Antibacterial action of chitosan

The antibacterial action of chitosan hydroglutamate (CH), chitosan lactate (CL) and chitosan derived from fungal mycelia was examined against both gram‐negative and gram‐positive bacteria. Plate counts indicated inactivation rates of one‐ to five‐log‐cycles within one hour. Fungal chitosan had significantly less antibiotic effect than CH and CL. The antibacterial action of CH and CL was very similar and shown to be concentration dependent with 0.1 mg/mL more effective than 2.0 and 5.0 mg/mL. When CH (or CL) and polygalacturonate were added to cell suspensions, death was prevented, possibly indicating that chitosan complexed with polygalacturonate could not penetrate the cell or disrupt the membrane. Leakage of intracellular components caused by chitosan was determined by exposing lactose‐induced Escherichia coli to chitosan with assay for ß‐galactosidase activity indicating that cell permeabilization occurred more extensively at the low chitosan concentrations. Microscopic examination showed that chitosan caused cell agglutination at pH 5.8. Injury to chitosan‐exposed Staphylococcus aureus MF‐31 could not be demonstrated using the criterion that sublethally stressed cells have increased sensitivity to high levels of sodium chloride.     

Mechanical properties of vinylester/glass and polyester/glass composites fabricated by resin transfer molding and hand lay‐up

This paper reports the comparative performance of vinylester/glass and polyester/glass laminates fabricated by resin transfer molding (RTM) and hand lay‐up. A resin transfer mold was designed and fabricated for preparing the laminates. Void content was much lower in Spartan II RTM specimens than in that of hand lay‐up. Ultimate tensile strength, Young's modulus, flexural strength, flexural modulus, impact strength, and interlaminar shear strength of RTM specimens were superior to that of the hand lay‐up for both vinylester/glass and polyester/glass. The improvements for vinylester/glass were 44%, 28%, 88%, 84%, 36%, and 78% for the respective properties. The corresponding improvements for polyester/glass were 21%, 52%, 70%, 74%, 57%, and 82%, respectively. Particle impact erosion rate was lower in RTM specimens than that of the hand lay‐up. J. VINYL ADDIT. TECHNOL. 21:166–173, 2015. © 2014 Society of Plastics Engineers     

Object-Oriented Framework for Genetic Algorithms with Application to Space Truss Optimization

Genetic algorithms have been shown to be very effective optimization tools for a number of engineering problems. Since the genetic processes typically operate independent of the actual problem, a core genetic algorithm library consisting of all the genetic operators having an interface to a generic objective function can serve as a very useful tool for learning as well as for solving a number of practical optimization problems. This paper discusses the object-oriented design and implementation of such a core library. Object-oriented design, apart from giving a more natural representation of information, also facilitates better memory management and code reusability. Next, it is shown how classes derived from the implemented libraries can be used for the practical size optimization of large space trusses, where several constructibility aspects have been incorporated to simulate real-world design constraints. Strategies are discussed to model the chromosome and to code genetic operators to handle such constraints. Strategies are also suggested for member grouping for reducing the problem size and implementing move-limit concepts for reducing the search space adaptively in a phased manner. The implemented libraries are tested on a number of large previously fabricated space trusses, and the results are compared with previously reported values. It is concluded that genetic algorithms implemented using efficient and flexible data structures can serve as a very useful tool in engineering design and optimization.     

The Nonlinearly Viscoelastic Response of a Wood-Thermoplastic Composite

This study considers the time-dependent response of a woodthermoplastic composite. The extruded material under considerationconsists of wood flour embedded in a high-density polyethylene (HDPE)matrix. The characterization study is based on a series of creep andrecovery tests. Stiffness reduction (i.e. damage) and permanentdeformation was observed in the material when the creep stress amplitudeexceeded a threshold value. The damage and permanent strains were foundto depend on creep stress amplitude and duration. The permanentdeformation was more efficiently accommodated by considering the coupontotal strain, however. A nonlinearly viscoelastic model is presentedthat incorporates damage and permanent deformation effects. Damage wasmodeled by considering an effective stress. The model is shown tocompare favorably with the experimental creep/recovery data as well astwo-step load history verification tests.     

Effect of hydrogen charging on the torsional fatigue behaviour of 2024 aluminium

Torsional fatigue tests have been carried out on overaged and hydrogen charged specimens of 2024 aluminium in gaseous hydrogen and humid air. Hydrogen charging was found to significantly increase the number of fatigue crack initiation sites compared with uncharged specimens tested in argon, resulting in an overall reduction in fatigue life. Fatigue testing in gaseous hydrogen and humid air influenced both initiation and propagation of cracks. The fracture sites of both charged and uncharged specimens were similar, and the fracture mode was predominantly tensile in all specimens. However, specimens tested in humid air showed small amounts of longitudinal and transverse fracture, with ≈5% shear at low humidity and 10% at high humidity.     

Visual speech recognition for small scale dataset using VGG16 convolution neural network

Multimedia Tools and Applications - Visual speech recognition is a method that comprehends speech from speakers lip movements and the speech is validated only by the shape and lip movement....     

Channel Statistics-Based RF Pre-Processing with Antenna Selection

We introduce two novel joint radio-frequency (RF)-baseband designs for receivers in a MIMO system with N_t transmit antennas, N _r receive antennas, but only L < N_r RF chains at the receiver. The joint design introduces an RF pre-processing matrix that processes the signals from the different antennas, and is followed by selection (if necessary), down-conversion, and further processing in the baseband. The schemes are similar to conventional antenna selection in that they use fewer RF chains than antenna elements, but achieve superior performance by exploiting the spatial correlation of the received signals. The first of our proposed designs uses an L times N _r RF pre-processing matrix that outputs only L streams followed by baseband signal processing, and, thus, eliminates the need for a selection switch. The second one uses an N_r times N _r RF pre-processing matrix that outputs N_r streams and is followed by a switch that selects L streams for baseband signal processing. Both spatial diversity and spatial multiplexing systems are considered and the optimum pre-processing matrices are derived for all cases. To accommodate practical RF design constraints, which prefer a variable phase-shifter-based implementation, a sub-optimal phase approximation is also introduced. Performance better than conventional antenna selection and close to the full complexity receiver is observed in both single cluster and multi-cluster wireless channels. A beam-pattern-based geometric intuition is also developed to illustrate the effectiveness of the optimal solutions     

Effect of basal plane dislocations on characteristics of diffused 4H-SiC p-i-n diodes

The effect of basal plane dislocations (BPDs) on the characteristics of diffused 4H-SiC p-i-n diodes was investigated. BPDs were intentionally introduced in the active regions of the device by means of epi-layer surface damage followed by high temperature annealing. Secondary electron microscopy images of the fabricated diodes clearly show the presence of the deliberately introduced BPDs. The current-voltage and electroluminescence spectra measurements did not reveal any noticeable effect of the BPDs on the electrical and optical properties of the diodes. All tested diodes with and without BPDs have no forward voltage drift during long-term on-state operation. A possible reason for stable device performance may be the immobilization of defects responsible for forward voltage drift due to interaction with the diffused dopants.     

Influence of contact architecture on the high-field characteristicsof planar silicon structures

The profile of the contact metallization is observed to play a significant role in the high-field behaviour of high-resistivity Si wafers used for photoconductive power switch applications. In this paper, we present the influence of five different contact geometries on the electric field distribution and leakage current variation in high-resistivity silicon wafers. Experimental results indicate that at high fields, current filamentation occurs due to local avalanche phenomena at high-stress locations when the field enhancement is concentrated in a narrow region forcing a high current density. The threshold for current filamentation is not solely determined by the magnitude of the field enhancement alone, but also the localization of the field enhancement in a narrow region and the consequent increase of current density in that localized region. The experimental results are supported by numerical field computations as well as by optical micrographs that confirm the occurrence of surface filamentation at concentrated high-stress locations. Based on the experimental and computational results, contact geometries suitable for high-field applications of planar Si structures is suggested and the maximum field up to which each geometry can be used without surface filamentation is compared