Directional laser generation and detection of ultrasound with arrays of optical fibers

Some aspects of the generation and detection of ultrasound with laser beams are presented. The objective of the study is (1) to present some experimental results on the generation of ultrasound with an array of optical fibers, (2) to discuss the possibility of generating directional surface waves with acousto-optic scanning in a very narrow frequency band, thus increasing the signal-to-noise ratio, and (3) to discuss the feasibility of the directional detection of ultrasound by using an array of optical fibers as a receiver, also with the goal of increasing the signal-to-noise ratio.     

A mapping tool using anisotropic unstructured meshes to study mixing in periodic flows

The objective of the present work is to describe a new mapping tool using anisotropic unstructured meshes to study mixing within a spatially periodic pipe flow. Instead of tracking the boundaries of elementary cell flow domains as it was done in the original mapping method established by Kruijt et al. (A.I.Ch.E. J. 47 (5) (2001a) 1005; Int. Polym. Process. 16 (2) (2001b) 151) and Galaktionov et al. (Comput. Fluids 30 (3) (2001) 271), the deformation of elementary triangles (only three nodal points) between the inlet and exit pipe cross-sections is followed. It is however necessary to adapt the initial mesh according to criteria which takes into account the spatial stretching and folding of fluid elements. The method developed is applied to the twisted curved pipes (TCP) three-dimensional (3D) flow. We show the evolution of concentration distributions along the TCP mixer for chaotic advection flow regimes. This method allows the emphasis of isolated unmixed regions (KAM islands). The flexibility of the method allows also the possibility of studying multiple stirring protocols, thus contributing to a better comprehension of the physical phenomena involved in chaotic mixing. The method developed is also applicable to 2D temporally periodic flows.     

Fabrication and performance of selectively oxidized vertical-cavitylasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range     

Red Fluorescent Turn‐On Ligands for Imaging and Quantifying G Protein‐Coupled Receptors in Living Cells

Classical fluorescence‐based approaches to monitor ligand–protein interactions are generally hampered by the background signal of unbound ligand, which must be removed by tedious washing steps. To overcome this major limitation, we report here the first red fluorescent turn‐on probes for a G protein‐coupled receptor (oxytocin receptor) at the surface of living cells. The peptide ligand carbetocin was conjugated to one of the best solvatochromic (fluorogenic) dyes, Nile Red, which turns on emission when reaching the hydrophobic environment of the receptor. We showed that the incorporation of hydrophilic octa(ethylene glycol) linker between the pharmacophore and the dye minimized nonspecific interaction of the probe with serum proteins and lipid membranes, thus ensuring receptor‐specific turn‐on response. The new ligand was successfully applied for background‐free imaging and quantification of oxytocin receptors in living cells.     

Finding the dominant source of distortion in two-stage op-amps

Although non-linear distortion is an important specification for op-amps, it is only determined at the end of the design in classical design flows, leaving the designers without a clue about its origin. Recently, the Best Linear Approximation (BLA) has been introduced to approximate non-linear systems. It allows to describe the behaviour of a non-linear system as a linear Frequency Response Function combined with a coloured noise source to describe respectively the wanted linear response and the distortion. To determine the dominant source of non-linear distortion, we combine the BLA with a classical noise analysis in this paper. The paper explains the BLA-based noise analysis and shows the result of this simulation-based analysis when applied to various op-amp architectures. The analysis pinpoints the non-linear hot-spots in an efficient way, without the use of special simulations, manual analytical calculations or modified transistor models.     

Sex differences in research funding,productivity and impact: an analysis of Québec university professors

Using the entire population of professors at universities in the province of Quebec (Canada), this article analyzes the relationship between sex and research funding, publication rates, and scientific impact. Since age is an important factor in research and the population pyramids of men and women are different, the role of age is also analyzed. The article shows that, after they have passed the age of about 38, women receive, on average, less funding for research than men, are generally less productive in terms of publications, and are at a slight disadvantage in terms of the scientific impact (measured by citations) of their publications. Various explanations for these differences are suggested, such as the more restricted collaboration networks of women, motherhood and the accompanying division of labour, women’s rank within the hierarchy of the scientific community and access to resources as well as their choice of research topics and level of specialization.     

Impact of agglomeration on the relaxometric properties of paramagnetic ultra-small gadolinium oxide nanoparticles

Ultra-small gadolinium oxide nanoparticles (US-Gd(2)O(3)) are used to provide 'positive' contrast effects in magnetic resonance imaging (MRI), and are being considered for molecular and cellular imaging applications. However, these nanoparticles can aggregate over time in aqueous medium, as well as when internalized into cells. This study is aimed at measuring in vitro, in aqueous medium, the impact of aggregation on the relaxometric properties of paramagnetic US-Gd(2)O(3) particles. First, the nanoparticle core size as well as aggregation behaviour was assessed by HRTEM. DLS (hydrodynamic diameter) was used to measure the hydrodynamic diameter of nanoparticles and nanoaggregates. The relaxometric properties were measured by NMRD profiling, as well as with (1)H NMR relaxometers. Then, the positive contrast enhancement effect was assessed by using magnetic resonance scanners (at 1.5 and 7 T). At every magnetic field, the longitudinal relaxivity (r(1)) decreased upon agglomeration, while remaining high enough to provide positive contrast. On the other hand, the transverse relaxivity (r(2)) slightly decreased at 0.47 and 1.41 T, but it was enhanced at higher fields (7 and 11.7 T) upon agglomeration. All NMRD profiles revealed a characteristic relaxivity peak in the range 60-100 MHz, suggesting the possibility to use US-Gd(2)O(3) as an efficient 'positive-T(1)' contrast agent at clinical magnetic fields (1-3 T), in spite of aggregation.     

Overall Thermodynamic Model of an Ultra Micro Turbine

The overall thermodynamic model of an ultra micro turbine engine has been established and applied in different situations in this tiny engine where heat transfer is dominant. The aerothermal conditions of the flow were calculated and analyzed. A corresponding calculation software (hot button software) was developed. The first results show that the non-adiabatic operation of the turbomachines leads to a strong penalty in performances. The dramatic influence of the compressor and turbine efficiency is confirmed in a non-adiabatic operation. A better knowledge of heat transfer coefficients at low Reynolds numbers in different components of the micro turbine has to be obtained to refine the results of this study.