Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Simultaneous pumping in atomic and ionic self-terminating transition laser

Solutions to the kinetic equations describing simultaneous pumping of working levels are obtained in quadratures for a laser operating on self-terminating transitions in the spectrum of an atom and an ion of the same element. The solutions reflect general features in the behavior of the population of resonance levels of the atom and ion depending on the electron concentration and make it possible to estimate the upper boundary of the energy parameters of lasing. By way of example, simultaneous pumping of working levels of the calcium atom and ion is considered. It is shown that the values of population of the levels, power, and energy of laser pulses of such an atomic-ionic laser are comparable. It is noted that the potentialities of ion lasers can be fully realized if appropriate conditions are created for level excitation during the propagation of the entire pump pulse (especially in its final phase).     

Stability of underexpanded supersonic jet flames burning H2-CO mixtures

It has been established experimentally that both natural gas and hydrogen discharges, through circular orifices larger than a critical diameter, sustain stable lifted flames irrespective of the reservoir pressure driving the release. At smaller diameters, however, stable burning will only be achieved at operating pressures higher than a particular, diameter-dependent, threshold. This latter is strongly fuel-type dependent but empirical correlations have been developed to describe such behaviour. Given the wide disparity of critical diameters depending upon the fuel type considered, the behaviour of multi-component gaseous mixtures involving hydrogen is much less predictable than the correlations for pure fuels might indicate. A series of experiments has been undertaken in which H₂-CO mixtures are discharged from a high pressure reservoir to ambient through convergent circular nozzles, varying in diameter from 1.3 to 5 mm. A wide range of driving pressures has been investigated, from 3 to 50 bar, embracing fuel mixtures containing up to 20% CO by volume. Stability curves have been derived that identify the region where stable burning is sustained relative to the pressure ratio (reservoir pressure/ambient pressure) and the CO concentration in the fuel mixture. The present experimental data are compared with existing correlations (Kalghatgi 1981), derived from subsonic releases, and Birch et al. (1988a), applied to underexpanded supersonic methane jet flames. Although these correlations reproduce the general trend observed experimentally, they appear to significantly over-estimate the stability region. Furthermore, they do not account for the high sensitivity of the diluent concentration on the blowout stability. A thorough investigation is carried out in order to determine the source of discrepancies observed between the empirical correlations and the present measurements. Differential diffusion between the fuel components is shown to be negligible. The introduction of additional information on the turbulent flowfield from numerical simulation of the isothermal underexpanded jet, immediately upstream of the flame stabilisation region, does not appear to yield discriminating evidence for incipient blow-off instability. The maximum burning velocity alone, a widely employed characterising parameter, does not appear to describe accurately the complex interactions between the turbulent flowfield and the chemical kinetics.     

Market Power Issues in Bid-Based Hydrothermal Dispatch

The objective of this work is to investigate market power issues in bid-based hydrothermal scheduling. Initially, market power was simulated with a single stage Cournot–Nash equilibrium model. In this static model the equilibrium was calculated analytically. It was shown that the total production of N strategic agents is smaller than the least-cost solution by a factor of (N/(N+1)). Market power analysis for multiple stages was then carried through a stochastic dynamic programming scheme, where the decision in each stage and state is the Cournot–Nash equilibrium of a multi-agent game. Case studies with data taken from the Brazilian system are presented.     

Convergence of Solutions to the Classic Dual Cosine Equation

Dual orthogonal series are a primary tool in the analysis of mixed boundary value problems for the potential in geometries conforming to separability conditions for the Laplace operator. Different formal solutions to the classic dual cosine equation, in the form of multiple singular integrals, have been developed by many authors, especially in connection with the study of brittle cracks. Recently an algorithmic representation for these solutions was developed to facilitate the writing of computer software. On the basis of this representation a rigorous proof of convergence for input functions of bounded variation is established. The proof utilizes only classical results in the theory of orthogonal expansions. In the first equation of the dual pair there is ordinary convergence, and in the second there is Abel-Poisson convergence which is not, in general, reducible to ordinary convergence.     

DNA replication in the third domain (of life)

DNA replication is the process underlying evolution and the propagation of living organisms. Since the discovery of DNA-dependent DNA polymerases more than 40 years ago, the mechanisms governing DNA replication have been extensively studied in bacteria and eukarya. During the last several years, these studies have been extended to the third domain of life, the archaea. Although archaea are prokaryotes, their replication machinery and the proteins participating in the initiation of DNA replication are more similar to those found in eukarya than bacteria. It appears, however, that replication in archaea is a simpler version of the eukaryotic one as fewer polypeptides participate in each phase of the replication process. The archaeal replication apparatus also has several unique features not found in eukaryotic organisms. Furthermore, like bacteria, members of this domain thrive under a broad range of environmental conditions including extreme temperature, high salt, pH, etc. Thus, the replication machinery had to adapt to these extreme conditions. This article summarizes our current understanding of the mechanisms governing DNA replication in archaea and highlights similarities and differences between archaeal replication and that of bacteria and eukarya.     

Structural studies of N-2-(6-picolyl)-N′-tolylthioureas

Reaction of 2-amino-6-picoline with 2-, 3-, and 4-tolyl isothiocyanates produces the three N-2-(6-picolyl)-N-tolylthioureas, 6PicTu2T, 6PicTu3T, and 6PicTu4T. 6PicTu2T is mono-clinic, space group P2₁/n with a = 8.1700(3) Å, b = 25.5840(6) Å, c = 12.6840(5) Å, = 98.8750(16)°, and V = 2619.5(2) ų with Z = 8, for d _calc = 1.305 g/cm³. 6PicTu3T is monoclinic, space group C2/c with a = 23.879(3) Å, b = 6.744(3) Å, c = 17.116(10) Å, = 99.26(4)°, and V = 2720(3) ų with Z = 8, for d _calc = 1.257 g/cm³. 6PicTu4T is triclinic, space group P-1 with a = 8.829(6) Å, b = 8.8950(15) Å, c = 10.495(3) Å, = 68.63(3)°, = 72.19(4)°, = 63.06(4)°, and V = 681.2(5) ų with Z = 2, for d _calc = 1.255 g/cm³. Intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen and the planarity of the thiourea are affected by the position of substitution on the aryl ring. ¹H NMR studies in CDCl₃ show the NH hydrogen resonance considerably downfield from other signals in the spectrum of each thiourea. The enthalpies of fusion of the present thioureas reflect the extent of intermolecular hydrogen bonding and are compared to other heterocyclic thioureas.