1,225 research outputs found
A multipurpose machine to study paramagnetic species on well defined single crystal surfaces
A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR)
spectrometer operating at 94 GHz to investigate paramagnetic centers on single
crystal surfaces is described. It is particularly designed to study
paramagnetic centers on well-defined model catalysts using epitaxial thin
oxide films grown on metal single crystals. The EPR setup is based on a
commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum
conditions using a home made Fabry Perot resonator. The key idea of the
resonator is to use the planar metal single crystal required to grow the
single crystalline oxide films as one of the mirrors of the resonator. EPR
spectroscopy is solely sensitive to paramagnetic species, which are typically
minority species in such a system. Hence, additional experimental
characterization tools are required to allow for a comprehensive investigation
of the surface. The apparatus includes a preparation chamber hosting
equipment, which is required to prepare supported model catalysts. In
addition, surface characterization tools such as low energy electron
diffraction (LEED)/Auger spectroscopy, temperature programmed desorption
(TPD), and infrared reflection absorption spectroscopy (IRAS) are available to
characterize the surfaces. A second chamber used to perform EPR spectroscopy
at 94 GHz has a room temperature scanning tunneling microscope attached to it,
which allows for real space structural characterization. The heart of the UHV
adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator
against atmosphere. To this end it is possible to use a thin sapphire window
glued to the backside of the coupling orifice of the Fabry Perot resonator.
With the help of a variety of stabilization measures reducing vibrations as
well as thermal drift it is possible to accumulate data for a time span, which
is for low temperature measurements only limited by the amount of liquid
helium. Test measurements show that the system can detect paramagnetic species
with a density of approximately 5 Ă 1011 spins/cm2, which is comparable to the
limit obtained for the presently available UHV-EPR spectrometer operating at
10 GHz (X-band). Investigation of electron trapped centers in MgO(001) films
shows that the increased resolution offered by the experiments at W-band
allows to identify new paramagnetic species, that cannot be differentiated
with the currently available methodology
Varieties of Limited Access Orders: The nexus between politics and economics in hybrid regimes
This article advances our understanding of differences in hybrid stability by going beyond existing regime typologies that separate the study of political institutions from the study of economic institutions. It combines the work of Douglass North, John Wallis, and Barry Weingast (NWW) on varieties of social orders with the literature on political and economic regime typologies and dynamics to understand hybrid regimes as Limited Access Orders (LAOs) that differ in the way dominant elites limit access to political and economic resources. Based on a measurement of political and economic access applied to seven postâSoviet states, the article identifies four types of LAOs. Challenging NWW's claim, it shows that hybrid regimes can combine different degrees of political and economic access to sustain stability. Our typology allows to form theoretical expectations about the kinds of political and/or economic changes that will move different types of LAOs toward more openness or closure
Challenging assumptions of the enlargement literature : the impact of the EU on human and minority rights in Macedonia
This article argues that from the very start of the transition process in Macedonia, a fusion of concerns about security and democratisation locked local nationalist elites and international organisations intoa political dynamic that prioritised security over democratisation. This dynamic resulted in little progress in the implementation of human and minority rights until 2009, despite heavy EU involvement in Macedonia after the internal warfare of 2001. The effects of this informally institutionalised relationship have been overlooked by scholarship on EU enlargement towards Eastern Europe, which has made generalisations based on assumptions relevant to the democratisation of countries in Eastern Europe, but not the Western Balkans
Large scale cosmic-ray anisotropy with KASCADE
The results of an analysis of the large scale anisotropy of cosmic rays in
the PeV range are presented. The Rayleigh formalism is applied to the right
ascension distribution of extensive air showers measured by the KASCADE
experiment.The data set contains about 10^8 extensive air showers in the energy
range from 0.7 to 6 PeV. No hints for anisotropy are visible in the right
ascension distributions in this energy range. This accounts for all showers as
well as for subsets containing showers induced by predominantly light
respectively heavy primary particles. Upper flux limits for Rayleigh amplitudes
are determined to be between 10^-3 at 0.7 PeV and 10^-2 at 6 PeV primary
energy.Comment: accepted by The Astrophysical Journa
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