14,898 research outputs found
The flow of the Antarctic circumpolar current over the North Scotia Ridge
The transports associated with the Subantarctic Front (SAF) and the Polar Front (PF) account for the majority of the volume transport of the Antarctic Circumpolar Current (ACC). After passing through Drake Passage, the SAF and the PF veer northward over the steep topography of the North Scotia Ridge. Interaction of the ACC with the North Scotia Ridge influences the sources of the Malvinas Current. This ridge is a major obstacle to the flow of deep water, with the majority of the deep water passing through the 3100 m deep gap in the ridge known as Shag Rocks Passage. Volume transports associated with these fronts were measured during the North Scotia Ridge Overflow Project, which included the first extensive hydrographic survey of the ridge, carried out in April and May 2003. The total net volume transport northward over the ridge was found to be . The total net transport associated with the SAF was approximately , and the total transport associated with the PF was approximately . Weddell Sea Deep Water was not detected passing through Shag Rocks Passage, contrary to some previous inferences
Depth-4 Lower Bounds, Determinantal Complexity : A Unified Approach
Tavenas has recently proved that any n^{O(1)}-variate and degree n polynomial
in VP can be computed by a depth-4 circuit of size 2^{O(\sqrt{n}\log n)}. So to
prove VP not equal to VNP, it is sufficient to show that an explicit polynomial
in VNP of degree n requires 2^{\omega(\sqrt{n}\log n)} size depth-4 circuits.
Soon after Tavenas's result, for two different explicit polynomials, depth-4
circuit size lower bounds of 2^{\Omega(\sqrt{n}\log n)} have been proved Kayal
et al. and Fournier et al. In particular, using combinatorial design Kayal et
al.\ construct an explicit polynomial in VNP that requires depth-4 circuits of
size 2^{\Omega(\sqrt{n}\log n)} and Fournier et al.\ show that iterated matrix
multiplication polynomial (which is in VP) also requires 2^{\Omega(\sqrt{n}\log
n)} size depth-4 circuits.
In this paper, we identify a simple combinatorial property such that any
polynomial f that satisfies the property would achieve similar circuit size
lower bound for depth-4 circuits. In particular, it does not matter whether f
is in VP or in VNP. As a result, we get a very simple unified lower bound
analysis for the above mentioned polynomials.
Another goal of this paper is to compare between our current knowledge of
depth-4 circuit size lower bounds and determinantal complexity lower bounds. We
prove the that the determinantal complexity of iterated matrix multiplication
polynomial is \Omega(dn) where d is the number of matrices and n is the
dimension of the matrices. So for d=n, we get that the iterated matrix
multiplication polynomial achieves the current best known lower bounds in both
fronts: depth-4 circuit size and determinantal complexity. To the best of our
knowledge, a \Theta(n) bound for the determinantal complexity for the iterated
matrix multiplication polynomial was known only for constant d>1 by Jansen.Comment: Extension of the previous uploa
Effective cooperation influencing performance: a study in Dutch hospitals
Objective: This study focuses on cooperation between physicians and managers and aspects of that cooperation that can provide leads for interventions aimed at enhancing hospital performance. - \ud
Design: We performed a qualitative study on cooperation between physicians and managers and the influence of that cooperation on hospital performance, and structured the resulting data according to the conditions of Allport's theory on intergroup conflicts. - \ud
Setting: General hospitals in the Netherlands. - \ud
Participants: Thirty physicians (surgical and internal) and managers (strategic, tactic and operational) working in five different hospitals. - \ud
Interventions: In-depth interviews exploring the influence of cooperation between physicians and managers on hospital performance. - \ud
Main Outcome Measures: Respondents confirmed the complexity of the relationship between physicians and managers and the link between their cooperation and hospital performance. Mentioned aspects such as power and status differences, clarity in decision-making and personal click, are important in determining the effectiveness of the cooperation between physicians and managers. - \ud
Results: Our study suggests that the effectiveness of cooperation between physicians and managers is related to the uptake of quality initiatives and hospital performance. - \ud
Conclusions: The complex relationship between physicians and managers can be referred to as an intergroup conflict situation. We combined Allport's Contact theory conditions with aspects found in our study leading to the following facilitating conditions: address common goals; create interdependent tasks; arrange the support of authorities and respect the medical domain. They will enhance intra-hospital cooperation and therewith hospital performance
Sums of products of polynomials in few variables : lower bounds and polynomial identity testing
We study the complexity of representing polynomials as a sum of products of
polynomials in few variables. More precisely, we study representations of the
form such that each is
an arbitrary polynomial that depends on at most variables. We prove the
following results.
1. Over fields of characteristic zero, for every constant such that , we give an explicit family of polynomials , where
is of degree in variables, such that any
representation of the above type for with requires . This strengthens a recent result of Kayal and Saha
[KS14a] which showed similar lower bounds for the model of sums of products of
linear forms in few variables. It is known that any asymptotic improvement in
the exponent of the lower bounds (even for ) would separate VP
and VNP[KS14a].
2. We obtain a deterministic subexponential time blackbox polynomial identity
testing (PIT) algorithm for circuits computed by the above model when and
the individual degree of each variable in are at most and
for any constant . We get quasipolynomial running
time when . The PIT algorithm is obtained by combining our
lower bounds with the hardness-randomness tradeoffs developed in [DSY09, KI04].
To the best of our knowledge, this is the first nontrivial PIT algorithm for
this model (even for the case ), and the first nontrivial PIT algorithm
obtained from lower bounds for small depth circuits
Superpolynomial lower bounds for general homogeneous depth 4 arithmetic circuits
In this paper, we prove superpolynomial lower bounds for the class of
homogeneous depth 4 arithmetic circuits. We give an explicit polynomial in VNP
of degree in variables such that any homogeneous depth 4 arithmetic
circuit computing it must have size .
Our results extend the works of Nisan-Wigderson [NW95] (which showed
superpolynomial lower bounds for homogeneous depth 3 circuits),
Gupta-Kamath-Kayal-Saptharishi and Kayal-Saha-Saptharishi [GKKS13, KSS13]
(which showed superpolynomial lower bounds for homogeneous depth 4 circuits
with bounded bottom fan-in), Kumar-Saraf [KS13a] (which showed superpolynomial
lower bounds for homogeneous depth 4 circuits with bounded top fan-in) and
Raz-Yehudayoff and Fournier-Limaye-Malod-Srinivasan [RY08, FLMS13] (which
showed superpolynomial lower bounds for multilinear depth 4 circuits). Several
of these results in fact showed exponential lower bounds.
The main ingredient in our proof is a new complexity measure of {\it bounded
support} shifted partial derivatives. This measure allows us to prove
exponential lower bounds for homogeneous depth 4 circuits where all the
monomials computed at the bottom layer have {\it bounded support} (but possibly
unbounded degree/fan-in), strengthening the results of Gupta et al and Kayal et
al [GKKS13, KSS13]. This new lower bound combined with a careful "random
restriction" procedure (that transforms general depth 4 homogeneous circuits to
depth 4 circuits with bounded support) gives us our final result
Celebrity culture and public connection: bridge or chasm?
Media and cultural research has an important contribution to make to recent debates about declines in democratic engagement: is for example celebrity culture a route into democratic engagement for those otherwise disengaged? This article contributes to this debate by reviewing qualitative and quantitative findings from a UK project on 'public connection'. Using self-produced diaries (with in-depth multiple interviews) as well as a nationwide survey, the authors argue that while celebrity culture is an important point of social connection sustained by media use, it is not linked in citizens' own accounts to issues of public concern. Survey data suggest that those who particularly follow celebrity culture are the least engaged in politics and least likely to use their social networks to involve themselves in action or discussion about public-type issues. This does not mean 'celebrity culture' is 'bad', but it challenges suggestions of how popular culture might contribute to effective democracy
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