230 research outputs found
Searching for a quantum critical point in YbCu5-xAux
Structural, magnetic, transport and thermal properties of YbCu5-xAux alloys
with Au concentration between the limit of structural stability of AuBe5 type
at x = 0.4 up to x = 0.7 are reported. The outstanding features of this system
are: i) the constant and record high values of Cm /T 7J/molK^2 below a
characteristic temperature T*, ranging between 150 mK and 350 mK. ii) A power
law thermal dependence dependence Cm/T(T>T*)=A/T^q, with q = 1.3 +/- 0.1, and
iii) an arising incoherent electronic scattering observed in the resistivity at
T < 1K for x < 0.6 despite the fact that Yb magnetic atoms are placed in a
lattice. Magnetic frustration, originated in the tetrahedral distribution of Yb
atoms, appears as the responsible of the exotic behavior of this system.Comment: 14 pages, 9 figure
YbPd2In : A promising candidate for strong entropy accumulation at very low temperature
We report on synthesis, crystal structure, magnetic, thermodynamic, and transport properties of the compound YbPd2In, crystallizing as a Heusler structure type. A trivalent state of the rare earth was determined by fitting the magnetic susceptibility with a Curie-Weiss law. This compound is characterized by showing very weak magnetic interactions and a negligible Kondo effect. A specific-heat jump was observed at T 48250mK, followed at higher temperature by a power-law decrease of CP(T)/T. The resulting large electronic entropy increase at very low temperature is rapidly shifted to higher temperature by the application of magnetic field. This magnetocaloric effect places YbPd2In as a very good candidate for adiabatic demagnetization cooling processes
The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy
We have investigated the intermediate valence narrow-gap semiconductor SmB6
at low temperatures using both conventional spear-anvil type point contacts as
well as mechanically controllable break junctions. The zero-bias conductance
varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the
spectral anomalies, which are related to the different activation energies and
band gaps of SmB6, did not depend on the the contact size. Two different
regimes of charge transport could be distinguished: Contacts with large zero -
bias conductance are in the diffusive Maxwell regime. They had spectra with
only small non-linearities. Contacts with small zero - bias conductance are in
the tunnelling regime. They had larger anomalies, but still indicating a finite
45 % residual quasiparticle density of states at the Fermi level at low
temperatures of T = 0.1 K. The density of states derived from the tunelling
spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and
Ed = 4.5 meV wide gaps, respectively.Comment: 9 pages incl. 13 figure
Constraints to Economic Development and Growth in the Middle East and North Africa
When comparing the speed and extent of economic development in different geographic
regions of the world over the past 20 years, the under-average performance of Arab countries
in general and Arab Mediterranean countries in particular is striking. This is despite
an overall favorable geo-strategic situation at the crossroads of three continents, with excellent
connections to sea and waterways and in direct proximity to the European Union,
one of the world’s economic hubs. It is also despite the minor importance of negative factors
such as a high-burden diseases or high levels of ethnic fractionalization.
In this paper, I focus on identifying the most important constraints on Arab Mediterranean
economic development. I use state-of-the-art econometric tools to quantify constraints that
have been identified through economic theory and studies of the political economy characteristics
of the region. The empirical results offer support for the central hypothesis that
limited technological capacities and political economy structures are the primary constraints
on economic development. With a view to international structural adjustment efforts,
my findings imply that the limited success of the Euro-Mediterranean policy to
stimulate the economic development of the Arab Mediterranean countries might be because
structural adjustment efforts do not tackle—or at least do not sufficiently tackle—
these constraints.Vergleicht man Geschwindigkeit und Umfang der wirtschaftlichen Entwicklung der verschiedenen
Weltregionen in den vergangenen zwanzig Jahren, so fällt insbesondere das
unterdurchschnittliche Abschneiden der arabischen Länder im Allgemeinen und der arabischen
Mittlemeerländer im Besonderen ins Auge, und dies trotz einer insgesamt vorteilhaften
geographischen Lage im Schnittpunkt dreier Kontinente mit exzellenten Anschlussmöglichkeiten
an See- und Wasserwege, trotz der direkten Nachbarschaft zum
Weltwirtschaftsdrehkreuz Europäische Union und trotz der relativ geringen Bedeutung
wichtiger entwicklungshemmender Faktoren, beispielsweise ethnische Zersplitterung oder
massive Ausbreitung von Krankheiten wie AIDS oder Malaria.
In diesem Aufsatz wird versucht, von den unterschiedlichen Hemmfaktoren wirtschaftlicher
Entwicklung, die in der wirtschaftstheoretischen Literatur und/oder in MENARegionalstudien
diskutiert werden, diejenigen herauszuarbeiten, die wirtschaftliche Entwicklung
am stärksten behindern oder möglicherweise stärker als andere. Dabei benutze
ich modernste ökonometrische Verfahren, um den Einfluss der verschiedenen erklärenden
Variablen zu quantifizieren. Die Ergebnisse stĂĽtzen die Eingangshypothese, dass insbesondere
mangelnde technologische Kapazitäten und Fähigkeiten sowie regionalspezifische
politökonomische Strukturen die wirtschaftliche Entwicklung in den arabischen Mittelmeerländern
behindern
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