2,446 research outputs found
Viscoelastic behaviour and fracture toughness of linear-low-density polyethylene reinforced with synthetic boehmite alumina nanoparticles
Toward reliable morphology assessment of thermosets via physical etching: Vinyl ester resin as an example
The morphology of peroxide-cured, styrene crosslinked, bisphenol A-based vinyl ester (VE) resin was investigated by atomic force microscopy (AFM) after ‘physical’ etching with different methods. Etching was achieved by laser ablation, atmospheric plasma treatment and argon ion bombardment. Parameters of the etching were varied to get AFM scans of high topography resolution. VE exhibited a nanoscaled nodular structure the formation of which was ascribed to complex intra- and intermolecular reactions during crosslinking. The microstructure resolved after all the above physical etching techniques was similar provided that optimized etching and suitable AFM scanning conditions were selected. Nevertheless, with respect to the ‘morphology visualization’ these methods follow the power ranking: argon bombardment > plasma treatment > laser ablation
The Lazy Bureaucrat Scheduling Problem
We introduce a new class of scheduling problems in which the optimization is
performed by the worker (single ``machine'') who performs the tasks. A typical
worker's objective is to minimize the amount of work he does (he is ``lazy''),
or more generally, to schedule as inefficiently (in some sense) as possible.
The worker is subject to the constraint that he must be busy when there is work
that he can do; we make this notion precise both in the preemptive and
nonpreemptive settings. The resulting class of ``perverse'' scheduling
problems, which we denote ``Lazy Bureaucrat Problems,'' gives rise to a rich
set of new questions that explore the distinction between maximization and
minimization in computing optimal schedules.Comment: 19 pages, 2 figures, Latex. To appear, Information and Computatio
Do airstream mechanisms influence tongue movement paths?
Velar consonants often show an elliptical pattern of tongue movement in symmetrical vowel contexts, but the forces responsible for this remain unclear. We here consider the role of overpressure (increased intraoral air pressure) behind the constriction by examining how movement patterns are modified when speakers change from an egressive to ingressive airstream. Tongue movement and respiratory data were obtained from 3 speakers. The two airstream conditions were additionally combined with two levels of speech volume. The results showed consistent reductions in forward tongue movement during consonant closure in the ingressive conditions. Thus, overpressure behind the constriction may partly determine preferred movement patterns, but it cannot be the only influence since forward movement during closure is usually reduced but not eliminated in ingressive speech
On the toughness of thermoplastic polymer nanocomposites as assessed by the essential work of fracture (EWF) approach
The essential work of fracture (EWF) approach is widely used to determine the plane stress fracture toughness of highly ductile polymers and related systems. To shed light on how the toughness is affected by nanofillers EWF-suited model polymers, viz. amorphous copolyester and polypropylene block copolymer were modified by multiwall carbon nanotube (MWCNT), graphene (GR), boehmite alumina (BA), and organoclay (MMT) in 1 wt% each. EWF tests were performed on deeply double-edge notched tensile-loaded specimens under quasistatic loading conditions. Data reduction occurred by energy partitioning between yielding and necking/tearing. The EWF prerequisites were not met with the nanocomposites containing MWCNT and GR by contrast to those with MMT and BA. Accordingly, the toughness of nanocomposites with homogeneously dispersed and low aspect ratio fillers may be properly determined using the EWF. Results indicated that incorporation of nanofillers may result in an adverse effect between the specific essential and non-essential EWF parameters
Assessment of the effectiveness of head only and back-of-the-head electrical stunning of chickens
The study assesses the effectiveness of reversible head-only and back-of-the-head electrical stunning of chickens using 130–950 mA per bird at 50 Hz AC
Distributed Minimum Cut Approximation
We study the problem of computing approximate minimum edge cuts by
distributed algorithms. We use a standard synchronous message passing model
where in each round, bits can be transmitted over each edge (a.k.a.
the CONGEST model). We present a distributed algorithm that, for any weighted
graph and any , with high probability finds a cut of size
at most in
rounds, where is the size of the minimum cut. This algorithm is based
on a simple approach for analyzing random edge sampling, which we call the
random layering technique. In addition, we also present another distributed
algorithm, which is based on a centralized algorithm due to Matula [SODA '93],
that with high probability computes a cut of size at most
in rounds for any .
The time complexities of both of these algorithms almost match the
lower bound of Das Sarma et al. [STOC '11], thus
leading to an answer to an open question raised by Elkin [SIGACT-News '04] and
Das Sarma et al. [STOC '11].
Furthermore, we also strengthen the lower bound of Das Sarma et al. by
extending it to unweighted graphs. We show that the same lower bound also holds
for unweighted multigraphs (or equivalently for weighted graphs in which
bits can be transmitted in each round over an edge of weight ),
even if the diameter is . For unweighted simple graphs, we show
that even for networks of diameter , finding an -approximate minimum cut
in networks of edge connectivity or computing an
-approximation of the edge connectivity requires rounds
Thermal, viscoelastic and mechanical behavior of polypropylene with synthetic boehmite alumina nanoparticles
Effects of nanofiller concentration and surface treatments on the morphology, thermal, viscoelastic and mechanical behaviors of polypropylene copolymer (PP)/boehmite alumina (BA) nanocomposites were investigated. Both untreated and treated BA particles with octylsilane (OS) and with sulphonic acid compound (OS2) were added up to 10 wt% to produce nanocomposites by melt mixing followed by film blow molding and hot pressing. Dispersion of BA was studied by scanning electron microscopy. Differential scanning calorimetry and wide-angle X-ray scattering were adopted to detect changes in the crystalline structure of PP. Thermooxidative degradation of the nanocomposites was assessed by thermogravimetrical analysis. Dynamic mechanical analysis served for studying the viscoelastic, whereas quasi-static tensile, creep and Elmendorf tear tests were used to detect changes in the mechanical performance. BA nanoparticles were finely dispersed in PP up to 10 wt%, even when they were not surface modified. The resistance to thermal degradation was markedly improved by BA nanomodification. Changes observed in the mechanical properties were attributed to BA dispersion, filler/matrix interactions and related effects because the crystalline characteristics of the PP matrix practically did not change with BA modification
Globally Optimal Crowdsourcing Quality Management
We study crowdsourcing quality management, that is, given worker responses to
a set of tasks, our goal is to jointly estimate the true answers for the tasks,
as well as the quality of the workers. Prior work on this problem relies
primarily on applying Expectation-Maximization (EM) on the underlying maximum
likelihood problem to estimate true answers as well as worker quality.
Unfortunately, EM only provides a locally optimal solution rather than a
globally optimal one. Other solutions to the problem (that do not leverage EM)
fail to provide global optimality guarantees as well. In this paper, we focus
on filtering, where tasks require the evaluation of a yes/no predicate, and
rating, where tasks elicit integer scores from a finite domain. We design
algorithms for finding the global optimal estimates of correct task answers and
worker quality for the underlying maximum likelihood problem, and characterize
the complexity of these algorithms. Our algorithms conceptually consider all
mappings from tasks to true answers (typically a very large number), leveraging
two key ideas to reduce, by several orders of magnitude, the number of mappings
under consideration, while preserving optimality. We also demonstrate that
these algorithms often find more accurate estimates than EM-based algorithms.
This paper makes an important contribution towards understanding the inherent
complexity of globally optimal crowdsourcing quality management
- …