223 research outputs found
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
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
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
Care leavers in early adulthood: How do they fare in Britain, Finland and Germany?
In this paper we examine the longer term outcomes of young people who experienced out of home care (OHC) as children, in Britain, Germany and Finland, countries characterised by different welfare regimes. While there is some evidence on immediate transitions after leaving care (up to age 21), there is less evidence on experiences around age 30, a phase of early adulthood. Drawing on existing longitudinal data for general population samples we focus on outcomes related to education, employment, family, health and receipt of welfare benefits for those who were ever in care and those who were not. We find evidence for continuing disadvantage regarding education and employment for those who were in care as children, but also indications of subjective wellbeing and commitment to family life – possibly a reflection of “normality” and efforts to “fit in” as parents. Surprisingly, despite variations in welfare system and differences in the scope and quality of available data, trends were similar in each of the countries, suggesting that none provide adequately for the needs of care experienced young adults. The findings point towards the need for a revised conceptualisation of the notion of “independence” which has to take into account the manifold and changing relationships between individuals and the state. Instead of a “cliff edge” approach there should be support for a more gradual shift from “dependence” to “independence” enabling those with care experience to develop their full potential. In interpreting the findings, limitations of the available data have to be acknowledged, pointing to the need for generating harmonised and longitudinal data on vulnerable subpopulations to enable effective monitoring of needs and provision
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
Non-liftable Calabi-Yau spaces
We construct many new non-liftable three-dimensional Calabi-Yau spaces in
positive characteristic. The technique relies on lifting a nodal model to a
smooth rigid Calabi-Yau space over some number field as introduced by the first
author and D. van Straten.Comment: 16 pages, 5 tables; v2: minor corrections and addition
Cluster structures on quantum coordinate rings
We show that the quantum coordinate ring of the unipotent subgroup N(w) of a
symmetric Kac-Moody group G associated with a Weyl group element w has the
structure of a quantum cluster algebra. This quantum cluster structure arises
naturally from a subcategory C_w of the module category of the corresponding
preprojective algebra. An important ingredient of the proof is a system of
quantum determinantal identities which can be viewed as a q-analogue of a
T-system. In case G is a simple algebraic group of type A, D, E, we deduce from
these results that the quantum coordinate ring of an open cell of a partial
flag variety attached to G also has a cluster structure.Comment: v2: minor corrections. v3: references updated, final version to
appear in Selecta Mathematic
Ising Universality in Three Dimensions: A Monte Carlo Study
We investigate three Ising models on the simple cubic lattice by means of
Monte Carlo methods and finite-size scaling. These models are the spin-1/2
Ising model with nearest-neighbor interactions, a spin-1/2 model with
nearest-neighbor and third-neighbor interactions, and a spin-1 model with
nearest-neighbor interactions. The results are in accurate agreement with the
hypothesis of universality. Analysis of the finite-size scaling behavior
reveals corrections beyond those caused by the leading irrelevant scaling
field. We find that the correction-to-scaling amplitudes are strongly dependent
on the introduction of further-neighbor interactions or a third spin state. In
a spin-1 Ising model, these corrections appear to be very small. This is very
helpful for the determination of the universal constants of the Ising model.
The renormalization exponents of the Ising model are determined as y_t = 1.587
(2), y_h = 2.4815 (15) and y_i = -0.82 (6). The universal ratio Q =
^2/ is equal to 0.6233 (4) for periodic systems with cubic symmetry.
The critical point of the nearest-neighbor spin-1/2 model is K_c=0.2216546
(10).Comment: 25 pages, uuencoded compressed PostScript file (to appear in Journal
of Physics A
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 Pert 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 [1], USB Test & Measurement [2], or, e.g., VXI-11 [3] 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. (C) 2018 The Author(s). Published by Elsevier B.V
Practitioner’s Section: Integrated Resource Efficiency Analysis for Reducing Climate Impacts in the Chemical Industry
Reducing greenhouse gas emissions of the material-intensive chemical industry requires an integrated analysis and optimization of the complex production systems including raw material and energy use, resulting costs and environmental and climate impacts. To meet this challenge, the research project InReff (Integrated Resource Efficiency Analysis for Reducing Climate Impacts in the Chemical Industry) has been established. It aims at the development of an IT-supported modeling and evaluation framework which is able to comprehensively address issues of resource efficiency and climate change within the chemical industry, e.g. the minimization of material and energy intensity and consequently greenhouse gas emissions, without compromising on production performance. The paper presents background information on resource efficiency and the research project, an ideal-typical decision model for resource efficiency analysis, the conceptual approach for an IT-based integration platform as well as the case study design at the industrial project partners’ sites. These first results are linked to future activities and further research questions are highlighted in the concluding section
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