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Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelectric response of a series of molecules featuring a quinoid core using density functional theory, as well as a semi-empirical interacting model Hamiltonian describing the π-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdrawing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S²G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices. [ABSTRACT FROM AUTHOR]

We present a set of benchmark calculations for the Kohn-Sham elastic transmission function of five representative single-molecule junctions. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential plane-wave code in combination with maximally localized Wannier functions and the norm-conserving pseudopotential code SIESTA which applies an atomic orbital basis set. All calculations have been converged with respect to the supercell size and the number of k∥ points in the surface plane. For all systems we find that the SIESTA transmission functions converge toward the plane-wave result as the SIESTA basis is enlarged. Overall, we find that an atomic basis with double zeta and polarization is sufficient (and in some cases, even necessary) to ensure quantitative agreement with the plane-wave calculation. We observe a systematic downshift of the SIESTA transmission functions relative to the plane-wave results. The effect diminishes as the atomic orbital basis is enlarged; however, the convergence can be rather slow. [ABSTRACT FROM AUTHOR]

Suspended chains consisting of single noble metal and oxygen atoms have been formed. We provide evidence that oxygen can react with and be incorporated into metallic one-dimensional atomic chains. Oxygen incorporation reinforces the linear bonds in the chain, which facilitates the creation of longer atomic chains. The mechanical and electrical properties of these diatomic chains have been investigated by determining local vibration modes of the chain and by measuring the dependence of the average chain-conductance on the length of the chain. Additionally, we have performed calculations that give insight into the physical mechanism of the oxygen-induced strengthening of the linear bonds and the conductance of the metal-oxygen chains. [ABSTRACT FROM AUTHOR]

The adrenal gland can be visualized using ultrasonography in at least 90% of fetuses of more than 26 weeks gestation. The fetal and neonatal adrenal gland is described as a structure having a characteristic V or Y shape. Despite the frequency of visualization of the neonatal adrenal gland, few reports of adrenal anomalies are present in the radiologic literature. The purpose of this paper is to describe and depict the sonographic appearance of the "horseshoe" and the "circumrenal" adrenal gland and to discuss adrenal anomalies in general. [ABSTRACT FROM AUTHOR]

Measurement of the speed of sound and the acoustic impedance, combined with a knowledge of ambient pressure and temperature, provide sufficient data for determining the relative abundance of constituents in a mixture of nitrogen, argon, and carbon dioxide. Sound absorption and dispersion yield additional information for checking the consistency of the results. An instrument has been developed to measure the acoustic properties of an unknown gas mixture. Laboratory results demonstrate the feasibility of determining the gas composition within a few percent. The technique of velocity measurement by use of phase comparison over several wavelengths is quite sensitive and may be useful in other applications. [ABSTRACT FROM AUTHOR]

Although malrotation is commonly found in infants with intestinal obstruction, the presence of malrotation in twins is rare. We report a set of twins who each had malrotation and non-bilious vomiting on the first day of life. [ABSTRACT FROM AUTHOR]