Desired Configuration Research Articles

Manipulating Dual Bound States in the Continuum for Efficient Spatial Light Modulator

Spatial light modulators (SLMs) that could control diverse optical properties are highly demanded by many optoelectronic systems. Recently, the integration of nonlinear χ(2) materials and metasurfaces has been recognized as a promising strategy for next-generation SLMs. However, their modulation efficiency still encounters challenges due to low quality factor and weak light-matter interaction. Here, we demonstrate an efficient SLM by manipulating the dual bound state in continuum (BIC) with the assistance of a binary-pore anodic alumina oxide template technique. The coexistence of symmetry-protected BIC and Fabry-Pérot BIC is obtained by a desirable sandwich configuration with a BIC metasurface and EO polymer, which efficiently restrain radiative loss and generate a strong quasi-BIC resonance. The assembled SLM with large absorption and Q-factor delivers a modulation depth of 77% and an f3dB of nearly 100 MHz. This dual BIC metasurface provides potential for applications including switches, LIDAR, augmented and virtual reality, and so on.

Passive-Circuit-Based Nonreciprocal Metamaterials: Controlling the Phase Gradient of Fields in Resonators and Antennas

In next- and future-generation wireless communication systems, demand for antenna technologies has continued to grow. This demand has fueled the development of design techniques that pursue more desirable configurations with simplification, electrically small size, and low profiles as well as multiple functionalities and higher performance with multiband, broad bandwidth, single/multibeam scanning, polarization control, and dispersionless group delay.

Dynamic modeling and analysis of large axially deployable spacecraft under gravity gradient

Many spacecrafts are designed with extendible, deployable, or inflatable appendages to achieve various desirable ultra-large configurations in space, which brings new challenges to the dynamic modeling and analysis of large spacecrafts. In this paper, flexible vibration and attitude angle coupling dynamic behavior of an axially deployable spacecraft considering the effects of gravity gradient are investigated. First, an improved spacecraft’s coupled dynamic model is constructed based on the Euler–Bernoulli beam theory and Hamilton’s principle while accounting for the axial motion and gravity gradient for the first time. Then, a practical deployment strategy is adopted to resolve the problem of speed residue. In addition, the effects of gravity gradient force and extension motion on deploying process, long-time evolution of the flexible vibration, and attitude motion of the spacecraft are investigated. The results indicate that the gravity gradient force and the coupling effects may alter the stability of the spacecraft system with a short deploying time, and result in a new absolute minimum value for the flexible vibration. This investigation provides constructive guidance for the attitude adjustment scheme and deployment strategy design of large-scale deployable spacecrafts.

"There's a lot of stereotypes going on": A cross-national qualitative analysis of the place of gender in declining youth drinking.

Significant declines in drinking among young people have been recorded in many high-income countries over the past 20 years. This analysis explored the role of gender - which we interpret as socially constructed and relational - to provide insight into whether and how gender might be implicated in declining youth drinking. Interview data from four independent qualitative studies from Australia, Denmark, Sweden and the UK (n=194; participants aged 15-19 years) were analysed by researchers in each country following agreement about analytical focus. Findings were collated by the lead author in a process of 'qualitative synthesis' which involved successive rounds of data synthesis and feedback from the broader research team. Our analysis raised two notable points in relation to the role of gender in declining youth drinking. The first concerned the consistency and vehemence across three of the countries at which drinkers and states of intoxication were pejoratively described in gendered terms (e.g., bitchy, sleazy). The second related to the opportunities non- and light-drinking offered for expressing alternate and desirable configurations of femininities and masculinities. We identified an intolerance towards regressive constructions of gender that emphasise weakness for women and strength for men and a valorisation of gendered expressions of maturity through controlled drinking. Though subtle differences in gendered drinking practices between and within countries were observed, our findings offer insight into how young people's enactions of gender are embedded in, and evolve alongside, these large declines in youth drinking.

Synthesis and application of new core-shell structure via Pickering emulsion polymerization stabilized by graphene oxide

Pickering structures significantly improve the compatibility and stability of composite polymer emulsions by virtue of their unique nanoparticle interfaces. An innovative application of Pickering structures to the synthesis of core-shell emulsions is proposed in this paper, two Pickering emulsions containing polystyrene acrylate-polysiloxane core-shell structures stabilized by graphene oxide (GO) were designed. The synthesized Pickering emulsions have excellent dispersibility and physical stability, while its particle size distribution is uniform and below 120 nm. The Pickering structure improves the grafting proportion between the PSA and polysiloxane components to over 87.8%. The GO interface gives the core-shell structure a desirable molecular configuration and high crosslinking degree, facilitating the formation of complete shielding films and stable hydrophobic layer on the cement hydrates. With a contact angle of over 130° and surface energy of below 15 mJ/m2, the capillary water absorption of the concrete decreased by 98.3% with the Pickering emulsions. Meanwhile, the Pickering coatings have the high corrosion potentials under chloride and sulfate attack, weakening the formation of Friedel's salts, gypsum, and ettringite in the cement substrates. Furthermore, the Pickering coating films are resistant to attack by aggressive ions and free radicals under acid/alkaline corrosion and photo-oxidative aging, effectively inhibiting the degradation of polymer molecules and adhesion failure on the cementitious materials.

A simulator of optical coherent-state evolution in quantum key distribution systems

Quantum key distribution (QKD) is believed to represent a viable solution to achieve theoretically unconditionally secure key generation. However, the available optical systems for experimental QKD, based on photon transmission, are flawed by non-idealities that ultimately limit the achievable performance. Classical simulation of the optical hardware employed in these systems may take on a determining role in engineering future QKD networks. In this article, attempts for developing a QKD simulator based on low-computational-cost models of the employed hardware are presented. In particular, the simulation infrastructure targets polarization-based QKD setups with faint laser sources, whose behaviour can be described by semiclassical coherent states and Mean Photon Number (MPN) per beam. The effects of passive optical components on the photonic qubit evolution are described by Jones matrices, whose coefficients, for some commercial devices, are stored in an ad-hoc library. Realistic eavesdropping attacks and non-idealities, such as optical losses, fibre attenuation, polarization misalignment and limited efficiency of single-photon detectors, are also taken into account. The infrastructure allows the user to describe the desired QKD configuration and it provides in output the MPN at the receiver and two fiducial performance parameters: Quantum Bit Error Rate (QBER) and secure key rate. The comparison of the simulation results with experimental data in the state-of-the-art literature highlights that this work is a step forward towards the definition of compact models for the hardware-dependent simulation of quantum-assisted communication networks.

Adaptive Fuzzy Fast Finite-Time Formation Control for Second-Order MASs Based on Capability Boundaries of Agents

This article addresses a new adaptive fuzzy fast finite-time state-constraint protocol for leader-follower formation control. Each agent in uncertain nonlinear dynamic multiagent systems is represented by second-order integrator, which synchronously governs its position and velocity. The fuzzy logic systems are employed to compensate and approximate uncertain functions. On the premise of maintaining formation structure and coupling communication topology, time-varying transformation equations containing exponential signals are introduced to ensure that state capability boundaries for different physical quantities of agents are not violated. It not only guarantees own state performance and collision avoidance among agents, but also realizes the specified transient and steady formation performance. Furthermore, focusing on convergence rate, the adaptive fuzzy fast finite-time strategy is designed that can guarantee all agents will follow the desired formation configuration in fast finite-time. Through the abovementioned approaches provide a good way to improve the convergence and ensure the security for decentralized formation control. Finally, the validity of the theoretical method is proved by fast finite-time stable theory and Lyapunov stability theory. The effectiveness of the protocol is verified by digital simulation and simulation comparison.

The application of solar integrated absorption cooling system to improve the air quality and reduce the energy consumption of the air conditioning systems in buildings – A full year model simulation

Due to the depletion of fossil fuels and increasing the atmospheric greenhouse gas emissions, employing equipment with low energy consumption levels, while benefiting the renewable energy sources have been wide spread these days. In this research, the application of a solar assisted absorption chiller/cooling system in a high cooling load required region of Iran was investigated. A building located in southeast region of the country as a high cooling load required region was considered for this purpose. The performance of the building existing cooling system was studied in terms of the provided indoor air conditions and energy consumption was using TRNSYS software. Then, the feasibility of replacing the existing cooling system with a solar assisted absorption chiller was explored. Three recommended standard solar panels, namely Evacuated Tube, Glazed Painted, and Unglazed solar collectors were examined to recommend the most desired configuration. The study was conducted based on two operating hours of 24 h. and 8 h. (office working hours) scenarios. The results showed that within the regular office working hours, the solar assisted absorption chiller system equipped with the Evacuated Tube, Glazed Painted, and Unglazed solar collectors improves the indoor temperature up to 3.08 °C, 1.68 °C, and 1.46 °C, respectively. It was also found that the reduction in power consumption by application of the solar assisted absorption chiller could be up to 84 %, 64 %, and 48 %, respectively compared to the currently used cooling system in the building. The performance comparison between the three examined solar thermal panels revealed that the solar absorption chiller equipped with the Evacuated Tube solar collector has the capability to provide the most desired indoor air conditions and power consumption level.

Structural optimization of a perovskite solar cell using single- and multi-objective particle swarm optimization method

In this paper, optimizing the efficiency characteristic parameters of a perovskite solar cell has been carried out by augmenting the particle swarm optimization algorithm to the SCAPS software. Unlike most of the performed studies in this field, instead of the equivalent circuit, actual structure of the solar device is optimized. In this regard, two approaches, being single- and multi-objective optimization have been employed to reach the desirable configuration, based on the optimum values of the internal efficiency parameters. These parameters include power conversion efficiency, fill factor, short-current density and open-circuit voltage, which were taken as different cost functions. Considering the results derived from the single-objective optimization, selection of different cost functions yield different optimum thickness for the layers. As for the multi-objective optimization, the weighted sum method accompanied with the particle swarm optimization are implemented. Applying different weights to the internal efficiency parameters results in different convergence rate for each cost function. Overall, a considerable enhancement in the power conversion efficiency, from 6.6945% to 23.7646%, reveals much better performance of the structure with the optimized layers compared to the initial structure.

UAV formation control based on distributed Kalman model predictive control algorithm

To address the perturbation of formation of multiple unmanned aerial vehicles (UAVs) subject to external disturbances, an algorithm of distributed Kalman model predictive control is proposed in this paper to improve the accuracy of maintaining a formation in flight. A UAV two-order discrete-time system model was built before devising a Kalman prediction model based on the standard prediction model. The desired formation configuration and neighbor Kalman optimal state estimation were conducted to determine the reference state of UAVs. While taking into account the formation tracking error and input stability, a logarithmic barrier function was introduced in the design of the overall cost function to ensure flight safety. Meanwhile, information was exchanged with neighbors with the directed and time-invariant communication topological structure. With the Lyapunov stability theorem, sufficient conditions were defined for the asymptotic stability of the formation system. Simulation results revealed that the algorithm could effectively suppress the perturbation in the formation of UAVs arising from external disturbances, allowing the formation to cope with the conflicts between individual UAVs.

Designing a novel small-scale parabolic trough solar thermal collector with secondary reflector for uniform heat flux distribution

This paper presents a new stepwise approach to design a medium-temperature solar parabolic trough collector with a secondary reflector, which is the fastest growing technology among concentrated solar power technology. The goal of the design is to have a homogeneous concentrated solar flux distribution with maximal output power over the receiver tube. Tonatiuh, a Monte Carlo ray-tracing based optical simulation software, has been used to conduct the ray-tracing analysis of the secondary reflector. Response surface methodology has been used to examine and select the desirable configuration of the solar collector system, and the findings have been analysed using the analysis of variance. It is found that the use of secondary reflector improves the uniformity of heat flux distribution to 0.58, whereas it is 1.0836 for the solar collector without the secondary reflector. For a target output power of 5.5 kW, the most attractive configuration has a maximum desirability value of 0.974. The computational fluid dynamics analysis has been performed in the configuration with better uniform heat flux and the collector without a secondary reflector, using the flux distribution acquired from the ray-tracing analysis. Results show that the use of secondary reflector significantly reduces the thermal gradient, and the heat flux distribution is found to be homogenous. By determining configurations with the best heat flux distribution against a specific output power, the approach provided in this paper lays the groundwork for future research on the design of parabolic trough solar collector systems with secondary reflectors.

Leaderless maneuver guidance and event-triggered formation control for distributed multi-space-robot systems

In this paper, the distributed displacement-based formation and leaderless maneuver guidance control problems of multi-space-robot systems are investigated by introducing event-triggered control update mechanism. A distributed formation and leaderless maneuver guidance control framework is first constructed, which includes two parallel controllers, namely an improved linear quadratic regulator and a distributed consensus-based formation controller. By applying this control framework, the desired formation configuration of multi-space-robot systems can be achieved and the center of leaderless formation can converge to the target point globally. Second, a pull-based event triggering mechanism is introduced to the distributed formation controller, which makes the control update independent of the events of neighboring robots, avoids unnecessary control updates, and saves the extremely limited energy of space robots. Furthermore, the potential Zeno behaviors have been excluded by proving a positive lower bound for the inter-event times. Finally, numerical simulation verifies the effectiveness of the theoretical results.

Modeling of Mechanisms Providing the Overall Control of Human Circulation

Multiple humoral and nervous mechanisms, each influencing the cardiovascular system (CVS) with its specific dynamics and power, had been evolutionarily saved both in animals and in human organisms. Most of such mechanisms are considered to be controllers of CVS’s function, but there is no concept clearly explaining the interaction of global and local controllers in intact human organisms under physiological or pathological conditions. Methodological and ethical constraints create practically insuperable obstacles while experiments on animals mainly concern artificial situations with certain switched-of mechanisms. Currently, mathematical modeling and computer simulations provide the most promising way for expanding and deepening our understanding of regulators’ interactions. As most of CVS’s models describe only partial control mechanisms, a special model (SM) capable of simulating every combination of control mechanisms is encouraged. This paper has three goals: i) to argue the uncial modeling concept and its physiological basis, ii) to describe SM, and iii) to give basic information about SM’s test research. SM describes human hemodynamics, which is under influence of arterial baroreceptor reflexes, peripheral chemoreceptor reflexes, central (CRAS) and local (lRAS) renin-angiotensin systems, local ischemia, and autoregulation of total brain flow. SM, performed in form of special software (SS), is tested under specific endogenous and/or exogenous alterations. The physiologist using SS can easily construct the desirable configuration of regulator mechanisms, their actual state, and scenarios of computer experiments. Tests illustrated the adequateness of SM, are the first step of SM’s research. Nuances of the interaction of modeled regulator mechanisms have to be illustrated in special publications.

A stochastic programming approach using multiple uncertainty sets for AC robust transmission expansion planning

We present a transmission expansion planning model to find the most desirable configuration of transmission grid under the robust optimization. Unlike the common existing approaches where only one uncertainty set is considered, we propose to model multiple uncertainty sets each with its own probability. In this regard, we devise a method to construct the corresponding uncertainty sets from the historical data based on minimum covering circle. Moreover, we introduce a new criterion for uncertainty budget based on which the planner can efficiently control the conservative level of the optimization problem. Using this new criterion, the planner is capable to make a trade-off between the tractability and solution quality. The robust planning method is formulated as a tri-level min–max–min optimization model in which the classic column-and-constraint generation technique is used to solve the problem. The proposed strategy is implemented on the IEEE 118-bus power system to show the effectiveness of the model. The results indicate the short-term uncertainties in demand and intermittent renewable generation can be efficiently captured by the presented strategy. The comparable results also corroborate the superiority of the model over the single uncertainty-set-based models as well as over the pure stochastic models. • A robust transmission expansion planning scheme is presented. • Short-term demand and wind speed uncertainties are taken into account. • Multiple uncertainty sets are considered rather than a single one. • A linearized network model is utilized. • The robust trilevel approach is solved using KKT and CCG.

Qubit-efficient encoding scheme for quantum simulations of electronic structure

Simulating electronic structure on a quantum computer requires encoding of fermionic systems onto qubits. Common encoding methods transform a fermionic system of $N$ spin-orbitals into an $N$-qubit system, but many of the fermionic configurations do not respect the required conditions and symmetries of the system so the qubit Hilbert space in this case may have unphysical states and thus can not be fully utilized. We propose a generalized qubit-efficient encoding (QEE) scheme that requires the qubit number to be only logarithmic in the number of configurations that satisfy the required conditions and symmetries. For the case of considering only the particle-conserving and singlet configurations, we reduce the qubit count to an upper bound of $\mathcal O(m\log_2N)$, where $m$ is the number of particles. This QEE scheme is demonstrated on an H$_2$ molecule in the 6-31G basis set and a LiH molecule in the STO-3G basis set using fewer qubits than the common encoding methods. We calculate the ground-state energy surfaces using a variational quantum eigensolver algorithm with a hardware-efficient ansatz circuit. We choose to use a hardware-efficient ansatz since most of the Hilbert space in our scheme is spanned by desired configurations so a heuristic search for an eigenstate is sensible. The simulations are performed on IBM Quantum machines and the Qiskit simulator with a noise model implemented from a IBM Quantum machine. Using the methods of measurement error mitigation and error-free linear extrapolation, we demonstrate that most of the distributions of the extrapolated energies using our QEE scheme agree with the exact results obtained by Hamiltonian diagonalization in the given basis sets within chemical accuracy. Our proposed scheme and results show the feasibility of quantum simulations for larger molecular systems in the noisy intermediate-scale quantum (NISQ) era.

Domain Engineering in Bulk Ferroelectric Ceramics via Mesoscopic Chemical Inhomogeneity.

Domain engineering in ferroelectrics endows flexibility for different functional applications. Whereas the domain engineering strategy for single crystals and thin films is diverse, there is only a limited number of strategies for bulk ceramics. Here, a domain engineering strategy for achieving a compact domain architecture with increased domain‐wall density in (K,Na)NbO3 (KNN)‐based ferroelectric ceramics via mesoscopic chemical inhomogeneity (MCI) is developed. The MCI‐induced interfaces can effectively hinder domain continuity and modify the domain configuration. Besides, the MCI effect also results in diffused phase transitions, which is beneficial for achieving enhanced thermal stability. Modulation of chemical inhomogeneity demonstrates great potential for engineering desirable domain configuration and properties in ferroelectric ceramics. Additionally, the MCI can be easily controlled by regulating the processing condition during solid‐state synthesis, which is advantageous to industrial production.

Multivariable run-to-run control of thermal atomic layer etching of aluminum oxide thin films

With the growing scarcity of semiconducting devices stemming from volatile prices, shortened supplies, and increased demand that are attributed to the Covid-19 pandemic, manufacturers are looking for efficient ways to facilitate the production of nanoscale semiconducting devices. Thermal atomic layer etching (ALE) is a promising method that can overcome the obstacles encountered during the production of semiconducting devices via conventional approaches by delivering precise dosages of reagent to etch monolayers of substrate surface material in a cyclic operation. However, thermal ALE has not been extensively studied and characterized to become fully embraced by the semiconductor manufacturing industry. Recent work by our group has led to the development of a multiscale computational fluid dynamics modeling framework that was used to optimally design a desirable reactor configuration and operating conditions for the thermal ALE process. Despite this progress, additional research is needed to ensure that the film quality is maintained in the presence of operational disturbances. Therefore, the present work is focused on the development of a multivariable run-to-run (R2R) control system to mitigate the impact of critical operational disturbances. It is demonstrated that the developed multivariable R2R control system can efficiently overcome the negative effects of unknown disturbances that may impact film uniformity by regulating input variables within a minimal number of batch runs.

Distributed time‐varying convex optimal consensus control for multi‐agent system with/without chattering restrain

AbstractIn this article, the consensus, collision avoidance, and distributed convex optimization problems of a class of multi‐agent systems with a time‐varying objective function are studied. Moreover, the proposed method in this article can reduce the chattering problem of the controller input caused by the sign function. First, the sign function is used to design the controller to improve the convergence rate of the system, on this basis, the optimization item is designed for the more complex time‐varying objective function to ensure that the value of the objective function is the smallest when the system achieves the speed consensus. Second, considering the chattering problem caused by the sign function, the designed controller is improved to reduce the chattering phenomenon. Third, two novel Lyapunov functions are constructed to verify the stability of the system and the distributed optimization objective. Due to the controller is designed for the time‐varying objective function, moreover, the tasks of the formation and collision avoidance are needed to take into account, therefore, the designed Lyapunov functions in this article are more difficult. Finally, the formation function is designed to ensure that the multi‐agent system achieves the desired formation configuration. The simulation results show the correctness of the theoretical design of this article and the superiority in extending the running time of the system.

Cyclic Shift Problems on Graphs

We study a new reconfiguration problem inspired by classic mechanical puzzles: a colored token is placed on each vertex of a given graph; we are also given a set of distinguished cycles on the graph. We are tasked with rearranging the tokens from a given initial configuration to a final one by using cyclic shift operations along the distinguished cycles. We first investigate a large class of graphs, which generalizes several classic puzzles, and we give a characterization of which final configurations can be reached from a given initial configuration. Our proofs are constructive, and yield efficient methods for shifting tokens to reach the desired configurations. On the other hand, when the goal is to find a shortest sequence of shifting operations, we show that the problem is NP-hard, even for puzzles with tokens of only two different colors.

Functionalized chitosan/spherical nanocellulose-based hydrogel with superior antibacterial efficiency for wound healing

Cellulose nanomaterials have received significant interest due to their superior physicochemical properties and biocompatibility. The nanomaterials-based hydrogel patches are widely explored for skin regeneration. However, the injectability and adhesiveness of the hydrogels are crucial challenges for tissue engineering applications. To overcome these, we synthesized an injectable and adhesive hydrogel of spherical nanocellulose (s-NC) reinforced carboxymethyl chitosan for rapid skin regeneration. The s-NC exhibited improved cellular activity than cellulose nanocrystals. The hydrogels exhibited adhesive and injectability potentials and were molded in the desired configurations. An enhanced conductivity was observed in s-NC added hydrogels than the pure polymer hydrogel. The skin regeneration potential of the hydrogel scaffolds was also examined in the rats using the wound healing model. The composite scaffolds also showed improved antibacterial potential. Taken together, the developed hydrogels have the potential and can be explored as a promising biomaterial for enhanced skin regeneration applications.