303 research outputs found
Sub-structural Niching in Estimation of Distribution Algorithms
We propose a sub-structural niching method that fully exploits the problem
decomposition capability of linkage-learning methods such as the estimation of
distribution algorithms and concentrate on maintaining diversity at the
sub-structural level. The proposed method consists of three key components: (1)
Problem decomposition and sub-structure identification, (2) sub-structure
fitness estimation, and (3) sub-structural niche preservation. The
sub-structural niching method is compared to restricted tournament selection
(RTS)--a niching method used in hierarchical Bayesian optimization
algorithm--with special emphasis on sustained preservation of multiple global
solutions of a class of boundedly-difficult, additively-separable multimodal
problems. The results show that sub-structural niching successfully maintains
multiple global optima over large number of generations and does so with
significantly less population than RTS. Additionally, the market share of each
of the niche is much closer to the expected level in sub-structural niching
when compared to RTS
Effect of Rare Earth Oxides (Y2O3, Nd2O3) on Oxidation Kinetics of Al-Li base alloy
The oxidation of Al-Li base alloy containing small amounts of rare earth (RE) oxides such as Y2O3 and d2O3 particles has been studied at temperatures between 300°Cand 550°C. The lithium is selectively oxidized in Al-Li alloys and the parabolic rate constants for the growth of the resulting oxides layer Li2O, LiAl5O8, Li2CO3 and Li5AlO4 are about an order of magnitude higher than those for growth of oxides on alloy (Al-Li) with RE oxides. Alloys used in this study were prepared by melting and casting in a permanent steel mould under controlled atmosphere. It was found that 0.2%Y2O3 containing alloys possess the lowest oxidation rate and show great improvements in oxidation resistance compared to the base alloy. Oxides found on base alloy are subjected to cracking and spalling during thermal shock at high temperature i.e. 500°Cand 550°C. Identification of oxidation kinetics was carried out by using weight gain measurements while scanning electron microscopy (SEM) and x-ray diffraction analysis were used for microstructural morphologies and phase identification of the oxide scales. The weight gain measurement results suggest that the oxidation kinetic of all studied alloys follows the parabolic law in most experimental tests under the different temperatures except at 300°C oxidation kinetic follows almost a logarithmic rate law
Parallel Nonbinary LDPC Decoding on GPU
Nonbinary Low-Density Parity-Check (LDPC) codes
are a class of error-correcting codes constructed over the Galois
field GF(q) for q > 2. As extensions of binary LDPC codes,
nonbinary LDPC codes can provide better error-correcting
performance when the code length is short or moderate, but
at a cost of higher decoding complexity. This paper proposes a
massively parallel implementation of a nonbinary LDPC decoding
accelerator based on a graphics processing unit (GPU) to
achieve both great flexibility and scalability. The implementation
maps the Min-Max decoding algorithm to GPU’s massively
parallel architecture. We highlight the methodology to partition
the decoding task to a heterogeneous platform consisting of the
CPU and GPU. The experimental results show that our GPUbased
implementation can achieve high throughput while still
providing great flexibility and scalability.National Science Foundation (NSF
Dual guidance in evolutionary multi-objective optimization by localization
In this paper, we propose a framework using local models for multi-objective optimization to guide the search heuristic in both the decision and objective spaces. The localization is built using a limited number of adaptive spheres in the decision space. These spheres are usually guided, using some direction information, in the decision space towards the areas with non-dominated solutions. We use a second mechanism to adjust the spheres to specialize on different parts of the Pareto front using the guided dominance technique in the objective space. With this dual guidance, we can easily guide spheres towards different parts of the Pareto front while also exploring the decision space efficiently
Flammability action of tires material after adding flame inhibitor
Magnesium hydroxide was used as flame inhibitor to increased flame resistance for tires .Magnesium hydroxide was adding with (5%,10%) weight percents to rubber master batch of tire and then exposed the resulting material to a flame generated from gas torch with (10 mm) exposure distance . Method of measuring the surface temperature opposite to the flame was used to determine the heat transferred through tire material. The results were obtained shows enhanced flame resistance for tire by added magnesium hydroxide and this resistance increased by increasing hydroxide Percentage
Study of Corrosion Behavior of Metal Matrix Composite Based on Al-Alloy (7020) Prepared by Atomization
An experimental procedure has been fully formulated and carried out toprepare composite material of an aluminum (alloy 7020) matrix reinforced by Al2O3 particles with weight percentages of 5%, 7% and 10% and its particle size of (+53-75)μm using molten metal atomization technique. These experiments involve the preparation of aluminum matrix composite (AMCS) materials and study their Corrosion resistance in 3.5% solution of NaCl at temperature degrees 30˚C, 38˚C and 45˚C using various testing techniques. These include electrochemical corrosion and optical microscopy .The corrosion rate was found to increase as the temperature was nominally raised from 30˚C to 38˚C and 45˚C for the 10%wt of alumina in atomized AMCS samples in 3.5% NaCl solution. At a temperature of 30˚C the corrosion rate was found to rise with increasing percentages of Al2O3 particles for 5%, 7% and 10% atomized samples. This is due to galvanic corrosion between the matrix and the second phases (MgAl2O4) and (MgO) in microstructure of AMCS. Optical microscope showed a profound appearance of general corrosion in all microstructural area and grain boundaries
A STUDY EFFECT OF SOME VARIABLES IN TIG SPOT WELDING FOR (ALUMINUM – MAGNESIUM) ALLOY
The present work investigates the effect of some of the variables in spot tungsten inert gas shielded
welding (TIG Spot) for (Aluminum-Magnesium) alloy type(5052-O) which is non–heat treatable
alloy for its wide industrial uses and applications in field of welding technology.
TIG Spot welding was performed by using tungsten electrode (EWTh2)of diameter (3.2mm) and
DC current with direct polarity (DCSP) at constant shielded gas flow rate (15litre/min).
The welded specimens were tested by using the Instron machine to determine the maximum shear
force (shear strength ) of spot welded and to define the optimum conditions of spot welding
variables in relation to the weld current, weld time and arc length of welding to produce an
acceptable weld. The metallurgical changes of the weld zone and heat affected zone were studied
under optimum conditions of welding.
It has been shown that the increase in the welding current and welding time tends to increase the
maximum shear force and it reaches maximum value and then decreases with high currents and
long times. The maximum shear force was 2.4KN at welding current of (90) Amp , welding time
( 7)sec and arc length (1.6mm ) for 1mm thickness.
It was also found that the highest value of hardness ( 53.5 Hv) was at the center of the spot welded
and decreases gradually from the center of the weld spot towards the base metal
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