1,048 research outputs found
Combining Model-Driven Design With Diverse Formal Verification
International audienceTwo historically diverse research streams are now delivering strong industrial performance in the engineering of high-integrity, software-intensive systems. The earlier of these is the use of source-language-based static analysis and formal verification. The more recent is the use of model-driven design coupled with automatic code generation. Although both have been effective, neither is without problems. Fortunately, these approaches are not mutually exclusive and combining them offers a route to ultra-high integrity at low cost. The paper exemplifies the approach by describing the combining of SPARK and SCADE and illustrating the benefits and opportunities that this brings
Climate change at the ecosystem scale: a 50-year record in New Hampshire
Observing the full range of climate change impacts at the local scale is difficult. Predicted rates of change are often small relative to interannual variability, and few locations have sufficiently comprehensive long-term records of environmental variables to enable researchers to observe the fine-scale patterns that may be important to understanding the influence of climate change on biological systems at the taxon, community, and ecosystem levels. We examined a 50-year meteorological and hydrological record from the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, an intensively monitored Long-Term Ecological Research site. Of the examined climate metrics, trends in temperature were the most significant (ranging from 0.7 to 1.3 °C increase over 40–50 year records at 4 temperature stations), while analysis of precipitation and hydrologic data yielded mixed results. Regional records show generally similar trends over the same time period, though longer-term (70–102 year) trends are less dramatic. Taken together, the results from HBEF and the regional records indicate that the climate has warmed detectably over 50 years, with important consequences for hydrological processes. Understanding effects on ecosystems will require a diversity of metrics and concurrent ecological observations at a range of sites, as well as a recognition that ecosystems have existed in a directionally changing climate for decades, and are not necessarily in equilibrium with the current climate
Cousins Of The Vendi Score: A Family Of Similarity-Based Diversity Metrics For Science And Machine Learning
Measuring diversity accurately is important for many scientific fields,
including machine learning (ML), ecology, and chemistry. The Vendi Score was
introduced as a generic similarity-based diversity metric that extends the Hill
number of order q=1 by leveraging ideas from quantum statistical mechanics.
Contrary to many diversity metrics in ecology, the Vendi Score accounts for
similarity and does not require knowledge of the prevalence of the categories
in the collection to be evaluated for diversity. However, the Vendi Score
treats each item in a given collection with a level of sensitivity proportional
to the item's prevalence. This is undesirable in settings where there is a
significant imbalance in item prevalence. In this paper, we extend the other
Hill numbers using similarity to provide flexibility in allocating sensitivity
to rare or common items. This leads to a family of diversity metrics -- Vendi
scores with different levels of sensitivity -- that can be used in a variety of
applications. We study the properties of the scores in a synthetic controlled
setting where the ground truth diversity is known. We then test their utility
in improving molecular simulations via Vendi Sampling. Finally, we use the
Vendi scores to better understand the behavior of image generative models in
terms of memorization, duplication, diversity, and sample quality.Comment: Code for evaluating diversity using the Vendi scores can be found at
https://github.com/vertaix/Vendi-Score. Code for using the scores within
Vendi Sampling can be found at https://github.com/vertaix/Vendi-Samplin
Heap Reference Analysis Using Access Graphs
Despite significant progress in the theory and practice of program analysis,
analysing properties of heap data has not reached the same level of maturity as
the analysis of static and stack data. The spatial and temporal structure of
stack and static data is well understood while that of heap data seems
arbitrary and is unbounded. We devise bounded representations which summarize
properties of the heap data. This summarization is based on the structure of
the program which manipulates the heap. The resulting summary representations
are certain kinds of graphs called access graphs. The boundedness of these
representations and the monotonicity of the operations to manipulate them make
it possible to compute them through data flow analysis.
An important application which benefits from heap reference analysis is
garbage collection, where currently liveness is conservatively approximated by
reachability from program variables. As a consequence, current garbage
collectors leave a lot of garbage uncollected, a fact which has been confirmed
by several empirical studies. We propose the first ever end-to-end static
analysis to distinguish live objects from reachable objects. We use this
information to make dead objects unreachable by modifying the program. This
application is interesting because it requires discovering data flow
information representing complex semantics. In particular, we discover four
properties of heap data: liveness, aliasing, availability, and anticipability.
Together, they cover all combinations of directions of analysis (i.e. forward
and backward) and confluence of information (i.e. union and intersection). Our
analysis can also be used for plugging memory leaks in C/C++ languages.Comment: Accepted for printing by ACM TOPLAS. This version incorporates
referees' comment
Study of Recursive Divide Architectures and Implementation for Division and Multiplication
Multipliers have been key and critical components for most application-specific and general-purpose computer architectures. However, these architectures have been transitioning towards multiple cores that can process large amounts of data through parallel approaches to computation. Unfortunately, traditional arithmetic functional units that worked well for single-core architectures have the side effect of incurring large amounts of area and power. Consequently, multi-core architecture need new ways of thinking about increased throughput to handle large amounts of data. This work discusses implementation of different divider algorithms and presents a recursive high radix divide unit that is modified to handle both multiplication and division targeted at multi-core architectures. Results are obtained with a 65nm technology and show a significant decrease in area and power while still maintaining a low total latency by utilizing high radix encoding within the functional unit.School of Electrical & Computer Engineerin
Longitudinal Eigenvibration of Multilayer Colloidal Crystals and the Effect of Nanoscale Contact Bridges
Longitudinal contact-based vibrations of colloidal crystals with a controlled
layer thickness are studied. These crystals consist of 390 nm diameter
polystyrene spheres arranged into close packed, ordered lattices with a
thickness of one to twelve layers. Using laser ultrasonics, eigenmodes of the
crystals that have out-of-plane motion are excited. The particle-substrate and
effective interlayer contact stiffnesses in the colloidal crystals are
extracted using a discrete, coupled oscillator model. Extracted stiffnesses are
correlated with scanning electron microscope images of the contacts and atomic
force microscope characterization of the substrate surface topography after
removal of the spheres. Solid bridges of nanometric thickness are found to
drastically alter the stiffness of the contacts, and their presence is found to
be dependent on the self-assembly process. Measurements of the eigenmode
quality factors suggest that energy leakage into the substrate plays a role for
low frequency modes but is overcome by disorder- or material-induced losses at
higher frequencies. These findings help further the understanding of the
contact mechanics, and the effects of disorder in three-dimensional micro- and
nano-particulate systems, and open new avenues to engineer new types of micro-
and nanostructured materials with wave tailoring functionalities via control of
the adhesive contact properties
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