200 research outputs found
Which canonical algebras are derived equivalent to incidence algebras of posets?
We give a full description of all the canonical algebras over an
algebraically closed field that are derived equivalent to incidence algebras of
finite posets. These are the canonical algebras whose number of weights is
either 2 or 3.Comment: 8 pages; slight revision; to appear in Comm. Algebr
Telegraph Noise in Coupled Quantum Dot Circuits Induced by a Quantum Point Contact
Charge detection utilizing a highly biased quantum point contact has become
the most effective probe for studying few electron quantum dot circuits.
Measurements on double and triple quantum dot circuits is performed to clarify
a back action role of charge sensing on the confined electrons. The quantum
point contact triggers inelastic transitions, which occur quite generally.
Under specific device and measurement conditions these transitions manifest
themselves as bounded regimes of telegraph noise within a stability diagram. A
nonequilibrium transition from artificial atomic to molecular behavior is
identified. Consequences for quantum information applications are discussed.Comment: 4 pages, 3 figures (as published
The structure of fluid trifluoromethane and methylfluoride
We present hard X-ray and neutron diffraction measurements on the polar
fluorocarbons HCF3 and H3CF under supercritical conditions and for a range of
molecular densities spanning about a factor of ten. The Levesque-Weiss-Reatto
inversion scheme has been used to deduce the site-site potentials underlying
the measured partial pair distribution functions. The orientational
correlations between adjacent fluorocarbon molecules -- which are characterized
by quite large dipole moments but no tendency to form hydrogen bonds -- are
small compared to a highly polar system like fluid hydrogen chloride. In fact,
the orientational correlations in HCF3 and H3CF are found to be nearly as small
as those of fluid CF4, a fluorocarbon with no dipole moment.Comment: 11 pages, 9 figure
Kondo effect in a one-electron double quantum dot: Oscillations of the Kondo current in a weak magnetic field
We present transport measurements of the Kondo effect in a double quantum dot
charged with only one or two electrons, respectively. For the one electron case
we observe a surprising quasi-periodic oscillation of the Kondo conductance as
a function of a small perpendicular magnetic field |B| \lesssim 50mT. We
discuss possible explanations of this effect and interpret it by means of a
fine tuning of the energy mismatch of the single dot levels of the two quantum
dots. The observed degree of control implies important consequences for
applications in quantum information processing
An electrostatically defined serial triple quantum dot charged with few electrons
A serial triple quantum dot (TQD) electrostatically defined in a GaAs/AlGaAs
heterostructure is characterized by using a nearby quantum point contact as
charge detector. Ground state stability diagrams demonstrate control in the
regime of few electrons charging the TQD. An electrostatic model is developed
to determine the ground state charge configurations of the TQD. Numerical
calculations are compared with experimental results. In addition, the tunneling
conductance through all three quantum dots in series is studied. Quantum
cellular automata processes are identified, which are where charge
reconfiguration between two dots occurs in response to the addition of an
electron in the third dot.Comment: 12 pages, 9 figure
Spatial inhomogeneities in ionic liquids, charged proteins and charge stabilized colloids from collective variables theory
Effects of size and charge asymmetry between oppositely charged ions or
particles on spatial inhomogeneities are studied for a large range of charge
and size ratios. We perform a stability analysis of the primitive model (PM) of
ionic systems with respect to periodic ordering using the collective variables
based theory. We extend previous studies [A. Ciach et al., Phys. Rev.E
\textbf{75}, 051505 (2007)] in several ways. First, we employ a non-local
approximation for the reference hard-sphere fluid which leads to the
Percus-Yevick pair direct correlation functions for the uniform case. Second,
we use the Weeks-Chandler-Anderson regularization scheme for the Coulomb
potential inside the hard core. We determine the relevant order parameter
connected with the periodic ordering and analyze the character of the dominant
fluctuations along the -lines. We show that the above-mentioned
modifications produce large quantitative and partly qualitative changes in the
phase diagrams obtained previously. We discuss possible scenarios of the
periodic ordering for the whole range of size- and charge ratios of the two
ionic species, covering electrolytes, ionic liquids, charged globular proteins
or nanoparticles in aqueous solutions and charge-stabilized colloids
Lab::Measurement - A portable and extensible framework for controlling lab equipment and conducting measurements
Lab::Measurement is a framework for test and measurement automatization using
Perl 5. While primarily developed with applications in mesoscopic physics in
mind, it is widely adaptable. Internally, a layer model is implemented.
Communication protocols such as IEEE 488, USB Test & Measurement, or, e.g.,
VXI-11 are addressed by the connection layer. The wide range of supported
connection backends enables unique cross-platform portability. At the
instrument layer, objects correspond to equipment connected to the measurement
PC (e.g., voltage sources, magnet power supplies, multimeters, etc.). The
high-level sweep layer automates the creation of measurement loops, with
simultaneous plotting and data logging. An extensive unit testing framework is
used to verify functionality even without connected equipment. Lab::Measurement
is distributed as free and open source software.Comment: Published version (open access, CC BY 4.0). 7 pages; refers to
Lab::Measurement 3.660, see https://www.labmeasurement.de
Anomalous relaxations and chemical trends at III-V nitride non-polar surfaces
Relaxations at nonpolar surfaces of III-V compounds result from a competition
between dehybridization and charge transfer. First principles calculations for
the (110) and (100) faces of zincblende and wurtzite AlN, GaN and InN
reveal an anomalous behavior as compared with ordinary III-V semiconductors.
Additional calculations for GaAs and ZnO suggest close analogies with the
latter. We interpret our results in terms of the larger ionicity (charge
asymmetry) and bonding strength (cohesive energy) in the nitrides with respect
to other III-V compounds, both essentially due to the strong valence potential
and absence of core states in the lighter anion. The same interpretation
applies to Zn II-VI compounds.Comment: RevTeX 7 pages, 8 figures included; also available at
http://kalix.dsf.unica.it/preprints/; improved after revie
Cluster algebras in algebraic Lie theory
We survey some recent constructions of cluster algebra structures on
coordinate rings of unipotent subgroups and unipotent cells of Kac-Moody
groups. We also review a quantized version of these results.Comment: Invited survey; to appear in Transformation Group
Toward polarized antiprotons: Machine development for spin-filtering experiments
The paper describes the commissioning of the experimental equipment and the
machine studies required for the first spin-filtering experiment with protons
at a beam kinetic energy of MeV in COSY. The implementation of a
low- insertion made it possible to achieve beam lifetimes of
s in the presence of a dense polarized hydrogen
storage-cell target of areal density . The developed techniques can be directly
applied to antiproton machines and allow for the determination of the
spin-dependent cross sections via spin filtering
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