1,462 research outputs found
Measurements of thermodynamic and transport properties of EuC: a low-temperature analogue of EuO
EuC is a ferromagnet with a Curie-temperature of K. It
is semiconducting with the particularity that the resistivity drops by about 5
orders of magnitude on cooling through , which is therefore called a
metal-insulator transition. In this paper we study the magnetization, specific
heat, thermal expansion, and the resistivity around this ferromagnetic
transition on high-quality EuC samples. At we observe well defined
anomalies in the specific heat and thermal expansion data.
The magnetic contributions of and can satisfactorily be
described within a mean-field theory, taking into account the magnetization
data. In zero magnetic field the magnetic contributions of the specific heat
and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in
finite fields. From an estimation of the pressure dependence of via
Ehrenfest's relation, we expect a considerable increase of under applied
pressure due to a strong spin-lattice coupling. Furthermore the influence of
weak off stoichiometries in EuC was studied. It is
found that strongly affects the resistivity, but hardly changes the
transition temperature. In all these aspects, the behavior of EuC strongly
resembles that of EuO.Comment: 7 pages, 6 figure
Thermal expansion of the magnetically ordering intermetallics RTMg (R = Eu, Gd and T = Ag, Au)
We report measurements of the thermal expansion for two Eu- and two
Gd-based intermetallics which exhibit ferro- or antiferromagnetic phase
transitions. These materials show sharp positive (EuAgMg and GdAuMg) and
negative (EuAuMg and GdAgMg) peaks in the temperature dependence of the thermal
expansion coefficient which become smeared and/or displaced in an
external magnetic field. Together with specific heat data we determine the
initial pressure dependences of the transition temperatures at ambient pressure
using the Ehrenfest or Clausius-Clapeyron relation. We find large pressure
dependences indicating strong spin-phonon coupling, in particular for GdAgMg
and EuAuMg where a quantum phase transition might be reached at moderate
pressures of a few GPa.Comment: 6 pages, 3 figure
Resistivity and Hall effect of LiFeAs: Evidence for electron-electron scattering
LiFeAs is unique among the broad family of FeAs-based superconductors,
because it is superconducting with a rather large K under
ambient conditions although it is a stoichiometric compound. We studied the
electrical transport on a high-quality single crystal. The resistivity shows
quadratic temperature dependence at low temperature giving evidence for strong
electron-electron scattering and a tendency towards saturation around room
temperature. The Hall constant is negative and changes with temperature, what
most probably arises from a van Hove singularity close to the Fermi energy in
one of the hole-like bands. Using band structure calculations based on angular
resolved photoemission spectra we are able to reproduce all the basic features
of both the resistivity as well as the Hall effect data.Comment: 6 pages, 3 figures included; V2 has been considerably revised and
contain a more detailed analysis of the Hall effect dat
The star-forming content of the W3 giant molecular cloud
We have surveyed a ~0.9-square-degree area of the W3 giant molecular cloud
and star-forming region in the 850-micron continuum, using the SCUBA bolometer
array on the James Clerk Maxwell Telescope. A complete sample of 316 dense
clumps was detected with a mass range from around 13 to 2500 Msun. Part of the
W3 GMC is subject to an interaction with the HII region and fast stellar winds
generated by the nearby W4 OB association. We find that the fraction of total
gas mass in dense, 850-micron traced structures is significantly altered by
this interaction, being around 5% to 13% in the undisturbed cloud but ~25 - 37%
in the feedback-affected region. The mass distribution in the detected clump
sample depends somewhat on assumptions of dust temperature and is not a simple,
single power law but contains significant structure at intermediate masses.
This structure is likely to be due to crowding of sources near or below the
spatial resolution of the observations. There is little evidence of any
difference between the index of the high-mass end of the clump mass function in
the compressed region and in the unaffected cloud. The consequences of these
results are discussed in terms of current models of triggered star formation.Comment: 13 pages, 8 figures, 1 table (full source table available on
request). Accepted for publication in Monthly Notices of the Royal
Astronomical Society (Main Journal
A Robust and Universal Metaproteomics Workflow for Research Studies and Routine Diagnostics Within 24 h Using Phenol Extraction, FASP Digest, and the MetaProteomeAnalyzer
The investigation of microbial proteins by mass spectrometry (metaproteomics) is a key technology for simultaneously assessing the taxonomic composition and the functionality of microbial communities in medical, environmental, and biotechnological applications. We present an improved metaproteomics workflow using an updated sample preparation and a new version of the MetaProteomeAnalyzer software for data analysis. High resolution by multidimensional separation (GeLC, MudPIT) was sacrificed to aim at fast analysis of a broad range of different samples in less than 24 h. The improved workflow generated at least two times as many protein identifications than our previous workflow, and a drastic increase of taxonomic and functional annotations. Improvements of all aspects of the workflow, particularly the speed, are first steps toward potential routine clinical diagnostics (i.e., fecal samples) and analysis of technical and environmental samples. The MetaProteomeAnalyzer is provided to the scientific community as a central remote server solution at www.mpa.ovgu.de.Peer Reviewe
The impact of geographic market definition on the stringency of hospital merger control in Germany and the Netherlands
In markets where hospitals are expected to compete, preventive merger control aims to prohibit anticompetitive mergers. In the hospital industry, however, the standard method for defining the relevant market (SSNIP) is difficult to apply and alternative approaches have proven inaccurate. Experiences from the United States show that courts, by identifying overly broad geographic markets, have underestimated the anticompetitive effects of hospital mergers. We examine how geographic hospital markets are defined in Germany and the Netherlands where market-oriented reforms have created room for hospital competition. For each country, we discuss a landmark case where definition of the geographic market played a decisive role. Our findings indicate that defining geographic hospital markets in both countries is less complicated than in the United States, where antitrust analysis must take managed care organisations into account. We also find that different methods result in much more stringent hospital merger control in Germany than in the Netherlands. Given the uncertainties in defining hospital markets, the German competition authority seems to be inclined to avoid the risk of being too permissive; the opposite holds for the Dutch competition authority. We argue that for society the costs of being too permissive with regard to hospital mergers may be larger than the costs of being too stringent
Diverging thermal expansion of the spin-ladder system (CHN)CuBr
We present high-resolution measurements of the -axis thermal
expansion and magnetostriction of piperidinium copper bromide \hp. The
experimental data at low temperatures is well accounted for by a two-leg
spin-ladder Hamiltonian. The thermal expansion shows a complex behaviour with
various sign changes and approaches a divergence at the critical
fields. All low-temperature features are semi-quantitatively explained within a
free fermion model; full quantitative agreement is obtained with Quantum Monte
Carlo simulations.Comment: 4 pages, 5 figures; version 2 is slightly shortened and typos are
correcte
- …