30,886 research outputs found

### Monochromatic Clique Decompositions of Graphs

Let $G$ be a graph whose edges are coloured with $k$ colours, and $\mathcal
H=(H_1,\dots , H_k)$ be a $k$-tuple of graphs. A monochromatic $\mathcal
H$-decomposition of $G$ is a partition of the edge set of $G$ such that each
part is either a single edge or forms a monochromatic copy of $H_i$ in colour
$i$, for some $1\le i\le k$. Let $\phi_{k}(n,\mathcal H)$ be the smallest
number $\phi$, such that, for every order-$n$ graph and every
$k$-edge-colouring, there is a monochromatic $\mathcal H$-decomposition with at
most $\phi$ elements. Extending the previous results of Liu and Sousa
["Monochromatic $K_r$-decompositions of graphs", Journal of Graph Theory},
76:89--100, 2014], we solve this problem when each graph in $\mathcal H$ is a
clique and $n\ge n_0(\mathcal H)$ is sufficiently large.Comment: 14 pages; to appear in J Graph Theor

### Flux-vector model of spin noise in superconducting circuits: Electron versus nuclear spins and role of phase transition

Superconducting Quantum Interference Devices (SQUIDs) and other
superconducting circuits are limited by intrinsic flux noise with spectral
density $1/f^{\alpha}$ with $\alpha<1$ whose origin is believed to be due to
spin impurities. Here we present a theory of flux noise that takes into account
the vectorial nature of the coupling of spins to superconducting wires. We
present explicit numerical calculations of the flux noise power (spectral
density integrated over all frequencies) for electron impurities and lattice
nuclear spins under several different assumptions. The noise power is shown to
be dominated by surface electron spins near the wire edges, with bulk lattice
nuclear spins contributing $\sim 5$% of the noise power in aluminum and niobium
wires. We consider the role of electron spin phase transitions, showing that
the spin-spin correlation length (describing e.g. the average size of
ferromagnetic spin clusters) greatly impacts the scaling of flux noise with
wire geometry. Remarkably, flux noise power is exactly equal to zero when the
spins are polarized along the flux vector direction, forming what we call a
poloidal state. Flux noise is non-zero for other spin textures, but gets
reduced in the presence of correlated ferromagnetic fluctuations between the
top and bottom wire surfaces, where the flux vectors are antiparallel. This
demonstrates that engineering spin textures and/or inter-surface correlation
provides a method to reduce flux noise in superconducting devices.Comment: New version accepted in PRB. Contains new discussion about the
poloidal stat

### The importance of target audiences in the design of training actions

This paper describes the process of definition, conceptualization and implementation of a business course addressed for logistic and industrial managers. This course was designed using a blended methodology, with training in classroom, visits to enterprises and self- study, supported by an eLearning platform. The aim of this work is to create an opportunity to reflect about the decisions and strategies implemented and point future developments

### Modelling a layer for real-time management of interactions in web based distance learning

In the last few years, the University of Aveiro, Portugal, has been offering several distance learning courses
over the Web, using e-learning platforms.
Experience showed that different editions of a same course, using the same contents and structure, and having
similar target learners, had different success rates. What would be the reason for that?
A hypothesis was considered: The level of success could be directly related with the remote follow-up of the
learners’ participation in the courses; the best results usually occur when the follow-up is closer.
The existing e-learning platforms offer and the standardization works being developed by organizations and
consortiums like IMS (IMS Global Learning Consortium, Inc), ADL SCORM (Advanced Distributed Learning
Sherable Content Object Reference Model), IEEE LTSC LOM (Institute of Electrical and Electronic Engineers
Learning Technologies Standard Committee Learning Object Metadata), ARIADNE (ARIADNE Foundation
for the European Knowledge Pool), AICC CMI (Aviation Industry CBT Committee Computer Managed
Instruction), etc, don’t cover the course monitorization concerns mentioned. Those projects were focused on
aspects like contents and its delivery in the context of the execution of the courses’ activities. This is even
true in the SCORM project that doesn’t include any reference to the management of the e-learning processes.
Recently, in the context of the IMS Global Consortium, a new project designated IMS LD (Learning Design) is
under development, providing a framework for the description of learning units under a three level model. In
the most recently defined level, the C level, some functionalities related to notifications were proposed,
expressing similar concerns to the ones that triggered our research. However, the extent at which IMS LD
takes the functionalities is, from our point of view, not complete.
This article describes a proposal of a reference model and functionalities towards a specification of a layer for
real-time management of user interactions on LMSs, and its possible integration with the ADL SCORM
standard proposal. The paper includes a discussion of the management metadata model for the LMS
sub-system and how the integration of the management module under SCORM may be achieved

### Dynamic Control of Tunable Sub-optimal Algorithms for Scheduling of Time-varying Wireless Networks

It is well known that for ergodic channel processes the Generalized
Max-Weight Matching (GMWM) scheduling policy stabilizes the network for any
supportable arrival rate vector within the network capacity region. This
policy, however, often requires the solution of an NP-hard optimization
problem. This has motivated many researchers to develop sub-optimal algorithms
that approximate the GMWM policy in selecting schedule vectors. One implicit
assumption commonly shared in this context is that during the algorithm
runtime, the channel states remain effectively unchanged. This assumption may
not hold as the time needed to select near-optimal schedule vectors usually
increases quickly with the network size. In this paper, we incorporate channel
variations and the time-efficiency of sub-optimal algorithms into the scheduler
design, to dynamically tune the algorithm runtime considering the tradeoff
between algorithm efficiency and its robustness to changing channel states.
Specifically, we propose a Dynamic Control Policy (DCP) that operates on top of
a given sub-optimal algorithm, and dynamically but in a large time-scale
adjusts the time given to the algorithm according to queue backlog and channel
correlations. This policy does not require knowledge of the structure of the
given sub-optimal algorithm, and with low overhead can be implemented in a
distributed manner. Using a novel Lyapunov analysis, we characterize the
throughput stability region induced by DCP and show that our characterization
can be tight. We also show that the throughput stability region of DCP is at
least as large as that of any other static policy. Finally, we provide two case
studies to gain further intuition into the performance of DCP.Comment: Submitted for journal consideration. A shorter version was presented
in IEEE IWQoS 200

### Enhancing web supported learning in higher education by adding a management layer to LMSs

There are many situations in the e-Learning experiences
that can compromise the success of the courses. Many
times simple reasons are great enough to motivate people
to abandon them. For example, if someone does not
execute a programmed activity inside the defined window
of time, it can compromise the rest of the course to that
person. In such situations it would be important that the
teacher knew about the situation in useful time, to be able
to take any corrective action.
Another example could be presented, involving the
professor and the learners. Let us assume that an activity
A2 is programmed to be executed by the learners and that
it depends on the previous knowledge of the result of the
evaluation of a work submitted by the learners to the
teacher (activity A1). If the teacher doesn’t inform the
learners about their classification in useful time, that can
compromise the execution of the activity A2.
It seems to be necessary to use mechanisms of automatic
management, in real time, of the envolvement of each
participant in a distance learning course using LMS
(Learning Management System). Such a functionality
allows the detection of deviations to the scheduled
activities planned for each actor. If it is the case, the
referred mechanism can initiate the process of sending
notifications to the relevant entities, enabling the
correction of these deviations.
Several organizations and consortiuns, involving the
industry, governmental institutions and universities, are
developing projects of standardization. It seemed
important to us to see how the referred aspects were
covered by those projects, and to perceive how it could be
possible to articulate our work with the ones that are
available from these organizations and consortiuns.
This article describes the work that the authors are
developing towards the specification of a layer for
real-time management of user interactions with LMSs,
during the operationalization of a course, and also
includes a management meta-data model, related to that
management layer

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