33,346 research outputs found
Some properties of the dissipative model of strain-gradient plasticity
A theoretical and computational investigation is carried out of a dissipative
model of rate-independent strain-gradient plasticity and its regularization. It
is shown that the flow relation, when expressed in terms of the Cauchy stress,
is necessarily global. The most convenient approach to formulating the flow
relation is through the use of a dissipation function. It is shown, however,
that the task of obtaining the dual version, in the form of a normality
relation, is a complex one. A numerical investigation casts further light on
the response using the dissipative theory in situations of non-proportional
loading. The elastic gap, a feature reported in recent investigations, is
observed in situations in which passivation has been imposed. It is shown
computationally that the gap may be regarded as an efficient path between a
load-deformation response corresponding to micro-free boundary conditions, and
that corresponding to micro-hard boundary conditions, in which plastic strains
are set equal to zero.Comment: 26 pages, 10 figure
Imaging compaction band propagation in Diemelstadt sandstone using acoustic emission locations
We report results from a conventional triaxial test performed on a specimen of Diemelstadt sandstone under an effective confining pressure of 110 MPa; a value sufficient to induce compaction bands. The maximum principal stress was applied normal to the visible bedding so that compaction bands propagated parallel to bedding. The spatio-temporal distribution of acoustic emission events greater than 40 dB in amplitude, and associated with the propagation of the first compaction band, were located in 3D, to within +/- 2 mm, using a Hyperion Giga-RAM recorder. Event magnitudes were used to calculate the seismic b- value at intervals during band growth. Results show that compaction bands nucleate at the specimen edge and propagate across the sample at approximately 0.08 mm s(-1). The seismic b-value does not vary significantly during deformation, suggesting that compaction band growth is characterized by small scale cracking that does not change significantly in scale
Extreme value statistics of mutation accumulation in renewing cell populations
The emergence of a predominant phenotype within a cell population is often triggered by the chance accumulation of a sequence of rare genomic DNA mutations within a single cell. For example, tumors may be initiated by a single cell in which multiple mutations cooperate to bypass their natural
defense mechanism. The risk of such an event is thus determined by the extremal accumulation of mutations across tissue cells. To address this risk, here we study the statistics of the maximum mutation numbers in a generic, but tested, model of a renewing cell population. By drawing an analogy between the genealogy of a cell population and the theory of branching random walks, we obtain analytical estimates for the probability of exceeding a threshold number of mutations to trigger a proliferative advantage of a cell over its neighbors, and determine how the statistical distribution of maximum mutation numbers scales with age and cell population size.EPSR
What difference does dance make? Critical conversations across dance, physical activity and public health
Critical conversations concerning if and how dance âfitsâ within current (dominant) discourse across physical activity (PA), public health (PH) and sport policy are presented here in the form of commentaries from a âcollectiveâ research base and individual âworldviewsâ that includes the director of an established community-based dance organisation, a local authority PH commissioner and three academic researchers (a sociologist, cultural geographer and technologist). Dynamic dialogue between all parties has been encouraged throughout the research process (JanuaryâDecember 2015). From our viewpoints, discursive differences and occasional disciplinary dilemmas are regarded as potentially knowledge producing. We share transcribed parts of our critical conversations to illustrate how evaluating dance as PA represents opportunities for challenging if not disrupting some discursive terrain, whilst concurrently being somewhat constrained by that terrain. Our broader research remit contributes to ongoing debates surrounding âwhat worksâ in relation to PA. Our dynamic interactions are thus constitutive of and productive within wider circuits or discourses of policy and provision. Paradigmatic rivalry or epistemological âtensionsâ may well be hindering attempts to demonstrate that dance does have positive impacts on health. Acknowledgement and engagement with these tensions can arguably inform policy and practice in effective and meaningful ways and contribute further to debates regarding an evidence base seeking to âproveâ the benefits of activity-based programmes and interventions as we look across PA, PH and sport
Large Networks of Diameter Two Based on Cayley Graphs
In this contribution we present a construction of large networks of diameter
two and of order for every degree , based on Cayley
graphs with surprisingly simple underlying groups. For several small degrees we
construct Cayley graphs of diameter two and of order greater than of
Moore bound and we show that Cayley graphs of degrees
constructed in this paper are the largest
currently known vertex-transitive graphs of diameter two.Comment: 9 pages, Published in Cybernetics and Mathematics Applications in
Intelligent System
Exhaustive generation of -critical -free graphs
We describe an algorithm for generating all -critical -free
graphs, based on a method of Ho\`{a}ng et al. Using this algorithm, we prove
that there are only finitely many -critical -free graphs, for
both and . We also show that there are only finitely many
-critical graphs -free graphs. For each case of these cases we
also give the complete lists of critical graphs and vertex-critical graphs.
These results generalize previous work by Hell and Huang, and yield certifying
algorithms for the -colorability problem in the respective classes.
Moreover, we prove that for every , the class of 4-critical planar
-free graphs is finite. We also determine all 27 4-critical planar
-free graphs.
We also prove that every -free graph of girth at least five is
3-colorable, and determine the smallest 4-chromatic -free graph of
girth five. Moreover, we show that every -free graph of girth at least
six and every -free graph of girth at least seven is 3-colorable. This
strengthens results of Golovach et al.Comment: 17 pages, improved girth results. arXiv admin note: text overlap with
arXiv:1504.0697
X-Ray Cone Beam Tomography with Two Tilted Circular Trajectories
Recently 3-D cone-beam tomography has become of interest for the nondestructive evaluation of advanced materials. The main field of application in nondestructive testing is the evaluation of structural ceramics. Study of such materials implies high density resolution and high sensitivity to cracks. In fact, with a single circular source trajectory, when the cone-beam aperture increases, density is underestimated and cone shaped artifacts may appear at interfaces in the sample even at relatively small aperture [1â3]. These artifacts limit the thickness we can examine with a planar source trajectory. To maintain optimal reconstruction accuracy with a circular source trajectory, the angular aperture must remain within ±10°. However Kudo and Saito [4] showed that this limit can be slightly overcome by using a special interpolation of the shadow area. But to examine greater thicknesses and to maintain resolution, we must widen the cone-beam aperture thereby decreasing accuracy. To overcome these aperture limitations, Tuy [5] introduced the double circular source trajectory idea
An adaptive prefix-assignment technique for symmetry reduction
This paper presents a technique for symmetry reduction that adaptively
assigns a prefix of variables in a system of constraints so that the generated
prefix-assignments are pairwise nonisomorphic under the action of the symmetry
group of the system. The technique is based on McKay's canonical extension
framework [J.~Algorithms 26 (1998), no.~2, 306--324]. Among key features of the
technique are (i) adaptability---the prefix sequence can be user-prescribed and
truncated for compatibility with the group of symmetries; (ii)
parallelizability---prefix-assignments can be processed in parallel
independently of each other; (iii) versatility---the method is applicable
whenever the group of symmetries can be concisely represented as the
automorphism group of a vertex-colored graph; and (iv) implementability---the
method can be implemented relying on a canonical labeling map for
vertex-colored graphs as the only nontrivial subroutine. To demonstrate the
practical applicability of our technique, we have prepared an experimental
open-source implementation of the technique and carry out a set of experiments
that demonstrate ability to reduce symmetry on hard instances. Furthermore, we
demonstrate that the implementation effectively parallelizes to compute
clusters with multiple nodes via a message-passing interface.Comment: Updated manuscript submitted for revie
Genome-wide profiling of uncapped mRNA
Gene transcripts are under extensive posttranscriptional regulation, including the regulation of their
stability. A major route for mRNA degradation produces uncapped mRNAs, which can be generated by
decapping enzymes, endonucleases, and small RNAs. Profiling uncapped mRNA molecules is important for
the understanding of the transcriptome, whose composition is determined by a balance between mRNA
synthesis and degradation. In this chapter, we describe a method to profile these uncapped mRNAs at the
genome scale
Automatic dispensing cabinets and governance of controlled drugs: an exploratory study in an intensive care unit.
BACKGROUND: Governance of controlled drugs (CDs) in hospitals is resource intensive but important for patient safety and policy compliance. OBJECTIVES: To explore whether and how storing CDs in an automated dispensing cabinet (ADC) in a children's hospital intensive care unit (ICU) contributes to the effectiveness and efficiency of CD governance. METHODS: We conducted a mixed-methods exploratory study, comprising observations, interviews and audits, 3âmonths after ADC implementation. We observed 54 hours of medications activities in the ICU medication room (with 42 hours of timed data); interviewed nurses (n=19), management (n=1) and pharmacy staff (n=3); reviewed 6âmonths of ICU incident reports pertaining to CD governance; audited 6âmonths of CD register data and extracted logs of all ADC transactions for the 3âmonths following implementation. Data analysis focused on four main CD governance activities: safekeeping/controlling access, documenting use, monitoring, and reporting/investigating. RESULTS: Nurses and pharmacists perceived spending less time on CD governance tasks with the ADC. The ADC supported CD governance through automated documentation of CD transactions; 'blind counts'; automated count discrepancy checks; electronic alerts and reporting functionalities. It changed quality and distribution of governance tasks, such as removing the requirement for 'nurses with keys' to access CDs, and allowing pharmacists to generate reports remotely, rather than reviewing registers on the ward. For CDs in the ADC, auditing and monitoring appeared to be ongoing rather than periodic. Such changes appeared to create positive reinforcing loops. However, the ADC also created challenges for CD governance. Most importantly, it was not suitable for all CDs, leading to workarounds and parallel use of a safe plus paper registers. CONCLUSIONS: ADCs can significantly alter CDs governance in clinical areas. Effects of an ADC on efficiency and effectiveness of governance tasks appear to be complex, going beyond simple time savings or more stringent controls
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