A comment on generalized Schwinger effect

A spatially homogeneous, time-dependent, electric field can produce charged particle pairs from the vacuum. When the electric field is constant, the mean number of pairs which are produced depends on the electric field and the coupling constant in a non-analytic manner, showing that this result cannot be obtained from the standard perturbation theory of quantum electrodynamics. When the electric field varies with time and vanishes asymptotically, the result may depend on the coupling constant either analytically or non-analytically. We investigate the nature of this dependence in detail. We show that the dependence of particle production on coupling constant is non-analytic for a class of time-dependent electric fields which vanish asymptotically when a specific condition is satisfied. We also demonstrate that for another class of electric fields, which vary rapidly, the dependence of particle production on coupling constant is analytic.Comment: published versio

Optimization of drafting zone variables in ring spinning for the production of cotton/milkweed blended yarns

Cotton/milkweed (60/40) blended yarn of 29.5 tex has been produced on a ring spinning system. The influence of fibre friction, front zone roller setting and front top roller pressure at speed frame and ring frame on yarn properties has been studied using the Box and Behnken design. The optimum conditions within the processing limits of the machines are established. It is observed that a higher fibre friction gives higher yarn tenacity and lower yarn unevenness, imperfection and hairiness. The roller setting and top roller pressure also influence the yarn properties at speed frame and ring frame. With the increase in roller setting the yarn tenacity increases initially and then decreases, while other yarn properties deteriorate at wider roller settings. The increase in top roller pressure leads to reduction in yarn unevenness, imperfection and hairiness due to better control of milkweed fibres in the drafting zone. In general, blends of cotton/alkali-treated milkweed fibres with moderate to lower roller setting and moderate to higher level of top roller pressure give better results

Spinnability of cotton/milkweed blends on ring, compact and rotor spinning systems

The physical characteristics of cotton/milkweed yarns spun on ring, compact and rotor spinning systems in relation to blend proportion and chemical treatment of milkweed fibres have been studied. During spinning of milkweed fibre blends, greater fibre losses in carding and flies during drafting are observed in further stages. It is observed that amongst the ring, compact and rotor yarns, the compact-spun blended yarns show higher yarn tenacity and elongation values followed by ring and rotor-spun yarns. The rotor-spun blended yarns show lower yarn unevenness, imperfections and hairiness values than compact and ring-spun yarns due to its mechanism of yarn formation. With the increase in milkweed proportion, the yarn quality deteriorates, irrespective of spinning systems due to lack of cohesiveness and brittleness of milkweed fibres, and drastic reduction in yarn quality is noticed for 40/60 cotton/milkweed blend. By considering the effect of chemical treatment of milkweed fibres, it is observed that the alkali-treated milkweed fibre blended yarns show better yarn properties due to improvement in fibre friction and elongation values followed by dyed and untreated milkweed fibres

Optimization of process variables in rotor spinning for the production of cotton/milkweed blended yarns

Cotton/milkweed (60/40) blended yarn of 29.5 tex has been produced on rotor spinning system. The influence of fibre friction, opening roller speed and sliver linear density on rotor yarn properties has been studied using Box and Behnken factorial design and the optimum conditions within the processing limits of the machines are established. The results show that fibre friction is the dominant factor in determining the tensile properties and other properties of rotor-spun yarn. It is observed that a higher fibre friction gives higher yarn tenacity, and lower yarn unevenness, imperfection and hairiness. The opening roller speed also has a greater influence on rotor yarn properties.  With an increase in opening roller speed, the number of points per fibre increases, which results in better fibre separation and improvement in yarn properties. But very high opening roller speed deteriorates the yarn properties and increases the end breakage rate mainly due to fibre breakage and low fibre straightness. Generally, heavier sliver weight leads to higher spinning draft which deteriorates the yarn properties

Analysis of structural properties of cotton/milkweed blended ring, compact and rotor yarns

This study has been conducted to explore the relationship between yarn structure and yarn characteristics of cotton/milkweed (C/M) blended yarns. The fibre migration index values reveal that the milkweed fibres are predominantly in the yarn sheath of C/M 80/20 yarn, whereas it occupies the yarn core in C/M 60/40 and 40/60 combinations as small clusters. Fibre migration studies reveal that the compact spun yarns have higher fibre migration factor which is responsible for their tenacity followed by ring- and rotor-spun yarns. The effective packing density of C/M blended yarn decreases with the increase in milkweed blend proportion due to less cohesiveness and poor self locking structure of fibres in the yarn cross-section

Investigation of structural, magnetic and optical properties of rare earth substituted bismuth ferrite

Polycrystalline BiFeO3 and rare earth substituted Bi 0.9R0.1FeO3 (BRFO, R=Y, Ho and Er) compounds were prepared by rapid solid state sintering technique. Structural phase analysis indicated that all the compounds stabilized in rhombohedral structure (R3c space group) and a small orthorhombic phase fraction was observed in BRFO compounds. From the Raman spectra results, the changes in the phonon frequencies (A1) and line widths suggested lattice distortion in the BRFO compounds as was evidenced in the XRD analysis. Compared to the linear variation of magnetization with magnetic field (M-H) shown by BFO, an obvious M-H loop was observed in BRFO compounds which could be due to the suppression of space modulated spin structure and was explained on the basis of weak ferromagnetism and field induced spin reorientation. UV-Vis spectroscopy evidenced a change in local FeO6 environment due to shift in the 6A 1g→4T2g energy transition band. BRFO compounds with improved remnant magnetization and coercive field are applicable for magnetoelectric devices

Thermal and sound insulation properties of chiengora blended nonwoven fabrics

A novel animal fibre chiengora has been explored for its potential application in textile. Chiengora fibres are made intononwoven fabrics by blending with polyester fibre in different proportions for their better strength. Nonwoven fabrics arealso produced from wool and polyester blends in different proportions for comparison. Hair of Lhasa Apso breed dog ischosen to blend with polyester to produce the nonwoven fabric and is analysed for its thermal and sound insulationcharacteristics. It is observed that 100% chiengora nonwoven fabric has thermal insulation value of 0.211 clo which is 42%higher than that of 100% wool nonwoven fabric (0.121 clo). The 70:30 chiengora/polyester fabric shows a thermalinsulation values of 0.141 clo which is higher than 100% wool nonwoven fabric. The chiengora nonwoven fabrics alsopossess similar sound insulation properties like wool [noise reduction coefficient value (NRC) of 0.23 for chiengora and0.22 for wool]. The increase in the chiengora and wool content in the blends reduces the tensile strength, tear strength andair permeability of the nonwoven fabrics. It is concluded that the chiengora blended nonwoven fabrics could be used as aneffective padding material because of their better thermal insulation and sound absorption properties