Self-similar pulse compression in a tapered Pb-silicate photonic crystal fiber at 2 µm.

We report a 2-µm all-fiber nonlinear pulse compressor based on a tapered Pb-silicate photonic crystal fiber (PCF), which is capable of achieving large compression with low pedestal energy. A tapered Pb-silicate photonic crystal fiber with increased nonlinear coefficients is proposed for achieving self-similar pulse compression (SSPC) at 2 µm. The dynamic evolution of the fundamental order soliton is numerically analyzed based on the designed tapered fiber. After pulse compression in a tapered fiber with a length of 2.2 m, an initial 1.76 ps pulse can be compressed to 88 fs, increasing the peak power from 4.4 to 86 W with a compression factor of 20 and a quality factor of 98%. The results reveal that exponential variation yields superior compression performance and provides a promising solution for generating high-power femtosecond pulses at 2 µm.

Simultaneous determination of residues of multiple pesticides and their metabolites in citrus and orange juice from markets in China: residue levels and dietary risk assessment.

Consumers are becoming more concerned about pesticide residues in food. Since citrus represent a significant portion of the diet, it is appropriate to monitor the pesticide residues in citrus. In this paper, we modified a QuEChERS method combined with HPLC-MS/MS to investigate residue levels of 15 pesticides and 3 metabolites in citrus (whole fruit and pulp) and orange juice from the markets in China. And the dietary exposure risks were evaluated by using the hazard quotient (HQ) and hazard index (HI) methods based on deterministic and probabilistic models. The recoveries of the modified method ranged from 70 to 112% at three spike levels of 0.005-0.5 mg/kg with relative standard deviations of 1.0-18.1%. Pesticide residues were detected in 85.84% of the whole citrus and 40.00% of pulp, with concentrations ranging from 0.005 to 0.47 mg/kg, which did not exceed their maximum residue limits (MRLs) in China. The HQ (0.01-11.41%) and HI (0.07-16.2%) were both less than 100%, demonstrating that chronic, acute, and cumulative dietary risks were acceptable. Notably, the risk for children (1-6 years old, 1.96-16.2%) was higher than that for the general population (0.76-6.25%). The results of our study can provide a valuable reference for regular monitoring to protect public health and ensure pesticide management.

Residue levels, household processing evolution, and risk assessment of chlorothalonil, SDS-3701, metalaxyl, and dimethomorph in Dendrobium officinale Kimura et Migo.

Dendrobium officinale, a minor crop with medicinal and edible value, is increasingly consumed by people, but the pesticide residues on it have received little attention. In this work, field trials were conducted under good agricultural practice conditions to investigate the residues of chlorothalonil, SDS-3701, metalaxyl, and dimethomorph in D. officinale; then the evolution of these pesticides after household processing was studied. The results indicated that chlorothalonil, SDS-3701, metalaxyl, and dimethomorph were 2.41-30.12, 0.20-1.23, 0.07-0.80, and 0.19-7.90 mg kg-1 , respectively, in stems at recommended preharvest interval (30 days). Washing and soaking removed the pesticides in fresh stems with processing factors 0.41-1.14 and 0.12-1.13, respectively. In the brewing test, the transfer rates of pesticides in dry stems decreased from the first time (4.27-95.40%) to the third time (3.89-15.57%). Intake risk assessments were also conducted, and the risk quotients were no more than 27.02% for all compounds in different samples, which indicated acceptable risks for consumers. As effective risk-reducing home-processing methods, washing, soaking, and multiple brewing were suggested in this work, hoping to help consumers with diet safety.

Residues and Safety Evaluation of Etoxazole, Bifenazate and Its Metabolite Bifenazate-diazene in Citrus Under Open-Field Conditions.

The residues of bifenazate (sum of bifenazate and bifenazate-diazene) and etoxazole in whole citrus and pulp collected from twelve regions of China were monitored and their chronic dietary risk to consumer were also evaluated. The citrus samples were extracted by a QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, and analyzed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The average recoveries of target compounds were ranged from 83 to 100% with relative standard deviations (RSDs) of 0.59-11.8%. The limits of quantification (LOQs) for three analytes were 0.01 mg/kg. At the interval to harvest of 20 and 30 days, the residues of total bifenazate and etoxazole were from below 0.02 to 0.26 mg/kg and from below 0.01 to 0.30 mg/kg in citrus samples. The chronic risk quotients (RQs) were below 100%, indicating no unacceptable risk to consumers.