126 research outputs found
Weak Localization Coexisting with a Magnetic Field in a Normal-Metal--Superconductor Microbridge
A random-matrix theory is presented which shows that breaking time-reversal
symmetry by itself does {\em not} suppress the weak-localization correction to
the conductance of a disordered metal wire attached to a superconductor.
Suppression of weak localization requires applying a magnetic field as well as
raising the voltage, to break both time-reversal symmetry and electron-hole
degeneracy. A magnetic-field dependent contact resistance obscured this anomaly
in previous numerical simulations.Comment: 8 pages, REVTeX-3.0, 1 figur
Adiabatic Dynamics of Superconducting Quantum Point Contacts
Starting from the quasiclassical equations for non-equilibrium Green's
functions we derive a simple kinetic equation that governs ac Josephson effect
in a superconducting quantum point contact at small bias voltages. In contrast
to existing approaches the kinetic equation is valid for voltages with
arbitrary time dependence. We use this equation to calculate
frequency-dependent linear conductance, and dc characteristics with
and without microwave radiation for resistively shunted quantum point contacts.
A novel feature of the characteristics is the excess current
appearing at small voltages. An important by-product of our
derivation is the analytical proof that the microscopic expression for the
current coincides at arbitrary voltages with the expression that follows from
the Bogolyubov-de Gennes equations, if one uses appropriate amplitudes of
Andreev reflection which contain information about microscopic structure of the
superconductors.Comment: 12 Pages, REVTEX 3.0, 3 figures available upon reques
Additive sustainability footprint: Rationale and pilot evaluation of a tool for assessing the sustainable use of PVC additives
© 2019 The Authors. Journal of Vinyl and Additive Technology published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers. PVC compounds contain additives necessary for processing and stability, and to modify the plastic's properties. The Europe-wide VinylPlusŸ voluntary commitment includes a challenge to make progress toward sustainable use of additives. Additive Sustainability Footprint (ASF) was developed to assess sustainable use of additives across the whole societal life cycles of finished PVC articles, taking a risk-based approach rather than simplistic hazard assessment. ASF addresses impacts across six life cycle assessment (LCA) stages established by ISO Standard 14040, using the four System Conditions (sustainability principles) developed by The Natural Step (TNS) covering social as well as environmental factors. For each LCA stage/System Condition combination, seven generically similar questions cover negative impacts (many covered by existing tools and regulations) but also the additive's positive contributions to the sustainability of finished articles. Positive contributions include ethical sourcing, longevity of service life, low maintenance inputs, and recyclability. Answers to questions determine a score, which can be combined across the life cycle and with other additives. Testing on a generic EU PVC window profile supported ASF development and demonstrated applicability and potential benefits including use for sensitivity analysis of alternative additives from different geopolitical regions or from recycled as opposed to virgin sources. J. VINYL ADDIT. TECHNOL., 2019. © 2019 The Authors. Journal of Vinyl and Additive Technology published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers
Dissipative Electron Transport through Andreev Interferometers
We consider the conductance of an Andreev interferometer, i.e., a hybrid
structure where a dissipative current flows through a mesoscopic normal (N)
sample in contact with two superconducting (S) "mirrors". Giant conductance
oscillations are predicted if the superconducting phase difference is
varied. Conductance maxima appear when is on odd multiple of due
to a bunching at the Fermi energy of quasiparticle energy levels formed by
Andreev reflections at the N-S boundaries. For a ballistic normal sample the
oscillation amplitude is giant and proportional to the number of open
transverse modes. We estimate using both analytical and numerical methods how
scattering and mode mixing --- which tend to lift the level degeneracy at the
Fermi energy --- effect the giant oscillations. These are shown to survive in a
diffusive sample at temperatures much smaller than the Thouless temperature
provided there are potential barriers between the sample and the normal
electron reservoirs. Our results are in good agreement with previous work on
conductance oscillations of diffusive samples, which we propose can be
understood in terms of a Feynman path integral description of quasiparticle
trajectories.Comment: 24 pages, revtex, 12 figures in eps forma
Stacked crop rotations and cultural practices for canola and flax yield and quality
Canola (Brassica napus L.) and flax (Linum usitatissimum L.) are important oilseed crops, but improved management practices to enhance their yields and quality are needed. We studied the effect of stacked versus alternateâyear crop rotations and traditional versus improved cultural practices on canola and flax growth, seed yield, oil concentration, and Nâuse efficiency from 2006 to 2011 in the northern Great Plains, USA. Stacked rotations were durum (Triticum turgidum L.)âdurumâcanolaâpea (Pisum sativum L.) (DDCP) and durumâdurumâflaxâpea (DDFP). Alternateâyear rotations were durumâcanolaâdurumâpea (DCDP) and durumâflaxâdurumâpea (DFDP). The traditional cultural practice included a combination of conventional tillage, recommended seed rate, broadcast N fertilization, and reduced stubble height. The improved cultural practice included a combination of noâtillage, increased seed rate, banded N fertilization, and increased stubble height. Canola stand count was 36â123% greater with the improved than the traditional cultural practice in 2006, 2009, 2010, and 2011. Canola pod number and oil concentration were 3â36% greater in the improved than the traditional practice in 2007 and 2010, but trends reversed by 5â19% in 2008. Flax stand count was 28% greater with DFDP than DDFP in 2007 and 56% greater in the improved than the traditional practice in 2010. Flax pod number, seed weight, seed yield, N content, Nâuse efficiency, and Nâremoval index varied with crop rotations, cultural practices, and years. Canola growth and oil concentration increased with the improved cultural practice as well as flax growth, yield, and quality enhanced with alternateâyear crop rotation and the improved cultural practice in wet years
Species trait shifts in vegetation and soil seed bank during fen degradation
Fens in Central Europe are characterised by waterlogged organic substrate and low productivity. Human-induced changes due to drainage and mowing lead to changes in plant species composition from natural fen communities to fen meadows and later to over-drained, degraded meadows. Moderate drainage leads to increased vegetation productivity, and severe drainage results in frequent soil disturbances and less plant growth. In the present article, we analyse changes in plant trait combinations in the vegetation and the soil seed bank as well as changes in the seed bank types along gradient of drainage intensity. We hypothesize that an increase in productivity enhances traits related to persistence and that frequent disturbance selects for regeneration traits. We use multivariate statistics to analyse data from three disturbance levels: undisturbed fen, slightly drained fen meadow and severely drained degraded meadow. We found that the abundance of plants regenerating from seeds and accumulating persistent seed banks was increasing with degradation level, while plants reproducing vegetatively were gradually eliminated along the same trajectory. Plants with strong resprouting abilities increased during degradation. We also found that shifts in trait combinations were similar in the aboveground vegetation and in soil seed banks. We found that the density of short-term persistent seeds in the soil is highest in fen meadows and the density of long-term persistent seeds is highest in degraded meadows. The increase in abundance of species with strong regeneration traits at the cost of species with persistence-related traits has negative consequences for the restoration prospects of severely degraded sites
Transmission formalism for supercurrent flow in multiprobe superconductor-semiconductor-superconductor devices
Recommended temperature metrics for carbon budget estimates, model evaluation and climate policy
Recent estimates of the amount of carbon dioxide that can still be emitted while achieving the Paris Agreement temperature goals are larger than previously thought. One potential reason for these larger estimates may be the different temperature metrics used to estimate the observed global mean warming for the historical period, as they affect the size of the remaining carbon budget. Here we explain the reasons behind these remaining carbon budget increases, and discuss how methodological choices of the global mean temperature metric and the reference period influence estimates of the remaining carbon budget. We argue that the choice of the temperature metric should depend on the domain of application. For scientific estimates of total or remaining carbon budgets, globally averaged surface air temperature estimates should be used consistently for the past and the future. However, when used to inform the achievement of the Paris Agreement goal, a temperature metric consistent with the science that was underlying and directly informed the Paris Agreement should be applied. The resulting remaining carbon budgets should be calculated using the appropriate metric or adjusted to reflect these differences among temperature metrics. Transparency and understanding of the implications of such choices are crucial to providing useful information that can bridge the scienceâpolicy gap
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