734 research outputs found
Radial orbit instability as a dissipation-induced phenomenon
This paper is devoted to Radial Orbit Instability in the context of
self-gravitating dynamical systems. We present this instability in the new
frame of Dissipation-Induced Instability theory. This allows us to obtain a
rather simple proof based on energetics arguments and to clarify the associated
physical mechanism.Comment: 15 pages. Published in Monthly Notices of the RAS by the Royal
Astronomical Society and Blackwell Publishing. Corrected for page style,
typos, and added reference
Systemic and central nervous system neuroinflammatory signatures of neuropsychiatric symptoms and related cognitive decline in older people.
Neuroinflammation may contribute to psychiatric symptoms in older people, in particular in the context of Alzheimer's disease (AD). We sought to identify systemic and central nervous system (CNS) inflammatory alterations associated with neuropsychiatric symptoms (NPS); and to investigate their relationships with AD pathology and clinical disease progression.
We quantified a panel of 38 neuroinflammation and vascular injury markers in paired serum and cerebrospinal fluid (CSF) samples in a cohort of cognitively normal and impaired older subjects. We performed neuropsychiatric and cognitive evaluations and measured CSF biomarkers of AD pathology. Multivariate analysis determined serum and CSF neuroinflammatory alterations associated with NPS, considering cognitive status, AD pathology, and cognitive decline at follow-up visits.
NPS were associated with distinct inflammatory profiles in serum, involving eotaxin-3, interleukin (IL)-6 and C-reactive protein (CRP); and in CSF, including soluble intracellular cell adhesion molecule-1 (sICAM-1), IL-8, 10-kDa interferon-γ-induced protein, and CRP. AD pathology interacted with CSF sICAM-1 in association with NPS. Presenting NPS was associated with subsequent cognitive decline which was mediated by CSF sICAM-1.
Distinct systemic and CNS inflammatory processes are involved in the pathophysiology of NPS in older people. Neuroinflammation may explain the link between NPS and more rapid clinical disease progression
Averaging out magnetic forces with fast rf-sweeps in an optical trap for metastable chromium atoms
We introduce a novel type of time-averaged trap, in which the internal state
of the atoms is rapidly modulated to modify magnetic trapping potentials. In
our experiment, fast radiofrequency (rf) linear sweeps flip the spin of atoms
at a fast rate, which averages out magnetic forces. We use this procedure to
optimize the accumulation of metastable chomium atoms into an optical dipole
trap from a magneto-optical trap. The potential experienced by the metastable
atoms is identical to the bare optical dipole potential, so that this procedure
allows for trapping all magnetic sublevels, hence increasing by up to 80
percent the final number of accumulated atoms.Comment: 4 pages, 4 figure
O18O and C18O observations of rho Oph A
Observations of the (N_J=1_1-1_0) ground state transition of O_2 with the
Odin satellite resulted in a about 5 sigma detection toward the dense core rho
Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam
width of 10', larger than the size of the dense core, so that the precise
nature of the emitting source and its exact location and extent are unknown.
The current investigation is intended to remedy this. Telluric absorption makes
ground based O_2 observations essentially impossible and observations had to be
done from space. mm-wave telescopes on space platforms were necessarily small,
which resulted in large, several arcminutes wide, beam patterns. Although the
Earth's atmosphere is entirely opaque to low-lying O_2 transitions, it allows
ground based observations of the much rarer O18O in favourable conditions and
at much higher angular resolution with larger telescopes. In addition, rho Oph
A exhibits both multiple radial velocity systems and considerable velocity
gradients. Extensive mapping of the region in the proxy C18O (J=3-2) line can
be expected to help identify the O_2 source on the basis of its line shape and
Doppler velocity. Line opacities were determined from observations of optically
thin 13C18O (J=3-2) at selected positions. During several observing periods,
two C18O intensity maxima in rho Oph A were searched for in the 16O18O
(2_1-0_1) line at 234 GHz with the 12m APEX telescope. Our observations
resulted in an upper limit on the integrated O18O intensity of < 0.01 K km/s (3
sigma) into the 26.5" beam. We conclude that the source of observed O_2
emission is most likely confined to the central regions of the rho Oph A cloud.
In this limited area, implied O_2 abundances could thus be higher than
previously reported, by up to two orders of magnitude.Comment: 7 pages, 6 figures (5 colour), Astronomy & Astrophysic
Radial orbit instability: review and perspectives
This paper presents elements about the radial orbit instability, which occurs
in spherical self-gravitating systems with a strong anisotropy in the radial
velocity direction. It contains an overview on the history of radial orbit
instability. We also present the symplectic method we use to explore stability
of equilibrium states, directly related to the dissipation induced instability
mechanism well known in theoretical mechanics and plasma physics.Comment: 10 pages, submitted to Transport Theory and Statistical Physics,
proceedings of Vlasovia 2009 International Conference. Corrected for typos,
redaction, and references adde
Accumulation of chromium metastable atoms into an Optical Trap
We report the fast accumulation of a large number of metastable 52Cr atoms in
a mixed trap, formed by the superposition of a strongly confining optical trap
and a quadrupolar magnetic trap. The steady state is reached after about 400
ms, providing a cloud of more than one million metastable atoms at a
temperature of about 100 microK, with a peak density of 10^{18} atoms.m^{-3}.
We have optimized the loading procedure, and measured the light shift of the
5D4 state by analyzing how the trapped atoms respond to a parametric
excitation. We compare this result to a theoretical evaluation based on the
available spectroscopic data for chromium atoms.Comment: 7 pages, 5 Figure
The RMS Survey: 13CO observations of candidate massive YSOs in the southern hemisphere
Abridged: The Red MSX Source (RMS) survey is an ongoing multi-wavelength
observational programme designed to return a large, well-selected sample of
massive young stellar objects (MYSOs). Here we present 13CO observations made
towards 854 MYSOs candidates located in the 3rd and 4th quadrants. We detected
13CO emission towards a total of 751 of the 854 RMS sources observed (~88%). In
total 2185 emission components are detected above 3 level. Multiple
emission profiles are observed towards the majority of these sources - 455
sources (~60%) - with an average of ~4 molecular clouds along the line of
sight. These multiple emission features make it difficult to assign a kinematic
velocity to many of our sample. We have used archival CS (J=2-1) and maser
velocities to resolved the component multiplicity towards 82 sources and have
derived a criterion which is used to identify the most likely component for a
further 202 multiple component sources. Combined with the single component
detections we have obtained unambiguous kinematic velocities towards 580
sources (~80% of the detections). The 171 sources for which we have not been
able to determine the kinematic velocity will require additional line data.
Using the rotation curve of Brand and Blitz (1993) and their radial velocities
we calculate kinematic distances for all components detected.Comment: Summitted to A&A, the resolution of figure 1 has been reduced,
samples of Table 3 and Figure 11 are now included but the full version will
only be available in the online version of the journa
Deformation of the N=Z nucleus 76Sr using beta-decay studies
A novel method of deducing the deformation of the N=Z nucleus 76Sr is
presented. It is based on the comparison of the experimental Gamow-Teller
strength distribution B(GT) from its beta decay with the results of QRPA
calculations. This method confirms previous indications of the strong prolate
deformation of this nucleus in a totally independent way. The measurement has
been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia",
newly installed at CERN-ISOLDE.Comment: Accepted in Phys. Rev. Letter
Determination of Matter Surface Distribution of Neutron-rich Nuclei
We demonstrate that the matter density distribution in the surface region is
determined well by the use of the relatively low-intensity beams that become
available at the upcoming radioactive beam facilities. Following the method
used in the analyses of electron scattering, we examine how well the density
distribution is determined in a model-independent way by generating pseudo data
and by carefully applying statistical and systematic error analyses. We also
study how the determination becomes deteriorated in the central region of the
density, as the quality of data decreases. Determination of the density
distributions of neutron-rich nuclei is performed by fixing parameters in the
basis functions to the neighboring stable nuclei. The procedure allows that the
knowledge of the density distributions of stable nuclei assists to strengthen
the determination of their unstable isotopes.Comment: 41 pages, latex, 27 figure
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