Synthesis and characterization of novel aromatic condensation polymers containing rigid benzoxazole pendent groups

A new aromatic diamine monomer containing benzoxazole substituents was prepared by a multistep synthesis starting from 1,4‐dibromo‐2,5‐difluorobenzene. The diamine was polymerized with commercial aromatic dianhydride or dicarboxylic acid chloride monomers to provide several different poly(amic acid)s and polyamides with their inherent viscosities in the range of 0.24–0.46 dL/g. Thermal properties of these polymers including thermal imidization of poly(amic acid)s into polyimides were investigated by using FTIR, DSC, and TGA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 178–185, 2004     

A novel spin-finishing method for antistatic modification of polyester fiber. Surface reaction onto amine-containing copoly(amide-ethers) blended with polyester fiber

Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 10⁶ to 10⁸ Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity.     

Morphology development in polymer blends

The major morphological changes during polymer blending occur during the initial softening stage. This work explains the evolution of phase morphology of polymer blends from pellets to submicron particles in a co-rotating twin-screw extruder. The extruder was opened and blend samples were taken along its length. The major phase component was extracted by means of a selective solvent so that the dispersed phase morphology could be viewed directly by using scanning electron microscopy. The two systems studied were 80:20 polystyrene/amorphous polyamide and 80:20 polystyrene/polypropylene. In both systems, the initial morphology consisted of sheets of dispersed phase. Holes form in the sheets, and these holes grow as a result of interfacial tension forces until they coalesce with each other, forming thin ligaments. These fluid ligaments are unstable and break up via mixer shear forces. Very large changes in dispersed phase size are observed during the softening stage. The particle size changes less after the polymers are completely melted. The extruder results are compared to results from a batch mixer. The same dispersed phase sheeting mechanism is seen in the initial morphology in the batch mixer and the breakup of the dispersed phase domains parallels the breakup seen in the extruder.     

Effects of Stearic Acid on the Injection Molding of Alumina

This research investigated the influence of stearic acid on the injection molding of alumina, by varying the concentration of stearic acid. The interaction between stearic acid and alumina was identified using transmission infrared spectroscopy, indicating stearic acid preferentially adsorbed onto the alumina powder surface. In addition to slightly modifying the intrinsic binder viscosity, stearic acid adsorbed onto the powder surface changed the flow behavior of the mixtures from dilatant flow to pseudoplastic flow at low temperatures. As a result, inhomogeneous distribution of binder in the injection-molded parts was minimized with increased stearic acid concentration. However, the possibility of forming bubbles in the mixtures arising from vaporization of stearic acid was enhanced. Additionally, the binder burnout temperature range was broadened with the increase of stearic acid concentration.     

An SDP Primal-Dual Algorithm for Approximating the Lovász-Theta Function

The Lovász ?-function (Lovász in IEEE Trans. Inf. Theory, 25:1–7, 1979) of a graph G=(V,E) can be defined as the maximum of the sum of the entries of a positive semidefinite matrix X, whose trace Tr(X) equals 1, and X _ij =0 whenever {i,j}∈E. This function appears as a subroutine for many algorithms for graph problems such as maximum independent set and maximum clique. We apply Arora and Kale’s primal-dual method for SDP to design an algorithm to approximate the ?-function within an additive error of δ>0, which runs in time $O(\frac{\vartheta ^{2} n^{2}}{\delta^{2}} \log n \cdot M_{e})$ , where ?=?(G) and M _e =O(n ³) is the time for a matrix exponentiation operation. It follows that for perfect graphs G, our primal-dual method computes ?(G) exactly in time O(? ² n ⁵logn). Moreover, our techniques generalize to the weighted Lovász ?-function, and both the maximum independent set weight and the maximum clique weight for vertex weighted perfect graphs can be approximated within a factor of (1+?) in time O(? ^?2 n ⁵logn).     

Formation of Azobenzenes and Azoxybenzenes from the Aqueous Reactions of Anilines and Ozone

Azobenzenes and azoxybenzenes are two of the products identified from the aqueous reaction of anilines with ozone. Aniline concentration and functional groups on the benzene ring of aniline affected the amount of azobenzenes and azoxybenzenes formed; (1) decreasing the aniline concentration significantly increased azobenzene formation, and (2) electron-withdrawing groups increased the formation of its related azobenzene and azoxybenzene, whereas electron-donating groups had the opposite effect.     

Extraction and implementation of muscle synergies in neuro-mechanical control of upper limb movement

This work faces the redundancy problem, a central concern in robotics, in a particular force-producing task by using muscle synergies to simplify the control. We extracted muscle synergies from human electromyograph signals and interpreted the physical meaning of the identified muscle synergies. Based on the human analysis results, we hypothesized a novel control framework that can explain the mechanism of the human motor control. The framework was tested in controlling a pneumatic-driven robotic arm to perform a reaching task. This control method, which uses only two synergies as manipulated variables for driving antagonistic pneumatic artificial muscles to generate desired movements, would be useful to deal with the redundancy problem; thus, suggesting a simple but efficient control for human-like robots to work safely and compliantly with humans.     

Shear-induced interactions in blends of HMMPE containing a small amount of thermotropic copolyester HBA/HQ/SA

Shear-induced interactions between high molecular mass polyethylene (HMMPE) melt and a thermotropic liquid crystalline copolyester, HBA/HQ/SA (TLCP) were investigated using large amplitude oscillatory shear and capillary shear. Polarized optical microscopy (POM) observations show that the mono-domain nematic TLCP droplets embedded inside a HMMPE melt may be readily elongated using large amplitude oscillatory shear. The HMMPE melt adjacent to the elongated TLCP filament was observed to crystallize faster than that in the matrix away from the interface. TEM analysis on the 1 wt% TLCP/HMMPE blend quenched after capillary shear shows that there are strong interfacial interactions between the elongated TLCP filament and the HMMPE matrix. Long range PE lamellae orientational order up to 2 μm away from the TLCP filament surface were observed, with all the lamellae surface normal parallel to the TLCP fiber. Additionally, a strong interfacial compatibility between the TLCP filament and the HMMPE matrix with an interfacial thickness of ∼30 nm has also been observed. The enhanced interfacial compatibility is attributed to the -CH₂- group interactions due to chain alignment in both components at their interface. These results provide a fundamental insight to other TLCP containing thermoplastics where compatibilities may be present due to segmental interactions.     

解决组合公钥共谋攻击和密钥碰撞的新方法

以解决组合公钥体制中共谋攻击和密钥碰撞问题为目的。首先,针对线性共谋攻击,提出了一种新的构造种子矩阵的方法,使得种子密钥和大于基点加法群的阶数,从而使密钥之间不能相互线性表示。其次在密钥的生产过程中,引入系数破坏了层不同和层互斥不同的关系,为解决选择共谋攻击提供了一种有效的方法,同时增强了抵御随机共谋攻击的能力。最后,在密钥产生的流程中,通过公钥对比来避免密钥碰撞,为解决密钥碰撞问题提出了一种新方法。     

应用静电纺丝法制备PZT纳米纤维薄膜

提出应用静电纺丝法制备PZT纳米纤维薄膜。研究中配制PZT溶液后再进行静电纺丝,获得了PZT纳米纤维薄膜,并且通过调整纺丝时间和沉积次数来控制纳米纤维薄膜的厚度。运用SEM对获得的热处理前后的薄膜进行了观察对比,测量其平均直径约为200 nm;运用XRD对退火后的样品进行分析,测得样品的主要成分为Pb(Zr0.52Ti0.48)O3,证明所制备的正是PZT薄膜;运用AFM测得薄膜的表面粗糙度为1.034 nm,说明该纳米薄膜材料非常的均匀整齐。