Preparation of bi-continuous macroporous polyamide copolymer membranes for cell culture

[[abstract]]Skinless bi-continuous macroporous membranes with extremely high porosity, ∼80%, were prepared by the non-solvent induced phase separation (NIPS) process, from casting dopes composed of Elvamide (co-polymer of Nylon-6, -66, and -610), chitosan, and formic acid that were immersed in a water bath maintained at 10 °C. The Chitosan, while functioned as a pore former, migrated along with out-diffusing formic acid into the bath during the NIPS process, thereby, breaking the top gel-layer and the boundaries between cellular pores to yield a morphology featuring interpenetration networks of pores and polymer host. The amount of chitosan added to the dope affected significantly the pore size and porosity of the membranes formed, as revealed by SEM observations. At the highest chitosan/Elvamide ratio of 0.155, very large pore size (∼30 μm) and porosity (83%) were achieved, whereas at the lowest ratio of 0.1, the membrane became asymmetric, and the pore size was reduced to ∼15 μm. 1H NMR analyses indicated that chitosan was completely removed during the precipitation process. Furthermore, L929 cells were cultured on various porous membranes. It is interesting to find that this cell was able to dwell on the pore walls in the cross sectional region, although with a smaller proliferation than on a flat nonporous surface.[[incitationindex]]SCI[[booktype]]電子

Variance-Optimal Offline and Streaming Stratified Random Sampling

Stratified random sampling (SRS) is a fundamental sampling technique that provides accurate estimates for aggregate queries using a small size sample, and has been used widely for approximate query processing. A key question in SRS is how to partition a target sample size among different strata. While Neyman allocation provides a solution that minimizes the variance of an estimate using this sample, it works under the assumption that each stratum is abundant, i.e., has a large number of data points to choose from. This assumption may not hold in general: one or more strata may be bounded, and may not contain a large number of data points, even though the total data size may be large. We first present VOILA, an offline method for allocating sample sizes to strata in a variance-optimal manner, even for the case when one or more strata may be bounded. We next consider SRS on streaming data that are continuously arriving. We show a lower bound, that any streaming algorithm for SRS must have (in the worst case) a variance that is {\Omega}(r) factor away from the optimal, where r is the number of strata. We present S-VOILA, a practical streaming algorithm for SRS that is locally variance-optimal in its allocation of sample sizes to different strata. Our result from experiments on real and synthetic data show that VOILA can have significantly (1.4 to 50.0 times) smaller variance than Neyman allocation. The streaming algorithm S-VOILA results in a variance that is typically close to VOILA, which was given the entire input beforehand

The DSC study on physical aging of PET

[[abstract]]Isothermal enthalpy relaxation in polyethylene terephthalate (PET) was measured at different annealing temperature below the glass transition temperature (Tg) on a differentia l scanning calorimeter (DSC) . The endothermic peaks below Tg were found on DSC scan curves and the peaks increased in magnitude and shifted to higher temperature with increasing aging time. We found the empirical fractional exponential function could describe the aging phenomena. The time constant r e in the fractional exponential function was lower at higher aging temperature It meant the aging rate was increasing with aging temperature. The temperature dependent activation energy obtained from this method was about 40 Kcal / mole. Also from the fractional exponential function fitting ,we found that the relaxation curves of samples aging at different temperatures couldn't be superimposed by a shift in time.[[sponsorship]]明志工業專科學校[[conferencetype]]國內[[conferencedate]]19901105~19901105[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]臺北縣, 臺

Asymmetric composite membranes from chitosan and tricalcium phosphate useful for guided bone regeneration

[[abstract]]To fulfill the properties of barrier membranes useful for guided bone tissue regeneration in the treatment of periodontitis, in this study a simple process combining lyophilization with preheating treatment to produce asymmetric barrier membranes from biodegradable chitosan (CS) and functional β-tricalcium phosphate (TCP) was proposed. By preheating TCP/CS (3:10, w/w) in an acetic acid solution at 40°C, a skin layer that could greatly increase the mechanical properties of the membrane was formed. The asymmetric membrane with a skin layer had a modulus value almost 4-times that of the symmetric porous membrane produced only by lyophilization. This is beneficial for maintaining a secluded space for the bone regeneration, as well as to prevent the invasion of other tissues. The subsequent lyophilization at -20°C then gave the rest of material an interconnected pore structure with high porosity (83.9-90.6%) and suitable pore size (50-150 μm) which could promote the permeability and adhesiveness to bone cells, as demonstrated by the in vitro cell-culture of hFOB1.19 osteoblasts. Furthermore, the TCP particles added to CS could further increase the rigidity and the cell attachment and proliferation of hFOB1.19. The TCP/CS asymmetric composite membrane thus has the potential to be used as the barrier membrane for guided bone regeneration.[[incitationindex]]SCI[[booktype]]電子

Synthesis of Modified Silica Spheres Used for the Preparation of Dual Ultraviolet- and Thermo-cured Epoxyacrylate/Silica Composites

[[abstract]]To investigate the interfacial effect on properties of epoxyacrylate–silica composites, submicron-sized silica spheres were synthesized by sol–gel reaction under a basic environment and their surfaces were endowed with vinyl functional groups by further modification with 3-methacryloxypropyl trimethoxy silane. The pure silica (PS) and the modified silica (MPS) spheres were characterized by Fourier transform infrared, 29Si- and 13C-nuclear magnetic resonance (NMR), scanning electron microscope (SEM), and particle size analyzer. The silica spheres were then added to the presynthesized difunctional epoxyacrylate resin with one vinyl group and one epoxide group at each end, in addition to the photo- and thermo-curing agents. After cure, thermal and mechanical properties of the obtained epoxyacrylate–silica composites were measured and compared. Tensile mechanical properties including initial modulus, ultimate tensile strength, and elongation at break, as well as the fracture energy of the epoxyacrylate–silica composite were all increased by increasing the content of silica spheres. Moreover, the composites filled with MPS had stronger interfacial strength between silica sphere and matrix than those with PS and thus exhibited an additional increase of tensile mechanical properties and fracture toughness. The increase of fracture toughness was owing to the crack deflection and particle–matrix debonding as evidenced by SEM pictures on the fracture surface.[[incitationindex]]SCI[[booktype]]電子

Structure characterizations and protein resistance of chitosan membranes selectively crosslinked by poly(ethylene glycol) dimethacrylate

[[abstract]]Chitosan (CS) is a fragile material with a high modulus of elasticity. Improving its flexibility as well as membrane permeability are the key aspects that need to be addressed for using CS as a biomaterial. Poly(ethylene glycol) (PEG) has several unique properties such as protein resistance, low toxicity, immunogenicity, and good solubility in both water and organic solvents. In this study, a vinyl compound was grafted to the C-6 position of CS by protection-grafting-deprotection. The vinyl CS was then crosslinked with PEG dimethacrylate (PEGDMA) selectively at its C-6 position to form CS-g-PEG copolymer membranes. Analyses from spectra of Fourier-transform infrared and nuclear magnetic resonance confirmed the chemical structure of the crosslinking CS-g-PEG copolymer membranes. Thermal and mechanical properties of the prepared CS-g-PEG membranes were measured and well-correlated to their structures. The incorporation of PEGDMA into the CS increased the material’s flexibility and thermal resistance. Finally, the CS-g-PEG membranes were found to have good protein resistance and blood compatibility; therefore, it has potential application as the biomedical material especially for hemodialysis.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子

應用柏克萊的動力網狀模型來描述PP的黏度性質

[[abstract]]D. S. Soong 提出了分子的動力網狀模型來描述高分于系統的流變行為。黏度受到剪切率的影響主要是由於隨著剪切率的增加，紐纏密度逐漸地減少。在穩定狀態下，紐纏的生成速率和消失速率達到一個動態平衡。而黏度即正比於紐纏數目。紐纏的消失速率主要是由於剪切率的關係，而假設和其a 次方成正比;紐纏的生民速率則和熱擴散運動有關，並且假設和剪切率無關。最後的方程式非常簡單，而且可以描述大部份高分于的流變性質[[sponsorship]]明志工業專科學校[[conferencetype]]國內[[conferencedate]]19891104~19891104[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]臺北縣, 臺

On the degree theory for general mappings of monotone type

AbstractDegree theory has been developed as a tool for checking the solution existence of nonlinear equations. In his classic paper published in 1983, Browder developed a degree theory for mappings of monotone type f+T, where f is a mapping of class (S)+ from a bounded open set Ω in a reflexive Banach space X into its dual X∗, and T is a maximal monotone mapping from X into X∗. This breakthrough paved the way for many applications of degree theoretic techniques to several large classes of nonlinear partial differential equations. In this paper we continue to develop the results of Browder on the degree theory for mappings of monotone type f+T. By enlarging the class of maximal monotone mappings and pseudo-monotone homotopies we obtain some new results of the degree theory for such mappings

Stratified Random Sampling from Streaming and Stored Data

Stratified random sampling (SRS) is a widely used sampling technique for approximate query processing. We consider SRS on continuously arriving data streams, and make the following contributions. We present a lower bound that shows that any streaming algorithm for SRS must have (in the worst case) a variance that is Ω(r ) factor away from the optimal, where r is the number of strata. We present S-VOILA, a streaming algorithm for SRS that is locally variance-optimal. Results from experiments on real and synthetic data show that S-VOILA results in a variance that is typically close to an optimal offline algorithm, which was given the entire input beforehand. We also present a variance-optimal offline algorithm VOILA for stratified random sampling. VOILA is a strict generalization of the well-known Neyman allocation, which is optimal only under the assumption that each stratum is abundant, i.e. has a large number of data points to choose from. Experiments show that VOILA can have significantly smaller variance (1.4x to 50x) than Neyman allocation on real-world data