9,151 research outputs found
Progressor: Personalized visual access to programming problems
This paper presents Progressor, a visualization of open student models intended to increase the student's motivation to progress on educational content. The system visualizes not only the user's own model, but also the peers' models. It allows sorting the peers' models using a number of criteria, including the overall progress and the progress on a specific topic. Also, in this paper we present results of a classroom study confirming our hypothesis that by showing a student the peers' models and ranking them by progress it is possible to increase the student's motivation to compete and progress in e-learning systems. © 2011 IEEE
A Model of the Ventral Visual System Based on Temporal Stability and Local Memory
The cerebral cortex is a remarkably homogeneous structure suggesting a rather generic computational machinery. Indeed, under a variety of conditions, functions attributed to specialized areas can be supported by other regions. However, a host of studies have laid out an ever more detailed map of functional cortical areas. This leaves us with the puzzle of whether different cortical areas are intrinsically specialized, or whether they differ mostly by their position in the processing hierarchy and their inputs but apply the same computational principles. Here we show that the computational principle of optimal stability of sensory representations combined with local memory gives rise to a hierarchy of processing stages resembling the ventral visual pathway when it is exposed to continuous natural stimuli. Early processing stages show receptive fields similar to those observed in the primary visual cortex. Subsequent stages are selective for increasingly complex configurations of local features, as observed in higher visual areas. The last stage of the model displays place fields as observed in entorhinal cortex and hippocampus. The results suggest that functionally heterogeneous cortical areas can be generated by only a few computational principles and highlight the importance of the variability of the input signals in forming functional specialization
Transverse Mercator with an accuracy of a few nanometers
Implementations of two algorithms for the transverse Mercator projection are
described; these achieve accuracies close to machine precision. One is based on
the exact equations of Thompson and Lee and the other uses an extension of
Krueger's series for the projection to higher order. The exact method provides
an accuracy of 9 nm over the entire ellipsoid, while the errors in the series
method are less than 5 nm within 3900 km of the central meridian. In each case,
the meridian convergence and scale are also computed with similar accuracy. The
speed of the series method is competitive with other less accurate algorithms
and the exact method is about 5 times slower.Comment: LaTeX, 10 pages, 3 figures. Includes some revisions. Supplementary
material is available at http://geographiclib.sourceforge.net/tm.htm
Superconducting proximity effect in interacting double-dot systems
We study subgap transport from a superconductor through a double quantum dot
with large on-site Coulomb repulsion to two normal leads. Non-local
superconducting correlations in the double dot are induced by the proximity to
the superconducting lead, detectable in non-local Andreev transport that splits
Cooper pairs in locally separated, spin-entangled electrons. We find that the
-- characteristics are strongly asymmetric: for a large bias voltage of
certain polarity, transport is blocked by populating the double dot with states
whose spin symmetry is incompatible with the superconductor. Furthermore, by
tuning gate voltages one has access to splitting of the Andreev excitation
energies, which is visible in the differential conductance.Comment: 5 pages, 4 figure
Contribution of Scalar Loops to the Three-Photon Decay of the Z
I corrected 3 mistakes from the first version: that were an omitted Feynman
integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in
eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed
drastically. Doing an expansion in the Higgs mass I show that the matrix
element is identically 0 in the order (MZ/MH)^2, which is due to gauge
invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is
that the scalar contribution to this decay rate is several orders of magnitude
smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail,
OCIP/C-93-5, UQAM-PHE-93/0
The Efficiency and Evolution of R&D Networks
This work introduces a new model to investigate the efficiency and evolution of networks of firms exchanging knowledge in R&D partnerships. We first examine the efficiency of a given network structure in terms of the maximization of total profits in the industry. We show that the efficient network structure depends on the marginal cost of collaboration. When the marginal cost is low, the complete graph is efficient. However, a high marginal cost implies that the efficient network is sparser and has a core-periphery structure. Next, we examine the evolution of the network struc- ture when the decision on collaborating partners is decentralized. We show the existence of mul- tiple equilibrium structures which are in general inefficient. This is due to (i) the path dependent character of the partner selection process, (ii) the presence of knowledge externalities and (iii) the presence of severance costs involved in link deletion. Finally, we study the properties of the emerg- ing equilibrium networks and we show that they are coherent with the stylized facts of R&D net- works.R&D networks, technology spillovers, network efficiency, network formation
Frequency-Dependent Current Noise through Quantum-Dot Spin Valves
We study frequency-dependent current noise through a single-level quantum dot
connected to ferromagnetic leads with non-collinear magnetization. We propose
to use the frequency-dependent Fano factor as a tool to detect single-spin
dynamics in the quantum dot. Spin precession due to an external magnetic and/or
a many-body exchange field affects the Fano factor of the system in two ways.
First, the tendency towards spin-selective bunching of the transmitted
electrons is suppressed, which gives rise to a reduction of the low-frequency
noise. Second, the noise spectrum displays a resonance at the Larmor frequency,
whose lineshape depends on the relative angle of the leads' magnetizations.Comment: 12 pages, 15 figure
An All-But-One Entropic Uncertainty Relation, and Application to Password-based Identification
Entropic uncertainty relations are quantitative characterizations of
Heisenberg's uncertainty principle, which make use of an entropy measure to
quantify uncertainty. In quantum cryptography, they are often used as
convenient tools in security proofs. We propose a new entropic uncertainty
relation. It is the first such uncertainty relation that lower bounds the
uncertainty in the measurement outcome for all but one choice for the
measurement from an arbitrarily large (but specifically chosen) set of possible
measurements, and, at the same time, uses the min-entropy as entropy measure,
rather than the Shannon entropy. This makes it especially suited for quantum
cryptography. As application, we propose a new quantum identification scheme in
the bounded quantum storage model. It makes use of our new uncertainty relation
at the core of its security proof. In contrast to the original quantum
identification scheme proposed by Damg{\aa}rd et al., our new scheme also
offers some security in case the bounded quantum storage assumption fails hold.
Specifically, our scheme remains secure against an adversary that has unbounded
storage capabilities but is restricted to non-adaptive single-qubit operations.
The scheme by Damg{\aa}rd et al., on the other hand, completely breaks down
under such an attack.Comment: 33 pages, v
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