5,116 research outputs found
Nutritional Management Post-AI to Enhance Pregnancy Outcomes
Effective replacement heifer development is a critical segment of the integrated management program in an efficient beef cow production system. The most critical factor determining the success of any heifer development program is nutrition. Most efforts are concentrated in providing the right amount and quality of feed to achieve gains from 1.5 to 2.0 lb/day, so heifers can reach 65% of their mature BW by the day of breeding. Approximately 80% of the U.S. cow-herds are spring calving, which means that producers utilizing estrous synchronization and AI are keeping their heifers in a feedlot environment until heifers are inseminated. Immediately following AI, heifers are typically moved to pasture. It is known that maternal recognition of pregnancy takes place around d 15 - 17 post-insemination and that transporting animals near this time compromises conception rates. However, moving heifers within the first 5 days post-insemination does not cause this reduction. Although, research suggests that conception rates are compromised when heifers are placed on early growth pasture forages. We hypothesized that feeding this high moisture pasture forage at turnout is limiting DMI which in turn causes a temporary energy deficiency that results in temporary heifer weight loss during the critical stages of early embryonic development and maternal recognition of pregnancy. Therefore, it is beneficial to ensure heifers maintain the same plane of nutrition after breeding, at least until day 25 when the embryo should be completely attached to the uterus. If this is true, maintaining a positive plane of nutrition on heifers after breeding will increase 1st service conception rates, improving herd fertility and longevity
Constraining Large Scale Structure Theories with the Cosmic Background Radiation
We review the relevant 10+ parameters associated with inflation and matter
content; the relation between LSS and primary and secondary CMB anisotropy
probes; COBE constraints on energy injection; current anisotropy band-powers
which strongly support the gravitational instability theory and suggest the
universe could not have reionized too early. We use Bayesian analysis methods
to determine what current CMB and CMB+LSS data imply for inflation-based
Gaussian fluctuations in tilted CDM, hCDM and oCDM model
sequences with age 11-15 Gyr, consisting of mixtures of baryons, cold (and
possibly hot) dark matter, vacuum energy, and curvature energy in open
cosmologies. For example, we find the slope of the initial spectrum is within
about 5% of the (preferred) scale invariant form when just the CMB data is
used, and for CDM when LSS data is combined with CMB; with both, a
nonzero value of is strongly preferred ( for a 13
Gyr sequence, similar to the value from SNIa). The CDM sequence prefers
, but is overall much less likely than the flat
sequence with CMB+LSS. We also review the rosy forecasts
of angular power spectra and parameter estimates from future balloon and
satellite experiments when foreground and systematic effects are ignored.Comment: 20 pages, LaTeX, 5 figures, 2 tables, uses rspublic.sty To appear in
Philosophical Transactions of the Royal Society of London A, 1998.
"Discussion Meeting on Large Scale Structure in the Universe," Royal Society,
London, March 1998. Text and colour figures also available at
ftp://ftp.cita.utoronto.ca/bond/roysoc9
Eutrophication and restoration in temperate lakes
Eutrophication affects many lakes and reservoirs worldwide. It is caused by excessive amounts of nutrients entering waterbodies from their catchments, mainly due to human activity. The main sources of these nutrients are discharges from industry and wastewater treatment systems, and agricultural runoff. The water quality problems caused by eutrophication, such as harmful algal blooms, affect the sustainable use of lakes for agriculture, fisheries, recreation, tourism and water supply. They also degrade habitat quality and threaten biodiversity. A range of methods for improving lake water quality are explored, including catchment management and in-lake restoration measures. The potential impacts of these on lake biodiversity are explored, including species interactions and ecosystem feedbacks that may confound the recovery process. A particular challenge is the fact that achieving sustainable recovery may take many years, mainly due to the impact of legacy pollution problems. This must be taken into account when planning and implementing eutrophication management options, because these slow recovery periods can exceed the timescales that people are willing to accept. While this review focuses on the many well documented studies of restoration and recovery processes in temperate lakes, it also highlights the need for similar research on tropical and sub-tropical systems
Issues for the Next Generation of Galaxy Surveys
I argue that the weight of the available evidence favours the conclusions
that galaxies are unbiased tracers of mass, the mean mass density (excluding a
cosmological constant or its equivalent) is less than the critical Einstein-de
Sitter value, and an isocurvature model for structure formation offers a viable
and arguably attractive model for the early assembly of galaxies. If valid
these conclusions complicate our work of adding structure formation to the
standard model for cosmology, but it seems sensible to pay attention to
evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st
Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime
Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias
A standard drift-diffusion model of space charge wave propagation in
semiconductors has been studied numerically and analytically under dc voltage
bias. For sufficiently long samples, appropriate contact resistivity and
applied voltage - such that the sample is biased in a regime of negative
differential resistance - we find chaos in the propagation of nonlinear fronts
(charge monopoles of alternating sign) of electric field. The chaos is always
low-dimensional, but has a complex spatial structure; this behavior can be
interpreted using a finite dimensional asymptotic model in which the front
(charge monopole) positions and the electrical current are the only dynamical
variables.Comment: 12 pages, 8 figure
Spherical collapse with dark energy
I discuss the work of Maor and Lahav [1], in which the inclusion of dark
energy into the spherical collapse formalism is reviewed. Adopting a
phenomenological approach, I consider the consequences of - a) allowing the
dark energy to cluster, and, b) including the dark energy in the virialization
process. Both of these issues affect the final state of the system in a
fundamental way. The results suggest a potentially differentiating signature
between a true cosmological constant and a dynamic form of dark energy. This
signature is unique in the sense that it does not depend on a measurement of
the value of the equation of state of dark energy.Comment: To appear in the proceedings of the ``Peyresq Physics 10" Workshop,
19 - 24 June 2005, Peyresq, Franc
QSO clustering and the AAT 2dF redshift survey
We review previous results on the clustering and environments of QSOs. We
show that the correlation length for QSOs derived from existing surveys is
r~5/h Mpc, similar to the observed correlation length for field galaxies at the
present epoch. The galaxy environment for z<1 radio-quiet QSOs is also
consistent with field galaxies. The evolution of the QSO correlation length
with redshift is currently uncertain, largely due to the small numbers of QSOs
(~2000) in surveys suitable for clustering analysis. We report on intial
progress with the AAT 2dF QSO redshift survey, which, once completed will
comprise almost 30000 QSOs. With over 1000 QSOs already observed, it is already
the largest single homogeneous QSO survey. We discuss prospects for deriving
limits on cosmological parameters from this survey, and on the evolution of
large-scale structure in the Universe.Comment: Invited talk at RS meeting on 'Large Scale Structure in the Universe'
held at the Royal Society on 25-26 March 1998 14 pages, 11 figre
Eddy Impacts on the Florida Current
The Gulf Stream in the Atlantic carries warm water northwards and forms both the return closure of the subtropical gyre as well as the upper limb of the meridional overturning circulation. Recent time series recorded east of the Bahamas at 26°N indicate that from May 2009 to April 2011, in contrast with past observations, the northward flowing Antilles Current covaried with the Gulf Stream in the Florida Straitsâthe Florida Currentâeven though the Florida and Antilles Currents are separated by banks and islands spanning 150?km. The peak-to-trough amplitude of transport variations during this period was 15?Ă?106?m3?s?1 for the Florida Current and 12?Ă?106?m3?s?1 for the Antilles Current, at time scales of 50?days to a year. From satellite observations, we show that the fluctuations in both the Florida and Antilles Currents between May 2009 and April 2011 are driven by eddy activity east of the Bahamas. Since the Florida Current time series is a critical time series for the state of the oceans, and often compared to climate models, this newly identified source of variability needs careful consideration when attributing the variability of the Florida Current to changes in the larger-scale circulations (e.g., gyre and overturning) or wind forcing.<br/
The velocity peaks in the cold dark matter spectrum on Earth
The cold dark matter spectrum on earth is expected to have peaks in velocity
space. We obtain estimates for the sizes and locations of these peaks. To this
end we have generalized the secondary infall model of galactic halo formation
to include angular momentum of the dark matter particles. This new model is
still spherically symmetric and it has self-similar solutions. Our results are
relevant to direct dark matter search experiments.Comment: 12 pages including 1 table and 4 figures, LaTeX, REVTEX 3.0 versio
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