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In this paper, a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared, in which a calculation method is firstly proposed to optimize the number of channels to a minimum. The induction of peristrophic multiplexing reduces the performance difference in one bulk of the grating, whereas there is no need to deliberately optimize the fabrication process. It is revealed that a discrete 2D angle deflection range of ±30° is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55% with a root-mean-square deviation of less than 3.4% in the same grating. The deviation of the Bragg incidence and exit angles from the expected values is less than 0.07°. It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.

The identification of cucumber fruit is an essential procedure in automated harvesting in greenhouses. In order to enhance the identification ability of object detection models for cucumber fruit harvesting, an extended RGB image dataset (n = 801) with 3943 positive and negative labels was constructed. Firstly, twelve channels in four color spaces (RGB, YCbCr, HIS, La*b*) were compared through the ReliefF method to choose the channel with the highest weight. Secondly, the RGB image dataset was converted to the pseudo-color dataset of the chosen channel (Cr channel) to pre-train the YOLOv5s model before formal training using the RGB image dataset. Based on this method, the YOLOv5s model was enhanced by the Cr channel. The experimental results show that the cucumber fruit recognition precision of the enhanced YOLOv5s model was increased from 83.7% to 85.19%. Compared with the original YOLOv5s model, the average values of AP, F1, recall rate, and mAP were increased by 8.03%, 7%, 8.7%, and 8%, respectively. In order to verify the applicability of the pre-training method, ablation experiments were conducted on SSD, Faster R-CNN, and four YOLOv5 versions (s, l, m, x), resulting in the accuracy increasing by 1.51%, 3.09%, 1.49%, 0.63%, 3.15%, and 2.43%, respectively. The results of this study indicate that the Cr channel pre-training method is promising in enhancing cucumber fruit detection in a near-color background.

Systems of controllable orbital angular momentum (OAM) require more compact, higher conversion efficiency and more tolerable wavelength or polarization. We introduce an optical vortex switch based on a multiplexed volume grating (MVG). The MVG recorded in a piece of photo-thermo-refractive (PTR) glass exhibits high diffraction efficiency (DE, also known as conversion efficiency in transporting), sensitive angular selectivity, and polarization-insensitivity. The effects of the incident divergence angle and polarization on the DE and the far-field diffraction profiles are demonstrated and investigated. It turns out that the divergence angle of the probe beam can greatly affect the DE. The fluctuation of the DE caused by polarization variation is less than 1.59%. This switch can be potentially applied in vortex tweezers, optical communication, and high power systems.

We propose a steady method to extract the effective constitutive parameters of a slab of bianisotropic split-ring resonator metamaterial from reflection and transmission coefficients. The effective permittivity, permeability and magnetoelectric coupling coefficient of bianisotropic metamaterial can be simply retrieved by our derived analytical inversion equations. In our retrieval method, the transmission and reflection coefficients in only one direction of wave propagation were applied. The method was verified by the retrieval constitutive parameters for different metamaterials, among which one is isotropic structure and the other one is bianisotropic metamaterial. The intrinsic difference between the normal isotropic metamaterial and the bianisotropic metamaterial was evidently revealed. The resonant characteristic of the split ring resonator metamaterial including electric coupling to magnetic resonance was verified by the extracted effective constitutive parameters. The proposed method can be effectively applied in investigation of bianisotropic performance of metamaterials.

In this work, a chirped volume Bragg grating (CVBG) with over 40 nm high efficiency broadband spectra for pulse compression of near 100 fs was studied. Based on the fundamental matrix method, the effects of various structural parameters of CVBG on its diffraction characteristics were analyzed and then a design of broadband and high efficiency CVBG was proposed. Afterward, the monolithic CVBG was utilized to stretch and recompress a 100 fs pulse with a center wavelength of 1030 nm. The result shows this device has a high diffraction efficiency (84%) and a fine reciprocity. For the fabrication of large-size broadband CVBGs, double cylindrical wave holographic interference in photo-thermorefractive (PTR) glass was applied to achieve a wide range uniform and stable light field, which could greatly minimize unnecessary space chirp.

Reflecting Bragg gratings (RBGs) recorded in photo-thermo-refractive (PTR) glasses have been widely used in narrowing and stabilization of the laser emission spectrum. As the center wavelength of RBGs determines the final output wavelength of lasers, it is necessary to carefully control the center wavelength of RBGs during the fabrication process. In this paper, the fabrication process of high-precision RBGs was investigated. We developed a two-step method and demonstrated both theoretically and experimentally that it is effective and can be used to guide the fabrication process of high-precision RBGs. The experimental results show that the center wavelength of the fabricated RBG deviates from the target center wavelength within ±10 pm.

The low-order harmonic generation induced by a strong laser field produces a bright, ultrashort, supercontinuum radiation ranging from the terahertz to ultraviolet band. By controlling the phase-delay and ellipticity of the bi-chromatic laser fields, the third harmonic generation is experimentally and theoretically investigated for elucidating the mechanism of the low-order harmonics. The third harmonic generation is found to be strongly suppressed in the counter-rotating bi-chromatic laser field due to the selection rule for harmonic emissions. The continuum-continuum transition in the strong field approximation is extended to explain the third harmonic generation as a function of the phase delay and ellipticity of the bi-chromatic laser fields. Compared with the semi-classical photocurrent model, the continuum-continuum transition on the basis of quantum-mechanical treatment achieves better agreement with the experimental observations. Our work indicates that the overlapping in continuum states via different quantum paths of a single electron plays a role in low-order harmonics generation under elliptical bi-chromatic laser fields.

OPTICA APPLICATA; 02/2017; ISSN 1429-7507

In this study, the realization of multiplexed volume Bragg gratings (VBGs) working as angle amplifiers in high power beam scanning system is theoretically and experimentally investigated. The design of the multiplexed VBG for the working wavelength of 1064 nm is described. We propose a cascaded multiplexed VBGs scheme that consists of 12 grating channels. Three 4-channel multiplexed VBGs were fabricated inside photo-thermo-refractive (PTR) glasses by multiple exposures and subsequent heat treatment. The test results show that this angle amplifier can achieve discrete angle deflection ranging from -45° to + 45°. The relative diffraction efficiency of all the grating channels is more than 80% and is almost polarization independent.

In this paper, we present a method for achieving precise evaluation of amplitude of refractive index modulation (RIM) inside the volume Bragg grating (VBG) recorded in photo-thermo-refractive (PTR) glasses. The Gaussian divergence characteristics of the incident beam is theoretically considered when calculating the angular selectivity of VBG, and the profiles of experimental angular selectivity curves are utilized to determine the value of RIM with one step. The effectiveness of our proposed method is experimentally verified. This method is applicable even if the full width at half maximum (FWHM) of VBG's angular selectivity curve has the same order of magnitude as or is less than the beam divergence.

Background Low-level DNA mutations play important roles in cancer prognosis and treatment. However, most existing methods for the detection of low-level DNA mutations are insufficient for clinical applications because of the high background of wild-type DNA. Design and method In this study, a novel assay based on Tm-dependent inhibition of wild type template amplification was developed. The defining characteristic of this assay is an additional annealing step was introduced into the ARMS-blocker PCR. The temperature of this additional annealing step is equal to the Tm of the blocker. Due to this additional annealing step, the blocker can preferentially and specifically bind the wild-type DNA. Thus, the inhibition of wild type template is realized and the mutant DNA is enriched. Results The sensitivity of this assay was between 10 − 4 and 10 − 5 , which is approximately 5 to 10 times greater than the sensitivity of the assay without the additional annealing step. To evaluate the performance of this assay in detecting K-ras mutation, we analyzed 100 formalin-fixed paraffin-embedded (FFPE) specimens from colorectal cancer patients using this new assay and Sanger sequencing. Of the clinical samples, 27 samples were positive for K-ras mutation by both methods. Conclusions Our results indicated that this new assay is a highly selective, convenient, and economical method for detecting rare mutations in the presence of higher concentrations of wild-type DNA.

The king oyster mushroom (Pleurotus eryngii) is one of the most popular mushrooms in Asia, Europe and North America. Its growth is influenced by environmental conditions, particularly air temperature and humidity. Using traditional methods of cultivation in plastic greenhouses, P. eryngii can be grown only in spring and autumn. However, mass cultivation using modern commercial methods is unrestricted by season, but precise environmental control is crucial, as the process is costly and a high energy consumption. Through experimentation and analysis of the effects of variations in air temperature and relative air humidity on morphological development, a mathematical model for these effects was developed. This model can be used to predict the optimal ranges of air temperature and humidity for various indices of morphological development of the fruiting body, and to guide commercial production. Using the model, standard values of morphological development, optimal environmental control ranges for each day of the fruiting body growth period were calculated. These values provide a reference suitable for application to actual production.

Understanding of the timing, orientation and transmission mode of crop disease spread is very important in prevention and treatment of crop diseases, especially for cross-border crop diseases. In this paper, we introduced the complex network approach to model trans-boundary spread of diseases. In the model, the process of crop disease spread is characterized as a network, where patches of crop planting are abstracted into nodes, and the diseases spread from a node to neighboring nodes. The edge between two nodes is connected, only if the Euclidean distance between two nodes does not exceed the radius of disease spread. We obtained wheat-growing distribution data of Beijing in 2007 by image classification, and further abstracted patches of wheat growing into network nodes, and finally constructed the disease spread network to analyze its topology characteristics. The experimental results show the heavy influence of spatial constraint on disease spread.

Accurate and reliable agricultural information is the basis of the implementation of digital agriculture. Currently, the processing of agricultural information collection and data acquisition is more complex. It urgently needs to develop a portable agricultural information collection system with high degree integration and a wide range of versatility. It can process information in "one-stop" service. It can capture the GPS coordinates of the farmland, the agricultural attribute data, image information, and sent to the monitoring system immediately using 3G network or GPRS network. In this paper, The system supports android and IOS system mobile phones, the Widgets technology and http communicationis technology is be used to develop a real-time agricultural information collection system, which is based on cross-platform mobile GIS.

In this paper, an approach to assessing ecological suitability of crop growth was developed using GIS, through a case study of maize planting in Jilin Province, in the northeast China, in order to improve the accuracy and objectivity of the evaluation, promote the rationality of crop distribution, and increase the efficiency of the agro-resource utility. Climate and soil conditions in the region were taken into consideration in the research. The crop potential productivity under the climatic condition of 46 meteorological stations in the region, namely photo-temperature-water climatic potential productivity, was calculated based on the meteorological data of the precipitation, temperature, wind speed and sunshine hours from 1980 to 2006, and the crop potential productivity was used as index to evaluate the climatic suitability for crop growth. The point data were interpolated in a GIS environment and formed climatic suitability map. The assessment of soil suitability for crop growth was derived from soil fertility map drawing on the basis of information on 12 parameters, such as terrain, depth of soil body, thickness of black earth, soil erosion and organic mater. The ecological suitability map is completed using methods of spatial overlay in GIS. Comparing with the crop yield map that based on the statistical yield of 30 years in each county, the result of ecological suitability assessment is consistent with the yield. Therefore this method is feasible to assess the ecological suitability in the region.

In this paper, through the research on two-dimensional bar codes of food source tracking; a set of traceability tracking system was designed based on the two bar coding algorithm and decoding algorithms. This system could generate PDF417 code based on food production, logistics and transport, supermarket and other storage information. Consumers could identify PDF417 code through a client based on B/S architecture so that a simple process of food traceability has been completed.

Mycelium is the vegetative part of a fungus or most microorganisms, consisting of a mass of branching, thread-like hyphae. It is through the hyphae that a fungus absorbs nutrients from its environment. For most fungi, the ability of nutrition translation from mycelium to fruit body is determined by growth status of hyphae. It is very necessary to study the effect of environmental factors on mycelium growth, and know the befitting environment condition. However, finding a good data acquisition method for measuring the mycelium is the key point.

International audience; An information collection system which was used to group characteristics of pleurotus eryngii was introduced. The group characteristics of pleurotus eryngii were quantified using machine vision in order to inspect and control the pleurotus eryngii house environment by an automated system. Its main contents include the following: collection of pleurotus eryngii image; image processing and pattern recognition. Finally, by analysing pleurotus eryngii image, the systems for group characteristics of pleurotus eryngii are proved to be greatly effective.

In this paper, an approach to assessing ecological suitability of crop growth was developed using GIS, through a case study of maize planting in Jilin Province, in the north-east of China, in order to improve the accuracy and objectivity of the evaluation and promote the rationality of crop distribution and increase the efficiency of the agro-resource utility. Climate and soil conditions in the region were taken into consideration in the research. The crop potential productivity under the climatic condition of 46 meteorological stations in the region, namely photo-temperature-water climatic potential productivity, were calculated based on the meteorological date of the p precipitation, temperature, wind speed and sunshine hours from 1980 to 2006, and used as index to evaluate the climatic suitability for crop growth. The point data were interpolated in a GIS environment and formed climatic suitability map. The assessment of soil suitability for crop growth was derived from soil fertility map drawing on the basis of information on 12 parameters, such as terrain, depth of soil body, thickness of black earth, soil erosion and organic mater. The ecological suitability map is completed using methods of spatial overlay in GIS. Comparing with the crop yield map that based on the statistical yield of 30 years in every county, the result of ecological suitability assessment is consistent with the yield. So this method is feasible to assess the ecological suitability in the region.

This research attempt to establish a grass cover change model based on cellular automata. It took the relationship between elevation, slope, aspect, settlement, road, water system and grass cover change as the foundation of the model, the dynamic progress of grass cover change was expressed by using cellular automata, the grass cover change model based on the basic geographical control condition which has been mentioned in above paragraph was constructed. The grass cover state of Madoi County in 2003 was simulated, and has been compared with the actual state of Madoi County in 2003. It was found that the grass cover change model has a high precision. The value of kappa index has reach 0.8801.