Search Results - (Author, Cooperation:L. Cabrera)

2018-03-06

Soil Science Society of America (SSSA)

0361-5995

1435-0661

Geosciences

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

2018-09-11

University of Barcelona, Faculty of Geology

1695-6133

1696-5728

Geosciences

2016-05-14

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-02-01

Institute of Physics Publishing (IOP)

1748-0221

Physics

1365-3091

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

A small, closed, lacustrine system developed during the restraining overstep stages of the Oligocene As Pontes strike-slip basin (Spain). The increase in basin accommodation and the headward spread of the drainage, which increased the water input, triggered a change from shallow, holomictic to deeper, meromictic conditions. The lower, shallow, lacustrine assemblage consists of mudstone–carbonate cycles recording lacustrine–palustrine ramp deposition in a saline lake. High Sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds. Early dolomitization took place together with widespread pedogenic activity. The upper, deep, freshwater, lacustrine assemblage includes bundles of carbonate–clay rhythmites and fine-grained turbidite beds. Primary calcite and diagenetic siderite make up the carbonate laminae. The Mg content of the primary carbonates records variations in Mg/Ca ratios in lacustrine waters. δ18O and δ13C covariance trends in calcite reinforce closed drainage conditions. δ18O data indicate that the lake system changed rapidly from short-lived isotopically light periods (i.e. from seasonal to pluriannual) to longer steady-state periods of heavier δ18O (i.e. from pluriannual to millennial). The small δ13C changes in the covariant trends were caused by dilute inflow, changing the contributions of dissolved organic carbon in the system and/or internal variations in lacustrine organic productivity and recycling. In both shallow and deep carbonate facies, sulphate reduction and methanogenesis may account, respectively, for the larger negative and positive δ13C shifts recorded in the early diagenetic carbonates (calcite, dolomite and siderite). The lacustrine system was very susceptible to high-frequency, climatically forced water balance variations. These climatic oscillations interfered with the low-frequency tectonic and morphological changes in the basin catchment. This resulted in the superposition of high-order depositional, mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence.

Electronic Resource

0022-3697

Oxygen ; cyclic voltametry ; diffusion ; fast conductor ; ionic conductor

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Physics

Electronic Resource

0031-9201

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Geosciences

Physics

Electronic Resource

0740-0020

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Process Engineering, Biotechnology, Nutrition Technology

Electronic Resource

0740-0020

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Process Engineering, Biotechnology, Nutrition Technology

Electronic Resource

0009-2614

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Physics

Electronic Resource

1432-1084

Key words: POEMS syndrome ; Plasmacytoma ; CT ; Scintigraphy

Springer Online Journal Archives 1860-2000

Medicine

Abstract. POEMS syndrome is a multisystemic disorder related to a plasma cell dyscrasia. Radiologically, this syndrome is characterized by sclerotic focal bone lesions with a normal radionuclide bone scan. We report a case of POEMS syndrome with an expansile lytic lesion in the sternum showing periosteal reaction and soft tissue mass, which revealed locally increased uptake of radiotracer in bone scintigraphy. These unusual findings and the differential diagnosis are discussed.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the40Ar/40K ratio. This technique has been replaced since 1966 by measurement of40Ar/39Ar ratio, after artificial production of39Ar from the39K(n,p)39Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the40Ar/40K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (41Ar and42K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction41K(n,p)41Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric40Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract The method described in a previous work to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with ammonium pyrrolidindithiocarbamate (APDC) at pH 1.5–2, has been applied to urine samples from 15 females patients suffering from cervical uterine cancer. With this type of sample the method reaches a maximum sensitivity (few ppb) with a good statistical variation (±12%). Since the highest concentration of selenium in human tissues is found in the kidney, and the elimination of this element is mainly by the urine, the method seems to be a powerful tool in the research about the human metabolism of selenium. This paper shows a possible relation of selenium concentration in human urine and the evolution time of cervical uterine cancer, in spite of limits imposed by the statistical error plus the inhomogeneity of the sample.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract A method is described to separate trace amounts of selenium in biological samples without using a carrier. This method is based on the adsorption on active carbon of the complex ion formed with APDC /ammonium salt of l-pyrrolidine carbodithioic acid/ at pH 1. The efficiency of the radiochemical separation described is measured by using carrier-free75Se labelled solutions of sodium selenite at selenium concentrations from 3.5×10−8 to 3.5×10−11 g ml−1. The results were between 95% and 98% with statistical variations from 2% to 10%. The determination of selenium can be made following this separation either through75Se in the traditional way, or through77mSe if the separation is performed prior to irradiation. The detection limits on the available conditions were 0.01 ppm for75Se and 0.1 ppm for77mSe. When the analysis is performed through75Se /t=120 d/, the statistical error is notably smaller because the counting time may be considerable, whereas through77mSe/t=17.5 s/it is higher than 20%, depending on the concentration and the available neutron flux. However, the advantages of gaining time and the fact of performing the trace separation from a non radioactive material, make both procedures competitive as useful tools for the research on the function of Se in vertebrates.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract A method is described to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with APDC at pH 1.5. The separation is made prior to the neutron irradiation and the correction for selenium in the reagents performed by the irradiation of a blank. The method has been successfully used in fodder samples as well as some other organic reference materials, using a fast pneumatic transfersystem, which takes the samples from the irradiation position to the counting position in 3s, with the only limitation of the thermal neutron flux available, 4.7·1011 cm−2·s−1. Detection limits of 0.1 μg are obtained under these experimental conditions.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract Gamma exposure rate and radon levels were measured in 75 single-family dwellings in Mexico City in order to correlate them with local environment. Radon monitoring was performed both indoors and outdoors using a continuous working level monitor for short-lived radon decay products; the gamma exposure rate was measured using CaSO4: Dy+PTFE. The results obtained show a log-normal distribution. The mean indoor radon concentration is lower than 45 Bq/m3 and the mean indoor gamma exposure rate was 11.29 μR/h.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract The classification of low and medium level radioactive wastes produced regularly by nuclear power plants is becoming ever more important in Mexico, after a few years of running the first of two units, 600 MeV each, in Laguna Verde nuclear power plant. This paper describes a method to separate and detect traces of the weak β-emitter63Ni, which is one of the activation products used to classify low and medium level radioactive wastes originating from the operation of nuclear power plants.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract Metallic pollutants were measured in dwellings in Mexico City by instrumental neutron activation analysis (INAA) and X-ray fluorescence techniques. Monitoring was performed in the west side of the city and in the winter season. In general the average concentration of contaminants collected, when compared with the average concentrations reported in a previous paper, have increased with time and in the particular case of lead and mercury some samples are above the indicative WHO maximum levels.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract This paper presents the annual radon gas concentrations obtained during the 1994–1995 monitoring campaign using passive electret system (type E-PERM). Radon levels were measured in 154 single family dwellings, in normal occupancy conditions (open house condition) in the metropolitan zone of Mexico City. At the same time radon monitoring was performed outdoors. The results show the general log-normal distribution of integrated indoor radon concentration with an annual indoor mean of 3.8 pCi·l−1. The seasonal variations show the minimum mean values in the summer season which are 39% lower than that in autumn. Equilibrium factors (F) were measured in 12 typical houses both in autumn and winter using a continuous working level monitor for short-lived radon decay products and H-chamber loaded with a short term electret (HST, E-PERM) for radon gas. The obtained total mean equilibrium factors are:F=0.41±0.17 andF=0.29±0.04 for indoor and outdoor, respectively. A quality program was also improved.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract Total solid particles (TSP), respirable particles (RP) PM10 and 17 metallic pollutants were measured in dwellings in the Metropolitan Zone of Mexico Valley (MZMV) by gravimetry and instrumental neutron activation analysis (INAA). Monitoring was performed in Northeast, Center, Southeast and Southwest Zones in the winter and spring seasons. In general, the average concentration of contaminants (derived from industrial activities) that we have determined have increased with time. TSP and RP PM10 are often above the US and Mexican norms.

Electronic Resource