An empirical model for stagnation pressure gain in rotating detonation combustors

This work investigates the stagnation pressure gain in rotating detonation combustors (RDC) and its dependency on the geometry and mass flux of the combustor. Using a Kiel probe to directly measure stagnation pressure in the high-enthalpy exhaust stream, results are presented for a systematic variation of these parameters. The best-performing configuration achieved a pressure gain of ?8%. A comparison with thrust-based equivalent available pressure data from literature shows that the Kiel probe measurements are in good agreement. It is observed that pressure gain increases with increasing air injector area, decreasing outlet throat area, increasing combustor mass flux, and is seen to be dependent on the operating mode. The data are then used to obtain an empirical model that describes pressure gain as a function of the three variables of injector area ratio, outlet area ratio, and combustor mass flux. The model is compared with measurements in this combustor and others, and is used to predict the pressure gain boundaries and to assess design corridors that potentially achieve positive pressure gain.     

A continuous stream flash evaporator for the calibration of an IR cavity ring-down spectrometer for the isotopic analysis of water

A new technique for high-resolution simultaneous isotopic analysis of δ¹⁸O and δD in liquid water is presented. A continuous stream flash evaporator has been designed that is able to vapourise a stream of liquid water in a continuous mode and deliver a stable and finely controlled water vapour sample to a commercially available infrared cavity ring-down spectrometer. Injection of sub-microlitre amounts of the liquid water is achieved by pumping liquid water sample through a fused silica capillary and instantaneously vapourising it with 100% efficiency in a home-made oven at a temperature of 170?°C. The system's simplicity, low power consumption and low dead volume together with the possibility for automated unattended operation provides a solution for the calibration of laser instruments performing isotopic analysis of water vapour. Our work is mainly driven by the possibility to perform high-resolution online water isotopic analysis on continuous-flow analysis (CFA) systems typically used to analyse the chemical composition of ice cores drilled in polar regions. In the following, we describe the system's precision and stability and sensitivity to varying levels of sample size and we assess the observed memory effects. A test run with standard waters of different isotopic compositions is presented, demonstrating the ability to calibrate the spectrometer's measurements on a VSMOW scale with a relatively simple and fast procedure.     

Improved particle filters for multi-target tracking

We present a novel approach for improving particle filters for multi-target tracking. The suggested approach is based on drift homotopy for stochastic differential equations. Drift homotopy is used to design a Markov Chain Monte Carlo step which is appended to the particle filter and aims to bring the particle filter samples closer to the observations while at the same time respecting the target dynamics. We have used the proposed approach on the problem of multi-target tracking with a nonlinear observation model. The numerical results show that the suggested approach can improve significantly the performance of a particle filter.     

All-semiconductor room-temperature terahertz time domain spectrometer

We report what we believe to be the first demonstration of an all-semiconductor room-temperature terahertz time domain spectrometer. An optical Stark mode-locked vertical-external-cavity surface-emitting laser with 480 fs pulses at 1044 nm was used to illuminate low-temperature-grown photoconductive antennae with 5 mum-gap bow-tie-shaped electrodes. The coherently detected spectrum has a bandwidth close to 1 THz, in which water absorption lines at 0.555 and 0.751 THz can be resolved.     

On the equilibrium personnel structure in the presence of vertical and horizontal mobility via multivariate Markov chains

The present paper employs the Multivariate Homogeneous Markov System (MHMS) in the context of Markov manpower planning modelling. The system is regulated by an embedded multivariate Markov process that allows us to distinguish employees’ mobility patterns that take place either within or among the existing divisions (departments) of an organization. The motivation behind this step arises from the generalization of univariate Markov manpower planning models in which the organization is considered a single (probably hierarchical) group and from the fact that departmental mobility is actually common in most realistic establishments. The first part of the paper presents the functional relations of the MHMS governing intra/inter-departmental transitions. Using these functional forms, we proceed by studying the system’s equilibrium behaviour. This asymptotic analysis reveals the inherent tendencies of the system to reach the limiting structures of specific forms and properties under conditions imposed in the long run.     

Preparation and investigation of rare earth magnesium hexaaluminate solid solutions

Conditions of preparation, by the method of solid state reactions, of rare-earth hexaaluminates RE_1?x?yM_xM’_yMgAl₁₁O₁₉ (RE = La, Sm; M, Mt’ = Gd, Yb, Lu, Y, Sc; x, y = 0, 0.15, 0.3), were investigated. For a number of compositions, high-degree single-phase products were obtained applying multi-step heat treatments in Ar/H₂ atmosphere at 1650–1690°C. Intense (107) and (114) diffraction lines typical for the hexaaluminate phase have been observed in X-ray diffraction patterns. Studies of microstructure and of elemental composition showed that magnesium deficiency on the sample surface may reach some 20%, while composition in the bulk is more homogeneous and close to stoichiometric. Our estimations of structural homogeneity and thermal conductivity show that lanthanum hexaaluminates La_1?x?yM_xM’_yMgAl₁₁O₁₉ with pair additives Gd-Yb, Gd-Y, Y-Yb, Y-Lu, Y-Sc (x = y = 0.15) and samarium hexaaluminates Sm_1?x?yM_xM’_yMgAl₁₁O₁₉ with pair additives Gd-Yb, Y-Yb (x = y = 0.15), as well as Sm_0.7Yb_0.3MgAl₁₁O₁₉, may present interest as thermal barrier coatings.     

The effect of CoPt-coated reduced-graphene oxide nanosheets upon the Smectic-A to Smectic-C* phase transition of a chiral liquid crystal

ABSTRACT

We report on high-resolution calorimetry and small-angle X-ray scattering measurements along the Smectic-A to chiral Smectic-C* phase transition of the liquid crystal 4-(2-methyl butyl) phenyl 4-n-octylbiphenyl-4-carboxylate with dispersed, CoPt nanoparticle-coated reduced-graphene oxide nanosheets. The temperature dependence of heat capacity and smectic layer spacing are obtained in the vicinity of Smectic-A to chiral Smectic-C* phase transition. Though no remarkable pretransitional effects are present, the critical fits show a crossover from mean-field near a tricritical point to classical mean-field compared to pure liquid crystal. The X-ray data yield a dilation of smectic layer thickness, indicating the assembly of graphene oxide nanosheets between the smectic layers.     

The interfacial properties of MgCl(2) thin films grown on Si(111)7 x 7

Photoelectron spectroscopy with synchrotron radiation and low energy electron diffraction (LEED) were used in order to study the MgCl(2)Si(111) system. At submonolayer coverage of MgCl(2), a new LEED pattern was observed corresponding to a (sqr rt 3 x sqr rt 3)R30 degrees overlayer superimposed on the underlying reconstructed Si(111)7 x 7. The surface species at this stage are mainly molecular MgCl(2) and MgCl(x) (x<2) or MgO(x)Cl(y) attached to the Si substrate through Cl bridges coexisting with monodentate SiCl. The interfacial interaction becomes more pronounced when the submonolayer coverage is obtained by annealing thicker MgCl(2) layers, whereby desorption of molecular MgCl(2) is observed leaving on the nonreconstructed silicon surface an approximately 0.2 ML thick MgCl(x) layer which again forms the (sqr rt 3 x sqr rt 3 )R30 degrees superstructure.     

Samarium Based High Surface Area Perovskite Type Oxides SmFe1-XAlXO3 (X=0.00, 0.50, 0.95).Part I, Synthesis and Characterization of Materials

High specific surface area (ssa) perovskite type solids based on samarium (SmFe_1-xAl_xO₃, x = 0.00, 0.50, 0.95) were prepared using hexadecyltrimethyl-ammonium bromide C16TAB as a precursor and gelating agent. The structure of perovskite is fully developed at 600oC for the SmFeO3 solid but not for the other materials. The ssa of the solids varies (33.5 m²g^-1 - 1 m²g^-1) depending on composition and calcination temperature.