1,992 research outputs found
Formation of pure two-electron triplet states in weakly coupled quantum dots attached to ferromagnetic leads
Weakly coupled quantum dots in the Pauli spin blockade regime are considered
with respect to spin-dependent transport. By attaching one half-metallic and
one non-magnetic lead, the Pauli spin blockade if formed by a pure triplet
state with spin moment or -1. Furthermore, additional spin blockade
regimes emerge because of full occupation in states with opposite spin to that
of the half-metallic lead.Comment: 6 pages, 2 figures, 1 table, minor changes to appear as publishe
Spin transport properties of a quantum dot coupled to ferromagnetic leads with noncollinear magnetizations
A correct general formula for the spin current through an interacting quantum
dot coupled to ferromagnetic leads with magnetization at an arbitrary angle
is derived within the framework of the Keldysh formalism. Under
asymmetric conditions, the spin current component J_{z} may change sign for
. It is shown that the spin current and spin tunneling
magnetoresistance exhibit different angle dependence in the free and Coulomb
blockade regimes. In the latter case, the competition of spin precession and
the spin-valve effect could lead to an anomaly in the angle dependence of the
spin current.Comment: 7 pages, 4 figures; some parts of the text has been revised in this
version accepted by J. Phys.: Condens. Matte
Chandra X-Ray Point Sources, including Supernova 1979C, in the Spiral Galaxy M100
Six x-ray point sources, with luminosities of in the 0.4--7 keV band, were detected in Chandra
observations of the spiral galaxy M100. One source is identified with supernova
SN 1979C and appears to have roughly constant x-ray flux for the period 16--20
years after the outburst. The x-ray spectrum is soft, as would be expected if
the x-ray emission is due to the interaction of supernova ejecta with
circumstellar matter. Most of the other sources are variable either within the
Chandra observation or when compared to archival data. None are coincident with
the peak of the radio emission at the nucleus. These sources have harder
spectra than the supernova and are likely x-ray binaries. M100 has more bright
x-ray sources than typical for spiral galaxies of its size. This is likely
related to active star formation occurring in the galaxy.Comment: accepted by the Astrophysical Journal, 7 page
Internal Migration and Regional Population Dynamics in Europe: Sweden Case Study
This paper describes the structure of internal migration and population change in Sweden in recent decades, focussing on the years 1988 and 1998 to capture change in the last decade.
Up to the 1970s and again in the early 1990s natural increase play an important role in regional population dynamics. In the late 1990s growing international migration, decreasing fertility and strong net internal migration into large cities increased the importance of migration at both national and local levels. In 1988 migration flows contributed to a pattern of relatively even deconcentration of population. Urban centres and surrounding communities experienced mixed patterns of growth. The pattern observed in 1998 was entirely different. It showed a strong movement up the urban hierarchy. Rural and remote areas, especially those in Norrland, depopulated. In 1998 migrants moved from low-density areas to high-density. High density areas had much higher population gains than low density over the 1988–1998 period.
There is a difference in migration pattern between the north of the country, which mostly loses population and the central and southern parts, which mostly gain people. The pattern of migration of the Swedish population is, to large extent, related to the level of unemployment. Low unemployment areas attract migrants; high unemployment areas lose them. However, the level of unemployment cannot be considered in isolation, because the level of unemployment is correlated with the level of urbanisation and with type of regional economy. Areas with an educated population have a very strong attraction for migrants. A high level of education is indispensable for high level services, including tertiary education, and for high technology enterprises, which attract migrants. Young people migrate to metropolitan areas and university towns out of the other types of municipality. Medium sized municipalities attract families. Outflows from industrial regions and Inner Norrland municipalities are visible in all age groups. Metropolitan areas are gaining popularity among families. The elderly population migrates to university and medium size municipalities
Stability analysis of boundary layers controlled by miniature vortex generators
It is currently known that Tollmien–Schlichting (TS) waves can be attenuated by the introduction of spanwise mean velocity gradients in an otherwise two-dimensional boundary layer (BL). The stabilizing effect, associated with an extra turbulence production term, is strong enough to obtain a delay in transition to turbulence induced by TS waves, with the implication of reducing skin-friction drag. Miniature vortex generators (MVGs), mounted in an array, have successfully been used to obtain velocity modulations by the generation of alternating high- and low-speed streaks in the spanwise direction to control the BL. Experimentally, an initial amplification of the TS waves has been reported, which takes place in the near-wake region of the MVG array. The higher the streak amplitude, the stronger the downstream stabilizing effect becomes, but with the drawback of experiencing an even stronger initial amplification. This can lead to a sub-critical transitional Reynolds number, which would not only mean that the control has failed but, even worse, also lead to an advancement of the transition location. Here, direct numerical simulations and a local spatial stability analysis have been performed in order to reach a deeper understanding of this behaviour. The results agree well with experiments and we propose an explanation of the described behavior in terms of stability properties of the controlled BL. This important knowledge can be used in future designs of BL modulators, which can lead to improved stability of the control and to an extended region of laminar flow
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