154,275 research outputs found
Strategic implications of critical fixities under continuous technological change
Includes bibliographical references (p. 27-28)
Towards an understanding of hole superconductivity
From the very beginning K. Alex M\"uller emphasized that the materials he and
George Bednorz discovered in 1986 were superconductors. Here I would
like to share with him and others what I believe to be key reason for why
high cuprates as well as all other superconductors are hole
superconductors, which I only came to understand a few months ago. This paper
is dedicated to Alex M\"uller on the occasion of his 90th birthday.Comment: Dedicated to Alex M\"uller on the Occasion of his 90th Birthday.
arXiv admin note: text overlap with arXiv:1703.0977
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Tracking surface photovoltage dipole geometry in bi2se3 with time-resolved photoemission
Topological insulators have been shown to exhibit strong and long-lived surface photovoltages when excited by an infrared pump. The ability to generate long-lived potentials on these surfaces provides opportunities to manipulate the spin-momentum locked topological surface states. Moreover, the photo-induced nature of this effect allows for localized excitation of arbitrary geometries. Knowing precisely how these potentials form and evolve is critical in understanding how to manage the effect in applications. The uniqueness of the photoemission experimental geometry, in which the photoelectron must traverse the induced surface field in vacuum, provides an interesting probe of the electric dipole shape generated by the surface photovoltage. In this study, we are able to match the observed decay of the geometric effect on the photoelectron to an essential electrodynamics model of the light-induced dipole thereby tracking the fluence-dependent evolution of the dipole geometry. By utilizing a standard time-resolved angle-resolved photoemission experiment, we are able to determine real-space information of the dipole while simultaneously recovering time-resolved band structure
Cosmological and Solar-System Tests of f(R) Modified Gravity
We investigate the cosmological and the local tests of the f(R) theory of
modified gravity via the observations of (1) the cosmic expansion and (2) the
cosmic structures and via (3) the solar-system experiments. To fit the possible
cosmic expansion histories under consideration, for each of them we reconstruct
f(R), known as "designer f(R)". We then test the designer f(R) via the
cosmic-structure constraints on the metric perturbation ratio Psi/Phi and the
effective gravitational coupling G_eff and via the solar-system constraints on
the Brans-Dicke theory with the chameleon mechanism. We find that among the
designer f(R) models specified by the CPL effective equation of state w_eff,
only the model closely mimicking general relativity with a cosmological
constant (LambdaCDM) can survive all the tests. Accordingly, these tests rule
out the frequently studied "w_eff = -1" designer f(R) models which are distinct
in cosmic structures from LambdaCDM. When considering only the cosmological
tests, we find that the surviving designer f(R) models, although exist for a
variety of w_eff, entail fine-tuning.Comment: 22 pages, 9 figures, LaTe
Some Grüss' Type Inequalities in 2-Inner Product Spaces and Applications for Determinantal Integral Inequalities
Some new Grüss type inequalities in 2-inner product spaces are given. Using this framework, some determinantal integral inequalities for synchronous functions are also derived
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Charge delocalization characteristics of regioregular high mobility polymers.
Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while the reorganizational energies calculated are quite similar across the molecular family. This work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties
Some Inequalities in 2-inner Product Spaces
In this paper we extend some results on the refinement of Cauchy-Buniakowski-Schwarz's inequality and Aćzel's inequality in inner product spaces to 2-inner product spaces
The anomalous U(1) global symmetry and flavors from an SU(5) x SU(5) GUT in orbifold compactification
In string compactifications, frequently there appears the anomalous U(1)
gauge symmetry which belonged to E8E8 of the heterotic string. This
anomalous U(1) gauge boson obtains mass at the compactification scale, just
below GeV, by absorbing one pseudoscalar (corresponding to the
model-independent axion) from the second rank anti-symmetric tensor field
.
Below the compactification scale, there results a global symmetry U(1) whose charge is the original gauge U(1) charge. This is
the most natural global symmetry, realizing the "invisible" axion. This global
symmetry U(1) is suitable for a flavor symmetry. In the simplest
compactification model with the flipped SU(5) grand unification, we calculate
all the low energy parameters in terms of the vacuum expectation values of the
standard model singlets.Comment: 18 pages, 4 figur
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