Roberto Piazza - Academia.edu (original) (raw)
Papers by Roberto Piazza
This review aims to provide a simple introduction to the application of optical correlation metho... more This review aims to provide a simple introduction to the application of optical correlation methods in colloidal science. In particular, I plan to show that full appraisal of the intimate relation between light scattering and microscopy allows designing novel powerful investigation techniques that combine their powers. An extended version of this paper will appear in "ColloidalFoundations of Nanoscience", edited by D. Berti and G. Palazzo, Elsevier (ISBN 978-0-444-59541-6). I am very grateful to the publisher for having granted me the permission to post this preprint on arXiv.
Journal of The Royal Society Interface, 2016
Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collec... more Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.
Journal of the Optical Society of America B, 1986
ABSTRACT
Physical Review E Statistical Physics Plasmas Fluids and Related Interdisciplinary Topics, Apr 1, 1994
An experimental investigation of the relaxation of electric birefringence in the critical binary ... more An experimental investigation of the relaxation of electric birefringence in the critical binary mixture n-butylbenzene-propylene carbonate is presented. The decay functions observed at different temperatures in the critical region are clearly nonexponential and show a scaling behavior. The experimental relaxation function is compared with theoretical predictions: the asymptotic decay is a stretched exponential with a stretch exponent 0.40+/-0.03, in good agreement with the dynamic droplet model, but the earlier stages are very well described also by the Onuki-Doi approach [Europhys. Lett. 17, 63 (1992)].
Journal of Physics Condensed Matter, Dec 31, 1998
ABSTRACT
Journal of the Optical Society of America B Optical Physics, 1986
ABSTRACT
Physical review letters, Jan 22, 2016
By experimenting on model colloids where depletion forces can be carefully tuned and quantified, ... more By experimenting on model colloids where depletion forces can be carefully tuned and quantified, we show that attractive interactions consistently "promote" particle settling, so much that the sedimentation velocity of a moderately concentrated dispersion can even exceed its single-particle value. At larger particle volume fraction ϕ, however, hydrodynamic hindrance eventually takes over. Hence, v(ϕ) actually displays a nonmonotonic trend that may threaten the stability of the settling front to thermal perturbations. Finally, by discussing a representative case, we show that these results are relevant to the investigation of protein association effects by ultracentrifugation.
Physical Review Letters, Dec 1, 1991
Page 1. VOLUME 67, NUMBER 27 PH YSICAL REVIEW LETTERS 30 DECEMBER 1991 Single-Particle Dynamics i... more Page 1. VOLUME 67, NUMBER 27 PH YSICAL REVIEW LETTERS 30 DECEMBER 1991 Single-Particle Dynamics in a Colloidal Crystal ... Dynamic depolarized scattering gives information about the"self-motion" of parti-cles within the crystal. ...
Structure and Dynamics of Strongly Interacting Colloids and Supramolecular Aggregates in Solution, 1992
Optics Communications, Aug 1, 1992
ABSTRACT
Journal of the Optical Society of America B
ABSTRACT
Europhysics News, 2015
Suppose that your house needs some restoration, and that you call a master mason asking for an es... more Suppose that your house needs some restoration, and that you call a master mason asking for an estimate. If the mason replies at once that he will quote 1000 € for himself, plus 500 € for each helper apprentice, you will likely be puzzled, if not annoyed. Surely you have good reasons to complain, reasoning that the job you ask for should be remunerated with a fixed amount, irrespective of the number of labourers involved. Yet, this is not a criterion that we usually apply when evaluating the CV of an applicant for an academic position or for a grant.
European Physical Journal E, 2004
This topical issue of The European Physical Journal E deals with mass transport effects driven by... more This topical issue of The European Physical Journal E deals with mass transport effects driven by thermal gradients, or, as we shall call them, with ``thermal forces''. In simple fluid mixtures, coupling of heat and mass diffusion is due to the Ludwig-Soret effect, also known as thermal diffusion. The Soret effect dramatically lowers the thermal convection threshold, since concentration gradients
Light Scattering and Photon Correlation Spectroscopy, 1997
Optics Communications, 1986
Jones matrix calculus for polarized light is used to derive some general properties of cascades o... more Jones matrix calculus for polarized light is used to derive some general properties of cascades of optical retarders. The obtained results are applied to the analysis of electric birefringence experiments on liquids. Our calculations suggest a simple correction method for the effect of stress-induced birefringence on the cell windows. The method is experimentally tested in a satisfactory way.
This review aims to provide a simple introduction to the application of optical correlation metho... more This review aims to provide a simple introduction to the application of optical correlation methods in colloidal science. In particular, I plan to show that full appraisal of the intimate relation between light scattering and microscopy allows designing novel powerful investigation techniques that combine their powers. An extended version of this paper will appear in "ColloidalFoundations of Nanoscience", edited by D. Berti and G. Palazzo, Elsevier (ISBN 978-0-444-59541-6). I am very grateful to the publisher for having granted me the permission to post this preprint on arXiv.
Journal of The Royal Society Interface, 2016
Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collec... more Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.
Journal of the Optical Society of America B, 1986
ABSTRACT
Physical Review E Statistical Physics Plasmas Fluids and Related Interdisciplinary Topics, Apr 1, 1994
An experimental investigation of the relaxation of electric birefringence in the critical binary ... more An experimental investigation of the relaxation of electric birefringence in the critical binary mixture n-butylbenzene-propylene carbonate is presented. The decay functions observed at different temperatures in the critical region are clearly nonexponential and show a scaling behavior. The experimental relaxation function is compared with theoretical predictions: the asymptotic decay is a stretched exponential with a stretch exponent 0.40+/-0.03, in good agreement with the dynamic droplet model, but the earlier stages are very well described also by the Onuki-Doi approach [Europhys. Lett. 17, 63 (1992)].
Journal of Physics Condensed Matter, Dec 31, 1998
ABSTRACT
Journal of the Optical Society of America B Optical Physics, 1986
ABSTRACT
Physical review letters, Jan 22, 2016
By experimenting on model colloids where depletion forces can be carefully tuned and quantified, ... more By experimenting on model colloids where depletion forces can be carefully tuned and quantified, we show that attractive interactions consistently "promote" particle settling, so much that the sedimentation velocity of a moderately concentrated dispersion can even exceed its single-particle value. At larger particle volume fraction ϕ, however, hydrodynamic hindrance eventually takes over. Hence, v(ϕ) actually displays a nonmonotonic trend that may threaten the stability of the settling front to thermal perturbations. Finally, by discussing a representative case, we show that these results are relevant to the investigation of protein association effects by ultracentrifugation.
Physical Review Letters, Dec 1, 1991
Page 1. VOLUME 67, NUMBER 27 PH YSICAL REVIEW LETTERS 30 DECEMBER 1991 Single-Particle Dynamics i... more Page 1. VOLUME 67, NUMBER 27 PH YSICAL REVIEW LETTERS 30 DECEMBER 1991 Single-Particle Dynamics in a Colloidal Crystal ... Dynamic depolarized scattering gives information about the"self-motion" of parti-cles within the crystal. ...
Structure and Dynamics of Strongly Interacting Colloids and Supramolecular Aggregates in Solution, 1992
Optics Communications, Aug 1, 1992
ABSTRACT
Journal of the Optical Society of America B
ABSTRACT
Europhysics News, 2015
Suppose that your house needs some restoration, and that you call a master mason asking for an es... more Suppose that your house needs some restoration, and that you call a master mason asking for an estimate. If the mason replies at once that he will quote 1000 € for himself, plus 500 € for each helper apprentice, you will likely be puzzled, if not annoyed. Surely you have good reasons to complain, reasoning that the job you ask for should be remunerated with a fixed amount, irrespective of the number of labourers involved. Yet, this is not a criterion that we usually apply when evaluating the CV of an applicant for an academic position or for a grant.
European Physical Journal E, 2004
This topical issue of The European Physical Journal E deals with mass transport effects driven by... more This topical issue of The European Physical Journal E deals with mass transport effects driven by thermal gradients, or, as we shall call them, with ``thermal forces''. In simple fluid mixtures, coupling of heat and mass diffusion is due to the Ludwig-Soret effect, also known as thermal diffusion. The Soret effect dramatically lowers the thermal convection threshold, since concentration gradients
Light Scattering and Photon Correlation Spectroscopy, 1997
Optics Communications, 1986
Jones matrix calculus for polarized light is used to derive some general properties of cascades o... more Jones matrix calculus for polarized light is used to derive some general properties of cascades of optical retarders. The obtained results are applied to the analysis of electric birefringence experiments on liquids. Our calculations suggest a simple correction method for the effect of stress-induced birefringence on the cell windows. The method is experimentally tested in a satisfactory way.