Neuron-neuron attraction shapes morphology and activity of tissue engineered brain constructs

The propensity of neuronal stem cells to aggregate is well established.Aggregation of differentiated neurons,particularly those of the brain regions such as the cortex,has been reported more recently(Hasan et al.,2019;Ming et al.,2020).However,the tendency of these cells to aggregate may play a significant role in the brain’s response to injury,and may also be important in developing regenerative therapies to treat brain injury.Some types of injury,including stroke and trauma,result in formation of liquid-filled cavities in the brain(Kazim et al.,2011;Moreau et al.,2012).Cavities are also produced by resection surgery in patients suffering from epilepsy or by surgical brain tumor removal.Brain cavitation represents a loss of neural circuitry and therefore leads to deficits in function and behavior.

Distributed Periodic Event-Triggered Optimal Control of DC Microgrids Based on Virtual Incremental Cost

This article presents a distributed periodic eventtriggered(PET)optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids.In order to accommodate the generation constraints of the distributed generators(DGs),a virtual incremental cost is firstly designed,based on which an optimality condition is derived to facilitate the control design.To meet the discrete-time(DT)nature of modern control systems,the optimal controller is directly developed in the DT domain.Afterward,to reduce the communication requirement among the controllers,a distributed event-triggered mechanism is introduced for the DT optimal controller.The event-triggered condition is detected periodically and therefore naturally avoids the Zeno phenomenon.The closed-loop system stability is proved by the Lyapunov synthesis for switched systems.The generation cost minimization and average bus voltage regulation are obtained at the equilibrium point.Finally,switch-level microgrid simulations validate the performance of the proposed optimal controller.

Distributed Control of Multiple-Bus Microgrid With Paralleled Distributed Generators

A microgrid is hard to control due to its reduced inertia and increased uncertainties. To overcome the challenges of microgrid control, advanced controllers need to be developed.In this paper, a distributed, two-level, communication-economic control scheme is presented for multiple-bus microgrids with each bus having multiple distributed generators(DGs) connected in parallel. The control objective of the upper level is to calculate the voltage references for one-bus subsystems. The objectives of the lower control level are to make the subsystems' bus voltages track the voltage references and to enhance load current sharing accuracy among the local DGs. Firstly, a distributed consensusbased power sharing algorithm is introduced to determine the power generations of the subsystems. Secondly, a discrete-time droop equation is used to adjust subsystem frequencies for voltage reference calculations. Finally, a Lyapunov-based decentralized control algorithm is designed for bus voltage regulation and proportional load current sharing. Extensive simulation studies with microgrid models of different levels of detail are performed to demonstrate the merits of the proposed control scheme.

Adaptive Decentralized Output-Constrained Control of Single-Bus DC Microgrids

A single-bus DC microgrid can represent a wide range of applications. Control objectives of such systems include high-performance bus voltage regulation and proper load sharing among multiple distributed generators(DGs) under various operating conditions. This paper presents a novel decentralized control algorithm that can guarantee both the transient voltage control performance and realize the predefined load sharing percentages. First, the output-constrained control problem is transformed into an equivalent unconstrained one. Second, a two-step backstepping control algorithm is designed based on the transformed model for bus-voltage regulation. Since the overall control effort can be split proportionally and calculated with locally-measurable signals, decentralized load sharing can be realized. The control design requires neither accurate parameters of the output filters nor load measurement. The stability of the transformed systems under the proposed control algorithm can indirectly guarantee the transient bus voltage performance of the original system. Additionally, the high-performance control design is robust, flexible, and reliable. Switch-level simulations under both normal and fault operating conditions demonstrate the effectiveness of the proposed algorithm.

Photoluminescence properties and energy transfer in Y_2O_3:Eu^(3+) nanophosphors

The photoluminescence （PL） properties of Y203 ：Eu^3＋ nanophosphors were systematically investigated with the goal of improving the color quality and quantum efficiency of Y2O3 ：Eu^3＋ nanophosphors for potential applications in nano-scale devices. The emission spectra, excitation spectra and fluorescence decay curves were employed to trace the energy transfer process from Eu^3＋ at C3i site to Eu^3＋ at C2 site. The experimental results show that the energy transfer process becomes more and more efficient with the increase in the Eu^3＋ concentration. The emission of Eu^3＋ at C2 site is favorable because it has high radiative efficiency and better color quality. The successful suppress of the emission Eu^3＋ at C3i is especially important for its applications in general illumination or display technology. The quantum efficiency and color quality of Y203 ：Eu^3＋ can be improved by controlling the energy transfer between the Eu^3＋ at S6 site and Eu^3＋ at C2 site.

Effect of packing density and packing geometry on light extraction of Ⅲ-nitride light-emitting diodes with microsphere arrays

The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.

Resonant Raman scattering in GaN single crystals and GaN-based heterostructures: feasibility for laser cooling

The recent progress on Raman scattering in GaN single crystals and GaN/A1N heterostructures is re- viewed. Anti-Stokes Raman scattering is used to determine electron-phonon scattering time and decay time constant for longitudinal-opticat phonons. In a typical high electron mobility transistor based on GaN/A1N heterostructures, strong resonances are reached for the first-order and second-order Raman scattering processes. Therefore, both Stokes and anti-Stokes Raman intensities are dramatically enhanced. The feasibility for laser cooling of a nitride structure is studied. A further optimization will enable us to reach the threshold for laser cooling. Raman scattering have potential applications in up-conversion lasers and laser cooling of nitride ultrafast electronic and optoelectronic devices.

Outage Detection for Distribution Networks Using Limited Number of Power Flow Measurements

Accurate topology estimation is crucial for effectively operating modern distribution networks.Line outages in a distribution network change the network topology by disconnecting some parts of the network from the main grid.In this paper,an outage detection(or topology estimation)algorithm for radial distribution networks is presented.The algorithm utilizes noisy power flow measurements collected from a subset of lines in the network,and statistical information characterizing errors in forecasting load demands.Additionally,a sensor placement scheme is presented.The sensor placement provides critical sensing for the outage detection algorithm so that any number of possible outages in the network can be detected.The performance of the proposed outage detection algorithm using the proposed sensor placement is demonstrated through several numerical results on the IEEE 123-node test feeder.

Near-infrared electroluminescence of AlGaN capped InGaN quantum dots formed by controlled growth on photoelectrochemical etched quantum dot templates

Near-infrared electroluminescence of InGaN quantum dots(QDs)formed by controlled growth on photoelectrochemical(PEC)etched QD templates is demonstrated.The QD template consists of PEC InGaN QDs with high density and controlled sizes,an AlGaN capping layer to protect the QDs,and a GaN barrier layer to planarize the surface.Scanning transmission electron microscopy(STEM)of Stranski-Krastanov(SK)growth on the QD template shows high-In-content InGaN QDs that align vertically to the PEC QDs due to localized strain.A highAl-content A1_(0.9)Ga_(0.1)N capping layer prevents the collapse of the SK QDs due to intermixing or decomposition during higher temperature GaN growth as verified by STEM.Growth of low-temperature(830℃)p-type layers is used to complete the p-n junction and further ensure QD integrity.Finally,electroluminescence shows a significant wavelength shift(800 nm to 500 nm),caused by the SK QDs’tall height,high In content,and strong polarization-induced electric fields.

Editorial for Special Issue on Terahertz Technologies and Applications

Terahertz radiation, defined in the frequency range of O. 1-10 THz, has been exploited to demonstrate unique properties that do not apply to the adjacent domains of the electromagnetic waves, such as infrared and microwave. Recent advances in terahertz science and technology hold promise for a wide variety of essential applications, particularly in spectroscopy, sensing, imaging,

Two-time-scale Congestion Management Scheme for Microgrid Integrated Distribution Networks

Microgrids(MGs)with high penetration of dis-tributed generators may cause congestion in the distribution net-work during operation.To address this issue,this paper proposes a two-time-scale congestion management scheme for multiple MGs integrated distribution networks.Day-ahead hourly-scale dynamic congestion management(DCM)is formulated as a con-strained optimization problem,which can be solved by utilizing the proposed alternating iterative method,with the privacy of both the distribution network and MGs being preserved.The sub-hourly-scale contract energy tracking aims at fully utilizing the controllable resources of the MGs to minimize the difference of the contract and actual exchanged energy between the MG and distribution network.Through coordination of the proposed two timescales of management schemes,the MGs integrated distribution networks can operate economically while avoiding the probable congestion predicament with high penetration of renewable energy.Simulation studies with a i3-bus system MGs integrated distribution network demonstrated this proposed approach is effective to manage the congestion problem in the distribution network,while the energy tracking approach can improve the welfare of the MGs engaged in energy contracts execution.IndexTerms-Alternating giterativemethod,congestion management,microgrids,renewable energy integration.

Wide-field ophthalmic space-division multiplexing optical coherence tomography

High-speed ophthalmic optical coherence tomography(OCT)systems are of interest because they allow rapid,motion-free,and wide-field retinal imaging.Space-division multiplexing optical coherence tomography(SDMOCT)is a high-speed imaging technology that takes advantage of the long coherence length of micro electro mechanical vertical cavity surface emitting laser sources to multiplex multiple images along a single imaging depth.We demonstrate wide-field retinal OCT imaging,acquired at an effective A-scan rate of 800,000 A-scans/s with volumetric images covering up to 12.5 mm×7.4 mm on the retina and captured in less than 1 s.A clinical feasibility study was conducted to compare the ophthalmic SDM-OCT with commercial OCT systems,illustrating the high-speed capability of SDM-OCT in a clinical setting.