576 research outputs found
Benefiting from past wrongdoing, human embryonic stem cell lines, and the fragility of the German legal position
This paper examines the logic and morality of the German Stem Cell Act of 2002. After a brief description of the lawâs scope and intent, its ethical dimensions are analysed in terms of symbolic threats, indirect consequences, and the encouragement of immorality. The conclusions are twofold. For those who want to accept the law, the arguments for its rationality and morality can be sound. For others, the emphasis on the uniqueness of the German experience, the combination of absolute and qualified value judgments, and the lingering questions of indirect encouragement of immoral activities will probably be too much.Peer reviewe
Determination of Li-6 -- He-4 interaction from multi-energy scattering data
We present the first successful potential model description of Li-6 -- He-4
scattering. The differential cross-sections for three energies and the vector
analyzing powers for two energies were fitted by a single potential with energy
dependent imaginary components. An essential ingredient is a set of Majorana
terms in each component. The potential was determined using a recently
developed direct data-to-potential inversion method which is a generalisation
of the IP S-matrix-to-potential inversion algorithm. We discuss the problems
related to this phenomenological approach, and discuss the relationship of our
results to existing and future theories.Comment: 9 pages plain LaTeX, 6 postscript figue
A pulsating white dwarf in an eclipsing binary
White dwarfs are the burnt-out cores of Sun-like stars and are the fate of 97 per cent of the stars in our Galaxy. The internal structure and composition of white dwarfs are hidden by their high gravities, which causes all elements apart from the lightest ones to settle out of their atmospheres. The most direct method of probing the inner structure of stars and white dwarfs in detail is via asteroseismology. Here we present a pulsating white dwarf in an eclipsing binary system, enabling us to place extremely precise constraints on the mass and radius of the white dwarf from the lightcurve, independent of the pulsations. This 0.325-solar-mass white dwarfâone member of the SDSS J115219.99+024814.4 systemâwill serve as a powerful benchmark with which to constrain empirically the core composition of low-mass stellar remnants and to investigate the effects of close binary evolution on the internal structure of white dwarfs
Tadpole Analysis of Orientifolded Plane-Waves
We study orientifolds of type IIB string theory in the plane-wave background
supported by null RR 3-form flux F^{(3)}. We describe how to extract the RR
tadpoles in the Green-Schwarz formalism in a general setting. Two models with
orientifold groups {1, \Omega} and {1,\Omega I_4}, which are T-dual to each
other, are considered. Consistency of these backgrounds requires 32 D9 branes
for the first model and 32 D5 branes for the second one. We study the spectra
and comment on the heterotic duals of our models.Comment: 22+1 pages, 3 figures References added, minor typos correcte
A 15.7-minAMâCVn binary discovered in K2
We present the discovery of SDSSâJ135154.46â064309.0, a short-period variable observed using 30-mincadence photometry in K2 Campaign 6. Follow-up spectroscopy and high-speed photometry support a classification as a new member of the rare class of ultracompact accreting binaries known as AMâCVn stars. The spectroscopic orbital period of 15.65 ± 0.12âmin makes this system the fourth-shortest-period AMâCVn known, and the second system of this type to be discovered by the Kepler spacecraft. The K2 data show photometric periods at 15.7306 ± 0.0003âmin, 16.1121 ± 0.0004âmin, and 664.82 ± 0.06âmin, which we identify as the orbital period, superhump period, and disc precession period, respectively. From the superhump and orbital periods we estimate the binary mass ratio q = M2/M1= 0.111 ± 0.005, though this method of mass ratio determination may not be well calibrated for helium-dominated binaries. This system is likely to be a bright foreground source of gravitational waves in the frequency range detectable by Laser Interferometer Space Antenna, and may be of use as a calibration source if future studies are able to constrain the masses of its stellar components
Induced Parity Nonconserving Interaction and Enhancement of Two-Nucleon Parity Nonconserving Forces
Two-nucleon parity nonconserving (PNC) interaction induced by the
single-particle PNC weak potential and the two-nucleon residual strong
interaction is considered. An approximate analytical formula for this Induced
PNC Interaction (IPNCI) between proton and neutron is derived (), and the
interaction constant is estimated. As a result of coherent contributions from
the nucleons to the PNC potential, IPNCI is an order of magnitude stronger
() than the residual weak two-nucleon interaction and has a
different coordinate and isotopic structure (e.g., the strongest part of IPNCI
does not contribute to the PNC mean field). IPNCI plays an important role in
the formation of PNC effects, e.g., in neutron-nucleus reactions. In that case,
it is a technical way to take into account the contribution of the distant
(small) components of a compound state which dominates the result. The absence
of such enhancement () in the case of T- and P-odd interaction
completes the picture.Comment: Phys. Rev. C, to appear; 17 pages, revtex 3, no figure
Spectroscopic and photometric periods of six ultracompact accreting binaries
Ultracompact accreting binary systems each consist of a stellar remnant accreting helium-enriched material from a compact donor star. Such binaries include two related sub-classes, AM CVn-type binaries and helium cataclysmic variables, in both of which the central star is a white dwarf. We present a spectroscopic and photometric study of six accreting binaries with orbital periods in the range of 40--70 min, including phase-resolved VLT spectroscopy and high-speed ULTRACAM photometry. Four of these are AM CVn systems and two are helium cataclysmic variables. For four of these binaries we are able to identify orbital periods (of which three are spectroscopic). SDSS J1505+0659 has an orbital period of 67.8 min, significantly longer than previously believed, and longer than any other known AM CVn binary. We identify a WISE infrared excess in SDSS J1505+0659 that we believe to be the first direct detection of an AM CVn donor star in a non-direct impacting binary. The mass ratio of SDSS J1505+0659 is consistent with a white dwarf donor. CRTS J1028-0819 has an orbital period of 52.1 min, the shortest period of any helium cataclysmic variable. MOA 2010-BLG-087 is co-aligned with a K-class star that dominates its spectrum. ASASSN-14ei and ASASSN-14mv both show a remarkable number of echo outbursts following superoutbursts (13 and 10 echo outbursts respectively). ASASSN-14ei shows an increased outburst rate over the years following its superoutburst, perhaps resulting from an increased accretion rate
Spallation reactions. A successful interplay between modeling and applications
The spallation reactions are a type of nuclear reaction which occur in space
by interaction of the cosmic rays with interstellar bodies. The first
spallation reactions induced with an accelerator took place in 1947 at the
Berkeley cyclotron (University of California) with 200 MeV deuterons and 400
MeV alpha beams. They highlighted the multiple emission of neutrons and charged
particles and the production of a large number of residual nuclei far different
from the target nuclei. The same year R. Serber describes the reaction in two
steps: a first and fast one with high-energy particle emission leading to an
excited remnant nucleus, and a second one, much slower, the de-excitation of
the remnant. In 2010 IAEA organized a worskhop to present the results of the
most widely used spallation codes within a benchmark of spallation models. If
one of the goals was to understand the deficiencies, if any, in each code, one
remarkable outcome points out the overall high-quality level of some models and
so the great improvements achieved since Serber. Particle transport codes can
then rely on such spallation models to treat the reactions between a light
particle and an atomic nucleus with energies spanning from few tens of MeV up
to some GeV. An overview of the spallation reactions modeling is presented in
order to point out the incomparable contribution of models based on basic
physics to numerous applications where such reactions occur. Validations or
benchmarks, which are necessary steps in the improvement process, are also
addressed, as well as the potential future domains of development. Spallation
reactions modeling is a representative case of continuous studies aiming at
understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie
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