The effect of glycolic acid monomer ratio on the emulsifying activity of PLGA in preparation of protein-loaded SLN

Our previous work demonstrated that lactic/glycolic acid copolymer (PLGA) was an efficient emulsifier for the primary w/o emulsion in the formulation of protein-loaded solid lipid nanoparticles (SLN) by w/o/w double emulsion-solvent evaporation technique. In this work, the effect of PLGA composition on the emulsifying activity was studied with PLGA of different lactic/glycolic acid ratios (90/10, 75/25, 50/50). The results demonstrated that the glycolic acid monomer ratio significantly affected the emulsifying activity of PLGA. Increasing the glycolic acid monomer ratio from 10% to 50% decreased the minimum PLGA content needed to produce stable w/o emulsions. With same PLGA contents, increase of the glycolic acid monomer ratio increased the stable time of the w/o emulsion, yielded smaller and narrower-distributed SLN, and enhanced the encapsulation efficiency and loading capacity.     

Fluorescein–formaldehyde oligomeric pH indicator: Facile synthesis,characterization, and potential application

A kind of fluorescent oligomeric pH indicator (fluorescein–formaldehyde product) was synthesized by the reaction of fluorescein with formaldehyde under alkaline conditions by a one‐pot method. The synthesized product was fully characterized with Fourier transform infrared, ¹H NMR, ultraviolet–visible spectra, luminescence spectra, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra. The results indicated that the reaction was a typical phenol–formaldehyde reaction and that the fluorescein–formaldehyde product contained dimer, trimer, tetramer, and even a little octamer. Visible spectra and luminescence spectra showed that the fluorescein–formaldehyde product could still provide pH sensitivity similar to that of fluorescein. In addition, the oligomeric pH indicator immobilized poly(vinyl alcohol) membranes could be easily fabricated and achieved better long‐term stability and fast equilibrium response. Thus, they are promising transparent membranes for optical pH sensors of a wide pH range (0.0–10.0) based on absorption and fluorescence. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3447–3453, 2005     

基于技术进步的经济增长因素分析

本文考虑技术进步的生产函数以及在规模收益可变的条件下,利用我国的年度数据对其进行了估计和检验;得到的结果区别于其他文献的结果:资本和劳动的投入是目前我国经济增长的主要动力并且规模报酬是递增的,技术进步对经济增长的影响很小并且是相反的.     

Evaluation of matrix solid‐phase dispersion extraction for 11 β‐agonists in swine feed by liquid chromatography with electrospray ionization tandem mass spectrometry

A sensitive liquid chromatography with tandem mass spectrometry method was developed for the determination of 11 β‐agonists (clenbuterol, salbutamol, ractopamine, terbutaline, fenoterol, cimaterol, isoxsuprine, mabuterol, mapenterol, clenproperol, and tulobuterol) in swine feed. This rapid, simple, and effective extraction method was based on matrix solid‐phase dispersion. The limit of quantification of clenbuterol, cimaterol, mabuterol, salbutamol, terbutaline, mapenterol, clenproperol, and tulobuterol was 1 μg/kg and that of ractopamine, fenoterol, and isoxsuprine was 2 μg/kg. The recoveries of β‐agonists spiked in swine feeds at a concentration range of 1–8 μg/kg were >83.1% with relative standard deviations <9.3%. This rapid and reliable method can be used to efficiently separate, characterize, and quantify the residues of 11 β‐agonists in swine feeds with advantages of simple pretreatment and environmental friendliness.     

E—matrices and Several Necessary and Sufficient Conditions

AER-x.,Aiscalledanonnegative(nonPositive)matrixifau>O(a,jO(aiirtO),markedA>O(AO(i#j),auO,wecallp(A)=max{IA,l,lA,l'.-.,lAnl},(whereA,,A2,..',A"areeigenva1ueofA)asspectralradiusofA.LemmalIfAe7'.,thenareanonnegativesquarematrxBandapositivenumberksuchthatA=B-kI(whereIistheidentitymatrixofordern).ProofLetbti=…     

A new type of high power composite ultrasonic transducer

A new type of high power composite ultrasonic transducer was proposed and studied. The composite transducer consists of a sandwich longitudinal piezoelectric transducer, an isotropic metal hollow cylinder with large radial dimension, and the front and back metal radiation mass. By means of its special structure and Poisson’s effect, the composite transducer can produce vibrations both in its longitudinal and radial directions, and therefore, it can radiate sound waves in three-dimensional space. The electro-mechanical equivalent circuit of the composite transducer was derived and the resonance frequency equation was obtained analytically. Numerical methods were used to simulate the vibration of the composite transducer, and the vibrational displacement distribution, the resonance frequency and the radiation sound field are given. Some composite transducers are designed and manufactured; their resonance frequencies and the radiation acoustic field are measured and compared with the analytical and numerical results. It can be seen that the measured frequencies and acoustic field contour are in good agreement with the analytical and numerical results. It is expected that this kind of composite ultrasonic transducer can be used in more and more power ultrasonic applications, such as ultrasonic cleaning, ultrasonic extraction, ultrasonic sonochemistry and other ultrasonic liquid processing, where high ultrasonic power and large ultrasonic processing space are needed increasingly.     

Preparation, characterization and pharmacokinetics of enrofloxacin-loaded solid lipid nanoparticles: influences of fatty acids

Enrofloxacin-loaded solid lipid nanoparticles (SLN) were prepared using fatty acids (tetradecanoic acid, palmitic acid, stearic acid) as lipid matrix by hot homogenization and ultrasonication method. The effect of fatty acids on the characteristics and pharmacokinetics of the SLN were investigated. The results showed that the encapsulation efficiency and loading capacity of nanoparticles varied with fatty acids in the order of stearic acid>palmitic acid>tetradecanoic acid. Furthermore, stearic acid-SLN had larger particle size, bigger polydispersity index (PDI) and higher zeta potential compared with the other two fatty acid formulated SLN. The SLN showed sustained releases in vitro and the released enrofloxacin had the same antibacterial activity as that of the native enrofloxacin. Although in vitro release exhibited similar patterns, within 24 h the releasing rates of the three formulations were significantly different (tetradecanoic acid-SLN>palmitic acid-SLN>stearic acid-SLN). Pharmacokinetic study after a single dose of intramuscular administration to mice demonstrated that tetradecanoic acid-SLN, palmitic acid-SLN, and stearic acid-SLN increased the bioavailability by 6.79, 3.56 and 2.39 folds, and extended the mean residence time (MRT) of the drug from 10.60 h to 180.36, 46.26 and 19.09 h, respectively. These results suggest that the enrofloxacin-fatty acid SLN are promising formulations for sustained release while fatty acids had significant influences on the characteristics and performances of the SLN.     

Assembly‐Induced Emission of Cellulose Nanocrystals for Hiding Information

Fluorescent‐labeled cellulose nanocrystal (CNC) films have been used to record and protect information in paper materials, whereas the fluorescent materials usually suffer photobleaching. Herein, a strategy of solid‐state emission induced by the vertical assembly of CNCs was established. The assembly‐induced emission starts from the structural diffraction of CNC, whose wavelength is adjusted into the ultraviolet (UV) region for hiding information under natural light. The small diameter (≈10 nm) of CNCs then promotes the resonance between the vertically assembled CNCs and the UV light, leading to a strong blue emission with an emitting quantum efficiency as high as 13.90%. By introducing the vertical‐assembly film with a specific pattern into paper materials, an anti‐counterfeiting image is obtained under a UV radiation. Since CNCs are a kind of cellulose with high crystallinity, this material can be a wear‐resistant anti‐counterfeiting material for banknotes or other paper applications.     

EFFICIENT LINEAR SCHEMES WITH UNCONDITIONAL ENERGY STABILITY FOR THE PHASE FIELD MODEL OF SOLID-STATE DEWETTING PROBLEMS

In this paper, we study linearly first and second order in time, uniquely solvable and unconditionally energy stable numerical schemes to approximate the phase field model of solid-state dewetting problems based on the novel "scalar auxiliary variable" (SAV) approach, a new developed efficient and accurate method for a large class of gradient flows. The schemes are based on the first order Euler method and the second order backward differential formulas (BDF2) for time discretization, and finite element methods for space discretization. The proposed schemes are proved to be unconditionally stable and the discrete equations are uniquely solvable for all time steps. Various numerical experiments are presented to validate the stability and accuracy of the proposed schemes.     

基于OTTOSEN准则的混凝土粘塑性力学模型

研究了混凝土的弹．粘塑性动态本构关系,提出一个应变率相关的非线性混凝土模型．模型改进Bicanic的混凝土塑性间断面变化规律和Ottosen的四参数屈服准则,建立冲击荷载下的混凝土本构方程,可以应用于地震和爆炸作用下混凝土材料响应的研究．根据混凝土动态实验结果对应变率和材料强度的关系提出合理假设,考虑以往被忽略的材料峰值应变和泊松比随应变率的变化．模型包含静水压力参数和动态塑性损伤因子,可以有效地反映混凝土的动态力学行为,为其动态问题的研究提供有益的思路和有效的工具．