Set-valued shortfall and divergence risk measures

Risk measures for multivariate financial positions are studied in a utility-based framework. Under a certain incomplete preference relation, shortfall and divergence risk measures are defined as the optimal values of specific set minimization problems. The dual relationship between these two classes of multivariate risk measures is constructed via a recent Lagrange duality for set optimization. In particular, it is shown that a shortfall risk measure can be written as an intersection over a family of divergence risk measures indexed by a scalarization parameter. Examples include set-valued versions of the entropic risk measure and the average value at risk. As a second step, the minimization of these risk measures subject to trading opportunities is studied in a general convex market in discrete time. The optimal value of the minimization problem, called the market risk measure, is also a set-valued risk measure. A dual representation for the market risk measure that decomposes the effects of the original risk measure and the frictions of the market is proved

Trade and Welfare Impacts of Partial Liberalization of U.S. Sugar TRQs: The Application of a PE/GE Modeling Approach

The sugar sector is one of the most heavily protected commodities in agriculture using a system of tariff rate quotas (TRQs) with a complex set of administration procedures. General equilibrium models are not suitable to analyze trade liberalization scenarios that involve numerous tariff-rate quotas across narrowly defined product lines. We use the Rutherford/Grant/Hertel modeling approach by embedding a detailed, partial equilibrium (PE) model into a standard, global general equilibrium (GE) framework. We use this PE/GE model to compare trade and welfare outcomes of two liberalization scenarios: Increasing quota levels by 25% and cutting over tariffs by 50%, versus increasing quota levels by 50% and cutting over-quota tariffs by 25%. We find that lowering over-quota tariffs relatively more has more positive welfare effects than increasing quota levels relatively more.International Relations/Trade,

Functional expression of horseradish peroxidase in Saccharomyces cerevisiae and Pichia pastoris

The ability to engineer proteins by directed evolution requires functional expression of the target polypeptide in a recombinant host suitable for construction and screening libraries of enzyme variants. Bacteria and yeast are preferred, but eukaryotic proteins often fail to express in active form in these cells. We have attempted to resolve this problem by identifying mutations in the target gene that facilitate its functional expression in a given recombinant host. Here we examined expression of HRP in Saccharomyces cerevisiae. Through three rounds of directed evolution by random point mutagenesis and screening, we obtained a 40-fold increase in total HRP activity in the S.cerevisiae culture supernatant compared with wild-type, as measured on ABTS [2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)] (260 units/l/OD_(600)). Genes from wild-type and two high-activity clones were expressed in Pichia pastoris, where the total ABTS activity reached 600 units/l/OD_(600) in shake flasks. The mutants show up to 5.4-fold higher specific activity towards ABTS and 2.3-fold higher specific activity towards guaiacol

Root system architecture determines fitness in an Arabidopsis mutant in competition for immobile phosphate ions but not for nitrate ions

Plant root systems often have complex branching patterns. Models indicate that a complex architecture is only required for the acquisition of immobile resources, such as phosphate; mobile ions, notably nitrate, can be effectively taken up by very restricted root systems. We have tested this prediction using the axr4 mutation of Arabidopsis thaliana, the principal phenotypic effect of which is to reduce the number of lateral roots. Arabidopsis thaliana is not a host for mycorrhizal fungi and so acquires all its nutrients through the root system. In both a pot experiment and a field experiment conducted under natural conditions for A. thaliana, we found that only phosphate, and not nitrate, affected the fitness of the mutant relative to the isogenic wild-type line, Columbia. These results confirm model predictions and have implications both for the evolution of complex root systems and for the design of efficient root systems for crops

Control of Volterra systems with scalar kernels

Volterra observations systems with scalar kernels are studied. New sufficient conditions for admissibility of observation operators are developed and some examples are discussed

Variability of the thrombin- and ADP-induced Ca2+ response among human platelets measured using fluo-3 and fluorescent videomicroscopy

AbstractThe intracellular free Ca2+ concentration ([Ca2+]cyt) of individual human platelets localized between siliconized glass cover slips was determined at rest and after stimulation with thrombin and ADP using the Ca2+ indicator fluo-3 (0.97 ± 0.30 mmol/1 cell volume) with fluorescence video microscopy. Resting [Ca2+]cyt in the presence of 2 mM external Ca2+ showed only small inter-platelet variability ([Ca2+]cyt = 86 ± 30 (S.D.) nM). Resting [Ca2+]cyt of individual fluo-3-loaded platelets measured as a function of time had a S.D. of 10 nM or 12% (S.D./mean). Individual platelets showed no affinity for the siliconized support and their [Ca2+]cyt showed no tendency to oscillate in either the resting or in the activated state. When 0.2 U/ml thrombin or 20 μM ADP were added, all platelets showed a characteristic Ca2+ transient whereby [Ca2+]cyt increased to peak values within 8–12 sec and then declined. The Ca2+ transients measured with fluo-3 were in approximate synchrony but peak [Ca2+]cyt values showed large inter-platelet variability. The ensemble average peak [Ca2+]cyt for thrombin and ADP were 672 ± 619 (S.D.) nM and 640 ± 642 (S.D.) nM, respectively. Thus inter-platelet variations (S.D./mean) were 92% or 100% as large as the average measured values. Mathematically-constructed averages of the single platelet experiments agreed reasonably well with platelet-averaged values obtained in parallel experiments with stirred platelet suspensions in a plastic cuvette, measured with a conventional spectrofluorometer. Peak [Ca2+]cyt values reflecting dense tubular Ca2+ release alone (external Ca2+ removed) also showed large interplatelet variation (171 ± 105 (S.D.) nM with thrombin and 183 ± 134 (S.D.) nM with ADP). Dense tubular Ca2+ release induced by cyclopiazonic acid (a dense tubular Ca2+-ATPase inhibitor) gave peak [Ca2+]cyt of 289 ± 170 nM. Thus the size of the dense tubular Ca2+ pool has an inter-platelet variation of 59% (S.D./mean). Variability of the dense tubular pool size accounts for some, but not all, of the large interplatelet variation in peak [Ca2+]cyt seen with thrombin and ADP activation