Prolactin

During an oral glucose tolerance test (OGTT) glucose and insulin levels were measured in 26 patients with prolactin-producing pituitary tumours without growth hormone excess. Basal glucose and insulin levels did not differ from the values of an age-matched control group. After glucose load the hyperprolactinaemic patients showed a decrease in glucose tolerance and a hyperinsulinaemia. Bromocriptine (CB 154), which suppressed PRL, improved glucose tolerance and decreased insulin towards normal in a second OGTT. — Human PRL or CB 154 had no significant influence on insulin release due to glucose in the perfused rat pancreas. — These findings suggest a diabetogenic effect of PRL. CB 154 might be a useful drug in improving glucose utilization in hormone-active pituitary tumours

Short term variations of tracer transit speed on alpine glaciers

We first present the results of a series of tracer experiments conducted on an alpine glacier (Gornergletscher, Switzerland) over a diurnal discharge cycle. For these injections, a moulin was used into which an ice marginal lake was draining, providing a relatively constant discharge. The measured tracer transit speeds show two diurnal maxima and minima. These findings are qualitatively different to existing observations from two series of injections conducted at Unteraargletscher (Switzerland) using a moulin fed by supraglacial meltwater having a high diurnal variability, which displayed one diurnal maximum and minimum. <br><br> We then develop and use a simple two-component model of the glacier drainage system, comprising a moulin and a channel element, to simulate the measured transit speeds for all three injection series. The model successfully reproduces all the observations and shows that the same underlying processes can produce the qualitatively different behaviour depending on the different moulin input discharge regimes. Using the model, we assess the relative importance of the different measurement quantities, show that frequent measurements of moulin input discharge are indispensable and propose an experiment design to monitor the development of the drainage system over several weeks

Morphology of supported polymer electrolyte ultra-thin films: a numerical study

Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin film morphology at different hydration levels. We use a mean-field-like model we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidences of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed

On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x

We have compared the ground-state energy of several observed or proposed " 2 \sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS), with those of "chain superstructures" (CS) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The model Hamiltonian contains i) the Madelung energy, ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and iii) covalency effects based on known results for $t-J$ models in one and two dimensions. The optimum distribution of charge is determined minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure, and long-range Coulomb interactions, are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb in Phys. Rev.

Doping Dependence of the Pseudogap in La(2-x)Sr(x)CuO(4)

We report the results of Raman scattering experiments on single crystals of La(2-x)Sr(x)CuO(4) that span the range from underdoped (x = 0.10) to overdoped (x =0.22). The spectra are consistent with the existence of a strong anisotropic quasiparticle interaction that results in a normal state depletion of spectral weight from regions of the Fermi surface located near the zone axes. The strength of the interaction decreases rapidly with increasing hole concentration and the spectral evidence for the pseudogap vanishes when the optimum doping level is reached. The results suggest that the pseudogap and superconducting gap arise from different mechanisms.Comment: 7 pages, 6 eps figures, added new sections, figures, reference

Evidence for Magnetic Pseudoscaling in Overdoped La(2-x)Sr(x)CuO(4)

We report the results of electronic Raman scattering experiments on an overdoped La(1.78)Sr(0.22)CuO(4) single crystal as a function of temperature. The scattering rate Gamma(w->0,T) has been determined from the normal state B(1g) spectra in the range 50 K < T < 300 K. Gamma(T) decreases linearly from 300 K to about 175 K and then undergoes a reduction with respect to the expected mean-field behavior. This trend suggests a crossover to pseudoscaling regime at about T(cr)=160 K. The results are in good agreement with the prediction of the nearly antiferromagnetic Fermi liquid model. There is no evidence of a pseudogap in the spectra obtained from this overdoped sample.Comment: RevTex, 4 pages with 3 PS figures included, replaced with minor changes in the text and reference

Graphene: A sub-nanometer trans-electrode membrane

Isolated, atomically thin conducting membranes of graphite, called graphene, have recently been the subject of intense research with the hope that practical applications in fields ranging from electronics to energy science will emerge. Here, we show that when immersed in ionic solution, a layer of graphene takes on new electrochemical properties that make it a trans-electrode. The trans-electrode's properties are the consequence of the atomic scale proximity of its two opposing liquid-solid interfaces together with graphene's well known in-plane conductivity. We show that several trans-electrode properties are revealed by ionic conductivity measurements on a CVD grown graphene membrane that separates two aqueous ionic solutions. Despite this membrane being only one to two atomic layers thick, we find it is a remarkable ionic insulator with a very small stable conductivity that depends on the ion species in solution. Electrical measurements on graphene membranes in which a single nanopore has been drilled show that the membrane's effective insulating thickness is less than one nanometer. This small effective thickness makes graphene an ideal substrate for very high-resolution, high throughput nanopore based single molecule detectors. Sensors based on modulation of graphene's in-plane electronic conductivity in response to trans-electrode environments and voltage biases will provide new insights into atomic processes at the electrode surfaces.Comment: Submitted 12 April 2010 to Nature, where it is under revie