131 research outputs found
Test them all, is it worth it? Assessing configuration sampling on the JHipster Web development stack
Many approaches for testing configurable software systems start from the same assumption: it is impossible to test all configurations. This motivated the definition of variability-aware abstractions and sampling techniques to cope with large configuration spaces. Yet, there is no theoretical barrier that prevents the exhaustive testing of all configurations by simply enumerating them if the effort required to do so remains acceptable. Not only this: we believe there is a lot to be learned by systematically and exhaustively testing a configurable system. In this case study, we report on the first ever endeavour to test all possible configurations of the industry-strength, open source configurable software system JHipster, a popular code generator for web applications. We built a testing scaffold for the 26,000+ configurations of JHipster using a cluster of 80 machines during 4 nights for a total of 4,376 hours (182 days) CPU time. We find that 35.70% configurations fail and we identify the feature interactions that cause the errors. We show that sampling strategies (like dissimilarity and 2-wise): (1) are more effective to find faults than the 12 default configurations used in the JHipster continuous integration; (2) can be too costly and exceed the available testing budget. We cross this quantitative analysis with the qualitative assessment of JHipster’s lead developers.</p
Local moment formation in quantum point contacts
Spin-density-functional theory of quantum point contacts (QPCs) reveals the
formation of a local moment with a net of one electron spin in the vicinity of
the point contact - supporting the recent report of a Kondo effect in a QPC.
The hybridization of the local moment to the leads decreases as the QPC becomes
longer, while the onsite Coulomb-interaction energy remains almost constant.Comment: 10 pages, 3 figures, accepted for publication in Physical Review
Letter
Kondo model for the "0.7 anomaly" in transport through a quantum point contact
Experiments on quantum point contacts have highlighted an anomalous
conductance plateau at , with features suggestive of the Kondo
effect. Here we present an Anderson model for transport through a point contact
which we analyze in the Kondo limit. Hybridization to the band increases
abruptly with energy but decreases with valence, so that the background
conductance and the Kondo temperature are dominated by different valence
transitions. This accounts for the high residual conductance above . A
spin-polarized current is predicted for Zeeman splitting .Comment: 4 page
Yo Variability! JHipster: A Playground for Web-Apps Analyses
International audienceThough variability is everywhere, there has always been a shortage of publicly available cases for assessing variability-aware tools and techniques as well as supports for teaching variability-related concepts. Historical software product lines contains industrial secrets their owners do not want to disclose to a wide audience. The open source community contributed to large-scale cases such as Eclipse, Linux kernels, or web-based plugin systems (Drupal, WordPress). To assess accuracy of sampling and prediction approaches (bugs, performance), a case where all products can be enumerated is desirable. As configuration issues do not lie within only one place but are scattered across technologies and assets, a case exposing such diversity is an additional asset. To this end, we present in this paper our efforts in building an explicit product line on top of JHipster, an industrial open-source Web-app configurator that is both manageable in terms of configurations (~ 163,000) and diverse in terms of technologies used. We present our efforts in building a variability-aware chain on top of JHipster's configurator and lessons learned using it as a teaching case at the University of Rennes. We also sketch the diversity of analyses that can be performed with our infrastructure as well as early issues found using it. Our long term goal is both to support students and researchers studying variability analysis and JHipster developers in the maintenance and evolution of their tools
Test them all, is it worth it? Assessing configuration sampling on the JHipster Web development stack
Many approaches for testing configurable software systems start from the same
assumption: it is impossible to test all configurations. This motivated the
definition of variability-aware abstractions and sampling techniques to cope
with large configuration spaces. Yet, there is no theoretical barrier that
prevents the exhaustive testing of all configurations by simply enumerating
them, if the effort required to do so remains acceptable. Not only this: we
believe there is lots to be learned by systematically and exhaustively testing
a configurable system. In this case study, we report on the first ever
endeavour to test all possible configurations of an industry-strength, open
source configurable software system, JHipster, a popular code generator for web
applications. We built a testing scaffold for the 26,000+ configurations of
JHipster using a cluster of 80 machines during 4 nights for a total of 4,376
hours (182 days) CPU time. We find that 35.70% configurations fail and we
identify the feature interactions that cause the errors. We show that sampling
strategies (like dissimilarity and 2-wise): (1) are more effective to find
faults than the 12 default configurations used in the JHipster continuous
integration; (2) can be too costly and exceed the available testing budget. We
cross this quantitative analysis with the qualitative assessment of JHipster's
lead developers.Comment: Submitted to Empirical Software Engineerin
Conductance anomalies and the extended Anderson model for nearly perfect quantum wires
Anomalies near the conductance threshold of nearly perfect semiconductor
quantum wires are explained in terms of singlet and triplet resonances of
conduction electrons with a single weakly-bound electron in the wire. This is
shown to be a universal effect for a wide range of situations in which the
effective single-electron confinement is weak. The robustness of this generic
behavior is investigated numerically for a wide range of shapes and sizes of
cylindrical wires with a bulge. The dependence on gate voltage, source-drain
voltage and magnetic field is discussed within the framework of an extended
Hubbard model. This model is mapped onto an extended Anderson model, which in
the limit of low temperatures is expected to lead to Kondo resonance physics
and pronounced many-body effects
Extreme sensitivity of the spin-splitting and 0.7 anomaly to confining potential in one-dimensional nanoelectronic devices
Quantum point contacts (QPCs) have shown promise as nanoscale spin-selective
components for spintronic applications and are of fundamental interest in the
study of electron many-body effects such as the 0.7 x 2e^2/h anomaly. We report
on the dependence of the 1D Lande g-factor g* and 0.7 anomaly on electron
density and confinement in QPCs with two different top-gate architectures. We
obtain g* values up to 2.8 for the lowest 1D subband, significantly exceeding
previous in-plane g-factor values in AlGaAs/GaAs QPCs, and approaching that in
InGaAs/InP QPCs. We show that g* is highly sensitive to confinement potential,
particularly for the lowest 1D subband. This suggests careful management of the
QPC's confinement potential may enable the high g* desirable for spintronic
applications without resorting to narrow-gap materials such as InAs or InSb.
The 0.7 anomaly and zero-bias peak are also highly sensitive to confining
potential, explaining the conflicting density dependencies of the 0.7 anomaly
in the literature.Comment: 23 pages, 7 figure
The Low-Temperature Fate of the 0.7 Structure in a Point Contact: A Kondo-like Correlated State in an Open System
Besides the usual conductance plateaus at multiples of 2e2/h, quantum point
contacts typically show an extra plateau at ~ 0.7(2e2/h), believed to arise
from electron-electron interactions that prohibit the two spin channels from
being simultaneously occupied. We present evidence that the disappearance of
the 0.7 structure at very low temperature signals the formation of a Kondo-like
correlated spin state. Evidence includes a zero-bias conductance peak that
splits in a parallel field, scaling of conductance to a modified Kondo form,
and consistency between peak width and the Kondo temperature
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