High-order gauge-invariant perturbations of a spherical spacetime

We complete the formulation of a general framework for the analysis of high-order nonspherical perturbations of a four-dimensional spherical spacetime by including a gauge-invariant description of the perturbations. We present a general algorithm to construct these invariants and provide explicit formulas for the case of second-order metric perturbations. We show that the well-known problem of lack of invariance for the first-order perturbations with l=0,1 propagates to increasing values of l for perturbations of higher order, owing to mode coupling. We also discuss in which circumstances it is possible to construct the invariants

Why do trees adjust water relations and hydraulic architecture in response to nutrient availability?

Studies on water relations, hydraulic architecture and effects of nutrients on growth in trees have been studied for many years in relative isolation. Only recently the functional relations of these groups of plant traits have been investigated with a more integrative approach (e.g. Harvey and van den Driessche, 1999; Clearwater and Meinzer 2001: Ewers et al. 2000, 2001; Bucci et al. 2006; Hacke et al. 2010; Faustino et al. 2013). In this commentary we attempt to answer the question of why water relations and the hydraulic architecture of trees are functionally related with their nutrient availability. We will focus on results of studies where nutrient limitations have been removed or alleviated by additions of the two most important macronutrients: nitrogen and phosphorous.Fil: Goldstein, Guillermo Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentina. University of Miami. Departament of Biology; Estados UnidosFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Comodoro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Comodoro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Lagrangian Variational Framework for Boundary Value Problems

A boundary value problem is commonly associated with constraints imposed on a system at its boundary. We advance here an alternative point of view treating the system as interacting "boundary" and "interior" subsystems. This view is implemented through a Lagrangian framework that allows to account for (i) a variety of forces including dissipative acting at the boundary; (ii) a multitude of features of interactions between the boundary and the interior fields when the boundary fields may differ from the boundary limit of the interior fields; (iii) detailed pictures of the energy distribution and its flow; (iv) linear and nonlinear effects. We provide a number of elucidating examples of the structured boundary and its interactions with the system interior. We also show that the proposed approach covers the well known boundary value problems.Comment: 41 pages, 3 figure

Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry

Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of ‘vulnerability segmentation’ between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate.Organismic and Evolutionary Biolog

Bell-Kochen-Specker theorem: A proof with 18 vectors

We present a ``state-independent'' proof of the Bell-Kochen-Specker theorem using only 18 four-dimensional vectors, which is a record for this kind of proof. This set of vectors contains subsets which allow us to develop a ``state-specific'' proof with 10 vectors (also a record) and a ``probabilistic'' proof with 7 vectors which reflects the algebraic structure of Hardy's nonlocality theorem.Comment: LaTeX, 10 page

Variações em atributos biofísicos e fisiológicos em nível de individuo e de parcela ao longo de um gradiente de densidade arbórea no Cerrado

O objetivo deste estudo foi caracterizar e compreender as variações morfológicas e fisiológicas em atributos relacionados à economia da água, em nível de indivíduo e de parcela, que ocorrem ao longo de um gradiente de densidade arbórea em uma savana neotropical (cerrado). Parcelas de vegetação de cerrado submetidas a um experimento de adubação de longo prazo e matas de galeria também foram incluídas na análise, a fim de expandir os eixos de variação do ecossistema. Mudanças consistentes em atributos biofísicos em nível de parcela foram observadas ao longo do gradiente de densidade crescente de árvores. Estas incluíram uma diminuição na densidade média ponderada da madeira, aumentos na área foliar por planta, na condutividade hidráulica específica da folha, na área foliar específica e na condutância estomática. Um modelo conceitual das interações entre as características biofísicas, morfológicas e fisiológicas foi desenvolvido em uma tentativa de explicar os determinantes da arquitetura hidráulica e variações na economia de água de árvores do Cerrado. Consistente com o modelo, os valores mínimos de potencial hídrico durante a estação seca foram maiores nas árvores de baixa densidade de madeira, em comparação com árvores de alta densidade de madeira, enquanto os maiores valores de potencial hídrico foliar estiveram associados com maior condutância estomática. Por outro lado, ao longo do gradiente de densidade arbórea, as variações em nível de parcela das características morfológicas e fisiológicas não puderam ser explicadas por variações de um único fator ambiental. Alguns dos fatores contribuintes potenciais são: maior concentração e disponibilidade de nutrientes do solo na porção superior do gradiente de densidade arbórea onde há um maior número de árvores e restrições no estabelecimento e crescimento pela inundação periódica e pela presença de concreções no perfil do solo onde a densidade de árvores é mais baixa.The objective of this study was to characterize and understand morphological and physiological variation in traits related to water economy, at the plant and stand level, along a gradient of tree density in a Neotropical savanna (Cerrado). Cerrado plots subjected to long-term fertilization and gallery forests were also included in the analysis to expand the axes of ecosystem variation. Consistent changes in stand level biophysical traits observed along the gradient of increasing tree density included a decrease in weighted-average wood density, and increases in leaf surface area per plant, leaf specific hydraulic conductivity, specific leaf area and stomatal conductance. A conceptual model of biophysical, morphological and physiological trait interactions was developed in an attempt to explain determinants of hydraulic architecture and variations in water economy of Cerrado trees. Consistent with the model minimum leaf water potentials were higher, during the dry season, in low wood density trees compared to high wood density trees, and higher leaf water potential was associated with higher stomatal conductance. On the other hand, variations in stand level physiological and morphological traits along the tree density gradient could not be explained by variations in single environmental factors. Some of the potential contributing factors are: higher concentration and availability of soil nutrients in the upper portion of the gradient where tree density is greatest and constrains to tree establishment and growth by waterlogging and presence of concretions in the soil profile where tree density is lowest

Relações hídricas e arquitetura hidráulica em árvores do cerrado : adequação às variações sazonais de disponibilidade hídrica e de demanda evaporativa

O objetivo deste estudo foi determinar os ajustamentos na morfologia e fisiologia que permitem árvores das savanas neotropicais do Brasil Central (Cerrado) de evitar déficits hídricos e de manter um balanço hídrico interno praticamente constante apesar das variações sazonais da precipitação e no déficit de saturação do ar (D). A precipitação na área de estudo é fortemente sazonal, com cerca de cinco meses praticamente sem chuva durante os quais D é duas vezes maior aos valores medidos na época chuvosa. Como conseqüência da flutuação sazonal das chuvas e de D, o potencial hídrico do solo muda substancialmente, nos primeiros 100 cm do solo, mas permanece quase constante abaixo de 2 m de profundidade. A arquitetura hidráulica e os parâmetros relacionados a relações hídricas das árvores do Cerrado se ajustaram durante a estação seca para evitar o déficit hídrico crescente e assegurar a homeostase nos valores mínimos de potencial hídrico foliar ΨL e na perda total diária de água pela planta (iso-hidria). O comportamento iso-hídrico das árvores do Cerrado foi o resultado de uma diminuição da superfície foliar total por árvore, um forte controle estomático das perdas por evaporação, um aumento na condutividade hidráulica específica da folha e na condutância hidráulica foliar e um aumento da quantidade de águas retirada dos reservatórios internos do caule, durante a estação seca. A eficiência no transporte de água aumentou, nas mesmas proporções, nas folhas e nos ramos terminais durante a estação seca. Todos estes ajustamentos sazonais foram importantes para a manutenção de ΨL acima de limiares críticos, com isto contribuindo para uma redução na formação de embolismos nos ramos e ajudando a evitar a perda de turgor em tecidos foliares durante a época seca. Esses ajustes permitem que os ramos das espécies lenhosas do Cerrado operem bem distanciados do ponto de disfunção catastrófica para a cavitação, enquanto as folhas operam próximas e sofrem embolismos em uma base diária, especialmente durante a estação seca.We determined adjustments in physiology and morphology that allow Neotropical savanna trees from central Brazil (Cerrado) to avoid water deficits and to maintain a nearly constant internal water balance despite seasonal changes in precipitation and air saturation deficit (D). Precipitation in the study area is highly seasonal with about five nearly rainless months during which D is two fold higher compared to wet season values. As a consequence of the seasonal fluctuations in rainfall and D, soil water potential changes substantially in the upper 100 cm of soil, but remains nearly constant below 2 m depth. Hydraulic architecture and water relations traits of Cerrado trees adjusted during the dry season to prevent increasing water deficits and insure homeostasis in minimum leaf water potential ΨL and in total daily water loss per plant (isohydry). The isohydric behavior of Cerrado trees was the result of a decrease in total leaf surface area per tree, a strong stomatal control of evaporative losses, an increase in leaf-specific hydraulic conductivity and leaf hydraulic conductance and an increase in the amount of water withdrawn from internal stem storage, during the dry season. Water transport efficiency increased in the same proportion in leaves and terminal stems during the dry season. All of these seasonal adjustments were important for maintaining ΨL above critical thresholds, which reduces the rate of embolism formation in stems and help to avoid turgor loss in leaf tissues still during the dry season. These adjustments allow the stems of most Cerrado woody species to operate far from the point of catastrophic dysfunction for cavitation, while leaves operate close to it and experience embolism on a daily basis, especially during the dry season

Multi-transmission-line-beam interactive system

We construct here a Lagrangian field formulation for a system consisting of an electron beam interacting with a slow-wave structure modeled by a possibly non-uniform multiple transmission line (MTL). In the case of a single line we recover the linear model of a traveling wave tube (TWT) due to J.R. Pierce. Since a properly chosen MTL can approximate a real waveguide structure with any desired accuracy, the proposed model can be used in particular for design optimization. Furthermore, the Lagrangian formulation provides for: (i) a clear identification of the mathematical source of amplification, (ii) exact expressions for the conserved energy and its flux distributions obtained from the Noether theorem. In the case of uniform MTLs we carry out an exhaustive analysis of eigenmodes and find sharp conditions on the parameters of the system to provide for amplifying regimes

Modeling multiple ecosystem services, biodiversity conservation, commodity production, and tradeoffs at landscape scales

Nature provides a wide range of benefits to people. There is increasing consensus about the importance of incorporating these ecosystem services into resource management decisions, but quantifying the levels and values of these services has proven difficult. We use a spatially explicit modeling tool, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST), to predict changes in ecosystem services, biodiversity conservation, and commodity production levels. We apply InVEST to stakeholder-defined scenarios of land-use/land-cover change in the Willamette Basin, Oregon. We found that scenarios that received high scores for a variety of ecosystem services also had high scores for biodiversity, suggesting there is little tradeoff between biodiversity conservation and ecosystem services. Scenarios involving more development had higher commodity production values, but lower levels of biodiversity conservation and ecosystem services. However, including payments for carbon sequestration alleviates this tradeoff. Quantifying ecosystem services in a spatially explicit manner, and analyzing tradeoffs between them, can help to make natural resource decisions more effective, efficient, and defensible. © The Ecological Society of America

Factores ambientales que modulan la fenología foliar de árboles del Bosque Atlántico

La fenología foliar responde de manera sensible a distintas señales ambientales. La coordinación entre las fases fenológicas y estas señales le permite a las especies ajustar el momento óptimo para expandir sus hojas y crecer, así como para evitar los posibles daños que causan las condiciones ambientales desfavorables. Por otro lado, en las especies deciduas, la altura de los árboles es otro factor clave, ya que los eventos de expansión y caída de las hojas de los individuos del dosel determinan la disponibilidad de luz para los de menor altura. El objetivo de nuestro trabajo fue conocer de qué manera los factores ambientales interactúan con la fenología foliar en especies arbóreas de diferente hábito foliar que coexisten en el extremo sur del Bosque Atlántico semideciduo. Para esto se monitoreó la fenología foliar de 10 especies arbóreas típicas del dosel del Bosque Atlántico semideciduo en la provincia de Misiones. En las especies deciduas y brevideciduas se identificaron patrones estacionales en las fases de expansión y caída de hojas, vinculados con las variaciones en las temperaturas y el fotoperíodo. En las siempreverdes, en cambio, no se encontró una asociación clara. Los árboles deciduos no dominantes adelantaron la expansión de hojas en comparación con los dominantes. Esto implicaría una estrategia para optimizar la captura de luz y la ganancia de carbono al inicio de la primavera extendiendo la estación de crecimiento. La fenología de las especies deciduas se acopló de forma estrecha a las variables ambientales, lo cual podría generar, en estas especies, mayor vulnerabilidad ante eventos extremos de estrés ambiental, como las bajas temperaturas y el déficit hídrico.Fil: Di Francescantonio, Débora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Villagra, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Goldstein, Guillermo Hernan. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Campanello, Paula Inés. Universidad Nacional de la Patagonia "san Juan Bosco". Facultad de Ingenieria - Sede Esquel. Centro de Estudios Ambientales Integrados.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin