Finitely concentrated partial molar excess properties of solvent/polymer [poly(4-methylstyrene) (PMS), poly(vinylbenzyl chloride) (PVBC)] systems

The finitely concentrated activity coefficients and partial molar excess properties of solvents were measured with inverse gas chromatography (IGC) in polymer solutions containing a poly(4-methylstyrene) (PMS) or a poly(vinylbenzyl chloride) (PVBC). The experimental temperature ranges were 373.15 K to 413.15 K for PMS and 353.15 K to 393.15 K for PVBC. They were over melting point or glass transition temperature of each polymer. Ten kinds of solvents (Acetone, n-Heptane, Cyclohexane, Chloroform, Methylisobutylketone, Trichlorobenzene, Benzene, Toluene, Ethylbenzene, Chlorobenzene) that are important in the chemical engineering field were arbitrarily chosen for binary polymer solutions. The external degree of freedom of original UNIFAC-FV model was empirically modified to give flexibility to itself as a C₁=A+BT from the experimental data in finite concentration. The UNIFAC-FV model included a new external degree of freedom as a function of temperature. The parameters (A, B) were estimated by correlating the activities of solvent with the modified model and extended to predict the partial molar excess properties of solvents in the finite-concentrated polymer solutions. The predicted values were compared with them by original UNIFAC-FV as well as the experimental data. The results obtained with the revised model using the new parameter showed the higher quality than the results obtained by original model.     

Implementation of intensity-modulated laser diodes in time-resolved, pump-probe fluorescence microscopy

We present the implementation of intensity-modulated laser diodes for applications in frequency-domain pump-probe fluorescence microscopy. Our technique, which is based on the stimulated-emission approach, uses two sinusoidally modulated laser diodes. One laser (635 nm) excites the chromophores under study, and the other laser (680 nm) is responsible for inducing stimulated emission from excited-state molecules. Both light sources are modulated in the 80-MHz range but with an offset of 5 kHz between them. The result of the interaction of the pump and the probe beams is that a cross-correlation fluorescence signal at 5 kHz is generated primarily at the focal volume. Microscope imaging at the cross-correlation signal results in images with high contrast, and time-resolved high-frequency information can be acquired without high-speed detection. A detailed experimental arrangement of our methodology is presented along with images acquired from a 4.0-mum-diameter fluorescent sphere and TOTO-3-labeled mouse STO cells. (TOTO-3 is a nucleic acid stain.) Our results demonstrate the feasibility of using sinusoidally modulated laser diodes for pump-probe imaging, creating the exciting possibility of high-contrast time-resolved imaging with low-cost laser-diode systems.     

Improving Quality of Service and Assuring Fairness in WLAN Access Networks

As public deployment of wireless local area networks (WLANs) has increased and various applications with different service requirements have emerged, fairness and quality of service (QoS) are two imperative issues in allocating wireless channels. This study proposes a fair QoS agent (FQA) to simultaneously provide per-class QoS enhancement and per-station fair channel sharing in WLAN access networks. FQA implements two additional components above the 802.11 MAC: a dual service differentiator and a service level manager. The former is intended to improve QoS for different service classes by differentiating service with appropriate scheduling and queue management algorithms, while the latter is to assure fair channel sharing by estimating the fair share for each station and dynamically adjusting the service levels of packets. FQA assures (weighted) fairness among stations in terms of channel access time without decreasing channel utilization. Furthermore, it can provide quantitative service assurance in terms of queuing delay and packet loss rate. FQA neither resorts to any complex fair scheduling algorithm nor requires maintaining per-station queues. Since the FQA algorithm is an add-on scheme above the 802.11 MAC, it does not require any modification of the standard MAC protocol. Extensive ns-2 simulations confirm the effectiveness of the FQA algorithm with respect to the per class QoS enhancement and per-station fair channel sharing     

Closed-Form RC and RLC Delay Models Considering Input Rise Time

The Elmore delay model is the most popular and efficient delay model used for analytical delay estimation. Closed-form delay formulas are useful for circuit design, timing-driven physical design, synthesis, and optimization. As signal rise time becomes faster and the line resistance becomes smaller from copper technology, the significance of inductance increases. Both RC and RLC delays are a strong function of signal rise time. We propose a novel and efficient delay modeling method based on nondimensionalization to consider finite input rise time as an improvement over the Elmore's approach. To further improve the accuracy of the delay model, a new correction method, effective distance correction factor (EDCF), is proposed to consider resistive shielding of downstream capacitance. EDCF can be used to correct the delays for both RC and RLC tree structures. The proposed delay modeling method was applied to a number of nets selected from an integrated circuit (IC) design, and the delay estimation results were compared with HSPICE simulations. The new delay model retains the efficiency and simplicity of the Elmore delay model with significantly improved accuracy.     

Experimental study of dynamic crushing of thin plates stiffened by stamping with V-grooves

Experimental study was made for the dynamic crushing of thin plates stiffened by stamping with 1–3 parallel V-grooves in a clamped-end condition. The length of the blanks was set at the same value of 300 mm, while the width was of 70, 140 and 210 mm at a thickness of 1 mm, otherwise specified. The depth of V-grooves was set at values of 4, 7 and 10 mm. In both static and dynamic tests, the results show that the ability of the plates to resist crushing and to absorb deformation energy was substantially enhanced by stamping with V-grooves. Stamped with 1 or 2 grooves of smaller values in depth, the plates 210 mm wide had larger resistance to dynamic crushing than those of greater values in depth did. In general, increases in number and depth of grooves caused an increase in the plates’ capacity of energy absorption. However, the ability of the plates to resist crushing and to absorb deformation energy cannot be determined only in accordance with the second moment of area of cross section, because the plates sufficiently wide stamped with any number of grooves deformed plastically before buckled in dynamic tests and, the interaction between deep grooves during deformation also enhanced the capacity of energy absorption.     

省略DVI 低价液晶到底值不值得购买

还是在液晶显示器最初普及的阶段,省略了DVI接口的产品曾经是霸占整个低端液晶市场的绝对主流。不过到了2007年,液晶显示器的发展开始快速变化,具备DVI＋VGA接口的液晶显示器已经成为了市场主流。而正是在这个时候,市场上还存留着一批省略了DVI接口的低价液晶。在这样的市场环境下,省略DVI的低价液晶到底值不值得购买？也就成为了人们争论的焦点。[编者按]     

Effects of display method,text display rate and observation angle on comprehension performance and subjective preferences for reading Chinese on an LED display

This study examined the effects of display method, text display rate, and observation angle on comprehension performance and subjective preferences for Chinese characters presented on an LED display. The factors and levels studied were as follows: four text display methods (rapid serial visual presentation ‘RSVP’, leading, paged view scrolling, and continuous scrolling), three text display rates (160 characters per min ‘cpm’, 240 cpm, and 320 cpm), and seven observation angles (−75°, −60°, −30°, 0°, 30°, 60°, and 75°). The results indicated that a display rate of 160 cpm was in general superior to 240 and 320 cpm for comprehension scores and subjective evaluations. The effects of display method and observation angle were found to be non significant. However, there was a significant interaction between display method and display rate. The results of this study were used to make ergonomics recommendations applicable to LED displays for determining optimum dynamic text display methods for Chinese characters.     

Bayesian network analysis for the dynamic prediction of early stage entrepreneurial activity index

Entrepreneurship plays a critical role for the development and well-being of society. Illustration of its dynamic relationship with entrepreneurial attitudes and aspirations can provide a guideline for the cause of such activities. However, a time-lagged causal relationship among these concepts has not yet been established. In this study, we examine a dynamic relationship among early stage entrepreneurial attitudes, activities, and aspirations using Bayesian network (BN) analysis. In addition, we propose an early stage entrepreneurial activity index that can predict the percentage of both nascent entrepreneur and new business owner using the variables related to entrepreneurial attitudes of the previous year. This index, in turn, can be used to predict various aspects of entrepreneurial aspiration of the following year. The proposed index turns out to have very high prediction accuracy and is expected to provide effective policies to boost future entrepreneurial activity and aspiration.     

Effect of the Pt precursor on the morphology and catalytic performance of Pt-impregnated on Pd/C for the oxygen reduction reaction in polymer electrolyte fuel cells

We describe how the morphology and electrocatalytic activity of Pt-Pd with low levels of Pt are dependent on the type of Pt precursor that is used for the impregnation on to Pd/C. When a Pt precursor with a negative charge (H₂PtCl₆) is used in the preparation medium (Pt-Pd/C-H), its electrostatic interaction with the carbon surface results in some Pt nanoparticles being deposited on the carbon separately from the Pd surface. Due to the absence of such an electrostatic interaction with the Pt(NH₃)₄Cl₂ precursor, more selective deposition of Pt can be achieved on the Pd surface (Pt-Pd/C-N). Depending on the morphology, different electrocatalytic performance in oxygen reduction reaction would be observed. Compared to Pt-Pd/C-H, Pt-Pd/C-N shows 180% (half-cell at 0.9 V) and 160% (unit-cell at 0.8 V) enhanced performance, which is comparable to that on Pt/C. It is believed that the interaction between the Pt and the Pd substrate is more extensive in Pt-Pd/C-N than in Pt-Pd/C-H, and this is responsible for the large difference in the catalytic performances between these two catalysts.     

Effects of deposition temperature and pressure of the surface roughness and the grain size of polycrystalline Si1−xGex films

The effects of temperature and pressure on the surface roughness and the grain size of poly-Si_1–x Ge _x films, and the effect of the initial surface state on the final film surface roughness and grain size, have been investigated. The deposition temperature and pressure were varied from 450 to 600 °C and from 1 to 50 Torr, respectively. The transition temperature from amorphous to polycrystalline during the deposition was about 525 °C for the Si_0.46Ge_0.54 alloy film and the average grain size of the film deposited at 600 °C and 3 Torr was measured approximately as 180 nm. As the temperature increased, the grain size and the rms (root mean square) surface roughness increased at constant pressure, whereas both were decreased with increasing pressure at constant temperature. The initial surface state of Si_1–x Ge _x film influenced the final film structure such as the surface roughness and grain size. The smooth surface was obtained at higher pressure and lower temperature.