensor noise (the noise resulting from the thermal e!ects of MRI scanning) as well as the geometric structure of the underlying Diffusion tensor neighborhoods. In this paper, we combine theoretical analysis, empirical analysis of simulated DTI data, and empirical analysis of real DTI scans to compare the noise removal performance of three kernel-based DTI smoothers that are based on Euclidean, log-Euclidean, and affine-invariant metrics. The results suggest, contrary to conventional wisdom, that imposing a simplistic Euclidean metric may in fact provide comparable or superior noise removal, especially in relatively unstructured regions and/or in the presence of moderate to high levels of sensor noise. On the contrary, log-Euclidean and affine-invariant metrics may lead to better noise removal in highly structured anatomical regions, especially when the sensor noise is of low magnitude. These findings emphasize the importance of considering the interplay of sensor noise magnitude and tensor field geometric structure when assessing Diffusion tensor smoothing options. They also point to the necessity for continued development of smoothing methods that perform well across a large range of scenarios. PMID:25419264
Lim, C. W.; Zhang, G.; Reddy, J. N.
2015-05-01
In recent years there have been many papers that considered the effects of material length scales in the study of mechanics of solids at micro- and/or nano-scales. There are a number of approaches and, among them, one set of papers deals with Eringen's differential nonlocal model and another deals with the strain gradient theories. The modified couple stress theory, which also accounts for a material length scale, is a form of a strain gradient theory. The large body of literature that has come into existence in the last several years has created significant confusion among researchers about the length scales that these various theories contain. The present paper has the objective of establishing the fact that the length scales present in nonlocal elasticity and strain gradient theory describe two entirely different physical characteristics of materials and structures at nanoscale. By using two principle kernel functions, the paper further presents a theory with application examples which relates the classical nonlocal elasticity and strain gradient theory and it results in a higher-order nonlocal strain gradient theory. In this theory, a higher-order nonlocal strain gradient elasticity system which considers higher-order stress gradients and strain gradient nonlocality is proposed. It is based on the nonlocal effects of the strain field and first gradient strain field. This theory intends to generalize the classical nonlocal elasticity theory by introducing a higher-order strain tensor with nonlocality into the stored energy function. The theory is distinctive because the classical nonlocal stress theory does not include nonlocality of higher-order stresses while the common strain gradient theory only considers local higher-order strain gradients without nonlocal effects in a global sense. By establishing the constitutive relation within the thermodynamic framework, the governing equations of equilibrium and all boundary conditions are derived via the variational
D=4, N=2 Gauged Supergravity coupled to Vector-Tensor Multiplets
Andrianopoli, Laura; D'Auria, Riccardo; Sommovigo, Luca; Trigiante, Mario
2011-01-01
We construct the general four-dimensional N=2 supergravity theory coupled to vector and vector-tensor multiplets only. Consistency of the construction requires the introduction of the vector fields dual to those sitting in the same supermultiplets as the antisymmetric tensors, as well as the scalar fields dual to the tensors themselves. Gauge symmetries also involving these additional fields guarantee the correct counting of the physical degrees of freedom.
Toward an improved determination of Earth's lithospheric magnetic field from satellite observations
Kotsiaros, S.
2016-12-01
An analytical and numerical analysis of the spectral properties of the gradient tensor, initially performed by Rummel and van Gelderen (1992) for the gravity potential, shows that when the tensor elements are grouped into sets of semi-tangential and pure-tangential parts, they produce almost identical signal content as the normal element. Moreover, simple eigenvalue relations can be derived between these sets and the spherical harmonic expansion of the potential. This theoretical development generally applies to any potential field. First, the analysis of Rummel and van Gelderen (1992) is adapted to the magnetic field case and then the elements of the magnetic gradient tensor are estimated by 2 years of Swarm data and grouped into Γ(1) = {[∇B]rθ,[∇B]rφ} resp. Γ(2) = {[∇B]θθ-[∇B]φφ, 2[∇B]θφ}. It is shown that the estimated combinations Γ(1) and Γ(2) produce similar signal content as the theoretical radial gradient [∇B]rr. These results demonstrate the ability of multi-satellite missions such as Swarm, which cannot directly measure the radial gradient, to retrieve similar signal content by means of the horizontal gradients. Finally, lithospheric field models are derived using the gradient combinations Γ(1) and Γ(2) and compared with models derived from traditional vector and gradient data. The model resulting from Γ(1) leads to a very similar, and in particular cases improved, model compared to models retrieved by using approximately three times more data, i.e. a full set of vector, North-South and East-West gradients. ReferencesRummel, R., and M. van Gelderen (1992), Spectral analysis of the full gravity tensor, Geophysical Journal International, 111 (1), 159-169.
Dillon, Joshua V.; Langmore, Ian; Tran, Dustin; Brevdo, Eugene; Vasudevan, Srinivas; Moore, Dave; Patton, Brian; Alemi, Alex; Hoffman, Matt; Saurous, Rif A.
2017-01-01
The TensorFlow Distributions library implements a vision of probability theory adapted to the modern deep-learning paradigm of end-to-end differentiable computation. Building on two basic abstractions, it offers flexible building blocks for probabilistic computation. Distributions provide fast, numerically stable methods for generating samples and computing statistics, e.g., log density. Bijectors provide composable volume-tracking transformations with automatic caching. Together these enable...
Holographic stress tensor for non-relativistic theories
International Nuclear Information System (INIS)
Ross, Simon F.; Saremi, Omid
2009-01-01
We discuss the calculation of the field theory stress tensor from the dual geometry for two recent proposals for gravity duals of non-relativistic conformal field theories. The first of these has a Schroedinger symmetry including Galilean boosts, while the second has just an anisotropic scale invariance (the Lifshitz case). For the Lifshitz case, we construct an appropriate action principle. We propose a definition of the non-relativistic stress tensor complex for the field theory as an appropriate variation of the action in both cases. In the Schroedinger case, we show that this gives physically reasonable results for a simple black hole solution and agrees with an earlier proposal to determine the stress tensor from the familiar AdS prescription. In the Lifshitz case, we solve the linearised equations of motion for a general perturbation around the background, showing that our stress tensor is finite on-shell.
Tensor Permutation Matrices in Finite Dimensions
Christian, Rakotonirina
2005-01-01
We have generalised the properties with the tensor product, of one 4x4 matrix which is a permutation matrix, and we call a tensor commutation matrix. Tensor commutation matrices can be constructed with or without calculus. A formula allows us to construct a tensor permutation matrix, which is a generalisation of tensor commutation matrix, has been established. The expression of an element of a tensor commutation matrix has been generalised in the case of any element of a tensor permutation ma...
Kim, Yun-Jeong; Chae, Joon-Seok; Chang, Jun Keun; Kang, Seong Ho
2005-08-12
We have developed a novel method for the ultra-fast analysis of genetically modified organisms (GMOs) in soybeans by microchip capillary gel electrophoresis (MCGE) using programmed field strength gradients (PFSG) in a conventional glass double-T microchip. Under the programmed electric field strength and 0.3% poly(ethylene oxide) sieving matrix, the GMO in soybeans was analyzed within only 11 s of the microchip. The MCGE-PFSG method was a program that changes the electric field strength during GMO analysis, and was also applied to the ultra-fast analysis of PCR products. Compared to MCGE using a conventional and constantly applied electric field, the MCGE-PFSG analysis generated faster results without the loss of resolving power and reproducibility for specific DNA fragments (100- and 250-bp DNA) of GM-soybeans. The MCGE-PFSG technique may prove to be a new tool in the GMO analysis due to its speed, simplicity, and high efficiency.
Dibb, Russell; Liu, Chunlei
2017-06-01
To develop a susceptibility-based MRI technique for probing microstructure and fiber architecture of magnetically anisotropic tissues-such as central nervous system white matter, renal tubules, and myocardial fibers-in three dimensions using susceptibility tensor imaging (STI) tools. STI can probe tissue microstructure, but is limited by reconstruction artifacts because of absent phase information outside the tissue and noise. STI accuracy may be improved by estimating a joint eigenvector from mutually anisotropic susceptibility and relaxation tensors. Gradient-recalled echo image data were simulated using a numerical phantom and acquired from the ex vivo mouse brain, kidney, and heart. Susceptibility tensor data were reconstructed using STI, regularized STI, and the proposed algorithm of mutually anisotropic and joint eigenvector STI (MAJESTI). Fiber map and tractography results from each technique were compared with diffusion tensor data. MAJESTI reduced the estimated susceptibility tensor orientation error by 30% in the phantom, 36% in brain white matter, 40% in the inner medulla of the kidney, and 45% in myocardium. This improved the continuity and consistency of susceptibility-based fiber tractography in each tissue. MAJESTI estimation of the susceptibility tensors yields lower orientation errors for susceptibility-based fiber mapping and tractography in the intact brain, kidney, and heart. Magn Reson Med 77:2331-2346, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.
Tensor Factorization for Low-Rank Tensor Completion.
Zhou, Pan; Lu, Canyi; Lin, Zhouchen; Zhang, Chao
2018-03-01
Recently, a tensor nuclear norm (TNN) based method was proposed to solve the tensor completion problem, which has achieved state-of-the-art performance on image and video inpainting tasks. However, it requires computing tensor singular value decomposition (t-SVD), which costs much computation and thus cannot efficiently handle tensor data, due to its natural large scale. Motivated by TNN, we propose a novel low-rank tensor factorization method for efficiently solving the 3-way tensor completion problem. Our method preserves the low-rank structure of a tensor by factorizing it into the product of two tensors of smaller sizes. In the optimization process, our method only needs to update two smaller tensors, which can be more efficiently conducted than computing t-SVD. Furthermore, we prove that the proposed alternating minimization algorithm can converge to a Karush-Kuhn-Tucker point. Experimental results on the synthetic data recovery, image and video inpainting tasks clearly demonstrate the superior performance and efficiency of our developed method over state-of-the-arts including the TNN and matricization methods.
Fouré, Alexandre; Ogier, Augustin C; Le Troter, Arnaud; Vilmen, Christophe; Feiweier, Thorsten; Guye, Maxime; Gondin, Julien; Besson, Pierre; Bendahan, David
2018-05-01
Purpose To demonstrate the reproducibility of the diffusion properties and three-dimensional structural organization measurements of the lower leg muscles by using diffusion-tensor imaging (DTI) assessed with ultra-high-field-strength (7.0-T) magnetic resonance (MR) imaging and tractography of skeletal muscle fibers. On the basis of robust statistical mapping analyses, this study also aimed at determining the sensitivity of the measurements to sex difference and intramuscular variability. Materials and Methods All examinations were performed with ethical review board approval; written informed consent was obtained from all volunteers. Reproducibility of diffusion tensor indexes assessment including eigenvalues, mean diffusivity, and fractional anisotropy (FA) as well as muscle volume and architecture (ie, fiber length and pennation angle) were characterized in lower leg muscles (n = 8). Intramuscular variability and sex differences were characterized in young healthy men and women (n = 10 in each group). Student t test, statistical parametric mapping, correlation coefficients (Spearman rho and Pearson product-moment) and coefficient of variation (CV) were used for statistical data analysis. Results High reproducibility of measurements (mean CV ± standard deviation, 4.6% ± 3.8) was determined in diffusion properties and architectural parameters. Significant sex differences were detected in FA (4.2% in women for the entire lower leg; P = .001) and muscle volume (21.7% in men for the entire lower leg; P = .008), whereas architecture parameters were almost identical across sex. Additional differences were found independently of sex in diffusion properties and architecture along several muscles of the lower leg. Conclusion The high-spatial-resolution DTI assessed with 7.0-T MR imaging allows a reproducible assessment of structural organization of superficial and deep muscles, giving indirect information on muscle function. © RSNA, 2018 Online supplemental material is
Dark energy in scalar-tensor theories
International Nuclear Information System (INIS)
Moeller, J.
2007-12-01
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of σ-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Dark energy in scalar-tensor theories
Energy Technology Data Exchange (ETDEWEB)
Moeller, J.
2007-12-15
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of {sigma}-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Fermionic topological quantum states as tensor networks
Wille, C.; Buerschaper, O.; Eisert, J.
2017-06-01
Tensor network states, and in particular projected entangled pair states, play an important role in the description of strongly correlated quantum lattice systems. They do not only serve as variational states in numerical simulation methods, but also provide a framework for classifying phases of quantum matter and capture notions of topological order in a stringent and rigorous language. The rapid development in this field for spin models and bosonic systems has not yet been mirrored by an analogous development for fermionic models. In this work, we introduce a tensor network formalism capable of capturing notions of topological order for quantum systems with fermionic components. At the heart of the formalism are axioms of fermionic matrix-product operator injectivity, stable under concatenation. Building upon that, we formulate a Grassmann number tensor network ansatz for the ground state of fermionic twisted quantum double models. A specific focus is put on the paradigmatic example of the fermionic toric code. This work shows that the program of describing topologically ordered systems using tensor networks carries over to fermionic models.
International Nuclear Information System (INIS)
Rao, J.R.; Tiwari, R.N.
1974-01-01
A theorem on obtaining exact solutions for a particular field structure from those of vacuum field equations of general theory as well as from some simpler solutions of unified theories is derived. With the help of this result the most general solution for the particular field structure is developed from the already known simpler solutions. The physical implications of this theorem in relation to some of the parallel work of other authors is discussed. (author)
Tensor norms and operator ideals
Defant, A; Floret, K
1992-01-01
The three chapters of this book are entitled Basic Concepts, Tensor Norms, and Special Topics. The first may serve as part of an introductory course in Functional Analysis since it shows the powerful use of the projective and injective tensor norms, as well as the basics of the theory of operator ideals. The second chapter is the main part of the book: it presents the theory of tensor norms as designed by Grothendieck in the Resumé and deals with the relation between tensor norms and operator ideals. The last chapter deals with special questions. Each section is accompanied by a series of exer
Notes on super Killing tensors
Energy Technology Data Exchange (ETDEWEB)
Howe, P.S. [Department of Mathematics, King’s College London,The Strand, London WC2R 2LS (United Kingdom); Lindström, University [Department of Physics and Astronomy, Theoretical Physics, Uppsala University,SE-751 20 Uppsala (Sweden); Theoretical Physics, Imperial College London,Prince Consort Road, London SW7 2AZ (United Kingdom)
2016-03-14
The notion of a Killing tensor is generalised to a superspace setting. Conserved quantities associated with these are defined for superparticles and Poisson brackets are used to define a supersymmetric version of the even Schouten-Nijenhuis bracket. Superconformal Killing tensors in flat superspaces are studied for spacetime dimensions 3,4,5,6 and 10. These tensors are also presented in analytic superspaces and super-twistor spaces for 3,4 and 6 dimensions. Algebraic structures associated with superconformal Killing tensors are also briefly discussed.
Tensor Train Neighborhood Preserving Embedding
Wang, Wenqi; Aggarwal, Vaneet; Aeron, Shuchin
2018-05-01
In this paper, we propose a Tensor Train Neighborhood Preserving Embedding (TTNPE) to embed multi-dimensional tensor data into low dimensional tensor subspace. Novel approaches to solve the optimization problem in TTNPE are proposed. For this embedding, we evaluate novel trade-off gain among classification, computation, and dimensionality reduction (storage) for supervised learning. It is shown that compared to the state-of-the-arts tensor embedding methods, TTNPE achieves superior trade-off in classification, computation, and dimensionality reduction in MNIST handwritten digits and Weizmann face datasets.
International Nuclear Information System (INIS)
Sato, Mitsugu; Ishitani, Tohru; Watanabe, Shunya; Nakagawa, Mine
2004-01-01
The depth of field (DoF) in scanning electron microscope (SEM) images has been determined by estimating the change of image sharpness or resolution near the exact focus position. The image sharpness or resolution along the optical axis is determined by calculating the information-passing capacity (IPC) of an optical system taking into account the effect of pixel size of the image. The change of image sharpness near the exact focus position is determined by measuring the slope gradient of the line profile in SEM images obtained at various focal positions of beam. The change of image sharpness along the optical axis determined by the IPC agrees well with those determined by the slope gradient of line profiles in SEM images when a Gaussian distribution having radius 0.86L p (L p : pixel size in image) at which the intensity has fallen to 1/e of the maximum is applied to the IPC calculation for each pixel intensity. The change of image sharpness near the exact focus position has also been compared with those determined by the CG (Contrast-to-Gradient) method. The CG method slightly underestimates the change of image sharpness compared with those determined by the IPC method
Directory of Open Access Journals (Sweden)
Zhen Chen
2017-01-01
Full Text Available Fractal and multi-fractal content area method finds application in a wide variety of geological, geochemical and geophysical fields. In this study, the fractal content-gradient method was used on 1:10,000 scale to delineate geochemical anomalies associated with copper mineralization. Analysis of geochemical data from the Yangla super large Cu-Pb-Zn polymetallic ore district using the fractal content-gradient method, combined with other geological data from this area, indicates that ore-prospecting in the ore district should focus on Cu as the main metal and Pb-Zn and Au as the auxiliary metals. The types of deposits include (in chronological order re-formed sedimentary exhalative (SEDEX, skarns, porphyries, and hydrothermal vein-type deposits. Three ore-prospecting targets are divided on a S–N basis: (1 the Qulong exploration area, in which the targets are porphyry-type Cu deposits; (2 the Zongya exploration area, where the targets are porphyry-type Cu and hydrothermal vein-type Cu-Pb polymetallic deposits; and (3 the Zarelongma exploration area, characterized mainly skarn-type “Yangla-style” massive sulfide Cu-Pb deposits. Our study demonstrates that the fractal content-gradient method is convenient, simple, rapid, and direct for delineating geochemical anomalies and for outlining potential exploration targets.
Canonical forms of tensor representations and spontaneous symmetry breaking
International Nuclear Information System (INIS)
Cummins, C.J.
1986-01-01
An algorithm for constructing canonical forms for any tensor representation of the classical compact Lie groups is given. This method is used to find a complete list of the symmetry breaking patterns produced by Higgs fields in the third-rank antisymmetric representations of U(n), SU(n) and SO(n) for n<=7. A simple canonical form is also given for kth-rank symmetric tensor representations. (author)
Gust, M; Buronfosse, T; Geffard, O; Coquery, M; Mons, R; Abbaci, K; Giamberini, L; Garric, J
2011-01-17
The Lot River is known to be contaminated by metals, mainly cadmium and zinc, due to a former Zn ore treatment plant in the watershed of the Riou-Mort, a tributary of the Lot River. Many studies have been performed to characterize contamination, but few have assessed its consequences on the biological responses of organisms along the gradient. We exposed adult and juvenile New Zealand freshwater mudsnails Potamopyrgus antipodarum at several sites along the gradient of metal contamination for 28 days. Biological responses were monitored at different levels: individual (survival, growth and fecundity), tissue and biochemical (energy status and vertebrate-like sex steroid levels) to better understand the toxicity mechanisms involved. Accumulation of Cd and Zn was high during exposure. Most of the biological effects observed could be linked to this contamination and were concentration-dependent. Histological lesions of the digestive gland were observed, with hypertrophy of calcium cells and vacuolization of digestive cells. Such effects are likely to explain the decrease of energy status (triglycerides and proteins), juvenile growth and adult fecundity observed at the most polluted site. However the magnitude of the fall in fecundity cannot be attributed only to these tissular effects, indicating another mode of action of Cd or possible confounding factors. Steroid accumulation in snails indicated only organic pollution. Histopathological effects proved the most sensitive endpoint to metal (Cd and Zn) contamination. Copyright © 2010 Elsevier B.V. All rights reserved.
Asymptotic tensor rank of graph tensors: beyond matrix multiplication
M. Christandl (Matthias); P. Vrana (Péter); J. Zuiddam (Jeroen)
2016-01-01
textabstractWe present an upper bound on the exponent of the asymptotic behaviour of the tensor rank of a family of tensors defined by the complete graph on $k$ vertices. For $k\\geq4$, we show that the exponent per edge is at most 0.77, outperforming the best known upper bound on the exponent per
Algebraic Rainich conditions for the fourth rank tensor V
International Nuclear Information System (INIS)
So, Lau Loi
2011-01-01
Algebraic conditions on the Ricci tensor in the Rainich-Misner-Wheeler unified field theory are known as the Rainich conditions. Penrose and more recently Bergqvist and Lankinen made an analogy from the Ricci tensor to the Bel-Robinson tensor B αβμν , a certain fourth rank tensor quadratic in the Weyl curvature, which also satisfies algebraic Rainich-like conditions. However, we found that not only does the tensor B αβμν fulfill these conditions, but so also does our recently proposed tensor V αβμν , which has many of the desirable properties of B αβμν . For the quasilocal small sphere limit restriction, we found that there are only two fourth rank tensors, B αβμν and V αβμν , which form a basis for good energy expressions. Both of them have the completely trace free and causal properties, these two form necessary and sufficient conditions. Surprisingly either completely traceless or causal is enough to fulfill the algebraic Rainich conditions.
Ostrom, N. E.; Ostrom, P. H.; Gandhi, H.; Millar, N.; Robertson, G. P.
2009-12-01
The microbial source of nitrous oxide in terrestrial ecosystems has long been debated. Both nitrification and denitrification produce nitrous oxide but their relative importance remains uncertain. Here we apply site preference, SP, (the difference in δ15N between the central and outer N atom in nitrous oxide), to estimate production of nitrous oxide from bacterial denitrification (including nitrifier denitrification). Soil flux chambers were deployed within 3 agricultural plots planted with wheat in corn-soybean wheat rotation as part of ongoing studies at the Kellogg Biological Stations Long-Term Ecosystem Research site. Distinct levels of urea-ammonium nitrate (28%) fertilizer were applied to each plot in the spring of 2007 to obtain totals of 0, 134, and 246 kg-N ha-1. Samples for nitrous oxide flux and isotopologue composition were collected approximately 4 times per week from May through December, 2007, in each of the plots. The average annual nitrous oxide flux weighted N isotope values increased along the fertilization gradient (-14.7, -12.3 and -9.1 ‰, for the no, medium and high N additions, respectively) whereas O isotope values decreased (33.2, 28.7 and 25.3 ‰, respectively). Flux weighted SP values along the fertilization gradient (0.7, 4.0 and 3.8 ‰, respectively) were low and consistent with an origin predominantly from denitrification based on SP values found for nitrification and denitrification in pure culture studies. Consequently, we find that irregardless of the level of fertilizer applied denitrification was the predominant source of nitrous oxide.
Indicial tensor manipulation on MACSYMA
International Nuclear Information System (INIS)
Bogen, R.A.; Pavelle, R.
1977-01-01
A new computational tool for physical calculations is described. It is the first computer system capable of performing indicial tensor calculus (as opposed to component tensor calculus). It is now operational on the symbolic manipulation system MACSYMA. The authors outline the capabilities of the system and describe some of the physical problems considered as well as others being examined at this time. (Auth.)
Urashima, Yasufumi; Sonoda, Takahiro; Fujita, Yuko; Uragami, Atsuko
2012-01-01
Growth inhibition due to continuous cropping of asparagus is a major problem; the yield of asparagus in replanted fields is low compared to that in new fields, and missing plants occur among young seedlings. Although soil-borne disease and allelochemicals are considered to be involved in this effect, this is still controversial. We aimed to develop a technique for the biological field diagnosis of growth inhibition due to continuous cropping. Therefore, in this study, fungal community structure and Fusarium community structure in continuously cropped fields of asparagus were analyzed by polymerase chain reaction/denaturing-gradient gel electrophoresis (PCR-DGGE). Soil samples were collected from the Aizu region of Fukushima Prefecture, Japan. Soil samples were taken from both continuously cropped fields of asparagus with growth inhibition and healthy neighboring fields of asparagus. The soil samples were collected from the fields of 5 sets in 2008 and 4 sets in 2009. We were able to distinguish between pathogenic and non-pathogenic Fusarium by using Alfie1 and Alfie2GC as the second PCR primers and PCR-DGGE. Fungal community structure was not greatly involved in the growth inhibition of asparagus due to continuous cropping. By contrast, the band ratios of Fusarium oxysporum f. sp. asparagi in growth-inhibited fields were higher than those in neighboring healthy fields. In addition, there was a positive correlation between the band ratios of Fusarium oxysporum f. sp. asparagi and the ratios of missing asparagus plants. We showed the potential of biological field diagnosis of growth inhibition due to continuous cropping of asparagus using PCR-DGGE.
An optimization approach for fitting canonical tensor decompositions.
Energy Technology Data Exchange (ETDEWEB)
Dunlavy, Daniel M. (Sandia National Laboratories, Albuquerque, NM); Acar, Evrim; Kolda, Tamara Gibson
2009-02-01
Tensor decompositions are higher-order analogues of matrix decompositions and have proven to be powerful tools for data analysis. In particular, we are interested in the canonical tensor decomposition, otherwise known as the CANDECOMP/PARAFAC decomposition (CPD), which expresses a tensor as the sum of component rank-one tensors and is used in a multitude of applications such as chemometrics, signal processing, neuroscience, and web analysis. The task of computing the CPD, however, can be difficult. The typical approach is based on alternating least squares (ALS) optimization, which can be remarkably fast but is not very accurate. Previously, nonlinear least squares (NLS) methods have also been recommended; existing NLS methods are accurate but slow. In this paper, we propose the use of gradient-based optimization methods. We discuss the mathematical calculation of the derivatives and further show that they can be computed efficiently, at the same cost as one iteration of ALS. Computational experiments demonstrate that the gradient-based optimization methods are much more accurate than ALS and orders of magnitude faster than NLS.
Killing-Yano tensors and Nambu mechanics
International Nuclear Information System (INIS)
Baleanu, D.
1998-01-01
Killing-Yano tensors were introduced in 1952 by Kentaro-Yano from mathematical point of view. The physical interpretation of Killing-Yano tensors of rank higher than two was unclear. We found that all Killing-Yano tensors η i 1 i 2 . .. i n with covariant derivative zero are Nambu tensors. We found that in the case of flat space case all Killing-Yano tensors are Nambu tensors. In the case of Taub-NUT and Kerr-Newmann metric Killing-Yano tensors of order two generate Nambu tensors of rank 3
Tambio, Sacris Jeru; Deschamps, Michaël; Sarou-Kanian, Vincent; Etiemble, Aurélien; Douillard, Thierry; Maire, Eric; Lestriez, Bernard
2017-09-01
Lithium-ion batteries are electrochemical storage devices using the electrochemical activity of the lithium ion in relation to intercalation compounds owing to mass transport phenomena through diffusion. Diffusion of the lithium ion in the electrode pores has been poorly understood due to the lack of experimental techniques for measuring its self-diffusion coefficient in porous media. Magic-Angle Spinning, Pulsed Field Gradient, Stimulated-Echo Nuclear Magnetic Resonance (MAS-PFG-STE NMR) was used here for the first time to measure the self-diffusion coefficients of the electrolyte species in the LP30 battery electrolyte (i.e. a 1 M solution of LiPF6 dissolved in 1:1 Ethylene Carbonate - Dimethyl Carbonate) in model composites. These composite electrodes were made of alumina, carbon black and PVdF-HFP. Alumina's magnetic susceptibility is close to the measured magnetic susceptibility of the LP30 electrolyte thereby limiting undesirable internal field gradients. Interestingly, the self-diffusion coefficient of lithium ions decreases with increasing carbon content. FIB-SEM was used to describe the 3D geometry of the samples. The comparison between the reduction of self-diffusion coefficients as measured by PFG-NMR and as geometrically derived from FIB/SEM tortuosity values highlights the contribution of specific interactions at the material/electrolyte interface on the lithium transport properties.
Efficient use of the velocity gradients tensor in flow modelling
Passchier, C.W.
1987-01-01
For models of fabric development in rocks, with vorticity as a variable parameter, the choice of an unsuitable reference frame for instantaneous flow can hamper clear presentation of results. The orientation of most fabric elements which develop in deforming rocks is attached to some principal
The lattice gradient flow at tree-level and its improvement
Fodor, Zoltan; Holland, Kieran; Kuti, Julius; Mondal, Santanu; Nogradi, Daniel; Wong, Chik Him
2014-09-01
The Yang-Mills gradient flow and the observable , defined by the square of the field strength tensor at t > 0, are calculated at finite lattice spacing and tree-level in the gauge coupling. Improvement of the flow, the gauge action and the observable are all considered. The results are relevant for two purposes. First, the discretization of the flow, gauge action and observable can be chosen in such a way that O( a 2), O( a 4) or even O( a 6) improvement is achieved. Second, simulation results using arbitrary discretizations can be tree-level improved by the perturbatively calculated correction factor normalized to one in the continuum limit.
Analyzing vortex breakdown flow structures by assignment of colors to tensor invariants.
Rütten, Markus; Chong, Min S
2006-01-01
Topological methods are often used to describe flow structures in fluid dynamics and topological flow field analysis usually relies on the invariants of the associated tensor fields. A visual impression of the local properties of tensor fields is often complex and the search of a suitable technique for achieving this is an ongoing topic in visualization. This paper introduces and assesses a method of representing the topological properties of tensor fields and their respective flow patterns with the use of colors. First, a tensor norm is introduced, which preserves the properties of the tensor and assigns the tensor invariants to values of the RGB color space. Secondly, the RGB colors of the tensor invariants are transferred to corresponding hue values as an alternative color representation. The vectorial tensor invariants field is reduced to a scalar hue field and visualization of iso-surfaces of this hue value field allows us to identify locations with equivalent flow topology. Additionally highlighting by the maximum of the eigenvalue difference field reflects the magnitude of the structural change of the flow. The method is applied on a vortex breakdown flow structure inside a cylinder with a rotating lid.
Renormalized energy-momentum tensor of λΦ4 theory in curved ...
Indian Academy of Sciences (India)
Renormalization of the energy-momentum tensor for λΦΦ4 theory. Our aim is to obtain finite expression for the energy-momentum tensor of a quantized scalar field interacting with classical Einstein gravitational field using momentum cut-off regular- ization technique. We have chosen the λΦ4 model of self-interaction, and ...
All-at-once Optimization for Coupled Matrix and Tensor Factorizations
DEFF Research Database (Denmark)
Evrim, Acar Ataman; Kolda, Tamara G.; Dunlavy, Daniel M.
2011-01-01
.g., the person by person social network matrix or the restaurant by category matrix, and higher-order tensors, e.g., the "ratings" tensor of the form restaurant by meal by person. In this paper, we are particularly interested in fusing data sets with the goal of capturing their underlying latent structures. We...... formulate this problem as a coupled matrix and tensor factorization (CMTF) problem where heterogeneous data sets are modeled by fitting outer-product models to higher-order tensors and matrices in a coupled manner. Unlike traditional approaches solving this problem using alternating algorithms, we propose...... an all-at-once optimization approach called CMTF-OPT (CMTF-OPTimization), which is a gradient-based optimization approach for joint analysis of matrices and higher-order tensors. We also extend the algorithm to handle coupled incomplete data sets. Using numerical experiments, we demonstrate...
Tensor analysis and elementary differential geometry for physicists and engineers
Nguyen-Schäfer, Hung
2017-01-01
This book comprehensively presents topics, such as Dirac notation, tensor analysis, elementary differential geometry of moving surfaces, and k-differential forms. Additionally, two new chapters of Cartan differential forms and Dirac and tensor notations in quantum mechanics are added to this second edition. The reader is provided with hands-on calculations and worked-out examples at which he will learn how to handle the bra-ket notation, tensors, differential geometry, and differential forms; and to apply them to the physical and engineering world. Many methods and applications are given in CFD, continuum mechanics, electrodynamics in special relativity, cosmology in the Minkowski four-dimensional spacetime, and relativistic and non-relativistic quantum mechanics. Tensors, differential geometry, differential forms, and Dirac notation are very useful advanced mathematical tools in many fields of modern physics and computational engineering. They are involved in special and general relativity physics, quantum m...
Cosmological magnetic fields - V
Indian Academy of Sciences (India)
Introduction. Magnetic fields seem to be everywhere that we can look in the universe, from our own sun out to high-redshift Lyman-« systems. The fields we ... is the field tensor, is the four-potential, and В is the four-current. The field tensor is observer-independent, while the electric and magnetic fields depend on the ...
MATLAB tensor classes for fast algorithm prototyping.
Energy Technology Data Exchange (ETDEWEB)
Bader, Brett William; Kolda, Tamara Gibson (Sandia National Laboratories, Livermore, CA)
2004-10-01
Tensors (also known as mutidimensional arrays or N-way arrays) are used in a variety of applications ranging from chemometrics to psychometrics. We describe four MATLAB classes for tensor manipulations that can be used for fast algorithm prototyping. The tensor class extends the functionality of MATLAB's multidimensional arrays by supporting additional operations such as tensor multiplication. The tensor as matrix class supports the 'matricization' of a tensor, i.e., the conversion of a tensor to a matrix (and vice versa), a commonly used operation in many algorithms. Two additional classes represent tensors stored in decomposed formats: cp tensor and tucker tensor. We descibe all of these classes and then demonstrate their use by showing how to implement several tensor algorithms that have appeared in the literature.
Energy Technology Data Exchange (ETDEWEB)
Fourrier, J.
2008-10-15
Radiotherapy uses particle beams to irradiate and kill cancer tumors while sparing healthy tissues. Bragg peak shape of the proton energy loss in matter allows a ballistic improvement of the dose deposition compared with X rays. Thus, the irradiated volume can be precisely adjusted to the tumour. This thesis, in the frame of the RACCAM project, aims to the study and the design of a proton therapy installation based on a fixed field alternating gradient (FFAG) accelerator in order to build a spiral sector FFAG magnet for validation. First, we present proton therapy to define medical specifications leading to the technical specifications of a proton therapy installation. Secondly, we introduce FFAG accelerators through their past and on-going projects which are on their way around the world before developing the beam dynamic theories in the case of invariant focusing optics (scaling FFAG). We describe modelling and simulation tools developed to study the dynamics in a spiral scaling FFAG accelerator. Then we explain the spiral optic parameter search which has leaded to the construction of a magnet prototype. Finally, we describe the RACCAM project proton therapy installation starting from the injector cyclotron and ending with the extraction system. (author)
Random SU(2) invariant tensors
Li, Youning; Han, Muxin; Ruan, Dong; Zeng, Bei
2018-04-01
SU(2) invariant tensors are states in the (local) SU(2) tensor product representation but invariant under the global group action. They are of importance in the study of loop quantum gravity. A random tensor is an ensemble of tensor states. An average over the ensemble is carried out when computing any physical quantities. The random tensor exhibits a phenomenon known as ‘concentration of measure’, which states that for any bipartition the average value of entanglement entropy of its reduced density matrix is asymptotically the maximal possible as the local dimensions go to infinity. We show that this phenomenon is also true when the average is over the SU(2) invariant subspace instead of the entire space for rank-n tensors in general. It is shown in our earlier work Li et al (2017 New J. Phys. 19 063029) that the subleading correction of the entanglement entropy has a mild logarithmic divergence when n = 4. In this paper, we show that for n > 4 the subleading correction is not divergent but a finite number. In some special situation, the number could be even smaller than 1/2, which is the subleading correction of random state over the entire Hilbert space of tensors.
Directory of Open Access Journals (Sweden)
P. A. Chaizy
Full Text Available Three main physical processes (and associated properties are currently used to describe the flux and anisotropy time profiles of solar energetic par- ticle events, called SEP profiles. They are (1 the particle scattering (due to magnetic waves, (2 the particle focusing (due to the decrease of the amplitude of the interplanetary magnetic field (IMF with the radial distance to the Sun and (3 the finite injection profile at the source. If their features change from one field line to another, i.e. if there is a cross IMF gradient (CFG, then the shape of the SEP profiles will depend, at onset time, on the relative position of the spacecraft to the IMF and might vary significantly on small distance scale (e.g. 10^{6} km. One type of CFG is studied here. It is called intensity CFG and considers variations, at the solar surface, only of the intensity of the event. It is shown here that drops of about two orders of magnitude over distances of ~10^{4} km at the Sun (1° of angular distance can influence dramatically the SEP profiles at 1 AU. This CFG can lead to either an under or overestimation of both the parallel mean free path and of the injection parameters by factor up to, at least, ~2-3 and 18, respectively. Multi-spacecraft analysis can be used to identify CFG. Three basic requirements are proposed to identify, from the observation, the type of the CFG being measured.
Key words: Solar physics, astrophysics, and astronomy (energetic particles; flares and mass ejections - Space plasma physics (transport processes
Vilanova, Anna; Burgeth, Bernhard; Visualization and Processing of Tensors and Higher Order Descriptors for Multi-Valued Data
2014-01-01
Arising from the fourth Dagstuhl conference entitled Visualization and Processing of Tensors and Higher Order Descriptors for Multi-Valued Data (2011), this book offers a broad and vivid view of current work in this emerging field. Topics covered range from applications of the analysis of tensor fields to research on their mathematical and analytical properties. Part I, Tensor Data Visualization, surveys techniques for visualization of tensors and tensor fields in engineering, discusses the current state of the art and challenges, and examines tensor invariants and glyph design, including an overview of common glyphs. The second Part, Representation and Processing of Higher-order Descriptors, describes a matrix representation of local phase, outlines mathematical morphological operations techniques, extended for use in vector images, and generalizes erosion to the space of diffusion weighted MRI. Part III, Higher Order Tensors and Riemannian-Finsler Geometry, offers powerful mathematical language to model and...
International Nuclear Information System (INIS)
Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Pérez-González, P. G.; Gallego, J.; Zamorano, J.; Muñoz-Mateos, J. C.; Sánchez, S. F.; Alonso-Herrero, A.; Boissier, S.
2012-01-01
We present an analysis of the full bidimensional optical spectral cube of the nearby spiral galaxy NGC 5668, observed with the Pmas fiber PAcK Integral Field Unit (IFU) at the Calar Alto observatory 3.5 m telescope. We make use of broadband imaging to provide further constraints on the evolutionary history of the galaxy. This data set will allow us to improve our understanding of the mechanisms that drive the evolution of disks. We investigated the properties of 62 H II regions and concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and chemical (oxygen) abundances. We find that while inward of r ∼36'' ∼ 4.4 kpc ∼ 0.36 (D 25 /2) the derived O/H ratio follows the radial gradient typical of spiral galaxies, the abundance gradient beyond r ∼ 36'' flattens out. The analysis of the multi-wavelength surface brightness profiles of NGC 5668 is performed by fitting these profiles with those predicted by chemo-spectrophotometric evolutionary models of galaxy disks. From this, we infer a spin and circular velocity of λ = 0.053 and v c = 167 km s –1 , respectively. The metallicity gradient and rotation curve predicted by this best-fitting galaxy model nicely match the values derived from the IFU observations, especially within r ∼36''. The same is true for the colors despite some small offsets and a reddening in the bluest colors beyond that radius. On the other hand, deviations of some of these properties in the outer disk indicate that a secondary mechanism, possibly gas transfer induced by the presence of a young bar, must have played a role in shaping the recent chemical and star formation histories of NGC 5668.
Retinal Vessel Segmentation via Structure Tensor Coloring and Anisotropy Enhancement
Directory of Open Access Journals (Sweden)
Mehmet Nergiz
2017-11-01
Full Text Available Retinal vessel segmentation is one of the preliminary tasks for developing diagnosis software systems related to various retinal diseases. In this study, a fully automated vessel segmentation system is proposed. Firstly, the vessels are enhanced using a Frangi Filter. Afterwards, Structure Tensor is applied to the response of the Frangi Filter and a 4-D tensor field is obtained. After decomposing the Eigenvalues of the tensor field, the anisotropy between the principal Eigenvalues are enhanced exponentially. Furthermore, this 4-D tensor field is converted to the 3-D space which is composed of energy, anisotropy and orientation and then a Contrast Limited Adaptive Histogram Equalization algorithm is applied to the energy space. Later, the obtained energy space is multiplied by the enhanced mean surface curvature of itself and the modified 3-D space is converted back to the 4-D tensor field. Lastly, the vessel segmentation is performed by using Otsu algorithm and tensor coloring method which is inspired by the ellipsoid tensor visualization technique. Finally, some post-processing techniques are applied to the segmentation result. In this study, the proposed method achieved mean sensitivity of 0.8123, 0.8126, 0.7246 and mean specificity of 0.9342, 0.9442, 0.9453 as well as mean accuracy of 0.9183, 0.9442, 0.9236 for DRIVE, STARE and CHASE_DB1 datasets, respectively. The mean execution time of this study is 6.104, 6.4525 and 18.8370 s for the aforementioned three datasets respectively.
Calculating contracted tensor Feynman integrals
International Nuclear Information System (INIS)
Fleischer, J.; Riemann, T.
2011-01-01
A recently derived approach to the tensor reduction of 5-point one-loop Feynman integrals expresses the tensor coefficients by scalar 1-point to 4-point Feynman integrals completely algebraically. In this Letter we derive extremely compact algebraic expressions for the contractions of the tensor integrals with external momenta. This is based on sums over signed minors weighted with scalar products of the external momenta. With these contractions one can construct the invariant amplitudes of the matrix elements under consideration, and the evaluation of one-loop contributions to massless and massive multi-particle production at high energy colliders like LHC and ILC is expected to be performed very efficiently.
Metric Tensor Vs. Metric Extensor
Fernández, V. V.; Moya, A. M.; Rodrigues Jr, Waldyr A.
2002-01-01
In this paper we give a comparison between the formulation of the concept of metric for a real vector space of finite dimension in terms of \\emph{tensors} and \\emph{extensors}. A nice property of metric extensors is that they have inverses which are also themselves metric extensors. This property is not shared by metric tensors because tensors do \\emph{not} have inverses. We relate the definition of determinant of a metric extensor with the classical determinant of the corresponding matrix as...
Calculating contracted tensor Feynman integrals
International Nuclear Information System (INIS)
Fleischer, J.
2011-05-01
A recently derived approach to the tensor reduction of 5-point one-loop Feynman integrals expresses the tensor coefficients by scalar 1-point to 4-point Feynman integrals completely algebraically. In this letter we derive extremely compact algebraic expressions for the contractions of the tensor integrals with externalmomenta. This is based on sums over signedminors weighted with scalar products of the external momenta. With these contractions one can construct the invariant amplitudes of the matrix elements under consideration, and the evaluation of one-loop contributions to massless and massive multi-particle production at high energy colliders like LHC and ILC is expected to be performed very efficiently. (orig.)
Multivariate Tensor-based Brain Anatomical Surface Morphometry via Holomorphic One-Forms
Wang, Yalin; Chan, Tony F.; Toga, Arthur W.; Thompson, Paul M.
2009-01-01
Here we introduce multivariate tensor-based surface morphometry using holomorphic one-forms to study brain anatomy. We computed new statistics from the Riemannian metric tensors that retain the full information in the deformation tensor fields. We introduce two different holomorphic one-forms that induce different surface conformal parameterizations. We applied this framework to 3D MRI data to analyze hippocampal surface morphometry in Alzheimer’s Disease (AD; 26 subjects), lateral ventricula...
A quantum gravity tensor equation formally integrating general relativity with quantum mechanics
Duan, Xu
2016-01-01
Extending black-hole entropy to ordinary objects, we propose kinetic entropy tensor, based on which a quantum gravity tensor equation is established. Our investigation results indicate that if N=1, the quantum gravity tensor equation returns to Schrodinger integral equation. When N becomes sufficiently large, it is equivalent to Einstein field equation. This illustrates formal unification and intrinsic compatibility of general relativity with quantum mechanics. The quantum gravity equation ma...
Homan, N.; Venne, B.B.; As, van H.
2010-01-01
Water flow through model porous media was studied in the presence of surface relaxation, internal magnetic field inhomogeneities and exchange with stagnant water pools with different relaxation behavior, demonstrating how the apparent flow parameters average velocity, volume flow and flow conducting
van Kalleveen, IML
2016-01-01
Adiabatic RF pulses are useful pulses for inhomogeneous B1 fields caused by surface RF coils, however the increase in SAR will lengthen the TR, and possibly also the TE if the adiabatic pulses become too long. Using the superadiabaticity theorem the increase in SAR can already be reduced, making it
DEFF Research Database (Denmark)
Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib
2017-01-01
and at the paranasal sinuses, however, this assumption is often broken. Herein, we explored a novel model that considers both linear and stochastic dependences of the phase evolution with echo time in the presence of weak and strong macroscopic field inhomogeneities. We tested the performance of the model at large...
International Nuclear Information System (INIS)
Hack, Thomas-Paul; Moretti, Valter
2012-01-01
We review a few rigorous and partly unpublished results on the regularization of the stress–energy in quantum field theory on curved spacetimes: (1) the symmetry of the Hadamard/Seeley–DeWitt coefficients in smooth Riemannian and Lorentzian spacetimes, (2) the equivalence of the local ζ-function and the Hadamard-point-splitting procedure in smooth static spacetimes and (3) the equivalence of the DeWitt–Schwinger- and the Hadamard-point-splitting procedure in smooth Riemannian and Lorentzian spacetimes. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical in honour of Stuart Dowker’s 75th birthday devoted to ‘Applications of zeta functions and other spectral functions in mathematics and physics’. (paper)
Tensor Product of Polygonal Cell Complexes
Chien, Yu-Yen
2017-01-01
We introduce the tensor product of polygonal cell complexes, which interacts nicely with the tensor product of link graphs of complexes. We also develop the unique factorization property of polygonal cell complexes with respect to the tensor product, and study the symmetries of tensor products of polygonal cell complexes.
International Nuclear Information System (INIS)
Hale, Beverley; Robertson, Paul
2016-01-01
Perennial plant communities in the proximity of metal smelters and refineries may receive substantial inputs of base metal particulate as well as sulphate from the co-emission of sulphur dioxide. The Ni refinery at Port Colborne (Canada) operated by Inco (now Vale Canada Ltd.) emitted Ni, Co and Cu, along with sulphur dioxide, between 1918 and 1984. The objectives were to determine if vascular plant community composition, including standing litter, in twenty-one woodlots on clay or organic soil, were related to soil Ni concentration which decreased in concentration with distance from the Ni refinery. The soil Ni concentration in the clay woodlots ranged from 16 to 4130 mg Ni/kg, and in the organic woodlots, ranged from 98 to 22,700 mg Ni/kg. The concentrations of Co and Cu in the soils were also elevated, and highly correlated with soil Ni concentration. In consequence, each series of woodlots constituted a ‘fixed ratio ray’ of metal mixture exposure. For each of the woodlots, there were 16 independent measurements of ‘woodlot status’ which were correlated with elevated soil Ni concentration. Of the 32 combinations, there were eight linear correlations with soil Ni concentration, considerably more than would be expected by chance alone at a p-value of 0.05. With the exception of mean crown rating for shrubs at the clay sites, the correlations were consistent with the hypothesis that increased soil metal concentrations would be correlated with decreased diversity, plant community health or fitness, and increased accumulation of litter. Only five of the eight linear correlations were from the organic woodlots, suggesting that the observations were not confounded with soil type nor range in soil metal concentrations. - Highlights: • Temperate woodlots on organic or clay soils with gradient of soil Ni were studied. • Soil Ni ranged up to 4100 mg/kg on clay and up to 22,700 mg/kg on organic. • Most indices of plant community status were not correlated
The normal conformal Cartan connection and the Bach tensor
International Nuclear Information System (INIS)
Korzynski, Mikolaj; Lewandowski, Jerzy
2003-01-01
The goal of this paper is to express the Bach tensor of a four-dimensional conformal geometry of an arbitrary signature by the Cartan normal conformal (CNC) connection. We show that the Bach tensor can be identified with the Yang-Mills current of the connection. It follows from that result that a conformal geometry whose CNC connection is reducible in an appropriate way has a degenerate Bach tensor. As an example we study the case of a CNC connection which admits a twisting covariantly constant twistor field. This class of conformal geometries of this property is known as given by the Fefferman metric tensors. We use our result to calculate the Bach tensor of an arbitrary Fefferman metric and show that it is proportional to the tensorial square of the four-fold eigenvector of the Weyl tensor. Finally, we solve the Yang-Mills equations imposed on the CNC connection for all the homogeneous Fefferman metrics. The only solution is the Nurowski-Plebanski metric
Mikkonen, Anu; Hakala, Kati P; Lappi, Kaisa; Kondo, Elina; Vaalama, Anu; Suominen, Leena
2012-03-01
Horizontal and vertical contaminant gradients in an old landfarming field for oil refinery waste were characterised with the aim to assess parallel changes in hydrocarbon groups and general, microbiological and ecotoxicological soil characteristics. In the surface soil polar compounds were the most prevalent fraction of heptane-extractable hydrocarbons, superseding GC-FID-resolvable and high-molar-mass aliphatics and aromatics, but there was no indication of their relatively higher mobility or toxicity. The size of the polar fraction correlated poorly with soil physical, chemical and microbiological properties, which were better explained by the total heptane-extractable and total petroleum hydrocarbons (TPH). Deleterious effects on soil microbiology in situ were observed at surprisingly low TPH concentrations (0.3%). Due to the accumulation of polar and complexed degradation products, TPH seems an insufficient measure to assess the quality and monitor the remediation of soil with weathered hydrocarbon contamination. Copyright © 2011 Elsevier Ltd. All rights reserved.
Hoarfrost, Megan L; Tyagi, Madhusudan; Segalman, Rachel A; Reimer, Jeffrey A
2012-07-19
The management of proton conductivity in the protic ionic liquid imidazolium bis(trifluoromethylsulfonyl)imide ([Im][TFSI]) is investigated via the use of quasi-elastic neutron scattering (QENS) and pulsed-field gradient NMR. The introduction of excess neutral imidazole to [Im][TFSI] leads to enhanced conductivity. We find that proton dynamics in [Im][TFSI] with excess imidazole are characterized by proton hopping that is encompassed in the slower of two translational processes, as identified by QENS. This relatively slow process contributes to long-range diffusion more than the faster process. NMR diffusion measurements show that proton hopping decreases with increasing temperature, but significant proton hopping persists even at the maximum experimental temperature of 120 °C. This, in combination with minimal ion aggregation, leads to high proton conductivity and a high proton transference number over a wide temperature range.
DEFF Research Database (Denmark)
Chougule, Abhijit S.; Mann, Jakob; Kelly, Mark C.
2017-01-01
A spectral tensor model is presented for turbulent fluctuations of wind velocity components and temperature, assuming uniform vertical gradients in mean temperature and mean wind speed. The model is built upon rapid distortion theory (RDT) following studies by Mann and by Hanazaki and Hunt, using...... the eddy lifetime parameterization of Mann to make the model stationary. The buoyant spectral tensor model is driven via five parameters: the viscous dissipation rate epsilon, length scale of energy-containing eddies L, a turbulence anisotropy parameter Gamma, gradient Richardson number (Ri) representing...
Czech Academy of Sciences Publication Activity Database
Zablotskyy, Vitaliy A.; Lunov, Oleg; Novotná, Božena; Churpita, Olexandr; Trošan, Peter; Holáň, Vladimír; Syková, Eva; Dejneka, Alexandr; Kubinová, Šárka
2014-01-01
Roč. 105, č. 10 (2014), "103702-1"-"103702-4" ISSN 0003-6951 R&D Projects: GA ČR GAP304/11/0653; GA ČR(CZ) GAP304/12/1370; GA MŠk LO1309 Grant - others:AV ČR(CZ) M100101219 Institutional support: RVO:68378271 ; RVO:68378041 Keywords : stem cell s * cytoskeleton * magnetic field * cell growth Subject RIV: BO - Biophysics; FH - Neurology (UEM-P) Impact factor: 3.302, year: 2014
Parallel implementation of electronic structure energy, gradient, and Hessian calculations
Lotrich, V.; Flocke, N.; Ponton, M.; Yau, A. D.; Perera, A.; Deumens, E.; Bartlett, R. J.
2008-05-01
ACES III is a newly written program in which the computationally demanding components of the computational chemistry code ACES II [J. F. Stanton et al., Int. J. Quantum Chem. 526, 879 (1992); [ACES II program system, University of Florida, 1994] have been redesigned and implemented in parallel. The high-level algorithms include Hartree-Fock (HF) self-consistent field (SCF), second-order many-body perturbation theory [MBPT(2)] energy, gradient, and Hessian, and coupled cluster singles, doubles, and perturbative triples [CCSD(T)] energy and gradient. For SCF, MBPT(2), and CCSD(T), both restricted HF and unrestricted HF reference wave functions are available. For MBPT(2) gradients and Hessians, a restricted open-shell HF reference is also supported. The methods are programed in a special language designed for the parallelization project. The language is called super instruction assembly language (SIAL). The design uses an extreme form of object-oriented programing. All compute intensive operations, such as tensor contractions and diagonalizations, all communication operations, and all input-output operations are handled by a parallel program written in C and FORTRAN 77. This parallel program, called the super instruction processor (SIP), interprets and executes the SIAL program. By separating the algorithmic complexity (in SIAL) from the complexities of execution on computer hardware (in SIP), a software system is created that allows for very effective optimization and tuning on different hardware architectures with quite manageable effort.
International Nuclear Information System (INIS)
Schellhorn, M; Rosenberger, M; Correns, M; Blau, M; Goepfert, A; Rueckwardt, M; Linss, G
2010-01-01
Within the field of industrial image processing the use of colour cameras becomes ever more common. Increasingly the established black and white cameras are replaced by economical single-chip colour cameras with Bayer pattern. The use of the additional colour information is particularly important for recognition or inspection. Become interesting however also for the geometric metrology, if measuring tasks can be solved more robust or more exactly. However only few suitable algorithms are available, in order to detect edges with the necessary precision. All attempts require however additional computation expenditure. On the basis of a new filter for edge detection in colour images with subpixel precision, the implementation on a pre-processing hardware platform is presented. Hardware implemented filters offer the advantage that they can be used easily with existing measuring software, since after the filtering a single channel image is present, which unites the information of all colour channels. Advanced field programmable gate arrays represent an ideal platform for the parallel processing of multiple channels. The effective implementation presupposes however a high programming expenditure. On the example of the colour filter implementation, arising problems are analyzed and the chosen solution method is presented.
Black holes in vector-tensor theories
Energy Technology Data Exchange (ETDEWEB)
Heisenberg, Lavinia [Institute for Theoretical Studies, ETH Zurich, Clausiusstrasse 47, 8092 Zurich (Switzerland); Kase, Ryotaro; Tsujikawa, Shinji [Department of Physics, Faculty of Science, Tokyo University of Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan); Minamitsuji, Masato, E-mail: lavinia.heisenberg@eth-its.ethz.ch, E-mail: r.kase@rs.tus.ac.jp, E-mail: masato.minamitsuji@tecnico.ulisboa.pt, E-mail: shinji@rs.kagu.tus.ac.jp [Centro Multidisciplinar de Astrofisica—CENTRA, Departamento de Fisica, Instituto Superior Tecnico—IST, Universidade de Lisboa—UL, Avenida Rovisco Pais 1, 1049-001 Lisboa (Portugal)
2017-08-01
We study static and spherically symmetric black hole (BH) solutions in second-order generalized Proca theories with nonminimal vector field derivative couplings to the Ricci scalar, the Einstein tensor, and the double dual Riemann tensor. We find concrete Lagrangians which give rise to exact BH solutions by imposing two conditions of the two identical metric components and the constant norm of the vector field. These exact solutions are described by either Reissner-Nordström (RN), stealth Schwarzschild, or extremal RN solutions with a non-trivial longitudinal mode of the vector field. We then numerically construct BH solutions without imposing these conditions. For cubic and quartic Lagrangians with power-law couplings which encompass vector Galileons as the specific cases, we show the existence of BH solutions with the difference between two non-trivial metric components. The quintic-order power-law couplings do not give rise to non-trivial BH solutions regular throughout the horizon exterior. The sixth-order and intrinsic vector-mode couplings can lead to BH solutions with a secondary hair. For all the solutions, the vector field is regular at least at the future or past horizon. The deviation from General Relativity induced by the Proca hair can be potentially tested by future measurements of gravitational waves in the nonlinear regime of gravity.
Physical and Geometric Interpretations of the Riemann Tensor, Ricci Tensor, and Scalar Curvature
Loveridge, Lee C.
2004-01-01
Various interpretations of the Riemann Curvature Tensor, Ricci Tensor, and Scalar Curvature are described. Also, the physical meanings of the Einstein Tensor and Einstein's Equations are discussed. Finally a derivation of Newtonian Gravity from Einstein's Equations is given.
Poisson-Jacobi reduction of homogeneous tensors
International Nuclear Information System (INIS)
Grabowski, J; Iglesias, D; Marrero, J C; Padron, E; Urbanski, P
2004-01-01
The notion of homogeneous tensors is discussed. We show that there is a one-to-one correspondence between multivector fields on a manifold M, homogeneous with respect to a vector field Δ on M, and first-order polydifferential operators on a closed submanifold N of codimension 1 such that Δ is transversal to N. This correspondence relates the Schouten-Nijenhuis bracket of multivector fields on M to the Schouten-Jacobi bracket of first-order polydifferential operators on N and generalizes the Poissonization of Jacobi manifolds. Actually, it can be viewed as a super-Poissonization. This procedure of passing from a homogeneous multivector field to a first-order polydifferential operator can also be understood as a sort of reduction; in the standard case-a half of a Poisson reduction. A dual version of the above correspondence yields in particular the correspondence between Δ-homogeneous symplectic structures on M and contact structures on N
Leote, Joao; Nunes, Rita G; Cerqueira, Luis; Loução, Ricardo; Ferreira, Hugo A
2018-01-01
Tractography studies for pre-surgical planning of primary brain tumors is typically done using diffusion tensor imaging (DTI), which cannot resolve crossing, kissing or highly angulated fibres. Tractography based on the estimation of the diffusion kurtosis (DK) tensor was recently demonstrated to enable tackling these limitations. However, its use in the clinical context at low 1.5T field has not yet been reported. To evaluate if the estimation of whole-brain tractography using the DK tensor is feasible for pre-surgical investigation of patients with brain tumors at 1.5T. Eight healthy subjects and 3 patients with brain tumors were scanned at 1.5T using a 12-channel head coil. Diffusion-weighted images were acquired with repetition/echo times of 5800/107 ms, 82 × 82 resolution, 3 × 3 × 3 mm 3 voxel size, b-values of 0, 1000, 2000 s/mm 2 and 64 gradient sensitising directions. Whole-brain tractography was estimated using the DK tensor and corticospinal tracts (CST) were isolated using regions-of-interest placed at the cerebral peduncles and motor gyrus. Tract size, DK metrics and CST deviation index (highest curvature point) were compared between healthy subjects and patients. Tract sizes did not differ between groups. The CST deviation index was significantly higher in patients compared to healthy subjects. Fractional anisotropy was significantly lower in patients, with higher mean kurtosis asymmetry index at the highest curvature point in patients. Corticospinal fibre bundles estimated using DK tensor in a 1.5T scanner presented similar properties in patients with brain gliomas as those reported in the literature using DTI-based tractography.
Energy Technology Data Exchange (ETDEWEB)
Ringholm, Magnus; Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Bast, Radovan [Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, S-10691 Stockholm (Sweden); PDC Center for High Performance Computing, Royal Institute of Technology, S-10044 Stockholm (Sweden); Oggioni, Luca [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Department of Physics G. Occhialini, University of Milano Bicocca, Piazza della scienza 3, 20126 Milan (Italy); Ekström, Ulf [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, 0315 Oslo (Norway)
2014-10-07
We present the first analytic calculations of the geometrical gradients of the first hyperpolarizability tensors at the density-functional theory (DFT) level. We use the analytically calculated hyperpolarizability gradients to explore the importance of electron correlation effects, as described by DFT, on hyper-Raman spectra. In particular, we calculate the hyper-Raman spectra of the all-trans and 11-cis isomers of retinal at the Hartree-Fock (HF) and density-functional levels of theory, also allowing us to explore the sensitivity of the hyper-Raman spectra on the geometrical characteristics of these structurally related molecules. We show that the HF results, using B3LYP-calculated vibrational frequencies and force fields, reproduce the experimental data for all-trans-retinal well, and that electron correlation effects are of minor importance for the hyper-Raman intensities.
Delcey, Mickaël G; Freitag, Leon; Pedersen, Thomas Bondo; Aquilante, Francesco; Lindh, Roland; González, Leticia
2014-05-07
We present a formulation of analytical energy gradients at the complete active space self-consistent field (CASSCF) level of theory employing density fitting (DF) techniques to enable efficient geometry optimizations of large systems. As an example, the ground and lowest triplet state geometries of a ruthenium nitrosyl complex are computed at the DF-CASSCF level of theory and compared with structures obtained from density functional theory (DFT) using the B3LYP, BP86, and M06L functionals. The average deviation of all bond lengths compared to the crystal structure is 0.042 Å at the DF-CASSCF level of theory, which is slightly larger but still comparable with the deviations obtained by the tested DFT functionals, e.g., 0.032 Å with M06L. Specifically, the root-mean-square deviation between the DF-CASSCF and best DFT coordinates, delivered by BP86, is only 0.08 Å for S0 and 0.11 Å for T1, indicating that the geometries are very similar. While keeping the mean energy gradient errors below 0.25%, the DF technique results in a 13-fold speedup compared to the conventional CASSCF geometry optimization algorithm. Additionally, we assess the singlet-triplet energy vertical and adiabatic differences with multiconfigurational second-order perturbation theory (CASPT2) using the DF-CASSCF and DFT optimized geometries. It is found that the vertical CASPT2 energies are relatively similar regardless of the geometry employed whereas the adiabatic singlet-triplet gaps are more sensitive to the chosen triplet geometry.
The tensor rank of tensor product of two three-qubit W states is eight
Chen, Lin; Friedland, Shmuel
2017-01-01
We show that the tensor rank of tensor product of two three-qubit W states is not less than eight. Combining this result with the recent result of M. Christandl, A. K. Jensen, and J. Zuiddam that the tensor rank of tensor product of two three-qubit W states is at most eight, we deduce that the tensor rank of tensor product of two three-qubit W states is eight. We also construct the upper bound of the tensor rank of tensor product of many three-qubit W states.
Lam, Mie K; de Greef, Martijn; Bouwman, Job G; Moonen, Chrit T W; Viergever, Max A; Bartels, Lambertus W
2015-10-07
The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method's performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method's ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.
Li, Yong; Jing, Haoqing; Zainal Abidin, Ilham Mukriz; Yan, Bei
2017-04-25
Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy.
Generalization of strain-gradient theory to finite elastic deformation for isotropic materials
Beheshti, Alireza
2017-03-01
This paper concerns finite deformation in the strain-gradient continuum. In order to take account of the geometric nonlinearity, the original strain-gradient theory which is based on the infinitesimal strain tensor is rewritten given the Green-Lagrange strain tensor. Following introducing the generalized isotropic Saint Venant-Kirchhoff material model for the strain-gradient elasticity, the boundary value problem is investigated in not only the material configuration but also the spatial configuration building upon the principle of virtual work for a three-dimensional solid. By presenting one example, the convergence of the strain-gradient and classical theories is studied.
Haaks, Michael; Martin, Steve W.; Vogel, Michael
2017-09-01
We use various 7Li NMR methods to investigate lithium ion dynamics in 70Li 2S-30 P 2S5 glass and glass-ceramic obtained from this glass after heat treatment. We employ 7Li spin-lattice relaxometry, including field-cycling measurements, and line-shape analysis to investigate short-range ion jumps as well as 7Li field-gradient approaches to characterize long-range ion diffusion. The results show that ceramization substantially enhances the lithium ion mobility on all length scales. For the 70Li 2S-30 P 2S5 glass-ceramic, no evidence is found that bimodal dynamics result from different ion mobilities in glassy and crystalline regions of this sample. Rather, 7Li field-cycling relaxometry shows that dynamic susceptibilities in broad frequency and temperature ranges can be described by thermally activated jumps governed by a Gaussian distribution of activation energies g (Ea) with temperature-independent mean value Em=0.43 eV and standard deviation σ =0.07 eV . Moreover, use of this distribution allows us to rationalize 7Li line-shape results for the local ion jumps. In addition, this information about short-range ion dynamics further explains 7Li field-gradient results for long-range ion diffusion. In particular, we quantitatively show that, consistent with our experimental results, the temperature dependence of the self-diffusion coefficient D is not described by the mean activation energy Em of the local ion jumps, but by a significantly smaller apparent value whenever the distribution of correlation times G (logτ ) of the jump motion derives from an invariant distribution of activation energies and, hence, continuously broadens upon cooling. This effect occurs because the harmonic mean, which determines the results of diffusivity or also conductivity studies, continuously separates from the peak position of G (logτ ) when the width of this distribution increases.
Tensor Target Polarization at TRIUMF
Energy Technology Data Exchange (ETDEWEB)
Smith, G
2014-10-27
The first measurements of tensor observables in $\\pi \\vec{d}$ scattering experiments were performed in the mid-80's at TRIUMF, and later at SIN/PSI. The full suite of tensor observables accessible in $\\pi \\vec{d}$ elastic scattering were measured: $T_{20}$, $T_{21}$, and $T_{22}$. The vector analyzing power $iT_{11}$ was also measured. These results led to a better understanding of the three-body theory used to describe this reaction. %Some measurements were also made in the absorption and breakup channels. A direct measurement of the target tensor polarization was also made independent of the usual NMR techniques by exploiting the (nearly) model-independent result for the tensor analyzing power at 90$^\\circ _{cm}$ in the $\\pi \\vec{d} \\rightarrow 2p$ reaction. This method was also used to check efforts to enhance the tensor polarization by RF burning of the NMR spectrum. A brief description of the methods developed to measure and analyze these experiments is provided.
Link prediction via generalized coupled tensor factorisation
DEFF Research Database (Denmark)
Ermiş, Beyza; Evrim, Acar Ataman; Taylan Cemgil, A.
2012-01-01
and higher-order tensors. We propose to use an approach based on probabilistic interpretation of tensor factorisation models, i.e., Generalised Coupled Tensor Factorisation, which can simultaneously fit a large class of tensor models to higher-order tensors/matrices with com- mon latent factors using...... different loss functions. Numerical experiments demonstrate that joint analysis of data from multiple sources via coupled factorisation improves the link prediction performance and the selection of right loss function and tensor model is crucial for accurately predicting missing links....
Holographic duality from random tensor networks
Energy Technology Data Exchange (ETDEWEB)
Hayden, Patrick; Nezami, Sepehr; Qi, Xiao-Liang; Thomas, Nathaniel; Walter, Michael; Yang, Zhao [Stanford Institute for Theoretical Physics, Department of Physics, Stanford University,382 Via Pueblo, Stanford, CA 94305 (United States)
2016-11-02
Tensor networks provide a natural framework for exploring holographic duality because they obey entanglement area laws. They have been used to construct explicit toy models realizing many of the interesting structural features of the AdS/CFT correspondence, including the non-uniqueness of bulk operator reconstruction in the boundary theory. In this article, we explore the holographic properties of networks of random tensors. We find that our models naturally incorporate many features that are analogous to those of the AdS/CFT correspondence. When the bond dimension of the tensors is large, we show that the entanglement entropy of all boundary regions, whether connected or not, obey the Ryu-Takayanagi entropy formula, a fact closely related to known properties of the multipartite entanglement of assistance. We also discuss the behavior of Rényi entropies in our models and contrast it with AdS/CFT. Moreover, we find that each boundary region faithfully encodes the physics of the entire bulk entanglement wedge, i.e., the bulk region enclosed by the boundary region and the minimal surface. Our method is to interpret the average over random tensors as the partition function of a classical ferromagnetic Ising model, so that the minimal surfaces of Ryu-Takayanagi appear as domain walls. Upon including the analog of a bulk field, we find that our model reproduces the expected corrections to the Ryu-Takayanagi formula: the bulk minimal surface is displaced and the entropy is augmented by the entanglement of the bulk field. Increasing the entanglement of the bulk field ultimately changes the minimal surface behavior topologically, in a way similar to the effect of creating a black hole. Extrapolating bulk correlation functions to the boundary permits the calculation of the scaling dimensions of boundary operators, which exhibit a large gap between a small number of low-dimension operators and the rest. While we are primarily motivated by the AdS/CFT duality, the main
Compact stars in vector-tensor-Horndeski theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Momeni, Davood; Myrzakulov, Kairat; Myrzakulov, Ratbay [Eurasian National University, Department of General and Theoretical Physics, Eurasian International Center for Theoretical Physics, Astana (Kazakhstan); Faizal, Mir [University of British Columbia-Okanagan, Irving K. Barber School of Arts and Sciences, Kelowna, BC (Canada); University of Lethbridge, Department of Physics and Astronomy, Lethbridge, AB (Canada)
2017-01-15
In this paper, we will analyze a theory of modified gravity, in which the field content of general relativity will be increased to include a vector field. We will use the Horndeski formalism to non-minimally couple this vector field to the metric. As we will be using the Horndeski formalism, this theory will not contain Ostrogradsky ghost degree of freedom. We will analyze compact stars using this vector-tensor-Horndeski theory. (orig.)
Phillips, J.D.; Nabighian, M.N.; Smith, D.V.; Li, Y.
2007-01-01
The Helbig method for estimating total magnetization directions of compact sources from magnetic vector components is extended so that tensor magnetic gradient components can be used instead. Depths of the compact sources can be estimated using the Euler equation, and their dipole moment magnitudes can be estimated using a least squares fit to the vector component or tensor gradient component data. ?? 2007 Society of Exploration Geophysicists.
Gao, Yang; Wang, Xuesong; Cheng, Yuhu; Wang, Z Jane
2015-08-01
To take full advantage of hyperspectral information, to avoid data redundancy and to address the curse of dimensionality concern, dimensionality reduction (DR) becomes particularly important to analyze hyperspectral data. Exploring the tensor characteristic of hyperspectral data, a DR algorithm based on class-aware tensor neighborhood graph and patch alignment is proposed here. First, hyperspectral data are represented in the tensor form through a window field to keep the spatial information of each pixel. Second, using a tensor distance criterion, a class-aware tensor neighborhood graph containing discriminating information is obtained. In the third step, employing the patch alignment framework extended to the tensor space, we can obtain global optimal spectral-spatial information. Finally, the solution of the tensor subspace is calculated using an iterative method and low-dimensional projection matrixes for hyperspectral data are obtained accordingly. The proposed method effectively explores the spectral and spatial information in hyperspectral data simultaneously. Experimental results on 3 real hyperspectral datasets show that, compared with some popular vector- and tensor-based DR algorithms, the proposed method can yield better performance with less tensor training samples required.