340 research outputs found
Parallel Evaluation of Multi-join Queries
A number of execution strategies for parallel evaluation of multi-join queries have been proposed in the literature. In this paper we give a comparative performance evaluation of four execution strategies by implementing all of them on the same parallel database system, PRISMA/DB. Experiments have been done up to 80 processors. These strategies, coming from the literature, are named: Sequential Parallel, Synchronous Execution, Segmented Right-Deep, and Full Parallel. Based on the experiments clear guidelines are given when to use which strategy.
This is an extended abstract; the full paper appeared in Proc. ACM SIGMOD'94, Minneapolis, Minnesota, May 24–27, 199
Characterization of antigen-presenting properties of tumour cells using virus-specific cytotoxic T lymphocytes
Immunotherapy of tumours by induction of tumour-specific cytotoxic T-lymphocytes (CTLs) will only be effective for tumours with a functional antigen processing and presentation machinery. However, many tumours are known to down-regulate expression of major histocompatibility complex (MHC) class I molecules and/or to impair antigen processing. It is therefore desirable to evaluate the ability of a given tumour to present antigenic epitopes before developing an immunotherapy protocol. In this study we have used influenza virus as a tool to determine the antigen-presenting capacities of the murine neuroblastoma C1300 cell line NB41A3, a frequently used model for human neuroblastoma. Immunofluorescence analyses revealed low and moderate expression of MHC class I molecules Ddand Kkrespectively. Nevertheless, infected NB41A3 cells were lysed efficiently by influenza-specific CTLs. These results demonstrate that all steps of the antigen-processing pathway function properly in the NB tumour cells, and that the limited MHC class I expression suffices for efficient recognition by CTLs. In addition, lysis of the NB tumour cells shows that the cells are susceptible to CTL-induced apoptosis, a pathway that is often impaired in tumour cells. These characteristics make neuroblastoma a suitable target for immunotherapy. The presented assay allows evaluation of various immunological properties of tumour cells and, thus, represents a valuable tool to assess whether a given tumour will be susceptible to immunotherapy or not. Copyright 2000 Cancer Research Campaign. © 2000 Cancer Research Campaig
On-line Excited-State Laser Spectroscopy of Trapped Short-Lived Ra Ions
As an important step towards an atomic parity violation experiment in one
single trapped Ra ion, laser spectroscopy experiments were performed with
on-line produced short-lived Ra ions. The isotope shift of
the 6\,^2D\,-\,7\,^2P and
6\,^2D\,-\,7\,^2P transitions and the hyperfine structure
constant of the 7\,^2S and 6\,^2D states in Ra
were measured. These values provide a benchmark for the required atomic theory.
A lower limit of ms for the lifetime of the metastable
6\,^2D state was measured by optical shelving.Comment: 4.2 pages, 6 figures, 2 tables
Isotope Shifts of the 6d\,^2D - 7p\,^2P Transition in Trapped Short-Lived Ra
Laser spectroscopy of short-lived radium isotopes in a linear Paul trap has
been performed. The isotope shifts of the 6d\,^2D -
7p\,^2P transition in Ra were measured, which are
sensitive to the short range part of the atomic wavefunctions. The results are
essential experimental input for improving the precision of atomic structure
calculation. This is indispensable for parity violation in Ra aiming at the
determination of the weak mixing angle.Comment: Accepted for publication in Physical Review A as a Rapid
Communicatio
Measurement of the half-life of the T= mirror decay of Ne and its implication on physics beyond the standard model
The superallowed mixed mirror decay
of Ne to F is excellently suited for high precision studies of
the weak interaction. However, there is some disagreement on the value of the
half-life. In a new measurement we have determined this quantity to be
= s, which differs
from the previous world average by 3 standard deviations. The impact of this
measurement on limits for physics beyond the standard model such as the
presence of tensor currents is discussed.Comment: 5 pages, 3 figures, 1 tabl
Evidence for Thermal Equilibration in Multifragmentation Reactions probed with Bremsstrahlung Photons
The production of nuclear bremsstrahlung photons (E 30 MeV) has
been studied in inclusive and exclusive measurements in four heavy-ion
reactions at 60{\it A} MeV. The measured photon spectra, angular distributions
and multiplicities indicate that a significant part of the hard-photons are
emitted in secondary nucleon-nucleon collisions from a thermally equilibrated
system. The observation of the thermal component in multi-fragment
Ar+Au reactions suggests that the breakup of the thermalized
source produced in this system occurs on a rather long time-scale.Comment: Revised version, accepted for publication in Physical Review Letters.
4 pages, 4 fig
A gas cell for stopping, storing and polarizing radioactive particles
A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The
stopped particles are polarized by optical pumping. The degree of polarization
that can be achieved is studied. A maximum polarization of 50% was found. The
dynamic processes in the cell are described with a phenomenological model.Comment: 16 pages, 6 figure
Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions
Photon energy spectra up to the kinematic limit have been measured in 190 MeV
proton reactions with light and heavy nuclei to investigate the influence of
the multiple-scattering process on the photon production. Relative to the
predictions of models based on a quasi-free production mechanism a strong
suppression of bremsstrahlung is observed in the low-energy region of the
photon spectrum. We attribute this effect to the interference of photon
amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let
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