Analysis of time-domain and spectral-domain two-beam interference including the effect of a variable spectral bandpass of a detecting system

Abstract

The effect of a variable Gaussian response function of a monochromator in a detecting system with a broadband detector is included in the theoretical and experimental analysis of time-domain and spectral-domain interference of two light beams from a source of a multimode Gaussian spectrum. The time-domain theoretical analysis gives the analytic expressions for the measured complex degree of temporal coherence of the light with and without the effect of variable spectral bandpass of the detecting system. The spectral-domain theoretical analysis of the two-beam interference gives the spectral interference law from which the visibility of the spectral interference fringes resolved for a given delay in the interferometer by a spectrometer is expressed as a function of the bandpass of the spectrometer. The theoretical conclusions are confirmed experimentally in the Michelson interferometer configuration using a laser diode operated below the threshold, a prism monochromator and a p-i-n photodetector. From the width of the central peak in the measured visibility dependence that narrows with increasing slit width of the monochromator, the spectral bandpass of the monochromator is evaluated. It is also shown how the visibility of the spectral interference fringes decreases as the slit width of the prism spectrometer increases.     

Two-dimensional linear model of elastic shell accounting for general anisotropy of material

A two-dimensional linearly elastic model of shells made of an anisotropic material described by 21 elastic moduli is developed. For this aim, the generalized Timoshenko–Reissner hypotheses are used. In contrast to the ordinary shell models, the tangential stress-resultants here depend not only on the tangential strains but also on the transverse shear. An asymptotic analysis of the obtained equations is fulfilled. The typical stress-strain states, namely the membrane state, the edge effect state, and the boundary layer, are constructed. The system of the Donnell type is delivered. As an example of general anisotropy, a composite material consisting of a matrix reinforced by the system of fibers inclined to the mid-surface is studied. Certain simple static problems and free vibration problems are solved for a cylindrical shell made of this material.     

Automated resolution of connector architectures using constraint solving (ARCAS method)

In current software systems, connectors play an important role by encapsulating the communication and coordination logic. Since they share common patterns (elements) depending on characteristics of the connections, the elements can be predefined and reused. A method of connector implementation based on a composition of predefined elements naturally comprises two steps: resolution of the connector architecture, and creation of the actual connector code based on the architecture. However, manual resolution of a connector architecture is very difficult due to the number of factors to be considered. Thus, the challenge is to come up with an automated method, able to address all the important factors. In this paper, we present a method for automated resolution of connector architectures based on constraint solving techniques. We exploit a propositional logic with relational calculus for defining a connector theory, a constraint specification reflecting both the predefined parts and the important resolution factors, and employ a constraint solver to find a suitable connector architecture as a model of the theory. As a proof of the concept, we show how the theory can be captured in the Alloy language and resolved via the Alloy Analyzer.     

Corrosion of NiTi Wires with Cracked Oxide Layer

Corrosion behavior of superelastic NiTi shape memory alloy wires with cracked TiO₂ surface oxide layers was investigated by electrochemical corrosion tests (Electrochemical Impedance Spectroscopy, Open Circuit Potential, and Potentiodynamic Polarization) on wires bent into U-shapes of various bending radii. Cracks within the oxide on the surface of the bent wires were observed by FIB–SEM and TEM methods. The density and width of the surface oxide cracks dramatically increase with decreasing bending radius. The results of electrochemical experiments consistently show that corrosion properties of NiTi wires with cracked oxide layers (static load keeps the cracks opened) are inferior compared to the corrosion properties of the straight NiTi wires covered by virgin uncracked oxides. Out of the three methods employed, the Electrochemical Impedance Spectroscopy seems to be the most appropriate test for the electrochemical characterization of the cracked oxide layers, since the impedance curves (Nyquist plot) of differently bent NiTi wires can be associated with increasing state of the surface cracking and since the NiTi wires are exposed to similar conditions as the surfaces of NiTi implants in human body. On the other hand, the potentiodynamic polarization test accelerates the corrosion processes and provides clear evidence that the corrosion resistance of bent superelastic NiTi wires degrades with oxide cracking.     

Comparison of arc stability and variability of geometry of welds obtained by MIG/MAG and FCAW processes

Despite their similarity, the MIG/MAG and Tubular Electrode processes display particular features with regard to arc stability and variability in the characteristics of the beads. Thus, selection of one of these processes for a specific application will have to consider how these particular features affect the quality of the welds. To support this choice, the present study aimed to investigate how changing the average current affects the stability and regularity of metal transfer in welds carried out with constant voltage and pulsed current and compare the variability in the geometry and dilution of these welds. To achieve these aims, automatic welding was carried out, with steel ABNT 1020 as base metal and wire AWS ER70S-6 and AWS E71T-1 as filler metals. Besides the welds with variation in the average current, the tests involved determination of the parameters for occurrence of stable short circuiting, drop and pulsed transfer. The results showed that the voltage that gives the highest stability in short circuiting transfer is independent of the welding speed and increases with the wire speed, and also showed that welds made with hollow wire displayed greater variability compared to solid wire.     

Regional differences in price levels across the European Union and their implications for its regional policy

Although regional price levels should be accounted for in any analysis of well-being in regions, the European Union fails to reflect them because they are not currently available for most EU member states. To fill this gap, we estimate regional price levels for all EU regions on the basis of available regional price level data from six EU countries. Once socio-economic indicators are recalculated using our estimates, substantially higher differences in living standards emerge. These results also have important implications for the European cohesion policy, with 9% of regions currently misclassified as a consequence of regional price levels not being used.     

Stable discretization of poroelasticity problems and efficient preconditioners for arising saddle point type matrices

Poroelastic models arise in reservoir modeling and many other important applications. Under certain assumptions, they involve a time-dependent coupled system consisting of Navier–Lamé equations for the displacements, Darcy’s flow equation for the fluid velocity and a divergence constraint equation. Stability for infinite time of the continuous problem and, second and third order accurate, time discretized equations are shown. Methods to handle the lack of regularity at initial times are discussed and illustrated numerically. After discretization, at each time step this leads to a block matrix system in saddle point form. Mixed space discretization methods and a regularization method to stabilize the system and avoid locking in the pressure variable are presented. A certain block matrix preconditioner is shown to cluster the eigenvalues of the preconditioned matrix about the unit value but needs inner iterations for certain matrix blocks. The strong clustering leads to very few outer iterations. Various approaches to construct preconditioners are presented and compared. The sensitivity of the number of outer iterations to the stopping accuracy of the inner iterations is illustrated numerically.