695 research outputs found
Variação nas estratégias de uso do nitrogênio e nas vias fotossintéticas entre epÃfitas vasculares na região central da Amazônia, Brasil
The variation in nitrogen use strategies and photosynthetic pathways among vascular epiphyte families was addressed in a white-sand vegetation in the Brazilian Central Amazon. Foliar nitrogen and carbon concentrations and their isotopic composition (δ15N and δ13C, respectively) were measured in epiphytes (Araceae, Bromeliaceae and Orchidaceae) and their host trees. The host tree Aldina heterophylla had higher foliar N concentration and lower C:N ratio (2.1 ± 0.06% and 23.6 ± 0.8) than its dwellers. Tree foliar δ15N differed only from that of the orchids. Comparing the epiphyte families, the aroids had the highest foliar N concentration and lowest C:N ratios (1.4 ± 0.1% and 34.9 ± 4.2, respectively). The orchids had more negative foliar δ15N values (-3.5 ± 0.2‰) than the aroids (-1.9 ± 0.7‰) and the bromeliads (-1.1 ± 0.6‰). Within each family, aroid and orchid taxa differed in relation to foliar N concentrations and C:N ratios, whereas no internal variation was detected within bromeliads. The differences in foliar δ15N observed herein seem to be related to the differential reliance on the available N sources for epiphytes, as well as to the microhabitat quality within the canopy. In relation to epiphyte foliar δ13C, the majority of epiphytes use the water-conserving CAM-pathway (δ13C values around -17‰), commonly associated with plants that live under limited and intermittent water supply. Only the aroids and one orchid taxon indicated the use of C3-pathway (δ13C values around -30‰).A variação nas estratégias de uso do nitrogênio e das vias fotossintéticas de famÃlias de epÃfitas vasculares foi investigada em uma vegetação de areia branca na Amazônia Central. Foram medidas as concentrações e composições isotópicas de nitrogênio e carbono (δ15N e δ13C, respectivamente) de folhas de epÃfitas (Araceae, Bromeliaceae e Orchidaceae), assim como de suas árvores hospedeiras. As folhas da árvore hospedeira Aldine heterophylla tiveram a maior concentração de nitrogênio foliar e menor razão C:N (2,1 ± 0,06% e 23,6 ± 0,8) que de suas hóspedes. O valor de δ15N foliar da árvore somente diferiu do valor das orquÃdeas. Ao comparar as famÃlias de epÃfitas, a maior concentração de nitrogênio foliar e menor razão C:N foi observada nas aráceas (1,4 ± 0,1% e 34,9 ± 4,2, respectivamente). As orquÃdeas tiveram valores mais negativos de δ15N foliar (-3,5 ± 0,2‰) que aráceas (-1,9 ± 0,7‰) e bromélias (-1,1 ± 0,6‰). Ao comparar os táxons de cada famÃlia, observou-se que tanto os táxons de aráceas como os de orquÃdeas diferiram em relação ao nitrogênio foliar e razão C:N, enquanto que não foi detectada variação entre os táxons de bromélias. As diferenças nos valores de δ15N foliar aqui observadas podem ser relacionadas à variação na dependência das fontes de nitrogênio disponÃveis para as epÃfitas, assim como na variação da qualidade do microhabitat no dossel. Em relação aos valores de δ13C foliar das epÃfitas analisadas, verificou-se que a maioria usa a via fotossintética CAM (valores em torno de -17‰), comumente associada com plantas que vivem em condições de suprimento de água limitado ou intermitente. Apenas as aráceas e um táxon de orquÃdea mostraram usar a via C3 (valores em torno de -30‰)
Que idade podem alcançar as castanheiras (Bertholletia excelsa) da Amazônia?
The age of a large Brazil-nut tree (Bertholletia excelsa) is measured by radiocarbon dating, and a discussion is made about their importance in the Amazon rain-forest ecosystem.A idade de uma castanheira (Bertholletia excelsa) grande é medida por datação radiocarbônica e uma discussão é feita a respeito de sua importância no ecosistema da floresta amazônica
Que idade podem alcançar as castanheiras (Bertholletia excelsa) da Amazônia?
The age of a large Brazil-nut tree (Bertholletia excelsa) is measured by radiocarbon dating, and a discussion is made about their importance in the Amazon rain-forest ecosystem.A idade de uma castanheira (Bertholletia excelsa) grande é medida por datação radiocarbônica e uma discussão é feita a respeito de sua importância no ecosistema da floresta amazônica
Extracting Spatial Information from Noise Measurements of Multi-Spatial-Mode Quantum States
We show that it is possible to use the spatial quantum correlations present
in twin beams to extract information about the shape of a mask in the path of
one of the beams. The scheme, based on noise measurements through homodyne
detection, is useful in the regime where the number of photons is low enough
that direct detection with a photodiode is difficult but high enough that
photon counting is not an option. We find that under some conditions the use of
quantum states of light leads to an enhancement of the sensitivity in the
estimation of the shape of the mask over what can be achieved with a classical
state with equivalent properties (mean photon flux and noise properties). In
addition, we show that the level of enhancement that is obtained is a result of
the quantum correlations and cannot be explained with only classical
correlations
High Temperature Expansions and Dynamical Systems
We develop a resummed high-temperature expansion for lattice spin systems
with long range interactions, in models where the free energy is not, in
general, analytic. We establish uniqueness of the Gibbs state and exponential
decay of the correlation functions. Then, we apply this expansion to the
Perron-Frobenius operator of weakly coupled map lattices.Comment: 33 pages, Latex; [email protected]; [email protected]
A genealogical critique of Beauchamp and Childress' for principles approach to medical ethics
<bold>Part Three</bold> examines the development of Beauchamp and Childress 'four principles' approach to medical ethics from the 1<super> st</super> to the 6<super>th</super> Editions of <italic>Principles of Biomedical Ethics,</italic> arguing that it has, thanks to changes in the authors' conception of philosophical moral theory, been able to productively incorporate the views of many of its critics over this time; that it is also able to incorporate features of different ethical approaches such as virtue ethics, narrative ethics and ethics of care; and that, properly understood, it continues to provide a good framework both for moral reflection in medicine and the provision of concrete action-guides. The thesis concludes by considering this view of the four principles in the light of the earlier sections' approach, and attempting to demonstrate further demonstrate their value through two case-studies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Nucleon Axial Form Factor from Lattice QCD
Results for the isovector axial form factors of the proton from a lattice QCD
calculation are presented for both point-split and local currents. They are
obtained on a quenched lattice at with Wilson
fermions for a range of quark masses from strange to charm. We determine the
finite lattice renormalization for both the local and point-split currents of
heavy quarks. Results extrapolated to the chiral limit show that the
dependence of the axial form factor agrees reasonably well with experiment. The
axial coupling constant calculated for the local and the point-split
currents is about 6\% and 12\% smaller than the experimental value
respectively.Comment: 8 pages, 5 figures (included in part 2), UK/93-0
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