Alfredo López - Academia.edu (original) (raw)
Papers by Alfredo López
Physical Review B, 1998
Spin models that have been proposed to describe dimerized chains, ladders, two dimensional antife... more Spin models that have been proposed to describe dimerized chains, ladders, two dimensional antiferromagnets, and other compounds are here studied when some spins are replaced by spinless vacancies, such as it occurs by Zn doping. A small percentage of vacancies rapidly destroys the spin gap, and their presence induces enhanced antiferromagnetic correlations near those vacancies. The study is performed with computational techniques which includes Lanczos, world-line Monte Carlo, and the Density Matrix Renormalization Group methods. Since the phenomenon of enhanced antiferromagnetism is found to occur in several models and cluster geometries, a common simple explanation for its presence may exist. It is argued that the resonating-valence-bond character of the spin correlations at short distances of a large variety of models is responsible for the presence of robust staggered spin correlations near vacancies and lattice edges. The phenomenon takes place regardless of the long distance properties of the ground state, and it is caused by a "pruning" of the available spin singlets in the vicinity of the vacancies. The effect produces a broadening of the low temperature NMR signal for the compounds analyzed here. This broadening should be experimentally observable in the structurally dimerized chain systems Cu(N O3)2 · 2.5H2O, CuW O4, (V O)2P2O7, and Sr14Cu24O41, in ladder materials such as SrCu2O3, in the spin-Peierls systems CuGeO3 and N aV2O5, and in several others since it is a universal effect common to a wide variety of models and compounds.
Recibido el 26 de julio del 2004; aceptado el 10 de diciembre del 2004 Abstract. Multivariate cal... more Recibido el 26 de julio del 2004; aceptado el 10 de diciembre del 2004 Abstract. Multivariate calibration with regression by partial least squares (PLS-1) is herein proposed as an alternative method for the spectrophotometric quantification of isoperoxisomicine A1 in peroxi- somicine A1 batches. In order to minimize the optimal factors neces- sary to obtain the calibration matrix, different parameters were
Toxicon, 2009
Karwinskia humboldtiana fruit (Kh) causes a neurological disorder 3-4 weeks after ingestion, char... more Karwinskia humboldtiana fruit (Kh) causes a neurological disorder 3-4 weeks after ingestion, characterized by flaccid, symmetrical, ascending paralysis, similar to the Guillain-Barre syndrome. In this polyneuropathy the lesion (demyelization) in peripheral nerves has been described in several animal species, both in acute and in chronic intoxication. However, no reports exist about the presence of lesions in the Central Nervous System (CNS), in chronic intoxication. We considered it important to evaluate, with histological techniques, the possible presence of lesions in the brain, by using a model of chronic intoxication that reproduces the same stages present in the human intoxication, to better understanding of this pathological process. In our present work we fed the ground Kh fruit to Wistar rats and samples of brain, cerebellum, and pons were embedded in paraffin. Sections were stained with Hematoxylin & Eosin (HE) and special stains for nerve tissue. Histopathological changes were evaluated in the CNS through the different stages of the polyneuropathy and comparison to a control group. With this methodology, we found lesions in the motor pathway. This is the first report about the presence of neuronal damage caused by Kh in the Central Nervous System in chronic intoxication.
Journal of Liquid Chromatography & Related Technologies, 2005
A quantitative gas-liquid chromatographic method for the determination of blood levels of ethosux... more A quantitative gas-liquid chromatographic method for the determination of blood levels of ethosuximide, phenobarbitone, primidone and diphenylhydantoin is described. All four compounds are determined using 1 ml of serum. A simple, direct extraction technique is employed. Ethosuximide is analysed without derivatization. Subsequent flash alkylation with trimethylanilinium hydroxide allows the simultaneous determination of phenobarbitone, primidone, and diphenylhydantoin.
Journal of Liquid Chromatography & Related Technologies, 2002
... de La Luz Salazar a , Pedro Luis Lopez De Alba b , Alfredo Pineyro López a & Noemi Wa... more ... de La Luz Salazar a , Pedro Luis Lopez De Alba b , Alfredo Pineyro López a & Noemi Waksman De Torres c ... liver and skin cell cultures, and is currently the subject of preclinical studies as an antitumor drug.[6]6. Piñeyro, A., Martínez, de Villarreal L. and González Alanis, R. 1994 ...
Biologia Plantarum, 1992
Biol. Plant. 34 (Suppl.): 523, 1992 Explants from single trees of Abies concolor (Gord. et Glend)... more Biol. Plant. 34 (Suppl.): 523, 1992 Explants from single trees of Abies concolor (Gord. et Glend) Lindl. • Abies grandis (mature embryo), Quercus robur L. (embryonic axis, young stem segments), Quercus rubra L. (young stem segments) and Castanea sativa L. (embryonic axis of mature embryo) were cultured on a callusinducing medium with NAb, or IBA (in Castanea) and BAP. Differentiation of tracheids tn both callus and explant tissues was preceeded by formation of cambium-like cells forming wound procambium zones of different shape. These zones produced tracheidal cells either on their convex side (cambium near to callus surface) or concave side (virtually wound cambium zones), where tracheid nests were produced. These were composed of irregulary arranged short or long and wound tracbeids surrounded by cells of the wound cambium. Tracheid nests originated in callus produced on hypocotyl-radicula region ofAbies explants were composed of nodal tracheids irregular in shape surrounded by the layer of the meristematic cells isodiametric in shape, capable of differentiation into tracheid cells. These tracheids as well as others differentiated in Abies explants had thickened secondary side walls with large circular bordered pits and sometimes, in addition, wound helical thickenings. On the other hand, in tracheids differentiated in callus of Quercus sp. and Castanea small circular or oval non-bordered pits or step-like thickening of secondary wail prevailed.
Physical Review B, 1998
Spin models that have been proposed to describe dimerized chains, ladders, two dimensional antife... more Spin models that have been proposed to describe dimerized chains, ladders, two dimensional antiferromagnets, and other compounds are here studied when some spins are replaced by spinless vacancies, such as it occurs by Zn doping. A small percentage of vacancies rapidly destroys the spin gap, and their presence induces enhanced antiferromagnetic correlations near those vacancies. The study is performed with computational techniques which includes Lanczos, world-line Monte Carlo, and the Density Matrix Renormalization Group methods. Since the phenomenon of enhanced antiferromagnetism is found to occur in several models and cluster geometries, a common simple explanation for its presence may exist. It is argued that the resonating-valence-bond character of the spin correlations at short distances of a large variety of models is responsible for the presence of robust staggered spin correlations near vacancies and lattice edges. The phenomenon takes place regardless of the long distance properties of the ground state, and it is caused by a "pruning" of the available spin singlets in the vicinity of the vacancies. The effect produces a broadening of the low temperature NMR signal for the compounds analyzed here. This broadening should be experimentally observable in the structurally dimerized chain systems Cu(N O3)2 · 2.5H2O, CuW O4, (V O)2P2O7, and Sr14Cu24O41, in ladder materials such as SrCu2O3, in the spin-Peierls systems CuGeO3 and N aV2O5, and in several others since it is a universal effect common to a wide variety of models and compounds.
Recibido el 26 de julio del 2004; aceptado el 10 de diciembre del 2004 Abstract. Multivariate cal... more Recibido el 26 de julio del 2004; aceptado el 10 de diciembre del 2004 Abstract. Multivariate calibration with regression by partial least squares (PLS-1) is herein proposed as an alternative method for the spectrophotometric quantification of isoperoxisomicine A1 in peroxi- somicine A1 batches. In order to minimize the optimal factors neces- sary to obtain the calibration matrix, different parameters were
Toxicon, 2009
Karwinskia humboldtiana fruit (Kh) causes a neurological disorder 3-4 weeks after ingestion, char... more Karwinskia humboldtiana fruit (Kh) causes a neurological disorder 3-4 weeks after ingestion, characterized by flaccid, symmetrical, ascending paralysis, similar to the Guillain-Barre syndrome. In this polyneuropathy the lesion (demyelization) in peripheral nerves has been described in several animal species, both in acute and in chronic intoxication. However, no reports exist about the presence of lesions in the Central Nervous System (CNS), in chronic intoxication. We considered it important to evaluate, with histological techniques, the possible presence of lesions in the brain, by using a model of chronic intoxication that reproduces the same stages present in the human intoxication, to better understanding of this pathological process. In our present work we fed the ground Kh fruit to Wistar rats and samples of brain, cerebellum, and pons were embedded in paraffin. Sections were stained with Hematoxylin & Eosin (HE) and special stains for nerve tissue. Histopathological changes were evaluated in the CNS through the different stages of the polyneuropathy and comparison to a control group. With this methodology, we found lesions in the motor pathway. This is the first report about the presence of neuronal damage caused by Kh in the Central Nervous System in chronic intoxication.
Journal of Liquid Chromatography & Related Technologies, 2005
A quantitative gas-liquid chromatographic method for the determination of blood levels of ethosux... more A quantitative gas-liquid chromatographic method for the determination of blood levels of ethosuximide, phenobarbitone, primidone and diphenylhydantoin is described. All four compounds are determined using 1 ml of serum. A simple, direct extraction technique is employed. Ethosuximide is analysed without derivatization. Subsequent flash alkylation with trimethylanilinium hydroxide allows the simultaneous determination of phenobarbitone, primidone, and diphenylhydantoin.
Journal of Liquid Chromatography & Related Technologies, 2002
... de La Luz Salazar a , Pedro Luis Lopez De Alba b , Alfredo Pineyro López a & Noemi Wa... more ... de La Luz Salazar a , Pedro Luis Lopez De Alba b , Alfredo Pineyro López a & Noemi Waksman De Torres c ... liver and skin cell cultures, and is currently the subject of preclinical studies as an antitumor drug.[6]6. Piñeyro, A., Martínez, de Villarreal L. and González Alanis, R. 1994 ...
Biologia Plantarum, 1992
Biol. Plant. 34 (Suppl.): 523, 1992 Explants from single trees of Abies concolor (Gord. et Glend)... more Biol. Plant. 34 (Suppl.): 523, 1992 Explants from single trees of Abies concolor (Gord. et Glend) Lindl. • Abies grandis (mature embryo), Quercus robur L. (embryonic axis, young stem segments), Quercus rubra L. (young stem segments) and Castanea sativa L. (embryonic axis of mature embryo) were cultured on a callusinducing medium with NAb, or IBA (in Castanea) and BAP. Differentiation of tracheids tn both callus and explant tissues was preceeded by formation of cambium-like cells forming wound procambium zones of different shape. These zones produced tracheidal cells either on their convex side (cambium near to callus surface) or concave side (virtually wound cambium zones), where tracheid nests were produced. These were composed of irregulary arranged short or long and wound tracbeids surrounded by cells of the wound cambium. Tracheid nests originated in callus produced on hypocotyl-radicula region ofAbies explants were composed of nodal tracheids irregular in shape surrounded by the layer of the meristematic cells isodiametric in shape, capable of differentiation into tracheid cells. These tracheids as well as others differentiated in Abies explants had thickened secondary side walls with large circular bordered pits and sometimes, in addition, wound helical thickenings. On the other hand, in tracheids differentiated in callus of Quercus sp. and Castanea small circular or oval non-bordered pits or step-like thickening of secondary wail prevailed.