Nanomatériaux Pour les Systèmes Sous Sollicitations Extrêmes

Since the pioneering studies of the 1960s, heart rate variability (HRV) has become an increasingly used non-invasive tool for examining cardiac autonomic functions and dysfunctions in various populations and conditions. Many calculation methods have been developed to address these issues, each with their strengths and weaknesses. Although its interpretation may remain difficult, this technique provides, from a non-invasive approach, reliable physiological information that was previously inaccessible, in many fields including death and health prediction, training and overtraining, cardiac and respiratory rehabilitation, sleep-disordered breathing, large cohort follow-ups, children’s autonomic status, anesthesia, or neurophysiological studies. In this context, we developed HRVanalysis, a software to analyse HRV, used and improved for over 20 years and, thus, designed to meet laboratory requirements. The main strength of HRVanalysis is its wide application scope. In addition to standard analysis over short and long periods of RR intervals, the software allows time-frequency analysis using wavelet transform as well as analysis of autonomic nervous system status on surrounding scored events and on preselected labeled areas. Moreover, the interface is designed for easy study of large cohorts, including batch mode signal processing to avoid running repetitive operations. Results are displayed as figures or saved in TXT files directly employable in statistical softwares. Recordings can arise from RR or EKG files of different types such as cardiofrequencemeters, holters EKG, polygraphs, and data acquisition systems. HRVanalysis can be downloaded freely from the Web page at: anslabtools.univ-st-etienne.fr. HRVanalysis is meticulously maintained and developed for in-house laboratory use. In this article, after a brief description of the context, we present an overall view of HRV analysis and we describe the methodological approach of the different techniques provided by the software.

STUDY OBJECTIVES: Sleep related breathing disorders (SRBD) are risk factors for cognitive dysfunction in middle-aged subjects, but this association has not been observed in the elderly. We assess the impact of SRBD on cognitive performance in a large cohort of healthy elderly subjects. DESIGN: Cross-sectional study examining the association between subjective memory test, neuropsychological battery testing and SRBD in the elderly. SETTING: Community-based sample in home and research clinical settings. PARTICIPANTS: 827 subjects, 58.5% women, aged 68 y at study entry, participated in the study. All were free of previously diagnosed SRBD, coronary heart disease, and neurological disorders, including stroke and dementia. Clinical interview, neurological assessment, polygraphy, and extensive cognitive testing were conducted for all participants. INTERVENTION: N/A. MEASUREMENT AND RESULTS: SRBD (apnea-hypopnea index [AHI] > 15 events/h) was diagnosed in 445 (53%) subjects, 167 (37%) of them with AHI > 30. Minimal daytime sleepiness was found in the group; 9.2% of the population had an Epworth Sleepiness Scale score > 10. No significant association was found between AHI, nocturnal hypoxemia, and cognitive scores. Comparison of mild vs severe cases showed a trend toward lower cognitive scores with AHI > 30, affecting delayed recall and Stroop test. CONCLUSIONS: The impact of undiagnosed SRBD on cognitive function appeared quite limited in a generally older healthy population, and only slightly affected severe cases. The implication of undiagnosed SRBD on the cognitive impairment in elderly subjects remains hypothetical and needs to be prospectively studied.

Obstructive sleep apnoea (OSA) affects females and males differently, and increases in prevalence with age. The aim of the present study was to characterise clinical, anthropometric and polygraphic sex differences in a large elderly OSA population. A total of 641 subjects aged 68 yrs were examined. Measurements of fat mass, using dual-energy X-ray absorptiometry (DEXA) and polygraphy, were obtained in all subjects. An apnoea/hypopnoea index (AHI) of >15 events·h⁻¹ identified the presence of OSA. OSA was diagnosed in 57% of the sample, 34% having a mild form and 23% having an AHI of >30 events·h⁻¹. Females with OSA exhibited a lower AHI, less severe hypoxaemia and greater peripheral fat mass, and frequently reported anxiety and depression. Comparison of females with and without OSA did not reveal significant differences in clinical, anthropometric and DEXA data. After adjustment for body mass index, hypertension, diabetes, smoking, anxiety and depression, logistic regression analysis revealed that the presence of hypertension was significantly associated with OSA risk in females (OR 1.52, p = 0.04). In a general community healthy population, the prevalence of undiagnosed OSA in females increases with age, with a risk similar to that in males. In females, the clinical spectrum, anthropometric data and fat distribution appear to be more sex-related than OSA-dependent. The occurrence of OSA contributes to hypertensive risk in elderly females.

TNT: Silicon microcantilevers modified with a three-dimensional layer of vertical titanium dioxide nanotubes (see picture) can be used in micromechanical sensors with optical signal detection to detect low levels of explosives such as 2,4,6-trinitrotoluene (TNT) in the gas phase, even in the presence of other volatile impurities such as n-heptane and ethanol.

MXenes are a young family of two-dimensional transition metal carbides, nitrides, and carbonitrides with highly controllable structure, composition, and surface chemistry to adjust for target applications. Here, we demonstrate the modifications of two-dimensional MXenes by low-energy ion implantation, leading to the incorporation of Mn ions in Ti3C2Tx (where Tx is a surface termination) thin films. Damage and structural defects caused by the implantation process are characterized at different depths by XPS on Ti 2p core-level spectra, by ToF-SIMS, and with electron energy loss spectroscopy analyses. Results show that the ion-induced alteration of the damage tolerant Ti3C2Tx layer is due to defect formation at both Ti and C sites, thereby promoting the functionalization of these sites with oxygen groups. This work contributes to the inspiring approach of tailoring 2D MXene structure and properties through doping and defect formation by low-energy ion implantation to expand their practical applications.

The detonation process is able to build new materials with a bottom-up approach. Diamond, the hardest material on earth, can be synthesized in this way. This unconventional synthesis route is possible due to the presence of carbon inside the high-explosive molecules: firing high-explosive mixtures with a negative oxygen balance in a non-oxidative environment leads to the formation of nanodiamond particles. Trinitrotoluene (TNT) and hexogen (RDX) are the explosives primarily used to synthesize nanodiamonds. Here we show that the use of nanostructured explosive charges leads to the formation of smaller detonation nanodiamonds, and it also provides new understanding of nanodiamond formation-mechanisms. The discontinuity of the explosive at the nanoscale level plays the key role in modifying the diamond particle size, and therefore varying the size with microstructured charges is impossible.

Historically, the synthesis of aqueous polymer dispersions has focused on radical chain-growth polymerization of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymerization, departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymerization process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an average diameter of 130 nm. After water evaporation, they yield a clear elastomeric film combining chemical resistance and high degree of crystallinity (55%).

A microelectromechanical-systems-based calorimeter designed for use on a synchrotron nano-focused X-ray beamline is described. This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤100000 K s(-1)) and temperature modulation frequencies (≤1 kHz). The calorimeter was used for high-resolution thermal imaging of nanogram-sized samples subjected to X-ray-induced heating. For a 46 ng indium particle, the measured temperature rise reaches ∼0.2 K, and is directly correlated to the X-ray absorption. Thermal imaging can be useful for studies of heterogeneous materials exhibiting physical and/or chemical transformations. Moreover, the technique can be extended to three-dimensional thermal nanotomography.

We report on the growth control of zinc oxide nanorods to point out the effect of the ZnO nanorods quality on the power conversion efficiency (PCE) of transparent conductive oxide (TCO)/ZnO nanorods/dye/spiro-OMeTAD/metal electrode photovoltaic devices. A promising PCE of 0.61% was measured for the best nanorods growth conditions. A careful control of all the growth parameters during the seeds layer deposition and the hydrothermal synthesis was necessary to reach such a high PCE for this kind of device. A regular nanorod layer with a flat upper surface was obtained for ethylenediamine to zinc acetate dihydrate molar ratio equal to 1.74 and a pH of 8.2. The growth was performed at 65 °C for 2 h to avoid zinc oxide brushes deposition on the surface, arising from zinc hydroxyacetate decomposition during the hydrothermal treatment. The effect of ZnO nanorods length (ranging from 1 to 3 μm) on solar cell efficiency was tested. Although the UV–vis absorption increases when the nanorods length increases, the best photovoltaic parameters were measured for the shortest nanorods length studied (1 μm).

Competitive swimming as a physical activity results in changes to the activity level of the autonomic nervous system (ANS). However, the precise relationship between ANS activity, fatigue and sports performance remains contentious. To address this problem and build a model to support a consistent relationship, data were gathered from national and regional swimmers during two 30 consecutive-week training periods. Nocturnal ANS activity was measured weekly and quantified through wavelet transform analysis of the recorded heart rate variability. Performance was then measured through a subsequent morning 400 meters freestyle time-trial. A model was proposed where indices of fatigue were computed using Banister's two antagonistic component model of fatigue and adaptation applied to both the ANS activity and the performance. This demonstrated that a logarithmic relationship existed between performance and ANS activity for each subject. There was a high degree of model fit between the measured and calculated performance (R(2)=0.84±0.14,p<0.01) and the measured and calculated High Frequency (HF) power of the ANS activity (R(2)=0.79±0.07, p<0.01). During the taper periods, improvements in measured performance and measured HF were strongly related. In the model, variations in performance were related to significant reductions in the level of 'Negative Influences' rather than increases in 'Positive Influences'. Furthermore, the delay needed to return to the initial performance level was highly correlated to the delay required to return to the initial HF power level (p<0.01). The delay required to reach peak performance was highly correlated to the delay required to reach the maximal level of HF power (p=0.02). Building the ANS/performance identity of a subject, including the time to peak HF, may help predict the maximal performance that could be obtained at a given time.

The interest in co-crystals of energetic materials is explained by the fact that they can offer better thermodynamic stability and tunable sensitivity and detonation performance. In the present work, a combination of DSC, ultrafast chip calorimetry, high-resolution X-ray powder diffraction, and nanofocus X-ray diffraction was employed to investigate the thermal behavior and structure formation in nanosized co-crystals of CL-20 with HMX and TNT prepared using Spray Flash Evaporation (SFE). The CL-20/HMX co-crystal does not reveal any thermal transitions up to the thermal decomposition. In contrast, CL-20/TNT exhibits an irreversible melting transition. Upon melting, it can rapidly crystallize on heating or, at a slower pace, at room temperature to form homocrystals of γCL-20, the polymorph stable at high temperature. These observations constitute the first evidence of a CL-20 crystallization process, which occurs from the melt and not from solution. The solid–liquid phase separation occurring during heating of a CL-20/TNT melt may explain its complex thermal decomposition process as compared to that of CL-20/HMX: the main exothermic peak of decomposition can be assigned to that of a pure CL-20.

Metal sulfates (Ba, Bi, Ca, Cu, Mg, Mn, Na, Zn, Zr) were used as oxidizers in reactive compositions with Al nanopowder. These new kinds of nanothermites have outstandingly high reaction heats (4-6 kJ g(-1) ) compared to conventional Al/metal oxides (1.5-4.8 kJ g(-1) ) and also have good combustion velocities (200-840 m s(-1) vs 100-2500 m s(-1) ). These compositions are extremely insensitive to friction making their preparation and handling easy and safe. The sulfate hydration water increases the reaction heats and has a significant effect on the sensitivity to impact and to electrostatic discharge. The reaction of Al with water is easier to initiate than the one with sulfate which leads to two possible decomposition modes for samples exposed to an open flame. The pyrotechnical properties observed with sulfates have also been found for other sulfur oxygenates (SO3 (2-) , S2 O3 (2-) , S2 O8 (2-) ) which opens up new horizons in the domain of metastable interstitial composites.

The main goal of doping detonation nanodiamonds with nitrogen is to obtain stable photoluminescence properties. Small quantities of nitrogen have already been evidenced in such nanodiamonds. This article deals with the possibility of increasing the nitrogen content inside nanodiamond samples. Electron energy loss spectroscopy is a very useful tool for determining the location and the quantity of nitrogen within individual nanodiamonds. The experimental results demonstrate that the nitrogen content strongly depends on the precursors used in the composition of the explosive charge: the incorporation of melamine leads to an increase by a factor 2 or 3 in the nitrogen content in the nanodiamond core. To the best of our knowledge, this is the first time that such high nitrogen contents have been obtained for detonation nanodiamonds. It is also shown that nitrogen is always present inside the nanodiamond core in an sp3 hybridization configuration.

Growth of Cu(OH)₂ and CuO nanotubes having a diameter of 100 nm on a silicon wafer.

BACKGROUND: ) cohort was built to establish, the normal autonomic maturation profile from birth up to 2 years, in a healthy population of full-term newborns. METHODS: software. RESULTS: Indices are dissociated according a temporal, geometrical, frequency, Poincaré, empirical mode decomposition, fractal, Chaos and DC/AC and entropy analysis. Each index is presented for five different periods of time, 0, 6, 12, 18 and 24 months and with smoothed values in the 3rd, 10th, 50th, 90th and 97th percentiles. Data are also presented for the full cohort and individualized by sex to account for gender variability. DISCUSSION & CONCLUSION: The physiological autonomic maturation profile from birth to 2 years in a healthy population of term neonates results in a fine-tuning autonomic maturation underlying progressively a new equilibrium and privileging the parasympathetic activity over the sympathetic activity.

Although pyrotechnic performance is fundamental, the strong mechanical and electrostatic intrinsic sensitivities of nanothermite energetic composites represent an obstacle to their development. The addition of a ternary component to the classical binary energetic composite appears to be a promising idea to overcome the problem. A carbon black additive (V3G) was used on a WO3/Al nanothermite. The effect of the pristine and modified carbon particles on the mechanical and electrical sensitivities of the composites was measured together with the pyrotechnic properties. The results show a complete desensitization to friction with a ball-milled carbon when the combustion velocity is slightly reduced.

Cantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with zinc oxide (ZnO) nanorods or nanotubes having a diameter of approximately 100 nm and a length of 1 µm. The nanostructure growth was first optimized on a silicon wafer and then transferred to the cantilevers. The ZnO nanorods were grown in an autoclave. The centre of the nanorods was dissolved in order to obtain nanotubes. The dissolution conditions were optimized in order to have the longest etching depth. After 1.25 h in a dissolution solution containing 0.75 wt% of NH 3(aq) and 0.75 wt% of cetyltrimethyl ammonium bromide, the longest etching depth was obtained. After the transfer of the syntheses to the cantilevers, nanorods/nanotubes grew on both sides of the cantilever, which prevents the reflection of the laser allowing the resonance frequency measurement. A masking procedure was developed in order to avoid the growth on one face of the cantilever of zinc oxide nanostructures. As far as the authors are concerned, for the first time, zinc oxide nanotubes were synthesized on only one face of cantilevers with optical readout.

Detonation nanodiamonds exhibit strong nonlinear optical properties depending on their electronic properties. In the present paper, the nanodiamond functional groups are chemically modified to obtain nanodiamonds with primary amines on their surface. The optical properties of such nanodiamonds placed in water suspensions are studied and compared with the one of classical detonation nanodiamonds. Transmission, scattering and Z-scan experiments are performed for two different wavelengths (532 nm and 1064 nm). A lower threshold for optical limiting associated to more pronounce non-linear optical effects is detected at the wavelength of 1064 nm compared to the one at 532 nm. This effect may be due to a stronger nonlinear backscattering behavior at 1064 nm. Moreover, a striking result obtained from the Z-scan experiments reveals a completely different behavior of the functionalized nanodiamonds for both wavelengths. This result is discussed in regard to the electronic properties of the material and possible charge transfer.

This paper reports on the first attempt to enclose diamond nanoparticles--produced by detonation--into a Kevlar matrix. A nanocomposite material (40 wt% diamond) was prepared by precipitation from an acidic solution of Kevlar containing dispersed nanodiamonds. In this material, the diamond nanoparticles (Ø = 4 nm) are entirely wrapped in a Kevlar layer about 1 nm thick. In order to understand the interactions between the nanodiamond surface and the polymer, the oxygenated surface functional groups of nanodiamond were identified and titrated by Boehm's method which revealed the exclusive presence of carboxyl groups (0.85 sites per nm2). The hydrogen interactions between these groups and the amide groups of Kevlar destroy the "rod-like" structure and the classical three-dimensional organization of this polymer. The distortion of Kevlar macromolecules allows the wrapping of nanodiamonds and leads to submicrometric assemblies, giving a cauliflower structure reminding a fractal object. Due to this structure, the macroscopic hardness of Kevlar doped by nanodiamonds (1.03 GPa) is smaller than the one of pure Kevlar (2.31 GPa). To our knowledge, this result is the first illustration of the change of the mechanical properties induced by doping the Kevlar with nanoparticles.

Nanothermites, combining a fuel with an oxidizer at the nanoscale, represent a class of energetic material that has been attracting increasing attention over the past decade. This intensive interest is due to their tuneable pyrotechnic performance, making the materials promising candidates for ordnance applications. However, the extreme mechanical and electrostatic sensitivities of energetic composites make handling them hazardous. In this study, a realistic desensitization method is suggested via the addition of polyaniline while maintaining an interesting combustion velocity in contrast to the literature values. This investigation claims a major scientific breakthrough in the preparation of safer energetic nanocomposites.