4,535 research outputs found
Characterisation of Charge Conduction Networks in Poly(3-hexylthiophene)/Polystyrene Blends using Noise Spectroscopy
1/f noise spectroscopy is used to investigate charge conduction networks within polymer blend space-charge-limited diodes (SCLDs) fabricated from regioregular poly(3-hexylthiophene) (P3HT) and either isotactic-polystyrene (i-PS) or amorphous-polystyrene (a-PS). Conducting AFM measurements showed that i-PS blends have heterogeneous conduction characterised by current ‘hotspots’, whereas a-PS blends showed homogeneous conduction. The difference in conducting networks between blends was clearly revealed when examining the noise spectra for the range of blend devices. Furthermore, the shape of the noise spectra suggested that as the blend composition changed, the charges sampled differing breadths of the density of states. These data suggest that noise measurements can be used as an informative technique to electrically characterise the effects of blend morphology and its effects within polymer electronic devices
Spatially Resolved Spitzer-IRS Spectroscopy of the Central Region of M82
We present high spatial resolution (~ 35 parsec) 5-38 um spectra of the
central region of M82, taken with the Spitzer Infrared Spectrograph. From these
spectra we determined the fluxes and equivalent widths of key diagnostic
features, such as the [NeII]12.8um, [NeIII]15.5um, and H_2 S(1)17.03um lines,
and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in
six representative regions and analysed the spatial distribution of these lines
and their ratios across the central region. We find a good correlation of the
dust extinction with the CO 1-0 emission. The PAH emission follows closely the
ionization structure along the galactic disk. The observed variations of the
diagnostic PAH ratios across M82 can be explained by extinction effects, within
systematic uncertainties. The 16-18um PAH complex is very prominent, and its
equivalent width is enhanced outwards from the galactic plane. We interpret
this as a consequence of the variation of the UV radiation field. The EWs of
the 11.3um PAH feature and the H_2 S(1) line correlate closely, and we conclude
that shocks in the outflow regions have no measurable influence on the H_2
emission. The [NeIII]/[NeII] ratio is on average low at ~0.18, and shows little
variations across the plane, indicating that the dominant stellar population is
evolved (5 - 6 Myr) and well distributed. There is a slight increase of the
ratio with distance from the galactic plane of M82 which we attribute to a
decrease in gas density. Our observations indicate that the star formation rate
has decreased significantly in the last 5 Myr. The quantities of dust and
molecular gas in the central area of the galaxy argue against starvation and
for negative feedback processes, observable through the strong extra-planar
outflows.Comment: 15 pages, 12 figures, 3 tables, ApJ, emulateap
An original interferometric study of NGC 1068 with VISIR BURST mode images
We present 12.8 microns images of the core of NGC 1068 obtained with the
BURST mode of the VLT/VISIR. We trace structures under the diffraction limit of
one UT and we investigate the link between dust in the vicinity of the central
engine of NGC 1068, recently resolved by interferometry with MIDI, and more
extended structures. This step is mandatory for a multi-scale understanding of
the sources of mid-infrared emission in AGNs. A speckle processing of VISIR
BURST mode images was performed to extract very low spatial-frequency
visibilities, first considering the full field of VISIR BURST mode images and
then limiting it to the mask used for the acquisition of MIDI data. Extracted
visibilities are reproduced with a multi-component model. We identify two major
sources of emission: one compact < 85 mas, associated with the dusty torus, and
an elliptical one, (< 140) mas x 1187 mas at P.A.=-4 degrees from N to E. This
is consistent with previous deconvolution processes. The combination with MIDI
data reveals the close environment of the dusty torus to contribute to about 83
percent of the MIR flux seen by MIDI. This strong contribution has to be
considered in modeling long baseline interferometric data. It must be related
to the NS elongated component which is thought to originate from individually
unresolved dusty clouds and is located inside the ionization cone. Low
temperatures of the dusty torus are not challenged, emphasizing the scenarios
of clumpy torus.Comment: 10 pages, 7 figures, accepted for publication in A&
Heating and cooling of the neutral ISM in the NGC4736 circumnuclear ring
The manner in which gas accretes and orbits within circumnuclear rings has
direct implications for the star formation process. In particular, gas may be
compressed and shocked at the inflow points, resulting in bursts of star
formation at these locations. Afterwards the gas and young stars move together
through the ring. In addition, star formation may occur throughout the ring, if
and when the gas reaches sufficient density to collapse under gravity. These
two scenarios for star formation in rings are often referred to as the `pearls
on a string' and `popcorn' paradigms. In this paper, we use new Herschel PACS
observations, obtained as part of the KINGFISH Open Time Key Program, along
with archival Spitzer and ground-based observations from the SINGS Legacy
project, to investigate the heating and cooling of the interstellar medium in
the nearby star-forming ring galaxy, NGC4736. By comparing spatially resolved
estimates of the stellar FUV flux available for heating, with the gas and dust
cooling derived from the FIR continuum and line emission, we show that while
star formation is indeed dominant at the inflow points in NGC 4736, additional
star formation is needed to balance the gas heating and cooling throughout the
ring. This additional component most likely arises from the general increase in
gas density in the ring over its lifetime. Our data provide strong evidence,
therefore, for a combination of the two paradigms for star formation in the
ring in NGC4736.Comment: accepted for publication in A&
- …