A method for detection of flumethrin residue in honey by high-performance liquid chromatography was established. After n-hexane-dichloromethane (4:6, vol/vol) extraction, the honey samples were ...concentrated by rotary evaporation, purified by an Oasis HLB solid-phase extraction column, and detected using a UV detector at 267 nm. The interference of the matrix was greatly reduced by optimizing pretreatment conditions; thus, the minimal detection limit of cyhalothrin was 0.005 mg/kg, the average recovery was 80.8 to 96.8%, and the coefficient of variation was 0.6 to 1.5%. The precision and reproducibility of this method was suitable and applicable for detecting flumethrin residue in honey. With this method, 135 honey samples from seven locations in the People's Republic of China were tested; 77 samples tested positive for flumethrin residue, resulting in a detection rate of 75.3%. Samples from the Guangdong province had the highest flumethrin residue level (0.122 mg/kg) of the locations tested. On the basis of analytical validation, the high-performance liquid chromatography has been shown to be a promising alternative for the analysis of flumethrin residue in honey samples.
Compared with the construction method of a tunnel with a middle drift, the construction method of a tunnel without a middle drift is a more advanced, novel, efficient, and energy efficient. Moreover, ...the blasting excavation of late-excavated tunnel parts exerts a vibration impact on the lining structure of early excavated tunnel parts. To analyze and predict the influence of late-excavated tunnel blasting on an early excavated tunnel and surrounding rocks in a triangular area, this study uses the Ansys LS-DYNA software to build a three-dimensional tunnel model simulating multihole blasting and the fluid-solid interaction method to assess the interaction of different materials. In addition, the different working conditions of surrounding rock levels and explosive equivalents are simulated. The distribution law of peak particle vibration velocity and maximum principal stress peak value of surrounding rocks and the lining along the transverse and longitudinal directions of the early excavated tunnel are generalized based on the numerical simulation results. The influence of the blasting of a late-excavated tunnel on the initial lining, secondary lining, and the middle triangular area of a double-arch tunnel is analyzed. The relationship between the surrounding rock level, explosive equivalent, and vibration velocity peak value is concluded. The field experiment-measured vibration velocities from the double-arch tunnel without a middle drift in the Chenjiachong tunnel of the Chuyao expressway in Yunnan Province, China, are in satisfactory agreement with the numerical simulation results. The results of this study are verified by the field blasting vibration data of the Chenjiachong and Changba tunnels and can provide reference and guidance for the blasting engineering practices of late-excavated double-arch tunnels without a middle drift.
Precise measurement under high counting rates has been a major challenge for γ-ray spectroscopy, where signals generally pile up with each other and their characteristic values are deeply coupled. An ...off-line pile-up pulse recovery algorithm based on template matching is developed for LaBr3 scintillation detectors and has been applied to data from China Spallation Neutron Source (CSNS) Back-n white neutron beamline. As an improvement to the traditional Template Matching methods, the predetermined template shape is associated with pulse amplitudes, which is found crucial to achieve the best fitting results. Moreover, a universal strategy of setting the initial values of fitting allows to resolve signals that are separated in time by less than the characteristic rise time. Processing of simulated pulses demonstrates that the lower limit of interval to distinguish successive events is 10 ns, which is a significant improvement to the previous works. The algorithm performs well under a counting rate of 6×107 s−1, and is still effective up to 108 s−1. Analysis of experimental data indicates that this algorithm recovers over 98% count yield under a counting rates of no more than 4×106 s−1 in this work, providing a more reliable approach to deduce neutron-induced reaction cross sections.
We present the first measurements of the electric and magnetic form factors of the neutron in the timelike (positive q^{2}) region as function of four-momentum transfer. We explored the differential ...cross sections of the reaction e^{+}e^{-}→nover ¯n with data collected with the BESIII detector at the BEPCII accelerator, corresponding to an integrated luminosity of 354.6 pb^{-1} in total at twelve center-of-mass energies between sqrts=2.0-2.95 GeV. A relative uncertainty of 18% and 12% for the electric and magnetic form factors, respectively, is achieved at sqrts=2.3935 GeV. Our results are comparable in accuracy to those from electron scattering in the comparable spacelike region of four-momentum transfer. The electromagnetic form factor ratio R_{em}≡|G_{E}|/|G_{M}| is within the uncertainties close to unity. We compare our result on |G_{E}| and |G_{M}| to recent model predictions, and the measurements in the spacelike region to test the analyticity of electromagnetic form factors.
PDF
