Phenomenological Lambda-Nuclear Interactions

Variational Monte Carlo calculations for ${_{\Lambda}^4}H$ (ground and excited states) and ${_{\Lambda}^5}He$ are performed to decipher information on ${\Lambda}$-nuclear interactions. Appropriate operatorial nuclear and ${\Lambda}$-nuclear correlations have been incorporated to minimize the expectation values of the energies. We use the Argonne $\upsilon_{18}$ two-body NN along with the Urbana IX three-body NNN interactions. The study demonstrates that a large part of the splitting energy in ${_{\Lambda}^4}H$ ($0^+-1^+$) is due to the three-body ${\Lambda}$ NN forces. $_{\Lambda}^{17}O$ hypernucleus is analyzed using the {\it s}-shell results. $\Lambda$ binding to nuclear matter is calculated within the variational framework using the Fermi-Hypernetted-Chain technique. There is a need to correctly incorporate the three-body ${\Lambda}$ NN correlations for $\Lambda$ binding to nuclear matter.Comment: 18 pages (TeX), 2 figure

Variational calculations of the Λ\Lambda-seperation energy of the Λ17_{\Lambda}^{17}O hypernucleus

Variational Monte Carlo calculations have been made for the $_{ \Lambda}^{17}$O hypernucleus using realistic two- and three-baryon interactions. A two pion exchange potential with spin- and space-exchange components is used for the $\Lambda$N potential. Three-body two-pion exchange and strongly repulsive dispersive $\Lambda$NN interactions are also included. The trial wave function is constructed from pair- and triplet-correlation operators acting on a single particle determinant. These operators consist of central, spin, isospin, tensor and three- baryon potential components. A cluster Monte Carlo method is developed for noncentral correlations and is used with up to four-baryon clusters in our calculations. The three-baryon $\Lambda$NN force is discussed.Comment: 24 pages, 2 figs available by fax., for publication in Phys. Rev.

CHARACTERISTICS OF RURAL SUBSISTENCE SMALL HOLDER LIVESTOCK PRODUCTION SYSTEM IN MOUNTAINOUS AREAS OF NWFP, PAKISTAN

A study was conducted in the rural mountainous areas of North West Frontier Province of Pakistan to characterize small holder’s subsistence livestock production system. Livestock farmers (n=82) were interviewed in 16 villages of Batagram and Mansehra districts. The farmers were keeping on an average 4 buffalos, 1 cattle, 12 sheep or 13 goats per household. More than 94% farmers were keeping 4 buffaloes per household as compared to only 40% keeping 1 or 2 cattle. Buffaloes were main dairy animals producing 7.9 liters of milk/day or 2370 liters per lactation of 300 days. Local non-descript cows were producing only 2.5 liters of milk per day. Animals of all species were found to be underfed, as they depended mostly on self growing local grasses for grazing. Only milking animals were offered some concentrates in the form of cottonseed cake and wheat bran. Milk was mostly consumed at the household level or converted into butter oil. Age at first calving and calving interval of buffaloes were longer than those of cows. Incidence of livestock diseases was high in the area. Major diseases in cattle and buffaloes were haemorrhagic septicaemia and internal parasites. Pleuropneumonia and parasitism were major disease problems in small ruminants. It was estimated that gross profit averaged Rs. 32475 per buffalo, Rs. 3320 per sheep and Rs. 5314 per goat per year. Gross margin for cattle was negative and the farmers were sustaining a loss of Rs. 1960 per cow per year. Keeping in view the poor production environments, the overall performance of animals was encouraging and offered considerable scope for improvement

Quantum optical non-linearities induced by Rydberg-Rydberg interactions: a perturbative approach

In this article, we theoretically study the quantum statistical properties of the light transmitted through or reflected from an optical cavity, filled by an atomic medium with strong optical non-linearity induced by Rydberg-Rydberg van der Waals interactions. Atoms are driven on a two-photon transition from their ground state to a Rydberg level via an intermediate state by the combination of a weak signal field and a strong control beam. By using a perturbative approach, we get analytic results which remain valid in the regime of weak feeding fields, even when the intermediate state becomes resonant. Therefore they allow us to investigate quantitatively new features associated with the resonant behaviour of the system. We also propose an effective non-linear three-boson model of the system which, in addition to leading to the same analytic results as the original problem, sheds light on the physical processes at work in the system

Microscopic calculations of Λ single-particle energies

A binding energy data for total baryon number A ≤ 208 and for Λ angular momenta ℓΛ ≤ 3 are analyzed in terms of phenomenological (but generally consistent with meson-exchange) ΛN and ΛNN potentials. The Fermi hypernetted chain technique is used to calculate the expectation values for the Λ binding to nuclear matter. Accurate effective ΛN and ΛNN potentials are obtained which are folded with the core-nucleus nucleon densities to calculate the Λ single-particle potential UΛ (r). We use a dispersive ANN potential but also include an explicit ρ dependence to allow for reduced repulsion in the surface, and the best fits have a large ρ dependence giving consistency with the variational Monte Carlo calculations for 5ΛHe. The exchange fraction of the ΛN space-exchange potential is found to be 0.2-0.3 corresponding to m*Λ ≃ (0.74 - 0.82)mΛ. Charge-symmetry breaking is found to be significant for heavy hypernuclei with a large neutron excess, with a strength consistent with that obtained from the A = 4 hypernuclei

Magnetic damping of a carbon nanotube NEMS resonator

A suspended, doubly clamped single wall carbon nanotube is characterized at cryogenic temperatures. We observe specific switching effects in dc-current spectroscopy of the embedded quantum dot. These have been identified previously as nano-electromechanical self-excitation of the system, where positive feedback from single electron tunneling drives mechanical motion. A magnetic field suppresses this effect, by providing an additional damping mechanism. This is modeled by eddy current damping, and confirmed by measuring the resonance quality factor of the rf-driven nano-electromechanical resonator in an increasing magnetic field.Comment: 8 pages, 3 figure