ARXPS-studies ofcˆ-axis textured YBa2Cu3Ox-films

YBa2Cu3Ox sputter deposited cold on MgO grows in O2 annealing epitaxially to a transparent, superconducting film with Tc 80K. The unscraped surfaces of these films are smooth showing XPS lines changing with photoelectron take-off angle. This enhanced data base allows to separate the different chemical compounds (hydroxide, peroxide, carbonate, carboxyle, cuprate, graphite ...) and to obtain their spatial distribution. This yields the compounds, their amount and distribution making up the cinder growing with O2-anneal at internal and external surfaces. The cinder stoichiometry gives insights in the chemistry going on in O2 annealing. Below the cinder the signature ofcˆ-axis oriented YBa2Cu3Ox is identified, showing that a Ba-oxide layer forms the stable surface. This coats insulating CuO2 and Y-oxide layers yielding so an intrinsic dead layer

Highly balanced gradiometer systems based on HTS-SQUIDs for the use in magnetically unshielded environment

Two different concepts for gradiometer formation were tested applying high-temperature rf SQUIDs operated at 77 K in liquid nitrogen. All gradiometer systems are fully based on magnetometers. The first concept applies a compensating magnetometer at different positions to actively cancel the magnetic field at the location of other magnetometers. These magnetometers were arranged in an axial direction. In parts, a system of superconducting plates was used to align the relative magnetic orientation of the magnetometers. The outputs of these sensors were used to form a highly balanced electronic gradiometer. The second concept is based on electronic noise cancellation. A set of three magnetometers arranged in an axial direction was used to form an electronic second-order gradiometer. Different types of reference systems based on HTS-SQUID magnetometers and fluxgate sensors were applied to the gradiometer signal for achieving a high common mode rejection of the environmental disturbances. The performance of the different systems is demonstrated in a magnetically unshielded environment as well as in a shielded environment and the common mode rejection of homogeneous magnetic fields is measured. To demonstrate the performance of the systems, biomagnetic measurements have been performed in shielded and unshielded environment

Measurement of the 187Re({\alpha},n)190Ir reaction cross section at sub-Coulomb energies using the Cologne Clover Counting Setup

Uncertainties in adopted models of particle+nucleus optical-model potentials directly influence the accuracy in the theoretical predictions of reaction rates as they are needed for reaction-network calculations in, for instance, {\gamma}-process nucleosynthesis. The improvement of the {\alpha}+nucleus optical-model potential is hampered by the lack of experimental data at astrophysically relevant energies especially for heavier nuclei. Measuring the Re187({\alpha},n)Ir190 reaction cross section at sub-Coulomb energies extends the scarce experimental data available in this mass region and helps understanding the energy dependence of the imaginary part of the {\alpha}+nucleus optical-model potential at low energies. Applying the activation method, after the irradiation of natural rhenium targets with {\alpha}-particle energies of 12.4 to 14.1 MeV, the reaction yield and thus the reaction cross section were determined via {\gamma}-ray spectroscopy by using the Cologne Clover Counting Setup and the method of {\gamma}{\gamma} coincidences. Cross-section values at five energies close to the astrophysically relevant energy region were measured. Statistical model calculations revealed discrepancies between the experimental values and predictions based on widely used {\alpha}+nucleus optical-model potentials. However, an excellent reproduction of the measured cross-section values could be achieved from calculations based on the so-called Sauerwein-Rauscher {\alpha}+nucleus optical-model potential. The results obtained indicate that the energy dependence of the imaginary part of the {\alpha}+nucleus optical-model potential can be described by an exponential decrease. Successful reproductions of measured cross sections at low energies for {\alpha}-induced reactions in the mass range 141{\leq}A{\leq}187 confirm the global character of the Sauerwein-Rauscher potential

Bench-scale photoelectrocatalytic reactor utilizing rGO-TiO2 photoanodes for the degradation of contaminants of emerging concern in water

Pharmaceuticals and personal care products are contaminants of emerging concern (CEC) in water. Photocatalysis (PC) and photoelectrocatalysis (PEC) are potential advanced oxidation processes for the effective degradation of these contaminants. In this work a bench-scale photoelectrocatalytic reactor utilizing a UVA-LED array was designed and tested for the degradation of diclofenac as a model CEC. Reduced graphene oxide-titanium dioxide (rGO-TiO2) composite, prepared by the photocatalytic reduction of rGO on TiO2, was immobilised on fluorine doped tin oxide (FTO) glass and evaluated as a photoanode. The influence of UVA intensity and rGO:TiO2 ratio on the degradation rate was studied. Surface modification of the TiO2 with 1% rGO gave the highest photocurrent and best degradation rate of diclofenac, as compared to unmodified TiO2. However, following repeat cycles of photoelectrocatalytic treatment there was an observed drop in the photocurrent with rGO-TiO2 anodes and the rate of diclofenac degradation decreased. Raman and XPS analysis indicated the re-oxidation of the rGO. Attempts to regenerate the rGO in-situ by electrochemical reduction did not prove successful, suggesting that the site of photoelectrocatalytic oxidation of rGO was different to the reduction site targeted in the photocatalytic reduction for the formation of the rGO-TiO2 composites

The Peopling of Europe from the Mitochondrial Haplogroup U5 Perspective

It is generally accepted that the most ancient European mitochondrial haplogroup, U5, has evolved essentially in Europe. To resolve the phylogeny of this haplogroup, we completely sequenced 113 mitochondrial genomes (79 U5a and 34 U5b) of central and eastern Europeans (Czechs, Slovaks, Poles, Russians and Belorussians), and reconstructed a detailed phylogenetic tree, that incorporates previously published data. Molecular dating suggests that the coalescence time estimate for the U5 is ∼25–30 thousand years (ky), and ∼16–20 and ∼20–24 ky for its subhaplogroups U5a and U5b, respectively. Phylogeographic analysis reveals that expansions of U5 subclusters started earlier in central and southern Europe, than in eastern Europe. In addition, during the Last Glacial Maximum central Europe (probably, the Carpathian Basin) apparently represented the area of intermingling between human flows from refugial zones in the Balkans, the Mediterranean coastline and the Pyrenees. Age estimations amounting for many U5 subclusters in eastern Europeans to ∼15 ky ago and less are consistent with the view that during the Ice Age eastern Europe was an inhospitable place for modern humans

Vortex trapping and expulsion in thin-film YBCO strips

A scanning SQUID microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBCO strips for strip widths W from 2 to 50 um. We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc. We present a simple model for the vortex exclusion process which takes into account the vortex - antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n=(Ba-BK)/Phi0 with BK = 1.65Phi0/W^2 and Phi0 = h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35 um wide strip was (2.89 + 1.91-0.93)Bc, consistent with a numerical prediction

GRAIL, an omni-directional gravitational wave detector

A cryogenic spherical and omni-directional resonant-mass detector proposed by the GRAIL collaboration is described.Comment: 5 pages, 4 figs., contribution to proceedings GW Data Analysis Workshop, Paris, nov. 199