4,433 research outputs found
Cross-language Wikipedia Editing of Okinawa, Japan
This article analyzes users who edit Wikipedia articles about Okinawa, Japan,
in English and Japanese. It finds these users are among the most active and
dedicated users in their primary languages, where they make many large,
high-quality edits. However, when these users edit in their non-primary
languages, they tend to make edits of a different type that are overall smaller
in size and more often restricted to the narrow set of articles that exist in
both languages. Design changes to motivate wider contributions from users in
their non-primary languages and to encourage multilingual users to transfer
more information across language divides are presented.Comment: In Proceedings of the SIGCHI Conference on Human Factors in Computing
Systems, CHI 2015. AC
Decay rate and other properties of the positronium negative ion
A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed
The complexity of 3-colouring H-colourable graphs.
We study the complexity of approximation on satisfiable instances for graph
homomorphism problems. For a fixed graph , the -colouring problem is to
decide whether a given graph has a homomorphism to . By a result of Hell and
Ne\v{s}et\v{r}il, this problem is NP-hard for any non-bipartite graph . In
the context of promise constraint satisfaction problems, Brakensiek and
Guruswami conjectured that this hardness result extends to promise graph
homomorphism as follows: fix any non-bipartite graph and another graph
with a homomorphism from to , it is NP-hard to find a homomorphism to
from a given -colourable graph. Arguably, the two most important special
cases of this conjecture are when is fixed to be the complete graph on 3
vertices (and is any graph with a triangle) and when is the complete
graph on 3 vertices (and is any 3-colourable graph). The former case is
equivalent to the notoriously difficult approximate graph colouring problem. In
this paper, we confirm the Brakensiek-Guruswami conjecture for the latter case.
Our proofs rely on a novel combination of the universal-algebraic approach to
promise constraint satisfaction, that was recently developed by Barto, Bul\'in
and the authors, with some ideas from algebraic topology.Comment: To appear in FOCS 201
Hardness of approximation for quantum problems
The polynomial hierarchy plays a central role in classical complexity theory.
Here, we define a quantum generalization of the polynomial hierarchy, and
initiate its study. We show that not only are there natural complete problems
for the second level of this quantum hierarchy, but that these problems are in
fact hard to approximate. Using these techniques, we also obtain hardness of
approximation for the class QCMA. Our approach is based on the use of
dispersers, and is inspired by the classical results of Umans regarding
hardness of approximation for the second level of the classical polynomial
hierarchy [Umans, FOCS 1999]. The problems for which we prove hardness of
approximation for include, among others, a quantum version of the Succinct Set
Cover problem, and a variant of the local Hamiltonian problem with hybrid
classical-quantum ground states.Comment: 21 pages, 1 figure, extended abstract appeared in Proceedings of the
39th International Colloquium on Automata, Languages and Programming (ICALP),
pages 387-398, Springer, 201
Lineage tree analysis of immunoglobulin variable-region gene mutations in autoimmune diseases: chronic activation, normal selection
Autoimmune diseases show high diversity in the affected organs, clinical manifestations and disease dynamics. Yet they all share common features, such as the ectopic germinal centers found in many affected tissues. Lineage trees depict the diversification, via somatic hypermutation (SHM), of immunoglobulin variable-region (IGV) genes. We previously developed an algorithm for quantifying the graphical properties of IGV gene lineage trees, allowing evaluation of the dynamical interplay between SHM and antigen-driven selection in different lymphoid tissues, species, and disease situations. Here, we apply this method to ectopic GC B cell clones from patients with Myasthenia Gravis, Rheumatoid Arthritis, and Sjögren’s Syndrome, using data scaling to minimize the effects of the large variability due to methodological differences between groups. Autoimmune trees were found to be significantly larger relative to normal controls. In contrast, comparison of the measurements for tree branching indicated that similar selection pressure operates on autoimmune and normal control clones
On k-Column Sparse Packing Programs
We consider the class of packing integer programs (PIPs) that are column
sparse, i.e. there is a specified upper bound k on the number of constraints
that each variable appears in. We give an (ek+o(k))-approximation algorithm for
k-column sparse PIPs, improving on recent results of and
. We also show that the integrality gap of our linear programming
relaxation is at least 2k-1; it is known that k-column sparse PIPs are
-hard to approximate. We also extend our result (at the loss
of a small constant factor) to the more general case of maximizing a submodular
objective over k-column sparse packing constraints.Comment: 19 pages, v3: additional detail
SACY - a Search for Associations Containing Young stars
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.Comment: 8 pages, 2 figures, to appear in the Proceedings of Open Issues in
Local Formation and Early Stellar Evolution, Ouro Preto, Brazi
- …