651 research outputs found
The layer disorders defect in coir fiber under thermal and chemical treatment
Natural coir fibers, subjectd to thermal treatments in the range of 0oC
to 200oC and alkali treatment with 5% to 30% concentration w/w, have been used in
the present investigation to determine the interlayer variability of the cellulose
planes (020), (110) and (110). Among the equatorial reflections (110), (110) and
(020), the extent of variability is found to be more with the proportion of such
affected planes less for (020) reflection in the native cellulose at lower
temperature while at higher temperature (110) and (110) become more affected by
variability defect. (110) and (1 10) planes are more affected also with alkali
treatment.The layer disorders defect in coir fiber under thermal and chemical treatment
D N Mahato*, B K Mathur and S Bhattacharjee
Department of Physics, Indian Institute of Technology,
Kharagpur-721 302, West Bengal, India
E-mail : [email protected] of Physics, Indian Institute of Technology,
Kharagpur-721 302, West Bengal, Indi
Aperiodic tumbling of microrods advected in a microchannel flow
We report on an experimental investigation of the tumbling of microrods in
the shear flow of a microchannel (40 x 2.5 x 0.4 mm). The rods are 20 to 30
microns long and their diameters are of the order of 1 micron. Images of the
centre-of-mass motion and the orientational dynamics of the rods are recorded
using a microscope equipped with a CCD camera. A motorised microscope stage is
used to track individual rods as they move along the channel. Automated image
analysis determines the position and orientation of a tracked rods in each
video frame. We find different behaviours, depending on the particle shape, its
initial position, and orientation. First, we observe periodic as well as
aperiodic tumbling. Second, the data show that different tumbling trajectories
exhibit different sensitivities to external perturbations. These observations
can be explained by slight asymmetries of the rods. Third we observe that after
some time, initially periodic trajectories lose their phase. We attribute this
to drift of the centre of mass of the rod from one to another stream line of
the channel flow.Comment: 14 pages, 8 figures, as accepted for publicatio
Surface Defects from Fractional Branes -- II
A generic half-BPS surface defect of supersymmetric U
Yang-Mills theory is described by a partition of and a
set of continuous parameters. We show that such a defect can be realized
by stacks of fractional D3-branes in Type II B string theory on a
orbifold background in which the brane world-volume is partially
extended along the orbifold directions. In this set up we show that the
continuous parameters correspond to constant background values of certain
twisted closed string scalars of the orbifold. These results extend and
generalize what we have presented for the simple defects in a previous paper.Comment: 37 page
Surface defects from fractional branes. Part I
We show that the Gukov-Witten monodromy defects of supersymmetric Yang-Mills theory can be realized in perturbative string theory by considering an orbifold background of the Kanno-Tachikawa type and placing stacks of fractional D3-branes whose world-volume partially extends along the orbifold directions. In particular, we show that turning on a constant background value for some scalar fields in the closed string twisted sectors induces a non-trivial profile for the gauge field and one of the complex scalars of the world-volume theory, and that this profile exactly matches the singular behavior that oneexpects for a Gukov-Witten surface defect in the N = 4 super Yang-Mills theory. To keep the presentation as simple as possible, in this work we restrict our analysis to surface defects corresponding to a \u21242 orbifold and defer the study of the most general case to a companion paper
Biomimetic synthesis of hybrid nanocomposite scaffolds by freeze-thawing and freeze-drying
The aim of this study is to biomimetically synthesize hydroxyapatite - hydrophilic polymer scaffolds for biomedical applications. This organic-inorganic hybrid has been structurally characterized and reveals a good microstructural control as seen by the SEM analysis and the nanosize of the particulates is confirmed by AFM microscopy. The characterization of such nano-structured composites would allow researchers to design new systems, tailoring properties for different applications. © Indian Academy of Sciences
Mega riverbed-patterns: linear and weakly nonlinear perspectives
In this paper, we explore the mega riverbed-patterns, whose longitudinal and vertical length dimensions scale with a few channel widths and the flow depth, respectively. We perform the stability analyses from both linear and weakly nonlinear perspectives by considering a steady-uniform flow in an erodible straight channel comprising a uniform sediment size. The mathematical framework stands on the dynamic coupling between the depth-averaged flow model and the particle transport model including both bedload and suspended load via the Exner equation, which drives the pattern formation. From the linear perspective, we employ the standard linearization technique by superimposing the periodic perturbations on the undisturbed system to find the dispersion relationship. From the weakly nonlinear perspective, we apply the centre-manifold-projection technique, where the fast dynamics of stable modes is projected on the slow dynamics of weakly unstable modes to obtain the Stuart-Landau equation for the amplitude dynamics. We examine the marginal stability, growth rate and amplitude of patterns for a given quintet formed by the channel aspect ratio, wavenumber of patterns, shear Reynolds number, Shields number and relative roughness number. This study highlights the sensitivity of pattern formation to the key parameters and shows how the classical results can be reconstructed on the parameter space. © 2021 The Authors
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