Polarization selective electro-optic polymer waveguide devices by direct electron beam writing

A novel technique for the fabrication of polarization selective electro-optic polymer waveguide devices with direct electron beam writing was described. Birefringence induced by the electric field poling in the electro-optic polymer film was erased in the electron beam exposed regions. The formed waveguides had stronger confinement for the light polarized along the poling direction. High fabrication resolution on the 100 nm scale or smaller could be achieved. Fabrication of polymer polarizer and polarization selective microring resonators with this technique was reported. The highest polarization extinction ratio was measured to be 21.4 dB.

Direct electron beam writing of electro-optic polymer microring resonators

Electro-optic polymer waveguides in electron beam sensitive polymethyl methacrylate (PMMA) polymer matrix doped with organic nonlinear chromophores could be directly patterned by electron beam exposure with high resolution and smoothness. The polymer in the exposed regions was removed with standard electron beam resist developer and without damaging the chromophore containing polymer waveguides. Feature sizes on the order of 100 nm could be clearly resolved. High quality microring resonators made of YL124/PMMA electro-optic polymer were successfully fabricated with this technique. The measured resonance extinction ratios were more than 16 dB and quality factors were in the range of 10(3) approximately 10(4).

A home-based exercise programme improves ankle range of motion in long-term venous ulcer patients

BACKGROUND AND OBJECTIVES

Decreased ankle mobility is associated with delayed healing of venous ulcers. The aim of this study was to assess the efficacy of a 24-week home-based exercise programme in increasing ankle range of motion and increasing the strength and endurance of the calf muscle. The secondary aim was to see whether subjects with venous ulcers were able to maintain a consistent exercise programme.

METHODS

Eleven patients with long-standing venous ulcers were encouraged to undertake a thrice-weekly 5-10 min ankle exercise programme using elastic resistance bands and stretching in a 24-week single-arm pilot study. Ankle range of motion was measured monthly using a bi-plane ankle goniometer. Pain scores and participation levels were also recorded.

RESULTS

There were significant improvements in ankle range of motion achieved at 12 and 24 weeks. Median pain scores (scale of 1-10) were reduced from 5.2 at baseline to 2.0 at weeks 12 and 24.

CONCLUSION

These results show that a simple, home-based exercise programme is effective in achieving gains in ankle range of motion and may help to reduce pain. Good participation levels show that it is not only effective, but also feasible. A larger randomized controlled study is needed to show whether there is a positive effect on ulcer healing.

von Willebrand factor: evidence for variable clearance in vivo according to Y/C1584 phenotype and ABO blood group

BACKGROUND

The plasma von Willebrand factor (VWF) level (VWF:Ag) is known to correlate with the VWF Y/C1584 variation and with ABO blood group. The ratio of the VWF propeptide (VWFpp) to VWF:Ag and the ratio of coagulation factor VIII (FVIII:C) to VWF:Ag have previously been used as indicators of VWF clearance and/or secretion.

OBJECTIVES AND METHODS

To investigate the mechanism underlying the relationship between VWF phenotype and VWF:Ag, the VWFpp/VWF:Ag ratio and FVIII:C/VWF:Ag ratio were determined for plasmas of phenotype Y/C1584, Y/Y1584, blood group O and blood group A (n = 50 for each set). The blood group O plasmas comprised two sets of 25 with low and high mean VWF levels (Low-O and High-O), respectively; similarly for group A (Low-A and High-A).

RESULTS AND CONCLUSIONS

The VWFpp/VWF:Ag ratio was greater than 1 (unity) for Y/C1584 plasmas and significantly higher than for Y/Y1584 plasmas; however, the FVIII:C/VWF:Ag ratio was near unity for both and was not significantly different. These results are consistent with increased clearance for Y/C1584 VWF. Similarly, the VWFpp/VWF:Ag ratio and FVIII:C/VWF:Ag ratio in combination were consistent with increased VWF clearance in blood group O compared with blood group A, and in Low-O and Low-A, respectively, compared with High-O and High-A. The data indicate that in vivo C1584 and blood group O are associated with increased VWF clearance, and that clearance contributes to differing VWF level within a given blood group.

Spontaneous generation of self-organized solitary wave structures at earth's magnetopause

Spontaneous formation of solitary wave structures has been observed in Earth's magnetopause, and is shown to be caused by the breakup of a zonal flow by the action of drift wave turbulence. Here we show matched observations and modeling of coherent, large-scale solitary electrostatic structures, generated during the interaction of short-scale drift wave turbulence and zonal flows at the Earth's magnetopause. The observations were made by the Cluster spacecraft and the numerical modeling was performed using the wave-kinetic approach to drift wave-zonal flow interactions. Good agreement between observations and simulations has been found, thus explaining the emergence of the observed solitary structures as well as confirming earlier theoretical predictions of their existence.

Theory-guided design and synthesis of multichromophore dendrimers: an analysis of the electro-optic effect

Extensive experimental and theoretical study suggests that interchromophore electrostatic interactions are among the most severe impediments to the induction and stability of large electro-optic coefficients in electric-field-poled organic materials. In this report, multichromophore-containing dendritic materials have been investigated as a means to minimize unwanted attenuation of nonlinear optical (electro-optic) activity at high chromophore loading. The dendritic molecular architectures employed were designed to provide optimized molecular scaffolding for electric-field-induced molecular reorientation. Design parameters were based upon past experimental results in conjunction with statistical and quantum mechanical modeling. The electro-optic behavior of these materials was evaluated through experimental and theoretical analysis. Experimental data collected from the dendrimer structures depict a reasonably linear relationship between chromophore number density (N) and electro-optic activity (r(33)) demonstrating a deviation from the dipolar frustration that typically limits r(33) in conventional chromophore/polymer composite materials. The observed linear dependence holds at higher chromophore densities than those that have been found to be practical in systems of organic NLO chromophores dispersed in polymer hosts. Theoretical analysis of these results using Monte Carlo modeling reproduces the experimentally observed trends confirming linear dependence of electro-optic activity on N in the dendrimer materials. These results provide new insight into the ordering behavior of EO dendrimers and demonstrate that the frequently observed asymptotic dependence of electro-optic activity on chromophore number density may be overcome through rational design.

Innexins in the lobster stomatogastric nervous system: cloning, phylogenetic analysis, developmental changes and expression within adult identified dye and electrically coupled neurons

Gap junctions play a key role in the operation of neuronal networks by enabling direct electrical and metabolic communication between neurons. Suitable models to investigate their role in network operation and plasticity are invertebrate motor networks, which are built of comparatively few identified neurons, and can be examined throughout development; an excellent example is the lobster stomatogastric nervous system. In invertebrates, gap junctions are formed by proteins that belong to the innexin family. Here, we report the first molecular characterization of two crustacean innexins: the lobster Homarus gammarus innexin 1 (Hg-inx1) and 2 (Hg-inx2). Phylogenetic analysis reveals that innexin gene duplication occurred within the arthropod clade before the separation of insect and crustacean lineages. Using in situ hybridization, we find that each innexin is expressed within the adult and developing lobster stomatogastric nervous system and undergoes a marked down-regulation throughout development within the stomatogastric ganglion (STG). The number of innexin expressing neurons is significantly higher in the embryo than in the adult. By combining in situ hybridization, dye and electrical coupling experiments on identified neurons, we demonstrate that adult neurons that express at least one innexin are dye and electrically coupled with at least one other STG neuron. Finally, two STG neurons display no detectable amount of either innexin mRNAs but may express weak electrical coupling with other STG neurons, suggesting the existence of other forms of innexins. Altogether, we provide evidence that innexins are expressed within small neuronal networks built of dye and electrically coupled neurons and may be developmentally regulated.

A method for cold storage and transport of viable embryonic kidney rudiments

Organ culture of mouse embryonic kidneys is a powerful system for studying normal renal development and for researching the developmental effects of experimental perturbations (drugs, antibodies, interfering RNA, and so on). In standard protocols, embryonic kidneys are isolated by delicate micro-dissection and placed in organ culture as soon as possible after the death of the donor mouse, before there is time to genotype them or to transport them elsewhere. This report demonstrates that fully viable embryonic kidneys can be isolated and cultured from crudely dissected caudal portions of embryos that have been stored on ice or at 4 degrees C for several days. This very simple technique can save considerable resources in laboratories that culture kidneys of transgenic mice: (i) cold storage allows embryos to be genotyped before their kidneys are cultured, and (ii) cold transport allows kidney research laboratories to study kidneys of transgenic mice raised elsewhere without the need for expensive importing of the mouse line itself. It will therefore substantially augment the ability of kidney research labs to perform pilot experiments on large numbers of different transgenic animals and to collaborate in new ways.

Designing follow-up intervals

When an examination is needed to determine if an event has occurred there will be a loss of efficiency in using the resulting interval-censored data instead of the exact event times. In designing follow-up intervals this loss for longer intervals needs to be weighed against extra visits required by shorter intervals. We obtain results to quantify this for the estimation of the median and mean survival and for covariates in parametric regression models with equally spaced examination times. Asymptotic information loss for the log-normal and Weibull distributions are similar when comparisons are made between corresponding members of the two families. For distributions with coefficients of variation of 50 per cent or more, a choice of interval from 0.25 to 0.7 times the median is recommended.

Real-time scanning tunnelling microscopy imaging of protein motion at electrode surfaces

A mutant (K27C) of the blue copper protein azurin [Eur. J. Biochem. 194 (1990) 109; J. Mol. Biol. 221 (1991) 765] for orientated immobilisation on gold surfaces was analysed by scanning tunnelling microscopy (STM) both in a resting state and following the application of a short potential pulse between the tip and sample.

Structural determinants of heparan sulphate modulation of GDNF signalling

Glial cell line-derived neurotrophic factor (GDNF) has many functions including regulation of kidney morphogenesis and of neuron growth and survival in the enteric, sensory and central nervous systems. Reports of GDNF being used against Parkinson's disease in human patients have sparked intense clinical interest in GDNF signalling. We recently showed that GDNF signalling requires cell surface heparan sulphate glycosaminoglycans (Barnett et al., 2002, J. Cell Sci. 115, 4495-4503). Here we use exogenous modified heparins to determine those structural features required to inhibit GDNF signalling in ex vivo assays. 2-O-sulphate groups were found to impart high activity but were not absolute requirements for the inhibition of GDNF signalling. These findings may explain the similarities between the phenotypes of transgenic mice lacking GDNF and those lacking heparan sulphate 2-sulphotransferase, the enzyme responsible for achieving 2-O-sulphation of uronic acids in vivo.

Non-selective and cyclo-oxygenase-2-specific non-steroidal anti-inflammatory drugs impair the hyperaemic response of skin to brief axillary artery occlusion

BACKGROUND

Cyclo-oxygenase-2 (COX-2)-specific inhibitors are marketed as safer analgesics than non-selective non-steroidal anti-inflammatory drugs. However, there has been conflicting evidence concerning endothelial function and cardiovascular risk after COX-2 inhibitor use. We investigated forearm skin vascular reactivity to brief axillary artery occlusion in healthy volunteers after a single dose of the non-steroidal anti-inflammatory drugs ibuprofen (non-selective) and rofecoxib (COX-2 specific).

METHODS

Ten healthy male volunteers were studied. Forearm skin blood flow was measured using laser Doppler flowmetry. Two non-invasive probes were placed on the volar surface of the forearm. The magnitude of hyperaemic response to brief (20 s) and prolonged (5 min) occlusion of the axillary artery was measured before and 2-3 h after administration of ibuprofen 800 mg or rofecoxib 25 mg. The transient hyperaemic response ratio (THRR), defined as the net peak hyperaemic flow-flux divided by the net baseline flow-flux, was calculated. Each volunteer received both drugs in random order at least 1 week apart.

RESULTS

Ibuprofen and rofecoxib increased net baseline blood flow (median (range): ibuprofen, from 23.3 (12.1-40.8) to 31.5 (17.4-77.3); rofecoxib, from 22.0 (14.6-41.0) to 29.9 (19.5-112.0); P<0.01). The net hyperaemic peak flow-flux after brief and prolonged occlusion was unchanged after both drugs. THRR was reduced by both drugs (ibuprofen, from 2.92 (2.38-3.86) to 2.09 (1.45-3.54); rofecoxib, from 3.36 (2.06-5.16) to 2.67 (1.15 -3.84); P<0.01).

CONCLUSIONS

Both COX-2 and non-selective non-steroidal anti-inflammatory drugs, when given to healthy volunteers as single therapeutic doses, decrease skin microvascular tone but do not impair maximal vasodilatory ability.

Effects of bilobalide on cerebral amino acid neurotransmission

Bilobalide is one of many active constituents found in EGb 761 (definition see editorial), which is extracted from Ginkgo biloba leaves. Whilst there is good, sound evidence that bilobalide exhibits neuroprotective actions in a variety of model systems, there is currently no consensus on its mechanism of action. This present communication summarises the results we have obtained with this compound on excitatory amino acid neurotransmission in the central nervous system using both neurochemical and electrophysiological techniques. Bilobalide was shown to reduce glutamate and aspartate release elicited by both high potassium-containing artificial cerebrospinal fluid (aCSF) or veratridine from mouse cortical slices. In addition, bilobalide had a very potent effect (IC (50) 2.7 microM) on glutamate release elicited by hypoxia/hypoglycaemia-induced release from rat cortical slices. Electrophysiologically, bilobalide also decreased the frequency of gamma-aminobutyric acid (GABA) uptake inhibitor-induced depolarisations in mouse cortical slices, an effect probably mediated by a decrease in glutamate release. No definitive conclusions can be reached concerning the mechanism of action of bilobalide, but an ability to decrease excitotoxic amino acid release, particularly glutamate, would suggest that this is a probable mechanism to account for its neuroprotective properties.

Effects of bilobalide on amino acid release and electrophysiology of cortical slices

This study investigated the effects of bilobalide, a constituent of Ginkgo biloba, on potassium and veratridine-induced release of glutamate and aspartate from mouse cortical slices. We also studied its effects on spontaneous and N-methyl-D-aspartate (NMDA)-induced depolarizations elicited in magnesium-free artificial cerebrospinal fluid (aCSF) as well as its effect on NO-711 (a gamma-aminobutyric acid (GABA) uptake inhibitor)-induced depolarizations. Bilobalide, 100 microM significantly reduced both glutamate and aspartate release elicited by potassium or veratridine. Bilobalide (5-100 microM) also significantly reduced the frequency of NO-711 induced depolarizations, however, it had no effect on spontaneous or on NMDA-induced depolarizations at 5-200 microM. These results suggest that the neuroactive properties of bilobalide may be mediated by a reduction in excitatory amino acid neurotransmitter release.