1,591 research outputs found
Evaluating Agricultural Banking Efficiency Using the Fourier Flexible Functional Form
This study applied more flexible cost functional form, Fourier Flexible Functional Form, and tested the validity of the Translog cost functional form as to estimate the cost function incorporating risk and loan's quality for banking industry. Meanwhile, the study extended four different cost efficiency measures for banking industry not only among different sized banks but also between commercial banks and agricultural banks. And thereafter, by evaluating these efficiency measures, banks will identify sources of inefficiency, which should aid banks in developing approaches to improve their operational policies, procedures, and performance.Agricultural Finance,
Combining WMAP and SDSS Quasar Data on Reionization Constrains Cosmological Parameters and the Star Formation Efficiency
We present constraints on cosmological and star formation parameters based on
combining observations of the Wilkinson Microwave Anisotropy Probe (WMAP) and
high-redshift quasars from the Sloan Digital Sky Survey (SDSS). We use a
semi-analytic model for reionization (Chiu and Ostriker 2000) that takes into
account a number of important physical processes both within collapsing halos
and in the intergalactic medium. Assuming that the efficiency of producing UV
photons per baryon is constant, we derive a constraint of the form sigma_8
Omega_0^0.5~0.33 in a flat, Lambda-dominated universe with h=0.72, n=0.99, and
Omega_b h^2=0.024. However, the calculated optical depth to electron scattering
of tau_es~0.06 is well below the value found by WMAP of 0.17+/-(0.04~0.07)
(Spergel et al 2003). Since the WMAP constraints on tau_es are somewhat
degenerate with the value of the spectral index n, we then permit the
primordial spectral index n to float and fix Omega_0 h^2=0.14, while
normalizing the power spectrum using WMAP. In addition, we allow the
UV-efficiency to have time-dependence. Combining the WMAP constraints with the
quasar transmission data, our analysis then favors a model with
tau_es=0.11^{+0.02}_{-0.03}, n=0.96^{+0.02}_{-0.03}$, implying
sigma_8=0.83^{+0.03}_{-0.05} (95% confidence), and an effective UV-efficiency
that was at least ~10x greater at z >> 6. These results indicate that the
quasar and WMAP observations are consistent. If future observations confirm an
optical depth to electron scattering tau_es~0.1, then it would appear that no
more "exotic" sources of UV-photons, such as mini-quasars or AGNs, are
necessary; but our analysis indicates that a determination of tau_es>~0.17
would require a more radical solution.Comment: 31 pages, 7 figures, 5 table
Hubble Advanced Camera for Surveys Observations of the z=6.42 Quasar SDSS 1148+5251: A Leak in the Gunn-Peterson Trough
The Hubble Advanced Camera for Surveys has been used to obtain a narrow-band
image of the weak emission peak seen at lambda=7205 A in the Gunn-Peterson Ly
beta absorption trough of the highest redshift quasar, SDSS J1148+5251. The
emission looks perfectly point-like; there is no evidence for the intervening
galaxy that we previously suggested might be contaminating the quasar spectrum.
We derive a more accurate astrometric position for the quasar in the two
filters and see no indication of gravitational lensing. We conclude that the
light in the Ly beta trough is leaking through two unusually transparent,
overlapping windows in the IGM absorption, one in the Ly beta forest at z ~ 6
and one in the Ly alpha forest at z ~ 5.
If there are significant optical depth variations on velocity scales small
compared with our spectral resolution (~150 km/s), the Ly alpha trough becomes
more transparent for a given Ly beta optical depth. Such variations can only
strengthen our conclusion that the fraction of neutral hydrogen in the IGM
increases dramatically at z>6. We argue that the transmission in the Ly beta
trough is not only a more sensitive measure of the neutral fraction than is Ly
alpha, it also provides a less biased estimator of the neutral hydrogen
fraction than does the Ly alpha transmission.Comment: Submitted to the Astronomical Journa
Exploiting the full power of temporal gene expression profiling through a new statistical test: Application to the analysis of muscular dystrophy data
Background: The identification of biologically interesting genes in a temporal expression profiling
dataset is challenging and complicated by high levels of experimental noise. Most statistical methods
used in the literature do not fully exploit the temporal ordering in the dataset and are not suited
to the case where temporal profiles are measured for a number of different biological conditions.
We present a statistical test that makes explicit use of the temporal order in the data by fitting
polynomial functions to the temporal profile of each gene and for each biological condition. A
Hotelling T2-statistic is derived to detect the genes for which the parameters of these polynomials
are significantly different from each other.
Results: We validate the temporal Hotelling T2-test on muscular gene expression data from four
mouse strains which were profiled at different ages: dystrophin-, beta-sarcoglycan and gammasarcoglycan
deficient mice, and wild-type mice. The first three are animal models for different
muscular dystrophies. Extensive biological validation shows that the method is capable of finding
genes with temporal profiles significantly different across the four strains, as well as identifying
potential biomarkers for each form of the disease. The added value of the temporal test compared
to an identical test which does not make use of temporal ordering is demonstrated via a simulation
study, and through confirmation of the expression profiles from selected genes by quantitative PCR
experiments. The proposed method maximises the detection of the biologically interesting genes,
whilst minimising false detections.
Conclusion: The temporal Hotelling T2-test is capable of finding relatively small and robust sets
of genes that display different temporal profiles between the conditions of interest. The test is
simple, it can be used on gene expression data generated from any experimental design and for any
number of conditions, and it allows fast interpretation of the temporal behaviour of genes. The R
code is available from V.V. The microarray data have been submitted to GEO under series
GSE1574 and GSE3523
DISCRETE AND CONTINUOUS TIME MODELS FOR FARM CREDIT MIGRATION ANALYSIS
This paper introduces two continuous time models, i.e. time homogenous and non-homogenous Markov chain models, for analyzing farm credit migration as alternatives to the traditional discrete time model cohort method. Results illustrate that the two continuous time models provide more detailed, accurate and reliable estimates of farm credit migration rates than the discrete time model. Metric comparisons among the three transition matrices show that the imposition of the potentially unrealistic assumption of time homogeneity still produces more accurate estimates of farm credit migration rates, although the equally reliable figures under the non-homogenous time model seem more plausible given the greater relevance and applicability of the latter model to farm business conditions.Agricultural Finance,
The C IV Mass Density of the Universe at Redshift 5
In order to search for metals in the Lyman alpha forest at redshifts z > 4,
we have obtained spectra of high S/N and resolution of three QSOs at z > 5.4
discovered by the Sloan Digital Sky Survey. These data allow us to probe to
metal enrichment of the intergalactic medium at early times with higher
sensitivity than previous studies. We find 16 C IV absorption systems with
column densities log N(C IV) = 12.50 - 13.98 over a total redshift path Delta X
= 3.29. In the redshift interval z = 4.5-5.0, where our statistics are most
reliable, we deduce a comoving mass density of C IV ions Omega(C IV) = (4.3 +/-
2.5) x 10(-8) (90% confidence limits) for absorption systems with log N(C IV) >
13.0 (for an Einstein-de Sitter cosmology with h = 0.65). This value of Omega(C
IV) is entirely consistent with those measured at z < 4; we confirm the earlier
finding by Songaila (2001) that neither the column density distribution of C IV
absorbers nor its integral show significant redshift evolution over a period of
time which stretches from 1.25 to 4.5 Gyr after the big bang. This somewhat
surprising conclusion may be an indication that the intergalactic medium was
enriched in metals at redshifts much greater than 5, perhaps by the sources
responsible for its reionization. Alternatively, the C IV systems we see may be
associated with outflows from massive star-forming galaxies at later times,
while the truly intergalactic metals may reside in regions of the Lyman alpha
forest of lower density than those probed up to now.Comment: 24 pages including 5 figures. Accepted for publication in the
Astrophysical Journal (September 10, 2003 issue
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