11,651 research outputs found
Synthesis Imaging of Dense Molecular Gas in the N113 HII Region of the Large Magellanic Cloud
We present aperture synthesis imaging of dense molecular gas in the Large
Magellanic Cloud, taken with the prototype millimeter receivers of the
Australia Telescope Compact Array (ATCA). Our observations of the N113 HII
region reveal a condensation with a size of ~6" (1.5 pc) FWHM, detected
strongly in the 1-0 lines of HCO+, HCN and HNC, and weakly in C_2H. Comparison
of the ATCA observations with single-dish maps from the Mopra Telescope and
sensitive spectra from the Swedish-ESO Submillimetre Telescope indicates that
the condensation is a massive clump of ~10^4 solar masses within a larger ~10^5
solar mass molecular cloud. The clump is centered adjacent to a compact,
obscured HII region which is part of a linear structure of radio continuum
sources extending across the molecular cloud. We suggest that the clump
represents a possible site for triggered star formation. Examining the
integrated line intensities as a function of interferometer baseline length, we
find evidence for decreasing HCO+/HCN and HCN/HNC ratios on longer baselines.
These trends are consistent with a significant component of the HCO+ emission
arising in an extended clump envelope and a lower HCN/HNC abundance ratio in
dense cores.Comment: 10 pages, 6 figures, to appear in Ap
Dynamical Instability in a Trimeric Chain of Interacting Bose-Einstein Condensates
We analyze thoroughly the mean-field dynamics of a linear chain of three
coupled Bose-Einstein condensates, where both the tunneling and the
central-well relative depth are adjustable parameters. Owing to its
nonintegrability, entailing a complex dynamics with chaos occurrence, this
system is a paradigm for longer arrays whose simplicity still allows a thorough
analytical study.We identify the set of dynamics fixed points, along with the
associated proper modes, and establish their stability character depending on
the significant parameters. As an example of the remarkable operational value
of our analysis, we point out some macroscopic effects that seem viable to
experiments.Comment: 5 pages, 3 figure
Complex Dynamics and Synchronization of Delayed-Feedback Nonlinear Oscillators
We describe a flexible and modular delayed-feedback nonlinear oscillator that
is capable of generating a wide range of dynamical behaviours, from periodic
oscillations to high-dimensional chaos. The oscillator uses electrooptic
modulation and fibre-optic transmission, with feedback and filtering
implemented through real-time digital-signal processing. We consider two such
oscillators that are coupled to one another, and we identify the conditions
under which they will synchronize. By examining the rates of divergence or
convergence between two coupled oscillators, we quantify the maximum Lyapunov
exponents or transverse Lyapunov exponents of the system, and we present an
experimental method to determine these rates that does not require a
mathematical model of the system. Finally, we demonstrate a new adaptive
control method that keeps two oscillators synchronized even when the coupling
between them is changing unpredictably.Comment: 24 pages, 13 figures. To appear in Phil. Trans. R. Soc. A (special
theme issue to accompany 2009 International Workshop on Delayed Complex
Systems
Network synchronization of groups
In this paper we study synchronized motions in complex networks in which
there are distinct groups of nodes where the dynamical systems on each node
within a group are the same but are different for nodes in different groups.
Both continuous time and discrete time systems are considered. We initially
focus on the case where two groups are present and the network has bipartite
topology (i.e., links exist between nodes in different groups but not between
nodes in the same group). We also show that group synchronous motions are
compatible with more general network topologies, where there are also
connections within the groups
Brain amyloid in preclinical Alzheimer\u27s disease is associated with increased driving risk
INTRODUCTION: Postmortem studies suggest that fibrillar brain amyloid places people at higher risk for hazardous driving in the preclinical stage of Alzheimer's disease (AD). METHODS: We administered driving questionnaires to 104 older drivers (19 AD, 24 mild cognitive impairment, and 61 cognitive normal) who had a recent (18)F-florbetapir positron emission tomography scan. We examined associations of amyloid standardized uptake value ratios with driving behaviors: traffic violations or accidents in the past 3 years. RESULTS: The frequency of violations or accidents was curvilinear with respect to standardized uptake value ratios, peaking around a value of 1.1 (model r(2) = 0.10, P = .002); moreover, this relationship was evident for the cognitively normal participants. DISCUSSION: We found that driving risk is strongly related to accumulating amyloid on positron emission tomography, and that this trend is evident in the preclinical stage of AD. Brain amyloid burden may in part explain the increased crash risk reported in older adults
Preparation of heteronuclear bridging methylene complexes
The reactions of the titanacyclobutane complexes (η^5-C_5H_5)_2TiCH_2CRR'CH_2 (la, R = R' = Me; lb, R = Me, R' = Pr) with M-X compounds (M =Ti, Zr, Rh, Ir, Pd, Pt; X = Cl, OMe) have been investigated. The titanacyclobutanes have been found to react as sources of (η^5-C_5H_5)_2TiCH_2, giving (η^5-C_5H_5)_2Ti(μ –CH_2)(μ-X)ML_n (L_n = ancillary ligands) products. Several such complexes have been isolated as crystalline solids; however, only (η^5-C_5H_5_2Ti(μ-CH_2)(μ-X)Rh(η^4-l,5-cyclooctadiene) is stable in solution at 25°C. The complex η^5-C_5H_5)_2iTi(μ-CH_2)(μ-Cl)Ti(η^5-C_5Me_5)Cl was found to react with CO to form the bridging ketene complex (η^5-C_5H_5)_2Ti-μ, η^2(C,O)-(OCCH_2)Ti(η^5-C_5Me_5)Cl_2
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