118 research outputs found
Consensus in Networks Prone to Link Failures
We consider deterministic distributed algorithms solving Consensus in
synchronous networks of arbitrary topologies. Links are prone to failures.
Agreement is understood as holding in each connected component of a network
obtained by removing faulty links. We introduce the concept of stretch, which
is a function of the number of connected components of a network and their
respective diameters. Fast and early-stopping algorithms solving Consensus are
defined by referring to stretch resulting in removing faulty links. We develop
algorithms that rely only on nodes knowing their own names and the ability to
associate communication with local ports. A network has nodes and it starts
with functional links. We give a general algorithm operating in time
that uses messages of bits. If we additionally restrict executions
to be subject to a bound on stretch, then there is a fast algorithm
solving Consensus in time using messages of bits. Let
be an unknown stretch occurring in an execution; we give an algorithm
working in time and using messages of bits. We
show that Consensus can be solved in the optimal time, but at the
cost of increasing message size to . We also demonstrate how to
solve Consensus by an algorithm that uses only non-faulty links and
works in time , while nodes start with their ports mapped to neighbors
and messages carry bits. We prove lower bounds on performance of
Consensus solutions that refer to parameters of evolving network topologies and
the knowledge available to nodes
Fast Agreement in Networks with Byzantine Nodes
We study Consensus in synchronous networks with arbitrary connected topologies. Nodes may be faulty, in the sense of either Byzantine or proneness to crashing. Let t denote a known upper bound on the number of faulty nodes, and D_s denote a maximum diameter of a network obtained by removing up to s nodes, assuming the network is (s+1)-connected. We give an algorithm for Consensus running in time t + D_{2t} with nodes subject to Byzantine faults. We show that, for any algorithm solving Consensus for Byzantine nodes, there is a network G and an execution of the algorithm on this network that takes ?(t + D_{2t}) rounds. We give an algorithm solving Consensus in t + D_{t} communication rounds with Byzantine nodes using authenticated messages of polynomial size. We show that for any numbers t and d > 4, there exists a network G and an algorithm solving Consensus with Byzantine nodes using authenticated messages in fewer than t + 3 rounds on G, but all algorithms solving Consensus without message authentication require at least t + d rounds on G. This separates Consensus with Byzantine nodes from Consensus with Byzantine nodes using message authentication, with respect to asymptotic time performance in networks of arbitrary connected topologies, which is unlike complete networks. Let f denote the number of failures actually occurring in an execution and unknown to the nodes. We develop an algorithm solving Consensus against crash failures and running in time ?(f + D_{f}), assuming only that nodes know their names and can differentiate among ports; this algorithm is also communication-efficient, by using messages of size ?(mlog n), where n is the number of nodes and m is the number of edges. We give a lower bound t+D_t-2 on the running time of any deterministic solution to Consensus in (t+1)-connected networks, if t nodes may crash
Optimal Algorithms for Free Order Multiple-Choice Secretary
Suppose we are given integer and boxes labeled
by an adversary, each containing a number chosen from an unknown distribution.
We have to choose an order to sequentially open these boxes, and each time we
open the next box in this order, we learn its number. If we reject a number in
a box, the box cannot be recalled. Our goal is to accept the largest of
these numbers, without necessarily opening all boxes. This is the free order
multiple-choice secretary problem. Free order variants were studied extensively
for the secretary and prophet problems. Kesselheim, Kleinberg, and Niazadeh KKN
(STOC'15) initiated a study of randomness-efficient algorithms (with the
cheapest order in terms of used random bits) for the free order secretary
problems.
We present an algorithm for free order multiple-choice secretary, which is
simultaneously optimal for the competitive ratio and used amount of randomness.
I.e., we construct a distribution on orders with optimal entropy
such that a deterministic multiple-threshold algorithm is
-competitive. This improves in three ways the previous
best construction by KKN, whose competitive ratio is .
Our competitive ratio is (near)optimal for the multiple-choice secretary
problem; it works for exponentially larger parameter ; and our algorithm is
a simple deterministic multiple-threshold algorithm, while that in KKN is
randomized. We also prove a corresponding lower bound on the entropy of optimal
solutions for the multiple-choice secretary problem, matching entropy of our
algorithm, where no such previous lower bound was known.
We obtain our algorithmic results with a host of new techniques, and with
these techniques we also improve significantly the previous results of KKN
about constructing entropy-optimal distributions for the classic free order
secretary
The great ephemeral tattooed skin
The skin is always and already a series of planes which signify race, gender, age and such. Tattooing creates a new surface of potential significance upon the body. Tattooing can call into question concepts of volition in reference to the power to inscribe and define one’s subjectivity through one’s own skin, and the social defining of the subject. Skin is the involution or event between subject and object, will and cultural inscription, the social and the self. Feminism, particularly corporeal feminists, have attempted to think ways in which the female flesh may be recognized and self-defined without risking essentialism through reification of the meaning of ‘woman’s body’. Thinking the tattooed female body thus resonates with some of the risks and benefits feminism has found in theorizing a marginalized body. Using Deleuze, Guattari, Lyotard and other major influences on corporeal feminists this article explores ways in which significance is sought in skin and possible configurations of skin and world which challenge the desire to read the flesh as a legible incarnation of subjectivity
Feminist phenomenology and the woman in the running body
Modern phenomenology, with its roots in Husserlian philosophy, has been taken up and utilised in a myriad of ways within different disciplines, but until recently has remained relatively under-used within sports studies. A corpus of sociological-phenomenological work is now beginning to develop in this domain, alongside a longer standing literature in feminist phenomenology. These specific social-phenomenological forms explore the situatedness of lived-body experience within a particular social structure. After providing a brief overview of key strands of phenomenology, this article considers some of the ways in which sociological, and particularly feminist phenomenology, might be used to analyse female sporting embodiment. For illustrative purposes, data from an autophenomenographic project on female distance running are also included, in order briefly to demonstrate the application of phenomenology within sociology, as both theoretical framework and methodological approach
Identification of Novel Pathogenicity Loci in Clostridium perfringens Strains That Cause Avian Necrotic Enteritis
Type A Clostridium perfringens causes poultry necrotic enteritis (NE), an enteric disease of considerable economic importance, yet can also exist as a member of the normal intestinal microbiota. A recently discovered pore-forming toxin, NetB, is associated with pathogenesis in most, but not all, NE isolates. This finding suggested that NE-causing strains may possess other virulence gene(s) not present in commensal type A isolates. We used high-throughput sequencing (HTS) technologies to generate draft genome sequences of seven unrelated C. perfringens poultry NE isolates and one isolate from a healthy bird, and identified additional novel NE-associated genes by comparison with nine publicly available reference genomes. Thirty-one open reading frames (ORFs) were unique to all NE strains and formed the basis for three highly conserved NE-associated loci that we designated NELoc-1 (42 kb), NELoc-2 (11.2 kb) and NELoc-3 (5.6 kb). The largest locus, NELoc-1, consisted of netB and 36 additional genes, including those predicted to encode two leukocidins, an internalin-like protein and a ricin-domain protein. Pulsed-field gel electrophoresis (PFGE) and Southern blotting revealed that the NE strains each carried 2 to 5 large plasmids, and that NELoc-1 and -3 were localized on distinct plasmids of sizes ∼85 and ∼70 kb, respectively. Sequencing of the regions flanking these loci revealed similarity to previously characterized conjugative plasmids of C. perfringens. These results provide significant insight into the pathogenetic basis of poultry NE and are the first to demonstrate that netB resides in a large, plasmid-encoded locus. Our findings strongly suggest that poultry NE is caused by several novel virulence factors, whose genes are clustered on discrete pathogenicity loci, some of which are plasmid-borne
Challenging Masculinity in CSR Disclosures: Silencing of Women’s Voices in Tanzania’s Mining Industry
This paper presents a feminist analysis of corporate social responsibility (CSR) in a male-dominated industry within a developing country context. It seeks to raise awareness of the silencing of women’s voices in CSR reports produced by mining companies in Tanzania. Tanzania is one of the poorest countries in Africa, and women are often marginalised in employment and social policy considerations. Drawing on work by Hélène Cixous, a post-structuralist/radical feminist scholar, the paper challenges the masculinity of CSR discourses that have repeatedly masked the voices and concerns of ‘other’ marginalised social groups, notably women. Using interpretative ethnographic case studies, the paper provides much-needed empirical evidence to show how gender imbalances remain prevalent in the Tanzanian mining sector. This evidence draws attention to the dynamics faced by many women working in or living around mining areas in Tanzania. The paper argues that CSR, a discourse enmeshed with the patriarchal logic of the contemporary capitalist system, is entangled with tensions, class conflicts and struggles which need to be unpacked and acknowledged. The paper considers the possibility of policy reforms in order to promote gender balance in the Tanzanian mining sector and create a platform for women’s concerns to be voiced
Transgenesis in Animal Agriculture: Addressing Animal Health and Welfare Concerns
The US Food and Drug Administration’s final Guidance for Industry on the regulation of transgenesis in animal agriculture has paved the way for the commercialization of genetically engineered (GE) farm animals. The production-related diseases associated with extant breeding technologies are reviewed, as well as the predictable welfare consequences of continued emphasis on prolificacy at the potential expense of physical fitness. Areas in which biotechnology could be used to improve the welfare of animals while maintaining profitability are explored along with regulatory schema to improve agency integration in GE animal oversight
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