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1
Hayes, Julie E., Margaret Pallotta, Ute Baumann, Bettina Berger, Peter Langridge et Tim Sutton. « Germanium as a tool to dissect boron toxicity effects in barley and wheat ». Functional Plant Biology 40, no 6 (2013) : 618. http://dx.doi.org/10.1071/fp12329.
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Tolerance to boron (B) toxicity in barley (Hordeum vulgare L.) is partially attributable to HvNIP2;1, an aquaporin with permeability to B, as well as to silicon, arsenic and germanium (Ge). In this study, we mapped leaf symptoms of Ge toxicity in a doubled-haploid barley population (Clipper × Sahara 3771). Two quantitative trait loci (QTL) associated with Ge toxicity symptoms were identified, located on Chromosomes 6H and 2H. These QTL co-located with two of four B toxicity tolerance loci previously mapped in the same population. The B toxicity tolerance gene underlying the 6H locus encodes HvNIP2;1, whereas the gene(s) and mechanisms underlying the 2H locus are as yet unknown. We provide examples of the application of Ge in studying specific aspects of B toxicity tolerance in plants, including screening of wheat (Triticum aestivum L.) and barley populations for altered function of HvNIP2;1 and related proteins. In particular, Ge may facilitate elucidation of the mechanism and gene(s) underlying the barley Chromosome 2H B tolerance locus.
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HWANG, J. K., J. H. HAMILTON et A. V. RAMAYYA. « N = 50 SHELL GAP EVOLUTION AND PARTICLE–HOLE EXCITATIONS IN 82Ge, 84Se AND 86Kr ». International Journal of Modern Physics E 21, no 03 (mars 2012) : 1250020. http://dx.doi.org/10.1142/s0218301312500206.
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The two excited 0+ states of the neutron-rich nuclei 82 Ge , 84 Se and 86 Kr are explained as 2-particle 2-hole (2p–2h) excited states associated with two different open-shells of Z = 28–50 and 28–40. Also, a configuration of 1p–1h 7+ state is assigned to the 3689 keV state in 82 Ge . These 1p–1h and 2p–2h excitation energies support the decreasing of the N = 50 shell gap when Z changes from 40 to 32. A N = 50 shell gap of 3.67 MeV for 78 Ni is extracted from an extrapolation of the known data.
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Vincent, Laetitia, Marcel A. Verheijen, Wouter Peeters, Hassan Melhem, Theo Van den Berg, Hafssa Ameziane, Gilles Patriarche et al. « Epitaxy of Hexagonal Ge-2H : Lessons from in Situ TEM Observations ». ECS Meeting Abstracts MA2024-02, no 32 (22 novembre 2024) : 2340. https://doi.org/10.1149/ma2024-02322340mtgabs.
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Silicon and Germanium crystallize in the cubic diamond structure 3C with which they dominate definitely the electronics. Playing on crystal phases in semiconductors occurs to be a valuable mean of electronic band engineering. Remarkably, the hexagonal 2H phase of SiGe turns to get a direct band gap with light emission capabilities within a specific composition range (Si<35%). This material holds the promise to fill the gap between electronics and photonics industry using group IV semiconductors. We use GaAs NWs with the wurtzite structure as a template to create both (1) core/shell and (2) trunk/nanobranches heterostructures [2,3]. The GaAs-wurtzite is an ideal template to copy the structure by epitaxy forcing the Ge to adopt the hexagonal crystal phase and in turn it is used here as a textbook case The growths are followed using the in situ TEM NANOMAX. This unique microscope can be implemented either with molecular beam epitaxy (MBE) sources or with a gas injector for chemical vapor deposition (CVD). Real time TEM observations at the atomic scale show the fundamental aspects of the epitaxy and the formation of growth-related staking faults in Ge-2H. 1) On core/shell configuration[1], depending on growth conditions, different growth regimes highly impact the crystal quality of the of Ge-2H shell. On {1-100} prismatic surfaces, a regular step flow supports a flat surface and a perfect replication of the hexagonal structure However, when the step flow is destabilized, original intrinsic I3 basal stacking faults (BSF) are formed during growth. We evidence their correlation with the growth modes related to surface diffusion. Understanding the nucleation of these defects is necessary to prevent their formation during epitaxy. Possible scenarios of I3 BSF formation are discussed. Theses defects show a faulted stacking ABACABAB with only one faulted basal plane bounded by a pair of partial dislocations along <11-20> with opposite Burger vectors b=+/-1/3<1-100>. Thermal annealing induces a motion of the dislocation and an expansion of the I3 BSF resulting in a 4H stacking in the core/shell structure. 2) On wurtzite GaAs nanowires, Au catalysts are deposited on the sidewalls. Nanobranches grow with an axial direction along <1-100> and exhibit a hexagonal crystal structure[2] . With in situ observations, we study the VLS and VSS growths of Au catalyzed Ge-2H branches depending on the growth temperature. [1] L. Vincent et al. Adv. Mat. Inter. 9-16 (2022) 2102340, doi.org/10.1002/admi.202102340 [2] A Li et al. Nanotechnology 34 (2023) 015601 doi: 10.1088/1361-6528/ac9317 Figure 1
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Nader, Richard, et Jörg Pezoldt. « Quantitative Evaluation of Strain in Epitaxial 2H-AlN Layers ». Advanced Materials Research 324 (août 2011) : 213–16. http://dx.doi.org/10.4028/www.scientific.net/amr.324.213.
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To improve the quality of AlN layer deposit on SiC/Si, different Ge amounts (0.25, 0.5, 1, 2ML) were deposited before the carbonization process at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers derives from the phonon frequency shifts of the E1(TO) phonon mode. The crystalline quality of the AlN layer is correlated to and investigated by the full width of the half maximum (FWHM) and the intensity of E1(TO) mode of the 2H-AlN. Best crystalline quality and lower stress value are found in the case where 1ML of Ge amount is predeposited. The E1(TO) mode phonon frequency shifts-down by 3 cm-1/GPa with respect to an unstrained layer.
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Galanopoulos, S., M. Serris, G. Perdikakis, M. Kokkoris, C. T. Papadopoulos, R. Vlastou, A. Lagoyannis et al. « Cross Section Measurements on Isotopes of Ge and Hf Using the Activation Technique ». HNPS Proceedings 14 (5 décembre 2019) : 167. http://dx.doi.org/10.12681/hnps.2267.
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Cross section measurements of neutron induced reactions on isotopes of Ge and Hf have been determined at energies 8.8, 9.6, 10.6, 11.1, 11.4 MeV using the activation technique. Neutrons produced by the 2H(d,n)3He reaction were used to irradiate pellets of natural Ge and Hf02- The neutron flux at the target position was determined using the 27Al(n,a)24Na, 93Nb(n,2n)92mNb and 197Au(n,2n)196Au reference reactions. HPGe detectors of relative efficiency εΓ=80% and 55% were used to determine the decay of the produced unstable nuclei. The cross section values were compared with those taken from the literature.
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Hinderberger, S., S. Q. Xiao, K. H. Westmacott et U. Dahmen. « Shape training of Ge precipitates in an Al-1.8at% Ge alloy ». Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994) : 690–91. http://dx.doi.org/10.1017/s0424820100171183.
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Ge precipitates in Al are known to form in a rich variety of shapes and orientation relationships. In this work it is shown that initial non-equilibrium shapes such as plates, laths, needles and tetrahedra can be induced to change to the equilibrium shape of an octahedron by proper temperature cycling. Analysis of this effect in bulk samples was complemented by direct observations of its mechanisms during in-situ temperature cycling.A bulk sample of an Al-1.8at%Ge alloy was solid solution annealed at 420°C for 2h, quenched in ice water, pre-aged at room temperature for 72h and then annealed for 5h at 250°C. Subsequently, part of the sample was repeatedly cycled between 250°C and 360°C. TEM specimens were prepared from both the cycled and non-cycled bulk sample by conventional electropolishing and examined in a JEOL 200CX electron microscope. The in-situ temperature cycling was carried out in a Kratos 1.5 MeV HVEM equipped with a double tilt heating stage.
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Bodé, Susan, Marianne Dreyer et Gorm Greisen. « Gastric Emptying and Small Intestinal Transit Time in Preterm Infants : a Scintigraphic Method ». Journal of Pediatric Gastroenterology and Nutrition 39, no 4 (octobre 2004) : 378–82. http://dx.doi.org/10.1002/j.1536-4801.2004.tb00870.x.
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ABSTRACTObjectives:Practical methods to determine gastric emptying (GE) and small intestinal transit time in preterm infants are required. The aim of this study was to develop a scintigraphic method to determine GE and small intestinal transit time in preterm infants which produce minimal radiation exposure and physical disturbance in these infants.Methods:Ten premature infants were studied. Median (and range) for gestational age was 28.9 (26–33) weeks, postnatal age was 19 (6–37) days, birth weight was 1194 (687–2300) grams and feeding volume was 173 (6–205) mL/kg/day. Nine of the patients were on nasal continuous positive airway pressure; one patient was on mechanical ventilation. A dose (0.2–0.4 MBq) of 99mTc‐DTPA (0.5 mL) was given at the end of a meal administered by naso‐gastric tube. Static images were obtained with a mobile gamma camera during the next 9 to 12 hours. The radiation dose was at most 0.30 mSv. Regions of interest (ROIs) were drawn around the stomach and the cecum. Time‐activity curves were generated. Gastric emptying half‐time (T½GE) was calculated. Residual gastric activity after 1 hour (R (1h)) and after 2 hours (R (2h)) was determined. Orocecal transit time was defined as the time until significant increase in activity was detected in the cecal ROI.Results:Images showed gastric emptying in all cases. Median (range) half time was 1.0 (0.5–3.0) h. R (1h) was 37.5% (19% to 100%), R (2h) was 23% (6% to 61%). In one patient the tracer did not reach the cecum within 12 hours. In the remaining nine patients orocecal transit time was 3.1 (1.3–6.1) h.Conclusions:We present a new scintigraphic method to determine GE and orocecal transit time. It appears safe and practicable as a research tool in preterm infants.
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Wu, Zhenyu, Xinlu Cheng et Hong Zhang. « Two-dimensional diamane-like Si2C(Ge)2H2 and Si2C(Ge)2H : Wide bandgap and bipolar magnetic semiconductors ». Journal of Magnetism and Magnetic Materials 566 (janvier 2023) : 170310. http://dx.doi.org/10.1016/j.jmmm.2022.170310.
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Pocha, Regina, et Dirk Johrendt. « Kristallstrukturen und elektronische Eigenschaften von Ge1/3NbS2 und Ge1/4NbS2 / Crystal Structures and Electronic Properties of Ge1/3NbS2 and Ge1/4NbS2 ». Zeitschrift für Naturforschung B 57, no 12 (1 décembre 2002) : 1367–74. http://dx.doi.org/10.1515/znb-2002-1205.
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Single crystals of the intercalation compounds Ge1/3NbS2 andGe1/4NbS2 have been prepared by heating of the elements at 1073 K and by chemical transport with iodine at 923 to 1073 K. Their crystal structures were determined by single crystal X-ray methods.Ge1/3NbS2 (P63/mcm, a=5.767(1), c=13.518(3) Å, Z = 6) crystallizes with a superstructureof 2H-NbS2, characterized by layers of edge-sharing NbS6 trigonal prisms. The Ge atoms in the octahedral voids of the van der Waals gap are sixfold coordinated by sulfur. The NbS2-sublattice of Ge1/4NbS2 (P63/mmc, a = 3.339(1), c = 37.326(7) Å , Z = 6) represents a new 6H-polymorph. Herein, the Ge atoms are located either in the centers of the octahedral voids (c. n. = 6) or shifted from this position along [001] (c. n. = 3 + 3). The unusual electronic state and the bonding situation of germanium in the van der Waal gaps of NbS2 and the metal-metal bonding are studied in detail by using DFT band structure calculations.
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Chasapoglou, Sotirios, Michael Axiotis, George Gkatis, Sotirios Harissopulos, Michael Kokkoris, Anastasios Lagoyannis, Claudia Lederer-Woods et al. « Cross Section Measurements of (n,x) Reactions at 17.9 MeV Using Highly Enriched Ge Isotopes ». HNPS Advances in Nuclear Physics 28 (17 octobre 2022) : 135–41. http://dx.doi.org/10.12681/hnps.3621.
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Τhe 70Ge(n,2n)69Ge, 72Ge(n,a)69mZn, 72Ge(n,p)72Ga and 73Ge(n,p)73Ga reactions have been measured by means of the activation technique at neutron energy 17.9 MeV. The quasimonoenergetic neutron beam was produced via the 2H(d,n)3He reaction at the 5.5 MV Tandem Van de Graaff accelerator of NCSR “Demokritos.” Isotopically highly enriched targets of 70Ge, 72Ge and 73Ge, provided by the nTOF collaboration at CERN, have been used, thus allowing accurate cross section measurements since no corrections are needed to compensate for the parasitic reactions from neighboring isotopes that exist in the case of using natural Ge target. The cross section has been deduced with respect to the 27Al(n,α)24Na reference reaction.
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Zamyshlyayeva, Olga, Zarina Shaliagina, Maria Simonova, Alexander Filippov et Maxim Baten’kin. « Properties in Langmuir Monolayers and Langmuir-Blodgett Films of a Block Copolymer Based on N-Isopropylacrylamide and 2,2,3,3-Tetrafluropropyl Methacrylate ». Polymers 14, no 23 (29 novembre 2022) : 5193. http://dx.doi.org/10.3390/polym14235193.
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The amphiphilic block copolymer poly(N-isopropylacrylamide)–Ge(C6F5)2–poly(2,2,3,3-tetrafluoropropyl methacrylate) was prepared by the reaction of chain transfer to bis-(pentafluorophenyl)germane during the polymerization of N-isopropylacrylamide and the subsequent postpolymerization of isolated functional polymers in 2,2,3,3–tetrafluoropropyl methacrylate. The conversion of the block copolymer was 68% and the molecular weight of the sample was 490,000 g/mol. The colloidal chemical properties of Langmuir monolayers and Langmuir-Blodgett films of synthesized block copolymer have been studied. For comparison, a functional polymer, namely, poly-N-isopropylacrylamide with terminal –Ge(C6F5)2H group, was synthesized and studied. The concentrations of spreading solutions were selected and the effect of subphase acidity on the formation of monolayers of macromolecules of the block copolymer was studied. It was found that regardless of the acidity of the subphase, high pressure of fracture of films are characteristic of monolayers of collapse pressures πmax = (48–61) mN/m. The morphology of the Langmuir-Blodgett films of functional polymer exhibit isolated elongated micelles with high densities in the form of “octopus” on the periphery of which there are terminal hydrophobic groups. For the Langmuir-Blodgett film of block copolymer, a comb-like structure is observed with characteristic protrusions.
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Vlastou, R., C. T. Papadopoulos, M. Kokkoris, G. Perdikakis, S. Galanopoulos, M. Serris, D. Giantsoudi, G. Argyropoulos, S. Kossionides et S. Harissopulos. « Neutron induced reactions at the Athens Tandem accelerator NCSR "Demokritos" ». HNPS Proceedings 14 (5 décembre 2019) : 1. http://dx.doi.org/10.12681/hnps.2238.
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The neutron facility at the 5.5 MV Tandem Tll/25 accelerator of NCSR "Demokritos" has been used to produce monoenergetic neutron beams in the energy range 120-650 keV and 4-11.5 MeV via the 7Li(p,n) and 2H(d,n) reactions, respectively. The flux variation of the neutron beam was monitored by using a BF3 detector, while an investigation of the energy dependence of the neutron fluence has been carried out with a liquid scintillator BC501A detector as well as with the multiple foil activation technique. The 232Th(n,2n)231Th and 241Am(n,2n)240Am as well as (n,2n), (n,p) and (η,α) reactions on natural Ge and Hf isotopes, have been investigated from threshold up to 11.5 MeV, by using the activation method.
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Schaeffer, Bernard. « Electric and Magnetic Coulomb Potentials in the Deuteron ». Advanced Electromagnetics 2, no 1 (27 septembre 2013) : 69. http://dx.doi.org/10.7716/aem.v2i1.218.
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After one century of nuclear physics, the underlying fun- damental laws of nuclear physics are still missing. Bohr had found a formula for the H atom and another for the H2 molecule but no equivalent formula exists for the deuteron 2H. The only known Coulomb interaction in a nucleus by the mainstream nuclear physics is the long range repulsion between protons, forgetting that the neutron contains elec- tric charges with no net charge. The neutron is attracted by the proton in a way discovered two millenaries ago by the Greeks. This attraction is equilibrated by the repulsion between the opposite magnetic moments of the proton and of the neutron in the deuteron. The bare application of ge- ometry together with electric and magnetic Coulomb’s in- teractions accounts for the binding energy of the deuteron, without fitting, with only 4 per cent discrepancy, proving the electromagnetic nature of the nuclear energy.
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Honkimäki, V., et P. Suortti. « Determination of thermal-motion parameters using energy-dispersive powder diffraction ». Journal of Applied Crystallography 25, no 2 (1 avril 1992) : 105–8. http://dx.doi.org/10.1107/s0021889891010798.
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An intrinsic Ge detector is used to analyze the energy spectrum of a well collimated X-ray beam of white radiation diffracted from powder samples of Al, Mg and Ti. Two spectra on each sample are measured at scattering angles where reflections hkl and 2h ′ 2k ′ 2l occur at the same energies. The Bragg reflections are separated by fitting a model for the different components of scattering to the total spectrum. The thermal-motion parameter B is determined from the intensity ratio of several pairs of reflections. Most of the uncertainties due to a non-ideal sample or errors in the experimental parameters cancel out in the expression for B. The values of B are 0.86 (2) Å2 for Al, Ba = 1.29 (8) Å2 and Bc = 1.60 (9) Å2 for Mg and Ba = 0.63 (4) Å2 and Bc = 0.73 (7) Å2 for Ti, where Ba is for directions perpendicular to the c axis and Bc for the direction of the c axis. The results are in agreement with published values of the thermal-motion parameters.
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Mallet, Anne-Flore, Olivier Gourhant, Christophe Duluard, Isabelle Berbezier et Luc Favre. « Stress Relaxation in SGOI Structure Obtained by Condensation ». ECS Meeting Abstracts MA2022-02, no 32 (9 octobre 2022) : 1217. http://dx.doi.org/10.1149/ma2022-02321217mtgabs.
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The development of effective buffer layer has required years of work in order to obtain relaxed SiGe substrates [1]. However, main drawback of this approach relies on the presence of embedded and numerous dislocations which can be detrimental for optimal applications. Recently, a surprising relaxation phenomenon has been observed on specific Silicon-Germanium On Insulator (SGOI) structures [4-5]. It has been observed that when the sample is heated, slippage is observed at the SGOI/Buried Oxide (BOX) interface. The phenomenon is not clearly understood. However, several explanations have been raised. It can be explained by the mechanical properties by Ge-O bonds which are weaker than the Si-O bonds at the SGOI/BOX interface causing the slip. [2] Also, the Ge atoms in the last crystalline layer at the BOX interface decreases the quantity of Si atoms inducing less bonds between the Si atoms of SGOI and the BOX. We suggest to take advantage of this phenomenon to obtain fully relaxed SGOI layers without dislocations. This new approach would allow to create high performance relaxed SGOI layers in industrial conditions with 300 mm wafers. This innovation is relevant for several applications, such as optical applications and the formation of base substrate to generate tensile Si epitaxy layer. It has to be noticed that any Ge concentration until pure GeOI structure is possible. Figure 1 shows the different process steps to obtain relaxed SGOI layer explained below. SiGe epitaxy (fig.1-a) is performed on an 300mm SOI wafer by Rapid Thermal Chemical Vapor Deposition (RT-CVD). Germane (GeH4) and Dichlorosilane (DCS) are used as precursor gases to obtain a 20nm thick fully strained Si0.8Ge0.2 layer. Upstream work is performed to improve the uniformity of the SiGe layer (thickness and composition) within the 300mm wafer. Indeed, they are key parameters impacting Ge concentration within wafer uniformity obtained after condensation.[3] Then, condensation is performed (fig.1-b) using thermal oxidation in a 300mm industrial furnace under N2/O2 atmosphere at 1000°C during several hours. Condensation is tuned to obtain the desired Ge concentration in the SGOI structure. Condensation allows to transform a SiGe/Si/BOX structure into SiGe/BOX structure called SGOI. Two mechanisms are involved in the condensation. The first mechanism is the Si-selective oxidation in the SiGe layer allowing Ge atoms to accumulate at the oxidation interface. The second mechanism is the Ge diffusion in the structure which allows SiGe inter-diffusion. The Ge atoms are maintained and homogenized in depth of the SGOI layer during the interdiffusion mechanism thanks to the BOX acting as a diffusion barrier. [2] During this work, the layer composition, the thickness as well as the stress were characterized by ellipsometry, XRR, XRD and SIMS. In addition, the surface was analyzed by AFM to detect any crystal defects. In this study, we propose to investigate the relaxation of SGOI layer with a concentration of Ge=50% because such structure shows no defects after condensation [2]. Thereafter, it will be possible to carry out GeOI in the future. Figure 2 shows SiGe thickness and density measurement by XRR. A thickness variation of 13.67 A and a density variation of 0.22g/cm3 of the SGOI layer after condensation on the whole wafer is obtained. The average density is 4,31g/cm3 with a concentration of %Ge=51% which was our target concentration. Then, the relaxation phenomenon is studied using anneals in the temperature range [700;900] °C during several hours. Indeed, we chose a temperature close to the SiO2 viscosity temperature and a long annealing time allowing to generate a slow slip thus limiting defects. Figure 3 shows a RSM map obtained by XRD of an Si0.5Ge0.5OI layer after annealing at 800°C for 2h. The mapping shows Si substrate as well as the layer relaxed along the (113) and (224) planes at an angle Φ=45°. RSM map allows to calculate the relaxation rate which is 22%. The relaxation on the sample is a success that remains to be improved by annealing time or temperatures to be optimized. This new approach would allow the realization a defect free relaxed SGOI layer under industrial conditions on a 300mm wafer. It would provide a new method for applications such as optical or the growth of tensile Si channels. [1] P.M.Mooney, Materials Science and Engineering, 1996 [2] F.Roze. PhD thesis, 2018 [3] D.Valenducq, PhD thesis, 2021 [4] V.Boureau et al., ECS, 2018 [5] Usuda, Koji, et al., Solid-State Electronics, 2013 Figure 1
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Реутова, О. В., Е. Л. Белоконева, О. В. Димитрова et А. С. Волков. « Силикат-германат Ba 2 K 2 In 2 [(Si 0.8 Ge 0.2 ) 6 O 18 ] · 2H 2 O – аналог природного цирконосиликата костылевита K 4 Zr 2 [Si 6 O 18 ] · 2H 2 O ». Кристаллография 65, no 5 (2020) : 740–44. http://dx.doi.org/10.31857/s0023476120050197.
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Kim, Kyoung Hwa, Gang Seok Lee, Hyung Soo Ahn, Jae Hak Lee, Jongseok Kim, Young Tea Chun, Min Yang, Sam Nyung Yi, Sun-Lyeong Hwang et Suck-Whan Kim. « Insights into the growth of hexagonal Si crystals using Al-based nano absorber ». Semiconductor Science and Technology 37, no 4 (8 mars 2022) : 045016. http://dx.doi.org/10.1088/1361-6641/ac579c.
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Abstract Although hexagonal (2H) silicon (Si) semiconductors exhibit excellent optical properties owing to their quasi-direct bandgap, their growth conditions, which require extremely high pressures, preclude their widespread use in industrial applications. The current study, therefore, proposes a novel approach for the facile growth of hexagonal Si at atmospheric pressure via a unique phenomenon known as Al-based nano absorber. A mixed-source hydride vapor phase epitaxy (HVPE) method was used for the growth of the hexagonal Si single crystals employing a rapid interaction between GaCl3, AlCl, and SiCln gases at a high temperature of 1200 °C using a source mixture of Ga, Al, and Si. In this process, the Al-based nano absorber was formed, which resulted in the absorbance of Si atoms, rather than the growth of Al-based nano absorber, to form the Si crystals due to the subsequent lack of GaCl3 and AlCl sources. The hexagonal Si structure of these Si crystals was confirmed using field emission scanning electron microscopy, high-resolution x-ray diffraction spectroscopy, and Raman spectroscopy. Thus, the current study establishes atmospheric pressure mixed-source HVPE as a facile approach for growing various allotropic crystals such as Si, C, or Ge via absorption of other atoms by an Al-based nano absorber.
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Hawkins, Stephen M., Peter B. Hitchcock, Michael F. Lappert et Audesh K. Rai. « Iridium(III) hydrides derived from an iridium(I) substrate by oxidative addition and cyclometallation of germanium(II) bis(trimethylsilyl)amide ; X-ray structures of [{CH2Me2SiN(R)(NR2)Ge}HIr(µ-Cl)2{Ge(NR2)N(R)SiMe2CH2}IrH{Ge(NR2)2}] and [lr{GeCl(NR2)N(R)SiMe2CH2}(CO)2H{Ge(NR2)2}](R = SiMe3) ». J. Chem. Soc., Chem. Commun., no 23 (1986) : 1689–90. http://dx.doi.org/10.1039/c39860001689.
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Гугнин, Дмитрий Владимирович, et Dmitry Vladimirovich Gugnin. « Любая надстройка и любая гомологическая сфера являются $2H$-пространствами ». Trudy Matematicheskogo Instituta imeni V.A. Steklova 318 (septembre 2022) : 51–65. http://dx.doi.org/10.4213/tm4277.
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Доказано, что приведенная надстройка $X = \Sigma Y$ над любым конечным или счетным связным полиэдром $Y$ допускает двузначное умножение $\mu \colon X\times X \to \mathrm {Sym}^2 X$, удовлетворяющее аксиоме единицы: $\mu (e,x) = \mu (x,e) = [x,x]$ для всех $x\in X$. Когда $X$ есть сфера $S^m$, $m = 1,3,7$, это классический результат; в случае $X=S^2$ это теорема В.М. Бухштабера 1990 г., в случае $X=S^{2k+1}$, $k\ne 0,1,3$, - теорема автора 2019 г. Аналогичное утверждение доказано также для всех $X$, являющихся сглаживаемыми гомологическими сферами произвольной размерности, и для $X=\mathbb R\mathrm P^m$, $m\ge 2$. Доказательство одного из основных результатов использует следующее утверждение, представляющее и самостоятельный интерес. Пусть даны связные конечные CW-комплексы $X$, $Y$ и непрерывное отображение $f\colon X\to Y$, индуцирующее изоморфизм целочисленных гомологий. Тогда для любого $n\ge 2$ отображение $\mathrm {Sym}^n f\colon \mathrm {Sym}^n X \to \mathrm {Sym}^n\kern 1pt Y$ также индуцирует изоморфизм целочисленных гомологий.
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Erdil, Tuncay, et Cigdem Toparli. « (Digital Presentation) The New 2H Hexagonal Double Perovskite Ba2CoMnO6 As a Superior OER Catalyst in Alkaline Media ». ECS Meeting Abstracts MA2022-01, no 34 (7 juillet 2022) : 1365. http://dx.doi.org/10.1149/ma2022-01341365mtgabs.
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Climate change has stimulated great interest in developing clean and renewable energy conversion and storage solutions. Emerging technologies for solutions, like unitized regenerative fuel cells, metal-air batteries, and water electrolyzers, depend on the reliable catalyst materials suited for long-term application in alkaline environments[1]. In particular, the demanding reaction in these systems is the oxygen evolution reaction involving complex multielectron/proton transfer processes and thus sluggish kinetic.[2] At present, the state-of-the-art OER catalysts are IrO2 and RuO2. However, the high cost and scarcity of these materials severely prevent the wide-scale application of these systems.[3] Perovskite oxide (e.g., single perovskite expressed as ABO3) electrocatalysts are particularly considered next-generation OER catalysts due to their adjustable physicochemical properties and, as a consequence, their catalytic properties by substitution of ions in the A and B sites.[4] Via doping both at A and B site, double perovskite oxides structure can form (AA′B2O5+δ), which were shown to have stable structure during the OER due to proper O p-band center position relative to the Fermi level. The previous research shows that hexagonal perovskites exhibit enhanced catalytic activity rather than cubic or tetragonal perovskites, which is associated with the face-sharing octahedral unit. [5,6] In this work, we systematically investigate doping of parent La2CoMnO6 with Ba to tune the crystal structure and electronic structure. A series of the double perovskites with the chemical formula of La2-xBaxCoMnO6 (x = 0, 0.5, 1.5, 2) were fabricated via the modified Sol-Gel Pechini method. According to Goldschmidt tolerance factor, it is expected that when Ba amount increases in the A site, the crystal structure changes from cubic to hexagonal, which can contribute to electrocatalytic OER activity based above discussions. Furthermore, it is anticipated that increasing Ba content at the A site should result in higher valence state of transition metals due to stabilizing charge balance of the structure. It is widely reported that presence of higher valence state of transition metals is beneficial for OER. The crystal structure was confirmed by combining powder X-ray diffraction (XRD) patterns and selected area electron diffraction (SAED) patterns. The two-layer hexagonal structure of Ba2CoMnO6 (BCM) was further characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The results show doping of Ba into parent La2CoMnO6 resulted in the hexagonal phase formation and BCM achieves a current density of 10 mA cm–2 at a low overpotential of 288 mV and has the highest intrinsic activity in the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2). Furthermore, BCM exhibits outstanding stability of 12 h in a 0.1 M KOH electrolyte. The electronic structure and surface work function values of the catalysts were examined with X-ray photoelectron spectroscopy (XPS). XPS analysis revealed that valence state of Co and Mn increases through Ba amount in the structure, indicating the double perovskite oxide charge balance is maintained. In addition to valence state analysis, we performed work function analysis of the catalysts tested in this work. The result shows work function of the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2) substantially decreases with Ba content. Here, we show that the high intrinsic activity of BCM is not only related with the hexagonal structure and also may be related with exhibiting lower work function value in the series. In addition, our approach presents a new strategy, air quenching method, to synthesize a phase pure 2H-hexagonal double perovskite oxide. [1] Y. Zhou, X. Guan, H. Zhou, K. Ramadoss, S. Adam, H. Liu, S. Lee, H. Shi, M. Tsuchiya, D. Fong and S. Ramanathan, Nature, 534, 231-234 (2016). [2] X. Cui, P. Ren, D. Deng, J. Deng and X. Bao, Energy & Environmental Science, 9, 123-129 (2016). [3] X. Qiu, Y. Zhang, Y. Zhu, C. Long, L. Su, S. Liu and Z. Tang, Advanced Materials, 33, 2001731 (2020). [4] W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li and Y. Yan, Energy & Environmental Science, 12, 442-462 (2019). [5] L. Tang, W. Zhang, D. Lin, Y. Ren, H. Zheng, Q. Luo, L. Wei, H. Liu, J. Chen and K. Tang, Inorganic Chemistry Frontiers, 7, 4488-4497 (2020). [6] C. Chen, G. King, R. M. Dickerson, P. A. Papin, S. Gupta, W. R. Kellogg and G. Wu, Nano Energy, 13, 423-432 (2015).
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Galanopoulos, S., R. Vlastou, P. Demetriou, M. Kokkoris, C. T. Papadopoulos, G. Perdikakis et M. Serris. « Statistical model calculations of 72,73Ge(n,p) and 72,74Ge(n,α) reactions on natural Ge ». HNPS Proceedings 15 (1 janvier 2020) : 104. http://dx.doi.org/10.12681/hnps.2626.
Texte intégralRésumé :
Systematic experimental and theoretical investigations of the 72,73Ge(n,p)72,73 Ga and 72,74Ge(n,α)69,71Znm reaction cross sections are presented in the energy range from thresh- old to about 17 MeV neutron energy. The above reaction cross sections were measured from 8.8 to 11.4 MeV by using the activation method, relative to the 27Al(n,α)24Na refer- ence reaction. The quasi-monoenergetic neutron beams were produced via the 2H(d,n)3He reaction at the 5 MV VdG Tandem T11/25 accelerator of NCSR “Demokritos”. Statisti- cal model calculations using the code EMPIRE-II (version 2.19) taking into consideration pre-equilibrium emission were performed on the data measured in this work as well as on data reported in literature.
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Li, Ang, Ikaros Hauge, Marcel A. Verheijen, Erik Bakkers, Ryan Tucker, Laetitia Vincent et Charles Renard. « Hexagonal silicon-germanium nanowire branches with tunable composition ». Nanotechnology, 20 septembre 2022. http://dx.doi.org/10.1088/1361-6528/ac9317.
Texte intégralRésumé :
Abstract Hexagonal SiGe-2H has been recently shown to have a direct bandgap, and holds the promise to be compatible with silicon technology. Hexagonal Si (Ge) has been grown on an epitaxial lattice matched template consisting of wurtzite GaP (GaAs). Here, we present the growth of hexagonal Si and SiGe nanowire branches grown from a wurtzite stem by the Vapor-Liquid-Solid (VLS) growth mode, which is substantiated by in-situ transmission electron microscopy. We show that the composition can be tuned through the whole range of stoichiometry from Si to Ge, and the possibility to realize Si and SiGe heterostructures in these branches.
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Tucker, Wesley, Jordan Patik, Bryon Curtis, Suwon Park, Michael Nelson et R. Matthew Brothers. « The Effect of a High‐Fat Meal on Vascular Stiffness in Young Healthy Males ». FASEB Journal 31, S1 (avril 2017). http://dx.doi.org/10.1096/fasebj.31.1_supplement.840.16.
Texte intégralRésumé :
Consumption of a high‐fat meal (HFM) has been implicated in the pathogenesis of cardiovascular disease (CVD). While the exact mechanism remains unclear, postprandial lipemia, low‐grade inflammation, and endothelial dysfunction are contributing factors. Whether impairments in other indices of vascular function, such as central aortic pressures and arterial stiffness, also occurs following a HFM remains unknown and was the focus of this investigation. Six (n=6) healthy young males (27±5 years) were randomized to the following conditions, performed on separate days following an overnight fast: a) HFM challenge (928 kcal, ~50% fat) or, b) time control (fasting). Measures were assessed at baseline, 2h‐, and 4h post‐HFM or at a similar time point on the fasting day. Peripheral blood pressure, central aortic blood pressure and augmentation indices (augmentation pressure [AP] and augmentation index normalized for heart rate 75 bpm [Aix@75]) were non‐invasively assessed by brachial pulse wave analysis (SphygmoCor System, ATCor Medical, Australia). Arterial stiffness was assessed by carotid‐femoral pulse wave velocity (cf‐PWV) using applanation tonometry (SphygmoCor System, ATCor Medical, Australia). Endothelial function was assessed as flow‐mediated dilation (FMD) of the brachial artery using high‐resolution 2D and Doppler ultrasound (GE Logiq P5, GE Healthcare, UK) and normalized for shear rate area under the curve (AUC). Blood triglycerides (TG) were assessed at baseline and 2h post‐meal for each condition. Two‐way repeated measures ANOVA was used to detect time, condition, or time × condition interaction effects. Consistent with previous reports, consumption of the HFM significantly elevated blood TG relative to the time control day (HFM: 101±38 to 169±77 mg/dl, Fasting day: 107±32 to 92±31 mg/dl, P=0.007). Likewise, endothelial function also tended to be reduced 2h following the HFM (Baseline: 0.17±0.13, 2h: 0.12±0.07 % FMD/shear AUC) compared to the fasting day which tended to increase at 2h (Baseline: 0.12±0.05, 2h: 0.15±0.10 % FMD/shear AUC) (p=0.09). In contrast to our hypothesis, the HFM had no effect on central systolic BP (p=0.43), central diastolic BP (p=0.81), AP (p=0.20), Aix @75 (p=0.21) and cf‐PWV (p=0.20). These preliminary data suggest that central aortic blood pressures and arterial stiffness do not change acutely following a HFM in young healthy males.
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Kumar, Sandeep, Leonard R. Maurer, Gregor Schnakenburg, Ujjal Das et Alexander C. Filippou. « NHC‐Supported 2‐Sila and 2‐Germavinylidenes : Synthesis, Dynamics, First Reactivity and Theoretical Studies ». Angewandte Chemie, 6 février 2024. http://dx.doi.org/10.1002/ange.202400227.
Texte intégralRésumé :
2‐tetrelavinylidenes (C=EH2; E = Si, Ge) are according to quantum chemical studies the least stable isomers on the [E,C,2H] potential energy hypersurface isomerizing easily via the trans‐bent tetrelaacetylenes HE≡CH to the thermodynamically most stable 1‐tetrelavinylidenes (E=CH2). Consequently, experimental studies on 2‐tetrelavinylidenes (C=ER2) are lacking. Herein we report experimental and theoretical studies of the first N‐heterocyclic carbene (NHC) supported 2‐silavinylidene (NHC)C=SiBr(Tbb) (1‐Si: NHC = C[N(Dipp)CH]2, Dipp = 2,6‐diisopropylphenyl, Tbb = 2,6‐bis[bis(trimethylsilyl)methyl]‐4‐tert‐butylphenyl) and the isovalent 2‐germavinylidenes (NHC)C=GeBr(R) (1‐Ge, 1‐GeMind: R = Tbb, Mind (1,1,3,3,5,5,7,7‐octamethyl‐s‐hydrindacene‐4‐yl)). The NHC‐supported 2‐tetrelavinylidenes were obtained from the 1,2‐dibromoditetrelenes (E)‐(R)BrE=EBr(R) using the diazoolefin (NHC)CN2 as vinylidene transfer reagent. 1‐E (E = Si, Ge) have a planar vinylidene core, a bent‐dicoordinated vinylidene carbon atom (CVNL), a very short E=CVNL bond and an almost orthogonal orientation of the NHC five‐membered ring to the vinylidene core. Quantum chemical analysis of the electronic structures of 1‐E suggest a significant bent 1‐tetrelaallene and tetrelyne character. NMR studies shed light into the dynamics of 1‐E involving NHC‐rotation around the CVNL−CNHC bond with a low activation barrier. Furthermore, the synthetic potential of 1‐E is demonstrated by the synthesis and full characterization of the unprecedented NHC‐supported bromogermynes BrGe=C(EBr2Tbb)(NHC) (2‐SiGe: E = Si; 2‐GeGe: E = Ge).
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Kumar, Sandeep, Leonard R. Maurer, Gregor Schnakenburg, Ujjal Das et Alexander C. Filippou. « NHC‐Supported 2‐Sila and 2‐Germavinylidenes : Synthesis, Dynamics, First Reactivity and Theoretical Studies ». Angewandte Chemie International Edition, 6 février 2024. http://dx.doi.org/10.1002/anie.202400227.
Texte intégralRésumé :
2‐tetrelavinylidenes (C=EH2; E = Si, Ge) are according to quantum chemical studies the least stable isomers on the [E,C,2H] potential energy hypersurface isomerizing easily via the trans‐bent tetrelaacetylenes HE≡CH to the thermodynamically most stable 1‐tetrelavinylidenes (E=CH2). Consequently, experimental studies on 2‐tetrelavinylidenes (C=ER2) are lacking. Herein we report experimental and theoretical studies of the first N‐heterocyclic carbene (NHC) supported 2‐silavinylidene (NHC)C=SiBr(Tbb) (1‐Si: NHC = C[N(Dipp)CH]2, Dipp = 2,6‐diisopropylphenyl, Tbb = 2,6‐bis[bis(trimethylsilyl)methyl]‐4‐tert‐butylphenyl) and the isovalent 2‐germavinylidenes (NHC)C=GeBr(R) (1‐Ge, 1‐GeMind: R = Tbb, Mind (1,1,3,3,5,5,7,7‐octamethyl‐s‐hydrindacene‐4‐yl)). The NHC‐supported 2‐tetrelavinylidenes were obtained from the 1,2‐dibromoditetrelenes (E)‐(R)BrE=EBr(R) using the diazoolefin (NHC)CN2 as vinylidene transfer reagent. 1‐E (E = Si, Ge) have a planar vinylidene core, a bent‐dicoordinated vinylidene carbon atom (CVNL), a very short E=CVNL bond and an almost orthogonal orientation of the NHC five‐membered ring to the vinylidene core. Quantum chemical analysis of the electronic structures of 1‐E suggest a significant bent 1‐tetrelaallene and tetrelyne character. NMR studies shed light into the dynamics of 1‐E involving NHC‐rotation around the CVNL−CNHC bond with a low activation barrier. Furthermore, the synthetic potential of 1‐E is demonstrated by the synthesis and full characterization of the unprecedented NHC‐supported bromogermynes BrGe=C(EBr2Tbb)(NHC) (2‐SiGe: E = Si; 2‐GeGe: E = Ge).
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Bada-Bosch, Isabel, María Dolores Blanco, Julio Arturo Cerdá, MARÍA FANJUL, Javier Ordóñez, María del Mar Tolín Hernani, Carmen Miranda Cid, César Sánchez Sánchez et Juan Carlos De Agustín. « CAN WE DO ANYTHING ELSE BEFORE REMOVING A BUTTON BATTERY FROM THE ESOPHAGUS ? HYALURONIC ACID ». European Journal of Pediatric Surgery, 5 juillet 2023. http://dx.doi.org/10.1055/a-2123-5214.
Texte intégralRésumé :
Aim: To test the protective effect of a commercially available mixture of hyaluronic acid, chondroitin sulfate and poloxamer 407 on the damage caused by the exposure of esophageal mucosa to button batteries in an animal model. Methods: Experimental study. 60 porcine esophageal samples distributed in three groups: control (CG), exposure (EG) and exposure-protection (EPG). In EG and EPG, one CR2032 button battery per sample was inserted, both were subdivided into 2h, 4h, 6h and 24h exposure subgroups, with subsequent battery removal. EPG samples were irrigated with the solution 1h after battery exposure. Esophageal pH and final voltage of the battery were measured. Results: pH in CG remained stable. No significant differences in pH at one hour were found between EG and EPG. In EPG, the pH of the mucosa exposed to the anode was lower than in GE at 2h (12.44 vs 11.89, p=0.203) and 4h (13.78 vs 11.77, p<0.0001). In the cathode pH was significantly higher in EG at 2h (2.5 vs 4.11, p<0.0001), 4h (2.33 vs 4.78, p<0.0001) and 6h (2.17 vs 2.91, p<0.0001). Significant voltage reduction at 1h was found in EG compared to EPG (0.48V vs 1.08V, p=0.004). Conclusion: Exposure to hyaluronic acid solution buffers the acidification on the side exposed to the cathode and basification on the anode. This effect can be maintained up to 3-5h, even after stopping its application. Our results suggest that a solution containing hyaluronic acid could be used as an esophageal protector after accidental ingestion of button batteries.
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Napolitano, Vito. « A new combinatorial characterization of (quasi)-Hermitian surfaces ». Journal of Geometry 114, no 2 (13 juillet 2023). http://dx.doi.org/10.1007/s00022-023-00681-7.
Texte intégralRésumé :
AbstractIn this paper, we present a combinatorial characterization of a quasi-Hermitian surface as a set $${\mathcal {H}}$$ H of points of $$\textrm{PG}(3,q)$$ PG ( 3 , q ) , $$q=p^{2h}$$ q = p 2 h $$h\ge 1$$ h ≥ 1 , p a prime number and $$q\ne 4$$ q ≠ 4 , having the same size as the Hermitian surface and containing no plane, such that either a line is contained in $${\mathcal {H}}$$ H or intersects $${\mathcal {H}}$$ H in at most $$\sqrt{q}+1$$ q + 1 points and every plane intersects $${\mathcal {H}}$$ H in at least $$q\sqrt{q}+1$$ q q + 1 points. Moreover, if there is no external line, the set $${\mathcal {H}}$$ H is a Hermitian surface.
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Vincent, Laetitia, Elham M. T. Fadaly, Charles Renard, Wouter H. J. Peeters, Marco Vettori, Federico Panciera, Daniel Bouchier, Erik P. A. M. Bakkers et Marcel A. Verheijen. « Growth‐Related Formation Mechanism of I3‐Type Basal Stacking Fault in Epitaxially Grown Hexagonal Ge‐2H ». Advanced Materials Interfaces, 4 mai 2022, 2102340. http://dx.doi.org/10.1002/admi.202102340.
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Pearton, S. J., C. R. Abernathy, C. B. Vartuli, R. G. Wilson et J. M. Zavada. « Diffusion of Implanted Dopants and Isolation Species in III-V Nitrides ». MRS Proceedings 354 (1994). http://dx.doi.org/10.1557/proc-354-159.
Texte intégralRésumé :
AbstractTwelve different elements used for doping or isolation were implanted into GaN, (and selected species into A1N and InN), and the resulting range parameters were measured by Secondary Ion Mass Spectrometry. For lighter elements such as Be, F and H the agreement between experimental range and range straggle dtermined using a Pearson IV computer fitting routine and those predicted by TRIM 92 calculations was good, but for heavier elements such as Ge and Se the discrepancy can be as much as a factor of two in range. There was little redistribution of any of the investigated species up to 700 °C, except for 2H in A1N and S in GaN. Elements such as F and Be which are generally rapid difiusers in III-V compounds do not display any redistribution in GaN for temperatures up to 800 °C.
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Rovaris, Fabrizio, Wouter H. J. Peeters, Anna Marzegalli, Frank Glas, Laetitia Vincent, Leo Miglio, Erik P. A. M. Bakkers, Marcel A. Verheijen et Emilio Scalise. « 2H–Si/Ge for Group-IV Photonics : on the Origin of Extended Defects in Core–Shell Nanowires ». ACS Applied Nano Materials, 15 avril 2024. http://dx.doi.org/10.1021/acsanm.4c00835.
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Avsarkisov, V., S. Hoyas, M. Oberlack et J. P. García-Galache. « Turbulent plane Couette flow at moderately high Reynolds number ». Journal of Fluid Mechanics 751 (17 juin 2014). http://dx.doi.org/10.1017/jfm.2014.323.
Texte intégralRésumé :
AbstractA new set of numerical simulations of turbulent plane Couette flow in a large box of dimension ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}20\pi h,\, 2h,\, 6\pi h$) at Reynolds number $(\mathit{Re}_{\tau }) =125$, 180, 250 and 550 is described and compared with simulations at lower Reynolds numbers, Poiseuille flows and experiments. The simulations present a logarithmic near-wall layer and are used to verify and revise previously known results. It is confirmed that the fluctuation intensities in the streamwise and spanwise directions do not scale well in wall units. The scaling failure occurs both near to and away from the wall. On the contrary, the wall-normal intensity scales in inner units in the near-wall region and in outer units in the core region. The spectral ridge found by Hoyas & Jiménez (Phys. Fluids, vol. 18, 2003, 011702) for the turbulent Poiseuille flow can also be seen in the present flow. Away from the wall, very large-scale motions are found spanning through all the length of the channel. The statistics of these simulations can be downloaded from the webpage of the Chair of Fluid Dynamics.
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Goud, Nerella Sridhar, Mahammad S. Ghouse, Chandana Nagaraju, Rose Dawn Bharath, Mallika Alvala et Pardeep Kumar. « Automated Radiosynthesis and Molecular Docking Studies of Coumarin-Triazole Hybrid with fluorine-18 : A feasibility study ». Current Radiopharmaceuticals 14 (29 janvier 2021). http://dx.doi.org/10.2174/1874471014666210129141221.
Texte intégralRésumé :
Background: Fluorine-18 is one of the promising radiotracers that can report target specific information related to its physiology to understand the disease status through PET modality. In current study, the radiochemical synthesis, purification and molecular docking studies of fluorine-18 (18F) radiolabeled coumarin-triazole hybrid have been performed. Objective: To develop target specific fluorine-18 radiotracer for the diagnosis in oncology. Methods: GE Tracer-lab FX2N module with few modifications in the line connections was used for the radiosynthesis and purification of target molecule [18F]SG-2, 4-((2,6-dimethylmorpholino) methyl)-7-((1-(4-(fluoro-18F) benzyl)-1H-1,2,3-triazol-4-yl) oxy)-2H-chromen-2-one, through the nucleophilic radiofluorination mechanism. The radiochemical purity was measured by HPLC, and TLC analytical methods. The kryptofix levels were also evaluated by using TLC method. The residual solvents like DMF, ethanol was measured using GC. The Schrödinger drug discovery suite 2018 was used to study the protein and ligand interactions. Results: The quality control parameters revealed the purity, chemical identity, and limits of residual solvents. The radiochemical purity was 95.5 ± 2.3 %, and dimethyl formamide solvent limit was 89 3 ppm. The molecular docking results had suggested that the cold target molecule has made strong electronic interactions and showed the possible pharmacokinetic (ADME) properties with galectin-1 protein. Overall, these results showed that [18F]SG-2 radiolabeling with 18F radionuclide was feasible, and support of molecular docking studies suggest possible interactions with Galectin-1. Conclusion: we reported feasibility study for labeling coumarin-triazole hybrid with fluorine-18 through aromatic nucleophilic fluorination reaction (SNAr).
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Kaminski, A. K., C. P. Caulfield et J. R. Taylor. « Transient growth in strongly stratified shear layers ». Journal of Fluid Mechanics 758 (7 octobre 2014). http://dx.doi.org/10.1017/jfm.2014.552.
Texte intégralRésumé :
AbstractWe investigate numerically transient linear growth of three-dimensional perturbations in a stratified shear layer to determine which perturbations optimize the growth of the total kinetic and potential energy over a range of finite target time intervals. The stratified shear layer has an initial parallel hyperbolic tangent velocity distribution with Reynolds number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Re}=U_0 h/\nu =1000$ and Prandtl number $\nu /\kappa =1$, where $\nu $ is the kinematic viscosity of the fluid and $\kappa $ is the diffusivity of the density. The initial stable buoyancy distribution has constant buoyancy frequency $N_0$, and we consider a range of flows with different bulk Richardson number ${\mathit{Ri}}_b=N_0^2h^2/U_0^2$, which also corresponds to the minimum gradient Richardson number ${\mathit{Ri}}_g(z)=N_0^2/(\mathrm{d}U/\mathrm{d} z)^2$ at the midpoint of the shear layer. For short target times, the optimal perturbations are inherently three-dimensional, while for sufficiently long target times and small ${\mathit{Ri}}_b$ the optimal perturbations are closely related to the normal-mode ‘Kelvin–Helmholtz’ (KH) instability, consistent with analogous calculations in an unstratified mixing layer recently reported by Arratia et al. (J. Fluid Mech., vol. 717, 2013, pp. 90–133). However, we demonstrate that non-trivial transient growth occurs even when the Richardson number is sufficiently high to stabilize all normal-mode instabilities, with the optimal perturbation exciting internal waves at some distance from the midpoint of the shear layer.
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Lin, Jiashi, Xiaoyue Yang et Yi Yan. « PO-024 Associations between the Sedentary Behavior and Cardiovascular Risk Factors in Adults of 40-49year ». Exercise Biochemistry Review 1, no 3 (3 octobre 2018). http://dx.doi.org/10.14428/ebr.v1i3.9373.
Texte intégralRésumé :
Objective Large amounts of pieces of evidence suggest sedentary behavior(SB) might have a negative impact on all-cause mortality, cardiovascular disease, and metabolic system. Our aim is to explore the associations between sedentary behavior and cardiovascular risk factors in adults of 40-49year.
Methods Participants(N=372) were adults 40-49 years old who had a survey by using adult sit-Q-7d. The indexes of body mass index(BMI) and Waist circumference(WC) were measured as per standard protocols and blood pressure measured using an automated sphygmomanometer (Carescape V100; GE Healthcare, UK) following five minutes seated rest. HDL cholesterol (HDL-C), LDL cholesterol (LDL-C), triglycerides(TG) and fasting plasma glucose(FPG) were assessed for blood sampling of venous blood following an overnight fast (Cholestech LDX; Alere Inc, USA). We analyzed data in 2 h/day and 1 h/day as segmentation criteria of sitting time were classified as 8 groups(0<2, 2-4, 4-6, 6-8, 8-10, >10 h/day) and 10 groups(<1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9，>9 h/day). Statistical analyses were performed using STATA software 15.0(STATA Corp, College Station, TX). We performed multiple linear regression models adjusting for health-related confounders to assess the associations between SB of difference range and risk factors of cardiovascular disease.
Results (1)When the sitting time as category criteria in 2 h/day, the relationship of LDL-C(β=0.651，95%CI=0.069 to 1.232, P=0.028) and HDL-C(β=0.129，95%CI=0.013 to 0.245, P=0.028) to sitting time in segment of 6-8h/day were statistically significant after adjustment for relative factor of risk; and the same in TC(β=0.932，95%CI=0.244 to 1.620, P=0.008) to sitting time in segment of 8-10h/day; (2) When the sitting time as category criteria in 1 h/day, in 3-4h/day segment, the index of BMI(β=1.550，95%CI=0.025 to 3.074, P=0.046) had a significant rise; in 7-8h/day segment, the index of LDL-C(β=0.919，95%CI=0.155 to 1.683, P=0.019) also had a significant rise; as well as, in 8-9h/day segment, the index of TC(β=1.531，95%CI=0.497 to 2.565, P=0.004) had a highly significant. (3) As has mentioned above, the threshold for each segment of sitting time for the index of LDL-C in 7-8h/day segment and the index of TC in 8-9h/day.
Conclusions This study suggests that (1) the different category criteria of sitting time, for categories criteria in 1h/d or 2h/d, will help reduce the risk of Cardiovascular risk in some degree and determining to their dose-response relationships. (2) For the 40-49year adult of health, the sitting time threshold is less than 7 h/d, in order to decrease the detrimental effects on metabolic markers associated with cardiovascular disease and metabolic system. (3) As well as the sitting time threshold is less than 3 h/d for adding to the negative aging effect on risk of cardiovascular markers.