Output Window Research Articles

GRAformer: A gated residual attention transformer for multivariate time series forecasting

Recurrent Neural Networks (RNNs), particularly when equipped with output windows – a standard practice in contemporary time series forecasting – have shown proficiency in handling short-term dependencies. Nonetheless, RNNs can encounter challenges in maintaining hidden states over extended forecasting periods, particularly in longer-term predictions where increased hidden state sizes and extended look-back windows can lead to gradient instability. In contrast, Transformer-based models, with their distinctive architecture designed to encode complex contextual relationships and enable computations to be done in parallel, are emerging as a popular alternative in this field. However, current research has mainly focused on modifying attention mechanisms, overlooking opportunities to improve the feedforward layer, which could lead to efficiency limitations. Moreover, prevailing methods often assume absolute independence between channels, disregarding distinct features among variables and failing to fully leverage channel-specific information. To address these gaps, we propose an efficient transformer design for multivariate time series prediction. Our approach integrates two key components: (i) a gated residual attention unit that enhances predictive accuracy and computational efficiency, and (ii) a channel embedding technique that differentiates between series and boosts performance. Theoretically, we prove that our model has recurrent dynamics introduced by the RNN layer. Through extensive experiments on real-world data, we demonstrate that our proposed method achieves competitive predictive accuracy compared to prior approaches while exhibiting accelerated processing relative to state-of-the-art transformers. Our code, data, and trained models are available at https://github.com/MythosAd/GRAformer.

Measurement of nonequilibrium vortex propagation dynamics in a nonlinear medium

We observe and measure the nonequilibrium dynamics of optical vortices as a function of propagation distance through a nonlinear medium. The precession of a tilted-core vortex is quantified as is vortex core sharpening, where the infinite width of a linear core subsequently shrinks and approaches the healing length of this nonlinear optical fluid. Experiments are performed with a variable-length nonlinear medium: a nonlinear fluid in a tank with an output window on a translating tube. This provides control over the distance the light propagates in the fluid and allows for the measurement of the dynamics throughout the propagation range. Results are compared with the predictions of a computational simulator to find the equivalent dimensionless nonlinear coefficient.

Investigation of Power Capacity in the Output Window for a High-Power W-Band Gyro-TWT

Investigation of Power Capacity in the Output Window for a High-Power <i>W</i>-Band Gyro-TWT

The Fabry-Perot effect suppression in gas cells used in THz absorption spectrometers

Gas cells are widely used in THz and IR absorption spectroscopy. However, reflections of an optical wave on cell input and output windows cause a gas sample measured spectrum distortion due to the Fabry-Perot effect. The hardware approach to decrease the Fabry-Perot effect in the THz spectral range is suggested. The approach is based on using a standard gas cell and the additional movable optically transparent window. To illustrate usefulness of the suggested approach, a simulation of registration of the sulfur dioxide absorption band near 660 GHz in the gas mixture consisted of 0.1 % SO2 and 99.9 % N2 was conducted. The absorption band profile fluctuations due to the Fabry-Perot effect were shown to be reduced by almost 4 times with the suggested approach implementation in relation to the default gas cell. This approach can be combined with other hardware and software variants of the Fabry-Perot effect suppression.

Effect of Transparency Increasing and Surface Relief of Polyvinyl Alcohol Thin Films with Graphene Oxide of Varied Concentrations: Possible Applications

Analysis of the experimentally established transmission variation (taking into account the transparency increasing) of polyvinyl alcohol thin films sensitized with graphene oxide of different concentrations was performed. The mechanical features of these solid-state compositions were studied. Transmission spectra in the visible and near-infrared ranges were registered. The microhardness of the studied materials was measured. The experimental results were confirmed by the quantum chemical modeling. A wide range of possible applications of the studied materials is proposed: display technology, light modulators, laser radiation converters, output windows of optoelectronic devices, biomedicine.

Measurement of Photoneutrons from Depleted Uranium and Comparison Study Using MCNPX-PoliMi

High-energy photon interrogation is a nondestructive technique that is used to detect special nuclear materials and characterize nuclear waste. The development of such systems is complex and requires Monte Carlo simulations to optimize system performance. Monte Carlo simulations rely on various scattering, absorption, and photonuclear cross-section data. While the scattering and absorption cross-section data have been extensively studied and validated with experiments, the results obtained from photonuclear simulations are often found to underpredict measured results, indicating uncertainties in the photonuclear cross sections themselves. Thus, there is a need for new measured results that can be used to quantify underpredictions in simulations using photonuclear cross-section data. In the present work, we interrogated depleted uranium with a 9-MV electron linac and detected photoneutrons with trans-stilbene organic scintillators. The measurement of photoneutrons with organic scintillators is challenging due to the presence of the intense photon flux, which causes issues such as pulse pile-up, detector saturation, and poor signal-to-background ratio. To mitigate these challenges, we used iron and polyethylene shielding of varying thicknesses around the depleted uranium target and a neural network–based digital pulse processing algorithm to recover neutron and photon information from piled-up events. Our goal was to compare the measured photoneutron count rate with the simulated rate obtained using the MCNPX-PoliMi transport code. For a light output window of 0.28 to 2.67 MeVee (1.66- to 6.85-MeV proton recoil energy), we found that the simulated count rate obtained using the ENDF/B-VII photonuclear cross-section library underpredicts the measured rate by 32.8% ± 3.2%. Additionally, we compared the simulated and measured photoneutron light output distributions. For the least thicknesses of shielding, the simulation was found to underpredict measurements in the 0.70- to 2.67-MeVee light output window. For the greatest thicknesses of shielding, the simulation was found to underpredict the measurement across the entire light output window of 0.28 to 2.67 MeVee.

Compact Efficient and Frequency Tunable Relativistic Magnetron With Reducing Coaxial Section and Tilted Tuners

In this article, we present a compact efficient and frequency tunable relativistic magnetron (RM) with what we have named a reducing coaxial section (RCS) and with tilted tuners. The RCS is a conical-shaped part inserted in front of the output window. The design is adapted to the compact Marx generator of the Concept Léger Aéroporté d’Illuminateur RadioElectrique (CEA)-Gramat demonstrator—Commissariat à l’Energie Atomique et aux Energies Alternatives (CLAIRE)—and meets technical requirements such as input impedance (specifically during frequency shifting), mechanical dimensions, power handling capacity, and electromagnetic (EM) mode. Special care has been taken to lower the EM mode competition, which occurs with specific geometry, extraction waveguide with high dimensions, and/or frequency shifting. To mitigate this effect, the output waveguide diameter was decreased by means of the RCS design. Another challenge was to operate frequency shifting by adding tuners while maintaining high power handling. The premise is that cathode endcap spheres and tilted tuners theoretically reduce the electric field strength from 600 to 280 kV/cm. Particle-in-cell (PIC) simulation exhibits an output power (averaged over the pulse duration) that reaches 680 MW at 1.85 GHz. The corresponding maximum power efficiency is about 50% when the applied voltage is 380 kV, and the current intensity is about 3.8 kA. The frequency operating range is above 19% from 1.85 to 2.25 GHz.

Quantitative Time-Resolved Visualization of Catalytic Degradation Reactions of Environmental Pollutants by Integrating Single-Drop Microextraction and Fluorescence Sensing.

Current methods for evaluating catalytic degradation reactions of environmental pollutants primarily rely on chromatography that often suffers from intermittent analysis, a long turnaround period, and complex sample pretreatment. Herein, we propose a quantitative time-resolved visualization method to evaluate the progress of catalytic degradation reactions by integrating sample pretreatment [single-drop microextraction, (SDME)], fluorescence sensing, and a smartphone detection platform. The dechlorination reaction of chlorobenzene derivatives was first investigated to validate the feasibility of this approach, in which SDME plays a critical role in direct sample pretreatment, and inorganic CsPbBr3 perovskite encapsulated in a metal-organic framework (MOF-5) was utilized as the fluorescent chromogenic agent (FLCA) in SDME to realize fast in situ colorimetric detection via the color switching from green (CsPbBr3) to blue (chlorine lead bromide, inorganic CsPbCl3 perovskite). The smartphone, which can calculate the B/G value of FLCA, serves as a data output window for quantitative time-resolved visualization. Further, a [Eu(PMA)]n (PMA= pyromellitic acid) fluorescent probe was constructed to use as an FLCA for the in situ evaluation of cinnamaldehyde and p-nitrophenol catalytic reduction. This approach not only minimizes the utilization of organic solvents and achieves quantitively efficient time-resolved visualization but also provides a feasible method for in situ monitoring of the progress of catalytic degradation reactions.

Realistic 3-D Particle-In-Cell Simulation of a Medical 2.1 MW 40-Vane X-Band Coaxial Magnetron

A medical 2.1 MW 40-vane <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band coaxial magnetron is designed and analyzed using a 3-D particle-in-cell (PIC) simulation. For realistic simulation, the magnetic field profile from the 3-D magnetic circuit and the structure of the output window are included in the simulation. A frequency tuner is located inside the coaxial resonator to control the operating frequency, and the output power is measured at the WR-112 waveguide located behind the output window. Using the operating conditions with an anode voltage of 35.8 kV and a magnetic field of 0.595 T, a maximum output power of 2.1 MW with an efficiency of 53.6% is measured in the stable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode resulting from the 20-electron spokes. The frequency tuner is moved down and up by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 300 \mu \text{m}$ </tex-math></inline-formula> along the axial direction, and the frequency bandwidth is 72 MHz from 9.272 to 9.344 GHz with the tuning parameter of 0.12 MHz/ <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> . In addition, the output performance is simulated to investigate the effect of dimensional parameters such as the coupling slot width and transformer length.

Compact Microstrip Patch Filtenna Array Based on Reusable High-Order SIW Cavity

In this letter, a compact microstrip patch (MP) filtenna array designed by reusing high-order substrate integrated waveguide (SIW) cavity is investigated. The SIW cavity operating at TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> mode not only acts as the first-stage resonator of the filter, but also serves for the four-way dividing realized by the mode power allocation. In addition, by appropriately controlling the coupling coefficient of the output window of the SIW cavity, the radiating 2 × 2 MP array can become the second-stage resonator of the filter. Finally, benefiting from the reuse of the employed high-order SIW cavity, the proposed filtenna array exhibits good performance such as low loss, high efficiency and compact structure. For demonstration, a filtenna array prototype centered at 13.6 GHz is fabricated and tested, showing 13 dBi peak gain and 90% peak efficiency. Good agreement is obtained between simulated and measured results.

Electromagnetic particle simulation of secondary electron multipactor characteristics in inner surface of 110 GHz microwave output window

The secondary electron multipactor on the inner surface of the output window is one of the main factors limiting the power capacity of high power microwave. Therefore, it is of great significance to carry out relevant research. In this work, the process of secondary electron multipactor and the resulting loss of power are numerically simulated by using the electromagnetic particle model with one-dimensional spatial distribution and three-dimensional velocity distribution at the microwave frequency of 110 GHz. The influences of microwave electric field at the surface and dielectric material type on the power loss are studied. The simulation results show that the electron number density is higher than the critical cut-off number density after the secondary electron multipactor has reached the steady state, but the microwave electric field does not show obvious change. This is because the electrons in a very high electrostatic field are mainly concentrated in the domain of several micrometers near the dielectric surface, which is far less than the corresponding skin depth. The electron number density in the multipactor steady state increases with the microwave electric field increasing, but the ratio of the power loss to the microwave power at the surface increases slowly. After the multipactor reaches the steady state, the number density of electrons near the sapphire surface is the highest, followed by the number density near the crystal quartz surface, and the number density near the fused quartz surface is the lowest, so the corresponding power loss decreases successively. In order to verify the accuracy of the model, the simulated value of the multipactor threshold is compared with the experimental data, and the difference between them is discussed.

DEFORMED STATE’S SIMULATION OF THE FIRST-GRADE TITANIUM FOIL OF THE ACCELERATOR OUTPUT WINDOW

The output accelerator windows, particularly the used metal foils are studied. The work was carried out to assess the strength of the first-strength grade titanium foil and the choice of variable parameters of the thickness of the foil. Depending on the latter, the simulation was performed by the finite element analysis in the ABAQUS automated software environment. The distributions of displacements, plastic strains of concavity caused by pressure differences, and radial and circumferential stresses have been studied in the foil's static state for 10 metal foils with a thickness of 50…500 microns. The basic dimensions of the titanium metal film are introduced: thickness and diameter. Atmospheric pressure was applied as an external force of influence, and the vacuum pressure was assumed to be zero. The metal shells were divided into a large number of nodes, which ensured higher accuracy for simulations. As a result of simulation, curves of the displacements of the selected points of the metal foil in the direction of the Y axis, depending on the values of the radiuses, and the curves of the strains intensities distributions of the metal foil were built, which were also analyzed. The metal foil of the output window was investigated so that simulation results could be applied to both output windows: mechanical connection and diffusion connection.

STFT-Domain Neural Speech Enhancement With Very Low Algorithmic Latency

Deep learning based speech enhancement in the short-time Fourier transform (STFT) domain typically uses a large window length such as 32 ms. A larger window can lead to higher frequency resolution and potentially better enhancement. This however incurs an algorithmic latency of 32 ms in an online setup, because the overlap-add algorithm used in the inverse STFT (iSTFT) is also performed using the same window size. To reduce this inherent latency, we adapt a conventional dual-window-size approach, where a regular input window size is used for STFT but a shorter output window is used for overlap-add, for STFT-domain deep learning based frame-online speech enhancement. Based on this STFT-iSTFT configuration, we employ complex spectral mapping for frame-online enhancement, where a deep neural network (DNN) is trained to predict the real and imaginary (RI) components of target speech from the mixture RI components. In addition, we use the DNN-predicted RI components to conduct frame-online beamforming, the results of which are used as extra features for a second DNN to perform frame-online postfiltering. The frequency-domain beamformer can be easily integrated with our DNNs and is designed to not incur any algorithmic latency. Additionally, we propose a future-frame prediction technique to further reduce the algorithmic latency. Evaluation on noisy-reverberant speech enhancement shows the effectiveness of the proposed algorithms. Compared with Conv-TasNet, our STFT-domain system can achieve better enhancement performance for a comparable amount of computation, or comparable performance with less computation, maintaining strong performance at an algorithmic latency as low as 2 ms.

Method for Calculating the Scanning Unit of a Laser Scanner and Optimizing Its Overall Dimensions

A prism deflector, which is a multifaceted prism with reflective edges, is the most common scanning element that allows fast filling of a wide scanning area with laser radiation pulses along one coordinate. To carry out the movement of laser radiation along the second coordinate of the region under study a second scanning element, for example, a flat oscillating mirror, should be used. The overall dimensions of the scanning elements and the scanning unit as a whole depend on the free parameters that are set at the system development stage. The paper proposes a mathematical model designed for automated calculation of a scanning unit consisting of a prism deflector, a fixed flat mirror, an oscillating flat mirror, and a laser exit window. The described model makes it possible to calculate the overall parameters of system optical elements and the layout of the block based on the required characteristics of the scanned area and free parameters, which include the angle of radiation supply to the face of the prism deflector, the tilt angle of the fixed mirror, and one of the coordinates of the laser output window position relatively to the center of the prism deflector. In this case, the first two mentioned parameters are of the greatest interest from the point of view of minimizing and optimizing the overall dimensions of the scanning elements and the scanning unit as a whole. Based on the above model, an analysis of the dependence of the overall dimensions of the scanning elements and the scanning unit as a whole was carried out. The paper describes the layout features of the scanning unit. Recommendations for choosing the value of such free parameters as the angle of radiation supply to the face of the prism deflector and the angle of inclination of a flat fixed mirror are given. The obtained results can be used in the development of automated systems for the design of laser scanning devices.

A 40.96-GOPS 196.8-mW Digital Logic Accelerator Used in DNN for Underwater Object Recognition

This investigation presents a digital logic accelerator (DLA) design of a neural network hardware that utilizes output reuse. The DLA is used in the detection mechanism of underwater objects that was deployed in an underwater vehicle. A modified YoloV3-tiny network was also implemented to detect more than 20 underwater objects. The proposed DLA uses processing units that have parallel architectures of output windows, and output channels. Moreover, a new Inter-Controller is designed to control the direct memory access (DMA) together with a new Reshape module to improve the performance and power efficiency. A detailed description of the design as well as the measurements on silicon are presented. The chip is realized using a typical 180-nm CMOS process. It showed a performance result of 40.96 GOPS and the power consumption is 196.8 mW. The DLA was tested to demonstrate 19.88 frames per second and 40.96 GOPS.

Design and analysis of the output windows of a doorknob structure for high-power P-band klystron

This article presents the design, analysis, and simulation for the klystron coaxial radio frequency (RF) output windows. Three new RF windows (Type-2, 3, and 4) are proposed based on the coaxial RF window with a doorknob structure (Type-1) to improve its performances. The proposed RF windows are simulated in high frequency simulator structure. At the operating frequency, the return loss are obtained as −49, −60, −56, and −52 dB, and the insert loss as −0.003 62, −0.002 51, −0.002 74, and −0.003 dB, respectively, for Type1, 2, 3, and 4. Moreover, for Type-1, the E-field near the short-circuit surface is significantly greater than that near the output port side due to the asymmetrical structure of RF window. However, this phenomenon has been greatly improved in the proposed RF windows. The heat load because of RF power absorption over the ceramic has been calculated. The distribution of heat load in three new windows is more uniform and less than that in Type-1, and the heat load in Type-2 is about half of that in Type-1. The thermal and structural analyses of RF windows predict the lower temperature and less mechanical deformation for the three new RF windows. Multipactor analysis is carried out to determine the safety at the operating power level.

Study of the Frequency Self-Modulation in Gyro-TWT Based on Two -Band Amplifiers

Periodical radiation spectrum with a frequency difference of ~160 MHz is observed in hot-test experiments of Ku-band gyrotron traveling-wave tubes (gyro-TWTs). By the means of eigenmode analyses and particle-in-cell (PIC) simulation considering the whole output transition section from the interaction circuit end to the output window, we found that the circuit oscillation is pronounced because of frequency self-modulation (FSM). As a comparison, the cutoff taper contributing to the FSM is removed and a new amplifier has been developed; hot-test results indicate that the periodical property has been greatly alleviated as expected and the stability of the amplifier is well improved.

Absolute response of a proton detector composed of a microchannel plate assembly and a charge-coupled device to laser-accelerated multi-MeV protons.

The absolute response of a real-time proton detector, composed of a microchannel plate (MCP) assembly, an imaging lens, and a charge-coupled device (CCD) camera, is calibrated for the spectral characterization of laser-accelerated protons, using a Thomson parabola spectrometer (TPS). A slotted CR-39 plate was used as an absolute particle-counting detector in the TPS, simultaneously with the MCP-CCD detector to obtain a calibration factor (count/proton). In order to obtain the calibration factor as a function of proton energy for a wide range of proton numbers, the absolute response was investigated for different operation parameters of the MCP-CCD detector, such as MCP voltage, phosphor voltage, and CCD gain. A theoretical calculation for the net response of the MCP was in good agreement with the calibrated response of the MCP-CCD detector, and allows us to extend the response to higher proton energies. The response varies in two orders of magnitude, showing an exponential increase with the MCP voltage and almost linear increase with the phosphor voltage and the CCD gain. The calibrated detector enabled characterization of a proton energy spectrum in a wide dynamic range of proton numbers. Moreover, two MCP assemblies having different structures of MCP, phosphor screen, and optical output window have been calibrated, and the difference in the absolute response was highlighted. The highly-sensitive detector operated with maximum values of the parameters enables measuring a single proton particle and evaluating an absolute spectrum at high proton energies in a single laser shot. The absolute calibrations can be applied for the spectral measurement of protons using different operating voltages and gains for optimized response in a large range of proton energy and number.

Off-axis propagation algorithm for partial reconstruction of wide-angle computer-generated holograms.

A method for reconstruction of partial off-axis areas of arbitrary size for wide-angle viewing computer generated holograms is presented. Proposed method employs paraxial spherical phase factors and modified propagation kernels. This significantly reduces the numerical space-bandwidth product needed for off-axis wave field calculations, which makes it an efficient propagation method. As a result, propagated wavefields of high-off axis and large size output windows can be obtained. To that end, a phase-space analysis for obtaining the proper condition for implementing spatial-frequency zero-padding for accurate wavefield propagation is carried out. Hence, suppression of aliased components and high spatial resolution is possible. Nevertheless, proposed algorithm faces a computer memory bottleneck when reconstructing very large off-axis areas due to too extensive zero-padding needed. To solve this problem, a memory optimized tiling implementation is introduced. Utility of the developed propagation tools are proven by partial reconstructions from a high-resolution hologram. The size of the reconstructions areas ranges from 100 × 100 mm2 up to 550 × 550 mm2.

Transient simulation of dielectric breakdown during high-power microwave propagation based on the SETD method

This article is mainly devoted to the research of dielectric breakdown phenomenon during high power microwave propagation. Under the force of the high-intensity fields, bound charges break free and a part of an insulator becomes electrically conductive, which may lead to electrical breakdown and thermal breakdown in high power microwave (HPM) devices or on the output window. A three-dimensional (3D) multi-physics electromagnetic-thermal model is developed and solved by spectral-element time-domain (SETD) method. The nonlinear conductivity caused by HPM is introduced into Maxwell's equations, which makes its nonlinear. The heat flux from transient power loss is utilized to construct the heat source for solving the thermal conduction equation. In the SETD process, the Galerkin's method and central difference scheme are employed for the space discretization and temporal discretization, respectively. The numerical results show that physical mechanism of electrical breakdown, thermal effect and nonlinear effect can be captured accurately during high power microwave propagation. Once the strength of the electric field exceeds the critical value experienced by the dielectric, the current increases rapidly, along with the temperature change is very severe. The validity and accuracy of the proposed method are demonstrated, and our research is beneficial for the HPM devices protection.