Distortional buckling in monosymmetric I-beams

This paper deals with distortional buckling of simply supported monosymmetric I-beams under three types of load: a central point load, a uniformly distributed load and a uniform sagging moment. ABAQUS is used for the investigation. Top-flange and bottom-flange load positions are considered for the first two load cases. It is found that for comparatively short beams, buckling may be governed by distortion of the web. Moment modification factors are calculated based on the present analysis, which accounts for the distortion of web and these are compared with those based on SSRC Guidelines, which are based on lateral-torsional buckling analysis only. It is seen that for short beams, provisions in SSRC Guide-1998 seriously overestimate the critical load.     

Single-frequency, high-power, continuous-wave fiber-laser-pumped Ti:sapphire laser

We demonstrate a high-power, continuous-wave (cw), single-frequency green source based on single-pass second-harmonic generation of a Yb-fiber laser in MgO:sPPLT as a viable pump source for a cw single-frequency Ti:sapphire ring laser. By careful design and optimization, the Ti:sapphire laser can provide as much as 2.3 W of cw single-frequency output across a 47 nm tuning range, limited by the reflectivity of the cavity mirrors. By implementing active stabilization of the laser frequency to an external reference, an ultrastable Fabry-Perot interferometer, we obtain a frequency stability better than 12 MHz over 10 min and continuous tunability greater than 180 MHz. Stable output power with peak-to-peak fluctuation of 5.4% over 75 min, in high spatial beam quality with M(2)<1.34, is achieved.     

One-step photochemical synthesis of permanent, nonleaching, ultrathin antimicrobial coatings for textiles and plastics

Antimicrobial copolymers of hydrophobic N-alkyl and benzophenone containing polyethylenimines were synthesized from commercially available linear poly(2-ethyl-2-oxazoline), and covalently attached to surfaces of synthetic polymers, cotton, and modified silicon oxide using mild photo-cross-linking. Specifically, these polymers were applied to polypropylene, poly(vinyl chloride), polyethylene, cotton, and alkyl-coated oxide surfaces using solution casting or spray coating and then covalently cross-linked rendering permanent, nonleaching antimicrobial surfaces. The photochemical grafting of pendant benzophenones allows immobilization to any surface that contains a C-H bond. Incubating the modified materials with either Staphylococcus aureus or Escherichia coli demonstrated that the modified surfaces had substantial antimicrobial capacity against both Gram-positive and Gram-negative bacteria (>98% microbial death).     

A smart spectrum utilization approach using multiantenna‐based cognitive relays in cognitive radio network

Efficient spectrum utilization is a promising technique for a prolonged unused radio frequency (RF) spectrum in a wireless network. In this paper, an adaptive spectrum sharing cognitive radio (CR) network has been proposed consisting of a primary user (PU) and secondary user transmitter (SU ? Tx) that communicates with secondary user receiver (SU ? Rx) via multiantenna‐based proactive decode‐and‐forward (DF) relay selection scheme. In our model, strategically an adaptable joint venture on underlay/overlay protocol is defined based on channel occupancy using spectrum sensing technique. Here, secondary transmitters (i.e., source transmitter) continuously sense the PU activities by energy detector and can simultaneously transmit to secondary receivers. Depending on sensing result secondary transmitters automatically switches in underlay mode if PU is active otherwise operates in overlay mode. The advantage of this scheme is that the joint mode of transmission allows the SUs to maximize their transmission rate. The outage performance at SU ? Rx and closed‐form expressions of joint underlay/overlay protocol has been evaluated. The power control policies at different transmitter nodes are taken care of. With the same diversity order, a trade‐off between multiantenna and multirelay is shown. This comparison shows improvement in outage behavior when the count in relays surpasses the number of antennas. Finally, the analytical model of smart efficient spectrum utilization without harming license users in CR is validated by MATLAB simulation.     

A novel concept on discrete samples for efficient microwave processing of materials

A novel concept on discrete samples has been introduced to analyze the efficient heating processes due to microwave radiations. A preliminary investigation on average power absorption within samples vs sample thickness has been carried out for continuous samples and various regimes have been identified such that these regimes may correspond to minima or maxima of average power. Two discrete sample pieces replace a continuous sample for each of these regimes such that the total thickness of the discrete samples is identical with the thickness of the continuous sample. Electric fields and temperature have been solved for each discrete sample layer and the intermediate air layer. The thickness of air layer plays a significant role to dramatically alter the interference of waves and power absorption within each sample layer. It is observed that the discrete sample layers exhibit larger heating rate than that within continuous sample especially for smaller sample thicknesses. Suitable ratios of discrete sample thickness and the thickness of air layer also show large heating rate for larger sample thicknesses. The discrete samples also play important role to optimize thermal runaway. Based on two factors: ‘large heating rate’ and ‘optimal thermal runaway’, the efficient heating strategy has been recommended for highly lossy food substances, and case studies are also demonstrated for low lossy substances.     

Studies on the structural properties of SiO:H films prepared from (SiH4+CO2+He) plasma in RF-PECVD

A comprehensive report on the structural studies on SiO:H films prepared at high growth rate from He-diluted (SiH₄+CO₂) plasma has been presented and extraction of some intriguing ideas that deserve high relevance for the potential development of nano-crystalline hydrogenated silicon oxide (nc-SiO:H) films has been tried. Poly-hydrogenation has been found as inherent to increasing alloying of the network; however, the bonded H-content reduces linearly with the degree of oxygen incorporation, i.e., the solubility of H in the SiO:H network decreases as the O-content increases in the presence of He. This result happens to be opposite to the conventional H₂-diluted plasma condition and appears to be attractive as well. In addition, He-dilution contributes to a high growth rate of the material. Dynamic interaction of He* in the formation of activated oxygen atoms in the plasma and their efficient mobilization on the surface reaction process at the growing network induces abstraction of H from the SiH_n groups and the terminal H atoms are replaced by bridging O atoms to form the SiO:H network. Abstraction of H from the network being an essential criteria for developing nanocrystallinity and it being inherent to oxygenation in Si network when prepared from He-diluted (SiH₄+CO₂) plasma in PECVD, the process could provide an appropriate pathway for preparing nc-SiO:H structures for solar cells, from such plasma in suitable parametric conditions.     

Toughening of epoxy resin with amine functional aniline acetaldehyde condensate

The diglycidyl ether of bisphenol-A (DGEBA) resin was modified with amine functional aniline acetaldehyde condensate (AFAAC) and cured with an ambient temperature curing agent triethylene tetramine. The resulting networks displayed significantly improved fracture toughness. The AFAAC was synthesized by the condensation reaction of aniline and acetaldehyde in the acid medium (pH 4) and characterized by FTIR and NMR spectroscopy, elemental analysis, viscosity measurements, and mole of primary and secondary amine analysis. The DGEBA and AFAAC were molecularly miscible but developed a two-phase microstructure upon network formation. Epoxy/AFAAC compositions were systematically varied to study the effect of AFAAC concentration on the impact, adhesive, tensile, and flexural properties of modified networks. The dynamic mechanical analysis and scanning electron microscopy studies showed two phase morphology in the cured networks, where AFAAC particles were dispersed. The AFAAC modified epoxy network was thermally stable up to around 280°C. POLYM. ENG. SCI., 47:1695–1702, 2007. © 2007 Society of Plastics Engineers     

Manufacturing-error-based maintenance for high-precision machine tools

Nowadays, the condition-based maintenance (CBM), in which repairs are triggered by the heuristic symptoms of the component faults, is finding increasing applications in the industrial fields. However, for the high-precision machine tools, the conventional CBM might not be the optimal option, which is uneconomic and incapable of ensuring their machining accuracy. In order to overcome these shortcomings, this paper propose the manufacturing-error-based maintenance (MEBM), where the repairs are initiated based on the manufacturing errors instead of the heuristic symptoms. In MEBM, repairs are taken properly at the occurrence of the excessive machining errors, and therefore, the premature and redundant maintenance can be avoided and the maintenance cost can be minimized; what is more, the machining errors are controlled in the closed loops, and therefore, the machining accuracy can be guaranteed. Based on the principles of the MEBM, a prototype maintenance system—the transient backlash error (TBE)-based maintenance system—is established. To achieve this aim, first, the width of the backlash in the mechanical chain is measured by utilizing the built-in encoders and the analytical mapping relationship between the backlash width and the TBE is derived. Relying on these foundations, the TBE can be indirectly estimated. Then, the warning threshold of the TBE is customized according to the permissible roundness error of the workpiece. Thus, the maintenance actions can be precisely implemented: when the monitored TBE exceeds its warning threshold, maintenance workers will be notified to lessen the backlash width, and meanwhile, the permissible maximal size for the backlash will also be informed.