[en] The Deer mouse, Peromyscus maniculatus, is being used more extensively as an animal model in biological research. At the Radiobiology Division of the University of Utah, preliminary studies have shown that the radionuclide retention characteristics of Peromyscus, especially involving bone and liver retention, are similar to a well defined beagle model and humans. Also, a colony of Peromyscus under study can be maintained more easily, at less cost, in much less space, and in greater numbers as compared to larger mammals. In addition, mouse studies can be conducted for the same proportion of the animals' life span in much less real time. For these reasons, a concerted effort is underway to define the normal biology of Peromyscus so that the model can be used in radionuclide studies designed to estimate human risk. One phase of this study was to characterize the normal Peromyscus hemogram because of dose-response relationships that exist between the cells of the peripheral blood and bone marrow irradiation. Results have already indicated that this animal model will be of value in estimating the toxicity of Pu-239 and possibly that of other actinide elements in humans

[en] Highlights: • Method to generate a thermally equivalent wall to that composed by hollow-blocks. • The thermal equivalence is valid for time-dependent conditions and for steady-state. • The equivalent wall is composed by a set of homogeneous layers. • This method can be implemented into whole-building simulations programs. - Abstract: An equivalent-homogeneous-layer-set (EHLS) method to account for the time-dependent heat transfer through a wall composed by hollow-blocks is proposed. This method considers the two-dimensional heat transfer due to conduction through the solid frame, the heat transfer by natural convection inside the air-cavities, and the heat transfer by radiation between air-cavity surfaces. The EHLS method gives an equivalent wall, composed by a set of homogeneous layers, that has a similar thermal behavior than the original hollow-block wall. Convection and radiation inside the air-cavities are considered by using temperature dependent heat coefficients and a radiative correction factor. This radiative correction factor is calculated for different values of the in-cavity fractional area and different aspect ratios of the air-cavities by comparing numerical results of the EHLS method with results of an experimentally validated two-dimensional model, in steady-state. This experimentally validated two-dimensional model, for time-dependent periodic conditions, is used to validate the EHLS method. Differences are up to 3.4% for the energy transferred through the wall, and 7% for both the sol–air decrement factor and the lag-time when the hollow-block wall is in a non-air conditioned room and up to 6% for the total thermal load when it is in an air-conditioned room. The EHLS method can be implemented into whole-building simulations programs and can be extended for other constructive systems for walls or roofs that have air-cavities inside, using the appropriate convective and radiative coefficients and radiative correction factor.

[en] We report reversible magnetization data and the scaling for the magnetization obtained for magnetic fields (H) applied at various tilt angles θ of the dc magnetic field with respect to the c axis in a single crystal of Bi₂Sr₂CaCu₂O₈. Our data show the crossover of the magnetization below the superconducting onset temperature, which indicates a dominant vortex fluctuation

[en] We report a crystallographic and magnetic characterization of the Sr₂FeMnO₆ novel polycrystalline complex manganite produced by the ceramic method. This material was mixed in volume percentages from 0% to 100% with the granular high temperature superconductor YBa₂Cu₃O_7-δ to conform Sr₂FeMnO₆/YBa₂Cu₃O_7-δ composites. Studies of chemical stability reveal that the Sr₂FeMnO₆ does not react with the YBa₂Cu₃O_7-δ superconductor. X-ray results show an excellent coupling between the respective lattice parameters. DC susceptibility measurements indicate that the superconductivity of the YBa₂Cu₃O_7-δ and the exotic magnetic properties of the Sr₂FeMnO₆ coexist up to 80% volume of this material in the composite. These characteristics permit to infer that these compounds would be utilized to the production of antiferromagnetic-superconductor multi-layer devices

[en] A comprehensive investigation of the general properties of the Sr_2DyRuO_6 complex perovskite was undertaken. Crystal structure characterization performed by X-ray diffraction measurements and Rietveld analysis allowed establishing that the material crystallizes in a distorted monoclinic perovskite-like structure belonging to the P2_1/n (#14) space group, with alternating distribution of Dy"3 "+ (2c: 0, 0.5, 0) and Ru"5 "+ (2d: 0.5, 0, 0). Because of the mismatch in the ionic radii, the DyO_6 and RuO_6 octahedra are forced to tilt around the cubic directions so as to optimize the Sr–O inter-atomic bond lengths. Morphological characterization carried out by scanning electron microscopy indicated a particle size D = 37.17 nm and an activation energy Q = 109.8 kJ/mol. Semi-quantitative compositional study, performed through energy-dispersive X-ray experiments, corroborated that the pure phase of the Sr_2DyRuO_6 was correctly obtained. Magnetic properties determined from the fit of the Curie–Weiss law to the curves of magnetic susceptibility as a function of temperature showed that Sr_2DyRuO_6 exhibits an antiferromagnetic-like behavior at low temperatures as a consequence of a magnetic transition at T = 38 K. Data collected with respect to the field dependence of the magnetization showed the existence of a weak ferromagnetic moment relationship with antiferromagnetic-like behavior. Density functional theory allowed establishing the optimum electronic structure for Sr_2DyRuO_6, and the study of the density of states showed that Dy"3 "+ and Ru"5 "+ are responsible for the magnetic character of the compound, with the prediction that at T = 0 K it behaves as a half-metallic material. The spin magnetic moment of the cell is close to 16 μ_B, and the integer number of Bohr magneton is a signature of half-metallic character. Evolution of crystal structure at high temperature revealed that Sr_2DyRuO_6 does not undergo any structural phase transitions, since the Bragg reflections [hkl] do not undergo changes, and the structure is preserved. - Highlights: • General properties of the Sr_2DyRuO_6 complex perovskite are widely discussed. • Structural description of octahedral distortions from X-ray diffraction analysis is performed. • Morphological and compositional characteristics are related with the physical properties reported. • Antiferromagnetic response is discussed form experimental results. • Theoretical calculations reveal the possible half-metallic character of material

[en] We report on fluctuation magnetoconductivity measurements in a granular sample of GdBa₂Cu₃O_7-δ. The experiments show that the resistive transition is a two-stage process in this sample. The pairing transition occurs at a higher temperature, where superconductivity is established in the grains. The critical thermodynamics for this transition is that of the 3D-XY universality class, with dynamic exponent z=1.5. At a lower temperature occurs the coherence transition, where the fluctuating phases of individual grains become long-range ordered and a zero resistance state sets in

[en] A complex perovskite oxide YSr₂SbO₆ has been synthesized by solid-state reaction. Structural ordering in this material has been studied by X-ray diffraction. The X-ray diffraction pattern reveals that YSr₂SbO₆ has an ordered complex cubic structure characteristic of A₂BB^'O₆ crystalline structure with lattice constant a=8.2561 Angst. The chemical stability of YSr₂SbO₆ with YBa₂Cu₃O_7-δ superconductors has been studied by X-ray diffraction and magnetic measurements on YSr₂SbO₆/YBa₂Cu₃O_7-δ composites. Magnetic measurements show that superconducting transition temperature of pure YBa₂Cu₃O_7-δ and YSr₂SbO₆/YBa₂Cu₃O_7-δ composites is 90 K. These studies show that YSr₂SbO₆ could be a potential candidate as a substrate material for films of YBa₂Cu₃O_7-δ. Furthermore, Percolation threshold V_C and critical exponent t are found in the YSr₂SbO₆, YBa₂Cu₃O_7-δ composite

[en] We report the study of the structural, magnetic and electrical properties of the multiferroic material with perovskite structure HoMn_1−xFe_xO₃ (x=0; 0.1 and 0.2) synthesized by the standard solid state reaction method. Structural analysis by X-ray diffraction (XRD) experiments shows the coexistence between two phases with the same chemical formula and with polyhedral distortions (MnO₃), a phase with hexagonal symmetry (P63cm # 185) which is characteristic of the non-doped material HoMnO₃ and other perovskite phase with orthorhombic symmetry (Pbnm # 62). Rietveld refinements of the experimental patterns show that the weight percentage of each phase (hexagonal or orthorhombic symmetry) depends on the degree of substitution of Fe in the Mn crystallographic sites. Measurements of polarization as a function of applied voltage at room temperature confirm a ferroelectric character for non-doped material with relative permittivity of 215.1. These measurements show that the ferroelectric behavior is deteriorated by the introduction of Fe, since in the configuration with x=0.1 (HoMn_0.9Fe_0.1O₃) we can see ferroelectric loops with dielectric losses to small values of applied voltage and finally in the configuration with x=0.2 (HoMn_0.8Fe_0.2O₃) the behavior is totally resistive at room temperature. Curves of magnetization as a function of temperature were carried out between 300 K and 860 K show an antiferromagnetic behavior in the three configurations of the HoMn_1−xFe_xO₃ material

No abstract available

[en] Between 2002 and 2003, an outbreak of a trout's mass death occurred at the intensive fish culture a Peruvian rural town (Marcara, Huaraz, Peru) where 15,000 from 20,000 fish died. Our objective in the present study was to investigate the high mortality of the trout biomass occurred in period of two months. This study was conducted after the peak of the outbreak has occurred. We collected samples of fishes, water and fish foodstuff which were examined for aflatoxin, metals, toxics and bacteria. We interviewed people who administered the feed pellet. Feed sample preparation, transport and storage. The processing of fish feed was at room temperature which was below 16 deg C. Once prepared the diet it was keep under an appropriate room for a few days before sending to Marcara town. Fishes. 20,000 immature trout larval of rainbow trout (Oncorhynchus mykiss) was acquired from an official Peruvian fish culture. The fishes were fed twice a day. Adjusted of feed ration was based from the monthly sample weight. Pellet sample analysis. The samples were analyzed for aflatoxin Bl (AFB1) according to the method previously published. The sensitivity is 0.1 μg per 1 kg of sample. During the fish development until the peak of the outbreak, the foodstuff to fishes was maintained in plastic bags. At this time the storage room temperature was 18-20 deg. C between 1.00-2.00 P.M. and the humidity rose close to 90 % at the Marcara facilities. Mortality development and Effect on survival. The fishes maintained in 4 pods had a normal surviving until end of November, less than 10 specimen dead by month. The fish outbreaks started the first week of December and continuing until the fourth week of January totalizing 15,000 dead fish from 20,000. The survival of the fish at the first month was less than 50 %. The mortality continues throughout January totalizing 15,000 dead fish and leaving only 25% survival. Laboratory data. The collected samples for analysis were frozen and transported in dry ice to the analysis laboratory. We took the samples on January 23 and it was analyzed on January 25. Aflatoxin Bl was detected in three samples of fish muscle and in the 3 samples of fish feed but it was negative in the 3 water samples. The AFB1 concentration was 10 times in the fish feed than in the fish muscle. In spite of heavy metal residues (lead, mercury and arsenic) were found in the fish samples, those concentrations were below the permissible levels. Volatile toxic residues were negative in water, fish and feed. Only the fish feed samples were contaminated by bacteria (Staphylococcus aureaus). Under favourable conditions of temperature and humidity, the Aspergillus flavus grows on certain foods and feeds, resulting in the production of aflatoxin Bl. For the trout, the highest admissible amount of AFBI in feed is 0.1 μg per kg. The data showed suggest that an improper handling of fish foodstuff (18-20 deg. C and 90 % humidity) was the cause growing of mould and/or spores and consequently it produced an increased concentration of AFBI in fish feed. Liver is strategically located between intestinal tract and general circulation. As AFBI concentration ranged in liver between 10 and 100 ppb, this level is capable to produce an acute hepatotoxicity in the fish stocks. (author)