The Lopingian series in the Lhasa Block, Tibet and its palaeogeographical implications

Latest investigation indicates that the Lopingian Series including both terrestrial and marine deposit s are developed in the Lhasa Block. The marine Lopinigian Series in the Lhasa Block contains the compound coral Waagenophyllum, fusulinid Reichelina, and foraminifer Colaniella faunas , and the terrestrial Lopingian Series is characterized by both Cathaysian floras and mixed floras consisting of Gondwanan element s such as Glossopteris , Noeggerathiopsis, Phyllotheca and Cathaysian elements such as Pecopteris ,Sphenopteris. An anlaysis of the Lopingian sequences in the Lhasa Block reveals that it experienced a regression stage f rom Guadalupian to Lopingian. By contrast , the Himalayan Tethys Zone south to the Lhasa Block is characterized by typical Gondwanan Glossopteris flora , coldwater brachiopod and solitary coral faunas. In addition, the Lopingian sequence in the Himalayan Tethys Zone reflect s a transgressive process from the terrestrial Qubu Formation to the shallow marine Qubuerga Formation. Therefore, the Lhasa Block shows significant differences in both biota and depositional features from the Himalayan Tethys Zone during the Lopingian, which implies that the Lhasa Block had rifted from the northern periGondwanan margin before the Lopingian.

Hydrogen bonded block copolymer systems : from microphase separation in solid state to self-assembly in aqueous solutions

Block copolymer systems with hydrogen bonding interactions have received relatively little attention. Recently, we have investigated the self-assembly and phase separation in such block copolymer systems with an attempt to elucidate the role of hydrogen bonding interactions both theoretically and experimentally [1-4]. In A-b-B/C diblock copolymer/homopolymer systems, the phase behavior was theoretically analyzed according to the random phase approximation and correlated with hydrogen bonding interactions in terms of the difference in inter-association constants (K). To examine how the hydrogen bonding determines the self-assembly and morphological transitions in these systems, we have introduced the K values as a new variable into the phase diagram which we established for the first time (Fig. 1). Multiple vesicular morphologies were formed in aqueous solution of A-b-B/A-b-C diblock copolymer complexes of PS-b-PAA and PS-b-PEO. Interconnected compound vesicles (ICCVs) were observed for the first time as a new morphology (Fig. 2), along with other aggregated nanostructures including vesicles, multilamellar vesicles, thick-walled vesicles and irregular aggregates. Complexation of two amphiphilic diblock copolymers provides a viable approach to vesicles in aqueous media.

Microphase separation in double crystalline poly (ethylene oxide)-block-poly (caprolactone)/poly (4-vinyl phenol) blends

We report microphase separation induced by competitive hydrogen bonding interactions in double crystalline diblock copolymer/homopolymer blends of poly(ethylene oxide)-block-poly(ɛ-caprolactone) (PEO-b-PCL) and poly(4-vinyl phenol) (PVPh). The diblock copolymer PEO-b-PCL consists of two immiscible crystallizable blocks wherein both PEO and PCL blocks can form hydrogen bonds with PVPh. In these A-b-B/C diblock copolymer/homopolymer blends, microphase separation takes place due to the disparity in intermolecular interactions; specifically PVPh and PEO block interact strongly whereas PVPh and PCL block interact weakly. The TEM and SAXS results show that the cubic PEO-b-PCL diblock copolymer changes into ordered hexagonal cylindrical morphology upon addition of 20 wt % PVPh followed by disordered bicontinuous phase in the blend with 40 wt % PVPh and then to homogenous phase at 60 wt% PVPh and above. Up to 40 wt % PVPh there is only weak interaction between PVPh and PCL due to the selective hydrogen bonding between PVPh and PEO. However, with higher PVPh concentration, the blends become homogeneous since a sufficient amount of PVPh is available to form hydrogen bonds with both PEO and PCL. A structural model was proposed to explain the self-assembly and morphology of these blends based on the experimental results obtained. The formation of nanostructures and changes in morphologies depend on the relative strength of hydrogen bonding interaction between each block of the block copolymer and the homopolymer (1-3).

A new route to nanostructured thermosets with block ionomer complexes

We report a novel approach to prepare nanostructured thermosets using block ionomer complexes. Neither block copolymer polystyrene-block-poly(ethylene-ran- butylene)-block-polystyrene (SEBS) nor block ionomer sulfonated SEBS (SSEBS) is miscible with diglycidyl ether of bisphenol A (DGEBA) type epoxy resin. It is thus surprising that the block ionomer complex of SSEBS with a tertiary amine-terminated poly(3-caprolactone) (PCL), denoted as SSEBS-c-PCL, can be used to prepare nanostructured epoxy thermosets. The block ionomer complex SSEBS-c-PCL is synthesized via neutralization of SSEBS with 3-dimethylamino- propylamine-terminated PCL. Sulfonation of SEBS yields the block ionomer SSEBS which is immiscible with epoxy. But the block ionomer complex SSEBS-c-PCL can be easily mixed with DGEBA. When the curing agent 4,4'-methylenedianiline (MDA) is added and the epoxy cures, the system retains the nanostructure. In cured epoxy thermosets containing up to 30 wt% SSEBS-c-PCL, the exclusion of the poly(ethylene-ran-butylene) (EB) phase forms spherical micro-domains surrounded by separated sulfonated polystyrene phase while the PCL side-chains of SSEBS-c-PCL are dissolved in the cured epoxy matrix. The spherical micro-domains are highly aggregated in the epoxy thermosets containing 40 and 50 wt% SSEBS-c-PCL. The existence of epoxy-miscible PCL side-chains in the block ionomer complex SSEBS-c-PCL avoids macro-phase separation. Hence, the block ionomer complex can act as an efficient modifier to achieve nanostructured epoxy thermosets.

Electrospinning of nanofibres with parallel line surface texture for improvement of nerve cell growth

Nanofibres having a parallel line surface texture were electrospun from cellulose acetate butyrate solutions using a solvent mixture of acetone and N,N'-dimethylacetamide. The formation mechanism of the unusual surface feature was explored and attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. The fast evaporation of a highly volatile solvent, acetone, from the polymer solution was found to play a key role in the formation of surface voids, while the high viscosity of the residual solution after the solvent evaporation ensured the line surface to be maintained after the solidification. Based on this principle, nanofibres having a similar surface texture were also electrospun successfully from other polymers, such as cellulose acetate, polyvinylidene fluoride, poly(methyl methacrylate), polystyrene and poly(vinylidene fluoride-co-hexafluoropropene), either from the same or from different solvent systems. Polarized Fourier transform infrared spectroscopy was used to measure the polymer molecular orientation within nanofibres. Schwann cells were grown on both aligned and randomly oriented nanofibre mats. The parallel line surface texture assisted in the growth of Schwann cells especially at the early stage of cell culture regardless of the fibre orientation. In contrast, the molecular orientation within nanofibres showed little impact on the cell growth.

Greater auricular nerve neuropraxia with beach chair positioning during shoulder surgery

Neuropraxia of the greater auricular nerve is an uncommon complication of shoulder surgery, with the patient in the beach chair position. The greater auricular nerve, a superficial branch of the cervical plexus, is vulnerable to neuropraxia due to its superficial anatomical location. In this case series, we present three cases of neuropraxia associated with direct compression by a horseshoe headrest, used in routine positioning for uncomplicated shoulder surgery. We outline the risk of using devices of this nature and discourage the use of similar headrest devices due to the potential complications in headrest devices that exert pressure on the posterior auricular area to maintain head position during surgery.

Rapid onset of renal sympathetic nerve activation in rabbits fed a high-fat diet

Hypertension and elevated sympathetic drive result from consumption of a high-calorie diet and deposition of abdominal fat, but the etiology and temporal characteristics are unknown. Rabbits instrumented for telemetric recording of arterial pressure and renal sympathetic nerve activity (RSNA) were fed a high-fat diet for 3 weeks then control diet for 1 week or control diet for 4 weeks. Baroreflexes and responses to air-jet stress and hypoxia were determined weekly. After 1 week of high-fat diet, caloric intake increased by 62%, accompanied by elevated body weight, blood glucose, plasma insulin, and leptin (8%, 14%, 134%, and 252%, respectively). Mean arterial pressure, heart rate, and RSNA also increased after 1 week (6%, 11%, and 57%, respectively). Whereas mean arterial pressure and body weight continued to rise over 3 weeks of high-fat diet, heart rate and RSNA did not change further. The RSNA baroreflex was attenuated from the first week of the diet. Excitatory responses to air-jet stress diminished over 3 weeks of high-fat diet, but responses to hypoxia were invariant. Resumption of a normal diet returned glucose, insulin, leptin, and heart rate to control levels, but body weight, mean arterial pressure, and RSNA remained elevated. In conclusion, elevated sympathetic drive and impaired baroreflex function, which occur within 1 week of consumption of a high-fat, high-calorie diet, appear integral to the rapid development of obesity-related hypertension. Increased plasma leptin and insulin may contribute to the initiation of hypertension but are not required for maintenance of mean arterial pressure, which likely lies in alterations in the response of neurons in the hypothalamus.

IMF®-Therapy (Intention controlled Myo-Feedback) — an innovative method in the treatment of peripheral nerve lesions

Physiotherapy is a well established part of the rehabilitation of peripheral nerve paralysis. The aim of this type of treatment is to re-establish arbitrary functions by improving the patients’ active and passive mobility as well as their strength and stamina. IMF®-Therapy (Intention controlled Myo-Feedback) is an innovative method in the treatment of peripheral nerve lesions that goes beyond the purely neuro-scientific framework and also takes into account methods and concepts of the psychology of learning. The essential assumption is that things learnt in the past are firmly established in the long term motor memory and can be reactivated by the patient. From results achieved in 32 patients treated with this therapy it can be concluded that IMF®-Therapy may be a promising additional rehabilitation tool in peripheral nerve lesion.

Nanostructured block copolymer blends and complexes via hydrogen bonding interactions

This thesis investigates the influence of hydrogen bonding interactions on the self-assembly, phase behaviour and nanostructures of the block copolymer/homopolymer systems. The different combinations of block copolymer blends and complexes of AB/C, AB/CD, and ABC/D mixtures open a convenient way to tailor various morphologies with controlled size and shape.

Overcoming interfacial affinity issues in natural fiber reinforced polylactide biocomposites by surface adsorption of amphiphilic block copolymers

This work demonstrates that the interfacial properties in a natural fiber reinforced polylactide biocomposite can be tailored through surface adsorption of amphiphilic and biodegradable poly (ethylene glycol)-b-poly-(L-lactide) (PEG-PLLA) block copolymers. The deposition from solvent solution of PEG-PLLA copolymers onto the fibrous substrate induced distinct mechanisms of molecular organization at the cellulosic interface, which are correlated to the hydrophobic/hydrophilic ratios and the type of solvent used. The findings of the study evidenced that the performance of the corresponding biocomposites with polylactide were effectively enhanced by using these copolymers as interfacial coupling agents. During the fabrication stage, diffusion of the polylactide in the melt induced a change in the environment surrounding block copolymers which became hydrophobic. It is proposed that molecular reorganization of the block copolymers at the interface occurred, which favored the interactions with both the hydrophilic fibers and hydrophobic polylactide matrix. The strong interactions such as intra- and intermolecular hydrogen bonds formed across the fiber−matrix interface can be accounted for the enhancement in properties displayed by the biocomposites. Although the results reported here are confined, this concept is unique as it shows that by tuning the amphiphilicity and the type of building blocks, it is possible to control the surface properties of the substrate by self-assembly and disassembly of the amphiphiles for functional materials.