840 research outputs found
Photometric brown-dwarf classification. II. A homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5 with accurate spectral types
We present a homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5
(of which 998 are new), from an effective area of 3070 deg2, classified by the
photo-type method to an accuracy of one spectral sub-type using izYJHKW1W2
photometry from SDSS+UKIDSS+WISE. Other than a small bias in the early L types,
the sample is shown to be effectively complete to the magnitude limit, for all
spectral types L0 to T8. The nature of the bias is an incompleteness estimated
at 3% because peculiar blue L dwarfs of type L4 and earlier are classified late
M. There is a corresponding overcompleteness because peculiar red (likely
young) late M dwarfs are classified early L. Contamination of the sample is
confirmed to be small: so far spectroscopy has been obtained for 19 sources in
the catalogue and all are confirmed to be ultracool dwarfs. We provide
coordinates and izYJHKW1W2 photometry of all sources. We identify an apparent
discontinuity, m 0.4 mag., in the Y-K colour between spectral
types L7 and L8. We present near-infrared spectra of nine sources identified by
photo-type as peculiar, including a new low-gravity source ULAS
J005505.68+013436.0, with spectroscopic classification L2{}. We provide
revised izYJHKW1W2 template colours for late M dwarfs, types M7 to M9.Comment: Accepted for publication in A & A, 17 pages, 14 figures, catalogue of
L and T dwarfs supplied here in source files (anc/ directory), and available
on CD
Synthesis and Properties of High Tilted Antiferroelectric Esters with Partially Fluorinated Alkoxyalkoxy Terminal Chains
Novel chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their phase transition temperatures, enthalpies, and electrooptical properties are reported. A helical pitch in pure compounds and their mixtures based on selective reflection of light is also characterized
Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies
We present precision calculations of the processes e+e- -> 4-fermions in
which the double resonant W+W- intermediate state occurs. Referring to this
latter intermediate state as the 'signal process', we show that, by using the
YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate
combination, we achieve a physical precision on the signal process, as isolated
with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge
invariance of our calculations and we compare our results with those of other
authors where appropriate. In particular, sample Monte Carlo data are
explicitly illustrated and compared with the results of the program RacoonWW of
Dittmaier {\it et al.}. In this way, we show that the total (physical plus
technical) precision tag for the WW signal process cross section is 0.4 per
cent for 200 GeV, for example. Results are also given for 500 GeV with an eye
toward the LC.Comment: 19 pages, 2 figs;corrected Tab. 3;improved refs.,figs.,text;improved
refs.,text;improved tex
Sneutrino Mass Measurements at e+e- Linear Colliders
It is generally accepted that experiments at an e+e- linear colliders will be
able to extract the masses of the selectron as well as the associated
sneutrinos with a precision of ~ 1% by determining the kinematic end points of
the energy spectrum of daughter electrons produced in their two body decays to
a lighter neutralino or chargino. Recently, it has been suggested that by
studying the energy dependence of the cross section near the production
threshold, this precision can be improved by an order of magnitude, assuming an
integrated luminosity of 100 fb^-1. It is further suggested that these
threshold scans also allow the masses of even the heavier second and third
generation sleptons and sneutrinos to be determined to better than 0.5%. We
re-examine the prospects for determining sneutrino masses. We find that the
cross sections for the second and third generation sneutrinos are too small for
a threshold scan to be useful. An additional complication arises because the
cross section for sneutrino pair to decay into any visible final state(s)
necessarily depends on an unknown branching fraction, so that the overall
normalization in unknown. This reduces the precision with which the sneutrino
mass can be extracted. We propose a different strategy to optimize the
extraction of m(\tilde{\nu}_\mu) and m(\tilde{\nu}_\tau) via the energy
dependence of the cross section. We find that even with an integrated
luminosity of 500 fb^-1, these can be determined with a precision no better
than several percent at the 90% CL. We also examine the measurement of
m(\tilde{\nu}_e) and show that it can be extracted with a precision of about
0.5% (0.2%) with an integrated luminosity of 120 fb^-1 (500 fb^-1).Comment: RevTex, 46 pages, 15 eps figure
Final State Radiative Effects for the Exact O(alpha) YFS Exponentiated (Un)Stable W+W- Production At and Beyond LEP2 Energies
We present the LL final state radiative effects for the exact O(alpha) YFS
exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte
Carlo event generator methods. The respective event generator, version 1.12 of
the program YFSWW3, wherein both Standard Model and anomalous triple gauge
boson couplings are allowed, generates n(\gamma) radiation both from the
initial state and from the intermediate W+ W- and generates the LL final state
W decay radiative effects. Sample Monte Carlo data are illustrated.Comment: 16 pages, 8 figures, 2 table
WW Cross-sections and Distributions
We present the results obtained by the "WW Cross-sections and Distributions"
working group during the CERN Workshop "Physics at LEP2" (1994/1995)Comment: 61 pages, tar'ed gzip'ed uuencoded files, LaTeX, 4 Postscript
figures. To appear in "Physics at LEP2", G.Altarelli and F.Zwirner eds., CERN
Report 199
Markovian MC simulation of QCD evolution at NLO level with minimum k_T
We present two Monte Carlo algorithms of the Markovian type which solve the
modified QCD evolution equations at the NLO level. The modifications with
respect to the standard DGLAP evolution concern the argument of the strong
coupling constant alpha_S. We analyze the z - dependent argument and then the
k_T - dependent one. The evolution time variable is identified with the
rapidity. The two algorithms are tested to the 0.05% precision level. We find
that the NLO corrections in the evolution of parton momentum distributions with
k_T - dependent coupling constant are of the order of 10 to 20%, and in a small
x region even up to 30%, with respect to the LO contributions.Comment: 32 pages, 9 pdf figure
Gauge Invariant YFS Exponentiation of (Un)stable Production At and Beyond LEP2 Energies
We present the theoretical basis and sample Monte Carlo data for the YFS
exponentiated calculation of at and beyond LEP2 energies, where the left-handed parts
of and are the respective upper and lower components of an
doublet, . The problem of gauge invariance of the radiation
from the unstable charged spin~1 is solved in an entirely physical
manner. Our formulas are illustrated in a proto-typical YFS Monte Carlo event
generator YFSWW2, wherein both Standard Model and anomalous triple gauge boson
couplings are allowed.Comment: Latex replaces postscript, 17 page
The Mossbauer spectroscopy studies of epsilon to cementite carbides transformation during isothermal heating from as-quenched state of high carbon tool steel
This work presents results of investigations using the Mossbauer spectroscopy technique and their interpretation concerning transformation of ² to cementite carbides during tempering in relation to the previously conducted
dilatometric, microscopic and mechanical investigations. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The in°uence of the tempering time on nucleation and solubility of ² carbides, and on cementite nucleation
and growth, was determined. The analysis of phase transformations during various periods of tempering using the Mossbauer spectroscopy technique made possible to reveal ¯ne details connected with the processes
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