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Roberto Rusconi

Bio: Roberto Rusconi is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Thermal conductivity & Nanofluid. The author has an hindex of 27, co-authored 41 publications receiving 3300 citations. Previous affiliations of Roberto Rusconi include École Polytechnique Fédérale de Lausanne & ETH Zurich.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors discuss the fluid physics governing the locomotion and feeding of individual planktonic microorganisms (≤ 1 mm) and provide a review of the recent advances in this area.
Abstract: The diversity of the morphologies, propulsion mechanisms, flow environments, and behaviors of planktonic microorganisms has long provided inspiration for fluid physicists, with further intrigue provided by the counterintuitive hydrodynamics of their viscous world. Motivation for studying the fluid dynamics of microplankton abounds, as microorganisms support the food web and control the biogeochemistry of most aquatic environments, particularly the oceans. In this review, we discuss the fluid physics governing the locomotion and feeding of individual planktonic microorganisms (≤1 mm). In the past few years, the field has witnessed an increasing number of exciting discoveries, from the visualization of the flow field around individual swimmers to linkages between microhydrodynamic processes and ecosystem dynamics. In other areas, chiefly the ability of microorganisms to take up nutrients and sense hydromechanical signals, our understanding will benefit from reinvigorated interest, and ample opportunities for breakthroughs exist. When it comes to the fluid mechanics of living organisms, there is plenty of room at the bottom.

462 citations

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TL;DR: It is shown that hydrodynamic shear, which creates forces and torques on bacterial suspensions, stimulates the attachment of bacteria to surfaces and seriously hinders chemotaxis.
Abstract: Bacteria often reside in fluids. Now, it is shown that hydrodynamic shear, which creates forces and torques on bacterial suspensions, stimulates the attachment of bacteria to surfaces and seriously hinders chemotaxis.

334 citations

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TL;DR: In this article, the authors show that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating,fractal confguration.
Abstract: We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating,fractal confguration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluids.

227 citations

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TL;DR: In this paper, a combination of static and continuous-flow biofilm experiments was used to show that Psl, one major polysaccharide in the Pseudomonas aeruginosa biofilm matrix, provides a generic first line of defense toward antibiotics with diverse biochemical properties during the initial stages of biofilm development.
Abstract: Bacteria within biofilms secrete and surround themselves with an extracellular matrix, which serves as a first line of defense against antibiotic attack. Polysaccharides constitute major elements of the biofilm matrix and are implied in surface adhesion and biofilm organization, but their contributions to the resistance properties of biofilms remain largely elusive. Using a combination of static and continuous-flow biofilm experiments we show that Psl, one major polysaccharide in the Pseudomonas aeruginosa biofilm matrix, provides a generic first line of defense toward antibiotics with diverse biochemical properties during the initial stages of biofilm development. Furthermore, we show with mixed-strain experiments that antibiotic-sensitive “non-producing” cells lacking Psl can gain tolerance by integrating into Psl-containing biofilms. However, non-producers dilute the protective capacity of the matrix and hence, excessive incorporation can result in the collapse of resistance of the entire community. Our data also reveal that Psl mediated protection is extendible to E. coli and S. aureus in co-culture biofilms. Together, our study shows that Psl represents a critical first bottleneck to the antibiotic attack of a biofilm community early in biofilm development.

219 citations

Journal ArticleDOI
TL;DR: The formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow is reported and a link between the accumulation of extracellular matrix and the development of these structures is identified.
Abstract: Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments.

190 citations


Cited by
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Journal ArticleDOI
TL;DR: The physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies, are reviewed and the hydrodynamic aspects of swimming are addressed.
Abstract: Locomotion and transport of microorganisms in fluids is an essential aspect of life. Search for food, orientation toward light, spreading of off-spring, and the formation of colonies are only possible due to locomotion. Swimming at the microscale occurs at low Reynolds numbers, where fluid friction and viscosity dominates over inertia. Here, evolution achieved propulsion mechanisms, which overcome and even exploit drag. Prominent propulsion mechanisms are rotating helical flagella, exploited by many bacteria, and snake-like or whip-like motion of eukaryotic flagella, utilized by sperm and algae. For artificial microswimmers, alternative concepts to convert chemical energy or heat into directed motion can be employed, which are potentially more efficient. The dynamics of microswimmers comprises many facets, which are all required to achieve locomotion. In this article, we review the physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies. Starting from individual microswimmers, we describe the various propulsion mechanism of biological and synthetic systems and address the hydrodynamic aspects of swimming. This comprises synchronization and the concerted beating of flagella and cilia. In addition, the swimming behavior next to surfaces is examined. Finally, collective and cooperate phenomena of various types of isotropic and anisotropic swimmers with and without hydrodynamic interactions are discussed.

1,220 citations

Journal ArticleDOI
TL;DR: In this article, the authors review the physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies, including synchronization and the concerted beating of flagella and cilia.
Abstract: Locomotion and transport of microorganisms in fluids is an essential aspect of life. Search for food, orientation toward light, spreading of off-spring, and the formation of colonies are only possible due to locomotion. Swimming at the microscale occurs at low Reynolds numbers, where fluid friction and viscosity dominates over inertia. Here, evolution achieved propulsion mechanisms, which overcome and even exploit drag. Prominent propulsion mechanisms are rotating helical flagella, exploited by many bacteria, and snake-like or whip-like motion of eukaryotic flagella, utilized by sperm and algae. For artificial microswimmers, alternative concepts to convert chemical energy or heat into directed motion can be employed, which are potentially more efficient. The dynamics of microswimmers comprises many facets, which are all required to achieve locomotion. In this article, we review the physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies. Starting from individual microswimmers, we describe the various propulsion mechanism of biological and synthetic systems and address the hydrodynamic aspects of swimming. This comprises synchronization and the concerted beating of flagella and cilia. In addition, the swimming behavior next to surfaces is examined. Finally, collective and cooperate phenomena of various types of isotropic and anisotropic swimmers with and without hydrodynamic interactions are discussed.

983 citations

Journal ArticleDOI
TL;DR: This review summarises both historical and recent scientific data in support of the known biofilm resistance and tolerance mechanisms and suggestions for future work in the field are provided.
Abstract: Biofilms are surface-attached groups of microbial cells encased in an extracellular matrix that are significantly less susceptible to antimicrobial agents than non-adherent, planktonic cells. Biofilm-based infections are, as a result, extremely difficult to cure. A wide range of molecular mechanisms contribute to the high degree of recalcitrance that is characteristic of biofilm communities. These mechanisms include, among others, interaction of antimicrobials with biofilm matrix components, reduced growth rates and the various actions of specific genetic determinants of antibiotic resistance and tolerance. Alone, each of these mechanisms only partially accounts for the increased antimicrobial recalcitrance observed in biofilms. Acting in concert, however, these defences help to ensure the survival of biofilm cells in the face of even the most aggressive antimicrobial treatment regimens. This review summarises both historical and recent scientific data in support of the known biofilm resistance and tolerance mechanisms. Additionally, suggestions for future work in the field are provided.

956 citations

Journal ArticleDOI
TL;DR: The International Nanofluid Property Benchmark Exercise (INPBE) as mentioned in this paper was held in 1998, where the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids" was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady state methods, and optical methods.
Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

942 citations

Journal ArticleDOI
TL;DR: In this article, the effects of particle volume fraction, temperature and particle size on thermal conductivity of alumina/water and copper oxide/water nanofluids were investigated.

886 citations