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Sheen P.,Cayetano Heredia Peruvian University | Ferrer P.,Cayetano Heredia Peruvian University | Christiansen G.,Cayetano Heredia Peruvian University | Moreno-Roman P.,Cayetano Heredia Peruvian University | And 11 more authors.
American Journal of Tropical Medicine and Hygiene | Year: 2012

Pyrazinamidase of Mycobacterium tuberculosis catalyzes the conversion of pyrazinamide to the active molecule pyrazinoic acid. Reduction of pyrazinamidase activity results in a level of pyrazinamide resistance. Previous studies have suggested that pyrazinamidase has a metal-binding site and that a divalent metal cofactor is required for activity. To determine the effect of divalent metals on the pyrazinamidase, the recombinant wild-type pyrazinamidase corresponding to the H37Rv pyrazinamide-susceptible reference strain was expressed in Escherichia coli with and without a carboxy terminal. His-tagged pyrazinamidase was inactivated by metal depletion and reactivated by titration with divalent metals. Although Co2+, Mn2+, and Zn2+ restored pyrazinamidase activity, only Co2+ enhanced the enzymatic activity to levels higher than the wild-type pyrazinamidase. Cu2+, Fe 2+, Fe3+, and Mg2+ did not restore the activity under the conditions tested. Various recombinant mutated pyrazinamidases with appropriate folding but different enzymatic activities showed a differential pattern of recovered activity. X-ray fluorescence and atomic absorbance spectroscopy showed that recombinant wild-type pyrazinamidase expressed in E. coli most likely contained Zn. In conclusion, this study suggests that M. tuberculosis pyrazinamidase is a metalloenzyme that is able to coordinate several ions, but in vivo, it is more likely to coordinate Zn2+. However, in vitro, the metal-depleted enzyme could be reactivated by several divalent metals with higher efficiency than Zn. Copyright © 2012 by The American Society of Tropical Medicine and Hygiene.

Lopez A.,National Autonomous University of Mexico | Lopez A.,Instituto Peruano Of Energia Nuclear | Lopez A.,University of Lima | Acosta D.,National Autonomous University of Mexico | And 3 more authors.
Powder Technology | Year: 2010

Transparent TiO2 thin films were deposited on soda lime glass at different substrate temperatures by a simple and reproducible spray pyrolysis technique from aqueous peroxo-polytitanic acid. Both the as-prepared and annealed films (3h thermal treatment in air at 500°C) were characterized by AFM, SEM, TEM, XRD, FT-IR and UV-visible spectroscopy. The as-prepared films present predominant low crystallized structure, low porosity, high surface roughness and grain agglomerates while the annealed films exhibit slightly better polycrystalline structure of brookite phase. The as-deposited TiO2 films prepared at low substrate temperatures (280°C) show the best photocatalytic activity, against methylene-blue, due principally to their small grain size and high surface area. © 2010 Elsevier B.V.

Orozco-Gonzalez P.,CINVESTAV | Castro-Roman M.,CINVESTAV | Martinez A.I.,CINVESTAV | Herrera-Trejo M.,CINVESTAV | And 3 more authors.
Intermetallics | Year: 2010

To contribute to the understanding of the Al-Fe-Mn-Si system, an exhaustive analysis of the intermetallic phases formed during thermal analysis experiments and specific isothermal treatments was carried out. In this work, three different phases were identified: the extensively reported β and α phases and the τh phase. The τh phase has been reported for the ternary Al-Fe-Si system, but not for the quaternary Al-Fe-Mn-Si system. Nonetheless, the present results suggest that the formation of the τh phase upon solidification of the alloy can be stabilized in the quaternary Al-Fe-Mn-Si system, with respect to the monoclinic θ-Al3Fe phase in the ternary Al-Fe-Si system, due to the Mn addition. The τh phase was unambiguously identified with the help of complementary techniques such as SEM/EDS, X-ray diffraction and Mössbauer spectroscopy. © 2010 Elsevier Ltd. All rights reserved.

Gonzalez-Hernandez R.,CINVESTAV | Martinez A.I.,CINVESTAV | Falcony C.,CINVESTAV | Lopez A.A.,Instituto Peruano Of Energia Nuclear | And 3 more authors.
Materials Letters | Year: 2010

ZnO and ZnO:F nanoparticles were successfully prepared by precipitation in the presence of oxalic acid. This procedure yields ZnO and ZnO:F nano-arrangements of different lengths consisting of chains of quasi-spherical nanoparticles of ∼ 30 nm in size. Only the wurtzite ZnO structure was detected for both undoped and fluorine doped ZnO nanoparticles. By absorption and photoluminescence measurements, a diminishing of singly ionized oxygen vacancies was detected when fluorine is present in the nanoparticles; while a blue shift of the exciton absorption was observed. Additionally, by NIR reflectance measurements, the creation of free carriers by the fluorine doping of ZnO nanoparticles was observed. © 2010 Elsevier B.V. All rights reserved.

PubMed | Health Canada, World Health Organization, Radiation and Nuclear Safety Authority, International Atomic Energy Agency and 12 more.
Type: | Journal: Radiation protection dosimetry | Year: 2016

The Global Health Security Initiative (GHSI) established a laboratory network within the GHSI community to develop collective surge capacity for radionuclide bioassay in response to a radiological or nuclear emergency as a means of enhancing response capability, health outcomes and community resilience. GHSI partners conducted an exercise in collaboration with the WHO Radiation Emergency Medical Preparedness and Assistance Network and the IAEA Response and Assistance Network, to test the participating laboratories (18) for their capabilities in in vitro assay of biological samples, using a urine sample spiked with multiple high-risk radionuclides (

PubMed | National University of Colombia, Brazilian Radiological Protection and Dosimetry Institute (IRD), Eletrobras, Hospital San Juan Of Dios and 14 more.
Type: Journal Article | Journal: Radiation protection dosimetry | Year: 2016

Internal dosimetry intercomparisons are essential for the verification of applied models and the consistency of results. To that aim, the First Regional Intercomparison was organised in 2005, and that results led to the Second Regional Intercomparison Exercise in 2013, which was organised in the frame of the RLA 9/066 and coordinated by Autoridad Regulatoria Nuclear of Argentina. Four simulated cases covering intakes of (131)I, (137)Cs and Tritium were proposed. Ninteen centres from thirteen different countries participated in this exercise. This paper analyses the participants results in this second exercise in order to test their skills and acquired knowledge, particularly in the application of the IDEAS Guidelines. It is important to highlight the increased number of countries that participated in this exercise compared with the first one and, furthermore, the improvement in the overall performance. The impact of the International Atomic Energy Agency (IAEA) Projects since 2003 has led to a significant enhancement of internal dosimetry capabilities that strengthen the radiation protection of workers.

Bedregal P.S.,Instituto Peruano Of Energia Nuclear | Mendoza P.A.,Instituto Peruano Of Energia Nuclear | Cohen I.M.,Secretaria de Ciencia | Cohen I.M.,University of Buenos Aires | And 2 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2012

A new approach for analysis of entire potsherds of archaeological interest by INAA, using the conventional relative method, is described. The analytical method proposed involves, primarily, the preparation of replicates of the original archaeological pottery, with well known chemical composition (standard), destined to be irradiated simultaneously, in a well thermalized external neutron beam of the RP-10 reactor, with the original object (sample). The basic advantage of this proposal is to avoid the need of performing complicated effect corrections when dealing with large samples, due to neutron self shielding, neutron self-thermalization and gamma ray attenuation. In addition, and in contrast with the other methods, the main advantages are the possibility of evaluating the uncertainty of the results and, fundamentally, validating the overall methodology. © Akadémiai Kiadó, Budapest, Hungary 2011.

Montoya E.,Instituto Peruano Of Energia Nuclear | Bedregal P.,Instituto Peruano Of Energia Nuclear | Mendoza P.,Instituto Peruano Of Energia Nuclear | Ubillus M.,Instituto Peruano Of Energia Nuclear | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2010

The k0 method was implemented at the Peruvian Institute of Nuclear Energy (IPEN), by 1993. Since the middle of 1994, almost all INAA work at IPEN is performed by the k0 method. The establishment, applications, development and future of the method in Peru are presented from a retrospective and prospective view. Attention is paid to difficult aspects, e.g. counting efficiency, characterization of irradiation facility; non-ideal behaviour of the epithermal neutron spectrum and consistency of nuclear input data. © 2010 Elsevier B.V. All rights reserved.

PubMed | Instituto Peruano Of Energia Nuclear
Type: Journal Article | Journal: Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2011

The structural evolution and dynamics of silver nanodrops Ag(2869) (4.4nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 10(13)Ks(-1) the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 10(12)Ks(-1)), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.

Montoya E.H.,Instituto Peruano Of Energia Nuclear | Mendoza P.A.,Instituto Peruano Of Energia Nuclear | Bedregal P.S.,Instituto Peruano Of Energia Nuclear | Baltuano O.R.,Instituto Peruano Of Energia Nuclear | And 2 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2012

A method that combines the use of nondestructive neutron activation analysis and high-resolution a spectrometry has been developed for determination of the activities of 234U and 238U in geological samples of low uranium content. The 238U content is determined by k0- based neutron activation analysis, whereas the 234U/238U relationship is measured by a spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3-40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty. © Akadémiai Kiadó, Budapest, Hungary 2011.

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