911 research outputs found
Formal total synthesis of (−)-haouamine A
A largely catalysis based approach to optically active haouamine A (−)-1 is presented, which provides the hexacyclic compound 25 previously used to construct this cytotoxic marine alkaloid
Nucleus polarizability contribution to the hydrogen-deuterium isotope shift
The correction to the hydrogen-deuterium isotope shift due to the proton and
deuteron polarizability is evaluated on the basis of modern experimental data
on the structure functions of inelastic lepton-nucleus scattering. The
numerical value of this contribution is equal 63\pm 12 Hz.Comment: 5 page
The effect of a Heat and Moisture Exchanger (Provox® HME) on pulmonary protection after total laryngectomy: a randomized controlled study
The goal of this randomized controlled study was to investigate the effect of Heat and Moisture Exchanger use on pulmonary symptoms and quality of life aspects in laryngectomized patients. Eighty laryngectomized patients were included and randomized into an HME and Control group. The effect of the HME was evaluated by means of Tally Sheets and Structured Questionnaires. The results showed a significant decrease in the frequency of coughing, forced expectoration, and stoma cleaning in the HME group. There were trends for the prosthetic speakers to report more fluent speech with the HME and for the HME group to report fewer sleeping problems. In conclusion, this study, performed in Poland, confirms the results of previous studies performed in other countries, showing that pulmonary symptoms decrease significantly with HME use and that related aspects such as speech and sleeping tend to improve, regardless of country or climate
Exclusive hadronic Tau decays in the resonance effective action of QCD
Until present the study of the form factors associated to the vector and
axial-vector components of the hadronic weak current has been carried out with
a plethora of modelizations of the underlying strong interactions. While of
importance to get an understanding of the dynamics involved, the amount and
quality of the experimental data start to show some discrepancies with the
analysed models. Moreover, and from a theoretical point of view, most of these
models are not consistent with quantum chromodynamics (QCD). We propose a
QCD-based model-independent procedure to analyse those decays through the use
of the resonance chiral theory, the low-energy effective action of QCD in the
relevant resonance region. Within this framework we study the hadronic
off-shell width of the Rho meson and the vector form factor of the pion in
Tau(-) -> Pi(-) Pi(0) nu_tau. We also comment on the Tau(-) -> (Pi Pi Pi)(-)
nu_tau decay.Comment: 8 pages, 4 figures. To appear in the proceedings of the 6th
International Workshop on Tau Lepton Physics, 18-21 September (2000),
Victoria (Canada
The Longitudinal Polarimeter at HERA
The design, construction and operation of a Compton back-scattering laser
polarimeter at the HERA storage ring at DESY are described. The device measures
the longitudinal polarization of the electron beam between the spin rotators at
the HERMES experiment with a fractional systematic uncertainty of 1.6%. A
measurement of the beam polarization to an absolute statistical precision of
0.01 requires typically one minute when the device is operated in the
multi-photon mode. The polarimeter also measures the polarization of each
individual electron bunch to an absolute statistical precision of 0.06 in
approximately five minutes. It was found that colliding and non-colliding
bunches can have substantially different polarizations. This information is
important to the collider experiments H1 and ZEUS for their future
longitudinally polarized electron program because those experiments use the
colliding bunches only.Comment: 21 pages (Latex), 14 figures (EPS
Spin alignment of vector meson in e+e- annihilation at Z0 pole
We calculate the spin density matrix of the vector meson produced in e+e-
annihilation at Z^0 pole. We show that the data imply a significant
polarization for the antiquark which is created in the fragmentation process of
the polarized initial quark and combines with the fragmenting quark to form the
vector meson. The direction of polarization is opposite to that of the
fragmenting quark and the magnitude is of the order of 0.5. A qualitative
explanation of this result based on the LUND string fragmentation model is
given.Comment: 15 pages, 2 fgiures; submitted to Phys. Rev.
CP violation and electric-dipole-moment at low energy production with polarized electrons
The new proposals for high luminosity B/Flavor factories, near and on top of
the resonances, allow for a detailed investigation of CP-violation
in the -pair production. In particular, bounds on the tau electric dipole
moment can be obtained from genuine CP-odd observables related to the
-pair production. We perform an independent analysis from low energy (10
GeV) data by means of linear spin observables. We show that, for a
longitudinally polarized electron beam, a CP-odd asymmetry, associated to the
normal polarization term, can be measured at these low energy facilities both
at resonant and non resonant energies. In this way, stringent and independent
bounds to the tau electric dipole moment, which are orders of magnitude below
other high or low energy bounds, can be obtained.Comment: 12 pages, 2 figure
A No-Lose Theorem for Higgs Searches at a Future Linear Collider
Assuming perturbativity up to a high energy scale GeV, we
demonstrate that a future linear collider operating at
500 GeV with 500 fb per year (such as the recently
proposed TESLA facility) will detect a Higgs boson signal regardless of the
complexity of the Higgs sector and of how the Higgs bosons decay.Comment: 4 pages, LaTe
CP violation and electric-dipole-moment at low energy tau-pair production
CP violation at low energy is investigated at the tau electromagnetic vertex.
High statistics at B factories, and on top of the Upsilon resonances, allows a
detailed investigation of CP-odd observables related to the tau-pair
production. The contribution of the tau electric dipole moment is considered in
detail. We perform an analysis independent from the high energy data by means
of correlation and linear spin observables at low energy. We show that
different CP-odd asymmetries, associated to the normal-transverse and
normal-longitudinal correlation terms can be measured at low energy
accelerators, both at resonant and non resonant energies. These observables
allow to put stringent and independent bounds to the tau electric dipole moment
that are competitive with other high or low energy results.Comment: 18 pages, 2 figures, references added, minor changes in section 3 and
5, to be published in Nucl.Phys.
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