267 research outputs found
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 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 and of the squared four-momentum transfer . The quantities \At and \bd are found to be
non-zero. The rise of \bd for decreasing values of 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 () and the target spin axis () 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 has been performed
in quasi-real photoproduction on a deuterium target through the decay channel
. No evidence for
a previously reported resonance is found in the 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 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 -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
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