1,635 research outputs found
Star Formation in the Circumnuclear Environment of NGC1068
We present near-infrared emission line images of the circumnuclear ring in
NGC1068. We have measured the Br_gamma fluxes in a number of star forming
complexes and derived extinctions for each of these by comparison with H_alpha.
We investigate the star forming histories of these regions and find that a
short burst of star formation occured co-evally throughout the ring within the
last 30-40 Myr, and perhaps as recently as 4-7 Myr ago. The 1-0 S(1) flux and
S(1)/Br_gamma ratios indicate that as well as fluorescence, shock excited H_2
emission contributes to the total flux. There is excess H_2 flux to the
North-West where the ionisation cone crosses the ring, and we have shown it is
possible that the non-stellar continuum from the Seyfert nucleus which produces
the high excitation lines could also be causing fluorescence at the edges of
molecular clouds in the ring. The nuclear 1-0 S(1) is more extended than
previously realised but only along the bar's major axis, and we consider
mechanisms for its excitation.Comment: 10 pages, 4 figures, LaTeX (mn.sty & psfig.sty). Accepted for
publication in MNRA
Detection of Non-Random Galaxy Orientations in X-ray Subclusters of the Coma Cluster
This study on the Coma cluster suggests that there are deviations from a
completely random galaxy orientation on small scales. Since we found a
significant coincidence of hot-gas features identified in the latest X-ray
observations of Coma with these local anisotropies, they may indicate regions
of recent mutual interaction of member galaxies within subclusters which are
currently falling in on the main cluster.Comment: 4 pages, 4 figures, 3 tables v2: Rewritten introduction, amendments
to the 'Interpretation' sectio
Controlled vaporization of the superconducting condensate in cuprate superconductors sheds light on the pairing boson
We use ultrashort intense laser pulses to study superconducting state
vaporization dynamics in La(2-x)Sr(x)CuO4 (x=0.1 and 0.15) on the femtosecond
timescale. We find that the energy density required to vaporize the
superconducting state is 2+- 0.8 K/Cu and 2.6 +- 1 K/Cu for x=0.1 and 0.15
respectively. This is significantly greater than the condensation energy
density, indicating that the quasiparticles share a large amount of energy with
the boson glue bath on this timescale. Considering in detail both spin and
lattice energy relaxation pathways which take place on the relevant timescale
of picoseconds, we rule out purely spin-mediated pair-breaking in favor of
phonon-mediated mechanisms, effectively ruling out spin-mediated pairing in
cuprates as a consequence.Comment: 5 pages of article plus 4 pages of supplementary materia
High-Tc superconductivity in entirely end-bonded multi-walled carbon nanotubes
We report that entirely end-bonded multi-walled carbon nanotubes (MWNTs) can
show superconductivity with the transition temperature Tc as high as 12K that
is approximately 40-times larger than those reported in ropes of single-walled
nanotubes. We find that emergence of this superconductivity is very sensitive
to junction structures of Au electrode/MWNTs. This reveals that only MWNTs with
optimal numbers of electrically activated shells, which are realized by the
end-bonding, can allow the superconductivity due to inter shell effects.Comment: 5 page
High-Energy Spin Dynamics in LaSrNiO
We have mapped out the spin dynamics in a stripe-ordered nickelate,
LaSrNiO with , using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: eV \AA, very similar to the velocity in the undoped, insulating
parent compound, LaNiO. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high- cuprates.Comment: 4 figure
Ionization Source of a Minor-axis Cloud in the Outer Halo of M82
The M82 `cap' is a gas cloud at a projected radius of 11.6 kpc along the
minor axis of this well known superwind source. The cap has been detected in
optical line emission and X-ray emission and therefore provides an important
probe of the wind energetics. In order to investigate the ionization source of
the cap, we observed it with the Kyoto3DII Fabry-Perot instrument mounted on
the Subaru Telescope. Deep continuum, Ha, [NII]6583/Ha, and [SII]6716,6731/Ha
maps were obtained with sub-arcsecond resolution. The superior spatial
resolution compared to earlier studies reveals a number of bright Ha emitting
clouds within the cap. The emission line widths (< 100 km s^-1 FWHM) and line
ratios in the newly identified knots are most reasonably explained by slow to
moderate shocks velocities (v_shock = 40--80 km s^-1) driven by a fast wind
into dense clouds. The momentum input from the M82 nuclear starburst region is
enough to produce the observed shock. Consequently, earlier claims of
photoionization by the central starburst are ruled out because they cannot
explain the observed fluxes of the densest knots unless the UV escape fraction
is very high (f_esc > 60%), i.e., an order of magnitude higher than observed in
dwarf galaxies to date. Using these results, we discuss the evolutionary
history of the M82 superwind. Future UV/X-ray surveys are expected to confirm
that the temperature of the gas is consistent with our moderate shock model.Comment: 7 pages, 5 figures, 2 tables; Accepted for publication in Ap
Strategies to enhance the excitation energy-transfer efficiency in a light-harvesting system using the intra-molecular charge transfer character of carotenoids
Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (∼95%) energy-transfer from fucoxanthin to chlorophyll a in the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids. In this study we were successful, for the first time, in incorporating fucoxanthin into a light-harvesting complex 1 from the purple photosynthetic bacterium, Rhodospirillum rubrum G9+ (a carotenoidless strain). Femtosecond pump-probe spectroscopy was applied to this reconstituted light-harvesting complex in order to determine the efficiency of excitation energy-transfer from fucoxanthin to bacteriochlorophyll a when they are bound to the light-harvesting 1 apo-proteins
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