Multiphase flows in microfluidics

Various aspects of microfluidic flows with different immiscible constituents are addressed. The fundamental physical characteristics are proposed, as well as the flow regimes which are determined by the wetting and surface tension properties. These fundamental aspects are followed by engineering applications that emerge in microfluidics, namely the creation of microbubbles or drops. Further applications are also discussed, such as the transfer of heat in bubbly flows, or the transport of colloids and emulsions. To cite this article: C.N. Baroud, H. Willaime, C. R. Physique 5 (2004).     

Luminescence induced by a scanning-tunneling microscope as a nanophotonic probe

The luminescence of nanostructured systems can be excited highly locally by the tip of a Scanning Tunneling Microscope (STM). We first present briefly the principles of this STM-induced luminescence. Then we present a review of selected results in STM-induced luminescence from the point of view of nano-scale photonics. We illustrate various contrast mechanisms with different examples of nanostructured systems. To cite this article: F. Silly, F. Charra, C. R. Physique 3 (2002) 493–500.     

The amazing phases of small systems

Small systems, notably clusters of tens or hundreds of atoms or molecules, exhibit forms almost precisely analogous to the phases of bulk systems. However their small sizes make these systems behave in ways quite different from their bulk counterparts. These differences can be elucidated and related to the behavior of bulk systems. Understanding these relationships gives us new insights into the traditional, classical bulk phase transitions, and shows us some unique properties of phases and phase equilibrium of nanoscale systems. To cite this article: R.S. Berry, C. R. Physique 3 (2002) 319–326.     

Vesicles and red blood cells in flow: From individual dynamics to rheology

The rheology of suspensions of soft particles, such as red blood cells, is a long-standing problem in science and engineering due to the complex interplay between deformable microstructure and the macroscale flow. The major challenge stems from the free-boundary nature of the particle interface. Lipid bilayer membranes that envelop cells and vesicles are particularly complex interfaces because of their unusual mechanics: the molecularly thin membrane is a highly-flexible incompressible fluid sheet. As a result, particles made of closed lipid bilayers (red cells and vesicles) can exhibit richer dynamics than would capsules and drops. We overview the key experimental observations and recent advances in the theoretical modeling of the vesicles and red blood cells in flow. To cite this article: P.M. Vlahovska et al., C. R. Physique 10 (2009).     

Quasistatic rheology and the origins of strain

Features of rheological laws applied to solid-like granular materials are recalled and confronted to microscopic approaches via discrete numerical simulations. We give examples of model systems with very similar equilibrium stress transport properties—the much-studied force chains and force distribution—but qualitatively different strain responses to stress increments. Results on the stability of elastoplastic contact networks lead to the definition of two different rheological regimes, according to whether a macroscopic fragility property (propensity to rearrange under arbitrary small stress increments in the thermodynamic limit) applies. Possible consequences are discussed. To cite this article: J.-N. Roux, G. Combe, C. R. Physique 3 (2002) 131–140.     

Review: Rheological properties of biological materials

Eukaryotic cells and biological materials are described from a rheological point of view. Single cells possess typical microrheological properties which can affect cell behaviour, in close connection with their adhesion properties. Single cell properties are also important in the context of multicellular systems, i.e. in biological tissues. Results from experiments are analyzed and models proposed both at the cellular scale and the macroscopic scale. To cite this article: C. Verdier et al., C. R. Physique 10 (2009).     

Sonochemical synthesis and characterization of three nano zinc(II) coordination polymers; Precursors for preparation of zinc(II) oxide nanoparticles

Nanostructures of three Zinc(II) coordination polymers, [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) {NNO: Nicotinic acid N-oxide, PNNO: Picolinic acid N-oxide and INNO: Isonicotinic acid N-oxide}, have been synthesized by a sonochemical process and reaction of ligands with Zn(CH₃COO)₂. The Zinc(II) oxide nano-particles have been synthesized from thermolysis of [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) at two different methods (with surfactant and without surfactant) and two temperatures (200 and 600 °C). The ZnO nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Comparison of the SEM images of ZnO nano-particles at two different methods and temperatures shows that higher temperature results in an increasing of agglomeration and thus small and spherical ZnO particles with good separation were produced by thermolysis of compounds at 200 °C and by use of surfactant.     

Modelling of electromagnetic wave interactions with the human body

Electromagnetic modelling plays a more and more important role in the study of complex systems involving Maxwell phenomena, such as the interactions of radiowaves with the human body. Simulation then becomes a credible means in decision making, related to the engineering of complex electromagnetic systems. To increase confidence in the models with respect to reality, validation and uncertainty estimation methods are needed. The different dimensions of model validation are illustrated through dosimetry, i.e., quantification of human exposure to electromagnetic waves. To cite this article: M.-F. Wong, J. Wiart, C. R. Physique 6 (2005).     

Derived thermodynamic design data for rankine power cycle systems operating on R22

Theoretical Rankine power cycle efficiencies ν_R and the pressure (PR) have been presented for rankine power cycles operating on R22. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 40–85°C in 5°C increments. Composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO - T_CO) illustrates the feasible operating range for R22 power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of the Rankine power cycle systems operating on R22.     

Derived thermodynamic design data for rankine power cycle systems operating on R502

Theoretical Rankine power cycle efficiencies ν_R and the pressure (PR) have been presented for Rankine power cycles operating on R502. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 35–80°C in 5°C increments. A composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO - T_CO illustrates the feasible operating range for R502 power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of Rankine power cycle systems operating on R502.     

Derived thermodynamic design data for rankine power cycle systems operating on R142b

Theoretical Rankine power cycle efficiencies ν_R and the (PR) have been presented for Rankine power cycles operating on R142b. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 25–125°C in 5°C increments. A composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO − T_CO) illustrates the feasible operating range for R142b power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of the Rankine power cycle systems operating on R142b.     

Life prediction for HLW containers – issues related to long-term extrapolation of corrosion resistance

Traditionally, the corrosion behaviour of container materials can be predicted by extrapolation from relatively short-term experiments. Approaches to life prediction are described for two kinds of materials: carbon steel (corrosion allowance material) which must resist general corrosion, and passive materials (corrosion-resistant materials) which may suffer localized corrosion phenomena (pitting and crevice corrosion). The current theoretical and empirical basis for extrapolating the behavior of these materials to long periods emphasizes the significant gaps in understanding. To improve the credibility of life prediction, and to prove the robustness of geological disposal systems, predictive models based on mechanistic understanding are needed. This work is probably more difficult for the corrosion-resistant materials than for corrosion-allowance materials. To cite this article: J.-M. Gras, C. R. Physique 3 (2002) 891–902.     

Magnetization process in cluster spin glass model in the low temperature region

An ensemble of magnetic clusters is approximated by an ensemble of two-singlet systems: at each lattice site l there are two levels, ?_l,1 and ?_l,2. ?_l,1 is associated with spin zero and ?_l,2 with spin 1 (or vice versa). Δ = ?_l,2??_l,1 originates from some intra-cluster interaction and some effective magnetic field; for the both some distribution is assumed. An exchange interaction between different clusters is also taken into account. The excitation spectrum of this ensemble as function of H_ext is calculated and applied to discuss the response of the system to some external magnetic field H_ext in the low-temperature region. Typical instabilities of magnetization as function of H_ext are obtained. Finally, possible applications of our results to spin-glass systems are discussed.     

Simulating pedestrian flow through narrow exits

Introduction: The flow of pedestrians through narrow doorways is one of the most common features of crowd motions and evacuations. It is particularly an important aspect of pedestrian simulations models since their accuracy depends highly on their ability to produce realistic exit flow rates. The problem has been extensively studied in the literature, but many aspects of it have remained controversial with mixed (and often contradictory) evidence emerging from different studies and different methods. Methods: We discuss the significance of parameter calibration for accurate simulation of pedestrian flow through narrow exits using social force model. Based on sensitivity analyses, we show how simulated exit throughput rate can vastly differ by changing the value of certain parameters. We identify the two parameters that are most critical, and then calibrate them based on a set of experimental observations (at macro level). Using these calibrated parameters, we then re-examine three fundamental questions related to pedestrian flow at bottlenecks, (1) the relation between desired velocity and simulated egress time; (2) the effect of barricade at exits; and (3) the effect of exit in the corner versus the middle. Results: Our numerical analyses showed that, with the calibrated parameters, increasing the desired velocity in the social-force model results in monotonically shorter egress times (at a marginal rate that rapidly diminishes as the desired velocity increases). We showed that placing a panel-like barricade at exit can facilitate the outflow and reduces the egress time, but its effect depends on the widths of exit, as well as the size of the barricade and its distance to exit. We show that the positioning the exit in the corner is also effective in terms of reducing egress time, but only for very narrow exits. The benefit diminishes quickly as the exit becomes wider. Applications: These outcomes demonstrated the significance of parameter calibration for accurate simulation of crowd flows. The findings may also help to identify simple modifications that can facilitate crowd flows at narrow bottlenecks.     

SPROM – an efficient program for NMR/MRI simulations of inter- and intra-molecular multiple quantum coherences

A software package has been designed to simulate nuclear magnetic resonance spectra and images. Combining the product operator matrix with the non-linear Bloch equations, the software can efficiently simulate classical and quantum effects including scalar coupling, dipolar coupling, translational diffusion, chemical shift, radiation damping, transverse relaxation, and longitudinal relaxation. One of the most unique features of the software is its ability to incorporate effects of inter- and intra-molecular multiple quantum coherences in complex multiple-spin coupled systems, which are difficult with other existing software packages. The software, written in Visual C++, has a friendly graphical user interface and is easy to use. To cite this article: C. Cai et al., C. R. Physique 9 (2008).     

Laser diode reliability: crystal defects and degradation modes

Degradation analysis is a crucial issue for the improvement of high power laser diodes. Degradation occurs in three different modes: rapid, gradual and catastrophic. It can be located inside the cavity or at the facet mirrors. Each type of degradation presents its own signature and different crystal defects appear associated with them. The main physical mechanisms responsible for laser degradation are analysed showing the relation between the main degradation modes and the different materials properties of the laser structures. To cite this article: J. Jiménez, C. R. Physique 4 (2003).     

Ab initio absorption spectra of 3-tert-butylcyclohexene

We present an ab initio investigation of the optical properties of 3-tert-butylcyclohexene in both its conformers. The optical spectra, here the photoabsorption cross section, have been obtained within density-functional theory at the independent-particle level, and within time-dependent density-functional theory. The optical spectra of the two conformers show small but visible differences, hence suggesting that optical absorption experiments can discriminate among the two molecular geometries. To cite this article: K. Gaál-Nagy et al., C. R. Physique 10 (2009).     

Stochastic equations arising from test particle problems: II. Application to the harmonic lattice and the electron plasma

To compare the different kinetic equations derived in a previous paper for weakly coupled systems, the results are applied to coupled harmonic oscillators and a one-component plasma in a magnetic field. Using the harmonic interaction as an example, it is demonstrated that reasonable results can be inferred only from the kinetic equation, which is characterized by an additional time average. Applying this equation to an electron plasma in a magnetic field B, the Balescu-Lenard equation is recovered for B = 0, but a modification is obtained for B ≠. For strong fields the diffusion coefficient is discussed.     

Phase separation in strained cation- and anion-deficient Nd0.52Sr0.48MnO3 films

The magnetic and transport properties of anion- and cation-deficient Nd_0.52Sr_0.48MnO₃ films with different thicknesses, as well as of two films from this system grown on different SrTiO₃ and LaAlO₃ substrates, are studied. Below Curie temperature T _C, the films with different thicknesses exhibit phase separation: they represent magnetic clusters (drops) embedded in a nonconducting paramagnetic (at T > T _N, where T _N is the Néel temperature) or antiferromagnetic (T < T _N) matrix. The temperature dependences of the resistivity of the films are well described in terms of the polaron mechanism of conduction. In external magnetic field H = 0.01 T, the drops may reach 15 nm in size. They consist of magnetic polarons with a small radius (1–2 nm). The drops are shown to interact with each other in the films. Because of competition between drop-drop dipole interaction and the magnetic energy, the drops disintegrate into droplets with a size comparable to that of a magnetic polaron in a field of 1 T. An explanation is given for the discrepancy between our results and the frequently observed growth of the drops with a rise in the external magnetic field. As the film gets thicker, the fraction of the ferromagnetic phase grows with thickness nonlinearly. In the film grown on SrTiO₃ (compressed by 0.9%), the characteristic Néel and Curie temperatures are lower than in the film grown on LaAlO₃. The diameters of ferromagnetic drops (both maximal at H = 0.01 T and minimal at H = 1 T) turn out to be roughly the same as in the films with different thicknesses.