1,637 research outputs found
An Ethical Defense of Federal Funding for Human Embryonic Stem Cell Research
Should the Federal Government fund human embryonic stem cell research? In addressing this question and answering it affirmatively, I will draw from testimony I was asked to prepare for the Hearing on Stem Cell Research conducted by the U.S. Senate Committee on Health, Education, Labor and Pensions, chaired by Senator Edward M. Kennedy, on September 5, 2001. Even though I did not testify on that occasion on behalf of the National Bioethics Advisory Commission (NBAC), on which I served until its demise at the end of September 2001, I drew, then as well as now, on the NBAC\u27s 1999 report on Ethical Issues in Human Stem Cell Research, which, as a commissioner, I helped to prepare and also endorsed
Anomalous exponents at the onset of an instability
Critical exponents are calculated exactly at the onset of an instability,
using asymptotic expansiontechniques. When the unstable mode is subject to
multiplicative noise whose spectrum at zero frequency vanishes, we show that
the critical behavior can be anomalous, i.e. the mode amplitude X scales with
departure from onset \mu as with an exponent
different from its deterministic value. This behavior is observed in a direct
numerical simulation of the dynamo instability and our results provide a
possible explanation to recent experimental observations
Magnetic domain wall propagation in a submicron spin-valve stripe: influence of the pinned layer
The propagation of a domain wall in a submicron ferromagnetic spin-valve
stripe is investigated using giant magnetoresistance. A notch in the stripe
efficiently traps an injected wall stopping the domain propagation. The authors
show that the magnetic field at which the wall is depinned displays a
stochastic nature. Moreover, the depinning statistics are significantly
different for head to head and tail-to-tail domain walls. This is attributed to
the dipolar field generated in the vicinity of the notch by the pinned layer of
the spin-valve
OzDES multifibre spectroscopy for the Dark Energy Survey: 3-yr results and first data release
We present results for the first three years of OzDES, a six year programme to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multiyear baseline and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17 000 objects, including the redshifts of 2566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise ratio (S/N), magnitude and exposure time, finding that our redshift success rate increases significantly at a S/N of 2–3 per 1-Å bin. We also find that the change in  S/N with exposure time closely matches the Poisson limit for stacked exposures as long as 10 h. We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as (i.e. the 4-m Multi-Object Spectroscopic Telescope, the Subaru Prime Focus Spectrograph and the Maunakea Spectroscopic Explorer). This work marks the first OzDES data release, comprising 14 693 redshifts. OzDES is on target to obtain over 30 000 redshifts over the 6-yr duration of the survey, including a yield of approximately 5700 supernova host-galaxy redshifts
OzDES multifibre spectroscopy for the Dark Energy Survey : 3-yr results and first data release
We present results for the first three years of OzDES, a six year programme to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multiyear baseline and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17 000 objects, including the redshifts of 2566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise ratio (S/N), magnitude and exposure time, finding that our redshift success rate increases significantly at a S/N of 2–3 per 1-Å bin. We also find that the change in S/N with exposure time closely matches the Poisson limit for stacked exposures as long as 10 h. We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as (i.e. the 4-m Multi-Object Spectroscopic Telescope, the Subaru Prime Focus Spectrograph and the Maunakea Spectroscopic Explorer). This work marks the first OzDES data release, comprising 14 693 redshifts. OzDES is on target to obtain over 30 000 redshifts over the 6-yr duration of the survey, including a yield of approximately 5700 supernova host-galaxy redshifts
Towards an experimental von Karman dynamo: numerical studies for an optimized design
Numerical studies of a kinematic dynamo based on von Karman type flows
between two counterrotating disks in a finite cylinder are reported. The flow
has been optimized using a water model experiment, varying the driving
impellers configuration. A solution leading to dynamo action for the mean flow
has been found. This solution may be achieved in VKS2, the new sodium
experiment to be performed in Cadarache, France. The optimization process is
described and discussed, then the effects of adding a stationary conducting
layer around the flow on the threshold, on the shape of the neutral mode and on
the magnetic energy balance are studied. Finally, the possible processes
involved into kinematic dynamo action in a von Karman flow are reviewed and
discussed. Among the possible processes we highlight the joint effect of the
boundary-layer radial velocity shear and of the Ohmic dissipation localized at
the flow/outer-shell boundary
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