High conductivity organic thin films for spintronics: the interface resistance bottleneck.

Highly electrochemically doped poly(2,5-bis(3-dodecyl-2-yl)-thieno[3,2-b]thiophene (pBTTT) thin films exhibiting remarkably high conductivities values reaching 3000-5000 Ω(-1) cm(-1) are investigated. Experimental evidence of delocalized transport properties of this material at the onset of metallicity makes it an ideal candidate for spin valve device integration. Nevertheless, the interface resistance between the polymer and metallic electrodes is orders of magnitudes larger than the expected spin resistance of the active channel. This prevents the collection of a spin current. This finding can explain the lack of success in making lateral organic spin valves reported in the literature, especially the related absence of spin signals in non-local spin valve and Hanle current measurements in organic thin films.

Extended tunability of Nd-doped fiber lasers operating at 872-936 nm.

Efficient operation of an Nd-doped fiber laser operating in a wavelength-tunable configuration using a volume Bragg grating (VBG) is reported in this Letter. A high-power operation on the 4F3/2-4I9/2 transition of Nd3+ at short wavelengths below 900 nm is demonstrated for the first time in silica fibers. A high-efficiency (47% laser conversion) output power up to 22 W and a narrow linewidth of 0.035 nm are achieved. This configuration is compared with a more conventional fiber laser setup using a bandpass filter and a highly reflective dichroic mirror.

Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO.

Research on advanced materials such as multiferroic perovskites underscores promising applications, yet studies on these materials rarely address the impact of defects on the nominally expected materials property. Here, we revisit the comparatively simple oxide MgO as the model material system for spin-polarized solid-state tunnelling studies. We present a defect-mediated tunnelling potential landscape of localized states owing to explicitly identified defect species, against which we examine the bias and temperature dependence of magnetotransport. By mixing symmetry-resolved transport channels, a localized state may alter the effective barrier height for symmetry-resolved charge carriers, such that tunnelling magnetoresistance decreases most with increasing temperature when that state is addressed electrically. Thermal excitation promotes an occupancy switchover from the ground to the excited state of a defect, which impacts these magnetotransport characteristics. We thus resolve contradictions between experiment and theory in this otherwise canonical spintronics system, and propose a new perspective on defects in dielectrics.

Cholinergic control of human and animal pulmonary vascular tone.

The regulation of pulmonary vascular tone by acetylcholine (ACh) involves the activation of different subtypes of muscarinic receptors as well as the cholinesterase activities which are responsible for ACh degradation. Most of the studies on the cholinergic control of the pulmonary vascular tone have been performed in vessels derived from animals. The ability of ACh to induce pulmonary vasoconstriction is species dependent. In vessels derived from sheep lung, ACh induced contractions in veins but not in arteries whereas in human pulmonary vessels the reverse was observed. The subtype(s) of the muscarinic receptors involved in the pulmonary vasoconstrictions is also dependent on the species which are studied. M1 receptors are implicated in the rabbit pulmonary vasoconstrictions, M3 in humans, whereas M1 and M2 receptors are involved in the dog. The cholinesterases are implicated in the vasoconstriction produced by ACh in human and rabbit pulmonary arteries. However, in these studies while acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) activities were detected in human vessels only acetylcholinesterase activity was found in rabbit vessels. The endothelium-dependent relaxation induced by ACh has been reported in isolated pulmonary vessels from different animals including man. However, the muscarinic receptors involved in the ACh-induced vasodilatation of rat and rabbit pulmonary artery are of the M3 subtype while those characterized in the human pulmonary artery are of the M3 and M1 subtypes. Together these results concerning the cholinergic control of the pulmonary vascular tone indicate that extrapolation of the data obtained in animal models to human vessels requires some caution. In addition, there is considerable evidence to demonstrate that ageing may modify cholinergic responses. However, little information is available concerning the pulmonary vascular bed during ageing.

Analysis of color-center-related contribution to Bragg grating formation in Ge:SiO 2 fiber based on a local Kramers -Kronig transformation of excess loss spectra.

UV-induced excess losses have been measured at various pulse energy densities and exposure times in germanosilicate optical fiber preform cores. The corresponding refractive-index changes have been determined through a Kramers -Kronig analysis. Because of the nonlinear behavior of the excess losses as a function of both exposure time and fluence per pulse, one should be careful when comparing the refractive-index modulation deduced from such measurements with that obtained from Bragg grating reflectivity. Indeed nonlinear effects such as saturation imply that it is necessary to take into account the local character of the change in absorption to calculate the evolution of the refractive-index modulation accurately as a function of the exposure time. Implications of these results are discussed.