19,866 research outputs found
Understanding the truth about subjectivity
Results of two experiments show childrenâs understanding of diversity in personal preference is incomplete. Despite acknowledging diversity, in Experiment 1(N=108), 6-
and 8-year-old children were less likely than adults to see preference as a legitimate basis for personal tastes and more likely to say a single truth could be found about a matter of taste. In Experiment 2 (N=96), 7- and 9-year-olds were less likely than 11- and 13-yearolds to say a dispute about a matter of preference might not be resolved. These data suggest that acceptance of the possibility of diversity does not indicate an adult-like understanding of subjectivity. An understanding of the relative emphasis placed on objective and subjective factors in different contexts continues to develop into adolescence
SQPR: Stream Query Planning with Reuse
When users submit new queries to a distributed stream processing system (DSPS), a query planner must allocate physical resources, such as CPU cores, memory and network bandwidth, from a set of hosts to queries. Allocation decisions must provide the correct mix of resources required by queries, while achieving an efficient overall allocation to scale in the number of admitted queries. By exploiting overlap between queries and reusing partial results, a query planner can conserve resources but has to carry out more complex planning decisions. In this paper, we describe SQPR, a query planner that targets DSPSs in data centre environments with heterogeneous resources. SQPR models query admission, allocation and reuse as a single constrained optimisation problem and solves an approximate version to achieve scalability. It prevents individual resources from becoming bottlenecks by re-planning past allocation decisions and supports different allocation objectives. As our experimental evaluation in comparison with a state-of-the-art planner shows SQPR makes efficient resource allocation decisions, even with a high utilisation of resources, with acceptable overheads
Gaia Stellar Kinematics in the Head of the Orion A Cloud: Runaway Stellar Groups and Gravitational Infall
This work extends previous kinematic studies of young stars in the Head of
the Orion A cloud (OMC-1/2/3/4/5). It is based on large samples of infrared,
optical, and X-ray selected pre-main sequence stars with reliable radial
velocities and Gaia-derived parallaxes and proper motions. Stellar kinematic
groups are identified assuming they mimic the motion of their parental gas.
Several groups are found to have peculiar kinematics: the NGC 1977 cluster and
two stellar groups in the Extended Orion Nebula (EON) cavity are caught in the
act of departing their birthplaces. The abnormal motion of NGC 1977 may have
been caused by a global hierarchical cloud collapse, feedback by massive Ori
OB1ab stars, supersonic turbulence, cloud-cloud collision, and/or slingshot
effect; the former two models are favored by us. EON groups might have
inherited anomalous motions of their parental cloudlets due to small-scale
`rocket effects' from nearby OB stars. We also identify sparse stellar groups
to the east and west of Orion A that are drifting from the central region,
possibly a slowly expanding halo of the Orion Nebula Cluster. We confirm
previously reported findings of varying line-of-sight distances to different
parts of the cloud's Head with associated differences in gas velocity.
Three-dimensional movies of star kinematics show contraction of the groups of
stars in OMC-1 and global contraction of OMC-123 stars. Overall, the Head of
Orion A region exhibits complex motions consistent with theoretical models
involving hierarchical gravitational collapse in (possibly turbulent) clouds
with OB stellar feedback.Comment: Accepted for publication in MNRAS. 26 pages, 13 figures. The two 3-D
stellar kinematic movies, aimed as Supplementary Materials, can be found on
YouTube at: https://youtu.be/B4GHCVvCYfo (`restricted' sample) and
https://youtu.be/6fUu8sP0QFI (`full' sample
Approximation Algorithms for the Max-Buying Problem with Limited Supply
We consider the Max-Buying Problem with Limited Supply, in which there are
items, with copies of each item , and bidders such that every
bidder has valuation for item . The goal is to find a pricing
and an allocation of items to bidders that maximizes the profit, where
every item is allocated to at most bidders, every bidder receives at most
one item and if a bidder receives item then . Briest
and Krysta presented a 2-approximation for this problem and Aggarwal et al.
presented a 4-approximation for the Price Ladder variant where the pricing must
be non-increasing (that is, ). We present an
-approximation for the Max-Buying Problem with Limited Supply and, for
every , a -approximation for the Price Ladder
variant
Tight local approximation results for max-min linear programs
In a bipartite max-min LP, we are given a bipartite graph \myG = (V \cup I
\cup K, E), where each agent is adjacent to exactly one constraint
and exactly one objective . Each agent controls a
variable . For each we have a nonnegative linear constraint on
the variables of adjacent agents. For each we have a nonnegative
linear objective function of the variables of adjacent agents. The task is to
maximise the minimum of the objective functions. We study local algorithms
where each agent must choose based on input within its
constant-radius neighbourhood in \myG. We show that for every
there exists a local algorithm achieving the approximation ratio . We also show that this result is the best possible
-- no local algorithm can achieve the approximation ratio . Here is the maximum degree of a vertex , and
is the maximum degree of a vertex . As a methodological
contribution, we introduce the technique of graph unfolding for the design of
local approximation algorithms.Comment: 16 page
Representations and -theory of Discrete Groups
Let be a discrete group of finite virtual cohomological dimension
with certain finiteness conditions of the type satisfied by arithmetic groups.
We define a representation ring for , determined on its elements of
finite order, which is of finite type. Then we determine the contribution of
this ring to the topological -theory , obtaining an exact
formula for the difference in terms of the cohomology of the centralizers of
elements of finite order in .Comment: 4 page
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