114,635 research outputs found
Read-Across of 90-day Rat Oral Repeated-Dose Toxicity: A Case Study for Selected n-Alkanols
n-Alkanols provide an excellent example where a category-approach to read-across may be used to estimate the repeated-dose endpoint for a number of untested derivatives (target chemicals) using experimental data for tested derivatives (source chemicals). n-Alkanols are non-reactive and exhibit the unspecific, reversible simple anaesthesia or non-polar narcosis mode of toxic action in that the metabolic products of the parent alcohols do not contribute to the toxic endpoint evaluated. In this case study, the chemical category is limited to the readily bioavailable (C5 to C13) analogues. The toxicokinetic premise includes rapid absorption via the gastrointestinal tract, distribution in the circulatory system, and first-pass metabolism in the liver resulting in metabolism via oxidation to CO2 and with minor elimination of oxidative intermediate as glucuronides. Two analogues have experimental 90-day oral repeated-dose toxicity data which exhibit qualitative and quantitative consistency. Typical findings include decreased body weight, slightly increased liver weight which, in some cases, is accompanied by clinical chemical and haematological changes but generally without concurrent histopathological effects at the Lowest Observed Effect Level (LOEL). Chemical similarity between the analogues is readily defined by a variety of structure-related properties; data uncertainty associated with toxicokinetic and toxicodynamic similarities is low. Uncertainty associated with mechanistic relevance and completeness of the read-across is reduced by the concordance of in vivo and in vitro results, as well as high throughput and in silico methods data. As shown in detail, the 90-day oral repeated-dose toxicity No Observed Effect Level (NOEL) value of 1000 mg/kg bw/d for 1-pentanol and 1-hexanol based on LOEL of very low systemic toxicity can be read across to fill the data gaps of the untested analogues in this category with acceptable uncertainty
Local Structure and Dynamics of Trans-polyisoprene oligomers
Mono- and poly-disperse melts of oligomers (average length 10 monomers) of
trans-1,4-polyisoprene are simulated in full atomistic detail. The force-field
is developed by means of a mixture of ab initio quantum-chemistry and an
automatic generation of empirical parameters. Comparisons to NMR and scattering
experiments validate the model. The local reorientation dynamics shows that for
CH vectors there is a two-stage process consisting of an initial decay and a
late-stage decorrelation originating from overall reorientation. The atomistic
model can be successfully mapped onto a simple model including only beads for
the monomers with bond springs and bond angle potentials. End-bridging Monte
Carlo as an equilibration stage and molecular dynamics as the subsequent
simulation method together prove to be a useful method for polymer simulations.Comment: 25 pages, 15 figures, accepted by Macromolecule
The element of uncertainty in the interpretation of feeding experiments / 165
Cover title.Bibliography: p. 578-579
Quasi-uniformity of Minimal Weighted Energy Points on Compact Metric Spaces
For a closed subset of a compact metric space possessing an
-regular measure with , we prove that whenever
, any sequence of weighted minimal Riesz -energy configurations
on (for `nice' weights) is
quasi-uniform in the sense that the ratios of its mesh norm to separation
distance remain bounded as grows large. Furthermore, if is an
-rectifiable compact subset of Euclidean space ( an integer)
with positive and finite -dimensional Hausdorff measure, it is possible
to generate such a quasi-uniform sequence of configurations that also has (as
) a prescribed positive continuous limit distribution with respect
to -dimensional Hausdorff measure. As a consequence of our energy
related results for the unweighted case, we deduce that if is a compact
manifold without boundary, then there exists a sequence of -point
best-packing configurations on whose mesh-separation ratios have limit
superior (as ) at most 2
Symmetric Shannon capacity is the independence number minus 1
A symmetric variant of Shannon capacity is defined and computed.Comment: 4 pages, submitted to Electronic Journal of Combinatoric
On the complete weight enumerators of some linear codes with a few weights
Linear codes with a few weights have important applications in authentication
codes, secret sharing, consumer electronics, etc.. The determination of the
parameters such as Hamming weight distributions and complete weight enumerators
of linear codes are important research topics. In this paper, we consider some
classes of linear codes with a few weights and determine the complete weight
enumerators from which the corresponding Hamming weight distributions are
derived with help of some sums involving Legendre symbol
Sparse halves in dense triangle-free graphs
Erd\H{o}s conjectured that every triangle-free graph on vertices
contains a set of vertices that spans at most
edges. Krivelevich proved the conjecture for graphs with minimum degree at
least . Keevash and Sudakov improved this result to graphs with
average degree at least . We strengthen these results by showing
that the conjecture holds for graphs with minimum degree at least
and for graphs with average degree at least for some absolute . Moreover, we show that the
conjecture is true for graphs which are close to the Petersen graph in edit
distance.Comment: 23 page
Multi-objective optimal designs in comparative clinical trials with covariates: The reinforced doubly adaptive biased coin design
The present paper deals with the problem of allocating patients to two
competing treatments in the presence of covariates or prognostic factors in
order to achieve a good trade-off among ethical concerns, inferential precision
and randomness in the treatment allocations. In particular we suggest a
multipurpose design methodology that combines efficiency and ethical gain when
the linear homoscedastic model with both treatment/covariate interactions and
interactions among covariates is adopted. The ensuing compound optimal
allocations of the treatments depend on the covariates and their distribution
on the population of interest, as well as on the unknown parameters of the
model. Therefore, we introduce the reinforced doubly adaptive biased coin
design, namely a general class of covariate-adjusted response-adaptive
procedures that includes both continuous and discontinuous randomization
functions, aimed to target any desired allocation proportion. The properties of
this proposal are described both theoretically and through simulations.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1007 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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