Transient Time Research Articles

The impact of vascular volume fraction and compressibility of the interstitial matrix on vascularised poroelastic tissues.

In this work we address the role of the microstructural properties of a vascularised poroelastic material, characterised by the coupling between a poroelastic matrix and a viscous fluid vessels network, on its overall response in terms of pressures, velocities and stress maps. We embrace the recently developed model (Penta and Merodio in Meccanica 52(14):3321-3343, 2017) as a theoretical starting point and present the results obtained by solving the full interplay between the microscale, represented by the intervessels' distance, and the macroscale, representing the size of the overall tissue. We encode the influence of the vessels' density and the poroelastic matrix compressibility in the poroelastic coefficients of the model, which are obtained by solving appropriate periodic cell problem at the microscale. The double-poroelastic model (Penta and Merodio 2017) is then solved at the macroscale in the context of vascular tumours, for different values of vessels' walls permeability. The results clearly indicate that improving the compressibility of the matrix and decreasing the vessels' density enhances the transvascular pressure difference and hence transport of fluid and drug within a tumour mass after a transient time. Our results suggest to combine vessel and interstitial normalization in tumours to allow for better drug delivery into the lesions.

Vibrational Dichroism of Chiral Valley Phonons.

Valley degrees of freedom in transition metal dichalcogenides thoroughly influence electron-phonon coupling and its nonequilibrium dynamics. We conducted a first-principles study of the quantum kinetics of chiral phonons following valley-selective carrier excitation with circularly polarized light. Our numerical investigations treat the ultrafast dynamics of electrons and phonons on equal footing within a parameter-free ab initio framework. We report the emergence of valley-polarized phonon populations in monolayer MoS2 that can be selectively excited at either the K or K' valleys depending on the light helicity. The resulting vibrational state is characterized by a distinctive chirality, which lifts time-reversal symmetry of the lattice on transient time scales. We show that chiral valley phonons can further lead to fingerprints of vibrational dichroism detectable by ultrafast diffuse scattering and persist beyond 10 ps. The valley polarization of nonequilibrium phonon populations could be exploited as an information carrier, thereby extending the paradigm of valleytronics to the domain of vibrational excitations.

Each step time-limited iterative learning control for a cushion robot with motion velocity constraints

An each step time-limited iterative learning control model was developed for a cushion robot with velocity constraints. A predictive modeling method was proposed to solve the velocity mutation problem by employing a kinematic model to constrain the velocity inputs, which can then constrain the robot’s actual velocity. Furthermore, a tracking error system was established that used constrained motion velocity and a dynamic model. A new iterative controller with each step time-limited learning was built to reduce the transient adjustment time. Simulation results and comparative analyses revealed that the proposed control method quickly stabilizes the system and ensures that the human–robot system operates at a safe velocity.

Abstract GS.11: Exercise Therapy During Doxorubicin Treatment Provides Sex-specific Cardioprotection

Moderate-intensity exercise is routinely prescribed to patients with cardiovascular diseases to improve cardiac function. It has also been recommended in patients undergoing anti-cancer chemotherapy to attenuate cardiotoxic effects. We recently identified that moderate endurance exercise in healthy mice causes the remodeling of cardiac physiology in a sex-specific manner. Therefore, we hypothesized that exercise therapy applied during doxorubicin chemotherapy would produce sex-specific cardioprotection. Male and female mice were divided into three groups, 1) sedentary control, 2) DOX - doxorubicin treated at 5 mg/kg/week for 6 weeks, and 3) EXDOX - 2 weeks of forced treadmill running for 2 weeks before DOX + exercise for an additional 6 weeks. Mouse health was tracked daily. Total body weight, echocardiography, and electrocardiography were assessed every 2 weeks. At the end of the protocol, triple parametric optical mapping was performed to determine the remodeling of cardiac metabolism-excitation-contraction coupling (MECC). DOX treatment increased morbidity and reduced total body weight in both males and females. DOX-induced action potential duration (APD) prolongation in both sexes and, additionally, in males alone, increased anisotropic ratio of conduction (index for arrhythmogenicity) and rise time of calcium transients (CaRT). In EXDOX mice, the onset of morbidity was delayed in both males and females compared to DOX mice. Total body weight in male EXDOX mice, but not females, was further reduced compared to DOX treatment alone. Echocardiography revealed increased LV wall thickness in male and female EXDOX mice vs DOX, while stroke volume was reduced in females alone. Next, DOX-induced APD prolongation was prevented in EXDOX females but not males. Furthermore, DOX-induced increase in CaRT was further increased in EXDOX males, in addition to increased calcium transient duration and reduced calcium decay constant. Taken together, these data suggest significant sex dimorphism in cardiac adaptation to DOX treatment and exercise therapy during DOX treatment. Female mice undergoing exercise therapy during DOX treatment demonstrated greater cardioprotection and attenuation of MECC remodeling.

A study on transient overvoltage caused by HVDC tie blocking in multi-rectifier systems

In a multi-rectifier AC-DC system the blocking of a HVDC tie can cause severe transient overvoltage problems, which may trip off the renewable energy sources, endangering the safe operation of the system. This paper shows that the blocking of a HVDC tie can introduce two types of transient overvoltage. For Type I overvoltage, which is caused by the surplus reactive power injection immediately after the blocking, a simple estimation formula is proposed. Suppression strategies that can decrease the key matrix are examined using a matrix-theoretic approach. The formula is applicable for system integrated with renewable energy sources and it has reasonable accuracy for overvoltage level of interest. To study Type II overvoltage, a reduced-order mathematical model is first derived with singular perturbation method. Then it is demonstrated that this type of overvoltage is due to the increase of transient electromotive force of synchronous machines, and an analytical calculation procedure is suggested. In addition, it is found that the voltage subsystem of a multi-rectifier system is an input–output monotonic system with nice order-preserving properties. Increasing the proportional gain constant of excitation system or choosing generators with large open-circuit transient time constant can monotonically decrease this type of overvoltage. The simulations of an actual large-scale multi-rectifier system in China are described to validate the introduced results.

Ultrafast Plasmonic Hot Hole Transfer and Plasmon Dynamics in a Dual Plasmonic Au@p‐Cu2−xSe Heterostructure

AbstractMetal‐semiconductor heterostructures have significant potential in harvesting plasmon induced hot charge carriers for photocatalytic and photovoltaic devices. Despite numerous studies, the field of hot hole transfer in heterostructures remains unexplored. In this work, the plasmon dynamics of a dual plasmonic core–shell Au@p‐Cu2−xSe heterostructure are investigated with the aid of femtosecond broadband pump probe spectroscopy. Ultrafast studies reveal that hot holes generated within the d and sp band after 400 and 800 nm excitations are injected from Au to copper selenide. Hot hole transfer substantially reduces the transient signal intensity and electron phonon relaxation time for Au plasmon. Increment in the transient signal intensity and slower kinetics for the semiconducting plasmon of Au@Cu2−xSe validate the hot hole transfer in the valence band of copper selenide. Fluence dependent studies reveal that d band hot holes extraction is more efficient than that of sp band hot holes.

Effects of Transient Liquid Phase Bonding Time on Microstructure, Mechanical and Corrosion Properties During Bonding of Inconel 617/AISI 310 Stainless Steel

Effects of Transient Liquid Phase Bonding Time on Microstructure, Mechanical and Corrosion Properties During Bonding of Inconel 617/AISI 310 Stainless Steel

Design of an integrated SEPIC and Buck Converter for High Step-down Applications

To overcome the issues related to special power supply called voltage regulator module (VRM) used for microprocessors, a special DC-DC converter will be designed in this work in which single-ended primary inductor (SEPIC) converter and the inverted form of buck converter are combine. As per available literature the problems associated with conventional VRM’s are slow transient response and narrow duty cycle. Other issue related to the voltage regulator module is the high voltage stress that occurs on switches of VRM. The solution to these problems is presented in the form of a new proposed dc-dc converter topology in which the single ended primary inductor is combined with the inverted form of buck converter. The proposed topology has the advantages of reducing the transient time at moderate duty cycle because of the parallel combination of the inductor. Similarly, the parallel combination of capacitor will step down the voltage from 12v to the appropriate voltage level required for the microprocessor. The steady state operation and transient state operation of the proposed VRM is discussed in this thesis. Various operating states of proposed converter are discussed and related equations for voltage gain, voltage stress and transient response have been derived. Output waveforms are plotted, and mathematical modeling is carried out. Simulation results for proposed and conventional VRM are obtained and from comparison of results, it is clear that proposed VRM is good in performances compared to conventional VRM’s.

Design of an integrated SEPIC and Buck Converter for High Step-down Applications

To overcome the issues related to special power supply called voltage regulator module (VRM) used for microprocessors, a special DC-DC converter will be designed in this work in which single-ended primary inductor (SEPIC) converter and the inverted form of buck converter are combine. As per available literature the problems associated with conventional VRM’s are slow transient response and narrow duty cycle. Other issue related to the voltage regulator module is the high voltage stress that occurs on switches of VRM. The solution to these problems is presented in the form of a new proposed dc-dc converter topology in which the single ended primary inductor is combined with the inverted form of buck converter. The proposed topology has the advantages of reducing the transient time at moderate duty cycle because of the parallel combination of the inductor. Similarly, the parallel combination of capacitor will step down the voltage from 12v to the appropriate voltage level required for the microprocessor. The steady state operation and transient state operation of the proposed VRM is discussed in this thesis. Various operating states of proposed converter are discussed and related equations for voltage gain, voltage stress and transient response have been derived. Output waveforms are plotted, and mathematical modeling is carried out. Simulation results for proposed and conventional VRM are obtained and from comparison of results, it is clear that proposed VRM is good in performances compared to conventional VRM’s.

Small-Signal Stability Modeling, Sensitivity Analysis, and Parameter Optimization of Improved Virtual Synchronous Machine Based Standalone Inverter

The virtual synchronous machine (VSM) concept is emerging as a flexible approach for controlling power electronic converters in grid-connected and standalone applications. In this study, we have used the mathematical model of a Virtual machine with a virtual exciter and governor for the standalone inverter to optimize the parameter for small-signal stability. Firstly, the small-signal models of virtual synchronous generator with load have developed, and subsequently, the system eigenvalues were obtained by solving the state Jacobian matrix. Next, the sensitivity of the eigenvalue location on controller parameters has been studied. The parameters are optimized on the basis of the location of dominant eigenvalues using a genetic algorithm. Finally, the optimal controller parameters are used to test the system’s dynamics by solving the model equations with Ordinary Differential Equation (ODE) solver. Moreover, our conclusions were also tested using the actual switching devices on Matlab/Simulink. The results indicate that the frequency stability can be enhanced drastically by optimizing a wide range of VSM parameters. The frequency stability sensitivity with respect to load variation has been improved. The transient settling time of system response for optimized values is 0.25 sec which is only 5% of that for general values. The results of this work are relevant for the VSM-based microgrid small-signal stability analysis.

A peak-current mode boost converter with fast linear transient response

This paper proposes a peak-current mode boost converter with fast linear transient response. To achieve this, a fast linear transient response circuit is proposed, which can directly reflect the change in the input voltage to the voltage on the zero-compensation capacitor of the error amplifier, thus effectively reducing the transient ripple and recovery time of the output voltage. The proposed circuit was simulated using a 90 nm BCD process. Results show that when the power supply voltage changes from 1.8V to 2.4V, the overshoot of the output voltage reduced from 189 mV to 62 mV, and the recovery time reduced from 117μs to 73μs. Similarly, when the power supply voltage changes from 2.4V to 1.8V, the undershoot of the output voltage reduced from 161 mV to 68 mV, and the recovery time reduced from 90μs to 45μs. In addition, the converter only occupies an area of 0.92 mm2. Its quiescent current is only 19 μA and the work efficiency is higher than 90%.

Efficacy of velocity feedback control for suppression of the friction-induced oscillation due to mode-coupling instability in a two degrees-of-freedom mechanical system

The present article focuses on suppressing mode-coupling instability in frictional systems, which can cause unwanted vibrations such as squeal in braking systems. Mode-coupling instability occurs when two or more modes of a system approach each other. This article proposes the use of resonant velocity feedback control to eliminate friction-induced oscillations generated by mode-coupling instability. A two degree-of-freedom linear model is used to capture the instability due to friction-induced mode coupling. The efficacy of the control is demonstrated through linear stability analysis, and by optimizing control parameters using pole crossover method to minimize the transient time of the response. The robustness analysis demonstrates the ability of the control to effectively mitigate the instability even under parametric perturbations. The controlled system is simulated in MATLAB Simulink to validate analytical results. The effects of time delay, which is commonly present in feedback systems, are also investigated. Finally, the effectiveness of the control is studied in the presence of nonlinearity in the system. The nonlinear dynamics are analyzed by creating bifurcation diagrams with different bifurcation parameters.

Microcontroller-Based Trapezoidal Slope Compensation Technique for Peak Current Mode Control at MHz Frequencies

Slope compensation is necessary for the peak cur-rent mode control technique to ensure the stability of the power converter. Micro-controllers (μCs) existing in the market implement the slope compensation using built-in digital to analog converters (DACs). DACs exhibit finite transient times, which can be negligible when the μCs are used to control the power converters at switching frequencies in the order of a few hundreds of kHz. However, for high device switching frequency (HDSF) operation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq 1\, \rm{MHz}$</tex-math></inline-formula> ), the DAC transient time becomes significant and can make it difficult, if not impossible, to achieve the conventional ramp slope compensation. Hence, in this paper, a novel concept of ‘trapezoidal’ slope compensation is proposed by considering the transient time of the μC. A detailed analysis is performed to understand the effect of the transient period on the converter stability. The proposed technique is validated with an experimental prototype of 400 W at 1 MHz switching frequency and it is shown to ensure stability of the converter at all operating points within the specification.

Criticality in transient behavior of coupled oscillator system toward chimera and synchronization.

Chimera states in spatiotemporal dynamical systems have been investigated in physical, chemical, and biological systems, while how the system is steering toward different final destinies upon spatially localized perturbation is still unknown. Through a systematic numerical analysis of the evolution of the spatiotemporal patterns of multi-chimera states, we uncover a critical behavior of the system in transient time toward either chimera or synchronization as the final stable state. We measure the critical values and the transient time of chimeras with different numbers of clusters. Then, based on an adequate verification, we fit and analyze the distribution of the transient time, which obeys power-law variation process with the increase in perturbation strengths. Moreover, the comparison between different clusters exhibits an interesting phenomenon, thus we find that the critical value of odd and even clusters will alternatively converge into a certain value from two sides, respectively, implying that this critical behavior can be modeled and enabling the articulation of a phenomenological model.

Statistical methods and its applications in Whey protein binding (Bos Taurus)

Milk is made up of two proteins, such as casein (80%) and whey (20%). These proteins, which include membrane globular proteins, glycoproteins, and lipoproteins, are mostly found in the outer layer of milk fat globule membranes. WP can be separated from the casein in milk or formed as a byproduct of cheese making and contains all nine essential amino acids with a low lactose content. Whey protein has many health benefits, including improving strength and body composition, promoting weight loss, boosting metabolism, stifling hunger, maintaining good health, avoiding nourishing the bones, reducing inflammation, promoting quick wound healing, lowering blood pressure, repairing and preserving muscle tissues etc. Many dairy and food-based industries eagerly explore the accurate retention time for the formation of health related new byproducts. As of date, there are very few studies available in the world literature citation database and too many micro and macro studies on WP are currently being undertaken globally, they provide insight into the binding of particular amino acids (Seq. peptides) and their accurate lag time of binding to the formation of "helixes and sheaths. In this paradigm, statistical tool are very important to determine average time and WP algorithms for analysis of seq amino acids and the metabolic pathway's action. Overall, the present research attempts to extrapolate the Seq peptide's binding capacity and its retention time for amino acids in order to fill the aforementioned research gap. For the model demonstration we used the commonly cited whey protein peptide (Seq) NCBS, which was considered to prove the hypothesis. The Markova two state random and Monte Carlo simulation (superimposed artificial neural network) models were formulated to extract transient probabilities and retention times of Seq peptides. As per the results, the binding capacity was found to be excellent with a good retention time (5 to 11.50 minutes) in cross-linked and unlinked cases (10 to 13.50 minutes). Bioinformatics, the dairy industry, and life scientists will find these more recent discoveries to be very helpful for measuring likelihoods and transient probabilities of binding.

Observer based incremental backstepping terminal sliding-mode control with learning rate for a multi-vectored propeller airship

The problem of finite-time trajectory tracking control for a multivectored propeller airship with model parameter uncertainties and unknown disturbances is addressed in the paper. In order to obtain a fast transient response and finite time convergence without singularity, an incremental backstepping nonsingular terminal sliding mode controller is designed to track desired trajectory within finite time. To overcome the limitation of backstepping terminal sliding-mode control design being dependant on prior knowledge, a nonlinear disturbance-observer is designed to estimate the external observable disturbances. Meanwhile, to reduce system chattering when the tracking error reaches the sliding mode surface, an adaptive learning rate design is proposed for the terminal sliding mode controller such that the tracking error approaches the sliding mode surface at a low speed and so the system chattering is restrained. The closed-loop trajectory tracking control system is proved to be stable and finite time convergence by using Lyapunov theory. The results are compared with traditional backstepping sliding mode control and different learning rate based control design, and they demonstrate the averaged tracking error in altitude and pitch motion is reduced more than 30% by using the disturbance-observer based incremental backstepping terminal sliding mode controller for the multivectored propeller airship to execute a realistic trajectory tracking mission, even in the presence of aerodynamic coefficient uncertainties, unknown disturbances.

Stereoelectroencephalography-guided radiofrequency ablation of the epileptogenic zone as a treatment and predictor of future success of further surgical intervention.

Stereoelectroencephalography (SEEG)-guided radiofrequency ablation (RFA) is increasingly being used as a treatment for drug-resistant localization-related epilepsy. The aim of this study is to analyze the successes and failures using RFA and how response correlates with surgical epilepsy treatment outcomes. We retrospectively reviewed 62 patients who underwent RFA via SEEGelectrodes. After excluding five, the remaining 57 were classified into subgroups based on procedures and outcomes. Forty patients (70%) underwent a secondary surgical procedure, of whom 32 were delayed: 26 laser interstitial thermal therapy (LITT), five resection, one neuromodulation. We determined the predictive value of RFA outcome upon subsequent surgical outcome by categorizing the delayed secondary surgery outcome as success (Engel I/II) versus failure (Engel III/IV). Demographic information, epilepsy characteristics, and the transient time of seizure freedom after RFA were calculated for each patient. Twelve of 49 patients (24.5%) who had RFA alone and delayed follow-up achieved Engel class I. Of the 32 patients who underwent a delayed secondary surgical procedure, 15 achieved Engel class I and nine Engel class II (24 successes), and eight were considered failures (Engel class III/IV). The transient time of seizure freedom after RFA was significantly longer in the success group (4 months, SD = 2.6) as compared to the failure group (.75 months, SD = 1.16; p < .001). Additionally, there was a higher portion of preoperative lesional findings in patients in the RFA alone and delayed surgical success group (p = .03) and a longer time to seizure recurrence in the presence of lesions (p < .05). Side effects occurred in 1% of patients. In this series, RFA provided a treatment during SEEG-guided intracranial monitoring that led to seizure freedom in ~25% of patients. Of the 70% who underwent delayed surgery, longer transient time of seizure freedom after RFA was predictive of the results of the secondary surgeries, 74% of which were LITT.

Exponentially Long Transient Time to Synchronization of Coupled Chaotic Circle Maps in Dense Random Networks.

We study the transition to synchronization in large, dense networks of chaotic circle maps, where an exact solution of the mean-field dynamics in the infinite network and all-to-all coupling limit is known. In dense networks of finite size and link probability of smaller than one, the incoherent state is meta-stable for coupling strengths that are larger than the mean-field critical coupling. We observe chaotic transients with exponentially distributed escape times and study the scaling behavior of the mean time to synchronization.

High-Fidelity Transient Analysis with STREAM Based on the Predictor-Corrector Quasi-Static Method

The predictor-corrector quasi-static method (PCQM) is used to solve the transient problem in the STREAM code, a steady-state and transient reactor analysis code with the method of characteristics. In PCQM, the angular neutron flux undergoes a factorized split to form the product of shape and amplitude functions. The time-dependent neutron transport equation is solved to obtain the shape function whereas the amplitude function is obtained by resolving the exact point kinetics equations (EPKEs). A two-level coarse mesh finite difference technique is implemented to reduce the transient running time of the transport solution. Moreover, high-order polynomial interpolation is applied to the kinetics parameters utilized in EPKEs to reduce the error when the reactivity insertion is nonlinear. Several numerical benchmarks are solved to justify the application of the procedure, proving that the method maintains solution accuracy.

Model of a Hybrid Electric Vehicle Equipped with Solid Oxide Fuel Cells Powered by Biomethane

To promote the development of new technologies that allow an intensive use of renewable green energies and to overcome the problem of the lack of range of full electric vehicles, an interesting energy source is biomethane. The Fuel Cells (FCs) systems benefit from high efficiency and zero emissions, and they are generally powered by hydrogen. One of the main problems related to hydrogen FCs is the current weak network of infrastructure’s need to supply the hydrogen itself. An alternative may be the development of FC vehicles powered by methane, or biomethane, to exploit a renewable energy source. The type of Fuel Cells that lends itself to a methane (or biomethane) power supply is the Solid Oxide Fuel Cell (SOFC). Considering the limitations of the SOFCs, a vehicle model powered by Fuel Cells fueled by methane (or biomethane) is created. This work concerns the creation of a vehicle model, and the sizing of the SOFC system (generator delivering a constant 3 kW) and battery pack (30 Ah), for a door-to-door waste collection vehicle, whose mission is known. The latter is a fundamental requirement due to the limitations found for Solid Oxide Fuel Cells: slow transient and long ignition times.