Dependence of chain conformation on degree of sulfonation and counterion dissociation of sodium poly(styrene sulfonate) in semidilute aqueous solution

The chain conformation of sodium poly(styrenesulfonate) (NaPSS) in the semidilute aqueous solution, estimated from the plots of reduced viscosity versus segmental concentration, was found to be dependent on the degree of sulfonation and dissociation extent of counterions. The latter, altered by the content of sodium chloride external salt, was estimated from the ionic conductivity measurements on the basis of the modified Manning's conductivity theories with consideration of the influence of chain overlapping in the semidilute regime. The results indicate that the increase of chain extension of NaPSS with counterion dissociation was further enhanced by increasing the degree of sulfonation.     

An approach to studying scale for students in higher education: a Rasch measurement model analysis

A questionnaire comprising 80 self-report items was designed to measure student Approaches to Studying in a higher education context. The items were conceptualized and designed from five learning orientations: a Deep Approach, a Surface Approach, a Strategic Approach, Clarity of Direction and Academic Self-Confidence, to include 40 attitude items and 40 corresponding behavior items. The study aimed to create a scale and investigate its psychometric properties using a Rasch measurement model. The convenience sample consisted of 350 students at an Australian university in 1998. The analysis supported the conceptual structure of the Scale as involving studying attitudes and behaviors towards five orientations to learning. Attitudes are mostly easier than behaviors, in line with the theory. Sixty-eight items fit the model and have good psychometric properties. The proportion of observed variance considered true is 92% and the Scale is well-targeted against the students. Some harder items are needed to improve the targeting and some further testing work needs to be done on the Surface Approach. In the Surface Approach and Clarity of Direction in Studying, attitudes make a lesser contribution than behaviors to the variable, Approaches to Studying.     

数字电视系列(7)HDMI兼容性测试

HDMI Licensing LLC目前授权两家HDMI授权测试中心(ATC),其中一家位于日本大阪,由Matsushita Electric Industries经营,另一家则位于美国加州Sunnyvale,由晶像公司(Silicon Image,Inc.)主持。HDM ILicensing LLC可能在日后授权其它ATC。     

Relation between bit and symbol error probabilities for DPSK andFSK with differential phase detection

In M-ary, Gray coded DPSK, and FSK with differential phase detection the bit error probability is usually approximated by the symbol error probability divided by the number of bits in a symbol. This approximation is known to be excellent for PSK with large signal-to-noise ratios in a Gaussian channel. In other cases this approximation may be questionable. Here we compute the exact values of bit error probability for DPSK and FSK in Gaussian, Rayleigh, and Rician channels. We also compute the relative error involved in this approximation. The conclusion is that except for very low values of signal-to-noise ratio the approximation is good for all channels     

Error motion of a kinematic spindle

A prototype spindle for low-force, low-speed applications that is kinematically constrained in accordance with the principles of exact constraint was designed, fabricated, and tested. In the prototype spindle, the position and orientation of the shaft (rotor) are constrained at five contact points; four constraints are arranged radially around the rotor, and one constraint is located at the end of the rotor. This paper describes the design of the prototype spindle and presents a study of its error motion for the hardened steel rotor sliding on brass and UHMW-PE bonded to ceramic. The error motion is observed to be highly repeatable with less than 100 nm asynchronous errors, and a simple analytical model enables the prediction of the synchronous error motion using measurements of the rotor’s roundness profiles.     

EXAMINING THE ROLE OF CUTTING FLUIDS IN MACHINING AND EFFORTS TO ADDRESS ASSOCIATED ENVIRONMENTAL/HEALTH CONCERNS

ABSTRACT

Cutting fluids have seen extensive use and have commonly been viewed as a required addition to high productivity and high quality machining operations. Cutting fluid related costs and health concerns associated with exposure to cutting fluid mist and a growing desire to achieve environmental sustainability in manufacturing have caused industry and academia to re-examine the role of these fluids and quantify their benefits. This work summarizes the traditional purposes of cutting fluids and reports on recent analytical and experimental research to critically examine these functions. To minimize or even eliminate the concerns associated with cutting fluid usage, several recent and novel approaches have been proposed and are examined.     

Enhancing the performance of dye-sensitized solar cells by incorporating nanosilicate platelets in gel electrolyte

Two kinds of gel-type dye-sensitized solar cells (DSSCs), composed of two types of electrolytes, were constructed and the respective cell performance was evaluated in this study. One electrolyte, TEOS-Triton X-100 gel, was based on a hybrid organic/inorganic gel electrolyte made by the sol–gel method and the other was based on poly(vinyidene fluoride-co-hexafluoro propylene) (PVDF-HFP) copolymer. TEOS-Triton X-100 gel was based on the reticulate structure of silica, formed by hydrolysis, and condensation of tetraethoxysilane (TEOS), while its organic subphase was a mixture of surfactant (Triton X-100) and ionic liquid electrolytes. Both DSSC gel-type electrolytes were composed of iodine, 1-propy-3-methyl-imidazolium iodide, and 3-methoxypropionitrile to create the redox couple of I₃⁻/I⁻. Based on the results obtained from the I–V characteristics, it was found that the optimal iodine concentrations for the TEOS-Triton X-100 gel electrolyte and PVDF-HFP gel electrolyte are 0.05 M and 0.1 M, respectively. Although the increase in the iodine concentration could enhance the short-circuit current density (J_SC), a further increase in the iodine concentration would reduce the J_SC due to increased dark current. Therefore, the concentration of I₂ is a significant factor in determining the performance of DSSCs.In order to enhance cell performance, the addition of nanosilicate platelets (NSPs) in the above-mentioned gel electrolytes was investigated. By incorporating NSP-Triton X-100 into the electrolytes, the J_SC of the cells increased due to the decrease of diffusion resistance, while the open circuit voltage (V_OC) remained almost the same. As the loading of the NSP-Triton X-100 in the TEOS-Triton X-100 gel electrolyte increased to 0.5 wt%, the J_SC and the conversion efficiency increased from 8.5 to 12 mA/cm² and from 3.6% to 4.7%, respectively. However, the J_SC decreased as the loading of NSP-Triton X-100 exceeded 0.5 wt%. At higher NSP-Triton X-100 loading, NSPs acted as a barrier interface between the electrolyte and the dye molecules, hindering electron transfer, hence, reducing the cell's photocurrent density. The same behavior was also observed in the PVDF-HFP gel electrolyte DSSC system.