O. Mesquita | Universidade São Francisco (original) (raw)

Papers by O. Mesquita

Physical review letters, Jan 27, 1993

We report the first systematic transient dynamics measurements of a cellular instability during d... more We report the first systematic transient dynamics measurements of a cellular instability during directional solidification on a nematic-isotropic interface of the liquid crystal 8cB. The time evolution of the most unstable spatial mode of the interface is well described by a third-order Landau-amplitude equation, as anticipated theoretically. Instability growth rates and nonlinear cubic coefficients are measured as a function of pulling velocity and temperature gradient. The results are compared with theories of directional solidification. PACS numbers: 81.30.Fb, 05.70.Ln, 61.30.Jf A theoretical explanation for morphological instabilities at the solid-liquid interface during solidification was first given by Mullins and Sekerka [1] for the case of free growth. Linear stability analysis of a planar interface during directional solidification of binary mixtures was later treated by the same authors [2l. A nonlinear analysis of this problem was performed by Wollkind and Segel [3] on the so-called "one-sided model," where diffusion of impurities in the solid was neglected. Langer [4] proposed the "symmetric model," where the diffusion of impurities in both phases was equal and the segregation coefficient was set to 1. The nature of the bifurcation is different for each model: In the symmetric model the cellular bifurcation is supercritical whereas for the one-sided model, the bifurcation is mostly subcritical. Caroli, Caroli, and Roulet [5,6] solved the nonlinear problem for the general case, where the impurity diffusivities in both phases could be different and the segregation coefficient could take different values. From the nonlinear analysis, Wollkind and Segel [3], Langer [4], and Caroli, Caroli and Roulet (CCR) [6] demonstrated that near the bifurcation from planar to cellular, the time evolution of the amplitude Ak of the most unstable spatial Fourier mode of the interface with wave vector k can be described by a third-order Landau-amplitude equation, namely,

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

ABSTRACT We present a detailed account of our videomicroscopy experiments on morphological instab... more ABSTRACT We present a detailed account of our videomicroscopy experiments on morphological instabilities of the nonequilibrium nematic-isotropic interface of the liquid crystal 8CB. For the parameter region chosen in our experiments, the time evolution of the amplitude of the most unstable spatial mode of the interface, during the planar-cellular bifurcation, can be well described by a third-order Landau-amplitude equation. Instability growth rates and cubic coefficients are in agreement with the two-sided model of solidification. Interface kinetics was also considered. In addition, we have made an analytical calculation of the Eckhaus boundary for solidification models. Even though we use an amplitude equation in our calculation, we have obtained a tilted Eckhaus boundary. This feature was previously believed to show up only in numerical calculations of complete models of solidification. We attempt to explain the final wave vectors measured in our experiments based on an Eckhaus instability. Another selection mechanism is mentioned.

Physical Review E, 1999

In a directional solidification apparatus, the recoil of the nonsteady planar nematic-isotropic i... more In a directional solidification apparatus, the recoil of the nonsteady planar nematic-isotropic interface of the liquid crystal 8CB doped with hexachloroethane was measured, for different pulling velocities. Results agree very well with the predictions of our two-sided extension of Warren and Langer's one-sided model [Phys. Rev. E 47, 2702 (1993)], therefore supporting the validity of their ansatz about the evolution of the dopant concentration field. From the comparison between experiment and theory we obtain values for the segregation and diffusion coefficients of hexachloroethane in 8CB comparable to those found in the literature and measured by other methods. Using the same procedure, we measured the value of the segregation coefficient of 8CB doped with water as a function of applied sinusoidal electric field perpendicular to the sample, along the homeotropic direction. The segregation coefficient increases with electric field. In addition, preliminary results on the cellular instability in this system show that the capillary length of the pattern also increases with electric field. To our knowledge, this is the first binary system with continuously tunable segregation coefficient and capillary length.

Physical Review E, 2003

With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine k... more With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine kidney cell and keep it suspended in the medium without touching the glass substrate or other cells. Since the optically trapped cell remains with a closely round shape, we can directly measure its volume by using videomicroscopy with digital image analysis. We submit this cell to a hyperosmotic shock ͑up-shock͒ and video record the process: the cell initially shrinks due to osmotic efflux of water and after a while, due to regulatory volume increase ͑RVI͒, an osmoregulation response, it inflates again ͑water influx͒ until it reaches a new volume ͑the regulatory volume V R ). In addition to considering standard osmotic water transport, we model RVI using a simple phenomenological model. We obtain an expression for cell volume variation as a function of time that fits very well with our experimental data, where two characteristic times appear naturally: one related to water transport and the other related to RVI. From the fit we obtain water permeability, osmolyte influx rate for RVI, and regulatory volume. With the addition of the hormone vasopressin, water permeability increases while the regulatory volume decreases until inhibition of RVI. In summary, we present a technique to measure directly volume changes of a single isolated kidney cell under osmotic shock and a phenomenological analysis of water transport that takes into account osmoregulation.

Physical Review E, 2002

Using a single microscope objective lens to optically trap, illuminate, and collect backscattered... more Using a single microscope objective lens to optically trap, illuminate, and collect backscattered light of a dielectric microsphere, we measure the temporal-intensity-autocorrelation functions (ACFs), and intensity profiles to obtain the trap stiffness and friction coefficient of the bead. This is an interesting study of an harmonically bound Brownian particle, with nanometer resolution. We extend the work of Bar-Ziv et al. [Phys. Rev. Lett. 78, 154 (1997)] to more general situations allowing for the use of our simpler geometry in other applications. As examples, we present measurements of the parallel Stokes friction coefficient on the trapped bead as a function of its distance from a surface and the entropic force of a single lambda-DNA molecule.

Physical Review E, 2003

Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom... more Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom used as a useful tool. We revisited the theory of defocusing and apply it to our optical microscope with optics corrected at infinity. In our approximation, we obtain that the image contrast is proportional to the two-dimensional ͑2D͒ Laplacian of the phase difference introduced by the phase object. If the index of refraction of the phase object is uniform the image obtained from defocusing microscopy is the image of curvature ͑Laplacian of the local thickness͒ of the phase object, while standard phase-contrast microscopy gives information about the thickness of the object. We made artificial phase objects and measured image contrasts with defocusing microscopy. Measured contrasts are in excellent agreement with our theoretical model. We use defocusing microscopy to study curvature fluctuations ͑ruffles͒ on the surface of macrophages ͑cell of the innate immune system͒, and try to correlate mechanical properties of macrophage surface and phagocytosis. We observe large coherent propagating structures: Their shape, speed, density are measured and curvature energy estimated. Inhomogeneities of cytoskeleton refractive index, curvature modulations due to thermal fluctuations and/or periodic changes in cytoskeleton-membrane interactions cause random fluctuations in image contrast. From the temporal and spatial contrast correlation functions, we obtain the decay time and correlation length of such fluctuations that are related to their size and the viscoelastic properties of the cytoskeleton. In order to associate the dynamics of cytoskeleton with the process of phagocytosis, we use an optical tweezers to grab a zymosan particle and put it into contact with the macrophage. We then measure the time for a single phagocytosis event. We add the drug cytochalasin D that depolymerizes the cytoskeleton F-actin network: It inhibits the large propagating coherent fluctuations on the cell surface, increases the relaxation time of cytoskeleton fluctuations, and increases the phagocytosis time. Our results suggest that the methods developed in this work can be of utility to assess the importance of cytoskeleton motility in the dynamics of cellular processes such as phagocytosis exhibited by macrophages.

Physical Review Letters, 1998

Stability of a uniformly spaced dendritic array against a spatial period doubling instability was... more Stability of a uniformly spaced dendritic array against a spatial period doubling instability was studied through UV thermal perturbations of every other dendrite tip. We observed that above a critical pulling speed the array is stable against these perturbations and we measured decreasing decay rates of the perturbed mode as we approached the critical speed. In the linear regime, our measurements are qualitatively consistent with the Warren-Langer linear stability analysis for a dendritic array [J.thinspA. Warren and J.thinspS. Langer, Phys.thinspthinspRev.thinspthinspA {bold 42}, 3518 (1990); Phys.thinspthinspRev.thinspthinspE {bold 47}, 2702 (1993)], while in the nonlinear regime fitting to a third order amplitude equation shows that the transition is subcritical. {copyright} {ital 1998} {ital The American Physical Society}

Physical Review A, 1992

We have investigated the phenomenon of intense dynamic light scattering at the nonequilibrium cry... more We have investigated the phenomenon of intense dynamic light scattering at the nonequilibrium crystal-melt interface in succinonitrile and naphthalene, in order to resolve the ongoing controversy over its origin. Of the several models that have been proposed to explain this phenomenon, the microbubble model of H. Z. Cummins {ital et} {ital al}. (Solid State Commun. 60, 857 (1986)) and the mesophase model proposed by J. Bilgram and co-workers (P. Boni, J. H. Bilgram, and W. Kanzig, Phys. Rev. A 28, 2953 (1983)) are the only two still considered to be consistent with most of the experimental observations. In these experiments the angular dependence of the scattered light was investigated. In the mesophase model the angular dependence of the scattered light is described by the Ornstein-Zernike form {ital I}({ital q})={ital I}â(1+{ital q}²ξ²)⁻¹, whereas light scattered by bubbles can be modeled by the Mie scattering theory. The data for both materials were found to be incompatible with the Ornstein-Zernike form, but could be reasonably well fit by the Mie theory. The behavior of the onset of scattering was also investigated, and it was found that the product {ital R}â{ital t0}{ital v{ital g}}² was a constant, where {ital R}â is the onset radius, {ital t}â the onset time, and {ital v}{sub {ital g}} the crystal growth velocity. This result is consistent with the analysis of Mesquita {ital et} {ital al}. (Phys. Rev. B 38, 1550 (1988)), in which the onset of the scattering was modeled by considering the rate of buildup of dissolved gas at the advancing crystal-melt interface. The time taken for the disappearance of the scattering after growth was terminated was also investigated. Lastly, the gases dissolved in our samples of succinonitrile were identified by mass spectroscopy and found to have a composition similar to air.

International Journal of Modern Physics C, 1998

We use molecular dynamics technique for simulating the zone melting process. By tuning the parame... more We use molecular dynamics technique for simulating the zone melting process. By tuning the parameters in the molecule-molecule potential we were able to reproduce segregation and fingering at the interface.

Physical review. A, Jan 15, 1991

ABSTRACT

Physical review. A, 1987

A strong-quasielastic laser light scattering at the growing crystal-melt interface of both biphen... more A strong-quasielastic laser light scattering at the growing crystal-melt interface of both biphenyl and naphthalene was observed in an experiment similar to the one first performed by Bilgram, Guttinger, and Kanzig [Phys. Rev. Lett. 40, 1394 (1978)]. Since its first observation, the origin of this light scattering remained unexplained. Cummins et al. [Solid State Commun. 60, 857 (1986)] suggested that

Physical Review B, 1984

Dynamic light-scattering measurements on the b face of a salol crystal growing into the melt reve... more Dynamic light-scattering measurements on the b face of a salol crystal growing into the melt revealed simultaneous lateral translation dynamics on the crystal surface and slow relaxational dynamics in a thin boundary layer of melt adjacent to the crystal. Analysis of the translational dynamics shows that crystal growth is mediated by highly polygonized screw dislocations. An explanation is suggested for

Applied Physics Letters, 2014

We present Defocusing Microscopy (DM), a bright-field optical microscopy technique able to perfor... more We present Defocusing Microscopy (DM), a bright-field optical microscopy technique able to perform total 3D imaging of transparent objects. By total 3D imaging we mean the determination of the actual shapes of the upper and lower surfaces of a phase object. We propose a new methodology using DM and apply it to red blood cells subject to different osmolality conditions: hypotonic, isotonic and hypertonic solutions. For each situation the shape of the upper and lower cell surface-membranes (lipid bilayer/cytoskeleton) are completely recovered, displaying the deformation of RBCs surfaces due to adhesion on the glass-substrate. The axial resolution of our technique allowed us to image surface-membranes separated by distances as small as 300 nm. Finally, we determine volume, superficial area, sphericity index and RBCs refractive index for each osmotic condition.

Springer Proceedings in Physics, 2000

Physical Review B, 1999

We use molecular dynamics to simulate the directional growth of binary mixtures. Our results comp... more We use molecular dynamics to simulate the directional growth of binary mixtures. Our results compare very well with analytical and experimental results. This opens up the possibility to probe growth situations which are difficult to reach experimentally, being an important tool for further experimental and theoretical developments in the area of crystal growth.

Laser Optics of Condensed Matter, 1988

Scandinavian Journal of Immunology, 2008

Herein, we described an experimental model of high-dose ethanol (EtOH) administration, able to in... more Herein, we described an experimental model of high-dose ethanol (EtOH) administration, able to induce in vitro impairment in macrophage phagocytic capacity, already observed at 24 h after the last EtOH administration. This phenomenon was characterized by enlarged time required for adhesion and internalization events. Parallel studies documented an overall impaired production of interleukin (IL)-6 and nitric oxide (NO) production by peritoneal macrophages in EtOH-treated mice following interferon (IFN)-c and lipopolysaccharide (LPS) stimuli. Although the impaired IL-6 response could not be restored by any of the experimental conditions tested, the lower NO response to INF-c and LPS was overturned by simultaneous IFN-c/LPS stimuli. It was interesting to notice that high-dose EtOH administration drives peritoneal macrophages towards long-term impairment in phagocytosis capacity with slower adhesion time, but with no impact on the time required for internalization. Moreover, 30 days after the last EtOH administration, lower IL-6 response to INF-c and impaired NO production were still observed in response to IFN-c/LPS stimuli, with the IL-6 response to IFN-c being restored by IFN-c/LPS stimuli. Histological studies showed that high-dose EtOH administration led to long-term in vivo impairment of antigen-clearance following OVA-driven delayed-type-hypersensitivity induction, characterized by the presence of a large amount of unprocessed OVA surrounded by dermal inflammatory infiltrate, suggesting defective activity of antigen-presenting cells. Together, these findings supported our hypothesis that the poor antigen clearance in vivo may be related to the impaired macrophage function in vitro. These observations in the murine experimental model may reflect some of the consequences of EtOH consumption by humans.

Physical Review Letters, 1991

JP Gollub, J. Clarke, M. Gharib, B. Lane, and ON Mesquita Department of Physics, Haverford Colleg... more JP Gollub, J. Clarke, M. Gharib, B. Lane, and ON Mesquita Department of Physics, Haverford College, Haverford, Pennsylvania 19041 Institute for Nonlinear Science, The University of California at San Diego, La Jolla, California 90237 Department of Physics, The University of ...

Physical review letters, Jan 27, 1993

We report the first systematic transient dynamics measurements of a cellular instability during d... more We report the first systematic transient dynamics measurements of a cellular instability during directional solidification on a nematic-isotropic interface of the liquid crystal 8cB. The time evolution of the most unstable spatial mode of the interface is well described by a third-order Landau-amplitude equation, as anticipated theoretically. Instability growth rates and nonlinear cubic coefficients are measured as a function of pulling velocity and temperature gradient. The results are compared with theories of directional solidification. PACS numbers: 81.30.Fb, 05.70.Ln, 61.30.Jf A theoretical explanation for morphological instabilities at the solid-liquid interface during solidification was first given by Mullins and Sekerka [1] for the case of free growth. Linear stability analysis of a planar interface during directional solidification of binary mixtures was later treated by the same authors [2l. A nonlinear analysis of this problem was performed by Wollkind and Segel [3] on the so-called "one-sided model," where diffusion of impurities in the solid was neglected. Langer [4] proposed the "symmetric model," where the diffusion of impurities in both phases was equal and the segregation coefficient was set to 1. The nature of the bifurcation is different for each model: In the symmetric model the cellular bifurcation is supercritical whereas for the one-sided model, the bifurcation is mostly subcritical. Caroli, Caroli, and Roulet [5,6] solved the nonlinear problem for the general case, where the impurity diffusivities in both phases could be different and the segregation coefficient could take different values. From the nonlinear analysis, Wollkind and Segel [3], Langer [4], and Caroli, Caroli and Roulet (CCR) [6] demonstrated that near the bifurcation from planar to cellular, the time evolution of the amplitude Ak of the most unstable spatial Fourier mode of the interface with wave vector k can be described by a third-order Landau-amplitude equation, namely,

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

ABSTRACT We present a detailed account of our videomicroscopy experiments on morphological instab... more ABSTRACT We present a detailed account of our videomicroscopy experiments on morphological instabilities of the nonequilibrium nematic-isotropic interface of the liquid crystal 8CB. For the parameter region chosen in our experiments, the time evolution of the amplitude of the most unstable spatial mode of the interface, during the planar-cellular bifurcation, can be well described by a third-order Landau-amplitude equation. Instability growth rates and cubic coefficients are in agreement with the two-sided model of solidification. Interface kinetics was also considered. In addition, we have made an analytical calculation of the Eckhaus boundary for solidification models. Even though we use an amplitude equation in our calculation, we have obtained a tilted Eckhaus boundary. This feature was previously believed to show up only in numerical calculations of complete models of solidification. We attempt to explain the final wave vectors measured in our experiments based on an Eckhaus instability. Another selection mechanism is mentioned.

Physical Review E, 1999

In a directional solidification apparatus, the recoil of the nonsteady planar nematic-isotropic i... more In a directional solidification apparatus, the recoil of the nonsteady planar nematic-isotropic interface of the liquid crystal 8CB doped with hexachloroethane was measured, for different pulling velocities. Results agree very well with the predictions of our two-sided extension of Warren and Langer's one-sided model [Phys. Rev. E 47, 2702 (1993)], therefore supporting the validity of their ansatz about the evolution of the dopant concentration field. From the comparison between experiment and theory we obtain values for the segregation and diffusion coefficients of hexachloroethane in 8CB comparable to those found in the literature and measured by other methods. Using the same procedure, we measured the value of the segregation coefficient of 8CB doped with water as a function of applied sinusoidal electric field perpendicular to the sample, along the homeotropic direction. The segregation coefficient increases with electric field. In addition, preliminary results on the cellular instability in this system show that the capillary length of the pattern also increases with electric field. To our knowledge, this is the first binary system with continuously tunable segregation coefficient and capillary length.

Physical Review E, 2003

With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine k... more With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine kidney cell and keep it suspended in the medium without touching the glass substrate or other cells. Since the optically trapped cell remains with a closely round shape, we can directly measure its volume by using videomicroscopy with digital image analysis. We submit this cell to a hyperosmotic shock ͑up-shock͒ and video record the process: the cell initially shrinks due to osmotic efflux of water and after a while, due to regulatory volume increase ͑RVI͒, an osmoregulation response, it inflates again ͑water influx͒ until it reaches a new volume ͑the regulatory volume V R ). In addition to considering standard osmotic water transport, we model RVI using a simple phenomenological model. We obtain an expression for cell volume variation as a function of time that fits very well with our experimental data, where two characteristic times appear naturally: one related to water transport and the other related to RVI. From the fit we obtain water permeability, osmolyte influx rate for RVI, and regulatory volume. With the addition of the hormone vasopressin, water permeability increases while the regulatory volume decreases until inhibition of RVI. In summary, we present a technique to measure directly volume changes of a single isolated kidney cell under osmotic shock and a phenomenological analysis of water transport that takes into account osmoregulation.

Physical Review E, 2002

Using a single microscope objective lens to optically trap, illuminate, and collect backscattered... more Using a single microscope objective lens to optically trap, illuminate, and collect backscattered light of a dielectric microsphere, we measure the temporal-intensity-autocorrelation functions (ACFs), and intensity profiles to obtain the trap stiffness and friction coefficient of the bead. This is an interesting study of an harmonically bound Brownian particle, with nanometer resolution. We extend the work of Bar-Ziv et al. [Phys. Rev. Lett. 78, 154 (1997)] to more general situations allowing for the use of our simpler geometry in other applications. As examples, we present measurements of the parallel Stokes friction coefficient on the trapped bead as a function of its distance from a surface and the entropic force of a single lambda-DNA molecule.

Physical Review E, 2003

Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom... more Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom used as a useful tool. We revisited the theory of defocusing and apply it to our optical microscope with optics corrected at infinity. In our approximation, we obtain that the image contrast is proportional to the two-dimensional ͑2D͒ Laplacian of the phase difference introduced by the phase object. If the index of refraction of the phase object is uniform the image obtained from defocusing microscopy is the image of curvature ͑Laplacian of the local thickness͒ of the phase object, while standard phase-contrast microscopy gives information about the thickness of the object. We made artificial phase objects and measured image contrasts with defocusing microscopy. Measured contrasts are in excellent agreement with our theoretical model. We use defocusing microscopy to study curvature fluctuations ͑ruffles͒ on the surface of macrophages ͑cell of the innate immune system͒, and try to correlate mechanical properties of macrophage surface and phagocytosis. We observe large coherent propagating structures: Their shape, speed, density are measured and curvature energy estimated. Inhomogeneities of cytoskeleton refractive index, curvature modulations due to thermal fluctuations and/or periodic changes in cytoskeleton-membrane interactions cause random fluctuations in image contrast. From the temporal and spatial contrast correlation functions, we obtain the decay time and correlation length of such fluctuations that are related to their size and the viscoelastic properties of the cytoskeleton. In order to associate the dynamics of cytoskeleton with the process of phagocytosis, we use an optical tweezers to grab a zymosan particle and put it into contact with the macrophage. We then measure the time for a single phagocytosis event. We add the drug cytochalasin D that depolymerizes the cytoskeleton F-actin network: It inhibits the large propagating coherent fluctuations on the cell surface, increases the relaxation time of cytoskeleton fluctuations, and increases the phagocytosis time. Our results suggest that the methods developed in this work can be of utility to assess the importance of cytoskeleton motility in the dynamics of cellular processes such as phagocytosis exhibited by macrophages.

Physical Review Letters, 1998

Stability of a uniformly spaced dendritic array against a spatial period doubling instability was... more Stability of a uniformly spaced dendritic array against a spatial period doubling instability was studied through UV thermal perturbations of every other dendrite tip. We observed that above a critical pulling speed the array is stable against these perturbations and we measured decreasing decay rates of the perturbed mode as we approached the critical speed. In the linear regime, our measurements are qualitatively consistent with the Warren-Langer linear stability analysis for a dendritic array [J.thinspA. Warren and J.thinspS. Langer, Phys.thinspthinspRev.thinspthinspA {bold 42}, 3518 (1990); Phys.thinspthinspRev.thinspthinspE {bold 47}, 2702 (1993)], while in the nonlinear regime fitting to a third order amplitude equation shows that the transition is subcritical. {copyright} {ital 1998} {ital The American Physical Society}

Physical Review A, 1992

We have investigated the phenomenon of intense dynamic light scattering at the nonequilibrium cry... more We have investigated the phenomenon of intense dynamic light scattering at the nonequilibrium crystal-melt interface in succinonitrile and naphthalene, in order to resolve the ongoing controversy over its origin. Of the several models that have been proposed to explain this phenomenon, the microbubble model of H. Z. Cummins {ital et} {ital al}. (Solid State Commun. 60, 857 (1986)) and the mesophase model proposed by J. Bilgram and co-workers (P. Boni, J. H. Bilgram, and W. Kanzig, Phys. Rev. A 28, 2953 (1983)) are the only two still considered to be consistent with most of the experimental observations. In these experiments the angular dependence of the scattered light was investigated. In the mesophase model the angular dependence of the scattered light is described by the Ornstein-Zernike form {ital I}({ital q})={ital I}â(1+{ital q}²ξ²)⁻¹, whereas light scattered by bubbles can be modeled by the Mie scattering theory. The data for both materials were found to be incompatible with the Ornstein-Zernike form, but could be reasonably well fit by the Mie theory. The behavior of the onset of scattering was also investigated, and it was found that the product {ital R}â{ital t0}{ital v{ital g}}² was a constant, where {ital R}â is the onset radius, {ital t}â the onset time, and {ital v}{sub {ital g}} the crystal growth velocity. This result is consistent with the analysis of Mesquita {ital et} {ital al}. (Phys. Rev. B 38, 1550 (1988)), in which the onset of the scattering was modeled by considering the rate of buildup of dissolved gas at the advancing crystal-melt interface. The time taken for the disappearance of the scattering after growth was terminated was also investigated. Lastly, the gases dissolved in our samples of succinonitrile were identified by mass spectroscopy and found to have a composition similar to air.

International Journal of Modern Physics C, 1998

We use molecular dynamics technique for simulating the zone melting process. By tuning the parame... more We use molecular dynamics technique for simulating the zone melting process. By tuning the parameters in the molecule-molecule potential we were able to reproduce segregation and fingering at the interface.

Physical review. A, Jan 15, 1991

ABSTRACT

Physical review. A, 1987

A strong-quasielastic laser light scattering at the growing crystal-melt interface of both biphen... more A strong-quasielastic laser light scattering at the growing crystal-melt interface of both biphenyl and naphthalene was observed in an experiment similar to the one first performed by Bilgram, Guttinger, and Kanzig [Phys. Rev. Lett. 40, 1394 (1978)]. Since its first observation, the origin of this light scattering remained unexplained. Cummins et al. [Solid State Commun. 60, 857 (1986)] suggested that

Physical Review B, 1984

Dynamic light-scattering measurements on the b face of a salol crystal growing into the melt reve... more Dynamic light-scattering measurements on the b face of a salol crystal growing into the melt revealed simultaneous lateral translation dynamics on the crystal surface and slow relaxational dynamics in a thin boundary layer of melt adjacent to the crystal. Analysis of the translational dynamics shows that crystal growth is mediated by highly polygonized screw dislocations. An explanation is suggested for

Applied Physics Letters, 2014

We present Defocusing Microscopy (DM), a bright-field optical microscopy technique able to perfor... more We present Defocusing Microscopy (DM), a bright-field optical microscopy technique able to perform total 3D imaging of transparent objects. By total 3D imaging we mean the determination of the actual shapes of the upper and lower surfaces of a phase object. We propose a new methodology using DM and apply it to red blood cells subject to different osmolality conditions: hypotonic, isotonic and hypertonic solutions. For each situation the shape of the upper and lower cell surface-membranes (lipid bilayer/cytoskeleton) are completely recovered, displaying the deformation of RBCs surfaces due to adhesion on the glass-substrate. The axial resolution of our technique allowed us to image surface-membranes separated by distances as small as 300 nm. Finally, we determine volume, superficial area, sphericity index and RBCs refractive index for each osmotic condition.

Springer Proceedings in Physics, 2000

Physical Review B, 1999

We use molecular dynamics to simulate the directional growth of binary mixtures. Our results comp... more We use molecular dynamics to simulate the directional growth of binary mixtures. Our results compare very well with analytical and experimental results. This opens up the possibility to probe growth situations which are difficult to reach experimentally, being an important tool for further experimental and theoretical developments in the area of crystal growth.

Laser Optics of Condensed Matter, 1988

Scandinavian Journal of Immunology, 2008

Herein, we described an experimental model of high-dose ethanol (EtOH) administration, able to in... more Herein, we described an experimental model of high-dose ethanol (EtOH) administration, able to induce in vitro impairment in macrophage phagocytic capacity, already observed at 24 h after the last EtOH administration. This phenomenon was characterized by enlarged time required for adhesion and internalization events. Parallel studies documented an overall impaired production of interleukin (IL)-6 and nitric oxide (NO) production by peritoneal macrophages in EtOH-treated mice following interferon (IFN)-c and lipopolysaccharide (LPS) stimuli. Although the impaired IL-6 response could not be restored by any of the experimental conditions tested, the lower NO response to INF-c and LPS was overturned by simultaneous IFN-c/LPS stimuli. It was interesting to notice that high-dose EtOH administration drives peritoneal macrophages towards long-term impairment in phagocytosis capacity with slower adhesion time, but with no impact on the time required for internalization. Moreover, 30 days after the last EtOH administration, lower IL-6 response to INF-c and impaired NO production were still observed in response to IFN-c/LPS stimuli, with the IL-6 response to IFN-c being restored by IFN-c/LPS stimuli. Histological studies showed that high-dose EtOH administration led to long-term in vivo impairment of antigen-clearance following OVA-driven delayed-type-hypersensitivity induction, characterized by the presence of a large amount of unprocessed OVA surrounded by dermal inflammatory infiltrate, suggesting defective activity of antigen-presenting cells. Together, these findings supported our hypothesis that the poor antigen clearance in vivo may be related to the impaired macrophage function in vitro. These observations in the murine experimental model may reflect some of the consequences of EtOH consumption by humans.

Physical Review Letters, 1991

JP Gollub, J. Clarke, M. Gharib, B. Lane, and ON Mesquita Department of Physics, Haverford Colleg... more JP Gollub, J. Clarke, M. Gharib, B. Lane, and ON Mesquita Department of Physics, Haverford College, Haverford, Pennsylvania 19041 Institute for Nonlinear Science, The University of California at San Diego, La Jolla, California 90237 Department of Physics, The University of ...