5,902 research outputs found
Keeping Continuous Deliveries Safe
Allowing swift release cycles, Continuous Delivery has become popular in
application software development and is starting to be applied in
safety-critical domains such as the automotive industry. These domains require
thorough analysis regarding safety constraints, which can be achieved by formal
verification and the execution of safety tests resulting from a safety analysis
on the product. With continuous delivery in place, such tests need to be
executed with every build to ensure the latest software still fulfills all
safety requirements. Even more though, the safety analysis has to be updated
with every change to ensure the safety test suite is still up-to-date. We thus
propose that a safety analysis should be treated no differently from other
deliverables such as source-code and dependencies, formulate guidelines on how
to achieve this and advert areas where future research is needed.Comment: 4 pages, 3 figure
Climate Change and Violent Conflict in Europe over the Last Millennium
We investigate the relationship between a thousand-year history of violent conflict in Europe and various reconstructions of temperature and precipitation. We find that conflict was more intense during colder periods. This relationship is weakening over time, and is not robust to the details of the climate reconstruction or to the sample period. We thus confirm Zhang et al. (2006, Climatic Change, 76, 459-477) that, at least in temperate climates, global warming would, if anything, lead to reduced violent conflict.history, violent conflict, Europe, climate change
Simulated Annealing for JPEG Quantization
JPEG is one of the most widely used image formats, but in some ways remains
surprisingly unoptimized, perhaps because some natural optimizations would go
outside the standard that defines JPEG. We show how to improve JPEG compression
in a standard-compliant, backward-compatible manner, by finding improved
default quantization tables. We describe a simulated annealing technique that
has allowed us to find several quantization tables that perform better than the
industry standard, in terms of both compressed size and image fidelity.
Specifically, we derive tables that reduce the FSIM error by over 10% while
improving compression by over 20% at quality level 95 in our tests; we also
provide similar results for other quality levels. While we acknowledge our
approach can in some images lead to visible artifacts under large
magnification, we believe use of these quantization tables, or additional
tables that could be found using our methodology, would significantly reduce
JPEG file sizes with improved overall image quality.Comment: Appendix not included in arXiv version due to size restrictions. For
full paper go to:
http://www.eecs.harvard.edu/~michaelm/SimAnneal/PAPER/simulated-annealing-jpeg.pd
Synthesis, Characterization and Application of Phosphazenyl Phosphines
The field of uncharged phosphorus superbases was expanded to include several new mono- and bisphosphazenyl phosphines. These novel bases have been systematically analyzed according to their basicity, nucleophilicity, chemical stability, donor capabilities and coordination behavior. They complement the missing link between extremely basic trisphosphazenyl phosphines and traditional tertiary phosphines by combining the stability and steric properties of tertiary phosphines like PtBu3 with the extreme donor capabilities of phosphazenyl phosphines. The aforementioned parameters that were established during this work allow the easy classification of newly synthesized bases. Several applications of these bases were presented, as ligands in transition metal catalysis as well as organocatalysts in a variety of transformations
Consumption habits and humps : [Version 23 June 2013]
We show that the optimal consumption of an individual over the life cycle can have the hump shape (inverted U-shape) observed empirically if the preferences of the individual exhibit internal habit formation. In the absence of habit formation, an impatient individual would prefer a decreasing consumption path over life. However, because of habit formation, a high initial consumption would lead to high required consumption in the future. To cover the future required consumption, wealth is set aside, but the necessary amount decreases with age which allows consumption to increase in the early part of life. At some age, the impatience outweighs the habit concerns so that consumption starts to decrease. We derive the optimal consumption strategy in closed form, deduce sufficient conditions for the presence of a consumption hump, and characterize the age at which the hump occurs. Numerical examples illustrate our findings. We show that our model calibrates well to U.S. consumption data from the Consumer Expenditure Survey
Impact of energy dissipation on interface shapes and on rates for dewetting from liquid substrates
We revisit the fundamental problem of liquid-liquid dewetting and perform a
detailed comparison of theoretical predictions based on thin-film models with
experimental measurements obtained by atomic force microscopy (AFM).
Specifically, we consider the dewetting of a liquid polystyrene (PS) layer from
a liquid polymethyl methacrylate (PMMA) layer, where the thicknesses and the
viscosities of PS and PMMA layers are similar. The excellent agreement of
experiment and theory reveals that dewetting rates for such systems follow no
universal power law, in contrast to dewetting scenarios on solid substrates.
Our new energetic approach allows to assess the physical importance of
different contributions to the energy-dissipation mechanism, for which we
analyze the local flow fields and the local dissipation rates.Comment: 15 pages, 5 figure
Stationary solutions of liquid two-layer thin film models
We investigate stationary solutions of a thin-film model for liquid two-layer
flows in an energetic formulation that is motivated by its gradient flow
structure. The goal is to achieve a rigorous understanding of the contact-angle
conditions for such two-layer systems. We pursue this by investigating a
corresponding energy that favors the upper liquid to dewet from the lower
liquid substrate, leaving behind a layer of thickness . After proving
existence of stationary solutions for the resulting system of thin-film
equations we focus on the limit via matched asymptotic analysis.
This yields a corresponding sharp-interface model and a matched asymptotic
solution that includes logarithmic switch-back terms. We compare this with
results obtained using -convergence, where we establish existence and
uniqueness of energetic minimizers in that limit
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