Finite amplitude pressure field of elliptical and rhomboid transducers in three dimensions

Design of different type of transducers to enhance image quality by forming narrow beams at the principals of nonlinear acoustics is considered in the paper. Thus, the nonlinear pressure fields of elliptical and rhomboid transducers were simulated in three dimensions. The simulation method presented in this study is based on Aanonsen’s model for circular sources, and closely follows the model that recently explored for the nonlinear wave propagation due to square and rectangular sources in three dimensions [Kaya et al. “Pressure field of rectangular transducers at finite amplitude in three dimensions,” Ultrasound in Med. Biol., vol. 32, no. 2, pp. 271–280, 2006]. It is assumed that elliptical and rhomboid sources are plane sources, and driven at 2.25 MHz fundamental frequency. Typical results of nonlinear acoustical pressure field simulation are presented there in three dimensions for elliptical and rhomboid sources and compared with the results for rectangular source. The similarities and differences between the nonlinear pressure field of rectangular, elliptical and rhomboid sources are discussed. The numerical results show that diffraction effects and acoustical beam cross section depend on the source geometry a lot. It is noticeable that the nonlinear pressure field of a rectangular source has a broader beam profile than elliptical and rhomboid source.     

Thermal QCD sum rules study of vector charmonium and bottomonium states

We calculate the masses and leptonic decay constants of the heavy vector quarkonia, J/ψ and ϒ mesons at finite temperature. In particular, considering the thermal spectral density as well as additional operators coming up at finite temperature, the thermal QCD sum rules are acquired. Our numerical calculations demonstrate that the masses and decay constants are insensitive to the variation of temperature up to T ≅ 100 MeV, however after this point, they start to fall altering the temperature. At deconfinement temperature, the decay constants attain roughly to 45% of their vacuum values, while the masses are diminished about 12%, and 2.5% for J/ψ and ϒ states, respectively. The obtained results at zero temperature are in good consistency with the existing experimental data as well as predictions of the other nonperturbative models.     

Determination of gross α and β activities in Ankara airborne particulate samples in 2003–2004

The complex formation of curium(III) with L2-aminobutyric acid was characterized by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3·10⁻⁷ M). The various curium(III) species, M_pH_qL_r, identified are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined log β₁₀₁ = 5.17±0.07, log β₁₀₂ = 9.00±0.07, and log β₁₀₃ = 11.30±0.09 at ionic strength I = 0.5M. Possible structures of the curium aminobutyrate species will be discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.     

Conformational analysis of methyl 2-methyl-2-(1-naphthyl)propionate

(S)-2-Methoxy-2-(1-naphthyl)propionic acid (MαNP acid 1) is used for enantioseparation of many secondary alcohols and for determining the stereogenic centers. In the liquid state, based on the ¹H NMR anisotropy effect and reported results, it was shown that the MαNP ester preferred a coplanar relation between the methyl and naphthyl groups and a synperiplanar relation between the Cα-OMe and CO groups. In the case of 1,2,3,4-tetrahydro-4-phenanthrenol, which is a secondary alcohol, the stereogenic center was determined by X-ray analysis. It was shown that MαNP ester adopted similar arrangements in the solid state. However, it was presumed that the strong repulsion between oxygen atoms may be disadvantageous in the solid state. Therefore, we carried out conformational analysis using the simplest MαNP methyl ester to clarify this unique relationship. From detailed results based on the energy surface determined using the RHF/STO-3G basis set, the synperiplanar positional relation was the most stable, and the calculated results agreed with many reported experimental results. At the same time, all conformational isomers of the MαNP methyl ester were used to clarify the internal conversion pathways.     

Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

Credit risk estimation using payment history data: a comparative study of Turkish retail stores

Our paper presents a comparative study applying logistic regression and multiple criteria decision analysis tools to the operations of wholesalers to assess the credit risk of their retailers using payment history data and to cluster the risky customers by ranking their risk levels. Our sample comprises approximately 6,000 retailer customers and 600.000 transactions of one of the major wholesalers of Turkey. Our findings emphasize the importance of using payment history and some non-financial factors data for predicting the creditworthiness of a firm.     

Supply chain contracts for capacity decisions under symmetric and asymmetric information

Central European Journal of Operations Research - Production capacity decision under random demand is an important factor that significantly effects supply chain profits. It is realized in...     

Markov–Dubins path via optimal control theory

Markov–Dubins path is the shortest planar curve joining two points with prescribed tangents, with a specified bound on its curvature. Its structure, as proved by Dubins in 1957, nearly 70 years after Markov posed the problem of finding it, is elegantly simple: a selection of at most three arcs are concatenated, each of which is either a circular arc of maximum (prescribed) curvature or a straight line. The Markov–Dubins problem and its variants have since been extensively studied in practical and theoretical settings. A reformulation of the Markov–Dubins problem as an optimal control problem was subsequently studied by various researchers using the Pontryagin maximum principle and additional techniques, to reproduce Dubins’ result. In the present paper, we study the same reformulation, and apply the maximum principle, with new insights, to derive Dubins’ result again. We prove that abnormal control solutions do exist. We characterize these solutions, which were not studied adequately in the literature previously, as a concatenation of at most two circular arcs and show that they are also solutions of the normal problem. Moreover, we prove that any feasible path of the types mentioned in Dubins’ result is a stationary solution, i.e., that it satisfies the Pontryagin maximum principle. We propose a numerical method for computing Markov–Dubins path. We illustrate the theory and the numerical approach by three qualitatively different examples.     

Vacuum ultraviolet absorption spectra of simple amides

Vacuum ultraviolet absorption spectra of six simple amides were measured. It was found that the positions of the firstπ→π ^* transition bands shift appreciably by the substitutions of methyl groups for hydrogen atoms of the NH₂ and\(\begin{gathered} | \hfill \\ H - C = O \hfill \\ \end{gathered} \) groups. A general tendency is that the substitution in the NH₂ group shifts the band toward longer wavelengths, in the\(\begin{gathered} | \hfill \\ H - C = O \hfill \\ \end{gathered} \) group however towards shorter wavelengths. This was explained satisfactorily by considering the nature of the band (intramolecular charge-transfer band) and the hyperconjugation effect of the methyl group.     

Comparing numerical methods for Helmholtz equation model problem

In this article, we implement a relatively new numerical technique, Adomian’s decomposition method for solving the linear Helmholtz partial differential equations. The method in applied mathematics can be an effective procedure to obtain for the analytic and approximate solutions. A new approach to a linear or nonlinear problems is particularly valuable as a tool for Scientists and Applied Mathematicians, because it provides immediate and visible symbolic terms of analytic solution as well as its numerical approximate solution to both linear and nonlinear problems without linearization [Solving Frontier Problems of Physics: The Decomposition Method, Kluwer Academic Publishers, Boston, 1994; J. Math. Anal. Appl. 35 (1988) 501]. It does also not require discretization and consequently massive computation. In this scheme the solution is performed in the form of a convergent power series with easily computable components. This paper will present a numerical comparison with the Adomian decomposition and a conventional finite-difference method. The numerical results demonstrate that the new method is quite accurate and readily implemented.