Influence of Surface Roughness on Corrosion and Tribological Behavior of CP-Ti After Thermal Oxidation Treatment

In this study, tribological and corrosion behavior of commercially pure titanium (CP-Ti) with different surface roughness values after thermal oxidation was investigated. The CP-Ti specimens were prepared with three different roughness values from silicon carbide paper, Ra = 0.1, 0.3, and 0.6 μm, and the thermal oxidization process was conducted at a temperature of 850 °C for 8 h in an O₂ atmosphere. Structural, mechanical, corrosion, and tribological properties of untreated and thermally oxidized CP-Ti with different surface roughness values were investigated through x-ray diffraction, scanning electron microscopy, microhardness, potensiostat, and pin-on-disk techniques. The corrosion and tribological behavior of CP-Ti improved as an oxide layer was formed by thermal oxidation. It was observed that the surface roughness had an effect on these characteristics. It was established that the decreased roughness improves the tribological and corrosion properties.     

Large-Format Voltage-Tunable Dual-Color Midwavelength Infrared Quantum-Well Infrared Photodetector Focal Plane Array

We report a large-format (640 times 512) voltage-tunable quantum-well infrared photodetector (QWIP) focal plane array (FPA) for dual-color imaging in the midwavelength infrared (3-5 mum) band. Voltage-tunable spectral response has been achieved through series connection of two eight-well stacks of AlGaAs-InGaAs epilayers grown by molecular beam epitaxy on GaAs substrate. The peak responsivity wavelength of the detectors is shifted from 4.1 mum (color 1) to 4.7 mum (color 2) as the bias is increased within the limit applicable by commercial read-out integrated circuits. The operability of the FPA is ~99.5% with noise equivalent temperature differences of ~60 and 30 mK (f/1.5) in color modes 1 and 2, respectively. To our knowledge, this is the first large-format voltage-tunable dual-color QWIP FPA reported for midwavelength thermal imaging.     

Live load distribution equations for integral bridge substructures

In this study, live load distribution equations (LLDEs) for integral bridge (IB) substructures are developed. For this purpose, numerous 3-D and corresponding 2-D structural models of typical IBs are built and analyzed under AASHTO live load. In the analyses, the effect of various superstructure and substructure properties such as span length, girder spacing, girder stiffness, abutment height, pile size, pile spacing and foundation soil stiffness are considered. The results from the 2-D and 3-D analyses are then used to calculate the live load distribution factors (LLDFs) for the abutments and piles of IBs as a function of the above mentioned properties. LLDEs are then developed to estimate the live load moments and shear in the abutments and piles of IBs using these LLDFs and nonlinear regression analysis methods. It is observed that the developed LLDEs yield a reasonably good estimate of live load moment and shear in the abutments and piles of IBs.     

A new approach to determine the base shear of steel frame structures

Base shear (V) is the maximum lateral force that will occur due to seismic ground motion at the base of a structure. Calculations of base shear depend on a lot of factors such as soil conditions, level of ductility, fundamental period of vibration of the structure, etc. A great number of methodologies have been developed to determine the dynamic responses of individual frameworks. However, there is no well established empirical solution of the dynamic response of the problem due to the base shear of the steel frames. In this study, a formulation based on NN to determine the dynamic response of both braced and unbraced plane steel frames are provided. The presented formulation is a function of number of stories (ns), bays of the frames (nb), and soil types (Z). The training and testing patterns of the proposed NN formulation are obtained from linear Finite Element Analysis (FEA) solution. The NN-based formulation results are compared with the results obtained from numerical and some current design codes. The NN- based formulation results are found to be more accurate.     

In situ surfactant generation as a means of miniemulsification?

In situ emulsification, where the surfactant is synthesized spontaneously at the oil/water interface, has been put forth as a simpler method for the preparation of miniemulsions‐like systems. Miniemulsions are relatively stable oil‐(e.g., monomer)‐in‐water emulsions having droplet sizes anywhere in the range of 50–500 nm, and are typically created with high shear and stabilized by the combination a surfactant and a costabilizer. Using the in situ method of preparation, emulsion stability and droplet and particle sizes were monitored and compared with conventional emulsions and miniemulsions. Styrene emulsions prepared by the in situ method do not demonstrate the stability of a comparable miniemulsion. Upon polymerization, the final particle size generated from the in situ emulsion did not differ significantly from the comparable conventional emulsion polymerization; the reaction mechanism for in situ emulsions is more like conventional emulsion polymerization rather than miniemulsion polymerization. Similar results were found when the in situ method was applied to controlled free radical polymerizations (CFRP), which have been advanced as a potential application of the method. Molecular weight control was found to be achieved via diffusion of the CFRP agents through the aqueous phase owing to limited water solubilities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Capacitive behavior of polycarbazole- and poly(N-vinylcarbazole)-coated carbon fiber microelectrodes in various solutions

The electrochemical behavior of polycarbazole (PCz) and poly(N-vinyl carbazole) P(NVCz) was investigated by means of electrochemical impedance spectroscopy (EIS). Supporting electrolytes made from various combinations of solvents (acetonitrile and propylene carbonate) and salts (sodium perchlorate, lithium perchlorate, and tetraethyl ammonium perchlorate) were employed in the investigation. Information on the double layer capacitance (C_dl) and specific capacitance (C_sp) of P(NVCz) was achieved by cyclic voltammetry (CV), chronoamperometry and chronopotentiometry. Carbon fiber microelectrodes (CFME) were electrocoated by cyclic voltammetry in a monomer-free solution and displayed film thicknesses in the range ~200 nm to ~4.8 μm. The capacitive behavior of the PCz- and P(NVCz)-coated carbon fiber microelectrodes was also investigated by CV. The effects of the type of electrolyte and solvent on the electrochemical impedance spectroscopic data were subsequently fitted with an ((R(C(R(Q(RW))))(CR))-equivalent circuit model to calculate the numerical values of the proposed components. The obtained experimental C_sp values for PCz/CFME and P(NVCz)/CFME, as measured in LiClO₄/ACN, were 280.5 mF g⁻¹ and 294.1 mF g⁻¹, respectively.     

Searchback Algorithms for TOA Estimation in Non-coherent Low-rate IR-UWB Systems

Non-coherent ultra-wideband (UWB) receivers offer an attractive low-complexity solution to ranging with UWB radios. They use a simple receiver architecture that can operate at very low sampling rates compared to the Nyquist rate. In this paper, time-of-arrival (TOA) estimation performances of two different searchback algorithms for non-coherent impulse radio UWB systems are analyzed: jump back and search forward (JBSF) and serial backward search (SBS). Average ranging errors for both algorithms are formulated using noise-based ranging thresholds and at sub-Nyquist sampling rates. For JBSF, a lower bound on the average ranging error is obtained using an error-minimizing threshold. Also, a semi-analytic technique for the selection of the searchback window length is presented. For SBS, noise-based threshold selection for both single-cluster and multi-cluster channels are introduced. Computer simulations in IEEE 802.15.4a channels provide insights on the selection of some of the critical parameters for accurate ranging. The simulation results show that JBSF typically performs better than SBS if the inter-cluster delay parameter (K) is not selected appropriately for SBS. In both cases, it is shown that even at sampling rates much smaller than the Nyquist rate, ranging accuracies on the order of 33 cm can be obtained using a non-coherent UWB receiver.

Free-space-optical mobile ad hoc networks: Auto-configurable building blocks

Existence of line of sight (LOS) and alignment between the communicating antennas is one of the key requirements for free-space-optical (FSO) communication. To ensure uninterrupted data flow, auto-aligning transmitter and receiver modules are necessary. We propose a new FSO node design that uses spherical surfaces covered with transmitter and receiver modules for maintaining optical links even when nodes are in relative motion. The spherical FSO node provides angular diversity in 3-dimensions, and hence provides an LOS at any orientation as long as there are no obstacles in between the communicating nodes. For proof-of-concept, we designed and tested an auto-configurable circuit, integrated with light sources and detectors placed on spherical surfaces. We demonstrated communication between a stationary and a mobile node using these initial prototypes of such FSO structures. We also performed the necessary theoretical analysis to demonstrate scalability of our FSO node designs to longer distances as well as feasibility of denser packaging of transceivers on such nodes.

Heat Transfer Analysis for Industrial AC Electric Arc Furnace

The heat transfer analysis was performed for an AC electric arc furnace (EAF). Heat losses by conduction, convection and radiation from outer surface, roof, bottom and electrodes of EAF were determined in detail. Some suggestions about decreasing heat losses were presented.     

Comparison of Minolta colorimeter and machine vision system in measuring colour of irradiated Atlantic salmon

BACKGROUND: Minolta and machine vision are two different instrumental techniques used for measuring the colour of muscle food products. Between these two techniques, machine vision has many advantages, such as its ability to determine L*, a*, b* values for each pixel of a sample's image and to analyse the entire surface of a food regardless of surface uniformity and colour variation. The objective of this study was to measure the colour of irradiated Atlantic salmon fillets using a hand‐held Minolta colorimeter and a machine vision system and to compare their performance. RESULTS: The L*, a*, b* values of Atlantic salmon fillets subjected to different electron beam doses (0, 1, 1.5, 2 and 3 kGy) were measured using a Minolta CR‐200 Chroma Meter and a machine vision system. For both Minolta and machine vision the L* value increased and the a* and b* values decreased with increasing irradiation dose. However, the machine vision system showed significantly higher readings for L*, a*, b* values than the Minolta colorimeter. Because of this difference, colours that were actually measured by the two instruments were illustrated for visual comparison. Minolta readings resulted in a purplish colour based on average L*, a*, b* values, while machine vision readings resulted in an orange colour, which was expected for Atlantic salmon fillets. CONCLUSION: The Minolta colorimeter and the machine vision system were very close in reading the standard red plate with known L*, a*, b* values. Hence some caution is recommended in reporting colour values measured by Minolta, even when the ‘reference’ tiles are measured correctly. The reason for this discrepancy in colour readings for salmon is not known and needs further investigation. Copyright © 2009 Society of Chemical Industry