1,820 research outputs found
Investigating Finite Sample Properties of Estimators for Approximate Factor Models When N Is Small
This paper examines the finite sample properties of estimators for approximate factor models when N is small via simulation study. Although the "rule-of-thumb" for factor models does not support using approximate factor models when N is small, we find that the principal component analysis estimator and quasi-maximum likelihood estimator proposed by Doz et al. (2008) perform very well even in this case. Our findings provide an opportunity for applying approximate factor models to low-dimensional data, which was thought to have been inappropriate for a long time.Approximate factor model, Principal components, Quasi-maximum likelihood
Reducing the Size Distortion of the KPSS Test
This paper proposes a new stationarity test based on the KPSS test with less size distortion. We extend the boundary rule proposed by Sul, Phillips and Choi (2005) to the autoregressive spectral density estimator and parametrically estimate the long-run variance. We also derive the finite sample bias of the numerator of the test statistic up to the 1/T order and propose a correction to the bias term in the numerator. Finite sample simulations show that the correction term effectively reduces the bias in the numerator and that the finite sample size of our test is close to the nominal one as long as the long-run parameter in the model satisfies the boundary condition.Stationary test, size distortion, boundary rule, bias correction
Gravitational Waves from Phase Transitions in Scale Invariant Models
We investigate the properties of the gravitational waves (GWs) generated
during a strongly first order electroweak phase transition (EWPT) in models
with the classical scale invariance (CSI). Here, we distinguish two parameter
space regions that correspond to the cases of (1) light dilaton and (2) purely
radiative Higgs mass (PRHM). In the CSI models, the dilaton mass, or the Higgs
mass in the PRHM case, in addition to some triple scalar couplings are fully
triggered by the radiative corrections (RCs). In order to probe the RCs effects
on the EWPT strength and on the GW spectrum, we extend the standard model by a
real singlet to assist the electroweak symmetry breaking and an additional
scalar field with multiplicity and mass . After imposing all
theoretical and experimental constraints, we show that a strongly first order
EWPT with detectable GW spectra can be realized for the two cases of light
dilaton and PRHM. We also show the corresponding values of the relative
enhancement of the cross section for the di-Higgs production process, which is
related to the triple Higgs boson coupling. We obtain the region in which the
GW spectrum can be observed by different future experiments such as LISA and
DECIGO. We also show that the scenarios (1) and (2) can be discriminated by
future GW observations and measurements of the di-Higgs productions at future
colliders.Comment: 18 pages, 6 figure
Isolation of a transcriptionally active element of high copy number retrotransposons in sweetpotato genome
Many plant retrotransposons have been characterized, but only three families (Tnt1, Tto1 and
Tos17) have been demonstrated to be transpositionally competent. We followed a novel approach
that enabled us to identify an active element of the Ty1-copia retrotransposon family with
estimated 400 copies in the sweetpotato genome. DNA sequences of Ty1 -copia reverse
transcriptase (RTase) from the sweetpotato genome were analyzed, and a group of
retrotransposon copies probably formed by recent transposition events was further analyzed.
3’RACE on callus cDNA amplified transcripts containing long terminal repeats (LTR) of this
group. The sequence -specific amplification polymorphism (S-SAP) patterns of the LTR sequence
in the genomic DNA were compared between a normal plant and callus lines derived from it. A
callus -specific S-SAP product was found into which the retrotransposon detected by the 3’RACE
had been transposed apparently during cell culture. We conclude that our approach provides an
effective way to identify active elements of retrotransposons with high copy numbers.</p
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