Influence of the Si–O–C interplayer on the flexural behaviors of C/Si–C–N composites

Carbon fiber reinforced Si–C–N matrix composite(C/Si–C–N) with a Si–O–C interlayer (C/Si–O–C/Si–C–N) was fabricated via CVI and PIP process. The flexural behaviors of C/Si–O–C/Si–C–N were investigated using the three-point-bending method and the SEM technique. The results indicated that the flexural strengh of the C/Si–O–C/Si–C–N increases with increasing temperature and the modulus of the composite is essentially unchanged. The strength of C/Si–O–C/Si–C–N is comparable to that of C/PyC/Si–C–N, and the role of Si–O–C interlayer in C/Si–C–N can rival that of the PyC interlayer. The weaker interfacial bonding and the larger thickness of Si–O–C interlayer make a contribution to this at RT while the thinner interlayer and unstable structure of Si–O–C interphase do it above 1300 °C.     

Numerical approximation of the Vlasov–Maxwell–Fokker–Planck system in two dimensions

A numerical method is developed for solving the Vlasov–Maxwell–Fokker–Planck system in two spatial dimensions. This system of equations is a model for a collisional plasma in the presence of a self consistent electromagnetic field. The numerical procedure is a type of deterministic particle method and is an extension to include the full electromagnetic field of the approximation method of Wollman and Ozizmir [S. Wollman, E. Ozizmir, Numerical approximation of the Vlasov–Poisson–Fokker–Planck system in two dimensions, J. Comput. Phys. 228 (2009) 6629–6669]. In addition, the long time asymptotic behavior of solutions is studied. It is determined that the solution to the Vlasov–Maxwell–Fokker–Planck system converges to the same steady state solution as that for the Vlasov–Poisson–Fokker–Planck system.     

A simple model to predict long-range atomic ordering temperatures in Cu-based shape memory alloys

The order–disorder and order–order phase transition temperatures in the austenitic phase of Cu-based shape memory alloys were used to obtain a set of first- and second-neighbour pair interchange energies. To this end, a mean field model was postulated. Then, the applicability to different alloys of this simple model was analysed. It was found that a good agreement with the experimental phase diagram is obtained for Cu–Zn–Al, Cu–Al–Ni and Cu–Al–Be alloys using composition-independent parameters. It was also found that for Cu–Al–Mn alloys, composition-dependent pair interchange energies need to be employed.     

Structural and electronic properties of a single Si chain doped zigzag AlN nanoribbon

The first-principles projector-augmented wave (PAW) potentials within the density function theory (DFT) framework have been used to determine the geometry structures and electronic properties of the zigzag edge AlN nanoribbons (ZAlNNRs) doped with a single Si chain under generalized gradient approximation (GGA). The average Al–Si, Si–Si, Al–N, Si–N, Al–H and N–H bond lengths are 2.39, 2.16, 1.83, 1.74, 1.59 and 1.03 Å, respectively. Pure 7-ZAlNNR is an indirect semiconductor with a large band gap of 2.235 eV, while a semiconductor to metal transformation is taken place after a single Si chain substituting for a single Al–N chain at various positions. In pure 7-ZAlNNR, the HVB and LCB are mainly attributed to the edge N and Al atoms, respectively, while in a single Si chain substituting doped 7-ZAlNNR, the HVB and LCB are mainly attributed to the Si atoms. The Al–N, Al–H and Al–Si bonds are ionic bond, the Si–Si and Si–H bonds are covalent bond, the N–H and N–Si bonds are covalent bond modified ionic bond.     

The current–voltage characteristic in an ultrasmall junction

The current–voltage characteristics of ultrasmall superconductor–insulator–normal metal (S–I–N), and a superconductor–insulator–superconductor (S–I–S) junctions are computed in the presence of a dissipative transmission line. The amplitude of the discontinuous jump at the energy gap of a single-particle current is greatly influenced by the size of the capacitance and the impedance of the external transmission line in the small junction. The results agree with Ambegaokar–Baratoff in the limit of vanishing impedance of a transmission line or large junction capacitance.     

Globally hyperbolic flat space–times

We consider (flat) Cauchy-complete GH space–times, i.e., globally hyperbolic flat Lorentzian manifolds admitting some Cauchy hypersurface on which the ambient Lorentzian metric restricts as a complete Riemannian metric. We define a family of such space–times—model space–times—including four subfamilies: translation space–times, Misner space–times, unipotent space–times, and Cauchy-hyperbolic space–times (the last family—undoubtful the most interesting one—is a generalization of standard space–times defined by G. Mess). We prove that, up to finite coverings and (twisted) products by Euclidean linear spaces, any Cauchy-complete GH space–time can be isometrically embedded in a model space–time, or in a twisted product of a Cauchy-hyperbolic space–time by flat Euclidean torus. We obtain as a corollary the classification of maximal GH space–times admitting closed Cauchy hypersurfaces. We also establish the existence of CMC foliations on every model space–time.     

New exact solutions to the space–time fractional nonlinear wave equation obtained by the ansatz and functional variable methods

In this paper, the ansatz method and the functional variable method are employed to find new analytic solutions for the space–time nonlinear fractional wave equation, the space–time fractional Kadomtsev–Petviashvili–Benjamin–Bona–Mahony equation and the space–time fractional modified Korteweg–de Vries–Zakharov–Kuznetsov equation. As a result, some exact solutions are obtained in terms of hyperbolic and periodic functions. It is shown that the proposed methods provide a more powerful mathematical tool for constructing exact solutions for many other nonlinear fractional differential equations occurring in nonlinear physical phenomena. We have also presented the numerical simulations for these equations by means of three dimensional plots.     

Effect of very small additions on the coercivity of Dy-free Nd–Fe–(Co)–B-sintered magnets

The effect of small substitutions on the coercivity of Nd–Fe–B and Nd–Fe–Co–B-sintered magnets has been investigated. Addition of 0.18 at% Ga was found to be the most effective for improving the coercivity in both Nd–Fe–B and Nd–Fe–Co–B without decreasing much the remanent magnetization. Scanning electron microscopy on Ga-free and Ga-added magnets did not reveal a noticeable difference in phase morphology. However, Fe and especially Co concentrations in the intergranular Nd-rich phase were found to be markedly increased after the small Ga addition. Combined addition of Co with a small amount of Cu did not increase the coercivity of the Dy-free magnets. However, none of the examined very small additives can yet be considered as an alternative to Dy for extending operating temperature range of the high-energy Nd–Fe–B magnets.     

Phase behavior of four homologous compounds of 4-n-alkyl-4′-isothiocyanatobiphenyl (nBT) under pressure

The phase behavior of four homologous compounds of 4-n-nonyl-, 4-n-decyl-, 4-n-undecyl-, and 4-n-dodecyl-4′-isothiocyanatobiphenyl (9BT, 10BT, 11BT, and 12BT) was re-investigated to characterize their high-pressure mesophases under pressures up to 150 MPa using a polarizing optical microscope equipped with a high-pressure optical cell and a wide-angle X-ray diffractometer equipped with a high-pressure sample vessel. The pressure-induced mesophases of 9BT and 10BT appearing under pressures above about 60 and 100 MPa, respectively, were identified as nematic (N) and SmA phases, which indicate the reversible Cr–CrE–N–I and Cr–CrE–SmA–I phase transitions under elevated pressure. 11BT and 12BT exhibited the reversible transition of Cr–CrE–SmA–I in the low-pressure regions below about 5 and 23 MPa, respectively. Both the stable CrE phases changed into the monotropic (and metastable) one under higher pressures, in which the Cr–SmA–I and I–SmA–CrE–Cr phase transitions on heating and cooling processes, respectively, were recognized.     

Temperature dependence of twinning stress – Analogy between Cu–Ni–Al and Ni–Mn–Ga shape memory single crystals

Abstract

To obtain a direct non-magnetic analogy to Ni–Mn–Ga 10M martensite with highly mobile twin boundaries, we present the recalculation of twinning systems in Cu–Ni–Al martensite. In this approach, the twinning planes denoted as Type I, Type II and compound have similar orientations for both alloys (Ni–Mn–Ga and Cu–Ni–Al). In Cu–Ni–Al, compound twinning exhibits the twinning stress of 1 to 2 MPa comparable to twining stress of Ni–Mn–Ga. In contrast Type II twinning stress of Cu–Ni–Al is approximately 20 MPa, i.e. much higher than twinning stress for Type II in Ni–Mn–Ga (0.1 to 0.3 MPa). Similarly to Ni–Mn–Ga, the twinning stress of Type II in Cu–Ni–Al is temperature independent. Moreover, no temperature dependence was found also for compound twinning in Cu–Ni–Al.     

A selective and sensitive tert-butylhydroquinone sensor based on synergy of CTAB and AuNPs–PVP–graphene nanohybrids

Gold nanoparticles (AuNPs)–polyvinylpyrrolidone (PVP)–graphene (Gr) nanohybrids were prepared by a facile one-pot green strategy. The obtained Au–PVP–Gr composites were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Then, a novel electrochemical sensor for highly sensitive and selective detection of tert-butylhydroquinone (TBHQ) is proposed based on cetyltrimethyl-ammonium bromide (CTAB) and Au–PVP–Gr modified glassy carbon electrode (GCE). Due to the synergistic effect of CTAB and Au–PVP–Gr, the developed sensor displays a wide linear range from 0.02 to 0.1 and 0.1 to 100.0 μM. A low detection limit of 0.009 μM was observed. Further, the sensitivity and selectivity of PVP–CTAB/Au–PVP–Gr/GCE was demonstrated by its practical application in the determination of TBHQ in real samples.     

Kinetic studies of the reaction of phenacyl bromide derivatives with sulfur nucleophiles

The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution S_N2 mechanism to give the corresponding 2‐sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ‐Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted‐type plot was linear with a α = ?0.41 ± 0.03. The kinetic data and structure‐reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k₄₅ versus log k₃₀, the plot log(k_x,3‐NO2/k_H) versus log(k_x/k_H), and the Brønsted‐type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd.     

Balance the oxidation resistance and mechanical properties of C/Si–C–N composite by a Si–O–C interphase

Carbon fiber reinforced Si–C–N matrix composite with a Si–O–C interphase (C/Si–O–C/Si–C–N) was fabricated via chemical vapor infiltration and polymer impregnation and pyrolysis process. The mechanical properties and oxidation behaviors of C/Si–O–C/Si–C–N were investigated using three-point-bending test and thermogravimetry. The results indicated that the oxidation resistance of C/Si–O–C/Si–C–N was improved as compared to C/Si–C–N with pyrolytic carbon (PyC) interphase (C/PyC/Si–C–N). The higher oxidation resistance of C/Si–O–C/Si–C–N attributed to the high inoxidizability of Si–O–C interlayer and low thermal stress in matrix. The flexural strength of C/Si–O–C/Si–C–N rivaled that of C/PyC/Si–C–N and the modulus was higher than that of C/PyC/Si–C–N. The suitable interphase and the optimized interface bonding can get the high oxidation resistance of the composites with the mechanical properties maintained.     

Magnetic properties of 3D nanocomposites consisting of an opal matrix with embedded spinel ferrite particles

The magnetic properties of 3D nanocomposites representing Mn–Zn, Ni–Zn, Co–Zn, La–Co–Zn, and Nd–Co–Zn spinel ferrite particles embedded in the interspherical spaces of opal matrices are studied. Experimental data are obtained in the temperature interval 2–300 K by measuring the magnetization at a static magnetic field strength of up to 50 kOe and the ac magnetic susceptibility at an alternating magnetic field amplitude of 4 kOe and a frequency of 80 Hz.     

A Z-scheme CuO–ZnO–ZnS–CuS quaternary nanocomposite for solar-light-driven photocatalytic performance

A quaternary CuO–CuS–ZnO–ZnS nanocomposite was successfully synthesized via a facile microwave irradiation based on the preprepared ZnS and CuO nanoparticles. CuO–CuS–ZnO–ZnS nanocomposite was a porous photocatalyst, providing excellent adsorption performance. It was sensitive to both ultraviolet and visible light, moreover, the photoelectrochemical measurements confirmed that there was a high separation rate and low recombination rate of photo-generated charge carriers in the nanocomposite, endowing excellent photocatalytic activity in the sunlight. Under the simulated solar light irradiation, the removal efficiency of rhodamine B (RhB) pollutant (30 mg/L) over CuO–CuS–ZnO–ZnS nanocomposite was 33.98 and 2.90 times of pristine CuO and ZnS, respectively. The outstandingt photocatalytic performance was attributed to Z-scheme charge transfer path.     

Exactly-solvable models derived from a generalized Gaudin algebra

We introduce a generalized Gaudin Lie algebra and a complete set of mutually commuting quantum invariants allowing the derivation of several families of exactly solvable Hamiltonians. Different Hamiltonians correspond to different representations of the generators of the algebra. The derived exactly-solvable generalized Gaudin models include the Hamiltonians of Bardeen–Cooper–Schrieffer, Suhl–Matthias–Walker, Lipkin–Meshkov–Glick, the generalized Dicke and atom–molecule, the nuclear interacting boson model, a new exactly-solvable Kondo-like impurity model, and many more that have not been exploited in the physics literature yet.     

Incommensurate–commensurate transition and nanoscale domain-like structure in iron doped Ti–Ni shape memory alloys

Precursor phenomena of displacive transformation have been studied by optical and transmission electron microscope observation and X-ray diffraction of Ti–(50???x)Ni–xFe (x?=?2,?4,?6,?8 in at.%) alloys. We found that a Ti–44Ni–6Fe alloy exhibits a second-order-like incommensurate–commensurate transition without latent heat and discontinuity in lattice parameters. In other words, diffuse scatterings appear in an electron diffraction pattern at an incommensurate position on cooling; they move gradually towards 1/3? 110? as the temperature decreases and lock into the commensurate position at 180?K. The commensurate phase is not expanded along one of the ? 111? directions, unlike the R-phase formed by a first-order transformation in Ti–48Ni–2Fe and Ti–46Ni–4Fe alloys. In addition, the commensurate phase shows a nanoscale domain-like structure, which is inherited from the incommensurate state of the parent phase. Thus, the anomalies in physical properties observed in the incommensurate state are most likely the precursor phenomena of the commensurate phase in the Ti–44Ni–6Fe alloy. In the case of a Ti–42Ni–8Fe alloy, the incommensurate state remains even at 19?K.     

Optimising the absorption and transmission properties of aircraft microperforated panels

A method for evaluating the absorption and transmission performances of multi-layer micro-perforated structures whose facings are excited by different noise sources is described here. It is applied to determine if the acoustical performances of a number of Micro-Perforated Panels (MPPs), optimised both in absorption and transmission, exceed those of typical aircraft panels undergoing internal and external acoustic excitations. A fully-coupled modal formulation is presented that accounts for the effects of the sub-structure volumetric resonances on the acoustical properties of the partitions. It is validated against full-scale measurements performed with a pressure–velocity probe and a laser vibrometer to estimate the absorption and transmission coefficients of single- and double-layer micro-perforated partitions. The model is used to optimise the sound power dissipated by three layouts obtained from a typical aircraft partition by micro-perforating the trim panel (MPP–Porous–Panel), removing the fibreglass material (MPP–Cavity–Panel) and adding a second MPP inside the separating cavity (MPP–MPP–Panel). It is concluded that the MPP–Porous–Panel and MPP–MPP–Panel layouts provide excess interior noise reduction above 1.8 kHz and 1.2 kHz respectively, whereas the MPP–Cavity–Panel is not acoustically more efficient than a typical aircraft panel.