4,726 research outputs found
USING A MULTIPLE PRODUCT AND MULTIPLE INPUT APPROACH TO DAIRY PROFIT MAXIMIZATION: A SIMULATION USING OPERATIONS RESEARCH METHODS
Dairy producers generally take a single output/multiple input approach when making production decisions. Under component pricing, with large variance in individual component prices, a multiple output/multiple input approach maximizes profits. This paper applied our approach to the individual farm milk production decision.Livestock Production/Industries, Productivity Analysis,
Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring
Spontaneous excitation of the dominant mode in a spin-wave active ring -- a
self-exciting positive-feedback system incorporating a spin-wave transmission
structure -- occurs at a certain threshold value of external gain. In general,
the wavenumber of the dominant mode is extremely sensitive to the properties
and environment of the spin-wave transmission medium, and is almost impossible
to predict. In this letter, we report on a backward volume magnetostatic
spin-wave active ring system incorporating a magnonic crystal. When mode
enhancement conditions -- readily predicted by a theoretical model -- are
satisfied, the ring geometry permits highly robust and consistent forced
dominant wavenumber selection.Comment: 4 pages, 3 figure
The evolution and star formation of dwarf galaxies in the Fornax Cluster
We present the results of a spectroscopic survey of 675 bright (16.5<Bj<18)
galaxies in a 6 degree field centred on the Fornax cluster with the FLAIR-II
spectrograph on the UK Schmidt Telescope. We measured redshifts for 516
galaxies of which 108 were members of the Fornax Cluster. Nine of these are new
cluster members previously misidentified as background galaxies. The cluster
dynamics show that the dwarf galaxies are still falling into the cluster
whereas the giants are virialised. Our spectral data reveal a higher rate of
star formation among the dwarf galaxies than suggested by morphological
classification: 35 per cent have H-alpha emission indicative of star formation
but only 19 per cent were morphologically classified as late-types. The
distribution of scale sizes is consistent with evolutionary processes which
transform late-type dwarfs to early-type dwarfs. The fraction of dwarfs with
active star formation drops rapidly towards the cluster centre. The
star-forming dwarfs are concentrated in the outer regions of the cluster, the
most extreme in an infalling subcluster. We estimate gas depletion time scales
for 5 dwarfs with detected HI emission: these are long (of order 10 Gyr),
indicating that active gas removal must be involved if they are transformed
into gas-poor dwarfs as they fall further into the cluster. In agreement with
our previous results, we find no compact dwarf elliptical (M32-like) galaxies
in the Fornax Cluster.Comment: To appear in Monthly Notices of the Royal Astronomical Societ
Oscillatory Energy Exchange Between Waves Coupled by a Dynamic Artificial Crystal
We describe a general mechanism of controllable energy exchange between waves
propagating in a dynamic artificial crystal. We show that if a spatial
periodicity is temporarily imposed on the transmission properties of a
wave-carrying medium whilst a wave is inside, this wave is coupled to a
secondary counter-propagating wave and energy oscillates between the two. The
oscillation frequency is determined by the width of the spectral band gap
created by the periodicity and the frequency difference between the coupled
waves. The effect is demonstrated with spin waves in a dynamic magnonic
crystal.Comment: 5 pages, 4 figure
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the
Astrophysical Journa
The FIRST-Optical-VLA Survey for Lensed Radio Lobes
We present results from a survey for gravitationally lensed radio lobes.
Lensed lobes are a potentially richer source of information about galaxy mass
distributions than lensed point sources, which have been the exclusive focus of
other recent surveys. Our approach is to identify radio lobes in the FIRST
catalog and then search optical catalogs for coincident foreground galaxies,
which are candidate lensing galaxies. We then obtain higher-resolution images
of these targets at both optical and radio wavelengths, and obtain optical
spectra for the most promising candidates. We present maps of several radio
lobes that are nearly coincident with galaxies. We have not found any new and
unambiguous cases of gravitational lensing. One radio lobe in particular, FOV
J0743+1553, has two hot spots that could be multiple images produced by a
z=0.19 spiral galaxy, but the lensing interpretation is problematic.Comment: 38 pages, 18 figures, aastex, accepted to A
Recommended from our members
How Porosity Modifies the Photovoltaic Effect in Nanocrystalline Solar Cells
The porosity of the nanocrystalline semiconductor affects many aspects of the photoconversion process in dye-sensitzed solar cells, thus distinguishing them mechanistically from conventional photovoltaic and photoelectro-chemical cells. We discuss several examples from our recent work
Antibiotic-resistant Escherichia Coli from Retail Poultry Meat with Different Antibiotic Use Claims
Background We sought to determine if the prevalence of antibiotic-resistant Escherichia coli differed across retail poultry products and among major production categories, including organic, âraised without antibioticsâ, and conventional. Results We collected all available brands of retail chicken and turkeyâincluding conventional, âraised without antibioticâ, and organic productsâevery two weeks from January to December 2012. In total, E. coli was recovered from 91% of 546 turkey products tested and 88% of 1367 chicken products tested. The proportion of samples contaminated with E. coli was similar across all three production categories. Resistance prevalence varied by meat type and was highest among E. coli isolates from turkey for the majority of antibiotics tested. In general, production category had little effect on resistance prevalence among E. coli isolates from chicken, although resistance to gentamicin and multidrug resistance did vary. In contrast, resistance prevalence was significantly higher for 6 of the antibiotics testedâand multidrug resistanceâamong isolates from conventional turkey products when compared to those labelled organic or âraised without antibioticsâ. E. coli isolates from chicken varied strongly in resistance prevalence among different brands within each production category. Conclusion The high prevalence of resistance among E. coli isolates from conventionally-raised turkey meat suggests greater antimicrobial use in conventional turkey production as compared to âraised without antibioticsâ and organic systems. However, among E. coli from chicken meat, resistance prevalence was more strongly linked to brand than to production category, which could be caused by brand-level differences during production and/or processing, including variations in antimicrobial use
The Fornax Spectroscopic Survey I. Survey Strategy and Preliminary Results on the Redshift Distribution of a Complete Sample of Stars and Galaxies
The Fornax Spectroscopic Survey will use the Two degree Field spectrograph
(2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample
of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on
the Fornax Cluster. By selecting all objects---both stars and
galaxies---independent of morphology, we cover a much larger range of surface
brightness and scale size than previous surveys. In this paper we present
results from the first 2dF field. Redshift distributions and velocity
structures are shown for all observed objects in the direction of Fornax,
including Galactic stars, galaxies in and around the Fornax Cluster, and for
the background galaxy population. The velocity data for the stars show the
contributions from the different Galactic components, plus a small tail to high
velocities. We find no galaxies in the foreground to the cluster in our 2dF
field. The Fornax Cluster is clearly defined kinematically. The mean velocity
from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They
show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be
traced behind the cluster to a redshift beyond z=0.3. Background compact
galaxies and low surface brightness galaxies are found to follow the general
galaxy distribution.Comment: LaTeX format; uses aa.cls (included). Accepted for publication in
Astronomy and Astrophysic
- âŠ