利用偏最小二乘回归从冬小麦冠层光谱提取叶片含水量

通过人为控制灌溉水平,在冬小麦3个发育期(孕穗、开花、乳熟)测定了冠层光谱和叶片含水量(leaf water content,LWC)。针对每期数据,结合偏最小二乘回归和迭代特征去除,建立了基于诊断波段的LWC回归模型。结果表明,叶片水分的光谱响应及反演精度受小麦生长状态的影响。在孕穗、开花和乳熟3个发育阶段,回归模型中光谱数据的最佳利用形式分别为对数光谱、导数光谱和反射率光谱;重要光谱区间为SWIR,NIR和SWIR;模型交叉验证决定系数(R2_CV)为0.750,0.889和0.696。研究结论对今后监测冬小麦旱情和开发作物水分遥感产品具有重要的指导作用。     

Direct numerical simulation of free and forced square jets

Direct numerical simulation (DNS) of incompressible, spatially developing square jets in the Reynolds number range of 500–2000 is reported. The three-dimensional unsteady Navier–Stokes equations are solved using high order spatial and temporal discretization. The objective of the present work is to understand the evolution of free and forced square jets by examining the formation of large-scale structures. Coherent structures and related interactions of free jets suggest control strategies that can be used to achieve enhanced spreading and mixing of the jet with the surrounding fluid. The critical Reynolds number for the onset on unsteadiness in an unperturbed free square jet is found to be 875–900 while it reduces to the range 500–525 in the presence of small-scale perturbations. Disturbances applied at the flow inlet cause saturation of KH-instability and early transition to turbulence. Forced jet calculations have been carried out using varicose perturbation with amplitude of 15%, while frequency is independently varied. Simulations show that the initial development of the square jet is influenced by the four corners leading to the appearance hairpin structures along with the formation of vortex rings. Farther downstream, adjacent vortices strongly interact leading to their rapid breakup. Excitation frequencies in the range 0.4–0.6 cause axis-switching of the jet cross-section. Results show that square jets achieve greater spreading but are less controllable in comparison to the circular ones.     

A Facile Strategy for Construction of Sensor for Detection of Ondansetron and Investigation of its Redox Behavior and Thermodynamic Parameters

A sodium dodecylsulfate‐doped polypyrrole (SDS‐PPy) film was elaborated on glassy carbon electrode (GCE) by an electrodeposition method in phosphate buffer solution (pH 2.0) containing pyrrole (Py) and sodium dodecyl sulfate (SDS). SDS‐PPy/GCE was used for the construction of sensor, which showed excellent electrochemical response for the detection of ondansetron (OND) compared to conventional PPy. The application of the square wave (SW), with the adsorptive accumulation, indicates a maximum response at 1.33 V in H₂SO₄ (0.5 M). The influence of experimental parameters on determination of OND is discussed. The adsorptive stripping technique showed to be more sensitive, giving responses twice as big as those of non‐accumulated OND. The substantial improvement of response permits the development of an electroanalytical technique with a linear concentration in the range (1.0–80 μM), low detection (0.09 μM), and quantification limits (0.3 μM), and acceptable relative standard deviations of repeatability (0.59 %), and reproducibility (1.51 %). Consequently, this electrode is promising candidate for an accurate electroanalytical determination of OND in pharmaceutical samples with high sensitivity and selectivity, good accuracy and precision. The electrooxidation of OND at SDS‐PPy/GCE at various temperatures were studied by cyclic voltammetry to evaluate both the kinetic (k_s and E_a) and thermodynamic (ΔG*, ΔH* and ΔS*) parameters.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.     

Acoustic absorbers at low frequency based on split-tube metamaterials

The remarkable properties of acoustic metamaterials have attracted massive researches and applications, especially on low-frequency sound absorptions. Currently, most of the acoustic metamaterial absorbers employ resonances in plastic cavities, and their structural strengths are important in many circumstances, especially in harsh environment. However, studies of metamaterials including this point are very scarce. Here, we propose an acoustic metamaterial for low-frequency (<500 Hz) absorptions, composed of three nested square split tubes with inverted opening directions. The efficiency of the absorber is investigated both numerically and experimentally, and absorptions at the peeks are found to exceed 90% and the frequency can be effectively adjusted by tuning its geometric parameters. We further test its yield strength under compression and confirm its buckling behavior happens from the outmost layer. This tunable acoustic metamaterial with a fairly good mechanical strength may lead to broad applications in noise reduction.     

Study of Convection in a Liquid with a Free Surface Using Exponential Fitting Discretization

The two-dimensional flow of viscous incompressible liquid in a square cavity with a Tree boundary and differentially heated vertical sides is considered in the present work. The influence of gravitational and thermocapillary convection on temperature and velocity fields is studied in a large range of dimensionless parameters and similarity criteria using method of exponential fitting discretization. Limiting cases of dimensionless parameters are analyzed numerically.     

Electrochemical Assay of Effects of Organophosphate Poisoning on Acetylcholinesterase from Pheretima via 2,6-Dimethyl-p-benzoquinone

Electroanalytical techniques could be a reliable and promising alternative to classical and sophisticated methods because of their simplicity(small and portable), easy use, the ability to deliver fast response with high sensitivity and selectivity. A square wave voltammetric method was developed for the assessment of organophosphorus(OPs) compound impact on acetylcholinesterase(AChE) of Pheretima with 2,6-dimethyl-p-benzoquinone(2,6- DMBQ) as a redox indicator. The substrate of acetylthiocholine is hydrolyzed by AChE and the produced thiocholine reacts with 2,6-DMBQ to give an obvious shift of electrochemical signal. The reduction peak of 2,6-DMBQ is located at around -0.18 V which is far away from the oxidation potential of possible interference components often present in biosample. The decreased rate of reduction current was related with the activity of AChE. The inhibition of parathion-methyl on AChE was assessed. The inhibiton rate of OPs on AChE activity increased quickly during the first 10 min inhibition, and after that the value of inhibition rate approached to be constant. AChE lost almost 29.3% of acti- vity after 10 min incubation with 1 mg/mL parathion-methyl and 67.5% of activity with 10 mg/mL parathion-methyl, while the activity that corresponds to 40 mg/mL parathion-methyl was nearly completely inhibited(94.9%). Compared to cyclic voltammetry and amperometry, Square wave voltammetry(SWV) method is a high sensitive electroanalysis with fast scan-rate(only several seconds for one signal value) which is useful to prevent the electrodes from possible fouling or passivation. This method can be employed to assess the inhibition of organophosphate on AChE and investigate OPs impact on environmental animals.     

微波溶样ICP-AES法测定甘肃东紫苏中的无机元素

将正交试验和方差分析应用于微波溶样ICP-AES法测定东紫苏地上部分K, Na, Ca, Ba, Pb, Zn, Mn, Cu, Mg, Fe和Al等无机元素的分析中,此方法简单、快速、灵敏度高、准确性好,且多种元素可同时测定,该方法的加标回收率为93.2%～104.1%, RSD(n=5)＜3.20%。结果表明: 东紫苏中含有丰富的对人体有益的微量元素,此结果可为探讨东紫苏中元素含量与其药效的相关性提供理论依据。