A three-year economic evaluation of a commercial heifer development program

In 1994, 1995, and 1996, a commercial heifer development operation purchased a total of 1542 potential replacement heifers. Heifers were purchased in the fall proceeding the spring breeding season and fed a silage-based diet during the developmental period. Before the breeding season began, heifers that failed to meet minimum requirements for pelvic area, average daily gain, body weight, disposition, or structural soundness were culled. During the first year, 42% of 483 heifers were culled, 17% of 468 heifers were culled in the second year, and 14% of 591 heifers in the third year. Estrus was synchronized and heifers were inseminated artificially (AI) for 30 days followed by 30 days of natural mating by cleanup bulls. First-service AI conception rates averaged 68% and overall pregnancy rates (AI + natural mating) averaged 95.1% over the 3-year period. Heifers culled prior to the breeding season realized a net profit of $9 per head, whereas heifers diagnosed nonpregnant after the breeding season lost$86, and heifers that aborted lost $133. Profits for pregnant heifers sold were$163 for first-service AI, $138 for second-service AI, and$83 for bull bred

Timing of gain does not alter puberty and reproductive performance of beef heifers fed a high-roughage diet

Eighty crossbred heifers (549 lb initial body weight) were developed in drylot and limit-fed a forage sorghum silage diet predicted to produce gains of either 1 lb/day for the entire developmental period (EVENGAIN) or .25 lb/day for the first two-thirds of the period followed by 2 lb/day during the last third (LATEGAIN). Treatments began on November 7, 1994 and continued until April 24, 1995 (onset of the breeding season). Actual daily gains over the entire feeding period averaged 1.18 and 1.10 lb/day for EVENGAIN and LATEGAIN heifers, respectively. Age and weight at puberty were not affected by feeding treatment. Body condition score, frame score, and pelvic area were similar at the end of the experiment regardless of growth regimen. At the conclusion of the 168-day feeding period, estrus was synchronized using two injections of prostaglandin F2 , and heifers were inseminated artificially during a 45-day breeding season. Open heifers were mated naturally for an additional 15 days. First service and overall pregnancy rates were similar between treatments. In summary, timing of gain did not affect the onset of puberty or breeding performance. These data indicate that bee f producers may be able to utilize low quality feedstuffs early in heifer development without adversely affecting reproductive performance. Because feed inputs are major costs for developing beef heifers, such a management alternative may decrease costs

Moving constraints as stabilizing controls in classical mechanics

The paper analyzes a Lagrangian system which is controlled by directly assigning some of the coordinates as functions of time, by means of frictionless constraints. In a natural system of coordinates, the equations of motions contain terms which are linear or quadratic w.r.t.time derivatives of the control functions. After reviewing the basic equations, we explain the significance of the quadratic terms, related to geodesics orthogonal to a given foliation. We then study the problem of stabilization of the system to a given point, by means of oscillating controls. This problem is first reduced to the weak stability for a related convex-valued differential inclusion, then studied by Lyapunov functions methods. In the last sections, we illustrate the results by means of various mechanical examples.Comment: 52 pages, 4 figure

Shot noise of spin polarized electrons

The shot noise of spin polarized electrons is shown to be generically dependent upon spin-flip processes. Such a situation represents perhaps the simplest instance where the two-particle character of current fluctuations out of equilibrium is explicit, leading to trinomial statistics of charge transfer in a single channel model. We calculate the effect of spin-orbit coupling, magnetic impurities, and precession in an external magnetic field on the noise in the experimentally relevant cases of diffusive wires and lateral semiconductor dots, finding dramatic enhancements of the Fano factor. The possibility of using the shot noise to measure the spin-relaxation time in an open mesoscopic system is raised.Comment: Published version. Minor clarifications and correction

Decoherence from a Chaotic Environment: An Upside Down "Oscillator" as a Model

Chaotic evolutions exhibit exponential sensitivity to initial conditions. This suggests that even very small perturbations resulting from weak coupling of a quantum chaotic environment to the position of a system whose state is a non-local superposition will lead to rapid decoherence. However, it is also known that quantum counterparts of classically chaotic systems lose exponential sensitivity to initial conditions, so this expectation of enhanced decoherence is by no means obvious. We analyze decoherence due to a "toy" quantum environment that is analytically solvable, yet displays the crucial phenomenon of exponential sensitivity to perturbations. We show that such an environment, with a single degree of freedom, can be far more effective at destroying quantum coherence than a heat bath with infinitely many degrees of freedom. This also means that the standard "quantum Brownian motion" model for a decohering environment may not be as universally applicable as it once was conjectured to be.Comment: RevTeX, 29 pages, 5 EPS figures. Substantially rewritten analysis, improved figures, additional references, and errors fixed. Final version (to appear in PRA

Magnetoresistance of Two-Dimensional Fermions in a Random Magnetic Field

We perform a semiclassical calculation of the magnetoresistance of spinless two-dimensional fermions in a long-range correlated random magnetic field. In the regime relevant for the problem of the half filled Landau level the perturbative Born approximation fails and we develop a new method of solving the Boltzmann equation beyond the relaxation time approximation. In absence of interactions, electron density modulations, in-plane fields, and Fermi surface anisotropy we obtain a quadratic negative magnetoresistance in the weak field limit.Comment: 12 pages, Latex, no figures, Nordita repor

Current in the light-front Bethe-Salpeter formalism II: Applications

We pursue applications of the light-front reduction of current matrix elements in the Bethe-Salpeter formalism. The normalization of the reduced wave function is derived from the covariant framework and related to non-valence probabilities using familiar Fock space projection operators. Using a simple model, we obtain expressions for generalized parton distributions that are continuous. The non-vanishing of these distributions at the crossover between kinematic regimes (where the plus component of the struck quark's momentum is equal to the plus component of the momentum transfer) is tied to higher Fock components. Moreover continuity holds due to relations between Fock components at vanishing plus momentum. Lastly we apply the light-front reduction to time-like form factors and derive expressions for the generalized distribution amplitudes in this model.Comment: 12 pages, 6 figures, RevTex

Fathers' experiences of supporting breastfeeding: challenges for breastfeeding promotion and education

Increasing breastfeeding rates is a strategic priority in the UK and understanding the factors that promote and encourage breastfeeding is critical to achieving this. It is established that women who have strong social support from their partner are more likely to initiate and continue breastfeeding. However, little research has explored the fathers' role in breastfeeding support and more importantly, the information and guidance he may need. In the current study, 117 men whose partner had given birth in the previous 2 years and initiated breastfeeding at birth completed an open-ended questionnaire exploring their experiences of breastfeeding, the information and support they received and their ideas for future breastfeeding education and promotion aimed at fathers and families. Overall, the findings showed that fathers were encouraging of breastfeeding and wanted to be able to support their partner. However, they often felt left out of the breastfeeding relationships and helpless to support their partner at this time. Many reported being excluded from antenatal breastfeeding education or being considered unimportant in post-natal support. Men wanted more information about breastfeeding to be directed towards them alongside ideas about how they could practically support their partner. The importance of support mechanisms for themselves during this time was also raised. The results highlight the need for health professionals to direct support and information towards fathers as well as the mother–infant dyad and to recognise their importance in promoting and enabling breastfeeding