935 research outputs found
Self-aligned charge read-out for InAs nanowire quantum dots
A highly sensitive charge detector is realized for a quantum dot in an InAs
nanowire. We have developed a self-aligned etching process to fabricate in a
single step a quantum point contact in a two-dimensional electron gas and a
quantum dot in an InAs nanowire. The quantum dot is strongly coupled to the
underlying point contact which is used as a charge detector. The addition of
one electron to the quantum dot leads to a change of the conductance of the
charge detector by typically 20%. The charge sensitivity of the detector is
used to measure Coulomb diamonds as well as charging events outside the dot.
Charge stability diagrams measured by transport through the quantum dot and
charge detection merge perfectly.Comment: 11 pages, 3 figure
Developing transferable management skills through Action Learning
There has been increasing criticism of the relevance of the Master of Business Administration (MBA) in developing skills and competencies. Action learning, devised to address problem-solving in the workplace, offers a potential response to such criticism. This paper offers an insight into one university’s attempt to integrate action learning into the curriculum. Sixty-five part-time students were questioned at two points in their final year about their action learning experience and the enhancement of relevant skills and competencies. Results showed a mixed picture. Strong confirmation of the importance of selected skills and competencies contrasted with weaker agreement about the extent to which these were developed by action learning. There was, nonetheless, a firm belief in the positive impact on the learning process. The paper concludes that action learning is not a panacea but has an important role in a repertoire of educational approaches to develop relevant skills and competencies
New quantum phases in a one-dimensional Josephson array
We examine the phase diagram of an ordered one-dimensional Josephson array of
small grains. The average grain charge in such a system can be tuned by means
of gate voltage. At small grain-to-grain conductance, this system is strongly
correlated because of the charge discreteness constraint (Coulomb blockade). At
the gate voltages in the vicinity of the charge degeneracy points, we find new
phases equivalent to a commensurate charge density wave and to a repulsive
Luttinger liquid. The existence of these phases can be probed through a special
dependence of the Josephson current on the gate voltage.Comment: 4 pages, including 1 eps figur
When does the action start and finish? Making the case for an ethnographic action research in educational research
This paper explores how ethnographic and action research methodologies can be justifiably combined to create a new methodological approach in educational research. It draws on existing examples in both educational research and
development studies that have discussed the use of ethnography and action research in specific projects. Interpretations of ethnography and action research
are developed that aim to minimise the epistemological differences between them.
The paper also contextualises an ‘ethnographic action research’ approach with reference to an example of the author’s research into participation in three ‘reception’ (first year of schooling) classes in the United Kingdom. It is argued that research into the theme of participation in early years education, using participative methods, was particularly suitable for this new methodological
approach
Ceramics studio to podiatry clinic: The impact of multi-media resources in the teaching of practical skills across diverse disciplines
This paper draws on the experiences of students from two vastly different disciplines to both explore the theoretical background supporting the use of multimedia resources to teach practical skills and provide a qualitative evaluation of student perceptions and experiences of using bespoke resources. Within ceramics and podiatry, practical skills are traditionally taught via an apprenticeship model within small groups. We explore the practical and pedagogic benefits of developing bespoke multimedia resources to teach practical skills, identifying common themes from these disparate discipline areas. Student focus groups revealed that, practically, the opportunity for repeated viewing at convenient times promoted less reliance on lecturers and better preparation prior to practical demonstrations. Pedagogically, time for reflection and sense making underpinned an increase in confidence which in turn led to increased creativity. The student voice was also used to identify recommendations and challenges driving future change
Quantum chaotic scattering in time-dependent external fields: random matrix approach
We review the random matrix description of electron transport through open
quantum dots, subject to time-dependent perturbations. All characteristics of
the current linear in the bias can be expressed in terms of the scattering
matrix, calculated for a time-dependent Hamiltonian. Assuming that the
Hamiltonian belongs to a Gaussian ensemble of random matrices, we investigate
various statistical properties of the direct current in the ensemble.
Particularly, even at zero bias the time-dependent perturbation induces
current, called photovoltaic current. We discuss dependence of the photovoltaic
current and its noise on the frequency and the strength of the perturbation. We
also describe the effect of time-dependent perturbation on the weak
localization correction to the conductance and on conductance fluctuations.Comment: 27 pages, 6 figures; contribution for the special issue of J. Phys.
A: "Trends in Quantum Chaotic Scattering
Josephson effects in dilute Bose-Einstein condensates
We propose an experiment that would demonstrate the ``dc'' and ``ac''
Josephson effects in two weakly linked Bose-Einstein condensates. We consider a
time-dependent barrier, moving adiabatically across the trapping potential. The
phase dynamics are governed by a ``driven-pendulum'' equation, as in
current-driven superconducting Josephson junctions. At a critical velocity of
the barrier (proportional to the critical tunneling current), there is a sharp
transition between the ``dc'' and ``ac'' regimes. The signature is a sudden
jump of a large fraction of the relative condensate population. Analytical
predictions are compared with a full numerical solution of the time dependent
Gross-Pitaevskii equation, in an experimentally realistic situation.Comment: 4 pages, 1 figur
Mean Field Theory of Josephson Junction Arrays with Charge Frustration
Using the path integral approach, we provide an explicit derivation of the
equation for the phase boundary for quantum Josephson junction arrays with
offset charges and non-diagonal capacitance matrix. For the model with nearest
neighbor capacitance matrix and uniform offset charge , we determine,
in the low critical temperature expansion, the most relevant contributions to
the equation for the phase boundary. We explicitly construct the charge
distributions on the lattice corresponding to the lowest energies. We find a
reentrant behavior even with a short ranged interaction. A merit of the path
integral approach is that it allows to provide an elegant derivation of the
Ginzburg-Landau free energy for a general model with charge frustration and
non-diagonal capacitance matrix. The partition function factorizes as a product
of a topological term, depending only on a set of integers, and a
non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure
Fermions and Type IIB Supergravity On Squashed Sasaki-Einstein Manifolds
We discuss the dimensional reduction of fermionic modes in a recently found
class of consistent truncations of type IIB supergravity compactified on
squashed five-dimensional Sasaki-Einstein manifolds. We derive the lower
dimensional equations of motion and effective action, and comment on the
supersymmetry of the resulting theory, which is consistent with N=4 gauged
supergravity in , coupled to two vector multiplets. We compute fermion
masses by linearizing around two vacua of the theory: one that breaks
N=4 down to N=2 spontaneously, and a second one which preserves no
supersymmetries. The truncations under consideration are noteworthy in that
they retain massive modes which are charged under a U(1) subgroup of the
-symmetry, a feature that makes them interesting for applications to
condensed matter phenomena via gauge/gravity duality. In this light, as an
application of our general results we exhibit the coupling of the fermions to
the type IIB holographic superconductor, and find a consistent further
truncation of the fermion sector that retains a single spin-1/2 mode.Comment: 43 pages, 2 figures, PDFLaTeX; v2: added references, typos corrected,
minor change
Quantal phases, disorder effects and superconductivity in spin-Peierls systems
In view of recent developments in the investigation on cuprate high-T superconductors and the spin-Peierls compound CuGeO, we study the
effect of dilute impurity doping on the spin-Peierls state in quasi-one
dimensional systems. We identify a common origin for the emergence of
antiferromagnetic order upon the introduction of static vacancies, and
superconductivity for mobile holes.Comment: 4 pages revtex; revised versio
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