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1

On MEG forward modelling using multipolar expansions  

Energy Technology Data Exchange (ETDEWEB)

Magnetoencephalography (MEG) is a non-invasive functional imaging modality based on the measurement of the external magnetic field produced by neural current sources within the brain. The reconstruction of the underlying sources is a severely ill-posed inverse problem typically tackled using either low-dimensional parametric source models, such as an equivalent current dipole (ECD), or high-dimensional minimum-norm imaging techniques. The inability of the ECD to properly represent non-focal sources and the over-smoothed solutions obtained by minimum-norm methods underline the need for an alternative approach. Multipole expansion methods have the advantages of the parametric approach while at the same time adequately describing sources with significant spatial extent and arbitrary activation patterns. In this paper we first present a comparative review of spherical harmonic and Cartesian multipole expansion methods that can be used in MEG. The equations are given for the general case of arbitrary conductors and realistic sensor configurations and also for the special cases of spherically symmetric conductors and radially oriented sensors. We then report the results of computer simulations used to investigate the ability of a first-order multipole model (dipole and quadrupole) to represent spatially extended sources, which are simulated by 2D and 3D clusters of elemental dipoles. The overall field of a cluster is analysed using singular value decomposition and compared to the unit fields of a multipole, centred in the middle of the cluster, using subspace correlation metrics. Our results demonstrate the superior utility of the multipolar source model over ECD models in providing source representations of extended regions of activity. (author)

Jerbi, K. [Signal and Image Processing Institute, University of Southern California, Los Angeles, CA (United States); Cognitive Neuroscience and Brain Imaging Laboratory, Hopital de la Salpetiere, CNRS, Paris (France); Mosher, J.C. [Los Alamos National Laboratory, Los Alamos, NM (United States); Baillet, S. [Cognitive Neuroscience and Brain Imaging Laboratory, Hopital de la Salpetiere, CNRS, Paris (France); Leahy, R.M. [Signal and Image Processing Institute, University of Southern California, Los Angeles, CA (United States)]. E-mail: leahy@sipi.usc.edu

2002-02-21

2

Magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

Although magnetoencephalography (MEG) may not be familiar to many pediatric radiologists, it is an increasingly available neuroimaging technique both for evaluating normal and abnormal intracranial neural activity and for functional mapping. By providing spatial, temporal, and time-frequency spectral information, MEG affords patients with epilepsy, intracranial neoplasia, and vascular malformations an opportunity for a sensitive and accurate non-invasive preoperative evaluation. This technique can optimize selection of surgical candidates as well as increase confidence in preoperative counseling and prognosis. Research applications that appear promising for near-future clinical translation include the evaluation of children with autism spectrum disorder, traumatic brain injury, and schizophrenia. (orig.)

Schwartz, Erin Simon [Children' s Hospital of Philadelphia, Lurie Family Foundations MEG Imaging Center, Department of Radiology, Philadelphia, PA (United States); Children' s Hospital of Philadelphia, Department of Radiology, Philadelphia, PA (United States); Edgar, J.C.; Gaetz, William C.; Roberts, Timothy P.L. [Children' s Hospital of Philadelphia, Lurie Family Foundations MEG Imaging Center, Department of Radiology, Philadelphia, PA (United States)

2010-01-15

3

Magnetoencephalography  

International Nuclear Information System (INIS)

[en] Although magnetoencephalography (MEG) may not be familiar to many pediatric radiologists, it is an increasingly available neuroimaging technique both for evaluating normal and abnormal intracranial neural activity and for functional mapping. By providing spatial, temporal, and time-frequency spectral information, MEG affords patients with epilepsy, intracranial neoplasia, and vascular malformations an opportunity for a sensitive and accurate non-invasive preoperative evaluation. This technique can optimize selection of surgical candidates as well as increase confidence in preoperative counseling and prognosis. Research applications that appear promising for near-future clinical translation include the evaluation of children with autism spectrum disorder, traumatic brain injury, and schizophrenia. (orig.)

2010-01-01

4

A wind-shell interaction model for multipolar planetary nebulae  

CERN Multimedia

We explore the formation of multipolar structures in planetary and pre-planetary nebulae from the interaction of a fast post-AGB wind with a highly inhomogeneous and filamentary shell structure assumed to form during the final phase of the high density wind. The simulations were performed with a new hydrodynamics code integrated in the interactive framework of the astrophysical modeling package SHAPE. In contrast to conventional astrophysical hydrodynamics software, the new code does not require any programming intervention by the user for setting up or controlling the code. Visualization and analysis of the simulation data has been done in SHAPE without external software. The key conclusion from the simulations is that secondary lobes in planetary nebulae, such as Hubble 5 and K3-17, can be formed through the interaction of a fast low-density wind with a complex high density environment, such as a filamentary circumstellar shell. The more complicated alternative explanation of intermittent collimated outflow...

Steffen, W; Esquivel, A; Garcia-Segura, G; Garcia-Diaz, Ma T; Lopez, J A; Magnor, M

2013-01-01

5

Ellipsoidal head model for fetal magnetoencephalography: forward and inverse solutions  

International Nuclear Information System (INIS)

Fetal magnetoencephalography (fMEG) is a non-invasive technique where measurements of the magnetic field outside the maternal abdomen are used to infer the source location and signals of the fetus' neural activity. There are a number of aspects related to fMEG modelling that must be addressed, such as the conductor volume, fetal position and orientation, gestation period, etc. We propose a solution to the forward problem of fMEG based on an ellipsoidal head geometry. This model has the advantage of highlighting special characteristics of the field that are inherent to the anisotropy of the human head, such as the spread and orientation of the field in relationship with the localization and position of the fetal head. Our forward solution is presented in the form of a kernel matrix that facilitates the solution of the inverse problem through decoupling of the dipole localization parameters from the source signals. Then, we use this model and the maximum likelihood technique to solve the inverse problem assuming the availability of measurements from multiple trials. The applicability and performance of our methods are illustrated through numerical examples based on a real 151-channel SQUID fMEG measurement system (SARA). SARA is an MEG system especially designed for fetal assessment and is currently used for heart and brain studies. Finally, since our model requires knowledge of the best-fitting ellipsoid's centre location and semiaxes lengths, we propose a method for estimating these parameters through a least-squares fit on anatomical information obtained from three-dimensional ultrasound images

2005-05-07

6

Description of. gamma. -transition multipolarities mixing in Pd and Cd nuclei by interacting boson model  

Energy Technology Data Exchange (ETDEWEB)

To check a possible use of one of the variants of the interacting boron model (IBM-1) for describing the excited states and ..gamma..-transitions in the sup(104, 106)Pd, sup(106+ 110)Cd nuclei, the multipolarity mixinq parameter delta(E2/Mt1) for ..gamma.. transitions between the levels in the 511.8-3239.5 keV range is calculated. The IBM-1 parameter values used for calculation and experimental values of energies of excited levels and delta parameters are tabulated. Perfect agreement between the calculation and experimental data is obtained for the /sup 110/Cd nucleus. The considered IBM-1 satisfactorily describes the ..gamma.. transition multipolarities mixing in the investigated nuclei.

Zykov, Yu.Yu.; Sychikov, G.I.

1983-11-01

7

Error bounds in MEG (Magnetoencephalography) multipole localization  

Energy Technology Data Exchange (ETDEWEB)

Magnetoencephalography (MEG) is a non-invasive method that enables the measurement of the magnetic field produced by neural current sources within the human brain. Unfortunately, MEG source estimation is a severely ill-posed inverse problem. The two major approaches used to tackle this problem are 'imaging' and 'model-based' methods. The first class of methods relies on a tessellation of the cortex, assigning an elemental current source to each area element and solving the linear inverse problem. Accurate tessellations lead to a highly underdetermined problem, and regularized linear methods lead to very smooth current distributions. An alternative approach widely used is a parametric representation of the neural source. Such model-based methods include the classic equivalent current dipole (ECD) and its multiple current dipole extension [1]. The definition of such models has been based on the assumption that the underlying sources are focal and small in number. An alternative approach reviewed in [4], [5] is to extend the parametric source representations within the model-based framework to allow for distributed sources. The multipolar expansion of the magnetic field about the centroid of a distributed source readily offers an elegant parametric model, which collapses to a dipole model in the limiting case and includes higher order terms in the case of a spatially extended source. While multipolar expansions have been applied to magnetocardiography (MCG) source modeling [2], their use in MEG has been restricted to simplified models [7]. The physiological interpretation of these higher-order components in non-intuitive, therefore limiting their application in this community (cf. [8]). In this study we investigate both the applicability of dipolar and multipolar models to cortical patches, and the accuracy with which we can locate these sources. We use a combination of Monte Carlo analyses and Cramer-Rao lower bounds (CRLBs), paralleling the work in [3] for the ECD. Results are presented for both point sources and cortical patches.

Jerbi, K. (Karim); Mosher, J. C. (John C.); Baillet, S. (Sylvain); Leahy, R. M. (Richard M.)

2001-01-01

8

A continuum solvent model of the multipolar dispersion solvation energy.  

UK PubMed Central (United Kingdom)

The dispersion energy is an important contribution to the total solvation energies of ions and neutral molecules. Here, we present a new continuum model calculation of these energies, based on macroscopic quantum electrodynamics. The model uses the frequency dependent multipole polarizabilities of molecules in order to accurately calculate the dispersion interaction of a solute particle with surrounding water molecules. It includes the dipole, quadrupole, and octupole moment contributions. The water is modeled via a bulk dielectric susceptibility with a spherical cavity occupied by the solute. The model invokes damping functions to account for solute-solvent wave function overlap. The assumptions made are very similar to those used in the Born model. This provides consistency and additivity of electrostatic and dispersion (quantum mechanical) interactions. The energy increases in magnitude with cation size, but decreases slightly with size for the highly polarizable anions. The higher order multipole moments are essential, making up more than 50% of the dispersion solvation energy of the fluoride ion. This method provides an accurate and simple way of calculating the notoriously problematic dispersion contribution to the solvation energy. The result establishes the importance of using accurate calculations of the dispersion energy for the modeling of solvation.

Duignan TT; Parsons DF; Ninham BW

2013-08-01

9

Hybrid MEG (Magnetoencephalography) source characterization by cortical remapping and imaging of parametric source models  

Energy Technology Data Exchange (ETDEWEB)

Reliable estimation of the local spatial extent of neural activity is a key to the quantitative analysis of MEG sources across subjects and conditions. In association with an understanding of the temporal dynamics among multiple areas, this would represent a major advance in electrophysiological source imaging. Parametric current dipole approaches to MEG (and EEG) source localization can rapidly generate a physical model of neural current generators using a limited number of parameters. However, physiological interpretation of these models is often difficult, especially in terms of the spatial extent of the true cortical activity. In new approaches using multipolar source models [3, 5], similar problems remain in the analysis of the higher-order source moments as parameters of cortical extent. Image-based approaches to the inverse problem provide a direct estimate of cortical current generators, but computationally expensive nonlinear methods are required to produce focal sources [1,4]. Recent efforts describe how a cortical patch can be grown until a best fit to the data is reached in the least-squares sense [6], but computational considerations necessitate that the growth be seeded in predefined regions of interest. In a previous study [2], a source obtained using a parametric model was remapped onto the cortex by growing a patch of cortical dipoles in the vicinity of the parametric source until the forward MEG or EEG fields of the parametric and cortical sources matched. The source models were dipoles and first-order multipoles. We propose to combine the parametric and imaging methods for MEG source characterization to take advantage of (i) the parsimonious and computationally efficient nature of parametric source localization methods and (ii) the anatomical and physiological consistency of imaging techniques that use relevant a priori information. By performing the cortical remapping imaging step by matching the multipole expansions of the original parametric source and the equivalent cortical patch, rather than their forward fields, we achieve significant reductions in computational complexity.

Baillet, S. (Sylvain); Mosher, J. C. (John C.); Jerbi, K. (Karim); Leahy, R. M. (Richard M.)

2001-01-01

10

Development of a generative model of magnetoencephalography noise that enables brain signal extraction from single-epoch data.  

UK PubMed Central (United Kingdom)

We presented a method of rejecting sensor-specific and environmental noise during magnetoencephalography (MEG) measurement that enables the extraction of brain signals from single-epoch data. The method assumes a parametric generative model of MEG data. The model's optimal parameters were determined from single-epoch data, and noise reduction was performed by the decomposition of data within the optimal model. We confirmed our method's validity through multiple experiments. Moreover, we compared our method's performance with that of several previous noise-reduction methods. Finally, we confirmed that the proposed method followed by spatial filtering reduced noise more efficiently.

Uno Y; Amano K; Takeda T

2013-08-01

11

Development of a generative model of magnetoencephalography noise that enables brain signal extraction from single-epoch data.  

Science.gov (United States)

We presented a method of rejecting sensor-specific and environmental noise during magnetoencephalography (MEG) measurement that enables the extraction of brain signals from single-epoch data. The method assumes a parametric generative model of MEG data. The model's optimal parameters were determined from single-epoch data, and noise reduction was performed by the decomposition of data within the optimal model. We confirmed our method's validity through multiple experiments. Moreover, we compared our method's performance with that of several previous noise-reduction methods. Finally, we confirmed that the proposed method followed by spatial filtering reduced noise more efficiently. PMID:23657832

Uno, Yutaka; Amano, Kaoru; Takeda, Tsunehiro

2013-05-09

12

Efficiency analysis of bipolar and multipolar radiofrequency ablation in an in vivo porcine kidney model using three-dimensional reconstruction of histologic section series.  

UK PubMed Central (United Kingdom)

BACKGROUND AND PURPOSE: Radiofrequency ablation (RFA) was established for minimally invasive treatment of small kidney tumors in multimorbid patients. Bipolar and multipolar RFA may allow the treatment of larger tumors. Safe tumor coagulation depends on total energy supplied and proper electrode placing. To investigate the influence of energy on ablation size and shape in intact kidneys, we used cooled bipolar and multipolar RFA in an in vivo pig model. MATERIALS AND METHODS: Twenty-five male pigs were treated with percutaneous bipolar (one electrode) or multipolar (two electrodes) RFA with various energy transfer under laparoscopic visual control. The animals were sacrificed 4 to 5 hours after RFA. Volume and shape of the coagulation zone was analyzed by three-dimensional reconstruction of hematoxylin and eosin and diaminobenzidine stained paraffin serial sections. Heat-induced cellular activation was addressed by immunohistologic detection of apoptosis marker proteins heat shock protein 70 (Hsp70) and caspase-3 (Casp3). RESULTS: Multipolar RFA led to significant larger tissue ablation than bipolar RFA. Increasing energy, however, did not result in significant enlargement of the coagulation volume. Shape control was better in bipolar RFA. Hsp70 and activated Casp3 immunoreactivity were increased close to the central coagulation zone and occasionally in the caliceal system. CONCLUSIONS: RFA causes minimal tissue damage beyond the primary coagulation zone, indicating that RFA is a safe, minimally invasive method for treatment of renal tumors. The ablation of larger volumes necessitates further improvement of multipolar RFA. These findings may be of general interest, because treatment failure correlates with mass size in monopolar RFA and cryoablative techniques as well.

Neuhaus J; Blachut L; Rabenalt R; Stein T; König F; Wehner M; Liatsikos E; Stolzenburg JU

2011-05-01

13

Accuracy and tractability of a kriging model of intramolecular polarizable multipolar electrostatics and its application to histidine.  

UK PubMed Central (United Kingdom)

We propose a generic method to model polarization in the context of high-rank multipolar electrostatics. This method involves the machine learning technique kriging, here used to capture the response of an atomic multipole moment of a given atom to a change in the positions of the atoms surrounding this atom. The atoms are malleable boxes with sharp boundaries, they do not overlap and exhaust space. The method is applied to histidine where it is able to predict atomic multipole moments (up to hexadecapole) for unseen configurations, after training on 600 geometries distorted using normal modes of each of its 24 local energy minima at B3LYP/apc-1 level. The quality of the predictions is assessed by calculating the Coulomb energy between an atom for which the moments have been predicted and the surrounding atoms (having exact moments). Only interactions between atoms separated by three or more bonds ("1, 4 and higher" interactions) are included in this energy error. This energy is compared with that of a central atom with exact multipole moments interacting with the same environment. The resulting energy discrepancies are summed for 328 atom-atom interactions, for each of the 29 atoms of histidine being a central atom in turn. For 80% of the 539 test configurations (outside the training set), this summed energy deviates by less than 1 kcal mol(-1).

Kandathil SM; Fletcher TL; Yuan Y; Knowles J; Popelier PL

2013-08-01

14

Multipolar proportional chambers  

International Nuclear Information System (INIS)

[en] The parameters of the multipolar proportional chamber, which is the new track detector used in SFINKS setup experiments, are presented. The characteristics of the chambers with different gaps between the anode wires are also investigated. 3 refs.; 7 figs.; 1 tab

1991-01-01

15

Searching for the best model: ambiguity of inverse solutions and application to fetal magnetoencephalography  

International Nuclear Information System (INIS)

Fetal brain signals produce weak magnetic fields at the maternal abdominal surface. In the presence of much stronger interference these weak fetal fields are often nearly indistinguishable from noise. Our initial objective was to validate these weak fetal brain fields by demonstrating that they agree with the electromagnetic model of the fetal brain. The fetal brain model is often not known and we have attempted to fit the data to not only the brain source position, orientation and magnitude, but also to the brain model position. Simulation tests of this extended model search on fetal MEG recordings using dipole fit and beamformers revealed a region of ambiguity. The region of ambiguity consists of a family of models which are not distinguishable in the presence of noise, and which exhibit large and comparable SNR when beamformers are used. Unlike the uncertainty of a dipole fit with known model plus noise, this extended ambiguity region yields nearly identical forward solutions, and is only weakly dependent on noise. The ambiguity region is located in a plane defined by the source position, orientation, and the true model centre, and will have a diameter approximately 0.67 of the modelled fetal head diameter. Existence of the ambiguity region allows us to only state that the fetal brain fields do not contradict the electromagnetic model; we can associate them with a family of models belonging to the ambiguity region, but not with any specific model. In addition to providing a level of confidence in the fetal brain signals, the ambiguity region knowledge in combination with beamformers allows detection of undistorted temporal waveforms with improved signal-to-noise ratio, even though the source position cannot be uniquely determined.

2007-02-07

16

A DETAILED SPATIOKINEMATIC MODEL OF THE CONICAL OUTFLOW OF THE MULTIPOLAR PLANETARY NEBULA NGC 7026  

Energy Technology Data Exchange (ETDEWEB)

We present extensive, long-slit, high-resolution coverage of the complex planetary nebula (PN) NGC 7026. We acquired 10 spectra using the Manchester Echelle Spectrometer at San Pedro Martir Observatory in Baja California, Mexico, and each shows exquisite detail, revealing the intricate structure of this object. Incorporating these spectra into the three-dimensional visualization and kinematic program SHAPE and using Hubble Space Telescope images of NGC 7026, we have produced a detailed structural and kinematic model of this PN. NGC 7026 exhibits remarkable symmetry consisting of three lobe pairs and four sets of knots, all symmetrical about the nucleus and displaying a conical outflow. Comparing the three-dimensional structure of this nebula to recent XMM-Newton X-ray observations, we investigate the extended X-ray emission in relation to the nebular structure. We find that the X-ray emission, while confined to the closed, northern lobes of this PN, shows an abrupt termination in the middle of the southeast lobe, which our long slit data show to be open. This is where the shocked fast wind seems to be escaping the interior of the nebula and the X-ray emission rapidly cools in this region.

Clark, D. M.; Lopez, J. A.; Steffen, W.; Richer, M. G., E-mail: dmclark@astro.unam.mx [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Campus Ensenada, Ensenada, Baja California, CA 22860 (United States)

2013-03-15

17

A Detailed Spatiokinematic Model of the Conical Outflow of the Multipolar Planetary Nebula, NGC 7026  

CERN Document Server

We present an extensive, long-slit, high-resolution coverage of the complex planetary nebula (PN), NGC 7026. We acquired ten spectra using the Manchester Echelle Spectrometer at San Pedro Martir Observatory in Baja California, Mexico, and each shows exquisite detail, revealing the intricate structure of this object. Incorporating these spectra into the 3-dimensional visualization and kinematic program, SHAPE, and using HST images of NGC 7026, we have produced a detailed structural and kinematic model of this PN. NGC 7026 exhibits remarkable symmetry consisting of three lobe-pairs and four sets of knots, all symmetrical about the nucleus and displaying a conical outflow. Comparing the 3-D structure of this nebula to recent, XMM-Newton X-ray observations, we investigate the extended X-ray emission in relation to the nebular structure. We find that the X-ray emission, while confined to the closed, northern lobes of this PN, shows an abrupt termination in the middle of the SE lobe, which our long slit data shows ...

Clark, D M; Steffen, W; Richer, M G

2012-01-01

18

Contributions to the application of the transferability principle and the multipolar modeling of H atoms: electron-density study of L-histidinium dihydrogen orthophosphate orthophosphoric acid. I.  

UK PubMed Central (United Kingdom)

The electron density of L-histidinium dihydrogen orthophosphate orthophosphoric acid has been determined from X-ray and neutron diffraction data at low temperature (120 K). Topological analysis of the electron density has been used to analyse the effect of the multipolar refinement strategy on the electron-density model in the hydrogen-bonding regions. The electron density at low temperature has also been used to acquire high-quality experimental thermal parameters at room temperature using the transferability principle. Molecular vibrations, TLS and normal mode analysis are discussed and studied at both temperatures.

Mata I; Espinosa E; Molins E; Veintemillas S; Maniukiewicz W; Lecomte C; Cousson A; Paulus W

2006-09-01

19

Clinical magnetoencephalography for neurosurgery.  

UK PubMed Central (United Kingdom)

Noninvasive neuroimaging aids in surgical planning and in counseling patients about possible risks of surgery. Magnetoencephalography (MEG) performs the most common types of surgical planning that the neurosurgeon faces, including localization of epileptic discharges, determination of the hemispheric dominance of verbal processing, and the ability to locate eloquent cortex. MEG is most useful when it is combined with structural imaging, most commonly with structural magnetic resonance (MR) imaging and MR diffusion imaging. This article reviews the history of clinical MEG, introduces the basic concepts about the biophysics of MEG, and outlines the basic neurosurgical applications of MEG.

Stufflebeam SM

2011-04-01

20

Multipolar ECR plasma characterization  

International Nuclear Information System (INIS)

There has been considerable interest in the development of intense negative ion sources for use in high-energy neutral beam heating and diagnostics systems for nuclear fusion plasmas. As it was shown by one of the authors overdense ECR plasmas seem to be an appropriate medium to produce H-ions at high rate. Overdense plasmas are a result of the microwave(?wave) power absorption in ECR plasma heating and magnetic field confinement. Our aim is to characterize the hydrogen plasma produced in a 2.45 GHz multipolar negative ion ECR source (ECRIN)

1995-08-04

 
 
 
 
21

Multipolar ECR plasma characterization  

Energy Technology Data Exchange (ETDEWEB)

There has been considerable interest in the development of intense negative ion sources for use in high-energy neutral beam heating and diagnostics systems for nuclear fusion plasmas. As it was shown by one of the authors overdense ECR plasmas seem to be an appropriate medium to produce H-ions at high rate. Overdense plasmas are a result of the microwave({mu}wave) power absorption in ECR plasma heating and magnetic field confinement. Our aim is to characterize the hydrogen plasma produced in a 2.45 GHz multipolar negative ion ECR source (ECRIN).

Ciubotariu, C.I. [Technical Univ., Iasi (Romania); Golovanivsky, K.S.; Bacal, M. [Laboratoire de Physique des Milieux Ionises Ecole Polytechnique, Palaiseau (France)

1995-12-31

22

Interictal networks in Magnetoencephalography.  

UK PubMed Central (United Kingdom)

Epileptic networks involve complex relationships across several brain areas. Such networks have been shown on intracerebral EEG (stereotaxic EEG, SEEG), an invasive technique. Magnetoencephalography (MEG) is a noninvasive tool, which was recently proven to be efficient for localizing the generators of epileptiform discharges. However, despite the importance of characterizing non-invasively network aspects in partial epilepsies, only few studies have attempted to retrieve fine spatiotemporal dynamics of interictal discharges with MEG. Our goal was to assess the relevance of magnetoencephalography for detecting and characterizing the brain networks involved in interictal epileptic discharges. We propose here a semi-automatic method based on independent component analysis (ICA) and on co-occurrence of events across components. The method was evaluated in a series of seven patients by comparing its results with networks identified in SEEG. On both MEG and SEEG, we found that interictal discharges can involve remote regions which are acting in synchrony. More regions were identified in SEEG (38 in total) than in MEG (20). All MEG regions were confirmed by SEEG when an electrode was present in the vicinity. In all patients, at least one region could be identified as leading according to our criteria. A majority (71%) of MEG leaders were confirmed by SEEG. We have therefore shown that MEG measurements can extract a significant proportion of the networks visible in SEEG. This suggests that MEG can be a useful tool for defining noninvasively interictal epileptic networks, in terms of regions and patterns of connectivity, in search for a "primary irritative zone." Hum Brain Mapp, 2013. © 2013 Wiley Periodicals, Inc.

Malinowska U; Badier JM; Gavaret M; Bartolomei F; Chauvel P; Bénar CG

2013-09-01

23

Magnetoencephalography: a tool for functional brain imaging.  

UK PubMed Central (United Kingdom)

At present, one of the most promising windows to the functional organization of the human brain is magnetoencephalography (MEG). By mapping the magnetic field distribution outside the head the sites of neural events can be located with an accuracy of a few millimeters and the temporal evolution of the activation can be traced with a millisecond resolution. This paper reviews some forward field calculation approaches suitable for the interpretation of the brain's electromagnetic signals. Inverse modelling with multiple dipoles is described in detail. An example of the analysis of the somatosensory evoked-responses illustrates the potential of multiple signal classification (MUSIC) algorithm in finding optimal dipole positions.

Hämäläinen MS

1992-01-01

24

On the complementarity of electroencephalography and magnetoencephalography  

Science.gov (United States)

We show that for the spherical model of the brain, the part of the neuronal current that generates the electric potential (and therefore the electric field) lives in the orthogonal complement of the part of the current that generates the magnetic potential (and therefore the magnetic induction field). This means that for a continuously distributed neuronal current, information missing in the electroencephalographic data is precisely information that is available in the magnetoencephalographic data, and vice versa. In this way, the notion of complementarity between the imaging techniques of electroencephalography and magnetoencephalography is mathematically defined. Using this notion of complementarity and expanding the neuronal current in terms of vector spherical harmonics, which by definition provide the angular dependence of the current, we show that if the electric and the magnetic potentials in the exterior of the head are given, then we can determine certain moments of the functions which provide the radial dependence of the neuronal current. In addition to the above notion of complementarity, we also present a notion of unification of electroencephalography and magnetoencephalography by showing that they are governed respectively by the scalar and the vector invariants of a unified dyadic field describing electromagnetoencephalography.

Dassios, G.; Fokas, A. S.; Hadjiloizi, D.

2007-12-01

25

Multipolar analysis of spinning binaries  

International Nuclear Information System (INIS)

We present a preliminary study of the multipolar structure of gravitational radiation from spinning black hole binary mergers. We consider three different spinning binary configurations: (1) one 'hang-up' run, where the black holes have equal masses and large spins initially aligned with the orbital angular momentum; (2) seven 'spin-flip' runs, where the holes have a mass ratio q ? M1/M2 = 4, the spins are anti-aligned with the orbital angular momentum, and the initial Kerr parameters of the holes j1 j2 = ji (where j ? J/M2) are fine-tuned to produce a Schwarzschild remnant after merger; (3) three 'super-kick' runs where the mass ratio q = 1, 2, 4 and the spins of the two holes are initially located on the orbital plane, pointing in opposite directions. For all of these simulations we compute the multipolar energy distribution and the Kerr parameter of the final hole. For the hang-up run, we show that including leading-order spin-orbit and spin-spin terms in a multipolar decomposition of the post-Newtonian waveforms improves agreement with the numerical simulation.

2008-06-07

26

Direct reconstruction algorithm of current dipoles for vector magnetoencephalography and electroencephalography  

International Nuclear Information System (INIS)

[en] This paper presents a novel algorithm to reconstruct parameters of a sufficient number of current dipoles that describe data (equivalent current dipoles, ECDs, hereafter) from radial/vector magnetoencephalography (MEG) with and without electroencephalography (EEG). We assume a three-compartment head model and arbitrary surfaces on which the MEG sensors and EEG electrodes are placed. Via the multipole expansion of the magnetic field, we obtain algebraic equations relating the dipole parameters to the vector MEG/EEG data. By solving them directly, without providing initial parameter guesses and computing forward solutions iteratively, the dipole positions and moments projected onto the xy-plane (equatorial plane) are reconstructed from a single time shot of the data. In addition, when the head layers and the sensor surfaces are spherically symmetric, we show that the required data reduce to radial MEG only. This clarifies the advantage of vector MEG/EEG measurements and algorithms for a generally-shaped head and sensor surfaces. In the numerical simulations, the centroids of the patch sources are well localized using vector/radial MEG measured on the upper hemisphere. By assuming the model order to be larger than the actual dipole number, the resultant spurious dipole is shown to have a much smaller strength magnetic moment (about 0.05 times smaller when the SNR = 16 dB), so that the number of ECDs is reasonably estimated. We consider that our direct method with greatly reduced computational cost can also be used to provide a good initial guess for conventional dipolar/multipolar fitting algorithms

2007-07-07

27

Direct reconstruction algorithm of current dipoles for vector magnetoencephalography and electroencephalography  

Energy Technology Data Exchange (ETDEWEB)

This paper presents a novel algorithm to reconstruct parameters of a sufficient number of current dipoles that describe data (equivalent current dipoles, ECDs, hereafter) from radial/vector magnetoencephalography (MEG) with and without electroencephalography (EEG). We assume a three-compartment head model and arbitrary surfaces on which the MEG sensors and EEG electrodes are placed. Via the multipole expansion of the magnetic field, we obtain algebraic equations relating the dipole parameters to the vector MEG/EEG data. By solving them directly, without providing initial parameter guesses and computing forward solutions iteratively, the dipole positions and moments projected onto the xy-plane (equatorial plane) are reconstructed from a single time shot of the data. In addition, when the head layers and the sensor surfaces are spherically symmetric, we show that the required data reduce to radial MEG only. This clarifies the advantage of vector MEG/EEG measurements and algorithms for a generally-shaped head and sensor surfaces. In the numerical simulations, the centroids of the patch sources are well localized using vector/radial MEG measured on the upper hemisphere. By assuming the model order to be larger than the actual dipole number, the resultant spurious dipole is shown to have a much smaller strength magnetic moment (about 0.05 times smaller when the SNR = 16 dB), so that the number of ECDs is reasonably estimated. We consider that our direct method with greatly reduced computational cost can also be used to provide a good initial guess for conventional dipolar/multipolar fitting algorithms.

Nara, Takaaki [Graduate School of Information Science and Technology, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-8656 (Japan); Oohama, Junji [Graduate School of Information Science and Technology, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-8656 (Japan); Hashimoto, Masaru [Graduate School of Information Science and Technology, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-8656 (Japan); Takeda, Tsunehiro [Graduate School of Frontier Science, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8561 (Japan); Ando, Shigeru [Graduate School of Information Science and Technology, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-8656 (Japan)

2007-07-07

28

Multipolar representation of protein structure  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background That the structure determines the function of proteins is a central paradigm in biology. However, protein functions are more directly related to cooperative effects at the residue and multi-residue scales. As such, current representations based on atomic coordinates can be considered inadequate. Bridging the gap between atomic-level structure and overall protein-level functionality requires parameterizations of the protein structure (and other physicochemical properties) in a quasi-continuous range, from a simple collection of unrelated amino acids coordinates to the highly synergistic organization of the whole protein entity, from a microscopic view in which each atom is completely resolved to a "macroscopic" description such as the one encoded in the three-dimensional protein shape. Results Here we propose such a parameterization and study its relationship to the standard Euclidian description based on amino acid representative coordinates. The representation uses multipoles associated with residue C? coordinates as shape descriptors. We demonstrate that the multipoles can be used for the quantitative description of the protein shape and for the comparison of protein structures at various levels of detail. Specifically, we construct a (dis)similarity measure in multipolar configuration space, and show how such a function can be used for the comparison of a pair of proteins. We then test the parameterization on a benchmark set of the protein kinase-like superfamily. We prove that, when the biologically relevant portions of the proteins are retained, it can robustly discriminate between the various families in the set in a way not possible through sequence or conventional structural representations alone. We then compare our representation with the Cartesian coordinate description and show that, as expected, the correlation with that representation increases as the level of detail, measured by the highest rank of multipoles used in the representation, approaches the dimensionality of the fold space. Conclusion The results described here demonstrate how a granular description of the protein structure can be achieved using multipolar coefficients. The description has the additional advantage of being immediately generalizable for any residue-specific property therefore providing a unitary framework for the study and comparison of the spatial profile of various protein properties.

Gramada Apostol; Bourne Philip E

2006-01-01

29

Multipolar Interactions in the Anderson Lattice with Orbital Degeneracy  

CERN Multimedia

Microscopic investigation is performed for intersite multipolar interactions in the orbitally degenerate Anderson lattice, with CeB$_6$ taken as an exemplary target. In addition to the $f^0$ intermediate state, $f^2$ Hund's-rule ground states are included as intermediate states for the interactions. The conduction-band states are taken as plane waves and the hybridization as spherically symmetric. The spatial dependences of multipolar interactions are given by the relative weight of partial wave components along the pair of sites. It is clarified how the the anisotropy arises in the interactions depending on the orbital degeneracy and the spatial configuration. The stability of the $\\Gamma_5$ antiferro-quadrupole order in the phase II of CeB$_6$ is consistent with our model. Moreover, the pseudo-dipole interactions follow a tendency required by the phenomenological model for the phase III.

Sakurai, G; Sakurai, Gen'ya; Kuramoto, Yoshio

2003-01-01

30

Multi-sensor magnetoencephalography with atomic magnetometers.  

UK PubMed Central (United Kingdom)

The authors have detected magnetic fields from the human brain with two independent, simultaneously operating rubidium spin-exchange-relaxation-free magnetometers. Evoked responses from auditory stimulation were recorded from multiple subjects with two multi-channel magnetometers located on opposite sides of the head. Signal processing techniques enabled by multi-channel measurements were used to improve signal quality. This is the first demonstration of multi-sensor atomic magnetometer magnetoencephalography and provides a framework for developing a non-cryogenic, whole-head magnetoencephalography array for source localization.

Johnson CN; Schwindt PD; Weisend M

2013-09-01

31

A new approach to neuroimaging with magnetoencephalography.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the application of beamforming techniques to the field of magnetoencephalography (MEG). We argue that beamformers have given us an insight into the dynamics of oscillatory changes across the cortex not explored previously with traditional analysis techniques that rely on averaged evoked r...

Hillebrand, A; Singh, KD; Holliday, IE; Furlong, PL; Barnes, GR

32

Excitation of single multipolar modes with engineered cylindrically symmetric fields  

CERN Multimedia

We present a new method to address multipolar resonances and to control the scattered field of a spherical scatterer. This method is based on the engineering of the multipolar content of the incident beam. We propose experimentally feasible techniques to generate light beams which contain only a few multipolar modes. The techniques uses incident beams with a well defined component of the angular momentum and appropriate focusing with aplanatic lenses. The control of the multipolar content of light beams allow for the excitation of single Mie resonances and unprecedented control of the scattered field from spherical particles.

Zambrana-Puyalto, Xavier; Molina-Terriza, Gabriel

2012-01-01

33

GENERALIZED SIDELOBE CANCELLER FOR MAGNETOENCEPHALOGRAPHY ARRAYS.  

UK PubMed Central (United Kingdom)

In the last decade, large arrays of sensors for magnetoencephalography (MEG) (and electroencephalography (EEG)) have become more commonplace, allowing new opportunities for the application of beamforming techniques to the joint problems of signal estimation and noise reduction. We introduce a new approach to noise cancellation, the generalized sidelobe canceller (GSC), itself an alternative to the linearly constrained minimum variance (LCMV) algorithm. The GSC framework naturally fits within the other noise reduction techniques that employ real or virtual reference arrays. Using expository human subject data with strong environmental and biological artifacts, we demonstrate a straightforward sequence of steps for practical noise filtering, applicable to any large array sensor design.

Mosher JC; Hämäläinen MS; Pantazis D; Hui HB; Burgess RC; Leahy RM

2009-08-01

34

GENERALIZED SIDELOBE CANCELLER FOR MAGNETOENCEPHALOGRAPHY ARRAYS.  

Science.gov (United States)

In the last decade, large arrays of sensors for magnetoencephalography (MEG) (and electroencephalography (EEG)) have become more commonplace, allowing new opportunities for the application of beamforming techniques to the joint problems of signal estimation and noise reduction. We introduce a new approach to noise cancellation, the generalized sidelobe canceller (GSC), itself an alternative to the linearly constrained minimum variance (LCMV) algorithm. The GSC framework naturally fits within the other noise reduction techniques that employ real or virtual reference arrays. Using expository human subject data with strong environmental and biological artifacts, we demonstrate a straightforward sequence of steps for practical noise filtering, applicable to any large array sensor design. PMID:20234848

Mosher, John C; Hämäläinen, Matti S; Pantazis, Dimitrios; Hui, Hua Brian; Burgess, Richard C; Leahy, Richard M

2009-08-01

35

Optical near fields of multipolar particle plasmons  

International Nuclear Information System (INIS)

[en] Nanoscale noble metal particles are well known for their ability to sustain resonant electron plasma oscillations, so-called particle plasmons. This phenomenon gives rise to spectrally selective light absorption and to an enhancement of the local electric field. Due to these properties, metal nanoparticles are of high current interest for applications and fundamental research in fields as surface enhanced Raman scattering or nanoscale waveguides. Most investigations and applications focus on the dipolar resonances of such particles. However, the particular near-field profiles and far-field scattering patterns of higher order excitations are of interest as well and might be advantageous for specific applications. In this presentation, we report on experimental and theoretical studies of multipolar optical excitations in prolate metal nanoparticles. The results of optical far-field extinction spectroscopy and optical near-field measurements on such particles can be qualitatively understood in a physical picture of standing plasmon-waves. The specific properties of the optical near-fields of the multipolar excitations compared to dipolar excitations are emphasized. (author)

2004-01-01

36

Colloidal nanocube supercrystals stabilized by multipolar Coulombic coupling.  

UK PubMed Central (United Kingdom)

We explore microscopic principles governing the self-assembly of colloidal octylamine-coated platinum nanocubes solvated in toluene. Our experiments show that regular nanocubes with an edge length of l(RC) = 5.5 nm form supercrystals with simple cubic packing, while slightly truncated nanocubes with an edge length of l(TC) = 4.7 nm tend to arrange in fcc packing. We model by averaged force fields and atomistic molecular dynamics simulations the coupling forces between these nanocrystals. Our detailed analysis shows that the fcc packing, which for cubes has a lower density than simple cubic packing, is favored by the truncated nanocubes due to their Coulombic coupling by multipolar electrostatic fields, formed during charge transfer between the octylamine ligands and the Pt cores.

Chan H; Demortière A; Vukovic L; Král P; Petit C

2012-05-01

37

Multipolar functions of BCL-2 proteins link energetics to apoptosis.  

UK PubMed Central (United Kingdom)

Classical apoptotic cell death is now sufficiently well understood to be interrogated with mathematical modeling and manipulated with targeted drugs for clinical benefit. However, a biological black hole has emerged with the realization that apoptosis regulators are functionally multipolar. BCL-2 family proteins appear to have much greater effects on cells than can be explained by their known roles in apoptosis. Although these effects may be observable simply because the cell is not dead, the general assumption is that BCL-2 proteins have undiscovered biochemical activities. Conversely, these as yet uncharacterized day-jobs also may underlie their profound effects on cell survival, challenging current assumptions about classical apoptosis. Even their sub-mitochondrial localizations remain controversial. Here we attempt to integrate seemingly conflicting information with the prospect that BCL-2 proteins themselves may be the critical crosstalk between life and death.

Hardwick JM; Chen YB; Jonas EA

2012-06-01

38

A magnetoencephalography study of choice bias.  

UK PubMed Central (United Kingdom)

Many factors can influence, or bias, human decision making. A considerable amount of research has investigated the neural correlates of such biases, mostly correlating hemodynamic responses in brain areas with some aspect of the decision. These studies, typically done using functional magnetic resonance imaging or positron emission tomography, have provided useful information about the location of processing in the brain. However, comparatively little research has examined when these processes occur. The present experiment addressed this question by using magnetoencephalography (MEG) to record brain activity while subjects chose preferred options from decision sets. We found that MEG signal deviations for biased decisions occurred as early as 250-750 ms following stimulus onset. Such deviations occurred earliest in sensors over the right anterior cortex. These findings improve our understanding of temporal dynamics of decision biases and suggest ways that existing explanations for this bias could be refined.

Hedgcock WM; Crowe DA; Leuthold AC; Georgopoulos AP

2010-04-01

39

SQUID-based multichannel system for Magnetoencephalography  

CERN Document Server

Here we present a multichannel system based on superconducting quantum interference devices (SQUIDs) for magnetoencephalography (MEG) measurements, developed and installed at Istituto di Cibernetica (ICIB) in Naples. This MEG system, consists of 163 full integrated SQUID magnetometers, 154 channels and 9 references, and has been designed to meet specifications concerning noise, dynamic range, slew rate and linearity through optimized design. The control electronics is located at room temperature and all the operations are performed inside a Magnetically Shielded Room (MSR). The system exhibits a magnetic white noise level of approximatively 5 fT/Hz1=2. This MEG system will be employed for both clinical and routine use. PACS numbers: 74.81.Fa, 85.25.Hv, 07.20.Mc, 85.25.Dq, 87.19.le, 87.85.Ng

Rombetto, S; Vettoliere, A; Trebeschi, A; Rossi, R; Russo, M

2013-01-01

40

Monte Carlo analysis of localization errors in magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

In magnetoencephalography (MEG), the magnetic fields created by electrical activity in the brain are measured on the surface of the skull. To determine the location of the activity, the measured field is fit to an assumed source generator model, such as a current dipole, by minimizing chi-square. For current dipoles and other nonlinear source models, the fit is performed by an iterative least squares procedure such as the Levenberg-Marquardt algorithm. Once the fit has been computed, analysis of the resulting value of chi-square can determine whether the assumed source model is adequate to account for the measurements. If the source model is adequate, then the effect of measurement error on the fitted model parameters must be analyzed. Although these kinds of simulation studies can provide a rough idea of the effect that measurement error can be expected to have on source localization, they cannot provide detailed enough information to determine the effects that the errors in a particular measurement situation will produce. In this work, we introduce and describe the use of Monte Carlo-based techniques to analyze model fitting errors for real data. Given the details of the measurement setup and a statistical description of the measurement errors, these techniques determine the effects the errors have on the fitted model parameters. The effects can then be summarized in various ways such as parameter variances/covariances or multidimensional confidence regions. 8 refs., 3 figs.

Medvick, P.A.; Lewis, P.S.; Aine, C.; Flynn, E.R.

1989-01-01

 
 
 
 
41

[Magnetoencephalography: its principles and clinical application  

UK PubMed Central (United Kingdom)

This review attempts to provide the basis of neuromagnetism and its clinical applications. The progress in this field has been connected with the introduction of SQUID (superconducting quantum interference device) magnetometer which was produced by the progress of low temperature physics. A magnetic field is generated by an electric current in accordance with 'the right hand law', and the magnetic field pattern inevitably crosses orthogonally that of the electric field. A SQUID magnetometer is able to only detect the magnetic field which is generated by the current dipole orientated parallel to the skull surface. Magnetoencephalography (MEG) has several advantages compared to electroencephalography (EEG). One is its more excellent spatial resolution than that of EEG, and the other is a non-contact measurement, i. e., a noninvasive method. Therefore, MEG measurement could not interfere with sweating on the skull skin or a depolarization between skin and electrodes. This advantage allows it to record the magnetic field generated by the direct current potential in the cortical surface, and one example, that is, direct current magnetic fields evoked by slow potential changes in rat brain during asphyxia, are shown.

Takanashi Y

1993-11-01

42

[Magnetoencephalography: its principles and clinical application].  

Science.gov (United States)

This review attempts to provide the basis of neuromagnetism and its clinical applications. The progress in this field has been connected with the introduction of SQUID (superconducting quantum interference device) magnetometer which was produced by the progress of low temperature physics. A magnetic field is generated by an electric current in accordance with 'the right hand law', and the magnetic field pattern inevitably crosses orthogonally that of the electric field. A SQUID magnetometer is able to only detect the magnetic field which is generated by the current dipole orientated parallel to the skull surface. Magnetoencephalography (MEG) has several advantages compared to electroencephalography (EEG). One is its more excellent spatial resolution than that of EEG, and the other is a non-contact measurement, i. e., a noninvasive method. Therefore, MEG measurement could not interfere with sweating on the skull skin or a depolarization between skin and electrodes. This advantage allows it to record the magnetic field generated by the direct current potential in the cortical surface, and one example, that is, direct current magnetic fields evoked by slow potential changes in rat brain during asphyxia, are shown. PMID:8283795

Takanashi, Y

1993-11-01

43

Magnetoencephalography (MEG) and other neurophysiological investigations.  

UK PubMed Central (United Kingdom)

Cortical generators of epileptic and certain physiological activity can be localized noninvasively by magnetoencephalography (MEG). MEG detects weak magnetic fields produced by the postsynaptic currents of pyramidal cortical cells in sulcal walls. Unlike EEG, MEG signals are not distorted by edema or bone defects, and unlike fMRI, abnormal hemodynamics do not alter the MEG. The patient's head is centered inside a helmet housing over a hundred magnetic field sensors. Cortical generators of MEG signals are determined with a useful spatial resolution and an excellent time resolution, which enable tracking of brain activity in successive points of, for example, an epileptic network. MEG sources can be co-registered and visualized on magnetic resonance images (MRI). MEG is highly sensitive for the detection of interictal epileptic discharges, and present techniques allow some degree of head movements enabling ictal recordings also. MEG is also useful for localizing the somatosensory, visual, and language areas before tailored surgery in the vicinity of eloquent cortex. In conjunction with other noninvasive modalities MEG provides nonredundant data in one-third of epilepsy surgery patients. Clinical MEG utilization is mainly focused on presurgical localization of the epileptogenic zone and eloquent cortex in epilepsy surgery candidates, including patients with Landau-Kleffner syndrome. However, MEG is also an excellent noninvasive tool to study the source distribution in childhood epilepsy syndromes and epileptic encephalopathies.

Paetau R; Mohamed IS

2013-01-01

44

Theory of multipolar excitations and neutron scattering spectra of CeB{sub 6}  

Energy Technology Data Exchange (ETDEWEB)

Multipolar excitations in the antiferroquadrupolar ordering phase of CeB{sub 6} are studied theoretically. We develop the method of boson expansion of multipoles, and apply it to the Ruderman-Kittel-Kasuya-Yosida model, which has been introduced previously for CeB{sub 6}. Then the neutron scattering spectra are calculated within the dipole approximation and compared with experimental results obtained by Bouvet. The origin of the characteristic peak structures and their dependence on the magnetic field are discussed.

Shiina, R [Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397 (Japan); Shiba, H [Department of Physics, Kobe University, Kobe 657-8501 (Japan); Thalmeier, P [Max-Planck-Institut fuer Chemische Physik fester Stoffe, 01187 Dresden (Germany); Takahashi, A [Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551 (Japan); Sakai, O [Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397 (Japan)

2003-07-23

45

Post-INF: Toward multipolar deterrence  

Energy Technology Data Exchange (ETDEWEB)

The NATO nations have never had enough conventional forces to deter the Soviets in Europe, and they have relied on NATO's nuclear forces--primarily American--for deterrence. As Soviet conventional and nuclear forces have grown larger and more threatening, the credibility of using U.S. nuclear forces in response to Soviet aggression in Europe has eroded. The decision to place U.S. Pershing II (PII) missiles and ground-launched cruise missiles (GLCMs) in Western Europe was intended to bolster this credibility. The intermediate nuclear forces agreement, which removes these missiles, although necessary for political reasons, is likely to further erode the credibility of the U.S. threat to use nuclear weapons in the defense of Europe. In the short run, some technical fixes could compensate somewhat for the removal of the PII and GLCM missiles. But, in the longer run, the current deterrence system, which relies on U.S. nuclear weapons to deter the Soviet Union, is likely to increasingly evolve toward a multipolar system including France, the United Kingdom and China, which possess growing nuclear arsenals playing a larger role in deterrence. Here we shall analyze the elements of deterrence and examine how U.S. nuclear forces have produced extended deterrence in Europe.

Wendt, J.C.; Wilson, P.A.

1988-02-01

46

Smoother thrust on multi-polar type linear DC motor  

Energy Technology Data Exchange (ETDEWEB)

A LDM has the merits of a high response and a direct linear motion. Therefore, a LDM is used widely in the fields of Factory Automation (FA). As compared with a mono-polar type Linear DC Motor (LDM), it is possible for a multi-polar type LDM to have a longer stroke and more thrust with thin shape. However, there are thrust ripple on multi-polar type one. In this paper, a design to prevent thrust ripple is discussed. In order to make a smoother thrust on multi-polar type LDM, the structure of the LDM is set as a 2-phase coil type. This paper clarifies that the thrust ripple of the LDM has the minimum value of 1.68%, the pole pitch of 15 mm, the coil width of 12 mm and the permanent magnet width of 10 mm.

Wakiwaka, H.; Senoh, S.; Yajima, H; Yamada, H. [Shinshu Univ., Wakasato, Nagano (Japan). Faculty of Engineering; Oda, J. [Ohkura Electric Co., Ltd., Shirako, Wakou (Japan)

1997-09-01

47

Design of outer-rotor type multipolar SR motor for electric vehicle  

International Nuclear Information System (INIS)

In this paper, we design an outer-rotor type multipolar switched reluctance (SR) motor, and examine an application of the SR motor to an electric vehicle (EV). The design is based on a nonlinear magnetic circuit model proposed by the authors. Using the model, we can calculate dynamic characteristics of a SR motor accurately. Furthermore, by combining the nonlinear magnetic circuit model with a motor drive circuit and motion equation of an EV, we can predict dynamic characteristics such as the maximum speed, acceleration torque, and a battery current of the EV.

2005-01-01

48

Hepatic radiofrequency ablation using multiple probes: vivo and in vivo comparative studies of monopolar versus multipolar modes  

Energy Technology Data Exchange (ETDEWEB)

We wanted to compare the efficiency of multipolar radiofrequency ablation (RFA) using three perfused-cooled electrodes with multiple overlapping- and simultaneous monopolar techniques for creating an ablation zone in ex vivo bovine livers and in in vivo porcine livers. In the ex vivo experiments, we used a 200 W generator (Valleylab, CC-3 model) and three perfused-cooled electrodes or internally cooled electrodes to create 30 coagulation zones by performing consecutive monopolar RFA (group A, n=10), simultaneous monopolar RFA (group B, n=10) or multipolar RFA (group C, n=10) in explanted bovine livers. In the consecutive mode, three ablation spheres were created by sequentially applying 150 watts radiofrequency (RF) energy to the internally cooled electrodes for 12 minutes each for a total of 36 minutes. In the simultaneous monopolar and multipolar modes, RF energy was concurrently applied to the three perfused-cooled electrodes for 20 minutes at 150 watt with instillation of 6% hypertonic saline at 2 mL/min. During RFA, we measured the temperatures of the treated area at its center. The changes in impedance, the current and liver temperature during RFA, as well as the dimensions of the thermal ablation zones, were compared among the three groups. In the in vivo experiments, three coagulations were created by performing multipolar RFA in a pig via laparotomy with using same parameter as the ex vivo study. In the ex vivo experiments, the impedance was gradually decreased during the RFA in groups B and C, but in group A, the impedance was increased during RFA and this induced activation by the pulsed RF technique. In groups A, B and C, the mean final-temperature values were 80 {+-} 10 {approx}, 69 {+-} 18 {approx} and 79 {+-} 12 {approx}, respectively ({rho} < 0.05). The multipolar mode created a larger volume of ablation than did the other modes: 37.6 {+-} 4.0 cm{sup 3} (group A); 44.9 {+-} 12.7 cm{sup 3} (group B); and 78.9 {+-} 6.9 cm{sup 3} (group C) ({rho} < 0.05). In the in vivo experiment, the pig well tolerated the RFA procedure and no major complications occurred during the 4 days of the follow-up period. The mean volume of coagulations produced by multipolar RFA in the pig liver was 60.5 {+-} 17.9 cm{sup 3}. For the multiple probe RFA, the multipolar mode with hypertonic saline instillation was more efficient in generating larger areas of thermal ablation than either the consecutive or simultaneous monopolar modes.

Lee, Jeong Min; Han, Joon Koo; Lee, Jae Young; Kim, Se Hyung; Choi, Jin Young; Lee, Min Woo; Choi, Seung Hong; Eo, Hong; Choi, Byung Ihn [Seoul National University College of Medicine, Seoul (Korea, Republic of)

2006-06-15

49

Aberrant functional organization and maturation in early-onset psychosis: Evidence from magnetoencephalography  

Science.gov (United States)

Studies of the location of somatosensory and auditory cortical responses have shown anomalous hemispheric asymmetries in a variety of neurodevelopmental disorders. Although to date, abnormal asymmetries in the somatosensory region have shown greater specificity being reported only in psychotic adults. This study examines functional organization of somatosensory cortices using magnetoencephalography in adolescents with childhood-onset psychotic disorders. Eighteen young outpatients with history of psychotic illness and 15 healthy adolescents participated. Both groups underwent stimulation of the index finger as magnetoencephalography was acquired from the contralateral hemisphere. Neural generators of the M50 somatosensory response were modeled using an equivalent current dipole for each hemisphere, and later investigated for systematic variation with diagnosis. Consistent with adult psychosis data, adolescent patients showed hemispheric symmetry in the anterior-posterior dimension. In controls, a reversed pattern of hemispheric asymmetry was observed relative to previous findings in normal adults (Reite et al., 2003), but trend-level correlations suggested source location became more adult-like during transition from adolescence to adulthood. Source parameters also exhibited robust inter-hemispheric correlations only in adolescent controls. In sum, source locations, patterns of cerebral lateralization, and inter-hemispheric correlations all distinguish patients from their normally developing cohort. These findings suggest aberrant maturation underlies the reduction in cerebral laterality associated with psychosis.

Wilson, Tony W.; Rojas, Donald C.; Teale, Peter D.; Hernandez, Olivia O.; Asherin, Ryan M.; Reite, Martin L.

2007-01-01

50

Multipolar radiation of quantum emitters with nanowire optical antennas  

Science.gov (United States)

Multipolar transitions other than electric dipoles are generally too weak to be observed at optical frequencies in single quantum emitters. For example, fluorescent molecules and quantum dots have dimensions much smaller than the wavelength of light and therefore emit predominantly as electric dipoles. Here we demonstrate controlled emission of a quantum dot into multipolar radiation through selective coupling to a linear nanowire antenna. The antenna resonance tailors the interaction of the quantum dot with light, effectively creating a hybrid nanoscale source beyond the simple Hertz dipole. Our findings establish a basis for the controlled driving of fundamental modes in nanoantennas and metamaterials, for the understanding of the coupling of quantum emitters to nanophotonic devices such as waveguides and nanolasers, and for the development of innovative quantum nano-optics components with properties not found in nature.

Curto, Alberto G.; Taminiau, Tim H.; Volpe, Giorgio; Kreuzer, Mark P.; Quidant, Romain; van Hulst, Niek F.

2013-01-01

51

Multipolar second harmonic generation from planar arrays of Au nanoparticles.  

Science.gov (United States)

We demonstrate optical Second Harmonic Generation (SHG) in planar arrays of cylindrical Au nanoparticles arranged in periodic and deterministic aperiodic geometries. In order to understand the respective roles of near-field plasmonic coupling and long-range photonic interactions on the SHG signal, we systematically vary the interparticle separation from 60 nm to distances comparable to the incident pump wavelength. Using polarization-resolved measurements under femtosecond pumping, we demonstrate multipolar SHG signal largely tunable by the array geometry. Moreover, we show that the SHG signal intensity is maximized by arranging Au nanoparticles in aperiodic spiral arrays. The possibility to engineer multipolar SHG in planar arrays of metallic nanoparticles paves the way to the development of novel optical elements for nanophotonics, such as nonlinear optical sensors, compact frequency converters, optical mixers, and broadband harmonic generators on a chip. PMID:22772269

Capretti, Antonio; Walsh, Gary F; Minissale, Salvatore; Trevino, Jacob; Forestiere, Carlo; Miano, Giovanni; Dal Negro, Luca

2012-07-01

52

Multipolar second harmonic generation from planar arrays of Au nanoparticles.  

UK PubMed Central (United Kingdom)

We demonstrate optical Second Harmonic Generation (SHG) in planar arrays of cylindrical Au nanoparticles arranged in periodic and deterministic aperiodic geometries. In order to understand the respective roles of near-field plasmonic coupling and long-range photonic interactions on the SHG signal, we systematically vary the interparticle separation from 60 nm to distances comparable to the incident pump wavelength. Using polarization-resolved measurements under femtosecond pumping, we demonstrate multipolar SHG signal largely tunable by the array geometry. Moreover, we show that the SHG signal intensity is maximized by arranging Au nanoparticles in aperiodic spiral arrays. The possibility to engineer multipolar SHG in planar arrays of metallic nanoparticles paves the way to the development of novel optical elements for nanophotonics, such as nonlinear optical sensors, compact frequency converters, optical mixers, and broadband harmonic generators on a chip.

Capretti A; Walsh GF; Minissale S; Trevino J; Forestiere C; Miano G; Dal Negro L

2012-07-01

53

Soil moisture estimation in cereal fields using multipolarized SAR data  

Science.gov (United States)

The retrieval of soil moisture from remote sensing data is an extremely active research topic with applications on a wide range of disciplines. Microwave observations represent the most viable approach due to the influence of soils' dielectric constant (and thus soil moisture) on both the emission and backscatter of waves in this region of the spectrum. Passive observations provide higher temporal resolutions, whereas active (SAR) observations have a higher spatial detail. Even if operational moisture products, based on passive data, exist, retrieval algorithms using active observations still face several problems. Surface roughness and vegetation cover are probably the disturbing factors most affecting the accuracy of soil moisture retrievals. In this communication the influence of vegetation cover is investigated and a retrieval technique based on multipolarized C band SAR observations is proposed. With this aim a dedicated field campaign was carried out in La Tejería watershed (north of Spain) from January to August 2010. Eight RADARSAT-2 Fine-Quadpol scenes were acquired in order to investigate the role of vegetation cover on the retrieval of soil moisture, as well as the sensitivity of different polarimetric parameters to vegetation cover condition. Coinciding with image acquisitions soil moisture, plant density and crop height measurements were acquired in eight control fields (cultivated with barley and wheat crops). The sensitivity of backscatter coefficients (in HH, HV and VV polarizations) and backscatter ratios (p=HH/VV and q=HV/VV) to soil moisture and crop condition were evaluated and the semi-empirical Water Cloud Model was fitted to the observations. The results obtained showed that the contribution of the cereal vegetation cover was minimal in HH and HV polarizations, whereas the VV channel appeared to be significantly attenuated by the cereal cover, so its value decreased as the crops grew. As a result, the ratios p and q showed a very good correlation with vegetation condition and resulted to be almost insensitive to soil moisture variations. These ratios were next used to parameterize cereal vegetation cover on a retrieval scheme based on the Water Cloud Model. Results were best on VV polarization where the correlation coefficients obtained were above 0.7. The approach proposed is very promising from an operational point of view since it corrects the influence of vegetation cover in the retrieval without requiring external information to describe it. Besides, the low variability of the empirical coefficients obtained for different fields, suggests that differences in surface roughness at this stage do not significantly affect soil moisture retrievals.

Alvarez-Mozos, J.; Izagirre, A.; Larrañaga, A.

2012-04-01

54

Infant speech perception activates Broca's area: a developmental magnetoencephalography study.  

Science.gov (United States)

Discriminative responses to tones, harmonics, and syllables in the left hemisphere were measured with magnetoencephalography in neonates, 6-month-old infants, and 12-month-old infants using the oddball paradigm. Real-time head position tracking, signal space separation, and head position standardization were applied to secure quality data for source localization. Minimum current estimates were calculated to characterize infants' cortical activities for detecting sound changes. The activation patterns observed in the superior temporal and inferior frontal regions provide initial evidence for the developmental emergence early in life of a perceptual-motor link for speech perception that may depend on experience. PMID:16791084

Imada, Toshiaki; Zhang, Yang; Cheour, Marie; Taulu, Samu; Ahonen, Antti; Kuhl, Patricia K

2006-07-17

55

Infant speech perception activates Broca's area: a developmental magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Discriminative responses to tones, harmonics, and syllables in the left hemisphere were measured with magnetoencephalography in neonates, 6-month-old infants, and 12-month-old infants using the oddball paradigm. Real-time head position tracking, signal space separation, and head position standardization were applied to secure quality data for source localization. Minimum current estimates were calculated to characterize infants' cortical activities for detecting sound changes. The activation patterns observed in the superior temporal and inferior frontal regions provide initial evidence for the developmental emergence early in life of a perceptual-motor link for speech perception that may depend on experience.

Imada T; Zhang Y; Cheour M; Taulu S; Ahonen A; Kuhl PK

2006-07-01

56

Detection of magnetic nanoparticles with magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

Superconducting quantum interference devices (SQUIDs) have been widely utilized in biomedical applications due to their extremely high sensitivity to magnetic signals. The present study explores the feasibility of a new type of nanotechnology-based imaging method using standard clinical magnetoencephalographic (MEG) systems equipped with SQUID sensors. Previous studies have shown that biological targets labeled with non-toxic, magnetized nanoparticles can be imaged by measuring the magnetic field generated by these particles. In this work, we demonstrate that (1) the magnetic signals from certain nanoparticles can be detected without magnetization using standard clinical MEG, (2) for some types of nanoparticles, only bound particles produce detectable signals, and (3) the magnetic field of particles several hours after magnetization is significantly stronger than that of un-magnetized particles. These findings hold promise in facilitating the potential application of magnetic nanoparticles to in vivo tumor imaging. The minimum amount of nanoparticles that produce detectable signals is predicted by theoretical modeling and computer simulation.

Jia Wenyan [Department of Neurosurgery, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Xu, Guizhi [Department of Neurosurgery, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Department of Biomedical Engineering, Hebei University of Technology, Tianjin, 300130 (China); Sclabassi, Robert J. [Department of Neurosurgery, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Zhu Jiangang [Department of Electrical and Computer Engineering, Carnegie Melon University, Pittsburgh, PA 15213 (United States); Bagic, Anto [Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Sun Mingui [Department of Neurosurgery, University of Pittsburgh, Pittsburgh, PA 15260 (United States)], E-mail: mrsun@neuronet.pitt.edu

2008-04-15

57

Retinotopic mapping of the human visual system with magnetoencephalography. Master's thesis  

Energy Technology Data Exchange (ETDEWEB)

A retinotopic mapping was verified using magnetoencephalography as the means to observe brain activity in one human subject. The stimulus consisted of 12 sectors of a hemicircle, 6 foveal and 6 peripheral out to about 17 degrees visual field angle. The sectors flashed individually for 63 milliseconds with an inter-stimulus-interval between .8 and 1.8 seconds. The recording computer was synchronized to the stimulus and recorded for .5 seconds after onset of stimulus. Thirty averages were taken for each stimulus section, for each of about 45 grid points on the scalp. The sectors were localized to distinct points in the primary visual cortex (area 17). The results did not verify the cruciform model of retinotopic mapping nor the theory that more visually eccentric stimuli produce deeper responses. The data seem to suggest and different type of mapping for foveal stimuli than peripheral, but this could also be due to the fold structure of the primary visual cortex.

Dowler, M.G.

1987-12-01

58

State-space solutions to the dynamic magnetoencephalography inverse problem using high performance computing  

CERN Multimedia

Determining the magnitude and location of neural sources within the brain that are responsible for generating magnetoencephalography (MEG) signals measured on the surface of the head is a challenging problem in functional neuroimaging. The number of potential sources within the brain exceeds by an order of magnitude the number of recording sites. As a consequence, the estimates for the magnitude and location of the neural sources will be ill-conditioned because of the underdetermined nature of the problem. One well-known technique designed to address this imbalance is the minimum norm estimator (MNE). This approach imposes an $L^2$ regularization constraint that serves to stabilize and condition the source parameter estimates. However, these classes of regularizer are static in time and do not consider the temporal constraints inherent to the biophysics of the MEG experiment. In this paper we propose a dynamic state-space model that accounts for both spatial and temporal correlations within and across candida...

Long, Christopher J; Temereanca, Simona; Desai, Neil U; Hämäläinen, Matti S; Brown, Emery N; 10.1214/11-AOAS483

2011-01-01

59

Hepatic radiofrequency ablation using multiple probes: vivo and in vivo comparative studies of monopolar versus multipolar modes  

International Nuclear Information System (INIS)

We wanted to compare the efficiency of multipolar radiofrequency ablation (RFA) using three perfused-cooled electrodes with multiple overlapping- and simultaneous monopolar techniques for creating an ablation zone in ex vivo bovine livers and in in vivo porcine livers. In the ex vivo experiments, we used a 200 W generator (Valleylab, CC-3 model) and three perfused-cooled electrodes or internally cooled electrodes to create 30 coagulation zones by performing consecutive monopolar RFA (group A, n=10), simultaneous monopolar RFA (group B, n=10) or multipolar RFA (group C, n=10) in explanted bovine livers. In the consecutive mode, three ablation spheres were created by sequentially applying 150 watts radiofrequency (RF) energy to the internally cooled electrodes for 12 minutes each for a total of 36 minutes. In the simultaneous monopolar and multipolar modes, RF energy was concurrently applied to the three perfused-cooled electrodes for 20 minutes at 150 watt with instillation of 6% hypertonic saline at 2 mL/min. During RFA, we measured the temperatures of the treated area at its center. The changes in impedance, the current and liver temperature during RFA, as well as the dimensions of the thermal ablation zones, were compared among the three groups. In the in vivo experiments, three coagulations were created by performing multipolar RFA in a pig via laparotomy with using same parameter as the ex vivo study. In the ex vivo experiments, the impedance was gradually decreased during the RFA in groups B and C, but in group A, the impedance was increased during RFA and this induced activation by the pulsed RF technique. In groups A, B and C, the mean final-temperature values were 80 ± 10 ?, 69 ± 18 ? and 79 ± 12 ?, respectively (? 3 (group A); 44.9 ± 12.7 cm3 (group B); and 78.9 ± 6.9 cm3 (group C) (? 3. For the multiple probe RFA, the multipolar mode with hypertonic saline instillation was more efficient in generating larger areas of thermal ablation than either the consecutive or simultaneous monopolar modes.

2006-01-01

60

Magnetar Giant Flares --- Flux Rope Eruptions in Multipolar Magnetospheric Magnetic Fields  

CERN Document Server

We address a primary question regarding the physical mechanism that triggers the energy release and initiates the onset of eruptions in the magnetar magnetosphere. A self-consistent stationary, axisymmetric model of the magnetar magnetosphere is constructed based on a force-free magnetic field configuration which contains a helically twisted force-free flux rope. Given the complex multipolar magnetic fields at the magnetar surface, we also develop a convenient numerical scheme to solve the GS equation. Depending on the surface magnetic field polarity, there exist two kinds of magnetic field configurations, inverse and normal. For these two kinds of configurations, variations of the flux rope equilibrium height in response to gradual surface physical processes, such as flux injections and crust motions, are carefully examined. We find that equilibrium curves contain two branches, one represents a stable equilibrium branch, the other an unstable equilibrium branch. As a result, the evolution of the system shows...

Yu, Cong

2012-01-01

 
 
 
 
61

Adaptive cluster analysis approach for functional localization using magnetoencephalography.  

UK PubMed Central (United Kingdom)

In this paper we propose an agglomerative hierarchical clustering Ward's algorithm in tandem with the Affinity Propagation algorithm to reliably localize active brain regions from magnetoencephalography (MEG) brain signals. Reliable localization of brain areas with MEG has been difficult due to variations in signal strength, and the spatial extent of the reconstructed activity. The proposed approach to resolve this difficulty is based on adaptive clustering on reconstructed beamformer images to find locations that are consistently active across different participants and experimental conditions with high spatial resolution. Using data from a human reaching task, we show that the method allows more accurate and reliable localization from MEG data alone without using functional magnetic resonance imaging (fMRI) or any other imaging techniques.

Alikhanian H; Crawford JD; Desouza JF; Cheyne DO; Blohm G

2013-01-01

62

Presence of Strong Harmonics During Visual Entrainment: A Magnetoencephalography Study  

Science.gov (United States)

Visual neurons are known to synchronize their firing with stimuli that flicker at a constant rate (e.g., 12 Hz). These so-called visual steady-state responses (VSSR) are a well-studied phenomenon, yet the underlying mechanisms are widely disagreed upon. Furthermore, there is limited evidence that visual neurons may simultaneously synchronize at harmonics of the stimulation frequency. We utilized magnetoencephalography (MEG) to examine synchronization at harmonics of the visual stimulation frequency (18 Hz). MEG data were analyzed for event-related-synchronization (ERS) at the fundamental frequency, 36, 54, and 72 Hz. We found strong ERS in all bands. Only 31% of participants showed maximum entrainment at the fundamental; others showed stronger entrainment at either 36 or 54 Hz. The cortical foci of these responses indicated that the harmonics involved cortices that were partially distinct from the fundamental. These findings suggest that spatially-overlapping subpopulations of neurons are simultaneously entrained at different harmonics of the stimulus frequency.

Heinrichs-Graham, Elizabeth; Wilson, Tony W.

2012-01-01

63

Multipolar Black Body Radiation Shifts for the Single Ion Clocks  

CERN Multimedia

Appraising the projected $10^{-18}$ fractional uncertainty in the optical frequency standards using singly ionized ions, we estimate the black-body radiation (BBR) shifts due to the magnetic dipole (M1) and electric quadrupole (E2) multipoles of the magnetic and electric fields, respectively. Multipolar scalar polarizabilities are determined for the singly ionized calcium (Ca$^+$) and strontium (Sr$^+$) ions using the relativistic coupled-cluster method; though the theory can be exercised for any single ion clock proposal. The expected energy shifts for the respective clock transitions are estimated to be $4.38(3) \\times 10^{-4}$ Hz for Ca$^+$ and $9.50(7) \\times 10^{-5}$ Hz for Sr$^+$. These shifts are large enough and may be prerequisite for the frequency standards to achieve the foreseen $10^{-18}$ precision goal.

Arora, Bindiya; Sahoo, B K

2011-01-01

64

Multipolar emission in the vicinity of metallic nanostructures  

Energy Technology Data Exchange (ETDEWEB)

Electromagnetic emission from finite-size multipoles very close to metal surfaces exhibiting plasmon resonances can have profound consequences on the characteristics of the emitted radiation in the far field in both its integrated intensity and its spatial distribution. The problem is relevant for many types of spectroscopies that use metals to enhance optical signals, but it also represents a complementary aspect to the recent interest in near-field imaging via surface plasmon resonances. The breakdown of selection rules for multipolar emission and the phenomenon of radiation funnelling in the far field are explicitly discussed. The relevance of these concepts for certain types of spectroscopy, like surface enhanced Raman scattering (SERS), is also highlighted.

Etchegoin, P G; Le Ru, E C [MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington (New Zealand)

2006-02-01

65

Wavenumber Dependence of Multipolar Interactions in the Anderson Lattice  

CERN Document Server

Multipolar interactions are derived in the orbitally degenerate Anderson lattice with a spherical Fermi surface and one conduction electron per unit cell of the simple cubic lattice. As the crystalline-electric-field (CEF) ground state of $f^1$ configuration, the four-fold degenerate $\\Gamma_8$ is mainly studied. Intersite interactions up to a sufficiently distant pair are Fourier transformed to the wavenumber space. For the $\\Gamma_8$ case, quadrupolar and octupolar interactions favor the staggered order with $\\mib{q} = (1/2,1/2,1/2)$, while the dipolar interaction favors an incommensurate magnetic structure with a long modulation period. The latter is due to a Kohn anomaly which is found to be sharply peaked for interaction channels with large angular momenta. Implications of results are discussed for multipole orders in CeB$_6$, and the incommensurate magnetic structure in a quasi-cubic system CeB$_2$C$_2$.

Sakurai, G; Sakurai, Gen'ya; Kuramoto, Yoshio

2004-01-01

66

Simulated multipolarized MAPSAR images to distinguish agricultural crops  

Directory of Open Access Journals (Sweden)

Full Text Available Many researchers have shown the potential of Synthetic Aperture Radar (SAR) images for agricultural applications, particularly for monitoring regions with limitations in terms of acquiring cloud free optical images. Recently, Brazil and Germany began a feasibility study on the construction of an orbital L-band SAR sensor referred to as MAPSAR (Multi-Application Purpose SAR). This sensor provides L-band images in three spatial resolutions and polarimetric, interferometric and stereoscopic capabilities. Thus, studies are needed to evaluate the potential of future MAPSAR images. The objective of this study was to evaluate multipolarized MAPSAR images simulated by the airborne SAR-R99B sensor to distinguish coffee, cotton and pasture fields in Brazil. Discrimination among crops was evaluated through graphical and cluster analysis of mean backscatter values, considering single, dual and triple polarizations. Planting row direction of coffee influenced the backscatter and was divided into two classes: parallel and perpendicular to the sensor look direction. Single polarizations had poor ability to discriminate the crops. The overall accuracies were less than 59 %, but the understanding of the microwave interaction with the crops could be explored. Combinations of two polarizations could differentiate various fields of crops, highlighting the combination VV-HV that reached 78 % overall accuracy. The use of three polarizations resulted in 85.4 % overall accuracy, indicating that the classes pasture and parallel coffee were fully discriminated from the other classes. These results confirmed the potential of multipolarized MAPSAR images to distinguish the studied crops and showed considerable improvement in the accuracy of the results when the number of polarizations was increased.

Wagner Fernando Silva; Bernardo Friedrich Theodor Rudorff; Antonio Roberto Formaggio; Waldir Renato Paradella; José Claudio Mura

2012-01-01

67

Simulated multipolarized MAPSAR images to distinguish agricultural crops  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english Many researchers have shown the potential of Synthetic Aperture Radar (SAR) images for agricultural applications, particularly for monitoring regions with limitations in terms of acquiring cloud free optical images. Recently, Brazil and Germany began a feasibility study on the construction of an orbital L-band SAR sensor referred to as MAPSAR (Multi-Application Purpose SAR). This sensor provides L-band images in three spatial resolutions and polarimetric, interferometric (more) and stereoscopic capabilities. Thus, studies are needed to evaluate the potential of future MAPSAR images. The objective of this study was to evaluate multipolarized MAPSAR images simulated by the airborne SAR-R99B sensor to distinguish coffee, cotton and pasture fields in Brazil. Discrimination among crops was evaluated through graphical and cluster analysis of mean backscatter values, considering single, dual and triple polarizations. Planting row direction of coffee influenced the backscatter and was divided into two classes: parallel and perpendicular to the sensor look direction. Single polarizations had poor ability to discriminate the crops. The overall accuracies were less than 59 %, but the understanding of the microwave interaction with the crops could be explored. Combinations of two polarizations could differentiate various fields of crops, highlighting the combination VV-HV that reached 78 % overall accuracy. The use of three polarizations resulted in 85.4 % overall accuracy, indicating that the classes pasture and parallel coffee were fully discriminated from the other classes. These results confirmed the potential of multipolarized MAPSAR images to distinguish the studied crops and showed considerable improvement in the accuracy of the results when the number of polarizations was increased.

Silva, Wagner Fernando; Rudorff, Bernardo Friedrich Theodor; Formaggio, Antonio Roberto; Paradella, Waldir Renato; Mura, José Claudio

2012-06-01

68

Toroidal Multipolar Expansion for Fast L-Mode Plasma Boundary Reconstruction in EAST  

Science.gov (United States)

A new method for plasma boundary reconstruction, based on the toroidal multipolar expansion (TME) scheme, is applied successfully in EAST. TME applies a limited number of toroidal multipolar moments based on toroidal coordinates to treat a two-dimensional problem of axisymmetric plasma equilibrium. The plasma boundary reconstructed by TME is consistent with the results by using EFIT. The method is sufficiently reliable and fast for real time shape control.

Guo, Yong; Xiao, Bingjia; Luo, Zhengping

2011-06-01

69

Toroidal Multipolar Expansion for Fast L-Mode Plasma Boundary Reconstruction in EAST  

International Nuclear Information System (INIS)

A new method for plasma boundary reconstruction, based on the toroidal multipolar expansion (TME) scheme, is applied successfully in EAST. TME applies a limited number of toroidal multipolar moments based on toroidal coordinates to treat a two-dimensional problem of axisymmetric plasma equilibrium. The plasma boundary reconstructed by TME is consistent with the results by using EFIT. The method is sufficiently reliable and fast for real time shape control. (magnetically confined plasma)

2011-01-01

70

Performance of a novel squid-based superconducting imaging-surface magnetoencephalography system  

Energy Technology Data Exchange (ETDEWEB)

Performance for a recently completed whole-head magnetoencephalography system using a superconducting imaging-surface (SIS) surrounding an array of 150 SQUID magnetometers is reported. The helmetlike SIS is hemispherical in shape with a brim. Conceptually, the SIS images nearby sources onto the SQUIDs while shielding sensors from distant 'noise' sources. A finite element method (FEM) description using the as-built geometry was developed to describe the SIS effect on source fields by imposing B(surface)=0. Sensors consist of 8mm x 8mm SQUID magnetometers with 0.84nT/F sensitivity and <3fT/vHz noise. A series of phantom experiments to verify system efficacy have been completed. Simple dry-wire phantoms were used to eliminate model dependence from our results. Phantom coils were distributed throughout the volume encompassed by the array with a variety of orientations. Each phantom coil was precisely machined and located to better than 25{micro}m and 10mRad accuracy. Excellent agreement between model-calculated and measured magnetic field distributions of all phantom coil positions and orientations was found. Good agreement was found between modeled and measured shielding of the SQUIDs from sources external to the array showing significant frequency-independent shielding. Phantom localization precision was better than 0.5mm at all locations with a mean of better than 0.3mm.

Matlochov, A. (Andrei); Espy, M. A. (Michelle A.); Volegov, P. (Petr); Maharajh, K. (Keeran); Flynn, E. R. (Edward. R.); Kraus, Robert H., Jr.

2001-01-01

71

Using variance information in magnetoencephalography measures of functional connectivity.  

UK PubMed Central (United Kingdom)

The use of magnetoencephalography (MEG) to assess long range functional connectivity across large scale distributed brain networks is gaining popularity. Recent work has shown that electrodynamic networks can be assessed using both seed based correlation or independent component analysis (ICA) applied to MEG data and further that such metrics agree with fMRI studies. To date, techniques for MEG connectivity assessment have typically used a variance normalised approach, either through the use of Pearson correlation coefficients or via variance normalisation of envelope timecourses prior to ICA. Here, we show that the use of variance information (i.e. data that have not been variance normalised) in source space projected Hilbert envelope time series yields important spatial information, and is of significant functional relevance. Further, we show that employing this information in functional connectivity analyses improves the spatial delineation of network nodes using both seed based and ICA approaches. The use of variance is particularly important in MEG since the non-independence of source space voxels (brought about by the ill-posed MEG inverse problem) means that spurious signals can exist in areas of low signal variance. We therefore suggest that this approach be incorporated into future studies.

Hall EL; Woolrich MW; Thomaz CE; Morris PG; Brookes MJ

2013-02-01

72

Noise-free magnetoencephalography recordings of brain function  

Energy Technology Data Exchange (ETDEWEB)

Perhaps the greatest impediment to acquiring high-quality magnetoencephalography (MEG) recordings is the ubiquitous ambient magnetic field noise. We have designed and built a whole-head MEG system using a helmet-like superconducting imaging surface (SIS) surrounding the array of superconducting quantum interference device (SQUID) magnetometers used to measure the MEG signal. We previously demonstrated that the SIS passively shields the SQUID array from ambient magnetic field noise, independent of frequency, by 25-60 dB depending on sensor location. SQUID 'reference sensors' located on the outside of the SIS helmet measure ambient magnetic fields in very close proximity to the MEG magnetometers while being nearly perfectly shielded from all sources in the brain. The fact that the reference sensors measure no brain signal yet are located in close proximity to the MEG sensors enables very accurate estimation and subtraction of the ambient field noise contribution to the MEG sensors using an adaptive algorithm. We have demonstrated total ambient noise reduction factors in excess of 10{sup 6} (>120 dB). The residual noise for most MEG SQUID channels is at or near the intrinsic SQUID noise floor, typically 2-3 f T Hz{sup -1/2}. We are recording MEG signals with greater signal-to-noise than equivalent EEG measurements.

Volegov, P; Matlachov, A; Mosher, J; Espy, M A; Kraus, R H Jr. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2004-05-21

73

Design and performance of the LANL 158-channel magnetoencephalography system  

Energy Technology Data Exchange (ETDEWEB)

Design and performance for a recently completed whole-head magnetoencephalography (MEG) system using a superconducting imaging-surface (SIS) surrounding an array of SQUID magnetometers is reported. The helmet-like SIS is hemispherical in shape with a brim. The SIS images nearby sources while shields sensors from ambient magnetic noise. The shielding factor depends on magnetometer position and orientation. Typical shielding values of 200 in central sulcus area have been observed. Nine reference channels form three vector magnetometers, which are placed outside SIS. Signal channels consist of 149 SQUID magnetometers with 0.84nT/{Phi}{sub 0} field sensitivity and less then 3 fT/{radical}Hz noise. Typical SQUID - room temperature separations are about 20mm in the cooled state. Twelve 16-channel flux-lock loop units are connected to two 96-channel control units allowing up to 192 total SQUID channels. The control unit includes signal conditioning circuits as well as system test and control circuits. After conditioning all signals are fed to 192-channel, 24-bit data acquisition system capable of sampling up to 48kSa/sec/channel. The SIS-MEG system enables high-quality human functional brain data to be recorded in a one-layer magnetically shielded room.

Matlachov, A. N. (Andrei N.); Kraus, Robert H., Jr.; Espy, M. A. (Michelle A.); Best, E. D. (Elaine D.); Briles, M. Carolyn; Raby, E. Y. (Eric Y.); Flynn, E. R.

2002-01-01

74

Neutron star deformation due to multipolar magnetic fields  

Science.gov (United States)

Certain multiwavelength observations of neutron stars, such as intermittent radio emissions from rotation-powered pulsars beyond the pair-cascade death line, the pulse profile of the magnetar SGR 1900+14 after its 1998 August 27 giant flare and X-ray spectral features of PSR J0821-4300 and SGR 0418+5729, suggest that the magnetic fields of non-accreting neutron stars are not purely dipolar and may contain higher order multipoles. Here, we calculate the ellipticity of a non-barotropic neutron star with (i) a quadrupole poloidal-toroidal field, and (ii) a purely poloidal field containing arbitrary multipoles, deriving the relation between the ellipticity and the multipole amplitudes. We present, as a worked example, a purely poloidal field comprising dipole, quadrupole and octupole components. We show the correlation between field energy and ellipticity for each multipole, that the l = 4 multipole has the lowest energy, and that l = 5 has the lowest ellipticity. We show how a mixed multipolar field creates an observationally testable mismatch between the principal axes of inertia (to be inferred from gravitational wave data) and the magnetic inclination angle. Strong quadrupole and octupole components (with amplitudes ˜102 times higher than the dipole) in SGR 0418+5729 still yield ellipticity ˜10-8, consistent with current gravitational wave upper limits. The existence of higher multipoles in fast-rotating objects (e.g. newborn magnetars) has interesting implications for the braking law and hence phase tracking during coherent gravitational wave searches.

Mastrano, A.; Lasky, P. D.; Melatos, A.

2013-09-01

75

Magnetoencephalography reveals early activation of V4 in grapheme-color synesthesia.  

UK PubMed Central (United Kingdom)

Grapheme-color synesthesia is a neurological phenomenon in which letters and numbers (graphemes) consistently evoke particular colors (e.g. A may be experienced as red). The cross-activation theory proposes that synesthesia arises as a result of cross-activation between posterior temporal grapheme areas (PTGA) and color processing area V4, while the disinhibited feedback theory proposes that synesthesia arises from disinhibition of pre-existing feedback connections. Here we used magnetoencephalography (MEG) to test whether V4 and PTGA activate nearly simultaneously, as predicted by the cross-activation theory, or whether V4 activation occurs only after the initial stages of grapheme processing, as predicted by the disinhibited feedback theory. Using our high-resolution MEG source imaging technique (VESTAL), PTGA and V4 regions of interest (ROIs) were separately defined, and activity in response to the presentation of achromatic graphemes was measured. Activation levels in PTGA did not significantly differ between synesthetes and controls (suggesting similar grapheme processing mechanisms), whereas activation in V4 was significantly greater in synesthetes. In synesthetes, PTGA activation exceeded baseline levels beginning 105-109ms, and V4 activation did so 5ms later, suggesting nearly simultaneous activation of these areas. Results are discussed in the context of an updated version of the cross-activation model, the cascaded cross-tuning model of grapheme-color synesthesia.

Brang D; Hubbard EM; Coulson S; Huang M; Ramachandran VS

2010-10-01

76

Resting state magnetoencephalography functional connectivity in traumatic brain injury.  

UK PubMed Central (United Kingdom)

OBJECT: Traumatic brain injury (TBI) is one of the leading causes of morbidity worldwide. One mechanism by which blunt head trauma may disrupt normal cognition and behavior is through alteration of functional connectivity between brain regions. In this pilot study, the authors applied a rapid automated resting state magnetoencephalography (MEG) imaging technique suitable for routine clinical use to test the hypothesis that there is decreased functional connectivity in patients with TBI compared with matched controls, even in cases of mild TBI. Furthermore, they posit that these abnormal reductions in MEG functional connectivity can be detected even in TBI patients without specific evidence of traumatic lesions on 3-T MR images. Finally, they hypothesize that the reductions of functional connectivity can improve over time across serial MEG scans during recovery from TBI. METHODS: Magnetoencephalography maps of functional connectivity in the alpha (8- to 12-Hz) band from 21 patients who sustained a TBI were compared with those from 18 age- and sex-matched controls. Regions of altered functional connectivity in each patient were detected in automated fashion through atlas-based registration to the control database. The extent of reduced functional connectivity in the patient group was tested for correlations with clinical characteristics of the injury as well as with findings on 3-T MRI. Finally, the authors compared initial connectivity maps with 2-year follow-up functional connectivity in a subgroup of 5 patients with TBI. RESULTS: Fourteen male and 7 female patients (17-53 years old, median 29 years) were enrolled. By Glasgow Coma Scale (GCS) criteria, 11 patients had mild, 1 had moderate, and 3 had severe TBI, and 6 had no GCS score recorded. On 3-T MRI, 16 patients had abnormal findings attributable to the trauma and 5 had findings in the normal range. As a group, the patients with TBI had significantly lower functional connectivity than controls (p < 0.01). Three of the 5 patients with normal findings on 3-T MRI showed regions of abnormally reduced MEG functional connectivity. No significant correlations were seen between extent of functional disconnection and injury severity or posttraumatic symptoms (p > 0.05). In the subgroup undergoing 2-year follow-up, the second MEG scan demonstrated a significantly lower percentage of voxels with decreased connectivity (p < 0.05) than the initial MEG scan. CONCLUSIONS: A rapid automated resting-state MEG imaging technique demonstrates abnormally decreased functional connectivity that may persist for years after TBI, including cases classified as "mild" by GCS criteria. Disrupted MEG connectivity can be detected even in some patients with normal findings on 3-T MRI. Analysis of follow-up MEG scans in a subgroup of patients shows that, over time, the abnormally reduced connectivity can improve, suggesting neuroplasticity during the recovery from TBI. Resting state MEG deserves further investigation as a prognostic and predictive biomarker for TBI.

Tarapore PE; Findlay AM; Lahue SC; Lee H; Honma SM; Mizuiri D; Luks TL; Manley GT; Nagarajan SS; Mukherjee P

2013-06-01

77

Neural effects of prolonged mental fatigue: A magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Mental fatigue, manifest as a reduced efficiency for mental work load, is prevalent in modern society. It is important to understand the neural mechanisms of mental fatigue and to develop appropriate methods for evaluating mental fatigue. In this study we quantified the effect of a long-duration mental fatigue-inducing task on neural activity. We used magnetoencephalography (MEG) to examine the time course change of neural activity over the long duration of the task trials. Nine healthy male volunteers participated in this study. They performed two mental fatigue-inducing tasks on separate days. The order of task presentation was randomized in a single-blinded, crossover fashion. Each task consisted of 25-min mental fatigue-inducing 0- or 2-back task session for three times. Subjective rating of mental fatigue sensation and electrocardiogram, and resting state MEG measurements were performed just before and after each task session. MEG data were analyzed using narrow-band adaptive spatial filtering methods. Alpha band (8-13Hz) power in the visual cortex decreased after performing the mental fatigue-inducing tasks, and the decrease of alpha power was greater when they performed 2-back task trials. The decrease in alpha power was positively associated with the self-reported level of mental fatigue sensation and sympathetic nerve activity level. These results demonstrate that performing the prolonged mental fatigue-inducing task causes overactivation of the visual cortex, manifest as decreased alpha power in this brain region. Our results increase understanding of the neural mechanisms of mental fatigue and can be used to develop new quantitative methods to assess mental fatigue.

Ishii A; Tanaka M; Shigihara Y; Kanai E; Funakura M; Watanabe Y

2013-09-01

78

The role of magnetoencephalography in children undergoing hemispherectomy.  

UK PubMed Central (United Kingdom)

OBJECT: Hemispherectomy is an established neurosurgical procedure for medication-resistant epilepsy in children. Despite the effectiveness of this technique, there are patients who do not achieve an optimum outcome after surgery; possible causes of suboptimal results include the presence of bilateral independent epileptogenic foci. Magnetoencephalography (MEG) is an emerging tool that has been found to be useful in the management of lesional and nonlesional epilepsy. The authors analyzed the relative contribution of MEG in patient selection for hemispherectomy. METHODS: The medical records of children undergoing hemispherectomy at the Hospital for Sick Children were reviewed. Those patients who underwent MEG as part of the presurgical evaluation were selected. RESULTS: Thirteen patients were included in the study. Nine patients were boys. The mean age at the time of surgery was 66 months (range 10-149 months). Seizure etiology was Rasmussen encephalitis in 6 patients, hemimegalencephaly in 2 patients, and cortical dysplasia in 4 patients. In 8 patients, video-EEG and MEG results were consistent to localize the primary epileptogenic hemisphere. In 2 patients, video-EEG lateralized the ictal onset, but MEG showed bilateral spikes. Two patients had bilateral video-EEG and MEG spikes. Engel Class I, II, and IV outcomes were seen in 10, 2, and 1 patients, respectively. In 2 of the patients who had an outcome other than Engel Class I, the MEG clusters were concentrated in the disconnected hemisphere. The third patient had bilateral clusters and potentially independent epileptogenic foci from bilateral cortical dysplasia. CONCLUSIONS: The presence of unilateral MEG spike waves correlated with good outcomes following hemispherectomy. In some cases, MEG provides information that differs from that obtained from video-EEG and conventional MR imaging studies. Further studies with a greater number of patients are needed to assess the role of MEG in the preoperative assessment of candidates for hemispherectomy.

Torres CV; Fallah A; Ibrahim GM; Cheshier S; Otsubo H; Ochi A; Chuang S; Snead OC; Holowka S; Rutka JT

2011-12-01

79

Sensitivity of scalp 10-20 EEG and magnetoencephalography.  

UK PubMed Central (United Kingdom)

Although previous studies have investigated the sensitivity of electroencephalography (EEG) and magnetoencephalography (MEG) to detect spikes by comparing simultaneous recordings, there are no published reports that focus on the relationship between spike dipole orientation or sensitivity of scalp EEG/MEG and the "gold standard" of intracranial recording (stereotactic EEG). We evaluated two patients with focal epilepsy; one with lateral temporal focus and the other with insular focus. Two MEG recordings were performed for both patients, each recorded simultaneously with initially scalp EEG, based on international 10-20 electrode placement with additional electrodes for anterior temporal regions, and subsequently stereotactic EEG. Localisation of MEG spike dipoles from both studies was concordant and all MEG spikes were detected by stereotactic EEG. For the patient with lateral temporal epilepsy, spike sensitivity of MEG and scalp EEG (relative to stereotactic EEG) was 55 and 0%, respectively. Of note, in this case, MEG spike dipoles were oriented tangentially to scalp surface in a tight cluster; the angle of the spike dipole to the vertical line was 3.6 degrees. For the patient with insular epilepsy, spike sensitivity of MEG and scalp EEG (relative to stereotactic EEG) was 83 and 44%, respectively; the angle of the spike dipole to the vertical line was 45.3 degrees. For the patient with lateral temporal epilepsy, tangential spikes from the lateral temporal cortex were difficult to detect based on scalp 10-20 EEG and for the patient with insular epilepsy, it was possible to evaluate operculum insular sources using MEG. We believe that these findings may be important for the interpretation of clinical EEG and MEG.

Kakisaka Y; Alkawadri R; Wang ZI; Enatsu R; Mosher JC; Dubarry AS; Alexopoulos AV; Burgess RC

2013-03-01

80

STATE-SPACE SOLUTIONS TO THE DYNAMIC MAGNETOENCEPHALOGRAPHY INVERSE PROBLEM USING HIGH PERFORMANCE COMPUTING.  

UK PubMed Central (United Kingdom)

Determining the magnitude and location of neural sources within the brain that are responsible for generating magnetoencephalography (MEG) signals measured on the surface of the head is a challenging problem in functional neuroimaging. The number of potential sources within the brain exceeds by an order of magnitude the number of recording sites. As a consequence, the estimates for the magnitude and location of the neural sources will be ill-conditioned because of the underdetermined nature of the problem. One well-known technique designed to address this imbalance is the minimum norm estimator (MNE). This approach imposes an L(2) regularization constraint that serves to stabilize and condition the source parameter estimates. However, these classes of regularizer are static in time and do not consider the temporal constraints inherent to the biophysics of the MEG experiment. In this paper we propose a dynamic state-space model that accounts for both spatial and temporal correlations within and across candidate intra-cortical sources. In our model, the observation model is derived from the steady-state solution to Maxwell's equations while the latent model representing neural dynamics is given by a random walk process. We show that the Kalman filter (KF) and the Kalman smoother [also known as the fixed-interval smoother (FIS)] may be used to solve the ensuing high-dimensional state-estimation problem. Using a well-known relationship between Bayesian estimation and Kalman filtering, we show that the MNE estimates carry a significant zero bias. Calculating these high-dimensional state estimates is a computationally challenging task that requires High Performance Computing (HPC) resources. To this end, we employ the NSF Teragrid Supercomputing Network to compute the source estimates. We demonstrate improvement in performance of the state-space algorithm relative to MNE in analyses of simulated and actual somatosensory MEG experiments. Our findings establish the benefits of high-dimensional state-space modeling as an effective means to solve the MEG source localization problem.

Long CJ; Purdon PL; Temereanca S; Desai NU; Hämäläinen MS; Brown EN

2011-06-01

 
 
 
 
81

Multipolar Interaction Derived from d--f Hybridization in Pr-Based Filled Skutterudite Compounds  

Science.gov (United States)

The conduction bands of the skutterudite compounds are composed of p orbitals of the pnictogen cages and d orbitals of the transition metal ions. In this paper, we address the effect of hybridization between the d bands and localized 4f states in relation with ordering and fluctuation of multipole moments in Pr-based filled skutterudites. First, we study the properties of a non-degenerate d band around the zone center in the framework of a tight-binding band model. Introducing a realistic form of the d--f hybridization, we show that the ag band can be hybridized only with the ?8 orbitals of f electrons. Then, we derive d--f multipolar interactions from the hybridization in the localized limit of f electrons in which the basis states are restricted to the singlet--triplet crystal field states. It is found that the quadrupolar interaction of the Oxy-type becomes predominant in the case of the singlet ground state, whereas the triplet ground state apparently favors the magnetic interaction. The relationship with experimental results in the Pr skutterudites, especially in PrOs4Sb12 and PrFe4As12, is discussed in view of the nature of quadrupolar and magnetic interactions. It is shown that the complex non-collinear magnetic structure of Fe ions observed in the latter material is reproduced well by the effective d--f interaction.

Shiina, Ryousuke

2012-02-01

82

Potential application of multipolarization SAR for pine-plantation biomass estimation  

Energy Technology Data Exchange (ETDEWEB)

This paper presents the techniques and the potential utility of multipolarization Synthetic Aperture Radar (SAR) data for pine-plantation biomass estimation. Three channels of SAR data, one from the Shuttle Imaging Radar SIR-A and the other two from the aircraft SAR, were acquired over the Baldwin County, Alabama, study area. The SIR-A data were acquired with HH polarization and the aircraft SAR data with VV and VH polarizations. Linear regression techniques are used to estimate the pine-plantation biomass, tree height, and age using 21 test plots. The results indicate that the multipolarization data are highly related to the plantation biomass. The results suggest a potential application of multipolarization SAR for pine-plantation biomass estimation.

Wu, S.T.

1987-05-01

83

Semantic and Phonological Task-Set Priming and Stimulus Processing Investigated Using Magnetoencephalography (MEG)  

Science.gov (United States)

|In this study the neural substrates of semantic and phonological task priming and task performance were investigated using single word task-primes. Magnetoencephalography (MEG) data were analysed using Synthetic Aperture Magnetometry (SAM) to determine the spatiotemporal and spectral characteristics of cortical responses. Comparisons were made…

McNab, F.; Rippon, G.; Hillebrand, A.; Singh, K. D.; Swithenby, S. J.

2007-01-01

84

The Influence of Semantic Processing on Phonological Decisions in Children and Adults: A Magnetoencephalography (MEG) Study  

Science.gov (United States)

Purpose: To examine the behavioral effects and neural activation patterns associated with implicit semantic processing influences on phonological judgments during reading in children and adults. Method: Whole-head magnetoencephalography (MEG) recordings were obtained from 2 groups, children (9-13 years) and adults, performing a homophone judgment…

Wehner, Daniel T.; Ahlfors, Seppo P.; Mody, Maria

2007-01-01

85

Semantic and Phonological Task-Set Priming and Stimulus Processing Investigated Using Magnetoencephalography (MEG)  

Science.gov (United States)

In this study the neural substrates of semantic and phonological task priming and task performance were investigated using single word task-primes. Magnetoencephalography (MEG) data were analysed using Synthetic Aperture Magnetometry (SAM) to determine the spatiotemporal and spectral characteristics of cortical responses. Comparisons were made…

McNab, F.; Rippon, G.; Hillebrand, A.; Singh, K. D.; Swithenby, S. J.

2007-01-01

86

Hydrogenic Lamb shift through the electric quadrupole approximations in radiation and multipolar gauge  

International Nuclear Information System (INIS)

A comparison of the Hydrogenic Lamb shift, calculated from the minimal-coupling and multipolar interaction's, is made. The transition frequency of 2S1/2 ? 2P1/2 in the electric-dipole approximation as well as the electric-quadrupole and magnetic-dipole approximations, is given. The two interactions, within the electric and magnetic dipole approximations yield identical results, while the electric quadrupole corrections are drastically different. The total transition frequency from the multipolar form is in complete agreement with experiment, indicating that this form is most suitable for perturbative calculations.

2001-01-01

87

Assessment of cortical dysfunction in human strabismic amblyopia using magnetoencephalography (MEG)  

Energy Technology Data Exchange (ETDEWEB)

The aim of this study was to use the technique of magnetoencephalography (MEG) to determine the effects of strabismic amblyopia on the processing of spatial information within the occipital cortex of humans. We recorded evoked magnetic responses to the onset of a chromatic (red/green) sinusoidal grating of periodicity 0.5-4.0 c deg{sup -1} using a 19-channel SQUID-based neuromagnetometer. Evoked responses were recorded monocularly on six amblyopes and six normally-sighted controls, the stimuli being positioned near the fovea in the lower right visual field of each observer. For comparison, the spatial contrast sensitivity function (CSF) for the detection of chromatic gratings was measured for one amblyope and one control using a two alternate forced-choice psychophysical procedure. We chose red/green sinusoids as our stimuli because they evoke strong magnetic responses from the occipital cortex in adult humans (Fylan, Holliday, Singh, Anderson and Harding. (1997). Neuroimage, 6, 47-57). Magnetic field strength was plotted as a function of stimulus spatial frequency for each eye of each subject. Interocular differences were only evident within the amblyopic group: for stimuli of 1-2 c deg{sup -1}, the evoked responses had significantly longer latencies and reduced amplitudes through the amblyopic eye (P<0.05). Importantly, the extent of the deficit was uncorrelated with either Snellen acuity or contrast sensitivity. Localization of the evoked responses was performed using a single equivalent current dipole model. Source localizations, for both normal and amblyopic subjects, were consistent with neural activity at the occipital pole near the V1/V2 border. We conclude that MEG is sensitive to the deficit in cortical processing associated with human amblyopia, and can be used to make quantitative neurophysiological measurements. The nature of the cortical deficit is discussed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

Anderson, S.J. [Department of Psychology, Royal Holloway, University of London, Egham, Surrey (United Kingdom); Holliday, I.E.; Harding, G.F.A. [Clinical Neurophysiology Unit, Department of Psychology, Aston University, Birmingham (United Kingdom)

1999-05-01

88

Can magnetoencephalography track the afferent information flow along white matter thalamo-cortical fibers?  

UK PubMed Central (United Kingdom)

White matter thalamo-cortical fibers allow the communication of distant brain regions by carrying neuronal signals. Mapping non-invasively the information flow within white matter fibers is regarded so far as impossible. We investigated here whether information flow propagating along thalamo-cortical fibers can be detected using magnetoencephalography (MEG). Somatosensory evoked fields (SEFs) were recorded from healthy subjects and a patient with a unilateral, prenatally acquired, white matter lesion, which had induced the development of an abnormal trajectory of thalamo-cortical fibers. Equivalent current dipole (ECD) was used to model sources of SEFs. ECD at ~15 ms after stimulus onset was located within or close to the contralateral thalamus at the proximity of a hemodynamic response detected during a similar fMRI experiment. At the M20 peak latency, ECD was localized within the hand area of the contralateral primary somatosensory cortex (Brodmann area 3b (BA3b)). In healthy subjects, ECD changed dynamically position from thalamus to BA3b following a curved path, which was partially overlapping the thalamo-cortical fibers reconstructed by tractography. In the patient, ECD followed a similar path only in the intact hemisphere. In the affected hemisphere, the dipole trajectory circumnavigated the extended lesion on its way to the preserved primary somatosensory cortex--similar to the trajectory findings. Evidence from different methodological approaches converges on the conclusion that MEG can track the afferent information flow along thalamo-cortical fibers and in contrast to the traditional view can localize under presuppositions deep thalamic sources.

Papadelis C; Leonardelli E; Staudt M; Braun C

2012-04-01

89

The use of contact heat evoked potential stimulator (CHEPS) in magnetoencephalography for pain research.  

UK PubMed Central (United Kingdom)

BACKGROUND: Contact heat evoked potentials (CHEP) is a thermal stimulus modality used in pain research. We examine a commercial CHEP stimulator (CHEPS) that is designed to work in an fMRI environment, but poorly understood in the MEG environment. The CHEPS attains target temperatures rapidly using sophisticated control signals that unfortunately induce artifacts in the MEG. In this paper, we summarize our experiences using the CHEPS in MEG to study pain using an experimental paradigm, and propose a novel method for managing its artifact. NEW METHOD: We introduce a novel damped sinusoid modeling (DSM) technique to remove the CHEPS artifact based on estimates of the underlying sinusoids and damping factors. We show comparisons to signal space projection (SSP) and temporal signal space separation (tSSS) methods. RESULTS: The CHEPS artifact is highly dynamic, yet deterministic, switching rapidly from one frequency to another, with different spatial components. The galvanic connection between the subject and the CHEPS probe alters its performance, making pre-characterization difficult. COMPARISON WITH EXISTING METHODS: SSP methods failed to remove the artifact completely. TSSS performed better than SSP; however, tSSS requires the use of a multipolar head model that decreases the dimensionality and possibly the information content of the data. In contrast, DSM offers a strictly temporal modeling approach in which the artifact is estimated as a sum of damped sinusoids which is subtracted from the data. CONCLUSION: Though the CHEPS increases the noise floor and introduces artifacts to the data, we believe the device can be successfully used in MEG if appropriate artifact removal techniques are followed.

Gopalakrishnan R; Machado AG; Burgess RC; Mosher JC

2013-08-01

90

p53 dependent centrosome clustering prevents multipolar mitosis in tetraploid cells.  

UK PubMed Central (United Kingdom)

BACKGROUND: p53 abnormality and aneuploidy often coexist in human tumors, and tetraploidy is considered as an intermediate between normal diploidy and aneuploidy. The purpose of this study was to investigate whether and how p53 influences the transformation from tetraploidy to aneuploidy. PRINCIPAL FINDINGS: Live cell imaging was performed to determine the fates and mitotic behaviors of several human and mouse tetraploid cells with different p53 status, and centrosome and spindle immunostaining was used to investigate centrosome behaviors. We found that p53 dominant-negative mutation, point mutation, or knockout led to a 2? 33-fold increase of multipolar mitosis in N/TERT1, 3T3 and mouse embryonic fibroblasts (MEFs), while mitotic entry and cell death were not significantly affected. In p53-/- tetraploid MEFs, the ability of centrosome clustering was compromised, while centrosome inactivation was not affected. Suppression of RhoA/ROCK activity by specific inhibitors in p53-/- tetraploid MEFs enhanced centrosome clustering, decreased multipolar mitosis from 38% to 20% and 16% for RhoA and ROCK, respectively, while expression of constitutively active RhoA in p53+/+ tetraploid 3T3 cells increased the frequency of multipolar mitosis from 15% to 35%. CONCLUSIONS: p53 could not prevent tetraploid cells entering mitosis or induce tetraploid cell death. However, p53 abnormality impaired centrosome clustering and lead to multipolar mitosis in tetraploid cells by modulating the RhoA/ROCK signaling pathway.

Yi Q; Zhao X; Huang Y; Ma T; Zhang Y; Hou H; Cooke HJ; Yang DQ; Wu M; Shi Q

2011-01-01

91

A study of the multipolar composition of the electrofission cross section of 237Np  

International Nuclear Information System (INIS)

[en] The electrofission cross section for 237Np was measured over the energy range from 0,6 to 60,0 MeV. The multipolar composition of this cross section was investigated using the virtual photons formalism with three different techniques of analysis: unfolding and two versions of multiple parameter regression. (A.C.A.S.)

1987-01-01

92

STATE-SPACE SOLUTIONS TO THE DYNAMIC MAGNETOENCEPHALOGRAPHY INVERSE PROBLEM USING HIGH PERFORMANCE COMPUTING.  

Science.gov (United States)

Determining the magnitude and location of neural sources within the brain that are responsible for generating magnetoencephalography (MEG) signals measured on the surface of the head is a challenging problem in functional neuroimaging. The number of potential sources within the brain exceeds by an order of magnitude the number of recording sites. As a consequence, the estimates for the magnitude and location of the neural sources will be ill-conditioned because of the underdetermined nature of the problem. One well-known technique designed to address this imbalance is the minimum norm estimator (MNE). This approach imposes an L(2) regularization constraint that serves to stabilize and condition the source parameter estimates. However, these classes of regularizer are static in time and do not consider the temporal constraints inherent to the biophysics of the MEG experiment. In this paper we propose a dynamic state-space model that accounts for both spatial and temporal correlations within and across candidate intra-cortical sources. In our model, the observation model is derived from the steady-state solution to Maxwell's equations while the latent model representing neural dynamics is given by a random walk process. We show that the Kalman filter (KF) and the Kalman smoother [also known as the fixed-interval smoother (FIS)] may be used to solve the ensuing high-dimensional state-estimation problem. Using a well-known relationship between Bayesian estimation and Kalman filtering, we show that the MNE estimates carry a significant zero bias. Calculating these high-dimensional state estimates is a computationally challenging task that requires High Performance Computing (HPC) resources. To this end, we employ the NSF Teragrid Supercomputing Network to compute the source estimates. We demonstrate improvement in performance of the state-space algorithm relative to MNE in analyses of simulated and actual somatosensory MEG experiments. Our findings establish the benefits of high-dimensional state-space modeling as an effective means to solve the MEG source localization problem. PMID:22081780

Long, Christopher J; Purdon, Patrick L; Temereanca, Simona; Desai, Neil U; Hämäläinen, Matti S; Brown, Emery N

2011-06-01

93

Fetal magnetoencephalography: a non-invasive method for the assessment of fetal neuronal maturation.  

UK PubMed Central (United Kingdom)

OBJECTIVE: To assess the maturation of auditory evoked cortical responses in the human fetus using fetal magnetoencephalography. DESIGN: Prospective case series over a three-year period. SETTING: Antenatal clinics, university hospital. POPULATION: Singleton pregnancies at 29-40 weeks of gestation. METHODS: We used a 31-channel-SQUID-biomagnetometer in a magnetically-shielded room to perform fetal magnetoencephalography. To record auditory evoked fields from the fetal brain we applied 500 monotonal bursts generated by a computerised sound generator directly to the maternal abdominal wall near the fetal head. The continuously recorded data sets were analysed stepwise using a specially developed heart artefact rejection software, Fourier filtering, principle component analysis and half split analysis of the averaged data. RESULTS: In 36 of 64 examinations we detected signals of auditory evoked fields comparable to the P2m component in adults. The earliest recording succeeded in the 29th gestational week. The latencies of the auditory evoked responses declined during the third trimester from 300 ms to nearly 150 ms at term. The maturation of different components of the auditory evoked field could be demonstrated from the 31st gestational week onwards. CONCLUSION: The maturation of a fetal auditory cortical function using fetal magnetoencephalography could be assessed directly for the first time. We believe that this method will add information to current indirect methods of assessing the normal maturation of the human fetal brain.

Schleussner E; Schneider U; Kausch S; Kähler C; Haueisen J; Seewald HJ

2001-12-01

94

Detailed angular correlation analysis with 4? spectrometers: Spin determinations and multipolarity mixing measurements in 128Ba  

Science.gov (United States)

We analyze for the first time the full ?? directional correlations from oriented states (DCO) in an experiment performed with the GASP detector array. Our analysis is based on a transformation of the directional information into expansion coefficients of an orthogonal basis. With this method, which we call SpeeDCO (spectral expansion of DCO), the complete DCO information is concentrated in 12 ?? coincidence spectra. The analysis is applicable to all detector arrays which uniformly cover the solid angle. We show that the complete DCO information can be used for a reliable and unique determination of spins and multipolarity mixing ratios in weakly populated bands. We were able to establish the spins and the positive parity of the ?I=1 ``M1 band'' in 128Ba and multipolarity mixing ratios of nine M1/E2 in-band transitions were derived as well. The measured values are in good agreement with those expected for a high-K rotational band.

Wiedenhöver, I.; Vogel, O.; Klein, H.; Dewald, A.; von Brentano, P.; Gableske, J.; Krücken, R.; Nicolay, N.; Gelberg, A.; Petkov, P.; Gizon, A.; Gizon, J.; Bazzacco, D.; Rossi Alvarez, C.; de Angelis, G.; Lunardi, S.; Pavan, P.; Napoli, D. R.; Frauendorf, S.; Dönau, F.; Janssens, R. V.; Carpenter, M. P.

1998-08-01

95

The emerging multi-polar world and China's grand game  

Energy Technology Data Exchange (ETDEWEB)

This talk outlines a scenario describing an emerging multipolar world that is aligned with geographical regions. The stability and security of this multipolar world is examined with respect to demographics, trade (economics), resource constraints, and development. In particular I focus on Asia which has two large countries, China and India, competing for resources and markets and examine the emerging regional relations, opportunities and threats. These relationships must overcome many hurdles - the Subcontinent is in a weak position politically and strategically and faces many threats, and China's growing power could help stabilize it or create new threats. Since the fate of 1.5 billion (2.4 billion by 2050) people depends on how the Subcontinent evolves, this talk is meant to initiates a discussion of what China and India can do to help the region develop and stabilize.

Gupta, Rajan [Los Alamos National Laboratory

2011-01-19

96

Bipolar versus multipolar radiofrequency (RF) ablation for the treatment of renal cell carcinoma: differences in technical and clinical parameters.  

UK PubMed Central (United Kingdom)

PURPOSE: This study aimed to compare retrospectively bipolar RF ablation with multipolar RF ablation for the treatment of renal cell carcinoma. MATERIALS AND METHODS: Between March 2009 and June 2012, 12 tumours (nine patients) treated with bipolar RF ablation (one applicator) and 14 tumours (11 patients) treated with multipolar RF ablation (two applicators) were compared systematically. Selection between bipolar RF ablation and multipolar RF ablation was operator choice considering tumour size. Study goals included differences in tumour and coagulation extent, and technical parameters (total RF energy delivery and RF ablation time per coagulation volume). RESULTS: Tumour maximum diameter was significantly larger for multipolar RF ablation compared with bipolar RF ablation (27.0?mm versus 19.4?mm; p?multipolar RF ablation compared with bipolar RF ablation (35.0?mm versus 26.5?mm, 27.5?mm versus 23.0?mm and 14.3?cm(3) versus 8.1?cm(3); p?multipolar RF ablation compared with bipolar RF ablation (52.0?kJ versus 28.6?kJ and 2.4?min/cm(3) versus 4.1?min/cm(3); p?Multipolar RF ablation creates a significantly larger coagulation width, but identical coagulation shape, compared with bipolar RF ablation. Additionally, multipolar RF ablation coagulates faster according to the shorter RF ablation time per coagulation volume.

Sommer CM; Lemm G; Hohenstein E; Stampfl U; Bellemann N; Teber D; Rassweiler J; Kauczor HU; Radeleff BA; Pereira PL

2013-01-01

97

Comparison of microwave ablation and multipolar radiofrequency ablation in vivo using two internally cooled probes.  

UK PubMed Central (United Kingdom)

OBJECTIVE: The objective of our study was to compare the effectiveness of microwave ablation (MWA) and multipolar radiofrequency ablation (RFA) in vivo using two internally cooled probes. MATERIALS AND METHODS: MWA (n=24) was performed by simultaneous application of double internally cooled-shaft antennae. Three power settings (60, 70, and 80 W) were used. Multipolar RFA (n=16) was also performed by simultaneously using two internally cooled bipolar applicators (lengths: 3-cm T30 and 4-cm T40) at 60 and 80 W. Probe spacing was 2 cm. Each power setting was applied for eight ablations with a 10-minute duration for each. The cooled-shaft probes were inserted approximately 7 cm into the liver parenchyma of seven adult Wuzhishan pigs under ultrasound guidance, and ablations were performed in various segments of porcine liver. The long-axis diameter (Dl), short-axis diameter (Ds) and the ratio Ds/Dl for each ablation was measured. Temperature curves at 0, 2, and 3 cm from the middle of the two probes and the time to reach 60°C at 0 cm from the parallel central line between the two probes were recorded. RESULTS: The long-axis diameter and short-axis diameter for all the power settings of MWA were significantly larger than that of both kinds of multipolar RFA (p<0.05). The rates of temperature rise to 60°C at 0 cm from the parallel central line between the two probes for all MWA power settings were significantly faster compared with RFA. CONCLUSION: MWA, by the simultaneous application of double antennae, can generate a larger ablation zone, in vivo, compared with multipolar RFA.

Fan W; Li X; Zhang L; Jiang H; Zhang J

2012-01-01

98

Multipolar polarizations of methane from isotropic and anisotropic collision-induced light scattering  

International Nuclear Information System (INIS)

[en] The anisotropic and isotropic binary collision-induced spectra scattered by gaseous methane have been measured in absolute units up to 900 cm-1 from the Rayleigh line. Corresponding theoretical intensities taking into account multipolar polarizabilities have been calculated using a semiclassical procedure. From the analysis of, mainly, our isotropic scattering data, values of the dipole-quadrupole and dipole-octopole polarizabilities are deduced. They are found to be in good agreement with recent ab initio calculations

2004-01-01

99

RP58 regulates the multipolar-bipolar transition of newborn neurons in the developing cerebral cortex.  

UK PubMed Central (United Kingdom)

Accumulating evidence suggests that many brain diseases are associated with defects in neuronal migration, suggesting that this step of neurogenesis is critical for brain organization. However, the molecular mechanisms underlying neuronal migration remain largely unknown. Here, we identified the zinc-finger transcriptional repressor RP58 as a key regulator of neuronal migration via multipolar-to-bipolar transition. RP58(-/-) neurons exhibited severe defects in the formation of leading processes and never shifted to the locomotion mode. Cre-mediated deletion of RP58 using in utero electroporation in RP58(flox/flox) mice revealed that RP58 functions in cell-autonomous multipolar-to-bipolar transition, independent of cell-cycle exit. Finally, we found that RP58 represses Ngn2 transcription to regulate the Ngn2-Rnd2 pathway; Ngn2 knockdown rescued migration defects of the RP58(-/-) neurons. Our findings highlight the critical role of RP58 in multipolar-to-bipolar transition via suppression of the Ngn2-Rnd2 pathway in the developing cerebral cortex.

Ohtaka-Maruyama C; Hirai S; Miwa A; Heng JI; Shitara H; Ishii R; Taya C; Kawano H; Kasai M; Nakajima K; Okado H

2013-02-01

100

Comparison of magnetoencephalography with other functional imaging techniques.  

UK PubMed Central (United Kingdom)

Recent advances in instrumentation and analysis in biomagnetism offer a unique tool for studying the spatiotemporal evolution of spontaneous brain activity as well as activity evoked by a stimulus. The overall performance characteristics of this and other techniques used to study the dynamics of brain function are compared. Particular emphasis is placed on defining the general spatiotemporal window of brain activity that each technique makes accessible. Similarities and differences associated with diverse modelling schemes for extracting source current density properties from electrographic recordings are stated.

Ioannides AA

1991-01-01

 
 
 
 
101

Post-Newtonian factorized multipolar waveforms for spinning, nonprecessing black-hole binaries  

International Nuclear Information System (INIS)

We generalize the factorized resummation of multipolar waveforms introduced by Damour, Iyer, and Nagar to spinning black holes. For a nonspinning test particle spiraling a Kerr black hole in the equatorial plane, we find that factorized multipolar amplitudes which replace the residual relativistic amplitude flm with its lth root, ?lm=flm1/l, agree quite well with the numerical amplitudes up to the Kerr-spin value q?0.95 for orbital velocities v?0.4. The numerical amplitudes are computed solving the Teukolsky equation with a spectral code. The agreement for prograde orbits and large spin values of the Kerr black-hole can be further improved at high velocities by properly factoring out the lower-order post-Newtonian contributions in ?lm. The resummation procedure results in a better and systematic agreement between numerical and analytical amplitudes (and energy fluxes) than standard Taylor-expanded post-Newtonian approximants. This is particularly true for higher-order modes, such as (2,1), (3,3), (3,2), and (4,4), for which less spin post-Newtonian terms are known. We also extend the factorized resummation of multipolar amplitudes to generic mass-ratio, nonprecessing, spinning black holes. Lastly, in our study we employ new, recently computed, higher-order post-Newtonian terms in several subdominant modes and compute explicit expressions for the half and one-and-half post-Newtonian contributions to the odd-parity (current) and even-parity (odd) multipoles, respectively. Those results can be used to build more accurate templates for ground-based and space-based gravitational-wave detectors.

2011-03-15

102

Study on the radiations in the 205At decay. Transition multipolarities in the 205Po  

International Nuclear Information System (INIS)

Spectra of radiations in the 205At decay (Tsub(1/2=26.2 min)) are studied by means of semiconductor detectors and iron-free toroidal ?-spectrometer. In the measurements was used the monoisotopic sources of the 205At. 148 ?-transitions have been discovered which accompany the 205At decay, information about 94 transition has been derived for the first time. The total 70 transition multipolarity has been determined, for 54 of them - for the first time. The measurements of e-? - coincidences were performed. (author).

1982-01-01

103

Determination of multipolarities and mixing ratios of some ? transitions following 125Sb decay by ?-? Angular Correlation  

International Nuclear Information System (INIS)

125Sb decays by ?- emission to 125Te with a half-life of 2.76 years. The angular correlations of some ?-ray transitions of this decay have been studied in order to determine their multipolarities and mixing ratios. The experimental set-up included a planar-Ge detector to measure the low-energy ?-rays, a coaxial Ge detector and a movable device to determine precisely the angle between the axes of the detectors. Results obtained in the experiments and other available data were processed to obtain the best values for the mixing ratios

1998-09-11

104

Transformation of the multipolar components of gravitational radiation under rotations and boosts  

CERN Document Server

We study the transformation of multipolar decompositions of gravitational radiation under rotations and boosts. Rotations to the remnant black hole's frame simplify the waveforms from the merger of generic spinning black hole binaries. Boosts may be important to get an accurate gravitational-wave phasing, especially for configurations leading to large recoil velocities of the remnant. As a test of our formalism we revisit the classic problem of point particles falling into a Schwarzschild black hole. Then we highlight by specific examples the importance of choosing the right frame in numerical simulations of unequal-mass, spinning binary black-hole mergers.

Gualtieri, L; Cardoso, V; Sperhake, U

2008-01-01

105

Comparison of three methods for localizing interictal epileptiform discharges with magnetoencephalography.  

UK PubMed Central (United Kingdom)

PURPOSE: To compare three methods of localizing the source of epileptiform activity recorded with magnetoencephalography: equivalent current dipole, minimum current estimate, and dynamic statistical parametric mapping (dSPM), and to evaluate the solutions by comparison with clinical symptoms and other electrophysiological and neuroradiological findings. METHODS: Fourteen children of 3 to 15 years were studied. Magnetoencephalography was collected with a whole-head 204-channel helmet-shaped sensor array. We calculated equivalent current dipoles and made minimum current estimate and dSPM movies to estimate the cortical distribution of interictal epileptiform discharges in these patients. RESULTS: The results for four patients with localization-related epilepsy and one patient with Landau-Kleffner Syndrome were consistent among all the three analysis methods. In the rest of the patients, minimum current estimate and dSPM suggested multifocal or widespread activity; in these patients, the equivalent current dipole results were so scattered that interpretation of the results was not possible. For 9 patients with localization-related epilepsy and generalized epilepsy, the epileptiform discharges were wide spread or only slow waves, but dSPM suggested a possible propagation path of the interictal epileptiform discharges. CONCLUSION: Minimum current estimate and dSPM could identify the propagation of epileptiform activity with high temporal resolution. The results of dSPM were more stable because the solutions were less sensitive to background brain activity.

Shiraishi H; Ahlfors SP; Stufflebeam SM; Knake S; Larsson PG; Hämäläinen MS; Takano K; Okajima M; Hatanaka K; Saitoh S; Dale AM; Halgren E

2011-10-01

106

Resting-state magnetoencephalography study of “small world” characteristics and cognitive dysfunction in patients with glioma  

Directory of Open Access Journals (Sweden)

Full Text Available Xin-Hua Hu, Ting Lei, Hua-Zhong Xu, Yuan-Jie Zou, Hong-Yi Liu Department of Neurosurgery, Brain Hospital Affiliated to Nanjing Medical University, Nanjing, People's Republic of China Background: The purpose of this study was to analyze “small world” characteristics in glioma patients in order to understand the relationship between cognitive dysfunction and brain functional connectivity network in the resting state. Methods: Resting-state magnetoencephalography was performed in 20 patients with glioma and 20 healthy subjects. The clustering coefficient of the resting functional connectivity network in the brain, average path length, and “small world” index (SWI) were calculated. Cognitive function was estimated by testing of attention, verbal fluency, memory, athletic ability, visual-spatial ability, and intelligence. Results: Compared with healthy controls, patients with glioma showed decreased cognitive function, and diminished low and high gamma band “small world” characteristics in the resting functional connectivity network. Conclusion: The SWI is associated with cognitive function and is diminished in patients with glioma, and is therefore correlated with cognition dysfunction. Keywords: glioma, cognitive dysfunction, “small world”, functional connectivity network, magnetoencephalography

Hu X; Lei T; Xu HZ; Zou YJ; Liu HY

2013-01-01

107

Spatiotemporal neural interactions underlying continuous drawing movements as revealed by magnetoencephalography.  

UK PubMed Central (United Kingdom)

Continuous and sequential movements are controlled by widely distributed brain regions. A series of studies have contributed to understanding the functional role of these regions in a variety of visuomotor tasks. However, little is known about the neural interactions underpinning continuous movements. In the current study, we examine the spatiotemporal neural interactions underlying continuous drawing movements and the association of them with behavioral components. We conducted an experiment in which subjects copied a pentagon continuously for ~45 s using an XY joystick, while neuromagnetic fluxes were recorded from their head using a 248-sensor whole-head magnetoencephalography (MEG) device. Each sensor time series was rendered stationary and non-autocorrelated by applying an autoregressive integrated moving average model and taking the residuals. We used the directional variability of the movement as a behavioral measure of the controls generated. The main objective of this study was to assess the relation between neural interactions and the variability of movement direction. That is, we divided the continuous recordings into consecutive periods (i.e., time-bins) of 51 steps duration and computed the pairwise cross-correlations between the prewhitened time series in each time-bin. The circular standard deviation of the movement direction within each time-bin provides an estimate of the directional variability of the 51-ms trajectory segment. We looked at the association between neural interactions and variability of movement direction, separately for each pair of sensors, by running a cross-correlation analysis between the strength of the MEG pairwise cross-correlations and the circular standard deviations. We identified two types of neuronal networks: in one, the neural interactions are correlated with the directional variability of the movement at negative time-lags (feedforward), and in the other, the neural interactions are correlated with the directional variability of the movement at positive time-lags (feedback). Sensors associated mostly with feedforward processes are distributed in the left hemisphere and the right occipital-temporal junction, whereas sensors related to feedback processes are distributed in the right hemisphere and the left cerebellar hemisphere. These results are in line with findings from a series of previous studies showing that specific brain regions are involved in feedforward and feedback control processes to plan, perform, and correct movements. Additionally, we looked at whether changes in movement direction modulate the neural interactions. Interestingly, we found a preponderance of sensors associated with changes in movement direction over the right hemisphere-ipsilateral to the moving hand. These sensors exhibit stronger coupling with the rest of the sensors for trajectory segments with high rather than low directional movement variability. We interpret these results as evidence that ipsilateral cortical regions are recruited for continuous movements when the curvature of the trajectory increases. To the best of our knowledge, this is the first study that shows how neural interactions are associated with a behavioral control parameter in continuous and sequential movements.

Christopoulos VN; Leuthold AC; Georgopoulos AP

2012-10-01

108

Spatiotemporal neural interactions underlying continuous drawing movements as revealed by magnetoencephalography.  

Science.gov (United States)

Continuous and sequential movements are controlled by widely distributed brain regions. A series of studies have contributed to understanding the functional role of these regions in a variety of visuomotor tasks. However, little is known about the neural interactions underpinning continuous movements. In the current study, we examine the spatiotemporal neural interactions underlying continuous drawing movements and the association of them with behavioral components. We conducted an experiment in which subjects copied a pentagon continuously for ~45 s using an XY joystick, while neuromagnetic fluxes were recorded from their head using a 248-sensor whole-head magnetoencephalography (MEG) device. Each sensor time series was rendered stationary and non-autocorrelated by applying an autoregressive integrated moving average model and taking the residuals. We used the directional variability of the movement as a behavioral measure of the controls generated. The main objective of this study was to assess the relation between neural interactions and the variability of movement direction. That is, we divided the continuous recordings into consecutive periods (i.e., time-bins) of 51 steps duration and computed the pairwise cross-correlations between the prewhitened time series in each time-bin. The circular standard deviation of the movement direction within each time-bin provides an estimate of the directional variability of the 51-ms trajectory segment. We looked at the association between neural interactions and variability of movement direction, separately for each pair of sensors, by running a cross-correlation analysis between the strength of the MEG pairwise cross-correlations and the circular standard deviations. We identified two types of neuronal networks: in one, the neural interactions are correlated with the directional variability of the movement at negative time-lags (feedforward), and in the other, the neural interactions are correlated with the directional variability of the movement at positive time-lags (feedback). Sensors associated mostly with feedforward processes are distributed in the left hemisphere and the right occipital-temporal junction, whereas sensors related to feedback processes are distributed in the right hemisphere and the left cerebellar hemisphere. These results are in line with findings from a series of previous studies showing that specific brain regions are involved in feedforward and feedback control processes to plan, perform, and correct movements. Additionally, we looked at whether changes in movement direction modulate the neural interactions. Interestingly, we found a preponderance of sensors associated with changes in movement direction over the right hemisphere-ipsilateral to the moving hand. These sensors exhibit stronger coupling with the rest of the sensors for trajectory segments with high rather than low directional movement variability. We interpret these results as evidence that ipsilateral cortical regions are recruited for continuous movements when the curvature of the trajectory increases. To the best of our knowledge, this is the first study that shows how neural interactions are associated with a behavioral control parameter in continuous and sequential movements. PMID:22923206

Christopoulos, Vassilios N; Leuthold, Arthur C; Georgopoulos, Apostolos P

2012-08-25

109

Detailed angular correlation analysis with 4? spectrometers: Spin determinations and multipolarity mixing measurements in 128Ba  

International Nuclear Information System (INIS)

We analyze for the first time the full ?? directional correlations from oriented states (DCO) in an experiment performed with the GASP detector array. Our analysis is based on a transformation of the directional information into expansion coefficients of an orthogonal basis. With this method, which we call SpeeDCO (spectral expansion of DCO), the complete DCO information is concentrated in 12 ?? coincidence spectra. The analysis is applicable to all detector arrays which uniformly cover the solid angle. We show that the complete DCO information can be used for a reliable and unique determination of spins and multipolarity mixing ratios in weakly populated bands. We were able to establish the spins and the positive parity of the ?I=1 'M1 band' in 128Ba and multipolarity mixing ratios of nine M1/E2 in-band transitions were derived as well. The measured values are in good agreement with those expected for a high-K rotational band. Copyright 1998 The American Physical Society.

1998-01-01

110

Dependence of the probabilities of the electric-multipole electron transitions in W24+ on multipolarity  

International Nuclear Information System (INIS)

Usually it is accepted that the probabilities of the electric-multipole electron transitions are rapidly decreasing functions of their multipolarity. Therefore while calculating the probabilities of electronic transitions between the configurations of certain chosen parities, it seems sufficient to take into account the first nonzero term, i.e., to consider the electron transitions of lowest multipolarity permitted by the exact selection rules. This paper aims at verifying this assumption on the example of electric-octupole transitions in W24+ ion. For this purpose the large-scale multiconfiguration Hartree-Fock and Dirac-Fock calculations have been performed for the configurations [Kr]4d104f4 and [Kr]4d104f35s energy levels of W24+ ion. The relativistic corrections were taken into account in the quasirelativistic Breit-Pauli and fully relativistic Breit (taking into account QED effects) approximations. The role of correlation, relativistic, and QED corrections is discussed. Line strengths, oscillator strengths, and transition probabilities in Coulomb and Babushkin gauges are presented for E1 and E3 transitions among these levels.

2011-01-01

111

The Fate of Chrysotile-Induced Multipolar Mitosis and Aneuploid Population in Cultured Lung Cancer Cells  

Science.gov (United States)

Chrysotile is one of the six types of asbestos, and it is the only one that can still be commercialized in many countries. Exposure to other types of asbestos has been associated with serious diseases, such as lung carcinomas and pleural mesotheliomas. The association of chrysotile exposure with disease is controversial. However, in vitro studies show the mutagenic potential of chrysotile, which can induce DNA and cell damage. The present work aimed to analyze alterations in lung small cell carcinoma cultures after 48 h of chrysotile exposure, followed by 2, 4 and 8 days of recovery in fiber-free culture medium. Some alterations, such as aneuploid cell formation, increased number of cells in G2/M phase and cells in multipolar mitosis were observed even after 8 days of recovery. The presence of chrysotile fibers in the cell cultures was detected and cell morphology was observed by laser scanning confocal microscopy. After 4 and 8 days of recovery, only a few chrysotile fragments were present in some cells, and the cellular morphology was similar to that of control cells. Cells transfected with the GFP-tagged ?-tubulin plasmid were treated with chrysotile for 24 or 48 h and cells in multipolar mitosis were observed by time-lapse microscopy. Fates of these cells were established: retention in metaphase, cell death, progression through M phase generating more than two daughter cells or cell fusion during telophase or cytokinesis. Some of them were related to the formation of aneuploid cells and cells with abnormal number of centrosomes.

de Araujo Cortez, Beatriz; Quassollo, Gonzalo; Caceres, Alfredo; Machado-Santelli, Glaucia Maria

2011-01-01

112

A new method for the determination of the multipolarity of prompt transitions and its application on the nuclides Nd-137 and Ir-189  

International Nuclear Information System (INIS)

A method is presentd, which allows the determination of multipolarities of high spin band transitions. By that, the spin dependent ? angular distribution is combined with the conversion electron angular distribution, which depends on the parameters of the conversion process. Model independent results on multipolarities of prompt transitions can be obtained by measurement of the cos2theta-term of the ? and e- decay angular distribution.A discussion of the findings on the basis of the three-axial and axially symmetric Coriolis coupling model shows that the 11/2- bands can be much better described by taking int account a hexadecapole deformation than by the introduction of a degree of freedom. From the calculations, small negative values result for the quadrupole and hexadecapole momentum (?2 ungefaehr -0.1 ?4 ungefaehr -0.008) of the isotopes with N=75, 77 and isotopes with Z=77. In Agreement with the system: atics of lifetimes, the parameters found permit an interpretation of the 11/2- states as shape-isomeric states as the ground states of the odd nuclei exhibit a prolate deformation which is sometimes quite high. A discussion of the findings on the basis of the three-axial and axillay symmetric coriolis coupling model shaws that the 11/2- bands can be much letter described by taking into account a hexadecapole deformation than by the introduction of a ? degree of freedom. From the calculations, small negative values result for the quadrupole and hexacapole momentum (?2 approximately -0.1, ?4 approximately -0.008) of isotopes with N=75, 77 and isotopes with Z=77. In agreement with the systemactics of lifetimes, the parameters found permit on interpretation of the 11/2- states as shape-isomeric states as the ground states of the cold nuclei exhibit a prolate deformation which is sometimes quite high. (orig./WL).

1978-01-01

113

Resting-state magnetoencephalography study of "small world" characteristics and cognitive dysfunction in patients with glioma.  

UK PubMed Central (United Kingdom)

BACKGROUND: The purpose of this study was to analyze "small world" characteristics in glioma patients in order to understand the relationship between cognitive dysfunction and brain functional connectivity network in the resting state. METHODS: Resting-state magnetoencephalography was performed in 20 patients with glioma and 20 healthy subjects. The clustering coefficient of the resting functional connectivity network in the brain, average path length, and "small world" index (SWI) were calculated. Cognitive function was estimated by testing of attention, verbal fluency, memory, athletic ability, visual-spatial ability, and intelligence. RESULTS: Compared with healthy controls, patients with glioma showed decreased cognitive function, and diminished low and high gamma band "small world" characteristics in the resting functional connectivity network. CONCLUSION: The SWI is associated with cognitive function and is diminished in patients with glioma, and is therefore correlated with cognition dysfunction.

Hu XH; Lei T; Xu HZ; Zou YJ; Liu HY

2013-01-01

114

Magnetoencephalography: From SQUIDs to neuroscience. Neuroimage 20th anniversary special edition.  

UK PubMed Central (United Kingdom)

Magnetoencephalography (MEG), with its direct view to the cortex through the magnetically transparent skull, has developed from its conception in physics laboratories to a powerful tool of basic and clinical neuroscience. MEG provides millisecond time resolution and allows real-time tracking of brain activation sequences during sensory processing, motor planning and action, cognition, language perception and production, social interaction, and various brain disorders. Current-day neuromagnetometers house hundreds of SQUIDs, superconducting quantum interference devices, to pick up signals generated by concerted action of cortical neurons. Complementary MEG measures of neuronal involvement include evoked responses, modulation of cortical rhythms, properties of the on-going neural activity, and interareal connectivity. Future MEG breakthroughs in understanding brain dynamics are expected through advanced signal analysis and combined use of MEG with hemodynamic imaging (fMRI). Methodological development progresses most efficiently when linked with insightful neuroscientific questions.

Hari R; Salmelin R

2012-06-01

115

Activation of the human sensorimotor cortex during error-related processing: a magnetoencephalography study.  

UK PubMed Central (United Kingdom)

We studied error-related processing using magnetoencephalography (MEG). Previous event-related potential studies have documented error negativity or error-related negativity after incorrect responses, with a suggested source in the anterior cingulate cortex or supplementary motor area. We compared activation elicited by correct and incorrect trials using auditory and visual choice-reaction time tasks. Source areas showing different activation patterns in correct and error conditions were mainly located in sensorimotor areas, both ipsi- and contralateral to the response, suggesting that activation of sensorimotor circuits accompanies error processing. Additional activation at various other locations suggests a distributed network of brain regions active during error-related processing. Activation specific to incorrect trials tended to occur later in MEG than EEG data, possibly indicating that EEG and MEG detect different neural networks involved in error-related processes.

Stemmer B; Vihla M; Salmelin R

2004-05-01

116

The retention of simultaneous tones in auditory short-term memory: a magnetoencephalography study.  

UK PubMed Central (United Kingdom)

We used magnetoencephalography (MEG) to localize brain activity related to the retention of tones differing in pitch. Participants retained one or two simultaneously presented tones. After a two second interval a test tone was presented and the task was to determine if that tone was in memory. We focused on brain activity during the retention interval that increased as the number of sounds retained in auditory short-term memory (ASTM) increased. Source analyses revealed that the superior temporal gyrus in both hemispheres is involved in ASTM. In the right hemisphere, the inferior temporal gyrus, the inferior frontal gyrus, and parietal structures also play a role. Our method provides good spatial and temporal resolution for investigating neuronal correlates of ASTM and, as it is the first MEG study using a memory load manipulation without using sequences of tones, it allowed us to isolate brain regions that most likely reflect the simple retention of tones.

Nolden S; Grimault S; Guimond S; Lefebvre C; Bermudez P; Jolicoeur P

2013-11-01

117

The retention of simultaneous tones in auditory short-term memory: A magnetoencephalography study.  

Science.gov (United States)

We used magnetoencephalography (MEG) to localize brain activity related to the retention of tones differing in pitch. Participants retained one or two simultaneously presented tones. After a two second interval a test tone was presented and the task was to determine if that tone was in memory. We focused on brain activity during the retention interval that increased as the number of sounds retained in auditory short-term memory (ASTM) increased. Source analyses revealed that the superior temporal gyrus in both hemispheres is involved in ASTM. In the right hemisphere, the inferior temporal gyrus, the inferior frontal gyrus, and parietal structures also play a role. Our method provides good spatial and temporal resolution for investigating neuronal correlates of ASTM and, as it is the first MEG study using a memory load manipulation without using sequences of tones, it allowed us to isolate brain regions that most likely reflect the simple retention of tones. PMID:23751862

Nolden, Sophie; Grimault, Stephan; Guimond, Synthia; Lefebvre, Christine; Bermudez, Patrick; Jolicoeur, Pierre

2013-06-07

118

Localizing the central sulcus by functional magnetic resonance imaging and magnetoencephalography.  

UK PubMed Central (United Kingdom)

To further validate the potential of functional magnetic resonance imaging (fMRI) for localization of the sensorimotor cortex, fMRI was compared with somatosensory evoked fields (SEFs) in eight normal volunteers. A conventional 1.5 T MRI scanner and an MRI-linked 66-channel whole head magnetoencephalography system were used. fMRI activated by unilateral hand squeeze movement indicated the highest activation on the central sulci that were localized by SEFs in all 16 contralateral hemispheres. This indicates that although the fMRI signal activation may originate from a vein running along the central sulcus, fMRI is reliable to detect the central sulcus. The pre-central gyrus also indicated some signal activation on fMRI implying better visualization of spatial distribution of activation. fMRI and SEFs are complementary methods for localizing the central sulcus.

Shimizu H; Nakasato N; Mizoi K; Yoshimoto T

1997-12-01

119

Prefrontal Cortex Modulation during Anticipation of Working Memory Demands as Revealed by Magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available During the anticipation of task demands frontal control is involved in the assembly of stimulus-response mappings based on current goals. It is not clear whether prefrontal modulations occur in higher-order cortical regions, likely reflecting cognitive anticipation processes. The goal of this paper was to investigate prefrontal modulation during anticipation of upcoming working memory demands as revealed by magnetoencephalography (MEG). Twenty healthy volunteers underwent MEG while they performed a variation of the Sternberg Working Memory (WM) task. Beta band (14–30?Hz) SAM (Synthetic Aperture Magnetometry) analysis was performed. During the preparatory periods there was an increase in beta power (event-related synchronization) in dorsolateral prefrontal cortex (DLPFC) bilaterally, left inferior prefrontal gyrus, left parietal, and temporal areas. Our results provide support for the hypothesis that, during preparatory states, the prefrontal cortex is important for biasing higher order brain regions that are going to be engaged in the upcoming task.

Mario Altamura; Terry E. Goldberg; Brita Elvevåg; Tom Holroyd; Frederick W. Carver; Daniel R. Weinberger; Richard Coppola

2010-01-01

120

Magnetoencephalography correlate of EEG POSTS (positive occipital sharp transients of sleep).  

UK PubMed Central (United Kingdom)

PURPOSE: In contrast to EEG, which has guidelines for interpretation and a plethora of textbooks, the full range of activity seen in magnetoencephalography (MEG) has not been fleshed out. Currently, magnetoencephalographers apply criteria for EEG waveforms to MEG signals based on an assumption that MEG activity should have morphology that is similar to EEG. The purpose of this article was to show the characteristic MEG profile of positive occipital sharp transients of sleep. METHODS: Simultaneous MEG-EEG recordings of two cases are shown. RESULTS: In both the cases, the morphologic features of positive occipital sharp transients of sleep in MEG vary and sometimes mimic epileptic spikes. CONCLUSION: This report raises a caution that a normal variant may have an even more epileptic appearance on MEG than on EEG. Using the simultaneously recorded EEG to avoid misinterpretation of spikey-looking positive occipital sharp transients of sleep in MEG is a natural and prudent practice.

Kakisaka Y; Wang ZI; Enatsu R; Dubarry AS; Mosher JC; Alexopoulos AV; Burgess RC

2013-06-01

 
 
 
 
121

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter  

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Highly electronegative plasmas were produced in Ar/SF 6 gas mixtures in a DC discharge with multipolar magnetic confinement and transversal magnetic filter. Langmuir probe and mass spectroscopy were used for plasma diagnostics. Plasma potential drift, the influence of small or large area bi...

122

The effect on the multipolar electromagnet for the levitation of thin iron plate  

Energy Technology Data Exchange (ETDEWEB)

The thin iron plate is needed to be transported without the degradation of the quality of surface, and magnetic levitation technology is one of the solutions to satisfy these requirements. Magnetic saturation in the objective, however, is a severe problem for the levitation of the thin iron plate. Design and evaluation method of the electromagnet is studied to avoid the saturation. In this paper, the shape of the electromagnet is studied to obtain the maximum attractive force without the saturation in the thin iron plate. The magnetic saturation position is investigated first, and it is proved that the saturation occurs in the iron plate especially when it is very thin. Therefore, the preferable shape of electromagnet should be investigated to secure the large cross sectional area of flux path in the plate. The authors propose the Multipolar electromagnet to solve this problem. The relationship between the electromagnet shape and the cross sectional area of flux path in the plate is studied. (orig.)

Osabe, H. [Dept. of Electrical and Electronic Engineering, Musashi Inst. of Technology, Tokyo (Japan); Watada, M. [Dept. of Electrical and Electronic Engineering, Musashi Inst. of Technology, Tokyo (Japan); Torii, S. [Dept. of Electrical and Electronic Engineering, Musashi Inst. of Technology, Tokyo (Japan); Ebihara, D. [Dept. of Electrical and Electronic Engineering, Musashi Inst. of Technology, Tokyo (Japan)

1995-12-31

123

Visualization of the corticospinal tract pathway using magnetic resonance axonography and magnetoencephalography for stereotactic irradiation planning of arteriovenous malformations  

International Nuclear Information System (INIS)

Corticospinal tract (CST) information using anisotropic diffusion-weighted imaging and magnetoencephalography were integrated into radiosurgical planning for two patients with deeply seated arteriovenous malformation. The volume of CST receiving >10 Gy, >15 Gy, and maximum dose of CST could be reduced when plans were created with the aid of CST information compared with plans without the information. The results indicate that the use of CST information might reduce the risk of post-radiosurgical motor disturbance resulting from radiation necrosis.

2003-01-01

124

The value of magnetoencephalography for seizure-onset zone localization in magnetic resonance imaging-negative partial epilepsy  

Science.gov (United States)

Surgical treatment of epilepsy is a challenge for patients with non-contributive brain magnetic resonance imaging. However, surgery is feasible if the seizure-onset zone is precisely delineated through intracranial electroencephalography recording. We recently described a method, volumetric imaging of epileptic spikes, to delineate the spiking volume of patients with focal epilepsy using magnetoencephalography. We postulated that the extent of the spiking volume delineated with volumetric imaging of epileptic spikes could predict the localizability of the seizure-onset zone by intracranial electroencephalography investigation and outcome of surgical treatment. Twenty-one patients with non-contributive magnetic resonance imaging findings were included. All patients underwent intracerebral electroencephalography investigation through stereotactically implanted depth electrodes (stereo-electroencephalography) and magnetoencephalography with delineation of the spiking volume using volumetric imaging of epileptic spikes. We evaluated the spatial congruence between the spiking volume determined by magnetoencephalography and the localization of the seizure-onset zone determined by stereo-electroencephalography. We also evaluated the outcome of stereo-electroencephalography and surgical treatment according to the extent of the spiking volume (focal, lateralized but non-focal or non-lateralized). For all patients, we found a spatial overlap between the seizure-onset zone and the spiking volume. For patients with a focal spiking volume, the seizure-onset zone defined by stereo-electroencephalography was clearly localized in all cases and most patients (6/7, 86%) had a good surgical outcome. Conversely, stereo-electroencephalography failed to delineate a seizure-onset zone in 57% of patients with a lateralized spiking volume, and in the two patients with bilateral spiking volume. Four of the 12 patients with non-focal spiking volumes were operated upon, none became seizure-free. As a whole, patients having focal magnetoencephalography results with volumetric imaging of epileptic spikes are good surgical candidates and the implantation strategy should incorporate volumetric imaging of epileptic spikes results. On the contrary, patients with non-focal magnetoencephalography results are less likely to have a localized seizure-onset zone and stereo electroencephalography is not advised unless clear localizing information is provided by other presurgical investigation methods.

Bouet, Romain; Delpuech, Claude; Ryvlin, Philippe; Isnard, Jean; Guenot, Marc; Bertrand, Olivier; Hammers, Alexander; Mauguiere, Francois

2013-01-01

125

The value of magnetoencephalography for seizure-onset zone localization in magnetic resonance imaging-negative partial epilepsy.  

UK PubMed Central (United Kingdom)

Surgical treatment of epilepsy is a challenge for patients with non-contributive brain magnetic resonance imaging. However, surgery is feasible if the seizure-onset zone is precisely delineated through intracranial electroencephalography recording. We recently described a method, volumetric imaging of epileptic spikes, to delineate the spiking volume of patients with focal epilepsy using magnetoencephalography. We postulated that the extent of the spiking volume delineated with volumetric imaging of epileptic spikes could predict the localizability of the seizure-onset zone by intracranial electroencephalography investigation and outcome of surgical treatment. Twenty-one patients with non-contributive magnetic resonance imaging findings were included. All patients underwent intracerebral electroencephalography investigation through stereotactically implanted depth electrodes (stereo-electroencephalography) and magnetoencephalography with delineation of the spiking volume using volumetric imaging of epileptic spikes. We evaluated the spatial congruence between the spiking volume determined by magnetoencephalography and the localization of the seizure-onset zone determined by stereo-electroencephalography. We also evaluated the outcome of stereo-electroencephalography and surgical treatment according to the extent of the spiking volume (focal, lateralized but non-focal or non-lateralized). For all patients, we found a spatial overlap between the seizure-onset zone and the spiking volume. For patients with a focal spiking volume, the seizure-onset zone defined by stereo-electroencephalography was clearly localized in all cases and most patients (6/7, 86%) had a good surgical outcome. Conversely, stereo-electroencephalography failed to delineate a seizure-onset zone in 57% of patients with a lateralized spiking volume, and in the two patients with bilateral spiking volume. Four of the 12 patients with non-focal spiking volumes were operated upon, none became seizure-free. As a whole, patients having focal magnetoencephalography results with volumetric imaging of epileptic spikes are good surgical candidates and the implantation strategy should incorporate volumetric imaging of epileptic spikes results. On the contrary, patients with non-focal magnetoencephalography results are less likely to have a localized seizure-onset zone and stereo electroencephalography is not advised unless clear localizing information is provided by other presurgical investigation methods.

Jung J; Bouet R; Delpuech C; Ryvlin P; Isnard J; Guenot M; Bertrand O; Hammers A; Mauguière F

2013-10-01

126

[The practical benefits of magnetoencephalography in comparison with electroencephalography in a patient with epilepsia partialis continua  

UK PubMed Central (United Kingdom)

A concurrent recording of electroencephalography (EEG), magnetoencephalography (MEG) and electromyography (EMG) was carried out in a patient with epilepsia partialis continua. He had continuous clonic jerks in his right hand and fingers. The EMG electrodes were placed on the thumb of his right hand. We observed numerous MEG spikes in the left central region and about half of them were accompanied by EMG potentials with a latency of about 20 msec. The EEG spikes appeared less frequently, had low amplitudes, and had unclear morphologies and further, no clear association with EMG potentials. MEG spikes were more reliably associated with individual jerks, exemplified by EMG potentials, than the EEG spikes. The MEG spikes were sharper than EEG spikes and were about 20 msec wide. The intracranial dipole localization of the MEG spikes was estimated by overlaying the calculated generator sites on magnetic resonance images. It was found that the spikes converged along a line, presumably the central sulcus. The practical benefits of the MEG as a diagnostic tool in epilepsy are illustrated.

Watanabe Y; Sato S; Nakamura F; Fukao K; Yagi K; Seino M

1995-04-01

127

Aberrant neuromagnetic activation in the motor cortex in children with acute migraine: a magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Migraine attacks have been shown to interfere with normal function in the brain such as motor or sensory function. However, to date, there has been no clinical neurophysiology study focusing on the motor function in children with migraine during headache attacks. To investigate the motor function in children with migraine, twenty-six children with acute migraine, meeting International Classification of Headache Disorders criteria and age- and gender-matched healthy children were studied using a 275-channel magnetoencephalography system. A finger-tapping paradigm was designed to elicit neuromagnetic activation in the motor cortex. Children with migraine showed significantly prolonged latency of movement-evoked magnetic fields (MEF) during finger movement compared with the controls. The correlation coefficient of MEF latency and age in children with migraine was significantly different from that in healthy controls. The spectral power of high gamma (65-150 Hz) oscillations during finger movement in the primary motor cortex is also significantly higher in children with migraine than in controls. The alteration of responding latency and aberrant high gamma oscillations suggest that the developmental trajectory of motor function in children with migraine is impaired during migraine attacks and/or developmentally delayed. This finding indicates that childhood migraine may affect the development of brain function and result in long-term problems.

Guo X; Xiang J; Wang Y; O'Brien H; Kabbouche M; Horn P; Powers SW; Hershey AD

2012-01-01

128

Magnetoencephalography reveals a unique neurophysiological profile of focal-onset epileptic spasms.  

UK PubMed Central (United Kingdom)

Epilepsy is defined as a disorder of the brain characterized by an enduring predisposition to experience epileptic seizures and the neurobiological, cognitive, psychological, and social difficulties relating to the condition. An epileptic spasm (ES) is a type of seizure characterized by clusters of short contractions involving axial muscles and proximal segments. However, the precise mechanism of ESs remains unknown. Despite the potential of magnetoencephalography (MEG) as a tool for investigating the neurophysiological mechanism of ESs, it has been difficult to use this methodology due to magnetic artifacts attributable to patient movement. We report on an 8-year-old girl suffering from intractable epileptic spasms from the age of 7 months. She was diagnosed with possible Aicardi syndrome [corrected] (AGS), characterized by the triad of callosal agenesis, infantile spasms, and chorioretinal lacunae. She is now intellectually delayed and suffers from intractable ES. We used both MEG and electroencephalography to investigate her epilepsy. The recording captured two series of spasm clusters. Spikes were clearly identified with MEG in about four-fifths of all spasms but were identified poorly or not at all in the remainder. MEG findings support previous studies that used intracranial electrodes to analyze patients with ESs and that showed variability in ES-associated spikes in terms of manner of cortical involvement and magnitude. Given the limitations of intracranial electrodes, such as sampling restrictions and invasiveness, MEG may be a helpful tool for non-invasively investigating the unique pathophysiological profile of focal-onset ESs.

Kakisaka Y; Gupta A; Enatsu R; Wang ZI; Alexopoulos AV; Mosher JC; Dubarry AS; Hino-Fukuyo N; Burgess RC

2013-01-01

129

Magnetoencephalography reveals a unique neurophysiological profile of focal-onset epileptic spasms.  

Science.gov (United States)

Epilepsy is defined as a disorder of the brain characterized by an enduring predisposition to experience epileptic seizures and the neurobiological, cognitive, psychological, and social difficulties relating to the condition. An epileptic spasm (ES) is a type of seizure characterized by clusters of short contractions involving axial muscles and proximal segments. However, the precise mechanism of ESs remains unknown. Despite the potential of magnetoencephalography (MEG) as a tool for investigating the neurophysiological mechanism of ESs, it has been difficult to use this methodology due to magnetic artifacts attributable to patient movement. We report on an 8-year-old girl suffering from intractable epileptic spasms from the age of 7 months. She was diagnosed with possible Aicardi syndrome [corrected] (AGS), characterized by the triad of callosal agenesis, infantile spasms, and chorioretinal lacunae. She is now intellectually delayed and suffers from intractable ES. We used both MEG and electroencephalography to investigate her epilepsy. The recording captured two series of spasm clusters. Spikes were clearly identified with MEG in about four-fifths of all spasms but were identified poorly or not at all in the remainder. MEG findings support previous studies that used intracranial electrodes to analyze patients with ESs and that showed variability in ES-associated spikes in terms of manner of cortical involvement and magnitude. Given the limitations of intracranial electrodes, such as sampling restrictions and invasiveness, MEG may be a helpful tool for non-invasively investigating the unique pathophysiological profile of focal-onset ESs. PMID:23343709

Kakisaka, Yosuke; Gupta, Ajay; Enatsu, Rei; Wang, Zhong I; Alexopoulos, Andreas V; Mosher, John C; Dubarry, Anne-Sophie; Hino-Fukuyo, Naomi; Burgess, Richard C

2013-01-01

130

Magnetoencephalography assessment of evoked magnetic fields and cognitive function in subcortical ischemic vascular dementia patients.  

UK PubMed Central (United Kingdom)

OBJECTIVE: To investigate the relationship between cognitive impairment and somatosensory evoked magnetic field and auditory evoked magnetic field changes in elderly male patients with subcortical ischemic vascular dementia (SIVD). METHODS: Magnetoencephalography (MEG) was used to record evoked magnetic field changes from 4 SIVD patients (76-88 years), 3 patients with vascular cognitive impairment with no dementia (VCI-ND; 74-87 years), and 6 healthy volunteers (72-85 years). Latency peaks, equivalent current dipole (ECD) strength, and bilateral ECD position were recorded. The MEG data were superimposed on magnetic resonance imaging to produce magnetic source imaging. RESULTS: Compared to controls, SIVD patients showed increased M20 latency and ECD strength. There were no significant differences in M20 inter-hemispheric positions across diagnostic categories. At M100, SIVD patients showed delayed auditory evoked magnetic field latency compared to controls. However, ECD strength and 3-dimensional inter-hemispheric differences were similar across the groups at the M100 measurement. CONCLUSIONS: Changes in somatosensory and auditory evoked magnetic field changes correlated with cognitive impairment in SIVD patients. Magnetic field latency measures may provide an objective and sensitive index for early dementia detection and monitoring of cognitive function.

Sun ZY; Wang JH; Sun JL; Wang TJ; Li L; Dong YH; Wu J; Cui WZ; Wu YJ; Lu PY

2013-01-01

131

Cortical somatosensory processing measured by magnetoencephalography predicts neurodevelopment in extremely low-gestational-age infants.  

UK PubMed Central (United Kingdom)

BACKGROUND: Higher cortical function during sensory processing can be examined by recording specific somatosensory-evoked magnetic fields (SEFs) with magnetoencephalography (MEG). We evaluated whether, in extremely low-gestational-age (ELGA) infants, abnormalities in MEG-recorded SEFs at term age are associated with adverse neurodevelopment at 2 y of corrected age. METHODS: SEFs to tactile stimulation of the index finger were recorded at term age in 30 ELGA infants (26.5?±?1.2?wk, birth weight: 884 g ± 181?g). Neurodevelopment was evaluated at 2 y of corrected age. Controls were 11 healthy term infants. RESULTS: In nine of the ELGA infants (30.0%), SEFs were categorized as abnormal on the basis of lack of response from secondary somatosensory cortex (SII). At 2 y, these infants had a significantly worse mean developmental quotient and locomotor subscale on the Griffiths Mental Development Scales than the ELGA infants with normal responses. Mild white matter abnormalities in magnetic resonance imaging at term age were detected in 21% of infants, but these abnormalities were not associated with adverse neurodevelopment. CONCLUSION: Abnormal SII responses at term predict adverse neuromotor development at 2 y of corrected age. This adverse development may not be foreseen with conventional neuroimaging methods, suggesting a role for evaluating SII responses in the developmental risk assessment of ELGA infants.

Rahkonen P; Nevalainen P; Lauronen L; Pihko E; Lano A; Vanhatalo S; Pesonen AK; Heinonen K; Räikkönen K; Valanne L; Autti T; Andersson S; Metsäranta M

2013-06-01

132

Maturation of somatosensory cortical processing from birth to adulthood revealed by magnetoencephalography.  

UK PubMed Central (United Kingdom)

OBJECTIVE: To evaluate the maturation of tactile processing by recording somatosensory evoked magnetic fields (SEFs) from healthy human subjects. METHODS: SEFs to tactile stimulation of the left index finger were measured from the contralateral somatosensory cortex with magnetoencephalography (MEG) in five age groups: newborns, 6- and 12-18-month-olds, 1.6-6-year-olds, and adults. The waveforms of the measured signals and equivalent current dipoles (ECDs) were analyzed in awake and sleep states in order to separate the effects of age and vigilance state on SEFs. RESULTS: There was an orderly, systematic change in the measured and ECD source waveforms of the initial cortical responses with age. The broad U-shaped response in newborns (M60) shifted to a W-shaped response with emergence of a notch by 6 months of age. The adult-type response with M30 and M50 components was present by 2 years. The ECDs of M60 and M30 were oriented anteriorly and that of M50 posteriorly. These maturational changes were independent of vigilance state. CONCLUSIONS: The most significant maturation of short latency cortical responses to tactile stimulation takes place during the first 2 years of life. SIGNIFICANCE: The maturational changes of somatosensory processing can noninvasively be evaluated with MEG already in infancy.

Pihko E; Nevalainen P; Stephen J; Okada Y; Lauronen L

2009-08-01

133

Neuroimaging studies of bilingual expressive language representation in the brain: potential applications for magnetoencephalography.  

UK PubMed Central (United Kingdom)

Bilingualism is the ability to use two or more languages with equal or near equal fluency. How the brain, often seamlessly, selects, controls, and switches between languages is an enigma. Neuroimaging studies offer the unique opportunity to probe the mechanisms underlying bilingual brain function. Non-invasive methods, in particular, functional MRI (fMRI) and event-related potentials (ERPs), have allowed examination in healthy control populations. Whole-head magnetoencephalography (MEG), a relatively new addition to the cadre of neuroimaging tools, offers a combination of the high spatial resolution of fMRI with the high temporal resolution of ERPs. Thus far, MEG has been applied to the studies of bilingual receptive language, or bilingual language comprehension. MEG has not yet been applied to the study of bilingual language production as such studies have faced more challenges (see Salmelin, 2007 for a review), and these have only recently been addressed. Here, we review the literature on MEG expressive language studies and point out a direction for the application of MEG to the study of bilingual language production.

Pang EW

2012-12-01

134

Neuroimaging studies of bilingual expressive language representation in the brain: potential applications for magnetoencephalography.  

Science.gov (United States)

Bilingualism is the ability to use two or more languages with equal or near equal fluency. How the brain, often seamlessly, selects, controls, and switches between languages is an enigma. Neuroimaging studies offer the unique opportunity to probe the mechanisms underlying bilingual brain function. Non-invasive methods, in particular, functional MRI (fMRI) and event-related potentials (ERPs), have allowed examination in healthy control populations. Whole-head magnetoencephalography (MEG), a relatively new addition to the cadre of neuroimaging tools, offers a combination of the high spatial resolution of fMRI with the high temporal resolution of ERPs. Thus far, MEG has been applied to the studies of bilingual receptive language, or bilingual language comprehension. MEG has not yet been applied to the study of bilingual language production as such studies have faced more challenges (see Salmelin, 2007 for a review), and these have only recently been addressed. Here, we review the literature on MEG expressive language studies and point out a direction for the application of MEG to the study of bilingual language production. PMID:23124647

Pang, Elizabeth W

2012-11-03

135

First results for a superconducting imaging-surface sensor array for magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

Magnetoencephalography (MEG) follows from the initial fundamental work of Cohen in 1968 and development by several groups, most notably at MIT and at NYU, based on the development of the Superconducting QUantum Interference Device (SQUID) using the Josephson effect. The SQUID`s incredible sensitivity to magnetic fields permits the measurement of the very weak magnetic fields emitted from the human brain due to intracellular neuronal currents. Current growth in MEG is dominated by multiple sensor arrays covering much of the head. These new large devices have primarily been developed and made commercially available by several companies including BTI in the US, CTF in Canada, and Neuromag in Finland. Large projects are also in place in Japan. These systems contain more than 100 sensors spaced at various intervals over the head using various configurations of magnetometers and gradiometers. The different designs available on the market are driven by factors such as detection efficiency, cost, and application. They now present a completely novel whole-head SQUID array system using a superconducting imaging-surface gradiometer concept derived at Los Alamos. Preliminary tests have demonstrated higher performance, lower noise, and additional shielding of background fields while using simpler fabrication techniques than existing whole-head MEG systems, which should reduce production costs.

Kraus, R.H. Jr.; Flynn, E.R.; Overton, W.; Espy, M.A.; George, J.S.; Matlachov, A.; Peters, M.V.; Ruminer, P.

1998-12-31

136

Magnetoencephalography---theory, instrumentation, and applications to noninvasive studies of the working human brain  

Energy Technology Data Exchange (ETDEWEB)

Magnetoencephalography (MEG) is a noninvasive technique for investigating neuronal activity in the living human brain. The time resolution of the method is better than 1 ms and the spatial discrimination is, under favorable circumstances, 2--3 mm for sources in the cerebral cortex. In MEG studies, the weak 10 fT--1 pT magnetic fields produced by electric currents flowing in neurons are measured with multichannel SQUID (superconducting quantum interference device) gradiometers. The sites in the cerebral cortex that are activated by a stimulus can be found from the detected magnetic-field distribution, provided that appropriate assumptions about the source render the solution of the inverse problem unique. Many interesting properties of the working human brain can be studied, including spontaneous activity and signal processing following external stimuli. For clinical purposes, determination of the locations of epileptic foci is of interest. The authors begin with a general introduction and a short discussion of the neural basis of MEG. The mathematical theory of the method is then explained in detail, followed by a thorough description of MEG instrumentation, data analysis, and practical construction of multi-SQUID devices. Finally, several MEG experiments performed in the authors' laboratory are described, covering studies of evoked responses and of spontaneous activity in both healthy and diseased brains. Many MEG studies by other groups are discussed briefly as well.

Haemaelaeinen, M.; Hari, R.; Ilmoniemi, R.J.; Knuutila, J.; Lounasmaa, O.V. (Low Temperature Laboratory, Helsinki University of Technology, 02150 Espoo (Finland))

1993-04-01

137

Assessment of cortical dysfunction in human strabismic amblyopia using magnetoencephalography (MEG)  

International Nuclear Information System (INIS)

The aim of this study was to use the technique of magnetoencephalography (MEG) to determine the effects of strabismic amblyopia on the processing of spatial information within the occipital cortex of humans. We recorded evoked magnetic responses to the onset of a chromatic (red/green) sinusoidal grating of periodicity 0.5-4.0 c deg-1 using a 19-channel SQUID-based neuromagnetometer. Evoked responses were recorded monocularly on six amblyopes and six normally-sighted controls, the stimuli being positioned near the fovea in the lower right visual field of each observer. For comparison, the spatial contrast sensitivity function (CSF) for the detection of chromatic gratings was measured for one amblyope and one control using a two alternate forced-choice psychophysical procedure. We chose red/green sinusoids as our stimuli because they evoke strong magnetic responses from the occipital cortex in adult humans (Fylan, Holliday, Singh, Anderson and Harding. (1997). Neuroimage, 6, 47-57). Magnetic field strength was plotted as a function of stimulus spatial frequency for each eye of each subject. Interocular differences were only evident within the amblyopic group: for stimuli of 1-2 c deg-1, the evoked responses had significantly longer latencies and reduced amplitudes through the amblyopic eye (P

1999-05-01

138

Interictal magnetoencephalography used in magnetic resonance imaging-negative patients with epilepsy.  

UK PubMed Central (United Kingdom)

PURPOSE: This study aims to investigate the contributions of magnetoencephalography (MEG) in magnetic resonance imaging (MRI)-negative patients. METHODS: A total of 18 MRI-negative patients diagnosed with refractory epilepsy, subjected to MEG investigation, and subsequently underwent surgery were selected for retrospective analysis. A 1.5-tesla Magnetom Sonata with an eight-channel head array coil was used. MEG data were obtained using a 74/248-channel system. RESULTS: A total of 16 patients (16/18) had positive MEG results, comprising 12 patients with monofocal localizations, five with multifocal localizations, and one with unremarkable results in MEG. In addition, 12 patients had indicative single photon-emission computed tomography (SPECT), five had indicative fluorodeoxyglucose positron emission tomography (FDG-PET), and all the patients had intracranial electroencephalography (EEG) (14 with subdural electrodes and four with electrocorticography). The intracranial EEG recordings of nine patients were guided by MEG informative results. Among these 18 patients, 10 exhibited good postoperative outcomes (Engel I and II), four of which were completely seizure-free. All these ten patients had clear monofocal localization in MEG, including nine with accordant indicative metabolic changes in either SPECT or FDG-PET, or both. None of the five patients with multifocal localizations achieved good postoperative outcomes. CONCLUSION: For cases with negative MRI findings, epilepsy surgery may be an alternative option for pharmaco-resistant patients if epileptogenic focus localizations by MEG are present in multimodal evaluation.

Wu XT; Rampp S; Buchfelder M; Kuwert T; Blümcke I; Dörfler A; Zhou D; Stefan H

2013-04-01

139

Neural correlation of successful cognitive behaviour therapy for spider phobia: A magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Cognitive behavioural therapy (CBT) can be an effective treatment for spider phobia, but the underlying neural correlates of therapeutic change are yet to be specified. The present study used magnetoencephalography (MEG) to study responses within the first half second, to phobogenic stimuli in a group of individuals with spider phobia prior to treatment (n=12) and then in nine of them following successful CBT (where they could touch and manage live large common house spiders) at least 9 months later. We also compared responses to a group of age-matched healthy control participants (n=11). Participants viewed static photographs of real spiders, other fear-inducing images (e.g. snakes, sharks) and neutral stimuli (e.g. kittens). Beamforming methods were used to localise sources of significant power changes in response to stimuli. Prior to treatment, participants with spider phobia showed a significant maximum response in the right frontal pole when viewing images of real spiders specifically. No significant frontal response was observed for either control participants or participants with spider phobia post-treatment. In addition, participants' subjective ratings of spider stimuli significantly predicted peak responses in right frontal regions. The implications for understanding brain-based effects of cognitive therapies are discussed.

Wright B; Alderson-Day B; Prendergast G; Kennedy J; Bennett S; Docherty M; Whitton C; Manea L; Gouws A; Tomlinson H; Green G

2013-10-01

140

Through a glass darkly: some insights on change talk via magnetoencephalography.  

UK PubMed Central (United Kingdom)

Motivational interviewing (MI) is a directive, client-centered therapeutic method employed in the treatment of substance abuse, with strong evidence of effectiveness. To date, the sole mechanism of action in MI with any consistent empirical support is "change talk" (CT), which is generally defined as client within-session speech in support of a behavior change. "Sustain talk" (ST) incorporates speech in support of the status quo. MI maintains that during treatment, clients essentially talk themselves into change. Multiple studies have now supported this theory, linking within-session speech to substance use outcomes. Although a causal chain has been established linking therapist behavior, client CT, and substance use outcome, the neural substrate of CT has been largely uncharted. We addressed this gap by measuring neural responses to clients' own CT using magnetoencephalography (MEG), a noninvasive neuroimaging technique with excellent spatial and temporal resolution. Following a recorded MI session, MEG was used to measure brain activity while participants heard multiple repetitions of their CT and ST utterances from that session, intermingled and presented in a random order. Results suggest that CT processing occurs in a right-hemisphere network that includes the inferior frontal gyrus, insula, and superior temporal cortex. These results support a representation of CT at the neural level, consistent with the role of these structures in self-perception. This suggests that during treatment sessions, clinicians who are able to evoke this special kind of language are tapping into neural circuitry that may be essential to behavior change.

Houck JM; Moyers TB; Tesche CD

2013-06-01

 
 
 
 
141

Improvement of an on-line electron spectrometer. Determination of transition multipolarity. Application to 102Ag and 108In  

International Nuclear Information System (INIS)

The aim of this work has been to optimize the transmission, resolution and background of an electron 'Orange' spectrometer, set-up on-line at the Grenoble isochronous cyclotron. The transitions multipolarities in 102Ag and 108In nuclei have been determined measuring the internal conversion coefficients and a cascade of five pure transitions Ml without cross-over E2 has been found in 108In.

1979-01-01

142

Neutron star deformation due to arbitrary-order multipolar magnetic fields  

CERN Multimedia

Certain multi-wavelength observations of neutron stars, such as intermittent radio emissions from rotation-powered pulsars beyond the pair-cascade death line, the pulse profile of the magnetar SGR 1900+14 after its 1998 August 27 giant flare, and X-ray spectral features of PSR J0821-4300 and SGR 0418+5729, suggest that the magnetic fields of non-accreting neutron stars are not purely dipolar and may contain higher-order multipoles. Here, we calculate the ellipticity of a non-barotropic neutron star with (i) a quadrupole poloidal-toroidal field, and (ii) a purely poloidal field containing arbitrary multipoles, deriving the relation between the ellipticity and the multipole amplitudes. We present, as a worked example, a purely poloidal field comprising dipole, quadrupole, and octupole components. We show the correlation between field energy and ellipticity for each multipole, that the l=4 multipole has the lowest energy, and that l=5 has the lowest ellipticity. We show how a mixed multipolar field creates an ob...

Mastrano, Alpha; Melatos, Andrew

2013-01-01

143

Parities and multipolarities of gamma rays in neutron-rich odd-mass Ba nuclei  

International Nuclear Information System (INIS)

The nuclei 143, 145, 147Ba produced in the spontaneous fission of 248Cm have been studied using the EUROGAM phase II array. The parities and multipolarities of ? rays in these nuclei have been assigned from triple angular correlation, directional linear-polarisation correlation and internal conversion coefficient measurements. These data confirm an alternating-parity sequence connected by strong electric dipole transitions in 143Ba. They also reveal a more weakly populated, complementary alternating-parity sequence. The two sequences together exhibit some characteristics of parity-doublet bands. Interpreting the E1 strengths in terms of a rotating intrinsic dipole moment gives a moment similar in size to that observed in 142Ba and 144Ba. No well-developed similar structure is seen in 145Ba, although E1 transitions are observed, from which a value of the dipole moment is obtained. This value is smaller than the moment observed in 143Ba. No features appropriate to strong octupole correlations were observed in 147Ba. (orig.)

1996-08-05

144

Parities and multipolarities of gamma rays in neutron-rich odd-mass Ba nuclei  

Energy Technology Data Exchange (ETDEWEB)

The nuclei {sup 143,} {sup 145,} {sup 147}Ba produced in the spontaneous fission of {sup 248}Cm have been studied using the EUROGAM phase II array. The parities and multipolarities of {gamma} rays in these nuclei have been assigned from triple angular correlation, directional linear-polarisation correlation and internal conversion coefficient measurements. These data confirm an alternating-parity sequence connected by strong electric dipole transitions in {sup 143}Ba. They also reveal a more weakly populated, complementary alternating-parity sequence. The two sequences together exhibit some characteristics of parity-doublet bands. Interpreting the E1 strengths in terms of a rotating intrinsic dipole moment gives a moment similar in size to that observed in {sup 142}Ba and {sup 144}Ba. No well-developed similar structure is seen in {sup 145}Ba, although E1 transitions are observed, from which a value of the dipole moment is obtained. This value is smaller than the moment observed in {sup 143}Ba. No features appropriate to strong octupole correlations were observed in {sup 147}Ba. (orig.).

Jones, M.A. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Urban, W. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Durell, J.L. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Leddy, M. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Phillips, W.R. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Smith, A.G. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Varley, B.J. [Manchester Univ. (United Kingdom). Dept. of Phys. and Astron.; Ahmad, I. [Argonne National Laboratory, Argonne, IL 60439 (United States); Morss, L.R. [Argonne National Laboratory, Argonne, IL 60439 (United States); Bentaleb, M. [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, 67037 Strasbourg (France); Lubkiewicz, E. [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, 67037 Strasbourg (France); Schulz, N. [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, 67037 Strasbourg (France)

1996-08-05

145

CT-guided Bipolar and Multipolar Radiofrequency Ablation (RF Ablation) of Renal Cell Carcinoma: Specific Technical Aspects and Clinical Results  

Energy Technology Data Exchange (ETDEWEB)

Purpose. This study was designed to evaluate the clinical efficacy of CT-guided bipolar and multipolar radiofrequency ablation (RF ablation) of renal cell carcinoma (RCC) and to analyze specific technical aspects between both technologies. Methods. We included 22 consecutive patients (3 women; age 74.2 {+-} 8.6 years) after 28 CT-guided bipolar or multipolar RF ablations of 28 RCCs (diameter 2.5 {+-} 0.8 cm). Procedures were performed with a commercially available RF system (Celon AG Olympus, Berlin, Germany). Technical aspects of RF ablation procedures (ablation mode [bipolar or multipolar], number of applicators and ablation cycles, overall ablation time and deployed energy, and technical success rate) were analyzed. Clinical results (local recurrence-free survival and local tumor control rate, renal function [glomerular filtration rate (GFR)]) and complication rates were evaluated. Results. Bipolar RF ablation was performed in 12 procedures and multipolar RF ablation in 16 procedures (2 applicators in 14 procedures and 3 applicators in 2 procedures). One ablation cycle was performed in 15 procedures and two ablation cycles in 13 procedures. Overall ablation time and deployed energy were 35.0 {+-} 13.6 min and 43.7 {+-} 17.9 kJ. Technical success rate was 100 %. Major and minor complication rates were 4 and 14 %. At an imaging follow-up of 15.2 {+-} 8.8 months, local recurrence-free survival was 14.4 {+-} 8.8 months and local tumor control rate was 93 %. GFR did not deteriorate after RF ablation (50.8 {+-} 16.6 ml/min/1.73 m{sup 2} before RF ablation vs. 47.2 {+-} 11.9 ml/min/1.73 m{sup 2} after RF ablation; not significant). Conclusions. CT-guided bipolar and multipolar RF ablation of RCC has a high rate of clinical success and low complication rates. At short-term follow-up, clinical efficacy is high without deterioration of the renal function.

Sommer, C. M., E-mail: christof.sommer@med.uni-heidelberg.de [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Lemm, G.; Hohenstein, E. [Minimally Invasive Therapies and Nuclear Medicine, SLK Kliniken Heilbronn GmbH, Clinic for Radiology (Germany); Bellemann, N.; Stampfl, U. [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Goezen, A. S.; Rassweiler, J. [Clinic for Urology, SLK Kliniken Heilbronn GmbH (Germany); Kauczor, H. U.; Radeleff, B. A. [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Pereira, P. L. [Minimally Invasive Therapies and Nuclear Medicine, SLK Kliniken Heilbronn GmbH, Clinic for Radiology (Germany)

2013-06-15

146

CT-guided bipolar and multipolar radiofrequency ablation (RF ablation) of renal cell carcinoma: specific technical aspects and clinical results.  

UK PubMed Central (United Kingdom)

PURPOSE: This study was designed to evaluate the clinical efficacy of CT-guided bipolar and multipolar radiofrequency ablation (RF ablation) of renal cell carcinoma (RCC) and to analyze specific technical aspects between both technologies. METHODS: We included 22 consecutive patients (3 women; age 74.2 ± 8.6 years) after 28 CT-guided bipolar or multipolar RF ablations of 28 RCCs (diameter 2.5 ± 0.8 cm). Procedures were performed with a commercially available RF system (Celon AG Olympus, Berlin, Germany). Technical aspects of RF ablation procedures (ablation mode [bipolar or multipolar], number of applicators and ablation cycles, overall ablation time and deployed energy, and technical success rate) were analyzed. Clinical results (local recurrence-free survival and local tumor control rate, renal function [glomerular filtration rate (GFR)]) and complication rates were evaluated. RESULTS: Bipolar RF ablation was performed in 12 procedures and multipolar RF ablation in 16 procedures (2 applicators in 14 procedures and 3 applicators in 2 procedures). One ablation cycle was performed in 15 procedures and two ablation cycles in 13 procedures. Overall ablation time and deployed energy were 35.0 ± 13.6 min and 43.7 ± 17.9 kJ. Technical success rate was 100 %. Major and minor complication rates were 4 and 14 %. At an imaging follow-up of 15.2 ± 8.8 months, local recurrence-free survival was 14.4 ± 8.8 months and local tumor control rate was 93 %. GFR did not deteriorate after RF ablation (50.8 ± 16.6 ml/min/1.73 m(2) before RF ablation vs. 47.2 ± 11.9 ml/min/1.73 m(2) after RF ablation; not significant). CONCLUSIONS: CT-guided bipolar and multipolar RF ablation of RCC has a high rate of clinical success and low complication rates. At short-term follow-up, clinical efficacy is high without deterioration of the renal function.

Sommer CM; Lemm G; Hohenstein E; Bellemann N; Stampfl U; Goezen AS; Rassweiler J; Kauczor HU; Radeleff BA; Pereira PL

2013-06-01

147

A preliminary study of the neural mechanisms of frustration in pediatric bipolar disorder using magnetoencephalography.  

UK PubMed Central (United Kingdom)

BACKGROUND: Irritability is prevalent and impairing in pediatric bipolar disorder (BD) but has been minimally studied using neuroimaging techniques. We used magnetoencephalography (MEG) to study theta band oscillations in the anterior cingulate cortex (ACC) during frustration in BD youth. ACC theta power is associated with attention to emotional stimuli, and the ACC may mediate responses to frustrating stimuli. METHODS: We used the affective Posner task, an attention paradigm that uses rigged feedback to induce frustration, to compare 20 medicated BD youth (14.9+/-2.0 years; 45% male) and 20 healthy controls (14.7+/-1.7 years; 45% male). MEG measured neuronal activity after negative and positive feedback; we also compared groups on reaction time, response accuracy, and self-reported affect. Patients met strict DSM-IV BD criteria and were euthymic. Controls had no psychiatric history. RESULTS: BD youth reported more negative affective responses than controls. After negative feedback, BD subjects, relative to controls, displayed greater theta power in the right ACC and bilateral parietal lobe. After positive feedback, BD subjects displayed lower theta power in the left ACC than did controls. Correlations between MEG, behavior, and affect were nonsignificant. CONCLUSION: In this first MEG study of BD youth, BD youth displayed patterns of theta oscillations in the ACC and parietal lobe in response to frustration-inducing negative feedback that differed from healthy controls. These data suggest that BD youth may display heightened processing of negative feedback and exaggerated self-monitoring after frustrating emotional stimuli. Future studies are needed with unmedicated bipolar youth, and comparison ADHD and anxiety groups.

Rich BA; Holroyd T; Carver FW; Onelio LM; Mendoza JK; Cornwell BR; Fox NA; Pine DS; Coppola R; Leibenluft E

2010-03-01

148

Neural mechanism of central inhibition during physical fatigue: A magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Central inhibition plays an important role in physical performance during physical fatigue. We tried to clarify the neural mechanism of central inhibition during physical fatigue using magnetoencephalography (MEG) and a classical conditioning technique. Twelve right-handed volunteers participated in this study. Participants underwent MEG recording during the imagery of maximum grips of the right hand guided by metronome sounds for 10min. Thereafter, fatigue-inducing maximum handgrip trials were performed for 10min; the metronome sounds were started 5min after the beginning of the handgrip trials. We used metronome sounds as conditioned stimuli and maximum handgrip trials as unconditioned stimuli to cause central inhibition. The next day, MEG recording during the imagery of maximum grips of the right hand guided by metronome sounds were measured for 10min. Levels of the fatigue sensation in the right hand and sympathetic nerve activity on the second day were significantly higher than those on the first day. In the right dorsolateral prefrontal cortex (Brodmann's area 46), the alpha-band event-related desynchronization (ERD) of the second MEG session relative to the first session with the time window of 200 to 300ms after the onset of handgrip cue sounds was identified. The ERD level in this brain region was positively associated with the change in subjective level of right hand fatigue after the conditioning session and was negatively associated with that of sympathetic nerve activity. We demonstrated that the right dorsolateral prefrontal cortex is involved in the neural substrates of central inhibition during physical fatigue.

Tanaka M; Ishii A; Watanabe Y

2013-09-01

149

Neural mechanisms of phonemic restoration for speech comprehension revealed by magnetoencephalography.  

UK PubMed Central (United Kingdom)

In daily communication, we can usually still hear the spoken words as if they had not been masked and can comprehend the speech when spoken words are masked by background noise. This phenomenon is known as phonemic restoration. Since little is known about the neural mechanisms underlying phonemic restoration for speech comprehension, we aimed to identify the neural mechanisms using magnetoencephalography (MEG). Twelve healthy male volunteers with normal hearing participated in the study. Participants were requested to carefully listen to and understand recorded spoken Japanese stories, which were either played forward (forward condition) or in reverse (reverse condition), with their eyes closed. Several syllables of spoken words were replaced by 300-ms white-noise stimuli with an inter-stimulus interval of 1.6-20.3s. We compared MEG responses to white-noise stimuli during the forward condition with those during the reverse condition using time-frequency analyses. Increased 3-5Hz band power in the forward condition compared with the reverse condition was continuously observed in the left inferior frontal gyrus [Brodmann's areas (BAs) 45, 46, and 47] and decreased 18-22Hz band powers caused by white-noise stimuli were seen in the left transverse temporal gyrus (BA 42) and superior temporal gyrus (BA 22). These results suggest that the left inferior frontal gyrus and left transverse and superior temporal gyri are involved in phonemic restoration for speech comprehension. Our findings may help clarify the neural mechanisms of phonemic restoration as well as develop innovative treatment methods for individuals suffering from impaired speech comprehension, particularly in noisy environments.

Sunami K; Ishii A; Takano S; Yamamoto H; Sakashita T; Tanaka M; Watanabe Y; Yamane H

2013-09-01

150

Oscillatory neuronal dynamics associated with manual acupuncture: a magnetoencephalography study using beamforming analysis  

Science.gov (United States)

Magnetoencephalography (MEG) enables non-invasive recording of neuronal activity, with reconstruction methods providing estimates of underlying brain source locations and oscillatory dynamics from externally recorded neuromagnetic fields. The aim of our study was to use MEG to determine the effect of manual acupuncture on neuronal oscillatory dynamics. A major problem in MEG investigations of manual acupuncture is the absence of onset times for each needle manipulation. Given that beamforming (spatial filtering) analysis is not dependent upon stimulus-driven responses being phase-locked to stimulus onset, we postulated that beamforming could reveal source locations and induced changes in neuronal activity during manual acupuncture. In a beamformer analysis, a two-minute period of manual acupuncture needle manipulation delivered to the ipsilateral right LI-4 (Hegu) acupoint was contrasted with a two-minute baseline period. We considered oscillatory power changes in the theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz), and gamma (30–100 Hz) frequency bands. We found significant decreases in beta band power in the contralateral primary somatosensory cortex and superior frontal gyrus (SFG). In the ipsilateral cerebral hemisphere, we found significant power decreases in beta and gamma frequency bands in only the SFG. No significant power modulations were found in theta and alpha bands. Our results indicate that beamforming is a useful analytical tool to reconstruct underlying neuronal activity associated with manual acupuncture. Our main finding was of beta power decreases in primary somatosensory cortex and SFG, which opens up a line of future investigation regarding whether this contributes toward an underlying mechanism of acupuncture.

Asghar, Aziz U. R.; Johnson, Robyn L.; Woods, William; Green, Gary G. R.; Lewith, George; MacPherson, Hugh

2012-01-01

151

Localization of epileptic foci in Children with childhood absence epilepsy by magnetoencephalography combined with synthetic aperture magnetometry?  

Science.gov (United States)

This present study was aimed to investigate the localizable diagnostic value of magnetoencephalography (MEG) combined with synthetic aperture magnetometry (SAM) in childhood absence epilepsy (CAE). Thirteen CAE patients underwent MEG detection at resting state and after hyperventilation, and then the epileptic foci were located by SAM. In the thirteen CAE patients, epileptic foci were found in five cases (38.5%), and they were all located in the bilateral frontal lobe, suggesting that the frontal lobe in some CAE patients may serve as the epileptic foci. Our findings indicate that MEG combined with SAM could be of diagnostic value in localizing the epileptic foci in certain CAE patients.

Hu, Xiuxiu; Dong, Jingde; Wang, Xiaoshan; Wu, Ting; Yang, Lu; Lu, Xiaopeng

2011-01-01

152

[Identification of the epileptic focus by the use of magnetoencephalography in a patient with refractory focal epilepsy].  

UK PubMed Central (United Kingdom)

Magnetoencephalography (MEG) is increasingly used in the non-invasive presurgical evaluation of patients with refractory focal epilepsy. Combination of MEG and magnetic resonance imaging of the brain can estimate the location of the epileptiform discharges. We report a case of a patient with paroxysmal sensory symptoms. All previous investigations where normal, but by the use of MEG we were able to identify the epileptic focus in the insular region. MEG has a better spatial resolution than electroencefalography, and it is more sensitive to tangentially oriented dipoles. MEG should be considered in the workup of patients with refractory focal epilepsy.

Duez L; Beniczky S; Fuglsang-Frederiksen A

2013-04-01

153

Invariant Form of Hyperfine Interaction with Multipolar Moments - Observation of Octupolar Moments in NpO$_{2}$ and CeB$_{6}$ by NMR -  

CERN Multimedia

The invariant form of the hyperfine interaction between multipolar moments and the nuclear spin is derived, and applied to discuss possibilities to identify the antiferro-octupolar (AFO) moments by NMR experiments. The ordered phase of NpO$_{2}$ and the phase IV of Ce$_{1-x}$La$_{x}$B$_{6}$ are studied in detail. Recent $^{17}$O NMR for polycrystalline samples of NpO$_{2}$ are discussed theoretically from our formulation. The observed feature of the splitting of $^{17}$O NMR spectrum into a sharp line and a broad line, their intensity ratio, and the magnetic field dependence of the shift and of the width can be consistently explained on the basis of the triple $\\bq$ AFO ordering model proposed by Paix\\~{a}o {\\it et. al.} Thus, the present theory shows that the $^{17}$O NMR spectrum gives a strong support to the model. The 4 O sites in the fcc NpO$_2$ become inequivalent due to the secondary triple $\\bq$ ordering of AF-quadrupoles: one cubic and three non-cubic sites. It turns out that the hyperfine field due ...

Sakai, O; Shiba, H; Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki

2004-01-01

154

FDG-PET and magnetoencephalography in presurgical workup of children with localization-related nonlesional epilepsy.  

UK PubMed Central (United Kingdom)

PURPOSE: 2-[18F]Fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) and magnetoencephalography (MEG) may assist in identifying the epileptogenic zone in children with nonlesional localization-related epilepsy. The aim of this study was to evaluate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FDG-PET, MEG, FDG-PET + MEG, and FDG-PET/MEG in children with nonlesional localization-related epilepsy. METHODS: Twenty-six children with localization-related epilepsy and who had normal or subtle changes on magnetic resonance imaging (MRI) underwent FDG-PET and MEG. Twenty-two patients had surgical resection, and surgical outcome was assessed using Engel classification. In patients with Engel I seizure outcome, we assessed the sensitivity, specificity, PPV, and NPV of lobar localization of MEG, FDG-PET, FDG-PET + MEG, and FDG-PET/MEG. KEY FINDINGS: Sixteen (72.7%) of 22 had Engel I seizure outcome. MEG was concordant with surgical resection in 18 patients, 14 had Engel I, and four had Engel II-IV outcomes. MEG was nonlocalizing or nonconcordant in four patients; two patients had Engel I and two had Engel II-IV outcomes. FDG-PET was concordant with surgical resection in 14 patients; 9 had Engel I outcome, and 5 had Engel II-IV outcome. FDG-PET was nonlocalizing or nonconcordant in seven patients with Engel I, and one with Engel III outcome. The sensitivity, specificity, PPV, and NPV of MEG were 85.0%, 99.1%, 94.4%, and 97.3%, respectively. The sensitivity, specificity, PPV, and NPV of FDG-PET were 65.0%, 94.4%, 68.4%, and 93.6%, respectively. There was no significant difference between MEG and FDG-PET for concordance with surgical resection (?(2)  = 2.794, p = 0.095). FDG-PET + MEG, defined as two tests concordant with surgical resection, had reduced sensitivity and NPV, but increased specificity and PPV (55.0%, 92.3%, 100%, and 100%, respectively) relative to individual tests. FDG-PET/MEG, defined as one or both test(s) concordant with surgical resection, had increased sensitivity and NPV but reduced specificity (95.0%, 99.0%, and 93.5%, respectively) relative to individual tests. SIGNIFICANCE: The two tests FDG-PET and MEG were complementary in the assessment of children with localization-related epilepsy, particularly when one test was nonlocalizing or nonconcordant.

Widjaja E; Shammas A; Vali R; Otsubo H; Ochi A; Snead OC; Go C; Charron M

2013-04-01

155

A phosphatidylinositol lipids system, lamellipodin, and Ena/VASP regulate dynamic morphology of multipolar migrating cells in the developing cerebral cortex.  

UK PubMed Central (United Kingdom)

In the developing mammalian cerebral cortex, excitatory neurons are generated in the ventricular zone (VZ) and subventricular zone; these neurons migrate toward the pial surface. The neurons generated in the VZ assume a multipolar morphology and remain in a narrow region called the multipolar cell accumulation zone (MAZ) for ?24 h, in which they extend and retract multiple processes dynamically. They eventually extend an axon tangentially and begin radial migration using a migratory mode called locomotion. Despite the potential biological importance of the process movement of multipolar cells, the molecular mechanisms remain to be elucidated. Here, we observed that the processes of mouse multipolar cells were actin rich and morphologically resembled the filopodia and lamellipodia in growth cones; thus, we focused on the actin-remodeling proteins Lamellipodin (Lpd) and Ena/vasodilator-stimulated phosphoprotein (VASP). Lpd binds to phosphatidylinositol (3,4)-bisphosphate [PI(3,4)P?] and recruits Ena/VASP, which promotes the assembly of actin filaments, to the plasma membranes. In situ hybridization and immunohistochemistry revealed that Lpd is expressed in multipolar cells in the MAZ. The functional silencing of either Lpd or Ena/VASP decreased the number of primary processes. Immunostaining and a Förster resonance energy transfer analysis revealed the subcellular localization of PI(3,4)P? at the tips of the processes. A knockdown experiment and treatment with an inhibitor for Src homology 2-containing inositol phosphatase-2, a 5-phosphatase that produces PI(3,4)P? from phosphatidylinositol (3,4,5)-triphosphate, decreased the number of primary processes. Our observations suggest that PI(3,4)P?, Lpd, and Ena/VASP are involved in the process movement of multipolar migrating cells.

Yoshinaga S; Ohkubo T; Sasaki S; Nuriya M; Ogawa Y; Yasui M; Tabata H; Nakajima K

2012-08-01

156

Detailed angular correlation analysis with 4{pi} spectrometers: Spin determinations and multipolarity mixing measurements in {sup 128}Ba  

Energy Technology Data Exchange (ETDEWEB)

We analyze for the first time the full {gamma}{gamma} directional correlations from oriented states (DCO) in an experiment performed with the GASP detector array. Our analysis is based on a transformation of the directional information into expansion coefficients of an orthogonal basis. With this method, which we call SpeeDCO (spectral expansion of DCO), the complete DCO information is concentrated in 12 {gamma}{gamma} coincidence spectra. The analysis is applicable to all detector arrays which uniformly cover the solid angle. We show that the complete DCO information can be used for a reliable and unique determination of spins and multipolarity mixing ratios in weakly populated bands. We were able to establish the spins and the positive parity of the {Delta}I=1 {open_quotes}M1 band{close_quotes} in {sup 128}Ba and multipolarity mixing ratios of nine M1/E2 in-band transitions were derived as well. The measured values are in good agreement with those expected for a high-K rotational band. thinsp thinsp thinsp {copyright} {ital 1998} {ital The American Physical Society}

Wiedenhoever, I.; Vogel, O.; Klein, H.; Dewald, A.; von Brentano, P.; Gableske, J.; Nicolay, N.; Gelberg, A. [Institut fuer Kernphysik der Universitaet zu Koeln, 50937 Koeln (Germany); Wiedenhoever, I.; Janssens, R.V.; Carpenter, M.P. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Kruecken, R. [W. A. Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520 (United States); Petkov, P. [Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, 1784 Sofia (Bulgaria); Gizon, A.; Gizon, J. [Institut des Sciences Nucleaires, Universite J. Fourier, F-38036 Grenoble Cedex (France); Bazzacco, D.; Rossi Alvarez, C.; Pavan, P. [Dipartimento di Fisica and INFN, Sezione di Padova, Padova (Italy); de Angelis, G.; Lunardi, S.; Napoli, D.R. [INFN, Laboratori Nazionali di Legnaro, Legnaro (Italy); Frauendorf, S.; Doenau, F. [Forschungszentrum Rossendorf, D-01219 Dresden (Germany)

1998-08-01

157

Excitatory cortical neurons with multipolar shape establish neuronal polarity by forming a tangentially oriented axon in the intermediate zone.  

UK PubMed Central (United Kingdom)

The formation of axon-dendrite polarity is crucial for neuron to make the proper information flow within the brain. Although the processes of neuronal polarity formation have been extensively studied using neurons in dissociated culture, the corresponding developmental processes in vivo are still unclear. Here, we illuminate the initial steps of morphological polarization of excitatory cortical neurons in situ, by sparsely labeling their neuroepithelial progenitors using in utero electroporation and then examining their neuronal progeny in brain sections and in slice cultures. Morphological analysis showed that an axon-like long tangential process formed in progeny cells in the intermediate zone (IZ). Time-lapse imaging analysis using slice culture revealed that progeny cells with multipolar shape, after alternately extending and retracting their short processes for several hours, suddenly elongated a long process tangentially. These cells then transformed into a bipolar shape, extending a pia-directed leading process, and migrated radially leaving the tangential process behind, which gave rise to an "L-shaped" axon. Our findings suggest that neuronal polarity in these cells is established de novo from a nonpolarized stage in vivo and indicate that excitatory cortical neurons with multipolar shape in the IZ initiate axon outgrowth before radial migration into the cortical plate.

Hatanaka Y; Yamauchi K

2013-01-01

158

Functional cortical hubs in the eyes-closed resting human brain from an electrophysiological perspective using magnetoencephalography.  

UK PubMed Central (United Kingdom)

It is not clear whether specific brain areas act as hubs in the eyes-closed (EC) resting state, which is an unconstrained state free from any passive or active tasks. Here, we used electrophysiological magnetoencephalography (MEG) signals to study functional cortical hubs in 88 participants. We identified several multispectral cortical hubs. Although cortical hubs vary slightly with different applied measures and frequency bands, the most consistent hubs were observed in the medial and posterior cingulate cortex, the left dorsolateral superior frontal cortex, and the left pole of the middle temporal cortex. Hubs were characterized as connector nodes integrating EC resting state functional networks. Hubs in the gamma band were more likely to include midline structures. Our results confirm the existence of multispectral cortical cores in EC resting state functional networks based on MEG and imply the existence of optimized functional networks in the resting brain.

Jin SH; Jeong W; Seol J; Kwon J; Chung CK

2013-01-01

159

Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography.  

Science.gov (United States)

We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography. PMID:12633462

Tass, P A; Fieseler, T; Dammers, J; Dolan, K; Morosan, P; Majtanik, M; Boers, F; Muren, A; Zilles, K; Fink, G R

2003-02-25

160

Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer.  

Science.gov (United States)

Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. PMID:22807201

Vesanen, Panu T; Nieminen, Jaakko O; Zevenhoven, Koos C J; Dabek, Juhani; Parkkonen, Lauri T; Zhdanov, Andrey V; Luomahaara, Juho; Hassel, Juha; Penttilä, Jari; Simola, Juha; Ahonen, Antti I; Mäkelä, Jyrki P; Ilmoniemi, Risto J

2012-07-17

 
 
 
 
161

Analysis of pain-related somatosensory evoked magnetic fields using the MUSIC (multiple signal classification) algorithm for magnetoencephalography.  

UK PubMed Central (United Kingdom)

We evaluated the effectiveness of the Multiple Signal Classification (MUSIC) algorithm by analysing pain-related somatosensory-evoked magnetic fields (SEFs) by 148-channel whole-head-type magnetoencephalography. MUSIC peaks of middle latency components were located around the primary somatosensory cortex (SI), contralateral to the stimulated finger. Long latency components were located around the bilateral secondary somatosensory cortices (SII) and cingulate gyri. Peaks at the SII and cingulate gyri were more prominent on very painful and moderately painful stimulation than on weak stimulation. The results were in very good agreement with results from single dipole estimation. These findings suggest that the MUSIC algorithm could be a useful tool for analysis of pain-related SEFs.

Ninomiya Y; Kitamura Y; Yamamoto S; Okamoto M; Oka H; Yamada N; Kuroda S

2001-06-01

162

Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer.  

UK PubMed Central (United Kingdom)

Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial whole-head MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device.

Vesanen PT; Nieminen JO; Zevenhoven KC; Dabek J; Parkkonen LT; Zhdanov AV; Luomahaara J; Hassel J; Penttilä J; Simola J; Ahonen AI; Mäkelä JP; Ilmoniemi RJ

2013-06-01

163

INTERACTIONS OF Si (III) SURFACE WITH H2, NH3, SiH4 MULTIPOLAR PLASMAS STUDIED BY IN SITU ELLIPSOMETRY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An ultra high vacuum system consisting in a plasma chamber and an analysis chamber is used to study the interactions of various multipolar plasmas (NH3- H2SiH4) with Si surfaces. The kinetics of interaction can be followed in real time by in situ ellipsometry at 310 nm. Using the same set up the sam...

Demay, Y.; Maurel, P.; Gourrier, S.

164

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter  

DEFF Research Database (Denmark)

Highly electronegative plasmas were produced in Ar/SF6 gas mixtures in a dc discharge with multipolar magnetic confinement and transversal magnetic filter. Langmuir probe and mass spectrometry were used for plasma diagnostics. Plasma potential drift, the influence of small or large area biased electrodes on plasma parameters, the formation of the negative ion sheath and etching rates by positive and negative ions have been investigated for different experimental conditions. When the electron temperature was reduced below 1 eV the density ratio of negative ion to electron exceeded 100 even for very low amounts of SF6 gas. The plasma potential drift could be controlled by proper wall conditioning. A large electrode biased positively had no effect on plasma potential for density ratios of negative ions to electrons larger than 50. For similar electronegativities or higher a negative ion sheath could be formed by applying a positive bias of a few hundred volts.

Draghici, Mihai; Stamate, Eugen

2010-01-01

165

Comparison of microwave ablation and multipolar radiofrequency ablation, both using a pair of internally cooled interstitial applicators: results in ex vivo porcine livers.  

UK PubMed Central (United Kingdom)

PURPOSE: To compare the effectiveness of microwave ablation (MWA) and multipolar radiofrequency ablation (RFA) in ex vivo porcine livers, in both cases using a pair of internally cooled interstitial applicators. MATERIALS AND METHODS: MWA was performed on ex vivo porcine livers (n?=?60) using a pair of simultaneously powered, internally cooled shaft interstitial antennae. Four power settings were used: 50?W, 60?W, 70?W and 80?W (n?=?15 per setting). Multipolar RFA was also performed on ex vivo porcine livers (n?=?30), also using a pair of simultaneously powered, internally cooled shaft interstitial bipolar applicators. This was performed for two applicator types T30 (3?cm length) and T40 (4?cm length) at a manufacturer prescribed power of 60?W and 80?W, respectively (n?=?15 per applicator). Spacing between the two probes was 2?cm in all cases. Each power setting was applied for 15 ablations for 10?min each. The long-axis diameter (Dl), short-axis diameter (Ds) and the ratio Ds/Dl for each ablation were measured. Temperature data were recorded at 10 positions. Temperature curves were recorded at 3 locations, as well as the time required for the temperature to rise to 50°C. RESULTS: Dl and Ds for all the power settings of MWA were significantly larger than that of both kinds of multipolar RFA (P?multipolar RF ablations. CONCLUSION: MWA by the simultaneous application of double antennae may be more advantageous for treating larger liver tumour than multipolar RFA.

Li X; Zhang L; Fan W; Zhao M; Wang L; Tang T; Jiang H; Zhang J; Liu Y

2011-01-01

166

Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia.  

UK PubMed Central (United Kingdom)

OBJECTIVE: Patients must remain immobile for magnetoencephalography (MEG) and MRI recordings to allow precise localization of brain function for pre-surgical functional mapping. In young children with epilepsy, this is accomplished with recordings during sleep or with anesthesia. This paper demonstrates that MEG can detect, characterize and localize somatosensory-evoked fields (SEF) in infants younger than 4 years of age with or without total intravenous anesthesia (TIVA). METHODS: We investigated the latency, amplitude, residual error (RE) and location of the N20m of the SEF in 26 infants (mean age=2.6 years). Seventeen patients underwent TIVA and 9 patients were tested while asleep, without TIVA. RESULTS: MEG detected 44 reliable SEFs (77%) in 52 median nerve stimulations. We found 27 reliable SEFs (79%) with TIVA and 13 reliable SEFs (72%) without TIVA. TIVA effects included longer latencies (p<0.001) and lower RE (p<0.05) compared to those without TIVA. Older patients and larger head circumferences also showed significantly shorter latencies (p<0.01). CONCLUSIONS: TIVA resulted in reliable SEFs with lower RE and longer latencies. SIGNIFICANCE: MEG can detect reliable SEFs in infants younger than 4 years old. When infants require TIVA for MEG and MRI acquisition, SEFs can still be reliably observed.

Bercovici E; Pang EW; Sharma R; Mohamed IS; Imai K; Fujimoto A; Ochi A; Viljoen A; Chu B; Holowka S; Chuang SH; Kemp SM; Rutka JT; Carter Snead O 3rd; Otsubo H

2008-06-01

167

SQUID-based systems for co-registration of ultra-low field nuclear magnetic resonance images and magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

The ability to perform magnetic resonance imaging (MRI) in ultra-low magnetic fields (ULF) of {approx}100 {mu}T, using superconducting quantum interference device (SQUID) detection, has enabled a new class of magnetoencephalography (MEG) instrumentation capable of recording both anatomical (via the ULF MRI) and functional (biomagnetic) information about the brain. The combined ULF MRI/MEG instrument allows both structural and functional information to be co-registered to a single coordinate system and acquired in a single device. In this paper we discuss the considerations and challenges required to develop a combined ULF MRI/MEG device, including pulse sequence development, magnetic field generation, SQUID operation in an environment of pulsed pre-polarization, and optimization of pick-up coil geometries for MRI in different noise environments. We also discuss the design of a 'hybrid' ULF MRI/MEG system under development in our laboratory that uses SQUID pick-up coils separately optimized for MEG and ULF MRI.

Matlashov, A.N., E-mail: matlach@lanl.gov [Los Alamos National Laboratory, P.O. Box 1663, MS-D454, Los Alamos, NM 87545 (United States); Burmistrov, E.; Magnelind, P.E.; Schultz, L.; Urbaitis, A.V.; Volegov, P.L.; Yoder, J.; Espy, M.A. [Los Alamos National Laboratory, P.O. Box 1663, MS-D454, Los Alamos, NM 87545 (United States)

2012-11-20

168

DC-magnetoencephalography and time-resolved near-infrared spectroscopy combined to study neuronal and vascular brain responses.  

UK PubMed Central (United Kingdom)

The temporal relation between vascular and neuronal responses of the brain to external stimuli is not precisely known. For a better understanding of the neuro-vascular coupling changes in cerebral blood volume and oxygenation have to be measured simultaneously with neuronal currents. With this motivation modulation dc-magnetoencephalography was combined with multi-channel time-resolved near-infrared spectroscopy to simultaneously monitor neuronal and vascular parameters on a scale of seconds. Here, the technique is described, how magnetic and optical signals can be measured simultaneously. In a simple motor activation paradigm (alternating 30 s of finger movement with 30 s of rest for 40 min) both signals were recorded non-invasively over the motor cortex of eight subjects. The off-line averaged signals from both modalities showed distinct stimulation related changes. By plotting changes in oxy- or deoxyhaemoglobin as a function of magnetic field a characteristic trajectory was created, which was similar to a hysteresis loop. A parametric analysis allowed quantitative results regarding the timing of coupling: the vascular signal increased significantly slower than the neuronal signal.

Sander TH; Liebert A; Mackert BM; Wabnitz H; Leistner S; Curio G; Burghoff M; Macdonald R; Trahms L

2007-06-01

169

Dynamics of cortical neurovascular coupling analyzed by simultaneous DC-magnetoencephalography and time-resolved near-infrared spectroscopy.  

UK PubMed Central (United Kingdom)

Functional magnetic resonance imaging (fMRI) visualizes activated brain areas with a high spatial resolution. The activation signal is determined by the local change of cerebral blood oxygenation, blood volume and blood flow which serve as surrogate marker for the neuronal signal itself. Here, the complex coupling between these parameters and the electrophysiologic activity is characterized non-invasively in humans during a simple motor task using simultaneously DC-magnetoencephalography (DC-MEG), for the detection of neuronal signals, and time-resolved near-infrared spectroscopy (trNIRS), for cortical metabolic/vascular responses: over the left primary motor cortex hand area of healthy subjects DC-fields and trNIRS parameters followed closely the 30 s motor task cycles, i.e., finger movements of the right hand alternating with rest. In subjects showing a sufficient signal-to-noise ratio the analysis of variance of photon time of flight proved that the task-related trNIRS changes originated from the cortex. While onset and relaxation started simultaneously, trNIRS signals reached 50% of the maximum level 1-4 s later than the DC-MEG-signals. The non-invasive 'dual' setup helps to characterize simultaneously the two complementary aspects of the 'hemodynamic inverse problem', i.e., the coupling of neuronal and vascular/metabolic signals, in healthy subjects and provides a new analysis perspective for pathophysiological coupling concepts in diverse diseases, e.g., in stroke, hypertension and Alzheimer's disease.

Mackert BM; Leistner S; Sander T; Liebert A; Wabnitz H; Burghoff M; Trahms L; Macdonald R; Curio G

2008-02-01

170

Long-term remission of nondysplastic Barrett's esophagus after multipolar electrocoagulation ablation: report of 139 patients with 10 years of follow-up.  

UK PubMed Central (United Kingdom)

BACKGROUND: Ablation of Barrett's esophagus (BE) has been advocated as a method to eliminate the risk of malignant transformation of BE. OBJECTIVE: To provide longer follow-up and determine safety and efficacy of multipolar ablation for nondysplastic BE. DESIGN: Prospective cohort study. SETTING: Gastroenterology Unit at the Policlinica Metropolitana, a tertiary care center in Caracas, Venezuela. PATIENTS: One hundred sixty-six patients with nondysplastic BE and histologic evidence of intestinal metaplasia. INTERVENTIONS: Patients underwent multipolar electrocoagulation ablation therapy to areas of BE identified with magnification chromoendoscopy. The identified areas were treated with a 50-W energy source and a 7F "gold" probe. After complete ablation, patients were followed on an annual basis with magnification chromoendoscopy. At annual visits, biopsy specimens were taken in areas identified at baseline as BE. Targeted biopsy specimens were taken in areas of recurrent BE identified by using magnification chromoendoscopy. MAIN OUTCOME MEASUREMENTS: Mortality, incidence of recurrent BE, incidence of adenocarcinoma in ablated BE, and morbidity associated with multipolar electrocoagulation. RESULTS: One hundred sixty-six patients were recruited for the study; 139 completed at least 10 years of follow-up. Complications developed in less than 5% of patients, all of which were minor. Recurrent BE occurred in less than 5% of patients. No adenocarcinoma or high-grade dysplasia of the esophagus developed in any of the patients. LIMITATION: Uncontrolled clinical trial. CONCLUSIONS: Long-term follow-up of ablation of BE with multipolar electrocoagulation ablation therapy indicates that this is a safe, effective method to ablate BE over the long term.

Allison H; Banchs MA; Bonis PA; Guelrud M

2011-04-01

171

Establishment of M1 multipolarity of a 6.5 mu_N^2 resonance in 172-Yb at E_gamma=3.3 MeV  

CERN Document Server

Two-step-cascade spectra in 172-Yb have been measured after thermal neutron capture. They are compared to calculations based on experimental values of the level density and radiative strength function (RSF) obtained from the 173-Yb(3-He,alpha gamma)172-Yb reaction. The multipolarity of a 6.5(15) mu_N^2 resonance at E_gamma=3.3(1) MeV in the RSF is determined to be M1 by this comparison.

Schiller, A; Algin, E; Becker, J A; Bernstein, L A; Garrett, P E; Guttormsen, M; Nelson, R O; Rekstad, J; Siem, S

2004-01-01

172

WAVE2-Abi2 complex controls growth cone activity and regulates the multipolar-bipolar transition as well as the initiation of glia-guided migration.  

UK PubMed Central (United Kingdom)

Glia-guided migration (glia-guided locomotion) during radial migration is a characteristic yet unique mode of migration. In this process, the directionality of migration is predetermined by glial processes and not by growth cones. Prior to the initiation of glia-guided migration, migrating neurons transform from multipolar to bipolar, but the molecular mechanisms underlying this multipolar-bipolar transition and the commencement of glia-guided migration are not fully understood. Here, we demonstrate that the multipolar-bipolar transition is not solely a cell autonomous event; instead, the interaction of growth cones with glial processes plays an essential role. Time-lapse imaging with lattice assays reveals the importance of vigorously active growth cones in searching for appropriate glial scaffolds, completing the transition, and initiating glia-guided migration. These growth cone activities are regulated by Abl kinase and Cdk5 via WAVE2-Abi2 through the phosphorylation of tyrosine 150 and serine 137 of WAVE2. Neurons that do not display such growth cone activities are mispositioned in a more superficial location in the neocortex, suggesting the significance of growth cones for the final location of the neurons. This process occurs in spite of the "inside-out" principle in which later-born neurons are situated more superficially.

Xie MJ; Yagi H; Kuroda K; Wang CC; Komada M; Zhao H; Sakakibara A; Miyata T; Nagata K; Oka Y; Iguchi T; Sato M

2013-06-01

173

Occurrence of multipolar mitoses and association with Aurora-A/-B kinases and p53 mutations in aneuploid esophageal carcinoma cells  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Aurora kinases and loss of p53 function are implicated in the carcinogenesis of aneuploid esophageal cancers. Their association with occurrence of multipolar mitoses in the two main histotypes of aneuploid esophageal squamous cell carcinoma (ESCC) and Barrett's adenocarcinoma (BAC) remains unclear. Here, we investigated the occurrence of multipolar mitoses, Aurora-A/-B gene copy numbers and expression/activation as well as p53 alterations in aneuploid ESCC and BAC cancer cell lines. Results A control esophageal epithelial cell line (EPC-hTERT) had normal Aurora-A and -B gene copy numbers and expression, was p53 wild type and displayed bipolar mitoses. In contrast, both ESCC (OE21, Kyse-410) and BAC (OE33, OE19) cell lines were aneuploid and displayed elevated gene copy numbers of Aurora-A (chromosome 20 polysomy: OE21, OE33, OE19; gene amplification: Kyse-410) and Aurora-B (chromosome 17 polysomy: OE21, Kyse-410). Aurora-B gene copy numbers were not elevated in OE19 and OE33 cells despite chromosome 17 polysomy. Aurora-A expression and activity (Aurora-A/phosphoT288) was not directly linked to gene copy numbers and was highest in Kyse-410 and OE33 cells. Aurora-B expression and activity (Aurora-B/phosphoT232) was higher in OE21 and Kyse-410 than in OE33 and OE19 cells. The mitotic index was highest in OE21, followed by OE33 > OE19 > Kyse-410 and EPC-hTERT cells. Multipolar mitoses occurred with high frequency in OE33 (13.8 ± 4.2%), followed by OE21 (7.7 ± 5.0%) and Kyse-410 (6.3 ± 2.0%) cells. Single multipolar mitoses occurred in OE19 (1.0 ± 1.0%) cells. Distinct p53 mutations and p53 protein expression patterns were found in all esophageal cancer cell lines, but complete functional p53 inactivation occurred in OE21 and OE33 only. Conclusions High Aurora-A expression alone is not associated with overt multipolar mitoses in aneuploid ESCC and BAC cancer cells, as specifically shown here for OE21 and OE33 cells, respectively. Additional p53 loss of function mutations are necessary for this to occur, at least for invasive esophageal cancer cells. Further assessment of Aurora kinases and p53 interactions in cells or tissue specimens derived from non-invasive dysplasia (ESCC) or intestinal metaplasia (BAC) are necessary to disclose a potential causative role of Aurora kinases and p53 for development of aneuploid, invasive esophageal cancers.

Fichter Christiane D; Herz Corinna; Münch Claudia; Opitz Oliver G; Werner Martin; Lassmann Silke

2011-01-01

174

Single-trial magnetoencephalography signals encoded as an unfolding decision process.  

UK PubMed Central (United Kingdom)

The model of a stochastic decision process unfolding in motor and premotor regions of the brain was encoded in single-trial magnetoencephalographic (MEG) recordings while ten healthy subjects performed a sensorimotor Reaction Time (RT) task. The duration of single-trial MEG signals preceding the motor response, recorded over the motor cortex contralateral to the responding hand, co-varied with RT across trials according to the model's prediction. Furthermore, these signals displayed the same properties of a "rising-to-a-fixed-threshold" decision process as posited by the model and observed in the activity of single neurons in the primate cortex. The present findings demonstrate that non-averaged, single-trial MEG recordings can be used to test models of cognitive processes, like decision-making, in humans.

Smyrnis N; Mylonas DS; Rezaie R; Siettos CI; Ventouras E; Ktonas PY; Evdokimidis I; Papanicolaou AC

2012-02-01

175

Fatigue sensation induced by the sounds associated with mental fatigue and its related neural activities: revealed by magnetoencephalography.  

UK PubMed Central (United Kingdom)

BACKGROUND: It has been proposed that an inappropriately conditioned fatigue sensation could be one cause of chronic fatigue. Although classical conditioning of the fatigue sensation has been reported in rats, there have been no reports in humans. Our aim was to examine whether classical conditioning of the mental fatigue sensation can take place in humans and to clarify the neural mechanisms of fatigue sensation using magnetoencephalography (MEG). METHODS: Ten and 9 healthy volunteers participated in a conditioning and a control experiment, respectively. In the conditioning experiment, we used metronome sounds as conditioned stimuli and two-back task trials as unconditioned stimuli to cause fatigue sensation. Participants underwent MEG measurement while listening to the metronome sounds for 6 min. Thereafter, fatigue-inducing mental task trials (two-back task trials), which are demanding working-memory task trials, were performed for 60 min; metronome sounds were started 30 min after the start of the task trials (conditioning session). The next day, neural activities while listening to the metronome for 6 min were measured. Levels of fatigue sensation were also assessed using a visual analogue scale. In the control experiment, participants listened to the metronome on the first and second days, but they did not perform conditioning session. MEG was not recorded in the control experiment. RESULTS: The level of fatigue sensation caused by listening to the metronome on the second day was significantly higher relative to that on the first day only when participants performed the conditioning session on the first day. Equivalent current dipoles (ECDs) in the insular cortex, with mean latencies of approximately 190 ms, were observed in six of eight participants after the conditioning session, although ECDs were not identified in any participant before the conditioning session. CONCLUSIONS: We demonstrated that the metronome sounds can cause mental fatigue sensation as a result of repeated pairings of the sounds with mental fatigue and that the insular cortex is involved in the neural substrates of this phenomenon.

Ishii A; Tanaka M; Iwamae M; Kim C; Yamano E; Watanabe Y

2013-01-01

176

Decreased inhibitory neuronal activity in patients with frontal lobe brain tumors with seizure presentation: Preliminary study using magnetoencephalography.  

UK PubMed Central (United Kingdom)

BACKGROUND: Although 30-50 % of patients with brain tumors experience epileptic seizure as the presenting clinical symptom, and another 10-30 % are at risk for developing epilepsy in the later stages of the disease, the mechanisms of tumor-related epileptogenesis are poorly understood. We used magnetoencephalography (MEG) to investigate sensory evoked fields (SEFs) in patients with frontal lobe brain tumors as a means of evaluating the neuronal activity of peri-tumoral cortex. METHODS: Twelve patients with frontal lobe brain tumors underwent MEG. We calculated the equivalent current dipole strength of two components of the primary sensory cortical response (N20m and P35m) and compared the P35m/N20m ratio in the tumor hemisphere vs. the normal hemisphere. There were two subsets of patients: group I, in which P35m/N20m was higher in the tumor hemisphere (n= 7), and group II, in which P35m/N20m was higher in the normal hemisphere (n=5). We looked for associations between clinical factors and P35m/N20m within each group. RESULTS: All patients with seizure presentation were in group I, whereas only two patients without seizure presentation were in group I (Fisher exact test, p=0.028). No other clinical factors were related to P35m/N20m. The mean ratio of P35m/N20m equivalent current dipole strength in patients with seizure presentation was 4.07 ± 2.38 in the tumor hemisphere and 2.00 ± 0.55 in the normal hemisphere. This difference was statistically significant (Mann-Whitney test, p=0.030). CONCLUSION: The paradoxical increase in P35m/N20m in patients with seizure presentation suggests that decreased inhibitory neuronal activity is a potential cause of tumorrelated epilepsy.

Chang WS; Kim BS; Jung HH; Kim K; Kwon HC; Lee YH; Chang JW

2013-08-01

177

Crisis del lóbulo temporal registrada mediante magnetoencefalografía: caso clínico/ Temporal lobe seizure recorded by magnetoencephalography: case report  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish La localización del inicio de las crisis es un factor importante para la evaluación prequirúrgica de la epilepsia. En este trabajo se describe la localización del inicio de una crisis registrada mediante magnetoencefalografía (MEG) en un niño de 12 años que presenta crisis parciales complejas farmacorresistentes. La RM muestra una lesión de 20mm de diámetro en el hipocampo izquierdo. EEG de superficie con ondas theta temporales izquierdas. Registro MEG interictal (more) con punta-onda aislada posterior e inferior a la lesión de la RM. Registro MEG ictal con punta-onda (2 Hz). La localización de los dipolos indica el inicio de la crisis en la circunvolución temporal inferior en la misma localización que la actividad interictal MEG. Esta actividad ictal se propaga bilateralmente a áreas frontales. El registro corticográfico intraquirúrgico confirma los resultados de la localización interictal mediante MEG. Abstract in english Ictal onset localization is a important factor in presurgical evaluation of epilepsy. This paper describes the localization of a seizure onset recorded by magnetoencephalography (MEG) from a 12-year-old male patient who suffered from complex partial drug-resistant seizures. MRI revealed a 20mm diameter lesion located in left hippocampus. Scalp EEG showed left temporal theta waves. Interictal MEG registrations detected isolated spike-wave activity posterior and inferior to (more) the MRI lesion. Ictal MEG showed continuous spike-wave activity (2 Hz). Dipole localization sited seizure onset in the inferior left temporal gyrus, the same localization of the interictal MEG activity. This ictal activity spreads bilaterally to frontal areas. Intrasurgical electrocorticography recording confirmed interictal MEG results.

Amo, Carlos; Santiuste, Marta; Maestú, Fernando; Fernández, Alberto; Egatz, Renata; González-Hidalgo, Mercedes; Saldaña, Cristóbal; Sáiz, Antonio; Ortiz, Tomás

2004-09-01

178

Total intravenous anesthesia affecting spike sources of magnetoencephalography in pediatric epilepsy patients: focal seizures vs. non-focal seizures.  

UK PubMed Central (United Kingdom)

PURPOSE: Magnetoencephalography (MEG) provides source localization of interictal spikes. This study evaluated the inhibitory effects of propofol on MEG spike sources (MEGSSs) among different types of seizures in patients who underwent two separate MEG studies with and without total intravenous anesthesia (TIVA) using propofol. METHODS: We studied 19 children (1-14 years; mean, 6.2 years) who had MEG with and without TIVA. TIVA was administered using propofol (0.03-0.06 mg/kg/min) to record MEG with simultaneous EEG. We analyzed number of spikes of MEG and MEGSSs comparing MEG studies done with and without TIVA. RESULTS: Seizures were divided into nine focal seizure (FS) with/without secondary generalization, five epileptic spasm (ES), and five generalized seizure (GS). TIVA significantly decreased the number of MEG spikes/min (from 4.5 to 2.0) in five FS without secondary generalization (p<0.05). The number of MEG spikes/min was significantly lower (1.9) in FS than that in non-FS (ES+GS, 6.1) (p<0.01). MEGSSs without TIVA were clustered in 15 patients (6FS; 4ES; 5GS), scattered in four (3FS; 1ES). MEG under TIVA showed clusters in 10 patients (1FS; 4ES; 5GS), scatters in three (2FS; 1ES) and no MEGSS in six patients with FS. Under TIVA, nine (90%) of ten patients with non-FS showed MEGSSs clusters compared to one (11%) of nine patients with FS (p<0.01). CONCLUSIONS: Reduction of MEGSSs occurred in patients with FS under TIVA. Diffuse/generalized spikes in non-FS are not affected by TIVA. Propofol may decrease focal spikes in the epileptic cortex in FS. Cortical hyperexcitability in non-FS group would be stronger or more extensive than that in the FS group of patients.

Hanaya R; Okamoto H; Fujimoto A; Ochi A; Go C; Snead CO 3rd; Widjaja E; Chuang SH; Kemp SM; Otsubo H

2013-08-01

179

Vibrational energy transfers from the v = 1 level of HBr, HCl, and DF to the v = 1 level of CO, NO, N/sub 2/, and to the 00/sup 0/1 level of CO/sub 2/ and N/sub 2/O: A rate constant calculation based upon long-range multipolar forces  

Energy Technology Data Exchange (ETDEWEB)

Rate constants for far-from-resonance V--V transfers in HX--M and DF--M systems, with X = Cl and Br and M = CO, NO, N/sub 2/, CO/sub 2/, and N/sub 2/O, have been calculated from the semiclassical method of Dillon and Stephenson: the transfer probability is calculated from an exponential form of the scattering operator, and long-range multipolar forces are assumed, involving not only interactions between vibrational transition moments but also interactions between permanent moments, the effect of which is to make the multiquanta rotational transitions efficient. The formalism, developed by these authors for HX--CO/sub 2/ systems, i.e., for the case of a dipole--dipole vibrational interaction and a dipole--quadrupole rotational interaction, has been extended to other cases involving a dipole--quadrupole vibrational interaction or a dipole--dipole rotational interaction, in order to treat systems such as HX--N/sub 2/ or HX--N/sub 2/O systems. The computations have been performed for temperatures between 300 and 900 K. The comparison between calculated and experimental values shows that, as expected from the analysis of the experimental results, long-range multipolar forces play certainly a preponderant role in these transfers, all the more as the temperature is lower. The limits of the model are discussed.

Seoudi, B.; Doyennette, L.; Margottin-Maclou, M.

1984-12-15

180

Vibrational energy transfers from the v = 1 level of HBr, HCl, and DF to the v = 1 level of CO, NO, N2, and to the 0001 level of CO2 and N2O: A rate constant calculation based upon long-range multipolar forces  

International Nuclear Information System (INIS)

Rate constants for far-from-resonance V--V transfers in HX--M and DF--M systems, with X = Cl and Br and M = CO, NO, N2, CO2, and N2O, have been calculated from the semiclassical method of Dillon and Stephenson: the transfer probability is calculated from an exponential form of the scattering operator, and long-range multipolar forces are assumed, involving not only interactions between vibrational transition moments but also interactions between permanent moments, the effect of which is to make the multiquanta rotational transitions efficient. The formalism, developed by these authors for HX--CO2 systems, i.e., for the case of a dipole--dipole vibrational interaction and a dipole--quadrupole rotational interaction, has been extended to other cases involving a dipole--quadrupole vibrational interaction or a dipole--dipole rotational interaction, in order to treat systems such as HX--N2 or HX--N2O systems. The computations have been performed for temperatures between 300 and 900 K. The comparison between calculated and experimental values shows that, as expected from the analysis of the experimental results, long-range multipolar forces play certainly a preponderant role in these transfers, all the more as the temperature is lower. The limits of the model are discussed.

1984-01-01

 
 
 
 
181

Statistical contribution in the giant multipolar resonance decay in hevay nuclei  

International Nuclear Information System (INIS)

Statistical calculations are made for the decay in the electric monopole giant resonance in 208Pb and electric dipole giant resonance in 209Bi, using the Hauser-Feshbach formalism. Calculations are done using the experimental energy levels of the corresponding residual nuclei. The particle-vibrator model is used for those experimental levels without spin and parity determination. The influence of different parametrizations of the optical potential in the statistical calculation result is also studied. (L.C.)

1986-01-01

182

A Rússia na ordem mundial: com o Ocidente, com o Oriente ou um pólo autônomo em um mundo multipolar?  

Directory of Open Access Journals (Sweden)

Full Text Available O artigo persegue o objetivo de definir o lugar e o papel da Rússia nas relações internacionais contemporâneas nos últimos anos. Ao se debruçar sobre o dilema tradicional da política externa russa - Ocidentalismo versus Orientalismo - o autor analisa o cenário de multipolaridade defendido pela nova concepção da política externa russa e o relaciona com a fase do pragmatismo e do multilateralismo que caracteriza a atuação internacional da Rússia de Putin, fazendo considerações, decorrentes do impacto dos ataques terroristas aos Estados Unidos em 11 de setembro de 2001 sobre a política externa russa. A atitude pragmática e a natureza multivetorial da política externa russa contribuem, segundo o autor, para o fortalecimento das posições internacionais da Rússia em comparação com a perda ou a natureza incerta das alianças e dos relacionamentos do período da transição pós-soviética.The article pursues the purpose to place Russia and its politics within the context of today's international relations. While discussing the traditional dilemma of the Russian foreign politics - Occidentalism versus Orientalism - the author analyses the scenario of multipolarity, backed up by the new Russian foreign policy concept. Hence it is related to the pragmatism and the multilateralism of the international posture of Putin's Russia, the author makes several considerations, which follow from the impact of the September 11th, 2001, terrorist attacks on the United States of America with regard to Russia's foreign policy. The pragmatic attitude and the multi-axis nature of the Russian foreign policy nowadays contribute, according to the author, to strengthen Russia's international background in comparison with the loss or the uncertain nature of alliances and relationships of the post-Soviet transition period.

Alexander Zhebit

2003-01-01

183

Low multipolarity magnetic transitions in 32S excited by electron scattering  

International Nuclear Information System (INIS)

Electron scattering cross section measurements on 32S have been made at incident electron energies between 34 and 74 MeV and at scattering angles of 162.40 and 1800. Form factors were deduced for transitions to states at 8.11, 9.68, 10.05, 10.78, 11.12, and 11.63 MeV. Additional peaks at 7.12, 12.02, and 13.36 MeV were observed in some spectra. Comparisons of cross sections at different angles show that the above six transitions are transverse. Comparison of the experimental form factors with those calculated using an oscillator shell model indicate that the 8.11, 9.68, 11.12, and 11.63 MeV transitions are M1. Transition probabilities B(M1)up-arrow = 1.14 +- 0.18, 0.69 +- 0.20, 2.40 +- 0.22, and 1.26 +- 0.20 ?02, respectively, were determined for these four transitions. The M1 form factors and transition probabilities are also compared with other theoretical shell model calculations. The transition at 10.78 MeV is probably M2, or a mixture of M2 and transverse E2 transitions to unresolved states at about that energy

1984-01-01

184

Low multipolarity magnetic transitions in /sup 32/S excited by electron scattering  

Energy Technology Data Exchange (ETDEWEB)

Electron scattering cross section measurements on /sup 32/S have been made at incident electron energies between 34 and 74 MeV and at scattering angles of 162.4/sup 0/ and 180/sup 0/. Form factors were deduced for transitions to states at 8.11, 9.68, 10.05, 10.78, 11.12, and 11.63 MeV. Additional peaks at 7.12, 12.02, and 13.36 MeV were observed in some spectra. Comparisons of cross sections at different angles show that the above six transitions are transverse. Comparison of the experimental form factors with those calculated using an oscillator shell model indicate that the 8.11, 9.68, 11.12, and 11.63 MeV transitions are M1. Transition probabilities B(M1)up-arrow = 1.14 +- 0.18, 0.69 +- 0.20, 2.40 +- 0.22, and 1.26 +- 0.20 ..mu../sub 0//sup 2/, respectively, were determined for these four transitions. The M1 form factors and transition probabilities are also compared with other theoretical shell model calculations. The transition at 10.78 MeV is probably M2, or a mixture of M2 and transverse E2 transitions to unresolved states at about that energy.

Burt, P.E.; Fagg, L.W.; Crannell, H.; Sober, D.I.; Stapor, W.; O' Brien, J.T.; Lightbody, J.W.; Maruyama, X.K.; Lindgren, R.A.; Sargent, C.P.

1984-03-01

185

Dipole localization of human induced focal afterdischarge seizure in simultaneous magnetoencephalography and electrocorticography.  

Science.gov (United States)

Localizations were compared for the same human seizure between simultaneously measured MEG and iEEG, which were both co-registered to MRI. The whole-cortex neuromagnetometer localized a dipole in a sphere phantom, co-registered to the MEG sensor array, with an error of 1.4 mm. A focal afterdischarge seizure was induced in a patient with partial epilepsy, by stimulation at a subdural electrocorticography (ECoG) electrode with a known location, which was co-registered to the MRI and to the MEG sensor array. The simultaneous MEG and ECoG during the 30-second seizure was measured and analyzed using the single, moving dipole model, which is the localization model used clinically. The dipole localizations from simultaneous whole cortex 68-channel MEG and 64-channel ECoG were then compared for the repetitive spiking at six different times during the seizure. There were two main regions of MEG and ECoG activity. The locations of these regions were confirmed by determining the location clusters of 8,000 dipoles on ECoG at consecutive time points during the seizure. The mean distances between the stimulated electrode location versus the dipole location of the MEG and versus the dipole location of the ECoG were each about one (1) centimeter. The mean distance between the dipole locations of the MEG versus the dipole locations of the ECoG was about 2 cm. These errors were compared to errors of MEG and ECoG reported previously for phantoms and for somatosensory evoked responses (SER) in patients. Comparing the findings from the present study to those from prior studies, there appeared to be the expected stepwise increase in mean localization error progressing from the phantom, to the SER, to the seizure. PMID:11797809

Sutherling, W W; Akhtari, M; Mamelak, A N; Mosher, J; Arthur, D; Sands, S; Weiss, P; Lopez, N; DiMauro, M; Flynn, E; Leah, R

2001-01-01

186

Determination of multipolarities and mixing ratios of some {gamma} transitions following {sup 125}Sb decay by {gamma}-{gamma} Angular Correlation  

Energy Technology Data Exchange (ETDEWEB)

{sup 125}Sb decays by {beta}{sup -} emission to {sup 125}Te with a half-life of 2.76 years. The angular correlations of some {gamma}-ray transitions of this decay have been studied in order to determine their multipolarities and mixing ratios. The experimental set-up included a planar-Ge detector to measure the low-energy {gamma}-rays, a coaxial Ge detector and a movable device to determine precisely the angle between the axes of the detectors. Results obtained in the experiments and other available data were processed to obtain the best values for the mixing ratios.

Roteta, Miguel; Garcia-Torano, Eduardo

1998-09-11

187

ZnO thin films with c-axis orientation prepared on the room temperature substrate by the ECR multipolar plasma sputtering method  

International Nuclear Information System (INIS)

Zinc oxide (ZnO) films with c-axis orientation have been prepared on the room temperature substrates by a reactive sputtering deposition utilizing electron-cyclotron-resonance multipolar (ECRM) plasma apparatus built with Nd-Fe-B magnets and 2.45 GHz, TE10 mode microwave. The plasma distributions in the axial direction were found to be sensitive to the magnetic field configurations in the plasma cavity. The XRD, TEM, SEM analyses indicated that the deposited ZnO films were of nanometre size, smoothness and dense with high c-axis orientation.

1992-01-01

188

Establishment of M1 multipolarity of a 6.5 (micro)2n resonance in 172Yb at E(gamma) = 3.3 MeV  

Energy Technology Data Exchange (ETDEWEB)

Two-step-cascade spectra in {sup 172}Yb have been measured after thermal neutron capture. they are compared to calculations based on experimental values of the level density and radiative strength function (RSF) obtained from the {sup 173}Yb(3{sup 3}He,{alpha}{gamma}){sup 172}Yb reaction. The multipolarity of a 6.5(15) {mu}{sub N}{sup 2} resonance at E{sub {gamma}} = 3.3(1) MeV in the RSF is determined to be M1 by this comparison.

Schiller, A; Voinov, A; Algin, E; Becker, J A; Bernstein, L A; Garrett, P E; Guttormsen, M; Nelson, R O; Rekstad, J; Siem, S

2004-02-04

189

Ab initio and multipolar characterisation of the induced dipole surface for CH4-CH4: Application to dipole-forbidden absorption in the Titan's atmosphere  

Science.gov (United States)

The present paper aims to further characterise the induced dipole surface for CH4-CH4 through either multipolar expansion or CCSD(T) ab initio calculations. Our calculations extend to evaluation of the collision-induced integrated intensity of absorption in the far infrared as well as to classical determination of the equilibrium constant for true bound methane dimer formation. Height profiles are simulated for the dimer mole fraction as well as for the portion of true bound dimer absorption in the integrated collision-induced absorption taking the Titan's atmosphere as an example.

Buryak, I. A.; Kalugina, Y. N.; Vigasin, A. A.

2013-09-01

190

Two types of exercise-induced neuroplasticity in congenital hemiparesis: a transcranial magnetic stimulation, functional MRI, and magnetoencephalography study.  

UK PubMed Central (United Kingdom)

AIM: Early unilateral brain lesions can lead to a persistence of ipsilateral corticospinal projections from the contralesional hemisphere, which can enable the contralesional hemisphere to exert motor control over the paretic hand. In contrast to the primary motor representation (M1), the primary somatosensory representation (S1) of the paretic hand always remains in the lesioned hemisphere. Here, we report on differences in exercise-induced neuroplasticity between individuals with such ipsilateral motor projections (ipsi) and individuals with early unilateral lesions but 'healthy' contralateral motor projections (contra). METHOD: Sixteen children and young adults with congenital hemiparesis participated in the study (contralateral [Contra] group: n=7, four females, three males; age range 10-30y, median age 16y; ipsilateral [Ipsi] group: n=9, four females, five males; age range 11-31y, median age 12y; Manual Ability Classification System levels I to II in all individuals in both groups). The participants underwent a 12-day intervention of constraint-induced movement therapy (CIMT), consisting of individual training (2h/d) and group training (8h/d). Before and after CIMT, hand function was tested using the Wolf Motor Function Test (WMFT) and diverging neuroplastic effects were observed by transcranial magnetic stimulation (TMS), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG). Statistical analysis of TMS data was performed using the non-parametric Wilcoxon signed-rank test for pair-wise comparison; for fMRI standard statistical parametric and non-parametric mapping (SPM5, SnPM3) procedures (first level/second level) were carried out. Statistical analyses of MEG data involved analyses of variance (ANOVA) and t-tests. RESULTS: While MEG demonstrated a significant increase in S1 activation in both groups (p=0.012), TMS showed a decrease in M1 excitability in the Ipsi group (p=0.036), but an increase in M1 excitability in the Contra group (p=0.043). Similarly, fMRI showed a decrease in M1 activation in the Ipsi group, but an increase in activation in the M1-S1 region in the Contra group (for both groups p<0.001 [SnPM3] within the search volume). INTERPRETATION: Different patterns of sensorimotor (re)organization in individuals with early unilateral lesions show, on a cortical level, different patterns of exercise-induced neuroplasticity. The findings help to improve the understanding of the general principles of sensorimotor learning and will help to develop more specific therapies for different pathologies in congenital hemiparesis.

Juenger H; Kuhnke N; Braun C; Ummenhofer F; Wilke M; Walther M; Koerte I; Delvendahl I; Jung NH; Berweck S; Staudt M; Mall V

2013-10-01

191

Does very premature birth affect the functioning of the somatosensory cortex?--A magnetoencephalography study.  

Science.gov (United States)

Increased survival of extremely low birth weight infants has led to a need for new prognostic methods to predict possible future neurological impairment. We investigated the early development of the somatosensory system by recording the somatosensory evoked magnetic fields (SEFs) during natural sleep at fullterm age in 16 very prematurely born infants and 16 healthy newborns born at term. The purpose was to determine possible changes in the function of the somatosensory cortex in the prematurely born infants by comparing the latency, strength, location and morphology of the SEFs with those of healthy fullterm newborns. We recorded reliable SEFs in all patients and controls. The equivalent current dipole (ECD) strength of the first cortical response, M60, was significantly lower in the patients. Otherwise, the general morphology and latency of the SEFs were similar in the two groups of babies. The similar response latencies in the two groups indicate normally developed conduction in the somatosensory system of the prematurely born infants. The attenuated ECD strength may reflect weaker synchrony in firing or a smaller number of the cortical neurons activated by the somatosensory stimulation. At the individual level, in four of the preterm infants, a later M200 response was not present or could not be modeled: all of them had lesions of the underlying hemisphere depicted by ultrasound and magnetic resonance imaging. PMID:18313161

Nevalainen, Päivi; Pihko, Elina; Metsäranta, Marjo; Andersson, Sture; Autti, Taina; Lauronen, Leena

2008-02-01

192

Does very premature birth affect the functioning of the somatosensory cortex?--A magnetoencephalography study.  

UK PubMed Central (United Kingdom)

Increased survival of extremely low birth weight infants has led to a need for new prognostic methods to predict possible future neurological impairment. We investigated the early development of the somatosensory system by recording the somatosensory evoked magnetic fields (SEFs) during natural sleep at fullterm age in 16 very prematurely born infants and 16 healthy newborns born at term. The purpose was to determine possible changes in the function of the somatosensory cortex in the prematurely born infants by comparing the latency, strength, location and morphology of the SEFs with those of healthy fullterm newborns. We recorded reliable SEFs in all patients and controls. The equivalent current dipole (ECD) strength of the first cortical response, M60, was significantly lower in the patients. Otherwise, the general morphology and latency of the SEFs were similar in the two groups of babies. The similar response latencies in the two groups indicate normally developed conduction in the somatosensory system of the prematurely born infants. The attenuated ECD strength may reflect weaker synchrony in firing or a smaller number of the cortical neurons activated by the somatosensory stimulation. At the individual level, in four of the preterm infants, a later M200 response was not present or could not be modeled: all of them had lesions of the underlying hemisphere depicted by ultrasound and magnetic resonance imaging.

Nevalainen P; Pihko E; Metsäranta M; Andersson S; Autti T; Lauronen L

2008-05-01

193

Degenerate two-photon absorption and effective optical-power-limiting properties of multipolar chromophores derived from 2,3,8-trisubstituted indenoquinoxaline.  

UK PubMed Central (United Kingdom)

Two analogous multipolar chromophores (1 and 2) that contained 2,3,8-trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two-photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi-branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical-power-limiting and stabilization behaviors in the nanosecond regime of dye molecule (2) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two-photon systems for quick-response and related broadband optical-suppressing applications, in particular for confronting laser pulses of a long duration.

Lin TC; Guo FL; Li MH; Liu CY

2013-09-01

194

Degenerate two-photon absorption and effective optical-power-limiting properties of multipolar chromophores derived from 2,3,8-trisubstituted indenoquinoxaline.  

Science.gov (United States)

Two analogous multipolar chromophores (1 and 2) that contained 2,3,8-trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two-photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi-branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical-power-limiting and stabilization behaviors in the nanosecond regime of dye molecule (2) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two-photon systems for quick-response and related broadband optical-suppressing applications, in particular for confronting laser pulses of a long duration. PMID:23744812

Lin, Tzu-Chau; Guo, Fang-Ling; Li, May-Hui; Liu, Che-Yu

2013-06-06

195

Effect of multi-polar magnetic field on the properties of nanocrystalline silicon thin film deposited by internal-type inductively coupled plasma.  

UK PubMed Central (United Kingdom)

An internal linear-type inductively coupled plasma (ICP) source with multi-polar permanent magnets was used to deposit nanocrystalline silicon thin films on a large-area substrate (470 mm x 370 mm), and the effects of a magnetic field on the characteristics of the plasma and deposited film were investigated. By applying the magnetic field, it was possible to obtain a high-density plasma of 2.8 x 10(11) cm(-3) at 15 mTorr Ar and 4000 W of RF power, which is about 50% higher than was obtained for the source without the magnetic field. The application of the multi-polar magnet field to the ICP source during the deposition of silicon film using SiH4/H2 also increased the deposition rates of the silicon thin films and the ratio Halpha*/SiH*, which transformed the structure of the silicon films deposited on the glass substrates from amorphous to nanocrystalline. Furthermore, the use of the magnetic field increased crystalline volume fraction and dark conductivity while decreasing the absorption coefficient. The improved characteristics were related to the increase in the ionization rate and the dissociation rate of SiH4/H2, which confined the plasma to the chamber volume and avoided losses to the chamber wall. The decrease in the absorption coefficient of the nanocrystalline silicon film deposited with a higher H2 percentage and with the magnetic field present is also related to the increase in the crystallization volume fraction. At 70% H2 with the magnetic field present, the nanocrystalline silicon thin films had a high crystalline volume fraction (68%), a dark conductivity of 3.4E-7 omega(-1) cm(-1), a deposition rate of 10 angstroms/s, and grain sizes of approximately 15 nm.

Kim HB; Lee HC; Kim KN; Kang SK; Yeom GY

2009-12-01

196

Effect of multi-polar magnetic field on the properties of nanocrystalline silicon thin film deposited by internal-type inductively coupled plasma.  

Science.gov (United States)

An internal linear-type inductively coupled plasma (ICP) source with multi-polar permanent magnets was used to deposit nanocrystalline silicon thin films on a large-area substrate (470 mm x 370 mm), and the effects of a magnetic field on the characteristics of the plasma and deposited film were investigated. By applying the magnetic field, it was possible to obtain a high-density plasma of 2.8 x 10(11) cm(-3) at 15 mTorr Ar and 4000 W of RF power, which is about 50% higher than was obtained for the source without the magnetic field. The application of the multi-polar magnet field to the ICP source during the deposition of silicon film using SiH4/H2 also increased the deposition rates of the silicon thin films and the ratio Halpha*/SiH*, which transformed the structure of the silicon films deposited on the glass substrates from amorphous to nanocrystalline. Furthermore, the use of the magnetic field increased crystalline volume fraction and dark conductivity while decreasing the absorption coefficient. The improved characteristics were related to the increase in the ionization rate and the dissociation rate of SiH4/H2, which confined the plasma to the chamber volume and avoided losses to the chamber wall. The decrease in the absorption coefficient of the nanocrystalline silicon film deposited with a higher H2 percentage and with the magnetic field present is also related to the increase in the crystallization volume fraction. At 70% H2 with the magnetic field present, the nanocrystalline silicon thin films had a high crystalline volume fraction (68%), a dark conductivity of 3.4E-7 omega(-1) cm(-1), a deposition rate of 10 angstroms/s, and grain sizes of approximately 15 nm. PMID:19908805

Kim, Hong Bum; Lee, Hyoung Cheol; Kim, Kyong Nam; Kang, Se Koo; Yeom, Geun Young

2009-12-01

197

'Is tinnitus accompanied by hemifacial spasm in normal-hearing patients also a type of hyperactive neurovascular compression syndrome? : A magnetoencephalography study.  

UK PubMed Central (United Kingdom)

BACKGROUND: Traditionally, tinnitus accompanied by hemifacial spasm has been considered a type of hyperactive neurovascular compression syndrome that is similar to hemifacial spasm alone because of the anatomically close relationship between the facial nerve and cochlear nerve as well as the hyperactive clinical nature. METHODS: Participants were 29 subjects who presented with hemifacial spasm and neuroradiological evidence of vascular compression of the cranial (facial/cochlear) nerve. We used magnetoencephalography (MEG) to estimate the activity of the cochlear nerve in patients with and without tinnitus on the ipsilateral side. We compared the difference in the latency and the ratio of the equivalent current dipole (ECD) strength between the ipsilateral and contralateral sides of the spasm and tinnitus. RESULTS: Cochlear nerve activity in patients with tinnitus was increased with a shorter latency (p?=?0.016) and stronger ECD strength (p?=?0.028) compared with patients without tinnitus. CONCLUSION: The MEG results from normal-hearing patients who had tinnitus accompanied by hemifacial spasm suggest that the hyperactivity of the auditory central nervous system may be a crucial pathophysiological factor in the generation of tinnitus in these patients. The neurovascular compression that causes sensory input from the pathologic facial nerve activity may contribute to this hyperactivity of the central auditory nervous system.

Chang WS; Kim BS; Lee JE; Jung HH; Kim K; Kwon HC; Lee YH; Chang JW

2013-01-01

198

'Is tinnitus accompanied by hemifacial spasm in normal-hearing patients also a type of hyperactive neurovascular compression syndrome? : A magnetoencephalography study  

Science.gov (United States)

Background Traditionally, tinnitus accompanied by hemifacial spasm has been considered a type of hyperactive neurovascular compression syndrome that is similar to hemifacial spasm alone because of the anatomically close relationship between the facial nerve and cochlear nerve as well as the hyperactive clinical nature. Methods Participants were 29 subjects who presented with hemifacial spasm and neuroradiological evidence of vascular compression of the cranial (facial/cochlear) nerve. We used magnetoencephalography (MEG) to estimate the activity of the cochlear nerve in patients with and without tinnitus on the ipsilateral side. We compared the difference in the latency and the ratio of the equivalent current dipole (ECD) strength between the ipsilateral and contralateral sides of the spasm and tinnitus. Results Cochlear nerve activity in patients with tinnitus was increased with a shorter latency (p?=?0.016) and stronger ECD strength (p?=?0.028) compared with patients without tinnitus. Conclusion The MEG results from normal-hearing patients who had tinnitus accompanied by hemifacial spasm suggest that the hyperactivity of the auditory central nervous system may be a crucial pathophysiological factor in the generation of tinnitus in these patients. The neurovascular compression that causes sensory input from the pathologic facial nerve activity may contribute to this hyperactivity of the central auditory nervous system.

2013-01-01

199

METHOD FOR DESIGNING COIL SYSTEMS FOR GENERATION OF MAGNETIC FIELDS OF DESIRED GEOMETRY, A MAGNETIC RESONANCE IMAGING OR MAGNETOENCEPHALOGRAPHY APPARATUS WITH A COIL ASSEMBLY AND A COMPUTER PROGRAM  

UK PubMed Central (United Kingdom)

The present invention introduces a method, apparatus and computer program for magnetic resonance imaging or magnetoencephalography applications in order to control currents of a coil assembly (20), and thus achieving desired magnetic fields precisely in the measuring volume (21). The approach is an algebraic method where a field vector is generated for the test currents of each coil (20). Vector and matrix algebra is applied and a linear set of equations is formed. Field components and their derivatives up to the desired order can be taken into account. Principal component analysis or independent component analysis can be applied for determination of the dominant external interference components. By checking the condition value for the matrix (33, 45), it is possible to investigate whether a reasonable solution of currents for desired magnetic fields is possible to achieve. Finally, solved currents can be installed into a current supply unit (29) feeding the coils of the assembly (20). The invention can be applied as an active compensation feature for different interference shapes in the MEG application (25), or for the precise creation of the fields and gradients in the MRI application (24).

SIMOLA JUHA; TAULU SAMU

200

Cellular and molecular characterization of multipolar Map5-expressing cells: a subset of newly generated, stage-specific parenchymal cells in the mammalian central nervous system.  

Science.gov (United States)

Although extremely interesting in adult neuro-glio-genesis and promising as an endogenous source for repair, parenchymal progenitors remain largely obscure in their identity and physiology, due to a scarce availability of stage-specific markers. What appears difficult is the distinction between real cell populations and various differentiation stages of the same population. Here we focused on a subset of multipolar, polydendrocyte-like cells (mMap5 cells) expressing the microtubule associated protein 5 (Map5), which is known to be present in most neurons. We characterized the morphology, phenotype, regional distribution, proliferative dynamics, and stage-specific marker expression of these cells in the rabbit and mouse CNS, also assessing their existence in other mammalian species. mMap5 cells were never found to co-express the Ng2 antigen. They appear to be a population of glial cells sharing features but also differences with Ng2+progenitor cells. We show that mMap5 cells are newly generated, postmitotic parenchymal elements of the oligodendroglial lineage, thus being a stage-specific population of polydendrocytes. Finally, we report that the number of mMap5 cells, although reduced within the brain of adult/old animals, can increase in neurodegenerative and traumatic conditions. PMID:23667595

Crociara, Paola; Parolisi, Roberta; Conte, Daniele; Fumagalli, Marta; Bonfanti, Luca

2013-05-07

 
 
 
 
201

Cellular and molecular characterization of multipolar Map5-expressing cells: a subset of newly generated, stage-specific parenchymal cells in the mammalian central nervous system.  

UK PubMed Central (United Kingdom)

Although extremely interesting in adult neuro-glio-genesis and promising as an endogenous source for repair, parenchymal progenitors remain largely obscure in their identity and physiology, due to a scarce availability of stage-specific markers. What appears difficult is the distinction between real cell populations and various differentiation stages of the same population. Here we focused on a subset of multipolar, polydendrocyte-like cells (mMap5 cells) expressing the microtubule associated protein 5 (Map5), which is known to be present in most neurons. We characterized the morphology, phenotype, regional distribution, proliferative dynamics, and stage-specific marker expression of these cells in the rabbit and mouse CNS, also assessing their existence in other mammalian species. mMap5 cells were never found to co-express the Ng2 antigen. They appear to be a population of glial cells sharing features but also differences with Ng2+progenitor cells. We show that mMap5 cells are newly generated, postmitotic parenchymal elements of the oligodendroglial lineage, thus being a stage-specific population of polydendrocytes. Finally, we report that the number of mMap5 cells, although reduced within the brain of adult/old animals, can increase in neurodegenerative and traumatic conditions.

Crociara P; Parolisi R; Conte D; Fumagalli M; Bonfanti L

2013-01-01

202

Restoration of Altered Somatosensory Cortical Representation With Spinal Cord Stimulation Therapy in a Patient With Complex Regional Pain Syndrome: A Magnetoencephalography Case Study.  

Science.gov (United States)

OBJECTIVES: Development of effective chronic pain treatment strategies has been hampered by the lack of an objective pain biomarker. Magnetoencephalography (MEG) has demonstrated cortical disorganization corresponding to the affected limb of complex regional pain syndrome (CRPS) patients and spinal cord stimulation (SCS) can acutely treat CRPS in a reversible and adjustable fashion. In order to better define a potential MEG-sensitive biomarker for chronic pain, our goal was to study the effects of therapeutic SCS on cortical disorganization in patients with unilateral limb CRPS. METHODS: Two patients treated with either thoracic or cervical SCS with leg or arm CRPS were studied with MEG. Baseline and tactile-evoked responses were recorded with and without effective SCS therapy. RESULTS: All MEG recordings were obtained with minimal interference. In the patient with arm CRPS, with the stimulator off, first and fifth digit primary somatosensory (SI) cortical representations (D1/D5) were significantly disorganized and spatially inverted as compared with the opposite unaffected limb. Effective SCS therapy was then able to acutely normalize or restore hand cortical organization in the affected CRPS limb. This restoration of cortical organization was partially maintained with lingering pain relief when the stimulator was subsequently turned off. CONCLUSIONS: This is the first report of a MEG study showing D1/D5 cortical disorganization and its apparent reversal or restoration with cervical SCS therapy. Ours also is the first report of an apparent acute reversible interchange in the cortical representations of D1 and D5. Our limited data demonstrate that disorganization of SI cortex might be a neurophysiologic marker of chronic pain as shown with instantaneous normalization of SI disorganization or restoration of SI organization with therapeutic SCS. As a clinically proven tool for functional mapping, MEG might be shown to provide an objective measure of chronic pain. More data are required to further investigate this possibility. PMID:23433264

Pahapill, Peter A; Zhang, Wenbo

2013-02-21

203

Restoration of Altered Somatosensory Cortical Representation With Spinal Cord Stimulation Therapy in a Patient With Complex Regional Pain Syndrome: A Magnetoencephalography Case Study.  

UK PubMed Central (United Kingdom)

OBJECTIVES: Development of effective chronic pain treatment strategies has been hampered by the lack of an objective pain biomarker. Magnetoencephalography (MEG) has demonstrated cortical disorganization corresponding to the affected limb of complex regional pain syndrome (CRPS) patients and spinal cord stimulation (SCS) can acutely treat CRPS in a reversible and adjustable fashion. In order to better define a potential MEG-sensitive biomarker for chronic pain, our goal was to study the effects of therapeutic SCS on cortical disorganization in patients with unilateral limb CRPS. METHODS: Two patients treated with either thoracic or cervical SCS with leg or arm CRPS were studied with MEG. Baseline and tactile-evoked responses were recorded with and without effective SCS therapy. RESULTS: All MEG recordings were obtained with minimal interference. In the patient with arm CRPS, with the stimulator off, first and fifth digit primary somatosensory (SI) cortical representations (D1/D5) were significantly disorganized and spatially inverted as compared with the opposite unaffected limb. Effective SCS therapy was then able to acutely normalize or restore hand cortical organization in the affected CRPS limb. This restoration of cortical organization was partially maintained with lingering pain relief when the stimulator was subsequently turned off. CONCLUSIONS: This is the first report of a MEG study showing D1/D5 cortical disorganization and its apparent reversal or restoration with cervical SCS therapy. Ours also is the first report of an apparent acute reversible interchange in the cortical representations of D1 and D5. Our limited data demonstrate that disorganization of SI cortex might be a neurophysiologic marker of chronic pain as shown with instantaneous normalization of SI disorganization or restoration of SI organization with therapeutic SCS. As a clinically proven tool for functional mapping, MEG might be shown to provide an objective measure of chronic pain. More data are required to further investigate this possibility.

Pahapill PA; Zhang W

2013-02-01

204

Potential of a no-touch pincer ablation procedure for small hepatocellular carcinoma that uses a multipolar radiofrequency ablation system: an experimental animal study.  

UK PubMed Central (United Kingdom)

AIM: Treatment of hepatocellular carcinoma located on the liver surface is frequently difficult because direct puncture of the tumor must be avoided during needle insertion. The aim of this study was to investigate the utility of a no-touch pincer ablation procedure that uses a multipolar radiofrequency ablation (RFA) system for a tumor located on the liver surface. METHODS: The experimental animals were 3 pigs, and RFA was performed with 2 internally cooled bipolar electrodes. Three ablative procedures were compared: linear insertion at regular 13-mm intervals (Pattern-1; virtual target tumor size, 10 mm), fan-shape insertion; maximum interval 20-mm (Pattern-2; virtual target tumor size, 15 mm), and 25-mm (Pattern-3; virtual target tumor size, 20 mm). All electrodes were inserted at a 30-mm depth. For Pattern-1 and Pattern-2, ablation was performed on three other parts of the liver, and for Pattern-3, ablation was performed on two other parts. RESULTS: For the median transverse and longitudinal diameter to the shaft, with the Pattern-1 procedure, the ablative areas were 32×30 mm, and with the Pattern-2 procedure, the ablative areas were 27×30 mm with carbonization of the liver surface. In contrast, with the Pattern-3 procedure, the ablative areas were 45×26 mm; however, the ablative margin did not reach the surface, and carbonization was not apparent. CONCLUSION: The no-touch pincer ablation procedure (with an electrode interval ?20 mm) may be useful when performed with two internally cooled bipolar electrodes for small nodules that protrude from the liver surface.

Kawamura Y; Ikeda K; Fukushima T; Hara T; Hosaka T; Kobayashi M; Saitoh S; Sezaki H; Akuta N; Suzuki F; Suzuki Y; Arase Y; Kumada H

2013-09-01

205

Imagens multipolarizadas do sensor Palsar/Alos na discriminação das fases fenológicas da cana?de?açúcar Multipolarized Palsar/Alos images to discriminate sugarcane phenological phases  

Directory of Open Access Journals (Sweden)

Full Text Available O objetivo deste trabalho foi avaliar o potencial das imagens multipolarizadas do sensor?radar Palsar/Alos em diferenciar as fases fenológicas da cana?de?açúcar. Valores digitais de quatro imagens do sensor, dos meses de fevereiro, maio, agosto e outubro de 2008, com polarizações HH (emissão e recebimento de onda na polarização horizontal) e HV (emissão de onda na polarização horizontal e recebimento na vertical), foram convertidos para coeficientes de retroespalhamento (?°), para a análise de dados de cana?de?açúcar, cultivadas em talhões na região nordeste do Estado de São Paulo. Foram selecionadas três variedades, em diferentes estágios fenológicos: RB85?5156, seis talhões; RB86?7515, dez talhões; e RB92?5345, dez talhões. As diferenças entre as fases fenológicas foram avaliadas para cada uma das variedades e, também, entre as variedades. A utilização simultânea ou não dos dados do sensor Palsar/Alos, obtidos em duas polarizações, foi capaz de discriminar as diferentes fases de crescimento da cana?de?açúcar, com exceção da fase de crescimento dos colmos e a fase de maturação, em que não foi observada diferença significativa.The objective of this work was to evaluate the potential of multipolarized Palsar/Alos satellite images to discriminate phenological phases of sugarcane. Digital values from four digital images of February, May, August, and October 2008, with HH (sending and receiving wave in horizontal polarization) and HV polarizations (sending wave in horizontal polarization and receiving in vertical polarization), were converted to backscattering coefficients (?°) for data analysis of sugarcane cultivated in the northeastern of the state of São Paulo, Brazil. Three varieties were selected at different phenological stages: RB85?5156, six stands; RB86?7515, ten stands; and RB92?5345, ten stands. The differences between the phenological phases were analyzed for each variety, and also between varieties. The single or dual?poralized Palsar/Alos data, obtained in two polarizations, were able of discriminating the different phases of sugarcane growth, except for the grand growth period and maturity phase, in which no significant difference was observed.

Michelle Cristina Araujo Picoli; Rubens Augusto Lamparelli; Edson Eyji Sano; Jansle Vieira Rocha

2012-01-01

206

Imagens multipolarizadas do sensor Palsar/Alos na discriminação das fases fenológicas da cana?de?açúcar/ Multipolarized Palsar/Alos images to discriminate sugarcane phenological phases  

Scientific Electronic Library Online (English)

Full Text Available Abstract in portuguese O objetivo deste trabalho foi avaliar o potencial das imagens multipolarizadas do sensor?radar Palsar/Alos em diferenciar as fases fenológicas da cana?de?açúcar. Valores digitais de quatro imagens do sensor, dos meses de fevereiro, maio, agosto e outubro de 2008, com polarizações HH (emissão e recebimento de onda na polarização horizontal) e HV (emissão de onda na polarização horizontal e recebimento na vertical), foram convertidos para coefic (more) ientes de retroespalhamento (?°), para a análise de dados de cana?de?açúcar, cultivadas em talhões na região nordeste do Estado de São Paulo. Foram selecionadas três variedades, em diferentes estágios fenológicos: RB85?5156, seis talhões; RB86?7515, dez talhões; e RB92?5345, dez talhões. As diferenças entre as fases fenológicas foram avaliadas para cada uma das variedades e, também, entre as variedades. A utilização simultânea ou não dos dados do sensor Palsar/Alos, obtidos em duas polarizações, foi capaz de discriminar as diferentes fases de crescimento da cana?de?açúcar, com exceção da fase de crescimento dos colmos e a fase de maturação, em que não foi observada diferença significativa. Abstract in english The objective of this work was to evaluate the potential of multipolarized Palsar/Alos satellite images to discriminate phenological phases of sugarcane. Digital values from four digital images of February, May, August, and October 2008, with HH (sending and receiving wave in horizontal polarization) and HV polarizations (sending wave in horizontal polarization and receiving in vertical polarization), were converted to backscattering coefficients (?°) for data analy (more) sis of sugarcane cultivated in the northeastern of the state of São Paulo, Brazil. Three varieties were selected at different phenological stages: RB85?5156, six stands; RB86?7515, ten stands; and RB92?5345, ten stands. The differences between the phenological phases were analyzed for each variety, and also between varieties. The single or dual?poralized Palsar/Alos data, obtained in two polarizations, were able of discriminating the different phases of sugarcane growth, except for the grand growth period and maturity phase, in which no significant difference was observed.

Picoli, Michelle Cristina Araujo; Lamparelli, Rubens Augusto; Sano, Edson Eyji; Rocha, Jansle Vieira

2012-09-01

207

Some models of non-newtonian fluids and their properties  

Energy Technology Data Exchange (ETDEWEB)

There are many possibilities how to describe a non-Newtonian flow. We present one of them, namely the bipolar isothermal non-Newtonian fluids, which includes two models: bipolar fluids and non-Newtonian fluids. Bipolar fluids are the special case of the multipolar fluids. The fundamental idea, that in the viscous flow the stress tensor has to depend on the higher order gradients of velocity, was given by Necas and Silhavy. The physical theory of multipolar fluids is compatible with the principle of thermodynamics and with the principle of material frame indifference. The non-Newtonian character of flow is described by the dependence of the coefficients of viscosity on the invariants of velocity fields. (orig.)

Matusu-Necasova, S. [Ceska Akademie Ved, Prague (Czech Republic). Matematicky Ustav; Lukacova-Medvidova, M. [Tech. Univ. of Brno (Czech Republic). Inst. of Mathematics

1997-12-31

208

Computer simulations of electrorheological fluids in the dipole-induced dipole model  

CERN Multimedia

We have employed the multiple image method to compute the interparticle force for a polydisperse electrorheological (ER) fluid in which the suspended particles can have various sizes and different permittivites. The point-dipole (PD) approximation being routinely adopted in computer simulation of ER fluids is shown to err considerably when the particles approach and finally touch due to multipolar interactions. The PD approximation becomes even worse when the dielectric contrast between the particles and the host medium is large. From the results, we show that the dipole-induced-dipole (DID) model yields very good agreements with the multiple image results for a wide range of dielectric contrasts and polydispersity. As an illustration, we have employed the DID model to simulate the athermal aggregation of particles in ER fluids both in uniaxial and rotating fields. We find that the aggregation time is significantly reduced. The DID model accounts for multipolar interaction partially and is simple to use in co...

Siu, Y L; Yu, K W; Wan, Jones T. K.

2001-01-01

209

Isoscalar giant resonances in a relativistic model  

International Nuclear Information System (INIS)

Isoscalar giant resonances in finite nuclei are studied in a relativistic Random Phase Approximation (RRPA) approach. The model is self-consistent in the sense that one set of coupling constants generates the Dirac-Hartree single-particle spectrum and the residual particle-hole interaction. The RRPA is used to calculate response functions of multipolarity L = 0,2,3, and 4 in light and medium nuclei. It is found that monopole and quadrupole modes exhibit a collective character. The peak energies are overestimated, but not as much as one might think if the bulk properties (compression modulus, effective mass) were the only relevant quantities.

1988-01-01

210

FIXATION HELIX AND MULTIPOLAR MEDICAL ELECTRODE  

UK PubMed Central (United Kingdom)

A cardiac rhythm management device that includes a lead and a pulse generator. The lead can comprise a lead body, a helical composite electrode, a composite conductor and a proximal connector. The helical composite electrode can have first and second electrodes in a co-axial configuration. The composite connector can electrically connect the first and second electrodes to the proximal connector. The proximal connector can be configured to couple to the pulse generator.

FOSTER ARTHUR J

211

Fixation helix and multipolar medical electrode  

UK PubMed Central (United Kingdom)

A cardiac rhythm management device that includes a lead and a pulse generator. The lead can comprise a lead body, a helical composite electrode, a composite conductor and a proximal connector. The helical composite electrode can have first and second electrodes in a coaxial configuration. The composite connector can electrically connect the first and second electrodes to the proximal connector. The proximal connector can be configured to couple to the pulse generator.

FOSTER ARTHUR J

212

Prospects for a multipolar international monetary system  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this DIIS Report, Dr Mansoor Dailami and Professor Paul Masson envisage a fundamental change in the international monetary system, one that is likely to recognize the growing economic and financial clout of emerging market economies, particularly China. The authors see three possible internationa...

Dailami, Mansoor; Masson, Paul

213

US ASAT Policy for a Multipolar World.  

Science.gov (United States)

Whether to pursue the continued development of a US ASAT in the 1990s will prove a difficult choice for defense planners. Making a case for the weapon system in the bipolar world seemed perhaps 'intuitively obvious' to ASAT advocates. The US was faced wit...

R. C. Hunter

1992-01-01

214

Clinical applications of magnetoencephalography in epilepsy  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetoencehalography (MEG) is being used with increased frequency in the pre-surgical evaluation of patients with epilepsy. One of the major advantages of this technique over the EEG is the lack of distortion of MEG signals by the skull and intervening soft tissue. In addition, the MEG preferentially records activity from tangential sources thus recording activity predominantly from sulci, which is not contaminated by activity from apical gyral (radial) sources. While the MEG is probably more sensitive than the EEG in detecting inter-ictal spikes, especially in the some locations such as the superficial frontal cortex and the lateral temporal neocortex, both techniques are usually complementary to each other. The diagnostic accuracy of MEG source localization is usually better as compared to scalp EEG localization. Functional localization of eloquent cortex is another major application of the MEG. The combination of high spatial and temporal resolution of this technique makes it an extremely helpful tool for accurate localization of visual, somatosensory and auditory cortices as well as complex cognitive functions like language. Potential future applications include lateralization of memory function.

Ray Amit; Bowyer Susan

2010-01-01

215

Multipolar ou apolar?: Um desconcertante mundo novo/ Multipolar or apolar: a confused new world  

Scientific Electronic Library Online (English)

Full Text Available Abstract in portuguese Com base numa reflexão sobre o mundo dez anos depois do 11 de Setembro, o artigo aprofunda a análise da organização do sistema internacional admitindo que estamos perante um mundo apolar. Depois de explorar a evolução do conceito de pólo, avalia os novos equilíbrios de poder com base em três elementos: a alteração dos equilíbrios de poder tradicional, a alteração da conflitualidade e lealdades e os grandes desafios emergentes. Abstract in english This article explores deeply the international system organization arguing that we are in an apolar world, bearing in mind a reflection about the 9/11. We will explore the evolution of the pole concept, and then evaluate the new balances of power through the analysis of three elements: the shifting of the traditional balances of power, the change on the rivalries and loyalties and the great emerging challenges.

Telo, António José

2011-09-01

216

Plasmon hybridization model generalized to conductively bridged nanoparticle dimers.  

UK PubMed Central (United Kingdom)

Charge transfer introduced by a conductive junction bridging a nanoparticle dimer can have a pronounced effect on the optical properties of the system. We have extended the plasmon hybridization model to include conductive junctions and charge transfer effects. From our model, we are able to derive all the plasmon resonances of the bridged dimer, including the charge transfer plasmon (CTP), and predict their trends when system parameters are varied. In particular, we find that CTP is a result of a sufficiently narrow monopole mode interacting with multipolar (including dipolar) modes. The screening arising from charge transfer induces a blueshift of the hybridized bonding dimer modes and decreases the electric field in the junction. Our model may serve as an important guide for optical properties of bridged nanoparticle aggregates.

Liu L; Wang Y; Fang Z; Zhao K

2013-08-01

217

Plasmon hybridization model generalized to conductively bridged nanoparticle dimers  

Science.gov (United States)

Charge transfer introduced by a conductive junction bridging a nanoparticle dimer can have a pronounced effect on the optical properties of the system. We have extended the plasmon hybridization model to include conductive junctions and charge transfer effects. From our model, we are able to derive all the plasmon resonances of the bridged dimer, including the charge transfer plasmon (CTP), and predict their trends when system parameters are varied. In particular, we find that CTP is a result of a sufficiently narrow monopole mode interacting with multipolar (including dipolar) modes. The screening arising from charge transfer induces a blueshift of the hybridized bonding dimer modes and decreases the electric field in the junction. Our model may serve as an important guide for optical properties of bridged nanoparticle aggregates.

Liu, Lifei; Wang, Yumin; Fang, Zheyu; Zhao, Ke

2013-08-01

218

A sensor-weighted overlapping-sphere head model and exhaustive head model comparison for MEG  

International Nuclear Information System (INIS)

The spherical head model has been used in magnetoencephalography (MEG) as a simple forward model for calculating the external magnetic fields resulting from neural activity. For more realistic head shapes, the boundary element method (BEM) or similar numerical methods are used, but at greatly increased computational cost. We introduce a sensor-weighted overlapping-sphere (OS) head model for rapid calculation of more realistic head shapes. The volume currents associated with primary neural activity are used to fit spherical head models for each individual MEG sensor such that the head is more realistically modelled as a set of overlapping spheres, rather than a single sphere. To assist in the evaluation of this OS model with BEM and other head models, we also introduce a novel comparison technique that is based on a generalized eigenvalue decomposition and accounts for the presence of noise in the MEG data. With this technique we can examine the worst possible errors for thousands of dipole locations in a realistic brain volume. We test the traditional single-sphere model, three-shell and single-shell BEM, and the new OS model. The results show that the OS model has accuracy similar to the BEM but is orders of magnitude faster to compute. (author)

1999-01-01

219

Integrating the disaster cycle model into traditional disaster diplomacy concepts.  

UK PubMed Central (United Kingdom)

Disaster diplomacy is an evolving contemporary model that examines how disaster response strategies can facilitate cooperation between parties in conflict. The concept of disaster diplomacy has emerged during the past decade to address how disaster response can be leveraged to promote peace, facilitate communication, promote human rights, and strengthen intercommunity ties in the increasingly multipolar modern world. Historically, the concept has evolved through two camps, one that focuses on the interactions between national governments in conflict and another that emphasizes the grassroots movements that can promote change. The two divergent approaches can be reconciled and disaster diplomacy further matured by contextualizing the concept within the disaster cycle, a model well established within the disaster risk management community. In particular, access to available health care, especially for the most vulnerable populations, may need to be negotiated. As such, disaster response professionals, including emergency medicine specialists, can play an important role in the development and implementation of disaster diplomacy concepts.

Callaway DW; Yim ES; Stack C; Burkle FM Jr

2012-03-01

220

Modelling the dispersion energy for Van der Waals complexes  

CERN Multimedia

Strictly ab initio calculations of the dispersion energy are unfeasible in practice but for the smallest systems. A sensible alternative is to model the dispersion contribution through a damped multipolar expansion. This thesis proposes to represent the dispersion energy by means of a non-empirical, atom-atom model using damping functions scaled from 'exact' results for one electron-one electron systems. We start by investigating the scalability of ab initio calculated damping functions for closed-shell atom-atom dimers. Ab initio scaling parameters are employed to assess the quality of the damping functions yielded by a predictor scheme based on the charge overlap between the interacting monomers. The investigation of the scaling properties is extended to atom-linear molecule systems, focusing on the dependence on orientation of the short-range dispersion energy and how to account for it using isotropic damping parameters. We study the possibilities of an 'atomic' (multicentre) representation of the dispersi...

Sanz-Garcia, A

2002-01-01

 
 
 
 
221

A mean-field formalism to model current source densities and extracellular potentials in biological tissue  

CERN Document Server

The standard model of electric fields and potentials in biological tissue assumes that current sources are exclusively made by dipoles, and that the surrounding medium is resistive and uniform. Because of these assumptions, this standard model cannot be used to estimate the contributions of monopolar sources or of non-resistive aspects of the extracellular medium. We propose here a general framework to model electric fields and potentials resulting from current source densities, without relying on such assumptions. We develop a mean-field formalism which is a generalization of the standard model, and which can directly incorporate macroscopic measurements of electric parameters and non-resistive (non-ohmic) properties of the extracellular medium, such as ionic diffusion effects. This formalism recovers the classic results of the standard model such as the current-source density (CSD) analysis, but can generalize the CSD approach to situations with non-resistive media and arbitrarily complex multipolar configu...

Bedard, Claude

2011-01-01

222

Effects of sutures and fontanels on MEG and EEG source analysis in a realistic infant head model.  

UK PubMed Central (United Kingdom)

In infants, the fontanels and sutures as well as conductivity of the skull influence the volume currents accompanying primary currents generated by active neurons and thus the associated electroencephalography (EEG) and magnetoencephalography (MEG) signals. We used a finite element method (FEM) to construct a realistic model of the head of an infant based on MRI images. Using this model, we investigated the effects of the fontanels, sutures and skull conductivity on forward and inverse EEG and MEG source analysis. Simulation results show that MEG is better suited than EEG to study early brain development because it is much less sensitive than EEG to distortions of the volume current caused by the fontanels and sutures and to inaccurate estimates of skull conductivity. Best results will be achieved when MEG and EEG are used in combination.

Lew S; Sliva DD; Choe MS; Grant PE; Okada Y; Wolters CH; Hämäläinen MS

2013-08-01

224

Model.  

Directory of Open Access Journals (Sweden)

Full Text Available Social scientists appear to be divided into two camps: those who use models and those who do not. In order to understand this phenomenon, a clear understanding of what a model is is required. Unfortunately, this is more complicated than one might think. To be sure, few social scientists would have trouble identifying what they consider to be a model: defining what a model is, however, is more difficult. To echo Associate Justice Potter Stewart's famous quote about pornography, most social ...

Zachary Patterson

2008-01-01

225

Evaluation of multiple-sphere head models for MEG source localization  

International Nuclear Information System (INIS)

Magnetoencephalography (MEG) source analysis has largely relied on spherical conductor models of the head to simplify forward calculations of the brain's magnetic field. Multiple- (or overlapping, local) sphere models, where an optimal sphere is selected for each sensor, are considered an improvement over single-sphere models and are computationally simpler than realistic models. However, there is limited information available regarding the different methods used to generate these models and their relative accuracy. We describe a variety of single- and multiple-sphere fitting approaches, including a novel method that attempts to minimize the field error. An accurate boundary element method simulation was used to evaluate the relative field measurement error (12% on average) and dipole fit localization bias (3.5 mm) of each model over the entire brain. All spherical models can contribute in the order of 1 cm to the localization bias in regions of the head that depart significantly from a sphere (inferior frontal and temporal). These spherical approximation errors can give rise to larger localization differences when all modeling effects are taken into account and with more complex source configurations or other inverse techniques, as shown with a beamformer example. Results differed noticeably depending on the source location, making it difficult to recommend a fitting method that performs best in general. Given these limitations, it may be advisable to expand the use of realistic head models.

2011-09-07

226

China's Soft Diplomacy in an Emerging Multi-polar World  

DEFF Research Database (Denmark)

Keynote presentation for the conference"The Growing Prominence of China on the World Stage: Exploring the Political, Economic, and Cultural Relations of China and Global Stakeholders" International Conference, Berlin, September 15th - 18th, 2011 - Held Parallel to the "Berlin - Asia Pacific Weeks Conference 2011

Schmidt, Johannes Dragsbæk

227

Multipolar Expansions for Closed and Open Systems of Relativistic Particles  

CERN Multimedia

Dixon's multipoles for a system of N relativistic positive-energy scalar particles are evaluated in the rest-frame instant form of dynamics. The Wigner hyper-planes (intrinsic rest frame of the isolated system) turn out to be the natural framework for describing multipole kinematics. Classical concepts like the {\\it barycentric tensor of inertia} turn out to be extensible to special relativity only by means of the quadrupole moments of the isolated system. Two new applications of the multipole technique are worked out for systems of interacting particles and fields. In the rest-frame of the isolated system of either free or interacting positive energy particles it is possible to define a unique world-line which embodies the properties of the most relevant centroids introduced in the literature as candidates for the collective motion of the system. This is no longer true, however, in the case of open subsystems of the isolated system. While effective mass, 3-momentum and angular momentum in the rest frame can ...

Alba, D

2004-01-01

228

Probing Electronic Correlations in Actinide Materials Using Multipolar Transitions  

Energy Technology Data Exchange (ETDEWEB)

We report nonresonant inelastic x-ray scattering from the semicore 5d levels of several actinide compounds. Dipole-forbidden, high-multipole features form a rich bound-state spectrum dependent on valence electron configuration and spin-orbit and Coulomb interactions. Cross-material comparisons, together with the anomalously high Coulomb screening required for agreement between atomic-multiplet theory and experiment, demonstrate sensitivity to the neighboring electronic environment, such as is needed to address longstanding questions of electronic localization and bonding in 5f compounds.

Bradley, J.A.; Gupta, S. Sen; Seidler, G.T.; Moore, K.T.; Haverkort, M.W.; Sawatzky, G.A.; Conradson, S.D.; Clark, D.L.; Kozimor, S.A.; Boland, K.S. (UWASH); (MXPL-SS); (LLNL); (UBC); (LANL)

2010-07-28

229

The filamentary multi-polar planetary nebula NGC 5189  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Presentamos un conjunto de imágenes ópticas e infrarrojas combinadas con espectros de rendija larga de mediana y alta dispersión de la Nebulosa Planetaria (NP) del sur NGC 5189. La compleja morfología de esta NP es desconcertante y no había sido estudiada en detalle hasta ahora. Nuestra investigación revela la presencia de un toroide denso y frío, en el infrarrojo, el cual probablemente generó uno de los dos flujos bipolares vistos en el óptico y podría, mediant (more) e un proceso de interacción, ser también responsable de la apariencia retorcida del toroide óptico. Los espectros de alta resolución del MES-AAT muestran claramente la presencia de nudos y estructuras filamentosas, así como tres burbujas en expansión. Nuestros hallazgos sugieren que NGC 5189 es una NP cuadrupolar con varios conjuntos de condensaciones simétricas en la cual la interacción de flujos determinó su compleja morfología. Abstract in english We present a set of optical and infrared images combined with long-slit, medium and high dispersion spectra of the southern planetary nebula (PN) NGC 5189. The complex morphology of this PN is puzzling and has not been studied in detailed so far. Our investigation reveals the presence of a new dense and cold infrared torus (alongside the optical one) which probably generated one of the two optically seen bipolar outflows and which might be responsible for the twisted appe (more) arance of the optical torus via an interaction process. The high-resolution MES-AAT spectra clearly show the presence of filamentary and knotty structures as well as three expanding bubbles. Our findings therefore suggest that NGC 5189 is a quadrupolar nebula with multiple sets of symmetrical condensations in which the interaction of outflows has determined its complex morphology.

Sabin, L.; Vázquez, R.; López, J. A.; García-Díaz, Ma. T.; Ramos-Larios, G.

2012-10-01

230

Photon angular momentum: selection rules and multipolar transition moments  

International Nuclear Information System (INIS)

The representation of electromagnetic radiation by means of vector spherical harmonics and Bessel functions is described and used to derive selection rules for atomic electronic transitions which, as expected, show that the angular momentum of the system-atom plus photon-is conserved and, more importantly, provide a very precise description of the angular momentum of the photon involved. Examples of matrix elements for electric dipole, electric quadrupole and magnetic dipole transition moments of the hydrogen atom are calculated and the results compared with those obtained by the usual plane-wave expansion and with more recent results obtained in connection with studies of 'twisted' beams.

2008-05-14

231

Photon angular momentum: selection rules and multipolar transition moments  

Science.gov (United States)

The representation of electromagnetic radiation by means of vector spherical harmonics and Bessel functions is described and used to derive selection rules for atomic electronic transitions which, as expected, show that the angular momentum of the system—atom plus photon—is conserved and, more importantly, provide a very precise description of the angular momentum of the photon involved. Examples of matrix elements for electric dipole, electric quadrupole and magnetic dipole transition moments of the hydrogen atom are calculated and the results compared with those obtained by the usual plane-wave expansion and with more recent results obtained in connection with studies of 'twisted' beams.

Grinter, Roger

2008-05-01

232

Photon angular momentum: selection rules and multipolar transition moments  

Energy Technology Data Exchange (ETDEWEB)

The representation of electromagnetic radiation by means of vector spherical harmonics and Bessel functions is described and used to derive selection rules for atomic electronic transitions which, as expected, show that the angular momentum of the system-atom plus photon-is conserved and, more importantly, provide a very precise description of the angular momentum of the photon involved. Examples of matrix elements for electric dipole, electric quadrupole and magnetic dipole transition moments of the hydrogen atom are calculated and the results compared with those obtained by the usual plane-wave expansion and with more recent results obtained in connection with studies of 'twisted' beams.

Grinter, Roger [School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ (United Kingdom)], E-mail: r.grinter@uea.ac.uk

2008-05-14

233

The filamentary Multi-Polar Planetary Nebula NGC 5189  

CERN Document Server

We present a set of optical and infrared images combined with long-slit, medium and high dispersion spectra of the southern planetary nebula (PN) NGC 5189. The complex morphology of this PN is puzzling and has not been studied in detail so far. Our investigation reveals the presence of a new dense and cold infrared torus (alongside the optical one) which probably generated one of the two optically seen bipolar outflows and which might be responsible for the twisted appearance of the optical torus via an interaction process. The high-resolution MES-AAT spectra clearly show the presence of filamentary and knotty structures as well as three expanding bubbles. Our findings therefore suggest that NGC 5189 is a quadrupolar nebula with multiple sets of symmetrical condensations in which the interaction of outflows has determined the complex morphology.

Sabin, L; López, J A; García-Díaz, Ma T; Ramos-Larios, G

2012-01-01

234

Tomographic electroencephalography/magnetoencephalography. Dynamics of human neural network switching.  

UK PubMed Central (United Kingdom)

New developments in multimodal registration of electroencephalography (EEG), magnetic resonance imaging (MRI), and positron emission tomography (PET) are presented as a method to create a tomographic EEG. Three-dimensional information about the x,y,z location of the sources of event-related potentials is corroborated through the use of experimental design and coregistration with MRI and PET. Once the three-dimensional location of event-related potential dipole sources is identified and corroborated, pseudoinverse procedures are used to derive a new EEG voltage sequence from each of the dipoles. Each derived EEG dipole time series is analogous to recording EEG from a deeply implanted electrode and constitutes a four-dimensional tomographic EEG (i.e., three-dimensional space plus time). EEG coherence and phase analyses are then performed on the dipole-derived time series to study the temporal and spatial dynamics of neural network switching during voluntary finger movements. The purpose of this article is to demonstrate a new method to exploit the time domain dynamics of neural network switching in behaving human subjects.

Thatcher RW

1995-01-01

235

Development and Evaluation of Data Processing Techniques in Magnetoencephalography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

With MEG, the tiny magnetic fields produced by neuronal currents within the brain can be measured completely non-invasively. But the signals are very small (~100 fT) and often obscured by spontaneous brain activity and external noise. So, a recurrent issue in MEG data analysis is the identification ...

Schönherr, Margit

236

Investigating neurophysiological correlates of metacontrast masking with magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available Early components of visual evoked potentials (VEP) in EEG seem to be unaffected by target visibility in visual masking studies. Bridgeman's reanalysis of Jeffreys and Musselwhite's (1986) data suggests that a later visual component in the VEP, around 250 ms reflects the perceptual effect of masking. We challenge this view on the ground that temporal interactions between targets and masks unrelated to stimulus visibility could account for Bridgeman's observation of a U-shaped time course in VEP amplitudes for this later component. In an MEG experiment of metacontrast masking with variable stimulus onset asynchrony, we introduce a proper control, a pseudo mask. In contrast to an effective mask, the pseudomask should produce neither behavioral masking nor amplitude modulations of late VEPs. Our results show that effective masks produced a strong U-shaped perceptual effect of target visibility while performance remained virtually perfect when a pseudomask was used. The visual components around 250 ms after target onset did not show a distinction between mask and pseudomask conditions. The results indicate that these visual evoked potentials do not reveal neurophysiological correlates of stimulus visibility but rather reflect dynamic interactions between superimposed potentials elicited by stimuli in close temporal proximity. However, we observed a postperceptual component around 340 ms after target onset, located over temporal-parietal cortex, which shows a clear effect of visibility. Based on P300 ERP literature, this finding could indicate that working memory related processes contribute to metacontrast masking.

Sandra I. van Aalderen-Smeets; Robert Oostenveld; Jens Schwarzbach

2006-01-01

237

Investigating the electrophysiological basis of resting state networks using magnetoencephalography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In recent years the study of resting state brain networks (RSNs) has become an important area of neuroimaging. The majority of studies have used functional magnetic resonance imaging (fMRI) to measure temporal correlation between blood-oxygenation-level–dependent (BOLD) signals from different brain ...

Brookes, Matthew J.; Woolrich, Mark; Luckhoo, Henry; Price, Darren; Hale, Joanne R.; Stephenson, Mary C.; Barnes, Gareth R.

238

Investigating the electrophysiological basis of resting state networks using magnetoencephalography.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In recent years the study of resting state brain networks (RSNs) has become an important area of neuroimaging. The majority of studies have used functional magnetic resonance imaging (fMRI) to measure temporal correlation between blood-oxygenation-level-dependent (BOLD) signals from different brain ...

Brookes, MJ; Woolrich, M; Luckhoo, H; Price, D; Hale, JR; Stephenson, MC

239

Experimental validation of a hybrid computational model for selective stimulation using transverse intrafascicular multichannel electrodes.  

UK PubMed Central (United Kingdom)

Recently a hybrid model based on the finite element method and on a compartmental biophysical representation of peripheral nerve fibers and intraneural electrodes was developed founded on experimental physiological and histological data. The model appeared to be robust when dealing with uncertainties in parameter selection. However, an experimental validation of the findings provided by the model is required to fully characterize the potential of this approach. The recruitment properties of selective nerve stimulation using transverse intrafascicular multichannel electrodes (TIME) were investigated in this work in experiments with rats and were compared to model predictions. Animal experiments were performed using the same stimulation protocol as in the computer simulations in order to rigorously validate the model predictions and understand its limitations. Two different selectivity indexes were used, and new indexes for measuring electrode performance are proposed. The model predictions are in decent agreement with experimental results both in terms of recruitment curves and selectivity values. Results show that these models can be used for extensive studies targeting electrode shape design, active sites shape, and multipolar stimulation paradigms. From a neurophysiological point of view, the topographic organization of the rat sciatic nerve, on which the model was based, has been confirmed.

Raspopovic S; Capogrosso M; Badia J; Navarro X; Micera S

2012-05-01

240

Rapidly recomputable EEG forward models for realistic head shapes.  

Science.gov (United States)

With the increasing availability of surface extraction techniques for magnetic resonance and x-ray computed tomography images, realistic head models can be readily generated as forward models in the analysis of electroencephalography (EEG) and magnetoencephalography (MEG) data. Inverse analysis of this data, however, requires that the forward model be computationally efficient. We propose two methods for approximating the EEG forward model using realistic head shapes. The 'sensor-fitted sphere' approach fits a multilayer sphere individually to each sensor, and the 'three-dimensional interpolation' scheme interpolates using a grid on which a numerical boundary element method (BEM) solution has been precomputed. We have characterized the performance of each method in terms of magnitude and subspace error metrics, as well as computational and memory requirements. We have also made direct performance comparisons with traditional spherical models. The approximation provided by the interpolative scheme had an accuracy nearly identical to full BEM, even within 3 mm of the inner skull surface. Forward model computation during inverse procedures was approximately 30 times faster than for a traditional three-shell spherical model. Cast in this framework, high-fidelity numerical solutions currently viewed as computationally prohibitive for solving the inverse problem (e.g. linear Galerkin BEM) can be rapidly recomputed in a highly efficient manner. The sensor-fitting method has a similar one-time cost to the BEM method, and while it produces some improvement over a standard three-shell sphere, its performance does not approach that of the interpolation method. In both methods, there is a one-time cost associated with precomputing the forward solution over a set of grid points. PMID:11324964

Ermer, J J; Mosher, J C; Baillet, S; Leah, R M

2001-04-01

 
 
 
 
241

A neuronal model of predictive coding accounting for the mismatch negativity.  

Science.gov (United States)

The mismatch negativity (MMN) is thought to index the activation of specialized neural networks for active prediction and deviance detection. However, a detailed neuronal model of the neurobiological mechanisms underlying the MMN is still lacking, and its computational foundations remain debated. We propose here a detailed neuronal model of auditory cortex, based on predictive coding, that accounts for the critical features of MMN. The model is entirely composed of spiking excitatory and inhibitory neurons interconnected in a layered cortical architecture with distinct input, predictive, and prediction error units. A spike-timing dependent learning rule, relying upon NMDA receptor synaptic transmission, allows the network to adjust its internal predictions and use a memory of the recent past inputs to anticipate on future stimuli based on transition statistics. We demonstrate that this simple architecture can account for the major empirical properties of the MMN. These include a frequency-dependent response to rare deviants, a response to unexpected repeats in alternating sequences (ABABAA…), a lack of consideration of the global sequence context, a response to sound omission, and a sensitivity of the MMN to NMDA receptor antagonists. Novel predictions are presented, and a new magnetoencephalography experiment in healthy human subjects is presented that validates our key hypothesis: the MMN results from active cortical prediction rather than passive synaptic habituation. PMID:22423089

Wacongne, Catherine; Changeux, Jean-Pierre; Dehaene, Stanislas

2012-03-14

242

A neuronal model of predictive coding accounting for the mismatch negativity.  

UK PubMed Central (United Kingdom)

The mismatch negativity (MMN) is thought to index the activation of specialized neural networks for active prediction and deviance detection. However, a detailed neuronal model of the neurobiological mechanisms underlying the MMN is still lacking, and its computational foundations remain debated. We propose here a detailed neuronal model of auditory cortex, based on predictive coding, that accounts for the critical features of MMN. The model is entirely composed of spiking excitatory and inhibitory neurons interconnected in a layered cortical architecture with distinct input, predictive, and prediction error units. A spike-timing dependent learning rule, relying upon NMDA receptor synaptic transmission, allows the network to adjust its internal predictions and use a memory of the recent past inputs to anticipate on future stimuli based on transition statistics. We demonstrate that this simple architecture can account for the major empirical properties of the MMN. These include a frequency-dependent response to rare deviants, a response to unexpected repeats in alternating sequences (ABABAA…), a lack of consideration of the global sequence context, a response to sound omission, and a sensitivity of the MMN to NMDA receptor antagonists. Novel predictions are presented, and a new magnetoencephalography experiment in healthy human subjects is presented that validates our key hypothesis: the MMN results from active cortical prediction rather than passive synaptic habituation.

Wacongne C; Changeux JP; Dehaene S

2012-03-01

243

A simple model of the chaotic eccentricity of Mercury  

CERN Multimedia

Mercury's eccentricity is chaotic and can increase so much that collisions with Venus or the Sun become possible (Laskar, 1989, 1990, 1994, 2008, Batygin & Laughlin, 2008, Laskar & Gastineau, 2009). This chaotic behavior results from an intricate network of secular resonances, but in this paper, we show that a simple integrable model with only one degree of freedom is actually able to reproduce the large variations in Mercury's eccentricity, with the correct amplitude and timescale. We show that this behavior occurs in the vicinity of the separatrices of the resonance g1-g5 between the precession frequencies of Mercury and Jupiter. However, the main contribution does not come from the direct interaction between these two planets. It is due to the excitation of Venus' orbit at Jupiter's precession frequency g5. We use a multipolar model that is not expanded with respect to Mercury's eccentricity, but because of the proximity of Mercury and Venus, the Hamiltonian is expanded up to order 20 and more in t...

Boué, Gwenaël; Farago, François

2012-01-01

244

A Model for the Escape of Solar-Flare Accelerated Particles  

CERN Multimedia

Impulsive solar energetic particles (SEP) bursts are frequently observed in association with so-called eruptive flares consisting of a coronal mass ejection (CME) and a flare. These highly prompt SEPs are believed to be accelerated by the flare rather than by a CME shock, but in the standard flare model the accelerated particles should remain trapped in the corona or in the ejected plas- moid. In this case, however, the particles would reach the Earth only after a delay of many hours to a few days. We present a new model that can account for the prompt injection of energetic particles onto open interplanetary magnetic flux tubes. The basic idea underlying the model is that magnetic reconnection between the ejection and external open field allows for the release of the ener- getic particles. We demonstrate the model using 2.5D MHD simulations of a CME/flare event. The model system consists of a multipolar field with a coro- nal null point and with photospheric shear imposed at a polarity inversion line, as in ...

Masson, Sophie; DeVore, C Rick

2013-01-01

245

Theoretical Models and Relevant Calculations of Photon Production and Photonuclear Reaction Data  

International Nuclear Information System (INIS)

Photon production and photonuclear reaction data, with emphasis on theoretical model aspects aimed at reliable evaluations, represent a challenge in many technological applications, from radiation shielding for different nuclear systems, including accelerators, to devices relevant to nuclear energy applications, particularly the ones concerning the Accelerator Driven Systems for nuclear waste transmutation. In this field of applied science, theoretical calculations complementing the existing experimental data play an essential role in performing valuable nuclear data evaluations, particularly when the measured quantities are discrepant, scarce, or even lacking. In this framework, new improved results of theoretical and evaluation activities carried out at ENEA, Division for Advanced Physics Technologies, are presented especially concerning photonuclear reaction cross sections. Relevant aspects of nuclear structure models are discussed together with a critical analysis of the related computing codes considered in the present ENEA evaluations, aimed at producing specific contributions to the above-mentioned nuclear programs and applications and at cooperating in the framework of the international initiatives and efforts on the inter-comparison of the evaluated data and of the relevant models and codes. An innovative method has been developed and utilized for microscopic and statistical models of nuclear structure, especially referring to algebraic models aimed at complementing the reaction models for the treatment of pre-equilibrium and compound-nucleus processes.The relevant microscopic algebraic model calculations are discussed, as they reasonably approximate the observed structure of photonuclear cross sections due to multi-polarity effects. Accordingly, theoretical calculation methods are presented for Ti and Mo isotopes, as materials relevant to nuclear applications, and significant results are reviewed for Ti natural isotopes and the element in comparison with the experimental data when available from the existing literature.

2005-05-24

246

Modeling the variability of EEG/MEG data through statistical machine learning  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Brain neural activity generates electrical discharges, which manifest as electrical and magnetic potentials around the scalp. Those potentials can be registered with magnetoencephalography (MEG) and electroencephalography (EEG) devices. Data acquired by M/EEG is extremely difficult to work with due ...

Zaremba, Wojciech

247

Sensitivity of MEG and EEG to Source Orientation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An important difference between magnetoencephalography (MEG) and electroencephalography (EEG) is that MEG is insensitive to radially oriented sources. We quantified computationally the dependency of MEG and EEG on the source orientation using a forward model with realistic tissue boundaries. Similar...

Hämäläinen, Matti S.; Ahlfors, Seppo P.; Han, Jooman; Belliveau, John William

248

Modeling the Impact of Alcohol on Cortical Development in a Dish: Strategies From Mapping Neural Stem Cell Fate  

Science.gov (United States)

Summary During the second trimester period, neuroepithelial stem cells give birth to millions of new neuroblasts, which migrate away from their germinal zones to populate the developing brain and terminally differentiate into neurons. During this period, large numbers of cells are also eliminated by programmed cell death. Therefore, the second trimester constitutes an important critical period for neuronal proliferation, migration, differentiation and apoptosis. Substantial evidence indicates that teratogens like ethanol can interfere with neuronal maturation. However, there is a paucity of good model systems to study early, second trimester events. In vivo models are inherently interpretatively complex because cell proliferation, migration, differentiation, and death mechanisms occur concurrently in regions like the cerebral cortex. This temporal overlap of multiple developmental critical periods makes it difficult to evaluate the relative vulnerability of any individual critical period. Our laboratory has elected to utilize fetal rodent cerebral cortical-derived neurosphere cultures as an experimental model of the second-trimester ventricular neuroepithelium. This model has enabled us to use flow cytometric approaches to identify neuroepithelial stem cell and progenitor sub-populations and to show that ethanol accelerates the maturation of neural stem cells. We have also developed a simplified mitogen-withdrawal/matrix-adhesion paradigm to model the exit of neuroepithelial cells from the ventricular zone towards the subventricular zone and cortical plate, and their maturation into multipolar neurons. We can treat neurosphere cultures with ethanol to mimic exposure during the period of neuroepithelial proliferation and by using the step-wise maturation model, ask questions about the impact of prior ethanol exposure on the subsequent maturation of neurons as they migrate and undergo terminal differentiation. The combination of neurosphere culture and stepwise maturation models will enable us to dissect out the contributions of specific developmental critical periods to the overall teratology of a drug of abuse like ethanol.

Miranda, Rajesh C.; Santillano, Daniel R.; Camarillo, Cynthia; Dohrman, Douglas

2010-01-01

249

Are collisions with neutral hydrogen important for modelling the Second Solar Spectrum of Ti I and Ca II ?  

CERN Document Server

The physical interpretation of scattering line polarization offers a novel diagnostic window for exploring the thermal and magnetic structure of the quiet regions of the solar atmosphere. Here we evaluate the impact of isotropic collisions with neutral hydrogen atoms on the scattering polarization signals of the 13 lines of multiplet 42 of Ti I and on those of the K line and of the IR triplet of Ca II, with emphasis on the collisional transfer rates between nearby J-levels. To this end, we calculate the linear polarization produced by scattering processes considering realistic multilevel models and solving the statistical equilibrium equations for the multipolar components of the atomic density matrix. We confirm that the lower levels of the 13 lines of multiplet 42 of Ti I are completely depolarized by elastic collisions. We find that upper-level collisional depolarization turns out to have an unnoticeable impact on the emergent linear polarization amplitudes, except for the ${\\lambda 4536$ line for which it...

Derouich, M; Sainz, R Manso

2007-01-01

250

[Catheter ablation of atrial fibrillation. Pulmonary vein isolation by using a new multipolar ablation catheter].  

UK PubMed Central (United Kingdom)

Catheter ablation of atrial fibrillation (AF) is an established therapeutical option, particularly in treatment of paroxysmal atrial fibrillation. This paper presents the results of using the PVAC multi-electrode ablation catheter (PVAC®, Medtronic Ablation Frontiers, Carlsbad, CA, USA). In 253 patients with paroxysmal or persistant AF, 1051 pulmonary veins were isolated, including ablation of 34 left common ostia and 1 right common ostium. Except one vein, all pulmonary veins in all patients were successfully isolated. In 23 patients with documented typical atrial flutter, the right atrial isthmus was additionally ablated within the same procedure. Follow-up (FU) visits were performed after 1, 3, 6 and 12 months with 12-lead-ECG, 24h-Holter-ECG and 4-days-Holter ECG. Mean FU was 11?±?7 months with 1.1 interventions per patient (24 redo cases). During FU, 122 of 181 patients with paroxysmal AF (69%) and 23 of 40 patients with persistant AF (58%) were in stable sinus rhythm (SR) after ablation. 159 (62.8%) patients wer under antiarrhythmic drugs after ablation, 214 (84.5%) patients with additional ?-blockers. Total procedure time was 71?±?19 min, and total fluoroscopy time was 16?±?6 min. In 3 cases (1.2%) procedure-related complications occured. Pulmonary vein isolation by using the PVAC-ablation catheter is a safe and effective method in treatment of paroxysmal and persistant AF.

Spitzer SG; Karolyi L

2011-05-01

251

Treatment of atrial fibrillation with radiofrequency ablation and simultaneous multipolar mapping of the pulmonary veins  

Directory of Open Access Journals (Sweden)

Full Text Available OBJECTIVE: To demonstrate the feasibility and safety of simultaneous catheterization and mapping of the 4 pulmonary veins for ablation of atrial fibrillation. METHODS: Ten patients, 8 with paroxysmal atrial fibrillation and 2 with persistent atrial fibrillation, refractory to at least 2 antiarrhythmic drugs and without structural cardiopathy, were consecutively studied. Through the transseptal insertion of 2 long sheaths, 4 pulmonary veins were simultaneously catheterized with octapolar microcatheters. After identification of arrhythmogenic foci radiofrequency was applied under angiographic or ultrasonographic control. RESULTS: During 17 procedures, 40 pulmonary veins were mapped, 16 of which had local ectopic activity, related or not with the triggering of atrial fibrillation paroxysms. At the end of each procedure, suppression of arrhythmias was obtained in 8 patients, and elimination of pulmonary vein potentials was accomplished in 4. During the clinical follow-up of 9.6±3 months, 7 patients remained in sinus rhythm, 5 of whom were using antiarrhythmic drugs that had previously been ineffective. None of the patients had pulmonary hypertension or evidence of stenosis in the pulmonary veins. CONCLUSION: Selective and simultaneous catheterization of the 4 pulmonary veins with microcatheters for simultaneous recording of their electrical activity is a feasible and safe procedure that may help ablation of atrial fibrillation.

Rocha Neto Almino C.; Farias Roberto Lima; de Paola Angelo A. V.

2001-01-01

252

Multipolar permanent-magnet synchronous generators intended for wind power plants  

Science.gov (United States)

The analytical method of calculating two-dimensional magnetic fields in the active section of permanent-magnet synchronous electrical rotating machines, as applied to their use in the wind energy industry, has been developed. The analytical relationships for calculating distribution of two-dimensional magnetic fields and determining output parameters with due regard for geometry of the active section, the number of pairs of poles, and magnetic characteristics of materials have been obtained. The criteria dependences needed for calculating the electromotive force and main inductive reactance of permanent-magnet synchronous electric machines, with consideration for the geometry of a machine and electrophysical properties of materials being used, have been derived. The procedure of evaluating parameters of permanent-magnet synchronous generators for large-size wind power plants is presented.

Kovalev, L. K.; Kovalev, K. L.; Tulinova, Ye. Ye.; Ivanov, N. S.

2012-12-01

253

Monitoring Subarctic Permafrost Changes Using Optical and Multi-Polarization SAR Imagery  

Science.gov (United States)

An integrated remote sensing methodology is being applied to map and monitor subarctic permafrost changes in Kobuk Valley, Alaska. Permafrost degradation is a slow process that is easier to quantify when monitored over a long period of time. Recent high resolution commercial satellite data and historical aerial photography are combined to map frozen ground and associated changes in soil moisture, and to detect vertical and lateral ground movements. A newly developed multispectral data displacement analysis (MDDA) methodology uses high-resolution imagery to map lateral ground displacements. MDDA is built upon the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique, which enable fine-scale measurements (i.e., ~ 1/15 of the image pixel size) of lateral movement, being especially useful in application to wave-action-enhanced permafrost degradation along thaw lake margins. Our previous study utilized MDDA to measure slow, subarctic dune migration and illustrates the value of applying this technique to reliably detect and monitor subtle changes in the permafrost landscape over wide areas. Trends in ground displacement over several decades can be observed by applying MDDA to historical aerial photography of Kobuk Valley (1951-1952 and 1978) and recent high-resolution optical satellite data. Recent soil moisture changes are mapped by means of SAR polarimetry using Japan Aerospace Exploration Agency’s (JAXA) Advanced Land Observation Satellite (ALOS) PALSAR imagery. Furthermore, radar interferometry based on ALOS PALSAR and high-resolution digital elevation maps (DEMs) constructed from ALOS PRISM imagery, are used to map vertical elevation changes associated with soil expansion/contraction. Preliminary results have detected horizontal and vertical changes over time, contributing to our understanding of permafrost degradation in subarctic Alaska. The advantage of this approach is that it extends the analysis to pre-satellite time frames, allowing a better understanding of the dynamics of permafrost processes as well as a detailed mapping of ground conditions at a greater or lesser risk of catastrophic ground movements.

Necsoiu, M.; Hooper, D. M.; Longépé, N.; Walter, G. R.

2010-12-01

254

Multipolarity of the 228.5-keV transition in {sup 80}Y  

Energy Technology Data Exchange (ETDEWEB)

We have unambiguously characterized the deexcitation of the 228.5-keV T{sub 1/2}=4.7-s isomer in {sup 80}Y as an M3 transition. This result determines, in conjunction with other experimental data, the spin and parity of the 228.5-keV isomer and the {sup 80}Y ground state as 1{sup -} and 4{sup -}, respectively. (c) 2000 The American Physical Society.

Piechaczek, A. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States); Zganjar, E. F. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States); Batchelder, J. C. [UNIRIB, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831 (United States); Bingham, C. R. [Department of Physics and Astronomy, University of Tennessee, Tennessee 37996-1200 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6371 (United States); Ginter, T. N. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Gross, C. J. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6371 (United States); Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831-0117 (United States); Grzywacz, R. [Department of Physics and Astronomy, University of Tennessee, Tennessee 37996-1200 (United States); Macdonald, B. D. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States); Paul, S. D. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6371 (United States); UNIRIB, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831 (United States); Rykaczewski, K. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6371 (United States); Warsaw University, PL-00681 Warsaw, (Poland)] (and others)

2000-04-01

255

Optimization of the CLIC Final Focus Dispersion without Using Extra Multipolar Components  

CERN Multimedia

We optimize the nominal final focus system for CLIC to maximize the luminosity at the IP. We investigate the effect of quadrupole optimization after sextupole optimization for high and low dispersion reductions. Finally we try to improve our optimization further via a small corrective optimization and check that the optimal dispersion reduction also holds for the entire Beam Delivery System (BDS).

Jarnhus, P R; CERN. Geneva. AB Department

2006-01-01

256

Ce site substitution effect on the multipolar ordering in CeB{sub 6}  

Energy Technology Data Exchange (ETDEWEB)

We have studied the Ce-cite substitution effect by R(=Pr, Nd) ion on the multipole interactions in CeB{sub 6}. We found that T{sub Q} of Ce{sub 0.9}Nd{sub 0.1}B{sub 6} in magnetic fields is higher than that of Ce{sub 0.9}Pr{sub 0.1}B{sub 6} and the magnetization is larger in the former than in the latter. The larger suppression of T{sub Q} in Ce{sub x}Pr{sub 1-x}B{sub 6} suggests the larger reduction of the T{sub xyz} antiferro-octupolar (AFO) interaction in this system considering that T{sub Q} at H=0 is nearly the same in both systems. The smaller magnetization in Ce{sub x}Pr{sub 1-x}B{sub 6} than in Ce{sub x}Nd{sub 1-x}B{sub 6} originates from the larger suppression of T{sub xyz} AFO interaction and also the larger Ce-Pr AF exchange interaction than in Ce{sub x}Nd{sub 1-x}B{sub 6}.

Sera, M. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan)]. E-mail: sera@sci.hiroshima-u.ac.jp; Kawaguchi, M. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Kishimoto, S. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Kondo, A. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Iwakubo, H. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Tou, H. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Umeo, K. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan); Iga, F. [Department of ADSM, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8530 (Japan)

2007-03-15

257

Ce site substitution effect on the multipolar ordering in CeB6  

International Nuclear Information System (INIS)

We have studied the Ce-cite substitution effect by R(=Pr, Nd) ion on the multipole interactions in CeB6. We found that TQ of Ce0.9Nd0.1B6 in magnetic fields is higher than that of Ce0.9Pr0.1B6 and the magnetization is larger in the former than in the latter. The larger suppression of TQ in CexPr1-xB6 suggests the larger reduction of the Txyz antiferro-octupolar (AFO) interaction in this system considering that TQ at H=0 is nearly the same in both systems. The smaller magnetization in CexPr1-xB6 than in CexNd1-xB6 originates from the larger suppression of Txyz AFO interaction and also the larger Ce-Pr AF exchange interaction than in CexNd1-xB6.

2007-01-01

258

Visual stress–induced migraine aura compared to spontaneous aura studied by magnetoencephalography.  

UK PubMed Central (United Kingdom)

DC MEG shifts, similarand complex in waveform, were observed in visually induced migraine with aura patients similar to spontaneous aura but not controls. Multiple cortical areas were activated in visually induced and spontaneous aura patients. In normal subjects activation was only observed in the primary visual cortex. Results support a spreading depression–like neuroelectric event as the basis of migraine aura that can arise spontaneously or be visually triggered in widespread regions of hyperexcitable occipital cortex.

Welch KMA; Bowyer SM; Aurora SK; Moran JE; Tepley N

2001-09-01

259

Coherence between magnetoencephalography and hand-action-related acceleration, force, pressure, and electromyogram.  

UK PubMed Central (United Kingdom)

Hand velocity and acceleration are coherent with magnetoencephalographic (MEG) signals recorded from the contralateral primary sensorimotor (SM1) cortex. To learn more of this interaction, we compared the coupling of MEG signals with four hand-action-related peripheral signals: acceleration, pressure, force, and electromyogram (EMG). Fifteen subjects performed self-paced repetitive hand-action tasks for 3.5min at a rate of about 3Hz. Either acceleration, pressure or force signal was acquired with MEG and EMG signals during (1) flexions-extensions of right-hand fingers, with thumb touching the other fingers (acceleration; free), (2) dynamic index-thumb pinches against an elastic rubber ball attached to a pressure sensor (pressure and acceleration; squeeze), and (3) brief fixed-finger-position index-thumb pinches against a rigid load cell (force; fixed-pinch). Significant coherence occurred between MEG and all the four peripheral measures at the fundamental frequency of the hand action (F0) and its first harmonic (F1). In all tasks, the cortical sources contributing to the cross-correlograms were located at the contralateral hand SM1 cortex, with average inter-source distance (mean±SEM) of 9.5±0.3mm. The coherence was stronger with respect to pressure (0.40±0.03 in squeeze) and force (0.38±0.04 in fixed-pinch) than acceleration (0.24±0.03 in free) and EMG (0.25±0.02 in free, and 0.29±0.04 in fixed-pinch). The results imply that the SM1 cortex is strongly coherent at F0 and F1 with hand-action-related pressure and force, in addition to the previously demonstrated EMG, velocity, and acceleration. All these measures, especially force and pressure, are potential tools for functional mapping of the SM1 cortex.

Piitulainen H; Bourguignon M; De Tiège X; Hari R; Jousmäki V

2013-05-01

260

Synchronized brain network associated with essential tremor as revealed by magnetoencephalography.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Despite the fact that essential tremor (ET) is the most prevalent movement disorder, the underlying pathological mechanisms are not fully understood. There is accumulating evidence that this specific type of tremor is mainly of central origin, in particular involving inferior olive, cerebellum, thal...

Schnitzler, A; Münks, C; Butz, M; Timmermann, L; Gross, J

 
 
 
 
261

The utility of magnetoencephalography in the presurgical evaluation of refractory insular epilepsy.  

UK PubMed Central (United Kingdom)

SIGNIFICANCE: MEG is useful in identifying patients who are likely to benefit from epilepsy surgery targeting the insula, particularly if a tight dipole cluster is identified even if other noninvasive modalities fail to produce localizing results.

Mohamed IS; Gibbs SA; Robert M; Bouthillier A; Leroux JM; Khoa Nguyen D

2013-09-01

262

Extension of Quantifiable Modification of sLORETA for Induced Oscillatory Changes in Magnetoencephalography.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantifiable modification of standardized low-resolution brain electromagnetic tomography (sLORETA-qm), which is one of the non-adaptive beamformer spatial filtering techniques, has been applied to source localization and quantification of evoked field or oscillatory changes in magnetoencephalograph...

Uda, T; Tsuyuguchi, N; Okumura, E; Shigihara, Y; Nagata, T; Terakawa, Y; Sakamoto, S; Ohata, K

263

Face area representation of primary somatosensory cortex in humans identified by whole-head magnetoencephalography.  

Science.gov (United States)

The feasibility of precise mapping was investigated noninvasively on the face component in predominantly unilateral primary somatosensory cortices (SI) in six healthy subjects. We recorded somatosensory evoked magnetic fields (SEFs) from the SI and secondary somatosensory cortices (SII) following the electrical stimulation of six skin sites: the infraorbital foramen, the angle of mouth, the upper lip, the lower lip, the mental foramen, and the mandibular angle. The median nerve at the wrist was stimulated as a standard of the map. The location of the equivalent current dipoles (ECDs) estimated from the distribution of magnetic fields was identified on MR images of the brain on each subject. The ECDs of the early components of SEF with peaks of 20-30 ms aligned along the SI in the hemisphere contralateral to the stimulation site. Late components with peaks of 80-150 ms were recorded from the bilateral hemispheres, and their ECDs were identified in the SII of the bilateral hemispheres. There was a distinct separation between the ECD locations representing discrete sites on the face and thumb in the SI of the contralateral hemisphere. Five sites of the face area in SI at the contralateral hemisphere were compatible with the conventional arrangement of homunculus in one subject. However, the remaining subjects had variations in the arrangement. The face area reorganization in the SI is possible to be related to the use-dependent cortical plasticity of the individual or to the perceptual experience by vision and proprioception. PMID:15182423

Suzuki, Takashi; Shibukawa, Yoshiyuki; Kumai, Toshifumi; Shintani, Masuro

2004-04-01

264

Functional reorganization of the human primary somatosensory cortex after acute pain demonstrated by magnetoencephalography.  

Science.gov (United States)

The somatosensory system is capable of functional reorganization following peripheral denervation or training. Studies on human amputees with phantom limb pain provided evidence that these reorganizational changes are modulated through nociceptive input. In the present study we used magnetoencephalographic recordings of six healthy volunteers to assess whether acute pain by itself causes a reorganization of the primary somatosensory cortex. After the induction of an intense experimental pain at the thenar of the left hand by intradermal injection of capsaicin, the extent of the cortical hand representation and the distance between the hand representation and the localization of the lip decreased. A likely mechanism for this acute reorganization is that pain induced hyperresponsiveness of the left thenar to tactile input from neighboring body sites. PMID:11165440

Sörös, P; Knecht, S; Bantel, C; Imai, T; Wüsten, R; Pantev, C; Lütkenhöner, B; Bürkle, H; Henningsen, H

2001-02-01

265

Use of superconducting plates and shells to deflect magnetic noise fields: Application to MEG (magnetoencephalography)  

Energy Technology Data Exchange (ETDEWEB)

Insertion of a superconducting plate or shell in a magnetic field causes a surface current distribution which opposes the applied field. Resultant fields near plate edges are higher while those near centers are much lower than applied fields. We make use of these principles in MEG by placing suitably oriented gradiometers at points where noise fields are smallest. Signals from nearby brain wave sources are enhanced because the net signal is a combination of that from the sources and that from its image. The principles of noise deflection and source imaging are applied to new concepts of gradiometry. 4 refs., 2 figs.

Overton, W.C. Jr.; van Hulsteyn, D.B.; Flynn, E.R. (Los Alamos National Lab., NM (USA))

1989-01-01

266

Modeling Model Slicers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Among model comprehension tools, model slicers are tools that extract a subset from a model, for a specific purpose. Model slicers are tools that let modelers rapidly gather relevant knowledge from large models. However, existing slicers are dedicated to one modeling language. This is an issue when ...

Blouin, Arnaud; Combemale, Benoit; Baudry, Benoit; Beaudoux, Olivier

267

Use of the isolated problem approach for multi-compartment BEM models of electro-magnetic source imaging  

Energy Technology Data Exchange (ETDEWEB)

The isolated problem approach (IPA) is a method used in the boundary element method (BEM) to overcome numerical inaccuracies caused by the high-conductivity difference in the skull and the brain tissues in the head. Haemaelaeinen and Sarvas (1989 IEEE Trans. Biomed. Eng. 36 165-71) described how the source terms can be updated to overcome these inaccuracies for a three-layer head model. Meijs et al (1989 IEEE Trans. Biomed. Eng. 36 1038-49) derived the integral equations for the general case where there are an arbitrary number of layers inside the skull. However, the IPA is used in the literature only for three-layer head models. Studies that use complex boundary element head models that investigate the inhomogeneities in the brain or model the cerebrospinal fluid (CSF) do not make use of the IPA. In this study, the generalized formulation of the IPA for multi-layer models is presented in terms of integral equations. The discretized version of these equations are presented in two different forms. In a previous study (Akalin-Acar and Gencer 2004 Phys. Med. Biol. 49 5011-28), we derived formulations to calculate the electroencephalography and magnetoencephalography transfer matrices assuming a single layer in the skull. In this study, the transfer matrix formulations are updated to incorporate the generalized IPA. The effects of the IPA are investigated on the accuracy of spherical and realistic models when the CSF layer and a tumour tissue are included in the model. It is observed that, in the spherical model, for a radial dipole 1 mm close to the brain surface, the relative difference measure (RDM*) drops from 1.88 to 0.03 when IPA is used. For the realistic model, the inclusion of the CSF layer does not change the field pattern significantly. However, the inclusion of an inhomogeneity changes the field pattern by 25% for a dipole oriented towards the inhomogeneity. The effect of the IPA is also investigated when there is an inhomogeneity in the brain. In addition to a considerable change in the scale of the potentials, the field pattern also changes by 15%. The computation times are presented for the multi-layer realistic head model.

Gencer, Nevzat G; Akalin-Acar, Zeynep [Department of Electrical and Electronics Engineering, Brain Research Laboratory, Middle East Technical University, 06531 Ankara (Turkey)

2005-07-07

268

How neurons migrate: a dynamic in-silico model of neuronal migration in the developing cortex  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Neuronal migration, the process by which neurons migrate from their place of origin to their final position in the brain, is a central process for normal brain development and function. Advances in experimental techniques have revealed much about many of the molecular components involved in this process. Notwithstanding these advances, how the molecular machinery works together to govern the migration process has yet to be fully understood. Here we present a computational model of neuronal migration, in which four key molecular entities, Lis1, DCX, Reelin and GABA, form a molecular program that mediates the migration process. Results The model simulated the dynamic migration process, consistent with in-vivo observations of morphological, cellular and population-level phenomena. Specifically, the model reproduced migration phases, cellular dynamics and population distributions that concur with experimental observations in normal neuronal development. We tested the model under reduced activity of Lis1 and DCX and found an aberrant development similar to observations in Lis1 and DCX silencing expression experiments. Analysis of the model gave rise to unforeseen insights that could guide future experimental study. Specifically: (1) the model revealed the possibility that under conditions of Lis1 reduced expression, neurons experience an oscillatory neuron-glial association prior to the multipolar stage; and (2) we hypothesized that observed morphology variations in rats and mice may be explained by a single difference in the way that Lis1 and DCX stimulate bipolar motility. From this we make the following predictions: (1) under reduced Lis1 and enhanced DCX expression, we predict a reduced bipolar migration in rats, and (2) under enhanced DCX expression in mice we predict a normal or a higher bipolar migration. Conclusions We present here a system-wide computational model of neuronal migration that integrates theory and data within a precise, testable framework. Our model accounts for a range of observable behaviors and affords a computational framework to study aspects of neuronal migration as a complex process that is driven by a relatively simple molecular program. Analysis of the model generated new hypotheses and yet unobserved phenomena that may guide future experimental studies. This paper thus reports a first step toward a comprehensive in-silico model of neuronal migration.

Setty Yaki; Chen Chih-Chun; Secrier Maria; Skoblov Nikita; Kalamatianos Dimitrios; Emmott Stephen

2011-01-01

269

Inverse modeling in magnetic source imaging: Comparison of MUSIC, SAM(g2), and sLORETA to interictal intracranial EEG.  

UK PubMed Central (United Kingdom)

Magnetoencephalography (MEG) is used in the presurgical work-up of patients with focal epilepsy. In particular, localization of MEG interictal spikes may guide or replace invasive electroencephalography monitoring that is required in difficult cases. From literature, it is not clear which MEG source localization method performs best in this clinical setting. Therefore, we applied three source localization methods to the same data from a large patient group for which a gold standard, interictal spikes as identified in electrocorticography (ECoG), was available. The methods used were multiple signal classification (MUSIC), Synthetic Aperture Magnetometry kurtosis [SAM(g2)], and standardized low-resolution electromagnetic tomography. MEG and ECoG data from 38 patients with refractory focal epilepsy were obtained. Results of the three source localization methods applied to the interictal MEG data were assigned to predefined anatomical regions. Interictal spikes as identified in ECoG were also assigned to these regions. Identified regions by each MEG method were compared to ECoG. Sensitivity and positive predictive value (PPV) of each MEG method were calculated. All three MEG methods showed a similar overall correlate with ECoG spikes, but the methods differ in which regions they detect. The choice of the inverse model thus has an unexpected influence on the results of magnetic source imaging. Combining inverse methods and seeking consensus can be used to improve specificity at the cost of some sensitivity. Combining MUSIC with SAM(g2) gives the best results (sensitivity = 38% and PPV = 82%). Hum Brain Mapp 34:2032-2044, 2013. © 2012 Wiley Periodicals, Inc.

de Gooijer-van de Groep KL; Leijten FS; Ferrier CH; Huiskamp GJ

2013-09-01

270

Inverse modeling in magnetic source imaging: Comparison of MUSIC, SAM(g2), and sLORETA to interictal intracranial EEG.  

Science.gov (United States)

Magnetoencephalography (MEG) is used in the presurgical work-up of patients with focal epilepsy. In particular, localization of MEG interictal spikes may guide or replace invasive electroencephalography monitoring that is required in difficult cases. From literature, it is not clear which MEG source localization method performs best in this clinical setting. Therefore, we applied three source localization methods to the same data from a large patient group for which a gold standard, interictal spikes as identified in electrocorticography (ECoG), was available. The methods used were multiple signal classification (MUSIC), Synthetic Aperture Magnetometry kurtosis [SAM(g2)], and standardized low-resolution electromagnetic tomography. MEG and ECoG data from 38 patients with refractory focal epilepsy were obtained. Results of the three source localization methods applied to the interictal MEG data were assigned to predefined anatomical regions. Interictal spikes as identified in ECoG were also assigned to these regions. Identified regions by each MEG method were compared to ECoG. Sensitivity and positive predictive value (PPV) of each MEG method were calculated. All three MEG methods showed a similar overall correlate with ECoG spikes, but the methods differ in which regions they detect. The choice of the inverse model thus has an unexpected influence on the results of magnetic source imaging. Combining inverse methods and seeking consensus can be used to improve specificity at the cost of some sensitivity. Combining MUSIC with SAM(g2) gives the best results (sensitivity = 38% and PPV = 82%). Hum Brain Mapp 34:2032-2044, 2013. © 2012 Wiley Periodicals, Inc. PMID:22431346

de Gooijer-van de Groep, Karin L; Leijten, Frans S S; Ferrier, Cyrille H; Huiskamp, Geertjan J M

2012-03-19

271

Effect of nuclear deformation on the alpha-decay half-life of even-even alpha emitters  

Energy Technology Data Exchange (ETDEWEB)

Alpha-decay half-life of even-even emitters has been calculated in terms of a tunnelling through a quantum mechanical potential barrier. A multipolar expansion of Coulomb potential has been developed taking into account the nuclear quadrupole, hexadecapole, and hexacontatetrapole deformations. We show that using a free-parameter model the calculated half-lives do not vary significantly with higher order multipolarities of the daughter nucleus deformation. (author)

Dimarco, A.; Duarte, S.B.; Tavares, O.A.P. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Goncalves, M. [Instituto de Radioprotecao e Dosimetria (IRD), Rio de Janeiro, RJ (Brazil); Garcia, F. [Universidade Estadual de Santa Cruz, Ilheus, BA (Brazil). Dept. de Ciencias Exatas e Tecnologicas; Rodriguez, O.; Guzman, F. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica

2000-03-01

272

Effect of nuclear deformation on the alpha-decay half-life of even-even alpha emitters  

International Nuclear Information System (INIS)

Alpha-decay half-life of even-even emitters has been calculated in terms of a tunnelling through a quantum mechanical potential barrier. A multipolar expansion of Coulomb potential has been developed taking into account the nuclear quadrupole, hexadecapole, and hexacontatetrapole deformations. We show that using a free-parameter model the calculated half-lives do not vary significantly with higher order multipolarities of the daughter nucleus deformation. (author)

2000-01-01

273

Increased p75 neurotrophin receptor expression in the canine distemper virus model of multiple sclerosis identifies aldynoglial Schwann cells that emerge in response to axonal damage.  

Science.gov (United States)

Gliogenesis under pathophysiological conditions is of particular clinical relevance since it may provide regeneration-promoting cells recruitable for therapeutic purposes. There is accumulating evidence that aldynoglial cells with Schwann cell-like growth-promoting properties emerge in the lesioned CNS. However, the characterization of these cells and the signals triggering their in situ generation have remained enigmatic. In the present study, we used the p75 neurotrophin receptor (p75(NTR) ) as a marker for Schwann cells to study gliogenesis in the well-defined canine distemper virus (CDV)-induced demyelination model. White matter lesions of CDV-infected dogs contained bi- to multipolar, p75(NTR) -expressing cells that neither expressed MBP, GFAP, BS-1, or P0 identifying oligodendroglia, astrocytes, microglia, and myelinating Schwann cells nor CDV antigen. Interestingly, p75(NTR) -expression became apparent prior to the onset of demyelination in parallel to the expression of ?-amyloid precursor protein (?-APP), nonphosphorylated neurofilament (n-NF), BS-1, and CD3, and peaked in subacute lesions with inflammation. To study the role of infiltrating immune cells during differentiation of Schwann cell-like glia, organotypic slice cultures from the normal olfactory bulb were established. Despite the absence of infiltrating lymphocytes and macrophages, a massive appearance of p75(NTR) -positive Schwann-like cells and BS-1-positive microglia was noticed at 10 days in vitro. It is concluded that axonal damage as an early signal triggers the differentiation of tissue-resident precursor cells into p75(NTR) -expressing aldynoglial Schwann cells that retain an immature pre-myelin state. Further studies have to address the role of microglia during this process and the regenerative potential of aldynoglial cells in CDV infection and other demyelinating diseases. PMID:22072443

Imbschweiler, Ilka; Seehusen, Frauke; Peck, Claas-Tido; Omar, Mohamed; Baumgärtner, Wolfgang; Wewetzer, Konstantin

2011-11-09

274

Increased p75 neurotrophin receptor expression in the canine distemper virus model of multiple sclerosis identifies aldynoglial Schwann cells that emerge in response to axonal damage.  

UK PubMed Central (United Kingdom)

Gliogenesis under pathophysiological conditions is of particular clinical relevance since it may provide regeneration-promoting cells recruitable for therapeutic purposes. There is accumulating evidence that aldynoglial cells with Schwann cell-like growth-promoting properties emerge in the lesioned CNS. However, the characterization of these cells and the signals triggering their in situ generation have remained enigmatic. In the present study, we used the p75 neurotrophin receptor (p75(NTR) ) as a marker for Schwann cells to study gliogenesis in the well-defined canine distemper virus (CDV)-induced demyelination model. White matter lesions of CDV-infected dogs contained bi- to multipolar, p75(NTR) -expressing cells that neither expressed MBP, GFAP, BS-1, or P0 identifying oligodendroglia, astrocytes, microglia, and myelinating Schwann cells nor CDV antigen. Interestingly, p75(NTR) -expression became apparent prior to the onset of demyelination in parallel to the expression of ?-amyloid precursor protein (?-APP), nonphosphorylated neurofilament (n-NF), BS-1, and CD3, and peaked in subacute lesions with inflammation. To study the role of infiltrating immune cells during differentiation of Schwann cell-like glia, organotypic slice cultures from the normal olfactory bulb were established. Despite the absence of infiltrating lymphocytes and macrophages, a massive appearance of p75(NTR) -positive Schwann-like cells and BS-1-positive microglia was noticed at 10 days in vitro. It is concluded that axonal damage as an early signal triggers the differentiation of tissue-resident precursor cells into p75(NTR) -expressing aldynoglial Schwann cells that retain an immature pre-myelin state. Further studies have to address the role of microglia during this process and the regenerative potential of aldynoglial cells in CDV infection and other demyelinating diseases.

Imbschweiler I; Seehusen F; Peck CT; Omar M; Baumgärtner W; Wewetzer K

2012-03-01

275

Model’s comparison  

DEFF Research Database (Denmark)

Three popular disease spread simulation models were used to simulate the spread of foot-and-mouth disease (FMD) in Denmark. The models’ predictions in term of disease spread, consequence, and the ranking of the applied control strategies were compared. The original Davis Animal Disease Spread (DADS version 0.05) was adapted to DTU-DADS, and this model as well as InterSpread Plus (ISP version 2.001.11) and the North American Animal Disease Spread Model (NAADSM version 3.0.81) were all used to simulate hypothetical spread of FMD in Denmark. Data on Danish herds were used including herd type, movements, and location in the period 1st October 2006 to 30th September 2007. The three models to the highest possible extend set up to simulate the same epidemics in 3 different control scenarios: 1) A basic scenario representing EU and Danish control strategies, 2) pre-emptive depopulation of susceptible herds in a 500 meters radius around the detected herds, and 3) suppressive vaccination of susceptible herds in a 1,000 meters radius around the detected herds. Depopulation and vaccination started either 14 days following the detection of the first infected herd or following detection of 50 infected herds. Five thousand index herds were selected randomly in which there were 1,000 cattle herds located in high density cattle area and 1,000 in low density cattle area, 1,000 swine herds located in high density swine area and 1,000 in low density swine area, and 1,000 sheep herds. Generally, NAADSM predicted the largest, longest duration and costliest epidemics. DTU-DADS predicted larger, longer duration and costlier epidemics than ISP, except when epidemics started in cattle herds located in high density cattle area. ISP predicted suppressive vaccination to be less costly than depopulation, while the least costly control strategy predicted by DTU-DADS differed depending on the species and density area of the index herd. It was not possible to run the depopulation scenarios in the NAADSM due to limitations in the model. Running several models in parallel gives better insight in disease spread, limits typing and coding errors and improves understanding of modeled processes. The chosen control strategy might depend on the chosen model.

Hisham Beshara Halasa, Tariq; Boklund, Anette

2012-01-01

276

Modelling SDL, Modelling Languages  

Directory of Open Access Journals (Sweden)

Full Text Available Today's software systems are too complex to implement them and model them using only one language. As a result, modern software engineering uses different languages for different levels of abstraction and different system aspects. Thus to handle an increasing number of related or integrated languages is the most challenging task in the development of tools. We use object oriented metamodelling to describe languages. Object orientation allows us to derive abstract reusable concept definitions (concept classes) from existing languages. This language definition technique concentrates on semantic abstractions rather than syntactical peculiarities. We present a set of common concept classes that describe structure, behaviour, and data aspects of high-level modelling languages. Our models contain syntax modelling using the OMG MOF as well as static semantic constraints written in OMG OCL. We derive metamodels for subsets of SDL and UML from these common concepts, and we show for parts of these languages that they can be modelled and related to each other through the same abstract concepts.

Michael Piefel; Markus Scheidgen

2007-01-01

277

Modelling the models  

CERN Multimedia

By analysing the production of mesons in the forward region of LHC proton-proton collisions, the LHCf collaboration has provided key information needed to calibrate extremely high-energy cosmic ray models.   Average transverse momentum (pT) as a function of rapidity loss ?y. Black dots represent LHCf data and the red diamonds represent SPS experiment UA7 results. The predictions of hadronic interaction models are shown by open boxes (sibyll 2.1), open circles (qgsjet II-03) and open triangles (epos 1.99). Among these models, epos 1.99 shows the best overall agreement with the LHCf data. LHCf is dedicated to the measurement of neutral particles emitted at extremely small angles in the very forward region of LHC collisions. Two imaging calorimeters – Arm1 and Arm2 – take data 140 m either side of the ATLAS interaction point. “The physics goal of this type of analysis is to provide data for calibrating the hadron interaction models – the well-known &...

Anaïs Schaeffer

2012-01-01

278

Intense ultra-broadband down-conversion in co-doped oxide glass by multipolar interaction process.  

UK PubMed Central (United Kingdom)

We report that Eu(2+) can be an efficient sensitizer for Yb(3+) and a broadband absorber for blue solar spectra in the host of oxide glass. The greenish 4f ? 5d transition of Eu(2+) and the characteristic near-infrared emission of Yb(3+) were observed, with the blue-light of xenon lamp excitation. The 5d energy can be adjusted by the host and the energy transfer efficiency can be enhanced. The quantum efficiency is up to 163.8%. Given the broad excitation band, high absorption coefficient and excellent mechanical, thermal and chemical stability, this system can be useful as down-conversion layer for solar cells.

Liu Z; Yang L; Dai N; Chu Y; Chen Q; Li J

2013-05-01

279

Promoting Models  

Science.gov (United States)

There can be multitudinous models specifying aspects of the same system. Each model has a bias towards one aspect. These models often override in specific aspects though they have different expressions. A specification written in one model can be refined by introducing additional information from other models. The paper proposes a concept of promoting models which is a methodology to obtain refinements with support from cooperating models. It refines a primary model by integrating the information from a secondary model. The promotion principle is not merely an academic point, but also a reliable and robust engineering technique which can be used to develop software and hardware systems. It can also check the consistency between two specifications from different models. A case of modeling a simple online shopping system with the cooperation of the guarded design model and CSP model illustrates the practicability of the promotion principle.

Li, Qin; Zhao, Yongxin; Wu, Xiaofeng; Liu, Si

280

Modelling Practice  

DEFF Research Database (Denmark)

This chapter deals with the practicalities of building, testing, deploying and maintaining models. It gives specific advice for each phase of the modelling cycle. To do this, a modelling framework is introduced which covers: problem and model definition; model conceptualization; model data requirements; model construction; model solution; model verification; model validation and finally model deployment and maintenance. Within the adopted methodology, each step is discussedthrough the consideration of key issues and questions relevant to the modelling activity. Practical advice, based on many years of experience is providing in directing the reader in their activities.Traps and pitfalls are discussed and strategies also given to improve model development towards “fit-for-purpose” models. The emphasis in this chapter is the adoption and exercise of a modelling methodology that has proven very successful in many model building activities. It is vital that good methodologies are adopted for both thoroughness andefficiency purposes. Asking good questions for each modelling stage can aid in getting to effective and efficient solutions in modelling practice. Modelling is very much a ‘goal oriented’ activity, under constraints of system insight, time, cost and human resources. The George Box dictum that “all models are wrong, some are useful” should be coupled with the parsimony principle to ensure optimal outcomes.

Cameron, Ian; Gani, Rafiqul

2011-01-01

 
 
 
 
281

Modeling Malaria  

Science.gov (United States)

In this module, we develop models of the effects of malaria on various populations of humans and mosquitoes. After considering differential equations to model a system, we create a model using the systems modeling tool STELLA. Projects involve various refinements of the model.

Shiflet, Angela B.; Shiflet, George W.

282

Potential role for magnetoencephalography in distinguishing low- and high-grade gliomas: a preliminary study with histopathological confirmation  

Science.gov (United States)

Gliomas are the most common form of tumor in the CNS and are exceptionally heterogeneous. Accurately characterizing gliomas, in terms of grade and type, is essential for predicting the rate of tumor progression. Histopathological grading and analysis based on biopsied tissue remains the gold standard, but non- and semi-invasive neuroimaging also plays a key role. Neuroimaging has been used to guide and optimize biopsies for several decades, but more recently molecular imaging and variants of MRI have shown promise in independently predicting glioma grade. Here we evaluated whether magnetoencephalographic (MEG) measurements of population-level physiology within the glioma space were predictive of the inherent grade of the tissue, based on definitive histopathological analyses. High-density MEG data were recorded from 11 patients who were undergoing functional mapping in preparation for resective surgery. The primary results indicated that glioma grade was positively correlated with the local amplitude of activity within the glioma space in the theta (4–7 Hz), alpha (8–14 Hz), and beta bands (14–30 Hz). Additionally, activity within the glioma was significantly elevated relative to the nonaffected homologue area in the same frequency bands. These results indicate that pathological levels of synchronization exist within the tumor space and that MEG may be a viable tool for noninvasively differentiating gliomas by their grade. Although these results should be considered preliminary and are only correlative in nature, these data suggest that MEG can potentially detect neurophysiological signatures or markers that predict the inherent grade of a glial tumor.

Wilson, Tony W.; Heinrichs-Graham, Elizabeth; Aizenberg, Michele R.

2012-01-01

283

Effects of Phonological Contrast on Auditory Word Discrimination in Children with and without Reading Disability: A Magnetoencephalography (MEG) Study  

Science.gov (United States)

Poor readers perform worse than their normal reading peers on a variety of speech perception tasks, which may be linked to their phonological processing abilities. The purpose of the study was to compare the brain activation patterns of normal and impaired readers on speech perception to better understand the phonological basis in reading…

Wehner, Daniel T.; Ahlfors, Seppo P.; Mody, Maria

2007-01-01

284

Models within models  

International Nuclear Information System (INIS)

Anyone who worries that physicists are running out of interesting challenges to tackle and important problems to solve should read the two, very different feature articles in this issue. In 'Climate change: complexity in action', Klaus Hasselmann and colleagues write about the challenges of including economic and political dimensions in computer simulations of climate change. It is hard to imagine a physics-based topic that has a greater impact on the world at large. In 'Quarks, diquarks and pentaquarks', Robert Jaffe and Frank Wilczek describe our current understanding of quantum chromodynamics and the strong nuclear force. In this case it is hard to think of many more difficult problems in fundamental physics. Traditional climate modelling is difficult enough because a whole range of effects in the atmosphere and the oceans have to be taken into account. It typically takes weeks for a state-of-the-art supercomputer to simulate 100 years of climate change with a horizontal resolution of 100 km. But climate change is about much more than solving difficult differential equations - there are crucial social, political and economic influences as well. Some researchers, including a significant number of physicists, have started to look at this integrated-assessment approach. The first challenge is to develop climate models that take minutes to run on a laptop. The next challenge is to develop analogous models that work in the social, political and economic arenas - which is not a trivial task - and then integrate all these different models and explore all the possible global-warming scenarios. Physicists also hope to integrate quantum chromodynamics (QCD) into the larger framework of a so-called theory of everything. Like climate modellers, particle theorists working on QCD require enormous computational resources for their calculations, and even then there are limits to what can be achieved (e.g. the mass of the proton has yet to be calculated from first principles). However, QCD can explain the results of an enormous range of experiments, and has recently been given some new particles - 'pentaquarks' - to get its teeth into. Moreover, physicists searching for a theory of everything can take heart from the fact that, unlike researchers working on integrated-assessment models, they already have highly successful theories for the phenomena they are trying to unify. However, the ultimate challenge for the climate community will be to persuade governments and big business that they need to do something to avoid the potentially disastrous consequences of climate change. The UK's chief scientific advisor, David King, made headlines recently when he wrote that, in his view, 'climate change is the most severe problem that we are facing today - more serious even than the threat of terrorism' (Science 303 176-177). It is too soon to say if the message is getting through, but at least climate scientists now have an unlikely ally in the shape of the climate-change disaster movie The Day After Tomorrow. (U.K.)

2004-01-01

285

Models within models  

Energy Technology Data Exchange (ETDEWEB)

Anyone who worries that physicists are running out of interesting challenges to tackle and important problems to solve should read the two, very different feature articles in this issue. In 'Climate change: complexity in action', Klaus Hasselmann and colleagues write about the challenges of including economic and political dimensions in computer simulations of climate change. It is hard to imagine a physics-based topic that has a greater impact on the world at large. In 'Quarks, diquarks and pentaquarks', Robert Jaffe and Frank Wilczek describe our current understanding of quantum chromodynamics and the strong nuclear force. In this case it is hard to think of many more difficult problems in fundamental physics. Traditional climate modelling is difficult enough because a whole range of effects in the atmosphere and the oceans have to be taken into account. It typically takes weeks for a state-of-the-art supercomputer to simulate 100 years of climate change with a horizontal resolution of 100 km. But climate change is about much more than solving difficult differential equations - there are crucial social, political and economic influences as well. Some researchers, including a significant number of physicists, have started to look at this {sup i}ntegrated-assessment approach{sup .} The first challenge is to develop climate models that take minutes to run on a laptop. The next challenge is to develop analogous models that work in the social, political and economic arenas - which is not a trivial task - and then integrate all these different models and explore all the possible global-warming scenarios. Physicists also hope to integrate quantum chromodynamics (QCD) into the larger framework of a so-called theory of everything. Like climate modellers, particle theorists working on QCD require enormous computational resources for their calculations, and even then there are limits to what can be achieved (e.g. the mass of the proton has yet to be calculated from first principles). However, QCD can explain the results of an enormous range of experiments, and has recently been given some new particles - 'pentaquarks' - to get its teeth into. Moreover, physicists searching for a theory of everything can take heart from the fact that, unlike researchers working on integrated-assessment models, they already have highly successful theories for the phenomena they are trying to unify. However, the ultimate challenge for the climate community will be to persuade governments and big business that they need to do something to avoid the potentially disastrous consequences of climate change. The UK's chief scientific advisor, David King, made headlines recently when he wrote that, in his view, 'climate change is the most severe problem that we are facing today - more serious even than the threat of terrorism' (Science 303 176-177). It is too soon to say if the message is getting through, but at least climate scientists now have an unlikely ally in the shape of the climate-change disaster movie The Day After Tomorrow. (U.K.)

Rodgers, Peter

2004-06-01

286

Toilet Model  

Science.gov (United States)

In this activity, PVC pipe, plastic water bottles and vinyl tubing are used to make a simple working toilet model. The model shows the role of a siphon in the flushing of a toilet. Educators can pre-assemble this model and use it for demonstration purposes or engage learners in the model building process.

Rathjen, Don

2005-01-01

287

Management models  

International Nuclear Information System (INIS)

Management models are used here as a vehicle to organize the ecological research tasks required for the biotic transport program. Three kinds of models are described: ecosystem level simulation models; radionuclide transport models; and optimization models. The ecosystem simulation model is included here as a coupling agent between climatic variables and waste management practices with the transport and optimization models. Certainly the potential for radionuclide transport depends to a large degree upon the density, type and vigor of plant species inhabiting burial sites. These parameters, in turn, are related to past management practices, precipitation patterns, and successional stages, all predictable using current techniques

1977-01-01

288

Polarimetric SAR Data for Urban Land Cover Classification Using Finite Mixture Model  

Science.gov (United States)

Image classification techniques play an important role in automatic analysis of remote sensing data. This paper demonstrates the potential of polarimetric synthetic aperture radar (PolSAR) for urban land cover mapping using an unsupervised classification approach. Analysis of PolSAR images often shows that non-Gaussian models give better representation of the scattering vector statistics. Hence, processing algorithms based on non-Gaussian statistics should improve performance, compared to complex Gaussian distributions. Several distributions could be used to model SAR image texture with different spatial correlation properties and various degrees of inhomogeneity [1-3]. Statistical properties are widely used for image segmentation and land cover classification of PolSAR data. The pixel-based approaches cluster individual pixels through analysis of their statistical properties. Those methods work well on the relatively coarse spatial resolution images. But classification results based on pixelwise analysis demonstrate the pepper-salt effect of speckle in medium and high resolution applications such as urban area monitoring [4]. Therefore, the expected improvement of the classification results is hindered by the increase of textural differences within a class. In such situation, enhancement could be made through exploring the contextual correlation among pixels by Markov random field (MRF) models [4, 5]. The potential of MRF models to retrieve spatial contextual information is desired to improve the accuracy and reliability of image classification. Unsupervised contextual polarimetric SAR image segmentation is addressed by combining statistical modeling and spatial context within an MRF framework. We employ the stochastic expectation maximization (SEM) algorithm [6] to jointly perform clustering of the data and parameter estimation of the statistical distribution conditioned to each image cluster and the MRF model. This classification method is applied on medium resolution L-band ALOS data from Tehran, Iran. Clustering results are presented and discussed in the full paper, also comparing the classification approach with other commonly used algorithms. References: [1] J.-S. Lee, M. Grunes, and R. Kwok, "Classification of multi-look polarimetric SAR imagery based on the complex Wishart distribution," Int. J Remote Sens., vol. 15, no. 11, pp. 2299-2311, Jul. 1994. [2] C. C. Freitas, A. C. Frery, and A. H. Correia, "The polarimetric G0 distribution for SAR data analysis," Environmetrics, vol. 16, no. 1, pp. 13-31, Feb. 2005. [3] A. P. Doulgeris, S. N. Anfinsen, and T. Eltoft, "Automated non-Gaussian clustering of polarimetric synthetic aperture radar images," IEEE Trans. Geosci. Remote Sens., vol. 49, no. 10, pp. 3665-3676, Oct. 2011. [4]. V. Akbari, A. P. Doulgeris, G. Moser, S. N. Anfinsen, T. Eltoft, and S. Serpico, "A textural-contextual model for unsupervised segmentation of multi-polarization synthetic aperture radar images," IEEE Transactions on Geoscience and Remote Sensing, in press. [5] S. Li, "Markov Random Field Modeling in Image Analysis," 3rd ed. London, U.K., Springer-Verlag, 2009.

Mahdianpari, Masoud; Akbari, Vahid; Mohammadimanesh, Fariba; Alioghli Fazel, Mohammad

2013-04-01

289

Modeling the purposes of models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Today, the purpose of a model is often kept implicit. The lack of explicit statements about a model's purpose hinders both its creation and its (re)use. In this paper, we adapt two goal modeling techniques, the Goal-Question-Metric paradigm and KAOS, an intentional modeling language, so that the pur...

Jeanneret, Cédric; Glinz, Martin; Baar, Thomas

290

Position models and language modeling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In statistical language modelling the classic model used is $n$-gram. This model is not able however to capture long term dependencies, \\emph{i.e.} dependencies larger than $n$. An alternative to this model is the probabilistic automaton. Unfortunately, it appears that preliminary experiments on the...

Zdziobeck, Arnaud; Thollard, Franck

291

Geotechnical modelling  

CERN Document Server

This book enables practising engineers to make informed decisions concerning soil model boundary conditions and the choice of elements in Finite Element models. Ideal for MSc and MEng students and for use on CPD courses.

Muir-Wood, David

2004-01-01

292

Hydrocarbon modelling  

Energy Technology Data Exchange (ETDEWEB)

The reliability of hydrocarbon modelling methods is a major problem due to uncertain data and parameter values. The usual procedures for inversion and variance analysis are complicated by the large calculational times of numerical basin models. Approximate methods for inversion and variance analysis, which can be applied in 1-, 2-, and 3-D basin models, have been developed for the case of thermal and maturity modelling. (au)

Nielsen, S.B. [Univ. of Aarhus, Dept. of Earth Sciences (Denmark)

1998-08-01

293

Computable models  

CERN Document Server

Computational models can be found everywhere in present day science and engineering. In providing a logical framework and foundation for the specification and design of specification languages, Raymond Turner uses this framework to introduce and study computable models. In doing so he presents the first systematic attempt to provide computational models with a logical foundation. Computable models have wide-ranging applications from programming language semantics and specification languages, through to knowledge representation languages and formalism for natural language semantics. They are al

Turner, Raymond

2009-01-01

294

Landscape Models  

Science.gov (United States)

In this assignment students model different scenarios of landscape evolution using an on-line landscape evolution model. The assignment takes them through several situations involving changes in commonly modeled landscape variables like overland flow, faulting and uplift, erosivity, and drainage incision. At the end I have students devise a situation (of variables) that tests a hypothesis or the sensitivity of the model to changes in a variable. Designed for a geomorphology course Uses online and/or real-time data

Marchetti, David

295

Modeling Convection  

Science.gov (United States)

Typically, teachers use simple models that employ differences in temperature and density to help students visualize convection. However, most of these models are incomplete or merely hint at (instead of model) convective circulation. In order to make the use of models more effective, the authors developed an alternative system that uses a simple, low-cost apparatus that not only maintains dynamic convective circulation, but also illustrates two adjacent cells that teaches students about Earth's processes.

Schulz, Amanda; Ebert, James R.; Elliott, Nancy A.

2004-09-01

296

Hysteresis modeling  

International Nuclear Information System (INIS)

[en] The theoretical modeling in complex physical systems may be aimed at an improved precision of empirical description or a deeper physical understanding of the phenomena. The Preisach-type empirical product model of hysteresis as well as a zero temperature Monte Carlo simulation of the magnetization process of an Ising-like dipolar system are discussed as an illustration of modeling examples

2000-06-02

297

Photocurrent modeling  

Energy Technology Data Exchange (ETDEWEB)

Mathematical models are described for time dependent photocurrent in a PN junction. The models incorporate high injection effects on lifetime, electric fields in the bulk quasi-neutral region, and diode length effects. A subroutine suitable for use in SPICE 2 implements the models.

Enlow, E.W.; Stuetzer, O.; Alexander, D.R.; Barnum, J.R.

1987-01-01

298

Marginal Models  

CERN Multimedia

Presents an overview of the basic principles of marginal modeling and offers a range of possible applications. This book includes many real world examples, explains the types of research questions for which marginal modeling is useful, and provides a description of how to apply marginal models for a great diversity of research questions.

Bergsma, Wicher; Hagenaars, Jacques A

2009-01-01

299

Correct Models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In previous reports, we have show how to transform a text $y_n$ in a random sequence by using functions of Fibonacci $T_q$. Now, in this report, we obtain a clearer result by proving that $T_q(y_n)$ has the IID model as correct model. But, it is necessary to define correctly a correct model. Then, w...

Blacher, René

300

Hysteresis modeling  

CERN Multimedia

The theoretical modeling in complex physical systems may be aimed at an improved precision of empirical description or a deeper physical understanding of the phenomena. The Preisach-type empirical product model of hysteresis as well as a zero temperature Monte Carlo simulation of the magnetization process of an Ising-like dipolar system are discussed as an illustration of modeling examples.

Kadar, G

2000-01-01

 
 
 
 
301

Animal models.  

UK PubMed Central (United Kingdom)

Epilepsy accounts for a significant portion of the dis-ease burden worldwide. Research in this field is fundamental and mandatory. Animal models have played, and still play, a substantial role in understanding the patho-physiology and treatment of human epilepsies. A large number and variety of approaches are available, and they have been applied to many animals. In this chapter the in vitro and in vivo animal models are discussed,with major emphasis on the in vivo studies. Models have used phylogenetically different animals - from worms to monkeys. Our attention has been dedicated mainly to rodents.In clinical practice, developmental aspects of epilepsy often differ from those in adults. Animal models have often helped to clarify these differences. In this chapter, developmental aspects have been emphasized.Electrical stimulation and chemical-induced models of seizures have been described first, as they represent the oldest and most common models. Among these models, kindling raised great interest, especially for the study of the epileptogenesis. Acquired focal models mimic seizures and occasionally epilepsies secondary to abnormal cortical development, hypoxia, trauma, and hemorrhage.Better knowledge of epileptic syndromes will help to create new animal models. To date, absence epilepsy is one of the most common and (often) benign forms of epilepsy. There are several models, including acute pharmacological models (PTZ, penicillin, THIP, GBL) and chronic models (GAERS, WAG/Rij). Although atypical absence seizures are less benign, thus needing more investigation, only two models are so far available (AY-9944,MAM-AY). Infantile spasms are an early childhood encephalopathy that is usually associated with a poor out-come. The investigation of this syndrome in animal models is recent and fascinating. Different approaches have been used including genetic (Down syndrome,ARX mutation) and acquired (multiple hit, TTX, CRH,betamethasone-NMDA) models.An entire section has been dedicated to genetic models, from the older models obtained with spontaneous mutations (GEPRs) to the new engineered knockout, knocking, and transgenic models. Some of these models have been created based on recently recognized patho-genesis such as benign familial neonatal epilepsy, early infantile encephalopathy with suppression bursts, severe myoclonic epilepsy of infancy, the tuberous sclerosis model, and the progressive myoclonic epilepsy. The contribution of animal models to epilepsy re-search is unquestionable. The development of further strategies is necessary to find novel strategies to cure epileptic patients, and optimistically to allow scientists first and clinicians subsequently to prevent epilepsy and its consequences.

Coppola A; Moshé SL

2012-01-01

302

Hydrological models are mediating models  

Directory of Open Access Journals (Sweden)

Full Text Available Despite the increasing role of models in hydrological research and decision-making processes, only few accounts of the nature and function of models exist in hydrology. Earlier considerations have traditionally been conducted while making a clear distinction between physically-based and conceptual models. A new philosophical account, primarily based on the fields of physics and economics, transcends classes of models and scientific disciplines by considering models as "mediators" between theory and observations. The core of this approach lies in identifying models as (1) being only partially dependent on theory and observations, (2) integrating non-deductive elements in their construction, and (3) carrying the role of instruments of scientific enquiry about both theory and the world. The applicability of this approach to hydrology is evaluated in the present article. Three widely used hydrological models, each showing a different degree of apparent physicality, are confronted to the main characteristics of the "mediating models" concept. We argue that irrespective of their kind, hydrological models depend on both theory and observations, rather than merely on one of these two domains. Their construction is additionally involving a large number of miscellaneous, external ingredients, such as past experiences, model objectives, knowledge and preferences of the modeller, as well as hardware and software resources. We show that hydrological models convey the role of instruments in scientific practice by mediating between theory and the world. It results from these considerations that the traditional distinction between physically-based and conceptual models is necessarily too simplistic and refers at best to the stage at which theory and observations are steering model construction. The large variety of ingredients involved in model construction would deserve closer attention, for being rarely explicitly presented in peer-reviewed literature. We believe that devoting more importance to identifying and communicating on the many factors involved in model development might increase transparency of model building.

L. V. Babel; D. Karssenberg

2013-01-01

303

Animal models.  

UK PubMed Central (United Kingdom)

Five well-established animal models in influenza research are discussed in a schematic fashion. Although there are clear parallels between these models, like viruses used, housing and handling conditions under biosafety conditions, routes of virus inoculation, sampling strategies, and necropsy techniques (mostly elaborated on in Subheading 4), each of these models involves specific differences in their practical applicability that need thorough assessment depending on the scientific question raised. In other words, there is no universal animal model for influenza and depending on the actual question to be answered the model and the experimental conditions should be carefully selected.

Kroeze EJ; Kuiken T; Osterhaus AD

2012-01-01

304

Dynamic modeling  

Energy Technology Data Exchange (ETDEWEB)

This chapter is based on the thesis, `Dynamic modeling and control of coal fired fluidized bed boilers` by J.M.P. van der Looij. The dynamic behaviour of a pressurised coal fired fluidised bed combustor was modelled by Kool` and Looij extended the model by adding horizontal mining of solids in the bed and recirculation of fly ash to the bed, in order to be able to accurately model the dynamic behaviour of the AKZO fluidized bed. The models are described in this paper. 45 refs., 8 figs.

Korving, A. [Delft University of Technology, Delft (Netherlands)

1995-05-01

305

Constitutive Models  

DEFF Research Database (Denmark)

This chapter presents various types of constitutive models and their applications. There are 3 aspects dealt with in this chapter, namely: creation and solution of property models, the application of parameter estimation and finally application examples of constitutive models. A systematic procedure is introduced for the analysis and solution of property models. Models that capture and represent the temperature dependent behaviour of physical properties are introduced, as well as equation of state models (EOS) such as the SRK EOS. Modelling of liquid phase activity coefficients are also covered, illustrating several models such as the Wilson equation and NRTL equation, along with their solution strategies. A section shows how to use experimental data to regress the property model parameters using a least squares approach. A full model analysis is applied in each example that discusses the degrees of freedom, dependent and independent variables and solution strategy. Vapour-liquid and solid-liquid equilibrium is covered, and applications to droplet evaporation and kinetic models are given.

Sales-Cruz, Mauricio; Piccolo, Chiara

2011-01-01

306

Ventilation Model  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this analysis and model report (AMR) for the Ventilation Model is to analyze the effects of pre-closure continuous ventilation in the Engineered Barrier System (EBS) emplacement drifts and provide heat removal data to support EBS design. It will also provide input data (initial conditions, and time varying boundary conditions) for the EBS post-closure performance assessment and the EBS Water Distribution and Removal Process Model. The objective of the analysis is to develop, describe, and apply calculation methods and models that can be used to predict thermal conditions within emplacement drifts under forced ventilation during the pre-closure period. The scope of this analysis includes: (1) Provide a general description of effects and heat transfer process of emplacement drift ventilation. (2) Develop a modeling approach to simulate the impacts of pre-closure ventilation on the thermal conditions in emplacement drifts. (3) Identify and document inputs to be used for modeling emplacement ventilation. (4) Perform calculations of temperatures and heat removal in the emplacement drift. (5) Address general considerations of the effect of water/moisture removal by ventilation on the repository thermal conditions. The numerical modeling in this document will be limited to heat-only modeling and calculations. Only a preliminary assessment of the heat/moisture ventilation effects and modeling method will be performed in this revision. Modeling of moisture effects on heat removal and emplacement drift temperature may be performed in the future.

H. Yang

1999-11-04

307

Turbulence modelling  

International Nuclear Information System (INIS)

This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-? two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the 'standard' (Rij-?) Reynolds tensions transport model and introduces more recent models called 'feasible'. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author).

1997-01-01

308

Phenomenological models  

Energy Technology Data Exchange (ETDEWEB)

The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. A range of models covering different endpoints and phenomena has developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified. 43 refs., 13 figs.

Braby, L.A.

1990-09-01

309

Model simulation  

Energy Technology Data Exchange (ETDEWEB)

This article reports on the development of a model of a generic atmospheric crude tower by Hypotech Ltd. Canada in its HYSYS software system which demonstrates the benefits of dynamic simulation and model predictive control of an atmospheric crude tower for increasing process understanding. Details are given of the simulation of a three sidestripper tower, and the PID control system. An overview of model predictive control is presented, and the implementation of dynamic matrix control is described. A case study is presented.

Hocking, D. [Hyprotech Ltd. (Canada)

2001-11-01

310

Floodplain Modeling  

Science.gov (United States)

Students explore the impact of changing river volumes and different floodplain terrain in experimental trials with table top-sized riverbed models. The models are made using modeling clay in an aluminum baking pans placed on a slight incline. Water added âupstreamâ at different flow rates and to different riverbed configurations simulates different potential flood conditions. Students study flood dynamics as they modify the riverbed with blockages or levees to simulate real-world scenarios.

Integrated Teaching And Learning Program

311

Model Volcanoes  

Science.gov (United States)

In this lesson, students will explore volcanoes by constructing models and reflect upon their learning through drawing sketches of their models. Once they have finished making their models, they will experiment with making their volcanoes erupt. They will observe how eruption changes the original form of their volcano models. In this way, students see first hand how this type of phenomena creates physical change. While students at this level may struggle to understand larger and more abstract geographical concepts, they will work directly with material that will help them build a foundation for understanding concepts of phenomena that sculpt the earth.

312

Ventilation Model  

International Nuclear Information System (INIS)

[en] The purpose of the Ventilation Model is to simulate the heat transfer processes in and around waste emplacement drifts during periods of forced ventilation. The model evaluates the effects of emplacement drift ventilation on the thermal conditions in the emplacement drifts and surrounding rock mass, and calculates the heat removal by ventilation as a measure of the viability of ventilation to delay the onset of peak repository temperature and reduce its magnitude. The heat removal by ventilation is temporally and spatially dependent, and is expressed as the fraction of heat carried away by the ventilation air compared to the fraction of heat produced by radionuclide decay. One minus the heat removal is called the wall heat fraction, or the remaining amount of heat that is transferred via conduction to the surrounding rock mass. Downstream models, such as the ''Multiscale Thermohydrologic Model'' (BSC 2001), use the wall heat fractions as outputted from the Ventilation Model to initialize their post-closure analyses. The Ventilation Model report was initially developed to analyze the effects of preclosure continuous ventilation in the Engineered Barrier System (EBS) emplacement drifts, and to provide heat removal data to support EBS design. Revision 00 of the Ventilation Model included documentation of the modeling results from the ANSYS-based heat transfer model. The purposes of Revision 01 of the Ventilation Model are: (1) To validate the conceptual model for preclosure ventilation of emplacement drifts and verify its numerical application in accordance with new procedural requirements as outlined in AP-SIII-10Q, Models (Section 7.0). (2) To satisfy technical issues posed in KTI agreement RDTME 3.14 (Reamer and Williams 2001a). Specifically to demonstrate, with respect to the ANSYS ventilation model, the adequacy of the discretization (Section 6.2.3.1), and the downstream applicability of the model results (i.e. wall heat fractions) to initialize post-closure thermal models (Section 6.6). (3) To satisfy the remainder of KTI agreement TEF 2.07 (Reamer and Williams 2001b). Specifically to provide the results of post-test ANSYS modeling of the Atlas Facility forced convection tests (Section 7.1.2). This portion of the model report also serves as a validation exercise per AP-SIII.10Q, Models, for the ANSYS ventilation model. (4) To further satisfy KTI agreements RDTME 3.01 and 3.14 (Reamer and Williams 2001a) by providing the source documentation referred to in the KTI Letter Report, ''Effect of Forced Ventilation on Thermal-Hydrologic Conditions in the Engineered Barrier System and Near Field Environment'' (Williams 2002). Specifically to provide the results of the MULTIFLUX model which simulates the coupled processes of heat and mass transfer in and around waste emplacement drifts during periods of forced ventilation. This portion of the model report is presented as an Alternative Conceptual Model with a numerical application, and also provides corroborative results used for model validation purposes (Section 6.3 and 6.4)

2002-01-01

313

Model Selection for Geostatistical Models  

Energy Technology Data Exchange (ETDEWEB)

We consider the problem of model selection for geospatial data. Spatial correlation is typically ignored in the selection of explanatory variables and this can influence model selection results. For example, the inclusion or exclusion of particular explanatory variables may not be apparent when spatial correlation is ignored. To address this problem, we consider the Akaike Information Criterion (AIC) as applied to a geostatistical model. We offer a heuristic derivation of the AIC in this context and provide simulation results that show that using AIC for a geostatistical model is superior to the often used approach of ignoring spatial correlation in the selection of explanatory variables. These ideas are further demonstrated via a model for lizard abundance. We also employ the principle of minimum description length (MDL) to variable selection for the geostatistical model. The effect of sampling design on the selection of explanatory covariates is also explored.

Hoeting, Jennifer A.; Davis, Richard A.; Merton, Andrew A.; Thompson, Sandra E.

2006-02-01

314

Model management  

Energy Technology Data Exchange (ETDEWEB)

The paper discusses the effect a new business model has had on coal trading by minimising risks and saving money. The economic foundation for the model rests on privatisation, deregulation and consolidation. Following success in the USA, Aquila commenced trading coal, both physically and financially, on Europe's OTC market at the beginning of 2002. 3 photos.

Stroud, V. [Aquila Merchant Services (United States)

2002-11-01

315

Modeling Daisyworld  

Science.gov (United States)

Daisyworld is a classic model of complex feedbacks in a simple climate system; this activity guides students through the construction of a STELLA model that can be used to experiment with the system, exploring the somewhat surprising dynamics that arise from the interplay of positive and negative feedbacks between daisies and the temperature of their environment.

Bice, David

316

Neurofuzzy Modelling  

DEFF Research Database (Denmark)

A neural network can approximate a function, but it is impossible to interpret the result in terms of natural language. The fusion of neural networks and fuzzy logic in neurofuzzy models provide learning as well as readability. Control engineers find this useful, because the models can be interpreted and supplemented by process operators.

Jantzen, Jan

1998-01-01

317

Hydrodynamic models  

CERN Multimedia

Recent developments based on relativistic hydrodynamic models in high energy heavy ion collisions are discussed. I focus especially on how hydrodynamics works at RHIC energies and how one can use the most of it in analyses of jet quenching and thermal electromagnetic radiations. I also comment on improvement of initial conditions and viscosity in hydrodynamic models.

Hirano, T

2004-01-01

318

Resolution Modeling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Very large graphics models are common in a number of application, and many different simplification methods have been recently developed. Some of them support the construction of multiresolution representations of the input meshes. On the basis of this innovative techniques, we foresee a modeling fr...

Cignoni P.; Montani C.; Rocchini C.; Scopigno R.

319

Volatility models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Chapter written for the Handbook of Volatility Models and their Applications, edited by Luc Bauwens, Christian Hafner, and Sébastien Laurent, forthcoming in 2012 (John Wiley & sons). This chapter presents an introductory review of volatility models and some applications. The review is linked with th...

Bauwens, Luc; Hafner, Christian; Laurent, Sébastien

320

Modeling Serviceflow  

UK PubMed Central (United Kingdom)

As e-business is invading the service industry and the public sector,there is a need for a serviceflow management of those processes, which consist ofa sequence of interrelated sub-services. Making use of the potentials of internetapplications, serviceflow management aims at providing these service in an efficientmanner, at improving customer relationship management in the field of tensionbetween routine and situated/personalized service provision, and at providingflexible IT support for service providers and/or clients at each service point. Basedon object oriented, workflow and user oriented modeling techniques, we modelserviceflow patterns by identifying sequences of service points, each capturing thespecific service tasks and their respective pre- and postconditions from the pro-vider's point of view. This serviceflow modeling approach may be supported bythe modeling tools Visioand Process@Work. We present some results from twocases of serviceflow modeling, each with a short case description and a discussionof the models' application for technical and organizational development.

Ralf Klischewski; Ingrid Wetzel; Ali Baharami

 
 
 
 
321

Model Execution  

Energy Technology Data Exchange (ETDEWEB)

A computer software-based model is typically designed to produce a trace of system evolution over time. The actual process of computing the model state and producing the state values as the simulation time is advanced is called model execution. Models could be designed with a specific execution technique in mind, or could be generally amenable to multiple different execution techniques. Two popular methods that are used to execute models are: time-stepped method and discrete-event method. Each of these methods could in turn be executed either sequentially (on a single processor), or in parallel (using multiple processors concurrently). In this chapter, we describe the time-stepped and discrete event execution methods and outline some of the common approaches to their sequential and parallel execution. Execution concepts common to the methods are described followed by implementation details of the methods.

Perumalla, Kalyan S [ORNL

2007-01-01

322

Linear Models  

CERN Multimedia

This 1971 classic on linear models is once again available--as a Wiley Classics Library Edition. It features material that can be understood by any statistician who understands matrix algebra and basic statistical methods.

Searle, Shayle R

2012-01-01

323

Technicolor model  

Energy Technology Data Exchange (ETDEWEB)

A one family Technicolor model without exact custodial symmetry is examined in the light of the oblique corrections. The effect of isospin breaking term in vector mesons on the oblique parameter S is discussed. (J.P.N.).

Morozumi, Takuya [Hiroshima Univ. (Japan). Dept. of Physics

1995-05-01

324

Segregation models.  

Science.gov (United States)

Many antigen receptors of the immune system belong to the family of multichain immune recognition receptors (MIRRs). Binding of ligand (antigen) to MIRR results in receptor phosphorylation, triggering downstream signaling pathways and cellular activation. How ligand binding induces this phosphorylation is not yet understood. In this Chapter, we discuss two models exploring the possibility that kinases and phosphatases are intermingled on the cell surface. Thus, in resting state, MIRR phosphorylation is counteracted by dephosphorylation. Upon ligand binding, phosphatases are removed from the vicinity of the MIRR and kinases, such that phosphorylated MIRRs can accumulate (segregation models). In the first model, clustering of MIRRs by multivalent ligand leads to their concentration in lipid rafts where kinases, but not phosphatases, are localized. The second model takes into account that the MIRR-ligandpair needs dose apposition of the two cell membranes, in cases where ligand is presented by an antigen-presenting cell. The intermembrane distance is too small to accommodate transmembrane phosphatases, which possess large ectodomains. Thus, phosphatases become spatially separated from the MIRRs and kinases (kinetic-segregation model). PMID:19065785

Dopfer, Elaine P; Swamy, Mahima; Siegers, Gabrielle M; Molnar, Eszter; Yang, Jianying; Schamel, Wolfgang W A

2008-01-01

325

Smashnova Model  

CERN Document Server

An alternate model for gamma ray bursts is suggested. For a white dwarf (WD) and neutron star (NS) very close binary system, the WD (close to Mch) can detonate due to tidal heating, leading to a SN. Material falling on to the NS at relativistic velocities can cause its collapse to a magnetar or quark star or black hole leading to a GRB. As the material smashes on to the NS, it is dubbed the Smashnova model. Here the SN is followed by a GRB. NS impacting a RG (or RSG) (like in Thorne-Zytkow objects) can also cause a SN outburst followed by a GRB. Other variations are explored.

Sivaram, C

2007-01-01

326

Environmental modeling  

CERN Multimedia

The book has two aims: to introduce basic concepts of environmental modelling and to facilitate the application of the concepts using modern numerical tools such as MATLAB. It is targeted at all natural scientists dealing with the environment: process and chemical engineers, physicists, chemists, biologists, biochemists, hydrogeologists, geochemists and ecologists. MATLAB was chosen as the major computer tool for modeling, firstly because it is unique in it's capabilities, and secondly because it is available in most academic institutions, in all universities and in the research departments of

Holzbecher, Ekkehard

2012-01-01

327

Daisyworld Model  

Science.gov (United States)

The Daisyworld model created by Andrew Watson and James Lovelock (1983, Tellus, v. 35B, p. 284-289) is a wonderful example of a self-regulating system incorporating positive and negative feedbacks. The model consists of a planet on which black and white daisies are growing. The growth of these daisies is governed by a parabolic shaped growth function regulated by planetary temperature and is set to zero for temperatures less than 5 ºC or greater than 40 ºC and optimized at 22.5 ºC. The model explores the effect of a steadily increasing solar luminosity on the growth of daisies and the resulting planetary temperature. The growth function for the daisies allows them to modulate the planet's temperature for many years, warming it early on as black daisies grow, and cooling it later as white daisies grow. Eventually, the solar luminosity increases beyond the daisies' capability to modulate the temperature and they die out, leading to a rapid rise in the planetary temperature. Students read Watson and Lovelock's original paper, and then use STELLA to create their own Daisyworld model with which they can experiment. Experiments include changing the albedos of the daisies, changing their death rates, and changing the rate at which energy is conducted from one part of the planet to another. In all cases, students keep track of daisy populations and of planetary temperature over time.

Menking, Kirsten

328

Cancer modeling  

Energy Technology Data Exchange (ETDEWEB)

This book contains 10 chapters. Some of the titles are: Intracellular electrolytes and their role in cancer etiology; Quantitative theories of carcinogenesis; Repair of radiation injury and the time factor in radiotherapy; and A modeling approach to metastatic progression of cancer.

Thompson, J.R. (Dept. of Statistics, Rice Univ., Houston, TX (US)); Brown, B.W. (Dept. of Biomathematics, Univ. of Texas, System Cancer Center, M.D. Anderson Hospital and Tumor Institute, Houston, TX (US))

1987-01-01

329

Modeling Business  

CERN Multimedia

Business concepts are studied using a metamodel-based approach, using UML 2.0. The Notation Independent Business concepts metamodel is introduced. The approach offers a mapping between different business modeling notations which could be used for bridging BM tools and boosting the MDA approach.

Vitolins, V; Vitolins, Valdis; Kalnins, Audris

2003-01-01

330

Diffusion Models  

Science.gov (United States)

Web-based intructional material describing the use of diffusion models in population ecology. This page is part of a set of on-line lectures on Quantitative Population Ecology produced by Alexei Sharov in the Department of Entomology at Virginia Tech.

Sharov, Alexei

331

Criticality Model  

International Nuclear Information System (INIS)

[en] The ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003) presents the methodology for evaluating potential criticality situations in the monitored geologic repository. As stated in the referenced Topical Report, the detailed methodology for performing the disposal criticality analyses will be documented in model reports. Many of the models developed in support of the Topical Report differ from the definition of models as given in the Office of Civilian Radioactive Waste Management procedure AP-SIII.10Q, ''Models'', in that they are procedural, rather than mathematical. These model reports document the detailed methodology necessary to implement the approach presented in the Disposal Criticality Analysis Methodology Topical Report and provide calculations utilizing the methodology. Thus, the governing procedure for this type of report is AP-3.12Q, ''Design Calculations and Analyses''. The ''Criticality Model'' is of this latter type, providing a process evaluating the criticality potential of in-package and external configurations. The purpose of this analysis is to layout the process for calculating the criticality potential for various in-package and external configurations and to calculate lower-bound tolerance limit (LBTL) values and determine range of applicability (ROA) parameters. The LBTL calculations and the ROA determinations are performed using selected benchmark experiments that are applicable to various waste forms and various in-package and external configurations. The waste forms considered in this calculation are pressurized water reactor (PWR), boiling water reactor (BWR), Fast Flux Test Facility (FFTF), Training Research Isotope General Atomic (TRIGA), Enrico Fermi, Shippingport pressurized water reactor, Shippingport light water breeder reactor (LWBR), N-Reactor, Melt and Dilute, and Fort Saint Vrain Reactor spent nuclear fuel (SNF). The scope of this analysis is to document the criticality computational method. The criticality computational method will be used for evaluating the criticality potential of configurations of fissionable materials (in-package and external to the waste package) within the repository at Yucca Mountain, Nevada for all waste packages/waste forms. The criticality computational method is also applicable to preclosure configurations. The criticality computational method is a component of the methodology presented in ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003). How the criticality computational method fits in the overall disposal criticality analysis methodology is illustrated in Figure 1 (YMP 2003, Figure 3). This calculation will not provide direct input to the total system performance assessment for license application. It is to be used as necessary to determine the criticality potential of configuration classes as determined by the configuration probability analysis of the configuration generator model (BSC 2003a)

2004-01-01

332

Criticality Model  

Energy Technology Data Exchange (ETDEWEB)

The ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003) presents the methodology for evaluating potential criticality situations in the monitored geologic repository. As stated in the referenced Topical Report, the detailed methodology for performing the disposal criticality analyses will be documented in model reports. Many of the models developed in support of the Topical Report differ from the definition of models as given in the Office of Civilian Radioactive Waste Management procedure AP-SIII.10Q, ''Models'', in that they are procedural, rather than mathematical. These model reports document the detailed methodology necessary to implement the approach presented in the Disposal Criticality Analysis Methodology Topical Report and provide calculations utilizing the methodology. Thus, the governing procedure for this type of report is AP-3.12Q, ''Design Calculations and Analyses''. The ''Criticality Model'' is of this latter type, providing a process evaluating the criticality potential of in-package and external configurations. The purpose of this analysis is to layout the process for calculating the criticality potential for various in-package and external configurations and to calculate lower-bound tolerance limit (LBTL) values and determine range of applicability (ROA) parameters. The LBTL calculations and the ROA determinations are performed using selected benchmark experiments that are applicable to various waste forms and various in-package and external configurations. The waste forms considered in this calculation are pressurized water reactor (PWR), boiling water reactor (BWR), Fast Flux Test Facility (FFTF), Training Research Isotope General Atomic (TRIGA), Enrico Fermi, Shippingport pressurized water reactor, Shippingport light water breeder reactor (LWBR), N-Reactor, Melt and Dilute, and Fort Saint Vrain Reactor spent nuclear fuel (SNF). The scope of this analysis is to document the criticality computational method. The criticality computational method will be used for evaluating the criticality potential of configurations of fissionable materials (in-package and external to the waste package) within the repository at Yucca Mountain, Nevada for all waste packages/waste forms. The criticality computational method is also applicable to preclosure configurations. The criticality computational method is a component of the methodology presented in ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003). How the criticality computational method fits in the overall disposal criticality analysis methodology is illustrated in Figure 1 (YMP 2003, Figure 3). This calculation will not provide direct input to the total system performance assessment for license application. It is to be used as necessary to determine the criticality potential of configuration classes as determined by the configuration probability analysis of the configuration generator model (BSC 2003a).

A. Alsaed

2004-09-14

333

Molecular Modeling  

Science.gov (United States)

Molecular modeling has trickled down from the realm of pharmaceutical and research laboratories into the realm of undergraduate chemistry instruction. It has opened avenues for the visualization of chemical concepts that previously were difficult or impossible to convey. I am sure that many of you have developed exercises using the various molecular modeling tools. It is the desire of this Journal to become an avenue for you to share these exercises among your colleagues. It is to this end that Ron Starkey has agreed to edit such a column and to publish not only the description of such exercises, but also the software documents they use. The WWW is the obvious medium to distribute this combination and so accepted submissions will appear online as a feature of JCE Internet. Typical molecular modeling exercise: finding conformation energies. Molecular Modeling Exercises and Experiments is the latest feature column of JCE Internet, joining Conceptual Questions and Challenge Problems, Hal's Picks, and Mathcad in the Chemistry Curriculum. JCE Internet continues to seek submissions in these areas of interest and submissions of general interest. If you have developed materials and would like to submit them, please see our Guide to Submissions for more information. The Chemical Education Resource Shelf, Equipment Buyers Guide, and WWW Site Review would also like to hear about chemistry textbooks and software, equipment, and WWW sites, respectively. Please consult JCE Internet Features to learn more about these resources at JCE Online. Email Announcements Would you like to be informed by email when the latest issue of the Journal is available online? when a new JCE Software title is shipping? when a new JCE Internet article has been published or is available for Open Review? when your subscription is about to expire? A new feature of JCE Online makes this possible. Visit our Guestbook to learn how. When you submit the form on this page, which includes your email address, you may choose to receive an email notice about a Journal event that interests you. Currently such events include availability of the latest issue of the Journal at JCE Online, expiration of your Journal subscription, shipment of a new JCE Software issue, publication of a new JCE Internet article or its availability for Open Review, and other announcements from the Journal. You may choose any number of these options independently. JCE Online Guestbook. Your Privacy JCE Online promises to you that we will not use the information that you provide in our Guestbook for anything other than our own internal information. We will not provide this information to third parties. We will use the information you provide only in our effort to help make the JCE serve you better. You only need to provide your email address to take advantage of this service; the other information you provide is optional. Molecular Modeling Exercises and Experiments: Mission Statement We are seeking in this JCE Internet feature column to publish molecular modeling exercises and experiments that have been used successfully in undergraduate instruction. The exercises will be published here on JCE Internet. An abstract of published submissions will appear in print in the Journal of Chemical Education. Acceptable exercises could be used in either a chemistry laboratory or a chemistry computer laboratory. The exercise could cover any area of chemistry, but should be limited to undergraduate instructional applications. We envision that most of the exercises/experiments will utilize one of the popular instructional molecular modeling software programs (e.g. HyperChem, Spartan, CAChe, PC Model). Exercises that are specific to a particular modeling program are acceptable, but those usable with any modeling program are preferred. Ideally the exercises/experiments will be of the type where the "correct"answer is not obvious so

Holmes, Jon L.

1999-06-01

334

Clustering models.  

Science.gov (United States)

Ligand binding to the multichain immune recognition receptors (MIRRs) leads to receptor triggering and subsequent lymphocyte activation. MIRR signal transduction pathways have been extensively studied, but it is still not clear how binding of the ligand to the receptor is initially communicated across the plasma membrane to the cells interior. Models proposed for MIRR triggering can be grouped into three categories. Firstly, ligand binding invokes receptor clustering, resulting in the approximation of kinases to the MIRR and receptor phosphorylation. Secondly, ligand binding induces a conformational change of the receptor. Thirdly, upon ligand-binding, receptors and kinases are segregated from phosphatases, leading to a net phosphorylation of the receptor. In this review, we focus on the homodclustering induced by multivalent ligands, the heterodustering induced by simultaneous binding of the ligand to the MIRR and a coreceptor and the pseudodimer model. PMID:19065784

Schamel, Wolfgang W A; Reth, Michael

2008-01-01

335

Modelling tsunamis  

International Nuclear Information System (INIS)

We doubt the relevance of soliton theory to the modelling of tsunamis, and present a case in support of an alternative view. Although the shallow-water equations do provide, we believe, an appropriate basis for this phenomenon, an asymptotic analysis of the solution for realistic variable depths, and for suitable background flows, is essential for a complete understanding of this phenomenon. In particular we explain how a number of tsunami waves can arrive at a shoreline. (letter to the editor)

2006-04-07

336

Gas Model  

Science.gov (United States)

This highly visual model demonstrates the atomic theory of matter which states that a gas is made up of tiny particles of atoms that are in constant motion, smashing into each other. Balls, representing molecules, move within a cage container to simulate this phenomenon. A hair dryer provides the heat to simulate the heating and cooling of gas: the faster the balls are moving, the hotter the gas. Learners observe how the balls move at a slower rate at lower "temperatures."

Exploratorium, The

2013-01-30

337

Modeling biomembranes.  

Energy Technology Data Exchange (ETDEWEB)

Understanding the properties and behavior of biomembranes is fundamental to many biological processes and technologies. Microdomains in biomembranes or ''lipid rafts'' are now known to be an integral part of cell signaling, vesicle formation, fusion processes, protein trafficking, and viral and toxin infection processes. Understanding how microdomains form, how they depend on membrane constituents, and how they act not only has biological implications, but also will impact Sandia's effort in development of membranes that structurally adapt to their environment in a controlled manner. To provide such understanding, we created physically-based models of biomembranes. Molecular dynamics (MD) simulations and classical density functional theory (DFT) calculations using these models were applied to phenomena such as microdomain formation, membrane fusion, pattern formation, and protein insertion. Because lipid dynamics and self-organization in membranes occur on length and time scales beyond atomistic MD, we used coarse-grained models of double tail lipid molecules that spontaneously self-assemble into bilayers. DFT provided equilibrium information on membrane structure. Experimental work was performed to further help elucidate the fundamental membrane organization principles.

Plimpton, Steven James; Heffernan, Julieanne; Sasaki, Darryl Yoshio; Frischknecht, Amalie Lucile; Stevens, Mark Jackson; Frink, Laura J. Douglas

2005-11-01

338

Polarized Neutron Radiative Capture Study of Giant Resonances in /sup 208/ Pb  

Energy Technology Data Exchange (ETDEWEB)

It is shown that predictions of the direct-semidirect model together with high-energy resoution data from radiative capture measurements with polarized neutrons can assist in obtaining information about the location, multipolarity, width and strength of giant multipole resonances.

Longo, G.

1988-12-15

339

Noncommutative Standard Model Model Building  

CERN Multimedia

A noncommutative version of the usual electro-weak theory is constructed. We discuss how to overcome the two major problems: 1) although we can have noncommutative U(n) (which we denote by $U_{\\star}(n)$) gauge theory we cannot have noncommutative SU(n) and 2) the charges in noncommutative QED are quantized to just $0, \\pm 1$. We show how the problem with charge quantization, as well as with the gauge group, can be resolved by taking $U_{\\star}(3)\\times U_{\\star}(2)\\times U_{\\star}(1)$ gauge group and reducing the extra U(1) factors in an appropriate way. Then we proceed with building the noncommutative version of the standard model by specifying the proper representations for the entire particle content of the theory, the gauge bosons, the fermions and Higgs. We also present the full action for the noncommutative Standard Model (NCSM). In addition, among several peculiar features of our model, we address the {\\it inherent} CP violation and new neutrino interactions.

Chaichian, Masud; Sheikh-Jabbari, M M; Tureanu, A

2001-01-01

340

Discrete choice models  

Directory of Open Access Journals (Sweden)

Full Text Available The paper systematically describes special regression methods – discrete choice models – known as probability models. The meaning of models and their methodological characteristics are described, as well as different types of models, especially binary-choice models and censored regression models. We considered three most commonly used approaches to estimating such models – logit, probit and tobit model.

Boštjan Kerbler

2006-01-01

 
 
 
 
341

Predictive Statistical Models for User Modeling  

UK PubMed Central (United Kingdom)

The limitations of traditional knowledge representation methods for modeling complex humanbehaviour led to the investigation of statistical models. Predictive statistical models enable the anticipationof certain aspects of human behaviour, such as goals, actions and preferences. In this paper, we motivate thedevelopment of these models in the context of the user modeling enterprise. We then review the two mainapproaches to predictive statistical modeling, content-based and collaborative, and discuss the main techniquesused to develop predictive statistical models. We also consider the evaluation requirements of these models inthe user modeling context, and propose topics for future research.

Ingrid Zukerman; David W. Albrecht

342

Modelling Consciousness  

UK PubMed Central (United Kingdom)

The relational mind" approach to the inner content of consciousness is developed in terms ofvarious control structures and processing strategies, and their possible neurobiological identificationsin brain sites. This leads naturally to a division of consciousness into a passive and an active part. Aglobal control structure for the single strand' aspect of consciousness is proposed as the thalamonucleusreticularis thalami-cortex coupled system, which is shown to support experimental data onelectrical stimulation of awareness [Libet (1964)]. Local control, in terms of excitatory transfer fromsites of semantic memory to working memory, is shown to explain subliminal perception timing[Marcel (1980)]. The inner content of consciousness is suggested as arising from the resultingrelational features between inputs and stored semantic and episodic memories.Long AbstractA possible physical model of consciousness is presented to allow for a solution to the problem ofanalysing what it i...

J. G. Taylor

343

Modeling sonoluminescence  

Energy Technology Data Exchange (ETDEWEB)

In single-bubble sonoluminescence, a bubble trapped by a sound wave in a flask of liquid is forced to expand and contract; exactly once per cycle, the bubble emits a very sharp ({lt}50 ps) pulse of visible light. This is a robust phenomenon observable to the naked eye, yet the mechanism whereby the light is produced is not well understood. One model that has been proposed is that the light is {open_quotes}vacuum radiation{close_quotes} generated by the coupling of the electromagnetic fields to the surface of the bubble. In this paper, we simulate vacuum radiation by solving Maxwell{close_quote}s equations with an additional term that couples the field to the bubble{close_quote}s motion. We show that, in the static case originally considered by Casimir [Proc. K. Ned. Akad. Nel. {bold 51}, 783 (1948)], we reproduce Casimir{close_quote}s result. In a simple purely time-dependent example, we find that an instability occurs and the pulse of radiation grows exponentially. In the more realistic case of spherically symmetric bubble motion, we again find exponential growth in the context of a small-radius approximation. {copyright} {ital 1999} {ital The American Physical Society}

Chodos, A. [Center for Theoretical Physics, Yale University, 217 Prospect Street, New Haven, Connecticut 06511-8167 (United States); Groff, S. [Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

1999-03-01

344

The IMACLIM model; Le modele IMACLIM  

Energy Technology Data Exchange (ETDEWEB)

This document provides annexes to the IMACLIM model which propose an actualized description of IMACLIM, model allowing the design of an evaluation tool of the greenhouse gases reduction policies. The model is described in a version coupled with the POLES, technical and economical model of the energy industry. Notations, equations, sources, processing and specifications are proposed and detailed. (A.L.B.)

NONE

2003-07-01

345

Time-constrained functional connectivity analysis of cortical networks underlying phonological decoding in typically developing school-aged children: a magnetoencephalography study.  

UK PubMed Central (United Kingdom)

The study investigated functional associations between left hemisphere occipitotemporal, temporoparietal, and inferior frontal regions during oral pseudoword reading in 58 school-aged children with typical reading skills (aged 10.4±1.6, range 7.5-12.5years). Event-related neuromagnetic data were used to compute source-current density waveforms using a minimum norm algorithm. Temporally-constrained contributions were established for four ROIs (STG, SMG, ANG, and IFG) by controlling for the autoregressive effects of activity in each ROI. Unique contributions made by activity in one ROI to subsequent activity in a second ROI were assessed through multiple regression analyses. Forward associations between lateral (LOC) and ventral occipitotemporal cortices (fusiform gyrus) to each of the four main ROIs were also examined. The earliest significant contributions to SMG and ANG activation (at 200-250ms) were made by preceding activity in the fusiform gyrus. The degree of activity in IFG appeared to be determined by earlier activity in ANG and STG.

Simos PG; Rezaie R; Fletcher JM; Papanicolaou AC

2013-05-01

346

Time-Constrained Functional Connectivity Analysis of Cortical Networks Underlying Phonological Decoding in Typically Developing School-Aged Children: A Magnetoencephalography Study  

Science.gov (United States)

The study investigated functional associations between left hemisphere occipitotemporal, temporoparietal, and inferior frontal regions during oral pseudoword reading in 58 school-aged children with typical reading skills (aged 10.4 [plus or minus] 1.6, range 7.5-12.5 years). Event-related neuromagnetic data were used to compute source-current…

Simos, Panagiotis G.; Rezaie, Roozbeh; Fletcher, Jack M.; Papanicolaou, Andrew C.

2013-01-01

347

Rotating universe models  

International Nuclear Information System (INIS)

A review is made of some properties of the rotating Universe models. Godel's model is identified as a generalized filted model. Some properties of new solutions of the Einstein's equations, which are rotating non-stationary Universe models, are presented and analyzed. These models have the Godel's model as a particular case. Non-stationary cosmological models are found which are a generalization of the Godel's metrics in an analogous way in which Friedmann is to the Einstein's model. (L.C.).

1984-01-01

348

Modeling natural gas reservoirs - a simple model  

Energy Technology Data Exchange (ETDEWEB)

A mathematical model is developed and tested for the production of natural gas with water encroachment and gas entrapment. The model is built on the material and volumetric balance relations, the Schilthuis water drive model, and a gas entrapment mechanism which assumes that the rate of gas entrapment is proportional to the volumetric rate of water influx. This model represents an alternative to the large grid models because of its low computer, maintenance, and manpower costs. 13 refs.

Collier, R.S.

1981-10-01

349

Weibull model selection for reliability modelling  

Energy Technology Data Exchange (ETDEWEB)

A large number of models have been derived from the two-parameter Weibull distribution and are referred to as Weibull models. They exhibit a wide range of shapes for the density and hazard functions, which makes them suitable for modelling complex failure data sets. The WPP and IWPP plot allows one to determine in a systematic manner if one or more of these models are suitable for modelling a given data set. This paper deals with this topic.

Prabhakar Murthy, D.N.; Bulmer, Michael; Eccleston, John A

2004-12-01

350

Weibull model selection for reliability modelling  

International Nuclear Information System (INIS)

A large number of models have been derived from the two-parameter Weibull distribution and are referred to as Weibull models. They exhibit a wide range of shapes for the density and hazard functions, which makes them suitable for modelling complex failure data sets. The WPP and IWPP plot allows one to determine in a systematic manner if one or more of these models are suitable for modelling a given data set. This paper deals with this topic

2004-01-01

351

Models of English text  

UK PubMed Central (United Kingdom)

The problem of constructing models of English text is considered. A number of applications of such models including cryptology, spelling correction and speech recognition are reviewed. The best current models of English text have been the result of research into compression. Not only is this an important application of such models but the amount of compression provides a measure of how well such models perform. Three main classes of models are considered: character based models, word based models, and models which use auxilary information in the form of parts of speech. These models are compared in terms of their memory usage and compression.

W. J. Teahan; John G. Cleary

352

Modeling Cholera Outbreaks.  

UK PubMed Central (United Kingdom)

Mathematical modeling can be a valuable tool for studying infectious disease outbreak dynamics and simulating the effects of possible interventions. Here, we describe approaches to modeling cholera outbreaks and how models have been applied to explore intervention strategies, particularly in Haiti. Mathematical models can play an important role in formulating and evaluating complex cholera outbreak response options. Major challenges to cholera modeling are insufficient data for calibrating models and the need to tailor models for different outbreak scenarios.

Chao DL; Longini IM Jr; Morris JG Jr

2013-02-01

353

Modeling, computation and optimization  

CERN Multimedia

This volume provides recent developments and a state-of-the-art review in various areas of mathematical modeling, computation and optimization. It contains theory, computation as well as the applications of several mathematical models to problems in statistics, games, optimization and economics for decision making. It focuses on exciting areas like models for wireless networks, models of Nash networks, dynamic models of advertising, application of reliability models in economics, support vector machines, optimization, complementarity modeling and games.

Neogy, S K

2009-01-01

354

Model selection for logistic regression models  

Science.gov (United States)

Model selection for logistic regression models decides which of some given potential regressors have an effect and hence should be included in the final model. The second interesting question is whether a certain factor is heterogeneous among some subsets, i.e. whether the model should include a random intercept or not. In this paper these questions will be answered with classical as well as with Bayesian methods. The application show some results of recent research projects in medicine and business administration.

Duller, Christine

2012-09-01

355

QSMSR QUALITATIVE MODEL  

Directory of Open Access Journals (Sweden)

Full Text Available Software architecture design and requirement engineering are core and independent areas of engineering. A lot of research, education and practice are carried on Requirement elicitation and doing refine it, but it is a major issue of engineering. QSMSR model act as a bridge between requirement and design there is a huge gap between these two areas of software architecture and requirement engineering. The QSMSR model divide into two sub model qualitative model and Principal model in this research we focus on Qualitative model which further divide into two sub models fabricated model and classified model. Classified model make the sub groups of the role and match it with components. The Fabricated model link QSMSR Principal Model to an architecture design. At the end it provides the QSMSR Architecture model of the system as output.

Shahbaz Nazeer; Tahir Abdullah

2012-01-01

356

Calogero Model(s) and Deformed Oscillators  

Directory of Open Access Journals (Sweden)

Full Text Available We briefly review some recent results concerning algebraical (oscillator) aspects of the N-body single-species and multispecies Calogero models in one dimension. We show how these models emerge from the matrix generalization of the harmonic oscillator Hamiltonian. We make some comments on the solvability of these models.

Marijan Milekovic; Stjepan Meljanac; Andjelo Samsarov

2006-01-01

357

China model: Energy modeling the modern dynasty  

Energy Technology Data Exchange (ETDEWEB)

In this paper a node-based microeconomic analysis is used to model the Chinese energy system. This model is run across multiple periods employing Lagrangian Relaxation techniques to achieve general equilibrium. Later, carbon dioxide emissions are added and the model is run to answer the question, {open_quotes}How can greenhouse gas emissions be reduced{close_quotes}?

Shaw, J.

1996-05-01

358

Sand-box modelling  

Energy Technology Data Exchange (ETDEWEB)

As the result of an enquiry into BHRA's physical-reservoir-modelling experience, the use of sand box models was investigated. The type of model was considered a possible means of confirmation of a numerical model. The problem facing the numerical model user was comparing the performance of inclined or horizontal oil wells with that of the conventional vertical well.

Avery, P.

1983-01-01

359

Bayesian Model Selection and Statistical Modeling  

CERN Document Server

Bayesian model selection is a fundamental part of the Bayesian statistical modeling process. The quality of these solutions usually depends on the goodness of the constructed Bayesian model. Realizing how crucial this issue is, many researchers and practitioners have been extensively investigating the Bayesian model selection problem. This book provides comprehensive explanations of the concepts and derivations of the Bayesian approach for model selection and related criteria, including the Bayes factor, the Bayesian information criterion (BIC), the generalized BIC, and the pseudo marginal lik

Ando, Tomohiro

2010-01-01

360

Object Models For Model Based Applications  

UK PubMed Central (United Kingdom)

In the enterprise information systems environment, web based systems in general, and e-commerceapplications in particular, are required to face a very high pace of change. The evolution of such systems iscaused both by adaptation to the customer needs and enterprise continuous improvement strategies. Suchrapid change can be achieved adopting a model-based approach in which the application is customizedaccording to a model. The concept of model proposed in this paper is more wide that the one adopted inmost modeling languages such as UML. We propose an object model that allows an application access themodel according to different perspectives and abstraction levels.

Giorgio Bruno; Marco Torchiano

 
 
 
 
361

Multivariate GARCH models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This article contains a review of multivariate GARCH models. Most common GARCH models are presented and their properties considered. This also includes semiparametric and nonparametric GARCH models. Existing specification and misspecification tests are discussed. Finally, there is an empirical examp...

Silvennoinen, Annastiina; Teräsvirta, Timo

362

Mathematics and Statistics Models  

Science.gov (United States)

Developed by Bob MacKay, Clark College. What are Mathematical and Statistical Models These types of models are obviously related, but there are also real differences between them. Mathematical Models: grow out of ...

363

Composite Linear Models  

Science.gov (United States)

Statistical Software Composite Linear Models (Written by Stuart G. Baker) The composite linear models software is a matrix approach to compute maximum likelihood estimates and asymptotic standard errors for models for incomplete multinomial data. It

364

Modelling Dependent Defaults  

UK PubMed Central (United Kingdom)

We consider the modelling of dependent defaults using latent variable models (theapproach that underlies KMV and CreditMetrics) and mixture models (the approachunderlying CreditRisk+). We explore the role of copulas in the latent variable frameworkand present results from a simulation study showing that even for xed assetcorrelation assumptions concerning the dependence of the latent variables can have alarge eect on the distribution of credit losses. We explore the eect of the tail of themixing-distribution for the tail of the credit-loss distributions. Finally, we discuss therelation between latent variable models and mixture models and provide general conditionsunder which these models can be mapped into each other. Our contribution canbe viewed as an analysis of the model risk associated with the modelling of dependencebetween credit losses.J.E.L. Subject Classication: G31, G11, C15Keywords: Portfolio Credit Risk Models, Model Risk, Dependence Modelling,Copulas, Mixture Models1

Alexander J. Mcneil; Eth Zentrum

365

Environmental Satellite Models for a Macroeconomic Model  

International Nuclear Information System (INIS)

To support national environmental policy, it is desirable to forecast and analyse environmental indicators consistently with economic variables. However, environmental indicators are physical measures linked to physical activities that are not specified in economic models. One way to deal with this is to develop environmental satellite models linked to economic models. The system of models presented gives a frame of reference where emissions of greenhouse gases, acid gases, and leaching of nutrients to the aquatic environment are analysed in line with - and consistently with - macroeconomic variables. This paper gives an overview of the data and the satellite models. Finally, the results of applying the model system to calculate the impacts on emissions and the economy are reviewed in a few illustrative examples. The models have been developed for Denmark; however, most of the environmental data used are from the CORINAIR system implemented in numerous countries.

2003-01-01

366

Mapping DEVS Models onto UML Models  

CERN Multimedia

Discrete event simulation specification (DEVS) is a formalism designed to describe both discrete state and continuous state systems. It is a powerful abstract mathematical notation. However, until recently it lacked proper graphical representation, which made computer simulation of DEVS models a challenging issue. Unified modeling language (UML) is a multipurpose graphical modeling language, a de-facto industrial modeling standard. There exist several commercial and open-source UML editors and code generators. Most of them can save UML models in XML-based XMI files ready for further automated processing. In this paper, we propose a mapping of DEVS models onto UML state and component diagrams. This mapping may lead to an eventual unification of the two modeling formalisms, combining the abstractness of DEVS and expressive power and ``computer friendliness'' of the UML.

Zinoviev, D

2005-01-01

367

Geologic Framework Model Analysis Model Report  

International Nuclear Information System (INIS)

The purpose of this report is to document the Geologic Framework Model (GFM), Version 3.1 (GFM3.1) with regard to data input, modeling methods, assumptions, uncertainties, limitations, and validation of the model results, qualification status of the model, and the differences between Version 3.1 and previous versions. The GFM represents a three-dimensional interpretation of the stratigraphy and structural features of the location of the potential Yucca Mountain radioactive waste repository. The GFM encompasses an area of 65 square miles (170 square kilometers) and a volume of 185 cubic miles (771 cubic kilometers). The boundaries of the GFM were chosen to encompass the most widely distributed set of exploratory boreholes (the Water Table or WT series) and to provide a geologic framework over the area of interest for hydrologic flow and radionuclide transport modeling through the unsaturated zone (UZ). The depth of the model is constrained by the inferred depth of the Tertiary-Paleozoic unconformity. The GFM was constructed from geologic map and borehole data. Additional information from measured stratigraphy sections, gravity profiles, and seismic profiles was also considered. This interim change notice (ICN) was prepared in accordance with the Technical Work Plan for the Integrated Site Model Process Model Report Revision 01 (CRWMS M and O 2000). The constraints, caveats, and limitations associated with this model are discussed in the appropriate text sections that follow. The GFM is one component of the Integrated Site Model (ISM) (Figure l), which has been developed to provide a consistent volumetric portrayal of the rock layers, rock properties, and mineralogy of the Yucca Mountain site. The ISM consists of three components: (1) Geologic Framework Model (GFM); (2) Rock Properties Model (RPM); and (3) Mineralogic Model (MM). The ISM merges the detailed project stratigraphy into model stratigraphic units that are most useful for the primary downstream models and the repository design. These downstream models include the hydrologic flow models and the radionuclide transport models. All the models and the repository design, in turn, will be incorporated into the Total System Performance Assessment (TSPA) of the potential radioactive waste repository block and vicinity to determine the suitability of Yucca Mountain as a host for the repository. The interrelationship of the three components of the ISM and their interface with downstream uses are illustrated in Figure 2.

2000-01-01

368

A Surficial Pronunciation Model  

UK PubMed Central (United Kingdom)

We argue for a surficial pronunciation model: a model without underlying forms. The surficial model outperforms a traditional generative model by a significant margin on conversational speech (Switchboard) as well as on read speech (TIMIT). Our results suggest that the true mapping from underlying forms to surface forms is too complex to be accurately modeled using current techniques, and that we would be best served to model the surface forms directly.

Eric Sven Ristad; Peter N. Yianilos

369

Modelling Food Webs  

CERN Multimedia

We review theoretical approaches to the understanding of food webs. After an overview of the available food web data, we discuss three different classes of models. The first class comprise static models, which assign links between species according to some simple rule. The second class are dynamical models, which include the population dynamics of several interacting species. We focus on the question of the stability of such webs. The third class are species assembly models and evolutionary models, which build webs starting from a few species by adding new species through a process of "invasion" (assembly models) or "speciation" (evolutionary models). Evolutionary models are found to be capable of building large stable webs.

Drossel, B

2002-01-01

370

Simplicity, Complexity and Modelling  

CERN Multimedia

Several points of disagreement exist between different modelling traditions as to whether complex models are always better than simpler models, as to how to combine results from different models and how to propagate model uncertainty into forecasts. This book represents the result of collaboration between scientists from many disciplines to show how these conflicts can be resolved. Key Features: Introduces important concepts in modelling, outlining different traditions in the use of simple and complex modelling in statistics. Provides numerous case studies on complex modelling, such as clima

Christie, Mike; Dawid, Philip; Senn, Stephen S

2011-01-01

371

QVT transformation by modelling - From UML Model to MD Model  

Directory of Open Access Journals (Sweden)

Full Text Available To provide a complete analysis of the organization, its business and its needs, it is necessary for leaders to have data that help decision making. Data warehouses are designed to meet such needs; they are an analysis and data management technology. This article describes an MDA (Model Driven Architecture) process that we have used to automatically generate the multidimensional schema of data warehouse. This process uses model transformation using several standards such as Unified Modeling Language, Meta-Object Facility, Query View Transformation, Object Constraint Language, ... From the UML model, especially the class diagram, a multidimensional model is generated as an XML file, the transformation is carried out by the QVT (Query View Transformation) language and the OCL (Object Constraint Language) Language. To validate our approach a case study is presented at the end of this work

I.Arrassen; A.Meziane; R.Sbai; M.Erramdani

2011-01-01

372

ROCK PROPERTIES MODEL ANALYSIS MODEL REPORT  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this Analysis and Model Report (AMR) is to document Rock Properties Model (RPM) 3.1 with regard to input data, model methods, assumptions, uncertainties and limitations of model results, and qualification status of the model. The report also documents the differences between the current and previous versions and validation of the model. The rock properties models are intended principally for use as input to numerical physical-process modeling, such as of ground-water flow and/or radionuclide transport. The constraints, caveats, and limitations associated with this model are discussed in the appropriate text sections that follow. This work was conducted in accordance with the following planning documents: WA-0344, ''3-D Rock Properties Modeling for FY 1998'' (SNL 1997, WA-0358), ''3-D Rock Properties Modeling for FY 1999'' (SNL 1999), and the technical development plan, Rock Properties Model Version 3.1, (CRWMS M&O 1999c). The Interim Change Notice (ICNs), ICN 02 and ICN 03, of this AMR were prepared as part of activities being conducted under the Technical Work Plan, TWP-NBS-GS-000003, ''Technical Work Plan for the Integrated Site Model, Process Model Report, Revision 01'' (CRWMS M&O 2000b). The purpose of ICN 03 is to record changes in data input status due to data qualification and verification activities. These work plans describe the scope, objectives, tasks, methodology, and implementing procedures for model construction. The constraints, caveats, and limitations associated with this model are discussed in the appropriate text sections that follow. The work scope for this activity consists of the following: (1) Conversion of the input data (laboratory measured porosity data, x-ray diffraction mineralogy, petrophysical calculations of bound water, and petrophysical calculations of porosity) for each borehole into stratigraphic coordinates; (2) Re-sampling and merging of data sets; (3) Development of geostatistical simulations of porosity; (4) Generation of derivative property models via linear coregionalization with porosity; (5) Post-processing of the simulated models to impart desired secondary geologic attributes and to create summary and uncertainty models; and (6) Conversion of the models into real-world coordinates. The conversion to real world coordinates is performed as part of the integration of the RPM into the Integrated Site Model (ISM) 3.1; this activity is not part of the current analysis. The ISM provides a consistent volumetric portrayal of the rock layers, rock properties, and mineralogy of the Yucca Mountain site and consists of three components: (1) Geologic Framework Model (GFM); (2) RPM, which is the subject of this AMR; and (3) Mineralogic Model. The interrelationship of the three components of the ISM and their interface with downstream uses are illustrated in Figure 1. Figure 2 shows the geographic boundaries of the RPM and other component models of the ISM.

Clinton Lum

2002-02-04

373

Integrated Site Model Process Model Report  

International Nuclear Information System (INIS)

The Integrated Site Model (ISM) provides a framework for discussing the geologic features and properties of Yucca Mountain, which is being evaluated as a potential site for a geologic repository for the disposal of nuclear waste. The ISM is important to the evaluation of the site because it provides 3-D portrayals of site geologic, rock property, and mineralogic characteristics and their spatial variabilities. The ISM is not a single discrete model; rather, it is a set of static representations that provide three-dimensional (3-D), computer representations of site geology, selected hydrologic and rock properties, and mineralogic-characteristics data. These representations are manifested in three separate model components of the ISM: the Geologic Framework Model (GFM), the Rock Properties Model (RPM), and the Mineralogic Model (MM). The GFM provides a representation of the 3-D stratigraphy and geologic structure. Based on the framework provided by the GFM, the RPM and MM provide spatial simulations of the rock and hydrologic properties, and mineralogy, respectively. Functional summaries of the component models and their respective output are provided in Section 1.4. Each of the component models of the ISM considers different specific aspects of the site geologic setting. Each model was developed using unique methodologies and inputs, and the determination of the modeled units for each of the components is dependent on the requirements of that component. Therefore, while the ISM represents the integration of the rock properties and mineralogy into a geologic framework, the discussion of ISM construction and results is most appropriately presented in terms of the three separate components. This Process Model Report (PMR) summarizes the individual component models of the ISM (the GFM, RPM, and MM) and describes how the three components are constructed and combined to form the ISM

2000-01-01

374

Modelling Holocene climate trends: A model intercomparison  

Science.gov (United States)

For the paleomodel intercomparison, we compared the results from scenarios with identical forcing for the mid-to-late Holocene period: varying Earth's orbital parameters, fixed level of greenhouse gas concentrations, fixed land-sea mask and orography. 18 paleoclimate modelling groups are involved in this initiative, working on transient Holocene simulations. One major issue of both the modelling and reconstruction side were the quantification of uncertainties, and the evaluation of trend and variability patterns beyond a single proxy and beyond a single model simulation. The goal is to obtain robust results of trend patterns, seasonality changes, as well as transitions on a regional scale. The major objective is to investigate the spatio-temporal pattern of temperature and precipitation changes during Holocene as derived from integrations with a set comprehensive global climate models (GCMs), Earth system models of intermediate complexity (EMICs), as well as conceptual-statistical models. In the conceptual-statistical model by Laepple and Lohmann (2009) a rigorous simple concept is proposed: The temperature response on astronomical timescales has the same function as the response to seasonal insolation variations. The general pattern of surface temperatures in the models shows a high latitude cooling and a low latitude warming. Our analysis shows common patterns of temperature changes, especially for the respective summer seasons. This is a common feature for all model considered. Due to strong differences in atmospheric dynamics and sea ice, we find significant differences in the winter patterns. The precipitation trends show a clear difference between GCMs and EMICs mainly because the treatment of the hydological cycle in the tropics. Most models show a southward movement of the ITCZ. Using statistical analysis of the model variability modes and their amplitude during the Holocene, we reveal a strong heterogeneity in temperature and precipitation pattern and no common response in trend and variability, although a tendency towards NAO- and SOI- (El Nino-like) is detected. Our approach is to obtain, through ensemble runs for climate model output, a range of solutions that can be then compared and evaluated for their consistency with the range of uncertainty given by the palaeoclimate proxies. This approach allows a much more congruent way of comparison between proxy data and model result because both investigations will provide a range of possible climate change where the errors in the estimates are accounted for. We compare the ocean temperature evolution of the Holocene as simulated by climate models and reconstructed from marine temperature proxies. Independently of the choice of the climate model, we observe significant mismatches between modelled and reconstructed amplitudes in the trends for the last 6000 years.

Lohmann, Gerrit

2013-04-01

375

Objective Bayes model selection in probit models.  

UK PubMed Central (United Kingdom)

We describe a new variable selection procedure for categorical responses where the candidate models are all probit regression models. The procedure uses objective intrinsic priors for the model parameters, which do not depend on tuning parameters, and ranks the models for the different subsets of covariates according to their model posterior probabilities. When the number of covariates is moderate or large, the number of potential models can be very large, and for those cases, we derive a new stochastic search algorithm that explores the potential sets of models driven by their model posterior probabilities. The algorithm allows the user to control the dimension of the candidate models and thus can handle situations when the number of covariates exceed the number of observations. We assess, through simulations, the performance of the procedure and apply the variable selector to a gene expression data set, where the response is whether a patient exhibits pneumonia. Software needed to run the procedures is available in the R package varselectIP.

Leon-Novelo L; Moreno E; Casella G

2012-02-01

376

Biosphere Model Report  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this report is to document the biosphere model, the Environmental Radiation Model for Yucca Mountain, Nevada (ERMYN), which describes radionuclide transport processes in the biosphere and associated human exposure that may arise as the result of radionuclide release from the geologic repository at Yucca Mountain. The biosphere model is one of the process models that support the Yucca Mountain Project (YMP) Total System Performance Assessment (TSPA) for the license application (LA), the TSPA-LA. The ERMYN model provides the capability of performing human radiation dose assessments. This report documents the biosphere model, which includes: (1) Describing the reference biosphere, human receptor, exposure scenarios, and primary radionuclides for each exposure scenario (Section 6.1); (2) Developing a biosphere conceptual model using site-specific features, events, and processes (FEPs), the reference biosphere, the human receptor, and assumptions (Section 6.2 and Section 6.3); (3) Building a mathematical model using the biosphere conceptual model and published biosphere models (Sections 6.4 and 6.5); (4) Summarizing input parameters for the mathematical model, including the uncertainty associated with input values (Section 6.6); (5) Identifying improvements in the ERMYN model compared with the model used in previous biosphere modeling (Section 6.7); (6) Constructing an ERMYN implementation tool (model) based on the biosphere mathematical model using GoldSim stochastic simulation software (Sections 6.8 and 6.9); (7) Verifying the ERMYN model by comparing output from the software with hand calculations to ensure that the GoldSim implementation is correct (Section 6.10); and (8) Validating the ERMYN model by corroborating it with published biosphere models; comparing conceptual models, mathematical models, and numerical results (Section 7).

M. A. Wasiolek

2003-10-27

377

Biosphere Model Report  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this report is to document the biosphere model, the Environmental Radiation Model for Yucca Mountain, Nevada (ERMYN), which describes radionuclide transport processes in the biosphere and associated human exposure that may arise as the result of radionuclide release from the geologic repository at Yucca Mountain. The biosphere model is one of the process models that support the Yucca Mountain Project (YMP) Total System Performance Assessment (TSPA) for the license application (LA), the TSPA-LA. The ERMYN model provides the capability of performing human radiation dose assessments. This report documents the biosphere model, which includes: (1) Describing the reference biosphere, human receptor, exposure scenarios, and primary radionuclides for each exposure scenario (Section 6.1); (2) Developing a biosphere conceptual model using site-specific features, events, and processes (FEPs), the reference biosphere, the human receptor, and assumptions (Section 6.2 and Section 6.3); (3) Building a mathematical model using the biosphere conceptual model and published biosphere models (Sections 6.4 and 6.5); (4) Summarizing input parameters for the mathematical model, including the uncertainty associated with input values (Section 6.6); (5) Identifying improvements in the ERMYN model compared with the model used in previous biosphere modeling (Section 6.7); (6) Constructing an ERMYN implementation tool (model) based on the biosphere mathematical model using GoldSim stochastic simulation software (Sections 6.8 and 6.9); (7) Verifying the ERMYN model by comparing output from the software with hand calculations to ensure that the GoldSim implementation is correct (Section 6.10); and (8) Validating the ERMYN model by corroborating it with published biosphere models; comparing conceptual models, mathematical models, and numerical results (Section 7).

D. W. Wu

2003-07-16

378

Dynamical Dirichlet Mixture Model  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this report, we propose a statistical model to deal with the discrete-distribution data varying over time. The proposed model -- HMM+DM -- extends the Dirichlet mixture model to the dynamic case: Hidden Markov Model with Dirichlet mixture output. Both the inference and parameter estimation proced...

Chen, Le; Barber, David; Odobez, Jean-Marc

379

On Multiobjective Evolution Model  

CERN Multimedia

Self-Organized Criticality (SOC) phenomena could have a significant effect on the dynamics of ecosystems. The Bak-Sneppen (BS) model is a simple and robust model of biological evolution that exhibits punctuated equilibrium behavior. Here we will introduce random version of BS model. Also we generalize the single objective BS model to a multiobjective one.

Ahmed, E

2004-01-01

380

Wastewater Treatment Models  

DEFF Research Database (Denmark)

The state-of-the-art level reached in modeling wastewater treatment plants (WWTPs) is reported. For suspended growth systems, WWTP models have evolved from simple description of biological removal of organic carbon and nitrogen in aeration tanks (ASM1 in 1987) to more advanced levels including description of biological phosphorus removal, physical–chemical processes, hydraulics, and settling tanks. For attached growth systems, biofilm models have progressed from analytical steady-state models to more complex 2-D/3-D dynamic numerical models. Plant-wide modeling is set to advance further the practice of WWTP modeling by linking the wastewater treatment line with the sludge handling line in one modeling platform. Application of WWTP models is currently rather time consuming and thus expensive due to the high model complexity, and requires a great deal of process knowledge and modeling expertise. Efficient and good modeling practice therefore requires the use of a proper set of guidelines, thus grounding the modeling studies on a general and systematic framework. Last but not least, general limitations of WWTP models – more specifically, activated sludge models – are introduced since these define a boundary of validity for WWTP model applications.

Gernaey, Krist; Sin, Gürkan

2008-01-01

 
 
 
 
381

The Model Confidence Set  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper introduces the model confidence set (MCS) and applies it to the selection of models. A MCS is a set of models that is constructed such that it will contain the best model with a given level of confidence. The MCS is in this sense analogous to a confidence interval for a parameter. The MCS ...

Hansen, Peter Reinhard; Lunde, Asger; Nason, James M.

382

Review of nonstandard models  

International Nuclear Information System (INIS)

After making the distinction between a solar-mass model and a model sun and commenting briefly on the way errors are handled in calculations, a description is given of some of the attempts that were made in the past ten years or so to produce solar models with low neutrino fluxes. These include a wide variety of models. 55 references.

1978-01-07

383

Modeling obsessive compulsive disorder.  

UK PubMed Central (United Kingdom)

A preliminary computational model for obsessive compulsive disorder is developed using neuro-circuitry information and systems biology principles. The model captures the salient features of the neuro-psychiatric disorder reported in the literature. Studies are on-going to model in more detail both the intra-cellular and extra-cellular features of the model, within the framework proposed.

Cline CH; Nair SS; Xu D; Nair J; Beitman B

2004-01-01

384

Multivariate GARCH models  

DEFF Research Database (Denmark)

This article contains a review of multivariate GARCH models. Most common GARCH models are presented and their properties considered. This also includes nonparametric and semiparametric models. Existing specification and misspecification tests are discussed. Finally, there is an empirical example in which several multivariate GARCH models are fitted to the same data set and the results compared.

Silvennoinen, Annastiina; Teräsvirta, Timo

2008-01-01

385

Conceptual Model for Communication  

CERN Multimedia

A variety of idealized models of communication systems exist, and all may have something in common. Starting with Shannons communication model and ending with the OSI model, this paper presents progressively more advanced forms of modeling of communication systems by tying communication models together based on the notion of flow. The basic communication process is divided into different spheres (sources, channels, and destinations), each with its own five interior stages, receiving, processing, creating, releasing, and transferring of information. The flow of information is ontologically distinguished from the flow of physical signals, accordingly, Shannons model, network based OSI models, and TCP IP are redesigned.

Fedaghi, Sabah Al; Fadel, Zahraa

2009-01-01

386

Calibrated Properties Model  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this Analysis/Model Report (AMR) is to document the Calibrated Properties Model that provides calibrated parameter sets for unsaturated zone (UZ) flow and transport process models for the Yucca Mountain Site Characterization Project (YMP). This work was performed in accordance with the AMR Development Plan for U0035 Calibrated Properties Model REV00 (CRWMS M&O 1999c). These calibrated property sets include matrix and fracture parameters for the UZ Flow and Transport Model (UZ Model), drift seepage models, drift-scale and mountain-scale coupled-processes models, and Total System Performance Assessment (TSPA) models as well as Performance Assessment (PA) and other participating national laboratories and government agencies. These process models provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic and thermal-loading conditions.

C.F. Ahlers, H.H. Liu

2001-12-18

387

Calibrated Properties Model  

International Nuclear Information System (INIS)

The purpose of this Analysis/Model Report (AMR) is to document the Calibrated Properties Model that provides calibrated parameter sets for unsaturated zone (UZ) flow and transport process models for the Yucca Mountain Site Characterization Project (YMP). This work was performed in accordance with the AMR Development Plan for U0035 Calibrated Properties Model REV00 (CRWMS M and O 1999c). These calibrated property sets include matrix and fracture parameters for the UZ Flow and Transport Model (UZ Model), drift seepage models, drift-scale and mountain-scale coupled-processes models, and Total System Performance Assessment (TSPA) models as well as Performance Assessment (PA) and other participating national laboratories and government agencies. These process models provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic and thermal-loading conditions.

2001-01-01

388

Calibrated Properties Model  

International Nuclear Information System (INIS)

The purpose of this Analysis/Model Report (AMR) is to document the Calibrated Properties Model that provides calibrated parameter sets for unsaturated zone (UZ) flow and transport process models for the Yucca Mountain Site Characterization Project (YMP). This work was performed in accordance with the ''AMR Development Plan for U0035 Calibrated Properties Model REV00. These calibrated property sets include matrix and fracture parameters for the UZ Flow and Transport Model (UZ Model), drift seepage models, drift-scale and mountain-scale coupled-processes models, and Total System Performance Assessment (TSPA) models as well as Performance Assessment (PA) and other participating national laboratories and government agencies. These process models provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic and thermal-loading conditions.

2000-01-01

389

Discrete chain graph models  

CERN Document Server

The statistical literature discusses different types of Markov properties for chain graphs that lead to four possible classes of chain graph Markov models. The different models are rather well understood when the observations are continuous and multivariate normal, and it is also known that one model class, referred to as models of LWF (Lauritzen--Wermuth--Frydenberg) or block concentration type, yields discrete models for categorical data that are smooth. This paper considers the structural properties of the discrete models based on the three alternative Markov properties. It is shown by example that two of the alternative Markov properties can lead to non-smooth models. The remaining model class, which can be viewed as a discrete version of multivariate regressions, is proven to comprise only smooth models. The proof employs a simple change of coordinates that also reveals that the model's likelihood function is unimodal if the chain components of the graph are complete sets.

Drton, Mathias

2009-01-01

390

Protein Models Comparator  

CERN Multimedia

The process of comparison of computer generated protein structural models is an important element of protein structure prediction. It has many uses including model quality evaluation, selection of the final models from a large set of candidates or optimisation of parameters of energy functions used in template free modelling and refinement. Although many protein comparison methods are available online on numerous web servers, their ability to handle a large scale model comparison is often very limited. Most of the servers offer only a single pairwise structural comparison, and they usually do not provide a model-specific comparison with a fixed alignment between the models. To bridge the gap between the protein and model structure comparison we have developed the Protein Models Comparator (pm-cmp). To be able to deliver the scalability on demand and handle large comparison experiments the pm-cmp was implemented "in the cloud". Protein Models Comparator is a scalable web application for a fast distributed comp...

Widera, Pawe?

2011-01-01

391

Lumped Thermal Household Model  

DEFF Research Database (Denmark)

In this paper we discuss two different approaches to model the flexible power consumption of heat pump heated households: individual household modeling and lumped modeling. We illustrate that a benefit of individual modeling is that we can overview and optimize the complete flexibility of a heat pump portfolio. Following, we illustrate two disadvantages of individual models, namely that it requires much computational effort to optimize over a large portfolio, and second that it is difficult to accurately model the houses in certain time periods due to local disturbances. Finally, we propose a lumped model approach as an alternative to the individual models. In the lumped model, the portfolio is seen as baseline consumption superimposed with an ideal storage of limited power and energy capacity. The benefit of such a lumped model is that the computational effort of flexibility optimization is significantly reduced. Further, the individual disturbances will smooth out as the number of houses in the portfolio increases.

Biegel, Benjamin; Andersen, Palle

2013-01-01

392

Knowledge and information modeling.  

UK PubMed Central (United Kingdom)

This chapter gives an educational overview of: * commonly used modelling methods what they represent * the importance of selecting the tools and methods suited to the health information system being designed * how the quality of the information or knowledge model is determined by the quality of the system requirements specification * differentiating between the purpose of information models and knowledge models * the benefits of the openEHR approach for health care data modeling.

Madsen M

2010-01-01

393

CISNET: Comparative Modeling  

Science.gov (United States)

Independent modeling efforts often yield disparate results that are difficult to reconcile. A comparative modeling approach explores differences between models in a systematic way. In joint collaborations, a set of common population inputs is shared across all models (e.g., dissemination patterns of screening and treatment, mortality from non-cancer causes), and common sets of intermediate and final outputs are developed. Results are then compared across models.

394