63,098 research outputs found
'Older people for older people' toolkit: developing social enterprise and service delivery in remote and rural areas
Z -> b\bar{b} Versus Dynamical Electroweak Symmetry Breaking involving the Top Quark
In models of dynamical electroweak symmetry breaking which sensitively
involve the third generation, such as top quark condensation, the effects of
the new dynamics can show up experimentally in Z->b\bar{b}. We compare the
sensitivity of Z->b\bar{b} and top quark production at the Tevatron to models
of the new physics. Z->b\bar{b} is a relatively more sensitive probe to new
strongly coupled U(1) gauge bosons, while it is generally less sensitive a
probe to new physics involving color octet gauge bosons as is top quark
production itself. Nonetheless, to accomodate a significant excess in
Z->b\bar{b} requires choosing model parameters that may be ruled out within run
I(b) at the Tevatron.Comment: LaTex file, 19 pages + 2 Figs., Fermilab-Pub-94/231-
Search for Narrow-Width ttbar Resonances in ppbar Collisions at center of mass energy = 1.8 TeV
We present a preliminary result on a search for narrow-width resonances that
decay into ttbar pairs using 130 pb^{-1} of lepton plus jets data in ppbar
collisions at center of mass energy = 1.8 TeV. No significant deviation from
Standard Model prediction is observed. 95% C.L. upper limits on the production
cross section of the narrow-width resonance times its branching fraction to
ttbar are presented for different resonance masses, M_X. We also exclude the
existence of a leptophobic topcolor particle, X, with M_X < 560 GeV/c^2 for a
width \Gamma_X = 0.012 M_X.Comment: 3 pages, 1 figure; Submitted for proceedings of 5th International
Conference on Quark Confinement and Hadron spectrum, held in Italy, from
11-14 Sep., 200
Spheromak formation and sustainment studies at the sustained spheromak physics experiment using high-speed imaging and magnetic diagnostics
A high-speed imaging system with shutter speeds as fast as 2 ns and double frame capability has been used to directly image the formation and evolution of the sustained spheromak physics experiment (SSPX) [E. B. Hooper et al., Nucl. Fusion 39, 863 (1999)]. Reproducible plasma features have been identified with this diagnostic and divided into three groups, according to the stage in the discharge at which they occur: (i) breakdown and ejection, (ii) sustainment, and (iii) decay. During the first stage, plasma descends into the flux conserver shortly after breakdown and a transient plasma column is formed. The column then rapidly bends and simultaneously becomes too dim to photograph a few microseconds after formation. It is conjectured here that this rapid bending precedes the transfer of toroidal to poloidal flux. During sustainment, a stable plasma column different from the transient one is observed. It has been possible to measure the column diameter and compare it to CORSICA [A. Tarditi et al., Contrib. Plasma Phys. 36, 132 (1996)], a magnetohydrodynamic equilibrium reconstruction code which showed good agreement with the measurements. Elongation and velocity measurements were made of cathode patterns also seen during this stage, possibly caused by pressure gradients or EĂ—B drifts. The patterns elongate in a toroidal-only direction which depends on the magnetic-field polarity. During the decay stage the column diameter expands as the current ramps down, until it eventually dissolves into filaments. With the use of magnetic probes inserted in the gun region, an X point which moved axially depending on current level and toroidal mode number was observed in all the stages of the SSPX plasma discharge
Multimegawatt thermionic reactor systems for space applications
Design features and performance characteristics of thermionic reactor systems for space application
Scanning apertureless microscopy below the diffraction limit: Comparisons between theory and experiment
The exact nature of the signal in scanning apertureless microscopy techniques is the subject of much debate. We have sought to resolve this controversy by carrying out simulations and experiments on the same structures. Simulations of a model of tip–sample coupling are shown to exhibit features that are in agreement with experimental observations at dimensions below the diffraction limit. The simulation of the optical imaging process is carried out using atomic force microscope data as a topographical template and a tip–sample dipole coupling model as the source of optical signal. The simulations show a number of key fingerprints including a dependence on the polarization of the external laser source, the size of the tip, and index of refraction of the sample being imaged. The experimental results are found to be in agreement with many of the features of the simulations. We conclude that the results of the dipole coupling theory agree qualitatively with experimental data and that apertureless microscopy measures optical properties, not just topography
Dynamics of Domain Walls for Split and Runaway Potentials
We demonstrate that the evolution of wall-like inhomogeneities in run-away
potentials, characteristic of dynamical supersymmetry breaking and moduli
stabilisation, is very similar to the evolution of domain wall networks
associated with double well potentials. Instabilities that would lead to a
rapid decay of domain walls can be significantly ameliorated by compensation
effects between a non-degeneracy of the vacua and a biased initial
distribution, which can be naturally expected in a wide class or particle
physics models that lead to out-of-equilibrium phase transitions. Within this
framework, it is possible to obtain domain walls that live long enough to be
relevant for the cosmic power spectrum and galaxy clustering, while being
compatible with the observed cosmic microwave background anisotropies.Comment: 30 pages, 9 figure
The AMBRE Project: Stellar Parameterisation of the ESO:UVES archived spectra
The AMBRE Project is a collaboration between the European Southern
Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA) that has been
established in order to carry out the determination of stellar atmospheric
parameters for the archived spectra of four ESO spectrographs.
The analysis of the UVES archived spectra for their stellar parameters has
been completed in the third phase of the AMBRE Project. From the complete
ESO:UVES archive dataset that was received covering the period 2000 to 2010,
51921 spectra for the six standard setups were analysed. The AMBRE analysis
pipeline uses the stellar parameterisation algorithm MATISSE to obtain the
stellar atmospheric parameters. The synthetic grid is currently constrained to
FGKM stars only.
Stellar atmospheric parameters are reported for 12,403 of the 51,921 UVES
archived spectra analysed in AMBRE:UVES. This equates to ~23.9% of the sample
and ~3,708 stars. Effective temperature, surface gravity, metallicity and alpha
element to iron ratio abundances are provided for 10,212 spectra (~19.7%),
while at least effective temperature is provided for the remaining 2,191
spectra. Radial velocities are reported for 36,881 (~71.0%) of the analysed
archive spectra. Typical external errors of sigmaTeff~110dex,
sigmalogg~0.18dex, sigma[M/H]~0.13dex, and sigma[alpha/Fe]~0.05dex with some
reported variation between giants and dwarfs and between setups are reported.
UVES is used to observe an extensive collection of stellar and non-stellar
objects all of which have been included in the archived dataset provided to OCA
by ESO. The AMBRE analysis extracts those objects which lie within the FGKM
parameter space of the AMBRE slow rotating synthetic spectra grid. Thus by
homogeneous blind analysis AMBRE has successfully extracted and parameterised
the targeted FGK stars (23.9% of the analysed sample) from within the ESO:UVES
archive.Comment: 19 pages, 16 figures, 11 table
- …