Fast Digital Convolutions using Bit-Shifts

An exact, one-to-one transform is presented that not only allows digital circular convolutions, but is free from multiplications and quantisation errors for transform lengths of arbitrary powers of two. The transform is analogous to the Discrete Fourier Transform, with the canonical harmonics replaced by a set of cyclic integers computed using only bit-shifts and additions modulo a prime number. The prime number may be selected to occupy contemporary word sizes or to be very large for cryptographic or data hiding applications. The transform is an extension of the Rader Transforms via Carmichael's Theorem. These properties allow for exact convolutions that are impervious to numerical overflow and to utilise Fast Fourier Transform algorithms.Comment: 4 pages, 2 figures, submitted to IEEE Signal Processing Letter

A Novel Tractor Operated Grass Seed Harvester Developed in India

The demand of green and dry fodder in India is estimated to increase to 1170 and 650 m tonne whereas availability is expected to be at 411.3 and 488 m tonne in 2025, respectively, depicting deficit of about 64.9% green fodder and 24.9% dry fodder (Vision 2030, ICAR - IGFRI, Jhansi, 2011). In forages, availability of quality seed is only 25-30% in cultivated fodder and less than 10 % in range grasses and legumes (Vision 2050, IGFRI). Prices paid for grass seeds of native species vary from Rs.5,000 to 6,500 per kg for clean, un-haired seeds due to excessive use of manual labour in seed collection and removing hairy portion. In order to increase the capacity of collection of grass seeds from standing crop, A tractor operated grass seed harvester was developed under a collaborative research project of Indian Council of Agricultural Research two Institutes viz. Indian Grassland and Fodder Research Institute and Central Institute of Agricultural Engineering, keeping in view the requirements of common grasses used as feed material in Indian context. This grass seed harvester was made using nylon brushes arranged in specific fashion on a rotating cylinder and a winding reel in front of rotating cylinder to collect grass seed from the grasses standing in the fields, where tractor can operate. The specific features of this machine were variable speed of rotating cylinder brush, helical arrangement of brushes on the cylinder to carry the detached seed in to the seed box, variable height of operation and front mounting of the machine on tractor. This machine was tested for seed collection in Pennisetum pedicellatum (Dinanath grass), Cenchrus cilliaris (Anjan grass ) and Megathyrsus maximum (Guinea grass). Seed collection capacity of the machine was 4.24 to 7.12 kg/h in Dinanath grass during 2nd operation, 2.10 to 3.56 kg/h in Anjan grass and 1.61 to 3.56 kg/h in Guinea grass at the full maturity of the grass seeds in two passes of the machine in to and fro direction. The field capacity of seed collection operation ranged from 0.21 to 0.47 ha/h for the grasses in which it was operated

Biomimicked Polymer Surfaces Exhibiting Superhydrophobic and Anti-Reflective Properties

Materials, objects and processes found in nature functions from macro-scale to the nanoscale. Bio-inspiration or biomimetics is a tool to mimic these natural objects to develop functional materials which provide desired properties. There are a large number of examples found in nature such as plants, bacteria, land animals, aquatic animals and insects which provide an inspiration to mimic some structural and functional properties owned by them. For example some plant leaves and flower petals like lotus leaf, rice leaf, taro leaf and rose petal are well known for their superhydrophobic and self-cleaning properties due to the multiscale structural patterns present on their surfaces. This self-cleaning phenomenon also known as “Lotus effect” is due to high contact angle and low contact angle hysteresis. India canna is a common garden plant however structural properties of its various parts such as petal, leaf and seedpod have not been studied in literature. In this work, we studied the super hydrophobic nature of India canna plant. In case of seedpod, it is the high aspect ratio multiscale structures that cause the superhydrophobicity however interestingly in case of leaf and petal, it is low aspect ratio bump like structures for similar behaviour. We mimicked these structural patterns into a number of polymers like PDMS and an organic (resorcinol formaldehyde) gel and found that these biomimicked polymer surfaces also exhibit superhydrophobic property. To add the novelty, polymer surfaces with these multiscale surface patterns has also been studied for their antireflective properties with an inspiration from the moth eye structure. The facile fabrication of superhydrophobic as well as antireflective polymer surfaces by a low cost and simple biomimicking route opens the possibilities of using such surfaces for a wide variety of engineering applications including energy storage devices

Improved Critical Current Density of MgB2 Carbon Nanotubes (CNTs) Composite

In the present study, we report a systematic study of doping/ admixing of carbon nanotubes (CNTs) in different concentrations in MgB2. The composite material corresponding to MgB2+ x at.%CNTs (35 at.% > x > 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/ microstructural characterization employing XRD, SEM and TEM techniques. The magnetization measurements were performed by PPMS and Tc & Jct measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB2-CNTs composites. A CNT connecting the MgB2 grains may enhance critical current density due to its size (~ 5-20 nm diameter) compatible with coherence length of MgB2 (~ 5-6 nm) and ballistic transport current carrying capability along the tube axis. The Jct of MgB2 samples with varying CNTs concentration have been found to vary significantly e.g. Jct of the MgB2 sample with 10 at.% CNT addition is ~2.3 x 10^3 A/cm2 and its value for MgB2 sample without CNT addition is ~7.2x10^2 A/cm2 at 20K. The optimum result on Jc is obtained for 10 at.% CNTs admixed MgB2 sample at 5K, the Jc reaches ~5.2 x10^6 A/cm2 in self field, ~1.6 x 10^6 A/cm2 at 1T, ~2.9 x 10^5 A/cm2 at 2.6T and \~3.9 x 10^4 A/cm2 at 4T. The high value of intragrain Jc in 10 at.% CNTs admixed MgB2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of MgB2, which are capable of providing effective flux pinning centres. A feasible correlation between microstructural features and superconducting properties has been put forward.Comment: 8 pages, 6 figures. To be published in J. Nanoscience and Nanotechnolog