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Biomedical subjects

L A Morales

Publications and source records attributed to L A Morales.

11 recordsLinked to original sources
PubMed2005

Unconventional superconductivity in PuCoGa5.

In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials--the copper oxides and a set of Ce- and U-based compounds. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa5 has a transition temperature intermediate between those classes and therefore may bridge these extremes. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa5, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.

Journal Article↗
PubMed2004

Structural tuning of unconventional superconductivity in PuMGa5 (M=Co,Rh).

The superconducting properties of the recently discovered PuMGa5 (M=Co,Rh) superconductors, including the power law behavior of the specific heat, the evolution of the superconducting transition T(c) temperature with pressure, and the linear relation between T(c) and ratio of tetragonal lattice parameters c/a, are compared to those of the heavy fermion CeMIn5 (M=Co,Rh,Ir) unconventional superconductors. The striking similarity of the properties between the two families of superconductors suggests a common physics and a common (magnetically mediated) mechanism of superconductivity.

Journal Article↗
PubMed2003

Photoemission and the electronic structure of PuCoGa5.

The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

Journal Article↗
PubMed2002

Plutonium-based superconductivity with a transition temperature above 18 K.

Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutonium's 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutonium's anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-T(c) copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, T(c) approximately 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent.

Journal Article↗
PubMed1985

Chromoblastomycosis in a renal transplant patient.

Chromoblastomycosis is a rare, deep mycosis seen mostly in tropical and subtropical regions. We have encountered a kidney transplant recipient with this subcutaneous mycosis developing as an asymptomatic mass in the right forearm. The lesion recurred after an initial local excision, but it is now apparently cured 10 months after wide surgical excision. The patient had previously been a shepherd. A 29-year-old kidney transplant recipient developed a rare deep chromoblastomycosis infection and was cured by aggressive diagnosis and surgical treatment.

Adult↗
PubMedDate not supplied

[The in-vitro digestive availability of lipase and trypsin in pancreatic supplements under different degrees of acidity].

We evaluated the in vitro disintegration time and the remanent digestive activity of eight pancreatic supplements under pH conditions similar to the gastrointestinal tract. They were incubated for 45 min at various pH levels (1, 3 or 6) and continued thereafter at pH 6, for another 135 min. The activities of lipase and trypsin were evaluated titrimetrically every 15 min. At pH 6, the products without an enteric coat and Creon, showed the shortest disintegration times; under acidic conditions, those times were longer in all the enteric coated products. At constant pH 6, lipase activity was greater in Creon, Pankreon and Cotazym-B; trypsin activity was greater in Nutrizym-C, Onoton and Cotazym-B. After acidic pH exposure enzyme bioavailability was decreased in all the products. Disintegration times and acid inactivation of enzymes, should be considered when prescribing PS.

Biological Availability↗