3,147 research outputs found
Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells
A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of
a monomeric dibromo indolenine squaraine dye. The resulting polymer has a
weight average molar mass in the order of Mw ~30.000-50.000 and a
polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC).
The electronic properties of monomer and polymer were investigated by cyclic
voltammetry, absorption and emission spectroscopy. Owing to exciton coupling
the absorption bands of the polymer are red-shifted and strongly broadened
compared to the monomer squaraine dye. Bulk heterojunction solar cells were
prepared from blends of the polysquaraine with the fullerene derivative
[6,6]-phenyl C61-butyric acid methyl ester (PCBM) in different weight ratios
(1:3 to 1:1). The power conversion efficiencies under simulated AM 1.5
conditions yielded 0.45 % for these non-optimized systems. The external quantum
efficiency (EQE) shows that the photoresponse spans the range from 300 to 850
nm, which illustrates the promising properties of this novel organic
semiconductor as a low band gap donor material in organic photovoltaics.Comment: 10 pages, 7 figure
Self-Similar Dynamical Relaxation of Dark Matter Halos in an Expanding Universe
We investigate the structure of cold dark matter halos using advanced models
of spherical collapse and accretion in an expanding Universe. These base on
solving time-dependent equations for the moments of the phase-space
distribution function in the fluid approximation; our approach includes
non-radial random motions, and most importantly, an advanced treatment of both
dynamical relaxation effects that takes place in the infalling matter:
phase-mixing associated to shell crossing, and collective collisions related to
physical clumpiness. We find self-similar solutions for the
spherically-averaged profiles of mass density rho(r), pseudo phase-space
density Q(r) and anisotropy parameter beta(r). These profiles agree with the
outcomes of state-of-the-art N-body simulations in the radial range currently
probed by the latter; at smaller radii, we provide specific predictions. In the
perspective provided by our self-similar solutions we link the halo structure
to its two-stage growth history, and propose the following picture. During the
early fast collapse of the inner region dominated by a few merging clumps,
efficient dynamical relaxation plays a key role in producing a closely
universal mass density and pseudo phase-space density profiles; in particular,
these are found to depend only weakly on the detailed shape of the initial
perturbation and the related collapse times. The subsequent inside-out growth
of the outer regions feeds on the slow accretion of many small clumps and
diffuse matter; thus the outskirts are only mildly affected by dynamical
relaxation but are more sensitive to asymmetries and cosmological variance.Comment: 31 pages, 16 figures. Typos corrected. Accepted by Ap
The role of tool geometry in process damped milling
The complex interaction between machining structural systems and the cutting process results in machining instability, so called chatter. In some milling scenarios, process damping is a useful phenomenon that can be exploited to mitigate chatter and hence improve productivity. In the present study, experiments are performed to evaluate the performance of process damped milling considering different tool geometries (edge radius, rake and relief angles and variable helix/pitch). The results clearly indicate that variable helix/pitch angles most significantly increase process damping performance. Additionally, increased cutting edge radius moderately improves process damping performance, while rake and relief angles have a smaller and closely coupled effect
The joint evolution of baryons and dark matter haloes
We have studied the dark matter (DM) distribution in a approx 10^12 h^-1
M_sun mass halo extracted from a simulation consistent with the concordance
cosmology, where the physics regulating the transformation of gas into stars
was allowed to change producing galaxies with different morphologies. The
presence of baryons produces the concentration of the DM halo with respect to
its corresponding dissipationless run, but we found that this response does not
only depend on the amount of baryons gathered in the central region but also on
the way they have been assembled. DM and baryons affect each other in a complex
way so the formation history of a galaxy plays an important role on its final
total mass distribution. Supernova (SN) feedback regulates the star formation
and triggers galactic outflows not only in the central galaxy but also in its
satellites. Our results suggest that, as the effects of SN feedback get
stronger, satellites get less massive and can even be more easily disrupted by
dynamical friction, transferring less angular momentum. We found indications
that this angular momentum could be acquired not only by the outer part of the
DM halo but also by the inner ones and by the stellar component in the central
galaxy. The latter effect produces stellar migration which contributes to
change the inner potential well, probably working against further DM
contraction. As a consequence of the action of these processes, when the halo
hosts a galaxy with an important disc structure formed by smooth gas accretion,
it is more concentrated than when it hosts a spheroidal system which
experienced more massive mergers and interactions. (abridged)Comment: 16 pages, 16 figures, accepted to MNRA
Late stage C―H activation of a privileged scaffold; synthesis of a library of benzodiazepines
A library of over twenty 5-(2-arylphenyl)-1,3-dihydro-2H-1,4-benzodiazepin-2-ones has been formed by a microwave-mediated late-stage palladium-catalysed arylation of 1,4-benzodiazepines using diaryliodonium salts. This can also be applied to nordazepam (7-chloro-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one), the active metabolite of diazepam, and subsequent N-alkylation and/or H/D exchange allows further diversification towards elaborated pharmaceuticals and their 3,3'-deuterated analogues
Galactic cannibalism and CDM density profiles
Using N-body simulations we show that the process of formation of the
brightest cluster galaxy through dissipationless galactic cannibalism can
affect the inner cluster dark matter density profile. In particular, we use as
realistic test case the dynamical evolution of the galaxy cluster C0337-2522 at
redshift z=0.59, hosting in its centre a group of five elliptical galaxies
which are likely to be the progenitor of a central giant elliptical. After the
formation of the brightest cluster galaxy, the inner cluster dark matter
density profile is significantly flatter (logarithmic slope 0.49<beta<0.90)
than the original cusp (beta=1), as a consequence of dynamical friction heating
of the massive galaxies against the diffuse cluster dark matter. In our
simulations we have assumed that the cluster galaxies are made of stars only.
We also show that the presence of galactic dark matter haloes can steepen the
cluster central density profile. We conclude that galactic cannibalism could be
a viable physical mechanism to reconcile - at least at the cluster scale - the
flat dark matter haloes inferred observationally in some galaxy clusters with
the steep haloes predicted by cosmological simulations.Comment: 6 pages with 3 figures. Version accepted for publication in MNRAS.
Longer than first version, with results from additional simulations.
Conclusions unchange
The impact of a major cluster merger on galaxy evolution in MACS\,J0025.4-1225
We present results of an extensive morphological, spectroscopic, and
photometric study of the galaxy population of MACS J0025.41225 (z=0.586), a
major cluster merger with clear segregation of dark and luminous matter, to
examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra
obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of
the cluster centre, and classified them using three spectroscopic types; we
find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and
6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a
monotonically increasing(decreasing) function of both projected galaxy density
and radial distance to the cluster center. More importantly, the 6 observed E+A
cluster members are all located between the dark-matter peaks of the cluster
and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in
other intermediate-redshift clusters which are usually found to avoid the core
region. In addition, we use Hubble Space Telescope imaging to classify cluster
members according to morphological type. We find the global fraction of spiral
and lenticular galaxies in MACS J0025 to be among the highest observed to date
in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular
type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per
cent between the dark-matter peaks. Combing the results of our analysis of the
spatial distribution, morphology, and spectroscopic features of the galaxy
population, we propose that the starburst phase of these E+A galaxies was both
initiated and terminated during the first core-passage about 0.5--1Gyr ago, and
that their morphology has already been transformed into S0 due to ram pressure
and/or tidal forces near the cluster core. By contrast, ongoing starbursts are
observed predominantly in infalling galaxies, and thus appears to be unrelated
to the cluster merger.Comment: 18 pages, 17 figures, accepted by MNRA
Cosmology Using Cluster Internal Velocity Dispersions
We compare the distribution of internal velocity dispersions of galaxy
clusters for an observational sample to those obtained from a set of N-body
simulations of seven COBE-normalised cosmological scenarios: the standard CDM
(SCDM) and a tilted (n=0.85) CDM (TCDM) model, a CHDM model with 25% of massive
neutrinos, two low-density LCDM models with Omega_0=0.3 and 0.5, two open OCDM
models with Omega_0=0.4 and 0.6. Simulated clusters are observed in projection
so as to reproduce the main observational biases and are analysed by applying
the same algorithm for interlopers removal and velocity dispersion estimate as
for the reference observational sample. Velocity dispersions for individual
clusters can be largely affected by observational biases in a model-dependent
way: models in which clusters had less time to virialize show larger
discrepancies between 3D and projected velocity dispersions. From the
comparison with real clusters we find that both SCDM and TCDM largely
overproduce clusters. The CHDM model marginally overproduces clusters and
requires a somewhat larger sigma_8 than a purely CDM model in order to produce
the same cluster abundance. The LCDM model with Omega_0=0.3 agrees with data,
while the open model with Omega_0=0.4 and 0.6 underproduces and marginally
overproduces clusters, respectively.Comment: 28 pages, LaTeX uses Elsevier style file, 7 postscript figures (3
bitmapped to lower res.) included. Submitted to New Astronom
An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277
All massive galaxies likely have supermassive black holes at their centers,
and the masses of the black holes are known to correlate with properties of the
host galaxy bulge component. Several explanations have been proposed for the
existence of these locally-established empirical relationships; they include
the non-causal, statistical process of galaxy-galaxy merging, direct feedback
between the black hole and its host galaxy, or galaxy-galaxy merging and the
subsequent violent relaxation and dissipation. The empirical scaling relations
are thus important for distinguishing between various theoretical models of
galaxy evolution, and they further form the basis for all black hole mass
measurements at large distances. In particular, observations have shown that
the mass of the black hole is typically 0.1% of the stellar bulge mass of the
galaxy. The small galaxy NGC4486B currently has the largest published fraction
of its mass in a black hole at 11%. Here we report observations of the stellar
kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x
10^11 Msun. From the data, we determine that the mass of the central black hole
is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have
properties similar to NGC 1277 and therefore may also contain over-sized black
holes. It is not yet known if these galaxies represent a tail of a
distribution, or if disk-dominated galaxies fail to follow the normal black
hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at
http://www.mpia.de/~bosch/blackholes.htm
The Galactic Center Black Hole Laboratory
The super-massive 4 million solar mass black hole Sagittarius~A* (SgrA*)
shows flare emission from the millimeter to the X-ray domain. A detailed
analysis of the infrared light curves allows us to address the accretion
phenomenon in a statistical way. The analysis shows that the near-infrared
flare amplitudes are dominated by a single state power law, with the low states
in SgrA* limited by confusion through the unresolved stellar background. There
are several dusty objects in the immediate vicinity of SgrA*. The source G2/DSO
is one of them. Its nature is unclear. It may be comparable to similar stellar
dusty sources in the region or may consist predominantly of gas and dust. In
this case a particularly enhanced accretion activity onto SgrA* may be expected
in the near future. Here the interpretation of recent data and ongoing
observations are discussed.Comment: 30 pages - 7 figures - accepted for publication by Springer's
"Fundamental Theories of Physics" series; summarizing GC contributions of 2
conferences: 'Equations of Motion in Relativistic Gravity' at the
Physikzentrum Bad Honnef, Bad Honnef, Germany, (Feb. 17-23, 2013) and the
COST MP0905 'The Galactic Center Black Hole Laboratory' Granada, Spain (Nov.
19 - 22, 2013
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