1,312 research outputs found
Properties of continuous Fourier extension of the discrete cosine transform and its multidimensional generalization
A versatile method is described for the practical computation of the discrete
Fourier transforms (DFT) of a continuous function given by its values
at the points of a uniform grid generated by conjugacy classes
of elements of finite adjoint order in the fundamental region of
compact semisimple Lie groups. The present implementation of the method is for
the groups SU(2), when is reduced to a one-dimensional segment, and for
in multidimensional cases. This simplest case
turns out to result in a transform known as discrete cosine transform (DCT),
which is often considered to be simply a specific type of the standard DFT.
Here we show that the DCT is very different from the standard DFT when the
properties of the continuous extensions of these two discrete transforms from
the discrete grid points to all points are
considered. (A) Unlike the continuous extension of the DFT, the continuous
extension of (the inverse) DCT, called CEDCT, closely approximates
between the grid points . (B) For increasing , the derivative of CEDCT
converges to the derivative of . And (C), for CEDCT the principle of
locality is valid. Finally, we use the continuous extension of 2-dimensional
DCT to illustrate its potential for interpolation, as well as for the data
compression of 2D images.Comment: submitted to JMP on April 3, 2003; still waiting for the referee's
Repor
Probing two topological surface bands of Sb2Te3 by spin-polarized photoemission spectroscopy
Using high resolution spin- and angle-resolved photoemission spectroscopy, we
map the electronic structure and spin texture of the surface states of the
topological insulator Sb2Te3. In combination with density functional
calculations (DFT), we directly show that Sb2Te3 exhibits a partially occupied,
single spin-Dirac cone around the Fermi energy, which is topologically
protected. DFT obtains a spin polarization of the occupied Dirac cone states of
80-90%, which is in reasonable agreement with the experimental data after
careful background subtraction. Furthermore, we observe a strongly spin-orbit
split surface band at lower energy. This state is found at 0.8eV below the
Fermi level at the gamma-point, disperses upwards, and disappears at about
0.4eV below the Fermi level into two different bulk bands. Along the gamma-K
direction, the band is located within a spin-orbit gap. According to an
argument given by Pendry and Gurman in 1975, such a gap must contain a surface
state, if it is located away from the high symmetry points of the Brillouin
zone. Thus, the novel spin-split state is protected by symmetry, too.Comment: 8 pages, 10 figure
Generalized iterated wreath products of cyclic groups and rooted trees correspondence
Consider the generalized iterated wreath product where . We
prove that the irreducible representations for this class of groups are indexed
by a certain type of rooted trees. This provides a Bratteli diagram for the
generalized iterated wreath product, a simple recursion formula for the number
of irreducible representations, and a strategy to calculate the dimension of
each irreducible representation. We calculate explicitly fast Fourier
transforms (FFT) for this class of groups, giving literature's fastest FFT
upper bound estimate.Comment: 15 pages, to appear in Advances in the Mathematical Science
Topological surface state under graphene for two-dimensional spintronics in air
Spin currents which allow for a dissipationless transport of information can
be generated by electric fields in semiconductor heterostructures in the
presence of a Rashba-type spin-orbit coupling. The largest Rashba effects occur
for electronic surface states of metals but these cannot exist but under
ultrahigh vacuum conditions. Here, we reveal a giant Rashba effect ({\alpha}_R
~ 1.5E-10 eVm) on a surface state of Ir(111). We demonstrate that its spin
splitting and spin polarization remain unaffected when Ir is covered with
graphene. The graphene protection is, in turn, sufficient for the spin-split
surface state to survive in ambient atmosphere. We discuss this result along
with evidences for a topological protection of the surface state.Comment: includes supplementary informatio
Photoemission of BiSe with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?
Topological insulators are characterized by Dirac cone surface states with
electron spins aligned in the surface plane and perpendicular to their momenta.
Recent theoretical and experimental work implied that this specific spin
texture should enable control of photoelectron spins by circularly polarized
light. However, these reports questioned the so far accepted interpretation of
spin-resolved photoelectron spectroscopy. We solve this puzzle and show that
vacuum ultraviolet photons (50-70 eV) with linear or circular polarization
probe indeed the initial state spin texture of BiSe while circularly
polarized 6 eV low energy photons flip the electron spins out of plane and
reverse their spin polarization. Our photoemission calculations, considering
the interplay between the varying probing depth, dipole selection rules and
spin-dependent scattering effects involving initial and final states explain
these findings, and reveal proper conditions for light-induced spin
manipulation. This paves the way for future applications of topological
insulators in opto-spintronic devices.Comment: Submitted for publication (2013
Recommended from our members
Nocturia as an Unrecognized Symptom of Uncontrolled Hypertension in Black Men Aged 35 to 49 Years.
Background Hypertension is assumed to be asymptomatic. Yet, clinically significant nocturia (≥2 nightly voids) constitutes a putative symptom of uncontrolled hypertension. Black men with hypertension may be prone to nocturia because of blunted nocturnal blood pressure ( BP ) dipping, diuretic drug use for hypertension, and comorbidity that predisposes to nocturia. Here, we test the hypothesis that nocturia is a common and potentially reversible symptom of uncontrolled hypertension in black men. Methods and Results We determined the strength of association between nocturia (≥2 nightly voids) and high BP (≥135/85 mm Hg) by conducting in-person health interviews and measuring BP with an automated monitor in a large community-based sample of black men in their barbershops. Because nocturia is prevalent and steeply age-dependent after age 50 years, we studied men aged 35 to 49 years. Among 1673 black men (mean age, 43±4 years [ SD ]), those with hypertension were 56% more likely than men with normotension to have nocturia after adjustment for diabetes mellitus and sleep apnea (adjusted odds ratio, 1.56; 95% CI , 1.25-1.94 [ P<0.0001]). Nocturia prevalence varied by hypertension status, ranging from 24% in men with normotension to 49% in men whose hypertension was medically treated but uncontrolled. Men with untreated hypertension were 39% more likely than men with normotension to report nocturia ( P=0.02), whereas men whose hypertension was treated and controlled were no more likely than men with normotension to report nocturia ( P=0.69). Conclusions Uncontrolled hypertension was an independent determinant of clinically important nocturia in a large cross-sectional community-based study of non-Hispanic black men aged 35 to 49 years. Clinical Trial Registration URL : http://www.clinicaltrials.gov . Unqiue identifier: NCT 02321618
Tolerance of topological surface states towards magnetic moments: Fe on Bi2Te3 and Bi2Se3
Topological insulators(1-8) are a novel form of matter which features
metallic surface states with quasirelativistic dispersion similar to
graphene(9). Unlike graphene, the locking of spin and momentum and the
protection by time-reversal symmetry(1-8) open up tremendous additional
possibilities for external control of transport properties(10-18). Here we show
by angle-resolved photoelectron spectroscopy that the topological sur-face
states of Bi2Te3 and Bi2Se3 are stable against the deposition of Fe without
opening a band gap. This stability extends to low submonolayer coverages
meaning that the band gap reported recently(19) for Fe on Bi2Se3 is incorrect
as well as to complete monolayers meaning that topological surface states can
very well exist at interfaces with ferromagnets in future devices.Comment: 10 pages, 3 figures, submitted to Nature Physics 22. July 201
High-Level Expression of Various Apolipoprotein (a) Isoforms by "Transferrinfection". The Role of Kringle IV Sequences in the Extracellular Association with Low-Density Lipoprotein
Characterization of the assembly of lipoprotein(a) [Lp(a)] is of fundamental importance to understanding the biosynthesis and metabolism of this atherogenic lipoprotein. Since no established cell lines exist that express Lp(a) or apolipoprotein(a) [apo(a)], a "transferrinfection" system for apo(a) was developed utilizing adenovirus receptor- and transferrin receptor-mediated DNA uptake into cells. Using this method, different apo(a) cDNA constructions of variable length, due to the presence of 3, 5, 7, 9, 15, or 18 internal kringle IV sequences, were expressed in cos-7 cells or CHO cells. All constructions contained kringle IV-36, which includes the only unpaired cysteine residue (Cys-4057) in apo(a). r-Apo(a) was synthesized as a precursor and secreted as mature apolipoprotein into the medium. When medium containing r-apo(a) with 9, 15, or 18 kringle IV repeats was mixed with normal human plasma LDL, stable complexes formed that had a bouyant density typical of Lp(a). Association was substantially decreased if Cys-4057 on r-apo(a) was replaced by Arg by site-directed mutagenesis or if Cys-4057 was chemically modified. Lack of association was also observed with r-apo(a) containing only 3, 5, or 7 kringle IV repeats without "unique kringle IV sequences", although Cys-4057 was present in all of these constructions. Synthesis and secretion of r-apo(a) was not dependent on its sialic acid content. r-Apo(a) was expressed even more efficiently in sialylation-defective CHO cells than in wild-type CHO cells. In transfected CHO cells defective in the addition of N-acetylglucosamine, apo(a) secretion was found to be decreased by 50%. Extracellular association with LDL was not affected by the carbohydrate moiety of r-apo(a), indicating a protein-protein interaction between r-apo(a) and apoB. These results show that, besides kringle IV-36, other kringle IV sequences are necessary for the extracellular association of r-apo(a) with LDL. Changes in the carbohydrate moiety of apo(a), however, do not affect complex formation
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