28,934 research outputs found
Resenha de: Un caso de bigamia transatlántica, por Cook, A. P. & N. D. Cook (1992): Reflexões sobre o livro de A. P. Cook e N. D. Cook, Un caso de bigamia transatlántica
No full textReflections on the book written by A. P. Cook and N. D. Cook (1992) titled Un caso de bigamia transatlántica. Madrid, Anaya y Muchnik Editores. Reflexiones sobre el libro escrito por A. P. Cook y N. D. Cook (1992) titulado Un caso de bigamia transatlántica. Madrid, Anaya y Muchnik Editores. Reflexões sobre o livro de A. P. Cook e N. D. Cook (1992) intitulado Um caso de bigamia transatlântica. Madrid, Anaya e Muchnik Editores
Extrusion without a motor:a new take on the loop extrusion model of genome organization
No full textChromatin loop extrusion is a popular model for the formation of CTCF loops and topological domains. Recent HiC data have revealed a strong bias in favour of a particular arrangement of the CTCF binding motifs that stabilize loops, and extrusion is the only model to date which can explain this. However, the model requires a motor to generate the loops, and although cohesin is a strong candidate for the extruding factor, a suitable motor protein (or a motor activity in cohesin itself) has yet to be found. Here we explore a new hypothesis: that there is no motor, and thermal motion within the nucleus drives extrusion. Using theoretical modelling and computer simulations we ask whether such diffusive extrusion could feasibly generate loops. Our simulations uncover an interesting ratchet effect (where an osmotic pressure promotes loop growth), and suggest, by comparison to recent in vitro and in vivo measurements, that diffusive extrusion can in principle generate loops of the size observed in the data. Extra View on : C. A. Brackley, J. Johnson, D. Michieletto, A. N. Morozov, M. Nicodemi, P. R. Cook, and D. Marenduzzo "Non-equilibrium chromosome looping via molecular slip-links", Physical Review Letters 119 138101 (2017).</p
Efficient Interactive Proofs for Non-Deterministic Bounded Space
No full textThe celebrated IP = PSPACE Theorem gives an efficient interactive proof for any bounded-space algorithm. In this work we study interactive proofs for non-deterministic bounded space computations. While Savitch’s Theorem shows that nondeterministic bounded-space algorithms can be simulated by deterministic bounded-space algorithms, this simulation has a quadratic overhead. We give interactive protocols for nondeterministic algorithms directly to get faster verifiers.
More specifically, for any non-deterministic space S algorithm, we construct an interactive proof in which the verifier runs in time Õ(n+S²). This improves on the best previous bound of Õ(n+S³) and matches the result for deterministic space bounded algorithms, up to polylog(S) factors.
We further generalize to alternating bounded space algorithms. For any language L decided by a time T, space S algorithm that uses d alternations, we construct an interactive proof in which the verifier runs in time Õ(n + S log(T) + S d) and the prover runs in time 2^O(S). For d = O(log(T)), this matches the best known interactive proofs for deterministic algorithms, up to polylog(S) factors, and improves on the previous best verifier time for nondeterministic algorithms by a factor of log(T). We also improve the best prior verifier time for unbounded alternations by a factor of S.
Using known connections of bounded alternation algorithms to bounded depth circuits, we also obtain faster verifiers for bounded depth circuits with unbounded fan-in
Djeboa unimaculata Cook 1966
No full textDjeboa unimaculata (Cook, 1966) (Figs. 34 A–F, 40 K–L) Mideopsis (Djeboa) unimaculata Cook, 1966: 236. Material examined: Type series: FMC, Liberia; holotype female, one mile north of Suehn, stream, 30.vi. 1958, Cook (Coll. 99); paratypes: same site as holotype, 20.ii. 1958 (Coll. 96); Coll. 88, 2/0/0 (details see Cook 1966). New records: Côte d’Ivoire, River N’zi near Fetekro (F), drift day, 13.i. 1977 Statzner 0/ 1 /0 (mounted); Ghana: Namini stream, Kakum NP, 5 º 23.396 N, 1 º 23.294 W, 12.ii. 2013 Smit 1 /0/0; Ankasa River, Ankasa NP, 5 º 13.011 N, 2 º 39.126 W, 13.ii. 2013 Smit 1 /0/0; tributary of Oguntwe, Ankasa NP, 5 º 16.563 N, 2 º 38.733 W, 78 m asl., 14.ii. 2013 Smit 0/ 1 /0; Ankasa Exploration Base stream, Ankasa NP, 5 º 16.413 N, 2 º 38.810 W, 81 m asl., 14.ii. 2013 Smit 1 / 1 /0; Ankasa Exploration Base trail stream, Ankasa NP, 5 º 16.415 N, 2 º 38.751 W, 80 m asl., 14.ii. 2013 Smit 1 / 1 /0; Plunge pool, Tsatsudo Falls, 7 º 07.390 N, 0º 23.365 E, 179 m asl., 22.ii. 2013 Smit 0/ 2 /0. General features: Dorsal shield oval (L/W ratio 1.1), with medial depression; muscle scars with little pronounced thickenings, located anterior and posterior to the postocularia; colour pattern consisting of an anterior blue patch (Figs. 40 K–L); gnathosomal bay Y-shaped, noticeably narrowing in posterior half; tips of Cx-I ending posterior to frontal margin; medial margin of Cx-IV reduced to a median angle; Cx-III and -IV with a series of longitudinal striae (four or five pairs on Cx-IV). Palp (Fig. 34 D): P- 1 with a dorsal seta; P- 2 with straight ventral and convexly bowed dorsal margin; P- 3 proximally thicker than distally, ventral margin concave; P- 4 slender, equally narrowing from the base to tip. Legs: I-L (Fig. 34 E) with I-L- 6 L/H ratio 2.0– 2.3, ventral margin strongly protruding; IV-L: Fig. 34 F. Remarks: The dorsal colour pattern of D. unimaculata resembles that of D. multidentata K. Viets, 1911, but in the latter the patch is violet in colour. Furthermore, the idiosoma of D. multidentata is much smaller and proportionally narrower and the palp segments are proportionally much shorter (Cook 1966). Distribution: Liberia (Cook 1966), Côte d’Ivoire (first record), Ghana (first record).Published as part of Pešić, Vladimir, Cook, David, Gerecke, Reinhard & Smit, Harry, 2013, The water mite family Mideopsidae (Acari: Hydrachnidia): a contribution to the diversity in the Afrotropical region and taxonomic changes above species level, pp. 1-75 in Zootaxa 3720 (1) on page 58, DOI: 10.11646/zootaxa.3720.1.1, http://zenodo.org/record/28502
Trading Time and Space in Catalytic Branching Programs
No full textAn m-catalytic branching program (Girard, Koucký, McKenzie 2015) is a set of m distinct branching programs for f which are permitted to share internal (i.e. non-source non-sink) nodes. While originally introduced as a non-uniform analogue to catalytic space, this also gives a natural notion of amortized non-uniform space complexity for f, namely the smallest value |G|/m for an m-catalytic branching program G for f (Potechin 2017).
Potechin (2017) showed that every function f has amortized size O(n), witnessed by an m-catalytic branching program where m = 2^(2ⁿ-1). We recreate this result by defining a catalytic algorithm for evaluating polynomials using a large amount of space but O(n) time. This allows us to balance this with previously known algorithms which are efficient with respect to space at the cost of time (Cook, Mertz 2020, 2021). We show that for any ε ≥ 2n^(-1), every function f has an m-catalytic branching program of size O_ε(mn), where m = 2^(2^(ε n)). We similarly recreate an improved result due to Robere and Zuiddam (2021), and show that for d ≤ n and ε ≥ 2d^(-1), the same result holds for m = 2^binom(n, ≤ ε d) as long as f is a degree-d polynomial over ₂. We also show that for certain classes of functions, m can be reduced to 2^(poly n) while still maintaining linear or quasi-linear amortized size.
In the other direction, we bound the necessary length, and by extension the amortized size, of any permutation branching program for an arbitrary function between 3n and 4n-4
Where Participatory Approaches Meet Pragmatism in Funded (Health) Research: The Challenge of Finding Meaningful Spaces
No full textThe term participatory research is now widely used as a way of categorising research that has moved beyond researching "on" to researching "with" participants. This paper draws attention to some confusions that lie behind such categorisation and the potential impact of those confusions on qualitative participatory research in practice. It illuminates some of the negative effects of "fitting in" to spaces devised by other types of research and highlights the importance of forging spaces for presenting participatory research designs that suit a discursive approach and that allow the quality and impact of such research to be recognised. The main contention is that the adoption of a variety of approaches and purposes is part of the strength of participatory research but that to date the paradigm has not been sufficiently articulated. Clarifying the unifying features of the participatory paradigm and shaping appropriate ways for critique could support the embedding of participatory research into research environments, funding schemes and administration in a way that better reflects the nature and purpose of authentic involvement
Finite Element Approximations for a linear Cahn-Hilliard-Cook equation driven by the space derivative of a space-time white noise
No full textWe consider an initial- and Dirichlet boundary- value problem for
a linear Cahn-Hilliard-Cook equation, in one space dimension,
forced by the space derivative of a space-time white noise.
First, we propose an approximate regularized stochastic parabolic
problem discretizing the noise using linear splines. Then
fully-discrete approximations to the solution of the
regularized problem are constructed using, for the discretization
in space, a Galerkin finite element method based on
piecewise polynomials, and, for time-stepping, the Backward
Euler method.
Finally, we derive strong a priori estimates for the modeling error and
for the numerical approximation error to the solution of the regularized problem
cook-room
No full textcook room n[PT] They got into this fight Christmas morning; they had a cook-room down there - that's where they used to....the Jerseymen used to stay in the cook-room. (at the place near the fushing grounds where cooking was done?)DNE-cit J. D. A. WIDDOWSON JUL 1973Used I and SupUsed I and SupUsed IChecked by Jordyn Hughes on Mon 20 Jun 201
Depletion effects and loop formation in self-avoiding polymers.
No full textLangevin dynamics is employed to study the looping kinetics of self-avoiding polymers both in ideal and crowded solutions. A rich kinetics results from the competition of two crowding-induced effects: the depletion attraction and the enhanced viscous friction. For short chains, the enhanced friction slows down looping, while for longer chains, the depletion attraction renders it more frequent and persistent. We discuss the possible relevance of the findings for chromatin looping in living cells
A draught of the harbour of Hallifax and the adjacent coast in Nova Scotia [cartographic material] : survey'd by order of Commodore Spry /
No full textNautical map of Halifax harbor and coast of Nova Scotia. Depth shown by bathymetric soundings.; The cartographer of this map should not be confused with his more famous namesake, the explorer Captain James Cook (1728-1779), who mapped the east coast of Australia in 1770.; Research by Black has found three James Cooks employed by the Royal Navy in the early 1760s. (Black, Jeanette D. Two many Cooks, in The Map Collector, 1986, no. 34, pp. 10-15); "Humbly dedicated to Henry Ellis esqr. F.R.S. late governor of Nova Scotia."; Prime meridian: London.; Kershaw, Kenneth. Early printed maps of Canada, vol. 3, no. 827.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-rm430
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