Mixing in the shear superposition micromixer: three-dimensional analysis

In this paper, we analyse mixing in an active chaotic advection micromixer. The micromixer consists of a main rectangular channel and three cross-stream secondary channels that provide ability for time-dependent actuation of the flow stream in the direction orthogonal to the main stream. Three-dimensional motion in the mixer is studied. Numerical simulations and modelling of the flow are pursued in order to understand the experiments. It is shown that for some values of parameters a simple model can be derived that clearly represents the flow nature. Particle image velocimetry measurements of the flow are compared with numerical simulations and the analytical model. A measure for mixing, the mixing variance coefficient (MVC), is analysed. It is shown that mixing is substantially improved with multiple side channels with oscillatory flows, whose frequencies are increasing downstream. The optimization of MVC results for single side-channel mixing is presented. It is shown that dependence of MVC on frequency is not monotone, and a local minimum is found. Residence time distributions derived from the analytical model are analysed. It is shown that, while the average Lagrangian velocity profile is flattened over the steady flow, Taylor-dispersion effects are still present for the current micromixer configuration.     

Application of the Gestalt principles to the detection of good continuations and corners in image level lines

In this paper, we propose an algorithm to automatically detect regular subcurves in a set of digital curves. The decision criterion is based on Helmholtz Principle introduced by Desolneux, Moisan and Morel and formulated in terms of number of false alarms. We apply our algorithm to low-level computer vision. Following Gestalt Theory, good continuation is indeed, one of the most important grouping laws entering into the early perception of objects. We check this on the level lines of images, which give a contrast invariant representation of images. The result is that most objects are good continuations. This experimentally shows that contrast invariance is a very sound hypothesis for low level vision and that objects can be detected independently of contrast. The parameters of the method may be reduced to a single one – the number of false alarms – and we can show that the detection has a very weak dependency on this number.     

Determination of firing times for the stochastic Fitzhugh-Nagumo neuronal model

We present for the first time an analytical approach for determining the time of firing of multicomponent nonlinear stochastic neuronal models. We apply the theory of first exit times for Markov processes to the Fitzhugh-Nagumo system with a constant mean gaussian white noise input, representing stochastic excitation and inhibition. Partial differential equations are obtained for the moments of the time to first spike. The observation that the recovery variable barely changes in the prespike trajectory leads to an accurate one-dimensional approximation. For the moments of the time to reach threshold, this leads to ordinary differential equations that may be easily solved. Several analytical approaches are explored that involve perturbation expansions for large and small values of the noise parameter. For ranges of the parameters appropriate for these asymptotic methods, the perturbation solutions are used to establish the validity of the one-dimensional approximation for both small and large values of the noise parameter. Additional verification is obtained with the excellent agreement between the mean and variance of the firing time found by numerical solution of the differential equations for the one-dimensional approximation and those obtained by simulation of the solutions of the model stochastic differential equations. Such agreement extends to intermediate values of the noise parameter. For the mean time to threshold, we find maxima at small noise values that constitute a form of stochastic resonance. We also investigate the dependence of the mean firing time on the initial values of the voltage and recovery variables when the input current has zero mean.     

Sugar interaction with metals in aqueous solution: indirect determination from infrared and direct determination from nuclear magnetic resonance spectroscopy

In this article, mid-infrared Fourier transform (Mid-FT-IR) and carbon thirteen nuclear magnetic resonance (13C NMR) spectroscopy have been used to determine possible interactions between sucrose and various alkali or alkaline earth metals in aqueous solution. In the presence of these metals, significant shifts in the absorption bands of sucrose were noted by mid-FT-IR coupled with principal component analysis (PCA). These shifts were explained on the basis of weakening of the H-bond network between sucrose and water and possible interactions between sucrose and the metal ion. Factorial maps were established and the spectral patterns obtained show that these interactions vary according to the nature of the metal ion. 13C NMR analysis showed that the carbon atoms of sucrose undergo shielding or deshielding in the presence of metal ions in aqueous solutions. Two factors were invoked to account for the variation of chemical shifts: the rupture of hydrogen bonds due to hydration of the metal ion and the possible coordination of the metal ion to the oxygen atoms of sucrose.     

Coregistration of diffuse optical spectroscopy and magnetic resonance imaging in a rat tumor model

We report coregistration of near-infrared diffuse optical spectroscopy (DOS) and magnetic resonance imaging (MRI) for the study of animal model tumors. A combined broadband steady-state and frequency-domain apparatus was used to determine tissue oxyhemoglobin, deoxyhemoglobin, and water concentration locally in tumors. Simultaneous MRI coregistration provided structural (T2-weighted) and contrast-enhanced images of the tumor that were correlated with the optical measurements. By use of Monte Carlo simulations, the optically sampled volume was superimposed on the MR images, showing precisely which tissue structure was probed optically. DOS and MRI coregistration measurements were performed on seven rats over 20 days and were separated into three tumor tissue classifications: viable, edematous, and necrotic. A ratio of water concentration to total hemoglobin concentration, as measured optically, was performed for each tissue type and showed values for edematous tissue to be greater than viable tissue (1.2 +/- 0.49 M/microM versus 0.48 +/- 0.15 M/microM). Tissue hemoglobin oxygen saturation (StO2) also showed a large variation between tissue types: viable tissue had an optically measured StO2 value of 61 +/- 5%, whereas StO2 determined for necrotic tissue was 43 +/- 6%.     

Decisional autonomy of planetary rovers

To achieve the ever increasing demand for science return, planetary exploration rovers require more autonomy to successfully perform their missions. Indeed, the communication delays are such that teleoperation is unrealistic. Although the current rovers (such as MER) demonstrate a limited navigation autonomy, and mostly rely on ground mission planning, the next generation (e.g., NASA Mars Science Laboratory and ESA Exomars) will have to regularly achieve long range autonomous navigation tasks. However, fully autonomous long range navigation in partially known planetary‐like terrains is still an open challenge for robotics. Navigating hundreds of meters without any human intervention requires the robot to be able to build adequate representations of its environment, to plan and execute trajectories according to the kind of terrain traversed, to control its motions, and to localize itself as it moves. All these activities have to be planned, scheduled, and performed according to the rover context, and controlled so that the mission is correctly fulfilled. To achieve these objectives, we have developed a temporal planner and an execution controller, which exhibit plan repair and replanning capabilities. The planner is in charge of producing plans composed of actions for navigation, science activities (moving and operating instruments), communication with Earth and with an orbiter or a lander, while managing resources (power, memory, etc.) and respecting temporal constraints (communication visibility windows, rendezvous, etc.). High level actions also need to be refined and their execution temporally and logically controlled. Finally, in such critical applications, we believe it is important to deploy a component that protects the system against dangerous or even fatal situations resulting from unexpected interactions between subsystems (e.g., move the robot while the robot arm is unstowed) and/or software components (e.g., take and store a picture in a buffer while the previous one is still being processed). In this article we review the aforementioned capabilities, which have been developed, tested, and evaluated on board our rovers (Lama and Dala). After an overview of the architecture design principle adopted, we summarize the perception, localization, and motion generation functions required by autonomous navigation, and their integration and concurrent operation in a global architecture. We then detail the decisional components: a high level temporal planner that produces the robot activity plan on board, and temporal and procedural execution controllers. We show how some failures or execution delays are being taken care of with online local repair, or replanning. © 2007 Wiley Periodicals, Inc.     

Functional expression in insect cells, one-step purification and characterization of a recombinant phospholipase D from cowpea (Vigna unguiculata L. Walp)

Phospholipase D (PLD) is an important enzyme involved in signaltransduction, vesicle trafficking and membrane metabolism. Inthis study, large amounts of a recombinant plant PLD were secretedinto the culture medium of baculovirus-infected insect cellsand purified to homogeneity in the form of a fully active enzyme.The transient production of recombinant PLD yielded a protein(rPLDa, 88 kDa) together with a shorter form (rPLDb, 87 kDa),which accumulated in the medium. N-Terminal amino acid sequencingof the rPLDa and rPLDb showed that rPLDb resulted from proteolyticcleavage at Gly8–Ile9. Immunoblotting showed that bothrPLDa and rPLDb are recognized by a polyclonal antibody previouslyraised against native soybean PLD. One-step calcium-dependentoctyl-Sepharose chromatography was used to obtain the two highlypurified forms of rPLD, as attested by gel electrophoresis,N-terminal amino acid sequence and mass spectrometry. The N-terminalregion of PLD is homologous with the C2 domains which are presentin a number of enzymes known to be involved in signal transductionand/or phospholipid metabolism. The truncated rPLDb lacks thefirst acidic amino acid in its N-terminus, which is probablyinvolved in the calcium binding site. The rPLDb was thus easilyeluted from the octyl-Sepharose column by decreasing the calciumconcentration of the buffer from 50 to 30 mM, whereas, the rPLDawas eluted after chelating calcium ions with EDTA. The purifiedrPLD yield reached a level of 10 mg per liter of serum-freeculture medium. The availability of baculovirus-derived rPLDconstitutes a valuable source of enzyme for future crystallographicstudies to determine its three-dimensional structure.     

Opportunities in nanometer sized Si wires for PV applications

Quantum-confined silicon material has been a very active field of research in the years 1990–2000 with the rapid development of opto-electronics. The main application targeted by this research was a light-emitting device (either LED, or laser). In the years 2000–2010, with the emerging need for efficient and cheap photovoltaic devices, new materials, and in particular new silicon-based materials trigger again a special interest. In particular, all-crystalline-Si tandem solar cells where the high-bandgap material is provided by the 2D confinement of excitons in nm-sized nanowires could provide the high-efficiency potential of a tandem device, while taking benefit of the decade-long buildup of knowhow of crystalline silicon material technology (both science and processing). In a first part of this review, we summarize the features described in the relevant literature for the functioning of a photovoltaic device based on Si NWs. This literature shows that from the conceptual point of view such an all-crystalline-Si-tandem solar cell using quantum confined nanowires should be feasible to produce in order to achieve the goal of inexpensive high efficiency (>30%) Si-based solar cells. Keeping the fabrication of efficient photovoltaic devices as driving theme, we review the dense literature of Si nanowires. The literature on the fabrication of nanometer-sized Si nanowires is reviewed in the second part.