1,724,511 research outputs found
Shreyas: An organisation for Sustainable Development
Get PDF Shreyas: An organisation for Sustainable Developmen
Episode 04: From Student to Founder
No full textIn this episode, UCW Alumni Shreyas Cotha a.k.a. Mr. Bean shares his passion for coffee and how curiosity led him to launch a successful business in British Columbia that adds happiness to our mornings.
MRKT; MGMT; BUS
Connectivity Lower Bounds in Broadcast Congested Clique
Get PDFWe prove three new lower bounds for graph connectivity in the 1-bit broadcast congested clique model, BCC(1). First, in the KT-0 version of BCC(1), in which nodes are aware of neighbors only through port numbers, we show an Ω(log n) round lower bound for Connectivity even for constant-error randomized Monte Carlo algorithms. The deterministic version of this result can be obtained via the well-known "edge-crossing" argument, but, the randomized version of this result requires establishing new combinatorial results regarding the indistinguishability graph induced by inputs. In our second result, we show that the Ω(log n) lower bound result extends to the KT-1 version of the BCC(1) model, in which nodes are aware of IDs of all neighbors, though our proof works only for deterministic algorithms. This result substantially improves upon the existing Ω(log^* n) deterministic lower bound (Jurdziński et el., SIROCCO 2018) for this problem. Since nodes know IDs of their neighbors in the KT-1 model, it is no longer possible to play "edge-crossing" tricks; instead we present a reduction from the 2-party communication complexity problem Partition in which Alice and Bob are given two set partitions on [n] and are required to determine if the join of these two set partitions equals the trivial one-part set partition. While our KT-1 Connectivity lower bound holds only for deterministic algorithms, in our third result we extend this Ω(log n) KT-1 lower bound to constant-error Monte Carlo algorithms for the closely related ConnectedComponents problem. We use information-theoretic techniques to obtain this result. All our results hold for the seemingly easy special case of Connectivity in which an algorithm has to distinguish an instance with one cycle from an instance with multiple cycles. Our results showcase three rather different lower bound techniques and lay the groundwork for further improvements in lower bounds for Connectivity in the BCC(1) model
Brief Announcement: Fast and Scalable Group Mutual Exclusion
Get PDFThe group mutual exclusion (GME) problem is a generalization of the classical mutual exclusion problem in which every critical section is associated with a type or session. Critical sections belonging to the same session can execute concurrently, whereas critical sections belonging to different sessions must be executed serially. The well-known read-write mutual exclusion problem is a special case of the group mutual exclusion problem.
In a shared memory system, locks based on traditional mutual exclusion or its variants are commonly used to manage contention among processes. In concurrent algorithms based on fine-grained synchronization, a single lock is used to protect access to a small number of shared objects (e.g., a lock for every tree node) so as to minimize contention window. Evidently, a large number of shared objects in the system would translate into a large number of locks. Also, when fine-grained synchronization is used, most lock accesses are expected to be uncontended in practice.
Most existing algorithms for the solving the GME problem have high space-complexity per lock. Further, all algorithms except for one have high step-complexity in the uncontented case. This makes them unsuitable for use in concurrent algorithms based on fine-grained synchronization. In this work, we present a novel GME algorithm for an asynchronous shared-memory system that has O(1) space-complexity per GME lock when the system contains a large number of GME locks as well as O(1) step-complexity when the system contains no conflicting requests
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Brief Announcement: Clock Distribution with Gradient TRIX
Get PDFGradient clock synchronisation (GCS) algorithms minimise the worst-case clock offset between the nodes in a distributed network of diameter D and size n. They achieve optimal offsets of Θ(log D) locally, i.e. between adjacent nodes [Lenzen et al., 2010], and Θ(D) globally [Biaz and Welch, 2001]. A key open problem in this area is to achieve fault tolerance at minimal overhead in terms of the number of edges.
In this work, we achieve this goal under the assumption of an average-case distribution of faults, i.e., nodes fail with independent probability p ∈ o(n^{-1/2}). In more detail, we present a self-stabilising GCS algorithm for a grid-like directed graph with in- and out-degrees of 3. Note that even for tolerating a single fault, this degree is necessary. Moreover, the failure probability p is the largest possible ensuring the necessary condition that for each node at most one in-neighbour fails with probability 1-o(1). Our algorithm achieves asymptotically optimal local skew of Θ(log D) with probability 1-o(1); this holds under general worst-case assumptions on link delay and clock speed variations, provided they change slowly relative to the speed of the system.
On the one hand, our results are of practical interest. As we discuss with care, the fault model is suitable for synchronously clocked hardware. Since our algorithm can simultaneously sustain a constant number of arbitrary changes due to faults in each clock cycle, it achieves sufficient robustness to dramatically increase the size of synchronously clocked Systems-on-Chip.
On the other hand, our result is of a theoretical and algorithmic nature. We show that for a worst-case distribution of f 1-local faulty nodes within our fault model’s locality constraints, our algorithm achieves a local skew of O(5^flog D), while for our model with probabilistic distribution of faults the algorithm achieves O(log D). Our work raises questions for further theoretical investigation on techniques for fault tolerance and trade-offs between fault distribution and edge density of graphs
Replication Data for: Public Health Advocacy in Times of Pandemic: An Analysis of the Medicare-For-All Debate on Twitter During COVID-19
No full textReplication Data for: Public Health Advocacy in Times of Pandemic: An Analysis of the Medicare-For-All Debate on Twitter During COVID-19
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Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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