Twinning and the mechanical behavior of magnesium alloys at very high strain rates

The dynamic mechanical behavior of magnesium and its alloys is a subject of interest primarily because of its high specific strength. This makes it attractive for structural components and vehicles. The hexagonal close packed crystal structure of magnesium makes it highly anisotropic in terms of its mechanical behavior. Extension twinning is a dominant deformation mechanism in these materials. This is often reflected in a characteristic sigmoidal profile of the stress–strain curve when crystals are compressed along directions perpendicular to the crystallographic c-axis. Past experiments have been limited to strain rates of 103 s–1 . This study focuses on microstructural twinning effects on the mechanical behavior of AZ31 magnesium alloy at higher strain rates. We perform very high-strain rate experiments on AZ31 magnesium alloy, using a miniature Kolsky compression bar apparatus coupled with a high speed camera for whole field imaging. This experiment is capable of achieving strain rates on the order of 105 s–1 . Experiments at these strain rates have shown substantial plastic deformation without failure when compared with the lower rates of loading. This is evidence of deformation mechanisms that tend to delay failure in the material. We also observe a change in the hardening rates between these experiments and experiments done at 103 s–1. Examination of the microstructure of deformed samples gives us information about the relative activation and growth of deformation mechanisms that cause plastic deformation at these rates

Twinning and the dynamic behavior of magnesium and its alloys

With a density two-thirds that of aluminum, magnesium has great potential to become the most sought-after structural metal. Naturally, many applications for structural metals require them to remain resilient under extreme conditions of pressure, temperature and loading rates (some common scenarios being car crashes, high speed machining, ballistic impact and micrometeorite impact). Most materials behave very differently when subjected to these extreme conditions in comparison to conventional quasi-static isothermal loading. In the context of magnesium, its asymmetric hexagonal close packed crystal structure results in an anisotropy in plastic deformation which can be linked back to two major plastic deformation mechanisms at the crystal scale: dislocation slip and deformation twinning. In this thesis, we focus on a mechanism-based approach to understand plastic deformation in magnesium under high rates of loading. Special focus has been placed on understanding deformation twinning under these loading conditions. We first investigate the macroscopic strength and ductility of a textured polycrystalline AZ31B magnesium alloy across 8 decades of strain rate (10^-4-10^4 /s) under uniaxial compression along different loading orientations relative to the material texture. The macroscopic flow stress and strain hardening are found to be a function of both strain rate and loading orientation. Post-mortem microscopy reveals both dislocation slip and twin-dominant deformation, depending on the loading orientation relative to the sample texture. We find that deformation twinning is more active at high strain rates than at quasi-static rates. This tends to affect both material strength and ductility. The next part of this thesis examines deformation twinning in greater detail. Using high strain rate experiments combined with in-situ high speed microscopy, we capture the dynamic evolution of deformation twins in single crystal magnesium. The measurements reveal the competition between twin nucleation and growth and its relation to macroscopic material response. A theoretical framework to predict twin propagation speeds is developed with significant potential to explain twin-twin and dislocation-twin interactions. Finally, we end with a discussion of the crystallographic nature of twins nucleated under both quasi-static and dynamic loading. The interplay between the mechanics of twinning (i.e. twin nucleation and growth kinetics) and the crystallography offers unique insights and may help improve predictive capabilities for the dynamic behavior of hcp crystals

HERMITIAN SYMMETRY BASED FIBER NON-LINEARITY COMPENSATION IN OPTICAL OFDM NETWORKS

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems such as standard 802.11a/b/g/n, Digital Video Broad casting Television (DVB-TV), and Long Term Evolution (LTE) in the next mobile generation, due to its capacity in solving the problems of Inter-Symbol Interference (ISI) caused by the effects of the dispersive channel. Very recently researches focus on applying OFDM technology in optical fiber communication systems. Optical OFDM is well suited for high speed transmission systems with high spectral efficiency and attracted significant attention from the optical communication community. One of the major issues that degrade the performance of optical OFDM networks is its fiber non-linearity. Fiber non-linearities represent the fundamental limiting mechanisms to the amount of data that can be transmitted on a single optical fiber. Non-linear effects arise as optical fiber data rates, transmission lengths, number of wavelengths, and optical power level increases. Therefore, the effect of non-linearity in high data rate optical networks needs to be controlled to enhance link performances. In this paper, a nonlinearity compensation technique (Hermitian Symmetry) is implemented to improve the performance of OFDM based optical networks. This would provide high spectral efficiency, low ISI and very good Bit Error Rate (BER) performances without increasing the complexity of the network. The optical OFDM transmission system with fiber non-linearity compensation is simulated using Virtual Photonics Integrated (VPI) software

Development and tribological characterization of fly ash reinforced iron based functionally gradient friction materials

The tribological and thermal properties enable iron based sintered materials with hard phase ceramic reinforcements as promising friction material for heavy-duty wind turbines. In wind turbines, the braking system consists of aerodynamic and mechanical braking systems. During application of mechanical brakes, the friction materials are pressed against the rotating low-speed shaft. The desired braking efficiency is achieved by utilizing a number of friction materials, which in turn are joined in a steel backing plate. Though this arrangement increases the braking efficiency, the hard phase ceramic reinforcement particles reduces the bonding strength between the friction material and steel backing plate. The joint failure leads to catastrophic failure of wind turbine. Therefore, the need of the hour is to develop friction materials with functional gradients that have high wear resistance (contact area) and high bond strength (interface). In this study, an attempt is made to fabricate and characterize a friction material with gradient profile of composition along the cross section to provide functional gradient property. The functional gradient friction material is synthesized by gradient deposition of Fe, Cu, Cg, SiC and fly ash powders which is then compacted and sintered. The prepared functional gradient friction material was characterized in terms of microstructure and microhardness. The tribological performance (wear rate and coefficient of friction) of the developed functionally gradient friction material was investigated at various loads using pin-on disc apparatus. The results show that as the load increases, the wear rate decreases and at the same time the COF tends to increase at higher loads. The predominant wear mechanism was deduced from the morphology of the worn surface

Changes in the Quality Attributes of Edible Vegetable Oils During Deep Frying Concerning Defence Ration

Deep fat frying is a popular cooking method that can significantly alter the physico-chemical properties of edible oils. This unit operation is very common both in civil as well as institutional level training, recreational and feeding centres owing to the high liking of fried products among all age groups. Frying is a high-temperature process where food material is normally exposed to longer periods depending upon its moisture content and results in the desirable colour, aroma and taste that is most acceptable to the consumers. But the quality of oil changes each after the frying cycle and leads to the onset of various physicochemical changes resulting in the accumulation of toxic compounds that may pose potential health risks. Various edible oils from plant sources have varied stability against high-temperature exposure, hence, the selection of appropriate edible vegetable oils for deep frying is critical to ensure its safety during repeated use. The current article summarizes the available literature on the changes in quality attributes of edible vegetable oils during deep frying along with the mechanisms of oil degradation, including oxidation and hydrolysis, formation of trans fats, and major concerns during deep frying. This also covers various methods of assessing the quality of frying oils, inclusive of measurement of free fatty acids, peroxide value, polar compounds, and oxidative stability. The impact of deep frying on the nutritional value of edible vegetable oils, such as changes in fatty acid composition, effects of different frying conditions, such as temperature and time, on the quality of the frying oil and the loss of antioxidant compounds is also discussed rationally The facts and finding covered under present manuscript will be useful to food manufacturers and consumers in selecting appropriate edible vegetable oils for deep frying, maintaining the desired food quality, and ensuring the safety of various edible oils and their blends concerning both civil and the Defence supplies

Seeing Beyond Cancer: Multi-Institutional Validation of Object Localization and 3D Semantic Segmentation using Deep Learning for Breast MRI

The clinical management of breast cancer depends on an accurate understanding of the tumor and its anatomical context to adjacent tissues and landmark structures. This context may be provided by semantic segmentation methods; however, previous works have been largely limited to a singular focus on the tumor alone and rarely other tissue types. In contrast, we present a method that exploits tissue-tissue interactions to accurately segment every major tissue type in the breast including: chest wall, skin, adipose tissue, fibroglandular tissue, vasculature and tumor via standard-of-care Dynamic Contrast Enhanced MRI. Comparing our method to prior state-of-the-art, we achieved a superior Dice score on tumor segmentation while maintaining competitive performance on other studied tissues across multiple institutions. Briefly, our method proceeds by localizing the tumor using 2D object detectors, then segmenting the tumor and surrounding tissues independently using two 3D U-nets, and finally integrating these results while mitigating false positives by checking for anatomically plausible tissue-tissue contacts. The object detection models were pre-trained on ImageNet and COCO, and operated on MIP (maximum intensity projection) images in the axial and sagittal planes, establishing a 3D tumor bounding box. By integrating multiple relevant peri-tumoral tissues, our work enables clinical applications in breast cancer staging, prognosis and surgical planning.Comment: 9 pages, 2 figures, to appear in SPIE: Medical Imaging 202

Tiny toxins, big problems: the hidden threat of microplastic in agroecosystems

Microplastic pollution has become a critical environmental challenge particularly in agricultural ecosystems, where excessive plastic use contributes to its accumulation in soils. Microplastic originate from various sources including plastic mulch films, irrigation systems, fertilizers, packaging materials and factories also gradually breaking down into microscopic particles that infiltrate the soil. Their presence disrupts soil structure, alters physicochemical properties and negatively affects water retention, nutrient cycling and microbial diversity ultimately reducing soil fertility and crop productivity. Besides disturbing soil health, microplastic enter the food chain through plant uptake, posing potential health risks to humans and even animals ingestit directly. Long-term exposure to microplastic has been linked to toxic effects including the accumulation of harmful chemicals and heavy metals. To mitigate these impacts, sustainable strategies such as biodegradable plastic alternatives, regulatory frameworks and bioremediation techniques involving plants and microorganisms must be implemented. Additionally, improved waste management practices particularly the 4Rs (Reduce, Reuse, Recycle and Recover) can significantly reduce microplastic contamination. Addressing microplastic pollution in agroecosystems requires a collaborative global effort involving policymakers, industries, researchers and local communities. By promoting sustainable agricultural practices and enforcing stricter regulations on plastic use, we can safeguard environmental health, ensure food security and protect future generations from the long-term consequences of microplastic pollution

Effect of Packaging Material on Moisture Migration and Textural Attributes of Bread During Storage

Bread as a commodity is included in the special inventory of Defence Forces, particularly as a morning or evening snack item. The present investigation pertains to the studies on the effect of various packaging materials, e.g. metalized polyester (MP-99.8 µm), low-density polyethylene with lower thickness (LDPE-1-78.33 µm), multi-layer flexible pouches (MLFP-106.2 µm), low-density polyethylene with higher thickness (LDPE-2-125.12 µm), and paper foil polyethylene (PFP-124.6 µm) on textural attributes of bread. Textural properties were significantly influenced by the change in moisture content which was clearly shifted from crumb to crust to the extent varying from -25.89% to +24.90% in LDPE-2; -29.11% to +29.77% in MP; -22.22% to +21.11%; in MLFP; -19.46% to +19.67% in PFP; -20.42% to +20.55% in LDPE-1 at the end of its expected shelf-life i.e. five days. Though overall bread moisture content was not much affected in PFP and MP, the marked difference was primarily observed in the case of bread packed in LDPE-2, LDPE-1, and MLFP. This difference may be attributed to the thickness and permeable properties of the packaging material used for the study. The hardness and resilience of samples depicted opposite trends, respectively, during their storage. The current study gives insight into physicochemical changes occurring in the bread system when  variety commonly practiced packaging materials is used and a perspective strategy for its extended life during varied field conditions.

Robot operating system based autonomous navigation platform with human robot interaction

In emerging technologies, indoor service robots are playing a vital role for people who are physically challenged and visually impaired. The service robots are efficient and beneficial for people to overcome the challenges faced during their regular chores. This paper proposes the implementation of autonomous navigation platforms with human-robot interaction which can be used in service robots to avoid the difficulties faced in daily activities. We used the robot operating system (ROS) framework for the implementation of algorithms used in auto navigation, speech processing and recognition, and object detection and recognition. A suitable robot model was designed and tested in the Gazebo environment to evaluate the algorithms. The confusion matrix that was created from 125 different cases points to the decent correctness of the model

Circular slot antenna for triband application

We recommend a circular monopole antenna (CMPA) with a central feed to operate in three bands. The antenna is circular and has an 8cm diameter. The suggested antennas' resonance frequency ranges are 2.43 GHz, 5.24 GHz, and 9.61 GHz. The planned CMPA is made up of two circle-shaped slots cut into the radiating patch. The whole structure is supplied via a microstrip feed line and analysed using CST Studio's electromagnetic simulator, which is based on finite integral technique (FIT). To check the structure, the return loss, radiation pattern, voltage standing wave ratio (VSWR), and gain are all examined. The structure's ideal dimensions are determined using a parametric study of three factors: feed position, feed breadth, and ground size. The proposed CMPA is capable of operating in several bands and has good matching impedance in all of them