767 research outputs found
Mechanisms for collaboration: a design and evaluation framework for multi-user interfaces
Multi-user interfaces are said to provide “natural” interaction in supporting collaboration, compared to individual and noncolocated technologies. We identify three mechanisms accounting for the success of such interfaces: high awareness of others' actions and intentions, high control over the interface, and high availability of background information. We challenge the idea that interaction over such interfaces is necessarily “natural” and argue that everyday interaction involves constraints on awareness, control, and availability. These constraints help people interact more smoothly. We draw from social developmental psychology to characterize the design of multi-user interfaces in terms of how constraints on these mechanisms can be best used to promote collaboration. We use this framework of mechanisms and constraints to explain the successes and failures of existing designs, then apply it to three case studies of design, and finally derive from them a set of questions to consider when designing and analysing multi-user interfaces for collaboration
Search for the Standard Model Higgs Boson with the OPAL Detector at LEP
This paper summarises the search for the Standard Model Higgs boson in e+e-
collisions at centre-of-mass energies up to 209 GeV performed by the OPAL
Collaboration at LEP. The consistency of the data with the background
hypothesis and various Higgs boson mass hypotheses is examined. No indication
of a signal is found in the data and a lower bound of 112.7GeV/C^2 is obtained
on the mass of the Standard Model Higgs boson at the 95% CL.Comment: 51 pages, 21 figure
Search for Yukawa Production of a Light Neutral Higgs Boson at LEP
Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in
the mass range of 4-12 GeV has been performed in the Yukawa process e+e- -> b
bbar A/h -> b bbar tau+tau-, using the data collected by the OPAL detector at
LEP between 1992 and 1995 in e+e- collisions at about 91 GeV centre-of-mass
energy. A likelihood selection is applied to separate background and signal.
The number of observed events is in good agreement with the expected
background. Within a CP-conserving 2HDM type II model the cross-section for
Yukawa production depends on xiAd = |tan beta| and xihd = |sin alpha/cos beta|
for the production of the CP-odd A and the CP-even h, respectively, where tan
beta is the ratio of the vacuum expectation values of the Higgs doublets and
alpha is the mixing angle between the neutral CP-even Higgs bosons. From our
data 95% C.L. upper limits are derived for xiAd within the range of 8.5 to 13.6
and for xihd between 8.2 to 13.7, depending on the mass of the Higgs boson,
assuming a branching fraction into tau+tau- of 100%. An interpretation of the
limits within a 2HDM type II model with Standard Model particle content is
given. These results impose constraints on several models that have been
proposed to explain the recent BNL measurement of the muon anomalous magnetic
moment.Comment: 24 pages, 9 figures, Submitted to Euro. Phys. J.
Measurement of triple gauge boson couplings from WW production at LEP energies up to 189 GeV
A measurement of triple gauge boson couplings is presented, based on W-pair
data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass
energy of 189 GeV with an integrated luminosity of 183 pb^-1. After combining
with our previous measurements at centre-of-mass energies of 161-183 GeV we
obtain k_g=0.97 +0.20 -0.16, g_1^z=0.991 +0.060 -0.057 and lambda_g=-0.110
+0.058 -0.055, where the errors include both statistical and systematic
uncertainties and each coupling is determined by setting the other two
couplings to their SM values. These results are consistent with the Standard
Model expectations.Comment: 28 pages, 8 figures, submitted to Eur. Phys. J.
Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP
A search was performed for charginos with masses close to the mass of the
lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209
GeV recorded by the OPAL detector at LEP. Events were selected if they had an
observed high-energy photon from initial state radiation, reducing the dominant
background from two-photon scattering to a negligible level. No significant
excess over Standard Model expectations has been observed in the analysed data
set corresponding to an integrated luminosity of 570pb-1. Upper limits were
derived on the chargino pair-productin cross-section, and lower limits on the
chargino mass were derived in the context of the Minimal Supersymmetric
Extension of the Standard Model for the gravity and anomaly mediated
Supersymmetry breaking scenarios.Comment: 26 pages, 9 figure
Measurement of the Hadronic Cross-Section for the Scattering of Two Virtual Photons at LEP
The interaction of virtual photons is investigated using the reaction e+e- ->
e+e- hadrons based on data taken by the OPAL experiment at e+e- centre-of-mass
energies sqrt(s_ee)=189-209 GeV, for W>5 GeV and at an average Q^2 of 17.9
GeV^2. The measured cross-sections are compared to predictions of the Quark
Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET to the
NLO prediction for the reaction e+e- -> e+e-qqbar, and to BFKL calculations.
PHOJET, NLO e+e- -> e+e-qqbar, and QPM describe the data reasonably well,
whereas the cross-section predicted by a Leading Order BFKL calculation is too
large.Comment: 30 pages, 10 figures, Submitted to Eur.Phys.J.
A Measurement of Semileptonic B Decays to Narrow Orbitally-Excited Charm Mesons
The decay chain b -> Bbar -> D^{**0} l nu X, D^{**0} -> D^{*+} pi^-, D^{*+}
-> D^0 pi^+, D^0 ->(Kpi or K3pi) is identified in a sample of 3.9 million
hadronic Z decays collected with the OPAL detector at LEP. The branching ratio
BR (b -> Bbar) x BR (Bbar -> D^0_1 l nu X) x BR (D^0_1 -> D^{*+} pi^-) is
measured to be (2.64 +- 0.79 (stat) +- 0.39 (syst)) X 10^-3 for the J^P = 1^+
(D^0_1) state. For decays into the J^P = 2^+ (D^{*0}_2) state, an upper limit
of 1.4 X 10^-3 is placed on the branching ratio at the 95% confidence level.Comment: 20 pages, 6 figure
Nucleation of a sodium droplet on C60
We investigate theoretically the progressive coating of C60 by several sodium
atoms. Density functional calculations using a nonlocal functional are
performed for NaC60 and Na2C60 in various configurations. These data are used
to construct an empirical atomistic model in order to treat larger sizes in a
statistical and dynamical context. Fluctuating charges are incorporated to
account for charge transfer between sodium and carbon atoms. By performing
systematic global optimization in the size range 1<=n<=30, we find that Na_nC60
is homogeneously coated at small sizes, and that a growing droplet is formed
above n=>8. The separate effects of single ionization and thermalization are
also considered, as well as the changes due to a strong external electric
field. The present results are discussed in the light of various experimental
data.Comment: 17 pages, 10 figure
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