Symbiotic bacteria and the structural specializations in the ileum of Cephalotes ants

Light, scanning, and transmission electron microscopy were used to examine the ultramorphology and ultrastructure of the ileum of Cephalotes atratus, Cephalotes clypeatus, and Cephalotes pusillus. Sections along the ileum revealed differences among the three main regions: proximal (or pylorus), medial, and distal. The structural specializations present in the ileum of these three ants have implications especially to the symbiotic bacteria harbored in this region of the digestive tract. The structural similarities are conspicuous for the three species examined, suggesting that this is the pattern adopted by the genus Cephalotes.     

About Approximation Numbers in Function Spaces

Sharp estimates for the approximation numbers of embeddings between the function spacesB^s_pqandF^s_pqon domains are given in a case not thoroughly studied by Edmunds and Triebel. Corresponding sharp estimates are also obtained for the counterparts of that case in the weighted function space setting.     

Visible absorption spectra of metal-catecholate and metal-tironate complexes

Interactions between metals and catechol (1,2-dihydroxybenzene) or other ortho-dihydroxy moieties are being found in an increasing number of biological systems with functions ranging from metal ion internalization to biomaterial synthesis. Although metal-catecholate interactions have been studied in the past, we present the first systematic study of an array of these compounds, all prepared under identical conditions. We report the ultraviolet-visible absorption (UV-vis) spectra for catecholate and tironate complexes of the first row transition elements. Generation and identification of these species were accomplished by preparing aqueous solutions with varied ligand:metal ratios and subsequently titrating with base (NaOH). Controlled ligand deprotonation and metal binding resulted in sequential formation of complexes with one, two, and sometimes three catecholate or tironate ligands bound to a metal ion. We prepared the mono-, bis- and tris-catecholates and -tironates of Fe(3+), V(3+), V(4+)and Mn(3+), the mono- and bis-catecholates and -tironates of Cu(2+), Co(2+), Ni(2+), Zn(2+), Cr(2+) and Mn(2+), and several Ti(4+) and Cr(3+) species. The UV-vis spectra of each complex are described, some of which have not been reported previously. These data can now be applied to characterization of biological metal-catecholate systems.     

Structural, electronic, and optical properties of CaCO3 aragonite

Density functional theory ab initio calculations of the structural parameters, electronic structure, carriers effective masses, and optical absorption of the CaCO₃ aragonite polymorph were performed within the local density and generalized gradient approximations, local density approximation (LDA) and generalized gradient approximation (GGA) respectively. A good agreement between the calculated lattice parameters and experimental results was obtained. Both the LDA and GGA results for CaCO₃ aragonite exhibit very close indirect and direct energy gaps, and the computed effective masses are heavy and anisotropic. Two optical absorption regimes related to distinct electronic transitions are predicted by the calculations.     

A Computational Model of Tonal Tension Profile of Chord Progressions in the Tonal Interval Space

In tonal music, musical tension is strongly associated with musical expression, particularly with expectations and emotions. Most listeners are able to perceive musical tension subjectively, yet musical tension is difficult to be measured objectively, as it is connected with musical parameters such as rhythm, dynamics, melody, harmony, and timbre. Musical tension specifically associated with melodic and harmonic motion is called tonal tension. In this article, we are interested in perceived changes of tonal tension over time for chord progressions, dubbed tonal tension profiles. We propose an objective measure capable of capturing tension profile according to different tonal music parameters, namely, tonal distance, dissonance, voice leading, and hierarchical tension. We performed two experiments to validate the proposed model of tonal tension profile and compared against Lerdahl’s model and MorpheuS across 12 chord progressions. Our results show that the considered four tonal parameters contribute differently to the perception of tonal tension. In our model, their relative importance adopts the following weights, summing to unity: dissonance (0.402), hierarchical tension (0.246), tonal distance (0.202), and voice leading (0.193). The assumption that listeners perceive global changes in tonal tension as prototypical profiles is strongly suggested in our results, which outperform the state-of-the-art models.     

Application of high temperature high resolution gas chromatography to paraffinic deposits in petroleum production pipelines

HTHRGC was found essential for optimizing representative preparation of high molecular weight samples and enabling fingerprinting of heavy fractions of crude oils and associated paraffinic deposits in production pipelines. Laboratory experiments aimed at simulating the process of paraffin deposition could also be easily evaluated. A comparative investigation of the performance of cold on-column and SPI (PTV type) injectors, in conjunction with high temperature capillary columns, for analysis of high molecular weight fractions, was also conducted during the course of this work.     

Sequencing-independent delocalization in a DNA-like double chain with base pairing

The question of whether or not DNA is intrinsically conducting is still a challenge. The ongoing debate on DNA molecules as an electronic material has so far underestimated a key distinction of the system: the role of base pairing in opposition to correlations along each chain. We show that a disordered base paired double chain presents truly or, at least, effectively delocalized states. This effect is irrespective to the sequencing along each chain.     

Inversive geometry and the hexlet

Geometriae Dedicata -     

Recombination centers and the spatial distribution of spontaneous emission in n-type GaAs at high excitation levels

We have investigated the excitation intensity dependence of the spatial distribution of the emission of photoluminescence from heavilly doped n-type GaAs.It was found that above a certain threshold of excitation, maximum emission originated from an anular zone surrounding the point of excitation rather than from that point.This new effect is explained in terms of the quasi Fermi level dependence of the rate of recombination through recombination centers.