Encapsulating Nickel-Iron Alloy Nanoparticles in a Polysilazane-Derived Microporous Si-C-O-N-Based Support to Stimulate Superior OER Activity.

The in situ confinement of nickel (Ni)-iron (Fe) nanoparticles (NPs) in a polymer-derived microporous silicon carboxynitride (Si-C-O-N)-based support is investigated to stimulate superior oxygen evolution reaction (OER) activity in an alkaline media. Firstly, we consider a commercial polysilazane (PSZ) and Ni and Fe chlorides to be mixed in N,N-dimethylformamide (DMF) and deliver after overnight solvent reflux a series of Ni-Fe : organosilicon coordination polymers. The latter are then heat-treated at 500 °C in flowing argon to form the title compounds. By considering a Ni : Fe ratio of 1.5, face centred cubic (fcc) NixFey alloy NPs with a size of 15-30 nm are in situ generated in a porous Si-C-O-N-based matrix displaying a specific surface area (SSA) as high as 237 m2 ⋅ g-1. Hence, encapsulated NPs are rendered accessible to promote electrocatalytic water oxidation. An OER overpotential as low as 315 mV at 10 mA ⋅ cm-2 is measured. This high catalytic performance (considering that the metal mass loading is as low as 0.24 mg cm-2) is rather stable as observed after an activation step; thus, validating our synthesis approach. This is clearly attributed to both the strong NP-matrix interaction and the confinement effect of the matrix as highlighted through post mortem microscopy observations.

Low temperature in situ immobilization of nanoscale fcc and hcp polymorphic nickel particles in polymer-derived Si-C-O-N(H) to promote electrocatalytic water oxidation in alkaline media.

We synthesized nickel (Ni) nanoparticles (NPs) in a high specific surface area (SSA) p-block element-containing inorganic compound prepared via the polymer-derived ceramics (PDC) route to dispatch the obtained nanocomposite towards oxygen evolution reaction (OER). The in situ formation of Ni NPs in an amorphous silicon carboxynitride (Si-C-O-N(H)) matrix is allowed by the reactive blending of a polysilazane, NiCl2 and DMF followed by the subsequent thermolysis of the Ni : organosilicon polymer coordination complex at a temperature as low as 500 °C in flowing argon. The final nanocomposite displays a BET SSA as high as 311 m2 g-1 while the structure of the NPs corresponds to face-centred cubic (fcc) Ni along with interstitial-atom free (IAF) hexagonal close-packed (hcp) Ni as revealed by XRD. A closer look into the compound through FEG-SEM microscopy confirms the formation of pure metallic Ni, while HR-TEM imaging reveals the occurrence of Ni particles featuring a fcc phase and surrounded by carbon layers; thus, forming core-shell structures, along with Ni NPs in an IAF hcp phase. By considering that this newly synthesized material contains only Ni without doping (e.g., Fe) with a low mass loading (0.15 mg cm-2), it shows promising OER performances with an overpotential as low as 360 mV at 10 mA cm-2 according to the high SSA matrix, the presence of the IAF hcp Ni NPs and the development of core-shell structures. Given the simplicity, the flexibility, and the low cost of the proposed synthesis approach, this work opens the doors towards a new family of very active and stable high SSA nanocomposites made by the PDC route containing well dispersed and accessible non-noble transition metals for electrocatalysis applications.

Mechanistic Investigation of the Formation of Nickel Nanocrystallites Embedded in Amorphous Silicon Nitride Nanocomposites.

Herein, we report the mechanistic investigation of the formation of nickel (Ni) nanocrystallites during the formation of amorphous silicon nitride at a temperature as low as 400 °C, using perhydropolysilazane (PHPS) as a preformed precursor and further coordinated by nickel chloride (NiCl2); thus, forming the non-noble transition metal (TM) as a potential catalyst and the support in an one-step process. It was demonstrated that NiCl2 catalyzed dehydrocoupling reactions between Si-H and N-H bonds in PHPS to afford ternary silylamino groups, which resulted in the formation of a nanocomposite precursor via complex formation: Ni(II) cation of NiCl2 coordinated the ternary silylamino ligands formed in situ. By monitoring intrinsic chemical reactions during the precursor pyrolysis under inert gas atmosphere, it was revealed that the Ni-N bond formed by a nucleophilic attack of the N atom on the Ni(II) cation center, followed by Ni nucleation below 300 °C, which was promoted by the decomposition of Ni nitride species. The latter was facilitated under the hydrogen-containing atmosphere generated by the NiCl2-catalyzed dehydrocoupling reaction. The increase of the temperature to 400 °C led to the formation of a covalently-bonded amorphous Si3N4 matrix surrounding Ni nanocrystallites.

In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems.

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000-1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiNxCy nanocrystals (x + y = 1) are homogeneously formed "in situ" in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si3N4, TiNxCy (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.

Characterization of Angle Accuracy and Precision of 3-Degree-of-Freedom Absolute Encoder Based on NanoGPS OxyO Technology.

An absolute encoder based on vision system nanoGPS OxyO was developed by HORIBA France. This encoder provides three types of position information, namely, two inplane co-ordinates and inplane angular orientation. This paper focuses on the characterization of its angular performance. To this aim, the nanoGPS OxyO system was compared with the national angle standard of the National Metrology Institute of Italy (INRIM) that had evaluated accuracy of about 0.1 µrad. The effect of image size and illumination conditions on angular measurements was studied. Precision better than 10 µrad and accuracy better than 63 µrad over 2π rotation were demonstrated. Moreover, the application of nanoGPS OxyO to the characterization of rotation bearing is presented. Small deviations from pure rotational behavior were evidenced that would have not been possible using laser interferometers. As a consequence of its accuracy and versatility, the nanoGPS OxyO encoder is expected to be useful for laboratory experiments and quality-control tasks.

Role of terminal and anastomotic circulation in the patency of arteries jailed by flow-diverting stents: from hemodynamic changes to ostia surface modifications.

OBJECTIVE The outcome for jailing arterial branches that emerge near intracranial aneurysms during flow-diverting stent (FDS) deployment remains controversial. In this animal study, the authors aimed to elucidate the role of collateral supply with regard to the hemodynamic changes and neointimal modifications that occur from jailing arteries with FDSs. To serve this purpose, the authors sought to quantify 1) the hemodynamic changes that occur at the jailed arterial branches immediately after stent placement and 2) the ostia surface values at 3 months after stenting; both parameters were investigated in the presence or absence of collateral arterial flow. METHODS After an a priori power analysis, 2 groups (Group A and Group B) were created according to an animal flow model for terminal and anastomotic arterial circulation; each group contained 7 Large White swine. Group A animals possessed an anastomotic-type arterial configuration to supply the territory of the right ascending pharyngeal artery (APhA), while Group B animals possessed a terminal-type arterial configuration to supply the right APhA territory. Subsequently, all animals underwent FDS placement, thereby jailing the right APhAs. Mean flow rates and velocities inside the jailed branches were quantified using time-resolved 3D phase-contrast MR angiography before and after stenting. Three months after stent placement, the jailed ostia surface values were quantified on scanning electron micrographs. The data were analyzed using descriptive statistics and group comparisons with parametric and nonparametric tests. RESULTS The endovascular procedures were feasible, and there were no findings of in situ thrombus formation on postprocedural optical coherence tomography or ischemia on postprocedural diffusion-weighted imaging. In Group A, the mean flow rate values at the jailed right APhAs were reduced immediately following stent placement as compared with values obtained before stent placement (p = 0.02, power: 0.8). In contrast, the mean poststenting flow rates for Group B remained similar to those obtained before stent placement. Three months after stent placement, the mean ostia surface values were significantly higher for Group B (527,911 ± 306,229 µm2) than for Group A (89,329 ± 59,762 µm2; p < 0.01, power: 1.00), even though the initial dimensions of the jailed ostia were similar between groups. A statistically significant correlation was found between groups (A or B), mean flow rates after stent placement, and ostia surface values at 3 months. CONCLUSIONS When an important collateral supply was present, the jailing of side arteries with flow diverters resulted in an immediate and significant reduction in the flow rate inside these arteries as compared with the prestenting values. In contrast, when competitive flow was absent, jailing did not result in significant flow rate reductions inside the jailed arteries. Ostium surface values at 3 months after stent placement were significantly higher in the terminal group of jailed arteries (Group B) than in the anastomotic group (Group A) and strongly correlated with poststenting reductions in the velocity value.

Jailed Artery Ostia Modifications After Flow-Diverting Stent Deployment at Arterial Bifurcations: A Scanning Electron Microscopy Translational Study.

BACKGROUND: Even though flow-diverting stents are being increasingly used to treat intracranial aneurysms, the fate of jailed side branches remains controversial, with recent clinical data contradicting finding of earlier animal studies that reported patency. OBJECTIVE: To quantify the surface area of the ostia after 3 months of jailing by flow-diverting stents as a more accurate means of patency evaluation. METHODS: Ten large white swine were stented by flow-diverting stents placed at common carotid-ascending pharyngeal arterial bifurcation sites. A dual antiplatelet regimen was initiated 72 hours before stenting and maintained during follow-up. Optical coherence tomography was used to search for per-procedural thrombus formation. Selective control digital subtraction angiography was performed 12 weeks post-stenting. Subsequently, the stented arterial segments were harvested en bloc and observed under scanning electron microscopy, photographed, and quantified. RESULTS: The absence of per-procedural thrombus formation was confirmed. All ostia were patent at 12 weeks (or 3 months) post stenting, with no angiographic or scanning electron microscopy-evident thrombus formation. The mean initial ostium surface was 2 048 617 ± 731 625 µm. At 3 months, the mean nonendothelialized ostium surface was 229 218 ± 140 172 µm, and mean endothelialized ostium surface was 1 819 399 ± 672 632 µm. A statistically significant difference (reduction) was observed between the initial and 12-week ostium surfaces (P < .001), with an significant statistical power (1.000). CONCLUSION: Jailed side branches remained patent after stenting, but the surface quantifications showed significant endothelial coverage, with a significant reduction of patent ostium surfaces at 12 weeks post-stenting. ABBREVIATIONS: APhA, ascending pharyngeal arteryCI, confidence interval3DRA, 3-dimensional rotational angiographyDSA, digital subtraction angiographyFDS, flow-diverting stentOCT, optical coherence tomographyOS, ostium surfaceSEM, scanning electron microscopy.

Role of terminal and anastomotic circulation in the patency of arteries jailed by flow-diverting stents: animal flow model evaluation and preliminary results.

OBJECTIVE The authors describe herein the creation of an animal model capable of producing quantifiable data regarding blood flow rate and velocity modifications in terminal and anastomotic types of cerebrofacial circulation. They also present the preliminary results of a translational study aimed at investigating the role of terminal and anastomotic types of circulation in arterial branches jailed by flow-diverting stents as factors contributing to arterial patency or occlusion. METHODS Two Large White swine were used to validate a terminal-type arterial model at the level of the right ascending pharyngeal artery (APhA), created exclusively by endovascular means. Subsequently 4 Large White swine, allocated to 2 groups corresponding to the presence (Group B) or absence (Group A) of terminal-type flow modification, underwent placement of flow-diverting stents. Blood flow rates and velocities were quantified using a dedicated time-resolved 3D phase-contrast MRA sequence before and after stenting. Three months after stent placement, the stented arteries were evaluated with digital subtraction angiography (DSA) and scanning electron microscopy (SEM). Patent (circulating) ostia quantification was performed on the SEM images. RESULTS Terminal-type flow modification was feasible; an increase of 75.8% in mean blood velocities was observed in the right APhAs. The mean blood flow rate for Group A was 0.31 ± 0.19 ml/sec (95% CI -1.39 to 2.01) before stenting and 0.21 ± 0.07 ml/sec (95% CI -0.45 to 0.87) after stenting. The mean blood flow rate for Group B was 0.87 ± 0.32 ml/sec (95% CI -1.98 to 3.73) before stenting and 0.76 ± 0.13 ml/sec (95% CI -0.41 to 1.93) after stenting. Mean flow rates after stenting showed a statistically significant difference between Groups A and B (Welch test). Mean and maximal blood velocities were reduced in Group A cases and did not decrease in Group B cases. Control DSA and SEM findings showed near occlusion of the jailed APhAs in both cases of anastomotic circulation (mean patent ostium surface 32,776 µm2) and patency in both cases of terminal-type circulation (mean patent ostium surface 422,334 µm2). CONCLUSIONS Terminal-type arterial modification in swine APhAs is feasible. Sufficient data were acquired to perform an a priori analysis for further research. Flow diversion at the level of the APhA ostium resulted in significant stenosis in cases of anastomotic circulation, while sufficient patency was observed in terminal-type circulation.

Intravascular optical coherence tomography for the evaluation of arterial bifurcations covered by flow diverters.

BACKGROUND AND OBJECTIVE: Due to its high spatial resolution, intravascular optical coherence tomography (OCT) has been used as a valid method for in vivo evaluation of several types of coronary stents at straight lumen and bifurcation sites. We sought to evaluate its effectiveness for flow diverting stents deployed in arterial bifurcation sites involving jailing of a side branch. METHODS: Four large white swine were stented with flow diverting stents covering the right common carotid artery-ascending pharyngeal artery bifurcation. After 12 weeks of follow-up the animals were evaluated by digital subtraction angiography and intravascular OCT and subsequently sacrificed. Neointimal thickness on the parent arteries and the free segments of the stent were measured. The stented arteries were harvested and underwent scanning electron microscopy (SEM) imaging. Ostia surface values were measured with OCT three-dimensional (3D) reconstructions and SEM images. RESULTS: All endovascular procedures and OCT pullback runs were feasible. Stent apposition was satisfactory on the immediate post-stent OCT reconstructions. At 12-week controls, all stents and jailed branches were patent. Mean neointimal thickness was 0.11±0.04 mm on the free segments of the stent. The mean ostia surface at 12 weeks was 319 750±345 533 µm2 with 3D-OCT reconstructions and 351 198±396 355 µm2 with SEM image-derived calculations. Good correlation was found for ostia surface values between the two techniques; the values did not differ significantly in this preliminary study. CONCLUSIONS: Intravascular OCT appears to be a promising technique for immediate and follow-up assessment of the orifice of arterial branches covered by flow diverting stents.

Scanning electron microscopy for flow-diverting stent research: technical tips and tricks.

Flow-diverting (FD) stents represent a new concept in the treatment of intracranial aneurysms with challenging anatomical dispositions. Having been introduced to clinical practice only in the last 5 years and featuring complex mechanisms of action, they are still under research. Scanning electron microscopy, as part of an animal research protocol, provides detailed surface observations of neointimal healing at the aneurysm's neck, as well as covered side branch ostia, allowing for the confirmation of scientific hypotheses and observations. Technical adaptations of preparation protocols are presented based on a pilot study on Large White pigs, stented with FD stents at carotid bifurcations.

The importance of fluctuations in fluid mixing.

A ubiquitous example of fluid mixing is the Rayleigh-Taylor instability, in which a heavy fluid initially sits atop a light fluid in a gravitational field. The subsequent development of the unstable interface between the two fluids is marked by several stages. At first, each interface mode grows exponentially with time before transitioning to a nonlinear regime characterized by more complex hydrodynamic mixing. Unfortunately, traditional continuum modeling of this process has generally been in poor agreement with experiment. Here, we indicate that the natural, random fluctuations of the flow field present in any fluid, which are neglected in continuum models, can lead to qualitatively and quantitatively better agreement with experiment. We performed billion-particle atomistic simulations and magnetic levitation experiments with unprecedented control of initial interface conditions. A comparison between our simulations and experiments reveals good agreement in terms of the growth rate of the mixing front as well as the new observation of droplet breakup at later times. These results improve our understanding of many fluid processes, including interface phenomena that occur, for example, in supernovae, the detachment of droplets from a faucet, and ink jet printing. Such instabilities are also relevant to the possible energy source of inertial confinement fusion, in which a millimeter-sized capsule is imploded to initiate nuclear fusion reactions between deuterium and tritium. Our results suggest that the applicability of continuum models would be greatly enhanced by explicitly including the effects of random fluctuations.

Rayleigh-Taylor instability experiments with precise and arbitrary control of the initial interface shape.

In a Rayleigh-Taylor instability a dense fluid sits metastably atop a less dense fluid, a configuration that can be stabilized using a magnetic field gradient when one fluid is highly paramagnetic. On switching off the magnetic field, the instability occurs as the dense fluid falls under gravity. By affixing appropriately shaped magnetically permeable wires to the outside of the cell, one may impose arbitrarily chosen and well-controlled initial perturbations on the interface. This technique is used to examine both the linear and nonlinear growth regimes for which the perturbation amplitudes, growth rates, and nonlinear growth coefficients are obtained.

Rayleigh-Taylor instability for immiscible fluids of arbitrary viscosities: a magnetic levitation investigation and theoretical model.

A magnetic field gradient was used to draw down a low density paramagnetic fluid below a more dense fluid in a Hele-Shaw cell. On turning off the field a Rayleigh-Taylor instability was observed in situ, and the growth of the most unstable wave vector was measured versus time. A theory for the instability that permits different viscosities for two immiscible fluids was developed, and good agreement was found with the experimental results. The technique of magnetic levitation promises to broaden significantly the accessible parameter space of gravitational interfacial instability experiments.

Two typical time scales of the piston effect.

The existence of a fourth mode of heat transfer near the critical point, named the piston effect, has been known for more than a decade. The typical time scale of temperature relaxation due to this effect was first predicted by Onuki [Phys. Rev A 41, 2256 (1990)], and this author's formula has been extensively used since then to predict the thermal behavior of near-critical fluids. Recent studies, however, pointed out that the critical divergence of the bulk viscosity could have a strong influence on piston-effect-related processes. In this paper, we conduct a theoretical analysis of near-critical temperature relaxation showing that the piston effect is not governed by one (as was until now believed) but by two typical time scales. These two time scales exhibit antagonistic asymptotic behaviors as the critical point is approached: while the classical piston-effect time scale (as predicted by Onuki ) goes to zero at the critical point (critical speeding up), the second time scale (related to bulk viscosity) goes to infinity (critical slowing down). Based on this property, an alternative method for measuring near-critical bulk viscosity is proposed.

Temperature and density relaxation close to the liquid-gas critical point: an analytical solution for cylindrical cells.

We present a study of the temperature and density equilibration near the liquid-gas critical point of a composite system consisting of a thin circular disk of near-critical fluid surrounded by a copper wall. This system is a simplified model for a proposed space experiment cell that would have 60 thin fluid layers separated by perforated copper plates to aid in equilibration. Upper and lower relaxation time limits that are based on radial and transverse diffusion through the fluid thickness are shown to be too significantly different for a reasonable estimate of the time required for the space experiment. We therefore have developed the first rigorous analytical solution of the piston effect in two dimensions for a cylindrically symmetric three-dimensional cell, including the finite conductivity of the copper wall. This solution covers the entire time evolution of the system after a boundary temperature step, from the early piston effect through the final diffusive equilibration. The calculation uses a quasistatic approximation for the copper and a Laplace-transform solution to the piston effect equation in the fluid. Laplace inversion is performed numerically. The results not only show that the equilibration is divided into three temporal regimes but also give an estimate of the amplitudes of the remaining temperature and density inhomogeneity in each regime. These results yield characteristic length scales for each of the regimes that are used to estimate the expected relaxation times in the one- and two-phase regions near the critical point.

Large cell neuroendocrine carcinoma of the lung: pathological study and clinical outcome of 18 resected cases.

Large cell neuroendocrine carcinoma of the lung (LCNEC) has been recently redefined by the World Health Organisation (WHO) classification but the appropriate treatment remains unclear. We reviewed 18 consecutive resected cases of LCNEC. Two pathologists assessed diagnosis by applying rigorously the last WHO criteria. We reported the pathological features and the clinical outcome of this particular tumour. All patients were men with a median age of 63 years. Clinicopathologic stages corresponded to stage I (n = 8), II (n = 8) and IIIA (n = 2). All patients were treated as non-small cell lung carcinoma (NSCLC) and underwent surgery without any adjuvant treatment except four post-operative radiotherapy for N2 or T3 disease. The evolution was pejorative for 14 patients: one patient died of post-operative complications and 13 patients relapsed with distant metastases that occurred in 10 cases within 6 months after surgery. One-year survival rate was 27% and survival rate at the end of follow-up was 22%, which were both less than expected for stage-comparable NSCLC. Survival was neither influenced by lymph node status nor by pathological or molecular findings. Among the 10 evaluable patients with metastatic disease that received palliative platin-etoposide chemotherapy only two had partial tumour regressions (20%). Our study suggests that applying to LCNEC the NSCLC standard treatment lead to poor prognosis even in localised disease with a high incidence of early metastatic spread and a low response rate to chemotherapy. This way of relapse underlies the necessity of an efficient chemotherapy in order to improve survival.

Diffuse infiltrative lung disease associated with flecainide. Report of two cases.

We present two patients who developed subacute diffuse infiltrative lung disease while receiving flecainide for supraventricular arrhythmia. They had bilateral subpleural lung opacities on computed tomography. Bronchoalveolar lavage revealed increased numbers of lymphocytes and eosinophils, and a low CD4/CD8 ratio. Nonspecific interstitial pneumonia was documented by open lung biopsy in patient 1. The outcome was favorable after flecainide withdrawal and prednisone treatment. Drug-induced pneumonitis should be suspected in patients treated with flecainide presenting with subacute diffuse infiltrative lung disease.

Scenarios for the onset of convection close to the critical point.

We perform a theoretical analysis of the onset of convection in a layer of near-critical 3He submitted to an unsteady bottom heating. A theoretical model previously presented [P. Carlès, Physica D 147, 36 (2000)] is adapted to the corresponding physical conditions, and a method is proposed to solve the associated equations. We predict, for different intensities of heating and different initial temperatures, when convection will start and what will be the shape of the dominant growing perturbations. A systematic parametric analysis shows that the onset of convection in a supercritical fluid can take place following four distinct scenarios, depending on the initial temperature and the intensity of the heating. Two of these scenarios are entirely specific to near-critical fluids, being impossible to observe in classical Boussinesq fluids.