Search

Locomotor and balance disorders are major limitations for subjects with hemiparesis. The Timed Up and Go (TUG) test is a complex navigational task involving oriented walking and obstacle circumvention. We hypothesized that subjects with hemiparesis adopt a cautious gait during complex locomotor tasks. The primary aim was to compare spatio-temporal gait parameters, indicators of cautious gait, between the locomotor subtasks of the TUG (Go, Turn, Return) and a Straight-line walk in people with hemiparesis. Our secondary aim was to analyze the relationships between TUG performance and balance measures, compare spatio-temporal gait parameters between fallers and non-fallers, and identify the biomechanical determinants of TUG performance. Biomechanical parameters during the TUG and Straight-line walk were analyzed using a motion capture system. A repeated measures ANOVA and two stepwise ascending multiple regressions (with performance variables and biomechanical variables) were conducted. Gait speed, step length, and % single support phase (SSP) of the 29 participants were reduced during Turn compared to Go and Return and the Straight-line walk, and step width and % double support phase were increased. TUG performance was related to several balance measures. Turn performance (R2 = 63%) and Turn trajectory deviation followed by % SSP on the paretic side and the vertical center of mass velocity during Go (R2 = 71%) determined TUG performance time. People with hemiparesis adopt a cautious gait during complex navigation at the expense of performance. [ABSTRACT FROM AUTHOR]

Several types of Quantum Dots (QDs) (CdS, CdSe and InP, as well as core‐shell QDs such as type I InP‐ZnS, quasi type‐II CdSe‐CdS and inverted type‐I CdS‐CdSe) were considered for generating α‐aminoalkyl free radicals. The feasibility of the oxidation of the N‐aryl amines and the generation of the desired radical was evidenced experimentally by quenching of the photoluminescence of the QDs and by testing a vinylation reaction using an alkenylsulfone radical trap. The QDs were tested in a radical [3+3]‐annulation reaction giving access to tropane skeletons and that requires the completion of two consecutive catalytic cycles. Several QDs such as CdS core, CdSe core and inverted type I CdS‐CdSe core‐shell proved to be efficient photocatalysts for this reaction. Interestingly, the addition of a second shorter chain ligand to the QDs appeared to be essential to complete the second catalytic cycle and to obtain the desired bicyclic tropane derivatives. Finally, the scope of the [3+3]‐annulation reaction was explored for the best performing QDs and isolated yields that compare well with classical iridium photocatalysis were obtained. [ABSTRACT FROM AUTHOR]

Flexible barriers can be used to trap woody debris or debris flows. However, their small scale modelling is challenging because of their possible deformation. This article addresses how to meet the partial mechanical similitude of manufactured flexible barriers. Relevant dimensionless parameters are defined from flow velocity, barrier geometry, and component mechanical properties. These similitude criteria are validated using numerical simulations of barriers exposed to a hydrodynamic loading at various scales. The simulations also confirm the importance of accounting for the mechanical characteristics of the barrier components when designing model barriers in view of achieving realistic deformations. Next, a real barrier with complex features is scaled to conduct flume experiments. This scaled barrier is 3D-printed with material selected to achieve the mechanical similitude criterion. Another validation of this approach is performed considering hydrostatic loading and checking that simulated and measured deformations are similar. As an application case, the deformations measured during the experiments performed with woody debris are also compared to the hydrostatic loading. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate the potential of ultrabright fluorescent silica-coated organic nanocrystals for two-photon in vivo imaging. These unique nanoparticles (NPs) containing a crystalline core of small push–pull dipolar dye are specifically designed to exhibit two-photon absorption for fluorescence imaging. The NPs can be easily functionalized using click chemistry in pure water, with preservation of the organic core. A novel small-volume DLS technique was used to evaluate the effect of PEGylation on the colloidal stability of the NPs in complex media containing salts and proteins, mimicking the composition of blood serum. The potential of these bright red-emitting NPs for two-photon fluorescence imaging is demonstrated both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

A novel and efficient method for ligand exchange on core-shell nanocrystals is described. Carbon disulfide reacts with amine-containing ligand during the process and the resulting dithiocarbamates are strongly bound to the surface of quantum dots giving a secure coating of the nanoparticle.

Background: French Guiana, a French overseas department located in South America between Brazil and Surinam, is the only European territory geographically located in the Amazonian forest complex and is considered endemic for yellow fever (YF). In the context of the emergent threat of YF in Latin America, we conducted a large household cross-sectional survey from June to October 2017 to estimate vaccination coverage in the population and to determine associations with sociodemographic and geographical characteristics. Methodology/Principal findings: In total, 1,415 households and 2,697 individuals were included from the 22 municipalities of French Guiana. YF vaccination coverage was estimated at 95.0% (95% CI: 93.4–96.2) in the entire territory but was spatially heterogeneous, with the lowest levels estimated in the western part of the territory along the Surinamese cross-border region, particularly in children under 16 years who were not enrolled in school, immigrant adults and disadvantaged populations with low socioeconomic indexes. Conclusions/Significance: Despite the good vaccination coverage against YF in the general population of French Guiana resulting from the compulsory nature of YF vaccination for residents and travelers, there is an urgent need to improve vaccination coverage in vulnerable populations living in the northwestern part of the territory to limit the risk of transmission in the context of the emerging YF threat in South America. Despite the relative rarity of YF and the significant number of infectious and tropical diseases in French Guiana, clinicians should adopt a high index of suspicion for YF, particularly in vulnerable and at-risk populations. [ABSTRACT FROM AUTHOR]

Here we demonstrate that the encapsulation of crystal-state emitters in sol–gel matrices is an efficient way to produce bright nanotracers for bioimaging applications. We report the development of a family of fluorescent organic@silicate core–shell nanoparticles (NPs) containing an organic core surrounded by a silicate shell, with a high loading of dyes (30–40 wt%), prepared by an original spray-drying technique combining sol–gel chemistry and nanocrystallization. Four dyes were encapsulated within the silicate nanoparticles. The crystallinity of the organic core is discussed on the basis of characterization by electron microscopy and fluorescence spectroscopy. Bright, red-emitting core–shell NPs have been produced, which are promising for use in bio-imaging. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) power devices are the only commercialized components to run at high voltage and high temperature. Normally on junction field-effect transistors (JFETs) have lower on-state resistance and lower output capacitance than other SiC switches, which reduces conduction and switching losses. However, normally on power devices induce a short-circuit in voltage-fed inverters (VFI) when the gate driver is not powered prior to the bus supply. This is a power-up limitation that has not received much attention in the literature, especially for safety systems that can be used in an integrated circuit capable of running at elevated temperature. This paper describes an original solution based on SiC JFETs to secure the inverter operation at power-up without gate driver supply for the SiC JFETs. The reliability test of the protection circuit and his impact on the ageing of the JFET of the VFI are also presented. The safety system is capable of running in elevated ambient temperatures. Experimental results have been carried out in a 540 V, 10 A inverter and at ambient temperatures from 27 to 200 °C. [ABSTRACT FROM AUTHOR]

Using a spray-drying process, we developed a versatile, one step synthesis, of two-photon luminescent silicate nanoparticles. The formation of the nanoparticles is based on the controlled drying of sol-gel droplets in a heated laminar flux inside a tubular furnace. Two types of nanoparticles were prepared, hybrid core-shell nanoparticles and silicate nanoparticles doped with an europium(III) complex. In the first case of hybrid (organic-silicate) coreshell nanoparticles the last evaporation of THF solvent enhance the polycondensation of the silicate network in the droplets, particularly at their surface. This induces first the formation of a silicate crust followed, at the end of the solvent evaporation, by the nucleation and growth of the organic dye in the core of the resulting dried nanoparticles. We studied the different physical and chemical parameters that influence the perfect and reproducible control of the confined nucleation and growth of dye nanocrystals in the sol-gel droplets. In the second case, silicate nanoparticles were doped with a functionalized tris-dipicolinate europium complex, which presents an important two-photon absorption cross section but exhibits a weak stability in water due to the dissociation of the complex. Two different compositions of the starting sols were tested to adjust the hydrophilic character of the nanoparticles and to avoid the dissociation of the europium complexes in water by closing the porosity of the silicate shell. [ABSTRACT FROM AUTHOR]

The discrete circle map is the archetypical example of a driven periodic system, showing a complex resonance structure under a change of the forcing frequency known as the devil's staircase. Adler's equation can be seen as the direct continuous equivalent of the circle map, describing locking effects in periodic systems with continuous forcing. This type of locking produces a single fundamental resonance tongue without higher-order resonances, and a devil's staircase is not observed. We show that, with harmonically modulated forcing, nonlinear oscillations close to a Hopf bifurcation generically reproduce the devil's staircase even in the continuous case. Experimental results on a semiconductor laser driven by a modulated optical signal show excellent agreement with our theoretical predictions. The locking appears as a modulation of the oscillation amplitude as well as the angular oscillation frequency. Our results show that by proper implementation of an external drive, additional regions of stable frequency locking can be introduced in systems which originally show only a single Adler-type resonance tongue. The induced resonances can be precisely controlled via the modulation parameters.

We show, both experimentally and theoretically, that a slave laser injected with an optical frequency comb can undergo two distinct locking mechanisms, both of which decrease the output optical comb's frequency spacing. We report that, for certain detuning and relative injection strengths, slave laser relaxation oscillations can become undamped and lock to rational frequencies of the optical comb spacing, creating extra comb tones by nonlinear dynamics of the injected laser. We also study the frequency locking of the slave laser at detunings in between the injected comb lines, which add the slave laser's frequency to the comb. Our results demonstrate the effect of the α parameter and stability of the locked states and indicate how the frequency of the relaxation oscillations affect both of these locking mechanisms. These optical locking mechanisms can be applied to regenerate or multiply optical combs.

We model the situation of two lasers in a face-to-face arrangement, optically coupled through an attenuating element, where the distance between the lasers is on a scale typical in photonic integration (hundreds of micrometers to millimeters). We account for the existence of a frequency difference between the two single-mode lasers. Modified versions of the Lang-Kobayashi equations were employed to describe the interaction. By solving this delay differential equation system, we characterized different dynamical regimes including one- and two-color states and self-pulsations. We focus on the effect varying coupling strength and detuning between the lasers has on the frequencies of the lasers. Using the results of this frequency study, we identify the bifurcations causing changes between the different frequency regimes.

The photophysical and nonlinear optical properties of water-soluble chromophore-functionalised tris-dipicolinate complexes [LnL3](3-) (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb(III) luminescence can be sensitized by a two-photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu4]3 [YbL3] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two-photon microscopy setup in a NIR-to-NIR configuration., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions., (© 2011 American Chemical Society)

Water soluble fluorescent nanocrystals were obtained by encapsulation of hydrophobic quantum dots (QDs) with amphiphilic phospholipids derived from the ring opening metathesis of norbornene-based monomers. The robustness of the newly coated quantum dots was assessed by comparative studies under various ionic conditions which indicated an overall enhancement of their fluorescence stability.