3,946 research outputs found
Atomic dynamics in evaporative cooling of trapped alkali atoms in strong magnetic fields
We investigate how the nonlinearity of the Zeeman shift for strong magnetic
fields affects the dynamics of rf field induced evaporative cooling in magnetic
traps. We demonstrate for the 87-Rb and 23-Na F=2 trapping states with wave
packet simulations how the cooling stops when the rf field frequency goes below
a certain limit (for the 85-Rb F=2 trapping state the problem does not appear).
We examine the applicability of semiclassical models for the strong field case
as an extension of our previous work [Phys. Rev. A 58, 3983 (1998)]. Our
results verify many of the aspects observed in a recent Rb experiment
[Phys. Rev. A 60, R1759 (1999)].Comment: 9 pages, RevTex, eps figures embedde
Reconstruction methods â P‾ANDA focussing-light guide disc DIRC
The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the P‾ANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the P‾ANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development
String Indexing for Patterns with Wildcards
We consider the problem of indexing a string of length to report the
occurrences of a query pattern containing characters and wildcards.
Let be the number of occurrences of in , and the size of
the alphabet. We obtain the following results.
- A linear space index with query time .
This significantly improves the previously best known linear space index by Lam
et al. [ISAAC 2007], which requires query time in the worst case.
- An index with query time using space , where is the maximum number of wildcards allowed in the pattern.
This is the first non-trivial bound with this query time.
- A time-space trade-off, generalizing the index by Cole et al. [STOC 2004].
We also show that these indexes can be generalized to allow variable length
gaps in the pattern. Our results are obtained using a novel combination of
well-known and new techniques, which could be of independent interest
Measurement of Strange Quark Contributions to the Nucleon's Form Factors at Q^2=0.230 (GeV/c)^2
We report on a measurement of the parity-violating asymmetry in the
scattering of longitudinally polarized electrons on unpolarized protons at a
of 0.230 (GeV/c)^2 and a scattering angle of \theta_e = 30^o - 40^o.
Using a large acceptance fast PbF_2 calorimeter with a solid angle of
\Delta\Omega = 0.62 sr the A4 experiment is the first parity violation
experiment to count individual scattering events. The measured asymmetry is
A_{phys} =(-5.44 +- 0.54_{stat} +- 0.27_{\rm sys}) 10^{-6}. The Standard Model
expectation assuming no strangeness contributions to the vector form factors is
. The difference is a direct measurement of the
strangeness contribution to the vector form factors of the proton. The
extracted value is G^s_E + 0.225 G^s_M = 0.039 +- 0.034 or F^s_1 + 0.130 F^s_2
= 0.032 +- 0.028.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Letters on Dec 11, 200
Evidence for Strange Quark Contributions to the Nucleon's Form Factors at = 0.108 (GeV/c)
We report on a measurement of the parity violating asymmetry in the elastic
scattering of polarized electrons off unpolarized protons with the A4 apparatus
at MAMI in Mainz at a four momentum transfer value of = \Qsquare
(GeV/c) and at a forward electron scattering angle of 30. The measured asymmetry is = (\Aphys
\Deltastat \Deltasyst) 10. The
expectation from the Standard Model assuming no strangeness contribution to the
vector current is A = (\Azero \DeltaAzero) 10. We
have improved the statistical accuracy by a factor of 3 as compared to our
previous measurements at a higher . We have extracted the strangeness
contribution to the electromagnetic form factors from our data to be +
\FakGMs = \GEsGMs \DeltaGEsGMs at = \Qsquare (GeV/c).
As in our previous measurement at higher momentum transfer for + 0.230
, we again find the value for + \FakGMs to be positive,
this time at an improved significance level of 2 .Comment: 4 pages, 3 figure
Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude
We report on a measurement of the asymmetry in the scattering of transversely
polarized electrons off unpolarized protons, A, at two Q values of
\qsquaredaveragedlow (GeV/c) and \qsquaredaveragedhighII (GeV/c) and a
scattering angle of . The measured transverse
asymmetries are A(Q = \qsquaredaveragedlow (GeV/c)) =
(\experimentalasymmetry alulowcorr \statisticalerrorlow
\combinedsyspolerrorlowalucor) 10 and
A(Q = \qsquaredaveragedhighII (GeV/c)) = (\experimentalasymme
tryaluhighcorr \statisticalerrorhigh
\combinedsyspolerrorhighalucor) 10. The first
errors denotes the statistical error and the second the systematic
uncertainties. A arises from the imaginary part of the two-photon
exchange amplitude and is zero in the one-photon exchange approximation. From
comparison with theoretical estimates of A we conclude that
N-intermediate states give a substantial contribution to the imaginary
part of the two-photon amplitude. The contribution from the ground state proton
to the imaginary part of the two-photon exchange can be neglected. There is no
obvious reason why this should be different for the real part of the two-photon
amplitude, which enters into the radiative corrections for the Rosenbluth
separation measurements of the electric form factor of the proton.Comment: 4 figures, submitted to PRL on Oct.
Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators
While the first binary post-AGB stars were serendipitously discovered, the
distinct characteristics of their Spectral Energy Distribution (SED) allowed us
to launch a more systematic search for binaries. We selected post-AGB objects
which show a broad dust excess often starting already at H or K, pointing to
the presence of a gravitationally bound dusty disc in the system. We started a
very extensive multi-wavelength study of those systems and here we report on
our radial velocity and photometric monitoring results for six stars of early F
type, which are pulsators of small amplitude. To determine the radial velocity
of low signal-to-noise time-series, we constructed dedicated auto-correlation
masks. The radial velocity variations were subjected to detailed analysis to
differentiate between pulsational variability and variability due to orbital
motion. Finally orbital minimalisation was performed to constrain the orbital
elements. All of the six objects are binaries, with orbital periods ranging
from 120 to 1800 days. Five systems have non-circular orbits. The mass
functions range from 0.004 to 0.57 solar mass and the companions are likely
unevolved objects of (very) low initial mass. We argue that these binaries must
have been subject to severe binary interaction when the primary was a cool
supergiant. Although the origin of the circumstellar disc is not well
understood, the disc is generally believed to be formed during this strong
interaction phase. The eccentric orbits of these highly evolved objects remain
poorly understood. With the measured orbits and mass functions we conclude that
the circumbinary discs seem to have a major impact on the evolution of a
significant fraction of binary systems.Comment: 13 pages, 15 figures, accepted for Astronomy and Astrophysic
Viewing Nature Scenes Positively Affects Recovery of Autonomic Function Following Acute-Mental Stress
A randomized crossover study explored whether viewing different scenes prior to a stressor altered autonomic function during the recovery from the stressor. The two scenes were (a) nature (composed of trees, grass, fields) or (b) built (composed of man-made, urban scenes lacking natural characteristics) environments. Autonomic function was assessed using noninvasive techniques of heart rate variability; in particular, time domain analyses evaluated parasympathetic activity, using root-mean-square of successive differences (RMSSD). During stress, secondary cardiovascular markers (heart rate, systolic and diastolic blood pressure) showed significant increases from baseline which did not differ between the two viewing conditions. Parasympathetic activity, however, was significantly higher in recovery following the stressor in the viewing scenes of nature condition compared to viewing scenes depicting built environments (RMSSD; 50.0 ± 31.3 vs 34.8 ± 14.8 ms). Thus, viewing nature scenes prior to a stressor alters autonomic activity in the recovery period. The secondary aim was to examine autonomic function during viewing of the two scenes. Standard deviation of R-R intervals (SDRR), as change from baseline, during the first 5 min of viewing nature scenes was greater than during built scenes. Overall, this suggests that nature can elicit improvements in the recovery process following a stressor. © 2013 American Chemical Society
The HypHI project: Hypernuclear spectroscopy with stable heavy ion beams and rare isotope beams at GSI and FAIR
The HypHI collaboration aims to perform a precise hypernuclear spectroscopy
with stable heavy ion beams and rare isotope beams at GSI and fAIR in order to
study hypernuclei at extreme isospin, especially neutron rich hypernuclei to
look insight hyperon-nucleon interactions in the neutron rich medium, and
hypernuclear magnetic moments to investigate baryon properties in the nuclei.
We are currently preparing for the first experiment with Li and C
beams at 2 AGeV to demonstrate the feasibility of a precise hypernuclear
spectroscopy by identifying H, H and
He. The first physics experiment on these hypernuclei is
planned for 2009. In the present document, an overview of the HypHI project and
the details of this first experiment will be discussed.Comment: 5 pages, 2 figures, French-Japanese symposium 2008, Paris (France
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