Search

Objective quality assessment and efficacious safety surveillance for agricultural and food products are inseparable from innovative techniques. Hyperspectral imaging (HSI), a rapid, nondestructive, and chemical-free method, is now emerging as a powerful analytical tool for product inspection by simultaneously offering spatial information and spectral signals from one object. This paper focuses on recent advances and applications of HSI in detecting, classifying, and visualizing quality and safety attributes of fruits and vegetables. First, the basic principles and major instrumental components of HSI are presented. Commonly used methods for image processing, spectral pretreatment, and modeling are summarized. More importantly, morphological calibrations that are essential for nonflat objects as well as feature wavebands extraction for model simplification are provided. Second, in spite of the physical and visual attributes (size, shape, weight, color, and surface defects), applications from the last decade are reviewed specifically categorized into textural characteristics inspection, biochemical components detection, and safety features assessment. Finally, technical challenges and future trends of HSI are discussed.

Hyperspectral imaging was exploited for its potential in direct and fast determination of Pseudomonas loads in raw chicken breast fillets. A line-scan hyperspectral imaging system (900-1700 nm) was employed to obtain sample images, which were then further corrected, modified and processed. The prepared images were correlated with the true Pseudomonas counts of these samples using partial least squares (PLS) regression. To enhance model performance, different spectral extraction approaches, spectral preprocessing methods as well as wavelength selection schemes based on genetic algorithm were investigated. The results revealed that extraction of mean spectra is more efficient for representation of sample spectra than computation of median spectra. The best full wavelength model was attained based on spectral images preprocessed with standard normal variate, and the correlation coefficients (R) and root mean squared errors (RMSEs) for the model were above 0.81 and below 0.80 log10 CFU g(-1), respectively. In development of simplified models, wavelengths were selected by using a proposed two-step method based on genetic algorithm. The best model utilized only 14 bands in five segments and produced R and RMSEs of 0.91 and 0.55 log10 CFU g(-1), 0.87 and 0.65 log10 CFU g(-1) as well as 0.88 and 0.64 log10 CFU g(-1) for calibration, cross-validation and prediction, respectively. Moreover, the prediction maps offered a novel way for visualizing the gradient of Pseudomonas loads on meat surface. Hyperspectral imaging is demonstrated to be an effective tool for nondestructive measurement of Pseudomonas in raw chicken breast fillets.

Near infrared (NIR) hyperspectral imaging (HSI) and different spectroscopic transforms were investigated for their potential in detecting total viable counts in raw chicken fillets. A laboratory-based pushbroom hyperspectral imaging system was utilized to acquire images of raw chicken breast fillets and the resulting reflectance images were corrected and transformed into hypercubes in absorbance and Kubelka-Munck (K-M) units. Full wavelength partial least regression models were established to correlate the three spectral profiles with measured bacterial counts, and the best calibration model was based on absorbance spectra, where the correlation coefficients (R) were 0.97 and 0.93, and the root mean squared errors (RMSEs) were 0.37 and 0.57 log10 colony forming units (CFU) per gram for calibration and cross validation, respectively. To simplify the models, several wavelengths were selected by stepwise regression. More robustness was found in the resulting simplified models and the model based on K-M spectra was found to be excellent with an indicative high ratio of performance to deviation (RPD) value of 3.02. The correlation coefficients and RMSEs for this model were 0.96 and 0.40 log10 CFU per gram as well as 0.94 and 0.50 log10 CFU per gram for calibration and cross validation, respectively. Visualization maps produced by applying the developed models to the images could be an alternative to test the adaptability of a calibration model. Moreover, multi-spectral imaging systems were suggested to be developed for online applications.

In this paper,the electromagnetic responses and potential applications of THz metamaterials are reviewed through the focus on fabrication,unit structure design,and material selection,respectively.It describes different kinds of fabrication technologies for obtaining metamaterials with special electromagnetic responses such as magnetic resonance and reconfigurable tunability,which is helpful for further understanding of electromagnetic resonances in metamaterials.The paper analyzes the electromagnetic response characteristics in detail and points out that the unit structure design can be used to obtain desired electromagnetic characteristics,such as anisotropy,bianisotropy,polarization modulation,multiband response,broadband response,asymmetric transmission,optical activity,and perfect absorption,etc.The dependence of electromagnetic responses upon surrounding dielectrics can be used not only to control resonant frequency by a proper substrate selection,but also for sensing applications.Furthermore,the introduction of functional materials with controllable dielectric properties by external optical field,electrical field,magnetic field and temperature has the potential to achieve tunable metamaterials,which is highly desirable for THz functional devices.Finally,the opportunities and challenges for further developments of THz metamaterials are briefly introduced.

Food safety is a great public concern, and outbreaks of food-borne illnesses can lead to disturbance to the society. Consequently, fast and nondestructive methods are required for sensing the safety situation of produce. As an emerging technology, hyperspectral imaging has been successfully employed in food safety inspection and control. After presenting the fundamentals of hyperspectral imaging, this paper provides a comprehensive review on its application in determination of physical, chemical, and biological contamination on food products. Additionally, other studies, including detecting meat and meat bone in feedstuffs as well as organic residue on food processing equipment, are also reported due to their close relationship with food safety control. With these applications, it can be demonstrated that miscellaneous hyperspectral imaging techniques including near-infrared hyperspectral imaging, fluorescence hyperspectral imaging, and Raman hyperspectral imaging or their combinations are powerful tools for food safety surveillance. Moreover, it is envisaged that hyperspectral imaging can be considered as an alternative technique for conventional methods in realizing inspection automation, leading to the elimination of the occurrence of food safety problems at the utmost.

The overall qualities of chestnuts are greatly affected by worm-eaten chestnuts, as they lead to a reduction of profits. Hence a fast, accurate and non-destructive method for sorting chestnuts is in great demand. In this study, the technology of machine vision was employed to grade chestnuts. A recognition method to identify worm-eaten chestnuts is presented based on the edge image of the wormhole. First, by applying a Sobel operator, binary images were gained through extracting the edges of the gray images, which were preprocessed with the denoising method of a Wiener filter. The binary image contained both the edge of the contour and the wormhole. The wormhole edges were obtained through separating the wormhole edge in light of the character that the gray degree of pixels in the neighborhood of the wormhole edge is lower than the threshold value set. Second, through morphological dilating and eroding, the denoised wormhole edge images were obtained. The connected component of the binary images of the wormhole edge were labeled, and the first three longest components were considered as feature values of the worm channel, which were then normalized. Third, the normalized data were input to a back-propagation (BP) neural network for training, where the hidden layer was 7. And only three steps were needed for iteration. When the model was utilized for prediction, the recognition rate was as high as 100%. The results showed that the proposed worm-eaten chestnut recognition method is accurate and fast, and it can provide a basis for on-line detection. Since the gray degree of the wormhole region is close to the normal region, this study used an enhanced boundary detection method to extract the edge of the worm channel solely, rather than the normally used region segmentation.

As an alternative energy of conventional resources, coalbed methane (CBM) has been studied globally. So far, the pressure distribution model for multi-stage fractured horizontal well (MFW) in stress sensitive coal seam is almost solved by numerical method. In this paper, a transient pressure behaviour model of MFW was established. Using perturbation transformation, Laplace transform, image theory and superposition principle the mathematical model was solved. According to the result of calculation, the flow process of MFW can be identified as six regimes. Stress-sensibility primarily influences the latter five stages. The well bore dimensionless pressure drop is several times larger comparing with the situation that does not take the stress sensitive into account. Accordingly, the influences of some of the critical parameters on the transient pressure behaviour were studied, including the fracture number, permeability modulus, storage ratio, and so on. [Received: August 25, 2016; Accepted: October 9, 2017]

Gated power supply is a key control circuit unit of image intensifier gated imaging. It has a great significance for the reduction of gated LLL image intensifier volume and the improvement of image intensifier imaging quality to carry out the research of small volume cathode high-voltage pulse circuit of gated power supply. By analyzing the photocathode gated operational principle of LLL image intensifier, this paper is to design a small volume cathode high-voltage pulse circuit for the gated image intensifier, and it gives the circuit block diagram and experimental results of gated power supply's cathode high-voltage pulse.

The image intensifier is special auto-gating power supply is an important component of the LLL image intensifier. It is the image intensifier tubes provide cathode, micro channel plate (MCP), anode the required voltage. It can realize automatic brightness control and image intensifier cathode protection function. The purpose of this paper is to design a cathode pulse control circuit which can protect the gating mode of auto-gating power supply and combining the independent cathode gating technology.