1,077 research outputs found
The Human Influence on Productivity in Harvester Operations
It is well-known that machine operators vary in their performance when undertaking mechanized forestry harvesting operations. Nevertheless, the human factor is still largely disregarded in productivity calculations. In the present study, operator performance is evaluated by analysing archived production data collected automatically by computers on-board single grip harvesters driven by 32 operators working in 3,351 stands over a period of three years. The experimental conditions were all approximately the same. The effect of the operators is modelled by a multilinear regression analysis. Seventeen operators were found to have performance levels that differed significantly from the mean model. Together, âtree volumeâ and âoperatorâ explained 84% of the overall variance. However, since 37.3% of the variance in productivity is explained by the operator, the influence of the operator on productivity is quite large. The minimum and maximum significant mean productivity values for all the operators differed by a factor of 2.2, which reduced to a factor of 1.8 if only data from experienced operators were analysed, although this still demonstrates that the best operators are nearly twice as productive as the worst. The operator, therefore, has an important influence on productivity and should be considered a key factor in productivity models
Pharmacophagy and pharmacophory: mechanisms of self-medication and disease prevention in the honeybee colony (Apis mellifera)
International audienceAbstractApitherapy promises cures for diseases in human folk medicine, but the effects of honeybee produced and foraged compounds on bee health are less known. Yet, hive products should chiefly facilitate medication and sanitation of the honeybees themselves rather than other organisms. We here review the impact of both self-produced gland secretions and foraged hive products (pharmacognosy) on colony health. Although foraged plant-derived compounds vary highly in antibiotic activity depending on the floral and regional origins, secondary plant metabolites in honey, pollen and propolis are important for the antibiotic activity against pathogens and parasites. However, specific bee health-enhancing activities of bee products should clearly be distinguished from the effects of an intact nutrition ensuring the basic immune competence of bees. Further unravelling the interactions among groups of active substances or individual compounds used in concert with specific behavioural adaptations will deepen our understanding of the natural potential of honeybees to maintain colony health
Masses of a Fourth Generation with Two Higgs Doublets
We use sampling techniques to find robust constraints on the masses of a
possible fourth sequential fermion generation from electroweak oblique
variables. We find that in the case of a light (115 GeV) Higgs from a single
electroweak symmetry breaking doublet, inverted mass hierarchies are possible
for both quarks and leptons, but a mass splitting more than M(W) in the quark
sector is unlikely. We also find constraints in the case of a heavy (600 GeV)
Higgs in a single doublet model. As recent data from the Large Hadron Collider
hints at the existence of a resonance at 124.5 GeV and a single Higgs doublet
at that mass is inconsistent with a fourth fermion generation, we examine a
type II two Higgs doublet model. In this model, there are ranges of parameter
space where the Higgs sector can potentially counteract the effects of the
fourth generation. Even so, we find that such scenarios produce qualitatively
similar fermion mass distributions.Comment: v2: 9 pages, 7 figures, improved analysis of Higgs decay constraints,
typos corrected and reference adde
Boundary State from Ellwood Invariants
Boundary states are given by appropriate linear combinations of Ishibashi
states. Starting from any OSFT solution and assuming Ellwood conjecture we show
that every coefficient of such a linear combination is given by an Ellwood
invariant, computed in a slightly modified theory where it does not trivially
vanish by the on-shell condition. Unlike the previous construction of
Kiermaier, Okawa and Zwiebach, ours is linear in the string field, it is
manifestly gauge invariant and it is also suitable for solutions known only
numerically. The correct boundary state is readily reproduced in the case of
known analytic solutions and, as an example, we compute the energy momentum
tensor of the rolling tachyon from the generalized invariants of the
corresponding solution. We also compute the energy density profile of
Siegel-gauge multiple lump solutions and show that, as the level increases, it
correctly approaches a sum of delta functions. This provides a gauge invariant
way of computing the separations between the lower dimensional D-branes.Comment: v2: 63 pages, 14 figures. Major improvements in section 2. Version
published in JHE
The Z-Z' Mass Hierarchy in a Supersymmetric Model with a Secluded U(1)'-Breaking Sector
We consider the Z'/Z mass hierarchy in a supersymmetric model in which the
U(1)' is broken in a secluded sector coupled to the ordinary sector only by
gauge and possibly soft terms. A large mass hierarchy can be achieved while
maintaining the normal sparticle spectra if there is a direction in which the
tree level potential becomes flat when a particular Yukawa coupling vanishes.
We describe the conditions needed for the desired breaking pattern, to avoid
unwanted global symmetries, and for an acceptable effective mu parameter. The
electroweak breaking is dominated by A terms rather than scalar masses, leading
to tan beta ~ 1. The spectrum of the symmetry breaking sector is displayed.
There is significant mixing between the MSSM particles and new standard model
singlets, for both the Higgs scalars and the neutralinos. A larger Yukawa
coupling for the effective mu parameter is allowed than in the NMSSM because of
the U(1)' contribution to the running from a high scale. The upper bound on the
tree-level mass of the lightest CP even Higgs doublet mass is about c x 174
GeV, where c is of order unity, but the actual mass eigenvalues are generally
smaller because of singlet mixing.Comment: Latex, 12 Tables, 22 page
Z' Bosons at Colliders: a Bayesian Viewpoint
We revisit the CDF data on di-muon production to impose constraints on a
large class of Z' bosons occurring in a variety of E_6 GUT based models. We
analyze the dependence of these limits on various factors contributing to the
production cross-section, showing that currently systematic and theoretical
uncertainties play a relatively minor role. Driven by this observation, we
emphasize the use of the Bayesian statistical method, which allows us to
straightforwardly (i) vary the gauge coupling strength, g', of the underlying
U(1)'; (ii) include interference effects with the Z' amplitude (which are
especially important for large g'); (iii) smoothly vary the U(1)' charges; (iv)
combine these data with the electroweak precision constraints as well as with
other observables obtained from colliders such as LEP 2 and the LHC; and (v)
find preferred regions in parameter space once an excess is seen. We adopt this
method as a complementary approach for a couple of sample models and find
limits on the Z' mass, generally differing by only a few percent from the
corresponding CDF ones when we follow their approach. Another general result is
that the interference effects are quite relevant if one aims at discriminating
between models. Finally, the Bayesian approach frees us of any ad hoc
assumptions about the number of events needed to constitute a signal or
exclusion limit for various actual and hypothetical reference energies and
luminosities at the Tevatron and the LHC.Comment: PDFLaTeX, 24 pages, 7 figures. Version with improved tables and
figure
Long-distance radiative corrections to the di-pion tau lepton decay
We evaluate the model-dependent piece of O(alpha) long-distance radiative
corrections to tau^- \to \pi^- \pi^0\nu_{\tau} decays by using a meson
dominance model. We find that these corrections to the di-pion invariant mass
spectrum are smaller than in previous calculations based on chiral perturbation
theory. The corresponding correction to the photon inclusive rate is tiny
(-0.15%) but it can be of relevance when new measurements reach better
precision.Comment: 4 pages, 2 figures. An estimate of the shift produced in the
evaluation of the h.v.p. contribution to the muon anomalous magnetic moment
is added. Version to appear in Phys. Rev.
Indications for an Extra Neutral Gauge Boson in Electroweak Precision Data
A new analysis of the hadronic peak cross section at LEP 1 implies a small
amount of missing invisible width in Z decays, while the effective weak charge
in atomic parity violation has been determined recently to 0.6% accuracy,
indicating a significantly negative S parameter. As a consequence of these two
deviations, the data are described well if the presence of an additional Z'
boson, such as predicted in Grand Unified Theories, is assumed. Moreover, the
data are now rich enough to study an arbitrary extra Z' boson and to determine
its couplings in a model independent way. An excellent best fit to the data is
obtained in this case, suggesting the possibility of a family non-universal Z'
with properties similar to ones predicted in a class of superstring theories.Comment: 5 pages of ReVTeX, 2 figure
A wide scalar neutrino resonance and b\bar{b} production at LEP
In supersymmetric models with R-parity violation, scalar neutrinos may be
produced as s-channel resonances in e^+e^- colliders. We note that within
current constraints, the scalar neutrino may have a width of several GeV into
b\bar{b} and be produced with large cross section, leading to a novel
supersymmetry discovery signal at LEP II. In addition, if the scalar neutrino
mass approximately equals m_Z, such a resonance necessarily increases R_b and
reduces A_{FB}(b), significantly improving the fit to electroweak data. Bounds
from B meson and top quark decays are leading constraints, and we stress the
importance of future measurements.Comment: 8 pages. LaTex + RevTex. Revised to include a discussion of ISR
effects. Version to appear in Phys. Rev. Let
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