506 research outputs found
New and Interesting Fungi. 1
This study introduces two new families, one new genus, 22 new species, 10 new combinations, four epitypes, and 16 interesting new host and / or geographical records. Cylindriaceae (based on Cylindrium elongatum) is introduced as new family, with three new combinations.Xyladictyochaetaceae (based on Xyladictyochaetalusitanica) is introduced to accommodate Xyladictyochaeta. Pseudoanungitea gen. nov. (based on P.syzygii)is described on stems of Vaccinium myrtillus(Germany). New species include: Exophiala eucalypticola on Eucalyptus obliqua leaf litter, Phyllosticta hakeicola on leaves of Hakea sp.,Setophaeosphaeriacitricola on leaves of Citrus australasica, and Sirastachyscyperacearum on leaves of Cyperaceae(Australia); Polyscytalum chilense on leaves of Eucalyptus urophylla (Chile); Pseudoanungitea vaccinii on Vaccinium myrtillus (Germany); Teichospora quercus on branch tissue of Quercus sp. (France); Fusiconidiumlycopodiellae on stems of Lycopodiella inundata,Monochaetiajunipericola on twig of Juniperus communis,Myrmecridiumsorbicola on branch tissues of Sorbus aucuparia, Parathyridariaphiladelphi on twigs of Philadelphus coronarius, and Wettsteininaphiladelphi on twigs of Philadelphus coronarius (Germany); Zygosporium pseudogibbum on leaves of Eucalyptus pellita (Malaysia); Pseudoanungiteavariabilis on dead wood (Spain); Alfaria acaciae on leaves of Acacia propinqua, Dictyochaeta mimusopis on leaves of Mimusops caffra,and Pseudocercosporabreonadiae on leaves of Breonadia microcephala (South Africa); Colletotrichumkniphofiae on leaves of Kniphofia uvaria,Subplenodomusiridicola on Iris sp., and Trochila viburnicola on twig cankers on Viburnum sp. (UK); Polyscytalum neofecundissimum on Quercus robur leaf litter, and Roussoellaeuonymi on fallen branches of Euonymus europaeus (Ukraine). New combinations include: Cylindrium algarvense on leaves of Eucalyptus sp. (Portugal), Cylindrium purgamentum on leaf litter (USA), Cylindrium syzygii on leaves of Syzygium sp. (Australia), Microdochium musae on leaves of Musa sp. (Malaysia), Polyscytalum eucalyptigenum on Eucalyptus grandis × pellita (Malaysia), P. eucalyptorum on leaves of Eucalyptus (Australia), P. grevilleae on leaves of Grevillea (Australia), P. nullicananum on leaves of Eucalyptus (Australia), Pseudoanungiteasyzygii on Syzygium cordatum leaf litter (South Africa), and Setophaeosphaeriasidae on leaves of Sida sp. (Brazil). New records include: Sphaerellopsis paraphysata on leaves of Phragmites sp., Vermiculariopsiella dichapetali on leaves of Melaleuca sp. and Eucalyptus regnans, and Xyladictyochaetalusitanica on leaf litter of Eucalyptus sp. (Australia); Camarosporidiella mackenziei on twigs of Caragana sp. (Finland); Cyclothyriella rubronotata on twigs of Ailanthus altissima, Rhinocladiella quercus on Sorbus aucuparia branches (Germany); Cytospora viticola on stems of Vitis vinifera (Hungary); Echinocatena arthrinioides on leaves of Acacia crassicarpa (Malaysia); Varicosporellopsis aquatilis from garden soil (Netherlands); Pestalotiopsis hollandica on needles of Cupressus sempervirens (Spain), Pseudocamarosporiumafricanum on twigs of Erica sp. (South Africa), Pseudocamarosporium brabeji on branch of Platanus sp. (Switzerland); Neocucurbitaria cava on leaves of Quercus ilex (UK); Chaetosphaeriamyriocarpaon decaying wood of Carpinus betulus,Haplograhium delicatum on decaying Carpinus betulus wood (Ukraine). Epitypes are designated for: Elsinoë mimosae on leaves of Mimosa diplotricha (Brazil), Neohendersonia kickxii on Fagus sylvatica twig bark (Italy), Caliciopsis maxima on fronds of Niphidium crassifolium (Brazil), Dictyochaeta septata on leaves of Eucalyptus grandis ×urophylla (Chile), and Microdochium musae on leaves of Musa sp. (Malaysia)
Inflationary Perturbations: the Cosmological Schwinger Effect
This pedagogical review aims at presenting the fundamental aspects of the
theory of inflationary cosmological perturbations of quantum-mechanical origin.
The analogy with the well-known Schwinger effect is discussed in detail and a
systematic comparison of the two physical phenomena is carried out. In
particular, it is demonstrated that the two underlying formalisms differ only
up to an irrelevant canonical transformation. Hence, the basic physical
mechanisms at play are similar in both cases and can be reduced to the
quantization of a parametric oscillator leading to particle creation due to the
interaction with a classical source: pair production in vacuum is therefore
equivalent to the appearance of a growing mode for the cosmological
fluctuations. The only difference lies in the nature of the source: an electric
field in the case of the Schwinger effect and the gravitational field in the
case of inflationary perturbations. Although, in the laboratory, it is
notoriously difficult to produce an electric field such that pairs extracted
from the vacuum can be detected, the gravitational field in the early universe
can be strong enough to lead to observable effects that ultimately reveal
themselves as temperature fluctuations in the Cosmic Microwave Background.
Finally, the question of how quantum cosmological perturbations can be
considered as classical is discussed at the end of the article.Comment: 49 pages, 6 figures, to appear in a LNP volume "Inflationary
Cosmology
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Measurement of the Strong Coupling alpha s from Four-Jet Observables in e+e- Annihilation
Data from e+e- annihilation into hadrons at centre-of-mass energies between
91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study
the four-jet rate as a function of the Durham algorithm resolution parameter
ycut. The four-jet rate is compared to next-to-leading order calculations that
include the resummation of large logarithms. The strong coupling measured from
the four-jet rate is alphas(Mz0)=
0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass)
in agreement with the world average. Next-to-leading order fits to the
D-parameter and thrust minor event-shape observables are also performed for the
first time. We find consistent results, but with significantly larger
theoretical uncertainties.Comment: 25 pages, 15 figures, Submitted to Euro. Phys. J.
Search for R-Parity Violating Decays of Scalar Fermions at LEP
A search for pair-produced scalar fermions under the assumption that R-parity
is not conserved has been performed using data collected with the OPAL detector
at LEP. The data samples analysed correspond to an integrated luminosity of
about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An
important consequence of R-parity violation is that the lightest supersymmetric
particle is expected to be unstable. Searches of R-parity violating decays of
charged sleptons, sneutrinos and squarks have been performed under the
assumptions that the lightest supersymmetric particle decays promptly and that
only one of the R-parity violating couplings is dominant for each of the decay
modes considered. Such processes would yield final states consisting of
leptons, jets, or both with or without missing energy. No significant
single-like excess of events has been observed with respect to the Standard
Model expectations. Limits on the production cross- section of scalar fermions
in R-parity violating scenarios are obtained. Constraints on the supersymmetric
particle masses are also presented in an R-parity violating framework analogous
to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.
Measurement of Rb in e+e- Collisions at 182 - 209 GeV
Measurements of Rb, the ratio of the bbbar cross-section to the qqbar cross-
section in e+e- collisions, are presented. The data were collected by the OPAL
experiment at LEP at centre-of-mass energies between 182 GeV and 209 GeV.
Lepton, lifetime and event shape information is used to tag events containing b
quarks with high efficiency. The data are compatible with the Standard Model
expectation. The mean ratio of the eight measurements reported here to the
Standard Model prediction is 1.055+-0.031+-0.037, where the first error is
statistical and the second systematic.Comment: 21 pages, 5 figures, Submitted to Phys. Letts
Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2
The hadronic structure function of the photon F_2^gamma is measured as a
function of Bjorken x and of the factorisation scale Q^2 using data taken by
the OPAL detector at LEP. Previous OPAL measurements of the x dependence of
F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of
F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted
by QCD, the data show positive scaling violations in F_2^gamma. Several
parameterisations of F_2^gamma are in agreement with the measurements whereas
the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001,
Ascona, Switzerlan
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons
We report the first observation of Z/gamma* production in Compton scattering
of quasi-real photons. This is a subprocess of the reaction e+e- to
e+e-Z/gamma*, where one of the final state electrons is undetected.
Approximately 55 pb-1 of data collected in the year 1997 at an e+e-
centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been
analysed. The Z/gamma* from Compton scattering has been detected in the
hadronic decay channel. Within well defined kinematic bounds, we measure the
product of cross-section and Z/gamma* branching ratio to hadrons to be
(0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV,
dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60
GeV, dominated by (e)egamma* production, this product is found to be
(4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo
event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
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