770 research outputs found

    Estimating threshold vector error-correction models with multiple cointegrating relationships

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    Hansen and Seo (2002) outline procedures to test for threshold cointegration, and to estimate a bi-variate model. However, in their conclusion they note that future research will have to find a way of estimating larger systems with multiple cointegrating vectors. This paper proposes a new algorithm that can be used to estimate such models. Simulation experiments are used to compare the algorithm´s performance with that of Hansen and Seo, and a practical application to the term structure of UK interest rates is also presented

    Asymmetries in Bank of England Monetary Policy

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    In this paper we estimate limited dependent variable models for Bank of England monetary policy using monthly data over the period June 1997 to March 2003. During this period the Bank has had operational independence to set the interest rate in order to meet the inflation target set by the Government. We find evidence that the Bank has responded to current output growth rather than inflation which is consistent with targeting future inflation when there is a lag in the response of inflation to the output gap. We also find evidence of an asymmetry in the sense that the link between the interest rate and output growth is stronger when an increase in the interest rate is required than when circumstances dictate it should be cut. On the other hand there is considerably more inertia for interest rate cuts in the sense that a cut in the rate in one month significantly increases the probability of a cut in the next month which is not the case for increases

    Allee effects driven by predation

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    The Role of Protein Kinase Cη in T Cell Biology

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    Protein kinase Cη (PKCη) is a member of the novel PKC subfamily, which also includes δ, ε, and θ isoforms. Compared to the other novel PKCs, the function of PKCη in the immune system is largely unknown. Several studies have started to reveal the role of PKCη, particularly in T cells. PKCη is highly expressed in T cells, and is upregulated during thymocyte positive selection. Interestingly, like the θ isoform, PKCη is also recruited to the immunological synapse that is formed between a T cell and an antigen-presenting cell. However, unlike PKCθ, which becomes concentrated to the central region of the synapse, PKCη remains in a diffuse pattern over the whole area of the synapse, suggesting distinctive roles of these two isoforms in signal transduction. Although PKCη is dispensable for thymocyte development, further analysis of PKCη- or PKCθ-deficient and double-knockout mice revealed the redundancy of these two isoforms in thymocyte development. In contrast, PKCη rather than PKCθ, plays an important role for T cell homeostatic proliferation, which requires recognition of self-antigen. Another piece of evidence demonstrating that PKCη and PKCθ have isoform-specific as well as redundant roles come from the analysis of CD4 to CD8 T cell ratios in the periphery of these knockout mice. Deficiency in PKCη or PKCθ had opposing effects as PKCη knockout mice had a higher ratio of CD4 to CD8 T cells compared to that of wild-type mice, whereas PKCθ-deficient mice had a lower ratio. Biochemical studies showed that calcium flux and NFκB translocation is impaired in PKCη-deficient T cells upon TCR crosslinking stimulation, a character shared with PKCθ-deficient T cells. However, unlike the case with PKCθ, the mechanistic study of PKCη is at early stage and the signaling pathways involving PKCη, at least in T cells, are essentially unknown. In this review, we will cover the topics mentioned above as well as provide some perspectives for further investigations regarding PKCη

    A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environments

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    Positive density-dependence occurs when individuals experience increased survivorship, growth, or reproduction with increased population densities. Mechanisms leading to these positive relationships include mate limitation, saturating predation risk, and cooperative breeding and foraging. Individuals within these populations may differ in age, size, or geographic location and thereby structure these populations. Here, I study structured population models accounting for positive density-dependence and environmental stochasticity i.e. random fluctuations in the demographic rates of the population. Under an accessibility assumption (roughly, stochastic fluctuations can lead to populations getting small and large), these models are shown to exhibit a dynamical trichotomy: (i) for all initial conditions, the population goes asymptotically extinct with probability one, (ii) for all positive initial conditions, the population persists and asymptotically exhibits unbounded growth, and (iii) for all positive initial conditions, there is a positive probability of asymptotic extinction and a complementary positive probability of unbounded growth. The main results are illustrated with applications to spatially structured populations with an Allee effect and age-structured populations experiencing mate limitation

    Algal Bloom Expansion Increases Cyanotoxin Risk in Food

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    As advances in global transportation infrastructure make it possible for out of season foods to be available year-round, the need for assessing the risks associated with the food production and expanded distribution are even more important. Risks for foodborne illness are associated with contamination by bacteria, viruses, mold, parasites, natural and synthetic toxins, chemical residues, and conditions that lead to contamination. An increase in the popularity of natural alternatives to pharmaceuticals, herbal remedies and the desire for consuming “super foods” is leading to a change in the dietary patterns of consumers. Similarly, dietary trends are plentiful, with more consumers adopting changes with little medical guidance to dietary plans that are supported by inadequate scientific data. In particular, U.S. consumers are acquiring novel foods that may not be adequately checked for the presence of marine toxins and heat stable toxins in dry or minimally processed foods. Some dry foods cultivated in or processed in regions that may utilize hypoxic agricultural waters high in cyanobacterial or algal contamination. These may perpetuate increased risks for chronic liver, kidney, and neurodegenerative disorders due to intoxication from preventable foodborne agents. Global climate change, which has the effect of potentially expanding the toxic waters into higher latitudes, forecasts an increase in the risk of food contamination with toxins

    Initiation of TCR Phosphorylation and Signal Transduction

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    Recent data with CD8+ T cells show that the initial phase of T cell receptor (TCR) binding to MHC–peptide (MHCp) is quickly followed by a second, stronger, binding phase representing the binding of CD8 to the MHCp. This second phase requires signaling by a Src-family kinase such as Lck. These data point out two aspects of the initial stage of TCR signaling that have not yet been clearly resolved. Firstly, how and by which Src-family kinase, is the initial phosphorylation of CD3ζ accomplished, given that the Lck associated with the co-receptors (CD4 or CD8) is not yet available. Secondly, what is the mechanism by which the co-receptor is brought close to the bound TCR before the co-receptor binds to MHCp

    Discovery of > 200 RR Lyrae Variables in M62: An Oosterhoff I Globular Cluster with a Predominantly Blue HB

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    We report on the discovery of a large number of RR Lyrae variable stars in the moderately metal-rich Galactic globular cluster M62 (NGC 6266), which places it among the top three most RR Lyrae-rich globular clusters known. Likely members of the cluster in our studied field, from our preliminary number counts, include about 130 fundamental-mode (RRab) pulsators, with = 0.548 d, and about 75 first-overtone (RRc) pulsators, with = 0.300 d. The average periods and the position of the RRab variables with well-defined light curves in the Bailey diagram both suggest that the cluster is of Oosterhoff type I. However, the morphology of the cluster's horizontal branch (HB) is strikingly similar to that of the Oosterhoff type II globular cluster M15 (NGC 7078), with a dominant blue HB component and a very extended blue tail. Since M15 and M62 differ in metallicity by about one dex, we conclude that metallicity, at a fixed HB type, is a key parameter determining the Oosterhoff status of a globular cluster and the position of its variables in the Bailey diagram.Comment: 5 pages, 4 figures. ApJ Letters, in pres

    Classical Cepheid Pulsation Models. III. The Predictable Scenario

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    Within the current uncertainties in the treatment of the coupling between pulsation and convection, limiting amplitude, nonlinear, convective models appear the only viable approach for providing theoretical predictions about the intrinsic properties of radial pulsators. In this paper we present the results of a comprehensive set of Cepheid models computed within such theoretical framework for selected assumptions on their original chemical composition.Comment: 24 pages, 1 latex file containing 6 tables, 10 postscript figures, accepted for publication on Ap

    Structure of the Large Magellanic Cloud from 2MASS

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    We derive structural parameters and evidence for extended tidal debris from star count and preliminary standard candle analyses of the Large Magellanic Cloud based on Two Micron All Sky Survey (2MASS) data. The full-sky coverage and low extinction in K_s presents an ideal sample for structural analysis of the LMC. The star count surface densities and deprojected inclination for both young and older populations are consistent with previous work. We use the full areal coverage and large LMC diameter to Galactrocentric distance ratio to infer the same value for the disk inclination based on perspective. A standard candle analysis based on a sample of carbon long-period variables (LPV) in a narrow color range, 1.6<J-K_s<1.7 allows us to probe the three-dimensional structure of the LMC along the line of sight. The intrinsic brightness distribution of carbon LPVs in selected fields implies that \sigma_M\simlt 0.2^m for this color cut. The sample provides a {\it direct} determination of the LMC disk inclination: 42.3±7.242.3^\circ\pm 7.2^\circ. Distinct features in the photometric distribution suggest several distinct populations. We interpret this as the presence of an extended stellar component of the LMC, which may be as thick as 14 kpc, and intervening tidal debris at roughly 15 kpc from the LMC.Comment: 24 pages, 9 figures. Submitted to Ap
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