Some Remarks on the Model Theory of Epistemic Plausibility Models

Classical logics of knowledge and belief are usually interpreted on Kripke models, for which a mathematically well-developed model theory is available. However, such models are inadequate to capture dynamic phenomena. Therefore, epistemic plausibility models have been introduced. Because these are much richer structures than Kripke models, they do not straightforwardly inherit the model-theoretical results of modal logic. Therefore, while epistemic plausibility structures are well-suited for modeling purposes, an extensive investigation of their model theory has been lacking so far. The aim of the present paper is to fill exactly this gap, by initiating a systematic exploration of the model theory of epistemic plausibility models. Like in 'ordinary' modal logic, the focus will be on the notion of bisimulation. We define various notions of bisimulations (parametrized by a language L) and show that L-bisimilarity implies L-equivalence. We prove a Hennesy-Milner type result, and also two undefinability results. However, our main point is a negative one, viz. that bisimulations cannot straightforwardly be generalized to epistemic plausibility models if conditional belief is taken into account. We present two ways of coping with this issue: (i) adding a modality to the language, and (ii) putting extra constraints on the models. Finally, we make some remarks about the interaction between bisimulation and dynamic model changes.Comment: 19 pages, 3 figure

Prediction of cortisol response to dexamethasone from age and basal cortisol in normal volunteers: A negative study

The dexamethasone suppression test (1 mg at 23 h and 4 P.M. blood collection) was performed in 22 normal subjects. In contrast to a previous study using 0.5 mg dexamethasone and a 8-9 A.M. post-dexamethasone blood sample, age and basal cortisol level did not significantly predict postdexamethasone cortisol levels. © 1986 Springer-Verlag

Reduction of food phatogens prevalence in dietary S.cerevisiae-fed poultry orally challenged with S.enteritidis and C. jejuni.

The effect of yeast supplementation in broiler chickens on Salmonella enteritidis and Campylobacter jejuni contamination in faeces, cecum, breast, and neck skin was evaluated. Two groups (12 replicates/group, 20 Hubbard female chickens 1d old/replicate) were fed pre-starter (0-10d), starter (11-20d) and growing (21-38d) diets, and administered (Y) or not (C) Levucell\uae SB20 (Saccharomyces cerevisiae type boulardii I-1079; 106 CFU/g feed through a 0.05% premix). Birds were orally challenged at 10 days of life (S. enteritidis, 1x105 CFU/bird, and C. jejuni, 3x105 CFU/bird). On day 10 and 28 post-infection (PI), 10 animals/replicate were slaughtered and pooled ceca content of 5 birds/replicate was analysed for Salmonella and Campylobacter detection and enumeration together with total yeast count. Neck and breast skin were tested for Salmonella and Campylobacter presence on 1 subject/replicate. Data were analysed by a GLM procedure of SAS considering two experimental periods, from 0 to 20 days and from 20 to 38 days. Growth performance and faecal coliforms content were not affected by treatment. Higher yeast and lactobacilli (P=0.01) faecal count, and a significant decreased Salmonella enumeration and frequency in neck (-41%, P=0.03) and tendency in faeces (-25%; P=0.06), cecum (-25%; P=0.06), and breast skin (-33%; P=0.08) were found in Y group on day 38. No fecal Campylobacter was detected at 10d (P<0.01) or 28d (P=0.06) PI in Y birds, while in neck skin absence of Campylobacter was only recorded on day 10 PI (P=0.01). Campylobacter was significantly lower in Y birds in cecum (-42%; P=0.01), and breast skin (-58%; P=0.04) on 10d PI, while on day 38 it was reduced in breast skin (-42%; P=0.02), and tended to decrease in faeces (-25%; P=0.06). Saccharomyces cerevisiae (CNCM I-1079) significantly controlled Campylobacter carriage in chickens with some positive results also on Salmonella contamination, thus reducing the contamination of carcasses with both food borne pathogens

First Measurement of the Tensor Structure Function b1b_1 of the Deuteron

The \Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of \Hera. The use of a tensor polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry \At and the tensor structure function \bd for average values of the Bj{\o}rken variable $0.01<0.45$ and of the squared four-momentum transfer $0.5 {\rm GeV^2} <5 {\rm GeV^2}$. The quantities \At and \bd are found to be non-zero. The rise of \bd for decreasing values of $x$ can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion ($\phi$) and the target spin axis ($\phi_S$) about the virtual photon direction and relative to the lepton scattering plane. The extracted Fourier component \cmpi is a signal of the previously unmeasured quark transversity distribution, in conjunction with the so-called Collins fragmentation function, also unknown. The Fourier component \smpi of the asymmetry arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson productio

Search for an exotic S=-2, Q=-2 baryon resonance at a mass near 1862 MeV in quasi-real photoproduction

A search for an exotic baryon resonance with $S=-2, Q=-2$ has been performed in quasi-real photoproduction on a deuterium target through the decay channel $\Xi^- \pi^- \to \Lambda \pi^- \pi^- \to p \pi^- \pi^- \pi^-$. No evidence for a previously reported $\Xi^{--}(1860)$ resonance is found in the $\Xi^- \pi^-$invariant mass spectrum. An upper limit for the photoproduction cross section of 2.1 nb is found at the 90% confidence level. The photoproduction cross section for the $\Xi^{0}(1530)$ is found to be between 9 and 24 nb

Double hadron leptoproduction in the nuclear medium

First measurement of double-hadron production in deep-inelastic scattering has been measured with the HERMES spectrometer at HERA using a 27.6 GeV positron beam with deuterium, nitrogen, krypton and xenon targets. The influence of the nuclear medium on the ratio of double-hadron to single-hadron yields has been investigated. Nuclear effects are clearly observed but with substantially smaller magnitude and reduced $A$-dependence compared to previously measured single-hadron multiplicity ratios. The data are in fair agreement with models based on partonic or pre-hadronic energy loss, while they seem to rule out a pure absorptive treatment of the final state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter

Subleading-twist effects in single-spin asymmetries in semi-inclusive deep-inelastic scattering on a longitudinally polarized hydrogen target

Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the subleading-twist contribution to the longitudinal case. This contribution is significantly positive for (\pi^+) mesons and dominates the asymmetries on a longitudinally polarized target previously measured by \hermes. The subleading-twist contribution for (\pi^-) mesons is found to be small