817 research outputs found

    Predicting Survival of East Texas Loblolly and Slash Pine Plantations Infected with Fusiform Rust

    Get PDF
    Repeated measurement during 1982-1992 of East Texas Pine Plantation Research Project permanent plots in loblolly( Pinus taedaL .) and slash( Pinus elliottii Engelm.) pine plantations throughout East Texas were used to develop equations for predicting the future number of trees per acre. A typical condition of East Texas pine plantations is the incidence of fusiform rust( Cronatrium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme). A regression procedure for fitting nonlinear systems of equations was used to fit survival models that considered the possibility that trees with no rust galls on the stem could either (1) remain uninfected and alive, (2) become infected yet still alive or (3) die. For infected stem so, only two possible outcomes were considered in the model:(1) remain infected and alive or (2) die.Analyses of the differences between predicted and observed values indicated no adverse trends for either of the two species. Apparently the models do represent observed survival patterns.South J. Appl. For. 20(1):30-35

    Preventing young farmers from leaving the farm: investigating the effectiveness of the young farmer payment using a behavioural approach

    Get PDF
    The number of young farmers has decreased over recent decades in several developed countries such as the United States and European countries. A recent strategy adopted by the European Union to address the resulting age imbalance is the Young Farmer Payment which provides an additional payment on top of the average basic payment introduced in the last Common Agricultural Policy reform. The objective of this study is to determine, by means of a behavioural approach, how this payment in fl uenced the incentives of young farmers to stay in the farm. Using the endogenous succession cycle model and the structural modelling technique, we found that the payment a ff ected young farmers ’ willingness to stay through its in fl uence on non-economic motivational goals. However, we also found that there are other factors that can be even more in fl uential, such as pessimism about farming, community and family integration, participation in decision making, and the opinion of neighbours, among others. Based on the results, we argue that similar policies could be adopted in other countries, although policies would be more e ff ective in addressing age imbalances if they are accompanied with complementary strategies aimed to deal with the identi fi ed social and psychological considerations

    Transverse momentum dependence in gluon distribution and fragmentation functions

    Get PDF
    We investigate the twist two gluon distribution functions for spin 1/2 hadrons, emphasizing intrinsic transverse momentum of the gluons. These functions are relevant in leading order in the inverse hard scale in scattering processes such as inclusive leptoproduction or Drell-Yan scattering, or more general in hard processes in which at least two hadrons are involved. They show up in azimuthal asymmetries. For future estimates of such observables, we discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure

    From E_8 to F via T

    Full text link
    We argue that T-duality and F-theory appear automatically in the E_8 gauge bundle perspective of M-theory. The 11-dimensional supergravity four-form determines an E_8 bundle. If we compactify on a two-torus, this data specifies an LLE_8 bundle where LG is a centrally-extended loopgroup of G. If one of the circles of the torus is smaller than sqrt(alpha') then it is also smaller than a nontrivial circle S in the LLE_8 fiber and so a dimensional reduction on the total space of the bundle is not valid. We conjecture that S is the circle on which the T-dual type IIB theory is compactified, with the aforementioned torus playing the role of the F-theory torus. As tests we reproduce the T-dualities between NS5-branes and KK-monopoles, as well as D6 and D7-branes where we find the desired F-theory monodromy. Using Hull's proposal for massive IIA, this realization of T-duality allows us to confirm that the Romans mass is the central extension of our LE_8. In addition this construction immediately reproduces the conjectured formula for global topology change from T-duality with H-flux.Comment: 25 pages, 4 eps figure

    Polymer Shape Anisotropy and the Depletion Interaction

    Full text link
    We calculate the second and third virial coefficients of the effective sphere-sphere interaction due to polymer depletion. By utilizing the anisotropy of a typical polymer conformation, we can consider polymers that are roughly the same size as the spherical inclusions. We argue that recent experiments can confirm this anisotropy.Comment: 4 pages, 4 eps figures, RevTe

    Universality of Z3 parafermions via edge-mode interaction and quantum simulation of topological space evolution with Rydberg atoms

    Get PDF
    Parafermions are Zn generalizations of Majorana quasiparticles, with fractional non-Abelian statistics. They can be used to encode topological qudits and perform Clifford operations by their braiding. Here we investigate the generation of quantum gates by allowing Z3 parafermions to interact in order to achieve universality. In particular, we study the form of the nontopological gate that arises through direct short-range interaction of the parafermion edge modes in a Z3 parafermion chain. We show that such an interaction gives rise to a dynamical phase gate on the encoded ground space, generating a non-Clifford gate which can be tuned to belong to even levels of the Clifford hierarchy. We illustrate how to access highly noncontextual states using this dynamical gate. Finally, we propose an experiment that simulates the braiding and dynamical evolutions of the Z3 topological states with Rydberg atom technology

    Null energy condition and superluminal propagation

    Get PDF
    We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimicking HË™>0\dot H>0 in scalar tensor theories of gravity.Comment: 46 pages, 6 figure

    Some Relations between Twisted K-theory and E8 Gauge Theory

    Full text link
    Recently, Diaconescu, Moore and Witten provided a nontrivial link between K-theory and M-theory, by deriving the partition function of the Ramond-Ramond fields of Type IIA string theory from an E8 gauge theory in eleven dimensions. We give some relations between twisted K-theory and M-theory by adapting the method of Diaconescu-Moore-Witten and Moore-Saulina. In particular, we construct the twisted K-theory torus which defines the partition function, and also discuss the problem from the E8 loop group picture, in which the Dixmier-Douady class is the Neveu-Schwarz field. In the process of doing this, we encounter some mathematics that is new to the physics literature. In particular, the eta differential form, which is the generalization of the eta invariant, arises naturally in this context. We conclude with several open problems in mathematics and string theory.Comment: 23 pages, latex2e, corrected minor errors and typos in published versio

    Supersymmetric Models with Higher Dimensional Operators

    Get PDF
    In 4D renormalisable theories, integrating out massive states generates in the low energy effective action higher dimensional operators (derivative or otherwise). Using a superfield language it is shown that a 4D N=1 supersymmetric theory with higher derivative operators in either the Kahler or the superpotential part of the Lagrangian and with an otherwise arbitrary superpotential, is equivalent to a 4D N=1 theory of second order (i.e. without higher derivatives) with additional superfields and renormalised interactions. We provide examples where a free theory with trivial supersymmetry breaking provided by a linear superpotential becomes, in the presence of higher derivatives terms and in the second order version, a non-trivial interactive one with spontaneous supersymmetry breaking. The couplings of the equivalent theory acquire a threshold correction through their dependence on the scale of the higher dimensional operator(s). The scalar potential in the second order theory is not necessarily positive definite, and one can in principle have a vanishing potential with broken supersymmetry. We provide an application to MSSM and argue that at tree-level and for a mass scale associated to a higher derivative term in the TeV range, the Higgs mass can be lifted above the current experimental limits.Comment: 36 pages; some clarifications and references adde
    • …
    corecore