Scattered Light in a Flood-plain Lake of Central Amazônia()

The light intensity below the surface of Lago Castanho was recorded at 10 minute intervals and compared to the total light intensity above the water surface. Scattered light of the lake water was rather constant and it was found to be sufficiently high to support the growth of photoautotrophic organisms in the near-surface layer. Below the floating plant communities scattered light was extremely low in intensity.Foram medidas, cada 10 minutos, a luz total incidindo sobre a superfície do Lago do Castanho e a luz difusa abaixo da superfície do lago. Verificou-se, nas camadas superficiais da água do lago, intensidade luminosa suficiente para assegurar o desenvolvimento de organismos foto-autotróficos, com variações mínimas durante o dia. Embaixo das massas de capim flutuante, a intensidade da luz difusa era extremamente baixa, máximo: 20 Lux

Light Environment in Tropical Rain Forest of Central Amazonia

Light intensity above the groundstoreys (120 cm) and inbetween the ground strata of a Riverine forest, a Carrasco forest and a terra firme Rain forest was recorded through two day periods of time in the rain season (April/May) and the dry season (August) of 1969. Measurements were undertaken between 6 a.m. and 18 p.m. in minute by minute intervals (51.840 readings). The relative frequency of light intensity was computed for seven intensity classes and three periods of time per day. The spectral composition of light was determined as relative frequency of light intensities for five filter ranges of wavelengths, seven intensity classes and three periods of time per day. The riverine forest (best light conditions for the undertorey plant communities) and the terra firme Rain forest (worst conditions) developed extremely oposite positions with respect to forest light climate, while the Carrasco forest showed up with a somewhat intermediate character, but with a strong shift to terra firme Rain forest conditions. The spectral composition of light received by the ground strata of all three forest stands was as follows1) light intensities peaked in the RG 630 filter range of wavelenths (5.920 ​​​Ǻ - 7.500 ​​​Ǻ), 2) a secondary intensity peak covered the VG 9 filter (4.420 ​​​Ǻ - 6.440 ​​​Ǻ) and 3) a less important secondary peak matched the BG 12 filter band (3.500 ​​​Ǻ - 5.150 ​​​Ǻ). Inbetween the understorey communities, spectral light intensities were pretty low and showed another considerable red-shift.O Autor apresenta um estudo comparativo do fator "luz" em três tipos de floresta na região central da Amazônia: floresta ribeirinha (floresta da baixa terra firme), carrasco e mata primária. São discutidas as dificuldades e a complexidade do problema enfatizando-se a importância das correlações entre luz e estrutura da floresta. É caracterizado o equipamento utilizado e descrito o procedimento seguido para a determinação da intensidade luminosa total, utilizando-se diferentes filtros em 51.840 determinações durante a estação chuvosa e a estação sêca, procurando verificar a intensidade luminosa total e espectral em cada stratum e como são aquelas intensidades distribuidas no tempo. A frequência relativa da intensidade luminosa foi computada em sete classes de intensidade e três períodos de tempo por dia. A composição espectral da luz foi determinada como frequência relativa de intensidades por meio de filtros para cinco faixas de comprimento de ondas. Na floresta ribeirinha foram encontradas as melhores condições de luz e na mata primária foram registrados os valores luminosos mais baixos. O carrasco ocupa uma posição intermediária, com nítida tendência às condições encontradas na mata primária. Quanto à composição espectral da luz recebida pelo stratum ao nível do solo nos três tipos de floresta, foi encontrado um pico de intensidade na faixa 5.950 ​​​Ǻ - 7.500 ​​​Ǻ, um pico secundário entre 4.420 e 6.440 ​​​Ǻ e um terceiro pico, menos importante, entre 3.500 a 5.150 ​​​

Non-singular radiation cosmological models

In this paper we analyse the possibility of constructing singularity-free inhomogeneous cosmological models with a pure radiation field as matter content. It is shown that the conditions for regularity are very easy to implement and therefore there is a huge number of such spacetimes.Comment: 13 pages, LaTex, ws-mpla, to appear in Modern Physics Letters

Investigation of the Spin-Peierls transition in CuGeO_3 by Raman scattering

Raman experiments on the spin-Peierls compound CuGeO$_3$ and the substituted (Cu$_{1- x}$,Zn$_x$)GeO$_3$ and Cu(Ge$_{1-x}$,Ga$_x$)O$_3$ compounds were performed in order to investigate the response of specific magnetic excitations of the one-dimensional spin-1/2 chain to spin anisotropies and substitution-induced disorder. In pure CuGeO$_3$, in addition to normal phonon scattering which is not affected at all by the spin-Peierls transition, four types of magnetic scattering features were observed. Below T$_{SP}$=14 K a singlet-triplet excitation at 30 cm$^{-1}$, two-magnon scattering from 30 to 227 cm$^{-1}$ and folded phonon modes at 369 and 819 cm$^{-1}$ were identified. They were assigned by their temperature dependence and lineshape. For temperatures between the spin-Peierls transition T$_{SP}$ and approximately 100 K a broad intensity maximum centered at 300 cm$^{-1}$ is observed.Comment: 7 pages, LaTex2e, including 3 figures (eps) to be published in Physica B (1996

Time dependency of hydrogen - ion concentration and electric conductivity measurements in river water samples of Central Amazonia()

The hypothesis was tested, whether hydrogen - ion concentration and electric conductivity in river water samples of the Tertiary region of central Amazonia were subject to changes in time and due to nature of storage. Over a period of about two months only changes in pH and conductivity of Rio Negro water samples were found to be significant. The total deviation of both parameters in rain forest stream samples was considered negligible for at least a period of 30 days, independant of the nature of storage (laboratory or icebox). The latter results may be generalized more or less unconditionally for the entire Tertiary formations of Amazonia.Algumas vêzes não é possível analisar no próprio local amostras d'água com relação aos valores de pH e condutibilidade elétrica, havendo por isso necessidade de posteriores determinações no laboratório. Foram investigadas as possíveis variações em uma série de 4 amostras colhidas em diversas profundidades no Rio Negro, bem como uma série de 4 amostras de diferentes igarapés da mata tropical ú8mida ao longo da rodovia BR-174, sendo obtidos os seguintes resultados após um período de armazenamento: a) As variações verificadas nas amostras do Rio Negro foram significantes em relação ao período de depósito das mesmas (dois meses); b) As amostras dos igarapés mantiveram-se mais ou menos estáveis durante 30 dias. De acôrdo com os resultados obtidos por outros autores para outras regiões terciárias da Amazônia, os valores analíticos mostram a possibilidade de serem elas analisadas depois de um mês desde a data da coleta; c) A natureza da conservação das amostras no laboratório (normal e refrigerador) não mostram variações significativas.", 'p

Natural Waters in Amazonia. VI-Soluble Calcium Properties ()

The principle sources of the calcium found in the water of the tertiary Amazonian region near Manaus, are the water running over the tree trunks and the total forest water. The soluble calcium content must come from the rain washing the tree crowns, stems, and leaves, and to a certain point from the dissolution of metabolic products of macro and micro-organisms. Generally, only traces of calcium are found in rain water, soil, and river water. Therefore, calcium can be considered as an element circulating in a closed system. Altogether the calcium content in the natural water of the tertiary Amazon region is extremely low.As principais fontes do cálcio encontrado na água na região terciária Amazônica próxima a Manaus, são a água escorrendo sobre os troncos e a água total da floresta. O teor em cálcio solúvel deve ser proveniente da lavagem, pela chuva, da copa, doa caules, folhas e, até um certo ponto, da dissolução de produtos metabólicos de macro e microorganismos. Na água da chuva, nas águas do solo e dos rios geralmente só foram encontrados traços de cálcio. Portanto, o cálcio pode ser encarado como elemento circulante num sistema fechado. De um modo geral, os teores de cálcio das águas naturais da região terciária Amazônica são extremamente baixos

Spectral Evolution of PKS 2155-304 observed with BeppoSAX during an Active Gamma-ray Phase

We present the results of BeppoSAX observations of PKS 2155-304 during an intense gamma-ray flare. The source was in a high X-ray state. A temporal analysis of the data reveals a tendency of the amplitude of variations to increase with energy, and the presence of a soft lag with a timescale of the order 10^3 s. A curved continuum spectrum, with no evidence of spectral features, extends up to ~50 keV, while there is indication of a flatter component emerging at higher energies, consistent with the interpretation of the broad band spectral energy distribution (SED) as due to synchrotron self-Compton (SSC) emission from a single region. Notably, the fitting of the SED with such a model is consistent with an interpretation of the detected soft lag as due to radiative cooling, supporting the idea that radiation losses play an important role in variability. The observed shifts of the SED peaks between the lowest and highest flux levels can be accounted for by an increase of the break energy in the relativistic particle spectrum. The model predicts emission at TeV energies in good agreement with the recently reported detection.Comment: 36 pages (8 figures), Latex with AAS macros, etc), accepted for publication on Astrophysical Journa

B Cell-Specific S1PR1 Deficiency Blocks Prion Dissemination between Secondary Lymphoid Organs

Many prion diseases are peripherally acquired (eg. orally or via lesions to skin or mucous membranes). After peripheral exposure prions replicate first upon follicular dendritic cells (FDC) in the draining lymphoid tissue before infecting the brain. However, after replication upon FDC within the draining lymphoid tissue, prions are subsequently propagated to most non-draining secondary lymphoid organs (SLO) including the spleen by a previously underdetermined mechanism. The germinal centres in which FDC are situated produce a population of B cells which can recirculate between SLO. We therefore reasoned that B cells were ideal candidates by which prion dissemination between SLO may occur. Sphingosine 1-phosphate receptor 1 (S1PR1) stimulation controls the egress of T and B cells from SLO. S1PR1 signalling-blockade sequesters lymphocytes within SLO resulting in lymphopenia in the blood and lymph. We show that in mice treated with the S1PR modulator FTY720, or with S1PR1-deficiency restricted to B cells, the dissemination of prions from the draining lymph node to non-draining SLO is blocked. These data suggest that B cells interacting with and acquiring surface proteins from FDC, and recirculating between SLO via the blood and lymph, mediate the initial propagation of prions from the draining lymphoid tissue to peripheral tissues

Air temperatures in Central Amazonia. II - The effect of near-surface temperatures on land-use in the Tertiary region of Central Amazonia

Maximum and minimum air temperatures were taken weekley at 10 different sites about 2 cm above ground level during the period of June 15th, 1968 to January 26th, 1970. Three temperature types were observed each of which has a specific ecological effect on land-use in Central Amazonia.Temperaturas máximas e mínimas do ar foram medidas em dez locais diferentes na Amazônia Central, a uma altura de 2 cm acima da superfície do solo. Como resultado destas medidas foram determinadas três tipos de temperatura, sendo que cada um dos três tipos apresentam influências especificas para a agricultura, silvicultura e pecuária em relação aos tipos de solos. Estas investigações foram realizadas em latossolos e solos arenosos, visto que, êsses dois tipos cobrem aproximadamente 90% dos solos da Estrada Manaus - Itacoatiara. Nos latossolos, os resultados obtidos demonstram que sem considerar outros fatôres limitantes, as queimadas em grande escala prejudicam até certo ponto o desenvolvimento da agricultura, silvicultura e pecuária, havendo por isso mesmo urgentes necessidades de modificar o sistema de exploração. Sem dúvida alguma, as áreas com areias brancas, não podem ser utilizadas por longo prazo para agricultura, silvicultura e pecuária em grande escala por sofrerem fortes influências da temperatura sem levar em consideração outros fatores limitantes. Essas áreas no momento são usadas para monoculturas (mandioca e abacaxi) porém em futuro elas devem permanecer conservadas

Air temperatures in Central Amazonia. III. - Vertical Temperature Distribution on a Clearcut Area and in a Secondary Forest near Manaus (Cold Front Conditions July 10 th. 1969)()

Air temperatures under cold front conditions were recorded on July 10th 1969 inside and outside a secondary forest at Ducke Forest Reserve Air temperatures were measured at 2 towers and 8 corresponding levels ranging from 10 cm to 900 cm height. The absolute daily minimum air temperature recorded was 11.0°C, which is exceptionally low for Central Amazonia and 16.0°C below the yearly average air temperature at Manaus measured over a 45-year period of temperature records. The maximum 30-min range of air temperature was observed in the clearing (8.1°C), 7 meters above the ground. The strongest impact of air temperatures in the forest stand was recorded in the canopy area and in the ground stratum due to the formation of cold air cells and cold air sinks. The temperature profiles inside and outside the secondary forest at Ducke Forest Preserve during cold front conditions did not conform with the established temperature patterns in a tropical environment.As temperaturas do ar durante a friagem do dia 10 de julho de 1969, foram registradas em uma clareira e uma capoeira na Reserva Florestal Ducke. As temperaturas foram medidas em duas torres improvisadas em 8 diferentes níveis na amplitude de 10 a 900 cm de altura. A temperatura mínima absoluta do dia foi de 11.0°C, sendo excepcionalmente baixa para a Amazônia Central e aproximadamente 16.0°C abaixo da temperatura média anual da cidade de Manaus. A amplitude máxima registrada em 30 minutos foi de 8.1°C na clareira a 7 m acima do nível do solo e o mais forte impacto das baixas temperaturas na capoeira foi registrada na área das copas e perto da superfície do solo de acordo com a formação das células e das caidas de ar frio. Os perfis da temperatura na clareira e na capoeira na Reserva Florestal Ducke durante a friagem, não se enquadram com a situação estabelecida para o ambiente tropical