7,664 research outputs found
Mobile game-based learning in secondary education:Students' immersion, game activities, team performance and learning outcomes
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
The quality of student dialogue in citizenship education
This study investigates the relationship between the quality of student dialogue and students’ ability to justify their viewpoints on a moral issue. A curriculum unit for dialogic citizenship education was developed and implemented in the 8th grade of secondary education. In the final lesson, students discussed a moral issue and then wrote an essay on it. The results show that students who made more value-related utterances during the discussion also referred more often and more explicitly in their individually written essays to moral values. This study indicates that the quality of the content of students’ dialogue is important for their ability to substantiate their opinion on moral issues with value-laden argumentation. Approaches to citizenship education in which dialogue is a central element should, therefore, pay specific attention to the validation of ideas in student dialogue
Strong nonlocality: A trade-off between states and measurements
Measurements on entangled quantum states can produce outcomes that are
nonlocally correlated. But according to Tsirelson's theorem, there is a
quantitative limit on quantum nonlocality. It is interesting to explore what
would happen if Tsirelson's bound were violated. To this end, we consider a
model that allows arbitrary nonlocal correlations, colloquially referred to as
"box world". We show that while box world allows more highly entangled states
than quantum theory, measurements in box world are rather limited. As a
consequence there is no entanglement swapping, teleportation or dense coding.Comment: 11 pages, 2 figures, very minor change
Noise resistance of adiabatic quantum computation using random matrix theory
Besides the traditional circuit-based model of quantum computation, several
quantum algorithms based on a continuous-time Hamiltonian evolution have
recently been introduced, including for instance continuous-time quantum walk
algorithms as well as adiabatic quantum algorithms. Unfortunately, very little
is known today on the behavior of these Hamiltonian algorithms in the presence
of noise. Here, we perform a fully analytical study of the resistance to noise
of these algorithms using perturbation theory combined with a theoretical noise
model based on random matrices drawn from the Gaussian Orthogonal Ensemble,
whose elements vary in time and form a stationary random process.Comment: 9 pages, 3 figure
Role of a "Local" Cosmological Constant in Euclidean Quantum Gravity
In 4D non-perturbative Regge calculus a positive value of the effective
cosmological constant characterizes the collapsed phase of the system. If a
local term of the form is
added to the gravitational action, where is a subset of the
hinges and are positive constants, one expects that the volumes
, , ... tend to collapse and that the excitations of the
lattice propagating through the hinges are damped. We study
the continuum analogue of this effect. The additional term may represent
the coupling of the gravitational field to an external Bose condensate.Comment: LaTex, 18 page
Optimal parametrizations of adiabatic paths
The parametrization of adiabatic paths is optimal when tunneling is
minimized. Hamiltonian evolutions do not have unique optimizers. However,
dephasing Lindblad evolutions do. The optimizers are simply characterized by an
Euler-Lagrange equation and have a constant tunneling rate along the path
irrespective of the gap. Application to quantum search algorithms recovers the
Grover result for appropriate scaling of the dephasing. Dephasing rates that
beat Grover imply hidden resources in Lindblad operators.Comment: 4 pages, 2 figures; To prevent from misunderstanding, we clarified
the discussion of an apparent speedup in the Grover algorithm; figures
improved + minor change
On SIC-POVMs in Prime Dimensions
The generalized Pauli group and its normalizer, the Clifford group, have a
rich mathematical structure which is relevant to the problem of constructing
symmetric informationally complete POVMs (SIC-POVMs). To date, almost every
known SIC-POVM fiducial vector is an eigenstate of a "canonical" unitary in the
Clifford group. I show that every canonical unitary in prime dimensions p > 3
lies in the same conjugacy class of the Clifford group and give a class
representative for all such dimensions. It follows that if even one such
SIC-POVM fiducial vector is an eigenvector of such a unitary, then all of them
are (for a given such dimension). I also conjecture that in all dimensions d,
the number of conjugacy classes is bounded above by 3 and depends only on d mod
9, and I support this claim with computer computations in all dimensions < 48.Comment: 6 pages, no figures. v3 Refs added, improved discussion of previous
work. Ref to a proof of the main conjecture also adde
Mg/Ti multilayers: structural, optical and hydrogen absorption properties
Mg-Ti alloys have uncommon optical and hydrogen absorbing properties,
originating from a "spinodal-like" microstructure with a small degree of
chemical short-range order in the atoms distribution. In the present study we
artificially engineer short-range order by depositing Pd-capped Mg/Ti
multilayers with different periodicities and characterize them both
structurally and optically. Notwithstanding the large lattice parameter
mismatch between Mg and Ti, the as-deposited metallic multilayers show good
structural coherence. Upon exposure to H2 gas a two-step hydrogenation process
occurs, with the Ti layers forming the hydride before Mg. From in-situ
measurements of the bilayer thickness L at different hydrogen pressures, we
observe large out-of-plane expansions of the Mg and Ti layers upon
hydrogenation, indicating strong plastic deformations in the films and a
consequent shortening of the coherence length. Upon unloading at room
temperature in air, hydrogen atoms remain trapped in the Ti layers due to
kinetic constraints. Such loading/unloading sequence can be explained in terms
of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by
diffusion calculations on a model multilayered systems. Absorption isotherms
measured by hydrogenography can be interpreted as a result of the elastic
clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces
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