High Frequency Area Research Articles

A Modified of Fourth-Order Partial Differential Equations Model Based on Isophote Direction to Noise Image Removal

Image denoising is one of the initial stages of image processing. Many models based on the diffusion method have been used to smooth the image. One of the problems, we face in the model based on the diffusion method is its possible loss of edges. The diffusion force is known to be more effective in areas of high frequency. So This paper suggests combining the direction of isophote and fourth-order partial differential equations to reduce the problem of loss edges and preserve important details of the image. The direction of the isophote can regulate the direction of diffusion. Thus, we have a proposed model that can remove the noise in the area while preserving the important edges and details of the image. We have proven the efficiency and superiority of the proposed model by applying it to a set of images and solving it numerically using the finite difference method (FDM).

Superconductivity of cubic MB6 (M = Na, K, Rb, Cs).

Previous studies have shown that NaB6, KB6, and RbB6 adopting Pm3̄m are superconductors with a relatively high Tc under ambient conditions. In this paper, we conducted systematic structural and related properties research on CsB6 through a genetic evolution algorithm and total energy calculations based on density functional theory between 0 and 20GPa. Our results reveal a cubic Pm3̄m CsB6, which is dynamically stable under the pressures we studied. We systematically calculated the formation enthalpies, electronic properties, and superconducting properties of Pm3̄m MB6 (M = Na, K, Rb, Cs). They all exhibit metallic features, and boron has high contributions to band structures, density of states, and electron-phonon coupling (EPC). The calculated results about the Helmholtz free energy difference of Pm3̄m CsB6 at 0, 10, and 20GPa indicate that it is stable upon chemical decomposition (decomposition to simple substances Cs and B) from 0 to 400K. The phonon density of states indicates that boron atoms occupy the high frequency area. The EPC results show that Pm3̄m CsB6 is a superconductor with Tc = 11.7K at 0GPa, close to NaB6 (13.1K), KB6 (11.7K), and RbB6 (11.3K) at 0GPa in our work, which indicates that boron atoms play an essential role in superconductivity: vibrations of B6 regular octagons lead to the high Tc of Pm3̄m MB6. Our work about Pm3̄m hexaborides provides a supplementary study on the borides of the group IA elements (without Fr and Li) and has an important guiding significance for the experimental synthesis of CsB6.

Spatial and temporal distribution characteristics of extreme wind and its effect on wind erosion in Northeast China

Under the background of climate change, extreme wind events occur frequently in Northeast China, and the soil erosion caused by these extreme wind events has attracted progressively more attention from scholars. We used the methods of linear analysis, Sen+Mann-Kendal trend analysis, and Kriging interpolation to analyze the spatial and temporal characteristics of extreme wind in Northeast China from 2005 to 2020, and used the RWEQ wind erosion estimation model to calculate the annual soil wind erosion of typical wind erosion sites and wind erosion under extreme wind conditions. The results showed that the extreme wind frequency in Northeast China presented a significant upward trend from 2005 to 2020, with an increase of 2.9 times·a-1. The annual average extreme wind frequency in Northeast China ranged from 1 to 49 times·a-1, and the high frequency areas were distributed in the northwest of Xilin Gol, the west of the Hulunbuir Plateau, and the northeast of Changbai Mountain. The average contribution rate of extreme wind to soil wind erosion in four typical sites (Xilinhot, New Barhu Right Banner, Nenjiang, and Tongyu) was 31%.

A Daubechies wavelet analysis on coupled radiation and conduction in absorbing and scattering medium under pulsed laser

This study examines how the wavelet is affected by the wavelet function and thermal parameters by combining radiative and conductive heat transfer with Daubechies discrete wavelet decomposition for signal processing. By comparing time-frequency information under different sampling time interval, we can deduce that the large sampling time interval causes the detail coefficients to focus on the high frequency area. Regarding the wavelet coefficient, the radiation characteristics, heating power, heating time, and actual random errors will affect the wavelet frequency. The thermal conductivity and extinction coefficient have a great influence on the detail coefficient, while the albedo has an impact on the temperature and the amplitude of the wavelet detail coefficient in the range of 0.5-0.9, and the asymmetry factor has a significant effect on the time of the temperature peak. The wavelet detail coefficient of the heating side temperature changes more dramatically than that of the cooling side. The detail coefficient of the low-frequency region is more affected by thermal physical factors whereas the high-frequency portion is more affected by random errors and heating power. This law can improve the accuracy of acquiring physical attributes by filtering out random errors in practical applications.

Study on acoustic properties of ultra-low-density polyurethane with Nano-Cellulose

Recently, polyurethane materials are commonly used as engine room sound-absorbing materials to reduce the weight of automobiles. Polyurethane materials have excellent sound absorption performance in the 800~2,000 Hz frequency range due to the structural characteristics of the material, but the sound absorption performance of more than 2,000 Hz is insufficient. In the case of electric vehicles, it is important to improve the high frequency noise generated by the motor, and the need for modification of polyurethane materials has increased. High frequency performance can be improved by improving the air permeability of polyurethane cells through the bonding structure of polyurethane materials, optimization of blowing and gelling reactivity, and the amount of foaming gas. Increased air permeability of polyurethane materials reduces density and strength. In this study, Nano-cellulose is a highly functional new material with light and high mechanical properties through a chain bundle structure. The dispersibility is improved by optimizing the content and particle size of nano-cellulose. The goal is to develop ultra-low-density polyurethane with excellent sound absorption performance in high frequency areas over 2,000 Hz and improved strength. The strength of hood insulation and dash outer products can be improved by applying the developed polyurethane material. In addition, the quality of lightweight engine room sound absorbing materials for electric vehicles can be improved.

Analysis of spatial and temporal changes and driving forces of arable land in the Weibei dry plateau region in China

Arable land is the lifeblood of food production, it is of great significance to promote the protection of arable land and ensure national food security by accurately understanding the change law of cultivated land and its driving mechanism. This study takes the Weibei dry plateau region of China as an example, explores its spatial and temporal change characteristics through the center of gravity shift and land use shift matrix, and couples the geographic probe model to reveal the driving mechanisms affecting arable land change. The results show that in the past 25 years, the total arable land area in the Weibei Dry Plateau Region of China has decreased by 5.58%, and the stability of arable land resources in the whole region has weakened. The center of gravity of arable land shifts to the northeast, and the standard deviation ellipse of arable land mainly undergoes the change process of "increase (1995–2015)-decrease (2015–2020)", and the spatial distribution of arable land tends to be dispersed. In the LISA frequency mapping, the proportion of stable constant and low-frequency areas is as high as 89.58%, and the spatial pattern of cultivated land is relatively stable. Medium and high frequency areas. The transformation mode is mainly "low-low" aggregation, "low–high" aggregation is not significant, and the decline of cultivated land in the study area is more obvious. In the past 25 years, a total of 1017.26 km2 of arable land was converted to construction land. The explanatory power of the influencing factors varies in each period (0.299 to 0.731), with total agricultural machinery power has the strongest explanatory power of 0.694, 0.592, and 0.731, respectively. The interaction between slope and annual average temperature and other factors being the highest, both greater than 0.8. Through the construction of LISA frequency mapping, combined with the center of gravity model and standard deviation ellipse, the spatial evolution trend of regional arable land is more comprehensively and dynamically grasped. By using the geodetector model, the driving mechanism of the changes of arable land is revealed comprehensively, which provides a theoretical basis for the scientific management and effective protection of arable land resources and a basis for decision-making.

Influence of Climate, Topography, and Hydrology on Vegetation Distribution Patterns—Oasis in the Taklamakan Desert Hinterland

Vegetation in natural desert hinterland oases is an important component of terrestrial ecosystems. Determining how desert vegetation responds to natural variability is critical for a better understanding of desertification processes and their future development. The aim of this study is to characterize the spatial distribution of vegetation in the natural desert hinterland and to reveal how different environmental factors affect vegetation changes. Taking a Taklamakan Desert hinterland oasis as our research object, we analyzed the effects of different environmental factors on desert vegetation using a time-series normalized difference vegetation index (NDVI) combined with meteorological, topographic, and hydrological data, including surface water and groundwater data. Vegetation was distributed in areas with high surface water frequency, shallow groundwater levels, relatively flat terrain, and dune basins. NDVI datasets show greening trends in oasis areas over the past 20 years. The frequency of surface water distribution influences water accessibility and effectiveness and shapes topography, thus affecting the spatial distribution pattern of vegetation. In this study, areas of high surface water frequency corresponded with vegetation distribution. The spatial distribution of groundwater depth supports the growth and development of vegetation, impacting the pattern of vegetation growth conditions. Vegetation is most widely distributed in areas where the groundwater burial depth is 3.5–4.5 m. This study provides data for restoring riparian vegetation, ecological water transfer, and sustainable development.

Spatiotemporal variation of drought in the Western Sichuan Plateau based on standardized precipitation evapotranspiration index.

Drought is a destructive natural disaster in the Western Sichuan Plateau. Understanding its spatiotemporal variations has important practical significance for drought prevention, ensuring agricultural production safety, and maintaining ecosystem health in the region. Based on the daily meteorological data from 48 meteorological stations in the Western Sichuan Plateau from 1980 to 2020, we used the Penman-Monteith model to calculate potential evapotranspiration and standardized precipitation evapotranspiration index (SPEI). The temporal and spatial variations of drought in the Western Sichuan Plateau were analyzed using linear trend analysis and drought characteristics analysis methods. The results showed that the annual and spring SPEI of the Western Sichuan Plateau showed a weak wetting trend from 1980 to 2020, while summer, autumn, and winter showed a drought trend. The southwest mountains and northeast grasslands in the study region were prone to drought. The range of interannual drought impact in the study area was weakly increasing, with a decreasing trend in spring and an increasing trend in summer, autumn, and winter. The overall drought frequency in the whole region was relatively high. The areas drought of low-frequency were mainly located in parts of west and northeast of the Western Sichuan Plateau, while the rest were high frequency areas.

The relationship between high dominant frequency and low voltage areas in patients with atrial fibrillation: digital twin study

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): a grant [2022R1I1A1A0106342211] from the Basic Science Research Program run by the National Research Foundation of Korea (NRF) which is funded by the Ministry of Science, ICT & Future Planning (MSIP) Background It has been suggested that the high dominant frequency (DF) site plays an atrial fibrillation (AF) driver, but its relationship with the atrial substrate voltage map (Vm) in the entire chamber AF map has yet to be studied. We explored the relationship between the DF site during AF and Vm in the entire chamber maps by applying the human left atrial (LA) electroanatomical map (EAM) to the digital twin AF map. Methods We acquired LA substrate Vm (at sinus rhythm, >800 points bipolar electrograms) of 110 patients with persistent AF (male 72.7%, 58.7±9.8 years old) who underwent AF catheter ablation. We applied EAM to digital twins (0.4 million nodes), reflecting anatomy, histology, and electrophysiology. We evaluated the highest 10% DF areas for 6 sec after inducing virtual AF. The correlation between the highest 10% DF and the low Vm areas (<0.2mV) was evaluated in the LA region of 10 segments. Results The mean voltage of the entire LA area was 1.96±0.85 mV (2.19±0.82 mV extra-PV area, 1.33±0.93 mV PV area) in 110 patients. The correlation between low Vm and high DF areas was not significant in the entire LA (r=0.106, p<0.001), extra-PV (r=0.157, p<0.001), and PV (r=0.079, p=0.097) areas. In the LA 10 segment regional analysis, 72 patients (65.5%) showed the co-localization of the highest DF in the region with the lowest Vm, and 14 patients (12.7%) had the lowest Vm segment in the region with the highest DF. The mean voltage where high DF appeared was 0.69±1.35 mV, and the mean voltage of the region where high DF did not appear was 0.59±1.15 mV (p=0.171). Conclusion High DF site, a parameter representing a localized focal source, had statistically significant but very poor correlations with LA extra-PV voltage substrate in patients with persistent AF.

A new local indicator of spatial autocorrelation identifies clusters of highrendakufrequency in Japanese place names

AbstractThe methods of spatial statistics have been successfully applied to the study of linguistic variation, especially for detecting the existence of spatial patterns in the geographical distribution of linguistic features. However, the use of local indicators of spatial autocorrelation for detecting spatial clusters have been limited to continuous variables, and we propose to apply the new method of Anselin and Li (2019) for categorical variables to linguistic data. We illustrate this method with the case of Japaneserendaku, or sequential voicing, whose dialectal variation is still poorly documented. Focusing on regional differences in the frequency of rendaku, we examined the occurrence of rendaku for four lexemes in 4,921 place names from all Japan. A statistical analysis of local spatial association and an unsupervised density-based cluster analysis revealed the existence of two cluster areas of high rendaku frequency centered around Wakayama and Fukushima-Yamagata prefectures. This suggests that rendaku is more frequent in those dialects, and we recommend that further studies in the dialectal variation of rendaku start by looking at those areas.

High-resolution spatiotemporal changes in dominant frequency and structural organization during persistent atrial fibrillation.

Analyze changes in frequency activity and structural organization that occur over time with persistent atrial fibrillation (AF). Little is known about the frequency characteristics of the epicardium during transition from paroxysmal to persistent AF. Accurate identification of areas of high dominant frequency (DF) is often hampered by limited spatial resolution. Improvements in electrode arrays provide high spatiotemporal resolution, allowing for characterization of the changes that occur during this transition. AF was induced in adult Yorkshire swine by atrial tachypacing. DF mapping was performed using personalized mapping arrays. Histological analysis and late gadolinium enhanced magnetic resonance imaging were performed to determine structural differences in fibrosis. The left atrial epicardium was associated with a significant increase in DF in persistent AF (6.5 ± 0.2 vs. 7.4 ± 0.5 Hz, P = 0.03). The organization index (OI) significantly decreased during persistent AF in both the left atria (0.3 ± 0.03 vs. 0.2 ± 0.03, P = 0.01) and right atria (0.33 ± 0.04 vs. 0.23 ± 0.02, P = 0.02). MRI analysis demonstrated increased ECV values in persistent AF (0.19 vs 0.34, paroxysmal vs persistent, P = 0.05). Tissue sections from the atria showed increase in fibrosis in pigs with persistent AF compared to paroxysmal AF. Staining demonstrated decreased myocardial fiber alignment and loss of anisotropy in persistent AF tissue. Changes in tissue organization and fibrosis are observed in the porcine model of persistent AF. Alterations in frequency activity and organization index can be captured with high resolution using flexible electrode arrays.

Evolution of Electrochemical Impedance Spectra Characteristics of Cementitious Materials after Capturing Carbon Dioxide

The electrochemical parameters of cement-based materials with different water–cement ratios in carbon curing and water curing were measured with electrochemical impedance spectroscopy (EIS). The optimized circuit model and corresponding electrical parameters were obtained to illustrate the variation of the microstructure of cementitious materials after carbon capturing. The results show that, to a large extent, the semicircle diameter in the high frequency area gradually increased along with carbon curing and water curing. However, carbon curing showed a difference that the semicircle diameter in the high frequency appeared at the minimal value at 3 days, which was higher than that at 1 day and 7 days. This should be the result of the joint influence of water content and porosity in the cement matrix. It was also found that the mass increase rates of carbonation with water–cement ratios of 0.4, 0.5, and 0.6 were basically stable at 3.4%, 5.0%, and 5.5%, respectively. The electrochemical parameters ρct2 of cement mortar corresponding to carbon curing were around three times that of water curing specimens, mainly due to the reduction of soluble materials and refinement of connecting pores in the microstructure of cementitious materials. A quadratic function correlation between the mass increase rate and ρct2 in the carbonation process of cement mortar was built, which proved that EIS analysis could be applied to monitor the carbon capturing of cement-based materials, either for newly mixed concrete or for recycled concrete aggregates.

Spectroradiometry of the Solar Corona on the RATAN-600

Modern studies of solar radio emission are complicated by continuous power amplification and multifrequency external interference, which often completely overlap important frequency ranges. Many topical problems in solar radio astronomy require large effective areas of radio telescopes, high frequency and time resolutions, accurate spatial measurements, and a large dynamic range. It becomes relevant to change the concept of receiving recording equipment. This paper deals with topical problems of the physics of the solar corona in combination with optimal methods of observation with large instruments. The features and difficulties of combining high parameters—dynamic, spatial, temporal, and frequency resolutions—are considered. The proposed solutions of the new-generation observation complex implement the possibilities of intelligent selection of registration conditions in a multioctave mode with multichannel over 8000 channels/GHz with temporary permission up to 8 ms/spectrum. A multiobject observation mode becomes available from powerful flaring objects to faint structures of various nature. High-speed data processing makes it possible to implement an online mode of interference elimination, which is based on a fast statistical analysis of the spectrum with the selection of non-Gaussian (interference) structures. Methods for high-speed analysis of large-volume data (the principal component analysis method) and their presentation to the user are proposed. Examples of the operation of the complex in the range of 1–3 GHz are given. The prospects of a new approach for multiobject radio astronomy observations in the implementation of the RATAN-600 tracking mode are considered: from recombination lines to wide-range spectra, from low-contrast fluctuations to fast changes in flares, etc.

자율신경검사의 해석과 임상적용

Autonomic nervous system (ANS) consists of sympathetic and parasympathetic components. ANS has a role in heart function and contraction and relaxation of smooth muscle in various internal organs. Several tests were introduced to assess ANS function. Heart rate variability (HRV) is the most common method to evaluate ANS function. HRV is defined as a physiologic variation between sinus beats, which is calculated into standard deviation of N-N interval. The indices derived from beat-to-beat variation are calculated based on time-domain analysis. Fourier transformation visualizes frequency-based graphs from the time-domain tachograms. Areas in the low frequency represent sympathetic predominant function, while high frequency areas show parasympathetic tone. Despite absence of the reference ranges of the HRV indices, studies have shown the ranges of the indices in their populations. Decrease in HRV may be a poor prognostic factor for heart disease, infection, and neuropsychiatric disorders. It is reported that HRV biofeedback improved various disorders related to ANS function. In addition, the results of HRV tests may guide functional approaches. In conclusion, the awareness on ANS function and HRV may help to provide patients with risk stratification and proper management.

Application of bioradiophotonics methods for the processing of bioelectric signals

The application of modern and perspective bioradiophotonics methods on the basis of optical and acousto-optic devices for the processing of bioelectric signals (BES) have been considered. The basic application difficulties of these methods are connected with the fact that the studied signals are of low frequencies, and development of special actions are required for the processing devices adapting. It has been proposed to introduce into acousto-optic processing system with time integration the bioelectric signals using method of high frequency carrier with linear frequency modulation which is modulated by low frequency signal. The system configuration has to provide the realization of convolution procedure; hence, the used Bragg cells must be oriented oppositely to each other. The performed analysis has shown that it is possible to realize both signal power spectrum calculation and its wavelet transform; the presence of carrier is obligatory for both kinds of processing. Also, the method of the preliminary BES compression has been proposed for its transmission into the high frequency area. In this case, the possibility occurs to introduce the signal into the acousto-optic processing system with spatial integration. In the simple acousto-optic correlator with the reference transparency the envelope of the correlation function is formed depending on time. Using the set of the reference transparencies in the multichannel correlator, it is possible to realize the prolonged BES wavelet analysis using the mother wavelet. The optical preliminary BES processing can be also performed using liquid crystal arrays. The analysis of the processing of electrocardiac signals obtained from the experimental animals (rats) has been listed using the liquid crystal array for the signal introduction into optical processing system. It has been shown that both spectral and wavelet processing can be realized in this case without using of the high frequency carrier by the low frequency signal. The use of the obtained results will make it possible to create a new family of devices for wavelet processing of bioelectrical signals implemented in real time which will make an important contribution to improving the diagnosis of diseases of the cardiovascular system, the cortex, and the central nervous system.

Prediction of Multi-Scale Meteorological Drought Characteristics over the Yangtze River Basin Based on CMIP6

Drought is a common and greatly influential natural disaster, yet its reliable estimation and prediction remain a challenge. The object of this paper is to investigate the spatiotemporal evolution of drought in the Yangtze River basin. The multi-time scale drought characteristics were analyzed based on 19 models and 3 emission scenarios of CMIP6. The results show that the CMIP6 model generally has moisture deviation in the Yangtze River basin, but the accuracy has been improved after correction and ensemble. The drought conditions in the near future (2030–2059) of the Yangtze River basin will be more severe than those in the historical period (1981–2010), with the drought intensity increasing by 7.47%, 18.24%, 18.34%, and 41.48% in the order of 1-month, 3-month, 6-month, and 12-month scales, but it will be alleviated in the far future (2070–2099) to 5.97%, 11.86%, −4.09%, and −8.97% of the historical period, respectively. The 1-month scale drought events are few, and the spatial heterogeneity is strong under different scenarios; areas of high frequency of the 3-month, 6-month, and 12-month scale drought events shift from the upper and middle reaches, middle and lower reaches in the historical period to the southwestern part of the entire basin in the future, and the harm of drought in these regions is also higher. The Yangtze River basin will get wetter, and the variability will increase in the future. The larger the time scale is, the more intense the change will be, with the 12-month scale varying about three times as much as the 1-month scale.

Surgical outcomes and observation in exotropia cerebral palsy children with cortical visual impairment

PurposeCortical visual impairment (CVI) is the common cause of pediatric visual impairment in cerebral palsy (CP) while exotropia is the most common strabismus associated with CP. We aim to observe the strabismic surgery outcomes in pediatric patients with CP and CVI.MethodOur medical records were collected from pediatric patients treated in our hospital from May 1, 2017 to Jan 1, 2022. With normal intelligence assessment and diagnosis of exotropia in children with CP and CVI, microsurgeries were performed under intravenous combined inhalation anesthesia. The strabismus was examined by the prism test under best vision correction and the contrast sensitivity testing (CST) was measured at five levels of spatial frequencies.ResultA total of 38 exotropia patients with CP and CVI were identified and included for analysis during the study period with age ranged from 5 to 12 years (mean 8.45 years) and mean follow up duration was 8.7 months (6–42 months). After bilateral lateral rectus recession (with/without medial rectus resection or inferior oblique transposition), the exotropia amount of participants were obviously revealed from − 30 ~ − 140 (median, IQR: − 50, 40) prism diopters (PD) preoperatively to 0 ~ − 15 (0, 5) PD postoperatively. Statistically significantly improvements were observed at all levels of spatial frequency on CST postoperatively, especially at high spatial frequency areas (p < 0.05).ConclusionOur results demonstrated that the effect of strabismus surgery on exotropia in children with CP and CVI were stable and monocular contrast sensitivity post- operation increased significantly at all spatial frequencies levels.

A climatological-dynamical analysis of tropopause folds over Southwest Asia in the period of 1989–2018

Tropopause folding is believed to be connected to the development of cyclonic systems in midlatitudes as well as the larger-scale, lower-frequency processes in the lower latitudes. To investigate such connections, a statistical and dynamical analysis of tropopause folds occurred in Southwest Asia is carried out for the period of 1989–2018. Tropopause folds are identified using the Era-Interim reanalysis dataset from the European Centre for Medium-Range Weather Forecasts. The spatial–temporal distributions of tropopause folding show that the frequency of folding is higher in the winter hemisphere than in the summer hemisphere and greater values of the frequency are found mostly within an elongated zonal band which is situated between 20 and 40 degrees latitude. Southwest Asia also has strong positive anomalous values of tropopause folding frequency and achieves the values more than five times the average of the Northern Hemisphere in the summer, especially in the northern latitudes of this region including Afghanistan, Iran and the eastern Mediterranean. This can be attributed mainly to the formation of summer monsoon in the subtropical latitudes of the Indian Ocean. In this regard, the examination of the effects of El Niño and La Niña on the spatial–temporal distributions of tropopause folding reveals that the values of 3-month running average of tropopause folding frequency coincident with La Niña tend to be larger than those with El Nino in both the hemispheres and Southwest Asia. This result is consistent with the previous findings on the tendency for higher occurrence of anticyclonic (cyclonic) baroclinic wave life cycles during La Niña (El Niño). Dynamically, the folds occurred in the study area are associated with the formation of waves at 500 hPa level and subsequently the creation of surface cyclones. In areas of high frequency of folding events, strong meridional shear of the zonal winds and jet stream amplification are observed at 200 hPa level. The analysis of wave activity flux and its divergence for the selected month of June 2015 shows two regions of wave propagation, one with a wave-packet like signature of flux divergence/convergence centers in the upper troposphere and one over the lower troposphere. The upper-tropospheric wave packet ends with an area of flux convergence related with the receipt and decay of Rossby waves, while in the lower troposphere, a flux divergence region as a source of stationary waves associated with the Indian monsoon activity is identified.

Research on Image Defogging Algorithms Based on Color Attenuation Prior

As for the defogging algorithm of color attenuation prior, an optimization algorithm based on color attenuation prior is proposed to solve the problem of image blurring in high frequency area of close-up view. Firstly, by improving the scene depth estimation information, the nonlinear model about scene depth is re-established to find the appropriate scene depth. Second, binary tree search algorithm is used to find the optimal atmospheric light value, and finally, a certain range of parameters are adjusted to achieve model optimization. The experimental results show that the algorithm solves the problem of blurring the close-up area and improves the speed of the algorithm.

Low quantum defect random Raman fiber laser.

The random Raman fiber laser (RRFL) has attracted great attention due to its wide applications in optical telecommunication, sensing, and imaging. The quantum defect (QD), as the main source of thermal load in fiber lasers, could threaten the stability and reliability of the RRFL. Conventional RRFLs generally adopt silica fiber to provide Raman gain, and the QD exceeds 4%. In this letter, we propose and demonstrate a phosphosilicate-fiber-based low-QD RRFL. There is a strong boson peak located at the frequency shift of 3.65 THz in the phosphosilicate fiber we employed. By utilizing this boson peak to provide Raman gain, we demonstrated an 11.71 W temporally stable random Raman laser at 1080 nm under a pump wavelength of 1066 nm. The corresponding QD is 1.3%, less than one third of the QD of the common silica-fiber-based RRFL. Compared with the full-cavity low-QD Raman fiber laser, this cavity-less low-QD RRFL has lower and flatter noise in the high frequency area (>100 kHz). This work provides a reference for suppressing thermal-induced effects, such as thermal-induced mode instability, thermal noise, and even fiber fusing in RRFLs.