Effect of Grain Size on the Weldability of Cast Alloy 718

Electron beam welding was conducted on cast alloy 718 with varying grain sizes obtained using Microcast (MX™) and conventional cast (CC) techniques. The average value per section of Total Crack Length (Av. TCL) was measured on each cross section and used to represent the material's weldability. It was found for the first time that the grain size had a reduced effect on the weldability of cast alloys, relative to that reported in the literature for wrought alloys; i.e., increased grain size in the range of 90-3000 microns resulted in improved weldability. This was determined to be related to the probability of welds intersecting grain boundaries and causing grain boundary microfissuring. The conclusion from the experimental analysis is corroborated by the use of a Weibull-type analysis to evaluate the probability of a weld microfissure occurring relative to the grain size. As grain size increases, the probability of the weld intersecting the grains is reduced, and thus, the likelihood of microfissuring is reduced. With regard to a single crystal, there are no grain boundaries intercepting the weld (probability = 0), and thus, microfissuring related to constitutional liquation of primary carbides, or segregation of species to grain boundaries would not occur.     

All Slot-Die Coated Non-Fullerene Organic Solar Cells with PCE 11%

Slot-die (SD) coating is used to fabricate fully solution processed organic solar cells (OSCs) based on a blend of high performance donor polymer (PTB7-Th) and a non-fullerene acceptor (IEICO-4F) for stable devices over extended periods of operation. The optimization of a sequential deposition process of transport and active layers, under ambient conditions, enable high efficiency slot-die coated solar cells with remarkable power conversion efficiencies (PCE) > 11.0% to bridge the gap between lab-to-fab. Fully slot-die coated inverted OSCs are demonstrated with efficiencies reaching 11% along with 1 cm² devices, proving the scalability and reproducibility of the proposed technique. Further, replacing the evaporated Ag electrode with solution processed Ag nanowire (AgNW) electrodes shows the highest light utilization efficiency of 5.26% for semi-transparent OSC with a PCE of 9.07% and average visible transmission of 58%.     

Discrimination of maize crop with hybrid polarimetric RISAT1 data

Microwave remote sensing provides an attractive approach to determine the spatial variability of crop characteristics. Synthetic aperture radar (SAR) image data provide unique possibility of acquiring data in all weather conditions. Several studies have used fully polarimetric data for extracting crop information, but it is limited by swath width. This study aimed to delineate maize crop using single date hybrid dual polarimetric Radar Imaging Satellite (RISAT)-1, Fine Resolution Stripmap mode (FRS)-1 data. Raney decomposition technique was used for explaining different scattering mechanisms of maize crop. Supervised classification on the decomposition image discriminated maize crop from other land-cover features. Results were compared with Resourcesat-2, Linear Imaging Self Scanner (LISS)-III optical sensor derived information. Spatial agreement of 91% was achieved between outputs generated from Resourcesat-2, LISS-III sensor and RISAT-1 data.     

A novel self‐healing key distribution scheme based on vector space access structure and MDS codes

Self‐healing group key distribution protocols are useful in applications that have a dynamic group structure. These include broadcast transmission systems and multicast networks such as pay‐per‐view television, embedded and sensor networks, and cellular and wireless networks. To cater to the requirements of these applications, several self‐healing group key distribution protocols are proposed in the literature. Many of these schemes are vulnerable to polynomial factorization or insider replay attacks. Some other schemes impose constraints on the users joining the group or revoked from the group. Motivated by these and other shortcomings of the existing schemes, we hereby propose a novel self‐healing group key distribution protocol. Some of the features of this scheme include that (a) the number and the set of revoked users is not constrained, (b) the communication group can consist of any set of users, and (c) a revoked user is allowed to rejoin the group in any of the later sessions. The scheme is analyzed for its security, and it is found to provide anywise forward and backward secrecy. It is also found to resist anywise collusion attack. Communication and computation complexity of the scheme is analyzed; while doing so, various possible realizations of the scheme is discussed. In addition to the theoretical analysis, the proposed scheme is experimentally verified for its correctness using OMNET++ network simulator.     

Kinetics of precipitation in Al-1 wt% Mn alloy

Precipitation kinetics in high purity Al-10 wt% Mn alloy has been investigated during the early stages of isothermal annealing between 823 and 698 K by resistivity measurements. Aged specimens were also examined by transmission electron microscopy. The precipitation kinetics can be represented by an Avrami type equation with the time exponentn=2/3 during the early stages of annealing. This can be attributed to the nucleation and growth of fiat needle-like precipitates on dislocations. The precipitates were Al₆ Mn at 773 K and the metastable G₂ -phase at 773 K. After prolonged annealing times at 848 K, isometric plates of Al₆Mn were also observed and the value ofn was found to be 1.0. However, at 698 K after longer annealing times, isometric needles of Al₁₂Mn, G-phase were observed along with flat needles of G₂ precipitate. At 698 K, the value ofn tends to decrease with time from 0.67 to 0.59.     

Storage of surface flows through groundwater recharge

The Ganga basin in India has a serious problem of water availability. The basin, which is only one twelfth of the United States in area, has a population greater than the totalus population, and is increasing at a rate of 2·5% per annum. About 77% of the population is engaged in agriculture which is totally dependent on irrigation, as almost 85% of the rainfall comes down in 2–3 monsoon months. Surface storage possibility is extremely limited, but groundwater recharge appears feasible, since sedimentary alluvial formations extend to depths of thousands of metres. Three alternative schemes of groundwater recharge have been proposed. One involves pumping heavily along perennial rivers prior to the monsoon so as to lower the water-table and promote induced groundwater recharge. The second proposes a similar approach along nonperennial rivers. The third involves irrigation during the monsoon with groundwater lowered adequately in the non-monsoon period so that enough induced groundwater recharge takes place to provide adequate supplies for non-monsoon months. A simulation-optimization model has been developed to study the surface flow-groundwater interaction and has been applied to study comparative cost effectiveness of the three alternate approaches. Sensitivity analysis has also been carried out. It is shown that the third scheme is the most attractive.     

Challenges and Developments in Secure Routing Protocols for Healthcare in WBAN: A Comparative Analysis

Wireless Personal Communications - The rise in life expectancy of humans, COVID-19 pandemic and growing cost of medical services has brought up huge challenges for the government and healthcare...     

A family of ISI-free polynomial pulses

A family of ISI free polynomial pulses that can have an asymptotic decay rate of t/sup -k/ for any integer value of k has been proposed. The proposed family provides flexibility in designing bandlimited pulses in accordance with the desired application, even after the roll-off factor /spl alpha/ has been chosen. Pulses obtained from this family have been found to be better than the currently known good pulses.     

Elimination of current non-uniformity in carbon nanotube field emitters

Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase in current resulted in region of positive slope in F–N curve, which can’t be explained by conventional F–N theory. Also the grown CNTs can be a mixture of metallic and semi conducting nature, which may cause deviation from the conventional F–N theory. We could eliminate abnormally active sites by electric field treatment, thereby increasing current uniformity and stability. The work is underway to understand the deviation in FN curve at high fields.