Source Width Research Articles

Enhancement Performance of High Electron Mobility Transistor (HEMT) Based on Dimensions Downscaling

This paper aims to enhance the performance of the High Electron Mobility Transistor (HEMT) according to downscaling dimensions based on the electrical properties and semiconductor materials (GaN, Si3N4, ALGaN and Si). This is to solve difficulties with reducing dimensions and ensuring HEMT has the highest performance possible. This goal was met when the physical scaling restrictions of channel diameters for different HEMTs were concurrently shrunk without compromising their performance. A simula-tion study was done using four variable factors (length, width, of the channel and length, width of the source and drain). Three electrical characteristics were used to assess the impact of altering dimensions on the performance of each kind of HEMT: threshold voltage Vt, ON-state/OFF-state current (ION/IOFF) ratio, and transconductance gm. To conduct experimental simulations under the specified situation, the well-known Silvaco TCAD simulation tool was used. The acquired simulation results revealed that the optimum performance for the downscaling device was achieved at the channel length of 1.6μm, the channel width of 0.3μm, the length of source and drain is 0.4μm and finally the width of source and drain is 0.05 μm.

Perceptual evaluation of an ambisonic auralization system of measured 3D acoustics

This paper presents a perceptual experiment aimed at assessing the spatial quality of acoustic environment rendering using a 4th order ambisonic auralization system. A novel test protocol is developed for this purpose, based on comparing the perceived spatial attributes of sound sources in both real (in-situ) and virtual listening conditions (loudspeaker-based ambisonic auralization of measured SRIRs). The perceptual evaluation is conducted using a specific reporting method combined with a virtual reality interface, enabling simultaneous assessment of perceived distance, angular position, and apparent width of sound sources. The test is conducted in three “office like” rooms, varying in reverberation properties and size. The results highlight differences in spatial perception between (a) real rooms and (b) their reproduction through the auralization system. Overall, localization performance is worse in auralized conditions than in real conditions, as evidenced by a clear increase in localization errors in azimuth and elevation, along with an increase in reported source width. This study also reveals that the spatial accuracy of the auralization depends on the rooms being auralized.

High-Aperture-Ratio Dual-View Integral Imaging Display.

Low aperture ratio is a problem in the conventional dual-view integral imaging (DVII) display using a point light source array. A high-aperture-ratio DVII display using a gradient width point light source array is reported in this work. The elemental Images 1 and 2, which are alternatively aligned on a liquid crystal panel, are illuminated by the light rays emitted from an assigned point light source. The optical path is optimized by optimizing the widths of the point light sources. The aperture ratio of the proposed DVII display was demonstrated as 1.88 times the conventional DVII display. Experiments showed that the vertical viewing range is related to the vertical width of the first row point light source, whereas the aperture ratio is related to the vertical widths of all point light sources. By optimizing the widths of the point light sources, the aperture ratio is enhanced without loss of viewing range.

Widely flexible and finely adjustable nonlocal dispersion cancellation with wavelength tuning.

In fiber-based quantum information processing with energy-time entangled photon pairs, optimized dispersion compensation is vital to preserve the strong temporal correlation of the photon pairs. We propose and experimentally verify that, by simply tuning the wavelength of the entangled photon pairs, nonlocal dispersion cancellation (NDC) can provide a widely flexible and finely adjustable solution for optimizing the dispersion compensation, which cannot be reached with the traditional local dispersion cancellation (LDC) instead. By way of example, when a 50 km-long single-mode fiber (SMF) is dispersion compensated by a 6.2-km-long commercial dispersion compensating fiber (DCF) based on the LDC configuration, it will lead to an almost invariant over-compensation in the wavelength range of 1500-1600 nm which restricts the observed temporal coincidence width of the self-developed energy-time entangled photon-pairs source to a minimum of ∼110 ps. While in the NDC configuration, the dispersion compensation can be readily optimized by tuning the signal wavelength to 1565.7 nm and a minimum coincidence width of 86.1 ± 0.7 ps is observed, which is mainly limited by the jitter of the single-photon detection system. Furthermore, such optimized dispersion compensation can also be achieved as the fiber length varies from 48 km to 60 km demonstrating the wide flexibility of NDC. Thanks to these capabilities, elaborate dispersion compensation modules are no longer required, which makes NDC a more versatile tool in fiber-based quantum information and metrology applications.

Power laws for accurate determination of landslide volume based on high-resolution LiDAR data

Landslide volume is critical in landslide risk management due to its close association with the landslide mobility and damage to elements at risk. Limited by accessibility, site conditions and availability of equipment, directly measuring the landslide volume on site is challenging. Instead, many empirical area-volume power-law models have been developed to estimate the landslide volume. Yet the validity of these power-law models for small-scale shallow landslides is in question considering the substantial uncertainty of field-estimated landslide volume data for developing these empirical power laws. In this study, two high-resolution LiDAR-derived digital terrain models taken in 2010 and 2020 are leveraged to interpret the volumes of 1326 shallow landslides that occurred in Hong Kong during the same period. The high precision of the digital terrain models ensures the accurate interpretation of landslides and the identification of landslide source and transport areas. On the basis of the interpreted landslide characteristics, new power-law models and a multivariate distribution model are proposed to accurately estimate the volumes of small-scale shallow landslides based on easy-to-obtain landslide source features such as source area, length, width or maximum depth. The multivariate distribution model rigorously expresses the conditional probability distribution of the landslide volume and quantifies the uncertainty of volume estimation. The models therefore enhance the capability of landslide risk assessment and management.

Quantitative analysis of photoinduced thermal force: Surface and volume responses

Herein, we provide comprehensive understanding of the photoinduced thermal force between the metal coated tip and organic sample in the context of surface and volume responses where the photoinduced dipole force is typically small enough. Surface response is caused by near-field tip-enhanced thermal expansion, whereas volume response is generated via far-field bulk thermal expansion. In this paper, we quantitatively characterize the two responses, which are mediated via interatomic tip-sample forces in photoinduced force microscopy. The major contributors to the surface sensitivity are the field enhancement at the tip end, the small oscillation of the driving amplitude, and the noncontact/gentle tapping force. Other possible parameters such as the repetition period, and the pulse width of the light source are also discussed. This paper offers insights into the quantitative analysis of surface-sensitive and volume-sensitive spectroscopic nanoimaging, which is of great interest to the scientific community.

Synchrotron Mössbauer source: trade-off between intensity and linewidth.

A synchrotron Mössbauer source (SMS) enables conventional (energy-domain) Mössbauer spectroscopy at synchrotron radiation facilities. In comparison with radioactive sources, SMS provides a beam of several micrometres in size, permitting studies of extremely small samples. The SMS linewidth can be narrowed at the expense of its intensity by varying the angular position and temperature of the key element of the SMS - an iron borate 57FeBO3 crystal. Here, in order to optimize the SMS performance, the angular and temperature dependencies of the SMS parameters have been studied and the optimal angular position and temperature of the crystal have been determined for highest intensity at specified source width. The results show that, when accepting broadening of the source width up to ∼6 natural widths, the intensity of the SMS at the European Synchrotron reaches more than 105 γ-quanta s-1. In the opposite extreme, the width of the source approaches the natural width with intensity decreasing toabout 103 γ-quanta s-1. These changes of intensity up to two orders of magnitude take place over a temperature range of about 0.5°C. For all temperature and angular conditions, the instrumental function of the source was derived; we also analyzed the modification of its shape when passing from the `low-width' to `high-intensity' extremes of SMS operation. Finally, we estimated the influence of the temperature instability and mosaicity of the iron borate crystal on the SMS performance.

An approach for quantification of the heterogeneity of DNAPL source zone geometries

Many studies have investigated the migration and entrapment processes of source zones from dense non-aqueous phase liquid (DNAPL) contamination under different conditions. However, the characterization of occupying area by source zone (or source shape) in water-saturated aquifers is still rudimentarily considered. In this study, we demonstrated this issue (1) by providing a brief review of existing approaches for source shape consideration, (2) by proposing an approach with simple shape parameters based on the non-uniformity of source widths, and (3) by providing exemplary applications of our proposed approach on shapes already published in previous research works. Our literature review suggested that the source zone in mathematical approaches is generally characterized as simple geometrical shapes (arbitrary lines or rectangles) or system-defined parameters that contrast to complex and discontinuous shapes observed in the real world. But the characterization of such complex shapes is still not possible with acceptable efforts. Therefore, we proposed an approach to parameterize the source shape by considering the variation of width and midpoints over the depth of the entire source zone and formulate four parameters based on population statistics (mean, standard deviation). To illustrate the suitability of our approach, we applied it to the results of lab experiments, and by analyzing these complex shapes, we highlighted the potential for improving the characterization techniques of non-uniformity of the source zones.

Development of Solution-Processed Perovskite Semiconductors Lasers

Lead halide perovskite is a new photovoltaic material with excellent material characteristics, such as high optical absorption coefficient, long carrier transmission length, long carrier lifetime and low defect state density. At present, the steady-state photoelectric conversion efficiency of all-perovskite laminated cells is as high as 28.0%, which has surpassed the highest efficiency of monocrystalline silicon cells (26.7%). In addition to its excellent photovoltaic properties, perovskite is also a type of direct bandgap semiconductor with low cost, solubilization, high fluorescence quantum efficiency and tunable radiation wavelength, which brings hope for the realization of electrically pumped low-cost semiconductor lasers. In recent years, a variety of perovskite lasers have emerged, ranging from the type of resonator, the wavelength and pulse width of the pump source, and the preparation process. However, the current research on perovskite lasers is only about the type of resonator, the type of perovskite and the pump wavelength, but the performance of the laser itself and the practical application of perovskite lasers are still in the initial stages. In this review, we summarize the recent developments and progress of solution-processed perovskite semiconductors lasers. We discuss the merit of solution-processed perovskite semiconductors as lasing gain materials and summarized the characteristics of a variety of perovskite lasers. In addition, in view of the issues of poor stability and high current density required to achieve electrically pumped lasers in perovskite lasers, the development trend of perovskite lasers in the future is prospected.

Induced gravitational waves from statistically anisotropic scalar perturbations

Scalar-induced gravitational waves (SIGWs) are attracting growing attention for probing extremely short-scale scalar perturbations via gravitational wave measurements. In this paper, we investigate the SIGWs from statistically anisotropic scalar perturbations, which are motivated in inflationary scenarios in the presence of, e.g., a vector field. While the ensemble average of the SIGW energy spectrum is isotropic for the standard statistically isotropic scalar perturbations, the statistical anisotropy in the source introduces the multipole moments of the differential SIGW energy spectrum. We consider quadrupole anisotropy in the scalar power spectrum and show that the SIGW spectrum has anisotropies up to $\ensuremath{\ell}=4$. We present generic formulas of the multipole moments and then apply them to the delta-function-like and log-normal source spectra. We find analytic expressions for the former case and show that the infrared scalings of the multipole moments are the same as the isotropic SIGWs. Interestingly, the monopole has an additional local minimum in the high-$k$ tail, a key feature to distinguish from the isotropic SIGWs. The latter log-normal case is analytic for the narrow-peak source, and we perform the numerical calculation for the broad peak. As one expects, the multipole moments become broader with increasing source width. Our results are helpful to test the isotropy of primordial density perturbations at extremely small scales through SIGWs.

Modulation of the solar microwave emission by sausage oscillations

ABSTRACT The modulation of the microwave emission intensity from a flaring loop by a standing linear sausage fast magnetoacoustic wave is considered in terms of a straight plasma slab with the perpendicular Epstein profile of the plasma density, penetrated by a magnetic field. The emission is of the gyrosynchrotron (GS) nature, and is caused by mildly relativistic electrons that occupy a layer in the oscillating slab, i.e. the emitting and oscillating volumes do not coincide. It is shown that the microwave response to the linear sausage wave is highly non-linear. The degree of the non-linearity, defined as a ratio of the Fourier power of the second harmonic to the Fourier power of the principal harmonic, is found to depend on the combination of the width of the GS source and the viewing angle, and is different in the optically thick and optically thin parts of the microwave spectrum. This effect could be considered as a potential tool for diagnostics of the transverse scales of the regions filled in by the accelerated electrons.

Evaluation of Eddy Covariance Footprint Models Through the Artificial Line Source Emission of Methane

AbstractThis paper evaluates the performance of footprint models through a line source (LS) system releasing methane (CH4) measured by an eddy covariance (EC) system in a rice‐wheat rotation agro‐ecosystem. Two footprint models namely Kormann and Meixner (KM) and Flux Footprint Prediction (FFP), are used. The “line source width (LW)” was introduced, which could highly impact the model estimation, leading to an error of ∼500% for the FFP and ∼200% for the KM. The surface roughness length (z0) also affects the FFP estimation, which is much weaker than the effect of LW with a 15% error. An overestimation of 217.8% is observed when the LS is close to the EC system, which reduces to 12.2% when the source stays distant. The analysis of different experimental configurations illustrated that the estimated emission calculated based on footprint model improves with increasing emission height, averaging period, and emission rate. The most accurate estimations are achieved by the configurations of canopy level (CL; 5.5% overestimation), 15 min averaging period (1% underestimation), and moderate emission (ME; 1.9% underestimation), respectively. For KM, the CL‐ME‐30 min setup leads to the best performance, while SL (soil level)‐ME‐15 min is the best configuration for the FFP estimation. A multivariate regression model is proposed to provide preliminary guidance for the footprint model application. The designed LS system is valuable for validating the performance of flux measurements in the specific ecosystems (e.g., grassland, sand land, and forest) as well as other greenhouse gases (e.g., N2O and NH3).

Numerical simulation of angled surface crack detection based on laser ultrasound

As an important branch of non-destructive testing, laser ultrasonic testing has attracted increasing attention in the field of material testing because of its instantaneity, non-contact and wide adaptability. Based on the finite element method, the process of laser-excited ultrasonic signal is numerically simulated, and the influence of angled cracks on the ultrasonic signal is analyzed. In this paper, the effects of the time function, pulse width, and spot radius of a Gaussian light source are analyzed through the transient field. The different modes of the ultrasonic signal are used to fit the crack’s angle, depth, and width to complete the characteristic analysis of the surface angled crack. The results show that the displacement peak-valley difference of the direct Rayleigh wave is negatively correlated with the crack angle. The displacement extremes of the transmitted Rayleigh wave boundary are negatively correlated with crack depth and width, while the transmitted Rayleigh wave is positively correlated. This paper presents a method for the quantitative analysis of surface-angled cracks and provides a theoretical basis for further experimental verification.

High-resolution, High-sensitivity, Low-frequency uGMRT View of Coma Cluster of Galaxies

We present high-resolution, high-sensitivity upgraded Giant Metrewave Radio Telescope observations of the Coma cluster (A1656) at 250–500 MHz and 550–850 MHz. At 250–500 MHz, 135 sources have extensions >0.′45 (with peak-to-local-noise ratio >4). Of these, 24 sources are associated with Coma-member galaxies. In addition, we supplement this sample of 24 galaxies with 20 ram pressure stripped (RPS) galaxies from (Chen et al. 2020, eight are included in the original extended radio source sample) and an additional five are detected and extended. We present radio morphologies, radio spectra, spectral index maps, and equipartition properties for these two samples. In general, we find the equipartition properties lie within a narrow range (e.g., = 1–3 × 10− 13 dynes cm−2). Only NGC 4874, one of the two brightest central Coma cluster galaxies, has a central energy density and pressure about five times higher and a radio source age about 50% lower than that of the other Coma galaxies. We find a diffuse tail of radio emission trailing the dominant galaxy of the merging NGC 4839 group that coincides with the slingshot tail seen in X-rays. The southwestern radio relic, B1253+275, has a large extent ≈32′ × 10′ (≃1.08 × 0.34 Mpc2). For NGC 4789, whose long radio tails merge into the relic and may be a source of its relativistic seed electrons, we find a transverse radio spectral gradient, a steepening from southwest to northeast across the width of the radio source. Finally, radio morphologies of the extended and RPS samples suggest that these galaxies are on their first infall into Coma on (predominantly) radial orbits.

Accurate estimation of thermal properties for AlGaN/GaN HEMTs on diamond

For accurate estimation of the thermal characteristics of AlGaN/GaN high electron mobility transistors on diamond, the anisotropic thermal conductivities of polycrystalline diamond (PCD) and GaN with their thickness dependences are included in the finite element simulation model, of which the PCD thermal conductivity kPCD is calculated through detailed analyses of the grain sizes in the directions parallel and vertical to the interface and relative phonon-grain boundary scatterings. In addition, the GaN thermal conductivity kGaN is the result of an approximate solution of the phonon Boltzmann transport equation. To investigate the effects of anisotropic GaN and PCD thermal conductivity, four cases of thermal conductivity models are compared: anisotropic kGaN and kPCD, anisotropic kGaN with constant kPCD, constant kGaN with anisotropic kPCD, and constant kGaN and kPCD. Then the maximum channel temperature simulated from the four above-mentioned models and the errors relative to the case of anisotropic kGaN and kPCD are investigated with respect to thermal boundary resistance, GaN layer thickness, gate pitch, heat source width, and power dissipation. The results show that the combination of anisotropic kPCD and constant kGaN overestimates the maximum channel temperature rise, and using constant kPCD and anisotropic kGaN underestimates the maximum channel temperature rise for almost all the simulations in the text. However, the channel temperature stemming from constant kPCD and kGaN is generally closer to the case with anisotropic PCD and GaN thermal conductivity.

Design and Implementation of a Direct Memory Access ControllerBased on Microcontroller Unit

With increasing IoT technology, the application of MCU is becoming more and more extensive, and higher requirements are put forward for the functions and data processing capabilities of MCU. This trend means the amount of data that the MCU needs to process in the system has increased sharply, so this paper proposes a hardware design scheme for a DMA controller based on the AHB-Lite protocol to replace the MCU to transfer data to improve system performance. The controller supports 8 transfer channels and adopts the method of fixed priority level arbitrating to select channels. The channel source and destination data width and burst type are configurable. In the process of data burst transfer, the condition of crossing the 1K address boundary is taken into consideration. At the same time, the design adopts the method that 8 transfer channels share a buffer FIFO to optimize the area of the controller.

Single photon imaging with multi-scale time resolution

To avoid echo photons to be submerged in noise in rough terrain or dynamic applications, a single photon imaging mechanism with multi-scale time resolution is proposed in this paper. Combining with adaptively thresholding technique, multiple histograms with different time resolutions are produced to cluster the echo photons into a time bin and then separate them from the noise. With microsecond-scale resolution, uncertainty in the position of an object can be reduced from several kilometers to 300 meters, and therefore the computational overheads are saved by only investigating depths with picosecond-scale resolution where an object is present. Reconstructed results of the two near surfaces show that the depth accuracy is less than 0.15 m in the conditions of 8 echo photons and 1 Mcps background count rate, even though the pulse width of laser source reaches 3.5 ns (equivalent to an uncertainty of 0.525 m). In addition, the echo can be distinguished from the noise clearly when the background count rate varies from 200 kcps to 1 Mcps. The proposed method is suitable for implementation in digital signal processor (DSP) due to low data volumes and computational overheads.

An electro-optical system for improving graphene nanopore DNA Sequencing

I propose a new electro-optical system for sequencing single-stranded DNA molecules. The localized plasmons in graphene combined with the nanopore-based DNA translocation have been suggested for sequencing DNA molecules and decreasing the translocation speed. These localized surface plasmon resonances in the graphene nanopore have three dominant modes. Every-mode peak wavelength is shifted while the DNA nucleobases are presented to the nanopore. The ultraviolet photodiodes with narrow-band filters can separate each mode individually. Then, the electrical-current to voltage convertor, differential pairs based on the bipolar transistors, combine all modes in the effective output voltage. The output voltage level of the circuit is sensitive to the DNA presence and is unique for each DNA nucleobase. Analyzes have been performed for different central wavelengths and spectral width of the light source. Results show that the best sensitivity to the DNA molecule is 6.04, and the best selectivity is 1.1. These factors are directly related to the method's applicability for DNA translocation sensing and DNA sequencing; they are enormously improved. The proposed method and results shed light on a higher selectivity for DNA nucleobases which is the main bottleneck for nanopore DNA sequencing.

Secondary Intrusion Formation of Multiphase Plumes

This work presents a new laboratory study for understanding secondary intrusions in multiphase plumes in quiescent, stratified environments. The study is driven by field observations of secondary intrusions during the Deepwater Horizon (DWH) oil spill. The smaller trap heights observed at DWH for secondary versus primary intrusions could have resulted, in part, from decreasing plume buoyancy (due to gas dissolution) and increasing ambient stratification with elevation above the source. We seek additional mechanisms responsible for the observed smaller secondary trap heights through controlled laboratory experiments where buoyancy and ambient stratification are nominally constant throughout. A novel approach is adopted in the experiments to increase the visibility of secondary intrusions, which are traditionally difficult to visualize, thus investigate. The study reveals that a wider plume source width can also cause the secondary intrusions to trap earlier, providing another plausible explanation for the shallower secondary intrusions observed in the field data.

Spatio-spectral deconvolution for high resolution spectral imaging with an application to the estimation of sun-induced fluorescence

We propose a signal deconvolution procedure for imaging spectrometer data, where a measured point spread function (PSF) is deconvolved itself before being used for deconvolution of the signal. We evaluate the effectiveness of our procedure for improvement of the spatio-spectral signal, as well as our target application, i.e. estimation of sun-induced fluorescence (SIF). Imaging spectrometers are well established instruments for remote sensing. When used for scientific purposes these instruments are usually calibrated on a regular basis. In our case the point spread function of the optics is measured in an elaborate procedure with a tunable monochromator point light source. PSFs are measured at different pixel positions of the imaging sensor, i.e. at different spatio-spectral locations, and averaged in order to get an as accurate PSF as possible. We investigate error sources in this calibration process by simulating the procedure in silico. Averaging as well as the spectral and spatial width of the point source introduce some smoothness in the measured PSF. We propose corrective measures, i.e. deconvolution of the PSF itself and median instead of mean averaging, leading to a set of sharper PSFs. We test the performance of these PSFs in deconvolving simulated as well as real hyperspectral images. For deconvolution we test a set of well-known, off the shelf deconvolution algorithms. Quantitatively in terms of PSNR (Peak Signal to Noise Ratio) a combination of Wiener filtering and sharpened PSFs yields strongest improvements, while using Wiener filtering with non-sharpened PSFs even deteriorates the signal. Comparing deconvolution results of the simulated data with results of real data reveals, that visually very similar effects can be observed. This well supports the assumption, that our findings are also valid for real spatio-spectral data. Surprisingly, the choice of PSF, sharpened or not, is of little effect for SIF estimation with the iFLD algorithm in the O2A band. Quantitatively we find that deconvolution reduces the overall error of SIF by a factor of 3.8, when using Wiener filtering instead of the currently used 1 iteration of vanCittert's method. For SIF estimation in the O2B band we observe a totally different behavior, where all deconvolution methods yield unreliable results with mostly well above 200% relative error and high standard deviations. In the discussion we can only speculate on possible reasons for this unreliability. As conclusion we therefore propose to use the O2A band for SIF estimation together with classic Wiener filtering for deconvolution of spatio-spectral data.