836 research outputs found
A correlated-polaron electronic propagator: open electronic dynamics beyond the Born-Oppenheimer approximation
In this work we develop a theory of correlated many-electron dynamics dressed
by the presence of a finite-temperature harmonic bath. The theory is based on
the ab-initio Hamiltonian, and thus well-defined apart from any
phenomenological choice of collective basis states or electronic coupling
model. The equation-of-motion includes some bath effects non-perturbatively,
and can be used to simulate line- shapes beyond the Markovian approximation and
open electronic dynamics which are subjects of renewed recent interest. Energy
conversion and transport depend critically on the ratio of electron-electron
coupling to bath-electron coupling, which is a fitted parameter if a
phenomenological basis of many-electron states is used to develop an electronic
equation of motion. Since the present work doesn't appeal to any such basis, it
avoids this ambiguity. The new theory produces a level of detail beyond the
adiabatic Born-Oppenheimer states, but with cost scaling like the
Born-Oppenheimer approach. While developing this model we have also applied the
time-convolutionless perturbation theory to correlated molecular excitations
for the first time. Resonant response properties are given by the formalism
without phenomenological parameters. Example propagations with a developmental
code are given demonstrating the treatment of electron-correlation in
absorption spectra, vibronic structure, and decay in an open system.Comment: 25 pages 7 figure
Stellar mass map and dark matter distribution in M31
Stellar mass distribution in M31 is estimated using optical and infrared
imaging data. Combining the derived stellar mass model with various kinematical
data, properties of the DM halo of the galaxy are constrained.
SDSS observations through the ugriz filters and the Spitzer imaging at 3.6
microns are used to sample the SED of the galaxy at each imaging pixel.
Intrinsic dust extinction effects are taken into account by using far-infrared
observations. Synthetic SEDs created with different stellar population
synthesis models are fitted to the observed SEDs, providing estimates for the
stellar mass surface density. The stellar mass distribution of the galaxy is
described with a 3D model consisting of a nucleus, a bulge, a disc, a young
disc and a halo component, each following the Einasto density distribution
(relations between different functional forms of the Einasto density
distribution are given in App. B). By comparing the stellar mass distribution
to the observed rotation curve and kinematics of outer globular clusters and
satellite galaxies, the DM halo parameters are estimated.
Stellar population synthesis models suggest that M31 is dominated by old
stars throughout the galaxy. The total stellar mass is (10-15)10^10Msun, 30% of
which is in the bulge and 56% in the disc. None of the tested DM distribution
models can be falsified on the basis of the stellar matter distribution and the
rotation curve of the galaxy. The virial mass of the DM halo is
(0.8-1.1)10^12Msun and the virial radius is 189-213kpc, depending on the DM
distribution. The central density of the DM halo is comparable to that of
nearby dwarf galaxies, low-surface-brightness galaxies and distant massive disc
galaxies, thus the evolution of central DM halo properties seems to be
regulated by similar processes for a broad range of halo masses, environments,
and cosmological epochs.Comment: 11 pages, 13 figures, 6 tables, accepted for publication in Astronomy
and Astrophysic
Human Resource Management of US multinationals in Germany and the UK.
This research examines human resource management (HRM) in subsidiaries of US multinational firms (MNCs) operating in the UK and Germany. Together with parallel studies in Ireland and Spain it explores the potential tensions resulting from a transfer of US-type human resource (HR) policies to Europe. Whilst we expected that the liberal
market British economy would not provide a major challenge for the transfer of US practices, we foresaw that the more densely institutionalized German business system would constitute a more serious barrier to transfer.
This report is based on case studies of four large US MNCs. In all four firms we conducted interviews in the British and German subsidiaries, as well as the US and/or European headquarters, with HR managers, line managers and non-managerial employees. For three substantive issues – diversity management, employee participation and pay – as well as for the processual issue of ‘centralization–decentralization’ this report analyses whether the four US MNCs studied have global policies, how these are transferred to Europe and the extent to which they have to be adapted to the British and German contexts.
Our findings support previous research which suggests that HR policies in US MNCs are not only relatively standardised, but also build on US domestic policies. However, the mechanisms of transfer appear to have changed. Whereas in the past, written guidelines, the transfer of home-country employees and extensive reporting seem to have been the major mechanisms employed to ensure that global policies were applied, today HR information systems, regional European headquarters and international teams of HR managers seem to play a more important role. Over the last decade, national subsidiaries in both countries have lost autonomy in HR decision-making. However, this has not been primarily in the form of recentralization towards headquarters, but rather towards the regional level and/or business unit.
Turning to substantive issues, as expected, the German institutional environment represents a stronger challenge for US MNCs than the British one. Of particular importance is codetermination which affects all four firms and which in at least three of them exerts pressure on local management to adjust global polices to local conditions.
However, in most cases the observed deviations were only marginal. Similarly, the German system of multi-employer bargaining does not constitute a major hurdle for US MNCs
seeking to apply global practices. Although in general German host-country pressures were stronger than those in the UK, we found that UK management was able to use its
role of interpreter of the local environment to force some adaptation of global policies, particularly in the substantive area of diversity management, suggesting that the extent to which local adaptation occurs is not entirely dependent on the strength of employment-relations institutions in the host country.
Regarding practical implications, our research points firmly to the limits of global policies. With their knowledge of the local context subsidiary-level managers can and should have some freedom to adapt global policies to the local context. At least in Germany they have
an additional role, as they have to manage a complex institutional environment. The system of collective bargaining and codetermination fosters collective HR policies that are often incompatible with the more individualistic global policies pursued by US MNCs.
Nevertheless, as the case studies show, US MNCs are able to manage these institutions in such a way that the need for adaptation is minimized. This process of institutional
arbitrage tends to be performed by local managers with a deep knowledge of the hostenvironment
Multimodality in galaxy clusters from SDSS DR8: substructure and velocity distribution
We search for the presence of substructure, a non-Gaussian, asymmetrical
velocity distribution of galaxies, and large peculiar velocities of the main
galaxies in galaxy clusters with at least 50 member galaxies, drawn from the
SDSS DR8. We employ a number of 3D, 2D, and 1D tests to analyse the
distribution of galaxies in clusters: 3D normal mixture modelling, the
Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests and others.
We find the peculiar velocities of the main galaxies, and use principal
component analysis to characterise our results. More than 80% of the clusters
in our sample have substructure according to 3D normal mixture modelling, the
Dressler-Shectman (DS) test shows substructure in about 70% of the clusters.
The median value of the peculiar velocities of the main galaxies in clusters is
206 km/s (41% of the rms velocity). The velocities of galaxies in more than 20%
of the clusters show significant non-Gaussianity. While multidimensional normal
mixture modelling is more sensitive than the DS test in resolving substructure
in the sky distribution of cluster galaxies, the DS test determines better
substructure expressed as tails in the velocity distribution of galaxies.
Richer, larger, and more luminous clusters have larger amount of substructure
and larger (compared to the rms velocity) peculiar velocities of the main
galaxies. Principal component analysis of both the substructure indicators and
the physical parameters of clusters shows that galaxy clusters are complicated
objects, the properties of which cannot be explained with a small number of
parameters or delimited by one single test. The presence of substructure, the
non-Gaussian velocity distributions, as well as the large peculiar velocities
of the main galaxies, shows that most of the clusters in our sample are
dynamically young.Comment: 15 pages, 11 figures, 2 online tables, accepted for publication in
Astronomy and Astrophysic
Multimodality of rich clusters from the SDSS DR8 within the supercluster-void network
We study the relations between the multimodality of galaxy clusters drawn
from the SDSS DR8 and the environment where they reside. As cluster environment
we consider the global luminosity density field, supercluster membership, and
supercluster morphology. We use 3D normal mixture modelling, the
Dressler-Shectman test, and the peculiar velocity of cluster main galaxies as
signatures of multimodality of clusters. We calculate the luminosity density
field to study the environmental densities around clusters, and to find
superclusters where clusters reside. We determine the morphology of
superclusters with the Minkowski functionals and compare the properties of
clusters in superclusters of different morphology. We apply principal component
analysis to study the relations between the multimodality parametres of
clusters and their environment simultaneously. We find that multimodal clusters
reside in higher density environment than unimodal clusters. Clusters in
superclusters have higher probability to have substructure than isolated
clusters. The superclusters can be divided into two main morphological types,
spiders and filaments. Clusters in superclusters of spider morphology have
higher probabilities to have substructure and larger peculiar velocities of
their main galaxies than clusters in superclusters of filament morphology. The
most luminous clusters are located in the high-density cores of rich
superclusters. Five of seven most luminous clusters, and five of seven most
multimodal clusters reside in spider-type superclusters; four of seven most
unimodal clusters reside in filament-type superclusters. Our study shows the
importance of the role of superclusters as high density environment which
affects the properties of galaxy systems in them.Comment: 16 pages, 12 figures, 2 online tables, accepted for publication in
Astronomy and Astrophysic
Shaping the BRCAness mutational landscape by alternative double-strand break repair, replication stress and mitotic aberrancies
Tumours with mutations in the BRCA1/BRCA2 genes have impaired double-stranded DNA break repair, compromised replication fork protection and increased sensitivity to replication blocking agents, a phenotype collectively known as 'BRCAness'. Tumours with a BRCAness phenotype become dependent on alternative repair pathways that are error-prone and introduce specific patterns of somatic mutations across the genome. The increasing availability of next-generation sequencing data of tumour samples has enabled identification of distinct mutational signatures associated with BRCAness. These signatures reveal that alternative repair pathways, including Polymerase θ-mediated alternative end-joining and RAD52-mediated single strand annealing are active in BRCA1/2-deficient tumours, pointing towards potential therapeutic targets in these tumours. Additionally, insight into the mutations and consequences of unrepaired DNA lesions may also aid in the identification of BRCA-like tumours lacking BRCA1/BRCA2 gene inactivation. This is clinically relevant, as these tumours respond favourably to treatment with DNA-damaging agents, including PARP inhibitors or cisplatin, which have been successfully used to treat patients with BRCA1/2-defective tumours. In this review, we aim to provide insight in the origins of the mutational landscape associated with BRCAness by exploring the molecular biology of alternative DNA repair pathways, which may represent actionable therapeutic targets in in these cells
IGBP-DIS soil data set for pedotransfer function development
At the request of the Global Soil Data Task (GSDT) of the Data and Information System of the International Geosphere Biosphere Programme (IGBP-DIS), ISRIC prepared a uniform soil data set for the development of pedotransfer functions. The necessary chemical and physical soil data have been derived from ISRIC's Soil Information System (ISIS) and the CD-ROM of the Natural Resources Conservation Service (USDA-NRCS). All soil samples were clustered into functional groups based on soil textural class and (calculated) activity of the clay minerals (9 classes), while samples from organic soils and allophanic soils were flagged. The digital set contains data for 131,472 samples, originating from 20,920 profiles. It is presented as a comma delimited ASCIIfile and in dBASE IV format. GSDT will use the data set to develop a number of pedotransfer functions for often required, yet seldom measured soil properties. Interaction with the global soil and modelling community led to the identification of four soil properties as being especially important and urgently needed: soil organic carbon, soil total nitrogen, water holding capacity, and soil thermal properties
IGBP-DIS soil data set for pedotransfer function development
This uniform soil data set for the development of pedotransfer functions was developed at the request of the Global Soil Data Task (GSDT) of the Data and Information System (DIS) of the International Geosphere Biosphere Programme (IGBP). The necessary chemical and physical soil data have been derived from ISRIC's Soil Information System (ISIS) and the soil CD-ROM of the Natural ... Resources Conservation Service (USDA-NRCS). Analytical data were clustered into functional groups based on soil textural class (FAO) and calculated activity of the clay size minerals. Samples from organic and allophanic soils were flagged as separate categories. The file contain analytical data for 131,472 soil samples, originating from 20,920 profiles. Being based on available data, there are several gaps in the measured data
An EAGLE view of the missing baryons
Context. A significant fraction of the predicted baryons remain undetected in the local Universe. We adopted the common assumption that a large fraction of the missing baryons correspond to the hot (log T(K) = 5.5–7) phase of the warm-hot intergalactic medium (WHIM). We base our missing baryons search on the scenario whereby the WHIM has been heated up via accretion shocks and galactic outflows, and it is concentrated towards the filaments of the cosmic web.
Aims. Our aim is to improve the observational search for the poorly detected hot WHIM.
Methods. We detected the filamentary structure within the EAGLE hydrodynamical simulation by applying the Bisous formalism to the galaxy distribution. To test the reliability of our results, we used the MMF/NEXUS+ classification of the large-scale environment of the dark matter component in EAGLE. We then studied the spatio-thermal distribution of the hot baryons within the extracted filaments.
Results. While the filaments occupy only ≈5% of the full simulation volume, the diffuse hot intergalactic medium in filaments amounts to ≈23%−25% of the total baryon budget, or ≈79%−87% of all the hot WHIM. The optimal filament sample, with a missing baryon mass fraction of ≈82%, is obtained by selecting Bisous filaments with a high galaxy luminosity density. For these filaments, we derived analytic formulae for the radial gas density and temperature profiles, consistent with recent Planck Sunyaev-Zeldovich and cosmic microwave background lensing observations within the central r ≈ 1 Mpc.
Conclusions. Results from the EAGLE simulation suggest that the missing baryons are strongly concentrated towards the filament axes. Since the filament finding methods used here are applicable to galaxy surveys, a large fraction of the missing baryons can be localised by focusing the observational efforts on the central ∼1 Mpc regions of the filaments. To optimise the observational signal, it is beneficial to focus on the filaments with the highest galaxy luminosity densities detected in the optical data
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