153 research outputs found
Quantum pumping in graphene nanoribbons at resonant transmission
Adiabatic quantum charge pumping in graphene nanoribbon double barrier
structures with armchair and zigzag edges in the resonant transmission regime
is analyzed. Using recursive Green's function method we numerically calculate
the pumped charge for pumping contours encircling a resonance. We find that for
armchair ribbons the whole resonance line contributes to the pumping of a
single electron (ignoring double spin degeneracy) per cycle through the device.
The case of zigzag ribbons is more interesting due to zero-conductance
resonances. These resonances separate the whole resonance line into several
parts, each of which corresponds to the pumping of a single electron through
the device. Moreover, in contrast to armchair ribbons, one electron can be
pumped from the left lead to the right one or backwards. The current direction
depends on the particular part of the resonance line encircled by the pumping
contour.Comment: 6 pages, 5 figures. This is an author-created, un-copyedited version
of an article accepted for publication in EPL. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at 10.1209/0295-5075/92/4701
Mammal fauna during the Late Pleistocene and Holocene in the far northeast of Europe
The paper summarises materials on the mammal remains in northeastern Europe, dated by radiocarbon. Altogether, 23 local faunas of small mammals and 47 local faunas of large mammals were analysed. Multidimensional statistical analysis shows a strong correlation between changes in small mammal fauna composition and climate changes throughout time. The correlations with the spatial gradients, however, are less pronounced. The faunas are classified into three groups: (1) faunas of Holocene age; (2) Late Pleistocene āstadialā assemblages; and (3) Late Pleistocene āinterstadialā assemblages. In some cases, changes in species abundance are better understood in terms of biotic interrelations rather than of climatic effects. The most pronounced change in small mammal fauna composition and structure occurred at the Preboreal/Boreal boundary, and a less conspicuous alteration took place at the LGM/Lateglacial transition. The most noticeable transformation in the large mammal fauna composition is dated to the early Holocene. Less significant changes are observed at the Middle Weichselian/LGM transition and at the LGM/Lateglacial transition. It is safely concluded that variations in the faunas of small and large mammals recorded in NE Europe during the last 35 000 years occurred synchronously and unidirectionally.
Late persistence and deterministic extinction of āhumid thermophilous plant taxa of East Asian affinityā (HUTEA) in southern Europe
Adiabatic quantum pumping in graphene with magnetic barriers
We study an adiabatic quantum pump effect in a two terminal graphene device with two
oscillating square electric barriers and a stationary magnetic barrier using the
scattering matrix approach. The model employs the low-energy Dirac approximation and
incorporates the possible existence of a finite band gap in graphene spectrum. We show
that in this case valley-polarized and pure valley currents can be pumped due to the
valley symmetry breaking. For a Ī“-function magnetic barrier we present
analytical expressions for bilinear total and valley pumping responses. These results are
compared to numerical ones for a double Ī“-function, a square and a triple
square magnetic barriers
Vegetation and climate changes during the Eemian interglacial in Central and Eastern Europe: comparative analysis of pollen data
Paradoxes of the Last Interglacial climate: reconstruction of the northern Eurasia climate based on palaeofloristic data
The effects of Pleistocene glaciations on the phylogeography of Melitaea cinxia (Lepidoptera: Nymphalidae)
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