597 research outputs found
The Financial Report of the Universities: maintaining academic standards? An empirical research to the size with explanation of the differences.
This paper describes research done concerning the size, level and explanation of the financial reports of 14 Dutch universities. Based on earlier research in the USA concerning the financial report of niversities, 14 Dutch financial reports are examined. See the Tables. In spite of the regulations the quantity and quality of the financial university reports diverge much, in particular the information provided about costs and output of education and research varies from university to university. For an explanation of the data a number well-known hypothesis such as Zimmerman''s size, debt/equity hypothesis were tested first. After that a disclosure index was developed for expressing the several information items in a unique report mark per university. The results can be explained by the kind of university, the size (number of students and revenues) and the long-term liabilities, in accordance with the research abroad. Therefore the main conclusion is that the findings of the research outside the Netherlands such as the importance of size and long-term liabilities hold largely in the Netherlands, too.accounting and auditing ;
Deeply-Virtual Compton Scattering on Deuterium and Neon at HERMES
We report the first observation of azimuthal beam-spin asymmetries in hard
electroproduction of real photons off nuclei. Attributed to the interference
between the Bethe-Heitler process and the deeply-virtual Compton scattering
process, the asymmetry gives access to the latter at the amplitude level. This
process appears to be the theoretically cleanest way to access generalized
parton distributions. The data presented here have been accumulated by the
HERMES experiment at DESY, scattering the HERA 27.6 GeV positron beam off
deuterium and neon gas targets.Comment: 5 pages, 6 figures. Talk given by F. Ellinghaus at the "15th
International Spin Physics Symposium", SPIN 2002, September 9-14, 2002, BNL,
Upton, NY, USA. To be published in the proceeding
Spin and charge transport in graphene-based spin transport devices with Co/MgO spin injection and spin detection electrodes
In this review we discuss spin and charge transport properties in
graphene-based single-layer and few-layer spin-valve devices. We give an
overview of challenges and recent advances in the field of device fabrication
and discuss two of our fabrication methods in more detail which result in
distinctly different device performances. In the first class of devices, Co/MgO
electrodes are directly deposited onto graphene which results in rough
MgO-to-Co interfaces and favor the formation of conducting pinholes throughout
the MgO layer. We show that the contact resistance area product (RA) is a
benchmark for spin transport properties as it scales with the measured spin
lifetime in these devices indicating that contact-induced spin dephasing is the
bottleneck for spin transport even in devices with large RA values. In a
second class of devices, Co/MgO electrodes are first patterned onto a silicon
substrate. Subsequently, a graphene-hBN heterostructure is directly transferred
onto these prepatterned electrodes which provides improved interface
properties. This is seen by a strong enhancement of both charge and spin
transport properties yielding charge carrier mobilities exceeding 20000
cm/(Vs) and spin lifetimes up to 3.7 ns at room temperature. We discuss
several shortcomings in the determination of both quantities which complicates
the analysis of both extrinsic and intrinsic spin scattering mechanisms.
Furthermore, we show that contacts can be the origin of a second charge
neutrality point in gate dependent resistance measurements which is influenced
by the quantum capacitance of the underlying graphene layer.Comment: 19 pages, 8 figure
Contact-induced charge contributions to non-local spin transport measurements in Co/MgO/graphene devices
Recently, it has been shown that oxide barriers in graphene-based non-local
spin-valve structures can be the bottleneck for spin transport. The barriers
may cause spin dephasing during or right after electrical spin injection which
limit spin transport parameters such as the spin lifetime of the whole device.
An important task is to evaluate the quality of the oxide barriers of both spin
injection and detection contacts in a fabricated device. To address this issue,
we discuss the influence of spatially inhomogeneous oxide barriers and
especially conducting pinholes within the barrier on the background signal in
non-local measurements of graphene/MgO/Co spin-valve devices. By both
simulations and reference measurements on devices with non-ferromagnetic
electrodes, we demonstrate that the background signal can be caused by
inhomogeneous current flow through the oxide barriers. As a main result, we
demonstrate the existence of charge accumulation next to the actual spin
accumulation signal in non-local voltage measurements, which can be explained
by a redistribution of charge carriers by a perpendicular magnetic field
similar to the classical Hall effect. Furthermore, we present systematic
studies on the phase of the low frequency non-local ac voltage signal which is
measured in non-local spin measurements when applying ac lock-in techniques.
This phase has so far widely been neglected in the analysis of non-local spin
transport. We demonstrate that this phase is another hallmark of the
homogeneity of the MgO spin injection and detection barriers. We link backgate
dependent changes of the phase to the interplay between the capacitance of the
oxide barrier to the quantum capacitance of graphene.Comment: 19 pages, 7 figure
Inter-valley dark trion states with spin lifetimes of 150 ns in WSe
We demonstrate long trion spin lifetimes in a WSe monolayer of up to 150
ns at 5 K. Applying a transverse magnetic field in time-resolved Kerr-rotation
measurements reveals a complex composition of the spin signal of up to four
distinct components. The Kerr rotation signal can be well described by a model
which includes inhomogeneous spin dephasing and by setting the trion spin
lifetimes to the measured excitonic recombination times extracted from
time-resolved reflectivity measurements. We observe a continuous shift of the
Kerr resonance with the probe energy, which can be explained by an
adsorbate-induced, inhomogeneous potential landscape of the WSe flake. A
further indication of extrinsic effects on the spin dynamics is given by a
change of both the trion spin lifetime and the distribution of g-factors over
time. Finally, we detect a Kerr rotation signal from the trion's higher-energy
triplet state when the lower-energy singlet state is optically pumped by
circularly polarized light. We explain this by the formation of dark trion
states, which are also responsible for the observed long trion spin lifetimes.Comment: 23 pages, 13 figure
Systematically extending classical nucleation theory
The foundation for any discussion of first-order phse transitions is
Classical Nucleation Theory(CNT). CNT, developed in the first half of the
twentieth century, is based on a number of heuristically plausible assumtptions
and the majority of theoretical work on nucleation is devoted to refining or
extending these ideas. Ideally, one would like to derive CNT from a more
fundamental description of nucleation so that its extension, development and
refinement could be developed systematically. In this paper, such a development
is described based on a previously established (Lutsko, JCP 136:034509, 2012 )
connection between Classical Nucleation Theory and fluctuating hydrodynamics.
Here, this connection is described without the need for artificial assumtions
such as spherical symmetry. The results are illustrated by application to CNT
with moving clusters (a long-standing problem in the literature) and the
constructrion of CNT for ellipsoidal clusters
Role of MgO barriers for spin and charge transport in Co/MgO/graphene non-local spin-valve devices
We investigate spin and charge transport in both single and bilayer graphene
non-local spin-valve devices. Similar to previous studies on bilayer graphene,
we observe an inverse dependence of the spin lifetime on the carrier mobility
in our single layer devices. This general trend is only observed in devices
with large contact resistances. Furthermore, we observe a second Dirac peak in
devices with long spin lifetimes. This results from charge transport underneath
the contacts. In contrast, all devices with low ohmic contact resistances only
exhibit a single Dirac peak. Additionally, the spin lifetime is significantly
reduced indicating that an additional spin dephasing occurs underneath the
electrodes.Comment: 5 pages, 3 figure
Emanzipierte Schul- und Bildungspolitik in Nordrhein-Westfalen:Auf dem Weg von der zentralen zur regionalen Schul- und Bildungspolitik
Gelingt es dem staatlichen Schulwesen in Nordrhein-Westfalen, allen Schülern die Chance zu bieten, die Schulen zu besuchen, die ihren Neigungen und Leistungsfähigkeiten entsprechen? Seinen Ausgang nimmt der Autor bei den Bildungsforschern der 50er und 60er Jahre des vorigen Jahrhunderts. Seine empirischen Forschungen knüpfen an die Methode der regionalen Bildungsforschung Hansgert Peiserts an. Daran knüpft er Fragen zur Gestaltung der Bildungs- und Schulpolitik durch den Landtag, zur Interpretation der Gesetze durch die Landesregierung und zur Umsetzung durch die Schulverwaltung sowie zur Gestaltung des kommunalen Schulwesens durch Gemeindeparlamente und -verwaltungen an.
Die Auswertung amtlicher Schulstatistiken zum Übergangsverhalten von Grundschülern in die Schulformen weiterführender Schulen ermöglicht die Identifizierung typischer Schullandschaften der Städte und Gemeinden des Landes NRW und bestätigt die Ausgangsthese, dass es dem Land NRW nicht gelingt, gleiche Zugangschancen für alle Schüler zu schaffen. <br/
Absence of non-trivial asymptotic scaling in the Kashchiev model of polynuclear growth
In this brief comment we show that, contrary to previous claims [Bartelt M C
and Evans J W 1993 {\it J.\ Phys.\ A} 2743], the asymptotic
behaviour of the Kashchiev model of polynuclear growth is trivial in all
spatial dimensions, and therefore lies outside the Kardar-Parisi-Zhang
universality class.Comment: 3 pages, 4 postscript figures, uses eps
Systematic Improvement of Classical Nucleation Theory
We reconsider the applicability of classical nucleation theory (CNT) to the
calculation of the free energy of solid cluster formation in a liquid and its
use to the evaluation of interface free energies from nucleation barriers.
Using two different freezing transitions (hard spheres and NaCl) as test cases,
we first observe that the interface-free-energy estimates based on CNT are
generally in error. As successive refinements of nucleation-barrier theory, we
consider corrections due to a non-sharp solid-liquid interface and to a
non-spherical cluster shape. Extensive calculations for the Ising model show
that corrections due to a non-sharp and thermally fluctuating interface account
for the barrier shape with excellent accuracy. The experimental solid
nucleation rates that are measured in colloids are better accounted for by
these non-CNT terms, whose effect appears to be crucial in the interpretation
of data and in the extraction of the interface tension from them.Comment: 20 pages (text + supplementary material
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