bluuebunny/crossref_metadata_2025 huggingface dataset:
Meiotic Regulators Ndt80 and Ime2 Have Different Roles in Saccharomyces and Neurospora
Authors: Hutchison Elizabeth A , Glass N Louise
Published: June 2010

Meiosis is a highly regulated process in eukaryotic species. The filamentous fungus Neurospora crassa has been shown to be missing homologs of a number of meiotic initiation genes conserved in Saccharomyces cerevisiae, but has three homologs of the well-characterized middle meiotic transcriptional regulator NDT80. In this study, we evaluated the role of all three NDT80 homologs in the formation of female reproductive structures, sexual development, and meiosis. We found that none of the NDT80 homologs were required for meiosis and that even the triple mutant was unaffected. However, strains containing mutations in NCU09915 (fsd-1) were defective in female sexual development and ascospore maturation. vib-1 was a major regulator of protoperithecial development in N. crassa, and double mutants carrying deletions of both vib-1 (NCU03725) and fsd-1 exhibited a synergistic effect on the timing of female reproductive structure (protoperithecia) formation. We further evaluated the role of the N. crassa homolog of IME2, a kinase involved in initiation of meiosis in S. cerevisiae. Strains containing mutations in ime-2 showed unregulated development of protoperithecia. Genetic analysis indicated that mutations in vib-1 were epistatic to ime-2, suggesting that IME-2 may negatively regulate VIB-1 activity. Our data indicate that the IME2/NDT80 pathway is not involved in meiosis in N. crassa, but rather regulates the formation of female reproductive structures.
Cytochrome P450-mediated 17β-estradiol metabolism in zebrafish (Danio rerio)
Authors: Scornaienchi Marcus L , Thornton Cammi , Willett Kristine L , Wilson Joanna Y
Published: June 2010

Cytochrome P4501 (CYP1) and CYP3A proteins are primarily responsible for the metabolism of 17β-estradiol (E2) in mammals. We have cloned and heterologously expressed CYP1A, CYP1B1, CYP1C1, CYP1C2, CYP1D1, and CYP3A65 from zebrafish (Danio rerio) to determine the CYP-mediated metabolism of E2 in a non-mammalian species. Constructs of each CYP cDNA were created using a leader sequence from the bacterial ompA gene to allow appropriate expression in Escherichia coli without 5′ modification of the gene. Membrane vesicles were purified, and functional CYP protein was verified using carbon monoxide difference spectra and fluorescent catalytic assays with the substrates 7-ethoxyresorufin and 7-benzyloxy-4-(trifluoromethyl)-coumarin. Rates of in vitro E2 metabolism into 4-hydroxyE2 (4-OHE2), 2-hydroxyE2 (2-OHE2), and 16α-hydroxyE1 (16α-OHE1) metabolites were determined by gas chromatography/mass spectrometry. The 2-OHE2 metabolite was produced by all CYPs tested, while 4-OHE2 was only detected following incubation with CYP1A, CYP1B1, CYP1C1, and CYP1C2. The 16α-OHE1 metabolite was only produced by CYP1A. The highest rates of E2 metabolism were from CYP1A and CYP1C1, followed by CYP1C2. CYP1B1, CYP1D1, and CYP3A65 had low rates of E2 metabolism. E2 metabolism by zebrafish CYP1A, CYP1C1, and CYP1C2 produced similar ratios of 4-OHE2 to 2-OHE2 as previous studies with mammalian CYP1As. CYP1B1 formed the highest ratio of 4-OHE2 to 2-OHE2 metabolites. Contrary to mammals, these results suggest that fish CYP1A and CYP1C proteins are primarily responsible for E2 metabolism, with only minor contributions from CYP3A65 and CYP1B1. Similar to mammals, 2-OHE2 is the predominant metabolite from CYP-mediated E2 metabolism in fish, suggesting that all vertebrate species produce the same major E2 metabolite.
Impact of elevated N input on soil N cycling and losses in old‐growth lowland and montane forests in Panama
Authors: Corre Marife D. , Veldkamp Edzo , Arnold Julia , Wright S. Joseph
Published: June 2010

Nitrogen deposition is projected to increase rapidly in tropical ecosystems, but changes in soil‐N‐cycling processes in tropical ecosystems under elevated N input are less well understood. We used N‐addition experiments to achieve N‐enriched conditions in mixed‐species, lowland and montane forests in Panama. Our objectives were to (1) assess changes in soil mineral N production (gross rates of N mineralization and nitrification) and retention (microbial immobilization and rapid reactions to organic N) during 1‐ and 9‐yr N additions in the lowland forest and during 1‐yr N addition in the montane forest and (2) relate these changes to N leaching and N‐oxide emissions.

In the old‐growth lowland forest located on an Inceptisol, with high base saturation and net primary production not limited by N, there was no immediate effect of first‐year N addition on gross rates of mineral‐N production and N‐oxide emissions. Changes in soil‐N processes were only apparent in chronic (9 yr) N‐addition plots: gross N mineralization and nitrification rates, NO3− leaching, and N‐oxide emissions increased, while microbial biomass and NH4+ immobilization rates decreased compared to the control. Increased mineral‐N production under chronic N addition was paralleled by increased substrate quality (e.g., reduced C:N ratios of litterfall), while the decrease in microbial biomass was possibly due to an increase in soil acidity. An increase in N losses was reflected in the increase in 15N signatures of litterfall under chronic N addition.

In contrast, the old‐growth montane forest located on an Andisol, with low base saturation and aboveground net primary production limited by N, reacted to first‐year N addition with increases in gross rates of mineral‐N production, microbial biomass, NO3− leaching, and N‐oxide emissions compared to the control. The increased N‐oxide emissions were attributed to increased nitrification activity in the organic layer, and the high NO3− availability combined with the high rainfall on this sandy loam soil facilitated the instantaneous increase in NO3− leaching. These results suggest that soil type, presence of an organic layer, changes in soil‐N cycling, and hydrological properties are more important indicators than vegetation as an N sink on how tropical forests respond to elevated N input.
Habitat heterogeneity and activity of an omnivorous ecosystem engineer control stream community dynamics
Authors: Brown Bryan L. , Lawson Raven L.
Published: June 2010

All communities vary through time. This variability originates from both intrinsic and extrinsic sources. Intrinsic sources are due to actions of organisms in a community, i.e., population dynamics and species interactions, while extrinsic variability is variability created by elements of habitat or environmental change. There is a growing appreciation that these two sources may interact, producing patterns of community variability that cannot be predicted or explained by focusing on a single source. We performed a field experiment that simultaneously manipulated trophic structure (intrinsic) and habitat heterogeneity (extrinsic) in order to examine the interaction between sources of variability in a South Carolina (USA) stream macroinvertebrate community. To manipulate trophic structure, we experimentally altered local abundances of crayfish which are keystone species and ecosystem engineers, while our manipulation of habitat was to alter stream substrate heterogeneity. We focused on two types of community variability as responses to our manipulations: aggregate variability (i.e., variability of summed species) and compositional variability (i.e., variability in relative abundances of species) by monitoring community composition through a 10‐week experiment. We found that community dynamics shifted from patterns in variability indicative of synchrony (high aggregate variability + low compositional) to variability indicative of compensation (low aggregate variability + high compositional) along a gradient of increasing habitat heterogeneity. However, the shift in community dynamics only occurred when crayfish were present in the community. Supporting evidence from the experiment suggested that sediment engineering effects of crayfish acted as a community‐wide perturbation in low‐heterogeneity habitat creating synchronous dynamics. However, in high‐heterogeneity enclosures, crayfish effects were moderated by refugia provided by a more complex substratum. The switch from synchronous to compensatory dynamics is significant since compensation stabilizes aggregate community properties and ecosystem functions while synchrony frequently exacerbates aggregate variability. Results from this experiment demonstrate that an interaction between intrinsic and extrinsic sources of variability can alter community dynamics and that such an alteration does not occur in the absence of an interaction.
Fire and grazing in a mesic tallgrass prairie: impacts on plant species and functional traits
Authors: Spasojevic Marko J. , Aicher Rebecca J. , Koch Gregory R. , Marquardt Emily S. , Mirotchnick Nicholas , Troxler Tiffany G. , Collins Scott L.
Published: June 2010

Fire is a globally distributed disturbance that impacts terrestrial ecosystems and has been proposed to be a global “herbivore.” Fire, like herbivory, is a top‐down driver that converts organic materials into inorganic products, alters community structure, and acts as an evolutionary agent. Though grazing and fire may have some comparable effects in grasslands, they do not have similar impacts on species composition and community structure. However, the concept of fire as a global herbivore implies that fire and herbivory may have similar effects on plant functional traits. Using 22 years of data from a mesic, native tallgrass prairie with a long evolutionary history of fire and grazing, we tested if trait composition between grazed and burned grassland communities would converge, and if the degree of convergence depended on fire frequency. Additionally, we tested if eliminating fire from frequently burned grasslands would result in a state similar to unburned grasslands, and if adding fire into a previously unburned grassland would cause composition to become more similar to that of frequently burned grasslands. We found that grazing and burning once every four years showed the most convergence in traits, suggesting that these communities operate under similar deterministic assembly rules and that fire and herbivory are similar disturbances to grasslands at the trait‐group level of organization. Three years after reversal of the fire treatment we found that fire reversal had different effects depending on treatment. The formerly unburned community that was then burned annually became more similar to the annually burned community in trait composition suggesting that function may be rapidly restored if fire is reintroduced. Conversely, after fire was removed from the annually burned community trait composition developed along a unique trajectory indicating hysteresis, or a time lag for structure and function to return following a change in this disturbance regime. We conclude that functional traits and species‐based metrics should be considered when determining and evaluating goals for fire management in mesic grassland ecosystems.
Recruitment facilitation can drive alternative states on temperate reefs
Authors: Baskett Marissa L. , Salomon Anne K.
Published: June 2010

How the combination of positive and negative species interactions acts to drive community dynamics is a fundamental question in ecology. Here we explore one aspect of this question by expanding the theory of predator‐mediated coexistence to include the potential role of facilitation between the predator and inferior competitor. To motivate and illustrate our simple model, we focus on sea‐urchin–algae interactions in temperate rocky reef systems and incorporate recruitment facilitation, a common characteristic of marine systems. Specifically, the model represents sea urchin grazing on macroalgae, macroalgal competition with crustose coralline algae (CCA), and facilitation of sea urchin recruitment to CCA. These interactions generate alternative stable states, one dominated by macroalgae and the other by urchins, which do not occur when recruitment facilitation of urchins to CCA is ignored. Therefore, recruitment facilitation provides a possible mechanism for alternative kelp forest and urchin barren states in temperate marine systems, where storm events or harvesting of urchins or their predators can drive switches between states that are difficult to reverse. In systems with such dynamics, spatial management such as no‐take marine reserves may play a crucial role in protecting community structure by increasing the resilience to shifts between states.
Impact of invertebrate herbivory in grasslands depends on plant species diversity
Authors: Stein Claudia , Unsicker Sybille B. , Kahmen Ansgar , Wagner Markus , Audorff Volker , Auge Harald , Prati Daniel , Weisser Wolfgang W.
Published: June 2010

Invertebrate herbivores are ubiquitous in most terrestrial ecosystems, and theory predicts that their impact on plant community biomass should depend on diversity and productivity of the associated plant communities. To elucidate general patterns in the relationship between invertebrate herbivory, plant diversity, and productivity, we carried out a long‐term herbivore exclusion experiment at multiple grassland sites in a mountainous landscape of central Germany. Over a period of five years, we used above‐ and belowground insecticides as well as a molluscicide to manipulate invertebrate herbivory at 14 grassland sites, covering a wide range of plant species diversity (13–38 species/m2) and aboveground plant productivity (272–1125 g·m−2·yr−1), where plant species richness and productivity of the sites were not significantly correlated.

Herbivore exclusion had significant effects on the plant communities: it decreased plant species richness and evenness, and it altered plant community composition. In particular, exclusion of belowground herbivores promoted grasses at the expense of herbs. In contrast to our expectation, herbivore effects on plant community biomass were not influenced by productivity. However, effect size of invertebrate herbivores was negatively correlated with plant diversity of the grasslands: the effect of herbivory on biomass tended to be negative at sites of high diversity and positive at sites of low diversity. In general, the effects of aboveground herbivores were relatively small as compared to belowground herbivores, which were important drivers of plant community composition. Our study is the first to show that variation in the effects of invertebrate herbivory on plant communities across a landscape is significantly influenced by plant species richness.
Native pollen thieves reduce the reproductive success of a hermaphroditic plant, Aloe maculata
Authors: Hargreaves Anna L. , Harder Lawrence D. , Johnson Steven D.
Published: June 2010

Pollen is unique among floral rewards in functioning as both a carrier of gametes and an attractant and nutritious resource for floral visitors. Animals that collect pollen without pollinating (pollen thieves) could reduce siring success of thieved plants and cause pollen limitation of seed set at the population level; however, such impacts on plant reproduction have not been demonstrated experimentally. To test these effects we added hives of native honey bees (Apis mellifera scutellata) to populations of a primarily bird‐pollinated plant, Aloe maculata, in eastern South Africa. In field and aviary trials, bee addition increased pollen removal from anthers but decreased pollen deposition on stigmas, and so reduced both male and female pollination components. Further, total seed production decreased with hive addition in the aviary experiment and in three of four field populations, indicating that population‐level pollen theft can also compromise reproductive success. In the field, naturally occurring allodapine bees also seemed to act as pollen thieves, outweighing the effect of honey bee hive addition at one of the four aloe populations. Our results highlight the importance of social bees as pollen thieves, even of plants that have evolved in their presence, and the role of dichogamy in promoting pollen theft. Given the commonness of both social bees and dichogamy, pollen theft is likely a much more common influence on floral ecology and evolution than suggested by the sparse literature.
Coexistence mechanisms and the paradox of the plankton: quantifying selection from noisy data
Authors: Fox Jeremy W. , Nelson William A. , McCauley Edward
Published: June 2010

Many species of phytoplankton typically co‐occur within a single lake, as do many zooplankton species (the “paradox of the plankton”). Long‐term co‐occurrence suggests stable coexistence. Coexistence requires that species be equally “fit” on average. Coexistence mechanisms can equalize species' long‐term average fitnesses by reducing fitness differences to low levels at all times, and by causing species' relative fitness to fluctuate over time, thereby reducing differences in time‐averaged fitness. We use recently developed time series analysis techniques drawn from population genetics to estimate the strength of net selection (time‐averaged selection over a year) and fluctuating selection (an index of the variation in selection throughout the year) in natural plankton communities. Analysis of 99 annual time series of zooplankton species dynamics and 49 algal time series reveals that within‐year net selection generally is statistically significant but ecologically weak. Rates of net selection are ~10 times faster in laboratory competition experiments than in nature, indicating that natural coexistence mechanisms are strong. Most species experience significant fluctuating selection, indicating that fluctuation‐dependent mechanisms may contribute to coexistence. Within‐year net selection increases with enrichment, implying that among‐year coexistence mechanisms such as trade‐offs between competitive ability and resting egg production are especially important at high enrichment. Fluctuating selection also increases with enrichment but is independent of the temporal variance of key abiotic factors, suggesting that fluctuating selection does not emerge solely from variation in abiotic conditions, as hypothesized by Hutchinson. Nor does fluctuating selection vary among lake‐years because more variable abiotic conditions comprise stronger perturbations to which species exhibit frequency‐dependent responses, since models of this mechanism fail to reproduce observed patterns of fluctuating selection. Instead, fluctuating selection may arise from internally generated fluctuations in relative fitness, as predicted by models of fluctuation‐dependent coexistence mechanisms. Our results place novel constraints on hypotheses proposed to explain the paradox of the plankton.
Many routes lead to Rome: potential causes for the multi‐route migration system of Red Knots, Calidris canutus islandica
Authors: Bauer Silke , Ens Bruno J. , Klaassen Marcel
Published: June 2010

Migrants, such as birds or representatives of other taxa, usually make use of several stopover sites to cover the distance between their site of origin and destination. Potentially, multiple routes exist, but often little is known about the causes and consequences of alternative migration routes. Apart from their geographical distribution, the suitability of potential sites might play an important role in the animals' decisions for a particular itinerary.

We used an optimal‐migration model to test three nonmutually exclusive hypotheses leading to variations in the spring migration routes of a subspecies of Red Knot, Calidris canutus islandica, which migrates from wintering grounds in Western Europe to breeding grounds in Greenland and the Canadian Arctic: the breeding location hypothesis, the energy budget hypothesis, and the predation risk hypothesis. Varying only breeding location, the model predicted that birds breeding in the Canadian Arctic and on West Greenland stop over on Iceland, whereas birds breeding in East and Northeast Greenland migrate via northern Norway, a prediction that is supported by empirical findings. Energy budgets on stopover sites had a strong influence on the choice of route and staging times. Varying foraging‐intensity and mass‐dependent predation risk prompted the birds to use less risky sites, if possible. The effect of simultaneous changes in the energy budget and predation risk strongly depended on the site where these occurred.

Our findings provide potential explanations for the observations that C. canutus islandica uses a diverse array of migration routes. Scrutinizing the three alternative driving forces for the choice of migratory routes awaits further, specific data collection in rapidly developing fields of research (e.g., predation risk assessment, GPS tracking). Generally, the type of modeling presented here may not only highlight alternative explanations, but also direct follow‐up empirical research.
Deciphering the relative contributions of multiple functions within plant–microbe symbioses
Authors: Sikes Benjamin A. , Powell Jeff R. , Rillig Matthias C.
Published: June 2010

For microbial symbioses with plants, such as mycorrhizas, we typically quantify either the net effects of one partner on another or a single function a symbiont provides. However, many microbial symbioses provide multiple functions to plants that vary based on the microbial species or functional group, plant species, and environment. Here we quantified the relative contributions of multiple functions provided by arbuscular mycorrhizal (AM) fungi to symbiont‐mediated changes in plant biomass. We used two published data sets, one that measured multiple functions (pathogen protection and nutrient uptake) on a single plant and one that measured a single function (pathogen protection) on multiple plants. Using structural equation modeling, we observed strong variation in the functional pathways by which AM fungi altered plant growth; changes in plant biomass were associated with different functions (and different AM fungal functional groups) for the different plant species. Utilizing this methodology across multiple partners and environments will allow researchers to gauge the relative importance of functions they isolate and, perhaps more importantly, those they did not consider. This baseline information is essential for establishing the specific mechanisms by which microbial symbioses influence plant diversity and to more effectively utilize these organisms in agriculture, restoration and conservation.
Survival Analysis on Pedigrees: A Marked Point Process Model
Authors: Macdonald Angus S.
Published: June 2010

Regulation of insurers' use of genetic information means actuaries are interested in age-at-onset of genetic disorders. Arjas & Haara (1984) suggested marked point processes (MPPs) as useful models for life history data with complex covariates. Age-at-onset distributions (or equivalently, hazard rates) in respect of inherited disorders are often estimated from pedigrees, which are life histories with unusually complex covariates, as well as strong dependencies induced by shared genes. Since Elston (1973) parametric models have often been used, conditioning the likelihood on known genotypes. However, a genotype identii ed by a presymptomatic genetic test is a form of internal covariate (Kalbfleisch & Prentice, 2002). We propose a very general MPP model of a pedigree, including presymptomatic genetic testing, (‘the full model’) and show under what circumstances the partial model leading to Elston's likelihood is valid. In practice, pedigrees are often ascertained retrospectively. Many such events can be modelled by augmenting the natural filtration of the MPP. We show that, except in simple special cases, the partial model is no longer valid, and the resulting likelihoods appear to be intractable. In particular, ascertainment interacts even with independent censoring so that likelihoods no longer factorize. For one simple special case — studies of sibships — we generalise a classical result to age-at-onset data. We conclude that the study of genetic conditions with variable age at onset gains insights from the underlying principles of survival analysis in their modern form, but that great care is needed in translating epidemiological studies into actuarial models.
On the Risk-Neutral Valuation of Life Insurance Contracts with Numerical Methods in View
Authors: Bauer Daniel , Bergmann Daniela , Kiesel Rüdiger
Published: June 2010

In recent years, market-consistent valuation approaches have gained an increasing importance for insurance companies. This has triggered an increasing interest among practitioners and academics, and a number of specific studies on such valuation approaches have been published.

In this paper, we present a generic model for the valuation of life insurance contracts and embedded options. Furthermore, we describe various numerical valuation approaches within our generic setup. We particularly focus on contracts containing early exercise features since these present (numerically) challenging valuation problems.

Based on an example of participating life insurance contracts, we illustrate the different approaches and compare their efficiency in a simple and a generalized Black-Scholes setup, respectively. Moreover, we study the impact of the considered early exercise feature on our example contract and analyze the influence of model risk by additionally introducing an exponential Lévy model.
Optimal Risk Control for The Excess of Loss Reinsurance Policies
Authors: Meng Hui , Zhang Xin
Published: June 2010

The primary objective of the paper is to explore using reinsurance as a risk management tool for an insurance company. We consider an insurance company whose surplus can be modeled by a Brownian motion with drift and that the surplus can be invested in a risky or riskless asset. Under the above Black-Scholes type framework and using the objective of minimizing the ruin probability of the insurer, we formally establish that the excess-of-loss reinsurance treaty is optimal among the class of plausible reinsurance treaties. We also obtain the optimal level of retention as well as provide an explicit expression of the minimal probability of ruin.
A Bootstrap Test for the Probability of Ruin in the Compound Poisson Risk Process
Authors: Baumgartner Benjamin , Gatto Riccardo
Published: June 2010

In this article we propose a bootstrap test for the probability of ruin in the compound Poisson risk process. We adopt the P-value approach, which leads to a more complete assessment of the underlying risk than the probability of ruin alone. We provide second-order accurate P-values for this testing problem and consider both parametric and nonparametric estimators of the individual claim amount distribution. Simulation studies show that the suggested bootstrap P-values are very accurate and outperform their analogues based on the asymptotic normal approximation.
Dispersion Estimates for Poisson and Tweedie Models
Authors: Rosenlund Stig
Published: June 2010

As a consequence of pointing out an ambiguity in Renshaw (1994), we show that the Overdispersed Poisson model cannot be generated by random independent intensities. Hence Pearson's chi-square-based estimate is normally unsuitable for GLM (Generalized Linear Model) log link claim frequency analysis in insurance. We propose a new dispersion parameter estimate in the GLM Tweedie model for risk premium. This is better than the Pearson estimate, if there are sufficiently many claims in each tariff cell. Simulation results are given showing the differences between it and the Pearson estimate.
Matrix-Form Recursions for a Family of Compound Distributions
Authors: Wu Xueyuan , Li Shuanming
Published: June 2010

In this paper, we aim to evaluate the distribution of the aggregate claims in the collective risk model. The claim count distribution is firstly assumed to belong to a generalised (a, b, 0) family. A matrix form recursive formula is then derived to evaluate the related compound distribution when individual claim amounts follow a discrete distribution on non-negative integers. The corresponding formula is also given for continuous individual claim amounts. Secondly, we pay particular attention to the recursive formula for compound phase-type distributions, since only certain types of discrete phase-type distributions belong to the generalised (a, b, 0) family. Similar recursive formulae are obtained for discrete and continuous individual claim amount distributions. Finally, numerical examples are presented for three counting distributions.
Numerical Evaluation of Continuous Time Ruin Probabilities for a Portfolio with Credibility Updated Premiums
Authors: Afonso Lourdes B. , Reis Alfredo D. Egídio dos , Waters Howard R.
Published: June 2010

The probability of ruin in continuous and finite time is numerically evaluated in a classical risk process where the premium can be updated according to credibility models and therefore change from year to year. A major consideration in the development of this approach is that it should be easily applicable to large portfolios. Our method uses as a first tool the model developed by Afonso et al. (2009), which is quite flexible and allows premiums to change annually. We extend that model by introducing a credibility approach to experience rating.

We consider a portfolio of risks which satisfy the assumptions of the Bühlmann (1967, 1969) or Bühlmann and Straub (1970) credibility models. We compute finite time ruin probabilities for different scenarios and compare with those when a fixed premium is considered.
Representations of Stream Processors Using Nested Fixed Points
Authors: Ghani Neil , Hancock Peter , Pattinson Dirk
Published: June 2010

We define representations of continuous functions on infinite streams of
discrete values, both in the case of discrete-valued functions, and in the case
of stream-valued functions. We define also an operation on the representations
of two continuous functions between streams that yields a representation of
their composite.
In the case of discrete-valued functions, the representatives are
well-founded (finite-path) trees of a certain kind. The underlying idea can be
traced back to Brouwer's justification of bar-induction, or to Kreisel and
Troelstra's elimination of choice-sequences. In the case of stream-valued
functions, the representatives are non-wellfounded trees pieced together in a
coinductive fashion from well-founded trees. The definition requires an
alternating fixpoint construction of some ubiquity.
Infinitary Combinatory Reduction Systems: Confluence
Authors: Ketema Jeroen , Simonsen Jakob Grue
Published: June 2010

We study confluence in the setting of higher-order infinitary rewriting, in
particular for infinitary Combinatory Reduction Systems (iCRSs). We prove that
fully-extended, orthogonal iCRSs are confluent modulo identification of
hypercollapsing subterms. As a corollary, we obtain that fully-extended,
orthogonal iCRSs have the normal form property and the unique normal form
property (with respect to reduction). We also show that, unlike the case in
first-order infinitary rewriting, almost non-collapsing iCRSs are not
necessarily confluent.
Observational Equivalence and Full Abstraction in the Symmetric Interaction Combinators
Authors: Mazza Damiano
Published: June 2010

The symmetric interaction combinators are an equally expressive variant of
Lafont's interaction combinators. They are a graph-rewriting model of
deterministic computation. We define two notions of observational equivalence
for them, analogous to normal form and head normal form equivalence in the
lambda-calculus. Then, we prove a full abstraction result for each of the two
equivalences. This is obtained by interpreting nets as certain subsets of the
Cantor space, called edifices, which play the same role as Boehm trees in the
theory of the lambda-calculus.
O-Minimal Hybrid Reachability Games
Authors: Bouyer Patricia , Brihaye Thomas , Chevalier Fabrice
Published: June 2010

In this paper, we consider reachability games over general hybrid systems, and distinguish between two possible observation frameworks for those games: either the precise dynamics of the system is seen by the players (this is the perfect observation framework), or only the starting point and the delays are known by the players (this is the partial observation framework). In the first more classical framework, we show that time-abstract bisimulation is not adequate for solving this problem, although it is sufficient in the case of timed automata . That is why we consider an other equivalence, namely the suffix equivalence based on the encoding of trajectories through words. We show that this suffix equivalence is in general a correct abstraction for games. We apply this result to o-minimal hybrid systems, and get decidability and computability results in this framework. For the second framework which assumes a partial observation of the dynamics of the system, we propose another abstraction, called the superword encoding, which is suitable to solve the games under that assumption. In that framework, we also provide decidability and computability results.
Guarded Second-Order Logic, Spanning Trees, and Network Flows
Authors: Blumensath Achim
Published: June 2010

According to a theorem of Courcelle monadic second-order logic and guarded
second-order logic (where one can also quantify over sets of edges) have the
same expressive power over the class of all countable $k$-sparse hypergraphs.
In the first part of the present paper we extend this result to hypergraphs of
arbitrary cardinality. In the second part, we present a generalisation dealing
with methods to encode sets of vertices by single vertices.
Weighted Logics for Nested Words and Algebraic Formal Power Series
Authors: Mathissen Christian
Published: June 2010

Nested words, a model for recursive programs proposed by Alur and Madhusudan, have recently gained much interest. In this paper we introduce quantitative extensions and study nested word series which assign to nested words elements of a semiring. We show that regular nested word series coincide with series definable in weighted logics as introduced by Droste and Gastin. For this we establish a connection between nested words and the free bisemigroup. Applying our result, we obtain characterizations of algebraic formal power series in terms of weighted logics. This generalizes results of Lautemann, Schwentick and Therien on context-free languages.
Infinitary Combinatory Reduction Systems: Normalising Reduction Strategies
Authors: Ketema Jeroen , Simonsen Jakob Grue
Published: June 2010

We study normalising reduction strategies for infinitary Combinatory
Reduction Systems (iCRSs). We prove that all fair, outermost-fair, and
needed-fair strategies are normalising for orthogonal, fully-extended iCRSs.
These facts properly generalise a number of results on normalising strategies
in first-order infinitary rewriting and provide the first examples of
normalising strategies for infinitary lambda calculus.
A Utility-Based Diffusion Model Applied to the Digital Camera Case
Authors: Orbach Yair , Fruchter Gila E.
Published: June 2010

We present a model that deals with the challenge of forecasting market acceptance and technology evolution along the product lifecycle, pre-launch. Market growth is driven by product's utility increase due to technology evolution, while firms' product improvements strategies are motivated by market growth and directed by market preferences. The interdependency between utility increase and market growth makes the problem inherently dynamic. To find the dependency of utility increase on market growth, we conduct an industry and technology analysis that follows industry financial policies, innovation orientation, industry players' inter-relations and technologic capabilities. For relating market preferences and purchase intentions to product's utility, we use data collected by a conjoint study. The ability to collect and interpret data about both demand and supply aspects, before the product is introduced, leads to a pre-launch forecasting. The evolution of the cumulative adoption level over time, as a result of the technology evolution, and vice versa, is based on both customer purchase decision processes and firms responses. We demonstrate the applicability of the model on the digital camera market.
The Effect of an Old-Age Demogrant on the Labor Supply and Time Use of the Elderly and Non-Elderly in Mexico
Authors: Juarez Laura
Published: June 2010

This paper estimates the effect of a generous demogrant for individuals age 70 and older that started in 2001 in Mexico City on the labor supply and time use of beneficiaries and of non-elderly family members who live with them. Using a triple differences approach, I find that the program has no significant effect on the time use of eligible individuals, except for the sharp decrease in the housework participation of elderly women who live with another potential beneficiary. Individuals 60 to 69 years old change their time use only if they live with a potential beneficiary, but not because they expect to receive the demogrant themselves in a few years. In particular, men in their 60s seem to retire early if they live with someone who qualifies for the transfer. Both men and women 18 to 59 years old increase their labor supply if they live with an eligible man, but decrease it if they live with an eligible woman. These results are consistent with income in the hands of elderly women being shared more with younger family members than income in the hands of elderly men.
The layer by layer selective laser synthesis of ruby
Authors: Vlasova M. , Ragulya A. , Stetsenko V. , Kakazey M. , Aguilar Marquez , Timofeeva I. , Tomila T. , Arellano Juarez
Published: June 2010

In the work, features of the layer-by-layer selective laser synthesis (SLS) of ruby from an Al2O3-Cr2O3 mixture are considered depending on the irradiation power, the laser beam traverse speed, the height and amount of the backfill of powder layers. It has been established that, under irradiation, a track consisting of polycrystalline textured ruby forms. The morphology of the surface of the track and its crystalline structure are determined by the irradiation conditions.
Master sintering curve: A practical approach to its construction
Authors: Pouchly V. , Maca K.
Published: June 2010

The concept of a Master Sintering Curve (MSC) is a strong tool for optimizing the sintering process. However, constructing the MSC from sintering data involves complicated and time-consuming calculations. A practical method for the construction of a MSC is presented in the paper. With the help of a few dilatometric sintering experiments the newly developed software calculates the MSC and finds the optimal activation energy of a given material. The software, which also enables sintering prediction, was verified by sintering tetragonal and cubic zirconia, and alumina of two different particle sizes.
Numerical modeling of microwave heating
Authors: Shukla A.K. , Mondal A. , Upadhyaya A.
Published: June 2010

The present study compares the temperature distribution within cylindrical samples heated in microwave furnace with those achieved in radiatively-heated (conventional) furnace. Using a two-dimensional finite difference approach the thermal profiles were simulated for cylinders of varying radii (0.65, 6.5, and 65 cm) and physical properties. The influence of susceptor-assisted microwave heating was also modeled for the same. The simulation results reveal differences in the heating behavior of samples in microwaves. The efficacy of microwave heating depends on the sample size and its thermal conductivity.
Mesenchymal Bone Morphogenetic Protein Signaling Is Required for Normal Pancreas Development
Authors: Ahnfelt-Rønne Jonas , Ravassard Philippe , Pardanaud-Glavieux Corinne , Scharfmann Raphaél , Serup Palle
Published: June 2010

OBJECTIVE

Pancreas organogenesis is orchestrated by interactions between the epithelium and the mesenchyme, but these interactions are not completely understood. Here we investigated a role for bone morphogenetic protein (BMP) signaling within the pancreas mesenchyme and found it to be required for the normal development of the mesenchyme as well as for the pancreatic epithelium.

RESEARCH DESIGN AND METHODS

We analyzed active BMP signaling by immunostaining for phospho-Smad1,5,8 and tested whether pancreas development was affected by BMP inhibition after expression of Noggin and dominant negative BMP receptors in chicken and mouse pancreas.

RESULTS

Endogenous BMP signaling is confined to the mesenchyme in the early pancreas and inhibition of BMP signaling results in severe pancreatic hypoplasia with reduced epithelial branching. Notably, we also observed an excessive endocrine differentiation when mesenchymal BMP signaling is blocked, presumably secondary to defective mesenchyme to epithelium signaling.

CONCLUSIONS

We conclude that BMP signaling plays a previously unsuspected role in the mesenchyme, required for normal development of the mesenchyme as well as for the epithelium.
Local Expression of Indoleamine 2,3 Dioxygenase in Syngeneic Fibroblasts Significantly Prolongs Survival of an Engineered Three-Dimensional Islet Allograft
Authors: Jalili Reza B. , Forouzandeh Farshad , Rezakhanlou Alireza Moeen , Hartwell Ryan , Medina Abelardo , Warnock Garth L. , Larijani Bagher , Ghahary Aziz
Published: June 2010

OBJECTIVE

The requirement of systemic immunosuppression after islet transplantation is of significant concern and a major drawback to clinical islet transplantation. Here, we introduce a novel composite three-dimensional islet graft equipped with a local immunosuppressive system that prevents islet allograft rejection without systemic antirejection agents. In this composite graft, expression of indoleamine 2,3 dioxygenase (IDO), a tryptophan-degrading enzyme, in syngeneic fibroblasts provides a low-tryptophan microenvironment within which T-cells cannot proliferate and infiltrate islets.

RESEARCH DESIGN AND METHODS

Composite three-dimensional islet grafts were engineered by embedding allogeneic mouse islets and adenoviral-transduced IDO–expressing syngeneic fibroblasts within collagen gel matrix. These grafts were then transplanted into renal subcapsular space of streptozotocin diabetic immunocompetent mice. The viability, function, and criteria for graft take were then determined in the graft recipient mice.

RESULTS

IDO-expressing grafts survived significantly longer than controls (41.2 ± 1.64 vs. 12.9 ± 0.73 days; P < 0.001) without administration of systemic immunesuppressive agents. Local expression of IDO suppressed effector T-cells at the graft site, induced a Th2 immune response shift, generated an anti-inflammatory cytokine profile, delayed alloantibody production, and increased number of regulatory T-cells in draining lymph nodes, which resulted in antigen-specific impairment of T-cell priming.

CONCLUSIONS

Local IDO expression prevents cellular and humoral alloimmune responses against islets and significantly prolongs islet allograft survival without systemic antirejection treatments. This promising finding proves the potent local immunosuppressive activity of IDO in islet allografts and sets the stage for development of a long-lasting nonrejectable islet allograft using stable IDO induction in bystander fibroblasts.
Increased Cytochrome P4502E1 Expression and Altered Hydroxyeicosatetraenoic Acid Formation Mediate Diabetic Vascular Dysfunction
Authors: Schäfer Andreas , Galuppo Paolo , Fraccarollo Daniela , Vogt Christian , Widder Julian D. , Pfrang Julia , Tas Piet , Barbosa-Sicard Eduardo , Ruetten Hartmut , Ertl Georg , Fleming Ingrid , Bauersachs Johann
Published: June 2010

OBJECTIVE

We investigated the mechanisms underlying vascular endothelial and contractile dysfunction in diabetes as well as the effect of HMR1766, a novel nitric oxide (NO)-independent activator of soluble guanylyl cyclase (sGC).

RESEARCH DESIGN AND METHODS

Two weeks after induction of diabetes by streptozotocin, Wistar rats received either placebo or HMR1766 (10 mg/kg twice daily) for another 2 weeks; thereafter, vascular function was assessed.

RESULTS

Endothelial function and contractile responses were significantly impaired, while vascular superoxide formation was increased in the aortae from diabetic versus healthy control rats. Using RNA microarrays, cytochrome P4502E1 (CYP2E1) was identified as the highest upregulated gene in diabetic aorta. CYP2E1 protein was significantly increased (16-fold) by diabetes, leading to a reduction in levels of the potent vasoconstrictor 20-hydroxy-eicosatetraenoic acid (20-HETE). Induction of CYP2E1 expression in healthy rats using isoniazide mimicked the diabetic noncontractile vascular response while preincubation of aortae from STZ-diabetic rats in vitro with 20-HETE rescued contractile function. Chronic treatment with the sGC activator HMR1766 improved NO sensitivity and endothelial function, reduced CYP2E1 expression and superoxide formation, enhanced 20-HETE levels, and reversed the contractile deficit observed in the diabetic rats that received placebo.

CONCLUSIONS

Upregulation of CYP2E1 is essentially involved in diabetic vascular dysfunction. Chronic treatment with the sGC activator HMR1766 reduced oxidative stress, decreased CYP2E1 levels, and normalized vasomotor function in diabetic rats.
Tauroursodeoxycholic Acid May Improve Liver and Muscle but Not Adipose Tissue Insulin Sensitivity in Obese Men and Women
Authors: Kars Marleen , Yang Ling , Gregor Margaret F. , Mohammed B. Selma , Pietka Terri A. , Finck Brian N. , Patterson Bruce W. , Horton Jay D. , Mittendorfer Bettina , Hotamisligil Gökhan S. , Klein Samuel
Published: June 2010

OBJECTIVE

Insulin resistance is commonly associated with obesity. Studies conducted in obese mouse models found that endoplasmic reticulum (ER) stress contributes to insulin resistance, and treatment with tauroursodeoxycholic acid (TUDCA), a bile acid derivative that acts as a chemical chaperone to enhance protein folding and ameliorate ER stress, increases insulin sensitivity. The purpose of this study was to determine the effect of TUDCA therapy on multiorgan insulin action and metabolic factors associated with insulin resistance in obese men and women.

RESEARCH DESIGN AND METHODS

Twenty obese subjects ([means ± SD] aged 48 ± 11 years, BMI 37 ± 4 kg/m2) were randomized to 4 weeks of treatment with TUDCA (1,750 mg/day) or placebo. A two-stage hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled tracer infusions and muscle and adipose tissue biopsies were used to evaluate in vivo insulin sensitivity, cellular factors involved in insulin signaling, and cellular markers of ER stress.

RESULTS

Hepatic and muscle insulin sensitivity increased by ∼30% (P < 0.05) after treatment with TUDCA but did not change after placebo therapy. In addition, therapy with TUDCA, but not placebo, increased muscle insulin signaling (phosphorylated insulin receptor substrateTyr and AktSer473 levels) (P < 0.05). Markers of ER stress in muscle or adipose tissue did not change after treatment with either TUDCA or placebo.

CONCLUSIONS

These data demonstrate that TUDCA might be an effective pharmacological approach for treating insulin resistance. Additional studies are needed to evaluate the target cells and mechanisms responsible for this effect.