IMPACT OF ALTERNATIVE GRID PRICING STRUCTURES ON CATTLE MARKETING DECISIONS

Quality grade, yield grade, and other feedlot performance factors explain much of the variation in profit under grid pricing. Thus, feedlot owners can change profits by adjusting time on feed to influence these performance factors. This research uses growth models, logistic regression, and an optimization process to determine how the optimal number of days on feed changes under different grid pricing structures. It was found that large quality or small yield discounts increases the optimal number of days on feed and small quality or large yield discounts result in fewer days on feed. Losses associated with a grid having large quality discounts are minimized as cattle fed for more days are able to obtain Choice premiums despite the discounts for more Yield Grade 4 and 5 carcasses. Given small quality discounts, cattle fed for a shorter length of time can obtain the Yield Grade 1 and 2 premiums without a large loss in revenue due to grading Select or Standard. Under cash pricing, cattle are fed for very long periods because there are no discounts applied to the carcasses and, therefore, the more weight they gain, the more revenue they generate. During periods of low feed prices, cattle can be fed longer so more cattle grade Prime but also have more Yield Grade 4 and 5 cattle.grid pricing, profits, animal growth, logistic regression, days on feed, Livestock Production/Industries, Marketing,

Determination of complex absorbing potentials from the electron self-energy

The electronic conductance of a molecule making contact to electrodes is determined by the coupling of discrete molecular states to the continuum electrode density of states. Interactions between bound states and continua can be modeled exactly by using the (energy-dependent) self-energy, or approximately by using a complex potential. We discuss the relation between the two approaches and give a prescription for using the self-energy to construct an energy-independent, non-local, complex potential. We apply our scheme to studying single-electron transmission in an atomic chain, obtaining excellent agreement with the exact result. Our approach allows us to treat electron-reservoir couplings independent of single electron energies, allowing for the definition of a one-body operator suitable for inclusion into correlated electron transport calculations.Comment: 11 pages, 8 figures; to be published in the J. Chem. Phy

Ballistic Conductance in Oxidized Si Nanowires

The influence of local oxidation in silicon nanowires on hole transport, and hence the effect of varying the oxidation state of silicon atoms at the wire surface, is studied using density functional theory in conjunction with a Green's function scattering method. For silicon nanowires with growth direction along [110] and diameters of a few nanometers, it is found that the introduction of oxygen bridging and back bonds does not significantly degrade hole transport for voltages up to several hundred millivolts relative to the valence band edge. As a result, the mean free paths are comparable to or longer than the wire lengths envisioned for transistor and other nanoelectronics applications. Transport along [100]-oriented nanowires is less favorable, thus providing an advantage in terms of hole mobilities for [110] nanowire orientations, as preferentially produced in some growth methods

Independent particle descriptions of tunneling from a many-body perspective

Currents across thin insulators are commonly taken as single electrons moving across classically forbidden regions; this independent particle picture is well-known to describe most tunneling phenomena. Examining quantum transport from a different perspective, i.e., by explicit treatment of electron-electron interactions, we evaluate different single particle approximations with specific application to tunneling in metal-molecule-metal junctions. We find maximizing the overlap of a Slater determinant composed of single particle states to the many-body current-carrying state is more important than energy minimization for defining single particle approximations in a system with open boundary conditions. Thus the most suitable single particle effective potential is not one commonly in use by electronic structure methods, such as the Hartree-Fock or Kohn-Sham approximations.Comment: 4+ pages, 4 figures; accepted to Phys. Rev. B Rapid Communication

Correlated electron transport in molecular electronics

Theoretical and experimental values to date for the resistances of single molecules commonly disagree by orders of magnitude. By reformulating the transport problem using boundary conditions suitable for correlated many-electron systems, we approach electron transport across molecules from a new standpoint. Application of our correlated formalism to benzene-dithiol gives current-voltage characteristics close to experimental observations. The method can solve the open system quantum many-body problem accurately, treats spin exactly, and is valid beyond the linear response regime

Structural and energetic origin of defects at the interface between germanium and a high-k dielectric from first principles

Atomic-scale models of the abrupt high-k/Ge interface with a range of suboxide stoichiometries GeO(x) are presented and compared to their Si analogs. Molecular dynamics and geometry optimization were carried out at the density functional theory level to yield structures and energetics. Cohesion across the interface becomes stronger with increasing oxidation of the Ge suboxide. Three-coordinate Ge is identified as the main defect and is formed at low energetic cost, which accounts for the observed abundance of defects at oxide/Ge interfaces. The optimum low temperature interface is defect-free, predominantly Ge(2+) with some Ge(+). (C) 2011 American Institute of Physics. (doi:10.1063/1.3554703

C-60 as a Faraday cage

Endohedral fullerenes have been proposed for a number of technological uses, for example, as a nanoscale switch, memory bit and as qubits for quantum computation. For these technology applications, it is important to know the ease with which the endohedral atom can be manipulated using an applied electric field. We find that the Buckminsterfullerene (C-60) acts effectively as a small Faraday cage, with only 25% of the field penetrating the interior of the molecule. Thus influencing the atom is difficult, but as a qubit the endohedral atom should be well shielded from environmental electrical noise. We also predict how the field penetration should increase with the fullerene radius. (C) 2004 American Institute of Physics. (DOI: 10.1063/1.1640783

Strain induced effects on electronic structure of semi-metallic and semiconducting tin nanowires

Semimetal nanowires are known to undergo a semimetal to semiconductor transition as a consequence of quantum confinement as their diameters are decreased. Using density functional theory calculations, the electronic structure of tin nanowires (SnNWs) under uniaxial strain within a range of 4% to þ4% is investigated. It is demonstrated that a [110]-oriented semi-metallic SnNW with a diameter of 4.2 nm can be made either more metallic or semiconducting by the application of tensile or compressive strain, respectively. On the contrary, a [100]-oriented semimetallic SnNW with a slightly larger diameter of 4.5 nm remains semiconducting with the application of either compressive or tensile strain. Carrier effective masses are calculated from the band structures; it is shown that for semimetal SnNW along [110] orientation the conduction and valence bands display near linear dispersion under both compressive and tensile strains (<3%) which leads to very small effective masses of 0.007m0. We also show that strain energies and Young modulus vary with nanowire diameter and crystal orientation. The effect of alloying on the generation of tensile and compressive strains in SnNWs is also investigated

Formation of contacts between doped carbon nanotubes and aluminum electrodes

A theoretical study of the a semiconducting carbon nanotube (CNT) bonding to an aluminum electrode is presented using density functional theory to determine the electronic structure, and charge transport across the junction is studied using non-equilibrium Green's functions. The properties of CNT-metal junctions are of interest for optimizing metal-semiconductor junctions for Schottky barrier transistors and for the formation of Ohmic contacts for nanoelectronics. We first consider the properties of an undoped (16,0) CNT bonded to an aluminum electrode, including an analysis of metal induced gap states and examination of the surface dipole. The junction is then modified by introduction of substitutional dopants into the CNT using nitrogen and boron to form n- and p-type semiconductors, respectively, and the resulting impact of the doping on current transport across the junctions is calculated. As an alternative doping strategy, tetrathiafulvalene is introduced endohedrally and found to act as an n-type dopant in agreement with previous experimental studies. From electron transmission and current voltage characteristics, it is found that the doped junctions can be engineered to have much lower onset resistances relative to the undoped junction. It is found that the current-voltage characteristics display increased resistance for larger forward and reverse biases: For one polarity, the resistance increase is associated with the introduction of the CNT band gap into the voltage bias window, whereas for the opposing voltage polarity, the resistance increase is due to large charge carrier-substitutional dopant scattering. For the case of the endohedral doping scheme, it is found that the carrier-dopant scattering is effectively absent. (C) 2013 AIP Publishing LLC