Application of Fluorescence to the Study of Crude Petroleum

Crude petroleum oils are complex mixtures of different compounds (mainly organic), which are obtained from an extensive range of different geological sources. The fluorescence of crude petroleum oils derives largely from the aromatic hydrocarbon fraction, and this fluorescence emission is strongly influenced by the chemical composition (e.g., fluorophore and quencher concentrations) and physical characteristics (e.g., viscosity and optical density) of the oil. The fluorescence spectroscopy (FS) is increasingly used in petroleum technology due the availability of better optical detection techniques, because FS offers high sensitivity, good diagnostic potential, and relatively simple instrumentation. In this work we analyzed crude petroleum at different dilution in Nujol, a transparent mineral oil. The main objective of this work was to verify the possibility to measure crude oil emission spectroscopic without use of volatile solvents. The mixtures of nujol with different -crude oil concentrations were measured with a 10 mm optical path cuvette thus simplifying the fluorescence spectroscopy signal detection. The emission spectra were obtained by exciting the samples with a 400 W Xenon lamp at 350 nm, 450 nm and 532 nm. The emissions of the samples were collected perpendicularly with the excitation axis.     

A Local Parabolic Monotonicity Formula on Riemannian Manifolds

In this article we establish a local parabolic almost monotonicity formula for two-phase free boundary problems on Riemannian manifolds.     

Space-time compactification/decompactification transitions via lightlike branes

We consider Einstein-Maxwell-Kalb-Ramond gravity-matter system in bulk space-time interacting self-consistently with two (widely separated) codimension-one electrically charged lightlike branes. The lightlike brane dynamics is explicitly given by manifestly reparametrization invariant world-volume actions in two equivalent dual to each other formulations (Polyakov-type and Nambu-Goto-type ones) proposed in our previous work. We find an explicit solution of the pertinent Einstein-Maxwell-Kalb-Ramond-lightlike-brane equations of motion describing a “two-throat” wormhole-like space-time consisting of a “left” compactified Bertotti-Robinson universe connected to a “middle” non-compact Reissner-Nordström- de-Sitter space-time region, which in turn is connected to another “right” compactified Bertotti-Robinson universe. Each of the lightlike branes automatically occupies one of the “throats”, so that they dynamically induce a sequence of spontaneous space-time compactification/decompactification transitions.     

Torsional response and dissipationless viscosity in topological insulators

We consider the viscoelastic response of the electronic degrees of freedom in 2D and 3D topological insulators (TI's). Our primary focus is on the 2D Chern insulator which exhibits a bulk dissipationless viscosity analogous to the quantum Hall viscosity predicted in integer and fractional quantum Hall states. We show that the dissipationless viscosity is the response of a TI to torsional deformations of the underlying lattice geometry. The viscoelastic response also indicates that crystal dislocations in Chern insulators will carry momentum density. We briefly discuss generalizations to 3D which imply that time-reversal invariant TI's will exhibit a quantum Hall viscosity on their surfaces.     

Crystallization mechanism of hard sphere glasses

In supercooled liquids, vitrification generally suppresses crystallization. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystallization of monodisperse hard-sphere glasses at constant volume (as in a colloid experiment). Multiple crystalline patches appear without particles having to diffuse more than one diameter. As these patches grow, the mobility in neighboring areas is enhanced, creating dynamic heterogeneity with positive feedback. The future crystallization pattern cannot be predicted from the coordinates alone: Crystallization proceeds by a sequence of stochastic micronucleation events, correlated in space by emergent dynamic heterogeneity.     

Fraunhofer diffraction of light with orbital angular momentum by a slit

We study the Fraunhofer diffraction problem while taking into account the orbital angular momentum of light. In this case, the phase singularity of the light beam is incident on the slit in two different cases: in one, it is incident slightly above the slit, and in the other it is centered on the slit. We observed that the symmetry and the fringe formation in the interference pattern strongly depend on the amount of orbital angular momentum and the slit position in relation to the beam.     

Iridium complexes of the doubly cyclometalated NHC ligand IMes'

Two consecutive C-H bond activations at the coordination sphere of Ir transform the commonly employed NHC ligand IMes into the new κ(3)-C fac-coordinating ligand IMes'. The preparation and structure of Ir(III) complexes featuring this ligand together with selected reactions toward small molecules that illustrate their reactivity keys are described.     

A convergent total synthesis of (±)-γ-rubromycin

An expeditious convergent total synthesis affords (±)-γ-rubromycin (1) in 4.4% overall yield. The longest linear sequence is 12 steps from commercial starting materials. The effort highlights a remarkable late-stage oxidative [3 + 2] cycloaddition for construction of the spiroketal, a regioselective carbonyl methylenation, a boron tribromide promoted deprotection, ortho- to para- naphthoquinone spiroketal rearrangement, and a tautomerization sequence.     

Characterization,thermal and ceramic properties of phyllite clays from southeast Spain

Journal of Thermal Analysis and Calorimetry - The present research studied a set of phyllite clays from several deposits in southeast Spain. These phyllite clays have traditionally been used as...     

Dimensional Matching versus Induced‐Fit Distortions: Binding Affinities of Planar and Curved Polyaromatic Hydrocarbons with a Tetragold Metallorectangle

A tetragold(I) rectangle‐like metallocage containing two pyrene‐bis‐imidazolylidene ligands and two carbazolyl‐bis‐alkynyl linkers is used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs), including corannulene. The binding affinities obtained for the encapsulation of the planar PAHs guests in CD₂Cl₂ are found to exponentially increase with the number of π‐electrons of the guest (1.3 > logK >6.6). For the bowl‐shaped molecule of corannulene, the association constant is much lower than the expected one according to its number of electrons. The molecular structure of the host–guest complex formed with corannulene shows that the molecule of the guest is compressed, while the host is expanded, thus showing an interesting case of artificial mutual induced‐fit arrangement.