基于偏振激光干涉技术的波长计

提出了一种基于偏振激光干涉技术的波长计,该波长计能在微米行程上实现10-6的测量精度,位移行程的缩减有效地减小了环境温度、波长漂移、空气折射率对测量精度的影响。给出了两种未知激光源（DL100-Toptica和Nd:YAG）的波长测量值及不确定度值,同时还给出了该波长计与商用波长计的比对结果。     

Preparation and characterization of coenzyme Q10-Eudragit solid dispersion

A solid dispersion of Coenzyme Q10 and Eudragit L 100-55 was prepared using solvent evaporation method. Solid dispersion, physical mixture, and pure compound were then characterized using differential scanning calorimetry and powder x-ray diffraction. Solubility of CoQ10 in different surfactant media was measured, and a suitable dissolution medium was developed to compare the dissolution patterns of the solid dispersion, physical mixture, and the pure compound. Combining labrasol with different surfactants in dissolution media demonstrated an additive effect on CoQ10 solubility. The solubility of CoQ10 in a 4% Labrasol/2% Cremophor EL solution was 562 microg/ml, which was five times higher than the combined solubility in 5% Labrasol (91 microg/ml) and 5% Cremophor EL (7.8 microg/ml). Moderate change in the crystalline pattern of CoQ10 was observed, which was attributed to solvent displacement rather than the degree of crystallinity change. The dissolution test indicated that the in-vitro release of Coenzyme Q10 from its solid dispersion was much faster than its physical mixture, which in turn was faster than the pure drug. The amount of drug released in 12 hours from solid dispersion, physical mixture, and the pure drug was 100, 26.5 and 12.5% respectively. CoQ10 was photostable throughout the dissolution experiments.     

International Expansion Decision for Construction Companies

There exist several reasons for construction firms to expand their business into international markets. But the complex international environment is affected by diverse factors and creates risks that are not well understood by companies that are active mostly in domestic markets. It is therefore essential for construction companies to follow a disciplined and well-informed strategy when deciding whether to enter international markets. Company strengths relative to conducting business in international markets, the threats and opportunities associated with overseas work, and the costs and benefits of undertaking construction projects in specific countries need to be considered in this decision. The interactions between the complex factors can be structured in a model that can help one to make a rational judgment. The International Expansion Decision Model developed in this study is based on the Analytic Hierarchy Process (AHP) improved by the addition of a Delphi survey. The main objective of this research study is to facilitate the entry decision into foreign markets and to highlight the importance of the factors involved in this decision. This study is of relevance to practitioners as it allows executives of construction companies to test if their company is ready for expansion into international markets in general and into a specific country in particular. It is also of relevance to researchers as it demonstrates the successful use of the combined Delphi and AHP methods.     

Modeling of a large electric power system for optimal control of dynamic stability

This paper describes a general state-variable form of mathematical modeling which may be used to control the dynamic stability of a larger power system optimally. Based on the linearization about the operating point of the system, a complete model for dynamic stability control is obtained by combining transmission network equations, full-order synchronous machine equations, the exciter and voltage regulator model, torque equations, and the governor-hydraulic model in a matrix form which includes supplementary excitation and governor control signals. The complete model may then be simplified as a low-order model by neglecting the governor effects, exciter time constant, and all but the field flux linkage variations of the machines in order to reduce computational requirements.     

Study of Metal and Ceramic Thermionic Vacuum arc Discharges

The thermionic vacuum arc （TVA） is a new type of plasma source, which generates a pure metal and ceramic vapour plasma containing ions with a directed energy. TVA discharges can be ignited in high vacuum conditions between a heated cathode （electron gun） and an anode （tungsten crucible） containing the material. The accelerated electron beam, incident on the anode, heats the crucible, together with its contents, to a high temperature. After establishing a steadystate density of the evaporating anode material atoms, and when the voltage applied is high enough, a bright discharge is ignited between the electrodes. We generated silver and Al2O3 TVA discharges in order to compare the metal and ceramic TVA discharges. The electrical and optical characteristics of silver and Al2O3 TVA discharges were analysed. The TVA is also a new technique for the deposition of thin films. The film condenses on the sample from the plasma state of the vapour phase of the anode material, generated by a TVA. We deposited silver and Al2O3 thin films onto an aluminium substrate layer-by-layer using their TVA discharges, and produced micro and/or nano-layer Ag-Al2O3 composite samples. The composite samples using scanning electron microscopy was also analysed.     

Nonlinear Optical Properties of Copolymers of Benzylaminofullerene with Methyl Methacrylate or Ethyl Methacrylate

Nonlinear optical properties of a C₆₀ derivative, benzylaminofullerene [C₆₀H_n(NHCH₂C₆H₅)_n] and its copolymers with methyl methacrylate or ethyl methacrylate were observed carefully by using the nanosecond laser pulses at 532 nm. These copolymers have been proved to be promising materials for optical limiting applications.     

The effect of dwell angle on vibration characteristics of camshaft bearing housings

Cam-follower mechanisms are affected by undesired dynamic forces which may disrupt the accuracy of the follower motion. These undesired dynamic forces create vibrations which cause noise, wear, and increasing operating costs for cam-follower mechanisms. Journal bearings are the most widely-used mechanical parts in internal combustion engines under high load and high operating speeds. In this study, the effect of the dwell angle on the vibration characteristics of camshaft bearing housings was investigated. Two camshafts having a 6 mm lift and different dwell angles were tested at operating speeds of 450, 900, 1350, 1920, and 2400 rpm. The collected data were analyzed in detail. It was observed that with the increasing of the camshaft rotational speed, vibration responses of greater magnitude were obtained. In general, the first and second peak values of the low dwell angle camshaft were higher than those of the high dwell angle camshaft.     

Nanomechanical characterization by double-pass force-distance mapping

We demonstrate high speed force-distance mapping using a double-pass scheme. The topography is measured in tapping mode in the first pass and this information is used in the second pass to move the tip over the sample. In the second pass, the cantilever dither signal is turned off and the sample is vibrated. Rapid (few kHz frequency) force-distance curves can be recorded with small peak interaction force, and can be processed into an image. Such a double-pass measurement eliminates the need for feedback during force-distance measurements. The method is demonstrated on self-assembled peptidic nanofibers.     

Application of SEBAL Model for Mapping Evapotranspiration and Estimating Surface Energy Fluxes in South-Central Nebraska

Knowledge of spatiotemporal distribution of evapotranspiration (ET) on large scales, as quantified by satellite remote sensing techniques, can provide important information on a variety of water resources issues such as evaluating water distributions, water use by different land surfaces, water allocations, water rights, consumptive water use and planning, and better management of ground and surface water resources. The objective of this study was to assess the operational characteristics and performance of the surface energy balance algorithm for land (SEBAL) model for estimating crop ET (ETc) and other energy balance components, and mapping spatial distribution and seasonal variation of ETc on a large scale in south-central Nebraska climatic conditions. A total of seven cloud free Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM) satellite images (May 19, June 20, July 22, August 7, September 8, September 16, and October 18, 2005) were processed to generate ETc maps and estimate surface energy fluxes. Predictions from the SEBAL model were compared with the Bowen ratio energy balance system (BREBS)-measured fluxes on an instantaneous and daily basis. The ETc maps generated by the model for seven Landsat overpass days showed a very good progression of ETc with time during the growing season in 2005 as the surface conditions continuously changed. The predictions for some surface energy fluxes were very good. Overall, a very good correlation was found between the BREBS-measured and SEBAL-estimated ETc with a good r2 of 0.73 and a root-mean-square difference (RMSD) of 1.04?mm?day?1. The estimated ETc was within 5% of the measured ETc. The model was able to predict growing season (from emergence to physiological maturity) cumulative daily corn ET reasonable well within 5% of the BREBS-measured values. The model overestimated the surface albedo by about 26% with a RMSD of 0.05. The difference between the measured and predicted albedo was the greatest on May 19, early in the growing season before the full canopy cover. The second largest difference between the two albedo values was on October 18, a day after harvest. The model significantly under predicted soil heat flux with a large RMSD of 80?W?m?2 and most of the underestimation occurred in the late growing season. Local calibration of soil heat flux significantly improved the agreement between the measured and predicted values. Furthermore, the sensible heat flux was underestimated between September 20 (after physiological maturity) and October 18 (a day after harvest). While our results showed that SEBAL can be a viable tool for generating ETc maps to assess and quantify spatiotemporal distribution of ET on large scales as well as estimating surface energy fluxes, its operational assessment for estimating sensible heat flux and ETc, especially during the drier periods for different surfaces, needs further development.