Dynamical Coulomb blockade and spin-entangled electrons

We consider the production of mobile and nonlocal pairwise spin-entangled electrons from tunneling of a BCS-superconductor (SC) to two normal Fermi liquid leads. The necessary mechanism to separate the two electrons coming from the same Cooper pair (spin-singlet) is achieved by coupling the SC to leads with a finite resistance. The resulting dynamical Coulomb blockade effect, which we describe phenomenologically in terms of an electromagnetic environment, is shown to be enhanced for tunneling of two spin-entangled electrons into the same lead compared to the process where the pair splits and each electron tunnels into a different lead. On the other hand in the pair-split process, the spatial correlation of a Cooper pair leads to a current suppression as a function of distance between the two tunnel junctions which is weaker for effectively lower dimensional SCs.Comment: 5 pages, 2 figure

Broaching the brook : daylighting, community and the ‘stickiness’ of water

Over the last century, under the modern hydraulic model, waterways across the world have been heavily canalized and culverted, driven into underground pipes, drains and sewers. This hydraulic approach has hardwired an isolated water network into the urban fabric, fragmenting erstwhile patterns and dynamics of life, both human and nonhuman. Ecologically, it has been hugely damaging, reducing water quality and biotic diversity, but also socially, disconnecting citizens from the waterways that service and characterize the city. Consequently, since the 1990s, waterway restoration has become widespread as a design solution to degraded rivers and streams, reinstating compromised hydrological, geomorphological and ecological processes. Deculverting or ‘daylighting’, the focus of this paper, is a radical form of restoration, opening up subterranean, culverted waterways often forgotten by communities above ground. Yet, as this paper emphasizes, waterway restoration has tended to privilege ecological over social objectives, while public engagement in project conceptualization has been limited, conducted ‘downstream’ subsequent to planning and design stages. Restoration schemes have therefore tended to reflect the concerns of professionals rather than communities, overlooking their potential for social renewal and change. Drawing on workshop data collected through participatory mapping exercises, this paper explores the case for daylighting a culverted brook in Urmston, Greater Manchester, focusing in particular on the preferences, concerns and knowledge of local residents. The paper compares professional and community perspectives on the preferred scheme design and potential benefits of daylighting, drawing out differences and tensions between them, temporarily ‘unblackboxing’ the brook. It is ventured that daylighting can unleash the social ‘stickiness’ of water, its proclivity to draw and bind together, to revitalize the park, enhancing connection to wildness, attachment to place and sense of community. This is particularly crucial in the face of decreased local authority funding and related crises in park management

Studies on charge production from Cs2Te photocathodes in the PITZ L-band normal conducting radio frequency photo injector

This paper discusses the behavior of electron bunch charge produced in an L-band normal conducting radio frequency cavity (RF gun) from Cs2Te photocathodes illuminated with ps-long UV laser pulses when the laser transverse distribution consists of a flat-top core with Gaussian-like decaying halo. The produced charge shows a linear dependence at low laser pulse energies as expected in the quantum efficiency limited emission regime, while its dependence on laser pulse energy is observed to be much weaker for higher values, due to space charge limited emission. However, direct plug-in of experimental parameters into the space charge tracking code ASTRA yields lower output charge in the space charge limited regime compared to measured values. The rate of increase of the produced charge at high laser pulse energies close to the space charge limited emission regime seems to be proportional to the amount of halo present in the radial laser profile since the charge from the core has saturated already. By utilizing core + halo particle distributions based on measured radial laser profiles, ASTRA simulations and semi-analytical emission models reproduce the behavior of the measured charge for a wide range of RF gun and laser operational parameters within the measurement uncertainties.Comment: 15 pages, 16 figures, 2 table

Meson-exchange enhancement in first-forbidden β\beta -transitions: the case of 50^{50}K and 38^{38}Ca

The $\beta$- decay of $^{50}$K and $^{38}$Ca have been investigated with the main motive of determining more accurately the first-forbidden $\beta$- branches, in particular the rank-zero, $\Delta$J = 0, $\,\beta$ -transitions. $^{50}$K and $^{38}$Ca have been produced by fragmentation of U and Ti targets respectively, with a 1 GeV proton beam and subsequent on-line mass separation. For $^{50}$K, $\gamma$-ray spectroscopy, as well as delayed neutron spectroscopy by time of flight, were carried out to obtain a detailed decay scheme to 20 (bound and unbound) levels in $^{50}$Ca. The level structur e of $^{50}$Ca can be compared to recent calculations which incorporate 1p1h excitations from the f$_{7/2}$ shell. The first-forbidden $\beta^-$ transition $^{50}$ K(0$^-$)$\,\to{}^{50}$Ca(0$^+$) g.s. has been evaluated for the first time by a direct measurement of $\beta$- and $\gamma$- activities. Its importance (61.0 $\pm$ 7.4$\%$) is interpreted as an effect of the meson-exchange current (MEC) l eading to an enhancement factor of 62(5)$\%$ in comparison with the value predicted by shell-model calculations using the impulse approximation. For the $^{38}$ Ca$\,\to{}^{38}$K decay, chemical selec tive production was obtained through separation of the molecular ion CaF$^+$ without contamination by isobars. In these conditions, the measurement of very weak $\beta$-branches, at a level of 10$^{-3}\%$ decays, could be made and a limit, at the 2$\sigma$-confidence level, has been obtained for the 0$^+\to$ 0$^-$ branch to the level at E$_x$ = 2993 keV (I$_\beta$ < 0.0046$\%$). Imp lications of these results on the general trend of meson-exchange enhancements of first-forbidden transitions within the framework of the spherical shell model are discussed

Half-Periodic Josephson Effect in an s-Wave Superconductor - Normal Metal -d-Wave Superconductor Junction

We predict that the Josephson current in a clean s-wave superconductor-normal metal-d-wave superconductor junction is periodic in superconducting phase difference $\phi$ with period $\pi$ instead of $2\pi$. The frequency of non-stationary Josephson effect is correspondingly $2\omega_J = 4eV.$ The effect is due to coexistence in the normal layer of current carrying Andreev levels with phase differences $\phi$ and $\phi+\pi.$Comment: 4 pages, REVTeX, 3 figure

Mechanisms of Spontaneous Current Generation in an Inhomogeneous d-Wave Superconductor

A boundary between two d-wave superconductors or an s-wave and a d-wave superconductor generally breaks time-reversal symmetry and can generate spontaneous currents due to proximity effect. On the other hand, surfaces and interfaces in d-wave superconductors can produce localized current-carrying states by supporting the T-breaking combination of dominant and subdominant order parameters. We investigate spontaneous currents in the presence of both mechanisms and show that at low temperature, counter-intuitively, the subdominant coupling decreases the amplitude of the spontaneous current due to proximity effect. Superscreening of spontaneous currents is demonstrated to be present in any d-d (but not s-d) junction and surface with d+id' order parameter symmetry. We show that this supercreening is the result of contributions from the local magnetic moment of the condensate to the spontaneous current.Comment: 4 pages, 5 figures, RevTe

Effect of Level of Surface Spoilage on the Nutritive Value of Maize Silage Diets

This study determined the effect of surface spoilage in the diet on feed intake and nutrient digestibilities using growing steers fed whole-plant maize silage-based diets. A bunker silo, 0.9 m in depth, and a 2.7 m diameter AgBag were filled with alternating loads of chopped forage. After 90 days, the bunker was sealed with a sheet of polyethylene, and this silage was designated “spoiled”. The silage in the AgBag was designated “normal”. The four diets contained 90% silage and 10% supplement (dry matter basis), and the proportions of silage in the diets were A) 100% normal, B) 75% normal: 25% spoiled; C) 50% normal: 50% spoiled; and D) 25% normal: 75% spoiled. Feed intake decreased linearly as the proportion of spoiled silage increased from 0 to 75%. Steers consuming the normal silage diet had the highest nutrient digestibilities. Spoiled silage also had negative associative effects on nutrient digestibilities, and the integrity of the forage mat in the rumen was partially destroyed

On reminder effects, drop-outs and dominance: evidence from an online experiment on charitable giving

We present the results of an experiment that (a) shows the usefulness of screening out drop-outs and (b) tests whether different methods of payment and reminder intervals affect charitable giving. Following a lab session, participants could make online donations to charity for a total duration of three months. Our procedure justifying the exclusion of drop-outs consists in requiring participants to collect payments in person flexibly and as known in advance and as highlighted to them later. Our interpretation is that participants who failed to collect their positive payments under these circumstances are likely not to satisfy dominance. If we restrict the sample to subjects who did not drop out, but not otherwise, reminders significantly increase the overall amount of charitable giving. We also find that weekly reminders are no more effective than monthly reminders in increasing charitable giving, and that, in our three months duration experiment, standing orders do not increase giving relative to one-off donations