1,287 research outputs found
ADE Double Scaled Little String Theories, Mock Modular Forms and Umbral Moonshine
We consider double scaled little string theory on . These theories are
labelled by a positive integer and an root lattice with Coxeter
number . We count BPS fundamental string states in the holographic dual of
this theory using the superconformal field theory . We show that the BPS fundamental string states that are counted
by the second helicity supertrace of this theory give rise to weight two mixed
mock modular forms. We compute the helicity supertraces using two separate
techniques: a path integral analysis that leads to a modular invariant but
non-holomorphic answer, and a Hamiltonian analysis of the contribution from
discrete states which leads to a holomorphic but not modular invariant answer.
From a mathematical point of view the Hamiltonian analysis leads to a mixed
mock modular form while the path integral gives the completion of this mixed
mock modular form. We also compare these weight two mixed mock modular forms to
those that appear in instances of Umbral Moonshine labelled by Niemeier root
lattices that are powers of root lattices and find that they are
equal up to a constant factor that we determine. In the course of the analysis
we encounter an interesting generalization of Appell-Lerch sums and
generalizations of the Riemann relations of Jacobi theta functions that they
obey.Comment: 1+56 page
Graphene-Dielectric Composite Metamaterials: Evolution from Elliptic to Hyperbolic Wavevector Dispersion and The Transverse Epsilon-Near-Zero Condition
We investigated a multilayer graphene-dielectric composite material,
comprising graphene sheets separated by subwavelength-thick dielectric spacer,
and found it to exhibit hyperbolic isofrequency wavevector dispersion at far-
and mid-infrared frequencies allowing propagation of waves that would be
otherwise evanescent in a dielectric. Electrostatic biasing was considered for
tunable and controllable transition from hyperbolic to elliptic dispersion. We
explored the validity and limitation of the effective medium approximation
(EMA) for modeling wave propagation and cutoff of the propagating spatial
spectrum due to the Brillouin zone edge. We found that EMA is capable of
predicting the transition of the isofrequency dispersion diagram under certain
conditions. The graphene-based composite material allows propagation of
backward waves under the hyperbolic dispersion regime and of forward waves
under the elliptic regime. Transition from hyperbolic to elliptic dispersion
regimes is governed by the transverse epsilon-near-zero (TENZ) condition, which
implies a flatter and wider propagating spectrum with higher attenuation, when
compared to the hyperbolic regime. We also investigate the tunable transparency
of the multilayer at that condition in contrast to other materials exhibiting
ENZ phenomena.Comment: to be published in Journal of Nanophotonic
Inference in partially identified models with many moment inequalities using Lasso
This paper considers inference in a partially identified moment (in)equality
model with many moment inequalities. We propose a novel two-step inference
procedure that combines the methods proposed by Chernozhukov, Chetverikov and
Kato (2018a) (CCK18, hereafter) with a first step moment inequality selection
based on the Lasso. Our method controls asymptotic size uniformly, both in
underlying parameter and data distribution. Also, the power of our method
compares favorably with that of the corresponding two-step method in CCK18 for
large parts of the parameter space, both in theory and in simulations. Finally,
we show that our Lasso-based first step can be implemented by thresholding
standardized sample averages, and so it is straightforward to implement.Comment: 1 figur
How Sensitive Are Bank Managers to Shareholder Value?
Cataloged from PDF version of article.We test for the existence of market discipline by shareholders of banks
with a wide range of ownership structures. Discipline by shareholders manifests
itself through monitoring banks’ level of risk as well as through influencing banks’
management actions. We find that shareholders utilize the relation between stock
returns and different types of risk measures to monitor risky banks. Shareholders
partially influence bank management by responding to decreasing stock returns with
a demand to improve loan quality. Moreover, the influence on management in small
banks is more pronounced compared to large banks
Fano collective resonance as complex mode in a two dimensional planar metasurface of plasmonic nanoparticles
Fano resonances are features in transmissivity/reflectivity/absorption that
owe their origin to the interaction between a bright resonance and a dark
(i.e., sub-radiant) narrower resonance, and may emerge in the optical
properties of planar two-dimensional (2D) periodic arrays (metasurfaces) of
plasmonic nanoparticles. In this Letter, we provide a thorough assessment of
their nature for the general case of normal and oblique plane wave incidence,
highlighting when a Fano resonance is affected by the mutual coupling in an
array and its capability to support free modal solutions. We analyze the
representative case of a metasurface of plasmonic nanoshells at ultraviolet
frequencies and compute its absorption under TE- and TM-polarized, oblique
plane-wave incidence. In particular, we find that plasmonic metasurfaces
display two distinct types of resonances observable as absorption peaks: one is
related to the Mie, dipolar resonance of each nanoparticle; the other is due to
the forced excitation of free modes with small attenuation constant, usually
found at oblique incidence. The latter is thus an array-induced collective Fano
resonance. This realization opens up to manifold flexible designs at optical
frequencies mixing individual and collective resonances. We explain the
physical origin of such Fano resonances using the modal analysis, which allows
to calculate the free modes with complex wavenumber supported by the
metasurface. We define equivalent array dipolar polarizabilities that are
directly related to the absorption physics at oblique incidence and show a
direct dependence between array modal phase and attenuation constant and Fano
resonances. We thus provide a more complete picture of Fano resonances that may
lead to the design of filters, energy-harvesting devices, photodetectors, and
sensors at ultraviolet frequencies.Comment: 6 pages, 5 figure
Double cantilever indirect tension testing for fracture of quasibrittle materials
The Double Cantilever Beam (DCB) Mode I fracture testing has been widely used in fracture testing of especially fiber reinforced polymer composites and adhesive joints. Application of classical DCB testing to plain concrete or unreinforced ceramic specimens is not straightforward and cannot be carried out as in fiber reinforced polymer composites. Instead, an indirect tension approach is proposed in this study. Tests of notched geometrically similar DCB specimens made of normal and high strength concretes loaded eccentrically at the cantilever beam-column ends in compression have been carried out. Classical Type II size effect analyses of peak loads obtained from these tests are performed. The Microplane Model M7 is calibrated independently using uniaxial compression tests and employed to predict the peak loads of both tested and virtual geometrically similar DCB specimens. The same size effect analyses are performed on the predicted peak loads and the errors in the fracture parameters of the classical size effect analysis are determined.Peer ReviewedPostprint (author's final draft
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Top quark physics at CDF
We present preliminary results on top quark physics recently obtained by the CDF collaboration. The data sample consists of 110 {ital pb}{sup -1} of {ital p{anti p}} collisions at {radical}{ital s} = 1.8 TeV, collected with the Collider Detector at Fermilab during the period 1992 - 1995. We report on the {ital t{anti t}} production cross section and on the top quark mass. The measurements are made in three topologies, corresponding to the decay modes of the {ital Wb} pairs in the final state: lepton + multi-jets, dilepton and all hadronic final state. The analysis performed on the single lepton sample yields the most accurate measurements, due to the good acceptance and the favorable signal to noise ratio obtained after applying some b-tagging techniques. In this channel we measure: {sigma}{sub {ital t{anti t}}} = 6.8{sup +2.3}{sub -1.8} pb M{sub {ital t}} = 175.6 {+-} 5.7 ({ital stat}) {+-} 7.1 ({ital syst.}) {ital GeV/c{sup 2}} Combining the cross sections measured with the lepton + multi-jet and dilepton data we obtain: {sigma}{sub {ital t{anti t}}} = 7.5{sup +1.9}{sub -1.6} {ital pb} A preliminary investigation of the production mechanism of the {ital t{anti t}} system is shown and compared to Standard Model expectations
Risk and career choice: Evidence from Turkey
In this paper, we examine the college major choice decision in a risk and return framework using university entrance exam data from Turkey. Specifically we focus on the choice between majors with low income risk such as education and health and others with riskier income streams. We use a unique dataset that allows us to control for the choice set of students and parental attitudes towards risk. Our results show that father's income, self-employment status and social security status are important factors influencing an individual in choosing a riskier career such as business over a less risky one such as education or health. © 2010 Elsevier Ltd
Photonuclear reactions with Zinc: A case for clinical linacs
The use of bremsstrahlung photons produced by a linac to induce photonuclear
reactions is wide spread. However, using a clinical linac to produce the
photons is a new concept. We aimed to induce photonuclear reactions on zinc
isotopes and measure the subsequent transition energies and half-lives. For
this purpose, a bremsstrahlung photon beam of 18 MeV endpoint energy produced
by the Philips SLI-25 linac has been used. The subsequent decay has been
measured with a well-shielded single HPGe detector. The results obtained for
transition energies are in good agreement with the literature data and in many
cases surpass these in accuracy. For the half-lives, we are in agreement with
the literature data, but do not achieve their precision. The obtained accuracy
for the transition energies show what is achievable in an experiment such as
ours. We demonstrate the usefulness and benefits of employing clinical linacs
for nuclear physics experiments
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