4,562 research outputs found
Estimating factor models for multivariate volatilities : an innovation expansion method
We introduce an innovation expansion method for estimation of factor models for conditional variance (volatility) of a multivariate time series. We estimate the factor loading space and the number of factors by a stepwise optimization algorithm on expanding the "white noise space". Simulation and a real data example are given for illustration
Low-energy electron transport with the method of discrete ordinates
The one-dimensional discrete ordinates code ANISN was adapted to transport low energy (a few MeV) electrons. Calculated results obtained with ANISN were compared with experimental data for transmitted electron energy and angular distribution data for electrons normally incident on aluminum slabs of various thicknesses. The calculated and experimental results are in good agreement for a thin slab (0.2 of the electron range), but not for the thicker slabs (0.6 of the electron range). Calculated results obtained with ANISN were also compared with results obtained using Monte Carlo methods
Growth of Stocker Channel Catfish to Large Market Size in Single-Batch Culture
Catfish farmers increasingly are producing fish larger than the traditional size of 0.45-0.57 kg/fish in order to meet processing plant requirements for larger fish. Production of larger channel catfish (Ictalurus punctatus) in multiple-batch culture has been investigated in a few studies, but the impact of understocked fingerlings on growth of carry-over fish is unknown. The present study was conducted to quantify growth, feed conversion ratio, net daily yield, and net and total yield of stocker channel catfish grown in single-batch, one-season culture to mean individual weights of 0.60, 0.72, 0.91, or 1.17 kg/fish. Channel catfish (mean weight = 0.26 kg/fish) were stocked into 12 0.1-ha ponds at 11,115 fish/ha. Fish were fed a 32% crude protein floating extruded feed once daily to apparent satiation. When the average weight of the fish population reached the target weight, three randomly selected ponds were harvested. Fish growth was linear in all treatments. Growth rates were similar for fish grown to 0.60, 0.72, and 0.91 kg/fish, and significantly lower (P \u3c 0.05) than for fish grown to 1.17 kg. Variation in individual fish weight increased linearly with increased duration of culture period. Feed conversion ratio averaged 1.9 and did not differ significantly among treatments. The percentage of the fish population at harvest that fell within the 0.57 to 2.04 kg-size range preferred by processing plants increased from 56.6 to 98.5% as the mean weight at harvest increased from 0.60 to 1.17 kg/fish
Lorentzian spin foam amplitudes: graphical calculus and asymptotics
The amplitude for the 4-simplex in a spin foam model for quantum gravity is
defined using a graphical calculus for the unitary representations of the
Lorentz group. The asymptotics of this amplitude are studied in the limit when
the representation parameters are large, for various cases of boundary data. It
is shown that for boundary data corresponding to a Lorentzian simplex, the
asymptotic formula has two terms, with phase plus or minus the Lorentzian
signature Regge action for the 4-simplex geometry, multiplied by an Immirzi
parameter. Other cases of boundary data are also considered, including a
surprising contribution from Euclidean signature metrics.Comment: 30 pages. v2: references now appear. v3: presentation greatly
improved (particularly diagrammatic calculus). Definition of "Regge state"
now the same as in previous work; signs change in final formula as a result.
v4: two references adde
Asymptotics of 4d spin foam models
We study the asymptotic properties of four-simplex amplitudes for various
four-dimensional spin foam models. We investigate the semi-classical limit of
the Ooguri, Euclidean and Lorentzian EPRL models using coherent states for the
boundary data. For some classes of geometrical boundary data, the asymptotic
formulae are given, in all three cases, by simple functions of the Regge action
for the four-simplex geometry.Comment: 10 pages, Proceedings for the 2nd Corfu summer school and workshop on
quantum gravity and quantum geometry, talk given by Winston J. Fairbair
Optimum harvest time in Aquaculture: an application of economic principles to a Nile tilapia, Oreochromis niloticus (L.), growth model
A simple method is presented for determining the optimum time to harvest fish and the effect of fertilization type on optimum harvest time for Aquaculture. Optimum harvest time was similar for either maximizing fish yield or maximizing profit of fish harvested (price of fish times fish yield minus fish production cost), because the daily change in fish production cost was low for the low-input Nile tilapia, Oreochromis niloticus (L.), production system in Thailand. At a harvest time of 150 days for an organic fertilization treatment compared to an inorganic fertilization treatment fish yield increased from l-505 t/ha to 2-295 t/ha, and profit of fish harvested increased from 15657·1 baht/ha (US 948-2/ha). For the organic treatment, optimum harvest time occurred at 191 days, with a fish yield of 2·328 t/ha and a profit of 25520·5baht/ha (US 605·1/ha).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73931/1/j.1365-2109.1992.tb00807.x.pd
Value at Risk models with long memory features and their economic performance
We study alternative dynamics for Value at Risk (VaR) that incorporate a slow moving component and information on recent aggregate returns in established quantile (auto) regression models. These models are compared on their economic performance, and also on metrics of first-order importance such as violation ratios. By better economic performance, we mean that changes in the VaR forecasts should have a lower variance to reduce transaction costs and should lead to lower exceedance sizes without raising the average level of the VaR. We find that, in combination with a targeted estimation strategy, our proposed models lead to improved performance in both statistical and economic terms
Excitation functions for (p,x) reactions of niobium in the energy range of E = 40-90 MeV
A stack of thin Nb foils was irradiated with the 100 MeV proton beam at Los
Alamos National Laboratory's Isotope Production Facility, to investigate the
Nb(p,4n)Mo nuclear reaction as a monitor for intermediate energy
proton experiments and to benchmark state-of-the-art reaction model codes. A
set of 38 measured cross sections for Nb(p,x) and
Cu(p,x) reactions between 40-90 MeV, as well as 5 independent
measurements of isomer branching ratios, are reported. These are useful in
medical and basic science radionuclide productions at intermediate energies.
The Cu(p,x)Co, Cu(p,x)Zn, and
Cu(p,x)Zn reactions were used to determine proton
fluence, and all activities were quantified using HPGe spectrometry. Variance
minimization techniques were employed to reduce systematic uncertainties in
proton energy and fluence, improving the reliability of these measurements. The
measured cross sections are shown to be in excellent agreement with literature
values, and have been measured with improved precision compared with previous
measurements. This work also reports the first measurement of the
Nb(p,x)Rb reaction, and of the independent cross
sections for Cu(p,x)Mn and
Nb(p,x)Y in the 40-90 MeV region. The effects of
Si(p,x)Na contamination, arising from silicone
adhesive in the Kapton tape used to encapsulate the aluminum monitor foils, is
also discussed as a cautionary note to future stacked-target cross section
measurements. \emph{A priori} predictions of the reaction modeling codes CoH,
EMPIRE, and TALYS are compared with experimentally measured values and used to
explore the differences between codes for the Nb(p,x) and
Cu(p,x) reactions.Comment: 34 pages, submitted to NIM-
One vertex spin-foams with the Dipole Cosmology boundary
We find all the spin-foams contributing in the first order of the vertex
expansion to the transition amplitude of the Bianchi-Rovelli-Vidotto Dipole
Cosmology model. Our algorithm is general and provides spin-foams of
arbitrarily given, fixed: boundary and, respectively, a number of internal
vertices. We use the recently introduced Operator Spin-Network Diagrams
framework.Comment: 23 pages, 30 figure
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