2,367 research outputs found
COMPOSITE SAMPLING TECHNIQUES FOR DETERMINING PESTICIDE CONCENTRATIONS
Composite sampling techniques are compared with random sampling methods for determining pesticide concentrations in agricultural fields. Estimates of mean pesticide concentrations and associated standard errors are presented for different experimental conditions. Variance components defined in extended forms of the Brown-Fisher model are estimated. The method of nonlinear least squares was employed to obtain numerical estimates of variance components by equating observed mean squares to expected mean squares for appropriate sampling designs
Flavor at the TeV Scale with Extra Dimensions
Theories where the Standard Model fields reside on a 3-brane, with a low
fundamental cut-off and extra dimensions, provide alternative solutions to the
gauge hierarchy problem. However, generating flavor at the TeV scale while
avoiding flavor-changing difficulties appears prohibitively difficult at first
sight. We argue to the contrary that this picture allows us to lower flavor
physics close to the TeV scale. Small Yukawa couplings are generated by
``shining'' badly broken flavor symmetries from distant branes, and flavor and
CP-violating processes are adequately suppressed by these symmetries. We
further show how the extra dimensions avoid four dimensional disasters
associated with light fields charged under flavor. We construct elegant and
realistic theories of flavor based on the maximal U(3)^5 flavor symmetry which
naturally generate the simultaneous hierarchy of masses and mixing angles.
Finally, we introduce a new framework for predictive theories of flavor, where
our 3-brane is embedded within highly symmetrical configurations of
higher-dimensional branes.Comment: 40 pages, 8 figure
Turbulence modeling in three-dimensional stenosed arterial bifurcations
Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar.
However, in the presence of a stenosis, the flow can become turbulent at the higher
Reynolds numbers during systole. There is growing consensus that the transitional k
? model is the best suited Reynolds averaged turbulence model for such flows. Further
confirmation of this opinion is presented here by a comparison with the RNG k? model
for the flow through a straight, nonbifurcating tube. Unlike similar validation studies
elsewhere, no assumptions are made about the inlet profile since the full length of the
experimental tube is simulated. Additionally, variations in the inflow turbulence quantities
are shown to have no noticeable affect on downstream turbulence intensity, turbulent
viscosity, or velocity in the k? model, whereas the velocity profiles in the transitional
k? model show some differences due to large variations in the downstream turbulence
quantities. Following this validation study, the transitional k? model is applied in a
three-dimensional parametrically defined computer model of the carotid artery bifurcation
in which the sinus bulb is manipulated to produce mild, moderate, and severe
stenosis. The parametric geometry definition facilitates a powerful means for investigating
the effect of local shape variation while keeping the global shape fixed. While turbulence
levels are generally low in all cases considered, the mild stenosis model produces
higher levels of turbulent viscosity and this is linked to relatively high values of turbulent
kinetic energy and low values of the specific dissipation rate. The severe stenosis model
displays stronger recirculation in the flow field with higher values of vorticity, helicity,
and negative wall shear stress. The mild and moderate stenosis configurations produce
similar lower levels of vorticity and helicity. DOI: 10.1115/1.240118
On the spectral density from instantons in quenched QCD
We investigate the contribution of instantons to the eigenvalue spectrum of
the Dirac operator in quenched QCD. The instanton configurations that we use
have been derived, elsewhere, from cooled SU(3) lattice gauge fields and, for
comparison, we also analyse a random `gas' of instantons. Using a set of
simplifying approximations, we find a non-zero chiral condensate. However we
also find that the spectral density diverges for small eigenvalues, so that the
chiral condensate, at zero quark mass, diverges in quenched QCD. The degree of
divergence decreases with the instanton density, so that it is negligible for
the smallest number of cooling sweeps but becomes substantial for larger number
of cools. We show that the spectral density scales, that finite volume
corrections are small and we see evidence for the screening of topological
charges. However we also find that the spectral density and chiral condensate
vary rapidly with the number of cooling sweeps -- unlike, for example, the
topological susceptibility. Whether the problem lies with the cooling or with
the identification of the topological charges is an open question. This problem
needs to be resolved before one can determine how important is the divergence
we have found for quenched QCD.Comment: 33 pages, 16 figures (RevTex), substantial revisions; to appear in
Phys.Rev.
What makes you not a Buddhist? : a preliminary mapping of values
This study sets out to establish which Buddhist values contrasted with or were shared by adolescents from a non-Buddhist population. A survey of attitude toward a variety of Buddhist values was fielded in a sample of 352 non-Buddhist schoolchildren aged between 13 and 15 in London. Buddhist values where attitudes were least positive concerned the worth of being a monk/nun or meditating, offering candles & incense on the Buddhist shrine, friendship on Sangha Day, avoiding drinking alcohol, seeing the world as empty or impermanent and Nirvana as the ultimate peace. Buddhist values most closely shared by non-Buddhists concerned the Law of Karma, calming the mind, respecting those deserving of respect, subjectivity of happiness, welfare work, looking after parents in old age and compassion to cuddly animals. Further significant differences of attitude toward Buddhism were found in partial correlations with the independent variables of sex, age and religious affiliation. Correlation patterns paralleled those previously described in theistic religions. Findings are applied to spiritual, moral, social and cultural development and for the teaching of religious to pupils of no faith adherence. The study recommends that quantitative psychometrics employed to conceptualize Buddhist values by discriminant validity in this study could be extended usefully to other aspects of the study of Buddhism, particularly in quest of validity in the conceptualization of Buddhist identity within specifically Buddhist populations
On the chirality of quark modes
A model for the QCD vacuum based on a domainlike structured background gluon
field with definite duality attributed to the domains has been shown elsewhere
to give confinement of static quarks, a reasonable value for the topological
susceptibility and indications that chiral symmetry is spontaneously broken. In
this paper we study in detail the eigenvalue problem for the Dirac operator in
such a gluon mean field. A study of the local chirality parameter shows that
the lowest nonzero eigenmodes possess a definite mean chirality correlated with
the duality of a given domain. A probability distribution of the local
chirality qualitatively reproduces histograms seen in lattice simulations.Comment: RevTeX4, 5 figures, 14 page
Higher Dimensional Recombination of Intersecting D-branes
We study recombinations of D-brane systems intersecting at more than one
angle using super Yang-Mills theory. We find the condensation of an
off-diagonal tachyon mode relates to the recombination, as was clarified for
branes at one angle in hep-th/0303204. For branes at two angles, after the
tachyon mode between two D2-branes condensed, D2-brane charge is distributed in
the bulk near the intersection point. We also find that, when two intersection
angles are equal, the off-diagonal lowest mode is massless, and a new stable
non-abelian configuration, which is supersymmetric up to a quadratic order in
the fluctuations, is obtained by the deformation by this mode.Comment: 18 pages, 2 figures, JHEP style. v3:references added, minor
corrections, English improve
Cosmological consequences of particle creation during inflation
Particle creation during inflation is considered. It could be important for
species whose interaction is of gravitational strength or weaker. A complete
but economical formalism is given for spin-zero and spin-half particles, and
the particle abundance is estimated on the assumption that the particle mass in
the early universe is of order the Hubble parameter . It is roughly the same
for both spins, and it is argued that the same estimate should hold for higher
spin particles in particular the gravitino. The abundance is bigger than that
from the usual particle collision mechanism if the inflationary energy scale is
of order , but not if it is much lower.Comment: 17 pages, no Figure
All clinically-relevant blood components transmit prion disease following a single blood transfusion: a sheep model of vCJD
Variant CJD (vCJD) is an incurable, infectious human disease, likely arising from the consumption of BSE-contaminated meat products. Whilst the epidemic appears to be waning, there is much concern that vCJD infection may be perpetuated in humans by the transfusion of contaminated blood products. Since 2004, several cases of transfusion-associated vCJD transmission have been reported and linked to blood collected from pre-clinically affected donors. Using an animal model in which the disease manifested resembles that of humans affected with vCJD, we examined which blood components used in human medicine are likely to pose the greatest risk of transmitting vCJD via transfusion. We collected two full units of blood from BSE-infected donor animals during the pre-clinical phase of infection. Using methods employed by transfusion services we prepared red cell concentrates, plasma and platelets units (including leucoreduced equivalents). Following transfusion, we showed that all components contain sufficient levels of infectivity to cause disease following only a single transfusion and also that leucoreduction did not prevent disease transmission. These data suggest that all blood components are vectors for prion disease transmission, and highlight the importance of multiple control measures to minimise the risk of human to human transmission of vCJD by blood transfusion
- …