bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of an interface boundary layer on the resonance properties of a buried structure
Authors: Karinski Y. S. , Shershnev V. V. , Yankelevsky D. Z. 
Published: January 2004

AbstractThis paper presents a model for the analysis of the diffraction of plane waves at a cavity in an infinite homogeneous linear elastic medium supported by a segmented lining. An elastic boundary layer is introduced between the cavity lining and the infinite medium. The boundary layer is simulated by ‘elastic boundary conditions’ in which the stress is proportional to the relative displacement of the lining and of the surrounding medium boundary.A closed‐form analytical solution of the problem was obtained using the Fourier–Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance.Using amplitude–frequency response analysis it was shown that the boundary layer produces additional ‘pseudo‐resonance’ frequencies that depend on the layer properties. These frequencies are almost identical to the eigenvalues obtained from the simple analysis of a segmented elastically supported lining. Copyright © 2003 John Wiley & Sons, Ltd.
Non‐linear seismic response of the rail‐counterweight system in elevators in buildings
Authors: Singh Mahendra P. , Rildova  , Suarez Luis E. 
Published: January 2004

AbstractElevators in buildings serve a very important function and are among the critical components of an essential facility. They have several mechanical and electrical components that are known to be susceptible to damage during earthquake occurrences. The counterweights, being the heaviest, are among their most vulnerable components. The ASME code has made several provisions to improve the performance of the counterweights in seismic events. To evaluate their performance under code‐mandated provisions, it is necessary that a comprehensive and realistic analytical model is used. This paper uses a detailed model of a counterweight of a traction elevator to study its in‐plane and out‐of‐plane dynamic behavior. The model incorporates the multiple support inputs and flexibilities of the counterweight guidance system along with their non‐linearities caused by the clearance limitations. The study examines the effect of changing clearances, variability of input motions, and the use of tie brackets on the system response, and evaluates the impact of some of the code provisions on the dynamic behavior of the system. Copyright © 2003 John Wiley & Sons, Ltd.
A discontinuous Galerkin method for seismic soil–structure interaction analysis in the time domain
Authors: Park Si‐Hwan , Antin Nicolas 
Published: January 2004

AbstractA technique for modeling transient wave propagation in unbounded media is extended and applied to seismic soil–structure interaction analysis in the time domain. The technique, based on the discontinuous Galerkin method, requires lower computational cost and less storage than the boundary element method, and the time‐stepping scheme resulting from Newmark's method in conjunction with the technique is unconditionally stable, allowing for efficient and robust time‐domain computations. To extend the technique to cases characterized by seismic excitation, the free‐field motion is used to compute effective forces, which are introduced on the boundary of the computational domain containing the structure and the soil in the vicinity of the structure. A numerical example on a dam–foundation system subjected to seismic excitation demonstrates the performance of the method. Copyright © 2003 John Wiley & Sons, Ltd.
Utilities privatization and the environmental processes employed by the Department of Defense—One firm's experience
Authors: Hammontree Jimmie 
Published: February 2004

AbstractC.H. Guernsey & Company (GUERNSEY) has played a key role in the Department of Defense Utility Privatization Initiative. This paper will provide a brief overview of the privatization initiative, environmental issues, and GUERNSEY's role in privatization. The presentation will outline the National Environmental Policy Act (NEPA) process and the Environmental Baseline Survey (EBS) process as they relate specifically to the privatization of utilities.GUERNSEY has identified several key elements necessary for successful completion of the environmental documentation that supports the privatization of utilities. Successful privatization projects depend heavily on communicating with the client, educating the client about how the environmental needs relate to the privatization process, and coordinating/interacting with the client from the beginning phases of scope generation to the delivery of the final documents. Environmental stewardship is also a must. © 2004 Wiley Periodicals, Inc.
Changes in effective connectivity models in the presence of task‐correlated motion: An fMRI study
Authors: Gavrilescu Maria , Stuart Geoffrey W. , Waites Anthony , Jackson Graeme , Svalbe Imants D. , Egan Gary F. 
Published: January 2004

AbstractWe investigated the effects of motion‐correction strategy and time course selection method when structural equation modeling is applied to fMRI data in the presence of task‐correlated motion. Three motion‐correction methods were employed for a group of 12 subjects performing an orthographic lexical retrieval task: (1) a rigid body realignment as implemented in SPM99, (2) a rigid body realignment combined with the inclusion of motion parameters in the statistical model, and (3) the FLIRT motion correction followed by an ICA analysis aiming to identify and remove the motion‐related components and the ghosting artifacts. For each motion correction, the time courses of the activated regions were selected in three ways: (1) using the voxels with the highest Z scores, (2) using the average across all the statistically significant voxels in the region of interest, and (3) using a within‐region, across‐subjects, singular value decomposition. The resulting models of effective connectivity were markedly different, although the activation pattern was not substantially altered by the motion‐correction method. Higher values for the path coefficients were obtained for the models fitted to the covariance matrices based on the average time courses than for the covariance matrices based on a single voxel time course. Our results suggest caution with the interpretation of task‐induced changes in effective connectivity since, for higher‐order cognitive brain functions, multiple models can be fitted to a given data set and these models cannot be rejected on an anatomical or cognitive basis. Hum. Brain Mapping 21:49–63, 2004. © 2003 Wiley‐Liss, Inc.
Effects of skull thickness, anisotropy, and inhomogeneity on forward EEG/ERP computations using a spherical three‐dimensional resistor mesh model
Authors: Chauveau Nicolas , Franceries Xavier , Doyon Bernard , Rigaud Bernard , Morucci Jean Pierre , Celsis Pierre 
Published: January 2004

AbstractBone thickness, anisotropy, and inhomogeneity have been reported to induce important variations in electroencephalogram (EEG) scalp potentials. To study this effect, we used an original three‐dimensional (3‐D) resistor mesh model described in spherical coordinates, consisting of 67,464 elements and 22,105 nodes arranged in 36 different concentric layers. After validation of the model by comparison with the analytic solution, potential variations induced by geometric and electrical skull modifications were investigated at the surface in the dipole plane and along the dipole axis, for several eccentricities and bone thicknesses. The resistor mesh permits one to obtain various configurations, as local modifications are introduced very easily. This has allowed several head models to be designed to study the effects of skull properties (thickness, anisotropy, and heterogeneity) on scalp surface potentials. Results show a decrease of potentials in bone, depending on bone thickness, and a very small decrease through the scalp layer. Nevertheless, similar scalp potentials can be obtained using either a thick scalp layer and a thin skull layer, and vice versa. It is thus important to take into account skull and scalp thicknesses, because the drop of potential in bone depends on both. The use of three different layers for skull instead of one leads to small differences in potential values and patterns. In contrast, the introduction of a hole in the skull highly increases the maximum potential value (by a factor of 11.5 in our case), because of the absence of potential drop in the corresponding volume. The inverse solution without any a priori knowledge indicates that the model with the hole gives the largest errors in both position and dipolar moment. Our results indicate that the resistor mesh model can be used as a robust and user‐friendly simulation tool in EEG or event‐related potentials. It makes it possible to build up real head models directly from anatomic magnetic resonance imaging without tessellation, and is able to take into account head heterogeneities very simply by changing volume elements conductivity. Hum. Brain Mapping 21:84–95, 2004. © 2003 Wiley‐Liss, Inc.
Functional brain mapping during free viewing of natural scenes
Authors: Bartels Andreas , Zeki Semir 
Published: January 2004

AbstractPrevious imaging studies have used mostly perceptually abstracted, idealized, or static stimuli to show segregation of function in the cerebral cortex. We wanted to learn whether functional segregation is maintained during more natural, complex, and dynamic conditions when many features have to be processed simultaneously, and identify regions whose activity correlates with the perception of specific features. To achieve this, we used functional magnetic resonance imaging (fMRI) to measure brain activity when human observers viewed freely dynamic natural scenes (a James Bond movie). The intensity with which they perceived different features (color, faces, language, and human bodies) was assessed psychometrically in separate sessions. In all subjects different features were perceived with a high degree of independence over time. We found that the perception of each feature correlated with activity in separate, specialized areas whose activity also varied independently. We conclude that even in natural conditions, when many features have to be processed simultaneously, functional specialization is preserved. Our method thus opens a new way of brain mapping, which allows the localization of a multitude of brain areas based on a single experiment using uncontrolled, natural stimuli. Furthermore, our results show that the intensity of activity in a specialized area is linearly correlated with the intensity of its perceptual experience. This leads us to suggest that each specialized area is directly responsible for the creation of a feature‐specific conscious percept (a microconsciousness). Hum. Brain Mapp. 21:75–83, 2004. © 2003 Wiley‐Liss, Inc.
Mapping the time course of nonconscious and conscious perception of fear: An integration of central and peripheral measures
Authors: Williams Leanne M. , Liddell Belinda J. , Rathjen Jennifer , Brown Kerri J. , Gray Jeffrey , Phillips Mary , Young Andy , Gordon Evian 
Published: January 2004

AbstractNeuroimaging studies using backward masking suggest that conscious and nonconscious responses to complex signals of fear (facial expressions) occur via parallel cortical and subcortical circuits. Little is known, however, about the temporal differentiation of these responses. Psychophysics procedures were first used to determine objective thresholds for both nonconscious detection (face vs. blank screen) and discrimination (fear vs. neutral face) in a backward masking paradigm. Event‐related potentials (ERPs) were then recorded (n = 20) using these thresholds. Ten blocks of masked fear and neutral faces were presented under each threshold condition. Simultaneously recorded skin conductance responses (SCRs) provided an independent index of stimulus perception. It was found that Fear stimuli evoked faster SCR rise times than did neutral stimuli across all conditions, indicating that emotional content influenced responses, regardless of awareness. In the first 400 msec of processing, ERPs dissociated the time course of conscious (enhanced N4 component) from nonconscious (enhanced N2 component) perception of fear, relative to neutral. Nonconscious detection of fear also elicited relatively faster P1 responses within 100 msec post‐stimulus. The N2 may provide a temporal correlate of the initial sensory processing of salient facial configurations, which is enhanced when top‐down cortical feedback is precluded. By contrast, the N4 may index the conscious integration of emotion stimuli in working memory, subserved by greater cortical engagement. Hum. Brain Mapping 21:64–74, 2004. © 2003 Wiley‐Liss, Inc.
Rollvection versus linearvection: Comparison of brain activations in PET
Authors: Deutschländer Angela , Bense Sandra , Stephan Thomas , Schwaiger Markus , Dieterich Marianne , Brandt Thomas 
Published: January 2004

AbstractWe conducted a PET study to directly compare the differential effects of visual motion stimulation that induced either rollvection about the line of sight or forward linearvection along this axis in the same subjects. The main question was, whether the areas that respond to vection are identical or separate and distinct for rollvection and linearvection. Eleven healthy volunteers were exposed to large‐field (100° × 60°) visual motion stimulation consisting of (1) dots accelerating from a focus of expansion to the edge of the screen (forward linearvection) and (2) dots rotating counterclockwise in the frontal plane (clockwise rollvection). These two stimuli, which induced apparent self‐motion in all subjects, were compared to each other and to a stationary visual pattern. Linearvection and rollvection led to bilateral activations of visual areas including medial parieto‐occipital (PO), occipito‐temporal (MT/V5), and ventral occipital (fusiform gyri) cortical areas, as well as superior parietal sites. Activations in the polar visual cortex around the calcarine sulcus (BA 17, BA 18) were larger and more significant during linearvection. Temporo‐parietal sites displayed higher activity levels during rollvection. Differential activation of PO or MT/V5 was not found. Both stimuli led to simultaneous deactivations of retroinsular regions (more pronounced during linearvection); this is compatible with an inhibitory interaction between the visual and the vestibular systems for motion perception. Hum. Brain Mapp. 21:143–153, 2004. © 2004 Wiley‐Liss, Inc.
Different areas of human non‐primary auditory cortex are activated by sounds with spatial and nonspatial properties
Authors: Hart Heledd C. , Palmer Alan R. , Hall Deborah A. 
Published: January 2004

AbstractIn humans, neuroimaging studies have identified the planum temporale to be particularly responsive to both spatial and nonspatial attributes of sound. However, a functional segregation of the planum temporale along these acoustic dimensions has not been firmly established. We evaluated this scheme in a factorial design using modulated sounds that generated a percept of motion (spatial) or frequency modulation (nonspatial). In addition, these sounds were presented in the context of a motion detection and a frequency‐modulation detection task to investigate the cortical effects of directing attention to different perceptual attributes of the sound. Motion produced stronger activation in the medial part of the planum temporale and frequency‐modulation produced stronger activation in the lateral part of the planum temporale, as well as an additional non‐primary area lateral to Heschl's gyrus. These separate subregions are consistent with the notion of divergent processing streams for spatial and nonspatial auditory information. Activation in the superior parietal cortex, putatively involved in the spatial pathway, was dependent on the task of motion detection and not simply on the presence of acoustic cues for motion. This finding suggests that the listening task is an important determinant of how the processing stream is engaged. Hum. Brain Mapping 21:178–190, 2004. © 2004 Wiley‐Liss, Inc.
Behavioral conflict, anterior cingulate cortex, and experiment duration: Implications of diverging data
Authors: Erickson Kirk I. , Milham Michael P. , Colcombe Stanley J. , Kramer Arthur F. , Banich Marie T. , Webb Andrew , Cohen Neal J. 
Published: January 2004

AbstractWe investigated the relationship between behavioral measures of conflict and the degree of activity in the anterior cingulate cortex (ACC). We reanalyzed an existing data set that employed the Stroop task using functional magnetic resonance imaging [Milham et al., Brain Cogn 2002;49:277–296]. Although we found no changes in the behavioral measures of conflict from the first to the second half of task performance, we found a reliable reduction in the activity of the anterior cingulate cortex. This result suggests the lack of a strong relationship between behavioral measurements of conflict and anterior cingulate activity. A concomitant increase in dorsolateral prefrontal cortex activity was also found, which may reflect a tradeoff in the neural substrates involved in supporting conflict resolution, detection, or monitoring processes. A second analysis of the data revealed that the duration of an experiment can dramatically affect interpretations of the results, including the roles in which particular regions are thought to play in cognition. These results are discussed in relation to current conceptions of ACC's role in attentional control. In addition, we discuss the implication of our results with current conceptions of conflict and of its instantiation in the brain. Hum. Brain Mapping 21:96–105, 2004. © 2003 Wiley‐Liss, Inc.
The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulation
Authors: Komssi Soile , Kähkönen Seppo , Ilmoniemi Risto J. 
Published: January 2004

AbstractTo better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS‐evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor‐cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS‐evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure‐of‐eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid‐shaped curve modeling the strength of TMS‐evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response‐stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154–164, 2004. © 2004 Wiley‐Liss, Inc.
Simple and complex movement‐associated functional MRI changes in patients at presentation with clinically isolated syndromes suggestive of multiple sclerosis
Authors: Filippi Massimo , Rocca Maria A. , Mezzapesa Domenico M. , Ghezzi Angelo , Falini Andrea , Martinelli Vittorio , Scotti Giuseppe , Comi Giancarlo 
Published: January 2004

AbstractUsing functional magnetic resonance imaging (fMRI), we investigated whether movement‐associated functional changes of the brain are present in patients who are, most likely, at the earliest stage of multiple sclerosis (MS). Functional MRI exams were obtained from 16 patients at presentation with clinically isolated syndromes (CIS) suggestive of MS and 15 sex‐ and age‐matched healthy volunteers during the performance of three simple and one more complex motor tasks with fully normal functioning extremities. fMRI analysis was performed using statistical parametric mapping (SPM99). Compared to healthy volunteers, CIS patients had increased activations of the contralateral primary sensorimotor cortex (SMC), secondary somatosensory cortex (SII), and inferior frontal gyrus (IFG), when performing a simple motor task with the dominant hand. The increased recruitment of the contralateral primary SMC was also found during the performance of the same motor task with the non‐dominant hand and with the dominant foot. In this latter case, an anterior shift of the center of activation of this region was detected. During the performance of a complex motor task with the dominant upper and lower limbs, CIS patients had an increased recruitment of a widespread network (including the frontal lobe, the insula, the thalamus), usually considered to function in motor, sensory, and multimodal integration processing. The comparison of brain activations during the performance of simple vs. complex motor tasks showed that the movement‐associated somatotopic organization of the cerebral and cerebellar cortices was retained in patients with CIS. Cortical reorganization occurs in patients at presentation with CIS highly suggestive of MS. Local synaptic reorganization, recruitment of parallel existing pathways, and reorganization of distant sites are all likely to contribute to the observed functional changes. Hum. Brain Mapping 21:106–115, 2004. © 2003 Wiley‐Liss, Inc.
Imaging a cognitive model of apraxia: The neural substrate of gesture‐specific cognitive processes
Authors: Peigneux Philippe , Van der Linden Martial , Garraux Gaetan , Laureys Steven , Degueldre Christian , Aerts Joel , Del Fiore Guy , Moonen Gustave , Luxen Andre , Salmon Eric 
Published: January 2004

AbstractThe present study aimed to ascertain the neuroanatomical basis of an influential neuropsychological model for upper limb apraxia [Rothi LJ, et al. The Neuropsychology of Action. 1997. Hove, UK: Psychology Press]. Regional cerebral blood flow was measured in healthy volunteers using H215O PET during performance of four tasks commonly used for testing upper limb apraxia, i.e., pantomime of familiar gestures on verbal command, imitation of familiar gestures, imitation of novel gestures, and an action‐semantic task that consisted in matching objects for functional use. We also re‐analysed data from a previous PET study in which we investigated the neural basis of the visual analysis of gestures. First, we found that two sets of discrete brain areas are predominantly engaged in the imitation of familiar and novel gestures, respectively. Segregated brain activation for novel gesture imitation concur with neuropsychological reports to support the hypothesis that knowledge about the organization of the human body mediates the transition from visual perception to motor execution when imitating novel gestures [Goldenberg Neuropsychologia 1995;33:63–72]. Second, conjunction analyses revealed distinctive neural bases for most of the gesture‐specific cognitive processes proposed in this cognitive model of upper limb apraxia. However, a functional analysis of brain imaging data suggested that one single memory store may be used for “to‐be‐perceived” and “to‐be‐produced” gestural representations, departing from Rothi et al.'s proposal. Based on the above considerations, we suggest and discuss a revised model for upper limb apraxia that might best account for both brain imaging findings and neuropsychological dissociations reported in the apraxia literature. Hum. Brain Mapp. 21:119–142, 2004. © 2004 Wiley‐Liss, Inc.