Multidimensional climatic niche conservatism and invasion risk of Phenacoccus solenopsis.

The cotton mealybug Phenacoccus solenopsis, a globally invasive insect, is listed as a national quarantine pest in agriculture and forestry, which seriously threatens biological safety of China. Niche conservatism is a key assumption of species distribution model. An evaluation of the applicability of using ecological niche models to assess the invasion risk of cotton mealybug, and further optimizing model complexity, are of both theoretical and practical significance. Based on 706 occurrence records and key bioclimatic variables, we used n-dimensional hypervolume niche analysis method to quantify the climatic niche hypervolumes of this pest in both native and invasive sites, and further tested the niche conservatism hypothesis. MaxEnt model parameters were optimized to predict the invasion risk of the mealybug under current and future climate scenarios in China. The results showed that four climatic variables (annual mean temperature, mean temperature of wettest quarter, mean temperature of warmest quarter, and precipitation of driest quarter) were the key climate factors affecting the distribution of cotton mealybug. Compared with native climatic niche (hypervolume volume, HV=40.43), the niche hypervolume of cotton mealybug in the invasive areas was significantly reduced (HV=6.04). Niche contraction (the net differences between the amount of space enclosed by each hypervolume was 0.84) explained 98.8% of niche differentiation, whereas niche shift (the replacement of space between hypervolumes was 0.01) contributed less than 2%. The direction of climatic niche contraction of the pest in different invasive areas was not exactly consistent. The default parameters of MaxEnt model were unreliable (ΔAICc=14.27), and the optimal parameter combination was obtained as follows: feature combination was linear-quadratic-hinge-product and regularization multiplier was 0.5. The most suitable habitats of cotton mealybug were concentrated in the south of Huaihe River-Qinling Mountains line, and the north-central provinces contained a large area of low suitable habitat. The increase of suitable habitat was not significant at the end of 21 century (SSP1-2.6: 1.7%, SSP5-8.5: 0.7%). The multidimensional climatic niche of P. solenopsis was highly conservative. The species distribution model was suitable for analyzing its invasion risk. The northward spread was obvious, and climate change had less impact on the pest.

A fast algorithm for nonnegative matrix factorization and its convergence.

Nonnegative matrix factorization (NMF) has recently become a very popular unsupervised learning method because of its representational properties of factors and simple multiplicative update algorithms for solving the NMF. However, for the common NMF approach of minimizing the Euclidean distance between approximate and true values, the convergence of multiplicative update algorithms has not been well resolved. This paper first discusses the convergence of existing multiplicative update algorithms. We then propose a new multiplicative update algorithm for minimizing the Euclidean distance between approximate and true values. Based on the optimization principle and the auxiliary function method, we prove that our new algorithm not only converges to a stationary point, but also does faster than existing ones. To verify our theoretical results, the experiments on three data sets have been conducted by comparing our proposed algorithm with other existing methods.

A negative-pressure flow-injection micro-electrode system for rapid and simultaneous determination of four electrolytes in human serums.

An automatic system for simultaneous determination of K(+), Na(+), Cl(-) and Ca(2+) in serums was established on the basis of a negative-pressure flow-injection using micro-electrodes, and parameters of the system were optimized. The total ionic strength adjustment buffer consisted of 0.25 mmol L(-1) K(+), 48.6 mmol L(-1) Na(+), 2.56 mmol L(-1) Cl(-), 0.25 mmol L(-1) Ca(2+) and 23 mmol L(-1) Na(2)B(4)O(7)-H(3)BO(3); the flow rate was 1.58 mL min(-1), the sampling volume was 45 µL, and the mixing coil length was 30 cm. The system could conduct 480 detections h(-1), and its RSD was less than 1.6%. Recoveries were 97.3 - 103.6%, and linear responses were 2.0 - 22.0 mmol L(-1) for K(+), 89.6 - 253.0 mmol L(-1) for Na(+), 20.1 - 248.2 mmol L(-1) for Cl(-), and 0.35 - 10.0 mmol L(-1) for Ca(2+), respectively. The ion concentration ranges were in ranges of human serum electrolytes. The system features minimized sorption of fibrin in sensors and prolonged sensor life.

Surface tension effects on the behavior of two cavities near a rigid wall.

Surface tension effects on the behavior of two initially spherical cavities growing and collapsing axisymmetrically above and near a rigid wall are investigated numerically by boundary integral method. The numerical simulations are performed for different dimensionless maximal cavity sizes, different dimensionless distances between the two cavities and those between the wall and the two cavities, and different values of Weber number. It is found that surface tension effects will resist the deformation of a cavity and make it closer to spherical during its growth phase, and make it collapse faster. For the case where the lower cavity is much smaller than the upper one, when the Weber number is less than or equal to 20, during the collapse phase, surface tension will have substantial effects on the behavior of the lower cavity such as change the form or the direction of its liquid jet if the Bjerknes forces to the lower cavity induced by the wall and the upper one are nearly equal. In all of the other cases, when the Weber number is greater than or equal to 10, surface tension will not have qualitative effects on the behavior of the cavity but change the length, width or sizes of its liquid jet. It is also found that for a convex cavity, surface tension has the effects on cavity behavior similar to those of the difference between the ambient pressure and the saturated vapor pressure inside the cavities. The above phenomena induced by surface tension effects are explained by this mechanism.

Surface tension effects on the behavior of a cavity growing, collapsing, and rebounding near a rigid wall.

Surface tension effects on the behavior of a pure vapor cavity or a cavity containing some noncondensible contents, which is growing, collapsing, and rebounding axisymmetrically near a rigid wall, are investigated numerically by the boundary integral method for different values of dimensionless stand-off parameter gamma, buoyancy parameter delta, and surface tension parameter beta. It is found that at the late stage of the collapse, if the resultant action of the Bjerknes force and the buoyancy force is not small, surface tension will not have significant effects on bubble behavior except that the bubble collapse time is shortened and the liquid jet becomes wider. If the resultant action of the two force is small enough, surface tension will have significant and in some cases substantial effects on bubble behavior, such as changing the direction of the liquid jet, making a new liquid jet appear, in some cases preventing the bubble from rebound before jet impact, and in other cases causing the bubble to rebound or even recollapse before jet impact. The mechanism of surface tension effects on the collapsing behavior of a cavity has been analyzed. The mechanisms of some complicated phenomena induced by surface tension effects are illustrated by analysis of the computed velocity fields and pressure contours of the liquid flow outside the bubble at different stages of the bubble evolution.