20,209 research outputs found
Norm Optimal Iterative Learning Control with Application to Problems in Accelerator based Free Electron Lasers and Rehabilitation Robotics
This paper gives an overview of the theoretical basis of the norm optimal approach to iterative learning control followed by results that describe more recent work which has experimentally benchmarking the performance that can be achieved. The remainder of then paper then describes its actual application to a physical process and a very novel application in stroke rehabilitation
Radiocarbon and blue optically stimulated luminescence chronologies of the Oitavos consolidated dune (Western Portugal)
The dune of Oitavos, the underlying paleosol, and Helix sp. gastropod shells found within the paleosol were dated using a combination of radiocarbon and blue optically stimulated luminescence (OSL). The organic component of the paleosol produced a significantly older age (~20,000 cal BP) than the OSL age measurement (~15,000 yr), while 14C age measurements on the inorganic component and the gastropods produced ages of ~35,000 yr and ~34,000 yr, respectively. Rare-earth
element analyses provide evidence that the gastropods incorporate geological carbonate, making them an unreliable indicator of the age of the paleosol. We propose that the 14C age of the small organic component of the paleosol is also likely to be unreliable due to incorporation of residual material. The OSL age measurement of the upper paleosol (~15,000 yr) is consistent with the age for the base of the dune (~14,500 yr). The younger OSL age for the top of the dune (~12,000 yr) suggests that it was built up by at least 2 sand pulses or that there was a remobilization of material at the top during its evolution, prior to consolidation
Principles of Control for Decoherence-Free Subsystems
Decoherence-Free Subsystems (DFS) are a powerful means of protecting quantum
information against noise with known symmetry properties. Although Hamiltonians
theoretically exist that can implement a universal set of logic gates on DFS
encoded qubits without ever leaving the protected subsystem, the natural
Hamiltonians that are available in specific implementations do not necessarily
have this property. Here we describe some of the principles that can be used in
such cases to operate on encoded qubits without losing the protection offered
by the DFS. In particular, we show how dynamical decoupling can be used to
control decoherence during the unavoidable excursions outside of the DFS. By
means of cumulant expansions, we show how the fidelity of quantum gates
implemented by this method on a simple two-physical-qubit DFS depends on the
correlation time of the noise responsible for decoherence. We further show by
means of numerical simulations how our previously introduced "strongly
modulating pulses" for NMR quantum information processing can permit
high-fidelity operations on multiple DFS encoded qubits in practice, provided
that the rate at which the system can be modulated is fast compared to the
correlation time of the noise. The principles thereby illustrated are expected
to be broadly applicable to many implementations of quantum information
processors based on DFS encoded qubits.Comment: 12 pages, 7 figure
Delta-like and gtl2 are reciprocally expressed, differentially methylated linked imprinted genes on mouse chromosome 12
AbstractThe distal portion of mouse chromosome 12 is imprinted. To date, however, Gtl2 is the only imprinted gene identified on chromosome 12. Gtl2 encodes multiple alternatively spliced transcripts with no apparent open reading frame. Using conceptuses with maternal or paternal uniparental disomy for chromosome 12 (UPD12), we found that Gtl2 is expressed from the maternal allele and methylated at the 5âČ end of the silent paternal allele. A reciprocally imprinted gene, Delta-like (Dlk), with homology to genes involved in the Notch signalling pathway was identified 80kb upstream of Gtl2. Dlk was expressed exclusively from the paternal allele in both the embryo and placenta, but the CpG-island promoter of Dlk was completely unmethylated on both parental alleles. Rather, a paternally methylated region was identified in the last exon of the active Dlk allele. The proximity, reciprocal imprinting and methylation in this domain are reminiscent of the co-ordinately regulated Igf2âH19 imprinted domain on mouse chromosome 7. Like H19 and Igf2, Gtl2 and Dlk were found to be co-expressed in the same tissues throughout development, though not after birth. These results have implications for the regulation, function and evolution of imprinted domains
An experimental study of the rearrangements of valence protons and neutrons amongst single-particle orbits during double {\beta} decay in 100Mo
The rearrangements of protons and neutrons amongst the valence
single-particle orbitals during double {\beta} decay of 100Mo have been
determined by measuring cross sections in (d,p), (p,d), (3He,{\alpha}) and
(3He,d) reactions on 98,100Mo and 100,102Ru targets. The deduced nucleon
occupancies reveal significant discrepancies when compared with theoretical
calculations; the same calculations have previously been used to determine the
nuclear matrix element associated with the decay probability of double {\beta}
decay of the 100Mo system.Comment: 18 pages, 13 figures, 37 pages of supplemental informatio
NGC 300: an extremely faint, outer stellar disk observed to 10 scale lengths
We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South
8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer
stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our
point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the
stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25
mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in
this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid
distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the
outermost field, and these are within 10% of the mean survey counts from both
Hubble Deep Fields. The luminosity profile is well described by a nucleus plus
a simple exponential profile out to 10 optical scale lengths. We reach an
effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55%
completeness which doubles the known radial extent of the optical disk. These
levels are exceedingly faint in the sense that the equivalent surface
brightness in B or V is about 32 mag/arcsec**2. We find no evidence for
truncation of the stellar disk. Only star counts can be used to reliably trace
the disk to such faint levels, since surface photometry is ultimately limited
by nonstellar sources of radiation. In the Appendix, we derive the expected
surface brightness of one such source: dust scattering of starlight in the
outer disk.Comment: ApJ accepted -- 30 pages, 13 figures -- see
ftp://www.aao.gov.au/pub/local/jbh/astro-ph/N300 for full resolution figures
and preprin
Change of nuclear configurations in the neutrinoless double- decay of Te Xe and Xe Ba
The change in the configuration of valence protons between the initial and
final states in the neutrinoless double- decay of Te
Xe and of Xe Ba has been
determined by measuring the cross sections of the (,He) reaction with
101-MeV deuterons. Together with our recent determination of the relevant
neutron configurations involved in the process, a quantitative comparison with
the latest shell-model and interacting-boson-model calculations reveals
significant discrepancies. These are the same calculations used to determine
the nuclear matrix elements governing the rate of neutrinoless double-
decay in these systems.Comment: 10 pages, 4 figures, 9 table
The Schrodinger-like Equation for a Nonrelativistic Electron in a Photon Field of Arbitrary Intensity
The ordinary Schrodinger equation with minimal coupling for a nonrelativistic
electron interacting with a single-mode photon field is not satisfied by the
nonrelativistic limit of the exact solutions to the corresponding Dirac
equation. A Schrodinger-like equation valid for arbitrary photon intensity is
derived from the Dirac equation without the weak-field assumption. The
"eigenvalue" in the new equation is an operator in a Cartan subalgebra. An
approximation consistent with the nonrelativistic energy level derived from its
relativistic value replaces the "eigenvalue" operator by an ordinary number,
recovering the ordinary Schrodinger eigenvalue equation used in the formal
scattering formalism. The Schrodinger-like equation for the multimode case is
also presented.Comment: Tex file, 13 pages, no figur
Accurate first principles detailed balance determination of Auger recombination and impact ionization rates in semiconductors
The technologically important problem of predicting Auger recombination
lifetimes in semiconductors is addressed by means of a fully first--principles
formalism. The calculations employ highly precise energy bands and wave
functions provided by the full--potential linearized augmented plane wave
(FLAPW) code based on the screened exchange local density approximation. The
minority carrier Auger lifetime is determined by two closely related
approaches: \emph{i}) a direct evaluation of the Auger rates within Fermi's
Golden Rule, and \emph{ii}) an indirect evaluation, based on a detailed balance
formulation combining Auger recombination and its inverse process, impact
ionization, in a unified framework. Calculated carrier lifetimes determined
with the direct and indirect methods show excellent consistency \emph{i})
between them for -doped GaAs and \emph{ii}%) with measured values for GaAs
and InGaAs. This demonstrates the validity and accuracy of the computational
formalism for the Auger lifetime and indicates a new sensitive tool for
possible use in materials performance optimization.Comment: Phys. Rev. Lett. accepte
More evidence for an intracluster planetary nebulae population in the Virgo cluster
We surveyed a 50 sq arcmin region in the Virgo cluster core to search for
intergalactic planetary nebulae, and found 11 candidates in the surveyed area.
The measured fluxes of these unresolved sources are consistent with these
objects being planetary nebulae from an intracluster population of stars. We
compute the cumulative luminosity function of these 11 planetary nebula
candidates. If we assume that they belong to the Virgo cluster, their
cumulative luminosity function is in good agreement with planetary nebula
luminosity function simulations. This comparison allows us to estimate the
surface mass density of the intracluster stellar population at the surveyed
field in the cluster core.Comment: ApJ Letters, in press. A .ps file is also available at:
http://www.usm.uni-muenchen.de:8001/people/mendez/preprints/preprints.htm
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