1,479 research outputs found
Numerical and experimental study of ethanol combustion in an industrial gas turbine
The application of ethanol as a biomass-derived fuel in OPRA’s 2 MWe class OP16 radial gas turbine has been studied both numerically and experimentally. The main purpose of this work is to validate the numerical model for future work on biofuel combustion.
For the experimental investigation a modified OP16 gas turbine combustor has been used. This reverse-flow tubular combustor is a diffusion type combustor that has been adjusted to be suitable for numerical validation. Two series of ethanol burning experiments have been conducted at atmospheric pressure with a thermal input ranging from 16 to 72 kW. Exhaust gas temperature and emissions (CO, CO2, O2, NOx) were measured at various fuel flow rates while keeping the air flow rate and air temperature constant. In addition, the temperature profile of the combustor liner has been determined by applying thermochromic paint.
CFD simulations have been performed in Ansys Fluent for four different operating conditions considered in the experiments. The simulations are based on a 3D RANS code. Fuel droplets representing the fuel spray are tracked throughout the domain while they interact with the gas phase. A temperature profile based on measurements has been prescribed on the liner to account for heat transfer through the flame tube wall. Detailed combustion chemistry is included by using the steady laminar flamelet model.
The predicted levels of CO2 and O2 in the exhaust gas are in good agreement with the experimental results. The calculated and measured exhaust gas temperatures show a close match for the low power condition, but more significant deviations are observed in the higher load cases. Also, the comparison pointed out that the CFD model needs to be improved regarding the prediction of the pollutants CO and NOx.
Chemiluminescence of CH radicals in the flame front indicated that the flame extends up to the liner, suggesting the presence of fuel near the surface. However, this result was not confirmed by liner temperature measurements using thermochromic paint.</jats:p
Biomechanical Performance of Variable and Fixed Angle Locked Volar Plates for the Dorsally Comminuted Distal Radius
Background The ideal treatment strategy for the dorsally comminuted distal radius fracture continues to evolve. Newer plate designs allow for variable axis screw placement while maintaining the advantages of locked technology. The purpose of this study is to compare the biomechanical properties of one variable axis plate with two traditional locked constructs. Methods Simulated fractures were created via a distal 1 cm dorsal wedge osteotomy in radius bone analogs. The analogs were of low stiffness and rigidity to create a worst-case strength condition for the subject radius plates. This fracture-gap model was fixated using one of three different locked volar distal radius plates: a variable axis plate (Stryker VariAx) or fixed axis (DePuy DVR, Smith & Nephew Peri-Loc) designs. The constructs were then tested at physiologic loading levels in axial compression and bending (dorsal and volar) modes. Construct stiffness was assessed by fracture gap motion during the different loading conditions. As a within-study control, intact bone analogs were similarly tested. Results All plated constructs were significantly less stiff than the intact control bone models in all loading modes (p\u3c0.040). Amongst the plated constructs, the VariAx was stiffest axially (p=0.032) and the Peri-Loc was stiffest in bending (p\u3c0.024). Conclusion In this analog bone fracture gap model, the variable axis locking technology was stiffer in axial compression than other plates, though less stiff in bending
Anyone Can Become a Troll: Causes of Trolling Behavior in Online Discussions
In online communities, antisocial behavior such as trolling disrupts
constructive discussion. While prior work suggests that trolling behavior is
confined to a vocal and antisocial minority, we demonstrate that ordinary
people can engage in such behavior as well. We propose two primary trigger
mechanisms: the individual's mood, and the surrounding context of a discussion
(e.g., exposure to prior trolling behavior). Through an experiment simulating
an online discussion, we find that both negative mood and seeing troll posts by
others significantly increases the probability of a user trolling, and together
double this probability. To support and extend these results, we study how
these same mechanisms play out in the wild via a data-driven, longitudinal
analysis of a large online news discussion community. This analysis reveals
temporal mood effects, and explores long range patterns of repeated exposure to
trolling. A predictive model of trolling behavior shows that mood and
discussion context together can explain trolling behavior better than an
individual's history of trolling. These results combine to suggest that
ordinary people can, under the right circumstances, behave like trolls.Comment: Best Paper Award at CSCW 201
A Markov Chain based method for generating long-range dependence
This paper describes a model for generating time series which exhibit the
statistical phenomenon known as long-range dependence (LRD). A Markov Modulated
Process based upon an infinite Markov chain is described. The work described is
motivated by applications in telecommunications where LRD is a known property
of time-series measured on the internet. The process can generate a time series
exhibiting LRD with known parameters and is particularly suitable for modelling
internet traffic since the time series is in terms of ones and zeros which can
be interpreted as data packets and inter-packet gaps. The method is extremely
simple computationally and analytically and could prove more tractable than
other methods described in the literatureComment: 8 pages, 2 figure
Kochen-Specker Sets and Generalized Orthoarguesian Equations
Every set (finite or infinite) of quantum vectors (states) satisfies
generalized orthoarguesian equations (OA). We consider two 3-dim
Kochen-Specker (KS) sets of vectors and show how each of them should be
represented by means of a Hasse diagram---a lattice, an algebra of subspaces of
a Hilbert space--that contains rays and planes determined by the vectors so as
to satisfy OA. That also shows why they cannot be represented by a special
kind of Hasse diagram called a Greechie diagram, as has been erroneously done
in the literature. One of the KS sets (Peres') is an example of a lattice in
which 6OA pass and 7OA fails, and that closes an open question of whether the
7oa class of lattices properly contains the 6oa class. This result is important
because it provides additional evidence that our previously given proof of noa
=< (n+1)oa can be extended to proper inclusion noa < (n+1)oa and that nOA form
an infinite sequence of successively stronger equations.Comment: 16 pages and 5 figure
Iterative Plug-In Algorithms for SEMIFAR Models—Definition, Convergence, and Asymptotic Properties
Type-Decomposition of a Pseudo-Effect Algebra
The theory of direct decomposition of a centrally orthocomplete effect
algebra into direct summands of various types utilizes the notion of a
type-determining (TD) set. A pseudo-effect algebra (PEA) is a (possibly)
noncommutative version of an effect algebra. In this article we develop the
basic theory of centrally orthocomplete PEAs, generalize the notion of a TD set
to PEAs, and show that TD sets induce decompositions of centrally orthocomplete
PEAs into direct summands.Comment: 18 page
- …