ABSTRACT In order to parametrize a leaf submodel of a canopy level gas‐exchange model, a series of photosynthesis and stomatal conductance measurements were made on leaves of white oak ( Quercus alba L.) and red maple ( Acer rubrum L.) in a mature deciduous forest near Oak Ridge, TN. Gas‐exchange characteristics of sun leaves growing at the top of a 30 m canopy and of shade leaves growing at a depth of 3–4 m from the top of the canopy were determined. Measured rates of net photosynthesis at a leaf temperature of 30°C and saturating photosynthetic photon flux density, expressed on a leaf area basis, were significantly lower (P = 0.01; n = 8) in shade leaves (7.9μmol m −2 s −1 ) than in sun leaves (11–5μmol m −2 s −1 ). Specific leaf area increased significantly with depth in the canopy, and when photosynthesis rates were expressed on a dry mass basis, they were not significantly different for shade and sun leaves. The percentage leaf nitrogen did not vary significantly with height in the canopy; thus, rates expressed on a per unit nitrogen basis were also not significantly different in shade and sun leaves. A widely used model integrating photosynthesis and stomatal conductance was parametrized independently for sun and shade leaves, enabling us to model successfully diurnal variations in photosynthesis and evapotranspiration of both classes of leaves. Key photosynthesis model parameters were found to scale with leaf nitrogen levels. The leaf model parametrizations were then incorporated into a canopy‐scale gas‐exchange model that is discussed and tested in a companion paper (Baldocchi & Harley 1995, Plant, Cell and Environment 18, 1157–1173).
In this edited version of the hour long talk, Omar Yaghi, director of the Molecular Foundry, sat down in conversation with Jeff Miller, head of Public Affairs, on July 11th, 2012 to discuss his fascination with the hidden world of chemistry and his work on Metal Organic Frameworks.
Since their introduction in 1985 by Tomalia et al. (1) and Newkome et al. (2), dendrimers have attracted much attention because of their fascinating structure and unique properties (3, 4). Dendrimers are globular, size monodisperse macromolecules in which all bonds emerge radially from a central focal point or core with a regular branching pattern and with repeat units that each contribute a branch point. Not all regularly branched molecules are dendrimers because properties of the dendritic state (4), such as core encapsulation (5, 6) and unusually low intrinsic viscosity in solution (7), are reached only when globularity is achieved at a certain generation or size threshold. Therefore, many low-generation dendrons or the early cascade molecules of Vogtle and coworkers (8) are too small to exhibit the properties of dendrimers, but they are frequently used as branched oligomeric building blocks in their construction, and have a size relationship to dendrimers somewhat akin to that between oligomers and polymers.
The "tapering talk" starting \n on May 22, 2013, when Federal Reserve Chairman Ben Bernanke \n first spoke of the possibility of the U.S. central bank \n reducing its security purchases, had a sharp negative impact \n on emerging markets. India was among those hardest hit. The \n rupee depreciated by 18 percent at one point, causing \n concerns that the country was heading toward a financial \n crisis. This paper contends that India was adversely \n impacted because it had received large capital flows in \n prior years and had large and liquid financial markets that \n were a convenient target for investors seeking to rebalance \n away from emerging markets. In addition, India's \n macroeconomic conditions had weakened in prior years, which \n rendered the economy vulnerable to capital outflows and \n limited the policy room for maneuver. The paper finds that \n the measures adopted to handle the impact of the tapering \n talk were not effective in stabilizing the financial markets \n and restoring confidence, implying that there may not be any \n easy choices when a country is caught in the midst of \n rebalancing of global portfolios. The authors suggest \n putting in place a medium-term policy framework that limits \n vulnerabilities in advance, while maximizing the policy \n space for responding to shocks. Elements of such a framework \n include a sound fiscal balance, sustainable current account \n deficit, and environment conducive to investment. In \n addition, India should continue to encourage relatively \n stable longer-term flows and discourage volatile short-term \n flows, hold a larger stock of reserves, avoid excessive \n appreciation of the exchange rate through interventions with \n the use of reserves and macroprudential policy, and prepare \n the banks and firms to handle greater exchange rate volatility.
Introduction and Objective: We introduce a heavy water (2H2 O) labeling technique to measure fluxes across a metabolome. The principle is that metabolic pathways comprise enzymatic reactions that exchange hydrogen between solvent water and covalent C-H bonds. Methods: The number (n) of exchangeable C-H sites is calculated from combinatorial probabilities (isotope ratios) after 2H2 O labeling, in a single LC-MS/MS analysis. This reveals contributions from different pathways traversed. Results: We first validated targeted fluxes in vivo in mice - e.g., hepatic glycolysis and glyceroneogenesis; plasma gluconeogenesis. We then measured untargeted fluxomics in central metabolism (Figure), including effects of inborn errors (Citrin deficiency) and T2D. Global flux ratios include sources of UDP-glucose, glycolytic and TCA cycle intermediates, acetyl-CoA, pentose phosphates, amino acids, purines and pyrimidines. The list can be expanded. Fig. Central metabolic fluxes in mouse liver. Numbers represent n (exchangeable C-H bonds), revealing pathway contributions. Conclusion: Labeling with 2H2 O has several benefits over 13C- methods. 13C- tracers enter locally whereas 2H2 O is distributed globally, is immune to non-linear error propagation and label recycling, and experimental logistics are simpler. This method has implications for diabetes research. Metabolic flux signatures, changes during diabetogenesis and effects of therapeutics can be explored. This fluxomics technique is translatable to humans. Disclosure N. Ziari: None. M.K. Hellerstein: Research Support; Lilly USA LLC. Consultant; Lilly USA LLC. Funding University of California CRCC predoctoral fellowship
Abstract This paper studies the three‐valued symbolic dynamics associated with the second‐order non‐linear digital filter which has been shown to be a chaotic system recently. A new necessary and sufficient condition is given for a periodic sequence to be an admissible one. the condition is further used to prove that four types of periodic sequences cannot be admissible.
