541 research outputs found
Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers
Epitaxially grown multilayer systems offer the possibility to study the
influence of ferromagnetism on superconductivity in a new and controlled way.
In this paper, we explore how the superconducting properties of high quality,
epitaxially-grown superconductor/normal-metal/ferromagnet trilayers evolve as a
function of the exchange splitting in the ferromagnet, and the thickness of the
normal metal layer. We report results for Nb(110)/Au(111)/Co(0001), and make a
detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use
quantitative FFT analysis to confirm the existence of a long-period (2.1 nm)
oscillation in the superconducting transition temperature Tc as a function of
the Au-layer thickness tAu, for tAu>2 nm, and highlight an additional
short-period (0.76 nm) oscillation for tAu<3 nm in Nb/Au/Co. This short-period
oscillation can be explained in terms of a damped RKKY-like oscillation of the
spin-polarization in Au. The robustness of the long-period oscillation against
the substitution of Co for Fe suggests that it is intrinsic to the Au(111)
layer on Nb, and may represent a new form of quantum interference in very clean
trilayer systems.Comment: 23 pages, 10 figure
Central Bank Independence and the Signaling Effect of Intervention : A Preliminary Exploration
Running title: Central Bank Independence and the Signaling Effect of Interventio
Fully-online Construction of Suffix Trees for Multiple Texts
We consider fully-online construction of indexing data structures for multiple texts. Let T = {T_1, ..., T_K} be a collection of texts. By fully-online, we mean that a new character can be appended to any text in T at any time. This is a natural generalization of semi-online construction of indexing data structures for multiple texts in which, after a new character is appended to the kth text T_k, then its previous texts T_1, ..., T_k-1 will remain static. Our fully-online scenario arises when we maintain dynamic indexes for multi-sensor data. Let N and sigma denote the total length of texts in T and the alphabet size, respectively. We first show that the algorithm by Blumer et al. [Theoretical Computer Science, 40:31-55, 1985] to construct the directed acyclic word graph (DAWG) for T can readily be extended to our fully-online setting, retaining O(N log sigma)-time and O(N)-space complexities. Then, we give a sophisticated fully-online algorithm which constructs the suffix tree for T in O(N log sigma) time and O(N) space. A key idea of this algorithm is synchronized maintenance of the DAWG and the suffix tree
Coupling between pore formation and phase separation in charged lipid membranes
We investigated the effect of charge on the membrane morphology of giant
unilamellar vesicles (GUVs) composed of various mixtures containing charged
lipids. We observed the membrane morphologies by fluorescent and confocal laser
microscopy in lipid mixtures consisting of a neutral unsaturated lipid
[dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid
[dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid
[dioleoylphosphatidylglycerol (DOPG)], a charged saturated
lipid [dipalmitoylphosphatidylglycerol (DPPG)], and
cholesterol (Chol). In binary mixtures of neutral DOPC/DPPC and charged
DOPC/DPPG, spherical vesicles were formed. On the other
hand, pore formation was often observed with GUVs consisting of
DOPG and DPPC. In a DPPC/DPPG/Chol
ternary mixture, pore-formed vesicles were also frequently observed. The
percentage of pore-formed vesicles increased with the DPPG
concentration. Moreover, when the head group charges of charged lipids were
screened by the addition of salt, pore-formed vesicles were suppressed in both
the binary and ternary charged lipid mixtures. We discuss the mechanisms of
pore formation in charged lipid mixtures and the relationship between phase
separation and the membrane morphology. Finally, we reproduce the results seen
in experimental systems by using coarse-grained molecular dynamics simulations.Comment: 34 pages, 10 figure
Charge-induced phase separation in lipid membranes
The phase separation in lipid bilayers that include negatively charged lipids
is examined experimentally. We observed phase-separated structures and
determined the membrane miscibility temperatures in several binary and ternary
lipid mixtures of unsaturated neutral lipid, dioleoylphosphatidylcholine
(DOPC), saturated neutral lipid, dipalmitoylphosphatidylcholine (DPPC),
unsaturated charged lipid, dioleoylphosphatidylglycerol
(DOPG), saturated charged lipid,
dipalmitoylphosphatidylglycerol (DPPG), and cholesterol.
In binary mixtures of saturated and unsaturated charged lipids, the combination
of the charged head with the saturation of hydrocarbon tail is a dominant
factor for the stability of membrane phase separation.
DPPG enhances phase separation, while
DOPG suppresses it. Furthermore, the addition of
DPPG to a binary mixture of DPPC/cholesterol induces phase
separation between DPPG-rich and cholesterol-rich phases.
This indicates that cholesterol localization depends strongly on the electric
charge on the hydrophilic head group rather than on the ordering of the
hydrocarbon tails. Finally, when DPPG was added to a
neutral ternary system of DOPC/DPPC/Cholesterol (a conventional model of
membrane rafts), a three-phase coexistence was produced. We conclude by
discussing some qualitative features of the phase behaviour in charged
membranes using a free energy approach.Comment: 17 pages, 6 figure
Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Fe(110) trilayers
In order to clarify the influence of ferromagnetism on superconductivity
through a normal metal layer, the superconducting properties of epitaxial
Nb(110)/Au(111)/Fe(110) trilayers were studied as a function of the thickness
tAu of the intervening Au layer. Structural characterization of the samples
revealed sharp interfaces, almost free from roughness. A strong suppression of
the superconducting transition temperature Tc was observed for tAu<10 A,
implying a strong spin-polarization of the Au layer in the vicinity of the
Au/Fe interface. A periodic change of Tc with a period of ~21 A (~9 atomic
monolayer of Au) was observed for 20 A<tAu<104 A. Neither the Fermi surface
nesting of the normal metal layer, nor Fulde-Ferrel-Larkin-Ovchinnikov
oscillations induced by a superconducting proximity effect in the ferromagnet
can by themselves account for the observed period. These results suggest that a
new and more subtle form of quantum interference occurs in very clean trilayer
systems.Comment: 15 pages, 6 figure
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