1,169 research outputs found
Lag Length Selection for Unit Root Tests in the Presence of Nonstationary Volatility
A number of recently published papers have focused on the problem of testing for a unit root in the case where the driving shocks may be unconditionally heteroskedastic. These papers have, however, assumed that the lag length in the unit root test regression is a deterministic function of the sample size, rather than data-determined, the latter being standard empirical practice. In this paper we investigate the finite sample impact of unconditional heteroskedasticity on conventional data-dependent methods of lag selection in augmented Dickey-Fuller type unit root test regressions and propose new lag selection criteria which allow for the presence of heteroskedasticity in the shocks. We show that standard lag selection methods show a tendency to over-fit the lag order under heteroskedasticity, which results in significant power losses in the (wild bootstrap implementation of the) augmented Dickey-Fuller tests under the alternative. The new lag selection criteria we propose are shown to avoid this problem yet deliver unit roots with almost identical finite sample size and power properties as the corresponding tests based on conventional lag selection methods when the shocks are homoskedastic.Unit root test, Lag selection, Information criteria, Wild bootstrap, Nonstationary volatility
Lag Length Selection for Unit Root Tests in the Presence of Nonstationary Volatility
A number of recently published papers have focused on the problem of testing for a unit root inthe case where the driving shocks may be unconditionally heteroskedastic. These papers have,however, assumed that the lag length in the unit root test regression is a deterministic functionof the sample size, rather than data-determined, the latter being standard empirical practice. Inthis paper we investigate the finite sample impact of unconditional heteroskedasticity onconventional data-dependent methods of lag selection in augmented Dickey-Fuller type unit roottest regressions and propose new lag selection criteria which allow for the presence ofheteroskedasticity in the shocks. We show that standard lag selection methods show a tendency toover-fit the lag order under heteroskedasticity, which results in significant power losses in the(wild bootstrap implementation of the) augmented Dickey-Fuller tests under the alternative. Thenew lag selection criteria we propose are shown to avoid this problem yet deliver unit root testswith almost identical finite sample size and power properties as the corresponding tests based onconventional lag selection methods when the shocks are homoskedastic.econometrics;
Lag Length Selection for Unit Root Tests in the Presence of Nonstationary Volatility
A number of recently published papers have focused on the problem of testing for a unit root in the case where the driving shocks may be unconditionally heteroskedastic. These papers have, however, assumed that the lag length in the unit root test regression is a deterministic function of the sample size, rather than data-determined, the latter being standard empirical practice. In this paper we investigate the ļ¬nite sample impact of unconditional heteroskedasticity on conventional data-dependent methods of lag selection in augmented Dickey-Fuller type unit root test regressions and propose new lag selection criteria which allow for the presence of heteroskedasticity in the shocks. We show that standard lag selection methods show a tendency to over-ļ¬t the lag order under heteroskedasticity, which results in signiļ¬cant power losses in the (wild bootstrap implementation of the) augmented Dickey-Fuller tests under the alternative. The new lag selection criteria we propose are shown to avoid this problem yet deliver unit roots with almost identical ļ¬nite sample size and power properties as the corresponding tests based on conventional lag selection methods when the shocks are homoskedastic
State-wide survey of boat-based recreational fishing in Western Australia 2013/14
Based on the outcomes of an international workshop on recreational fishing survey methods in 2010, the Department of Fisheries developed an integrated survey involving several methods to provide a robust and cost-effective approach for obtaining annual estimates of recreational catch by boat-based fishers at both state-wide and bioregional levels
Can one see the fundamental frequency of a drum?
We establish two-sided estimates for the fundamental frequency (the lowest
eigenvalue) of the Laplacian in an open subset G of R^n with the Dirichlet
boundary condition. This is done in terms of the interior capacitary radius of
G which is defined as the maximal possible radius of a ball B which has a
negligible intersection with the complement of G. Here negligibility of a
subset F in B means that the Wiener capacity of F does not exceed gamma times
the capacity of B, where gamma is an arbitrarily fixed constant between 0 and
1. We provide explicit values of constants in the two-sided estimates.Comment: 18 pages, some misprints correcte
Abelian and nonabelian vector field effective actions from string field theory
The leading terms in the tree-level effective action for the massless fields
of the bosonic open string are calculated by integrating out all massive fields
in Witten's cubic string field theory. In both the abelian and nonabelian
theories, field redefinitions make it possible to express the effective action
in terms of the conventional field strength. The resulting actions reproduce
the leading terms in the abelian and nonabelian Born-Infeld theories, and
include (covariant) derivative corrections.Comment: 49 pages, 1 eps figur
Scaling Laws and Effective Dimension in Lattice SU(2) Yang-Mills Theory with a Compactified Extra Dimension
Monte Carlo simulations are performed in a five-dimensional lattice SU(2)
Yang-Mills theory with a compactified extra dimension, and scaling laws are
studied. Our simulations indicate that as the compactification radius
decreases, the confining phase spreads more and more to the weak coupling
regime, and the effective dimension of the theory changes gradually from five
to four. Our simulations also indicate that the limit with
kept fixed exists both in the confining and deconfining phases if is
small enough, where is the lattice spacing in the four-dimensional
direction. We argue that the color degrees of freedom in QCD are confined only
for , where a rough estimate shows that lies
in the TeV range. Comments on deconstructing extra dimensions are given.Comment: 15 pages, TeX, 5 figure
Towards a Resolution of the Cosmological Singularity in Non-local Higher Derivative Theories of Gravity
One of the greatest problems of standard cosmology is the Big Bang
singularity. Previously it has been shown that non-local ghostfree
higher-derivative modifications of Einstein gravity in the ultra-violet regime
can admit non-singular bouncing solutions. In this paper we study in more
details the dynamical properties of the equations of motion for these theories
of gravity in presence of positive and negative cosmological constants and
radiation. We find stable inflationary attractor solutions in the presence of a
positive cosmological constant which renders inflation {\it geodesically
complete}, while in the presence of a negative cosmological constant a cyclic
universe emerges. We also provide an algorithm for tracking the super-Hubble
perturbations during the bounce and show that the bouncing solutions are free
from any perturbative instability.Comment: 38 pages, 6 figures. V2: Added: a word to the title, clarifications,
an appendix, many references. To appear in JCA
UV and EUV Instruments
We describe telescopes and instruments that were developed and used for
astronomical research in the ultraviolet (UV) and extreme ultraviolet (EUV)
regions of the electromagnetic spectrum. The wavelength ranges covered by these
bands are not uniquely defined. We use the following convention here: The EUV
and UV span the regions ~100-912 and 912-3000 Angstroem respectively. The
limitation between both ranges is a natural choice, because the hydrogen Lyman
absorption edge is located at 912 Angstroem. At smaller wavelengths,
astronomical sources are strongly absorbed by the interstellar medium. It also
marks a technical limit, because telescopes and instruments are of different
design. In the EUV range, the technology is strongly related to that utilized
in X-ray astronomy, while in the UV range the instruments in many cases have
their roots in optical astronomy. We will, therefore, describe the UV and EUV
instruments in appropriate conciseness and refer to the respective chapters of
this volume for more technical details.Comment: To appear in: Landolt-Boernstein, New Series VI/4A, Astronomy,
Astrophysics, and Cosmology; Instruments and Methods, ed. J.E. Truemper,
Springer-Verlag, Berlin, 201
The Nkx6.1 homeodomain transcription factor suppresses glucagon expression and regulates glucose-stimulated insulin secretion in islet beta cells
We have previously described rat insulinoma INS-1 derived cell lines with robust or poor glucose-stimulated insulin secretion (GSIS). In the current study, we have further resolved these lines into three classes: class 1, glucose-unresponsive glucagon-expressing; class 2, glucose-unresponsive glucagon-negative; and class 3, glucose-responsive glucagon-negative. The transcription factor Nkx2.2 was expressed with relative abundance of 3.3, 1.0, and 1.0 in class 1, class 2, and class 3 cells, respectively, whereas Nkx6.1 expression had the opposite trend: 1.0, 2.6, and 6.4 in class 1, class 2, and class 3 cells, respectively. In class 1 cells, overexpressed Nkx6.1 suppressed glucagon expression but did not affect the levels of several other prominent beta cell transcription factors. RNA interference (RNAi)-mediated suppression of Nkx6.1 in class 3 cells resulted in a doubling of glucagon mRNA, with no effect on Pdx1 levels, whereas suppression of Pdx1 in class 3 cells caused a 12-fold increase in glucagon transcript levels, demonstrating independent effects of Nkx6.1 and Pdx1 on glucagon expression in beta cell lines. RNAi-mediated suppression of Nkx6.1 expression in class 3 cells also caused a decrease in GSIS from 13.9- to 3.7-fold, whereas suppression of Pdx1 reduced absolute amounts of insulin secretion without affecting fold response. Finally, RNAi-mediated suppression of Nkx6.1 mRNA in primary rat islets was accompanied by a significant decrease in GSIS relative to control cells. In sum, our studies have revealed roles for Nkx6.1 in suppression of glucagon expression and control of GSIS in islet beta cells
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