12,673 research outputs found
Bernal and the structure of water
Bernal recognised early on the importance of water in biological systems and processes, and hence the need to understand the structure of the liquid if he was to understand its biological functionality. Although the structure of crystalline ice had been solved only a few years earlier, and little was understood about the structures of liquids in general, in 1933 he published what is still regarded as a seminal paper which treated not only the structure of liquid water itself, but also addressed an impressively wide range of problems of ice and ionic solutions. Imaginatively exploiting ideas that were developing at the time, he proposed a model for water that reproduced the main features of its x-ray diffraction pattern. Despite the success of this model, however, he subsequently found it unsatisfactory – ''a delusive approach, postulating a greater degree of order in the liquid than actually exists there''. Building on the very successful ''random packing'' model of simple liquids that he developed in the 1950s and 60s, he was ultimately led to a ''random network'' model that was consistent with the known properties of the individual water molecules, and that again could reproduce a range of experimental data – but this time without the model being too ordered. Todays state of the art experiments essentially verify the underlying validity of his ideal model. And even his 1933 model of the water molecule itself is mimicked in some of the more successful molecular models used in todays computer simulations of aqueous systems
On Verifying Complex Properties using Symbolic Shape Analysis
One of the main challenges in the verification of software systems is the
analysis of unbounded data structures with dynamic memory allocation, such as
linked data structures and arrays. We describe Bohne, a new analysis for
verifying data structures. Bohne verifies data structure operations and shows
that 1) the operations preserve data structure invariants and 2) the operations
satisfy their specifications expressed in terms of changes to the set of
objects stored in the data structure. During the analysis, Bohne infers loop
invariants in the form of disjunctions of universally quantified Boolean
combinations of formulas. To synthesize loop invariants of this form, Bohne
uses a combination of decision procedures for Monadic Second-Order Logic over
trees, SMT-LIB decision procedures (currently CVC Lite), and an automated
reasoner within the Isabelle interactive theorem prover. This architecture
shows that synthesized loop invariants can serve as a useful communication
mechanism between different decision procedures. Using Bohne, we have verified
operations on data structures such as linked lists with iterators and back
pointers, trees with and without parent pointers, two-level skip lists, array
data structures, and sorted lists. We have deployed Bohne in the Hob and Jahob
data structure analysis systems, enabling us to combine Bohne with analyses of
data structure clients and apply it in the context of larger programs. This
report describes the Bohne algorithm as well as techniques that Bohne uses to
reduce the ammount of annotations and the running time of the analysis
Locating Vagueness
The claim that all vagueness must be a feature of language or thought is the current orthodoxy. This is a claim about the “location” of vagueness. “Locating Vagueness” argues that this claim is false, largely by defending the possibility of borderline cases in the absence of language and thought. If the orthodoxy about the location of vagueness is false, then so too is any account of the “nature” of vagueness that implies that orthodoxy. So this paper concludes that various accounts of the nature of vagueness are false. Among such accounts, so this paper argues, are the standard versions of supervaluationism and the standard versions of epistemicism. So I conclude that those accounts are false. Along the way, I present, and uncover ways to motivate, several heretical accounts of the nature of vagueness, including nonstandard versions of both supervaluationism and epistemicism
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Excavations and survey at Coats Hill, near Moffat, 1990-1
This report describes the results of the survey and sample excavations of small cairns,
annular structures and other remains on Coats Hill, near Moffat. The difficulties of assessing
the dates and functions of certain of the structures are discussed. The project formed
part of the archaeological studies for the North Western Ethylene Pipeline (NWEP) Project
for Shell Chemicals UK Ltd, which wholly funded the archaeological work and the publication
of this report
Polymorphic Endpoint Types for Copyless Message Passing
We present PolySing#, a calculus that models process interaction based on
copyless message passing, in the style of Singularity OS. We equip the calculus
with a type system that accommodates polymorphic endpoint types, which are a
variant of polymorphic session types, and we show that well-typed processes are
free from faults, leaks, and communication errors. The type system is
essentially linear, although linearity alone may leave room for scenarios where
well-typed processes leak memory. We identify a condition on endpoint types
that prevents these leaks from occurring.Comment: In Proceedings ICE 2011, arXiv:1108.014
Dip-coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project
The objective of this research program is to investigate the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. The past quarter demonstrated significant progress in several areas. Seeded growth of silicon-on-ceramic (SOC) with an EFG ribbon seed was demonstrated. Different types of mullite were successfully coated with silicon. A new method of deriving minority carrier diffusion length, L sub n from spectral response measurements was evaluated. ECOMOD cost projections were found to be in good agreement with the interim SAMIS method proposed by JPL. On the less positive side, there was a decrease in cell performance which we believe to be due to an unidentified source of impurities
Memory Mangement in the PoSSo Solver
AbstractA uniform general purpose garbage collector may not always provide optimal performance. Sometimes an algorithm exhibits a predictable pattern of memory usage that could be exploited, delaying as much as possible the intervention of the collector. This requires a collector whose strategy can be customized to the need of an algorithm. We present a dynamic memory management framework which allows such customization, while preserving the convenience of automatic collection in the normal case. The Customizable Memory Management (CMM) organizes memory in multiple heaps, each one encapsulating a particular storage discipline. The default heap for collectable objects uses the technique of mostly copying garbage collection, providing good performance and memory compaction. Customization of the collector is achieved through object orientation by specialising the collector methods for each heap class. We describe how the CMM has been exploited in the implementation of the Buchberger algorithm, by using a special heap for temporary objects created during polynomial reduction. The solution drastically reduces the overall cost of memory allocation in the algorithm
Incremental Network Design with Minimum Spanning Trees
Given an edge-weighted graph and a set , the
incremental network design problem with minimum spanning trees asks for a
sequence of edges minimizing
where is the weight of a minimum spanning tree
for the subgraph and . We prove that this problem can be solved by a greedy
algorithm.Comment: 9 pages, minor revision based on reviewer comment
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