Institut Franco-Allemand de Recherches de Saint-Louis

Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.

We demonstrate for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility. The plasma density was optimized by adjusting the chirp, the focusing and beam diameter. The interaction of filaments with transparent and opaque targets was studied.

There is no standard method for the diagnosis of prosthetic joint infection (PJI). The contribution of 16S rRNA gene PCR sequencing on a routine basis remains to be defined. We performed a prospective multicenter study to assess the contributions of 16S rRNA gene assays in PJI diagnosis. Over a 2-year period, all patients suspected to have PJIs and a few uninfected patients undergoing primary arthroplasty (control group) were included. Five perioperative samples per patient were collected for culture and 16S rRNA gene PCR sequencing and one for histological examination. Three multicenter quality control assays were performed with both DNA extracts and crushed samples. The diagnosis of PJI was based on clinical, bacteriological, and histological criteria, according to Infectious Diseases Society of America guidelines. A molecular diagnosis was modeled on the bacteriological criterion (≥ 1 positive sample for strict pathogens and ≥ 2 for commensal skin flora). Molecular data were analyzed according to the diagnosis of PJI. Between December 2010 and March 2012, 264 suspected cases of PJI and 35 control cases were included. PJI was confirmed in 215/264 suspected cases, 192 (89%) with a bacteriological criterion. The PJIs were monomicrobial (163 cases [85%]; staphylococci, n = 108; streptococci, n = 22; Gram-negative bacilli, n = 16; anaerobes, n = 13; others, n = 4) or polymicrobial (29 cases [15%]). The molecular diagnosis was positive in 151/215 confirmed cases of PJI (143 cases with bacteriological PJI documentation and 8 treated cases without bacteriological documentation) and in 2/49 cases without confirmed PJI (sensitivity, 73.3%; specificity, 95.5%). The 16S rRNA gene PCR assay showed a lack of sensitivity in the diagnosis of PJI on a multicenter routine basis.

We present a technique to overcome the depth resolution limitation for 3D active imaging. Applying microsecond laser pulses and sensor gate width, a scene of several hundred meters is illuminated and recorded in a single image. The trapezoid-shaped range intensity profile is analyzed to obtain both the reflectivity and the depth of scene. We demonstrate a 3D scene reconstruction in a depth of 650 to 1550 m from only three images with an accuracy of <30 m. This depth accuracy is 10 times better than estimated from the classical resolution limit obtained for depth scanning active imaging with a similar number of images. Therefore, this technique enables superresolution depth mapping with a reduction of image data processing.

We investigate the depth imaging of objects through various densities of different obscurants (water fog, glycol-based vapor, and incendiary smoke) using a time-correlated single-photon detection system which had an operating wavelength of 1550 nm and an average optical output power of approximately 1.5 mW. It consisted of a monostatic scanning transceiver unit used in conjunction with a picosecond laser source and an individual Peltier-cooled InGaAs/InP single-photon avalanche diode (SPAD) detector. We acquired depth and intensity data of targets imaged through distances of up to 24 meters for the different obscurants. We compare several statistical algorithms which reconstruct both the depth and intensity images for short data acquisition times, including very low signal returns in the photon-starved regime.

The fabrication of Schottky diodes withstanding breakdown voltages up to 10 kV is demonstrated. A corresponding electric field of 7.7 MV/cm at the center of the diode is evaluated with the help of a two-dimensional finite elements software. These properties result from a net shallow acceptor concentration below 1016 cm−3 in the first micrometers of an epitaxial film with optimized crystalline quality and a special oxidizing treatment of its surface, allowing the true dielectric strength of bulk diamond to be revealed.

The observation of objects located in inaccessible regions is a recurring challenge in a wide variety of important applications. Recent work has shown that using rare and expensive optical setups, indirect diffuse light reflections can be used to reconstruct objects and two-dimensional (2D) patterns around a corner. Here we show that occluded objects can be tracked in real time using much simpler means, namely a standard 2D camera and a laser pointer. Our method fundamentally differs from previous solutions by approaching the problem in an analysis-by-synthesis sense. By repeatedly simulating light transport through the scene, we determine the set of object parameters that most closely fits the measured intensity distribution. We experimentally demonstrate that this approach is capable of following the translation of unknown objects, and translation and orientation of a known object, in real time.

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. Wire array metamaterials can be used to beat the fundamental diffraction limit of light, but most demonstrations have been limited to microwaves and very short propagation lengths. Tuniz et al. scale these metamaterial fibres up to the terahertz region over longer distances and show focussing down to λ/28.

Numerical simulation of three-dimensional dynamic stall has been undertaken using computational fluid dynamics. The full Navier–Stokes equations, coupled with a two-equation turbulence model, where appropriate, have been solved on multiblock strucured grids in a time-accurate fashion. Results have neen obtained for wings of square planform and of NACA 0012 section. Efforts have been devoted to the accurate modeling of the flow near the wing tips, which, for this case, were sharp without tip caps. The obtained results revealed the time evolution of the dynamic stall vortex, which, for this case, takes the shape of a capital omega+spanning the wing. The obtained results compare well against experimental data both for the surface pressure distribution on the wing and the flow topology. Of significant importance is the interaction between the three-dimensional dynamic stall vortex and the tip vortex. The present results indicate that once the two vortices are formed both appear to originate from the same region, which is located near the leading edge of the tip. During the ramping of the wing, the two vortices grow significantly in size. The dynamic stall vortex dettaches from the wing in the inboard region but remains close to the wing’s leading edge near the tip. The overall configuration of the developed vortical system takes a form. To our knowledge, this is the first detailed numerical study of three-dimensional dynamic stall appearing in the literature.

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.

This paper investigates the relaxor ferroelectric polymer-poly(vinylidene fluoride/trifluoroethylene/chlorofluoroethylene) terpolymer for energy storage capacitors. It is found that the high dielectric constant (>50 at 1 kHz) and high reversible polarization in the terpolymer lead to a high electric energy density ~ 10 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3 </sup> , achieved under an electric field of more than 350 MV/m. The high dielectric constant also causes the polarization saturation at fields much below the breakdown field and whereby the discharged energy density increases nearly linearly with applied field, distinctively different from the low dielectric constant linear dielectric polymers whose energy density rises with square of the applied field. The strong frequency dispersion and nonlinear polarization response (polarization saturation) of the relaxor terpolymer result in a low effective capacitance at the beginning of the discharge and the effective capacitance increases with time during the discharge. Furthermore, due to the frequency dispersion and nonlinear effect, the discharged energy density of the terpolymer to a resistor load R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> increases with R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . A large R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> will lead to high discharge efficiency in the terpolymer capacitor

The dynamic stall process on a pitching NACA 0012 airfoil was investigated by two experimental techniques-particle image velocimetry (PIV) and laser-sheet visualizations-and a numerical code based on the Navier-Stokes equations. The freestream velocity was 28 m/s, leading to a Reynolds number (based on airfoil chord) of 3.73 X 10 5 . The airfoil motion was a sinusoidal function between 5 and 25 deg of incidence, with a frequency of 6.67 Hz corresponding to a reduced frequency (based on airfoil half-chord) of 0.15. The out-of-plane component of the vorticity could be derived from the PIV velocity fields. The comparison between experimental and numerical results was conducted for the four main phases of the dynamic stall process, i.e., attached flow, development of the dynamic stall vortex, poststall vortex shedding, and reattachment. In general, the computational results agreed very well with the experimental results. However, some discrepancies were observed and discussed. The cycle-to-cycle nonreproducibility of the flowfield during the phase of massive separation is also mentioned.

The computational tools available for prediction of sound propagation through the atmosphere have increased dramatically during the past decade. The numerical techniques include analytical solutions for selected index of refraction profiles, ray trace techniques which include interaction with a complex impedance boundary, a Gaussian beam ray trace algorithm, and more sophisticated approximate solutions to the full wave equation; the fast field program (FFP) and the parabolic equation (PE) solutions. This large array of computational approaches raises questions concerning under what conditions the various approaches are reliable and concerns about possible errors in specific implementations. This paper presents comparisons of predictions from the several models assuming a complex impedance ground and four atmospheric conditions. For the cases studied, it was found that the FFP and PE algorithms agree to within numerical accuracy over the full range of conditions and agree with the analytical solutions where available. Comparisons to ray solutions define regimes where ray approaches can be used. There is no attempt to compare calculated transmission losses to measurements.

Making use of defects modification to P(VDF-TrFE) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor k/sub 31/ of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, /spl sim/ 1 J/cm/sup 3/. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chlorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a nonpolar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the nonpolar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/cm/sup 3/ can be induced under a low applied field of 13 V//spl mu/m. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.

A diode-pumped Q-switched Tm(3+)-doped double-clad silica fiber laser is reported providing average powers of up to 30 W at pulse widths of only 41 ns and repetition rates in the range of 10-125 kHz. Up to 270 microJ pulse energy was produced. Amplified spontaneous emission (ASE) buildup limits the maximum peak power, and the pump power and average output power at the point of ASE induced clamping were found to depend linearly on the repetition rate.

With growing interest in switchable devices for the THz frequency range, there is a strong demand for liquid crystals (LC) exhibiting both a high birefringence and a low absorption. We present the refractive index and absorption coefficient of the liquid crystal mixtures 1852 and 1825 in the frequency range between 0.2 and 2.5 THz. Both mixtures are designed specifically for high birefringence Δn of 0.32 and 0.38, respectively, in the THz region. In addition, they show low absorption coefficients for both ordinary and extraordinary polarization. This low absorbance in combination with the high birefringence makes these LCs particularly well suited for applications in switchable devices for THz optics.

Ferroelectric materials are intrinsically multifunctional and have found a broad range of applications. A new class of semicrystalline terpolymers comprising vinylidene fluoride (VDF), trifluoroethylene (TrFE), and 1,1-chlorofluoroethylene (CFE), were prepared at Institut de Saint-Louis (ISL) via a suspension polymerization process. Relevant studies and results show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The terpolymer exhibits high electrostrictive strain (>7%) with relatively high modulus (>0.3GPa). It has been also observed that the large electrostrictive strain is nearly constant in the temperature range from 20 to 80 degC. The high room temperature relative dielectric constant (~50), which is the highest among all the known polymers), high induced polarization (~0.05 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and high electric breakdown field (>400 MV/m) lead to very high volume efficiency for the electric energy storage operated under high voltage (~10 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> )

A reduced-size wideband single-feed circularly polarized patch antenna is introduced for telemetry applications in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -band around 2300 MHz. The proposed structure consists of a slot-loaded patch antenna printed over an optimized metamaterial-inspired reactive impedance substrate (RIS). We demonstrate, step by step, the main role of each antenna element by comparing numerically and experimentally the performance of various antenna configurations: antenna over a single- or dual-layer substrate, standard patch or slot-loaded patch, antenna with or without RIS. The final optimized structure exhibits an axial-ratio bandwidth of about 15% and an impedance bandwidth better than 11%, which is much wider than the conventional printed antenna on the same materials.

We report a compact Ho:YAG laser that is intracavity pumped by a diode-pumped Tm:YLF laser. Both lasers exhibit pulse mode behavior. Operating both crystals at room temperature (25 degrees C), we obtained 1.6 W of average output at 2.09 microm from the Ho:YAG laser for 15.4 W of diode power incident upon the Tm:YLF rod and a slope efficiency of 21%.

This article presents a complete design concerning the guidance and autopilot modules for a class of spin-stabilized fin-controlled projectiles. The proposed concept is composed of two sections: the rapidly spinning aft part contains the charge, whereas the front part, which is roll decoupled from the aft, includes all the necessary electronic equipment and actuator devices needed for guidance and control. As far as the front section is concerned, a skid-to-turn control configuration is adopted, employing two pairs of movable trajectory correction aerodynamic surfaces, whereas a coaxial motor is added for nose roll angle positioning. The main advantage of the overall setup is that, on the one hand, it maintains the inherent dynamic stability properties of a rapidly spinning body due to the aft part, while at the same time, the front part, containing the guidance fuse, remains easy to be fit to any unguided projectile, hence transforming it into a guided one. The design of the guidance and control modules for this configuration still remains a challenging task because the rapid spinning of the body creates a heavy coupling between the normal and lateral projectile dynamics, which must be eliminated. Furthermore, the rapidly changing operating conditions, the extended flight envelope, and the limited actuator and sensor bandwidths make this task even more demanding. A thorough yet practical procedure for the treatment of the preceding issues is described in this work involving several steps, such as nonlinear modeling of the projectile dynamics, equilibrium point computation, and linear parameter-varying modeling, autopilot design as well as guidance algorithms. Finally, complete nonlinear simulations based on realistic scenarios are performed to demonstrate the robustness of the proposed solution with respect to uncertain initial launch conditions.