Spin-polarized Shapiro steps and spin-precession-assisted multiple Andreev reflection

We investigate the charge and spin transport of a voltage-biased superconducting point contact coupled to a nanomagnet. The magnetization of the nanomagnet is assumed to precess with the Larmor frequency, $\omega_L$, due to ferromagnetic resonance. The interplay between the ac Josephson current and the magnetization dynamics leads to spin-polarized Shapiro steps at voltages $|V|=\hbar \omega_L/2en$ for $n=1,2,...$ and the subharmonic steps with $n>1$ are a consequence of multiple Andreev reflection (MAR). Moreover, the spin-precession-assisted MAR generates quasiparticle scattering amplitudes that, due to interference, lead to current-voltage characteristics of the dc charge and spin currents with subharmonic gap structures displaying an even-odd effect.Comment: 5 pages, 4 figure

Spin transport and tunable Gilbert damping in a single-molecule magnet junction

We study time-dependent electronic and spin transport through an electronic level connected to two leads and coupled with a single-molecule magnet via exchange interaction. The molecular spin is treated as a classical variable and precesses around an external magnetic field. We derive expressions for charge and spin currents by means of the Keldysh non-equilibrium Green's functions technique in linear order with respect to the time-dependent magnetic field created by this precession. The coupling between the electronic spins and the magnetization dynamics of the molecule creates inelastic tunneling processes which contribute to the spin currents. The inelastic spin currents, in turn, generate a spin-transfer torque acting on the molecular spin. This back-action includes a contribution to the Gilbert damping and a modification of the precession frequency. The Gilbert damping coefficient can be controlled by the bias and gate voltages or via the external magnetic field and has a non-monotonic dependence on the tunneling rates.Comment: 11 pages, 9 figures, final version including corrections to published articl

Spillningsinventering för bestämning av älgbetesbelastning på ungskog

In the 1980’s the moose population in Sweden grew explosively due to big changes in the silviculture with clear cuttings instead of single-tree selection. Clear cuttings brought big areas of young forest and therefore a lot of fodder in one place. Since this change, the discussion about how to manage the moose population has grown into a very big problem. Forest owners think that the population needs to be strongly reduced because of all the damage that is done to the young forest when the moose seeks its food, and the economic losses because of that. At the same time hunters think that the moose population should be maintained at a level that allows a yearly yield, so that they can continue hunting on a yearly basis, which is a large part of the Swedish culture. Both forest owners and hunters are starting to understand that they must begin to cooperate in order to come up with a long lasting solution. Nowadays the attempt is to detect which amount of forest damage that is economically acceptable and on that basis determine how many moose that can be allowed in our forests. Independently on how many moose we should have, we must know have many we do have to be able to manage the population. To find this out, inventories of the moose population needs to be done. One of the most efficient ways of doing this is by droppings inventory and this has also proven to be the most economical way. We know approximately how many times a moose leave droppings every day and by counting all the droppings in one area we then, roughly, know how many moose there are. Most damage done by moose is during wintertime when the food situation is at its worst state. Young forests are then exposed because they are one of the few places moose can find fodder wintertime, due to its accessible branches and tops. Earlier studies show that grazing pressure on young forests are about five times higher than in other forests this time of the year. So to make this all a little more complex, we also need to know how big areas of young forests these moose have access to, to be able to foresee the damages that the moose can do. This is where this study comes in, for the purpose of it is to be the initial element in the quest of enlarging knowledge concerning the quantity and quality of fodder from young forests. Another reason for this study to be done, is for the sake of having a more recent study within the subject of grazing pressure on young forests and the final purpose is to find out if the results from droppings inventory can be used to produce statistically significant key figures that can be used to find out what the grazing pressure in one area really looks like. To be able to find this out, comparisons have been done to the earlier studies that say that the grazing pressure approximately would be about five times higher in young forests

Josephson current through a precessing classical spin

International audienceA study of the dc Josephson current between two superconducting leads in the presence of a precessing classical spin is presented. The precession gives rise to a time-dependent tunnel potential which not only implies different tunneling probabilities for spin-up and spin-down quasiparticles, but introduces also a time-dependent spin-flip term. We provide an exact general analytic solution for the out-of-equilibrium steady-state permanent current between two spin-singlet superconductors as a function of the superconducting phase difference, the precession frequency and for arbitrary junction transparency. As an application we focus on the effects of the spin-flip term alone and show that the magnitude and nature of the Josephson current are indeed strongly affected by the precession of the classical spin

Smuggling

Smuggling – Innehållsförteckning: – Gästskribenten Sandra Bergqvist / Det unika måste få ett eget språk – Notiser – Tack! / Pia Prost och Cecilia Lundberg – Fakta om förbudstiden 1919–1932 / Pia Prost – Romantik och ryslighet / Fredrik Nilsson – En skärgård som gjord för smuggling / Liselott Nyström Forsén – ”Den bästa tiden var spiritiden” / Keth Strömdahl – Smugglingen blir permanent i Rönnäs / Thure Malmberg – Berättelser från förbudstiden blev en smuggelbok / Cecilia Lundberg – Fotoalbum berättar / Marianne Ström – Då människor och tidningar smugglades genom Åbolands skärgård / Pia Heikkilä – Öppen kritik i dagspressen – ålänningarnas syn på förbudstiden / Hanna Dahlbom – Vi hade svultit ihjäl om inte spriten kommit / Olof Öström – Smugglare och förbjuden sprit i Västnyland / Carolina Holmqvist – Smugglare och smuggelgods av dags dato / Pia Prost – En ar i taget / Mikko Jokinen, Jouko Lehtonen och RiittaLiisa Pettersson – Min ö Replot / Linda Ahlbäck – Skärinytt – Sista bilde

Fiber Mediated Receptor Masking in Non-Infected Bystander Cells Restricts Adenovirus Cell Killing Effect but Promotes Adenovirus Host Co-Existence

The basic concept of conditionally replicating adenoviruses (CRAD) as oncolytic agents is that progenies generated from each round of infection will disperse, infect and kill new cancer cells. However, CRAD has only inhibited, but not eradicated tumor growth in xenograft tumor therapy, and CRAD therapy has had only marginal clinical benefit to cancer patients. Here, we found that CRAD propagation and cancer cell survival co-existed for long periods of time when infection was initiated at low multiplicity of infection (MOI), and cancer cell killing was inefficient and slow compared to the assumed cell killing effect upon infection at high MOI. Excessive production of fiber molecules from initial CRAD infection of only 1 to 2% cancer cells and their release prior to the viral particle itself caused a tropism-specific receptor masking in both infected and non-infected bystander cells. Consequently, the non-infected bystander cells were inefficiently bound and infected by CRAD progenies. Further, fiber overproduction with concomitant restriction of adenovirus spread was observed in xenograft cancer therapy models. Besides the CAR-binding Ad4, Ad5, and Ad37, infection with CD46-binding Ad35 and Ad11 also caused receptor masking. Fiber overproduction and its resulting receptor masking thus play a key role in limiting CRAD functionality, but potentially promote adenovirus and host cell co-existence. These findings also give important clues for understanding mechanisms underlying the natural infection course of various adenoviruses

Studies on hybrid superconducting junctions

In the field of nanoelectronics, one seeks to combine quantum mechanical effects with macroscopic entities such as currents in order to find new ways of storing and manipulating information. One possibility to accomplish this is to use the quantum correlations found in superconductors. Teaming superconductors with normal metals and magnetic systems, one can obtain novel correlation and fluctuation effects. In the first work of this thesis, we examine how charge correlations in a metallic dot are modified due to the presence of a capacitively coupled superconducting island. It is possible to overcome the Coulomb repulsion between electrons in a hybrid double-dot system consisting of a metallic island coupled capacitively to a Cooper-pair box. The superconducting island S acts as a dynamic gate on the metallic island N and in the strong coupling regime the electric charge of the Cooper pairs in S and their fluctuations are able to overscreen the repulsion between electrons in N. This produces an attractive interaction between two additional electrons in the metallic island and results in a non-monotonous charging curve of the metallic island. The second part of the thesis considers how the dynamics of a precessing molecular magnetic moment affects the Josephson current. The precession gives rise to a time-dependent tunnel potential which not only creates different tunneling probabilities for spin-up and spin-down quasiparticles, but also introduces a time-dependent spin-flip term. In particular, we study the effects of the spin-flip term alone on the Josephson current between two spin-singlet superconductors as a function of precession frequency and junction transparency. The system displays a nonequilibrium steady-state solution which depends on the precession frequency of the classical spin