Photon heat transport in low-dimensional nanostructures

At low temperatures when the phonon modes are effectively frozen, photon transport is the dominating mechanism of thermal relaxation in metallic systems. Starting from a microscopic many-body Hamiltonian, we develop a nonequilibrium Green's function method to study energy transport by photons in nanostructures. A formally exact expression for the energy current between a metallic island and a one-dimensional electromagnetic field is obtained. From this expression we derive the quantized thermal conductance as well as show how the results can be generalized to nonequilibrium situations. Generally, the frequency-dependent current noise of the island electrons determines the energy transfer rate.Comment: 4 pages, 3 Fig

Huge thermoelectric effects in ferromagnet-superconductor junctions in the presence of a spin-splitting field

We show that a huge thermoelectric effect can be observed by contacting a superconductor whose density of states is spin-split by a Zeeman field with a ferromagnet with a non-zero polarization. The resulting thermopower exceeds $k_B/e$ by a large factor, and the thermoelectric figure of merit $ZT$ can far exceed unity, leading to heat engine efficiencies close to the Carnot limit. We also show that spin-polarized currents can be generated in the superconductor by applying a temperature bias.Comment: 5 pages, 4 figure

Odelman typpilannoituksen ja niittoajan vaikutus timoteinurmen satoon

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Thermal conductance of a proximity superconductor

We study heat transport in hybrid normal metal - superconductor - normal metal (NSN) structures. We find the thermal conductance of a short superconducting wire to be strongly enhanced beyond the BCS value due to inverse proximity effect. The measurements agree with a model based on the quasiclassical theory of superconductivity in the diffusive limit. We determine a crossover temperature below which quasiparticle heat conduction dominates over the electron-phonon relaxation.Comment: 4+ pages, 3 figure

Effects of sodium sulphate and potassium chloride fertilizers on the nutritive value of timothy grown on different soils

Third harvest samples from a pot experiment were analysed to study the effects of sodium (Na) (0, 200 and 400 mg dm-3 of soil in a single application as Na2SO4 . 10H2O) and potassium (K) application (0, 100 and 200 mg dm-3 applied at each harvest as KCl) on the nutritive value of timothy grown on three different soil types (clay, loam and organogenic soil). The effects of fertilization on concentrations of crude protein, neutral detergent fibre (NDF) and non-structural carbohydrates, although statistically significant, were relatively minor in absolute terms. Na applications increased and K applications decreased sulphur and phosphorus concentrations, the magnitude of which was dependent on soil type. The increase in sulphur concentration can be attributed to sulphate in Na-fertilizer. The effects of fertilizers on in vitro organic matter digestibility and the potential extent of dry matter (DM) and NDF digestibility were small. Digestion kinetic parameters estimated from fermentative gas production measured using a fully automated system were used in a rumen simulation model to estimate digestibility. Total gas volume and the rate of gas production from the rapidly digestible fraction were negatively correlated with timothy S and N concentrations. Na application had no effect, but K application increased true rumen DM digestibility, the effect being most profound on organogenic soil. The results suggest that Na application does not elicit substantial positive effects on the nutritive value of timothy which has often been reported for perennial ryegrass, but K application can improve the nutritive value of timothy grown on K deficient soil.;Tutkimuksen tavoitteena oli selvitettää natrium- ja kaliumlannoituksen vaikutusta timotein ravintoarvoon. Näytteet olivat Peltovuoren ja Yli-Hallan (1997) astiakokeesta, jossa selvitettiin Na- ja K-lannoituksen vaikutusta timotein Na, K,Ca ja Mg-pitoisuuteen ja satoon savi-, hieta- ja turvemaalla. Käytetyt ravinnemäärät olivat 0, 200 tai 400 mg Na l-1 kokeen alussa natriumsulfaattina ja 0, 100 tai 200 mg K 1-1 joka sadolle kaliumkloridina. Tähän tutkimukseen valittiin kolmannen sadon näytteet, koska niissä Na-pitoisuuden vaihtelu oli suurin (0,16-7,13 g kg-1). Vaikka timotei luetaan ns. natrofobisiin kasveihin, jotka ottavat huonosti natriumia versoihin, nousi timotein natriumpitoisuus huomattavasti. Na- ja K-lannoituksen vaikutusta timotein ravintoarvoon tutkittiin in vitro -kokein ja lisäksi määritettiin typpi, neutraalideterkenttikuitu (NDF), sokeri, rikki ja fosfori. Orgaanisen aineen in vitro -sulavuus määritettiin sellulaasimenetelmällä ja potentiaalinen kuiva-aineen ja NDF:n pötsisulavuus inkuboimalla näytettä 12 vrk nailonpussissa kahden lehmän pötsissä (in situ). Sulatuskinetiikan parametrit määritettiin mikrobikäymisen tuottaman kaasuntuotannon mittauksella ajan funktiona automaattisella mittauslaitteella, ja dynaamisen ja pötsimallin perusteella laskettiin potentiaalisesti sulavan kuiva-aineen pötsisulavuus ja kuiva-aineen todellinen pötsisulavuus. Lannoituksen vaikutus raakavalkuais-, NDF- ja sokeripitoisuuteen oli pieni. Na-lannoitus lisäsi hieman ja K-lannoitus vähensi typpipitoisuutta ja molemmat vähensivät laskennallista sokeripitoisuutta. NDF-pitoisuus nousi hieman Na-lannoituksella. Na-lannoitus lisäsi ja K-lannoitus vähensi rikki- ja fosforipitoisuutta vaikutuksen riippuessa maalajista. Na-lannoituksen vaikutukset orgaanisen aineen in vitro sulavuuteen sekä potentiaaliseen kuiva-aineen ja NDF:n pötsisulavuuteen olivat pieniä, vaikkakin tilastollisesti merkitseviä. Kokonaiskaasutuotanto ja nopeasti sulavan fraktion kaasutuotannon nopeus vähenivät, kun timotein typpi-, rikki-, kalsium-, magnesium-, fosfori- ja natriumpitoisuudet nousivat. Na-lannoituksella ei ollut vaikutusta sulatuskinetiikan parametreihin ja estimoituun potentiaalisesti sulavan kuiva-aineen pötsisulavuuteen tai kuiva-aineen todelliseen pötsisulavuuteen, kun taas K-lannoitus lisäsi hieman nopeasti sulavan fraktion kaasutuotannon nopeutta ja todellista kuiva-aineen pötsisulavuutta. Kaliumin vaikutus oli selvin turvemaalla. Maalajien välillä oli eroja kaasuntuotannon määrässä ja potentiaalisesti sulavan kuiva-aineen ja todellisessa kuiva-aineen pötsisulavuudessa, savimaa ruoho oli huonoiten ja turvemaan ruoho parhaiten sulavaa. Näiden tulosten mukaan Na-lannoituksella ei näytä olevan samanlaisia myönteistä vaikutusta timotein ravintoarvoon kuin brittiläistutkimuksissa on usein esitetty englannin raiheinällä, mutta K-lannoitus voi parantaa timotein ravintoarvoa K-puutteesta kärsivillä mailla

Energy relaxation in graphene and its measurement with supercurrent

We study inelastic energy relaxation in graphene for low energies to find out how electrons scatter with acoustic phonons and other electrons. By coupling the graphene to superconductors, we create a strong dependence of the measured signal, i.e.,\ critical Josephson current, on the electron population on different energy states. Since the relative population of high- and low-energy states is determined by the inelastic scattering processes, the critical current becomes an effective probe for their strength. We argue that the electron-electron interaction is the dominant relaxation method and, in our model of two-dimensional electron-electron scattering, we find a scattering time $\tau_{e-e}=5... 13$ ps at T=500 mK, 1-2 orders of magnitude smaller than predicted by theory.Comment: 10 pages, 13 figures submitted to Physical Review

Microwave response of an NS ring coupled to a superconducting resonator

A long phase coherent normal (N) wire between superconductors (S) is characterized by a dense phase dependent Andreev spectrum . We probe this spectrum in a high frequency phase biased configuration, by coupling an NS ring to a multimode superconducting resonator. We detect a dc flux and frequency dependent response whose dissipative and non dissipative components are related by a simple Debye relaxation law with a characteristic time of the order of the diffusion time through the N part of the ring. The flux dependence exhibits $h/2e$ periodic oscillations with a large harmonics content at temperatures where the Josephson current is purely sinusoidal. This is explained considering that the populations of the Andreev levels are frozen on the time-scale of the experiments.Comment: 5 pages,4 figure

Absorption of heat into a superconductor-normal metal-superconductor junction from a fluctuating environment

We study a diffusive superconductor-normal metal-superconductor junction in an environment with intrinsic incoherent fluctuations which couple to the junction through an electromagnetic field. When the temperature of the junction differs from that of the environment, this coupling leads to an energy transfer between the two systems, taking the junction out of equilibrium. We describe this effect in the linear response regime and show that the change in the supercurrent induced by this coupling leads to qualitative changes in the current-phase relation and for a certain range of parameters, an increase in the critical current of the junction. Besides normal metals, similar effects can be expected also in other conducting weak links.Comment: 5 pages, 4 figures - supplementary information included: 3 pages, 1 figure; minor modifications to the text and Fig. 2, added Ref. 1