Luis Felipe del Castillo

Tectonic Evolution of the Southern Gulf of Mexico

A detailed magnetic survey in the southern Gulf of Mexico shows subdued irregular magnetic anomalies that are similar in wave length to those attributed to sea-floor spreading on present-day oceanic rises. The small amplitude of these anomalies, about 75γ, would be compatible with an oceanic basalt source at a depth of 10 km, and previous seismic refraction studies in this area have shown that layer 2 of the oceanic crust (presumed to be basalt) does indeed lie at approximately that depth. Palynomorphs in Deep Sea Drilling Project samples of cap-rock material from the Sigsbee Knolls have shown the associated salt to be Jurassic. A crustal model, based on seismic refraction evidence and on new gravity data, suggests that, whereas the salt-dome belt of the southern gulf is underlain by a thick layer with a density of 2.2 g per cm 3 (presumed to be halite rock), adjacent deeper areas of the basin seem to lack this low density layer. In northeastern Mexico, Triassic red beds fill grabens that are correlative with the Newark Group of the Atlantic Coast and suggest that the Gulf of Mexico originated at the time of the initial rifting of the North Atlantic. When the gulf was about half-opened during the Jurassic, oceanic circulation was restricted; and thick deep-basin evaporite deposits, analogous to those found in the Mediterranean Sea by the Deep Sea Drilling Project, were laid down. Further opening established normal salinity and led to the development of salt-free areas of oceanic crust that separated the Sigsbee Escarpment (together with adjacent ridges of offshore Mexico) from the Sigsbee Knolls and salt domes of Cuba. The subsequent structural evolution of the Gulf of Mexico basin is believed to have been mainly a result of interaction between it and tectonic plates of the Pacific area. After opening of the gulf, subduction began along the Cuban arc, where Atlantic rifting had created a nearly uninterrupted tract of oceanic crust extending from the Pacific between Yucatan and Colombia. Then, folding and gravity sliding associated with Laramide deformation on the west side of the gulf led to salt anticlines that underlie the ridges offshore from Mexico. Except for continued diapirism and subsidence associated with sediment loading, present tectonic activity is confined to the southwestern corner of the gulf, where volcanism and intermediate-focus earthquakes are a distant manifestation of subduction along the Middle America Trench on the Pacific side of Mexico.

Singly and binary grafted poly(vinyl chloride) urinary catheters that elute ciprofloxacin and prevent bacteria adhesion

Acrylic acid (AAc) and poly(ethylene glycol) methacrylate (PEGMA) were singly and dually grafted onto poly(vinyl chloride) (PVC) urinary catheters with the aim of preventing biofouling by endowing the catheters with the ability to load and release antimicrobial agents and to avoid bacteria adhesion. The polymers were grafted applying an oxidative pre-irradiation ((60)Co source) method in two steps. Grafting percentage and kinetics were evaluated by varying the absorbed pre-irradiation dose, reaction time, monomer concentration, and reaction temperature. Catheters with grafting percentages ranging from 8 to 207% were characterized regarding thermal stability, surface hydrophilicity, mechanical properties, swelling, and lubricity. The modified catheters proved to have better compatibility with fibroblast cells than PVC after long exposure times. Furthermore, grafted catheters were able to load ciprofloxacin and sustained its release in urine medium for several hours. Ciprofloxacin-loaded catheters inhibited the growth of Escherichia coli and Staphylococcus aureus in the catheter surroundings and prevented bacteria adhesion.

Radiation grafting of dimethylaminopropylacrylamide and dimethylaminopropylmethacrylamide onto polyethylene

Abstract Radiation-induced grafting of dimethylaminopropylacrylamide and dimethylamino-propylmethacrylamide onto polyethylene films, by direct grafting of the vinyl monomers to a polymer by mutual irradiation, has been investigated. The kinetics of the reaction were studied at different irradiation temperatures, monomer concentration and dose rates of gamma rays, and the appropriate reaction conditions for graft polymerization were determined. The thermal and mechanical behavior of the grafted films by means of DMA, TMA, DSC and TGA were also investigated.

Synthesis and crystal structure of three new cadmium tartrates with open frameworks

Four metal–organic coordination polymers: {[Cd3(C4H4O6)3(H2O)]·H2O}nI, {[Cd3(C4H3O6)2(H2O)2]·5.5H2O}nII, {[Cd2(C4H4O6)2(H2O)]·3H2O}nIII, and [Cd(C4H4O6)]nIV were obtained under hydrothermal conditions and characterized by IR spectroscopy and single crystal X-ray diffraction. The structural analysis reveals that compounds I–III exhibit new 3D open frameworks filled with water molecules, which according to thermogravimetric analysis evolve at temperatures significantly lower than onset temperatures for decomposition. Compound I exhibits an 8-c net; uninodal net (eci net) with Schlafli symbol {36·412·510}, where Cd atoms are connected by μ4,κ6-mode and μ4,κ5-mode tartrate ligands. Compound II is a rare example of a tartrate trianion complex formed by μ5,κ6-mode ligands creating a (6,3)-connected net with Schlafli symbol (4·62)2(42·610·83). Compound III exhibits a 3,3,4,4-connected, 4-nodal net with Schlafli symbol {4·82}{4·84·10}, built up by dimers of two octahedral Cd atoms linked by μ4,κ6-mode and μ3,κ5-mode tartrate ligands. Compound IV was previously reported although being obtained under different synthetic conditions and can be described as a 5,5,11-connected, 3-nodal net with the Schlafli symbol of {32·46·52}2{34·414·516·618·72·8}{34·43·52·6}. None of the compounds reported here are topologically related, evidencing the versatility of the tartrate ligand for the framework formation of coordination polymers.

Diffusion and Monod kinetics model to determine in vivo human corneal oxygen-consumption rate during soft contact lens wear

PURPOSE We present an analysis of the corneal oxygen consumption Qc from non-linear models, using data of oxygen partial pressure or tension (P(O2) ) obtained from in vivo estimation previously reported by other authors. (1) METHODS: Assuming that the cornea is a single homogeneous layer, the oxygen permeability through the cornea will be the same regardless of the type of lens that is available on it. The obtention of the real value of the maximum oxygen consumption rate Qc,max is very important because this parameter is directly related with the gradient pressure profile into the cornea and moreover, the real corneal oxygen consumption is influenced by both anterior and posterior oxygen fluxes. RESULTS Our calculations give different values for the maximum oxygen consumption rate Qc,max, when different oxygen pressure values (high and low P(O2)) are considered at the interface cornea-tears film. CONCLUSION Present results are relevant for the calculation on the partial pressure of oxygen, available at different depths into the corneal tissue behind contact lenses of different oxygen transmissibility.

Experimental transmission of murine malaria by the oral route

A total of 116 young male CD1 mice were orally inoculated with mouse blood; half of the animals received 0.2 ml of uninfected blood and the others were given 0.2 ml ofPlasmodium berghei yoelii-infected blood in six experiments performed at different times. Almost 30% of the experimental mice acquired malaria as demonstrated by the observation of parasites in their blood. In no case were parasites found in the blood of control mice. Rodent malaria parasites may be transmitted to CD1 mice by the ingestion of mouse blood parasitized byP. b. yoelii. As far as we know, this study represents the first demonstration of oral transmission of murine malaria. Oral transmission studies in this mouse-Plasmodium model may produce very important information on the biology of the malaria parasites.

Experimental and computational conductivity study of multilayer graphene in polypropylene nanocomposites

We study the electric conductivity of compounds formed by multilayer graphene in polypropylene. Our study makes a comparative analysis between the experimental and computational results. To obtain an experimental measurement of the electronic properties, we deposited multilayer graphene (MLG) nanoparticles over a polypropylene matrix. The deposition was made over several stages, in which we added to the polymer matrix different percentages of MLG nanoparticles using the melt compounding technique, and we studied the conductivities of the nanocomposites by means of electrochemical impedance spectroscopy (EIS). The second part consists of computational calculations, in which we studied the electronic properties of a graphene sheet under a polypropylene molecule with different slabs in the monomer. In both analyses, there is a strong percolation phenomenon with a percolation threshold of around 18% of the MLG nanoparticles. Before the percolation threshold, the charge carriers are constrained in the polypropylene molecule, making the system an insulating material and creating p-type doping. After the percolation threshold, the charge carriers are constrained in the graphene, making the system a conductor material and creating n-type doping with conductivity values of around 20 S m−1. This phenomenon is a consequence of a change in the mechanism of charge transfer in the interface between the polypropylene molecule and graphene sheet. To describe the charge transfer mechanism, it is necessary to consider the quantum effect. The incorporation of the quantum effects and the percolation phenomenon make it possible for the theoretical conductivity to be close to the conductivity measured experimentally.

Synthesis, characterization, and crystal structure of two zinc linear dicarboxylates

Two different crystalline structures corresponding to a zinc adipate and a zinc succinate were determined combining: X-ray powder and single-crystal diffraction, infrared spectroscopy, thermal analysis, and true densities experiments. The zinc succinate crystal structure was determined by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space-group Cccm with unit-cell parameters a = 4.792(1) A, b = 21.204(6) A, c = 6.691(2) A, V = 679.8(3) A 3 , and Z = 8. Zinc adipate crystal structure was refined from the laboratory X-ray powder diffraction data by the Rietveld method. It crystallizes in the monoclinic space group P 2/ c with unit-cell parameters, a = 16.2037(17)A, b = 4.7810(2)A, c = 9.2692(6)A, β = 90.329(3)°, V = 718.07(9) A 3 , and Z = 4. The thermal expansion of it was estimated in 5.40 × 10 −5 K −1 . This contribution is a step on the way to systematize the regularities in the coordination diversity between linear dicarboxylates and transition metal–inorganic buildings units of metal–organic frameworks.