27,906 research outputs found
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A conceptual and empirical framework to analyze the economics of consumer food waste
We develop a microeconomic model to understand food waste of consumers. We capture at-home and away-from home food consumption and distinguish between food purchases and food consumption. We allow the consumer to choose the rate of food waste at home optimally to maximize her utility. We show that consumer purchases can decline or increase with a cut in the rate of consumer waste, depending on the elasticity of food demand. Using the UK data for poultry in 2012, we also show a case where for a price elastic demand food consumption increases with a reduction in the food waste rate, but food purchases (retail sales) increase
Are the Nuclei of Seyfert 2 Galaxies Viewed Face-On?
We show from modeling the Fe Kalpha line in the ASCA spectra of four X-ray
bright narrow emission line galaxies (Seyfert types 1.9 and 2) that two equally
viable physical models can describe the observed line profile. The first is
discussed by Turner et al. (1998) and consists of emission from a nearly
pole-on accretion disk. The second, which is statistically preferred, is a
superposition of emission from an accretion disk viewed at an intermediate
inclination of about 48 degrees and a distinct, unresolved feature that
presumably originates some distance from the galaxy nucleus. The intermediate
inclination is entirely consistent with unified schemes and our findings
challenge recent assertions that Seyfert 2 galaxies are preferentially viewed
with their inner regions face-on. We derive mean equivalent widths for the
narrow and disk lines of =60 eV and = 213 eV, respectively. The
X-ray data are well described by a geometry in which our view of the active
nucleus intersects and is blocked by the outer edges of the obscuring torus,
and therefore do not require severe misalignments between the accretion disk
and the torus.Comment: 19 pages, 3 postscript figures. Accepted for publication in ApJ
Energetic Impact of Jet Inflated Cocoons in Relaxed Galaxy Clusters
Jets from active galactic nuclei (AGN) in the cores of galaxy clusters have
the potential to be a major contributor to the energy budget of the
intracluster medium (ICM). To study the dependence of the interaction between
the AGN jets and the ICM on the parameters of the jets themselves, we present a
parameter survey of two-dimensional (axisymmetric) ideal hydrodynamic models of
back-to-back jets injected into a cluster atmosphere (with varying Mach numbers
and kinetic luminosities). We follow the passive evolution of the resulting
structures for several times longer than the active lifetime of the jet. The
simulations fall into roughly two classes, cocoon-bounded and non-cocoon
bounded sources. We suggest a correspondence between these two classes and the
Faranoff-Riley types. We find that the cocoon-bounded sources inject
significantly more entropy into the core regions of the ICM atmosphere, even
though the efficiency with which energy is thermalized is independent of the
morphological class. In all cases, a large fraction (50--80%) of the energy
injected by the jet ends up as gravitational potential energy due to the
expansion of the atmosphere.Comment: 12 pages, Accepted for publication in Ap
Three-dimensional time dependent computation of turbulent flow
The three-dimensional, primitive equations of motion are solved numerically for the case of isotropic box turbulence and the distortion of homogeneous turbulence by irrotational plane strain at large Reynolds numbers. A Gaussian filter is applied to governing equations to define the large scale field. This gives rise to additional second order computed scale stresses (Leonard stresses). The residual stresses are simulated through an eddy viscosity. Uniform grids are used, with a fourth order differencing scheme in space and a second order Adams-Bashforth predictor for explicit time stepping. The results are compared to the experiments and statistical information extracted from the computer generated data
School violence, school differences and school discourses
This article highlights one strand of a study which investigated the concept of the violenceresilient school. In six inner-city secondary schools, data on violent incidents in school and violent crime in the neighbourhood were gathered, and compared with school practices to minimise violence, accessed through interviews. Some degree of association between the patterns of behaviour and school practices was found: schools with a wider range of wellconnected practices seemed to have less difficult behaviour. Interviews also showed that the different schools had different organisational discourses for construing school violence, its possible causes and the possible solutions. Differences in practices are best understood in connection with differences in these discourses. Some of the features of school discourses are outlined, including their range, their core metaphor and their silences. We suggest that organisational discourse is an important concept in explaining school effects and school differences, and that improvement attempts could have clearer regard to this concept
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Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera
Effects of increased ammonia and/or arginine
absorption on net splanchnic (portal-drained viscera
[PDV] plus liver) metabolism of nonnitrogenous
nutrients and hormones in cattle were examined. Six
Hereford × Angus steers (501 ± 1 kg BW) prepared with
vascular catheters for measurements of net flux across
the splanchnic bed were fed a 75% alfalfa:25% (as-fed
basis) corn and soybean meal diet (0.523 MJ of ME/[kg
BW0.75.d]) every 2 h without (27.0 g of N/kg of DM) and
with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a
split-plot design. Net flux measurements were made
immediately before and after a 72-h mesenteric vein
infusion of L-arginine (15 mmol/h). There were no treatment
effects onPDVor hepaticO2 consumption. Dietary
urea had no effect on splanchnic metabolism of glucose
or L-lactate, but arginine infusion decreased net hepatic
removal of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine
infusion (P < 0.07), and both dietary urea (P <
0.09) and arginine infusion (P < 0.05) increased net
hepatic removal of n-butyrate. Dietary urea also increased
total splanchnic acetate output (P < 0.06),
tended to increase arterial glucagon concentration (P
< 0.11), and decreased arterial ST concentration (P <
0.03). Arginine infusion increased arterial concentration
(P < 0.07) and net PDV release (P < 0.10) and
tended to increase hepatic removal (P < 0.11) of insulin,
as well as arterial concentration (P < 0.01) and total
splanchnic output (P < 0.01) of glucagon. Despite
changes in splanchnic N metabolism, increased ammonia
and arginine absorption had little measurable effect
on splanchnic metabolism of glucose and other nonnitrogenous
components of splanchnic energy metabolism
Radiative transfer in highly scattering materials - numerical solution and evaluation of approximate analytic solutions
Numerical solutions for radiative transport in a class of anisotropically scattering materials are presented. Conditions for convergence and divergence of the iterative method are given and supported by computed results. The relation of two flux theories to the equation of radiative transfer for isotropic scattering is discussed. The adequacy of the two flux approach for the reflectance, radiative flux and radiative flux divergence of highly scattering media is evaluated with respect to solutions of the radiative transfer equation
Occultation Mapping of the Central Engine in the Active Galaxy MCG -6-30-15
The colossal power output of active galactic nuclei (AGN) is believed to be
fueled by the accretion of matter onto a supermassive black hole. This central
accreting region of AGN has hitherto been spatially unresolved and its
structure therefore unknown. Here we propose that a previously reported `deep
minimum' in the X-ray intensity of the AGN MCG-6-30-15, was due to a unique
X-ray occultation event and that it probes structure of the central engine on
scales < 1e14 cm, or 1.4e-7 arcseconds. The data are consistent with a bright
central source surrounded by a less intense ring, which we identify with the
inner edge of an accretion disk. These may be the first direct measurements of
the spatial structure and geometry of the accreting black-hole system in an
active galaxy.If the ring of X-ray emission is identified with the inner edge
of an accretion disk, upper limits on the BH mass can be derived. Our
occultation interpretation is controversial in the sense that X-ray variability
in AGNs is normally attributed to intrinsic physical changes in the X-ray
emission region, such as disk or coronal instabilities.Comment: 15 pages, 2 Figures. Latex with separate postscript figure files.
Accepted for publication in ApJ Letter
Jet power extracted from ADAF and the applications to X-ray binaries and radio galaxy FR dichotomy
We calculate the jet power of the classical Blandford-Znajek(BZ) model and
hybrid model developed by Meier based on the global solutions of advection
dominated accretion flows (ADAFs) surrounding Kerr black holes. We find that
the jet power of the hybrid model is larger than that of the pure BZ model. The
jet power will dominate over the accretion power, and the objects will enter
into "jet-power-dominated advective systems", when the accretion rate is less
than a critical value mdot_c=Mdot_c/Mdot_Edd, where 3*10^-4 < mdot_c < 5*10^-3
is a function of black hole spin parameter. The accretion power will be
dominant when mdot<mdot_c and the objects will enter into
"accretion-power-dominated advective systems." This is roughly consistent with
that constrained from the low/hard-state black hole X-ray binaries (e.g.,
Fender et al.). We calculate the maximal jet power as a function of black hole
mass with the hybrid jet formation model, and find it can roughly reproduce the
dividing line of the Ledlow-Owen relation for FR I/FR II dichotomy in the jet
power-black hole(BH) mass plane (Q_jet-M_BH) if the dimensionless accretion
rate mdot~0.01 and BH spin parameter j~0.9-0.99 are adopted. This accretion
rate mdot~0.01 is consistent with that of the critical accretion rate for the
accretion mode transition of a standard disk to an ADAF constrained from the
state transition of X-ray binaries. Our results imply that most FR I galaxies
may be in the ADAF accretion mode similar to the low/hard-state XRBs.Comment: 6 pages, 3 color figures, ApJ in press, edited with ApJ style and
English is improved as suggested by Edito
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