Integration-based approach to evaluate the sub-threshold slope of MOSFETs

We propose the use of simple integration-based methods to extract the sub-threshold current slope factor of MOSFETs as an alternative to traditional extraction processes based on differentiating the sub-threshold transfer characteristics. The purpose is to lessen the effects of error and noise often present in the measurement of very small currents, which are aggravated by the differentiation processes. The effectiveness of the proposed methods is compared to the traditional Transconductance-to-Current Ratio method using the measured transfer characteristics of two experimental devices as application examples.     

Fuel sensor-less control of a liquid feed fuel cell under dynamic loading conditions for portable power sources (I)

This work presents a novel fuel sensor-less control scheme for a liquid feed fuel cell system that operates under dynamic loading conditions and is suitable for portable power sources. The proposed technique utilizes the operating characteristics of a fuel cell, such as voltage, current and power, to control the supply of liquid fuel and regulate its concentration. As verified by systematic experiments, this scheme controls effectively the supply of fuel under dynamic loading conditions and pushes the system toward higher power output. The primary features and advantages of sensor-less fuel control are as follows. When the fuel concentration sensor is excluded, the cost of a liquid feed fuel cell system is decreased and system volume and weight are reduced, thereby increasing specific energy density and design simplicity, and shortening system response time. Notably, temperature compensation for measurement data is unnecessary. With a decreased number of components, the control scheme improves durability and reliability of liquid feed fuel cells. These advantages will help commercialization of liquid feed fuel cells as portable power sources.     

Kinetics investigation of antioxidant capacity and total phenols of low‐temperature steeping Bi Luo Chun green tea

Traditionally, tea is steeped in boiled water in Taiwan. In this study, Bi Luo Chun (250 μg mL^?1) steeped at 4, 22, 30, 40 and 50 °C reached the saturation of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging capacity at the time of 15, 8, 2, 0.17 (10 s) and 0.17 min (10 s), respectively. The result indicated that tea steeped in cold water (under 22 °C) still can reach a saturation of antioxidant capacity in 15 min. However, the initial scavenging rate (% min^?1) was quick and decreased with time at all steeping temperatures (r: ?0.98 to ?1.00). Total phenols and the DPPH scavenging capacity of Bi Luo Chun showed excellent correlation with time. However, the plot of DPPH scavenging capacity vs. total phenols was not always correlated. The result indicated that polyphenol infusion at different times may have a different DPPH scavenging capacity.     

Fixture analysis under dynamic machining

This paper presents a fixture generation methodology that takes into account dynamic machining conditions which occur when the machining forces and moments travel or change with respect to time. This is more realistic than previous systems which have treated the machining conditions as static. It also increases the difficulty of fixture generation since the machining conditions are always changing. In this paper, a comprehensive methodology based on linear programming has been developed to circumvent this problem. It takes into account the maximum forces and moments during all time and the desirable characteristics of a fixture such as: positive reaction forces at the locators for all time, deterministic positioning, strong accessibility, stability of the workpart in the fixture while under no external forces, and a positive clamping sequence. In order to reduce the total computation time, the linear programming technique is used to formulate the deterministic positioning and accessibility characteristics of a fixture. Finally, force planes, similar to distributed load diagrams, are created to act as guides in the slight repositioning of locators for modular fixturing. Two case studies are presented to demonstrate the capabilities of the methodology.     

A DNA methylation assay for detection of ovarian cancer cells using a HpaII/MspI digestion-based PCR assay in an integrated microfluidic system

Early and accurate diagnosis of cancer plays a very important role in favorable clinical outcomes. DNA methylation of tumor suppressor genes has been recognized as a diagnostic biomarker for early carcinogenesis. The presence of 5-methylcytosine in the CpG islands in the promoter region of a tumor suppressor gene is an important indicator of DNA methylation. However, the standard detection assay utilizing a bisulfite treatment and HpaII/MspI endonuclease digestion is a tedious and lengthy process and requires a relatively large amount of DNA for testing. In this study, the methylated DNAs of various tumor suppressor genes, HAAO, HOXA9 and SFRP5, were chosen as candidates for detection of ovarian cancer cells. The entire experimental process for the DNA methylation assay, including target DNA isolation, HpaII/MspI endonuclease digestion, and nucleic acid amplification has been realized in an integrated microfluidic system. The limit of detection using this developed system has been experimentally determined to be 10² cells/reaction. The entire process from sample loading to analysis of the results only took 3 h which is much faster than the existing protocols. Different sources of biosamples, such as cells, ascites and serums, could be detected with the methylated DNA, indicating that this developed microfluidic system could be adapted for clinical use. Thus, this developed microsystem may be a promising platform for the rapid and early diagnosis of cancers.     

Preparation and characterization of a star‐shaped polystyrene‐b‐poly(ethylene‐co‐propylene) block copolymer as a viscosity index improver of lubricant

A saturated star‐shaped polystyrene‐b‐poly(ethylene‐co‐propylene) block copolymer, (SEP)_star, was synthesized for use as a viscosity index improver in lubricants. Polystyrene‐b‐polyisoprene arms were first made anionically, followed by a linking reaction at the optimum temperature of 60°C with divinylbenzene. The resulting star‐shaped (SI)_star was hydrogenated to eliminate the double bonds on the polyisoprene segment, thus forming the star‐shaped (SEP)_star. The number of arms on each molecule increased with an increase in the mol ratio of divinylbenzene to n‐butyllithium. Increasing the arm length adversely affected the linking efficiency but caused a slight increase in the degree of branching. The T_g of the poly(ethylene‐co‐propylene) block was 13°C higher than that of the original polyisoprene block. Compared with (SI)_star, (SEP)_star has a thermal decomposition temperature 50°C higher but independent of the arm length or the degree of branching. Viscosity measurements for (SEP)_star revealed that intrinsic viscosity depends only on the arm length, but not on the degree of branching. Adding 1 wt % of (SEP)_star markedly increased the viscosity index of a HN base oil. With a fixed arm length, a (SEP)_star having a higher degree of branching increased the viscosity index more than that having a lower degree of branching. On the other hand, the viscosity index increased with an increase in the arm length when the degree of branching was fixed. The addition of 1wt % of (SEP)_star increased the vioscosity index up to a number between 111 and 166, with the exact number depending upon its arm length and degree of branching. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1838–1846, 2001     

Synthesis and properties of new poly(amide‐imide)s based on 2,5‐bis(trimellitimido)chlorobenzene

A series of new aromatic poly(amide‐imide)s were synthesized by the triphenyl phosphite‐activated polycondensation of the diimide‐diacid, 2,5‐bis(trimellitimido)chlorobenzene (I) with various aromatic diamines in a medium consisting of N‐methyl‐2‐pyrrolidone (NMP), pyridine, and calcium chloride. The poly(amide‐imide)s had inherent viscosities of 0.76–1.42 dL g⁻¹. The diimide‐diacid monomer (I) was prepared from 2‐chloro‐p‐phenylenediamine with trimellitic anhydride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents, including NMP and N,N‐dimethylacetamide. Transparent, flexible, and tough films of these polymers could be cast from N,N‐dimethylacetamide or NMP solutions. Their cast films had tensile strengths ranging from 74 to 95 MPa, elongations at break from 7 to 11%, and initial moduli from 1.38 to 3.25 GPa. The glass transition temperatures of these polymers were in the range of 233°–260°C, and the 10% weight loss temperatures were above 450°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1691–1701, 1999     

Synthesis and characterization of new poly(amide‐imide)s based on 1,4‐bis(trimellitimido)‐2,5‐dichlorobenzene

A series of new aromatic poly(amide‐imide)s were synthesized by the triphenyl phosphite‐activated polycondensation of the diimide‐diacid, 1,4‐bis(trimellitimido)‐2,5‐dichlorobenzene (I), with various aromatic diamines in a medium consisting of N‐methyl‐2‐pyrrolidone (NMP), pyridine, and calcium chloride. The poly(amide‐imide)s had inherent viscosities of 0.88–1.27 dL g⁻¹. The diimide‐diacid monomer (I) was prepared from 2,5‐dichloro‐p‐phenylenediamine with trimellitic anhydride. All the resulting polymers were amorphous and were readily soluble in a variety of organic solvents, including NMP and N,N‐dimethylacetamide. Transparent, flexible, and tough films of these polymers could be cast from N,N‐dimethylacetamide or NMP solutions. Cast films had tensile strengths ranging from 92 to 127 MPa, elongations at break from 4 to 24%, and initial moduli from 2.59 to 3.65 GPa. The glass transition temperatures of these polymers were in the range of 256°–317°C, and the 10% weight loss temperatures were above 430°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 271–278, 1999     

Preparation and characterization of crosslinked and heat-treated PVA-MA films

Two kinds of water-insoluble PVA-MA hydrogel films were prepared from PVA-MA, an esterification product of poly(vinyl alcohol) and maleic anhydride, by heat treatment and a crosslinking reaction, respectively. Both films changed their dimensions upon environmental pH changes. The crosslinked gel expanded to approximately 230% of its original length, with most changes occurring in the pH range of 2–7. The heat-treated PVA-MA film swelled stepwisely, with about 45% of the total expansion occurring at pH 2–7 and the remaining 55% at pH 9–12. Results from IR spectra analysis and acid-base titration suggest that the ionization of carboxylic acid accounts for the pH-induced gel swelling irrespective of the differences in the swelling behavior of these two gels. The pK_a values of the heat-treated PVA-MA gel increased from 4 to 10 while the degree of dissociation varied from 0 to 80%, whereas that of the crosslinked PVA-MA film is limited in a range of 3.3–4.2. The permeability of glucose across the crosslinked PVA-MA film increased when pH was raised from 2 to 7. No significant change of permeability was noticed between pH 7 and 12. For the heat-treated PVA-MA film, glucose permeability increased when pH was changed from 2 to 7 and from 7 to 12. © 1996 John Wiley & Sons, Inc.