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Abstract Injection of fluids in deep subsurface geological formations has created a series of challenges in recent decades. Possibility of upward fluid leakage along nearby wells and faults is one of the main issues related to these operations. It is important to ensure that such conduits, if present, can be detected, characterized and treated. Looking for pressure abnormalities in intervals above the injection zones, is one the methods used to monitor for these conduits. We propose an analytical solution to detect and characterize the vertical leakage from a fault of finite length using pressure data collected from monitoring zones. The proposed closed form analytical model would allow to not only distinguish the pressure signal of leakage from a fault of finite length from other possible leakage conduits but also to estimate the leakage rate, length of leaky section of the fault and relative position of the fault with respect to the location of monitoring well. Highlights • For first time based on Theis solution a mathematical solution for fault leakage is derived. • Derived analytical solution were used to study fluid movement out of a linear-finite fault [ABSTRACT FROM AUTHOR]

Highlights • Transient model was built to analyze unsteady thermal behaviors of PTCs. • It was validated with experiment data measured from a utility-scale loop of PTCs. • Parametric studies were made to analyze essential impact factors. Abstract Solar resources are inherently unsteady and their energy density on the earth is low. Thereby, when the solar energy is converted into thermal energy through concentrating the sunlight, how to predict the transient performance of parabolic trough solar collectors under the operating conditions is necessary for the steady useful output and the efficient use of the energy. So this paper describes a mathematical model of the transient thermal behaviors of parabolic trough solar collectors. Then, to validate this transient model, its numerical results are compared with the experimental data. These data were collected from a utility-scale loop of parabolic trough solar collectors. The comparison between the model predictions and the experimental data shows a consistent and reasonable agreement. Furthermore, the primary interest of this study is to determine how the temperature distributions of the absorber, the glass envelope and the heat transfer fluid evolve from initial conditions with specified optical and thermal parameters. Thus, this model is used to carry out parametric studies to make analyses of essential impact factors on transient behaviors of parabolic trough solar collectors. These factors include the temperature of the heat transfer fluid at the inlet, the initial conditions, and the optical efficiency. Moreover, this model has the function of continuous adjustment of the flow rate to satisfy the requirement of the temperature of the heat transfer fluid at the outlet according to varying boundary conditions. Hence, another analysis is performed to investigate transient processes when the flow rate is continuously adjusted at various DNI ramp rates. [ABSTRACT FROM AUTHOR]

We study the accuracy and the robustness of the Geometrical Finite Element Model Updating method proposed in Touzeau et al. [Touzeau, C., Magnain, B., Emile, B., Laurent, H. and Florentin, E. (2016) "Identification in transient dynamic using a geometry-based cost function in finite element model updating method," Finite Elements Anal. Des.122, 49–60]. In this work, the method is applied to transient dynamic in finite transformations to identify mechanical material parameters. A stochastic approach is performed to determine accuracy and robustness. The method is illustrated on numerical test cases and compared to a classical FEMU method. Uncertainties on the loading are taken into account in the identification using an original approach. [ABSTRACT FROM AUTHOR]

The current study describes a detailed steady-state analysis and transient operation of a multi-effect desalination plant with a thermal vapor compressor unit (MED-TVC). The model developed is based on solving the basic conservation equations of mass, energy, and salt. It can predict steady-state operation and transient behavior when the plant is subject to abrupt changes in the main input parameters including motive steam flow rate (m ms ), cooling seawater flow rate (m cw ) and cooling seawater temperature (T cw ). These sudden changes simulate the conditions a MED-TVC plant may be exposed to. Both the steady-state and dynamic aspects of the model are validated against published experimental data. Monitoring the variation of four state variables (vapor temperature, brine level, brine and vapor flow rates) in each effect shows that disturbances in the motive steam flow rate and the cooling seawater temperature have a significant effect on the plant performance. On the other hand, the disturbance in the cooling seawater mass flow rate has only a moderate effect. For all applied disturbances, the change in the brine level is the slowest compared to the changes in vapor temperature, and brine and vapor flow rates. Furthermore, the effect of changing seawater salinity shows a slight effect on the total distillate production and the specific heat transfer area. [ABSTRACT FROM AUTHOR]

Meteosat Third Generation (MTG) is the next generation of European meteorological geostationary satellites, set to be launched in 2021. Besides ensuring continuity with Meteosat Second Generation imagery mission, the new series will feature new instruments, such as the Lightning Imager (LI), a high-speed optical detector providing near real-time lightning detection capabilities over Europe and Africa. The instrument will register events on pixels, where a lightning pulse generates a transient in the acquired radiance. In parallel, signal variations due to a number of unwanted sources, e.g., acquisition noise or jitter movement, are expected to produce false events. The challenge for on-board and on-ground processing is, thus, to discard as many false events as possible while keeping a majority of the true lightning events. This paper discusses a chain of algorithms that can be used by the LI for the detection of lightning and for the filtering of false events. Some of these algorithms have been developed in the framework of internal research and simulations conducted by the MTG team at the European Space Agency on an in-house LI simulator and therefore will not necessarily reflect the ultimate operational processing chain. The application of the chain on a representative scenario shows that 99.5% of the false events can be eliminated while keeping 83.6% of the true events, before generating the LI higher level data products. Machine learning techniques have also been studied as an alternative for on-ground event processing, and preliminary results indicate promising potential. [ABSTRACT FROM AUTHOR]

The complexity and safety requirements for Nuclear power plants (NPP) warrant a reliable fault diagnosis approach. In this paper, we present a fault diagnosis method based on Correlation Analysis and Deep Belief Network. We utilized the feature selection capability of Correlation Analysis for dimensionality reduction and deep belief network for fault identification. We also discussed the implementation of the algorithm and the process of model building that is characteristics of NPP. To illustrate the performance of the proposed fault diagnosis model, we utilized Personal Computer Transient Analyzer (PCTRAN). In addition, we also compared the fault diagnostic results from back-propagation neural network and support vector machine with our method. The results show that the proposed method has obvious advantages over other methods, and would be of profound guiding significance to the fault diagnosis of NPP. [ABSTRACT FROM AUTHOR]

The nonintrusive Chebyshev interval method is used to analyze the transient response of a rotor system. The main idea is to analyze the uncertainty in speed-varying rotor systems and reduce the error in the calculation. The hybrid analysis procedure, which combines the black-box modeling and overestimation controlling, is proposed via the Chebyshev approximation and searching the extreme values of the approximation function for the uncertain response. It can both increase accuracy and improve the computational efficiency of the proposed method. Effects of the uncertain parameters on response bounds and estimation errors of the system are investigated, e.g., supporting stiffness and damping. The accuracy and efficiency of the proposed method are verified via comparing with the scanning method. Overestimation effects caused by the interval arithmetic can be controlled, particularly the sensitive domains near the critical speed. It can provide guidance for general uncertain transient mechanical systems, particularly those that have severe fluctuations near resonances. [ABSTRACT FROM AUTHOR]

The aim of the present study was to identify the effect of heme oxygenase (HO)-1 gene on cerebral ischemia- reperfusion injury. Sprague-Dawley rats were divided randomly into four groups: Sham group, vehicle group, empty adenovirus vector (Ad) group and recombinant HO-1 adenovirus (Ad-HO-1) transfection group. Rats in the vehicle, Ad and Ad-HO-1 groups were respectively injected with saline, Ad or Ad-HO-1 for 3 days prior to cerebral ischemia-reperfusion injury. Subsequently, the middle cerebral artery occlusion method was used to establish the model of cerebral ischemia-reperfusion injury. Following the assessment of neurological function, rats were sacrificed, and the infarction volume and apoptotic index in rat brains were measured. Furthermore, the protein expression levels of HO-1 in brain tissues were detected using western blot analysis. Results indicated that the neurological score of the Ad-HO-1 group was significantly increased compared with the Ad or vehicle groups, respectively (P<0.001). The volume of cerebral infarction and the index score of neuronal apoptosis in the vehicle and Ad groups was significantly increased compared with the Ad-HO-1 group (P<0.01). The death of neuronal cells following cerebral ischemia-reperfusion injury reduced remarkably induced by over-expression of HO-1. These findings suggest a neuroprotective role of HO-1 against brain injury induced by transient cerebral ischemia-reperfusion injury. [ABSTRACT FROM AUTHOR]

The article proposes a power system fault-recognition technique founded on waveform analysis to identify and categorize short circuit faults in large power systems. The main criticism against waveform-based approaches is their huge computational burden and relatively slow processing, making them unsuitable for on-line applications. This article efficiently handles the computational load by applying a novel zone partitioning concept, where a large power system is partitioned, forming smaller hypothetical zones with fewer number of buses and lines. Crude determination of fault zone is first performed by a neural network (NN)-based zone classifier. A succeeding module of classifier, then determines the exact fault nature and its precise location within a hypothetical zone. Transient recorders installed at optimal monitoring buses, in each partitioned zone, collect the preliminary wave-data, which is then passed-on to an extended Kalman filter (EKF)-based feature extraction module, to filter-out relevant fault features. The EKF-NN combination is found to be highly efficient and precise in determining fault nature and location when tested on WECC-200-bus practical system. Hypothetical-zone partitioning has been established as a highly efficient technique, reducing the computation burden and CPU usage considerably, and rendering the scheme suitable for on-line implementation. The method also improved the fault-recognition accuracy phenomenally. [ABSTRACT FROM AUTHOR]

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload, or vice versa, for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10-kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. Depending on the application for both machines, a short-duty transient operation in overload conditions could be required. In particular, the automotive starter-generator must accomplish engine cranking and torque assistance during the vehicle acceleration and braking, while the industrial induction machine could operate in intermittent service in overload conditions when used in machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach, and, subsequently, the model has been validated during operative overload conditions. [ABSTRACT FROM AUTHOR]

The material point method (MPM) enhanced with B-spline basis functions, referred to as B-spline MPM (BSMPM), is developed and demonstrated using representative quasi-static and dynamic example problems. Smooth B-spline basis functions could significantly reduce the cell-crossing error as known for the original MPM. A Gauss quadrature scheme is designed and shown to be able to diminish the quadrature error in the BSMPM analysis of large-deformation problems for the improved accuracy and convergence, especially with the quadratic B-splines. Moreover, the increase in the order of the B-spline basis function is also found to be an effective way to reduce the quadrature error and to improve accuracy and convergence. For plate impact examples, it is demonstrated that the BSMPM outperforms the generalized interpolation material point (GIMP) and convected particle domain interpolation (CPDI) methods in term of the accuracy of representing stress waves. Thus, the BSMPM could become a promising alternative to the MPM, GIMP, and CPDI in solving certain types of transient problems. [ABSTRACT FROM AUTHOR]

Rotor dynamic systems require considerably higher power/torque to accelerate through the structural resonance. However, most sources of mechanical power are non-ideal, i.e., they can only provide a limited amount of power. If there is insufficient power to overcome the resonance then the rotor speed may get caught at resonance and the persistent high vibrations can damage the machine. Various proposed solutions to this problem deal with modifications to the mechanical structure and active/semi-active control of structural parameters. This article proposes modification to the prime mover so that peak available power is delivered exactly at the structural resonance frequency. The limited power/non-ideal prime mover considered in this article is a direct current (DC) motor and the structural resonance happens due to forcing from an eccentric rotor disk and vibrations of a flexible weakly damped foundation. Various control strategies to modify the torque-speed characteristics of permanent magnet, shunt and series wound DC motors to promote escape through resonance are considered. Also, the characteristic curves for rotor/motor speed versus the DC supply voltage are obtained for the considered DC motor types from which the unattainable steady angular speeds and the speed jumps due to Sommerfeld effect are computed. Transient simulations are performed using bond graph models for this multi-energy domain (here, electro-mechanical) system. It is shown that a switched control permitting to switch between shunt and series DC motor configurations gives better regulation over the power delivery at the resonant frequency as well as super-critical operating speeds in the neighborhood of structural resonance. [ABSTRACT FROM AUTHOR]

A marching-on-in-time (MOT) based time domain thin dielectric sheet (TDS) method is proposed for analyzing the transient electromagnetic scattering from the perfect electrically conducting (PEC) body coated with thin dispersive material. The sources in the thin dielectric layer are all replaced by the current densities of PEC. A recursive convolution method is utilized to deal with the dispersive properties. The performance of accuracy and stability are investigated numerically. [ABSTRACT FROM AUTHOR]

Features of transient liquid phase (TLP) bondability of high-volume fraction (70 vol.%) SiC particle-reinforced A356 composite for popular Cu interlayer were investigated. Although Cu foil was melted, molten Cu was completely expulsed, indicating that the numerous SiC particles significantly deteriorated wettability not only at particle/braze metal (P/M) interface, but also at the matrix/braze metal (M/M) interface. For the reason of poor wettability at P/M interface, a model showing there is a 'window period' for actual wetting reaction (allowing liquid phase to be in contact with surficial SiC particles) much shorter than nominal isothermal solidification time during TLP bonding of the composite containing sintered ceramic preform was proposed. For the poor wettability at M/M interface, both size effect of too small matrix unit (2 ~ 20 μm) and restraint effect of the rigid porous ceramic preform on suppressing oxide film crack on the small matrix unit surface were proposed. Thus, chemical route to disrupt oxide film on the small matrix unit surface should be preferred in braze composition design. For example, Al-27Cu-5Si-2Mg-1Ti braze was developed by co-addition of Mg and Ti to improve wettability and to in situ reinforce bond seam, respectively; Ti also could remedy Mg loss for improving wettability. [ABSTRACT FROM AUTHOR]

The characterization of the CuInSe 2 (CIS), CuInGaSe (CIGS) and CuGaSe 2 (CGS) based semiconductor thin films are very important role for solar cell and various nonlinear optical applications. In this paper, the amorphous CuIn 0.7 Ga 0.3 (Se 1−x Te x ) 2 semiconductor thin films (0 ≤ x ≤ 1) were prepared with 60 nm thicknesses by using vacuum evaporation technique. The nonlinear absorption properties and ultrafast transient characteristics were investigated by using open aperture Z-scan and ultrafast pump-probe techniques. The energy bandgap values were calculated by using linear absorption spectra. The bandgap values are found to be varying from 0.67 eV to 1.25 eV for CuIn 0.7 Ga 0.3 Te 2 , CuIn 0.7 Ga 0.3 Se 1.6 Te 0.4 , CuIn 0.7 Ga 0.3 Se 0.4 Te 1.6 and CuIn 0.7 Ga 0.3 Se 2 thin films. The energy bandgap values decrease with increasing telluride (Te) doping ratio in mixed CuIn 0.7 Ga 0.3 (Se 1−x Te x ) 2 films. This affects nonlinear characteristics and ultrafast dynamics of amorphous thin films. Ultrafast pump-probe experiments indicated that decreasing of bandgap values with increasing the Te amount switches from the excited state absorption signals to ultrafast bleaching signals. Open aperture Z-scan experiments show that nonlinear absorption properties enhance with decreasing bandgaps values for 65 ps pulse duration at 1064 nm. Highest nonlinear absorption coefficient was found for CuIn 0.7 Ga 0.3 Te 2 thin film due to having the smallest energy bandgap. [ABSTRACT FROM AUTHOR]

The pre-conceptual design for a European pulsed fusion reactor (DEMO1) is ongoing and one of the most challenging activities within scenario modeling studies deals with numerical investigations of DEMO1 transient phases. This paper presents an investigation on both ramp-up and ramp-down phases by selected plasma trajectories. Plasma evolution has a clear impact on the engineering design of the reactor, e.g. on auxiliary power systems, current ramp-rates and requirements on the coil system. Studies on ramp-up have been carried out with the fast tokamak simulator METIS to highlight the effects of different ramp-up options in terms of robustness of access to the desired flat-top scenario. Particular attention has been paid to requirements on heating systems and plasma position controllability. A dedicated heating power during ramp-up, in addition to the one required during flat-top, appears to be necessary for reliable access to H-mode. The ramp-down phase poses specific issues on vertical stability due to the complex plasma evolution. Ramp-down trajectories with controllable plasma boundaries generated by the CREATE NL code have been coupled to 1.5D transport simulations by means of the JINTRAC transport suite of codes. The results show the necessity of additional ramp-down heating power to avoid a radiative plasma collapse and to control the current density profile. Reducing the current ramp-rate in the ramp-down phase can help the controllability of the plasma. [ABSTRACT FROM AUTHOR]

Shell has developed a novel mono-diameter well concept for oil and gas wells as opposed to the traditional telescopic well design. A Mono- diameter well contains multiple casing sections with the same internal diameter. This is achieved by expansion of the casing sections concerned using an expansion cone. Since the well is drilled in stages and casings are inserted to support the open hole, an overlap section between two consecutive (expandable) casings exists which has to be expanded. When the cone enters the overlap section, the expansion force increases dramatically due to the expansion of two casings, cured cement and formation layers. When the cone finalizes the expansion of the overlap section it pops out, the expansion force vanishes and the cone accelerates upwards and it generates an empty volume to be filled by the well fluid (mud). As a result of this, fluid starts to flow through the drill pipe, around the cone and the fluid volume below the cone starts to decompress. This induces a surge pressure wave traveling upwards and a swab pressure wave in the expanded casing traveling downwards. If the pressure difference between outside and inside of the expanded casing exceeds the collapse rating of the casing, the casing will collapse which leads to the loss of the concerned well section. Repair of such a failure costs time and money, therefore this swab pressure must be well predicted to enable the installation process to be designed such that this collapse can be avoided. A model of fully coupled fluid-structure interaction between cone and the well fluid is built for calculating the swab pressure propagating downward and surge pressure propagating upward resulted from transient process occurring after cone pops out. This model has shown an effective tool for predicting the swabbing pressure in field deployments performed lately in Gulf of Mexico and according to its output the suitable cone is selected in order to avoid the casing collapse. [ABSTRACT FROM AUTHOR]

This paper presents human–robot cooperation with adaptive behavior of the robot, which helps the human operator to perform the cooperative task and optimizes its performance. A novel adaptive impedance control is proposed for the robotic manipulator, whose end-effector's motions are constrained by human arm motion limits. In order to minimized motion tracking errors and acquire an optimal impedance mode of human arms, the linear quadratic regulation (LQR) is formulated; then, integral reinforcement learning (IRL) has been proposed to solve the given LQR with little information of the human arm model. Considering human–robot interaction force during the robot performing manipulation, a novel barrier-Lyapunov-function-based adaptive impedance control incorporating adaptive parameter learning is developed for physical limits, transient perturbations, and time-varying dynamics. Experimental results validate that the proposed controller is effective in assisting the operator to perform the human–robot cooperative task. [ABSTRACT FROM PUBLISHER]

A new non-fullerene small molecule with an acceptor-donor-acceptor (A-D-A) structure, FDNCTF, incorporating fluorenedicyclopentathiophene as core and naphthyl-fused indanone as end groups, was designed and synthesized. Compared with the previous molecule FDICTF with the phenyl-fused indanone as the end groups, the extended π-conjugation at the end group has only little impact on its molecular orbital energy levels, and thus, the open-circuit voltage (Voc) of its solar cell devices has been kept high. However, its light absorption and mobility, together with the short-current density (Jsc) and the fill factor (FF), of its devices have been all improved simultaneously. Through morphology, transient absorption, and theoretical studies, it is believed that these favorable changes are caused by (1) the appropriately enhanced molecular interaction between donor/acceptor which makes the charge separation at the interface more efficient, and (2) enhanced light absorption and more ordered packing at solid state, all due to the extended end-group conjugation of this molecule. With these, the solar cells with FDNCTF as the acceptor and a wide band gap polymer PBDB-T as the donor demonstrated a high power conversion efficiency (PCE) of 11.2% with an enhanced Jsc and a maintained high Voc, and significantly improved FF of 72.7% compared with that of the devices of FDICTF with the phenyl-fused indanone as the end groups. These results indicate that the unexplored conjugation size of the end group plays a critical role for the performance of their solar cell devices. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic thermal-mechanical model to investigate the thermal characteristics in a spindle-bearing system. In this model, transient thermal analysis, static structure analysis and calculation of the boundary conditions are conducted as a solution loop. The transient boundary conditions, such as bearing stiffness, bearing heat generation and thermal contact conductance, are calculated with the appropriate formulas and solution methodology. The thermal feedbacks, which are seldom considered in the previous studies, are calculated in details. In order to validate the prediction accuracy, thermal equilibrium experiment is conducted on a test rig of spindle-bearing system. The predictions of the proposed model, such as bearing preload, temperature and thermal displacements, are in close agreement with the experiment results. The comparisons of the proposed model with two traditional simulations show that, the thermal feedbacks on the boundary conditions and thermal contact conductance are of great importance to the real-time estimation of the thermal characteristics. The proposed model provides a practical method to improve the prediction accuracy. It could also be generalized in other mechanical systems to investigate the dynamic thermal characteristics. [ABSTRACT FROM AUTHOR]

Meta-C−H functionalization of benzylamines has been developed using a PdII/transient mediator strategy. Using 2-pyridone ligands and 2-carbomethoxynorbornene (NBE-CO2Me) as the mediator, arylation, amination, and chlorination of benzylamines are realized. This protocol features a broad substrate scope and is compatible with heterocylic coupling partners. Moreover, the loading of the Pd can be lowered to 2.5 mol % by using the optimal ligand. [ABSTRACT FROM AUTHOR]

Transient-based methods for fault diagnosis of induction machines (IMs) are attracting a rising interest, due to their reliability and ability to adapt to a wide range of IM’s working conditions. These methods compute the time–frequency (TF) distribution of the stator current, where the patterns of the related fault components can be detected. A significant amount of recent proposals in this field have focused on improving the resolution of the TF distributions, allowing a better discrimination and identification of fault harmonic components. Nevertheless, as the resolution improves, computational requirements (power computing and memory) greatly increase, restricting its implementation in low-cost devices for performing on-line fault diagnosis. To address these drawbacks, in this paper, the use of the short-frequency Fourier transform (SFFT) for fault diagnosis of induction machines working under transient regimes is proposed. The SFFT not only keeps the resolution of traditional techniques, such as the short-time Fourier transform, but also achieves a drastic reduction of computing time and memory resources, making this proposal suitable for on-line fault diagnosis. This method is theoretically introduced and experimentally validated using a laboratory test bench. [ABSTRACT FROM AUTHOR]

For the digital signal processors (DSP), a new approach of detecting soft errors is proposed to overcome the transient fault, named EDIO. The goal of EDIO is to enhance the reliability of a DSP software system with reduced performance overhead, compared to former software fault tolerant techniques. EDIO employs diverse instructions for the sake of furthest exploring errors and increasing performance. The loop optimization delays the fault tolerance latency between errors detecting and errors handling, only in this way can EDIO schedule the software pipeline to reduce performance overhead significantly. We evaluate EDIO by the performance experiments and the ion irradiation experiments, which demonstrate exceptional fault coverage with a reasonable performance cost. Compared to the well-known software approach, EDIO demonstrates 6.4 times average speedup while remaining the ability to detect faults. [ABSTRACT FROM AUTHOR]

The shear-compression specimen was employed to study the hot deformation behavior and microstructure evolution of 7050 aluminum alloy at transient conditions. Rapid drop of the flow curves after the peak stress was the common feature at low temperatures, which resulted in the strain localization along the edges of the deformation zone. The combined deformation features with a competition between compression and shear were proved. In the early stage of the deformation, the compression strain played the dominated role. Instead, the shear strain became the main strain path in the subsequent stage. For the large equivalent strain and high strain rate, the dynamic microstructure evolution was enhanced. Moreover, the dynamic recrystallization exhibited multiple features in term of geometric, discontinuous and continuous recrystallization. Finally, the relations between flow behavior and microstructure evolution were presented and discussed. [ABSTRACT FROM AUTHOR]

Sparsity-aware adaptive algorithms present some advantages over standard ones, specially due to the fact that they have faster convergence rate. This paper proposes a stochastic model for both l 0 -LMS and l 0 -NLMS algorithms, and carries out an accurate transient analysis of these algorithms without requiring the input signal to be white. Some previously unreported learning properties of these algorithms are revealed by the proposed framework, which are confirmed by experimental evidence. [ABSTRACT FROM AUTHOR]

The application of queueing network models to real-world applications often involves the task of estimating the service demand placed by requests at queueing nodes. In this article, we propose a methodology to estimate service demands in closed multiclass queueing networks based on Gibbs sampling. Our methodology requires measurements of the number of jobs at resources and can accept prior probabilities on the demands. Gibbs sampling is challenging to apply to estimation problems for queueing networks since it requires one to efficiently evaluate a likelihood function on the measured data. This likelihood function depends on the equilibrium solution of the network, which is difficult to compute in closed models due to the presence of the normalizing constant of the equilibrium state probabilities. To tackle this obstacle, we define a novel iterative approximation of the normalizing constant and show the improved accuracy of this approach, compared to existing methods, for use in conjunction with Gibbs sampling. We also demonstrate that, as a demand estimation tool, Gibbs sampling outperforms other popular Markov Chain Monte Carlo approximations. Experimental validation based on traces from a cloud application demonstrates the effectiveness of Gibbs sampling for service demand estimation in real-world studies. [ABSTRACT FROM AUTHOR]

In the planning of steady-state simulations, a central issue is the initial transient problem, in which an initial segment of the simulation output is adversely contaminated by initialization bias. Our article makes several contributions toward the analysis of this computational challenge. To begin, we introduce useful ways for measuring the magnitude of the initial transient effect in the single replication setting. We then analyze the marginal standard error rule (MSER) and prove that MSER&#8217;s deletion point is determined, as the simulation time horizon tends to infinity, by the minimizer of a certain random walk. We use this insight, together with fluid limit intuition associated with queueing models, to generate two nonpathological examples in which at least one variant of MSER fails to accurately predict the duration of the initial transient. Our results suggest that the efficacy of a deletion procedure is sensitive to the choice of performance measure, and that the set of standard test problems on which initial transient procedures are tested should be significantly broadened. [ABSTRACT FROM AUTHOR]

Structured models are population models in which the individuals are characterized with respect to the value of some variable of interest, called the structure variable. In the present paper, we propose a glycemia-structured population model, based on a linear partial differential equation with variable coefficients. The model is characterized by three rate functions: a new-adult population glycemic profile, a glycemia-dependent mortality rate and a glycemia-dependent average worsening rate. First, we formally analyze some properties of the solution, the transient behavior and the equilibrium distribution. Then, we identify the key parameters and functions of the model from real-life data and we hypothesize some plausible modifications of the rate functions to obtain a more beneficial steady-state behavior. The interest of the model is that, while it summarizes the evolution of diabetes in the population in a completely different way with respect to previously published Monte Carlo aggregations of individual-based models, it does appear to offer a good approximation of observed reality and of the features expected in the clinical setting. The model can offer insights in pharmaceutical research and be used to assess possible public health intervention strategies. [ABSTRACT FROM AUTHOR]

In this paper we investigate the applicability of flow equivalence to transient analysis with the specific aim of reducing the computational complexity of the solution of complex queuing networks. It is well-known that flow equivalent servers lead to exact steady state solution in many cases, and specifically when applied for the steady-state analysis of Product Form Queuing Networks (PFQN). We show that exact results can be obtained even in the transient phase of the study of PFQNs, but the definition of the equivalent server requires the analysis of the whole original network. We propose thus to use approximate aggregate servers whose characterization demands much less computation. Specifically, the characterization corresponds to the steady state equivalent server of the stations that we aim to aggregate and thus can be achieved by analyzing the involved stations in isolation. This way, approximations can be derived for any queuing network, but the precision of the results depends heavily on the topology and on the parameters of the model. To identify the cases in which the approach is likely to provide acceptable results, structural and behavioral criteria are proposed that are computationally inexpensive and that can be preliminarily applied to a queuing network before starting its analysis. We motivate our findings with the study of several small models, but we subsequently show the relevance of our methodology by applying it to a web service case study derived from the literature. Results are computed to assess the effectiveness of possible design choices and the impact of certain reconfiguration strategies on the possibility of satisfying possible Service Level Agreements. [ABSTRACT FROM AUTHOR]

This work describes the development of a hybrid finite element strategy for modeling the nonlinear, strongly coupled electromechanical equations governing micro-electro-mechanical systems (MEMS) structures in general and the phenomena of static and dynamic pull-in exhibited by such structures in particular. It is known that conventional finite elements 'lock' severely for thin plate or shell-type structures (which is typical of geometries that occur in microsystems). The developed hybrid finite element formulation is based on a two-field variational formulation and involves an independent interpolation of the displacement and stress fields. In a conventional structural analysis, it is known that hybrid finite elements are much more immune to volumetric, shear, and membrane locking compared with conventional elements. This work extends the hybrid finite element method to the analysis of MEMS structures. Such an extension is not straightforward due to the strong coupling with the electric field variables. The formulation is based on a total Lagrangian description and is monolithic. This combination of the hybrid strategy and the monolithic scheme results in very good coarse-mesh accuracy and quadratic convergence both within the context of the static and transient formulations that have been developed. Numerous examples from the literature are considered to demonstrate the high efficacy of the developed method. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this article, large displacement static and transient behavior of moderately thick deep functionally graded curved beams with constant curvature are investigated using generalized differential quadrature method. Equilibrium equations for static and dynamic responses are obtained using the virtual work principle. Spatial derivatives in the equilibrium equations are expressed with the generalized differential quadrature method. Large displacements are taken into account using Green–Lagrange nonlinear strain–displacement relations that are derived from elasticity theory equations. Transverse shear effect is considered through the first-order shear deformation theory. Static and dynamic equilibrium equations are solved using Newton and Newmark methods respectively. Several curved beam problems with different level of deepness is solved with the proposed method. Effect of functionally graded material properties on the behavior of curved beam is investigated using various ceramic and metal combinations such as Zirconia/Aluminum, Alumina/Aluminum, Zirconia/Monel, Silicon Nitride/Steel and Alumina/Steel materials in analyses. [ABSTRACT FROM AUTHOR]

The transient overvoltages associated to the interruption of high direct currents with high current derivative, at the base of the operation of a Quench Protection System for Superconducting Coils, have been studied, with particular reference to the JT-60SA project, which adopt edge technology solutions for current interruption: a Hybrid mechanical-static Circuit Breaker as main circuit breaker in series with a PyroBreaker as backup protection. The paper reports in particular on the analyses of the intervention of the backup circuit breaker in the final circuital conditions, considering the actual power connections that will be implemented on Site. The key elements which influence the peak value of the voltage and the relation existing among the different stray impedances of the circuit are identified, thus giving general guidelines for the design of the layout of the power connections. The specific case of JT-60SA is considered, but general criteria can be derived. [ABSTRACT FROM AUTHOR]

A shunt for measuring pulse currents with an amplitude of up to 200 kA, the resistive part of which takes the form of a corrugated tube, is proposed. This enables the length of the shunt to be increased without increasing the inductance, and it increases the strength of the tube and reduces the wall thickness, and hence reduces the rise time of the transient characteristic (it broadens the passband). [ABSTRACT FROM AUTHOR]

Most researches on shale gas production and pressure transient analysis placed more emphasis on single-phase flow, the two-phase flow caused by flowback after hydrofracture in shale gas reservoirs does not attract much attention. This paper presents a two-phase pressure transient analysis model of multi-stage fractured horizontal well with the consideration of wellbore storage, skin effect, two-phase saturation, hydraulic fractures parameters and desorption characteristics of shale gas reservoirs. Accurate solution to this flow model is obtained by the use of source function theory, Laplace transform, three-dimensional eigenvalue method and orthogonal transformation. Pseudo-pressure and pseudo-pressure derivative type curve is plotted by using the Stehfest algorithm. Seven different flow regimes have been identified and the effects of influence factors such as initial saturation, skin factor, absorption index, fracture stages, horizontal well lateral length and wellbore storage coefficient have also been discussed. The presents research could be used to interpret the pressure behavior more accurately and effectively of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

In the framework of the current IFMIF Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) phase, ENEA is responsible for the design of the European concept of the IFMIF lithium target system which foresees the possibility to periodically replace only the most irradiated and thus critical component (i.e., the backplate) while continuing to operate the rest of the target for a longer period (bayonet backplate concept). With the objective of evaluating the performances of the system in terms of temperature, stress and displacement fields evolution during start-up and shutdown phases, an uncoupled thermomechanical transient analysis has been performed in close collaboration with the University of Palermo by means of a qualified finite element (FE) thermomechanical code. The calculations employed a realistic 3D time-dependent FE model which takes into account all the mechanical and thermal loads including the nuclear heating due to neutron and prompt gamma fields during start-up and decay power of activated products during shutdown. The nuclear data have been calculated by ENEA as part of a parallel extensive neutronic analysis carried out through the MCNP transport code and the EASY-2010 activation code package and then passed as input to the thermomechanical FE model. In this paper, the results of the above transient analyses are reported, highlighting the relevant indications obtained with respect to the fulfillment of the design requirements and possible hints for improving the system design. In particular, it is found that ITER design rules taking into account secondary loads are not always fulfilled during the transient, whereas the predicted displacements allow to exclude any contact of the target system with the surrounding structures. [ABSTRACT FROM AUTHOR]

This paper focuses on the motion control of a camless engine valve actuation system during both steady state and transient engine operation. The precise tracking performance obtained using controllers based on the internal model principle for the constant speed case motivates the investigation under engine speed transients. The cyclic but aperiodic reference signal to be tracked is modeled using two different methods, i.e., as a combination of frequency varying sinusoids in the time domain or as a repetitive (periodic) signal in the rotational angle domain. The recently developed time-varying internal model-based controller is ideally suited for both the approaches. The details associated with the design of the controller for each of the approaches are first documented. A quantitative analysis comparing various performance metrics for both the approaches helps to highlight the relative advantages of each method. The experimental results from a prototype camless engine valve actuation system are then presented to help in validating the overall effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Abstract: We present a CMOS low-dropout voltage regulator with a high-speed NMOS compact driver suitable for supplying on-chip voltages for the digital core of a SoC. The LDO is part of a power management controller hardblock integrated within a microcontroller. The die area of the circuit implemented in a 90nm CMOS process is only 0.054mm2. Experimental results show that the developed LDO can supply up to 15mA and it presents a very fast transient response, with a settling time of approximately 30ns and a voltage drop of 200mV when the load current changes from 100nA to 9mA. [Copyright &y& Elsevier]

Abstract: We develop a pseudo two-dimensional, isothermal transient model for a high temperature proton exchange membrane fuel cell. It takes into account the dynamic change of oxygen concentration in the cathode gas diffusion layer and in the cathode channel. The model can be used to simulate and analyze electrochemical impedance spectra of the cell in both potentiostatic and galvanostatic modes, current interrupt results and step changes in the cell current or potential. The model is validated by fitting experimental data. [Copyright &y& Elsevier]

This paper deals with the two most used arresters models applied in digital simulations with the Alternative Transients Program, the conventional, and IEEE models. It presents a model analysis and parameter adjustment procedures to the conventional model. It also presents an application to both models of different types of current and voltage surges and even power frequency voltage, with a comparison of the results obtained with both models and with typical manufacturer data. While adjustment of the IEEE model was difficult and laborious, the conventional model presented a straightforward procedure. The results obtained show that there is a close agreement between the two models when the surge front time is above 1/2\ \mus. The conventional model always presents higher values for the limiting and residual voltages, and better agreement with the typical manufacturer data. Thus, the conventional model presents the advantages of simplicity and more conservative results. [ABSTRACT FROM PUBLISHER]

We have studied the optical response and dynamical behavior of photocarriers in BiFeO3 thin films by means of transient absorption (TA) and photocurrent (PC) measurements. PC and absorption spectroscopy indicate that BiFeO3 thin films have an indirect band gap energy of ∼2.4 eV. The TA and PC decay dynamics have fast (∼1 ns) and slow (∼ 100 ns) components that are attributed to the localization of free carriers to shallow trap states and the recombination of trapped carriers, respectively. The long decay time of the PC is caused by the thermal activation of trapped carriers into the conduction band. Long-lived trapped photocarriers can be linked to the ferroelectricity and give rise to unique photoinduced phenomena in BiFeO3. [ABSTRACT FROM AUTHOR]

Compared with the traditional load monitoring system, a nonintrusive load monitoring (NILM) system is simple to install and does not need an individual sensor for each load. Accordingly, the NILM system can be applied for wide load monitoring and become a powerful energy management and measurement system. Although several NILM algorithms have been developed during the last two decades, recognition accuracy and computational efficiency remain as challenges. To minimize training time and improve recognition accuracy, particle swarm optimization is adopted in this paper to optimize parameters of training algorithms in artificial neural networks. The proposed algorithm is verified through the combination of Electromagnetic Transients Program simulations and field measurements. The results indicate that the proposed method significantly improves recognition accuracy and computational efficiency under multiple operation conditions. [ABSTRACT FROM AUTHOR]

In this paper the operation and construction of a protective relay tester based on the PCs will be studied. Since this tester has computer, it is capable of programming to test different types of protective relays. On the other hand, because of its 3 phases voltage and current outputs, the hardware of this device makes it possible to test different types of electromagnetic, static, and digital relays. One of the main characteristics of this device is to real time reconstruction of the signals obtained in transient states. Other capabilities of this device include the ability of sending digital signals to the relay in adjustable times, which is widely used including in testing protective plans with telecommunication signals. At the end of paper, the results of some sample tests will be presented that show the good performance using this device in the test of different types of relays. [ABSTRACT FROM AUTHOR]

It was experimentally observed that the electrolysis reaction continues a short period of time - time to relax τc - after the cell power supply is interrupted. This paper presents an analysis of transient phenomena occurring and pr opose technical solutions. [ABSTRACT FROM AUTHOR]

The incoming downward shortwave solar irradiance is harvested to an increasing extent by solar power plants. However, the variable nature of this energy source poses an operational challenge for solar power plants and electrical grids. Intra hour solar irradiance nowcasts with a high temporal and spatial resolution could be used to tackle this challenge. All sky imager (ASI) based nowcasting systems fulfill the requirements in terms of temporal and spatial resolution. However, ASI nowcasts can only be used if the required accuracies for applications in solar power plants and electrical grids are fulfilled. Scalar error metrics, such as mean absolute deviation, root mean square deviation, and skill score are commonly used to estimate the accuracy of nowcasting systems. However, these overall error metrics represented by a single number per metric are neither suitable to determine the real time accuracy of a nowcasting system in the actual weather situation, nor suitable to describe any spatially resolved nowcast accuracy. The performance of ASI-based nowcasting systems is strongly related to the prevailing weather conditions. Depending on weather conditions, large discrepancies between the overall and current system uncertainties are conceivable. Furthermore, the nowcast accuracy varies strongly within the irradiance map as higher errors may occur at transient zones close to cloud shadow edges. In this paper, we present a novel approach for the spatially resolved real-time uncertainty specification of ASI-based nowcasting systems. The current irradiance conditions are classified in one of eight distinct temporal direct normal irradiance (DNI) variability classes. For each class and lead-time, an upper and lower uncertainty value is derived from historical data, which describes a coverage probability of 68.3%. This database of uncertainty values is based on deviations of the irradiance maps, compared to three reference pyrheliometers in Tabernas, Andalucia over two years (2016 and 2017). Increased uncertainties due to transient effects are considered by detecting transient zones close to cloud shadow edges within the DNI map. The width of the transient zones is estimated by the current average cloud height, cloud speed, lead-time, and Sun position. The final spatially resolved uncertainties are validated with three reference pyrheliometers, using a data set consisting of the entire year 2018. Furthermore, we developed a procedure based on the DNI temporal variability classes to estimate the expected average uncertainties of the nowcasting system at any geographical location. The novel method can also be applied for global tilted or horizontal irradiance and is assumed to improve the applicability of the ASI nowcasts. [ABSTRACT FROM AUTHOR]

Constant on-time (COT) control has been widely applied in industrial applications due to its fast transient response. However, the conventional COT controlled buck converter has poor output-regulation accuracy. A new control method, called improved COT (ICOT) control, that provides both high output-regulation accuracy and fast transient response for the buck converter is proposed. Circuit simulation results validate the correctness of the theoretical analysis. [ABSTRACT FROM AUTHOR]