WorldWideScience
 
 
1

MEG (Magnetoencephalography) multipolar modeling of distributed sources using RAP-MUSIC (Recursively Applied and Projected Multiple Signal Characterization)  

Energy Technology Data Exchange (ETDEWEB)

We describe the use of truncated multipolar expansions for producing dynamic images of cortical neural activation from measurements of the magnetoencephalogram. We use a signal-subspace method to find the locations of a set of multipolar sources, each of which represents a region of activity in the cerebral cortex. Our method builds up an estimate of the sources in a recursive manner, i.e. we first search for point current dipoles, then magnetic dipoles, and finally first order multipoles. The dynamic behavior of these sources is then computed using a linear fit to the spatiotemporal data. The final step in the procedure is to map each of the multipolar sources into an equivalent distributed source on the cortical surface. The method is illustrated through an application to epileptic interictal MEG data.

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

2001-01-01

2

On MEG forward modelling using multipolar expansions  

International Nuclear Information System (INIS)

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 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)

3

Magnetoencephalography  

International Nuclear Information System (INIS)

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.)

4

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

5

Optical Photometry of BY Cam Modeled Using a Multipolar Magnetic Field Structure  

Science.gov (United States)

We present new high-speed broad-band optical photometry of the asynchronous polar (magnetic cataclysmic variable) BY Cam. Observations were obtained at the 2.1-m Otto Struve Telescope of McDonald observatory with 3s integration times. In an attempt to understand the complex changes in accretion flow geometry, we performed full 3D MHD simulations assuming a variety of white dwarf magnetic field structures including both aligned and non-aligned dipole plus quadrupole field components. We compare model predictions with photometry and various phases of the beat cycle and find that synthetic light curves derived from a multipolar field structure are consistent with the optical photometry.

Morales, John; Mason, P. A.; Zhilkin, A.; Bisikalo, D. V.; Robinson, E. L.

2014-01-01

6

A study on decoding models for the reconstruction of hand trajectories from the human magnetoencephalography.  

Science.gov (United States)

Decoding neural signals into control outputs has been a key to the development of brain-computer interfaces (BCIs). While many studies have identified neural correlates of kinematics or applied advanced machine learning algorithms to improve decoding performance, relatively less attention has been paid to optimal design of decoding models. For generating continuous movements from neural activity, design of decoding models should address how to incorporate movement dynamics into models and how to select a model given specific BCI objectives. Considering nonlinear and independent speed characteristics, we propose a hybrid Kalman filter to decode the hand direction and speed independently. We also investigate changes in performance of different decoding models (the linear and Kalman filters) when they predict reaching movements only or predict both reach and rest. Our offline study on human magnetoencephalography (MEG) during point-to-point arm movements shows that the performance of the linear filter or the Kalman filter is affected by including resting states for training and predicting movements. However, the hybrid Kalman filter consistently outperforms others regardless of movement states. The results demonstrate that better design of decoding models is achieved by incorporating movement dynamics into modeling or selecting a model according to decoding objectives. PMID:25050324

Yeom, Hong Gi; Hong, Wonjun; Kang, Da-Yoon; Chung, Chun Kee; Kim, June Sic; Kim, Sung-Phil

2014-01-01

7

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

8

Libration driven multipolar instabilities  

CERN Document Server

We consider rotating flows in non-axisymmetric enclosures that are driven by libration, i.e. by a small periodic modulation of the rotation rate. Thanks to its simplicity, this model is relevant to various contexts, from industrial containers (with small oscillations of the rotation rate) to fluid layers of terrestial planets (with length-of-day variations). Assuming a multipolar $n$-fold boundary deformation, we first obtain the two-dimensional basic flow. We then perform a short-wavelength local stability analysis of the basic flow, showing that an instability may occur in three dimensions. We christen it the Libration Driven Multipolar Instability (LDMI). The growth rates of the LDMI are computed by a Floquet analysis in a systematic way, and compared to analytical expressions obtained by perturbation methods. We then focus on the simplest geometry allowing the LDMI, a librating deformed cylinder. To take into account viscous and confinement effects, we perform a global stability analysis, which shows that...

Cébron, David; Herreman, Wietze

2014-01-01

9

Comparison of three-shell and simplified volume conductor models in magnetoencephalography.  

Science.gov (United States)

Experimental MEG source imaging studies have typically been carried out with either a spherically symmetric head model or a single-shell boundary-element (BEM) model that is shaped according to the inner skull surface. The concepts and comparisons behind these simplified models have led to misunderstandings regarding the role of skull and scalp in MEG. In this work, we assess the forward-model errors due to different skull/scalp approximations and due to differences and errors in model geometries. We built five anatomical models of a volunteer using a set of T1-weighted MR scans and three common toolboxes. Three of the models represented typical models in experimental MEG, one was manually constructed, and one contained a major segmentation error at the skull base. For these anatomical models, we built forward models using four simplified approaches and a three-shell BEM approach that has been used as reference in previous studies. Our reference model contained in addition the skull fine-structure (spongy bone). We computed signal topographies for cortically constrained sources in the left hemisphere and compared the topographies using relative error and correlation metrics. The results show that the spongy bone has a minimal effect on MEG topographies, and thus the skull approximation of the three-shell model is justified. The three-shell model performed best, followed by the corrected-sphere and single-shell models, whereas the local-spheres and single-sphere models were clearly worse. The three-shell model was the most robust against the introduced segmentation error. In contrast to earlier claims, there was no noteworthy difference in the computation times between the realistically-shaped and sphere-based models, and the manual effort of building a three-shell model and a simplified model is comparable. We thus recommend the realistically-shaped three-shell model for experimental MEG work. In cases where this is not possible, we recommend a realistically-shaped corrected-sphere or single-shell model. PMID:24434678

Stenroos, Matti; Hunold, Alexander; Haueisen, Jens

2014-07-01

10

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

Science.gov (United States)

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). PMID:23720381

Kandathil, Shaun M; Fletcher, Timothy L; Yuan, Yongna; Knowles, Joshua; Popelier, Paul L A

2013-08-01

11

Magnetoencephalography: Basic principles.  

Science.gov (United States)

Magnetoencephalography (MEG) is the measurement of the magnetic field generated by the electrical activity of neurons. It is usually combined with a magnetic resonance imaging to get what is called magnetic source imaging. The technology that has helped record these minute magnetic fields is super-conducting quantum interference detector which is like a highly sensitive magnetic field meter. To attenuate the external magnetic noise the MEG is housed inside a magnetically shielded room. The actual sensors recording magnetic fields are magnetometers and/or gradiometers. MEG fields pass through the head without any distortion. This is a significant advantage of MEG over electroencephalography. MEG provides a high spatial and temporal resolution. The recording and identification information should be according to the American Clinical Magnetoencephalography Society guidelines published in 2011. MEG currently has two approved indications in the United States, one is for pre-operative brain mapping and the other is for use in epilepsy surgery. MEG studies have shown functional brain tissue inside brain tumors. PMID:24791076

Singh, Sanjay P

2014-03-01

12

The scalar magnetic potential in magnetoencephalography  

Energy Technology Data Exchange (ETDEWEB)

Two results on Magnetoencephalography (MEG) are reported in this presentation. First, we present an integral formula connecting the scalar magnetic potential with the values of the electric potential on the boundary of a conductive region. This formula provides the magnetic potential analogue of the well known Geselowitz formula. Second, we construct the scalar magnetic potential for the realistic ellipsoidal model of the brain, as an eigenfunction expansion in terms of surface ellipsoidal harmonics.

Dassios, G [Department of Applied Mathematics and Theoretical Physics University of Cambridge, Cambridge (United Kingdom)], E-mail: G.Dassios@damtp.cam.ac.uk

2008-07-15

13

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

14

Magnetoencephalography in pediatric epilepsy  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetoencephalography (MEG records the magnetic field generated by electrical activity of cortical neurons. The signal is not distorted or attenuated, and it is contactless recording that can be performed comfortably even for longer than an hour. It has excellent and decent temporal resolution, especially when it is combined with the patient’s own brain magnetic resonance imaging (magnetic source imaging. Data of MEG and electroencephalography are not mutually exclusive and it is recorded simultaneously and interpreted together. MEG has been shown to be useful in detecting the irritative zone in both lesional and nonlesional epilepsy surgery. It has provided valuable and additive information regarding the lesion that should be resected in epilepsy surgery. Better outcomes in epilepsy surgery were related to the localization of the irritative zone with MEG. The value of MEG in epilepsy surgery is recruiting more patients to epilepsy surgery and providing critical information for surgical planning. MEG cortical mapping is helpful in younger pediatric patients, especially when the epileptogenic zone is close to the eloquent cortex. MEG is also used in both basic and clinical research of epilepsy other than surgery. MEG is a valuable diagnostic modality for diagnosis and treatment, as well as research in epilepsy.

Hunmin Kim

2013-10-01

15

Progress in magneto-encephalography; Les progres de la magnetoencephalographie  

Energy Technology Data Exchange (ETDEWEB)

Researchers looking for a higher temporal resolution of cognitive functions are turning to magneto-encephalography (MEG) as an extension to MRI. Progress made in MEG imaging, especially in terms of the sensors employed, is opening up a broader range of applications. (authors)

Dehaene, St. [CEA Saclay, Institut d' Imagerie Biomedicale - NeuroSpin, Dir. des Sciences du Vivant, 91 - Gif-sur-Yvette (France); Fermon, C. [CEA Saclay, Direction des Sciences de la Matiere, 91 - Gif-sur-Yvette (France)

2008-07-01

16

Multiprocessors for multipolar responses  

International Nuclear Information System (INIS)

For the first time, a complete microscopic simulation has allowed us to predict the multipolar responses of U238. This simulation is based on the QRPA (Quasiparticle Random Phase Approximation) approach that is an extension of the RPA approach developed in the seventies. The random phase approximation allowed the description of the collective excitations of the nucleus as coherent states of the excitations of particle-hole pairs. In the seventies RPA was limited to spherical symmetry without taking into account pairing effects. Now the power of computers has enabled RPA to deal with axial symmetry and to use the concept of quasiparticle (the quasiparticle can be both particle and hole) that is particularly well adapted for the processing of pair correlations. (A.C.)

17

Progress in magneto-encephalography  

International Nuclear Information System (INIS)

Researchers looking for a higher temporal resolution of cognitive functions are turning to magneto-encephalography (MEG) as an extension to MRI. Progress made in MEG imaging, especially in terms of the sensors employed, is opening up a broader range of applications. (authors)

18

MULTIPOLAR PLANETARY NEBULAE: NOT AS GEOMETRICALLY DIVERSIFIED AS THOUGHT  

Energy Technology Data Exchange (ETDEWEB)

Planetary nebulae (PNe) have diverse morphological shapes, including point-symmetric and multipolar structures. Many PNe also have complicated internal structures such as tori, lobes, knots, and ansae. A complete accounting of all the morphological structures through physical models is difficult. A first step toward such an understanding is to derive the true three-dimensional structure of the nebulae. In this paper, we show that a multipolar nebula with three pairs of lobes can explain many such features, if orientation and sensitivity effects are taken into account. Using only six parameters-the inclination and position angles of each pair-we are able to simulate the observed images of 20 PNe with complex structures. We suggest that multipolar structure is an intrinsic structure of PNe and the statistics of multipolar PNe have been severely underestimated in the past.

Chong, S.-N.; Imai, H.; Chibueze, J. [Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan); Kwok, Sun [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Tafoya, D., E-mail: chongsnco@gmail.com, E-mail: sunkwok@hku.hk [Onsala Space Observatory, SE-439 92 Onsala (Sweden)

2012-12-01

19

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

20

Strategies for Business Schools in a Multi-Polar World  

Science.gov (United States)

Purpose: The purpose of this paper is to examine the contours of the emerging business education and institutions in a multi-polar world and to identify the causes of the strategic convergence of management education, to explore the limitations of the dominant models of management education and to propose a range of strategic alternatives for…

Dameron, Stephanie; Durand, Thomas

2013-01-01

 
 
 
 
21

Multi-sensor magnetoencephalography with atomic magnetometers  

International Nuclear Information System (INIS)

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. (paper)

22

Multi-sensor magnetoencephalography with atomic magnetometers.  

Science.gov (United States)

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. PMID:23939051

Johnson, Cort N; Schwindt, P D D; Weisend, M

2013-09-01

23

Lithologic mapping in a sedimentary environment using multipolarization SAR images  

Science.gov (United States)

Multipolarization Synthetic Aperture Radar (SAR) data from the NASA/JPL aircraft SAR were used in conjunction with LANDSAT Thematic Mapper (TM), Thermal Infrared Multispectral Scanner (TIMS), and Airborne Imaging Spectrometer (AIS) data as part of a three-year research program to evaluate the utility of remote sensing measurements for analysis of sedimentary basins. The purpose of this research effort is to construct stratigraphic columns, map variations in the lithology, geometry, and structure of sedimentary rocks in the Wind River/Bighorn Basin area, Wyoming, and to integrate remote sensing data with conventional rain models of basin formation and evolution.

Evans, D. L.; Schenck, L. R.

1985-01-01

24

Multipolar x-ray diffraction study of the canted magnetic structure of TbMg  

International Nuclear Information System (INIS)

Earlier neutron powder diffraction measurements on the CsCl compound TbMg showed that a canted magnetic structure is stabilized at T=4.2 K. This structure mixes ferromagnetic and antiferromagnetic, , components. Accounting for the anisotropy, several consistent models of structures could be proposed. In order to identify the best one, we performed x-ray diffraction measurements on a single crystal. A set of charge satellites originating from multipolar 4f scattering and related to the wavevectors were observed. Analysing the experimental data, within the framework recently proposed for multipolar scattering in cubic systems, a model is selected for the magnetic structure of TbMg. (author)

25

Softened potentials and the multipolar expansion  

Directory of Open Access Journals (Sweden)

Full Text Available Cuando se calcula el desarrollo multipolar del potencial gravitatorio, los distintos multipolos quedan bien definidos, correspondiendo cada uno a una suma finita de términos de la serie. Sin embargo, al usar el potencial gravitatorio en simulaciones numéricas, suele desarrollarse en serie una versión suavizada del mismo. Ocurre que, en estos casos, el desarrollo multipolar estándar que suele utilizarse ya no aísla los multipolos, sino que cada uno de ellos queda distribuido en infinitos términos. En este artículo se muestra cómo recuperar los multipolos completos en estos casos. Afortunadamente, la diferencia entre usar multipolos incompletos y completos es despreciable en los casos de interés, por ejemplo, en su uso en códigos árbol.

Felipe C. Wachlin

2006-01-01

26

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

27

Magnetoencephalography from signals to dynamic cortical networks  

CERN Document Server

"Magnetoencephalography (MEG) provides a time-accurate view into human brain function. The concerted action of neurons generates minute magnetic fields that can be detected---totally noninvasively---by sensitive multichannel magnetometers. The obtained millisecond accuracycomplements information obtained by other modern brain-imaging tools. Accurate timing is quintessential in normal brain function, often distorted in brain disorders. The noninvasiveness and time-sensitivityof MEG are great assets to developmental studies, as well. This multiauthored book covers an ambitiously wide range of MEG research from introductory to advanced level, from sensors to signals, and from focal sources to the dynamics of cortical networks. Written by active practioners of this multidisciplinary field, the book contains tutorials for newcomers and chapters of new challenging methods and emerging technologies to advanced MEG users. The reader will obtain a firm grasp of the possibilities of MEG in the study of audition, vision...

Aine, Cheryl

2014-01-01

28

NQR investigation on multipolar ordering systems  

International Nuclear Information System (INIS)

We have carried out nuclear quadrupolar resonance (NQR) measurements on SmRu4P12 and YbAl3C3, both of which have attracted much interest in terms of multipolar ordering. Although no structural anomalies have been detected by diffraction experiments so far, the NQR resonance frequencies ?Q's of both compounds show marked anomalies just below each phase transition temperature, which probably probes the order parameters. The results provide important information to shed light on the ordered structures in the low temperature phases of these compounds

29

Magnetoencephalography in stroke: a 1-year follow-up study.  

Science.gov (United States)

Recovery after stroke is closely linked to cerebral plasticity. Magnetoencephalography (MEG) is a non-invasive technique, which allows location of cerebral cells activities. In the present work, a cohort of patients has been studied with MEG. Twelve patients with a recent ischemic or hemorragic stroke were included as soon as possible after onset of stroke. Neurologic assessment, including standard neurologic examination, functional independence measure (FIM) and Orgogozo's scale was performed for 1 year in addition to a study of the somatosensory evoked field (SEF) using a 37-channel Biomagnetometer system. No response could be recorded in five patients at the first SEF exploration. In three cases, no response was ever recorded during the study. All these patients had a bad recovery. The location of the SEF sources was always in the normal non-infarcted cortex of the postcentral gyrus. Sensory recovery seemed to be linked to the reorganization of the persistent functional cortex, which was a limiting factor for recovery. These observations confirm the experimental results obtained in animal models. After stroke it can be assumed that in the case of incomplete lesion, an intensive sensory peripheral stimulation could maximize the use of residual sensory function and then contribute to improve the sensory deficit. In case of total sensory loss other techniques have to be used, such as visual monitoring of hand activity in order to improve hand function. PMID:12823488

Gallien, P; Aghulon, C; Durufle, A; Petrilli, S; de Crouy, A C; Carsin, M; Toulouse, P

2003-07-01

30

High multipolarity electroexcitations in 207Pb and 206Pb  

International Nuclear Information System (INIS)

We report the identification of new high multipolarity transitions in 207 Pb and 206Pb by the measurement of their form factor. A comparison to the corresponding excitations in 208Pb is presented. (orig.)

31

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

32

Electrokinetic behavior of two touching inhomogeneous biological cells and colloidal particles: Effects of multipolar interactions  

CERN Document Server

We present a theory to investigate electro-kinetic behavior, namely, electrorotation and dielectrophoresis under alternating current (AC) applied fields for a pair of touching inhomogeneous colloidal particles and biological cells. These inhomogeneous particles are treated as graded ones with physically motivated model dielectric and conductivity profiles. The mutual polarization interaction between the particles yields a change in their respective dipole moments, and hence in the AC electrokinetic spectra. The multipolar interactions between polarized particles are accurately captured by the multiple images method. In the point-dipole limit, our theory reproduces the known results. We find that the multipolar interactions as well as the spatial fluctuations inside the particles can affect the AC electrokinetic spectra significantly.

Huang, J P; Yu, K W; Dong, L; Gu, G Q; Karttunen, Mikko

2004-01-01

33

Estimation of soil moisture with L-band multipolarization radar  

Science.gov (United States)

This paper reports an attempt in improving surface soil moisture radar algorithm for Hydrosphere State Mission (Hydros). We used a Radiative Transfer Model to simulate a wide range surface dielectric, roughness, vegetation with random orientated disks database for our algorithm development under HYDROS radar sensor (L-band multi-polarizations and 40¦ incidence) configuration. Through analyses of the model simulated database, we developed a technique to estimate surface soil moisture. This technique includes two steps. First, it decomposes the total backscattering signals into two components - the surface scattering components (the bare surface backscattering signals attenuated by the overlaying vegetation layer) and the sum of the direct volume scattering components and surface-volume interaction components at different polarizations. From the model simulated data-base, our decomposition technique works quit well in estimation of the surface scattering components with RMSEs of 0.12, 0.25, and 0.55 dB for VV, HH, and VH polarizations, respectively. Then, we use the decomposed surface backscattering signals to estimate the soil moisture and the combined surface roughness and vegetation attenuation correction factors with all three polarizations. Test of this algorithm using all simulated data showed that an accuracy for the volumetric soil moisture estimation in terms of Root Mean Square Error (RMSE) of 4.6 % could be achievable.

Shi, Jiancheng; Chen, K. S.; Kim, Y.; Van Zyl, J. J.; Njoku, E.; Sun, G.; O'Neill, P.; Jackson, T.; Entekhabi, D.

2004-12-01

34

Compact multipolar representation of the electrostatic potential for flexible molecules  

Science.gov (United States)

A new method for generating a compact multipolar representation of the electrostatic potential (EP) for flexible molecules is presented. The method is based on a constrained minimization of the difference between the quantum mechanical and the classical EP. The fitting procedure used adopts the least absolute shrinkage and selection operator technique [R. Tibshirani, J. Roy. Stat. Soc. B 58, 267 (1996)] which can be seen as penalized ordinary least squares. The penalty function optimized for the particular molecule of interest effectively removes redundant multipoles. It is shown that the use of multiple conformations is crucial for the predictive ability of the EP model for flexible molecules. The multipole local coordinate systems are chosen in a way that best reflects the key conformational changes. It was demonstrated that such an approach improves the predictive ability of EP models. It also allows to exploit equivalence of atoms in the calculation of multipoles components. In the case of polar flexible molecules, the augmentation of the EP model based on charges by higher multipoles decreases the relative root mean square error by a factor of 1.5-5. The corresponding effect of enlargement of the set of multipoles was significantly reduced.

Chodkiewicz, Michal Leszek

2005-06-01

35

Magnetar Giant Flares in Multipolar Magnetic Fields. I. Fully and Partially Open Eruptions of Flux Ropes  

Science.gov (United States)

We propose a catastrophic eruption model for the enormous energy release of magnetars during giant flares, in which a toroidal and helically twisted flux rope is embedded within a force-free magnetosphere. The flux rope stays in stable equilibrium states initially and evolves quasi-statically. Upon the loss of equilibrium, the flux rope cannot sustain the stable equilibrium states and erupts catastrophically. During the process, the magnetic energy stored in the magnetosphere is rapidly released as the result of destabilization of global magnetic topology. The magnetospheric energy that could be accumulated is of vital importance for the outbursts of magnetars. We carefully establish the fully open fields and partially open fields for various boundary conditions at the magnetar surface and study the relevant energy thresholds. By investigating the magnetic energy accumulated at the critical catastrophic point, we find that it is possible to drive fully open eruptions for dipole-dominated background fields. Nevertheless, it is hard to generate fully open magnetic eruptions for multipolar background fields. Given the observational importance of the multipolar magnetic fields in the vicinity of the magnetar surface, it would be worthwhile to explore the possibility of the alternative eruption approach in multipolar background fields. Fortunately, we find that flux ropes may give rise to partially open eruptions in the multipolar fields, which involve only partial opening of background fields. The energy release fractions are greater for cases with central-arcaded multipoles than those with central-caved multipoles that emerged in background fields. Eruptions would fail only when the centrally caved multipoles become extremely strong.

Huang, Lei; Yu, Cong

2014-04-01

36

Somatosensory cortical plasticity in adult humans revealed by magnetoencephalography.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Microelectrode recordings in adult mammals have clearly demonstrated that somatosensory cortical maps reorganize following peripheral nerve injuries and functional modifications; however, such reorganization has never been directly demonstrated in humans. Using magnetoencephalography, we have been able to demonstrate the somatotopic organization of the hand area in normal humans with high spatial precision. Somatosensory cortical plasticity was detected in two adults who were studied before a...

Mogilner, A.; Grossman, J. A.; Ribary, U.; Joliot, M.; Volkmann, J.; Rapaport, D.; Beasley, R. W.; Llina?s, R. R.

1993-01-01

37

Induction of structural and numerical changes of chromosome, centrosome abnormality, multipolar spindles and multipolar division in cultured Chinese hamster V79 cells by exposure to a trivalent dimethylarsenic compound.  

Science.gov (United States)

Dimethylarsine iodide (DMI) was used as a model compound of trivalent dimethylarsenicals [DMA(III)], and the biological effects were extensively investigated in cultured Chinese hamster V79 cells. When the cytotoxic effects of DMA(III) were compared with those of inorganic arsenite and dimethylarsinic acid [DMA(V)], DMA(III) was about 10,000 times more potent than DMA(V), and it was even 10 times more toxic than arsenite. Depletion of cell glutathione (GSH) did not influence the cytotoxic effects of DMA(III), whereas it enhanced the cytotoxicity of arsenite. Chromosome structural aberrations, such as gaps, breaks and pulverizations, and numerical changes, such as aneuploidy, hyper- and hypo-tetraploidy, were induced by DMA(III) in a concentration-dependent manner. Mitotic index increased 9-12h after the addition of DMA(III), and then declined. By contrast, the incidence of multinucleated cells increased conversely with the decrease in mitotic index at and after 24h of exposure. The mitotic cell-specific abnormality of centrosome integrity and multipolar spindles were induced by DMA(III) in a time- and concentration-dependent manner. Moreover, DMA(III) caused abnormal cytokinesis (multipolar division) at concentrations that were effective in causing centrosome abnormality, multipolar spindles and aneuploidy. These results showed that DMA(III) was genotoxic on cultured mammalian cells. Results also suggest that DMA(III)-induced multipolar spindles and multipolar division may be associated with the induction of aneuploidy. In addition, the centrosome may be a primary target for cell death via multinucleated cells. PMID:14563531

Ochi, Takafumi; Suzuki, Tosihide; Isono, Hideo; Schlagenhaufen, Claudia; Goessler, Walter; Tsutsui, Takeki

2003-09-29

38

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

39

DISCOVERY OF A MULTIPOLAR STRUCTURE WITH AN EQUATORIAL DISK IN NGC 6072  

International Nuclear Information System (INIS)

From near-infrared and molecular hydrogen imaging observations, we have discovered that the planetary nebula NGC 6072 has a multipolar structure with a prominent equatorial ring. We have modeled the object by a double bipolar system, each with an equatorial ring and a pair of bipolar lobes. The bipolar axes of the two systems are estimated to be separated by 47 deg. The existence of such a double bipolar system suggests that the object has undergone separate fast outflow episodes separated by several thousand years.

40

Mapping diverse forest cover with multipolarization airborne radar  

Science.gov (United States)

Imaging radar backscatter in continuously forested areas contains information about the forest canopy; it also contains data about topography, landforms, and terrain texture. For purposes of radar image interpretation and geologic mapping researchers were interested in identifying and separating forest canopy effects from geologic or geomorphic effects on radar images. The objectives of this investigation was to evaluate forest canopy variables in multipolarization radar images under conditions where geologic and topographic variables are at a minimum. A subsidiary objective was to compare the discriminatory capabilities of the radar images with corresponding optical images of similar spatial resolution. It appears that the multipolarization images discriminate variation in tree density, but no evidence was found for discrimination between evergreen and deciduous forest types.

Ford, J. P.; Wickland, D. E.; Sharitz, R. R.

1985-01-01

 
 
 
 
41

Optical Torque from Enhanced Scattering by Multipolar Plasmonic Resonance  

CERN Document Server

We present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field, thereby producing scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamateria...

Lee, Yoonkyung E; Jin, Dafei; Fang, Nicholas

2014-01-01

42

Multipolar nonlinear light-matter interactions with Gaussian vector beams  

Science.gov (United States)

We show that surface second-harmonic generation (SHG) with focused Gaussian vector beams can be described in terms of effective Mie-type multipolar contributions to the SHG signal even in the electric dipole approximation of constitutive relations. Traditionally, Mie-type multipoles arise from field retardation across nanoparticles. In our case, the multipolar light-matter interaction is due to excitation with Gaussian vector beams and the tensorial properties of the SH response. As different multipoles have different radiative properties, we demonstrate the presence of multipoles by measuring strongly asymmetric SH emission into reflected and transmitted directions from a nonlinear thin film with isotropic surface symmetry, where symmetric emission is expected using traditional formalisms based on plane-wave excitation. The proposed multipole approach provides a convenient way to explain the measured asymmetric emission. Secondly, we generalize the treatment beyond the electric dipole approximation and propose that analogous vector excitation-induced multipolar effects could also occur in the microscopic light-matter interaction. Our results may allow new possibilities to designing confined and thin nonlinear sources with desired radiation patterns.

Huttunen, Mikko J.; Mäkitalo, Jouni; Bautista, Godofredo; Kauranen, Martti

2014-05-01

43

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

44

Adaptive cluster analysis approach for functional localization using magnetoencephalography.  

Science.gov (United States)

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. PMID:23675314

Alikhanian, Hooman; Crawford, J Douglas; Desouza, Joseph F X; Cheyne, Douglas O; Blohm, Gunnar

2013-01-01

45

Phase shift detection in thalamocortical oscillations using magnetoencephalography in humans.  

Science.gov (United States)

Magnetoencephalography was used to investigate exogenously stimulated oscillatory activity between cortex and thalamus resulting from clicks presented binaurally at the rate of 40 Hz. Analysis of the responses demonstrated activation of left and right auditory cortex, medial parietal cortex, thalamus, and cerebellum. Cross-correlations of the source waveforms revealed synchronicity between the auditory cortex sources (r > 0.9), auditory cortex and thalamic sources (r > 0.7), and thalamic and parietal sources (r > 0.7). The 40 Hz response in auditory cortex occurred 6 ms after thalamic activation. Supporting earlier findings, the results demonstrate the networks involved in the maintenance of 40 Hz auditory steady-state response and will prove useful for the interrogation of dysfunction in disorders demonstrating thalamocortical dysrhythmia, such as schizophrenia, Parkinson's disease, and depression. PMID:15147778

Bish, Joel Pearson; Martin, Tim; Houck, Jon; Ilmoniemi, Risto J; Tesche, Claudia

2004-05-13

46

The role of angular momentum in the construction of electromagnetic multipolar fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Multipolar solutions of Maxwell's equations are used in many practical applications and are essential for the understanding of light-matter interactions at the fundamental level. Unlike the set of plane wave solutions of electromagnetic fields, the multipolar solutions do not share a standard derivation or notation. As a result, expressions originating from different derivations can be difficult to compare. Some of the derivations of the multipolar solutions do not explicitl...

Tischler, Nora; Zambrana-puyalto, Xavier; Molina-terriza, Gabriel

2012-01-01

47

Multipolar excitations in small metallic spheres  

International Nuclear Information System (INIS)

A dielectric function E(?,l) appropriate to a small metallic sphere is obtained within the semiclassical infinite barrier model, where l is the multipole order. An excitation diagram in the l,? plane based on the structure of this function is proposed. It represents the spherical analog of the excitation structure of an infinite medium in the k,? plane. 8 refs., 1 fig

48

Multichannel System Based on a High Sensitivity Superconductive Sensor for Magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available We developed a multichannel system based on superconducting quantum interference devices (SQUIDs for magnetoencephalography measurements. Our system consists of 163 fully-integrated SQUID magnetometers, 154 channels and 9 references, and all of the operations are performed inside a magnetically-shielded room. The system exhibits a magnetic field noise spectral density of approximatively 5 fT/Hz1=2. The presented magnetoencephalography is the first system working in a clinical environment in Italy.

Sara Rombetto

2014-07-01

49

Challenges of a Multi-Polar Nuclear World  

Directory of Open Access Journals (Sweden)

Full Text Available Nuclear warfare, being calamitous, is nevertheless, unlike popular perception, far from being apocalyptic. In the article, we consider possible scenarios of nuclear war in a multi-polar nuclear world, arguing that a democratic society has good chances of victory against a totalitarian nuclear-possessing state. Afterwards, we focus on two technical issues of primary importance – targeting doctrine and civil defense. We conclude that a steadfast and determined stance together with properly conceived and well planned policies for dealing with aggression is the price democratic societies must be willing to pay in order to effectively battle aggression at all levels.

Yehoshua Socol

2012-06-01

50

Impact of polydispersity on multipolar resonant scattering in emulsions.  

Science.gov (United States)

The influence of size polydispersity on the resonant acoustic properties of dilute emulsions, made of fluorinated-oil droplets, is quantitatively investigated. Ultrasound attenuation and dispersion measurements on various samples with controlled size polydispersities, ranging from 1% to 13%, are found to be in excellent agreement with predictions based on the independent scattering approximation. By relating the particle-size distribution of the synthesized emulsions to the quality factor of the predicted multipolar resonances, the number of observable acoustic resonances is shown to be imposed by the sample polydispersity. These results are briefly discussed into the context of metamaterials for which scattering resonances are central to their effective properties. PMID:23556570

Mascaro, Benoit; Brunet, Thomas; Poncelet, Olivier; Aristégui, Christophe; Raffy, Simon; Mondain-Monval, Olivier; Leng, Jacques

2013-04-01

51

Multipolar localized resonances for multi-band metamaterial perfect absorbers  

Science.gov (United States)

A metamaterial structure, comprising of metallic circular micro-discs (gold or aluminum) separated from a metallic thin film by a dielectric zinc sulphide film, behaves as a multi-band perfect absorber at infra red wavelengths due to the excitation of multipole resonances. With micro-discs of 3.2 ?m diameter, the fabricated metamaterial absorber shows peak absorbance of over 90% in multiple selected bands spanning the 3-14 ?m wavelengths. Absorption bands corresponding to the different resonance modes have been measured and computational simulations show these resonances originate from the higher order multipolar resonances of the disk.

Dayal, Govind; Ramakrishna, S. Anantha

2014-09-01

52

Anatomy of the binary black hole recoil: A multipolar analysis  

International Nuclear Information System (INIS)

We present a multipolar analysis of the gravitational recoil computed in recent numerical simulations of binary black hole coalescence, for both unequal masses and nonzero, nonprecessing spins. We show that multipole moments up to and including l=4 are sufficient to accurately reproduce the final recoil velocity (within ?2%) and that only a few dominant modes contribute significantly to it (within ?5%). We describe how the relative amplitudes, and more importantly, the relative phases, of these few modes control the way in which the recoil builds up throughout the inspiral, merger, and ringdown phases. We also find that the numerical results can be reproduced by an 'effective Newtonian' formula for the multipole moments obtained by replacing the radial separation in the Newtonian formulas with an effective radius computed from the numerical data. Beyond the merger, the numerical results are reproduced by a superposition of three Kerr quasinormal modes. Analytic formulas, obtained by expressing the multipole moments in terms of the fundamental quasinormal modes of a Kerr black hole, are able to explain the onset and amount of 'antikick' for each of the simulations. Lastly, we apply this multipolar analysis to help explain the remarkable difference between the amplitudes of planar and nonplanar kicks for equal-mass spinning black holes

53

Wavelet-based localization of oscillatory sources from magnetoencephalography data.  

Science.gov (United States)

Transient brain oscillatory activities recorded with Eelectroencephalography (EEG) or magnetoencephalography (MEG) are characteristic features in physiological and pathological processes. This study is aimed at describing, evaluating, and illustrating with clinical data a new method for localizing the sources of oscillatory cortical activity recorded by MEG. The method combines time-frequency representation and an entropic regularization technique in a common framework, assuming that brain activity is sparse in time and space. Spatial sparsity relies on the assumption that brain activity is organized among cortical parcels. Sparsity in time is achieved by transposing the inverse problem in the wavelet representation, for both data and sources. We propose an estimator of the wavelet coefficients of the sources based on the maximum entropy on the mean (MEM) principle. The full dynamics of the sources is obtained from the inverse wavelet transform, and principal component analysis of the reconstructed time courses is applied to extract oscillatory components. This methodology is evaluated using realistic simulations of single-trial signals, combining fast and sudden discharges (spike) along with bursts of oscillating activity. The method is finally illustrated with a clinical application using MEG data acquired on a patient with a right orbitofrontal epilepsy. PMID:22410322

Lina, J M; Chowdhury, R; Lemay, E; Kobayashi, E; Grova, C

2014-08-01

54

A magnetoencephalography study of visual processing of pain anticipation.  

Science.gov (United States)

Anticipating pain is important for avoiding injury; however, in chronic pain patients, anticipatory behavior can become maladaptive, leading to sensitization and limiting function. Knowledge of networks involved in pain anticipation and conditioning over time could help devise novel, better-targeted therapies. With the use of magnetoencephalography, we evaluated in 10 healthy subjects the neural processing of pain anticipation. Anticipatory cortical activity elicited by consecutive visual cues that signified imminent painful stimulus was compared with cues signifying nonpainful and no stimulus. We found that the neural processing of visually evoked pain anticipation involves the primary visual cortex along with cingulate and frontal regions. Visual cortex could quickly and independently encode and discriminate between visual cues associated with pain anticipation and no pain during preconscious phases following object presentation. When evaluating the effect of task repetition on participating cortical areas, we found that activity of prefrontal and cingulate regions was mostly prominent early on when subjects were still naive to a cue's contextual meaning. Visual cortical activity was significant throughout later phases. Although visual cortex may precisely and time efficiently decode cues anticipating pain or no pain, prefrontal areas establish the context associated with each cue. These findings have important implications toward processes involved in pain anticipation and maladaptive pain conditioning. PMID:24790165

Machado, Andre G; Gopalakrishnan, Raghavan; Plow, Ela B; Burgess, Richard C; Mosher, John C

2014-07-15

55

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

56

Noise-free magnetoencephalography recordings of brain function  

International Nuclear Information System (INIS)

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 106 (>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-1/2. We are recording MEG signals with greater signal-to-noise than equivalent EEG measurements

57

Real-time robust signal space separation for magnetoencephalography.  

Science.gov (United States)

In this paper, we develop a robust signal space separation (rSSS) algorithm for real-time magnetoencephalography (MEG) data processing. rSSS is based on the spatial signal space separation (SSS) method and it applies robust regression to automatically detect and remove bad MEG channels so that the results of SSS are not distorted. We extend the existing robust regression algorithm via three important new contributions: 1) a low-rank solver that efficiently performs matrix operations; 2) a subspace iteration scheme that selects bad MEG channels using low-order spherical harmonic functions; and 3) a parallel computing implementation that simultaneously runs multiple tasks to further speed up numerical computation. Our experimental results based on both simulation and measurement data demonstrate that rSSS offers superior accuracy over the traditional SSS algorithm, if the MEG data contain significant outliers. Taking advantage of the proposed fast algorithm, rSSS achieves more than 75 x runtime speedup compared to a direct solver of robust regression. Even though rSSS is currently implemented with MATLAB, it already provides sufficient throughput for real-time applications. PMID:20176529

Guo, Chenlei; Li, Xin; Taulu, Samu; Wang, Wei; Weber, Douglas J

2010-08-01

58

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 decreasments, 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

59

Whole Brain Functional Connectivity Using Phase Locking Measures Of Resting State Magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available The analysis of spontaneous functional connectivity reveals the statistical connections between regions of the brain consistent with underlying functional communication networks within the brain. In this work, we describe the implementation of a complete all-to-all network analysis of resting state neuronal activity from magnetoencephalography (MEG. Using graph theory to define networks at the dipole level, we established functionally defined regions by k-means clustering cortical surface locations using Eigenvector centrality scores from the all-to-all adjacency model. Permutation testing was used to estimate regions with statistically significant connections compared to empty room data, which adjusts for spatial dependencies introduced by the MEG inverse problem. In order to test this model, we preformed a series of numerical simulations investigating the effects of the MEG reconstruction on connectivity estimates. We subsequently applied the approach to subject data to investigate the effectiveness of our method in obtaining whole brain networks. Our findings indicated that our model provides statistically robust estimates of functional region networks. Application of our phase locking network methodology to real data produced networks with similar connectivity to previously published findings, specifically, we found connections between contralateral areas of the arcuate fasciculus that have been previously investigated. The use of data-driven methods for neuroscientific investigations provides a new tool for researchers in identifying and characterizing whole brain functional connectivity networks.

BenjaminTSchmidt

2014-06-01

60

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

 
 
 
 
61

Note: Unshielded bilateral magnetoencephalography system using two-dimensional gradiometers  

Science.gov (United States)

Magnetoencephalography (MEG) noninvasively measures neuronal activity with high temporal resolution. The aim of this study was to develop a new type of MEG system that can measure bilateral MEG waveforms without a magnetically shielded room, which is an obstacle to reducing both the cost and size of an MEG system. An unshielded bilateral MEG system was developed using four two-dimensional (2D) gradiometers and two symmetric cryostats. The 2D gradiometer, which is based on a low-Tc superconducting quantum interference device and wire-wound pickup coil detects a magnetic-field gradient in two orthogonal directions, or ?/?x(?2Bz/?z2), and reduces environmental magnetic-field noise by more than 50 dB. The cryostats can be symmetrically positioned in three directions: vertical, horizontal, and rotational. This makes it possible to detect bilateral neuronal activity in the cerebral cortex simultaneously. Bilateral auditory-evoked fields (AEF) of 18 elderly subjects were measured in an unshielded hospital environment using the MEG system. As a result, both the ipsilateral and the contralateral AEF component N100m, which is the magnetic counterpart of electric N100 in electroencephalography and appears about 100 ms after the onset of an auditory stimulus, were successfully detected for all the subjects. Moreover, the ipsilateral P50m and the contralateral P50m were also detected for 12 (67%) and 16 (89%) subjects, respectively. Experimental results demonstrate that the unshielded bilateral MEG system can detect MEG waveforms, which are associated with brain dysfunction such as epilepsy, Alzheimer's disease, and Down syndrome.

Seki, Yusuke; Kandori, Akihiko; Ogata, Kuniomi; Miyashita, Tsuyoshi; Kumagai, Yukio; Ohnuma, Mitsuru; Konaka, Kuni; Naritomi, Hiroaki

2010-09-01

62

Neural effects of prolonged mental fatigue: a magnetoencephalography study.  

Science.gov (United States)

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 (8-13 Hz) 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. PMID:23880373

Ishii, Akira; Tanaka, Masaaki; Shigihara, Yoshihito; Kanai, Etsuko; Funakura, Masami; Watanabe, Yasuyoshi

2013-09-01

63

THE EU-US RELATIONS IN AN EMERGING MULTIPOLAR WORLD  

Directory of Open Access Journals (Sweden)

Full Text Available In the context of an emerging multipolar world, the transatlantic partnership faces various challenges in the attempt to maintain the Western-shaped and dominated liberal order. This article aims to synthesize and rationalize the central argumentative positions on the ever-evolving transatlantic relationship provided by the following theories of international relations: neorealism, neoliberalism and constructivism. A combination of the main assumptions of the three approaches brings useful insights into the policy debates on the role of the transatlantic partnership in the process of forging the global governance. Nevertheless, where the systemic theories such as neorealism and neoliberalism fall short in explaining the transatlantic relations, constructivism, with its focus on actor identity succeeds in offering a dynamic account of them.

Roxana Hincu

2014-08-01

64

Anatomy of the binary black hole recoil: A multipolar analysis  

CERN Document Server

We present a multipolar analysis of the gravitational recoil computed in recent numerical simulations of binary black hole (BH) coalescence, for both unequal masses and non-zero, non-precessing spins. We show that multipole moments up to and including l=4 are sufficient to accurately reproduce the final recoil velocity (within ~2%) and that only a few dominant modes contribute significantly to it (within ~5%). We describe how the relative amplitudes, and more importantly, the relative phases, of these few modes control the way in which the recoil builds up throughout the inspiral, merger, and ringdown phases. We also find that the numerical results can be reproduced by an ``effective Newtonian'' formula for the multipole moments obtained by replacing the radial separation in the Newtonian formulae with an effective radius computed from the numerical data. Beyond the merger, the numerical results are reproduced by a superposition of three Kerr quasi-normal modes (QNMs). Analytic formulae, obtained by expressin...

Schnittman, Jeremy D; van Meter, James R; Baker, John G; Boggs, William D; Centrella, Joan; Kelly, Bernard J; McWilliams, Sean T

2007-01-01

65

Rf multipolar plasma for broad and reactive ion beams  

International Nuclear Information System (INIS)

Hot cathode dc multipolar plasma sources are very efficient but have lifetime and contamination problems when they are operated with chemically active gases. As an alternative solution the rf excitation of a triode structure immersed in a multicusp magnetic field has been developed. The structure has an internal cathode, an anode around which are the magnet lines, and a third electrode which is either the target electrode in the case of 'plasma processing' or the beam forming electrode in the case of 'ion beam processing'. The source has been operated with oxygen and fluorocarbon gases without any lifetime problems. The discharge may be run down to 10-4 torr (within source chamber) and creates a plasma which is homogeneous to +- 1.5% over 175 mm diameter section and which delivers at the beam forming electrode a current density of about 1 mAcm-2 for 500 W rf power. (author)

66

Multipolar Black Body Radiation Shifts for the Single Ion Clocks  

CERN Document Server

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

67

Simulated multipolarized MAPSAR images to distinguish agricultural crops  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English 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 orb [...] ital 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.

2012-06-01

68

Sequential Monte Carlo samplers for semi-linear inverse problems and application to magnetoencephalography  

Science.gov (United States)

We discuss the use of a recent class of sequential Monte Carlo methods for solving inverse problems characterized by a semi-linear structure, i.e. where the data depend linearly on a subset of variables and nonlinearly on the remaining ones. In this type of problems, under proper Gaussian assumptions one can marginalize the linear variables. This means that the Monte Carlo procedure needs only to be applied to the nonlinear variables, while the linear ones can be treated analytically; as a result, the Monte Carlo variance and/or the computational cost decrease. We use this approach to solve the inverse problem of magnetoencephalography, with a multi-dipole model for the sources. Here, data depend nonlinearly on the number of sources and their locations, and depend linearly on their current vectors. The semi-analytic approach enables us to estimate the number of dipoles and their location from a whole time-series, rather than a single time point, while keeping a low computational cost.

Sommariva, Sara; Sorrentino, Alberto

2014-11-01

69

Internal electron conversion spectra of 202Bi. Transition multipolarities of 202Pb  

International Nuclear Information System (INIS)

To refine and supplement data on multipolarity of 202Pb transitions, internal conversion electrons (ICE) spectra with 202Bi monoisotopic sources have been studied. Special attention is paid to determination of > 1000 keV transition multipolarity. Results of measurements in the energy range of 80-1700 keV are tabulated. Wei.ohted average values of ICE intensity corresponding to more than 80 transitions in 202Pb are given. Intensity values for 42 transitions were determined for the first time. Obtained refined data and new data on transition multipolarities confirm quantum characteristics suggested earlier for 202Pb levels and for some levels-refine them

70

High-resolution imaging and spectroscopy of multipolar plasmonic resonances in aluminum nanoantennas.  

Science.gov (United States)

We report on the high resolution imaging of multipolar plasmonic resonances in aluminum nanoantennas using electron energy loss spectroscopy (EELS). Plasmonic resonances ranging from near-infrared to ultraviolet (UV) are measured. The spatial distributions of the multipolar resonant modes are mapped and their energy dispersion is retrieved. The losses in the aluminum antennas are studied through the full width at half-maximum of the resonances, unveiling the weight of both interband and radiative damping mechanisms of the different multipolar resonances. In the blue-UV spectral range, high order resonant modes present a quality factor up to 8, two times higher than low order resonant modes at the same energy. This study demonstrates that near-infrared to ultraviolet tunable multipolar plasmonic resonances in aluminum nanoantennas with relatively high quality factors can be engineered. Aluminum nanoantennas are thus an appealing alternative to gold or silver ones in the visible and can be efficiently used for UV plasmonics. PMID:25207386

Martin, Jérôme; Kociak, Mathieu; Mahfoud, Zackaria; Proust, Julien; Gérard, Davy; Plain, Jérôme

2014-10-01

71

A novel microtubule-modulating noscapinoid triggers apoptosis by inducing spindle multipolarity via centrosome amplification and declustering.  

Science.gov (United States)

We have previously shown that a non-toxic noscapinoid, EM011 binds tubulin without altering its monomer/polymer ratio. EM011 is more active than the parent molecule, noscapine, in inducing G2/M arrest, inhibiting cellular proliferation and tumor growth in various human xenograft models. However, the mechanisms of mitotic-block and subsequent cell death have remained elusive. Here, we show that EM011-induced attenuation of microtubule dynamics was associated with impaired association of microtubule plus-end tracking proteins, such as EB1 and CLIP-170. EM011 treatment then led to the formation of multipolar spindles containing 'real' centrioles indicating drug-induced centrosome amplification and persistent centrosome declustering. Centrosome amplification was accompanied by an upregulation of Aurora A and Plk4 protein levels, as well as a surge in the kinase activity of Aurora A, suggesting a deregulation of the centrosome duplication cycle. Cell-cycle phase-specific experiments showed that the 'cytotoxicity-window' of the drug encompasses the late S-G2 period. Drug-treatment, excluding S-phase, not only resulted in lower sub-G1 population but also attenuated centrosome amplification and spindle multipolarity, suggesting that drug-induced centrosome amplification is essential for maximal cell death. Subsequent to a robust mitotic arrest, EM011-treated cells displayed diverse cellular fates suggesting a high degree of intraline variation. Some 'apoptosis-evasive' cells underwent aberrant cytokinesis to generate rampant aneuploidy that perhaps contributed to drug-induced cell death. These data indicate that spindle multipolarity induction by means of centrosome amplification has an exciting chemotherapeutic potential that merits further investigation. PMID:21052096

Karna, P; Rida, P C G; Pannu, V; Gupta, K K; Dalton, W B; Joshi, H; Yang, V W; Zhou, J; Aneja, R

2011-04-01

72

Ambipolar diffusion of a collisional plasma through an inhomogeneous magnetic field. Application to a multipolar discharge  

International Nuclear Information System (INIS)

Making use of an ambipolar diffusion theory, the differential equation governing the electronic density of a collisional plasma diffusing through an inhomogeneous magnetic field is established. The diffusion equation is solved numerically in the case of a multipolar field and the profile of the potential is calculated. The results enable to interpret the fact that density are located in the vicinity of the wall as well as the occurrence of high potential regions in a multipolar discharge

73

Average multipolarity of continuum transitions in nuclei at high angular momentum  

International Nuclear Information System (INIS)

The multipolarity of continuum transitions deexciting high-spin states has been deduced from measured conversion coefficients. The investigated 146Nd(20Ne, 4n or 5n) 162 161Yb reactions were selected by gating on discrete lines. The average multipolarity gradually changes from E2 at 0.5 MeV to E1 above 1.5 MeV. (Auth.)

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

First-principles theory of multipolar order in actinide dioxides  

Science.gov (United States)

Magnetic phase transitions that involve multipolar degrees of freedom have been widely studied during the last couple of decades, challenging the common approximation which assumes that the physical properties of a magnetic material could be effectively described by purely dipolar degrees of freedom. Due to the complexity of the problem and to the large number of competing interactions involved, the simple (fcc) crystal structure of the actinide dioxides made them the ideal playground system for such theoretical and experimental studies. In the present paper, we summarize our recent attempts to provide an ab initio description of the ordered phases of UO2, NpO2, and AmO2 by means of state-of-the-art LDA+U first-principles calculations. This systematic analysis of the electronic structures is here naturally connected to the local crystalline fields of the 5f states in the actinide dioxide series. Related to these we find that the mechanisms which lead to the experimentally observed insulating ground states work in distinctly different ways for each compound. xml:lang="fr"

Magnani, Nicola; Suzuki, Michi-To; Oppeneer, Peter M.

2014-08-01

76

Possible multipolar transition in NdB {sub 4}  

Energy Technology Data Exchange (ETDEWEB)

Physical properties of neodymium tetraboride NdB{sub 4} which crystallizes in the ThB{sub 4}-type structure belonging to space group D{sub 4h}{sup 5} - P4/mbm have been studied. The specific heat measurement on single crystal of NdB{sub 4} shows that this material undergoes successive phase transitions at T{sub Q} = 17.2 K (second-order transition), T{sub N1} = 7.0 K (second-order transition) and T{sub N2} = 4.8 K (first-order transition). The magnetic entropy of approximately R ln2 and R ln 4 is released below T{sub N1} and T{sub C}, respectively. The crystalline electric field (CEF) ground state of NdB{sub 4} is a pseudo-quartet consisting of two Kramers doublets. At around T{sub Q}, no anomalies of the magnetic susceptibility along the c-direction which is easy axis of magnetization are observed. Moreover, the susceptibility within the ab-plane shows only a very small peak. These results seem to indicate that NdB{sub 4} undergoes a quadrupolar (or higher rank multipolar) transition at T{sub Q} followed by two magnetic transitions since the behaviors are quite different from those of conventional magnet.

Watanuki, Ryuta; Kobayashi, Toshihiko; Noguchi, Ryo; Suzuki, Kazuya, E-mail: ryu-wat@ynu.ac.j [Department of Advanced Materials Chemistry, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama (Japan)

2009-03-01

77

Determination of discrete transition multipolarity using the generalized oscillator strength  

International Nuclear Information System (INIS)

The generalized oscillator strengths (GOS's) for quadrupole and monopole (and their sums) excitation of the outer np?(n+1)p,(n+2)p levels of the noble gas atoms Ne, Ar, Kr, and Xe are investigated over the broad range of momentum transfer q values, from q=0 up to q=8 a.u., the region of their accessibility. The purpose of this investigation is to understand and delineate the relative contributions to the GOS of the various discrete transition multipolarities to guide measurements. This study has been motivated by recent absolute measurements of the GOS's for the lowest nondipole discrete transition in Ar [X. W. Fan and K. T. Leung, Phys. Rev. A 62, 062703 (2000)] and their subsequent reinterpretation.. The calculations are performed in the one-electron Hartree-Fock approximation and with many-electron correlation effects taken into account within the random phase approximation with exchange for the quadrupole and monopole excitations. We find that the GOS's for the quadrupole np?(n+1)p transitions of Ne, Ar, Kr, and Xe are characterized by two maxima, while the corresponding GOS's for monopole excitations have only a single maximum

78

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

79

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<0.05). Importantly, the extent of the deficit was uncorrelated with either Snellen acuity or contrast sensitivity. Localization of the evoked responses was peocalization 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.)

80

A trivalent dimethylarsenic compound, dimethylarsine iodide, induces cellular transformation, aneuploidy, centrosome abnormality and multipolar spindle formation in Syrian hamster embryo cells.  

Science.gov (United States)

The abilities of dimethylarsine iodide (DMI), a model compound of trivalent dimethylarsenicals, to induce cellular transformation, aneuploidy, centrosome abnormality, and multipolar spindle formations were investigated using the Syrian hamster embryo (SHE) cell model. Cellular growth was decreased in a concentration-dependent manner by treatment with DMI at concentrations over 0.1 microM. Treatment with DMI at concentrations from 0.1 to 1.0 microM induced morphological transformation in SHE cells. The transforming activity of DMI, determined by the frequency of morphologically transformed colonies, was approximately 30 times higher than that induced by treatment with the same concentration of sodium arsenite. Flow cytometry suggested an increase in the aneuploid population caused by DMI, as shown by the appearance of hypo-2N, hypo-4N and hypo-8N. DMI also caused abnormal staining of gamma-tubulin, indicating loss of centrosome integrity and a resultant induction of multipolar spindles in mitotic cells. Mitotic cells with centrosomes that coalesced partly at the cell periphery, not the cell center, were detected as early changes that resulted in multipolar spindles. These findings indicate that DMI has transforming activity in SHE cells. Moreover, the results suggest the importance of centrosome abnormalities as a causal change of DMI-induced aneuploidy. PMID:15363591

Ochi, Takafumi; Suzuki, Toshihide; Barrett, J Carl; Tsutsui, Takeki

2004-10-15

 
 
 
 
81

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

82

Magnetar Giant Flares in Multipolar Magnetic Fields --- II. Flux Rope Eruptions With Current Sheets  

CERN Document Server

We propose a physical mechanism to explain giant flares and radio afterglows in terms of a magnetospheric model containing both a helically twisted flux rope and a current sheet (CS). With the appearance of CS, we solve a mixed boundary value problem to get the magnetospheric field based on a domain decomposition method. We investigate properties of the equilibrium curve of the flux rope when the CS is present in background multipolar fields. In response to the variations at the magnetar surface, it quasi-statically evolves in stable equilibrium states. The loss of equilibrium occurs at a critical point and, beyond that point, it erupts catastrophically. New features show up when the CS is considered. Especially, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. The released magnetic energy is sufficient to drive giant flares. The flux rope would go away from the magnetar quasi-statically, which is ...

Huang, Lei

2014-01-01

83

Magnetoencephalography based on high-Tc superconductivity: a closer look into the brain?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetoencephalography (MEG) enables the study of brain activity by recording the magnetic fields generated by neural currents and has become an important technique for neuroscientists in research and clinical settings. Unlike the liquid-helium cooled low-Tc superconducting quantum interference devices (SQUIDs) that have been at the heart of modern MEG systems since their invention, high-Tc SQUIDs can operate with liquid nitrogen cooling. The relaxation of thermal insulation...

O?isjo?en, F.; Schneiderman, J. F.; Figueras, G. A.; Chukharkin, M. L.; Kalabukhov, A.; Hedstro?m, A.; Elam, M.; Winkler, D.

2011-01-01

84

Gamma band pitch responses in human auditory cortex measured with magnetoencephalography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have previously used direct electrode recordings in two human subjects to identify neural correlates of the perception of pitch (Griffiths, Kumar, Sedley et al., Direct recordings of pitch responses from human auditory cortex, Curr. Biol. 22 (2010), pp. 1128–1132). The present study was carried out to assess virtual-electrode measures of pitch perception based on non-invasive magnetoencephalography (MEG). We recorded pitch responses in 13 healthy volunteers using a passive listening para...

Sedley, William; Teki, Sundeep; Kumar, Sukhbinder; Overath, Tobias; Barnes, Gareth R.; Griffiths, Timothy D.

2012-01-01

85

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2012-01-01

86

Word repetition priming induced oscillations in auditory cortex: a magnetoencephalography study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetoencephalography was used in a passive repetition priming paradigm. Words in two frequency bins (high/low) were presented to subjects auditorily. Subjects’ brain responses to these stimuli were analyzed using synthetic aperture magnetometry. The main finding is that single word repetition of low frequency word pairs significantly attenuated the post-second word event related desynchronization in the theta-alpha (5–15Hz) bands, 200–600ms post second word stimulus onset. Peak signif...

Tavabi, Kambiz; Embick, David; Roberts, Timothy P. L.

2011-01-01

87

Potential Utility of Resting-State Magnetoencephalography as a Biomarker of CNS Abnormality in HIV Disease  

Digital Repository Infrastructure Vision for European Research (DRIVER)

There is a lack of a neuroimaging biomarker for HIV-Associated Neurocognitive Disorder. We report magnetoencephalography (MEG) data from patients with HIV disease and risk-group appropriate controls that were collected to determine the MEG frequency profile during the resting state, and the stability of the profile over 24 weeks. 17 individuals (10 HIV+, 7 HIV?) completed detailed neurobehavioral evaluations and 10 minutes of resting-state MEG acquisition with a 306-channel whole-head syste...

Becker, James T.; Fabrizio, Melissa; Sudre, Gustavo; Haridis, Anna; Ambrose, Timothy; Aizenstein, Howard J.; Eddy, William; Lopez, Oscar L.; Wolk, David; Parkkonen, Lauri; Bagic, Anto

2012-01-01

88

Study on radiation following the 205At decay. Multipolarities of the 205Po transitions  

International Nuclear Information System (INIS)

A study is performed of spectra of #betta#-rays, conversion electrons and e#betta#-coincidences with the use of monoisotopic 205At sources. The admixture of 206At and 207At made up approximately 1%, that of 208At - about 0.3%, by activity. A study of the 205At ? 205Po decay shows 148 #betta#-transitions, 94 of them being observed for the first time. Multipolarities for 70 #betta#-transitions have been determined, for 54 of them - for the first time. For 20 #betta#-transitions the internal conversion coefficients are estimated and, respectively, probable multipolarity

89

Magnetic structures and x-ray 4f multipolar scattering in cubic systems  

International Nuclear Information System (INIS)

Thomson scattering by rare-earth multipoles is a valuable technique for determining orbital structures in rare-earth systems. In the present paper, the formalism describing the relation between the magnetic and multipolar structures in cubic systems is extended to the fourth- and sixth-order multipoles. The associated x-ray scattering amplitudes are written using the cubic irreducible representations and calling in play appropriate Stevens equivalent operators. This paper is intended to provide a rigorous framework for the interpretation of multipolar scattering experiments on magnetically or orbitally ordered systems. (author)

90

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

International Nuclear Information System (INIS)

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.)

91

Magnetar Giant Flares in Multipolar Magnetic Fields. II. Flux Rope Eruptions with Current Sheets  

Science.gov (United States)

We propose a physical mechanism to explain giant flares and radio afterglows in terms of a magnetospheric model containing both a helically twisted flux rope and a current sheet (CS). With the appearance of a CS, we solve a mixed boundary value problem to get the magnetospheric field based on a domain decomposition method. We investigate properties of the equilibrium curve of the flux rope when the CS is present in background multipolar fields. In response to the variations at the magnetar surface, it quasi-statically evolves in stable equilibrium states. The loss of equilibrium occurs at a critical point and, beyond that point, it erupts catastrophically. New features show up when the CS is considered. In particular, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. This released magnetic energy is sufficient to drive giant flares, and the flux rope would, therefore, go away from the magnetar quasi-statically, which is inconsistent with the radio afterglow. Fortunately, in the latter case, i.e., the catastrophic escape, the flux rope could escape the magnetar and go to infinity in a dynamical way. This is more consistent with radio afterglow observations of giant flares. We find that the minor radius of the flux rope has important implications for its eruption. Flux ropes with larger minor radii are more prone to erupt. We stress that the CS provides an ideal place for magnetic reconnection, which would further enhance the energy release during eruptions.

Huang, Lei; Yu, Cong

2014-11-01

92

Evidence for Early Morphological Decomposition: Combining Masked Priming with Magnetoencephalography  

Science.gov (United States)

Are words stored as morphologically structured representations? If so, when during word recognition are morphological pieces accessed? Recent masked priming studies support models that assume early decomposition of (potentially) morphologically complex words. The electrophysiological evidence, however, is inconsistent. We combined masked…

Lehtonen, Minna; Monahan, Philip J.; Poeppel, David

2011-01-01

93

Multipolar radiofrequency ablation using internally cooled electrodes in ex vivo bovine liver: Correlation between volume of coagulation and amount of applied energy  

International Nuclear Information System (INIS)

Purpose: To evaluate the relationship between applied energy and volume of coagulation induced by multipolar radiofrequency (RF) ablation. Methods and materials: Multipolar RF ablations (n = 80) were performed in ex vivo bovine liver. Three bipolar applicators with two electrodes located on each applicator shaft were placed in a triangular array. The power-output (75–225 W) and the distance between the different applicators (2, 3, 4, 5 cm) were systematically varied. The volume of confluent white coagulation and the amount of applied energy were assessed. Based on our experimental data the relationship between the volume of coagulation and applied energy was assessed by nonlinear regression analysis. The variability explained by the model was determined by the parameter r2. Results: The volume of coagulation increases with higher amounts of applied energy. The maximum amount of energy was applied at a power-output of 75 W and an applicator distance of 5 cm. The corresponding maximum volume of coagulation was 324 cm3 and required an application of 453 kJ. The relationship between amount of applied energy (E) and volume (V) of coagulation can be described by the function, V = 4.39E0.7 (r2 = 0.88). By approximation the volume of coagulation can be calculated by the linear function V = 0.61E + 40.7 (r2 = 0.87). Conclusion: Ex vivo the relationship between volume of coagulation and amount of applied energy can be des and amount of applied energy can be described by mathematical modeling. The amount of applied energy correlates to the volume of coagulation and may be a useful parameter to monitor multipolar RF ablation.

94

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

2013-04-01

95

Multipolar excitations in the antiferroquadrupolar phase of CeB{sub 6}  

Energy Technology Data Exchange (ETDEWEB)

The hexaboride compound CeB{sub 6} exhibits quadrupolar O{sub xy} type and magnetic order due to the four-fold degenerate Ce{sup 3+}-{gamma}{sub 8} CEF-states. The B-T phase diagram shows anomalous large positive slope of the critical field curve. This is due to a new type of induced octupolar T{sub xyz} order parameter. Inelastic neutron scattering experiments by Bouvet have provided direct evidence for the existence of collective excitations. Their nature is shown to be of mixed multipolar character and their dispersion and intensities are calculated using a RPA-type approach and a Holstein-Primakoff approach which show excellent agreement. Temperature and field dependence of the multipolar excitations are calculated and the latter is compared to experimental results.

Thalmeier, P.; Shiina, R.; Shiba, H.; Takahashi, A.; Sakai, O

2004-07-15

96

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

97

Cytotoxicity of paclitaxel in breast cancer is due to chromosome missegregation on multipolar spindles.  

Science.gov (United States)

The blockbuster chemotherapy drug paclitaxel is widely presumed to cause cell death in tumors as a consequence of mitotic arrest, as it does at concentrations routinely used in cell culture. However, we determine here that paclitaxel levels in primary breast tumors are well below those required to elicit sustained mitotic arrest. Instead, cells in these lower concentrations of drug proceed through mitosis without substantial delay and divide their chromosomes on multipolar spindles, resulting in chromosome missegregation and cell death. Consistent with these cell culture data, most mitotic cells in primary human breast cancers contain multipolar spindles after paclitaxel treatment. Contrary to the previous hypothesis, we find that mitotic arrest is dispensable for tumor regression in patients. These results demonstrate that mitotic arrest is not responsible for the efficacy of paclitaxel, which occurs because of chromosome missegregation on highly abnormal, multipolar spindles. This mechanistic insight may be used to improve selection of future antimitotic drugs and to identify a biomarker with which to select patients likely to benefit from paclitaxel. PMID:24670687

Zasadil, Lauren M; Andersen, Kristen A; Yeum, Dabin; Rocque, Gabrielle B; Wilke, Lee G; Tevaarwerk, Amye J; Raines, Ronald T; Burkard, Mark E; Weaver, Beth A

2014-03-26

98

Cytotoxicity of paclitaxel in breast cancer is due to chromosome missegregation on multipolar spindles  

Science.gov (United States)

The blockbuster chemotherapy drug paclitaxel is widely presumed to cause cell death in tumors as a consequence of mitotic arrest, as it does at concentrations routinely used in cell culture. However, we determine here that paclitaxel levels in primary breast tumors are well below those required to elicit sustained mitotic arrest. Instead, cells in these lower concentrations of drug proceed through mitosis without substantial delay and divide their chromosomes on multipolar spindles, resulting in chromosome missegregation and cell death. Consistent with these cell culture data, the majority of mitotic cells in primary human breast cancers contain multipolar spindles after paclitaxel treatment. Contrary to the previous hypothesis, we find that mitotic arrest is dispensable for tumor regression in patients. These results demonstrate that mitotic arrest is not responsible for the efficacy of paclitaxel, which occurs due to chromosome missegregation on highly abnormal, multipolar spindles. This mechanistic insight may be used to improve selection of future anti-mitotic drugs and to identify a biomarker with which to select patients likely to benefit from paclitaxel. PMID:24670687

Zasadil, Lauren M.; Andersen, Kristen A.; Yeum, Dabin; Rocque, Gabrielle B.; Wilke, Lee G.; Tevaarwerk, Amye J.; Raines, Ronald T.; Burkard, Mark E.; Weaver, Beth A.

2014-01-01

99

Early visual processing is affected by clinical subtype in patients with unilateral spatial neglect: A magnetoencephalography study.  

Directory of Open Access Journals (Sweden)

CONCLUSIONS: These results demonstrate that early VEFs are disrupted in patients with unilateral spatial neglect and support the concept that deficits in visual processing differ according to the clinical subtype of unilateral spatial neglect and the lesion location. This study also demonstrates the feasibility of using magnetoencephalography to explore subtypes of neglect.

KatsuhiroMizuno

2013-07-01

100

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.

Richard Coppola

2010-01-01

 
 
 
 
101

Epistemics for Learning Disabilities: Contributions from Magnetoencephalography, a Functional Neuroimaging Tool  

Directory of Open Access Journals (Sweden)

Full Text Available The syndrome known as Learning Disabilities (LD was described by S. Kirk in 1963. From that point on, institutions from the US, Canada and Spain have engaged in refining the concept and classification of LDs. The Complutense University in Spain, has proposed a descriptive and all-embracing definition, and has studied the different manifestations of LD, pursuing the description of biological markers and neurological features of LD’s main expressions: dyslexia, dyscalculia, dysorthographia, Attention Deficit and Hyperactivity Disorder –ADHD, and so forth. Findings in LD using functional neuroimaging techniques, namely Magnetoencephalography (MEG, are described. MEG is a non-invasive technique, which records magnetic fields naturally generated by the brain and their spatial distribution. It allows simultaneous functional and structural information. MEG is therefore used in the study of primary and superior cognitive functions, in surveillance of patterns of normal cognitive function and those specific to the different LD clinical manifestations.

VÍCTOR SANTIUSTE-BERMEJO

2008-01-01

102

The neurochemical basis of human cortical auditory processing: combining proton magnetic resonance spectroscopy and magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background A combination of magnetoencephalography and proton magnetic resonance spectroscopy was used to correlate the electrophysiology of rapid auditory processing and the neurochemistry of the auditory cortex in 15 healthy adults. To assess rapid auditory processing in the left auditory cortex, the amplitude and decrement of the N1m peak, the major component of the late auditory evoked response, were measured during rapidly successive presentation of acoustic stimuli. We tested the hypothesis that: (i the amplitude of the N1m response and (ii its decrement during rapid stimulation are associated with the cortical neurochemistry as determined by proton magnetic resonance spectroscopy. Results Our results demonstrated a significant association between the concentrations of N-acetylaspartate, a marker of neuronal integrity, and the amplitudes of individual N1m responses. In addition, the concentrations of choline-containing compounds, representing the functional integrity of membranes, were significantly associated with N1m amplitudes. No significant association was found between the concentrations of the glutamate/glutamine pool and the amplitudes of the first N1m. No significant associations were seen between the decrement of the N1m (the relative amplitude of the second N1m peak and the concentrations of N-acetylaspartate, choline-containing compounds, or the glutamate/glutamine pool. However, there was a trend for higher glutamate/glutamine concentrations in individuals with higher relative N1m amplitude. Conclusion These results suggest that neuronal and membrane functions are important for rapid auditory processing. This investigation provides a first link between the electrophysiology, as recorded by magnetoencephalography, and the neurochemistry, as assessed by proton magnetic resonance spectroscopy, of the auditory cortex.

Tollkötter Melanie

2006-08-01

103

Distribution and character of water in a surge-type glacier revealed by multifrequency and multipolarization ground-penetrating radar  

Science.gov (United States)

We have investigated the distribution and character of radar scatterers in the glacier Bakaninbreen, Svalbard, using ground-penetrating radar (GPR). The GPR profiles showed scattering regions with an undulating upper boundary in both along- and across-glacier orientations. The simplest interpretation of such scattering regions would be a layer of randomly distributed scatterers with an undulating upper boundary, underlying a layer without scatterers. We propose an alternative model of scatterer distribution, in which the scatterers are confined to obliquely dipping planes. This model is shown to be able to reproduce the shape of the scattering regions observed in the field data and is consistent with previous observations of dipping thrust features in Bakaninbreen from radar data and in outcrop. Multifrequency profiles (50, 100, and 200 MHz) contained scatterers with similar measured power, indicating that the scatterers have decimeter-scale dimensions. Multipolarized antenna configurations were used to detect a preferred polarization direction for scattered radiation, which was approximately across glacier, suggesting that the scatterers are nonspherical and aligned across glacier. The scatterers are thought to be large water bodies confined to dipping planar features and elongated in the strike orientation of the planes.

Barrett, B. E.; Murray, T.; Clark, R.; Matsuoka, K.

2008-12-01

104

Left atrial voltage remodeling after pulmonary venous isolation with multipolar radiofrequency ablation  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: Pulmonary vein isolation (PVI is the accepted primary endpoint for catheter ablation of atrial fibrillation (AF. The aim of this study was to evaluate the level of PVI by PVAC, a multipolar circular catheter utilizing bipolar/unipolar radiofrequency (RF energy. Methods: Twenty patients with paroxysmal AF underwent PVAC ablation. PVI was validated by voltage reduction and pacing tests. Before and after RF ablation, left atrium (LA and PV electroanatomic mapping (EAM were performed by EnSite NavX system. Voltage abatement was considered for potentials 24mm: 9/20 (45% vs 11/57 (19%, p

Francesco Laurenzi

2013-11-01

105

Effective medium multipolar tensor analysis of second-harmonic generation from metal nanoparticles  

Science.gov (United States)

We present a detailed multipolar tensor analysis of second-harmonic (SH) generation from arrays of L-shaped gold nanoparticles. We define three effective nonlinear tensors, which include electric dipoles only (Aeee) and lowest-order magnetic (and quadrupole) effects at the fundamental (Aeem) and the SH (Amee) frequency. The components of the various tensors are distinguished through their different transformations as the experimental geometry is varied. The response is dominated by electric-dipole effects. However, the higher multipoles also play a significant role and are more important at the fundamental frequency than at the SH frequency. The results correlate well with the particles' plasmonic resonances and symmetry rules.

Zdanowicz, Mariusz; Kujala, Sami; Husu, Hannu; Kauranen, Martti

2011-02-01

106

Abnormal thalamocortical dynamics may be altered by deep brain stimulation: using magnetoencephalography to study phantom limb pain.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Deep brain stimulation (DBS) is used to alleviate chronic pain. Using magnetoencephalography (MEG) to study the mechanisms of DBS for pain is difficult because of the artefact caused by the stimulator. We were able to record activity over the occipital lobe of a patient using DBS for phantom limb pain during presentation of a visual stimulus. This demonstrates that MEG can be used to study patients undergoing DBS provided control stimuli are used to check the reliability of the data. We then ...

Ray, Nj; Jenkinson, N.; Kringelbach, Ml; Hansen, Pc; Pereira, Ea; Brittain, Js; Holland, P.; Holliday, Ie; Owen, S.; Stein, J.; Aziz, T.

2009-01-01

107

Anisotropic multipolar exchange interactions in systems with strong spin-orbit coupling  

Science.gov (United States)

We introduce a theoretical framework for computations of anisotropic multipolar exchange interactions found in many spin-orbit coupled magnetic systems and propose a method to extract these coupling constants using a density functional total energy calculation. This method is developed using a multipolar expansion of local density matrices for correlated orbitals that are responsible for magnetic degrees of freedom. Within the mean-field approximation, we show that each coupling constant can be recovered from a series of total energy calculations via what we call the "pair-flip" technique. This technique flips the relative phase of a pair of multipoles and computes the corresponding total energy cost associated with the given exchange constant. To test it, we apply our method to uranium dioxide, which is a system known to have pseudospin J =1 superexchange induced dipolar, and superexchange plus spin-lattice induced quadrupolar orderings. Our calculation reveals that the superexchange and spin-lattice contributions to the quadrupolar exchange interactions are about the same order with ferro- and antiferromagnetic contributions, respectively. This highlights a competition rather than a cooperation between them. Our method could be a promising tool to explore magnetic properties of rare-earth compounds and hidden-order materials.

Pi, Shu-Ting; Nanguneri, Ravindra; Savrasov, Sergey

2014-07-01

108

An analysis of the electromagnetic field in multi-polar linear induction system  

International Nuclear Information System (INIS)

In this paper a new method for determination of the electromagnetic field vectors in a multi-polar linear induction system (LIS) is described. The analysis of the electromagnetic field has been done by four dimensional electromagnetic potentials in conjunction with theory of the magnetic loops . The electromagnetic field vectors are determined in the Minkovski's space as elements of the Maxwell's tensor. The results obtained are compared with those got from the analysis made by the finite elements method (FEM).With the method represented in this paper one can determine the electromagnetic field vectors in the multi-polar linear induction system using four-dimensional potential. A priority of this method is the obtaining of analytical results for the electromagnetic field vectors. These results are also valid for linear media. The dependencies are valid also at high speeds of movement. The results of the investigated linear induction system are comparable to those got by the finite elements method. The investigations may be continued in the determination of other characteristics such as drag force, levitation force, etc. The method proposed in this paper for an analysis of linear induction system can be used for optimization calculations. (Author)

109

Multi-polar resistance switching and memory effect in copper phthalocyanine junctions  

Science.gov (United States)

Copper phthalocyanine junctions, fabricated by magnetron sputtering and evaporating methods, show multi-polar (unipolar and bipolar) resistance switching and the memory effect. The multi-polar resistance switching has not been observed simultaneously in one organic material before. With both electrodes being cobalt, the unipolar resistance switching is universal. The high resistance state is switched to the low resistance state when the bias reaches the set voltage. Generally, the set voltage increases with the thickness of copper phthalocyanine and decreases with increasing dwell time of bias. Moreover, the low resistance state could be switched to the high resistance state by absorbing the phonon energy. The stability of the low resistance state could be tuned by different electrodes. In Au/copper phthalocyanine/Co system, the low resistance state is far more stable, and the bipolar resistance switching is found. Temperature dependence of electrical transport measurements demonstrates that there are no obvious differences in the electrical transport mechanism before and after the resistance switching. They fit quite well with Mott variable range hopping theory. The effect of Al2O3 on the resistance switching is excluded by control experiments. The holes trapping and detrapping in copper phthalocyanine layer are responsible for the resistance switching, and the interfacial effect between electrodes and copper phthalocyanine layer affects the memory effect.

Qiao, Shi-Zhu; Kang, Shi-Shou; Qin, Yu-Feng; Li, Qiang; Zhong, Hai; Kang, Yun; Yu, Shu-Yun; Han, Guang-Bing; Yan, Shi-Shen; Mei, Liang-Mo

2014-05-01

110

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

CERN Document Server

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 f_{l m} with its l-th root, \\rho_{l m} = f_{l m}^{1/l}, agree quite well with the numerical amplitudes up to the Kerr-spin value q \\leq 0.95 for orbital velocities v \\leq 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 \\rho_{l m}. 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 mode...

Pan, Yi; Fujita, Ryuichi; Racine, Etienne; Tagoshi, Hideyuki

2010-01-01

111

Improved resummation of post-Newtonian multipolar waveforms from circularized compact binaries  

International Nuclear Information System (INIS)

We improve and generalize a resummation method of post-Newtonian multipolar waveforms from circular (nonspinning) compact binaries introduced in Refs. 1,2. One of the characteristic features of this resummation method is to replace the usual additive decomposition of the standard post-Newtonian approach by a multiplicative decomposition of the complex multipolar waveform hlm into several (physically motivated) factors: (i) the Newtonian waveform, (ii) a relativistic correction coming from an 'effective source', (iii) leading-order tail effects linked to propagation on a Schwarzschild background, (iv) a residual tail dephasing, and (v) residual relativistic amplitude corrections flm. We explore here a new route for resumming flm based on replacing it by its l-th root: ?lm=flm1/l. In the extreme-mass-ratio case, this resummation procedure results in a much better agreement between analytical and numerical waveforms than when using standard post-Newtonian approximants. We then show that our best approximants behave in a robust and continuous manner as we deform them by increasing the symmetric mass ratio ??m1m2/(m1+m2)2 from 0 (extreme-mass-ratio case) to 1/4 (equal-mass case). The present paper also completes our knowledge of the first post-Newtonian corrections to multipole moments by computing ready-to-use explicit expressions for the first post-Newtonian contributions to the odd-parity (current) multipoles.

112

Multipolar hepatic radiofrequency ablation using up to six applicators: preliminary results  

Energy Technology Data Exchange (ETDEWEB)

Purpose: to evaluate the clinical feasibility and safety of hepatic radiofrequency (RF) ablation using a multipolar RF system permitting the simultaneous use of up to six electrodes. Materials and methods: ten patients (3 female, 7 male, mean age 61) suffering from 29 hepatic metastases (range: 1-5) of different tumors were treated with a modified multipolar RF system (CelonLab Power, Celon Medical Instruments, Teltow, Germany) operating four to six needle-shaped internally cooled RF applicators. The procedure duration, applied energy and generator output were recorded during the intervention. The treatment result and procedure-related complications were analyzed. The achieved coagulation volume was calculated on the basis of contrast-enhanced CT scans 24 hours after RF ablation. Results: complete tumor ablation was achieved in all cases as determined by the post-interventional lack of contrast enhancement in the target region using four applicators in five patients, five applicators in one patient and six applicators in four patients. A mean energy deposition of 353.9 {+-} 176.2 kJ resulted in a mean coagulation volume of 115.9 {+-} 79.5 cm{sup 3}. The mean procedure duration was 74.9 {+-} 21.2 minutes. Four patients showed an intraabdominal hemorrhage which necessitated further interventional treatment (embolization; percutaneous histoacryl injection) in two patients. (orig.)

Bruners, P.; Schmitz-Rode, T. [RWTH Aachen (Germany). Lehrstuhl fuer Angewandte Medizintechnik; Guenther, R.W.; Mahnken, A. [Universitaetsklinikum RWTH Aachen (Germany). Klinik fuer Radiologische Diagnostik

2008-03-15

113

Differential spectral power alteration following acupuncture at different designated places revealed by magnetoencephalography  

Science.gov (United States)

As an ancient therapeutic technique in Traditional Chinese Medicine, acupuncture has been used increasingly in modern society to treat a range of clinical conditions as an alternative and complementary therapy. However, acupoint specificity, lying at the core of acupuncture, still faces many controversies. Considering previous neuroimaging studies on acupuncture have mainly employed functional magnetic resonance imaging, which only measures the secondary effect of neural activity on cerebral metabolism and hemodynamics, in the current study, we adopted an electrophysiological measurement technique named magnetoencephalography (MEG) to measure the direct neural activity. 28 healthy college students were recruited in this study. We filtered MEG data into 5 consecutive frequency bands (delta, theta, alpha, beta and gamma band) and grouped 140 sensors into 10 main brain regions (left/right frontal, central, temporal, parietal and occipital regions). Fast Fourier Transformation (FFT) based spectral analysis approach was further performed to explore the differential band-limited power change patterns of acupuncture at Stomach Meridian 36 (ST36) using a nearby nonacupoint (NAP) as control condition. Significantly increased delta power and decreased alpha as well as beta power in bilateral frontal ROIs were observed following stimulation at ST36. Compared with ST36, decreased alpha power in left and right central, right parietal as well as right temporal ROIs were detected in NAP group. Our research results may provide additional evidence for acupoint specificity.

You, Youbo; Bai, Lijun; Dai, Ruwei; Xue, Ting; Zhong, Chongguang; Liu, Zhenyu; Wang, Hu; Feng, Yuanyuan; Wei, Wenjuan; Tian, Jie

2012-03-01

114

Large-scale spontaneous fluctuations and correlations in brain electrical activity observed with magnetoencephalography.  

Science.gov (United States)

Knowledge about the intrinsic functional architecture of the human brain has been greatly expanded by the extensive use of resting-state functional magnetic resonance imaging (fMRI). However, the neurophysiological correlates and origins of spontaneous fMRI signal changes remain poorly understood. In the present study, we characterized the power modulations of spontaneous magnetoencephalography (MEG) rhythms recorded from human subjects during wakeful rest (with eyes open and eyes closed) and light sleep. Through spectral, correlation and coherence analyses, we found that resting-state MEG rhythms demonstrated ultraslow (<0.1 Hz) spontaneous power modulations that synchronized over a large spatial distance, especially between bilaterally homologous regions in opposite hemispheres. These observations are in line with the known spatio-temporal properties of spontaneous fMRI signals, and further suggest that the coherent power modulation of spontaneous rhythmic activity reflects the electrophysiological signature of the large-scale functional networks previously observed with fMRI in the resting brain. PMID:20123024

Liu, Zhongming; Fukunaga, Masaki; de Zwart, Jacco A; Duyn, Jeff H

2010-05-15

115

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

Science.gov (United States)

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. PMID:24139305

Wright, Barry; Alderson-Day, Ben; Prendergast, Garreth; Kennedy, Juliette; Bennett, Sophie; Docherty, Mary; Whitton, Clare; Manea, Laura; Gouws, Andre; Tomlinson, Heather; Green, Gary

2013-12-30

116

The neural processing of musical instrument size information in the brain investigated by magnetoencephalography  

Science.gov (United States)

The specific cortical representation of size was investigated by recording auditory evoked fields (AEFs) elicited by changes of instrument size and pitch. In Experiment 1, a French horn and one scaled to double the size played a three note melody around F3 or its octave, F4. Many copies of these four melodies were played in random order and the AEF was measured continuously. A similar procedure was applied to saxophone sounds in a separate run. In Experiment 2, the size and type of instrument (French horn and saxophone) were varied without changing the octave. AEFs were recorded in five subjects using magnetoencephalography and evaluated by spatio-temporal source analysis with one equivalent dipole in each hemisphere. The morphology of the source waveforms revealed that each note within the melody elicits a well-defined P1-N1-P2 AEF-complex with adaptation for the 2nd and 3rd note. At the transition of size, pitch, or both, a larger AEF-complex was evoked. However, size changes elicited a stronger N1 than pitch changes. Furthermore, this size-related N1 enhancement was larger for French horn than saxophone. The results indicate that the N1 plays an important role in the specific representation of instrument size.

Rupp, Andre; van Dinther, Ralph; Patterson, Roy D.

2005-04-01

117

Magnetoencephalography based on high-Tc superconductivity: a closer look into the brain?  

CERN Document Server

Magnetoencephalography (MEG) enables the study of brain activity by recording the magnetic fields generated by neural currents and has become an important technique for neuroscientists in research and clinical settings. Unlike the liquid-helium cooled low-Tc superconducting quantum interference devices (SQUIDs) that have been at the heart of modern MEG systems since their invention, high-Tc SQUIDs can operate with liquid nitrogen cooling. The relaxation of thermal insulation requirements allows for a reduction in the stand-off distance between the sensor and the room-temperature environment from a few centimeters to less than a millimeter, where MEG signal strength is significantly higher. Despite this advantage, high-Tc SQUIDs have only been used for proof-of-principle MEG recordings of well-understood evoked activity. Here we show high-Tc SQUID-based MEG may be capable of providing novel information about brain activity due to the close proximity of the sensor to the head. We have performed single- and two-...

Öisjöen, F; Figueras, G A; Chukharkin, M L; Kalabukhov, A; Hedström, A; Elam, M; Winkler, D

2011-01-01

118

Combination of PET and magnetoencephalography in the presurgical assessment of MRI-negative epilepsy  

Directory of Open Access Journals (Sweden)

Full Text Available Despite major advances in neuroimaging, no lesion is visualized on MRI in up to a quarter of patients with drug-resistant focal epilepsy presenting for presurgical evaluation. These patients demonstrate poorer surgical outcomes than those with lesion seen on MRI. Accurate localization of the seizure onset zone is more difficult in MRI-negative patients and often requires invasive EEG recordings. Positron emission tomography (PET and magnetoencephalography (MEG have been proposed as clinically relevant tools to localize the seizure onset zone prior to intracranial EEG recordings. However, there is no consensus regarding the optimal gold standard that should be used for assessing the performance of these pre-surgical investigations. Here, we review the current knowledge concerning the usefulness of PET and MEG for presurgical assessment of MRI-negative epilepsy. Beyond the individual diagnostic performance of MEG and of different PET tracers, including [18F]-fluorodeoxyglucose, [11C]flumazenil, and markers of 5-HT1A receptors, recent data suggest that the combination of PET and MEG might provide greater sensitivity and specificity than that of each of the two individual tests in patients with normal MRI.

SylvainRheims

2013-11-01

119

Simultaneous measurement of neuronal activity and cortical hemodynamics by unshielded magnetoencephalography and near-infrared spectroscopy  

Science.gov (United States)

The correlation between neuronal activity and cortical hemodynamics, namely, neurovascular coupling (NVC), is important to shed light on the mechanism of a variety of brain functions or neuronal diseases. NVC can be studied by simultaneously measuring neuronal activity and cortical hemodynamics. Consequently, noninvasive measurements of the NVC have been widely studied using both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). However, electromagnetic interference between EEG and fMRI is still a major problem. On the other hand, near-infrared spectroscopy (NIRS) is another promising tool for detecting cortical hemodynamics because it can be combined with EEG or magnetoencephalography (MEG) without any electromagnetic interference. Accordingly, in the present study, a simultaneous measurement system-combining an unshielded MEG using a two-dimensional gradiometer based on a low-T superconducting quantum interference device (SQUID) and an NIRS using nonmagnetic thin probes-was developed. This combined system was used to simultaneously measure both an auditory-evoked magnetic field and blood flow change in the auditory cortex. It was experimentally demonstrated that the combined unshielded MEG/NIRS system can simultaneously measure neuronal activity and cortical hemodynamics.

Seki, Yusuke; Miyashita, Tsuyoshi; Kandori, Akihiko; Maki, Atsushi; Koizumi, Hideaki

2012-10-01

120

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

International Nuclear Information System (INIS)

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

 
 
 
 
121

Cognitive Impairments in Schizophrenia as Assessed Through Activation and Connectivity Measures of Magnetoencephalography (MEG) Data.  

Science.gov (United States)

The cognitive dysfunction present in patients with schizophrenia is thought to be driven in part by disorganized connections between higher-order cortical fields. Although studies utilizing electroencephalography (EEG), PET and fMRI have contributed significantly to our understanding of these mechanisms, magnetoencephalography (MEG) possesses great potential to answer long-standing questions linking brain interactions to cognitive operations in the disorder. Many experimental paradigms employed in EEG and fMRI are readily extendible to MEG and have expanded our understanding of the neurophysiological architecture present in schizophrenia. Source reconstruction techniques, such as adaptive spatial filtering, take advantage of the spatial localization abilities of MEG, allowing us to evaluate which specific structures contribute to atypical cognition in schizophrenia. Finally, both bivariate and multivariate functional connectivity metrics of MEG data are useful for understanding how these interactions in the brain are impaired in schizophrenia, and how cognitive and clinical outcomes are affected as a result. We also present here data from our own laboratory that illustrates how some of these novel functional connectivity measures, specifically imaginary coherence (IC), are quite powerful in relating disconnectivity in the brain to characteristic behavioral findings in the disorder. PMID:21160543

Hinkley, Leighton B N; Owen, Julia P; Fisher, Melissa; Findlay, Anne M; Vinogradov, Sophia; Nagarajan, Srikantan S

2010-01-01

122

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

Science.gov (United States)

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. PMID:23185541

Guo, Xinyao; Xiang, Jing; Wang, Yingying; O'Brien, Hope; Kabbouche, Marielle; Horn, Paul; Powers, Scott W; Hershey, Andrew D

2012-01-01

123

Plasma diffusion through a two-dimensional magnetic field. Application to multipolar discharge  

International Nuclear Information System (INIS)

In this work, a collisional plasma diffusion theory through a two dimensional magnetic field is presented. This study allows to define two types of diffusion domains: the weak field domain, where diffusion is practically isotropic, and strong field domain where diffusion is only parallel to field lines. The inversion and ion confinement by ambipolar electric field, perpendicular to line fields, is also understood. This theory is applied to a multipolar discharge. A sheath thickness can be defined, which is the width of the region in which the plasma diffusion is limited by the magnetic field. Little dependence with magnetic field is found. All these results have been observed experimentally. The diffusion equation numerical solution allows to find the density and potential profiles. The comparison of the density in the middle of the plasma with and without multicusp field is done

124

Role of pairing degrees of freedom and higher multipolarity deformations in spontaneous fission process  

CERN Document Server

Spontaneous fission (T sub s sub f) and alpha-decay half-lives (T subalpha) of the heaviest nuclei with atomic number 100 <= Z <= 114 are calculated on the basis of the deformed Woods-Saxon potential. The calculations of (T sub s sub f) are performed by the WKB approximation, in the multi-dimensional dynamical-programing method (MDP). We have examined three different effects: the effect of higher even-multipolarity shape parameters (beta sub 6 and beta sub 8), the role of reflection-asymmetry (beta sub 3 and beta sub 5) and the influence of pairing degrees of freedom (DELTA sub p and DELTA sub n). Alpha-decay half-lives (T subalpha) have been calculated by the Viola-Seaborg (V-S) formula with the parameters modified to the latest experimental data.

Lojewski, Z

1999-01-01

125

Level spin-parities and ?-ray transition multipolarities in 140Ce  

International Nuclear Information System (INIS)

The ?? directional correlation method was used to determine the spins of levels in 140Ce populated following the ? decay of 140La. The multipolarities of ?-ray transitions were measured and, on the basis of the dominant multipole and published ICC data, parity assignments were made. Past ambiguities in the decay have been removed, and from the present measurements unique spin-parity assignments are made to the following levels: 2350.0 keV, 5+; 2516.1 keV, 3+; 2548.0 keV, 1+. The level systematics of nuclei in this region are examined and it is found that the change from a vibrational- to a rotational-like structure is not so well defined as in heavier isotopes such as Sm or Gd. The behaviour of the 3- level energy as a function of Z value is examined for a group of isotones in this mass region and is found to be linear. (author)

126

Age-related sex differences in language lateralization: A magnetoencephalography study in children.  

Science.gov (United States)

It is well supported by behavioral and neuroimaging studies that typical language function is lateralized to the left hemisphere in the adult brain and this laterality is less well defined in children. The behavioral literature suggests there maybe be sex differences in language development, but this has not been examined systematically with neuroimaging. In this study, magnetoencephalography was used to investigate the spatiotemporal patterns of language lateralization as a function of age and sex. Eighty typically developing children (46 female, 34 male; 4-18 years) participated in an overt visual verb generation task. An analysis method called differential beamforming was used to analyze language-related changes in oscillatory activity referred to as low-gamma event-related desynchrony (ERD). The proportion of ERD over language areas relative to total ERD was calculated. We found different patterns of laterality between boys and girls. Boys showed left-hemisphere lateralization in the frontal and temporal language-related areas across age groups, whereas girls showed a more bilateral pattern, particularly in frontal language-related areas. Differences in patterns of ERD were most striking between boys and girls in the younger age groups, and these patterns became more similar with increasing age, specifically in the preteen years. Our findings show sex differences in language lateralization during childhood; however, these differences do not seem to persist into adulthood. We present possible explanations for these differences. We also discuss the implications of these findings for presurgical language mapping in children and highlight the importance of examining the question of sex-related language differences across development. (PsycINFO Database Record (c) 2014 APA, all rights reserved). PMID:25069054

Yu, Vickie Y; MacDonald, Matt J; Oh, Anna; Hua, Gordon N; De Nil, Luc F; Pang, Elizabeth W

2014-09-01

127

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

Science.gov (United States)

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 3-5 Hz 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 18-22 Hz 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. PMID:24055105

Sunami, Kishiko; Ishii, Akira; Takano, Sakurako; Yamamoto, Hidefumi; Sakashita, Tetsushi; Tanaka, Masaaki; Watanabe, Yasuyoshi; Yamane, Hideo

2013-11-01

128

Correlation between fetal brain activity patterns and behavioral states: an exploratory fetal magnetoencephalography study.  

Science.gov (United States)

The fetal brain remains inaccessible to neurophysiological studies. Magnetoencephalography (MEG) is being assessed to fill this gap. We performed 40 fetal MEG (fMEG) recordings with gestational ages (GA) ranging from 30 to 37 weeks. The data from each recording were divided into 15 second epochs which in turn were classified as continuous (CO), discontinuous (DC), or artifact. The fetal behavioral state, quiet or active sleep, was determined using previously defined criteria based on fetal movements and heart rate variability. We studied the correlation between the fetal state, the GA and the percentage of CO and DC epochs. We also analyzed the spectral edge frequency (SEF) and studied its relation with state and GA. We found that the odds of a DC epoch decreased by 6% per week as the GA increased (P = 0.0036). This decrease was mainly generated by changes during quiet sleep, which showed 52% DC epochs before a 35 week GA versus 38% after 35 weeks (P = 0.0006). Active sleep did not show a significant change in DC epochs with GA. When both states were compared for MEG patterns within each GA group (before and after 35 weeks), the early group was found to have more DC epochs in quiet sleep (54%) compared to active sleep (42%) (P = 0.036). No significant difference in DC epochs between the two states was noted in the late GA group. Analysis of SEF showed a significant difference (P = 0.0014) before and after a 35 week GA, with higher SEF noted at late GA. However, when both quiet and active sleep states were compared within each GA group, the SEF did not show a significant difference. We conclude that fMEG shows reproducible variations in gross features and frequency content, depending on GA and behavioral state. Fetal MEG is a promising tool to investigate fetal brain physiology and maturation. PMID:21237155

Haddad, Naim; Govindan, Rathinaswamy B; Vairavan, Srinivasan; Siegel, Eric; Temple, Jessica; Preissl, Hubert; Lowery, Curtis L; Eswaran, Hari

2011-04-01

129

Suppressive responses by visual food cues in postprandial activities of insular cortex as revealed by magnetoencephalography.  

Science.gov (United States)

'Hara-Hachibu' in Japanese means a subjective sense by which we stop eating just before the motivation to eat is completely lost, a similar concept to caloric restriction (CR). Insular cortex is a critical platform which integrates sensory information into decision-making processes in eating behavior. We compared the responses of insular cortex, as assessed by magnetoencephalography (MEG), immediately after presentation of food images in the Fasting condition with those in the 'Hara-Hachibu' condition. Eleven healthy, right-handed males [age, 27.2±9.6 years; body mass index, 22.6±2.1kg/m(2) (mean±SD)] were enrolled in a randomized, two-crossover experiment (Fasting and 'Hara-Hachibu' conditions). Before the MEG recordings in the 'Hara-Hachibu' condition, the participants consumed rice balls as much as they judged themselves to have consumed shortly before reaching satiety. During the MEG recordings, they viewed food pictures projected on a screen. The intensities of MEG responses to viewing food pictures were significantly lower in the 'Hara-Hachibu' condition than those in the Fasting condition (P<0.05). The intensities of the MEG responses to the visual food stimuli in the 'Hara-Hachibu' condition was positively associated with the factor-3 (food tasted) (r=0.693, P=0.018) and aggregated scores (r=0.659, P=0.027) of the Power of Food Scale, a self-report measure of hedonic hunger. These findings may help to elucidate the neural basis of variability of appetite phenotypes under the condition of CR among individuals, and to develop possible strategies for the maintenance of adequate CR in daily life. PMID:24768717

Yoshikawa, Takahiro; Tanaka, Masaaki; Ishii, Akira; Watanabe, Yasuyoshi

2014-06-01

130

Dynamic neural activity recorded from human amygdala during fear conditioning using magnetoencephalography.  

Science.gov (United States)

Magnetoencephalography (MEG) was used to record the dynamics of amygdala neuronal population activity during fear conditioning in human participants. Activation during conditioning training was compared to habituation and extinction sessions. Conditioned stimuli (CS) were visually presented geometric figures, and unconditioned stimuli (US) were aversive white-noise bursts. The CS+ was paired with the US on 50% of presentations and the CS- was never paired. The precise temporal resolution of MEG allowed us to address the issue of whether the amygdala responds to the onset or offset of the CS+, and/or the expectation of the initiation or offset of the an omitted auditory US. Fear conditioning elicited differential amygdala activation for the unpaired CS+ compared to the CS-, extinction and habituation. This was especially robust in the right hemisphere at CS onset. The strongest peaks of amygdala activity occurred at an average of 270 ms in the right and 306 ms in the left hemisphere following unpaired CS+ onset, and following offset at 21 ms in the left and 161 ms in the right (corresponding to an interval of 108 ms and 248 ms after the anticipated onset of the US, respectively). However, the earliest peaks in this epoch preceded US onset in most subjects. Thus, the activity dynamics suggest that the amygdala both differentially responds to stimuli and anticipates the arrival of stimuli based on prior learning of contingencies. The amygdala also shows stimulus omission-related activation that could potentially provide feedback about experienced stimulus contingencies to modify future responding during learning and extinction. PMID:17259013

Moses, Sandra N; Houck, Jon M; Martin, Tim; Hanlon, Faith M; Ryan, Jennifer D; Thoma, Robert J; Weisend, Michael P; Jackson, Eric M; Pekkonen, Eero; Tesche, Claudia D

2007-03-15

131

Neural effects of mental fatigue caused by continuous attention load: a magnetoencephalography study.  

Science.gov (United States)

Mental fatigue can be defined as a psychobiological state caused by prolonged periods of demanding cognitive activity and manifests as a reduced efficiency in cognitive performance. Mental fatigue is one of the most significant causes of accidents in modern society. Therefore, understanding the neural mechanisms of mental fatigue is important. However, the neural mechanisms of mental fatigue are not fully understood. In this study, we investigated the neural activity that results from mental fatigue caused by a continuous attention load. We used magnetoencephalography (MEG) to evaluate the neural activities during the attention task. Ten healthy male volunteers participated in this study. They performed a continuous attention task lasting 10 min. Subjective ratings of mental fatigue, mental stress, boredom, and sleepiness were performed just after the task trial. MEG data were analyzed using narrow-band adaptive spatial filtering methods. An increase in the beta-frequency band (13-25 Hz) power in the right inferior and middle frontal gyri (Brodmann?s areas 44 and 9 respectively) was caused by the mental fatigue. The increase in the beta-frequency band power in the right middle frontal gyrus was negatively associated with the self-reported level of mental stress and was positively associated with those of boredom and sleepiness. These results demonstrate that performing a continuous mental fatigue-inducing task causes changes in the activation of the prefrontal cortex, and manifests as an increased beta-frequency power in this brain area as well as sleepiness. Our results contribute to greater understanding of the neural mechanisms of mental fatigue. PMID:24642273

Tanaka, Masaaki; Ishii, Akira; Watanabe, Yasuyoshi

2014-05-01

132

The Neural Mechanisms Underlying the Decision to Rest in the Presence of Fatigue: A Magnetoencephalography Study  

Science.gov (United States)

Adequate rest is essential to avoid fatigue and disruption of homeostasis. However, the neural mechanisms underlying the decision to rest are not well understood. In the present study, we aimed to clarify the neural mechanisms of this decision-making process using magnetoencephalography. Fifteen healthy volunteers participated in decision and control experiments performed in a cross-over fashion. In the decision experiment, participants performed 1,200 reverse Stroop test trials and were intermittently asked to decide whether they wanted to take a rest or continue. In the control experiments, participants performed 1,200 reverse Stroop test trials and were instructed to press a response button intermittently without making any decision. Changes in oscillatory brain activity were assessed using a narrow-band adaptive spatial filtering method. The levels of decrease in theta (4–8 Hz) band power in left Brodmann's area (BA) 31, alpha (8–13 Hz) band power in left BA 10 and BA 9, and beta (13–25 Hz) band power in right BA 46 and left BA 10 were greater in trials when the participant opted to rest (rest trials) than those in control trials. The decrease in theta band power in BA 31 in the rest trials was positively correlated with the subjective level of fatigue after the decision experiment. These results demonstrated that the dorsolateral prefrontal cortex, frontal pole, and posterior cingulate cortex play a role in the decision to rest in the presence of fatigue. These findings may help clarify the neural mechanisms underlying fatigue and fatigue-related problems. PMID:25303465

Ishii, Akira; Tanaka, Masaaki; Watanabe, Yasuyoshi

2014-01-01

133

High-Tc superconducting quantum interference device recordings of spontaneous brain activity: Towards high-Tc magnetoencephalography  

Science.gov (United States)

We have performed single- and two-channel high transition temperature (high-Tc) superconducting quantum interference device (SQUID) magnetoencephalography (MEG) recordings of spontaneous brain activity in two healthy human subjects. We demonstrate modulation of two well-known brain rhythms: the occipital alpha rhythm and the mu rhythm found in the motor cortex. We further show that despite higher noise-levels compared to their low-Tc counterparts, high-Tc SQUIDs can be used to detect and record physiologically relevant brain rhythms with comparable signal-to-noise ratios. These results indicate the utility of high-Tc technology in MEG recordings of a broader range of brain activity.

Öisjöen, F.; Schneiderman, J. F.; Figueras, G. A.; Chukharkin, M. L.; Kalabukhov, A.; Hedström, A.; Elam, M.; Winkler, D.

2012-03-01

134

Eficacia de los imanes permanentes multipolares en el tratamiento del dolor crónico en pacientes con osteoartrosis generalizada / Effectiveness of the multipolar permanent magnets in the treatment of chronic pain in patients with generalized osteoarthrosis  

Scientific Electronic Library Online (English)

Full Text Available SciELO Cuba | Language: Spanish Abstract in spanish Se efectuó un estudio longitudinal y controlado de 100 pacientes con osteoartrosis generalizada, atendidos en el Servicio de Medicina Natural y Tradicional del Hospital Provincial Docente Clinicoquirúrgico "Saturnino Lora Torres" de Santiago de Cuba, desde enero hasta diciembre del 2010, a fin de ev [...] aluar la eficacia de los imanes permanentes multipolares en el tratamiento del dolor crónico en los afectados. Estos imanes se ubicaron y fijaron en diferentes puntos de acupunturas para aliviar la dolencia. Los niveles de dolor se cuantificaron mediante la Escala Visual Análoga, por sexo y rango de edades; se evaluaron a los 0, 30, 60 y 90 días durante la terapia. Se demostró la factibilidad del uso de los imanes permanentes multipolares en el alivio del dolor de los pacientes con osteoartrosis generalizada por ser simples, seguros, eficaces y no inducir efectos adversos en el organismo. Abstract in english A longitudinal and controlled study of 100 patients with generalized osteoarthrosis, assisted in the Service of Natural and Traditional Medicine of "Saturnino Lora Torres" Clinical Surgical Teaching Provincial Hospital in Santiago de Cuba was carried out from January to December, 2010, in order to e [...] valuate the effectiveness of the multipolar permanent magnets in the treatment of the chronic pain in those affected. These magnets were placed and fixed in different acupuncture points to reduce pain. The pain levels were quantified by means of the Analogue Visual Scale, by sex and age range; they were evaluated at the 0, 30, 60 and 90 days during the therapy. The feasibility of the use of the multipolar permanent magnets was demonstrated in the relief of pain of the patients with generalized osteoarthrosis as they are simple, sure, effective and induce no adverse effects in the organism.

Mario, Hechavarría Sánchez; Mercedes, Gay Muguercia; César, Hernández Acosta; Luis Enrique, Bergues Cabrales.

2013-11-01

135

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2011-01-01

136

Multipolar radiofrequency ablation using 4–6 applicators simultaneously: A study in the ex vivo bovine liver  

Energy Technology Data Exchange (ETDEWEB)

In this study the volume and shape of coagulation zones after multipolar radiofrequency ablation (RFA) with simultaneous use of 4–6 applicators in the ex vivo bovine liver were investigated. The RF-applicators were positioned in 13 different configurations to simulate ablation of large solitary tumors and simultaneous ablation of multiple lesions with 120 kJ of applied energy/session. In total, 110 coagulation zones were induced. Standardized measurements of the volume and shape of the coagulation zones were carried out on magnetic resonance images and statistically analyzed. The coagulation zones induced with solitary applicators and with 2 applicators were imperceptibly small and incomplete, respectively. At 20 mm applicator distance, the total ablated volume was significantly larger if all applicators were arranged in a single group compared to placement in 2 distant applicator groups, each consisting of 3 applicators (p = .001). The mean total coagulated volume ranged from immeasurably small (if 6 solitary applicators were applied simultaneously) to 74.7 cc (if 6 applicators at 30 mm distance between neighboring applicators were combined to a single group). Applicator distance, number and positioning array impacted time and shape. The coagulation zones surrounding groups with 4–6 applicators were regularly shaped, homogeneous and completely fused, and the axial diameters were almost constant. In conclusion, multipolar RFA with 4–6 applicators is feasible. The multipolar simultaneous mode should be applied for large and solitary lesions only, small and multiple tumors should be ablated consecutively in standard multipolar mode with up to 3 applicators.

Stoffner, Rudolf, E-mail: rudi_stoffner@hotmail.com [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria); Kremser, Christian, E-mail: Christian.Kremser@i-med.ac.at [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria); Schullian, Peter, E-mail: Peter.Schullian@i-med.ac.at [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria); Haidu, Marion, E-mail: Marion.Haidu@i-med.ac.at [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria); Widmann, Gerlig, E-mail: Gerlig.Widmann@i-med.ac.at [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria); Bale, Reto J., E-mail: Reto.Bale@i-med.ac.at [Innsbruck Medical University, Department of Radiology, Anichstr. 35, A-6020 Innsbruck (Austria)

2012-10-15

137

Multipolar radiofrequency ablation using 4–6 applicators simultaneously: A study in the ex vivo bovine liver  

International Nuclear Information System (INIS)

In this study the volume and shape of coagulation zones after multipolar radiofrequency ablation (RFA) with simultaneous use of 4–6 applicators in the ex vivo bovine liver were investigated. The RF-applicators were positioned in 13 different configurations to simulate ablation of large solitary tumors and simultaneous ablation of multiple lesions with 120 kJ of applied energy/session. In total, 110 coagulation zones were induced. Standardized measurements of the volume and shape of the coagulation zones were carried out on magnetic resonance images and statistically analyzed. The coagulation zones induced with solitary applicators and with 2 applicators were imperceptibly small and incomplete, respectively. At 20 mm applicator distance, the total ablated volume was significantly larger if all applicators were arranged in a single group compared to placement in 2 distant applicator groups, each consisting of 3 applicators (p = .001). The mean total coagulated volume ranged from immeasurably small (if 6 solitary applicators were applied simultaneously) to 74.7 cc (if 6 applicators at 30 mm distance between neighboring applicators were combined to a single group). Applicator distance, number and positioning array impacted time and shape. The coagulation zones surrounding groups with 4–6 applicators were regularly shaped, homogeneous and completely fused, and the axial diameters were almost constant. In conclusion, multipolar RFA with 4–6 applicators is feasible. The multipolar simultaneous mode should be applied for large and solitary lesions only, small and multiple tumors should be ablated consecutively in standard multipolar mode with up to 3 applicators

138

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.)

139

The Evolutionary Dynamics of Biofuel Value Chains : From Unipolar and Government-Driven to Multipolar Governance  

DEFF Research Database (Denmark)

In this paper I propose to push the frontier of global value chain (GVC) governance analysis through the concept of ‘polarity’. Much of the existing GVC literature has focused on ‘unipolar’ value chains, where one group of ‘lead firms’ inhabiting a specific function in a chain plays a dominant role in governing it. Some scholars have explored the dynamics of governance in GVCs characterized as ‘bipolar’, where two sets of actors in different functional positions both drive the chain. I expand this direction further to suggest conceptualizing governance within a continuum between unipolarity and multipolarity. Empirically, I do so by examining the evolutionary dynamics of governance in biofuel value chains, with specific focus on the key regulatory and institutional features that facilitated their emergence and expansion. First, I examine the formation, evolution, and governance of three national/regional value chains (in Brazil, the US, and the EU); then, I provide evidence to support a trend towards the increasing but still partial formation of a global biofuel value chain and examine its governance traits.

Ponte, Stefano

2014-01-01

140

Neutron star deformation due to arbitrary-order multipolar magnetic fields  

CERN Document Server

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

 
 
 
 
141

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

142

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

International Nuclear Information System (INIS)

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 m2 before RF ablation vs. 47.2 ± 11.9 ml/min/1.73 m2 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.

143

An iterative algorithm for sparse and constrained recovery with applications to divergence-free current reconstructions in magneto-encephalography  

CERN Document Server

We propose an iterative algorithm for the minimization of a $\\ell_1$-norm penalized least squares functional, under additional linear constraints. The algorithm is fully explicit: it uses only matrix multiplications with the three matrices present in the problem (in the linear constraint, in the data misfit part and in penalty term of the functional). None of the three matrices must be invertible. Convergence is proven in a finite-dimensional setting. We apply the algorithm to a synthetic problem in magneto-encephalography where it is used for the reconstruction of divergence-free current densities subject to a sparsity promoting penalty on the wavelet coefficients of the current densities. We discuss the effects of imposing zero divergence and of imposing joint sparsity (of the vector components of the current density) on the current density reconstruction.

Loris, Ignace

2012-01-01

144

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

Science.gov (United States)

The ability to perform magnetic resonance imaging (MRI) in ultra-low magnetic fields (ULF) of ?100 ?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.; Burmistrov, E.; Magnelind, P. E.; Schultz, L.; Urbaitis, A. V.; Volegov, P. L.; Yoder, J.; Espy, M. A.

2012-11-01

145

Bilateral parietal and contralateral responses during maintenance of unilaterally encoded objects in visual short-term memory: evidence from magnetoencephalography.  

Science.gov (United States)

A component of the event-related magnetic field (ERMF) response was observed in magnetoencephalographic signals recorded during the maintenance of information in visual short-term memory (VSTM). This sustained posterior contralateral magnetic (SPCM) field is likely the magnetic equivalent of the sustained posterior contralateral negativity (SPCN) found in electrophysiology. Magnetoencephalography data showed, at the sensor level, a bilateral activation over the parietal cortex that increased in amplitude for higher memory load. Others sensors, also over the parietal cortex, showed an activation pattern similar to the SPCN with higher activation for the hemisphere contralateral to the visual field from which visual information was encoded. These two activation patterns suggest that the SPCN and SPCM are generated by a network of cortical sources that includes bilateral parietal loci, likely intra-parietal/intra-occipital cortex, and contralateral parietal sources. PMID:19497007

Robitaille, Nicolas; Grimault, Stephan; Jolicoeur, Pierre

2009-09-01

146

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

CERN Document Server

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

147

Building on the EGIPPS performance assessment: the multipolar framework as a heuristic to tackle the complexity of performance of public service oriented health care organisations  

Science.gov (United States)

Background Performance of health care systems is a key concern of policy makers and health service managers all over the world. It is also a major challenge, given its multidimensional nature that easily leads to conceptual and methodological confusion. This is reflected by a scarcity of models that comprehensively analyse health system performance. Discussion In health, one of the most comprehensive performance frameworks was developed by the team of Leggat and Sicotte. Their framework integrates 4 key organisational functions (goal attainment, production, adaptation to the environment, and values and culture) and the tensions between these functions. We modified this framework to better fit the assessment of the performance of health organisations in the public service domain and propose an analytical strategy that takes it into the social complexity of health organisations. The resulting multipolar performance framework (MPF) is a meta-framework that facilitates the analysis of the relations and interactions between the multiple actors that influence the performance of health organisations. Summary Using the MPF in a dynamic reiterative mode not only helps managers to identify the bottlenecks that hamper performance, but also the unintended effects and feedback loops that emerge. Similarly, it helps policymakers and programme managers at central level to better anticipate the potential results and side effects of and required conditions for health policies and programmes and to steer their implementation accordingly. PMID:24742181

2014-01-01

148

Critical excitation-rate enhancement of a dipolar scatterer close to a plasmonic nanosphere and importance of multipolar self-coupling  

Science.gov (United States)

We develop an electrodynamic model based on dyadic Green's functions for analyzing the near-field interactions between a dipolar scatterer (DS) and a plasmonic nanosphere (PN) under external excitation, accounting for multipolar contributions in the evaluation of the scattered fields. In particular, we include all the radiative and nonradiative field interactions between the DS and the PN, particularly the physical mechanism of DS's self-coupling through the PN, which is either neglected or approximated in previous work. Our objective is to show under which conditions self-coupling is important for strong excitation-rate enhancement of the DS and provide a description of the system's properties. We analytically investigate the conditions under which the excitation rate of a DS, such as an organic dye or a quantum dot, is enhanced when located in close proximity to a PN. We show the existence of critical conditions in terms of polarizabilities and distances that lead to large enhancement based on self-coupling and how to predict it.

Tork Ladani, Faezeh; Campione, Salvatore; Guclu, Caner; Capolino, Filippo

2014-09-01

149

Comparative analysis of transverse intrafascicular multichannel, longitudinal intrafascicular and multipolar cuff electrodes for the selective stimulation of nerve fascicles  

Science.gov (United States)

The selection of a suitable nerve electrode for neuroprosthetic applications implies a trade-off between invasiveness and selectivity, wherein the ultimate goal is achieving the highest selectivity for a high number of nerve fascicles by the least invasiveness and potential damage to the nerve. The transverse intrafascicular multichannel electrode (TIME) is intended to be transversally inserted into the peripheral nerve and to be useful to selectively activate subsets of axons in different fascicles within the same nerve. We present a comparative study of TIME, LIFE and multipolar cuff electrodes for the selective stimulation of small nerves. The electrodes were implanted on the rat sciatic nerve, and the activation of gastrocnemius, plantar and tibialis anterior muscles was recorded by EMG signals. Thus, the study allowed us to ascertain the selectivity of stimulation at the interfascicular and also at the intrafascicular level. The results of this study indicate that (1) intrafascicular electrodes (LIFE and TIME) provide excitation circumscribed to the implanted fascicle, whereas extraneural electrodes (cuffs) predominantly excite nerve fascicles located superficially; (2) the minimum threshold for muscle activation with TIME and LIFE was significantly lower than with cuff electrodes; (3) TIME allowed us to selectively activate the three tested muscles when stimulating through different active sites of one device, both at inter- and intrafascicular levels, whereas selective activation using multipolar cuff (with a longitudinal tripolar stimulation configuration) was only possible for two muscles, at the interfascicular level, and LIFE did not activate selectively more than one muscle in the implanted nerve fascicle.

Badia, Jordi; Boretius, Tim; Andreu, David; Azevedo-Coste, Christine; Stieglitz, Thomas; Navarro, Xavier

2011-06-01

150

Injection and Confinement of Plasma in a Stellarator with a Multipolar (? =2) Helical Field  

International Nuclear Information System (INIS)

We give the results of external injection of plasma into a closed magnetic trap and on the investigation of the effect of helical fields on the maintenance of the plasma. The ''L-I'' apparatus consists of a toroidal magnetic trap of stellarator type with a continuous ''double-thread'' multipolar (? = 2) helical field. The large diameter of the torus is 120 cm and the diameter of the vacuum chamber section 10 cm. The maximum value of the longitudinal field H is 104 Oe. The magnetic field of the stellarator is variable in time, to enable a study of adiabatic heating of the plasma in a trap of this type. The L-I stellarator and low-energy electron beams were used to investigate the structure of the magnetic surfaces. The method made it possible to determine the existence and form of closed magnetic surfaces over a wide range of the ratio of the helical and longitudinal fields. Resonance perturbations of the magnetic surfaces were detected that led to splitting of the latter and the formation of rosettes. Magnetic measurements confirmed the theoretical postulates regarding the magnetic surfaces and the effect of perturbations in resonance and non-resonance cases. Filling of the trap with plasma was effected by injecting plasma jets from spark guns into the transverse magnetic field. The total number of charged particles generated at each injection was ?5 x 1014. Injection could be made both .while the field was growing, with subsequent adiabatic compression of the plasma, and while the field was quasi-constant. Filling of the trap took place over a time of the order of tens of us. The inital density of the plasma was ?1011 cm-3, and the electron temperature ?15 eV. The density of the plasma was measured by the resonance ultra-high-frequency method and its distribution over the section was determined by twin Langmuir probes. The experiments showed the effective influence of a helical field on plasma. In the absence of a helical field, the density distribution was non-symmetrical relative to the centre of the chamber and the plasma drifted towards the external wall of the torus; its lifetime was the order of 100 to 200 ?s. When a helical field was applied then density distribution was symmetrical about the axis of the chamber and was determined by the form of the magnetic surfaces; the constant of density fall-off time was ?1 to 2 ms. The measured lifetime of the plasma when the apparatus is working as a stellarator cannot be explained by conventional diffusion. The spectrum of oscillations in the plasma electric fields was studied, and we discuss the various mechanisms capable of explaining the anomalously high plasma diffusion rates that we observed. (author)

151

The stability of source localization in a whole-head magnetoencephalography system demonstrated by auditory evoked field measurements  

Science.gov (United States)

Superconducting quantum interference device (SQUID), which is a very sensitive magnetic sensor, has been widely used to detect the ultra-small magnetic signals in many different territories, especially in the biomagnetic measurement. In this study, a 128-channel SQUID first-order axial gradiometer system for whole-head magnetoencephalography (MEG) measurements was setup to characterize the auditory evoked magnetic fields (AEFs). A 500 Hz monaural pure tone persisting 425 ms with the sound pressure level of 80 dB was randomly applied to the left ear of subject with the inter-stimulus interval of 1.5 ˜ 2.8 s to prevent fatigue of nerves. We demonstrated the characteristic waveforms of AEFs can be accurately recorded and analyzed. Using source localization processes, the origins of AEFs were successfully calculated to be at the auditory cortices which are brain areas known for responsive to sound stimulus. A phantom experiment also proved the good localization accuracy of the established MEG system and measurement procedures. The validated performance of the SQUID system suggests that this technique can also be employed in other brain research.

Chen, Kuen-Lin; Yang, Hong-Chang; Tsai, Sung-Ying; Liu, Yu-Wei; Liao, Shu-Hsien; Horng, Herng-Er; Lee, Yong-Ho; Kwon, Hyukchan

2011-10-01

152

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

153

Many-body dipole-induced dipole model for electrorheological fluids  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Theoretical investigations on electrorheological (ER) fluids usually rely on computer simulations. An initial approach for these studies would be the point-dipole (PD) approximation, which is known to err considerably when the particles approach and finally touch due to many-body and multipolar interactions. Thus various work attempted to go beyond the PD model. Being beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar...

Huang, J. P.; Yu, K. W.

2002-01-01

154

Application of high-quality SiO2 grown by multipolar ECR source to Si/SiGe MISFET  

Science.gov (United States)

A 5 nm-thick SiO2 gate was grown on an Si(p+)/Si(0.8)Ge(0.2) modulation-doped heterostructure at 26 C with an oxygen plasma generated by a multipolar electron cyclotron resonance source. The ultrathin oxide has breakdown field above 12 MV/cm and fixed charge density about 3 x 10 exp 10/sq cm. Leakage current as low as 1/micro-A was obtained with the gate biased at 4 V. The MISFET with 0.25 x 25 sq m gate shows maximum drain current of 41.6 mA/mm and peak transconductance of 21 mS/mm.

Sung, K. T.; Li, W. Q.; Li, S. H.; Pang, S. W.; Bhattacharya, P. K.

1993-01-01

155

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

156

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 SciELO Brazil | Language: Spanish 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 farmac [...] orresistentes. La RM muestra una lesión de 20mm de diámetro en el hipocampo izquierdo. EEG de superficie con ondas theta temporales izquierdas. Registro MEG interictal 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 diame [...] ter lesion located in left hippocampus. Scalp EEG showed left temporal theta waves. Interictal MEG registrations detected isolated spike-wave activity posterior and inferior to 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.

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

157

Study of fundamental mode multipolar kicks in double- and single-feed power couplers for the CLIC main linac accelerating structure  

CERN Document Server

Multipolar kicks from the fundamental mode have been calculated in the CLIC baseline accelerating structure with double-feed input and output power couplers. The influence of such multipolar kicks on the main linac beam dynamics has been investigated. Furthermore, an alternative design of the couplers with single-feed has been studied and compared with the double-feed. Such an alternative would significantly simplify the waveguide system of the main linac but potentially introduce an harmful dipolar kick from the fundamental mode. The geometry of the coupler has been optimized in order to minimize such a dipolar kick and keep it below threshold levels determined with beam dynamics simulations. Influence of the higher order multipoles has been investigated as well and acceptable levels have been determined.

Latina, A; Schulte, D

2012-01-01

158

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

159

Change vector analysis method for inundation change detection using multi-temporal multi-polarized SAR images  

Science.gov (United States)

With the all-weather and day-night imaging capability, synthetic aperture radar (SAR) plays an important role in inundation extent change detection. Inundation extent change detection using SAR will be easy as a result of the dark image tones yielded by specular reflection. Change vector analysis (CVA) method, an effective change detection method, is also a valuable inundation extent change detection method. In CVA method, change magnitude and change direction can be generated separately, which can be used to determine change areas and change types. CVA method also has the ability to process any number of spectral bands and to produce detailed change information. In this paper, CVA method was applied to inundation extent change detection using multi-temporal multi-polarization ENVISAT ASAR alternative polarization images acquired on 2004-08-29, 2004-12-12 and 2005-03-27. The test site is located in Poyang Lake wetland, where land surface had different inundation extent when images were acquired. Firstly these 3 phases of images were registered together. Then the change vectors were calculated using these images. After that change magnitude and direction cosine images were produced. At last the change areas and the corresponding change type were extracted separately using decision tree method. The result indicates that CVA method has potential utility in inundation extent change detection.

Shen, Guozhuang; Guo, Huadong; Liao, Jingjuan

2007-11-01

160

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.

Münch Claudia

2011-04-01

 
 
 
 
161

Sensitivity analysis on the relationship between vegetation growth and multi-polarized radar data  

Science.gov (United States)

Spatially distributed soil moisture is required for watershed applications such as drought and flood prediction, crop irrigation scheduling, etc. In particular, an accurate assessment of the spatial and temporal variation of soil moisture is necessary to improve the predictive capability of runoff models, and for improving and validating hydrological processes forecasting. In recent years, several models have been developed in order to retrieve soil moisture using RADAR data. However, these models need precise prior knowledge about surface roughness. Within this framework, the present research aims to investigate the capabilities of multi polarimetric RADAR images to overcome the use of in situ data for surface roughness assessment. The research is carried out on a 24 km² test-site of DEMMIN (Görmin farm), Mecklenburg Vorpommern, in the North-East of Germany approximately 150 km north from Berlin. Data were acquired within ESA-funded project AgriSAR 2006 between April and July 2006. Images used include L-band in HH, VV and HV polarizations acquired from the airborne sensor E-SAR system operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt - DLR). Two models have been coupled in order to obtain a rms Surface Roughness Index (rSRI) that is related to terrain physical characteristics as well as vegetation surface properties. These are the PSEM (Polarimetric Semi-Empirical Model) published by Oh et al. in 2002 and a semi empirical model developed by Dubois in 1995. A finite difference iterative solution allowed rSRI retrieval without the use of in situ data. Results have been compared both with in situ rms roughness over bare soil and with Normalized Difference Vegetation Index (NDVI) obtained from Airborne Hyperspectral Scanner (AHS) optical images collected over the whole phenological cycle. They show a good agreement with bare soil in situ data, describing its whole range of variability well, and moreover the NDVI vs. rSRI relationship seems similar to that occurring between NDVI and Leaf Area Index (LAI) for most crop types meaning that rSRI can be considered as LAI look like.

Capodici, F.; La Loggia, G.; D'Urso, G.; Maltese, A.; Ciraolo, G.

2009-09-01

162

Steady-state direct-current plasma immersion ion implantation using a multipolar magnetic field electron cyclotron resonance plasma source  

International Nuclear Information System (INIS)

In semiconductor plasma immersion ion implantation (PIII) applications such as the synthesis of silicon-on-insulator by hydrogen PIII and ion cut, only ions arriving at the top surface of the sample stage are important. The ions implanted into the other surfaces of the sample chuck actually not only decrease the efficiency of the power supply and plasma source but also give rise to metallic contamination. In addition, low energy ions introduced by the initial plasma sheath propagation, pulse rise time, and pulse fall time introduce a large surface hydrogen concentration that creates surface damage and affects the wafer bonding efficacy. We have theoretically demonstrated direct-current PIII (DC-PIII) which retains the x-y immersion characteristic while simultaneously reducing this low energy ion component, obviating the need for the expensive power modulator, and extending the voltage ceiling that is no longer limited by the vacuum chamber and power modulator. In this article, we describe our hydrogen DC-PIII experiments using a conducting grid placed between the wafer stage and a multipolar electron cyclotron resonance plasma source. The grounded grid stops the propagation of the plasma sheath, thereby removing the vacuum chamber size limitation. Ions are formed in the plasma sustained by an external plasma source above the grid and accelerated through the lower zone to be implanted into the wafer biased by only a dc power supply. Atomic force microscopy, hydrogen fopply. Atomic force microscopy, hydrogen forward scattering, and secondary ion mass spectrometry analyses indicate uniform hydrogen PIII into a 100 mm silicon wafer and the surface hydrogen component is indeed reduced significantly compared to conventional pulsed PIII

163

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese 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. Abstract in english 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 ne [...] w 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.

164

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

2003-06-01

165

Experimental investigation of microwave interaction with magnetoplasma in miniature multipolar configuration using impedance measurements  

Science.gov (United States)

A miniature microwave plasma source employing both radial and axial magnetic fields for plasma confinement has been developed for micro-propulsion applications. Plasma is initiated by launching microwaves via a short monopole antenna to circumvent geometrical cutoff limitations. The amplitude and phase of the forward and reflected microwave power is measured to obtain the complex reflection coefficient from which the equivalent impedance of the plasma source is determined. Effect of critical plasma density condition is reflected in the measurements and provides insight into the working of the miniature plasma source. A basic impedance calculation model is developed to help in understanding the experimental observations. From experiment and theory, it is seen that the equivalent impedance magnitude is controlled by the coaxial discharge boundary conditions, and the phase is influenced primarily by the plasma immersed antenna impedance.

Dey, Indranuj; Toyoda, Yuji; Yamamoto, Naoji; Nakashima, Hideki

2014-09-01

166

Magnetar Giant Flares in Multipolar Magnetic Fields --- I. Fully and Partially Open Eruptions of Flux Ropes  

CERN Document Server

We propose a catastrophic eruption model for magnetar's enormous energy release during giant flares, in which a toroidal and helically twisted flux rope is embedded within a force-free magnetosphere. The flux rope stays in stable equilibrium states initially and evolves quasi-statically. Upon the loss of equilibrium point is reached, the flux rope cannot sustain the stable equilibrium states and erupts catastrophically. During the process, the magnetic energy stored in the magnetosphere is rapidly released as the result of destabilization of global magnetic topology. The magnetospheric energy that could be accumulated is of vital importance for the outbursts of magnetars. We carefully establish the fully open fields and partially open fields for various boundary conditions at the magnetar surface and study the relevant energy thresholds. By investigating the magnetic energy accumulated at the critical catastrophic point, we find that it is possible to drive fully open eruptions for dipole dominated background...

Huang, Lei

2014-01-01

167

The Fate of Sub-micron Circumplanetary Dust Grains II: Multipolar Fields  

CERN Document Server

We study the radial and vertical stability of dust grains launched with all charge-to-mass ratios at arbitrary distances from rotating planets with complex magnetic fields. We show that the aligned dipole magnetic field model analyzed by Jontof-Hutter and Hamilton (2012) is an excellent approximation in most cases, but that fundamentally new physics arises with the inclusion of non-axisymmetric magnetic field terms. In particular, large numbers of distant negatively-charged dust grains, stable in a magnetic dipole, can be driven to escape by a more complex field. We trace the origin of the instability to overlapping Lorentz resonances which are extremely powerful when the gravitational and electromagnetic forces on a dust grain are comparable. These resonances enable a dust grain to tap the spin energy of the planet to power its escape. We also explore the relatively minor influence of different launch speeds and the far more important effects of variable grain charge. Only the latter are capable of significa...

Jontof-Hutter, Daniel

2012-01-01

168

Parametrized post-Newtonian theory of reference frames, multipolar expansions and equations of motion in the N-body problem  

International Nuclear Information System (INIS)

r. Scalar-tensor equations of the gravitational field are solved by making use of the post-Newtonian approximations so that the metric tensor and the scalar field are obtained as functions of the global and local coordinates. A correspondence between the local and global coordinate frames is found by making use of asymptotic expansion matching technique. This technique allows us to find a class of the post-Newtonian coordinate transformations between the frames as well as equations of translational motion of the origin of the local frame along with the law of relativistic precession of its spatial axes. These transformations depend on the PPN parameters ? and ?, generalize general relativistic transformations of the IAU 2000 resolutions, and should be used in the data processing of the solar system gravitational experiments aimed to detect the presence of the scalar field. These PPN transformations are also applicable in the precise time-keeping metrology, celestial mechanics, astrometry, geodesy and navigation.We consider a multipolar post-Newtonian expansion of the gravitational and scalar fields and construct a set of internal and external gravitational multipoles depending on the parameters ? and ?. These PPN multipoles generalize the Thorne-Blanchet-Damour multipoles defined in harmonic coordinates of general theory of relativity. The PPN multipoles of the scalar-tensor theory of gravity are split in three classes-active, conformal, and scalar multipoles. Only two of them are algebraically independent and we chose to work with the conformal and active multipoles. We derive the laws of conservations of the multipole moments and show that they must be formulated in terms of the conformal multipoles. We focus then on the law of conservation of body's linear momentum which is defined as a time derivative of the conformal dipole moment of the body in the local coordinates. We prove that the local force violating the law of conservation of the body's linear momentum depends exclusively on the active multipole moments of the body along with a few other terms which depend on the internal structure of the body and are responsible for the violation of the strong principle of equivalence (the Nordtvedt effect).The PPN translational equations of motion of extended bodies in the global coordinate frame and with all gravitational multipoles taken into account are derived from the law of conservation of the body's linear momentum supplemented by the law of motion of the origin of the local frame derived from the matching procedure. We use these equations to analyze transnational motion of shperically symmetric and rigidly rotating bodies having finite size. Spherical symmetry is defined in the local frame of each body through a set of conditions imposed on the shape of the body and the distribution of its internal density, pressure and velocity field. We prove that our formalism brings about the parametrized post-Newtonian EIH equations of motion of the bodies if the finite-size effects are neglected. Analysis of the finite-size effects reveal that they are proportional to the parameter ? coupled with the second and higher-order rotational moments of inertia of the bodies. The finite-size effects in the translational equations of motion can be appreciably large at the latest stage of coalescence of binary neutron stars and can be important in calculations of gravitational waveform templates for the gravitational-wave interferometers.The PPN rotational equations of motion for each extended body possessing an arbitrary multipolar structure of its gravitational field, have been derived in body's local coordinates. Spin of the body is defined phenomenologically in accordance with the post-Newtonian law of conservation of angular momentum of an isolated system. Torque consists of a general relativistic part and the PPN contribution due to the presence of the scalar field. The PPN scalar-field-dependent part is proportional to the difference between active and conformal dipole moments of the body which disappears in general relativ

169

Using Structural Equation Modeling to Assess Functional Connectivity in the Brain: Power and Sample Size Considerations  

Science.gov (United States)

The present study assessed the impact of sample size on the power and fit of structural equation modeling applied to functional brain connectivity hypotheses. The data consisted of time-constrained minimum norm estimates of regional brain activity during performance of a reading task obtained with magnetoencephalography. Power analysis was first…

Sideridis, Georgios; Simos, Panagiotis; Papanicolaou, Andrew; Fletcher, Jack

2014-01-01

170

During visual word recognition, phonology is accessed within 100 ms and may be mediated by a speech production code: evidence from magnetoencephalography.  

Science.gov (United States)

Debate surrounds the precise cortical location and timing of access to phonological information during visual word recognition. Therefore, using whole-head magnetoencephalography (MEG), we investigated the spatiotemporal pattern of brain responses induced by a masked pseudohomophone priming task. Twenty healthy adults read target words that were preceded by one of three kinds of nonword prime: pseudohomophones (e.g., brein-BRAIN), where four of five letters are shared between prime and target, and the pronunciation is the same; matched orthographic controls (e.g., broin-BRAIN), where the same four of five letters are shared between prime and target but pronunciation differs; and unrelated controls (e.g., lopus-BRAIN), where neither letters nor pronunciation are shared between prime and target. All three priming conditions induced activation in the pars opercularis of the left inferior frontal gyrus (IFGpo) and the left precentral gyrus (PCG) within 100 ms of target word onset. However, for the critical comparison that reveals a processing difference specific to phonology, we found that the induced pseudohomophone priming response was significantly stronger than the orthographic priming response in left IFG/PCG at approximately 100 ms. This spatiotemporal concurrence demonstrates early phonological influences during visual word recognition and is consistent with phonological access being mediated by a speech production code. PMID:20392945

Wheat, Katherine L; Cornelissen, Piers L; Frost, Stephen J; Hansen, Peter C

2010-04-14

171

Parametrized post-Newtonian theory of reference frames, multipolar expansions and equations of motion in the N-body problem  

Science.gov (United States)

Post-Newtonian relativistic theory of astronomical reference frames based on Einstein's general theory of relativity was adopted by General Assembly of the International Astronomical Union in 2000. This theory is extended in the present paper by taking into account all relativistic effects caused by the presumable existence of a scalar field and parametrized by two parameters, ? and ?, of the parametrized post-Newtonian (PPN) formalism. We use a general class of the scalar-tensor (Brans-Dicke type) theories of gravitation to work out PPN concepts of global and local reference frames for an astronomical N-body system. The global reference frame is a standard PPN coordinate system. A local reference frame is constructed in the vicinity of a weakly self-gravitating body (a sub-system of the bodies) that is a member of the astronomical N-body system. Such local inertial frame is required for unambiguous derivation of the equations of motion of the body in the field of other members of the N-body system and for construction of adequate algorithms for data analysis of various gravitational experiments conducted in ground-based laboratories and/or on board of spacecrafts in the solar system. We assume that the bodies comprising the N-body system have weak gravitational field and move slowly. At the same time we do not impose any specific limitations on the distribution of density, velocity and the equation of state of the body's matter. Scalar-tensor equations of the gravitational field are solved by making use of the post-Newtonian approximations so that the metric tensor and the scalar field are obtained as functions of the global and local coordinates. A correspondence between the local and global coordinate frames is found by making use of asymptotic expansion matching technique. This technique allows us to find a class of the post-Newtonian coordinate transformations between the frames as well as equations of translational motion of the origin of the local frame along with the law of relativistic precession of its spatial axes. These transformations depend on the PPN parameters ? and ?, generalize general relativistic transformations of the IAU 2000 resolutions, and should be used in the data processing of the solar system gravitational experiments aimed to detect the presence of the scalar field. These PPN transformations are also applicable in the precise time-keeping metrology, celestial mechanics, astrometry, geodesy and navigation. We consider a multipolar post-Newtonian expansion of the gravitational and scalar fields and construct a set of internal and external gravitational multipoles depending on the parameters ? and ?. These PPN multipoles generalize the Thorne-Blanchet-Damour multipoles defined in harmonic coordinates of general theory of relativity. The PPN multipoles of the scalar-tensor theory of gravity are split in three classes—active, conformal, and scalar multipoles. Only two of them are algebraically independent and we chose to work with the conformal and active multipoles. We derive the laws of conservations of the multipole moments and show that they must be formulated in terms of the conformal multipoles. We focus then on the law of conservation of body's linear momentum which is defined as a time derivative of the conformal dipole moment of the body in the local coordinates. We prove that the local force violating the law of conservation of the body's linear momentum depends exclusively on the active multipole moments of the body along with a few other terms which depend on the internal structure of the body and are responsible for the violation of the strong principle of equivalence (the Nordtvedt effect). The PPN translational equations of motion of extended bodies in the global coordinate frame and with all gravitational multipoles taken into account are derived from the law of conservation of the body's linear momentum supplemented by the law of motion of the origin of the local frame derived from the matching procedure. We use these equations to analyze translational motion of shperical

Kopeikin, Sergei; Vlasov, Igor

2004-11-01

172

Consistencia epistémica del síndrome de Dificultades del Aprendizaje: aportaciones de la magnetoencefalografía como técnica de neuroimagen funcional / Epistemics for Learning Disabilities: Contributions from Magnetoencephalography, a Functional Neuroimaging Tool  

Scientific Electronic Library Online (English)

Full Text Available SciELO Colombia | Language: Spanish Abstract in spanish El síndrome Dificultades del Aprendizaje (DA) fue descrito en 1963 por S. Kirk. Desde entonces, diversas escuelas en EE.UU., Canadá y España han afinado su concepto y clasificación. La UCM en España ha propuesto una definición descriptiva y totalizadora, y ha estudiado empíricamente distintas manife [...] staciones, intentando descubrir sus marcadores biológicos y las características neurológicas de sus principales manifestaciones (dislexia, discalculia, disortografia, TDA, TDAH, etc.). Se describen los hallazgos en DA a partir de estudios como la magnetoencefalografía (MEG), técnica inocua que recoge campos magnéticos generados naturalmente por el cerebro y analiza su distribución espacial para localizar los generadores neuronales responsables, proporcionando información simultánea sobre la estructura y la función cerebral en patrones de normalidad en el procesamiento cognitivo y patrones aberrantes propios de las particulares manifestaciones clínicas del síndrome DA. Abstract in english The syndrome known as Learning Disabilities (LD) was described by S. Kirk in 1963. From that point on, institutions from the US, Canada and Spain have engaged in refining the concept and classification of LDs. The Complutense University in Spain, has proposed a descriptive and all-embracing definiti [...] on, and has studied the different manifestations of LD, pursuing the description of biological markers and neurological features of LD’s main expressions: dyslexia, dyscalculia, dysorthographia, Attention Deficit and Hyperactivity Disorder -ADHD, and so forth. Findings in LD using functional neuroimaging techniques, namely Magnetoencephalography (MEG), are described. MEG is a non-invasive technique, which records magnetic fields naturally generated by the brain and their spatial distribution. It allows simultaneous functional and structural information. MEG is therefore used in the study of primary and superior cognitive functions, in surveillance of patterns of normal cognitive function and those specific to the different LD clinical manifestations.

VÍCTOR, SANTIUSTE-BERMEJO; MARTA, SANTIUSTE-DÍAZ.

2008-12-01

173

Binary black hole coalescence in the extreme-mass-ratio limit: Testing and improving the effective-one-body multipolar waveform  

International Nuclear Information System (INIS)

We discuss the properties of the effective-one-body (EOB) multipolar gravitational waveform emitted by nonspinning black-hole binaries of masses ? and M in the extreme-mass-ratio limit ?/M=?-4 rad and maintain then a remarkably accurate phase coherence during the long inspiral (?33 orbits), accumulating only about -2x10-3 rad until the last stable orbit, i.e. ??/??-5.95x10-6. We obtain such accuracy without calibrating the analytically resummed EOB waveform to numerical data, which indicates the aptitude of the EOB waveform for studies concerning the Laser Interferometer Space Antenna. We then improve the behavior of the EOB waveform around merger by introducing and tuning next-to-quasicircular corrections in both the gravitational wave amplitude and phase. For each multipole we tune only fr each multipole we tune only four next-to-quasicircular parameters by requiring compatibility between EOB and Regge-Wheeler-Zerilli waveforms at the light ring. The resulting phase difference around the merger time is as small as ±0.015 rad, with a fractional amplitude agreement of 2.5%. This suggest that next-to-quasicircular corrections to the phase can be a useful ingredient in comparisons between EOB and numerical-relativity waveforms.

174

Modeling Choices in Nuclear Warfighting: Two Classroom Simulations on Escalation and Retaliation  

Science.gov (United States)

Two classroom simulations--"Superpower Confrontation" and "Multipolar Asian Simulation"--are used to teach and test various aspects of the Borden versus Brodie debate on the Schelling versus Lanchester approach to nuclear conflict modeling and resolution. The author applies a Schelling test to segregate high from low empathic students, and assigns…

Schofield, Julian

2013-01-01

175

A novel microtubule-modulating noscapinoid triggers apoptosis by inducing spindle multipolarity via centrosome amplification and declustering  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have previously shown that a non-toxic noscapinoid, EM011 binds tubulin without altering its monomer/polymer ratio. EM011 is more active than the parent molecule, noscapine, in inducing G2/M arrest, inhibiting cellular proliferation and tumor growth in various human xenograft models. However, the mechanisms of mitotic-block and subsequent cell death have remained elusive. Here, we show that EM011-induced attenuation of microtubule dynamics was associated with impaired association of microt...

Karna, P.; Rida, P. C. G.; Pannu, V.; Gupta, K. K.; Dalton, W. B.; Joshi, H.; Yang, V. W.; Zhou, J.; Aneja, R.

2011-01-01

176

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 SciELO Brazil | Language: Portuguese 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 receb [...] imento 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. 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 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.

1307-13-01

177

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 SciELO Brazil | Language: Portuguese 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 receb [...] imento 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. 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 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.

178

Electric Multipole Interactions in an Extended BEG Model  

Digital Repository Infrastructure Vision for European Research (DRIVER)

General 2D dielectric phase diagrams and phase transitions for multipolar molecules adsorbed to a square ionic crystal are presented. The adsorbed molecules are modeled using a dilute spin-one Ising model in the Blume-Emery-Griffiths formalism, using a mean-field approximation. Physical constants such as the electricmultipole moments and binding energies are used to uniquely determine the interaction parameters over the full range of physically-relevant values. We find that temperature- and c...

Burns, Teresa; Dennison, Jr

2013-01-01

179

Quantifying the dynamics of water bodies, wetlands and biomass in the Poyang Lake region: A multi-polarization SAR remote sensing approach  

Science.gov (United States)

Field measurements were combined with synthetic aperture radar (SAR) images to evaluate the use of C-band multi-polarized radar remote sensing for estimating plant parameters (plant height, fresh biomass, dry biomass and vegetation water content) of wetland vegetation, and mapping the dynamics of water bodies, wetlands (natural wetlands and rice paddies) and flooding extents in the Poyang Lake region. The capacity of L-band SAR in land cover mapping was also investigated by integrating with optical imagery. Hydrological patterns in Poyang Lake are the dominant factor controlling the spatial and temporal variations of wetland species in Poyang Lake. Water levels in this region are primarily governed by five rivers (Ganjiang river, Xiushui river, Raohe river, Fuhe river, and Xinjiang river). Its northern region is also influenced by the backflow from Yangtze River. The above-ground total biomass increased steadily from March following the hydrological cycle. Wetland species colonizing at different altitudes were gradually flooded from late spring to summer. Carex spp. died during flooding periods and started another growth cycle in autumn after flooding receded. Canopy volume dominates the radar backscattering mechanism in Carex spp. wetlands during their growth period, but the temporal variation of radar backscatter from these wetlands is mainly influenced by flooding. Tall wetland species (Miscanthus sacchariflorus, Phragmites communis Trin., and others) still emerged above water surfaces during flooding peaks and started to senesce in autumn. Surface backscattering mechanism is dominant during the early growing stage and the senescent period of tall vegetation. Plant canopy variation controlled the temporal dynamics of radar backscatters from Phragmites communis Min. Radar backscattering mechanisms from Miscanthus sacchariflorus wetlands were more complicated during the flooding periods. The variations of ground water depth and plant structure of Miscanthus sacchariflorus during its growth period result in over 10 dB spatial and temporal variation in ASAR backscatter in HH- and HV-polarization. The relationship of canopy height with ASAR backscattering coefficient is the most significant among the influencing factors (plant height, fresh biomass, dry biomass, vegetation water content) on radar backscattering mechanism (R2=0.9 for HH-polarization and R2=0.59 for HV-polarization) from Phragmites cummunis Trin. HH- and HV-backscatters are more sensitive to the variation of dry biomass (R2=0.76 for HH and R2=0.56 for HV) than to that of fresh biomass (R 2=0.07 for HV and R2=0.42 for HH). Plant water content plays a negative role and attenuates the backscattering signals in both polarizations. For Phragmites communis Trin. with tall stalks (over 2m) and long, blade-like leaves, HH-polarization is more sensitive to vegetation parameters than HV-polarization for C-band SAR signals. Similar to Phragmites communis Trin., ASAR backscattering coefficient in both polarizations is more sensitive to plant height and dry biomass of non-flooded Miscanthus sacchariflorus, and their regression coefficients (R2) are over 0.5 for HH-polarization and over 0.4 for HV-polarization. Plant water content has no evident effect on the variation of ASAR backscatter. HV-polarization is more sensitive to the variation of above-water canopy parameters than HH-polarization for flooded Miscanthus saccharifiorus. HH- and HV-polarized radar backscatters from Carex spp. wetlands increased significantly with the variation of plant height, fresh biomass and dry biomass, but they reach saturated when vegetation grows up to 30cm. Compared with those tall grass with stalks and long blade-like leaves, the correlation of fresh biomass with HV-polarization is more pronounced (R 2=0.78) than that with HH-polarization (R2=0.41) for Carex spp. Vegetation structure play a more important role in radar backscattering mechanism than plant water content for these three wetland species. Temporal profiles of C-band multi-polarized backscatter coefficients for individual lan

Sang, Huiyong

180

Functions and structure of nuclear deterrence in the post-cold war world. More for less - an arms control strategy for the 1990s. A SIOP for Perestroika. Theater nuclear forces and extended deterrence in a multipolar world. Special series report  

Energy Technology Data Exchange (ETDEWEB)

This Publication includes: Essay (1). The Function and Structure of Nuclear Deterrence in the Post-Cold War World. Essay (2). More for Less-An Arms Control Strategy for the 1990s. Essay (3). A SIOP for Perestroika. Essay (4). Theater Nuclear Forces and Extended Deterrence in a Multipolar World.

Snow, D.M.; Wooten, R.E.; Sundberg, E.E.; Szafranski, R.; Booker, D.L.

1992-06-01

 
 
 
 
181

A morphometric analysis of bipolar and multipolar TH-IR neurons treated with the neurotoxin MPP+ in co-cultures from mesencephalon and striatum of embryonic C57BL/6 mice.  

Science.gov (United States)

Mesencephalic cultures contain two morphologically different tyrosine hydroxylase (TH)-immunoreactive (IR) neurons, fusiform bipolar, and pyramidal multipolar, which project to different anatomical structures (ventral striatum and neostriatum). The possibility of functional difference of these cells in Parkinson's disease led us study the effect of 1-methyl-4-phenylpyridinium (MPP+) on them. Survival and morphology of the two groups was studied in dissociated co-cultures from mesencephalon and striatum of embryonic C57BL/6 mice. Cells were grown at first in serum containing medium and then in serum free medium supplemented with hormones. Cultures were exposed to different concentrations of MPP+ on day 9 and 13 for 24 hr. They were fixed and stained with an anti-TH antibody. 0.1-1.0 microM MPP+ caused a dramatic reduction of the total area of TH-IR neurons. At 0.1 microM MPP+ some area was reduced, at 0.5 microM it appeared similar to controls, and decreased further at 1.0 microM. The relation of soma to total area showed that the decrease of the neuronal size was mainly due to the degeneration of the neuronal processes. The length of neuronal tree as well as the number of terminal segments were reduced dose dependently when cells were treated with the toxin. Similar results were obtained for bipolar and multipolar neurons. A significant difference in the decrease in total area was observed between the two age groups when cells were treated with MPP+, as older cells appeared to be more sensitive. When other parameters were checked no apparent difference was present. PMID:7650755

Koutsilieri, E; Chen, T S; Kruzik, P; Rausch, W D

1995-06-01

182

Analysis and Realization on MIMO Channel Model  

Directory of Open Access Journals (Sweden)

Full Text Available In order to build the MIMO (Multiple Input Multiple Output channel model based on IEEE 802.16, the way and analysis on how to build good MIMO channel model are described in this study. By exploiting the spatial freedom of wireless channels, MIMO systems have the potential to achieve high bandwidth efficiency, promoting MIMO to be a key technique in the next generation communication systems. As a basic researching field of MIMO technologies, MIMO channel modeling significantly serve to the performance evaluation of space-time encoding algorithms as well as system level calibration and simulation. Having the superiorities of low inner-antenna correlation and small array size, multi-polarization tends to be a promising technique in future MIMO systems. However, polarization characteristics have not yet been modeled well in current MIMO channel models, so establishing meaningful multi-polarized MIMO channel models has become a hot spot in recent channel modeling investigation. In this study, I have mainly made further research on the related theories in the channel models and channel estimation and implementation algorithms on the others’ research work.

Liu Hui

2014-04-01

183

Multipolar interference for directed light emission.  

Science.gov (United States)

By directing light, optical antennas can enhance light-matter interaction and improve the efficiency of nanophotonic devices. Here we exploit the interference among the electric dipole, quadrupole, and magnetic dipole moments of a split-ring resonator to experimentally realize a compact directional optical antenna. This single-element antenna design robustly directs emission even when covered with nanometric emitters at random positions, outperforming previously demonstrated nanoantennas with a bandwidth of 200 nm and a directivity of 10.1 dB from a subwavelength structure. The advantages of this approach bring directional optical antennas closer to practical applications. PMID:24279805

Hancu, Ion M; Curto, Alberto G; Castro-López, Marta; Kuttge, Martin; van Hulst, Niek F

2014-01-01

184

The Stark ball: A programmable multipolar environment  

Science.gov (United States)

A device is described and mathematically analyzed which creates electrostatic multipole potentials at least up to rank 3 in a 2 cm diam spherical region. The fields in the Stark ball are produced by the application of programmed voltages to 24 conducting rods that are inserted symmetrically in an empty 5 cm conducting cavity. Three mutually orthogonal unobstructed paths through the center of the device between the rods are provided for access of light and particle beams, and four other tetrahedrally located openings can be added for beams, detectors, or imaging. The device is intended for application in atom or molecule trapping and cooling, recoil-ion momentum spectroscopy, particulate analysis, reactive scattering, and coherent control. Potential distributions can be established, altered, and rotated on subnanosecond time scales, and frequencies higher than 20 GHz can be introduced via the same electrodes. Uniform fields, i.e., first-rank multipoles, quadrupole, and octupole potentials can be programmed and superposed with arbitrary and independent time profiles, so that the device may be applied to the study of orientational properties of complex anisotropic molecules, pollens, grains of dust, and other particulates. The device is nonmagnetic. An extensive analysis of fields in the center region, fringing fields, and multipole purity up to rank 7 has been carried out, and recipes are given for pure (l,m)=(1,0), (2,0), and (3,0) multipoles. The principles and methods laid out here and applied to a "truncated octahedron" can be applied to the design of electrostatic environments having fewer or more independent electrodes in any polyhedral geometry.

MacAdam, K. B.; Hwang, C. S.

2003-04-01

185

Scaling laws, force balances and dynamo generation mechanisms in numerical dynamo models: influence of boundary conditions  

Science.gov (United States)

We investigate the influence of different thermal and velocity boundary conditions on numerical geodynamo models. We concentrate on the implications for magnetic field morphology, heat transport scaling laws, force balances and generation mechanisms. The field morphology most strongly depends on the local Rossby number, but there is some variation in the dipolarity of the field with boundary condition. Scaling laws also depend on the boundary conditions, but a diffusivity-free scaling is a good first order approximation for all our dipolar models. Our multipolar models, however, obey different scaling laws from dipolar models implying a different force balance in these models. We find that our dipolar models have a stronger degree of Lorentz-Coriolis balance compared to our multipolar models which have a stronger degree of Lorentz-inertial balance.The models with a stronger Lorentz-Coriolis dominance can be generated by either ??, ?2? or ?2 mechanisms whereas the models with a stronger Lorentz-inertial balance are all ?2 dynamos. These results imply that some caution is necessary when extrapolating results from dynamo models to Earth-like parameters since the choice of boundary conditions can have important effects.

Dharmaraj, G.; Stanley, S.; Qu, A. C.

2014-10-01

186

Modelling Sporangiospore-yeast transformation of Dimorphomyces strain.  

Science.gov (United States)

Two types of buffered media, strictly defined-Ammonium sulphate-basal salts and complex Peptone-basal salts, were used for the cultivation of Dimorphomyces pleomorphis, one of two dimorphic fungi isolated from fermenting juice of soursop fruit, Annona muricata L. The growth count was taken every twenty-four hours. Transient morphologies were observed to change from sporangiospores through enlarged globose cells, to granular particles and eventually, polar budding yeast cells in the strictly defined medium at 15 degrees, 20 degrees, or 37 degrees C, but the complex medium casually terminally induced polar budding yeast cells and multipolar budding yeast like cells in between the growth phases, at 15 degrees and 20 degrees C, while mainly multipolar budding yeastlike morphology was observed at elevated temperature. There was obvious influence of nutritional factor or morphological expression (p < 0.01). After analysis of variance, the growth data could not fit into predictive quadratic polynomial model because the organism's response curves were incongruent with basic assumptions of the model. Furthermore, a stepwise regression analysis gave very low coefficients of determination, r2, for the interactive combinations. They were therefore, considered unfit for the data. Construction of the pII-profiles led to inference being drawn from the chemiosmotic theory, polyelectrolyte theory to account for the behaviour in the buffered multiionic media. It was also thought that inherent cellular mitotic division and glycolytic activity led to a prelogarithmic growth response. PMID:9676041

Omoifo, C O

1996-01-01

187

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

Directory of Open Access Journals (Sweden)

Full Text Available 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.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.

António José Telo

2011-09-01

188

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: Portuguese 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 element [...] os: 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.

António José, Telo.

189

Linear polarization measurement of interband transitions in superdeformed 190hg: model-independent evidence for octupole vibrational structures.  

Science.gov (United States)

The linear polarization of gamma rays between excited and yrast superdeformed (SD) states in 190Hg was measured using the four-element CLOVER detectors of the EUROBALL IV gamma-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the A approximately 190 region in terms of octupole excitations. PMID:11290029

Korichi, A; Wilson, A N; Hannachi, F; Lopez-Martens, A; Rejmund, M; Schück, C; Vieu, C; Chmel, G; Görgen, A; Hübel, H; Rossbach, D; Schönwasser, S; Bergström, M; Nyakó, B M; Timár, J; Bazzacco, D; Lunardi, S; Rossi-Alvarez, C; Bednarczyk, P; Kintz, N; Naguleswaran, S; Astier, A; Cullen, D M; Sharpey-Schafer, J F; Lauritsen, T; Wadsworth, R

2001-03-26

190

Probabilistic forward model for electroencephalography source analysis  

Energy Technology Data Exchange (ETDEWEB)

Source localization by electroencephalography (EEG) requires an accurate model of head geometry and tissue conductivity. The estimation of source time courses from EEG or from EEG in conjunction with magnetoencephalography (MEG) requires a forward model consistent with true activity for the best outcome. Although MRI provides an excellent description of soft tissue anatomy, a high resolution model of the skull (the dominant resistive component of the head) requires CT, which is not justified for routine physiological studies. Although a number of techniques have been employed to estimate tissue conductivity, no present techniques provide the noninvasive 3D tomographic mapping of conductivity that would be desirable. We introduce a formalism for probabilistic forward modeling that allows the propagation of uncertainties in model parameters into possible errors in source localization. We consider uncertainties in the conductivity profile of the skull, but the approach is general and can be extended to other kinds of uncertainties in the forward model. We and others have previously suggested the possibility of extracting conductivity of the skull from measured electroencephalography data by simultaneously optimizing over dipole parameters and the conductivity values required by the forward model. Using Cramer-Rao bounds, we demonstrate that this approach does not improve localization results nor does it produce reliable conductivity estimates. We conclude that the conductivity of the skull has to be either accurately measured by an independent technique, or that the uncertainties in the conductivity values should be reflected in uncertainty in the source location estimates.

Plis, Sergey M [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); George, John S [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Jun, Sung C [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Ranken, Doug M [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Volegov, Petr L [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Schmidt, David M [MS-D454, Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2007-09-07

191

Detailed magnetic model simulations of the H- injection chicane magnets for the CERN PS Booster Upgrade, including eddy currents and influence on beam dynamics  

CERN Document Server

The CERN PS Booster will be upgraded with an H- injection system. The chicanemagnets for the injection bump ramp-down in 5 ms and generate eddy currents in the inconel vacuum chamber which perturb the homogeneity of the magnetic field. The multipolar field components are extracted from 3D OPERA simulations and are included in the lattice model. The -beating correction is computed all along the ramp and complete tracking simulations including space-charge are performed to evaluate the impact of these perturbations and correction on beam dynamics.

Benedetto, E; Borburgh, J; Carli, C; Martini, M; Forte, V

2014-01-01

192

Giant resonance of electrical multipole from droplet model  

International Nuclear Information System (INIS)

The formalism of the electrical multipole resonance developed from the Droplet nuclear model is presented. It combines the approaches of Goldhaber-Teller (GT) and Steinwedel-Jensen (SJ) and it shows the relative contribution of Coulomb, superficial and neutron excess energies. It also discusses the calculation of half-width. The model evaluates correctly the resonance energies as a function of nuclear mass and allows, through the Mixture Index, the prediction of the complementary participation of modes SJ and GT in the giant nuclear resonance. Values of the mixture index, for each multipolarity, reproduce well the form factors obtained from experiments of charged particle inelastic scattering. The formalism presented for the calculation of the half-width gives a macroscopic description of the friction mechanism. The establishment of the macroscopic structure of the Dissipation Function is used as a reference in the comparison of microscopic calculations. (Author)

193

Electro-magneto-encephalography for the three-shell model: numerical implementation via splines for distributed current in spherical geometry  

International Nuclear Information System (INIS)

The basic inverse problems for the functional imaging techniques of electroencephalography (EEG) and magnetoencephalography (MEG) consist in estimating the neuronal current in the brain from the measurement of the electric potential on the scalp and of the magnetic field outside the head. Here we present a rigorous derivation of the relevant formulae for a three-shell spherical model in the case of independent as well as simultaneous MEG and EEG measurements. Furthermore, we introduce an explicit and stable technique for the numerical implementation of these formulae via splines. Numerical examples are presented using the locations and the normal unit vectors of the real 102 magnetometers and 70 electrodes of the Elekta Neuromag (R) system. These results may have useful implications for the interpretation of the reconstructions obtained via the existing approaches. (paper)

194

Adaptive Cluster Analysis Approach for Functional Localization Using Magnetoencephalography  

Directory of Open Access Journals (Sweden)

Full Text Available 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 magnetorencephalography (MEG brain signals. Reliable localization of brain areas with MEG has been difficult due to variations in signal strength, and the spatial extend 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.

HoomanAlikhanian

2013-05-01

195

Nonparametric Statistical Thresholding for Sparse Magnetoencephalography Source Reconstructions  

Directory of Open Access Journals (Sweden)

Full Text Available Uncovering brain activity from MEG data requires solving an ill-posed inverse problem, greatly confounded by noise, interference, and correlated sources. Sparse reconstruction algorithms, such as Champagne, show great promise in that they provide focal brain activations robust to these confounds. In this paper, we address the technical considerations of statistically thresholding brain images obtained from sparse reconstruction algorithms. The source power distribution of sparse algorithms makes this class of algorithms ill-suited to "conventional" techniques. We propose two nonparametric resampling methods hypothesized to be compatible with sparse algorithms. The first adapts the maximal statistic procedure to sparse reconstruction results and the second departs from maximal statistics, putting forth a less stringent procedure that protects against spurious peaks. Three MEG data sets are utilized to demonstrate the efficacy of the proposed methods. Two sparse algorithms, Champagne and generalized minimum current estimation (G-MCE, are compared to two non-sparse algorithms, a variant of minimum-norm estimation, sLORETA, and an adaptive beamformer. The results, in general, demonstrate that the already sparse images obtained from Champagne and G-MCE are further thresholded by both proposed statistical thresholding procedures. While non-sparse algorithms are thresholded by the maximal statistic procedure, they are not made sparse. The work presented here is one of the first attempts to address the problem of statistically thresholding sparse reconstructions, and aims to improve upon this already advantageous and powerful class of algorithm.

JuliaParsonsOwen

2012-12-01

196

Distorted cortical networks in dislexia: findings using Magnetoencephalography (MEG  

Directory of Open Access Journals (Sweden)

Full Text Available In dyslexic children a functional deficit in the brain circuitry supporting some of the cognitive operations taking place while they learn how the printed words maps onto spoken language is suspected. Until recently, however, no information existed regarding the functional status of this circuit during the early stages of reading acquisition. In the context of three studies we sought to address key issues in the pathophysiology of this condition using Magnetoencephalograhy (MEG at the University of Texas-Houston. The first study, including 30 kindergarten children at risk for developing reading problems and 15 not-at-risk controls, ascertained that the aberrant neural circuit that underlies reading problems appears to be present in the initial stages of reading acquisition. A subset of these children were retested a year later using identical procedures in a second study. Children in the at-risk group showed the most prominent changes in brain activation profiles and successfully predicted individual differences in the growth of reading skill measures. The results of a third study showed clearly that the aberrant activation profile can be normalized following intensive behavioral instruction. These findings are consistent with the view that dyslexia represents a functional deficit in the neural network that mediates the conversion of print to sound, which is amenable to change given adequate instruction.

Eduardo M. Catillo

2008-04-01

197

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.

Jens Schwarzbach

2006-01-01

198

Magnetoencephalography of frontotemporal dementia: spatiotemporally localized changes during semantic decisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Behavioural variant frontotemporal dementia is a neurodegenerative disorder with dysfunction and atrophy of the frontal lobes leading to changes in personality, behaviour, empathy, social conduct and insight, with relative preservation of language and memory. As novel treatments begin to emerge, biomarkers of frontotemporal dementia will become increasingly important, including functionally relevant neuroimaging indices of the neurophysiological basis of cognition. We used magnetoencephalogra...

Hughes, Laura E.; Nestor, Peter J.; Hodges, John R.; Rowe, James B.

2011-01-01

199

Thalamocortical dysrhythmia: A neurological and neuropsychiatric syndrome characterized by magnetoencephalography.  

Science.gov (United States)

Spontaneous magnetoencephalographic activity was recorded in awake, healthy human controls and in patients suffering from neurogenic pain, tinnitus, Parkinson's disease, or depression. Compared with controls, patients showed increased low-frequency theta rhythmicity, in conjunction with a widespread and marked increase of coherence among high- and low-frequency oscillations. These data indicate the presence of a thalamocortical dysrhythmia, which we propose is responsible for all the above mentioned conditions. This coherent theta activity, the result of a resonant interaction between thalamus and cortex, is due to the generation of low-threshold calcium spike bursts by thalamic cells. The presence of these bursts is directly related to thalamic cell hyperpolarization, brought about by either excess inhibition or disfacilitation. The emergence of positive clinical symptoms is viewed as resulting from ectopic gamma-band activation, which we refer to as the "edge effect." This effect is observable as increased coherence between low- and high-frequency oscillations, probably resulting from inhibitory asymmetry between high- and low-frequency thalamocortical modules at the cortical level. PMID:10611366

Llinás, R R; Ribary, U; Jeanmonod, D; Kronberg, E; Mitra, P P

1999-12-21

200

Chaotic analysis approach in neonatal magneto-encephalography.  

Science.gov (United States)

The aim of this study was to investigate the presence of any non-linearity in the magneto-encephalographic recordings (MEG) in neonates born to pre-eclamptic mothers in comparison with the ones born to mothers having uncomplicated pregnancies, in order to find out differences in the mechanisms underlying their brain waves. Our study population consisted of 40 term neonates who were delivered normally, without any clinical signs of brain damage. Thirty of them had a normal pregnancy and labour with normal Apgar scores, umbilical cord pH, and birth weight, while 10 neonates had suffered a pre-eclamptic pregnancy. The above analysis of the MEG in the neonatal pre-eclamptic brain showed a lower dimension complexity as compared with the normal neonatal brain and a lower first Lyapunov exponent which means lower information processing. The non-linear analysis of the MEG activities in neonates may offer important perspectives to understand significant features of their brain function. PMID:14504445

Kotini, A; Koutlaki, N; Anninos, P; Adamopoulos, A; Liberis, V; Anastasiadis, P

2003-01-01

 
 
 
 
201

Automatic procedure for realistic 3D finite element modelling of human brain for bioelectromagnetic computations  

International Nuclear Information System (INIS)

Realistic computer modelling of biological objects requires building of very accurate and realistic computer models based on geometric and material data, type, and accuracy of numerical analyses. This paper presents some of the automatic tools and algorithms that were used to build accurate and realistic 3D finite element (FE) model of whole-brain. These models were used to solve the forward problem in magnetic field tomography (MFT) based on Magnetoencephalography (MEG). The forward problem involves modelling and computation of magnetic fields produced by human brain during cognitive processing. The geometric parameters of the model were obtained from accurate Magnetic Resonance Imaging (MRI) data and the material properties - from those obtained from Diffusion Tensor MRI (DTMRI). The 3D FE models of the brain built using this approach has been shown to be very accurate in terms of both geometric and material properties. The model is stored on the computer in Computer-Aided Parametrical Design (CAD) format. This allows the model to be used in a wide a range of methods of analysis, such as finite element method (FEM), Boundary Element Method (BEM), Monte-Carlo Simulations, etc. The generic model building approach presented here could be used for accurate and realistic modelling of human brain and many other biological objects.

202

Duifhuis pitch: neuromagnetic representation and auditory modeling.  

Science.gov (United States)

When a high harmonic is removed from a cosine-phase harmonic complex, we hear a sine tone pop out of the perception; the sine tone has the pitch of the high harmonic, while the tone complex has the pitch of its fundamental frequency, f0. This phenomenon is commonly referred to as Duifhuis Pitch (DP). This paper describes, for the first time, the cortical representation of DP observed with magnetoencephalography. In experiment 1, conditions that produce the perception of a DP were observed to elicit a classic onset response in auditory cortex (P1m, N1m, P2m), and an increment in the sustained field (SF) established in response to the tone complex. Experiment 2 examined the effect of the phase spectrum of the complex tone on the DP activity: Schroeder-phase negative waves elicited a transient DP complex with a similar shape to that observed with cosine-phase waves but with much longer latencies. Following the transient DP activity, the responses of the negative and positive Schroeder-phase waves converged, and the increment in the SF slowly died away. In the absence of DP, the two Schroeder-phase conditions with low peak factors both produced larger SFs than cosine-phase waves with large peak factors. A model of the auditory periphery that includes coupling between adjacent frequency channels is used to explain the early neuromagnetic activity observed in auditory cortex. PMID:25143548

Andermann, Martin; Patterson, Roy D; Geldhauser, Michael; Sieroka, Norman; Rupp, André

2014-11-15

203

Evaluation of multiple-sphere head models for MEG source localization  

Energy Technology Data Exchange (ETDEWEB)

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.

Lalancette, M; Cheyne, D [Department of Diagnostic Imaging, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario M5G 1X8 (Canada); Quraan, M, E-mail: marc.lalancette@sickkids.ca, E-mail: douglas.cheyne@utoronto.ca [Krembil Neuroscience Centre, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 (Canada)

2011-09-07

204

The filamentary multi-polar planetary nebula NGC 5189  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English 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 investigació [...] n 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, mediante 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 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 its complex morphology.

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

2012-10-01

205

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

206

Bipolar and multipolar Jets in protoplanetary and planetary nebulae  

Directory of Open Access Journals (Sweden)

Full Text Available Uno de los retos m as emocionantes con que actualmente se enfrentan las teor as de evoluci on posterior a la secuencia principal, es entender c omo estrellas AGB (ingl. "Asymptotic Giant Branch" y sus envolturas cicunestelares esf ericas (siglas en ingl es: CSEs se transforman en nebulosas planetarias (NPs con su asombrosa variedad de morfolog as asf ericas. El modelo m as exitoso para dar forma a los NPs|el modelo generalizado de vientos estelares interactuantes, en el cual un viento esf erico de alta velocidad (> 1000 km s...

Sahai Raghvendra

2002-01-01

207

RF Multipolar Characterization of the Latest LHC Deflecting Cavities  

CERN Document Server

Deflecting cavity geometries considered for the Large Hadron Collider (LHC) crab scheme lack axial symmetry resulting in non-zero higher-order components of the deflecting field. A formalism to express the higher-order multipoles was developed and applied on previous cavity designs to characterize their influence on the beam stability. In this paper, the radio frequency (RF) multipoles are numerically estimated for the latest cavity geometries and compared to the older versions. A sensitivity study is carried out to understand the numerical errors levels and define mechanical tolerances.

Navarro-Tapia, M; Calaga, R

2013-01-01

208

Multipolar ordering in NpO2 probed by NMR  

International Nuclear Information System (INIS)

We have initiated the first 17O-NMR measurements in the ordered state of NpO2. From the 17O-NMR spectrum, we have confirmed the occurrence of two inequivalent oxygen sites below T0=26K. It has also been shown that the 17O-NMR spectrum in the ordered state can be understood by considering an unconventional hyperfine interaction between the 17O nuclear spins and field-induced antiferromagnetic moments arising from the longitudinal triple-q antiferro-quadrupolar order. These NMR results give strong evidence for the occurrence of the longitudinal triple-q multipole structure in NpO2

209

Possible form of multi-polar interaction in cubic lattice  

Energy Technology Data Exchange (ETDEWEB)

The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection.

Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki

2003-05-01

210

Possible form of multi-polar interaction in cubic lattice  

International Nuclear Information System (INIS)

The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection

211

The filamentary multi-polar planetary nebula NGC 5189  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English 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 investigació [...] n 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, mediante 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 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 its complex morphology.

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

212

New modes of nuclear excitations in microscopic and collective model description  

Energy Technology Data Exchange (ETDEWEB)

A microscopic approach based on density functional theory and multi-phonon QRPA methods is successfully applied for investigations of pygmy resonances and other excitations of different multipolarities and energies in stable and exotic nuclei. From systematic studies of nuclear response functions a clear indication of close connection between low-energy excited states related to pygmy resonances and nuclear skin oscillations is observed. This is confirmed also in analyses of transition densities and currents. A useful link to collective model approaches is used for distinction of pygmy resonance from other modes of excitations related low-energy multi-phonon vibrations, twist modes or giant resonances observed in response functions and data. Furthermore, nuclear skins are found to affect M1 strength distributions in nuclei, as confirmed by recent experiments. The fine structure of the spin-flip M1 resonance is discussed and compared to experimental data.

Tsoneva, Nadia [Institut fuer Theoretische Physik, Universitaet Giessen (Germany); INRNE, BAS, Sofia (Bulgaria); Lenske, Horst [Institut fuer Theoretische Physik, Universitaet Giessen (Germany)

2013-07-01

213

New modes of nuclear excitations in microscopic and collective model description  

International Nuclear Information System (INIS)

A microscopic approach based on density functional theory and multi-phonon QRPA methods is successfully applied for investigations of pygmy resonances and other excitations of different multipolarities and energies in stable and exotic nuclei. From systematic studies of nuclear response functions a clear indication of close connection between low-energy excited states related to pygmy resonances and nuclear skin oscillations is observed. This is confirmed also in analyses of transition densities and currents. A useful link to collective model approaches is used for distinction of pygmy resonance from other modes of excitations related low-energy multi-phonon vibrations, twist modes or giant resonances observed in response functions and data. Furthermore, nuclear skins are found to affect M1 strength distributions in nuclei, as confirmed by recent experiments. The fine structure of the spin-flip M1 resonance is discussed and compared to experimental data.

214

Refined modeling of superconducting double helical coils using finite element analyses  

International Nuclear Information System (INIS)

Double helical coils are becoming more and more attractive for accelerator magnets and other applications. Conceptually, a sinusoidal modulation of the longitudinal position of the turns allows virtually any multipolar field to be produced and maximizes the effectiveness of the supplied ampere turns. Being intrinsically three-dimensional, the modeling of such structures is very complicated, and several approaches, with different degrees of complexity, can be used. In this paper we present various possibilities for solving the magnetostatic problem of a double helical coil, through both finite element analyses and direct integration of the Biot–Savart law, showing the limits and advantages of each solution and the corresponding information which can be derived. (paper)

215

Refined modeling of superconducting double helical coils using finite element analyses  

Science.gov (United States)

Double helical coils are becoming more and more attractive for accelerator magnets and other applications. Conceptually, a sinusoidal modulation of the longitudinal position of the turns allows virtually any multipolar field to be produced and maximizes the effectiveness of the supplied ampere turns. Being intrinsically three-dimensional, the modeling of such structures is very complicated, and several approaches, with different degrees of complexity, can be used. In this paper we present various possibilities for solving the magnetostatic problem of a double helical coil, through both finite element analyses and direct integration of the Biot-Savart law, showing the limits and advantages of each solution and the corresponding information which can be derived.

Farinon, S.; Fabbricatore, P.

2012-06-01

216

Nonequilibrium properties of linear polar Kihara fluids from molecular dynamics. Results for models and for liquid acetonitrile  

Science.gov (United States)

Molecular dynamics simulations for polar Kihara fluids are reported for linear models of different lengths at several dipole and quadrupole values and at three different thermodynamic states. Two of these states are close to the vapor-liquid equilibrium curve and the third one is at the same density as the first and at the same temperature as the second. Self-correlation functions and translational and orientational times are calculated and analyzed. Transport properties, diffusion, thermal conductivity, and shear viscosity are also reported and discussed in terms of multipolar forces. Correlation terms are used to calculate band broadening in different kinds of molecular spectra. Finally, it is shown how it is possible to discriminate between two models of acetonitrile that fit equilibrium properties equally well by using dynamic properties.

Calero, S.; Garzón, B.; MacDowell, L. G.; Lago, S.

1997-08-01

217

Neural Masses and Fields in Dynamic Causal Modelling  

Directory of Open Access Journals (Sweden)

Full Text Available Dynamic causal modelling (DCM provides a framework for the analysis of effective connectivity among neuronal subpopulations that subtend invasive (electrocorticograms and local field potentials and non-invasive (electroencephalography and magnetoencephalography electrophysiological responses. This paper reviews the suite of neuronal population models including neural masses, fields and conductance–based models that are used in DCM. These models are expressed in terms of sets of differential equations that allow one to model the synaptic underpinnings of connectivity. We describe early developments using neural mass models, where convolution-based dynamics are used to generate responses in laminar-specific populations of excitatory and inhibitory cells. We show that these models, though resting on only two simple transforms, can recapitulate the characteristics of both evoked and spectral responses observed empirically. Using an identical neuronal architecture, we show that a set of conductance based models – that consider the dynamics of specific ion-channels – present a richer space of responses; owing to nonlinear interactions between conductances and membrane potentials. We propose that conductance-based models may be more appropriate when spectra present with multiple resonances. Finally, we outline a third class of models, where each neuronal subpopulation is treated as a field; in other words, as a manifold on the cortical surface. By explicitly accounting for the spatial propagation of cortical activity through partial differential equations, we show that the topology of connectivity – through local lateral interactions among cortical layers – may be inferred, even in the absence of spatially resolved data. We also show that these models allow for a detailed analysis of structure–function relationships in the cortex. Our review highlights the relationship among these models and how the hypothesis asked of empirical data suggests an appropriate model class.

RosalynJMoran

2013-05-01

218

Bayesian mixture models for source separation in MEG  

International Nuclear Information System (INIS)

This paper discusses the problem of imaging electromagnetic brain activity from measurements of the induced magnetic field outside the head. This imaging modality, magnetoencephalography (MEG), is known to be severely ill posed, and in order to obtain useful estimates for the activity map, complementary information needs to be used to regularize the problem. In this paper, a particular emphasis is on finding non-superficial focal sources that induce a magnetic field that may be confused with noise due to external sources and with distributed brain noise. The data are assumed to come from a mixture of a focal source and a spatially distributed possibly virtual source; hence, to differentiate between those two components, the problem is solved within a Bayesian framework, with a mixture model prior encoding the information that different sources may be concurrently active. The mixture model prior combines one density that favors strongly focal sources and another that favors spatially distributed sources, interpreted as clutter in the source estimation. Furthermore, to address the challenge of localizing deep focal sources, a novel depth sounding algorithm is suggested, and it is shown with simulated data that the method is able to distinguish between a signal arising from a deep focal source and a clutter signal. (paper)

219

Mental imagery of speech and movement implicates the dynamics of internal forward models  

Directory of Open Access Journals (Sweden)

Full Text Available The classical concept of efference copies in the context of internal forward models has stimulated productive research in cognitive science and neuroscience. There are compelling reasons to argue for such a mechanism, but finding direct evidence in the human brain remains difficult. Here we investigate the dynamics of internal forward models from an unconventional angle: mental imagery, assessed while recording high temporal resolution neuronal activity using magnetoencephalography (MEG. We compare two overt and covert tasks; our covert, mental imagery tasks are unconfounded by overt input/output demands – but in turn necessitate the development of appropriate multi-dimensional topographic analyses. Finger tapping (studies 1-2 and speech experiments (studies 3-5 provide temporally constrained results that implicate the estimation of an efference copy. We suggest that one internal forward model over parietal cortex subserves the kinesthetic feeling in motor imagery. Secondly, observed auditory neural activity ~170 ms after motor estimation in speech experiments (studies 3-5 demonstrates the anticipated auditory consequences of planned motor commands in a second internal forward model in imagery of speech production. Our results provide neurophysiological evidence from the human brain in favor of internal forward models deploying efference copies in somatosensory and auditory cortex, in finger tapping and speech production tasks, respectively, and also suggest the dynamics and sequential updating structure of internal forward models.

DavidPoeppel

2010-10-01

220

Using Structural Equation Modeling to Assess Functional Connectivity in the Brain: Power and Sample Size Considerations  

Science.gov (United States)

The present study assessed the impact of sample size on the power and fit of structural equation modeling applied to functional brain connectivity hypotheses. The data consisted of time-constrained minimum norm estimates of regional brain activity during performance of a reading task obtained with magnetoencephalography. Power analysis was first conducted for an autoregressive model with 5 latent variables (brain regions), each defined by 3 indicators (successive activity time bins). A series of simulations were then run by generating data from an existing pool of 51 typical readers (aged 7.5-12.5 years). Sample sizes ranged between 20 and 1,000 participants and for each sample size 1,000 replications were run. Results were evaluated using chi-square Type I errors, model convergence, mean RMSEA (root mean square error of approximation) values, confidence intervals of the RMSEA, structural path stability, and D-Fit index values. Results suggested that 70 to 80 participants were adequate to model relationships reflecting close to not so close fit as per MacCallum et al.'s recommendations. Sample sizes of 50 participants were associated with satisfactory fit. It is concluded that structural equation modeling is a viable methodology to model complex regional interdependencies in brain activation in pediatric populations.

Sideridis, Georgios; Simos, Panagiotis; Papanicolaou, Andrew; Fletcher, Jack

2014-01-01

 
 
 
 
221

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

2008-11-01

222

Mercado Simbólico: um modelo de comunicação para políticas públicas / The symbolic market: a communication model for public policies / Mercado Simbólico: un modelo de comunicación para políticas públicas  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese O trabalho tem como objetivo propor um modelo para análise e planejamento estratégico da comunicação nas políticas públicas, considerando que os modelos correntes não dão conta adequadamente da prática comunicativa nos processos de intervenção social, frustrando os altos investimentos e expectativas [...] que despertam. O "Modelo do Mercado Simbólico", em rede, descentrado e multipolar, é composto por uma formulação teórica, uma representação gráfica dos principais componentes e suas relações e de uma matriz de análise e planejamento estratégico das relações comunicativas. A representação gráfica contempla: a rede de sentidos sociais, os interlocutores e seus contextos e "lugar de interlocução". A matriz inclui fontes, campos, instâncias, comunidades discursivas e uma tipologia de fatores de mediação. Abstract in spanish El trabajo tiene como objetivo proponer un modelo para análisis y planificación estratégica de la comunicación en las políticas públicas, considerando que los modelos corrientes no sustentan adecuadamente la práctica comunicativa en los procesos de intervención social, frustrando las altas inversion [...] es y expectativas que despiertan. El "Modelo del Mercado Simbólico", en red, descentrado y multipolar, es compuesto por una formulación teórica, una representación gráfica de los principales componentes y sus relaciones y de una matriz de análisis y planificación estratégica de las relaciones comunicativas. La representación gráfica contempla: la red de sentidos sociales, los interlocutores y sus contextos y "lugar de interlocución". La matriz incluye fuentes, campos, instancias, comunidades discursivas y una tipología de factores de mediación. Abstract in english The purpose of this paper is to put forth a model for the analysis and strategic planning of the communication of public policies, given that the current models fail to adequately fulfill communication requirements in the processes of social intervention, frustrating the high investments and expecta [...] tions that they give rise to. The "Symbolic Market Model", in network form, both decentralized and multipolar, is comprised of (i) a theoretical formulation, (ii) a graphical representation of the main components and the relations between them and (iii) an analysis and strategic planning matrix of communicative relations. The graphic representation takes into account: the network of social senses, the interlocutors and their contexts, and the "place of dialogue". The matrix includes sources, fields, instances, discursive communities and a typology of mediation factors.

Inesita Soares de, Araújo.

223

Mercado Simbólico: um modelo de comunicação para políticas públicas / The symbolic market: a communication model for public policies / Mercado Simbólico: un modelo de comunicación para políticas públicas  

Scientific Electronic Library Online (English)

Full Text Available SciELO Public Health | Language: Portuguese Abstract in portuguese O trabalho tem como objetivo propor um modelo para análise e planejamento estratégico da comunicação nas políticas públicas, considerando que os modelos correntes não dão conta adequadamente da prática comunicativa nos processos de intervenção social, frustrando os altos investimentos e expectativas [...] que despertam. O "Modelo do Mercado Simbólico", em rede, descentrado e multipolar, é composto por uma formulação teórica, uma representação gráfica dos principais componentes e suas relações e de uma matriz de análise e planejamento estratégico das relações comunicativas. A representação gráfica contempla: a rede de sentidos sociais, os interlocutores e seus contextos e "lugar de interlocução". A matriz inclui fontes, campos, instâncias, comunidades discursivas e uma tipologia de fatores de mediação. Abstract in spanish El trabajo tiene como objetivo proponer un modelo para análisis y planificación estratégica de la comunicación en las políticas públicas, considerando que los modelos corrientes no sustentan adecuadamente la práctica comunicativa en los procesos de intervención social, frustrando las altas inversion [...] es y expectativas que despiertan. El "Modelo del Mercado Simbólico", en red, descentrado y multipolar, es compuesto por una formulación teórica, una representación gráfica de los principales componentes y sus relaciones y de una matriz de análisis y planificación estratégica de las relaciones comunicativas. La representación gráfica contempla: la red de sentidos sociales, los interlocutores y sus contextos y "lugar de interlocución". La matriz incluye fuentes, campos, instancias, comunidades discursivas y una tipología de factores de mediación. Abstract in english The purpose of this paper is to put forth a model for the analysis and strategic planning of the communication of public policies, given that the current models fail to adequately fulfill communication requirements in the processes of social intervention, frustrating the high investments and expecta [...] tions that they give rise to. The "Symbolic Market Model", in network form, both decentralized and multipolar, is comprised of (i) a theoretical formulation, (ii) a graphical representation of the main components and the relations between them and (iii) an analysis and strategic planning matrix of communicative relations. The graphic representation takes into account: the network of social senses, the interlocutors and their contexts, and the "place of dialogue". The matrix includes sources, fields, instances, discursive communities and a typology of mediation factors.

Inesita Soares de, Araújo.

224

Modelling  

CERN Document Server

Modeling of technical machines became a standard technique since computer became powerful enough to handle the amount of data relevant to the specific system. Simulation of an existing physical device requires the knowledge of all relevant quantities. Electric fields given by the surrounding boundary as well as magnetic fields caused by coils or permanent magnets have to be known. Internal sources for both fields are sometimes taken into account, such as space charge forces or the internal magnetic field of a moving bunch of charged particles. Used solver routines are briefly described and some bench-marking is shown to estimate necessary computing times for different problems. Different types of charged particle sources will be shown together with a suitable model to describe the physical model. Electron guns are covered as well as different ion sources (volume ion sources, laser ion sources, Penning ion sources, electron resonance ion sources, and H$^-$-sources) together with some remarks on beam transport.

Spädtke, P

2013-01-01

225

Remote sensing of forest ecosystem dynamics: Measurements and modeling  

Science.gov (United States)

The development of an integrated approach to the modeling of forest dynamics encompassing submodels of forest growth and succession, soil processes and radiation interactions, is reported. Remote sensing technology is a key element of this study in that it provides data for developing, initializing, updating, and validating the models. The objectives are reviewed, the data collected and models in use are discussed, and a framework for studying interactions between the forest growth, soil process and energy interaction components, is described. Remote sensing technology used in the study includes optical and microwave field, aircraft and satellite borne instruments. The types of data collected during intensive field and aircraft campaigns included bidirectional reflectance, thermal emittance and multifrequency, multipolarization synthetic aperture radar backscatter. Synthetic imagery of derived products such as forest biomass and NDVI (Normalized Difference Vegetative Index), and collections of ground data are being assembled in a georeferenced data base. These data are used to drive or test multidiscipline simulations of forested ecosystems. Enhancements to the modeling environment permit considerable flexibility in configuring simulations and selecting results for reporting and graphical display.

Williams, Darrel L.; Ranson, K. Jon; Knox, Robert G.; Levine, Elissa R.

1994-01-01

226

Models  

Directory of Open Access Journals (Sweden)

Full Text Available Conventionally, multilevel analysis of covariance (ML-ANCOVA has been therecommended approach for analyzing treatment effects in quasi-experimental multilevel designswith treatment application at the cluster-level. In this paper, we introduce the generalizedML-ANCOVA with linear effect functions that identifies average and conditional treatment effectsin the presence of treatment-covariate interactions. We show how the generalized ML-ANCOVAmodel can be estimated with multigroup multilevel structural equation models that offerconsiderable advances compared to traditional ML-ANCOVA. The proposed model takes intoaccount measurement error in the covariates, sampling error in contextual covariates,treatment-covariate interactions, and stochastic predictors. We illustrate the implementation ofML-ANCOVA with an example from educational effectiveness research where we estimateaverage and conditional effects of early transition to secondary schooling on readingcomprehension.

BenjaminNagengast

2014-04-01

227

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

228

Modeling multi-frequency diurnal backscatter from a walnut orchard  

Science.gov (United States)

The Michigan Microwave Canopy Scattering Model (MIMICS) is used to model scatterometer data that were obtained during the August 1987 EOS (Earth Observing System) synergism study. During this experiment, truck-based scatterometers were used to measure radar backscatter from a walnut orchard in Fresno County, California. Multipolarized L- and X-band data were recorded for orchard plots for which dielectric and evapotranspiration characteristics were monitored. MIMICS is used to model a multiangle data set in which a single orchard plot was observed at varying impedance angles and a series of diurnal measurements in which backscatter from this same plot was measured continuously over several 24-h periods. MIMICS accounts for variations in canopy backscatter driven by changes in canopy state that occur diurnally as well as on longer time scales. L-band backscatter is dependent not only on properties of the vegetation but also on properties of the underlying soil surface. The behavior of the X-band backscatter is dominated by properties of the tree crowns.

Mcdonald, Kyle C.; Dobson, Myron C.; Ulaby, Fawwaz T.

1991-01-01

229

Modeling  

Directory of Open Access Journals (Sweden)

Full Text Available Recently, there have been a large number of studies using resting state fMRI to characterize abnormal brain connectivity in patients with a variety of neurological, psychiatric and developmental disorders. However, interpreting what the differences in resting state functional connectivity (rsfMRI-FC actually reflect in terms of the underlying neural pathology has proved to be elusive because of the complexity of brain anatomical connectivity. The same is the case for task-based fMRI studies. In the last few years, several groups have used large-scale neural modeling to help provide some insight into the relationship between brain anatomical connectivity and the corresponding patterns of fMRI-FC. In this paper we review several efforts at using large-scale neural modeling to investigate the relationship between structural connectivity and functional/effective connectivity to determine how alterations in structural connectivity are manifested in altered patterns of functional/effective connectivity. Because the alterations made in the anatomical connectivity between specific brain regions in the model are known in detail, one can use the results of these simulations to determine the corresponding alterations in rsfMRI-FC. Many of these simulation studies found that structural connectivity changes do not necessarily result in matching changes in functional/effective connectivity in the areas of structural modification. Often, it was observed that increases in functional/effective connectivity in the altered brain did not necessarily correspond to increases in the strength of the anatomical connection weights. Note that increases in rsfMRI-FC in patients have been interpreted in some cases as resulting from neural plasticity. These results suggest that this interpretation can be mistaken. The relevance of these simulation findings to the use of functional/effective fMRI connectivity as biomarkers for brain disorders is also discussed.

BarryHorwitz

2013-11-01

230

Modelling  

International Nuclear Information System (INIS)

will also soon be published by the IAEA. This is the reason why the IAEA was involved in the co-ordination required for preparation of this volume; the material presented is a condensed overview prepared by some of the scientists that were involved in the above cited IAEA activities. This volume VI providing such an overview was included into the series to make this series self-sufficient in its coverage of the field of Isotope Hydrology. A special chapter on the methodologies and concepts related to geochemical modelling in groundwater systems would have been most desirable to include. The reader is referred to IAEA-TECDOC-910 and other relevant publications for guidance in this specific field

231

A simple model of the chaotic eccentricity of Mercury  

CERN Document Server

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

232

A Skew-t space-varying regression model for the spectral analysis of resting state brain activity.  

Science.gov (United States)

It is known that in many neurological disorders such as Down syndrome, main brain rhythms shift their frequencies slightly, and characterizing the spatial distribution of these shifts is of interest. This article reports on the development of a Skew-t mixed model for the spatial analysis of resting state brain activity in healthy controls and individuals with Down syndrome. Time series of oscillatory brain activity are recorded using magnetoencephalography, and spectral summaries are examined at multiple sensor locations across the scalp. We focus on the mean frequency of the power spectral density, and use space-varying regression to examine associations with age, gender and Down syndrome across several scalp regions. Spatial smoothing priors are incorporated based on a multivariate Markov random field, and the markedly non-Gaussian nature of the spectral response variable is accommodated by the use of a Skew-t distribution. A range of models representing different assumptions on the association structure and response distribution are examined, and we conduct model selection using the deviance information criterion. (1) Our analysis suggests region-specific differences between healthy controls and individuals with Down syndrome, particularly in the left and right temporal regions, and produces smoothed maps indicating the scalp topography of the estimated differences. PMID:22614763

Ismail, Salimah; Sun, Wenqi; Nathoo, Farouk S; Babul, Arif; Moiseev, Alexader; Beg, Mirza Faisal; Virji-Babul, Naznin

2013-08-01

233

A Model for the Escape of Solar-Flare Accelerated Particles  

CERN Document Server

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

234

Bayesian multi-dipole modelling of a single topography in MEG by adaptive sequential Monte Carlo samplers  

Science.gov (United States)

In this paper, we develop a novel Bayesian approach to the problem of estimating neural currents in the brain from a fixed distribution of magnetic field (called topography), measured by magnetoencephalography. Differently from recent studies that describe inversion techniques, such as spatio-temporal regularization/filtering, in which neural dynamics always plays a role, we face here a purely static inverse problem. Neural currents are modelled as an unknown number of current dipoles, whose state space is described in terms of a variable-dimension model. Within the resulting Bayesian framework, we set up a sequential Monte Carlo sampler to explore the posterior distribution. An adaptation technique is employed in order to effectively balance the computational cost and the quality of the sample approximation. Then, both the number and the parameters of the unknown current dipoles are simultaneously estimated. The performance of the method is assessed by means of synthetic data, generated by source configurations containing up to four dipoles. Eventually, we describe the results obtained by analysing data from a real experiment, involving somatosensory evoked fields, and compare them to those provided by three other methods.

Sorrentino, Alberto; Luria, Gianvittorio; Aramini, Riccardo

2014-04-01

235

Complex polarity reversals in a geodynamo model  

Science.gov (United States)

Complex polarity reversals in numerical dynamos driven by thermo-chemical convection are analyzed in terms of magnetic field intensity variations, transitional field structure, and other observable characteristics. Our most Earth-like dynamos are characterized by long stable polarity chrons with dipole-dominant magnetic fields punctuated by occasional polarity reversals, and are found within a transition region of parameter space between non-reversing strongly dipolar dynamos and chaotic multi-polar-type dynamos. Dynamos in the transition region have elevated dipole terms, reduced quadrupole terms, magnetic energy that decreases slowly with spherical harmonic degree, and broadband dipole frequency spectra. Their axial dipole intensity histograms are trimodal, with large modes representing the stable polarity states and an intermediate mode representing the transitional multi-polar state. The dipole family intensity exceeds the quadrupole family intensity on the core-mantle boundary during stable polarity times, but during transitions the two families are similar. A complex dynamo model reversal is compared with paleomagnetic reconstructions around the Matuyama-Brunhes polarity transition. Both start with a gradual decrease of the dipole intensity, followed by a precursor reversal and transient polarity recovery, then a rapid dipole collapse and a final reversal that initiates with reverse flux generation in one hemisphere. Virtual geomagnetic poles (VGPs) from sites near the reverse flux trace complex paths and cross the equator several thousand years before the simpler VGP paths from more distant sites, and magnetic intensity variations during the dynamo model reversal correlate with intensity variations inferred for the Matuyama-Brunhes transition.

Olson, Peter L.; Glatzmaier, Gary A.; Coe, Robert S.

2011-04-01

236

The breakdown of dipolar magnetic field generation in planetary dynamo models (Invited)  

Science.gov (United States)

Magnetic field measurements show that each dynamo in our solar system is distinct with field strengths that differ by many orders of magnitude and morphologies that range from titled dipoles to nearly axisymmetric dipole-quadrupoles to non-axisymmetric multipoles. The characteristics of stellar and astrophysical magnetic fields are similarly wide-ranging. Towards understanding the diversity of this dynamo zoo, we investigate the breakdown of dipole-dominated magnetic fields in a suite of planetary dynamo and otherwise identical non-magnetic simulations where the convective vigor and rotation rate are varied systematically. This survey considers models with Prandtl number Pr=1, magnetic Prandtl numbers up to Pm = 5, Ekman numbers in the range 1e-3 transition from dipolar to multipolar dynamos is observed in models with moderate to high Ekman numbers. This breakdown of the dipole happens when inertial and viscous forces become comparable and coincides with a degradation of helicity in the flow, which also occurs when no magnetic field is present. Large-scale poloidal magnetic fields in these models then appear to be generated by a viscously controlled, macro-scale alpha-effect. Our lowest Ekman number cases, however, suggest that the dynamics may be changing as the viscous force decreases. Since viscosity is expected to be negligible in planetary and stellar interiors, an extrapolation of our results implies that moderate Ekman number models may not simulate the physical mechanisms of magnetic field generation in these bodies correctly.

Soderlund, K. M.; King, E. M.; Aurnou, J. M.

2013-12-01

237

The structure of {sup 193}Au within the Interacting Boson Fermion Model  

Energy Technology Data Exchange (ETDEWEB)

A ?? angular correlation experiment investigating the nucleus {sup 193}Au is presented. In this work the level scheme of {sup 193}Au is extended by new level information on spins, multipolarities and newly observed states. The new results are compared with theoretical predictions from a general Interacting Boson Fermion Model (IBFM) calculation for the positive-parity states. The experimental data is in good agreement with an IBFM calculation using all proton orbitals between the shell closures at Z=50 and Z=126. As a dominant contribution of the d{sub 3/2} orbital to the wave function of the lowest excited states is observed, a truncated model of the IBFM using a Bose–Fermi symmetry is applied to the describe {sup 193}Au. Using the parameters of a fit performed for {sup 193}Au, the level scheme of {sup 192}Pt, the supersymmetric partner of {sup 193}Au, is predicted but shows a too small boson seniority splitting. We obtained a common fit by including states observed in {sup 192}Pt. With the new parameters a supersymmetric description of both nuclei is established.

Thomas, T., E-mail: tim.thomas@ikp.uni-koeln.de [Institute for Nuclear Physics, University of Cologne, Zülpicher Straße 77, D-50937 Köln (Germany); WNSL, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States); Bernards, C. [Institute for Nuclear Physics, University of Cologne, Zülpicher Straße 77, D-50937 Köln (Germany); WNSL, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States); Régis, J.-M.; Albers, M.; Fransen, C.; Jolie, J.; Heinze, S.; Radeck, D.; Warr, N.; Zell, K.-O. [Institute for Nuclear Physics, University of Cologne, Zülpicher Straße 77, D-50937 Köln (Germany)

2014-02-15

238

Ordering and Fluctuation of Quantum Multipoles in CeB6  

International Nuclear Information System (INIS)

The effect of multipolar fluctuations on the quadrupolar phase transition in CeB6 is investigated theoretically. It is shown that the fluctuations become strong and field-dependent, reflecting the competition of coupled multipolar interactions. Some unusual phenomena around the transition in CeB6 are shown to be reasonably explained within the RKKY model. (author)

239

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%). PMID:22431346

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

2013-09-01

240

An Asymmetric Jet-launching Model for the Protoplanetary Nebula CRL 618  

Science.gov (United States)

We propose an asymmetrical jet-ejection mechanism in order to model the mirror symmetry observed in the lobe distribution of some protoplanetary nebulae (pPNs), such as the pPN CRL 618. Three-dimensional hydrodynamical simulations of a precessing jet launched from an orbiting source were carried out, including an alternation in the ejections of the two outflow lobes, depending on which side of the precessing accretion disk is hit by the accretion column from a Roche lobe-filling binary companion. Both synthetic optical emission maps and position-velocity diagrams were obtained from the numerical results with the purpose of carrying out a direct comparison with observations. Depending on the observer's point of view, multipolar morphologies are obtained that exhibit a mirror symmetry at large distances from the central source. The obtained lobe sizes and their spatial distributions are in good agreement with the observed morphology of the pPN CRL 618. We also obtain that the kinematic ages of the fingers are similar to those obtained in the observations.

Velázquez, Pablo F.; Riera, Angels; Raga, Alejandro C.; Toledo-Roy, Juan C.

2014-10-01

 
 
 
 
241

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

242

Prediction of vapor-liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part II: Application to H2O-NaCl and CO2-H2O-NaCl System  

Science.gov (United States)

The SAFT-LJ equation of state improved by Sun and Dubessy (2010) can represent the vapor-liquid equilibrium and PVTx properties of the CO2-H2O system over a wide P-T range because it accounts for the energetic contribution of the main types of molecular interactions in terms of reliable molecular based models. Assuming that NaCl fully dissociates into individual ions (spherical Na+ and Cl-) in water and adopting the restricted primitive model of mean spherical approximation to account for the energetic contribution due to long-range electrostatic forces between ions, this study extends the improved SAFT-LJ EOS to the H2O-NaCl and the CO2-H2O-NaCl systems at temperatures below 573 K. The EOS parameters for the interactions between ion and ion and between ion and water were determined from the mean ionic activity coefficient data and the density data of the H2O-NaCl system. The parameters for the interactions between ion and CO2 were evaluated from CO2 solubility data of the CO2-H2O-NaCl system. Comparison with the experimental data shows that this model can predict the mean ionic activity coefficient, osmotic coefficient, saturation pressure, and density of aqueous NaCl solution and can predict the vapor-liquid equilibrium and PVTx properties of the CO2-H2O-NaCl system over the range from 273 to 573 K, from 0 to 1000 bar, and from 0 to 6 mol/kg NaCl with high accuracy.

Sun, Rui; Dubessy, Jean

2012-07-01

243

Modeling extracellular electrical neural stimulation: from basic understanding to MEA-based applications.  

Science.gov (United States)

Extracellular electrical stimulation of neural networks has been widely used empirically for decades with individual electrodes. Since recently, microtechnology provides advanced systems with high-density microelectrode arrays (MEAs). Taking the most of these devices for fundamental goals or developing neural prosthesis requires a good knowledge of the mechanisms underlying electrical stimulation. Here, we review modeling approaches used to determine (1) the electric potential field created by a stimulation and (2) the response of an excitable cell to an applied field. Computation of the potential field requires solving the Poisson equation. While this can be performed analytically in simple electrode-neuron configurations, numerical models are required for realistic geometries. In these models, special care must be taken to model the potential drop at the electrode/tissue interface using appropriate boundary conditions. The neural response to the field can then be calculated using compartmentalized cell models, by solving a cable equation, the source term of which (called activating function) is proportional to the second derivative of the extracellular field along the neural arborization. Analytical and numerical solutions to this equation are first presented. Then, we discuss the use of approximated solutions to intuitively predict the neuronal response: Either the "activating function" or the "mirror estimate", depending on the pulse duration and the cell space constant. Finally, we address the design of optimal electrode configurations allowing the selective activation of neurons near each stimulation site. This can be achieved using either multipolar configurations, or the "ground surface" configuration, which can be easily integrated in high-density MEAs. Overall, models highlighting the mechanisms of electrical microstimulation and improving stimulating devices should help understanding the influence of extracellular fields on neural elements and developing optimized neural prostheses for rehabilitation. PMID:22036892

Joucla, Sébastien; Yvert, Blaise

2012-01-01

244

Alpha-band hypersynchronization in progressive mild cognitive impairment: a magnetoencephalography study.  

Science.gov (United States)

People with mild cognitive impairment (MCI) show a high risk to develop Alzheimer's disease (AD; Petersen et al., 2001). Nonetheless, there is a lack of studies about how functional connectivity patterns may distinguish between progressive (pMCI) and stable (sMCI) MCI patients. To examine whether there were differences in functional connectivity between groups, MEG eyes-closed recordings from 30 sMCI and 19 pMCI subjects were compared. The average conversion time of pMCI was 1 year, so they were considered as fast converters. To this end, functional connectivity in different frequency bands was assessed with phase locking value in source space. Then the significant differences between both groups were correlated with neuropsychological scores and entorhinal, parahippocampal, and hippocampal volumes. Both groups did not differ in age, gender, or educational level. pMCI patients obtained lower scores in episodic and semantic memory and also in executive functioning. At the structural level, there were no differences in hippocampal volume, although some were found in left entorhinal volume between both groups. Additionally, pMCI patients exhibit a higher synchronization in the alpha band between the right anterior cingulate and temporo-occipital regions than sMCI subjects. This hypersynchronization was inversely correlated with cognitive performance, both hippocampal volumes, and left entorhinal volume. The increase in phase synchronization between the right anterior cingulate and temporo-occipital areas may be predictive of conversion from MCI to AD. PMID:25355209

López, María Eugenía; Bruña, Ricardo; Aurtenetxe, Sara; Pineda-Pardo, José Ángel; Marcos, Alberto; Arrazola, Juan; Reinoso, Ana Isabel; Montejo, Pedro; Bajo, Ricardo; Maestú, Fernando

2014-10-29

245

Sparse Multiview Methods for Classification of Musical Genre from Magnetoencephalography Recordings  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Classification of musical genre from audio is a well-researched area of music research. However to the authors’ knowledge no studies have been performed that attempt to identify the genre of music a person is listening to from recordings of their brain activity. It is believed that with the appropriate choice of experimental stimuli and analysis procedures, this discrimination is possible. The main goal of this experiment is to see whether it is possible to detect the genre of music that a ...

Diethe, Tom; Teodoru, Gabi; Furl, Nick; Shawe-taylor, John

2009-01-01

246

Development of Theory of Mind Stimuli in Magnetoencephalography for Nursing Evaluation  

Directory of Open Access Journals (Sweden)

Full Text Available We introduce the development of animation stimuli for theory of mind (ToM in magnetoencepalography (MEG. We will discuss apparatus for presenting animation stimuli and a technical problem like an eye movement signal generated from following triangles in the animations, and its rejection using independent component analysis (ICA. With the ToM animations and the apparatus, we conducted MEG measurements for 8 normal controls and 6 schizophrenic patients. We present a preliminary assessment result for the developed animation stimuli as a tool for ToM test, which has been obtained by scoring in the followingup interview after the MEG measurement.

Sungwon Park

2009-09-01

247

Cortical activity associated with the detection of temporal gaps in tones: a magnetoencephalography study  

Science.gov (United States)

We used magnetoencephalogram (MEG) in two experiments to investigate spatio-temporal profiles of brain responses to gaps in tones. Stimuli consisted of leading and trailing markers with gaps between the two markers of 0, 30, or 80 ms. Leading and trailing markers were 300 ms pure tones at 800 or 3200 Hz.Two conditions were examined: the within-frequency (WF) condition in which the leading and trailing markers had identical frequencies, and the between-frequency (BF) condition in which they had different frequencies. Using minimum norm estimates (MNE), we localized the source activations at the time of the peak response to the trailing markers. Results showed that MEG signals in response to 800 and 3200 Hz tones were localized in different regions within the auditory cortex, indicating that the frequency pathways activated by the two markers were spatially represented.The time course of regional activity (RA) was extracted from each localized region for each condition. In Experiment 1, which used a continuous tone for the WF 0-ms stimulus, the N1m amplitude for the trailing marker in the WF condition differed depending on gap duration but not tonal frequency. In contrast, N1m amplitude in BF conditions differed depending on the frequency of the trailing marker. In Experiment 2, in which the 0-ms gap stimulus in the WF condition was made from two markers and included an amplitude reduction in the middle, the amplitude in WF and BF conditions changed depending on frequency, but not gap duration.The difference in temporal characteristics betweenWF and BF conditions could be observed in the RA.

Mitsudo, Takako; Hironaga, Naruhito; Mori, Shuji

2014-01-01

248

Evaluation of CNS-function in CAPD patients using magnetoencephalography (MEG): comparison with hemodialysis patients.  

Science.gov (United States)

In order to evaluate the CNS-function of uremic patients, the magnetic activity emitted from the brain of 20 pts (10 pts on CAPD and 10 on HD) was measured. MEG consisted of taking 32 consecutive records from the 32 equally spaced points chosen on the skull in uremic pts around our reference points T3, T4, P4, F3, F4 of the international 10-20 electrode placement point system. MEG data were converted using an AD-converter with sampling frequency 256 Hz and stored in a P/C. Our results showed significant differences between the two groups. In all HD pts there was abnormal magnetic brain activity with high spectral amplitudes (in the band 2-7 Hz) which was more prominent in pts in hemo for more than 4 years. The magnetic activity was within normal ranges in all CAPD pts. We conclude that: 1) There is high magnetic brain activity in HD pts, which in accordance with the EEG findings are signs of diffuse encephalopathy. 2) CAPD pts show a very low magnetic brain activity which must be interpreted as normal brain function, and 3) MEG can be useful in further measurement of adequacy of dialysis. PMID:1361782

Thodis, E; Anninos, P A; Pasadakis, P; Adamopoulos, A V; Panagoutsos, S; Vargemezis, V

1992-01-01

249

Tinnitus perception and distress is related to abnormal spontaneous brain activity as measured by magnetoencephalography.  

Directory of Open Access Journals (Sweden)

Full Text Available BACKGROUND: The neurophysiological mechanisms underlying tinnitus perception are not well understood. Surprisingly, there have been no group studies comparing abnormalities in ongoing, spontaneous neuronal activity in individuals with and without tinnitus perception. METHODS AND FINDINGS: Here, we show that the spontaneous neuronal activity of a group of individuals with tinnitus (n = 17 is characterised by a marked reduction in alpha (8-12 Hz power together with an enhancement in delta (1.5-4 Hz as compared to a normal hearing control group (n = 16. This pattern was especially pronounced for temporal regions. Moreover, correlations with tinnitus-related distress revealed strong associations with this abnormal spontaneous activity pattern, particularly in right temporal and left frontal areas. Overall, effects were stronger for the alpha than for the delta frequency band. A data stream of 5 min, recorded with a whole-head neuromagnetometer under a resting condition, was sufficient to extract the marked differences. CONCLUSIONS: Despite some limitations, there are arguments that the regional pattern of abnormal spontaneous activity we found could reflect a tinnitus-related cortical network. This finding, which suggests that a neurofeedback approach could reduce the adverse effects of this disturbing condition, could have important implications for the treatment of tinnitus.

2005-06-01

250

Joint EEG/fMRI state space model for the detection of directed interactions in human brains--a simulation study.  

Science.gov (United States)

An often addressed challenge in neuroscience research is the assignment of different tasks to specific brain regions. In many cases several brain regions are activated during a single task. Therefore, one is also interested in the temporal evolution of brain activity to infer causal relations between activated brain regions. These causal relations may be described by a directed, task specific network which consists of activated brain regions as vertices and directed edges. The edges describe the causal relations. Inference of the task specific brain network from measurements like electroencephalography (EEG) or functional magnetic resonance imaging (fMRI) is challenging, due to the low spatial resolution of the former and the low temporal resolution of the latter. Here, we present a simulation study investigating a possible combined analysis of simultaneously measured EEG and fMRI data to address the challenge specified above. A nonlinear state space model is used to distinguish between the underlying brain states and the (simulated) EEG/fMRI measurements. We make use of a modified unscented Kalman filter and a corresponding unscented smoother for the estimation of the underlying neural activity. Model parameters are estimated using an expectation-maximization algorithm, which exploits the partial linearity of our model. Inference of the brain network structure is then achieved using directed partial correlation, a measure for Granger causality. The results indicate that the convolution effect of the fMRI forward model imposes a big challenge for the parameter estimation and reduces the influence of the fMRI in combined EEG-fMRI models. It remains to be investigated whether other models or similar combinations of other modalities such as, e.g., EEG and magnetoencephalography can increase the profit of the promising idea of combining various modalities. PMID:22027197

Lenz, Michael; Musso, Mariachristina; Linke, Yannick; Tüscher, Oliver; Timmer, Jens; Weiller, Cornelius; Schelter, Björn

2011-11-01

251

Distinguishing mechanisms of gamma frequency oscillations in human current source signals using a computational model of a laminar neocortical network  

Directory of Open Access Journals (Sweden)

Full Text Available Gamma frequency rhythms have been implicated in numerous studies for their role in healthy and abnormal brain function. The frequency band has been described to encompass as broad a range as 30–150 Hz. Crucial to understanding the role of gamma in brain function is an identification of the underlying neural mechanisms, which is particularly difficult in the absence of invasive recordings in macroscopic human signals such as those from magnetoencephalography (MEG and electroencephalography (EEG. Here, we studied features of current dipole (CD signals from two distinct mechanisms of gamma generation, using a computational model of a laminar cortical circuit designed specifically to simulate CDs in a biophysically principled manner (Jones et al., 2007; Jones et al., 2009. We simulated spiking pyramidal interneuronal gamma (PING whose period is regulated by the decay time constant of GABAA-mediated synaptic inhibition and also subthreshold gamma driven by gamma-periodic exogenous excitatory synaptic drive. Our model predicts distinguishable CD features created by spiking PING compared to subthreshold driven gamma that can help to disambiguate mechanisms of gamma oscillations in human signals. We found that gamma rhythms in neocortical layer 5 can obscure a simultaneous, independent gamma in layer 2/3. Further, we arrived at a novel interpretation of the origin of high gamma frequency rhythms (100–150 Hz, showing that they emerged from a specific temporal feature of CDs associated with single cycles of PING activity and did not reflect a separate rhythmic process. Last we show that the emergence of observable subthreshold gamma required highly coherent exogenous drive. Our results are the first to demonstrate features of gamma oscillations in human current source signals that distinguish cellular and circuit level mechanisms of these rhythms and may help guide understanding of their functional role.

ShaneLee

2013-12-01

252

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 c...

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

2011-01-01

253

Resonant X-ray scattering and multipolar order in actinide dioxides  

International Nuclear Information System (INIS)

on both the U and Np ions, and quadrupolar ordering was also found associated with both ions. However, these were different from those in pure NpO2. Whereas a longitudinal (L) 3-k configuration was found for NpO2, the x = 0.25 sample was found to have a transverse (T) 3-k configuration. The understanding of these different configurations then allowed an experiment to be performed in 2005 on a single crystal of UO2. The azimuthal dependence of the intensity from non-specular reflections reveals 3-k T anti-ferro-electric-quadrupolar order also UO2. The complication in UO2 is that both dipole ordering and an internal distortion of the oxygen atoms due to the quadrupole ordering are present; these have contrived to make it difficult to observe directly the quadrupole ordering in UO2, although such ordering was predicted almost 40 years ago, and the oxygen displacements reported 30 years ago [5]. These experiments also suggest a qualitative explanation of the unusual behaviour of the mixed oxides with 0.40 < x < 0.80. In this region there is competition between the L and T quadrupole ordering, resulting in quadrupolar frustration and only short-range dipole and quadrupole ordering. (authors)

254

Preliminary results from the NASA/JPL multifrequency, multipolarization synthetic aperture radar  

Science.gov (United States)

A brief description is given of the three-frequency polarimetric synthetic-aperture radar built and tested at the Jet Propulsion Laboratory. The radar has the capability to simultaneously acquire fully polarimetric data at P-, L-, and C-bands from a DC-8 airborne platform. The radar has an instantaneous data rate of approximately 2.1 Gb/s and has selectable record rates between 80-240 Mb/s. The system has a wide dynamic range featuring 8-b analog-to-digital converters and full digital floating-point processing. The processing is accomplished offline on a minicomputer system assisted by an array processor. Sample images are presented.

Held, Daniel N.; Brown, Walter E.; Miller, Timothy W.

1988-01-01

255

The star fish twins: Two young planetary nebulae with extreme multipolar morphology  

Science.gov (United States)

We present alpha images of two objects, He 2-47 and M1-37, obtained during a Hubble Space Telescope imaging survey of young planetary nebulae (PNs) selected on the basis of their low-excitation characteristics.

Sahai, R.

2000-01-01

256

Multipolar ordering in NpO{sub 2} probed by NMR  

Energy Technology Data Exchange (ETDEWEB)

We have initiated the first {sup 17}O-NMR measurements in the ordered state of NpO{sub 2}. From the {sup 17}O-NMR spectrum, we have confirmed the occurrence of two inequivalent oxygen sites below T{sub 0}=26K. It has also been shown that the {sup 17}O-NMR spectrum in the ordered state can be understood by considering an unconventional hyperfine interaction between the {sup 17}O nuclear spins and field-induced antiferromagnetic moments arising from the longitudinal triple-q antiferro-quadrupolar order. These NMR results give strong evidence for the occurrence of the longitudinal triple-q multipole structure in NpO{sub 2}.

Tokunaga, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: tokunaga.yo@jaea.go.jp; Homma, Y. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Kambe, S. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); Aoki, D. [IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Sakai, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); Yamamoto, E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); Nakamura, A. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); IMR Tohoku University, 2145-2 Narita Oarai Higashiibaraki Ibaraki 311-1313 (Japan); Walstedt, R.E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan); Yasuoka, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, 2-4 Shirane, Tokai, Ibaraki 319-1195 (Japan)

2006-05-01

257

Antihydrogen formation dynamics in a multipolar neutral anti-atom trap  

International Nuclear Information System (INIS)

Antihydrogen production in a neutral atom trap formed by an octupole-based magnetic field minimum is demonstrated using field-ionization of weakly bound anti-atoms. Using our unique annihilation imaging detector, we correlate antihydrogen detection by imaging and by field-ionization for the first time. We further establish how field-ionization causes radial redistribution of the antiprotons during antihydrogen formation and use this effect for the first simultaneous measurements of strongly and weakly bound antihydrogen atoms. Distinguishing between these provides critical information needed in the process of optimizing for trappable antihydrogen. These observations are of crucial importance to the ultimate goal of performing CPT tests involving antihydrogen, which likely depends upon trapping the anti-atom.

258

Antihydrogen formation dynamics in a multipolar neutral anti-atom trap  

CERN Document Server

Antihydrogen production in a neutral atom trap formed by an octupole-based magnetic field minimum is demonstrated using field-ionization of weakly bound anti-atoms. Using our unique annihilation imaging detector, we correlate antihydrogen detection by imaging and by field-ionization for the first time. We further establish how field-ionization causes radial redistribution of the antiprotons during antihydrogen formation and use this effect for the first simultaneous measurements of strongly and weakly bound antihydrogen atoms. Distinguishing between these provides critical information needed in the process of optimizing for trappable antihydrogen. These observations are of crucial importance to the ultimate goal of performing CPT tests involving antihydrogen, which likely depends upon trapping the anti-atom.

Andresen, G B; Bowe, P D; Bray, C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Humphries, A J; Hydomako, R; Jørgensen, L V; Kerrigan, S J; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; van der Werf, D P; Wurtele, J S; Yamazaki, Y

2010-01-01

259

NGC 6309, a Planetary Nebula that Shifted from Round to Multipolar  

CERN Document Server

We present new narrow-band Ha, [N II], and [O III] high-resolution images of the quadrupolar planetary nebula (PN) NGC 6309 that show in great detail its bipolar lobes and reveal new morphological features. New high- and low-dispersion long-slit spectra have been obtained to help in the investigation of the new nebular components. The images and spectra unveil two diffuse blobs, one of them located at 55 arcsec from the central star along the NE direction (PA= +71) and the other at 78 arcsec in the SW direction (PA= -151). Therefore, these structures do not share the symmetry axes of the inner bipolar outflows. Their radial velocities relative to the system are quite low: +3 and -4 km/s, respectively. Spectroscopic data confirm a high [O III] to Ha ratio, indicating that the blobs are being excited by the UV flux from the central star. Our images convincingly show a spherical halo 60 arcsec in diameter encircling the quadrupolar nebula. The expansion velocity of this shell is low, 66 km/s. The software SHAPE ...

Rubio, Gabriel; Ramos-Larios, Gerardo; Guerrero, Martin A; Olguin, Lorenzo; Guillen, Pedro F; Mata, Hector

2014-01-01

260

Reshaping Europe In A Multipolar World: Can The EU Rise To The Challenge?  

Directory of Open Access Journals (Sweden)

Full Text Available Globalisation and the emergence of economic players such as Brazil, Russia, India and China (BRIC have led to predictions that US hegemony will quickly decline as a new world order emerges. With the European Union (EU also facing a downgrading of its own status – as economic, political and cultural power shifts from west to east – now is the time to ensure the Union has a strategy in place to remain an influential global actor despite its lack of natural resources and member state sovereign debt arising from the 2008/9 economic crisis. Only concerted efforts at institutional future-proofing (or widening and deepening plus by the EU and a global vision for the supranational body will ensure its survival and prosperity.

Dean Carroll

2011-09-01

 
 
 
 
261

High-order multipolar hyperpolarizabilities with imaginary frequency for H and He  

International Nuclear Information System (INIS)

Calculations are reported of Xzz,zz,z,z3(-i?; i?, 0,0), Xzz,zz,x,x3 (-i?; i?; 0,0), Xzzz,z,z,z3(-i?; i?,0,0), Xzz,z,z,z,z4(-i?; i?, 0,0,0), and Xzz,x,x,z,z4(-i?; i?, 0,0,0) for H and He. These are the independent components of the atomic (quadrupole)2-(dipole)2, (octupole)-(dipole)3, and (quadrupole)-(dipole)4 hyperpolarizability tensors for an imaginary frequency i?. The first three quantities have been used for the determination of the R-8 dispersion contribution to the H-H, H-He, and He-He collision-induced pair polarizability functions. The last two quantities will be needed in future calculations of the leading order (R-7) dispersion contributions to the collision-induced first hyperpolarizability (?) for the H-He pair. The calculations were based on sum-over-states formulations with near-exact wave functions for H and highly accurate explicitly electron-correlated wave functions for He. For this reason the authors believe them to be of benchmark quality. 8 refs., 3 tabs

262

Multipolarity or cosmopolitanism? A critique of Mouffe from a hegemony-theoretical perspective  

DEFF Research Database (Denmark)

In a series of publications Chantal Mouffe (2004, 2005a, 2005b, 2008, 2009, 2013) has criticized cosmopolitanism for its lack of conceptualization of power, conflict and struggle, in short of politics. Even though this critique is largely well placed, the conclusions drawn from the analysis by Mouffe are flawed. As she puts it, if a cosmopolitan democracy “was ever realized, it could only signify the world hegemony of a dominant power that would have been able to impose its conception of the world on the entire planet and which, identifying its interests with those of humanity, would treat any disagreement as an illegitimate challenge to its ‘rational’ leadership”. Mouffe, On the Political pp. 106–7. I argue that Mouffe paradoxically seems to be using a traditional 'realist' conceptualization of hegemony, signifying simply domination. Against this I argue that a post-structuralist understanding of hegemony – as developed by herself and Laclau in Hegemony and Socialist Strategy, (Laclau and Mouffe,1985), precisely allows us to see the distance between universal values, such as freedom and equality for all, and their actual interpretation and use. The fact that the West are using democracy and human rights as legitimating devises for non-democratic goals, should not make us abandon the realization of these values on the global scale as the political goal.

Hansen, Allan Dreyer

263

Multi-Polarization ASAR Backscattering from Herbaceous Wetlands in Poyang Lake Region, China  

Directory of Open Access Journals (Sweden)

Full Text Available Wetlands are one of the most important ecosystems on Earth. There is an urgent need to quantify the biophysical parameters (e.g., plant height, aboveground biomass and map total remaining areas of wetlands in order to evaluate the ecological status of wetlands. In this study, Environmental Satellite/Advanced Synthetic Aperture Radar (ENVISAT/ASAR dual-polarization C-band data acquired in 2005 is tested to investigate radar backscattering mechanisms with the variation of hydrological conditions during the growing cycle of two types of herbaceous wetland species, which colonize lake borders with different elevation in Poyang Lake region, China. Phragmites communis (L. Trin. is semi-aquatic emergent vegetation with vertical stem and blade-like leaves, and the emergent Carex spp. has rhizome and long leaves. In this study, the potential of ASAR data in HH-, HV-, and VV-polarization in mapping different wetland types is examined, by observing their dynamic variations throughout the whole flooding cycle. The sensitivity of ASAR backscattering coefficients to vegetation parameters of plant height, fresh and dry biomass, and vegetation water content is also analyzed for Phragmites communis (L. Trin. and Carex spp. The research for Phragmites communis (L. Trin. shows that HH polarization is more sensitive to plant height and dry biomass than HV polarization. ASAR backscattering coefficients are relatively less sensitive to fresh biomass, especially in HV polarization. However, both are highly dependent on canopy water content. In contrast, the dependence of HH- and HV- backscattering from Carex community on vegetation parameters is poor, and the radar backscattering mechanism is controlled by ground water level.

Huiyong Sang

2014-05-01

264

A modelling study to inform specification and optimal electrode placement for imaging of neuronal depolarization during visual evoked responses by electrical and magnetic detection impedance tomography  

International Nuclear Information System (INIS)

Electrical impedance tomography (EIT) has the potential to achieve non-invasive functional imaging of fast neuronal activity in the human brain due to opening of ion channels during neuronal depolarization. Local changes of resistance in the cerebral cortex are about 1%, but the size and location of changes recorded on the scalp are unknown. The purpose of this work was to develop an anatomically realistic finite element model of the adult human head and use it to predict the amplitude and topography of changes on the scalp, and so inform specification for an in vivo measuring system. A detailed anatomically realistic finite element (FE) model of the head was produced from high resolution MRI. Simulations were performed for impedance changes in the visual cortex during evoked activity with recording of scalp potentials by electrodes or magnetic flux density by magnetoencephalography (MEG) in response to current injected with electrodes. The predicted changes were validated by recordings in saline filled tanks and with boundary voltages measured on the human scalp. Peak changes were 1.03 ± 0.75 µV (0.0039 ± 0.0034%) and 27 ± 13 fT (0.2 ± 0.5%) respectively, which yielded an estimated peak signal-to-noise ratio of about 4 for in vivo averaging over 10 min and 1 mA current injection. The largest scalp changes were over the occipital cortex. This modelling suggests, for the first time, that reproducible changes could be recorded on the scalp in vivo in single channels, although a higher SNR would be desirable for accurate image production. The findings suggest that an in vivo study is warranted in order to determine signal size but methods to improve SNR, such as prolonged averaging or other signal processing may be needed for accurate image production

265

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

International Nuclear Information System (INIS)

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

266

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

267

Damping of the giant resonances in a fluid-dynamical model  

International Nuclear Information System (INIS)

The relevance to the damping of the giant resonances, of the anharmonic coupling between the normal modes, is investigated in a fluid dynamical mode. It is found that this mechanism leads to a weak damping which, however, increases very drastically with the wavevector, implying a very short life time for high multipolarity modes. (Author)

268

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

LENUS (Irish Health Repository)

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

2011-09-30

269

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.

Skoblov Nikita

2011-09-01

270

Analysis of Growth and Decay Rates of the Axial Dipole in Geodynamo Models  

Science.gov (United States)

Observations of the Earth's magnetic field made at the surface reveal temporal variations in the field originating in the outer core. PADM2M is a reconstruction of the 0 to 2 Ma paleomagnetic axial dipole moment. Ziegler & Constable, 2011 showed that for periods longer than 25 kyr the rate of growth of the geomagnetic dipole is greater than its decay rate. This asymmetry is not limited to times when the field is reversing; this may be indicative of a key physical process of secular variation. To investigate the possible core processes underlying this observation we have analyzed a suite of numerical dynamo simulations, specifically the temporal variation of their axial dipole moments. We use the magnetic diffusion time to scale the simulations' nondimensional time, as this is more appropriate for the periods of interest here. An advantage to analyzing simulations is that they do not suffer from the same limitations in spatial and temporal resolution as the data; however, simulations cannot yet run with Earth-like rotational rates or diffusivities. All of our simulations span multiple diffusion times. We have chosen a broad range of simulations with different reversal regimes (dipole-dominated, non-reversing; dipole-dominated, reversing; multipolar, reversing) and with different heating modes (bottom, internal, or a combination of the two). For each simulation we conduct the same analysis that was applied to PADM2M. Families of smoothed axial dipole models are constructed using penalized smoothing splines as an effective low-pass filter to see at what timescales any asymmetry exist. The first derivatives of each axial dipole record are calculated in order to examine the rates of growth and decay. The results vary with the nature of the simulations. Further analysis is needed to determine what dynamo parameters, and related physical properties, determine the relative rates of growth and decay.

Avery, M. S.; Constable, C.; Davies, C.; Gubbins, D.

2013-12-01

271

Testing the geomagnetic dipole and reversing dynamo models over Earth's cooling history  

Science.gov (United States)

Continental drift reconstructions rely on the assumption that Earth's mean magnetic field has been a geocentric axial dipole over geologic time. However, the coupled dynamics of mantle and core convection may have had profound effects on the magnetic field in the distant past. Previous dynamo models have linked differences between polar and equatorial mantle heat flow to apparently anomalous paleomagnetic fields, and changes in reversal frequency. Here we use the inclination test (Evans, 1976) to interpret observational magnetic field models and polarity-reversing numerical dynamos representing various convective states of the mantle and core. Dynamo models with uniform buoyancy flux represent three convective states of the mantle and core: (1) present era Earth, driven thermo-chemically at the inner core boundary; (2) mantle overturn, with elevated heat flux at the core-mantle boundary, and (3) ancient Earth prior to inner core nucleation, with buoyancy production solely at the CMB. Consistent with Earth's present magnetic field, dynamos driven by buoyancy due to inner core growth are nearly dipolar. In contrast, elevated CMB heat flow yields small to moderate inclination flattening due to a persistent octupole that reverses synchronously with the dipole. For the ancient Earth models the relatively strong octupole component tends to stabilize the dynamo and decrease the reversal frequency. Our results, along with evidence of a young inner core, imply that an entirely liquid core contributed to shallow inclinations in Precambrian time. We also run models with latitudinally variable heat flux boundary conditions to further investigate the relationship between dynamo flow fields, the octupole component, magnetic inclinations and reversal frequency. For models with increased polar CMB heat flux we find that the relative strength of the octupole component increases in proportion to latitudinal heat flux variation. On the other hand, models are very sensitive to enhanced equatorial CMB cooling, which rapidly leads to unstable, multipolar dynamos with high reversal frequencies. This asymmetry in sensitivity to latitudinal variations in CMB heat flux implies that such variations are likely to yield only small inclination anomalies.

Heimpel, Moritz; Evans, Ted

2014-05-01

272

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

273

Reconstructing Coherent Networks from Electroencephalography and Magnetoencephalography with Reduced Contamination from Volume Conduction or Magnetic Field Spread  

Science.gov (United States)

Volume conduction (VC) and magnetic field spread (MFS) induce spurious correlations between EEG/MEG sensors, such that the estimation of functional networks from scalp recordings is inaccurate. Imaginary coherency [1] reduces VC/MFS artefacts between sensors by assuming that instantaneous interactions are caused predominantly by VC/MFS and do not contribute to the imaginary part of the cross-spectral densities (CSDs). We propose an adaptation of the dynamic imaging of coherent sources (DICS) [2] - a method for reconstructing the CSDs between sources, and subsequently inferring functional connectivity based on coherences between those sources. Firstly, we reformulate the principle of imaginary coherency by performing an eigenvector decomposition of the imaginary part of the CSD to estimate the power that only contributes to the non-zero phase-lagged (NZPL) interactions. Secondly, we construct an NZPL-optimised spatial filter with two a priori assumptions: (1) that only NZPL interactions exist at the source level and (2) the NZPL CSD at the sensor level is a good approximation of the projected source NZPL CSDs. We compare the performance of the NZPL method to the standard method by reconstructing a coherent network from simulated EEG/MEG recordings. We demonstrate that, as long as there are phase differences between the sources, the NZPL method reliably detects the underlying networks from EEG and MEG. We show that the method is also robust to very small phase lags, noise from phase jitter, and is less sensitive to regularisation parameters. The method is applied to a human dataset to infer parts of a coherent network underpinning face recognition. PMID:24349088

Drakesmith, Mark; El-Deredy, Wael; Welbourne, Stephen

2013-01-01

274

Frequency-pattern functional tomography of magnetoencephalography data allows new approach to the study of human brain organization  

Directory of Open Access Journals (Sweden)

Full Text Available A method based on a set of new theorems for the analysis of multichannel time series is described, based on precise Fourier transform and coherence analysis of the restored signals from a detailed set of frequency components. Magnetic field recordings of spontaneous and evoked activity by means of magnetic encephalography demonstrated that multichannel precise Fourier spectrum contains a very large set of harmonics with high coherence. The inverse problem can be solved with great precision based on coherent harmonics, so the technique is a promising platform of general analysis in brain imaging. The analysis method makes it possible to reconstruct sites and timing of electrical activity generated by both spontaneous and evoked brain function at different depths in the brain in the millisecond time range.

RodolfoRLlinás

2014-04-01

275

An iterative algorithm for sparse and constrained recovery with applications to divergence-free current reconstructions in magneto-encephalography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose an iterative algorithm for the minimization of a $\\ell_1$-norm penalized least squares functional, under additional linear constraints. The algorithm is fully explicit: it uses only matrix multiplications with the three matrices present in the problem (in the linear constraint, in the data misfit part and in penalty term of the functional). None of the three matrices must be invertible. Convergence is proven in a finite-dimensional setting. We apply the algorithm ...

Loris, Ignace; Verhoeven, Caroline

2012-01-01

276

Neural responses to auditory stimulus deviance under threat of electric shock revealed by spatially-filtered magnetoencephalography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Stimulus novelty or deviance may be especially salient in anxiety-related states due to sensitization to environmental change, a key symptom of anxiety disorders such as posttraumatic stress disorder (PTSD). We aimed to identify human brain regions that show potentiated responses to stimulus deviance during anticipatory anxiety. Twenty participants (14 men) were presented a passive oddball auditory task in which they were exposed to uniform auditory stimulation of tones with occasional deviat...

Cornwell, Brian R.; Baas, Johanna M. P.; Johnson, Linda; Holroyd, Tom; Carver, Frederick W.; Lissek, Shmuel; Grillon, Christian

2007-01-01

277

Las relaciones entre Colombia y Brasil en un contexto de regionalización diversificada en Suramérica y de un mundo multipolar emergente / The Relationship between Colombia and Brazil in the Context of Regional Diversification in South America and an Increasingly Multipolar World  

Scientific Electronic Library Online (English)

Full Text Available SciELO Colombia | Language: Spanish Abstract in spanish El artículo interpreta los desafíos que tiene la política exterior colombiana, tanto en el plano regional como en el global, de cara a la proyección de Brasil como potencia regional y jugador global. Para ello, en primer lugar, se lleva a cabo un acercamiento teórico al escenario regional actual y a [...] l horizonte de las relaciones colombo-brasileñas, desde la perspectiva de algunos presupuestos del realismo neoclásico (predominantemente) y del neoliberalismo institucional (subsidiariamente). En segundo lugar, se examinan las fuentes y alcances de la presunta caída de la hegemonía norteamericana y el ascenso gradual de la hegemonía brasileña en Suramérica. En tercer lugar, se analiza la calidad de Colombia como potencia secundaria, luego la diversificación geográfica y temática de su política exterior a partir de agosto de 2010, y sus estrategias de competencia y cooperación con respecto a Brasil en la región. Finalmente, se identifican y se interpretan las perspectivas bilaterales y multilaterales de la profundización de los intercambios y compromisos entre Colombia y Brasil, que tendrían un alto potencial para institucionalizar una alianza estratégica multitemática con repercusiones importantes para impulsar y afianzar el proceso de regionalización en Suramérica. Abstract in english This article interprets the challenges of Colombia's foreign policy, both on a regional and global level, with regard to Brazil's ambitions as a regional power and global player. First, a theoretical analysis of the current regional scenario and the horizon of the Colombian-Brazilian relations is do [...] ne, mainly from various neoclassical realist positions and also from institutional neoliberal viewpoints. Second, sources and impact of the proclaimed decay of the North American hegemony and the gradual rise of a Brasilian hegemony in South America are examined. Third, Colombia's capacity as a secondary power is analized, followed by an analysis of the geographic and thematic diversification of its foreign policy since August 2010, as well as its strategy of competition and cooperation with Brazil in the region. Finally, those bilateral and multilateral perspectives of profundization of the exchanges and committments between Brazil and Colombia are identified and interpreted, which would have a high potential to be institutionalized as a strategic multithematic alliance with an important impact to promote and strengthen the regionalization process in South America.

Eduardo, Pastrana Buelvas; Diego, Vera Piñeros.

2013-12-01

278

Política e acção pública: Entre uma regulação centralizada e uma regulação multipolar / Politique et action publique.: D’une régulation centrale à une régulation multipolaire / Policy and public action.: From central regulation to multipolar regulation  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: Portuguese Abstract in portuguese Este texto situa-se no campo alargado da análise política e tem o propósito de contribuir para a compreensão do processo de construção e regulação das políticas públicas, dando conta da complexidade do processo que vai muito para além do momento da decisão, implicando diferentes instâncias e uma gra [...] nde multiplicidade de actores. Constitui uma reflexão, construída a partir das análises, interrogações, comentários e críticas produzidas por diferentes autores, a partir de diferentes prismas, que incidiram sobre a política educativa portuguesa das últimas décadas, no que diz respeito à autonomia das escolas e aos efeitos observados na aplicação das medidas que a invocaram, particularmente no que se refere aos projectos, aqui considerados como instrumentos para resolver problemas e criar oportunidades na fronteira entre o social e o político. Representa ainda a oportunidade de mostrar a importância do tempo na construção e análise das políticas públicas. Abstract in english This text provides an overview of the broadened field of the policy analysis with the aim of contributing for the understanding of the process of construction and regulation of public policies. It gives account of the complexity of the process that goes beyond the moment of decision, implying differ [...] ent spaces and a great multiplicity of actors. Our reflection derives from the critical analyses, interrogations and commentaries on the Portuguese educational policy, made by different authors, and from different prisms, in the last decades, on the autonomy of the schools, and the effects observed in the implementation of the measures invoked by that autonomy. Particularly, we will consider projects, considered here as tools to solve problems and create opportunities on the borders between the social and the political. It also represents an opportunity to show the importance of the space and temporal dimension for the construction and analysis of the public policies.

Maria Madalena, Fontoura.

279

Maternal inheritance of mitochondria: multipolarity, multiallelism and hierarchical transmission of mitochondrial DNA in the true slime mold Physarum polycephalum.  

Science.gov (United States)

Direct evidence of digestion of paternal mitochondrial DNA (mtDNA) has been found in the true slime mold Physarum polycephalum. This is the first report on the selective digestion of mtDNA inside the zygote, and is striking evidence for the mechanism of maternal inheritance of mitochondria. Moreover, two mitochondrial nuclease activities were detected in this organism as-candidates for the nucleases responsible for selective digestion of mtDNA. In the true slime mold, there is an additional-feature of the uniparental inheritance of mitochondria.Although mitochondria are believed to be inherited from the maternal lineage in nearly all eukaryotes, the mating types of the true slime mold P. polycephalum is not restricted to two: there are three mating loci--matA, matB,and matC--and these loci have 16, 15, and 3 alleles,-respectively. Interestingly, the transmission patterns of mtDNA are determined by the matA locus, in a hierarchical-fashion (matA hierarchy) as follows: matA7[matA2[matA11[matA12[matA15/matA16[matA1[matA6.The strain possessing the higher status of matA would be the mtDNA donor in crosses. Furthermore, we have found that some crosses showed biparental inheritance of mitochondria.This review describes the phenomenon of hierarchical transmission of mtDNA in true slime molds, and discusses the presumed molecular mechanism of maternal and biparental inheritance. PMID:20082112

Moriyama, Yohsuke; Kawano, Shigeyuki

2010-03-01

280

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

 
 
 
 
281

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

2007-02-01

282

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

283

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.)

284

Fair Model  

Science.gov (United States)

The Fair model web site includes a freely available United States macroeconomic econometric model and a multicounty econometric model. The models run on the Windows OS. Instructors can use the models to teach forecasting, run policy experiments, and evaluate historical episodes of macroeconomic behavior. The web site includes extensive documentation for both models. The simulation is for upper-division economics courses in macroeconomics or econometrics. The principle developer is Ray Fair at Yale University.

Blecha, Betty

285

Design of mini-orange spectrometers and their application to nuclear structure studies  

International Nuclear Information System (INIS)

The design and properties of a mini-orange spectrometer for internal conversion experiments are described. The application of such a system to the study of the decay of Coulomb excited /sup 191,193/Ir nuclei is presented. Some E2/M1 mixing ratios of the transitions with mixed multipolarities are deduced. The experimental energy levels and reduced matrix elements of the excited /sup 191,193/Ir are compared with two model calculations, namely the particle-plus-triaxial rotor model and the interacting boson fermion model. A mini-orange spectrometer was also used to study the multipolarities of the decay of high spin continuum states in 130Ce

286

Energy modeling  

Energy Technology Data Exchange (ETDEWEB)

The Energy Modeling and Forecasting Group at the Centre for Advanced Computing and Decision Support (CACDS) has contributed to the development of energy forecasting models for South Africa. Most energy models exist to attain a specific objective. At the CACDS two energy forecasting models are used. The first of these is an energy demand model, the ENVRAAG model, which is based on the US model COAL2. The COAL2 model was modified to incorporate the characteristics of the South African energy-economic demand system. The Group is now working on the second model, namely an energy supply model named SAMARKAL, which is based on the internationally used MARKAL supply model. The objective is to transform this model to simulate the South African energy supply for the future. Eventually, these two energy models will be inter-connected in a way that will enable the supply of energy to be brought into balance with the demand for energy in South Africa. Both models are briefly described.

van Niekerk, G.D.

1988-04-01

287

Supermatrix models  

International Nuclear Information System (INIS)

Radom matrix models based on an integral over supermatrices are proposed as a natural extension of bosonic matrix models. The subtle nature of superspace integration allows these models to have very different properties from the analogous bosonic models. Two choices of integration slice are investigated. One leads to a perturbative structure which is reminiscent of, and perhaps identical to, the usual Hermitian matrix models. Another leads to an eigenvalue reduction which can be described by a two component plasma in one dimension. A stationary point of the model is described

288

Differential Model  

Directory of Open Access Journals (Sweden)

Full Text Available In order to push table tennis into more cutting-edge area, we need to conduct sound research and simulation for the flying condition of table tennis in the air. This study analyzes the force characteristic of objects moving in the air and establishes differential equation model of three force conditions for the characteristics of table tennis, namely the flight model of table tennis only by gravity, the flight model of table tennis only by gravity and air resistance, as well as the flight model of table tennis only by gravity and air resistance and Magnus force. The research results: For the table tennis flight condition of the first model and the third model it conducts Matlab trajectory situation and achieves good simulation results. The model and simulation methods established in this study provide a theoretical basis for the flight conditions of table tennis in the air and provide a model-based simulation for the movement.

Ping Du

2013-01-01

289

Geochemical modeling  

International Nuclear Information System (INIS)

Contributions to the workshop 'Geochemical modeling' from 19 to 20 September 1990 at the Karlsruhe Nuclear Research Centre. The report contains the programme and a selection of the lectures held at the workshop 'Geochemical modeling'. (BBR)

290

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

291

SIR Model  

Science.gov (United States)

This worksheet implements an SIR (Susceptible/ Infected/ Resistant) model of epidemiology for vector-borne diseases. Up to three microbial strains with different virulence and transmission parameters can be modeled and the results graphed. Originally designed to explore coevolution of myxoma and rabbits, the model is easily generalized to other systems.

Tony Weisstein (Truman State University;Biology)

2007-06-20

292

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

2013-08-01

293

Actor Model  

CERN Document Server

The Actor model is a mathematical theory that treats "Actors" as the universal primitives of concurrent digital computation. The model has been used both as a framework for a theoretical understanding of concurrency, and as the theoretical basis for several practical implementations of concurrent systems. Unlike previous models of computation, the Actor model was inspired by physical laws. It was also influenced by the programming languages Lisp, Simula 67 and Smalltalk-72, as well as ideas for Petri Nets, capability-based systems and packet switching. The advent of massive concurrency through client-cloud computing and many-core computer architectures has galvanized interest in the Actor model.

Hewitt, Carl

2010-01-01

294

ICRF modelling  

International Nuclear Information System (INIS)

This lecture provides a survey of the methods used to model fast magnetosonic wave coupling, propagation, and absorption in tokamaks. The validity and limitations of three distinct types of modelling codes, which will be contrasted, include discrete models which utilize ray tracing techniques, approximate continuous field models based on a parabolic approximation of the wave equation, and full field models derived using finite difference techniques. Inclusion of mode conversion effects in these models and modification of the minority distribution function will also be discussed. The lecture will conclude with a presentation of time-dependent global transport simulations of ICRF-heated tokamak discharges obtained in conjunction with the ICRF modelling codes. 52 refs., 15 figs

295

ICRF modelling  

Energy Technology Data Exchange (ETDEWEB)

This lecture provides a survey of the methods used to model fast magnetosonic wave coupling, propagation, and absorption in tokamaks. The validity and limitations of three distinct types of modelling codes, which will be contrasted, include discrete models which utilize ray tracing techniques, approximate continuous field models based on a parabolic approximation of the wave equation, and full field models derived using finite difference techniques. Inclusion of mode conversion effects in these models and modification of the minority distribution function will also be discussed. The lecture will conclude with a presentation of time-dependent global transport simulations of ICRF-heated tokamak discharges obtained in conjunction with the ICRF modelling codes. 52 refs., 15 figs.

Phillips, C.K.

1985-12-01

296

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

297

Ventilation Model  

International Nuclear Information System (INIS)

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)

298

FINANCIAL MODELS  

Directory of Open Access Journals (Sweden)

Full Text Available The idea of using models is not a new one, but it is an idea that kept the interest of many researchers in different fields of activity for a very long time now. The present paper looks at models starting from the very general forms (divided according to the way they are expressed or to the kind of research they support to the ones that are specific for the financial field. Financial models are useful as they give managers and other categories of users the possibility to innovate, manage and plan the financial information. The paper provides a theoretical approach to financial models and their importance in the management of different companies. Financial models are very technical instruments that have to be exact enough in order to provide the users with accurate results regarding the financial state of the company. They give users the possibility to examine both past and future events and the quality of the financial decisions highly depends on them. Models that are not based on reality lead to wrong decisions that are incorrect and have adverse effects. Models generate the decision support information. The financial models are based on the normal, natural succession of processing information regarding the transactions and their effects. Such models offer the possibility to imagine what would happen in case of different decisions without having to expose the company to the associated risks of those decisions. Of course that models also have certain shortcomings and they have to be revised all the time. The model used generates results that need to be analyzed, explained and applied. The financial models are applied in order to facilitate the financial decision and the choice of one model over another highly depends on the results the manager expects to obtain and on the degree of exactitude expected.

Cristea Horia

2014-07-01

299

Gimbal Model  

Science.gov (United States)

The Gimbal Model illustrates the pitch, roll and yaw of a 3D object. Independent axis mode allows each axes to be rotated without affecting the others axes. If this mode is not selected, the model can be used to explore the phenomena of gimbal lock. This model tests the Java 3D implementation of the EJS 3D library. If the Java 3D option is selected, a airplane VMRL file (wrl) is rendered inside the gimbals. A warning message will appear if the Java 3D library is not available. The Gimbal Model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ntnu_Gimbal.jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Hwang, Fu-Kwun; Wee, Loo K.

2011-12-30

300

Modelling sustainability  

Energy Technology Data Exchange (ETDEWEB)

This article examines the concept that the actual process of production is one of entropy reduction, and that physical capital stock such as equipment, personnel, and fuel are all essential inputs to produce a service or goods. The natural capital accounting (NCA) procedure of modelling the economy in terms of energy, the quantification of sustainability, and the ECCO model (Evolution of Capital Creation Options) which is an operational version of NCA are described. A diagram of the core loops in an ECCO model is provided, and sources of data for ECCO, the incorporation of energy policies into the model, the simulation of the economy, and output variables are discussed. (UK)

Slesser, Malcolm

1999-12-09

 
 
 
 
301

Ventilation Model  

Energy Technology Data Exchange (ETDEWEB)

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).

V. Chipman

2002-10-05

302

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

303

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

304

BF Models  

International Nuclear Information System (INIS)

The problem of investigating consistent interactions that can be added to a set of scalar fields, two collections of one-forms and a system of two-forms, described in the free limit by a sum of abelian BF models, is reported. The couplings of this class of BF models to matter fields and vector fields are also discussed. (author)

305

VENTILATION MODEL  

International Nuclear Information System (INIS)

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 postclosure analyses

306

OSPREY Model  

Energy Technology Data Exchange (ETDEWEB)

The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and REcoverY (OSPREY) models the adsorption of off-gas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data is obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data and parameters were input into the adsorption model to develop models specific for krypton adsorption. The same can be done for iodine, xenon, and tritium. The model will be validated with experimental breakthrough curves. Customers will be given access to OSPREY to used and evaluate the model.

Veronica J. Rutledge

2013-01-01

307

Stereometric Modelling  

Science.gov (United States)

These mandatory guidelines are provided for preparation of papers accepted for publication in the series of Volumes of The The stereometric modelling means modelling achieved with : - the use of a pair of virtual cameras, with parallel axes and positioned at a mutual distance average of 1/10 of the distance camera-object (in practice the realization and use of a stereometric camera in the modeling program); - the shot visualization in two distinct windows - the stereoscopic viewing of the shot while modelling. Since the definition of "3D vision" is inaccurately referred to as the simple perspective of an object, it is required to add the word stereo so that "3D stereo vision " shall stand for "three-dimensional view" and ,therefore, measure the width, height and depth of the surveyed image. Thanks to the development of a stereo metric model , either real or virtual, through the "materialization", either real or virtual, of the optical-stereo metric model made visible with a stereoscope. It is feasible a continuous on line updating of the cultural heritage with the help of photogrammetry and stereometric modelling. The catalogue of the Architectonic Photogrammetry Laboratory of Politecnico di Bari is available on line at: target="_blank">http://rappresentazione.stereofot.it:591/StereoFot/FMPro?-db=StereoFot.fp5&-lay=Scheda&-format=cerca.htm&-view

Grimaldi, P.

2012-07-01

308

Modeling Arcs  

CERN Document Server

Although vacuum arcs were first identified over 110 years ago, they are not yet well understood. We have since developed a model of breakdown and gradient limits that tries to explain, in a self-consistent way: arc triggering, plasma initiation, plasma evolution, surface damage and gra- dient limits. We use simple PIC codes for modeling plasmas, molecular dynamics for modeling surface breakdown, and surface damage, and mesoscale surface thermodynamics and finite element electrostatic codes for to evaluate surface properties. Since any given experiment seems to have more variables than data points, we have tried to consider a wide variety of arcing (rf structures, e beam welding, laser ablation, etc.) to help constrain the problem, and concentrate on common mechanisms. While the mechanisms can be comparatively simple, modeling can be challenging.

Insepov, Zeke; Veitzer, Seth; Mahalingam, Sudhakar

2011-01-01

309

Linear Models  

CERN Document Server

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

310

Geochemical modeling  

International Nuclear Information System (INIS)

This paper discusses the need for prediction over time periods of up to 100,000 years of factors involved in nuclear waste disposal. Experimental programs are presented. Geochemical modeling codes are addressed

311

Energy Models  

Science.gov (United States)

Energy models characterize the energy system, its evolution, and its interactions with the broader economy. The energy system consists of primary resources, including both fossil fuels and renewables; power plants, refineries, and other technologies to process and convert these r...

312

Programming models  

Energy Technology Data Exchange (ETDEWEB)

A programming model is a set of software technologies that support the expression of algorithms and provide applications with an abstract representation of the capabilities of the underlying hardware architecture. The primary goals are productivity, portability and performance.

Daniel, David J [Los Alamos National Laboratory; Mc Pherson, Allen [Los Alamos National Laboratory; Thorp, John R [Los Alamos National Laboratory; Barrett, Richard [SNL; Clay, Robert [SNL; De Supinski, Bronis [LLNL; Dube, Evi [LLNL; Heroux, Mike [SNL; Janssen, Curtis [SNL; Langer, Steve [LLNL; Laros, Jim [SNL

2011-01-14

313

Modelling Constructs  

DEFF Research Database (Denmark)

There are many different notations and formalisms for modelling business processes and workflows. These notations and formalisms have been introduced with different purposes and objectives. Later, influenced by other notations, comparisons with other tools, or by standardization efforts, these notations have been extended in order to increase expressiveness and to be more competitive. This resulted in an increasing number of notations and formalisms for modelling business processes and in an increase of the different modelling constructs provided by modelling notations, which makes it difficult to compare modelling notations and to make transformations between them. One of the reasons is that, in each notation, the new concepts are introduced in a different way by extending the already existing constructs. In this chapter, we go the opposite direction: We show that it is possible to add most of the typical extensions on top of any existing notation or formalism—without changing the formalism itself. Basically, we introduce blocks with some additional attributes defining their initiation and termination behaviour. This serves two purposes: First, it gives a clearer understanding of the basic constructs and how they can be combined with more advanced constructs. Second, it will help combining different modelling notations with each other. Note that, though we introduce a notation for blocks in this chapter, we are not so much interested in promoting this notation here. The notation should just prove that it is possible to separate different issues of a modelling notation, and this way making its concepts clearer and the interchange of models easier. A fully-fledged block notation with a clear and simple interface to existing formalisms is yet to be developed.

Kindler, Ekkart

2009-01-01

314

Modelling Entrepreneurship  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two approaches can be distinguished with respect to modelling entrepreneurship: (i) the approach focusing on the net development of the number of entrepreneurs in an equilibrium framework and (ii) the approach focusing on the entries and exits of entrepreneurs. In this paper we unify these ap- proaches to arrive at a model explaining the equilibrium and actual number of entrepreneurs and the entry and exit rate of entrepreneurs simultaneously and consistently. We apply our unified approach to...

Bosma, N.; Wit, G.; Carree, M. A.

2003-01-01

315

Experimental and database-transferred electron-density analysis and evaluation of electrostatic forces in coumarin-102 dye.  

Science.gov (United States)

The electron-density distribution of a new crystal form of coumarin-102, a laser dye, has been investigated using the Hansen-Coppens multipolar atom model. The charge density was refined versus high-resolution X-ray diffraction data collected at 100?K and was also constructed by transferring the charge density from the Experimental Library of Multipolar Atom Model (ELMAM2). The topology of the refined charge density has been analysed within the Bader `Atoms In Molecules' theory framework. Deformation electron-density peak heights and topological features indicate that the chromen-2-one ring system has a delocalized ?-electron cloud in resonance with the N (amino) atom. The molecular electrostatic potential was estimated from both experimental and transferred multipolar models; it reveals an asymmetric character of the charge distribution across the molecule. This polarization effect is due to a substantial charge delocalization within the molecule. The molecular dipole moments derived from the experimental and transferred multipolar models are also compared with the liquid and gas-phase dipole moments. The substantial molecular dipole moment enhancements observed in the crystal environment originate from the crystal field and from intermolecular charge transfer induced and controlled by C-H···O and C-H···N intermolecular hydrogen bonds. The atomic forces were integrated over the atomic basins and compared for the two electron-density models. PMID:23165601

Bibila Mayaya Bisseyou, Yvon; Bouhmaida, Nouhza; Guillot, Benoit; Lecomte, Claude; Lugan, Noel; Ghermani, Noureddine; Jelsch, Christian

2012-12-01

316

The impact of the new Earth gravity models from CHAMP and GRACE on the detection of the Lense-Thirring effect with existing or proposed laser-ranged satellites  

Science.gov (United States)

One of the most important source of systematic errors in the performed or proposed attempts to measure the gravitomagnetic Lense-Thirring effect in the gravitational field of Earth by analyzing the time series of the nodes and the perigees of the orbits of currently existing, or proposed, laser-ranged satellites is represented by the mismodelling in the low degree even zonal harmonic coefficients of the multipolar expansion of the terrestrial gravitational field. Several observables have been used or proposed in order to suitably cancel or, at least, reduce the impact of such aliasing effects (linear combinations of many orbital elements, sum of the nodes and difference of the perigees of satellites in supplementary orbits). In this talk first we analyze in detail the role played by the various even zonal harmonics on the different observables adopted or proposed. Then, we investigate the impact of the new Earth gravity models from CHAMP and, especially, GRACE missions on such attempts. It turns out that the notable improvements in the determination of the mid-high degree even zonal harmonics might allow to use also the orbital data of the nodes of the other existing geodetic laser-tracked satellites in addition to LAGEOS and LAGEOS II. A LAGEOS-LAGEOS II node-only combination is also examined. The present-day accuracy with the recently released GGM01C Erath gravity model, which includes also the first data from GRACE, is of the order of 15% or better. Further improvements might yield the systematic error due to geopotential to a some percent level if the currently existing satellites are used. The use of a three-nodes combination with the data of the existing LAGEOS, LAGEOS II and of the proposed LARES (or OPTIS in a LAGEOS-like orbital configuration) would reduce such error to 0.06%. Another favorable consequence of the increasing accuracy in our knowledge of the Earth gravity field is that the impact of the orbital injection errors in the inclination of LARES/OPTIS is greately reduced. This could allow to reduce the costs of a possible launch by using a rocket of not too high quality.

Iorio, L.

317

Mechanistic models  

Energy Technology Data Exchange (ETDEWEB)

Several models and theories are reviewed that incorporate the idea of radiation-induced lesions (repairable and/or irreparable) that can be related to molecular lesions in the DNA molecule. Usually the DNA double-strand or chromatin break is suggested as the critical lesion. In the models, the shoulder on the low-LET survival curve is hypothesized as being due to one (or more) of the following three mechanisms: (1) ``interaction`` of lesions produced by statistically independent particle tracks; (2) nonlinear (i.e., linear-quadratic) increase in the yield of initial lesions, and (3) saturation of repair processes at high dose. Comparisons are made between the various approaches. Several significant advances in model development are discussed; in particular, a description of the matrix formulation of the Markov versions of the RMR and LPL models is given. The more advanced theories have incorporated statistical fluctuations in various aspects of the energy-loss and lesion-formation process. An important direction is the inclusion of physical and chemical processes into the formulations by incorporating relevant track structure theory (Monte Carlo track simulations) and chemical reactions of radiation-induced radicals. At the biological end, identification of repair genes and how they operate as well as a better understanding of how DNA misjoinings lead to lethal chromosome aberrations are needed for appropriate inclusion into the theories. More effort is necessary to model the complex end point of radiation-induced carcinogenesis.

Curtis, S.B.

1990-09-01

318

Mechanistic models  

Energy Technology Data Exchange (ETDEWEB)

Several models and theories are reviewed that incorporate the idea of radiation-induced lesions (repairable and/or irreparable) that can be related to molecular lesions in the DNA molecule. Usually the DNA double-strand or chromatin break is suggested as the critical lesion. In the models, the shoulder on the low-LET survival curve is hypothesized as being due to one (or more) of the following three mechanisms: (1) interaction'' of lesions produced by statistically independent particle tracks; (2) nonlinear (i.e., linear-quadratic) increase in the yield of initial lesions, and (3) saturation of repair processes at high dose. Comparisons are made between the various approaches. Several significant advances in model development are discussed; in particular, a description of the matrix formulation of the Markov versions of the RMR and LPL models is given. The more advanced theories have incorporated statistical fluctuations in various aspects of the energy-loss and lesion-formation process. An important direction is the inclusion of physical and chemical processes into the formulations by incorporating relevant track structure theory (Monte Carlo track simulations) and chemical reactions of radiation-induced radicals. At the biological end, identification of repair genes and how they operate as well as a better understanding of how DNA misjoinings lead to lethal chromosome aberrations are needed for appropriate inclusion into the theories. More effort is necessary to model the complex end point of radiation-induced carcinogenesis.

Curtis, S.B.

1990-09-01

319

Beats Model  

Science.gov (United States)

The Ejs Beats model displays the result of adding two waves with different frequencies. The simulation displays the superposition of the two waves as well as a phasor diagram that shows how the waves add up at one point in space. The ratio of the wave amplitudes, the ratio of the frequencies, and the phase shift between the two waves can be changed via textboxes. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. Ejs Beats model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ehu_oscillations_beats.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Aguirregabiria, Juan

2008-10-13

320

Damping rates of surface plasmons for particles of size from nano- to micrometers; reduction of the nonradiative decay  

International Nuclear Information System (INIS)

Damping rates of multipolar, localized surface plasmons (SPs) of gold and silver nanospheres of radii up to 1000 nm were found with the tools of classical electrodynamics. The significant increase in damping rates followed by noteworthy decrease for larger particles takes place along with substantial red-shift of plasmon resonance frequencies as a function of particle size. We also introduced interface damping into our modeling, which substantially modifies the plasmon damping rates of smaller particles. We demonstrate unexpected reduction of the multipolar SP damping rates in certain size ranges. This effect can be explained by the suppression of the nonradiative decay channel as a result of the lost competition with the radiative channel. We show that experimental dipole damping rates [H. Baida, et al., Nano Lett. 9(10) (2009) 3463, and C. Sönnichsen, et al., Phys. Rev. Lett. 88 (2002) 077402], and the resulting resonance quality factors can be described in a consistent and straightforward way within our modeling extended to particle sizes still unavailable experimentally. -- Highlights: ? We model plasmon damping rates up to the uncommonly large particles of 1000 nm. ? We demonstrate reduction of multipolar SP damping rates below its low size limit. ? We show that the radiative decay competes with the nonradiative processes. ? We model the quality Q-factor of SP multipolar resonances as a function of size. ? We confront our size characteristics with the experimental results of other authors.

 
 
 
 
321

Transition probabilities between first excited state and ground state in the N=81 nuclei 139Ce, 141Nd, 143Sm and 145Gd  

International Nuclear Information System (INIS)

The half-life of the 108 keV level in 143Sm (Tsub(1/2) = 800 +- 50 ps) has been measured by delayed e- - ? coincidences and the multipolarity of the deexciting transition has been determined (E2/M1 139Ce, 141Nd and 145Gd from the literature. This systematics is interpreted in terms of intermediate coupling model calculations

322

Subcomponent models  

International Nuclear Information System (INIS)

According to the instruction given by Professor Lanius and Professor Uhlman, the Conference Chairmen, and by Professor Ranft and Professor Nowak, the Chairmen of the Program Committee, I have organized the Session B04 ''Subcomponent Models'' in the following way: First, I have tried to review recent theoretical works on composite models of quarks and leptons, including twenty-six contributed papers allocated to this session, with the title of ''Composite Models''. Next, I have asked Professor Yamada from University of Tokyo to review recent experimental works related to this subject, including three contributed papers allocated to this session, with the title of ''Experimental Search for Compositeness''. After that, I have invited Professor Mohapatra from University of Maryland and Professor Nielsen from Niels Bohr Institute to give talks on their own recent works contributed to this session, with the titles of ''Fermion Generations and Compositeness'' and ''Field Theories without Fundamental (Gauge) Symmetry'', respectively. (author)

323

Molecular modeling  

Directory of Open Access Journals (Sweden)

Full Text Available The use of computational chemistry in the development of novel pharmaceuticals is becoming an increasingly important tool. In the past, drugs were simply screened for effectiveness. The recent advances in computing power and the exponential growth of the knowledge of protein structures have made it possible for organic compounds to be tailored to decrease the harmful side effects and increase the potency. This article provides a detailed description of the techniques employed in molecular modeling. Molecular modeling is a rapidly developing discipline, and has been supported by the dramatic improvements in computer hardware and software in recent years.

Sharma Aarti

2009-01-01

324

Supernova models  

International Nuclear Information System (INIS)

Recent progress in understanding the observed properties of Type I supernovae as a consequence of the thermonuclear detonation of white dwarf stars and the ensuing decay of the 56Ni produced therein is reviewed. Within the context of this model for Type I explosions and the 1978 model for Type II explosions, the expected nucleosynthesis and gamma-line spectra from both kinds of supernovae are presented. Finally, a qualitatively new approach to the problem of massive star death and Type II supernovae based upon a combination of rotation and thermonuclear burning is discussed

325

Why Model?  

Directory of Open Access Journals (Sweden)

Full Text Available Next generation sequencing technologies are bringing about a renaissance of mining approaches. A comprehensive picture of the genetic landscape of an individual patient will be useful, for example, to identify groups of patients that do or do not respond to certain therapies. The high expectations may however not be satisfied if the number of patient groups with similar characteristics is going to be very large. I therefore doubt that mining sequence data will give us an understanding of why and when therapies work. For understanding the mechanisms underlying diseases, an alternative approach is to model small networks in quantitative mechanistic detail, to elucidate the role of gene and proteins in dynamically changing the functioning of cells. Here an obvious critique is that these models consider too few components, compared to what might be relevant for any particular cell function. I show here that mining approaches and dynamical systems theory are two ends of a spectrum of methodologies to choose from. Drawing upon personal experience in numerous interdisciplinary collaborations, I provide guidance on how to model by discussing the question "Why model?"

OlafWolkenhauer

2014-01-01

326

Cosmological models  

Science.gov (United States)

An LRS Bianchi type II cosmological model is built with a state equation that is a function of the cosmic time t. The ratio p/? is 1/3 when t? 0 and is insignificant when t??. Thus, the matter content behaves like radiation for small t and like dust for large t.

Hajj-Boutros, J.

1989-04-01

327

Cosmological models  

Energy Technology Data Exchange (ETDEWEB)

An LRS Bianchi type II cosmological model is built with a state equation that is a function of the cosmic time t. The ratio p/{mu} is 1/3 when t {yields} 0 and is insignificant when t {yields} {infinity}. Thus, the matter content behaves like radiation for small t and like dust for large t.

Hajj-Boutros, J. (Lebanese Univ., Mansourieh-El-Maten (Lebanon))

1989-04-01

328

Cosmological models  

International Nuclear Information System (INIS)

An LRS Bianchi type II cosmological model is built with a state equation that is a function of the cosmic time t. The ratio p/? is 1/3 when t ? 0 and is insignificant when t ? ?. Thus, the matter content behaves like radiation for small t and like dust for large t

329

Defect modelling  

International Nuclear Information System (INIS)

Calculations, drawing principally on developments at AERE Harwell, of the relaxation about lattice defects are reviewed with emphasis on the techniques required for such calculations. The principles of defect modelling are outlined and various programs developed for defect simulations are discussed. Particular calculations for metals, ionic crystals and oxides, are considered. (UK)

330

Quasimolecular modelling  

CERN Document Server

In this book the author has tried to apply "a little imagination and thinking" to modelling dynamical phenomena from a classical atomic and molecular point of view. Nonlinearity is emphasized, as are phenomena which are elusive from the continuum mechanics point of view. FORTRAN programs are provided in the Appendices.

Greenspan, Donald

1991-01-01

331

Biotran model  

International Nuclear Information System (INIS)

The BIOTRAN model was developed at Los Alamos to help predict short- and long-term consequences to man from releases of radionuclides into the environment. It is a dynamic model that simulates on a daily and yearly basis the flux of biomass, water, and radionuclides through terrestrial and aquatic ecosystems. Biomass, water, and radionuclides are driven within the ecosystems by climate variables stochastically generated by BIOTRAN each simulation day. The climate variables influence soil hydraulics, plant growth, evapotranspiration, and particle suspension and deposition. BIOTRAN has 22 different plant growth strategies for simulating various grasses, shrubs, trees, and crops. Ruminants and humans are also dynamically simulated by using the simulated crops and forage as intake for user-specified diets. BIOTRAN has been used at Los Alamos for long-term prediction of health effects to populations following potential accidental releases of uranium and plutonium. Newly developed subroutines are described: a human dynamic physiological and metabolic model; a soil hydrology and irrigation model; limnetic nutrient and radionuclide cycling in fresh-water lakes. 7 references

332

BF models  

International Nuclear Information System (INIS)

The problem of investigating consistent interactions that can be added to a set of scalar fields, two collections of one-forms and a system of two-forms, described in the free limit by a sum of abelian BF models, is reviewed. (authors)

333

Criticality Model  

International Nuclear Information System (INIS)

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)

334

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

335

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

336

Lens Model  

DEFF Research Database (Denmark)

Firms consist of people who make decisions to achieve goals. How do these people develop the expectations which underpin the choices they make? The lens model provides one answer to this question. It was developed by cognitive psychologist Egon Brunswik (1952) to illustrate his theory of probabilistic functionalism, and concerns the environment and the mind, and adaptation by the latter to the former. This entry is about the lens model, and probabilistic functionalism more broadly. Focus will mostly be on firms and their employees, but, to fully appreciate the scope, we have to keep in mind the fact that probabilistic functionalism extends to all purposive organisms. Probabilistic functionalism is currently experiencing growing interest among strategy scholars, and some very recent papers are highlighted in conclusion.

Nash, Ulrik William

2014-01-01

337

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

338

Gyroscope Model  

Science.gov (United States)

The Gyroscope example computes and displays the dynamics of gyroscope under the influence of a gravitational torque acting on the center of mass. The gyroscope is supported at one end and given an initial angular velocity component about its axis of symmetry and a component perpendicular to its axis of symmetry. The numerical solution shows the motion for all initial conditions including zero initial angular momentum. The model is designed to show the cycloidal motion (precession and nutation) of the gyroscope axle when the initial angular velocity is large. Users can very the position and radius of the spinning mass as well as the initial angle and can display the angular momentum, angular velocity, and torque vectors. A second window shows the elevation angle of the axle and the angular momentum vector.   Units are chosen such that the total mass M and the acceleration of gravity g are one. The rotor is an ellipsoid with a uniform mass distribution and with major axes 2*R and minor axis R/5. The ellipsoid's moment of inertia through the center of mass is 4MR2/5 about the major axes and 26MR2/125 about the minor axis. The Gyroscope model is a supplemental simulation for the article "It Has to Go Down a Little, in Order to Go Around" by Svilen Kostov and Daniel Hammer in The Physics Teacher 49(4), 216-219 (2011) and has been approved by the authors and The Physics Teacher editor. The model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_csm_ch17_Gyroscope.jar file will run the program if Java is installed.

Christian, Wolfgang

2011-02-10

339

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

340

DTN Modeling in OPNET Modeler  

Directory of Open Access Journals (Sweden)

Full Text Available Traditional wireless networks use the concept of the point-to-point forwarding inherited from reliable wired networks which seems to be not ideal for wireless environment. New emerging applications and networks operate mostly disconnected. So-called Delay-Tolerant networks (DTNs are receiving increasing attentions from both academia and industry. DTNs introduced a store-carry-and-forward concept solving the problem of intermittent connectivity. Behavior of such networks is verified by real models, computer simulation or combination of the both approaches. Computer simulation has become the primary and cost effective tool for evaluating the performance of the DTNs. OPNET modeler is our target simulation tool and we wanted to spread OPNET’s simulation opportunity towards DTN. We implemented bundle protocol to OPNET modeler allowing simulate cases based on bundle concept as epidemic forwarding which relies on flooding the network with messages and the forwarding algorithm based on the history of past encounters (PRoPHET. The implementation details will be provided in article.

PAPAJ Jan

2014-05-01

 
 
 
 
341

Multipolarity of statistical #betta#-rays from f-p shell nuclei produced in deep-inelastic heavy-ion reactions  

International Nuclear Information System (INIS)

Measurements of the circular polarization and the angular correlation of #betta#-rays from highly excited polarized nuclei, produced in 16O+58Ni deep-inelastic reactions, indicate a strong quadrupole component in the spectra of statistical #betta#-decay at Esub(#betta#)>2 MeV. Differences in the anisotropies observed for the 16O+58Ni and the 16O+48Ti reactions are attributed to the influence of nuclear structure. (orig.)

342

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

343

Modeling materials with phase field crystal models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The phase field crystal (PFC) model is a novel approach for modeling phenomena on atomistic length and diffusive time scales. In this dissertation, we present new advances in the methodology of the PFC model and describe applications to solidification and grain boundaries. We present an extended phase diagram for the original formulation of the PFC model that allows to model three dimensional hexagonal and cubic close-packed crystal structures. The original PFC model is also applied to study ...

Jaatinen, Akusti

2010-01-01

344

Model Awal Dan Model Klasik Struktur Informasi  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper describes early models of information structure and classical models of information structure. Early models of information structure consist of (1) subject- predicate structure, (2) the early psychological model, (3) the communicative model, and (4) linguistics, psychology, and information structure. Classical models is begun from the Prague school, Halliday and the American structuralists, Chafe on givenness, and Chomsky on focus and presupposition. The most characteristic feat...

Widayati, Dwi

2010-01-01

345

Skylab Model  

Science.gov (United States)

This photograph is of a model of the Skylab with the Command/Service Module being docked. In an early effort to extend the use of Apollo for further applications, NASA established the Apollo Applications Program (AAP) in August of 1965. The AAP was to include long duration Earth orbital missions during which astronauts would carry out scientific, technological, and engineering experiments in space by utilizing modified Saturn launch vehicles and the Apollo spacecraft. Established in 1970, the Skylab Program was the forerurner of the AAP. The goals of the Skylab were to enrich our scientific knowledge of the Earth, the Sun, the stars, and cosmic space; to study the effects of weightlessness on living organisms, including man; to study the effects of the processing and manufacturing of materials utilizing the absence of gravity; and to conduct Earth resource observations. The Skylab also conducted 19 selected experiments submitted by high school students. Skylab's 3 different 3-man crews spent up to 84 days in Earth orbit. The Marshall Space Flight Center (MSFC) had responsibility for developing and integrating most of the major components of the Skylab: the Orbital Workshop (OWS), Airlock Module (AM), Multiple Docking Adapter (MDA), Apollo Telescope Mount (ATM), Payload Shroud (PS), and most of the experiments. MSFC was also responsible for providing the Saturn IB launch vehicles for three Apollo spacecraft and crews and a Saturn V launch vehicle for the Skylab.

1967-01-01

346

Modeling sonoluminescence  

International Nuclear Information System (INIS)

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 (<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 radiationclose 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's equations with an additional term that couples the field to the bubble's motion. We show that, in the static case originally considered by Casimir [Proc. K. Ned. Akad. Nel. 51, 783 (1948)], we reproduce Casimir'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 1999 The American Physical Society

347

Modelling Sonoluminescence  

CERN Document Server

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 ($< 50 ps$) 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 "vacuum radiation" generated by the coupling of the electromagnetic fields to the surface of the bubble. In this paper, we simulate vacuum radiation by solving Maxwell's equations with an additional term that couples the field to the bubble's motion. We show that, in the static case originally considered by Casimir, we reproduce Casimir'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.

Chodos, A; Chodos, Alan; Groff, Sarah

1999-01-01

348

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

349

Impedance model for nanostructures  

Directory of Open Access Journals (Sweden)

Full Text Available The application of the impedance model for nanoelectronic quantum-mechanical structures modelling is described. Characteristics illustrating the efficiency of the model are presented.

R. S. Akhmedov

2007-06-01

350

Model Selection Principles in Misspecified Models  

CERN Document Server

Model selection is of fundamental importance to high dimensional modeling featured in many contemporary applications. Classical principles of model selection include the Kullback-Leibler divergence principle and the Bayesian principle, which lead to the Akaike information criterion and Bayesian information criterion when models are correctly specified. Yet model misspecification is unavoidable when we have no knowledge of the true model or when we have the correct family of distributions but miss some true predictor. In this paper, we propose a family of semi-Bayesian principles for model selection in misspecified models, which combine the strengths of the two well-known principles. We derive asymptotic expansions of the semi-Bayesian principles in misspecified generalized linear models, which give the new semi-Bayesian information criteria (SIC). A specific form of SIC admits a natural decomposition into the negative maximum quasi-log-likelihood, a penalty on model dimensionality, and a penalty on model miss...

Lv, Jinchi

2010-01-01

351

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

352

Geologic Framework Model Analysis Model Report  

International Nuclear Information System (INIS)

ed 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

353

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.)

354

Modeling Mercury  

Science.gov (United States)

Mercury has a tenuous exosphere created by the combined effects of solar radiation and micrometeoroid bombardment on the surface and the interaction of the solar wind with Mercury's magnetic field and surface. Observations of this exosphere provide essential data necessary for understanding the composition and evolution of Mercury's surface, as well as the interaction between Mercury's magnetosphere with the solar wind. The sodium component of the exosphere has been well observed from the ground (see review by Killen et al., 2007). These observations have revealed a highly variable and inhomogeneous exosphere with emission often peaking in the polar regions. Radiation acceleration drives exospheric escape producing a sodium tail pointing away from the sun which has been detected up to 1400 Mercury radii from the planet (Potter et al. 2002; Baumgardner et al. 2008). Calcium has also been observed in Mercury's exosphere showing a distribution distinct from sodium, although also variable (Killen et al. 2005). During the first two encounters with Mercury by MESSENGER, observations of the exosphere were made by the UltraViolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). Sodium and calcium emission were detected during both flybys, and magnesium was detected for the first time in Mercury's exosphere during the second flyby. The spatial distributions of these species showed significant, unexpected differences which suggest differences in the mechanisms responsible for releasing them from the surface. We present a Monte-Carlo model of sodium, magnesium, and calcium in Mercury's exosphere. The important source mechanisms for ejecting these species from the surface are sputtering by solar wind ions, photon-stimulated desorption, and micrometeoroid impact vaporization. Thermal desorption on the dayside does not supply enough energy to significantly populate the exosphere, although it does play a role in redistributing volatiles over the surface. In addition, atomic calcium can be produced from the dissociation of Ca-bearing molecules, such as CaO, which can be formed in impact vapors. The primary loss processes are the escape of neutrals ejected with sufficient energy and photoionization. The former process is supplemented by radiation pressure which accelerates neutrals anti-sunward such that escaping neutrals form a tail pointing away from the sun. Because Mercury's heliocentric distance and radial velocity vary during its orbit, both loss processes are functions of Mercury's true anomaly. We also consider the spatial distribution of the surface source. Impact vaporization is roughly isotropic over the surface, although there may be a leading/trailing asymmetry in the impact rate due to Mercury's orbital motion. Sputtering is confined to regions where the solar wind can impact the surface, which is shielded somewhat by the internal magnetic field. The surface regions vulnerable depend on the solar wind conditions. References: Baumgardner et al., GRL, 35, L03201, 2008. Killen, R.M. et al., Space Sci. Rev. 132, 433-509, 2007. Killen, R.M. et al., Icarus, 173, 300-311, 2005. Potter et al., Meteoritics & Planetary Sci., 37, 1165, 2002.

Burger, M. H.; Killen, R. M.; M, N.; Sarantos, M.; Crider, D. H.; Vervak, R. J.

2009-04-01

355

Common Modeling Language for Model Checkers  

Directory of Open Access Journals (Sweden)

Full Text Available Problem statement: There are many different model checkers that have been developed. Each of the model checkers is based on different input languages and they are suitable for model checking different types of systems. Thus it is important for us to choose the right model checker or modeling and verifying a given system. However, moving from one model checker to another is not an easy task since we have to deal with different input languages. Approach: In order to solve the problem we propose a common modeling language that is based on UML state chart. Some translation rules for translating the model described in the common modeling language into the input languages of model checkers are also presented. Results: The result of the case study shows that our approach has been successfully applied in modeling the control system through the process of transformation and translation. Conclusion: Common modeling language can be used as a front end to help users to properly model a system before it is translated into input language of model checkers.

Pathiah A.  Samat

2012-01-01

356

Cognitive models embedded in system simulation models  

International Nuclear Information System (INIS)

If we are to discuss and consider cognitive models, we must first come to grips with two questions: (1) What is cognition; (2) What is a model. Presumably, the answers to these questions can provide a basis for defining a cognitive model. Accordingly, this paper first places these two questions into perspective. Then, cognitive models are set within the context of computer simulation models and a number of computer simulations of cognitive processes are described. Finally, pervasive issues are discussed vis-a-vis cognitive modeling in the computer simulation context

357

Bayesian model comparison of solar radiation models  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we propose a new statistical method: the Bayesian Model Comparison (BMC) method for selecting an adequate hourly diffuse fraction correlation. Six models are investigated and compared according to the BMC method. The selection of the best model is based on a Bayesian criterion called the Deviance Information Criterion (DIC). In this article, we demonstrate the usefulness of the DIC criterion in the model selection process and we issue a caution regarding the selection of a model with standard statistical methods. The aim of this paper is also to introduce the DIC to the solar radiation modeling community. (orig.)

Lauret, Philippe; Riviere, Carine [Lab. de Physique du Batiment et des Systemes, Saint-Denis (France)

2008-07-01

358

Modeling, computation and optimization  

CERN Document Server

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

359

Business Model Innovation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The chapter offers a broad review of the literature at the nexus between Business Models and innovation studies, and examines the notion of Business Model Innovation in three different situations: Business Model Design in newly formed organizations, Business Model Reconfiguration in incumbent firms, and Business Model Innovation in the broad context of sustainability. Tools and perspectives to make sense of Business Models and support managers and entrepreneurs in dealing with Business Model ...

Dodgson, Mark; Gann, David; Phillips, Nelson; Massa, Lorenzo; Tucci, Christopher

2014-01-01

360

Functional connectivity in slow-wave sleep: identification of synchronous cortical activity during wakefulness and sleep using time series analysis of electroencephalographic data.  

Science.gov (United States)

Sleep is a behavioral state ideal for studying functional connectivity because it minimizes many sources of between-subject variability that confound waking analyses. This is particularly important for potential connectivity studies in mental illness where cognitive ability, internal milieu and active psychotic symptoms can vary widely across subjects. We, therefore, sought to adapt techniques applied to magnetoencephalography for use in high-density electroencephalography (EEG), the gold-standard in brain-recording methods during sleep. Autoregressive integrative moving average modeling was used to reduce spurious correlations between recording sites (electrodes) in order to identify functional networks. We hypothesized that identified network characteristics would be similar to those found with magnetoencephalography, and would demonstrate sleep stage-related differences in a control population. We analysed 60-s segments of low-artifact data from seven healthy human subjects during wakefulness and sleep. EEG analysis of eyes-closed wakefulness revealed widespread nearest-neighbor positive synchronous interactions, similar to magnetoencephalography, though less consistent across subjects. Rapid eye movement sleep demonstrated positive synchronous interactions akin to wakefulness but weaker. Slow-wave sleep (SWS), instead, showed strong positive interactions in a large left fronto-temporal-parietal cluster markedly more consistent across subjects. Comparison of connectivity from early SWS to SWS from a later sleep cycle indicated sleep-related reduction in connectivity in this region. The consistency of functional connectivity during SWS within and across subjects suggests this may be a promising technique for comparing functional connectivity between mental illness and health. PMID:21281369

Langheim, Frederick J P; Murphy, Michael; Riedner, Brady A; Tononi, Giulio

2011-12-01

 
 
 
 
361

Orthogonal Meta-Modeling  

Directory of Open Access Journals (Sweden)

Full Text Available This article introduces meta-modeling hierarchies additional to the conventional meta-modeling hierarchy in a model-driven architecture. Additional hierarchies are introduced orthogonal to the conventional meta-modeling hierarchy for an appropriate correlation of information on combined hierarchies. In particular, orthogonal meta-modeling enables the grouping of models on the same conventional meta-modeling layer based on additional semantic dependencies. For the enhancement of conventional meta-modeling this paper discusses the creation of orthogonal meta-modeling hierarchies, the specification of semantic dependencies in meta-modeling hierarchies, semantic instances as well as the inheritance of semantic dependencies in meta-modeling hierarchies in general. Furthermore, the paper outlines the impact of orthogonal semantic meta-modeling on automated model transformation.

Katharina Gorlach

2014-04-01

362

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.

Tahir Abdullah

2012-02-01

363

Modelling of Hydraulic Robot  

DEFF Research Database (Denmark)

This paper describes a case study of identifying the physical model (or the grey box model) of a hydraulic test robot. The obtained model is intended to provide a basis for model-based control of the robot. The physical model is formulated in continuous time and is derived by application of the laws of physics on the system. The unknown (or uncertain) parameters are estimated with Maximum Likelihood (ML) parameter estimation. The identified model has been evaluated by comparing the measurements with simulation of the model. The identified model was much more capable of describing the dynamics of the system than the deterministic model.

Madsen, Henrik; Zhou, Jianjun

1997-01-01

364

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

2006-03-01

365

Armas estratégicas e poder no sistema internacional: o advento das armas de energia direta e seu impacto potencial sobre a guerra e a distribuição multipolar de capacidades / Strategic weapons and power in international system: the arise of direct energy weapons and their potential impact over the war and multipolar distribution of capabilities  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese O pós-Guerra Fria (1991-2006) apresenta uma mudança significativa no cenário estratégico: a maior acessibilidade da tecnologia militar e o surgimento de novas armas capazes de modificar o poder coercitivo dos países - como as armas de energia direta - acabam pondo em xeque a ideia de que a primazia [...] nuclear é condição suficiente para garantir a unipolaridade. Focando-se no atual recrudescimento das tensões entre EUA e Rússia - especialmente com a proposta norte-americana de implementação do Escudo Antimíssil no Leste Europeu - e analisando as relações de poder entre os três países, procuramos revelar que tipo de competição ocorrerá no sistema internacional nas próximas décadas. O presente artigo analisa as reais possibilidades de que a primazia nuclear norte-americana se torne efetiva, uma vez que, para tanto, é necessário o desarmamento estratégico das demais potências. Como uma guerra nuclear entre os três países possui um custo político muito elevado, as disputas tendem a ser decididas na esfera das operações. Para ilustrar esta última afirmação, usamos um cenário contrafactual de guerra nuclear limitada entre Estados Unidos, Rússia e China, por meio do qual tentamos evidenciar as precondições táticas e operacionais para uma eventual vitória da coalizão sino-russa. Abstract in english The evolution of the Post-Cold War (1991-2006) international system shows a significant amount of change regarding the strategic capabilities of United States, Russia, and China. The rise of a new class of strategic weapons called directed energy weapons (lasers and high power microwaves), as well a [...] s the great costs associated with the quest for nuclear primacy, demand closer examination of the current assumption about the links between nuclear primacy and unipolar distribution of power in the International System. Starting with the current tensions between US and Russia, we try to reveal in this article what kind of competition might be observed in the international system over the next decade. The present work analyzes the real possibilities of the USA achieving an effective nuclear primacy condition, which requires the complete disarmament of all other powers. Since a nuclear war between the three countries has a very high political cost, disputes tend to be settled on the operational sphere. In order to demonstrate this final point, we made comparative use of two nuclear war scenarios. The article concludes by establishing the tactical and operational conditions that Russia and China seems to counting with in order to defeat United States if a shooting war comes.

Fabrício Schiavo, Ávila; José Miguel, Martins; Marco, Cepik.

2009-04-01

366

Armas estratégicas e poder no sistema internacional: o advento das armas de energia direta e seu impacto potencial sobre a guerra e a distribuição multipolar de capacidades / Strategic weapons and power in international system: the arise of direct energy weapons and their potential impact over the war and multipolar distribution of capabilities  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese O pós-Guerra Fria (1991-2006) apresenta uma mudança significativa no cenário estratégico: a maior acessibilidade da tecnologia militar e o surgimento de novas armas capazes de modificar o poder coercitivo dos países - como as armas de energia direta - acabam pondo em xeque a ideia de que a primazia [...] nuclear é condição suficiente para garantir a unipolaridade. Focando-se no atual recrudescimento das tensões entre EUA e Rússia - especialmente com a proposta norte-americana de implementação do Escudo Antimíssil no Leste Europeu - e analisando as relações de poder entre os três países, procuramos revelar que tipo de competição ocorrerá no sistema internacional nas próximas décadas. O presente artigo analisa as reais possibilidades de que a primazia nuclear norte-americana se torne efetiva, uma vez que, para tanto, é necessário o desarmamento estratégico das demais potências. Como uma guerra nuclear entre os três países possui um custo político muito elevado, as disputas tendem a ser decididas na esfera das operações. Para ilustrar esta última afirmação, usamos um cenário contrafactual de guerra nuclear limitada entre Estados Unidos, Rússia e China, por meio do qual tentamos evidenciar as precondições táticas e operacionais para uma eventual vitória da coalizão sino-russa. Abstract in english The evolution of the Post-Cold War (1991-2006) international system shows a significant amount of change regarding the strategic capabilities of United States, Russia, and China. The rise of a new class of strategic weapons called directed energy weapons (lasers and high power microwaves), as well a [...] s the great costs associated with the quest for nuclear primacy, demand closer examination of the current assumption about the links between nuclear primacy and unipolar distribution of power in the International System. Starting with the current tensions between US and Russia, we try to reveal in this article what kind of competition might be observed in the international system over the next decade. The present work analyzes the real possibilities of the USA achieving an effective nuclear primacy condition, which requires the complete disarmament of all other powers. Since a nuclear war between the three countries has a very high political cost, disputes tend to be settled on the operational sphere. In order to demonstrate this final point, we made comparative use of two nuclear war scenarios. The article concludes by establishing the tactical and operational conditions that Russia and China seems to counting with in order to defeat United States if a shooting war comes.

Fabrício Schiavo, Ávila; José Miguel, Martins; Marco, Cepik.

367

Armas estratégicas e poder no sistema internacional: o advento das armas de energia direta e seu impacto potencial sobre a guerra e a distribuição multipolar de capacidades Strategic weapons and power in international system: the arise of direct energy weapons and their potential impact over the war and multipolar distribution of capabilities  

Directory of Open Access Journals (Sweden)

Full Text Available O pós-Guerra Fria (1991-2006 apresenta uma mudança significativa no cenário estratégico: a maior acessibilidade da tecnologia militar e o surgimento de novas armas capazes de modificar o poder coercitivo dos países - como as armas de energia direta - acabam pondo em xeque a ideia de que a primazia nuclear é condição suficiente para garantir a unipolaridade. Focando-se no atual recrudescimento das tensões entre EUA e Rússia - especialmente com a proposta norte-americana de implementação do Escudo Antimíssil no Leste Europeu - e analisando as relações de poder entre os três países, procuramos revelar que tipo de competição ocorrerá no sistema internacional nas próximas décadas. O presente artigo analisa as reais possibilidades de que a primazia nuclear norte-americana se torne efetiva, uma vez que, para tanto, é necessário o desarmamento estratégico das demais potências. Como uma guerra nuclear entre os três países possui um custo político muito elevado, as disputas tendem a ser decididas na esfera das operações. Para ilustrar esta última afirmação, usamos um cenário contrafactual de guerra nuclear limitada entre Estados Unidos, Rússia e China, por meio do qual tentamos evidenciar as precondições táticas e operacionais para uma eventual vitória da coalizão sino-russa.The evolution of the Post-Cold War (1991-2006 international system shows a significant amount of change regarding the strategic capabilities of United States, Russia, and China. The rise of a new class of strategic weapons called directed energy weapons (lasers and high power microwaves, as well as the great costs associated with the quest for nuclear primacy, demand closer examination of the current assumption about the links between nuclear primacy and unipolar distribution of power in the International System. Starting with the current tensions between US and Russia, we try to reveal in this article what kind of competition might be observed in the international system over the next decade. The present work analyzes the real possibilities of the USA achieving an effective nuclear primacy condition, which requires the complete disarmament of all other powers. Since a nuclear war between the three countries has a very high political cost, disputes tend to be settled on the operational sphere. In order to demonstrate this final point, we made comparative use of two nuclear war scenarios. The article concludes by establishing the tactical and operational conditions that Russia and China seems to counting with in order to defeat United States if a shooting war comes.

Fabrício Schiavo Ávila

2009-04-01

368

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

369

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

370

Modeling in Computer Graphics  

Science.gov (United States)

A discussion of different modeling techniques in computer graphics including t polygon mesh, parametric cubic curves and patches, implicit functions such as metaballs, procedural modeling (plants and flowers) and modeling transformations.

2003-02-15

371

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

372

Predictive Models for Music  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Modeling long-term dependencies in time series has proved very difficult to achieve with traditional machine learning methods. This problem occurs when considering music data. In this paper, we introduce generative models for melodies. We decompose melodic modeling into two subtasks. We first propose a rhythm model based on the distributions of distances between subsequences. Then, we define a generative model for melodies given chords and rhythms based on modeling sequences of Narmour featur...

Paiement, Jean-franc?ois; Grandvalet, Yves; Bengio, Samy

2008-01-01

373

Linear stochastic volatility models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we investigate general linear stochastic volatility models with correlated Brownian noises. In such models the asset price satisfies a linear SDE with coefficient of linearity being the volatility process. This class contains among others Black-Scholes model, a log-normal stochastic volatility model and Heston stochastic volatility model. For a linear stochastic volatility model we derive representations for the probability density function of the arbitrage pri...

Jakubowski, Jacek; Wisniewolski, Maciej

2009-01-01

374

Survival modelling with frailty  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the survival analysis literature, the standard model for data analysis is the semi-parametric Proportional Hazard (PH) model of Cox (1972). MacKenzie (1996) introduced the Generalised Time Dependent Logistic (GTDL) family of non-PH parametric survival models, which compete with Cox’s PH model. This thesis develops the GTDL model side-by-side with the PH Weibull model. In many datasets, some attributes that might be deemed relevant may not be available. The effect of ...

Lynch, Joseph

2011-01-01

375

Operator spin foam models  

International Nuclear Information System (INIS)

ay we tend to view 4D quantum gravity, starting with the BC model and continuing with the Engle-Pereira-Rovelli-Livine (EPRL) or Freidel-Krasnov (FK) models. That makes our framework directly applicable to those models. Specifically, our operator spin foam framework can be translated into the language of spin foams and partition functions. Among our natural spin foam models there are the BF spin foam model, the BC model, and a model corresponding to the EPRL intertwiners. Our operator spin foam framework can also be used for more general spin foam models which are not symmetric with respect to one or more moves we consider.

376

Simplicity, Complexity and Modelling  

CERN Document Server

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

377

Modelling Food Webs  

CERN Document Server

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

378

DIPOLE COLLAPSE AND DYNAMO WAVES IN GLOBAL DIRECT NUMERICAL SIMULATIONS  

Energy Technology Data Exchange (ETDEWEB)

Magnetic fields of low-mass stars and planets are thought to originate from self-excited dynamo action in their convective interiors. Observations reveal a variety of field topologies ranging from large-scale, axial dipoles to more structured magnetic fields. In this article, we investigate more than 70 three-dimensional, self-consistent dynamo models in the Boussinesq approximation obtained by direct numerical simulations. The control parameters, the aspect ratio, and the mechanical boundary conditions have been varied to build up this sample of models. Both strongly dipolar and multipolar models have been obtained. We show that these dynamo regimes in general can be distinguished by the ratio of a typical convective length scale to the Rossby radius. Models with a predominantly dipolar magnetic field were obtained, if the convective length scale is at least an order of magnitude larger than the Rossby radius. Moreover, we highlight the role of the strong shear associated with the geostrophic zonal flow for models with stress-free boundary conditions. In this case the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. We interpret our results in terms of dynamo eigenmodes using the so-called test-field method. We can thus show that models in the dipolar regime are characterized by an isolated 'single mode'. Competing overtones become significant as the boundary to multipolar dynamos is approached. We discuss how these findings relate to previous models and to observations.

Schrinner, Martin; Dormy, Emmanuel [MAG (ENS/IPGP), LRA, Ecole Normale Superieure, 24 Rue Lhomond, 75252 Paris Cedex 05 (France); Petitdemange, Ludovic, E-mail: martin@schrinner.eu [Previously at Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany. (Germany)

2012-06-20

379

Biosphere Model Report  

International Nuclear Information System (INIS)

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 iosphere 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)

380

Bounded LTL Model Checking with Stable Models  

CERN Document Server

In this paper bounded model checking of asynchronous concurrent systems is introduced as a promising application area for answer set programming. As the model of asynchronous systems a generalisation of communicating automata, 1-safe Petri nets, are used. It is shown how a 1-safe Petri net and a requirement on the behaviour of the net can be translated into a logic program such that the bounded model checking problem for the net can be solved by computing stable models of the corresponding program. The use of the stable model semantics leads to compact encodings of bounded reachability and deadlock detection tasks as well as the more general problem of bounded model checking of linear temporal logic. Correctness proofs of the devised translations are given, and some experimental results using the translation and the Smodels system are presented.

Heljanko, K; Heljanko, Keijo; Niemel\\"a, Ilkka

2003-01-01

 
 
 
 
381

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