Manufacture of slow-release matrix granules by wet granulation with an aqueous dispersion of quaternary poly(meth)acrylates in the fluidized bed

Slow-release matrix granules were manufactured in the fluidized bed using an aqueous dispersion of quaternary poly(meth)acrylates (Eudragit® RS 30 D) as binder for granulation. A factorial design was carried out to investigate the influence of the following parameters, spraying rate, applied polymer amount, and inlet air temperature, on various granule properties. Prerequisites for a slow release of the model drug theophylline are high spraying rate, high amount of polymer, and low inlet air temperature. No considerable decrease of the drug release rate can be achieved without a subsequent curing of the dry granules. A clear correlation exists between the moisture content of the fluidized bed, indicated by the terminal moisture content (TMC), and the mean dissolution time for 80% of the drug (MDT₈₀).     

Modeling the sorption kinetics of divalent metal ions to hematite

The sorption kinetics of the divalent metals Zn, Co, Ni, and Cd to hematite were studied in single sorbate systems with high sorbate/sorbent ratios (from 1.67 to 3.33mol sorbate/mol sorption sites) in 10mM Na-piperazine N,N'-bis 2-ethane sulfonic acid (Na-PIPES) solution at pH 6.8. The experimental data showed a rapid initial sorption (half-time about 1min) followed by slower sorption that continued for 1-5 days. The sequence of fast to slow sorption kinetics was modeled by slow inner-sphere (IS) complexation in equilibrium with outer-sphere (OS) complexes. Although the OS reaction was fast and considered to be in equilibrium, the extent of OS complexation changed over time due to increased surface potential from the IS complexes. For example, the model showed that the dimensionless OS complexation function, K(os), decreased from 0.014 initially to 0.0016 at steady state due to sorption of 4x10(-5)M Zn(II) to 2gL(-1) hematite. Sorption rate constants, k(ads), for the various divalent metals ranged from 6.1 to 82.5M(-1)s(-1). Desorption rate constants, k(des), ranged from 5.2x10(-7) to 6.7x10(-5)s(-1). This study suggests that the conversion from OS to IS complex was the rate-determining step for the sorption of divalent metals on crystalline adsorbents.     

用低应变速率方法测定919铝合金的应力腐蚀敏感性

用低应变速率方法测定了３种热处理状态的９１９铝合金的应力腐蚀敏感性，结果表明，３种状态合金的应力腐蚀敏感性顺序与在恒载荷试验中获得的结果具有很好的相关性。因而，低应变速率方法适用于９１９及其同类合金的应力腐蚀性能研究。     

飞行时间法测量真空电子偶素产额研究低能离子溅射诱导的缺陷损伤

利用飞行时间谱直接测量了低能正电子与表面相互作用时的真空Ｐｓ产额．该方法比通常的峰法和峰－谷法准确、简单：利用该方法研究了Ａｒ＋溅射在Ｓｉ（１００）面上诱导的缺陷损伤及退火行为。     

On a stability criterion for continuous slow adaptation

A self-contained proof is given of a stability criterion for slow adaptation. The proof is based on a novel open-loop representation of the parameter adjustment feedback.     

保水剂与肥料互作及保水缓/控释肥料研究展望

保水剂在农业上的作用日益重要,肥料与保水剂一体化使用是水肥调控的重要技术,是肥料研究的国际前沿。保水剂是吸水量超过自身重量数百倍以上的亲水性高聚物。保水剂一般分为天然的,合成的及半合成的。保水剂与肥料可以通过物理混合、包膜或化学合成三种方式结合为一体化的保水缓/控释肥料。保水剂具有吸水吸肥功能,保水剂可吸附大量中性分子,对阳离子养分也有较强吸附作用,对阴离子养分吸附弱。肥料种类与盐浓度影响保水剂的吸附作用与膨胀能力。保水缓/控释肥料在土壤中对肥料养分有延迟释放作用。保水缓/控释肥料可改善土壤持蓄水分和水肥交互作用,促进植物对养分的吸收和作物增产。保水缓/控释肥料发展方向是包膜和化成保水缓/控释肥料。保水缓/控释肥料湿润及养分控释机理研究也需要加强。     

螺距对螺旋慢波系统色散和耦合阻抗的影响

螺距是慢波系统的一个重要参数,直接影响螺旋慢波系统的色散特性和耦合阻抗.严格求解螺距对慢波系统色散和耦合阻抗的影响是不方便的,而通过计算机模拟可以方便快速地研究螺距对慢波系统色散和耦合阻抗的影响.模拟结果表明,对于工程项目当螺距变化小于4%时,螺距对色散和耦合阻抗的影响是很小的.     

Tailoring the time delay of optical pulse/sequence employing cascaded SOA and band-pass filter

Abstract

A tunable time delay for a 100-ps pulse is achieved via a SOA cascaded band-pass filter, which can be tailored by tuning the filter or changing the SOA injection current. For a single pulse, when the pulse propagates through the cascaded system, a delay of 99.6 ps and an advance of 42.6 ps can be achieved by altering the SOA injection current at two different wavelengths located in the red band and blue band of the filter, respectively. The corresponding tunable delay range is 165 ps, and the maximum delay-bandwidth product (DBP) is 1.65. For an optical sequence, to our knowledge, it is the first time that the time delay is tailored over 145.6 ps corresponding to a DBP of 1.46 by tuning the wavelength from 1556.075 to 1556.955 nm, and 45.2 ps (95.6 ps) advance (delay) by tuning the injection current from 100 to 500 mA at 1556.155 nm (1556.955 nm). The dependence of the time delay on the injection current and filtering configuration has been discussed based on plenty of experiments data. Based on SOA’s fast switching, this device can be used for signal synchronization and bit-by-bit signal processing in a communication system.     

A numerical study on the thermal initiation of a confined explosive in 2-D geometry

Insensitive munitions design against thermal stimuli like slow or fast cook-off has become a significant requirement for today's munitions. In order to achieve insensitive munitions characteristics, the response of the energetic material needs to be predicted against heating stimuli. In this study, a 2D numerical code was developed to simulate the slow and fast cook-off heating conditions of confined munitions and to obtain the response of the energetic materials. Computations were performed in order to predict the transient temperature distribution, the ignition time, and the location of ignition in the munitions. These predictions enable the designers to have an idea of when and at which location the energetic material ignites under certain adverse surrounding conditions. In the paper, the development of the code is explained and the numerical results are compared with available experimental and numerical data in the literature. Additionally, a parametric study was performed showing the effect of dimensional scaling of munitions and the heating rate on the ignition characteristics.     

Effect of bainitic microstructure on the susceptibility of pipeline steels to hydrogen induced cracking

Hydrogen induced cracking (HIC) of API X80 and API X100 pipeline steels have been investigated in high pH carbonate-bicarbonate environment using slow strain rate testing (SSRT) method. It has been found that while both steels are highly susceptible to HIC, and diffusible hydrogen content is higher in API X80 than in API X100, the later steel is more vulnerable than the former at high (more negative) cathodic potential. This higher susceptibility can be primarily attributed to the combined effect of (1) separation of bainitic lath boundaries due to hydrogen trapping in these locations, (2) mobile hydrogen, and (3) stress. The charging-discharging experiments followed by SSRT experiments in air suggest that, the cracks that appeared due to lath boundary separation did not cause the reduction of ductility by themselves, rather it was the diffusible hydrogen that forced these cracks to propagate and, ruptured the steel with very low percent reduction of area (%RA). Despite the fact that the mobile hydrogen content plays a key role in causing the embrittlement, the large number of cracks in API X100 steel, resulting from the bainitic lath boundary separation at high cathodic potential, superseded the effect of higher diffusible hydrogen content in API X80 steel. The general conclusion is that bainitic lath type microstructure is more vulnerable to HIC at high cathodic potential than the ferritic/granular bainitic ones. It has been also found that applying cathodic protection can lead to excessive hydrogen embrittlement in both of the abovementioned steels in high pH carbonate-bicarbonate environment and, therefore, efforts need to be invested in developing nobler (more positive corrosion potential) and better HIC resistant steels.