33,403 research outputs found
Monte Carlo simulations of interfaces in polymer blends
We review recent simulation studies of interfaces between immiscible
homopolymer phases. Special emphasis is given to the presentation of efficient
simulation techniques and powerful methods of data analysis, such as the
analysis of capillary wave spectra. Possible reasons for polymer
incompatibility and ways to relate model dependent interaction parameters to an
effective Flory Huggins parameter are discussed. Various interfaces are then
considered and characterised with respect to their microscopic structure and
thermodynamic properties. In particular, interfaces between homopolymers of
equal or disparate stiffness are studied, interfaces containing diblock
copolymers, and interfaces confined in thin films. The results are related to
the phase behaviour of ternary homopolymer/copolymer systems, and to wetting
transitions in thin films.Comment: To appear in Annual Reviews of Computational Physics, edt. D.
Stauffe
Raman Scattered He II 6545 Line in the Symbiotic Star V1016 Cygni
We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 m
Canada-France-Hawaii Telescope, in order to illustrate a method to measure the
covering factor of the neutral scattering region around the giant component
with respect to the hot emission region around the white dwarf component. In
the spectrum, we find broad wings around H and a broad emission feature
around 6545 that is blended with the [N II] 6548 line.
These two features are proposed to be formed by Raman scattering by atomic
hydrogen, where the incident radiation is proposed to be UV continuum radiation
around Ly in the former case and He II 1025 emission line
arising from transitions for the latter feature. We remove the
H wings by a template Raman scattering wing profile and subtract the [N
II] 6548 line using the 3 times stronger [N II] 6583
feature in order to isolate the He II Raman scattered 6545 \AA line. We obtain
the flux ratio of the He II 6560 emission
line and the 6545 \AA feature for V1016 Cyg. Under the assumption that the He
II emission from this object is isotropic, this ratio is converted to the ratio
of the number of the incident photons and that
of the scattered photons. This implies that the scattering region with H I
column density covers 17 per cent of the
emission region. By combining the presumed binary period yrs of this
system we infer that a significant fraction of the slow stellar wind from the
Mira component is ionized and that the scattering region around the Mira
extends a few tens of AU, which is closely associated with the mass loss
process of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap
Disorder Induced Stripes in d-Wave Superconductors
Stripe phases are observed experimentally in several copper-based high-Tc
superconductors near 1/8 hole doping. However, the specific characteristics may
vary depending on the degree of dopant disorder and the presence or absence of
a low- temperature tetragonal phase. On the basis of a Hartree-Fock decoupling
scheme for the t-J model we discuss the diverse behavior of stripe phases. In
particular the effect of inhomogeneities is investigated in two distinctly
different parameter regimes which are characterized by the strength of the
interaction. We observe that small concen- trations of impurities or vortices
pin the unidirectional density waves, and dopant disorder is capable to
stabilize a stripe phase in parameter regimes where homogeneous phases are
typically favored in clean systems. The momentum-space results exhibit
universal features for all coexisting density-wave solutions, nearly unchanged
even in strongly disordered systems. These coexisting solutions feature
generically a full energy gap and a particle-hole asymmetry in the density of
states.Comment: 28 pages, 8 figure
Leadership Structure and Corporate Governance in Switzerland
The question of whether the CEO should also serve as chairman of the board is one of the most hotly debated issues in the recent corporate governance discussion. While agencytheoretic arguments advocate a separation of decision and control functions, the empirical evidence focusing on U.S. companies is not conclusive. In this context evidence from a country with a different practice of CEO succession may provide important new insights with respect to the question of whether one leadership structure should generally be preferred to the other one. This article fills this gap by investigating the valuation effects of leadership structure in Switzerland where – in contrast to the U.S. – a separation of the CEO and chairman functions is common. Consistent with the majority of prior research focusing on the U.S., the authors found no evidence of a systematic and significant difference in valuation between firms with combined and firms with separated functions. They also investigated whether leadership structure is related to firm-level corporate governance characteristics and found a similar curvilinear relationship between leadership structure and managerial shareholdings as is observed between firm value and managerial shareholdings. An implication is that possible agency costs associated with a combined function are mitigated by a higher incentive alignment of the CEO/chairman through an adequate level of managerial shareholdings. Over the last few years corporate governance became an important investment criterion, which is for example reflected in the emergence of various corporate governance ratings. The authors of this article additionally investigated whether firm value is significantly related to firm level corporate governance as measured by a broad survey-based index for a representative sample of Swiss firms. They documented a positive and significant relationship between the corporate governance index and firm valuation. This finding is robust to controlling for a series of additional governance mechanisms related to ownership structure, board characteristics, and leverage as well as a potential endogeneity of these mechanisms.Leadership structure; Firm valuation; Corporate governance; Managerial shareholdings
Spectropolarimetry of the borderline Seyfert 1 galaxy ESO 323-G077
We report the detection of high linear polarization in the bright Seyfert 1
galaxy ESO 323-G077. Based on optical spectropolarimetry with FORS1 at the VLT
we find a continuum polarization which ranges from 2.2 % at 8300A to 7.5 % at
3600A. Similar amounts of linear polarization are found for the broad emission
lines, while the narrow lines are not polarized. The position angle of the
polarization is independent of the wavelength and found to be perpendicular to
the orientation of the extended [OIII] emission cone of this galaxy. Within the
standard model of Seyfert nuclei the observations can be well understood
assuming that this AGN is observed at an inclination angle where the nucleus is
partially obscured and seen mainly indirectly in the light scattered by dust
clouds within or above the torus and the illuminated inner edge of the dust
torus itself. Hence we conclude that ESO 323-G077 is a borderline Seyfert 1
galaxy which can provide important information on the geometric properties of
active nuclei
Exact exchange optimized effective potential and self-compression of stabilized jellium clusters
In this work, we have used the exchange-only optimized effective potential in
the self-consistent calculations of the density functional Kohn-Sham equations
for simple metal clusters in stabilized jellium model with self-compression.
The results for the closed-shell clusters of Al, Li, Na, K, and Cs with 2,
8, 18, 20, 34, and 40 show that the clusters are 3% more compressed here than
in the local spin density approximation. On the other hand, in the LSDA,
neglecting the correlation results in a contraction by 1.4%.Comment: 7 pages, RevTex, 5 eps figures, 2 table
On the Melting of Bosonic Stripes
We use quantum Monte Carlo simulations to determine the finite temperature
phase diagram and to investigate the thermal and quantum melting of stripe
phases in a two-dimensional hard-core boson model. At half filling and low
temperatures the stripes melt at a first order transition. In the doped system,
the melting transitions of the smectic phase at high temperatures and the
superfluid smectic (supersolid) phase at low temperatures are either very
weakly first order, or of second order with no clear indications for an
intermediate nematic phase.Comment: 4 pages, 5 figure
Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density
By means of extensive Monte Carlo simulations of the bond fluctuation model,
we study the effect of adding AB diblock copolymers on the properties of an
interface between demixed homopolymer phases. The parameters are chosen such
that the homopolymers are strongly segregated, and the whole range of copolymer
concentrations in the two phase coexistence region is scanned. We compare the
``mushroom'' regime, in which copolymers are diluted and do not interact with
each other, with the ``wet brush'' regime, where copolymers overlap and
stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is
never entered for our choice of chain lengths. ``Intrinsic'' profiles are
calculated using a block analysis method introduced by us in earlier work. We
discuss density profiles, orientational profiles and contact number profiles.
In general, the features of the profiles are similar at all copolymer
concentrations, however, the profiles in the concentrated regime are much
broader than in the dilute regime. The results compare well with
self-consistent field calculations.Comment: to appear in J. Chem. Phy
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