High-performance nanoadhesive bonding of titanium for aerospace and space applications

In this investigation, attempts are made to prepare high-performance nanoadhesive bonding of titanium for its essential applications to aviation and space. The high-performance nanoadhesive is prepared by dispersing silicate nanoparticles into the ultra-high-temperature-resistant epoxy adhesive at 10 wt% ratio with the matrix adhesive followed by modification of the nanoadhesive after curing under high-energy radiation for 6 h in the pool of SLOWPOKE-2 nuclear reactor with a dose rate of 37 kGy/h to promote crosslink into the adhesive. Prior to bonding, the surfaces of the titanium sheets are mechanically polished by wire brushing, ultrasonically cleaned by acetone and thereafter the titanium sheets are modified by plasma ion implantation using plasma nitriding. The titanium surface is characterized by X-ray photoelectron spectroscopy (XPS). The thermal characteristics of the epoxy adhesive and the high-performance nanoadhesive are carried out by thermal gravimetric analysis (TGA). The TGA studies clearly shows that for the basic adhesive there is a weight loss of the adhesive, however, in the case of epoxy–silicate nanoadhesive, there is almost 100% retention of weight of the adhesive, when the adhesive is heated up to 350 °C. Lap shear tensile strength of the joint increases considerably, when the titanium surface is modified by plasma-nitriding implantation. There is a further massive increase in joint strength, when the plasma-nitriding implanted titanium joint is prepared by nanosilicate–epoxy adhesive and further modification of the adhesive joint under high-energy radiation results a further significant increase in joint strength. In order to simulate with aviation and space climatic conditions, the joints are separately exposed to cryogenic (?196 °C) and elevated temperature (+300 °C) for 100 h and thermal fatigue tests of the joints are carried out under 10 cycles by exposing the joint for 2 h under the above temperatures. When the joint completely kept at ambient condition and the joint strength compared with those joints exposed to aviation and space climatic conditions, it is observed that the joint could retain 95% of the joint strength. Finally, to understand the behavior of the high-performance silicate–epoxy nanoadhesive bonding of titanium, the fractured surfaces of the joints are examined by scanning electron microscope.     

Density of xNa2S.(1 – x)B2S3 (x = 0 to 0.8) Glasses: Correlation with Short-Range Order

The densities of xNa₂S + (1 – x)B₂S₃ glasses have been measured for 0 ≤ x ≤ 0.80. The variation of the density with x is quite strong and is characterized by a sharp maximum at x ∼0.30. The density increases on the low-alkali side of the maximum from 1.7 g/mL for vitreous B₂S₃ up to 2.2 g/mL for the x = 0.3 glass and decreases on the highalkali side to 1.8 g/mL. The increase in the density at low alkali is associated with the increasing fraction of the heavy mass and relatively small volume tetrahedral boron group, Na⁺BS₄^–. The density decrease in the high-alkali range is associated with the decreasing fraction of these groups with the concomitant increase in the fraction of trigonal boron groups with increasing numbers of nonbridging (terminal) sulfurs. To model the density, a weighted fractional mass and volume model was used. The molar volumes of the individual short-range order (SRO) groups were determined from compositions where a particular SRO group was the single group in the glass, by fitting the density data, and by interpolating between groups of known volume. The composition dependence of the fractions of the individual SRO groups was developed by combining spectroscopic evidence with chemically reasonable hypotheses of the SRO of the glasses. In this way, the density was calculated from first principles with one adjustable parameter, that of the volume of the tetrahedral boron group. The calculated densities were found to agree well with the experimental values.     

Growth analysis of corn and soybean response to allelopathic effects of weed residues at various temperatures and photosynthetic photon flux densities

The effects of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setariaglauca (L.) Beauv.] residues on corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were evaluated at various temperatures and photosynthetic photon flux densities (PPFD) in a Biotron. Mathematical growth analysis techniques were used for the evaluation. Redroot pigweed markedly reduced leaf area duration (LAD), leaf weight ratio (LWR), and total dry matter production in both crops. Yellow foxtail residue inhibited total dry matter production in corn and soybeans 20 and 30 days after planting (DAP). It also reduced growth rate (GR) and LAD in corn and biomass increment ( W) in soybeans. Biomass increment was more closely correlated to LAD than net assimilation rate (NAR) in soybeans, whereas in corn NAR contributed more to W than LAD. The 30/20 ° C temperature with a PPFD of 380 E/m²/sec produced a larger W with a greater NAR and larger LAD in corn, resulting in maximum dry matter accumulation than 20/10 ° C and other levels of PPFD. Under similar conditions, soybeans showed little or no response to the changes. The results demonstrate the allelopathic effects of weed residues on growth and dry matter production, affecting LAD, LWR, and GR. The results also show that environmental temperature and PPFD may alter the allelopathic effects of weeds on crops. The possible interference with photosynthesis and the partitioning of biomass into leaf component relative to the total biomass produced by the plant may be the inhibitory effects of allelochemicals present in redroot pigweed and yellow foxtail residues.     

Multiple-reflection effects in photoelastic stress analysis

The interpretation of fringes observed in photoelastic stress measurements made with coherent well-collimated optical radiation such as a laser beam and slab specimens with parallel surfaces is affected by multiple internal reflections of light within the sample, which are usually negligible when incoherent light is used. An analysis of the multiple-reflection effects in photoelastic measurements involving the plane polariscope configuration is presented. The results show that the isochromatic fringes are modified by the interference of multiply reflected waves. The multipass differential phase accumulations that display oscillatory magnitudes as functions of the model thickness and the optical wavelength result in a shifted and altered intensity profile across the isochromatic fringes. It is shown that for large values of reflectivity, as in the case of samples with reflective coating or partial mirrors, the bright fringes split into multiple peaks.     

Polygonal optical cavities

A general class of multifacet optical resonators that have uniform polygonal geometries is described. Expressions for the transmission of light through classical refractive escape from the cavities are presented. The conventional Fabry-Perot resonator is shown to be a special case of this general class of cavities. The effects of absorption and scattering of optical radiation on the transmission properties and cavity-quality factors are analyzed. These resonator structures have significant applications in a wide variety of optical devices.     

Operating temperatures of linear solar concentrators for optimum power output

In this paper, operating temperatures of linear solar concentrators for optimum power output have been calculated considering the operating temperature, emissivity of absorber and wind velocity dependence of the heat loss factor. Results are presented graphically and discussed.     

Convoy Tree Based Fuzzy Target Tracking in Wireless Sensor Network

One important application area of wireless sensor network (WSN) is tracking mobile target. When a target enters in a monitoring region and moves around it, the deployed WSN is used to collect information about the target and send it to the nearby base station. In this paper, we propose a fuzzy based target tracking algorithm (CTFTT). The algorithm constructs a convoy tree around the target and dynamically moves the tree along with the target by adding new nodes into the tree and removing old nodes from the tree. The expansion, contraction and reconfiguration of the tree is done using a fuzzy based sensing model. Important advantages are (1) convoy tree provides 100% coverage, (2) fuzzy mechanism helps to localize the evevts such as tree expansion, contraction and reconfiguration. This in turn helps to reduce the energy consumption in the network. Localized events also reduce communication overhead. Thus CTFTT is able to support the tracking of even fast moving objects. Extensive simulation shows that our algorithm performs better than the existing tree based algorithms in terms of coverage and energy.     

Application of rice husk ash in brick aggregate concrete to improve the permeability and resistance against acid and sulfate attack

Brick-aggregate-concrete with a greater permeability is susceptible to decay at a faster rate under the action of acid and sulfate. This study tries to improve the durability of brick aggregate concrete by the addition of rice husk ash, which has been termed brick-ash concrete in this paper. The permeability and sorptivity of stone-aggregate-concrete, brick-aggregate concrete, and brick-ash concrete samples with different percentages of rice husk ash and different water-to-binder ratios were investigated. The concrete samples were also exposed to 1.5 % hydrochloric acid and 5 % sodium sulfate along with periodic drying and wetting cycle and periodic observations in terms of compressive strength, weight loss, and ultrasonic pulse velocity test for 360 days. 5 % to 10 % rice husk ash can significantly improve the permeability and resistance to the harsh environment of brick aggregate concrete. Additionally, this study also presents the equations to predict the actual strength from ultrasonic pulse velocity values for the brick ash concrete specimen exposed to acid and sulfate environments.     

Scalable watermark extraction for real-time authentication of JPEG 2000 images

This paper proposes a novel scalable authentication scheme that utilizes the progressive enhancement functionality in JPEG 2000 scalable image coding. The proposed method first models the wavelet-based quality scalable coding to identify the effect of the quantization and de-quantization on wavelet coefficient magnitudes and the data embedded within such coefficients as a watermark. A relationship is then established between the watermark extraction rule and the embedding rule, using the magnitudes of the reconstructed and original coefficients. It ranks the wavelet coefficients according to their ability to retain the embedded watermark data intact under various quantization levels corresponding to quality enhancements. Then watermark data is embedded into wavelet coefficients according to their rank followed by JPEG 2000 embedded coding. At the decoder as more and more quality and resolution layers are decoded the authentication metric is improved, thus resulting in gradually increasing complexity of the authentication process according to the number of quality and resolution enhancements. The low complexity authentication is available at low quality low resolution decoding, enabling real-time authentication for resource constrained applications without affecting the authentication metric. Compared to the existing methods, the proposed method results in highly robust scalable authentication of JPEG 2000 coded images.