先进栅叠层的在线光谱分析法

量测平台的复杂性和光学原理上的局限性制约着测量系统的应用,直到真空紫外光谱反射仪的出现,这种状况才得到改变。     

Open DRM and the Future of Media

This article offers an analysis of the various methods for implementing interoperable digital rights management platforms.     

Kinematic instabilities in two-layer eccentric annular flows,part 1: Newtonian fluids

Primary-cementing displacement flows occur in long narrow eccentric annuli during the construction of oil and gas wells. A common problem is that the displacing fluid fingers up the upper wide side of the annulus, leaving behind a “mud channel” of displaced fluid on the lower narrow side of the annulus. Tehrani et al. report that the interface between displacing fluid and mud channel can in certain circumstances become unstable, and a similar phenomenon has been observed in our ongoing experiments. Here an explanation for these instabilities is provided via analysis of the stability of two-layer eccentric annular Hele-Shaw flows, using a transient version of the usual Hele-Shaw approach, in which fluid acceleration terms are retained. Two Newtonian fluids are considered, as a simplification of the general case in which the fluids are shear-thinning yield-stress fluids. It is shown that negative azimuthal buoyancy gradients are in general stabilizing in inclined wells, but that buoyancy may also have a destabilizing effect via axial buoyancy forces that influence the base-flow interfacial velocity. In a variety of special cases where buoyancy is not dominant, it is found that instability is suppressed by a positive product of interfacial velocity difference and reduced Reynolds-number difference between fluids. Even a small positive azimuthal buoyancy gradient, (heavy fluid over light fluid), can be stabilized in this way. Eccentricity of the annulus seems to amplify the effect of buoyancy on stability or instability, e.g. stably stratified fluid layers become more stable as the eccentricity is increased.     

Comprehensive control for unified power quality conditioners

This paper presents a comprehensive control strategy for unified power quality conditioners（UPQCs） to compensate for both voltage and current quality problems.The controllers for the series and shunt components of the UPQC are, equally, divided into three blocks: à main controller, which deals with the fundamental-frequency issues such as active and reactive power flow; ` harmonic controller, which ensures zero-error tracking while compensating voltage and current harmonics; ′ the set-point generation block, which handles the different control objectives of the UPQC. The controller design procedure has been simplified to the selection of three parameters for each converter. Furthermore, the proposed strategy can be implemented measuring only four variables, which represents a reasonable number of sensors. In addition, a pulse width modulation（PWM）-based modulation with fixed switching frequency is used for both converters. The proposed control strategy has been validated experimentally under different conditions, including grid-frequency variations.     

Optimal Design of Hybrid Microgrid in Isolated Communities of Ecuador

In rural territories, the communities use energy sources based on fossil fuels to supply themselves with electricity, which may address two main problems: greenhouse gas emissions and high fuel prices. Hence, there is an opportunity to include renewable resources in the energy mix. This paper develops an optimization model to determine the optimal sizing, the total annual investment cost in renewable generation, and other operating costs of the components of a hybrid microgrid. By running a k-means clustering algorithm on a meteorological dataset of the community under study, the hourly representative values become input parameters in the proposed optimization model. The method for the optimal design of hybrid microgrid is analyzed in six operating scenarios considering:（1） 24-hour continuous power supply;（2） load shedding percentage;（3） diesel power generator（genset） curtailment;（4） the worst meteorological conditions;（5） the use of renewable energy sources including battery energy storage systems（BESSs）; and（6） the use of genset. A mathematical programming language（AMPL） tool is used to find solutions of the proposed optimization model. Results show that the total costs of microgrid in the scenarios that cover 100% of the load demand（without considering the scenario with 100% renewables） increase by over 16% compared with the scenario with genset operation limitation. For the designs with power supply restrictions, the total cost of microgrid in the scenario with load shedding is reduced by over 27% compared with that without load shedding.     

Evaluation of ACE inhibitory activity of dipeptides generated by the action of porcine muscle dipeptidyl peptidases

Dipeptidyl peptidases (DPP) constitute a group of proteolytic enzymes able to release a good number of dipeptides from the N-terminus of both synthetic substrates and natural polypeptides. Specific sequences generated by the action of DPP purified from porcine skeletal muscle have been assayed to evaluate their capacity to inhibit the activity of angiotensin-I converting enzyme (ACE; EC 3.4.15.1). A fluorimetric assay based on the hydrolysis of the internally quenched fluorescent substrate o-aminobenzoylglycyl-p-nitrophenylalanylproline by the action of ACE was used for this purpose. The generated fluorescence of the product (the o-aminobenzoylglycine group) was continuously monitored in a microtiter-plate multiscan fluorometer.     

Topology optimization of periodic microstructures with a penalization of highly localized buckling modes

The problem of determining highly localized buckling modes in perfectly periodic cellular microstructures of infinite extent is addressed. A double scale asymptotic technique is applied to the linearized stability problem for a periodic structure built from linearly elastic microstructures. The obtained stability condition for the microscale level is then used to establish a comparative analysis between different material distributions in the base cell subjected to the same strain field at the macroscale level. The idea is illustrated by some two‐dimensional finite element examples and used to design materials with optimal elastic properties that are less prone to localized instability in the form of local buckling modes at the scale of the microstructure. Copyright © 2002 John Wiley & Sons, Ltd.