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In the human brain, aversive and appetitive processing have been studied with controlled stimuli in rather static settings. In addition, the extent to which aversive-related and appetitive-related processing engage distinct or overlapping circuits remains poorly understood. Here, we sought to investigate the dynamics of aversive and appetitive processing while male and female participants engaged in comparable trials involving threat avoidance or reward seeking. A central goal was to characterize the temporal evolution of responses during periods of threat or reward imminence. For example, in the aversive domain, we predicted that the bed nucleus of the stria terminalis (BST), but not the amygdala, would exhibit anticipatory responses given the role of the former in anxious apprehension. We also predicted that the periaqueductal gray (PAG) would exhibit threatproximity responses based on its involvement in proximal-threat processes, and that the ventral striatum would exhibit threat-imminence responses given its role in threat escape in rodents. Overall, we uncovered imminence-related temporally increasing ("ramping") responses in multiple brain regions, including the BST, PAG, and ventral striatum, subcortically, and dorsal anterior insula and anterior midcingulate, cortically. Whereas the ventral striatum generated anticipatory responses in the proximity of reward as expected, it also exhibited threat-related imminence responses. In fact, across multiple brain regions, we observed a main effect of arousal. In other words, we uncovered extensive temporally evolving, imminence-related processing in both the aversive and appetitive domain, suggesting that distributed brain circuits are dynamically engaged during the processing of biologically relevant information regardless of valence, findings further supported by network analysis. [ABSTRACT FROM AUTHOR]

In the present fMRI study, we examined how anxious apprehension is processed in the human brain. A central goal of the study was to test the prediction that a subset of brain regions would exhibit sustained response profiles during threat periods, including the anterior insula, a region implicated in anxiety disorders. A second important goal was to evaluate the responses in the amygdala and the bed nucleus of the stria terminals, regions that have been suggested to be involved in more transient and sustained threat, respectively. A total of 109 participants performed an experiment in which they encountered "threat" or "safe" trials lasting approximately 16 sec. During the former, they experienced zero to three highly unpleasant electrical stimulations, whereas in the latter, they experienced zero to three benign electrical stimulations (not perceived as unpleasant). The timing of the stimulation during trials was randomized, and as some trials contained no stimulation, stimulation delivery was uncertain. We contrasted responses during threat and safe trials that did not contain electrical stimulation, but only the potential that unpleasant (threat) or benign (safe) stimulation could occur. We employed Bayesian multilevel analysis to contrast responses to threat and safe trials in 85 brain regions implicated in threat processing. Our results revealed that the effect of anxious apprehension is distributed across the brain and that the temporal evolution of the responses is quite varied, including more transient and more sustained profiles, as well as signal increases and decreases with threat. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) in elderly adds substantially to socioeconomic burden necessitating early diagnosis. While recent studies in rodent models of AD have suggested diagnostic and therapeutic value for gamma rhythms in brain, the same has not been rigorously tested in humans. In this case-control study, we recruited a large population (N = 244; 106 females) of elderly (>49 years) subjects from the community, who viewed large gratings that induced strong gamma oscillations in their electroencephalogram (EEG). These subjects were classified as healthy (N = 227), mild cognitively impaired (MCI; N = 12), or AD (N = 5) based on clinical history and Clinical Dementia Rating scores. Surprisingly, stimulus-induced gamma rhythms, but not alpha or steady-state visually evoked responses, were significantly lower in MCI/AD subjects compared to their age- and gender-matched controls. This reduction was not due to differences in eye movements or baseline power. Our results suggest that gamma could be used as a potential screening tool for MCI/AD in humans. [ABSTRACT FROM AUTHOR]

Recent studies have shown the existence of two gamma rhythms in the hippocampus subserving different functions but, to date, primate studies in primary visual cortex have reported a single gamma rhythm. Here, we show that large visual stimuli induce a slow gamma (25- 45 Hz) in area V1 of two awake adult female bonnet monkeys and in the EEC of 15 human subjects (7 males and 8 females), in addition to the traditionally known fast gamma (45-70 Hz). The two rhythms had different tuning characteristics for stimulus orientation, contrast, drift speed, and size. Further, fast gamma had short latency, strongly entrained spikes and was coherent over short distances, reflecting short-range processing, whereas slow gamma appeared to reflect long-range processing. Together, two gamma rhythms can potentially provide better coding or communication mechanisms and a more comprehensive biomarker for diagnosis of mental disorders. [ABSTRACT FROM AUTHOR]

This task force paper presents multi-domain tools and their interfacing issues to perform simulations that require expertise in multiple areas of physics, such as electrothermal, electromechanical, electrochemical, and electromagnetic simulations, etc. Features of single multi-domain simulation tools, which are capable of simulating more than one system such as electrical chemical, mechanical, etc., are discussed. In addition, programs that are not capable of performing multi-domain simulation independently but can be interfaced with other programs to perform multi-domain simulation are also covered. Two case studies are reported where multi-domain simulations are performed in offline and real-time environments through the interfacing of more than one simulation tool. [ABSTRACT FROM PUBLISHER]

Real-time testing of new and more sophisticated distributed resource interfaces during transients, representing the different physical parts (mechanical, thermal, hydraulic, chemical, electrical, electronics) of a nonconventional generator in a single platform, or analyzing the interactions of distribution systems with distributed generators, energy markets, and customer behaviors are scenarios that cannot be studied with current software packages. This paper analyzes the present status and discusses the future development of tools that could cope with these simulation challenges. This paper includes test cases that will illustrate the scope of some of these simulation tools. [ABSTRACT FROM AUTHOR]

Transient stability (TS) and electromagnetic transient (EMT) programs are widely used simulation tools in power systems, with distinct applications but competing requirements. TS programs are fast which makes them suitable for handling large-scale networks, however, the modeling is not sufficiently detailed. On the other hand, EMT simulators are highly detailed, but limited in speed; consequently, they are used to simulate only small portions of the network. Integrating these two types of simulators generates a hybrid simulator which inherits the merits of both programs. A hybrid simulator can fulfill the modeling requirements of a large network by providing a fast as well as a detailed simulation. Establishing a connection between two different programs brings up several important issues which have been addressed, classified, and explained in this paper. An alternative integrated modeling of TS and EMT is also discussed using the concept of frequency shifting. [ABSTRACT FROM AUTHOR]

Visual stimulus-induced gamma oscillations in electroencephalogram (EEG) recordings have been recently shown to be compromised in subjects with preclinical Alzheimer's Disease (AD), suggesting that gamma could be an inexpensive biomarker for AD diagnosis provided its characteristics remain consistent across multiple recordings. Previous magnetoencephalography studies in young subjects have reported consistent gamma power over recordings separated by a few weeks to months. Here, we assessed the consistency of stimulus-induced slow (20–35 Hz) and fast gamma (36–66 Hz) oscillations in subjects (n  = 40) (age: 50–88 years) in EEG recordings separated by a year, and tested the consistency in the magnitude of gamma power, its temporal evolution and spectral profile. Gamma had distinct spectral/temporal characteristics across subjects, which remained consistent across recordings (average intraclass correlation of ~0.7). Alpha (8–12 Hz) and steady-state-visually evoked-potentials were also reliable. We further tested how EEG features can be used to identify 2 recordings as belonging to the same versus different subjects and found high classifier performance (AUC of ~0.89), with temporal evolution of slow gamma and spectral profile being most informative. These results suggest that EEG gamma oscillations are reliable across sessions separated over long durations and can also be a potential tool for subject identification. [ABSTRACT FROM AUTHOR]

This study presents a methodology for analysing the transient behaviour of harmonics associated with the interfacing of a synchronous generator and a transmission line. The algorithm is derived entirely in the dynamic harmonic domain that is based on an orthogonal basis and on operational matrices. The main characteristics of the proposed method are: its capability to accurately follow the harmonic content of a transient without the aid of a post-processing tool and its ability to serve as a visually active indicator of the steady-state and transient conditions in a signal. The proposed method is validated by comparing its results against those obtained through a time-domain technique. [ABSTRACT FROM AUTHOR]

The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results. [ABSTRACT FROM AUTHOR]

A fast and stable approach for the simulation of transformer nonlinearities during transient and unbalanced operating conditions is given. The proposed scheme implements separate magnetic and electric equivalent circuits. The solution of the transformer nonlinear mathematical model is carried out using the Newton-Raphson iterative method. Introducing the magnetic circuit nonlinearities into the model as either continuous or piecewise functions eliminated the difficulty of the Jacobian formation. The method was verified against experimental and computed results. The application of the Jacobian iterative method increased the stability and convergence of the solution as compared to a predictor corrector scheme. The proposed method was able to accurately simulate the transformer behaviour under switching and no-load conditions. [ABSTRACT FROM AUTHOR]

This paper discusses design and application of the multiagent simulation technology aiming to meet smart grid requirements. The difference between multiagent systems and multiagent simulation in smart grid applications is clarified. The state-of-the-art applications of multiagent simulation in power and energy systems are classified based on the simulation environment. The paper also addresses the interface issues including synchronization and data distribution for multiagent co-simulation. In addition, the emerging research paradigms in smart grid multiagent simulation are identified. [ABSTRACT FROM PUBLISHER]

This paper presents a review with a concise description and analysis of the fundamentals, characteristics, analytical details, merits, and drawbacks associated with existing methods in frequency and time domain for harmonic analysis in practical power networks. The description and analysis are centered on methods developed in the harmonic domain, hybrid frequency-time domain, and time domain, respectively. Validation of the reviewed methods for harmonic analysis, against one of the widely accepted digital simulators, such as EMTP, EMTDC, or MATLAB/SIMULINK, is reported in the cited individual contributions. [ABSTRACT FROM PUBLISHER]

This paper proposes large-scale transient stability simulation based on the massively parallel architecture of multiple graphics processing units (GPUs). A robust and efficient instantaneous relaxation (IR)-based parallel processing technique which features implicit integration, full Newton iteration, and sparse LU-based linear solver is used to run the multiple GPUs simultaneously. This implementation highlights the combination of coarse-grained algorithm-level parallelism with fine-grained data-parallelism of the GPUs to accelerate large-scale transient stability simulation. Multithreaded parallel programming makes the entire implementation highly transparent, scalable, and efficient. Several large test systems are used for the simulation with a maximum size of 9,984 buses and 2,560 synchronous generators all modeled in detail resulting in matrices that are larger than 20\,000\times 20\,000. [ABSTRACT FROM AUTHOR]

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation. [ABSTRACT FROM PUBLISHER]

This paper presents a brief review of techniques available for reducing large systems to smaller equivalents. This paper is divided into high frequency equivalents, low frequency equivalents, and wideband equivalents. Numerical examples are presented to demonstrate selected methods of high frequency equivalencing. [ABSTRACT FROM PUBLISHER]

Distribution software packages were primarily designed for analyzing radial systems with very limited capabilities for representing distributed resources (DR). Software manufacturers are presently updating and expanding the capabilities of their tools. The challenges, however, are many, since the new tools should be able to represent a wide range of power component models, efficiently compute steady-state and transient unbalanced operating conditions, or cope with DR interconnections whose design cannot be anticipated yet. This paper summarizes the main types of studies related to planning, analysis, and design of distribution networks, analyzes the models required for representing distributed resources, and discusses the future capabilities of distribution software packages. This paper includes test cases that illustrate some of the studies related to planning, analysis, and design of distribution networks with penetration of DR. [ABSTRACT FROM AUTHOR]

This paper deals with the current state-of-the-art in interfacing issues related to real-time digital simulators employed in the simulation of power systems and power-electronic systems. This paper provides an overview of technical challenges encountered and their solutions as the real-time digital simulators evolved. Hardware-in-the-loop interfacing for controller hardware and power apparatus hardware are also presented. [ABSTRACT FROM AUTHOR]

Modeling and analysis of power and power-electronic systems' transients using digital programs enables testing new design concepts in modern electric grid and many industrial and commercial products and applications. This paper gives an overview of dynamic average-value modeling techniques for representing static switching converters for the system-level studies. Concepts and desirable properties of averaged models for conducting large-signal time-domain transient studies and small-signal frequency-domain analysis for control design tasks are discussed. Basic approaches for developing average models for dc/dc and dc/ac converters are briefly reviewed and summarized. Finally, the desirable properties of the average-value models are demonstrated through an example system. [ABSTRACT FROM PUBLISHER]

Some of the most remarkable issues related to interharmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interharmonic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolution and of the computational burden associated with the analysis of periodic steady-state waveforms. Finally, modeling of different kinds of interharmonic sources and the extension of the classical models developed for power system harmonic analysis to include interharmonics are discussed. Numerical results for the issues presented are given with references to case studies constituted by popular schemes of adjustable speed drives. [ABSTRACT FROM AUTHOR]