Análise da influência de superfícies refletivas nas perdas de calor de sistema térmicos

The use of reflective surfaces functioning as thermal insulator has grown significantly over the years. Reflective thermal insulator are materials that have several characteristics such as low emissivity, low absorptivity and high reflectivity in the infrared spectrum. The use of these materials has grown a lot lately, since it contains several important radioactive properties that minimize the heat loss of thermal systems and cooling systems that are used to block the heat on the roof of buildings. A system made of three surfaces of 316 stainless steel mirror was built to analyze the influence of reflective surfaces as a way to reduce the heat loss and thereby conserve the energy of a thermal system. The system was analyzed both with and without the presence of vacuum, and then compared with a system that contained glass wool between the stainless steel mirror walls, since this isolator is considered resistive and also broadly used around the world in thermal systems. The reflectivity and emissivity of the surfaces used were also measured in this experiment. A type K thermocouple was fixed on the wall of the system to obtain the temperature of the stainless steel mirror surfaces and to analyze the thermal behavior of each configuration used. The results showed an efficiency of 13% when the reflective surfaces were used to minimize the heat loss of the thermal system. However, the system with vacuum had the best outcome, a 60% efficiency. Both of these were compared to the system made of glass wool as a thermal insulator

Estudo do aproveitamento do rejeito da mineração de esmeraldas na produção de refratários conformados isolantes

Emerald mining is an important area of the economy in Brazil, country which is in second place among the exporting nations of this gem. Due to the process of extraction, a great amount of reject is generated. Since there is no appropriate destination, the reject is abandoned around the mining industries, contributing to environment degradation. Nowadays, some of the most relevant things to an industry in general are: energy conservation, cost reduction, quality and productivity enhancement. The production of isolating, transformed refractory materials achieves the sustainability dimension when protection of the environment is incorporated to such process. This work investigates the use of emerald mining rejects in the ceramic body of refractory materials, aiming at obtaining a product whose characteristics are compatible with commercial products and, at the same time, allow the use of such rejects to solve the environmental issue caused by its disposal in nature. X-ray fluorescence analysis show that the emerald reject obtained after the flotation to extract molybdenum and mica has 70% of silica and alumina (SiO2+Al2O3) and 21% of a basic oxides and alkaline metals and earthy alkaline mixture (Na2O, K2O, CaO e MgO). Because of the significant amount of silica and alumina present in the reject, four refractory ceramic bodies were prepared. Samples with a rectangular shape and dimensions 100x50x10 mm were pressed in a steel mold at 27,5 MPa and sintered at 1200ºC for 40 min. under environment atmosphere in a resistive oven. The sintered samples were characterized in relation to the chemical composition (FRX), mineralogical composition (DRX), microstructure (MEV) and physical and mechanical properties. The results indicate that the mixture with 45% of reject, 45% of alumina and 10% of kaolin presents a refractory quality of 1420ºC, dimensional linear variation below 2.00%, apparent specific mass of 1,56 g/cm3 and porosity of 46,68%, which demonstrates the potential use of the reject as raw material for the industry of isolating transformed refractory materials

Modelos analíticos para rádio fontes extragalácticas

The great majority of analytical models for extragalactic radio sources suppose self-similarity and can be classified into three types: I, II and III. We have developed a model that represents a generalization of most models found in the literature and showed that these three types are particular cases. The model assumes that the area of the head of the jet varies with the jet size according to a power law and the jet luminosity is a function of time. As it is usually done, the basic hypothesis is that there is an equilibrium between the pressure exerted both by the head of the jet and the cocoon walls and the ram pressure of the ambient medium. The equilibrium equations and energy conservation equation allow us to express the size and width of the source and the pressure in the cocoon as a power law and find the respective exponents. All these assumptions can be used to calculate the evolution of the source size, width and radio luminosity. This can then be compared with the observed width-size relation for radio lobes and the power-size (P-D) diagram of both compact (GPS and CSS) and extended sources from the 3CR catalogue. In this work we introduce two important improvement as compared with a previous work: (1)We have put together a larger sample of both compact and extended radio sources

Criação da matéria em cosmologias com velocidade da luz variável e eletrônico não-linear

In this work we obtain the cosmological solutions and investigate the thermodynamics of matter creation in two diferent contexts. In the first we propose a cosmological model with a time varying speed of light c. We consider two diferent time dependence of c for a at Friedmann-Robertson- Walker (FRW) universe. We write the energy conservation law arising from Einstein equations and study how particles are created as c decreases with cosmic epoch. The variation of c is coupled to a cosmological Λ term and both singular and non-singular solutions are possible. We calculate the "adiabatic" particle creation rate and the total number of particles as a function of time and find the constrains imposed by the second law of thermodynamics upon the models. In the second scenario, we study the nonlinearity of the electrodynamics as a source of matter creation in the cosmological models with at FRW geometry. We write the energy conservation law arising from Einstein field equations with cosmological term Λ, solve the field equations and study how particles are created as the magnetic field B changes with cosmic epoch. We obtain solutions for the adiabatic particle creation rate, the total number of particles and the scale factor as a function of time in three cases: Λ = 0, Λ = constant and Λ α H2 (cosmological term proportional to the Hubble parameter). In all cases, the second law of thermodynamics demands that the universe is not contracting (H ≥ 0). The first two solutions are non-singular and exhibit in ationary periods. The third case studied allows an always in ationary universe for a suficiently large cosmological term

Modelos cosmológicos com velocidade da luz variável

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Efeitos da privação do sono em tarefas cognitivas

Learning and memory are important mechanism for species, since its allows to recognize conspecifics, routes and food place. Sleep is one of behaviors known by facilitate learning, it is a widespread phenomenon, present in most of vertebrates lives and highly investigated in many aspects. It is known that sleep deprivation modifies physiologic behavioral processes in animals, however, sleep function in organism is still debatable. Hypothesis range from energy conservation to memory consolidation, with different roles in animal’s evolution. The zebrafish (Danio rerio) emerg e in the last years as vertebrate model in genetics and developmental biology and quickly become popular in behavioral studies, as learning and memory. Despite the fact that zebrafish is a diurnal animal and have well characterized sleep behavior, zebrafish fish still has advantages due to its small size and low cost of maintenance, whichestablishes this species as interesting model for research on sleep. In this study we aimed to analyze the effects of partial and total sleep deprivation on learning acquisition, as well the concomitant administration of alcohol and melatonin. For this, the research was divided in three phases, each one with a different kind of conditioning: (1) object Recognition, (2) avoidance conditioning and (3) appetitive conditioning. The results showed the fish partially sleep deprived and totally sleep deprived + et hanol could perform the tasks just like the control group, however, fish totally sleep deprived and totally sleep deprived + melatonin showed impairments in attention and memory during the tests. Our results suggest that only one night of sleep deprivation is enough to harm the zebrafish performance in cognitive tasks. In addition, ethanol exposure on the night previously the test seems to suppress the negative effects of sleep deprivation, while the melatonin treatment seems not to be enough to promote sleep state, at least on the protocol applied here.

Efeitos da privação do sono em tarefas cognitivas

Learning and memory are important mechanism for species, since its allows to recognize conspecifics, routes and food place. Sleep is one of behaviors known by facilitate learning, it is a widespread phenomenon, present in most of vertebrates lives and highly investigated in many aspects. It is known that sleep deprivation modifies physiologic behavioral processes in animals, however, sleep function in organism is still debatable. Hypothesis range from energy conservation to memory consolidation, with different roles in animal’s evolution. The zebrafish (Danio rerio) emerg e in the last years as vertebrate model in genetics and developmental biology and quickly become popular in behavioral studies, as learning and memory. Despite the fact that zebrafish is a diurnal animal and have well characterized sleep behavior, zebrafish fish still has advantages due to its small size and low cost of maintenance, whichestablishes this species as interesting model for research on sleep. In this study we aimed to analyze the effects of partial and total sleep deprivation on learning acquisition, as well the concomitant administration of alcohol and melatonin. For this, the research was divided in three phases, each one with a different kind of conditioning: (1) object Recognition, (2) avoidance conditioning and (3) appetitive conditioning. The results showed the fish partially sleep deprived and totally sleep deprived + et hanol could perform the tasks just like the control group, however, fish totally sleep deprived and totally sleep deprived + melatonin showed impairments in attention and memory during the tests. Our results suggest that only one night of sleep deprivation is enough to harm the zebrafish performance in cognitive tasks. In addition, ethanol exposure on the night previously the test seems to suppress the negative effects of sleep deprivation, while the melatonin treatment seems not to be enough to promote sleep state, at least on the protocol applied here.

O uso da abordagem CTSA para o ensino de energia tendo o desenvolvimento sustentável como eixo temático

In recent decades, humanity has become increasingly concerned with environmental problems. Proofs of this are increasing initiatives in civil society organizations, private institutions and government actions, either local, state or national actions to promote environmental protection. The goal of this research is to contribute to the formation of citizens more aware of their responsibilities to sustainable development issues, simultaneously to their learning of physics in the secondary school. Thus, we have designed a research project that aims to evaluate the effectiveness of the adoption of the concept of sustainable development as a central theme in physics classes in high school. From this goal, we designed, implemented and evaluate lesson plans that aim not only to construct and apply the concept of energy, but also to understand their transformations and conservation law, as well as their processes of production, distribution and consume in the context of physical laws in which it is involved. Then, it was deliberately provided to students, during classes, to read, interpret and produce texts, by this way being able to think and start to have a critical view of the world around him, as well as absorb the energy concept and understand his occurrence in phenomena of nature and in technologies. The approach used for this was that constraining science, technology, society and environment - STSE. This teaching methodology has been applied in the IFRN Ipanguaçu campus, for students of two classes of first year of high school integrated course in agroecology and in technical computing. The survey results show the effectiveness of both methods with respect to the viewpoints of students in relation to the guidelines of sustainable development and the learning of physics content proposed. It is hoped with this dissertation to contribute to the formation of future men and women as citizens environmentally friendly, but also as a source of inspiration for teachers who wish to foster in its students such a critical position about civic education, from their classes

Precificação de energia eólica offshore no Brasil

Offshore wind power emits low amounts of gases, is renewable and has better performance than onshore due to its greater stability and higher wind power density, less visual and noise impact, among others. Brazil has a high capacity of generation, but has not yet developed any offshore projects. High costs are a strong impediment. This study is an effort towards pricing offshore resources through Livelized Cost of Energy - LCOE, which represents the minimum return to cover the costs of development, production and maintenance of a wind project. Initially LCOE was calculated for all Brazilian onshore wind farms listed at Bloomberg New Energy Finance R○, accounting for 71 farms. Then hypothetical offshore wind farms were created from the onshore farms, tripling the cost of generation, which is consistent with the literature, and estimating the offshore energy for two locations off the Brazilian coast using satellite data extracted from National Oceanic and Atmospheric Administration. The results demonstrate that offshore resources have the potential to significantly reduce the energy price due to the better performance of the wind at sea

Parâmetros citogenéticos de espécies comerciais de carangidae (perciformes), com vistas a sua empregabilidade na conservação biológica e piscicultura marinha

Worldwide, families Carangidae and Rachycentridae represent one of the groups most important commercial fish, used for food, and great potential for marine aquaculture. However, the genetic bases that can underpin the future cultivation of these species, cytogenetic between these aspects are very weak. The chromosomal patterns have provided basic data for the exploration of biotechnological processes aimed at handling chromosomal genetic improvement, such as induction of polyploidy, androgenesis and ginogenesis, as well as obtaining monosex stocks and interspecific hybridizations. This paper presents a comprehensive cytogenetic survey in 10 species, seven of the family Carangidae and the monotypic family Rachycentridae. Classical cytogenetic analysis and in situ mapping of multigene sequences were employed, and additionally for the genus Selene and morphotypes of Caranx lugubris, comparisons were made using geometric morphometrics. In general, conservative species exhibit a marked chromosome number (2n=48). Although present in large part, different karyotypic form, retain many characteristics typical of chromosomal Order Perciformes, the high number of elements monobrachyal, Ag-NORs/18S rDNA sites and heterochromatin simply reduced, preferably centromeric. The main mechanisms involved in karyotypic diversification are the pericentric inversions, with secondary action of centric fusions. In addition to physical mapping and chromosome detail for the species are presented and discussed patterns of intra-and interspecific diversity, cytotaxonomic markers. This data set provides a better understanding of these patterns caryoevolutyonary groups and conditions for the development of protocols based on Biotechnology for chromosomal manipulation Atlantic these species

Estudo da moagem de alta energia e sinterização de pós compósitos W-Cu

The Tungsten/copper composites are commonly used for electrical and thermal objectives like heat sinks and lectrical conductors, propitiating an excellent thermal and electrical conductivity. These properties are dependents of the composition, crystallite size and production process. The high energy milling of the powder of W-Cu produces an dispersion high and homogenization levels with crystallite size of W very small in the ductile Cu phase. This work discusses the effect of the HEM in preparation of the W-25Cu composite powders. Three techniques of powder preparation were utilized: milling the dry with powder of thick Cu, milling the dry with powder of fine Cu and milling the wet with powder of thick Cu. The form, size and composition of the particles of the powders milled were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) was used to analyse the phases, lattice parameters, size and microstrain of the crystallite. The analyse of the crystalline structure of the W-25Cu powders milled made by Rietveld Method suggests the partial solid solubility of the constituent elements of the Cu in lattice of the W. This analyse shows too that the HEM produces the reduction high on the crystallite size and the increase in the lattice strain of both phases, this is more intense in the phase W

Efeito da moagem de alta energia na microestrutura e nas propriedades magnéticas do compósito wc-10%p.Co

This work a studied the high energy milling effect in microstructure and magnetic properties of the WC-10wt.%Co composite. The composite powders were prepared by mechanical mixed and milled at 2 hours, 100 hours, 200 hours and 300 hours in planetary milling. After this process the composite were compacted in stainless steel die with cylindrical county of 10 mm of diameter, at pressure 200 Mpa and sintered in a resistive furnace in argon atmosphere at 1400 oC for 5 min. The sintered composite were cutted, inlaid, sandpapered, and polished. The microestrutural parameters of the composite was analyzed by X-ray diffraction, scanning electronic microscopy, optical microscopy, hardness, magnetic propriety and Rietveld method analyze. The results shows, with milling time increase the particle size decrease, it possibility minor temperature of sintering. The increase of milling time caused allotropic transformation in cobalt phase and cold welding between particles. The cold welding caused the formation of the particle composite. The X-ray diffraction pattern of composite powders shows the WC peaks intensity decrease with the milling time increase. The X-ray diffraction pattern of the composite sintered samples shows the other phases. The magnetic measurements detected a significant increase in the coercitive field and a decrease in the saturation magnetization with milling time increase. The increase coercitive field it was also verified with decrease grain size with milling time increase. For the composite powders the increase coercitive field it was verified with particle size reduction and saturation magnetization variation is relate with the variation of free cobalt. The Rietveld method analyze shows at milling time increase the mean crystalline size of WC, and Co-cfc phases in composite sintered sample are higher than in composite powders. The mean crystallite size of Co-hc phase in composite powders is higher than in composite sintered sample. The mean lattice strains of WC, Co-hc and Co-cfc phases in composite powders are higher than in composite sintered samples. The cells parameters of the composite powder decrease at milling time increase this effect came from the particle size reduction at milling time increase. In sintered composite the cells parameters is constant with milling time increase

Caracterização de compósitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase líquida

In this work, was studied the formation of a composite of the refractory metal niobium with copper, through the process of high-energy milling and liquid phase sintering. The HEM can be used to synthesize composite powders with high homogeneity and fine size particle distribution. It may also produce the solid solubility in immiscible systems such as Nb-Cu, or extend the solubility of systems with limited solubility. Therefore, in the immiscible system Cu-Nb, the high-energy milling was successfully used to obtain the composite powder particles. Initially, the formation of composite particles during the HEM and the effect of preparation technique on the microstructure of the material was evaluated. Four loads of Nb and Cu powders containing 20%wt Cu were synthesized by MAE in a planetary type ball mill under different periods of grinding. The influence of grinding time on the metal particles is evaluated during the process by the withdrawal of samples at intermediate times of milling. After compaction under different forces, the samples were sintered in a vacuum furnace. The liquid phase sintering of these samples prepared by HEM produced a homogeneous and fine grained. The composite particles forming the sintered samples are the addition of a hard phase (Nb) with a high melting point, and a ductile phase (Cu) with low melting point and high thermal and electrical conductivities. Based on these properties, the Nb-Cu system is a potential material for many applications, such as electrical contacts, welding electrodes, coils for generating high magnetic fields, heat sinks and microwave absorbers, which are coupled to electronic devices. The characterization techniques used in this study, were laser granulometry, used to evaluate the homogeneity and particle size, and the X-ray diffraction, in the phase identification and to analyze the crystalline structure of the powders during milling. The morphology and dispersion of the phases in the composite powder particles, as well the microstructures of the sintered samples, were observed by scanning electron microscopy (SEM). Subsequently, the sintered samples are evaluated for density and densification. And finally, they were characterized by techniques of measuring the electrical conductivity and microhardness, whose properties are analyzed as a function of the parameters for obtaining the composite

Síntese e caracterização de ferrita ni-zn pelo método dos precursores poliméricos calcinada por energia de microondas

Magnetic ceramics have been widely investigated, especially with respect to intrinsic and extrinsic characteristics of these materials. Among the magnetic ceramic materials of technological interest, there are the ferrites. On the other hand, the thermal treatment of ceramic materials by microwave energy has offered various advantages such as: optimization of production processes, high heat control, low consumption of time and energy among others. In this work were synthesized powders of Ni-Zn ferrite with compositions Ni1- xZnxFe2O4 (0.25 ≤ x ≤ 0.75 mols) by the polymeric precursor route in two heat treatment conditions, conventional oven and microwave energy at 500, 650, 800 and 950°C and its structural, and morphological imaging. The materials were characterized by thermal analysis (TG/ DSC), X-ray diffraction (XRD), absorption spectroscopy in the infrared (FTIR), scanning electron microscopy (SEM), X-ray spectroscopy and energy dispersive (EDS) and vibrating sample magnetometry (VSM). The results of X-ray diffraction confirmed the formation of ferrite with spinel-type cubic structure. The extrinsic characteristics of the powders obtained by microwave calcination and influence significantly the magnetic behavior of ferrites, showing particles ferrimagnéticas characterized as soft magnetic materials (soft), is of great technological interest. The results obtained led the potential application of microwave energy for calcining powders of Ni-Zn ferrite

Diversidade de invertebrados em cavernas calcárias do oeste potiguar : subsídios para a determinação de áreas prioritárias para conservação.

It is estimated that the Brazilian karst areas sum about 200.000 km2. The caves, one of the main components of karst, are important windows into the biological studies on hypogean environments. In Rio Grande do Norte are known 563 caves, and 476 of them are in the municipalities of Baraúna, Felipe Guerra, Governador Dix-Sept Rosado, Apodi and Mossoró, the Western region of the State. However, like in the rest of the country, the cave fauna of the State is still poorly understood. This study used data from invertebrates harvested in 47 caves and aimed to analyze the effect of environmental change between the dry and rainy seasons in the communities of cave invertebrates, characterize these communities and evaluate the relationships between morphological and biotic variables of the caves and surroundings, and to define priority areas for conservation of cave environments of the study area from biotic parameters. Strong effects were found in the community structure of cave invertebrates due environmental changes between seasons, with values of total richness, abundance, diversity and ecological complexity significantly higher in the rainy season. It was possible to assess how the morphology of the cave and the external environment variables affect the biotic system, so that the variety of resources, forest cover in the vicinity, the area of the cave and its entrance were the variables that best explained the structure communities of cave invertebrates in the region. High values of total richness of invertebrates (36,62 ± 14,04 spp / cave) and troglomorphic species (61 species, mean 1,77 ± 2,34 spp / cave) were found and, given the biological relevance in the context of the area national and the imminent anthropogenic pressures existing, we defined four priority areas for actions aiming cave biodiversity conservation in the region.