1,084 research outputs found
Positron states at vacancy-impurity pairs in semiconductors
Positron states at pure monovacancies and divacancies and vacancy-phosphorus pairs in Si as well as at As vacancies and As-vacancy–As-antisite pairs in GaAs are calculated. The dependence of the positron lifetime on the lattice relaxation around the defects is studied, and the effects related to the screening of positrons are discussed. The calculations are based on superimposing free atoms. The ability of the method to describe positron states at charged defects is demonstrated.Peer reviewe
Composite repetition-aware data structures
In highly repetitive strings, like collections of genomes from the same
species, distinct measures of repetition all grow sublinearly in the length of
the text, and indexes targeted to such strings typically depend only on one of
these measures. We describe two data structures whose size depends on multiple
measures of repetition at once, and that provide competitive tradeoffs between
the time for counting and reporting all the exact occurrences of a pattern, and
the space taken by the structure. The key component of our constructions is the
run-length encoded BWT (RLBWT), which takes space proportional to the number of
BWT runs: rather than augmenting RLBWT with suffix array samples, we combine it
with data structures from LZ77 indexes, which take space proportional to the
number of LZ77 factors, and with the compact directed acyclic word graph
(CDAWG), which takes space proportional to the number of extensions of maximal
repeats. The combination of CDAWG and RLBWT enables also a new representation
of the suffix tree, whose size depends again on the number of extensions of
maximal repeats, and that is powerful enough to support matching statistics and
constant-space traversal.Comment: (the name of the third co-author was inadvertently omitted from
previous version
Suffix Tree of Alignment: An Efficient Index for Similar Data
We consider an index data structure for similar strings. The generalized
suffix tree can be a solution for this. The generalized suffix tree of two
strings and is a compacted trie representing all suffixes in and
. It has leaves and can be constructed in time.
However, if the two strings are similar, the generalized suffix tree is not
efficient because it does not exploit the similarity which is usually
represented as an alignment of and .
In this paper we propose a space/time-efficient suffix tree of alignment
which wisely exploits the similarity in an alignment. Our suffix tree for an
alignment of and has leaves where is the sum of
the lengths of all parts of different from and is the sum of the
lengths of some common parts of and . We did not compromise the pattern
search to reduce the space. Our suffix tree can be searched for a pattern
in time where is the number of occurrences of in and
. We also present an efficient algorithm to construct the suffix tree of
alignment. When the suffix tree is constructed from scratch, the algorithm
requires time where is the sum of the lengths
of other common substrings of and . When the suffix tree of is
already given, it requires time.Comment: 12 page
Developing LCA-based benchmarks for sustainable consumption - for and with users
This article presents the development process of a consumer-oriented, illustrative benchmarking tool enabling consumers to use the results of environmental life cycle assessment (LCA) to make informed decisions. Active and environmentally conscious consumers and environmental communicators were identified as key target groups for this type of information. A brochure presenting the benchmarking tool was developed as an participatory, iterative process involving consumer focus groups, stakeholder workshops and questionnaire-based feedback. In addition to learning what works and what does not, detailed suggestions on improved wording and figures were obtained, as well as a wealth of ideas for future applications
Screening of positrons in semiconductors and insulators
Theoretical models are presented for the enhancement of the electron density at a positron in a semiconductor or insulator host. The model better suited for typical semiconductors is based on the many-body theory for the screening of a positron in electron gas. The starting point of the model for insulators is the atomic polarizability. The common parameter in both models is the high-frequency dielectric constant. Moreover, the enhancement depends on the ambient electron density in the semiconductor model and on the unit-cell volume in the insulator model. With use of the models developed, positron lifetimes in perfect semiconductor and insulator crystals have been calculated. In the calculations, three-dimensional electron densities and electrostatic potentials are obtained by atomic superposition and the fully three-dimensional positron wave functions are solved by a relaxation method. The calculated positron lifetimes agree with the experimental ones within a few picoseconds. Moreover, we have used the model to predict lifetimes of positrons trapped by lattice defects such as vacancies and vacancy clusters.Peer reviewe
Intraoperative Complications and Mid-Term Follow-Up of Large-Diameter Head Metal-on-Metal Total Hip Arthroplasty and Hip Resurfacing Arthroplasty
Background and Aims: Large-diameter head total hip arthroplasty and hip resurfacing arthroplasty were popular in Finland from 2000 to 2012 for the treatment of hip osteoarthritis. The aim of this retrospective study was to investigate the mid-term survival of large-diameter head total hip arthroplasty patients operated on in three university hospitals and to compare these results to the survival of hip resurfacing arthroplasty patients. Material and Methods: A total of 3860 hip arthroplasties (3029 large-diameter head total hip arthroplasties in 2734 patients and 831 hip resurfacing arthroplasties in 757 patients) were operated on between January 2004 and December 2009. The mean follow-up was 4.3years (range: 0.3-8.0years) in the total hip arthroplasty group and 5.1years (range: 1.7-7.9years) in the hip resurfacing arthroplasty group. Cox multiple regression model and Kaplan-Meier survival analysis were used to study the survival of the total hip arthroplasties and the hip resurfacing arthroplasties. Intraoperative complications and reasons for revisions were also evaluated. Results: In Cox regression analysis, the hazard ratio for revision of hip resurfacing arthroplasty was 1.5 compared with large-diameter head total hip arthroplasty (95% confidence interval: 1.0-2.2) (p=0.029). The cumulative Kaplan-Meier survival rate was 90.7% at 7.7years for the large-diameter head total hip arthroplasty (95% confidence interval: 86.8-94.6) and 92.2% at 7.6years for hip resurfacing arthroplasty (95% confidence interval: 89.9-94.6). There were a total of 166/3029 (5.5%) intraoperative complications in the large-diameter head total hip arthroplasty group and 20/831 (2.4%) in the hip resurfacing arthroplasty group (p=0.001). Revision for any reason was performed on 137/3029 (4.5%) of the arthroplasties in the large-diameter head total hip arthroplasty group and 52/831 (6.3%) in the hip resurfacing arthroplasty group (p=0.04). Conclusion: The mid-term survival of both of these devices was poor, and revisions due to adverse reactions to metal debris will most likely rise at longer follow-up. There were more intraoperative complications in the large-diameter head total hip arthroplasty group than in the hip resurfacing arthroplasty group.Peer reviewe
Quasiparticle scattering measurements of laminar and turbulent vortex flow in the spin-down of superfluid 3He-B
The dynamics of quantized vortices is studied in superfluid 3He-B after a
rapid stop of rotation. We use Andreev reflection of thermal excitations to
monitor vortex motion with quartz tuning fork oscillators in two different
experimental setups at temperatures below 0.2Tc. Deviations from ideal
cylindrical symmetry in the flow environment cause the early decay to become
turbulent. This is identified from a rapid initial overshoot in the vortex
density above the value before the spin-down and its subsequent decay with a
t^(-3/2) time dependence. The high polarization of the vortices along the
rotation axis significantly suppresses the effective turbulent kinematic
viscosity below the values reported for more homogeneous turbulence and leads
to a laminar late-time response. The vortex dissipation down to T < 0.15Tc is
determined from the precession frequency of the polarized vortex configuration.
In the limit of vanishing normal component density, the laminar dissipation is
found to approach a temperature-independent value, whose origin is currently
under discussion.Comment: 8 pages, 5 figure
Compressed Data Structures for Dynamic Sequences
We consider the problem of storing a dynamic string over an alphabet
in compressed form. Our representation
supports insertions and deletions of symbols and answers three fundamental
queries: returns the -th symbol in ,
counts how many times a symbol occurs among the
first positions in , and finds the position
where a symbol occurs for the -th time. We present the first
fully-dynamic data structure for arbitrarily large alphabets that achieves
optimal query times for all three operations and supports updates with
worst-case time guarantees. Ours is also the first fully-dynamic data structure
that needs only bits, where is the -th order
entropy and is the string length. Moreover our representation supports
extraction of a substring in optimal time
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