5,166 research outputs found
Improving Irrigation Scheduling and Water use Efficiency in Cotton
Cotton (Gossypium hirsutum L) is an important crop in the southern United States. The crop is grown in both irrigated and rainfed situations and is seldom free from periods of water shortages at some stage during the season. In recent years the need for consistency in yields and a stable cash flow has resulted in a rapid expansion in the number of irrigated acres of cotton in the Mississippi Delta. Irrigation research has, however, not kept pace with this expansion. This project represents a start at meeting this urgent need. The influence of weather patterns necessitates that these studies be conducted over several years, and the results given here are, therefore, only preliminary observations. The early termination of irrigation has not resulted in any significant decrease in yield or lint quality on the Sharkey clay, although there was a slight detrimental trend when irrigation was terminated too early in August. These studies have helped to clarify the relationship between soil-moisture deficit and plant stress, especially as relates to yield, for cotton cropped on a Sharkey clay soil. Evaluation of crop indicators of water deficit showed that leaf water potential and the air-canopy temperature differential are reliable indicators of the onset of water stress. Leaf extension growth is also a sensitive indicator, but of no practical value in irrigation management. With further research, leaf water potential and canopy-air temperature differentials could provide useful indicators for use in conjunction with traditional methods of scheduling irrigation for cotton in the humid mid-south. A better understanding of the irrigation requirements of the crop will improve management and will have a very significant dollar reduction in the cost of production of the crop
Multiparton Interactions in Photoproduction at HERA
The high energy photoproduction of jets is being observed at the ep collider,
HERA. It may be that the HERA centre-of-mass energy is sufficiently large that
the production of more than one pair of jets per ep collision becomes possible,
owing to the large number density of the probed gluons. We construct a Monte
Carlo model of such multiparton interactions and study their effects on a wide
range of physical observables. The conclusion is that multiple interactions
could have very significant effects upon the photoproduction final state and
that this would for example make extractions of the gluon density in the photon
rather difficult. Total rates for the production of many (i.e. > 2) jets could
provide direct evidence for the presence of multiple interactions, although
parton showering and hadronization significantly affect low transverse energy
jets.Comment: 21 pages, 8 figures include
Viewpoint consistency in Z and LOTOS: A case study
Specification by viewpoints is advocated as a suitable method of specifying complex systems. Each viewpoint describes the envisaged system from a particular perspective, using concepts and specification languages best suited for that perspective. Inherent in any viewpoint approach is the need to check or manage the consistency of viewpoints and to show that the different viewpoints do not impose contradictory requirements. In previous work we have described a range of techniques for consistency checking, refinement, and translation between viewpoint specifications, in particular for the languages LOTOS and Z. These two languages are advocated in a particular viewpoint model, viz. that of the Open Distributed Processing (ODP) reference model. In this paper we present a case study which demonstrates how all these techniques can be combined in order to show consistency between a viewpoint specified in LOTOS and one specified in Z. Keywords: Viewpoints; Consistency; Z; LOTOS; ODP
Diffractive deeply inelastic scattering of hadronic states with small transverse size
Diffractive deeply inelastic scattering from a hadron is described in terms
of diffractive quark and gluon distributions. If the transverse size of the
hadronic state is sufficiently small, these distributions are calculable using
perturbation theory. We present such a calculation and discuss the underlying
dynamics. We comment on the relation between this dynamics and the pattern of
scaling violation observed in the hard diffraction of large-size states at
HERA.Comment: 8 pages including 3 figures, REVTE
Quiescent consistency: Defining and verifying relaxed linearizability
Concurrent data structures like stacks, sets or queues need to be highly optimized to provide large degrees of parallelism with reduced contention. Linearizability, a key consistency condition for concurrent objects, sometimes limits the potential for optimization. Hence algorithm designers have started to build concurrent data structures that are not linearizable but only satisfy relaxed consistency requirements. In this paper, we study quiescent consistency as proposed by Shavit and Herlihy, which is one such relaxed condition. More precisely, we give the first formal definition of quiescent consistency, investigate its relationship with linearizability, and provide a proof technique for it based on (coupled) simulations. We demonstrate our proof technique by verifying quiescent consistency of a (non-linearizable) FIFO queue built using a diffraction tree. © 2014 Springer International Publishing Switzerland
Verifying linearizability on TSO architectures
Linearizability is the standard correctness criterion for fine-grained, non-atomic concurrent algorithms, and a variety of methods for verifying linearizability have been developed. However, most approaches assume a sequentially consistent memory model, which is not always realised in practice. In this paper we define linearizability on a weak memory model: the TSO (Total Store Order) memory model, which is implemented in the x86 multicore architecture. We also show how a simulation-based proof method can be adapted to verify linearizability for algorithms running on TSO architectures. We demonstrate our approach on a typical concurrent algorithm, spinlock, and prove it linearizable using our simulation-based approach. Previous approaches to proving linearizabilty on TSO architectures have required a modification to the algorithm's natural abstract specification. Our proof method is the first, to our knowledge, for proving correctness without the need for such modification
Correlated Resource Models of Internet End Hosts
Understanding and modelling resources of Internet end hosts is essential for
the design of desktop software and Internet-distributed applications. In this
paper we develop a correlated resource model of Internet end hosts based on
real trace data taken from the SETI@home project. This data covers a 5-year
period with statistics for 2.7 million hosts. The resource model is based on
statistical analysis of host computational power, memory, and storage as well
as how these resources change over time and the correlations between them. We
find that resources with few discrete values (core count, memory) are well
modeled by exponential laws governing the change of relative resource
quantities over time. Resources with a continuous range of values are well
modeled with either correlated normal distributions (processor speed for
integer operations and floating point operations) or log-normal distributions
(available disk space). We validate and show the utility of the models by
applying them to a resource allocation problem for Internet-distributed
applications, and demonstrate their value over other models. We also make our
trace data and tool for automatically generating realistic Internet end hosts
publicly available
Can One Distinguish Tau Neutrinos from Antineutrinos in Neutral-Current Pion Production Processes?
A potential way to distinguish tau-neutrinos from antineutrinos, below the
tau-production threshold, but above the pion production one, is presented. It
is based on the different behavior of the neutral current pion production off
the nucleon, depending on whether it is induced by neutrinos or antineutrinos.
This procedure for distinguishing tau-neutrinos from antineutrinos neither
relies on any nuclear model, nor it is affected by any nuclear effect
(distortion of the outgoing nucleon waves, etc...). We show that
neutrino-antineutrino asymmetries occur both in the totally integrated cross
sections and in the pion azimuthal differential distributions. To define the
asymmetries for the latter distributions we just rely on Lorentz-invariance.
All these asymmetries are independent of the lepton family and can be
experimentally measured by using electron or muon neutrinos, due to the lepton
family universality of the neutral current neutrino interaction. Nevertheless
and to estimate their size, we have also used the chiral model of
hep-ph/0701149 at intermediate energies. Results are really significant since
the differences between neutrino and antineutrino induced reactions are always
large in all physical channels.Comment: Revised version. 8 pages, 3 figures. The abstract has been changed
and discussion extende
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