Sharath Ananthamurthy - Academia.edu (original) (raw)
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Papers by Sharath Ananthamurthy
AIP Conference Proceedings (American Institute of Physics); (USA), Oct 20, 1989
We have studied Ca-He spin changing collisions using far wing laser scattering half-collision... more We have studied Ca-He spin changing collisions using far wing laser scattering half-collision'' techniques. We have observed a strong red wing-blue wing asymmetry which we interpret in terms of an orbital alignment preference in the energy transfer cross section. This orbital alignment effect approaches 100%.
arXiv (Cornell University), Feb 15, 2011
We have carried out a comparative study of the microrheological properties of silk fibroin soluti... more We have carried out a comparative study of the microrheological properties of silk fibroin solutions formed from a variety of silks indigenous to the Indian subcontinent. We present the measured viscoelastic moduli of Tasar silk fibroin solution using both a single and dual optical tweezer at 0.16% and 0.25% (w/v). The bandwidth of the measurements carried out using optical tweezers is extended down to the lower frequency regime by a video microscopy measurement. Further, we have measured the viscoelastic moduli of Eri and Muga varieties of silk fibroin solutions at a higher concentration (1.00% w/v) limiting the tool of measurement to video microscopy, as the reduced optical transparencies of these solutions at higher concentration preclude an optical tweezer based investigation. The choice of a higher concentration of fibroin solution of the latter silk varieties is so as to enable a comparison of the shear moduli obtained from optical methods with their corresponding fibre stiffness obtained from wide angle X-ray scattering data. We report a correlation between the microstructure and microrheological parameters of these silk varieties for the concentration of fibroin solutions studied.
Bulletin of Materials Science, Jun 1, 2008
We have investigated the rheological properties of regenerated silk fibroin (RSF), a viscoelastic... more We have investigated the rheological properties of regenerated silk fibroin (RSF), a viscoelastic material at micro and nano length scales, by video microscopy. We describe here the principles and technique of video microscopy as a tool in such investigations. In this work, polystyrene beads were dispersed in the matrix of RSF polymer and the positions of the embedded beads diffusing were tracked using video microscopy. An optical tweezer was used to transport and locate the bead at any desired site within the micro-volume of the sample, to facilitate the subsequent free-bead video analysis. The position information of the beads was used to obtain the time dependant mean squared displacement (MSD) of the beads in the medium and hence to calculate the dynamic moduli of the medium. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. The technique is complementary to other microrheological techniques to characterize the material, but additionally enables one to characterize local inhomogeneities in the medium, features that get averaged out in bulk characterization procedures.
BASI, Dec 1, 2004
CCD photometric observations of three open clusters Berkeley 15 (=OCl 414), Czernik 18 (=OCl 426)... more CCD photometric observations of three open clusters Berkeley 15 (=OCl 414), Czernik 18 (=OCl 426) and NGC 2401 (=OCl 588), obtained for the first time in UBVRI filters down to V=20 mag, are presented here. They are located at distances of 1259, 955 and 3467 parsecs with their respective ages estimated as ~5 x 109 years, ~0.8 to 1 x
Journal of Molecular Liquids, Jul 1, 2019
At the room temperature, the rotational reorientations times of three probes 7-DHB, Qu-390, and C... more At the room temperature, the rotational reorientations times of three probes 7-DHB, Qu-390, and C-6H have been examined in primary alcohol solvent series, by employing the steady-state fluorescence depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Experimental observation shows that C-6H probe rotates slower in solvents when compared to the other two probe molecules. 7-DHB and Qu-390 probes show relatively same rotational reorientation time with 10% of deviation. Hydrodynamic models-Stokes Einstein's Debye theory (SED) with a stick, slip boundary conditions limits, Quasihydrodynamic models-Dote-Kivelson-Schwartz and Geirer-Wirtz were, used to determine mechanical friction and the results are found interesting trend towards super stick behavior. Also, dielectric frictional theories-Nee-Zwanzig and van der Zwan-Hynes were used to examine dielectric friction. Both dielectric friction models, overestimate dielectric friction contributions for all the three probes is observed in alcohol series. Outcomes are explained in the context of the theoretical models, size effects were not noticed and the probability of hydrogen bonding among an amino functional group of the solute molecules and-OH functional group of the alcohols.
Journal of Chemical Physics, Feb 1, 1995
We have measured the product alignment resulting from the collisional redistribution of polarized... more We have measured the product alignment resulting from the collisional redistribution of polarized light in Sr–He inelastic spin-changing energy transfer collisions. The experimental results are in good agreement with the predictions of an analytic theoretical model, based on a standard orbital-locking and following approximation, but generalized to this inelastic collision process. The good agreement indicates a clear understanding of the energy transfer dynamics in this case, and suggests that this simple analytic approach may be generalized to a much broader range of collisional phenomena.
Indian Journal of Physics, Aug 1, 2010
Since the first proposal and demonstration of an optical trap to hold micron sized particles by A... more Since the first proposal and demonstration of an optical trap to hold micron sized particles by Ashkin in 1986, optical tweezer-based techniques for control and manipulation of particles has seen tremendous progress and enabled the exploration of the structure and dynamics of materials at the nano length scale. In biophysical applications, these techniques have enabled a range of activities from measurements of very small forces (at sub-pN levels) at operation within cells thus assisting in the elucidation of intracellular transport mechanisms, to obtaining elastic parameters of biomolecules. The techniques have helped in gaining insights on the viscoelastic properties at micro and nano length scales of a range of soft materials such as colloids, polymer melts, bio membranes etc. The paper describes some of the studies carried out by us to understand polymer structure and elasticity of these materials in solution. The domains of "passive" and "active" rheology are explained with examples of studies undertaken to address these domains. The work using video microscopy to study silk fibroin solutions is used to exemplify the domain of passive rheology. We present recent work on bacterial solutions wherein live bacteria influence the optical trap region and thereby help us study the local viscoelasticity of such a medium.
Pramana, Oct 1, 2005
The optical tweezer is a versatile setup that can be employed in a wide variety of studies invest... more The optical tweezer is a versatile setup that can be employed in a wide variety of studies investigating the microscopic properties of materials. In particular, this setup has in recent times been gainfully employed in probing rheological properties of materials that exhibit viscoelasticity. These measurements can provide data at the micro and nanometer scales, not normally accessible by rheometers that are used for measurements on bulk samples. In this work we describe a single laser beam optical tweezer setup , which is built around an inverted open microscope. The trapped polystyrene particle bead's deviation from the trap potential minimum is monitored by laser backscattering technique and the bead position measured by a quadrant photodiode detector. Additionally, a provision is made for video microscopic studies on dispersed beads using a CCD camera. A single particle microrheological experiment that can be performed using the setup is described with relevant calculations.
Asian Journal of Physics, 2011
We have built a low-cost Scanning Fabry Perot Interferometer for use in student laboratory. Our s... more We have built a low-cost Scanning Fabry Perot Interferometer for use in student laboratory. Our setup consists of two highly reflecting concave mirrors facing each other and mounted on a home built chassis. One of the mirrors is attached to a piezo buzzer extracted from a motorcycle horn and is driven with a triangular wave from a signal generator, or through a 50 Hz AC output from a variac. Light from a laser source to be diagnosed is made to enter the Fabry Perot cavity. The beam that undergoes multiple reflections emerges from a hole through the mirror-PZT combination and is made incident on a fast photodiode. A simple amplifier circuit optimizes the signal monitored on an oscilloscope. The Free Spectral Range (FSR) of the device is 5 GHz, and much larger than the FSR of the laser under test. Using this we were able to clearly resolve the longitudinal modes of a He-Ne 3mW laser. The FSR of the laser is measured to be 838 MHz. The Fabry-Perot setup alone costs less than Rs. 1500 to build. The design is simple and can be built as student projects, and is an ideal tool for laser diagnostics. It can be used to make accurate measurements without having to resort to commercially available interferometers that are expensive.
arXiv (Cornell University), 2008
The polarization of radiation by scattering on an atom embedded in combined external quadrupole e... more The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Analytic formulae are derived for the scattering phase matrix. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed.
Nucleation and Atmospheric Aerosols, 2002
We have experimentally investigated the behaviour of an electron cloud confined in a Penning trap... more We have experimentally investigated the behaviour of an electron cloud confined in a Penning trap at weak superimposed magnetic fields. Exciting the motional frequencies of the electrons by an external drive field we found the axial mode split into two components which were identified as center-of-mass and individual electron oscillations. When the trapping potential was varied, rapid electron loss appeared at numerous values of the applied voltage. They are determined by the relation nto, + n,,o,, = q. 0)o, 0 m, qý are the axial, magnetron, and cyclotron frequency of the trapped electrons, respectively. The reason for this loss is attributed to higher order contributions to the ideal quadrupole trapping potential.
AIP Conference Proceedings (American Institute of Physics); (USA), Oct 20, 1989
We have studied Ca-He spin changing collisions using far wing laser scattering half-collision... more We have studied Ca-He spin changing collisions using far wing laser scattering half-collision'' techniques. We have observed a strong red wing-blue wing asymmetry which we interpret in terms of an orbital alignment preference in the energy transfer cross section. This orbital alignment effect approaches 100%.
arXiv (Cornell University), Feb 15, 2011
We have carried out a comparative study of the microrheological properties of silk fibroin soluti... more We have carried out a comparative study of the microrheological properties of silk fibroin solutions formed from a variety of silks indigenous to the Indian subcontinent. We present the measured viscoelastic moduli of Tasar silk fibroin solution using both a single and dual optical tweezer at 0.16% and 0.25% (w/v). The bandwidth of the measurements carried out using optical tweezers is extended down to the lower frequency regime by a video microscopy measurement. Further, we have measured the viscoelastic moduli of Eri and Muga varieties of silk fibroin solutions at a higher concentration (1.00% w/v) limiting the tool of measurement to video microscopy, as the reduced optical transparencies of these solutions at higher concentration preclude an optical tweezer based investigation. The choice of a higher concentration of fibroin solution of the latter silk varieties is so as to enable a comparison of the shear moduli obtained from optical methods with their corresponding fibre stiffness obtained from wide angle X-ray scattering data. We report a correlation between the microstructure and microrheological parameters of these silk varieties for the concentration of fibroin solutions studied.
Bulletin of Materials Science, Jun 1, 2008
We have investigated the rheological properties of regenerated silk fibroin (RSF), a viscoelastic... more We have investigated the rheological properties of regenerated silk fibroin (RSF), a viscoelastic material at micro and nano length scales, by video microscopy. We describe here the principles and technique of video microscopy as a tool in such investigations. In this work, polystyrene beads were dispersed in the matrix of RSF polymer and the positions of the embedded beads diffusing were tracked using video microscopy. An optical tweezer was used to transport and locate the bead at any desired site within the micro-volume of the sample, to facilitate the subsequent free-bead video analysis. The position information of the beads was used to obtain the time dependant mean squared displacement (MSD) of the beads in the medium and hence to calculate the dynamic moduli of the medium. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. The technique is complementary to other microrheological techniques to characterize the material, but additionally enables one to characterize local inhomogeneities in the medium, features that get averaged out in bulk characterization procedures.
BASI, Dec 1, 2004
CCD photometric observations of three open clusters Berkeley 15 (=OCl 414), Czernik 18 (=OCl 426)... more CCD photometric observations of three open clusters Berkeley 15 (=OCl 414), Czernik 18 (=OCl 426) and NGC 2401 (=OCl 588), obtained for the first time in UBVRI filters down to V=20 mag, are presented here. They are located at distances of 1259, 955 and 3467 parsecs with their respective ages estimated as ~5 x 109 years, ~0.8 to 1 x
Journal of Molecular Liquids, Jul 1, 2019
At the room temperature, the rotational reorientations times of three probes 7-DHB, Qu-390, and C... more At the room temperature, the rotational reorientations times of three probes 7-DHB, Qu-390, and C-6H have been examined in primary alcohol solvent series, by employing the steady-state fluorescence depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Experimental observation shows that C-6H probe rotates slower in solvents when compared to the other two probe molecules. 7-DHB and Qu-390 probes show relatively same rotational reorientation time with 10% of deviation. Hydrodynamic models-Stokes Einstein's Debye theory (SED) with a stick, slip boundary conditions limits, Quasihydrodynamic models-Dote-Kivelson-Schwartz and Geirer-Wirtz were, used to determine mechanical friction and the results are found interesting trend towards super stick behavior. Also, dielectric frictional theories-Nee-Zwanzig and van der Zwan-Hynes were used to examine dielectric friction. Both dielectric friction models, overestimate dielectric friction contributions for all the three probes is observed in alcohol series. Outcomes are explained in the context of the theoretical models, size effects were not noticed and the probability of hydrogen bonding among an amino functional group of the solute molecules and-OH functional group of the alcohols.
Journal of Chemical Physics, Feb 1, 1995
We have measured the product alignment resulting from the collisional redistribution of polarized... more We have measured the product alignment resulting from the collisional redistribution of polarized light in Sr–He inelastic spin-changing energy transfer collisions. The experimental results are in good agreement with the predictions of an analytic theoretical model, based on a standard orbital-locking and following approximation, but generalized to this inelastic collision process. The good agreement indicates a clear understanding of the energy transfer dynamics in this case, and suggests that this simple analytic approach may be generalized to a much broader range of collisional phenomena.
Indian Journal of Physics, Aug 1, 2010
Since the first proposal and demonstration of an optical trap to hold micron sized particles by A... more Since the first proposal and demonstration of an optical trap to hold micron sized particles by Ashkin in 1986, optical tweezer-based techniques for control and manipulation of particles has seen tremendous progress and enabled the exploration of the structure and dynamics of materials at the nano length scale. In biophysical applications, these techniques have enabled a range of activities from measurements of very small forces (at sub-pN levels) at operation within cells thus assisting in the elucidation of intracellular transport mechanisms, to obtaining elastic parameters of biomolecules. The techniques have helped in gaining insights on the viscoelastic properties at micro and nano length scales of a range of soft materials such as colloids, polymer melts, bio membranes etc. The paper describes some of the studies carried out by us to understand polymer structure and elasticity of these materials in solution. The domains of "passive" and "active" rheology are explained with examples of studies undertaken to address these domains. The work using video microscopy to study silk fibroin solutions is used to exemplify the domain of passive rheology. We present recent work on bacterial solutions wherein live bacteria influence the optical trap region and thereby help us study the local viscoelasticity of such a medium.
Pramana, Oct 1, 2005
The optical tweezer is a versatile setup that can be employed in a wide variety of studies invest... more The optical tweezer is a versatile setup that can be employed in a wide variety of studies investigating the microscopic properties of materials. In particular, this setup has in recent times been gainfully employed in probing rheological properties of materials that exhibit viscoelasticity. These measurements can provide data at the micro and nanometer scales, not normally accessible by rheometers that are used for measurements on bulk samples. In this work we describe a single laser beam optical tweezer setup , which is built around an inverted open microscope. The trapped polystyrene particle bead's deviation from the trap potential minimum is monitored by laser backscattering technique and the bead position measured by a quadrant photodiode detector. Additionally, a provision is made for video microscopic studies on dispersed beads using a CCD camera. A single particle microrheological experiment that can be performed using the setup is described with relevant calculations.
Asian Journal of Physics, 2011
We have built a low-cost Scanning Fabry Perot Interferometer for use in student laboratory. Our s... more We have built a low-cost Scanning Fabry Perot Interferometer for use in student laboratory. Our setup consists of two highly reflecting concave mirrors facing each other and mounted on a home built chassis. One of the mirrors is attached to a piezo buzzer extracted from a motorcycle horn and is driven with a triangular wave from a signal generator, or through a 50 Hz AC output from a variac. Light from a laser source to be diagnosed is made to enter the Fabry Perot cavity. The beam that undergoes multiple reflections emerges from a hole through the mirror-PZT combination and is made incident on a fast photodiode. A simple amplifier circuit optimizes the signal monitored on an oscilloscope. The Free Spectral Range (FSR) of the device is 5 GHz, and much larger than the FSR of the laser under test. Using this we were able to clearly resolve the longitudinal modes of a He-Ne 3mW laser. The FSR of the laser is measured to be 838 MHz. The Fabry-Perot setup alone costs less than Rs. 1500 to build. The design is simple and can be built as student projects, and is an ideal tool for laser diagnostics. It can be used to make accurate measurements without having to resort to commercially available interferometers that are expensive.
arXiv (Cornell University), 2008
The polarization of radiation by scattering on an atom embedded in combined external quadrupole e... more The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Analytic formulae are derived for the scattering phase matrix. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed.
Nucleation and Atmospheric Aerosols, 2002
We have experimentally investigated the behaviour of an electron cloud confined in a Penning trap... more We have experimentally investigated the behaviour of an electron cloud confined in a Penning trap at weak superimposed magnetic fields. Exciting the motional frequencies of the electrons by an external drive field we found the axial mode split into two components which were identified as center-of-mass and individual electron oscillations. When the trapping potential was varied, rapid electron loss appeared at numerous values of the applied voltage. They are determined by the relation nto, + n,,o,, = q. 0)o, 0 m, qý are the axial, magnetron, and cyclotron frequency of the trapped electrons, respectively. The reason for this loss is attributed to higher order contributions to the ideal quadrupole trapping potential.