Efeitos de interface em bicamadas magnéticas acopladas

We have developed a theoretical study of magnetic bilayers composed by a ferromagnetic film grown in direct contact on an antiferromagnetic one. We have investigated the interface effects in this systems due to the interfilms coupling. We describe the interface effects by a Heisenberg like coupling with an additional unidirectional anisotropy. In the first approach we assume that the magnetic layers are thick enough to be described by the bulk parameters and they are coupled through the interaction between the magnetic moments located at the interface. We use this approach to calculate the modified dynamical response of each material. We use the magnetic permeability of the layers (with corrections introduced by interface interactions) to obtain a correlation between the interface characteristics and the physical behavior of the magnetic excitations propagating in the system. In the second model, we calculated an effective susceptibility of the system considering a nearly microscopical approach. The dynamic response obtained by this approach was used to study the modifications in the spectrum of the polaritons and its consequences on the attenuated total reflection (ATR). In addition, we have calculated the oblique reflectivity. We compare our result with those obtained for the dispersion relation of the magnetostatic modes in these systems

Excitações em cristais fotônicos unidimensionais

In this work, we present a theoretical study of the propagation of electromagnetic waves in multilayer structures called Photonic Crystals. For this purpose, we investigate the phonon-polariton band gaps in periodic and quasi-periodic (Fibonacci-type) multilayers made up of both positive and negative refractive index materials in the terahertz (THz) region. The behavior of the polaritonic band gaps as a function of the multilayer period is investigated systematically. We use a theoretical model based on the formalism of transfer matrix in order to simplify the algebra involved in obtaining the dispersion relation of phonon-polaritons (bulk and surface modes). We also present a quantitative analysis of the results, pointing out the distribution of the allowed polaritonic bandwidths for high Fibonacci generations, which gives good insight about their localization and power laws. We calculate the emittance spectrum of the electromagnetic radiation, in THZ frequency, normally and obliquely incident (s and p polarized modes) on a one-dimensional multilayer structure composed of positive and negative refractive index materials organized periodically and quasi-periodically. We model the negative refractive index material by a effective medium whose electric permittivity is characterized by a phonon-polariton frequency dependent dielectric function, while for the magnetic permeability we have a Drude like frequency-dependent function. Similarity to the one-dimensional photonic crystal, this layered effective medium, called polaritonic Crystals, allow us the control of the electromagnetic propagation, generating regions named polaritonic bandgap. The emittance spectra are determined by means of a well known theoretical model based on Kirchoff s second law, together with a transfer matrix formalism. Our results shows that the omnidirectional band gaps will appear in the THz regime, in a well defined interval, that are independent of polarization in periodic case as well as in quasiperiodic case

Composição ictiofaunística e estratégias reprodutivas de quatro espécies de peixes nativos da Bacia Hidrográfica Piranhas - Assu, Rio Grande do Norte

This study focuses on the fish fauna composition and reproductive strategies of four native fish species in relation to environmental variables of the Piranhas-Assu hydrographic basin of the Caatinga biome, Rio Grande do Norte, Brazil. Fish and environmental data were collected monthly during the period September 2008 to February 2010, in the Marechal Dutra reservoir and River Acauã a tributary of Piranhas- Assu. The fish were measured, weighed and dissected, and the gonads were removed, weighed and examined macroscopically for identification and determination of gonad maturation stages. The results of this work generated seven articles. The first article is about the fish fauna composition of the Piranhas-Assu hydrographic basin, Rio Grande do Norte. The 602 fish samples captured were distributed in four orders (Characiformes, Perciformes, Siluriformes and Synbranchiformes), 11 families and 22 species, of which 17 are endemic to the Caatinga ecoregion. The order Characiformes was more representative followed by Perciformes, Siluriformes and Synbranchiformes. The second article is about the length-weight relationship and growth of seven native fish species Crenicichla menezesi, Cichlasoma orientale, Triportheus angulatus, Psectrogaster rhomboides, Pimelodella gracilis, Prochilodus brevis and Leporinus piau from a semiarid Brazilian reservoir. The third article is about the reproductive aspects of Crenicichla menezesi. Males were larger, heavier and with a slight predominance as compared to females. Four stages of gonadal development were characterized, being immature, maturing, mature and spent. The females reached sexual maturity earlier than males, with an average fecundity of 398 oocytes per batch. The spawning was partial with a long reproductive period. The fourth article deals with the reproductive strategy of Leporinus piau a neotropical freshwater fish in semi-arid region of Brazil. The population of L. piau (n = 211) showed a slight predominance of males (55%), with larger and heavier females. The males matured earlier than the females. This species presented total spawning, with an average fecundity of 55,000 mature oocytes. Rainfall and concentration of dissolved oxygen acted as influential factors during the spawning season. L. piau shows a seasonal reproductive strategy. The fifth article is related to the morphometric-meristic characteristics and reproductive aspects of freshwater sardine, Triportheus angulatus from River Acauã of the Caatinga biome. There was a predominance of larger females, reaching first maturation before males. There was total spawning during the rainy period of the region. The sixth article reports on the reproductive strategy of Psectrogaster rhomboides. The sex ratio was 1M: 1F, with negative allometric growth. Males reached sexual maturity earlier than females Females and males showed four stages of gonadal development and spawned during the rainy season. The fecundity was low and this species presented total spawning. The seventh article reports on the dynamics of territorial behavior of Crenicichla menezesi. Ten agonistic behaviors displayed by the males were observed: frontal and lateral threat, chasing, circular chasing, perpendicular, lateral and mouth attacks, escape, parallel positioning and stationary. The formation of four social groups was observed among males: without interaction; interaction with submission and escape; with frontal and lateral agonistic interactions. In social interactions between males and females, it was observed that the larger males interacted more among themselves and with the larger females. The large male established its territory and the two small males along with the small female were excluded from the other groups. These studies clarified the fish fauna composition and reproductive strategies of four native species Crenicichla menezesi, Leporinus piau, Triportheus angulatus and Psectrogaster rhomboides of the Piranhas- Assu hydrographic basin of the Caatinga biome, Rio Grande do Norte, Brazil.

Caracterização comportamental e avaliação da qualidade de leite em caprinos da raça saanen no semiárido nordestino

Goats are social animals which groups are organized from dominance hierarchies, established by agonistic behaviors. The quality and productivity of the goat s milk can be influenced by the dominance hierarchy. In this context, the objectives of our work were describe the social and food behavior of Saanen goats in a semi-extensive production system; characterize the social organization from the assessment of dominance hierarchies in two seasonal periods and correlate the physicochemical quality of the goats milk according hierarchical position. The experiment was conducted in the EMPARN s experimental station, located in the district of Cruzeta/RN. We utilized 17 multiparous goats of the Saanen race, with different age and weight. The observations were performed in precipitation and drought phases. The scan method recorded the trough permanence and agonistic interactions by method "all occurrences" in the pasture the alimentary behaviors of eat, ruminate on foot, ruminate lying, leisure on foot, leisure lying and walk, by the focal animal sampling method. The goats milk was submitted to analyzes of: density, protein, fat, lactose, CSS and total solids. The animals spend most of the time feeding themselves, and the activities that demand greater energy expenditure are done in the morning. The animals changed the hierarchical structure during the seasonal periods because of the withdrawal of some individuals of the group, having more aggressive behavior in the rainy season. The dominant animal the lowet production, the more CSS and the lesser fat, the goat in the middle of the hierarchy was the one that obtained the best production and quality. We conclude that the Saanen goats adapt to the environment and the conditions of the group to ensure better survival and its production is influenced by the internal dynamics of the group

Variações horárias na entrada e saída dos golfinhos-rotadores e sua relação com fatores ambientais, na Baía dos Golfinhos em Fernando de Noronha PE

The dolphins are found in all world s marine environments, except for poles. On Brazil, the major concentration of this animals is on Fernando de Noronha Islands, wich have a tropical climate with two well-defined rainfall seasons: dry and rainy season. The Baía dos Golfinhos, wich is the most crowded piece of dolphins on the archipelago. These research looks for to characterize the circadian rhythms of the spinner dolphin behavior, Stenella longirostris, on the Baía dos Golfinhos occupation, at the Fernando de Noronha islands, Brazil s northeast, according to the fluctuations of environment that they all are inserted. The research was realized daily between 1991 January and 2009 December, with observations from a fixed point up to Mirante dos Golfinhos, located on Baía dos Golfinhos. The data was examined with the PASW Statistics 18 program, up to nonparametric tests, being analyzed on the incoming and out coming time of the spinner dolphins and the relationship with moon phases, the wind incidence, and the rainfall season, the dolphins were inserted. The spinner dolphins diurnal rhythms are influenced by moon phases, the spinner dolphins arrival at Baía dos Golfinhos earlier when it s full moon because of the high luminosity at night cause a bigger food efficiency for these animals. The outgoing time of spinner dolphins didn t show statistic difference between moon phases, despite follows the same pattern for the incoming time. When the spinner dolphins are submitted to bigger wind incidence conditions around the archipelago, the dolphins come early to the Baía dos Golfinhos, since that one is protected from wind that reaches Fernando de Noronha, the spinner dolphins tends to arrive later and leave earlier of the bay because the rain may cause adverse conditions for your rest.

Estudo das características magnéticas e absorvedoras das ferritas de nizn, niznmn, mnzn, nimg, nicuzn e nicuznmg obtidas via método do citrato precursor

Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350°C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100ºC/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500°C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100ºC/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100ºC/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation.

Qualidade de água como tema para a socialização do conhecimento científico em região semi-árida brasileira

During the dry and rainy periods, in the Piranhas-Assu river hydrographic basin, variations in bacterioplankton and trophic state indexes were studied in the lotic and lentic environments. The means of total bacterial density wavered in the order of 107 organisms. mL-1 and they were higher in the rainy period. Cocci bacteria were numerically predominant in all sampling points, influencing the total abundance of bacterioplankton. Total bacterial biomass varied from 659 to 1997,3 µgC.L-1 due to the high values of filaments cellular volume. Total phosphorus amounted 108 µg.L-1 and it had a positive correlation with chlorophyll a (r = 0,94; p < 0,05) during dry period, when these variables presented higher concentrations. There wasn t a high spatial variation. The low transparency of water and the phosphorus and chlorophyll concentrations indicated eutrophic or hipereutrophic levels in studied points of reservoir. These variables, associated with high density and biomass values found, alert to the necessity of a constant monitoring of the semi-arid aquatic ecosystems, where the quality of water is affected by dry occurrence

Culicídeos vetores em uma unidade de conservação da caatinga na região do seridó no Rio Grande do Norte aspectos da transmissão de doenças

The scarcity of occurrence records of culicid species, transmitting insects of etiologic agents for arboviruses, protozoan diseases and philarioses, and lack of information about their interactions with the forest environment make the Caatinga one of the most unknown biomes in Brazil. The aim of this study was to identify culicid species in a conservation unit located in a preserved area of the Caatinga and the possible associations with local abiotic factors, as well as characterize the natural and artificial ecotopes present in the Caatinga of Rio Grande do Norte state. The Ecological Station of Serido (ESEC-Seridó) is a Caatinga Conservation Unit located in a rural area of Rio Grande do Norte. The hot and dry climate of the Caatinga, along with a short rainy season, favor the adaptation and resistance of plants, resulting in completely distinct landscapes over the course of the year. The study took place over the course of one year, with monthly collections between 10h-12h, 14h-16h and 18h-20h. Adult mosquitoes were collected in a forest area using a manual suction trap with human bait as attractant at the three times and a Shannon trap for night collections. During the rainy season ovitraps were randomly distributed at different sites. The different capture sites were observed and photographed. Immature and adult insects captured were taken to the laboratory for identification. Of the 5081 insects collected in human-bait and Shannon traps, 75% were Mansonia wilsoni. In addition, Aedeomyia, Aedes, Anopheles, Coquillettidia, Culex, Haemagogus, Mansonia and Psorophora were identified. Of the 92 Haemagogus eggs found, 71 were collected on the banks of a reservoir. Mosquito larvae were found and photographed in an artificial breeding site of a neighboring rural area. Humidity had the greatest influence on culicid density in the Caatinga. Rain was important in the appearance of Haemagogus, Anopheles, Aedes and Psorophora. Temperature had a negative influence on Anopheles triannulatus. The occurence of important vector species of diseases in a little known preserved area of the Caatinga as well as environmental and sociocultural questions are factors that favor the emergence of transmitting insects, making these areas potential subject to the resurgence of diseases

Experiências de inverno no seridó potiguar

The knowledge known as "winter experiences" has been developed for centuries among country people in the Brazilian Northeast hinterlands. It consists in the systematic observation of the nature to forecast and protect people against the effects of droughts. This knowledge is transmitted orally through generations. These experiences are guided by the observation of the behavior of fauna, flora, stars, the weather in the holy days and other very specific aspects of the lives of country people. Almost all country people living in the rural area know at least one experience, but the Prophets of Rain are known as the communicators of winter prophecies formulated from the observation of the experiences. The country person is identified as a Prophet of Rain because of his close relationship with nature and his ability to forecast. No matter if the prophecies are always right, he possesses a vital social role, as his practices contribute to prevent, ease and encourage other people. The main aim of this work is to analyze the role of the winter experiences for the country people in the Seridó Potiguar. In this sense, we sought to understand to what extent this knowledge still orients the productive practices of farmers living in this region and identify which factors instigate the observation of winter experiences nowadays. 241 questionnaires were applied to farmers in the rural cities of Acari, Caicó, Parelhas and Lagoa Nova and interviews were conducted with 15 Prophets in the Seridó. The methodological framework of this work is the analysis of content proposed by Bardin (2010). In this study area, the experiences exert influence and relevance to the country people in the Seridó, because they consider them as a way to ease their anguishes face the possible drought in the region. The major role of the Prophet is to feed the hope of country people for better days, rather than contribute for the organization of the productive activities. Among the interviewed people, the forecast from the observation of winter experiences have greater credibility than the meteorological and disseminated by media. The Prophets of Rain base their prophecies on the set of natural elements present in the environment. Many factors stimulate the winter experiences by the Prophets nowadays, as cultural transmission, age, relationship with nature, level of education, faith, among others, but specially the productive activities (agriculture and cattle raising) and the droughts. The winter means abundance and happiness in this region and the experience is one of the ways that people find to minimize the anxiety and, according to their possibilities, to prepare for a year of droughts or for winter

Comunidade fitoplanctônica como discriminador ambiental em açude eutrófico tropical semiárido (Barragem Armando Ribeiro Gonçalves, RN) e divulgação científica para reflexão social

The knowledge of the phytoplankton community, as an integral and dynamic processes of eutrophication, provides information essential for proper management and handling. A growing problem of cyanobacteria in reservoirs around the world as a result of artificial eutrophication processes, generating a particular concern, because some species produce cyanotoxins, which can cause adverse effects on human health. The present work aims to characterize the spatial and temporal dynamics of phytoplankton, assessing their potential as ecological indicator of water quality in reservoirs semiarid region. The samples of water were collected monthly between 2009 and 2011, at three points along the dam Armando Ribeiro Gonçalves / RN. In each sample were measured physico - chemical analysis of water and biological components. We conducted a scientific dissemination activity, with distribution and reading primer on eutrophication, informative talk about water quality, questionnaires and performing a play in a public school in the city of Itajá / RN. The reservoir was considered eutrophic in three points, taking into account the values of chlorophyll -a and phosphorus, adopted to characterize eutrophic environments of semi-arid areas. High density of cyanobacteria, with a maximum value of 2.227.862 cél.ml- 1 and minimum of 43.456 cél.ml- 1 was recorded in lentic and semilêntico points throughout the study, exceeding the levels of drinking water (20.000 cél.ml- 1) established in 2.914/2011 Ordinance of the Ministry of Health of Brazil. All samples contained microcystin, and 44 % had values superiores1μg L- 1. The thermal pattern of the water column showed micro stratifications with differences of less than 1 ° C from five feet deep. The distribution pattern was the type profile clinogrado with oxygen deficit in the bottom of the reservoir. Oxiclina from 10 meters depth was observed during the rainy season (May-June) in the two years of study. The phytoplankton community was represented by 10 functional groups: S1, M, H1, Lo, P, F, Sn, P, W2 and R. The assessment of the ecological status of the system by the index Q showed poor water quality. The results of the study show that the vertical variations were less pronounced than the seasonal variations of cyanobacteria and phytoplankton community in general in the reservoir. The presence of cyanotoxins confirms the need for the monitoring of water quality and measures to reduce eutrophication in water supply reservoirs semiarid RN and demonstrates the challenge for water managers and health authorities to ensure water quality and consequently minimize risks to human health. Compared to the lecture, the primer was considered more efficient in sensitizing the participants, featuring a dynamic practice, differentiated learning, create opportunities for students to rethink attitudes of respect and care for the environment, and shall have the opportunity to learn the subject content from your reality and living environment. The knowledge generated from the activity of scientific were seen as essential for raising awareness of some of the region`s environmental problems , such as eutrophication

Biomonitoramento da qualidade da água e ações em educação ambiental em dois açudes da bacia hidrográfica Apodi-Mossoró, RN

Water scarcity is a reality for the inhabitants of the Brazilian semiarid region. The problem, in quantitative terms , is caused due to local climatic conditions due mostly to a water deficit. Qualitatively, results of multiple uses and resulting contamination by human activities. Eutrophication is presented as a threat to the sustainable use of water resources, in order to favor the predominance of dense populations of cyanobacteria, which can be potentially harmful to human health. The aim of this study is to understand the population dynamics of phytoplankton and cyanobacteria to assess water quality of reservoirs Santa Cruz do Apodi and Pau dos Ferros belonging to bacia Apodi Mossoró-RN . Water samples were collected monthly between October 2011 and May 2012 in reservoirs Santa Cruz do Apodi and Pau dos Ferros, in this latter , in Jan/12 we performed a diel profile . The abiotic variables obtained in the field and in the laboratory were: water temperature , dissolved oxygen , pH , turbidity , transparency , total nitrogen and total phosphorus . Phytoplankton samples were collected with a plankton net and bottle of Van dorn . Were performed : identification , quantification , calculation of biovolume , classification into functional groups and index calculation phytoplankton assembly ( Q ) , cyanotoxins were quantified by ELISA . Statistical analyzes supported the evaluation of the dynamics between biotic and abiotic factors. A questionnaire was conducted to examine the conceptions of the population, education professionals and students. The reservoir of Pau dos Ferros, shallow , turbid and eutrophic showed dominance of the functional group SN throughout the sample period . The phytoplankton biomass ranged from 20 to 70 mm ³ . L - 1, the lowest values coincided with the increase of the mixing zone and transparency, which contributed to the occurrence of a change in species composition phytoplankton . The application of the index Q proved relevant, the reservoir of Pau dos Ferros , depending on the species present , was classified ecologically as bad for almost the entire sample period . The reservoir Santa Cruz do Apodi showed low biomass ( 0.04 and 4.31 mm ³ . L - 1 ) and greater diversity in the phytoplankton composition . According to the index assembly (Q ), it showed moderate condition during most of the period influenced by different functional groups of typical meso- eutrophic environment (K S0, H1, C, F , J , E, D and N) . Associations of diatoms and green algae D and X1 succeeded populations of cyanobacteria in periods marked by greater instability in the system , caused by wind or rain. In summary , the occurrence of drought has a direct influence on the hydrological conditions of the reservoirs , in general, these events, reducing the reservoir level is directly related to decreased water quality and increased density of phytoplankton occurring predominance of cyanobacteria , the index Q reflected well to changes in phytoplankton composition , being a good indicator for biomonitoring of reservoirs in this study and survey of previous conceptions showed the need to work on environmental awareness for the preservation of water resources by conducting workshops for Environmental Education

Espectros fractais em sistemas nanoestruturados e cristais fotônicos

The study of the elementary excitations such as photons, phonons, plasmons, polaritons, polarons, excitons and magnons, in crystalline solids and nanostructures systems are nowdays important active field for research works in solid state physics as well as in statistical physics. With this aim in mind, this work has two distinct parts. In the first one, we investigate the propagation of excitons polaritons in nanostructured periodic and quasiperiodic multilayers, from the description of the behavior for bulk and surface modes in their individual constituents. Through analytical, as well as computational numerical calculation, we obtain the spectra for both surface and bulk exciton-polaritons modes in the superstructures. Besides, we investigate also how the quasiperiodicity modifies the band structure related to the periodic case, stressing their amazing self-similar behavior leaving to their fractal/multifractal aspects. Afterwards, we present our results related to the so-called photonic crystals, the eletromagnetic analogue of the electronic crystalline structure. We consider periodic and quasiperiodic structures, in which one of their component presents a negative refractive index. This unusual optic characteristic is obtained when the electric permissivity and the magnetic permeability µ are both negatives for the same range of angular frequency ω of the incident wave. The given curves show how the transmission of the photon waves is modified, with a striking self-similar profile. Moreover, we analyze the modification of the usual Planck´s thermal spectrum when we use a quasiperiodic fotonic superlattice as a filter.

Análise do Efeito Goos-Hanchen e Não-reciprocidade do fluxo de potência em antiferromagnéticos

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Propriedades estruturais e optoeletrônicas dos compostos SrSnO3, SrxBa1-xSnO3 e BaSnO3

In this work we present a study for the structural, electronic and optical properties, at ambient conditions of SrSnO3, SrxBa1

Monitoramento da qualidade das ásguas de chuvas conforme a atuação dos sistemas sinóticos na cidade de Natal/RN

Acid rain is a major assault on the environment, a consequence of burning fossil fuels and industrial pollutants the basis of sulfur dioxide released into the atmosphere. The objective of this research was to monitor and analyze changes in water quality of rain in the city of Natal, seeking to investigate the influence of quality on a local, regional and global, in addition to possible effects of this quality in the local landscape. Data collection was performed from December 2005 to December 2007. We used techniques of nefanálise in identifying systems sinóticos, field research in the search for possible effects of acid rain on the landscape, and collect and analyze data of precipitation and its degree of acidity. Used descriptive statistics (standard deviation and coefficient of variation) used to monitor the behavior of chemical precipitation, and monitoring of errors in measurements of pH, level of confidence, Normalized distribution of Gauss, confidence intervals, analysis of variance ANOVA were also used. Main results presented as a variation of pH between 5,021 and 6,836, with an average standard deviation of 5,958 and 0,402, showing that the average may represent the sample. Thus, we can infer that, according to the CONAMA Resolution 357 (the index for fresh water acidity should be between 6.0 and 9.0), the precipitation of Natal / RN is slightly acidic. It appears that the intertropical convergence zone figures showed the most acidic among the systems analyzed sinóticos, taking its average value of pH of 5,617, which means an acid value now, with a standard deviation of 0,235 and the coefficient of variation of 4,183% which shows that the average may represent the sample. Already in field research and found several places that suffer strongly the action of acid rain. However, the results are original and need further investigation, including the use of new methodologies