Forward Sweep Research Articles

Optimal treatment strategies to control acute HIV infection.

Various antiretroviral therapies (ART) are administered to symptomatic human immunodeficiency virus (HIV) infected individuals to improve their health. The treatment effectiveness may depend on suppressing development of drug resistance, reduce evolution of new viral strains, minimize serious side effects and the costs of drugs. This paper deals with some results concerning optimal drug administration scheme successful in improving patients' health especially in poorly resourced settings. The model under consideration describes the interaction between the uninfected cells, the latently infected cells, the productively infected cells, and the free viruses. Generally, in viral infection, the drug strategy aspects either the virus infectivity or reduce the virion production. The mathematical model proposed here, deals with both situations with the objective function based on a combination of maximizing benefit relied on T cells count (the white cells that coordinate activities of the immune system) and minimizing the systemic cost. The existence of the optimal control pair is established and the Pontryagin's minimum principle is used to characterize these two optimal controls. The optimality system is derived and solved numerically using the forward and backward sweep method (FBSM). Our results indicate that early initiation of treatment makes a profound impact in both improving the quality of life and reducing the economic costs of therapy.

Sensitivity analysis of an unsteady char particle combustion

Simulations of unsteady char particle combustion rely on various models that are necessary in order to correctly predict the governing flow and combustion processes. These models, in turn, rely on model parameters, which are determined by experiments or small scale simulations and contain a certain level of uncertainty. It is therefore, essential to correctly determine the sensitivities of quantities of interest measured using such simulations, with respect to the existing parameters. In this study, a discrete adjoint algorithm is employed to extract sensitivities of various quantities of interest with respect to physical and model parameters. This adjoint framework bears a great advantage in cases where a large input space is analyzed, since a single forward and backward sweep provides sensitivity information with respect to all parameters of interest. Sensitivities are extracted for relevant quantities of interest, such as burning rate and particle temperature, and are then compared as free stream composition changes from air to oxy atmosphere. The evolution of sensitivities in time is shown to be dependent on the selected quantity of interest. Model sensitivities with respect to heterogeneous reaction parameters (oxidation of carbon, in particular) are shown to be the highest, whereas the sensitivities with respect to free stream composition are shown to be significantly lower.

Effect of transient behavior on off-state current in poly-Si junctionless nanowire thin-film transistor

For forward sweeping of V GS, the unpredicted negative drain current is observed in our L-type double-gated junctionless transistor. This reveals that in addition to gate-induced drain leakage, there is an another mechanism that causes this negative drain current. According to some measurements, it is found that the negative drain current is related to the steep V GS transition, and the large reduction of hole density in the nanowire channel induces a transient negative drain current. Based on this mechanism, for reverse sweeping of V GS, the positive drain current is measured due to an increment of hole density in the nanowire channel. To explain the mechanism well, the hole density in the Si channel is simulated and an AC model is proposed. Finally, it is likely that the transient negative current of the drain is also affected by the gate transient current, besides the large reduction of hole density.

Adjoint-based sensitivity analysis of steady char burnout

Simulations of pulverised coal combustion rely on various models, required in order to correctly approximate the flow, chemical reactions, and behaviour of solid particles. These models, in turn, rely on multiple model parameters, which are determined through experiments or small-scale simulations and contain a certain level of uncertainty. The competing effects of transport, particle physics, and chemistry give rise to various scales and disparate dynamics, making it a very challenging problem to analyse. Therefore, the steady combustion process of a single solid particle is considered as a starting point for this study. As an added complication, the large number of parameters present in such simulations makes a purely forward approach to sensitivity analysis very expensive and almost infeasible. Therefore, the use of adjoint-based algorithms, to identify and quantify the underlying sensitivities and uncertainties, is proposed. This adjoint framework bears a great advantage in this case, where a large input space is analysed, since a single forward and backward sweep provides sensitivity information with respect to all parameters of interest. In order to investigate the applicability of such methods, both discrete and continuous adjoints are considered, and compared to the conventional approaches, such as finite differences, and forward sensitivity analysis. Various quantities of interest are considered, and sensitivities with respect to the relevant combustion parameters are reported for two different free-stream compositions, describing air and oxy atmospheres. This study serves as a benchmark for future research, where unsteady and finally turbulent cases will be considered.

Optimal control of an online game addiction model with positive and negative media reports

In the spread of infectious diseases, media reports have played a positive role. However, in the process of game communication, there are not only positive but also negative media reports. Therefore, in this paper, we establish a model with positive and negative media reports to analyze the role of media reports in the process of game communication. First, we study its positivity and boundedness, and calculate the basic reproduction number $$R_{0}$$ under three different incidence rates. The existence and stability of the equilibria are proved. Secondly, the optimal control problem is studied by adding two dynamic variables of media reports. Finally, in the simulation we simulate the stability of the equilibria, so as to verify the correctness of the theory. Then the influence of media parameters on $$R_{0}$$ is analyzed. The numerical results of optimal control are simulated by forward and backward sweep method. By comparing the results of the optimal control and without control, the media coverage should be controlled according to the optimal control measures shown in this paper. The serious situation of game addiction will be greatly alleviated, which can reduce the infection rate by at least 90%.

Voltage violation in four‐wire distribution networks integrated with rooftop PV systems

Integration of rooftop photovoltaic (PV) systems in a three-phase four-wire distribution network cause voltage-violations namely voltage-rise and voltage unbalance. This study investigates the factors that affect both the voltage-rise and voltage unbalance in low voltage distribution network integrated with the rooftop PV systems. The concerning factors are classified into active factors such as; loads active powers, PV active powers, and bus reactive powers, and passive factors such as; numbers of feeder buses and neutral-grounded resistances. The study also determines the factors conditions at which the highest values of both voltage-rise and voltage unbalance occurred. Moreover, the most and least significant effects of individual factors on both voltage-rise and voltage unbalance are studied. The studied system is simulated and implemented in MATLAB software environment and the feeder loads are modelled based on Back–Forward Sweep method. The simulation results identify that the conditions of the worst voltage-rise and voltage unbalance cases depend on the collective influence of the studied factors.

Air flow model development and application in a complex combined sewer system.

A steady-state air flow model was developed and applied in a complex combined sewer system in the city of Edmonton, Alberta, Canada. The model solves the continuity at each junction and the momentum equation for the links coupled with dropshaft and other manholes. The dropshaft pressure gradient is computed using the dropshaft equation and air flow rate through manhole pickholes is computed considering the opening as an orifice. A leakage factor is used as a calibration parameter to represent the area through which air can leak from the manholes into the neighborhood. The model uses an iterative solution algorithm with a forward sweep for the continuity and backward sweep for the momentum equation. An underrelaxation is applied to update pressure in each iteration for model stability. The model was calibrated and validated by using the measured air flow rate and manhole pressure in the sewer network, with good results. An analysis of the air flow characteristics shows that a significant amount of air is brought into the system due to a large headspace in the upstream trunk but over 70% of this air is released into the neighborhood due to reduced headspace in the downstream trunk.

A Robust Electric Spring Model and Modified Backward Forward Solution Method for Microgrids with Distributed Generation

The electric spring (ES) is a contemporary device that has emerged as a viable alternative for solving problems associated with voltage and power stability in distributed generation-based smart grids (SG). In order to study the integration of ESs into the electrical network, the steady-state simulation models have been developed as an essential tool. Typically, these models require an equivalent electrical circuit of the in-test networks, which implies adding restrictions for its implementation in simulation software. These restrictions generate simplified models, limiting their application to specific scenarios, which, in some cases, do not fully apply to the needs of modern power systems. Therefore, a robust steady-state model for the ES is proposed in this work to adequately represent the power exchange of multiples ESs in radial micro-grids (µGs) and renewable energy sources regardless of their physical location and without the need of additional restrictions. For solving and controlling the model simulation, a modified backward–forward sweep method (MBFSM) is implemented. In contrast, the voltage control determines the operating conditions of the ESs from the steady-state solution and the reference voltages established for each ES. The model and algorithms of the solution and the control are validated with dynamic simulations. For the quasi-stationary case with distributed renewable generation, the results show an improvement higher than 95% when the ESs are installed. On the other hand, the MBFSM reduces the number of iterations by 34% on average compared to the BFSM.

Power loss minimization in radial distribution systems with obstructed solar astronomical model and temperature effect using grey wolf optimization technique

ABSTRACT This article presents implementation of a solar energy-based DG (Distribution Generation) system, which is optimally designed by taking combined effect of solar irradiation and temperature into consideration to minimize the power loss in the Radial Distribution Systems (RDS). A power gap of 35 W/panel is reduced when the solar panel is considered under ambient temperature effect. Novelty of this work lies in the implementation of the obstructed solar astronomical model to improve the accuracy in the prediction of radiation level. In this work, the considered radiation level is determined to be 14.86% of the global radiation data. Consideration of self-shadowing losses for maximum efficiency from PV panels is another significant aspect of this work. Two different test systems are designed by integrating the proposed DG system to IEEE-15 and IEEE-28 RDS. Load Impedance Matrix (LIM) method is adopted to perform load flow in above mentioned test systems due to its single step analysis with faster results unlike traditional Backward Forward Sweep (BFS) method. Grey Wolf Optimization (GWO) technique is used to obtain optimal location of DG for both the test systems for its simple evaluation, good flexibility, avoidance of local optimal point and derivation free tool, which makes this technique popular among the other heuristic methods. Following DG allocation in IEEE-15 bus RDS, it is observed that active power loss is reduced by 39.69%. Similarly, for IEEE-28 bus RDS, reduction in active power loss is found to be 41.20% after integration of a DG unit. There is also a remarkable improvement in voltage profile in both systems after integration of DG units.

Hydrogen Oxidation on Ni-Based Electrocatalysts: The Role of the Synthetic Method

Hydrogen electrooxidation is one of the key reactions underlying the fuel cell technology for electromobility and stationary power supply, the critical segments of the hydrogen economy of the future. Progress in alkaline anion exchange membranes (AAEMs) may lead to fuel cells employing catalysts that are less costly than those of the platinum-group metals required by the PEM technology1 - 6. To this end Ni appears to be a well suited metal, and development and implementation of affordable Ni-based electrocatalysts as a replacement for the cost-intensive platinum group metals would significantly facilitate the progress in AAEM fuel cells. However, the low catalytic activity of Ni for the hydrogen oxidation reaction (HOR) and inevitable (electro)chemical passivation of the metallic surface impede the advancement of the technology. In this work, we have synthesized two series of binary Ni3M/C (M=Fe, Cu, Co) catalysts using two different synthesis techniques, viz. low-temperature chemical reduction (CR) and high temperature solvothermal reduction (STR). We have undertaken a comprehensive experimental study using transmission electron microscopy (TEM), scannin-transmission electron microscopy (STEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), cyclic voltammetry (CV), and methods based on rotating disc electrodes (RDEs) to understand the role of the synthetic methods in determining the structural (the formation of true alloys or mechanical mixtures), (electro)chemical, and catalytic properties of Ni-based catalysts in the HOR. We show that neither the degree of alloying nor the degree of phase crystallinity is critical in determining the HOR catalytic activity. The chemical and electrochemical oxidation of the surface on the other hand, are critical to the catalytic activity, and these are in turn dependent on the chemical nature of the dopant and on its surface concentration, as well as the synthetic technique used. Due to the oxophilic properties, the Ni-M surface promotes the bifunctional HOR catalysis better than the monometallic Ni surface. However, for the same reason, doping of nickel by Co, Cu and Fe also promotes the electrochemical oxidation of the Ni surface and thus has an adverse effect on the overpotential range over which the catalyst will be active.Due to the formation of NiOH and Ni(OH)2 and possibly other species at the catalyst surface, establishing credible Tafel plots are difficult from experimental data. We therefore interpreted voltammograms recorded in hydrogen-saturated solutions of KOH in terms of dynamic microkinetic models for the HOR that also includes odxidation of the Ni surface7, 8. The figure shows the results of such fits to experimental data for a numerical model that includes the Tafel, Heyrovsky, and Volmer steps for the HOR and steps for the formation of NiOH and Ni(OH)2 and a simplified, approximate model for the forward sweep.

Understanding of Polarization-Induced Threshold Voltage Shift in Ferroelectric-Gated Field Effect Transistor for Neuromorphic Applications

A ferroelectric-gated fin-shaped field effect transistor (Fe-FinFET) is fabricated by connecting a Pb(Zr0.2Ti0.8)O3-based ferroelectric capacitor into the gate electrode of FinFET. The ferroelectric capacitor shows coercive voltages of approximately −1.5 V and 2.25 V. The polarization-induced threshold voltage shift in the Fe-FinFET is investigated by regulating the gate voltage sweep range. When the maximum positive gate to source voltage is varied from 4 V to 2 V with a fixed starting negative gate to source voltage, the threshold voltage during the backward sweep is increased from approximately −0.60 V to 1.04 V. In the case of starting negative gate to source voltage variation from −4 V to −0.5 V with a fixed maximum positive gate to source voltage of 4 V, the threshold voltage during the forward sweep is decreased from 1.66 V to 0.87 V. Those results can be elucidated with polarization domain states. Lastly, it is observed that the threshold voltage is mostly increased/decreased when the positive/negative gate voltage sweep range is smaller/larger than the positive/negative coercive voltage, respectively.

Modeling of distributed generators and converters control for power flow analysis of networked islanded hybrid microgrids

This paper proposes the incorporation of distributed and decentralized control models of generators and converters into the power flow analysis of islanded hybrid microgrids (IHMG). The absence of a slack bus in an islanded microgrid presents challenges to its frequency and voltage regulation as well as power flow calculation. While droop mechanism as the primary control has been well incorporated into load flow analysis, distributed secondary control has only recently been developed for islanded microgrids. This paper proposes a distributed secondary control for a) generators in an AC subgrid of an IHMG and b) interlinking converters in networked IHMGs. Both the distributed and droop control are incorporated into a three-phase power flow calculation based on a modified Backward Forward Sweep method. The algorithm has been tested on several case studies, and the power flow results have been verified against a time-domain simulation. The proposed method proves to be accurate and useful for the planning and design of three-phase networked IHMGs.

Giant Flying Jaws: Aerodynamic Effects and Constraints on Cranial Hypertrophy in Pterosaurs

Pterosaurs are most well‐known for their expanded and altered forelimbs, which supported muscular membrane wings. Indeed, pterosaurs possessed one of the most derived hand morphologies of any vertebrate animal. However, several pterosaur lineages also possessed enormously expanded cranial and cervical proportions. The most extreme cases occur within ornithocheiroid and azhdarchoid pterosaurs, for which the cranial length, even excluding display crests, regularly exceeded 3.5 times the shoulder to hip distance.The enlarged heads and necks of many pterosaurs had implications for their flight and ecology. Understanding the costs and mechanisms of cranial hypertrophy in pterosaurs also has implications for understanding the evolution of the vertebrate skull, more generally. Investigating this problem is made particularly challenging by the fact that pterosaurs have no living descendants. A numerical modeling approach, using first principles, is likely the most effective way to investigate the evolution of cranial hypertrophy in pterosaurs.I addressed the performance impacts of cranial expansion in pterosaurs through a modeling approach combining aeromechanics and beam mechanics. I focused particularly on azhdarchids. These include some of the most extreme cases of cranial hypertrophy and possessed cervical anatomy amenable to beam theory applications (azhdarchids possessed highly derived cervical vertebrae with an elongate, tubular morphology). I used CT imaging to resolve cortical bone thickness in key elements. I created updated soft tissue reconstruction estimates, and I then applied both volumetric and scaling methods to estimate body masses and mass distribution.The results of this analysis provide new insights regarding the soft tissue morphology, flight dynamics, and wing positions of large pterosaurs. While the skulls were relatively light, the neck of azhdarchoid pterosaurs may have been much more robust than previously suggested. The Relative Cantilever Failure Force (RCFF) values of the cervical vertebrae range from roughly equal to nearly double that of the humeri. The expanded skull and neck of azhdarchid pterosaurs did have a substantial impact on center of mass (COM). To align the center of lift with the forward center of mass, a forward sweep of the wings was required. Rather than being a costly wing position, this would have improved low speed performance by delaying stall of the wingtip. Stability could be achieved dynamically through leading edge adjustments of the propatagium and passively with a wing dihedral and inboard reflex camber. Pterosaurs therefore may have obtained flight advantages from their expanded cranial and cervical proportions, in addition to any advantages to signaling or feeding.I suggest that cranial hypertrophy in pterosaurs is best explained as a case of constraint release, rather than an unusual selective regime. Other flying animals would probably obtain similar advantages from a forward center of mass, but developmental, anatomical, and ecological constraints most likely prevent extreme increases in head size in other flying taxa.Support or Funding InformationI wish to thank Gretchen Augustyn and Family for their financial support of research activities in the Dinosaur Institute of the NHMLAInstallation of two life sized Quetzalcoatlus sculptures by Blue Rhino Studio, demonstrating the giant size and extreme cranial proportions of these pterosaurs.Figure 1

Analysis Method of Compressor Stability Based on Eigenvalue Theory

Abstract In order to analyze the flow stability of compressors rapidly in the design stage, a fast analysis method is developed in this paper. This method takes the base flow on each streamline at different spanwise locations as the research object and characterizes the effect of blade rows on the internal flow by establishing a body force model. Therefore, it is capable of taking the complex three-dimensional blade geometry and the abundant flow details into account, and what's more, it has a significantly high computational efficiency, which makes it available to engineering practice. Based on the eigenvalue theory, the flow stability problem is transformed into the eigenvalue problem, and the system stability is determined by the eigenvalue obtained by utilizing the singular value decomposition method. The flow stability of NASA Rotor 37 is analyzed to validate the reliability of the developed approach, and the results show that this analysis method is able to capture the process of stability deterioration with throttling and identify the blade tip region as the most unstable area. In order to further study the influence of blade geometry on compressor stability, a number of swept rotors are designed by modifying the stacking line of NASA Rotor 37. The assessment results via the developed method indicate that the forward sweep defined in this work can significantly improve the stability of the flow field in the tip region, while the backward sweep has the opposite effect.

Numerical Investigation of Forward Sweep Rotor Effect on Internal Flow under Inflow Distortion

Numerical Investigation of Forward Sweep Rotor Effect on Internal Flow under Inflow Distortion

Fabrication and optimization of nanocube mixed halide perovskite films for solar cell application

In this article, we report the tailoring of nanostructured mixed halide perovskite MAPb(I1-xBrx)3 films with tunable band gap fabricated by anion exchange reaction. In this process, we used PbBr2 and methyl ammonium iodide (MAI) in order to fabricate mixed halide perovskite films. We have observed an uncommon shape transformation from nanocube-hollow tetraoids-nanocubes/plate. The underlying mechanism of shape transformation was discussed based on experimental results. The driving force for such shape transformation is combined effect of anion exchange reaction between I− and Br− at the solid/liquid interface of PbBr2 and MAI, and mechanical driving force exerted by the spin coating process. The shape transformation is highly reproducible, verified by two step process, dipping as well as spinning process. The best performing device using the nanostructured perovskite films in a device architecture FTO/TiO2/MAPb(I1-xBrx)3/Spiri-OMeTAD/Au shows a current density (Jsc,) of 23.58 mA/cm2, open circuit voltage (Voc) of 0.891 V and fill factor (FF) of 0.608, with a power conversion efficiency (η) of 12.79% in forward sweep. In reverse sweep, the device shows the Jsc (mA/cm2), Voc (V), FF, and η (%) are 23.852, 0.891, 0.716 and 15.237, respectively.

Material anisotropy and sweep effects on the hydroelastic response of lifting surfaces

The objective is to study the hydroelastic response of composite cantilevered plates as a combined function of the material anisotropy and geometric sweep angle. For plates with a positive incidence angle, if the fibers are aligned towards the leading edge, nose-down deformations occur, which reduces lift and delays static divergence. If the fibers are aligned towards the aft, nose-up deformations occur, and the deformations increase (decrease) with forward (backward) sweep. For the cases examined, coupled-mode flutter was observed for plates in air. In water, however, flutter was caused by the emergence of a new low-frequency mode at high flow speeds. Backward sweep accelerates flutter in air, but delays flutter in water. The effect of the sweep angle was found to be secondary in contrast to the effective fiber angle. For the plates in air, the highest critical speed corresponds to a foil with a slight forward sweep with fibers aligned along the spanwise direction. For the same plate in water, a backward swept hydrofoil with fibers aligned toward the inflow was found to be the best combination to avoid divergence and flutter.

Optimal Integration of Distributed Generation in Distribution System: A Case Study of Sallaghari Feeder from Thimi Switching Station, Bhaktapur, Nepal

The modern power distribution network is constantly being faced with an ever-growing load demand resulting into increased burden and reduced voltage, which leads to find alternative source of energy to meet it. In Nepal, the electricity supply is based on hydropower primarily, which are situated very far from load centers and hence the generated power are to be transmitted through transmission and distributed system. Among the systems, radial distribution system is popular because of low cost and simple design, but it has power quality issues like low voltage profile and higher loss. In response to the problem of increased load demand, efforts have been made to decentralize this infrastructure through the use of distributed generators. However, the improper sizing and placement of DG unit may lead to higher power loss and power instability. The optimization problem of DG unit placement and its capacity determination were performed in this research. The study has been carried out for Thimi-Sallaghari Feeder and this feeder has low voltage profile and higher power loss. The IEEE 33 bus test system was examined as a test case to demonstrate the effectiveness of the proposed approach. The study has been carried out in MATLAB using “Backward and Forward Sweep Method” for load flow analysis and Genetic Algorithm for optimization. The number of DG unit of different size integrated was varied from one to ten. The result of this study showed that the voltage at minimum voltage node, maximum active and reactive loss reduction of Thimi-Sallaghari feeder have been improved by 3.69% (from 0.942 p.u. to 0.976 p.u), 75.88 % and 75.88 % respectively with placement of DG units at three bus locations of total 658.2019 kW and 395.873 kVAR capacity. Likewise, the voltage at minimum voltage node, maximum active and reactive loss of IEEE- 33 bus system have been improved by 6.88 %, 90.11% and 89.9% respectively with placement of DG units of total 2215.488 kW and 1176.059 kVAR at 6 different locations of the network.

Dual technique of reconfiguration and capacitor placement for distribution system

Radial Distribution System (RDS) suffer from high real power losses and lower bus voltages. Distribution System Reconfiguration (DSR) and Optimal Capacitor Placement (OCP) techniques are ones of the most economic and efficient approaches for loss reduction and voltage profile improvement while satisfy RDS constraints. The advantages of these two approaches can be concentrated using of both techniques together. In this study two techniques are used in different ways. First, the DSR technique is applied individually. Second, the dual technique has been adopted of DSR followed by OCP in order to identify the technique that provides the most effective performance. Three optimization algorithms have been used to obtain the optimal design in individual and dual technique. Two IEEE case studies (33bus, and 69 bus) used to check the effectiveness of proposed approaches. A Direct Backward Forward Sweep Method (DBFSM) has been used in order to calculate the total losses and voltage of each bus. Results show the capability of the proposed dual technique using Modified Biogeography Based Optimization (MBBO) algorithm to find the optimal solution for significant loss reduction and voltage profile enhancement. In addition, comparisons with literature works done to show the superiority of proposed algorithms in both techniques.

A two‐stage approach to shunt capacitor‐based optimal reactive power compensation using loss sensitivity factor and cuckoo search algorithm

AbstractReactive power compensation on radial distribution systems is a challenging issue. Electric power distribution systems are being bedeviled by high active power loss and severe voltage violation especially on the buses that are far from distribution substations. This article presents a two‐stage approach for sizing shunt capacitors and identifying the locations where their placement would be most beneficial within radial distribution systems. A multiobjective function capturing real power loss minimization and bus voltage profile enhancement was formulated and weighted approach was engaged to transform the function into single objective one. While backward forward sweep approach was used for the load flow analysis, loss sensitivity factor was employed to predetermine suitable sites for capacitor installation, with the optimal sites and sizes determined using cuckoo search algorithm. This approach was implemented on IEEE 15‐bus and Yale 17‐bus/11 kV feeder. Results obtained using the method was thereafter compared with those obtained through other methods as obtained from literature and the comparison shows that cuckoo search algorithm outsmarts others. Significant reduction in real power loss, coupled with appreciable enhancement in voltage profile, is achieved on the Yale 17‐bus/11 kV feeder. The approach is therefore viable for addressing reactive power compensation problems confronting practical radial distribution systems.