5,236 research outputs found
Controlling turbulence in coupled map lattice systems using feedback techniques
We report the suppression of spatiotemporal chaos observed in coupled map lattices. Suppression is achieved using different feedback techniques, most of which are applicable to actual experimental situations. Results from application of feedback control to a single chaotic element (single map) are presented to demonstrate similarities in the dynamical response of a single system and an extended system under the influence of external feedback
Resolving velocity space dynamics in continuum gyrokinetics
Many plasmas of interest to the astrophysical and fusion communities are
weakly collisional. In such plasmas, small scales can develop in the
distribution of particle velocities, potentially affecting observable
quantities such as turbulent fluxes. Consequently, it is necessary to monitor
velocity space resolution in gyrokinetic simulations. In this paper, we present
a set of computationally efficient diagnostics for measuring velocity space
resolution in gyrokinetic simulations and apply them to a range of plasma
physics phenomena using the continuum gyrokinetic code GS2. For the cases
considered here, it is found that the use of a collisionality at or below
experimental values allows for the resolution of plasma dynamics with
relatively few velocity space grid points. Additionally, we describe
implementation of an adaptive collision frequency which can be used to improve
velocity space resolution in the collisionless regime, where results are
expected to be independent of collision frequency.Comment: 20 pages, 11 figures, submitted to Phys. Plasma
Design and development of adapters for electromagnetic trackers to perform navigated laparoscopic radiofrequency ablation
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies
We present CO observations of a large sample of ultraluminous IR galaxies out
to z = 0.3. Most of the galaxies are interacting, but not completed mergers.
All but one have high CO(1-0) luminosities, log(Lco [K-km/s-pc^2]) = 9.92 +/-
0.12. The dispersion in Lco is only 30%, less than that in the FIR luminosity.
The integrated CO intensity correlates Strongly with the 100 micron flux
density, as expected for a black body model in which the mid and far IR
radiation are optically thick. We use this model to derive sizes of the FIR and
CO emitting regions and the enclosed dynamical masses. Both the IR and CO
emission originate in regions a few hundred parsecs in radius. The median value
of Lfir/Lco = 160 Lsun/(K-km/s-pc^2), within a factor of two of the black body
limit for the observed FIR temperatures. The entire ISM is a scaled up version
of a normal galactic disk with densities a factor of 100 higher, making even
the intercloud medium a molecular region. Using three different techniques of
H2 mass estimation, we conclude that the ratio of gas mass to Lco is about a
factor of four lower than for Galactic molecular clouds, but that the gas mass
is a large fraction of the dynamical mass. Our analysis of CO emission reduces
the H2 mass from previous estimates of 2-5e10 Msun to 0.4-1.5e10 Msun, which is
in the range found for molecular gas rich spiral galaxies. A collision
involving a molecular gas rich spiral could lead to an ultraluminous galaxy
powered by central starbursts triggered by the compression of infalling
preexisting GMC's.Comment: 34 pages LaTeX with aasms.sty, 14 Postscript figures, submitted to
ApJ Higher quality versions of Figs 2a-f and 7a-c available by anonymous FTP
from ftp://sbast1.ess.sunysb.edu/solomon/
Doping nature of native defects in 1T-TiSe2
The transition metal dichalcogenide 1T-TiSe2 is a quasi two-dimensional
layered material with a charge density wave (CDW) transition temperature of
TCDW 200 K. Self-doping effects for crystals grown at different temperatures
introduce structural defects, modify the temperature dependent resistivity and
strongly perturbate the CDW phase. Here we study the structural and doping
nature of such native defects combining scanning tunneling
microscopy/spectroscopy and ab initio calculations. The dominant native single
atom dopants we identify in our single crystals are intercalated Ti atoms, Se
vacancies and Se substitutions by residual iodine and oxygen.Comment: 5 pages, 3 figure
Revealing the environs of the remarkable southern hot core G327.3-0.6
We present a submm study of the massive hot core G327.3-0.6 that constrains
its physical parameters and environment. The APEX telescope was used to image
CO and N2H+ emission, to observe lines from other molecules toward a hot and a
cold molecular core, and to measure the continuum flux density of the hot core.
In the C18O J=3-2 line, two clumps were found, one associated with the HII
region G327.3-0.5 and the other associated with the hot core. An additional
cold clump is found 30 arcsec (0.4 pc) northeast of the hot core in bright N2H+
emission. From the the continuum data, we calculate a mass of 420 Msol and a
size of 0.1 pc for the hot core. A new, more accurate position of the hot core
is reported, which allows the association of the core with a bright
mid-infrared source. The luminosity of the hot core is estimated to be between
5 and 15 10^4 Lsol. This study revealed several different evolutionary stages
of massive star formation in the G327.3-0.6 region.Comment: APEX A&A special issue, accepte
STM microscopy of the CDW in 1T-TiSe2 in the presence of single atom defects
We present a detailed low temperature scanning tunneling microscopy study of
the commensurate charge density wave (CDW) in 1-TiSe in the presence of
single atom defects. We find no significant modification of the CDW lattice in
single crystals with native defects concentrations where some bulk probes
already measure substantial reductions in the CDW phase transition signature.
Systematic analysis of STM micrographs combined with density functional theory
modelling of atomic defect patterns indicate that the observed CDW modulation
lies in the Se surface layer. The defect patterns clearly show there are no
2-polytype inclusions in the CDW phase, as previously found at room
temperature [Titov A.N. et al, Phys. Sol. State 53, 1073 (2011). They further
provide an alternative explanation for the chiral Friedel oscillations recently
reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125, (2011)].Comment: 5 pages, 4 figure
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