370 research outputs found
Enhancing ordering dynamics in solvent-annealed block-copolymer films by lithographic hard masks supports
We studied solvent-driven ordering dynamics of block copolymer films
supported by a densely cross-linked polymer network designed as organic hard
mask (HM) for lithographic fabrications. The ordering of microphase separated
domains at low degrees of swelling corresponding to intermediate/strong
segregation regimes was found to proceed significantly faster in films on a HM
layer as compared to similar block copolymer films on silicon wafers. The
ten-fold enhancement of the chain mobility was evident in the dynamics of
morphological phase transitions and of related process of terrace-formation on
a macroscale, as well as in the degree of long-range lateral order of
nanostructures. The effect is independent of the chemical structure and on the
volume composition (cylinder-/ lamella-forming) of the block copolymers.
In-situ ellipsometric measurements of the swelling behavior revealed a
cumulative increase in 1-3 vol. % in solvent up-take by HM-block copolymer
bilayer films, so that we suggest other than dilution effect reasons for the
observed significant enhancement of the chain mobility in concentrated block
copolymer solutions. Another beneficial effect of the HM-support is the
suppression of the film dewetting which holds true even for low molecular
weight homopolymer polystyrene films at high degrees of swelling. Apart from
immediate technological impact in block copolymer-assisted nanolithography, our
findings convey novel insight into effects of molecular architecture on
polymer-solvent interactions.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Macromolecules, copyright
\c{opyright} American Chemical Society after peer review. To access the final
edited and published work see http://pubs.acs.org/doi/abs/10.1021/ma500561
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
Polarized Proton Beams from Laser-induced Plasmas
We report on the concept of an innovative source to produce polarized
proton/deuteron beams of a kinetic energy up to several GeV from a laser-driven
plasma accelerator. Spin effects have been implemented into the PIC simulation
code VLPL to make theoretical predictions about the behavior of proton spins in
laser-induced plasmas. Simulations of spin-polarized targets show that the
polarization is conserved during the acceleration process. For the experimental
realization, a polarized HCl gas-jet target is under construction using the
fundamental wavelength of a Nd:YAG laser system to align the HCl bonds and
simultaneously circular polarized light of the fifth harmonic to
photo-dissociate, yielding nuclear polarized H atoms. Subsequently, their
degree of polarization is measured with a Lamb-shift polarimeter. The final
experiments, aiming at the first observation of a polarized particle beam from
laser-generated plasmas, will be carried out at the 10 PW laser system SULF at
SIOM/Shanghai.Comment: 7 pages, 7 figure
UBVI Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group
We present UBVI surface photometry for 20.'5 X 20.'5 area of a late-type
spiral galaxy NGC 300. In order to understand the morphological properties and
luminosity distribution characteristics of NGC 300, we have derived isophotal
maps, surface brightness profiles, ellipticity profiles, position angle
profiles, and color profiles. By merging the I-band data of our surface
brightness measurements with those of Boeker et al. (2002) based on Hubble
Space Telescope observations, we have made combined I-band surface brightness
profiles for the region of 0."02 < r < 500" and decomposed the profiles into
three components: a nucleus, a bulge, and an exponential disk.Comment: 16 pages(cjaa209.sty), Accepted by the Chinese J. Astron. Astrophys.,
Fig 2 and 8 are degraded to reduce spac
A Young Stellar Cluster in the Nucleus of NGC 4449
We have obtained 1-2 A resolution optical Echellette spectra of the nuclear
star cluster in the nearby starburst galaxy NGC 4449. The light is clearly
dominated by a very young (6-10 Myr) population of stars. For our age dating,
we have used recent population synthesis models to interpret the observed
equivalent width of stellar absorption features such as the HI Balmer series
and the CaII triplet around 8500 A. We also compare the observed spectrum of
the nuclear cluster to synthesized spectra of simple stellar populations of
varying ages. All these approaches yield a consistent cluster age. Metallicity
estimates based on the relative intensities of various ionization lines yield
no evidence for significant enrichment in the center of this low mass galaxy:
the metallicity of the nuclear cluster is about one fourth of the solar value,
in agreement with independent estimates for the disk material of NGC 4449.Comment: 24 pages (incl. 7 figures), accepted by AJ, March 2001 issue revised
version with minor changes and additions, one additional figur
HST/STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass On Hubble Type
(Abridged) We study the nuclear star clusters in spiral galaxies of various
Hubble types using spectra obtained with STIS on-board HST. We observed the
nuclear clusters in 40 galaxies, selected from two previous HST/WFPC2 imaging
surveys. The spectra provide a better separation of cluster light from
underlying galaxy light than is possible with ground-based spectra. To infer
the star formation history, metallicity and dust extinction, we fit weighted
superpositions of single-age stellar population templates to the spectra. The
luminosity-weighted age ranges from 10 Myrs to 10 Gyrs. The stellar populations
of NCs are generally best fit as a mixture of populations of different ages.
This indicates that NCs did not form in a single event, but instead they had
additional star formation long after the oldest stars formed. On average, the
sample clusters in late-type spirals have a younger luminosity-weighted mean
age than those in early-type spirals (log(age/yr) = 8.37+/-0.25 vs.
9.23+/-0.21). The average cluster masses are smaller in late-type spirals than
in early-type spirals (log(M/Msun) = 6.25+/-0.21 vs. 7.63+/-0.24), and exceed
the masses typical of globular clusters. The cluster mass correlates strongly
with both the Hubble type of the host galaxy and the luminosity of its bulge.
The latter correlation has the same slope as the well-known correlation between
supermassive black hole mass and bulge luminosity. The properties of both
nuclear clusters and black holes are therefore intimately connected to the
properties of the host galaxy.Comment: AJ submitted (original submission Nov 30, 2005, present version
includes changes based on referee recommendations). 69 pages, 16 figures, 7
table
Multi-density model of the ionised gas in NGC 253 using radio recombination lines
We have imaged the H92alpha (8.3 GHz), H75alpha (15 GHz), and H166alpha (1.4
GHz) Radio Recombination Lines (RRLs) from NGC 253 at resolutions of 4.5 pc
(0.4"), 2.5 pc (0.2") and 53 pc (4.5") respectively. The H92alpha line arises
from individual compact sources, most of which possess radio continuum
counterparts. The line widths range from ~200 km/s for the sources near the
radio nucleus to 70-100 km/s for the extranuclear ones. These lines are emitted
by gas at a density ~10000 /cc. The remainder of the cm-wave RRLs arise in
lower density gas (~500 /cc) with a higher area filling factor and with ten
times highermass. A third component of higher density gas (>10000 /cc) is
required to explain the mm-wave RRLs.Comment: Accepted by A&A; Changed to fit all figures within pag
Block Copolymer at Nano-Patterned Surfaces
We present numerical calculations of lamellar phases of block copolymers at
patterned surfaces. We model symmetric di-block copolymer films forming
lamellar phases and the effect of geometrical and chemical surface patterning
on the alignment and orientation of lamellar phases. The calculations are done
within self-consistent field theory (SCFT), where the semi-implicit relaxation
scheme is used to solve the diffusion equation. Two specific set-ups, motivated
by recent experiments, are investigated. In the first, the film is placed on
top of a surface imprinted with long chemical stripes. The stripes interact
more favorably with one of the two blocks and induce a perpendicular
orientation in a large range of system parameters. However, the system is found
to be sensitive to its initial conditions, and sometimes gets trapped into a
metastable mixed state composed of domains in parallel and perpendicular
orientations. In a second set-up, we study the film structure and orientation
when it is pressed against a hard grooved mold. The mold surface prefers one of
the two components and this set-up is found to be superior for inducing a
perfect perpendicular lamellar orientation for a wide range of system
parameters
The Quintuplet Cluster III. Hertzsprung-Russell diagram and cluster age
The Quintuplet, one of three massive stellar clusters in the Galactic center,
is located about 30pc in projection from Sagittarius A*. Based on near-infrared
K-band spectra we determine temperatures and luminosities for all stars in our
sample and construct the Herztsprung-Russell diagram. We find two distinct
groups: early-type OB stars and late-type KM stars, well separated from each
other. By comparison with Geneva stellar evolution models we derive initial
masses exceeding 8 solar masses for the OB stars, that are located along an
isochrone corresponding to a cluster age of about 4 million years. In addition,
we derive number ratios (e. g. N_WR/N_O) and compare them with predictions of
population synthesis models. We find that an instantaneous burst of star
formation at about 3.3 to 3.6\,Myr ago is the most likely scenario to form the
Quintuplet cluster. The late-type stars in the sample are red giant branch
(RGB) stars or red supergiants (RSGs) according to their spectral signatures.
It is discussed if they could physically belong to the Quintuplet cluster.
Furthermore, we apply a mass-luminosity relation to construct the initial mass
function (IMF) of the cluster. We find indications for a slightly top-heavy
IMF.Comment: 10 pages, 9 figures, 2 tables, accepted for publication in A&
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