524 research outputs found
Energy of bond defects in quantum spin chains obtained from local approximations and from exact diagonalization
We study the influence of ferromagnetic and antiferromagnetic bond defects on
the ground-state energy of antiferromagnetic spin chains. In the absence of
translational invariance, the energy spectrum of the full Hamiltonian is
obtained numerically, by an iterative modification of the power algorithm. In
parallel, approximate analytical energies are obtained from a local-bond
approximation, proposed here. This approximation results in significant
improvement upon the mean-field approximation, at negligible extra
computational effort.Comment: 3 pages, 2 figures. Manuscript accepted by Journal of Magnetism and
Magnetic Materials, special issue for LAWMMM 2007 conferenc
Structure And Composition Of Amorphous Ge1-xsnx Thin Films
The composition and bonding configuration of amorphous germanium-tin (a-Ge1-xSnx) thin films are reported (0≤x<0.3). Mössbauer spectroscopy analyses show that under the reported deposition conditions all tin atoms enter the a-Ge network in a perfect substitutional way, i.e., in a covalent tetrahedral configuration. The absence of defect structures in the tin sites is discussed and compared with results on films prepared under different conditions.63115596559
Utjecaj korozijskih inhibitora na krivulje ohlađivanja sredstva za kaljenje na bazi sojinog ulja
The relative inhibitory effect of a series of common yellow-metal (brass)
corrosion inhibitors was studied potentiodynamically in a saline solution.
The results of this study showed that all of the corrosion inhibitors examined
could potentially exhibit substantial cooling time and rate reduction. The
magnitude of this effect was corrosion inhibitor specific. Corrosion and
cooling curve supporting data are provided.Relativni inhibitorski efekt niza korozijskih inhibitora obojenih metala
(bronca) istraživani su potencijo-dinamički u solnim kupkama. Rezultati
istraživanja pokazali su da svi ispitani korozijski inhibitori mogu utjecati
na vrijeme ohlađivanja i smanjenje brzine ohlađivanja. Veličina tih efekata
ovisila je o pojedinom korozijskom inhibitoru. Prikazani su podaci za
koroziju kao i utjecaji na krivulje ohlađivanja
Response surface for biodiesel production from soybean oil by ethylic route
Petroleum has been the most consumed energy source in the world, but it tends to run
out due its non-renewable character. Among biofuels, biodiesel has emerged as the main
candidate to substitute petroleum diesel. The present study aimed to identify the maximum yield
point of biodiesel production by generating a response surface using molar ratio, temperature and
agitation time as independent variables, and yield as a dependent variable. From the response
surface, it is observed that the increase in temperature and reaction time leads to reduced yield.
The configuration that resulted in maximum yield of 93.30% was 12:1 molar ratio, 30 °C
temperature and 30-minute reaction time. From the chromatographic analysis it was possible to
identify five different fatty acids in the composition of the biodiesels. Total saturated fatty acids
(palmitic and stearic acids) ranged from 41.53% to 42.09% and total unsaturated fatty acids
including monounsaturated and polyunsaturated fatty acids (oleic, linoleic and linolenic acids)
ranged from 57.92% to 58.48%. According to the results of the physicochemical analyses, the
specific mass at 68°F is in agreement with Brazilian, American and European specifications,
ranging from 877.46 kg m-3
to 879.64 kg m-3
. The kinematic viscosity at 104 °F ranged from
4.49 mm² s
-1
to 4.82 mm² s
-1
. The acid value obtained did not vary within the limits established
by the norms, and values between 0.54 and 2.74 mg KOH g
-1 were observed
Use of analysis and processing of digital images for evaluation and control of animal behavior in hot climates
The world production of meats is mainly concentrated in the countries with a hot climate. Among these countries,
Brazil, considered "world's breadbasket", is located in the intertropical zone, with hot climates and presents lower thermal
amplitude. Brazilian poultry is a leader in the production and export of broilers. Brazil has the second largest cattle herd in the
world, has the largest commercial herd besides being the largest exporter of beef. Brazilian swine breeding, among the most
advanced production chains in the world, occupy the position of fourth largest producer of pork in the world. Projections for
Brazil's meat production sector indicate strong growth in the coming years, with countries in hot climates that will continue to
sustain future growth in world meat production, ensuring food security in many countries. One of the factors responsible for the
success or failure of animal production is the environment, defined by the sum of all physical and biological factors that affect
animals. In these regions of hot climates, climatic factors are among the main limiting factors to the development of animal
production, which may compromise animal welfare and productivity indices. Behavioral information can aid in the analysis of
problems arising from environmental conditions unfavorable to animals, helping both decision making and the use of different
environmental conditioning systems. The introduction of technification in the animal behavior evaluation processes, through the
use of video cameras and image processing programs, allowed a better interpretation of the behavioral responses, quickly,
accurately and non-invasively, gradually being used with greater frequency in the animal production sectors. The study of animal
behavior assumes an important role in animal production, since, to rationalize the breeding methods, management, feeding and
facilities techniques have been developed that interfere with animal behavior. In this context, the use of digital image analysis
techniques, where the animals themselves are used as biosensors in response to environmental conditions, contributes to the
analysis of animal behavior, and consequently also to the assessment of the internal environment of the production in hot weather.
Keywords: animal production, animal welfare, information technolog
Productive efficiency and density and viscosity studies of biodiesels from vegetable oil mixtures
Received: January 31st, 2021 ; Accepted: April 10th, 2021 ; Published: April 29th, 2021 ; Correspondence: [email protected] in Brazil the minimum content of biodiesel in mixtures is 11% and,
according to Brazilian laws, the goal is to reach 15% in volume in diesel fuel available for final
consumers by 2023. Therefore, studies about different matrices of biodiesel and distinct mixtures
are essential. The present work had two goals, the first one was to analyse physico-chemical
properties of 16 biofuels produced from soybean and cotton oils, using S10 diesel, in mixtures
B8, B10, B20 and B30. The second goal was to verify the vantages and disadvantages of biodiesel
production through prior mixing of the oils, before and after the transesterification process. All
biofuels produced presented results of specific mass values at 20 °C and kinematic viscosity at
40 °C within the limits established by ANP Resolution no 30/2016 and International Resolutions.
The soybean B20 biofuel showed the best overall results, with the second highest production
yield of 65.36%, the fifth lowest kinematic viscosity with 3.48 mm s
-1
. The mixture of soybean
and cotton oils before the transesterification process presented the highest production yield when
compared with the production from a single oil or biodiesel mixtures. The results found proved
to be satisfactory and corroborate to continue with the increase of biodiesel in the mixture with
diesel to B15 until 2023 and support the possibility of planning for a gradual increase of this
mixture in the following years
Neurology training around the world
Lancet Neurol. 2003 Sep;2(9):572-9.
Neurology training around the world.
Hooker J, Eccher M, Lakshminarayan K, Souza-Lima FC, Rejdak K, Kwiecinski H, Corea F, Lima JM.
The National Hospital for Neurology and Neurosurgery, Queen Square, WC1N 3BG, London, UK.
Comment in:
Lancet Neurol. 2003 Oct;2(10):594; discussion 594
Orthogonal cut of SPS-sintered composites with ferrous matrix and Fe Mo S particles: Numerical and experimental analysis
Metal-matrix composites with solid lubricant reinforcements may present a suitable alternative to improve the tribological behavior of sintered components. Besides the performance during the application, the presence of solid lubricants may also modify component manufacture, for example, during machining operations to achieve complex shapes not directly obtained from the sintering process. This work describes a numerical and experimental analysis on the orthogonal cut of metal-matrix composites composed of FeMoS particles embedded in an Astaloy 85 Mo (Höganäes AB) matrix. Specimens were prepared using the Spark-Plasma Sintering (SPS) technique, from mixtures containing powders of Astaloy 85 Mo steel and 2 wt% or 4 wt% of molybdenum disulfide (MoS2). An unreinforced Astaloy 85 Mo specimen (without MoS2) was also included in the analysis. Different microstructures were observed after SPS. The unreinforced specimen presented a ferrite-pearlite structure with a porosity level below 2% and the specimen sintered with 2 wt% of MoS2 presented iron sulfide particles dispersed in the steel matrix. The structure of the specimen sintered with 4 wt % was more complex, with two distinct phases dispersed in the Astaloy 85 Mo matrix. Experimental orthogonal cuts were conducted on the three specimens using a shaper machine tool equipped with a tungsten carbide (WCCo) cutting insert. Tests were recorded using a high-speed camera. The machined surfaces were later analyzed with an optical profilometer and in a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS). The chips were also characterized. The cutting operation was simulated by two-dimensional (2D) finite-element analysis. The meshes were prepared based on the specimen microstructures and considering the properties of the individual phases. Results have indicated significant differences in the cutting process. Observation of the chip surfaces indicates plastic deformation on the unreinforced specimen, in opposition to more uniform scratches on the composite surfaces, especially that of the specimen sintered with 4 wt % of MoS2
Antiretroviral therapy initiation alters the redox system of asymptomatic HIV-Infected individuals
Background. The combination antiretroviral therapy (cART) increases the oxidative stress in HIV-infected people, which in turn favors the onset and aggravation of non-AIDS comorbidities, a common situation affecting these individuals. We aimed to evaluate the influence of cART initiation on oxidative stress parameters. This is a longitudinal study including 30 asymptomatic patients divided according to their CD4+ T cell count (G1: 500 cell/mL) before (M0) and after (M1) cART initiation. We analyzed total antioxidant capacity (TAC), fat-soluble vitamins, malondialdehyde, 8-isoprostane, and DNA damage. Results. Results showed a decrease in TAC, retinol, \u3b1-tocopherol, and some carotenoids, in addition to a significant increase in DNA damage at M1. These changes were more evident in G2 subjects. Moreover, there was a significant 8-isoprostane increase at M1 in individuals belonging to G1. Conclusion. The results indicate that cART interfered in the redox system, mainly by reducing the antioxidant defenses. In addition, patients who had CD4+ T counts higher than 500 cells/mm3 showed more susceptibility to genotoxicity, while patients with less CD4+ T counts displayed more damage triggered by lipoperoxidation. Considering the early beginning of cART, its chronic use, and its capacity to alter the redox status, further long-term studies on larger cohorts are needed to define the best time to initiate therapy and to investigate new strategies to delay the development of non-AIDS diseases
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