3,035 research outputs found
Renormalization of hole-hole interaction at decreasing Drude conductivity
The diffusion contribution of the hole-hole interaction to the conductivity
is analyzed in gated GaAs/InGaAs/GaAs heterostructures. We show
that the change of the interaction correction to the conductivity with the
decreasing Drude conductivity results both from the compensation of the singlet
and triplet channels and from the arising prefactor in the
conventional expression for the interaction correction.Comment: 6 pages, 5 figure
The quantum speed up as advanced knowledge of the solution
With reference to a search in a database of size N, Grover states: "What is
the reason that one would expect that a quantum mechanical scheme could
accomplish the search in O(square root of N) steps? It would be insightful to
have a simple two line argument for this without having to describe the details
of the search algorithm". The answer provided in this work is: "because any
quantum algorithm takes the time taken by a classical algorithm that knows in
advance 50% of the information that specifies the solution of the problem".
This empirical fact, unnoticed so far, holds for both quadratic and exponential
speed ups and is theoretically justified in three steps: (i) once the physical
representation is extended to the production of the problem on the part of the
oracle and to the final measurement of the computer register, quantum
computation is reduction on the solution of the problem under a relation
representing problem-solution interdependence, (ii) the speed up is explained
by a simple consideration of time symmetry, it is the gain of information about
the solution due to backdating, to before running the algorithm, a
time-symmetric part of the reduction on the solution; this advanced knowledge
of the solution reduces the size of the solution space to be explored by the
algorithm, (iii) if I is the information acquired by measuring the content of
the computer register at the end of the algorithm, the quantum algorithm takes
the time taken by a classical algorithm that knows in advance 50% of I, which
brings us to the initial statement.Comment: 23 pages, to be published in IJT
Giant suppression of the Drude conductivity due to quantum interference in disordered two-dimensional systems
Temperature and magnetic field dependences of the conductivity in heavily
doped, strongly disordered two-dimensional quantum well structures
GaAs/InGaAs/GaAs are investigated within wide conductivity and
temperature ranges. Role of the interference in the electron transport is
studied in the regimes when the phase breaking length crosses over the
localization length with lowering temperature,
where and are the Fermi quasimomentum and mean free path,
respectively. It has been shown that all the experimental data can be
understood within framework of simple model of the conductivity over
delocalized states. This model differs from the conventional model of the weak
localization developed for and by one point: the
value of the quantum interference contribution to the conductivity is
restricted not only by the phase breaking length but by the
localization length as well. We show that just the quantity
rather than
, where is the dephasing time and
, is responsible for the temperature and
magnetic field dependences of the conductivity over the wide range of
temperature and disorder strength down to the conductivity of order .Comment: 11 pages, 15 figure
Diffusion and ballistic contributions of the interaction correction to the conductivity of a two-dimensional electron gas
The results of an experimental study of interaction quantum correction to the
conductivity of two-dimensional electron gas in AB semiconductor
quantum well heterostructures are presented for a wide range of
-parameter (), where is the transport
relaxation time. A comprehensive analysis of the magnetic field and temperature
dependences of the resistivity and the conductivity tensor components allows us
to separate the ballistic and diffusion parts of the correction. It is shown
that the ballistic part renormalizes in the main the electron mobility, whereas
the diffusion part contributes to the diagonal and does not to the off-diagonal
component of the conductivity tensor. We have experimentally found the values
of the Fermi-liquid parameters describing the electron-electron contribution to
the transport coefficients, which are found in a good agreement with the
theoretical results.Comment: 11 pages, 11 figure
One-dimensional collision carts computer model and its design ideas for productive experiential learning
We develop an Easy Java Simulation (EJS) model for students to experience the
physics of idealized one-dimensional collision carts. The physics model is
described and simulated by both continuous dynamics and discrete transition
during collision. In the field of designing computer simulations, we discuss
briefly three pedagogical considerations such as 1) consistent simulation world
view with pen paper representation, 2) data table, scientific graphs and
symbolic mathematical representations for ease of data collection and multiple
representational visualizations and 3) game for simple concept testing that can
further support learning. We also suggest using physical world setup to be
augmented complimentary with simulation while highlighting three advantages of
real collision carts equipment like tacit 3D experience, random errors in
measurement and conceptual significance of conservation of momentum applied to
just before and after collision. General feedback from the students has been
relatively positive, and we hope teachers will find the simulation useful in
their own classes. 2015 Resources added:
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/46-one-dimension-collision-js-model
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/195-elastic-collisionComment: 6 pages, 8 figures, 1 table, 1 L. K. Wee, Physics Education 47 (3),
301 (2012); ISSN 0031-912
Localized states and interaction induced delocalization in Bose gases with quenched disorder
Very diluted Bose gas placed into a disordered environment falls into a
fragmented localized state. At some critical density the repulsion between
particles overcomes the disorder. The gas transits into a coherent superfluid
state. In this article the geometrical and energetic characteristics of the
localized state at zero temperature and the critical density at which the
quantum phase transition from the localized to the superfluid state proceeds
are found.Comment: 17 pages, 5 figur
Top Management Team Diversity: A systematic Review
Empirical research investigating the impact of top management team (TMT)
diversity on executives’ decision making has produced inconclusive results.
To synthesize and aggregate the results on the diversity-performance
link, a meta-regression analysis (MRA) is conducted. It integrates more
than 200 estimates from 53 empirical studies investigating TMT diversity
and its impact on the quality of executives’ decision making as reflected
in corporate performance. The analysis contributes to the literature by
theoretically discussing and empirically examining the effects of TMT diversity
on corporate performance. Our results do not show a link between TMT
diversity and performance but provide evidence for publication bias. Thus,
the findings raise doubts on the impact of TMT diversity on performance
Blaming the victim, all over again: Waddell and Aylward's biopsychosocial (BPS) model of disability
The biopsychosocial (BPS) model of mental distress, originally conceived by the American psychiatrist George Engel in the 1970s and commonly used in psychiatry and psychology, has been adapted by Gordon Waddell and Mansell Aylward to form the theoretical basis for current UK Government thinking on disability. Most importantly, the Waddell and Aylward version of the BPS has played a key role as the Government has sought to reform spending on out-of- work disability benefits. This paper presents a critique of Waddell and Aylward’s model, examining its origins, its claims and the evidence it employs. We will argue that its potential for genuine inter-disciplinary cooperation and the holistic and humanistic benefits for disabled people as envisaged by Engel are not now, if they ever have been, fully realized. Any potential benefit it may have offered has been eclipsed by its role in Coalition/Conservative government social welfare policies that have blamed the victim and justified restriction of entitlements
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