Rise Time Research Articles

Remarkably High Dielectric Constant and Capacitance Density by Ni/ZrO2/TiN Using Nanosecond Laser and Surface Plasma Effect

Rapid thermal annealing (RTA) has been widely used in semiconductor device processing. However, the rise time of RTA, limited to the millisecond (ms) range, is unsuitable for advanced nanometer-scale electronic devices. Using sub-energy bandgap (EG) 532 nm ultra-fast 15 nanosecond (ns) pulsed laser annealing, a record-high dielectric constant (high-κ) of 67.8 and a capacitance density of 75 fF/μm2 at −0.2 V were achieved in Ni/ZrO2/TiN capacitors. According to heat source and diffusion equations, the surface temperature of TiN can reach as high as 870 °C at a laser energy density of 16.2 J/cm2, effectively annealing the ZrO2 material. These record-breaking results are enabled by a novel annealing method—the surface plasma effect generated on the TiN metal. This is because the 2.3 eV (532 nm) pulsed laser energy is significantly lower than the 5.0–5.8 eV energy bandgap (EG) of ZrO2, making it unabsorbable by the ZrO2 dielectric. X-ray diffraction analysis reveals that the large κ value and capacitance density are attributed to the enhanced crystallinity of the cubic-phase ZrO2, which is improved through laser annealing. This advancement is critical for monolithic three-dimensional device integration in the backend of advanced integrated circuits.

Ultraviolet Photoresponse and Electroluminescence of Exfoliated Ga2O3 Flake on p-type GaN

Abstract β-phase Ga2O3 (β-Ga2O3) is a promising candidate for deep ultraviolet (UV) solar-blind photodetector due to its large bandgap of 4.9 eV. A high crystal quality two-dimensional β-Ga2O3 flake on p-type GaN (p-GaN) surface was formed using a facile mechanical exfoliation and transfer method, and the heterojunction photodiode consisting of an n-type β-Ga2O3 flake on a p-type GaN substrate was fabricated. The device exhibited a distinctive rectifying current-voltage (I-V) characteristics with a rectification ratio of 4.0×105 at ±2 V. The photodetector responded to both 365 nm and 254 nm UV light irradiation with a photocurrent to dark current ratio of 5.64×10⁵% for 365 nm and 3.38×10⁵% for 254 nm UV. The rise and decay time constants for 365 nm and 254 nm deep UV exposure were obtained through dynamic time-dependent photocurrent measurements. In addition, electroluminescence of the p-type GaN/n-type Ga2O3 heterojunction diode was observed under high forward bias condition.

Electron beam monitoring of a modified conventional medical accelerator with a portable current transformer system traceable to primary electrical standards.

Ultra-high dose rate radiotherapy (UHDR) delivers therapeutic doses at rates >40Gy/s in a fraction of a second, aiming to enhance the therapeutic ratio through the FLASH effect. The substantial increase in UHDR beam current poses serious challenges for conventional active dosimeters. Integrating current transformers (ICT) offer a nondestructive solution for accurate monitoring, enabling the type of fast transient readout that will be crucial for UHDR treatment verification. The aim of this study is to build and characterize a clinically deployable ICT system and to develop an accurate calibration methodology for absolute charge determination that is traceable to primary electrical standards. The ICT was constructed from a Super MuMetal® toroid, and its secondary winding was made from 50 Ω coaxial cable. A 3D-printed case with an internal conductive coating shields the toroid assembly from interference. The ICT readout involves a custom differential amplifier and a commercial flash analog-to-digital converter. The system was calibrated using a bespoke sub-µs current pulser in the range of (2 to 16) mA, which itself is traceable to electrical standards via an in-house built electrometer with a calibrated feedback capacitor. The performance of the ICT was evaluated as a milliampere-scale beam monitor against concurrent absorbed dose graphite calorimetry irradiation measurements acquired on a specially tuned medical accelerator for UHDR delivery. The ICT responses for nominal test pulses, generated by a function generator and a current pulser, exhibited accurate reproduction of rise and fall times within the 1ns sampling frequency. A systematic droop effect of 0.6(1)%/µs was observed but is accounted for through the calibration chain. The calibration of the current pulser exhibited a repeatability typically better than 0.05%, with a slowly-varying leakage that can be subtracted using a linear regression of the leakage current. The ICT charge calibration demonstrated a repeatability in the range of (0.5 to<0.05)% for charge per pulse values in the range of (0.5 to 50)nC, respectively. The ICT response showed a strong linear relationship (adj-R2=0.99997) to charge per pulse. The in-beam comparison with a graphite calorimeter demonstrated the effectiveness of the ICT as an online beam monitor, independent of pulse repetition frequency in the range of (25 to 200)Hz, reducing the mean excess (i.e., independent of accelerator output) calorimeter variation to 0.3% (0.1% standard error on the mean). This work demonstrates the feasibility of accurately calibrating the ICT in terms of absolute charge and applying it as a clinically deployable monitoring system of mA-scale electron beams delivered by a medical accelerator.

Investigating charge injection, transport, and electronic performance in rGO-integrated TIPS pentacene blend devices

Abstract This study demonstrates the successful integration of reduced graphene oxide (rGO) into the TIPS pentacene framework, leading to significant enhancements in device performance. The fabricated devices exhibit ideality factors ranging from 2.1 to 2.6, indicating that trap-assisted Shockley Read Hall (SRH) recombination dominates the charge recombination mechanism. The Schottky barrier height (SBH) values, estimated using both the Richardson-Schottky (RS) thermionic emission model and an alternative calculation method, show excellent consistency, confirming the reliability of both approaches. Leakage current is primarily dictated by a direct tunnelling mechanism, while charge conduction is well-explained by the space-charge-limited current (SCLC) model. Optimal device performance, characterized by peak hole mobility and shortest rise times, is achieved with 3% rGO concentration, highlighting its potential for high-speed switching applications. Capacitance-frequency (C–f) analysis reveals a slight frequency dependence at lower frequencies, attributed to charge traps, while the dielectric constants obtained from C–f measurements align with those derived from the RS thermionic emission model. These findings demonstrate the suitability of rGO-doped TIPS pentacene for advanced electronic devices, particularly in high-speed applications.

Cascaded AC-DC parallel boost-flyback converter for power factor correction

A two-stage power factor correction (PFC) topology achieves a higher power factor quality and lower harmonic distortion than a single-stage converter. This paper introduces a two-stage PFC topology using a parallel boost and flyback converter which is employed as a voltage regulator The main boost converter is used for PFC and the other is the active filter circuit. The filter is implemented to improve the quality of phase-current and eliminate the switching loss. Furthermore, a reaction curve of Ziegler-Nichol’s method determines the controller parameter for cascaded PFC converter circuit. Simulated and experimental results are presented to validate the proposed method. The total harmonic distortion (THD) value decreases significantly from 83.35% become 0.98% in the simulation. In addition, experimental results show that the current response has good performances, including less harmonics, higher power factor, and lower THD value compared to without a PFC circuit. The PF increased from 0.43 become 0.96, the THD value decreased from 49.4% become 16.2%, and contains a small number of harmonics. The proposed controller method has better responses than the conventional one, including small steady-state error, fast rise time and settling time. A microcontroller (MCU), type STM32F407VG, produced by STMicroelectronics is used to execute the proposed control in both converters.

Enhanced plasma wave excitation in a tapered plasma channel through chirped laser beatwaves

The excitation of plasma waves by the beatwave of two-color laser beams within a tapered plasma channel has been investigated both analytically and through particle-in-cell (PIC) simulations. This study presents a promising approach for beatwave accelerators. The design aims to achieve a more stable and enhanced plasma wave amplitude, even under non-resonant conditions, compared to untapered channels. For the analytical description, we solved the plasma wave equation generated by two beating laser beams propagating through a tapered channel with a linear radial density profile. The study further validates its results by comparing the analytical predictions with PIC simulations of the beatwave phenomenon in the tapered channel. The findings confirm that this design significantly enhances plasma wave amplitude compared to untapered channels. In addition, we demonstrated that employing a chirped laser pulse with a fast rise time can significantly increase the strength of the plasma wave.

Voltage profile enhancement of an AVR system using ant lion optimization algorithm

Abstract This paper addresses voltage regulation, which is a critical issue in power systems. The automatic voltage regulator (AVR) plays a crucial role in maintaining voltage regulation within permissible limits The AVR system's dynamic behaviour is improved by applying the Proportional (KP) Integral (KI) Derivative (KD) (PID) controller. The primary challenges of using a PID controller in AVR include difficulties in tuning parameters to handle nonlinearities, load disturbances, and system dynamics, leading to potential instability, overshoot, or slow response. The controller parameters are tuned with Ant Lion Optimisation (ALO) algorithm and Integral Time Absolute Error (ITAE) as an objective function. Also, the proposed system has the ability to improve the transient response of AVR by decreasing the maximum overshoot, settling time, rise time, and peak time magnitudes of the generator terminal voltage with eliminating the steady state error. Once the suggested method had produced the best values for the three gains i.e., KP, KI, and KD of the PID controller, a transient response analysis is examined and compared with some of the existing techniques such as Bat Algorithm (BA), Grey Wolf Optimisation (GWO) and Biogeography Based Optimisation (BBO) algorithm to highlight the novelty of the proposed ALO optimized PID controller. Transient response analysis, root locus analysis, and bode analysis are used to assess the AVR system's stability. Comparisons to three well-known optimization techniques corroborate the findings. The results show that this new suggested method performs exceptionally well even when there are significant variations in power system parameters and load uncertainties.

Value of Spleen Dynamic Contrast-enhanced Ultrasound Parameters in Predicting Hepatic Vein Pressure Gradient for Patients With Liver Cirrhosis.

To explore dynamic contrast-enhanced ultrasound (CEUS) parameters in predicting hepatic vein pressure gradient (HVPG) for patients with liver cirrhosis (LC). Noninvasive diagnosis of HVPG remains a challenge. This prospective study included patients with LC undergoing hepatic vein catheterization and pressure measurement at the hospital from May 2021 to January 2023. The CEUS images (Mindray Resona R9, 1-6-MHz probe frequency; mechanical index=0.08; image depth=10cm; focus at the lowest point of the diaphragm; dynamic range=70dB; optimal gain; single SonoVue bolus injection) were taken for 60 seconds after injection and analyzed using VueBox. HVPG (ie, the gold standard for portal hypertension) was measured routinely by catheterization. Fifty patients with LC were included in the study. The rise time (r=0.6, P<0.01), the fall time (r=0.7, P<0.01), the peak time (r=0.6, P<0.01), wash-in area under the curve (AUC) (r=0.5, P<0.01), the wash-out phase AUC (r=0.4, P<0.01) and wash-in and wash-out phase AUC (r=0.4, P<0.01) of the dynamic spleen CEUS were positively correlated with HVPG. The optimal fall time cutoff levels to predict HVPG ≥10mmHg and ≥12mmHg were 27.0 and 36.4 seconds, with the AUC being 0.958 and 0.941, respectively. The optimal area under the wash-in area cutoff level to predict HVPG ≥10mmHg and ≥12mmHg was 1,658,967.38 (a.u) and 4,244,015.90 (a.u), with the AUC being 0.865 and 0.877, respectively. The fall time and wash-in AUC obtained by dynamic CEUS may help diagnose HVPG in patients with LC without requiring invasive hepatic vein catheterization.

A magnetic field compatible readout circuit for enhanced coincidence time resolution in BGO Cherenkov radiation-based TOF-PET detectors.

Developing time-of-flight positron emission tomography/magnetic resonance imaging (TOF-PET/MRI) detectors that exploit prompt Cherenkov photons from bismuth germanate (BGO) crystals for estimating 511keV photon arrival time. To present a low-noise, high-speed electronic readout circuit design for BGO-based TOF-PET detectors that achieves enhanced coincidence time resolution (CTR) in presence of a strong magnetic field. The CTR of a BGO-based TOF-PET test detector employing a high-speed, low-noise electronic readout chain was evaluated in a strong magnetic field produced by a permanent magnet placed directly on top of the circuit. For these experiments, which exploit Cherenkov radiation for precise measurement of annihilation photon time arrival time difference, a point source of 22Na was positioned between a pair of 3×3×15mm3 polished BGO crystals wrapped in Teflon tape and optically coupled to 3×3mm2 ultra-violet (UV)-sensitive silicon photomultipliers (SiPMs). By incorporating both Cherenkov (prompt) and standard (slow) luminescence components, 283±8ps and 275±10ps full-width-half-maximum(FWHM) CTR were achieved without and with the permanent magnet present, respectfully. These values improved to 236±4ps and 216±17ps FWHM when only the Cherenkov components of the timing signal (events with the fastest rise time) were considered. Results indicate we have designed a high-performance readout circuit that achieves significantly the same CTR in BGO with or without a strong magnetic field present. This further demonstrates that UV SiPMs can effectively operate in a strong magnetic field while remaining highly advantageous for detecting Cherenkov radiation, thus highlighting their potential to be used in BGO-based TOF-PET/MRI scanners.

High-Voltage Pulsed Power Generator for Beam Injection Systems

Beam injection systems in hadron colliders require kickers generating ±50 kV peak voltages into a 50 Ω impedance, with peak currents of 1000 A and sub-10 ns rise and fall times. This paper presents a novel high-voltage pulse power generator utilizing a distributed pulser architecture. It combines gallium nitride (GaN) transistors in a Marx topology with an inductive adder, achieving nanosecond-scale switching speeds and high-power efficiency. Compared to other solutions such as based on MOSFETs or fast ionization dynistors, our development offers superior peak and average power performance, reduced system complexity, and enhanced reliability, marking a significant step forward in high-voltage pulse generation for accelerator applications.

Measurement and spectral analysis of medical shock wave parameters based on flexible PVDF sensors.

Extracorporeal shock wave therapy (ESWT) achieves its therapeutic purpose mainly through the biological effects produced by the interaction of shock waves with tissues, and the accurate measurement and calculation of the mechanical parameters of shock waves in tissues are of great significance in formulating the therapeutic strategy and evaluating the therapeutic effect. This study utilizes the approach of implanting flexible polyvinylidene fluoride (PVDF) vibration sensors inside the tissue-mimicking phantom of various thicknesses to capture waveforms at different depths during the impact process in real time. Parameters including positive and negative pressure changes (P+, P-), pulse wave rise time ([Formula: see text]), and energy flux density (EFD) are calculated, and frequency spectrum analysis of the waveforms is conducted. The dynamic response, propagation process, and attenuation law of the shock wave in the phantom under different impact intensities were analyzed. Results showed that flexible PVDF sensors could precisely acquire the characteristics of pulse waveform propagating within the phantom. At the same depth, as the driving pressure increases, P+ and P- increase linearly, and [Formula: see text] remains constant. At the same driving pressure, P+, P-, and EFD decay exponentially with increasing propagation depth. At the same depth, the spectra of pulse waveforms are similar, and the increasing driving pressure does not cause significant changes in carrier frequency and modulation frequency. The research findings could provide a reference for developing ESWT devices, improving treatment strategies, and enhancing the safety of clinical applications.

Temperature and pump modulation investigation of an Er:Yb co-doped fiber laser with optimized SWaP

This paper presents the results of experimental and theoretical studies of the influence of temperature and pump modulation on an erbium:ytterbium co-doped fiber laser in context for an optimized size, weight, and power (SWaP) integration. The fiber laser setup including the active fiber and pump diode lasers are heated up or cooled down for ranging temperatures from 0°C till 60°C and in parallel the output power is measured. Experimental results show that the slope efficiency of the fiber laser is constant over the measured temperature range. A slight decrease of the electro-optical conversion efficiency with increasing temperature is observed. Furthermore, the erbium:ytterbium co-doped fiber laser is pump modulated and the rise time as well as the frequency response is measured. The experimental results of the pump modulated fiber laser are compared with a time resolved simulation. The investigation shows that a minimum rise time of 36.6 µs and a maximum modulation depth of 9.4 dB can be reached. Moreover, the modulated laser amplitude is measured. The laser amplitude experiences a 3 dB attenuation at a modulation frequency of 20 kHz that agrees with the simulation results taking partly coupled ytterbium ions into account.

Optically Pumped Ultrafast and Broadband Terahertz Modulation with Scalable Molecular Beam Epitaxy Grown MoTe2/Si Heterostructures

AbstractDespite advancements in terahertz (THz) modulators, achieving a balance between large modulation depth (MD) and fast modulation speed in scalable devices remains a significant challenge. Optically pumped THz modulators with high MD, broad bandwidth, and fast response times are essential for progress in THz technology. Here, scalable MoTe2/Si van der Waals (vdW) heterostructures are grown via molecular beam epitaxy (MBE) as an optically pumped THz modulators, leveraging its favorable band alignment and seamless integration with silicon complementary metal‐oxide semiconductor (CMOS) technology. High‐quality bilayer, 5‐layer, and 7‐layer MoTe2 films are grown on high‐resistivity silicon, with the bilayer modulator achieving a maximum 74.6% modulation depth under 355 nm illumination of 4.8 W mm−2 at 0.25 THz. The bilayer device exhibited fast rise and fall times of 1.8 and 0.6 µs, respectively, and provided broadband modulation across the 0.1 to 1.0 THz range. Furthermore, this work demonstrates that higher modulation depth significantly enhances THz imaging quality with promising applications in detecting pharmaceutical forgeries. Overall, these ultrafast, broadband THz modulators provide a promising route for advancing next‐generation THz technology, enhancing applications in wireless communication, precision detection, and high‐resolution THz imaging, fostering future innovation.

Evaluation value of contrast enhanced ultrasound quantitative parameters in ischemic-type biliary lesions after liver transplantation-a prospectively study.

To explore the evaluation value of contrast enhanced ultrasound (CEUS) quantitative parameters in ischemic-type biliary lesions after liver transplantation to assist its early-diagnosis. Patients who underwent liver transplantation and intravenous CEUS at Beijing Friendship Hospital, Capital Medical University from June 25, 2020 to December 28, 2022 and were diagnosed with Ischemic-type biliary lesions (ITBLs) by Magnetic Resonance Cholangiopancreatography (MRCP) or Endoscopic Retrograde Cholangiopancreatography (ERCP) or Percutaneous Transhepatic Cholangiography (PTC) were prospectively enrolled. SonoLiver software was used to quantitatively analyze the contrast images, transplanted livers with normal biliary tracts as the control group. SPSS 25.0 software was used to analyze the data. There was a total of 35 patients enrolled in the study, and 15 ITBLs and 30 normal biliary tract of transplanted livers, respectively. The dynamic vascular patterns (DVP) curve of the ITBLs group was negative wave, while the DVP curve of the normal biliary tract group was positive wave. Compared with the patients with normal biliary tract, the Maximum intensity (IMAX), Rise slope 50% (Rs50), Area under curve (AUC), Area under curve in Wash-in phase (WinAUC), Wash in Rate (WinR), Rise slope 10-90% (Rs1090), and Wash out Rate (WouR) of the ITBLs group were lower, while the Fall slope (Fs50) was higher. There was no significant difference in Rise time (RT), Time to Peak (TTP), Fall half time (FHT), Mean transit time (mTT), Fall time (FT), WioAUC ((WioAUC = WinAUC + WouAUC)), and Area under curve in Wash-out phase (WouAUC) between the two groups (P > 0.05). The ROC curve results showed that Fs50 > -2.64 was the cutoff value for predicting ITBLs, with an area under the curve of 0.816 (95%CI: 0.683-0.949), and a sensitivity and specificity of 0.846 and 0.607; Rs50 < 7.08, AUC < 39761.7050, WinR < 101.7 and WouR < 474.52 were the cutoff values ​​for predicting ITBLs, with areas under the curve of 0.853 (95%CI: 0.728-0.979), 0.911 (95%CI: 0.783-1.000), 0.756 (95%CI: 0.615-0.896) and 0.700 (95%CI: 0.536-0.864). The quantitative parameters of CEUS imaging, such as IMAX, Rs50, AUC, WinAUC, WinR, Rs1090, WouR, and Fs50, are helpful in predicting ITBLs and improving the reproducibility of diagnosis. The threshold of these quantitative parameters will aid in the early diagnosis of ischemic-type biliary lesions after liver transplantation.

Low-cost physiology and behavioral monitor for intravital imaging in small mammals.

Functional brain imaging experiments in awake animals require meticulous monitoring of animal behavior to screen for spontaneous behavioral events. Although these events occur naturally, they can alter cell signaling and hemodynamic activity in the brain and confound functional brain imaging measurements. We developed a centralized, user-friendly, and stand-alone platform that includes an animal fixation frame, compact peripheral sensors, and a portable data acquisition system. The affordable, integrated platform can benefit imaging experiments by monitoring animal behavior for motion detection and alertness levels as complementary readouts for brain activity measurements. A custom acquisition system was designed using a powerful, inexpensive microcomputer. We customized an accelerometer and miniature camera modules for efficient, real-time monitoring of animal motion detection and pupil diameter. We then tested and validated the platform's performance with optical intrinsic signal imaging and GCaMP fluorescence calcium imaging in functional activation experiments in awake mice. The integrated platform shows promise for detecting spontaneous motion and pupil dilation while imaging. Stimulus-induced pupil dilation was found to initiate earlier than cortical hemodynamics with a slower rise time. Compared with neuronal calcium response, stimulus-induced pupil dilation initiated later with a slower rise time. We developed an integrated platform to monitor animal motion and pupil dynamics. The device can be easily coupled and synchronized with optical brain imaging systems to monitor behavior, alertness, and spontaneous motion for awake animal studies.

Anomalous Ultra‐Broadband Photoresponse Based on PdSe2 with Asymmetric Contact

AbstractAnomalous photoresponse with negative photoconductance (NPC) is rarely observed which is quite different from the common semiconductor with positive photoconductance (PPC) as the light can induce additional carriers. NPC effect is not widely studied because the performance of the NPC is limited and the device fabrication is uncontrollable. Here, a controllable way is reported to fabricate an anomalous photoresponse device through asymmetric metal contact with the PdSe2. A mirror electrode‐enhanced vertical asymmetric contact (VAC) PdSe2 device is designed. The VAC PdSe2 device demonstrated the NPC effect in an ultra‐broadband spectral range from 637 nm to the long‐wave infrared (LWIR) 10.6 µm. Notably, the device exhibits excellent uncooled mid‐wave infrared (MWIR) and LWIR detection ability with a high photoresponsivity (R) of 128.4 AW−1 and 38.2 AW−1, respectively. Furthermore, the lateral asymmetric contact (LAC) PdSe2 device is also investigated. The LAC PdSe2 device demonstrated competitive performance including high photovoltaic responsivity up to 0.22 AW−1 and external quantum efficiency (EQE) of 67.5%, fast photoresponse speed with rise time τr = 28.7 µs and decay time τd = 31.2 µs, and anisotropic dichroic ratio (γ) of ≈1.15. The results open a new platform for studying anomalous photoresponse with high performance in uncooled LWIR photodetection.

Increased motor performance and responsivity in physical fitness after high-intensity functional training in excess weight adolescents

Introduction: Motor competence (MC) is essential for motor development and an active lifestyle. However, adolescents with excess weight face challenges like low physical fitness and cardiometabolic alterations that affect MC. While high-intensity functional training (HIFT) improves physical fitness and reduces cardiometabolic risks, its effects on MC remain underexplored. Objective: This study aimed to investigate the impact of different types of physical training on motor competence and physical fitness in excess weight adolescents. Methodology: The sample had 46 adolescents of both sexes, aged 10 to 16 years, distributed into HIFT(n=10), high-intensity interval training (HIIT, n=12), moderate-intensity continuous training (MICT, n=12), and control group (CG, n=12). Anthropometric measurements, body composition, physical fitness, and motor competence with supine-to-stand time (STSTIME) were assessed before and after the intervention. Repeated measures ANOVA, effect size, and prevalence of respondents were used for statistical analysis. Results: HIFT had a decrease in BMI (p=0.04), WHtR (p=0.050), and %FM (p&lt;0.001), an increase in %FFM (p&lt;0.001), ABD strength (p&lt;0.01), and flexibility (p&lt;0.03), and very beneficial improvement in STSTIME (p&lt; 0.001) in relation to the other groups. On the other hand, HIIT (p&lt;0.003) and MICT (p&lt;0.02) had greater handgrip strength than HIFT. Furthermore, higher frequencies of HIFT respondents had a decrease in BMI and %FM and an increase in %FFM (p&lt;0.05), flexibility, and STSTIME in relation to the other groups (p=0.001). Conclusions: HIFT was significantly more effective than the other protocols in improving body composition, abdominal strength, flexibility, and floor rise time.

The Impact of Optical Undersampling on the Ca2+ Signal Resolution in Ca2+ Imaging of Spontaneous Neuronal Activity.

In neuroscience, Ca2+ imaging is a prevalent technique used to infer neuronal electrical activity, often relying on optical signals recorded at low sampling rates (3 to 30 Hz) across multiple neurons simultaneously. This study investigated whether increasing the sampling rate preserves critical information that may be missed at slower acquisition speeds. Primary neuronal cultures were prepared from the cortex of newborn pups. Neurons were loaded with Oregon Green BAPTA-1 AM (OGB1-AM) fluorescent indicator. Spontaneous neuronal activity was recorded at low (14 Hz) and high (500 Hz) sampling rates, and the same neurons (n = 269) were analyzed under both conditions. We compared optical signal amplitude, duration, and frequency. Although recurring Ca2+ transients appeared visually similar at 14 Hz and 500 Hz, quantitative analysis revealed significantly faster rise times and shorter durations (half-widths) at the higher sampling rate. Small-amplitude Ca2+ transients, undetectable at 14 Hz, became evident at 500 Hz, particularly in the neuropil (putative dendrites and axons), but not in nearby cell bodies. Large Ca2+ transients exhibited greater amplitudes and faster temporal dynamics in dendrites compared with somas, potentially due to the higher surface-to-volume ratio of dendrites. In neurons bulk-loaded with OGB1-AM, cell nucleus-mediated signal distortions were observed in every neuron examined (n = 57). Specifically, two regions of interest (ROIs) on different segments of the same cell body displayed significantly different signal amplitudes and durations due to dye accumulation in the nucleus. Our findings reveal that Ca2+ signal undersampling leads to three types of information loss: (1) distortion of rise times and durations for large-amplitude transients, (2) failure to detect small-amplitude transients in cell bodies, and (3) omission of small-amplitude transients in the neuropil.

High-Performance Ultraviolet Photodetector Based on the Vertical GaSe/GaN Heterojunction.

Ultravioletlight detection is essential for environmental monitoring, hazard alerting, and optical communication. Here,a vertical UV photodetector is proposed and demonstrated by stacking the freestanding GaN-film on the 2DGaSe flake. Benefits from the vertical heterostructure and built-in electric field, the photodetector exhibits excellent photoresponse properties, including a high responsivity of 1.38 × 105 A/W and a high specific detectivity of 1.40 × 1016 Jones under 362nm wavelength illumination. Additionally, the device demonstrates fast rise and decay time of 18.0 and 21.8 µs, respectively. This work paves the way for design and realization of the high-performance GaN-based photodetectors.

Estimation of Equivalent Series Resistance (ESR) of Supercapacitors Using Charging/Discharging Kinetics.

One of the key parameters that affects efficiency, power density and performance of a supercapacitor (SC) is the equivalent series resistance (ESR). In this study we propose a method to estimate ESR from the charging kinetics which has practical applications. Therefore, to study the ESR of the SC we must look at the different factors that affect this resistance. In this study, the rise time extracted from the charging kinetics curves of the SC was used as an indirect method to investigate the ESR of the SC. Three different parameters were taken into account: ionic mobility, solvent material and pore cavity size of the porous electrode. The results offer enlightening information for optimizing the design of the SC with higher performance and smaller ESR values that will be translated into a better energy storage technologies.