28,925 research outputs found
Asymptotics for penalized additive B-spline regression
This paper is concerned with asymptotic theory for penalized spline estimator
in bivariate additive model. The focus of this paper is put upon the penalized
spline estimator obtained by the backfitting algorithm. The convergence of the
algorithm as well as the uniqueness of its solution are shown. The asymptotic
bias and variance of penalized spline estimator are derived by an efficient use
of the asymptotic results for the penalized spline estimator in marginal
univariate model. Asymptotic normality of estimator is also developed, by which
an approximate confidence interval can be obtained. Some numerical experiments
confirming theoretical results are provided.Comment: 24 pages, 6 figure
Symplectic structure and monopole strength in 12C
The relation between the monopole transition strength and existence of
cluster structure in the excited states is discussed based on an algebraic
cluster model. The structure of C is studied with a 3 model, and
the wave function for the relative motions between clusters are
described by the symplectic algebra , which corresponds to the
linear combinations of states with different multiplicities.
Introducing algebra works well for reducing the number of the basis
states, and it is also shown that states connected by the strong monopole
transition are classified by a quantum number of the
algebra.Comment: Phys. Rev. C in pres
Atomically straight steps on vicinal Si (111) surfaces prepared by step-parallel current in the kink-up direction
We demonstrate that annealing of a vicinal Si(111) surface at about 800 C
with a direct current in the direction that ascends the kinks enhances the
formation of atomically straight step edges over micrometer lengths, while
annealing with a current in the opposite direction does not. Every straight
step edge has the same atomic configuration U(2,0), which is useful as a
template for the formation of a variety of nanostructures. A phenomenological
model based on electromigration of charged mobile atoms explains the observed
current-polarity dependent behavior.Comment: Accepted for publication in Appl. Phys. Lett. Numbers of pages and
figures are 12 and 4, respectivel
Constraints on the origin of the ultra-high energy cosmic-rays using cosmic diffuse neutrino flux limits: An analytical approach
Astrophysical neutrinos are expected to be produced in the interactions of
ultra-high energy cosmic-rays with surrounding photons. The fluxes of the
astrophysical neutrinos are highly dependent on the characteristics of the
cosmic-ray sources, such as their cosmological distributions. We study possible
constraints on the properties of cosmic-ray sources in a model-independent way
using experimentally obtained diffuse neutrino flux above 100 PeV. The
semi-analytic formula is derived to estimate the cosmogenic neutrino fluxes as
functions of source evolution parameter and source extension in redshift. The
obtained formula converts the upper-limits on the neutrino fluxes into the
constraints on the cosmic-ray sources. It is found that the recently obtained
upper-limit on the cosmogenic neutrinos by IceCube constrains the scenarios
with strongly evolving ultra-high energy cosmic-ray sources, and the future
limits from an 1 km^3 scale detector are able to further constrain the
ultra-high energy cosmic-rays sources with evolutions comparable to the cosmic
star formation rate.Comment: 9 pages, 3 figures and 1 table. Accepted by Phys. Rev.
Fabrication of graphene nanoribbon by local anodic oxidation lithography using atomic force microscope
We conducted local anodic oxidation (LAO) lithography in single-layer,
bilayer, and multilayer graphene using tapping-mode atomic force microscope.
The width of insulating oxidized area depends systematically on the number of
graphene layers. An 800-nm-wide bar-shaped device fabricated in single-layer
graphene exhibits the half-integer quantum Hall effect. We also fabricated a
55-nm-wide graphene nanoribbon (GNR). The conductance of the GNR at the charge
neutrality point was suppressed at low temperature, which suggests the opening
of an energy gap due to lateral confinement of charge carriers. These results
show that LAO lithography is an effective technique for the fabrication of
graphene nanodevices.Comment: 4 pages, 4 figure
Stability of Neutral Fermi Balls with Multi-Flavor Fermions
A Fermi ball is a kind of non-topological soliton, which is thought to arise
from the spontaneous breaking of an approximate symmetry and to
contribute to cold dark matter. We consider a simple model in which fermion
fields with multi-flavors are coupled to a scalar field through Yukawa
coupling, and examine how the number of the fermion flavors affects the
stability of the Fermi ball against the fragmentation. (1)We find that the
Fermi ball is stable against the fragmentation in most cases even in the lowest
order thin-wall approximation. (2)We then find that in the other specific
cases, the stability is marginal in the lowest order thin-wall approximation,
and the next-to-leading order correction determines the stable region of the
coupling constants; We examine the simplest case where the total fermion number
and the Yukawa coupling constant of each flavor are common to
the flavor, and find that the Fermi ball is stable in the limited region of the
parameters and has the broader region for the larger number of the flavors.Comment: 10 pages, 3 eps figures, ReVTeX
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