Parameterized Distributed Algorithms

In this work, we initiate a thorough study of graph optimization problems parameterized by the output size in the distributed setting. In such a problem, an algorithm decides whether a solution of size bounded by k exists and if so, it finds one. We study fundamental problems, including Minimum Vertex Cover (MVC), Maximum Independent Set (MaxIS), Maximum Matching (MaxM), and many others, in both the LOCAL and CONGEST distributed computation models. We present lower bounds for the round complexity of solving parameterized problems in both models, together with optimal and near-optimal upper bounds. Our results extend beyond the scope of parameterized problems. We show that any LOCAL (1+epsilon)-approximation algorithm for the above problems must take Omega(epsilon^{-1}) rounds. Joined with the (epsilon^{-1}log n)^{O(1)} rounds algorithm of [Ghaffari et al., 2017] and the Omega (sqrt{(log n)/(log log n)}) lower bound of [Fabian Kuhn et al., 2016], the lower bounds match the upper bound up to polynomial factors in both parameters. We also show that our parameterized approach reduces the runtime of exact and approximate CONGEST algorithms for MVC and MaxM if the optimal solution is small, without knowing its size beforehand. Finally, we propose the first o(n^2) rounds CONGEST algorithms that approximate MVC within a factor strictly smaller than 2

The effect of different post-exercise beverages with food on ad libitum fluid recovery, nutrient provision, and subsequent athletic performance

This study investigated the effect of consuming either water or a carbohydrate (CHO)-electrolyte sports beverage (‘Sports Drink’) ad libitum with food during a 4 h post-exercise recovery period on fluid restoration, nutrient provision and subsequent endurance cycling performance. On two occasions, 16 endurance-trained cyclists; 8 male [M] (age: 31 ± 9 y; VO2max: 54 ± 6 mL·kg−1·min−1) and 8 female [F] (age: 33 ± 8 y; VO2max: 50 ± 7 mL·kg−1·min−1); lost 2.3 ± 0.3% and 1.6 ± 0.3% of their body mass (BM), respectively during 1 h of fixed-intensity cycling. Participants then had ad libitum access to either Water or Sports Drink and food for the first 195 min of a 4 h recovery period. At the conclusion of the recovery period, participants completed a cycling performance test consisting of a 45 min fixed-intensity pre-load and an incremental test to volitional exhaustion (peak power output, PPO). Beverage intake; total water/nutrient intake; and indicators of fluid recovery (BM, urine output, plasma osmolality [POSM]) were assessed periodically throughout trials. Participants returned to a similar state of net positive fluid balance prior to recommencing exercise, regardless of the beverage provided (Water: +0.4 ± 0.5 L; Sports Drink: +0.3 ± 0.3 L, p = 0.529). While Sports Drink increased post-exercise energy (M: +1.8 ± 1.0 MJ; F: +1.3 ± 0.5 MJ) and CHO (M: +114 ± 31 g; F: +84 ± 25 g) intake (i.e. total from food and beverage) (p's < 0.001), this did not improve subsequent endurance cycling performance (Water: 337 ± 40 W [M] and 252 ± 50 W [F]; Sports Drink: 340 ± 40 W [M] and 258 ± 47 W [F], p = 0.242). Recovery beverage recommendations should consider the post-exercise environment (i.e. the availability of food), an individual's tolerance for food and fluid pre−/post-exercise, the immediate requirements for refuelling (i.e. CHO demands of the activity) and the athlete's overall dietary goals.Full Tex

Optimal Distributed Covering Algorithms

We present a time-optimal deterministic distributed algorithm for approximating a minimum weight vertex cover in hypergraphs of rank f. This problem is equivalent to the Minimum Weight Set Cover problem in which the frequency of every element is bounded by f. The approximation factor of our algorithm is (f+epsilon). Let Delta denote the maximum degree in the hypergraph. Our algorithm runs in the congest model and requires O(log{Delta} / log log Delta) rounds, for constants epsilon in (0,1] and f in N^+. This is the first distributed algorithm for this problem whose running time does not depend on the vertex weights nor the number of vertices. Thus adding another member to the exclusive family of provably optimal distributed algorithms. For constant values of f and epsilon, our algorithm improves over the (f+epsilon)-approximation algorithm of [Fabian Kuhn et al., 2006] whose running time is O(log Delta + log W), where W is the ratio between the largest and smallest vertex weights in the graph. Our algorithm also achieves an f-approximation for the problem in O(f log n) rounds, improving over the classical result of [Samir Khuller et al., 1994] that achieves a running time of O(f log^2 n). Finally, for weighted vertex cover (f=2) our algorithm achieves a deterministic running time of O(log n), matching the randomized previously best result of [Koufogiannakis and Young, 2011]. We also show that integer covering-programs can be reduced to the Minimum Weight Set Cover problem in the distributed setting. This allows us to achieve an (f+epsilon)-approximate integral solution in O((1+f/log n)* ((log Delta)/(log log Delta) + (f * log M)^{1.01}* log epsilon^{-1}* (log Delta)^{0.01})) rounds, where f bounds the number of variables in a constraint, Delta bounds the number of constraints a variable appears in, and M=max {1, ceil[1/a_{min}]}, where a_{min} is the smallest normalized constraint coefficient. This improves over the results of [Fabian Kuhn et al., 2006] for the integral case, which combined with rounding achieves the same guarantees in O(epsilon^{-4}* f^4 * log f * log(M * Delta)) rounds

Time to failure prediction in rubber components subjected to thermal ageing: A combined approach based upon the intrinsic defect concept and the fracture mechanics

In this contribution, we attempt to derive a tool allowing the prediction of the stretch ratioat failure in rubber components subjected to thermal ageing. To achieve this goal, the mainidea is to combine the fracture mechanics approach and the intrinsic defect concept. Using an accelerated ageing procedure for an Ethylene–Propylene–Diene Monomer (EPDM), it is first shown that the average molar mass of the elastically active chains (i.e. between crosslinks) can be used as the main indicator of the macromolecular network degradation. Byintroducing the time–temperature equivalence principle, a shift factor obeying to an Arrhenius law is derived, and master curves are built as well for the average molar mass as for the ultimate mechanical properties. Fracture mechanics tests are also achieved and the square root dependence of the fracture energy with the average molar mass is pointed out. Moreover, it is shown that the mechanical response could be approximated by the phantom network theory, which allows to relate the strain energy density function to the average molar mass. Assuming that the fracture of a smooth specimen is the consequence of a virtual intrinsic defect whose the size can be easily estimated, the stretch ratio at break can be therefore computed for any thermal ageing condition. The estimated values are found in a very nice agreement with EPDM experimental data, making this approach a useful tool when designing rubber components for moderate to high temperature environments

Web Crippling Behaviour of Channels with Flanges Restrained

The paper presents a comparison of web crippling tests of cold-formed unlipped channels with flanges restrained or unrestrained. The tests were performed under end and interior two-flange loading conditions specified in the Australian/New Zealand Standard (AS/NZS 4600, 1996) and the American Iron and Steel Institute (AISI, 1996) Specification for cold-formed steel structures, namely End-Two-Flange (ETF) and Interior-Two-Flange (ITF) loading conditions. The concentrated load was applied by a bearing plate at the top flange of the channels, and the reaction force applied by an identical bearing plate at the bottom flange of the channels. The bearing plates acted across the full flange widths of the channels. The flanges of the channels were bolted to the bearing plates for the specimens with flanges restrained. The web crippling test strengths are compared with the current design strengths obtained using the AS/NZS 4600 and the AISI Specification. It is shown that the design strengths predicted by the specifications are unconservative for the tested channels with flanges restrained or unrestrained

Web Crippling Behaviour of Cold-formed Unlipped Channels

An experimental investigation of cold-formed unlipped channels subject to web crippling is described. The tests were carried out under four loading conditions according to the AISI Specification, namely End-One-Flange (EOF), Interior-One-Flange (IOF), End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loading. The concentrated load or reaction forces were applied by means of bearing plates which acted across the full flange widths of the channels. The web crippling test results are compared with the American Iron and Steel Institute (AISI 1996) Specification and the Australian/New Zealand Standard (AS/NZS 4600-1996) for cold-formed steel structures. The design web crippling strength predictions given by the specifications have been found to be very unconservative for the unlipped channel sections tested. In this paper, simple plastic mechanism formulae for web crippling strength of unlipped channels are proposed

All-optical hyperpolarization of electron and nuclear spins in diamond

Low thermal polarization of nuclear spins is a primary sensitivity limitation for nuclear magnetic resonance. Here we demonstrate optically pumped (microwave-free) nuclear spin polarization of $^{13}\mathrm{C}$ and $^{15}\mathrm{N}$ in $^{15}\mathrm{N}$-doped diamond. $^{15}\mathrm{N}$ polarization enhancements up to $-2000$ above thermal equilibrium are observed in the paramagnetic system $\mathrm{N_s}^{0}$. Nuclear spin polarization is shown to diffuse to bulk $^{13}\mathrm{C}$ with NMR enhancements of $-200$ at room temperature and $-500$ at $\mathrm{240~K}$, enabling a route to microwave-free high-sensitivity NMR study of biological samples in ambient conditions.Comment: 5 pages, 5 figure

Does Neuronal Synchrony Underlie Visual Feature Grouping?

SummaryPrevious research suggests that synchronous neural activity underlies perceptual grouping of visual image features. The generality of this mechanism is unclear, however, as previous studies have focused on pairs of neurons with overlapping or collinear receptive fields. By sampling more broadly and employing stimuli that contain partially occluded objects, we have conducted a more incisive test of the binding by synchrony hypothesis in area MT. We find that synchrony in spiking activity shows little dependence on feature grouping, whereas gamma band synchrony in field potentials can be significantly stronger when features are grouped. However, these changes in gamma band synchrony are small relative to the variability of synchrony across recording sites and do not provide a robust population signal for feature grouping. Moreover, these effects are reduced when stimulus differences nearby the receptive fields are eliminated using partial occlusion. Our findings suggest that synchrony does not constitute a general mechanism of visual feature binding