Paleomagnetic Results of Later Paleozolic Rocks From Alashan Area of Western North China Block

In order to contribute to the Apparent Polar Wander Path (APWP) of the North China Block (NCB) , we collected paleomagnetic samples of Late Paleozoic rocks from the northern and southern margins of the Alashan (Alxa) terrane (the western part of Inner Mongolia and northern parts of Gansu and Ningxia Provinces) and adjacent regions. Laboratory work revealed different types of demagnetization behavior and isolated a higher temperature characteristic component in most of the samples. Results of IRM experiments show high thermal stability and high coercivities for the magnetic carriers in these rocks. The characteristic component passed the fold and/or reversal tests, suggesting that the characteristic components were probably primary. On the basis of comparing the paleomagnetic results with the geologic evidence, we discuss the tectonic implications. In the Late Paleozoic, the Alashan region had been part of the NCB and was not connected with the northern and southern blocks. During the Carboniferous Alash     

Synthesis of an Anti-1,3-Diol Type Chiral Building Block

Duringthelastdecade,1,3-dioltypechiralbuildingbIocksofvariousconfigurationshavebeensynthesizedandappliedwidelyinthetotalsynthesisofnaturalpolyenemacrolideantibiotics1'2andla,25-dihydroxyvitaminD3analogues'.RecentlyWeigandandBrucker4synthesizedachiralbuildingblock(4R,6R)-2,2-dimethyl-5-tert-butyldip4-hydroxymethyl-l,3-dioxane1inlOsteps.Herein,wereportasyntheticrouteofnewbuildingblock(4S,6S)-2,2-dimethyl-5-tert-butyldip2,anenantiomerofl,startingfromreadilyavailableandinexpensiveD( )-xylose3i…     

Surface forces in foam films from ABA block copolymer: a dynamic method study

The thinning of foam films from aqueous solutions of an ABA triblock copolymer of polyethylene oxide and polypropylene oxide (average molecular weight 14,000 g/mol) is studied experimentally. The dependence of the surface forces on film thickness is obtained by the dynamic method of Scheludko and Exerowa.The total surface force measured in foam films (radius 60–70 m) from 10^–5 M (0.014 wt%) polymer solution with 0.1 M NaCl is positive at thicknesses from about 800 down to 460 . The electrostatic repulsion is negligible while the contribution of van der Waals attraction is small (within 15%). Therefore a positive surface force component predominates. Most probably it arises from steric interactions between the hydrophilic polyethylene oxide tails of the polymer. The dynamic method appears to be a suitable technique for exploring the stabilization of foam films from ABA copolymers.     

交联网络和浓溶液中高分子链运动的NMR研究Ⅲ.质子自旋-晶格弛豫时间与凝胶和浓溶液体系中高分子链段的运动

用自旋－晶格弛豫时间（Ｔ１）研究了溶胀的交联聚丙烯酰胺－丙烯酸网络和线型聚苯乙烯溶液中质子的弛豫行为。交联网络中，随着交联度增大，Ｔ１ＣＨ／Ｔ１ＣＨ２的值由１．１７逐渐趋近于１；而线型聚苯乙烯溶液中，Ｔ１ＣＨ／Ｔ１ＣＨ２的值由最稀浓度下的１．７过渡到１。说明在交联网络中，交联度很低时，链段的运动已经相当受约束；但交联度很大时，充分溶胀的交联网络中链段运动仍有一定自由度。而在线型高分子浓溶液中，链段的运动严重受阻，导致自旋扩散效应非常完全，彻底平均掉了各质子间Ｔ１时间的差异。     

Polyarylate–polystyrene block copolymer from macro-azoinitiator: Synthesis and its thermal properties

A macro-azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy-terminated polyarylates having viscosity-average molecular weights of 6200, 8100, and 12 400. These macro-azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate-polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc.     

A rigorous control of logarithmic corrections in four-dimensional ϕ4 spin systems

Using Gawedzki and Kupiainen's rigorous block spin transformation method, we study critical phenomena in ⁴ spin systems in four dimensions. In Part I of this work we investigate in detail the renormalization group trajectory of the system not exactly at the critical point.     

Infrared asymptotic freedom of a hierarchical φ 3 6 lattice theory

For the weakly coupled lattice ₃ ⁶ theory in a hierarchical model approximation a nonperturbative renormalization group analysis in the spirit of Gawedzki and Kupiainen is performed to study the flow of the effective actions. We deduce a domain of attraction to the tricritical (Gaussian) fixed point. The two relevant coupling constants of the problem are controlled by analytic continuation to complex domains, tracing their images under the renormalization group iterations.     

Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.     

Micellization and gelation of aqueous solutions of star-shaped PEG-PCL block copolymers consisting of branched 4-arm poly(ethylene glycol) and polycaprolactone blocks

Star-shaped block copolymers consisting of non-toxic poly(ethylene glycol) and biodegradable polycaprolactone ((PEG5K-PCL)₄) were synthesized by ring-opening polymerization of the ε-caprolactone monomer with hydroxyl-terminated 4-armed PEG as initiator. These biodegradable, amphiphilic star block copolymers showed micellization and sol-gel transition behaviors in aqueous solution with varying concentration and temperature. In the dilute aqueous solutions of star block copolymers, micellization behavior occurred over specific concentration. The 1,6-diphenyl-1,3,5-hexatriene (DPH) solubilization method was used to determine the critical micellization concentration (CMC) of star block copolymers. The obtained micelle size increased with increasing hydrophobic PCL block length. In high-concentration solutions, the star block copolymers showed temperature-sensitive sol-gel transition behavior. The morphology of the micelle and gel was investigated by atomic force microscopy (AFM). As a result, the micelles showed a core-corona spherical structure at concentration near CMC, while the gel showed a mountain-chain-like morphology picture. It was proposed that with increasing the micelle concentration the worm-like micelle clusters formed firstly and the gel was constructed by the packing of micelle clusters.