Fast methods for spatially correlated multilevel functional data
Staicu, Ana-Maria; Crainiceanu, Ciprian M.; Carroll, Raymond J.
2010-01-01
We propose a new methodological framework for the analysis of hierarchical functional data when the functions at the lowest level of the hierarchy are correlated. For small data sets, our methodology leads to a computational algorithm that is orders of magnitude more efficient than its closest competitor (seconds versus hours). For large data sets, our algorithm remains fast and has no current competitors. Thus, in contrast to published methods, we can now conduct routine simulations, leave-one-out analyses, and nonparametric bootstrap sampling. Our methods are inspired by and applied to data obtained from a state-of-the-art colon carcinogenesis scientific experiment. However, our models are general and will be relevant to many new data sets where the object of inference are functions or images that remain dependent even after conditioning on the subject on which they are measured. Supplementary materials are available at Biostatistics online. PMID:20089508
NASA Technical Reports Server (NTRS)
Edelson, R. A.; Krolik, J. H.
1988-01-01
A method of measuring correlation functions without interpolating in the temporal domain, the discrete correlation function, is introduced. It provides an assumption-free representation of the correlation measured in the data, and allows meaningful error estimates. This method does not produce spurious correlations at zero lag due to correlated errors. It is shown that physical interpretation of active galactic nuclei cross-correlation functions requires knowledge of the input function's fluctuation power spectrum, involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias. This technique was used to find a correlation in published IUE data for NGC 4151, which indicates that the broad C IV feature emanates from a shell 15 to 75 light-days in radius, assuming spherical symmetry.
Vijaya Kumar, B K; Mahalanobis, A; Takessian, A
2000-01-01
Correlation methods are becoming increasingly attractive tools for image recognition and location. This renewed interest in correlation methods is spurred by the availability of high-speed image processors and the emergence of correlation filter designs that can optimize relevant figures of merit. In this paper, a new correlation filter design method is presented that allows one to optimally tradeoff among potentially conflicting correlation output performance criteria while achieving desired correlation peak value behavior in response to in-plane rotation of input images. Such controlled in-plane rotation response is useful in image analysis and pattern recognition applications where the sensor follows a pre-arranged trajectory while imaging an object. Since this new correlation filter design is based on circular harmonic function (CHF) theory, we refer to the resulting filters as optimal tradeoff circular harmonic function (OTCHF) filters. Underlying theory, OTCHF filter design method, and illustrative numerical results are presented.
NASA Astrophysics Data System (ADS)
Rader, Michael; Hebenstreit, Martin; Zillich, Robert E.
2017-03-01
We present a method for calculating the dynamics of a bosonic mixture, the multicomponent correlated-basis-function (CBF) method. For a single component, CBF results for the excitation energies agree quite well with experimental results, even for highly correlated systems like 4He, and recent systematic improvements of CBF achieve perfect agreement. We give a full derivation of multicomponent CBF, and apply the method to a dipolar Bose gas cut into two-dimensional layers by a deep optical lattice, with coupling between layers due to the long-ranged dipole-dipole interaction. We consider the case of strong coupling, leading to large positive interlayer correlations. We calculate the spectrum for a system of eight layers and show that the strong coupling can lead to a simpler spectrum than in the uncoupled case, with a single peak carrying most of the spectral weight.
Liu, Yu; Wu, Jianzhong
2014-02-28
Efficient and accurate prediction of the correlation functions of uniform electron gases is of great importance for both practical and theoretical applications. This paper presents a bridge-functional-based classical mapping method for calculating the correlation functions of uniform spin-unpolarized electron gases at finite temperature. The bridge functional is formulated by following Rosenfeld's universality ansatz in combination with the modified fundamental measure theory. The theoretical predictions are in good agreement with recent quantum Monte Carlo results but with negligible computational cost, and the accuracy is better than a previous attempt based on the hypernetted-chain approximation. We find that the classical mapping method is most accurate if the effective mass of electrons increases as the density falls.
Orientation function of optical mouse realized by digital speckle correlation method
NASA Astrophysics Data System (ADS)
Zhen, ZhiQiang; Tang, ZhengXin; Yan, Haitao; Lai, Fangming
2008-12-01
Used digital speckle correlation method (DSCM) to realize orientation function of optical mouse is researched. The experiment is designed to obtain the dynamic speckle patterns which are shot by CCD, Then the DSCM is used to process the sequential images and also the experiment is simulated. The experimental results show the DSCM can confirm orientation function of the optical mouse, and have a good agreement with the simulation results, and the resolution we obtained is higher than the resolution of mouse on the market.
Used digital speckle correlation method to realize orientation function of optical mouse
NASA Astrophysics Data System (ADS)
Yan, Haitao; Wang, Ming; Ge, Yixian; Zhou, Junping
2008-09-01
Used digital speckle correlation method (DSCM) to realize orientation function of optical mouse is researched. The experiment is designed to obtain the dynamic speckle patterns which are shot by CCD, then the DSCM is used to process the sequential images and also the experiment is simulated. The experimental results show the DSCM can confirm orientation function of the optical mouse, and have a good agreement with the simulation results, and the resolution we obtained is higher than the resolution of mouse on the market.
A novel joint sparse partial correlation method for estimating group functional networks.
Liang, Xiaoyun; Connelly, Alan; Calamante, Fernando
2016-03-01
Advances in graph theory have provided a powerful tool to characterize brain networks. In particular, functional networks at group-level have great appeal to gain further insight into complex brain function, and to assess changes across disease conditions. These group networks, however, often have two main limitations. First, they are popularly estimated by directly averaging individual networks that are compromised by confounding variations. Secondly, functional networks have been estimated mainly through Pearson cross-correlation, without taking into account the influence of other regions. In this study, we propose a sparse group partial correlation method for robust estimation of functional networks based on a joint graphical models approach. To circumvent the issue of choosing the optimal regularization parameters, a stability selection method is employed to extract networks. The proposed method is, therefore, denoted as JGMSS. By applying JGMSS across simulated datasets, the resulting networks show consistently higher accuracy and sensitivity than those estimated using an alternative approach (the elastic-net regularization with stability selection, ENSS). The robustness of the JGMSS is evidenced by the independence of the estimated networks to choices of the initial set of regularization parameters. The performance of JGMSS in estimating group networks is further demonstrated with in vivo fMRI data (ASL and BOLD), which show that JGMSS can more robustly estimate brain hub regions at group-level and can better control intersubject variability than it is achieved using ENSS.
A new method for improving functional-to-structural MRI alignment using local Pearson correlation.
Saad, Ziad S; Glen, Daniel R; Chen, Gang; Beauchamp, Michael S; Desai, Rutvik; Cox, Robert W
2009-02-01
Accurate registration of Functional Magnetic Resonance Imaging (FMRI) T2-weighted volumes to same-subject high-resolution T1-weighted structural volumes is important for Blood Oxygenation Level Dependent (BOLD) FMRI and crucial for applications such as cortical surface-based analyses and pre-surgical planning. Such registration is generally implemented by minimizing a cost functional, which measures the mismatch between two image volumes over the group of proper affine transformations. Widely used cost functionals, such as mutual information (MI) and correlation ratio (CR), appear to yield decent alignments when visually judged by matching outer brain contours. However, close inspection reveals that internal brain structures are often significantly misaligned. Poor registration is most evident in the ventricles and sulcal folds, where CSF is concentrated. This observation motivated our development of an improved modality-specific cost functional which uses a weighted local Pearson coefficient (LPC) to align T2- and T1-weighted images. In the absence of an alignment gold standard, we used three human observers blinded to registration method to provide an independent assessment of the quality of the registration for each cost functional. We found that LPC performed significantly better (p<0.001) than generic cost functionals including MI and CR. Generic cost functionals were very often not minimal near the best alignment, thereby suggesting that optimization is not the cause of their failure. Lastly, we emphasize the importance of precise visual inspection of alignment quality and present an automated method for generating composite images that help capture errors of misalignment.
Buttgereit, R; Roths, T; Honerkamp, J; Aberle, L B
2001-10-01
Dynamic light scattering experiments have become a powerful tool in order to investigate the dynamical properties of complex fluids. In many applications in both soft matter research and industry so-called "real world" systems are subject of great interest. Here, the dilution of the investigated system often cannot be changed without getting measurement artifacts, so that one often has to deal with highly concentrated and turbid media. The investigation of such systems requires techniques that suppress the influence of multiple scattering, e.g., cross correlation techniques. However, measurements at turbid as well as highly diluted media lead to data with low signal-to-noise ratio, which complicates data analysis and leads to unreliable results. In this article a multiangle regularization method is discussed, which copes with the difficulties arising from such samples and enhances enormously the quality of the estimated solution. In order to demonstrate the efficiency of this multiangle regularization method we applied it to cross correlation functions measured at highly turbid samples.
Hexagonalization of correlation functions
NASA Astrophysics Data System (ADS)
Fleury, Thiago; Komatsu, Shota
2017-01-01
We propose a nonperturbative framework to study general correlation functions of single-trace operators in N = 4 supersymmetric Yang-Mills theory at large N . The basic strategy is to decompose them into fundamental building blocks called the hexagon form factors, which were introduced earlier to study structure constants using integrability. The decomposition is akin to a triangulation of a Riemann surface, and we thus call it hexagonalization. We propose a set of rules to glue the hexagons together based on symmetry, which naturally incorporate the dependence on the conformal and the R-symmetry cross ratios. Our method is conceptually different from the conventional operator product expansion and automatically takes into account multi-trace operators exchanged in OPE channels. To illustrate the idea in simple set-ups, we compute four-point functions of BPS operators of arbitrary lengths and correlation functions of one Konishi operator and three short BPS operators, all at one loop. In all cases, the results are in perfect agreement with the perturbative data. We also suggest that our method can be a useful tool to study conformal integrals, and show it explicitly for the case of ladder integrals.
Accuracy of Frequencies Obtained with the Aid of Explicitly Correlated Wave Function Based Methods.
Schmitz, Gunnar; Christiansen, Ove
2017-08-08
We asses the basis set convergence of harmonic frequencies using different explicitly correlated wave function based methods. All commonly available CCSD(T) variants as well as MP2-F12 and MP4(F12*) are considered, and a hierarchy of the different approaches is established. As for reaction and atomization energies, CCSD(F12*)(T*) is a close approximation to CCSD(F12)(T*) and clearly superior to the other tested approximations. The used scaling for the triples correction enhances the accuracy relative to CCSD(F12*)(T) especially for small basis sets and is very attractive since no additional computational costs are added. However, this scaling slightly breaks size consistency, and therefore we additionally study the accuracy of CCSD(F12*)(T*) and CCSD(F12*)(T) in the context of calculating anharmonic frequencies to check if this causes problems in the generation of the potential energy surface (PES). We find a fast basis set convergence for harmonic and anharmonic frequencies. Already in the cc-pVDZ-F12 basis, the RMSD to the CBS limit is only around 4-5 cm(-1).
NASA Astrophysics Data System (ADS)
Proynov, Emil; Liu, Fenglai; Kong, Jing
2012-02-01
Becke's B05 method for nondynamic correlation is simplified for self-consistent implementation. An alternative form is proposed for the nondynamic correlation factors that do not require solving a complicated nonlinear algebraic equation. The four linear parameters of B05 are re-optimized together with one extra parameter in a modified expression for the second-order same-spin energy contribution. The latter is co-linear with the exact-exchange energy density and does not require higher moments of the relaxed exchange hole. Preliminary tests of this method show that it leads to a slight improvement over the resolution-of-identity B05 results reported previously for atomization energies, and to a definite improvement for reaction barriers of Hydrogen abstraction.
Ghosh, Soumen; Cramer, Christopher J; Truhlar, Donald G; Gagliardi, Laura
2017-04-01
Predicting ground- and excited-state properties of open-shell organic molecules by electronic structure theory can be challenging because an accurate treatment has to correctly describe both static and dynamic electron correlation. Strongly correlated systems, i.e., systems with near-degeneracy correlation effects, are particularly troublesome. Multiconfigurational wave function methods based on an active space are adequate in principle, but it is impractical to capture most of the dynamic correlation in these methods for systems characterized by many active electrons. We recently developed a new method called multiconfiguration pair-density functional theory (MC-PDFT), that combines the advantages of wave function theory and density functional theory to provide a more practical treatment of strongly correlated systems. Here we present calculations of the singlet-triplet gaps in oligoacenes ranging from naphthalene to dodecacene. Calculations were performed for unprecedently large orbitally optimized active spaces of 50 electrons in 50 orbitals, and we test a range of active spaces and active space partitions, including four kinds of frontier orbital partitions. We show that MC-PDFT can predict the singlet-triplet splittings for oligoacenes consistent with the best available and much more expensive methods, and indeed MC-PDFT may constitute the benchmark against which those other models should be compared, given the absence of experimental data.
Filatov, Michael; Liu, Fang; Kim, Kwang S.; Martínez, Todd J.
2016-12-22
Here, the spin-restricted ensemble-referenced Kohn-Sham (REKS) method is based on an ensemble representation of the density and is capable of correctly describing the non-dynamic electron correlation stemming from (near-)degeneracy of several electronic configurations. The existing REKS methodology describes systems with two electrons in two fractionally occupied orbitals. In this work, the REKS methodology is extended to treat systems with four fractionally occupied orbitals accommodating four electrons and self-consistent implementation of the REKS(4,4) method with simultaneous optimization of the orbitals and their fractional occupation numbers is reported. The new method is applied to a number of molecular systems where simultaneous dissociation of several chemical bonds takes place, as well as to the singlet ground states of organic tetraradicals 2,4-didehydrometaxylylene and 1,4,6,9-spiro[4.4]nonatetrayl.
Filatov, Michael; Liu, Fang; Kim, Kwang S.; ...
2016-12-22
Here, the spin-restricted ensemble-referenced Kohn-Sham (REKS) method is based on an ensemble representation of the density and is capable of correctly describing the non-dynamic electron correlation stemming from (near-)degeneracy of several electronic configurations. The existing REKS methodology describes systems with two electrons in two fractionally occupied orbitals. In this work, the REKS methodology is extended to treat systems with four fractionally occupied orbitals accommodating four electrons and self-consistent implementation of the REKS(4,4) method with simultaneous optimization of the orbitals and their fractional occupation numbers is reported. The new method is applied to a number of molecular systems where simultaneous dissociationmore » of several chemical bonds takes place, as well as to the singlet ground states of organic tetraradicals 2,4-didehydrometaxylylene and 1,4,6,9-spiro[4.4]nonatetrayl.« less
NASA Astrophysics Data System (ADS)
Filatov, Michael; Liu, Fang; Kim, Kwang S.; Martínez, Todd J.
2016-12-01
The spin-restricted ensemble-referenced Kohn-Sham (REKS) method is based on an ensemble representation of the density and is capable of correctly describing the non-dynamic electron correlation stemming from (near-)degeneracy of several electronic configurations. The existing REKS methodology describes systems with two electrons in two fractionally occupied orbitals. In this work, the REKS methodology is extended to treat systems with four fractionally occupied orbitals accommodating four electrons and self-consistent implementation of the REKS(4,4) method with simultaneous optimization of the orbitals and their fractional occupation numbers is reported. The new method is applied to a number of molecular systems where simultaneous dissociation of several chemical bonds takes place, as well as to the singlet ground states of organic tetraradicals 2,4-didehydrometaxylylene and 1,4,6,9-spiro[4.4]nonatetrayl.
Scaled density functional theory correlation functionals.
Ghouri, Mohammed M; Singh, Saurabh; Ramachandran, B
2007-10-18
We show that a simple one-parameter scaling of the dynamical correlation energy estimated by the density functional theory (DFT) correlation functionals helps increase the overall accuracy for several local and nonlocal functionals. The approach taken here has been described as the "scaled dynamical correlation" (SDC) method [Ramachandran, J. Phys. Chem. A 2006, 110, 396], and its justification is the same as that of the scaled external correlation (SEC) method of Brown and Truhlar. We examine five local and five nonlocal (hybrid) DFT functionals, the latter group including three functionals developed specifically for kinetics by the Truhlar group. The optimum scale factors are obtained by use of a set of 98 data values consisting of molecules, ions, and transition states. The optimum scale factors, found with a linear regression relationship, are found to differ from unity with a high degree of correlation in nearly every case, indicating that the deviation of calculated results from the experimental values are systematic and proportional to the dynamic correlation energy. As a consequence, the SDC scaling of dynamical correlation decreases the mean errors (signed and unsigned) by significant amounts in an overwhelming majority of cases. These results indicate that there are gains to be realized from further parametrization of several popular exchange-correlation functionals.
Wang, Yikai; Kang, Jian; Kemmer, Phebe B.; Guo, Ying
2016-01-01
Currently, network-oriented analysis of fMRI data has become an important tool for understanding brain organization and brain networks. Among the range of network modeling methods, partial correlation has shown great promises in accurately detecting true brain network connections. However, the application of partial correlation in investigating brain connectivity, especially in large-scale brain networks, has been limited so far due to the technical challenges in its estimation. In this paper, we propose an efficient and reliable statistical method for estimating partial correlation in large-scale brain network modeling. Our method derives partial correlation based on the precision matrix estimated via Constrained L1-minimization Approach (CLIME), which is a recently developed statistical method that is more efficient and demonstrates better performance than the existing methods. To help select an appropriate tuning parameter for sparsity control in the network estimation, we propose a new Dens-based selection method that provides a more informative and flexible tool to allow the users to select the tuning parameter based on the desired sparsity level. Another appealing feature of the Dens-based method is that it is much faster than the existing methods, which provides an important advantage in neuroimaging applications. Simulation studies show that the Dens-based method demonstrates comparable or better performance with respect to the existing methods in network estimation. We applied the proposed partial correlation method to investigate resting state functional connectivity using rs-fMRI data from the Philadelphia Neurodevelopmental Cohort (PNC) study. Our results show that partial correlation analysis removed considerable between-module marginal connections identified by full correlation analysis, suggesting these connections were likely caused by global effects or common connection to other nodes. Based on partial correlation, we find that the most significant
Wang, Yikai; Kang, Jian; Kemmer, Phebe B; Guo, Ying
2016-01-01
Currently, network-oriented analysis of fMRI data has become an important tool for understanding brain organization and brain networks. Among the range of network modeling methods, partial correlation has shown great promises in accurately detecting true brain network connections. However, the application of partial correlation in investigating brain connectivity, especially in large-scale brain networks, has been limited so far due to the technical challenges in its estimation. In this paper, we propose an efficient and reliable statistical method for estimating partial correlation in large-scale brain network modeling. Our method derives partial correlation based on the precision matrix estimated via Constrained L1-minimization Approach (CLIME), which is a recently developed statistical method that is more efficient and demonstrates better performance than the existing methods. To help select an appropriate tuning parameter for sparsity control in the network estimation, we propose a new Dens-based selection method that provides a more informative and flexible tool to allow the users to select the tuning parameter based on the desired sparsity level. Another appealing feature of the Dens-based method is that it is much faster than the existing methods, which provides an important advantage in neuroimaging applications. Simulation studies show that the Dens-based method demonstrates comparable or better performance with respect to the existing methods in network estimation. We applied the proposed partial correlation method to investigate resting state functional connectivity using rs-fMRI data from the Philadelphia Neurodevelopmental Cohort (PNC) study. Our results show that partial correlation analysis removed considerable between-module marginal connections identified by full correlation analysis, suggesting these connections were likely caused by global effects or common connection to other nodes. Based on partial correlation, we find that the most significant
NASA Astrophysics Data System (ADS)
Goïc, Gaëtan Le; Bigerelle, Maxence; Samper, Serge; Favrelière, Hugues; Pillet, Maurice
2016-01-01
This study investigates the correlations between the topography of different damaged rough surfaces and process conditions. Several surfaces are measured and compared to determine if they can be discriminated. The analysis is performed by using Gaussian Filtering, Wavelet Transform and a more recent approach named Discrete Modal Decomposition. Standardized 3D roughness parameters are computed for each multiscale method, filter (e.g., high-pass, low-pass and band-pass) and available scale. The relevance (i.e., the ability to discriminate surface topographies corresponding to different process conditions) is then investigated using a statistical analysis based on the MesRugTM expert system. The results indicate clear differences between the multiscale methods and show that the Wavelet approach is useful when characterizing localized surface defects while Gaussian Filtering is more appropriate for highly periodic morphological structures. For more complex topographies, this study also clearly shows that the Discrete Modal Decomposition exhibits compelling abilities that fall between those of the Gaussian and Wavelet approaches; this method is clearly more relevant than the Gaussian method in the case of localized defects and less relevant in the case of highly periodical structures and fractal surfaces (1 /fα spectrum). This can be explained by the modulated frequency/amplitude descriptors generated via the modal basis.
Kinetic theory of correlated fluids: from dynamic density functional to Lattice Boltzmann methods.
Marconi, Umberto Marini Bettolo; Melchionna, Simone
2009-07-07
Using methods of kinetic theory and liquid state theory we propose a description of the nonequilibrium behavior of molecular fluids, which takes into account their microscopic structure and thermodynamic properties. The present work represents an alternative to the recent dynamic density functional theory, which can only deal with colloidal fluids and is not apt to describe the hydrodynamic behavior of a molecular fluid. The method is based on a suitable modification of the Boltzmann transport equation for the phase space distribution and provides a detailed description of the local structure of the fluid and its transport coefficients. Finally, we propose a practical scheme to solve numerically and efficiently the resulting kinetic equation by employing a discretization procedure analogous to the one used in the Lattice Boltzmann method.
Applications of methods beyond density functional theory to the study of correlated electron systems
NASA Astrophysics Data System (ADS)
Sims, Hunter Robert
The difficulty in accurately treating systems in which electron-electron interactions are the dominant physics has plagued condensed matter physics for decades. Currently, there exist many different computational techniques designed to improve upon density functional theory to varying degrees of accuracy. To date, no unified, parameter-free method exists that is guaranteed to yield the correct answer for all materials. Consequently, proper treatment of such systems often requires a combination of several methods, allowing one to check them against one another when their regions of validity overlap and to expand one's reach when a single method cannot reliably describe all of the physics at work. In this dissertation, I present discussion and, when appropriate, brief derivations of several of the most prominent electronic structure methods currently in use---from the local density approximation through LDA+DMFT. I then present several investigations into the electronic and magnetic structure of materials of potential interest for information technology that also illustrate the current state of affairs in computational condensed matter physics. I explore the intersite exchange interactions in CrO2 within density functional theory (with and without Hubbard "+U" corrections) and evaluate these results through analytic and numerical means. I study the dependence of the mysterious magnetization of Fe16N2 on crystal and electronic structure and employ a wide range of techniques in an attempt to bring greater rigor and deeper understanding to the widely-varying reports on this material. In conjunction with others' careful experimental analysis, I provide a picture of the band structure of the magnetic insulator NiFe2O4 that reveals a novel hierarchy in its band gaps and suggests applications in spintronics and possibly other areas. Finally, I employ dynamical mean-field theory to study the behavior of impurity states in elemental semiconductors, using H impurities in Ge as
Pisutha-Arnond, N; Chan, V W L; Iyer, M; Gavini, V; Thornton, K
2013-01-01
We introduce a new approach to represent a two-body direct correlation function (DCF) in order to alleviate the computational demand of classical density functional theory (CDFT) and enhance the predictive capability of the phase-field crystal (PFC) method. The approach utilizes a rational function fit (RFF) to approximate the two-body DCF in Fourier space. We use the RFF to show that short-wavelength contributions of the two-body DCF play an important role in determining the thermodynamic properties of materials. We further show that using the RFF to empirically parametrize the two-body DCF allows us to obtain the thermodynamic properties of solids and liquids that agree with the results of CDFT simulations with the full two-body DCF without incurring significant computational costs. In addition, the RFF can also be used to improve the representation of the two-body DCF in the PFC method. Last, the RFF allows for a real-space reformulation of the CDFT and PFC method, which enables descriptions of nonperiodic systems and the use of nonuniform and adaptive grids.
Correlation dynamics of Green functions
NASA Astrophysics Data System (ADS)
Shun-Jin, Wang; Wei, Zuo; Wolfgang, Cassing
1994-06-01
We generalize the methods used in the theory of correlation dynamics and establish a set of equations of motion for many-body correlation Green functions in the nonrelativistic case. These nonlinear and coupled equations of motion describe the dynamical evolution of correlation Green functions of different order and transparently show how many-body correlations are generated by the different interaction terms in a genuine nonperturbative framework. The nonperturbative results of the conventional Green function theory are included in the present formalism as two limiting cases (the so-called ladder-diagram summation and ring-diagram summation) as well as the familiar correlation dynamics of density matrices in the equal-time limit. We present explicit expressions for three- and four-body correlation functions that can be used to dynamically restore the trace relations for spin-symmetric Fermi systems and study numerically the relative importance of two-, three- and four-body correlations for nuclear configurations close to the ground state.
Palma, Juliana
2009-03-28
A simple mixed quantum/classical (mixed-Q/C) implementation of the flux-flux correlation function method has been applied to evaluate rate constants for a two-dimensional model system. The model consists of an Eckart barrier resembling the collinear H + H(2) reaction, linearly coupled to a harmonic oscillator. Results are presented for a broad range of parameters for temperatures between 140 and 300 K. It is found that the mixed-Q/C method gives fairly accurate results as long as the reaction does not involve too many recrossings. This suggests that the methodology could be extended to treat direct polyatomic reactions in gas phase.
Functional Multiple-Set Canonical Correlation Analysis
ERIC Educational Resources Information Center
Hwang, Heungsun; Jung, Kwanghee; Takane, Yoshio; Woodward, Todd S.
2012-01-01
We propose functional multiple-set canonical correlation analysis for exploring associations among multiple sets of functions. The proposed method includes functional canonical correlation analysis as a special case when only two sets of functions are considered. As in classical multiple-set canonical correlation analysis, computationally, the…
Functional Multiple-Set Canonical Correlation Analysis
ERIC Educational Resources Information Center
Hwang, Heungsun; Jung, Kwanghee; Takane, Yoshio; Woodward, Todd S.
2012-01-01
We propose functional multiple-set canonical correlation analysis for exploring associations among multiple sets of functions. The proposed method includes functional canonical correlation analysis as a special case when only two sets of functions are considered. As in classical multiple-set canonical correlation analysis, computationally, the…
NASA Astrophysics Data System (ADS)
Campana, L. S.; Cavallo, A.; Cesare, L. De; Esposito, U.; Naddeo, A.
2017-04-01
In the present paper we investigate the paramagnetic susceptibility and the short-range order correlation functions of a d-dimensional classical isotropic ferromagnetic Heisenberg model with short-range exchange interactions by employing the two-time Green function method in classical statistical mechanics. Here we use Tyablikov-Callen-like decouplings for higher order Green functions and a formula for magnetization recently obtained by extension of the well known Callen method developed many years ago for the quantum isotropic Heisenberg model. Although our analysis is true for any temperature and dimensionality, we focus on one-, and some two- and three-dimensional lattices of experimental interest and derive asymptotic expressions for susceptibility and correlation functions within the paramagnetic phase close to the phase boundary and in the high-temperature regime. Besides, we present a Fourier series expansion method for deriving the high-temperature behaviors of the correlation functions. Our predictions, as obtained from a genuine classical many-body framework, may constitute a good reference point for the quantum counterparts emerging in the classical limit at the same level of approximation. Of course, although the classical spin models have unrealistic properties at sufficiently low temperatures, our classical analysis provides, in a relatively simple way as compared to a quantum treatment, an experimentally interesting scenario at finite temperature and dimensionalities d ≥ 1.
Causo, Maria Serena; Ciccotti, Giovanni; Bonella, Sara; Vuilleumier, Rodolphe
2006-08-17
Linearized mixed quantum-classical simulations are a promising approach for calculating time-correlation functions. At the moment, however, they suffer from some numerical problems that may compromise their efficiency and reliability in applications to realistic condensed-phase systems. In this paper, we present a method that improves upon the convergence properties of the standard algorithm for linearized calculations by implementing a cumulant expansion of the relevant averages. The effectiveness of the new approach is tested by applying it to the challenging computation of the diffusion of an excess electron in a metal-molten salt solution.
NASA Astrophysics Data System (ADS)
Bodek, K.; Kępka, D.; Rozpędzik, D.; Zejma, J.; Kozela, A.
2017-04-01
A self-calibrating double-Mott polarimeter is proposed for measurement of the spin correlation function of relativistic electron pairs produced in Møller scattering. The polarization of outgoing electrons (appearing when the beam is polarized) is utilized for calibration of effective analyzing powers in the secondary Mott scattering used for spin analysis. The experiment will measure the newly introduced relative spin correlation function. This new observable can be measured with a significantly better accuracy than the regular spin correlation function in a small scale experiment. It is shown that both the spin correlation function and the relative spin correlation function are theoretically equivalent. A specific experimental data analysis scenario is proposed, which effectively eliminates the systematic effects related to the imperfect geometry and detector efficiency.
Global Method for Electron Correlation
NASA Astrophysics Data System (ADS)
Piris, Mario
2017-08-01
The current work presents a new single-reference method for capturing at the same time the static and dynamic electron correlation. The starting point is a determinant wave function formed with natural orbitals obtained from a new interacting-pair model. The latter leads to a natural orbital functional (NOF) capable of recovering the complete intrapair, but only the static interpair correlation. Using the solution of the NOF, two new energy functionals are defined for both dynamic (Edyn) and static (Esta) correlation. Edyn is derived from a modified second-order Møller-Plesset perturbation theory (MP2), while Esta is obtained from the static component of the new NOF. Double counting is avoided by introducing the amount of static and dynamic correlation in each orbital as a function of its occupation. As a result, the total energy is represented by the sum E˜ HF+Edyn+Esta , where E˜ HF is the Hartree-Fock energy obtained with natural orbitals. The new procedure called NOF-MP2 scales formally as O (M5) (where M is the number of basis functions), and is applied successfully to the homolytic dissociation of a selected set of diatomic molecules, paradigmatic cases of near-degeneracy effects. The size consistency has been numerically demonstrated for singlets. The values obtained are in good agreement with the experimental data.
Iterative method for generating correlated binary sequences
NASA Astrophysics Data System (ADS)
Usatenko, O. V.; Melnik, S. S.; Apostolov, S. S.; Makarov, N. M.; Krokhin, A. A.
2014-11-01
We propose an efficient iterative method for generating random correlated binary sequences with a prescribed correlation function. The method is based on consecutive linear modulations of an initially uncorrelated sequence into a correlated one. Each step of modulation increases the correlations until the desired level has been reached. The robustness and efficiency of the proposed algorithm are tested by generating sequences with inverse power-law correlations. The substantial increase in the strength of correlation in the iterative method with respect to single-step filtering generation is shown for all studied correlation functions. Our results can be used for design of disordered superlattices, waveguides, and surfaces with selective transport properties.
Goodpaster, Jason D; Barnes, Taylor A; Manby, Frederick R; Miller, Thomas F
2012-12-14
Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexa-aquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in the dispersion interactions due to conventional exchange-correlation (XC) functionals while simultaneously avoiding errors due to subsystem partitioning across covalent bonds. Application of WFT-in-DFT embedding to the calculation of the low-spin/high-spin splitting energy in the hexaaquairon(II) cation reveals that the majority of the dependence on the DFT XC functional can be eliminated by treating only the single transition-metal atom at the WFT level; furthermore, these calculations demonstrate the substantial effects of open-shell contributions to the embedding potential, and they suggest that restricted open-shell WFT-in-DFT embedding provides better accuracy than unrestricted open-shell WFT-in-DFT embedding due to the removal of spin contamination.
Two-particle correlation function and dihadron correlation approach
Vechernin, V. V. Ivanov, K. O.; Neverov, D. I.
2016-09-15
It is shown that, in the case of asymmetric nuclear interactions, the application of the traditional dihadron correlation approach to determining a two-particle correlation function C may lead to a form distorted in relation to the canonical pair correlation function {sub C}{sup 2}. This result was obtained both by means of exact analytic calculations of correlation functions within a simple string model for proton–nucleus and deuteron–nucleus collisions and by means of Monte Carlo simulations based on employing the HIJING event generator. It is also shown that the method based on studying multiplicity correlations in two narrow observation windows separated in rapidity makes it possible to determine correctly the canonical pair correlation function C{sub 2} for all cases, including the case where the rapidity distribution of product particles is not uniform.
Two-particle correlation function and dihadron correlation approach
NASA Astrophysics Data System (ADS)
Vechernin, V. V.; Ivanov, K. O.; Neverov, D. I.
2016-09-01
It is shown that, in the case of asymmetric nuclear interactions, the application of the traditional dihadron correlation approach to determining a two-particle correlation function C may lead to a form distorted in relation to the canonical pair correlation function C 2. This result was obtained both by means of exact analytic calculations of correlation functions within a simple string model for proton-nucleus and deuteron-nucleus collisions and by means of Monte Carlo simulations based on employing the HIJING event generator. It is also shown that the method based on studying multiplicity correlations in two narrow observation windows separated in rapidity makes it possible to determine correctly the canonical pair correlation function C 2 for all cases, including the case where the rapidity distribution of product particles is not uniform.
NASA Astrophysics Data System (ADS)
Elward, Jennifer Mary
Semiconductor nanoparticles, or quantum dots (QDs), are well known to have very unique optical and electronic properties. These properties can be controlled and tailored as a function of several influential factors, including but not limited to the particle size and shape, effect of composition and heterojunction as well as the effect of ligand on the particle surface. This customizable nature leads to extensive experimental and theoretical research on the capabilities of these quantum dots for many application purposes. However, in order to be able to understand and thus further the development of these materials, one must first understand the fundamental interaction within these nanoparticles. In this thesis, I have developed a theoretical method which is called electron-hole explicitly correlated Hartee-Fock (eh-XCHF). It is a variational method for solving the electron-hole Schrodinger equation and has been used in this work to study electron-hole interaction in semiconductor quantum dots. The method was benchmarked with respect to a parabolic quantum dot system, and ground state energy and electron-hole recombination probability were computed. Both of these properties were found to be in good agreement with expected results. Upon successful benchmarking, I have applied the eh-XCHF method to study optical properties of several quantum dot systems including the effect of dot size on exciton binding energy and recombination probability in a CdSe quantum dot, the effect of shape on a CdSe quantum dot, the effect of heterojunction on a CdSe/ZnS quantum dot and the effect of quantum dot-biomolecule interaction within a CdSe-firefly Luciferase protein conjugate system. As metrics for assessing the effect of these influencers on the electron-hole interaction, the exciton binding energy, electron-hole recombination probability and the average electron-hole separation distance have been computed. These excitonic properties have been found to be strongly infuenced by the
Basire, Marie; Borgis, Daniel; Vuilleumier, Rodolphe
2013-08-14
Langevin dynamics coupled to a quantum thermal bath (QTB) allows for the inclusion of vibrational quantum effects in molecular dynamics simulations at virtually no additional computer cost. We investigate here the ability of the QTB method to reproduce the quantum Wigner distribution of a variety of model potentials, designed to assess the performances and limits of the method. We further compute the infrared spectrum of a multidimensional model of proton transfer in the gas phase and in solution, using classical trajectories sampled initially from the Wigner distribution. It is shown that for this type of system involving large anharmonicities and strong nonlinear coupling to the environment, the quantum thermal bath is able to sample the Wigner distribution satisfactorily and to account for both zero point energy and tunneling effects. It leads to quantum time correlation functions having the correct short-time behavior, and the correct associated spectral frequencies, but that are slightly too overdamped. This is attributed to the classical propagation approximation rather than the generation of the quantized initial conditions themselves.
Chen, Shentan; Raugei, Simone; Rousseau, Roger J.; Dupuis, Michel; Bullock, R. Morris
2010-12-09
A systematic assessment of theoretical methods applicable to the accurate characterization of catalytic cycles of homogeneous catalysts for H2 oxidation and evolution is reported. For these catalysts, H2 bond breaking or formation involve di-hydrogen, di-hydride, hydride-proton, and di-proton complexes. The key elementary steps have heterolytic character. In the context of Density Functional Theory (DFT) we investigated the use of functionals in the generalized gradient approximation (GGA) as well as hybrid functionals. We compared the results with wavefunction theories based on perturbation theory (MP2 and MP4) and on coupled-cluster expansions (CCSD and CCSD(T)). Our findings suggest that DFT results based on Perdew functionals are in semi-quantitative agreement with the CCSD(T) results, with deviations of a few kcal/mol only. On the other hand, the B3LYP functional is not even in qualitative agreement with CCSD[T]. Surprisingly the MP2 results are found to be extremely poor, a finding that we attribute to the limited treatment in MP2 theory of dynamic electron correlation effects in Ni(0) oxidation state. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.
Functional CAR models for large spatially correlated functional datasets.
Zhang, Lin; Baladandayuthapani, Veerabhadran; Zhu, Hongxiao; Baggerly, Keith A; Majewski, Tadeusz; Czerniak, Bogdan A; Morris, Jeffrey S
2016-01-01
We develop a functional conditional autoregressive (CAR) model for spatially correlated data for which functions are collected on areal units of a lattice. Our model performs functional response regression while accounting for spatial correlations with potentially nonseparable and nonstationary covariance structure, in both the space and functional domains. We show theoretically that our construction leads to a CAR model at each functional location, with spatial covariance parameters varying and borrowing strength across the functional domain. Using basis transformation strategies, the nonseparable spatial-functional model is computationally scalable to enormous functional datasets, generalizable to different basis functions, and can be used on functions defined on higher dimensional domains such as images. Through simulation studies, we demonstrate that accounting for the spatial correlation in our modeling leads to improved functional regression performance. Applied to a high-throughput spatially correlated copy number dataset, the model identifies genetic markers not identified by comparable methods that ignore spatial correlations.
NASA Astrophysics Data System (ADS)
Suhai, Sándor
1995-06-01
Structural and energetic aspects of the Peierls-type lattice dimerization were investigated in infinite, one-dimensional, periodic trans-polyacetylene (t-PA) using many-body perturbation theory (MBPT) and density-functional theory (DFT). Cohesive properties and dimerization parameters were obtained first for the classical Coulomb potential in the Hartree approximation and then by gradually turning on exchange and correlation potentials. Besides the nonlocal Hartree-Fock exchange, several other exchange functionals were used incorporating gradient corrections as well. For MBPT, electron correlation was included up to the fourth order of the Mo/ller-Plesset scheme and the behavior of lattice sums for different PT terms was analyzed in detail. The electrostatic part of the infinite lattice sums was computed by the multipole expansion technique. In solving the polymer Kohn-Sham equations, the performance of several different correlation potentials was studied again including different gradient corrections. Atomic basis sets of systematically increasing size, in the range of double-zeta to triple-zeta (TZ) up to TZ (3df,3p2d), were used in all calculations to construct the symmetry-adapted (Bloch-type) polymer wave functions, to fully optimize the structures, and to extrapolate different physical quantities to the limit of a hypothetical infinite basis set. Comparison of the different DFT results with MBPT and with experiments demonstrated the importance of gradient terms both for exchange and correlation. On the other hand, the best DFT functional, using a medium-size atomic basis set, excellently reproduced the cohesive and dimerization energies obtained for infinite t-PA at the MP4/TZ(3d2f,3p2d) level and provided dimerization parameters close to experiment. The experimentally observed lattice spacing of 2.46+/-0.01 Å will be correctly predicted both at the MBPT and DFT levels with 2.48 and 2.44 Å, respectively.
Ways to improve your correlation functions
NASA Technical Reports Server (NTRS)
Hamilton, A. J. S.
1993-01-01
This paper describes a number of ways to improve on the standard method for measuring the two-point correlation function of large scale structure in the Universe. Issues addressed are: (1) the problem of the mean density, and how to solve it; (2) how to estimate the uncertainty in a measured correlation function; (3) minimum variance pair weighting; (4) unbiased estimation of the selection function when magnitudes are discrete; and (5) analytic computation of angular integrals in background pair counts.
Nakashima, Hiroyuki; Nakatsuji, Hiroshi
2013-07-28
We propose here fast antisymmetrization procedures for the partially correlated wave functions that appear in the free complement-local Schrödinger equation (FC-LSE) method. Pre-analysis of the correlation diagram, referred to as dot analysis, combined with the determinant update technique based on the Laplace expansion, drastically reduces the orders of the antisymmetrization computations. When the complement functions include only up to single-correlated terms, the order of computations is O(N(3)), which is the same as the non-correlated case. Similar acceleration is obtained for general correlated functions as a result of dot analysis. This algorithm has been successfully used in our laboratory in actual FC-LSE calculations for accurately solving the many-electron Schrödinger equations of atoms and molecules. The proposed method is general and applicable to the sampling-type methodology of other partially correlated wave functions like those in the quantum Monte Carlo and modern Hylleraas-type methods.
Nakashima, Hiroyuki; Nakatsuji, Hiroshi
2013-07-28
We propose here fast antisymmetrization procedures for the partially correlated wave functions that appear in the free complement-local Schrödinger equation (FC-LSE) method. Pre-analysis of the correlation diagram, referred to as dot analysis, combined with the determinant update technique based on the Laplace expansion, drastically reduces the orders of the antisymmetrization computations. When the complement functions include only up to single-correlated terms, the order of computations is O(N{sup 3}), which is the same as the non-correlated case. Similar acceleration is obtained for general correlated functions as a result of dot analysis. This algorithm has been successfully used in our laboratory in actual FC-LSE calculations for accurately solving the many-electron Schrödinger equations of atoms and molecules. The proposed method is general and applicable to the sampling-type methodology of other partially correlated wave functions like those in the quantum Monte Carlo and modern Hylleraas-type methods.
Grabowski, Ireneusz Śmiga, Szymon; Buksztel, Adam; Fabiano, Eduardo; Teale, Andrew M.; Sala, Fabio Della
2014-07-14
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn–Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite–spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
NASA Astrophysics Data System (ADS)
Grabowski, Ireneusz; Fabiano, Eduardo; Teale, Andrew M.; Śmiga, Szymon; Buksztel, Adam; Della Sala, Fabio
2014-07-01
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn-Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite-spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
Grabowski, Ireneusz; Fabiano, Eduardo; Teale, Andrew M; Śmiga, Szymon; Buksztel, Adam; Della Sala, Fabio
2014-07-14
The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn-Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite-spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort.
NASA Astrophysics Data System (ADS)
Deguchi, Tetsuo; Matsui, Chihiro
2010-06-01
For the integrable higher-spin XXX and XXZ spin chains we present multiple-integral representations for the correlation function of an arbitrary product of Hermitian elementary matrices in the massless ground state. We give a formula expressing it by a single term of multiple integrals. In particular, we explicitly derive the emptiness formation probability (EFP). We assume 2s-strings for the ground-state solution of the Bethe-ansatz equations for the spin-s XXZ chain, and solve the integral equations for the spin-s Gaudin matrix. In terms of the XXZ coupling Δ we define ζ by Δ=cos ζ, and put it in a region 0⩽ζ<π/2s of the gapless regime: -1<Δ⩽1 (0⩽ζ<π), where Δ=1 (ζ=0) corresponds to the antiferromagnetic point. We calculate the zero-temperature correlation functions by the algebraic Bethe-ansatz, introducing the Hermitian elementary matrices in the massless regime, and taking advantage of the fusion construction of the R-matrix of the higher-spin representations of the affine quantum group.
Improved Digital Image Correlation method
NASA Astrophysics Data System (ADS)
Mudassar, Asloob Ahmad; Butt, Saira
2016-12-01
Digital Image Correlation (DIC) is a powerful technique which is used to correlate two image segments to determine the similarity between them. A correlation image is formed which gives a peak known as correlation peak. If the two image segments are identical the peak is known as auto-correlation peak otherwise it is known as cross correlation peak. The location of the peak in a correlation image gives the relative displacement between the two image segments. Use of DIC for in-plane displacement and deformation measurements in Electronic Speckle Photography (ESP) is well known. In ESP two speckle images are correlated using DIC and relative displacement is measured. We are presenting background review of ESP and disclosing a technique based on DIC for improved relative measurements which we regard as the improved DIC method. Simulation and experimental results reveal that the proposed improved-DIC method is superior to the conventional DIC method in two aspects, in resolution and in the availability of reference position in displacement measurements.
Pair correlation function integrals: Computation and use
NASA Astrophysics Data System (ADS)
Wedberg, Rasmus; O'Connell, John P.; Peters, Günther H.; Abildskov, Jens
2011-08-01
We describe a method for extending radial distribution functions obtained from molecular simulations of pure and mixed molecular fluids to arbitrary distances. The method allows total correlation function integrals to be reliably calculated from simulations of relatively small systems. The long-distance behavior of radial distribution functions is determined by requiring that the corresponding direct correlation functions follow certain approximations at long distances. We have briefly described the method and tested its performance in previous communications [R. Wedberg, J. P. O'Connell, G. H. Peters, and J. Abildskov, Mol. Simul. 36, 1243 (2010);, 10.1080/08927020903536366 Fluid Phase Equilib. 302, 32 (2011)], 10.1016/j.fluid.2010.10.004, but describe here its theoretical basis more thoroughly and derive long-distance approximations for the direct correlation functions. We describe the numerical implementation of the method in detail, and report numerical tests complementing previous results. Pure molecular fluids are here studied in the isothermal-isobaric ensemble with isothermal compressibilities evaluated from the total correlation function integrals and compared with values derived from volume fluctuations. For systems where the radial distribution function has structure beyond the sampling limit imposed by the system size, the integration is more reliable, and usually more accurate, than simple integral truncation.
NASA Astrophysics Data System (ADS)
Bai, Ruixiang; Jiang, Hao; Lei, Zhenkun; Li, Weikang
2017-03-01
Compared with the traditional forward compositional matching strategy, the inverse compositional matching strategy has almost the same accuracy, but has an obviously higher efficiency than the former in digital image correlation (DIC) algorithms. Based on the inverse compositional matching strategy and the auxiliary displacement functions, a more accurate inverse compositional Gauss-Newton (IC-GN2) algorithm with a new second-order shape operator is proposed for nonuniform and large deformation measurements. A theoretical deduction showed that the new proposed second-order shape operator is invertible and can steadily attain second-order precision. The result of the numerical simulation showed that the matching accuracy of the new IC-GN2 algorithm is the same as that of the forward compositional Gauss-Newton (FC-GN2) algorithm and is relatively better than in IC-GN2 algorithm. Finally, a rubber tension experiment with a large deformation of 27% was performed to validate the feasibility of the proposed algorithm.
Multitime correlation functions in nonclassical stochastic processes
NASA Astrophysics Data System (ADS)
Krumm, F.; Sperling, J.; Vogel, W.
2016-06-01
A general method is introduced for verifying multitime quantum correlations through the characteristic function of the time-dependent P functional that generalizes the Glauber-Sudarshan P function. Quantum correlation criteria are derived which identify quantum effects for an arbitrary number of points in time. The Magnus expansion is used to visualize the impact of the required time ordering, which becomes crucial in situations when the interaction problem is explicitly time dependent. We show that the latter affects the multi-time-characteristic function and, therefore, the temporal evolution of the nonclassicality. As an example, we apply our technique to an optical parametric process with a frequency mismatch. The resulting two-time-characteristic function yields full insight into the two-time quantum correlation properties of such a system.
NASA Astrophysics Data System (ADS)
Suhai, Sándor
1994-11-01
Linear equidistant and bond-alternating infinite chains of hydrogen atoms have been investigated by the ab initio crystal-orbital method at the Hartree-Fock (HF) level, by including electron correlation up to the complete fourth order of the Mo/ller-Plesset perturbation theory (MP4-PT), and by using different versions of density-functional theory (DFT). The Bloch functions have been expanded in all cases in a series of high-quality atomic-orbital basis sets and complemented by extended sets of polarization functions up to 6s3p2d1f per H atom. In order to compare the performance of the PT and DFT methods, several physical properties have been computed at all theoretical levels including lattice geometry, cohesive energy, mechanisms of bond alternation (Peierls instability), and energetic features of nonequilibrium configurations (dissociation). For these latter quantities, both spin-restricted (RHF) and unrestricted (UHF) wave functions have been employed in all orders of PT. The methods described have been used parallel to infinite chains and to the H2 molecule, to be able to check their accuracy on experiments. In the case of the DFT, six different functionals (combining Slater and Becke exchange with local and gradient-corrected correlation potentials) have been utilized to test their accuracy in comparison with the MP4 results.
NASA Astrophysics Data System (ADS)
Pérez, Alejandro; Tuckerman, Mark E.; Müser, Martin H.
2009-05-01
The problems of ergodicity and internal consistency in the centroid and ring-polymer molecular dynamics methods are addressed in the context of a comparative study of the two methods. Enhanced sampling in ring-polymer molecular dynamics (RPMD) is achieved by first performing an equilibrium path integral calculation and then launching RPMD trajectories from selected, stochastically independent equilibrium configurations. It is shown that this approach converges more rapidly than periodic resampling of velocities from a single long RPMD run. Dynamical quantities obtained from RPMD and centroid molecular dynamics (CMD) are compared to exact results for a variety of model systems. Fully converged results for correlations functions are presented for several one dimensional systems and para-hydrogen near its triple point using an improved sampling technique. Our results indicate that CMD shows very similar performance to RPMD. The quality of each method is further assessed via a new χ2 descriptor constructed by transforming approximate real-time correlation functions from CMD and RPMD trajectories to imaginary time and comparing these to numerically exact imaginary time correlation functions. For para-hydrogen near its triple point, it is found that adiabatic CMD and RPMD both have similar χ2 error.
Speeding up local correlation methods
Kats, Daniel
2014-12-28
We present two techniques that can substantially speed up the local correlation methods. The first one allows one to avoid the expensive transformation of the electron-repulsion integrals from atomic orbitals to virtual space. The second one introduces an algorithm for the residual equations in the local perturbative treatment that, in contrast to the standard scheme, does not require holding the amplitudes or residuals in memory. It is shown that even an interpreter-based implementation of the proposed algorithm in the context of local MP2 method is faster and requires less memory than the highly optimized variants of conventional algorithms.
Law, A D; Buzza, D M A
2009-09-07
The structure and stability of colloidal monolayers depend crucially on the effective pair potential u(r) between colloidal particles. In this paper, we develop a two-dimensional (2D) predictor-corrector method for extracting u(r) from the pair correlation function g(r) of dense colloidal monolayers. The method is based on an extension of the three-dimensional scheme of Rajagopalan and Rao [Phys. Rev. E 55, 4423 (1997)] to 2D by replacing the unknown bridge function B(r) with the hard-disk bridge function B(d)(r); the unknown hard-disk diameter d is then determined using an iterative scheme. We compare the accuracy of our predictor-corrector method to the conventional one-step inversion schemes of hypernetted chain closure (HNC) and Percus-Yevick (PY) closure. Specifically we benchmark all three schemes against g(r) data generated from Monte Carlo simulation for a range of 2D potentials: exponential decay, Stillinger-Hurd, Lennard-Jones, and Derjaguin-Landau-Verwey-Overbeek. We find that for all these potentials, the predictor-corrector method is at least as good as the most accurate one-step method for any given potential, and in most cases it is significantly better. In contrast the accuracy of the HNC and PY methods relative to each other depends on the potential studied. The proposed predictor-corrector scheme is therefore a robust and more accurate alternative to these conventional one-step inversion schemes.
Elucidation of SESANS correlation functions through model
Shew, Chwen-Yang; Chen, Wei-Ren
2012-01-01
Several single-modal Debye correlation functions are closely examined to elucidate the behavior of their corresponding SESANS (Spin Echo Small Angle Neutron Scattering) correlation functions. We nd that the upper bound of a Debye correlation function and of its SESANS correlation func- tion is identical. For discrete Debye correlation functions, the peak of SESANS correlation function emerges at their rst discrete point, whereas for continuous Debye correlation functions with greater width, the peak position shifts to a greater value. In both cases, the intensity and shape of the peak of the SESANS correlation function are determined by the width of the normalized Debye correlation functions. In the application, we mimic the intramolecular and intermolecular Debye correlation functions of liquids composed of interacting particles by using the simple models to elucidate their competition in the SESANS correlation function. Our calculations show that the position of the rst minimum of SESANS correlation function shifts to a smaller value as inter- molecular attraction or correlation is enhanced. The minimum value can be positive or negative, and the positive values are observed for the cases equivalent to stronger intermolecular attraction, consistent with literature results based on more sophisticated liquid state theory and simulations.
Loops in inflationary correlation functions
NASA Astrophysics Data System (ADS)
Tanaka, Takahiro; Urakawa, Yuko
2013-12-01
We review the recent progress regarding the loop corrections to the correlation functions in the inflationary universe. A naive perturbation theory predicts that the loop corrections generated during inflation suffer from various infrared (IR) pathologies. Introducing an IR cutoff by hand is neither satisfactory nor enough to fix the problem of a secular growth, which may ruin the predictive power of inflation models if the inflation lasts sufficiently long. We discuss the origin of the IR divergences and explore the regularity conditions of the loop corrections for the adiabatic perturbation, the iso-curvature perturbation, and the tensor perturbation, in turn. These three kinds of perturbations have qualitative differences, but in discussing the IR regularity there is a feature common to all cases, which is the importance of the proper identification of observable quantities. Genuinely, observable quantities should respect the gauge invariance from the view point of a local observer. Interestingly, we find that the requirement of the IR regularity restricts the allowed quantum states.
Theoretical methods in fluorescence correlation spectroscopy
NASA Astrophysics Data System (ADS)
Torres, Tedman Anthony
2009-12-01
analysis of the data. Also, a method is presented to eliminate the effect of diffusion in experimental correlation-functions of conformational reaction studies by means of auto/cross-correlation ratios. This method eliminates the need to utilize a separate diffusion-characterizing sample in a second experiment. Changes in confocal volume shape between experiments are also eliminated, providing more reliable parameter extraction.
Matrix elements from moments of correlation functions
Chang, Chia Cheng; Bouchard, Chris; Orginos, Konstantinos; Richards, David G.
2016-10-01
Momentum-space derivatives of matrix elements can be related to their coordinate-space moments through the Fourier transform. We derive these expressions as a function of momentum transfer Q2 for asymptotic in/out states consisting of a single hadron. We calculate corrections to the finite volume moments by studying the spatial dependence of the lattice correlation functions. This method permits the computation of not only the values of matrix elements at momenta accessible on the lattice, but also the momentum-space derivatives, providing {\\it a priori} information about the Q2 dependence of form factors. As a specific application we use the method, at a single lattice spacing and with unphysically heavy quarks, to directly obtain the slope of the isovector form factor at various Q2, whence the isovector charge radius. The method has potential application in the calculation of any hadronic matrix element with momentum transfer, including those relevant to hadronic weak decays.
Method of Second Cross-Correlation
NASA Astrophysics Data System (ADS)
Tanimoto, T.; Alvizuri, C.
2008-12-01
In a high frequency band above 1 Hz, the Noise Cross-Correlation method works because of multiple scattering but in a lower frequency band, say below 0.2 Hz, it works mainly because of wide distribution of sources as effects from multiple scattering are much smaller. As noise-source locations change seasonably, seasonal variations are often seen in the correlated seismograms (first correlogram). In Southern California, weaker signals are seen in summer because of weaker ocean waves. Source distribution also introduces another problem; near the coast, it is often found that the paths perpendicular to the coast show good signal in correlograms but the paths parallel to the coast do not necessarily contain good signals. This is directly related to the source locations, i.e., ocean waves in low frequency bands. This feature does harm in tomographic studies, especially for the recovery of azimuthal anisotropy, as measurements from all azimuths are the key to its success. One method to circumvent this problem is the method of Second Cross-Correlation. This method computes cross-correlations of Greens function that have been obtained by the noise cross-correlation method. We call it here as Second Cross-Correlation and refer to correlated seismograms as second correlograms. Campillo et al. (2008) showed an application to coda in Greens functions for the first time but in this study we focus on the entire waveforms. We present theoretical analysis of this method with some examples from Southern California. It works for a relatively dense array of network only, but such dense arrays are available in many parts of the world now. We extend our theoretical analysis in Tanimoto (2008) for first correlograms which was a full normal-mode- theory version of theories developed by Snieder (2004), Roux et al. (2005) and Wapenaar (2004). There are some distinct features in second correlograms; for example, while an ordinary (first) correlogram depends on f**2, where f is the source
On soft limits of inflationary correlation functions
Assassi, Valentin; Baumann, Daniel; Green, Daniel E-mail: dbaumann@damtp.cam.ac.uk
2012-11-01
Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.
On soft limits of inflationary correlation functions
NASA Astrophysics Data System (ADS)
Assassi, Valentin; Baumann, Daniel; Green, Daniel
2012-11-01
Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.
Nuclear correlation functions in lattice QCD
Detmold, William; Orginos, Konstantinos
2013-06-01
We consider the problem of calculating the large number of Wick contractions necessary to compute states with the quantum numbers of many baryons in lattice QCD. We consider a constructive approach and a determinant-based approach and show that these methods allow the required contractions to be performed for certain choices of interpolating operators. Examples of correlation functions computed using these techniques are shown for the quantum numbers of the light nuclei, $^4$He, $^8$Be, $^{12}$C, $^{16}$O and $^{28}$Si.
Bikondoa, Oier
2017-04-01
Multi-time correlation functions are especially well suited to study non-equilibrium processes. In particular, two-time correlation functions are widely used in X-ray photon correlation experiments on systems out of equilibrium. One-time correlations are often extracted from two-time correlation functions at different sample ages. However, this way of analysing two-time correlation functions is not unique. Here, two methods to analyse two-time correlation functions are scrutinized, and three illustrative examples are used to discuss the implications for the evaluation of the correlation times and functional shape of the correlations.
On the use of two-time correlation functions for X-ray photon correlation spectroscopy data analysis
Bikondoa, Oier
2017-01-01
Multi-time correlation functions are especially well suited to study non-equilibrium processes. In particular, two-time correlation functions are widely used in X-ray photon correlation experiments on systems out of equilibrium. One-time correlations are often extracted from two-time correlation functions at different sample ages. However, this way of analysing two-time correlation functions is not unique. Here, two methods to analyse two-time correlation functions are scrutinized, and three illustrative examples are used to discuss the implications for the evaluation of the correlation times and functional shape of the correlations. PMID:28381968
RECONSTRUCTING THE SHAPE OF THE CORRELATION FUNCTION
Huffenberger, K. M.; Galeazzi, M.; Ursino, E.
2013-06-01
We develop an estimator for the correlation function which, in the ensemble average, returns the shape of the correlation function, even for signals that have significant correlations on the scale of the survey region. Our estimator is general and works in any number of dimensions. We develop versions of the estimator for both diffuse and discrete signals. As an application, we apply them to Monte Carlo simulations of X-ray background measurements. These include a realistic, spatially inhomogeneous population of spurious detector events. We discuss applying the estimator to the averaging of correlation functions evaluated on several small fields, and to other cosmological applications.
BONNSAI: correlated stellar observables in Bayesian methods
NASA Astrophysics Data System (ADS)
Schneider, F. R. N.; Castro, N.; Fossati, L.; Langer, N.; de Koter, A.
2017-02-01
In an era of large spectroscopic surveys of stars and big data, sophisticated statistical methods become more and more important in order to infer fundamental stellar parameters such as mass and age. Bayesian techniques are powerful methods because they can match all available observables simultaneously to stellar models while taking prior knowledge properly into account. However, in most cases it is assumed that observables are uncorrelated which is generally not the case. Here, we include correlations in the Bayesian code Bonnsai by incorporating the covariance matrix in the likelihood function. We derive a parametrisation of the covariance matrix that, in addition to classical uncertainties, only requires the specification of a correlation parameter that describes how observables co-vary. Our correlation parameter depends purely on the method with which observables have been determined and can be analytically derived in some cases. This approach therefore has the advantage that correlations can be accounted for even if information for them are not available in specific cases but are known in general. Because the new likelihood model is a better approximation of the data, the reliability and robustness of the inferred parameters are improved. We find that neglecting correlations biases the most likely values of inferred stellar parameters and affects the precision with which these parameters can be determined. The importance of these biases depends on the strength of the correlations and the uncertainties. For example, we apply our technique to massive OB stars, but emphasise that it is valid for any type of stars. For effective temperatures and surface gravities determined from atmosphere modelling, we find that masses can be underestimated on average by 0.5σ and mass uncertainties overestimated by a factor of about 2 when neglecting correlations. At the same time, the age precisions are underestimated over a wide range of stellar parameters. We conclude that
Detecting correlations among functional-sequence motifs
NASA Astrophysics Data System (ADS)
Pirino, Davide; Rigosa, Jacopo; Ledda, Alice; Ferretti, Luca
2012-06-01
Sequence motifs are words of nucleotides in DNA with biological functions, e.g., gene regulation. Identification of such words proceeds through rejection of Markov models on the expected motif frequency along the genome. Additional biological information can be extracted from the correlation structure among patterns of motif occurrences. In this paper a log-linear multivariate intensity Poisson model is estimated via expectation maximization on a set of motifs along the genome of E. coli K12. The proposed approach allows for excitatory as well as inhibitory interactions among motifs and between motifs and other genomic features like gene occurrences. Our findings confirm previous stylized facts about such types of interactions and shed new light on genome-maintenance functions of some particular motifs. We expect these methods to be applicable to a wider set of genomic features.
Correlation functions on a curved background
NASA Astrophysics Data System (ADS)
Knorr, Benjamin; Lippoldt, Stefan
2017-09-01
We investigate gravitational correlation functions in a curved background with the help of nonperturbative renormalization group methods. Beta functions for eleven couplings are derived, two of which correspond to running gauge parameters. A unique ultraviolet fixed point is found, suitable for a UV completion in the sense of Asymptotic Safety. To arrive at a well-behaved flow in a curved background, the regularization must be chosen carefully. We provide two admissible choices to solve this issue in the present approximation. We further demonstrate by an explicit calculation that the Landau limit is a fixed point also for quantum gravity, and additionally show that in this limit, the gauge parameter β does not flow.
Dynamic functional network connectivity using distance correlation
NASA Astrophysics Data System (ADS)
Rudas, Jorge; Guaje, Javier; Demertzi, Athena; Heine, Lizette; Tshibanda, Luaba; Soddu, Andrea; Laureys, Steven; Gómez, Francisco
2015-01-01
Investigations about the intrinsic brain organization in resting-state are critical for the understanding of healthy, pathological and pharmacological cerebral states. Recent studies on fMRI suggest that resting state activity is organized on large scale networks of coordinated activity, in the so called, Resting State Networks (RSNs). The assessment of the interactions among these functional networks plays an important role for the understanding of different brain pathologies. Current methods to quantify these interactions commonly assume that the underlying coordination mechanisms are stationary and linear through the whole recording of the resting state phenomena. Nevertheless, recent evidence suggests that rather than stationary, these mechanisms may exhibit a rich set of time-varying repertoires. In addition, these approaches do not consider possible non-linear relationships maybe linked to feed-back communication mechanisms between RSNs. In this work, we introduce a novel approach for dynamical functional network connectivity for functional magnetic resonance imaging (fMRI) resting activity, which accounts for non-linear dynamic relationships between RSNs. The proposed method is based on a windowed distance correlations computed on resting state time-courses extracted at single subject level. We showed that this strategy is complementary to the current approaches for dynamic functional connectivity and will help to enhance the discrimination capacity of patients with disorder of consciousness.
Dynamical dimer-dimer correlation functions from exact diagonalization
Werner, Ralph
2001-05-01
A regularization method is presented to deduce dynamic correlation functions from exact diagonalization calculations. It is applied to dimer-dimer correlation functions in quantum spin chains relevant for the description of spin-Peierls systems. Exact results for the XY model are presented. The analysis draws into doubt that the dimer-dimer correlation functions show the same scale invariance as spin-spin correlation functions. The results are applied to describe the quasielastic scattering in CuGeO{sub 3} and the hardening of the Peierls-active phonons.
Pfaffian Correlation Functions of Planar Dimer Covers
NASA Astrophysics Data System (ADS)
Aizenman, Michael; Valcázar, Manuel Laínz; Warzel, Simone
2017-01-01
The Pfaffian structure of the boundary monomer correlation functions in the dimer-covering planar graph models is rederived through a combinatorial/topological argument. These functions are then extended into a larger family of order-disorder correlation functions which are shown to exhibit Pfaffian structure throughout the bulk. Key tools involve combinatorial switching symmetries which are identified through the loop-gas representation of the double dimer model, and topological implications of planarity.
Note on correlation functions in conformal quantum mechanics
NASA Astrophysics Data System (ADS)
Khodaee, Sadi; Vassilevich, Dmitri
2017-09-01
We suggest a method to compute the correlation functions in conformal quantum mechanics (CFT1) for the fields that transform under a nonlocal representation of 𝔰𝔩(2) basing on the invariance properties. Explicit calculations of two- and three-point correlation functions are presented.
Accurate method for computing correlated color temperature.
Li, Changjun; Cui, Guihua; Melgosa, Manuel; Ruan, Xiukai; Zhang, Yaoju; Ma, Long; Xiao, Kaida; Luo, M Ronnier
2016-06-27
For the correlated color temperature (CCT) of a light source to be estimated, a nonlinear optimization problem must be solved. In all previous methods available to compute CCT, the objective function has only been approximated, and their predictions have achieved limited accuracy. For example, different unacceptable CCT values have been predicted for light sources located on the same isotemperature line. In this paper, we propose to compute CCT using the Newton method, which requires the first and second derivatives of the objective function. Following the current recommendation by the International Commission on Illumination (CIE) for the computation of tristimulus values (summations at 1 nm steps from 360 nm to 830 nm), the objective function and its first and second derivatives are explicitly given and used in our computations. Comprehensive tests demonstrate that the proposed method, together with an initial estimation of CCT using Robertson's method [J. Opt. Soc. Am. 58, 1528-1535 (1968)], gives highly accurate predictions below 0.0012 K for light sources with CCTs ranging from 500 K to 10^{6} K.
NASA Astrophysics Data System (ADS)
Myo, Takayuki; Toki, Hiroshi; Ikeda, Kiyomi; Horiuchi, Hisashi; Suhara, Tadahiro
2017-09-01
We developed a new variational method for tensor-optimized antisymmetrized molecular dynamics (TOAMD) for nuclei. In TOAMD, the correlation functions for the tensor force and the short-range repulsion are introduced and used in the power series form of the wave function, which is different from the Jastrow method. Here, nucleon pairs are correlated in multisteps with different forms, while they are correlated only once including all pairs in the Jastrow correlation method. Each correlation function in every term is independently optimized in the variation of total energy in TOAMD. For s -shell nuclei using the nucleon-nucleon interaction, the energies in TOAMD are better than those in the variational Monte Carlo method with the Jastrow correlation function. This means that the power series expansion using the correlation functions in TOAMD describes the nuclei better than the Jastrow correlation method.
Off-forward quark-quark correlation function
Casanova, Sabrina
2006-09-01
The properties of the nonforward quark-quark correlation function are examined. We derive constraints on the correlation function from the transformation properties of the fundamental fields of QCD occurring in its definition. We further develop a method to construct an Ansatz for this correlator. We present the complete leading order set of generalized parton distributions in terms of the amplitudes of the Ansatz. Finally we conclude that the number of independent generalized parton helicity changing distributions is four.
On the measurability of quantum correlation functions
NASA Astrophysics Data System (ADS)
de Lima Bernardo, Bertúlio; Azevedo, Sérgio; Rosas, Alexandre
2015-05-01
The concept of correlation function is widely used in classical statistical mechanics to characterize how two or more variables depend on each other. In quantum mechanics, on the other hand, there are observables that cannot be measured at the same time; the so-called incompatible observables. This prospect imposes a limitation on the definition of a quantum analog for the correlation function in terms of a sequence of measurements. Here, based on the notion of sequential weak measurements, we circumvent this limitation by introducing a framework to measure general quantum correlation functions, in principle, independently of the state of the system and the operators involved. To illustrate, we propose an experimental configuration to obtain explicitly the quantum correlation function between two Pauli operators, in which the input state is an arbitrary mixed qubit state encoded on the polarization of photons.
On the measurability of quantum correlation functions
Lima Bernardo, Bertúlio de Azevedo, Sérgio; Rosas, Alexandre
2015-05-15
The concept of correlation function is widely used in classical statistical mechanics to characterize how two or more variables depend on each other. In quantum mechanics, on the other hand, there are observables that cannot be measured at the same time; the so-called incompatible observables. This prospect imposes a limitation on the definition of a quantum analog for the correlation function in terms of a sequence of measurements. Here, based on the notion of sequential weak measurements, we circumvent this limitation by introducing a framework to measure general quantum correlation functions, in principle, independently of the state of the system and the operators involved. To illustrate, we propose an experimental configuration to obtain explicitly the quantum correlation function between two Pauli operators, in which the input state is an arbitrary mixed qubit state encoded on the polarization of photons.
Generalized hydrodynamic correlations and fractional memory functions
NASA Astrophysics Data System (ADS)
Rodríguez, Rosalio F.; Fujioka, Jorge
2015-12-01
A fractional generalized hydrodynamic (GH) model of the longitudinal velocity fluctuations correlation, and its associated memory function, for a complex fluid is analyzed. The adiabatic elimination of fast variables introduces memory effects in the transport equations, and the dynamic of the fluctuations is described by a generalized Langevin equation with long-range noise correlations. These features motivate the introduction of Caputo time fractional derivatives and allows us to calculate analytic expressions for the fractional longitudinal velocity correlation function and its associated memory function. Our analysis eliminates a spurious constant term in the non-fractional memory function found in the non-fractional description. It also produces a significantly slower power-law decay of the memory function in the GH regime that reduces to the well-known exponential decay in the non-fractional Navier-Stokes limit.
From correlation functions to event shapes
NASA Astrophysics Data System (ADS)
Belitsky, A. V.; Hohenegger, S.; Korchemsky, G. P.; Sokatchev, E.; Zhiboedov, A.
2014-07-01
We present a new approach to computing event shape distributions or, more precisely, charge flow correlations in a generic conformal field theory (CFT). These infrared finite observables are familiar from collider physics studies and describe the angular distribution of global charges in outgoing radiation created from the vacuum by some source. The charge flow correlations can be expressed in terms of Wightman correlation functions in a certain limit. We explain how to compute these quantities starting from their Euclidean analogues by means of a nontrivial analytic continuation which, in the framework of CFT, can be performed elegantly in Mellin space. The relation between the charge flow correlations and Euclidean correlation functions can be reformulated directly in configuration space, bypassing the Mellin representation, as a certain Lorentzian double discontinuity of the correlation function integrated along the cuts. We illustrate the general formalism in N=4 SYM, making use of the well-known results on the four-point correlation function of half-BPS scalar operators. We compute the double scalar flow correlation in N=4 SYM, at weak and strong coupling and show that it agrees with known results obtained by different techniques. One of the remarkable features of the N=4 theory is that the scalar and energy flow correlations are proportional to each other. Imposing natural physical conditions on the energy flow correlations (finiteness, positivity and regularity), we formulate additional constraints on the four-point correlation functions in N=4 SYM that should be valid at any coupling and away from the planar limit. presence of intrinsic infrared (IR) divergences; integration over the phase space of the final state and subsequent intricate IR cancellations; necessity for summation over all final states. Let us comment on each of these points. They are very well understood in the context of perturbation theory no IR divergences are present in the correlation
Chen, Shentan; Raugei, Simone; Rousseau, Roger; Dupuis, Michel; Bullock, R. Morris
2010-12-09
A systematic assessment of theoretical methods applicable to the accurate characterization of catalytic cycles of homogeneous catalysts for H_{2} oxidation and evolution is reported. The key elementary steps involve heterolytic cleavage of the H-H bond and formation/cleavage of Ni-H and N-H bonds. In the context of density functional theory (DFT), we investigated the use of functionals in the generalized gradient approximation (GGA) as well as hybrid functionals. We compared the results with wave-function theories based on perturbation theory (MP2 and MP4) and on coupled-cluster expansions [CCD, CCSD, and CCSD(T)]. Our findings indicate that DFT results based on Perdew correlation functionals are in semiquantitative agreement with the CCSD(T) results, with deviations of only a few kilocalories/mole. On the other hand, the B3LYP functional is not even in qualitative agreement with CCSD(T). Surprisingly, the MP2 results are found to be extremely poor, in particular for the diproton Ni(0) and dihydride Ni(IV) species on the reaction potential energy surface. The Hartree-Fock reference wave function in MP2 theory gives a poor reference state description for these states that are electron rich on Ni, giving rise to erroneous MP2 energies. Finally, we present a detailed potential-energy diagram for the oxidation of H_{2} by these catalysts after accounting for the effects of solvation, as modeled by a polarizable continuum, and of free energy estimated at the harmonic level of theory.
Garofalo, Matteo; Nieus, Thierry; Massobrio, Paolo; Martinoia, Sergio
2009-01-01
Functional connectivity of in vitro neuronal networks was estimated by applying different statistical algorithms on data collected by Micro-Electrode Arrays (MEAs). First we tested these “connectivity methods” on neuronal network models at an increasing level of complexity and evaluated the performance in terms of ROC (Receiver Operating Characteristic) and PPC (Positive Precision Curve), a new defined complementary method specifically developed for functional links identification. Then, the algorithms better estimated the actual connectivity of the network models, were used to extract functional connectivity from cultured cortical networks coupled to MEAs. Among the proposed approaches, Transfer Entropy and Joint-Entropy showed the best results suggesting those methods as good candidates to extract functional links in actual neuronal networks from multi-site recordings. PMID:19652720
Image correlation method for DNA sequence alignment.
Curilem Saldías, Millaray; Villarroel Sassarini, Felipe; Muñoz Poblete, Carlos; Vargas Vásquez, Asticio; Maureira Butler, Iván
2012-01-01
The complexity of searches and the volume of genomic data make sequence alignment one of bioinformatics most active research areas. New alignment approaches have incorporated digital signal processing techniques. Among these, correlation methods are highly sensitive. This paper proposes a novel sequence alignment method based on 2-dimensional images, where each nucleic acid base is represented as a fixed gray intensity pixel. Query and known database sequences are coded to their pixel representation and sequence alignment is handled as object recognition in a scene problem. Query and database become object and scene, respectively. An image correlation process is carried out in order to search for the best match between them. Given that this procedure can be implemented in an optical correlator, the correlation could eventually be accomplished at light speed. This paper shows an initial research stage where results were "digitally" obtained by simulating an optical correlation of DNA sequences represented as images. A total of 303 queries (variable lengths from 50 to 4500 base pairs) and 100 scenes represented by 100 x 100 images each (in total, one million base pair database) were considered for the image correlation analysis. The results showed that correlations reached very high sensitivity (99.01%), specificity (98.99%) and outperformed BLAST when mutation numbers increased. However, digital correlation processes were hundred times slower than BLAST. We are currently starting an initiative to evaluate the correlation speed process of a real experimental optical correlator. By doing this, we expect to fully exploit optical correlation light properties. As the optical correlator works jointly with the computer, digital algorithms should also be optimized. The results presented in this paper are encouraging and support the study of image correlation methods on sequence alignment.
Image Correlation Method for DNA Sequence Alignment
Curilem Saldías, Millaray; Villarroel Sassarini, Felipe; Muñoz Poblete, Carlos; Vargas Vásquez, Asticio; Maureira Butler, Iván
2012-01-01
The complexity of searches and the volume of genomic data make sequence alignment one of bioinformatics most active research areas. New alignment approaches have incorporated digital signal processing techniques. Among these, correlation methods are highly sensitive. This paper proposes a novel sequence alignment method based on 2-dimensional images, where each nucleic acid base is represented as a fixed gray intensity pixel. Query and known database sequences are coded to their pixel representation and sequence alignment is handled as object recognition in a scene problem. Query and database become object and scene, respectively. An image correlation process is carried out in order to search for the best match between them. Given that this procedure can be implemented in an optical correlator, the correlation could eventually be accomplished at light speed. This paper shows an initial research stage where results were “digitally” obtained by simulating an optical correlation of DNA sequences represented as images. A total of 303 queries (variable lengths from 50 to 4500 base pairs) and 100 scenes represented by 100 x 100 images each (in total, one million base pair database) were considered for the image correlation analysis. The results showed that correlations reached very high sensitivity (99.01%), specificity (98.99%) and outperformed BLAST when mutation numbers increased. However, digital correlation processes were hundred times slower than BLAST. We are currently starting an initiative to evaluate the correlation speed process of a real experimental optical correlator. By doing this, we expect to fully exploit optical correlation light properties. As the optical correlator works jointly with the computer, digital algorithms should also be optimized. The results presented in this paper are encouraging and support the study of image correlation methods on sequence alignment. PMID:22761742
Triplet correlation functions in liquid water
Dhabal, Debdas; Chakravarty, Charusita; Singh, Murari; Wikfeldt, Kjartan Thor
2014-11-07
Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O–O–O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O–O–O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed.
Triplet correlation functions in liquid water
NASA Astrophysics Data System (ADS)
Dhabal, Debdas; Singh, Murari; Wikfeldt, Kjartan Thor; Chakravarty, Charusita
2014-11-01
Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O-O-O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O-O-O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed.
Correlation function of the luminosity distances
NASA Astrophysics Data System (ADS)
Biern, Sang Gyu; Yoo, Jaiyul
2017-09-01
We present the correlation function of the luminosity distances in a flat ΛCDM universe. Decomposing the luminosity distance fluctuation into the velocity, the gravitational potential, and the lensing contributions in linear perturbation theory, we study their individual contributions to the correlation function. The lensing contribution is important at large redshift (z gtrsim 0.5) but only for small angular separation (θ lesssim 3°), while the velocity contribution dominates over the other contributions at low redshift or at larger separation. However, the gravitational potential contribution is always subdominant at all scale, if the correct gauge-invariant expression is used. The correlation function of the luminosity distances depends significantly on the matter content, especially for the lensing contribution, thus providing a novel tool of estimating cosmological parameters.
Noninvasive measurement of dynamic correlation functions
NASA Astrophysics Data System (ADS)
Uhrich, Philipp; Castrignano, Salvatore; Uys, Hermann; Kastner, Michael
2017-08-01
The measurement of dynamic correlation functions of quantum systems is complicated by measurement backaction. To facilitate such measurements we introduce a protocol, based on weak ancilla-system couplings, that is applicable to arbitrary (pseudo)spin systems and arbitrary equilibrium or nonequilibrium initial states. Different choices of the coupling operator give access to the real and imaginary parts of the dynamic correlation function. This protocol reduces disturbances due to the early-time measurements to a minimum, and we quantify the deviation of the measured correlation functions from the theoretical, unitarily evolved ones. Implementations of the protocol in trapped ions and other experimental platforms are discussed. For spin-1 /2 models and single-site observables we prove that measurement backaction can be avoided altogether, allowing for the use of ancilla-free protocols.
Hierarchy of equations of multiple-time correlation functions
Alonso, Daniel; Vega, Ines de
2007-05-15
In this paper we derive the evolution equations for non-Markovian multiple-time correlation functions of an open quantum system without using any approximation. We find that these equations conform an open hierarchy in which N-time correlation functions are dependent on (N+1)-time correlations. This hierarchy of equations is consistently obtained with two different methods: A first one based on Heisenberg equations of system operators, and a second one based on system propagators. The dependency on higher order correlations, and therefore the open hierarchy structure, only disappears in certain particular cases and when some hypothesis or approximations are considered in the equations. In this paper we consider a perturbative approximation and derive the general evolution equation for N-time correlations. This equation turns to depend only on N-time and lower order correlation functions, conforming a closed hierarchy structure that is useful for computational purposes.
Correlation functions of Coulomb branch operators
NASA Astrophysics Data System (ADS)
Gerchkovitz, Efrat; Gomis, Jaume; Ishtiaque, Nafiz; Karasik, Avner; Komargodski, Zohar; Pufu, Silviu S.
2017-01-01
We consider the correlation functions of Coulomb branch operators in four-dimensional N = 2 Superconformal Field Theories (SCFTs) involving exactly one antichiral operator. These extremal correlators are the "minimal" non-holomorphic local observables in the theory. We show that they can be expressed in terms of certain determinants of derivatives of the four-sphere partition function of an appropriate deformation of the SCFT. This relation between the extremal correlators and the deformed four-sphere partition function is non-trivial due to the presence of conformal anomalies, which lead to operator mixing on the sphere. Evaluating the deformed four-sphere partition function using supersymmetric localization, we compute the extremal correlators explicitly in many interesting examples. Additionally, the representation of the extremal correlators mentioned above leads to a system of integrable differential equations. We compare our exact results with previous perturbative computations and with the four-dimensional tt ∗ equations. We also use our results to study some of the asymptotic properties of the perturbative series expansions we obtain in N = 2 SQCD.
SMJ's analysis of Ising model correlation functions
NASA Astrophysics Data System (ADS)
Kadanoff, Leo P.; Kohmoto, Mahito
1980-05-01
In a series of recent publications Sato, Miwa, and Jimbo (SMJ) have shown how to derive multispin correlation functions of the two-dimensional Ising model in the continuum, or scaling, limit by analyzing the behavior of the solutions to the two-dimensional version of the Dirac equation. The major purpose of the present work is to describe SMJ's analysis more discursively and in terms closer to that used in previous studies of the Ising model. In addition, new and more compact expressions for their basic equations are derived. A single new answer is obtained: the form of the three-spin correlation function at criticality.
Semiclassical approximations to quantum time correlation functions
NASA Astrophysics Data System (ADS)
Egorov, S. A.; Skinner, J. L.
1998-09-01
Over the last 40 years several ad hoc semiclassical approaches have been developed in order to obtain approximate quantum time correlation functions, using as input only the corresponding classical time correlation functions. The accuracy of these approaches has been tested for several exactly solvable gas-phase models. In this paper we test the accuracy of these approaches by comparing to an exactly solvable many-body condensed-phase model. We show that in the frequency domain the Egelstaff approach is the most accurate, especially at high frequencies, while in the time domain one of the other approaches is more accurate.
Group entropies, correlation laws, and zeta functions
NASA Astrophysics Data System (ADS)
Tempesta, Piergiulio
2011-08-01
The notion of group entropy is proposed. It enables the unification and generaliztion of many different definitions of entropy known in the literature, such as those of Boltzmann-Gibbs, Tsallis, Abe, and Kaniadakis. Other entropic functionals are introduced, related to nontrivial correlation laws characterizing universality classes of systems out of equilibrium when the dynamics is weakly chaotic. The associated thermostatistics are discussed. The mathematical structure underlying our construction is that of formal group theory, which provides the general structure of the correlations among particles and dictates the associated entropic functionals. As an example of application, the role of group entropies in information theory is illustrated and generalizations of the Kullback-Leibler divergence are proposed. A new connection between statistical mechanics and zeta functions is established. In particular, Tsallis entropy is related to the classical Riemann zeta function.
Permutation method for evaluating topographic craniofacial correlations.
Halazonetis, Demetrios J
2011-03-01
Correlations between cephalometric measurements are frequently assumed to represent biologic associations. However, a significant portion of such correlations might arise from purely geometric dependencies, when measurements share common landmarks. Analytic calculation of this topographic component is difficult. The purpose of this study was to propose a permutation method for evaluating the topographic component of cephalometric correlations. The method consisted of creating a virtual sample of cephalometric tracings (landmark configurations) from the original biologic sample under investigation. Each novel landmark configuration was constructed by assigning coordinates to the cephalometric points; the coordinates of each point were taken randomly from the original sample, each from a potentially different subject. Correlation analysis was performed separately on both samples and the results compared. Biologic meaning was ascribed only when there was a significant difference in correlation values between the samples. Confidence intervals for assessing statistical significance were calculated by using a randomization approach. The method was tested on a sample of 170 radiographs to evaluate the correlation between cranial base angle (NSBa) and angles SNA and SNB, as well as between ANB angle and the Wits appraisal. No biologic association was found between ANB and Wits, or between NSBa and SNA. The biologic correlation between NSBa and SNB was statistically significant but low (r(2) = 12%). Topographic associations between cephalometric measurements are ubiquitous and difficult to assess. The proposed method enables evaluation of their relative strength without the need for analytic solutions. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.
Correlation Functions Aid Analyses Of Spectra
NASA Technical Reports Server (NTRS)
Beer, Reinhard; Norton, Robert H., Jr.
1989-01-01
New uses found for correlation functions in analyses of spectra. In approach combining elements of both pattern-recognition and traditional spectral-analysis techniques, spectral lines identified in data appear useless at first glance because they are dominated by noise. New approach particularly useful in measurement of concentrations of rare species of molecules in atmosphere.
Self-calibrated correlation imaging with k-space variant correlation functions.
Li, Yu; Edalati, Masoud; Du, Xingfu; Wang, Hui; Cao, Jie J
2017-07-07
Correlation imaging is a previously developed high-speed MRI framework that converts parallel imaging reconstruction into the estimate of correlation functions. The presented work aims to demonstrate this framework can provide a speed gain over parallel imaging by estimating k-space variant correlation functions. Because of Fourier encoding with gradients, outer k-space data contain higher spatial-frequency image components arising primarily from tissue boundaries. As a result of tissue-boundary sparsity in the human anatomy, neighboring k-space data correlation varies from the central to the outer k-space. By estimating k-space variant correlation functions with an iterative self-calibration method, correlation imaging can benefit from neighboring k-space data correlation associated with both coil sensitivity encoding and tissue-boundary sparsity, thereby providing a speed gain over parallel imaging that relies only on coil sensitivity encoding. This new approach is investigated in brain imaging and free-breathing neonatal cardiac imaging. Correlation imaging performs better than existing parallel imaging techniques in simulated brain imaging acceleration experiments. The higher speed enables real-time data acquisition for neonatal cardiac imaging in which physiological motion is fast and non-periodic. With k-space variant correlation functions, correlation imaging gives a higher speed than parallel imaging and offers the potential to image physiological motion in real-time. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.
Nonclassicality criteria: Quasiprobability distributions and correlation functions
NASA Astrophysics Data System (ADS)
Alexanian, Moorad
2016-10-01
We use the exact calculation of the quantum mechanical, temporal characteristic function χ (η ) and the degree of second-order coherence g(2 )(τ ) for a single-mode, degenerate parametric amplifier for a system in the Gaussian state, viz., a displaced-squeezed thermal state, to study the different criteria for nonclassicality. In particular, we contrast criteria that involve only one-time functions of the dynamical system, for instance, the quasiprobability distribution P (β ) of the Glauber-Sudarshan coherent or P representation of the density of state and the Mandel QM(τ ) parameter, versus the criteria associated with the two-time correlation function g(2 )(τ ) .
Correlates of functional capacity among centenarians.
Martin, Peter; MacDonald, Maurice; Margrett, Jennifer; Siegler, Ilene; Poon, Leonard W; Jazwinski, S M; Green, R C; Gearing, M; Markesbery, W R; Woodard, J L; Johnson, M A; Tenover, J S; Rodgers, W L; Hausman, D B; Rott, C; Davey, A; Arnold, J
2013-04-01
This study investigated correlates of functional capacity among participants of the Georgia Centenarian Study. Six domains (demographics and health, positive and negative affect, personality, social and economic support, life events and coping, distal influences) were related to functional capacity for 234 centenarians and near centenarians (i.e., 98 years and older). Data were provided by proxy informants. Domain-specific multiple regression analyses suggested that younger centenarians, those living in the community and rated to be in better health were more likely to have higher functional capacity scores. Higher scores in positive affect, conscientiousness, social provisions, religious coping, and engaged lifestyle were also associated with higher levels of functional capacity. The results suggest that functional capacity levels continue to be associated with age after 100 years of life and that positive affect levels and past lifestyle activities as reported by proxies are salient factors of adaptation in very late life.
Vyboishchikov, Sergei F
2017-09-03
We propose a simple method of calculating the electron correlation energy density e_c(r) and the correlation potential V_c(r) from second-order Møller-Plesset amplitudes and its generalization for the case of a Configuration Interaction wavefunction, based on Nesbet's theorem. The correlation energy density obtained by this method for free and spherically confined Be and He atoms was employed to fit a local analytical density functional based on Wigner's functional. The functional is capable to reproduce a strong increase of the correlation energy with decreasing the confined radius for the Be atom. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Efficient quantum algorithm for computing n-time correlation functions.
Pedernales, J S; Di Candia, R; Egusquiza, I L; Casanova, J; Solano, E
2014-07-11
We propose a method for computing n-time correlation functions of arbitrary spinorial, fermionic, and bosonic operators, consisting of an efficient quantum algorithm that encodes these correlations in an initially added ancillary qubit for probe and control tasks. For spinorial and fermionic systems, the reconstruction of arbitrary n-time correlation functions requires the measurement of two ancilla observables, while for bosonic variables time derivatives of the same observables are needed. Finally, we provide examples applicable to different quantum platforms in the frame of the linear response theory.
A method for detecting complex correlation in time series
NASA Astrophysics Data System (ADS)
Alfi, V.; Petri, A.; Pietronero, L.
2007-06-01
We propose a new method for detecting complex correlations in time series of limited size. The method is derived by the Spitzer's identity and proves to work successfully on different model processes, including the ARCH process, in which pairs of variables are uncorrelated, but the three point correlation function is non zero. The application to financial data allows to discriminate among dependent and independent stock price returns where standard statistical analysis fails.
The correlation function of galaxy ellipticities produced by gravitational lensing
NASA Technical Reports Server (NTRS)
Miralda-Escude, Jordi
1991-01-01
The correlation of galaxy ellipticities produced by gravitational lensing is calculated as a function of the power spectrum of density fluctuations in the universe by generalizing an analytical method developed by Gunn (1967). The method is applied to a model where identical objects with spherically symmetric density profiles are randomly laid down in space, and to the cold dark matter model. The possibility of detecting this correlation is discussed. Although an ellipticity correlation can also be caused by an intrinsic alignment of the axes of galaxies belonging to a cluster or a supercluster, a method is suggested by which one type of correlation can be distinguished from another. The advantage of this ellipticity correlation is that it is one of the few astronomical observations that can directly probe large-scale mass fluctuations in the universe.
Baryons with functional methods
NASA Astrophysics Data System (ADS)
Fischer, Christian S.
2017-01-01
We summarise recent results on the spectrum of ground-state and excited baryons and their form factors in the framework of functional methods. As an improvement upon similar approaches we explicitly take into account the underlying momentum-dependent dynamics of the quark-gluon interaction that leads to dynamical chiral symmetry breaking. For light octet and decuplet baryons we find a spectrum in very good agreement with experiment, including the level ordering between the positive- and negative-parity nucleon states. Comparing the three-body framework with the quark-diquark approximation, we do not find significant differences in the spectrum for those states that have been calculated in both frameworks. This situation is different in the electromagnetic form factor of the Δ, which may serve to distinguish both pictures by comparison with experiment and lattice QCD.
A Kinematically Consistent Two-Point Correlation Function
NASA Technical Reports Server (NTRS)
Ristorcelli, J. R.
1998-01-01
A simple kinematically consistent expression for the longitudinal two-point correlation function related to both the integral length scale and the Taylor microscale is obtained. On the inner scale, in a region of width inversely proportional to the turbulent Reynolds number, the function has the appropriate curvature at the origin. The expression for two-point correlation is related to the nonlinear cascade rate, or dissipation epsilon, a quantity that is carried as part of a typical single-point turbulence closure simulation. Constructing an expression for the two-point correlation whose curvature at the origin is the Taylor microscale incorporates one of the fundamental quantities characterizing turbulence, epsilon, into a model for the two-point correlation function. The integral of the function also gives, as is required, an outer integral length scale of the turbulence independent of viscosity. The proposed expression is obtained by kinematic arguments; the intention is to produce a practically applicable expression in terms of simple elementary functions that allow an analytical evaluation, by asymptotic methods, of diverse functionals relevant to single-point turbulence closures. Using the expression devised an example of the asymptotic method by which functionals of the two-point correlation can be evaluated is given.
Multiple soft limits of cosmological correlation functions
Joyce, Austin; Khoury, Justin; Simonović, Marko E-mail: jkhoury@sas.upenn.edu
2015-01-01
We derive novel identities satisfied by inflationary correlation functions in the limit where two external momenta are taken to be small. We derive these statements in two ways: using background-wave arguments and as Ward identities following from the fixed-time path integral. Interestingly, these identities allow us to constrain some of the O(q{sup 2}) components of the soft limit, in contrast to their single-soft analogues. We provide several nontrivial checks of our identities both in the context of resonant non-Gaussianities and in small sound speed models. Additionally, we extend the relation at lowest order in external momenta to arbitrarily many soft legs, and comment on the many-soft extension at higher orders in the soft momentum. Finally, we consider how higher soft limits lead to identities satisfied by correlation functions in large-scale structure.
Redshift distortions of galaxy correlation functions
NASA Technical Reports Server (NTRS)
Fry, J. N.; Gaztanaga, Enrique
1994-01-01
To examine how peculiar velocities can affect the two-, three-, and four-point redshift correlation functions, we evaluate volume-average correlations for configurations that emphasize and minimize redshift distortions for four different volume-limited samples from each of the CfA, SSRS, and IRAS redshift catalogs. We present the results as the correlation length r(sub 0) and power index gamma of the two-point correlations, bar-xi(sub 0) = (r(sub 0)/r)(exp gamma), and as the hierarchical amplitudes of the three- and four-point functions, S(sub 3) = bar-xi(sub 3)/bar-xi(exp 2)(sub 2) and S(sub 4) = bar-xi(sub 4)/bar-xi(exp 3)(sub 2). We find a characteristic distortion for bar-xi(sub 2), the slope gamma is flatter and the correlation length is larger in redshift space than in real space; that is, redshift distortions 'move' correlations from small to large scales. At the largest scales (up to 12 Mpc), the extra power in the redshift distribution is compatible with Omega(exp 4/7)/b approximately equal to 1. We estimate Omega(exp 4/7)/b to be 0.53 +/- 0.15, 1.10 +/- 0.16, and 0.84 +/- 0.45 for the CfA, SSRS, and IRAS catalogs. Higher order correlations bar-xi(sub 3) and bar-xi(sub 4) suffer similar redshift distortions but in such a way that, within the accuracy of our ananlysis, the normalized amplitudes S(sub 3) and S(sub 4) are insensitive to this effect. The hierarchical amplitudes S(sub 3) and S(sub 4) are constant as a function of scale between 1 and 12 Mpc and have similar values in all samples and catalogs, S(sub 3) approximately equal to 2 and S(sub 4) approximately equal to 6, despite the fact that bar-xi(sub 2), bar-xi(sub 3), and bar-xi(sub 4) differ from one sample to another by large factors (up to a factor of 4 in bar-xi(sub 2), 8 for bar-xi(sub 3), and 12 for bar-xi(sub 4)). The agreement between the independent estimations of S(sub 3) and S(sub 4) is remarkable given the different criteria in the selection of galaxies and also the difference in the
Redshift distortions of galaxy correlation functions
NASA Astrophysics Data System (ADS)
Fry, J. N.; Gaztanaga, Enrique
1994-04-01
To examine how peculiar velocities can affect the two-, three-, and four-point redshift correlation functions, we evaluate volume-average correlations for configurations that emphasize and minimize redshift distortions for four different volume-limited samples from each of the CfA, SSRS, and IRAS redshift catalogs. We present the results as the correlation length r0 and power index gamma of the two-point correlations, bar-xi0 = (r0/r)gamma, and as the hierarchical amplitudes of the three- and four-point functions, S3 = bar-xi3/bar-xi22 and S4 = bar-xi4/bar-xi32. We find a characteristic distortion for bar-xi2, the slope gamma is flatter and the correlation length is larger in redshift space than in real space; that is, redshift distortions 'move' correlations from small to large scales. At the largest scales (up to 12 Mpc), the extra power in the redshift distribution is compatible with Omega4/7/b approximately equal to 1. We estimate Omega4/7/b to be 0.53 +/- 0.15, 1.10 +/- 0.16, and 0.84 +/- 0.45 for the CfA, SSRS, and IRAS catalogs. Higher order correlations bar-xi3 and bar-xi4 suffer similar redshift distortions but in such a way that, within the accuracy of our analysis, the normalized amplitudes S3 and S4 are insensitive to this effect. The hierarchical amplitudes S3 and S4 are constant as a function of scale between 1 and 12 Mpc and have similar values in all samples and catalogs, S3 approximately equal to 2 and S4 approximately equal to 6, despite the fact that bar-xi2, bar-xi3, and bar-xi4 differ from one sample to another by large factors (up to a factor of 4 in bar-xi2, 8 for bar-xi3, and 12 for bar-xi4). The agreement between the independent estimations of S3 and S4 is remarkable given the different criteria in the selection of galaxies and also the difference in the resulting range of densities, luminosities, and locations between samples.
Redshift distortions of galaxy correlation functions
NASA Astrophysics Data System (ADS)
Fry, J. N.; Gaztanaga, E.
1993-05-01
To examine how peculiar velocities can affect the 2-, 3-, and 4-point correlation functions, we evaluate volume-average correlations for configurations that emphasize and minimize distortions for four different volume-limited samples from each of the CfA, SSRS, and IRAS redshift catalogs. We present the results as the correlation length r0 and power index gamma of the 2-point correlation, bar-xi2 = (r0/r)gamma), and as the hierarchical amplitudes of the 3- and 4-point functions, S3 = bar-xi3/bar-xi22 and S4 = bar-xi/bar-xi)23. We find a characteristic distortion for bar-xi2: The slope gamma is flatter and the correlation length is larger in redshift space than in real space; that is, redshift distortions 'move' correlations from small to large scales. At the largest scales, extra power in the redshift distribution is compatible with Omega4/7/b approx. 1; we find 0.53 plus/minus 0.15, 1.10 plus/minus 0.16 and 0.84 plus/minus 0.45 for the CfA, SSRS and IRAS catalogs. Higher order correlations bar-xi3 and bar-xi4 suffer similar redshift distortions, but in such a way that, within the accuracy of our analysis, the normalized amplitudes S3 and S4 are insensitive to this effect. The hierarchical amplitudes S3 and S4 are constant as a function of scale between 1-12 h-1 Mpc and have similar values in all samples and catalogues, S3 approx. 2 and S4 approx. 6, despite the fact that bar-xi2, bar-xi3, and bar-xi4 differ from one sample to another by large factors. The agreement between the independent estimations of S3 and S4 is remarkable given the different criteria in the selection of galaxies and also the difference in the resulting range of densities, luminosities and locations between samples.
Correlation Functions of the Magnetization in Thin Films
NASA Astrophysics Data System (ADS)
Rebei, A.; Simionato, M.; Parker, G. J.
2003-05-01
We calculate the correlation functions of uniform magnetization in thin ferromagnetic films for small deviations from equilibrium, by using a functional formalism. To take account of dissipation and fluctuations consistently, the magnetization is coupled to a bosonic heat bath. The correlation functions show strong dependence on the nature of the coupling between the bath and the system. Depending on what coupling we choose, we show how the recent results $(\\text{J. Appl. Phys. 90, 5768 (2001); Phys. Rev. B 65, 172417 (2002)}) $ obtained by macroscopic methods can be related to the microscopic treatment adopted here.
Measuring Omega and the real correlation function from the redshift correlation function
NASA Technical Reports Server (NTRS)
Hamilton, A. J. S.
1992-01-01
Peculiar velocities distort the correlation function of galaxies in redshift space. In the linear regime, the distortion has a characteristic quadrupole plus hexadecapole form. The amplitude of the distortion depends on the cosmological density parameter Omega. Practical formulas are derived here which can be applied to redshift galaxy catalogs to measure Omega in the linear regime. The formulas also yield the real underlying correlation function in the linear regime, corrected for peculiar velocities.
Unified Green's Function Retrieval by Cross Correlation
Wapenaar, Kees; Slob, Evert; Snieder, Roel
2006-12-08
It has been shown by many authors that the cross correlation of two recordings of a diffuse wave field at different receivers yields the Green's function between these receivers. Recently the theory has been extended for situations where time-reversal invariance does not hold (e.g., in attenuating media) and where source-receiver reciprocity breaks down (in moving fluids). Here we present a unified theory for Green's function retrieval that captures all these situations and, because of the unified form, readily extends to more complex situations, such as electrokinetic Green's function retrieval in poroelastic or piezoelectric media. The unified theory has a wide range of applications in ''remote sensing without a source.''.
New angles on energy correlation functions
Moult, Ian; Necib, Lina; Thaler, Jesse
2016-12-29
Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/H tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: M_{i}, N_{i}, and U_{i}. The Mi series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The N_{i} series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the U_{i} series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.
New angles on energy correlation functions
Moult, Ian; Necib, Lina; Thaler, Jesse
2016-12-29
Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/Hmore » tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: Mi, Ni, and Ui. The Mi series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The Ni series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the Ui series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.« less
New angles on energy correlation functions
NASA Astrophysics Data System (ADS)
Moult, Ian; Necib, Lina; Thaler, Jesse
2016-12-01
Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/H tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: M i , N i , and U i . The M i series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The N i series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the U i series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.
Efficient reconstruction of multiphase morphologies from correlation functions
Rozman, M. G.; Utz, Marcel
2001-06-01
A highly efficient algorithm for the reconstruction of microstructures of heterogeneous media from spatial correlation functions is presented. Since many experimental techniques yield two-point correlation functions, the restoration of heterogeneous structures, such as composites, porous materials, microemulsions, ceramics, or polymer blends, is an inverse problem of fundamental importance. Similar to previously proposed algorithms, the new method relies on Monte Carlo optimization, representing the microstructure on a discrete grid. An efficient way to update the correlation functions after local changes to the structure is introduced. In addition, the rate of convergence is substantially enhanced by selective Monte Carlo moves at interfaces. Speedups over prior methods of more than two orders of magnitude are thus achieved. Moreover, an improved minimization protocol leads to additional gains. The algorithm is ideally suited for implementation on parallel computers. The increase in efficiency brings new classes of problems within the realm of the tractable, notably those involving several different structural length scales and/or components.
Two-point correlation functions in inhomogeneous and anisotropic cosmologies
NASA Astrophysics Data System (ADS)
Marcori, Oton H.; Pereira, Thiago S.
2017-02-01
Two-point correlation functions are ubiquitous tools of modern cosmology, appearing in disparate topics ranging from cosmological inflation to late-time astrophysics. When the background spacetime is maximally symmetric, invariance arguments can be used to fix the functional dependence of this function as the invariant distance between any two points. In this paper we introduce a novel formalism which fixes this functional dependence directly from the isometries of the background metric, thus allowing one to quickly assess the overall features of Gaussian correlators without resorting to the full machinery of perturbation theory. As an application we construct the CMB temperature correlation function in one inhomogeneous (namely, an off-center LTB model) and two spatially flat and anisotropic (Bianchi) universes, and derive their covariance matrices in the limit of almost Friedmannian symmetry. We show how the method can be extended to arbitrary N-point correlation functions and illustrate its use by constructing three-point correlation functions in some simple geometries.
Effective theory of squeezed correlation functions
Mirbabayi, Mehrdad; Simonović, Marko E-mail: markos@ias.edu
2016-03-01
Various inflationary scenarios can often be distinguished from one another by looking at the squeezed limit behavior of correlation functions. Therefore, it is useful to have a framework designed to study this limit in a more systematic and efficient way. We propose using an expansion in terms of weakly coupled super-horizon degrees of freedom, which is argued to generically exist in a near de Sitter space-time. The modes have a simple factorized form which leads to factorization of the squeezed-limit correlation functions with power-law behavior in k{sub long}/k{sub short}. This approach reproduces the known results in single-, quasi-single-, and multi-field inflationary models. However, it is applicable even if, unlike the above examples, the additional degrees of freedom are not weakly coupled at sub-horizon scales. Stronger results are derived in two-field (or sufficiently symmetric multi-field) inflationary models. We discuss the observability of the non-Gaussian 3-point function in the large-scale structure surveys, and argue that the squeezed limit behavior has a higher detectability chance than equilateral behavior when it scales as (k{sub long}/k{sub short}){sup Δ} with Δ < 1—where local non-Gaussianity corresponds to Δ = 0.
MESON CORRELATION FUNCTIONS AT HIGH TEMPERATURES.
WISSEL, S.; DATTA, S.; KARSCH, F.; LAERMANN, E.; SHCHEREDIN, S.
2005-07-25
We present preliminary results for the correlation- and spectral functions of different meson channels on the lattice. The main focus lies on gaining control over cut-off as well as on the finite-volume effects. Extrapolations of screening masses above the deconfining temperature are guided by the result of the free (T = {infinity}) case on the lattice and in the continuum. We study the quenched non-perturbatively improved Wilson-clover fermion as well as the hypercube fermion action which might show less cut-off effects.
Pair correlation function for spin glasses
NASA Astrophysics Data System (ADS)
Fernández, Julio F.; Alonso, Juan J.
2012-10-01
We extract a pair correlation function (PCF) from probability distributions of the spin-overlap parameter q. The distributions come from Monte Carlo simulations. A measure, w, of the thermal fluctuations of magnetic patterns follows from the PCFs. We also obtain rms deviations (over different system samples) δp away from average probabilities for q. For the linear system sizes L that we have studied, w and δp are independent of L in the Edwards-Anderson model but scale as 1/L and L, respectively, in the Sherrington-Kirkpatrick model.
Van Hove correlation functions for identical fermions
NASA Astrophysics Data System (ADS)
Macke, Wilhelm; Miesenböck, Helga M.; Hingerl, Kurt; Bachlechner, Martina E.
1989-02-01
For a quantum system of identical fermions a partition of the density-density correlation function in its ``self'' and ``distinct'' part is presented. These quantities show different properties than their classical counterparts, e.g., they violate the ``detailed balance'' and are not necessarily real. Nevertheless it can be expected that they will provide a good tool for a better description of the self-motion in many-particle systems and are therefore investigated in second-order perturbation theory of the interparticle potential.
Understanding GRETINA using angular correlation method
NASA Astrophysics Data System (ADS)
Austin, Madeline
2015-10-01
The ability to trace the path of gamma rays through germanium is not only necessary for taking full advantage of GRETINA but also a promising possibility for homeland security defense against nuclear threats. This research tested the current tracking algorithm using the angular correlation method by comparing results from raw and tracked data to the theoretical model for Co-60. It was found that the current tracking method is unsuccessful in reproducing angular correlation. Variations to the tracking algorithm were made in the FM value, tracking angle, number of angles of separation observed, and window of coincidence in attempt to improve correlation results. From these variations it was observed that having a larger FM improved results, reducing the number of observational angles worsened correlation, and that overall larger tracking angles improved with larger windows of coincidence and vice-verse. Future research would be to refine the angle of measurement for raw data and to explore the possibility of an energy dependence by testing other elements. This work is supported by the United States Department of Energy, Office of Science, under Contract Number DE-AC02-06CH11357
Statistical properties and correlation functions for drift waves
NASA Technical Reports Server (NTRS)
Horton, W.
1986-01-01
The dissipative one-field drift wave equation is solved using the pseudospectral method to generate steady-state fluctuations. The fluctuations are analyzed in terms of space-time correlation functions and modal probability distributions. Nearly Gaussian statistics and exponential decay of the two-time correlation functions occur in the presence of electron dissipation, while in the absence of electron dissipation long-lived vortical structures occur. Formulas from renormalized, Markovianized statistical turbulence theory are given in a local approximation to interpret the dissipative turbulence.
Functional Magnetic Resonance Imaging Methods
Chen, Jingyuan E.; Glover, Gary H.
2015-01-01
Since its inception in 1992, Functional Magnetic Resonance Imaging (fMRI) has become an indispensible tool for studying cognition in both the healthy and dysfunctional brain. FMRI monitors changes in the oxygenation of brain tissue resulting from altered metabolism consequent to a task-based evoked neural response or from spontaneous fluctuations in neural activity in the absence of conscious mentation (the “resting state”). Task-based studies have revealed neural correlates of a large number of important cognitive processes, while fMRI studies performed in the resting state have demonstrated brain-wide networks that result from brain regions with synchronized, apparently spontaneous activity. In this article, we review the methods used to acquire and analyze fMRI signals. PMID:26248581
CMB anisotropy in compact hyperbolic universes. I. Computing correlation functions
NASA Astrophysics Data System (ADS)
Bond, J. Richard; Pogosyan, Dmitry; Souradeep, Tarun
2000-08-01
Cosmic microwave background (CMB) anisotropy measurements have brought the issue of global topology of the universe from the realm of theoretical possibility to within the grasp of observations. The global topology of the universe modifies the correlation properties of cosmic fields. In particular, strong correlations are predicted in CMB anisotropy patterns on the largest observable scales if the size of the universe is comparable to the distance to the CMB last scattering surface. We describe in detail our completely general scheme using a regularized method of images for calculating such correlation functions in models with nontrivial topology, and apply it to the computationally challenging compact hyperbolic spaces. Our procedure directly sums over images within a specified radius, ideally many times the diameter of the space, effectively treats more distant images in a continuous approximation, and uses Cesaro resummation to further sharpen the results. At all levels of approximation the symmetries of the space are preserved in the correlation function. This new technique eliminates the need for the difficult task of spatial eigenmode decomposition on these spaces. Although the eigenspectrum can be obtained by this method if desired, at a given level of approximation the correlation functions are more accurately determined. We use the 3-torus example to demonstrate that the method works very well. We apply it to power spectrum as well as correlation function evaluations in a number of compact hyperbolic (CH) spaces. Application to the computation of CMB anisotropy correlations on CH spaces, and the observational constraints following from them, are given in a companion paper.
Two-point correlation function for Dirichlet L-functions
NASA Astrophysics Data System (ADS)
Bogomolny, E.; Keating, J. P.
2013-03-01
The two-point correlation function for the zeros of Dirichlet L-functions at a height E on the critical line is calculated heuristically using a generalization of the Hardy-Littlewood conjecture for pairs of primes in arithmetic progression. The result matches the conjectured random-matrix form in the limit as E → ∞ and, importantly, includes finite-E corrections. These finite-E corrections differ from those in the case of the Riemann zeta-function, obtained in Bogomolny and Keating (1996 Phys. Rev. Lett. 77 1472), by certain finite products of primes which divide the modulus of the primitive character used to construct the L-function in question.
[Correlation between heel vessel and human balance function].
Tian, Hui; Bian, Di; Sui, Yuejiao; Ren, Lu; Ma, Tieming
2015-04-01
The heel vessel belongs to the eight extra meridians in human meridian system, which is closely related to the human motion function. Balance function plays an essential role in successful completion of activities in daily life, so the physiological function and pathology of heel vessel as well as human balance function are analyzed, and from the aspect of running course of heel vessel and syndrome, the correlation between heel vessel and human balance function is explored, and the application status of acupoints related to heel vessel for balance dysfunction is introduced. It is believed that heel vessel is closely related to human balance function, especially the motion regulation mechanisms of balance function, and it is hoped that new ideas and methods can be provided for acupuncture treatment for the balance function disorders.
Generating partially correlated noise—A comparison of methods
Hartmann, William M.; Cho, Yun Jin
2011-01-01
There are three standard methods for generating two channels of partially correlated noise: the two-generator method, the three-generator method, and the symmetric-generator method. These methods allow an experimenter to specify a target cross correlation between the two channels, but actual generated noises show statistical variability around the target value. Numerical experiments were done to compare the variability for those methods as a function of the number of degrees of freedom. The results of the experiments quantify the stimulus uncertainty in diverse binaural psychoacoustical experiments: incoherence detection, perceived auditory source width, envelopment, noise localization∕lateralization, and the masking level difference. The numerical experiments found that when the elemental generators have unequal powers, the different methods all have similar variability. When the powers are constrained to be equal, the symmetric-generator method has much smaller variability than the other two. PMID:21786899
Multi-reference vibration correlation methods
Pfeiffer, Florian; Rauhut, Guntram
2014-02-14
State-specific vibration correlation methods beyond the vibrational multi-configuration self-consistent field (VMCSCF) approximation have been developed, which allow for the accurate calculation of state energies for systems suffering from strong anharmonic resonances. Both variational multi-reference configuration interaction approaches and an implementation of approximate 2nd order vibrational multi-reference perturbation theory are presented. The variational approach can be significantly accelerated by a configuration selection scheme, which leads to negligible deviations in the final results. Relaxation effects due to the partitioning of the correlation space and the performance of a VMCSCF modal basis in contrast to a standard modal basis obtained from vibrational self-consistent field theory have been investigated in detail. Benchmark calculations based on high-level potentials are provided for the propargyl cation and cis-diazene.
Toward correlating functional MRI and EEG sources
NASA Astrophysics Data System (ADS)
Singh, Manbir; Khosla, Deepak
1996-04-01
Though excellent spatial resolution (on the order of 1 mm) is obtainable in functional MRI (fMRI), its temporal resolution is limited to about 1 second by hemodynamics. On the other hand, magnetoencephalography (MEG) and electroencephalography (EEG) provide millisecond temporal resolution but a relatively crude (on the order of 1 cm) spatial resolution to localized sources. Thus, techniques that could combine the high temporal resolution of MEG or EEG with the high spatial resolution of fMRI would be of great significance in imaging the spatiotemporal distribution of neuronal activation. With the ultimate objective of combining fMRI and EEG activation studies, we have conducted experiments to determine how pixels activated in fMRI correlate with underlying EEG sources in a given subject during visual stimulation. Results of a three-subject study suggest good correlation between the center-of-gravity of activated pixels seen in fMRI and the center-of-gravity of regions localized through EEG measurements.
Bringing the cross-correlation method up to date
NASA Technical Reports Server (NTRS)
Statler, Thomas
1995-01-01
The cross-correlation (XC) method of Tonry & Davis (1979, AJ, 84, 1511) is generalized to arbitrary parametrized line profiles. In the new algorithm the correlation function itself, rather than the observed galaxy spectrum, is fitted by the model line profile: this removes much of the complication in the error analysis caused by template mismatch. Like the Fourier correlation quotient (FCQ) method of Bender (1990, A&A, 229, 441), the inferred line profiles are, up to a normalization constant, independent of template mismatch as long as there are no blended lines. The standard reduced chi(exp 2) is a good measure of the fit of the inferred velocity distribution, largely decoupled from the fit of the spectral template. The updated XC method performs as well as other recently developed methods, with the added virtue of conceptual simplicity.
Bringing the cross-correlation method up to date
NASA Astrophysics Data System (ADS)
Statler, Thomas
1995-03-01
The cross-correlation (XC) method of Tonry & Davis (1979, AJ, 84, 1511) is generalized to arbitrary parametrized line profiles. In the new algorithm the correlation function itself, rather than the observed galaxy spectrum, is fitted by the model line profile: this removes much of the complication in the error analysis caused by template mismatch. Like the Fourier correlation quotient (FCQ) method of Bender (1990, A&A, 229, 441), the inferred line profiles are, up to a normalization constant, independent of template mismatch as long as there are no blended lines. The standard reduced chi2 is a good measure of the fit of the inferred velocity distribution, largely decoupled from the fit of the spectral template. The updated XC method performs as well as other recently developed methods, with the added virtue of conceptual simplicity.
Optimization of an exchange-correlation density functional for water
NASA Astrophysics Data System (ADS)
Fritz, Michelle; Fernández-Serra, Marivi; Soler, José M.
2016-06-01
We describe a method, that we call data projection onto parameter space (DPPS), to optimize an energy functional of the electron density, so that it reproduces a dataset of experimental magnitudes. Our scheme, based on Bayes theorem, constrains the optimized functional not to depart unphysically from existing ab initio functionals. The resulting functional maximizes the probability of being the "correct" parameterization of a given functional form, in the sense of Bayes theory. The application of DPPS to water sheds new light on why density functional theory has performed rather poorly for liquid water, on what improvements are needed, and on the intrinsic limitations of the generalized gradient approximation to electron exchange and correlation. Finally, we present tests of our water-optimized functional, that we call vdW-DF-w, showing that it performs very well for a variety of condensed water systems.
Variational adaptive correlation method for flow estimation.
Becker, Florian; Wieneke, Bernhard; Petra, Stefania; Schröder, Andreas; Schnörr, Christoph
2012-06-01
A variational approach is presented to the estimation of turbulent fluid flow from particle image sequences in experimental fluid mechanics. The approach comprises two coupled optimizations for adapting size and shape of a Gaussian correlation window at each location and for estimating the flow, respectively. The method copes with a wide range of particle densities and image noise levels without any data-specific parameter tuning. Based on a careful implementation of a multiscale nonlinear optimization technique, we demonstrate robustness of the solution over typical experimental scenarios and highest estimation accuracy for an international benchmark data set (PIV Challenge).
Modeling the three-point correlation function
Marin, Felipe; Wechsler, Risa; Frieman, Joshua A.; Nichol, Robert; /Portsmouth U., ICG
2007-04-01
We present new theoretical predictions for the galaxy three-point correlation function (3PCF) using high-resolution dissipationless cosmological simulations of a flat {Lambda}CDM Universe which resolve galaxy-size halos and subhalos. We create realistic mock galaxy catalogs by assigning luminosities and colors to dark matter halos and subhalos, and we measure the reduced 3PCF as a function of luminosity and color in both real and redshift space. As galaxy luminosity and color are varied, we find small differences in the amplitude and shape dependence of the reduced 3PCF, at a level qualitatively consistent with recent measurements from the SDSS and 2dFGRS. We confirm that discrepancies between previous 3PCF measurements can be explained in part by differences in binning choices. We explore the degree to which a simple local bias model can fit the simulated 3PCF. The agreement between the model predictions and galaxy 3PCF measurements lends further credence to the straightforward association of galaxies with CDM halos and subhalos.
Using of Correlating monomineral thermobarometry for mantle peridotites (correlating methods).
NASA Astrophysics Data System (ADS)
Ashchepkov, I. V.; Pokhilenko, N. P.; Sobolev, N. V.; Rotman, A. Y.; Afanasiev, V. P.; Logvinova, A. M.; Vladykin, N. V.; Kostrovitsky, S. I.; Karpenko, M. A.; Vishnyakova, E. V.
2005-12-01
Correlating monomineral thermobarometry using kimberlite mega- and xenocrysts and xenoliths allows to determine mantle layering with concentrate from kimberlites or placers. Orthopyroxene method (Brey, Kohler,1990)-(McGregor, 1974) was used for calibration of others. Clinopyroxene. Po =0.04*Kd *ToC/(1-2.4*Fe)-5.5 where KD = Na/Ca *Mg/(Al+Cr)and polynomial P = 0.00006*Po3 - 0.0156*Po2 + 1.6757*Po (R2 = 0.8245). The ToC (Nimis -Taylor, 2000) are corrected ToC= 000001*TooC**2 +0.9575*TooC+107.01 Garnet. Thermometers based on: 1) OPx's (Brey, Kohler,1990) estimates, ToC =5272.5*(Ln(KD)/P)3+10265* (Ln(KD)/P)2+ 6472* Ln(KD)/P +2113 where KD= MgO*TiO2/((CaO+MgO)2* FeO*Al2O3 2) CPx (Nimis, Taylor, 2000), : T0oC =362.05*(Ln(KD)/P)3+1880.4* (Ln(KD))/P2+2659.6* Ln(KD)/P +1695.5 where KD= Na2O*MnO*TiO2/(CaO+MgO)* FeO*Al2O3, 3) Gar-Cpx (Krogh, 1988) KD= Na2O*MnO*TiO2/(CaO+MgO)* FeO*Al2O3, 4)Ni in garnet thermometry (Griffin, 1989) with Ni(ppm) =88,877*E**(-5.021*Ni'), (R2=0.69) where Ni' =MnO*ln(FeO)/ln(MgO)*1.1-0.193*TiO2 +0.003*ln(Na2O)- 0.003*Cr2O3+0.0035*CaO+0.004*Al2O3 ToC =0.0004*Ni3-0.0304*Ni2 +7.6318*Ni+ 597.2 ( R2 = 0.69) Chromite P=0.86347*(Cr/(Cr+Al)* ToC/14+Ti*0.1) the second approximation P=0.0004*Po3-0.0342*Po2+1.5323*Po The temperatures are determined using monomineral version of the Ol-Sp thermometer (Taylor et al.,1998) Fo=0.06+0.0005*P for P >30 kbar and Fo=0.095+0.0001*Po for the lower pressures. The Sp-Ol oxybarometer (Taylor et al ., 1998) give the lineal correlation with monomineral version made in the same manner (R-0,96). Ilmenite. P= (TiO2-23.)*2.15-(ToC-700)/20*MgO*Cr2O3-1.5*MnO)*ToC/1273 and further P=10*(60-Po)/60+Po. Monomineral version Ol-Il thermometer (Taylor et al ., 1998) where Fo=0.11+0.00025*P for pressures lower then 30 kbar and Fo=0.10+0.00025*P for greater pressures. The monomineral fO2 oxybarometer same Fo content . Data for 7 kimberlite fields in Yakutia show large scale variations of the mantle different part of Siberian platform
Analysis of spectra using correlation functions
NASA Technical Reports Server (NTRS)
Beer, Reinhard; Norton, Robert H.
1988-01-01
A novel method is presented for the quantitative analysis of spectra based on the properties of the cross correlation between a real spectrum and either a numerical synthesis or laboratory simulation. A new goodness-of-fit criterion called the heteromorphic coefficient H is proposed that has the property of being zero when a fit is achieved and varying smoothly through zero as the iteration proceeds, providing a powerful tool for automatic or near-automatic analysis. It is also shown that H can be rendered substantially noise-immune, permitting the analysis of very weak spectra well below the apparent noise level and, as a byproduct, providing Doppler shift and radial velocity information with excellent precision. The technique is in regular use in the Atmospheric Trace Molecule Spectroscopy (ATMOS) project and operates in an interactive, realtime computing environment with turn-around times of a few seconds or less.
Neuroanatomical correlates of cognitive functioning in prodromal Huntington disease
Harrington, Deborah L; Liu, Dawei; Smith, Megan M; Mills, James A; Long, Jeffrey D; Aylward, Elizabeth H; Paulsen, Jane S
2014-01-01
Introduction The brain mechanisms of cognitive impairment in prodromal Huntington disease (prHD) are not well understood. Although striatal atrophy correlates with some cognitive abilities, few studies of prHD have investigated whether cortical gray matter morphometry correlates in a regionally specific manner with functioning in different cognitive domains. This knowledge would inform the selection of cognitive measures for clinical trials that would be most sensitive to the target of a treatment intervention. Method In this study, random forest analysis was used to identify neuroanatomical correlates of functioning in five cognitive domains including attention and information processing speed, working memory, verbal learning and memory, negative emotion recognition, and temporal processing. Participants included 325 prHD individuals with varying levels of disease progression and 119 gene-negative controls with a family history of HD. In intermediate analyses, we identified brain regions that showed significant differences between the prHD and the control groups in cortical thickness and striatal volume. Brain morphometry in these regions was then correlated with cognitive functioning in each of the domains in the prHD group using random forest methods. We hypothesized that different regional patterns of brain morphometry would be associated with performances in distinct cognitive domains. Results The results showed that performances in different cognitive domains that are vulnerable to decline in prHD were correlated with regionally specific patterns of cortical and striatal morphometry. Putamen and/or caudate volumes were top-ranked correlates of performance across all cognitive domains, as was cortical thickness in regions related to the processing demands of each domain. Conclusions The results underscore the importance of identifying structural magnetic resonance imaging (sMRI) markers of functioning in different cognitive domains, as their relative
Isotope correlations for safeguards surveillance and accountancy methods
Persiani, P.J.; Kalimullah
1982-01-01
Isotope correlations corroborated by experiments, coupled with measurement methods for nuclear material in the fuel cycle have the potential as a safeguards surveillance and accountancy system. The ICT allows the verification of: fabricator's uranium and plutonium content specifications, shipper/receiver differences between fabricator output and reactor input, reactor plant inventory changes, reprocessing batch specifications and shipper/receiver differences between reactor output and reprocessing plant input. The investigation indicates that there exist predictable functional relationships (i.e. correlations) between isotopic concentrations over a range of burnup. Several cross-correlations serve to establish the initial fuel assembly-averaged compositions. The selection of the more effective correlations will depend not only on the level of reliability of ICT for verification, but also on the capability, accuracy and difficulty of developing measurement methods. The propagation of measurement errors through the correlations have been examined to identify the sensitivity of the isotope correlations to measurement errors, and to establish criteria for measurement accuracy in the development and selection of measurement methods. 6 figures, 3 tables.
Correlation fluorescence method of amine detection
NASA Astrophysics Data System (ADS)
Myslitsky, Valentin F.; Tkachuk, Svetlana S.; Rudeichuk, Volodimir M.; Strinadko, Miroslav T.; Slyotov, Mikhail M.; Strinadko, Marina M.
1997-12-01
The amines fluorescence spectra stimulated by UV laser radiation are investigated in this paper. The fluorescence is stimulated by the coherent laser beam with the wavelength 0.337 micrometers . At the sufficient energy of laser stimulation the narrow peaks of the fluorescence spectra are detected besides the wide maximum. The relationship between the fluorescence intensity and the concentration of amines solutions are investigated. The fluorescence intensity temporal dependence on wavelength 0.363 micrometers of the norepinephrine solution preliminarily radiated by UV laser with wavelength 0.337 micrometers was found. The computer stimulated and experimental investigations of adrenaline and norepinephrine mixtures fluorescence spectra were done. The correlation fluorescent method of amines detection is proposed.
Charmonium correlators and spectral functions at finite temperature
Ding,H.T.; Kaczmarek, O.; Karsch, F.; Satz, H.
2008-09-01
We present an operational approach to address the in-medium behavior of charmonium and analyze the reliability of maximum entropy method (MEM). We study the dependences of the ratio of correlators to the reconstructed one and the free one on the resonance's width and the continuum's threshold. Furthermore, we discuss the issue of the default model dependence of the spectral function obtained from MEM.
Method of phased magnitude correlation using binary sequences
NASA Astrophysics Data System (ADS)
Pender, Michael; Tom, Donald
1994-02-01
A method for allowing a correlation function to be applied to binary codes of length 3 to length 255 is presented. A user may specify the desired length of the binary codes for correlation processing, whether the binary code is to use a phase sidelobe level as the threshold or a sidelobe amplitude as the threshold. The user will also be asked to specify the threshold as well as an in phase coefficient referred to as beta and in out of phase coefficient referred to as a alpha. When the user has specified the parameters for correlation processing of the binary code length selected by the user, the program of the present invention will process the binary codes eliminating allomorphic forms of the codes from correlation and then display the results to the user.
Path integral based calculations of symmetrized time correlation functions. II.
Bonella, S; Monteferrante, M; Pierleoni, C; Ciccotti, G
2010-10-28
Schofield's form of quantum time correlation functions is used as the starting point to derive a computable expression for these quantities. The time composition property of the propagators in complex time is exploited to approximate Schofield's function in terms of a sequence of short time classical propagations interspersed with path integrals that, combined, represent the thermal density of the system. The approximation amounts to linearization of the real time propagators and it becomes exact with increasing number of propagation legs. Within this scheme, the correlation function is interpreted as an expectation value over a probability density defined on the thermal and real path space and calculated by a Monte Carlo algorithm. The performance of the algorithm is tested on a set of benchmark problems. Although the numerical effort required is considerable, we show that the algorithm converges systematically to the exact answer with increasing number of iterations and that it is stable for times longer than those accessible via a brute force, path integral based, calculation of the correlation function. Scaling of the algorithm with dimensionality is also examined and, when the method is combined with commonly used filtering schemes, found to be comparable to that of alternative semiclassical methods.
Neuroanatomical correlates of cognitive functioning in prodromal Huntington disease.
Harrington, Deborah L; Liu, Dawei; Smith, Megan M; Mills, James A; Long, Jeffrey D; Aylward, Elizabeth H; Paulsen, Jane S
2014-01-01
The brain mechanisms of cognitive impairment in prodromal Huntington disease (prHD) are not well understood. Although striatal atrophy correlates with some cognitive abilities, few studies of prHD have investigated whether cortical gray matter morphometry correlates in a regionally specific manner with functioning in different cognitive domains. This knowledge would inform the selection of cognitive measures for clinical trials that would be most sensitive to the target of a treatment intervention. In this study, random forest analysis was used to identify neuroanatomical correlates of functioning in five cognitive domains including attention and information processing speed, working memory, verbal learning and memory, negative emotion recognition, and temporal processing. Participants included 325 prHD individuals with varying levels of disease progression and 119 gene-negative controls with a family history of HD. In intermediate analyses, we identified brain regions that showed significant differences between the prHD and the control groups in cortical thickness and striatal volume. Brain morphometry in these regions was then correlated with cognitive functioning in each of the domains in the prHD group using random forest methods. We hypothesized that different regional patterns of brain morphometry would be associated with performances in distinct cognitive domains. The results showed that performances in different cognitive domains that are vulnerable to decline in prHD were correlated with regionally specific patterns of cortical and striatal morphometry. Putamen and/or caudate volumes were top-ranked correlates of performance across all cognitive domains, as was cortical thickness in regions related to the processing demands of each domain. The results underscore the importance of identifying structural magnetic resonance imaging (sMRI) markers of functioning in different cognitive domains, as their relative sensitivity depends on the extent to which
Nonlocal density-functional description constructed from a correlated many-body wave function
NASA Astrophysics Data System (ADS)
Umezawa, Naoto; Tsuneyuki, Shinji
2004-03-01
We suggest a new approach to the nonlocal density-functional theory. In our method, the nonlocal correlation functional is derived from a correlated many-body wave function using the transcorrelated similarity transformation [1,2]. Our formalism is rigorous in principle if the v-representable density is assumed. In practice, Jastrow-Slater-type wave function is adopted and the correlation functional consists of many-body interactions originated from the Jastrow factor. Instead of struggling with these higher order interactions, we retain only 2-body interactions multiplying an adjusting parameter so that it can reproduce the exact correlation energy for the homogeneous electron gas. Therefore, the computational cost is comparable to the exact exchange method. Moreover, parameters in the Jastrow factor are determined by the two conditions: the cusp conditions and the random-phase approximation without empirical fitting. We found that our correlation functional gives fairly good results for small atoms and ions (He, Li^+, Be^2+, Li, and Be). [1]S. F. Boys and N. C. Handy, Proc. Roy. Soc. A, 309, 209; 310, 43; 310, 63; 311, 309. [2] N. Umezawa and S. Tsuneyuki, J. Chem. Phys. 119, 10015 (2003).
Nonlocal exchange correlation in screened-exchange densityfunctional methods
Lee, Byounghak; Wang, Lin-Wang; Spataru, Catalin D.; Louie,Steven G.
2007-04-22
We present a systematic study on the exchange-correlationeffects in screened-exchange local density functional method. Toinvestigate the effects of the screened-exchange potential in the bandgap correction, we have compared the exchange-correlation potential termin the sX-LDA formalism with the self-energy term in the GWapproximation. It is found that the band gap correction of the sX-LDAmethod primarily comes from the downshift of valence band states,resulting from the enhancement of bonding and the increase of ionizationenergy. The band gap correction in the GW method, on the contrary, comesin large part from the increase of theconduction band energies. We alsostudied the effects of the screened-exchange potential in the totalenergy by investigating the exchange-correlation hole in comparison withquantum Monte Carlo calculations. When the Thomas-Fermi screening isused, the sX-LDA method overestimates (underestimates) theexchange-correlation hole in short (long) range. From theexchange-correlation energy analysis we found that the LDA method yieldsbetter absolute total energy than sX-LDA method.
NASA Astrophysics Data System (ADS)
Tran, Fabien; Blaha, Peter; Schwarz, Karlheinz; Novák, Pavel
2006-10-01
For the treatment of strongly correlated electrons, the corresponding Hartree-Fock exchange energy is used instead of the local density approximation (LDA) or generalized gradient approximation (GGA) functional, as suggested recently [P. Novák , Phys. Status Solidi B 243, 563 (2006)]. If this is done only inside the atomic spheres, using an augmented plane wave scheme, a significant simplification and reduction of computational cost is achieved with respect to the usual but costly implementation of the Hartree-Fock formalism in solids. Starting from this, we construct exchange-correlation energy functionals of the hybrid form like B3PW91, PBE0, etc. These functionals are tested on the transition-metal monoxides MnO, FeO, CoO, and NiO, and the results are compared with the LDA, GGA, LDA+U , and experimental ones. The results show that the proposed method, which does not contain any system-dependent input parameter, gives results comparable or superior to the ones obtained with LDA+U which is designed to improve significantly over the LDA and GGA results for systems containing strongly correlated electrons. The computational efficiency, similar to the LDA+U one, and accuracy of the proposed method show that it represents a very good alternative to LDA+U .
NASA Astrophysics Data System (ADS)
Joubert, Daniel P.
2012-03-01
It is shown that the density-functional-theory exchange and correlation functionals satisfy 0=γEhx[ρN]+2Ecγ[ρN]-γEhx[ρN-1γ]-2Ecγ[ρN-1γ]+2∫d3r'[ρN-10(r)-ρN-1γ(r)]v0([ρN];r)+∫d3r'[ρN-10(r)-ρN-1γ(r)]r·∇v0([ρN];r)+∫d3r'ρN(r)r·∇vcγ([ρN];r)-∫d3r'ρN-1γ(r)r·∇vcγ([ρN-1γ];r)-∫d3r'fγ(r)r·∇vhxcγ([ρN];r)-2∫d3r'fγ(r)vhxcγ([ρN];r). In the derivation of this equation the adiabatic connection formulation is used, where the ground-state density of an N-electron system ρN is kept constant independent of the electron-electron coupling strength γ. Here Ehx[ρ] is the Hartree plus exchange energy, Ecγ[ρ] is the correlation energy, vhxcγ[ρ] is the Hartree plus exchange-correlation potential, vc[ρ] is the correlation potential, and v0[ρ]is the Kohn-Sham potential. The charge densities ρN and ρN-1γ are the N- and (N-1)-electron ground-state densities of the same Hamiltonian at electron-electron coupling strength γ. fγ(r)=ρN(r)-ρN-1γ(r) is the Fukui function. This equation can be useful in testing the internal self-consistency of approximations to the exchange and correlation functionals. As an example the identity is tested on the analytical Hooke's atom charge density for some frequently used approximate functionals.
Lai, X; Torp, H
1999-01-01
The cross-correlation method (CCM) for blood flow velocity measurement using Doppler ultrasound is based on time delay estimation of echoes from pulse-to-pulse. The sampling frequency of the received signal is usually kept as low as possible in order to reduce computational complexity, and the peak in the correlation function is found by interpolating the correlation function. The parabolic-fit interpolation method introduces a bias at low sampling rate to the ultrasound center frequency ratio. In this study, four different methods are suggested to improve the estimation accuracy: (1) Parabolic interpolation with bias-compensation, derived from a theoretical signal model. (2) Parabolic interpolation combined with linear filter interpolation of the correlation function. (3) Parabolic interpolation to the complex correlation function envelope. (4) Matched filter interpolation applied to the correlation function. The new interpolation methods are analyzed both by computer simulated signals and RF-signals recorded from a patient with time delay larger than 1/f(0), where f(0) is the center frequency. The simulation results show that these methods are more accurate than the parabolic-fit method. From the simulation, the worst estimation accuracy is about 1.25% of 1/f(0) for the parabolic-fit interpolation, and it is improved by the above methods to less than 0.5% of 1/f(0) when the sampling rate is 10 MHz, the center frequency is 2.5 MHz and the bandwidth is 1 MHz. This improvement also can be observed in the experimental data. Furthermore, the matched filter interpolation gives the best performance when signal-to-noise ratio (SNR) is low. This is verified both by simulation and experimentation.
Density Functional Plus Dynamical Mean Field Theory of Correlated Oxides
NASA Astrophysics Data System (ADS)
Millis, Andrew
2015-03-01
The density functional plus dynamical mean field method is outlined and a few recent successes including applications to spin crossover molecules, oxide superlattices and metal-insulator transitions in bulk transition metals are outlined. Insights from the method into the essential role played by lattice distortions (both rotations and bond length changes) in determining the phase diagrams of correlated materials are presented. The key theoretical issue of the double counting correction is outlined, different approaches are compared, and a connection to the energy level differences between strongly and weakly correlated orbitals is presented. Charge transfer across oxide interfaces shown to depend crucially on the double counting correction, suggesting that experiments on oxide superlattices may provide insights into this important problem. Future directions are discussed. This work is performed in collaboration with Jia Chen, Hung Dang, Hyowon Park and Chris Marianetti. This research supported by the DOE Office of Science, Grant ER 046169.
Structural and functional neural correlates of music perception.
Limb, Charles J
2006-04-01
This review article highlights state-of-the-art functional neuroimaging studies and demonstrates the novel use of music as a tool for the study of human auditory brain structure and function. Music is a unique auditory stimulus with properties that make it a compelling tool with which to study both human behavior and, more specifically, the neural elements involved in the processing of sound. Functional neuroimaging techniques represent a modern and powerful method of investigation into neural structure and functional correlates in the living organism. These methods have demonstrated a close relationship between the neural processing of music and language, both syntactically and semantically. Greater neural activity and increased volume of gray matter in Heschl's gyrus has been associated with musical aptitude. Activation of Broca's area, a region traditionally considered to subserve language, is important in interpreting whether a note is on or off key. The planum temporale shows asymmetries that are associated with the phenomenon of perfect pitch. Functional imaging studies have also demonstrated activation of primitive emotional centers such as ventral striatum, midbrain, amygdala, orbitofrontal cortex, and ventral medial prefrontal cortex in listeners of moving musical passages. In addition, studies of melody and rhythm perception have elucidated mechanisms of hemispheric specialization. These studies show the power of music and functional neuroimaging to provide singularly useful tools for the study of brain structure and function.
Correlation of Thyroid Functions with Severity and Outcome of Pregnancy
Kharb, S; Sardana, D; Nanda, S
2013-01-01
Background: During normal pregnancy, changes in thyroid function are well documented; however, information regarding thyroid function in preeclampsia is scanty. Aim: The present study was planned to study thyroid hormones in mild and severe preeclamptic women and normotensive women and correlate them with outcome of pregnancy. Subject and Methods: Thyroid hormones were analyzed in mild (n = 50) and severe (n = 50) cases of preeclamptic women and normotensive women (n = 100). Results: Thyroid-stimulating hormone (TSH) and TT4 levels were higher in mild preeclampsia as compared with severe preeclampsia (P < 0.001 and P < 0.01, respectively). TT3 levels were lower in preeclampsia (more so in severe preeclamptics as compared with normotensive pregnant and non-pregnant women). Preeclamptic with raised TSH levels had significantly higher mean arterial blood pressure and low birth weight (BW). A negative correlation was observed between BW and TSH levels (r = 0.296, P < 0.001) and BW and TT4 levels. A positive correlation was observed between BW and TT3 levels. Conclusion: These findings indicate that there is a state of biochemical hypothyroidism that correlates with severity of preeclampsia and influences obstetric outcome in these women. Identification of thyroid hormone in pregnancy might be of help in predicting occurrence of preeclampsia. PMID:23634328
Multichannel correlation recognition method of optical images
NASA Astrophysics Data System (ADS)
Wang, Hongxia; He, Junfa; Sun, Honghui
2000-10-01
In this paper a multi-channel real-time hybrid joint transform correlator is proposed. In this correlator, the computer control is used to divide the screen into several equal size windows, reference images of the windows are all the same one and object images are adopted from different frames of image sequences by CCD, twice Fourier transforms of every channel images are realized by using hololens array. Areas of LCLV and the output light energy can be used effectively. The correlation performance can be improved.
Properties of polyelectrolyte chains from analysis of angular correlation functions
NASA Astrophysics Data System (ADS)
Cannavacciuolo, Luigi; Pedersen, Jan Skov
2002-11-01
An empirical expression for the angular correlation function (ACF) of charged (Debye-Huckel) wormlike chains (WLC) with excluded volume (EV) is introduced. It reproduces the Monte Carlo (MC) data of a previous study very well. Using this expression analytical calculations for the persistence length (Lp), radius of gyration (Rg), and end-to-end distance (R) are given in the form of Taylor series. It is shown that the above quantities can be expressed as a weighted sum over the corresponding quantities (Lph, Rgh, Rh) of a set of ideal wormlike chains {Ch} h=0,1,ellipsis . Both the set {Ch} and the coefficients in the Taylor expansions are defined as functions of three parameters which are determined by fitting the ACF expression to the MC data. A comparison of the calculated Rg and R shows excellent agreement with the corresponding sampled values. The persistence length Lp is in good agreement with the values determined by fitting the sampled scattering functions by model expressions for neutral chains with excluded volume interactions, provided that a contribution due to EV is subtracted from Lp. Moreover, the method here proposed allows one to determine the persistence length of very short chains which is not possible by fitting the scattering function. The new expression for the angular correlation function, as well as the expressions derived for Rg and R are a natural generalization of well known results for ideal WLC, when EV and/or electrostatic interactions are present.
Can density cumulant functional theory describe static correlation effects?
Mullinax, J Wayne; Sokolov, Alexander Yu; Schaefer, Henry F
2015-06-09
We evaluate the performance of density cumulant functional theory (DCT) for capturing static correlation effects. In particular, we examine systems with significant multideterminant character of the electronic wave function, such as the beryllium dimer, diatomic carbon, m-benzyne, 2,6-pyridyne, twisted ethylene, as well as the barrier for double-bond migration in cyclobutadiene. We compute molecular properties of these systems using the ODC-12 and DC-12 variants of DCT and compare these results to multireference configuration interaction and multireference coupled-cluster theories, as well as single-reference coupled-cluster theory with single, double (CCSD), and perturbative triple excitations [CCSD(T)]. For all systems the DCT methods show intermediate performance between that of CCSD and CCSD(T), with significant improvement over the former method. In particular, for the beryllium dimer, m-benzyne, and 2,6-pyridyne, the ODC-12 method along with CCSD(T) correctly predict the global minimum structures, while CCSD predictions fail qualitatively, underestimating the multireference effects. Our results suggest that the DC-12 and ODC-12 methods are capable of describing emerging static correlation effects but should be used cautiously when highly accurate results are required. Conveniently, the appearance of multireference effects in DCT can be diagnosed by analyzing the DCT natural orbital occupations, which are readily available at the end of the energy computation.
On the correlation function of 1/ f noise
NASA Astrophysics Data System (ADS)
Hooge, F. N.; Bobbert, P. A.
1997-02-01
The correlation function is derived of noise with a 1/ f spectrum between a low-frequency fl and a high-frequency h. The essential term in the correlation function is a - ln t term. The usual interpretation of 1/ f noise as a summation of Lorentzian spectra is discussed. The model of 1/ f noise from a random series of t - {1}/{2} pulses is correct. The - ln t correlation function is also derived from such a series.
Method of reflection point correlation seismic surveying
Barbier, M.G.; Staron, P.J.
1982-02-16
A method of seismic exploration comprises transmitting waves from transmission sources into the medium to be explored and picking up signals in a receiver and recording these as traces, the signals being produced by reflection in the medium, the sequential transmission of the sources taking place at intervals less than the reflection time of the longest transmitted waves, the repeated transmission of any one source taking place at intervals at least equal to the said reflection time and therein being an intercorrelation function of a series of transmission instants of all the sources and a series of transmission instants of any one of the sources to give a relationship between the maximum peak amplitude and the secondary residue amplitude greater than a predetermined value and grouping the recorded traces corresponding to the same reflection point, adjusting the traces in relation to the associated source providing the information relating to the reflection point and adding together the adjusted traces relating to the same reflection point.
NASA Astrophysics Data System (ADS)
Zhang, Jin-Ping; Cheng, Xin-Lu; Zhang, Hong; Yang, Xiang-Dong
2011-06-01
Three low-lying electronic states (X1Σ+, a3Σ+, and A1Π) of NO+ ion are studied using the complete active space self-consistent-field (CASSCF) method followed by highly accurate valence internally contracted multi-reference configuration interaction (MRCI) approach in combination of the correlation-consistent sextuple basis set augmented with diffuse functions, aug-cc-pV6Z. The potential energy curves (PECs) of the NO+(X1Σ+, a3Σ+, A1Π) are calculated. Based on the PECs, the spectroscopic parameters Re, De, ωe, ωeχe, αe, Be, and D0 are reproduced, which are in excellent agreement with the available measurements. By numerically solving the radial Schrödinger equation of nuclear motion using the Numerov method, the first 20 vibrational levels, inertial rotation and centrifugal distortion constants of NO+(X1Σ+, a3Σ+, A1Π) ion are derived when the rotational quantum number J is equal to zero (J = 0) for the first time, which accord well with the available measurements. Finally, the analytical potential energy functions of these states are fitted, which are used to accurately derive the first 20 classical turning points when J = 0. These results are compared in detail with those of previous investigations reported in the literature.
Brain structure and function correlates of cognitive subtypes in schizophrenia.
Geisler, Daniel; Walton, Esther; Naylor, Melissa; Roessner, Veit; Lim, Kelvin O; Charles Schulz, S; Gollub, Randy L; Calhoun, Vince D; Sponheim, Scott R; Ehrlich, Stefan
2015-10-30
Stable neuropsychological deficits may provide a reliable basis for identifying etiological subtypes of schizophrenia. The aim of this study was to identify clusters of individuals with schizophrenia based on dimensions of neuropsychological performance, and to characterize their neural correlates. We acquired neuropsychological data as well as structural and functional magnetic resonance imaging from 129 patients with schizophrenia and 165 healthy controls. We derived eight cognitive dimensions and subsequently applied a cluster analysis to identify possible schizophrenia subtypes. Analyses suggested the following four cognitive clusters of schizophrenia: (1) Diminished Verbal Fluency, (2) Diminished Verbal Memory and Poor Motor Control, (3) Diminished Face Memory and Slowed Processing, and (4) Diminished Intellectual Function. The clusters were characterized by a specific pattern of structural brain changes in areas such as Wernicke's area, lingual gyrus and occipital face area, and hippocampus as well as differences in working memory-elicited neural activity in several fronto-parietal brain regions. Separable measures of cognitive function appear to provide a method for deriving cognitive subtypes meaningfully related to brain structure and function. Because the present study identified brain-based neural correlates of the cognitive clusters, the proposed groups of individuals with schizophrenia have some external validity. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
Method of phased magnitude correlation using binary sequences
NASA Astrophysics Data System (ADS)
Pender, Michael
1994-07-01
This patent discloses a method for allowing a correlation function to be applied to binary codes of length 3 to length 128. A user may specify the desired length of the binary codes for correlation processing; whether the binary code is to use a phase sidelobe level as the threshold or a sidelobe amplitude as the threshold. The user will also be asked to specify the threshold as well as an in phase coefficient referred to as alpha and an out of phase coefficient referred to as a beta. The user may also specify that the codes be expanded which results in correlated compounds having a length twice that of the specified length being displayed to the user. When the user has specified the parameters for correlation processing of the binary code length selected by the user, the program of the present invention will process the binary codes eliminating allomorphic and symmetrical forms of the codes from correlation and then display the results to the user.
Neurobiological correlates of social functioning in autism.
Neuhaus, Emily; Beauchaine, Theodore P; Bernier, Raphael
2010-08-01
Although autism is defined by deficits in three areas of functioning (social, communicative, and behavioral), impairments in social interest and restricted behavioral repertoires are central to the disorder. As a result, a detailed understanding of the neurobiological systems subserving social behavior may have implications for prevention, early identification, and intervention for affected families. In this paper, we review a number of potential neurobiological mechanisms--across several levels of analysis--that subserve normative social functioning. These include neural networks, neurotransmitters, and hormone systems. After describing the typical functioning of each system, we review available empirical findings specific to autism. Among the most promising potential mechanisms of social behavioral deficits in autism are those involving neural networks including the amygdala, the mesocorticolimbic dopamine system, and the oxytocin system. Particularly compelling are explanatory models that integrate mechanisms across biological systems, such as those linking dopamine and oxytocin with brain regions critical to reward processing.
Functional brain correlates of heterosexual paedophilia.
Schiffer, Boris; Paul, Thomas; Gizewski, Elke; Forsting, Michael; Leygraf, Norbert; Schedlowski, Manfred; Kruger, Tillmann H C
2008-05-15
Although the neuronal mechanisms underlying normal sexual motivation and function have recently been examined, the alterations in brain function in deviant sexual behaviours such as paedophilia are largely unknown. The objective of this study was to identify paedophilia-specific functional networks implicated in sexual arousal. Therefore a consecutive sample of eight paedophile forensic inpatients, exclusively attracted to females, and 12 healthy age-matched heterosexual control participants from a comparable socioeconomic stratum participated in a visual sexual stimulation procedure during functional magnetic resonance imaging. The visual stimuli were sexually stimulating photographs and emotionally neutral photographs. Immediately after the imaging session subjective responses pertaining to sexual desire were recorded. Principally, the brain response of heterosexual paedophiles to heteropaedophilic stimuli was comparable to that of heterosexual males to heterosexual stimuli, including different limbic structures (amygdala, cingulate gyrus, and hippocampus), the substantia nigra, caudate nucleus, as well as the anterior cingulate cortex, different thalamic nuclei, and associative cortices. However, responses to visual sexual stimulation were found in the orbitofrontal cortex in healthy heterosexual males, but not in paedophiles, in whom abnormal activity in the dorsolateral prefrontal cortex was observed. Thus, in line with clinical observations and neuropsychological studies, it seems that central processing of sexual stimuli in heterosexual paedophiles may be altered by a disturbance in the prefrontal networks, which, as has already been hypothesized, may be associated with stimulus-controlled behaviours, such as sexual compulsive behaviours. Moreover, these findings may suggest a dysfunction (in the functional and effective connectivity) at the cognitive stage of sexual arousal processing.
Analog computation of auto and cross-correlation functions
NASA Technical Reports Server (NTRS)
1974-01-01
For analysis of the data obtained from the cross beam systems it was deemed desirable to compute the auto- and cross-correlation functions by both digital and analog methods to provide a cross-check of the analysis methods and an indication as to which of the two methods would be most suitable for routine use in the analysis of such data. It is the purpose of this appendix to provide a concise description of the equipment and procedures used for the electronic analog analysis of the cross beam data. A block diagram showing the signal processing and computation set-up used for most of the analog data analysis is provided. The data obtained at the field test sites were recorded on magnetic tape using wide-band FM recording techniques. The data as recorded were band-pass filtered by electronic signal processing in the data acquisition systems.
Cumulants and correlation functions versus the QCD phase diagram
Bzdak, Adam; Koch, Volker; Strodthoff, Nils
2017-05-12
Here, we discuss the relation of particle number cumulants and correlation functions. It is argued that measuring couplings of the genuine multiparticle correlation functions could provide cleaner information on possible nontrivial dynamics in heavy-ion collisions. We also extract integrated multiproton correlation functions from the presently available experimental data on proton cumulants. We find that the STAR data contain significant four-proton correlations, at least at the lower energies, with indication of changing dynamics in central collisions. We also find that these correlations are rather long ranged in rapidity. Finally, using the Ising model, we demonstrate how the signs of the multiprotonmore » correlation functions may be used to exclude certain regions of the phase diagram close to the critical point.« less
The Boundary Function Method. Fundamentals
NASA Astrophysics Data System (ADS)
Kot, V. A.
2017-03-01
The boundary function method is proposed for solving applied problems of mathematical physics in the region defined by a partial differential equation of the general form involving constant or variable coefficients with a Dirichlet, Neumann, or Robin boundary condition. In this method, the desired function is defined by a power polynomial, and a boundary function represented in the form of the desired function or its derivative at one of the boundary points is introduced. Different sequences of boundary equations have been set up with the use of differential operators. Systems of linear algebraic equations constructed on the basis of these sequences allow one to determine the coefficients of a power polynomial. Constitutive equations have been derived for initial boundary-value problems of all the main types. With these equations, an initial boundary-value problem is transformed into the Cauchy problem for the boundary function. The determination of the boundary function by its derivative with respect to the time coordinate completes the solution of the problem.
Structure-Function Correlation of the Human Central Retina
Charbel Issa, Peter; Troeger, Eric; Finger, Robert; Holz, Frank G.; Wilke, Robert; Scholl, Hendrik P. N.
2010-01-01
Background The impact of retinal pathology detected by high-resolution imaging on vision remains largely unexplored. Therefore, the aim of the study was to achieve high-resolution structure-function correlation of the human macula in vivo. Methodology/Principal Findings To obtain high-resolution tomographic and topographic images of the macula spectral-domain optical coherence tomography (SD-OCT) and confocal scanning laser ophthalmoscopy (cSLO), respectively, were used. Functional mapping of the macula was obtained by using fundus-controlled microperimetry. Custom software allowed for co-registration of the fundus mapped microperimetry coordinates with both SD-OCT and cSLO datasets. The method was applied in a cross-sectional observational study of retinal diseases and in a clinical trial investigating the effectiveness of intravitreal ranibizumab in macular telangietasia type 2. There was a significant relationship between outer retinal thickness and retinal sensitivity (p<0.001) and neurodegeneration leaving less than about 50 µm of parafoveal outer retinal thickness completely abolished light sensitivity. In contrast, functional preservation was found if neurodegeneration spared the photoreceptors, but caused quite extensive disruption of the inner retina. Longitudinal data revealed that small lesions affecting the photoreceptor layer typically precede functional detection but later cause severe loss of light sensitivity. Ranibizumab was shown to be ineffective to prevent such functional loss in macular telangietasia type 2. Conclusions/Significance Since there is a general need for efficient monitoring of the effectiveness of therapy in neurodegenerative diseases of the retina and since SD-OCT imaging is becoming more widely available, surrogate endpoints derived from such structure-function correlation may become highly relevant in future clinical trials. PMID:20877651
Timing Correlations in Proteins Predict Functional Modules and Dynamic Allostery.
Lin, Milo M
2016-04-20
How protein structure encodes functionality is not fully understood. For example, long-range intraprotein communication can occur without measurable conformational change and is often not captured by existing structural correlation functions. It is shown here that important functional information is encoded in the timing of protein motions, rather than motion itself. I introduce the conditional activity function to quantify such timing correlations among the degrees of freedom within proteins. For three proteins, the conditional activities between side-chain dihedral angles were computed using the output of microseconds-long atomistic simulations. The new approach demonstrates that a sparse fraction of side-chain pairs are dynamically correlated over long distances (spanning protein lengths up to 7 nm), in sharp contrast to structural correlations, which are short-ranged (<1 nm). Regions of high self- and inter-side-chain dynamical correlations are found, corresponding to experimentally determined functional modules and allosteric connections, respectively.
Landau gauge Yang-Mills correlation functions
NASA Astrophysics Data System (ADS)
Cyrol, Anton K.; Fister, Leonard; Mitter, Mario; Pawlowski, Jan M.; Strodthoff, Nils
2016-09-01
We investigate Landau gauge S U (3 ) Yang-Mills theory in a systematic vertex expansion scheme for the effective action with the functional renormalization group. Particular focus is put on the dynamical creation of the gluon mass gap at nonperturbative momenta and the consistent treatment of quadratic divergences. The nonperturbative ghost and transverse gluon propagators as well as the momentum-dependent ghost-gluon, three-gluon and four-gluon vertices are calculated self-consistently with the classical action as the only input. The apparent convergence of the expansion scheme is discussed and within the errors, our numerical results are in quantitative agreement with available lattice results.
Correlation Functions in Hard and - Processes
NASA Astrophysics Data System (ADS)
Schlegel, M.; Meißner, S.; Metz, A.
2009-04-01
Possible relations between two a priori different classes of parton distributions, the Generalized Parton Distributions (GPDs) and the Transverse Momentum Dependent parton distributions (TMDs), are discussed in this note. Although these relations were proven to hold exactly only in simple models they imply an appealingly simple and intuitive explanation for single-spin asymmetries in semi-inclusive deep-inelastic scattering. In this context we perform a first classification of common mother functions of GPDs and TMDs, so-called Generalized Transverse Momentum Dependent parton distributions (GTMDs), investigate their GPD- and TMD-limits, and gain new insight into the nature of these relations.
A Representation for Fermionic Correlation Functions
NASA Astrophysics Data System (ADS)
Feldman, Joel; Knörrer, Horst; Trubowitz, Eugene
Let dμS(a) be a Gaussian measure on the finitely generated Grassmann algebra A. Given an even W(a)∈A, we construct an operator R on A such that
Analytical correlation functions for motion through diffusivity landscapes.
Roosen-Runge, Felix; Bicout, Dominique J; Barrat, Jean-Louis
2016-05-28
Diffusion of a particle through an energy and diffusivity landscape is a very general phenomenon in numerous systems of soft and condensed matter. On the one hand, theoretical frameworks such as Langevin and Fokker-Planck equations present valuable accounts to understand these motions in great detail, and numerous studies have exploited these approaches. On the other hand, analytical solutions for correlation functions, as, e.g., desired by experimentalists for data fitting, are only available for special cases. We explore the possibility to use different theoretical methods in the specific picture of time-dependent switching between diffusive states to derive analytical functions that allow to link experimental and simulation results to theoretical calculations. In particular, we present a closed formula for diffusion switching between two states, as well as a general recipe of how to generalize the formula to multiple states.
STRUCTURAL-FUNCTIONAL CORRELATION IN PATIENTS WITH DIABETIC MACULAR EDEMA.
Edington, Magdalena; Sachdev, Amun; Morjaria, Rupal; Chong, Victor
2017-05-01
Previous studies have shown that patients with diabetic macular edema (DME) with relatively good visual acuity can have slow reading speed. The aim of this study was to evaluate the structural-functional correlation in a cohort of patients with DME and to assess whether the central four retinal points on microperimetry (MP4) could be used as a potentially faster and more reliable method of assessing retinal function in patients with DME than reading speed. The study was performed on patients with clinically significant DME. The best-corrected visual acuity (BCVA) was recorded with letter counting on a modified ETDRS chart, the maximal reading speed (MRS) was recorded with MNREAD, the retinal sensitivity (MP28 and MP4) was measured with Optos OCT/ Scanning Laser Ophthalmoscopy and the central subfield thickness was measured by Heidelberg Spectralis Spectral Domain Optical Coherent Topography. Of 100 eyes analyzed, 76 eyes were included in the study. The mean BCVA was 76.5 letters (Snellen equivalent 6/18), the mean MRS was 156.8 words per minute, the mean MP4 was 9.81 dB per point, and the mean central subfield thickness was 309.3 microns. It was found that faster MRS is correlated with younger age (P = 0.001), better BCVA (P < 0.0001), and better retinal sensitivity (P < 0.0001) for both MP28 and MP4, but not with central subfield thickness (P = 0.66). Central subfield thickness is correlated with MP28 (P = 0.05) but not with age (P = 0.812), BCVA (P = 0.113), or MP4 (P = 0.485). After correction for age and BCVA, MRS is still correlated with MP28 (P = 0.001) and MP4 (P = 0.015). Patients with DME can have reduced reading speed despite good visual acuity. Maximal reading speed is often reported to be difficult to perform, inconsistent, and affected by language and educational level. However, in this study, the authors found that the central MP4 points are quick and easy to test in most of the patients, and are highly correlated with MRS. Microperimetry might
Bedirian, Ricardo; Neves, Mario Fritsch; Oigman, Wille; Gismondi, Ronaldo Altenburg Odebrecht Curi; Pozzobon, Cesar Romaro; Ladeira, Marcia Cristina Boaventura; Castier, Marcia Bueno
2016-01-01
Background: Endothelial dysfunction may be involved in the pathophysiology of cardiac abnormalities in patients with diabetes mellitus (DM). A correlation between endothelial dysfunction and diastolic dysfunction in patients with type 1 DM has been demonstrated, but this relationship has not been well investigated in type 2 DM. Objective: Compare groups of patients with type 2 DM and hypertension with and without diastolic dysfunction using endothelial function indexes, and to assess whether correlations exist between the diastolic function and the endothelial function indexes. Method: This was a cross-sectional study of 34 men and women with type 2 DM and hypertension who were aged between 40 and 70 years and were categorized based on assessments of their Doppler echocardiographic parameters as having normal (14 patients) and abnormal (20 patients) diastolic function. Flow-mediated dilatation (FMD) assessments of the brachial artery evaluated the patients’ endothelial function. Results: The mean maximum FMD was 7.15 ± 2.80% for the patients with diastolic dysfunction and it was 11.85 ± 4.77% for the patients with normal diastolic function (p = 0.004). Correlations existed between the maximum FMD and the E/e' ratio (p = 0.040, r = -0.354) and the early wave velocity (e') at the lateral mitral annulus (p = 0.002, r = 0.509). Conclusion: The endothelial function assessed by FMD was worse in hypertensive diabetic patients with diastolic dysfunction. There were correlations between the diastolic function indexes and the endothelial function indexes in our sample. PMID:27867429
Calculation of phonon dispersion relation using new correlation functional
NASA Astrophysics Data System (ADS)
Jitropas, Ukrit; Hsu, Chung-Hao
2017-06-01
To extend the use of Local Density Approximation (LDA), a new analytical correlation functional is introduced. Correlation energy is an essential ingredient within density functional theory and used to determine ground state energy and other properties including phonon dispersion relation. Except for high and low density limit, the general expression of correlation energy is unknown. The approximation approach is therefore required. The accuracy of the modelling system depends on the quality of correlation energy approximation. Typical correlation functionals used in LDA such as Vosko-Wilk-Nusair (VWN) and Perdew-Wang (PW) were obtained from parameterizing the near-exact quantum Monte Carlo data of Ceperley and Alder. These functionals are presented in complex form and inconvenient to implement. Alternatively, the latest published formula of Chachiyo correlation functional provides a comparable result for those much more complicated functionals. In addition, it provides more predictive power based on the first principle approach, not fitting functionals. Nevertheless, the performance of Chachiyo formula for calculating phonon dispersion relation (a key to the thermal properties of materials) has not been tested yet. Here, the implementation of new correlation functional to calculate phonon dispersion relation is initiated. The accuracy and its validity will be explored.
Correlation studies on surface particle detection methods
NASA Technical Reports Server (NTRS)
Peterson, Ronald V.; White, James C.
1988-01-01
The accurate determination of dust levels on optical surfaces is necessary to assess sensor system performance. A comparison study was made on several particle measurement methods including those based on direct imaging and light scattering. The effectiveness of removing the particles from the surface prior to determining particle size distributions was also assessed. These studies revealed that some methods, especially those requiring particle removal before analysis, are subject to large systematic errors affecting particle size distributions. Thus, an understanding of the particle measurement methods employed is necessary before any surface cleanliness or obstruction value assignments are accepted as true representations of an optical surface contamination condition.
NASA Astrophysics Data System (ADS)
Takeuchi, Tsutomu T.
2010-08-01
We provide an analytic method to construct a bivariate distribution function (DF) with given marginal distributions and correlation coefficient. We introduce a convenient mathematical tool, called a copula, to connect two DFs with any prescribed dependence structure. If the correlation of two variables is weak (Pearson's correlation coefficient |ρ| < 1/3), the Farlie-Gumbel-Morgenstern (FGM) copula provides an intuitive and natural way to construct such a bivariate DF. When the linear correlation is stronger, the FGM copula cannot work anymore. In this case, we propose using a Gaussian copula, which connects two given marginals and is directly related to the linear correlation coefficient between two variables. Using the copulas, we construct the bivariate luminosity function (BLF) and discuss its statistical properties. We focus especially on the far-infrared-far-ulatraviolet (FUV-FIR) BLF, since these two wavelength regions are related to star-formation (SF) activity. Though both the FUV and FIR are related to SF activity, the univariate LFs have a very different functional form: the former is well described by the Schechter function whilst the latter has a much more extended power-law-like luminous end. We construct the FUV-FIR BLFs using the FGM and Gaussian copulas with different strengths of correlation, and examine their statistical properties. We then discuss some further possible applications of the BLF: the problem of a multiband flux-limited sample selection, the construction of the star-formation rate (SFR) function, and the construction of the stellar mass of galaxies (M*)-specific SFR (SFR/M*) relation. The copulas turn out to be a very useful tool to investigate all these issues, especially for including complicated selection effects.
Acoustic ship signature measurements by cross-correlation method.
Fillinger, Laurent; Sutin, Alexander; Sedunov, Alexander
2011-02-01
Cross-correlation methods were applied for the estimation of the power spectral density and modulation spectrum of underwater noise generated by moving vessels. The cross-correlation of the signal from two hydrophones allows the separation of vessel acoustic signatures in a busy estuary. Experimental data recorded in the Hudson River are used for demonstration that cross-correlation method measured the same ship noise and ship noise modulation spectra as conventional methods. The cross-correlation method was then applied for the separation of the acoustic signatures of two ships present simultaneously. Presented methods can be useful for ship traffic monitoring and small ship classification, even in noisy harbor environments.
Understanding volatility correlation behavior with a magnitude cross-correlation function
NASA Astrophysics Data System (ADS)
Jun, Woo Cheol; Oh, Gabjin; Kim, Seunghwan
2006-06-01
We propose an approach for analyzing the basic relation between correlation properties of the original signal and its magnitude fluctuations by decomposing the original signal into its positive and negative fluctuation components. We use this relation to understand the following phenomenon found in many naturally occurring time series: the magnitude of the signal exhibits long-range correlation, whereas the original signal is short-range correlated. The applications of our approach to heart rate variability signals and high-frequency foreign exchange rates reveal that the difference between the correlation properties of the original signal and its magnitude fluctuations is induced by the time organization structure of the correlation function between the magnitude fluctuations of positive and negative components. We show that this correlation function can be described well by a stretched-exponential function and is related to the nonlinearity and the multifractal structure of the signals.
42 CFR 476.86 - Correlation of Title XI functions with Title XVIII functions.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 42 Public Health 4 2011-10-01 2011-10-01 false Correlation of Title XI functions with Title XVIII functions. 476.86 Section 476.86 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF...) Qio Review Functions § 476.86 Correlation of Title XI functions with Title XVIII functions. (a...
42 CFR 476.86 - Correlation of Title XI functions with Title XVIII functions.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 42 Public Health 4 2010-10-01 2010-10-01 false Correlation of Title XI functions with Title XVIII functions. 476.86 Section 476.86 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF...) Qio Review Functions § 476.86 Correlation of Title XI functions with Title XVIII functions. (a...
Direct measurement of correlation functions in a lattice Lorentz gas
NASA Technical Reports Server (NTRS)
Binder, P.-M.; Frenkel, D.
1990-01-01
Simulations of a two-dimensional ballistic Lorentz gas on a lattice are reported. A moment-propagation technique allows direct measurements of the velocity correlation function and its moments with low relative errors for all times. The predicted 1/t-sq algebraic tails in the velocity correlation function are observed at all studied scatterer densities, unlike what has been reported for continuous systems. In the square lattice a fast oscillation is observed, consistent with the existence of staggered density modes. For the second-rank tensor correlation function, an extremely slow approach to the expected 1/t exp 3 tail is found.
Correlating Function and Imaging Measures of the Medial Longitudinal Fasciculus
Sakaie, Ken; Takahashi, Masaya; Remington, Gina; Wang, Xiaofeng; Conger, Amy; Conger, Darrel; Dimitrov, Ivan; Jones, Stephen; Frohman, Ashley; Frohman, Teresa; Sagiyama, Koji; Togao, Osamu
2016-01-01
Objective To test the validity of diffusion tensor imaging (DTI) measures of tissue injury by examining such measures in a white matter structure with well-defined function, the medial longitudinal fasciculus (MLF). Injury to the MLF underlies internuclear ophthalmoparesis (INO). Methods 40 MS patients with chronic INO and 15 healthy controls were examined under an IRB-approved protocol. Tissue integrity of the MLF was characterized by DTI parameters: longitudinal diffusivity (LD), transverse diffusivity (TD), mean diffusivity (MD) and fractional anisotropy (FA). Severity of INO was quantified by infrared oculography to measure versional disconjugacy index (VDI). Results LD was significantly lower in patients than in controls in the medulla-pons region of the MLF (p < 0.03). FA was also lower in patients in the same region (p < 0.0004). LD of the medulla-pons region correlated with VDI (R = -0.28, p < 0.05) as did FA in the midbrain section (R = 0.31, p < 0.02). Conclusions This study demonstrates that DTI measures of brain tissue injury can detect injury to a functionally relevant white matter pathway, and that such measures correlate with clinically accepted evaluation indices for INO. The results validate DTI as a useful imaging measure of tissue integrity. PMID:26800522
Molteni, Matteo; Weigel, Udo M; Remiro, Francisco; Durduran, Turgut; Ferri, Fabio
2014-11-17
We present a new hardware simulator (HS) for characterization, testing and benchmarking of digital correlators used in various optical correlation spectroscopy experiments where the photon statistics is Gaussian and the corresponding time correlation function can have any arbitrary shape. Starting from the HS developed in [Rev. Sci. Instrum. 74, 4273 (2003)], and using the same I/O board (PCI-6534 National Instrument) mounted on a modern PC (Intel Core i7-CPU, 3.07GHz, 12GB RAM), we have realized an instrument capable of delivering continuous streams of TTL pulses over two channels, with a time resolution of Δt = 50ns, up to a maximum count rate of 〈I〉 ∼ 5MHz. Pulse streams, typically detected in dynamic light scattering and diffuse correlation spectroscopy experiments were generated and measured with a commercial hardware correlator obtaining measured correlation functions that match accurately the expected ones.
Green's Function Application for Pairing Correlations and the Optical Potential
NASA Astrophysics Data System (ADS)
Ding, Dong
Pairing in asymmetric nuclear matter has been studied incorporating the effect of finite total momentum. We employ the generalized Cooper eigenvalue equation, which can be used to demonstrate the pairing instability and also generates reasonable pairing gaps compared to the traditional Bardeen-Cooper-Schrieffer (BCS) gap equation. From phase space arguments and the resulting strength of the pairing gap, we learn that the Larkin-Ovchinnikov-Fulde-Ferrell phase with a finite total momentum is favored over the conventional phase in asymmetric nuclear matter, but not in symmetric nuclear matter. To address open questions in neutron star cooling, neutron matter pairing gaps of the 1S0 and the 3P2 - 3F2 channels in a wide range of densities have been calculated using three different realistic interactions. Instead of the mean-field BCS procedure, we incorporate the influence of short- and long-range correlations in calculating the pairing gaps. Short-range correlations are treated to include the fragmentation of single-particle states, suppressing the gaps substantially. Long-range correlations dress the pairing interaction via density and spin modes, and provide a smaller correction. The results provide input for neutron-star cooling scenarios and are parametrized in a user friendly way. The results are of particular relevance in view of the recent observational data on Cassiopeia A. To study the nucleon-nucleus scattering problem in an ab-initio way, the optical potential in the momentum vector basis beyond the mean-field has been calculated employing the T x rho folding as the first step of the self-consistent Green's function method. The deuteron pole structure of T- matrix has been properly avoided using the spectral functions from the dispersive optical model. A comparison of the resulting real and imaginary part of the self-energy at 100 MeV with the corresponding dispersive-optical-model potentials shows reasonable agreement.
Sudomotor innervation in transthyretin amyloid neuropathy: Pathology and functional correlates
Huang, Cho‐Min; Chiang, Hao‐Hua; Luo, Kai‐Ren; Kan, Hung‐Wei; Yang, Naomi Chu‐Chiao; Chiang, Hao; Lin, Whei‐Min; Lai, Shu‐Mei; Lee, Ming‐Jen; Shun, Chia‐Tung; Hsieh, Sung‐Tsang
2015-01-01
Objective Autonomic neuropathy is a major component of familial amyloid polyneuropathy (FAP) due to mutated transthyretin, with sudomotor failure as a common manifestation. This study aimed to investigate the pathology and clinical significance of sudomotor denervation. Methods Skin biopsies were performed on the distal leg of FAP patients with a follow‐up duration of 3.8 ± 1.6 years. Sudomotor innervation was stained with 2 markers: protein gene product 9.5 (PGP 9.5), a general neuronal marker, and vasoactive intestinal peptide (VIP), a sudomotor nerve functional marker, followed by quantitation according to sweat gland innervation index (SGII) for PGP 9.5 (SGIIPGP 9.5) and VIP (SGIIVIP). Results There were 28 patients (25 men) with Ala97Ser transthyretin and late onset (59.9 ± 6.0 years) disabling neuropathy. Autonomic symptoms were present in 22 patients (78.6%) at the time of skin biopsy. The SGIIPGP 9.5 and SGIIVIP of FAP patients were significantly lower than those of age‐ and gender‐matched controls. The reduction of SGIIVIP was more severe than that of SGIIPGP 9.5 (p = 0.002). Patients with orthostatic hypotension or absent sympathetic skin response at palms were associated with lower SGIIPGP 9.5 (p = 0.019 and 0.002, respectively). SGIIPGP 9.5 was negatively correlated with the disability grade at the time of skin biopsy (p = 0.004), and was positively correlated with the interval from the time of skin biopsy to the time of wheelchair usage (p = 0.029). Interpretation This study documented the pathological evidence of sudomotor denervation in FAP. SGIIPGP 9.5 was functionally correlated with autonomic symptoms, autonomic tests, ambulation status, and progression of disability. Ann Neurol 2015;78:272℃283 PMID:25973863
NASA Technical Reports Server (NTRS)
Mcclelland, J.; Silk, J.
1979-01-01
The evolution of the two-point correlation function for the large-scale distribution of galaxies in an expanding universe is studied on the assumption that the perturbation densities lie in a Gaussian distribution centered on any given mass scale. The perturbations are evolved according to the Friedmann equation, and the correlation function for the resulting distribution of perturbations at the present epoch is calculated. It is found that: (1) the computed correlation function gives a satisfactory fit to the observed function in cosmological models with a density parameter (Omega) of approximately unity, provided that a certain free parameter is suitably adjusted; (2) the power-law slope in the nonlinear regime reflects the initial fluctuation spectrum, provided that the density profile of individual perturbations declines more rapidly than the -2.4 power of distance; and (3) both positive and negative contributions to the correlation function are predicted for cosmological models with Omega less than unity.
NASA Technical Reports Server (NTRS)
Mcclelland, J.; Silk, J.
1979-01-01
The evolution of the two-point correlation function for the large-scale distribution of galaxies in an expanding universe is studied on the assumption that the perturbation densities lie in a Gaussian distribution centered on any given mass scale. The perturbations are evolved according to the Friedmann equation, and the correlation function for the resulting distribution of perturbations at the present epoch is calculated. It is found that: (1) the computed correlation function gives a satisfactory fit to the observed function in cosmological models with a density parameter (Omega) of approximately unity, provided that a certain free parameter is suitably adjusted; (2) the power-law slope in the nonlinear regime reflects the initial fluctuation spectrum, provided that the density profile of individual perturbations declines more rapidly than the -2.4 power of distance; and (3) both positive and negative contributions to the correlation function are predicted for cosmological models with Omega less than unity.
Functional connectivity disruptions correlate with cognitive phenotypes in Parkinson's disease.
Hassan, M; Chaton, L; Benquet, P; Delval, A; Leroy, C; Plomhause, L; Moonen, A J H; Duits, A A; Leentjens, A F G; van Kranen-Mastenbroek, V; Defebvre, L; Derambure, P; Wendling, F; Dujardin, K
2017-01-01
Cognitive deficits in Parkinson's disease are thought to be related to altered functional brain connectivity. To date, cognitive-related changes in Parkinson's disease have never been explored with dense-EEG with the aim of establishing a relationship between the degree of cognitive impairment, on the one hand, and alterations in the functional connectivity of brain networks, on the other hand. This study was aimed at identifying altered brain networks associated with cognitive phenotypes in Parkinson's disease using dense-EEG data recorded during rest with eyes closed. Three groups of Parkinson's disease patients (N = 124) with different cognitive phenotypes coming from a data-driven cluster analysis, were studied: G1) cognitively intact patients (63), G2) patients with mild cognitive deficits (46) and G3) patients with severe cognitive deficits (15). Functional brain networks were identified using a dense-EEG source connectivity method. Pairwise functional connectivity was computed for 68 brain regions in different EEG frequency bands. Network statistics were assessed at both global (network topology) and local (inter-regional connections) level. Results revealed progressive disruptions in functional connectivity between the three patient groups, typically in the alpha band. Differences between G1 and G2 (p < 0.001, corrected using permutation test) were mainly frontotemporal alterations. A statistically significant correlation (ρ = 0.49, p < 0.001) was also obtained between a proposed network-based index and the patients' cognitive score. Global properties of network topology in patients were relatively intact. These findings indicate that functional connectivity decreases with the worsening of cognitive performance and loss of frontotemporal connectivity may be a promising neuromarker of cognitive impairment in Parkinson's disease.
Charge-Charge Correlation Functions in Ultra Dense Plasmas.
1983-06-22
functions appearing in the memory operator and had to approximate those correlations by their Debye - Huckel limits. We are now able to calculate the direct...results for S (kz) with one important difference. The results presented here contain the exact static correlation functions rather than their Debye - Huckel ...The types of theories of interest here are microscopic theories based upon formally exact kinetic equations derived from projection operator 10- 12
Corrfunc: Blazing fast correlation functions on the CPU
NASA Astrophysics Data System (ADS)
Sinha, Manodeep
2017-03-01
Corrfunc is a suite of high-performance clustering routines. The code can compute a variety of spatial correlation functions on Cartesian geometry as well Landy-Szalay calculations for spatial and angular correlation functions on a spherical geometry and is useful for, for example, exploring the galaxy-halo connection. The code is written in C and can be used on the command-line, through the supplied python extensions, or the C API.
Dynamic Correlation Functions of Adsorption Stochastic Systems with Diffusional Relaxation
NASA Astrophysics Data System (ADS)
Grynberg, Marcelo D.; Stinchcombe, Robin B.
1995-02-01
We investigate the nonequilibrium behavior of dynamic correlation functions of random sequential adsorption processes with diffusional relaxation. Depending on the relative values of the transition probability rates, in one dimension these systems reduce to a soluble problem of many fermions. In contrast to the standard diffusive relaxation of the macroscopic density, the correlation functions exhibit a faster decay. Our results are supported and compared with Monte Carlo simulations.
ZeldovichRecon: Halo correlation function using the Zeldovich approximation
NASA Astrophysics Data System (ADS)
White, Martin
2015-12-01
ZeldovichRecon computes the halo correlation function using the Zeldovich approximation. It includes 3 variants:zelrecon.cpp, which computes the various contributions to the correlation function; zelrecon_ctypes.cpp, which is designed to be called from Python using the ctypes library; and a version which implements the "ZEFT" formalism of "A Lagrangian effective field theory" [arxiv:1506.05264] including the alpha term described in that paper.
Structural and Functional Cerebral Correlates of Hypnotic Suggestibility
Huber, Alexa; Lui, Fausta; Duzzi, Davide; Pagnoni, Giuseppe; Porro, Carlo Adolfo
2014-01-01
Little is known about the neural bases of hypnotic suggestibility, a cognitive trait referring to the tendency to respond to hypnotic suggestions. In the present magnetic resonance imaging study, we performed regression analyses to assess hypnotic suggestibility-related differences in local gray matter volume, using voxel-based morphometry, and in waking resting state functional connectivity of 10 resting state networks, in 37 healthy women. Hypnotic suggestibility was positively correlated with gray matter volume in portions of the left superior and medial frontal gyri, roughly overlapping with the supplementary and pre-supplementary motor area, and negatively correlated with gray matter volume in the left superior temporal gyrus and insula. In the functional connectivity analysis, hypnotic suggestibility was positively correlated with functional connectivity between medial posterior areas, including bilateral posterior cingulate cortex and precuneus, and both the lateral visual network and the left fronto-parietal network; a positive correlation was also found with functional connectivity between the executive-control network and a right postcentral/parietal area. In contrast, hypnotic suggestibility was negatively correlated with functional connectivity between the right fronto-parietal network and the right lateral thalamus. These findings demonstrate for the first time a correlation between hypnotic suggestibility, the structural features of specific cortical regions, and the functional connectivity during the normal resting state of brain structures involved in imagery and self-monitoring activity. PMID:24671130
Characterization of maximally random jammed sphere packings: Voronoi correlation functions.
Klatt, Michael A; Torquato, Salvatore
2014-11-01
We characterize the structure of maximally random jammed (MRJ) sphere packings by computing the Minkowski functionals (volume, surface area, and integrated mean curvature) of their associated Voronoi cells. The probability distribution functions of these functionals of Voronoi cells in MRJ sphere packings are qualitatively similar to those of an equilibrium hard-sphere liquid and partly even to the uncorrelated Poisson point process, implying that such local statistics are relatively structurally insensitive. This is not surprising because the Minkowski functionals of a single Voronoi cell incorporate only local information and are insensitive to global structural information. To improve upon this, we introduce descriptors that incorporate nonlocal information via the correlation functions of the Minkowski functionals of two cells at a given distance as well as certain cell-cell probability density functions. We evaluate these higher-order functions for our MRJ packings as well as equilibrium hard spheres and the Poisson point process. It is shown that these Minkowski correlation and density functions contain visibly more information than the corresponding standard pair-correlation functions. We find strong anticorrelations in the Voronoi volumes for the hyperuniform MRJ packings, consistent with previous findings for other pair correlations [A. Donev et al., Phys. Rev. Lett. 95, 090604 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.090604], indicating that large-scale volume fluctuations are suppressed by accompanying large Voronoi cells with small cells, and vice versa. In contrast to the aforementioned local Voronoi statistics, the correlation functions of the Voronoi cells qualitatively distinguish the structure of MRJ sphere packings (prototypical glasses) from that of not only the Poisson point process but also the correlated equilibrium hard-sphere liquids. Moreover, while we did not find any perfect icosahedra (the locally densest possible structure in which a
NASA Astrophysics Data System (ADS)
Rogers, Jeremy D.
2016-03-01
Numerous methods have been developed to quantify the light scattering properties of tissue. These properties are of interest in diagnostic and screening applications due to sensitivity to changes in tissue ultrastructure and changes associated with disease such as cancer. Tissue is considered a weak scatterer because that the mean free path is much larger than the correlation length. When this is the case, all scattering properties can be calculated from the refractive index correlation function Bn(r). Direct measurement of Bn(r) is challenging because it requires refractive index measurement at high resolution over a large tissue volume. Instead, a model is usually assumed. One particularly useful model, the Whittle-Matern function includes several realistic function types such as mass fractal and exponential. Optical scattering properties for weakly scattering media can be determined analytically from Bn(r) by applying the Rayleigh-Gans-Debye (RGD) or Born Approximation, and so measured scattering properties are used to fit parameters of the model function. Direct measurement of Bn(r) would provide confirmation that the function is a good representation of tissue or help in identifying the length scale at which changes occur. The RGD approximation relates the scattering phase function to the refractive index correlation function through a Fourier transform. This can be inverted without approximation, so goniometric measurement of the scattering can be converted to Bn(r). However, geometric constraints of the measurement of the phase function, angular resolution, and wavelength result in a band limited measurement of Bn(r). These limits are discussed and example measurements are described.
Aggregating and Testing Intra-Individual Correlations: Methods and Comparisons.
Zhang, Qian Jackie; Wang, Lijuan Peggy
2014-01-01
From a longitudinal study, we have repeatedly measured data from multiple individuals at multiple occasions. For each individual, the relation between 2 variables can be measured by the Pearson's correlation. The question is how to aggregate the multiple correlations and conduct statistical inference on the aggregated intra-individual correlation. Several methods are proposed to aggregate and test intra-individual correlations: (a) a meta-analysis method based on Fisher's Z transformed correlations, (b) a meta-analysis method based on the Pearson's correlations, and (c) a multilevel modeling method using data standardized within each individual. The performance of the methods after bias corrections was compared using simulations with considering factors including numbers of individuals, numbers of time points, population effect sizes, and their distribution forms (homogeneous vs heterogeneous). The results from the simulation studies show that estimation biases were found using the meta-analytic methods and suggestions on when and how to correct biases were provided based on the simulation results. Furthermore, the performance of the 3 methods after necessary bias corrections was found to be comparable and reasonably good, indicating that all 3 methods worked for aggregating and testing intra-individual correlations. An empirical daily diary data set was then used to illustrate the applications of the 3 methods. The assumptions, advantages and disadvantages, and possible extensions of the 3 methods were discussed.
Wave function methods for fractional electrons.
Steinmann, Stephan N; Yang, Weitao
2013-08-21
Determining accurate chemical potentials is of considerable interest in various chemical and physical contexts: from small molecular charge-transfer complexes to bandgap in bulk materials such as semi-conductors. Chemical potentials are typically evaluated either by density functional theory, or, alternatively, by computationally more intensive Greens function based GW computations. To calculate chemical potentials, the ground state energy needs to be defined for fractional charges. We thus explore an extension of wave function theories to fractional charges, and investigate the ionization potential and electron affinity as the derivatives of the energy with respect to the electron number. The ultimate aim is to access the chemical potential of correlated wave function methods without the need of explicitly changing the numbers of electrons, making the approach readily applicable to bulk materials. We find that even though second order perturbation theory reduces the fractional charge error considerably compared to Hartree-Fock and standard density functionals, higher order perturbation theory is more accurate and coupled-cluster approaches are even more robust, provided the electrons are bound at the Hartree-Fock level. The success of post-HF approaches to improve over HF relies on two equally important aspects: the integer values are more accurate and the Coulomb correlation between the fractionally occupied orbital and all others improves the straight line behavior significantly as identified by a correction to Hartree-Fock. Our description of fractional electrons is also applicable to fractional spins, illustrating the ability of coupled-cluster singles and doubles to deal with two degenerate fractionally occupied orbitals, but its inadequacy for three and more fractional spins, which occur, for instance, for spherical atoms and when dissociating double bonds. Our approach explores the realm of typical wave function methods that are applied mostly in molecular
Wave function methods for fractional electrons
NASA Astrophysics Data System (ADS)
Steinmann, Stephan N.; Yang, Weitao
2013-08-01
Determining accurate chemical potentials is of considerable interest in various chemical and physical contexts: from small molecular charge-transfer complexes to bandgap in bulk materials such as semi-conductors. Chemical potentials are typically evaluated either by density functional theory, or, alternatively, by computationally more intensive Greens function based GW computations. To calculate chemical potentials, the ground state energy needs to be defined for fractional charges. We thus explore an extension of wave function theories to fractional charges, and investigate the ionization potential and electron affinity as the derivatives of the energy with respect to the electron number. The ultimate aim is to access the chemical potential of correlated wave function methods without the need of explicitly changing the numbers of electrons, making the approach readily applicable to bulk materials. We find that even though second order perturbation theory reduces the fractional charge error considerably compared to Hartree-Fock and standard density functionals, higher order perturbation theory is more accurate and coupled-cluster approaches are even more robust, provided the electrons are bound at the Hartree-Fock level. The success of post-HF approaches to improve over HF relies on two equally important aspects: the integer values are more accurate and the Coulomb correlation between the fractionally occupied orbital and all others improves the straight line behavior significantly as identified by a correction to Hartree-Fock. Our description of fractional electrons is also applicable to fractional spins, illustrating the ability of coupled-cluster singles and doubles to deal with two degenerate fractionally occupied orbitals, but its inadequacy for three and more fractional spins, which occur, for instance, for spherical atoms and when dissociating double bonds. Our approach explores the realm of typical wave function methods that are applied mostly in molecular
Correlation of Two Anthocyanin Quantification Methods: HPLC and Spectrophotometric Methods
USDA-ARS?s Scientific Manuscript database
The pH differential method and HPLC are methods that are commonly used by researchers and the food industry for quantifying anthocyanins in a sample. This study was conducted to establish a relationship between the two analytical methods. Seven juice samples containing an array of different individu...
Kim, Junghi; Wozniak, Jeffrey R.; Mueller, Bryon A.
2015-01-01
Abstract Resting-state functional magnetic resonance imaging allows one to study brain functional connectivity, partly motivated by evidence that patients with complex disorders, such as Alzheimer's disease, may have altered functional brain connectivity patterns as compared with healthy subjects. A functional connectivity network describes statistical associations of the neural activities among distinct and distant brain regions. Recently, there is a major interest in group-level functional network analysis; however, there is a relative lack of studies on statistical inference, such as significance testing for group comparisons. In particular, it is still debatable which statistic should be used to measure pairwise associations as the connectivity weights. Many functional connectivity studies have used either (full or marginal) correlations or partial correlations for pairwise associations. This article investigates the performance of using either correlations or partial correlations for testing group differences in brain connectivity, and how sparsity levels and topological structures of the connectivity would influence statistical power to detect group differences. Our results suggest that, in general, testing group differences in networks deviates from estimating networks. For example, high regularization in both covariance matrices and precision matrices may lead to higher statistical power; in particular, optimally selected regularization (e.g., by cross-validation or even at the true sparsity level) on the precision matrices with small estimation errors may have low power. Most importantly, and perhaps surprisingly, using either correlations or partial correlations may give very different testing results, depending on which of the covariance matrices and the precision matrices are sparse. Specifically, if the precision matrices are sparse, presumably and arguably a reasonable assumption, then using correlations often yields much higher powered and more
Correlation singularities of partially coherent beams with multi-Gaussian correlation function
NASA Astrophysics Data System (ADS)
Zhang, Yongtao; Wang, Haixia; Ding, Chaoliang; Pan, Liuzhan
2017-08-01
Correlation singularities of partially coherent beams with multi-Gaussian correlation function (i.e., multi-Gaussian Schell-model beams) are studied. It is shown that there exist correlation singularities for scalar multi-Gaussian Schell-model (MGSM) beams, both in the source plane and in the output plane. We find the simple relation between the correlation singularities and the beam index M of MGSM beams, i.e., the number of ring dislocations equals M - 1, which may be used to determine the beam index M.
Design of exchange-correlation functionals through the correlation factor approach
Pavlíková Přecechtělová, Jana E-mail: Matthias.Ernzerhof@UMontreal.ca
2015-10-14
The correlation factor model is developed in which the spherically averaged exchange-correlation hole of Kohn-Sham theory is factorized into an exchange hole model and a correlation factor. The exchange hole model reproduces the exact exchange energy per particle. The correlation factor is constructed in such a manner that the exchange-correlation energy correctly reduces to exact exchange in the high density and rapidly varying limits. Four different correlation factor models are presented which satisfy varying sets of physical constraints. Three models are free from empirical adjustments to experimental data, while one correlation factor model draws on one empirical parameter. The correlation factor models are derived in detail and the resulting exchange-correlation holes are analyzed. Furthermore, the exchange-correlation energies obtained from the correlation factor models are employed to calculate total energies, atomization energies, and barrier heights. It is shown that accurate, non-empirical functionals can be constructed building on exact exchange. Avenues for further improvements are outlined as well.
Pair-correlation function of a metastable helium Bose-Einstein condensate
Zin, Pawel; Trippenbach, Marek; Gajda, Mariusz
2004-02-01
The pair-correlation function is one of the basic quantities to characterize the coherence properties of a Bose-Einstein condensate. We calculate this function in the experimentally important case of a zero temperature Bose-Einstein condensate in a metastable triplet helium state using the variational method with a pair-excitation ansatz. We compare our result with a pair-correlation function obtained for the hard-sphere potential with the same scattering length. Both functions are practically indistinguishable for distances greater than the scattering length. At smaller distances, due to interatomic interactions, the helium condensate shows strong correlations.
Garashchuk, Sophya
2007-04-21
The de Broglie-Bohm formulation of the Schrodinger equation implies conservation of the wave function probability density associated with each quantum trajectory in closed systems. This conservation property greatly simplifies numerical implementations of the quantum trajectory dynamics and increases its accuracy. The reconstruction of a wave function, however, becomes expensive or inaccurate as it requires fitting or interpolation procedures. In this paper we present a method of computing wave packet correlation functions and wave function projections, which typically contain all the desired information about dynamics, without the full knowledge of the wave function by making quadratic expansions of the wave function phase and amplitude near each trajectory similar to expansions used in semiclassical methods. Computation of the quantities of interest in this procedure is linear with respect to the number of trajectories. The introduced approximations are consistent with approximate quantum potential dynamics method. The projection technique is applied to model chemical systems and to the H+H(2) exchange reaction in three dimensions.
Universal spatial correlation functions for describing and reconstructing soil microstructure.
Karsanina, Marina V; Gerke, Kirill M; Skvortsova, Elena B; Mallants, Dirk
2015-01-01
Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification
Universal Spatial Correlation Functions for Describing and Reconstructing Soil Microstructure
Skvortsova, Elena B.; Mallants, Dirk
2015-01-01
Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification
NASA Astrophysics Data System (ADS)
M, Y. Ali; J, Poulter
2013-06-01
In this work we study the correlation function of the ground state of a two-dimensional fully frustrated Ising model as well as spin glass. The Pfaffian method is used to calculate free energy and entropy as well as the correlation function. We estimate the exponent of spin correlation function for the fully frustrated model and spin glass. In this paper an overview of the latest results on the spin correlation function is presented.
Revealing quantum correlation by negativity of the Wigner function
NASA Astrophysics Data System (ADS)
Taghiabadi, Razieh; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen
2016-05-01
We analyze two two-mode continuous variable separable states with the same marginal states. We adopt the definition of classicality in the form of well-defined positive Wigner function describing the state and find that although the states possess positive local Wigner functions, they exhibit negative Wigner functions for the global states. Using the negativity of Wigner function as an indicator of nonclassicality, we show that despite these states possess different negativities of the Wigner function, they do not reveal this difference as phase space nonclassicalities such as negativity of the Mandel Q parameter or quadrature squeezing. We then concentrate on quantum correlation of these states and show that quantum discord and local quantum uncertainty, as two well-defined measures of quantum correlation, manifest the difference between negativity of the Wigner functions. The non-Gaussianity of these states is also examined and show that the difference in behavior of their non-Gaussianity is the same as the difference between negativity of their Wigner functions. We also investigate the influence of correlation rank criterion and find that when the states can be produced locally from classical states, the Wigner functions cannot reveal their quantum correlations.
Determination of transfer function of COPE correlation interferometer instrument
NASA Technical Reports Server (NTRS)
Twitty, J.; Kindle, E. C.
1976-01-01
The comparison of theoretical and instrument response functions and its use as a procedure for determining the transfer function of the COPE correlation interferometer are summarized. Data show qualitative agreement can be obtained when discrepancies between theory and instrument are investigated and instrument components are analyzed in detail. Data were obtained using a set of calibration data and computer algorithms.
Correlated Monte Carlo wave functions for the atoms He through Ne
Schmidt, K.E. ); Moskowitz, J.W. )
1990-09-15
We apply the variational Monte Carlo method to the atoms He through Ne. Our trial wave function is of the form introduced by Boys and Handy. We use the Monte Carlo method to calculate the first and second derivatives of an unreweighted variance and apply Newton's method to minimize this variance. We motivate the form of the correlation function using the local current conservation arguments of Feynman and Cohen. Using a self-consistent field wave function multiplied by a Boys and Handy correlation function, we recover a large fraction of the correlation energy of these atoms. We give the value of all variational parameters necessary to reproduce our wave functions. The method can be extended easily to other atoms and to molecules.
Functional profiling methods in cancer.
Dopazo, Joaquín
2010-01-01
The introduction of new high-throughput methodologies such as DNA microarrays constitutes a major breakthrough in cancer research. The unprecedented amount of data produced by such technologies has opened new avenues for interrogating living systems although, at the same time, it has demanded of the development of new data analytical methods as well as new strategies for testing hypotheses. A history of early successful applications in cancer boosted the use of microarrays and fostered further applications in other fields. Keeping the pace with these technologies, bioinformatics offers new solutions for data analysis and, what is more important, permits the formulation of a new class of hypotheses inspired in systems biology, more oriented to pathways or, in general, to modules of functionally related genes. Although these analytical methodologies are new, some options are already available and are discussed in this chapter.
Craig, Ian R; Manolopoulos, David E
2004-08-22
We propose an approximate method for calculating Kubo-transformed real-time correlation functions involving position-dependent operators, based on path integral (Parrinello-Rahman) molecular dynamics. The method gives the exact quantum mechanical correlation function at time zero, exactly satisfies the quantum mechanical detailed balance condition, and for correlation functions of the form C(Ax)(t) and C(xB)(t) it gives the exact result for a harmonic potential. It also works reasonably well at short times for more general potentials and correlation functions, as we illustrate with some example calculations. The method provides a consistent improvement over purely classical molecular dynamics that is most apparent in the low-temperature regime.
Correlation function of four spins in the percolation model
NASA Astrophysics Data System (ADS)
Dotsenko, Vladimir S.
2016-10-01
By using the Coulomb gas technics we calculate the four-spin correlation function in the percolation q → 1 limit of the Potts model. It is known that the four-point functions define the actual fusion rules of a particular model. In this respect, we find that fusion of two spins, of dimension Δσ =5/96, produce a new channel, in the 4-point function, which is due to the operator with dimension Δ = 5 / 8.
A new 'Implicit correlation' method for cross-correlation sampling in MCNPX-PoliMi
Marcath, M. J.; Larsen, E. W.; Clarke, S. D.; Pozzi, S. A.
2013-07-01
Monte Carlo particle transport codes used to accurately model detector response are traditionally run in fully analog mode. Analog simulations of cross-correlation measurements with these codes are extremely time-consuming because the probability of correlated detection is extremely small, approximately equal to the product of the probabilities of a single detection in each detector. The new 'implicit correlation' method described here increases the number of correlation event scores thereby reducing variance and required computation times. The cost of the implicit correlation method is comparable to the cost of simulating single event detection for the lowest absolute detector efficiency in the problem. This method is especially useful in the nuclear non-proliferation and safeguards fields for simulating correlation measurements of shielded special nuclear material. The new method was implemented in MCNPX-PoliMi for neutron-neutron cross-correlations with a Cf-252 spontaneous fission source measured by two detectors of variable stand-offs. The method demonstrated good agreement with analog simulation results for multiple measurement geometries. Small differences between non-analog and analog cross-correlation distributions are attributed to known features of the specific problem simulated that will not be present in practical applications. (authors)
Correlation Function Analysis of Fiber Networks: Implications for Thermal Conductivity
NASA Technical Reports Server (NTRS)
Martinez-Garcia, Jorge; Braginsky, Leonid; Shklover, Valery; Lawson, John W.
2011-01-01
The heat transport in highly porous fiber structures is investigated. The fibers are supposed to be thin, but long, so that the number of the inter-fiber connections along each fiber is large. We show that the effective conductivity of such structures can be found from the correlation length of the two-point correlation function of the local conductivities. Estimation of the parameters, determining the conductivity, from the 2D images of the structures is analyzed.
Static structure factor and pair correlation function of graphene.
Ashraf, S S Z; Mishra, Kavita N; Sharma, A C
2010-09-08
We report our theoretical investigations on the static structure factor and pair correlation function using both the density-density and spin-density response functions of a doped single graphene sheet based on the random phase approximation and on graphene's massless Dirac fermions concept. The static structure factor and pair correlation function are obtained by regularizing the dynamical polarization function, which otherwise is clearly divergent due to the interaction energy of the infinite Dirac sea of negative energy states. The local field effects have been considered in the simplistic Hubbard approximation. We find the structure factor to be dependent on the dimensionless coupling constant α, and for high values of coupling constant the magnetic structure factor indicates paramagnetic instability which is also corroborated from other theoretical investigations. The spin symmetric pair correlation function computed in the simplistic Hubbard approximation begins from zero at zero separation only at very high densities but the results for parallel spin and anti-parallel spin pair correlation functions expose the shortcoming of this local field approximation. This work should stimulate more investigations testing various other local field schemes and also quantum Monte Carlo based simulations.
Prevalence and correlates of functional dependence among maintenance dialysis patients.
Kavanagh, Niall T; Schiller, Brigitte; Saxena, Anjali B; Thomas, I-Chun; Kurella Tamura, Manjula
2015-10-01
Functional dependence is an important determinant of longevity and quality of life. The purpose of the current study was to determine the prevalence and correlates of functional dependence among patients with end-stage renal disease (ESRD) receiving maintenance dialysis. We enrolled 148 participants with ESRD from five clinics. Functional status, as measured by basic and instrumental activities of daily living (ADL, IADL), was ascertained by validated questionnaires. Functional dependence was defined as needing assistance in at least one of seven IADLs or at least one of four ADLs. Demographic characteristics, chronic health conditions, anthropometric measurements, and laboratories were assessed by a combination of self-report and chart review. Cognitive function was assessed with a neurocognitive battery, and depressive symptoms were assessed by questionnaire. Mean age of the sample was 56.2 ± 14.6 years. Eighty-seven participants (58.8%) demonstrated dependence in ADLs or IADLs, 70 (47.2%) exhibited IADL dependence alone, and 17 (11.5%) exhibited combined IADL and ADL dependence. In a multivariable-adjusted model, stroke, cognitive impairment, and higher systolic blood pressure were independent correlates of functional dependence. We found no significant association between demographic characteristics, chronic health conditions, depressive symptoms or laboratory measurements, and functional dependence. Impairment in executive function was more strongly associated with functional dependence than memory impairment. Functional dependence is common among ESRD patients and independently associated with stroke, systolic blood pressure, and executive function impairment.
Chiral and UA(1) Symmetry in Correlation Functions in Medium
NASA Astrophysics Data System (ADS)
Lee, Su Houng; Cho, Sungtae
2013-03-01
In this review, we will discuss how the chiral symmetry and UA(1) breaking effects are reflected in the correlation functions. Using the Banks-Casher formula, one can identify the density of zero eigenvalues to be the common ingredient that governs the chiral symmetry breaking in correlation functions between currents composed of light quarks with or without a heavy quark. Similarly, the presence of the UA(1) breaking effect is determined through the contribution of the topologically nontrivial configurations that depends on the number of flavors. We also discuss how the symmetry breaking effects are reflected in the gluon correlation functions. Finally, we review the Witten-Veneziano (WV) formula for the η' mass in medium.
Correlation functions of higher-dimensional automatic sequences
NASA Astrophysics Data System (ADS)
Barbé, A.; von Haeseler, F.
2004-11-01
A procedure for calculating the (auto)correlation function \\gamma_f(k), k\\in {\\bb Z}^m , of an m-dimensional complex-valued automatic sequence f:{\\bb Z}^m\\rightarrow {\\bb C} , is presented. This is done by deriving a recursion for the vector correlation function Γker(f)(k) whose components are the (cross)correlation functions between all sequences in the finite set ker(f), the so-called kernel of f which contains all properly defined decimations of f. The existence of Γker(f)(k), which is defined as a limit, for all k\\in {\\bb Z}^m , is shown to depend only on the existence of Γker(f)(0). This is illustrated for the higher-dimensional Thue-Morse, paper folding and Rudin-Shapiro sequences.
Wilsonian renormalisation of CFT correlation functions: field theory
NASA Astrophysics Data System (ADS)
Lizana, J. M.; Pérez-Victoria, M.
2017-06-01
We examine the precise connection between the exact renormalisation group with local couplings and the renormalisation of correlation functions of composite operators in scale-invariant theories. A geometric description of theory space allows us to select convenient non-linear parametrisations that serve different purposes. First, we identify normal parameters in which the renormalisation group flows take their simplest form; normal correlators are defined by functional differentiation with respect to these parameters. The renormalised correlation functions are given by the continuum limit of correlators associated to a cutoff-dependent parametrisation, which can be related to the renormalisation group flows. The necessary linear and non-linear counterterms in any arbitrary parametrisation arise in a natural way from a change of coordinates. We show that, in a class of minimal subtraction schemes, the renormalised correlators are exactly equal to normal correlators evaluated at a finite cutoff. To illustrate the formalism and the main results, we compare standard diagrammatic calculations in a scalar free-field theory with the structure of the perturbative solutions to the Polchinski equation close to the Gaussian fixed point.
Decomposition of Proteins into Dynamic Units from Atomic Cross-Correlation Functions.
Calligari, Paolo; Gerolin, Marco; Abergel, Daniel; Polimeno, Antonino
2017-01-10
In this article, we present a clustering method of atoms in proteins based on the analysis of the correlation times of interatomic distance correlation functions computed from MD simulations. The goal is to provide a coarse-grained description of the protein in terms of fewer elements that can be treated as dynamically independent subunits. Importantly, this domain decomposition method does not take into account structural properties of the protein. Instead, the clustering of protein residues in terms of networks of dynamically correlated domains is defined on the basis of the effective correlation times of the pair distance correlation functions. For these properties, our method stands as a complementary analysis to the customary protein decomposition in terms of quasi-rigid, structure-based domains. Results obtained for a prototypal protein structure illustrate the approach proposed.
Gutzwiller density functional theory for correlated electron systems
Ho, K. M.; Schmalian, J.; Wang, C. Z.
2008-02-04
We develop a density functional theory (DFT) and formalism for correlated electron systems by taking as reference an interacting electron system that has a ground state wave function which exactly obeys the Gutzwiller approximation for all one-particle operators. The solution of the many-electron problem is mapped onto the self-consistent solution of a set of single-particle Schroedinger equations, analogously to standard DFT-local density approximation calculations.
Correlation Green's Functions for the Gulf of California
NASA Astrophysics Data System (ADS)
Clayton, R. W.
2005-12-01
Green's functions for the Gulf of California region have been determined from ambient noise measurements recorded by the broadband networks in the region (NARS and RESBAN). The correlations are one-sided for energy in the microseism band ( 5-30 sec) and two-sided for the 30-100 sec band. The Green's functions appear to exhibit significant multipathing. Synthetic tests have been conducted to rule out heterogeneity in the source distribution as the cause of this.
Russo, Cesare; Jin, Zhezhen; Homma, Shunichi; Rundek, Tatjana; Elkind, Mitchell S V; Sacco, Ralph L; Di Tullio, Marco R
2012-01-01
Objective Left atrial (LA) maximum volume (LAVmax) is an indicator of left ventricular (LV) diastolic function. However, LAVmax is also influenced by systolic events, whereas the LA minimum volume (LAVmin) is directly exposed to LV pressure. The authors hypothesised that LAVmin may be a better correlate of LV diastolic function than LAVmax. Design Cross-sectional. Setting University hospital. Patients 357 participants from a community-based cohort study. Methods LA volumes and reservoir function, measured as total LA emptying volume (LAEV) and LA emptying fraction (LAEF), were assessed by real-time three-dimensional echocardiography. LV diastolic function was assessed by trans-mitral early (E) and late (A) Doppler velocities and mitral early diastolic velocity by tissue-Doppler (e′). LV systolic function was assessed by LV ejection fraction (LVEF) and global longitudinal strain (GLS) by speckle-tracking. Results LAVmin significantly increased with worsening diastolic dysfunction (p<0.001), whereas the increase in LAVmax was less pronounced (p=0.07). LAEV and LAEF decreased with worsening diastolic dysfunction (both p<0.001). In linear regressions, LAVmin and LAVmax were significant predictors of E/e′, with higher parameter estimates for LAVmin. In multivariate models, LAVmin resulted strongly associated with E/e′ (β=0.45, p<0.001), whereas LAVmax was not (β=− 0.16, p=0.08). LA reservoir function was better associated with GLS than LVEF. In multivariate analyses, GLS was significantly associated with LAVmax (β=− 0.15, p=0.002), LAEV (β=−0.37, p<0.001) and LAEF (β=−0.28, p<0.001) but not with LAVmin. Conclusions LAVmin is a better correlate of LV diastolic function than LAVmax. The impact of LV longitudinal systolic function on LA reservoir function might explain the weaker relation between LAVmax and LV diastolic function. PMID:22543839
Cross-correlation function of acoustic fields generated by random high-frequency sources.
Godin, Oleg A
2010-08-01
Long-range correlations of noise fields in arbitrary inhomogeneous, moving or motionless fluids are studied in the ray approximation. Using the stationary phase method, two-point cross-correlation function of noise is shown to approximate the sum of the deterministic Green's functions describing sound propagation in opposite directions between the two points. Explicit relations between amplitudes of respective ray arrivals in the noise cross-correlation function and the Green's functions are obtained and verified against specific problems allowing an exact solution. Earlier results are extended by simultaneously accounting for sound absorption, arbitrary distribution of noise sources in a volume and on surfaces, and fluid inhomogeneity and motion. The information content of the noise cross-correlation function is discussed from the viewpoint of passive acoustic characterization of inhomogeneous flows.
Methods of making functionalized nanorods
Gur, Ilan [San Francisco, CA; Milliron, Delia [Berkeley, CA; Alivisatos, A Paul [Oakland, CA; Liu, Haitao [Berkeley, CA
2012-01-10
A process for forming functionalized nanorods. The process includes providing a substrate, modifying the substrate by depositing a self-assembled monolayer of a bi-functional molecule on the substrate, wherein the monolayer is chosen such that one side of the bi-functional molecule binds to the substrate surface and the other side shows an independent affinity for binding to a nanocrystal surface, so as to form a modified substrate. The process further includes contacting the modified substrate with a solution containing nanocrystal colloids, forming a bound monolayer of nanocrystals on the substrate surface, depositing a polymer layer over the monolayer of nanocrystals to partially cover the monolayer of nanocrystals, so as to leave a layer of exposed nanocrystals, functionalizing the exposed nanocrystals, to form functionalized nanocrystals, and then releasing the functionalized nanocrystals from the substrate.
NASA Astrophysics Data System (ADS)
Faerman, V. A.; Cheremnov, A. G.; Avramchuk, V. V.; Luneva, E. E.
2014-08-01
In the current work the relevance of nondestructive test method development applied for pipeline leak detection is considered. It was shown that acoustic emission testing is currently one of the most widely spread leak detection methods. The main disadvantage of this method is that it cannot be applied in monitoring long pipeline sections, which in its turn complicates and slows down the inspection of the line pipe sections of main pipelines. The prospects of developing alternative techniques and methods based on the use of the spectral analysis of signals were considered and their possible application in leak detection on the basis of the correlation method was outlined. As an alternative, the time-frequency correlation function calculation is proposed. This function represents the correlation between the spectral components of the analyzed signals. In this work, the technique of time-frequency correlation function calculation is described. The experimental data that demonstrate obvious advantage of the time-frequency correlation function compared to the simple correlation function are presented. The application of the time-frequency correlation function is more effective in suppressing the noise components in the frequency range of the useful signal, which makes maximum of the function more pronounced. The main drawback of application of the time- frequency correlation function analysis in solving leak detection problems is a great number of calculations that may result in a further increase in pipeline time inspection. However, this drawback can be partially reduced by the development and implementation of efficient algorithms (including parallel) of computing the fast Fourier transform using computer central processing unit and graphic processing unit.
Correlative Light Electron Microscopy: Connecting Synaptic Structure and Function
Begemann, Isabell; Galic, Milos
2016-01-01
Many core paradigms of contemporary neuroscience are based on information obtained by electron or light microscopy. Intriguingly, these two imaging techniques are often viewed as complementary, yet separate entities. Recent technological advancements in microscopy techniques, labeling tools, and fixation or preparation procedures have fueled the development of a series of hybrid approaches that allow correlating functional fluorescence microscopy data and ultrastructural information from electron micrographs from a singular biological event. As correlative light electron microscopy (CLEM) approaches become increasingly accessible, long-standing neurobiological questions regarding structure-function relation are being revisited. In this review, we will survey what developments in electron and light microscopy have spurred the advent of correlative approaches, highlight the most relevant CLEM techniques that are currently available, and discuss its potential and limitations with respect to neuronal and synapse-specific applications. PMID:27601992
Correlation between thoracolumbar curvatures and respiratory function in older adults
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were −46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=−0.23, P<0.05; forced vital capacity: r=−0.32, P<0.05), quiet expiration intercostal thickness (r=−0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=−0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=−0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=−0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar
Correlation between thoracolumbar curvatures and respiratory function in older adults.
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were -46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=-0.23, P<0.05; forced vital capacity: r=-0.32, P<0.05), quiet expiration intercostal thickness (r=-0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=-0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=-0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=-0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar curvatures
Upper Limb Assessment in Tetraplegia: Clinical, Functional and Kinematic Correlations
ERIC Educational Resources Information Center
Cacho, Enio Walker Azevedo; de Oliveira, Roberta; Ortolan, Rodrigo L.; Varoto, Renato; Cliquet, Alberto
2011-01-01
The aim of this study was to correlate clinical and functional evaluations with kinematic variables of upper limp reach-to-grasp movement in patients with tetraplegia. Twenty chronic patients were selected to perform reach-to-grasp kinematic assessment using a target placed at a distance equal to the arm's length. Kinematic variables (hand peak…
Correlations and functional connections in a population of grid cells.
Dunn, Benjamin; Mørreaunet, Maria; Roudi, Yasser
2015-02-01
We study the statistics of spike trains of simultaneously recorded grid cells in freely behaving rats. We evaluate pairwise correlations between these cells and, using a maximum entropy kinetic pairwise model (kinetic Ising model), study their functional connectivity. Even when we account for the covariations in firing rates due to overlapping fields, both the pairwise correlations and functional connections decay as a function of the shortest distance between the vertices of the spatial firing pattern of pairs of grid cells, i.e. their phase difference. They take positive values between cells with nearby phases and approach zero or negative values for larger phase differences. We find similar results also when, in addition to correlations due to overlapping fields, we account for correlations due to theta oscillations and head directional inputs. The inferred connections between neurons in the same module and those from different modules can be both negative and positive, with a mean close to zero, but with the strongest inferred connections found between cells of the same module. Taken together, our results suggest that grid cells in the same module do indeed form a local network of interconnected neurons with a functional connectivity that supports a role for attractor dynamics in the generation of grid pattern.
Finite size effect on the magnon's correlation functions
Lee, Bum-Hoon; Park, Chanyong
2011-10-15
We calculate the finite size correction on the three-point correlation function between two giant magnons and one marginal operator, which is dual to a dilaton field of the bulk gravity theory. We also check that the structure constant in the string setup is exactly the same as one of the renormalization group analyses in the gauge theory.
Upper Limb Assessment in Tetraplegia: Clinical, Functional and Kinematic Correlations
ERIC Educational Resources Information Center
Cacho, Enio Walker Azevedo; de Oliveira, Roberta; Ortolan, Rodrigo L.; Varoto, Renato; Cliquet, Alberto
2011-01-01
The aim of this study was to correlate clinical and functional evaluations with kinematic variables of upper limp reach-to-grasp movement in patients with tetraplegia. Twenty chronic patients were selected to perform reach-to-grasp kinematic assessment using a target placed at a distance equal to the arm's length. Kinematic variables (hand peak…
Spatial Correlation Function of the Chandra Selected Active Galactic Nuclei
NASA Technical Reports Server (NTRS)
Yang, Y.; Mushotzky, R. F.; Barger, A. J.; Cowie, L. L.
2006-01-01
We present the spatial correlation function analysis of non-stellar X-ray point sources in the Chandra Large Area Synoptic X-ray Survey of Lockman Hole Northwest (CLASXS). Our 9 ACIS-I fields cover a contiguous solid angle of 0.4 deg(exp 2) and reach a depth of 3 x 10(exp -15) erg/square cm/s in the 2-8 keV band. We supplement our analysis with data from the Chandra Deep Field North (CDFN). The addition of this field allows better probe of the correlation function at small scales. A total of 233 and 252 sources with spectroscopic information are used in the study of the CLASXS and CDFN fields respectively. We calculate both redshift-space and projected correlation functions in co-moving coordinates, averaged over the redshift range of 0.1 < z < 3.0, for both CLASXS and CDFN fields for a standard cosmology with Omega(sub Lambda) = 0.73,Omega(sub M) = 0.27, and h = 0.71 (H(sub 0) = 100h km/s Mpc(exp -1). The correlation function for the CLASXS field over scales of 3 Mpc< s < 200 Mpc can be modeled as a power-law of the form xi(s) = (S/SO)(exp - gamma), with gamma = 1.6(sup +0.4 sub -0.3) and S(sub o) = 8.0(sup +.14 sub -1.5) Mpc. The redshift-space correlation function for CDFN on scales of 1 Mpc< s < 100 Mpc is found to have a similar correlation length so = 8.55(sup +0.74 sub -0.74) Mpc, but a shallower slope (gamma = 1.3 +/- 0.1). The real-space correlation functions derived from the projected correlation functions, are found to be tau(sub 0 = 8.1(sup +1.2 sub -2.2) Mpc, and gamma = 2.1 +/- 0.5 for the CLASXS field, and tau(sub 0) = 5.8(sup +.1.0 sub -1.5) Mpc, gamma = 1.38(sup +0.12 sub -0.14 for the CDFN field. By comparing the real- and redshift-space correlation functions in the combined CLASXS and CDFN samples, we are able to estimate the redshift distortion parameter Beta = 0.4 +/- 0.2 at an effective redshift z = 0.94. We compare the correlation functions for hard and soft spectra sources in the CLASXS field and find no significant difference between the
LIBXC: A library of exchange and correlation functionals for density functional theory
NASA Astrophysics Data System (ADS)
Marques, Miguel A. L.; Oliveira, Micael J. T.; Burnus, Tobias
2012-10-01
The central quantity of density functional theory is the so-called exchange-correlation functional. This quantity encompasses all non-trivial many-body effects of the ground-state and has to be approximated in any practical application of the theory. For the past 50 years, hundreds of such approximations have appeared, with many successfully persisting in the electronic structure community and literature. Here, we present a library that contains routines to evaluate many of these functionals (around 180) and their derivatives. Program summary Program title: LIBXC Catalogue identifier: AEMU_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEMU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU Lesser General Public License version 3 No. of lines in distributed program, including test data, etc.: 87455 No. of bytes in distributed program, including test data, etc.: 945365 Distribution format: tar.gz Programming language: C with Fortran bindings. Computer: All. Operating system: All. RAM: N.A. Classification: 7.3, 16.1. Nature of problem: Evaluation of the exchange-correlation energy functional and its derivatives. This is a fundamental part of any atomic, molecular, or solid-state code that uses density-functional theory. Solution method: The values of the energy functional and its derivatives are given in a real grid of mesh points. Running time: Typically much smaller than the remainder of the electronic structure code. The running time has a natural linear scaling with the number of grid points.
Local-hybrid functional based on the correlation length
Johnson, Erin R.
2014-09-28
Local-hybrid functionals involve position-dependent mixing of Hartree-Fock and density-functional exchange, which should allow improved performance relative to conventional hybrids by reducing the inherent delocalization error and improving the long-range behaviour. Herein, the same-spin correlation length, obtained from the Fermi-hole radius, is used as the mixing parameter. The performance of the resulting local-hybrid functional is assessed for standard thermochemical and kinetics benchmarks. The local hybrid is shown to perform significantly better than the corresponding global hybrid in almost all cases.
Extension of local-type inequality for the higher order correlation functions
Suyama, Teruaki; Yokoyama, Shuichiro E-mail: shu@a.phys.nagoya-u.ac.jp
2011-07-01
For the local-type primordial perturbation, it is known that there is an inequality between the bispectrum and the trispectrum. By using the diagrammatic method, we develop a general formalism to systematically construct the similar inequalities up to any order correlation function. As an application, we explicitly derive all the inequalities up to six and eight-point functions.
ERIC Educational Resources Information Center
Gegenfurtner, Andreas; Kok, Ellen M.; van Geel, Koos; de Bruin, Anique B. H.; Sorger, Bettina
2017-01-01
Functional neuroimaging is a useful approach to study the neural correlates of visual perceptual expertise. The purpose of this paper is to review the functional-neuroimaging methods that have been implemented in previous research in this context. First, we will discuss research questions typically addressed in visual expertise research. Second,…
Spatiotemporal velocity-velocity correlation function in fully developed turbulence
NASA Astrophysics Data System (ADS)
Canet, Léonie; Rossetto, Vincent; Wschebor, Nicolás; Balarac, Guillaume
2017-02-01
Turbulence is a ubiquitous phenomenon in natural and industrial flows. Since the celebrated work of Kolmogorov in 1941, understanding the statistical properties of fully developed turbulence has remained a major quest. In particular, deriving the properties of turbulent flows from a mesoscopic description, that is, from the Navier-Stokes equation, has eluded most theoretical attempts. Here, we provide a theoretical prediction for the functional space and time dependence of the velocity-velocity correlation function of homogeneous and isotropic turbulence from the field theory associated to the Navier-Stokes equation with stochastic forcing. This prediction, which goes beyond Kolmogorov theory, is the analytical fixed point solution of nonperturbative renormalization group flow equations, which are exact in the limit of large wave numbers. This solution is compared to two-point two-times correlation functions computed in direct numerical simulations. We obtain a remarkable agreement both in the inertial and in the dissipative ranges.
Entropy and correlation functions of a driven quantum spin chain
Cherng, R. W.; Levitov, L. S.
2006-04-15
We present an exact solution for a quantum spin chain driven through its critical points. Our approach is based on a many-body generalization of the Landau-Zener transition theory, applied to a fermionized spin Hamiltonian. The resulting nonequilibrium state of the system, while being a pure quantum state, has local properties of a mixed state characterized by finite entropy density associated with Kibble-Zurek defects. The entropy and the finite spin correlation length are functions of the rate of sweep through the critical point. We analyze the anisotropic XY spin-1/2 model evolved with a full many-body evolution operator. With the help of Toeplitz determinant calculus, we obtain an exact form of correlation functions. The properties of the evolved system undergo an abrupt change at a certain critical sweep rate, signaling the formation of ordered domains. We link this phenomenon to the behavior of complex singularities of the Toeplitz generating function.
Atmospheric pollution measurement by optical cross correlation methods - A concept
NASA Technical Reports Server (NTRS)
Fisher, M. J.; Krause, F. R.
1971-01-01
Method combines standard spectroscopy with statistical cross correlation analysis of two narrow light beams for remote sensing to detect foreign matter of given particulate size and consistency. Method is applicable in studies of generation and motion of clouds, nuclear debris, ozone, and radiation belts.
NASA Astrophysics Data System (ADS)
Verdebout, S.; Jönsson, P.; Gaigalas, G.; Godefroid, M.; Froese Fischer, C.
2010-04-01
Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core-valence correlation effects. This in turn leads to huge numbers of configuration state functions (CSFs), many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the multiconfiguration Hartree-Fock (MCHF) method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double-excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional complete active space (CAS)-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations.
Correlation Between Vision and Cognitive Function in the Elderly
Spierer, Oriel; Fischer, Naomi; Barak, Adiel; Belkin, Michael
2016-01-01
Abstract The correlation between vision and cognition is not fully understood. Visual impairment in the elderly has been associated with impaired cognitive function, dementia, and Alzheimer disease. The aim was to study the correlation between near visual acuity (VA), refraction, and cognitive state in an elderly population. Subjects ≥75 years were enrolled in this cross-sectional study. Refraction and near VA was tested. Cognitive function was evaluated with a version of the mini-mental state examination for the visually impaired (MMSE-blind). The eye with better VA and no cataract or refractive surgery was analyzed. One-hundred ninety subjects (81.6 ± 5.1 years, 69.5% female) were included. Good VA (≤J3) was associated with high MMSE-blind (>17) (OR = 3.18, 95% CI = 1.57–6.43, P = 0.001). This remained significant adjusting for sex, age, and years of education. Wearing reading glasses correlated significantly with high MMSE-blind after adjustment for sex and age (OR = 2.14, 95% CI = 1.16–3.97, P = 0.016), but reached borderline significance after adjustment for education. There was a trend toward correlation between myopia and better MMSE-blind (r = −0.123, P = 0.09, Pearson correlation). Good VA and wearing glasses seem to correlate with better cognitive function. Reading glasses can serve as a protective factor against cognitive deterioration associated with sensory (visual) deprivation in old age. The association between myopia and cognition requires further investigation. PMID:26817872
Rangaprakash, D; Hu, Xiaoping; Deshpande, Gopikrishna
2013-04-01
It is increasingly being recognized that resting state brain connectivity derived from functional magnetic resonance imaging (fMRI) data is an important marker of brain function both in healthy and clinical populations. Though linear correlation has been extensively used to characterize brain connectivity, it is limited to detecting first order dependencies. In this study, we propose a framework where in phase synchronization (PS) between brain regions is characterized using a new metric "correlation between probabilities of recurrence" (CPR) and subsequent graph-theoretic analysis of the ensuing networks. We applied this method to resting state fMRI data obtained from human subjects with and without administration of propofol anesthetic. Our results showed decreased PS during anesthesia and a biologically more plausible community structure using CPR rather than linear correlation. We conclude that CPR provides an attractive nonparametric method for modeling interactions in brain networks as compared to standard correlation for obtaining physiologically meaningful insights about brain function.
Large N correlation functions in superconformal field theories
NASA Astrophysics Data System (ADS)
Rodriguez-Gomez, Diego; Russo, Jorge G.
2016-06-01
We compute correlation functions of chiral primary operators in mathcal{N}=2 super-conformal theories at large N using a construction based on supersymmetric localization recently developed by Gerchkovitz et al. We focus on mathcal{N}=4 SYM as well as on supercon-formal QCD. In the case of mathcal{N}=4 we recover the free field theory results as expected due to non-renormalization theorems. In the case of superconformal QCD we study the planar expansion in the large N limit. The final correlators admit a simple generalization to a finite N formula which exactly matches the various small N results in the literature.
Generalized parton correlation functions for a spin-0 hadron
Meissner, Stephan; Metz, Andreas; Schlegel, Marc; Goeke, Klaus
2008-08-01
The fully unintegrated, off-diagonal quark-quark correlator for a spin-0 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects are of relevance for the phenomenology of certain hard exclusive reactions. In particular, they can be considered as mother distributions of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum dependent parton distributions. As a by-product we obtain the first complete classification of generalized parton distributions beyond leading twist.
The role of exchange and correlation in time-dependent density-functional theory for photoionization
NASA Astrophysics Data System (ADS)
Stener, M.; Decleva, P.; Görling, A.
2001-05-01
Atomic photoionization cross sections are calculated by time-dependent density-functional (TDDF) methods using different exchange-correlation potentials including the exact one. The exchange-correlation kernel is treated in the adiabatic local density approximation (ALDA). Results for the exact full and the exact exchange-only Kohn-Sham (KS) potential are very similar, the calculated photo cross section agree very well with experimental data. Thus the exact correlation potential seems to have no influence on photoionization and the ALDA for the exchange-correlation kernel seems to be sufficient for most features of the cross sections. The TDDF method employing the exact exchange-only KS potential in combination with the ALDA exchange-correlation kernel therefore is a promising approach to describe photoionization. Deviations from experiment are observed for the widths and shape of the autoionization resonances and have to be attributed to deficiencies of the ALDA exchange-correlation kernel. The calculation of widths and shapes of autoionization resonances therefore may serve as a severe test for new approximate exchange-correlation density-functionals. The asymptotically exact exchange-correlation potential of van Leeuwen and Baerends also leads to quite good photo cross section, which, however, shows deficiencies close to the ionization threshold and in the energetic position of the autoionization resonances. Supplementation of the exact exchange potential with the LDA correlation potential leads to a worsening of the photo cross section because the LDA correlation potential is too attractive.
Long-range correlation energy calculated from coupled atomic response functions
Ambrosetti, Alberto; Reilly, Anthony M.; Tkatchenko, Alexandre; DiStasio, Robert A.
2014-05-14
An accurate determination of the electron correlation energy is an essential prerequisite for describing the structure, stability, and function in a wide variety of systems. Therefore, the development of efficient approaches for the calculation of the correlation energy (and hence the dispersion energy as well) is essential and such methods can be coupled with many density-functional approximations, local methods for the electron correlation energy, and even interatomic force fields. In this work, we build upon the previously developed many-body dispersion (MBD) framework, which is intimately linked to the random-phase approximation for the correlation energy. We separate the correlation energy into short-range contributions that are modeled by semi-local functionals and long-range contributions that are calculated by mapping the complex all-electron problem onto a set of atomic response functions coupled in the dipole approximation. We propose an effective range-separation of the coupling between the atomic response functions that extends the already broad applicability of the MBD method to non-metallic materials with highly anisotropic responses, such as layered nanostructures. Application to a variety of high-quality benchmark datasets illustrates the accuracy and applicability of the improved MBD approach, which offers the prospect of first-principles modeling of large structurally complex systems with an accurate description of the long-range correlation energy.
NASA Astrophysics Data System (ADS)
Gori-Giorgi, Paola
I will present some recent results based on the strictly-correlated electrons (SCE) functional: 1) a rigorous method to set lower bounds to the optimal particle-number dependent constant appearing in the Lieb-Oxford bound, and 2) an investigation of exact properties in the time domain, including an analytical expression for the kernel in one-dimension, with an analysis of its behavior for the case of bond-breaking excitations. ERC Consolidator Grant 648932.
Analytic height correlation function of rough surfaces derived from light scattering
NASA Astrophysics Data System (ADS)
Zamani, M.; Shafiei, F.; Fazeli, S. M.; Downer, M. C.; Jafari, G. R.
2016-10-01
We derive an analytic expression for the height correlation function of a homogeneous, isotropic rough surface based on the inverse wave scattering method of Kirchhoff theory. The expression directly relates the height correlation function to diffuse scattered intensity along a linear path at fixed polar angle. We test the solution by measuring the angular distribution of light scattered from rough silicon surfaces and comparing extracted height correlation functions to those derived from atomic force microscopy (AFM). The results agree closely with AFM over a wider range of roughness parameters than previous formulations of the inverse scattering problem, while relying less on large-angle scatter data. Our expression thus provides an accurate analytical equation for the height correlation function of a wide range of surfaces based on measurements using a simple, fast experimental procedure.
Correlation functions of the chiral stress-tensor multiplet in SYM
NASA Astrophysics Data System (ADS)
Chicherin, Dmitry; Doobary, Reza; Eden, Burkhard; Heslop, Paul; Korchemsky, Gregory P.; Mason, Lionel; Sokatchev, Emery
2015-06-01
We give a new method for computing the correlation functions of the chiral part of the stress-tensor supermultiplet that relies on the reformulation of SYM in twistor space. It yields the correlation functions in the Born approximation as a sum of Feynman diagrams on twistor space that involve only propagators and no integration vertices. We use this unusual feature of the twistor Feynman rules to compute the correlation functions in terms of simple building blocks which we identify as a new class of off-shell superconformal invariants. Making use of the duality between correlation functions and planar scattering amplitudes, we demonstrate that these invariants represent an off-shell generalisation of the on-shell invariants defining tree-level scattering amplitudes in SYM.
NASA Astrophysics Data System (ADS)
Wang, Qian; Mei, Hai-Ping; Qian, Xian-Mei; Rao, Rui-Zhong
2016-10-01
A theory about scales in atmospheric optical turbulence vortex from the point view of spatial correlation function is described. Then an experiment is carried out to prove this theory by the fiber optical turbulence sensor array near the ground. Results show that the outer scale has a mean value of 0.62m and varies from 0.34m to 0.95m by doing a nonlinear fitting on spatial correlation functions. With this method, the value of the outer scale can be given directly without any hypothesis when the optical turbulence is well-developed. A question about how the trend of the spatial correlation function show when the displacement approaches the outer scale is solved. This research can be regarded as a progress about understanding the characters of spatial correlation function in optical turbulence.
QSO clustering - II. The correlation function of IRAS seyfert galaxies.
NASA Astrophysics Data System (ADS)
Georgantopoulos, I.; Shanks, T.
1994-12-01
We investigate the clustering properties of 192 Seyfert galaxies from the IRAS all-sky survey. Using the spatial correlation function, we detect evidence of Seyfert clustering at the 2σ confidence level at < 10 h^-1^ Mpc separations, and at the 3{SIGMA} level at < 20 h^-1^ Mpc separations. Comparison of the QSO correlation function amplitude at high redshifts, z = 1.4, with that of Seyferts below 10 h^-1^ comoving Mpc leads us to reject the stable model of AGN clustering evolution at the 4σ level, whereas a comoving model where QSOs randomly sample the galaxy distribution is more consistent. The main uncertainty here now lies in the statistical error on the amplitude of the clustering in the faint QSO surveys at z = 1.4. The Seyfert-QDOT cross-correlation function is measured to be approximately a factor of 2 higher than the QDOT galaxy autocorrelation function, suggesting an enhanced environment for Seyferts with respect to IRAS galaxies, but it is not clear whether this is also the case with respect to optical galaxies. We conclude that the comoving model is probably favoured overall, at least on the r < 10 h^-1^ Mpc scales investigated here, but it is not yet possible to rule out intermediate models: for example, an enhanced-environment, stable model with ξ(r)=(r/3)^-1.8^ at z = 1.4, which is statistically consistent with the faint QSO data.
Compressed correlation functions and fast aging dynamics in metallic glasses
NASA Astrophysics Data System (ADS)
Ruta, B.; Baldi, G.; Monaco, G.; Chushkin, Y.
2013-02-01
We present x-ray photon correlation spectroscopy measurements of the atomic dynamics in a Zr67Ni33 metallic glass, well below its glass transition temperature. We find that the decay of the density fluctuations can be well described by compressed, thus faster than exponential, correlation functions which can be modeled by the well-known Kohlrausch-Williams-Watts function with a shape exponent β larger than one. This parameter is furthermore found to be independent of both waiting time and wave-vector, leading to the possibility to rescale all the correlation functions to a single master curve. The dynamics in the glassy state is additionally characterized by different aging regimes which persist in the deep glassy state. These features seem to be universal in metallic glasses and suggest a nondiffusive nature of the dynamics. This universality is supported by the possibility of describing the fast increase of the structural relaxation time with waiting time using a unique model function, independently of the microscopic details of the system.
Cheng, Jin; Yu, Kuang; Libisch, Florian; Dieterich, Johannes M; Carter, Emily A
2017-03-14
Quantum mechanical embedding theories partition a complex system into multiple spatial regions that can use different electronic structure methods within each, to optimize trade-offs between accuracy and cost. The present work incorporates accurate but expensive correlated wave function (CW) methods for a subsystem containing the phenomenon or feature of greatest interest, while self-consistently capturing quantum effects of the surroundings using fast but less accurate density functional theory (DFT) approximations. We recently proposed two embedding methods [for a review, see: Acc. Chem. Res. 2014 , 47 , 2768 ]: density functional embedding theory (DFET) and potential functional embedding theory (PFET). DFET provides a fast but non-self-consistent density-based embedding scheme, whereas PFET offers a more rigorous theoretical framework to perform fully self-consistent, variational CW/DFT calculations [as defined in part 1, CW/DFT means subsystem 1(2) is treated with CW(DFT) methods]. When originally presented, PFET was only tested at the DFT/DFT level of theory as a proof of principle within a planewave (PW) basis. Part 1 of this two-part series demonstrated that PFET can be made to work well with mixed Gaussian type orbital (GTO)/PW bases, as long as optimized GTO bases and consistent electron-ion potentials are employed throughout. Here in part 2 we conduct the first PFET calculations at the CW/DFT level and compare them to DFET and full CW benchmarks. We test the performance of PFET at the CW/DFT level for a variety of types of interactions (hydrogen bonding, metallic, and ionic). By introducing an intermediate CW/DFT embedding scheme denoted DFET/PFET, we show how PFET remedies different types of errors in DFET, serving as a more robust type of embedding theory.
Relaxation method of compensation in an optical correlator
NASA Technical Reports Server (NTRS)
Juday, Richard D.; Daiuto, Brian J.
1987-01-01
An iterative method is proposed for the sharpening of programmable filters in a 4-f optical correlator. Continuously variable spatial light modulators (SLMs) permit the fine adjustment of optical processing filters so as to compensate for the departures from ideal behavior of a real optical system. Although motivated by the development of continuously variable phase-only SLMs, the proposed sharpening method is also applicable to amplitude modulators and, with appropriate adjustments, to binary modulators as well. A computer simulation is presented that illustrates the potential effectiveness of the method: an image is placed on the input to the correlator, and its corresponding phase-only filter is adjusted (allowed to relax) so as to produce a progressively brighter and more centralized peak in the correlation plane. The technique is highly robust against the form of the system's departure from ideal behavior.
Relaxation method of compensation in an optical correlator
NASA Technical Reports Server (NTRS)
Juday, Richard D.; Daiuto, Brian J.
1987-01-01
An iterative method is proposed for the sharpening of programmable filters in a 4-f optical correlator. Continuously variable spatial light modulators (SLMs) permit the fine adjustment of optical processing filters so as to compensate for the departures from ideal behavior of a real optical system. Although motivated by the development of continuously variable phase-only SLMs, the proposed sharpening method is also applicable to amplitude modulators and, with appropriate adjustments, to binary modulators as well. A computer simulation is presented that illustrates the potential effectiveness of the method: an image is placed on the input to the correlator, and its corresponding phase-only filter is adjusted (allowed to relax) so as to produce a progressively brighter and more centralized peak in the correlation plane. The technique is highly robust against the form of the system's departure from ideal behavior.
Yuan, Naiming; Fu, Zuntao; Zhang, Huan; Piao, Lin; Xoplaki, Elena; Luterbacher, Juerg
2015-01-01
In this paper, a new method, detrended partial-cross-correlation analysis (DPCCA), is proposed. Based on detrended cross-correlation analysis (DCCA), this method is improved by including partial-correlation technique, which can be applied to quantify the relations of two non-stationary signals (with influences of other signals removed) on different time scales. We illustrate the advantages of this method by performing two numerical tests. Test I shows the advantages of DPCCA in handling non-stationary signals, while Test II reveals the “intrinsic” relations between two considered time series with potential influences of other unconsidered signals removed. To further show the utility of DPCCA in natural complex systems, we provide new evidence on the winter-time Pacific Decadal Oscillation (PDO) and the winter-time Nino3 Sea Surface Temperature Anomaly (Nino3-SSTA) affecting the Summer Rainfall over the middle-lower reaches of the Yangtze River (SRYR). By applying DPCCA, better significant correlations between SRYR and Nino3-SSTA on time scales of 6 ~ 8 years are found over the period 1951 ~ 2012, while significant correlations between SRYR and PDO on time scales of 35 years arise. With these physically explainable results, we have confidence that DPCCA is an useful method in addressing complex systems. PMID:25634341
Distance correlation methods for discovering associations in large astrophysical databases
Martínez-Gómez, Elizabeth; Richards, Mercedes T.; Richards, Donald St. P. E-mail: mrichards@astro.psu.edu
2014-01-20
High-dimensional, large-sample astrophysical databases of galaxy clusters, such as the Chandra Deep Field South COMBO-17 database, provide measurements on many variables for thousands of galaxies and a range of redshifts. Current understanding of galaxy formation and evolution rests sensitively on relationships between different astrophysical variables; hence an ability to detect and verify associations or correlations between variables is important in astrophysical research. In this paper, we apply a recently defined statistical measure called the distance correlation coefficient, which can be used to identify new associations and correlations between astrophysical variables. The distance correlation coefficient applies to variables of any dimension, can be used to determine smaller sets of variables that provide equivalent astrophysical information, is zero only when variables are independent, and is capable of detecting nonlinear associations that are undetectable by the classical Pearson correlation coefficient. Hence, the distance correlation coefficient provides more information than the Pearson coefficient. We analyze numerous pairs of variables in the COMBO-17 database with the distance correlation method and with the maximal information coefficient. We show that the Pearson coefficient can be estimated with higher accuracy from the corresponding distance correlation coefficient than from the maximal information coefficient. For given values of the Pearson coefficient, the distance correlation method has a greater ability than the maximal information coefficient to resolve astrophysical data into highly concentrated horseshoe- or V-shapes, which enhances classification and pattern identification. These results are observed over a range of redshifts beyond the local universe and for galaxies from elliptical to spiral.
Characterizing Intra-Die Spatial Correlation Using Spectral Density Fitting Method
NASA Astrophysics Data System (ADS)
Fu, Qiang; Luk, Wai-Shing; Tao, Jun; Yan, Changhao; Zeng, Xuan
In this paper, a spectral domain method named the SDF (Spectral Density Fitting) method for intra-die spatial correlation function extraction is presented. Based on theoretical analysis of random field, the spectral density, as the spectral domain counterpart of correlation function, is employed to estimate the parameters of the correlation function effectively in the spectral domain. Compared with the existing extraction algorithm in the original spatial domain, the SDF method can obtain the same quality of results in the spectral domain. In actual measurement process, the unavoidable measurement error with arbitrary frequency components would greatly confound the extraction results. A filtering technique is further developed to diminish the high frequency components of the measurement error and recover the data from noise contamination for parameter estimation. Experimental results have shown that the SDF method is practical and stable.
A Correlation between Protein Function and Ligand Binding Profiles
Shortridge, Matthew D.; Bokemper, Michael; Copeland, Jennifer C.; Stark, Jaime L.; Powers, Robert
2011-01-01
We report that proteins with the same function bind the same set of small molecules from a standardized chemical library. This observation led to a quantifiable and rapidly adaptable method for protein functional analysis using experimentally-derived ligand binding profiles. Ligand binding is measured using a high-throughput NMR ligand affinity screen with a structurally diverse chemical library. The method was demonstrated using a set of 19 proteins with a range of functions. A statistically significant similarity in ligand binding profiles was only observed between the two functionally identical albumins and between the five functionally similar amylases. This new approach is independent of sequence, structure or evolutionary information, and therefore, extends our ability to analyze and functionally annotate novel genes. PMID:21366353
Ramos, J G G S; Barbosa, A L R; Carlson, B V; Frederico, T; Hussein, M S
2016-01-01
We derive analytical expressions for the correlation functions of the electronic conductance fluctuations of an open quantum dot under several conditions. Both the variation of energy and that of an external parameter, such as an applied perpendicular or parallel magnetic fields, are considered in the general case of partial openness. These expressions are then used to obtain the ensemble-averaged density of maxima, a measure recently suggested to contain invaluable information concerning the correlation widths of chaotic systems. The correlation width is then calculated for the case of energy variation, and a significant deviation from the Weisskopf estimate is found in the case of two terminals. The results are extended to more than two terminals. All of our results are analytical. The use of these results in other fields, such as nuclei, where the system can only be studied through a variation of the energy, is then discussed.
NASA Astrophysics Data System (ADS)
Ramos, J. G. G. S.; Barbosa, A. L. R.; Carlson, B. V.; Frederico, T.; Hussein, M. S.
2016-01-01
We derive analytical expressions for the correlation functions of the electronic conductance fluctuations of an open quantum dot under several conditions. Both the variation of energy and that of an external parameter, such as an applied perpendicular or parallel magnetic fields, are considered in the general case of partial openness. These expressions are then used to obtain the ensemble-averaged density of maxima, a measure recently suggested to contain invaluable information concerning the correlation widths of chaotic systems. The correlation width is then calculated for the case of energy variation, and a significant deviation from the Weisskopf estimate is found in the case of two terminals. The results are extended to more than two terminals. All of our results are analytical. The use of these results in other fields, such as nuclei, where the system can only be studied through a variation of the energy, is then discussed.
Correlated Protein Function Prediction via Maximization of Data-Knowledge Consistency.
Wang, Hua; Huang, Heng; Ding, Chris
2015-06-01
Conventional computational approaches for protein function prediction usually predict one function at a time, fundamentally. As a result, the protein functions are treated as separate target classes. However, biological processes are highly correlated in reality, which makes multiple functions assigned to a protein not independent. Therefore, it would be beneficial to make use of function category correlations when predicting protein functions. In this article, we propose a novel Maximization of Data-Knowledge Consistency (MDKC) approach to exploit function category correlations for protein function prediction. Our approach banks on the assumption that two proteins are likely to have large overlap in their annotated functions if they are highly similar according to certain experimental data. We first establish a new pairwise protein similarity using protein annotations from knowledge perspective. Then by maximizing the consistency between the established knowledge similarity upon annotations and the data similarity upon biological experiments, putative functions are assigned to unannotated proteins. Most importantly, function category correlations are gracefully incorporated into our learning objective through the knowledge similarity. Comprehensive experimental evaluations on the Saccharomyces cerevisiae species have demonstrated promising results that validate the performance of our methods.
Decay of random correlation functions for unimodal maps
NASA Astrophysics Data System (ADS)
Baladi, Viviane; Benedicks, Michael; Maume-Deschamps, Véronique
2000-10-01
Since the pioneering results of Jakobson and subsequent work by Benedicks-Carleson and others, it is known that quadratic maps tfa( χ) = a - χ2 admit a unique absolutely continuous invariant measure for a positive measure set of parameters a. For topologically mixing tfa, Young and Keller-Nowicki independently proved exponential decay of correlation functions for this a.c.i.m. and smooth observables. We consider random compositions of small perturbations tf + ωt, with tf = tfa or another unimodal map satisfying certain nonuniform hyperbolicity axioms, and ωt chosen independently and identically in [-ɛ, ɛ]. Baladi-Viana showed exponential mixing of the associated Markov chain, i.e., averaging over all random itineraries. We obtain stretched exponential bounds for the random correlation functions of Lipschitz observables for the sample measure μωof almost every itinerary.
On the application of correlation function matrices in OMA
NASA Astrophysics Data System (ADS)
Brincker, Rune
2017-03-01
In this paper the theoretical solution for the correlation function matrix of the random response of a structural system is re-visited. It is shown that using the classical definition of the correlation functions, the row space is defined by the mode shapes of the system, whereas the column space is defined by the modal participation vectors. This means that only the rows can be used for unbiased modal identification in operational modal analysis and if the columns are used for identification, then bias will be introduced on the mode shape estimates. It is pointed out that the mode shape bias is strongly dependent on the frequency distance between the modes, i.e. bias will significantly increase in case of closely spaced modes. The identification errors on the estimated biased and unbiased mode shapes are studied in a simulation example.
CFT correlation functions from AdS/CFT correspondence
NASA Astrophysics Data System (ADS)
Matusis, Alec
In this thesis we discuss correlation functions of N = 4, d = 4 Super-Yang-Mills theory in the strong coupling regime. Namely, the recent conjecture of the equivalence of the string theory in AdS5 x S5 background to the N = 4, d = 4 SYM theory with SU( N) gauge group allows to find correlation functions of the CFT in the limit of large t'Hooft coupling and at large N by evaluating relatively simple tree-level supergravity amplitudes. We discuss the basic ideas of the AdS supergravity computations, and establish the techniques for evaluating tree-level AdS supergravity scattering amplitudes with fixed rates of fall-offs of the fields as they approach AdS boundary. We translate these supergravity results into field theory language and learn several interesting things. First, at the level of the two-point correlation functions we learn about the necessity for the introduction of a cut-off in seemingly convergent AdS supergravity computations. Next, we find a non-renormalization property of certain 3-point functions. Finally, we find an explicit expression for certain 4-point functions, which deviate from free-field approximation in perturbation theory, thus providing some new non- perturbative information about SYM. We study various limits of these 4-point functions, with intention to give them an OPE interpretation. We find logarithmic singularities in all limits, and discuss their compatibility with existence of an OPE at strong coupling. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
Elongation measurement using 1-dimensional image correlation method
NASA Astrophysics Data System (ADS)
Phongwisit, Phachara; Kamoldilok, Surachart; Buranasiri, Prathan
2016-11-01
Aim of this paper was to study, setup, and calibrate an elongation measurement by using 1- Dimensional Image Correlation method (1-DIC). To confirm our method and setup correctness, we need calibration with other methods. In this paper, we used a small spring as a sample to find a result in terms of spring constant. With a fundamental of Image Correlation method, images of formed and deformed samples were compared to understand the difference between deformed process. By comparing the location of reference point on both image's pixel, the spring's elongation were calculated. Then, the results have been compared with the spring constants, which were found from Hooke's law. The percentage of 5 percent error has been found. This DIC method, then, would be applied to measure the elongation of some different kinds of small fiber samples.
Linearized path integral approach for calculating nonadiabatic time correlation functions.
Bonella, Sara; Montemayor, Daniel; Coker, David F
2005-05-10
We show that quantum time correlation functions including electronically nonadiabatic effects can be computed by using an approach in which their path integral expression is linearized in the difference between forward and backward nuclear paths while the electronic component of the amplitude, represented in the mapping formulation, can be computed exactly, leading to classical-like equations of motion for all degrees of freedom. The efficiency of this approach is demonstrated in some simple model applications.
CCFpams: Atmospheric stellar parameters from cross-correlation functions
NASA Astrophysics Data System (ADS)
Malavolta, Luca; Lovis, Christophe; Pepe, Francesco; Sneden, Christopher; Udry, Stephane
2017-07-01
CCFpams allows the measurement of stellar temperature, metallicity and gravity within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, the technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. Literature stellar parameters of high signal-to-noise (SNR) and high-resolution HARPS spectra of FGK Main Sequence stars are used to calibrate the stellar parameters as a function of CCF areas.
Statistical Study of Turbulence: Spectral Functions and Correlation Coefficients
NASA Technical Reports Server (NTRS)
Frenkiel, Francois N.
1958-01-01
In reading the publications on turbulence of different authors, one often runs the risk of confusing the various correlation coefficients and turbulence spectra. We have made a point of defining, by appropriate concepts, the differences which exist between these functions. Besides, we introduce in the symbols a few new characteristics of turbulence. In the first chapter, we study some relations between the correlation coefficients and the different turbulence spectra. Certain relations are given by means of demonstrations which could be called intuitive rather than mathematical. In this way we demonstrate that the correlation coefficients between the simultaneous turbulent velocities at two points are identical, whether studied in Lagrange's or in Euler's systems. We then consider new spectra of turbulence, obtained by study of the simultaneous velocities along a straight line of given direction. We determine some relations between these spectra and the correlation coefficients. Examining the relation between the spectrum of the turbulence measured at a fixed point and the longitudinal-correlation curve given by G. I. Taylor, we find that this equation is exact only when the coefficient is very small.
Trait correlates and functional significance of heteranthery in flowering plants.
Vallejo-Marín, Mario; Da Silva, Elizabeth M; Sargent, Risa D; Barrett, Spencer C H
2010-10-01
• Flowering plants display extraordinary diversity in the morphology of male sexual organs, yet the functional significance of this variation is not well understood. Here, we conducted a comparative analysis of floral correlates of heteranthery - the morphological and functional differentiation of anthers within flowers - among angiosperm families to identify traits associated with this condition. • We performed a phylogenetic analysis of correlated evolution between heteranthery and several floral traits commonly reported from heterantherous taxa. In addition, we quantified the effect of phylogenetic uncertainty in the observed patterns of correlated evolution by comparing trees in which polytomous branches were randomly resolved. • Heteranthery is reported from 12 angiosperm orders and is phylogenetically associated with the absence of floral nectaries, buzz-pollination and enantiostyly (mirror-image flowers). These associations are robust to particularities of the underlying phylogenetic hypothesis. • Heteranthery has probably evolved as a result of pollinator-mediated selection and appears to function to reduce the conflict of relying on pollen both as food to attract pollinators and as the agent of male gamete transfer. The relative scarcity of heteranthery among angiosperm families suggests that the conditions permitting its evolution are not easily met despite the abundance of pollen-collecting bees and nectarless flowers.
Hydrodynamic Waves and Correlation Functions in Dusty Plasmas
NASA Astrophysics Data System (ADS)
Bhattacharjee, A.; Wang, Xiaogang
1997-11-01
A hydrodynamic description of strongly coupled dusty plasmas is given when physical quantities vary slowly in space and time and the system can be assumed to be in local thermodynamic equilibrium. The linear waves in such a system are analyzed. In particular, a dispersion equation is derived for low-frequency dust acoustic waves, including collisional damping effects, and compared with experimental results. The linear response of the system is calculated from the fluctuation-dissipation theorem and the hydrodynamic equations. The requirement that these two calculations coincide constrains the particle correlation function for slowly varying perturbations [L. P. Kadanoff and P. C. Martin, Ann. Phys. 24, 419 (1963)]. It is shown that in the presence of the slow dust-acoustic waves, the dust auto-correlation function is of the Debye-Hekel form and the shielding distance is the dust Debye length. In the short-wavelength regime, an integral equation is derived from kinetic theory and solved numerically to yield particle correlation functions that display ``liquid-like'' behavior and have been observed experimentally [R. A.. Quinn, C. Cui, J. Goree, J. B. Pieper, H. Thomas and G. E. Morfill, Phys. Rev. E 53, R2049 (1996)].
Functional correlates of military sexual assault in male veterans.
Schry, Amie R; Hibberd, Rachel; Wagner, H Ryan; Turchik, Jessica A; Kimbrel, Nathan A; Wong, Madrianne; Elbogen, Eric E; Strauss, Jennifer L; Brancu, Mira
2015-11-01
Despite research findings that similar numbers of male and female veterans are affected by military sexual trauma (MST), there has been considerably less research on the effects of MST specific to male veterans. The aim of the present study was to provide preliminary data describing functional correlates of military sexual assault (MSA) among male Iraq/Afghanistan-era veterans to identify potential health care needs for this population. We evaluated the following functional correlates: posttraumatic stress disorder (PTSD) symptoms, depression symptoms, alcohol use, drug use, suicidality, social support, violent behavior in the past 30 days, incarceration, disability eligibility status, and use of outpatient mental health treatment. We compared 3 groups: (a) male veterans who endorsed a history of MSA (n = 39), (b) a general non-MSA sample (n = 2,003), and (c) a matched non-MSA sample (n = 39) identified by matching algorithms on the basis of factors (e.g., age, education, adult premilitary sexual trauma history, childhood sexual and physical trauma history, and race) that could increase veterans' vulnerability to the functional correlates examined. MSA in men was associated with greater PTSD symptom severity, greater depression symptom severity, higher suicidality, and higher outpatient mental health treatment, above and beyond the effects of vulnerability factors. These findings suggest that, for male veterans, MSA may result in a severe and enduring overall symptom profile requiring ongoing clinical management. (c) 2015 APA, all rights reserved).
Correlation between Pediatric Balance Scale and Functional Test in Children with Cerebral Palsy
Duarte, Natália de A. C.; Grecco, Luanda André Collange; Franco, Renata Calhes; Zanon, Nelci; Oliveira, Cláudia Santos
2014-01-01
[Purpose] To investigate the correlation of functional balance with the functional performance of children with cerebral palsy. [Subjects and Methods] This was a cross-sectional study of children with cerebral palsy with mild to moderate impairment. The children were divided into 3 groups based on motor impairment. The evaluation consisted of the administration of the Pediatric Balance Scale (PBS) and the Pediatric Evaluation Disability Inventory. Correlations between the instruments were determined by calculating Pearson’s correlation coefficients. [Results] In Group 1, a strong positive correlation was found between the PBS and the mobility dimension of the Pediatric Evaluation Disability Inventory (r=0.82), and a moderate correlation was found between the PBS and self-care dimension of the Pediatric Evaluation Disability Inventory (r=0.51). In Group 2, moderate correlations were found between the PBS and both the self-care dimension (r=0.57) and mobility dimension (r=0.41) of the Pediatric Evaluation Disability Inventory. In Group 3, the PBS was weakly correlated with the self-care dimension (r=0.11) and moderately correlated with the mobility dimension (r=0.55). [Conclusion] The PBS proved to be a good auxiliary tool for the evaluation of functional performance with regard to mobility, but cannot be considered a predictor of function in children with cerebral palsy. PMID:25013281
A double-correlation tremor-location method
NASA Astrophysics Data System (ADS)
Li, Ka Lok; Sgattoni, Giulia; Sadeghisorkhani, Hamzeh; Roberts, Roland; Gudmundsson, Olafur
2016-12-01
A double-correlation method is introduced to locate tremor sources based on stacks of complex, doubly-correlated tremor records of multiple triplets of seismographs back projected to hypothetical source locations in a geographic grid. Peaks in the resulting stack of moduli are inferred source locations. The stack of the moduli is a robust measure of energy radiated from a point source or point sources even when the velocity information is imprecise. Application to real data shows how double correlation focuses the source mapping compared to the common single correlation approach. Synthetic tests demonstrate the robustness of the method and its resolution limitations which are controlled by the station geometry, the finite frequency of the signal, the quality of the used velocity information and noise level. Both random noise and signal or noise correlated at time shifts that are inconsistent with the assumed velocity structure can be effectively suppressed. Assuming a surface-wave velocity, we can constrain the source location even if the surface-wave component does not dominate. The method can also in principle be used with body waves in three dimensions, although this requires more data and seismographs placed near the source for depth resolution.
A double-correlation tremor-location method
NASA Astrophysics Data System (ADS)
Li, Ka Lok; Sgattoni, Giulia; Sadeghisorkhani, Hamzeh; Roberts, Roland; Gudmundsson, Olafur
2017-02-01
A double-correlation method is introduced to locate tremor sources based on stacks of complex, doubly-correlated tremor records of multiple triplets of seismographs back projected to hypothetical source locations in a geographic grid. Peaks in the resulting stack of moduli are inferred source locations. The stack of the moduli is a robust measure of energy radiated from a point source or point sources even when the velocity information is imprecise. Application to real data shows how double correlation focuses the source mapping compared to the common single correlation approach. Synthetic tests demonstrate the robustness of the method and its resolution limitations which are controlled by the station geometry, the finite frequency of the signal, the quality of the used velocity information and noise level. Both random noise and signal or noise correlated at time shifts that are inconsistent with the assumed velocity structure can be effectively suppressed. Assuming a surface wave velocity, we can constrain the source location even if the surface wave component does not dominate. The method can also in principle be used with body waves in 3-D, although this requires more data and seismographs placed near the source for depth resolution.
Cross-correlation of point series using a new method
NASA Technical Reports Server (NTRS)
Strothers, Richard B.
1994-01-01
Traditional methods of cross-correlation of two time series do not apply to point time series. Here, a new method, devised specifically for point series, utilizes a correlation measure that is based in the rms difference (or, alternatively, the median absolute difference) between nearest neightbors in overlapped segments of the two series. Error estimates for the observed locations of the points, as well as a systematic shift of one series with respect to the other to accommodate a constant, but unknown, lead or lag, are easily incorporated into the analysis using Monte Carlo techniques. A methodological restriction adopted here is that one series be treated as a template series against which the other, called the target series, is cross-correlated. To estimate a significance level for the correlation measure, the adopted alternative (null) hypothesis is that the target series arises from a homogeneous Poisson process. The new method is applied to cross-correlating the times of the greatest geomagnetic storms with the times of maximum in the undecennial solar activity cycle.
[Assessment of the correlation between taste and smell functioning].
Dzaman, Karolina; Jadczak, Marcin; Rapiejko, Piotr; Syryło, Agnieszka; Jurkiewicz, Dariusz
2005-09-01
There are few studies examining relationship between taste and smell. However their clinical unity is more often indicated. Smell perception abnormalities cause modification in taste of food intensity, disabling perception of taste as a consequence of taste's sniffing failure. Thus disturbances of these senses, which often commonly coexist could cause great discomfort in patients, however taste sense is estimated as less important comparing to smell sense. The aim of that study was to compare the taste perception in patients with normal smell function and patients with hyposmia and anosmia. There was analyzed correlation between the patients' subjective estimation of smell and taste senses and results of gustometry and olfactometry examinations. there were indicated three groups of patients based on smell examination with usage of Elsberga--Levy'ego olfactometr in Pruszewicz modification. The first group included patients with normosmia, the second--patients with hyposmia or anosmia related to every smell, the third--patients with hyposmia on few smells and normal smell feeling of others. The Bornstein's method gustometry modified by us was performed for all groups. Moreover patients presented their subjective estimation of smell and taste senses. All results were statistically analyzed, taking into consideration results with alpha < or = 0.05. All (100%) patients with normosmia correctly identified sour, bitter and salty tastes, while only 53% of patients with hyposmia and anosmia got similar results. However 76.5% of patients from the second group subjectively estimated their sense of taste as a normal perception. Patients with smell disturbances significantly more often have abnormalities in taste perception than patients with normosmia and their subjective estimation of taste and smell senses is much more different than gustometry and olfactometry results.
Capturing correlations in chaotic diffusion by approximation methods.
Knight, Georgie; Klages, Rainer
2011-10-01
We investigate three different methods for systematically approximating the diffusion coefficient of a deterministic random walk on the line that contains dynamical correlations that change irregularly under parameter variation. Capturing these correlations by incorporating higher-order terms, all schemes converge to the analytically exact result. Two of these methods are based on expanding the Taylor-Green-Kubo formula for diffusion, while the third method approximates Markov partitions and transition matrices by using a slight variation of the escape rate theory of chaotic diffusion. We check the practicability of the different methods by working them out analytically and numerically for a simple one-dimensional map, study their convergence, and critically discuss their usefulness in identifying a possible fractal instability of parameter-dependent diffusion, in the case of dynamics where exact results for the diffusion coefficient are not available.
An Explicitly Correlated Wavelet Method for the Electronic Schroedinger Equation
Bachmayr, Markus
2010-09-30
A discretization for an explicitly correlated formulation of the electronic Schroedinger equation based on hyperbolic wavelets and exponential sum approximations of potentials is described, covering mathematical results as well as algorithmic realization, and discussing in particular the potential of methods of this type for parallel computing.
Insights on why graphic correlation (Shaw's method) works.
Edwards, L.E.
1984-01-01
In 1964 A.B.Shaw presented a method of correlating fossilferous sedimentary rocks based on interpretation of graphic plots of first- and last-occurrences of taxa. Because there is no way to determine the true total ranges of fossil taxa, it is instructive to test the accuracy of the method using hypothetical datasets. The dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation. In all graphs, a single straight-line correlation was a reasonable interpretation. The resulting ranges after the first and third rounds of compositing reproduce the 'true' ranges but with small errors. Slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them. Shaw's method works well because, whereas actually sampled ranges will be shorter than true ranges, errors in correlation will be likely to extend some ranges. This or any exercise using simulated data is useful only if the hypothetical situation resembles real geologic situations and if insights derived from the hypothetical dataset provide insights into real situations. The method is only as good as the available data. -Author
Conformal Window and Correlation Functions in Lattice Conformal QCD
NASA Astrophysics Data System (ADS)
Iwasaki, Y.
We discuss various aspects of Conformal Field Theories on the Lattice. We mainly investigate the SU(3) gauge theory with Nf degenerate fermions in the fundamental representation, employing the one-plaquette gauge action and the Wilson fermion action. First we make a brief review of our previous works on the phase structure of lattice gauge theories in terms of the gauge coupling constant and the quark mass. We thereby clarify the reason why we conjecture that the conformal window is 7 ≤ Nf ≤ 16. Secondly, we introduce a new concept, "conformal theories with IR cutof" and point out that any numerical simulation on a lattice is bounded by an IR cutoff ∧IR. Then we make predictions that when Nf is within the conformal window, the propagator of a meson G(t) behaves at large t, as G(t) = c exp (-mHt)/tα, that is, a modified Yukawa-type decay form, instead of the usual exponential decay form exp (-mHt), in the small quark mass region. This holds on an any lattice for any coupling constant g, as far as g is between 0 and g*, where g* is the IR fixed point. We verify that numerical results really satisfy the predictions for the Nf = 7 case and the Nf = 16 case. Thirdly, we discuss small number of flavors (Nf = 2 ˜ 6) QCD at finite temperatures. We point out theoretically and verify numerically that the correlation functions at T/Tc > 1 exhibit the characteristics of the conformal function with IR cutoff, an exponential decay with power correction. Investigating our numerical data by a new method which we call the "local-analysis" of propagators, we observe that the Nf = 7 case and the Nf = 2 at T ˜ 2Tc case are similar to each other, while the Nf = 16 case and the Nf = 2 at T = 102 ˜ 105Tc cases are similar to each other. Further, we observe our data are consistent with the picture that the Nf = 7 case and the Nf = 2 at T ˜ 2Tc case are close to the meson unparticle model. On the other hand, the Nf = 16 case and the Nf = 2 at T = 102 ˜ 105Tc cases are close to
Two-Dimensional Correlation Method for Polymer Analysis
Herman, Matthew Joseph
2015-06-08
Since its introduction by Noda in 1986 two-dimension correlation spectroscopy has been offering polymer scientists an opportunity to look more deeply into collected spectroscopic data. When the spectra are recorded in response to an external perturbation, it is possible to correlate the spectra and expand the information over a separate spectra axis allow for enhancement of spectral resolution, the ability to determine synchronous change, and a unique way to organize observed changes in the spectra into sequential order following a set of three simple rules. By organizing the 2D spectra into synchronous change plots and asynchronous change plots it is possible to correlate change between spectral regions and develop their temporal relationships to one another. With the introduction of moving-window correlation-spectroscopy by Thomas and Richardson in 2000, a method of binning and processing data, it became possible to directly correlate relationships generated in the spectra from the change in the perturbation variable. This method takes advantage of the added resolution of two-dimension spectroscopy and has been applied to study very week transitions found in polymer materials. Appling both of these techniques we are beginning to develop an understanding of how polymers decay under radiolytic aging, to develop a stronger understanding of changes in mechanical properties and the service capabilities of materials.
Exact correlation functions in SU(2) N=2 superconformal QCD.
Baggio, Marco; Niarchos, Vasilis; Papadodimas, Kyriakos
2014-12-19
We report an exact solution of 2- and 3-point functions of chiral primary fields in SU(2) N=2 super-Yang-Mills theory coupled to four hypermultiplets. It is shown that these correlation functions are nontrivial functions of the gauge coupling, obeying differential equations which take the form of the semi-infinite Toda chain. We solve these equations recursively in terms of the Zamolodchikov metric that can be determined exactly from supersymmetric localization on the four-sphere. Our results are verified independently in perturbation theory with a Feynman diagram computation up to 2 loops. This is a short version of a companion paper that contains detailed technical remarks, additional material, and aspects of an extension to the SU(N) gauge group.
Writing CFT correlation functions as AdS scattering amplitudes
NASA Astrophysics Data System (ADS)
Penedones, Joao
2011-03-01
We explore the Mellin representation of conformal correlation functions recently proposed by Mack. Examples in the AdS/CFT context reinforce the analogy between Mellin amplitudes and scattering amplitudes. We conjecture a simple formula relating the bulk scattering amplitudes to the asymptotic behavior of Mellin amplitudes and show that previous results on the flat space limit of AdS follow from our new formula. We find that the Mellin amplitudes are particularly useful in the case of conformal gauge theories in the planar limit. In this case, the four point Mellin amplitudes are meromorphic functions whose poles and their residues are entirely determined by two and three point functions of single-trace operators. This makes the Mellin amplitudes the ideal objects to attempt the conformal bootstrap program in higher dimensions.
Invariant Markov processes on compact groups and correlation functions
NASA Astrophysics Data System (ADS)
Zimpel, Zbigniew
1990-04-01
Random processes governing the time evolution of probability distributions of many physical systems can be described by continuous homogeneous Markov processes taking values from compact groups. Assuming the transition probability function of the process to be invariant in the sense that Pt( x, B) = Pt( e, x-1B) with e being the neutral element of the group, the harmonic analysis (Weyl theory) is applied to study the properties of the Markov semi-group. The infinitesimal operator and generating functional are decomposed using the Levy-Khinchin formula. Under some auxiliary assumptions the components of this decomposition are interpreted as generators of a one parameter subgroup, Brownian motion and a jump process. The formalism is illustrated for several models of processes taking values from compact Lie groups. The properties of the correlation functions of time dependent random variables are investigated.
Reduced density-matrix functional theory: Correlation and spectroscopy
Di Sabatino, S.; Romaniello, P.; Berger, J. A.; Reining, L.
2015-07-14
In this work, we explore the performance of approximations to electron correlation in reduced density-matrix functional theory (RDMFT) and of approximations to the observables calculated within this theory. Our analysis focuses on the calculation of total energies, occupation numbers, removal/addition energies, and spectral functions. We use the exactly solvable Hubbard dimer at 1/4 and 1/2 fillings as test systems. This allows us to analyze the underlying physics and to elucidate the origin of the observed trends. For comparison, we also report the results of the GW approximation, where the self-energy functional is approximated, but no further hypothesis is made concerning the approximations of the observables. In particular, we focus on the atomic limit, where the two sites of the dimer are pulled apart and electrons localize on either site with equal probability, unless a small perturbation is present: this is the regime of strong electron correlation. In this limit, using the Hubbard dimer at 1/2 filling with or without a spin-symmetry-broken ground state allows us to explore how degeneracies and spin-symmetry breaking are treated in RDMFT. We find that, within the used approximations, neither in RDMFT nor in GW, the signature of strong correlation is present, when looking at the removal/addition energies and spectral function from the spin-singlet ground state, whereas both give the exact result for the spin-symmetry broken case. Moreover, we show how the spectroscopic properties change from one spin structure to the other.
Güven, Can; Hinczewski, Michael; Berker, A Nihat
2010-11-01
The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature.
NASA Astrophysics Data System (ADS)
Güven, Can; Hinczewski, Michael; Berker, A. Nihat
2011-03-01
The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature. This research was supported by the Alexander von Humboldt Foundation, the Scientific and Technological Research Council of Turkey (TÜBITAK), and the Academy of Sciences of Turkey.
NASA Astrophysics Data System (ADS)
Güven, Can; Hinczewski, Michael; Berker, A. Nihat
2010-11-01
The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability for the entire temperature range down to the percolation threshold at zero temperature.
Uncertainties in the cluster-cluster correlation function
NASA Astrophysics Data System (ADS)
Ling, E. Nisel; Barrow, John D.; Frenk, C. S.
1986-12-01
The bootstrap resampling technique is applied to estimate sampling errors and significance levels of the two-point correlation functions determined for a subset of the CfA redshift survey of galaxies and a redshift sample of 104 Abell clusters. The angular correlation function for a sample of 1664 Abell clusters is also calculated. The standard errors in xi(r) for the Abell data are found to be considerably larger than quoted 'Poisson errors'. The best estimate for the ratio of the correlation length of Abell clusters (richness class R greater than or equal to 1, distance class D less than or equal to 4) to that of CfA galaxies is 4.2 + 1.4 or - 1.0 (68 percentile error). The enhancement of cluster clustering over galaxy clustering is statistically significant in the presence of resampling errors. The uncertainties found do not include the effects of possible systematic biases in the galaxy and cluster catalogs and could be regarded as lower bounds on the true uncertainty range.
Course 4: Density Functional Theory, Methods, Techniques, and Applications
NASA Astrophysics Data System (ADS)
Chrétien, S.; Salahub, D. R.
Contents 1 Introduction 2 Density functional theory 2.1 Hohenberg and Kohn theorems 2.2 Levy's constrained search 2.3 Kohn-Sham method 3 Density matrices and pair correlation functions 4 Adiabatic connection or coupling strength integration 5 Comparing and constrasting KS-DFT and HF-CI 6 Preparing new functionals 7 Approximate exchange and correlation functionals 7.1 The Local Spin Density Approximation (LSDA) 7.2 Gradient Expansion Approximation (GEA) 7.3 Generalized Gradient Approximation (GGA) 7.4 meta-Generalized Gradient Approximation (meta-GGA) 7.5 Hybrid functionals 7.6 The Optimized Effective Potential method (OEP) 7.7 Comparison between various approximate functionals 8 LAP correlation functional 9 Solving the Kohn-Sham equations 9.1 The Kohn-Sham orbitals 9.2 Coulomb potential 9.3 Exchange-correlation potential 9.4 Core potential 9.5 Other choices and sources of error 9.6 Functionality 10 Applications 10.1 Ab initio molecular dynamics for an alanine dipeptide model 10.2 Transition metal clusters: The ecstasy, and the agony... 10.3 The conversion of acetylene to benzene on Fe clusters 11 Conclusions
Temporal Correlation-Based Spatial Filtering of Rician Noise for Functional MRIs
NASA Astrophysics Data System (ADS)
Amir., A. Khaliq; M. Qureshi, I.; Jawad., A. Shah
2012-01-01
A novel correlation-based filter is presented for de-noising functional magnetic resonance imaging (fMRI) data. Temporal correlation-based exponential weights are defined for spatial smoothing of the data, with bias reduction using estimated noise variance. The proposed scheme is tested on simulated and real fMRI data. Finally, the results are compared with conventional filters. The method is found to be effectively suppressing the Rician noise in fMRI data, while improving the SNR.
Kumar, B V; Ng, T K
1996-04-10
The circular-harmonic-function correlation filter originally proposed by Hsu and Arsenault [Appl. Opt. 21, 4016 (1982)] for in-plane rotation invariance uses only one harmonic, which results in poor discrimination capability of the filter. Various methods to use multiple harmonics were explored previously by different researchers. We present a new method to combine multiple circular harmonics into a single filter that can provide the desired correlation response to in-plane rotation while minimizing the correlation-plane energy. Since multiple harmonics are included, the filter can discriminate well, and since correlation-plane energy is minimized, correlation peaks tend to be sharp. Since the designer can specify the desired in-plane rotation response, a variety of filter behaviors (including complete invariance to input rotations) can be obtained. Underlying theory is discussed, and simulation results are presented.
Casanova, David; Krylov, Anna I.
2016-01-07
A new method for quantifying the contributions of local excitation, charge resonance, and multiexciton configurations in correlated wave functions of multichromophoric systems is presented. The approach relies on fragment-localized orbitals and employs spin correlators. Its utility is illustrated by calculations on model clusters of hydrogen, ethylene, and tetracene molecules using adiabatic restricted-active-space configuration interaction wave functions. In addition to the wave function analysis, this approach provides a basis for a simple state-specific energy correction accounting for insufficient description of electron correlation. The decomposition scheme also allows one to compute energies of the diabatic states of the local excitonic, charge-resonance, and multi-excitonic character. The new method provides insight into electronic structure of multichromophoric systems and delivers valuable reference data for validating excitonic models.
An extension of stochastic hierarchy equations of motion for the equilibrium correlation functions
NASA Astrophysics Data System (ADS)
Ke, Yaling; Zhao, Yi
2017-06-01
A traditional stochastic hierarchy equations of motion method is extended into the correlated real-time and imaginary-time propagations, in this paper, for its applications in calculating the equilibrium correlation functions. The central idea is based on a combined employment of stochastic unravelling and hierarchical techniques for the temperature-dependent and temperature-free parts of the influence functional, respectively, in the path integral formalism of the open quantum systems coupled to a harmonic bath. The feasibility and validity of the proposed method are justified in the emission spectra of homodimer compared to those obtained through the deterministic hierarchy equations of motion. Besides, it is interesting to find that the complex noises generated from a small portion of real-time and imaginary-time cross terms can be safely dropped to produce the stable and accurate position and flux correlation functions in a broad parameter regime.
Shape determination of unidimensional objects: the virtual image correlation method
NASA Astrophysics Data System (ADS)
Francois, M.; Semin, B.; Auradou, H.; Vatteville, J.
2010-06-01
The proposed method, named Virtual Image Correlation, allows one to identify an analytical expression of the shape of a curvilinear object from its image. It uses a virtual beam, whose curvature field is expressed as a truncated mathematical series. The virtual beam width only needs to be close to the physical one; its gray level (in the transverse direction) is bell-shaped. The method consists in finding the coefficients of the series for which the correlation between physical and virtual beams is the best. The accuracy and the robustness of the method is shown by the mean of two examples. The first details a Young’s modulus identification from a cantilever beam image. The second is relative to a thermal plume image, that have a weak contrast and a lot of noise.
The "Mixed" Green's Function Approach to Quantum Kinetics with Initial Correlations
NASA Astrophysics Data System (ADS)
Morozov, V. G.; Röpke, G.
1999-12-01
A method for deriving quantum kinetic equations with initial correlations is developed on the basis of the nonequilibrium Green's function formalism. The method is applicable to a wide range of correlated initial states described by nonequilibrium statistical thermodynamics. Initial correlations and the real-time evolution are treated by a unified technique employing many-component "mixed" Green's functions. The Dyson equation for the mixed Green's function leads to a set of equations for real-time Green's functions and new (cross) components linking initial correlations with dynamical processes. These equations are used to formulate a generalized Kadanoff-Baym ansatz for correlated initial states. A non-Markovian short-time kinetic equation is derived within the T-matrix approximation for the self-energies. The properties of the memory kernels in this equation are considered in detail in Born approximation for the T-matrices. The kinetic equation is demonstrated to conserve the total energy of the system. An explicit expression for the time-dependent correlation energy is obtained.
Correlation functions for pairs and groups of galaxies
NASA Technical Reports Server (NTRS)
Kalinkov, M.; Kuneva, I.
1990-01-01
There are many studies on the correlation functions of galaxies, of clusters of galaxies, even of superclusters (e.g., Groth and Peebles 1977; Davies and Peebles 1983; Kalinkov and Kuneva 1985, 1986; Bahcall 1988 and references therein) but not so many on pairs and groups of galaxies. Results of the calculations of two-point correlation fuctions for some catalogs of pairs and groups of galaxies are given. It is assumed that the distances to pairs and groups of galaxies are given by their mean redshifts according to R = sigma (sup n, sub i-1) V sub i/nH (sub 0), where n is the number of galaxies in the system and H sub 0 = 100 km s(exp -1) Mpc(exp -1).
Spectral functions of strongly correlated extended systems via an exact quantum embedding
NASA Astrophysics Data System (ADS)
Booth, George H.; Chan, Garnet Kin-Lic
2015-04-01
Density matrix embedding theory (DMET) [Phys. Rev. Lett. 109, 186404 (2012), 10.1103/PhysRevLett.109.186404], introduced an approach to quantum cluster embedding methods whereby the mapping of strongly correlated bulk problems to an impurity with finite set of bath states was rigorously formulated to exactly reproduce the entanglement of the ground state. The formalism provided similar physics to dynamical mean-field theory at a tiny fraction of the cost but was inherently limited by the construction of a bath designed to reproduce ground-state, static properties. Here, we generalize the concept of quantum embedding to dynamic properties and demonstrate accurate bulk spectral functions at similarly small computational cost. The proposed spectral DMET utilizes the Schmidt decomposition of a response vector, mapping the bulk dynamic correlation functions to that of a quantum impurity cluster coupled to a set of frequency-dependent bath states. The resultant spectral functions are obtained on the real-frequency axis, without bath discretization error, and allows for the construction of arbitrary dynamic correlation functions. We demonstrate the method on the one- (1D) and two-dimensional (2D) Hubbard model, where we obtain zero temperature and thermodynamic limit spectral functions, and show the trivial extension to two-particle Green's functions. This advance therefore extends the scope and applicability of DMET in condensed-matter problems as a computationally tractable route to correlated spectral functions of extended systems and provides a competitive alternative to dynamical mean-field theory for dynamic quantities.
The leak location package for assessment of the time-frequency correlation method for leak location
NASA Astrophysics Data System (ADS)
Faerman, V. A.; Cheremnov, A. G.; Avramchuk, V. S.; Shepetovsky, D. V.
2017-01-01
The paper describes the simplest implementation of a software and hardware package for acoustic correlation leak location and results of its performance assessment for location of water leaks from a metallic pipe in laboratory conditions. A distinctive feature of this leak locator is the use of the software based on the time-frequency correlation analysis of signals, which was proposed in our previous papers. Comparative analysis results are given for the information content of classical and time-frequency cross-correlation functions as obtained during processing of experimental data. The results obtained justify comparatively higher efficiency of a time-frequency cross correlation method to solve the leak location task. Improved efficiency is determined by bandpass filtration embedded into the time-frequency cross-correlation function calculation.
Brains online: structural and functional correlates of habitual Internet use.
Kühn, Simone; Gallinat, Jürgen
2015-03-01
In the past decades, the Internet has become one of the most important tools to gather information and communicate with other people. Excessive use is a growing concern of health practitioners. Based on the assumption that excessive Internet use bears resemblance with addictive behaviour, we hypothesized alterations of the fronto-striatal network in frequent users. On magnetic resonance imaging scans of 62 healthy male adults, we computed voxel-based morphometry to identify grey matter (GM) correlates of excessive Internet use, assessed by means of the Internet Addiction Test (IAT) and functional connectivity analysis and amplitude of low-frequency fluctuation (ALFF) measures on resting state data to explore the functional networks associated with structural alterations. We found a significant negative association between the IAT score and right frontal pole GM volume (P < 0.001, family wise error corrected). Functional connectivity of right frontal pole to left ventral striatum was positively associated with higher IAT scores. Furthermore, the IAT score was positively correlated to ALFF in bilateral ventral striatum. The alterations in the fronto-striatal circuitry associated with growing IAT scores could reflect a reduction of top-down modulation of prefrontal areas, in particular, the ability to maintain long-term goals in face of distraction. The higher activation of ventral striatum at rest may indicate a constant activation in the context of a diminished prefrontal control. The results demonstrate that excessive Internet use may be driven by neuronal circuits relevant for addictive behaviour.
Duan, L-M
2006-03-17
We propose a detection method for ultracold atoms which allows reconstruction of the full one-particle and two-particle correlation functions from the measurements. The method is based on Fourier sampling of the time-of-flight images through two consecutive impulsive Raman pulses. For applications of this method, we discuss a few examples, including detection of phase separation between superfluid and Mott insulators, various types of spin or superfluid orders, entanglement, exotic or fluctuating orders.
Noise cross correlation functions in a noisy region
NASA Astrophysics Data System (ADS)
Gaudot, I.; Beucler, E.; Mocquet, A.; Schimmel, M.; Le Feuvre, M.; Leparoux, D.; Côte, P.
2013-12-01
The geology of the western France can be roughly split into two main domains: the Armorican massif that contains imprints of the old Cadomian and Variscan orogens; and the Bay of Biscay which present signatures of more recent tectonic events closely related to the opening of North Atlantic ocean. Due to the lack of seismic stations deployment, it exists very few pictures of the deep structures below the Armorican Massif and the Bay of Biscay. Recently, a broadband array of seismometers has been deployed over the south and west of France, providing a good opportunity to get reliable images at depth. Since the region is surrounded by the seas, the seismic ambient noise tomography technique has been proposed to reveal the crustal and uppermost mantle features beneath this area. The first step consists in the computation of noise correlation functions (NCFs) between each station pairs. The ability to obtain empirical Green's functions from NCFs relies on the efficiency of the randomization. Classic ambient noise tomography studies use long-time series (typically several months) to help the randomization including all the scattering effects due to Earth's heterogeneities. However, additionnal signal processing steps such as temporal and/or spectral whitening are most often required for the signals to be representative of a random wavefield. These techniques rely on nonlinear operations which corrupt the integrity of the original record. In the literature, alternatives have been proposed to avoid, at least partially, such non linear operations. One of them is the instantaneous phase cross correlation (PCC). This correlation technique is intrinsically little sensitive to large amplitude transient signals. Using a set of data from a temporary broad band array, we explore the features of the PCC as compared to the time domain geometrically normalized cross correlation (CCGN). In the 0.02Hz-1Hz frequency band, different time series are extracted to investigate the effects of
The derivative discontinuity of the exchange-correlation functional.
Mori-Sánchez, Paula; Cohen, Aron J
2014-07-28
The derivative discontinuity is a key concept in electronic structure theory in general and density functional theory in particular. The electronic energy of a quantum system exhibits derivative discontinuities with respect to different degrees of freedom that are a consequence of the integer nature of electrons. The classical understanding refers to the derivative discontinuity of the total energy as a function of the total number of electrons (N), but it can also manifest at constant N. Examples are shown in models including several hydrogen systems with varying numbers of electrons or nuclear charge (Z), as well as the 1-dimensional Hubbard model (1DHM). Two sides of the problem are investigated: first, the failure of currently used approximate exchange-correlation functionals in DFT and, second, the importance of the derivative discontinuity in the exact electronic structure of molecules, as revealed by full configuration interaction (FCI). Currently, all approximate functionals, including hybrids, miss the derivative discontinuity, leading to basic errors that can be seen in many ways: from the complete failure to give the total energy of H2 and H2(+), to the missing gap in Mott insulators such as stretched H2 and the thermodynamic limit of the 1DHM, or a qualitatively incorrect density in the HZ molecule with two electrons and incorrect electron transfer processes. Description of the exact particle behaviour of electrons is emphasised, which is key to many important physical processes in real systems, especially those involving electron transfer, and offers a challenge for the development of new exchange-correlation functionals.
The Shane-Wirtanen counts. [in galaxy correlation function
NASA Technical Reports Server (NTRS)
Geller, M. J.; Kurtz, M. J.; De Lapparent, V.
1984-01-01
It is shown that the 2.5 degree-break in the galaxy correlation function derived from the Shane-Wirtanen star counts is indistinguishable from an artifact introduced by residual systematic variations in the effective magnitude limit from plate to plate. In order to avoid the introduction of a break, the maximum error from plate to plate must be no more than about 0.05 mag. Other large scale features in the data which are also affected by the systematic variations are discussed.
Functional connectivity correlates of response inhibition impairment in anorexia nervosa.
Collantoni, Enrico; Michelon, Silvia; Tenconi, Elena; Degortes, Daniela; Titton, Francesca; Manara, Renzo; Clementi, Maurizio; Pinato, Claudia; Forzan, Monica; Cassina, Matteo; Santonastaso, Paolo; Favaro, Angela
2016-01-30
Anorexia nervosa (AN) is a disorder characterized by high levels of cognitive control and behavioral perseveration. The present study aims at exploring inhibitory control abilities and their functional connectivity correlates in patients with AN. Inhibitory control - an executive function that allows the realization of adaptive behavior according to environmental contingencies - has been assessed by means of the Stop-Signal paradigm. The study involved 155 patients with lifetime AN and 102 healthy women. A subsample underwent resting-state functional magnetic resonance imaging and was genotyped for COMT and 5-HTTLPR polymorphisms. AN patients showed an impaired response inhibition and a disruption of the functional connectivity of the ventral attention circuit, a neural network implicated in behavioral response when a stimulus occurs unexpected. The 5-HTTLPR genotype appears to significantly interact with the functional connectivity of ventral attention network in explaining task performance in both patients and controls, suggesting a role of the serotoninergic system in mechanisms of response selection. The disruption of the ventral attention network in patients with AN suggests lower efficiency of bottom-up signal filtering, which might be involved in difficulties to adapt behavioral responses to environmental needs. Our findings deserve further research to confirm their scientific and therapeutic implications. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
The Intermediate Scattering Function in Fluorescence Correlation Spectroscopy
NASA Astrophysics Data System (ADS)
Guerra, Rodrigo; Andrews, Ballard; Sen, Pabitra
2006-03-01
We formulate the autocorrelation function for Fluorescence Correlation Spectroscopy (FCS) GD(τ) in reciprocal space in terms of the of the Intermediate Scattering Function ISF(k,t) and the fourier transform of the Optical Response Function ORF(k). In this way we may extend the use of FCS to processes that have been studied using NMR, DLS, and neutron scattering. This formalism is useful for the complicated propagators involved in confined systems and in the study of diffusion in cells: where diffusion is either restricted or permeation through membrane is important. Calculations in k-space produce approximate expressions for the ORF using cumulant expansions that are accurate for small wavevectors. This provides descriptions for longer timescales better suited for studying time-dependent diffusion ISF(k,t)->exp[-tD(t)k^2] and provides a natural separation of contributions from system dynamics and from optical artifacts and aberrations. We will show an explicit derivation of a semi-analytical fit function for free diffusion based on standard electromagnetic analysis of a confocal optical apparatus. This fit function is then used to analyze a representative data set and has no free fit parameters other than the diffusion constant.
Pion correlations as a function of atomic mass in heavy ion collisions
Chacon, A.D.
1989-11-26
The method of two pion interferometry was used to obtain source-size and lifetime parameters for the pions produced in heavy ion collisions. The systems used were 1.70 {center dot} A GeV {sup 56}Fe + Fe, 1.82 {center dot} A GeV {sup 40}Ar + KCl and 1.54 {center dot} A GeV {sup 93}Nb + Nb, allowing for a search for dependences on the atomic number. Two acceptances (centered, in the lab., at {approximately} 0{degrees} and 45{degrees}) were used for each system, allowing a search for dependences on the viewing angle. The correlation functions were calculated by comparing the data samples to background (or reference) samples made using the method of event mixing, where pions from different events are combined to produce a data sample in which the Bose-Einstein correlation effect is absent. The effect of the correlation function on the background samples is calculated, and a method for weighting the events to remove the residual correlation effect is presented. The effect of the spectrometer design on the measured correlation functions is discussed, as are methods for correcting for these effects during the data analysis. 58 refs., 39 figs., 18 tabs.
Mantini, Dante; Hasson, Uri; Betti, Viviana; Perrucci, Mauro G.; Romani, Gian Luca; Corbetta, Maurizio; Orban, Guy A.; Vanduffel, Wim
2012-01-01
Evolution-driven functional changes in the primate brain are typically assessed by aligning monkey and human activation maps using cortical surface expansion models. These models use putative homologous areas as registration landmarks, assuming they are functionally correspondent. In cases where functional changes have occurred in an area, this assumption prohibits to reveal whether other areas may have assumed lost functions. Here we describe a method to examine functional correspondences across species. Without making spatial assumptions, we assess similarities in sensory-driven functional magnetic resonance imaging responses between monkey (Macaca mulatta) and human brain areas by means of temporal correlation. Using natural vision data, we reveal regions for which functional processing has shifted to topologically divergent locations during evolution. We conclude that substantial evolution-driven functional reorganizations have occurred, not always consistent with cortical expansion processes. This novel framework for evaluating changes in functional architecture is crucial to building more accurate evolutionary models. PMID:22306809
Mantini, Dante; Hasson, Uri; Betti, Viviana; Perrucci, Mauro G; Romani, Gian Luca; Corbetta, Maurizio; Orban, Guy A; Vanduffel, Wim
2012-02-05
Evolution-driven functional changes in the primate brain are typically assessed by aligning monkey and human activation maps using cortical surface expansion models. These models use putative homologous areas as registration landmarks, assuming they are functionally correspondent. For cases in which functional changes have occurred in an area, this assumption prohibits to reveal whether other areas may have assumed lost functions. Here we describe a method to examine functional correspondences across species. Without making spatial assumptions, we assessed similarities in sensory-driven functional magnetic resonance imaging responses between monkey (Macaca mulatta) and human brain areas by temporal correlation. Using natural vision data, we revealed regions for which functional processing has shifted to topologically divergent locations during evolution. We conclude that substantial evolution-driven functional reorganizations have occurred, not always consistent with cortical expansion processes. This framework for evaluating changes in functional architecture is crucial to building more accurate evolutionary models.
NASA Astrophysics Data System (ADS)
Fu, Qiang; Luk, Wai-Shing; Tao, Jun; Zeng, Xuan; Cai, Wei
In this paper, a novel intra-die spatial correlation extraction method referred to as MLEMTC (Maximum Likelihood Estimation for Multiple Test Chips) is presented. In the MLEMTC method, a joint likelihood function is formulated by multiplying the set of individual likelihood functions for all test chips. This joint likelihood function is then maximized to extract a unique group of parameter values of a single spatial correlation function, which can be used for statistical circuit analysis and design. Moreover, to deal with the purely random component and measurement error contained in measurement data, the spatial correlation function combined with the correlation of white noise is used in the extraction, which significantly improves the accuracy of the extraction results. Furthermore, an LU decomposition based technique is developed to calculate the log-determinant of the positive definite matrix within the likelihood function, which solves the numerical stability problem encountered in the direct calculation. Experimental results have shown that the proposed method is efficient and practical.
Porous Organic Materials: Strategic Design and Structure-Function Correlation.
Das, Saikat; Heasman, Patrick; Ben, Teng; Qiu, Shilun
2017-02-08
Porous organic materials have garnered colossal interest with the scientific fraternity due to their excellent gas sorption performances, catalytic abilities, energy storage capacities, and other intriguing applications. This review encompasses the recent significant breakthroughs and the conventional functions and practices in the field of porous organic materials to find useful applications and imparts a comprehensive understanding of the strategic evolution of the design and synthetic approaches of porous organic materials with tunable characteristics. We present an exhaustive analysis of the design strategies with special emphasis on the topologies of crystalline and amorphous porous organic materials. In addition to elucidating the structure-function correlation and state-of-the-art applications of porous organic materials, we address the challenges and restrictions that prevent us from realizing porous organic materials with tailored structures and properties for useful applications.
An improved image reconstruction method for optical intensity correlation Imaging
NASA Astrophysics Data System (ADS)
Gao, Xin; Feng, Lingjie; Li, Xiyu
2016-12-01
The intensity correlation imaging method is a novel kind of interference imaging and it has favorable prospects in deep space recognition. However, restricted by the low detecting signal-to-noise ratio (SNR), it's usually very difficult to obtain high-quality image of deep space object like high-Earth-orbit (HEO) satellite with existing phase retrieval methods. In this paper, based on the priori intensity statistical distribution model of the object and characteristics of measurement noise distribution, an improved method of Prior Information Optimization (PIO) is proposed to reduce the ambiguous images and accelerate the phase retrieval procedure thus realizing fine image reconstruction. As the simulations and experiments show, compared to previous methods, our method could acquire higher-resolution images with less error in low SNR condition.
Strength of functional signature correlates with effect size in autism.
Ballouz, Sara; Gillis, Jesse
2017-07-07
Disagreements over genetic signatures associated with disease have been particularly prominent in the field of psychiatric genetics, creating a sharp divide between disease burdens attributed to common and rare variation, with study designs independently targeting each. Meta-analysis within each of these study designs is routine, whether using raw data or summary statistics, but combining results across study designs is atypical. However, tests of functional convergence are used across all study designs, where candidate gene sets are assessed for overlaps with previously known properties. This suggests one possible avenue for combining not study data, but the functional conclusions that they reach. In this work, we test for functional convergence in autism spectrum disorder (ASD) across different study types, and specifically whether the degree to which a gene is implicated in autism is correlated with the degree to which it drives functional convergence. Because different study designs are distinguishable by their differences in effect size, this also provides a unified means of incorporating the impact of study design into the analysis of convergence. We detected remarkably significant positive trends in aggregate (p < 2.2e-16) with 14 individually significant properties (false discovery rate <0.01), many in areas researchers have targeted based on different reasoning, such as the fragile X mental retardation protein (FMRP) interactor enrichment (false discovery rate 0.003). We are also able to detect novel technical effects and we see that network enrichment from protein-protein interaction data is heavily confounded with study design, arising readily in control data. We see a convergent functional signal for a subset of known and novel functions in ASD from all sources of genetic variation. Meta-analytic approaches explicitly accounting for different study designs can be adapted to other diseases to discover novel functional associations and increase
Spectral methods and cluster structure in correlation-based networks
NASA Astrophysics Data System (ADS)
Heimo, Tapio; Tibély, Gergely; Saramäki, Jari; Kaski, Kimmo; Kertész, János
2008-10-01
We investigate how in complex systems the eigenpairs of the matrices derived from the correlations of multichannel observations reflect the cluster structure of the underlying networks. For this we use daily return data from the NYSE and focus specifically on the spectral properties of weight W=|-δ and diffusion matrices D=W/sj-δ, where C is the correlation matrix and si=∑jW the strength of node j. The eigenvalues (and corresponding eigenvectors) of the weight matrix are ranked in descending order. As in the earlier observations, the first eigenvector stands for a measure of the market correlations. Its components are, to first approximation, equal to the strengths of the nodes and there is a second order, roughly linear, correction. The high ranking eigenvectors, excluding the highest ranking one, are usually assigned to market sectors and industrial branches. Our study shows that both for weight and diffusion matrices the eigenpair analysis is not capable of easily deducing the cluster structure of the network without a priori knowledge. In addition we have studied the clustering of stocks using the asset graph approach with and without spectrum based noise filtering. It turns out that asset graphs are quite insensitive to noise and there is no sharp percolation transition as a function of the ratio of bonds included, thus no natural threshold value for that ratio seems to exist. We suggest that these observations can be of use for other correlation based networks as well.
NASA Astrophysics Data System (ADS)
Rontani, Massimo; Molinari, Elisa; Maruccio, Giuseppe; Janson, Martin; Schramm, Andreas; Meyer, Christian; Matsui, Tomohiro; Heyn, Christian; Hansen, Wolfgang; Wiesendanger, Roland
2007-04-01
We show both theoretically and experimentally that scanning tunneling spectroscopy (STS) images of semiconductor quantum dots may display clear signatures of electron-electron correlation. We apply many-body tunneling theory to a realistic model, which fully takes into account correlation effects and dot anisotropy. Comparing measured STS images of freestanding InAs quantum dots with those calculated by the full configuration interaction method, we explain the wave-function sequence in terms of images of one- and two-electron states. The STS map corresponding to double charging is significantly distorted by electron correlation with respect to the noninteracting case.
Pair correlation functions of strongly coupled two-temperature plasma
NASA Astrophysics Data System (ADS)
Shaffer, Nathaniel R.; Tiwari, Sanat Kumar; Baalrud, Scott D.
2017-09-01
Using molecular dynamics simulations, we perform the first direct tests of three proposed models for the pair correlation functions of strongly coupled plasmas with species of unequal temperature. The models are all extensions of the Ornstein-Zernike/hypernetted-chain theory used to good success for equilibrium plasmas. Each theory is evaluated at several coupling strengths, temperature ratios, and mass ratios for a model plasma in which the electrons are positively charged. We show that the model proposed by Seuferling et al. [Phys. Rev. A 40, 323 (1989)] agrees well with molecular dynamics over a wide range of mass and temperature ratios, as well as over a range of coupling strength similar to that of the equilibrium hypernetted-chain (HNC) theory. The SVT model also correctly predicts the strength of interspecies correlations and exhibits physically reasonable long-wavelength limits of the static structure factors. Comparisons of the SVT model with the Yukawa one-component plasma (YOCP) model are used to show that ion-ion pair correlations are well described by the YOCP model up to Γe≈1 , beyond which it rapidly breaks down.
Haney, Matthew M.; Mikesell, T. Dylan; van Wijk, Kasper; Nakahara, Hisashi
2012-01-01
Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations were not considered in the development of the SPAC method. The method originally addressed the vertical–vertical (ZZ), RR and TT correlations, hence the name spatial autocorrelation. The theoretical expressions we derive for the ZR and RZ correlations offer additional ways to measure Rayleigh wave dispersion within the SPAC framework. Expanding on the results for isotropic incidence, we derive the complete correlation matrix in the case of generally anisotropic incidence. We show that the ZR and RZ correlations have advantageous properties in the presence of an out-of-plane directional wavefield compared to ZZ and RR correlations. We apply the results for mixed-component correlations to a data set from Akutan Volcano, Alaska and find consistent estimates of Rayleigh wave phase velocity from ZR compared to ZZ correlations. This work together with the recently discovered connections between the SPAC method and time-domain correlations of ambient noise provide further insights into the retrieval of surface wave Green’s functions from seismic noise.
Compositions and methods for hydrocarbon functionalization
Gunnoe, Thomas Brent; Fortman, George; Boaz, Nicholas C.; Groves, John T.
2017-03-28
Embodiments of the present disclosure provide for methods of hydrocarbon functionalization, methods and systems for converting a hydrocarbon into a compound including at least one group ((e.g., hydroxyl group) (e.g., methane to methanol)), functionalized hydrocarbons, and the like.
Large N correlation functions N = 2 superconformal quivers
NASA Astrophysics Data System (ADS)
Pini, Alessandro; Rodriguez-Gomez, Diego; Russo, Jorge G.
2017-08-01
Using supersymmetric localization, we consider four-dimensional N = 2 superconformal quiver gauge theories obtained from Z_n orbifolds of N = 4 Super Yang-Mills theory in the large N limit at weak coupling. In particular, we show that: 1) The partition function for arbitrary couplings can be constructed in terms of universal building blocks. 2) It can be computed in perturbation series, which converges uniformly for |λ I | < π2, where λ I are the 't Hooft coupling of the gauge groups. 3) The perturbation series for two-point functions can be explicitly computed to arbitrary orders. There is no universal effective coupling by which one can express them in terms of correlators of the N = 4 theory. 4) One can define twisted and untwisted sector operators. At the perturbative orbifold point, when all the couplings are the same, the correlators of untwisted sector operators coincide with those of N = 4 Super Yang-Mills theory. In the twisted sector, we find remarkable cancellations of a certain number of planar loops, determined by the conformal dimension of the operator.
[Correlation between structural and functional analysis in glaucoma suspects].
Chiseliţă, D; Danielescu, C; Apostol, Alina
2008-01-01
To establish correlations between structural and functional parameters in glaucoma suspects. In 43 patients (83 eyes) of glaucoma patients we have performed standard automated perimetry, scanning laser polarimetry (GDx-VCC) of the retinal nerve fiber layer (RNFL) and optical coherence tomography (Stratus OCT) of the RNFL and optic disc. Diagnostic concordance (achieved if one eye is deemed normal--respectively abnormal--by both tests) was 60.24% between perimetry and OCT respectively 61.44% between perimetry and GDx. The Areas under the Receiver Operating Characteristic curve were between 0.524-0.574 for OCT parameters and 0.518-0.548 for GDx parameters (considering the visual field examination as "gold standard"). The correlation between RNFL measurements in OCT and GDx took values between r = 0.481 and r = 0.352. Structural and functional damage are not consistent with each other in early glaucoma, resulting in the fact that both tests should be used in the diagnostic strategy
Omega from the anisotropy of the redshift correlation function
NASA Technical Reports Server (NTRS)
Hamilton, A. J. S.
1993-01-01
Peculiar velocities distort the correlation function of galaxies observed in redshift space. In the large scale, linear regime, the distortion takes a characteristic quadrupole plus hexadecapole form, with the amplitude of the distortion depending on the cosmological density parameter omega. Preliminary measurements are reported here of the harmonics of the correlation function in the CfA, SSRS, and IRAS 2 Jansky redshift surveys. The observed behavior of the harmonics agrees qualitatively with the predictions of linear theory on large scales in every survey. However, real anisotropy in the galaxy distribution induces large fluctuations in samples which do not yet probe a sufficiently fair volume of the Universe. In the CfA 14.5 sample in particular, the Great Wall induces a large negative quadrupole, which taken at face value implies an unrealistically large omega 20. The IRAS 2 Jy survey, which covers a substantially larger volume than the optical surveys and is less affected by fingers-of-god, yields a more reliable and believable value, omega = 0.5 sup +.5 sub -.25.
Correlation between static balance and functional autonomy in elderly women.
de Noronha Ribeiro Daniel, Fernanda; de Souza Vale, Rodrigo Gomes; Giani, Tania Santos; Bacellar, Silvia; Escobar, Tatiane; Stoutenberg, Mark; Dantas, Estélio Henrique Martin
2011-01-01
The purpose of the present study was to verify the correlation between static balance and functional autonomy in elderly women. The sample was a random selection of 32 sedentary elderly women (mean age=67.47 ± 7.37 years, body mass index=BMI=27.30 ± 5.07 kg/m(2)), who live in the city of Teresina in the state of Piauí, Brazil. Static balance was analyzed by stabilometric assessment using an electronic baropodometer which measured the average of the amplitude of postural oscillations in the right (RLD) and left (LLD) lateral displacements, anterior (AD) and posterior (PD) displacements, and in the elliptical area (EA) formed by the body's center of gravity. Functional autonomy was evaluated by a battery of tests from the LADEG protocol which is composed of: a 10 m walk (10 mW), getting up from a seated position (GSP), getting up from the prone position (GPP), getting up from a chair and movement around the house (GCMH), and putting on and taking off a shirt (PTS). The Spearman's correlation coefficient (r) indicated a positive and significant correlation between GPP and LLD (r=0.382; p=0.031), GPP and PD (r=0.398; p=0.024) and GPP and EA (r=0.368; p=0.038). These results show that sedentary elderly women who spent the greatest amount of time performing the GPP test achieved the largest mean amplitude of displacement leading to greater levels of instability.
A functional correlate of severity in alternating hemiplegia of childhood.
Li, Melody; Jazayeri, Dana; Corry, Ben; McSweeney, K Melodi; Heinzen, Erin L; Goldstein, David B; Petrou, Steven
2015-05-01
Mutations in ATP1A3, the gene that encodes the α3 subunit of the Na(+)/K(+) ATPase, are the primary cause of alternating hemiplegia of childhood (AHC). Correlations between different mutations and AHC severity were recently reported, with E815K identified in severe and D801N and G947R in milder cases. This study aims to explore the molecular pathological mechanisms in AHC and to identify functional correlates for mutations associated with different levels of disease severity. Human wild type ATP1A3, and E815K, D801N and G947R mutants were expressed in Xenopus laevis oocytes and Na(+)/K(+) ATPase function measured. Structural homology models of the human α3 subunit containing AHC mutations were created. The AHC mutations examined all showed similar levels of reduction in forward cycling. Wild type forward cycling was reduced by coexpression with any mutant, indicating dominant negative interactions. Proton transport was measured and found to be selectively impaired only in E815K. Homology modeling showed that D801 and G947 lie within or near known cation binding sites while E815 is more distal. Despite its effect on proton transport, E815K was also distant from the proposed proton transport route. Loss of forward cycling and dominant negativity are common and likely necessary pathomechanisms for AHC. In addition, loss of proton transport correlated with severity of AHC. D801N and G947R are likely to directly disrupt normal Na(+)/K(+) binding while E815K may disrupt forward cycling and proton transport via allosteric mechanisms yet to be elucidated. Copyright © 2015 Elsevier Inc. All rights reserved.
Phase demodulation method from a single fringe pattern based on correlation with a polynomial form.
Robin, Eric; Valle, Valéry; Brémand, Fabrice
2005-12-01
The method presented extracts the demodulated phase from only one fringe pattern. Locally, this method approaches the fringe pattern morphology with the help of a mathematical model. The degree of similarity between the mathematical model and the real fringe is estimated by minimizing a correlation function. To use an optimization process, we have chosen a polynomial form such as a mathematical model. However, the use of a polynomial form induces an identification procedure with the purpose of retrieving the demodulated phase. This method, polynomial modulated phase correlation, is tested on several examples. Its performance, in terms of speed and precision, is presented on very noised fringe patterns.
Functional correlates of distractor suppression during spatial working memory encoding.
Toepper, M; Gebhardt, H; Beblo, T; Thomas, C; Driessen, M; Bischoff, M; Blecker, C R; Vaitl, D; Sammer, G
2010-02-17
Executive working memory operations are related to prefrontal regions in the healthy brain. Moreover, neuroimaging data provide evidence for a functional dissociation of ventrolateral and dorsolateral prefrontal cortex. Most authors either suggest a modality-specific or a function-specific prefrontal cortex organization. In the present study we particularly aimed at the identification of different prefrontal cerebral areas that are involved in executive inhibitory processes during spatial working memory encoding. In an fMRI study (functional magnetic resonance imaging) we examined the neural correlates of spatial working memory processing by varying the amount of executive demands of the task. Twenty healthy volunteers performed the Corsi Block-Tapping test (CBT) during fMRI. The CBT requires the storage and reproduction of spatial target sequences. In a second condition, we presented an adapted version of the Block-Suppression-Test (BST). The BST is based on the original CBT but additionally requires the active suppression of visual distraction within the target sequences. In comparison to the CBT performance, particularly the left dorsolateral prefrontal cortex (BA 9) showed more activity during the BST condition. Our results show that the left dorsolateral prefrontal cortex plays a crucial role for executive controlled inhibition of spatial distraction. Furthermore, our findings are in line with the processing model of a functional dorsolateral-ventrolateral prefrontal cortex organization.
Two-dimensional signal reconstruction: The correlation sampling method
Roman, H. E.
2007-12-15
An accurate approach for reconstructing a time-dependent two-dimensional signal from non-synchronized time series recorded at points located on a grid is discussed. The method, denoted as correlation sampling, improves the standard conditional sampling approach commonly employed in the study of turbulence in magnetoplasma devices. Its implementation is illustrated in the case of an artificial time-dependent signal constructed using a fractal algorithm that simulates a fluctuating surface. A statistical method is also discussed for distinguishing coherent (i.e., collective) from purely random (noisy) behavior for such two-dimensional fluctuating phenomena.
Cathodic protection design using the regression and correlation method
Niembro, A.M.; Ortiz, E.L.G.
1997-09-01
A computerized statistical method which calculates the current demand requirement based on potential measurements for cathodic protection systems is introduced. The method uses the regression and correlation analysis of statistical measurements of current and potentials of the piping network. This approach involves four steps: field potential measurements, statistical determination of the current required to achieve full protection, installation of more cathodic protection capacity with distributed anodes around the plant and examination of the protection potentials. The procedure is described and recommendations for the improvement of the existing and new cathodic protection systems are given.
Analysis/forecast experiments with a flow-dependent correlation function using FGGE data
NASA Technical Reports Server (NTRS)
Baker, W. E.; Bloom, S. C.; Carus, H.; Nestler, M. S.
1986-01-01
The use of a flow-dependent correlation function to improve the accuracy of an optimum interpolation (OI) scheme is examined. The development of the correlation function for the OI analysis scheme used for numerical weather prediction is described. The scheme uses a multivariate surface analysis over the oceans to model the pressure-wind error cross-correlation and it has the ability to use an error correlation function that is flow- and geographically-dependent. A series of four-day data assimilation experiments, conducted from January 5-9, 1979, were used to investigate the effect of the different features of the OI scheme (error correlation) on forecast skill for the barotropic lows and highs. The skill of the OI was compared with that of a successive correlation method (SCM) of analysis. It is observed that the largest difference in the correlation statistics occurred in barotropic and baroclinic lows and highs. The comparison reveals that the OI forecasts were more accurate than the SCM forecasts.
Analysis/forecast experiments with a flow-dependent correlation function using FGGE data
NASA Technical Reports Server (NTRS)
Baker, W. E.; Bloom, S. C.; Carus, H.; Nestler, M. S.
1986-01-01
The use of a flow-dependent correlation function to improve the accuracy of an optimum interpolation (OI) scheme is examined. The development of the correlation function for the OI analysis scheme used for numerical weather prediction is described. The scheme uses a multivariate surface analysis over the oceans to model the pressure-wind error cross-correlation and it has the ability to use an error correlation function that is flow- and geographically-dependent. A series of four-day data assimilation experiments, conducted from January 5-9, 1979, were used to investigate the effect of the different features of the OI scheme (error correlation) on forecast skill for the barotropic lows and highs. The skill of the OI was compared with that of a successive correlation method (SCM) of analysis. It is observed that the largest difference in the correlation statistics occurred in barotropic and baroclinic lows and highs. The comparison reveals that the OI forecasts were more accurate than the SCM forecasts.
Correlation functions from a unified variational principle: Trial Lie groups
Balian, R.; Vénéroni, M.
2015-11-15
Time-dependent expectation values and correlation functions for many-body quantum systems are evaluated by means of a unified variational principle. It optimizes a generating functional depending on sources associated with the observables of interest. It is built by imposing through Lagrange multipliers constraints that account for the initial state (at equilibrium or off equilibrium) and for the backward Heisenberg evolution of the observables. The trial objects are respectively akin to a density operator and to an operator involving the observables of interest and the sources. We work out here the case where trial spaces constitute Lie groups. This choice reduces the original degrees of freedom to those of the underlying Lie algebra, consisting of simple observables; the resulting objects are labeled by the indices of a basis of this algebra. Explicit results are obtained by expanding in powers of the sources. Zeroth and first orders provide thermodynamic quantities and expectation values in the form of mean-field approximations, with dynamical equations having a classical Lie–Poisson structure. At second order, the variational expression for two-time correlation functions separates–as does its exact counterpart–the approximate dynamics of the observables from the approximate correlations in the initial state. Two building blocks are involved: (i) a commutation matrix which stems from the structure constants of the Lie algebra; and (ii) the second-derivative matrix of a free-energy function. The diagonalization of both matrices, required for practical calculations, is worked out, in a way analogous to the standard RPA. The ensuing structure of the variational formulae is the same as for a system of non-interacting bosons (or of harmonic oscillators) plus, at non-zero temperature, classical Gaussian variables. This property is explained by mapping the original Lie algebra onto a simpler Lie algebra. The results, valid for any trial Lie group, fulfill
Correlation between two methods of florbetapir PET quantitative analysis.
Breault, Christopher; Piper, Jonathan; Joshi, Abhinay D; Pirozzi, Sara D; Nelson, Aaron S; Lu, Ming; Pontecorvo, Michael J; Mintun, Mark A; Devous, Michael D
2017-01-01
This study evaluated performance of a commercially available standardized software program for calculation of florbetapir PET standard uptake value ratios (SUVr) in comparison with an established research method. Florbetapir PET images for 183 subjects clinically diagnosed as cognitively normal (CN), mild cognitive impairment (MCI) or probable Alzheimer's disease (AD) (45 AD, 60 MCI, and 78 CN) were evaluated using two software processing algorithms. The research method uses a single florbetapir PET template generated by averaging both amyloid positive and amyloid negative registered brains together. The commercial software simultaneously optimizes the registration between the florbetapir PET images and three templates: amyloid negative, amyloid positive, and an average. Cortical average SUVr values were calculated across six predefined anatomic regions with respect to the whole cerebellum reference region. SUVr values were well correlated between the two methods (r2 = 0.98). The relationship between the methods computed from the regression analysis is: Commercial method SUVr = (0.9757*Research SUVr) + 0.0299. A previously defined cutoff SUVr of 1.1 for distinguishing amyloid positivity by the research method corresponded to 1.1 (95% CI = 1.098, 1.11) for the commercial method. This study suggests that the commercial method is comparable to the published research method of SUVr analysis for florbetapir PET images, thus facilitating the potential use of standardized quantitative approaches to PET amyloid imaging.
Törnberg, Anna; Wadell, Karin
2016-01-01
Purpose: To examine the correlation between limb muscle function (endurance and strength) and functional capacity in upper limbs (ULs) and lower limbs (LLs) of people with chronic obstructive pulmonary disease (COPD). Method: This article describes a secondary analysis of data from a randomized controlled trial. A stationary dynamometer was used to measure isokinetic muscle strength and endurance; the 6-minute walk test, the 6-minute pegboard and ring test, and the unsupported UL exercise test were used to measure functional capacity. Results: Participants were 44 adults with COPD. Muscle strength and endurance in ULs and LLs demonstrated a moderate to strong correlation with functional capacity. When controlling for muscle strength, muscle endurance was moderately correlated with functional capacity in ULs and LLs, but when controlling for muscle endurance, there was no positive and significant correlation between muscle strength and functional capacity for the ULs or LLs. Conclusions: Functional capacity seems to be more closely related to limb muscle endurance than to limb muscle strength in people with COPD. PMID:27504047
Petascale Many Body Methods for Complex Correlated Systems
NASA Astrophysics Data System (ADS)
Pruschke, Thomas
2012-02-01
Correlated systems constitute an important class of materials in modern condensed matter physics. Correlation among electrons are at the heart of all ordering phenomena and many intriguing novel aspects, such as quantum phase transitions or topological insulators, observed in a variety of compounds. Yet, theoretically describing these phenomena is still a formidable task, even if one restricts the models used to the smallest possible set of degrees of freedom. Here, modern computer architectures play an essential role, and the joint effort to devise efficient algorithms and implement them on state-of-the art hardware has become an extremely active field in condensed-matter research. To tackle this task single-handed is quite obviously not possible. The NSF-OISE funded PIRE collaboration ``Graduate Education and Research in Petascale Many Body Methods for Complex Correlated Systems'' is a successful initiative to bring together leading experts around the world to form a virtual international organization for addressing these emerging challenges and educate the next generation of computational condensed matter physicists. The collaboration includes research groups developing novel theoretical tools to reliably and systematically study correlated solids, experts in efficient computational algorithms needed to solve the emerging equations, and those able to use modern heterogeneous computer architectures to make then working tools for the growing community.
Van Raemdonck, Mario; Alcoba, Diego R; Poelmans, Ward; De Baerdemacker, Stijn; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E; Van Neck, Dimitri; Bultinck, Patrick
2015-09-14
A class of polynomial scaling methods that approximate Doubly Occupied Configuration Interaction (DOCI) wave functions and improve the description of dynamic correlation is introduced. The accuracy of the resulting wave functions is analysed by comparing energies and studying the overlap between the newly developed methods and full configuration interaction wave functions, showing that a low energy does not necessarily entail a good approximation of the exact wave function. Due to the dependence of DOCI wave functions on the single-particle basis chosen, several orbital optimisation algorithms are introduced. An energy-based algorithm using the simulated annealing method is used as a benchmark. As a computationally more affordable alternative, a seniority number minimising algorithm is developed and compared to the energy based one revealing that the seniority minimising orbital set performs well. Given a well-chosen orbital basis, it is shown that the newly developed DOCI based wave functions are especially suitable for the computationally efficient description of static correlation and to lesser extent dynamic correlation.
Baladandayuthapani, Veerabhadran; Mallick, Bani K.; Hong, Mee Young; Lupton, Joanne R.; Turner, Nancy D.; Carroll, Raymond J.
2009-01-01
Summary In this article, we present new methods to analyze data from an experiment using rodent models to investigate the role of p27, an important cell-cycle mediator, in early colon carcinogenesis. The responses modeled here are essentially functions nested within a two-stage hierarchy. Standard functional data analysis literature focuses on a single stage of hierarchy and conditionally independent functions with near white noise. However, in our experiment, there is substantial biological motivation for the existence of spatial correlation among the functions, which arise from the locations of biological structures called colonic crypts: this possible functional correlation is a phenomenon we term crypt signaling. Thus, as a point of general methodology, we require an analysis that allows for functions to be correlated at the deepest level of the hierarchy. Our approach is fully Bayesian and uses Markov chain Monte Carlo methods for inference and estimation. Analysis of this data set gives new insights into the structure of p27 expression in early colon carcinogenesis and suggests the existence of significant crypt signaling. Our methodology uses regression splines, and because of the hierarchical nature of the data, dimension reduction of the covariance matrix of the spline coefficients is important: we suggest simple methods for overcoming this problem. PMID:17608780
Probing the twist-3 multi-gluon correlation functions by p↑p → DX
NASA Astrophysics Data System (ADS)
Koike, Yuji; Yoshida, Shinsuke
2011-05-01
We study the single spin asymmetry (SSA) for the D-meson production ADN in the pp collision, p↑p → DX in the framework of the collinear factorization. Since the charm quark is mainly produced through the cbar c-pair creation from the gluon-fusion process, this is an ideal process to probe the twist-3 triple-gluon correlation functions in the polarized nucleon. We derive the corresponding cross section formula for the contribution of the triple-gluon correlation function to ADN in p↑p → DX, applying the method developed for ep↑ → eDX in our previous study. As in the case of ep↑ → eDX, our result differs from a previous study in the literature.We will also present a simple estimate of the triple-gluon correlation functions based on the preliminary data on ADN by RHIC.
CORRELATION BETWEEN VISUAL GAIT ANALYSIS AND FUNCTIONAL ASPECTS IN CEREBRAL PALSY
FOLLE, MAIRA RECH; TEDESCO, ANA PAULA; NICOLINI-PANISSON, RENATA D´AGOSTINI
2016-01-01
ABSTRACT Objective: To verify the correlation between visual gait analysis (VGA) by the Edinburgh visual gait score (EVGS) and functional aspects using the Timed Up and Go Test (TUG) and Gross Motor Function Classification System (GMFCS) in individuals with cerebral palsy (CP). Methods: Retrospective cross sectional study of 35 patients with CP. The mean age 12.61 years old, 94.3% were spastic; 34.4% hemiplegic, 54.3% diplegic, 11.4% triplegic; 45.7% were level II GMFCS, 42.9% level I, 5.7% level III and 5.7% level IV. VGA was analyzed by the Edinburgh visual gait score (EVGS), functional mobility was assessed by TUG and functionality through GMFCS. The Spearman correlation was used for statistical analysis. Results: The mean EVGS score was 18.97. The mean TUG was 13.71sec. EVGS showed moderate correlation with TUG (r=0.46, p=0.03) and GMFCS (r=0.45, p=0.00). Conclusion: Worse VGA scores correlate to worse functionality and mobility performance. Due to the observed correlation, it is possible to assert that VGA is a useful tool on evaluation of CP patients. Level of Evidence III, Retrospective Comparative Study. PMID:28149192
Correlation between pouch function and sexual function in patients with IPAA.
Sunde, Marie Louise; Øresland, Tom; Engebreth Færden, Arne
2016-03-01
Restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA) is the treatment of choice for ulcerative colitis refractory to medical treatment and familial adenomatous polyposis. The objective of this study was to study the impact of postoperative pouch function on sexual function. Sexual function after IPAA surgery has also been compared to sexual function in the average Norwegian population. All patients having undergone IPAA from 2000 to June 2013 were identified from the hospital medical record files and sent validated questionnaires regarding their sexual function. Pouch function was scored according to Oresland score through a phone interview. Patients operated on or before June 2012 were asked to answer the same questionnaires twice with an interval of one year to see how stable sexual function is over time. Sixty-eight out of 100 consecutive patients answered the questionnaire regarding both sexual function and pouch function (44 men, 24 women). There was no significant relationship between pouch and sexual function in men (p-value 0.158, corr. coefficient - 0.216). In women there was a significant relationship (p-value - 0.01, corr. coefficient 0.517). There was no significant shift in sexual function during the study period. We found no significant correlation between sexual function and pouch function in men. In women, we found a significant correlation between poor pouch function and impaired sexual function. As similar studies have found, sexual function remains good after IPAA surgery. This is an important information for patients and physicians, both to inform patients correctly prior to surgery, and in the postoperative follow-up.
A method for correlating performance data of a terrestrial solar cell array
NASA Technical Reports Server (NTRS)
Simon, F. F.
1979-01-01
An analytical method was proposed for characterizing array power output, in the region of maximum power, as a function of environmental variables. The correlation provided a way of evaluating the output of an array under environmental conditions that differ from those encountered during testing. Power data obtained at one location was used to predict array performance at other locations.
A fast digital image correlation method for deformation measurement
NASA Astrophysics Data System (ADS)
Pan, Bing; Li, Kai
2011-07-01
Fast and high-accuracy deformation analysis using digital image correlation (DIC) has been increasingly important and highly demanded in recent years. In literature, the DIC method using the Newton-Rapshon (NR) algorithm has been considered as a gold standard for accurate sub-pixel displacement tracking, as it is insensitive to the relative deformation and rotation of the target subset and thus provides highest sub-pixel registration accuracy and widest applicability. A significant drawback of conventional NR-algorithm-based DIC method, however, is its extremely huge computational expense. In this paper, a fast DIC method is proposed deformation measurement by effectively eliminating the repeating redundant calculations involved in the conventional NR-algorithm-based DIC method. Specifically, a reliability-guided displacement scanning strategy is employed to avoid time-consuming integer-pixel displacement searching for each calculation point, and a pre-computed global interpolation coefficient look-up table is utilized to entirely eliminate repetitive interpolation calculation at sub-pixel locations. With these two approaches, the proposed fast DIC method substantially increases the calculation efficiency of the traditional NR-algorithm-based DIC method. The performance of proposed fast DIC method is carefully tested on real experimental images using various calculation parameters. Results reveal that the computational speed of the present fast DIC is about 120-200 times faster than that of the traditional method, without any loss of its measurement accuracy
Estimating time-correlation functions by sampling and unbiasing dynamically activated events.
Athènes, Manuel; Marinica, Mihai-Cosmin; Jourdan, Thomas
2012-11-21
Transition path sampling is a rare-event method that estimates state-to-state time-correlation functions in many-body systems from samples of short trajectories. In this framework, it is proposed to bias the importance function using the lowest Jacobian eigenvalue moduli along the dynamical trajectory. A lowest eigenvalue modulus is related to the lowest eigenvalue of the Hessian matrix and is evaluated here using the Lanczos algorithm as in activation-relaxation techniques. This results in favoring the sampling of activated trajectories and enhancing the occurrence of the rare reactive trajectories of interest, those corresponding to transitions between locally stable states. Estimating the time-correlation functions involves unbiasing the sample of simulated trajectories which is done using the multi-state Bennett acceptance ratio (MBAR) method. To assess the performance of our procedure, we compute the time-correlation function associated with the migration of a vacancy in α-iron. The derivative of the estimated time-correlation function yields a migration rate in agreement with the one given by transition state theory. Besides, we show that the information relative to rejected trajectories can be recycled within MBAR, resulting in a substantial speed-up. Unlike original transition path-sampling, our approach does not require computing the reversible work to confine the trajectory endpoints to a reactive state.
Speckle correlation method used to detect an object's surface slope
Smid, Petr; Horvath, Pavel; Hrabovsky, Miroslav
2006-09-20
We present a technique employing a speckle pattern correlation method for detection of the slope of an object's surface. Controlled translation of an object under investigation and numerical correlation of speckle patterns recorded during its motion give information used to evaluate the tilt of the object. The proposed optical setup uses a symmetrical arrangement of detection planes in the image field and enables one to detect the tilt of an object's surface within the interval(10 deg. -30 deg. ). Simulation analysis shows how to control the measuring range. The presented theory, simulation analysis, and setup are verified through an experiment by measurement of the slope of a surface of a cube made out of steel.
Speckle correlation method used to detect an object's surface slope.
Smíd, Petr; Horváth, Pavel; Hrabovský, Miroslav
2006-09-20
We present a technique employing a speckle pattern correlation method for detection of the slope of an object's surface. Controlled translation of an object under investigation and numerical correlation of speckle patterns recorded during its motion give information used to evaluate the tilt of the object. The proposed optical setup uses a symmetrical arrangement of detection planes in the image field and enables one to detect the tilt of an object's surface within the interval (10 degrees-30 degrees). Simulation analysis shows how to control the measuring range. The presented theory, simulation analysis, and setup are verified through an experiment by measurement of the slope of a surface of a cube made out of steel.
Application of the Graphic Correlation method to Pliocene marine sequences
Dowsett, H.J.
1989-01-01
Biostratigraphy - the use of paleontological evidence to establish relative chronologies, forms the cornerstone of many sedimentary geological investigations. Several different approaches to biochronology are available. Traditional interval zones, defined on lowest and/or highest occurrences of selected taxa, are used to place bodies of rock in a relative chronological framework. Fossil datum levels, which are more numerous than zones, are often used as chronohorizons for correlation purposs. The Graphic Correlation method, like interval zonations, synthesizes information from a number of different taxa but does not assume synchrony of any one taxon. A magnetobiostratigraphic model for deep-sea Pliocene sequences has been constructed by graphic correlation of Deep Sea Drilling project cores from the North Atlantic (606), Caribbean Sea (502), South Atlantic (516), Tasman Sea (590), Equatorial Pacific (573) and North Pacific (577). All cores are hydraulic piston cores which contain abundant planktonic foraminifers, calcareous nannofossils and which record many of the magnetic reversals expected in the Pliocene. The model is based on internally consistent paleontologic data gathered by the author. This study demonstrates the advantages of graphic correlation over conventional biostratigraphic procedures. Accurate inter-regional correlations can be made between core sites without resorting to multiple microfossil zonations and without invoking synchrony of fossil events. Important results of this study are: (1) many Pliocene planktonic foraminifer and calcareous nannofossil events are diachronous by more than 0.20 m.y., (2) Globorotalia truncatulinoides first occurs in the Southwest Pacific Ocean, approximately 0.50 m.y. earlier than previously reported, (3) a previously undetected hiatus of short duration (0.38 m.y.) exists just above the Cochiti subchron at DSDP 577A. ?? 1989.
Fish functional traits correlated with environmental variables in a temperate biodiversity hotspot.
Keck, Benjamin P; Marion, Zachary H; Martin, Derek J; Kaufman, Jason C; Harden, Carol P; Schwartz, John S; Strange, Richard J
2014-01-01
The global biodiversity crisis has invigorated the search for generalized patterns in most disciplines within the natural sciences. Studies based on organismal functional traits attempt to broaden implications of results by identifying the response of functional traits, instead of taxonomic units, to environmental variables. Determining the functional trait responses enables more direct comparisons with, or predictions for, communities of different taxonomic composition. The North American freshwater fish fauna is both diverse and increasingly imperiled through human mediated disturbances, including climate change. The Tennessee River, USA, contains one of the most diverse assemblages of freshwater fish in North America and has more imperiled species than other rivers, but there has been no trait-based study of community structure in the system. We identified 211 localities in the upper Tennessee River that were sampled by the Tennessee Valley Authority between 2009 and 2011 and compiled fish functional traits for the observed species and environmental variables for each locality. Using fourth corner analysis, we identified significant correlations between many fish functional traits and environmental variables. Functional traits associated with an opportunistic life history strategy were correlated with localities subject to greater land use disturbance and less flow regulation, while functional traits associated with a periodic life history strategy were correlated with localities subject to regular disturbance and regulated flow. These are patterns observed at the continental scale, highlighting the generalizability of trait-based methods. Contrary to studies that found no community structure differences when considering riparian buffer zones, we found that fish functional traits were correlated with different environmental variables between analyses with buffer zones vs. entire catchment area land cover proportions. Using existing databases and fourth corner
Fish Functional Traits Correlated with Environmental Variables in a Temperate Biodiversity Hotspot
Keck, Benjamin P.; Marion, Zachary H.; Martin, Derek J.; Kaufman, Jason C.; Harden, Carol P.; Schwartz, John S.; Strange, Richard J.
2014-01-01
The global biodiversity crisis has invigorated the search for generalized patterns in most disciplines within the natural sciences. Studies based on organismal functional traits attempt to broaden implications of results by identifying the response of functional traits, instead of taxonomic units, to environmental variables. Determining the functional trait responses enables more direct comparisons with, or predictions for, communities of different taxonomic composition. The North American freshwater fish fauna is both diverse and increasingly imperiled through human mediated disturbances, including climate change. The Tennessee River, USA, contains one of the most diverse assemblages of freshwater fish in North America and has more imperiled species than other rivers, but there has been no trait-based study of community structure in the system. We identified 211 localities in the upper Tennessee River that were sampled by the Tennessee Valley Authority between 2009 and 2011 and compiled fish functional traits for the observed species and environmental variables for each locality. Using fourth corner analysis, we identified significant correlations between many fish functional traits and environmental variables. Functional traits associated with an opportunistic life history strategy were correlated with localities subject to greater land use disturbance and less flow regulation, while functional traits associated with a periodic life history strategy were correlated with localities subject to regular disturbance and regulated flow. These are patterns observed at the continental scale, highlighting the generalizability of trait-based methods. Contrary to studies that found no community structure differences when considering riparian buffer zones, we found that fish functional traits were correlated with different environmental variables between analyses with buffer zones vs. entire catchment area land cover proportions. Using existing databases and fourth corner
Field methods to measure surface displacement and strain with the Video Image Correlation method
NASA Technical Reports Server (NTRS)
Maddux, Gary A.; Horton, Charles M.; Mcneill, Stephen R.; Lansing, Matthew D.
1994-01-01
The objective of this project was to develop methods and application procedures to measure displacement and strain fields during the structural testing of aerospace components using paint speckle in conjunction with the Video Image Correlation (VIC) system.
Song, Linze; Shi, Qiang
2015-11-21
Based on recent findings in the hierarchical equations of motion (HEOM) for correlated initial state [Y. Tanimura, J. Chem. Phys. 141, 044114 (2014)], we propose a new stochastic method to obtain the initial conditions for the real time HEOM propagation, which can be used further to calculate the equilibrium correlation functions and symmetrized correlation functions. The new method is derived through stochastic unraveling of the imaginary time influence functional, where a set of stochastic imaginary time HEOM are obtained. The validity of the new method is demonstrated using numerical examples including the spin-Boson model, and the Holstein model with undamped harmonic oscillator modes.
Song, Linze; Shi, Qiang
2015-11-21
Based on recent findings in the hierarchical equations of motion (HEOM) for correlated initial state [Y. Tanimura, J. Chem. Phys. 141, 044114 (2014)], we propose a new stochastic method to obtain the initial conditions for the real time HEOM propagation, which can be used further to calculate the equilibrium correlation functions and symmetrized correlation functions. The new method is derived through stochastic unraveling of the imaginary time influence functional, where a set of stochastic imaginary time HEOM are obtained. The validity of the new method is demonstrated using numerical examples including the spin-Boson model, and the Holstein model with undamped harmonic oscillator modes.
Preparation method: structure-bioactivity correlation in mesoporous bioactive glass
NASA Astrophysics Data System (ADS)
Shih, Shao-Ju; Chou, Yu-Jen; Borisenko, Konstantin B.
2013-06-01
Mesoporous bioactive glasses (MBGs) are receiving increased attention because of their superior bioactive properties and possible applications as drug-releasing carriers, bone implants and sealing materials in dentistry. We report here the results of investigation of structures and bioactivities of two types of MBG particles prepared by two different techniques, the sol-gel method and spray pyrolysis (SP). In this study, we used transmission electron microscopy and selected area electron diffraction to characterize particle morphology and atomistic structures of the particles correlating these observations with nitrogen adsorption measurements to determine surface areas of the particles and in vitro bioactivity tests. It is found that the preparation method can influence the final composition of the particles and that SP method offers a better control over the composition. The SP particles have higher bioactivity than the sol-gel particles due to their higher surface area and possibly more favourable atomistic structure for promoting deposition of pure hydroxyl apatite phase.
A new class of methods for functional connectivity estimation
NASA Astrophysics Data System (ADS)
Lin, Wutu
Measuring functional connectivity from neural recordings is important in understanding processing in cortical networks. The covariance-based methods are the current golden standard for functional connectivity estimation. However, the link between the pair-wise correlations and the physiological connections inside the neural network is unclear. Therefore, the power of inferring physiological basis from functional connectivity estimation is limited. To build a stronger tie and better understand the relationship between functional connectivity and physiological neural network, we need (1) a realistic model to simulate different types of neural recordings with known ground truth for benchmarking; (2) a new functional connectivity method that produce estimations closely reflecting the physiological basis. In this thesis, (1) I tune a spiking neural network model to match with human sleep EEG data, (2) introduce a new class of methods for estimating connectivity from different kinds of neural signals and provide theory proof for its superiority, (3) apply it to simulated fMRI data as an application.
Exploring correlations in the CGC wave function: Odd azimuthal anisotropy
NASA Astrophysics Data System (ADS)
Kovner, Alex; Lublinsky, Michael; Skokov, Vladimir
2017-07-01
We extend the color glass condensate (CGC) approach to a calculation of the double inclusive gluon production by including the high density effect in the CGC wave function of the projectile (proton). Our main result is that these effects lead to the appearance of odd harmonics in the two particle correlation C (k ,p ) . We find that in the high momentum limit, |k |,|p |≫Qs , this results in a positive c1{2 }. Additionally when the magnitudes of the two momenta are approximately equal, |k |/|p |≈1 , the density effects also generate a positive third harmonic c3{2 }, which translates into a nonvanishing v3 when the momenta of the trigger and an associated particle are in the same momentum bin. The sign of c3{2 } becomes negative when |k |/|p |>1.1 suggesting an interesting experimental signature.
A maximum likelihood approach to estimating correlation functions
Baxter, Eric Jones; Rozo, Eduardo
2013-12-10
We define a maximum likelihood (ML for short) estimator for the correlation function, ξ, that uses the same pair counting observables (D, R, DD, DR, RR) as the standard Landy and Szalay (LS for short) estimator. The ML estimator outperforms the LS estimator in that it results in smaller measurement errors at any fixed random point density. Put another way, the ML estimator can reach the same precision as the LS estimator with a significantly smaller random point catalog. Moreover, these gains are achieved without significantly increasing the computational requirements for estimating ξ. We quantify the relative improvement of the ML estimator over the LS estimator and discuss the regimes under which these improvements are most significant. We present a short guide on how to implement the ML estimator and emphasize that the code alterations required to switch from an LS to an ML estimator are minimal.
Exploring correlations in the CGC wave function: Odd azimuthal anisotropy
Kovner, Alex; Lublinsky, Michael; Skokov, Vladimir
2017-07-17
In this paper, we extend the color glass condensate (CGC) approach to a calculation of the double inclusive gluon production by including the high density effect in the CGC wave function of the projectile (proton). Our main result is that these effects lead to the appearance of odd harmonics in the two particle correlation C(k,p). We find that in the high momentum limit, |k|, |p| >> Qs, this results in a positive c1{2}. Additionally when the magnitudes of the two momenta are approximately equal, |k|/|p| ≈ 1, the density effects also generate a positive third harmonic c3{2}, which translates intomore » a nonvanishing v3 when the momenta of the trigger and an associated particle are in the same momentum bin. Finally, the sign of c3{2} becomes negative when |k|/|p| > 1.1 suggesting an interesting experimental signature.« less
Functional cortical network in alpha band correlates with social bargaining.
Billeke, Pablo; Zamorano, Francisco; Chavez, Mario; Cosmelli, Diego; Aboitiz, Francisco
2014-01-01
Solving demanding tasks requires fast and flexible coordination among different brain areas. Everyday examples of this are the social dilemmas in which goals tend to clash, requiring one to weigh alternative courses of action in limited time. In spite of this fact, there are few studies that directly address the dynamics of flexible brain network integration during social interaction. To study the preceding, we carried out EEG recordings while subjects played a repeated version of the Ultimatum Game in both human (social) and computer (non-social) conditions. We found phase synchrony (inter-site-phase-clustering) modulation in alpha band that was specific to the human condition and independent of power modulation. The strength and patterns of the inter-site-phase-clustering of the cortical networks were also modulated, and these modulations were mainly in frontal and parietal regions. Moreover, changes in the individuals' alpha network structure correlated with the risk of the offers made only in social conditions. This correlation was independent of changes in power and inter-site-phase-clustering strength. Our results indicate that, when subjects believe they are participating in a social interaction, a specific modulation of functional cortical networks in alpha band takes place, suggesting that phase synchrony of alpha oscillations could serve as a mechanism by which different brain areas flexibly interact in order to adapt ongoing behavior in socially demanding contexts.
[Correlations of consciousness and the default function of the brain].
Gyulaházi, Judit; Varga, Katalin
2014-01-30
Neural correlation with consciousness represents a main topic of neuroscience studies. New results of consciousness researches proved that based on a coherent function in between its components the default mode network activity is the condition for awake consciousness. The subject of consciousness is self. Tasks related with the self were proving a high default mode network activity. Using connections inside the network, results which were related with self, could be considered to represent a polymodal integration system are they are participating in fine processing of the highly integrated associative information. It could be a result of the convergence of cognitive binding. There is a strong connection between the level of consciousness and praecuneal activation. It was proved that the network activity is changing during sleeping (normal condition), trauma or under drug induced altered consciousness. The default network activity can be considered as the neural correlate of consciousness. Further researches are warranted to answer the question: is the activity of the network the cause or is just accompanying the development of human consciousness?
Functional Cortical Network in Alpha Band Correlates with Social Bargaining
Billeke, Pablo; Zamorano, Francisco; Chavez, Mario; Cosmelli, Diego; Aboitiz, Francisco
2014-01-01
Solving demanding tasks requires fast and flexible coordination among different brain areas. Everyday examples of this are the social dilemmas in which goals tend to clash, requiring one to weigh alternative courses of action in limited time. In spite of this fact, there are few studies that directly address the dynamics of flexible brain network integration during social interaction. To study the preceding, we carried out EEG recordings while subjects played a repeated version of the Ultimatum Game in both human (social) and computer (non-social) conditions. We found phase synchrony (inter-site-phase-clustering) modulation in alpha band that was specific to the human condition and independent of power modulation. The strength and patterns of the inter-site-phase-clustering of the cortical networks were also modulated, and these modulations were mainly in frontal and parietal regions. Moreover, changes in the individuals’ alpha network structure correlated with the risk of the offers made only in social conditions. This correlation was independent of changes in power and inter-site-phase-clustering strength. Our results indicate that, when subjects believe they are participating in a social interaction, a specific modulation of functional cortical networks in alpha band takes place, suggesting that phase synchrony of alpha oscillations could serve as a mechanism by which different brain areas flexibly interact in order to adapt ongoing behavior in socially demanding contexts. PMID:25286240
Hadronic correlation functions in the random instanton-dyon ensemble
NASA Astrophysics Data System (ADS)
Larsen, Rasmus; Shuryak, Edward
2017-08-01
It is known since the 1980s that the instanton-induced 't Hooft effective Lagrangian not only can solve the so-called U (1 )a problem, by making the η' meson heavy etc., but it can also lead to chiral symmetry breaking. In the 1990s it was demonstrated that, taken to higher orders, this Lagrangian correctly reproduces effective forces in a large set of hadronic channels, mesonic and baryonic ones. Recent progress in understanding gauge topology at finite temperatures is related with the so-called instanton-dyons, the constituents of the instantons. Some of them, called L -dyons, possess the antiperiodic fermionic zero modes, and thus form a new version of the 't Hooft effective Lagrangian. This paper is our first study of a wide set of hadronic correlation function. We found that, at the lowest temperatures at which this approach is expected to be applicable, those may be well compatible with what is known about them based on phenomenological and lattice studies, provided L and M type dyons are strongly correlated.
Functional neural correlates of social approval in schizophrenia
Lepage, Martin
2016-01-01
Social approval is a reward that uses abstract social reinforcers to guide interpersonal interactions. Few studies have specifically explored social reward processing and its related neural substrates in schizophrenia. Fifteen patients with schizophrenia and fifteen healthy controls participated in a two-part study to explore the functional neural correlates of social approval. In the first session, participants were led to believe their personality would be assessed based on their results from various questionnaires and an interview. Participants were then presented with the results of their supposed evaluation in the scanner, while engaging in a relevant fMRI social approval task. Subjects provided subjective reports of pleasure associated with receiving self-directed positive or negative feedback. Higher activation of the right parietal lobe was found in controls compared with individuals with schizophrenia. Both groups rated traits from the high social reward condition as more pleasurable than the low social reward condition, while intergroup differences emerged in the low social reward condition. Positive correlations were found in patients only between subjective ratings of positive feedback and right insula activation, and a relevant behavioural measure. Evidence suggests potential neural substrates underlying the cognitive representation of social reputation in schizophrenia. PMID:26516171
Functional neural correlates of social approval in schizophrenia.
Makowski, Carolina S; Lepage, Martin; Harvey, Philippe-Olivier
2016-03-01
Social approval is a reward that uses abstract social reinforcers to guide interpersonal interactions. Few studies have specifically explored social reward processing and its related neural substrates in schizophrenia. Fifteen patients with schizophrenia and fifteen healthy controls participated in a two-part study to explore the functional neural correlates of social approval. In the first session, participants were led to believe their personality would be assessed based on their results from various questionnaires and an interview. Participants were then presented with the results of their supposed evaluation in the scanner, while engaging in a relevant fMRI social approval task. Subjects provided subjective reports of pleasure associated with receiving self-directed positive or negative feedback. Higher activation of the right parietal lobe was found in controls compared with individuals with schizophrenia. Both groups rated traits from the high social reward condition as more pleasurable than the low social reward condition, while intergroup differences emerged in the low social reward condition. Positive correlations were found in patients only between subjective ratings of positive feedback and right insula activation, and a relevant behavioural measure. Evidence suggests potential neural substrates underlying the cognitive representation of social reputation in schizophrenia.
Exponential series expansion for correlation functions of many-body systems.
Barocchi, Fabrizio; Guarini, Eleonora; Bafile, Ubaldo
2014-09-01
We demonstrate that in Hamiltonian many-body systems at equilibrium, any kind of time dependent correlation function c(t) can always be expanded in a series of (complex) exponential functions of time when its Laplace transform C̃(z) has single poles. The characteristic frequencies can be identified as the eigenfrequencies of the correlation. This is done without introducing the concepts of fluctuating forces and memory functions, due to Mori and Zwanzig and extensively used in the literature in the last decades. Our method is based on a different projection technique in the Hilbert space S of the system and shows that appropriate approximations of the exponential series are related to the contraction of S to a finite, usually small, number of dimensions. The time dependence of correlation functions is always described in detail by a multiple-exponential functionality also at long times. This result is therefore also valid for correlation functions of many-body Hamiltonian systems for which a power-law dependence, observed in restricted time ranges and predicted to be the asymptotic one, can be considered at most as a useful approximate modeling of long-time behavior.
a Task-Oriented Disaster Information Correlation Method
NASA Astrophysics Data System (ADS)
Linyao, Q.; Zhiqiang, D.; Qing, Z.
2015-07-01
With the rapid development of sensor networks and Earth observation technology, a large quantity of disaster-related data is available, such as remotely sensed data, historic data, case data, simulated data, and disaster products. However, the efficiency of current data management and service systems has become increasingly difficult due to the task variety and heterogeneous data. For emergency task-oriented applications, the data searches primarily rely on artificial experience based on simple metadata indices, the high time consumption and low accuracy of which cannot satisfy the speed and veracity requirements for disaster products. In this paper, a task-oriented correlation method is proposed for efficient disaster data management and intelligent service with the objectives of 1) putting forward disaster task ontology and data ontology to unify the different semantics of multi-source information, 2) identifying the semantic mapping from emergency tasks to multiple data sources on the basis of uniform description in 1), and 3) linking task-related data automatically and calculating the correlation between each data set and a certain task. The method goes beyond traditional static management of disaster data and establishes a basis for intelligent retrieval and active dissemination of disaster information. The case study presented in this paper illustrates the use of the method on an example flood emergency relief task.
A density functional for core-valence correlation energy
NASA Astrophysics Data System (ADS)
Ranasinghe, Duminda S.; Frisch, Michael J.; Petersson, George A.
2015-12-01
A density functional, ɛCV-DFT(ρc, ρv), describing the core-valence correlation energy has been constructed as a linear combination of ɛLY Pcorr(ρc), ɛV WN5corr(ρc, ρv), ɛPBEcorr(ρc, ρv), ɛSlaterex(ρc, ρv), ɛHCTHex(ρc, ρv), ɛHFex(ρc, ρv), and F CV -DFT (" separators=" N i , Z i ) , a function of the nuclear charges. This functional, with 6 adjustable parameters, reproduces (±0.27 kcal/mol rms error) a benchmark set of 194 chemical energy changes including 9 electron affinities, 18 ionization potentials, and 167 total atomization energies covering the first- and second-rows of the periodic table. This is almost twice the rms error (±0.16 kcal/mol) obtained with CCSD(T)/MTsmall calculations, but less than half the rms error (±0.65 kcal/mol) obtained with MP2/GTlargeXP calculations, and somewhat smaller than the rms error (±0.39 kcal/mol) obtained with CCSD/MTsmall calculations. The largest positive and negative errors from ɛCV-DFT(ρc, ρv) were 0.88 and -0.75 kcal/mol with the set of 194 core-valence energy changes ranging from +3.76 kcal/mol for the total atomization energy of propyne to -9.05 kcal/mol for the double ionization of Mg. Evaluation of the ɛCV-DFT(ρc, ρv) functional requires less time than a single SCF iteration, and the accuracy is adequate for any model chemistry based on the CCSD(T) level of theory.
Correlation between functional disability and quality of life in patients with adhesive capsulitis
Fernandes, Marcos Rassi
2015-01-01
OBJECTIVE: To determine the correlation between functional disability and quality of life of patients with adhesive capsulitis. METHODS: Two instruments (WHOQOL-BREF and DASH) were applied to evaluate the quality of life and functional capacity of patients with adhesive capsulitis. Inclusion criteria were age between 35 and 75 years old and achievement of shoulder imaging. Each domain of the WHOQOL-BREF was correlated with DASH. Pearson's correlation coefficient was used for parametric variables and Spearman's correlation coefficient was used when at least one variable had a non-normal distribution. The level of significance was p <0.05. RESULTS: Forty three patients with mean age of 54.7 years old were evaluated. The mean values found in the physical, psychological, social and environmental domains of the WHOQOL-BREF and DASH were 45.3, 63.9, 68.2, 60.2 and 61.6, respectively. A moderate negative correlation was found between DASH and the physical domain of WHOQOL-BREF (r= - 0.583, p<0.001). CONCLUSION: The only domain where WHOQOL-BREF correlates with DASH is the physical domain, suggesting that measures to promote the improvement of functional capacity may lead to better quality of life of patients with adhesive capsulitis. Level of Evidence IV, Prospective Study. PMID:27069405
Iutaka, Natalia A.; Grochowski, Rubens A.; Kasahara, Niro
2017-01-01
Purpose: To evaluate the correlation between visual field index (VFI) and both structural and functional measures of the optic disc in primary open angle glaucoma patients and suspects. Methods: In this retrospective study, 162 glaucoma patients and suspects underwent standard automated perimetry (SAP), retinography, and retinal nerve fiber layer (RNFL) measurement. The optic disc was stratified according to the vertical cup/disc ratio (C/D) and sorted by the disc damage likelihood scale (DDLS). RNFL was measured with the optical coherence tomography. The VFI perimetry was correlated with the mean deviation (MD) and pattern standard deviation (PSD) obtained by SAP, and structural parameters by Pearson's correlation coefficients. Results: VFI displayed strong correlation with MD (R = 0.959) and PSD (R = −0.744). The linear correlations between VFI and structural measures including C/D (R = −0.179, P = 0.012), DDLS (R = −0.214, P = 0.006), and RNFL (R = 0.416, P < 0.001) were weak but statistically significant. Conclusion: VFI showed a strong correlation with MD and PSD but demonstrated a weak correlation with structural measures. It can possibly be used as a marker for functional impairment severity in patients with glaucoma. PMID:28299007
Zhou, Yongxi; Ernzerhof, Matthias; Bahmann, Hilke
2015-09-28
Drawing on the adiabatic connection of density functional theory, exchange-correlation functionals of Kohn-Sham density functional theory are constructed which interpolate between the extreme limits of the electron-electron interaction strength. The first limit is the non-interacting one, where there is only exchange. The second limit is the strong correlated one, characterized as the minimum of the electron-electron repulsion energy. The exchange-correlation energy in the strong-correlation limit is approximated through a model for the exchange-correlation hole that is referred to as nonlocal-radius model [L. O. Wagner and P. Gori-Giorgi, Phys. Rev. A 90, 052512 (2014)]. Using the non-interacting and strong-correlated extremes, various interpolation schemes are presented that yield new approximations to the adiabatic connection and thus to the exchange-correlation energy. Some of them rely on empiricism while others do not. Several of the proposed approximations yield the exact exchange-correlation energy for one-electron systems where local and semi-local approximations often fail badly. Other proposed approximations generalize existing global hybrids by using a fraction of the exchange-correlation energy in the strong-correlation limit to replace an equal fraction of the semi-local approximation to the exchange-correlation energy in the strong-correlation limit. The performance of the proposed approximations is evaluated for molecular atomization energies, total atomic energies, and ionization potentials.
Incalzi, Raffaele Antonelli; Pennazza, Giorgio; Scarlata, Simone; Santonico, Marco; Petriaggi, Massimo; Chiurco, Domenica; Pedone, Claudio; Arnaldo; D'Amico
2012-01-01
Background The electronic nose (e nose) provides distinctive breath fingerprints for selected respiratory diseases. Both reproducibility and respiratory function correlates of breath fingerprint are poorly known. Objectives To measure reproducibility of breath fingerprints and to assess their correlates among respiratory function indexes in elderly healthy and COPD subjects. Method 25 subjects (5 COPD patients for each GOLD stage and 5 healthy controls) over 65 years underwent e-nose study through a seven sensor system and respiratory function tests at times 0, 7, and 15 days. Reproducibility of the e nose pattern was computed. The correlation between volatile organic compound (VOC) pattern and respiratory function/clinical parameters was assessed by the Spearman's rho. Measurements and Main Results VOC patterns were highly reproducible within healthy and GOLD 4 COPD subjects, less among GOLD 1–3 patients.VOC patterns significantly correlated with expiratory flows (Spearman's rho ranging from 0.36 for MEF25% and sensor Co-Buti-TPP, to 0.81 for FEV1% and sensor Cu-Buti-TPP p<0.001)), but not with residual volume and total lung capacity. Conclusions VOC patterns strictly correlated with expiratory flows. Thus, e nose might conveniently be used to assess COPD severity and, likely, to study phenotypic variability. However, the suboptimal reproducibility within GOLD 1–3 patients should stimulate further research to identify more reproducible breath print patterns. PMID:23077492
A Flexible Method of Estimating Luminosity Functions
NASA Astrophysics Data System (ADS)
Kelly, Brandon C.; Fan, Xiaohui; Vestergaard, Marianne
2008-08-01
We describe a Bayesian approach to estimating luminosity functions. We derive the likelihood function and posterior probability distribution for the luminosity function, given the observed data, and we compare the Bayesian approach with maximum likelihood by simulating sources from a Schechter function. For our simulations confidence intervals derived from bootstrapping the maximum likelihood estimate can be too narrow, while confidence intervals derived from the Bayesian approach are valid. We develop our statistical approach for a flexible model where the luminosity function is modeled as a mixture of Gaussian functions. Statistical inference is performed using Markov chain Monte Carlo (MCMC) methods, and we describe a Metropolis-Hastings algorithm to perform the MCMC. The MCMC simulates random draws from the probability distribution of the luminosity function parameters, given the data, and we use a simulated data set to show how these random draws may be used to estimate the probability distribution for the luminosity function. In addition, we show how the MCMC output may be used to estimate the probability distribution of any quantities derived from the luminosity function, such as the peak in the space density of quasars. The Bayesian method we develop has the advantage that it is able to place accurate constraints on the luminosity function even beyond the survey detection limits, and that it provides a natural way of estimating the probability distribution of any quantities derived from the luminosity function, including those that rely on information beyond the survey detection limits.
High Resolution Pulse Compression Imaging Using Super Resolution FM-Chirp Correlation Method (SCM)
NASA Astrophysics Data System (ADS)
Fujiwara, M.; Okubo, K.; Tagawa, N.
This study addresses the issue of the super-resolution pulse compression technique (PCT) for ultrasound imaging. Time resolution of multiple ultrasonic echoes using the FM-Chirp PCT is limited by the bandwidth of the sweep-frequency. That is, the resolution depends on the sharpness of auto-correlation function. We propose the Super resolution FM-Chirp correlation Method (SCM) and evaluate its performance. This method is based on the multiple signal classification (MUSIC) algorithm. Our simulations were made for the model assuming multiple signals reflected from some scatterers. We confirmed that SCM detects time delay of complicated reflected signals successfully with high resolution.
NASA Astrophysics Data System (ADS)
Shi, F.; Lowe, M. J. S.; Craster, R. V.
2017-02-01
We propose an ultrasonic methodology to reconstruct the height correlation function of remotely inaccessible random rough surfaces in solids. The inverse method is based on the Kirchhoff approximation(KA), and it requires measuring the angular distribution of diffuse scattering intensities by sending in a narrow band incident pulse. Near field scattering effects are also included by considering the Fresnel assumption. The proposed approach is successfully verified by simulating the scattering from multiple realizations of rough surfaces whose correlation function is known, calculating the mean scattering intensities from these received signals, and then deploying the inverse method on these to reconstruct the original correlation function. Very good agreement between the reconstructed correlation function and the original is found, for a wide range of roughness parameters. In addition, the effect of reducing the number of realizations to approximate the mean intensity are investigated, providing confidence bounds for the experiment. An experiment on a corrugated rough surface is performed with a limited number of scans using a phased array, which further validates the proposed inversion algorithm.
Modeling the Galaxy Three-Point Correlation Function
Marin, Felipe; Wechsler, Risa; Frieman, Joshua A.; Nichol, Robert; /Portsmouth U., ICG
2007-06-05
We present new theoretical predictions for the galaxy three-point correlation function (3PCF) using high-resolution dissipationless cosmological simulations of a flat Lambda CDM Universe which resolve galaxy-size halos and subhalos. We create realistic mock galaxy catalogs by assigning luminosities and colors to dark matter halos and subhalos, and we measure the reduced 3PCF as a function of luminosity and color in both real and redshift space. As galaxy luminosity and color are varied, we find small differences in the amplitude and shape dependence of the reduced 3PCF, at a level qualitatively consistent with recent measurements from the SDSS and 2dFGRS. We confirm that discrepancies between previous 3PCF measurements can be explained in part by differences in binning choices. We explore the degree to which a simple local bias model can fit the simulated 3PCF. The agreement between the model predictions and galaxy 3PCF measurements lends further credence to the straightforward association of galaxies with CDM halos and subhalos.
Extraction of noise cross-correlation function with topography
NASA Astrophysics Data System (ADS)
Ping, P.; Chu, R.; Zhang, Y.
2016-12-01
Due to the increasing popularity of analyzing empirical Green's functions obtained from ambient noise, more regional tomographical studies based on short-period surface waves are published. The propagation of surface waves from noise cross-correlation function (NCF) could potentially be biased in local regions where topography is not small compared with the wavelength and penetration of the waves. We investigate these effects of topography on the extraction of NCF by synthetic data in a typical 3D topography model. Sufficient surface wave dispersion bias analysis on this type of topography is also presented. Different thicknesses of the layers along the topography may generate different scale dispersion perturbations. These phenomena suggest a cautious preprocessing for high SNR NCF extraction in the topographic region. An apparent statistical regularity drawn from the numerical experiments can favor a possible guidance for accurate NCF extractions. Through the numerical validations, we can conclude that: 1) when the stations are located on the topographic regions, the SNR of NCF could be enhanced with the vertical station component rotation perpendicular to the inclined surface; 2) the dispersion curves move to low frequencies, which lead to false thickness reductions of the near surface layers; 3) An error plane can be built for this perturbation on the true thickness of the layers and the topography scale to eliminate this misleading in practical dispersion analysis of NCFs.
Behavioral correlates of anxiety in well-functioning older adults.
Losada, Andrés; Márquez-González, María; Pachana, Nancy A; Wetherell, Julie L; Fernández-Fernández, Virginia; Nogales-González, Celia; Ruiz-Díaz, Miguel
2015-07-01
Research on the behavioral correlates of anxiety in older adults is sparse. The aim of this study was to explore the association of anxiety with behavioral patterns defined by health, activity, emotional and social variables. A convenience sample of 395 older adults completed measures of health, activity, emotions, social variables and experiential avoidance. Cross-sectional data were analysed using cluster analysis. Five clusters were identified: active healthy, healthy, active vulnerable, lonely inactive and frail lonely. Participants in the active healthy and healthy clusters showed the highest scores on health variables (vitality and physical function), and adaptive scores on the rest of variables. They also reported the lowest scores on anxiety and included the lowest number of cases with clinically significant anxiety levels. Active vulnerable showed high scores on social support, leisure activities and capitalization on them but low scores in vitality and physical functioning. Participants in the lonely inactive cluster reported the highest mean score in experiential avoidance and high scores on boredom and loneliness, and low scores on social support, leisure activities capitalizing on pleasant activities and health variables. Frail lonely represent a particularly vulnerable profile of participants, similar to that of lonely inactive, but with significantly lower scores on health variables and higher scores on boredom and hours watching TV. Anxiety in older adults is not only linked to poor health, but also to dysfunctional social behavior, loneliness, boredom and experiential avoidance. Maladaptive profiles of older adults with regard to these variables have been identified.
Statistical functions and relevant correlation coefficients of clearness index
NASA Astrophysics Data System (ADS)
Pavanello, Diego; Zaaiman, Willem; Colli, Alessandra; Heiser, John; Smith, Scott
2015-08-01
This article presents a statistical analysis of the sky conditions, during years from 2010 to 2012, for three different locations: the Joint Research Centre site in Ispra (Italy, European Solar Test Installation - ESTI laboratories), the site of National Renewable Energy Laboratory in Golden (Colorado, USA) and the site of Brookhaven National Laboratories in Upton (New York, USA). The key parameter is the clearness index kT, a dimensionless expression of the global irradiance impinging upon a horizontal surface at a given instant of time. In the first part, the sky conditions are characterized using daily averages, giving a general overview of the three sites. In the second part the analysis is performed using data sets with a short-term resolution of 1 sample per minute, demonstrating remarkable properties of the statistical distributions of the clearness index, reinforced by a proof using fuzzy logic methods. Successively some time-dependent correlations between different meteorological variables are presented in terms of Pearson and Spearman correlation coefficients, and introducing a new one.
Probing quantum correlation functions through energy-absorption interferometry
NASA Astrophysics Data System (ADS)
Withington, S.; Thomas, C. N.; Goldie, D. J.
2017-08-01
An interferometric technique is described for determining the spatial forms of the individual degrees of freedom through which a many-body system can absorb energy from its environment. The method separates out the spatial forms of the coherent excitations present at any single frequency; it is not necessary to sweep the frequency and then infer the spatial forms of possible excitations from resonant absorption features. The system under test is excited with two external sources, which create generalized forces, and the fringe in the total power dissipated is measured as the relative phase between the sources is varied. If the complex fringe visibility is measured for different pairs of source locations, the anti-Hermitian part of the complex-valued nonlocal correlation tensor can be determined, which can then be decomposed to give the natural dynamical modes of the system and their relative responsivities. If each source in the interferometer creates a different kind of force, the spatial forms of the individual excitations that are responsible for cross-correlated response can be found. The technique is related to holography, but measures the state of coherence to which the system is maximally sensitive. It can be applied across a wide range of wavelengths, in a variety of ways, to homogeneous media, thin films, patterned structures, and components such as sensors, detectors, and energy-harvesting absorbers.
Study of quantum correlation swapping with relative entropy methods
NASA Astrophysics Data System (ADS)
Xie, Chuanmei; Liu, Yimin; Chen, Jianlan; Zhang, Zhanjun
2016-02-01
To generate long-distance shared quantum correlations (QCs) for information processing in future quantum networks, recently we proposed the concept of QC repeater and its kernel technique named QC swapping. Besides, we extensively studied the QC swapping between two simple QC resources (i.e., a pair of Werner states) with four different methods to quantify QCs (Xie et al. in Quantum Inf Process 14:653-679, 2015). In this paper, we continue to treat the same issue by employing other three different methods associated with relative entropies, i.e., the MPSVW method (Modi et al. in Phys Rev Lett 104:080501, 2010), the Zhang method (arXiv:1011.4333 [quant-ph]) and the RS method (Rulli and Sarandy in Phys Rev A 84:042109, 2011). We first derive analytic expressions of all QCs which occur during the swapping process and then reveal their properties about monotonicity and threshold. Importantly, we find that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed. In addition, we simply compare our present results with our previous ones.
Luteogenesis in cyclic ewes: echotextural, histological, and functional correlates.
Duggavathi, R; Bartlewski, P M; Pierson, R A; Rawlings, N C
2003-08-01
To date, it has not been possible to detect corpus luteum (CL) by ultrasonography, immediately following ovulation, in the ewe. Early CL detection is essential to be able to relate luteal outcome to the developmental pattern of the ovulated follicle and to confirm ovulation. Image analysis of the CL may be useful in providing a noninvasive picture of CL differentiation and function. The present study was designed to use high-resolution ultrasonography to monitor and to correlate the echotextural, histological, and functional attributes of the developing ovine CL from Days 1 to 3 after ovulation. Ten ewes underwent twice-daily transrectal ultrasonography and blood sampling from the day of synchronized estrus. Ewes were ovariectomized at 12-24, 36-48, and 60-72 h after ovulation. Ovaries collected were scanned in a water bath before processing for histology. Ultrasonographic images of CL were analyzed for echotexture. Histological sections were analyzed for the percentage area of the CL occupied by blood clot or luteal tissue. Serum samples were analyzed for progesterone concentration. Numerical pixel value, heterogeneity, and percentage of the CL occupied by blood clot declined (P<0.05) from 12-24 to 60-72 h after ovulation. Luteal area and serum progesterone concentration increased (P<0.05) from 12-24 to 60-72 h. The results indicated that it was possible to visualize developing CL as early as 12-24 h after ovulation in the ewe. Echotexture of the CL was closely associated with its morphological and functional characteristics; image analysis holds promise for noninvasive monitoring of CL differentiation and growth.
Explicitly Correlated Methods within the ccCA Methodology.
Mahler, Andrew; Wilson, Angela K
2013-03-12
The prediction of energetic properties within "chemical accuracy" (1 kcal mol(-1) from well-established experiment) can be a major challenge in computational quantum chemistry due to the computational requirements (computer time, memory, and disk space) needed to achieve this level of accuracy. Methodologies such as coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) combined with very large basis sets are often required to reach this level of accuracy. Unfortunately, such calculations quickly become cost prohibitive as system size increases. Our group has developed an ab initio composite method, the correlation consistent Composite Approach (ccCA), which enables such accuracy to be possible, on average, but at reduced computational cost as compared with CCSD(T) in combination with a large basis set. While ccCA has proven quite useful, computational bottlenecks still occur. In this study, the means to reduce the computational cost of ccCA without compromising accuracy by utilizing explicitly correlated methods within ccCA have been considered, and an alternative formulation is described.
Ruse, Stacy A.; Harvey, Philip D.; Davis, Vicki G.; Atkins, Alexandra S.; Fox, Kolleen H.; Keefe, Richard S.E.
2014-01-01
Introduction Assessment of functional capacity is an intrinsic part of determining the functional relevance of response to treatment of cognitive impairment in schizophrenia. Existing methods are highly and consistently correlated with performance on neuropsychological tests, but most current assessments of functional capacity are still paper and pencil simulations. We developed a computerized virtual reality assessment that contains all of the components of a shopping trip. Methods We administered the Virtual Reality Functional Capacity Assessment Tool (VRFCAT) to 54 healthy controls and to 51 people with schizophrenia to test its feasibility. Dependent variables for the VRFCAT included time to completion and errors on 12 objectives and the number of times that an individual failed to complete an objective. The MATRICS Consensus Cognitive Battery (MCCB) and a standard functional capacity measure, the UCSD Performance-Based Skills Assessment-Brief (UPSA-B) were administered to the patients with schizophrenia. Results Patients with schizophrenia performed more poorly than healthy controls on 10/11 of the time variables, as well as 2/12 error scores and 2/12 failed objectives. Pearson correlations for 7 of 15 VRFCAT variables with MCCB composite scores were statistically significant. Conclusion These results provide support for the possibility of computerized functional capacity assessment, but more substantial studies are required. PMID:25083416
Ps-Ps scattering via the correlated Gaussian hyperspherical method
NASA Astrophysics Data System (ADS)
Daily, Kevin; von Stecher, Javier; Greene, Chris
2014-05-01
There is renewed interest in systems of electrons and positrons since it may be possible to create a Bose-Einstein condensate of spin-triplet positronium atoms [P. M. Platzman and A. P. Mills, Jr., Phys. Rev. B 49, 454 (1994)]. We study the four-body system consisting of two positrons and two electrons. Using a basis of correlated Gaussians at fixed hyperradius, we utilize a new technique [K. M. Daily and C. H. Greene, Phys. Rev. A 89, 012503 (2014)] to efficiently calculate the adiabatic potentials and non-adiabatic couplings as a function of the hyperradius. The R-matrix is propagated to large hyperradius and scattering properties are derived. We gratefully acknowledge support by the NSF.
Hierarchical Ensemble Methods for Protein Function Prediction
2014-01-01
Protein function prediction is a complex multiclass multilabel classification problem, characterized by multiple issues such as the incompleteness of the available annotations, the integration of multiple sources of high dimensional biomolecular data, the unbalance of several functional classes, and the difficulty of univocally determining negative examples. Moreover, the hierarchical relationships between functional classes that characterize both the Gene Ontology and FunCat taxonomies motivate the development of hierarchy-aware prediction methods that showed significantly better performances than hierarchical-unaware “flat” prediction methods. In this paper, we provide a comprehensive review of hierarchical methods for protein function prediction based on ensembles of learning machines. According to this general approach, a separate learning machine is trained to learn a specific functional term and then the resulting predictions are assembled in a “consensus” ensemble decision, taking into account the hierarchical relationships between classes. The main hierarchical ensemble methods proposed in the literature are discussed in the context of existing computational methods for protein function prediction, highlighting their characteristics, advantages, and limitations. Open problems of this exciting research area of computational biology are finally considered, outlining novel perspectives for future research. PMID:25937954
Hierarchical ensemble methods for protein function prediction.
Valentini, Giorgio
2014-01-01
Protein function prediction is a complex multiclass multilabel classification problem, characterized by multiple issues such as the incompleteness of the available annotations, the integration of multiple sources of high dimensional biomolecular data, the unbalance of several functional classes, and the difficulty of univocally determining negative examples. Moreover, the hierarchical relationships between functional classes that characterize both the Gene Ontology and FunCat taxonomies motivate the development of hierarchy-aware prediction methods that showed significantly better performances than hierarchical-unaware "flat" prediction methods. In this paper, we provide a comprehensive review of hierarchical methods for protein function prediction based on ensembles of learning machines. According to this general approach, a separate learning machine is trained to learn a specific functional term and then the resulting predictions are assembled in a "consensus" ensemble decision, taking into account the hierarchical relationships between classes. The main hierarchical ensemble methods proposed in the literature are discussed in the context of existing computational methods for protein function prediction, highlighting their characteristics, advantages, and limitations. Open problems of this exciting research area of computational biology are finally considered, outlining novel perspectives for future research.
Galaxy Redshifts from Discrete Optimization of Correlation Functions
NASA Astrophysics Data System (ADS)
Lee, Benjamin C. G.; Budavári, Tamás; Basu, Amitabh; Rahman, Mubdi
2016-12-01
We propose a new method of constraining the redshifts of individual extragalactic sources based on celestial coordinates and their ensemble statistics. Techniques from integer linear programming (ILP) are utilized to optimize simultaneously for the angular two-point cross- and autocorrelation functions. Our novel formalism introduced here not only transforms the otherwise hopelessly expensive, brute-force combinatorial search into a linear system with integer constraints but also is readily implementable in off-the-shelf solvers. We adopt Gurobi, a commercial optimization solver, and use Python to build the cost function dynamically. The preliminary results on simulated data show potential for future applications to sky surveys by complementing and enhancing photometric redshift estimators. Our approach is the first application of ILP to astronomical analysis.
Transport through correlated systems with density functional theory.
Kurth, S; Stefanucci, G
2017-10-18
We present recent advances in density functional theory (DFT) for applications in the field of quantum transport, with particular emphasis on transport through strongly correlated systems. We review the foundations of the popular Landauer-Büttiker(LB) + DFT approach. This formalism, when using approximations to the exchange-correlation (xc) potential with steps at integer occupation, correctly captures the Kondo plateau in the zero bias conductance at zero temperature but completely fails to capture the transition to the Coulomb blockade (CB) regime as the temperature increases. To overcome the limitations of LB + DFT, the quantum transport problem is treated from a time-dependent (TD) perspective using TDDFT, an exact framework to deal with nonequilibrium situations. The steady-state limit of TDDFT shows that in addition to an xc potential in the junction, there also exists an xc correction to the applied bias. Open shell molecules in the CB regime provide the most striking examples of the importance of the xc bias correction. Using the Anderson model as guidance we estimate these corrections in the limit of zero bias. For the general case we put forward a steady-state DFT which is based on one-to-one correspondence between the pair of basic variables, steady density on and steady current across the junction and the pair local potential on and bias across the junction. Like TDDFT, this framework also leads to both an xc potential in the junction and an xc correction to the bias. Unlike TDDFT, these potentials are independent of history. We highlight the universal features of both xc potential and xc bias corrections for junctions in the CB regime and provide an accurate parametrization for the Anderson model at arbitrary temperatures and interaction strengths, thus providing a unified DFT description for both Kondo and CB regimes and the transition between them.
Transport through correlated systems with density functional theory
NASA Astrophysics Data System (ADS)
Kurth, S.; Stefanucci, G.
2017-10-01
We present recent advances in density functional theory (DFT) for applications in the field of quantum transport, with particular emphasis on transport through strongly correlated systems. We review the foundations of the popular Landauer–Büttiker(LB) + DFT approach. This formalism, when using approximations to the exchange-correlation (xc) potential with steps at integer occupation, correctly captures the Kondo plateau in the zero bias conductance at zero temperature but completely fails to capture the transition to the Coulomb blockade (CB) regime as the temperature increases. To overcome the limitations of LB + DFT, the quantum transport problem is treated from a time-dependent (TD) perspective using TDDFT, an exact framework to deal with nonequilibrium situations. The steady-state limit of TDDFT shows that in addition to an xc potential in the junction, there also exists an xc correction to the applied bias. Open shell molecules in the CB regime provide the most striking examples of the importance of the xc bias correction. Using the Anderson model as guidance we estimate these corrections in the limit of zero bias. For the general case we put forward a steady-state DFT which is based on one-to-one correspondence between the pair of basic variables, steady density on and steady current across the junction and the pair local potential on and bias across the junction. Like TDDFT, this framework also leads to both an xc potential in the junction and an xc correction to the bias. Unlike TDDFT, these potentials are independent of history. We highlight the universal features of both xc potential and xc bias corrections for junctions in the CB regime and provide an accurate parametrization for the Anderson model at arbitrary temperatures and interaction strengths, thus providing a unified DFT description for both Kondo and CB regimes and the transition between them.
Temporal discrimination, a cervical dystonia endophenotype: penetrance and functional correlates.
Kimmich, Okka; Molloy, Anna; Whelan, Robert; Williams, Laura; Bradley, David; Balsters, Joshua; Molloy, Fiona; Lynch, Tim; Healy, Daniel G; Walsh, Cathal; O'Riordan, Seán; Reilly, Richard B; Hutchinson, Michael
2014-05-01
The pathogenesis of adult-onset primary dystonia remains poorly understood. There is variable age-related and gender-related expression of the phenotype, the commonest of which is cervical dystonia. Endophenotypes may provide insight into underlying genetic and pathophysiological mechanisms of dystonia. The temporal discrimination threshold (TDT)-the shortest time interval at which two separate stimuli can be detected as being asynchronous-is abnormal both in patients with cervical dystonia and in their unaffected first-degree relatives. Functional magnetic resonance imaging (fMRI) studies have shown that putaminal activation positively correlates with the ease of temporal discrimination between two stimuli in healthy individuals. We hypothesized that abnormal temporal discrimination would exhibit similar age-related and gender-related penetrance as cervical dystonia and that unaffected relatives with an abnormal TDT would have reduced putaminal activation during a temporal discrimination task. TDTs were examined in a group of 192 healthy controls and in 158 unaffected first-degree relatives of 84 patients with cervical dystonia. In 24 unaffected first-degree relatives, fMRI scanning was performed during a temporal discrimination task. The prevalence of abnormal TDTs in unaffected female relatives reached 50% after age 48 years; whereas, in male relatives, penetrance of the endophenotype was reduced. By fMRI, relatives who had abnormal TDTs, compared with relatives who had normal TDTs, had significantly less activation in the putamina and in the middle frontal and precentral gyri. Only the degree of reduction of putaminal activity correlated significantly with worsening of temporal discrimination. These findings further support abnormal temporal discrimination as an endophenotype of cervical dystonia involving disordered basal ganglia circuits.
The Galaxy Count Correlation Function in Redshift Space Revisited
NASA Astrophysics Data System (ADS)
Campagne, J.-E.; Plaszczynski, S.; Neveu, J.
2017-08-01
In the near future, cosmology will enter the wide and deep galaxy survey era, enabling high-precision studies of the large-scale structure of the universe in three dimensions. To test cosmological models and determine their parameters accurately, it is necessary to use data with exact theoretical expectations expressed in observational parameter space (angles and redshift). The data-driven, galaxy number count fluctuations on redshift shells can be used to build correlation functions ξ (θ ,{z}1,{z}2) on and between shells to probe the baryonic acoustic oscillations and distance-redshift distortions, as well as gravitational lensing and other relativistic effects. To obtain a numerical estimation of ξ (θ ,{z}1,{z}2) from a cosmological model, it is typical to use either a closed form derived from a tripolar spherical expansion or to compute the power spectrum {C}{\\ell }({z}1,{z}2) and perform a Legendre polynomial {P}{\\ell }(\\cos θ ) expansion. Here, we present a new derivation of a ξ (θ ,{z}1,{z}2) closed form using the spherical harmonic expansion and proceeding to an infinite sum over multipoles thanks to an addition theorem. We demonstrate that this new expression is perfectly compatible with the existing closed forms but is simpler to establish and manipulate. We provide formulas for the leading density and redshift-space contributions, but also show how Doppler-like and lensing terms can be easily included in this formalism. We have implemented and made publicly available software for computing those correlations efficiently, without any Limber approximation, and validated this software with the CLASSgal code. It is available at https://gitlab.in2p3.fr/campagne/AngPow.
On the Angular Correlation Functions of the Hubble Deep Field
NASA Astrophysics Data System (ADS)
Roukema, B. F.
Roukema & Valls-Gabaud (1997, RVG) reinforce the conclusion of Colley et al. (1996, 1997) that the Hubble Deep Field (HDF) ``galaxies'' are probably star-forming regions, not ``building-blocks''. Consider a ``building-block'' hypothesis: (1) all (colour-selected high z) HDF galaxy-like objects are galaxies; (2) these objects have a spatial correlation function xi(r,z) = b2 (r0 / r)gamma (1+z)-(3+epsilon-gamma) where b >> 1 is a strong bias factor at high z; and b > = 1, db/dr < 0 for all r,z; such that the projection of xi (3-D) into w (angular correlation; 2-D) (via Limber's equation) matches Figs 1a, 1d of Colley et al. (1996). Since w(1 arcsecond) > approx 1 in Figs 1a,1d of Colley et al. (1996), at least 50% of the 1 arcsecond object pairs can be considered ``excess pairs''. Table 1 of RVG therefore shows, conservatively, that of all the 1 arcsecond object pairs, and under the above hypotheses, 25% are spatially separated by a median of only 3-7h-1 kpc (proper units), and 45% are spatially separated by a median of 12-30h-1 kpc$, taking into account projection effects. Many excess pairs have theta approx 0.25 arcseconds. Hence, for a pure ``building-block'' model, galaxy formation models would have to post-dict the existence of many Rhalo << 2 kpc, very highly biased galaxies, at 2.5 < z < 5. This result is little sensitive to epsilon, Omega0, lambda0 or zmedian.
Development of a transfer function method for dynamic stability measurement
NASA Technical Reports Server (NTRS)
Johnson, W.
1977-01-01
Flutter testing method based on transfer function measurements is developed. The error statistics of several dynamic stability measurement methods are reviewed. It is shown that the transfer function measurement controls the error level by averaging the data and correlating the input and output. The method also gives a direct estimate of the error in the response measurement. An algorithm is developed for obtaining the natural frequency and damping ratio of low damped modes of the system, using integrals of the transfer function in the vicinity of a resonant peak. Guidelines are given for selecting the parameters in the transfer function measurement. Finally, the dynamic stability measurement technique is applied to data from a wind tunnel test of a proprotor and wing model.
Blair, S.C.; Berge, P.A.; Berryman, J.G.
1993-08-01
We have developed an image-processing method for characterizing the microstructure of rock and other porous materials, and for providing a quantitative means for understanding the dependence of physical properties on the pore structure. This method is based upon the statistical properties of the microgeometry as observed in scanning electron micrograph (SEM) images of cross sections of porous materials. The method utilizes a simple statistical function, called the spatial correlation function, which can be used to predict bounds on permeability and other physical properties. We obtain estimates of the porosity and specific surface area of the material from the two-point correlation function. The specific surface area can be related to the permeability of porous materials using a Kozeny-Carman relation, and we show that the specific surface area measured on images of sandstones is consistent with the specific surface area used in a simple flow model for computation of permeability. In this paper, we discuss the two-point spatial correlation function and its use in characterizing microstructure features such as pore and grain sizes. We present estimates of permeabilities found using SEM images of several different synthetic and natural sandstones. Comparison of the estimates to laboratory measurements shows good agreement. Finally, we briefly discuss extension of this technique to two-phase flow.
Convergence Properties of KKR Green Function Methods
NASA Astrophysics Data System (ADS)
Moghadam, N. Y.; Stocks, G. M.; Zhang, X.-G.; Nicholson, D. M. C.; Shelton, W. A.; Wang, Yang; Faulkner, J. S.
1998-03-01
Most multiple scattering theory (MST) electronic structure methods (e.g. KKR, KKR-CPA, impurity Greens function, O[N] LSMS method(Yang Wang et al. Phys. Rev. Letters 75), 2867,(1995)) make use of a expression for the single particle Green function that is based on a single center expansion(J. S. Faulkner and G. M. Stocks, Phys. Rev. B 21),3222, (1980). Because the electronic structure is rapidly convergent in angular momentum, l, the multiple scattering equations are typically truncated at l_max <= 4. Using the LSMS method as illustrative we show that the Green function and, therefore, the cell densities of states and charge density converge more slowly requiring l_max ~ 8 arrow 12 even for muffin-tin potentails. We discuss the consequences of this for previous MST based work, and show that this slow convergence can be trivially accommodated within the LSMS method.
Bayraktar Bilen, Neslihan; Hepsen, Ibrahim F.; Arce, Carlos G.
2016-01-01
AIM To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus. METHODS Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є2), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices. RESULTS The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672) (P<0.001 for all). Root mean square (RMS) was 4.3±1.81 µm, spherical aberration (SA) was -0.4±0.67 µm, vertical and horizontal coma were -2.1±1.47 and -0.4±0.72 µm. All wavefront data (except horizontal coma), AAI, Є2 and maximum BFS correlated significantly with the visual function (P≤0.001 for all). CONCLUSION In this study, CS is more affected than CDVA as a visual function. The quantity and quality of vision is significantly correlated with well-known and new topographic indices. There is not a significant correlation between visual function and pachymetric parameters. The significantly correlated indices can be used in staging keratoconus and to follow the outcome of a treatment. PMID:27588266
NASA Astrophysics Data System (ADS)
Erhard, Jannis; Bleiziffer, Patrick; Görling, Andreas
2016-09-01
A power series approximation for the correlation kernel of time-dependent density-functional theory is presented. Using this approximation in the adiabatic-connection fluctuation-dissipation (ACFD) theorem leads to a new family of Kohn-Sham methods. The new methods yield reaction energies and barriers of unprecedented accuracy and enable a treatment of static (strong) correlation with an accuracy of high-level multireference configuration interaction methods but are single-reference methods allowing for a black-box-like handling of static correlation. The new methods exhibit a better scaling of the computational effort with the system size than rivaling wave-function-based electronic structure methods. Moreover, the new methods do not suffer from the problem of singularities in response functions plaguing previous ACFD methods and therefore are applicable to any type of electronic system.
NASA Astrophysics Data System (ADS)
Gould, Tim; Dobson, John F.
2013-01-01
By exploiting freedoms in the definitions of "correlation," "exchange," and "Hartree" physics in ensemble systems, we better generalise the notion of "exact exchange" (EXX) to systems with fractional occupations of the frontier orbitals, arising in the dissociation limit of some molecules. We introduce the linear EXX ("LEXX") theory whose pair distribution and energy are explicitly piecewise linear in the occupations f^{σ }i. We provide explicit expressions for these functions for frontier s and p shells. Used in an optimised effective potential (OEP) approach the LEXX yields energies bounded by the piecewise linear "ensemble EXX" (EEXX) energy and standard fractional optimised EXX energy: EEEXX ⩽ ELEXX ⩽ EEXX. Analysis of the LEXX explains the success of standard OEP methods for diatoms at large spacing, and why they can fail when both spins are allowed to be non-integer so that "ghost" Hartree interactions appear between opposite spin electrons in the usual formula. The energy ELEXX contains a cancellation term for the spin ghost case. It is evaluated for H, Li, and Na fractional ions with clear derivative discontinuities for all cases. The p-shell form reproduces accurate correlation-free energies of B-F and Al-Cl. We further test LEXX plus correlation energy calculations on fractional ions of C and F and again we find both derivative discontinuities and good agreement with exact results.
Gould, Tim; Dobson, John F
2013-01-07
By exploiting freedoms in the definitions of "correlation," "exchange," and "Hartree" physics in ensemble systems, we better generalise the notion of "exact exchange" (EXX) to systems with fractional occupations of the frontier orbitals, arising in the dissociation limit of some molecules. We introduce the linear EXX ("LEXX") theory whose pair distribution and energy are explicitly piecewise linear in the occupations f(i)(σ). We provide explicit expressions for these functions for frontier s and p shells. Used in an optimised effective potential (OEP) approach the LEXX yields energies bounded by the piecewise linear "ensemble EXX" (EEXX) energy and standard fractional optimised EXX energy: E(EEXX) ≤ E(LEXX) ≤ E(EXX). Analysis of the LEXX explains the success of standard OEP methods for diatoms at large spacing, and why they can fail when both spins are allowed to be non-integer so that "ghost" Hartree interactions appear between opposite spin electrons in the usual formula. The energy E(LEXX) contains a cancellation term for the spin ghost case. It is evaluated for H, Li, and Na fractional ions with clear derivative discontinuities for all cases. The p-shell form reproduces accurate correlation-free energies of B-F and Al-Cl. We further test LEXX plus correlation energy calculations on fractional ions of C and F and again we find both derivative discontinuities and good agreement with exact results.
A self-constrained inversion of magnetic data based on correlation method
NASA Astrophysics Data System (ADS)
Sun, Shida; Chen, Chao
2016-12-01
Geologically-constrained inversion is a powerful method for producing geologically reasonable solutions in geophysical exploration problems. But in many cases, except the observed geophysical data to be inverted, the geological information is insufficiently available for improving reliability of recovered models. To deal with these situations, self-constraints extracted from preprocessing observed data have been applied to constrain the inversion. In this paper, we present a self-constrained inversion method based on correlation method. In our approach the correlation results are first obtained by calculating the cross-correlation between theoretical data and horizontal gradients of the observed data. Subsequently, we propose two specific strategies to extract the spatial variation from the correlation results and then translate them into spatial weighting functions. Incorporating the spatial weighting functions into the model objective function, we obtain self-constrained solutions with higher reliability. We presented two synthetic and one field magnetic data example to test the validity. All results demonstrate that the solution from our self-constrained inversion can delineate the geological bodies with clearer boundaries and much more concentrated physical property.
Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions
NASA Technical Reports Server (NTRS)
Miles, Jeffrey H.
2009-01-01
Cross-correlation and coherence functions are used to look for periodic acoustic components in turbofan engine combustor time histories, to investigate direct and indirect combustion noise source separation based on signal propagation time delays, and to provide information on combustor acoustics. Using the cross-correlation function, time delays were identified in all cases, clearly indicating the combustor is the source of the noise. In addition, unfiltered and low-pass filtered at 400 Hz signals had a cross-correlation time delay near 90 ms, while the low-pass filtered at less than 400 Hz signals had a cross-correlation time delay longer than 90 ms. Low-pass filtering at frequencies less than 400 Hz partially removes the direct combustion noise signals. The remainder includes the indirect combustion noise signal, which travels more slowly because of the dependence on the entropy convection velocity in the combustor. Source separation of direct and indirect combustion noise is demonstrated by proper use of low-pass filters with the cross-correlation function for a range of operating conditions. The results may lead to a better idea about the acoustics in the combustor and may help develop and validate improved reduced-order physics-based methods for predicting direct and indirect combustion noise.
Choi, Ji Yeh; Hwang, Heungsun; Yamamoto, Michio; Jung, Kwanghee; Woodward, Todd S
2016-02-08
Functional principal component analysis (FPCA) and functional multiple-set canonical correlation analysis (FMCCA) are data reduction techniques for functional data that are collected in the form of smooth curves or functions over a continuum such as time or space. In FPCA, low-dimensional components are extracted from a single functional dataset such that they explain the most variance of the dataset, whereas in FMCCA, low-dimensional components are obtained from each of multiple functional datasets in such a way that the associations among the components are maximized across the different sets. In this paper, we propose a unified approach to FPCA and FMCCA. The proposed approach subsumes both techniques as special cases. Furthermore, it permits a compromise between the techniques, such that components are obtained from each set of functional data to maximize their associations across different datasets, while accounting for the variance of the data well. We propose a single optimization criterion for the proposed approach, and develop an alternating regularized least squares algorithm to minimize the criterion in combination with basis function approximations to functions. We conduct a simulation study to investigate the performance of the proposed approach based on synthetic data. We also apply the approach for the analysis of multiple-subject functional magnetic resonance imaging data to obtain low-dimensional components of blood-oxygen level-dependent signal changes of the brain over time, which are highly correlated across the subjects as well as representative of the data. The extracted components are used to identify networks of neural activity that are commonly activated across the subjects while carrying out a working memory task.
Atmospheric stellar parameters from cross-correlation functions
NASA Astrophysics Data System (ADS)
Malavolta, L.; Lovis, C.; Pepe, F.; Sneden, C.; Udry, S.
2017-08-01
The increasing number of spectra gathered by spectroscopic sky surveys and transiting exoplanet follow-up has pushed the community to develop automated tools for atmospheric stellar parameters determination. Here we present a novel approach that allows the measurement of temperature (Teff), metallicity ([Fe/H]) and gravity (log g) within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, our technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. We use literature stellar parameters of high signal-to-noise (SNR), high-resolution HARPS spectra of FGK main-sequence stars to calibrate Teff, [Fe/H] and log g as a function of CCF parameters. Our technique is validated using low-SNR spectra obtained with the same instrument. For FGK stars we achieve a precision of σ _{{T_eff}} = 50 K, σlog g = 0.09 dex and σ _{{{[Fe/H]}}} =0.035 dex at SNR = 50, while the precision for observation with SNR ≳ 100 and the overall accuracy are constrained by the literature values used to calibrate the CCFs. Our approach can easily be extended to other instruments with similar spectral range and resolution or to other spectral range and stars other than FGK dwarfs if a large sample of reference stars is available for the calibration. Additionally, we provide the mathematical formulation to convert synthetic equivalent widths to CCF parameters as an alternative to direct calibration. We have made our tool publicly available.
Bharadwaj, Atul S; Singh, Swarn L; Singh, Yashwant
2013-08-01
A free-energy functional for a crystal that contains both the symmetry-conserved and symmetry-broken parts of the direct pair-correlation function has been used to investigate the crystallization of fluids in three dimensions. The symmetry-broken part of the direct pair-correlation function has been calculated using a series in ascending powers of the order parameters and which contains three- and higher-body direct correlation functions of the isotropic phase. It is shown that a very accurate description of freezing transitions for a wide class of potentials is found by considering the first two terms of this series. The results found for freezing parameters including the structure of the frozen phase for fluids interacting via the inverse power potential u(r)=ε(σ/r)(n) for n ranging from 4 to ∞ are in very good agreement with simulation results. It is found that for n>6.5 the fluid freezes into a face-centered cubic (fcc) structure while for n≤6 the body-centered cubic (bcc) structure is preferred. The fluid-bcc-fcc triple point is found to be at 1/n=0.158, which is in good agreement with simulation result.
Krause, Christine; Werner, Hans-Joachim
2012-06-07
Explicitly correlated local coupled-cluster (LCCSD-F12) methods with pair natural orbitals (PNOs), orbital specific virtual orbitals (OSVs), and projected atomic orbitals (PAOs) are compared. In all cases pair-specific virtual subspaces (domains) are used, and the convergence of the correlation energy as a function of the domain sizes is studied. Furthermore, the performance of the methods for reaction energies of 52 reactions involving 58 small and medium sized molecules is investigated. It is demonstrated that for all choices of virtual orbitals much smaller domains are needed in the explicitly correlated methods than without the explicitly correlated terms, since the latter correct a large part of the domain error, as found previously. For PNO-LCCSD-F12 with VTZ-F12 basis sets on the average only 20 PNOs per pair are needed to obtain reaction energies with a root mean square deviation of less than 1 kJ mol(-1) from complete basis set estimates. With OSVs or PAOs at least 4 times larger domains are needed for the same accuracy. A new hybrid method that combines the advantages of the OSV and PNO methods is proposed and tested. While in the current work the different local methods are only simulated using a conventional CCSD program, the implications for low-order scaling local implementations of the various methods are discussed.
Disorders of Microtubule Function in Neurons: Imaging Correlates
Mutch, Christopher A.; Poduri, Annapurdi; Sahin, Mustafa; Barry, Brenda; Walsh, Christopher A.; Barkovich, A. James
2015-01-01
Background and Significance A number of recent studies have described malformations of cortical development with mutations of components of microtubules and microtubule-associated proteins. Despite examinations of large numbers of MRIs, good phenotype-genotype correlations have been elusive. Additionally, most of these studies focused exclusively on cerebral cortical findings. Materials and Methods MRIs from18 patients with confirmed tubulin mutations (8 TUBA1A, 5 TUBB2B, and 5 TUBB3) and 15 patients with known mutations of the genes encoding microtubule-associated proteins (5 LIS1, 4 DCX, and 6 DYNC1H1) were carefully visually analyzed and compared. Specific note was made of cortical gyral pattern, basal ganglia and white matter to assess internal capsular size, cortical thickness, ventricular and cisternal size, and size and contours of the brain stem, cerebellar hemispheres and vermis, and the corpus callosum of patients with tubulin and microtubule-associated protein gene mutations. Results were determined by unanimous consensus of the authors. Results All patients had abnormal MRI scans. Large proportions of patients with tubulin gene mutations were found to have multiple cortical and subcortical abnormalities including microcephaly, ventriculomegaly, abnormal gyral and sulcal patterns (termed dysgyria), small or absent corpus callosum and small pons. All patients with microtubule-associated proteins mutations also had abnormal cerebral cortices (predominantly pachygyria and agyria), but fewer subcortical abnormalities were noted. Conclusion Comparison of MRIs from patients with known mutations of tubulin genes and microtubule-associated proteins allows for the establishment of some early correlations of phenotype with genotype and may assist in identification and diagnosis of these rare disorders. PMID:26564436
A marked correlation function for constraining modified gravity models
NASA Astrophysics Data System (ADS)
White, Martin
2016-11-01
Future large scale structure surveys will provide increasingly tight constraints on our cosmological model. These surveys will report results on the distance scale and growth rate of perturbations through measurements of Baryon Acoustic Oscillations and Redshift-Space Distortions. It is interesting to ask: what further analyses should become routine, so as to test as-yet-unknown models of cosmic acceleration? Models which aim to explain the accelerated expansion rate of the Universe by modifications to General Relativity often invoke screening mechanisms which can imprint a non-standard density dependence on their predictions. This suggests density-dependent clustering as a `generic' constraint. This paper argues that a density-marked correlation function provides a density-dependent statistic which is easy to compute and report and requires minimal additional infrastructure beyond what is routinely available to such survey analyses. We give one realization of this idea and study it using low order perturbation theory. We encourage groups developing modified gravity theories to see whether such statistics provide discriminatory power for their models.
Translating ceRNA Susceptibilities into Correlation Functions.
Martirosyan, Araks; Marsili, Matteo; De Martino, Andrea
2017-07-11
Competition to bind microRNAs induces an effective positive cross talk between their targets, which are therefore known as "competing endogenous RNAs" (ceRNAs). Although such an effect is known to play a significant role in specific situations, estimating its strength from data and experimentally in physiological conditions appears to be far from simple. Here, we show that the susceptibility of ceRNAs to different types of perturbations affecting their competitors (and hence their tendency to cross talk) can be encoded in quantities as intuitive and as simple to measure as correlation functions. This scenario is confirmed by extensive numerical simulations and validated by re-analyzing phosphatase and tensin homolog's cross-talk pattern from The Cancer Genome Atlas breast cancer database. These results clarify the links between different quantities used to estimate the intensity of ceRNA cross talk and provide, to our knowledge, new keys to analyze transcriptional data sets and effectively probe ceRNA networks in silico. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.
EEG correlates of time-varying BOLD functional connectivity
Chang, Catie; Liu, Zhongming; Chen, Michael C.; Liu, Xiao; Duyn, Jeff H.
2013-01-01
Recent resting-state fMRI studies have shown that the apparent functional connectivity (FC) between brain regions may undergo changes on time-scales of seconds to minutes, the basis and importance of which are largely unknown. Here, we examine the electrophysiological correlates of within-scan FC variations during a condition of eyes-closed rest. A sliding window analysis of simultaneous EEG-fMRI data was performed to examine whether temporal variations in coupling between three major networks (default mode; DMN, dorsal attention; DAN, and salience network; SN) are associated with temporal variations in mental state, as assessed from the amplitude of alpha and theta oscillations in the EEG. In our dataset, alpha power showed a significant inverse relationship with the strength of connectivity between DMN and DAN. In addition, alpha power covaried with the spatial extent of anticorrelation between DMN and DAN, with higher alpha power associated with larger anticorrelation extent. Results suggest an electrical signature of the time-varying FC between the DAN and DMN, potentially reflecting neural and state-dependent variations. PMID:23376790
The double-soft limit in cosmological correlation functions and graviton exchange effects
NASA Astrophysics Data System (ADS)
Alinea, Allan L.; Kubota, Takahiro; Misumi, Nobuhiko
2017-01-01
The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and (1‑ns) ≈ 0.042, where ns is the scalar spectral index. It is argued that the graviton exchange effects are more dominant than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.
Extension of the Nakajima-Zwanzig approach to multitime correlation functions of open systems
NASA Astrophysics Data System (ADS)
Ivanov, Anton; Breuer, Heinz-Peter
2015-09-01
We extend the Nakajima-Zwanzig projection operator technique to the determination of multitime correlation functions of open quantum systems. The correlation functions are expressed in terms of certain multitime homogeneous and inhomogeneous memory kernels for which suitable equations of motion are derived. We show that under the condition of finite memory times, these equations can be used to determine the memory kernels by employing an exact stochastic unraveling of the full system-environment dynamics. The approach thus allows us to combine exact stochastic methods, feasible for short times, with long-time master equation simulations. The applicability of the method is demonstrated by numerical simulations of two-dimensional spectra for a donor-acceptor model, and by comparison of the results with those obtained from the reduced hierarchy equations of motion. We further show that the formalism is also applicable to the time evolution of a periodically driven two-level system initially in equilibrium with its environment.
Analysis of Green functions obtained by cross-correlations for MASE stations
NASA Astrophysics Data System (ADS)
Padilla, G. V. Vera
2012-04-01
We used continuous records of broadband seismic stations of the MASE experiment to obtain observed Green's functions using the method of ambient noise cross-correlations. The experiment consisted of 100 stations distributed along a perpendicular line to the Mesoamerican trench across the Valley of Mexico. The stations recorded continuously at 100 sps for more than two years. The geometry of the array provide a good opportunity to study the attenuation effects along the coast-perpendicular structure. The method we used to compute Green functions involves a strong data pre-processing (temporal normalization and spectral whitening). However, our results show that the amplitude of the cross-correlations still contains information about the surface waves attenuation and probably local amplification effects. Records from two regional earthquakes located close to Acapulco were used for comparison.
Hybrid star structure with the Field Correlator Method
NASA Astrophysics Data System (ADS)
Burgio, G. F.; Zappalà, D.
2016-03-01
We explore the relevance of the color-flavor locking phase in the equation of state (EoS) built with the Field Correlator Method (FCM) for the description of the quark matter core of hybrid stars. For the hadronic phase, we use the microscopic Brueckner-Hartree-Fock (BHF) many-body theory, and its relativistic counterpart, i.e. the Dirac-Brueckner (DBHF). We find that the main features of the phase transition are directly related to the values of the quark-antiquark potential V1, the gluon condensate G2 and the color-flavor superconducting gap Δ. We confirm that the mapping between the FCM and the CSS (constant speed of sound) parameterization holds true even in the case of paired quark matter. The inclusion of hyperons in the hadronic phase and its effect on the mass-radius relation of hybrid stars is also investigated.
Cross correlation method application to prompt fission neutron investigation
NASA Astrophysics Data System (ADS)
Zeynalova, O. V.; Zeynalov, Sh.; Nazarenko, M. A.; Hambsch, F.-J.; Oberstedt, S.
2012-10-01
Do The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying cross correlation method and digital signal processing algorithms. A new mathematical approach for neutron/gamma pulse shape separation was developed and implemented for prompt fission neutron (PFN) time-of-flight measurement. The main goal was development of automated data analysis algorithms and procedures for data analysis with minimum human intervention. Experimental data was taken with a twin Frisch-grid ionization chamber and a NE213-equivalent neutron detector in an experimental setup similar to well work of C. Budtz-Jorgensen and H.-H. Knitter [1]. About 2*107 fission events were registered with 2*105 neutron/gamma detection in coincidence with fission fragments. Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12 bit waveform digitizer.
Brain structural and functional correlates of resilience to Bipolar Disorder
Frangou, Sophia
2011-01-01
Background: Resilient adaptation can be construed in different ways, but as used here it refers to adaptive brain responses associated with avoidance of psychopathology despite expressed genetic predisposition to Bipolar Disorder (BD). Although family history of BD is associated with elevated risk of affective morbidity a significant proportion of first-degree relatives remain free of psychopathology. Examination of brain structure and function in these individuals may inform on adaptive responses that pre-empt disease expression. Methods: Data presented here are derived from the Vulnerability to Bipolar Disorders Study (VIBES) which includes BD patients, asymptomatic relatives and controls. Participants underwent extensive investigations including brain structural (sMRI) and functional magnetic resonance imaging (fMRI). We present results from sMRI voxel-based-morphometry and from conventional and connectivity analyses of fMRI data obtained during the Stroop Colour Word Test (SCWT), a task of cognitive control during conflict resolution. All analyses were implemented using Statistical Parametric Mapping software version 5 (SPM5). Resilience in relatives was operationalized as the lifetime absence of clinical-range symptoms. Results: Resilient relatives of BD patients expressed structural, functional, and connectivity changes reflecting the effect of genetic risk on the brain. These included increased insular volume, decreased activation within the posterior and inferior parietal regions involved in selective attention during the SCWT, and reduced fronto-insular and fronto-cingulate connectivity. Resilience was associated with increased cerebellar vermal volume and enhanced functional coupling between the dorsal and the ventral prefrontal cortex during the SCWT. Conclusions: Our findings suggests the presence of biological mechanisms associated with resilient adaptation of brain networks and pave the way for the identification of outcome-specific trajectories given
Pair-correlated coupled cluster theory: An alternative multireference coupled cluster method
NASA Astrophysics Data System (ADS)
Li, Shuhua; Ma, Jing; Jiang, Yuansheng
2003-04-01
We describe an alternative multireference coupled cluster (MRCC) method, pair-correlated coupled cluster (PCCC) theory, for treating the ground state of closed-shell systems with degeneracy or quasidegeneracy. With the separated electron pair (SEP) wave function as a reference, the PCCC wave function is truncated according to how many electron pairs are explicitly correlated. The inclusion of only two-pair correlation defines the PCCC2 scheme, and the inclusion of up to three-pair correlation gives the PCCC3 scheme. The PCCC theory is well defined within the natural orbital (of the SEP reference) description and size extensive. We present the formalism of the PCCC theory by taking the PCCC2 scheme as an example, and implement the PCCC2 and PCCC3 schemes at the ab initio level with various basis sets. Then illustrative applications are presented for systems such as the perpendicular insertion reaction path of Be into H2, the simultaneous bond stretching in AlH3 and H2O. The results show that the overall performance of PCCC methods is competitive to that of the RCCSD(T) or UCCSD(T) method at stretched geometries, but slightly inferior to that of the CCSD(T) method at the equilibrium geometry.
NASA Astrophysics Data System (ADS)
Jukić, Damir; Denić-Jukić, Vesna
2015-11-01
Time series of rainfall and karst-spring discharge are influenced by various space-time-variant processes involved in the transfer of water in hydrological cycle. The effects of these processes can be exhibited in auto-correlation and cross-correlation functions. Consequently, ambiguities with respect to the effects encoded in the correlation functions exist. To solve this problem, a new statistical method for investigating relationships between rainfall and karst-spring discharge is proposed. The method is based on the determination and analysis of higher-order partial correlation functions and their spectral representations. The study area is the catchment of the Jadro Spring in Croatia. The analyzed daily time series are the air temperature, relative humidity, spring discharge, and rainfall at seven rain-gauges over a period of 19 years, from 1995 to 2013. The application results show that the effects of spatial and temporal variations of hydrological time series and the space-time-variant behaviours of the karst system can be separated from the correlation functions. Specifically, the effect of evapotranspiration can be separated to obtain the forms of correlation functions that represent the hydrogeological characteristics of the karst system. Using the proposed method, it is also possible to separate the effects of the process of groundwater recharge that occurs in neighbouring parts of a catchment to identify the specific contribution of each part of the catchment to the karst-spring discharge. The main quantitative results obtained for the Jadro Spring show that the quick-flow duration is 14 days, the intermediate-flow duration is 80 days, and the pure base flow starts after 80 days. The base flow consists of an inter-catchment groundwater flow. The system memory of the spring is 80 days. The presented results indicate the far-reaching applicability of the proposed method in the analyses of relationships between rainfall and karst-spring discharge; e
Non-oscillatory flux correlation functions for efficient nonadiabatic rate theory.
Richardson, Jeremy O; Thoss, Michael
2014-08-21
There is currently much interest in the development of improved trajectory-based methods for the simulation of nonadiabatic processes in complex systems. An important goal for such methods is the accurate calculation of the rate constant over a wide range of electronic coupling strengths and it is often the nonadiabatic, weak-coupling limit, which being far from the Born-Oppenheimer regime, provides the greatest challenge to current methods. We show that in this limit there is an inherent sign problem impeding further development which originates from the use of the usual quantum flux correlation functions, which can be very oscillatory at short times. From linear response theory, we derive a modified flux correlation function for the calculation of nonadiabatic reaction rates, which still rigorously gives the correct result in the long-time limit regardless of electronic coupling strength, but unlike the usual formalism is not oscillatory in the weak-coupling regime. In particular, a trajectory simulation of the modified correlation function is naturally initialized in a region localized about the crossing of the potential energy surfaces. In the weak-coupling limit, a simple link can be found between the dynamics initialized from this transition-state region and an generalized quantum golden-rule transition-state theory, which is equivalent to Marcus theory in the classical harmonic limit. This new correlation function formalism thus provides a platform on which a wide variety of dynamical simulation methods can be built aiding the development of accurate nonadiabatic rate theories applicable to complex systems.
Non-oscillatory flux correlation functions for efficient nonadiabatic rate theory
Richardson, Jeremy O. Thoss, Michael
2014-08-21
There is currently much interest in the development of improved trajectory-based methods for the simulation of nonadiabatic processes in complex systems. An important goal for such methods is the accurate calculation of the rate constant over a wide range of electronic coupling strengths and it is often the nonadiabatic, weak-coupling limit, which being far from the Born-Oppenheimer regime, provides the greatest challenge to current methods. We show that in this limit there is an inherent sign problem impeding further development which originates from the use of the usual quantum flux correlation functions, which can be very oscillatory at short times. From linear response theory, we derive a modified flux correlation function for the calculation of nonadiabatic reaction rates, which still rigorously gives the correct result in the long-time limit regardless of electronic coupling strength, but unlike the usual formalism is not oscillatory in the weak-coupling regime. In particular, a trajectory simulation of the modified correlation function is naturally initialized in a region localized about the crossing of the potential energy surfaces. In the weak-coupling limit, a simple link can be found between the dynamics initialized from this transition-state region and an generalized quantum golden-rule transition-state theory, which is equivalent to Marcus theory in the classical harmonic limit. This new correlation function formalism thus provides a platform on which a wide variety of dynamical simulation methods can be built aiding the development of accurate nonadiabatic rate theories applicable to complex systems.
Physiological correlates of pulmonary function in children with cystic fibrosis.
Wells, Greg D; Wilkes, Donna L; Schneiderman, Jane E; Thompson, Sara; Coates, Allan L; Ratjen, Felix
2014-09-01
Although peak aerobic capacity (VO(2peak)) has been linked to outcome in patients with cystic fibrosis (CF), measuring is time consuming, and requires expensive equipment and expertise that is not readily available in all centers. Other fitness parameters such as peak anaerobic power, measures of power and strength may be simpler to deliver in the clinic. The relationship between these measures and established outcomes such as forced expiratory volume in one second (FEV(1)) and peak aerobic power (VO(2peak)) in CF remains unclear. Therefore we evaluated (a) aerobic fitness, (b) anaerobic fitness, and (c) upper and lower body muscle strength to determine their relationship to FEV(1) and VO(2peak) in children with CF. Eighty-two patients (7-18 years) with CF (40 female) from the CF clinic at The Hospital for Sick Children in Toronto performed a maximal incremental cycling test to exhaustion. Anaerobic power (W) for 10 and 30 sec cycling trials as well as vertical jump (VJ) and hand grip strength (HG) were compared to FEV(1) and VO(2peak). Absolute VO(2peak) (R(2) = 0.16, P < 0.001), anaerobic power (R(2) = 0.21, P < 0.001), and hand grip strength (R(2) = 0.10, P = 0.003) were significantly correlated to lung function whereas measures of explosive lower body strength (VJ) were not. Anaerobic power (R(2) = 0.16, P = 0.001) and hand grip strength (R(2) = 0.08, P = 0.01) were related to VO(2peak). Vertical jump was correlated with VO(2peak) (R(2) = 0.29, P < 0.001) but not FEV(1). Simple fitness tests such as hand grip strength and anaerobic cycle tests may be useful indicators of lung health and fitness. © 2013 Wiley Periodicals, Inc.
NASA Astrophysics Data System (ADS)
Sridhar, Srivatsan; Maurogordato, Sophie; Benoist, Christophe; Cappi, Alberto; Marulli, Federico
2017-04-01
Context. The next generation of galaxy surveys will provide cluster catalogues probing an unprecedented range of scales, redshifts, and masses with large statistics. Their analysis should therefore enable us to probe the spatial distribution of clusters with high accuracy and derive tighter constraints on the cosmological parameters and the dark energy equation of state. However, for the majority of these surveys, redshifts of individual galaxies will be mostly estimated by multiband photometry which implies non-negligible errors in redshift resulting in potential difficulties in recovering the real-space clustering. Aims: We investigate to which accuracy it is possible to recover the real-space two-point correlation function of galaxy clusters from cluster catalogues based on photometric redshifts, and test our ability to detect and measure the redshift and mass evolution of the correlation length r0 and of the bias parameter b(M,z) as a function of the uncertainty on the cluster redshift estimate. Methods: We calculate the correlation function for cluster sub-samples covering various mass and redshift bins selected from a 500 deg2 light-cone limited to H < 24. In order to simulate the distribution of clusters in photometric redshift space, we assign to each cluster a redshift randomly extracted from a Gaussian distribution having a mean equal to the cluster cosmological redshift and a dispersion equal to σz. The dispersion is varied in the range σ(z=0)=\\frac{σz{1+z_c} = 0.005,0.010,0.030} and 0.050, in order to cover the typical values expected in forthcoming surveys. The correlation function in real-space is then computed through estimation and deprojection of wp(rp). Four mass ranges (from Mhalo > 2 × 1013h-1M⊙ to Mhalo > 2 × 1014h-1M⊙) and six redshift slices covering the redshift range [0, 2] are investigated, first using cosmological redshifts and then for the four photometric redshift configurations. Results: From the analysis of the light-cone in
Methods for incomplete Bessel function evaluation
NASA Astrophysics Data System (ADS)
Harris, Frank E.; Fripiat, J. G.
Presented here are detailed methods for evaluating the incomplete Bessel functions arising when Gaussian-type orbitals are used for systems periodic in one spatial dimension. The scheme is designed to yield these incomplete Bessel functions with an absolute accuracy of ±1 × 10-10, for the range of integer orders 0 ≤ n ≤ 12 [a range sufficient for a basis whose members have angular momenta of up to three units (s, p, d, or f atomic functions)]. To reach this accuracy level within acceptable computation times, new rational approximations were developed to compute the special functions involved, namely, the exponential integral E1(x) and the modified Bessel functions K0(x) and K1(x), to absolute accuracy ±1 × 10-15.
NASA Astrophysics Data System (ADS)
Nafziger, Jonathan; Wasserman, Adam
2015-12-01
One of the most important open challenges in modern Kohn-Sham (KS) density-functional theory (DFT) is the correct treatment of systems involving fractional electron charges and spins. Approximate exchange-correlation functionals struggle with such systems, leading to pervasive delocalization and static correlation errors. We demonstrate how these errors, which plague density-functional calculations of bond-stretching processes, can be avoided by employing the alternative framework of partition density-functional theory (PDFT) even using the local density approximation for the fragments. Our method is illustrated with explicit calculations on simple systems exhibiting delocalization and static-correlation errors, stretched H2+, H2, He2+, Li2+, and Li2. In all these cases, our method leads to greatly improved dissociation-energy curves. The effective KS potential corresponding to our self-consistent solutions displays key features around the bond midpoint; these are known to be present in the exact KS potential, but are absent from most approximate KS potentials and are essential for the correct description of electron dynamics.
NASA Astrophysics Data System (ADS)
Higuchi, Katsuhiko; Niwa, Hiroyasu; Higuchi, Masahiko
2017-10-01
We present the current-density functional theory for the superconductor immersed in the magnetic field. The order parameter of the superconducting state, transverse component of the paramagnetic current-density, and electron density are chosen as basic variables that uniquely determine the equilibrium properties of the system. In order to construct this theory, the development of the approximate form of the exchange-correlation (xc) energy functional is indispensable as well as the derivation of the effective single-particle equation which makes it possible to reproduce the equilibrium densities mentioned above. The rigorous expression of the xc-energy functional is derived using the technique of the coupling-constant integration. Furthermore, the approximate form of the xc energy functional is proposed such that the energy gap resulting from the effective single-particle equation is consistent with the attractive interaction energy of the system.
NASA Astrophysics Data System (ADS)
Mattsson, Ann E.; Wills, John M.
2013-03-01
The inability to computationally describe the physics governing the properties of actinides and their alloys is the poster child of failure of existing Density Functional Theory exchange-correlation functionals. The intricate competition between localization and delocalization of the electrons, present in these materials, exposes the limitations of functionals only designed to properly describe one or the other situation. We will discuss the manifestation of this competition in real materials and propositions on how to construct a functional able to accurately describe properties of these materials. I addition we will discuss both the importance of using the Dirac equation to describe the relativistic effects in these materials, and the connection to the physics of transition metal oxides. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Method of making low work function component
Robinson, Vance; Weaver, Stanton Earl; Michael, Joseph Darryl
2011-11-15
A method for fabricating a component is disclosed. The method includes: providing a member having an effective work function of an initial value, disposing a sacrificial layer on a surface of the member, disposing a first agent within the member to obtain a predetermined concentration of the agent at said surface of the member, annealing the member, and removing the sacrificial layer to expose said surface of the member, wherein said surface has a post-process effective work function that is different from the initial value.
NASA Astrophysics Data System (ADS)
Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.
2015-07-01
Modern extensions of density functional theory such as the density functional theory plus U and the density functional theory plus dynamical mean field theory require choices, including selection of variable (charge vs spin density) for the density functional and specification of the correlated subspace. This paper examines these issues in the context of the "plus U" extensions of density functional theory, in which additional correlations on specified correlated orbitals are treated using a Hartree-Fock approximation. Differences between using charge-only or spin-density-dependent exchange-correlation functionals and between Wannier and projector-based definitions of the correlated orbitals are considered on the formal level and in the context of the structural energetics of the rare-earth nickelates. It is demonstrated that theories based on spin-dependent exchange-correlation functionals can lead to large and in some cases unphysical effective on-site exchange couplings. Wannier and projector-based definitions of the correlated orbitals lead to similar behavior near ambient pressure, but substantial differences are observed at large pressures. Implications for other beyond density functional methods such as the combination of density functional and dynamical mean field theory are discussed.
NASA Astrophysics Data System (ADS)
Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii
2016-12-01
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi-long-range antiferromagnetic order in the lightly doped regime.
Explicitly-correlated coupled cluster method for long-range dispersion coefficients
NASA Astrophysics Data System (ADS)
Bokhan, Denis; Trubnikov, Dmitrii N.; Perera, Ajith; Bartlett, Rodney J.
2017-03-01
A method of calculation of long-range dispersion C6 coefficients with wavefunctions, corresponding to linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model, has been developed. Designed approach uses CCSD(F12) wave functions for the calculation of dynamic polarizabilities at complex frequencies with further utilization of Casimir-Polder formula. As a part of the algorithm, the explicitly-correlated version of the coupled-perturbed CCSD equations for the case of complex frequencies has also been implemented. Numerical tests, conducted for the set of molecules show good agreement between dispersion coefficients, calculated with developed explicitly-correlated method and corresponding complete basis set results in regular CCSD already at triple- ζ level.
Keijser, Klara; Nowinski, Daniel
2016-01-01
Background: Unilateral cleft lip and palate (UCLP) affects nasal function and appearance. There is a lack of objective measurements to evaluate these features. This study analyzes whether objective measurements on photographs correlate with nasal function and/or appearance among adults treated for UCLP. Methods: All patients with UCLP born from 1960 to 1987 treated at the Uppsala University Hospital were invited (n = 109). Participation rate was 68% (n = 74); mean follow-up was 35 years. An age-matched control group (n = 61) underwent the same tests. Nostril area, nasal tip deviation angle, and width of the nostril were measured on photographs and were compared with functional tests and with appearance as assessed by self-assessment questionnaire, professional panel, or laymen panel. Results: The photographically measured nostril area correlated with nasal volume (acoustic rhinometry) among UCLP patients, both cleft side and noncleft side, and controls (0.331, P = 0.005; 0.338, P = 0.004; and 0.420, P < 0.001, respectively). For the patients’ noncleft side and controls, the area correlated inversely with airflow resistance at inspiration (noncleft side: −0.245, P = 0.043; controls: −0.226, P = 0.013). Laymen assessment of nasal appearance correlated with width ratio of the patients (0.27, P = 0.022) and with nasal tip deviation angle and area ratio of the controls (0.26, P = 0.041, and 0.31, P = 0.015, respectively). Conclusions: Photographic measurements correlate partially with both functional tests of the nose and panel ratings of appearance. No correlation was found with self-assessment of appearance. Evaluation of photographs needs to be combined with patient-reported outcome measures to be a valuable endpoint of nasal appearance. PMID:27579244
TANG, NING; ZHANG, YAPING; LIU, ZEYU; FU, TAO; LIANG, QINGHONG; AI, XUEMEI
2016-01-01
The aim of the present study was to investigate the correlation between four serum biomarkers of liver fibrosis and liver function in infants with cholestasis. A total of 30 infants with cholestasis and 20 healthy infants were included in the study. Biochemical assays based on the initial rate method and colorimetric assays were conducted to determine the levels of liver function markers in the serum [such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), direct bilirubin (DBIL), indirect bilirubin (IBIL), γ-glutamyl transferase (γ-GT), cholinesterase (CHE) and total bile acids (TBA)] and four serum biomarkers of liver fibrosis were measured using radioimmunoassays [hyaluronic acid (HA), procollagen type III (PCIII), laminin (LN) and collagen type IV (cIV)]. The serum levels of ALT, AST, TBIL, DBIL, IBIL, γ-GT and TBA in the infants with cholestasis were significantly higher compared to the healthy infants (P<0.01); the serum levels of CHE in the infants with cholestasis were significantly lower compared to the healthy infants (P<0.01). The serum levels of HA, PCIII, and cIV in the infants with cholestasis were significantly higher compared to the healthy infants (P<0.01). Correlation analyses between liver function and the four biomarkers of liver fibrosis showed that HA was positively correlated with AST and γ-GT (P<0.05) and negatively correlated with ALT, CHE and TBA (P<0.05). cIV was positively correlated with γ-GT (P<0.05) and negatively correlated with CHE (P<0.05). In conclusion, statistically significant differences were identified for the liver function markers (ALT, AST, TBIL, DBIL, IBIL, γ-GT and TBA) and the biomarkers HA, PCIII and cIV of liver fibrosis between infants with cholestasis and healthy infants. Thus, the serum levels of HA, cIV, γ-GT and CHE are sensitive markers for cholestatic liver fibrosis in infants. PMID:27347413
Arterial endothelial function measurement method and apparatus
Maltz, Jonathan S; Budinger, Thomas F
2014-03-04
A "relaxoscope" (100) detects the degree of arterial endothelial function. Impairment of arterial endothelial function is an early event in atherosclerosis and correlates with the major risk factors for cardiovascular disease. An artery (115), such as the brachial artery (BA) is measured for diameter before and after several minutes of either vasoconstriction or vasorelaxation. The change in arterial diameter is a measure of flow-mediated vasomodification (FMVM). The relaxoscope induces an artificial pulse (128) at a superficial radial artery (115) via a linear actuator (120). An ultrasonic Doppler stethoscope (130) detects this pulse 10-20 cm proximal to the point of pulse induction (125). The delay between pulse application and detection provides the pulse transit time (PTT). By measuring PTT before (160) and after arterial diameter change (170), FMVM may be measured based on the changes in PTT caused by changes in vessel caliber, smooth muscle tone and wall thickness.
Anisotropic extinction distortion of the galaxy correlation function
NASA Astrophysics Data System (ADS)
Fang, Wenjuan; Hui, Lam; Ménard, Brice; May, Morgan; Scranton, Ryan
2011-09-01
Similar to the magnification of the galaxies’ fluxes by gravitational lensing, the extinction of the fluxes by comic dust, whose existence is recently detected by [B. Ménard, R. Scranton, M. Fukugita, and G. Richards, Mon. Not. R. Astron. Soc.MNRAA40035-8711 405, 1025 (2010)DOI: 10.1111/j.1365-2966.2010.16486.x.], also modifies the distribution of a flux-selected galaxy sample. We study the anisotropic distortion by dust extinction to the 3D galaxy correlation function, including magnification bias and redshift distortion at the same time. We find the extinction distortion is most significant along the line of sight and at large separations, similar to that by magnification bias. The correction from dust extinction is negative except at sufficiently large transverse separations, which is almost always opposite to that from magnification bias (we consider a number count slope s>0.4). Hence, the distortions from these two effects tend to reduce each other. At low z (≲1), the distortion by extinction is stronger than that by magnification bias, but at high z, the reverse holds. We also study how dust extinction affects probes in real space of the baryon acoustic oscillations (BAO) and the linear redshift distortion parameter β. We find its effect on BAO is negligible. However, it introduces a positive scale-dependent correction to β that can be as large as a few percent. At the same time, we also find a negative scale-dependent correction from magnification bias, which is up to percent level at low z, but to ˜40% at high z. These corrections are non-negligible for precision cosmology, and should be considered when testing General Relativity through the scale-dependence of β.
Genotype-phenotype correlation for pulmonary function in cystic fibrosis
de Gracia, J; Mata, F; Alvarez, A; Casals, T; Gatner, S; Vendrell, M; de la Rosa, D; Guarner, L; Hermosilla, E
2005-01-01
Background: Since the CFTR gene was cloned, more than 1000 mutations have been identified. To date, a clear relationship has not been established between genotype and the progression of lung damage. A study was undertaken of the relationship between genotype, progression of lung disease, and survival in adult patients with cystic fibrosis (CF). Methods: A prospective cohort of adult patients with CF and two CFTR mutations followed up in an adult cystic fibrosis unit was analysed. Patients were classified according to functional effects of classes of CFTR mutations and were grouped based on the CFTR molecular position on the epithelial cell surface (I–II/I–II, I–II/III–V). Spirometric values, progression of lung disease, probability of survival, and clinical characteristics were analysed between groups. Results: Seventy four patients were included in the study. Patients with genotype I–II/I–II had significantly lower current spirometric values (p<0.001), greater loss of pulmonary function (p<0.04), a higher proportion of end-stage lung disease (p<0.001), a higher risk of suffering from moderate to severe lung disease (odds ratio 7.12 (95% CI 1.3 to 40.5)) and a lower probability of survival than patients with genotype I–II/III, I–II/IV and I–II/V (p<0.001). Conclusions: The presence of class I or II mutations on both chromosomes is associated with worse respiratory disease and a lower probability of survival. PMID:15994263
Killgore, William D. S.
2013-01-01
Study Objectives: Prior research suggests that sleep deprivation is associated with declines in some aspects of emotional intelligence and increased severity on indices of psychological disturbance. Sleep deprivation is also associated with reduced prefrontal-amygdala functional connectivity, potentially reflecting impaired top-down modulation of emotion. It remains unknown whether this modified connectivity may be observed in relation to more typical levels of sleep curtailment. We examined whether self-reported sleep duration the night before an assessment would be associated with these effects. Design: Participants documented their hours of sleep from the previous night, completed the Bar-On Emotional Quotient Inventory (EQ-i), Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT), and Personality Assessment Inventory (PAI), and underwent resting-state functional magnetic resonance imaging (fMRI). Setting: Outpatient neuroimaging center at a private psychiatric hospital. Participants: Sixty-five healthy adults (33 men, 32 women), ranging in age from 18-45 y. Interventions: N/A. Measurements and Results: Greater self-reported sleep the preceding night was associated with higher scores on all scales of the EQ-i but not the MSCEIT, and with lower symptom severity scores on half of the psychopathology scales of the PAI. Longer sleep was also associated with stronger negative functional connectivity between the right ventromedial prefrontal cortex and amygdala. Moreover, greater negative connectivity between these regions was associated with higher EQ-i and lower symptom severity on the PAI. Conclusions: Self-reported sleep duration from the preceding night was negatively correlated with prefrontal-amygdala connectivity and the severity of subjective psychological distress, while positively correlated with higher perceived emotional intelligence. More sleep was associated with higher emotional and psychological strength. Citation: Killgore WDS. Self
NASA Astrophysics Data System (ADS)
Yang, Yang; Brorsen, Kurt R.; Culpitt, Tanner; Pak, Michael V.; Hammes-Schiffer, Sharon
2017-09-01
Multicomponent density functional theory (DFT) enables the consistent quantum mechanical treatment of both electrons and protons. A major challenge has been the design of electron-proton correlation (epc) functionals that produce even qualitatively accurate proton densities. Herein an electron-proton correlation functional, epc17, is derived analogously to the Colle-Salvetti formalism for electron correlation and is implemented within the nuclear-electronic orbital (NEO) framework. The NEO-DFT/epc17 method produces accurate proton densities efficiently and is promising for diverse applications.
Yang, Yang; Brorsen, Kurt R; Culpitt, Tanner; Pak, Michael V; Hammes-Schiffer, Sharon
2017-09-21
Multicomponent density functional theory (DFT) enables the consistent quantum mechanical treatment of both electrons and protons. A major challenge has been the design of electron-proton correlation (epc) functionals that produce even qualitatively accurate proton densities. Herein an electron-proton correlation functional, epc17, is derived analogously to the Colle-Salvetti formalism for electron correlation and is implemented within the nuclear-electronic orbital (NEO) framework. The NEO-DFT/epc17 method produces accurate proton densities efficiently and is promising for diverse applications.
Booth, George H; Chan, Garnet Kin-Lic
2012-11-21
In this communication, we propose a method for obtaining isolated excited states within the full configuration interaction quantum Monte Carlo framework. This method allows for stable sampling with respect to collapse to lower energy states and requires no uncontrolled approximations. In contrast with most previous methods to extract excited state information from quantum Monte Carlo methods, this results from a modification to the underlying propagator, and does not require explicit orthogonalization, analytic continuation, transient estimators, or restriction of the Hilbert space via a trial wavefunction. Furthermore, we show that the propagator can directly yield frequency-domain correlation functions and spectral functions such as the density of states which are difficult to obtain within a traditional quantum Monte Carlo framework. We demonstrate this approach with pilot applications to the neon atom and beryllium dimer.
Correlation of Objective Audiometric and Caloric Function in Ménière's Disease.
McMullen, Kyle P; Lin, Chen; Harris, Michael S; Adunka, Oliver F
2017-02-01
Objective Ménière's disease affects the vestibular and audiologic systems; however, little is known about the relationship between audiometric and caloric function with increasing duration of disease. We employed a novel methodology to understand the longitudinal correlation between audiometric and caloric function in Ménière's patients. Study Design Case series with chart review. Setting Neuro-otologic tertiary care practice. Subjects and Methods Charts of 19 patients with unilateral Ménière's disease, as classified by the 1995 American Academy of Otolaryngology-Head and Neck Foundation criteria, were examined. We included patients with ≥2 videonystagmograms and audiograms. We excluded those with bilateral Ménière's, prior audiovestibular destruction, or symptoms suggesting concomitant vestibular pathology. Spearman's rank correlation of audiometric status (pure tone average [PTA], low PTA, and word recognition score [WRS]) and vestibular function (bithermal calorics) was performed. The study was Institutional Review Board approved (protocol 2015H0266). Results A total of 112 audiograms and 42 videonystagmographies were performed. There was a decline in affected ear hearing PTA and WRS with duration of disease ( r = 0.602, P < .001, and r = -0.573, P < .001, respectively). Similarly, there was a decline in vestibular function with increasing duration of disease ( r = 0.709, P < .001). There were moderate correlations between vestibular weakness and PTA, low PTA, and WRS ( r = 0.464, P = .002; r = 0.498, P = .001; and r = -0.518, P = .001, respectively). Conclusions There is a correlation between decline in objective hearing and horizontal semicircular canal function with time. As expected, this correlation is not 1:1, indicating differential involvement of both systems. Understanding this relationship may assist in counseling patients with regard to prognosis, natural history, and therapeutic interventions.
Generalized summability methods of functions using ideals
NASA Astrophysics Data System (ADS)
Savaş, Ekrem
2015-09-01
In this paper, we shall make a new approach to two well known summability methods by using ideals and introduce new notions, namely, ℐ-statistical convergence and ℐ-lacunary statistical convergence by taking a nonnegative real-valued Lebesque measurable function in the interval (1, ∞) and mainly investigate their relationship and also make some observations about these classes.
Burns, Rebekah; Olson, Inger; Kazmucha, Jeffrey; Balise, Raymond; Chin, Rita; Chin, Clifford
2010-10-01
Although exercise testing is an important objective method used to assess cardiopulmonary function, subjective assessment often is used as a proxy in the clinical setting. This study aimed to determine whether responses to a subjective functional capacity questionnaire administered to parents and patients in a pediatric exercise laboratory correlate with objective assessment of functional capacity, measured by peak oxygen consumption during maximal voluntary exercise testing. Subjective questionnaire responses and exercise test results collected over 10 years were retrospectively analyzed. Symptoms and physical capabilities were assessed using a 6-point Likert scale regarding the ability to attend school/work, walk, climb stairs, and run, as well as the frequency of fatigue, palpitations, and chest pain. Values of 0 to 3 were considered abnormal, whereas values of 4-5 were regarded as normal. Exercise testing was performed on a stationary cycle ergometer with a continuous ramping protocol. Heart rate and oxygen saturation were continuously monitored. Blood pressures and electrocardiograms (ECGs) were obtained at 2-min intervals. Metabolic gas analysis was performed using a breath-by-breath method. The results of the exercise testing were normalized for body size and expressed as a percentage of predicted peak oxygen consumption (%pVO(2)). Very weak but statistically significant correlations (τ < 0.25; P < 0.05) between the scores of the school/work, walking, stair climbing, running, and fatigue items and %pVO(2) were found using Kendall's rank correlations. The subjective Likert scales used to assess basic physical capacity and cardiac-associated symptoms have limited ability to predict actual functional capacity as measured by %pVO(2) achieved. The very weak rank-order correlation between %pVO(2) achieved and the subjective reporting of the ability to attend school/work, walk, climb stairs, and run has low clinical significance and will not be useful in
Liao, Ying; Yuan, Wen-yu; Zheng, Wen-ke; Luo, Ao-xue; Fan, Yi-jun
2015-11-01
To compare the radical scavenging activity of five different acidic polysaccharides, and to find the correlation with the functional groups. Alkali extraction method and Stepwise ethanol precipitation method were used to extract and concentrate the five Dendrobium polysaccharides, and to determine the contents of sulfuric acid and uronic acid of each kind of acidic polysaccharides, and the scavenging activity to ABTS+ radical and hydroxyl radical. Functional group structures were examined by FTIR Spectrometer. Five kinds of Dendrobium polysaccharides had different ability of scavenging ABTS+ free radical and hydroxyl free radical. Moreover, the study had shown that five kinds of antioxidant activity of acidic polysaccharides had obvious correlation withuronic acid and sulfuric acid. The antioxidant activity of each sample was positively correlated with the content of uronic acid, and negatively correlated with the content of sulfuric acid. Sulfuric acid can inhibit the antioxidant activity of acidic polysaccharide but uronic acid can enhance the free radical scavenging activity. By analyzing the structure characteristics of five acidic polysaccharides, all samples have similar structures, however, Dendrobium denneanum, Dendrobium devonianum and Dendrobium officinale which had β configuration have higher antioxidant activity than Dendrobium nobile and Dendrobium fimbriatum which had a configuration.
MIC as an Appropriate Method to Construct the Brain Functional Network
Yi, Ming; Wu, Xia
2015-01-01
Using an effective method to measure the brain functional connectivity is an important step to study the brain functional network. The main methods for constructing an undirected brain functional network include correlation coefficient (CF), partial correlation coefficient (PCF), mutual information (MI), wavelet correlation coefficient (WCF), and coherence (CH). In this paper we demonstrate that the maximal information coefficient (MIC) proposed by Reshef et al. is relevant to constructing a brain functional network because it performs best in the comprehensive comparisons in consistency and robustness. Our work can be used to validate the possible new functional connection measures. PMID:25710031
Hybrid functionals and GW approximation in the FLAPW method
NASA Astrophysics Data System (ADS)
Friedrich, Christoph; Betzinger, Markus; Schlipf, Martin; Blügel, Stefan; Schindlmayr, Arno
2012-07-01
We present recent advances in numerical implementations of hybrid functionals and the GW approximation within the full-potential linearized augmented-plane-wave (FLAPW) method. The former is an approximation for the exchange-correlation contribution to the total energy functional in density-functional theory, and the latter is an approximation for the electronic self-energy in the framework of many-body perturbation theory. All implementations employ the mixed product basis, which has evolved into a versatile basis for the products of wave functions, describing the incoming and outgoing states of an electron that is scattered by interacting with another electron. It can thus be used for representing the nonlocal potential in hybrid functionals as well as the screened interaction and related quantities in GW calculations. In particular, the six-dimensional space integrals of the Hamiltonian exchange matrix elements (and exchange self-energy) decompose into sums over vector-matrix-vector products, which can be evaluated easily. The correlation part of the GW self-energy, which contains a time or frequency dependence, is calculated on the imaginary frequency axis with a subsequent analytic continuation to the real axis or, alternatively, by a direct frequency convolution of the Green function G and the dynamically screened Coulomb interaction W along a contour integration path that avoids the poles of the Green function. Hybrid-functional and GW calculations are notoriously computationally expensive. We present a number of tricks that reduce the computational cost considerably, including the use of spatial and time-reversal symmetries, modifications of the mixed product basis with the aim to optimize it for the correlation self-energy and another modification that makes the Coulomb matrix sparse, analytic expansions of the interaction potentials around the point of divergence at k = 0, and a nested density and density-matrix convergence scheme for hybrid-functional
Excited states of boron isoelectronic series from explicitly correlated wave functions.
Gálvez, F J; Buendía, E; Sarsa, A
2005-04-15
The ground state and some low-lying excited states arising from the 1s2 2s2p2 configuration of the boron isoelectronic series are studied starting from explicitly correlated multideterminant wave functions. One- and two-body densities in position space have been calculated and different expectation values such as
Correlation between head posture and proprioceptive function in the cervical region
Yong, Min-Sik; Lee, Hae-Yong; Lee, Mi-Young
2016-01-01
[Purpose] The aim of the present study was to investigate correlation between head posture and proprioceptive function in the cervical region. [Subjects and Methods] Seventy-two subjects (35 males and 37 females) participated in this study. For measurement of head posture, the craniovertebral angle was calculated based on the angle between a horizontal line passing through C7 and a line extending from the tragus of the ear to C7. The joint position sense was evaluated using a dual digital inclinometer (Acumar, Lafayette Instrument, Lafayette, IN, USA), which was used to measure the joint position error for cervical flexion and extension. [Results] A significant negative correlation was observed between the craniovertebral angle and position sense error for flexion and extension. [Conclusion] Forward head posture is correlated with greater repositioning error than a more upright posture, and further research is needed to determine whether correction of forward head posture has any impact on repositioning error. PMID:27134372
Muscle MRI Findings in Childhood/Adult Onset Pompe Disease Correlate with Muscle Function
Figueroa-Bonaparte, Sebastián; Segovia, Sonia; Llauger, Jaume; Belmonte, Izaskun; Pedrosa, Irene; Alejaldre, Aída; Mayos, Mercè; Suárez-Cuartín, Guillermo; Gallardo, Eduard; Illa, Isabel; Díaz-Manera, Jordi
2016-01-01
Objectives Enzyme replacement therapy has shown to be effective for childhood/adult onset Pompe disease (AOPD). The discovery of biomarkers useful for monitoring disease progression is one of the priority research topics in Pompe disease. Muscle MRI could be one possible test but the correlation between muscle MRI and muscle strength and function has been only partially addressed so far. Methods We studied 34 AOPD patients using functional scales (Manual Research Council scale, hand held myometry, 6 minutes walking test, timed to up and go test, time to climb up and down 4 steps, time to walk 10 meters and Motor Function Measure 20 Scale), respiratory tests (Forced Vital Capacity seated and lying, Maximun Inspiratory Pressure and Maximum Expiratory Pressure), daily live activities scales (Activlim) and quality of life scales (Short Form-36 and Individualized Neuromuscular Quality of Life questionnaire). We performed a whole body muscle MRI using T1w and 3-point Dixon imaging centered on thighs and lower trunk region. Results T1w whole body muscle MRI showed a homogeneous pattern of muscle involvement that could also be found in pre-symptomatic individuals. We found a strong correlation between muscle strength, muscle functional scales and the degree of muscle fatty replacement in muscle MRI analyzed using T1w and 3-point Dixon imaging studies. Moreover, muscle MRI detected mild degree of fatty replacement in paraspinal muscles in pre-symptomatic patients. Conclusion Based on our findings, we consider that muscle MRI correlates with muscle function in patients with AOPD and could be useful for diagnosis and follow-up in pre-symptomatic and symptomatic patients under treatment. Take home message Muscle MRI correlates with muscle function in patients with AOPD and could be useful to follow-up patients in daily clinic. PMID:27711114
Empirical Synthesis of Green functions from the correlation of diffuse waves
NASA Astrophysics Data System (ADS)
Campillo, M.; Larose, E.; Margerin, L.; Paul, A.; van Tiggelen, B.; Derode, A.; Abers, G.
2003-12-01
We show the existence of long range field correlations in the seismic coda of regional records in both Mexico and Alaska. The cross-correlation tensor between the coda records at two points is measured for a set of distant earthquakes. Remarkably, while individual correlations have a random character, the source- averaged correlations exhibit deterministic arrivals that obey the same symmetry rules as the Green tensor between the two points. In addition, the arrival times of these waves coincide with propagating surface waves between the two stations. Thus, we propose to identify the averaged correlation signals with the surface wave part of the Green tensor. However, while time reversal symmetry theoretically imposes that the Green function appears at both negative and positive times, we find experimentally this symmetry to be broken when the distribution of earthquakes is not isotropic around the stations. We explain this observation by the long lasting anisotropy of the diffuse field. This point is further discussed in a companion paper where we prove both experimentally and theoretically that a dominant flux of energy coming from the source can persist in the late coda. Finally, we show that averaged cross-correlations of ambient noise enable the reconstruction of some coherent arrivals. These examples illustrate a novel empirical method that provides synthetic seismograms between two stations, without the knowledge of the precise location and origin times of the sources.
Bleicher, Lucas; Lemke, Ney; Garratt, Richard Charles
2011-01-01
Correlated mutation analysis has a long history of interesting applications, mostly in the detection of contact pairs in protein structures. Based on previous observations that, if properly assessed, amino acid correlation data can also provide insights about functional sub-classes in a protein family, we provide a complete framework devoted to this purpose. An amino acid specific correlation measure is proposed, which can be used to build networks summarizing all correlation and anti-correlation patterns in a protein family. These networks can be submitted to community structure detection algorithms, resulting in subsets of correlated amino acids which can be further assessed by specific parameters and procedures that provide insight into the relationship between different communities, the individual importance of community members and the adherence of a given amino acid sequence to a given community. By applying this framework to three protein families with contrasting characteristics (the Fe/Mn-superoxide dismutases, the peroxidase-catalase family and the C-type lysozyme/α-lactalbumin family), we show how our method and the proposed parameters and procedures are related to biological characteristics observed in these protein families, highlighting their potential use in protein characterization and gene annotation. PMID:22205928
White-Matter Changes Correlate with Cognitive Functioning in Parkinson’s Disease
Theilmann, Rebecca J.; Reed, Jason D.; Song, David D.; Huang, Mingxiong X.; Lee, Roland R.; Litvan, Irene; Harrington, Deborah L.
2013-01-01
Diffusion tensor imaging (DTI) findings from emerging studies of cortical white-matter integrity in Parkinson’s disease (PD) without dementia are inconclusive. When white-matter changes have been found, their relationship to cognitive functioning in PD has not been carefully investigated. To better characterize changes in tissue diffusivity and to understand their functional significance, the present study conducted DTI in 25 PD patients without dementia and 26 controls of similar ages. An automated tract-based DTI method was used. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were analyzed. Neuropsychological measures of executive functioning (working memory, verbal fluency, cognitive flexibility, inhibitory control) and visuospatial ability were then correlated with regions of interest that showed abnormal diffusivity in the PD group. We found widespread reductions in FA and increases in MD in the PD group relative to controls. These changes were predominantly related to an increase in RD. Increased AD in the PD group was limited to specific frontal tracks of the right hemisphere, possibly signifying more significant tissue changes. Motor symptom severity did not correlate with FA. However, different measures of executive functioning and visuospatial ability correlated with FA in different segments of tracts, which contain fiber pathways to cortical regions that are thought to support specific cognitive processes. The findings suggest that abnormal tissue diffusivity may be sensitive to subtle cognitive changes in PD, some of which may be prognostic of future cognitive decline. PMID:23630517
Correlation between upper limb function and oral health impact in stroke survivors
da Silva, Fernanda C.; da Silva, Daniela F. T.; Mesquita-Ferrari, Raquel A.; Fernandes, Kristianne P. S.; Bussadori, Sandra K.
2015-01-01
[Purpose] The aim of the present study was to evaluate the relationship between upper limb impairment and oral health impact in individuals with hemiparesis stemming from a stroke. [Subjects and Methods] The study subjects were conducted with a sample of 27 stroke survivors with complete or partial hemiparesis with brachial or crural predominance. The 14-item short version of the Oral Health Impact Profile was used to evaluate perceptions of oral health. The Brazilian version of the Stroke Specific Quality of Life Scale was used to evaluate perceptions regarding quality of life. [Results] A statistically significant association was found between the upper extremity function subscale of the SSQOL-Brazil and the impact of oral health evaluated using the OHIP-14, with a strong correlation found for the physical pain subscale, moderate correlations with the functional limitation, psychological discomfort, physical disability, social disability and social handicap subscales as well as a weak correlation with the psychological disability subscale. Analyzing the OHIP-14 scores with regard to the impact of oral health on quality of life, the most frequent classification was weak impact, with small rates of moderate and strong impact. [Conclusion] Compromised upper limb function and self-perceived poor oral health, whether due to cultural resignation or functional disability, exert a negative impact on the quality of life of individuals with hemiparesis stemming from a stroke. PMID:26310352
Borroni, Barbara; Grassi, Mario; Agosti, Chiara; Paghera, Barbara; Alberici, Antonella; Di Luca, Monica; Perani, Daniela; Padovani, Alessandro
2007-01-01
Background Frontotemporal Lobar Degeneration (FTLD) thus recently renamed, refers to a spectrum of heterogeneous conditions. This same heterogeneity of presentation represents the major methodological limit for the correct evaluation of clinical designation and brain functional correlates. At present, no study has investigated clinical clusters due to specific cognitive and behavioural disturbances beyond current clinical criteria. The aim of this study was to identify clinical FTLD presentation, based on cognitive and behavioural profile, and to define their SPECT functional correlations. Methods Ninety-seven FTLD patients entered the study. A clinical evaluation and standardised assessment were preformed, as well as a brain SPECT perfusion imaging study. Latent Profile Analysis on clinical, neuropsychological, and behavioural data was performed. Voxel-basis analysis of SPECT data was computed. Results Three specific clusters were identified and named "pseudomanic behaviour" (LC1), "cognitive" (LC2), and "pseudodepressed behaviour" (LC3) endophenotypes. These endophenotypes showed a comparable hypoperfusion in left temporal lobe, but a specific pattern involving: medial and orbitobasal frontal cortex in LC1, subcortical brain region in LC2, and right dorsolateral frontal cortex and insula in LC3. Conclusion These findings provide evidence that specific functional-cluster symptom relationship can be delineated in FTLD patients by a standardised assessment. The understanding of the different functional correlates of clinical presentations will hopefully lead to the possibility of individuating diagnostic and treatment algorithms. PMID:17506892
Genuine N -partite entanglement without N -partite correlation functions
NASA Astrophysics Data System (ADS)
Tran, Minh Cong; Zuppardo, Margherita; de Rosier, Anna; Knips, Lukas; Laskowski, Wiesław; Paterek, Tomasz; Weinfurter, Harald
2017-06-01
A genuinely N -partite entangled state may display vanishing N -partite correlations measured for arbitrary local observables. In such states the genuine entanglement is noticeable solely in correlations between subsets of particles. A straightforward way to obtain such states for odd N is to design an "antistate" in which all correlations between an odd number of observers are exactly opposite. Evenly mixing a state with its antistate then produces a mixed state with no N -partite correlations, with many of them genuinely multiparty entangled. Intriguingly, all known examples of "entanglement without correlations" involve an odd number of particles. Here we further develop the idea of antistates, thereby shedding light on the different properties of even and odd particle systems. We conjecture that there is no antistate to any pure even-N -party entangled state making the simple construction scheme unfeasible. However, as we prove by construction, higher-rank examples of entanglement without correlations for arbitrary even N indeed exist. These classes of states exhibit genuine entanglement and even violate an N -partite Bell inequality, clearly demonstrating the nonclassical features of these states as well as showing their applicability for quantum information processing.
2011-06-01
USING SPECTRAL CORRELATION FUNCTION THESIS Mujun Song, Captain, ROKA AFIT/GCE/ENG/11-09 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR... CORRELATION FUNCTION THESIS Presented to the Faculty Department of Electrical and Computer Engineering Graduate School of Engineering and...cyclostationarity of a signal to detect its presence. Signals that have cyclostationarity exhibit correlations between widely separated spectral components
Delta function convolution method (DFCM) for fluorescence decay experiments
NASA Astrophysics Data System (ADS)
Zuker, M.; Szabo, A. G.; Bramall, L.; Krajcarski, D. T.; Selinger, B.
1985-01-01
A rigorous and convenient method of correcting for the wavelength variation of the instrument response function in time correlated photon counting fluorescence decay measurements is described. The method involves convolution of a modified functional form F˜s of the physical model with a reference data set measured under identical conditions as the measurement of the sample. The method is completely general in that an appropriate functional form may be found for any physical model of the excited state decay process. The modified function includes a term which is a Dirac delta function and terms which give the correct decay times and preexponential values in which one is interested. None of the data is altered in any way, permitting correct statistical analysis of the fitting. The method is readily adaptable to standard deconvolution procedures. The paper describes the theory and application of the method together with fluorescence decay results obtained from measurements of a number of different samples including diphenylhexatriene, myoglobin, hemoglobin, 4', 6-diamidine-2-phenylindole (DAPI), and lysine-trytophan-lysine.
Shankar, R; Vishwanath, Ashvin
2011-09-02
For certain systems, the N-particle ground-state wave functions of the bulk happen to be exactly equal to the N-point spacetime correlation functions at the edge, in the infrared limit. We show why this had to be so for a class of topological superconductors, beginning with the p+ip state in D=2+1. Varying the chemical potential as a function of Euclidean time between weak and strong pairing states is shown to extract the wave function. Then a Euclidean rotation that exchanges time and space and approximate Lorentz invariance lead to the edge connection. This framework readily generalizes to other dimensions. We illustrate it with a D=3+1 example, superfluid 3He- B, and a p-wave superfluid in D=1+1. Our method works only when the particle number is not conserved, as in superconductors.
Pillet, N.; Berger, J.-F.; Caurier, E.
2008-08-15
Applying a variational multiparticle-multihole configuration mixing method whose purpose is to include correlations beyond the mean field in a unified way without particle number and Pauli principle violations, we investigate pairing-like correlations in the ground states of {sup 116}Sn, {sup 106}Sn, and {sup 100}Sn. The same effective nucleon-nucleon interaction, namely, the D1S parametrization of the Gogny force, is used to derive both the mean field and correlation components of nuclear wave functions. Calculations are performed using an axially symmetric representation. The structure of correlated wave functions, their convergence with respect to the number of particle-hole excitations, and the influence of correlations on single-particle level spectra and occupation probabilities are analyzed and compared with results obtained with the same two-body effective interaction from BCS, Hartree-Fock-Bogoliubov, and particle number projected after variation BCS approaches. Calculations of nuclear radii and the first theoretical excited 0{sup +} states are compared with experimental data.
Fujimoto, Shuhei; Kon, Noriko
2016-04-01
[Purpose] The purpose of this study was to elucidate how well patients' perceptions related to the improvements in their hand function during hospitalization. [Subjects] Sixteen patients who were hospitalized after hand surgery. [Methods] Using the Japanese Society for Surgery of the Hand edition of the Quick-Disabilities of the Arm, Shoulder, and Hand questionnaire; tactile roughness discrimination acuity, motor imagery, motor function, sensory function, and pain of the upper limb were assessed at admission and discharge. Spearman's rank-order correlation coefficients were calculated using the differences in all assessment items at admission and discharge. A multiple regression analysis (stepwise method) was performed to investigate factors that correlated with improvements in Quick-Disabilities of the Arm, Shoulder, and Hand scores. [Results] The improvement of tactile roughness discrimination acuity was significantly associated with patient perception of improved hand function. [Conclusion] The results suggest that an improvement in tactile roughness discrimination acuity was most strongly correlated with patient perception of improved hand function.
Erdal, Barbaros Selnur; Yildiz, Vedat; King, Mark A.; Patterson, Andrew T.; Knopp, Michael V.; Clymer, Bradley D.
2012-01-01
Background: Chest CT scans are commonly used to clinically assess disease severity in patients presenting with pulmonary sarcoidosis. Despite their ability to reliably detect subtle changes in lung disease, the utility of chest CT scans for guiding therapy is limited by the fact that image interpretation by radiologists is qualitative and highly variable. We sought to create a computerized CT image analysis tool that would provide quantitative and clinically relevant information. Methods: We established that a two-point correlation analysis approach reduced the background signal attendant to normal lung structures, such as blood vessels, airways, and lymphatics while highlighting diseased tissue. This approach was applied to multiple lung fields to generate an overall lung texture score (LTS) representing the quantity of diseased lung parenchyma. Using deidentified lung CT scan and pulmonary function test (PFT) data from The Ohio State University Medical Center’s Information Warehouse, we analyzed 71 consecutive CT scans from patients with sarcoidosis for whom simultaneous matching PFTs were available to determine whether the LTS correlated with standard PFT results. Results: We found a high correlation between LTS and FVC, total lung capacity, and diffusing capacity of the lung for carbon monoxide (P < .0001 for all comparisons). Moreover, LTS was equivalent to PFTs for the detection of active lung disease. The image analysis protocol was conducted quickly (< 1 min per study) on a standard laptop computer connected to a publicly available National Institutes of Health ImageJ toolkit. Conclusions: The two-point image analysis tool is highly practical and appears to reliably assess lung disease severity. We predict that this tool will be useful for clinical and research applications. PMID:22628487
An optimum approximation of n-point correlation functions of random heterogeneous material systems.
Baniassadi, M; Safdari, M; Garmestani, H; Ahzi, S; Geubelle, P H; Remond, Y
2014-02-21
An approximate solution for n-point correlation functions is developed in this study. In the approximate solution, weight functions are used to connect subsets of (n-1)-point correlation functions to estimate the full set of n-point correlation functions. In previous related studies, simple weight functions were introduced for the approximation of three and four-point correlation functions. In this work, the general framework of the weight functions is extended and derived to achieve optimum accuracy for approximate n-point correlation functions. Such approximation can be utilized to construct global n-point correlation functions for a system when there exist limited information about these functions in a subset of space. To verify its accuracy, the new formulation is used to approximate numerically three-point correlation functions from the set of two-point functions directly evaluated from a virtually generated isotropic heterogeneous microstructure representing a particulate composite system. Similarly, three-point functions are approximated for an anisotropic glass fiber/epoxy composite system and compared to their corresponding reference values calculated from an experimental dataset acquired by computational tomography. Results from both virtual and experimental studies confirm the accuracy of the new approximation. The new formulation can be utilized to attain a more accurate approximation to global n-point correlation functions for heterogeneous material systems with a hierarchy of length scales.
An optimum approximation of n-point correlation functions of random heterogeneous material systems
Baniassadi, M.; Garmestani, H.; Ahzi, S.; Remond, Y.
2014-02-21
An approximate solution for n-point correlation functions is developed in this study. In the approximate solution, weight functions are used to connect subsets of (n-1)-point correlation functions to estimate the full set of n-point correlation functions. In previous related studies, simple weight functions were introduced for the approximation of three and four-point correlation functions. In this work, the general framework of the weight functions is extended and derived to achieve optimum accuracy for approximate n-point correlation functions. Such approximation can be utilized to construct global n-point correlation functions for a system when there exist limited information about these functions in a subset of space. To verify its accuracy, the new formulation is used to approximate numerically three-point correlation functions from the set of two-point functions directly evaluated from a virtually generated isotropic heterogeneous microstructure representing a particulate composite system. Similarly, three-point functions are approximated for an anisotropic glass fiber/epoxy composite system and compared to their corresponding reference values calculated from an experimental dataset acquired by computational tomography. Results from both virtual and experimental studies confirm the accuracy of the new approximation. The new formulation can be utilized to attain a more accurate approximation to global n-point correlation functions for heterogeneous material systems with a hierarchy of length scales.
The Course and Correlates of Everyday Functioning in Schizophrenia
Reichenberg, Abraham; Feo, Concetta; Prestia, Davide; Bowie, Christopher R.; Patterson, Thomas L.; Harvey, Philip D.
2014-01-01
Previously institutionalized older patients with schizophrenia show changes in cognitive and functional capacity over time. This study examined changes in real-world functioning in a sample of people with schizophrenia who varied in their history of long-term institutionalization and related changes in real world functioning to changes in cognition and functional capacity over the follow-up period. Older patients with schizophrenia (n=111) were examined with assessments of cognitive functioning, functional capacity, clinical symptoms, and everyday functioning. They were then followed up to 45 months and examined up to two times. Mixed-model regression was used to examine changes in real-world functioning in social, everyday living, and vocational domains over the follow-up period and identify potential predictors of change. Everyday functioning worsened over time in all three domains. Although length of longest hospitalization predicted worsening, this influence was eliminated when the course of functional capacity was used to predict the course of everyday functioning. For both vocational and everyday living domains, as well as the composite score on functional status, worsening in performance based measures of everyday functioning and social competence predicted worsening in real world functioning. Changes in negative symptoms further predicted worsening in the everyday living domain. Worsening in everyday functioning is found in people with schizophrenia and those with a history of greater chronicity and severity of illness seem more affected. These influences seem to be expressed through worsening in the ability to perform everyday functional skills. Potential causes of these changes and implications for reducing these impairments are discussed. PMID:25045625
Density-Functional Theory Studies of Correlation Energy Effects at Metallic Surfaces.
NASA Astrophysics Data System (ADS)
Mohammed, Abdel-Raouf Eid
In this thesis we study the effects of correlation in the inhomogeneous electron gas at metallic surfaces. These studies are performed within the context of density-functional theory (DFT). Using accurate representations of the electronic density profile, we have estimated variationally the surface correlation energy of jellium metal. The accuracy of these estimates is founded in the assumption that the exchange -correlation energy functional of the density is approximated accurately by the wave-vector analysis method, and by the fact that the non-local exchange energy contributions are treated exactly. In contrast to the previously accepted conclusion that for surfaces correlation effects are as significant as exchange, our results indicate the ratio of these energies to lie between 34% - 97% over the metallic density range, the smaller ratios corresponding to the higher density metals. In this work we have also examined the local density (LDA) and gradient expansion approximations (GEA) (to O((DEL)('2))) for the correlation energy. We have demonstrated for realistic metal surface densities the cancellation of the errors in the LDA for exchange and correlation, and shown that the density profiles at surfaces would have to be unphysically slowly varying for the correlation energy GEA to converge. We have also studied the effects of correlation at surfaces by screening the exchange, and observe that the surface exchange energy for screened-Coulomb interaction decreases as the screening length is reduced. Thus, the more short-ranged the interaction, the easier it is to split the crystal in two. In addition we have derived the DFT first gradient correction coefficient in the GEA for the screened-Coulomb exchange energy, and shown it to be the same as that obtained within Hartree -Fock theory (HFT) for finite screening. This coefficient reduces to the DFT bare-Coulomb interaction value in the limit of no screening in which limit the HFT coefficient is singular. The GEA
A nonparametric method for penetrance function estimation.
Alarcon, F; Bonaïti-Pellié, C; Harari-Kermadec, H
2009-01-01
In diseases caused by a deleterious gene mutation, knowledge of age-specific cumulative risks is necessary for medical management of mutation carriers. When pedigrees are ascertained through at least one affected individual, ascertainment bias can be corrected by using a parametric method such as the Proband's phenotype Exclusion Likelihood, or PEL, that uses a survival analysis approach based on the Weibull model. This paper proposes a nonparametric method for penetrance function estimation that corrects for ascertainment on at least one affected: the Index Discarding EuclideAn Likelihood or IDEAL. IDEAL is compared with PEL, using family samples simulated from a Weibull distribution and under alternative models. We show that, under Weibull assumption and asymptotic conditions, IDEAL and PEL both provide unbiased risk estimates. However, when the true risk function deviates from a Weibull distribution, we show that the PEL might provide biased estimates while IDEAL remains unbiased.
Finite difference methods for approximating Heaviside functions
NASA Astrophysics Data System (ADS)
Towers, John D.
2009-05-01
We present a finite difference method for discretizing a Heaviside function H(u(x→)), where u is a level set function u:Rn ↦ R that is positive on a bounded region Ω⊂Rn. There are two variants of our algorithm, both of which are adapted from finite difference methods that we proposed for discretizing delta functions in [J.D. Towers, Two methods for discretizing a delta function supported on a level set, J. Comput. Phys. 220 (2007) 915-931; J.D. Towers, Discretizing delta functions via finite differences and gradient normalization, Preprint at http://www.miracosta.edu/home/jtowers/; J.D. Towers, A convergence rate theorem for finite difference approximations to delta functions, J. Comput. Phys. 227 (2008) 6591-6597]. We consider our approximate Heaviside functions as they are used to approximate integrals over Ω. We prove that our first approximate Heaviside function leads to second order accurate quadrature algorithms. Numerical experiments verify this second order accuracy. For our second algorithm, numerical experiments indicate at least third order accuracy if the integrand f and ∂Ω are sufficiently smooth. Numerical experiments also indicate that our approximations are effective when used to discretize certain singular source terms in partial differential equations. We mostly focus on smooth f and u. By this we mean that f is smooth in a neighborhood of Ω, u is smooth in a neighborhood of ∂Ω, and the level set u(x)=0 is a manifold of codimension one. However, our algorithms still give reasonable results if either f or u has jumps in its derivatives. Numerical experiments indicate approximately second order accuracy for both algorithms if the regularity of the data is reduced in this way, assuming that the level set u(x)=0 is a manifold. Numerical experiments indicate that dependence on the placement of Ω with respect to the grid is quite small for our algorithms. Specifically, a grid shift results in an O(hp) change in the computed solution
Lacey, R.A.; Elmaani, A.; Lauret, J.; Li, T.; Bauer, W.; Craig, D.; Cronqvist, M.; Gualtieri, E.; Hannuschke, S.; Reposeur, T.; Vander Molen, A.; Westfall, G.D.; Wilson, W.K.; Winfield, J.S.; Yee, J.; Yennello, S.; Nadasen, A.; Tickle, R.S.; Norbeck, E. National Superconducting Cyclotron Laboratory Department of Physics, Michigan State University, East Lansing, Michigan 48824-1321 Department of Physics, University of Michigan at Dearborn, Dearborn, Michigan 48128 Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120 Department of Physics, University of Iowa, Iowa City, Iowa 52242 )
1993-03-01
Multifragment azimuthal correlation functions have been measured as a function of beam energy and impact parameter for the Ar+Sc system ([ital E]/[ital A]=35 to 115 MeV). The observed azimuthal correlation functions---which do not require corrections for dispersion of the reaction plane---exhibit strong asymmetries which are dependent on impact parameter and beam energy. Rotational collective motion and flow seem to dominate the correlation functions at low beam energies. It is proposed that multifragment azimuthal correlation functions can provide a useful probe for intermediate energy heavy ion reaction dynamics.
ERIC Educational Resources Information Center
Dumenci, Levent; Yates, Phillip D.
2012-01-01
Estimation problems associated with the correlated-trait correlated-method (CTCM) parameterization of a multitrait-multimethod (MTMM) matrix are widely documented: the model often fails to converge; even when convergence is achieved, one or more of the parameter estimates are outside the admissible parameter space. In this study, the authors…
Power, Jonathan D; Barnes, Kelly A; Snyder, Abraham Z; Schlaggar, Bradley L; Petersen, Steven E
2012-02-01
Here, we demonstrate that subject motion produces substantial changes in the timecourses of resting state functional connectivity MRI (rs-fcMRI) data despite compensatory spatial registration and regression of motion estimates from the data. These changes cause systematic but spurious correlation structures throughout the brain. Specifically, many long-distance correlations are decreased by subject motion, whereas many short-distance correlations are increased. These changes in rs-fcMRI correlations do not arise from, nor are they adequately countered by, some common functional connectivity processing steps. Two indices of data quality are proposed, and a simple method to reduce motion-related effects in rs-fcMRI analyses is demonstrated that should be flexibly implementable across a variety of software platforms. We demonstrate how application of this technique impacts our own data, modifying previous conclusions about brain development. These results suggest the need for greater care in dealing with subject motion, and the need to critically revisit previous rs-fcMRI work that may not have adequately controlled for effects of transient subject movements. Copyright © 2011 Elsevier Inc. All rights reserved.
NASA Technical Reports Server (NTRS)
Ma, Q.; Tipping, R. H.; Lavrentieva, N. N.
2012-01-01
By adopting a concept from signal processing, instead of starting from the correlation functions which are even, one considers the causal correlation functions whose Fourier transforms become complex. Their real and imaginary parts multiplied by 2 are the Fourier transforms of the original correlations and the subsequent Hilbert transforms, respectively. Thus, by taking this step one can complete the two previously needed transforms. However, to obviate performing the Cauchy principal integrations required in the Hilbert transforms is the greatest advantage. Meanwhile, because the causal correlations are well-bounded within the time domain and band limited in the frequency domain, one can replace their Fourier transforms by the discrete Fourier transforms and the latter can be carried out with the FFT algorithm. This replacement is justified by sampling theory because the Fourier transforms can be derived from the discrete Fourier transforms with the Nyquis rate without any distortions. We apply this method in calculating pressure induced shifts of H2O lines and obtain more reliable values. By comparing the calculated shifts with those in HITRAN 2008 and by screening both of them with the pair identity and the smooth variation rules, one can conclude many of shift values in HITRAN are not correct.
Electronic correlation effects in a fullerene molecule studied by the variational Monte Carlo method
Krivnov, V.Y. ); Shamovsky, I.L. Chemistry Department, University of West Indies Mona Campus, St. Andrew, Kingston 7 ); Tornau, E.E. ); Rosengren, A. )
1994-10-15
Electron-correlation effects in the fullerene molecule and its ions are investigated in the framework of the Hubbard model. The variational Monte Carlo method and the Gutzwiller wave function are used. Most attention is paid to the case of intermediate interactions, but also the strong coupling limit, where the Hubbard model reduces to the antiferromagnetic Heisenberg model, is considered for the fullerene molecule. In this case we obtain a very low variational ground state energy. Futher, we have calculated the main spin correlation functions in the ground state. Only short-range order is found. The pairing energy of two electrons added to a fullerene molecule or to a fullerene ion is also calculated. Contrary to the results obtained by second-order perturbation theory, pair binding is not found.
Holland, Jason P; Green, Jennifer C
2010-04-15
The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) < 3.5% and epsilon(SF) values close to unity (>0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes. 2009 Wiley Periodicals, Inc.
Volume Functions of Historical Texts and the Amplitude Correlation Principle.
ERIC Educational Resources Information Center
Fomenko, Anatoliy T.; Rachev, Svetlozar T.
1990-01-01
Proposes an empirico-statistical model to differentiate dependent and independent historical texts. Formulates a regard for information principle and an amplitude correlation principle. Experimentally examines and validates the model and both principles using specific historical texts. Includes tables and graphs. Appends further discussion of the…
Park, Gi-Tae; Kim, Mihyun
2016-01-01
[Purpose] The purpose of this study was to investigate the relationship between mobility assessed by the Modified Rivermead Mobility Index and variables associated with physical function in stroke patients. [Subjects and Methods] One hundred stroke patients (35 males and 65 females; age 58.60 ± 13.91 years) participated in this study. Modified Rivermead Mobility Index, muscle strength (manual muscle test), muscle tone (Modified Ashworth Scale), range of motion of lower extremity, sensory function (light touch and proprioception tests), and coordination (heel to shin and lower-extremity motor coordination tests) were assessed. [Results] The Modified Rivermead Mobility Index was correlated with all the physical function variables assessed, except the degree of knee extension. In addition, stepwise linear regression analysis revealed that coordination (heel to shin test) was the explanatory variable closely associated with mobility in stroke patients. [Conclusion] The Modified Rivermead Mobility Index score was significantly correlated with all the physical function variables. Coordination (heel to shin test) was closely related to mobility function. These results may be useful in developing rehabilitation programs for stroke patients. PMID:27630440
NASA Astrophysics Data System (ADS)
Xue, Qian; Wang, Huaxiang; Yang, Chengyi; Cui, Ziqiang
2012-08-01
In a twin-plane electrical capacitance tomography (ECT) system, velocity measurement of two-phase flow is transformed into the time delay estimation problem, while the nongaussianity and nonstationarity of two-phase flow signals have put the validity of the conventional cross-correlation algorithm in jeopardy. To improve the robustness and reliability of flow velocity measurement, an alternative method is proposed based on the dynamical lag correlation exponent and applied to coal ash measurement in a pneumatic pipeline. Different from the cross-correlation method which picks the peak point of the cross-correlation function as the delayed frames between the upstream and downstream signals, the proposed method determines the delayed frames by finding the minimum point of the dynamical lag correlation exponent. The preliminary results of flow velocity measurement indicate that the proposed method is capable of detecting various velocities (8-25 m s-1), which is useful for monitoring and predicting flow instability.
Liu, Jian; Miller, William H.
2008-08-01
The maximum entropy analytic continuation (MEAC) method is used to extend the range of accuracy of the linearized semiclassical initial value representation (LSC-IVR)/classical Wigner approximation for real time correlation functions. The LSC-IVR provides a very effective 'prior' for the MEAC procedure since it is very good for short times, exact for all time and temperature for harmonic potentials (even for correlation functions of nonlinear operators), and becomes exact in the classical high temperature limit. This combined MEAC+LSC/IVR approach is applied here to two highly nonlinear dynamical systems, a pure quartic potential in one dimensional and liquid para-hydrogen at two thermal state points (25K and 14K under nearly zero external pressure). The former example shows the MEAC procedure to be a very significant enhancement of the LSC-IVR, for correlation functions of both linear and nonlinear operators, and especially at low temperature where semiclassical approximations are least accurate. For liquid para-hydrogen, the LSC-IVR is seen already to be excellent at T = 25K, but the MEAC procedure produces a significant correction at the lower temperature (T = 14K). Comparisons are also made to how the MEAC procedure is able to provide corrections for other trajectory-based dynamical approximations when used as priors.
NASA Astrophysics Data System (ADS)
Montoya-Castillo, Andrés; Reichman, David R.
2017-02-01
The ability to efficiently and accurately calculate equilibrium time correlation functions of many-body condensed phase quantum systems is one of the outstanding problems in theoretical chemistry. The Nakajima-Zwanzig-Mori formalism coupled to the self-consistent solution of the memory kernel has recently proven to be highly successful for the computation of nonequilibrium dynamical averages. Here, we extend this formalism to treat symmetrized equilibrium time correlation functions for the spin-boson model. Following the first paper in this series [A. Montoya-Castillo and D. R. Reichman, J. Chem. Phys. 144, 184104 (2016)], we use a Dyson-type expansion of the projected propagator to obtain a self-consistent solution for the memory kernel that requires only the calculation of normally evolved auxiliary kernels. We employ the approximate mean-field Ehrenfest method to demonstrate the feasibility of this approach. Via comparison with numerically exact results for the correlation function Cz z(t ) =Re ⟨σz(0 ) σz(t ) ⟩ , we show that the current scheme affords remarkable boosts in accuracy and efficiency over bare Ehrenfest dynamics. We further explore the sensitivity of the resulting dynamics to the choice of kernel closures and the accuracy of the initial canonical density operator.
Mirage in temporal correlation functions for baryon-baryon interactions in lattice QCD
NASA Astrophysics Data System (ADS)
Iritani, T.; Doi, T.; Aoki, S.; Gongyo, S.; Hatsuda, T.; Ikeda, Y.; Inoue, T.; Ishii, N.; Murano, K.; Nemura, H.; Sasaki, K.
2016-10-01
Single state saturation of the temporal correlation function is a key condition to extract physical observables such as energies and matrix elements of hadrons from lattice QCD simulations. A method commonly employed to check the saturation is to seek for a plateau of the observables for large Euclidean time. Identifying the plateau in the cases having nearby states, however, is non-trivial and one may even be misled by a fake plateau. Such a situation takes place typically for a system with two or more baryons. In this study, we demonstrate explicitly the danger from a possible fake plateau in the temporal correlation functions mainly for two baryons (ΞΞ and N N ), and three and four baryons (3He and 4He) as well, employing (2+1)-flavor lattice QCD at m π = 0 .51GeV on four lattice volumes with L = 2.9, 3.6, 4.3 and 5.8 fm. Caution is required when drawing conclusions about the bound N N , 3 N and 4 N systems based only on the standard plateau fitting of the temporal correlation functions. [Figure not available: see fulltext.
Montoya-Castillo, Andrés; Reichman, David R
2017-02-28
The ability to efficiently and accurately calculate equilibrium time correlation functions of many-body condensed phase quantum systems is one of the outstanding problems in theoretical chemistry. The Nakajima-Zwanzig-Mori formalism coupled to the self-consistent solution of the memory kernel has recently proven to be highly successful for the computation of nonequilibrium dynamical averages. Here, we extend this formalism to treat symmetrized equilibrium time correlation functions for the spin-boson model. Following the first paper in this series [A. Montoya-Castillo and D. R. Reichman, J. Chem. Phys. 144, 184104 (2016)], we use a Dyson-type expansion of the projected propagator to obtain a self-consistent solution for the memory kernel that requires only the calculation of normally evolved auxiliary kernels. We employ the approximate mean-field Ehrenfest method to demonstrate the feasibility of this approach. Via comparison with numerically exact results for the correlation function Czz(t)=Re⟨σz(0)σz(t)⟩, we show that the current scheme affords remarkable boosts in accuracy and efficiency over bare Ehrenfest dynamics. We further explore the sensitivity of the resulting dynamics to the choice of kernel closures and the accuracy of the initial canonical density operator.
The galaxy correlation function as a constraint on galaxy formation physics
NASA Astrophysics Data System (ADS)
van Daalen, Marcel P.; Henriques, Bruno M. B.; Angulo, Raul E.; White, Simon D. M.
2016-05-01
We introduce methods which allow observed galaxy clustering to be used together with observed luminosity or stellar mass functions to constrain the physics of galaxy formation. We show how the projected two-point correlation function of galaxies in a large semi-analytic simulation can be estimated to better than ˜10 per cent using only a very small subsample of the subhalo merger trees. This allows measured correlations to be used as constraints in a Monte Carlo Markov Chain exploration of the astrophysical and cosmological parameter space. An important part of our scheme is an analytic profile which captures the simulated satellite distribution extremely well out to several halo virial radii. This is essential to reproduce the correlation properties of the full simulation at intermediate separations. As a first application, we use low-redshift clustering and abundance measurements to constrain a recent version of the Munich semi-analytic model. The preferred values of most parameters are consistent with those found previously, with significantly improved constraints and somewhat shifted `best' values for parameters that primarily affect spatial distributions. Our methods allow multi-epoch data on galaxy clustering and abundance to be used as joint constraints on galaxy formation. This may lead to significant constraints on cosmological parameters even after marginalizing over galaxy formation physics.
NASA Technical Reports Server (NTRS)
Mcclelland, J.; Silk, J.
1978-01-01
Higher-order correlation functions for the large-scale distribution of galaxies in space are investigated. It is demonstrated that the three-point correlation function observed by Peebles and Groth (1975) is not consistent with a distribution of perturbations that at present are randomly distributed in space. The two-point correlation function is shown to be independent of how the perturbations are distributed spatially, and a model of clustered perturbations is developed which incorporates a nonuniform perturbation distribution and which explains the three-point correlation function. A model with hierarchical perturbations incorporating the same nonuniform distribution is also constructed; it is found that this model also explains the three-point correlation function, but predicts different results for the four-point and higher-order correlation functions than does the model with clustered perturbations. It is suggested that the model of hierarchical perturbations might be explained by the single assumption of having density fluctuations or discrete objects all of the same mass randomly placed at some initial epoch.
NASA Technical Reports Server (NTRS)
Huang, K.-N.
1977-01-01
A computational procedure for calculating correlated wave functions is proposed for three-particle systems interacting through Coulomb forces. Calculations are carried out for the muonic helium atom. Variational wave functions which explicitly contain interparticle coordinates are presented for the ground and excited states. General Hylleraas-type trial functions are used as the basis for the correlated wave functions. Excited-state energies of the muonic helium atom computed from 1- and 35-term wave functions are listed for four states.
NASA Astrophysics Data System (ADS)
Karsanina, M.; Gerke, K.; Vasilyev, R.; Skvortsova, E. B.; Korost, D. V.; Mallants, D.
2013-12-01
It is now well-established that structure of porous or composite media (i.e., distribution of different materials or phases) defines all physical properties, including multi-phase flow and solute transport. To characterize soil structure conventional soil science uses such metrics as grain size distribution, morphology or numerous classifications. However, all these descriptors provide only limited and often qualitative information about structural properties, cannot be used to reconstruct real structure or predict physical properties. With the progress of modern non-destructive analysis tools we can obtain detailed 3D structure information and use it for calculation of any physical property. Such 3D data is a valuable verification dataset to check the usefulness of soil structure description using stochastic measures such as correlation functions. Any potential soil structure descriptor should possess two main features: 1) represent structure in some mathematical way, 2) reconstruction based on this mathematical function alone should be statistically equal to the original structure (e.g., have similar pore size distributions, physical properties, etc.). To check the applicability to soil science, we choose different 2D and 3D segmented soil images and calculated their correlation function. The modified Yeong-Torquato procedure was then used to reconstruct images based on calculated correlation functions. This method was applied to three different soil datasets: 1) a set of 2D thin-sections, 2) 3D images of soils with known hydraulic properties (Ksat and WRC), 3) 3D images of soils and aggregates from the same soil profile, but different genetic horizons. In the first case, we use conventional morphological descriptors in 2D original and reconstructed images (pore size, shapes and orientations) to quantify reconstructions quality. In the second case, we use pore-network models extracted from original and reconstructed 3D images to calculate Ksat, WRC and relative
Goodpaster, Jason D.; Barnes, Taylor A.; Miller, Thomas F.; Manby, Frederick R.
2014-05-14
We analyze the sources of error in quantum embedding calculations in which an active subsystem is treated using wavefunction methods, and the remainder using density functional theory. We show that the embedding potential felt by the electrons in the active subsystem makes only a small contribution to the error of the method, whereas the error in the nonadditive exchange-correlation energy dominates. We test an MP2 correction for this term and demonstrate that the corrected embedding scheme accurately reproduces wavefunction calculations for a series of chemical reactions. Our projector-based embedding method uses localized occupied orbitals to partition the system; as with other local correlation methods, abrupt changes in the character of the localized orbitals along a reaction coordinate can lead to discontinuities in the embedded energy, but we show that these discontinuities are small and can be systematically reduced by increasing the size of the active region. Convergence of reaction energies with respect to the size of the active subsystem is shown to be rapid for all cases where the density functional treatment is able to capture the polarization of the environment, even in conjugated systems, and even when the partition cuts across a double bond.
Giger, Maryellen L.; Chen, Chin-Tu; Armato, Samuel; Doi, Kunio
1999-10-26
A method and system for the computerized registration of radionuclide images with radiographic images, including generating image data from radiographic and radionuclide images of the thorax. Techniques include contouring the lung regions in each type of chest image, scaling and registration of the contours based on location of lung apices, and superimposition after appropriate shifting of the images. Specific applications are given for the automated registration of radionuclide lungs scans with chest radiographs. The method in the example given yields a system that spatially registers and correlates digitized chest radiographs with V/Q scans in order to correlate V/Q functional information with the greater structural detail of chest radiographs. Final output could be the computer-determined contours from each type of image superimposed on any of the original images, or superimposition of the radionuclide image data, which contains high activity, onto the radiographic chest image.
Cai, Yangjian; Chen, Yahong; Wang, Fei
2014-09-01
Partially coherent beams with nonconventional correlation functions have displayed many extraordinary properties, such as self-focusing and self-splitting, which are totally different from those of partially coherent beams with conventional Gaussian correlated Schell-model functions and are useful in many applications, such as optical trapping, free-space optical communications, and material thermal processing. In this paper, we present a review of recent developments on generation and propagation of partially coherent beams with nonconventional correlation functions.
A nonlinear correlation function for selecting the delay time in dynamical reconstructions
NASA Astrophysics Data System (ADS)
Aguirre, Luis Antonio
1995-02-01
Numerical results discussed in this paper suggest that a function which detects nonlinear correlations in time series usually indicates shorter correlation times than the linear autocorrelation function which is often used for this purpose. The nonlinear correlation function can also detect changes in the data which cannot be distinguished by the linear counterpart. This affects a number of approaches for the selection of the delay time used in the reconstruction of nonlinear dynamics from a single time series based on time delay coordinates.
Structure of the correlation function at the accumulation points of the logistic map
NASA Astrophysics Data System (ADS)
Karamanos, K.; Mistakidis, I. S.; Mistakidis, S. I.
2017-03-01
The correlation function of the trajectory exactly at the Feigenbaum point of the logistic map is investigated and checked by numerical experiments. Taking advantage of recent closed analytical results on the symbol-to-symbol correlation function of the generating partition, we are in position to justify the deep algorithmic structure of the correlation function apart from numerical constants. A generalization is given for arbitrary $m\\cdot 2^{\\infty}$ Feigenbaum attractors.
Development of Colle-Salvetti type electron-nucleus correlation functional for MC-DFT
Udagawa, Taro; Tsuneda, Takao; Tachikawa, Masanori
2015-12-31
A Colle-Salvetti type electron-nucleus correlation functional for multicomponent density-functional theory is proposed. We demonstrate that our correlation functional quantitatively reproduces the quantum nuclear effects of protons; the mean absolute deviation value is 2.8 millihartrees for the optimized structure of hydrogen-containing molecules. We also show other practical calculations with our new electron-deuteron and electron-triton correlation functionals. Since this functional is derived without any unphysical assumption, the strategy taken in this development will be a promising recipe to make new functionals for the potentials of other particles’ interactions.
Development of Colle-Salvetti type electron-nucleus correlation functional for MC_DFT
NASA Astrophysics Data System (ADS)
Udagawa, Taro; Tsuneda, Takao; Tachikawa, Masanori
2015-12-01
A Colle-Salvetti type electron-nucleus correlation functional for multicomponent density-functional theory is proposed. We demonstrate that our correlation functional quantitatively reproduces the quantum nuclear effects of protons; the mean absolute deviation value is 2.8 millihartrees for the optimized structure of hydrogen-containing molecules. We also show other practical calculations with our new electron-deuteron and electron-triton correlation functionals. Since this functional is derived without any unphysical assumption, the strategy taken in this development will be a promising recipe to make new functionals for the potentials of other particles' interactions.
Modified Interior Distance Functions (Theory and Methods)
NASA Technical Reports Server (NTRS)
Polyak, Roman A.
1995-01-01
In this paper we introduced and developed the theory of Modified Interior Distance Functions (MIDF's). The MIDF is a Classical Lagrangian (CL) for a constrained optimization problem which is equivalent to the initial one and can be obtained from the latter by monotone transformation both the objective function and constraints. In contrast to the Interior Distance Functions (IDF's), which played a fundamental role in Interior Point Methods (IPM's), the MIDF's are defined on an extended feasible set and along with center, have two extra tools, which control the computational process: the barrier parameter and the vector of Lagrange multipliers. The extra tools allow to attach to the MEDF's very important properties of Augmented Lagrangeans. One can consider the MIDFs as Interior Augmented Lagrangeans. It makes MIDF's similar in spirit to Modified Barrier Functions (MBF's), although there is a fundamental difference between them both in theory and methods. Based on MIDF's theory, Modified Center Methods (MCM's) have been developed and analyzed. The MCM's find an unconstrained minimizer in primal space and update the Lagrange multipliers, while both the center and the barrier parameter can be fixed or updated at each step. The MCM's convergence was investigated, and their rate of convergence was estimated. The extension of the feasible set and the special role of the Lagrange multipliers allow to develop MCM's, which produce, in case of nondegenerate constrained optimization, a primal and dual sequences that converge to the primal-dual solutions with linear rate, even when both the center and the barrier parameter are fixed. Moreover, every Lagrange multipliers update shrinks the distance to the primal dual solution by a factor 0 less than gamma less than 1 which can be made as small as one wants by choosing a fixed interior point as a 'center' and a fixed but large enough barrier parameter. The numericai realization of MCM leads to the Newton MCM (NMCM). The
Veatch, Sarah L.; Machta, Benjamin B.; Shelby, Sarah A.; Chiang, Ethan N.; Holowka, David A.; Baird, Barbara A.
2012-01-01
We present an analytical method using correlation functions to quantify clustering in super-resolution fluorescence localization images and electron microscopy images of static surfaces in two dimensions. We use this method to quantify how over-counting of labeled molecules contributes to apparent self-clustering and to calculate the effective lateral resolution of an image. This treatment applies to distributions of proteins and lipids in cell membranes, where there is significant interest in using electron microscopy and super-resolution fluorescence localization techniques to probe membrane heterogeneity. When images are quantified using pair auto-correlation functions, the magnitude of apparent clustering arising from over-counting varies inversely with the surface density of labeled molecules and does not depend on the number of times an average molecule is counted. In contrast, we demonstrate that over-counting does not give rise to apparent co-clustering in double label experiments when pair cross-correlation functions are measured. We apply our analytical method to quantify the distribution of the IgE receptor (FcεRI) on the plasma membranes of chemically fixed RBL-2H3 mast cells from images acquired using stochastic optical reconstruction microscopy (STORM/dSTORM) and scanning electron microscopy (SEM). We find that apparent clustering of FcεRI-bound IgE is dominated by over-counting labels on individual complexes when IgE is directly conjugated to organic fluorophores. We verify this observation by measuring pair cross-correlation functions between two distinguishably labeled pools of IgE-FcεRI on the cell surface using both imaging methods. After correcting for over-counting, we observe weak but significant self-clustering of IgE-FcεRI in fluorescence localization measurements, and no residual self-clustering as detected with SEM. We also apply this method to quantify IgE-FcεRI redistribution after deliberate clustering by crosslinking with two
Multiconfiguration Pair-Density Functional Theory: A New Way To Treat Strongly Correlated Systems.
Gagliardi, Laura; Truhlar, Donald G; Li Manni, Giovanni; Carlson, Rebecca K; Hoyer, Chad E; Bao, Junwei Lucas
2017-01-17
The electronic energy of a system provides the Born-Oppenheimer potential energy for internuclear motion and thus determines molecular structure and spectra, bond energies, conformational energies, reaction barrier heights, and vibrationa