DC Response Research Articles

Quantized Integrated Shift Effect in Multigap Topological Phases

We show that certain three-dimensional multigap topological insulators can host quantized integrated shift photoconductivities due to bulk invariants that are defined under reality conditions imposed by additional symmetries. We recast the quantization in terms of the integrated torsion tensor and the non-Abelian Berry connection constituting Chern-Simons forms. Physically, we recognize that the topological quantization emerges purely from virtual transitions contributing to the optical response. Our findings provide another quantized electromagnetic dc response due to the nontrivial band topology, beyond the quantum anomalous Hall effect of Chern insulators and quantized circular photogalvanic effect found in Weyl semimetals. Published by the American Physical Society 2024

Structure and dielectric spectroscopy of double perovskite La2-xPrxCoFe1-yMnyO6 system

Double perovskites have shown promise in the development of spin polarized conduction and ferromag semiconductors. In this category of double perovskite, we report on the lanthanum ferrocobaltite, co-doped with Pr and Mn. The polycrystalline ceramics were analysed for its structural properties by using Rietveld refinement of X-ray diffraction (XRD) and Raman spectroscopy measurements. The pristine and co-doped samples possess monoclinic structure with P21/n space group. In the pristine compound Co and Fe octahedra are ordered periodically which later gets distorted upon cationic substitution. Scanning electron microscopy (SEM) and energy dispersive spectra (EDS) reveals the grain morphology and elemental analysis. The samples were investigated for their dc and ac electrical responses. The two-probe dc resistance was measured from room temperature RT to 575 K. Dielectric spectroscopy in the RT to 650 K temperature range was performed in the frequency range of 50 kHz to 5 MHz. We observed that introducing Pr at La-site and Mn at Fe site creates structural disorder and tilt in octahedra which results in decreasing the dielectric constant at RT but increases significantly at higher temperature with low dielectric loss. ac conductivity was found to increase with increasing temperature indicating the thermally governed hopping mechanism. All these features validate their potential applications as a high temperature capacitor and can be widely used in automotive and aerospace domains for the storage device application.

Adaptive fuzzy integrated LMS based control strategy for voltage power quality enhancement

In this paper, an adaptive Takagi Sugeno (TS) Fuzzy integrated Mixed Order Normalized Least Mean Square/Fourth Algorithm (MONLMS/F) is proposed for the unresolved voltage power quality issues in distribution system. The proposed control utilizes the cost function of mixed order of errors, which are based on second and fourth order and the feature of cost function overcomes the demerit of traditional basic least mean square method, which is based on second-order error. The implemented control technique has two main objectives. Firstly, the fundamental estimation of correct active and reactive signals from polluted grid voltage for computing the reference load voltages and second is the DC link voltage regulation. A correct weight estimation is achieved by Mixed Order Normalized Least Mean Square/Fourth Algorithm (MONLMS/F) and voltage regulation is performed by Takagi Sugeno Fuzzy (TSF) approach. The proposed integrated control enhances the capability of system against voltage deviation from the reference voltage and successfully eliminates the harmonics from polluted grid voltages. A bio-inspired optimizer like Spotted Hyena (SH) is integrated with TSF for self-tuning of the membership functions (MFs) and fuzzy rule to adapt the system variations and regulate fluctuations in the DC link for dynamic conditions. However, auto-tunned TS-Fuzzy have a fast transient response of DC and AC link voltage based on dynamic indicators like settling time (ts=0.12 s), undershoot (Us=3.4 %) and peak overshoot (Mp=5.6 %) are compared to classical PI controller. Nonetheless, the proposed TS-MONLMS/F control strategy outperforms the other classical control with low oscillations at any power quality scenario with improved dynamic response. The significant MATLAB simulation and experimental results are evaluated, and its performance is demonstrated with the dSPACE (DS1202) processor for experimental realization.

A Low-Power, 65 nm 24.6-to-30.1 GHz Trusted LC Voltage-Controlled Oscillator Achieving 191.7 dBc/Hz FoM at 1 MHz

This work presents a novel trusted LC voltage-controlled oscillator (VCO) with an embedded compact analog Physically Unclonable Function (PUF) used for authentication. The trusted VCO is implemented in a 1P9M 65 nm standard CMOS process and consumes 1.75 mW. It exhibits a measured phase noise (PN) of −104.8 dBc/Hz @ 1 MHz and −132.2 dBc/Hz @ 10 MHz offset, resulting in Figures of Merit (FoMs) of 191.7 dBc/Hz and 199.1 dBc/Hz, respectively. With the measured frequency tuning range (TR) of ~5.5 GHz, the FoM with tuning (FoMT) reaches 197.6 dBc/Hz and 205.0 dBc/Hz at 1 MHz and 10 MHz offset, respectively. The analog PUF consists of CMOS cross-coupled pairs in the main VCO to change analog characteristics. Benefiting from the impedance change and parasitic capacitance of the cross-coupled pairs, the AC and DC responses of the VCO are utilized for multiple responses for each input. The PUF consumes 0.83 pJ/bit when operating at 1.5 Gbps. The proposed PUF exhibits a measured Inter-Hamming Distance (HD) of 0.5058b and 0.4978b, with Intra-HD reaching 0.0055b and 0.0053b for the current consumption and fosc, respectively. The autocorrelation function (ACF) of 0.0111 and 0.0110 is obtained for the current consumption and fosc, respectively, at a 95% confidence level.

Nanoelectromechanical Control of Spin-Photon Interfaces in a Hybrid Quantum System on Chip.

Color centers (CCs) in nanostructured diamond are promising for optically linked quantum technologies. Scaling to useful applications motivates architectures meeting the following criteria: C1 individual optical addressing of spin qubits; C2 frequency tuning of spin-dependent optical transitions; C3 coherent spin control; C4 active photon routing; C5 scalable manufacturability; and C6 low on-chip power dissipation for cryogenic operations. Here, we introduce an architecture that simultaneously achieves C1-C6. We realize piezoelectric strain control of diamond waveguide-coupled tin vacancy centers with ultralow power dissipation necessary. The DC response of our device allows emitter transition tuning by over 20 GHz, combined with low-power AC control. We show acoustic spin resonance of integrated tin vacancy spins and estimate single-phonon coupling rates over 1 kHz in the resolved sideband regime. Combined with high-speed optical routing, our work opens a path to scalable single-qubit control with optically mediated entangling gates.

A Predictive Control Method for LCC HVDC Participated Black Start With Commutation Failure Prevention

Line-commutated converter (LCC) based HVDC systems can significantly speed up the restoration of infeed power systems in blackout states. But they are fragile to commutation failure (CF) under the adverse black-start conditions. To improve the adaptability of LCC HVDC systems in such situations, a predictive control method is proposed in this paper. It includes the linear discrete time predictive model, receding horizon regulator, state estimator, and CF prevention (CFPREV) module. The model is based on the quasi-dynamic and transient-state analysis of load disturbances, where the black-start state is forecasted according to voltage sags caused by inrush currents. The regulator operates in real-time to optimize reference inputs for the HVDC controller. In the estimator, process error and measurement noise are modeled and the optimal system state is estimated with a Kalman filter. Moreover, the dc current setting for CFPREV is calculated using the predicted and estimated state variables. The CFPREV module and regulator work in coordination for secure and fast dc power recovery under abnormal conditions. Small-signal stability analysis and EMT simulations are implemented on the CIGRE benchmark model based black start test grid. The results show that the proposed method i) improves dc power response to black start load startups and ii) presents better recovery performance after the fault.

An Enhanced Method to Achieve Exact DC Values for Frequency-dependent Transmission lines

This paper proposes an improved method to enhance the dc response of a frequency-dependent transmission line model used in EMT studies. A modification to the rational function approximation of propagation and characteristic admittance matrices of a transmission line is introduced to enforce exact dc values at 0 Hz. Furthermore, weighting factors are applied to improve accuracy at low frequencies. Finally, the order of the propagation function is reduced to decrease the computational effort.The validity of the proposed approach is demonstrated using examples involving underground cables and overhead lines. First, the effect of dc correction is demonstrated by comparing transmission line frequency domain characteristics. In addition, time domain simulations via open and short circuit conditions show a more accurate simulation of HVDC transmission lines with the proposed method.

Frequency dependent impedance response analysis of nanocrystalline ZnO chemiresistors

ZnO is a widely studied gas sensor material and is used in many commercial sensor devices. However, selectivity towards any particular gas remains an issue due to lack of complete knowledge of the gas sensing mechanism of oxide surfaces. In this paper, we have studied the frequency dependent gas sensor response of ZnO nanoparticles of a diameter of nearly 30 nm. A small rise of synthesis temperature from 85 °C to 95 °C in the solvothermal process, shows coarsening by joining and thereby distinct loss of grain boundaries as seen from transmission electron micrographs. This leads to a substantial reduction in impedance, Z (GΩ to MΩ), and rises in resonance frequency f res (from 1 to 10 Hz) at room temperature. From temperature dependent studies it is observed that the grain boundaries show a Correlated Barrier Hopping mechanism of transport and the hopping range in the grain boundary region is typically 1 nm with a hopping energy of 153 meV. On the other hand, within the grain, it shows a change of transport type from low temperature tunneling to beyond 300 °C as polaron hopping. The presence of disorder (defects) as the hopping sites. The temperature dependence of f res agrees with different predicted oxygen chemisorbed species between 200 °C to 400 °C. As opposed to the traditional DC response, the AC response in the imaginary part of (Z″) shows gas specific resonance frequencies for each gas, such as NO2, ethanol, and H2. Among the two reducing gases, ethanol and hydrogen; the former shows good dependence on concentration in Z″ whereas the latter shows a good response in f res as well as capacitance. Thus, the results of frequency dependent response allow us to investigate greater details of the gas sensing mechanism in ZnO, which may be exploited for selective gas sensing.

Dual-focus contact lenses for myopia control modify central retinal electrophysiology in humans.

Dual-focus contact lenses create two focal planes, one providing a clear retinal image while the other imposes myopic defocus on the retina to slow myopia progression. This study used global-flash multifocal electroretinogram (gmfERG) response amplitudes to compare central versus peripheral retinal responses under dual-focus conditions and to assess the optimal degree of myopic defocus compared with a single-vision control lens. Twenty participants each underwent three gmfERG trials, wearing a spectacle correction over dual-focus contact lenses with plano central power and peripheral secondary focal powers of either +2.00D, +4.00D or a plano single-vision lens. We compared amplitudes and latencies of the gmfERG direct and induced components (DC and IC) within participants, between the three different contact lens powers and at different retinal eccentricities (gmfERG ring). We observed significant differences in the gmfERG responses between the single-vision and dual-focus contact lenses. Overall, DC amplitudes peaked between zero and +2.00D secondary power, while IC amplitudes were maximal between +2.00D and +4.00D. Compared with the single-vision control, the greatest increase in DC and IC amplitudes while wearing dual-focus lenses occurred within the central 10° of the retina. There was no interaction effect between gmfERG ring (eccentricity) and secondary power, and no difference in the latency of the gmfERG responses between different powers. We found that dual-focus contact lenses with a +2.00D secondary power are close to that expected to induce the greatest increase in gmfERG responses relative to a single-vision lens. Dual-focus lenses produced the highest DC and IC response amplitudes relative to a single-vision lens in the central 10° of the retina. This suggests that dual-focus contact lenses slow myopia progression by modifying central rather than peripheral retinal activity.

Identifying and targeting a subpopulation of dendritic cells with enhanced activation of adaptive responses - identifying first responders.

Abstract Dendritic cell (DC) activation via pathogen-associated molecular patterns (PAMPs) is critical for antigen presentation and development of adaptive immune responses, but the stochastic distribution of DC responses to PAMP signaling, especially during the initial stages of immune activation, is poorly understood. In this study, we isolate a unique DC subpopulation via preferential phagocytosis of microparticles (MPs) and characterize this subpopulation of “first responders” (FRs). We present results that show these cells (1) can be isolated and studied via both increased accumulation of the micron-sized particles and combinations of cell surface markers, (2) show increased responses to PAMPs, (3) facilitate adaptive immune responses by providing the initial paracrine signaling, and (4) can be selectively targeted by vaccines to modulate both antibody and T cell responses in vivo. This study presents insights into a temporally controlled, distinctive cell population that influences downstream immune responses. Furthermore, it demonstrates potential for improving vaccine designs via FR targeting. 7U01AI124286-03, 5 F32 AI147517

Electrochemical impedance spectroscopy for studying the SO2 electrocatalytic oxidation on Pt electrodes

The generation of green hydrogen for a more environmentally friendly and energetic environment is in the spotlight of electrocatalysis for a while. One emerging strategy is assisted water electrolysis, in which the oxidative reaction, the limiting one, can be substituted and the SO2 oxidation reaction (SO2OR) is an interesting candidate since it will consume a lethal atmospheric pollutant, at lower potentials. To better comprehend the electrochemical kinetics of this process, in the present work, we applied electrochemical impedance spectroscopy (EIS) as a tool to understand the electrolyte composition's influence on the activity. In this way, we have shown that, despite the three tested electrolytes, 0.5 mol L−1 H2SO4, HClO4, and 1:1 mixture of these two, presented the same DC response, EIS has shown that the adsorption kinetic is different for them all, presenting the different potential of zero charge values, double layer capacitance vs applied potential profiles and very different charge transfer resistance Tafel plots.

Observation of the Superconducting Proximity Effect from Surface States in SmB_{6}/YB_{6} Thin Film Heterostructures via Terahertz Spectroscopy.

The ac conduction of epitaxially grown SmB_{6} thin films and superconducting heterostructures of SmB_{6}/YB_{6} are investigated via time-domain terahertz spectroscopy. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB_{6} thin films, demonstrating the presence of surface states in SmB_{6}. While the observed reductions in the simultaneously measured superconducting gap, transition temperature, and superfluid density of SmB_{6}/YB_{6} heterostructures relative to bare YB_{6} indicate the penetration of proximity-induced superconductivity into the SmB_{6} overlayer; the corresponding SmB_{6}-thickness independence between different heterostructures indicates that the induced superconductivity is predominantly confined to the interface surface state of the SmB_{6}. This study demonstrates the ability of terahertz spectroscopy to probe proximity-induced superconductivity at an interface buried within a heterostructure, and our results show that SmB_{6} behaves as a predominantly insulating bulk surrounded by conducting surface states in both the normal and induced-superconducting states in both terahertz and dc responses, which is consistent with the topological Kondo insulator picture.

Pediatric Ethics Consultation Services, Scope, and Staffing.

National standards and guidelines call for a mechanism to address ethical concerns and conflicts in children's hospitals. The roles, responsibilities, and reach of pediatric ethics consultation services (PECS) remain unmeasured. The purpose of this study is to quantify staffing, structure, function, scope, training, and funding of PECS. Cross-sectional online survey was shared with an ethics informant at 181 children's hospitals in the United States from March to June 2022. Data were summarized descriptively and with semantic content analyses. One hundred seventeen surveys were received from individual children's hospitals in 45 states and Washington DC (response rate 65%), with 104 qualifying for survey completion. Almost one-quarter of settings received 50 or more pediatric ethics consults in the past 12 months. On average, 7.4 people at each institution have responsibility for completing ethics consults. Estimated full-time equivalent salary support for ethics is on average 0.5 (range 0-3, median 0.25). One-third (33%) of facilities do not offer any salary support for ethics and three-quarters do not have an institutional budget for the ethics program. Clinical staff primarily initiate consults. End-of-life, benefits versus burdens of treatments, and staff moral distress were the most frequently consulted themes. Almost one-quarter (21%) of children's hospitals do not receive any consults from patients or families. The findings from this study reveal wide variation in PECS practices and raise concern about the lack of financial support provided for PECS despite substantial workloads.

Influence of Bulk Doping and Halos on the TID Response of I/O and Core 150 nm nMOSFETs

The total ionizing dose sensitivity of planar 150 nm CMOS technology is evaluated by measuring the DC responses of nMOSFETs at several irradiation steps up to 125 krad(SiO2). Different TID sensitivities are measured for transistors built with different channel dimensions and operating voltages (I/O and core). The experimental results evidence strong relations between TID sensitivity and the doping profiles in the channel. I/O transistors have the highest TID sensitivity due to their thicker gate oxide and lower bulk doping compared with core devices. In general, narrow-channel devices have the worst degradation with negative threshold voltage shifts, transconductance variations and increased subthreshold leakage currents, suggesting charge trapping in shallow trench isolation (STI). The enhanced TID tolerance of short-channel core devices is most likely related to the increased channel doping induced by the overlapping of halo implantations. Finally, transistors fabricated for low-leakage applications exhibit near insensitivity to TID due to higher bulk doping used during the fabrication to minimize the drain-to-source leakage current.

Design of a PEM fuel cell powered autonomous quadcopter

The purpose of this paper is to design a PID controller for a detailed nonlinear model of a custom-made quadcopter and utilise the power requirements in designing a proton exchange membrane (PEM) fuel cell system. The first principles methodology to commence with unmanned aerial vehicle architecture is delineated. The empirical actuator response of the brushless DC (BLDC) is obtained which further adds accuracy to the mathematical model of the system. The paper also presents simulations for nonlinear open loop and closed loop feedback with PID controller. The controller gains are obtained from the simulations for hover flight mode. The experimental implementation of battery powered quadcopter is validated with simulation results of PID control design. Finally, for the designed quadcopter, a mathematical model of a PEM fuel cell system to replace battery-specific power requirements is obtained. The key limitation of this paper is the absence of experimental data for fuel cell model due their high cost and low-availability.

Fungal lipase dampens DC response.

Fungal lipase dampens DC response.

Ant colony based optimization model for QoS-based task scheduling in cloud computing environment

Cloud computing has evolved with various techniques for satisfying the needs of users to reduce costs and offer better results. The users' needs may include sharing of resources like memories, processors, apps, information, data, applications, etc., whereas, performance should be in terms of improved DC processing period & response time. Apart from the above-said, there is also a requirement to manage the stability of the system and be flexible to make amendments to the system. Static data is used to optimize the project schedule. However, the traditional does not take into account the personnel allocation matrix when scheduling projects. The ACO model is not a suitable solution to the scheduling problem. The classic ACO methodology operates in two phases: the first phase uses an event-based scheduler to address the complex planning issue. Planning and allocating resources for a project are both constrained by these two approaches. The event-based ACO model was developed to match the resource restrictions and activity schedule to handle dynamic data allocation. When it comes to multi-objective scheduling, EBS with ACO is not an adequate approach. An updated ACO technique to optimum global search employing a neural network approach was presented to schedule many activities to tackle the difficulty of multiple objectives. Using the suggested multi-objective technique, an activity with a defined number of tasks and necessary resources may be optimally organized. The algorithm LBACO is the most effective one to apply for optimizing the objective function, according to the test results, as well as the fastest. An advantage of ACO over other techniques is its ability to provide better plans with higher statistics and mean access times, as well as more consistent job assignments.

A SiGe/Si Phototransistor With High FOM of Gain*VA Using 0.35-μm BiCMOS Technology

A novel SiGe/Si phototransistor with high figure of merit (FOM) of gain*early voltage for optical communication was designed and fabricated in a standard 0.35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> BiCMOS process. A compound base consisting of a P-Si layer and a P+-SiGe layer was designed to achieve a good optical response through relieving the negative influence induced by doped ion’s mutual diffusion in device fabrication. The fabricated surface-illuminated SiGe/Si heterojunction phototransistor (HPT) was measured under 850-nm incident light with a variety of optical powers at 1-V collector bias. When the incident optical power was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.29~\mu \text{W}$ </tex-math></inline-formula> , the collector current reached <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.45~\mu \text{A}$ </tex-math></inline-formula> . The maximum gain exceeded 6.925 with the dark current of about 100 pA. The FOM of gain*early voltage of the proposed SiGe/Si HPT can achieve 100.97. Its optical DC and RF responses under high light power were analyzed with a physically based simulation model, which considered the process effects of device fabrication detailed. The optical gain may promote to 13.3 but with the deteriorated output performance and a smaller early voltage. The maximum optical characteristic frequency may reach 17.6 GHz.

OFDM-Based Intrinsically Safe Power and Signal Synchronous Transmission for CC-PT-Controlled Buck Converters

Intrinsically safe power converters have been highly demanded in many harsh industrial environments, such as gas stations, chemical plants, and mine tunnels, to realize accurate voltage or current regulations with minimum safety risks. Communication among different devices is the key to realizing important operations, such as coordinated control, fault detection, and state update, for intrinsically safe converters. In this article, a capacitor current pulse train (CC-PT) control strategy is designed to increase the dynamic response of dc–dc converter with intrinsic operational safety. An orthogonal frequency-division multiplexing (OFDM) based power and signal synchronous transmission (PSST) method is then proposed. The mathematical models of signal modulation are established, and the intrinsic safety region is drawn in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L–C</i> parameters plane, considering the requirements of electric performance, the inductor disconnection discharging, and output short-circuit tests. Simulations and prototype experiments are conducted and presented to verify the feasibility of the OFDM-based PSST in the CC-PT-controlled buck converter with intrinsically safe parameters.

A comparative analysis of Danionella cerebrum and zebrafish (Danio rerio) larval locomotor activity in a light-dark test.

The genus Danionella comprises some of the smallest known vertebrate species and is evolutionary closely related to the zebrafish, Danio rerio. With its optical translucency, rich behavioral repertoire, and a brain volume of just 0.6 mm3, Danionella cerebrum (Dc) holds great promise for whole-brain in vivo imaging analyses with single cell resolution of higher cognitive functions in an adult vertebrate. Little is currently known, however, about the basic locomotor activity of adult and larval Danionella cerebrum and how it compares to the well-established zebrafish model system. Here, we provide a comparative developmental analysis of the larval locomotor activity of Dc and AB wildtype as well as crystal zebrafish in a light-dark test. We find similarities but also differences in both species, most notably a striking startle response of Dc following a sudden dark to light switch, whereas zebrafish respond most strongly to a sudden light to dark switch. We hypothesize that the different startle responses in both species may stem from their different natural habitats and could represent an opportunity to investigate how neural circuits evolve to evoke different behaviors in response to environmental stimuli.