The Experts below are selected from a list of 9348 Experts worldwide ranked by ideXlab platform

Suresh Narayanan - One of the best experts on this subject based on the ideXlab platform.

  • sub microsecond resolved multi speckle x ray Photon Correlation Spectroscopy with a pixel array detector
    Journal of Synchrotron Radiation, 2018
    Co-Authors: Qingteng Zhang, Eric M. Dufresne, Suresh Narayanan, P Grybos, P Maj, R Szczygiel, Anna Koziol, M R Sutton, Alec Sandy
    Abstract:

    Small-angle X-ray Photon Correlation Spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a Photon-counting pixel array detector with a dynamic range of 0-3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame-1 or 826 ns frame-1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi-speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm-radius gold and 57 nm-radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one- and two-Photon counts was examined by comparing the statistical distribution of Photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel-response dead-time.

  • hard sphere like dynamics in highly concentrated alpha crystallin suspensions
    Physical Review E, 2018
    Co-Authors: Preeti Vodnala, George M. Thurston, Nuwan Karunaratne, Michael Vega, Elizabeth R Gaillard, L. B. Lurio, Qingteng Zhang, Suresh Narayanan, Alec Sandy, Eric M. Dufresne
    Abstract:

    The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray Photon Correlation Spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

  • submillisecond x ray Photon Correlation Spectroscopy from a pixel array detector with fast dual gating and no readout dead time
    Journal of Synchrotron Radiation, 2016
    Co-Authors: Qingteng Zhang, Eric M. Dufresne, Suresh Narayanan, P Grybos, Piotr Kmon, P Maj, G Deptuch, R Szczygiel, Alec Sandy
    Abstract:

    Small-angle scattering X-ray Photon Correlation Spectroscopy (XPCS) studies were performed using a novel Photon-counting pixel array detector with dual counters for each pixel. Each counter can be read out independently from the other to ensure there is no readout dead-time between the neighboring frames. A maximum frame rate of 11.8 kHz was achieved. Results on test samples show good agreement with simple diffusion. The potential of extending the time resolution of XPCS beyond the limit set by the detector frame rate using dual counters is also discussed.

  • a 960 960 fast frame store ccd detector for x ray Photon Correlation Spectroscopy
    Nuclear Science Symposium and Medical Imaging Conference, 2014
    Co-Authors: John Weizeorick, T Madden, Suresh Narayanan, Alec Sandy, Sufeng Niu, Devis Contarato, P Denes, Dionisio Doering, J Joseph, Patrick Mcvittie
    Abstract:

    This paper describes a 960×960 Frame Store Fast Charge-Coupled Device (CCD) x-ray detector being used for x-ray Photon Correlation Spectroscopy (XPCS) at the Advanced Photon Source (APS) on the 8-ID-I beam line. The detector is typically operated in either the 960 × 960 pixel mode at 100 frames per second (fps) or in the 960×90 pixel mode at 1000 fps. The vacuum subsystems consist of a top board with a custom CCD sensor, two digitizer boards with 12 custom readout chips, and a CCD clock driver board. The digitized data from the detector head is sent to a Camera Interface Node (CIN) located inside an Advanced Telecommunication Computing Architecture (ATCA) chassis. One or more processor blades in the ATCA chassis use the Message Passing Interface (MPI) protocol to perform real time parallel processing on the incoming data. When the image processing is complete, the data is stored, where it is available for further processing.

  • Dynamics of Cadmium Sulfide Nanoparticles within Polystyrene Melts
    2014
    Co-Authors: Woo-sik Jang, Suresh Narayanan, Alec Sandy, Peter Koo, Kyle Bryson, Thomas P. Russell, S G J Mochrie
    Abstract:

    We present a detailed study of the dynamics of cadmium sulfide nanoparticles suspended in polystyrene homopolymer matrices using X-ray Photon Correlation Spectroscopy for temperatures between 120 and 180 °C. For low molecular weight polystyrene homopolymers, the observed dynamics show a crossover from diffusive to hyper-diffusive behavior with decreasing temperatures. For higher molecular weight polystyrene, the nanoparticle dynamics appear hyper-diffusive at all temperatures studied. The relaxation time and characteristic velocity determined from the measured hyper-diffusive dynamics reveal that the activation energy and underlying forces determined are on the order of 2.14 × 10–19 J and 87 pN, respectively

Alec Sandy - One of the best experts on this subject based on the ideXlab platform.

  • sub microsecond resolved multi speckle x ray Photon Correlation Spectroscopy with a pixel array detector
    Journal of Synchrotron Radiation, 2018
    Co-Authors: Qingteng Zhang, Eric M. Dufresne, Suresh Narayanan, P Grybos, P Maj, R Szczygiel, Anna Koziol, M R Sutton, Alec Sandy
    Abstract:

    Small-angle X-ray Photon Correlation Spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a Photon-counting pixel array detector with a dynamic range of 0-3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame-1 or 826 ns frame-1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi-speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm-radius gold and 57 nm-radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one- and two-Photon counts was examined by comparing the statistical distribution of Photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel-response dead-time.

  • hard sphere like dynamics in highly concentrated alpha crystallin suspensions
    Physical Review E, 2018
    Co-Authors: Preeti Vodnala, George M. Thurston, Nuwan Karunaratne, Michael Vega, Elizabeth R Gaillard, L. B. Lurio, Qingteng Zhang, Suresh Narayanan, Alec Sandy, Eric M. Dufresne
    Abstract:

    The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray Photon Correlation Spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

  • submillisecond x ray Photon Correlation Spectroscopy from a pixel array detector with fast dual gating and no readout dead time
    Journal of Synchrotron Radiation, 2016
    Co-Authors: Qingteng Zhang, Eric M. Dufresne, Suresh Narayanan, P Grybos, Piotr Kmon, P Maj, G Deptuch, R Szczygiel, Alec Sandy
    Abstract:

    Small-angle scattering X-ray Photon Correlation Spectroscopy (XPCS) studies were performed using a novel Photon-counting pixel array detector with dual counters for each pixel. Each counter can be read out independently from the other to ensure there is no readout dead-time between the neighboring frames. A maximum frame rate of 11.8 kHz was achieved. Results on test samples show good agreement with simple diffusion. The potential of extending the time resolution of XPCS beyond the limit set by the detector frame rate using dual counters is also discussed.

  • a 960 960 fast frame store ccd detector for x ray Photon Correlation Spectroscopy
    Nuclear Science Symposium and Medical Imaging Conference, 2014
    Co-Authors: John Weizeorick, T Madden, Suresh Narayanan, Alec Sandy, Sufeng Niu, Devis Contarato, P Denes, Dionisio Doering, J Joseph, Patrick Mcvittie
    Abstract:

    This paper describes a 960×960 Frame Store Fast Charge-Coupled Device (CCD) x-ray detector being used for x-ray Photon Correlation Spectroscopy (XPCS) at the Advanced Photon Source (APS) on the 8-ID-I beam line. The detector is typically operated in either the 960 × 960 pixel mode at 100 frames per second (fps) or in the 960×90 pixel mode at 1000 fps. The vacuum subsystems consist of a top board with a custom CCD sensor, two digitizer boards with 12 custom readout chips, and a CCD clock driver board. The digitized data from the detector head is sent to a Camera Interface Node (CIN) located inside an Advanced Telecommunication Computing Architecture (ATCA) chassis. One or more processor blades in the ATCA chassis use the Message Passing Interface (MPI) protocol to perform real time parallel processing on the incoming data. When the image processing is complete, the data is stored, where it is available for further processing.

  • Dynamics of Cadmium Sulfide Nanoparticles within Polystyrene Melts
    2014
    Co-Authors: Woo-sik Jang, Suresh Narayanan, Alec Sandy, Peter Koo, Kyle Bryson, Thomas P. Russell, S G J Mochrie
    Abstract:

    We present a detailed study of the dynamics of cadmium sulfide nanoparticles suspended in polystyrene homopolymer matrices using X-ray Photon Correlation Spectroscopy for temperatures between 120 and 180 °C. For low molecular weight polystyrene homopolymers, the observed dynamics show a crossover from diffusive to hyper-diffusive behavior with decreasing temperatures. For higher molecular weight polystyrene, the nanoparticle dynamics appear hyper-diffusive at all temperatures studied. The relaxation time and characteristic velocity determined from the measured hyper-diffusive dynamics reveal that the activation energy and underlying forces determined are on the order of 2.14 × 10–19 J and 87 pN, respectively

Andrzej Dobek - One of the best experts on this subject based on the ideXlab platform.

  • effect of ions on the polymorphism effective charge and stability of human telomeric dna Photon Correlation Spectroscopy and circular dichroism studies
    Journal of Physical Chemistry B, 2005
    Co-Authors: Agnieszka Wlodarczyk, Przemyslaw R Grzybowski, A Patkowski, Andrzej Dobek
    Abstract:

    The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)4 has been studied by Photon Correlation Spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K+, Na+, Rb+, Li+, Cs+, and Sr2+ ions were recorded by CD Spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 °C has shown that the presence of a single Sr2+ ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl2 at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr2+ ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)4 is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients DT of the ...

  • effect of ions on the polymorphism effective charge and stability of human telomeric dna Photon Correlation Spectroscopy and circular dichroism studies
    Journal of Physical Chemistry B, 2005
    Co-Authors: Agnieszka Wlodarczyk, Przemyslaw R Grzybowski, A Patkowski, Andrzej Dobek
    Abstract:

    The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by Photon Correlation Spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K(+), Na(+), Rb(+), Li(+), Cs(+), and Sr(2+) ions were recorded by CD Spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 degrees C has shown that the presence of a single Sr(2+) ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl(2) at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr(2+) ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)(4) is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients D(T) of the structures present in solution have been determined by Photon Correlation Spectroscopy and the effective charges on the structures have been calculated by combining the experimental data with the results based on the coupled mode theory. Analysis of the melting points monitored by the CD method has permitted a determination of Deltan, the number of ions released in the process of thermal denaturation. All the results are in good agreement with the predictions based on the theory of polyelectrolytes. The effect of ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by Photon Correlation Spectroscopy and circular dichroism.

S G J Mochrie - One of the best experts on this subject based on the ideXlab platform.

  • Dynamics of Cadmium Sulfide Nanoparticles within Polystyrene Melts
    2014
    Co-Authors: Woo-sik Jang, Suresh Narayanan, Alec Sandy, Peter Koo, Kyle Bryson, Thomas P. Russell, S G J Mochrie
    Abstract:

    We present a detailed study of the dynamics of cadmium sulfide nanoparticles suspended in polystyrene homopolymer matrices using X-ray Photon Correlation Spectroscopy for temperatures between 120 and 180 °C. For low molecular weight polystyrene homopolymers, the observed dynamics show a crossover from diffusive to hyper-diffusive behavior with decreasing temperatures. For higher molecular weight polystyrene, the nanoparticle dynamics appear hyper-diffusive at all temperatures studied. The relaxation time and characteristic velocity determined from the measured hyper-diffusive dynamics reveal that the activation energy and underlying forces determined are on the order of 2.14 × 10–19 J and 87 pN, respectively

  • the static and dynamic structure factor of a diblock copolymer melt via small angle x ray scattering and x ray Photon Correlation Spectroscopy
    Macromolecules, 2013
    Co-Authors: Woo-sik Jang, Suresh Narayanan, Alec Sandy, Peter K Koo, Marcin Sykorsky, S G J Mochrie
    Abstract:

    We present a detailed X-ray scattering study of the static and dynamic behavior of a styrene–isoprene diblock copolymer melt with a styrene volume fraction of 0.3468. At 115 and 120 °C, we observe splitting of the principal Bragg peak, which we attribute to phase coexistence of hexagonal cylindrical and cubic double-gyroid structure. In the disordered phase, above 130 °C, we have characterized the dynamics of composition fluctuations via X-ray Photon Correlation Spectroscopy. Near the peak of the static structure factor, these fluctuations show stretched-exponential relaxations, characterized by a stretching exponent of about 0.36 for a range of temperatures immediately above the MST. The corresponding characteristic relaxation times vary exponentially with temperature, changing by a factor of 2 for each 2 °C change in temperature. At low wavevectors, the measured relaxations are diffusive with relaxation times that change by a factor of 2 for each 8 °C change in temperature.

  • dynamic signatures of microphase separation in a block copolymer melt determined by x ray Photon Correlation Spectroscopy and rheology
    Macromolecules, 2010
    Co-Authors: Amish J Patel, Suresh Narayanan, Alec Sandy, S G J Mochrie, Hiroshi Watanabe, Nitash P Balsara
    Abstract:

    The relationship between structure and dynamics in a polystyrene-polyisoprene block copolymer melt in the vicinity of the order−disorder transition was studied by small-angle X-ray scattering (SAXS), X-ray Photon Correlation Spectroscopy (XPCS), and rheology. Rheological measurements on the disordered state indicate the presence of a fast process arising from the relaxation of polyisoprene chains and a slow process resulting predominantly from the relaxation of concentration fluctuations. In contrast, XPCS measurements of the disordered phase are dominated by diffusion of micelles. Time-resolved SAXS, XPCS, and rheology experiments on samples quenched from disorder-to-order reveal the existence of two regimes. While the microscopic relaxation time, measured by XPCS, increases after all of the quenches, SAXS and rheological signatures of ordering are only seen when the quench depth exceeds a critical value of 10 °C. For quenches 5 °C below the order-to-disorder transition temperature, no changes in the SAX...

  • how a liquid becomes a glass both on cooling and on heating
    Physical Review Letters, 2008
    Co-Authors: S G J Mochrie, Suresh Narayanan, Alec Sandy, Michael Sprung
    Abstract:

    The onset of structural arrest and glass formation in a concentrated suspension of silica nanoparticles in a water-lutidine binary mixture near its consolute point is studied by exploiting the near-critical fluid degrees of freedom to control the strength of an attraction between particles and multispeckle x-ray Photon Correlation Spectroscopy to determine the particles' collective dynamics. This model system undergoes a glass transition both on cooling and on heating, and the intermediate liquid realizes unusual logarithmic relaxations. How vitrification occurs for the two different glass transitions is characterized in detail and comparisons are drawn to recent theoretical predictions for glass formation in systems with attractive interactions.

  • crossover from stretched to compressed exponential relaxations in a polymer based sponge phase
    Physical Review Letters, 2006
    Co-Authors: P Falus, Suresh Narayanan, Alec Sandy, M A Borthwick, S G J Mochrie
    Abstract:

    X-ray Photon Correlation Spectroscopy was used to characterize the wave vector- and temperature-dependent dynamics of spontaneous thermal fluctuations in a sponge (L3) phase that occurs in a blend of a symmetric poly(styrene-ethylene/butylene-styrene) triblock copolymer with a polystyrene homopolymer. Measurements of the intermediate scattering function reveal a crossover from stretched- to compressed-exponential relaxations as the temperature is lowered from 180 to 120 degrees C.

Agnieszka Wlodarczyk - One of the best experts on this subject based on the ideXlab platform.

  • effect of ions on the polymorphism effective charge and stability of human telomeric dna Photon Correlation Spectroscopy and circular dichroism studies
    Journal of Physical Chemistry B, 2005
    Co-Authors: Agnieszka Wlodarczyk, Przemyslaw R Grzybowski, A Patkowski, Andrzej Dobek
    Abstract:

    The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)4 has been studied by Photon Correlation Spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K+, Na+, Rb+, Li+, Cs+, and Sr2+ ions were recorded by CD Spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 °C has shown that the presence of a single Sr2+ ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl2 at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr2+ ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)4 is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients DT of the ...

  • effect of ions on the polymorphism effective charge and stability of human telomeric dna Photon Correlation Spectroscopy and circular dichroism studies
    Journal of Physical Chemistry B, 2005
    Co-Authors: Agnieszka Wlodarczyk, Przemyslaw R Grzybowski, A Patkowski, Andrzej Dobek
    Abstract:

    The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by Photon Correlation Spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K(+), Na(+), Rb(+), Li(+), Cs(+), and Sr(2+) ions were recorded by CD Spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 degrees C has shown that the presence of a single Sr(2+) ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl(2) at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr(2+) ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)(4) is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients D(T) of the structures present in solution have been determined by Photon Correlation Spectroscopy and the effective charges on the structures have been calculated by combining the experimental data with the results based on the coupled mode theory. Analysis of the melting points monitored by the CD method has permitted a determination of Deltan, the number of ions released in the process of thermal denaturation. All the results are in good agreement with the predictions based on the theory of polyelectrolytes. The effect of ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by Photon Correlation Spectroscopy and circular dichroism.