PAPR Reduction Using Low Complexity PTS to Construct OFDM Signal

Orthogonal frequency division multiplexing has become evident due to its higher frequency multiplicity to achieve high data rate and greater immunity to multipath fading. The imperative drawback of OFDM is its high peak-to-average power ratio which results in power inefficiency. There are numerous techniques used to overcome problem of high PAPR in OFDM modulation system. Partial transmit sequence (PTS) is most prominent peak-to-average power ratio (PAPR) reduction techniques proposed for orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of the conventional PTS (C-PTS) is its higher computational complexity and transmission of several side information bits. A new PTS with simple detector is recommended here to deal with these drawbacks of C-PTS. The candidates can be generated by cyclically shift of each sub block sequence in time domain and combining them in a recursive manner. At the receiver, by using the natural diversity of phase constellation for different candidates, the detector can successfully regain the original signal without side information. The probability of detecting failure of the side information found that detector can work without any side information with high reliability. The scheme in this paper achieves almost the same bit error rate (BER) performance as the C-PTS with perfect side information, under additive white Gaussian noise (AWGN) channel and Rayleigh fading channel

Climate change and its impacts in Southern Africa: A synthesis of existing evidence in support of the World Food Programme’s 2021 Climate Change Position Paper

Approximately 30% of the whole SADC region is exposed to a variety of climate hazards and their combinations. Decreased suitable land for cropping and reduced crop and livestock production would exacerbate water scarcity and insecurity, and decrease national self-sufficiency ratios, and impact food availability locally, with devastating effects on food insecurity in the region. Water, energy and food are inextricably linked across multiple scales in SADC and are heavily interdependent. Therefore, actions to address climate change need to be regionwide. Furthermore, addressing existing and emerging water-energy-food issues requires understanding and shaping ongoing food systems transformations in the region

Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process

FEATURES OF CNC MACHINES AND SYSTEMS

This paper deals with configuration and implementation of latest state of art CNC system for Automation.The apparatus required in CNC system,PLC software HMI software, electronic AC Servo Motors drivers, Position Feedback Devices. A thorough understanding of the physical configuration of CNC machining centre and its various functions are presented here. A study of CNC & PLC system, AC Servomotor, drivers and feedback elements and automation of machine functions using these devices.The introduction of CNC has radically changed the manufacturing industry implementation of latest CNC and AC Servo Motors and drivers allows reduced cycle time, higher productivity and higher level of accuracy and flexibility in the manufacturing processors. Moreover technically it has rugged and designed to withstand vibrations, temperature, humidity and noise. It has interfacing for inputs and outputs already inside the controllers which is easily programmable

Features Of Cnc Machines And Systems

This paper deals with configuration and implementation of latest state of art CNC system for Automation.The apparatus required in CNC system,PLC software HMI software, electronic AC Servo Motors drivers, Position Feedback Devices. A thorough understanding of the physical configuration of CNC machining centre and its various functions are presented here. A study of CNC & PLC system, AC Servomotor, drivers and feedback elements and automation of machine functions using these devices.The introduction of CNC has radically changed the manufacturing industry implementation of latest CNC and AC Servo Motors and drivers allows reduced cycle time, higher productivity and higher level of accuracy and flexibility in the manufacturing processors. Moreover technically it has rugged and designed to withstand vibrations, temperature, humidity and noise. It has interfacing for inputs and outputs already inside the controllers which is easily programmable

Neural network models of peak temperature, torque, traverse force, bending stress and maximum shear stress during friction stir welding

Tool and workpiece temperatures, torque, traverse force and stresses on the tools are affected by friction stir welding (FSW) variables such as plate thickness, welding speed, tool rotational speed, shoulder and pin diameters, pin length and tool material. Because of the large number of these welding variables, their effects cannot be realistically mapped by experiments. Here, we develop, test and make available a set of five neural networks to calculate the peak temperature, torque, traverse force and bending and equivalent stresses on the tool pin for the FSW of an aluminium alloy. The neural networks are trained and tested with the results from a well tested, comprehensive, three-dimensional heat and material flow model. The predictions of peak temperature and torque are also compared with appropriate experimental data for various values of shoulder radius and tool revolutions per minute. The models can be used even beyond the range of training with predictable levels of uncertainty

Tool durability maps for friction stir welding of an aluminium alloy

Friction stir welding is not used for hard alloys because of premature tool failure. A scheme is created that exploits the physical three-dimensional heat and mass flow models, and implements them into a fast calculation algorithm, which, when combined with damage accumulation models, enables the plotting of tool durability maps that define the domains of satisfactory tool life. It is shown that fatigue is an unlikely mechanism for tool failure, particularly for the welding of thin plates. Plate thickness, welding speed, tool rotational speed, shoulder, and pin diameters and pin length all affect the stresses and temperatures experienced by the tool. The large number of these variables makes the experimental determination of their effects on stresses and temperatures intractable and the use of a well-tested, efficient friction stir welding model a realistic undertaking. An artificial neural network that is trained and tested with results from a phenomenological model is used to generate tool durability maps that show the ratio of the shear strength of the tool material to the maximum shear stress on the tool pin for various combinations of welding variables. These maps show how the thicker plates and faster welding speeds adversely affect tool durability and how that can be optimized

Investigation on laser engineered net shaping of multilayered structures in H13 tool steel

Laser engineered net shaping process is widely used to build multilayered structures for critical applications by melting and solidification of metallic powders in a layer by layer manner using a focused laser beam. An a-priori estimation of the influence of laser beam power and scanning speed on the layerwise build dimensions, thermal cycles, and mechanical properties is requisite in laser engineered net shaping process. We present here a three-dimensional heat transfer model to estimate the temperature field and layer profile in single line multilayer depositions of H13 tool steel. A novel approach is undertaken to account for the laser beam energy input to the substrate and the depositing powder materials considering the attenuation of the beam power. The computed build profiles are validated with the corresponding experimentally measured results. The computed cooling rates show a reducing trend from the bottom to the top layers while that in the transformation temperature range tend to increase toward the top layer. The measured hardness shows a gentle reducing trend from the top to the bottom layers but exhibits a relatively steep increase in the layers near to the substrate. (C) 2015 Laser Institute of America