Structure and microporous formation of cellulose/silk fibroin blend membranes: Part II. Effect of post-treatment by alkali

Blend membranes (RCF1) were prepared from mixture solution of cellulose and silk fibroin (SF) in cuoxam by coagulating with acetone–acetic acid (4:1 by volume). The blend membranes were subjected to post-treatment with 10% NaOH aqueous solution, and their structure and properties were characterized by FT-IR, X-ray diffraction, DSC, SEM and DMTA. In previous work, cellulose/SF blend membranes (RCF2) prepared by coagulating with 10% NaOH aqueous solution formed a microporous structure, in which the SF as a pore former was almost completely removed from the membrane. However, when the blend membranes RCF1 were immersed in 10% NaOH aqueous solution for post-treatment, a strong hydrogen bonding between cellulose and SF inhibited the removal of SF. Although alkali is a good solvent for SF, the blend membranes RCF1 such obtained from cellulose and SF were alkali resistant. The crystallinity and the mean pore size of the blend membranes slightly decreased with increasing post-treatment time. This work provided a cellulose/silk blend membrane, which can be used under alkaline medium.     

Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures

The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl₂+CaCl₂ with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl₂ concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC _p and apparent molar heat capacities C_p, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g^–1-K^–1 and –2.6 J-mol^–1-K^–1, respectively).     

Aqueous partial molar heat capacities and volumes for NaTcO4 and NaReO4

A flow microcalorimeter/densimeter system has been commissioned to measure heat capacities and densities of solutions containing radioactive species as a function of temperature. Measurements were made for NaTcO₄(aq) at six temperatures (189.15 K to 373.15 K for the heat capacities, 287.43 K to 396.67 K for the densities) over the molality range 0.01 to 0.29 mol-kg^–1. Measurements for NaReO₄(aq) (NaReO₄ is a common nonradioactive analogue for NaTcO₄) were made under similar conditions, but for eight temperatures and a more extensive range of molalities, 0.05 to 0.65 mol-kg^–1. Heat capacities of NaCl(aq) reference solutions were also measured from 293.15 K to 398.15 K.The heat capacity and density data are analysed using Pitzer's ioninteraction model. Equations for the apparent molar heat capacities and volumes are reported. Values of the NaReO₄(aq) partial molar heat capacities are compared to literature values based on integral heats of solution. The agreement between the two sets of NaReO₄ results is good below 330 K, but only fair at the higher temperatures. Values of the partial molar volumes have also been derived. Using literature values and the results of our experiments, it is calculated that the disproportionation of hydrated TcO₂(s) to form TcO ₄ ^– (aq) and Tc(cr) occurs more readily at high temperatures. The uncertainties introduced by using thermodynamic values for ReO ₄ ^– (aq), in the absence of values for TcO ₄ ^– (aq), are discussed.     

5-Aminolaevulinic acid-mediated photodynamic therapy in multidrug resistant leukemia cells

To verify if photodynamic therapy (PDT) could overcome multidrug resistance (MDR) when it it applied to eradicate minimal residual disease in patients with leukemia, we investigated the fluorescence kinetics of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) and the effect of subsequent photodynamic therapy on MDR leukemia cells, which express P-glycoprotein (P-gp), as well as on their parent cells. Evaluation of PpIX accumulation by flow cytometry showed that PpIX accumulated at higher levels in mdr-1 gene-transduced MDR cells (NB4/MDR) and at lower levels in doxorubicin-induced MDR cells (NOMO-1/ADR) than in their parent cells. A P-gp inhibitor could not increase PpIX accumulation. Measurement of extracellular PpIX concentration by fluorescence spectrometry showed that P-gp did not mediate the fluorescence kinetics of ALA-induced PpIX production. Assessment of ferrochelatase activity using high-performance liquid chromatography indicated that PpIX accumulation in drug-induced MDR cells was probably regulated by this enzyme. Assessment of phototoxicity of PDT using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that PDT was effective in NB4, NB4/MDR, NOMO-1 and NOMO-1/ADR cells, which accumulated high levels of PpIX, but not effective in K562 and K562/ADR cell lines, which accumulated relatively low levels of PpIX. These findings demonstrate that P-gp does not mediate the ALA-fluorescence kinetics, and multidrug resistant leukemia cells do not have cross-resistance to ALA-PDT.     

Photochemical aging of in situ polymerized blends of polystyrene and poly[acrylonitrile-g-(ethylene-co-propylene-co-diene)-g-styrene] (AES)

The influence of photochemical aging of in situ polymerized PS/AES blends on their mechanical properties has been studied. The PS/AES blends were subjected to photochemical aging for 168 h and 720 h. Tensile properties and Izod impact resistance of aged and non-aged samples were evaluated. The mechanical properties of the PS/AES blends are influenced by the polymerization temperature and blend composition and represent a balance between the toughness of EPDM and the stiffness of SAN in the PS matrix. Even though the impact resistance and strain at break of HIPS are higher than those of the PS/AES blends, after the aging period all PS/AES blends showed higher strain at break than HIPS. PS/AES blends present higher photochemical stability than HIPS.     

Electrical Conductance and Volumetric Studies in Aqueous Solutions of DL-Pyroglutamic Acid

Conductivity measurements of DL-pyroglutamic acid and sodium pyroglutamate in dilute aqueous solutions were performed in the 288.15–323.15 K temperature range. The limiting molar conductances of pyroglutamate anion, λ^o(pGlu⁻, T) and the dissociation constants of pyroglutamic acid, K(T) were derived from the Onsager, and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.5 mol-kg⁻¹ were determined at 5 K intervals from T = 288.15 K to 333.15 K. Densities served to evaluate the apparent molar volumes, V_2,φ(m, T), the cubic expansion coefficients, α (m,T) and the changes of the isobaric heat capacities with respect to pressure, (∂ C_P/∂ P)_T,m. They were correlated qualitatively with the changes in the structure of water when pyroglumatic acid is dissolved in it.     

脉冲泄流时土壤条件对冲击接地阻抗的影响

 为了探寻电流脉冲泄流时，设备的接地是否有效可靠，用FDTD法分析了脉冲泄流时均一土壤、分层土壤及局部改善土壤的电导率对冲击接地阻抗（TGR）的影响。结果表明：大地电导率对冲击接地阻抗的影响很大；对均一土壤，TGR随大地电导率的增大而减小，大地电导率越大，TGR对接地体的埋深越不敏感。对分层土壤，接地体要埋在大地电导率大的土壤层中，且不要靠近交界面；局部改善大地导电性能对降低TGR效果明显，TGR对改善区域的体积非常敏感，而当电导率大于一定值时，大地电导率的再增加，对TGR的影响不明显。     

Thermal Resistance Measurement across a Wick Structure Using a Novel Thermosyphon Test Chamber

A novel system is developed for measuring the thermal resistance across thin layers of sintered copper wicks of varying porosity. Wicks to be tested are integrated into a passive vertical thermosyphon system, and the resistance is measured for a series of input power levels. The wicks are sintered to a thermally conducting pedestal above a pool of deionized water and heated from below. The apparent thermal resistance across the wick (from the pedestal/wick interface to the vapor space) under the evaporative operating conditions encountered in heat pipes is measured using thermocouples. The apparent thermal resistance across the wick is measured to be as low as 0.01°C/W, corresponding to an evaporative heat transfer coefficient of greater than 128,000 W/m²K.