2,024 research outputs found
Random Block Operators
We study fundamental spectral properties of random block operators that are
common in the physical modelling of mesoscopic disordered systems such as dirty
superconductors. Our results include ergodic properties, the location of the
spectrum, existence and regularity of the integrated density of states, as well
as Lifshits tails. Special attention is paid to the peculiarities arising from
the block structure such as the occurrence of a robust gap in the middle of the
spectrum. Without randomness in the off-diagonal blocks the density of states
typically exhibits an inverse square-root singularity at the edges of the gap.
In the presence of randomness we establish a Wegner estimate that is valid at
all energies. It implies that the singularities are smeared out by randomness,
and the density of states is bounded. We also show Lifshits tails at these band
edges. Technically, one has to cope with a non-monotone dependence on the
random couplings.Comment: 22 pages, 3 figure
Lifshitz tails for spectra of Erd\H{o}s--R\'{e}nyi random graphs
We consider the discrete Laplace operator on
Erd\H{o}s--R\'{e}nyi random graphs with vertices and edge probability
. We are interested in the limiting spectral properties of
as in the subcritical regime where no giant cluster
emerges. We prove that in this limit the expectation value of the integrated
density of states of exhibits a Lifshitz-tail behavior at the
lower spectral edge E=0.Comment: Published at http://dx.doi.org/10.1214/1050516000000719 in the Annals
of Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Molecular equilibria determined by van der Waals' attraction.
This thesis is primarily concerned with a nuclear magnetic resonance study on the effect of intramolecular van der Waals' attractive forces between alkyl groups. This phenomenon is investigated by devising certain two-fold conformational equilibria, such that one side of the equilibrium has two alkyl groups positioned relatively close to one another and attracting one another, the other side has the alkyl groups further apart and experiencing a greatly reduced interaction. The valence bond isomerisation between 1,4 and 1,6-dialkylcyclooctatetraenes 7(R=Me), 8(R=Et), 9(R=ipr), 10(R='Bu) is observed to favour the more compact 1,6-isomers in solution. This preference is attributed to van der Waals' attraction between the pendant alkyl groups. Molecular mechanics agree as to the preferred valence isomer and confirm it has greater attractive steric interactions. The two-fold 1-(3-alkylphenyl)-group rotational equilibrium in 1 (e)-(3-alkylphenyl)-2(e),6(e)-dimethylcyclohexan-1 -ols 23(R=Me), 24(R='Bu) and 1 (e)(3-alkylphenyl)-2(e),6(e)-dimethylcyclohexanes 25(R=Me), 26(R='Bu) is observed to favour the more compact conformer for 23, 24 but the less compact conformer for 26, while no preference is seen for 25. A combination of buttressing and attractive steric effects are postulated to explain these preferences, the results being supplemented with molecular mechanics calculations. The l-(l-methylneopentyl) rotational equlibrium in 1-(1-methylneopentyl)-3-alkylbenzenes 33(R=Me), 34(R='Bu) and 3-(1-methylneopentyl)phenanthrene 35 favours the less compact conformers for 34 and 35, while no preference is seen for 33. Buttressing is invoked to explain the observed conformational preferences, the results being supplemented with molecular mechanics calculations. The rotational conformations of a 2-methylalkyl-group in 2-methylalkyl-4,4-dimethyl-1,3-dioxanes 39(R=ipr), 40(R=1-Ad), 41(R=Ph) are investigated via analysis of the three bond methyl 1H-NMR coupling constants. For 41, two unequally populated gauche conformations are indicated while for 39,40 no population difference is observed about the indicated bond. However, spin decoupling at the 2-H ring hydrogen in 39 suggests a preferred conformation about the ipr-CH2 bond in this compound. These results are interpreted in terms of buttressing and attractive steric effects. An assignment of NMR signals to rotamers for 23, 24, 25, 26 is performed via an NOE difference experiment on 1 (a)-(3-tBuphenyl)-2(e),6(e)-dimethylcyclohexane, 30. Signal assignment for meta-alkylbenzenes 33, 34, 35 is via an NOE difference experiment on 35
Protected steel and composite connections in fire, Simulation of the mechanical behaviour of steel and composite connections protected by intumescent coating in fire
Actual developments in numerical simulations of the structural behaviour in fire situation are focussed on taking into consideration the interaction of all structural members in a global approach. Therefore it is necessary to simulate the load bearing behaviour of connections.With this motivation, the authors conducted experiments and thermal FE-simulations on two different connection types. In this paper, the accompanying mechanical FE-simulations of both investigated connection types will be described. The joints are defined as an end plate connection in a steel structure and a fin plate connection in a composite structure. Besides the validation of the numerical models, the results of the described investigations show that it is possible to activate a significant moment resistance within fin plate connections of composite structures. The main requirement for this activation is sufficient reinforcement strength
Characterization of Water Dissociation on -AlO: Theory and Experiment
The interaction of water with -alumina (i.e. -AlO
surfaces is important in a variety of applications and a useful model for the
interaction of water with environmentally abundant aluminosilicate phases.
Despite its significance, studies of water interaction with
-AlO surfaces other than the are extremely
limited. Here we characterize the interaction of water (DO) with a well
defined -AlO surface in UHV both
experimentally, using temperature programmed desorption and surface-specific
vibrational spectroscopy, and theoretically, using periodic-slab density
functional theory calculations. This combined approach makes it possible to
demonstrate that water adsorption occurs only at a single well defined surface
site (the so-called 1-4 configuration) and that at this site the barrier
between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV.
A subset of OD stretch vibrations are parallel to this dissociation coordinate,
and thus would be expected to be shifted to low frequencies relative to an
uncoupled harmonic oscillator. To quantify this effect we solve the vibrational
Schr\"odinger equation along the dissociation coordinate and find fundamental
frequencies red-shifted by more than 1,500 cm. Within the context
of this model, at moderate temperatures, we further find that some fraction of
surface deuterons are likely delocalized: dissociatively and molecularly
absorbed states are no longer distinguishable.Comment: Paper: 22 pages, 9 figures , ESI: 6 pages, 1 figur
The Role of the Federal Energy Regulatory Commission in Protecting Non-Consumptive Water Uses
55 pages
Recommended from our members
Random block operators
We study fundamental spectral properties of random block operators that
are common in the physical modelling of mesoscopic disordered systems such as
dirty superconductors. Our results include ergodic properties, the location
of the spectrum, existence and regularity of the integrated density of
states, as well as Lifshits tails. Special attention is paid to the
peculiarities arising from the block structure such as the occurrence of a
robust gap in the middle of the spectrum. Without randomness in the
off-diagonal blocks the density of states typically exhibits an inverse
square-root singularity at the edges of the gap. In the presence of
randomness we establish a Wegner estimate that is valid at all energies. It
implies that the singularities are smeared out by randomness, and the density
of states is bounded. We also show Lifshits tails at these band edges.
Technically, one has to cope with a non-monotone dependence on the random
coupling
Einflussfaktoren der öffentlichen Förderung in Ostdeutschland : eine Auswertung des IAB-Betriebspanels
In diesem Beitrag wird zunächst ein Überblick über die Ausgestaltung des Förderinstrumentariums für ostdeutsche Betriebe im Bereich der betrieblichen Wirtschafts- und betriebsnahen Arbeitsmarktpolitik gegeben. Darauf aufbauend wird die Inanspruchnahme der diskutierten Maßnahmen zwischen 1997 und 2002 untersucht. Ein besonderes Augenmerk wird dabei auf die Rolle des Betriebsrats gelegt. Anschließend wird über die Anwendung multivariater Verfahren analysiert, welche Einflussgrößen dafür verantwortlich sind, dass Betriebe Fördermaßnahmen nutzen. --
Ansichten vom Irawadi: Die Kapitänsfrau Eugenie Rosenberger berichtet aus Burma, 1893 bis 1897
In the years 1893 to 1897, Eugenie Rosenberger accompanied her husband, a sailing ship captain, on four journeys from European ports to the Irrawaddy delta in Burma (Myanmar). It was the age of the "rice voyages" with sailing ships, which were facing increasing competition in rice transport from the faster steamers. After her last journey, Rosenberger consolidated her diaries and letters and, in 1899, published her book Auf Großer Fahrt. It would become a bestseller. Rosenberger's descriptions of the ports of Bassein (Pathein) and Rangoon
(Yangon) inspired the author of this article to illustrate her literary images with historical photos as well as many he took on the Irawaddy himself in 1988. The text outlines the political and economic situation in Burma in the 1890s. The author describes the water vehicles mentioned by Rosenberger and explains why the water world on the Irawaddy, which he experienced
firsthand in 1988, is comparable to that of the nineteenth century. The concluding section sketches the political and economic history of Burma as well as its economic downfall, as a result of which ancient Asia was still quite discernible there in many places in 1988 - much in contrast to the neighbouring countries
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