286 research outputs found
Five year prognosis in patients with angina identified in primary care : incident cohort study
Peer reviewedPublisher PD
Telerobotics: A simulation facility for university research
An experimental telerobotics (TR) simulation suitable for studying human operator (H.O.) performance is described. Simple manipulator pick-and-place and tracking tasks allowed quantitative comparison of a number of calligraphic display viewing conditions. A number of control modes could be compared in this TR simulation, including displacement, rate and acceleratory control using position and force joysticks. A homeomorphic controller turned out to be no better than joysticks; the adaptive properties of the H.O. can apparently permit quite good control over a variety of controller configurations and control modes. Training by optimal control example seemed helpful in preliminary experiments. An introduced communication delay was found to produce decrease in performance. In considerable part, this difficulty could be compensated for by preview control information. That neurological control of normal human movement contains a data period of 0.2 second may relate to this robustness of H.O. control to delay. The Ames-Berkeley enhanced perspective display was utilized in conjunction with an experimental helmet mounted display system (HMD) that provided stereoscopic enhanced views
Quasiparticle entanglement: redefinition of the vacuum and reduced density matrix approach
A scattering approach to entanglement in mesoscopic conductors with
independent fermionic quasiparticles is discussed. We focus on conductors in
the tunneling limit, where a redefinition of the quasiparticle vacuum
transforms the wavefunction from a manybody product state of noninteracting
particles to a state describing entangled two-particle excitations out of the
new vacuum. The approach is illustrated with two examples (i) a
normal-superconducting system, where the transformation is made between
Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system,
where the transformation is made between electron quasiparticles and
electron-hole pairs. This is compared to a scheme where an effective
two-particle state is derived from the manybody scattering state by a reduced
density matrix approach.Comment: Submitted to New Journal of Physics, Focused Issue on "Solid State
Quantum Information". 19 pages, 7 figure
The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\circ 3248
We have combined new high-resolution spectra obtained with the Hubble Space
Telescope (HST) and ground-based facilities to make a comprehensive new
abundance analysis of the metal-poor, halo star BD +17^\circ 3248. We have
detected the third r-process peak elements osmium, platinum, and (for the first
time in a metal-poor star) gold, elements whose abundances can only be reliably
determined using HST. Our observations illustrate a pattern seen in other
similar halo stars with the abundances of the heavier neutron-capture elements,
including the third r-process peak elements, consistent with a scaled solar
system r-process distribution. The abundances of the lighter neutron-capture
elements, including germanium and silver, fall below that same scaled solar
r-process curve, a result similar to that seen in the ultra-metal-poor star CS
22892--052. A single site with two regimes or sets of conditions, or perhaps
two different sites for the lighter and heavier neutron-capture elements, might
explain the abundance pattern seen in this star. In addition we have derived a
reliable abundance for the radioactive element thorium. We tentatively identify
U II at 3859 A in the spectrum of BD +17^\circ 3248, which makes this the
second detection of uranium in a very metal-poor halo star. Our combined
observations cover the widest range in proton number (from germanium to
uranium) thus far of neutron-capture elements in metal-poor Galactic halo
stars. Employing the thorium and uranium abundances in comparison with each
other and with several stable elements, we determine an average
cosmochronological age for BD +17^\circ 3248 of 13.8 +/- 4 Gyr, consistent with
that found for other similar metal-poor halo stars.Comment: 58 pages, 4 tables, 11 figures; To appear in ApJ Typo correcte
Optogalvanic Spectroscopy of Metastable States in Yb^{+}
The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest
for applications in metrology and quantum information and also act as dark
states in laser cooling. These metastable states are commonly repumped to the
ground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm
^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic
spectroscopy of these transitions in Yb^{+} ions generated in a discharge. We
measure the pressure broadening coefficient for the 638.6 nm transition to be
70 \pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the
638.6 nm isotope splitting and show that our observations are consistent with
theory for the hyperfine splitting. Our measurements of the 935.2 nm transition
extend those made by Sugiyama et al, showing well-resolved isotope and
hyperfine splitting. We obtain high signal to noise, sufficient for laser
stabilisation applications.Comment: 8 pages, 5 figure
Theory and applications of atomic and ionic polarizabilities
Atomic polarization phenomena impinge upon a number of areas and processes in
physics. The dielectric constant and refractive index of any gas are examples
of macroscopic properties that are largely determined by the dipole
polarizability. When it comes to microscopic phenomena, the existence of
alkaline-earth anions and the recently discovered ability of positrons to bind
to many atoms are predominantly due to the polarization interaction. An
imperfect knowledge of atomic polarizabilities is presently looming as the
largest source of uncertainty in the new generation of optical frequency
standards. Accurate polarizabilities for the group I and II atoms and ions of
the periodic table have recently become available by a variety of techniques.
These include refined many-body perturbation theory and coupled-cluster
calculations sometimes combined with precise experimental data for selected
transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index
measurements in microwave cavities, ab initio calculations of atomic structures
using explicitly correlated wave functions, interferometry with atom beams, and
velocity changes of laser cooled atoms induced by an electric field. This
review examines existing theoretical methods of determining atomic and ionic
polarizabilities, and discusses their relevance to various applications with
particular emphasis on cold-atom physics and the metrology of atomic frequency
standards.Comment: Review paper, 44 page
Photoassociation spectroscopy of cold calcium atoms
Photoassociation spectroscopy experiments on 40Ca atoms close to the
dissociation limit 4s4s 1S0 - 4s4p 1P1 are presented. The vibronic spectrum was
measured for detunings of the photoassociation laser ranging from 0.6 GHz to 68
GHz with respect to the atomic resonance. In contrast to previous measurements
the rotational splitting of the vibrational lines was fully resolved. Full
quantum mechanical numerical simulations of the photoassociation spectrum were
performed which allowed us to put constraints on the possible range of the
calcium scattering length to between 50 a_0 and 300 a_0
Effect of multivitamin and multimineral supplementation on cognitive function in men and women aged 65 years and over : a randomised controlled trial
Background: Observational studies have frequently reported an association between cognitive function and nutrition in later life but randomised trials of B vitamins and antioxidant supplements have mostly found no beneficial effect. We examined the effect of daily supplementation with 11 vitamins and 5 minerals on cognitive function in older adults to assess the possibility that this could help to prevent cognitive decline. Methods: The study was carried out as part of a randomised double blind placebo controlled trial of micronutrient supplementation based in six primary care health centres in North East Scotland. 910 men and women aged 65 years and over living in the community were recruited and randomised: 456 to active treatment and 454 to placebo. The active treatment consisted of a single tablet containing eleven vitamins and five minerals in amounts ranging from 50–210 % of the UK Reference Nutrient Intake or matching placebo tablet taken daily for 12 months. Digit span forward and verbal fluency tests, which assess immediate memory and executive functioning respectively, were conducted at the start and end of the intervention period. Risk of micronutrient deficiency at baseline was assessed by a simple risk questionnaire. Results: For digit span forward there was no evidence of an effect of supplements in all participants or in sub-groups defined by age or risk of deficiency. For verbal fluency there was no evidence of a beneficial effect in the whole study population but there was weak evidence for a beneficial effect of supplementation in the two pre-specified subgroups: in those aged 75 years and over (n 290; mean difference between supplemented and placebo groups 2.8 (95% CI -0.6, 6.2) units) and in those at increased risk of micronutrient deficiency assessed by the risk questionnaire (n 260; mean difference between supplemented and placebo groups 2.5 (95% CI -1.0, 6.1) units). Conclusion: The results provide no evidence for a beneficial effect of daily multivitamin and multimineral supplements on these domains of cognitive function in community-living people over 65 years. However, the possibility of beneficial effects in older people and those at greater risk of nutritional deficiency deserves further attention.Peer reviewedPublisher PD
Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
A previous study (Nissen & Schuster 2010) of 94 dwarf stars with -1.6 <
[Fe/H] < -0.4 has revealed the existence of two distinct halo populations with
a systematic difference in [alpha/Fe] at a given metallicity. In continuation
of that work, abundances of Mn, Cu, Zn, Y, and Ba are determined for the same
sample of stars. Equivalent widths of atomic lines are measured from high
resolution VLT/UVES and NOT/FIES spectra and used to derive precise abundance
ratios from an LTE analysis based on MARCS model atmospheres. Systematic
differences between the `high-alpha' and `low-alpha' halo populations are found
for [Cu/Fe], [Zn/Fe], and [Ba/Y], whereas there is no significant difference in
the case of [Mn/Fe]. At a given metallicity, [Cu/Fe] shows a large scatter that
is closely correlated with a corresponding scatter in [Na/Fe] and [Ni/Fe]. The
metallicity trends of [Cu/Fe], [Zn/Fe], and [Ba/Y] can be explained from
existing nucleosynthesis calculations if the high-alpha stars formed in regions
with such a high star formation rate that only massive stars and Type II
supernovae contributed to the chemical enrichment. The low-alpha stars, on the
other hand, most likely originate from systems with a slower chemical
evolution, characterized by additional enrichment from Type Ia supernovae and
low-mass AGB stars.Comment: Accepted for publication in A&
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