Transient Aspects Research Articles

DC Microgrid Grounding Impact on Power Electronic Interfaces in Fault Condition

This paper deals with assessment of grounding systems impacts on power electronic interfaces. To this end, transient overvoltage and overcurrent are analyzed in different fault situations considering various grounding conditions from the power electronic switches point of view. A new model for a neutral point clamped power electronic interface is presented that is suitable for this assessment. Plenty of simulations are carried out; from their results one can offer some valuable comments regarding ground condition impacts on the transients. It will be confirmed that grounding resistance and structure of dc microgrids have considerable impacts on the transients experienced by power electronic switches. The permissible range of the grounding resistance and the worst states of the switching template from transient voltage and current aspects are determined. By real-time monitoring of the grounding resistance and taking into account the simulations outcomes, one can alleviate transients experienced by the switches and promote fault ride through capability of the converter. Since computational burden of the proposed simple model is relatively low, it is applicable in real-time monitoring of the ground systems in practice.

Transient Aspects and Ultrafast Dynamical Processes of Amplified Spontaneous Emission in Conjugated Polymers.

Experimental research has revealed that the stimulated emission in organic semiconductors is associated with lattice vibrations. To reveal the dynamical aspects of the excited state of the conjugated polymer, the electron-transition process has been incorporated into the molecular dynamics, making it possible to simulate in detail the whole ultrafast process of amplified spontaneous emission (ASE). A typical conjugated polymer, poly( p-phenylene vinylene), is chosen as a model for the research. When an external laser beam of 60 μJ/cm2 is applied to photoexcite the polymer, the energy levels begin to oscillate within 100 fs. Thanks to the prominent self-trapping effect of the conjugated polymer, the laser beam also drives the lattice of the polymer chain to strongly vibrate. Until about 200 fs, four energy levels are pulled to the center of the energy gap, resulting in a transient discrete four-energy-level electronic structure for ASE. Simultaneously, in this ultrafast dynamical process, within the first 1 ps, inversion of the electron population occurs along with the appearance of a localized electronic cloud and locally distorted alternating bonds of the polymer chain. This detailed description of the whole ultrafast process of ASE helps in the understanding of the microscopic dynamical evolution of excitation in conjugated polymers.

Transient aspects of plasma luminescence induced by triboelectrification of polymers

Transient electric gas discharges that occur around sliding interfaces during contact electrification of polymers were studied at millisecond timescales and with micrometre resolution. Deduced vibrational temperatures indicate cold plasma resulting from positive corona discharge. At millisecond timescales, previously unseen rapid discharge events are observed, and modelling suggests that these result from streamer development, triggered by electron emission from the polymer surface. Those which occur over a period of several seconds are shown to be caused by competition between charge generation and the formation of polymer films. The findings explain the interplay between charging and plasma generation and their dependence on wear processes.

Identification of generator criticality and transient instability by supervising real-time rotor angle trajectories employing RBFNN

Identification of transient stability state in real-time and maintaining stability through preventive control technology are challenging tasks for a large power system while integrating deregulation constraints. Widely employment of the phasor measurement units (PMUs) in a power system and development of wide area management systems (WAMS) give relaxation to monitoring, measurement and control hurdles. This paper focuses on two research objectives; the first is transient stability assessment (TSA) and second is selection of the appropriate member for the control operation in unstable operating scenario. A model based on the artificial machine learning and PMU data is constructed for achieving both the objectives. This model works through prompt TSA status with radial basis function neural network (RBFNN) and validates it with PMU data to determine the criticality level of the generators. To reduce the complexity of the model a transient stability index (TSI) is proposed in this paper. A RBFNN is used to determine the transient stability aspects like stability status of system, coherent group and criticality rank of generator and preventive control action, following a large perturbation. PMUs measure post-fault rotor angle values and these are used as input for training RBFNN. The proposed approach is demonstrated on the IEEE 10-generator 39-bus, 16-generator 68-bus and 50-generator 145-bus test power systems successfully and the effectiveness of the approaches is discussed.

A numerical study on the transient aspects of porous flows and the applicability of Darcy’s friction flow relation

In recent developments of shale reservoirs, it is important to estimate the permeabilities of hydraulic fractures accompanying the Non- Darcy effects and geometric changes. Accordingly, a new permeability estimation method that considers the varying geometric features under different flow regions is demanded. To this end, the present study introduces the generalized Darcy’s friction flow relation, especially for examining the friction factor-Reynolds number (f · Re) relationship of porous flow, which is originally used in general internal friction flow analyses. Moreover, simple hydraulic fractures comprising structured microbeads are simulated via computational fluid dynamics during fracture aperture variations under different flow conditions from laminar to turbulent. Frictional flow features, e.g., the preservation characteristics of f · Re values, are examined under different geometry and flow conditions, and the transient flow characteristics are investigated using streamline analyses. Consequently, it is verified that the f · Re values vary slightly in proportion to the geometric changes caused by aperture reduction in each medium. Even though the variations in the f · Re values are much smaller than the permeability variations, it seems to be contrary to our expectation. Otherwise, the almost linear-variation aspects of f · Re values were observed in both directional flow cases. The linear-variation aspect of f · Re values is expected to be useful in the permeability-variation estimations in porous media with changing basic geometric factors, such as hydraulic fracture closing. Moreover, it is demonstrated that regardless of aperture reduction in the same type of medium, each porous flow has a very similar power-law relation between f and Re values when the flow velocity changes from the laminar to the turbulent condition. This aspect can be effectively used for obtaining permeability estimations of the varied media, particularly under different flow conditions.

Physics of the Stress Overshoot and Chain Stretch Dynamics of Entangled Polymer Liquids Under Continuous Startup Nonlinear Shear.

We construct a new theory for transient aspects of the shear rheology of entangled chain liquids. Within an established tube model constitutive equation framework, four new physical features are introduced: a tension blob scaling derivation of the interchain grip force that generates chain stretch, a force imbalance condition for the termination of affine stretch deformation, a delayed chain retraction process that after loss of grip is accelerated for fast deformations, and a distribution of tube diameters. Nonclassical predictions are made for the stress-strain curve to just beyond the overshoot, the existence of a master curve, and fractional power law scaling of the overshoot strain and stress at high shear rates, all in good agreement with experiment and simulation. Testable new predictions are made for chain stretch dynamics.

Distinguishing transient versus stable aspects of depression in New Zealand Pacific Island children using Generalizability Theory

BackgroundThe distinction between temporary versus enduring or state/trait aspects of depression is important. More precise distinction would improve understanding of the aetiology of depression and those aspects most amenable to intervention thus identifying more homogeneous, dynamic targets for clinical trials. Generalizability Theory has been proposed as useful for disentangling state and trait components of psychopathology. MethodsWe applied Generalizability Theory to determine the relative contributions of temporary and enduring aspects of depression in a widely used screening measure of depression the – 10-item Children's Depression Inventory (CDI-10; Kovacs, 1985). Participants were children of Pacific Island descent living in New Zealand (n = 668). Data were collected at ages – 9, 11, and 14 years. ResultsThe CDI-10 demonstrated acceptable generalizability across occasions (G = 0.79) with about one third of variance in total scores attributed to temporary and two thirds to more enduring aspects of depression. There were no other significant sources of error variance. Two items were identified as more sensitive than the remaining eight to more dynamic symptoms. LimitationsStudies with briefer test-retest intervals are warranted. Use of this Pacific Island cohort limits generalizability of findings to other cultures and ethnicities. No data were collected on whether participants had received intervention for depression. ConclusionsWhile the CDI-10 reliably measures both stable and transient aspects of depression in children, the scale does not permit clear distinction between them. We advocate application of Generalizability Theory for developing state/trait depression measures and determining which existing measures are most suitable for capturing modifiable features of depression.

Enhanced In-Plane Heat Transport in Embedded Mini Heat Pipes PCB

AbstractWe demonstrate the embedding of heat pipes as a solution for heat management in high density applications where heat spreading and heat guiding can be extremely important. Measurements results describe the advantages of the presented technology in comparison with thick copper inlays in the PCB. Further, this paper will also discuss the transient aspects of the heat transport in PCBs with embedded heat pipes.

Design and Analysis of Counter-Rotating Dual Rotors Permanent Magnet Compensated Pulsed Alternator

This paper presents the methodology for the electromagnetic design and analysis of air-cored pulsed alternators, which is based on a new type counter-rotating dual rotor permanent magnet compensated pulsed alternator (CRDR-PMCPA). The application of the CRDR topology in the field of CPA is used to decrease the large transient torque transmitted to the combat vehicle platform. Based on the air-cored structures and the pulse operation duty, the special design flowchart was presented. Halbach array permanent magnet rotors were designed for using the characteristic of unilateral magnetism gathering in the CRDR-PMCPA. The parameters of the air-cored dual rotors pulsed alternators were calculated and compared by the analytical method and finite-element analysis (FEA) method (FEM). The inductance of the armature winding is important for obtaining the pulsed current waveform accurately. The inductance of the armature winding is calculated by the numerical method and FEM, respectively. The mechanical design of the CRDR-PMCPA was done. The transient discharge process was simulated in detail for evaluating the design performance, and the operation risks of permanent magnets were also evaluated. The special problems for dual rotors rotating were investigated. The electromagnetic design and analysis is the base for accurately calculating the transient thermal rise and mechanical impulse aspects. Thermal and structural analysis was done by the multiphysics coupling analysis. And the results were used to evaluate the demagnetization risk of permanent magnets and evaluate the safety of the whole machine and the discharge system.

PERSONALITY TRAITS, ANGER AND PSYCHIATRIC SYMPTOMS RELATED TO QUALITY OF LIFE IN PATIENTS WITH NEWLY DIAGNOSED DIGESTIVE SYSTEM CANCER.

The presence of psychiatric symptoms, anger, and personality characteristics are factors that affect the quality of life of newly diagnosed digestive system cancer patients. This study aims to identify which stable characteristics of the individual's personality interfere with quality of life, even when reactive emotional characteristics of falling ill are controlled. A cross-sectional study was performed at the Oncology Clinic ( Hospital das Clínicas ), Marília/SP, Brazil, in which 50 adult patients with digestive system cancer and diagnosed less than 6 months answered the State-Trait Anger Expression Inventory, Temperament and Character Inventory, Hospital Anxiety and Depression Scale and WHOQOL-BREF. Multiple regression was performed to verify if quality of life was related to stable characteristics of the subject's personality (anger trait, temperament and character) after controlling to the transient emotional aspects (anger state, psychiatric symptoms). The quality of life psychological health score was higher in presence of self-directedness character and reward dependence temperament and quality of life environment score was higher in presence of self-directedness character and lower in presence of harm avoidance temperament. The psychological well-being and the adaptive needs to the environment that favoring a better quality of life were reinforced mainly by the self-directedness character; which means that patients more autonomous cope better with the disease. On the other hand, the harm avoidance temperament (meaning the patient has fear of aversive situations) impaired the adaptive capacity to deal with the changes of the day-to-day imposed by the disease. Understanding these personality traits is important to the health professionals drive the patient to more successful treatment.

Transient aspects of the Hadley circulation forced by an idealized off‐equatorial ITCZ

AbstractThis paper presents analytical solutions of large‐scale, zonally symmetric overturning circulations in the tropical free troposphere forced by transient diabatic heating in the off‐equatorial intertropical convergence zone (ITCZ). The dynamics are discussed in the context of the time‐dependent meridional circulation equation arising in an equatorial β‐plane model. The solutions of these differential equations contain terms for the slow, quasi‐balanced part of the response and terms for the transient, zonally symmetric, inertia‐gravity wave part of the response. When the off‐equatorial (north of the equator) ITCZ diabatic heating is switched on at various rates, both parts of the response reveal a basic asymmetry between the southern and northern hemispheres, with the southern hemisphere side containing most of the quasi‐balanced compensating subsidence and transient inertia‐gravity wave activity. The inertia‐gravity waves travel in wave packets that bounce off a spectrum of turning latitudes and are analyzed in the context of an average conservation law approach. These traveling wave packets cause the mass flux in the southern and northern Hadley cells to pulsate on timescales of about 1, 2, and 3 days for diabatic heating of the external, first internal, and second internal vertical modes, respectively. The spectral characteristics of the vertical motion in the ITCZ and subsidence regions are slightly more complicated and depend on ITCZ location.

Transient aspects of drag reducing plane Couette flows

The addition of a small amount of polymers of high molecular weight can lead to a decrease in the pressure drop in turbulent flows. Over the years, numerous studies have been conducted in attempts to make practical use of polymer-induced drag reduction. However, many aspects concerning its main mechanism are still unclear. One of those aspects is the development of the turbulent structures and polymer deformation over time in the beginning of the phenomenon. As an attempt to further understand the drag reduction over this developing time, we analyse a turbulent Couette flow of a FENE-P fluid with the aid of direct numerical simulations. We show that the initial interactions between the mean shear flow, turbulent structures, and polymer stretching are the key to understanding the step-by-step evolution of the drag reduction (DR). A few instants after the beginning of the simulation, the DR assumes a significantly negative value before starting to increase and reaches its maximum. When the DR is a minimum, the polymers experience their highest deformation state. The energy necessary to initially stretch them comes mainly from the mean shear flow, which causes a decrease of the DR until its minimum and negative value. After this point, the polymers start to strongly interact with the turbulent structures, which are partially suppressed, and the DR starts to increase. Part of the energy stored by the molecules is then released to the mean flow, increasing the DR to a maximum level while the polymer extension decreases. Lastly, DR reduces, reaching an asymptotic and positive value, which indicates the beginning of the statistical steady flow state.

An extension of the Hill–Mandel principle for transient heat conduction in heterogeneous media with heat generation incorporating finite RVE thermal inertia effects

SummaryIn this work, we propose a homogenization formulation to model transient heat conduction in heterogeneous media that takes into account thermal inertia contributions, which arise from a finite description of the microscale. Rewriting the variational form of the transient heat conduction problem and making use of key assumptions, we arrive at a mathematical formulation that suggests an extension of the Hill–Mandel principle when considering non‐null heat flux divergence in the representative volume element (RVE). Along the manuscript, we highlight that the main results of the proposed formulation are in agreement with recent advances in the field of computational homogenization applied to transient mechanical and heat flow problems. The proposed extension of the Hill–Mandel principle contributes to the understanding of the microscale thermal inertia effects incorporation into the multiscale framework. We also present the calculations needed for implementing the model and numerical results, which give support to the theoretical model developed. The numerical results highlight the importance of considering full transient aspects when dealing with multiscale heat conduction in heterogeneous media which are subjected to high thermal gradients. Copyright © 2016 John Wiley & Sons, Ltd.

General and emotion-specific alterations to cognitive control in women with a history of childhood abuse

BackgroundAlthough limited, the literature suggests alterations in activation of cognitive control regions in adults and adolescents with a history of childhood abuse. The current study examined whether such alterations are increased in the face of emotionally-distracting as compared to emotionally neutral information, and whether such alterations occur in brain regions that exert cognitive control in a more top-down sustained manner or a more bottom-up transient manner.MethodsParticipants were young adult women (ages 23–30): one group with a history of childhood physical or sexual abuse (N = 15) and one with no trauma exposure (N = 17), as assessed through the Trauma History Questionnaire and a two-stage interview adapted from the National Crime Victims Survey. Participants underwent fMRI scanning while completing hybrid block/event-related versions of a classic color-word and an emotional Stroop paradigm (threat and positive words). This paradigm allowed us to examine both sustained (activation persisting across blocks) and transient (event-specific activation) aspects of cognitive control.ResultsWomen with a history of childhood abuse demonstrated decreased recruitment of frontal-parietal regions involved in cognitive control and enhanced recruitment of a ventral attention surveillance network during blocks of both versions of the Stroop task. Additionally, they had less suppression of brain regions involved in self-referential processes for threat blocks, but greater suppression of these regions for positive blocks. Severity of avoidance symptoms was associated with sustained activation in lateral prefrontal regions, whereas hyperarousal/re-experiencing symptoms were associated with sustained activity in temporal regions. No differential effects were observed for transient control.ConclusionsResults suggest exposure to childhood abuse is associated with blunted recruitment of brain regions supporting task-set maintenance but hypervigilance for task-irrelevant information, regardless of whether distractors are emotionally neutral or emotional. Exposure to childhood abuse is also associated with less suppression of default mode brain regions associated with self-referential processing in the face of irrelevant threat information, but heightened ability to suppress similar processing for irrelevant positive information.

Rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model

AbstractClassical rate‐and‐state friction (RSF) laws are widely applied in modeling earthquake dynamics but generally using empirically determined parameters with little or no knowledge of, or quantitative account for, the controlling physical mechanisms. Here a mechanism‐based microphysical model is developed for describing the frictional behavior of carbonate fault gouge, assuming that the frictional behavior seen in lab experiments is controlled by competing processes of rate‐strengthening intergranular sliding versus contact creep by pressure solution. By solving the controlling equations, derived from kinematic and energy/entropy balance considerations, and employing a microphysical model for rate‐strengthening grain boundary friction plus standard creep equations for pressure solution, we simulate typical lab‐frictional tests, namely, “velocity stepping” and “slide‐hold‐slide” test sequences, for velocity histories and environmental conditions employed in previous experiments. The modeling results capture all of the main features and trends seen in the experimental results, including both steady state and transient aspects of the observed behavior, with reasonable quantitative agreement. To our knowledge, ours is the first mechanism‐based model that can reproduce RSF‐like behavior in terms of microstructurally verifiable processes and state variables. Since it is microphysically based, we believe that our modeling approach can provide an improved framework for extrapolating friction data to natural conditions.

Unbearable Lightness: Some Modern Instances in Auden, Stevens and Eliot

In this essay I examine the implicit paradox that, although in conventional consideration ‘light’ is good and ‘darkness’, by antithesis, bad, the antithesis itself implies interconnection and, especially in poetry, the evocation of light can equally imply the possibility of darkness. Further, I suggest that poets have found intermediate or qualified illumination to be a more productive resource than light unmoderated by shadow, whose erasure of uncertainty is potentially disabling. My principal examples are drawn from modern poetry, in W. H. Auden, Wallace Stevens and T. S. Eliot, preceded by a consideration of some nineteenth-century precursors; by means of these I show how their verse takes animation from the transient and transitional aspects of light, rather than from its plenitude. The implications of this, in a culture shaped by traditional Christian associations between ‘God’ and ‘light’, are suggestive throughout the essay, but become especially resonant in the case of Eliot's overtly Christian poetry.

Neural substrates of sexual arousal in heterosexual males: event-related fMRI investigation.

BackgroundSexual behavior is an important role for the survival of species. The advancement of brain imaging methods has enabled the understanding of the brain mechanism related to sexual arousal. The previous studies on the brain mechanism related to sexual arousal have mostly conducted on block design paradigm.MethodsDespite its requirement for stricter experimental control, the event-related paradigm is known to be more efficient in detecting instant emotional and cognitive responses. The paradigm also enables the observation of hemodynamic responses through time. Therefore, this study used the event-related fMRI to examine the brain activation in various areas associated with sexual arousal as well as changes in hemodynamic responses with time.ResultsStrong activations were observed in the various areas associated with sexual arousal comprised of various factors: (1) activation areas related to cognitive factors: the occipital lobe and parietal lobe; (2) activation areas related to emotional factors: the thalamus and amygdala; (3) activation areas related to motivational factors: the anterior cingulate gyrus, orbitofrontal cortex, and insula; and (4) activation areas related to physiological factors: the precentral gyrus, putamen, and globus pallidus. We also identified the activation of the putamen and globus pallidus that were not well observed in previous block design studies. In the result of the hemodynamic response, the neural activity in those areas showed more transient aspects of the hemodynamic responses relative to the neural activity of other areas.ConclusionsThese results suggested that the event-related paradigm is better at detecting the neural activity of the brain regions, which tend to appear suddenly, but disappear soon.

The steady-state and transient electron transport within bulk zinc-blende indium nitride: The impact of crystal temperature and doping concentration variations

Within the framework of a semi-classical three-valley Monte Carlo electron transport simulation approach, we analyze the steady-state and transient aspects of the electron transport within bulk zinc-blende indium nitride, with a focus on the response to variations in the crystal temperature and the doping concentration. We find that while the electron transport associated with zinc-blende InN is highly sensitive to the crystal temperature, it is not very sensitive to the doping concentration selection. The device consequences of these results are then explored.

A cross-bridge based model of force depression: Can a single modification address both transient and steady-state behaviors?

Force depression (FD), the reduction of isometric force following active shortening, is a phenomenon of skeletal muscle that has received significant attention in biomechanical and physiological literature, yet the mechanisms underlying FD remain unknown. Recent experiments identified a slower rate of force redevelopment with increasing amounts of steady-state FD, suggesting that FD may be caused, at least in part, by a decrease in cross-bridge binding rate (Corr and Herzog, 2005; Koppes et al., 2014). Herein, we develop a cross-bridge based model of FD in which the binding rate function, f, decreases with the mechanical work performed during shortening. This modification incorporates a direct relationship between steady-state FD and muscle mechanical work (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008), and is consistent with a proposed mechanism attributing FD to stress-induced inhibition of cross-bridge attachments (Herzog, 1998; Maréchal and Plaghki, 1979). Thus, for an increase in mechanical work, the model should predict a slower force redevelopment (decreased attachment rate) to a more depressed steady-state force (fewer attached cross-bridges), and a reduction in contractile element stiffness (Ford et al., 1981). We hypothesized that since this modification affects the cross-bridge kinetics, a corresponding model would be able to account for both transient and steady-state FD behaviors. Comparisons to prior experiments (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008) show that both steady-state and transient aspects of FD, as well as the relationship of FD with respect to speed and amplitude of shortening, are well captured by this model. Thus, this relatively simple cross-bridge based model of FD lends support to a mechanism involving the inhibition of cross-bridge binding, and indicates that cross-bridge kinetics may play a critical role in FD.

Anhedonia is associated with reduced incentive cue related activation in the basal ganglia.

Research has shown that reward incentives improve cognitive control in motivationally salient situations. Much previous work in this domain has focused on incentive cue-related activity in a number of brain regions, including the dorsolateral prefrontal cortex (DLPFC) and striatum. However, the more sustained changes in functional brain activity during task contexts with incentives have been relatively less explored. Here, we examined both the cue-related and sustained effects of rewards (i.e., monetary incentives) on cognitive control, with a particular focus on the roles of the DLPFC and striatum, using a mixed state-item design. We investigated whether variability in a reward-related trait (i.e., anhedonia) would modulate the sustained and/or the cue-related transient aspects of motivated cognitive control. Twenty-seven healthy individuals performed a modified response conflict task (Padmala & Pessoa, Journal of Cognitive Neuroscience, 23, 3419-3432, 2011) during scanning, in which participants were asked to categorize images as either houses or buildings with either congruent or incongruent overlaid words. Participants performed a baseline condition without knowledge of monetary incentives, followed by reward blocks with monetary incentives on some cued trials (reward cues) for fast and correct responses. We replicated previous work by showing increases in both sustained activity during reward versus baseline blocks and transient. cue-related activity in bilateral DLPFC and the basal ganglia. Importantly, healthy individuals with higher anhedonia showed less of an increase in trial-by-trial activity as a function of reward in the lateral globus pallidus. Together, our results suggest that reduced hedonic experience may be related to abnormality of reward cue-related activity in the basal ganglia.