Millisecond Range Research Articles

Synthesis and optical properties of Tb3+ or Dy3+-doped MgAl2O4 transparent ceramics

MgAl2O4 ceramics doped with rare earth ions (Tb3+ and Dy3+ ions) were fabricated by SPS technique. Optical properties and pulse cathodoluminescence (PCL) spectra were studied. The redshift effect of the absorption boundary for rare earth (RE) ions doped ceramics was shown. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63 eV caused by F-type centers. It has been demonstrated that the introduction of terbium and dysprosium ions practically does not change the intensity ratio of the bands at 2.72, 3.01, 3.37 eV, but leads to an increase in the band at 3.63 eV in nanosecond time range. There are emission bands related to intrinsic host defects, RE ions dopants (Dy3+, Tb3+), and trace elements (Cr3+ ions) in PCL spectra measured in millisecond time range. The dependences of kinetic characteristics of spinel ceramics were studied. In nanosecond time range, decay kinetics of the MAS ceramics is described by the sum of two exponentials with luminescence decay times are 30 ± 5 ns and 0.8 ± 0.1 μs In the millisecond time interval, the luminescence decay time depends on the dopant ions.

Perceptual timing in children with attention-deficit/hyperactivity disorder (ADHD) as measured by computer-based experiments versus real-life tasks: protocol for a cross-sectional experimental study in an ambulatory setting

IntroductionThe goal of this study is to get a better understanding of the fundamentals of perceptual timing deficits, that is, difficulties with estimating durations of explicitly attended temporal intervals, in...

Arbitrary spectral matching using multi-LED lighting systems

Spectrally tunable light sources for general lighting have recently attracted much attention as versatile solutions that can be used in humancentric lighting implementations provided with excellent color rendering and increased user perception. However, temperature and age-dependent color shifts and flux variations in the light-emitting diode (LED) emission are nonresolved challenges that need to be overcome in order to be used in final applications. We demonstrate two strategies that can be used to efficiently and precisely generate arbitrary spectral power distributions (SPDs) using multichannel LED engines. First, we introduce different methods to match a given SPD and select an algorithm (simulated annealing) in virtue of its speed (in the milliseconds range) and accuracy (color shifts Δu ′ v ′ < 5 × 10 − 4). Then, we propose a closed-loop feedback control (PID) to compensate for spectral shifts due to temperature changes or lumen decay of the LEDs. Both methods can be used independently, but only a combination of them (which uses the output of the first method as an initial guess for the second) offers fast computational times and high spectral accuracy and precision. Computation times are important because these algorithms are intended to be executed on dedicated microprocessors integrated in the LED modules, often sharing scarce memory and processing resources. The results presented here are aimed to be universal and hold for different implementations of the light engine and any number of LED channels.

Imaging photoinduced surface potentials on hybrid perovskites by real-time Scanning Electron Microscopy

We introduce laser-assisted Time-Resolved SEM (TR-SEM), joining Scanning Electron Microscopy and laser light excitation, to probe the long-term temporal evolution of optically excited charge distributions at the surface of Metal Ammonium Lead Triiodide (MAPbI3) hybrid perovskite thin films. Laser-assisted TR-SEM relies on the optically induced local modification of Secondary Electron (SE) detection yield to provide mapping of photoexcited potentials and charge dynamics at surfaces, and qualifies as a complementary approach to near-field probe microscopies and nonlinear photoemission spectroscopies for photovoltage measurements. Real-time imaging of evolving field patterns are provided on timescales compatible with SEM scanning rates, so that temporal resolution in the millisecond range can be ultimately envisaged. MAPbI3 is an outstanding light-sensitive material candidate for applications in solar light harvesting and photovoltaics, also appealing as an active system for light generation. In this work, the real time temporal evolution of optically induced SE contrast patterns in MAPbI3 is experimentally recorded, both under illumination by a 405 nm blue laser and after light removal, showing the occurrence of modifications related to photoinduced positive charge fields at surface. The long term evolution of these surface fields are tentatively attributed to ion migration within the film, under the action of the illumination gradient and the hole collecting substrate. This optical excitation is fully reversible in MAPbI3 over timescales of hours and a complete recovery of the system occurs within days.Permanent irradiation damage of the material is avoided by operating the SEM at 5 keV of energy and 1–10 pA of primary current. Optical excitation is provided by intense above-bandgap illumination (up to 50 W/cm2). TR-SEM patterns show a strong dependence on the geometry of SE collection. Measurements are taken at different axial orientations of the sample with respect to the entrance of the in-column detection system of the SEM and compared with numerical modeling of the SE detection process. This enables to single out the information regarding the local potential distribution. Results are interpreted by combining data about the spectral distribution of emitted SEs with the configuration of the electric and magnetic fields in the specimen chamber. The present modeling sets a robust basis for the understanding of photoinduced SE electron contrast.

Capturing the spatiotemporal dynamics of self-generated, task-initiated thoughts with EEG and fMRI

The temporal structure of self-generated cognition is a key attribute to the formation of a meaningful stream of consciousness. When at rest, our mind wanders from thought to thought in distinct mental states. Despite the marked importance of ongoing mental processes, it is challenging to capture and relate these states to specific cognitive contents. In this work, we employed ultra-high field functional magnetic resonance imaging (fMRI) and high-density electroencephalography (EEG) to study the ongoing thoughts of participants instructed to retrieve self-relevant past episodes for periods of 22sec. These task-initiated, participant-driven activity patterns were compared to a distinct condition where participants performed serial mental arithmetic operations, thereby shifting from self-related to self-unrelated thoughts. BOLD activity mapping revealed selective enhanced activity in temporal, parietal and occipital areas during the memory compared to the mental arithmetic condition, evincing their role in integrating the re-experienced past events into conscious representations during memory retrieval. Functional connectivity analysis showed that these regions were organized in two major subparts, previously associated to “scene-reconstruction” and “self-experience” subsystems. EEG microstate analysis allowed studying these participant-driven thoughts in the millisecond range by determining the temporal dynamics of brief periods of stable scalp potential fields. This analysis revealed selective modulation of occurrence and duration of specific microstates in the memory and in the mental arithmetic condition, respectively. EEG source analysis revealed similar spatial distributions of the sources of these microstates and the regions identified with fMRI. These findings imply a functional link between BOLD activity changes in regions related to a certain mental activity and the temporal dynamics of mentation, and support growing evidence that specific fMRI networks can be captured with EEG as repeatedly occurring brief periods of integrated coherent neuronal activity, lasting only fractions of seconds.

Design and optimization of optical passive elements using artificial neural networks

Artificial neural networks (ANNs) have been recognized as a fast and flexible tool for microwave modeling, design, and optimization. Similarly, ANNs can be utilized in the design and optimization of photonic devices to provide fast simulation and speed up the design process. ANN models can produce great efficiency in design and optimization processes when repetitive computationally intensive simulations are required for modeling of optical passive elements using commercial tools. In this paper we explore how trained ANNs can be utilized for the fast simulation of optical passive elements, while attaining high accuracy. We present the design of four fundamental optical passive elements using commercial tools and compare the results with our trained ANN model. In all four examples illustrated, the error ranges from 0.5% to 1.7% while the simulation time is in the range of milliseconds instead of minutes or hours. Finally, we discuss possible uses of these trained ANNs with respect to the design, optimization, and statistical validation of photonic devices.

Dynamic Modeling and Characteristic Analysis of Cantilever Piezoelectric Bimorph

The analytical model of an axially precompressed cantilever bimorph is established using the Hamilton’s principle in this study, and the static characteristics are obtained. The dynamic equations of the cantilever bimorph in generalized coordinates are established using a numerical method, and the dynamic characteristics are analyzed. Finally, simulations are performed and experiments are conducted to verify the validity of the theory. The results show that increase of axial force has significant amplification effects on the steady-state response amplitude of the displacement, and it reduces the resonance frequency. The response time is still in the millisecond range under a large axial force, which indicates that the bimorph has excellent dynamic characteristics as an actuator.

Silicon Nitride Barrier Layers Mitigate Minority-Carrier Lifetime Degradation in Silicon Wafers During Simulated MBE Growth of III–V Layers

We observe a degradation of the minority-carrier lifetime in silicon substrates after a temperature cycle in a molecular beam epitaxy (MBE) chamber that is representative of the growth of III–V materials. This decrease in the lifetime is from milliseconds to microseconds, and in some cases into the sub-microsecond range. The degradation appears to be caused by thermally activated diffusion of metals from the back side of the substrate, occurring at temperatures above 500 °C. This impacts the ability to achieve high-performance monolithic III–V/Si multi-junction solar cells, since the epitaxial growth usually requires high-temperature steps (over 700 °C) for surface de-oxidation or surface reconstruction and temperatures of 400–600 °C during the epitaxial growth. We show that, through phosphorous diffusion gettering, the lifetimes of degraded wafers can be recovered to the millisecond range. Further, we demonstrate that a silicon nitride coating functions both as a diffusion barrier and as an interfacial gettering or hydrogenation agent, enabling high minority-carrier lifetimes directly out of the MBE chamber. This approach allows for the silicon minority-carrier lifetime to be maintained in the millisecond range without the need for post-growth recovery, providing a path to achieve high-efficiency III–V/Si solar cells.

Spin transport in the bulk of two-dimensional Hall insulator

Magneto-fermionic condensate under study is a Bose-Einstein condensate of cyclotron spin-flip magnetoexcitons in a quantum Hall insulator. This condensate features unique properties such as millisecond range lifetime and hundreds of micrometers of propagation length. In this study, utilizing the photo-induced resonant reflection technique, we measured the exciton escape time. Finally, we estimated the exciton condensate propagation velocity as 25 m/s, which is much higher than a single particle propagation velocity. We also proposed a mechanism of exciton condensation.

Ultrasonic Fabrication of Polymer Plate Reactors with a Surface Coating

AbstractMicroreactors offer several advantages compared to the industrial scale when developing new chemical processes. Especially the production and investment costs are low if polymer microreactors are generated by ultrasonic processes. In order to observe the chemical reaction and the flow configuration, these microreactors need to be optically transparent, mechanically stable, and chemically inert to several reagents. The manufacturing process of a transparent polymer plate reactor with a chemically inert surface coating by ultrasonic fabrication is described. Experimental characterization of the microreactors showed that they are leak tight up to a pressure difference of at least 300 kPa and the mixing times are in the range of milliseconds.

Solar blind Schottky photodiode based on an MOCVD-grown homoepitaxial β-Ga2O3 thin film

We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 Å thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths &amp;lt; 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.

Kinetic Measurements of Singlet Oxygen Phosphorescence in Hydrogen-Free Solvents by Time-Resolved Photon Counting.

Solvents lacking hydrogen atoms are very convenient models for elucidating the properties of singlet oxygen, since the lifetime of singlet oxygen in these solvents reaches tens milliseconds. Measuring intrinsic infrared (IR) phosphorescence of singlet oxygen at 1270 nm is the most reliable method of singlet oxygen detection. However, efficient application of the phosphorescence method to these models requires an equipment allowing reliable measurement of the phosphorescence kinetic parameters in the millisecond time range at low rates of singlet oxygen generation, which is a technically difficult problem. Here, we describe a highly sensitive LED (laser) spectrometer recently constructed in our laboratory for the steady-state and time-resolved measurements of the millisecond phosphorescence of singlet oxygen. In the steady-state mode, this spectrometer allows detection of singlet oxygen phosphorescence upon direct excitation of oxygen molecules in the region of dark-red absorption bands at 690 and 765 nm. For kinetic measurements, we used phenalenone as a photosensitizer, microsecond pulses of violet (405 nm) LED for excitation (irradiance intensity, ≤50 μW/cm2), a photomultiplier and a computer multichannel scaler for time-resolved photon counting. The decays of singlet oxygen in air-saturated CCl4, C6F6, and Freon 113 and quenching of singlet oxygen by phenalenone and dissolved molecules of triplet oxygen were measured. The relative values of the radiative rate constants of singlet oxygen in these media were determined. The results were compared with the absorption coefficients of oxygen measured by our group using the methods of laser photochemistry. Critical discussion of the obtained results and the data of other researchers is presented.

A software framework for embedded nonlinear model predictive control using a gradient-based augmented Lagrangian approach (GRAMPC)

A nonlinear MPC framework is presented that is suitable for dynamical systems with sampling times in the (sub)millisecond range and that allows for an efficient implementation on embedded hardware. The algorithm is based on an augmented Lagrangian formulation with a tailored gradient method for the inner minimization problem. The algorithm is implemented in the software framework GRAMPC and is a fundamental revision of an earlier version. Detailed performance results are presented for a test set of benchmark problems and in comparison to other nonlinear MPC packages. In addition, runtime results and memory requirements for GRAMPC on ECU level demonstrate its applicability on embedded hardware.

Broadband Ultraviolet Photodetector Based on Vertical Ga2O3/GaN Nanowire Array with High Responsivity

AbstractBroadband ultraviolet (BUV) photodetectors responding to the multiband spectrum can effectively reduce false alarm rates and improve the accuracy and versatility of detection systems in various situations. A high‐responsivity BUV photodetector based on vertical Ga2O3/GaN nanowire array is proposed and demonstrated. Ga2O3/GaN nanowires are obtained by partially thermally oxidizing GaN nanowires grown by molecular beam epitaxy and used to combine with a monolayer graphene film to form graphene/Ga2O3/GaN heterojunction. Moreover, the oxidation mechanism of GaN nanowires is further investigated by the developed thermal oxidation model. The fabricated devices exhibit excellent performance with a broadband spectral response of exceeding 550 A W−1 at −5 V and a fast‐response speed in the millisecond range, which can be attributed to the optical properties of vertical nanowire array structure and the internal gain mechanism of graphene/Ga2O3/GaN heterojunction.

Platelet-based Detection of Nitric Oxide in Blood by Measuring VASP Phosphorylation.

Platelets are the blood components responsible for proper blood clotting. Their function is highly regulated by various pathways. One of the most potent vasoactive agents, nitric oxide (NO), can also act as a powerful inhibitor of platelet aggregation. Direct NO detection in blood is very challenging due to its high reactivity with cell-free hemoglobin that limits NO half-life to the millisecond range. Currently, NO changes after interventions are only estimated based on measured changes of nitrite and nitrate (members of the nitrate-nitrite-NO metabolic pathway). However precise, these measurements are rather difficult to interpret vis a vis actual NO changes, due to the naturally high baseline nitrite and nitrate levels that are several orders of magnitude higher than expected changes of NO itself. Therefore, the development of direct and simple methods that would allow one to detect NO directly is long overdue. This protocol addresses a potential use of platelets as a highly sensitive NO sensor in blood. It describes initial platelet rich plasma (PRP) and washed platelet preparations and the use of nitrite and deoxygenated red blood cells as NO generators. Phosphorylation of VASP at serine 239 (P-VASPSer239) is used to detect the presence of NO. The fact that VASP protein is highly expressed in platelets and that it is rapidly phosphorylated when NO is present leads to a unique opportunity to use this pathway to directly detect NO presence in blood.

A new fast algorithm to compute continuous moments defined in a rectangular region

In this research, we have developed a new algorithm to compute the moments defined in a rectangular region. By applying the recurrent formulas, symmetry properties, and particularly the parallelized matrix operations, our proposed computational method can improve the efficiency of computing Legendre, Gegenbauer, and Jacobi moments extensively with highly satisfied accuracy. To verify this new computational algorithm, the image reconstructions from the higher orders of Legendre, Gegenbauer, and Jacobi moments are performed on a testing image sized at 1024 × 1024 with very encouraging results. It took only a few seconds to compute moments and conduct the image reconstructions from the 1000-th order of the Legendre, Gegenbauer, and Jacobi moments with the PSNR values up to 45. By utilizing our new algorithm, image analysis and recognition applications using the higher orders of moments defined in a rectangular region in the range of milliseconds will be possible.

Soft inequality constraints in gradient method and fast gradient method for quadratic programming

A quadratic program (QP) with soft inequality constraints with both linear and quadratic costs on constraint violation can be solved with the dual gradient method (GM) or the dual fast gradient method (FGM). The treatment of the constraint violation influences the efficiency and usefulness of the algorithm. We improve on the classical way of extending the QP: our novel contribution is that we obtain the solution to the soft-constrained QP without explicitly introducing slack variables. This approach is more efficient than solving the extended QP with GM or FGM and results in a similar algorithm than if the soft constraints were replaced with hard ones. The approach is intended for applications in model predictive control with fast system dynamics, where QPs of this type are solved at every sampling time in the millisecond range.

Spatial and Spectral Auditory Temporal-Order Judgment (TOJ) Tasks in Elderly People Are Performed Using Different Perceptual Strategies.

The Temporal-Order Judgment (TOJ) paradigm has been widely investigated in previous studies as an accurate measure of temporal resolution and sequencing abilities in the millisecond time range. Two auditory TOJ tasks are often used: (1) a spatial TOJ task, in which two identical stimuli are presented in rapid succession monaurally and the task is to indicate which ear received the first stimulus and which ear received the second one (left-right or right-left), and (2) a spectral TOJ task, in which two tones of different frequencies are presented asynchronously to both ears binaurally and the task is to report the sequence of these tones (low-high or high-low). The previous literature studies conducted on young volunteers indicated that the measured temporal acuity on these two tasks depended on the procedure used. As considerable data are now available about age-related decline in temporal resolution ability, the aim of the present study was to compare in elderly subjects the pattern of performance on these two tasks. A total of 40 normal healthy volunteers aged from 62 to 78 years performed two TOJ tasks. The measurement was repeated in two consecutive sessions. Temporal resolution was indexed by the Auditory Temporal-Order Threshold (ATOT), i.e., the minimum time gap between successive stimuli necessary for a participant to report a before-after relation with 75% correctness. The main finding of the present study was the indication of differences in the elderly in performance on two tasks. In the spatial task, the distribution of obtained ATOT values did not deviate from the Gaussian distribution. In contrast, the distribution of data in the spectral task deviated significantly from the Gaussian and was spread more to the right. Although lower ATOT values were usually observed in Session 2 than in Session 1, such difference was significant only in the spectral task. We conclude that although temporal acuity and sequencing abilities in the millisecond time range are probably based in neuronal oscillatory activity, the measured ATOTs in the elderly seem to be stimulus-dependent, procedure-related, and influenced by the perceptual strategies used by participants.

Direct measurement of the magnetocaloric effect on micrometric Ni-Mn-(In,Sn) ribbons by the mirage effect under pulsed magnetic field

In this work, we report on the direct measurement of the magnetic field induced temperature change in a series of micrometric thick ribbons of Ni-Mn-In-Sn Heusler alloys, performed with an innovative experimental technique based on the thermo-optical “Mirage Effect.” The technique combines very fast measurement time, 1 T pulsed magnetic field in the millisecond range, and contactless temperature detection. These features make the technique ideal for the characterization of thin samples with a thickness down to a few micrometers. In this work, we demonstrate this by directly measuring the magnetocaloric effect (MCE) of micrometric-thick ribbons of Heusler alloys at the Curie transition, which was tuned on a wide temperature range by varying the Sn to In ratio. The direct test of the MCE in thin samples is fundamental for the development of refrigerant elements with a large heat-transfer coefficient and for the design of solid state micro devices for cooling and energy harvesting.

A hierarchically patterned, bioinspired e-skin able to detect the direction of applied pressure for robotics.

Tactile sensing is required for the dexterous manipulation of objects in robotic applications. In particular, the ability to measure and distinguish in real time normal and shear forces is crucial for slip detection and interaction with fragile objects. Here, we report a biomimetic soft electronic skin (e-skin) that is composed of an array of capacitors and capable of measuring and discriminating in real time both normal and tangential forces. It is enabled by a three-dimensional structure that mimics the interlocked dermis-epidermis interface in human skin. Moreover, pyramid microstructures arranged along nature-inspired phyllotaxis spirals resulted in an e-skin with increased sensitivity, minimal hysteresis, excellent cycling stability, and response time in the millisecond range. The e-skin provided sensing feedback for controlling a robot arm in various tasks, illustrating its potential application in robotics with tactile feedback.