2,449 research outputs found
Intermediate inflation in light of the three-year WMAP observations
The three-year observations from the Wilkinson Microwave Anisotropy Probe
have been hailed as giving the first clear indication of a spectral index
n_s<1. We point out that the data are equally well explained by retaining the
assumption n_s=1 and allowing the tensor-to-scalar ratio r to be non-zero. The
combination n_s=1 and r>0 is given (within the slow-roll approximation) by a
version of the intermediate inflation model with expansion rate H(t) \propto
t^{-1/3}. We assess the status of this model in light of the WMAP3 data.Comment: 4 pages RevTeX4 with one figure. Minor changes to match PRD accepted
versio
Population dynamics of Pacific herring and humpback whales, Sitka Sound, Alaska 1981-2011
Thesis (Ph.D.) University of Alaska Fairbanks, 2015Humpback whales are a major predator in Sitka Sound, possibly consuming as much as a half-ton of Pacific herring per day. These large migratory baleen whales congregate in Sitka Sound to feed on schools of Pacific herring which spawn in April. In recent decades humpback whale abundance has increased tremendously in Sitka Sound after recovering from near extinction due to commercial whaling. In order to assess the long-term impact on herring by humpback whales, I estimated humpback whale abundance from 1981 to 2011. To do so I developed a Bayesian mark-recapture method for small sample sizes. I also modified a multi-strata Hilborn model to account for sporadic availability of whales in Sitka Sound. The multi-million dollar sac roe fishery in Sitka Sound is managed by the Alaska Department of Fish and Game (ADF&G) with an Age-Structured Assessment model (ASA). I modified the standard ASA model by including the humpback whale abundance estimates as a covariate for herring natural mortality. I found that there is no significant effect of humpback whales on herring mortality. In fact, both Pacific herring and humpback whale abundance have increased together, reaching their maximum values in 2011. This suggests that some other factor, perhaps better marine survival for both species, is driving their upwards trend
Revisiting carbon Kuznets curves with endogenous breaks modeling: evidence of decoupling and saturation (but few inverted-Us) for individual OECD countries
Future fuels and engines for railroad locomotives. Volume 1: Summary
The potential for reducing the dependence of railroads on petroleum fuel, particularly Diesel No. 2 was investigated. Two approaches are studied: (1) to determine how the use of Diesel No. 2 can be reduced through increased efficiency and conservation, and (2) to use fuels other than Diesel No. 2 both in Diesel and other types of engines. Because synthetic hydrocarbon fuels are particularly suited to medium speed diesel engines, the first commercial application of these fuels may be by the railroad industry
The Small Scale Velocity Dispersion of Galaxies: A Comparison of Cosmological Simulations
The velocity dispersion of galaxies on small scales ( Mpc),
, can be estimated from the anisotropy of the galaxy-galaxy
correlation function in redshift space. We apply this technique to
``mock-catalogs'' extracted from N-body simulations of several different
variants of Cold Dark Matter dominated cosmological models to obtain results
which may be consistently compared to similar results from observations. We
find a large variation in the value of in different
regions of the same simulation. We conclude that this statistic should not be
considered to conclusively rule out any of the cosmological models we have
studied. We attempt to make the statistic more robust by removing clusters from
the simulations using an automated cluster-removing routine, but this appears
to reduce the discriminatory power of the statistic. However, studying
as clusters with different internal velocity dispersions are
removed leads to interesting information about the amount of power on cluster
and subcluster scales. We also compute the pairwise velocity dispersion
directly and compare this to the values obtained using the Davis-Peebles
method, and find that the agreement is fairly good. We evaluate the models used
for the mean streaming velocity and the pairwise peculiar velocity distribution
in the original Davis-Peebles method by comparing the models with the results
from the simulations.Comment: 20 pages, uuencoded (Latex file + 8 Postscript figures), uses AAS
macro
Dynamics of Logamediate Inflation
A computation of the inflationary observables n_{s} and r is made for
`logamediate' inflation where the cosmological scale factor expands as , and is compared to their predicted values in the
intermediate inflationary theory, where . Both versions prove
to be consistent with observational measurements of the cosmic background
radiation. It is shown that the dynamics of a single inflaton field can be
mimicked by a system of several fields in an analogous manner to that created
by the joint evolution of the fields in assisted power-law inflation.Comment: 7 pages, 5 figures. Extended introductio
Can Inflation be Falsified?
Despite its central role in modern cosmology, doubts are often expressed as
to whether cosmological inflation is really a falsifiable theory. We
distinguish two facets of inflation, one as a theory of initial conditions for
the hot big bang and the other as a model for the origin of structure in the
Universe. We argue that the latter can readily be excluded by observations, and
that there are also a number of ways in which the former can find itself in
conflict with observational data. Both aspects of the theory are indeed
falsifiable.Comment: 7 pages LaTeX file with two figures incorporated by epsf. Fifth Prize
in Gravity Research Foundation Essay Competition. To appear, General
Relativity and Gravitatio
Gamma-rays from ultracompact minihalos: potential constraints on the primordial curvature perturbation
Ultracompact minihalos (UCMHs) are dense dark matter structures which can
form from large density perturbations shortly after matter-radiation equality.
If dark matter is in the form of Weakly Interacting Massive Particles (WIMPs),
then UCMHs may be detected via their gamma-ray emission. We investigate how the
{\em{Fermi}} satellite could constrain the abundance of UCMHs and place limits
on the power spectrum of the primordial curvature perturbation. Detection by
{\em Fermi} would put a lower limit on the UCMH halo fraction. The smallest
detectable halo fraction, , is for . If gamma-ray emission from UCMHs is not detected, an
upper limit can be placed on the halo fraction. The bound is tightest, , for . The
resulting upper limit on the power spectrum of the primordial curvature
perturbation in the event of non-detection is in the range on scales . This is substantially tighter than the existing constraints from
primordial black hole formation on these scales, however it assumes that dark
matter is in the form of WIMPs and UCMHs are not disrupted during the formation
of the Milky Way halo.Comment: 5 pages, 2 figures, version to appear in Phys. Rev. D, minor change
Maximum-Likelihood Comparisons of Tully-Fisher and Redshift Data: Constraints on Omega and Biasing
We compare Tully-Fisher (TF) data for 838 galaxies within cz=3000 km/sec from
the Mark III catalog to the peculiar velocity and density fields predicted from
the 1.2 Jy IRAS redshift survey. Our goal is to test the relation between the
galaxy density and velocity fields predicted by gravitational instability
theory and linear biasing, and thereby to estimate where is the linear bias parameter for IRAS galaxies.
Adopting the IRAS velocity and density fields as a prior model, we maximize the
likelihood of the raw TF observables, taking into account the full range of
selection effects and properly treating triple-valued zones in the
redshift-distance relation. Extensive tests with realistic simulated galaxy
catalogs demonstrate that the method produces unbiased estimates of
and its error. When we apply the method to the real data, we model the presence
of a small but significant velocity quadrupole residual (~3.3% of Hubble flow),
which we argue is due to density fluctuations incompletely sampled by IRAS. The
method then yields a maximum likelihood estimate
(1-sigma error). We discuss the constraints on and biasing that follow
if we assume a COBE-normalized CDM power spectrum. Our model also yields the
1-D noise noise in the velocity field, including IRAS prediction errors, which
we find to be be 125 +/- 20 km/sec.Comment: 53 pages, 20 encapsulated figures, two tables. Submitted to the
Astrophysical Journal. Also available at http://astro.stanford.edu/jeff
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