Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2

In this study, the outcome of operating conditions of extrusion assisted by supercritical CO₂ for the manufacture of poly(lactic acid) foams was investigated. It was found that the temperature before and inside the die was the most prominent parameter to tune the foam properties. Foam porosity as high as 96% could be obtained (for die temperature between 109 and 112 °C), representing a total expansion exceeding 30. In this temperature range, low crystallinity (≈6%) was induced giving foams with high radial expansion i.e., large diameters and open porosity. At 112 °C, the CO₂ was able to greatly expand the foams, providing 73% of its potential blowing effect. On the other hand, a low die temperature (below a die temperature of 107 °C) induces a significantly higher level of crystallinity resulting in foams with closed‐porosity and a large longitudinal expansion due to higher strength of the polymer melt. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45067.     

Structure and analgesic properties of layered double hydroxides intercalated with low amounts of ibuprofen

Ibuprofen‐intercalated layered double hydroxides (LDH‐IBU) have been successfully synthesized via a coprecipitation method with a nominal [Al³⁺]/[Mg²⁺] ratio of 0.5 and a variable molar IBU/([Al³⁺]+[Mg²⁺]) ratio of 0, 0.15, 0.18, 0.24, 0.36, and 0.72. After an accurate determination of the composition, the nature of the intercalated species and the effective intercalation yield from to IBU, it is shown that the synthesis route used allows a good control of the quantity of intercalated IBU within the LDH framework. This results in different samples with full or partial IBU intercalation in the interlayer space in exchange of nitrate anions. The analysis of the X‐ray diffraction basal reflections reveals that the intercalation of IBU in the framework only increases the basal distances with no alteration of the brucite‐type layers. Also, a computational study used to model the positions and shapes of the basal reflections showed that the structure of the nonfully intercalated compounds follows a random interstratification scheme. Finally, three samples ranging from slightly to fully IBU‐intercalated galleries were selected for preliminary in vivo assays. These tests showed a strong tendency that after 24 hours the low yield of IBU‐intercalated compounds are almost as efficient as the fully intercalated sample.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

Influence of pressure and dwell time on pressure-assisted sintering of calcium cobaltite

Calcium cobaltite Ca₃Co₄O₉, abbreviated Co349, is a promising thermoelectric material for high-temperature applications in air. Its anisotropic properties can be assigned to polycrystalline parts by texturing. Tape casting and pressure-assisted sintering (PAS) are a possible future way for a cost-effective mass-production of thermoelectric generators. This study examines the influence of pressure and dwell time during PAS at 900°C of tape-cast Co349 on texture and thermoelectric properties. Tape casting aligns lentoid Co349. PAS results in a textured Co349 microstructure with the thermoelectrically favorable ab-direction perpendicular to the pressing direction. By pressure variation during sintering, the microstructure of Co349 can be tailored either toward a maximum figure of merit as required for energy harvesting or toward a maximum power factor as required for energy harvesting. Moderate pressure of 2.5 MPa results in 25% porosity and a textured microstructure with a figure of merit of 0.13 at 700°C, two times higher than the dry-pressed, pressureless-sintered reference. A pressure of 7.5 MPa leads to 94% density and a high power factor of 326 µW/mK² at 800°C, which is 11 times higher than the dry-pressed reference (30 MPa) from the same powder.     

Selective Oxidation of Chromium by O2 Impurities in CO2 During Initial Stages of Oxidation

This study shows that the corrosion behaviour of 12 wt% Cr steel in CO₂ at 550 °C is determined in the first stage of oxidation by reaction with O₂ impurities. Depending on the amount of theses impurities and the thermal ramp rate, selective oxidation of chromium could lead to the formation of a protective chromium-rich oxide. An oxidation model describing qualitatively the nature of the oxide layer formed in the initial period of oxidation is presented. From these observations, surface engineering processes for protecting 9–12 wt% chromium steels from fast corrosion rate have emerged.     

Role of ABCA7 in Human Health and in Alzheimer’s Disease

Several studies, including genome wide association studies (GWAS), have strongly suggested a central role for the ATP-binding cassette transporter subfamily A member 7 (ABCA7) in Alzheimer’s disease (AD). This ABC transporter is now considered as an important genetic determinant for late onset Alzheimer disease (LOAD) by regulating several molecular processes such as cholesterol metabolism and amyloid processing and clearance. In this review we shed light on these new functions and their cross-talk, explaining its implication in brain functioning, and therefore in AD onset and development.     

Cross-influence of membrane polyunsaturated fatty acids and hypoxia-reoxygenation on α- and β-adrenergic function of rat cardiomyocytes

The purpose of the present investigation was to determine whether the beneficial effects of polyunsaturated fatty acids (PUFA) may influence ischemia-reperfusion-induced alterations of myocardial α- and β-adrenoceptor (α-AR, β-AR) responsiveness. This study was carried out using monolayer cultures of neonatal rat ventricular myocytes in a substrate-free, hypoxia-reoxygenation model of ischemia. The cardiomyocytes (CM) were incubated during 4 days in media enriched either with n−6 PUFA (arachidonic acid, AA) or with n−3 PUFA (eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA). The n−6/n−3 ratio in n−3 CM was close to 1.2, compared to 20.1 in n−6 CM. The contractile parameters of n−6 CM and n−3 CM were similar in basal conditions as well as during hypoxia and reoxygenation. In basal conditions, the phospholipid (PL) enrichment with long chain n−3 PUFA resulted in an increased chronotropic response to isoproterenol (ISO) and to phenylephrine (PHE). After posthypoxic reoxygenation, the chronotropic response to β-AR activation in n−6 CM was significantly enhanced as compared with the control response in normoxia. In opposition, the ISO-induced rise in frequency in n−3 CM in control normoxia and after reoxygenation was similar. In these n−3 CM, the changes in contractile parameters, which accompanied the chronotropic response, were also similar in reoxygenation and in normoxic periods, although the rise in shortening velocity was slightly increased after reoxygenation. In response to PHE addition, only the chronotropic effect of n−6 CM appeared significantly enhanced after hypoxic treatment. These results suggested that increasing n−3 PUFA in PL reduced the increase in α- and β-AR functional responses observed after hypoxia-reoxygenation. This effect may partly account for the assumed cardiac protective effect of n−3 PUFA, through the attenuation of the functional response to catecholamines in the ischemic myocardium.     

Building blocks for a two-frequency laser lidar-radar: a preliminary study

A new principle of lidar-radar is theoretically and experimentally investigated. The proposed architecture is based on the use of an rf modulation of the emitted light beam and a direct detection of the backscattered intensity. Use of a radar-processing chain allows one to obtain range and Doppler measurements with the advantages of lidar spatial resolution. We calculate the maximum range of this device, taking into account different possible improvements. In particular, we show that use of a pulsed two-frequency laser and a spatially multimode optical preamplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility of both range and Doppler measurements. The building blocks of this lidar-radar are tested experimentally: The radar processing of an rf-modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. In addition, signal-to-noise ratio improvement by optical pre-amplification is demonstrated at 1.06 microm. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits two-frequency pulses with tunable pulse duration (from 18 to 240 ns) and beat frequency (from 0 to 2.65 GHz) to be obtained.     

Toward tunable thin-film filters for wavelength division multiplexing applications

We provide a detailed analysis of the various problems connected with the development of tunable thin-film filters for wavelength-division multiplexing applications. We examine the relation between the change in layer thickness and the central wavelength shift for various configurations and point out the significance of the structure of the reflectors, the spacer thickness, and the location of the active layers. We describe and compare practical arrangements using either temperature or an electric field as the driving parameter.